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Improvement of steel quality by using hydrocarbon gas in a converter Lee, Dong-Ryeol 2006

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Improvement of Steel Quality by Using Hydrocarbon Gas in a Converter by Dong-Ryeol Lee B.Sc, Pusan National University, Pusan, Korea, 1990 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in The Faculty of Graduate Studies (Materials Engineering) The University of British Columbia March 2006 © Dong-Ryeol Lee, 2006 ABSTRACT Minimizing alumina (AI2O3) or other nonmetallic oxide inclusions formed during deoxidation is an important factor in producing 'quality' steel. Although a variety of practices are employed to encourage floatation of such deoxidation products prior to solidification, complete removal is never achieved. The amount of AI2O3 formed during deoxidation is determined by the residual dissolved oxygen present in the steel after decarburization. In a combined practice converter with Ar and/or N2 gas bottom-blowing, thermodynamics suggests [%C] x [%0] ~ 0.0021 at the end of the blow. In practice, the dissolved oxygen content is •— 525 ppm at 0.04% C which is consistent with thermodynamic predictions and indicates that, for a given %C, the combined blowing practice has achieved its lowest possible (equilibrium) oxygen level. Thermodynamic calculations indicate that injection of gaseous hydrocarbons such as methane (CH4), partly replacing Ar and/or N2 , might allow significantly lower residual oxygen levels to be achieved; i.e. based on thermodynamics, [%C]x[%0] ~ 0.000009 which translates into ~ 2 ppm dissolved oxygen at 0.04%C. In addition, the products of the deoxidation reaction are gaseous CO, CO2 and H2O rather solid or liquid AI2O3 or Si02 that can be difficult to completely remove prior to solidification. Substituting relatively cheap CH4 for traditional deoxidizing additions such as aluminum or ferro-silicon might also lower overall costs. This research involved experimental investigation of methane deoxidation backed-up by thermodynamic modeling to assess the theoretical limits for the process. The work also examined deoxidation rate and the impact of H and C solution into the steel. During the trials —20 ppm residual oxygen was achieved. Although greater than thermodynamic predictions, this suggests the process might be of commercial interest. ii LIST OF CONTENTS ABSTRACT ii LIST OF CONTENTS iii LIST OF TABLES v LIST OF FIGURES vi ACKNOWLEDGEMENTS viii 1. Introduction 1 2. Literature Review • 8 2.1 Introduction 8 2.2 Iron making process 8 2.3 Pretreatment Process of Hot Metal 8 2.4 BOF Process 10 2.5 Secondary refining process 22 3. Thermodynamic Review 25 3.1 Characteristic of Hydrocarbon Gases 25 3.2 Thermodynamic calculations 27 3.2.1 Oxygen content with a conventional combined blowing process 27 3.2.2 Oxygen value with CH 4 blowing 29 3.2.3 Hydrogen content in conventional combined blowing 30 3.2.4 Hydrogen content with CH4 blowing 31 3.3 Summary of the Thermodynamics Review 33 4. Objectives 34 5. Experimental Apparatus and Procedure 35 5.1. Experimental Apparatus 35 5.2. Experimental Methodology 38 5.2.1. Experimental Design 38 5.2.2. Experimental Procedure 42 6. Results and Discussion 44 6.1 Deoxidation form 'Low' Initial Dissolved Oxygen 44 6.1.1 Results for 200cc/min CH 4 44 6.1.2 Results for 150cc/min CH 4 44 iii 6.1.3 Results for 120cc/min CH 4 44 6.1.4 Comparison of Experimenatal and Thermodynamic Results 46 6.2 Depxidation form 'High' Initial Dissolved Oxygen 49 6.2.1 Results for 150cc/min of CH 4 49 6.2.2 Results for lOOcc/min of CH 4 50 6.2.3 Carbon Pick-up (Recarburization) 51 6.2.4 The Role of Carbon in the Process 54 6.3 Hydrogen Pick up 56 7.Summary and Conclusions 58 REFERENCES 60 APPENDIX 62 iv LIST OF TABLES TABLE 1.1 THE MAJOR COMBINED BLOWN CONVERTERS 4 TABLE 2.1 THE EXPERIMENTAL CONDITIONS 11 TABLE 2.2 TYPES OF TOP, BOTTOM AND PROTECTIVE GAS IN B O F AND Q-BOP. 14 TABLE 2.3 DISSOLVED OXYGEN AT TAPPING AND RELATED VARIABLES 18 TABLE 2.4 RESULTS OBTAINED DURING LADLE TREATMENT BY BOTTOM ARGON OR NATURAL GAS INJECTION IN FOUR DIFFERENT HEATS IN EMIS 24 TABLE 3.1 THE SPECIFICATIONS OF HYDROCARBON GASES 26 TABLE 3.2 CHANGES OF GIBBS FREE ENERGY IN REACTIONS INVOLVING C H 4 GAS AT 1873K 26 TABLE 3.3 THE EQUILIBRIUM CONTENT OF DISSOLVED OXYGEN 28 TABLE 3.4 THE EQUILIBRIUM CONTENT OF DISSOLVED OXYGEN 29 TABLE 5.1 SPECIFICATIONS OF THE GASES USED IN THE EXPERIMENTS (PRAXAIR) 40 TABLE 5.2 EXPERIMENTAL CONDITIONS ON FLOW RATE, TEMPERATURE AND INITIAL [O]. 43 v LIST OF FIGURES FIGURE 1.1 SCHEMATIC DIAGRAM OF CURRENT IRON AND STEELMAKING OPERATIONS 3 FIGURE 1.2 GENERAL CONVERTER CLASSIFICATION 3 FIGURE 1.3 THE CHANGES OF [%C]x[%0] WITH NORMAL LD OPERATION AND COMBINED-BLOWING ( B A P ) OPERATION 4 FIGURE 1.4 DISSOLVED OXYGEN AS A FUNCTION OF FINAL CARBON FOR B O P (TOP-BLOWING) AND L B E - B O P (COMBINED BLOWING) 7 FIGURE 2.1 SCHEMATIC DIAGRAM OF THE HISMELT SMELT REDUCTION VESSEL 9 FIGURE 2.2 THE EXPERIMENTAL APPARATUS FOR THE COMBINED PROCESS 11 FIGURE 2.3 COMPARISON OF 0 2 /CH 4 AND 0 2 /N 2 AS BOTTOM BLOWING GASES 13 FIGURE 2.4 RELATIONSHIP BETWEEN [H] AND OXYGEN CONSUMPTION OF THE BOTTOM BLOWING 13 FIGURE 2.5 SCHEMATIC DIAGRAM OF THE COMBINED BLOWING B O F AND Q - B O P 14 FIGURE 2.6 BOTTOM BLOWING SYSTEM LAYOUT IN No.2 SHOP AHMS A IN MEXICO 16 FIGURE 2.7 BOTTOM GAS BLOWING PATTERN AT AHMS A IN MEXICO 16 FIGURE 2.8 CARBON OXYGEN CONTENT AT TURNDOWN (THE SECOND CAMPAIGN OF COMBINED BLOWING) 17 FIGURE 2.9 [%0] VERSUS [%C] IN LD AND COMBINED BLOWING WITH HYDROCARBON GAS 17 FIGURE 2.10 DEPHOSPHORIZATION EFFECT BY POST STIRRING (THE THIRD CAMPAIGN OF COMBINED BLOWING) 18 FIGURE 2.11 [H] IN THE LADLE VERSUS TOTAL ARGON VOLUME DURING B O F POST STIRRING. 19 FIGURE 2.12 [H] IN THE LADLE VERSUS [ O ] AT B O F TAPPING. 20 FIGURE 2.13 ABSORPTION OF HYDROGEN IN LIQUID STEEL FROM CONTACTING WITH H2O VAPOUR 20 FIGURE 2.14. [%H] PPM IN THE LADLE VERSUS [%MN] 21 FIGURE 2.15 LADLE METALLURGY PILOT PLANT AT IMIS 23 FIGURE 3.1 EQUILIBRIUM CARBON AND OXYGEN CONTENT AT 1600TJ 28 FIGURE 3.2 THE CARBON-HYDROGEN EQUILIBRIUM FOR SEVERAL PARTIAL PRESSURES OF CH 4 33 FIGURE 5.1 THE EXPERIMENTAL APPARATUS SHOWING BOTH THE FURNACE (FOREGROUND) AND POWER SUPPLY/CONTROL PANEL (BACKGROUND) 36 FIGURE 5.2 DETAILS OF THE CONTROL PANEL FOR THE FURNACE 36 VI FIGURE 5.3 THE VACUUM PUMP (TOP) AND FURNACE (BOTTOM) 37 FIGURE 5.4 SCHEMATIC DIAGRAM OF THE EXPERIMENTAL APPARATUS 38 FIGURE 5.5 THE OXYGEN AND HYDROGEN SAMPLERS 41 FIGURE 6.1 DISSOLVED OXYGEN VERSUS CUMULATIVE C H 4 (200 CC/MIN STARTING FROM 'LOW' INITIAL OXYGEN) 45 FIGURE 6.2 DISSOLVED OXYGEN VERSUS CUMULATIVE C H 4 (150 CC/MIN STARTING FROM 'LOW' INITIAL OXYGEN) 45 FIGURE 6.3 DISSOLVED OXYGEN VERSUS CUMULATIVE C H 4 (120 CC/MIN STARTING FROM 'LOW' INITIAL OXYGEN) 46 FIGURE 6.4 EMF VERSUS DISSOLVED OXYGEN AT 1600°C USING SCHMARZRIED'S RELATIONSHIP 48 FIGURE 6.5 [O] VERSUS CUMULATIVE QUANTITY OF C H 4 (150CC/MIN) 49 FIGURE 6.6 [O] VERSUS CUMULATIVE QUANTITY OF CH4(100CC/MIN) 50 FIGURE 6.7 [O] AND CARBON VERSUS CUMULATIVE CH4 STARTING FROM 'LOW' INITIAL OXYGEN (15 OCC/MIN) 51 FIGURE 6.8 [O] AND CARBON VERSUS CUMULATIVE CH4 STARTING FROM 'HIGH' INITIAL OXYGEN (100CC/MIN) 53 FIGURE 6.9 [O] AND CARBON VERSUS CUMULATIVE CH4 STARTING FROM 'HIGH' INITIAL OXYGEN (150CC/MIN) 53 FIGURE 6.10 CARBON UTILIZATION FOR DEOXIDATION 54 FIGURE 6.11 CARBON UTILIZATION FOR RECARBURIZATION 55 FIGURE 6.12 TOTAL CARBON UTILIZATION AT 100CC/MIN CH4 56 FIGURE 6.13 TOTAL CARBON UTILIZATION AT 15OCC/MIN CH4 56 FIGURE 6.14 DISSOLVED HYDROGEN AND OXYGEN AS FUNTION OF CUMMULATIVE CH4 ..57 vii A C K N O W L E D G E M E N T S Even one small achievement usually cannot be done by oneself. This work is a result of many people's help and I would like to express heartfelt thanks. First of all, I would like to thank my supervisors Professors Ray Meadowcroft and Peter Barr for providing me the opportunity to work with them in the Department of Materials Engineering at UBC. Their advice, instruction and encouragement were very helpful and made the project an enjoyable learning experience. Assistance with the experiment work provided by Milaim Dervishaj is really appreciated. Thanks are also due to many faculty and staff in the department for advice and assistance. I would like to thank Dr. Hyeon-Soo Choi in the Steelmaking Research Group at POSCO for his advice and help. Financial support for this work by UBC and Pohang Iron and Steel Co, Ltd. (POSCO) is gratefully acknowledged. viii 1. Introduction The Basic Oxygen Steelmaking (BOS) process is the dominant steelmaking technology that is used by approximately 60% of the world's steel producers. Figure 1.1 shows a schematic diagram of the iron and steelmaking process. In the converter process, the pure oxygen injected removes carbon as carbon monoxide CO and carbon dioxide CO2 gas. Other