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Coal drying and comminution in a spouted bed Sun, Shang Liang 1988

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COAL DRYING AND COMMINUTION IN A SPOUTED BED by Shang Liang SUN East China Institute of Chemical Technology, 1964 A THESIS SUBMITTED IN PARTIAL FULFILMENT OFTHE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMICAL ENGINEERING We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA DECEMBER 1988 © S h a n g Liang SUN , 1988 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date DE-6 (2/88) Abstract The simultaneous comminution and drying of coal in spouted beds at various temperatures and structural conditions was studied in a column with 152 mm internal diameter. Size reduction in the spouted bed occurs by three different mechanisms: impaction, shear (attrition) and crushing. The size reduction process depends on the physical parameters and the operating conditions in the spouted bed. The key parameters are the design features of the insert, the spouting velocity, the chosen feedrate and the drying temperature. The feedrate for a continuous run can be determined from the instantaneous production rates of the related semi-batch run at the same operating conditions. In this study, the operating conditions were kept constant in each run, except for the inlet gas temperature, while the grinding medium was either glass beads or a special static insert. The results show that the size reduction rate is more rapid with the special insert than with the glass beads. At elevated temperature the rate of size reduction is also more rapid than that at room temperature. The moisture content and particle size distribution of the products with various inlet gas tem-peratures were measured for each run. The particle size distribution of the product was dependent on the outlet gas velocity. The energy input to a spouted bed during a comminution and drying operation includes both kinetic energy and thermal energy. The kinetic energy has a direct effect, that is, it provides comminution energy to the particles, whereas the thermal energy influences the comminution of the particles due to the change in their physical properties. These two kinds of energy can complement each other and improve both the efficiency and the capacity of the comminution. The total energy equation, therefore, can provide a simple method to estimate the energy requirement for the coal comminution. ii T A B L E O F C O N T E N T S Abstract ii List of tables v List of figures vii Acknowledgment viii 1. INTRODUCTION AND SUMMARY 1 1.1 Motivation and Objectives 1 1.2 The Spouted Bed 1 1.3 Summary 4 2. LITERATURE REVIEW ON DRYING AND COMMINUTION 5 2.1 Drying in general and in spouted beds 5 2.1.1 Literature on drying in general 5 2.1.2 Literature on drying in spouted beds 5 2.2 Comminution in general and in spouted beds 7 2.2.1 Literature on comminution in general 7 2.2.2 Literature on comminution in spouted beds 11 3. EXPERIMENTAL SET-UP AND THE PARTICULATE MATERIAL 13 3.1 Experimental flow sheet 13 3.2 The main equipment and the accessories 15 3.2.1 Spouted Bed 15 3.2.2 Rotary table feeder 16 3.2.3 Screen separator 18 3.2.4 Static insert 19 3.3 The particles used 19 3.3.1 Glass Beads 19 3.3.2 Coal Feed-stock 19 4. EXPERIMENTAL CONDITIONS AND TECHNIQUES 23 4.1 Spouting velocity 23 4.2 Drying of Forestburg coal 23 4.3 Coal and inerts loading 25 4.4 Experimental conditions 27 4.4.1 Experimental conditions at room temperature 27 4.4.2 Experimental conditions at elevated temperatures 28 4.4.3 Determination of the feedrate for a continuous run 28 4.5 Experimental technique 30 5. EXPERIMENTAL RESULTS AND DISCUSSION 33 5.1 The experiments results using glass beads as a dynamic grinding aid 33 iii 5.1.1 The experimental results using combined bottom and top product discharge 33 5.1.2 The experimental results using only the top product discharge 36 5.2 The experimental results using a specially designed static grinding aid in conjunction with top product discharge 40 5.3 Discussion 45 6. DISCUSSION ON THE SIZE REDUCTION MECHANISM 46 6.1 Comminution mechanism at room temperature 46 6.2 Comminution mechanism at elevated temperature 48 7. ENERGY REQUIREMENT 52 7.1 Energy for size reduction 52 7.2 Energy requirement 53 8. CONCLUSIONS AND SUGGESTIONS 57 8.1 Conclusions 57 8.2 Suggestions 58 Nomenclature 59 References 60 Appendix 1. Calibration curve of rotameter 62 Appendix 2. Calibration curve of coal feeder 63 Appendix 3. The choice of coal sample and the properties of the coal 64 Appendix 4. Laboratory convective dryer 66 Appendix 5. The air flowrates maintained at different temperatures 67 Appendix 6. Analysis of moisture content, relative humidity and size of the coal particles 68 Appendix 7. Sample calculations 69 Appendix 8. Summary table of experiments 75 A. Raw data on the semi-batch experiments No. ST-2 to ST-2 m and No. SCI-1 to SCI-1 76 B. Raw data on experiments other than No. ST-2 to ST-2'" and SCI-1 to SCI-1"" 86 iv L IST O F T A B L E S 4.1 4.2 2.1 3.2 3.1 Selection of comminution equipment (modified from Lowrison, 1974). Particulars of the equipment. Data on specific properties of the coal. Spouting velocity and related data. Drying conditions in the convective dryer. 25 22 23 21 8 5.1 Results under various drying conditions using combined bottom and top product discharge. Spouting of coal and glass beads. 34 5.2 Results under various drying conditions with top discharge only. Spouting of coal and glass beads. 36 5.3 Average results of continuous runs at various temperatures using the special insert and top discharge. 42 5.4 Results at several intermediate periods during the continuous runs (CI-2 at 20° C and HCI-1 at 95°C) using the special insert and top discharge. 42 5.5 The results of the spouted bed comminution at elevated temperature with glass beads as grinding aid compared to the results with the insert. 45 6.1 Weight distributions of comminution products in continuous runs at room temperature, with glass beads (run TC-3) and with static insert (run CI-2). 47 6.2 Weight distributions of comminution products in continuous runs at elevated temperatures, with glass beads (run TCH-7) and with static insert (run HCI-1). 50 7.1 Analysis of energy consumption of a ball mill. 52 7.2 Values of Ek, n1/4 / P1/2 and k s from the continuous runs. 56 A3.1 Measured coal particle moisture content and hardness. 64 A6.1 Sieve series used in this experiment. 68 A6.2 Sieve average diameters. 68 v L IST O F F I G U R E S 1.1 Schematic diagram of a spouted bed. 2 1.2 Schematic diagram of a spouted bed comminution rig. 3 2.1 Typical results for a co-current rotary dryer obtained by solving differential moisture and heat-balance equations coupled with expressions for the forward transport of solids (modified from Sharpies, 1964). 6 2.2 Temperature history of a recirculating particle, including transient intra-particle gradients developed during its passage through the spout (modified from Mathur and Gishler, 1955). 7 2.3 Particle size range and energy requirement for different size reduction theories (modified from Hukki, 1962). 8 2.4 Effect of progressive grinding on size distribution (modified from Heywood, 1950). 9 2.5 Emperical energy chart. 10 2.6 Schematic diagram of experimental comminution apparatus used by Mathur and co-workers (1972). 11 3.1 Flowsheet of experimental setup. 13 3.2 Photographs of the experimental equipment. 14 3.3 Schematic diagram of the spouted bed. 15 3.4 Schematic diagram of the rotary table feeder. 16 3.5 Photograph of the rotary table feeder. 17 3.6 Schematic diagram of the screen separator. 18 3.7 Photograph of the screen separator. 18 3.8 Position of the static insert. 20 3.9 Picture of the static insert. 20 3.10 Schematic diagram of the static insert. 20 4.1 2.80-3.35 mm coal & glass beads: photo at minimum spouting velocity. 24 4.2 With a static insert, 2.36-2.80 mm coal: photo at minimum spouting velocity. 24 4.3 Drying curves of Forestburg coal. 26 4.4 Forestburg coal drying curve measured by thermogravimetric analysis. dp = 2.80-3.35 mm, initial moisture content - 24%, T = 200°C. 26 4.5 A diagram showing the relation between the semi-batch production rate and the required feedrate for continuous production (after Khoe, 1987). 29 4.6 The production rate graph of a semi-batch and its related continuous run. (Average values in each 5 minute period). 31 4.7 Product rate changing with time in semi-batch run. 31 5.1 The results of continuous operation at different inlet air temperatures using top and bottom outlets. 33 5.2 Sieve analysis of the bed holdup using several different inlet air temperatures; 6-minute semi-batch run (exception: 15 minutes for C-19-9), with combined top and bottom discharge. Spouting of coal and glass beads. 34 5.3 Sieve analysis of the bed holdup using several different inlet air temperatures; continuous run, with combined top and bottom discharge.Spouting of coal and glass beads. 35 5.4 Sieve analysis of the bottom product using several different inlet air temperatures; continuous run, with combined top and bottom discharge. Spouting of coal and glass beads. 35 vi 5.5 The results of continuous operation at different inlet air temperatures (using top discharge only). 37 5.6 Sieve analysis of the bed holdup at several intermediate periods during an experiment (using top discharge only). Semi-batch run, initial coal size: 2.80-3.35 mm and initial M.C.: 24.54%. T=20°C. 38 5.7 Sieve analysis of the product at several intermediate periods during an experiment (using top discharge only). Semi-batch run, initial coal size: 2.80-3.35 mm and initial M.C.: 24.54%. T=20°C. 38 5.8 Sieve analysis of the bed holdup from continuous runs at room and at elevated temperatures (using top discharge only). Initial coal size: 2.80-3.35 mm. Spouting coal and glass beads. 39 5.9 Sieve analysis of the product from continuous runs at room and at elevated temperatures (using top discharge only). Initial coal size: 2.80-3.35 mm. Spouting coal and glass beads. 39 5.10 Moisture content of the product as a function of operating time, at different inlet air temperatures (top discharge only). Spouting coal and glass beads. 40 5.11 Sieve analysis of the bed holdup at different operating times. 41 5.12 Sieve analysis of the product at different operating times. 41 5.13 Product moisture content and production rates at several periods during continuous experiments at 20°C and 95°C (with insert and top discharge). 43 5.14 Sieve analysis of the bed holdup and product, at various temperatures. 44 6.1 Sieve analysis of products at room temperature, continuous runs. 47 6.2 Sieve analysis of initial and final bed holdup at room temperature, continuous runs. 48 6.3 Sieve analysis of products at elevated temperature, continuous runs. 49 6.4 Sieve analysis of holdup and products, continuous runs at elevated temperatures using glass beads as grinding aid. 50 6.5 Sieve analysis of holdup and products, continuous runs at elevated temperatures using metal insert as grinding aid. 51 7.1 Emperical energy chart showing the total energy consumption for coal comminution in spouted beds. 55 7.2 Total energy input into the spouted bed as a function of temperature, with the glass beads and with the insert. 55 A l Caliberation curve for spouted air flow. 62 A2 Caliberation curve for coal feeder 63 A3 Coal feedrates at different moisture contents. 65 A4 Convective drying rig. 66 A5 The graph of production rate versus time in a semi-batch run and its related continuous run intervals (average values in each 5 minute interval). 87 vii Acknowledgements I would like to express my appreciation to Dr. N. Epstein and Dr. C.J. Lim for their guidance and supervision. I am grateful to Dr. G.K. Khoe for his supervision, advice and assistance. With their advice and encouragement this thesis was carried out. Special thanks are also due to the gentlemen of the Chemical Engineering Department workshop and stores for their invaluable assistance. viii 1 1. INTRODUCTION AND SUMMARY 1.1 Mot ivat ion and Objectives Research in the field of spouted bed drying has been extensive since its first introduction by Mathur and Gishler in 1955. In 1970, Mathur first suggested spouting as a means for comrninution. Since then several research projects on spouted bed comminution were carried out under his supervision in the Chemical Engineering Department at the U B C . After Dr . Mathur died, this line of research was continued in 1980 with emphasis on individual comminution mechanisms and on a mechanistic approach which involves simulation by matrix models. The present work is an attempt to combine drying and comminution of coal into a single spouted bed process, and to find its optimum configuration and operating conditions. Three different configurations were studied: 1. Cbmminution and drying with glass beads as dynamic grinding aid and the utilization of: a. Combined product discharge from the top by air elutriation and from the bottom by gravity. b. Total product discharge from the top by elutriation at increased air-exhaust velocities. 2. Comrrrinution and drying with a specially designed static grinding aid in the form of an insert installed above the air inlet orifice in the conical section of the bed, and the use of a top discharge as in L b . above. The present experimental procedure was designed in such a way that the data could be analyzed using the Matrix Mode l (Broadbent and Callcott, 1956). For this reason the present experiments used a very narrowly sized cut of coal as the feedstock to approach a monosized stock. Although the Matrix Model itself is not expected to be part of the present thesis, this monosized approach wi l l gready simplify the subsequent matrix modelling which is expected to contribute positively to the understanding o f the governing mechanisms for simultaneous comminution and drying. A novel aspect of the present experiments of prospective importance is that for each set of conditions, semi-batch as well as continuous runs were carried out, in which the continuous feedrate was first calculated from the semi-batch data to ensure a chosen product size range. Future breakage and selection matrices w i l l rely on the semi-batch data, the validity of which can be tested on the data for the continuous counterpart. 1.2 The Spouted Bed The spouted bed technique was first developed and employed successfully for drying wheat by Mathur and Gishler (1955). Since then the spouted bed technique has been used industrially, or in some cases only experimentally, for operations such as heating or cooling of solids, drying of solutions and suspensions onto an inert bed of particles, particle coating, granulation, solids blending, comminution, aerosol collection from a gas stream, combustion and gasification of coal, shale pyrolysis, ore roasting, cement clinker production and thermal cracking of petroleum A complete review of spouted bed technology was presented by Mathur and Epstein (1974) and more recently reviews were published by Epstein and Grace (1984) and Bridgwater (1985). 2 Figure 1.1 illustrates schematically a typical spouted bed. The central core is called the spout, and the peripheral annular region is referred to as the annulus. The particles in the spout are lifted by the high velocity inlet air jet. As the spout particle velocity decreases towards the top, the particles simulate a fountain and fall onto the annular section, forming a moving packed bed with flow mainly downwards, but also laterally towards the center, until the particles are once again lifted by the air jet and recycled to the top. The air stream enters from the bottom at a high velocity and travels upward in the spout, and at the same time spreads through the void space of the annular moving packed bed, so that, in al l but shallow beds, most of the air eventually moves up the annulus. Fountain {'-."" V; — Bed surface — .- r-s-s-s ; — Annulus .••..%••.< -. - —»-„ ':- — Spout - annulus interface Figure 1.1 Schematic diagram of a spouted bed The idea of using a spouted bed as a means for comminution of particulate solids was first proposed by Mathur and the related experiments were carried out at the University of British Columbia in 1970. In the comminution apparatus, the particles were subjected to attrition and impaction by the spouting air, and most size reduction occured in the so-called main comminution region, i.e. in the conical bottom of the spouted bed as shown in Figure 1.2, when inert solid particles such as glass beads were used as the grinding aid. 3 Gas out Spout wall Solid streamlines Main comminution region Solids disengagement fountain Annulus Spout Gas streamlines Gas entry Figure 12. Schematic diagram of a spouted bed coniminution rig. The few preliminary tests dating from 1974 and earlier have already shown the feasibility of spouted beds for comminution. More recently, as coal combustion and gasification processes were developed, the requirement for prelirxrinary comminution and drying of the coal has given rise to the need for a simple device which can do this task efficiently. The use of spouted beds could improve the efficiency of coal preparation and could also lower the investment cost. In order to obtain a quantitatively better understanding of the combined corxuiiinution and drying process, the study of continuous runs at steady state is necessary and important As a device for comminution and drying, spouted beds have special advantages over fluidized beds for this particular application. This is true despite the larger air consumption in spouted beds than in fluidized beds of comparable size. The special advantages are that: 1. The combination of the two processes, comminution and drying, occur simultaneously. The apparatus is simple in its construction and the size of the products can be controlled by simple means. This dual purpose is a new application of the spouting technique not possible with conventional fluidized beds where lower gas velocities prevail. 4 2. The comminution process helps to increase the drying rate, and at the same time the drying process enhances the comminution process. Both intensify the heat and mass transfer, leading to higher drying and comminudon efficiencies, than occur for each process in the absence of the other. The construction, operating costs and energy consumption will be compared with other grinding equipment having similar selectivity, size reduction ratio and size range. 1.3 Summary This thesis includes eight chapters: • The motivation and objective of this research and applications of the spouted bed technique are briefly described in Chapter 1. • A Mterature review about drying and comminution in general, and in spouted beds specifi-cally, are given in Chapter 2. • The experimental set-up and the particulate materials used are described in Chapter 3, which includes the experimental flow sheet as well as details of the equipment parts, including the static insert. • Chapter 4 lists the experimental conditions and the variables studied. The relation between the semi-batch and the continuous runs, the determination of the feedrate for the continuous runs and the experimental techniques are also given in this chapter, while the next chapter presents and discusses the experimental results. • The discussion on the mechanisms of comminution and drying in spouted beds are presented in Chapter 6. • The total energy requirement in a spouted bed is discussed in Chapter7, while the conclusions and some suggestions are given in Chapter 8. • The appendices contain the coal properties and analysis, the calibration curves for the spouting air flowrate and the coal feeder, the experimental data and sample calculations. 