UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Coal combustion in spouted and spout-fluid beds Zhao, Jiansheng 1986

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1986_A7 Z52.pdf [ 12.41MB ]
Metadata
JSON: 831-1.0058691.json
JSON-LD: 831-1.0058691-ld.json
RDF/XML (Pretty): 831-1.0058691-rdf.xml
RDF/JSON: 831-1.0058691-rdf.json
Turtle: 831-1.0058691-turtle.txt
N-Triples: 831-1.0058691-rdf-ntriples.txt
Original Record: 831-1.0058691-source.json
Full Text
831-1.0058691-fulltext.txt
Citation
831-1.0058691.ris

Full Text

c. COAL COMBUSTION IN SPOUTED AND S P O U T - F L U I D BEDS by J I A N S H E N G ZHAO A T H E S I S S U B M I T T E D IN P A R T I A L F U L F I L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF A P P L I E D S C I E N C E i n THE F A C U L T Y OF GRADUATE S T U D I E S CHEMICAL E N G I N E E R I N G We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H COLUMBIA F E B R U A R Y , 1 9 8 6 © J I A N S H E N G ZHAO, F E B R U A R Y , 1 9 8 6 -7 B In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r an advanced degree a t the The U n i v e r s i t y of B r i t i s h C olumbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by t h e Head of my Department or by h i s or her r e p r e s e n t a t i v e s . I t i s un d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . CHEMICAL ENGINEERING The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date: FEBRUARY,1986 ABSTRACT T h i s study of c o a l combustion was c a r r i e d out i n a h a l f - c o l u m n s p o u t - f l u i d bed combustor, i n which F o r e s t b e r g c o a l , a sub-bituminous A l b e r t a c o a l , was burned i n i n e r t beds of sand. The combustor c o n s i s t s of a h a l f c y l i n d r i c a l s t a i n l e s s s t e e l column of 0.152 m I . D. and 1.06 m l o n g , a h a l f c y l i n d r i c a l cone f i t t e d w i t h an i n l e t o r i f i c e of 15.9 mm and a p e r f o r a t e d p l a t e as d i s t r i b u t o r s u r r o unded by a plenum chamber, and a f l a t s t a i n l e s s s t e e l p a n e l w i t h q u a r t z g l a s s windows. A s p e c t s s t u d i e d i n c l u d e d hydrodynamic and combustion p a t t e r n s , a x i a l and r a d i a l t e mperature p r o f i l e s , a x i a l oxygen c o n c e n t r a t i o n p r o f i l e s and burnout t i m e s of c o a l p a r t i c l e s . Depending on o p e r a t i n g c o n d i t i o n s and p r o p e r t i e s of bed m a t e r i a l s , f o u r d i f f e r e n t f l o w p a t t e r n s were e s t a b l i s h e d : S t a b l e s p o u t i n g , p u l s a t o r y s p o u t i n g , j e t - i n - f l u i d i z e d - b e d and s l u g g i n g . I t was found t h a t the maximum s t a b l e s p o u t i n g h e i g h t d e c r e a s e d as the bed temp e r a t u r e i n c r e a s e d . A x i a l t e mperature p r o f i l e s i n the spout and ann u l u s were found t o be u n i f o r m f o r both spouted and s p o u t - f l u i d beds except f o r a s h o r t d i s t a n c e above the i n l e t o r i f i c e . However, a temperature i n c r e a s e was found i n the f o u n t a i n above the spout when f i n e r c o a l p a r t i c l e s were employed. Above the annulus the t e m p e r a t u r e s i n c r e a s e d s u b s t a n t i a l l y . More u n i f o r m a x i a l t e m p e r a t u r e p r o f i l e s c o u l d be a c h i e v e d by i n t r o d u c i n g a u x i l i a r y a i r t o c r e a t e a s p o u t - f l u i d bed. i i R a d i a l t emperature p r o f i l e s were u n i f o r m both i n the an n u l u s and i n the f o u n t a i n r e g i o n . A x i a l oxygen c o n c e n t r a t i o n p r o f i l e s were found t o be c l o s e l y r e l a t e d t o the f l o w p a t t e r n s and s o l i d s p r o p e r t i e s . When l a r g e r c o a l p a r t i c l e s (1mm) were used the oxygen c o n c e n t r a t i o n p r o f i l e s were u n i f o r m w i t h i n and above the spou t , but a d e c r e a s e of c o n c e n t r a t i o n was obser v e d when f i n e c o a l p a r t i c l e s (0.6 mm) were used. In the a n n u l u s a sharp d e c l i n e of c o n c e n t r a t i o n s t a r t e d near the bed s u r f a c e , and a minimum was reached i n the f o u n t a i n r e g i o n . C o n c e n t r a t i o n p r o f i l e s became more u n i f o r m when a u x i l i a r y a i r was i n t r o d u c e d . Compared w i t h d a t a r e p o r t e d i n l i t e r a t u r e f o r f l u i d i z e d bed c o m b u s t i o n , the burnout t i m e s of c o a l p a r t i c l e s i n spouted and s p o u t - f l u i d beds were found t o be s i g n i f i c a n t l y s h o r t e r . A model f o r e s t i m a t i n g the burnout t i m e s was proposed and t e s t e d a g a i n s t the e x p e r i m e n t a l d a t a . For the p a r t i c l e s i z e and temperature range t e s t e d , the combustion was m a i n l y c o n t r o l l e d by c h e m i c a l r e a c t i o n . T a b l e of C o n t e n t s ABSTRACT i i LIST OF TABLES v i i LIST OF FIGURES v i i i ACKNOWLEDGEMENT x i i 1. INTRODUCTION 1 1.1 S i g n i f i c a n c e of the P r e s e n t Work 1 1.2 O b j e c t i v e s of the P r e s e n t Work 5 2. LITERATURE REVIEW 7 2.1 Hydrodynamics of Spouted and S p o u t - f l u i d Beds ..7 2.2 C h a r a c t e r i s t i c s of Spouted and S p o u t - f l u i d Bed Combustion 11 2.3 J u s t i f i c a t i o n of Use of Half-Column Bed 15 3. EXPERIMENTAL APPARATUS AND SOLIDS PROPERTIES 17 3.1 E x p e r i m e n t a l Equipment 17 3.1.1 Combustor 17 3.1.2 Other A u x i l i a r y Equipment 20 3.2 E x p e r i m e n t a l I n s t r u m e n t a t i o n 20 3.3 P r o p e r t i e s of S o l i d s 29 3.3.1 P r o p e r t i e s of Sand 29 3.3.2 P r o p e r t i e s of C o a l 32 4. OPERATING PROCEDURE AND CHOICE OF EXPERIMENTAL CONDITIONS 35 4.1 O p e r a t i n g P r o c e d u r e ......35 4.2 C h o i c e of Base E x p e r i m e n t a l C o n d i t i o n s 36 4.3 Range of E x p e r i m e n t a l C o n d i t i o n s 37 5. HYDRODYNAMIC AND COMBUSTION PATTERNS 38 5.1 E x p e r i m e n t a l Technique 38 5.2 R e s u l t s and D i s c u s s i o n 40 5.2.1 Hydrodynamic and Combustion P a t t e r n s ....40 5.2.2 E f f e c t of Bed He i g h t on Flow P a t t e r n s ...55 5.2.3 E f f e c t of S o l i d s P r o p e r t i e s on the Flow P a t t e r n s 63 5.2.4 S h i f t i n g of Flow P a t t e r n s a t E l e v a t e d Temperature 67 5.2.5 Other O b s e r v a t i o n s 67 6. TEMPERATURE PROFILES 71 6.1 E x p e r i m e n t a l Technique 71 6.1.1 A x i a l Temperature Measurement 71 6.1.2 R a d i a l Temperature Measurement 72 6.2 R e s u l t s and D i s c u s s i o n 72 6.2.1 A x i a l Temperature P r o f i l e s i n and above the Spout 72 6.2.2 A x i a l Temperature P r o f i l e s i n the Annulus .76 6.2.3 R a d i a l Temperature P r o f i l e s 76 7. OXYGEN CONCENTRATION PROFILES 79 7.1 E x p e r i m e n t a l Technique 79 7.1.1 S y r i n g e Gas Sampling 79 7.1.2 Gas Probe Sampling 80 7.2 R e s u l t s and D i s c u s s i o n 83 7.2.1 Spouted Bed Combustion 83 7.2.2 S p o u t - F l u i d Bed Combustion 87 7.2.3 Other Phenomena 88 8. ELUTRIATION OF SOLIDS 90 8.1 S i z e D i s t r i b u t i o n and Carbon Content of E n t r a i n e d S o l i d s 90 8.2 S i z e Change of Bed M a t e r i a l s 92 9. COAL PARTICLE BURNOUT TIMES 94 v 9 .1 B a c k g r o u n d 94 9 . 2 E x p e r i m e n t a l T e c h n i q u e 98 9 . 3 R e s u l t s a n d D i s c u s s i o n 99 9 . 3 . 1 O b s e r v a t i o n 99 9 . 3 . 2 C o a l P a r t i c l e B u r n o u t t i m e s 100 9 . 3 . 3 M o d e l i n g o f B u r n o u t T i m e s 100 9 . 3 . 4 C o m p a r i s o n o f B u r n o u t T i m e s 106 10 . CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK 114 10.1 C o n c l u s i o n s 114 1 0 . 2 S u g g e s t i o n s f o r F u r t h e r Work 115 NOMENCLATURE 116 R E F E R E N C E S 119 A P P E N D I X I C A L I B R A T I O N CURVES OF ROTAMETERS 126 A P P E N D I X I I C A L I B R A T I O N CURVES OF COAL F E E D E R 128 A P P E N D I X I I I E S T I M A T I O N OF GAS SAMPLING FLOWRATE 129 A P P E N D I X I V A MODEL FOR E S T I M A T I N G COAL BURNOUT T I M E S . . . 1 3 1 A P P E N D I X V E X P E R I M E N T A L DATA 140 v i LIST OF TABLES Table 2.1 S t u d i e s of spouted bed combustion 12 Ta b l e 3.1 P a r t i c u l a r s of major equipment 25 Ta b l e 3.2 P r o p e r t i e s of Ottawa sand 31 Ta b l e 3.3 S i z e d i s t r i b u t i o n s of c o a l 33 Ta b l e 3.4 A n a l y s i s of C o a l 34 T a b l e 5.1 Terminology of f l o w p a t t e r n s i n l i t e r a t u r e 53 T a b l e 8.1 S i z e d i s t r i b u t i o n and carbon c o n t e n t of a s h . . . . 91 Ta b l e 8.2 Change of sand s i z e d i s t r i b u t i o n 93 Ta b l e 9.1 O p e r a t i n g c o n d i t i o n s of f l u i d i z e d bed combustors from l i t e r a t u r e 110 T a b l e 9.2 C o a l a n a l y s e s from l i t e r a t u r e 111 T a b l e A1 E x p e r i m e n t a l c o n d i t i o n s 137 Ta b l e A2 Comparison of c a l c u l a t e d burnout t i m e s 138 v i i LIST OF FIGURES F i g . 1.1 Schematic diagram of a spouted bed ,. 2 F i g . 1.2 Schematic diagram of s p o u t - f l u i d beds 4 F i g . 2.1 Regime map due t o D u m i s t r e s c u (1977) 9 F i g . 2.2 Regime map due t o S u t a n t o et a l (1985) 10 F i g . 3.1 Schematic diagram of the combustor 18 F i g . 3.2 F l a t t e n e d s u r f a c e of the c o n i c a l p e r f o r a t e d d i s t r i b u t o r 19 F i g . 3.3 E x p e r i m e n t a l Equipment 21 F i g . 3.4 P i c t u r e s of e x p e r i m e n t a l s e t - u p 22 F i g . 3.5 R o t a r y v a l v e f o r c o a l f e e d i n g 23 F i g . 3.6 P i c t u r e of c o a l f e e d e r 24 F i g . 3.7 Gas sampl i n g probe 27 F i g . 3.8 Gas sampl i n g system 28 F i g . 3.9 P o s i t i o n s of gas probe i n the combustor 30 F i g . 5.1 P h y s i c a l appearence of the f l o w p a t t e r n s ....41 F i g . 5.2 S t a b l e s p o u t i n g a t room temperature 42 F i g . 5.3 S t a r t u p of spouted bed combustion 42 F i g . 5.4 S t a b l e s p o u t i n g (T b=590 C, U/U m s=1.2 r H o = 0.3 m) .43 F i g . 5.5 P u l s a t o r y s p o u t i n g (T b=650 C, U/U m s=1.2, H o = 0.3 m) 45 F i g . 5.6 P u l s a t o r y s p o u t i n g (T b=650 C, U/U m s=1.4, H o = 0.3 m) 46 F i g . 5.7 J e t i n f l u i d i z e d bed ( I ) (T f a=650 C, q/Q T=0.2, H o = 0.3 m) 47 F i g . 5.8 J e t i n f l u i d i z e d bed ( I I ) (T f a=650 C, q/Q T=0.4, v i i i H o = 0.3 m) 49 F i g . 5.9 R i s i n g b u b b l e s i n J F ( I I ) 50 F i g . 5.10 S l u g g i n g (T b=650 C, q/Q T=0.6, H o = 0.2 m) 51 F i g . 5.11 S t a r t u p of combustion (T f a=460 C, U/U m s=1.2, H o = 0.2 m) 56 F i g . 5.12 S t a r t u p of combustion (T b=544 C, U/U m s=1.2, H o = 0.2 m) , 56 F i g . 5.13 S t a b l e s p o u t i n g (T b=650 C, U/U m s=1.2, H o = 0.2 m) 57 F i g . 5.14 P u l s a t o r y s p o u t i n g (T f a=630 C, U/U m s=1.3, H o = 0. 2 m) 58 F i g . 5.15 P u l s a t o r y s p o u t i n g (T f a=630 C, U/U m s=1.5, H o = 0.2 m) 59 F i g . 5.16 J e t i n f l u i d i z e d bed ( I ) (T b=640 C, q/Q T=0.2, H o = 0.2 m) 60 F i g . 5.17 J e t i n f l u i d i z e d bed ( I I ) (T f a=630 C, q/Q T=0.4, H o = 0.2 m) 61 F i g . 5.18 S l u g g i n g (T b=650 C, q/Q T=0.6, H o = 0.2 m) 62 F i g . 5.19 M a l d i s t r i b u t i o n of c o a l i n a spouted bed.. 66 F i g . 5.20 S t r a t i f i e d sand and ash 66 F i g . 5.21 Regime map of s p o u t - f l u i d bed a t room temp e r a t u r e 68 F i g . 5.22 Regime map of s p o u t - f l u i d bed a t h i g h t e m p e r a t u r e 69 F i g . 6.1 P o s i t i o n s of a x i a l t e mperature measurement...... 73 i x F i g . 6.2 P o s i t i o n s of r a d i a l t emperature measurement 73 F i g . 6.3 A x i a l t e mperature p r o f i l e s i n and above the spout 74 F i g . 6.4 A x i a l t e m p e r a t u r e p r o f i l e s i n s l u g g i n g bed 75 F i g . 6.5 A x i a l t e mperature p r o f i l e s (q/Q T:0-0.4) 77 F i g . 6.6 R a d i a l t emperature p r o f i l e s 78 F i g . 7.1 L o c a t i o n s of gas s a m p l i n g p o i n t s 81 F i g . 7.2 Oxygen c o n c e n t r a t i o n p r o f i l e s (sand s i z e : 1 . 6 5 - 2 . 3 6 mm, c o a l s i z e : 0 . 8 5 - 1 . 1 8 mm) 84 F i g . 7.3 Oxygen c o n c e n t r a t i o n p r o f i l e s (sand s i z e : 1 . 6 5 - 2 . 3 6 mm, c o a l s i z e : 0 . 6 0 - 0 . 8 5 mm) 85 F i g . 7.4 Oxygen c o n c e n t r a t i o n p r o f i l e s (sand s i z e : 1 . 1 8 - 1 . 6 5 mm, c o a l s i z e : 0 . 8 5 - 1 . 1 8 mm) 86 F i g . 7.5 Oxygen c o n c e n t r a t i o n p r o f i l e i n a f l u i d i z e d bed due t o Gibbs and Hedley (1978) 89 F i g . 9.1 C o a l p a r t i c l e burnout t i m e s i n spouted bed 101 F i g . 9.2 C o a l p a r t i c l e burnout t i m e s i n s p o u t - f l u i d bed. 102 F i g . 9.3 Schematic diagram of c o a l p a r t i c l e s b u r n i n g i n the an n u l u s of a spouted bed 104 F i g . 9.4 Comparison of c o a l burnout t i m e s from l i t e r a t u r e 107 F i g . 9.5 Comparison of c o a l burnout t i m e s f o r d i f f e r e n t t y p e s of c o a l (T b=875 C) 108 F i g . 9.6 Comparison of c o a l burnout t i m e s f o r d i f f e r e n t t y p e s of c o a l (T b= 1010 C) 109 F i g . A1 C a l i b r a t i o n c u r v e f o r s p o u t i n g a i r f l o w 126 F i g . A2 C a l i b r a t i o n c u r v e f o r a u x i l i a r y a i r f l o w 127 x F i g . A3 C a l i b r a t i o n c u r v e s f o r c o a l f e e d e r ....128 x i ACKNOWLEDGEMENT I would l i k e t o e x p r e s s my a p p r e c i a t i o n t o Dr. J . R. Grace and Dr. C. J . Lim f o r t h e i r e x c e l l e n t s u p e r v i s i o n and guidance; under t h e i r a d v i c e and encouragement t h i s work was c a r r i e d o u t . I am a l s o g r a t e f u l t o Dr. N. E p s t e i n f o r h i s h e l p f u l d i s c u s s i o n s and s u g g e s t i o n s . I would l i k e t o thank the N a t u r a l S c i e n c e s and E n g i n e e r i n g R esearch C o u n c i l of Canada, who funded the r e s e a r c h c o n t r a c t under which t h i s work was done. S p e c i a l thanks a r e a l s o due t o the gentlemen of the workshop, s t o r e s and c o a l l a b of the Department of Che m i c a l E n g i n e e r i n g f o r t h e i r e n t h u s i a s t i c and i n v a l u a b l e a s s i s t a n c e . F i n a l l y , I am d e e p l y i n d e b t e d t o the l a t e P r o f e s s o r L i n Hao of Tsing h u a U n i v e r s i t y , whose support and i n s p i r a t i o n accompanied me throughout t h i s work. x i i 1. INTRODUCTION 1.1 S IGN IF ICANCE OF THE PRESENT WORK The s p o u t e d bed t e c h n i q u e was d e v e l o p e d by G i s h l e r and M a t h u r (1955) f o r d r y i n g w h e a t . S i n c e t h e n , a s an a l t e r n a t i v e t o f l u i d i z e d bed s f o r h a n d l i n g c o a r s e p a r t i c l e s , s p o u t e d b e d s have been u s e d f o r a l a r g e v a r i e t y o f p r o c e s s e s s u c h a s d r y i n g o f g r a n u l a r s o l i d s , t a b l e t c o a t i n g , s o l i d s b l e n d i n g and g a s i f i c a t i o n o f c o a l . A c o m p l e t e r e v i e w o f s p o u t e d bed t e c h n o l o g y was p r e s e n t e d i n t h e monograph by M a t h u r and E p s t e i n ( 1 9 7 4 ) . More r e c e n t r e v i e w s a r e g i v e n by E p s t e i n and G r a c e (1984) and B r i d g w a t e r ( 1 9 8 5 ) . F i g u r e 1.1 i l l u s t r a t e s s c h e m a t i c a l l y a t y p i c a l s p o u t e d b e d . In a v e s s e l f i l l e d w i t h c o a r s e p a r t i c l e s , f l u i d i s i n j e c t e d v e r t i c a l l y t h r o u g h a c e n t r a l l y l o c a t e d s m a l l o p e n i n g a t t h e b o t t o m . The p a r t i c l e s a r e e n t r a i n e d i n t h e c e n t r a l h o l l o w e d s p o u t i n t o a f o u n t a i n a b o v e t h e bed s u r f a c e where t h e y r a i n back o n t o t h e s u r f a c e , t h e y t h e n move downwards s l o w l y a s a m o v i n g p a c k e d b e d i n an a n n u l u s r e g i o n s u r r o u n d i n g t h e s p o u t . The o v e r a l l bed t h e r e b y becomes a c o m p o s i t e o f a d i l u t e p h a s e c e n t r a l c o r e , w i t h upward m o v i n g s o l i d s e n t r a i n e d by c o c u r r e n t f l o w o f f l u i d , and a d e n s e p h a s e a n n u l u s r e g i o n , w i t h c o u n t e r c u r r e n t p e r c o l a t i o n o f f l u i d . V a r i o u s m o d i f i c a t i o n s t o s t a n d a r d s p o u t e d bed s h a v e r e s u l t e d i n a w ide r a n g e o f u s e f u l a p p l i c a t i o n s (Ma thur and E p s t e i n , 1 9 7 4 ) . One o f them i s t h e s p o u t - f l u i d b e d , w h i c h i s 1 2 FOUNTAIN BED SURFACE SPOUT ANNULUS S P O U T - A N N U L U S INTERFACE CONICAL B A S E FLUID INLET F i g . 1 .1 . Schematic diagram of a spouted bed 3 shown i n F i g . 1.2. In a d d i t i o n t o s u p p l y i n g s p o u t i n g f l u i d t h rough a c e n t r a l l y l o c a t e d o p e n i n g , a u x i l i a r y f l u i d i s s u p p l i e d t h r o u g h a c o n i c a l or f l a t porous or p e r f o r a t e d d i s t r i b u t o r . S p o u t - f l u i d beds show b e t t e r s o l i d s m i x i n g and a n n u l a r s o l i d - f l u i d c o n t a c t than s t a n d a r d spouted beds ( C h a t t e r j e e , 1970; Madonna et a l , 1980) and l e s s tendency f o r p a r t i c l e s t o adhere t o the w a l l s or base of the column (Kono, 1981). In s p i t e of numerous a p p l i c a t i o n s of the spouted bed t e c h n i q u e , i t s a p p l i c a t i o n t o combustion d i d not come u n t i l Khoshnoodi and Weinberg (1978) used a spouted bed combustor t o burn l e a n gases. S i n c e then more work has been done, i n c l u d i n g combustion of l i q u i d f u e l s ( A r b i b and Levy, 1982) and s o l i d f u e l s (Lim e t a l , 1984) i n spouted beds. As p o i n t e d out by Lim e t a l (1984), spouted beds have a number of advantages over c o n v e n t i o n a l f l u i d i z e d bed combustion: (a) Because of the s h e a r i n g a c t i o n of the h i g h v e l o c i t y j e t or s p o u t , spouted beds can be used t o p r o c e s s c a k i n g s o l i d f u e l s . (b) Spouted beds a r e c a p a b l e of p r o c e s s i n g c o a r s e r p a r t i c l e s than f l u i d i z e d beds, (c) The p r e s s u r e d r o p a c r o s s spouted beds i s t y p i c a l l y o n l y about s e v e n t y - f i v e p e r c e n t of t h a t a c r o s s a f l u i d i z e d bed of the same bed h e i g h t , (d) Spouted beds have been proven t o be a b l e t o burn low q u a l i t y f u e l s . (e)The r e g u l a r movement of s o l i d s and gases of spouted beds makes them e a s i e r t o model and s c a l e - u p . ( f ) F u e l p a r t i c l e s can be r e a d i l y f e d w i t h the s p o u t i n g a i r w i t h o u t the need f o r overbed f e e d i n g or e x t r a SPOUTING FLUID INLET F i g . 1.2a Schematic diagram of a s p o u t - f l u i d bed with c o n i c a l base d i s t r i b u t o r . F i g . 1.2b Schematic diagram of a s p o u t - f l u i d bed with f l a t base d i s t r i b u t o r . 