components such as Mn, Si and P are oxidized and combine with lime (CaO) and FeO formed by the oxidation of Fe to form a molten slag. The oxygen blowing time is 15 to 20 minutes. Because the oxygen flow rate to the lance is adjusted to the melt weight, blowing time is essentially constant for heats ranging anywhere from 70 to 400 tonnes. The charging and discharging of steel and slag, including sampling for temperature and analysis of the melt, extends the tap to tap time of a converter to around 40 minutes. The high productivity and steel of low impurity content process are the main feature of the converter. As shown in Fig. 1.1, steel from the converter is transferred to the continuous caster via a refractory lined ladle. Metallurgical operations within the ladle usually include deoxidation and alloy addition. Roughly 50% of steel production is also vacuum degassed, in this instance by the RH process (Ruhrstahl-Heraeus) in which the steel is circulated from the ladle by gas injection into one leg of a vacuum chamber (to lower the density and induce upward flow to the vacuum chamber) and the degassed steel flows back to the ladle through the second leg. Vacuum treatment achieves reduction of the hydrogen content to less than 2 ppm and also allows decarburization to as low as 30 ppm. Since the first commercial operation of the top-blown converter in the early 1950s at Linz and Donawitz (LD converter), other variations have been developed using bottom or . 1 combined (top and bottom) blowing. In 1968, hydrocarbon-protected tuyeres were developed and applied commercial operations. These new 'shielded' tuyeres relied on the endothermic reaction of the cracking of the gas to cool the annular tuyere. This development made possible the birth of bottom blowing oxygen steelmaking processes such as OBM (Germany, Maxmillianhutte) and Q-BOP(US, US Steel) in the early 1970s. Further developments have been made to take advantage of top blowing and bottom blowing converters. Figure 1.2 and Table 1.1 show bottom and combined blowing processes with stirring gases such as N2, Ax and CO2. Since the early days of oxygen steelmaking, the quality of steel from a converter, often expressed by the product of. carbon and free oxygen content at turndown, has steadily improved. Generally speaking, the [%C]x[%0] from combined blowing converter is lower than that of LD converter due to the stirring effects of the bottom gas, i.e. the effect of bottom blowing can improve the efficiency of mass transfer for carbon in molten steel to the oxygen in the converter so the system can more closely approach the equilibrium. Figure 1.3 shows the effects of bottom stirring gas in the converter. The values of the [%C]x[%0] from the LD converter and combined blowing converter are 0.0033±0.0002 and 0.0021±0.0002 respectively. 2 (Oe-S, P) (De-C, P) Tapping RH degasser Continuous Casting (De-Oxidation, (De-C, N, H) (Slab, Bloom, Billet) Ferro-alloy) Figure 1.1 Schematic diagram of current iron and steelmaking operations (typical). Oxygen lanes Hydrocarbon Oxygen— t t N 2 Ar BOF Figure 1.2 General converter classification. 3 Table 1.1 The major combined blown converters. Process Developer Bottom gases injected Bottom gas flow rate (Nm /minute-ton) Bottom wear Rate (mm/heat) LBE ARBED-IRSID N 2 ,Ar 0.01-0.10 0.3-0.6 LD-CB NSC (Nippon Steel Corp) C0 2 , N 2 ,Ar 0.02-0.06 0.3-0.8 LD-KGC KSC (Kawasaki Steel Corp.) CO,N 2 ,Ar 0.01-0.20 0.2-0.3 LD-OTB Kobe Steel Corp. CO,N 2 ,Ar 0.01-0.10 0.2-0.3 NK-CB NKK (Nippon Kokan Corp.) C0 2 , N 2 , Ar 0.02-0.10 0.7-0.9 o 50 E 40 c d : 5 s 30 i £ 2 0 10 Normal LD mean value = 33.6 * Y ^ V BAP operation mean value = 20.8 I I i i ••• 0 200 400 600 800: Heat 1000 1200 1400 Figure 1.3 The changes of [%C]x[%0] with normal LD operation and combined-blowing (BAP) operation.3) 4 Figure 1.4 shows the relationship between carbon and oxygen content at the blow end in a converter from plant data. The BOP and LBE-BOP process represent top blowing and combined blowing respectively. The oxygen content from the combined blowing process is lower than that of the top blowing process at the same carbon content. For example, at 0.05%C the dissolved oxygen of the BOP and LBE-BOP are approximately 630ppm and 450ppm respectively due to the effect of the bottom gas (in case of the LBE-BOP). However, for current converter operations, unless bottom blowing includes species which are reactive with dissolved oxygen there is little opportunity for further reducing dissolved oxygen levels from the converter. The dissolved oxygen in molten steel must be largely removed before casting, otherwise it will cause quality problems such as pin holes which may occur due to entrapped gas or shrinkage during solidification. This is normally accomplished by the addition, downstream of the converter, of elements such as Al, Si or Mn that have a strong affinity for oxygen to form AI2O3, Si02 or MnO, called nonmetallic inclusions. For ingot casting a variety of deoxidation levels have been employed ranging (in order of decreasing final oxygen) from rimmed to semi-killed and finally killed. For modern continuous casting operations, virtually all steel is killed. To prevent quality problems, carry-over of inclusions into the solidified steel product must be minimized by a combination of reducing the amount generated during deoxidation and effective flotation prior to casting. Techniques include argon bubbling and optimization of slag composition in the ladle, vacuum treatment to reduce hydrogen and nitrogen, and Ar sealing of the molten steel against atmosphere. Clearly, lower dissolved oxygen in the steel from the converter will reduce the amount of inclusions formed during deoxidation (and 5 presumably the amount finding its way into the solidified steel) which is why the oxygen level in the converter at turndown can be regarded as an index of steelmaking technology and quality of the molten steel. One option for reducing dissolved oxygen from the converter is the injection of a hydrocarbon gas to react with dissolved oxygen to form H2O and some CO/CO2. This would most likely be done during the late stages of oxygen blowing and up to tapping or even in the ladle. In any event, using hydrocarbon gases for deoxidation is advantageous in that the deoxidation products are gases CO, C0 2 or H 2 0 which flow freely from the melt rather than solid or liquid oxide inclusions having a small density difference to drive flotation from the liquid metal. However, hydrocarbon injection raises issues such as recarburization (since oxygen levels are now below the [C]-[0] equilibrium carbon will go into solution) and hydrogen dissolution. Regardless of where hydrocarbon deoxidation is practiced, any reduction in the reliance on traditional (expensive) aluminum or ferro-silicon deoxidants has the potential for reduced costs. As noted earlier, hydrocarbon gas has been used as the cooling medium for the bottom tuyeres by the endothermic 'cracking' reaction. However, the quantity of gas is too small to play any significant role in deoxidation. The focus of the current work was to examine the feasibility of using CH4 gas in relatively large quantities for the purpose of lowering dissolved oxygen from the converter. Additional factors, such as the dissolution behaviour of hydrogen, would also be examined. 6 7 2. Literature Review 2.1 Introduction hydrocarbon gas has been reported that it is widely used as a reactive, cooling and stirring medium for iron making and steelmaking processes. In this chapter, the effects of hydrocarbon gas in various processes such as iron making, hot metal pretreatment, converter and secondary refining processes are reviewed. 2.2 Iron making process The HIsmelt process that is shown in Figure 2.1 is one of the direct smelting processes for iron ore. Hydrocarbon gas is supplied to provide supplementary cooling of the tuyere. Endothermic cracking of hydrocarbon gas injected through the outer annulus of the tuyere is the chemical cooling mechanism. It can reduce the wear rate of the bottom tuyere. 2.3 Pretreatment Process of Hot Metal5) IMIS, a Mexican research institute, reported that hydrocarbon gas was used as a bottom stirring gas. According to research at IMIS, it was used to effect desulfurization of hot metal through the addition of sodium metalsilicate reagents to the empty ladle just before hot metal charging, followed by injection of hydrocarbon gas to the hot metal charging ladle. The application of hydrocarbon gas was proved to be effective in the industrial trials with a 100 ton hot metal charging ladle. The results of industrial performance are as follows; 1) Using 8~10kg of gas per ton of iron, sulfur was reduced to about 50ppm which is about 80% removal. 8 2) The use of additional equipment and lance for powder injection is eliminated and cost reduction in a hot metal desulfurization process was achieved. 