2. L I T E R A T U R E R E V I E W O N D R Y I N G A N D C O M M I N U T I O N 2.1 Drying in general and in spouted beds 2.1.1 Literature on drying in general Convective drying is the unit operation of passing a gas over, or through the interstices of, a nonvolatile solid to remove adherent or loosely combined moisture by vaporizing it into the gas. A description of the theory and fundamental concepts of the drying of solids can be found in many books, such as those by Perry and Chilton (1984), and Coulson and Richardson (1977). There are many hundreds of dryer designs available on the market. Probably the most thorough classification of dryer types has been made by Kroll (1965), who has presented a decemalised system based on the following factors: 1) temperature and pressure in the dryer, 2) the method of heating, 3) the means by which moist material is transported through the dryer, 4) any mechanical aids aimed at improving drying, 5) the method by which the air is circulated, 6) the way in which the moist material is supported, 7) the heating medium, and 8) the nature of the wet feed and the way it is introduced into the dryer. Many papers have discussed heat transfer to particles drying in different types of dryers. For example, in the case of pneumatic conveying dryers, the heat transfer coefficient between particles and gas, was given by Ranz and Marshall (1952) for the water-air system For a fluidized bed dryer, the coefficient of heat transfer between coal particles and air was given by Fedorov (1955) for the coal particle size range from 0.5-10 mm and Re from 20 to 500. The changing temperature and moisture content of gas and solids in the drying process are important. Sharpies (1964) has solved the differential moisture and heat-balance equations coupled with expressions for the forward transport of solids, in a co-current rotary dryer, allowing for solids being cascaded by lifting baffles. Figure 2.1 shows typical results for co-current drying of 11.3 kg/ s of fertilizer granules with 9.1 kg/s of air in a rotary dryer 2.6 m in diameter and 16 m long, with a one degree slope. 2.1.2 Literature on drying in spouted beds The spouted bed wheat dryer used by Mathur and Gishler (1955) may be regarded as a typical continuous granular-solids drying system. The dryer had a 15-inch diameter heater and 12-inch diameter cooler side by side. Up to 270 kg/hr of wheat, through a dry basis moisture range of 4%, could be dried in a system of this size, using 177°C inlet air. The first industrial scale spouted bed drier for agricultural products such as peas, lentils and flax was installed in 1962 in Canada (Peterson, 1962). The drier, of 0.6 m diameter with a bed depth of about 2 m, was capable of safely drying up 2 Mg/hr of peas through an 8% moisture range, dry basis, using about 3 Mg/h of air at temperatures 6 Moisture content (kg/kg) o.oa 0.03 0.04 O.03 0.02 0.01 800 700 «oo 500 400 300 Temperature (K) Position along dryer (m) Figure 2.1 Typical results for a co-current rotary dryer obtained by solving differential moisture and heat-balance equations coupled with expressions for the forward transport of solids (modified from Sharpies, 1964). up to 557 K. The chief advantage of a spouted bed dryer is the same as that of a fluidized bed dryer, namely good solids agitation combined with effective gas-solids contact. A theoretical study of particle movement in the annulus and spout of spouted beds has been carried out by Lim and Mathur (1978), a force balance being employed in the spouL The main disadvantages of a spouted bed dryer are the large amount of air required and the high pressure drop across the inlet nozzle. The former can be eliminated by use of a draft tube, which permits a smaller air flux to maintain the solids circulation, as reported by Buchanan and Wilson (1965). Drying of rice in a draft tube spouted bed has been studied over a range of draft tube geometries by Khoe and Van Brakel (1980). Most of the early work on drying, and on heat and mass transfer, in spouted beds has been reviewed by Mathurand Epstein (1974). Ruid-to-panicleheattransferratesin theannulus, spoutand fountain regions are different. These coefficients are in the order of 50W/nvK in the annulus and about eight times this value in the spout. Figure 2.2 shows the theoretical fluid and particle temperature profiles given by Mathur and Gishler (1955) for wheat drying. From Figure 2.2 it is apparent that good heat and mass transfer in the spouted bed occurs in the bottom region of the cone. 7 BUI. It 8E0 TEMPERATURE O ' 0.1 OX O i . 0.4 O i 0.6 0.7 0.8 C » I.O I / H Figure 2.2 Temperature history of a recirculating particle, deluding transient intra-particle gradients developed during its passage through the spout (modified from Mathur and Gishler, 1955). 2.2 Comminution in general and in spouted beds The term "comnnnution" is used to describe those operations in which solid particles are cut or broken into smaller pieces. Comminution theory is concerned with the relationship between energy input and product particle size distributions from a given feed size. It is also concerned with the properties of solids and the mechanisms of size reduction. 2.2.1 Literature on comminution in general Crushing is the first step in the process of size reduction, but for many chemical processes it is usually followed by grmding to produce a fine-sized powder. Though many articles have been published on corrumnution (over 4000 up to 1974, as estimated by Marshall (1974)), the subject remains essentially empirical. A fuller treatment of crushing and grinding should refer to the book by Lowrison (1974). There is no universal method of size reduction of solids because all solids are not the same in their response to size reduction methods. There are three basic size reduction theories or laws: Rittinger's Law: E = K (l/d2 - 1/di) 2.1 Kick's Law: E = K log(di/d2) 2.2 Bond's Law: E = 10 Wi(l/\/d2 - 1/Vdi) 2.3 Each of the three 'laws' has a range of particle size for which it is the most applicable, as shown in Figure 2.3. Hukki (1962) showed that for practical applications these equations generally give a big error. Therefore, the designer must rely on experience and on the equipment manufacturers' 8 o c c o 5 o O 10 1 0 5 1 0 4 1 0 3 1 0 2 1 0 1 1 O - l C O M P O S I T E C U R V E R I T T I N G E R B O N D -K ICK, 1A 1/Jtm 1mm 10m L O G P A R T I C L E S I Z E Figure 2.3 Particle size range and energy requirement for different size reduction theories (modified from Ffukki, 1962). information to estimate the power requirement of comminution equipment The selection guide given by Lowrison (1974) and Marshall (1974), reproduced in Table 2.1, can be used to make a preliminary selection based on particle size and material hardness. The most commonly used equipment for coarse size reduction are jaw crushers and rotary crushers: and for grinding, ball nulls or their variants such as pebble, rod and tube mills. Descriptions of most of the equipment can be found in Lowrison (1974), and in Perry and Chilton (1984). Table 2.1 Selection of comminution equipment (modified from Lowrison, 1974). fiongt of f**d to product sit* Typfcot S'lt rtduclron rot to 1 t O ^ m -(1mm J 10* SO Hohs hardness af mot trial tiondtt<f tO 9 8 7 6 S £ 3 2 I Die mood Soppfurt Topoz Ovcrti feldspar Apotitt Ftuorspof Cotdtt Gypsum Tote —Jow crushers - O y r o l o r y crushers-Rolory Impoctws-Stomp mitts - R o l l crushers -Autogenous miUs (d ry ) -*»<m mill (dry) Rod-tooded Bott-iooded tumbling mill I lumoMn Hommer mltl-g mill (<Jry|-f—Ultro-rotor-t d r y l -Rlng toll ond ring boU milts--Vlbrotlort mil i l (dry) r - S a n d mills -- F l u i d - e n e r g y mi l ls --Cotto'.d mi l ls -Sticky mo tt rioti The effect of the progress of grinding on the size distribution of coal has been well illustrated by a series of experiments on the grinding of coal in a small mill by Hcywood (1950). Their results arc shown in Figure 2.4, in which the distribution of particle size in the product is given as a function of the number of revolutions of the mill. The initial size distribution shows a single mode corresponding to a relatively coarse size, but as the degree of crushing is gradually increased this mode progressively decreases in magnitude and a second mode develops at a particular size. This process continues until the first mode has completely disappeared. The second mode is then characteristic of the material and is known as the persistent mode, while the first is known as the transitory mode. It will be seen later that measured size distributions inside a spouted bed at different operating times show similar changes to those displayed by Figure 2.4. 1.0O U J _) ^ 0.75 CC „ < O Q. UJ !- O.SO o O 2 O O Z ( - 0.25 O ^ < o CC u. ZCO <0O 600 800 WOO 1200 l " 0 O 1SO0 P A R T I C L E S I Z E , y-Figure 2.4 Effect of progressive grinding on size distribution (modified from Heywood, 1950). The energy required to effect cornrninution is related to the internal structure of the material, since the comminution process really consists of two parts: firsdy, opening up any small fissures which are already present and secondly, forming new surface. A material, such as coal, contains a number of small cracks and tends to break along these first, and therefore large pieces are broken up more readily than the small ones. Further, since a very much greater increase in surface results from sub-dividing a large quantity of fines as opposed to a small number of coarse particles, fine grinding requires very much more power per unit mass of material. Theoverall energy efficiency of comminution is absurdly low (Carey and Hahon 1974). It has been observed that most of the applied energy is lost because of the difficulty of transmission of the applied forces to those panicles in ihe mill that most need to be comminuted. The culprit is 10 intcrparoclc fricdon. This difficulty is coupled wiih the fact that roost materials processed by cx>rnrninuDon arc substantially weaker in tension than in compression and that, for the most part, the applied forces arc not tensile in ajrnrninudorL Despite thcscdifficuldcs, considerable effort has been made to relate energy consumption to product characteristics. Based on a large number of experimental results Bond and Wang (1950) developed a Sfrain Energy Theory. The theory can be used to calculate the total energy required for conrnunution under room temperature conditions. Their final equation was: E3c=k n , / 4/P1/2=h [hp-h/short ton) 2.4 where Ek= total energy input k = constant. n = reduction ratio at product size = F / P F = feed size, screen aperture in inches through which 80% of the feed passes. P = product size, screen aperture in inches through which 80% of the product passes. The energy required to crush and grind many different materials in different machines was tabulated and plotted in various ways. Bond and Wang (1950) found that these data could be shown consistently on a log-log plot of the energy input required in hp-hr per short ton vs. the square root of the quantity, feed size F divided by the cube of the product size P, which is equivalent to the square root of the reduction ratio n, divided by P, or "Vn~7 P. The slope of the plot was 1/2. 0-1 0-2 0-t OS 08 I ? 1 ( |I0 2 t S 8 100 .2 I 6 81000 2 t 6 8 K)000 \/ n •>/ fird\»it»o*» aol iQ j T » — : Figure 2.5 Empirical energy chart. 11 The plot is shown in Figure 2.5. This plot has been of considerable practical value in predicting approximate energy requirements. It can be used whenever the feed and product sizes are known, and an assumption can be made regarding the relative resistance of the material to comminution. Since Broadbent and Callcott (1956) developed their "Matrix Simulation Model", it has become increasingly popular in research on size reduction. This approach gives rise to the concept of "individual comrninution mechanisms", introduced by Rumpf (1965) as a method to analyze and to synthesize a model for specific equipment. 2.2.2 Literature on comminution in spouted beds Conventional ball mills, which are currently being utilized to comminute coal in order to meet the various size distributions required for different processes, have high capital and operating costs associated with them, and are energy inefficient These facts have motivated researchers at U.B.C. to investigate the comminution process of coal in spouted beds. Preliminary tests of spouted bed comminution were conducted by Mathur and co-workers (1972). Figure 2.6 showing the schematic diagram of his apparatus. The bed diameter was I.D. 152 mm. Later, Sion (1982), Nakano (1982), Figure 2.6 Schematic diagram of experimental comminution apparatus used by Mathur and co-workers (1972). 12 Amlani (1984) and Khoe et al. (1984) also studied batch comminution at room temperature. Their results showed that the overall process of comminution in a spouted bed occurs through three different mechanisms, namely, impaction, crushing and attrition. Using 6 mm glass beads as a grinding medium, studies (Nakano 1982, Khoe et al.1984) have been conducted to determine the relative importance of the three individual mechanisms which cause the size reduction, and to locate the parts of the spouted bed in which they occur. With the aid of results from a study on the three individual comminution mechanisms (Sion 1982), Khoe et al. (1984) concluded that, under normal spouting conditions, the dominant comrninution mechanisms are attrition and mild impaction in the spout. Crushing by compression, on the other hand, is relatively unimportant Further studies (Khoe et al., 1984) have also been carried out to test the effects of special bed inserts, and of spouting velocity, on the comminution mechanisms. These studies have shown that installation of a target plate insert in the fountain accentuates the impaction mechanism but does not qualitatively affect the comminution kinetics. The kinetics changed qualitatively only after instal-lation above the orifice of an additional crossed-blades insert which accentuated impaction and particle-to-wall abrasion in the spout. Finally, increasing the spouting velocity with both inserts only served to intensify the latter kinetics. Increasing the surface area of the grinding aid also changed the character of the comminution kinetics, which continued to hold even with the installation of the crossed-blades insert (Amlani, 1984). Khoe et al. (1984) used an energy and simulation model in matrix form of the particle size distribution before and after comminution. Therefore, in the present work the experiments have been performed and the experimental data treated to facilitate future application of the developed Matrix Simulation Model. 13 3. EXPERIMENTAL SET-UP AND THE PARTICULATE MATERIAL 3.1 Experimental flow sheet Figure 3.1 shows the flow sheet for the present study and Figure 3.2 two photographs of the experimental equipment. Air from the building compressor (1) was fed through a pressure regulator to reduce its pressure to 20 psi gauge before it entered the surge tank (2). The air flowrate was adjusted and monitored using a control valve (3) and a rotameter (4), respectively. Thereafter the air temperature was raised using a preheater (5). Once the hot air flowed through the three way valve (6) which provided a by-pass for start-up and shut down, it entered the spouted bed (7) through the inlet orifice. The crushed coal particles entrained by the air were collected in a screen separator (14) and a cyclone (15). In the experiments in which bottom discharge was used, the coarse product fractions left the bed through a grid covering the top end of four discharge pipes. The coal fed from the hopper (12) was regulated by the rotary table feeder (11). It entered the bed through an inlet shut-off valve (9). Valves (8) and (13) were used to shut off the coal discharge to the bottom and the top outlets, respectively. 1. Compressor 2. Surge tank 3. Control valve 4. Rotameter 5. Preheater 6. Three way by-pass valve 7. Spouted bed 8. Coal discharge pipe & valve 9. Coal feed pipe & valve 10. Variable speed electrical motor 11. Rotary table feeder 12. Coal hopper 13. Tops product discharge valve 14. Screen separator 15. Cyclone Figure 3.1 Flowsheet of experimental setup. Figure 3.2 Photographs of the experimental equipment. 15 3.2 The main equipment and the accessories 3.2.1 Spouted Bed The spouted bed used in these experiments is shown in Figure 3.3. The glass column used was 152 mm in I.D. and 1.80 m in length. Its brass conical bottom had an included angle of 30 degrees . The flat base of the cone was 57 mm in diameter, and had a variable-diameter inlet orifice formed by a multi-vane shutter. In these experiments the inlet opening was kept constant at 20 mm diameter. A ring channel built in the multi-vane shutter facilitated measurement of the pressure immediately above the orifice plane. The main air inlet pipe leading to the orifice had a honeycomb insert which acted as straightening vanes. Except in the experiments using a combined bottom and top discharge, the top of the column was coupled to a 75 mm I.D. brass pipe in order to ensure a specific carry-over velocity. The pipe had a variable mounting position. In these experiments it was kept constant at 685 mm above the inlet orifice. The various measuring points are indicated in Figure 3.3. The temperature, pressure drop, inlet and outlet moisture contents of air were monitored. (?) c jv s Z \ o CO O O 4>57 Figure 3.3 Schematic diagram of the spouted bed. A l l dimensions are in mm. P = pressure gauge. T = thermometer. 16 3.2.2 Rotary table feeder In order to control the feedrate reliably in this experiment, a rotary table feeder of 100 mm 1. D. was specially made for these experiments. This type of rotary table feeder can be used to feed particulate solids as well as powder materials; it can also handle feedstock with a rather wide range of moisture content. The coal particles leaving the feeder drop by gravity into the spouted bed. The rotational speed of the table feeder was controlled by a variable speed motor through a reduction gear. Details of the table feeder are shown in Figure 3.4 and a photograph in Figure 3.5. The range of feed-rate for the coal size presently used (2.80-3.35 mm and 2.36-2.80 mm) at 24% moisture content wet basis was between 20 and 200 g/min. The calibration curve of this coal feeder is shown in Appendix 2. The sensitivity of coal feedrate to coal moisture content is illustrated in Figure A3 of Appendix 3. o o ~ I A 70 «--o 51 o CO o A—A Figure 3.4 Schematic diagram of the rotary table feeder. Figure 3.5 Photograph of the rotary table feeder. 18 3.2.3 Screen separator In order to recover particles entrained to the top of the bed, a screen separator was used. This separator had a low pressure drop and showed no secondary comminution. A sketch of the separator is shown in Figure 3.6 and its photograph in Figure 3.7. The top part of the filter had a screen area of about 0.138 m J and was made of 100 pm stainless steel sieve material. The superficial air velocity through the filter was less than 0.18 m/sec. Figure 3.6 Schematic diagram of the screen separator. Figure 3.7 Photograph of the screen separator. 19 3.2.4 Static insert A special static insert was designed and used to accentuate the size reduction by providing additional surface for attrition and impaction in the main comminution zone. This insert was in-stalled in the conical section of the spouted bed along the axis of the spout (See Figure 3.8.). A photograph of the insert is shown in Figure 3.9. It was employed in several experiments in which no glass beads were used as grmding aid. A design drawing is shown in Figure 3.10. The design characteristics of the above pieces of equipment are listed in Table 3.1. 3 3 The particles used 3.3.1 Glass Beads 6 mm glass beads manufactured by Fisher Scientific Co. were used as a dynamic grinding aid. Their true density was 2.69 g/cm3 and bulk density 1.595 g/cm3 (as given by the manufacturer). After an initial break-in period in which the bead surface was slightly roughened, no noticeable weight loss was subsequently found after each experiment. 