5 a i r f o r f e e d i n g from below. The r e s e r v e s of s o l i d f u e l s , e s p e c i a l l y c o a l and waste m a t e r i a l s , a r e r e l a t i v e l y abundant i n many c o u n t r i e s such as Canada and C h i n a . New t e c h n i q u e s s h o u l d be sought i n an e f f o r t t o d e v e l o p s u i t a b l e p r o c e s s e s t h a t can e f f i c i e n t l y u t i l i z e t h e s e m a t e r i a l s . The development of combustion i n spouted beds needs a d e t a i l e d s t u d y of the mechanism of c o a l combustion i n spouted and s p o u t - f l u i d beds. T h i s i s the t o p i c of the p r e s e n t work. 1.2 OBJECTIVES OF THE PRESENT WORK Because of the s h o r t h i s t o r y of spouted bed combustion, because l i t t l e work has been done i n s p o u t - f l u i d bed comb u s t i o n , and a l s o because the knowledge of the spouted bed b e h a v i o u r a t e l e v a t e d temperature i s f a r from s u f f i c i e n t , the main purpose of the p r e s e n t work i s t o study the hydrodynamics and combustion p a t t e r n s under v a r y i n g o p e r a t i n g c o n d i t i o n s . V a r i a b l e s i n c l u d e s p o u t i n g a i r f l o w r a t e , a u x i l i a r y a i r f l o w r a t e , f e e d r a t e of c o a l , bed h e i g h t , and s i z e s of i n e r t bed p a r t i c l e s and c o a l p a r t i c l e s . V i s u a l o b s e r v a t i o n i n a h a l f - c o l u m n p r o v i d e s a good method to a c c o m p l i s h t h i s o b j e c t i v e . A nother o b j e c t i v e i s t o measure the a x i a l and r a d i a l t e m p e r a t u r e p r o f i l e s and a x i a l oxygen c o n c e n t r a t i o n p r o f i l e s . These d a t a w i l l h e l p i n the development of r e a c t o r models and s c a l e - u p methods. F i n a l l y , the burnout times of c o a l p a r t i c l e s of v a r i o u s s i z e s a r e measured under d i f f e r e n t 6 o p e r a t i n g c o n d i t i o n s and compared w i t h d a t a r e p o r t e d i n the l i t e r a t u r e f o r f l u i d i z e d bed combustion. . . In o r d e r t o f u l f i l l t h e s e o b j e c t i v e s , i t was f i r s t n e c e s s a r y t o d e s i g n and b u i l d a h a l f - c o l u m n s p o u t - f l u i d bed combustor and i t s a u x i l i a r y equipment. 2. LITERATURE REVIEW 2.1 HYDRODYNAMICS OF SPOUTED AND SPOUT-FLUID BEDS Without a u x i l i a r y f l u i d , a s p o u t - f l u i d bed becomes a s t a n d a r d spouted bed. There have been many s t u d i e s on hydrodynamics of spouted bed. For r e v i e w s see Mathur and E p s t e i n (1974), and E p s t e i n and Grace (1984). T h e r e f o r e the p r e s e n t review on hydrodynamics i s c o n f i n e d t o s p o u t - f l u i d beds. The study of hydrodynamics of s p o u t - f l u i d beds seems t o have s t a r t e d w i t h C h a t t e r j e e (1970) and Pomortseva and Baskakov (1970). A c c o r d i n g t o C h a t t e r j e e , who used a spouted bed w i t h a f l a t - b o t t o m d i s t r i b u t o r t o i n t r o d u c e f l u i d i z i n g a i r , s p o u t - f l u i d beds overcome the l i m i t a t i o n s of s t r a t i f i c a t i o n and s l u g g i n g which a r e o f t e n e n c o u n t e r e d i n f l u i d i z e d beds, but w i t h o u t the l i m i t a t i o n s i n p a r t i c l e s i z e and bed d e p t h , which a r e i n h e r e n t i n spouted beds. He a l s o c o n c l u d e d t h a t the s p o u t - f l u i d beds g i v e much h i g h e r r a t e s of c i r c u l a t i o n and b e t t e r m i x i n g of s o l i d s and. f l u i d s than o t h e r f l u i d - s o l i d c o n t a c t i n g t e c h n i q u e s . T h i s p o i n t was s u p p o r t e d by o b s e r v a t i o n s of Pomorstseva and Baskakov (1970) made i n a s e m i c i r c u l a r column. Regime maps, which r e p r e s e n t a number of d i f f e r e n t t y p e s of s p o u t - f l u i d bed b e h a v i o u r , have been e x p e r i m e n t a l l y d e t e r m i n e d by s e v e r a l i n v e s t i g a t o r s ( N a g a r k a t t i and C h a t t e r j e e , 1974; L i t t m a n e t a l , l 9 7 4 ; Dumistresy,1977; S u t a n t o e t a l , l 9 8 5 ) . One such diagram p r e s e n t e d by 7 8 D u m i s t r e s c u (1977) i s r e p r o d u c e d i n F i g . 2 . 1 . T h i s shows t h a t d i f f e r e n t h y d r o d y n a m i c p a t t e r n s e x i s t d e p e n d i n g on t h e c o m b i n a t i o n o f s p o u t i n g and a u x i l i a r y f l o w r a t e . A d e t a i l e d s t u d y o f h y d r o d y n a m i c s o f s p o u t - f l u i d bed s was a c c o m p l i s h e d by S u t a n t o e t a l ( 1 9 8 5 ) . A c y l i n d r i c a l h a l f - c o l u m n s p o u t - f l u i d bed was u s e d i n t h e i r s t u d y . F i g u r e 2.2 i s a t y p i c a l r e g i m e map g i v e n by S u t a n t o e t a l ( 1 9 8 5 ) . F o u r f a i r l y d i s t i n c t f l o w p a t t e r n s a r e d e l i n e r a t e d : s p o u t i n g w i t h a e r a t i o n ( S A ) ; s p o u t - f l u i d i z a t i o n ( S F ) , i n w h i c h t h e bed s u r f a c e i s f l u i d i z e d ; s u b m e r g e d j e t i n f l u i d i z e d b e d ( J F ) , and p a c k e d b e d ( P ) . Two d i f f e r e n t f l o w p a t t e r n s were o b s e r v e d u n d e r t h e c o n d i t i o n o f a submerged j e t i n f l u i d i z e d b e d . A t h i g h e r a u x i l i a r y f l o w , s l u g g i n g o f s o l i d m a t e r i a l i n t h e u p p e r s e c t i o n o f bed was o b s e r v e d . T h i s c a s e was d e n o t e d a s J F ( I ) . A t l o w e r a u x i l i a r y f l o w s a r e g i m e , d e n o t e d a s J F ( I I ) , was f o u n d where b u b b l e s b r o k e t h e b e d s u r f a c e . The t r a n s i t i o n be tween J F ( I ) and J F ( I I ) was g r a d u a l . No s t a b l e s p o u t i n g c o u l d be a c h i e v e d i n t h e s p o u t - f l u i d i z a t i o n r e g i m e . The " s p o u t " u n d e r t h i s c o n d i t i o n was i n f a c t a s u c c e s s i o n o f r i s i n g b u b b l e s . S u t a n t o e t a l (1985) a l s o s t u d i e d o t h e r c h a r a c t e r i s t i c s o f s p o u t - f l u i d b e d s , s u c h a s minimum s p o u t i n g v e l o c i t y , b e d p r e s s u r e d r o p , v e l o c i t y d i s t r i b u t i o n i n t h e a n n u l u s , p a r t i c l e c i r c u l a t i o n , and h e i g h t and shape o f t h e f o u n t a i n . 9 F i g . 2.1 Regime map due t o D u m i s t r e s c u (1977) M a t e r i a l : p o l y e t h y l e n e p e l l e t P a r t i c l e s i z e : 3 mm d i a m e t e r , 1.5-4 mm l o n g Column d i a m e t e r : 0.15 m I n l e t o r i f i c e d i a m e t e r : 2.21 mm H=0.25 m F l u i d used: a i r q /Qmf 10 1.6 1.4 1.2 0.4 0.2 0 • Ob se r ved spout - f l u i d i z a t i o n O Obse rved s p o u t i n g w i t h a e r a t i o n Jet in f luidized bed (s lugging) / JF(I) / Spout-f luidization ' (SF) TD cr \ J F ( I I ) o o o Spouting with aeration (SA) Packed bed ( P) ^ \^bubbllsjg) \ \ F \ A 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Qs/Qmf F i g . 2.2 Regime Map due to Sutanto et a l (1985) [system: p o l y s t y r e n e , d = 1.91 cm, H= 60cm] 11 2.2 CHARACTERISTICS OF SPOUTED AND SPOUT-FLUID BED  COMBUSTION No l i t e r a t u r e r e g a r d i n g s p o u t - f l u i d bed combustion i s a v a i l a b l e except f o r Lim et a l (1984). A p p l i c a t i o n of s p o u t - f l u i d beds t o combustion i s a t an e a r l y s t a g e . Because s p o u t - f l u i d beds share some common c h a r a c t e r i s t i c s w i t h spouted beds ( S u t a n t o e t a l , 1985), the emphasis here i s on spouted bed combustion. Table 2.1 summarizes the work done i n s pouted bed combustion. Khoshnoodi and Weinberg (1978) burned gaseous m i x t u r e s of methanol and a i r i n a s i l i c a tube of 40 mm d i a m e t e r . They found t h a t gaseous m i x t u r e s h a v i n g o n l y h a l f of the normal f l a m m a b i l i t y c o u l d be burned i n t h e i r s m a l l combustor. T h i s i s because a spouted bed can work as a c o u n t e r - c u r r e n t heat exchanger, l e a d i n g t o p r e h e a t i n g of the gaseous m i x t u r e b e f o r e i t reaches the f o u n t a i n . As a r e s u l t , gas was ob s e r v e d t o burn i n the f o u n t a i n r e g i o n . I t was a l s o found t h a t under c e r t a i n c o n d i t i o n s , presumably when v i s c o s i t y i n c r e a s e s s u f f i c i e n t l y due t o the r i s e i n t e m p e r a t u r e , a second f l u i d i z e d bed formed above the bed s u r f a c e . U s i n g a spouted bed combustor, A r b i b and Levy (1982) burned a v a r i e t y of low c a l o r i f i c v a l u e l i q u i d f u e l s , such as methanol-water m i x t u r e s and o i l - w a t e r e m u l s i o n s . The l i q u i d f u e l s were f e d i n t o the bed w i t h the s p o u t i n g a i r t h r o u g h the bottom i n l e t . I t was p r o v e d t h a t a spouted bed combustor has the a b i l i t y t o burn l o w - q u a l i t y f u e l s , which a r e i n c o m b u s t i b l e by o t h e r methods. TABLE 2.1 STUDIES OF SPOUTED BED COMBUSTION I n v e s t i g a t o r Column Type Column D i ameter (mm) Bed M a t e r i a l (dp;mm) Fuel A s p e c t s Stud i ed Khoshnoodi and Weinberg (1978) d r c u l a r 40 slMca(I.O) methane/a 1r m i x t u r e s t a b i 1 i ty H u n , temperature p r o f i l e A r b i b e t a l . (1981) c i r c u l a r 53 s i 1 i ca, a 1 urn 1na. mul 1i te(0.5-2 ) methane/a i r m i x t u r e combust i o n Ums, s t a b i 1 i t y , t r a n s f e r modes, f 1 ame heat Arb i b ( 1982a) and Levy c i r c u l a r 48 a 1 urn i na(1.0) t o l u e n e / a i r , o i 1 / w a t e r , methanol/water m i x t u r e 1ean l i m i t A r b i b and Levy c i r c u l a r 53 , s i n t e r e d b a u x i t e methane, methanol f e a s i b i l i t y of (1982b) (2.4-3.3) r e v e r s e f l o w spouted bed combustor Khoe and Weve s e m i c i r c u l a r 90 r i v e r sand, molding p r o p a n e / a i r f l o w regimes and (1983) sand(0.8-1) combustion modes Lim e t a l (1984) c i r c u l a r 305 g r a v e l ( 2 - 3 ) c o a l ( 1 - 3 ) f e a s i b i l i t y . temperature p r o f i l e , heat t r a n s f e r 13 A s t u d y o f h y d r o d y n a m i c s o f s p o u t e d b e d s u n d e r c o m b u s t i o n c o n d i t i o n s was c o n d u c t e d by A r b i b e t a l ( 1 9 8 1 ) . Two q u a r t z c o l u m n s w i t h d i f f e r e n t d i m e n s i o n s were u s e d . When b u r n i n g g a s e o u s m i x t u r e s o f methane and a i r , d i f f e r e n t c o m b u s t i o n p a t t e r n s were f o u n d : t h e s e r a n g e d f r o m p a c k e d b e d , f l u i d i z e d b e d , p u l s a t i n g s p o u t e d b e d , t o s t a b l e s p o u t e d bed a s f l o w r a t e i n c r e a s e d . P u l s a t i n g c o m b u s t i o n was more f r e q u e n t l y o b s e r v e d w i t h s m a l l ( 0 . 5 mm) t h a n w i t h l a r g e ( 2 . 0 mm) p a r t i c l e s . The t e m p e r a t u r e was q u i t e u n i f o r m t h r o u g h o u t t h e b e d . A d e t a i l e d s t u d y o f t h e f l o w r e g i m e s d u r i n g s p o u t e d bed c o m b u s t i o n o f gas was r e p o r t e d by Khoe and Weve ( 1 9 8 3 ) . A h a l f c o l u m n s p o u t e d b e d o f 90 mm d i a m e t e r w i t h a g l a s s f r o n t p a n e l was u s e d . F l o w r e g i m e s and c o m b u s t i o n p a t t e r n s u n d e r v a r y i n g o p e r a t i n g c o n d i t i o n s were d i s t i n g u i s h e d . A t a g i v e n p r o p a n e t o a i r r a t i o , t h e s p o u t e d bed e x h i b i t e d t h e f o l l o w i n g r e g i m e s a s t h e i n l e t mass f l o w r a t e was i n c r e a s e d : (1) I n t e r n a l s p o u t . T h i s p a t t e r n i s q u i t e s i m i l a r t o i n t e r n a l s p o u t i n g w i t h o u t c o m b u s t i o n . (2) B u b b l e e r u p t i o n . In t h i s c a s e , e x p a n s i o n o f gas c a u s e s a c h a i n o f b u b b l e s t o emerge f r o m t h e t o p o f t h e i n t e r n a l s p o u t . (3) R e g u l a r p u l s i n g s p o u t . The o v e r a l l s o l i d s c i r c u l a t i o n i s s i m i l a r t o t h a t i n t h e s t a b l e s p o u t i n g mode, bu t t h e t o p l a y e r s o f t h e a n n u l u s r e g u l a r l y s l i p down i n t o t h e s p o u t w i t h o u t e n t i r e l y b l o c k i n g 14 the passage. (4) S t a b l e s p o u t i n g . In t h i s regime, the flame s t a b l i z e s below the f o u n t a i n a t the t o p of the spout, and the sour c e of i g n i t i o n i s at the t o p s u r f a c e of the a n n u l u s . I t was found t h a t the f o u n t a i n i s much h i g h e r f o r t h i s case than where no combustion i s o c c u r r i n g . Other a s p e c t s such as the e f f e c t of n o z z l e s i z e and bed h e i g h t on combustion modes were a l s o examined by Khoe and Weve. Study of t h e combustion of s o l i d f u e l s i n spouted beds was s t a r t e d i n the Department of Chemical E n g i n e e r i n g a t the U n i v e r s i t y of B r i t i s h Columbia i n 1980 (Lim e t a l , 1984). A 0.3 m d i a m e t e r spouted bed combustor p i l o t p l a n t was completed i n e a r l y 1981 and has been o p e r a t i n g s i n c e t h e n . Low grade c o a l s , i n c l u d i n g washery r e j e c t s w i t h up t o 89% ash and h e a t i n g v a l u e s as low as 3500 k j / k g have been s u c c e s s f u l l y burned i n t h i s combustor. H i g h l y c a k i n g c o a l and peat have a l s o been used as f u e l s . I t has been proven t h a t spouted beds a r e u s e f u l not o n l y f o r b u r n i n g l e a n gases and l i q u i d s but a l s o f o r b u r n i n g l o w - q u a l i t y s o l i d f u e l s . The o v e r a l l bed-to-immersed tube heat t r a n s f e r c o e f f i c i e n t i n a spouted bed undergoing combustion was found t o be c l o s e t o t h a t found i n f l u i d i z e d bed combustors. A p r e l i m i n a r y study of c o a l combustion i n a s p o u t - f l u i d bed was a l s o c a r r i e d out by Lim e t a l (1984). When a u x i l i a r y a i r was i n t r o d u c e d t o produce the s p o u t - f l u i d bed combustion 15 mode, the a x i a l t e m p e r a t u r e p r o f i l e s were found t o be more u n i f o r m than i n s t a n d a r d spouted bed combustors. S i m i l a r f i n d i n g s i n a p r e h e a t e d s p o u t - f l u i d bed were r e p o r t e d by Madonna et a l (1980). From the above r e v i e w , some c o n c l u s i o n s can be drawn r e g a r d i n g spouted and s p o u t - f l u i d bed combustion: (1) Spouted beds can be e f f e c t i v e combustors f o r a v a r i e t y of f u e l s , i n c l u d i n g l o w - q u a l i t y and s t i c k y f u e l s which may cause problems i n more c o n v e n t i o n a l combustors such as moving packed beds, p u l v e r i z e d f u e l b u r n e r s and f l u i d i z e d bed combustors. (2) C o r r e s p o n d i n g t o d i f f e r e n t o p e r a t i n g c o n d i t i o n s , s u b s t a n t i a l l y d i f f e r e n t hydrodynamic regimes and f l o w p a t t e r n s e x i s t i n s p o u t - f l u i d beds. The combustion p r o c e s s i s l i k e l y t o depend on the regimes of hydrodynamic b e h a v i o u r . (3) Spouted beds share some c h a r a c t e r i s t i c s of f l u i d i z e d bed c o m b u s t i o n . For example, bed-to-tube heat t r a n s f e r c o e f f i c i e n t s a r e of the same o r d e r of magnitude and bed t e m p e r a t u r e tends t o be q u i t e u n i f o r m i n both c a s e s . 2.3 JUSTIFICATION OF USE OF HALF-COLUMN BED The h a l f column spouted bed i s w e l l known as a t e c h n i q u e f o r v i s u a l i z a t i o n of the i n t e r n a l b e h a v i o r of spouted beds. However, the q u e s t i o n i s f r e q u e n t l y asked whether the d a t a and f l o w regimes o b t a i n e d from a h a l f column bed can r e p r e s e n t the r e a l s i t u a t i o n i n a f u l l column 16 bed. Mathur and G i s h l e r (1955) showed t h a t p a r t i c l e v e l o c i t i e s a t the w a l l and p r e s s u r e drop p r o f i l e s f o r f u l l and h a l f columns a r e i d e n t i c a l . S i n c e then many works (Mathur and E p s t e i n , 1974; Lim and Mathur,1978; W h i t i n g and G e l d a r t , 1980; G e l d a r t et a l , 1981) have demonstrated t h a t the d i f f e r e n c e s i n b e h a v i o r between f u l l and h a l f columns a r e r e l a t i v e l y minor. I t i s a l s o noteworthy t h a t i t has been shown r e c e n t l y ( H a t ate e t a l , 1985) t h a t measured v a l u e s i n a s e m i c y l i n d r i c a l f l u i d i z e d bed a r e i n agreement w i t h p u b l i s h e d d a t a f o r t h r e e - d i m e n s i o n a l f l u i d i z e d beds. Based on the above e v i d e n c e , a h a l f column s p o u t - f l u i d bed combustor was d e s i g n e d and c o n s t r u c t e d f o r the p r e s e n t work. 3. EXPERIMENTAL APPARATUS AND SOLIDS PROPERTIES 3.1 EXPERIMENTAL EQUIPMENT 3.1.1 COMBUSTOR The combustor p r o p e r i s shown i n F i g . 3.1. C o n s t r u c t e d of s t a i n l e s s s t e e l , the combustor i t s e l f i s 1.19 m h i g h and c o n s i s t s of two s e c t i o n s : (1) A h a l f c y l i n d r i c a l s e c t i o n of 0.152 m I.D. by 1.06 m l o n g w i t h a w a l l of t h i c k n e s s 6.4 mm. T h i s s e c t i o n was a l s o f u r n i s h e d w i t h s o l i d s d i s c h a r g e l i n e s a t t h r e e d i f f e r e n t l e v e l s : 0.25, 0.35 0,45 m above the i n l e t o r i f i c e . (2) A t r u n c a t e d 60° h a l f c o n i c a l s e c t i o n 0.13 m h i g h w i t h a c e n t r e d 15.9 mm d i a m e t e r s e m i - c i r c u l a r o r i f i c e as s p o u t i n g gas i n l e t and a p e r f o r a t e d p l a t e , f o r m i n g the cone and surrounded by a plenum chamber f o r i n d e p e n d e n t l y i n t r o d u c i n g a u x i l i a r y a i r i n t o the a n n u l u s i n o r d e r t o c r e a t e a s p o u t - f l u i d bed. T h i s p e r f o r a t e d cone was c o v e r e d by a p i e c e of 100 mesh (0.15 mm) s c r e e n t o p r e v e n t p a r t i c l e s from d r o p p i n g i n t o the gas chamber. A f l a t s t a i n l e s s s t e e l p a n e l on which t h r e e 6.4 mm t h i c k g l a s s windows were mounted f o r d i r e c t o b s e r v a t i o n s e r v e d as the combustor f r o n t . Both q u a r t z g l a s s and w i r e - r e i n f o r c e d g l a s s were used d u r i n g the e x p e r i m e n t s . D e t a i l s of the p e r f o r a t e d d i s t r i b u t o r a r e g i v e n i n F i g . 3.2. The combustor was e x t e r n a l l y i n s u l a t e d by c e r a m i c f i b r e i n s u l a t i o n of t h i c k n e s s 20 mm. Seven measuring p o r t s of 17 18 F i g 3.1 Schematic Diagram of Combustor 1. S p o u t i n g Flow L i n e 2 . Gas Chamber and D i s t r i b u t o r 3 . A u x i l i a r y Flow L i n e 4 . S o l i d s D i s c h a r g e L i n e 5. M e a s u r i n g P o r t 6. Half-Column 7. O f f - g a s L i n e 8. P o r t f o r Gas Sampling Probe 9. F r o n t P a n e l 10. Quartz G l a s s Window ( A l l d i m e n s i o n s i n t h i s t h e s i s a r e i n mm.) F i g . 3.2 F l a t t e n e d S u r f a c e of the C o n i c a l P e r f o r a t e d D i s t r i b u t o r 20 d i a m e t e r 12 .7 mm were l o c a t e d a l o n g t h e back o f t h e c o m b u s t o r a t 0 .10 m i n t e r v a l s f o r m o u n t i n g t h e r m o c o u p l e s and t a k i n g gas s a m p l e s . 3 . 1 . 2 OTHER AUXIL IARY EQUIPMENT The s p o u t - f l u i d bed c o m b u s t o r w i t h i t s a u x i l i a r y e q u i p m e n t i s shown i n F i g s . 3.3 and 3 . 4 . A r o t a r y v a l v e , c o n s i s t i n g o f a b r a s s c a s i n g and a r u b b e r i m p e l l e r o f d i a m e t e r 32 mm, was u s e d a s c o a l f e e d e r . W i t h t h e h e l p o f g r a v i t y , t h e c o a l p a r t i c l e s f e l l i n t o t h e s p o u t i n g a i r l i n e f r o m a h o p p e r t h r o u g h t h e r o t a r y v a l v e , t h e r o t a t i o n s p e e d o f w h i c h was c o n t r o l l e d by a v a r i a b l e s p e e d moto r of- 62 W ( M o d e l 8 P 3 2 2 5 , G . H. K. C o . ) t h r o u g h a g e a r r e d u c t i o n ( B o s t o n G e a r ) . D e t a i l s o f t h e r o t a r y v a l v e a r e shown i n F i g . 3.5 and F i g . 3 . 6 . O t h e r e q u i p m e n t i n c l u d e a 75 mm d i a m e t e r c y c l o n e f o r r e c o v e r i n g p a r t i c l e s w h i c h e s c a p e f r o m t h e c o m b u s t o r , a 10.8 kW e l e c t r i c a l p r e h e a t e r and i t s c o n t r o l s y s t e m f o r p r e h e a t i n g t h e a i r d u r i n g s t a r t u p , and a f l u e gas s c r u b b e r f o r c l e a n i n g and c o o l i n g t h e o f f - g a s . D e t a i l s o f t h e s e d e v i c e s a r e g i v e n i n T a b l e 3 . 1 . 3.2 EXPERIMENTAL INSTRUMENTATION A i r f l o w r a t e s were c o n t r o l l e d and m o n i t o r e d by r o t a m e t e r s . C a l i b r a t i o n s were c a r r i e d o u t w i t h a d r y ga s m e t e r . The c a l i b r a t i o n c u r v e s a r e g i v e n i n A p p e n d i x I. C o a l f e e d i n g r a t e was m o n i t o r e d by t h e s e t t i n g o f t h e v a r i a b l e U : ~\ A F i g 3.3 E x p e r i m e n t a l Equipment 1. S p o u t i n g Flow L i n e 2 . A u x i l i a r y Flow L i n e 3. C o a l Feeding L i n e 4. Rotameter 5 . P r e h e a t e r 6. C o a l Hopper 7. Rotary V a l v e 8. Gear R e d u c t i o n 9 . Motor 1 0 . Thermocouple D i s p l a y 1 1 . Motor C o n t r o l l e r 1 2 . Cyclone 13. Ash C o n t a i n e r 14. Combustor 1 5 . Scrubber Q u e e n i n g Gas C y l i n d e r Hopper and C o a l F e e d e r F i g . 