3) The operation was more reliable in operation than that with conventional lance injection in a desulfurization process. Figure 2.1 Schematic diagram of the HIsmelt smelt reduction vessel.' 9 2.4 BOF Process Hydrocarbon gas is generally applied as part of the bottom gas in a combined blowing converter. Generally speaking, the purpose of bottom blowing in the converter is lowering the level of final dissolved oxygen in molten steel and total Fe- oxide in slag. The types of bottom blowing gas are as follows; 1) Inert stirring gases such as Ar and N2 2) Reactive and stirring gases such as O2 and hydrocarbon gases 3) Protective gases for the bottom tuyere such as CO2 and hydrocarbon gas. Two different effects of hydrocarbon gas as a bottom blowing gas in combined blowing converters were reviewed. One of the main uses of hydrocarbon gas is as a cooling medium for the bottom tuyere (nozzle) in a converter process. Chongqing University in China studied the effects of hydrocarbon gas with the experimental apparatus shown in Figure 2.2 and the experimental condition in Table 2.1. After iron pieces were melted and the temperature measured and adjusted, the first turn of slag materials and then top blowing was applied. At the same time, bottom blowing gas was changed from nitrogen to oxygen. The oxygen of the top blowing was stopped when a carbon flame appeared. Thereafter, the second turn of slag material was added and the top lance was dropped again. 10 conyer/cer °^ yj|r i nauetor. d | ~ V - top-bicst lb.nc» Udrke - protecting brick bottom-blast lance Figure 2.2 The experimental apparatus for the combined blowing process. Table 2.1 The experimental conditions. Model converter lOOkW induction furnace and 1/240 scale model in weight of the real converter. Top lance nozzle Tube-shaped bobbin with inner diameter of 25mm Bottom nozzle - Two concentric tubes (diameter of inner tube was 1mm and the width of seem is 0.20~0.25mm.) - Location: center or eccentrically at the 0.3 diameter position of the converter bottom. Average oxygen blown amount 59Nm3/t with outlet pressure of 0.4~0.55MPa (oxygen flow rate through the top and bottom lances varied in the range of 4.5-5.5 and 0.20-0.35 Nm3/min-t respectively.) Quantity and species of hydrocarbon gas - Species: natural gas - Quantity: 12-18% of the bottom oxygen-blown amount. Material composition 3.68-4.20% C, 0.45-0.60% Si, 0.35-0.65% M n and 0.30-0.85% P Slag forming materials Lime (90~100kg/t), mica (4~8kg/t), iron scale (8~12kg/t) 11 Figure 2.3 shows the variation of bath composition during bottom blowing by O2- CH4 and O2-N2. It was observed that O2-CH4 as a bottom gas showed a higher reaction rate and shorter blowing time than that of O2-N2 gas. Based on these experimental results, it could be considered that natural gas had a high possibility for good metallurgical characteristics such as low [P] content and fast blowing time. In spite of excellent metallurgical characteristics, there was a problem with hydrogen pickup in molten steel as shown in Figure 2.4 when natural gas was used as cooling medium for the bottom blowing with oxygen nozzle. Therefore, this experimental study revealed that the rate of bottom blowing with oxygen gas must be controlled to a certain extent depending on the different steel grades with their limit of hydrogen in steel. An example of using hydrocarbon gas in steelmaking plants is shown in Figure 2.5 showing the combined blowing and Q-BOP converter. Table 2.2 shows the types of top blowing, bottom blowing and protective gas for tuyeres. In the case of LD-OB, K-BOP and Q-BOP, oxygen gas is supplied from the bottom tuyere and hydrocarbon gas is injected into the bath through the outer tuyere to protect the bottom tuyere. The main function of hydrocarbon gas is protection of the tuyere, not lowering of the level of dissolved oxygen in molten steel. 12 cooling medium Cfy cooling medium N2 5 s 0.61 a 25 50 75 Blowing process,*/* Figure 2.3 Comparison of O2/CH4 and O2/N2 as bottom blowing gases.9) 8 0 tHl=3.66ew o o0R • r=0.95 (Cl OB-0.25*/. 0 3 ft OBR . % ,1 Figure 2.4 Relationship between [H] and oxygen consumption of the bottom blowing K 13 /7 C O Ar N 2 r /7 Inner tube j f ^ r._., O2 — , N 2 -Ar -CO2-O2 wr// Outer tube (Coolant) C 3 H 8 LD-KGC T / 7 ^ Inner tube ^f^| r O2 — N 2 — I Ar -K-BOP Outer tube (Coolant) C 3 H 8 Q-BOP Figure 2.5 Schematic diagram of the combined blowing BOF and Q-BOP. Table 2.2 Types of top, bottom and protective gas in BOF and Q-BOP. 1 2 ) LD-KGC LD-OB K-BOP Q-BOP Top blowing gas Oxygen Oxygen Oxygen -Bottom blowing gas Ar, N 2 , CO 0 2 ,Ar ,N 2 , CO 02,N 2,Ar, C0 2 0 2 ,Ar Protective gas for tuyere - Natural gas Natural gas Natural gas 14 In addition to the use of hydrocarbon gas for protection of the tuyere, it is also used as a reactive gas from the bottom tuyere(nozzle) in a converter process. This performance was reported by IMIS and AHMS A Steelmaking plant, a steel research institute and steel works in Mexico respectively. Figure 2.6 shows the bottom blowing system layout in No.2 shop AHMSA which has two 150 ton BOF combined blowing converters. The bottom blowing pattern for the production of low carbon aluminum killed steel at No.2 shop is shown in Figure 2.7. Hydrocarbon gas from natural gas is injected during refining and standby while argon gas is injected during re-blowing and post-stirring. The metallurgical results show that bottom blowing with hydrocarbon gas allowed rapid and improved gas-slag-metal interaction as shown in Figure 2.8. These performance values were lower than the theoretical carbon-oxygen relationship found with the LD process. The [%C] x [%0] for combined blowing with hydrocarbon gas was lower than that of LD as shown in Figure 2.9. This has very important consequences on the metallurgy of the steelmaking process as shown by Table 2.3 that compares the oxidation level at tapping between the LD operation and the combined blown process with hydrocarbon gas. It is noted that the decrease of (%FeO) and reduction of slag volume resulted in lower flux consumption and increase in metallic yield by 1.6 percent. The low dissolved oxygen level using hydrocarbon as a bottom gas can reduce the unit consumption of deoxidation materials and alloying additions. In addition, it was possible to get higher dephosphorization during the post-stirring period as shown in Figure 2.10. 15 t IQ I ID A KG/ON P » " i : • 15 bat EVAPORATORS N A T I R A L O A S MTROO EN • I 4 k f VI I R0 0 f S n • 5 k j .- m • l l l l l l l P U R G E N I T R O G E N Til IN ST R II M EN T A T ION K E Y B O A R D Figure 2.6 Bottom blowing system layout in No.2 shop AHMSA in Mexico.I3) —1 9 c\j 'as O X 5 o 2 1.5 1 7 6 5 4 3 2 1 1 Blowing Post-Stirring Reblowifig Tapping Charging 10 20 30 Time (min.) 40 Figure 2.7 Bottom gas blowing pattern at AHMSA in Mexico.14) 16 900 800 I 700 gj 600 8 300 o > V) Z 400 300 200 T » I624«C Equilibrium Pco • lotm. 0.015 0.025 0.035 0.043 CARBON CONTENT {%) n d 0.053 Figure 2.8 Carbon oxygen content at turndown (2 campaign of combined blowing) 15) [Olppm O Combined blowing • LD (%C) Figure 2.9 [%0] versus [%C] in LD and combined blowing with hydrocarbon gas.16) 17 Table 2.3 Dissolved oxygen at tapping and related variables. LD Combined blowing Campaign 98 Campaign 1 Campaign 2 Campaign 3 [0], ppm 694 562 430 330 [%C] 0.039 0.030 0.027 0.024 (%FeO) 32 28 24 24 Metallic Yield, % 91.1 91.5 92.0 92.7 o a 2 0.0? 0.03 (%P) BLOW ENO 0.04 0.05 Figure 2.10 Dephosphorization effect by post stirring (3rd campaign of combined blowing). 18 When Ar gas was blown after the main oxygen blow, it was found that 3~4ppm of the reduction of hydrogen was possible as shown in Figure 2.11. In the case of bottom blowing using pure hydrocarbon gas, the hydrogen content was 7.3ppm. Hydrogen content was lowered to the normal level of conventional LD converter by the application of Ar after top blowing end. This measurement was consistent with a relatively low level of dissolved oxygen at tapping compared with normal hydrogen contents obtained in the conventional LD converter. As shown in Figure 2.12 the oxidation level at turndown had a very clear effect on hydrogen level. The hydrogen content in molten steel increased when the oxidation level decreased. Absorption of hydrogen in liquid steel is affected by moisture also. As shown in Figure 2.13, absorption of hydrogen in liquid steel under dry winter weather is lower than that of any other circumstances such as wet summer or steam due to the decrease of the partial pressure of the water vapour in air. 7- • 6-s--[H] 4 " ppm 3 - • 2 -1 -• -4- -+- -+- -+-COMBINED BLOWING A36-1 -4- - 4 - -t" -+- -+- -+-0. 