3.3.2 Coal Feed-stock The sub-bituminous coal used in all the experiments came from the Forestburg colliery of AlbertaPowerLtd.. It was crushed and sieved to obtain a narrowly sized feedstock (through 3.35 mm sieve and retained on 2.80 mm). For those experiments with the static insert, the coal feed particles were 2.36-2.80 mm in size. Table 3.2 lists the properties of the coal. The moisture content of sieved coal was carefully controlled at -24% (wet basis) because any variation in moisture could affect the experimental results. Nearly 90 to 92% of the coal moisture was on the surface of the particles as shipped. When the coal was crushed, the resulting particles belonged partly to the original surface and partly to the original kernels with their very different moisture contents. The only way to control the moisture to a definite value was to mix the particles well and to seal them in a barrel for two or three days, after which the air and the particles in the barrel were in moisture equilibrium. A sample analysis of the coal particle moisture content was -24% (wet basis). A plastic barrel with internal mixing vanes and a well sealed lid was used as storage conditioner. The barrel was rolled on its side to ensure that the coal was evenly rnixed before being taken out as feedstock. A discussion on the selection and properties of coal is included in Appendix 3. The bulk density of Forestburg coal was measured by partially filling a 250 cm3 graduate cylinder with a known weight of coal. This cylinder was inverted with its open end covered and was then quickly reinverted again to its original position. The volume occupied by the coal after this Inserting procedure was recorded and used to calculate the bulk density. This method has been used by other workers (e.g., Lim, 1975). The loosely packed bulk porosity was determined from the true density and bulk density of the particles. The angle of repose of the particles was measured as the angle formed between a horizontal plane and the sloping line extending along the face of a heap formed by pouring the coal particles Figure 3.10 Schematic diagram of the static insert. Table 3.1 Particulars of the equipment. Spouted bed column Diameter Height Cone Angle Inlet orifice Outlet diameter Material I.D. 152 mm - 1.8 m 30* opening at 20 mm I.D. 75 mm brass, glass and plexiglass Surge tank Diameter Length Material I.D. 600 mm 750 mm stainless steel Preheater Type : electrical heater, three sections in series. Capacity : 0.9x0.66x0.4 m3 Power : 9kW Heating pipe diameter: 20 mm Heating pipe length : 800 mm Coal hopper Diameter Height Cone Angle Material I.D. 120 mm 450 mm 15* plexiglass Coal feeder Type Table Diameter Height Material Feed capacity Screen separator Diameter Height Filter area Material rotary table feeder 100 mm 200 m stainless steel 1.2-12 kg/hr I.D. 420 mm -800 mm 0.138 m2 stainless steel Cyclone Diameter : I.D. 150 mm Cylinder height : 320 mm Cone height : 300 mm Static Insert Height Top diameter Bottom diameter Material 180 mm 152 mm 20 mm. spring-steel 22 onto a horizontal surface. The coal particle heap was formed by natural means. The moisture content of the coal was measured before and after crushing. A sample of 5 grams was used in each determination and dried in the oven for one hour at 100-110°C. An aluminum weighing dish was used to contain the sample. The weight loss was used to calculate the moisture content The weight was measured using an electronic analytical balance. The smallest unit on this balance was 0.0001 g. Table 3.2 Data on specific properties of the coal Particles size: before comminution : 2.80-3.35 mm after comminution Density Bulk density Angle of repose Moisture content before drying after (2.36-2.80 mm with insert) 0.125-1.4 mm 1.35 Mg/m>* 0.688 Mg/m' 33.7° -24% =9% The true density of the Forestburg coal as given by General Testing Lab. 2 3 4. EXPERIMENTAL CONDITIONS AND TECHNIQUES A period of debugging and preliminary tests were necessary in order to find the limits of the set-up and to establish a good experimental methodology within these limits. These tests included consideration of the initial moisture content and particle size, the weight ratio of coal to glass-beads, the drying characteristics of the coal, the method of feeding, the determination of spouting velocity and a suitable drying temperature. The key parameters in this situation of combined comminution and drying are the spouting velocity, the drying temperature and the structure of the spouted bed. The Umits and the key parameters were determined at room and at elevated (50-105°C) temperatures. 4.1 Spouting velocity The most critical key parameter of comminution and drying in a spouted bed is the spouting velocity. Part of the velocity related data that were determined during the debugging period and during the preliminary tests are shown in Table 4.1. In these experiments the inlet velocity through the orifice was always kept at the same value. In order to maintain a constant inlet velocity regardless of the inlet temperature, the air flowrate was adjusted upstream of the heater. The air flowrates at different inlet temperatures are shown in Appendix 5. The minimum spouting velocity measured for the mixture of glass beads and coal (of 2.8-3.35 mm size fraction) was 1.16 m/s (See Figure 4.1). During the experiments, U/Ums for this rnixture was sustained at 1.53. When the insert was used with coal of2.36-2.80 mm size fraction (which has a Ums of 0.88-0.90 m/sec, see Figure 4.2), the operating value of U/Ums was maintained at 2. Table 4.1 Spouting velocity and related data. Mass flowrate of air 2.18 kg/nun Air flowrate 1.92 m'/min Spouted orifice diameter 20 mm Velocity of gas through the orifice 102 m/s Superficial gas velocity 1.78 m/s Minimum spouting velocity (measured) 1.16 m/s U/Ums 1.53 4.2 Drying of Forestburg coal The moisture present in coal exists in two different forms. The moisture held by physical forces (in the capillary holes and cracks) and by chemical forces (such as water of crystallization) within the coal structure is considered bound moisture. The bound moisture in coal (in this study all the moisture contents are expressed on a wet basis unless otherwise stated) is generally around 10-11% of the total moisture content, of which the water of crystallization, which is approximately 3-Figure 4.1 2.80-3.35 m m coal & glass beads: photo at rmnimum spouting velocity. Figure 4.2 With a static insert, 2.36-2.80 mm coal: photo at minimum spouting velocity. 2 5 5% of the total moisture, is hard to remove. The unbound moisture of coal mainly covers the surface of the particles and its value is around 90% of the total. In this work, the moisture content of coal particles was reduced from =24% to =9%. Coal particles with =9% moisture content are generally suitable for coal combustion or gasification and for trouble-free solids feeding. Different coal types may exhibit different drying characteristics. Therefore, in order to determine the specific drying characteristics of the present coal particles, preliminary studies on drying of coal particles were carried out. The drying curves for Forestburg coal particles were collected using a laboratory convective dryer, the details of which are shown in Appendix 4. Figure 4.3 shows the drying curves measured and the corresponding drying condition is listed in Table 4.2. Figure 4.3 shows that, even with an air temperature below 50° C, the surface moisture of coal can be removed with ease. The drying curves of the same type of coal obtained through thermo-gravimetric analysis are shown in Figure 4.4 (measured by Shanghai Research Institute of Chemical Industry, China). In the chemical industry, waste gas or spent steam can be used to heat up the air to 110-150°C. Therefore, the inlet air temperatures were chosen to be lower than 110°C for the main experiments. Table 4.2 Drying conditions in the convective dryer. Temperature Air flowrate Moisture content (M.C.) of coal: at the start final Total weight of coal Drying time Coal particle size 32-33°C, 50°C 3.94 m/sec =63% =10% 10 g 26 min (at 32-33°C) 10 min (at 50°C) 2.80-3.35 mm 43 Coal and inerts loading There are two test modes of tests in these experiments. In the first mode a certain quantity of coal particles mixed at a fixed ratio with glass beads (or coal particles only) was carefully put into the bed. The initial size of coal particles was always kept the same. The coal particles were crushed and discharged continuously during the process, but no coal feed was added, which caused the value of the bed holdup to decrease with the operating time. This mode is termed the semi-batch mode and was used to measure both the quantity and the particle size distribution of the product, as well as the bed holdup, at different moments after the initial start. In the second mode, the bed holdup as prepared in the related semi-batch mode remained inside the bed. When the spouting air entered the bed, the coal feeder was started. During the entire operating time the quantity of holdup is almost constant. The feeder and discharge run continuously. This is the continuous mode. Moisture content [kg moisture 1 kg dry solidsj A AirRJ l . 41.3% Coal size 2.8-335 mm Air temperature 32-33"C Air velocity 3.96 m/s Initial moisture content 63.76% 26 40.6% 2.8-3J5mm 50*C 3.96 m/s 63.54% Drying time (min) Figure 4.3 Drying curves of Forestburg coal. 0 6 Moisture content kg moisture ~\ .kg dry solids J 0 4 0-50*C, losses 835mg; 50-70*C. losses 10-55mg; 70-90'C. losses 13.50mg. 2 0 0 150 1 0 0 Particle surface temperature CC) Drying time (min) Figure 4.4 Forestburg coal drying curve measured by themiogravimctric analysis, dp = 2.80-3.35 mm, initial moisture content = 24%, T =-200*C. 27 The narrowly sized coal particles were 2.80 to 3.35 mm in diameter and the moisture content was controlled at =24%. The grinding aid used was 6 mm diameter glass beads and the quantity used in each experiment was 3 kg for all the runs. The quantity of coal was 1.2 kg per batch in every semi-batch mode and the coal holdup varied between 0.7 and 0.9 kg in the continuous mode. This quantity was determined based on the gas supply and spouting condition. The initial coal and glass holdups in the semi-batch experiments were selected to match those used earlier (Khoe et al., 1984). No glass beads were used as comminution aid for runs with the static insert. In the semi-batch mode with the insert, the quantity of coal per batch was 2.0-2.7 kg. The coal feed was 2.35-2.80 mm in diameter, slightly smaller than in the experiments with grinding aid, but with its moisture content the same (=24%). 4.4 Experimental conditions 4.4.1 Experimental conditions at room temperature The operating conditions and range of some variables are as follows: Operating temperature Pressure Air flowrate Superficial gas velocity Bed pressure drop Initial coal particles size Glass beads Holdup of coal Coal/Glass beads mass ratio Coal moisture content 20°C Atmospheric 1.93 m'/min (operating state) 1.78 m/s (operating state) 1250-1300 mm ELO 2.80-3.35 mm 2.36-2.80 mm (with insert) : 6 mm diameter (3 kg) : Semi-Batch, Initial 1.2 kg (dry basis) Continuous, =0.7-0.9 kg (dry basis) Continuous, (with insert) =2 kg (dry basis) : Semi-batch, 0.4 Continuous, 0.23-0.30 : Semi-batch, initial = 24% Feedrate Continuous, feed=24% =27 g/min (with products discharge from the top) =47 g/min (with products discharge from the bottom) 55-68 g/min (with insert and top product discharge) Minimum spouting velocity for: 1.16 m/s (measured) 1.53 (experimental setting) 0.88-0.90 m/sec (measured) ~2 (experimental setting) Glass beads and coal mixture U/Ums Coal only (using static insert) U/Ums 28 4.4.2 Experimental conditions at elevated temperatures The operating conditions and range of some variables are as follows: Operating temperature Pressure Air flowrate Superficial gas velocity Bed pressure drop Initial coal particle size Glass Beads Holdup of Coal Coal/Glass beads mass ratio Coal Moisture Content 50-105'C Atmospheric 1.93 m'/min (operating state) 1.78 m/s (operating state) 1200-1300 mm H p 2.80-3.35 mm 2.36-2.80 mm (with insert) : 6 mm diameter (3 kg) : Semi-batch, Initial 1.2 kg (dry basis) Continuous, =0.7-0.9 kg (dry basis) Continuous, (with insert) 2.1-2.3 kg (dry basis) : Semi-batch, 0.4 Continuous, 0.23-0.30 : Semi-batch, initial =24% Continuous, feed =24% Feedrate : 54-102 g/min, increasing with the operating temperature Minimum Spouting velocity for: 1.16 m/s (measured) 1.53 (experimental setting) 0.88-0.90 m/s (measured) =2 (experimental setting) Glass beads and coal mixture U/Ums Coal only (using static insert) U/Ums 4.4.3 Extermination of the feedrate for a continuous run The diagram in Figure 4.5 shows the relation between a semi-batch and its related continuous run. It explains the novel method (as proposed by Khoe, 1987) of how to determine the feedrate of the continuous run which has the same operating parameters as the semi-batch. Considering the similarities between a batch run in a spouted bed and a ball mill, the effects of progressive grinding with time on the holdup size distribution will be equivalent to that in Figure 2.4. If the product is allowed to discharge as in a semi-batch process, then the weight of the cumulatively collected product will vary with time according to Figure 4.5.A. The initial production rate is relatively low, but as the particle surface of the holdup increases, and the comminution conditions become more violent as the bed height drops, the rate of product collection will steadily rise. The limitation of this rising production rate is the consistency of the spouted bed, the height of which will steadily become too low and ultimately cease to exist This will cause the instantaneous production rate to drop after a peak or a plateau has been reached, and the few particles left in a dilute bed are then difficult to grind (see Figure 4.5.B). 0 I , 1 0 Time (min) Figure 4.5 A diagram showing the relation between the semi-batch production rate and the required feedrate for continuous production starting with a fixed bed loading (after Khoe, 1987). Along with the changing values of the cumulatively collected product weight and the produc-tion rate, the size distribution of the collected product will also change as one can qualitatively deduce from Figure 2.4. Quantitatively, the size distribution of the product will vary depending on the choice of the grinding aid, the grid size covering the bottom discharge, the elutriation velocity of the top discharge and the spouting conditions. This is the main reason why for each set of operating conditions a semi-batch test is required to find the time span after start which will produce the acceptable product size distribution, such as point 1 or point 2 in Figure 4.5.B. Once the product 30 complies with the acceptable size distribution, its continuous production can be commenced by matching the instantaneous production rate at point 1 or point 2 with a continuous feedrate of equal magnitude. This wili ensure a steady state continuous production, depicted by the horizontal lines from point 1 or point 2 in Figure 4.5.B. Controllability of the continuous process is good in a range between points a and b, because of the ever changing production rate. The near constant rate such as seen between points b and c, however, can cause drifting and unwelcome variations in the bed height followed by other negative consequences. Therefore, with a near constant production rate such as this, a close watch on the bed level together with a few corrective adjustments on the feedrate might be required. The above described relation between a semi-batch run and its continuous counterpart can be seen in Figure 4.6 with run C-19-9 to C-19-9"' as the chosen example. A typical production rate during a semi-batch test is shown in Figure 4.7, which was constructed using data from run ST-2 up to run ST-2"'. Each of these runs has a five minute duration, after which the quantities and the size distribution of the holdup and the product are deterrnined. The earliest production rate recorded is therefore the one measured between time zero and five minutes, which is the average production rate at two and one half minutes. When the operation ran under continuous conditions, and all the operating parameters were controlled at a certain value, this represented a steady state of comminution for the spouted bed at room or elevated temperatures. Thus for the steady state at room temperature, the feedrate was controlled at a given value. The velocity of gas through the orifice and the carry-out velocity of the bed remained unchanged. The height of the bed was controlled by the feedrate. The total cumulative product and the losses were equal to the cumulative feed. The horizontal line in Figure 4.6 represents the comminution run under a steady state condition. At this condition the feedrate was almost unchanged. The production rate also remained nearly constant and close to the feedrate. The moisture content of the products were almost constant, and so were the size distribution of the holdup and the product at 30,45 and 60 minutes (See the data in Appendix 8). Therefore, if we could control the initial size distribution of the bed holdup, the feedrate, the bed height, the inlet spouting gas tempera-ture, the spouting velocity and the carry-out velocity, the spouted bed conjrninution could run con-tinuously at a steady state condition, and the production rate and product size distribution would thus be controlled. Continuous runs were performed for up to 2.5 mean residence times. Some continuous runs were performed independently of the semi-batch runs (See summary table on page 15b). 4.5 Experimental technique Coal forms a special kind of irregularly shaped particle, and consequently the experiments and their analysis must be handled with this understanding to obtain consistent data. The bed contents prior to any run must be prepared by gently rriixing coal and glass beads homogeneously and by inserting the mixture inside the bed carefully so as not to cause any crushing before the experiment. The relative humidity of inlet air was measured before each run. The gas flowrate was regulated and 31 Conditions in run C-19-9: T = 20*C Initial coal size 2.80-335 mm Spouted bed height 232-235 mm Prod. = Bottoms + Tops + Losses. 8 O i 1 • 1 • 1 • 1 • 1 • 1 Prod, rate (g/min) 6 0 4 o 2 0 (C-l9-9)Seni H-C.Stact-24-SUl M . C . E n d =18.84% . 1 (C-19-9*) F e e d > 4 7 . 3 0 9 / » i n M.C."24.241 ProJ . "=4S. 539/ " i n H . C . M 8 . 7 1 1 (C-19-9") Feed=47.169/oin H . C . - 2 4 . 7 6 * Prod.=46.21g/nin H.C.=18.26* (C-19-9") Feed>47 .2Sg/u in H.C.-25.034 p r o d . " 4 5 . 3 7 9 / u i o M.C.=17.74* O 1 o 20 3 0 4 O 5 0 6 0 Time after start (min) Figure 4.6 The production rate graph of a semi-batch and its related continuous run. (Average values in each 5 minute period). Prod, rate (g/min) 3 5 30 -25 -20 Run No. + ST-2 * ST-2' o ST-2" • ST-2" Time (min) 0-5 5-10 10-15 15-20 Conditions: T = 20*C Semi-batch Initial coal size 2.80-335 mm Initial coal M. .C 24.54% Product from top discharge 5 I O 15 20 25 Time after start (min) 30 Figure 4.7 Product rate changing with time in semi-batch run. 32 steadied at the operating value prior to the actual start of the experiment. The gas was passed through the by-pass pipe to avoid any coal-air contact during this period, in which the temperature was allowed to increase and reach the operating point Only after the gas flowrate and the temperature have reached a steady state was the three-way valve switched abruptly (=zero time) to allow the au-to enter the bed, and at the same time the coal feeder was started. The air entering the bed will spout the contents of the bed. With part of the products discharged from the four bottom outlets, which need to be opened at the same time, about 17 to 22% of particles with dp<0.75 mm were entrained by the air in the freeboard (IT). 152 mm) and collected as tops. Care was taken to monitor and keep the spouting flowrate constant at all times. The feedrate during the continuous runs was carefully monitored and sometimes corrected to keep the operating bed level unchanged. The pressure, pressure drop and temperature of the bed were recorded. The oudet gas moisture content was measured at steady state conditions. The product moisture content was measured immediately after each experiment and the product was sieved after the each run to find the particle size distribution. The results of these measurements, i.e. the coal moisture content, the relative humidity of the gas and the size distribution of the coal particles are shown in Appendix 6. 33 5. EXPERIMENTAL RESULTS AND DISCUSSION 5.1 The experiments results using glass beads as a dynamic grinding aid 5.1.1 The experimental results using combined bottom and top product discharge The results of continuous operation at steady state at various drying temperatures are shown in Figure 5.1. Increasing the inlet air temperature improves bom coal commmution and drying. The production rate and the final moisture content of coal using various drying conditions are listed in Table 5.1. o Total product rates • Product rates of dp=0.125-1.40 mm A Moisture content of products Run T No. C O C-19-9" 20 CH-8' 75 CH-9' 85 CH-7' 95 CH-5' 105 Figure 5.1 The results of continuous operation at different inlet air temperatures using top and bottom outlets. 