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UBC Theses and Dissertations

Spouted bed process for suplhur-coating fertilizers Weiss, Phillippe J. 1981

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SPOUTED BED PROCESS FOR SULPHUR-COATING FERTILIZERS by PHILLIPPE J . WEISS B.A.Sc., N a t i o n a l U n i v e r s i t y o f E n g i n e e r i n g , P e r u , 1971 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES Ch e m i c a l E n g i n e e r i n g U n i v e r s i t y o f B r i t i s h C o l u m b i a 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 t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1981 (c; P h i l l i p p e J . W e i s s , 1981 I n 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 o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e 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 a n d s t u d y . I f u r t h e r a g r e e 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 o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s m a y b e g r a n t e d b y t h e h e a d o f my d e p a r t m e n t o r b y h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f 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 n o t b e 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 . D e p a r t m e n t o f T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a 2 0 7 5 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V 6 T 1W5 11 /no, \ ABSTRACT The work u n d e r t a k e n was f o r t h e p u r p o s e o f d e v e l o p i n g r e l a t i o n s h i p s between key v a r i a b l e s i n s u l p h u r c o a t i n g o f u r e a t o p e r m i t d e s i g n o f a se m i - c o m m e r c i a l s c a l e p l a n t . I n o r d e r t o g e n e r a t e s t u d y d a t a , i t was n e c e s s a r y t o c o m p l e t e l y r e d e s i g n and r e b u i l d t h e e x i s t i n g s p o u t e d bed c o a t i n g f a c i l i t i e s owing t o d e f i c i e n c i e s e n c o u n t e r e d by p r e v i o u s r e s e a r c h e r s . The s p o u t e d bed ( u s u a l l y g r a n u l a t e d u r e a ) was c o n t a i n e d i n a c y l i n d r i c a l column, 0.154 m ID x 0.91 m h i g h , w i t h a c o n i c a l bottom. M o l t e n s u l p h u r was s p r a y e d t h r o u g h a s p e c i a l l y d e s i g n e d n o z z l e i n t o t h e bottom o f t h e bed c o n c u r r e n t l y w i t h t h e s p o u t i n g a i r . The a i r c o u l d be p r e h e a t e d and s p e c i a l p r e c a u t i o n s were t a k e n t o remove p a r t i c u l a t e m a t t e r from t h e o f f - g a s l e a v i n g t h e bed. The p i l o t p l a n t was o n l y c a p a b l e o f o p e r a t i n g i n t h e b a t c h - w i s e mode. The p r o d u c t q u a l i t y was e x p r e s s e d i n terms o f t h e 7-day d i s s o l u t i o n o f a sample immersed i n w a t e r under c o n d i t i o n s s p e c i f i e d by t h e Tennessee V a l l e y A u t h o r i t y . The dependence o f t h e d i s s o l u t i o n r a t e on t h e f o l l o w i n g o p e r a t i n g p a r a m e t e r s was examined: bed t e m p e r a t u r e (58-85°C), s u l p h u r t e m p e r a t u r e (157-159°C), s u l p h u r f l o w r a t e (34-260 g/min), a t o m i z i n g a i r f l o w r a t e (0.402-0.785 m 3 / h r ) , bed de p t h (0.28-0.47 m). The bed t e m p e r a t u r e had t h e g r e a t e s t e f f e c t on p r o d u c t q u a l i t y . The q u a l i t y i n c r e a s e s ( i . e . t h e 7-day d i s s o l u t i o n r a t e d e c r e a s e s ) up t o a bed t e m p e r a t u r e o f a p p r o x i m a t e l y 80°C and t h e n d e c r e a s e s a g a i n . - S i m i l a r l y , t h e p r o d u c t q u a l i t y improves w i t h s u l p h u r i n j e c t i o n r a t e p r o v i d e d a l l o t h e r o p e r a t i n g v a r i a b l e s a r e k e p t c o n s t a n t . These measurements c o u l d be e x p l a i n e d i n terms o f t h e t r a n s i t i o n o f s u l p h u r from t h e rh o m b i c t o t h e m o n o c l i n i c form and a l s o t h e d r o p l e t s i z e w h i c h i i strongly affects the cooling rates of the sulphur f i l m and hence the tr a n s i t i o n rates. Electron micrographs are presented to support these explanations. A technical and preliminary economic analysis was performed for two semi-commercial coating f a c i l i t i e s with production capacities of 0.78 and 1.26 t/day. Both processes were assumed to operate i n the batch-wise mode. The production costs per ton of sulphur-coated urea were estimated to be $523.00 and $448.00 for the two plants. However, r e l a t i v e l y minor process modifications would enable continuous operation and lead to greatly increased plant capacities as well as reduced operating costs. DEDICATED TO MY WIFE ROSANNA AND TO MY PARENTS i v T i t l e Table of Contents Abstract