20 4<f 60 80 100 120 140 160 180 200 220 240 260 Argon (M3) . Figure 2.11 [H] in the ladle versus total argon volume during BOF post stirring.19-* 19 7 h S A E / A I S I GRADE A 1070 % 1041 O 1065 4 h 3 \-« 300 400 500 600 700 800 900 [0] ppm Figure 2.12 [H] in the ladle versus [O] at BOF tapping.20^ 8 oc a v X O. I O. 5 O. 2 O. I O. 005 0 .0027 O.OOOZJ O.OOOl *t6 S A J _ U ^ A T E D _ S j r E A r £ J ^ ^ P H g g = I -O A T ^ K J 0.002' O. OOS O. 02 0 . 0 5 O. OOI O. Ol O X Y G E N (%) O I gure 2.13 Absorption of hydrogen in liquid steel contacting with H2O vapour.' 20 Figure 2.14 indicates the changes of hydrogen content with manganese level in three steel grades which were produced in AHMSANo.2 shop. It was observed that the hydrogen level was notably increased with increased manganese addition, such as ferro-manganese to the ladle. A H M S A S T E E L G R A D E S 7 T A M - I U I raocm It o 9 i » 4. l o o * v e I • • 3 1 1 1 as «v» x L% M n J Figure 2.14. [%H] ppm in the ladle versus [%Mn].22) 21 2.5 Secondary refining process Research work on the use of hydrocarbon gas in ladle metallurgy was carried out by IMIS which commissioned a ladle metallurgy pilot plant. The principal components of this plant are shown in Figure 2.15. On the basis of research at the ladle metallurgy pilot plant, IMIS developed a technology for the use of hydrocarbon gas not only as a bubbling gas, but also as a metallurgical component in the refining reactions. Industrial work was carried out in a 130 ton ladle furnace of AHMS A. Table 2.4 indicates related parameters obtained during ladle treatment by bottom argon or natural gas injection in four different heats at AHMSA. According to these industrial results, hydrocarbon gas was more effective in lowering dissolved oxygen during ladle treatment by bottom blowing than argon gas. Temperature drop by endothermic reaction and absorption of hydrogen in molten steel was not a concern due to the application of vacuum treatment. Therefore, vacuum treatment in ladle treatment was essential to lower hydrogen in molten steel. 22 Fig. 1 • Ladle metallurgy pilot plant at IMIS 1 Cover vessel 2 Vessel 3 Vessel car 4 Vacuum line 5 Cyclon 6 Bag filter 7 Vacuum system B Double hopper system 9 Oxygen lance 10 Ladle tumace station Figure 2.15 Ladle metallurgy pilot plant at IMIS. 23 Table 2.4 Results obtained during ladle treatment by bottom argon or natural gas injection in four different heats in EVIIS.24) Heat No. Parameters ~ — 350 Argon 351 Natural gas 352 Natural gas 353 Argon Steel grade 1030 1030 1030 13CrMo44 Initial temperature ( °C) 1650 1645 1670 1650 Total oxygen at the beginning of the ladle treatment (ppm) 61 48 80 72 Total time of reheating (min.) 9 13 8 8 Initial temperature at vacuum ( °C) 1685 1685 1690 1680 Total time of vacuum (min.) 10 10 10 10 Maximum vacuum obtained (MBAR) 7 7 7 7 Final temperature at vacuum ( °C) 1610 1607 1618 1619 Total oxygen at the end of the ladle treatment (ppm) 29 19 30 50 Total argon injected during the ladle treatment (LTS) 927 - - 900 Total natural gas injected during the ladle treatment (LTS) - 1020 930 -Hydrogen at the end of the ladle treatment (ppm) 1.90 2.00 1.20 1.24 24 3. Thermodynamic Review 3.1 Characteristics of Hydrocarbon Gases Methane gas represents over 95% of the hydrocarbon gases in the world. Therefore, it has been used widely in industry. Table 3.1 shows the specifications of hydrocarbon gases. Generally LNG (Liquefied Natural Gas: C H 4 ) can be made from natural gas and LPG (Liquefied Petroleum Gas: mixture of C3H8 and C4H10) can be extracted from distilling of petroleum. The cracking temperature of methane is about 820°C and the reaction is; CH 4 ( g) = C(S) + 2H2(g) Considering the Gibbs free energy, some possible reactions at 1873K are shown in Table 3.2. Based on the thermodynamic free energy calculations, reaction R7 in the table is the most feasible; i.e. CH4(g) + 20(%) = 2H20(g)+C(%), AG°= -155644-31.25T (joules) If this reaction dominates hydrogen pick-up will be low but appreciable carbon dissolution can be expected by the use of CH4 gas. 25 Table 3.1 The specifications of hydrocarbon gases. Species LNG LPG Main composition Methane (CH4) Propane (C3H8) Butane (C4H10) Specific gravity 0.55 1.5 2.0 Ignition temperature(°C) 537 346 406 Liquefied Temperature(°C) -162 -42 -0.5 Table 3.2 Changes of Gibbs free energy in reactions involving C H 4 gas at 1873K. No. Reaction AG 0, joules AG 0 1873K, joules Rl C(%)+Q(%)=CO(g) -22,3 84-41.17T -99,496.9 R2 H20(g)=2H(%)+0(%) 207,694+0.29T 208,242.3 R3 CH4(g)=C(s)+2H2(g) 92,466-110.67T -114,812.5 R4 C(s)=C(%) 21,338-41.84T -57,027.9 R5 H2(g)=2H(%) 72,969+60.92T 187,070.3 R6=R3+R4+2*R5 R7=R6-2*R2 R8=R1+R6 CH4(g)=C(%)+4H(%) CH4(g)+20(%)=2H20(g)+C(%) CH4(g)+0(%)=CO(g)+4H(%) 259,743-30.67T -155,645-31.25T 237,358+8.99T 202,300.2 -214,184.4 254,207.1 26 3.2 Thermodynamic calculations 3.2.1 Oxygen content with a conventional combined blowing process The main reaction is: C (%) + 0(%) = CO(g), AG 0 = -22,384-41.17T, at 1873K AG 0 = -99,497 joules K = exp(^l^) = 596 where K is the equilibrium constant. Assume that the solutes approaches Henrian standard behavior, the activity can be written as ht = / , x ( % i ) log/,=Ie/.%/ Where hj = the Henrian activity, fj = the Henrian activity coefficient, e,J = the interaction coefficient of i on j P P rco _ rco K = K-K fc-%c-f„-%o where, e c c = 2 2 x 10"2' e 0 ° = - 2 0 x 10" 2 , assume P c o = latm = 1 The results of the above calculation, dissolved oxygen at equilibrium can be expressed as Table 3.3. According to the results of calculation [%C]x[%0] is 0.0021 as shown in Figure 3.1. This value is consistent with actual plant data which is 0.0022~0.0024 depending on the condition of the bottom nozzle. The present combined blowing practice using inert gas as bottom gas reaches close to its equilibrium level. Therefore there is not much room to improve dissolved oxygen by this practice. 27 Table 3.3 The equilibrium content of dissolved oxygen. %c fc fo %0- equation O (ppm) %C*%0 0.50 1.29 1.00 0.0032 1.000 32 0.0016 0.40 1.22 1.00 0.0043 1.000 43 0.0017 0.30 1.16 1.00 0.0060 1.000 60 0.0018 0.20 1.11 1.00 0.0095 1.000 95 0.0019 0.15 1.08 0.99 0.0130 1.000 130 0.0019 0.10 1.05 0.99 0.0200 1.000 200 0.0020 0.08 1.04 0.99 0.0254 1.000 254 0.0020 0.06 1.03 0.98 0.0343 1.000 343 0.0021 0.05 1.03 0.98 0.0415 1.000 415 0.0021 0.04 1.02 0.98 0.0524 1.000 524 0.0021 0.03 1.02 0.97 0.0708 0.999 708 0.0021 0.02 • 1.01 0.95 0.1086 1.000 1086 0.0022 Conventional Oxygen Bowing 1200 i 0.00 0.10 0.20 0.30 0.40 0.50 C&rbon content (%) Figure 3.1 Equilibrium carbon and oxygen content at 1600°C. 28 3.2.2 Oxygen value with CH4 blowing With the same assumptions and calculation procedure in section 3.2.1, the main reaction is expressed as follows; CH 4 + 20(%) = 2H20(g) + C(%), AG 0 =-155,645-31.25T, A G ° , 8 7 3 K = -214,184(joules) K =  P » ™ - f c % C ^ = (Z^1) = 940,647 PCH^fo%02 RT assuming PCH4 = PH20 = latm The results of the above calculation, dissolved oxygen at equilibrium using C H 4 gas is shown in Table 3.4. Theoretically the equilibrium oxygen content using C H 4 gas as stirring gas instead of inert gases is 2ppm at 0.04%C and 1600 ° C . This means nearly all of the dissolved oxygen can be removed by the use of CH 4 as stirring gas. Table 3.4 The equilibrium content of dissolved oxygen. %c fc fo % 0 equation O %(ppm) %C*%0 0.10 1.05 1.00 0.0004 1.000 4 0.00004 0.08 1.04 1.00 0.0003 1.000 3 0.00003 0.06 1.03 1.00 0.0003 1.000 3 0.00002 0.05 1.03 1.00 0.0003 1.000 3 0.00001 0.04 1.02 1.00 0.0002 1.000 2 0.00001 0.03 1.02 1.00 0.0002 1.000 2 0.00001 0.02 . 1.01 1.00 0:0002 1.000 2 0.00000 29 3.2.3 Hydrogen content in conventional combined blowing The main reaction with water vapour in air is: H 2 0 (g) = 2H (%) + O (%), AG 0 - 207,694 + 0.29T Goules) at 1873K , AG 0 = 208,242.3 joules JC = o q < ^ « l ) = 1 . 6 x l O - K=ti-H*™ ^°<%> Kl FH2Q where, e H H = 0 (fH =1), e0° = -20 X 10"2 1) Assume P H 2 o = 0.06atm (wet summer) * r e f : F i g u r e 2 -fc : fo %0 O(ppm) %H . . H (ppm) 0.15 1.08 0.99 0.0130 130 0.0027 27 0.10 1.05 0.99 0.0200 200 0.0022 22 0.08 1.04 0.99 0.0254 254 0.0020 20 0.06 1.03 0.98 0.0343 343 0.0017 17 0.05 1.03 0.98 0.0415 415 0.0015 15 0.04 1.02 0.98 0.0524 524 0.0014 14 0.03 1.02 0.97 0.0708 708 0.0012 12 0.02 1.01 0.95 0.1086 1086 0.0010 10 2) Assume P H 2 O = 0.0003atm (dry winter) %c . fc fo %0 ^M(ppm) ' %H H (ppm) 0.15 1.08 0.99 0.0130 130 0.0002 2 0.10 1.05 0.99 0.0200 200 0.0002 2 0.08 1.04 0.99 0.0254 254 0.0001 1 0.06 1.03 0.98 0.0343 343 0.0001 1 0.05 1.03 0.98 0.0415 415 0.0001 1 0.04 1.02 0.98 0.0524 524 0.0001 1 0.03 1.02 0.97 0.0708 708 0.0001 1 0.02 1.01 0.95 0.1086 1086 0.0001 1 Considering 2~4ppm of hydrogen content at the blowing end in a converter, the actual partial pressure of the H 2 0 in the surroundings might be in the range of 0.00 latm to 0.005atm. 30 3.2.4 Hydrogen content with CH4 blowing The main reaction is: CH4(g) = C (%) + 4H (%), AG 0 = 259,742 - 30.67 T at 1873K , AG 0 = 202,300 joules K = e x p ( ^ ) = 2.28x10- K = C(%)-/^ 4 (%) where, eHH = 0(fH=l) 1) Case 1 : PCH4 = latm %c fc fo % 0 O (ppm) %H H (ppm) 0 . 