34 Table 5.1 Results under various drying conditions using combined bottom and top product discharge. Spouting of coal and glass beads. Run Air Oper- Production Production M.C. of 0.5-1.0mm Under- Over- Mean No. temp- ating rate rate products size crushing crushing resi-erature time (total) (in terms of fraction rate rate dence dp=0.125- in product time 1.4 mm) C O (min) (g/min) (g/min) (%) (g/min) (g/min) (g/min) (min) C-19-9' 20 15 46.53 37.81 18.17 14.10 028 0.24 17.07 CH-81 75 6 84.54 71.41 1226-13.40 28.28 0.43 0.33 10.91 CH-9' 85 6 88.50 76.78 10.53-11.40 32.20 0.50 0.46 11.33 CH-7 95 6 123.16 105.01 7.90-9.90 48.42 0.65 0.64 5.95 CH-5' 105 15 106.43 98.99 822 41.% 0.28 0.23 7.65 The results of sieve analysis of the bed holdup in some semi-batch runs are shown in Figure 5.2, and related continuous runs in Figure 5.3. These two figures show the uniform trend of change in the size distribution of the bed holdup as function of temperature. At room temperature the size distributions of the holdup are almost the identical. With increasing inlet air temperture the size distribution mode of the holdup seems to move from dp=1.7 mm to dp =0.75 mm. This shows the increasing effectiveness of coal comminution in a spouted bed with increasing inlet air temperature. Figure 5.2 Sieve analysis of the bed holdup using several different inlet air temperatures; o^ minute semi-batch run (exception: 15 minutes for C-l 9-9), with combined top and bottom discharge. Spouting of coal and glass beads. 100 Wt% = total remaining coal holdup. (Mode can be determined from corresponding histogram, e.g. for Run C-19-9, the mode would be 1.7 mm.) 35 Run T Final Run T Final No. CC) M.C. No. C O M.C. (%) (%) C-19-9' 20 18.71 CH-5' 105 11.37 CH-8' 75 13.96 CH-5" 105 11.35 CH-9' 85 14.16 CH-6' 105 11.15 CH-7' 95 13.00 CH-6" 105 11.07 30 T Sieve size (mm) Figure 5.3 Sieve analysis of the bed holdup using several different inlet air temperatures; continuous run, with combined top and bottom discharge. Spouting of coal and glass beads. 100 Wt% = total remaining coal holdup. The product main size-range falls between 0.125 mm and 1.4 mm. The bottom product size-fraction of 0.75 mm particles increases from 29.76 Wt% at 20°C to 40 Wt% at 105°C (as shown in Figure 5.4.). From Figure 5.1 and the data in Table 5.1 it is evident that increasing the temperature is advantageous for the comminution. Because of the increasing production at 105°C, the four bottom discharge openings, which are covered with grids, proved to be insufficiently sized. Part of the grids tended to get blocked by the particles, resulting in a smaller production rate at 105°C (Figure 5.1) than at 95°C. Therefore, bottom discharge was only suitable for room or intermediate temperatures. 36 0 Xaasa^S 1 1 1 1 —5*n X X X 0.106 0.125 025 0.5 1 1.4 2 2.36 2.8 3.35 Sieve size [mm] Figure 5.4 Sieve analysis of the bottom product using several different inlet air temperatures; continuous run, with combined top and bottom discharge. Spouting of coal and glass beads. 100 Wt% = total coal feed for run. 5.1.2 The experimental results using only the top product discharge In these experiments only the top discharge was used and the entrainment velocity was util-ized to control the product size. Therefore, the outlet pipe diameter from the freeboard was changed from 152 mm I.D. to 75 mm I.D. (see Figure 3.4). Table 5.2 summarizes the experimental data at room and elevated inlet air temperatures. The final moisture content and the production rates with inlet air temperatures varying from Table 5.2 Results under various drying conditions with top discharge only. Spouting of coal and glass beads. Run Air Run Feed Produc- Produc- M.C. 0.5-1.0mm Under- Over- Mean No. temp- time rate tion tion rate of size crushing crushing resi-erature rale (in terms of pro- fraction rate rate dence (total) dp=0.125- ducts in product time 1.4 mm) CQ (min) (g/min) (g/min) (g/min) (%) Oi/min) (g/min) 0i/min) (min) TC-3 20 20 27.10 26.09 20.92 16.93 9.91 0.32 0.175 29.40 TCH-6 50 30 55.43 54.68 46.03 12.25 29.73 0.48 1.40 14.08 TCH-5 75 25 68.25 67.97 58.63 9.20 37.38 0.17 1.80 12.05 TCH-4 95 25 75.40 71.40 59.96 8.86 39.12 0.55 0.71 12.15 TCH-4' 95 25 75.30 75.14 57.82 8.10 39.48 0.40 2.15 11.60 TCH-7 95 22.5 92.25 86.05 72.80 8.20 48.41 0.77 2.80 10.27 37 20*C to 95*C are shown in Figure 5.5. The production rate increased by a factor of 3 and the mean residence time of the coal decreased by a factor of 2 to 3, when the air inlet temperature was increased from room to 95*C. At 95*C the product moisture content was down to 8.1 %, as compared to 16.93% moisture content at room temperature. Figure 5.5 shows that using top discharge for continuous operation at various inlet air temperatures gave more reasonable results than using it in combination with bottom discharge (Figure 5.1). The products size was controlled by the carry-out velocity and the top discharge remained clear. Figure 5.6 and Figure 5.7 show the results of sieve analysis of the holdup and of the product, Run No. TC-3 TCH-6 TCH-5 TCH-4* Temp. C O 20 50 75 95 o Total product rates • Product rates of dp=0.125-1.40 mm A Moisture content of products Moisture content (%) 2 5 2 0 -6 0 1 0 0 8 0 4 0 Produc-tion rate (g/min) o 2 0 4 0 6 0 8 0 1 0 0 1 2 0 Temperature (°C) Figure 5.5 The results of continuous operation at different inlet air temperatures (using top discharge only). respectively, in the semi-batch runs as a function of time (up to 25 minutes). The sieve analysis of the holdup under continuous operating conditions are shown in Figure 5.8. When the inlet air temperature increased from 20*C to 95*C the mode value of the size distribution curve moved from 1.7 mm to 0.75 mm. Figure 5.8 also shows that the size distributions of the holdup at 75*C and at 95*C are almost identical. Figure 5.9 indicates that, with the inlet air temperature ranging from 50*C 50 45 40 35 + 30 Wt% retained 25 on 20 15 --10 --5 0 • 0.106 0.125 0.25 0.5 1 1.4 2 Sieve size (mm) 38 Run Time Final (min) E C . (%) ST-2 0- 5 22.28 o- ST-2' 5-10 19.88 m- ST-2" 10-15 18.70 r> ST-2"' 15-20 16.65 3.35 Figure 5.6 Sieve analysis of the bed holdup at several intermediate periods during an experiment (using top discharge only). Semi-batch run, initial coal size: 2.80-3.35 mm and initial M.C.: 24.54%. T=20°C. 100 Wt% = initial coal holdup. Run H 1 ,-~^Q 0.106 0.125 0.25 0.5 1 o-1.4 Time (min) ••- ST-2 0- 5 o- ST-21 5-10 • - ST-2" 10-15 n- ST-2'" 15-20 2.36 2.8 3.35 Final M.C. (%) 22.28 19.88 18.70 16.65 Sieve size (mm) Figure 5.7 Sieve analysis of the product at several intermediate periods during an experiment (using top discharge only). Semi-batch run, initial coal size: 2.80-3.35 mm and initial M.C.: 24.54%. T=20°C. 100 Wt% s initial coal holdup. 39 30 T 25 -. 20 + Wt% retained 15 - • on 10 + Run Temp. No. CC) -•- TC-3 20 o- TCH-6 50 •~ TCH-5 75 TCH-4 95 TCH-4' 95 -A- TCH-7 95 0.106 0.125 0.25 1 1.4 Sieve size (mm) 2.36 2.8 3.35 Figure 5.8 Sieve analysis of the bed holdup from continuous runs at room and at elevated temperatures (using top discharge only). Initial coal size: 2.80-3.35 mm. Spouting coal and glass beads. 100 Wt% = total remaining coal holdup. to 95°C, the product size distribution curves are basically identical. With the temperature increasing from 20°C to 50°C, 75°C and 95°C the product (dp=0.5-1.0 mm) weight percentage increases from 38% to 53%, and the over-crushing rate (defined as the wt% of particles having dp < 0.125 mm ) remains less than 3%. Figure 5.10 shows the various steady state moisture contents of the product with increasing inlet air temperature and time. 0.106 0.125 0.25 0.5 1 1.4 2 2.36 2.8 3.35 Sieve size (mm) Figure 5.9 Sieve analysis of the product from continuous runs at room and at elevated temperatures (using top discharge only). Initial coal size: 2.80-3.35 mm. Spouting coal and glass beads. 100 Wt% = total coal feed for run. 40 25 Run No. o TC-3 A TCH-6 o TCH-5 • TCH-4' Temp. CC) 20 50 75 95 20 -5 O 0 10 15 2 0 25 Drying time (min) 30 Figure 5.10 Moisture content of the product as a function of operating time, at different inlet air temperatures (top discharge only). Spouting coal and glass beads. 5.2 The experimental results using a specially designed static grinding aid in conjunction with top product discharge A specially designed insert to enhance corrnrunution (shown in Figure 3.9) was installed on the bottom cone of the spouted bed. In these experiments 2.36-2.80 mm coal particles were used as a feedstock as a substitute for the previously used fraction of 2.8-3.35 mm, which was out of stock. The initial moisture content of this coal was =24%. Figures 5.11 and 5.12 show the results of sieve analysis on the holdup and product in the semi-batch run which was extended up to 25 minutes. The results of the continuous run are given in Table 5.3 and Table 5.4, and the graphs in Figure 5.13 show the change of production rate and product 41 80 j 70 -• 60 -• 50 --Wt% retained 40 -• on 30 -• 20 -• 10 -• Run No. SCI-1 sci-r sci-r sci-r SCI-l"" Time (min) 0-5 5-10 10-15 15-20 20-25 Conditions: T = 20*C Semi-batch Insert used Initial coal size 236-2.80 mm Initial coal M..C. 2324 % Product from top discharge only ••- SCI-1 O- SCI-1' •- SCI-1" sci-r A- SCI-1"" 0 B 0.106 0.125 3.35 Sieve size (mm) Figure 5.11 Sieve analysis of the bed holdup at different operating times. 100 Wt% = initial coal holdup. Run No. Time Conditions: T = 20*C Semi-batch Insert used Initial coal size 236-2.80 mm Initial coal M..C. 23.24 % Product from top discharge only SCI-1 o- SCI-1' •- sa-r n- sa-r •A- sa-i" 0.106 0.125 0.25 0.5 1 1.4 2 Sieve size (mm) 3.35 Figure 5.12 Sieve analysis of the product at different operating times. 100 Wt% = initial coal holdup. 42 moisture content with time. The particle sieve analysis of the holdup and the product at different temperatures are shown in Figure 5.14. From this figure it is obvious that the modes of the size distribution spectra of the holdup are shifting towards smaller sizes, starting at 2.1 mm for the semi-batch operation through 1.7 mm for continuous operation, both at room temperature down to 1.2 mm at 95*C, in a continuous run. The mode of the product size distribution spectra is at dp=0.75 mm. Increasing the inlet air temperature from room temperature to 95°C caused the weight percentage of the particle fraction between 0.5 and 1.0 mm (with the average at dp=0.75 mm) to increase from 40% to 66%. The production rate was increased from 70 g/min to 131 g/min as a result of the increased temperature. The production rate for the range of dp=0.125-1.4 mm was increased from 52 g/min to 128 g/min at the same time as the mean residence time of the solids (irrespective of size) was decreased from 30 min to 17.5 min. There was not enough coal left over which had the same properties as the one used in this run, Table 5.3 Average results of continuous runs at various temperatures using the special insert and top discharge. Run Air Run Feed Produc- Production M.C. of 0.5-1.0mm Under- Over- Mean No. temp- time rate tion rate products size crush- crushing resi-erature rate (in terms fraction ing rate dence (total) ofdp=0.125- in product rate time 1.4 mm) CC) (min) (g/min) (g/min) (g/min) (%) (g/min) (g/min) (g/min) (min) CI-1 23 20 55.70 56.00 48.55 18.47 23.97 2.01 0.95 39.55 CI-2 23 32 70.58 64.39 56.15 17.87 30.18 3.36 1.78 32.70 HCI-1 95 30 121.99 114.98 104.78 11.53 76.15 0.37 2.27 20.00 Table 5.4 Results at several intermediate periods during the continuous runs (CI-2 at 20°C and HCI-1 at 95°C) using the special insert and top discharge. Run Product moist. Production Average Mean residence 100% holdup time content rate feed rate time 20*C 95*C 20*C 95'C 20*C 95*C 20*C 95-C 20*C 95*C (min) (%) (%) (g/min) (g/min) (g/min) (g/min) (min) (min) (g) (g) 5 17.87 14.41 5136 54.93 70.58 121.99 41.00 41.87 2105 2300 10 17.87 11.77 58.76 105.81 35.83 21.74 15 17.87 11.46 66.68 119.08 30.58 19.31 20 17.87 11.92 70.08 129.07 30.09 17.82 25 17.87 11.24 6929 130.81 30.39 17.58 30 17.87 11.25 69.99 131.01 30.08 17.56 Initial coal size: dp = 2.36-2.80 mm Initial coal M.C.: = 24 % Urns = 0.88-0.90 m/s U/Ums = 2 Spouted bed height = 275 mm 43 3 0 Moisture content (%) 1 5 0 1 2 5 1 0 0 - 7 5 5 0 2 5 Produc-tion rate (g/min) O 5 1 0 15 2 0 2 5 3 0 Drying time (min) Figure 5.13 Product moisture content and production rates at several periods during continuous experiments at 20°C and 95"C (with insert and top discharge). Time Production rates dp=0.10-2.58 mm dp=0.20-1.20 CI-2 HCI-1 HCI-1 20'C 95°C 95*C • . • A O • (min) (g/min) (g/min) (g/min) 5 51.36 54.93 52.16 10 58.76 105.81 100.24 15 66.68 119.08 114.45 20 70.08 129.07 126.30 25 69.29 130.81 128.09 30 69.99 131.01 128.18 44 Run No. Mode Temp. CC) SCI-l"' semi-batch 21.5 CI-2 continuous 24 HCI-1 continuous 95 Conditions: Initial coal size 2.36-2.80 mm Insert used Product from top discharge only 70 T Wt% retained on 0.11 0.13 0.25 0.5 1 1.4 2 Sieve size (mm) ss a 2.36 2.8 3.35 ••- SCI-1'" holdup o- SCI-1'" product CI-2 CI-2 HCI-1 -A- HCI-1 holdup product holdup product Figure 5.14 Sieve analysis of the bed holdup and product, at various temperatures. For open points, 100 Wt% s total feed for run; for solid points, 100 Wt% = total remaining coal holdup. to make other experiments. Nevertheless, these results show that using an insert in a spouted bed can gready improve its cormninution capability. The holdup of coal using the insert was 2 to 3 times greater than in the case of glass beads used as grinding aid. If the product moisture contents, such as the ones obtained in these experiments, need to be reduced further, e.g. from an average of 11% down to 9%, then the required setting of the inlet air temperature can be estimated by calculation. The calculation in Appendix 7 shows that the temperature should be set between 105 to 110°C. ! 45 5.3 Discussion 1. The combination of bottom and top product discharge was originally meant for separating different sizes, the coarse product from the bottom oudet and the fines from the top. However, this combination has some disadvantages. They are: a. The residence time of particles varies widely, b. The size distribution of the coarse product can only be changed by changing the size of the grid covering the four outlet openings in the bottom. 2. The results using only the top discharge show that increasing the inlet air temperature was beneficial for coal comtrunution. The nearly identical size distributions of the holdups at 75 and at 95°C air inlet, and the differences found in the comminution rate and the mean residence time suggest the following: using the spouting velocities applied in these experiments, the required product size distribution can be reached by adjusting the feedrate while maintaining the size distribution of the hold-up and the bed level constant The disadvantage of using glass beads as grinding aid is that they are practical only on a small or laboratory scale. Spouting glass beads is an energy wasting process, and is therefore less than ideal for industrial or scaled-up application. 3. The insert, used as a static grinding aid in the spouted bed, can gready improve the commi-nution effects. The advantage of an insert as grinding aid is that it can be used not only on a laboratory scale but also on an industrial scale. The mechanical energy utilization in a spouted bed equipped with a static insert is more favourable than with inert particles as grinding aid. 4. The spouted bed performs well as a grinding device for a gas-solid system at elevated temperatures, in which coal comminution and drying of unbound moisture occurs simultaneously. Calculations, using the experimental results, show that the evaporation intensity, the thermal effi-ciency and the grinding intensity were relatively high (see Table 5.5). Table 5.5 The results of the spouted bed comminution at elevated temperature with glass beads as grinding aid compared to the results with the insert Run Temperature Coal Air humidity Run Bed Produc- Load- Evapo- Ther- Grind-No. Air Bed Prod, prod. In Out time height tion ing ration mal ing In Out M.C. rate quan- inten- effi- inten-tity sity* ciency sity* C Q C Q (*C) (*C) (%) kgH2Q (min) (mm) (kg/hr) (g) kg_H20 (%) kg coal kg dry air m\h m\h TCH-5 75 41 47 36 9.2 0.0025 0.0130 25 220 4.08 819.0 88.28 40.10 453.3 TCH-4* 95 47 55 42 8.1 0.0050 0.0160 25 220 4.50 871.2 104.60 3928 500.0 TCH-7 95 49 56 46 8.2 0.0070 0.0195 22.5 230 5.40 883.6 124.70 46.96 600.0 (Coal feed size: 2.80-3.35 mm; 3 kg glass beads) HCI-1 95 40 45 32 11.53 0.0070 0.0220 30 275 7.80 2300 141.10 53.00 866.7 ((Coal feed size: 2.36-2.80 mm; insert) *Based on chamber volume = 0.009 m1 (= volume of spouting chamber to fountain top) Inlet air flow : 1.91-1.92 m'/min (held constant at all temperatures) M.C. of coal feed : = 24% Thermal efficiency defined as: [heat of moisture evaporation + heat to increase the coal particle temperature] / [inlet air enthalpy] Reference conditions: air and initial coal at room conditions 46 6. DISCUSSION ON THE SIZE REDUCTION MECHANISM The size reduction mechanism in a spouted bed can be described as follows. A stream of high speed gas coming from the orifice at the bottom of the cone forms a high speed jeL At elevated temperature the jet forms a high temperature region around it. Heat transfer and size reduction mainly happen in this region where coal particles and grinding aid (glass beads or static insert) move relative to each other and are subjected to mechanical stresses which result in simultaneous comminution and drying. The particles are broken by being subjected to compression, to shear forces and to impaction effects. This lower part of the bed will further be referred to as the comminution zone. So far there has been no literature which gives details on the relationship between the relevant forces and the size reduction mechanism in spouted beds. Therefore, a general qualitative approach will be attempted in the following paragraphs. The factors that affect the size reduction process in a spouted bed can be divided into five categories: 1. the properties of the material to be reduced 2. the characteristics of the grinding aid 3. the properties of the spouting fluid 4. the size and settings of the spouted bed 5. operating time There are of the dozens of variables related to these categories of which only the following have been varied in the present experiments: air temperature, feedrate, grinding aid and operating time. Variables such as: spouting velocity, initial particle size and moisture content, bed depth, carry-out velocity, and the size of the spouted bed have been deliberately kept constant in order to follow a systematic experimental approach. 