Table of Contents List of Tables List of Figures List of Plates Acknowledgement 1. INTRODUCTION 1.1 Controlled Release Fert i l i z e r s 1.2 The TVA Process 1.3 The UBC Spouted Bed Process 1.4 Objectives of this Thesis 2. LITERATURE REVIEW 2.1 Industrial Process for Sulphur Coating of Urea 2.1.1 TVA Process Development 2.1.2 TVA Demonstration Scale Plant 2.2 The University of British Columbia (UBC) Proces 2.3 Select Physical Properties of Sulphur 3. EXPERIMENTAL APPARATUS AND PROCEDURE 3.1 Apparatus 3.1.1 The spouted bed 3.1.2 The sulphur supply system a) The sulphur melter b) The f i l t e r c) Sulphur rotameter d) Sulphur lines e) Nitrogen supply T i t l e Page 3.1.3 The Nozzle Assembly 42 a) The perforated plate 42 b) The bayonet 42 c) The nozzle 50 3.1.4 Dust Collectors 50 3.1.5 Air and supplies 50 3.2 Experimental Procedures 53 3.2.1 Start Up 53 3.2.2 Coating Procedure 53 3.2.3 Shutdown 57 3.2.4 Special Operations 57 3.2.5 Measurement of Operating Variables 57 a) Fluid flow measurement 57 b) Temperature measurement 57 c) Solids elutriation 59 d) Raw materials and product weight 59 e) Spout height and bed weight level 59 3.2.6 Analysis and Quality Control 59 a) Raw materials 59 b) Product Analysis 59 b.l Dissolution test 62 b.2 Total sulphur content 62 b.3 Dissolution rate, 62 4. RESULTS AND DISCUSSION 64 4.1 Calculation of the Average Sulphur Flow Rate 64 4.2 Effect of Sulphur Flow Rate on Dissolution Value, 65 4.3 Corrected Dissolution Value, D^ 67 4.4 Effect of Atomizing Air Flow Rate on D^,- 68 v i T i t l e Page 4 . 5 E f f e c t o f Bed T e m p e r a t u r e on 68 4 . 6 E l e c t r o n M i c r o g r a p h s o f S u l p h u r C o a t e d U r e a 68 4 . 6 . 1 E f f e c t o f bed t e m p e r a t u r e on C o a t A p p e a r a n c e 73 4 . 6 . 2 E f f e c t o f s u l p h u r f l o w r a t e on C o a t A p p e a r a n c e 73 4 . 7 Q u a l i t a t i v e M o d e l o f C o a t i n g P r o c e s s 79 4 . 7 . 1 D r o p l e t s i z e 79 4 . 7 . 2 S p r e a d i n g o f s u l p h u r d r o p l e t s 79 4 . 7 . 3 S e a l i n g o f p o r e s 82 4 . 8 E f f e c t o f Bed We igh t on D' 82 4 . 9 E f f e c t o f S i l i c o n e A d d i t i v e on D ^ 86 4 . 1 0 E f f e c t o f T ime on D 2 5 90 4 . 1 1 E f f e c t o f S u b s t r a t e ( F e r t i l i z e r M a t e r i a l ) on D ^ 91 5 . CONCEPTUAL DESIGN OF A SEMICOMMERCIAL COATING F A C I L I T Y 93 5 .1 T e c h n i c a l D e s i g n o f S e m i c o m m e r c i a l C o a t i n g F a c i l i t i e s 93 5 . 1 . 1 D e s i g n C o n s i d e r a t i o n s 93 a) S p o u t e d Bed 93 b ) Min imum s p o u t i n g v e l o c i t y 94 c ) S p o u t i n g a i r and b l o w e r r e q u i r e m e n t s 94 d) E s t i m a t i o n o f h e a t i n g and c o o l i n g t i m e s 97 e) E s t i m a t i o n o f c o a t i n g t i m e 97 5 . 2 E n v i r o n m e n t a l and S a f e t y F e a t u r e s 98 5 . 3 E c o n o m i c s 98 5 . 4 C o n t i n u o u s o p e r a t i o n 100 6 . CONCLUSIONS AND RECOMMENDATIONS 102 6 .1 L a b o r a t o r y T e s t s 102 6 . 2 S e m i c o m m e r c i a l U n i t s 102 6 . 3 Recommendat ions 102 7 . REFERENCES 104 v i i T i t l e Page Appendices 106 I. Dissolution Test Results and Average Operating Conditions 107 I I . Calibration Curves for Rotameters and Refractometer 119 v i i i L i s t o f T a b l e s T a b l e Page 2 . 1 Opt imum O p e r a t i n g T e m p e r a t u r e s f o r S u l p h u r C o a t i n g o f U r e a i n t h e TVA 900 k g / h o u r P l a n t 15 2 . 2 Summary o f D i s s o l u t i o n R a t e s f o r P n e u m a t i c and H y d r a u l i c A t o m i z a t i o n ( w i t h and w i t h o u t s e a l a n t ) TVA PROCESS 17 2 . 3 M a i n P r o c e s s V a r i a b l e s and P r o d u c t C h a r a c t e r i s t i c s o f TVA D e m o n s t r a t i o n S c a l e P l a n t ( C a p a c i t y : 9 . 0 7 m T o n / h r ) 20 2 . 4 P h y s i c a l and C h e m i c a l P r o p e r t i e s o f S u l p h u r 33 2 . 5 P r o p e r t i e s o f Common S u l p h u r A l l o t r o p e s 34 3.1 F l u i d F l o w measurement equ ipmen t 58 3 . 2 Cominco U r e a S c r e e n A n a l y s i s 58 3 . 3 Cominco Ammonium P h o s p h a t e A n a l y s i s 61 4 . 1 D i s s o l u t i o n vs A t o m i z i n g A i r F l o w R a t e ( S u l p h u r C o a t e d 70 U r e a ) 4 . 2 D i s s o l u t i o n vs Bed T e m p e r a t u r e ( S u l p h u r C o a t e d U rea ) 72 4 . 3 E f f e c t o f Bed We igh t on D ^ 5 ( S u l p h u r C o a t e d U rea ) 86 4 . 4 S o l i d s C i r c u l a t i o n i n a S p o u t e d Bed f o r S u l p h u r C o a t i n g 88 o f U r e a 4 . 5 E f f e c t o f S i l i c o n e A d d i t i v e on D ^ 5 ( S u l p h u r C o a t e d U r e a ) 8 9 4 . 6 E f f e c t o f T ime on D^^ ( S u l p h u r C o a t e d U r e a ) 90 4 . 