3 . 4 P i c t u r e s of E x p e r i m e n t a l S e t - u p 1 A-A View U A ro F i g 3.5 R o t a r y V a l v e f o r C o a l F e e d i n g w 1. P l e x i g l a s s L i d 2. Rubber I m p e l l e r 3. S h a f t 4. B r a s s C a s i n g 2 4 F i g . 3 .6 P i c t u r e of the C o a l Feeder T A B L E 3 . 1 P A R T I C U L A R S O F M A J O R E Q U I P M E N T 25 Spouted Bed Column Diameter: 0.152 m ( h a l f column) Height: 1.19 m ( i n c l u d i n g c o n i c a l s e c t i o n ) Cone Angle: 60° C o n i c a l D i s t r i b u t o r : p e r f o r a t e d , p l a t e with 35 h o l e s of diameter of 3.2 mm evenly spaced I n l e t O r i f i c e Diameter: 15.9 mm M a t e r i a l : 316 s t a i n l e s s s t e e l except f o r windows Coal Hopper Diameter: 0.30 m Height: 0.2 5 m Cone Angle: 60° M a t e r i a l : m i l d s t e e l Coal Feeder Type: r o t a r y v a l v e connected to v a r i a b l e speed motor Impeller Diameter: 32 mm C a p a c i t y : 8 kg/h Preheater Type: e l e c t r i c a l heater, three s e c t i o n s i n s e r i e s Power: 3.6 kW/section, 10.8 kW i n t o t a l Heating Pipe Diameter: 51 mm• Heating Pipe Length: 2.25 m Cyclone Diameter: 75/25 mm C y l i n d e r Height: 0.125 m Cone Height: 0.177 m Scrubber Type: packed c o u n t e r c u r r e n t spray column Diameter: 0.57 m 26 speed motor. T h i s was c a l i b r a t e d f o r d i f f e r e n t p a r t i c l e s i z e s . C a l i b r a t i o n c u r v e s a r e p r o v i d e d i n Appendix I I . Temperatures c o u l d be measured e i t h e r by seven thermocouples mounted a t the back of combustor f l u s h w i t h the c u r v e d i n n e r w a l l s u r f a c e a t 0.1 m i n t e r v a l s , or by a s i n g l e thermocouple i n s e r t e d i n s i d e a gas probe as d i s c u s s e d below. The l a t t e r was more f l e x i b l e f o r temperature measurement s i n c e i t c o u l d be l o c a t e d a t d i f f e r e n t p o s i t i o n s . A l l e i g h t thermocouples were of Chromel-Alumel type and were connected t o a thermocouple d i s p l a y t h r o u g h a c o n t r o l b o a r d . In o r d e r t o measure the oxygen c o n c e n t r a t i o n c o n t i n u o u s l y , a gas sa m p l i n g probe was d e s i g n e d as shown i n F i g . 3.7. The probe c o n s i s t s of a 6.4 mm O.D. by 1.25 m l o n g s t a i n l e s s s t e e l tube lowered from above. Mounted a t one end of the tube i s a 12.7 mm O.D. porous s t a i n l e s s s t e e l f i l t e r w i t h an average pore opening of 90 m i c r o n s . In o r d e r t o be a b l e t o measure the temperature of the s u c t i o n p o i n t , a 1.6 mm thermocouple was i n s e r t e d i n s i d e the tube. T h i s arrangement i s a c h i e v e d by u s i n g a branch t e e as shown i n F i g . 3.7. As i l l u s t r a t e d s c h e m a t i c a l l y i n F i g . 3.8, the c o n t i n u o u s oxygen c o n c e n t r a t i o n m o n i t o r i n g system c o n s i s t s of the f o l l o w i n g p a r t s : a c o o l i n g c o i l made of a p i e c e of 2m l o n g s t a i n l e s s s t e e l tube w i t h 6.4 mm I . D., a gas d r y i n g u n i t of a 60 mm I . D. by 200 mm h i g h packed column f i l l e d w i t h anhydrous CaSO, p a r t i c l e s (W. A. Hammond D r i e r i t e C o . ) , 1. S t a i n l e s s S t e e l F i l t e r 2. High Temperature Cement 3. 3.2 mm Thermocouple 4. 6.4 mm I.D. S t a i n l e s s S t e e l Tube 5. Tee F i g 3.7 Gas Sampling Probe tsj 3 F i g 3.8 Gas Sampling System 1. Gas Probe 2. Combustor 3. C o o l i n g C o i l s 4. Gas D r y i n g U n i t 5. Rotameter 6. C o n t r o l V a l v e 7. E x t r a c t i o n Pump 8. Oxygen M o n i t o r ro co 29 a r o t a m e t e r , a vacuum pump o f 746 W (M0A -P101 -AA , MFG C o . ) and an oxygen m o n i t o r (Mode l 7 1 5 , B e c k m a n ) . The d u s t - f r e e gas s a m p l e drawn f r o m t h e c o m b u s t o r was f i r s t p a s s e d t h r o u g h t h e c o o l i n g c o i l t o be c o o l e d , and t h e n t h r o u g h t h e d r y i n g u n i t i n w h i c h most o f t h e m o i s t u r e was r e m o v e d . F i n a l l y , a f t e r p a s s i n g t h r o u g h t h e r o t a m e t e r and t h e vacuum pump, t h e d r y gas r e a c h e d t h e o x y g e n m o n i t o r . The s a m p l i n g r a t e was c o n t r o l l e d by a v a l v e and m o n i t o r e d by t h e r o t a m e t e r , a s shown i n F i g . 3 . 8 . As shown i n F i g . 3 . 9 , t h e gas p r o b e was d e s i g n e d and c o n s t r u c t e d s u c h t h a t by r o t a t i n g t h e p r o b e , t h e o x y g e n c o n c e n t r a t i o n a t d i f f e r e n t p o s i t i o n s i n s i d e t h e c o m b u s t o r c o u l d be m e a s u r e d . 3.3 PROPERTIES OF SOLIDS 3.3.1 PROPERTIES OF SAND O t t a w a s a n d , w h i c h b e l o n g s t o t h e g r o u p D p a r t i c l e s ( G e l d a r t , 1 9 7 3 ) , was u s e d a s bed m a t e r i a l i n t h i s s t u d y . The p r o p e r t i e s o f t h e s a n d a r e p r o v i d e d i n T a b l e 3 . 2 . The s a n d was s c r e e n e d t o a r e l a t i v e l y n a r r o w s i z e r a n g e b e f o r e p a r t i c l e d e n s i t y and p a r t i c l e s i z e s were m e a s u r e d . T h r e e d i f f e r e n t s i z e s were p r e p a r e d a n d t h e i r s i z e d i s t r i b u t i o n s were d e t e m i n e d . The d e n s i t y o f s a n d was o b t a i n e d by m e a s u r i n g t h e vo l ume o f w a t e r d i s p l a c e d by a known w e i g h t o f p a r t i c l e s . B e c a u s e t h e s a n d p a r t i c l e s may be p e r m e a b l e t o w a t e r , t h e F r o n t P a n e l 2. Half-Column 3. Gas Probe F i g 3.9 P o s i t i o n s of Gas Probe (1) i n spout (2) i n a n n u l u s TABLE 3.2 S I Z E DISTRIBUTION OF OTTAWA SAND 31 Wt. f r a c t i o n (%) S i e v e S i z e S i z e 1 S i z e 2 S i z e (mm) 2.0-2.36 1 4.87 0 0 1 .68-2.00 63. 1 5 1 .04 0 1 .41-1.68 21 .06 25.38 0 1.19-1.41 0.85 55. 1 7 0.12 1 .00-1.19 0.10 18.27 43.4 0.85-1.00 0 0.12 46.4 0.60-0.85 0 0 9.93 0.43-0.60 0 0 0.07 Mean dp*(mm) 1 .84 1.31 0.96 Bulk D e n s i t y 1229 1245 1252 (kg/m 3) Voidage 0.53 0.52 0.52 Density=2605 kg/m 3 * mean d_ = 1 32 p a r t i c l e s were c o a t e d w i t h w a t e r - s e a l b e f o r e t h e vo l ume measu rement t o e l i m i n a t e u n d e s i r e d e r r o r . In d e n s i t y m e a s u r e m e n t , a 100 c m 3 v o l u m e t r i c f l a s k and a h i g h a c c u r a c y ( 0 . 0 5 g) b a l a n c e were e m p l o y e d . The vo l ume o c c u p i e d by t h e s a n d was c a l c u l a t e d f r o m vo lume d i f f e r e n c e . F o u r m e a s u r e m e n t s o f t h e d e n s i t y were made, and t h e v a l u e i n T a b l e 3.2 i s an a v e r a g e o f t h o s e m e a s u r e d v a l u e s . B u l k d e n s i t y o f l o o s e l y p a c k e d s a n d was m e a s u r e d by p a r t i a l l y f i l l i n g a 250 c m 3 g r a d u a t e c y l i n d e r w i t h a known w e i g h t o f s a n d . T h i s c y l i n d e r was i n v e r t e d w i t h i t s open end c o v e r e d and was t h e n q u i c k l y i n v e r t e d a g a i n t o i t s o r i g i n a l p o s i t i o n . The vo l ume o c c u p i e d by t h e s and a f t e r t h i s l o o s e n i n g p r o c e d u r e was r e c o r d e d and u s e d t o c a l c u l a t e t h e b u l k d e n s i t y . T h i s method h a s been u s e d by o t h e r w o r k e r s ( e . g . L i m , 1 9 7 5 ) . L o o s e l y p a c k e d s o l i d v o i d a g e s were d e t e r m i n e d f r o m t h e d e n s i t y and b u l k d e n s i t y . 3 . 3 . 2 PROPERTIES OF COAL A s u b - b i t u m i n o u s A l b e r t a F o r e s t b e r g c o a l was u s e d a s t h e f u e l i n a l l t h e e x p e r i m e n t s . T h i s c o a l was f i r s t c r u s h e d a n d a i r - d r i e d , t h e n s c r e e n e d t o t h e d e s i r e d s i z e r a n g e s . T h r e e d i f f e r e n t s i z e f r a c t i o n s were p r e p a r e d , a s shown i n T a b l e 3 . 3 . The p r o x i m a t e and u l t i m a t e a n a l y s e s o f t h e F o r e s t b e r g c o a l , w h i c h was made by G e n e r a l T e s t i n g L a b o r a t o r i e s , a r e l i s t e d i n T a b l e 3 . 4 . TABLE 3.3 S I Z E DISTRIBUTION OF COAL Wt. f r a c t i o n (%) S i e v e S i z e S i z e 1 S i z e 2 S i z e (mm) 1.68-2.00 0 . 1 8 0 0 1.41-1.68 11.47 0 0 1.19-1.41 16.33 0.59 0 1.00-1.19 5.30 54.20 0 0.85-1.00 3.00 35.60 3.60 0.60-0.85 58.53 9.49 87.8 0.35-0.60 5.40 0.20 8.10 <0. 35 0 0 0.49 Mean dp*(mm) 0.83 1 .04 0.69 Bu l k Density=684 kg/m 3 1 * mean d_ = TABLE 3.4 ANALYSES OF FORESTBERG COAL P r o x i m a t e A n a l y s i s (Wt. %) M o i s t u r e 11.9 V o l a t i l e 30.8 Ash 25.9 F i x e d Carbon 31.4 U l t imate A n a l y s i s (Wt. %) As R e c e i v e d MAF M o i s t u r e 1 1 .90 0.0 Ash 25.89 0.0 Carbon 33.79 52.60 Hydrogen 3.92 6.11 N i t r o g e n 0.72 1.12 Su l p h u r 0.29 0.45 Oxygen 23.49 39.42 C a l o r i f i c V a l u e ( a s r e c e i v e d ) : 17,970 k J / k g Free S w e l l i n g Index: 1.0 4. OPERATING PROCEDURE AND CHOICE OF EXPERIMENTAL CONDITIONS 4.1 OPERATING PROCEDURE About 3 kg c o a l was poured i n t o the c o a l hopper b e f o r e o p e r a t i o n s t a r t e d . A i r was t u r n e d on n e x t , then sand was s l o w l y poured i n t o the combustor from the t o p . The a i r v e l o c i t y i n the s p o u t i n g a i r i n l e t p i p e was m a i n t a i n e d a t a l e v e l s u f f i c i e n t t o p r e v e n t sand from s e t t l i n g down i n the i n l e t p i p e . A f t e r the r e q u i r e d s t a t i c bed. h e i g h t was reached, the p r e h e a t e r was s w i t c h e d on..The bed was he a t e d up s l o w l y by the hot a i r coming from the p r e h e a t e r . The o f f - g a s s c r u b b e r was put i n t o o p e r a t i o n by t u r n i n g on water . When the bed t e m p e r a t u r e , as r e c o r d e d by thermocouples i n the a n n u l u s , reached 400 C, the c o a l f e e d e r was t u r n e d on. C o a l p a r t i c l e s were then dropped i n t o the main a i r l i n e , where t h e y were p n e u m a t i c a l l y c a r r i e d i n t o the combustor. Once the c o a l s t a r t s b u r n i n g , the bed temperature i n c r e a s e d g r a d u a l l y . A f t e r i t reached 500 C, the p r e h e a t e r was s w i t c h e d o f f so t h a t room tem p e r a t u r e a i r was f e d i n . The combustion c o u l d then be s u s t a i n e d w i t h c o l d a i r . Because t h e r e was no c o o l i n g c o i l i n s i d e the combustor, the bed t e m p e r a t u r e was c o n t r o l l e d by the c o a l f e e d i n g r a t e , a i r f l o w r a t e and amount of i n s u l a t i o n . When the bed temperature exceeded 500 C, the i n s u l a t i o n on the f r o n t p a n e l was ta k e n o f f a l l o w i n g v i s u a l o b s e r v a t i o n . D u r i n g the t r i a l runs where w i r e - r e i n f o r c e d g l a s s was employed, c r a c k s appeared on the g l a s s windows of the f r o n t 35 36 p a n e l . A s p e c i a l h i g h - t e m p e r a t u r e cement was u s e d t o p a t c h up t h e c r a c k s i n o r d e r t o p r e v e n t gas f r o m l e a k i n g . A l l o f t h e r u n s w h i c h y i e l d e d d a t a p r e s e n t e d i n t h i s t h e s i s were c a r r i e d o u t w i t h h i g h t e m p e r a t u r e q u a r t z g l a s s . When a run was c o m p l e t e d , t h e c o a l f e e d i n g r a t e was g r a d u a l l y r e d u c e d and p r e h e a t i n g a i r was s w i t c h e d on t o m a i n t a i n t h e d e s i r e d c o o l i n g r a t e t o a v o i d a r a p i d t e m p e r a t u r e d r o p w h i c h may have c a u s e d a d d i t i o n a l c r a c k i n g o f g l a s s . 4 .2 CHOICE OF BASE EXPERIMENTAL CONDITIONS B e f o r e any u s e f u l d a t a c o u l d be o b t a i n e d , 10 t r i a l r u n s were c a r r i e d ou t i n o r d e r t o d e b u g t h e e x p e r i m e n t a l s y s t e m . A c c o r d i n g t o E p s t e i n and G r a c e ( 1 9 8 4 ) , a s p o u t e d bed i s u s u a l l y o p e r a t e d w i t h a bed h e i g h t - t o - d i a m e t e r r a t i o o f 1 t o 5. T h e r e f o r e , i n i t i a l l y a s t a t i c bed h e i g h t o f 0.3 m was c h o s e n a s a b a s e b e d h e i g h t d u r i n g t h e t r i a l r u n s . I t was f o u n d t h a t t h e bed b e h a v i o u r c h a n g e d s u b s t a n t i a l l y a t e l e v a t e d t e m p e r a t u r e s , p a r t i c u l a r l y f o r t h e f i n e r p a r t i c l e s . F o r t h e r u n s w i t h a s and s i z e o f 0 . 8 5 - 1 . 1 8 mm, p u l s a t i o n o f t h e s p o u t s t a r t e d when t h e b e d t e m p e r a t u r e was o v e r 200 C . W i t h a s a n d s i z e o f 1 . 1 8 - 1 . 6 5 mm, no s t a b l e s p o u t i n g c o u l d be m a i n t a i n e d when t h e bed t e m p e r a t u r e was a b o u t 500 C o r h i g h e r . T h i s i n s t a b i l i t y i s p r e s u m a b l y c a u s e d by r e a c h i n g t h e maximum s t a b l e s p o u t i n g bed h e i g h t a t t h e e l e v a t e d t e m p e r a t u r e . A f t e r s u r v e y i n g t h e r a n g e o f o p e r a t i n g c o n d i t i o n s , t h e l a r g e s t s a n d s i z e among t h e t h r e e p r e p a r e d a n d a s t a t i c bed h e i g h t o f 0 .3 m were c h o s e n a s b a s e 37 c o n d i t i o n s . U n d e r t h e s e c o n d i t i o n s a l l f l o w r e g i m e s i n t r o d u c e d i n S e c t i o n 2.1 c o u l d be o b t a i n e d . 4 .3 RANGE OF EXPERIMENTAL CONDITIONS Ba se o p e r a t i n g c o n d i t i o n s and t h e r a n g e o f some v a r i a b l e s a r e l i s t e d a s f o l l o w s : Bed D i a m e t e r : 152 mm ( 6 " ) I n l e t O r i f i c e D i a m e t e r : 15 .9 mm (5 /8 " ) S t a t i c Bed H e i g h t : 0.3 m ( 1 2 " ) Mean Sand S i z e : 1.84 mm Mean C o a l S i z e : 1.0 mm U / U m s = 1 . 1 - 1 . 5 ( U m s = 1 . 1 m/s a t 650 C and 1 atm) A u x i l i a r y f l o w r a t e / T o t a l q / Q T = 0 - 0 . 6 Bed T e m p e r a t u r e ( m e a s u r e d i n a n n u l u s ) : 6 0 0 - 7 0 0 C A l l e x p e r i m e n t s were a t a t m o s p h e r i c p r e s s u r e w i t h a i r a s t h e s p o u t i n g and a u x i l i a r y g a s . 5. HYDRODYNAMIC AND COMBUSTION PATTERNS 5.1 EXPERIMENTAL TECHNIQUE A f t e r f o l l o w i n g the o p e r a t i n g p r o c e d u r e g i v e n i n S e c t i o n 4.1, v i s u a l o b s e r v a t i o n s t a r t e d when the bed temperature reached 650 C. At t h i s t emperature combustion c o u l d be s u s t a i n e d a f t e r ' s p o u t i n g a i r was s w i t c h e d from p r e h e a t e d a i r t o a i r a t room t e m p e r t u r e . I t was found t h a t d i f f e r e n t f l o w p a t t e r n s c o u l d be o b t a i n e d f o r d i f f e r e n t c o m b i n a t i o n s of s p o u t i n g and a u x i l i a r y a i r f l o w r a t e s , denoted as Q s and q, r e s p e c t i v e l y . Both e f f e c t s of U / U m s and q/Q T on hydrodynamic and combustion p a t t e r n s were s t u d i e d . Without i n t r o d u c i n g a u x i l i a r y a i r ( i . e . q/QT=0 and Q S=Q T) U m s a t a g i v e n t e m p e r a t u r e was d e t e r m i n e d by g r a d u a l l y r e d u c i n g the s p o u t i n g a i r f l o w r a t e u n t i l t he sudden c o l l a p s e of the spout o c c u r r e d . The r e a d i n g of the ro t a m e t e r a t t h i s p o i n t was r e c o r d e d and used t o d e t e r m i n e Q m s « The s p o u t i n g a i r f l o w r a t e was then a d j u s t e d t o the d e s i r e d Q s so t h a t U/U m s was e q u a l t o a p r e d e t e r m i n e d v a l u e . In the s p o u t - f l u i d bed where q/Q T > 0 when the a u x i l i a r y a i r f l o w r a t e was i n t r o d u c e d , the s p o u t i n g a i r f l o w r a t e was a d j u s t e d t o m a i n t a i n the t o t a l a i r f l o w r a t e Q T c o n s t a n t . At a g i v e n bed h e i g h t a temperature change c o u l d cause a change of f l o w p a t t e r n . T h e r e f o r e m a i n t a i n i n g a c o n s t a n t t e m p e r a t u r e became a c r u c i a l problem f o r t h e s e e x p e r i m e n t s . The bed t e m p e r a t u r e , r e c o r d e d by a thermocouple i n the 38 39 annulus about 50 mm below the bed s u r f a c e , was c o n t r o l l e d by the a i r f l o w r a t e , c o a l f e e d i n g r a t e and the amount of i n s u l a t i o n i n the f r o n t p a n e l . When the bed temperature was i n the range between 650 and 750 C, the -temperature i n the f r e e b o a r d c o u l d r e a c h 800-900 C. In o r d e r t o p r e v e n t c r a c k i n g of the q u a r t z g l a s s due t o expansion s t r e s s e s , the bed t e m p e r a t u r e was m a i n t a i n e d i n the range 650 t o 700 C f o r most of the r u n s . When the a i r f l o w r a t e was changed i n o r d e r t o run the combustor a t d i f f e r e n t U/U m s, the c o a l f e e d i n g r a t e was a d j u s t e d t o m a i n t a i n c o n s t a n t bed te m p e r a t u r e . D u r i n g most of the runs t e m p e r a t u r e f l u c t u a t i o n s were c o n t r o l l e d w i t h i n ±15 C. Three methods were employed t o r e c o r d hydrodynamic and combustion p a t t e r n s f o r l a t e r d e t a i l e d s t u d y : (a) S t i l l p hotographs were taken w i t h d i f f e r e n t exposure t i m e s . Longer exposure t i m e s ( e . g . 1 second) c o u l d g i v e the t r a j e c t o r y of s o l i d s b o t h i n the annulus and i n the f r e e b o a r d . (b) V i d e o f i l m s were t a k e n u s i n g a SONY v i d e o camera. W i t h the a i d of slow motion when the r e c o r d e d tape was p l a y e d back, v i d e o p r o v i d e a u s e f u l method t o r e v e a l the d e t a i l s of the gas and s o l i d s movement. (c) A 16 mm c i n e camera (BOLEX) was used t o shoot moving p i c t u r e a t the speed of 24 frames per second w i t h h i g h speed c o l o u r f i l m (Eastman Ektachrome v i d e o news f i l m , ASA 400). U s i n g a v i e w e r e d i t o r ( M i n e t t e , Model 16), 40 a n a l y s i s of the f i l m s was c a r r i e d out frame by frame. 5.2 RESULTS AND DISCUSSION 5.2.1 HYDRODYNAMIC AND COMBUSTION PATTERNS Four f a i r l y d i s t i n c t f l o w p a t t e r n s and t h e i r c o r r e s p o n d i n g combustion p a t t e r n s were o b s e r v e d : s t a b l e s p o u t i n g ( S S ) , p u l s a t o r y s p o u t i n g ( P S ) , j e t i n f l u i d i z e d b e d ( J F ) and s l u g g i n g ( S ) , as shown i n F i g . 5.1. T h e i r f e a t u r e s and a s s o c i a t e d o p e r a t i n g c o n d i t i o n s were as f o l l o w s : (a) S t a b l e S p o u t i n g (SS) The p h y s i c a l appearance of t h i s p a t t e r n i s v e r y s i m i l a r t o t h a t of a s t a n d a r d spouted bed w i t h o u t c o m bustion. The f o u n t a i n had a w e l l - d e f i n e d shape above the bed s u r f a c e . S t a r t i n g from the c o l d s t a t e , t h i s p a t t e r n remained unchanged u n t i l the bed temperature reached about 600 °C f o r a bed h e i g h t of 0.3 m (base c o n d i t i o n s ) . C o a l burned i n the f o u n t a i n and i n the a n n u l u s . F i g u r e s 5.2, 5.3 and 5.4 show photographs of t h i s p a t t e r n a t d i f f e r e n t bed t e m p e r a t u r e s . Comparison of F i g s . 5.3 and 5.4 shows t h a t more c o a l p a r t i c l e s were b u r n i n g i n the a nnulus a t the h i g h e r t e m p e r a t u r e . (b) P u l s a t o r y S p o u t i n g (PS) In t h i s p a t t e r n , the o v e r a l l p a r t i c l e movement was s i m i l a r t o t h a t i n s t a b l e s p o u t i n g , but the shape and s t r u c t u r e of the f o u n t a i n was e n t i r e l y d i f f e r e n t . The h e i g h t (c) (d) (e) F i g . 5 . 1 Flow P a t t e r n s : (a) S t a b l e S p o u t i n g (b) P u l s a t o r y S p o u t i n g (c) J e t i n F l u i d i z e d Bed ( I ) (d) J e t i n F l u i d i z e d Bed ( I I ) (e) S l u g g i n g F i g . 