6.1 Comminution mechanism at room temperature The comminution mechanism in the spouted bed can be described as follows. The mcoming high speed gas stream spouts the coal particles and glass beads (or the coal particles through and against the insert) and transfers energy to them. Since coal and glass particles have different masses, their speeds and momentums are different These differences cause the two kinds of particles to collide, whereupon the coal particles suffer impaction, shear and friction. These effects mainly occur in the comminution zone. When the insert is used, the coal particles are entrained by the high speed spouting fluid, and caused to impact and shearrepeatedly (KhoeetaL, 1983) on a specially shaped fixed structure (insert) in the bottom part of the spouted bed. On the average, the relative velocity between the coal particles and the insert is larger than the relative velocity between the coal particles and the glass beads, and therefore the insert is a more effective aid than the glass beads. Comparison of results using glass beads with those using the insert at room temperature shows that the size distribution of the products are very similar (see Figure 6.1). The production rate, 4 7 Wt% retained on 20 T = 20-C •- CI-2 (insert) O- TC-3 (glass beads) 0 P 1 1 1 1 h 0.106 0.125 0.25 03 1 1.4 2 Sieve size (mm) Figure 6.1 Sieve analysis of products at room temperature, continuous runs. 100 Wt% = total coal feed for run. however, was 2 to 3 times higher when the insert was used. The experimental data are listed in Table 6.1. From these data, which were measured at the same spouting velocity, it can be concluded that comminution with the insert is better than with the glass beads. Table 6.1 Weight distributions of comminution products in continuous runs at room temperature, with glass beads (run TC-3) and with static insert (run CI-2). dp dp avg. TC-3 CI-2 Sieve size Products Products (mm) (mm) (g) (Wt%) (g) (Wt%) 335-2.80 3.08 0 0 0 0 2.80-236 2.58 2.16 0.41 13.06 035 236-2.00 2.18 423 0.81 54.12 228 2.00-1.40 1.70 17.69 338 116.13 4.90 1.40-1.00 1.20 50.18 9.61 259.20 10.93 1.00-030 0.75 1982 9 38.00 965.85 40.72 030-025 0375 141.63 27.14 498.45 2523 025-0.125 0.188 63.63 12.19 18233 7.69 .125-0.106 0.116 130 0.29 34.25 1.44 < 0.106 0.053 2.00 038 1.40 0.06 Conditions TC-3 CI-2 Operating temperature (°Q 20 20 Operating time (min) 20 32 Feedrate (g/min) 27.1 70.6 Initial coal M.C. (%) 243 24.0 Initial coal size (screen size) (mm) 335-Z8 2.8-236 Coal product M.C. (%) 16.9 17.9 Production rate(.125<dp<1.4 mm) (g/min) 20.9 56.2 Total production rate (g/min) 26.1 64.4 Air flowrate at orifice (m'/min) 1.92 1.92 Spouted bed height (mm) 228 275 Urns (m/s) 1.16 0.88-0.90 U/Ums 133 2.0 Mean residence time (min) 293 32.7 Coal holdup (g) 767.2 2105.6 48 The process of size reduction of coal particles from the initial size down to the fines can be followed by monitoring the size distribution of the holdup during a semi-batch run. During this period, no steady state prevailed and the production rate recorded at any moment after the initial start was an instantaneous rate. The transformation of the semi-batch into a continuous run occurred when the instantaneous production rate, which is equal to the instantaneous disappearance rate of the original size, was converted into a continuous production rate by balancing the instantaneous disappearance rate with a continuous feed of equal rate (Khoe, 1987). When coal is first fed continuously into the bed, the small number of particles of the initial size thus introduced relative to the number already in the bed will not noticeably change the holdup size distribution because they immediately start to join the size reduction process experienced before by the bed holdup during the semi-batch period, and will subsequently be discharged as products. Therefore, with correct handling of the experiment, the size distribution of the holdup will remain unaltered. Typical results of sieve analysis of the holdup during continuous runs C-19-9' to C-19-9'" are shown in Figure 6.2. 0.106 0.125 0.25 0.5 1 1.4 2 236 2.8 335 Sieve size (mm) Figure 6.2 Sieve analysis of initial and final bed holdup at room temperature, continuous runs. 100 Wt% = total remaining coal holdup. 6.2 Comminution mechanism at elevated temperature The gas is initially heated and thereby increased in its thermal energy. The heated gas coming in contact with the surface of the coal particles results in dryingof the coal. In turn, the dried particle surfaces have an increased brittleness, which results in them being more readily damaged. When the temperature rises, the drying rate is increased, and with it the rate of size reduction also increases. The present experiments showed that this rate could increase several fold. From Figure 5.9 and 5.14 one can see the difference between the product size distribution at room and at elevated temperature. 49 The high temperature thus helps the size reduction process. On the other hand, damaging the dried layers will expose new underlying layers which are still wet and simultaneously increase the total surface, which causes the drying rate to increase. Drying and corrirriinution processes in the spouted bed thus occur simultaneously and mutually intensify each other, ie. they are synergistic. Since size reduction and heat transfer mainly happen in the comnunution zone, the size reduction effect is small in the greater part of the annulus. However, after the outer layer of each particles is rapidly (see Figure 2.2) heated up in the comminution zone, each particle will travel further up the spout and down the annulus, during which the heat gained is used to evaporate the moisture and a longer time period is allowed for mass transfer (Khoe and Brakel, 1980). When the particles pass the comminution zone a second time, the dry and brittle outer layers will be damaged and new moist layers will be exposed, which superficially turns the situation back to that of the first cycle. The difference lies in the fact that the second cycle ends up with a multiple of the initial particle surface. When the particle diameter is reduced to a certain size for which its fall velocity equals the air exhaust velocity, it will be elutriated by the airstream and carried out of the bed. In the case of a combined top and bottom discharge, the particles will tend to leave the bed as soon as their size equals the size of the grid covering the four bottom discharge openings. Figure 6.3 shows the sieve analysis Sieve size (mm) Figure 6.3 Sieve analysis of products at elevated temperature, continuous runs. 100 Wt% = total coal feed for run. of the products using glass beads compared to the one using a static insert to aid size reduction at elevated temperatures. The experimental data are listed in Table 6.2. 50 Table 6.2 Weight distributions of comminution products in continuous runs at elevated temperatures, with glass beads (run TCH-7) and with static insert (run HCI-1). dp dp avg TCH-7 HCI-1 Sieve size Products Products (mm) (mm) (g) (Wt%) (g) (Wt%) 335-2.80 3.08 0 0 - -2.80-236 238 0 0 0 0 236-2.00 2.18 173 0.86 11.41 033 2.00-1.40 1.70 3524 1.74 26.85 0.77 1.40-1.00 120 90.25 4.47 11421 33 1.00-030 0.75 108930 53.91 2284.48 65.94 030-025 0375 43273 21.41 56338 1626 025-0.125 0.188 150.18 7.43 285.03 823 .125-0.106 0.116 59.26 2.93 63.11 1.82 < 0.106 0.053 3.66 0.18 5.10 0.15 Conditions TCH-7 HCI-1 Operating temperature CC) 95 95 Operating rime (min) 223 30.0 Feed rate (g/min) 923 122.0 Initial coal M.C. (%) 23.6 24.0 Initial coal size (screen size) (mm) 335-280 2.80-236 Coal product M.C. (%) 8.2 113 Production rate (.125<dp<l .4 mm) (g/min) 72.8 104.8 Total production rate (g/min) 86.1 115.0 Air flowrate at orifice (m'/min) 1.92 1.92 Spouted bed height (mm) 230 275 Urns (m/s) 1.16 0.88-0.90 U/Ums 133 2.00 Mean residence time (min) 103 20.0 Coal holdup (g) 883.9 2300.0 From Figure 6.4 and 6.5 one can see that, for the same initial particle size (dp=2.5-3 mm) and the same air effluent velocity, one can obtain approximately the same separation between the product and the holdup. The mode value of the product is 0.75 mm. 60 T o Sieve size (mm) Figure 6.4 Sieve analysis of holdup and products, continuous runs at elevated temperatures using glass beads as grinding aid. For open points, 100 Wt% = total coal feed for run; for solid points, 100 Wt% = total remaining coal holdup. Figure 6.5 Sieve analysis of holdup and products, continuous runs at elevated temperatures using metal insert as grinding aid. For open points, 100 Wt% = total coal feed for run; for solid points, 100 Wt% = total remaining coal holdup. 52 7. ENERGY REQUIREMENT 7.1 Energy for size reduction When a solid particle is subjected to crushing, it will be broken when external forces exerted on the particle exceed the internal forces that originally tie the particle elements together. The energy consumption for size reduction is composed of the following aspects: 1. Friction of the crushing machine. 2. Deformation energy of particles before breaking. 3. Increase of surface energy by the production of smaller particles. 4. Rearrangement of surface structure of the particles. 5. Rearrangement of crystal structure of the particles. 6. The friction between the particles and their surroundings, and vibration of the particles. The crushing phenomenon is the result of several forces. These forces are transferred by certain components of the machine to the particles. The mechanism of the crushing is still not yet fully understood: The most pertinent explanation so far is that when the particles are subjected to certain forces, the deformation energy is stored in the particles because of strain. When the local deformation energy exceeds a critical value, breaking occurs at some weak points. Hence, there are two major types of energy needed in crushing. One is deformation energy before breakage which is related to the volume of the particles. The other is surface energy after breakage which is related to the new surface area of the particles. The remaining energy comsumption is related to the friction between the particles. At the critical state the deformation energy is related to the particle volume. Since a large particle has a larger possibility of having gaps and defects than a small one, the critical stress on large particles is lower than that on small ones, which is also true for the deformation energy consumed. This is why crushing of smaller sized particles is relatively more difficulL In the operation of crushing, the energy consumption related to the production of new surface area is only a small part of the total energy consumption. Table 7.1 shows the results of an analysis Table 7.1 Analysis of energy consumption of a ball mill * Classification Amount of total energy (%) 1. Losses at the machine transmission 12.3 2. Heat carried by crushed products 47.6 3. Radiation heat lost by equipment 6.4 4. Heat carried by air exhaust flow 31.0 5. Surface energy for new surface 0.6 6. Others: 2.1 Friction of the crushing machine (1.1) Heat dispersed and temperature increase of the crushing machine (0.4) Vibration and evaporation of water and others (0.6) Total 100.0 * Chemical Engineers' Handbook, Vol. 23, "Crushing, Classification and Size Enlargement", ed. Ren De Shu, Chem. Ind. Publishing Ltd. Beijing. 53 of energy consumption for a ball mill. It is impossible to estimate accurately the value of the minimum energy requirement; and there is also no pertinent mature theory. Combination of the experimental results with the energy consumption analysis to describe the crushing process is apparently the only practical approach. So far, the practical design for crushing equipment is based on experimental results and experience. 7.2 Energy requirement The study of crushing in a spouted bed is a relatively new topic, since it is different from that in other crushing equipment In a spouted bed there are no mechanical moving parts to participate in the crushing process and the major crushing energy is provided by the spouting fluid stream. The other form of energy input is the heat transfer . Based on the energy conservation principles to describe the transfer of energy for spouted bed cornminution, a suitable and practical energy equation can be set up. The basic assumptions for the energy equation are: 1. The crushing energy for a certain moisture content of material is provided by the kinetic and thermal energy of the spouting gas stream. These two kinds of energy affect each other and follow the energy conservation principle. 2. The input energy overcomes the binding force in the solid particles, and the particles are then broken. This energy increases with increase in surface area and is proportional to the difference between initial and final particle sizes. 3. The drying rate of the particle surface moisture increases with increase in the hot gas stream temperature. 4. The britdeness of the particle surface is related to the surface moisture content of the par-ticles. The higher the temperature, the faster the rate of drying and the more readily the particle surfaces become brittie. According to the Strain Energy Theory of Bond and Wang (1950), the total energy input for crushing in a comminution device such as a spouted bed can be expressed by: Ek = ksn"7P1/2 hp-h/short ton 7.1 where n = F/P F = particle size before crushing (inch) P = particle size after crushing, 80% undersize (inch) ks = spouted bed crushing energy coefficient Ek = total energy input in a spouted bed per unit mass of crushed product, e.g. coal, (hp-h/short ton) 54 In spouted bed comminution at room temperature the crushing energy could only be obtained from the kinetic energy of the inlet gas stream. When the inlet gas is heated, this kinetic energy is supplemented by the thermal energy. The energy provided by the gas stream for comminution in a spouted bed is: Ek = £ Gs [(Vi2 - Ve2) P. + c> (Pi/pi - Pe/pe) + fr Cp(Ti-Te)]/W 7.2 where Gs = mass flowrate of spouted gas (kg/min) W = coal comminution rate (short tons/min) Vi = gas velocity at the spouted bed inlet pipe (m/s) Ve = gas velocity at the spouted bed exit pipe (m/s) Pi = gas pressure at the spouted bed inlet pipe (rrimFteO) Pe = gas pressure at the spouted bed exit pipe (mmH20) pi = gas density at Pi condition (kg/m3) pe = gas density at Pe condition (kg/m3) C P = heat capacity of air = 4187x0.24 = 1004.88 (J/kg/C) Ti = inlet spouting gas temperature (°C) Te = exit gas temperature (°C) fr = energy distribution coefficient (%) c\ = conversion factor = 3.725xl0"7 (hp-h/J) bp = pressure conversion factor = 9.798 (N/m2)/mmH20 Equation 7.2, therefore, can be written as: Ek = 3.725x10-7 Gs [(Vi2- Ve2) /2 + 9.798 (Pi/pi - Pe/pe)]/W + 3.743xlO-4GsfTCP(Ti-Te)]/W 7.3 The energy distribution coefficient fr is a parameter to express the fraction of energy used for crushing, as opposed to drying, in the spouted bed. According to the experimental results of the operation from 50 to 105"C (see Appendix 7), the thermal energy consumption to dry the coal varied from 83 to 89%. Thus the coal panicles could obtain only 17 to 11 % of the available heat for crushing. That is fr = 0.11 - 0.17, depending on the operating temperature and with an increase of the temperatute fr decreased. When the crushing is carried out at room temperature, the inlet and exit gas temperatures are the same. In that case, the last term of Equation 7.3 becomes zero. In the present experiments the coal particles were reduced from an initial average size of 3 mm to an average size of 0.75 mm of the product. The calculation results of the total energy input Ek and the parameter Vn/P, which expresses the size change before and after comminution, are shown in Figure 7.1. It can be seen that the energy needed in a spouted bed is higher than in a hammer mill for a certain comminution result, that is at a certain Vn/P. The curves of the total energy input into the spouted bed as a function of temperature, with the glass beads and with the insert, are shown in Figure 7.2. It can be seen that the higher the 55 hp-h per short ton = h = B c 100 t Jaw crusher 0 Hammer mill © Cyniory crusher 0 Rod mill 0 Cnuhinf rolli O B«llmill Q o 0-? 0-t frS OJ l ( l 8 10 i % slOO * t & »1000 j t & »10000 ^ = Vn~/ p = V Reduction ratio / Product size in inches Figure 7.1 Empirical energy chart showing the total energy consumption for coal corjirninution in spouted beds. hp-h per 1 0 0 short ton so Spouted bed commi-nution of coat - O static insert A glass beads - -o - - -^ _ A -^__ ~ ~ — ^ — _ _ _ _ ~ " A - A ~ ~ ~ ~ O i . i i i O 20 40 60 80 100 120 Temperature (*C) Figure 7.2 Total energy input into the spouted bed as a function oftcnipcrature, with the glass beads and with the insert. 56 temperature, the lower the total energy input. Comparing the Ek values using the insert with those using the glass beads, one can see that the latter are 2.0 to 2.4 times the former at room temperature. The values of Ek for operation with glass beads as grinding aid at 50 to 105*C are, however, about 15 to 38% lower than those using the insert at room temperature. Thus the effect of the operating temperature is greater than that of the insert This effect may be caused by the increase of the internal energy of the coal particles. The rate of water evaporation at the particle surface increases with tem-perature, which causes the particle surface to become more brittle and the particles are then more readily broken by the external forces. It is difficult to measure the effect of the rate of surface drying on surface britdeness. A quantitative description of the relationship is therefore still impossible. It is also very difficult to determine the quantitative relationship between the surface britdeness and the energy efficiency of crushing at different temperatures. Some qualitative conclusions however, can be drawn from our experimental results. The coefficient of comrrhnution energy, ks, in a spouted bed is apparendy a function of spouting velocity, temperature and bed structure. The values of ks with different temperatures and grmding aids are listed in Table 7.2. The relationship between the conmiinution energy in a spouted bed and the crushing results can be expressed by Equation 7.1, after Bond and Wang (1950), with ks coefficients evaluated from the experimental data. The homologous data of Ek vs. Vn/P for other systems are plotted in the empirical energy chart, Figure 7.1. The comininution energy coefficient, ks, in a spouted bed could be estimated from such a chart if more data were available at both lower and higher values of "Vn/P than those obtained in the present study and plotted on Figure 7.1. This coefficient is useful in the design and scale-up of a spouted bed dryer and crusher. Table 12. Values of Ek, n1/4 / P 1 / 2 and ks from the continuous runs. Run Temp. Time Coal Ek nl/4/pl/2 ks No. comminution (eq.7.F rate C O (min) (metric tons/min) (hp-h/short ton) (-) (-) using glass beads: TC-3 20 20 2.40xl0-5 145.90 8.13 17.94 TCH-6 50 30 5.27xl0-5 57.42 8.13 7.06 TCH-5 75 25 6.58xl0-5 51.42 8.13 6.32 TCH-7 95 22.5 8.34xl0-5 50.96 8.13 6.27 using static insert: CI-1 20 20 5.60xl0-5 62.53 7.84 7.97 CI-2 20 32 6.64xl0-5 55.52 7.84 7.08 HCI-1 95 30 11.18xl0-5 41.26 7.84 5.26 57 8. C O N C L U S I O N S A N D S U G G E S T I O N S 8.1 Conclusions The experiments on simultaneous comminution and drying of coal (initial particle size 2.8 to 3.35 mm and 2.36 to 2.8 mm with the initial moisture content at circa 24%) at various drying temperatures in a spouted bed of 152 mm internal diameter with a fixed inlet velocity have shown that: 1. the spouted bed is a new size reduction device with stable operation in the continuous mode. The key parameters closely related to this stability are the design features of the spouted bed including the insert, the spouting velocity, the chosen feedrate and the drying temperature. The experiments also confirm that the feedrate for a continuous run can be determined from the instantaneous production rates of the related semi-batch run at the same operating conditions. This method ensures a rapid attainment of stable operation in which the size distribution of the holdup remains unaltered. 2. the energy input for spouted bed coiriminution and drying includes two parts: the kinetic energy and the thermal energy. The kinetic energy has a direct effect on the comminution of particles. The thermal energy affects the comrninution of the particles by changing their physical properties. Subjected to force, these particles can break more easily. These two kinds of energy can complement each other and improve both the comminution efficiency and the capacity. 3. at room temperature the energy used for comminution is only a small fraction of the total input This is especially true when glass beads are used as a dynamic grinding aid. The comminu-tion energy is supplied and transmitted by the spouting air, which reaches its highest velocity in the comininution zone on the axis of the conical base immediately above the orifice. In this zone the relative velocity between the coal particles and the grinding aid also reaches a maximum, which causes the violent condition needed for size reduction. 4. the rate of size reduction is increased at elevated temperatures, which is due to the effect of drying the outer skin of the coal particles. This dry outer skin becomes more brittle and is chipped off more easily at the moment when coal particles re-enter the cornminution zone. Therefore, at elevated temperatures, as the coal particles follow the regular circulation pattern, the two processes of comminution and drying follow each other in a cyclical manner, which results in a mutual magnifying effect 5. the product size distribution can be controlled to match a required specification, most con-veniendy with top discharge. The air discharge velocity and its elutriation effects can be adjusted to obtain the expected cut-size diameter between the product and the bed holdup. The use of grid-covered discharge openings on the conical bottom is less satisfactory due to blinding effects. 