7 E f f e c t o f Bed T e m p e r a t u r e on D ^ (Ammonium P h o s p h a t e ) 91 5 .1 S p e c i f i c a t i o n s f o r a B a t c h w i s e P l a n t P r o d u c i n g 1 9 6 . 3 t / y e a r 95 o f S u l p h u r C o a t e d U r e a 5 . 2 S p e c i f i c a t i o n s f o r a B a t c h w i s e P l a n t P r o d u c i n g 3 1 4 . 8 t / y e a r o f S u l p h u r C o a t e d U r e a ^6 5 . 3 P r e l i m i n a r y E c o n o m i c s o f S e m i c o m m e r c i a l F a c i l i t i e s f o r S u l p h u r C o a t i n g o f U r e a 5 . 5 C o m p a r i s o n o f B a t c h w i s e and C o n t i n u o u s O p e r a t i o n o f S u l p h u r C o a t i n g F a c i l i t i e s . 99 5 . 4 Raw M a t e r i a l s R e q u i r e m e n t s and C o s t s 100 101 1.1 D i s s o l u t i o n T e s t R e s u l t s ' 107 i x T i t l e Page 1.2 Average Operating Conditions 114 x L i s t o f F i g u r e s F i g u r e s Page 1.1 F l o w s h e e t o f TVA P r o c e s s f o r S u l p h u r C o a t i n g o f Urea 3 (900 kg/hour F a c i l i t y ) 1.2 UBC Spouted Bed 5 2.1 TVA P r o c e s s f o r S u l p h u r C o a t i n g o f Urea (136 kg/hour F a c i l i t y ) 13 2.2 I n t e r n a l s o f t h e C o a t i n g Drum, TVA P r o c e s s (900 kg/hour F a c i l i t y ) 2.3 S u l p h u r S p r a y Header System and Spray N o z z l e s D e t a i l 14 TVA P r o c e s s , (900 kg/hour F a c i l i t y ) 2.4 E f f e c t o f S u b s t r a t e Temperature on D i s s o l u t i o n Rates 16 TVA P r o c e s s ( S h i r l e y and M e l i n e ) 1 3 2.5 TVA D e m o n s t r a t i o n S c a l e P l a n t f o r S u l p h u r C o a t i n g o f 19 Urea (9.07 m t o n / h o u r ) 2.6 UBC Spouted Bed f o r S u l p h u r C o a t i n g o f Urea ( I n i t i a l P r o t o t y p e d e s i g n e d by Mathur and Meisen) 22 2.7 UBC Spouted Bed f o r S u l p h u r C o a t i n g o f Urea ( M o d i f i c a t i o n d e s i g n e d by Mathur, M e i s e n and Zee) 24 2.8 N o z z l e arrangement (Mathur, M e i s e n and Zee) 25 2.9 UBC Spouted Bed f o r S u l p h u r C o a t i n g o f Urea ( M o d i f i c a t i o n d e s i g n e d by Mathur, M e i s e n and Lim) 28 2.10 Steam Heated S u l p h u r M e l t e r (Mathur, M e i s e n and Lim) 29 2.11 N o z z l e arrangement (Mathur, M e i s e n and Lim) 30 2.12 V i s c o s i t y o f S u l p h u r , Low Temperature Range 35 3.1 S i m p l i f i e d d i a g r a m o f UBC Spouted Bed F a c i l i t y Used i n t h i s Work ( D e s i g n e d by Me i s e n and Weiss) 37 3.2 Spouted Bed Column (Mathur, M e i s e n , and Lim) 38 3.3 S h u t t e r Assembly (Mathur, M e i s e n , and Lim) 39 3.4 (a) S e c t i o n a l View o f S u l p h u r M e l t e r 40 3.4 (b) S u l p h u r M e l t e r Top View 41 3.5 (a) S e c t i o n a l View o f S u l p h u r F i l t e r 43 3.5 ( b l Top P l a t e o f S u l p h u r F i l t e r 44 x i 3.6 (a) Sectional View of Sulphur Rotameter 45 3.6 (b) Various Views of Rotameter ends 46 3.6 (c) General View of Sulphur Rotameter 47 3.7 Sectional View of Nozzle Arrangement and General Assembly 48 3.8 Perforated Plate, Upper Flange and Nozzle Sectional View 49 3.9 Dust Collection System 51 3.10 Air and Sulphur Lines 52 3.11 Steam and Condensate System Layout 54 3.12 Thermocouple location 60 3.13 D 2 5 Determination 4.1 Effect of Sulphur Flow Rate on D 2 5 66 4.2 Effect of Atomizing Air Flow Rate on Normalized Dissolution 69 Rate, D 2 5 4.3 Effect of Bed Temperature on D 2 5 71 4.4 First Layer of Sulphur Onto Urea Surface (Low Temperature) 83 4.5 First Layer of Sulphur Onto Urea Surface (High Temperature) 83 4.6 Deposition of Second Layer of Sulphur 84 4.7 Effect of Bed Weight on D^5 8 7 4.8 Effect of Bed Temperature on D^5 of Sulphur-Coated 92 Ammonium Phosphate 11.1 Calibration Curve for Cooling Air Rotameter 120 11.2 Calibration Curve for Spouting Air Rotameter 121 11.3 Calibration Curve for Atomizing Air Rotameter 122 11.4 Calibration Curve for Sulphur Rotameter 123 11.5 Abbe Refractometer Calibration for Aqueous Solutions of Urea 124 11.6 Abbe Refractometer Calibration Curve for Aqueous Solutions 125 ,of Ammonium Phosphate x i i L i s t of Plates Plates 4.1 Uncoated Urea Surface (Magnification: lOOx) 4.2 Uncoated Urea Surface (Magnification: 400x) 4.3 Uncoated Urea Surface (Magnification: 2000x) 4.4 Sulphur Coated Urea (Magnification: 20x) Bed Temperature 4.5 Sulphur Coated Urea (Magnification: 20x) Bed Temperature 4.6 Sulphur Coated Urea Surface (Magnification: lOOOx) Bed Temperature: 58°C 4.7 Sulphur Coated Urea Surface (Magnification: lOOOx) Bed Temperature: 67°C 4.8 Sulphur Coated Urea Surface (Magnification: lOOOx) Bed Temperature: 76°C 4.9 Sulphur Coated Urea Surface (Magnification: lOOOx) Bed Temperature: 67°C Q = 94 g/min, Q = 0.594 m3/hr S 3. L 4.10 Sulphur Coated Urea Surface (Magnification: 800x) Bed Temperature 76°C Q = 94 g/min, Q = 0.594 m3/hr S 3.T 4.11 Sulphur Coated Urea