5 . 2 S t a b l e S p o u t i n g a t Room T e m p e r a t u r e T b = 2 0 C r H o = 0 . 3 m U / U m s = 1 . 1 , q / Q T = 0 U m s = 1 . 0 m/s (a) e x p o s u r e t i m e = 1 / 8 s (b) e x p o s u r e t i m e = 1 s F i g . 5.3 S t a r t u p of S p o u t e d B e d C o m b u s t i o n Tb=500 C , H o=0.3 m U / U m s =1 . 2 , q/Q T =0 U m s=1.2 m / s , rh = 0.2 g / s (b) (a) F i g 5.4 S t a b l e S p o u t i n g Tb=590 C, H o=0.3 m U/U m s = 1.2 r q/Q T=0 U m s= 1.2 m/s, m=0.3 g/s 44 of the f o u n t a i n o s c i l l a t e d between a maximum and a minimum v a l u e w i t h a f r e q u e n c y of 4-5 s ~ 1 . As seen i n F i g . 5.5 ( a ) - ( c ) , f o r m a t i o n and r e l e a s e of the bu b b l e s a t the bed s u r f a c e caused the change of f o u n t a i n h e i g h t and the f l u c t u a t i o n of spout d i a m e t e r . A p p a r e n t l y a t t h i s bed h e i g h t and t e m p e r a t u r e the maximum s t a b l e s p o u t i n g bed h e i g h t had been r e a c h e d . F i g u r e 5.6 i n d i c a t e s t h a t an i n c r e a s e of a i r f l o w r a t e , Q s ( i . e . h i g h e r U/U m s) d i d not a f f e c t the f l o w p a t t e r n , but bu b b l e s e r u p t e d more v i g o r o u s l y , (c) J e t i n F l u i d i z e d bed (JF) A spouted bed and a f l u i d i z e d bed c o e x i s t e d i n t h i s p a t t e r n . Depending on the amount of a u x i l i a r y a i r i n t r o d u c e d , t h i s p a t t e r n can be d i v i d e d i n t o two s u b - p a t t e r n s , J F ( I ) and J F ( I I ) . When a s m a l l amount of a u x i l i a r y a i r was i n t r o d u c e d , J F ( l ) appeared. For most of the t i m e , a j e t was submerged i n s i d e t h e bed, and bubbles were r e l e a s e d from the t o p of t h i s i n t e r n a l j e t . These b u b b l e s , w i t h s i z e s up t o 90% of the column d i a m e t e r , e r u p t e d a t the bed s u r f a c e w i t h a f r e q u e n c y of about 2 s _ 1 , e j e c t i n g s o l i d s i n t o the f r e e b o a r d . O c c a s i o n a l l y , the j e t broke t h r o u g h the bed s u r f a c e , swaying l a t e r a l l y . T h i s s u b - p a t t e r n i s shown i n F i g . 5 . 7 ( a ) - ( c ) . A downward movement of s o l i d s i n the annulus was ob s e r v e d . When more a u x i l i a r y a i r was i n t r o d u c e d , b u b b l e s were formed a few c e n t i m e t e r s above the i n l e t o r i f i c e . U n l i k e J F ( I ) where bubbles rose a l o n g the c e n t r e l i n e of the (b) ( c ) F i g . 5.5 P u l s a t o r y S p o u t i n g T b=650 C, H o=0.3 m U/Um S=1.2, q/Q T-0 U m s = 1.2 m/s, rh=0.4 g/s cn F i g . 5.6 P u l s a t o r y S p o u t i n g ( h i g h e r U/U m s) T b=650 C, H o=0.3 m U/U m s=1.4, q / Q T=0 U m s=1.2 m/s, m=0.4 g/s F i g . 5.7 J e t i n F l u i d i z e d Bed ( I ) T b=650 C, H o=0.3 m U/U m s='.2, q/Q T=0.2 U m s = 1 . 2 m/s, m=0.4 g/s 48 combustor, the b u b b l e s i n J F ( I I ) emerged a t the bed s u r f a c e randomly. Bubbles were a l s o found t o be s m a l l e r , a p p r o x i m a t e l y h a l f the diameter of those i n J F ( I ) , but the frequency a t which bubbles were produced was the same, about 2 s 1. No j e t b r e a k t h r o u g h was o b s e r v e d i n J F ( I I ) , and the s o l i d s c i r c u l a t i o n r a t e d e c r e a s e d s u b s t a n t i a l l y . T h i s s u b - p a t t e r n i s shown i n F i g . 5 . 8 ( a ) - ( c ) and F i g . 5.9. T r a n s f o r m a t i o n from J F ( I ) t o J F ( I I ) was g r a d u a l . In j e t i n f l u i d i z e d bed the p a r t of the j e t near the o r i f i c e was found t o f l u c t u a t e w i t h a f r e q u e n c y of 7-8 s ~ 1 , something which was not o b s e r v e d f o r p a t t e r n s SS and PS. (d) S l u g g i n g (S) At much h i g h e r a u x i l i a r y f l o w r a t e ( e . g . q/Q T > 0.5), bubbles w i t h s i z e s e q u a l t o or l a r g e r than column d i a m e t e r were formed near the bottom, c a u s i n g the p a r t i c l e s of the whole c r o s s - s e c t i o n t o move up and down f i e r c e l y , as shown i n F i g . 5.10. Severe s t r a t i f i c a t i o n of sand and c o a l r e s u l t e d . Much l e s s c o a l burned i n s i d e the bed, and the bed t e m p e r a t u r e dropped d r a s t i c a l l y . Combustion c o u l d not be s u s t a i n e d i n t h i s p a t t e r n i f c o a r s e r sand (1.65-2.36 mm) was used as bed m a t e r i a l . Some of the f l o w p a t t e r n s found i n the p r e s e n t experiment resemble those found by o t h e r w o r k e r s . Khoshnoodi et a l ( 1978) n o t i c e d t h a t as the a i r flojwrate i n c r e a s e d , a " p u l s a t i n g spouted combustion" was d e v e l o p e d b e f o r e s t a b l e s p o u t i n g c o u l d be a c h i e v e d . A regime map w i t h gas combustion which i n c l u d e d " p u l s a t i n g s p o u t " as one of the f l o w p a t t e r n s U3 U M S = 1 . 2 m/s, m=0 . 4 g/s 50 F i g . 5.10 S l u g g i n g Tb=650 C, H o=0.2 m u/Um S=1-2, q/Q T=0.6 ums=1.0 m/s, rh=0.4 g/s 52 was p r o v i d e d by Khoe and Weve (1984). That p u l s a t o r y s p o u t i n g took p l a c e when the temperature i n c r e a s e d w h i l e o t h e r c o n d i t i o n s remained unchanged i n d i c a t e s t h a t the maximum s t a b l e s p o u t i n g bed h e i g h t d e c r e a s e s as bed t e m p e r a t u r e i n c r e a s e s . J e t i n f l u i d i z e d bed ( J F ) i s s i m i l a r t o " j e t submerged i n the f l u i d i z e d bed" d e f i n e d by S u t a n t o et a l ( l 9 8 5 ) . In s t u d y i n g the c h a r a c t e r i s t i c s of s p o u t - f l u i d beds, H e i l (1982) obs e r v e d s e v e r a l f l o w p a t t e r n s : s t a b l e s p o u t i n g , p u l s a t i n g , and f l u i d i z e d bed. These p a t t e r n s were a l s o found i n the p r e s e n t work. The t e r m i n o l o g y used by d i f f e r e n t workers r e g a r d i n g the f l o w p a t t e r n s i n s p o u t - f l u i d beds i s l i s t e d i n T a b l e 5.1. The e x i s t e n c e of J F ( I ) and J F ( I I ) i n a s p o u t - f l u i d bed i s c o n s i s t a n t w i t h the o b s e r v a t i o n of V u k o v i c e t a l (1984) who found t h a t t h r e e regimes c o u l d be d i s t i n g u i s h e d when a u x i l i a r y a i r was i n t r o d u c e d i n t o a s p o u t - f l u i d bed w i t h a f l a t bottom d i s t r i b u t o r : a s p o u t - f l u i d bed w i t h H < H m s j , denoted as Regime 1; a s p o u t - f l u i d bed w i t h H > H m s £ , l a b e l l e d as Regime 2; and j e t i n a f u l l y f l u i d i z e d bed, denoted as Regime 3. Regime 1 i s s i m i l a r t o the f l o w regime of a s t a n d a r d spouted bed. In Regime 2 t h e s p o u t - f l u i d bed e x h i b i t e d two zones: a lower spouted bed of h e i g h t H m s ^ and an upper f l u i d i z e d bed of h e i g h t H - H m s j . As the a u x i l i a r y f l o w r a t e i n c r e a s e d w h i l e s p o u t i n g a i r f l o w r a t e was m a i n t a i n e d c o n s t a n t , f l u i d i z a t i o n was found t o be i n i t i a t e d a t lower and lower l e v e l s i n the a n n u l u s . S i m i l a r hydrodynamic p a t t e r n s were found i n the p r e s e n t work. TABLE 5.1 TERMNOLOGY REGARDING FLOW PATTERNS OF SPOUT-FLUID BEDS This work Nagarkatt1 and Chatterjee (1974) Hell (1982) Dumistrescu (1977) Stable spouting, Fig.5.1(a) Spouted and spout-f l u i d bed Stable spouting Spouting Littman et al(1976) Spout-fluid bed and Vukovlc et al with H<H msf (1984) Sutanto et al (1985) Spouting with Pulsatory spouting, F1g.5.1(b) Unstable spouted bed Pulsating spouting Pulsed jet Spout-fluid bed with H>H „ msf Spout F l u i d i z a t i o n det 1n f l u i d i z e d bed, Slugging, Fig.5.1(c) and (d) Fig.5.1(e) Unstable spout-fluid F l u i d i z e d bed bed Slugging Fl u i d i z e d bed F l u i d i z a t i o n (bubbling) Fl u i d i z e d bed with local spout Jet in f l u i d i z e d bed Slugging aerat i on OI 54 Comparing F i g . 5.7(a) w i t h 5 . 8 ( a ) , i t can be seen t h a t the l e n g t h of the j e t a p p a r e n t l y d e c r e a s e d as the a u x i l i a r y a i r f l o w r a t e i n c r e a s e d . J F ( I I ) appeared when the a u x i l i a r y f l o w r a t e approached the v a l u e needed f o r minimum f l u i d i z a t i o n of the s o l i d s a t the bottom. The d i f f e r e n c e of bubble s i z e i n J F ( I ) and J F ( I I ) , as shown i n F i g . 5.1(c) and ( d ) , was r e l a t e d t o the d i a m e t e r of the i n t e r n a l j e t from which t h e b u b b l e s were r e l e a s e d . In J F ( I I ) b ubbles were formed o n l y a few c e n t i m e t e r s above the o r i f i c e where the j e t had a d i a m e t e r c l o s e t o t h a t of i n l e t o r i f i c e , but i n J F ( I ) , because of the gas e x p a n s i o n , the l o n g e r j e t had a much l a r g e r d i a m e t e r a t i t s end (about 1/3 of column d i a m e t e r ) , c a u s i n g l a r g e r b ubbles t o be r e l e a s e d . S l u g g i n g may be promoted by p e n e t r a t i o n of a u x i l i a r y a i r i n t o the i n t e r n a l j e t , e s p e c i a l l y f o r h i g h a u x i l i a r y a i r f l o w r a t e s , as shown i n F i g . 5 . 1 ( e ) . No s u b s t a n t i a l d i f f e r e n c e between the p a r t i c l e c i r c u l a t i o n r a t e s i n s t a b l e s p o u t i n g and p u l s a t o r y s p o u t i n g was found. F i g u r e 5.3(b) shows the t r a j e c t o r i e s of p a r t i c l e s i n s t a b l e s p o u t i n g . In j e t i n f l u i d i z e d bed p a r t i c l e movement had two d i f f e r e n t forms: In the lower p a r t of the bed, from the i n l e t o r i f i c e t o the t o p of t h e i n t e r n a l j e t , p a r t i c l e s moved i n the same way as i n the bottom of a s t a n d a r d spouted bed; i n the upper p a r t p a r t i c l e movement was a p p a r e n t l y caused by r i s i n g b u b b l e s , as shown i n F i g . 5.8(a) and ( b ) . Slow downward movement of s o l i d s i n the upper p a r t of the bed, found by e x a m i n a t i o n of the movie and 5 5 v i d e o f i l m s , i n d i c a t e s t h a t s o l i d s were b r o u g h t t o t h e bed s u r f a c e by b u b b l e s . When s l u g g i n g t o o k p l a c e , l i t t l e o r no o v e r a l l c i r c u l a t i o n was o b s e r v e d ; i n s t e a d , s o l i d s movement r e s u l t e d f r o m t h e p e r i o d i c r i s e and f a l l o f s l u g s . The d e c r e a s e o f s o l i d s c i r c u l a t i o n r a t e s i n s p o u t - f l u i d b e d s was o b s e r v e d by H e i l ( 1 9 8 2 ) and S u t a n t o e t a l ( 1 9 8 5 ) . H e i l s u g g e s t e d t h a t l a r g e b u b b l e s w h i c h a s c e n d f r o m t h e i n l e t o r i f i c e t o t h e t o p o f t h e bed i n t e r f e r e w i t h t h e downward s o l i d s f l o w i n t h e a n n u l u s and r e s u l t i n a l o w e r s o l i d s c i r c u l a t i o n r a t e . 5 . 2 . 2 E F F E C T OF BED HEIGHT ON FLOW PATTERNS As d i s c u s s e d a b o v e , h y d r o d y n a m i c p a t t e r n s were d e t e r m i n e d by o p e r a t i n g c o n d i t i o n s s u c h a s s p o u t i n g and a u x i l i a r y a i r f l o w r a t e s , bed t e m p e r a t u r e , s o l i d s p r o p e r t i e s , and most i m p o r t a n t , b e d h e i g h t . F i g u r e s 5 . 1 1 - 5 . 1 8 show t h e h y d r o d y n a m i c and c o m b u s t i o n p a t t e r n s o f r u n 1 7 , where t h e s t a t i c bed h e i g h t was 0 . 2 0 m, one t h i r d l o w e r t h a n t h a t o f t h e b a s e c o n d i t i o n s . A l l f o u r p a t t e r n s u n d e r b a s e c o n d i t i o n s a l s o a p p e a r e d a t t h i s l o w e r b e d h e i g h t . H o w e v e r , t h i s bed h e i g h t t e n d s t o s h i f t t h e p a t t e r n s f r o m p u l s a t o r y s p o u t i n g t o s t a b l e s p o u t i n g a t t h e same bed t e m p e r a t u r e , a s i n d i c a t e d by c o m p a r i n g F i g . 5 . 1 3 ( a ) w i t h F i g . 5 . 5 ( a ) - ( c ) . I t was f o u n d t h a t t h e i n t e r n a l j e t , w i t h i t s h e i g h t e q u a l t o H m s f r d e c r e a s e d a s a u x i l i a r y f l o w r a t e i n c r e a s e d . A s p o u t - f l u i d b e d w i t h a bed h e i g h t e x c e e d i n g t h e maximum s t a b l e bed h e i g h t c o n s i s t s o f two p a r t s : a s p o u t e d bed h a v i n g a u x i l i a r y a i r 5.11 S t a r t u p ( S t a b l e s p o u t i n g ) T b = 4 6 0 C , H o = 0 . 2 m U / U m s = 1 . 2 , q / Q T = 0 U m s = 0 . 9 m / s , rh= 0 . 1 5 g / s F i g . 5 . 1 2 S t a r t u p ( S t a b l e s p o u t i n g ) T b = 5 4 4 C , H o = 0 . 2 m U / U m s = 1 - 2 » q / Q T = n \j = 1 . 1 m / s , m = 0 . 1 9 g / s (a) (b) F i g . 5.13 S t a b l e S p o u t i n g T b=650 C, H o=0.2 m U/Ums=1-2, q/QT=0 ums =1-0 m/s, m=0.3 g/s F i g . 5.14 P u l s a t o r y S p o u t i n g T b=630 C, H o-0.2 m U/U m s=1.3, q/QT=0 Ums=1.0 m/s, rh=0. 4 g / s cn CD F i g . 5.15 P u l s a t o r y S p o u t i n g ( h i g h e r U / U m s ) Tb=630 C, H o=0.2 m U / U m s = 1 . 5 , q / Q T=0 U m s =1•0 m / s t m = 0 • 4 9/ s F i g . 5.16 J e t in F l u i d i z e d Bed (I) Tb=640 C, Ho=0.2 m U/Ums=1.2, q/QT=0.2 u m s = 1 .0 m/s, rh=0.5 g/s F i g . 5.18 S l u g g i n g T b=650 C, Ho=0.2 m U/U m s=1.2, q/Q T=0.6 U m s=l.O m/s,m=0.5 g/s 63 p a s s i n g t h r o u g h i t s a n n u l u s w i t h a bed h e i g h t o f H m s £ a t t h e b o t t o m a b o v e w h i c h i s a f l u i d i z e d bed w i t h h e i g h t H - H m s j . 5 . 2 . 3 E F F E C T OF SOLIDS PROPERTIES ON THE FLOW PATTERNS F o r some r u n s i n w h i c h a w i d e r s i z e r a n g e c o a l was u s e d , s e c o n d a r y f l u i d i z a t i o n and s o l i d s s e g r e g a t i o n were o b s e r v e d . I t was f o u n d t h a t c o a l p a r t i c l e s were n o t w e l l d i s t r i b u t e d o v e r t h e w h o l e b e d , a s shown i n F i g . 5.5 and 5 . 6 . S o l i d s s e g r e g a t i o n i n s p o u t e d bed s ha s been s t u d i e d q u i t e e x t e n s i v e l y i n t h e l a s t t e n y e a r s ( P i c c i n i n i e t a l , 1977; Cook and B r i d g w a t e r , 1978; McNab a n d B r i d g w a t e r , 1979; P i c c i n i n i , 1980; K u t l u o g l u e t a l , 1983; Uemaki e t a l , 1 9 8 3 ) . In s p o u t e d bed s s o l i d s s e g r e g a t i o n o c c u r s a c c o r d i n g t o p a r t i c l e d i a m e t e r , w i t h b i g g e r p a r t i c l e s c o n g r e g a t i n g i n t h e u p p e r i n s i d e p a r t o f t h e a n n u l u s ( P i c c i n i n i e t a l , 1 9 7 7 ) . When p a r t i c l e s w i t h d i f f e r e n t d e n s i t y a r e e m p l o y e d , t h e h e a v i e r s o l i d s s e t t l e t o t h e i n s i d e p a r t o f t h e a n n u l u s f o r s h a l l o w b e d s . H o w e v e r , t h e s i t u a t i o n r e v e r s e s f o r d e e p e r b e d s . I t was a l s o f o u n d t h a t l i g h t e r c o m p o n e n t s s t a y e d n e a r t h e f r e e s u r f a c e (Cook a n d B r i d g w a t e r , 1 9 7 8 ) . In t h e p r e s e n t work s a n d p a r t i c l e s have a mean d i a m e t e r a n d d e n s i t y a p p r o x i m a t e l y t w i c e t h o s e o f t h e c o r r e s p o n d i n g c o a l p a r t i c l e s . S e g r e g a t i o n s h o u l d r e s u l t f r o m t h e d i f f e r e n c e s b o t h i n d e n s i t y a n d i n s i z e . In o r d e r t o d i s t i n g u i s h t h e s e g r e g a t i o n c a u s e d by s i z e a n d d e n s i t y d i f f e r e n c e and t h a t c a u s e d by t h e c o m b u s t i o n o f 64 c o a l , one run was conducted at room t e m p e r a t u r e . The s o l i d s d i s t r i b u t i o n i n the bed appeared t o be c l o s e l y r e l a t e d t o the s o l i d s movement a f t e r p a r t i c l e s are brought t o the bed s u r f a c e . I t was found t h a t s e p a r a t i o n of c o a l and sand s t a r t e d i n the f o u n t a i n r e g i o n . H e a v i e r sand p a r t i c l e s f e l l on the bed s u r f a c e c l o s e r t o the s p o u t , w h i l e the l i g h t e r c o a l p a r t i c l e s were e i t h e r e n t r a i n e d i n the f r e e b o a r d or f e l l onto the o u t e r p a r t of bed s u r f a c e . T h i s i s i n agreement w i t h the o b s e r v a t i o n of K u t l u o g l u e t a l (1983). F i g u r e 5.19 shows a p o s s i b l e way by which c o a l p a r t i c l e s s p r e a d over the lower s e c t i o n of the a n n u l u s . Secondary f l u i d i z a t i o n was found i n some ca s e s w i t h a f l u i d i z e d bed of b u r n i n g c o a l o b s e r v e d above the s u r f a c e of a spouted bed of sand. T h i s became more s u b s t a n t i a l when the wider s i z e range c o a l w i t h a h i g h f r a c t i o n of f i n e p a r t i c l e s or when s m a l l c o a l p a r t i c l e s were used. In those c ases b u r n i n g c o a l p a r t i c l e s w i t h b r i g h t f l e c k s s t a y e d above the bed s u r f a c e . The f l o a t i n g of c o a l p a r t i c l e s on the s u r f a c e of a f l u i d i z e d bed combustor w h i l e u n d e r g o i n g d e v o l a t i l i z a t i o n was o b s e r v e d by A t i m t a y (1980). She a l s o o b t a i n e d an e x p r e s s i o n f o r the r a d i a l v e l o c i t y of the e m i t t e d v o l a t i l e m a t t e r : Q V R = (5.1) 7 r d c 2 N where Q i s the v o l u m e t r i c f l o w r a t e of v o l a t i l e s , N i s the number of the c o a l p a r t i c l e s and d i s the c o a l p a r t i c l e 65 d i a m e t e r . V R , the r a d i a l v e l o c i t y of v o l a t i l e s , was found t o be of the same o r d e r of magnitude as the U m f , which causes the b u r n i n g p a r t i c l e s t o f l o a t above the bed s u r f a c e . Another reason f o r f l o a t i n g may be t h a t the gas v e l o c i t y a t the bed s u r f a c e was h i g h e r than U m£ of the f i n e r and l i g h t e r c o a l p a r t i c l e s , c a u s i n g them t o be f l u i d i z e d . A s s o c i a t e d w i t h the secondary f l u i d i z a t i o n , s t r a t i f i c a t i o n was observed when j e t i n f l u i d i z e d bed o c c u r r e d . An ash l a y e r was formed above the bed s u r f a c e , and p e r i o d i c a l l y d i s r u p t e d by the b u r s t of b u b b l e s . A b r i g h t f l a m e , p o s s i b l y caused by the combustion of v o l a t i l e s , was observ e d above the bed s u r f a c e , as shown i n F i g s . 5 . 7 ( a ) - ( c ) and 5 . 8 ( a ) - ( c ) . F i g u r e 5.20 shows t h a t an ash l a y e r s t a y e d a t the t o p of the bed a f t e r a run was completed. No e f f o r t was made t o d i s c h a r g e the ash or r e t u r n the unburned c o a l c a p t u r e d i n the c y c l o n e i n t o the combustor d u r i n g the r u n s . When o t h e r c o n d i t i o n s remained unchanged but the bed m a t e r i a l was changed t o the s m a l l e r s i z e sand (1.18-1.65 mm), the f l o w p a t t e r n s d i f f e r e d from the p r e v i o u s runs i n which the c o a r s e r sand (1.65-2.36 mm) was used. P u l s a t o r y s p o u t i n g s t a r t e d a t a lower bed t e m p e r a t u r e , 550 C i n s t e a d of 600 C. At h i g h e r temperature (630 C) the p a t t e r n was t r a n s f o r m e d from p u l s a t o r y s p o u t i n g i n t o s l u g g i n g d i r e c t l y , even w i t h o u t i n t r o d u c i n g a u x i l i a r y a i r . I t i s noteworthy, however, t h a t i n t h i s case no s t r a t i f i c a t i o n of s o l i d s was ob s e r v e d . A c c u m u l a t i o n of C o a l A b s e n c e of C o a l O Sand • C o a l F i g . 5.19 M a l d i s t r i b u t i o n o f C o a l F i g . 5.20 S t r a t i f i e d Sand and A s h 67 5.2.4 SHIFTING OF FLOW PATTERNS AT ELEVATED TEMPERATURE In o r d e r t o i n v e s i g a t e the e f f e c t of temperature on the hydrodynamic p a t t e r n s , a regime map was d e t e r m i n e d a t room te m p e r a t u r e . T h i s regime map i s s i m i l a r t o t h a t o b t a i n e d by S u t a n t o e t a l ( l 9 8 5 ) , as shown i n F i g . 