6. the energy equation, Equation 7.1 provides a simple method to estimate the energy require-ment for comminution. It has been found that ks is dependent on the bed configuration (including bed dimensions) and on the operating temperature. 7. the total energy needed for comminution in a spouted bed at room temperature is much more than that in a hammer mill. When the drying temperature increases, however, this energy require-58 ment decreases markedly and may eventually reach the level of the hammer mill. Thus an economic benefit can be obtained by operating the spouted bed grinder at higher temperature, in which case the spouted bed is not only a comminution device but also a dryer. The lower construction and maintenance costs may give the spouted bed additional advantages. 8. the accuracy of the present feeding system was crucial for the success of the experimental work. The system consists of a pressure equalized bin and a rotary table feeder. 8.2 Suggestions The combination of comminution drying in spouted beds is relatively new and many questions still remain unanswered. To reach wide acceptance for.practical use, further research needs to be carried out covering: 1. different insert designs to find the optimum shape and configuration which can give peak efficiency. 2. higher temperature ranges for the inlet air, eventually approaching the conditions of flash drying. 3. the use of other inlet velocities and several feedrates for each condition, and the processing of materials other than coal. 4. further work to establish the energy equation for spouted bed comminution. For example, to estimate the coefficient ks more reliably, the value of Vn/P should be changed over a wider range. 5. an empirical or semi-empirical equation which can be applied for design and scale-up. Nomenclature. C P Heat capacity of air = 1004.88 J/kg°C di Initial particle diameter, m d2 Final particle diameter, m E Energy per unit mass, J /kg Ek Total energy input for crushing, hp-h/short ton ft Energy distribution efficiency, % F Particle size before grinding, inch g Gravity acceleration, m/s2 Gs Mass flowrate of the spouted gas stream, kg/min h Total energy input, Hp-hr per short ton k Constant in Equation 2.4 ' ks Spouted bed crushing energy coefficient defined by Equation 7.1 K Work index n Reduction ratio at product size = F/P P Particle size after grinding (80% passes screen), inch Pe Gas pressure at the spouted bed exit pipe, mmH20 Pi Gas pressure at the spouted bed inlet pipe, rrrmHiO t Crushing time, min T Total crushed coal product, ton Ti Inlet spouting gas temperature, °C Te Exit gas temperature, °C U Superficial gas velocity, m/s Urns Minimum spouting velocity, m/s Ve Exit spouting velocity, m/s V i Inlet spouting velocity, m/s Wi Work index of Bond's law Greek Symbols t, Conversion factor = 3.725xl0"7 hp-h/J p^ Pressure conversion factor = 9.798 (N/m2)/mm HzO pe Gas density at Pe condition (1 atm), kg/m3 pi Gas density at Pi condition, kg/m3 X = V n / P 60 References. Amlani, A., BA.Sc. Thesis, "Batch Comminution of Coal in a Spouted Bed", Univ. of British Columbia, Vancouver, B.C. (1984). Bond, F.C. and Jen-Tung Wang, "A New Theory of Comminution", Mining Engineering, Trans-actions ATME 1 £ L 871-878 (1950). Bridgwater, J., Chapter 6 in Fluidization, 2nd edition, Edited by J.F. Davidson, R. Clift and D. Harrison, London, (1958), p. 201-224. Broadbent, S. R. and T. G. Callcott, "A New Analysis of Coal Breakage Process", J. Inst, Fuel 29, 524-539, (1956). Buchanan, R.A. and B.Wilson, "The Fluid-Lift Solids Recirculator", Mech. Chem. Eng. Trans. 1117-124(1965). Carey, W. F. and E. F. Halton, "Energy Flowsheet in Milling Particles", Trans. Inst. Chem. Engrs.(1974). Quoted by Stairmand in "Power in Industry", Society of Chemical Industry Monograph, London No.14 (1961), p.23. Coulson, J. M. and J. F. Richardson, "Chemical Engineering", Vol. No. 2 (1977). Epstein, N. and J. R. Grace, "Spouting of Particlulate Solids", Chapter 11 in "Handbook of Powder Science and Technology," ed. M. E. Fayed and L. Otten, Van Nostrand Reinhold Company Inc., New York (1984), p.507-536. Fedorov, I. M., Troriya i raschot protzessa, sushki vo vzveshennom sostoynii Gosenergoizdat, Moscow (1955). Heywood, H., J. Imp. College Chem. Eng. Soc. iL26-35 (1950-52). Hukki, R.T. Trans. AJME 223 (1962): 402. American Institute of Mining, Metallurgical and Petroleum Engineers. Khoe, G.K., Personal Communications, Univ. of British Columbia, Vancouver, B.C. (1987) Khoe, G. K., M. M. Ruda, and N. Epstein, "Batch Comminution of Coal in a Spouted Bed", Powder Technology, 39,249-262 (1984). Khoe, G. K. and J. Van Brakel, "A draft tube spouted bed as small scale grain dryer", Inst Chem. Eng. Symp. Ser 59, 6:6/1-14 (1980). Kroll, K., 'Trockner, Einteilen, Ordnen, Benennen, Benumnem.", Schilde Schriftenreihe 6 (Schilde Bed Hersgeld, 1965). Lim, C. J., "Gas Residence Time Distribution and Related Patterns in Spouted Beds", Ph.D. Thesis, University of British Columbia, Vancouver, Canada (1975). Lim, C. J. and K. B. Mathur, "Modeling of Particle Movement in Spouted Beds." In Fluidization proceedings of the second Engineering Foundation Conference, ed. J. F. Davidsion and D. L. Keaims, Cambridge Univ. Press., 104-109 (1978). Lowrison, G. C , "Crushing and Grinding", (Butterworths, London, 1974). Marshall, V. C , "Comminution" (I. Chem. E., London, 1974). Mathur, K. B., "A new technique for grinding of particulate solids.", Patent proposal, 1972. Prelim. work reported in B.A.Sc. Thesis by C. L. Connaghan, 1970 and D. G. Miller 1971, Univ. of Brit. Colunbia, Vancouver, Canada. Mathur, K. B. and N. Epstein, "Spouted Beds", Academic Press, New York, 1974. Mathur, K. B. andP.E. Gishler, " A study of the application of the spouted bed, technique to wheat drying", J. Appl. Chem. 5.624 (1955). Nakano, K., B.A.Sc. Thesis, "Comminution of Coal in a Spouted Bed", Univ. of British Columbia, (1982). Perry, R. H. and C. H. Chilton, (Eds), "Chemical Engineers' Handbook", 6th ed. (McGraw-Hill), New York, (1984). Peterson, W. S., "Spouted bed drier", Can. J. Chem. Eng. 40,226 -230 (1962). Ranz, W.E. and W.R. Marshall, Jr., "Evaporation from Drops", Chem. Eng. Progress, 4&, No.3,4. (1952). Rumpf, H., 'Tiinzelkornzerkleinerung als Grundlage einer Techn. Zerkleinerungs-Wissenschaft", Chem. Ing. Techn. 32,108-127 (1965). Sharpies, K., P.G. Gliken, and R.Warne, "Complete simulation of rotary dryers", Trans, Inst Chem. Eng. 42 (1964), T 275. Sion, S., B .A.Sc. Thesis," Individual Comminution Mechanisms in a Spouted Bed", Univ. of British Columbia, (1982). Wu, Stanley W. M., M .A.Sc. Thesis," Hydrodynamics of Gas Spouting at High Temperature", Univ. of British Columbia (1986). APPENDIX 1. Calibration curve of rotameter. A P P E N D I X 2. Calibration curve of coal feeder. 63 Speed of variable speed motor (r.p.m.) 4 0 0 1 1 1 I 9 0 120 150 180 Coal feedrate (g/min) Figure A2. Calibration curve for coal feeder. 64 APPENDIX 3. The choice of coal sample and the properties of the coal. A Forestburg sub-bituminous coal was used in the experiment As required by the experiment the particle properties such as hardness, initial moisture content, angle of repose and drying curve, etc. have been measured. It was found that coal particle properties varied remarkably as the moisture content changed, as illustrated in Table A3.1. Figure A3.1 shows the effect of the moisture content on the solid feeding rate. There are a few important coal particle properties which may strongly affect the coal comminution, mcluding moisture content for different particle sizes (surface moisture and internal moisture), the effect of temperature on surface hardness, fragility and the effect of crack structure on corrrminution. Unfortunately, very litde work has been done on studying these properties. In the early stage of the present work, difficulty and confusion were encountered because of the lack of useful information about Forestburg coal, when an effort was made to summarize and correlate the data obtained. As shown in Figure A3.1, as litde as 1.73% difference in moisture content produced a large difference in the feeding rate. Because of the strong effect of moisture content on comminution, the coal particles size and moisture content were controlled in an appropriate range, and foreach run the initial particle size and moisture content were kept constant Other properties such as hardness and fragility could not be controlled, therefore they were assumed to be the same for different runs. During the particle preparation, coal was crushed and screened to size 2.80-3.35 mm. Particles in this range were well mixed and kept in a sealed plastic container. The moisture content of these particles were =24% and the angle of repose was 33.7°. Before each run, particles in the container would be analysed. Mixing vanes were installed in the container to achieve good niixing by rolling it on its side. Because the percentage of surface moisture and interal moisture (water in pores and cracks) can not be separately measured, it was assumed that moisture losses in this study are mainly surface moisture. Moisture content was reduced from =24% to =9% in the experiments. Table A3.1. Measured coal particle moisture content and hardness. Sample# 1 2 3 4 5 6 Knoop hardness 8.822 10.24 3.23 104.50 26.48 61.70 test 7.26 10.43 6.32 127.50 18.09 13.26 53.00 45.67 (sample from the container, coal particles 2.8-3.35) 9.8 12.6 12.6 65 Moisture content of coal A 22.68% • 24.41% Coal feedrate (g/min) Figure A3. Coal feedrates at different moisture contents. APPENDIX 4. Laboratory convective dryer. 66 The drying characteristics of Forestburg coal were studied as a preliminary to the spouted bed drying investigation. A laboratory convective dryer was used to measured the coal drying curve. The convective dryer is shown in Figure A4. The centrifugal blower sent the air through the wind tunnel, where it was heated by the electric heater. The wet and dry bulb thermometers measured the air temperature and moisture content. The coal sample measured sat on the plate. The weight loss could be read from the balance at different drying times. The time was measured with a stopwatch. A typical drying curve measured in this convective dryer is shown in Figure 4.1. Tliermocouplc Thermocouple Viewing port (wet bulb) (dry bulb) Wind tunnel Centrifugal fan Balance Wet bulb water reservoir Electric heater Figure A4. Convective drying rig. APPENDIX 5. The air flowrates maintained at different temperatures. Inlet air Rotameter Volumetric Mass A/PSTD.PR/PS Actual Temp. Density reading flowrate flowrate flowrate (20*C, 1 atm) C C ) (kg/m5) (mVmin) (kg/min) (m3/min) 20 1.205 70 1.81 2.18 1.06 1.92 50 1.093 65 1.67 1.83 1.05 1.93 75 1.014 60 1.55 1.57 1.04 1.91 85 0.986 59 1.51 1.49 1.04 1.92 95 0.959 58 1.48 1.42 1.04 1.93 105 0.932 57 1.46 1.36 1.03 1.93 Equation and sample calculation: V S = volumetric flowrate before the spouted V S = V S T D ( T S / T R ) V P S T D . P R / P S WU (1986) bed oriGce (m'/min) V S T D = volumetric flowrate taken from the calibration curve (m'/min) P S T D = 1 atm V S = 1.46 (378/293) V760x950/827 P R = absolute pressure of the rotameter (atm) = 1.93 m3/rmn P S = absolute pressure of the spouted bed (atm) T R = temperature of the rotameter (K) TS = temperature of the spouted bed inlet air (K) 68 APPENDIX 6. Analysis of moisture content, relative humidity and size of the coal particles. 1. Moisture analysis: Moisture content of coal was indirectly measured. The sample of coal with a known weight was dried in an oven at 100-110°C. The weight lost during drying would be the content of the surface moisture. The sample weight was 5 grams and the drying time was 1 hour for the moisture measurement Moisture content was calculated by following formula: M.C.% = [(G-G')/G] 100 where G = weight before drying. G' = weight after drying. 2. Analysis of relative humidity of air. It was found that the error in relative humidity measurement above room temperature was much larger when a relative humidity meter was used than the error involved in using wet and dry bulb thermometers. Therefore all the relative humidities were measured by the latter device in the experiments, including the spouting runs at different temperatures. The relative humidity could thus be easily obtained from standard charts if the temperature difference between the dry and wet bulb was known. 3. Analysis of size distribution of coal after comminution After each run, coal in the spouted bed was collected and screened by using a set of screens with standard sieves, listed in Tables A6.1 and A6.2. The effectiveness of the comminution was reflected in these size distribution analyses. To reduce loss of sample and minimize the error in the analysis, screening was done manually. Table A6.1. Sieve series used in this experiment. Mesh No. Standard (nun) Mesh No. Standard (mm) 6 3350 18 1.000 7 2.830 35 0500 8 2360 60 0250 10 2.000 120 0.125 14 1.410 140 0.105 Table A6.2. Sieve average diameters. Sieves davg. Ad (mm) (mm) -6 +7 3.08 032 -7 +8 238 0.47 -8 +10 2.18 036 -10 +14 1.70 059 -14 +18 1.2 0.41 -18 +35 0.75 030 -35 +60 0375 025 -60 +120 0.188 0.125 -120 +140 0.116 0.02 -140 =0.053 APPENDIX 7. SAMPLE CALCULATIONS (all symbols which do not appear in Nomenclature are defined here) 1. D r y i n g calculation i n spouted bed* -. Heat balance The total heat consumption inside the bed is Qo = Qi+Q2 + Q3 + Q4 (1) where Qo = total heat carried by inlet air Q i = heat consumption for evaporating water Q2 = heat consumption for heating the coal Q3 = heat lost from the equipment Q4 = heat carried by the outlet air -. Calculation of water evaporation from coal i n the spouted bed G i = G2(10O-u2)/(10O-u1) where G l = Feedrate of coal (wet basis) kg/hr G2 = Production rate of coal (wet basis) kg/hr Uj == Moisture content of coal before drying (wet basis) % u 2 = Moisture content of coal after drying (wet basis) % Evaporated water in the spouted bed is given by W = G1-G2 -. Heat consumption for evaporating water Q i = W ( i e - i | ) (4) where i : The enthalpy of exit water vapour (at exit temperature) kcal/kg L: The enthalpy of inlet coal moisture (at init ial condition) kcal/kg The enthalpy of steam at t ^ C is equal to the latent heat of water at (TC evaporating to 0 ° C steam, adding the heat for increasing the steam temperature from 0 ° C to t ^ C (for water and steam system). Assumed reference condition: H2O as liquid at CTC. i e = 595 + 0.46^ i = c e = 0 , ( c =1) 1 w 1 I s- ' 8j= coal inlet temperature °C 02= coal exit temperature °C cw= heat capacity of water = 1 kcal/kg°C tj = air exit temperature °C The latent heat of water at (TC = 595 kcal/kg H2O The heat capacity of water vapour = 0.46 kcal/kg*C Therefore Equation (4) can be written as Q ,=W(595 + 0.46^-8,) (5) -. Heat consumption for heating the coal particles Q2 = G 2 C . ( V 0 , ) «>> -. Effective heat for removing water Q' = Qi + Q2 (7) -. Heat lost, assuming similar heat loss as in fluidized bed Q3 = 10%Q' (8) -. Total heat carried by inlet air Qo = L(0.24 -fO^x,)^- t) (9) -. Additional heat carried out by the exit air 04=^(0.24 + 0.46x^-0 (10) -. Total heat for drying XQ = Qi + Q2 + Q3 +04 (11) * This drying calculation method is according to the textbook "Fundamentals of Chemical Engineering", Vol. 3, Science and Technology Publishing Ltd., Beijing (1982). Example: Run No. HCI-1 Data: Air inlet Air outlet Room Coal feed Coal products Coal inside bed Heat capacity of coal Air mass flowrate Temperature t, = 95°C ^=40^ t =20°C Oj = 20°C 82= 33°C 0 = 45°C Humidity Xj = 0.007 kg H20/kg dry air x^ = 0.022 kg HXVkg dry air Moisture content u = 24 % u2=11.53% Cs= 0.3 kcal/kg°C L = 1.42 kg/min = 85.2 kg/hr Coal production rate G2= 130 g/min = 7.8 kg/hr Latent heat of water 595 kcal/kg H2O (at 0*C) Heat capacity of dry air 0.24 kcal/kg°C Heat capacity of water vapour: 0.46 kcal/kg°C Solution: Evaporated water Using Eq. (2) and (3) Gl = 7.8 (1- 0.1153)/(1 - 0.24) = 9.07 kg/hr > W = 9.07 - 7.8 = 1.27 kg/hr Heat consumption for evaporating water Using Eq. (5) Qi = 1.27 (595 + 0.46x40 - 20) = 753.618 kcal/hr Heat consumption for heating the coal: Using Eq. (6) Q2 = 7.8x0.3 (33-20) = 30.42 kcal/hr Effective heat for drying: Using Eq.(7) Q' = 753.618 +30.42 = 784.04 kcal/hr Heat losses : Using Eq.(8) Q3=784.04xl0% = 78.4 kcal/hr Total heat carried by inlet ain Using Eq.(9) Qo = 85.2(0.24 + 0.46x0.007)(95 - 20) = 1552.77 kcal/hr Additional heat carried out by the exit ain Using Eq.(10) CM = 85.2 (0.24 + 0.46x0.007)(40-20) = 414.45 kcal/hr Total heat for drying: Using Eq. (11) Z Q = 753.618 + 30.42 + 78.4 + 414.45 = 1276.89 kcal/hr Thermal efficiency for evaporating water: TI =784.04/1552.77 = 50.5% Thermal energy consumption for drying: TJD = 1276.89/1552.77 = 82.23% The energy consumptions for drying at different temperatures are listed below. ti fC) 50 75 95 105 TID(%) 82.23 81.2 88.66 87.87 (glass beads) 82.23 - (insert) Volume of the spouted bed, assuming fountain volume + cone volume = volume of cylinder having height equal to that of cone: Spouted bed diameter =150 mm, Spouted bed height = 500 mm. V = 0.785 (O.IS)^ = 0.009 m3 Evaporation intensity: 1.27/0.009 = 141.1 kg H20/m3hr Grinding intensity: 7.8/0.009 = 866.7 kg coal/m3hr 2. Estimation calculation for drying in spouted bed at 110 *C. Data: Air inlet temperature: 110°C Air inlet humidity: 0.008 kg H207kg dry air Air oudet temperature: 50*C Coal inlet temperature: 20°C Coal exit temperature: 35*C Coal inlet moisture content: 24% Room temperature: 20*C Air flowrate (at 110*C): 1.35 kg/min = 81 kg/hr Coal production rate: 7.8 kg/hr Thermal efficiency for evaporating water = 53%** **The experimental results for thermal efficiency of water evaporation in spouted bed at different drying temperatures are listed below. Drying temperature C C ) : 50 75 95 105 Thermal efficiency (rj): 41.17 39.11 45-50 50-53 Therefore, for 110°C drying temperature, the assumption of a thermal efficiency of 53% for evaporating water is conservative. -. Total heat carried by the inlet air: Using Eq.(9) Qo = 81(0.24 + 0.46x0.008)(110 - 20) = 1776.43 kcal/hr -. Heat consumption for hearing the coal particles: Q2= 7.8x0.3(35 - 20) = 35.1 kcal/hr Q ' = T I Q O Qi + Q2 = Q' = 1776.43x53% = 941.51 kcal/hr Qi = 945.51 - 35.1= 906.41 kcal/hr Using Eq.(5), the evaporated water is: W = 906.41/ (595 + 0.46x50 - 20) = 1.52 kg/hr If it is required to reduce the moisture content from 24% to 9%, the evaporated water is calcu-lated as follows: Gl = 7.8 (0.91/0.76) = 9.34 kg/hr W = 9.34-7.8= 1.54 kg/hr Thus W » W Therefore, choosing 110'C inlet air temperature could dry the coal particles to a moisture content of 9%. 