Surface (Magnification: 800x) Bed Temperature 77°C Q =187.9 g/min, Q = 0.278 m3/hr S Si c 4.12 Sulphur Coated Urea Surface (Magnification: 800x) Bed Temperature 77°C Q = 273.4 g/min, Q = 0.278 m3/hr 5 3.X 4.13 Pore i n a Sulphur Coating (Magnification: 400x) x i i i ACKNOWLEDGEMENT I w i s h t o thank Dr. A x e l M e i s e n , under whose d i r e c t i o n t h i s i n v e s t i g a t i o n was u n d e r t a k e n , f o r h i s h e l p f u l g u i d a n c e and encouragement i n a l l s t a g e s o f t h i s work. I a l s o w i s h t o thank t h e f a c u l t y and s t a f f o f t h e C h e m i c a l E n g i n e e r i n g Department o f t h e U n i v e r s i t y o f B r i t i s h C o lumbia f o r t h e i r w i l l i n g a s s i s t a n c e and c o o p e r a t i o n . The a s s i s t a n c e p r o v i d e d by t h e p e r s o n n e l o f t h e Workshop and t h e S t o r e s o f t h e C h e m i c a l E n g i n e e r i n g Department i s h i g h l y a p p r e c i a t e d . I am v e r y g r a t e f u l t o t h e Department o f M e t a l l u r g y o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a f o r l e t t i n g me work w i t h t h e i r S c a n n i n g E l e c t r o n M i c r o s c o p e . The f i n a n c i a l s u p p o r t p r o v i d e d by t h e Government o f B r i t i s h C o l u m b i a ( t h r o u g h t h e G.R.E.A.T. scheme) and Green V a l l e y F e r t i l i z e r s and C h e m i c a l Co. L t d . i s g r a t e f u l l y acknowledged. x i v 1. INTRODUCTION Crops r e q u i r e v a r i o u s elements suc h as n i t r o g e n , p o t a s s i u m , phosphorous and s u l p h u r f o r p r o p e r growth. To e n s u r e t h a t adequate n u t r i e n t l e v e l s a r e m a i n t a i n e d i n t h e s o i l , f e r t i l i z e r s have t o be added. Among n i t r o g e n f e r t i l i z e r s , u r e a has t h e h i g h e s t n i t r o g e n c o n t e n t by w e i g h t ( 4 6 . 6 % * ) . Most n i t r o g e n f e r t i l i z e r s i n p r e s e n t use a r e h i g h l y w a t e r s o l u b l e and t h e r e f o r e t e n d t o be l o s t by r u n - o f f o r l e a c h i n g b e f o r e t h e y can be a s s i m i l a t e d by t h e p l a n t s . F o r example, i n t h e case o f u r e a , t y p i c a l l y 50% o f t h e s u p p l i e d n i t r o g e n i s a b s o r b e d b u t , i n r e g i o n s w i t h h i g h i n t e r -m i t t e n t r a i n f a l l , t h e f i g u r e may be as low as 2 5 % ^ . F e r t i l i z e r r u n - o f f n o t o n l y r e p r e s e n t s a l o s s o f v a l u a b l e u r e a b u t may a l s o s t i m u l a t e u n d e s i r a b l e growth o f weeds and a l g a e i n l o c a l b o d i e s o f w a t e r . M i n i m i z i n g t h e r u n - o f f p r o b l e m by r e p e a t e d a p p l i c a t i o n s o f s m a l l f e r t i l i z e r dosages i s f r e q u e n t l y u n e c o n o m i c a l . Due t o t h e h i g h c o s t o f l a b o u r , r e p e a t e d f e r t i l i z e r a p p l i c a t i o n s ( i . e . s p r e a d i n g ) i s a major c o s t i n t h e use o f f e r t i l i z e r s . An a l t e r n a t e approach i s t o d e v e l o p f e r t i l i z e r s w i t h c o n t r o l l e d and s l o w n u t r i e n t r e l e a s e r a t e s w h i c h match c r o p r e q u i r e m e n t s . 1.1 C o n t r o l l e d R e l e a s e F e r t i l i z e r s One method o f a c h i e v i n g c o n t r o l l e d n u t r i e n t r e l e a s e i s t o e n c a p s u l a t e g r a n u l a r f e r t i l i z e r s w i t h a s l i g h t l y p o r o u s , i n s o l u b l e c o a t . M c C l e l l a n and S c h e i b ^ o f t h e Tennesee V a l l e y A u t h o r i t y (TVA), as w e l l as o t h e r s ^ , have examined a v a r i e t y o f f e r t i l i z e r - c o a t c o m b i n a t i o n s b u t , t h u s f a r , o n l y s u l p h u r * Weight p e r c e n t a g e s a r e used t h r o u g h o u t t h i s t h e s i s . 1 2 c o a t e d u r e a has a t t r a c t e d major i n t e r e s t and i s b e i n g p r o d u c e d c o m m e r c i a l l y . f 51 S u l p h u r i s an abundant, low c o s t m a t e r i a l w h i c h , under c e r t a i n c i r c u m -s t a n c e s , i s c a p a b l e o f f o r m i n g a good c o a t . I n a d d i t i o n , i t i s an e s s e n t i a l p l a n t n u t r i e n t and must t h e r e f o r e be added t o s o i l s d e f i c i e n t i n s u l p h u r , However, t h e low s t r e n g t h o f t h e s u l p h u r and i t s p o o r a d h e s i o n t o u r e a c r e a t e problems i n p r o d u c i n g a h i g h q u a l i t y , s l o w - r e l e a s e f e r t i l i z e r . Two p r o c e s s e s have been s t u d i e d f o r m a n u f a c t u r i n g s u l f u r c o a t e d u r e a , i . e . t h e TVA r o t a r y drum p r o c e s s and t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a (U.B.C.) s p o u t e d bed p r o c e s s . B r i e f d e s c r i p t i o n s a r e g i v e n below w i t h f u r t h e r d e t a i l s b e i n g p r o v i d e d i n t h e n e x t c h a p t e r . 