5.21. A t r a n s i t i o n r e g i o n e x i s t e d where the upper p a r t of the bed was f l u i d i z e d b e f o r e s t a b l e s p o u t i n g was e s t a b l i s h e d . I t was found t h a t i n c r e a s i n g bed temperature c o u l d s h i f t the d i f f e r e n t f l o w regimes c l o c k w i s e around the o r i g i n of the c o o r d i n a t e s on the regime map. A t e n t a t i v e regime map f o r a s p o u t - f l u i d bed a t a h i g h t emperature i s g i v e n i n F i g . 5.22. Comparison of regime maps a t d i f f e r e n t t e m p e r a t u r e s shows t h a t s t a b l e s p o u t i n g d i s a p p e a r e d a t h i g h t e m p e r a t u r e s , and p u l s a t o r y s p o u t i n g c o u l d be a c h i e v e d even w i t h o u t a u x i l i a r y a i r . I t i s c l e a r t h a t the maximum s t a b l e s p o u t i n g bed h e i g h t d e c r e a s e s as bed t e m p e r a t u r e i n c r e a s e s , c a u s i n g a t r a n s f o r m a t i o n of f l o w p a t t e r n s . S i m i l a r f i n d i n g s have been r e p o r t e d by Wu (1986) . 5.2.5 OTHER OBSERVATIONS (a) D i s a p p e a r a n c e of s t a g n a n t zone As shown i n F i g s . 5.5 and 5.13, a stagnant s o l i d s - zone was formed on the c o n i c a l d i s t r i b u t o r . T h i s i s because the s c r e e n which c o v e r e d the p e r f o r a t e d p l a t e caused f i n e p a r t i c l e s t o s t i c k t o i t . F r i c t i o n a l r e s i s t a n c e then h i n d e r e d the movement of the s o l i d s . When a u x i l i a r y a i r was i n t r o d u c e d , t h i s s t a g n a n t zone was d e s t r o y e d due t o the 68 1.4 1.2 h o c r 0 . 8 h 0 . 6 h 0 . 4 h 0 . 2 h 9 S t a b l e S p o u t i n g O P u l s a t o r y S p o u t i n g D J e t i n F l u i d i z e d Bed v* S l u g g i n g P u l s a t o r y S p o u t i n g S t a b l e S p o u t i n g 0 . 2 0 . 4 0 . 6 0 . 8 Q s / Q m f 1.2 1.4 F i g . 5.21 Regime Map of S p o u t - F l u i d Bed a t Room Temperature T D=10 C, H o=0.3 m U mf=1.05 m/s ( a t T=10 C) Sand S i z e : 1.65-2.36 mm 69 O P u l s a t o r y S p o u t i n g • J e t i n F l u i d i z e d Bed e S t a b l e S p o u t i n g (Tb=580 C) v S l u g g i n g 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Q s / Q m f g. 5.22 T e n t a t i v e Regime Map of S p o u t - F l u i d Bed a t H i g h Temperature T D=650 C, H o=0.3 m U m f = 1 . l 5 m/s (at T=650 C) Sand S i z e : 1.65-2.36 mm 70 f l u i d i z a t i o n of the s o l i d s , as shown i n F i g . 5 . 8 ( a ) - ( c ) . (b) Temperature of c o a l p a r t i c l e s From the v i d e o f i l m s i t was found t h a t l a r g e c o a l p a r t i c l e s burned more b r i g h t l y than f i n e r p a r i c l e s . Presumably l a r g e c o a l p a r t i c l e s had h i g h e r s u r f a c e t e m p e r a t u r e s than f i n e p a r t i c l e s . 6. TEMPERATURE PROFILES 6.1 EXPERIMENTAL TECHNIQUE 6.1.1 AXIAL TEMPERATURE MEASUREMENT In the p r e l i m i n a r y r u n s , a x i a l t e m p e r a t u r e p r o f i l e s were measured by seven thermocouples mounted a t the back of the combustor w i t h a s p a c i n g of 0.1 m, as shown i n F i g . 6.1. However, t h i s arrangement o n l y a l l o w s two temperature r e a d i n g s t o be taken i n the a n n u l u s , which i s not s u f f i c i e n t t o d e termine the temperature p r o f i l e s i n the a n n u l u s . T h e r e f o r e , a x i a l t e m p e r a t u r e p r o f i l e s were d e t e r m i n e d by u s i n g a m o b i l e l o n g thermocouple i n s e r t e d from above. T h i s 1.6 mm I.D. thermocouple was i n s t a l l e d i n s i d e the gas probe, as d i s c u s s e d i n S e c t i o n 3.2. A l l a x i a l t e m p e r a t u r e s i n t h e a n n u l u s were measured a t the m i d d l e p o i n t , h a l f way from the w a l l of the combustor t o the s p o u t - a n n u l u s i n t e r f a c e . When the d e s i r e d bed t e m p e r a t u r e was r e a c h e d , the l o n g thermocouple was moved down t o the c o n i c a l s e c t i o n , where the f i r s t r e a d i n g was t a k e n . Then the thermocouple was moved upwards 50 mm a t a t i m e , u n t i l a l l wanted p o s i t i o n s had been c o v e r e d . Depending on the t e m p e r a t u r e d i f f e r e n c e between two n e i g h b o u r i n g p o i n t s , two t o f i v e minutes were r e q u i r e d f o r the t e mperature r e a d i n g s t o be s t e a d y . By r o t a t i n g the gas probe i n which the thermocouple was i n s t a l l e d , t e m p e r a t u r e s c o u l d be measured both i n the a n n u l u s and i n the spout. 71 72 6.1.2 RADIAL TEMPERATURE MEASUREMENT As i l l u s t r a t e d s c h e m a t i c a l l y i n F i g . 6.2, r a d i a l t e m p e r a t u r e measurements were made by moving the wall-mounted thermocouples t o g i v e n p o s i t i o n s r a d i a l l y . Measurement was s t a r t e d i n the spout, 2 mm from the f r o n t p a n e l . Thermocouples were then p u l l e d out 15 mm each time t o measure r a d i a l t e mperature p r o f i l e s i n s i d e the a n n u l u s . 6.2 RESULTS AND DISCUSSION 6.2.1 AXIAL TEMPERATURE PROFILES IN AND ABOVE THE SPOUT F i g u r e 6.3 g i v e s the r e s u l t s of two d i f f e r e n t r u n s . e Temperature p r o f i l e s were found t o be s t r o n g l y dependent on s o l i d s p r o p e r t i e s and were a l s o a f f e c t e d by the combustion p a t t e r n s . When c o a r s e r c o a l p a r t i c l e s w i t h a narrow s i z e range (0.85-1.19 mm) were f e d t o the combustor, the temperature p r o f i l e s were q u i t e u n i f o r m . However, f o r f i n e r c o a l p a r t i c l e s or a w i d e r s i z e range c o a l w i t h a h i g h f r a c t i o n of f i n e s , t e m p e r a t u r e s i n c r e a s e d s h a r p l y above the bed s u r f a c e . F i g u r e 6.3 a l s o shows t h a t a x i a l t e m p e r a t u r e p r o f i l e s i n s i d e the spout were r a t h e r u n i f o r m . The tempe r a t u r e p r o f i l e s i n the spout were measured o n l y f o r spouted bed combustion (q/Q T=0), because a f t e r a u x i l i a r y a i r was i n t r o d u c e d , the spout would reduce t o a j e t submerged i n a f l u i d i z e d bed. As shown i n F i g . 6.4, i n the s l u g g i n g bed when f i n e r sand was used, t h e r e was o n l y s m a l l d i f f e r e n c e between a x i a l t e m p e r a t u r e p r o f i l e s w i t h and w i t h o u t F i g . 6.1 Schematic Diagram of A x i a l Temperature Measurement F i g . 6.2 Schematic Diagram of R a d i a l Temperature Measurement oo 74 C J , Q) D ~o CP G L E 1000 900 -800 700 -600 -500 -400 O A-. O . •o Sand S i z e : 1.65-2.36 mm C o a l S i z e : O 0.85-1.18 mm A 0.60-1.65 mm 0.0 .0.1 0.2 0.3 0.4 0.5 0.6 Distance above Inlet Orifice (m) F i g . 6.3 A x i a l Temperature P r o f i l e s i n and above Spout U/U m s=1.2, U m s=1.1 m/s ( a t T=650 C) g/Q T=0, H o=0.3 m 0.7 75 900 i _ 15 -4— o CD CL E .CD 800 700 600 -500 O o C e n t r e l i n e , q/Qy=0 © A n n u l u s , q/QT=0 • A n n u l u s , q/Q_T=0.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Distance above Inlet Orifice (m) 0.7 0.8 F i g . 6 . 4 A x i a l Temperature P r o f i l e s i n S l u g g i n g Bed T b=660 C, H o=0.3 m U/U mf=1.2, U mf=0.7 m/s(at T=660 C) Sand S i z e : 1.18-1.65 mm C o a l S i z e : 0.85-1.18 mm 76 i n t r o d u c i n g a u x i l i a r y a i r . 6 . 2 . 2 AX IAL TEMPERATURE PROFILES IN THE ANNULUS F i g u r e 6.5 g i v e s t y p i c a l t e m p e r a t u r e p r o f i l e s i n t h e a n n u l u s f o r s p o u t e d and s p o u t - f l u i d bed c o m b u s t i o n . B o t h F i g s . 6.4 and 6.5 show t h a t a s t h e a u x i l i a r y a i r f l o w r a t e i n c r e a s e d , t h e o v e r a l l t e m p e r a t u r e p r o f i l e s became more u n i f o r m e x c e p t f o r a s h o r t d i s t a n c e a b o v e t h e i n l e t o r i f i c e where h i g h e r a u x i l i a r y a i r f l o w r a t e s c a u s e d a g r e a t e r t e m p e r a t u r e r i s e . T h i s i s i n a g r e e m e n t w i t h L i m e t a l ( 1 9 8 4 ) . The r e m a r k a b l e i n c r e a s e o f t e m p e r a t u r e i n t h e f o u n t a i n r e g i o n , e s p e c i a l l y when t h e r e was no a u x i l i a r y a i r , i n d i c a t e s t h a t c o m b u s t i o n was i n t e n s i f i e d i n t h e f o u n t a i n o r a b o v e t h e bed s u r f a c e . As p o i n t e d ou t by G r a c e a n d M a t h u r ( 1 9 7 8 ) , t h e f o u n t a i n may p l a y a v e r y i m p o r t a n t r o l e when c h e m i c a l r e a c t i o n s t a k e p l a c e i n s p o u t e d bed r e a c t o r s . 6 . 2 . 3 RADIAL TEMPERATURE PROFILES F i g u r e 6.6 shows t h a t t e m p e r a t u r e g r a d i e n t s i n t h e r a d i a l d i r e c t i o n were m i n o r , and t h e r e was no s u d d e n t e m p e r a t u r e c h a n g e b e t w e e n t h e s p o u t and a n n u l u s . A s l i g h t d e c r e a s e o f t e m p e r a t u r e o c c u r r e d n e a r t h e f r o n t w a l l o f t h e c o l u m n , p r e s u m a b l y due t o h e a t l o s s e s , b e c a u s e t h e i n s u l a t i o n on t h e f r o n t was t a k e n o f f f o r v i s u a l o b s e r v a t i o n when t e m p e r a t u r e m e a s u r e m e n t s were made. 77 1000 900 CD L_ D ~o v_ OJ Q_ E 800 700 600 500 ° i n and a b o v e s p o u t , q/QT=0 9 i n a n n u l u s , q/Q/r=0 • i n a n n u l u s , q /QT=0.2 A i n a n n u l u s , q/Qi<=0.4 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Distance above Inlet Orifice (m) 0.7 0.8 F i g . 6 . 5 A x i a l T e m p e r a t u r e P r o f i l e s 0 / U m s = 1 . 2 ; U m s = 1 . 1 m/s ( a t T=650 C) H o = 0 . 3 m Sand S i z e : 1 . 6 5 - 2 . 3 6 mm C o a l S i z e : 0 . 6 0 - 1 . 6 5 mm 78 900 800 ,0 CD 700 CD CL £ 600 O- •o- "O -o-• -o • 500 -400 1 1 1— 1 1 I i | 0 10 20 30 40 50 60 70 80 Distance f rom Front Panel (mm) F i g . 6 . 6 R a d i a l Temperature P r o f i l e s o 0.41 m above i n l e t o r i f i c e U/U m s=1.1, U m s=1.1 m/s (at T=650 C) q/QT=0 H o=0.3 m Sand S i z e : 1.65-2.36 mm C o a l S i z e : 0.60-1.65 mm • 0.41 m above i n l e t o r i f i c e • 0.31 m above i n l e t o r i f i c e U/U m s=1.2, ums= 1- 1 m / s < a t T=650 C) q/QT=0.2 H o=0.3 m Sand S i z e : 1.18-1.65 mm C o a l S i z e : 0.85-1.18 mm 7. OXYGEN CONCENTRATION PROFILES 7.1 EXPERIMENTAL TECHNIQUE Two methods were used i n the e x p e r i m e n t s t o determine a x i a l oxygen c o n c e n t r a t i o n p r o f i l e s : S y r i n g e gas s a m p l i n g and c o n t i n u o u s gas probe s a m p l i n g . The l a t t e r was found t o be more f l e x i b l e and r e l i a b l e . 7.1.1 SYRINGE GAS SAMPLING A t o t a l of 15 p r e s s u r e - l o c k gas s y r i n g e s were p r e p a r e d f o r gas s a m p l i n g on t h r e e s e p a r a t e o c c a s i o n s . F i v e measuring p o r t s a t which the thermocouples had p r e v i o u s l y been mounted f o r t e m p e r a t u r e measurement were chosen as s a m p l i n g p o r t s . A f t e r the d e s i r e d bed t e m p e r a t u r e , measured by a l o n g thermocouple suspended from above, had been reached, s y r i n g e s were i n s e r t e d i n t o the combustor t o t a k e gas samples. A l l the samples were a n a l y s e d by a gas chromatograph (Model HP 571 OA) a f t e r c o m p l e t i o n of the r u n . In a d d i t i o n t o measuring oxygen c o n c e n t r a t i o n , t h i s method can p r o v i d e c o n c e n t r a t i o n s of o t h e r gases such as H 2, CO, C0 2 and CH 0. However, a c o n t i n u o u s gas probe s a m p l i n g system was d e s i g n e d and i n s t a l l e d t o det e r m i n e the a x i a l oxygen c o n c e n t r a t i o n p r o f i l e s because of s e v e r a l problems w i t h the gas s y r i n g e s a m p l i n g methods: (a) Long a n a l y s i n g t i m e , a p p r o x i m a t e l y 20 minutes f o r each sample, was needed f o r gas chromatograph a n a l y s i s . 79 80 (b) P r e s s u r e - l o c k s y r i n g e s a r e v e r y d e l i c a t e . When a l a r g e number of them was h a n d l e d , the p o s s i b i l i t y of gas lea k a g e i n c r e a s e d . Leakage l e a d s t o i n a c c u r a c i e s i n d e t e r m i n i n g oxygen c o n c e n t r a t i o n p r o f i l e s and c o n c e n t r a t i o n s of o t h e r s p e c i e s . (c) As d i s c u s s e d i n S e c t i o n 6.1, the sa m p l i n g p o s i t i o n s were f i x e d and a t the bed h e i g h t employed o n l y one or two p o i n t s were i n s i d e the a n n u l u s . As a r e s u l t , i t was not p o s s i b l e t o det e r m i n e t h e p r o f i l e s w i t h i n t h e ann u l u s u s i n g t h i s method. 7.1.2 GAS PROBE SAMPLING Because of the drawbacks of s y r i n g e s a m p l i n g as d e t a i l e d above, a m o b i l e gas probe was c o n s t r u c t e d t o p r o v i d e a l l of the a x i a l oxygen c o n c e n t r a t i o n p r o f i l e s i n the p r e s e n t work. The d e t a i l s of t h i s s a m p l i n g system were d e s c r i b e d i n S e c t i o n 3.1, and the a u x i l i a r y d e v i c e s a re s c h e m a t i c a l l y i l l u s t r a t e d i n F i g s . 3.7 and 3.8. F i g u r e 7.1 shows the l o c a t i o n s i n the combustor where the samples were o b t a i n e d . By r o t a t i n g the gas probe oxygen c o n c e n t r a t i o n s c o u l d be measured both i n the ann u l u s and i n the spout. When measurements were made i n the a n n u l u s , the gas probe • was r o t a t e d t o such an a n g l e t h a t the oxygen c o n c e n t r a t i o n a t the m i d d l e p o i n t from the w a l l t o s p o u t - a n n u l u s i n t e r f a c e was measured. B e f o r e the run was s t a r t e d , the s t a i n l e s s f i l t e r a t the end of the gas probe was purged from i n s i d e by f r e s h a i r t o c l e a n out any dust s t u c k i n the por e s of the F i g . 7.1 L o c a t i o n s of Sampling P o i n t s i n the Combustor. 82 f i l t e r . To a s s u r e the a c c u r a c y of the measurements the i s o k i n e t i c s a m p l i n g t e c h n i q u e was employed, by which the s a m p l i n g v e l o c i t y i s e q u a l t o the gas v e l o c i t y a t the s a m p l i n g p o s i t i o n . The e s t i m a t i o n of the s a m p l i n g f l o w r a t e i s g i v e n i n Appendix I I I . A l t h o u g h the gas s a m p l i n g v e l o c i t y i n the a n n u l u s w i l l be d i f f e r e n t a t d i f f e r e n t l e v e l s , i t was found t h a t the oxygen c o n c e n t r a t i o n s were not s e n s i t i v e t o the s a m p l i n g f l o w r a t e : When the f l o w r a t e , m o n i t o r e d by a s m a l l r o t a m e t e r , was changed by 100%, o n l y a 3% change i n oxygen c o n c e n t r a t i o n was o b s e r v e d ; t h i s i s w i t h i n the a c c u r a c y of the oxygen m o n i t o r . Hence an average s a m p l i n g f l o w r a t e , e s t i m a t e d f o r t y p i c a l c o n d i t i o n s , was chosen f o r a l l gas s a m p l i n g . The s a m p l i n g was s t a r t e d from the l o w e s t p o s i t i o n a t the bottom, then the gas probe was g r a d u a l l y r a i s e d u n t i l the h i g h e s t p o s i t i o n i n the f r e e b o a r d was reached. A f t e r a complete s e t of d a t a had been o b t a i n e d , one p o s i t i o n was chosen f o r a r e p e a t measurement, and the r e s u l t was compared w i t h the p r e v i o u s one. The r e p r o d u c i b i l i t y was always w i t h i n ±5%. Because the amount of i n s u l a t i o n which c o u l d be removed e a s i l y was l i m i t e d , t h e e x c e s s i v e a i r needed t o m a i n t a i n the bed t e m p e r a t u r e was i n the range 20% t o 90%. The combustion e f f i c i e n c y was not s t u d i e d i n the p r e s e n t work. 83 7.2 RESULTS AND DISCUSSION Combustion i s s t r o n g l y a f f e c t e d by t e m p e r a t u r e and l o c a l oxygen c o n c e n t r a t i o n s . As w i t h the t e m p e r a t u r e p r o f i l e d i s c u s s e d i n Chapter 6, oxygen c o n c e n t r a t i o n s were r e l a t e d t o the hydrodynamic and combustion p a t t e r n s and s o l i d s p r o p e r t i e s . F i g u r e s 7.2, 7.3 and 7.4 g i v e t y p i c a l oxygen c o n c e n t r a t i o n p r o f i l e s f o r d i f f e r e n t o p e r a t i n g c o n d i t i o n s and s o l i d s p r o p e r t i e s . 7.2.1 SPOUTED BED COMBUSTION (a) Oxygen c o n c e n t r a t i o n s i n and above the s p o u t : When l a r g e r (0.85-1.18 mm) c o a l p a r t i c l e s were used, F i g . 7 . 2 shows t h a t the oxygen c o n c e n t r a t i o n d e c r e a s e d o n l y s l i g h t l y i n the spout and then became c o n s t a n t above the bed s u r f a c e . A p p a r e n t l y , because of the h i g h a i r - t o - c o a l r a t i o and the s h o r t r e s i d e n c e time of c o a l i n the spout v e r y l i t t l e oxygen was consumed t h e r e . F i g u r e 7.3 i n d i c a t e s t h a t a l t h o u g h the same t r e n d s were found i n the spout as i n F i g . 7 . 2 , the oxygen c o n c e n t r a t i o n d e c r e a s e d more s h a r p l y above th e spout when f i n e r (0.60-0.85 mm) c o a l was used. When f i n e r sand was employed as the bed m a t e r i a l , the bed was i n the s l u g g i n g regime. In t h i s c a s e , t h e r e i s no d i s t i n g u i s h a b l e spout or a n n u l u s , and a s t r o n g e r r e d u c t i o n of oxygen c o n c e n t r a t i o n above the bed s u r f a c e was found, as shown i n F i g . 7 . 4 (b) Oxygen c o n c e n t r a t i o n i n and above the a n n u l u s : 84 25 c o £ o > c CD cn >. X O 20 15 10 o i n and above s p o u t , q/Q>p=0 • i n a n n u l u s , q/QT = n • i n a n n u l u s , q/Q>p=0.2 _1 I I I 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Distance above Inlet Orifice (m) F i g . 7.2 Oxygen C o n c e n t r a t i o n p r o f i l e s Tb=640 C, H o=0.3 m 0.7 U/U m s=1.1 Sand S i z e : C o a l S i z e : U m s=1.1 m/s(at T=640 C) 1.65-2.36 mm 0.85-1.18 mm 0.8 85 O i n and above spout, q/QT=0 e i n a n n u l u s , q/QT=0 • i n a n n u l u s , q/Q>p=0.2 A i n a n n u l u s , q/QT=0.4 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Distance above Inlet Orifice (m) F i g . 7.3 Oxygen C o n c e n t r a t i o n P r o f i l e s Tb=650 C, H o=0.3 m U/U m s=1.2, U m s=1.1 m/s(at T=650 C) Sand S i z e : 1.65-2.36 mm Co a l S i z e : 0.60-0.85 mm 86 25 O on c e n t r e l i n e , q/QT=0 • a t m i d p o i n t from w a l l t o c e n t r e l i n e , q/QT=0 B a t m i d p o i n t from w a l l t o c e n t r e l i n e , q/Q/r=0.2 20 15 10 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Distance above Inlet Orifice (m) F i g . 7.4 Oxygen C o n c e n t r a t i o n P r o f i l e s ( i n s l u g g i n g regime) T b=660 C, H o=0.3 m U/U mf=1.2, U mf=0.7 m/s(at T=660 C) Sand S i z e : 1.18-1.65 mm C o a l S i z e : 0.85-1.18 mm 87 G e n e r a l l y , oxygen c o n c e n t r a t i o n s d e c r e a s e d g r a d u a l l y i n the annulus w h i l e more d r a s t i c changes took p l a c e near the bed s u r f a c e . A minimum c o n c e n t r a t i o n was u s u a l l y reached w i t h i n the f o u n t a i n r e g i o n , f o l l o w e d by an i n c r e a s e of oxygen c o n c e n t r a t i o n i n the f r e e b o a r d . These t r e n d s a re i l l u s t r a t e d by the c u r v e s w i t h q/QT=0 i n F i g s . 7 . 2 and 7.3. The minima a r e l i k e l y due t o the m i x i n g of gases which emerged from the spout and an n u l u s w i t h d i f f e r e n t oxygen c o n c e n t r a t i o n s . F i g u r e 7.4 i n d i c a t e s t h a t when the bed was i n the s l u g g i n g regime w i t h the f i n e r sand, the oxygen c o n c e n t r a t i o n p r o f i l e s a t o t h e r r a d i a l p o s i t i o n s were s i m i l a r t o t h a t a l o n g the c e n t r e l i n e of the combustor. 7.2.2 SPOUT-FLUID BED COMBUSTION When a u x i l i a r y a i r was i n t r o d u c e d , the p r o f i l e s of oxygen c o n c e n t r a t i o n i n the a n n u l u s were changed. A l t h o u g h the minimum was s t i l l r eached i n s i d e the f o u n t a i n r e g i o n , the subsquent i n c r e a s e of oxygen c o n c e n t r a t i o n was s u b s t a n t i a l l y l e s s than f o r the case where t h e r e was no a u x i l i a r y a i r , as shown i n F i g . 7 . 