1 5 1 . 0 8 0 . 9 9 0 . 0 1 3 0 1 3 0 0 . 0 6 2 4 6 2 4 0 . 1 0 1 . 0 5 0 . 9 9 0 . 0 2 0 0 2 0 0 0 . 0 6 9 1 6 9 1 0 . 0 8 1 . 0 4 0 . 9 9 0 . 0 2 5 4 2 5 4 0 . 0 7 3 1 7 3 1 0 . 0 6 1 . 0 3 0 . 9 8 0 . 0 3 4 3 3 4 3 0 . 0 7 8 5 7 8 5 0 . 0 5 1 . 0 3 0 . 9 8 0 . 0 4 1 5 4 1 5 0 . 0 8 2 2 8 2 2 0.04 1.02 0.98 0.0524 524 0.0869 869 0 . 0 3 1 . 0 2 0 . 9 7 0 . 0 7 0 8 7 0 8 0 . 0 9 3 4 9 3 4 0 . 0 2 1 . 0 1 0 . 9 5 0 . 1 0 8 6 1 0 8 6 0 . 1 0 3 3 1 0 3 3 2) Case 2 : PCH4 = 2.0atm % c fc fo % 0 O (ppm) %H H (ppm) 0 . 1 5 1 . 0 8 0 . 9 9 0 . 0 1 3 0 1 3 0 0 . 0 7 4 2 7 4 2 0 . 1 0 1 . 0 5 0 . 9 9 0 . 0 2 0 0 2 0 0 0 . 0 8 2 2 8 2 2 0 . 0 8 1 . 0 4 0 . 9 9 0 . 0 2 5 4 2 5 4 0 . 0 8 6 9 8 6 9 0 . 0 6 1 . 0 3 0 . 9 8 0 . 0 3 4 3 3 4 3 0 . 0 9 3 4 9 3 4 0 . 0 5 1 . 0 3 0 . 9 8 0 . 0 4 1 5 4 1 5 0 . 0 9 7 7 9 7 7 0.04 1.02 0.98 0.0524 524 0.1033 1033 0 . 0 3 1 . 0 2 0 . 9 7 0 . 0 7 0 8 7 0 8 0 . 1 1 1 0 1 1 1 0 0 . 0 2 1 . 0 1 0 . 9 5 0 . 1 0 8 6 1 0 8 6 0 . 1 2 2 9 1 2 2 9 3) Case 3 : P C H 4 = 3.0atm % c • fc , . -fo % 0 O (ppm) %H H (ppm) 0 . 1 5 1 . 0 8 0 . 9 9 0 . 0 1 3 0 1 3 0 0 . 0 8 2 2 8 2 2 0 . 1 0 1 . 0 5 0 . 9 9 0 . 0 2 0 0 2 0 0 0 . 0 9 0 9 9 0 9 0 . 0 8 1 . 0 4 0 . 9 9 0 . 0 2 5 4 2 5 4 0 . 0 9 6 1 9 6 1 0 . 0 6 1 . 0 3 0 . 9 8 0 . 0 3 4 3 3 4 3 0 . 1 0 3 3 1 0 3 3 0 . 0 5 1 . 0 3 0 . 9 8 0 . 0 4 1 5 4 1 5 0 . 1 0 8 1 1 0 8 1 0.04 1.02 0.98 0.0524 524 0.1143 1143 0 . 0 3 1 . 0 2 0 . 9 7 0 . 0 7 0 8 7 0 8 0 . 1 2 2 9 1 2 2 9 0 . 0 2 1 . 0 1 0 . 9 5 0 . 1 0 8 6 1 0 8 6 0 . 1 3 6 0 1 3 6 0 31 The gas pressure in the bottom of the vessel (assume 300t converter at #2BOF of POSCO in Korea) is approximately 3atmospheres; i.e. P = P 0 + pgh, where P is gas partial pressure and P 0 is atmosphere. = 101.3 kPa + (7800kg/m3 x 9.8m/sec2 x 2.5m) = 101.3 kPa + 191,100kg/m-sec2 = 101.3 kPa+ 191.1 kPa = 292.4 kPa Considering the results of the above three case, the equilibrium hydrogen content is too high considering the literature review. For example, 869 ppm at PcH4=latm, 1033 ppm at PcH4=2atm and 1143 ppm at PcH4=3atm and 0.04%C respectively as shown in Figure 3.2. Therefore, another reaction should occur after C H 4 gas cracks to form carbon and hydrogen. The following reaction can be considered: 4H (ppm) + 20(%) = 2H 2 0 ( g ) , AG°I 8 7 3K = -145,388 + 306.85 T = 159,351 joules K = Qxp(-^-) = 3.596 xlO"5 K= P f i 2 0 RT f"H-H\ppm)-f2-02(%) Equilibrium hydrogen content on partial pressure of H2O after CH4 cracking at 0.05%O is shown in below. This might be a reasonable reaction considering the literature review. PH20 =0.1 atm 0.01 atm 0.005atm 0.002atm H(ppm) 18 6 4 2 Therefore, it can be expected two reactions would be occurred during blowing CH4 gas into molten steel in a converter as follows: CH 4 = C (%) + 4H (%) (-»[H] Pick up) and 4H (ppm) + 20(%) = 2H20 (g) (-> deoxidation) 32 1400 1300 1200 1100 I, 1000 900 800 700 600 0.02 0.03 0.04 0.05 0.06 0.08 0.10 0.15 Carbon content (°/) Figure 3.2 The carbon-hydrogen equilibrium for several partial pressures of CH 4 . 3.3 Summary of the Thermodynamic Review In summary, the results of the thermodynamic calculations indicate that: • For inert-gas stirring the plant data for [%C]x[%0] at the blowing end is close to theoretical values. • Applying CFI4 as reducing gas, the theoretical limitation of the dissolved oxygen in equilibrium is 2ppm, a very low value (assume PCH4= PH20 = latm). • It is difficult to assess the theoretical hydrogen content when CH4 is used as stirring gas. However, another reaction could occur after CH4 cracking. 33 4 . Objectives The objectives of the work can be summarized as follows: • To carry-out a theoretical investigation to determine the thermodynamic limitations for dissolved oxygen using submerged injection of methane. • To determine experimentally the minimum [O] achievable and compare the theoretical value. • To assess the impact of variables such as gas flow rate and blowing time on carbon pick-up in molten steel. • To assess hydrogen pick-up from C H 4 gas and compare this to that for conventional combined blown processes. The benefits of such a process might include: • Improvement in steel quality by decreasing non-metallic inclusions such as AI2O3 and Si02 by means of reducing dissolved oxygen at the turndown of converter. • Cost reduction by the decrease of deoxidation materials and alloying additions. 34 5. Experimental Apparatus and Procedure 5.1. Experimental apparatus The experiments were performed using the ASTRO Systems vacuum furnace and power supply shown in Figure 5.1. Heating is via a graphite resistance element (5"/4.25" OD/ID by 13.5" long) and the furnace chamber can be evacuated down to about 13 kPa via a mechanical vacuum pump. For the resistance element used for the trials the maximum temperature of the furnace is about 2500°C. The temperature of the furnace is controlled by power setting at the control panel (Figure 5.2) A vacuum furnace was employed to protect the graphite heating element against oxidation by air during melting (Figure 5.3). A schematic diagram of the experimental apparatus is shown in Figure 5.4. The detailed information about the resistance furnace is given below. To minimize oxidation of the graphite heating element by residual oxygen within the graphite insulting blanket, during initial heating the furnace pressure was held at about 13 kPa up to the 1300°C using the mechanical vacuum pump. Above this temperature the pressure was brought up atmosphere and an Ar gas flow was maintained through the unit to minimize any further oxidation of the element. The actual experiments were carried out at 1600°C. Melt was contained in a high purity alumina crucible (60 mm ED, Al203^98%) and graphite crucible was installed at the outside to protect the furnace in the event of cracking of the alumina crucible. 35 Figure 5.1 The experimental apparatus showing both the furnace (foreground) and power supply/control panel (background) Figure 5.2 Details of the control panel for the furnace. 36 Figure 5.3 The vacuum pump (top) and furnace (bottom). 37 Gas outlet Thermo couple Ar inlet 1. Alumina tube 2. Graphite crucible 3. A l 2 0 3 crucible 5. Sampling hole 4. Molten metal 6. Heating element Figure 5.4 Schematic diagram of the experimental apparatus. 5.2. Experimental methodology 5.2.1. Experimental Design Variables For the trials about 1 kg of electrolytic iron (0.013%C) was used as the starting material. Note that the carbon level is significantly below the 0.04% level typical of commercial steelmaking converters. For the 60 mm ID alumina crucible used for containment, this yielded a liquid melt depth of about 46mm. 38 • Variables : Initial dissolved oxygen and the CH 4 flow rate 1) The trials employed two different ranges of initial dissolved oxygen; i.e. 'high' 600~700ppm and Tow' 50~150ppm. The Tow' initial oxygen trials were to investigate the limitation of the deoxidation compared to the theoretical result and the 'high' oxygen trials were to simulate commercial converter levels after blowing and to determine the kinetics of deoxidation using C H 4 . After initial melting, oxygen levels in the electrolytic iron were within the 50~150ppm range used for the Tow' oxygen trials. For the 'high' oxygen trials compressed air was injected into the melt at 400cc/min for 8~10min in order to reach the desired 600-700 ppm range. The actual controlled values were 70~171ppm and 508~834ppm respectively. 2) The CH4 flow rate was the other main variable for the trials, the objective being to assess the impact on deoxidation rate. Four values were used; 100, 120, 150 and 200 cc/min. which approximate the upper range of typical industrial bottom gas injection rates, 0.05-0.20 Nm per ton of steel per minute (lOOcc/min corresponds to 0.10 Nm3/ton-min). Method Before using three flow meters they were calibrated against a bubble calibrator to ensure accuracy in a low flow rate regime. For all trials, argon gas at 700cc/min was supplied by 4mm stainless tube at the bottom of furnace to protect the graphite heating element. For the trials methane was injected at rates ranging from 100~200cc/min via an alumina tube (600mm long, 5 mm ID, 8 mm OD) submerged to a depth of about 20mm from the melt surface (total melt depth was about 46 mm). In all trials, the samples were melted and brought up to 1600°C prior to starting the 39 methane gas flow. For Trials 4 through 7 the samples were also blown with compressed air (400cc/min) prior to starting the methane flow in order to bring the initial dissolved oxygen up to about 700 ppm which is more typical of industrial levels for steel from the converter. Details of the gases used are given in Table 5.1. Table 5.1 Specifications of the gases used in the experiments (Praxair). Item Part No. Specification CH 4 ME 2.0 Methane 99.0%, O2<50ppm,H2O<1 