1.2 The TVA P r o c e s s The p r o c e s s d e v e l o p e d by TVA (See F i g . 1.1) c o n s i s t s e s s e n t i a l l y o f a r o t a r y drum i n t o w h i c h p r e h e a t e d (52-79°C) u r e a i s f e d ; m o l t e n s u l p h u r O 154°C) i s s p r a y e d o n t o t h e u r e a g r a n u l e s t h r o u g h a t o m i z i n g n o z z l e s . The p r o d u c t l e a v i n g t h e drum s t i l l has i m p e r f e c t i o n s i n t h e s u l p h u r c o a t w h i c h a r e s e a l e d w i t h wax i n a subsequent o p e r a t i o n . The TVA p r o c e s s was s e l e c t e d by C a n a d i a n I n d u s t r i e s L i m i t e d ( C I L) f o r i t s p l a n t i n C o u r t r i g h t , O n t a r i o and a s i m i l a r , b u t l a r g e r f a c i l i t y , has been b u i l t i n Alabama, U.S.A. The s u l p h u r c o a t e d u r e a m a n u f a c t u r e d by CIL i s r e g i s t e r e d under t h e t r a d e name o f SCU. The q u a l i t y o f s u l p h u r c o a t e d u r e a may be e v a l u a t e d by means o f l a b o r a t o r y and f i e l d t e s t s . I n t h e l a b o r a t o r y t e s t s , t h e q u a l i t y o f c o a t e d u r e a i s u s u a l l y e x p r e s s e d i n terms o f D 2 5 > i . e . t h e p e r c e n t a g e o f u r e a w h i c h d i s s o l v e s when 50g o f c o a t e d u r e a c o n t a i n i n g 25% s u l p h u r a r e p l a c e d i n 250 ml o f w a t e r a t 37.8°C f o r 7 days. D i s s o l u t i o n v a l u e s o f c o a t e d u r e a p r o d u c e d by t h e TVA p r o c e s s range GRANULAR UREA Ij PREHEATING DRUM (RADIANT HEAT) 6 3 - 6 6 ° C I 5 2 - 7 9 ° C ) SULFUR FROM •TANK CAR I 5 4 . 4 ° ( ( I 5 4 . 4 ° C ] SULFUR COATING DRUM SULFUR PUMP »c\ ° C ) \ 8 - S P R A Y 7 4 - 7 7 ° NOZZLES ( 7 4 - 9 0 ° 'HEATED ATOMIZING AIR (NO AIR USED WITH HYDRAULIC SPRAY NOZZLES) WAX |COATING| DRUM 07 - 110 ° C '7 110 °C ) PREHEATED WAX I 6 - 3 8 ° C (16 3 8 ° C ) INLET + AIR 6 8 - 7 l ° C (68 8 2 ° C ) DISCHARGE AIR COOLER 4 I ° C ( 4 I ° C MAX MAX) CONDITIONING AGENT L. CONDITIONING DRUM 1 SCALPINGj SCREEN PRODUCT F i g u r e 1.1: F l o w s h e e t o f TVA P r o c e s s f o r S u l p h u r C o a t i n g o f Urea (900 kg/hour F a c i l i t y ) ( F i g u r e s i n p a r e n t h e s i s i n d i c a t e p r o c e s s t e m p e r a t u r e s f o r h y d r a u l i c s p r a y i n g . ) from about 17.5% t o 35%. The e x a c t f i g u r e depends p r i m a r i l y on t h e c o a t i n g t e m p e r a t u r e , s u l p h u r a t o m i z a t i o n , c o a t i n g t h i c k n e s s and, t o a l e s s e r e x t e n t , t h e s e a l a n t and c o n d i t i o n e r . S u l p h u r c o a t e d u r e a has been e v a l u a t e d i n a v a r i e t y o f s o i l s and c r o p s ( A l l e n , 1 9 7 1 ( 6 " 1 ; L i e g e l , 1976*-7-1; Sharma, 1976 (' 8' ); J a r a m i l l o , 1 9 7 6 ( 9 ) ) . F o r example, when a p p l i e d t o B e r m u d a ^ g r a s s , s u l p h u r c o a t e d u r e a gave more u n i f o r m u p t a k e o f n i t r o g e n and 13% h i g h e r g r a s s y i e l d s t h a n u n c o a t e d u r e a . I t has a l s o been s h o w n ^ t h a t s u l p h u r c o a t e d u r e a can be used e f f e c t i v e l y f o r t u r f , p a s t u r e , and hay p r o d u c t i o n , where h i g h l e a c h i n g and d e c o m p o s i t i o n l o s s e s a r e p r e v a l e n t . The e f f i c a c y o f t h e p r o d u c t has a l s o been d e m o n s t r a t e d w i t h l o n g t e r m c r o p s ( P i n e a p p l e , Sugar-cane and T i m b e r ) ^ . 1;3 The U.B.C. Spouted Bed P r o c e s s Development o f t h e s p o u t e d bed s u l p h u r c o a t i n g p r o c e s s s t a r t e d i n 1975 by Mathur and M e i s e n ^ ^ . The equipment c o n s i s t e d (see F i g . 1.2) m a i n l y o f a c y l i n d r i c a l v e s s e l w i t h a c o n i c a l b ase f i l l e d w i t h u r e a g r a n u l e s . A h i g h v e l o c i t y a i r j e t e n t e r s t h e b o t t o m o f t h e bed and c a r r i e s upwards p a r t i c l e s l o c a t e d i n t h e c e n t r a l r e g i o n o f t h e bed ( o r " s p o u t " ) u n t i l t h e y r e a c h t h e t o p o f t h e bed where t h e y f a l l back i n t o t h e " a n n u l u s " . The annulus behaves as a s l o w l y d e s c e n d i n g p a c k e d bed. Near t h e bottom o f t h e bed t h e p a r t i c l e s r e - e n t e r t h e s p o u t and a r e once a g a i n c a r r i e d upwards. C o a t i n g i s a c c o m p l i s h e d by s p r a y i n g m o l t e n s u l p h u r i n t o t h e bottom o f t h e bed c o a x i a l l y w i t h t h e s p o u t i n g a i r . Each t i m e a u r e a p