3. Total input energy calculation Comminution energy: Inlet coal size (average) F = 3 mm = 0.118 inch Product coal size (average) P = 0.75 mm = 0.03 inch n = F/P = 0.118/0.03 = 3.93 x = Vn/P = V3.39/0.03 = 66.11 Inlet coal size (average) F = 2.58 mm = 0.102 inch Product coal size (average) P= 0.75 mm = 0.03 inch n = 0.102/0.03 = 3.38 y= Vn/P = V3.38/0.03 = 61.46 The inlet and exit gas density at different temperatures and pressure are listed below: T Pressure (kg/m3) (kg/m3) CC) (mm H2O absolute) 20 11828 1.280 1.2050 50 11654 1.164 1.0920 75 11581 1.080 1.0145 95 11613 1.020 0.9590 105 11559 1.000 0.9340 Vi= 1.92/0.785(0.057)260 = 1.92/0.153 = 12.55 m/s Ve = 1.92/0.785(0.075)260 =1.92/0.265 = 7.24 m/s Using Equation 7.2 for run No. TC-3 whenTi=Te = 20'C, Mass flowrate of spouting air = 2.18 kg/min, Production rate W = 2.09xl0"5 metric ton/min, 73 Pi = 11828 mm H 2 O , Pe = = 10553 mm H2O, S = 3.725xl07 hp-h/J, 9.798 N/m 2 /mmH20 Ek = = i;Gs[(Vi2-Ve2)/2 + p^(Ps/pi-P p^e)]AV Ek = = 3.725xl0-7x2.18 [(12.59-1 .lA 7)/! + 9.798(11828/1.28 - 10553/1.205)]/2.09x 10 = 3.725xl0-7x2.18[52.54+ 0.47x1Cfyi.WxlOr5 = 3.885xl0-3/2.09xl0-5 = 185.88 hp-h/metric ton = 168.6 hp-h/short ton ForranNo.HCI-1 When Ti =95 °C,Te = 4 5 ° C Mass flowrate of spouting air = 1.48 kg/min Production rate W = 10.47xl0"5 ton/rnin Pi = 11613 mm H2O, Pe = 10513 mm H2O. pi= 1.02 kg/m3, pe = 0.959 kg/m3, fT= 10% Ek = 3.725xl0-7xl.48[52.54 + 0.414xl04]/10.47xl0-5 + 3.743xl0"5xl.48 (95 -45)/10.47xl0-5 = 21.92+ 26.45 = 48.37 hp-h/metric ton = 43.88 hp-h/short ton The calculated data are listed below: T Gs i;p(R/pi-Pe/pe) W Ek ks CC) kg/m' J/kg metric ton/min hp-h/short ton Eq.7.1 Glass beads 20 2.18 0.470X104 2.40xl0;s 145.90 17.94 50 1.67 0.360X104 521xl0r s 57.42 7.06 75 1.55 0.359X104 6.58xl0"5 51.42 6.32 95 1.48 0.453X104 8.34xia5 50.96 6.27 Static insert 20 2.18 0.470X104 5.60xl0-5 62.53 7.97 20 2.18 0.495X104 6.64xl0-5 55.52 7.08 95 1.48 0.414X104 11.18xl0-5 41.26 5.26 For initial coal size 2.80-3.35 mm and final coal size 0.75 mm (0.03 inch), n i A y p i / 2 = 3.93i*/o.031/2= 8.13 For initial coal size 2.36-2.80 mm and final coal size 0.75 mm, nw/pm = 338W/0.03172 = 7.84 4. Water balance for the drying system Calculation of water carried by the oudet gas W' : Water carried by the oudet gas (kg/hr) Xj : Air inlet humidity (kg H20/kg dry air) x2 : Air oudet humidity (kg H20/kg dry air) L : Air mass flowrate (kg dry air/hr) For run No. HCI-1 W" = (0.022 - 0.007) 1.42 x 60 = 1.278 kg/hr Evaporated water removed from coal = W = 1.27 kg/hr % deviation = ((1.27 - 1.278) / 1.278) x 100 = -0.63% APPENDIX 8. Raw data Summary table of experiments Run Date Discharge conditions Temp- BedAP Operating conditions No. Top& Top erature Semi- Conti-bottom only CQ (mmffiO) batch nuous Using glass beads as grinding aid C-19-8 22.87 V Room 1316 V C-19-8' 23.87 V Room 1278 V C-19-8" 2.4.87 Room 1329 V C-19-8"' 2.5.87 V Room 1312 C-19-9 2.13.87 V Room 1320 C-19-9' 2.16.87 V Room 1267 C-19-9" 2.17.87 Room 1255 C-19-9"' 2.18.87 Room 1264 SCH-5 3.5.87 V" 105 1175 V CH-5' 3.5.87 V 105 1188 CH-5" 3.12.87 105 1223 SCH-6 3.9.87 105 1198 V CH-6' 3.10.87 105 -CH-6" 3.12.87 105 1212 CH-6m 320.87 105 1182 SCH-7 3.19.87 95 1208 V. CH-7' 3.23.87 95 1168 V CH-7" 325.87 95 1180 V SCH-8 324.87 V 75 1190 CH-8' 325.87 75 1150 V SCH-9 326.87 • V 85 1199 CH-9' 326.87 V 85 1174 V ST-2 327.87 Room 1349 ST-2' 327.87 V Room 1340 V ST-2" 328.87 V Room 1361 ST-2"' 328.87 Room 1352 V TC-3 328.87 Room 1275 TCH-4 331.87 95 1225 V* TCH-4' 4.1.87 95 1238 V* TCH-5 62.87 75 1074 V* TCH-6 5.16.87 50 1123 V* TCH-7 621.87 V 95 1140 V* Using insert as grinding aid V SCH-1 524.87 Room 1279 SCH-1' 524.87 Room 1429 V SCH-1" 525.87 Room 1419 SCH-1'" 525.87 Room 1430 SCH-1'"' 525.87 V Room 1440 a - i 526.87 Room 1304 V* a-2 72.87 Room 1470 V* HCI-1 7.10.87 V 95 1100 * performed independent of semi-batch. 76 RAW DATA ON THE SEMI-BATCH EXPERIMENTS No. ST-2 TO ST-2'" AND No.SCI-1 TO SCI-1"" These experiments have been performed to find the size distribution of the holdup and the product after every 5 minute interval. The results show the progress in the spouted bed coal comminution process. As a consequence of the above mentioned intention, the weight percent in the sieve analysis refers to the weight of coal forming the bed holdup at the very start (dp=2.80-3.35mm). Run No.ST-2 Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 49.12 0 -2.80 - 2.36 2.58 25.85 0 -2.36 - 2.00 2.18 10.06 0 -2.00-1.40 1.70 5.67 0 -1.40 - 1.00 1.20 2.30 0 -1.00 - 0.50 0.75 1.97 0.39 -0.50 - 0.25 0.375 0.32 1.66 -0.25 - 0.125 0.188 0.06 1.36 -0.125-0.106 0.116 0.007 0.03 -> 0.106 0.053 0 0 -Coal M.C. after run (%) 22.28 22.28 _ Coal mass after run (g) 1151.52 41.73 -Production rate (0.125mm<dp<1.4 mm) (g/min) 8.25 Total product (g) 41.27 Products from cyclone (g) 5.73 Total coal losses (g) 8.38 Initial coal holdup (g) 1207.36 OPERATING CONDITIONS Inlet air temperature (*C) 20 Operating time (min) 5 Feed (initial) coal M.C. (%) 24.54 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 290-282 * see Figure 5.6 (holdup) and Figure 5.7 (product). Run No.ST-2' Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run * dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 32.36 0 -2.80 - 2.36 2.58 21.65 0 -2.36 - 2.00 2.18 14.43 0.06 -2.00- 1.40 1.70 10.46 0.08 -1.40-1.00 1.20 5.40 0.23 -1.00 - 0.50 0.75 3.97 1.86 -0.50 - 0.25 0.375 0.54 4.02 -0.25 - 0.125 0.188 0.03 2.78 -0.125-0.106 0.116 0 0.06 -> 0.106 0.053 0 0.02 -Coal M . C . after run (%) 19.88 19.88 -Coal mass after run (g) 1072.60 68.27 -Production rate (0.125mm<dp<1.4 mm) (g/min) 13.22 Total product (g) 66.11 Products from cyclone (g) 5.50 Total coal losses (g) 6.25 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature C O 20 Operating time (min) 5 Feed (initial) coal M . C . (%) -Feed (initial) coal size (mm) -Coal feedrate (g/min) -A i r flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 268 * see Figure 5.6 (holdup) and Figure 5.7 (product). Run No.ST-2" Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 8.62 0 -2.80 - 2.36 2.58 19.39 0.21 -2.36 - 2.00 2.18 15.16 0.30 -2.00-1.40 1.70 17.39 0.71 -1.40-1.00 1.20 9.58 1.42 -1.00 - 0.50 0.75 5.10 5.83 -0.50 - 0.25 0.375 0.69 7.60 -0.25-0.125 0.188 0.09 4.89 -0.125 - 0.106 0.116 0.007 0.12 -> 0.106 0.053 0 0.05 -Coal M.C. after run (%) 18.70 18.70 -Coal mass after run (g) 917.87 145.20 . -Production rate (0.125mm<dp<1.4 mm) (g/min) 26.18 Total product (g) 130.98 Products from cyclone (g) 5.85 Total coal losses (g) 3.68 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 20 Operating time (min) 5 Feed (initial) coal M.C. (%) -Feed (initial) coal size (mm) -Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 240 * see Figure 5.6 (holdup) and Figure 5.7 (product). Run No.ST-2'" Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 5.06 0 -2.80 - 2.36 2.58 10.76 0.3 -2.36 - 2.00 2.18 11.81 0.46 -2.00-1.40 1.70 16.98 1.43 -1.40 - 1.00 1.20 11.13 2.55 -1.00 - 0.50 0.75 5.57 10.15 -0.50 - 0.25 0.375 0.90 11.09 -0.25-0.125 0.188 0.78 9.69 -0.125-0.106 0.116 0.11 0.17 -> 0.106 0.053 0.01 0.09 -Coal M.C. after run (%) 15.99 15.99 Coal mass after run (g) 746.97 147.67 -Production rate (0.125mm<dp<1.4 mm) (g/min) 26.97 Total product (g) 134.83 Products from cyclone (g) 5.75 Total coal losses (g) 17.48 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 20 Operating time (min) 5 Feed (initial) coal M.C. (%) -Feed (initial) coal size (mm) -Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (rnin) -Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 230 * see Figure 5.6 (holdup) and Figure 5.7 (product). Run No.SCH-1 Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 76.96 0 -2.36 - 2.00 2.18 13.47 0.01 -2.00-1.40 1.70 1.85 0.01 -1.40-1.00 1.20 1.15 0.014 -1.00 - 0.50 0.75 1.23 0.57 -0.50 - 0.25 0.375 0.14 1.0 -0.25 - 0.125 0.188 0.014 0.53 -0.125 - 0.106 0.116 0 0.33 -> 0.106 0.053 0 0.03 -Coal M.C. after run (%) 22.56 22.56 _ Coal mass after run (g) 2620.49 69.24 -Production rate (0.125mm<dp<1.4 mm) (g/min) 11.76 Total product (g) 85.78 Products from cyclone (g) 6.81 Total coal losses is) 66.82 Initial coal holdup (g) 2763.36 OPERATING CONDITIONS Inlet air temperature CC) 21 Operating time (min) 5 Feed (initial) coal M.C. (%) 23.24 Feed (initial) coal size (mm) 2.36-2.80 Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 0.88-0.90 U/Ums 2.0 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 365-350 * see Figure 5.11 (holdup) and Figure 5.12 (product). Run No.SCH-1' Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 58.54 0 -2.36 - 2.00 2.18 16.63 0.01 -2.00 - 1.40 1.70 8.84 0.05 -1.40 - 1.00 1.20 3.70 0.16 -1.00 - 0.50 0.75 1.86 3.44 -0.50 - 0.25 0.375 0.11 1.98 -0.25-0.125 0.188 0.01 1.32 -0.125 - 0.106 0.116 0.003 0.50 -> 0.106 0.053 0 0.045 -Coal M.C. after run (%) 21.16 21.16 Coal mass after run (g) 2478.98 138.36 -Production rate (0.125mm<dp<1.4 mm) (g/min) 26.38 Total product (g) 131.90 Products from cyclone (g) 5.12 Total coal losses (g) 27.67 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 21 Operating time (rriin) 5 Feed (initial) coal M.C. (%) -Feed (initial) coal size (mm) -Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 0.88 U/Ums 2.0 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 330 * see Figure 5.11 (holdup) and Figure 5.12 (product). Run No.SCH-1" Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 44.01 0 -2.36 - 2.00 2.18 16.21 0.07 -2.00 - 1.40 1.70 12.40 0.16 -1.40-1.00 1.20 6.10 0.40 -1.00 - 0.50 0.75 2.57 6.67 -0.50 - 0.25 0.375 0.19 3.91 -0.25 - 0.125 0.188 0.02 2.17 -0.125-0.106 0.116 0.006 0.82 -> 0.106 0.053 0 0.07 -Coal M.C. after run (%) 20.16 20.16 -Coal mass after run (g) 2252.84 186.98 -Production rate (0.125mm<dp<1.4 mm) (g/min) 34.55 Total product (g) 172.77 Products from cyclone (g) 7.50 Total coal losses (g) 31.66 Initial coal holdup (g) -OPERATING CONDITIONS Inlet air temperature C Q Operating time (min) Feed (initial) coal M.C. (%) Feed (initial) coal size (mm) Coal feedrate (g/min) Air flowrate at orifice (mVniin) Ums (m/s) UAJms Mean residence time (min) Moisture content of air In/Out (kg water/kg dry air) Spouted bed height (mm) * see Figure 5.11 (holdup) and Figure 5.12 (product). Run No.SCH-1"' Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 17.88 0 -2.36 - 2.00 2.18 25.23 0.26 -2.00- 1.40 1.70 17.71 0.41 -1.40- 1.00 1.20 9.00 0.98 -1.00-0.50 0.75 2.70 11.16 -0.50 - 0.25 0.375 0.21 5.63 -0.25-0.125 0.188 0.02 2.99 -0.125-0.106 0.116 0.006 1.07 -> 0.106 0.053 0 0.08 -Coal M.C. after ran (%) 19.23 19.23 _ Coal mass after run (g) 2011.98 228.97 -Production rate (0.125mm<dp<1.4 mm) (g/min) 42.01 Total product (g) 210.07 Products from cyclone (g) 6.86 Total coal losses (g) 5.12 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 21 Operating time (min) 5 Feed (initial) coal M.C. (%) -Feed (initial) coal size (mm) -Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 0.88-0.90 U/Ums 2.0 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 263 * see Figure 5.11 (holdup) and Figure 5.12 (product). Run No.SCH-1"" Semi-batch (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 9.87 0 -2.36 - 2.00 2.18 20.14 1.38 -2.00 - 1.40 1.70 15.56 1.78 -1.40-1.00 1.20 9.85 2.93 -1.00-0.50 0.75 3.58 15.90 -0.50 - 0.25 0.375 0.32 7.96 -0.25 - 0.125 0.188 0.05 3.87 -0.125-0.106 0.116 0.006 1.42 -> 0.106 0.053 0 0.10 -Coal M.C. after run (%) 18.17 18.17 _ Coal mass after run (g) 1640.94 352.83 -Production rate (0.125mm<dp<1.4 mm) (g/min) 54.71 Total product (g) 273.66 Products from cyclone (g) 8.10 Total coal losses (g) 10.02 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 21 Operating time (min) 5 Feed (initial) coal M.C. (%) -Feed (initial) coal size . (mm) -Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 0.88-0.90 U/Ums 2.0 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 225 * see Figure 5.11 (holdup) and Figure 5.12 (product). 86 RAW DATA ON EXPERIMENTS OTHER THAN No. ST-2 TO ST-2"' AND No. SCI-1 TO SCI-1"" The results of the sieve analysis on the holdup remaining at the end of each (semi-batch or continuous) run interval are presented in terms of Wt% retained on the sieve, where 100% is the total mass of coal holdup remaining. This method of presentation was chosen because, in the continuous runs, the holdup was kept almost constant In the semi-batch experiments, the results of the sieve analysis on the products are expressed as Wt% retained on the sieve, where 100% is the total mass of coal holdup at the very start. This was done to follow the progress of corruninution from the start. In the continuous experiments, the results of the sieve analysis on the products are expressed as Wt% retained on the sieve, where 100% is the coal feedrate times the duration of the run interval, i.e. 100% represents the total feed during the given interval. 87 80 Produc-tion rate 4 0 (g/min) 1— • 1 •• I • • « - ^ (C-19-8)Serai . M.C.Start=25.15% M.C.End =19.10% • • * * (C-19-8') . (C-19-8") Feed=53.46g/min Feed=42.16g/min M.C.=23.87% • M.C.=24.79% Prod.=48.1g/min Prod.=45.09g/min M.C=18.90% M.C.=17.84% (C-19-8"') Feed=44.53g/min -M.C.=24.06% Prod.=48.03g/min . M.C.=17.69* 1 0 10 20 30 40 50 60 Time after start (min) Figure A5. The graph of production rate versus time in a semi-batch and run its related continu-ous run intervals (average values in each 5 minute interval). Conditions in run C-19-8: T = 20*C Initial coal size 2.80-3.35 mm Spouted bed height 237-242 mm Product = Bottoms + Tops + Losses. Run No.C-19-8 Semi-batch (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run dp dp (mm) (mm) 3.35- 2.80 3.08 2.80- 2.36 2.58 2.36- 2.00 2.18 2.00- 1.40 1.70 1.40- 1.00 1.20 1.00- 0.50 0.75 0.50- 0.25 0.375 0.25- 0.125 0.188 0.125 - 0.106 0.116 > 0.106 0.053 Coal M.C. after run (%) Coal mass after run (g) Holdup Products Top Bottom (Wt%) (Wt%) (Wt%) 9.26 0 0 7.58 0 0.25 24.07 0 0.75 34.50 0 3.90 15.99 0 6.30 6.96 0 9.43 1.34 5.5 8.70 0.24 4.57 4.73 0.02 0.14 0.16 0.02 0.07 0.07 19.1 _ 19.1 692.25 123.33 288.33 (g/min) (g) (g) 14.18 (g) 76.19 (g) H97.6 Production rate (0.125mm<dp<1.4 mm) Total product Products from cyclone Total coal losses Initial coal holdup OPERATING CONDITIONS Inlet air temperature (*C) 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 25.15 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 237-290 Run No.C-19-8* Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 10.29 0 0 2.80 - 2.36 2.58 20.02 0 0 2.36 - 2.00 2.18 21.00 0 0.52 2.00-1.40 1.70 26.46 0 7.53 1.40 - 1.00 1.20 14.09 0 17.43 1.00-0.50 0.75 6.89 0 21.30 0.50 - 0.25 0.375 1.0 7.38 8.48 0.25-0.125 0.188 0.22 4.98 0.30 0.125-0.106 0.116 0.008 0.20 0.03 > 0.106 0.053 0 0.12 0 Coal M.C. after run (%) 18.90 _ 18.90 Coal mass after run (g) 900.04 101.69 445.81 Production rate (0.125mm<dp<1.4 mm) (g/min) 32.00 Total product (g) 480.11 Products from cyclone (g) 15.17 Total coal losses (g) 31.49 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 23.87 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 53.46 Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 22.72 Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 237 Run No.C-19-8" Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 11.07 0 0 2.80 - 2.36 2.58 18.83 0 0 2.36 - 2.00 2.18 21.62 0 0.55 2.00 - 1.40 1.70 23.66 0 10.17 1.40-1.00 1.20 14.05 0 24.76 1.00-0.50 0.75 9.13 0 33.44 0.50 - 0.25 0.375 1.49 11.48 13.09 0.25 - 0.125 0.188 0.14 6.43 0.49 0.125-0.106 0.116 0.009 0.22 0.04 > 0.106 0.053 0 0.18 0 Coal M.C. after run (%) 17.84 - 17.84 Coal mass after run (g) 865.09 115.85 522.12 Production rate (0.125mm<dp<1.4 mm) (g/min) 37.82 Total product (g) 567.32 Products from cyclone (g) 15.86 Total coal losses (g) 22.48 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature C O 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 24.16 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 42.16 Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 18.98 Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 242 Run No.C-19-8'" Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 10.86 0 0 2.80 - 2.36 2.58 18.48 0 0 2.36 - 2.00 2.18 20.33 0 0.53 2.00-1.40 1.70 26.05 0 8.59 1.40- 1.00 1.20 14.11 0 23.20 1.00 - 0.50 0.75 8.56 0.21 34.91 0.50 - 0.25 0.375 1.35 12.68 13.60 0.25 - 0.125 0.188 0.18 5.10 0.55 0.125-0.106 0.116 0.01 0.26 0.03 > 0.106 0.053 0 0.21 0 Coal M.C. after run (%) 17.69 _ 17.69 Coal mass after run (g) 803.51 121.49 543.80 Production rate (0.125mm<dp<1.4 mm) (g/min) 40.06 Total product (g) 601.02 Products from cyclone (g) 15.48 Total coal losses (g) 39.71 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature C O 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 24.16 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 44.53 Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 16.73 Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 237 Run No.C-19-9 Semi-batch (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 10.00 0 0 2.80 - 2.36 2.58 18.06 0 0.19 2.36-2.00 2.18 20.63 0 0.71 2.00 - 1.40 1.70 27.99 0 3.44 1.40-1.00 1.20 15.59 0 6.21 1.00 - 0.50 0.75 6.59 0.007 9.28 0.50 - 0.25 0.375 1.03 5.60 3.17 0.25 - 0.125 0.188 0.10 2.90 0.13 0.125-0.106 0.116 0.01 0.19 0.02 > 0.106 0.053 0 0.12 0 Coal M.C. after run (%) 18.84 _ 18.84 Coal mass after run (g) 782.94 106.80 279.28 Production rate (0.125mm<dp<1.4 mm) (g/min) -Total product (g) -Products from cyclone (g) 13.47 Total coal losses (g) 24.23 Initial coal holdup (g) 1206.72 OPERATING CONDITIONS Inlet air temperature (*C) 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 24.16 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 237 * see Figure 5.2 (holdup) and Figure 4.6 (production rate). Run No.C-19-9' Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 9.93 0 0 2.80 - 2.36 2.58 18.18 0 0 2.36 - 2.00 2.18 20.46 0 0.6 2.00 - 1.40 1.70 27.11 0 10.16 1.40 -1.00 1.20 13.66 0 22.73 1.00 - 0.50 0.75 9.14 0.06 29.26 0.50 - 0.25 0.375 1.32 9.58 12.05 0.25-0.125 0.188 0.18 5.3 0.46 0.125 - 0.106 0.116 0.01 0.27 0.03 > 0.106 0.053 0 0.2 0 Coal M.C. after run (%) 18.71 _ 18.71 Coal mass after run (g) 794.52 109.42 537.73 Production rate (0.125rnm<dp<1.4 mm) (g/min) 37.81 Total product (g) 567.17 Products from cyclone (g) 15.04 Total coal losses (g) 35.72 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 24.24 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 47.30 Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 17.07 Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 232 * see Figure 5.3 (holdup) and Figure 5.4 (bottom product). Run No.C-19-9" Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run dp dp (mm) (mm) 3.35- 2.80 3.08 2.80- 2.36 2.58 2.36- 2.00 2.18 2.00- 1.40 1.70 1.40- 1.00 1.20 1.00- 0.50 0.75 0.50- 0.25 0.375 0.25- 0.125 0.188 0.125 - 0.106 0.116 > 0.106 0.053 Coal M.C. after run (%) Coal mass after run (g) Holdup Products Top Bottom (Wt%) (Wt%) (Wt%) 9.86 0 0 17.74 0 0 21.13 0 0.70 27.19 0 11.12 13.51 0 21.51 9.08 0.011 31.93 1.32 9.0 10.87 0.15 6.64 0.43 0.01 0.27 0.03 0 0.25 0 18.26 _ 18.26 808.73 114.52 541.82 (g/min) 37.90 (g) 568.51 (g) 15.45 (g) .21.36 (g) Production rate (0.125mm<dp<1.4 mm) Total product Products from cyclone Total coal losses Initial coal holdup OPERATING CONDITIONS Inlet air temperature CC) 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 24.78 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 47.16 Air flowrate at orifice (mVmin) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 17.50 Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 237 Run No.C-19-9"' Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 9.67 0 0 2.80 - 2.36 2.58 18.61 0 0 2.36 - 2.00 2.18 20.62 0 0.73 2.00 - 1.40 1.70 26.88 0 10.11 1.40 - 1.00 1.20 14.37 0 20.63 1.00 - 0.50 0.75 8.43 0.01 31.97 0.50 - 0.25 0.375 1.23 10.82 11.88 0.25 - 0.125 0.188 0.18 4.04 0.46 0.125-0.106 0.116 0.01 0.22 0.03 > 0.106 0.053 0 0.14 0 Coal M.C. after run (%) 17.74 . 