Oppm, N2<2000ppm Ar AR5.0UH Argon 99.999%, 02<lppm,H20<3ppm, N2<4ppm Sampling Technique Dissolved oxygen was measured using the sensor system shown in Fig.5.5. As shown, it consists of a molybdenum wire for a melt and an oxygen sensor for a reference electrode. The signal from the sensor was logged using a chart recorder. The hydrogen probe used for the trials, also shown in Figure 5.5 and consists of two parts. The first component is a conventional pin sample which retains some part of the initial hydrogen. The second component is the outer tube which captures the hydrogen which diffuses out of the pin during cooling. After analyzing for the diffusible hydrogen, residual hydrogen can then be determined. A quartz tube was used to take steel samples for checking carbon pick up. 40 Oxygen sensor Figure 5.5 The oxygen and hydrogen samplers. Dissolved oxygen levels were calculated from the emf data using the equation proposed by Schmarzried(26): RT , Po 2 I I 1 / 4 + Pe 1 / 4 emf = ln — — r — — J F Po 2 I 1 / 4 + Pe 1 / 4 where: P02 I is the O2 partial pressure of the sample P 02II is the O2 partial pressure of the standard Pe is the partial electron conductivity parameter R is the gas constant F is the Faraday constant The hydrogen content was analyzed using a LECO Hydrogen analyzer at POSCO in Korea. Steel samples were collected during the blowing of CH4 gas and analyzed for carbon at IPL (International Plasma Laboratory LTD). 4 1 5.2.2. Experimental Procedure The experimental procedure was as follows: • The furnace was charged with 1 kg of electrolytic iron and closed. The pressure was then reduced to 0.13 atmospheres and heating commenced. In order to protect the graphite heating element from oxidation, this reduced pressure was maintained up to 1300°C. • Upon reaching 1300°C the pressure was increased to atmospheric and the flow of argon purge gas started. • Upon reaching 1600°C (fully liquid melt) the dissolved oxygen was measured (via the oxygen probe) and samples taken for subsequent carbon and hydrogen analysis. • For the high initial oxygen trials, air was injected at 400cc/min for 8-10 minutes in order to reach the desired 600-700 ppm [ O ] . The methane flow was then started. For the low initial oxygen trials methane injection was started as soon as the initial sampling was completed. • During the methane blow temperature and [O ] were measured and samples taken for [C] and [H] analysis at 5-8 minute intervals. • The methane flow was continued until the dissolved oxygen was reduced to < 30 ppm and the level had stabilized. 42 Experimental conditions are summarized in Table 5.2. Table 5.2 Experimental conditions on flow rate, temperature and initial [O]. Trial Flow rate (cc/min) Temperature, target (°C) Initial [0]ppm (target) Sample CH 4 Air [C] [H] 1 200 0 1600 50-150 2 150 0 1600 50-150 o o 3 120 0 1600 50-150 o 4 150 400 1600 600-700 5 150 400 1600 600-700 o 6 100 400 1600 600-700 o o 7 100 400 1600 600-700 o o 43 6. Results and Discussion 6.1 Deoxidation from 'Low' Initial Dissolved Oxygen As noted three methane flows were employed for the trials; 120cc/min, 150cc/min and 200cc/min. and these will be considered on an individual basis. 6.1.1 Results for 200cc/min CH 4 In order to determine repeatability, the initial dissolved oxygen level was measured twice at the same conditions, giving 162ppm and 171ppm (average 166ppm), +/-2.5% relative to the average indicating good repeatability. For this trial the initial dissolved oxygen was 166 ppm. The measured dissolved oxygen content (down to 27 ppm) is plotted against cumulative CH 4 supplied in Figure 6.1. 6.1.2 Results for 150cc/min CH 4 The initial dissolved oxygen was 71 ppm. The dissolved oxygen reached 23ppm after 32 minutes of CH 4 injection. The measured dissolved oxygen is plotted against cumulative CH 4 in Fig.6.2. 6.1.3 Results for 120cc/min CH 4 The initial dissolved oxygen was 48ppm. The dissolved oxygen reached 22 ppm after blowing for 33 minutes. The measured dissolved oxygen is plotted against cumulative CH4 in Figure 6.3. 44 Figure 6.1 Dissolved oxygen versus cumulative CH4 (200 cc/min starting from ' low ' initial oxygen). a. 40 L 7 1 6 . .33 1 33 23 0 1000 2000 3000 4000 5000 Cumulative quantity of CH4 (cc) Figure 6.2 Dissolved oxygen versus cumulative CH4 (150 cc/min. starting from ' low ' initial oxygen) 45 50 45 40 O 30 25 20 15 10 0 1000 2000 3000 4000 5000 Cumulative quantity of CH4 (cc) Figure 6.3 Dissolved oxygen versus cumulative CH4 (120 cc/min. starting from 'low' initial oxygen) 6.1.4 Comparison Experimental and Thermodynamic Results Comparison of the theoretical and experimental values for dissolved oxygen (Figure 6.4) indicate that either equilibrium is not achieved or other reactions may play a role. Based on the thermodynamic modeling, the theoretical value of dissolved oxygen is 2 ppm and the minimum experimental result is 22 ppm and the average is ~25 ppm. Extended CH4 blowing was unable to achieve any further reduction in dissolved oxygen.. In order to explore this result further, aluminum was added to determine whether dissolved oxygen could be reduced to thermodynamic (and practical) values achievable with Al deoxidation; ~5 ppm. In each instance, sufficient Al was added to reach thermodynamic equilibrium. With Al addition and starting from 32 ppm [O] (21mV signal) and 34 ppm [O] (36mV) in molten steel, dissolved oxygen was reduced to 16 ppm (-39mV, Al 11.4g) and 18 ppm (-6mV, Al 5.6g), 46 respectively, both levels being well above what can be expected of Al deoxidation. The reason that the dissolved oxygen did not reach 4 ppm (fully killed) but leveled out at 16~18ppm may be the inappropriateness of the oxygen probe at very low oxygen levels. Two types of the oxygen probes are employed in steelmaking operations, one for 'high' oxygen levels in the converter and a second type for the Tow' oxygen levels encountered during secondary refining, for the ladle furnace or RH degasser. The split between high and low oxygen is approximately 0 mV signal which corresponds to 30ppm. Both probes employ the same reference electrode, powder mixtures (Cr 2%-Cr203 98%) and solid oxide electrolyte (8%MgO-92%Zr02). However, to increase accuracy of the oxygen measurement through improved wetability of the reference electrode, the surface of the solid oxide electrolyte is coated with MgF2 for high oxygen probes and for CaF2 low oxygen probes. The trials employed only the 'high' oxygen type probe which may have resulted in significant error for the measurements taken late in the experiments. This may explain why Al deoxidation did not approach theoretical levels. Another possible reason might have been dissolution of oxygen into the melt from the refractory or furnace atmosphere. 47 [O] Vs mV (1600°C) 300 -150 4 -200 i» -250 <• -300 [OJppm T e m p ( ° C ) m v [0]ppm m v K Pe Po 1600 250 772.2463 250 26041896 5.21E-16 1.16E-12 • 1600 200 407.2943 200 26041896 5.21E-16 1.16E-12 1600 100 1 10.3707 100 26041896 5.21E-16 1.16E-12 1600 50 56.27839 50 26041896 5.21E-16 1.16E-12 1600 30 42.74301 30 26041896 5.21E-16 1.16E-12 1600 20 37.19489 20 26041896 5.21E-16 1.16E-12 1600 10 32.33155 10 26041896 5.21E-16 1.16E-12 1600 5 30.13062 5 26041896 5.21E-16 1.16E-12 1600 0 28.07088 0 26041896 5.21E-16 1.16E-12 1600 -5 26.14359 -5 26041896 5.21E-16 1.16E-12 1600 -10 24.34051 -10 26041896 5.21E-16 1.16E-12 1600 -20 21.07659 -20 26041896 5.21E-16 1.16E-12 1600 -30 18.22287 -30 26041896 5.21E-16 1.16E-12 1600 -50 13.55353 -50 26041896 5.21E-16 1.16E-12 1600 -100 6.227391 -100 26041896 5.21E-16 1.16E-12 1600 -150 2.641823 -150 26041896 5.21E-16 1.16E-12 1600 -200 0.974245 -200 26041896 5.21E-16 1.16E-12 1600 -250 0.269095 -250 26041896 5.21E-16 1.16E-12 Figure 6.4 E m f versus dissolved oxygen at 1600°C using Schmarzried's relationship. 48 6.2 Deoxidation from 'High' Initial Oxygen The objective of this campaign was to simulate the starting point for typical industrial conditions (i.e. steel from the converter) and to examine issues such as CH4 utilization and recarburization of the steel. As noted earlier, before starting the CH4 injection, air was injected into molten bath to bring the initial oxygen to within the range of the desired starting point. 6.2.1 Results for 150cc/min CH4 flow As shown in Figure 6.5 the dissolved oxygen content of oxidized samples were reduced from 834ppm to 58ppm and 508ppm to 28ppm after blowing with 4200cc and 6000cc of CH4 respectively. Approximately 50% of the dissolved oxygen (300ppm) was reduced after blowing 1500cc of CH4 gas (lOminuites). At about 2000cc CH4 and around 100 ppm oxygen the rate of deoxidation declines significantly and CH4 utilization becomes poor. 900 800 700 600 I 500 g 400 300 200 100 0 0 1000 2000 3000 4000 5000 6000 7000 Cumulative quantity of CH4 (CC) Figure 6.5 Dissolved oxygen versus cumulative CH4 (150cc/min). 