a r t i c l e p a s s e s t h r o u g h t h e s p r a y - z o n e , i t a c q u i r e s a l a y e r o f s u l p h u r w h i c h s o l i d i f i e s by t h e t i m e t h e p a r t i c l e r e a c h e s t h e t o p o f t h e bed. Due t o t h e r e p e a t e d passage t h r o u g h t h e s p r a y zone i m p e r f e c t i o n s i n t h e c o a t t e n d t o be c o r r e c t e d . The q u a l i t y o f t h e p r o d u c t was d e t e r m i n e d by t h e t e s t d e s c r i b e d 5 f i g u r e 1.2: U.B.C. Spouted Bed (Arrows i n d i c a t e d i r e c t i o n o f s o l i d s movement) 6 above; the values were found to be strongly dependent on bed temperature and sulphur flow rate. I n i t i a l runs and dissolution tests showed poor reproducib i 1 i t y . Due to several operational problems with the o r i g i n a l plant (e.g. nozzle plugging, sulphur f i l t r a t i o n problems, molten sulphur handling d i f f i c u l t i e s ) a complete redesign and modification of the f a c i l i t i e s was needed. 1.4 Objectives of t h i s Thesis The main objectives of t h i s thesis were as follows: (a) Redesigning the spouted bed coating f a c i l i t y to overcome the operational problems previously mentioned. (b) Developing a r e l i a b l e and reproducible procedure for determining product quality i n terms of D^^ values. (c) Confirming the influence of different process variables on the product quality as determined by the D2g test. (d) Studying the coating process and the effects of sulphur additives such as s i l i c o n e s . (e) Examining scale-up problems and presenting a conceptual design of small, commercial coating f a c i l i t i e s (including preliminary cost estimates). 2. LITERATURE REVIEW 2.1 I n d u s t r i a l P r o c e s s f o r S u l p h u r C o a t i n g o f Urea 2.1.1 Tl/A Vfiocte* Vzv&lopmzrvt I n i t i a l work on s u l p h u r c o a t i n g o f u r e a was p e r f o r m e d by R i n d t , B l o u i n and G e t z i n g e r , who d e v e l o p e d a b a t c h - w i s e p r o c e s s i n w h i c h t h e u r e a was p l a c e d i n a r o t a r y pan and s p r a y e d w i t h m o l t e n s u l p h u r . The p r o d u c t q u a l i t y was t e s t e d i n t h e l a b o r a t o r y by d e t e r m i n i n g t h e d i s s o l u t i o n o f 2 g o f sample i n 10 ml o f w a t e r a t 37.8°C a f t e r one and f i v e days. The one-day t e s t was t a k e n t o i n d i c a t e t h e p r o p o r t i o n o f p a r t i c l e s w i t h i m p e r f e c t c o a t i n g . The average o f t h e d a i l y d i s s o l u t i o n r a t e s f o r t h e n e x t 4 days was r e g a r d e d as an i n d i c a t i o n o f m o i s t u r e p e n e t r a t i o n i n t o w e l l c o a t e d p a r t i c l e s . Most o f t h e work was p e r f o r m e d w i t h p a n - g r a n u l a t e d u r e a p r o d u c e d by TVA. However, o t h e r f e r t i l i z e r s u b s t r a t e s were a l s o t e s t e d . I t was fo u n d t h a t f e r t i l i z e r s s u c h as diammonium phosphate c r y s t a l s and g r a n u l e s , ammonium phosphate n i t r a t e g r a n u l e s , and p o t a s s i u m c h l o r i d e g r a n u l e s a l s o gave p r o m i s i n g r e s u l t s . Two t y p e s o f s u l p h u r were examined: " b r i g h t " and " d a r k " grades o f com m e r c i a l s u l p h u r . Both t y p e s gave s i m i l a r r e s u l t s i n t h e d i s s o l u t i o n t e s t s . (41 Based on t h e s e s t u d i e s R i n d t e t a l c o n c l u d e d t h a t a c o a t c o n s i s t i n g e n t i r e l y o f s u l p h u r was n o t an e f f e c t i v e m o i s t u r e b a r r i e r , due t o t h e p r e s e n c e o f m i c r o s c o p i c c r a c k s and p o r e s . To s o l v e t h i s p r o b l e m two approaches were t a k e n : 1. Use o f a d d i t i v e s t o m i n i m i z e c r a c k s and p o r e s i n t h e s u l p h u r s h e l l and 2. S e a l i n g t h e c o a t w i t h wax. The f i r s t a p p r o a c h was s t u d i e d e x t e n s i v e l y and v a r i o u s a d d i t i v e s (such as o r g a n i c p o l y s u l f i d e s , n a p h t h a l e n e , i n o r g a n i c o x i d e s ) were t r i e d . However, no 7 8 s i g n i f i c a n t improvement was a c h i e v e d . R i n d t e t a l t h e r e f o r e c o n c e n t r a t e d on s e a l i n g t h e s u l p h u r c o a t w i t h a l a y e r o f a b i o d e g r a d a b l e wax. The wax s e a l a n t p r e s e n t e d two p r o b l e m s : p r o d u c t a g g l o m e r a t i o n , w h i c h was s o l v e d by t h e a d d i t i o n o f an a n t i c a k i n g agent such as diatomaceous e a r t h ; m i c r o b i a l a t t a c k w h i c h was overcome by t h e a d d i t i o n o f m i c r o b i c i d e s . (4) R i n d t e t a l a l s o f ound t h a t t h e p r o d u c t q u a l i t y was