2 . The o v e r a l l oxygen c o n c e n t r a t i o n p r o f i l e s became more u n i f o r m as q/Q T i n c r e a s e d . • As shown i n F i g . 7 . 3 , i n c r e a s i n g a u x i l i a r y a i r appeared t o cause somewhat h i g h e r oxygen c o n c e n t r a t i o n s i n the a n n u l u s . I t i s noteworthy t h a t the boundary between the an n u l u s and f o u n t a i n was e v i d e n t i n temperature p r o f i l e s (see F i g . 6 . 5 ) . On the o t h e r hand, the change of oxygen 88 c o n c e n t r a t i o n s between the an n u l u s and f o u n t a i n was g r a d u a l , as shown i n F i g . 7 . 2 . F i g u r e 7.5 shows oxygen c o n c e n t r a t i o n p r o f i l e s p r o v i d e d by Gibbs and Hedley (1978) f o r f l u i d i z e d bed combustion. In t h a t c a s e , the oxygen c o n c e n t r a t i o n s d e c r e a s e d r a p i d l y i n the r e g i o n i m m e d i a t e l y above the d i s t r i b u t o r . However, i n the spouted and s p o u t - f l u i d bed a s u b s t a n t i a l change i n the oxygen c o n c e n t r a t i o n o n l y s t a r t e d a t about two t h i r d s of the expanded bed h e i g h t , as shown i n F i g s . 7.2 and 7.3. 7.2.3 OTHER PHENOMENA When s y r i n g e s a m p l i n g was employed, s m a l l amounts of hydrogen and methane ( t y p i c a l l y 0.8%v/v H 2 and 0 . 0 1 % V / V CH«) were found i n the upper p a r t of the bed and i n the f o u n t a i n r e g i o n . T h i s was p o s s i b l y caused by d e v o l a t i l i z a t i o n and c r a c k i n g or g a s i f i c a t i o n a c c o r d i n g t o the f o l l o w i n g r e a c t i o n s , due t o the h i g h m o i s t u r e c o n t e n t of the c o a l used: C + 1/20 2 — * CO C + 2H 20 — * C0 2 + H 2 CO + 3H 2 — * H 20 + CH« 89 25 c o o o i t CD c CD X O 20 15 10 -5 " C o a l S i z e : © <1.4 mm O 6-25 mm 0.0 0.1 0.2 0.3 0.4 0.5 Distance above Distributor (m) F i g . 7.5 Oxygen C o n c e n t r a t i o n P r o f i l e s i n a F l u i d i z e d Bed Combustor,Gibbs and Hedley (1978) Sand S i z e : 0.5-1.0 mm Tfc>: 700-800 C H= 0.6 m Combustor Dimension: 0.3X0.3X1.83 m3 8. ELUTRIATION OF SOLIDS 8.1 SIZE DISTRIBUTION AND CARBON CONTENT OF ENTRAINED SOLIDS The s o l i d p a r t i c l e s captured by the cyclone were not re t u r n e d to the combustor. A f t e r each run was completed, those p a r t i c l e s were removed, and the s i z e d i s t r i b u t i o n and carbon content were determined. Table 8.1 g i v e s the r e s u l t s of two runs i n which sand p a r t i c l e s with d i f f e r e n t s i z e ranges were used. D e t a i l e d study of carbon a t t r i t i o n d u r i n g f l u i d i z e d bed combustion of c o a l has been c a r r i e d out by Arena et a l (1983) and more r e c e n t l y by Chirone et a l (1985). According to Arena et a l , a t t r i t i o n i s enhanced by combustion and i n c r e a s e d when i n c r e a s i n g the s i z e of bed m a t e r i a l . Chirone et a l . i n d i c a t e d that combustion and a t t r i t i o n of char p a r t i c l e s occur i n p a r a l l e l , and two types of a t t r i t i o n were d i s t i n g u i s h e d : (a) p u r e l y mechanical a t t r i t i o n and (b) com b u s t i o n - a s s i s t e d a t t r i t i o n , where detachable a s p e r i t i e s are c o n t i n u o u s l y renewed by i r r e g u l a r movement of the combustion f r o n t . The l a t t e r was found to be one order of magnitude l a r g e r than the former. The s i z e d i s t r i b u t i o n and carbon content given i n Table 8.1 f o r two d i f f e r e n t runs are comparable. About 70% of the captured ash was sma l l e r than 250 jum, i n d i c a t i n g that c o a l p a r t i c l e s shrunk to a small s i z e before being c a r r i e d out of the combustor. The carbon content of the ash was reduced somewhat when the combustor was operated at a higher 90 TABLE 8.1 SIZE DISTRIBUTION AND CARBON CONTENT OF ASH Run 20 28 T b (C) 620 700 T i m e o f Run (h) 4 . 7 5 4 . 0 U ( m / s ) 1 . 3 - 1 . 4 0 . 9 - 1 . 2 S a n d s i z e (mm) 1 . 6 5 - 2 . 3 6 1 . 1 8 - 1 . 6 5 F e e d c o a l s i z e (mm) 0 . 7 1 - 1 . 1 8 0 . 7 1 - 1 . 1 8 T o t a l W t . o f a s h (g) 504 708 S i e v e S i z e (mn) Wt (%) Wt (%) 590-850 1.3 2.1 350-590 11.0 11.2 250-350 15.1 12.6 150-250 24.0 22.8 61-150 20.5 21.5 <61 27.8 29.8 mean d i a m e t e r d p (Aim)* 76 73 c a r b o n c o n t e n t ( % ) 13.1 11.1 * mean d 1 92 t e m p e r a t u r e . T a b l e 8.1 a l s o shows t h a t w i t h t h e same p e r i o d of t i m e more s o l i d s were e l u t r i a t e d when f i n e r bed m a t e r i a l was e m p l o y e d . 8.2 S I Z E CHANGE OF BED MATERIALS T a b l e 8.2 g i v e s t h e s i z e change of s a n d i n r u n 23. B e s i d e s t h e change of t h e s a n d p a r t i c l e d i a m e t e r t h e shape of t h e p a r t i c l e s were a l s o c h a n g e d from a n g u l a r t o n e a r l y s p h e r i c a l . F i v e p e r c e n t o f a s h was f o u n d i n t h e bed a f t e r t h e run was c o m p l e t e d . 93 TABLE 8.2 CHANGE OF SAND S I Z E DISTRIBUTION T f a = 670 C Time of run = 4 h 20 m i n . U = 1.2-1.5 (m/s) S i e v e S i z e (nun) Wt (%), F r e s h Wt (%), Used 2.38-2.83 rj.5 0.0 2.00-2.38 21.6 9.0 1.68-2.00 62.5 47.8 1.41-1.68 14.2 27.7 1.19-1.41 14.0 9.9 1.00-1.19 0.2 4.2 0.84-1.00 0.0 1.5 mean d (mm)* 1.84 1.70 * mean d_ = 1 9. COAL PARTICLE BURNOUT TIMES 9.1 BACKGROUND S i n c e the e a r l y 1970's much work has been performed on c o a l combustion mechanisms i n f l u i d i z e d beds, and a number of models have been proposed t o d e s c r i b e f l u i d i z e d c o mbustion ( e. g. A v e d e s i a n and D a v i d s o n , 1973; Basu e t a l , 1975; C h a k r a b o r t y and Howard, 1978 and 1981; Leung and Smi t h , 1979; Yat e s e t a l , 1980; Ross and Davidson,1981; P i l l a i , 1981; LaNauze and Jung,.1982; S t u b i n g t o n , 1985). A re v i e w of f l u i d i z e d bed combustion models was g i v e n by P y l e (1977), and more r e c e n t l y a comprehensive r e v i e w of f l u i d i z e d bed combustion was p r o v i d e d by LaNauze (1985). A v e d e s i a n and Davidson (1973) s t u d i e d combustion of bat c h e s of char p a r t i c l e s i n a f l u i d i z e d bed of ash (0.5 mm). T h e i r t h e o r e t i c a l t r e a t m e n t was combined w i t h an e x p e r i m e n t a l study b u r n i n g b a t c h char p a r t i c l e s of dia m e t e r 0.23 t o 2.61 mm. The burnout t i m e s , o f f - g a s oxygen and carbon d i o x i d e c o n c e n t r a t i o n s were measured under a v a r i e t y of c o n d i t i o n s . The fundamental assumption was t h a t the combustion r a t e i s c o n t r o l l e d by the r a t e of d i f f u s i o n of oxygen t o the b u r n i n g p a r t i c l e and t h a t the temperature employed (900 C) has no i n f l u e n c e on o v e r a l l k i n e t i c s due t o the f a s t c h e m i c a l r e a c t i o n . They proposed a double f i l m d i f f u s i o n c o n t r o l as the mechanism of combustion t a k i n g p l a c e a t the p a r t i c l e s u r f a c e . The p r i m a r y p r o d u c t was s a i d t o be CO which d i f f u s e s away and burns t o C 0 2 i n a 94 95 homogeneous gas phase r e a c t i o n i n a zone c l o s e t o the carbon s u r f a c e . U s i n g an e q u a t i o n f o r the o v e r a l l consumption of oxygen based on the f l u i d i z e d bed r e a c t o r model of Davidson and H a r r i s o n (1963) and n e g l e c t i n g the c h e m i c a l r e s i s t a n c e , the a u t h o r s o b t a i n e d the f o l l o w i n g e x p r e s s i o n f o r burnout time of a b a t c h char i n a bed of c r o s s - s e c t i o n a r e a A: m p c d 0 2 t = + •— (9.1) 12AC 0 [ U - ( U - U m f ) e x p ( - X ) ] 96ShD gC 0 where C 0 i s t h e i n l e t oxygen c o n c e n t r a t i o n , pQ i s the carbon d e n s i t y , d 0 i s the i n i t i a l p a r t i c l e d i a m e t e r , m i s the mass of c a r b o n , Dg i s the gas d i f f u s i o n c o e f f i c i e n t and X i s the i n t e r p h a s e mass t r a n s f e r c o e f f i c i e n t d e f i n e d by Davidson and H a r r i s o n (1963). The Sherwood number, Sh, was t r e a t e d as a c o n s t a n t w i t h a v a l u e of 1.4. Measured burnout t i m e s were i n good agreement w i t h the proposed model. However, the assumption of f a s t c h e m i c a l r e a c t i o n has been q u e s t i o n e d by many w o r k e r s . C h a k r a b o r t y and Howard (1978) measured the b u r n i n g r a t e s of carbon p a r t i c l e s of d i a m e t e r 6 t o 12 mm i n a s h a l l o w f l u i d i z e d bed and found the r a t e t o v a r y p r o p o r t i o n a l l y t o d 0 n , where 1.8<n<1.97. On the b a s i s t h a t n s h o u l d be r e s p e c t i v e l y 1 and 2 f o r d i f f u s i o n and k i n e t i c c o n t r o l , t hey c o n c l u d e d t h a t the combustion was m a i n l y k i n e t i c a l l y c o n t r o l l e d . In o r d e r t o i n v e s t i g a t e the importance of c h e m i c a l k i n e t i c s , Ross and Davidson (1981) m o d i f i e d the model proposed by A v e d e s i a n and o b t a i n e d the e x p r e s s i o n : 96 m 1 2 A C 0 [ U - ( U - U m f ) e x p ( - X ) ] ap d 0 2 7 P c d 0 + °- + £ (9.2) 48ShD C 0 2 4 k c C 0 Here k c i s a r e a c t i o n r a t e c o n s t a n t w h i l e a and 7 a r e c o n s t a n t s whose v a l u e s depend on the r e a c t i o n s assumed t o occ u r a t the p a r t i c l e s u r f a c e : a 7 ( i ) C + 1/20 2~*C0 1/2 1 ( i i ) C + 0 2-*C0 2 1 1 ( i i i ) C + C0 2^*2CO 1/2 1/2 The e x p e r i m e n t a l r e s u l t s and model, which a re i n good agreement, showed t h a t the combustion r a t e i s c o n t r o l l e d by a c o m b i n a t i o n of d i f f u s i o n and c h e m i c a l r e a c t i o n . They c o n c l u d e d t h a t f o r l a r g e r p a r t i c l e s (1-3 mm) the combustion r a t e i s c o n t r o l l e d by d i f f u s i o n of oxygen t o the p a r t i c l e s u r f a c e , but f o r s m a l l p a r t i c l e s ( l e s s than 1 mm) combustion i s p r i m a r i l y c o n t r o l l e d by t h e k i n e t i c s of the r e a c t i o n : C + 1/2 0 2 —"-C0, the CO then b u r n i n g i n the sand around the c a r b o n . The e f f e c t of sand s i z e on the combustion r a t e , which may have a s t r o n g impact i n spouted bed combustion because c o a r s e r sand i s u s u a l l y used, has not r e c e i v e d much a t t e n t i o n . However, C h a k r a b o r t y and Howard (1978) showed t h a t the b u r n i n g r a t e i n c r e a s e d w i t h an i n c r e a s e of i n e r t p a r t i c l e s i z e . The p r e d i c t i o n of combustion r a t e s needs knowledge of the r a t e of oxygen t r a n s f e r t h r o u g h the dense phase t o the 97 b u r n i n g p a r t i c l e c h a r a c t e r i z e d by the Sherwood number. A v e d e s i a n and Davidson (1973) and Ross and Davidson(1981) t r e a t e d Sh as a c o n s t a n t , a l t h o u g h t h e i r v a l u e s were d i f f e r e n t . LaNauze and Jung (1982) s t u d i e d the change of Sherwood number by b u r n i n g p e t r o l e u m coke i n a f l u i d i z e d bed. I t was found t h a t Sh changed from 12 t o 4 when p a r t i c l e s i z e d e c r e a s e d from 14 t o 3 mm. A c o r r e l a t i o n m o d i f i e d from the p r e v i o u s work was proposed, i n which the e x i s t a n c e of i n e r t s was i n c o r p o r a t e d : -Sh = 2e + 0 . 6 9 ( R e / e ) 1 / 2 S C 1 / 3 (9.3) where e i s the voidage of the f l u i d i z e d bed, Re i s Reynolds number based on the c o a l p a r t i c l e d i a m e t e r and s u p e r f i c i a l gas v e l o c i t y , and Sc i s the Schmidt number. P a r t i c l e t e mperature i s e s s e n t i a l f o r d e t e r m i n a t i o n of the k i n e t i c r a t e c o n s t a n t . U n f o r t u n a t e l y , i t has not y e t been p o s s i b l e t o p r e d i c t b u r n i n g p a r t i c l e t e m p e r a t u r e s a c c u r a t e l y d e s p i t e a number of s t u d i e s i n t h i s a r e a ( C h a k r a b o r t y and Howard, 1980; Roscoe et a l , l 9 8 0 ; Ross and D a v i d s o n , 1981; S t u b i n g t o n , 1985). Roscoe e t a l (1980) photographed a s m a l l b a t c h of coke p a r t i c l e s (2.41-2.81 mm) which had been added t o an ash bed (0.6-0.7 mm) a t 930 C. The t e m p e r a t u r e d i f f e r e n c e between the b u r n i n g p a r t i c l e and the bed was found t o be 130 t o 160 C. S t u b i n g t o n ( 1 9 8 5 ) mounted a char p a r t i c l e on a v e r y f i n e thermocouple and burned i t i n a f l u i d i z e d bed w h i l e the p a r t i c l e was o s c i l l a t i n g . The maximum p a r t i c l e t e m p e r a t u r e was found t o be 98 C h i g h e r than the bed t e m p e r a t u r e , w h i l e the p r e d i c t e d 98 d i f f e r e n c e was 132 C. One of the o b j e c t i v e s of the p r e s e n t work i s t o measure the burnout t i m e s of b a t c h c o a l i n spouted and s p o u t - f l u i d bed and compare the r e s u l t s w i t h the d a t a o b t a i n e d from f l u i d i z e d bed combustion. A l s o a m a t h e m a t i c a l model i s t o be proposed which can p r e d i c t the burnout t i m e s i n spouted bed combust i o n . 9.2 EXPERIMENTAL TECHNIQUE Four s m a l l batches of r e l a t i v e l y u n i f o r m s i z e c o a l p a r t i c l e s were p r e p a r e d by s c r e e n i n g a s m a l l amount of F o r e s t b e r g c o a l . These b a t c h e s had mean d i a m e t e r of 0.55, 1.10, 1.55, and 2.20 mm and c o r r e s p o n d i n g range of 0.50-0.60, 1.00-1.19, 1.41-1.68 and 2.00-2.39 mm. B e f o r e the burnout time measurements were s t a r t e d , the bed was heated up by p r e h e a t i n g the s p o u t i n g a i r and by b u r n i n g c o a l i n the combustor. D u r i n g the runs the e n t i r e a r e a of the f r o n t p a n e l was i n s u l a t e d except f o r a s m a l l s l o t , 25mm by 150 mm, l e f t f o r v i s u a l o b s e r v a t i o n . A b a l l v a l v e was i n s t a l l e d on the t o p of t h e combustor. A b a t c h of c o a l of known weight (2 g) was s t o r e d i n the v a l v e . The burnout t i m e s were d e t e r m i n e d under the base c o n d i t i o n s (see S e c t i o n 4.3). A f t e r the d e s i r e d bed tem p e r a t u r e was reached, the c o a l f e e d e r was t u r n e d o f f . As soon as a l l the p r e v i o u s i n v e n t o r y of c o a l i n t h e combustor had burned o u t , the b a t c h of c o a l s t o r e d i n the b a l l v a l v e was r e l e a s e d t o f a l l i n t o the combustor from above. F i r s t , the bed temperature d e c r e a s e d , 99 then i n c r e a s e d a f t e r t h i s b a t c h of c o a l s t a r t e d b u r n i n g , and d e c r e a s e d a g a i n as c o a l burned o u t . V i s u a l o b s e r v a t i o n t h r o u g h the t r a n s p a r e n t f r o n t f a c e p r o v i d e d a s i m p l e means of measuring burnout t i m e s w i t h a s t o p watch. D u r i n g the runs the b u r n i n g c o a l p a r t i c l e s c o u l d be seen as b r i g h t r e d and w h i t e s p o t s and s t r e a k s . The burnout time was de t e r m i n e d by n o t i n g the time from i n j e c t i o n of the c o a l t o the time when the s e b r i g h t s p o t s and s t r e a k s d i s a p p e a r e d . A f t e r the measurement was made, the c o a l f e e d e r was s w i t c h e d on t o i n c r e a s e the bed temp e r a t u r e t o the p r e v i o u s l e v e l . The tempe r a t u r e change was w i t h i n ±15 C d u r i n g the burnout time measurements. The r e p r o d u c i b i l i t y of burnout time measurements was w i t h i n ±5%.. 9.3 RESULTS AND DISCUSSION 9.3.1 OBSERVATION Combustion of s m a l l b a t c h e s of c o a l of u n i f o r m s i z e p r o v i d e d a way t o st u d y the d i f f e r e n t b e h a v i o u r of b u r n i n g p a r t i c l e s depending on t h e i r s i z e s . A f t e r the c o a l p a r t i c l e s of d i a m e t e r 0.55 mm were dropped i n t o the combustor, they f l o a t e d on the bed s u r f a c e f o r m i n g a secondary bed, as d i s c u s s e d i n S e c t i o n 5.2. P a r t i c l e s l a r g e r t h a n 1.1 mm mixed w i t h the sand t r a v e l l i n g downwards i n the a n n u l u s , emerging i n t e r m i t t e n t l y from t h e bed s u r f a c e . 100 9.3.2 COAL PARTICLE BURNOUT TIMES F i g u r e s 9.1 and 9.2 g i v e the burnout t i m e s under a v a r i e t y of c o n d i t i o n s . Apparent l i n e a r r e l a t i o n s h i p s between p a r t i c l e s i z e s and burnout t i m e s i n d i c a t e t h a t combustion was m a i n l y k i n e t i c a l l y c o n t r o l l e d a t the bed ( a n n u l u s ) t e m p e r a t u r e t e s t e d ( 8 l 0 C ) . As shown i n F i g . 9.1, the e f f e c t of c h a n g i n g U/U m s was not a p p r e c i a b l e . However, l o n g e r burnout t i m e s were found when a u x i l i a r y a i r was i n t r o d u c e d , as shown i n F i g . 9.2. T h i s may be caused by the change of hydrodynamic p a t t e r n s from p u l s a t o r y s p o u t i n g t o j e t - i n - f l u i d i z e d - b e d where a b u b b l i n g bed was formed a t the upper p a r t of the bed. T h i s became more e v i d e n t when the combustor o p e r a t e d a t h i g h q/Q T. 9.3.3 MODELING OF BURNOUT TIMES D e t a i l s of the d e r i v a t i o n of a s i m p l i f i e d combustion model a r e g i v e n i n Appendix IV. The assumptions made i n the model d e r i v a t i o n a r e as f o l l o w s : (a) C o a l p a r t i c l e s spend most of t h e i r time i n the a n n u l u s . The t i m e s spent i n the spout and i n the f o u n t a i n a r e i g n o r e d , s i n c e the average p a r t i c l e v e l o c i t y i n the spout i s two o r d e r of magnitude l a r g e r than t h a t i n the a n n u l u s . The t i m e s r e q u i r e d f o r p a r t i c l e heat-up and d e v o l a t i l i a z t i o n a r e a l s o i g n o r e d . (b) A r e p r e s e n t a t i v e or average oxygen c o n c e n t r a t i o n , Cg, i s adopted throughout the a n n u l u s . A l t h o u g h p l u g f l o w i s u s u a l l y assumed i n the a n n u l u s (Lim and Mathur, 1974), a 101 70 w i t h U/U m s=1.3) 0 " 1 1 ; 1 1 1 1 0 0.5 1 1.5 2 2.5 3 Coal Particle Diameter (mm) F i g . 9.1 C o a l Burnout Time i n Spouted Bed Tb=8l0 C, H o=0.3 m U m s=1.1 m/s(at T=810 C) Sand S i z e : 1.65-2.36 mm (See T a b l e 9.1 f o r o p e r a t i n g c o n d i t i o n s ) 102 • %/ • 1 / i i 0 q/QT=0 D q/QT=0.1 • q/QT=0.3 • q/QT=0-5 . T h e o r e t i c a l (from Eq(9.4) w i t h q/QT=0) 1 1 i 0 .0.5 1 1.5 2 2.5 3 Coal Particle Diameter (mm) F i g . 9.2 C o a l Burnout Time i n S p o u t - F l u i d Bed T D=810 C, H o=0.3 m U/U m s=1.3, U m s=1.1 m/s(at T=810 C) Sand S i z e : 1.65-2.36 mm (See T a b l e 9.1 f o r o p e r a t i n g c o n d i t i o n s ) 103 s i n g l e v a l u e of the oxygen c o n c e n t r a t i o n p r o v i d e s a f i r s t a p p r o x i m a t i o n towards d e v e l o p i n g a more comprehensive model. (c) The p a r t i c l e temperature Tp i s c o n s t a n t r e g a r d l e s s of t h e i r s i z e s , w i t h Tp 130-160 C h i g h e r than the bed te m p e r a t u r e . T h i s i s based on the d a t a from Roscoe e t a l ( 1980) . (d) As shown i n F i g . 9.3, the s i n g l e f i l m model i s chosen. T h i s i s based on the c o n c l u s i o n by Bukur and Amundson (1981). They found t h a t char p a r t i c l e t e m p e r a t u r e s under the c o n d i t i o n s p r e v a i l i n g i n f l u i d i z e d bed combustors (800-950 C) a r e too low t o s u s t a i n the endothemic carbon d i o x i d e r e d u c t i o n a t the p a r t i c l e s u r f a c e , i m p l y i n g t h a t the double f i l m t h e o r y i s not r e a l i s t i c . T h e i r c o n c l u s i o n was su p p o r t e d by the study of Ross and Davidson (1981). Based on above a s s u m p t i o n s , a t h e o r e t i c a l model has been d e r i v e d t o e s t i m a t e the burnout t i m e s (see Appendix I V ) : m . P c d 0 2 P c d 0 t = + X + 2 4 U a H A a C 0 9 6 S h 0 D g C 0 2 4 k c C 0 (9.4) where X i s a f a c t o r which a c c o u n t s f o r the change of Sherwood number d u r i n g combustion: 4 S h 0 S h 0 3 X = [ 3 e S h 0 2 + 1 2 e 2 S h 0 ( S h 0 - 2e) f t 3 S h 0 44e 3 - 8 e 3 l n ( ) - ] (9.5) 2e 3 A z Annulus OQ6Q Q>*OlV c o a l s u r f a c e C + 1/2 O,-*- CO F i g 9.3 C o a l P a r t i c l e s B u r n i n g i n t h e Annulus of a Spouted Bed o 105 where S h 0 i s the i n i t i a l Sherwood number based on the the i n i t i a l c o a l p a r t i c l e d i a m e t e r ( E q ( 9 . 