49 6.2.2 Results for lOOcc/min CH 4 For the two trials performed at 100 cc/min CFI4, the dissolved oxygen was reduced from 746ppm to 34ppm and 682ppm to 31ppm after blowing 3700cc and 4500cc of C H 4 respectively (Fig.6.6). As in the 150 cc/min trial, deoxidation down to about 100 ppm is relatively fast but the rate then declines sharply and CH4 utilization drops off correspondingly. Comparing Figs. 6.5 and 6.6, which show the influence of injection rate on C H 4 utilization, it is clear that operating at the higher flow should offer advantages in terms of deoxidation time to -lOOppm. CH4 Vs [0]ppm (100cc/min) 800 r-700 2 600 -c 500 -c Q . Q . ^ * 400 -J 300 -200 -100 -0 1000 2000 3000 4000 Cumulative quantity of CH4 (cc) 5000 Figure 6.6 Dissolved oxygen versus cumulative CH4 (lOOcc/min). 50 6.2.3 Carbon Pick-up (Recarburization) 6.2.3.1 Recarburization at 150cc/min CH4 (Starting from 'Low' Initial Oxygen) During the trial the carbon content of the steel increased from 0.013%C to 0.099%C. This might be of concern since the specification for carbon is normally targeted at +0.01%C in a commercial process. As shown in Figure 6.7 recarburization was initially slow but accelerated significantly late in the process. Carbon pick up in molten steel had a strong relationship with the oxygen level. At the high oxygen potential, carbon dissociated from CH4 can react via C(s) + O = CO(g) but this reaction is suppressed by low oxygen potential, likely due oxygen transport control of the reaction rate. 0.120 0.100 0.080 0.060 O 0.040 0.020 0.000 0 750 2100 3000 3750 4800 Curriiative quantity of CH4 (cc) Figure 6.7 Dissolved oxygen and carbon versus cumulative CH4 starting from 'low' initial oxygen (150cc/min). 51 6.2.3.2 Recarburization from 'High' Initial Oxygen Results at lOOcc/min CH4 As a result of air injection to bring the oxygen level up, the initial carbon was down from 0.013% to an initial 0.004% due to the oxygen in compressed air. During CH4 gas blowing, the carbon content increased from the initial 0.004% to 0.033%. As shown in Figure 6.8, the initial rate of recarburization was slow but again accelerated at low oxygen levels. Results at 150cc/min CH 4 During the trial, carbon levels went from 0.004% to 0.047%. As shown in Figure 6.9, the behavior followed the same pattern as before with most of the recarburization occurring at low oxygen levels. In general, the results indicate that recarburization should not be a significant issue above 200 ppm dissolved oxygen as total carbon pick up was only 0.003-0.008% which is within range of the carbon specification in commercial steelmaking. Actually, compared with 0.04% of the carbon content in the blowing end of the commercial converter, 0.004% carbon for the electrolytic iron is very low value. Therefore in actual converter, the oxygen levels at which recarburization becomes significant might differ from that observed in the experiments. 52 800 700 600 500 400 300 200 100 0 - » - [ 0 ] p p m — A - [ q wt% -—JR^ i 0.035 0.030 0.025 0.020 O 0.015 0.010 0.005 0.000 0 400 700 1400 2100 2800 3500 4000 4500 Cumulative quantity of CH4 (cc) Figure 6.8 Dissolved oxygen and carbon versus cumulative CH4 starting from 'high' initial oxygen (lOOcc/min CH4). 600 500 400 U 3 0 0 200 100 0 - * - [ 0 ] p p m - ± - [ Q wt% -• • • -- - — • • i i i 0.050 0.045 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0.000 750 1500 2250 3000 3750 4500 5250 6000 Cumulative quantity of CH4 (cc) O Figure 6.9 Dissolved oxygen and carbon versus cumulative CH4 starting from 'high' initial oxygen (150cc/min CH4). 53 6.2.4 The Role of Carbon in the Process 6.2.4.1 Carbon Consumption for Deoxidation The carbon mass balance is calculated without considering the effect of the hydrogen cracked CH4 because it can not be measured exact quantity of the hydrogen due to furnace condition exposed atmosphere. To assess the carbon utilization on the flow rate of CH4, the carbon efficiency is employed. The carbon efficiency is defined as the ratio of quantity of carbon reacted with the dissolve oxygen to total quantity of input carbon from CH4. Fig 6.10 indicates the change of the efficiency of carbon contributed to reduce the oxygen. It can be evaluated that a low flow rate of CH4 (lOOcc/min.) is the high efficiency of carbon to react with the oxygen (average efficiencies of carbon are 32% for 100cc/min., 17% for 150cc/min.). Figure 6.10 Carbon utilization for deoxidation. 54 6.2.4.2 Carbon Consumption for Recarburization Carbon consumption due to recarburization as a function of time at 100 and 150 cc/minute is shown in Fig 6.11. The carbon efficiency for recarburization is defined as the ratio of quantity of carbon pick up into the molten bath to total quantity of input carbon from CH4. As can be seen, <10% of carbon in the CH4 goes to recarburization and the injection rate is not a major factor in controlling recarburization. >< o c <D O c. o \ OS O 1.0 0.8 0.6 0.4 •CH4(100cc/min) •CH4(150cc/min) 10 20 30 40 Blowing time (min) 50 Figure 6.11 Carbon utilization for recarburization 6.2.4.3 Efficiency of the carbon for the reduction of [O] and the carbon pick up Fig 6.12 and 6.13 show total carbon utilization (deoxidation and recarburization) at 100 and 150 cc/min. C H 4 . Carbon from C H 4 contributed to deoxidation high oxygen concentrations but recarburization becomes significant at low oxygen levels. It can be seen that the carbon efficiency of the low flow rate (lOOcc/min.) is higher than that of the 150cc/min. flow rate. 55 Figure 6.12 Total carbon utilization at lOOcc/min CH4 0 10 20 30 40 50 Blowing time (min) Figure 6.13 Total carbon utilization at 150cc/min CH 4 6.3 Hydrogen Pick up Sampling for dissolved hydrogen was performed for 3 trials. However, for two of these trials the results considered invalid due to infiltration of water into the sampling tube during cooling. Results for the one trial not affected by this problem are shown in Figure 6.14 which plots dissolved oxygen and hydrogen (diffusible and residual hydrogen in the sample) as functions of cumulative CH4. As can be seen the two species move in opposite directions, 56 hydrogen going from 4 to 26 ppm while oxygen goes from 71 to 27 ppm. Relative to the literature review 2 7 ) concerned with hydrogen dissolution from CH4 injection the hydrogen at 26 ppm is high relative to commercial process. Since only one trial was involved, further work on hydrogen dissolution is warranted. 57 7. Summary and Conclusions The work examined the feasibility of deoxidizing liquid steel using submerged injection of C H 4 in order to avoid the formation of potential contaminants such as AI2O3 as in conventional deoxidation with aluminum. It involved both thermodynamic assessments and bench-scale trials. The experiments involved two campaigns, one involving Tow' initial oxygen concentrations (-100 ppm) and a second at 'high' initial oxygen levels (-700 ppm) more typical of industrial converter operations. In each campaign the effect of C H 4 injection rate on gas utilization, deoxidation rate and recarburization was assessed. Very limited amounts of data were also collected for hydrogen pick-up by the liquid steel. The results lead to the following conclusions: 1. Although thermodynamics would suggest that CH4 deoxidation is possible down to about 2 ppm, ~ 22 ppm was the lowest level achieved in the trials. Over the entire campaign, final oxygen levels were within the range 22-58 ppm, with typical values being about 30 ppm. The high of 58 ppm occurred at the lowest total amount of CH 4 injection. 2. It is unclear whether the failure to more closely approach equilibrium reflects experimental error at low oxygen levels (related to the choice of oxygen sensor), oxygen pick-up from other sources or factors such as reactions not considered in the thermodynamic modeling. 3. Although the apparent final oxygen achieved was an order of magnitude greater than the thermodynamic predictions, two attempts to further deoxidize by aluminum addition after CH 4 deoxidation resulted in 16 and 18 ppm oxygen which is also well above the equilibrium (~4 ppm) for a deoxidant that normally achieves close to equilibrium oxygen levels. This would suggest that under industrial conditions, CH 4 might achieve 58 . deoxidation down to levels comparable to Al. 4. In starting from high initial oxygen levels and going down to about 100 ppm the deoxidation rate is essentially independent of oxygen concentration and directly proportion to the CH 4 injection rate which suggests hydrogen or carbon transport control. During this period, the process is reasonably efficient in terms of gas utilization. 5. Below 100 ppm oxygen the rate of deoxidation slows, perhaps indicating a shift to oxygen transport control for the reaction. Gas utilization is not good in this regime indicating that a modulated injection rate linked to dissolved oxygen might be appropriate. 