17.74 Coal mass after run (g) 836.98 107.93 537.46 Production rate (0.125mm<dp<1.4 mm) (g/min) 37.71 Total product (g) 565.70 Products from cyclone (g) 14.14 Total coal losses (g) 20.0 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature C Q 20 Operating time (min) 15 Feed (initial) coal M.C. (%) 25.08 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 47.25 Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 18.45 Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 235 Run No.SCH-5 Semi-batch (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 4.13 0 0 2.80 - 2.36 2.58 , 9.24 0 0.14 2.36 - 2.00 2.18 11.11 0 0.34 2.00 - 1.40 1.70 19.21 0 2.66 1.40 - 1.00 1.20 22.39 0 6.11 1.00 - 0.50 0.75 27.47 0.02 11.87 0.50 - 0.25 0.375 5.88 6.85 4.37 0.25 - 0.125 0.188 0.54 3.74 0.01 0.125-0.106 0.116 0.01 0.16 0.01 > 0.106 0.053 0 0.09 0 Coal M.C. after run (%) 10.79 11.43 14.13-1: Coal mass after run (g) 751.77 115.85 311.55 Production rate (0.125mm<dp<1.4 mm) (g/min) 64.46 Total product (g) 386.78 Products from cyclone (g) 15.15 Total coal losses (g) 11.12 Initial coal holdup (g) 1205.44 OPERATING CONDITIONS Inlet air temperature CC) 105 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.66 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) 0.003/ -Spouted bed height (mm) 220 * see Figure 5.2 (holdup). Run No.CH-5' Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 10.02 0 0 2.80 - 2.36 2.58 16.75 0 0 2.36 - 2.00 2.18 15.46 0 0.24 2.00- 1.40 1.70 15.23 0 3.47 1.40 - 1.00 1.20 14.36 0 12.14 1.00-0.50 0.75 21.2 0.09 37.26 0.50 - 0.25 0.375 6.23 16.48 4.88 0.25 - 0.125 0.188 0.70 4.04 1.33 0.125-0.106 0.116 0.01 0.08 0.03 > 0.106 0.053 0 0.10 0 Coal M.C. after run (%) 11.37 7.88 8.22 Coal mass after run (g) 813.78 350.33 1200.41 Production rate (0.125mm<dp<1.4 mm) (g/min) 98.99 Total product (g) 1484.79 Products from cyclone (g) 41.14 Total coal losses (g) 4.53 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 105 Operating time (min) 15 Feed (initial) coal M.C. (%) 24.10 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 112.36 Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 •U/Ums 1.53 Mean residence time (min) 7.65 Moisture content of air In/Out (kg water/kg dry air) 0.003/-Spouted bed height (mm) 220 * see Figure 5.3 (holdup) and Figure 5.4 (product). Run No.CH-5" Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 8.52 0 0 2.80 - 2.36 2.58 15.30 0 0 2.36 - 2.00 2.18 14.78 0 0.33 2.00 - 1.40 1.70 17.35 0 4.11 1.40-1.00 1.20 13.53 0 16.16 1.00 - 0.50 0.75 21.74 0 48.89 0.50 - 0.25 0.375 7.84 0 11.00 0.25 - 0.125 0.188 0.90 12.53 0.40 0.125-0.106 0.116 0.04 6.598 0.05 > 0.106 0.053 0 0.20 0 Coal M.C. after run (%) 11.35 7.79 8.77 Coal mass after run (g) 709.64 252.74 1044.78 Production rate (0.125mm<dp<1.4 mm) (g/min) 102.86 Total product (g) 1234.42 Products from cyclone (g) 35.41 Total coal losses (g) 52.04 Initial coal holdup < (g) OPERATING CONDITIONS Inlet air temperature C O 105 Operating time (min) 12 Feed (initial) coal M.C. (%) 24.84 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 107.54 Air flowrate at orifice (mVirun) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 6.58 Moisture content of air In/Out (kg water/kg dry air) 0.0035/-Spouted bed height (mm) 217 * see Figure 5.3 (holdup) and Figure 5.4 (product). Run No.SCH-6 Semi-batch (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 4.13 0 0 2.80 - 2.36 2.58 9.67 0 0.06 2.36 - 2.00 2.18 12.55 0 0.41 2.00 - 1.40 1.70 18.57 0 1.51 1.40- 1.00 1.20 21.90 0 5.37 1.00-0.50 0.75 21.73 0 10.27 0.50 - 0.25 0.375 5.24 6.57 10.27 0.25-0.125 0.188 0.90 3.19 4.40 0.125-0.106 0.116 0.01 0.188 0.01 > 0.106 0.053 0 0.12 0 Coal M.C. after run (%) 11.86 12.77 15.73-1: Coal mass after run (g) 796.44 105.02 268.48 Production rate (0.125mm<dp<1.4 mm) (g/min) 57.72 Total product (g) 346.30 Products from cyclone (g) 17.38 Total coal losses (g) 8.36 Initial coal holdup (g) 1195.68 OPERATING CONDITIONS Inlet air temperature (°C) 105 Operating time (min) 6 Feed (initial) coal M.C. (%) 25.27 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) Air flowrate at orifice (m3/min) 1.91 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) Moisture content of air In/Out (kg water/kg dry air) 0.003/ -Spouted bed height (mm) 225 * see Figure 5.2 (holdup). Run No.CH-6' Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 7.17 0 0 2.80 - 2.36 2.58 14.28 0 0 2.36 - 2.00 2.18 14.53 0 0.46 2.00 - 1.40 1.70 17.11 0 4.73 1.40 - 1.00 1.20 15.62 0 14.64 1.00-0.50 0.75 23.87 0.15 36.98 0.50-0.25 0.375 6.84 12.75 14.69 0.25 - 0.125 0.188 0.56 6.54 1.26 0.125-0.106 0.116 0.01 0.27 0.03 > 0.106 0.053 0 0.27 0 Coal M.C. after run (%) 11.15 7.32 6.77-7J Coal mass after run (g) 823.11 136.42 497.05 Production rate (0.125mm<dp<1.4 mm) (g/min) 99.02 Total product (g) 594.15 Products from cyclone (g) 14.24 Total coal losses (g) 8.41 Initial coal holdup (g) 1206.72 OPERATING CONDITIONS Inlet air temperature CC) 105 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.57 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 113.80 Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 7.53 Moisture content of air In/Out (kg water/kg dry air) 0.004/-Spouted bed height (mm) 225 * see Figure 5.3 (holdup) and Figure 5.4 (product). Run No.CH-6" Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 10.00 0 0 2.80 - 2.36 2.58 16.93 0 0 2.36 - 2.00 2.18 16.29 0 0.65 2.00 - 1.40 1.70 17.81 0 5.32 1.40 - 1.00 1.20 13.86 0 13.06 1.00 - 0.50. 0.75 20.18 0.09 40.19 0.50 - 0.25 0.375 5.90 13.25 20.34 0.25-0.125 0.188 0.58 6.14 1.16 0.125 - 0.106 0.116 0.01 0.24 0.03 > 0.106 0.053 0 0.19 0 Coal M.C. after run (%) 11.07 7.94 7.86-8.' Coal mass after run (g) 795.56 135.79 551.02 Production rate (0.125mm<dp<1.4 mm) (g/min) 107.16 Total product Cg) 642.96 Products from cyclone (g) 15.54 Total coal losses (g) 7.69 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature C Q 105 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.57 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 113.75 Air flowrate at orifice (mVrnin) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 6.72 Moisture content of air In/Out (kg water/kg dry air) 0.004/-Spouted bed height (mm) 226 * see Figure 5.3 (holdup) and Figure 5.4 (product). Run No.CH-6'" Continuous (products from top and bottom) 102 EXPERIMENTAL RESULTS Sieve analysis after run dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 11.59 0 0 2.80 - 2.36 2.58 18.33 0 0.06 2.36 - 2.00 2.18 15.92 0 0.75 2.00 - 1.40 1.70 19.25 0 6.81 1.40-1.00 1.20 12.56 0 13.59 1.00 - 0.50 0.75 17.09 0 40.02 0.50 - 0.25 0.375 4.74 11.75 19.70 0.25 - 0.125 0.188 0.49 6.15 1.09 0.125-0.106 0.116 0.01 0.20 0.03 > 0.106 0.053 0 0.15 0 Coal M.C. after run (%) 11.45 8.80 7.13-9.7 Coal mass after run (g) 759.85 121.30 545.32 Production rate (0.125rnm<dp<1.4 mm) (g/min) 102.47 Total product (g) 614.81 Products from cyclone (g) 15.10 Total coal losses (g) 18.55 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 105 Operating time (min) 6 Feed (initial) coal M.C. (%) 25.0 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 110.76 Air flowrate at orifice (mVmin) 1.92 Urns (m/s) 1.16 U/LTms 1.53 Mean residence time (min) 6.51 Moisture content of air In/Out (kg water/kg dry air) 0.0035/0.027 Spouted bed height (mm) 220 Run No.SCH-7 Semi-batch (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 3.05 0 0 2.80 - 2.36 2.58 8.46 0 0.11 2.36 - 2.00 2.18 11.52 0 0.36 2.00 - 1.40 1.70 18.86 0 2.06 1.40- 1.00 1.20 23.80 0 5.63 1.00 - 0.50 0.75 27.05 0.01 14.63 0.50 - 0.25 0.375 6.52 6.64 5.40 0.25-0.125 0.188 0.72 3.24 0.34 0.125-0.106 0.116 0.025 0.16 0.02 > 0.106 0.053 0 0.09 0 Coal M.C. after run (%) 10.50 10.09 11.95-11 Coal mass after run (g) 697.17 124.83 348.53 Production rate (0.125mm<dp<1.4 mm) (g/rain) 73.16 Total product (g) 438.98 Products from cyclone (g) 18.60 Total coal losses (g) 38.46 Initial coal holdup (g) 1223.68 OPERATING CONDITIONS Inlet air temperature CC) 95 Operating time (min) 6 Feed (initial) coal M.C. (%) 23.52 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) 0.0025/-Spouted bed height (mm) 216 * see Figure 5.2 (holdup). Run No.CH-7' Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp (mm) (mm) 3.35- 2.80 3.08 2.80- 2.36 2.58 2.36- 2.00 2.18 2.00- 1.40 1.70 1.40- 1.00 1.20 1.00- 0.50 0.75 0.50- 0.25 0.375 0.25- 0.125 0.188 0.125 -0.106 0.116 > 0.106 0.053 Coal M.C. after run (%) Coal mass after run (g) Holdup Products Top Bottom (Wt%) (Wt%) (Wt%) 12.15 0 0 19.42 0 0 16.67 0 0.53 16.86 0 4.88 12.94 0 15.83 17.13 0 39.09 4.27 9.73 13.10 0.52 6.43 0.86 0.02 0.25 0 0 0.25 0 13.00 8.42 7.91-9.98 732.63 124.73 549.25 Production rate (0.125mm<dp<1.4 mm) (g/min) 105.01 Total product (g) 630.09 Products from cyclone (g) 16.70 Total coal losses (g) 10.34 Initial coal holdup (g) -OPERATING CONDITIONS Inlet air temperature CC) 95 Operating time (min) 6 Feed (initial) coal M.C. (%) 23.26 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 123.17 Air flowrate at orifice (m3/min) 1.91 Urns (m/s) 1.16 TJ/Ums 1.53 Mean residence time (min) 5.95 Moisture content of air In/Out (kg water/kg dry air) 0.003/0.014 Spouted bed height (mm) 225 * see Figure 5.3 (holdup) and Figure 5.4 (product). 105 Run No.CH-7" Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 11.45 0 0 2.80 - 2.36 2.58 17.86 0 0 2.36 - 2.00 2.18 16.42 0 0.53 2.00 - 1.40 1.70 17.69 0 4.36 1.40-1.00 1.20 14.64 0 9.76 1.00 - 0.50 0.75 17.34 0 31.49 0.50 - 0.25 0.375 4.13 11.02 11.62 0.25-0.125 0.188 0.43 5.97 0.61 0.125-0.106 0.116 0.20 0.17 0 > 0.106 0.053 0 0.18 0 Coal M.C. after run (%) 11.84 8.70 8.81-10. Coal mass after run (g) 874.38 130.64 439.59 Production rate (0.125mm<dp<1.4 mm) (g/min) 88.41 Total product (g) 530.49 Products from cyclone (g) 15.08 Total coal losses (g) 15.64 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 95 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.73 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 125.45 Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 UAJms 1.53 Mean residence time (min) 8.73 Moisture content of air In/Out (kg water/kg dry air) 0.0045/0.016 Spouted bed height (mm) 232 Run No.SCH-8 Semi-batch (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 10.19 0 0 2.80 - 2.36 2.58 18.57 0 0.16 2.36 - 2.00 2.18 18.19 0 0.47 2.00 -1.40 1.70 21.24 0 1.54 1.40-1.00 1.20 15.67 0 2.73 1.00 - 0.50 0.75 13.14 0.03 5.95 0.50 - 0.25 0.375 2.54 4.20 1.87 0.25-0.125 0.188 0.27 3.17 0.10 0.125-0.106 0.116 0.18 0.13 0.01 > 0.106 0.053 0 0.07 0 Coal M.C. after run (%) 15.82 15.26 20.50-11 Coal mass after run (g) 918.98 91.85 154.97 Production rate (0.125mm<dp<1.4 mm) (g/min) 36.33 Total product (g) 217.97 Products from cyclone (g) 12.09 Total coal losses (g) 29.15. Initial coal holdup (g) 1207.04 OPERATING CONDITIONS Inlet air temperature C O 75 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.56 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.91 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) 0.003/0.013 Spouted bed height (mm) 242 * see Figure 5.2 (holdup). Run No.CH-8' Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 13.30 0 0 2.80-2.36 2.58 17.38 0 0 2.36 - 2.00 2.18 16.27 0 0.51 2.00- 1.40 1.70 19.25 0 6.43 1.40 - 1.00 1.20 15.87 0 18.00 1.00 - 0.50 0.75 14.80 0.45 32.78 0.50 - 0.25 0.375 2.83 11.72 13.35 0.25-0.125 0.188 0.29 6.98 0.63 0.125 - 0.106 0.116 0.01 0.21 0.03 > 0.106 0.053 0 0.14 0 Coal M.C. after run (%) 13.96 11.18 12.26-L Coal mass after run (g) 922.34 98.57 366.34 Production rate (0.125mm<dp<1.4 mm) (g/min) 71.41 Total product (g) 428.49 Products from cyclone (g) 13.41 Total coal losses (g) 27.93 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 75 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.41 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 85.1 Air flowrate at orifice (m3/min) 1.91 Urns (m/s) 1.16 LVUms 1.53 Mean residence time (min) 10.91 Moisture content of air In/Out (kg water/kg dry air) 0.004/0.0135 Spouted bed height (mm) 236 * see Figure 5.3 (holdup) and Figure 5.4 (product). Run No.SCH-9 Semi-batch (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 7.43 0 0 2.80 - 2.36 2.58 14.23 0 0.11 2.36 - 2.00 2.18 15.48 0 0.30 2.00 -1.40 1.70 20.13 0 2.17 1.40- 1.00 1.20 18.42 0 5.28 1.00-0.50 0.75 19.70 0.09 10.79 0.50 - 0.25 0.375 4.12 5.78 3.96 0.25-0.125 0.188 0.47 3.12 0.18 0.125 - 0.106 0.116 0.01 0.14 0.01 > 0.106 0.053 0 0.08 0 Coal M.C. after run (%) 14.34 13.82 13.93-L Coal mass after run (g) 779.07 111.18 275.18 Production rate (0.125mm<dp<1.4 mm) (g/min) 58.76 Total product (g) 352.53 Products from cyclone (g) 12.91 Total coal losses (g) 28.54 Initial coal holdup (g) 1206.88 OPERATING CONDITIONS Inlet air temperature (*C) 85 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.57 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) -Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 UAJms 1.53 Mean residence time (min) -Moisture content of air In/Out (kg water/kg dry air) 0.004/-Spouted bed height (mm) 277 * see Figure 5.2 (holdup). 109 Run No.CH-9' Continuous (products from top and bottom) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 14.83 0 0 2.80 - 2.36 2.58 19.23 0 0 2.36 - 2.00 2.18 16.50 0 0.37 2.00-1.40 1.70 16.72 0 3.76 1.40 - 1.00 1.20 12.79 0 10.26 1.00 - 0.50 0.75 16.09 0.15 25.40 0.50 - 0.25 0.375 3.46 7.02 11.26 0.25-0.125 0.188 0.36 6.23 0.61 0.125 - 0.106 0.116 0.01 0.17 0.02 > 0.106 0.053 0 0.20 0 Coal M.C. after run (%) 14.15 9.43 10.53-1 Coal mass after run (g) 1003.90 104.16 390.74 Production rate (0.125mm<dp<1.4 mm) (g/min) 76.78 Total product (g) 460.68 Products from cyclone (g) 12.59 Total coal losses (g) 23.67 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature (*C) 85 Operating time (min) 6 Feed (initial) coal M.C. (%) 24.25 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 126 Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (rnin) 11.33 Moisture content of air In/Out (kg water/kg dry air) 0.004/0.015 Spouted bed height (mm) 240 * see Figure 5.3 (holdup) and Figure 5.4 (product). Run No.TC-3 Continuous (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 8.50 0 -2.80 - 2.36 2.58 18.28 0.41 -2.36 - 2.00 2.18 16.82 0.81 -2.00 - 1.40 1.70 26.12 3.38 -1.40 - 1.00 1.20 17.84 9.61 -1.00 - 0.50 0.75 11.34 38.00 -0.50 - 0.25 0.375 0.95 27.14 -0.25-0.125 0.188 0.14 12.19 -0.125-0.106 0.116 0 0.29 -> 0.106 0.053 0 0.38 -Coal M.C. after run (%) 17.0 16.93 Coal mass after run (g) 767.16 481.31 -Production rate (0.125mm<dp<1.4 mm) (g/min) 20.92 Total product (g) 418.45 Products from cyclone (g) 20.27 Total coal losses (g) 20.27 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 20 Operating time (min) 20 Feed (initial) coal M.C. (%) 24.54 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 27.10 Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 29.5 Moisture content of air In/Out (kg water/kg dry air) 0.005/-Spouted bed height (mm) 228 * see Figure 5.8 (holdup) and Figure 5.9 (product). Run No.TCH-4 Continuous (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 7.87 0 -2.80 - 2.36 2.58 15.18 0.24 -2.36 - 2.00 2.18 11.54 0.54 -2.00 - 1.40 1.70 16.37 1.71 -1.40 - 1.00 1.20 21.32 5.00 -1.00 - 0.50 0.75 23.97 54.78 -0.50 - 0.25 0.375 3.27 21.44 -0.25 - 0.125 0.188 0.39 8.69 -0.125-0.106 0.116 0.08 0.87 -> 0.106 0.053 0.01 0.12 -Coal M.C. after run (%) 11.37 8.86 _ Coal mass after run (g) 867.16 1667.31 -Production rate (0.125mm<dp<1.4 mm) (g/min) 59.96 Total product (g) 1499.10 Products from cyclone (g) 54.72 Total coal losses (g) 62.99 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature C O 95 Operating time (min) 25 Feed (initial) coal M.C. (%) 23.42 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 75.40 Air flowrate at orifice (m3/min) 1.92 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 12.15 Moisture content of air In/Out (kg water/kg dry air) 0.006/-Spouted bed height (mm) 227 * see Figure 5.8 (holdup) and Figure 5.9 (product). Run No.TCH-4' Continuous (products from top only) 112 EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 8.68 0 -2.80 - 2.36 2.58 15.32 0.16 -2.36 - 2.00 2.18 11.29 0.37 -2.00 - 1.40 1.70 16.61 1.19 -1.40-1.00 1.20 20.86 3.87 -1.00 - 0.50 0.75 23.05 52.43 -0.50 - 0.25 0.375 3.55 21.38 -0.25 - 0.125 0.188 0.54 7.68 -0.125 - 0.106 0.116 0.103 2.73 -> 0.106 0.053 0 0.12 Coal M.C. after run (%) 10.00 8.10 Coal mass after run (g) 871.16 1693.33 -Production rate (0.125mm<dp<1.4 mm) (g/min) 57.82 Total product (g) 1445.40 Products from cyclone (g) 65.30 Total coal losses (g) 19.88 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 95 Operating time (rnin) 25 Feed (initial) coal M.C. (%) 24.20 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 75.30 Air flowrate at orifice (mVmin) 1.91 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 11.60 Moisture content of air In/Out (kg water/kg dry air) 0.005/0.016 Spouted bed height (mm) 220 * see Figure 5.8 (holdup) and Figure 5.9 (product). Run No.TCH-5 Continuous (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 9.60 0 -2.80 - 2.36 2.58 13.27 0.09 -2.36 - 2.00 2.18 13.20 0.14 -2.00-1.40 1.70 16.67 1.68 -1.40-1.00 1.20 19.84 3.50 -1.00 - 0.50 0.75 23.42 53.15 -0.50 - 025 0.375 3.51 25.19 -0.25-0.125 0.188 0.41 7.29 -0.125-0.106 0.116 0.066 2.44 -> 0.106 0.053 0 0.12 -Coal M.C. after run (%) 10.59 9.20 _ Coal mass after run (g) 819.36 1644.37 -Production rate (0.125mm<dp<1.4 mm) (g/min) 58.63 Total product • (g) 1465.60 Products from cyclone (g) 54.95 Total coal losses (g) 58.94 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature (°C) 75 Operating time (min) 25 Feed (initial) coal M.C. (%) 23.93 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 68.25 Air flowrate at orifice (m3/min) 1.91 Ums (m/s) 1.16 UAJms 1.53 Mean residence time (min) 12.43 Moisture content of air In/Out (kg water/kg dry air) 0.0025/0.013 Spouted bed height (mm) 222 * see Figure 5.8 (holdup) and Figure 5.9 (product). Run No.TCH-6 Continuous (products from top only) 114 EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 10.38 0 -2.80 - 2.36 2.58 14.87 0.09 -2.36-2.00 2.18 14.48 0.14 -2.00- 1.40 1.70 18.65 1.68 -1.40 - 1.00 1.20 19.84 3.50 -1.00 - 0.50 0.75 19.31 53.15 • -0.50 - 0.25 0.375 2.06 25.19 -0.25-0.125 0.188 0.34 7.29 -0.125-0.106 0.116 0.06 2.44 -> 0.106 0.053 0 0.12 -Coal M.C. after run (%) 13.32 12.25 _ Coal mass after run (g) 769.79 1579.96 -Production rate (0.125mm<dp<1.4 mm) (g/min) 46.03 Total product (g) 1380.90 Products from cyclone (g) 60.53 Total coal losses (g) 72 Initial coal holdup (g) -)PERATING CONDITIONS Inlet air temperature CC) 50 Operating time (min) 30 Feed (initial) coal M.C. (%) 23.88 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 55.43 Air flowrate at orifice (m3/min) 1.93 Urns (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 14.50 Moisture content of air In/Out (kg water/kg dry air) 0.005/0.0095 Spouted bed height (mm) 220 * see Figure 5.8 (holdup) and Figure 5.9 (product). Run No.TCH-7 Continuous (products from top only) 115 EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 9.47 0 -2.80 - 2.36 2.58 16.66 0 -2.36 - 2.00 2.18 13.17 0.86 -2.00 - 1.40 1.70 16.10 1.74 -1.40-1.00 1.20 17.99 4.47 -1.00 - 0.50 0.75 23.71 53.91 -0.50 - 0.25 0.375 2.54 21.41 -0.25-0.125 0.188 0.28 7.43 -0.125-0.106 0.116 0.07 2.93 -> 0.106 0.053 0 0.18 -Coal M.C. after run (%) 10.15 8.20 _ Coal mass after run (g) 883.86 1877.92 -Production rate (0.125mm<dp<1.4 mm) (g/min) 72.80 Total product (g) 1637.92 Products from cyclone (g) 58.27 Total coal losses (g) 84.57 Initial coal holdup (g) -OPERATING CONDITIONS Inlet air temperature C Q 95 Operating rime (min) 22.5 Feed (initial) coal M.C. (%) 23.57 Feed (initial) coal size (mm) 2.80-3.35 Coal feedrate (g/min) 92.25 Air flowrate at orifice (m3/min) 1.91 Ums (m/s) 1.16 U/Ums 1.53 Mean residence time (min) 9.84 Moisture content of air In/Out (kg water/kg dry air) 0.007/0.0195 Spouted bed height (mm) 230 * see Figure 5.8 (holdup) and Figure 5.9 (product). Run No.CI-1 Continuous (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 19.59 1.91 -2.36 - 2.00 2.18 29.84 3.87 -2.00 - 1.40 1.70 28.54 6.34 -1.40 - 1.00 1.20 18.28 11.88 -1.00-0.50 0.75 3.41 43.02 -0.50 - 0.25 0.375 0.27 21.74 -0.25 - 0.125 0.188 0.15 10.06 -0.125-0.106 0.116 0.02 1.58 -> 0.106 0.053 0 0.13 -Coal M.C. after ran (%) 19.32 18.47 _ Coal mass after run (g) 2214.83 1119.97 -Production rate (0.125mm<dp<1.4 mm) (g/min) 48.55 Total product (g) 971 Products from cyclone (g) 56.40 Total coal losses (g) -Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 23 Operating time (min) 20 Feed (initial) coal M.C. (%) 24.08 Feed (initial) coal size (mm) 2.36-2.80 Coal feedrate (g/min) 55.70 Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 0.88-0.90 U/Ums 2.0 Mean residence time (min) 39.76 Moisture content of air In/Out (kg water/kg dry air) -/-Spouted bed height (mm) 275 Run No.CI-2 Continuous (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 11.03 0.55 -2.36 - 2.00 2.18 22.48 2.28 -2.00 - 1.40 1.70 33.51 4.90 -1.40 - 1.00 1.20 25.35 10.93 -1.00-0.50 0.75 7.07 40.72 -0.50 - 0.25 0.375 0.45 25.25 -0.25-0.125 0.188 0.08 7.69 -0.125 - 0.106 0.116 0.03 1.44 -> 0.106 0.053 0 0.06 -Coal M.C. after run (%) 19.17 17.87 _ Coal mass after run (g) 2105.64 2124.79 -Production rate (0.125mm<dp<1.4 mm) (g/min) 56.15 Total product (g) 1796.93 Products from cyclone (g) 70.06 Total coal losses (g) 173.82 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 23 Operating time (min) 32 Feed (initial) coal M.C. (%) 23.99 Feed (initial) coal size (mm) 2.36-2.80 Coal feedrate (g/min) 68.44 Air flowrate at orifice (mVrnin) 1.92 Urns (m/s) 0.88-0.90 U/Ums 2.0 Mean residence time (min) 32.70 Moisture content of air In/Out (kg water/kg dry air) - / -Spouted bed height (mm) 275 * see Figure 5.14 (holdup and product). 118 Run No.HCI-1 Continuous (products from top only) EXPERIMENTAL RESULTS Sieve analysis after run* dp dp Holdup Products Top Bottom (mm) (mm) (Wt%) (Wt%) (Wt%) 3.35 - 2.80 3.08 - - -2.80 - 2.36 2.58 8.84 0 -2.36 - 2.00 2.18 13.06 0.33 -2.00-1.40 1.70 25.45 0.77 -1.40-1.00 1.20 37.98 3.33 -1.00 - 0.50 0.75 13.79 65.94 -0.50 - 0.25 0.375 0.66 16.26 -0.25-0.125 0.188 0.20 8.23 -0.125-0.106 0.116 0.037 1.82 -> 0.106 0.053 0 0.15 -Coal M.C. after run (%) 13.02 11.53 _ Coal mass after run (g) 2300.01 3353.57 -Production rate (0.125mm<dp<1.4 mm) (g/min) 104.78 Total product (g) 3143.30 Products from cyclone (g) 95.74 Total coal losses (g) 16.05 Initial coal holdup (g) OPERATING CONDITIONS Inlet air temperature CC) 95 Operating time (min) 30 Feed (initial) coal M.C. (%) 24.02 Feed (initial) coal size (mm) 2.36-2.80 Coal feedrate (g/min) 121.99 Air flowrate at orifice (m3/min) 1.92 Ums (m/s) 0.88-0.90 U/Ums 2.0 Mean residence time (min) 20 Moisture content of air In/Out (kg water/kg dry air) 0.007/0.022 Spouted bed height (mm) 275 * see Figure 5.14 or Figure 6.5 (holdup and product). 

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