3 ) ) . The t h r e e terms on the r i g h t - h a n d s i d e of Eq.(9.4) have the f o l l o w i n g s i g n i f i c a n c e : the l a s t term a c c o u n t s f o r the c h e m i c a l r e a c t i o n . When k c approaches i n f i n i t y , t h i s term w i l l v a n i s h . The second term a c c o u n t s f o r e x t e r n a l mass t r a n s f e r . When d 0 i s v e r y s m a l l ( e . g . <0.5 mm) or S h 0 i s l a r g e , t h i s term becomes n e g l i g i b l e . The f i r s t term r e p r e s e n t s the f i n i t e time needed f o r s u f f i c i e n t oxygen t o be i n t r o d u c e d t o s t o i c h i o m e t r i c a l l y c o n v e r t the c o a l p a r t i c l e s i n the an n u l u s . As d i s c u s s e d below, i n the p r e s e n t study the l a s t term was dominant under the c o n d i t i o n s t e s t e d . The k i n e t i c r a t e c o n s t a n t , k c , can be e s t i m a t e d from the e q u a t i o n of F i e l d e t a l (1967) as 149227 k = 595T exp( ) (9.6) P RT p F i g u r e s 9.1 and 9.2 show t h a t the c a l c u l a t e d v a l u e s a re i n good agreement w i t h the e x p e r i m e n t a l d a t a . N e v e r t h l e s s , the s i m p l i f i e d model has t h e f o l l o w i n g l i m i t a t i o n s : (a) The use of a s i n g l e r e p r e s e n t a t i v e gas c o n c e n t r a t i o n i n the ann u l u s makes the model o v e r s i m p l i f i e d . P l u g f l o w ( w i t h a f a l l i n g c o n c e n t r a t i o n ) i s a more a p p r o p r i a t e approach. (b) The r e a c t i o n s i n the spout and f o u n t a i n a re n e g l e c t e d , which would l e a d t o an o v e r e s t i m a t i o n of t . 106 The good a g r e e m e n t be tween t h e p r o p o s e d mode l and t h e e x p e r i m a n t a l d a t a may be b e c a u s e t h e f a c t o r s m e n t i o n e d a b o v e o f f s e t one a n o t h e r . 9 . 3 . 4 COMPARISON OF BURNOUT TIMES F i g u r e 9.4 g i v e s t h e c o m p a r i s o n o f b u r n o u t t i m e s i n t h e p r e s e n t work and t h o s e o b t a i n e d f r om t h e l i t e r a t u r e ( A v e d e s i a n and D a v i d s o n , 1973; A t i m t a y , 1980; Ro s s and D a v i d s o n , 1981; C h a k r a b o r t y and H o w a r d , 1981b) b a s e d on t h e same mass o f c a r b o n b u r n t . I t s h o u l d be n o t e d t h a t t h e bed t e m p e r a t u r e i n t h e p r e s e n t s t u d y was 100 C l o w e r t h a n t h a t u s e d by t h e o t h e r w o r k e r s . To e l i m i n a t e t h e e f f e c t o f c o a l t y p e on b u r n o u t t i m e s , t h e d a t a f o r 10 t y p e s o f c o a l f r o m P i l l a i (1981b) a r e g i v e n i n F i g s . 9.5 and 9 . 6 . The c o a l t y p e s and e x p e r i m e n t a l c o n d i t i o n s w h i c h l e d t o t h e d a t a i n F i g s . 9 . 4 , 9 .5 and 9.6 a r e l i s t e d i n T a b l e s 9.1 and 9 . 2 . The c o a l p a r t i c l e b u r n o u t t i m e s i n s p o u t e d and s p o u t - f l u i d beds a r e s i g n i f i c a n t l y s h o r t e r t h a n t h o s e i n f l u i d i z e d b e d s . The p o s s i b l e r e a s o n s a r e : (a ) No b u b b l e s b y p a s s t h e a n n u l u s . In f l u i d i z e d bed s ° t h e r e c a n be an a p p r e c i a b l e r e s i s t a n c e t o i n t e r p h a s e t r a n s f e r f r o m t h e b u b b l e p h a s e t o t h e d e n s e p h a s e . As shown i n F i g . 9 . 2 , when s u f f i c i e n t a u x i l i a r y a i r was i n t r o d u c e d f o r a b u b b l i n g bed t o be o b s e r v e d , t h e b u r n o u t t i m e s were s l i g h t l y i n c r e a s e d due t o b u b b l e b y p a s s i n g . (b) B e c a u s e o f t h e e x i s t e n c e of t h e h i g h v e l o c i t y s p o u t i n t h e s p o u t e d b e d s , t h e a s h l a y e r may be r a p i d l y p e e l e d o f f 1 07 300 1 2 3 4 Coal Particle Diameter (mm) F i g . 9.4 Comparison of C o a l Burnout Times A A v e d e s i a n and Davidson (1973) Tb=900 C, U=0.38 m/s, Sand S i z e : 0.39 mm O Ross and Davidson (1981) Tb=900 C, U=.50 m/s, Sand S i z e : 0.55 mm • O C h a k r a b o r t y and Howard (1981b) Tb=800 C, U=0.25 m/s, Sand S i z e : 0.33 mm Tb=900 C, U=0.27 m/s, Sand S i z e : 0.33 mm Tb=900 C, U=0.71 m/s, Sand S i z e : 0.78 mm Tb=900 C, U=0.71 m/s, Sand S i z e : 0.33 mm • P r e s e n t Work Tb=8l0 C, U=1.4 m/s, Sand S i z e : 1.84 mm 108 150 g 100 5 0 P i l l a i (1981b) T b=875 C C o a l Type: "- C: N i e d e r b e r g a n t h r a c i t i c — D : Lohberg b i t u m i n o u s --E: Glen Brook b i t u m i n o u s P r e s e n t Work T D=810 C F o r e s t b e r g s u b - b i t u m i n o u s 2 3 Coal Particle Diameter (mm) F i g . 9.5 Comparison of Burnout Times f o r D i f f e r e n t Types of C o a l i n F l u i d i z e d and Spouted Beds (See T a b l e s 9.1 and 9.2 f o r more i n f o r m a t i o n . ) 109 250 200 150 100 50 P i l l a i ( 1981b ) T b = l 0 l 0 C C o a l T y p e : R e x c o c h a r N i e d e r b e r g a n t h r a c i t i c L o h b e r g b i t u m i n o u s G l e n B r o o k b i t u m i n o u s / P i t t s b u r g h No . 8 b i t u m i n o u s / N o s t e l l b i t u m i o u s ^ O s t e r f e l d b i t u m i n o u s » ••' A r i g n a h i g h - a s h / s^.—• Hat C r e e k h i g h - a s h / T e x a s l i g n i t e S P r e s e n t Work T b = 8 l 0 C F o r e s t b e r g s u b - b i t u m i n o u s I I 0 1 2 3 4 5 Coal Particle Diameter (mm) F i g . 9.6 C o m p a r i s o n o f B u r n o u t T i m e s f o r D i f f e r e n t T y p e s o f C o a l i n F l u i d i z e d and S p o u t e d Beds (See T a b l e s 9.1 and 9.2 f o r more i n f o r m a t i o n . ) TABLE 9.1 OPERATING CONDITIONS OF FLUIDIZED AND SPOUTED BED COMBUSTORS Parameters chakraborty and Avedesian and Ross and Howard(1981b) Dav1dson(1973) Dav1dson(1981) P)llai(1981b) The present work Bed Diameter (mm) 71.5 76 100 100 154 Bed Material s11ica sand ash sand refractory Ottawa sand Inert P a r t i c l e Size (mm) 0.327,0.55,0.78 0.39 0. 55 0.62 1 .84 Inert Density (kg/m3) 2630 2360 2650 2700 2605 St a t i c Bed Height (mm) 30 82 150 70 300 Bed Temperature (C) 800,900 900 900 775,875,1010 810 Sup e r f i c i a l Velocity (m/s) 0.27,0.71 0. 38 0.50 1.2, 1 .35, 1 .5 1.4 Coal Size (mm) 1.84-4.38 1.30-2.60 1.30-2.20 0.50-8.00 0.55-2.20 TABLE 9.2 COAL ANALYSIS FROM LITERATURE AND PRESENT WORK Coa l Type P i l l a i (1981b) A ,Rexco C, N i e d e r b e r g D, Lohberg E. G l e n Brook F, P 1 t t s b u r g h G. N o s t e l 1 H. O s t e r f e l d I , Ar1gna J . H a t Creek L .Texas 1 I g n i t e C h a r ( A v e d e s i a n and D a v i d s o n , 1973; Ross and D a v i d s o n , 1 9 8 1 ) C h a r ( C h a k r a b o r t y and Howard,1981b) F o r e s t b e r g Coa l ( p r e s e n t work) P rox imate a n a l y s i s ( W t . %) M o i s t u r e V o l a t i l e Ash F i x e d Carbon S w e l l i n g C a l o r i f i c Number V a l u e ( k J / k g ) 3.3 12.0 12.4 2.0 9.2 5.6 1.8 31.0 6.7 3.0 33.5 15.0 1.9 33.10 9.7 5.0 29.5 23.5 1.9 21.2 33.5 1.8 14.1 56.2 8.0 23.9 47.2 17.3 31.5 20.7 2.8 20.0 5.2 72.3 0 28790 83.2 0.5 33230 60.5 7.5 32410 48.5 7 27912 55.1 7 30982 42 .0 1 23670 43.4 2.5 22014 27.9 0 12235 20.9 - 10914 30.5 0 17757 72 .0 I . 1 27.1 4.4 67.5 I I . 9 30.8 25.9 31.4 1 17910 1 1.2 by a t t r i t i o n , a l l o w i n g more f r e s h s u r f a c e a r e a t o be exposed f o r r e a c t i o n . (c) The l a r g e i n e r t p a r t i c l e s cause a much h i g h e r i n t e r s t i t i a l gas v e l o c i t y , l e a d i n g t o a s i g n i f i c a n t r e d u c t i o n i n the i n t e r s t i t i a l - g a s - t o - p a r t i c l e mass t r a n s t e r r e s i s t a n c e . (d) Because a c o a r s e r bed m a t e r i a l was used i n the spouted bed, the c o a l p a r t i c l e t e m p e r a t u r e may be h i g h e r than t h a t i n f l u i d i z e d beds ( C h a k r a b o r t y and Howard, 1978). T h i s has been s u p p o r t e d by the c a l c u l a t i o n i n which the p a r t i c l e t e mperature was assumed t o be 150 C h i g h e r than the bed t e m p e r a t u r e . T h i s v a l u e i s h i g h e r than the v a l u e o b t a i n e d by S t u b i n g t o n (98 C) and c l o s e t o the upper l i m i t r e p o r t e d by Roscoe e t a l (130-160 C ) . The s h o r t e r burnout t i m e s i n spouted beds can a l s o be e x p l a i n e d by comparison of the model proposed by Ross and Davidson (1981) w i t h t h a t d e r i v e d i n the p r e s e n t s t u d y . S u b s t i t u t i n g a=l/2 and 7=1, Eq(9.2) becomes m t = 1 2 A C 0 [ U - ( U - U m f ) e x p ( - X ) ] p d 0 2 P c d 0 + - + — (9.7) 96ShD gC 0 2 4 k c C 0 As i n d i c a t e d by the v a l u e s p r e s e n t e d i n T a b l e A2 of Appendix IV, which were c a l c u l a t e d from Eqs.(9.4) and (9.7) based on the c o n d i t i o n s g i v e n i n T a b l e A1, the v a l u e s of the f i r s t two terms i n Eq.(9.4) a r e s m a l l e r than the c o r r e s p o n d i n g 1 13 terms of Eq(9.7) because of the g r e a t e r U m£ and Sh. I t i s a l s o seen t h a t the combustion i n the p r e s e n t study was m a i n l y c o n t r o l l e d by c h e m i c a l r e a c t i o n , which a c c o u n t s f o r 80% of the t o t a l burnout t i m e s . 10. CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK 10.1 CONCLUSIONS Four d i f f e r e n t f l o w p a t t e r n s and t h e i r c o r r e s p o n d i n g combustion p a t t e r n s were o b s e r v e d : S t a b l e s p o u t i n g , p u l s a t o r y s p o u t i n g , j e t i n f l u i d i z e d bed and s l u g g i n g . The p a t t e r n s depend on the o p e r a t i n g c o n d i t i o n s and s o l i d s p r o p e r t i e s . I t was found t h a t the maximum s t a b l e s p o u t i n g h e i g h t d e c r e a s e d as the bed temperture i n c r e a s e d . A s p o u t - f l u i d bed a t e l e v a t e d t e m p e r a t u r e s can be c o n s i d e r e d t o c o n s i s t of a spouted bed w i t h a h e i g h t H m s £ i n the lower p a r t of the bed and a f l u i d i z e d bed w i t h a h e i g h t H-H m s£ i n the upper p a r t . At a g i v e n t e m p e r a t u r e , H m S £ d e c r e a s e d as the a u x i l i a r y a i r f l o w r a t e i n c r e a s e d w h i l e the t o t a l a i r f l o w r a t e was m a i n t a i n e d unchanged. A x i a l temperature p r o f i l e s i n the spout and ann u l u s were found t o be u n i f o r m f o r both spouted and s p o u t - f l u i d beds except f o r a s h o r t d i s t a n c e above the i n l e t o r i f i c e . However, a temperature i n c r e a s e was found above the spout when f i n e r c o a l p a r t i c l e s were employed. Above the ann u l u s the t e m p e r a t u r e s i n c r e a s e d s u b s t a n t i a l l y , i n d i c a t i n g t h a t combustion was i n t e n s i f i e d i n the f o u n t a i n r e g i o n . More u n i f o r m a x i a l t emperature p r o f i l e s c o u l d be a c h i e v e d by i n t r o d u c i n g the a u x i l i a r y a i r t o c r e a t e a s p o u t - f l u i d bed. R a d i a l t e m p e r a t u r e p r o f i l e s were u n i f o r m b o t h i n the a n n u l u s and i n the f o u n t a i n r e g i o n . No a b r u p t temperature change was found a t the s p o u t - a n n u l u s i n t e r f a c e . 114 1 15 A x i a l oxygen c o n c e n t r a t i o n p r o f i l e s were found t o be c l o s e l y r e l a t e d t o the f l o w p a t t e r n s and s o l i d s p r o p e r t i e s . When l a r g e r c o a l p a r t i c l e s (1mm) were used the oxygen c o n c e n t r a t i o n p r o f i l e s were u n i f o r m w i t h i n and above the spou t , but a d e c r e a s e of c o n c e n t r a t i o n was obser v e d when f i n e c o a l p a r t i c l e s (0.6 mm) were used. I n the a n n u l u s a r a p i d d e c r e a s e of c o n c e n t r a t i o n s t a r t e d near the bed s u r f a c e , and a minimum v a l u e was reached i n the f o u n t a i n r e g i o n . C o n c e n t r a t i o n p r o f i l e s became more u n i f o r m when a u x i l i a r y a i r was i n t r o d u c e d . The burnout t i m e s of c o a l p a r t i c l e s i n spouted and s p o u t - f l u i d beds were found t o be s i g n i f i c a n t l y s h o r t e r than those found i n f l u i d i z e d bed combustion. A model f o r e s t i m a t i n g the burnout t i m e s was proposed. For the p a r t i c l e s i z e and temp e r a t u r e range t e s t e d , the combustion appeared t o be c o n t r o l l e d by c h e m i c a l r e a c t i o n . ,10.2 SUGGESTIONS FOR FURTHER WORK Flow regime maps of s p o u t - f l u i d bed a t e l e v a t e d t e m p e r a t u r e s s h o u l d be d e t e r m i n e d . A g e n e r a l t h e o r e t i c a l model which can d e s c r i b e the performance of the s p o u t - f l u i d bed combustor s h o u l d be dev e l o p e d and t e s t e d a g a i n s t the expermental r e s u l t s of t h i s work. The s e g r e g a t i o n and s t r a t i f i c a t i o n of s o l i d s d u r i n g combustion s h o u l d r e c e i v e f u r t h e r a t t e n t i o n . NOMENCLATURE Roman L e t t e r s A C r o s s - s e c t i o n a l a r e a of the combustor, m2 A a C r o s s - s e c t i o n a l a r e a of the a n n u l u s , m2 A s C r o s s - s e c t i o n a l a r e a of the sp o u t , m2 C a Oxygen c o n c e n t r a t i o n i n the a n n u l u s , kmol/m 3 C a' R e p r e s e n t a t i v e oxygen c o n c e n t r a t i o n i n the an n u l u s , kmol/m 3 C a H Oxygen c o n c e n t r a t i o n i n t h e ann u l u s a t z=H, kmol/m 3 C e E x i t oxygen c o n c e n t r a t i o n , kmol/m 3 C s H Oxygen c o n c e n t r a t i o n i n the spout a t z=H, kmol/m 3 C 0 I n l e t oxygen c o n c e n t r a t i o n , kmol/m 3 D M o l e c u l a r d i f f u s i o n c o e f f i c i e n t i n gas phase, y m 2/s d c C o a l p a r t i c l e d i a m e t e r , m dp Mean p a r t i c l e d i a m e t e r d e f i n e d i n T a b l e 3.1, m d 0 I n i t i a l c o a l p a r t i c l e d i a m e t e r , m H Expanded bed h e i g h t , m H m Maximum s p o u t a b l e h e i g h t , m H m s £ Maximum s t a b l e bed h e i g h t i n the s p o u t - f l u i d bed, m H 0 S t a t i c bed h e i g h t , m 116 1 17 m Mass of ca r b o n , kg rii C o a l f e e d i n g r a t e , g/s K O v e r a l l r a t e c o n s t a n t , m/s k c C h e m i c a l r e a c t i o n r a t e c o n s t a n t , m/s k m Mass t r a n s f e r c o e f f i c i e n t , m/s N Number of the c o a l p a r t i c l e s i n the b a t c h Q V o l a t i l e e m i s s i o n r a t e , m 3/s Q m f Minimum f l u i d i z i n g a i r f l o w r a t e , m 3/s Q m s Minimum s p o u t i n g a i r f l o w r a t e , m 3/s Q s S p o u t i n g a i r f l o w r a t e , m 3/s Q T T o t a l a i r f l o w r a t e , m 3/s q A u x i l i a r y a i r f l o w r a t e , m 3/s q s a m Gas s a m p l i n g f l o w r a t e , m 3/s R Gas c o n s t a n t , R=8.314 kJ/kmol'K R c C o a l b u r n i n g r a t e , kmol/s T Temperature, C T^ Bed t e m p e r a t u r e , C Tp 1 . C o a l p a r t i c l e t e m p e r a t u r e , C t Time, s t c Burnout time of c o a l , s U S u p e r f i c i a l gas v e l o c i t y , m/s U a H S u p e r f i c i a l gas v e l o c i t y i n the annulus a t z=H, m/s U m f Minimum f l u i d i z i n g v e l o c i t y , m/s 118 U m s Minimum s p o u t i n g v e l o c i t y , m/s U s H S u p e r f i c i a l gas v e l o c i t y i n the spout a t z=H, m/s V R E m i s s i o n v e l o c i t y of v o l a t i l e , m/s X Number of i n t e r p h a s e mass t r a n s f e r u n i t s Greek L e t t e r s a R e a c t i o n mechanism c o n s t a n t , Eq.(9.2) 7 R e a c t i o n mechanism c o n s t a n t , Eq.(9.2) e Loose packed bed v o i d a g e X F a c t o r d e f i n e d by Eq(9.5) v K i n e t i c gas v i s c o s i t y , m 2/s P c Carbon d e n s i t y , kg/m 3 D i m e n s i o n l e s s Group Re Reynolds number=Ud c/f Sh Sherwood number=k md c/Dg S h 0 I n i t i a l Sh of c o a l p a r t i c l e a t t=0 Sc Schmidt number=p/D REFERENCES A r b i b , H. A. and Levy, A. Combustion of Low H e a t i n g V a l u e F u e l s and Wastes i n the Spouted Beds, Can. J . Chem. Eng., 60, 528-531(1982a) A r b i b ; H. A. and Levy, A., The R e v e r s e - f l o w Spouted Bed Combustor, Combustion S c i e c e and Technology, 29, 83-86(1982b) A r b i b , H. A., Sawyer, R. F. and Weinberg, J . , The Combustion C h a r a c t e r i s t i c s of Spouted Beds, 18th I n t e r n a t i o n a l Symposium on Combustion, The Combustion I n s t . , 233-241(1981) Arena, U., D'Amore, M. and M a s s i m i l l a , L., Carbon A t t r i t i o n D u r i n g the F l u i d i z e d Combustion of a C o a l , AIChE J . , 29, 40-49C1983) A t i m t a y , A., Combustion of V o l a t i l e M a t t e r i n F l u i d i z e d Beds, i n F l u i d i z a t i o n , eds. J . R. Grace and J . M. Matsen, Plenum P r e s s , New York, 159-166(1980) A v e d e s i a n , M. M. and D a v i d s o n , J . F., Combustion of Carbon P a r t i c l e s i n a F l u i d i z e d Bed, T r a n s . I n s t . Chem. En g r s , 51,, 1 21-131( 1 973) Basu, P. Broughton, J . and E l l i o t t , D. E., Combustion of S i n g l e C o a l P a r t i c l e s i n F l u i d i z e d Beds, F l u i d i z e d Combustion C o n f e r e n c e , I n s t . F u e l Symp. S e r . No.1, A3: 1-10(1975), London Bukur, D. B. and Amundson, N. R., F l u i d i z e d Bed Char Combustion D i f f u s i o n L i m i t e d M o dels, Chem. Eng. S c i . , 30, 1239-1254(1981) 119 120 B r i d g w a t e r , J . , Chapter 6 i n F l u i d i z a t i o n , 2nd ed., ed. J . F. D a v i d s o n , R. C l i f t and D. H a r r i s o n , London, 201-224(1985) C h a k r a b o r t y , R. K. and Howard, J . R., B u r n i n g R a tes and Temperatures of Carbon P a r t i c l e s i n a S h a l l o w F l u i d i z e d - B e d Combustor, J . I n s t . Energy, 51, 220-224(1978) C h a k r a b o r t y , R. K. and Howard, J . R., Combustion of S i n g l e Carbon P a r t i c l e s i n F l u i d i z e d Beds of H i g h - d e n s i t y A l u m i n a , J . I n s t . Energy, 54, 5 5 - 5 8 ( l 9 8 l a ) C h a k r a b o r t y , R. K. and Howard, J . R., Combustion of Char i n Sh a l l o w F l u i d i z e d Bed Combustors: I n f l u e n c e of Some Design and O p e r a t i n g P a r a m e t e r s , J . I n s t . Energy, 54, 48-54(1981b) C h a t t e r j e e , A., S p o u t - f l u i d Bed Technique, I n d . Eng. Chem. P r o g r e s s Des. D e v e l p . , No.2, 9, 340-341(1970) C h i r o n e , R., D'amore, M. M a s s m i l l a , L. and Mazza, A., Char A t t r i t i o n D u r i n g the B a t c h F l u i d i z e d Bed Combustion of a C o a l , AIChE J . , 3J_, 812-820( 1 985) Cook, H. H. and B r i d g w a t e r , J . , S e g r e g a t i o n i n Spouted Beds, Can. J . Chem. Eng., 56, 636-638(1978) D a v i d s o n , J . F. and H a r r i s o n , D., F l u i d i z e d P a r t i c l e s , Cambridge: The U n i v e r s i t y P r e s s , 1963 D u m i s t r e s c u , C , The Hydrodynamical A s p e c t s of a Spouted Bed M o d i f i e d by the I n t r o d u c t i o n of an A d d i t i o n a l Flow, R e v i s t a de Chimie 2 8 ( 8 ) , Roumania, 746-754(1977) E p s t e i n , N. and Grace, J . R., S p o u t i n g of P a r t i c u l a t e 121 S o l i d s , Chapter 11 i n Handbook of Powder S c i e n c e and Technology, ed. M. E. Fayed and L. O t t e n , Van N o s t r a n d R e i n h o l d Company I n c . , New York, 507-536(1984) E p s t e i n , N., Lim, C. J . and Mathur, K. B., Data and Models f o r Flow D i s t r i b u t i o n and P r e s s u r e Drop i n Spouted Beds, Can. J . Chem. Eng., 56, 436-447(1978) F i e l d , M. A., G i l l , D. W., Morgan, B. B. and Hawskley, P. G. W., Combustion of C o a l V o l a t i l e s , i n Combustion of P u l v e r i z e d C o a l , BCURA, L e a t h e r h e a d , U. K., 1967 G e l d a r t , D., Types of Gas F l u i d i z a t i o n , Powder T e c h n o l o g y , 2 , 285-292(1973) G e l d a r t , D., Hemsworth, A., Sundavadra, R. and