6. Recarburization was not significant until dissolved oxygen goes below —200 ppm. Although reliable data on hydrogen pick-up were obtained for only one trial, the results also suggest that this becomes an issue only when deoxidation is inefficient. 7. The efficiency of carbon for deoxidation was approximately 17-32% indicating that hydrogen was the dominant factor. 59 REFERENCES ^.E.T.Turkdogan, Fundfamentals of Steelmaking, Institute of Materials, 1996 (Version 1.) , 210 (Figure 8.1), 222 (Table 8.1), 225 (Figure 8.12), 225 (Figure 8.13). 5. A.Lazcano-Navarro and GVargas-Gutierrez, Improving Quality and Productive through Natural Gas Bottom Blowing in Iron and Steelmaking, Proceedings of the Emerging Technologies for New Materials & Product-mix of the Steel Industry, 1991,282. 6 . G.J.Hardie, I.F.Taylor, J.M.Ganser, L.K.Wright, M.P.Davis and C.W.Boon, Adaptation of Injection Technology fot the Fflsmelt Process, Proceedings of the Savard/Lee International Symposium on Bath Smelting, 1992, 623-628, 627 (Figure 3). 7 ~ 1 0 .YAN Guangting, TANG Ping and ZHANG Shujun, Metallurgical Reaction Characteristic for the Combined Blowing Process of Top-Bottom Blown Oxyen and Bottom Blown Natural Gas, Chin.J.Met.Sci.Technol.,Vol.7,1991,50-54,51 (Figure 1),50,53 (Figure 8),53 (Figure 9). u~12.Yasuo Kishimoto, Toshikazu Sakuraya and Tetsuya Fujii, Recent Advances in Top and Bottom Blowing Converters Based on a Mathematical Model, Proceedings of the Savard/Lee International Symposium on Bath Smelting, 1992, 293-298, 297 (Fig. 4), 297 (Table 1). .LUISJ.Velez, Juan.M.Fuentes, Hervey Zamora and Cesar Santillana, Operational and Metallurgical Results of Combined Blowing at AHMS A's No.2 Steel Shop, Steelmaking Conference Proceedings, 1998, 137-140, 137 (Figure 1). 1 4 . Arturo Lazcano and Gregorio Vargas, Use of natural gas in combined blowing technology, Steel Technology International, 1991, pp.83-87, 83 (Figure 1). 1 5 . Arturo Lazcano and Gregorio Vargas, Start up results of EVIIS combined blowing Technology Using Natural Gas At AHMSA BOF-1, Steelmaking Conference Proceedings, 1989, 447-454, 450 (Figure 9). 60 16.A.Lazcano-Navarro and GVargas-Gutierrez, Improving Quality and Productive through Natural Gas Bottom Blowing in Iron and Steelmaking, Proceedings of the Emerging Technologies for New Materials & Product-mix of the Steel Industry, 1991,278 (Figure 2). 17~18.Arturo Lazcano and Gregorio Vargas, Start up results of IMIS combined blowing Technology Using Natural Gas At AHMS A BOF-1, Steelmaking Conference Proceedings, 1989, 447-454, 450 (Table 1), 450 (Figure 10). 19~20.Arturo Lazcano and Gregorio Vargas, Use of natural gas in combined blowing technology, Steel Technology International, 1991, pp.83-87, 87 (Figure 6), 87 (Figure 7). 2I.Arturo Lazcano and Gregorio Vargas, Start up results of IMIS combined blowing Technology Using Natural Gas At AHMS A BOF-1, Steelmaking Conference Proceedings, 1989, 447-454, 454 (Figure 11). 22 .A.Lazcano-Navarro and GVargas-Gutierrez, Improving Quality and Productive through Natural Gas Bottom Blowing in Iron and Steelmaking, Proceedings of the Emerging Technologies for New Materials & Product-mix of the Steel Industry, 1991,280 (Figure 4). 23~24.Ing.Arturo Lazcano Navarro and Dr.Gregorio Vargas Gutierrez, Research and Development Activities on Ladle Metallurgy at IMIS, Metalurgia International, Vol.2, No.7, September 1989, 189-197, 190 (Fig. 1), 191 (Table 3). John F.Elliott, Molly Gleiser and V.Ramakrishna, Thermochemistry For Steelmaking, Vol 2, 1963,618-621. .Axel Weyl, Shi Wei Tu and Dieter Janke, Sensors based on new oxide electrolyte and oxygen reference materials for on-line measurements in steel melts, Steel research 65, 1994, No 5, 167-172. 27 . Arturo Lazcano and Gregorio Vargas, Use of natural gas in combined blowing technology, Steel Technology International, 1991, pp.87 (Figure 6). 61 APPENDIX. EXPERIMENTAL DATA 1. 200cc/min (without air blowing) blow(min) CH4 (cc) T(°C) [0]ppm mv K Pe Po 0 0 1595 162 132 26662621 4.08E-16 1.03E-12 0 0 1595 171 136 26662621 4.08E-16 1.03E-12 4 800 1598 88 84 26288036 4.72E-16 1.11E-12 4 800 1598 71 68 26288036 4.72E-16 1.11E-12 10 2000 1586 27 4 27826329 2.62E-16 8.21E-13 10 2000 1586 27 6 27826329 2.62E-16 8.21E-13 10 2000 1586 27 6 27826329 2.62E-16 8.21 E-13 2. 15 Occ/min (without air blowing) Time CH4(cc/min) Temp [0]ppm mv K Pe Po 0 0 1605 71 64 25438813 6.65E-16 1.31E-12 5 750 1625 56 36 23191557 1.74E-15 2.13E-12 14 2100 1585 33 12 27959439 2.49E-16 8.01E-13 20 3000 1605 33 8 25438813 6.65E-16 1.31E-12 25 3750 1583 27 6 28228009 2.26E-16 7.62E-13 32 4800 1571 23 2 29907501 1.24E-16 5.63E-13 3. 120cc/min (without air blowing) Time CH4(cc/min) Temp [0]ppm mv K Pe Po 0 0 1591 48 44 27172308 3.35E-16 9.3E-13 6 720 1583 33 20 28228009 2.26E-16 7.62E-13 12 1440 1565 27 16 30793068 9.14E-17 4.83E-13 16 1920 1559 24 12 31710916 6.74E-17 4.14E-13 20 2400 1564 24 8 30943764 8.69E-17 4.71E-13 28 3360 1562 22 4 31247872 7.85E-17 4.47E-13 33 3960 1560 22 4 31555642 7.09E-17 4.25E-13 62 4. 150cc/min (with air blowing) *.Data 1) CH4 (cc) T(°C) [0]ppm mv K Pe Po 0 ' 1600 834 256 26041896 5.21E-16 1.16E-12 375 1580 588 240 28636817 1.94E-16 7.06E-13 825 1590 442 212 27301592 3.19E-16 9.07E-13 1950 1620 96 78 23729691 1.37E-15 1.89E-12 4200 1538 58 88 35198145 2.28E-17 2.4E-13 *.Data 2) CH4(cc/min) Temp [OJppm mv K Pe Po 0 1595 508 220 26662621 4.08E-16 1.03E-12 750 1595 430 207 26662621 4.08E-16 1.03E-12 1500 1591 314 185 27172308 3.35E-16 9.3E-13 2250 1584 75 80 28093331 2.37E-16 7.81 E-13 3000 1585 66 70 27959439 2.49E-16 8.01 E-13 3750 1584 36 27 28093331 2.37E-16 7.81E-13 4500 1584 35 24 28093331 2.37E-16 7.81E-13 5250 1584 32 17 28093331 2.37E-16 7.81E-13 6000 1584 28 8 28093331 2.37E-16 7.81 E-13 5. lOOcc/min (with air blowing) *.Data 1) Time CH4(cc/min) Temp [0]ppm mv K Pe Po 0 0 1570 746 264 30052910 1.18E-16 5.48E-13 8 800 1570 547 240 30052910 1.18E-16 5.48E-13 13 1300 1570 279 188 30052910 1.18E-16 5.48E-13 18 1800 1568 223 172 30346333 1.06E-16 5.21E-13 22 2200 1568 181 156 30346333 1.06E-16 5.21 E-13 27 2700 1564 73 90 30943764 8.69E-17 4.71E-13 32 3200 1564 41 48 30943764 8.69E-17 4.71E-13 37 3700 1560 34 36 31555642 7.09E-17 4.25E-13 *.Data2) Time CH4(cc/min) Temp [OJppm mv K Pe Po 0 0 1579 682 252 28774696 1.85E-16 6.89E-13 4 400 1579 555 236 28774696 1.85E-16 6.89E-13 7 700 1573 443 222 29619257 1.37E-16 5.92E-13 14 1400 1579 242 172 28774696 1.85E-16 6.89E-13 21 2100 1579 197 156 28774696 1.85E-16 6.89E-13 28 2800 1579 67 75 28774696 1.85E-16 6.89E-13 35 3500 1576 45 48 29193237 1.59E-16 6.39E-13 40 4000 1576 42 42 29193237 1.59E-16 6.39E-13 45 4500 1576 31 21 29193237 1.59E-16 6.39E-13 63 6. 150cc/min (without air blowing) — carbon pick up *.Data 1) Time CH4(cc/min) Temp [0]ppm mv [C] wt% 0 0 1605 71 64 0.013 5 750 1625 56 36 0.019 14 2100 1585 33 12 0.022 20 3000 1605 33 8 0.062 25 3750 1583 27 6 0.073 32 4800 1571 23 2 0.099 7. lOOcc/min (with air blowing) — carbon pick up *.Data 1) Time CH4(cc/min) Temp [0]ppm mv [C] wt% 0 0 1579 682 252 0.004 4 400 1579 555 236 -7 700 1573 443 222 0.005 14 1400 1579 242 172 0.007 21 2100 1579 197 156 0.007 28 2800 1579 67 75 0.015 35 3500 1576 45 48 0.017 40 4000 1576 42 42 0.025 45 4500 1576 31 21 0.033 8. 150cc/min (with air blowing) — carbon pick up *.Data 1) Time CH4(cc/min) Temp [0]ppm mv [C] wt% 0 0 1595 508 220 0.004 5 750 1595 430 207 0.007 10 1500 1591 314 185 0.008 15 2250 1584 75 80 0.012 20 3000 1585 66 70 0.014 25 3750 1584 36 27 0.024 30 4500 1584 35 24 0.027 35 5250 1584 32 17 0.031 40 6000 1584 28 8 0.047 64 9.100cc/min : Efficiency carbon Time CH4(cc/min) Temp [0]ppm C p ick up 0 reduc t ion to ta l 0 0 1579 682 0 0 0 7 700 1573 443 0.03 0.48 0.50 14 1400 1579 242 0.04 0.44 0.48 21 2100 1579 197 0.03 0.32 0.35 28 2800 1579 67 0.07 0.31 0.38 35 3500 1576 45 0.07 0.25 0.32 40 4000 1576 42 0.10 0.22 0.32 45 4500 1576 31 0.12 0.20 0.32 10.150cc/min : Efficiency carbon Time CH4(cc/min) Temp [0 ]ppm mv [C] wt% C p i c k u p 0 r e d u c t i o n t o t a l 0 0 1595 508 220 0.004 0 0 0 5 750 1595 430 207 0.007 0.07 0.15 0.22 10 1500 1591 314 185 0.008 0.05 0.18 0.23 15 2250 1584 75 80 0.012 0.07 0.27 0.34 20 3000 1585 66 70 0.014 0.06 0.21 0.27 25 3750 1584 36 27 0.024 0.10 0.18 0.28 30 4500 1584 35 24 0.027 0.10 0.15 0.24 35 5250 1584 32 17 0.031 0.10 0.13 0.22 40 6000 1584 28 8 0.047 0.13 0.11 0.25 11. 15 Occ/min (without air blowing) — Hydrogen pick up Time CH4(cc/min) Temp [0]ppm mv K Pe Po [C] wt% [Hlppm D [H]ppm R [Hlppm T 0 0 1605 71 64 25438813 6.65E-16 1.31E-12 0.013 4 0 4 5 750 1625 56 36 23191557 1.74E-15 2.13E-12 0.019 19 2 20 14 2100 1585 33 12 27959439 2.49E-16 8.01E-13 0.022 21 1 22 20 3000 1605 33 8 25438813 6.65E-16 1.31E-12 0.062 20 1 21 25 3750 1583 27 6 28228009 2.26E-16 7.62E-13 0.073 26 0 26 32 4800 1571 23 2 29907501 1.24E-16 5.63E-13 0.099 65 

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