W h i t i n g , K. J . , A Comparison of S p o u t i n g and J e t t i n g i n Round and H a l f - r o u n d F l u i d i z e d Beds, Can. J . Chem. Eng., 59, 638-639(1980) G i b b s , B. M. and He d l e y , A. B., Combustion of Large C o a l P a r t i c l e s i n a F l u i d i z e d Bed, i n F l u i d i z a t i o n , eds. J . F. Davidson and D. L. K e a i r n s , Cambridge, E n g l a n d , 235-240(1978) Grace, J . R. and Mathur, K. B., H e i g h t and S t r u c t u r e of the F o u n t a i n Region above Spouted Beds, Can. J . Chem. Eng., 56, 533(1978) H a t a t e , Y . K i n g , D. F., M i g i t a , M. and I k a r i , A., B e h a v i o u r of B ubbles i n a S e m i - c y l i n d r i c a l G a s - s o l i d F l u i d i z e d Bed, Japan J . Chem. Eng., No.2, J_8, 99-104(1985) H e i l , C., Some P r o p e r t i e s of S p o u t - F l u i d Beds, Ph. D. D i s s e r t a t i o n , Eindhoven U n i v e r s i t y of Technology, 122 N e t h e r l a n d , 1982 Khoe, G. K. and Weve,D., V i s u a l O b s e r v a t i o n s of Spouted Bed Gas Combustion Modes and t h e i r Flow Regimes, Can. J . Chem. Eng., 6J_, 460-467 (1983) Khoshnoodi, M. and Weinberg, F. J . , Combustion i n Spouted Beds, Combustion and Flame, 33, 11-21(1978) Kono, H., G r a n u l a t i o n of S m a l l G r a n u l e s from F i n e Powder i n Spouted F l u i d i z e d Bed G r a n u l a t o r s , I n t . Symp. on Powder Te c h o l o g y , Sept. 27 - Oct. 1, 1981, Kyo t o , Japan. K u t l u o g l u , E., Grace, J . R. M u r c h i e , K. W. and Cavanagh, P. H., P a r t i c l e S e g r e g a t i o n i n Spouted Beds, Can. J . Chem. Eng., 61_, 308-316(1983) LaNauze, R. D., Fundamentals of C o a l Combustion, Chapter 19 i n F l u i d i z a t i o n , eds. J . F. D a v i d s o n , R. C l i f t and D. H a r r i s o n , Academic P r e s s , London, 1985 LaNauze, R. D. and Jung, K., The K i n e t i c s of Combustion of P e t r o l e u m Coke P a r t i c l e s i n a F l u i d i z e d Bed Combustor, N i n e t e e n t h Symp. ( I n t . ) on Combustion, 1087-1092(1982) Leung, S. L. and Sm i t h , I . W., The Role of F u e l R e a c t i v i t y i n F l u i d i z e d Bed Combustion, F u e l , 58, 354-360(1979) Lim, C. J . , Gas Re s i d e n c e Time D i s t r i b u t i o n and R e l a t e d Flow P a t t e r n s i n Spouted Beds, Ph.D. d i s s e r t a t i o n , U n i v e r s i t y of B. C , 1975 Lim, C. J . , Barua, S. K., E p s t e i n , N., G r a c e , J . R. and Wa t k i n s o n , A. P., Spouted Bed and S p o u t - f l u i d Bed Combustion of S o l i d s F u e l , i n F l u i d i z e d Combustion, P r o c e e d i n g s of I n t e r n a t i o n a l Conference on Combustion, 1 23 London, E n g l a n d , 72-79(1984) Lim, C. J . and Mathur, K. B., Residence Time D i s t r i b u t i o n of Gas i n Spouted Beds, Can. J . Chem. Eng., 52, 150-153(1974) Madonna, L. A., B o o r n a z i a n , L., B e n c e l , B. K.and Geveke, D., Some C h a r a c t e r i s t i c s of a S p o u t - f l u i d Bed, I n t e r n a t i o n a l C o n f e r e n c e on A l t e r n a t i v e Energy Sources Three, ed. T. No j o t V e z i r o g l o u s , No.6, 3, 257-282(1980) Mamuro, T. and H a t t o r i , H., Flow P a t t e r n of F l u i d i n Spouted Beds, J . Chem. Eng. Ja p . , J_, 1-5(1968) Mathur, K. B. and E p s t e i n , N., Spouted Beds, Academic P r e s s , New Y o r k , 1974 Mathur, K. B. and G i s h l e r , P. E., A Technique f o r C o n t a c t i n g Gases w i t h Coarse S o l i d P a r t i c l e s , AIChE J . , J_, 157-164(1955) McNab, G. S. and B r i d g w a t e r , J . , S o l i d s M i x i n g and S e g r e g a t i o n i n Spouted Beds, P r o c e e d i n g of T h i r d European Conference'on M i x i n g , 125-140(1979) N a g a r k a t t i , A. and C h a t t e r j e e , A., P r e s s u r e and Flow C h a r a c t e r i s t i c s of a Gas Phase S p o u t - F l u i d Bed and t h e Minimum S p o u t - F l u i d C o n d i t i o n , Can. J . Chem. Eng., 52, 185-195(1974) P i c c i n i n i , N., P a r t i c l e S e g r e g a t i o n i n C o n t i n u o u s l y O p e r a t i n g Spouted Bed, i n F l u i d i z a t i o n , ed. J . R. Grace and J . M. Matsen, Plenum P r e s s , New Y o r k , 279-286(1980) P i c c i n i n i , N., B e r h n a r d , A. Campagna, P. and V a l l a n a , F., S e g r e g a t i o n Phenomenon i n Spouted Beds, Can. J . Chem. 124 Eng., 55, 122-125(1977) P i l l a i , K. K., B u r n i n g Rates of C o a l i n F l u i d i z e d Bed Combustion, F u e l , 6_0, 1 63-1 64 ( 1 98 1 a) P i l l a i , K. K., The I n f l u e n c e of C o a l Type on D e v o l a t i 1 i z a t i o n and Combustion i n F l u i d i z e d Beds, J . I n s t . Energy, 54, 142-150(1981b) Pomortseva, A. A. and Baskakov, A. P., Hydrodynamics and Heat T r a n s f e r i n F l u i d i z e d Beds of F i n e l y G r a n u l a r M a t e r i a l w i t h a L o c a l S p o u t i n g Zone, K h i m i y a i T e k h n o l o g i y a T o p l i v i Mase, J_2, 34-37(1970), U.S.S.R. P y l e , D. L., F l u i d i z e d Combustion Models, I n s t i t u t e of F u e l Symposium S e r i e s No.1: F l u i d i z e d Combustion, 1977 Roscoe, J . C , W i t k o w s k i , A. R. and H a r r i s o n , D., The Temperature of Coke P a r t i c l e s i n a F l u i d i z e d Combustor, T r a n s . I n s t . Chem. Eng., 58, 69-72(1980) Ross, I . B. and D a v i d s o n , J . F., The Combustion of Carbon P a r t i c l e s i n a F l u i d i z e d Bed, T r a n s . I n s t . Chem. Eng., 59, 108-114(1981) S t u b i n g t o n , J . F., Comparison of Techniques f o r Measuring the Temperature of Char P a r t i c l e s B u r n i n g i n a F l u i d i z e d Bed, Chem. Eng. Res. Des. 63, 241-249(1985) S u t a n t o , W., E p s t e i n , N. and Grace, J . R., Hydrodynamics of Spouted Beds, Powder Technology, 44, 205-212(1985) Uemaki, 0., Yamada, R. and Kugo, M., P a r t i c l e S e g r e g a t i o n i n a Spouted Bed of B i n a r y M i x t u r e s of P a r t i c l e s , Can. J . Chem. Eng., 6J_, 303-307(1983) V u k o v i c , D. V., H a d z i s m a j l o v i c , Dz. E., G r b a v c i c , Z. B., 125 G a r i c , R. V. and L i t t m a n , H., Flow Regimes f o r S p o u t - f l u i d Beds, Can. J . Chem. Eng.,6_2, 825-829(1984) W h i t i n g , K. J . and G e l d a r t , D ., A Comparison of C y l i n d r i c a l and S e m i - c y l i n d r i c a l Spouted Beds of Coarse P a r t i c l e s , Chem. Eng. S c i . , 35, 1499-1501(1979) Wu, S., Hydrodynamics of Gas S p o u t i n g a t Hig h Temperature, Master T h e s i s , U n i v e r s i t y of B. C , 1986 Ya t e s J . G., Fundamentals of F l u i d i z e d Bed Chemical P r o c e s s , T h e t f o r d P r e s s L t d , T h e t f o r d , N o r f o l k , 1983 Y a t e s , J . G. M a c g i l l i v r y , H. J . and Cheesman, D. J . , C o a l D e v o l a t i l i z a t i o n i n F l u i d i z e d Bed Combustors, Chem. Eng. S c i . , 35, 2360-2361(1980) 8 > z a i—i o 0 0 5 0 100 1 5 0 2 0 0 Rotameter Reading 2 5 0 F i g . A1 C a l i b r a t i o n Curve f o r S p o u t i n g A i r Flow > n to W > n o z n a < o w o ra -3 w w in 0 2 4 6 8 10 Rotameter Reading F i g . A2 C a l i b r a t i o n Curve f o r A u x i l i a r y A i r Flow _ 1 28 APPENDIX I I CALIBRATION CURVES OF COAL FEEDER APPENDIX I I I ESTIMATION OF GAS SAMPLING FLOWRATE The i s o k i n e t i c gas s a m p l i n g t e c h n i q u e , i n which the sam p l i n g v e l o c i t y i s e q u a l t o the l o c a l gas v e l o c i t y , was chosen i n t h i s e x p e r i m e n t . As d i s c u s s e d i n S e c t i o n 7.1, because the oxygen c o n c e n t r a t i o n i s not s e n s i t i v e t o the sam p l i n g f l o w r a t e , a r e p r e s e n t a t i v e s a m p l i n g f l o w r a t e based on the f l o w a t z=H/2, was used throughout the e x p e r i m e n t s . A c c o r d i n g t o Mamuro and H a t t o r i (1968), the gas v e l o c i t y i n the annulus a t h e i g h t z can be e x p r e s s e d as U a ( z ) / U m f = 1 " ( I " z/H m ) 3 ( D where H m, the maximum s p o u t a b l e h e i g h t , can be c o n s i d e r e d t o be e q u a l t o H under the c o n d i t i o n s t e s t e d . U m j i s c a l c u l a t e d t o be 1.14 m/s a t T b = 650 C. From E q . ( 1 ) , U a(H/2)= 1.14x[ 1 - ( 1 - 1 / 2 ) 3 ] = 1.0 m/s The i n t e r s t i t i a l gas v e l o c i t y i n the a n n u l u s , U a', i s U a'=U a(H/2)/e = 1.0/0.53 = 1.88 m/s The gas s a m p l i n g f l o w r a t e , q s a m » a t T b= 650 C i s then ^sam = u a A p r o b e = 1 . 8 8 X 7 T X ( 6 . 3 5 X 1 0 - 3 ) 2 / 4 = 5.95X10" 5 m 3/s Here A p r o D e ^ s t f t e c r o s s - s e c t i o n a l a r e a of the opening on the gas pro b e . A f t e r c o o l i n g , the gas s a m p l i n g f l o w passes through t h e r o t a m e t e r a t T=20 C i s q_ '= 5.95x10" 5x(20+273)/(650+273) 129 130 = 1 .80X 1 0 " 5 m 3/s APPENDIX IV A MODEL FOR ESTIMATING COAL BURNOUT TIMES A l t h o u g h a spouted bed c o n s i s t s of t h r e e r e g i o n s : an a n n u l u s , a spout and a f o u n t a i n , as a f i r s t a p p r o x i m a t i o n o n l y the annulus i s taken i n t o a c c o u n t . R e a c t i o n i n the spout and f o u n t a i n a re n e g l e c t e d due t o the much s h o r t e r t i m e s t h a t c o a l p a r t i c l e s s t a y i n thes e two r e g i o n s . The ti m e s r e q u i r e d f o r p a r t i c l e heat-up and d e v o l a t i l i z a t i o n a r e a l s o i g n o r e d . F o l l o w i n g the r e a s o n i n g of Ross and Davidson (1981), the b u r n i n g r a t e of a s i n g l e c o a l p a r t i c l e i n the annulus can be e x p r e s s e d a s : R c = ffdc2KCa ( 1 ) where R c i s b u r n i n g r a t e of c a r b o n , d c i s c o a l p a r t i c l e d i a m e t e r , K i s o v e r a l l r a t e c o n s t a n t , d e f i n e d i n Eq ( 2 ) , and C Q i s oxygen c o n c e n t r a t i o n i n the a n n u l u s . A c c o r d i n g t o Ross and D a v i d s o n , 1 7 acL — = + (2) K k c ShD g where k c i s t he k i n e t i c r a t e c o n s t a n t , Sh i s sherwood number and Dg i s the gas d i f f u s i o n c o e f f i c i e n t . a and 7 are c o n s t a n t s whose v a l u e s depend on the r e a c t i o n assumed t o be o c c u r r i n g a t the p a r t i c l e s u r f a c e as f o l l o w s : 131 132 a 7 ( i ) C + 1/2 0 2—-CO 1/2 1 ( i i ) C + 0 2 — * C0 2 1 1 ( i i i ) C + C0 2—*• 2CO 1/2 1/2 The f i r s t term i n Eq(2) a c c o u n t s f o r c h e m i c a l r e a c t i o n and the second f o r e x t e r n a l d i f f u s i o n . Because i n spouted beds a t t r i t i o n i s l i k e l y t o cause ash l a y e r s t o be p e e l e d o f f and c o a l p a r t i c l e s t o s h r i n k , Sh i s t r e a t e d as a f u n c t i o n of c o a l p a r t i c l e d i a m e t e r d c , as g i v e n by LaNauze and Jung (1982): Sh = 2e + 0 . 6 9 ( R e / e ) 1 / 2 S C 1 / 3 (3) where Sc i s Schmidt number, Re i s Reynolds number d e f i n e d as Here e i s the bed v o i d a g e and v i s the k i n e t i c gas v i s c o s i t y . The b u r n i n g r a t e can a l s o be e x p r e s s e d as consumption of carbon i n moles per u n i t t i m e : 7 r p _ d c 2 d(d_) R c = — (4) 24 dt where p c i s carbon d e n s i t y which has been assumed t o be c o n s t a n t , c o n s i s t a n t w i t h the n e g l e c t of any r e s i s t a n c e term f o r i n t e r n a l d i f f u s i o n i n Eq(2) above. As a s i m p l e approach, a u n i f o r m c o m p o s i t i o n of gases and of s o l i d s i n the a n n u l u s i s assumed. A m a t e r i a l b a l a n c e over the whole a n n u l u s g i v e s : 133 N 7 T P c d c 2 d ( c L ) UA(C 0 - C e) = ^ °- (5) 24 d t where A i s the c r o s s - s e c t i o n a l a r e a of the combustor, C 0 i s the i n l e t oxygen c o n c e n t r a t i o n , C e i s the e x i t oxygen c o n c e n t r a t i o n , U i s the s u p e r f i c i a l gas v e l o c i t y and N i s the number of c o a l p a r t i c l e s c h a r g e d . From a mass b a l a n c e a t z=H, we can w r i t e C e = ( u a H A a C a H + " s H ^ s H ^ <6> where U a H and U s H a r e the gas v e l o c i t i e s i n the an n u l u s and spout a t h e i g h t H, C a H and C s H a r e the oxygen c o n c e n t r a t i o n s i n the a n n u l u s and spout a t h e i g h t H and A Q, A g a r e the c r o s s - s e c t i o n a l a r e a of the an n u l u s and s p o u t , assumed independent of h e i g h t . From the e x p e r i m e n t a l r e s u l t s d i s c u s s e d i n S e c t i o n 7.2, C s H i s q u i t e u n i f o r m and c l o s e t o C 0, so we s e t C s H = C 0 (7) A r e p r e s e n t a t i v e oxygen c o n c e n t r a t i o n i n the a n n u l u s , C a', may be d e f i n e d by C a' = ( C 0 + C a H ) / 2 (8) C o r r e s p o n d i n g l y , E q ( l ) becomes R c - * d c 2 K C a ' Combining E q s ( l ) ' - ( 8 ) , a d i f f e r e n t i a l e q u a t i o n f o r d c ( t ) can be o b t a i n e d . From (8) C a H = 2 C a ' " C ° ( 9 ) and c o m b ining (6) and (9) y i e l d s c e = [ U a H A a ( 2C a' - C 0 ) + U s H A s C 0 ]/UA S u b s t i t u t i o n of 1 34 U s H A s = U A - U a H A a g i v e s , a f t e r some a l g e b r a 2U. HA C e = C 0 S i L 5 ( C 0 " C ' ) (10) UA S u b s t i t u t i n g Eq(!0) i n t o E q ( 5 ) , we o b t a i n Nrrp.d 2 d(d_) 2 U a H A a ( C 0 - C a' ) = £-£- — S - ' (11) 24 dt Combining E q s ( l ) ' and (3) y i e l d s Pc d ( d c ) C ' = (12) 24K dt S u b s t i t u t i o n of Eq(2) i n t o E q ( l 2 ) g i v e s p 7 ad d(d_) C • = - - C - ( + — £ - ) g -24 k c ShD g d t (13) C ' can be e l i m i n a t e d by combining E q ( l l ) and (13) a f t e r s u b s t i t u t i o n of Eq(3) i n t o ( 1 3 ) : Nrrp d 2 d ( d ) p 7 = 2 U a H A a { C 0 + — [ 24 dt 24 k c ad,, d(d_) ] } ( 1 1 ) ' ( 2e + 0.69( Re/e ) l / 2 S c l / 3 ) D g dt R e a r r a n g i n g and i n t e g r a t i n g E q ( l l ) ' l e a d s t o 135 m P c a d 0 2 P c7d 0 t c = •+ :\ + 2 4 U a H A a C 0 4 8 S h 0 D g C 0 2 4 k c C 0 (14) a f t e r s u b s t i t u t i n g 6m N = -T d 03 p c Here t c i s the burnout t i m e , d 0 i s the i n i t i a l c o a l p a r t i c l e d i a m e t e r , and X, which a c c o u n t s f o r changes of Sherwood number d u r i n g c o m b u s t i o n , i s a f u n c t i o n of i n i t i a l Sherwood number, S h 0 : 4Sh 0 S h 0 3 X = — [ 3 e S h 0 2 + 1 2 e 2 S h 0 ( S h 0 - 2e )• 3 S h 0 44e 3 - 8 e 3 l n ( ) ] (15) 2e 3 For a change of S h 0 from 3 t o 5, X i s i n the range 1.17 t o 1.22 f o r e = 0.53. As S h 0 approaches the l i m i t 2e, a c o n s t a n t , X i s e q u a l t o 1.0. As p o i n t e d out by Y a t e s (1983), f o r the temperature and p r e s s u r e c o n d i t i o n s t e s t e d , the r e a c t i o n which i s most l i k e l y t o o c c u r a t the p a r t i c l e s u r f a c e (see F i g . 9.3) i s C + 1/2 0 2—"CO Hence we may s e t a and 7 e q u a l t o 1/2 and 1, r e s p e c t i v e l y . W i t h t h e s e v a l u e s , Eq(14) becomes 136 m P c d ° 2 p c d ° t c = + x + 2 4 U a H A a C 0 9 6 S h 0 D g C 0 2 4 k c C 0 (16) T h i s e q u a t i o n can be used t o e s t i m a t e burnout t i m e s . At a bed t e m p e r a t u r e of 810 C, the bed had reached i t s maximum s p o u t a b l e bed depth. Hence U a H i s a p p r o x i m a t e l y e q u a l t o U m f ( E p s t e i n e t a l , l 9 7 8 ) . The k i n e t i c r a t e c o n s t a n t k c i s e s t i m a t e d from the well-known e q u a t i o n of F i e l d e t a l d 9 6 7 ) : 149227 k r = 595T n exp( ) (17) P RT p where Tp i s the p a r t i c l e t e mperature and R i s the gas c o n s t a n t . The e x p e r i m e n t a l c o n d i t i o n s of t h i s work and of Ross and Davidson (1981) a r e l i s t e d i n T a b l e A1. T y p i c a l v a l u e s of the d i f f e r e n t terms of t c c a l c u l a t e d from E q ( l 6 ) a r e g i v e n i n T a b l e A2. For c o m p a r i s o n , v a l u e s a r e a l s o g i v e n f o r the c o r r e s p o n d i n g e q u a t i o n d e r i v e d by Ross and D a v i d s o n : m t = : 12AC 0[ U - ( U - U m f ) e x p ( - X ) ] p d 0 2 P c d 0 + + — 9 6 S h 0 D g C 0 2 4 k c C 0 (18) where the f i r s t term d i f f e r s from the f i r s t term i n E q ( l 6 ) because of the i n t e r p h a s e (bubble phase t o dense phase) mass t r a n s f e r r e s i s t a n c e which i s a f e a t u r e of b u b b l i n g f l u i d i z e d beds, X b e i n g the number of i n t e r p h a s e mass t r a n s f e r u n i t s 137 TABLE A l EXPERIMENTAL CONDITIONS VARIABLE T f a (C) T p (C) m (kg/m 3) A (m 2) A a (m 2 U (m/s) U a H (m/s) Umf ( m/ s> X p c (kg/m 3) D g (m 2/s) C 0 (kmol/m 3) Sh Sand S i z e (mm) p s (kg/m 3) e Sc PRESENT WORK 810 960 6.28- 10-" 9 . 1 2 - 1 0 - 3 8 . 1 4 - 1 0 - 3 1 .50 1.14 1.14 403 2.02-10- f l 2.33- 10' 3 3-5 1.65-2.36 2605 0.53 0.896 ROSS AND DAVIDSON 900 1030 6.28- 10-" 8.11 - 10" 3 0.50 0.11 2.0 720 2.08-10-" 2 . 1 8 - 1 0" 3 1 .75 0.55 2650 0.50 138 TABLE A2 COMPARISON OF CALCULATED BURNOUT TIMES FOR DIFFERENT TERMS ( i n seconds) PRESENT WORK d 0 (mm) 0.55 1.10 2.20 F i r s t Term i n Eq(16) 1 .30 1 .30 1 .30 Second Term i n E q ( l 6 ) 1.31 4.17 12.96 T h i r d Term i n E q 0 6) 1 1 .32 22.65 45.30 T o t a l ( t c ) 13.9 28.1 59.6 ROSS AND DAVIDSON F i r s t Term i n E q ( l 8 ) 6.60 6.60 6.60 Second Term i n E q ( l 8 ) 2.86 1 1 .44 45.75 T h i r d Term i n E q ( l 8 ) 9.85 19.69 39.38 T o t a l ( t c ) 19.3 37.7 91 .7 d e f i n e d by Davidson and H a r r i s o n (1963). APPENDIX V EXPERIMENTAL DATA Run 1 8 C o n d i t i o n s : T b=640 C, H o=0.3 m U/U m s=1.1, U m s=1.1 m/s ( a t 640 C) Sand s i z e : 1.65-2.36 mm C o a l s i z e : 0.85-1.18 mm A x i a l Oxygen C o n c e n t r a t i o n s : z (m) 0 2 (%v/v) spout a n n u l u s annulus (q/Q T=0) (q/Q T=0) (q/Q T=0 0.10 19.5 18.5 18.8 0.15 - 19.6 19.0 0.20 19.0 19.5 18.2 0.25 17.5 17.5 16.5 0.30 17.0 14.5 14.0 0.35 - 8.0 10.0 0.40 17.5 8.2 11.5 0.45 - 5.5 10.5 0.50 17.0 7.0 12.0 0.55 - 12.0 12.0 0.60 17.0 14.0 12.5 0.65 -0.70 - 15.0 12.3 140 141 Run 21 C o n d i t i o n s : T b = 8 l 0 C, H o=0.3 m Sand s i z e : 1.65-2.36 mm Burnout Times: d 0 (mm) t c (s) °/ Ums = 1- 1 U / U m s = 1 - 3 U/ Ums= 1' 3 U / U m s = 1 - 3 U/ Ums q/QT=0 q/QT=0 q/QT=0.1 q/QT=0.3 q/QT= 0.55 14.0 16.6 18.0 18.8 20.7 1.10 24.5 24. 1 27.3 23.5 34.7 1 .55 42.2 38.8 42.9 42.6 43.4 2.20 59.0 60.6 57.4 59.6 65.2 Run 22 C o n d i t i o n s : Tfa=650 C, H o=0.3 m U/U m s=1.2, U m s=1.1 m/s ( a t 650 C) Sand s i z e : 1.65-2.36 mm C o a l s i z e : 0.60-1.65 mm A x i a l Temperatures: z (m) T (C) spout a n n u l u s annulus a n n u l u s (q/Q T=0) (q/Q T=0) (q/Q T=0.2) (q/Q T=0.4) 0. 10 - 675 660 520 0.15 687 715 712 695 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 688 686 686 693 890 847 805 714 706 708 714 870 873 850 813 775 71 1 708 7 1 5 735 830' 834 815 784 760 709 717 733 773 815 815 800 771 743 Run 26 C o n d i t i o n s : T b=650 C, H o=0.3 m U/U m s=1.2, U m s=1.1 m/s ( a t 650 C) Sand s i z e : 1.65-2.36 mm C o a l s i z e : 0.60-0.85 mm A x i a l Oxygen C o n c e n t r a t i o n s : z (m) 0 2 (%v/v) spout a n n u l u s annulus a n n u l u s (q/Q T=0) (q/Q T=0) (q/Q T=0.2) (q/Q T=0, 0.075 19.0 -0.10 - 18.3 18.4 19.0 0.15 19.5 17.0 17.4 18.5 0.20 19.5 17.0 16.8 17.9 0.25 18.5 16.4 15.5 17.2 0.30 18.5 12.5 11.5 14.0 0.35 - 5.5 6.5 7.6 0.40 16.0 7.0 8.0 8.2 0.45 - 7.4 8.5 8.3 0.50 15.0 7.5 8.0 7.9 0.55 - - 8.2 7.9 0.60 13.8 9.5 8.5 8.1 0.70 13.0 9.0 8.2 7.5 Run 28 C o n d i t i o n s : T^=660 C, H o=0.3 m ( s l u g g i n g regime) U/U m f=1.2, U m f=0.7 m/s ( a t 660 C) Sand s i z e : 1.18-1.65 mm C o a l s i z e : 0.85-1.18 mm A x i a l Oxygen C o n c e n t r a t i o n s : z (m) 0 2 (%v/v) c e n t r e l i n e a nnulus annulus (q/Q T= 0) (q/Q T= 0) (q/Q T= 0, 0.075 19.5 0.10 19.7 19.0 20.4 0.15 19.6 19.0 20.3 0.20 19.4 18.5 19.0 0.25 18.6 15.0 17.0 0.30 17.2 14.2 15.0 0.35 15.4 11.6 12.8 0.40 11.9 7.2 9.5 0.45 11.0 6.5 9.0 0.50 10.5 6.6 9.4 0.55 - 7.2 9.0 0.60 9.8 - -0.65 - 8.2 9.4 0.70 9.4 — A x i a l Temperatures: z (m) T (C) c e n t r e l i n e a n nulus annulus (q/Q T=0) (q/Q T=0) (q/Q T=0 0.075 640 - -0.10 664 623 570 0.15 664 650 652 0.20 655 662 662 0.25 655 663 663 0.30 659 662 667 0.35 665 668 677 0.40 738 778 740 0.45 754 769 747 0.50 735 735 714 0.55 - 710 690 0.60 691 0.65 - 678 660 0.70 626 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0058691/manifest

Comment

Related Items