s t r o n g l y i n f l u e n c e d by t h e t e m p e r a t u r e s o f t h e m o l t e n s u l p h u r , a t o m i z i n g a i r and s u b s t r a t e d u r i n g t h e c o a t i n g o p e r a t i o n . O p t i m a l t e m p e r a t u r e s f o r t h e s u l p h u r and a t o m i z i n g a i r were found t o l i e between 135°C and 140°C. T h i s c o r r e s p o n d s f a i r l y c l o s e l y t o t h e r e g i o n where t h e s u l p h u r v i s c o s i t y i s a minimum. The s u b s t r a t e t e m p e r a t u r e was a l s o f o u n d t o have a s t r o n g e f f e c t on p r o d u c t q u a l i t y . The d i s s o l u t i o n d e c r e a s e d s h a r p l y w i t h t e m p e r a t u r e up t o 65.5°C and t h e n i n c r e a s e d a g a i n s l o w l y . B e s t r e s u l t s were o b t a i n e d i n t h e range o f 65.5°C t o 76.6°C. (41 The f o l l o w i n g r e a s o n was g i v e n f o r t h i s b e h a v i o u r : "At t h e l o w e r t e m p e r a t u r e , t h e c o a t i n g was rough and d i f f i c u l t t o s e a l because o f p r e m a t u r e f r e e z i n g o f t h e s u l p h u r d r o p l e t s . At t h e h i g h e r t e m p e r a t u r e s t h e s u l p h u r d i d n o t s o l i d i f y r a p i d l y enough and r a n o f f t h e s u b s t r a t e " . The e f f e c t o f s u b s t r a t e t e m p e r a t u r e d u r i n g wax a p p l i c a t i o n was a l s o i n v e s t i g a t e d . The b e s t r e s u l t s were o b t a i n e d between 65.5°C and 71.1°C. The e f f e c t o f t h e amount o f s u l p h u r c o a t i n g and s e a l a n t was a l s o s t u d i e d ; d i s s o l u -t i o n d e c r e a s e d w i t h c o a t t h i c k n e s s . The b e s t c o m b i n a t i o n f o r low d i s s o l u t i o n r a t e s (0.2 % d a i l y ) was: 16% s u l p h u r , 3% h a r d wax, 0.5% m i c r o b i c i d e and 1% c o n d i t i o n e r . (These f i g u r e s r e f e r t o t h e w e i g h t p e r c e n t i n t h e f i n a l p r o d u c t ) . Based on t h e b a t c h - w i s e , pan c o a t i n g e x p e r i m e n t s , a c o n t i n u o u s p r o c e s s (31 was a l s o d e v e l o p e d by B l o u i n e t a l ; i t c o n s i s t e d p r i n c i p a l l y o f a 0.914 m ID by 1.219 m l o n g r o t a r y drum i n t o w h i c h u r e a was p a s s e d c o n t i n u o u s l y a t r a t e s 9 up to 136 kg/hour (see Fig. 2.1). The drum was divided into three compartments. The f i r s t one was a pre-heating section where the urea temperature was raised to about 71°C by jet s of hot a i r (137.8°C). In the second compartment molten sulphur (at 148.9-154.4°C) was sprayed onto the urea through three a i r atomizing nozzles. The sulphur coated granules then passed to the t h i r d section where they were coated (between 65.5 and 71°C) with molten wax (at 93.3 to 104°C) containing a microbicide (8% wt). The coated p a r t i c l e s were discharged into a second drum, where they were cooled to about 38°C and conditioned with diatomaceous earth or clay. (13) Blouin, Rindt and Moorev ^ who performed t r i a l s with t h i s f a c i l i t y f i r s t developed a new and more representative test for product quality. This test consisted of immersing 50 g of sample i n 250 ml of water at 37.8°C for specified periods of time. The amount of dissolved urea was determined by the s p e c i f i c gravity of the solution. The r e l a t i v e l y high dissolution (2.5% daily) during the f i r s t seven days period was thought to resul t from imper-fect coating; subsequent dissolution (0.5% daily) occurred by slow leaching from well-coated material. The best settings of operating variables for the batch plant served as the starting point and a new set of optimum operating temperatures was obtained (see Fig. 2.1). As i n previous experiments, the dissolution rates were found to decrease with increasing coat thickness. Between 27 and 30% sulphur, the urea dissolution (over 10 days) varied from 4 to 27% as the urea p a r t i c l e size range was changed from 99% + 3.36 mm (+ 6 mesh) to 75% - 2.00 mm (-10 mesh), respectively. For urea p r i l l s 95% - 3.36 mm + 1.41 mm (-6 +14 mesh) the effect of sulphur spray conditions was also studied and i t was found that the dissolution rates decreased with an increase i n atomizing a i r pressure. A si m i l a r effect was observed for granular urea (99% - 3.36 + 2.00 mm). Spray patterns produced by diff e r e n t nozzles had a pronounced effect on Coal Tar p H Z w b - G w Metering Pump Atomizing A i r •—1489°C Molfen Sulfur Conditioner Feeder Metering Pump Screen^ Product ( 3 6 % N M 7 8 % Urea 1 7 % Sulfur 3 % Wax 0 2 % Coal Tar 1.6% Conditioner "Oversize F i g u r e 2.1: TVA P r o c e s s f o r S u l p h u r C o a t i n g o f Urea (136 kg/hour F a c i l i t y ) 11 d i s s o l u t i o n r a t e s . The b e s t p r o d u c t was o b t a i n e d w i t h an e x t e r n a l - m i x s p r a y n o z z l e h a v i n g d i a m e t r i c a l l y opposed wing t i p a i r j e t s . The seven day-d i s s o l u t i o n was 5% f o r a sample c o n t a i n i n g 28% o f c o a t i n g m a t e r i a l . T e s t s were a l s o p e r f o r m e d t o d e t e r m i n e t h e s t o r a g e and h a n d l i n g c h a r a c t e r i s t i c s o f t h e c o a t e d m a t e r i a l w h i c h had a c c e p t a b l e d i s s o l u t i o n r a t e s . I t was c o n c l u d e d t h a t normal s t o r a g e and h a n d l i n g p r o c e d u r e s d i d n o t r e s u l t i n s e r i o u s d e g r a d a t i o n o f t h e p r o d u c t . M o i s t u r e a b s o r t i o n o f t h e c o a t e d m a t e r i a l s was 5 t o 12% o f t h a t o f s i m i l a r l y exposed u n c o a t e d m a t e r i a l . A t y p i c a l f i n i s h e d p r o d u c t h a v i n g a 7-days d i s s o l u t i o n r a t e o f 15% c o n t a i n e d 17% s u l p h u r , 3% wax, 0.2% c o a l t a r ( m i c r o b i c i d e ) , and 1.8% a n t i c a k i n g a g e n t . Based on t h e e x p e r i e n c e g a i n e d w i t h t h e 136 kg/hour p l a n t TVA d e s i g n e d and b u i l t a 900 kg/hour d e m o n s t r a t i o n f a c i l i t y ^ 1 2 ^ * ' f!4") ^  I n t ^ s c a s e t h e p r e h e a t i n g , s u l p h u r c o a t i n g and wax c o a t i n g were p e r f o r m e d i n s e p a r a t e d u n i t s as shown i n F i g . 1.1. The r o t a r y drum h e a t e r r a i s e d t h e u r e a t e m p e r a t u r e t o about 80°C. The p r e h e a t e d u r e a was t h e n f e d i n t o t h e s u l p h u r c o a t i n g drum, where t h e s u l p h u r s p r a y (produced by pneumatic o r h y d r a u l i c a t o m i z a t i o n ) was d i r e c t e d o n t o t h e u r e a . Both t y p e s o f a t o m i z a t i o n were e v a l u a t e d and a r e d i s c u s s e d l a t e r . The s u l p h u r - c o a t e d u r e a was t h e n t r a n s f e r r e d by a b u c k e t e l e v a t o r i n t o a wax c o a t i n g drum ( o p e r a t i n g temp. 76.7-110°C). A m i c r o c r i s t a l l i n e wax was s p r a y e d o n t o t h e c o a t e d u r e a p a r t i c l e s (approx. 2% o f t h e f i n a l p r o d u c t ) , t o s e a l any i m p e r f e c t i o n s . The use o f m i c r o b i c i d e s was d i s c o n t i n u e d because agronomic t e s t s had d e m o n s t r a t e d t h e i r i n e f f e c t i v e n e s s . The p r o d u c t was t h e n c o o l e d i n a f l u i d i z e d bed c o o l e r ( a t 15.6 t o 37.8°C) and d i s c h a r g e d t o a c o n d i t i o n i n g drum. Diatomaceous e a r t h was used as a c o n d i t i o n e r t o p r e v e n t p r o d u c t c a k i n g d u r i n g s t o r a g e . The f i n a l p r o c e s s i n g s t e p was s c r e e n i n g t o remove any o v e r s i z e m a t e r i a l . S h i r l e y and M e l i n e ( J " J J have p e r f o r m e d e x t e n s i v e t e s t s w i t h t h i s f a c i l i t y . T h e i r work was m a i n l y o r i e n t e d t o w a r d s f i n d i n g t h e b e s t c o n d i t i o n s when o p e r a t i n g w i t h p n e u m a t i c o r h y d r a u l i c s u l p h u r a t o m i z i n g s y s t e m s . Based on e x p e r i e n c e w i t h t h e p r e v i o u s p i l o t p l a n t (136 k g / h o u r ) p n e u m a t i c n o z z l e s were i n i t i a l l y u s e d . The i n t e r n a l s o f t h e c o a t i n g drum a r e shown i n F i g . 2 . 2 ( a ) . The m o l t e n s u l p h u r was p a s s e d t h r o u g h 177 ym, 149 ym, and 250 ym f i l t e r s b e f o r e s p r a y i n g t o p r e v e n t n o z z l e p l u g g i n g . The i m p u r i t i e s i n t h e s u l p h u r a r e m a i n l y CARSUL, w h i c h i s a s o l i d c a r b o n - s u l p h u r comp lex fo rmed by t h e r e a c t i o n o f h y d r o c a r b o n s w i t h m o l t e n s u l p h u r . ( R e c o v e r e d s u l p h u r f r o m t h e p e t r o l e u m i n d u s t r y i n v a r i a b l y c o n t a i n s s m a l l amounts o f h y d r o c a r b o n s ) . The s u l p h u r was t h e n d i s t r i b u t e d t h r o u g h a s team h e a t e d - h e a d e r e q u i p p e d w i t h e i g h t a i r - a t o m i z i n g n o z z l e s ( see F i g . 2 . 3 ( a ) , and t h e i r p o s i t i o n was a r r a n g e d t o s p r a y v e r t i c a l l y downwards and d i r e c t l y o n t o t h e f a s t e s t mov ing p o r t i o n o f t h e r o l l i n g b e d . P a r a m e t e r s examined were t o t a l c o a t i n g w e i g h t o f s u l p h u r , wax and c o n d i t i o n e r ; s i z e and c o n d i t i o n o f t h e u r e a ; t y p e and s i z e o f p n e u m a t i c s p r a y i n g n o z z l e s , number o f s u l p h u r n o z z l e s , p o s i t i o n o f s u l p h u r n o z z l e s ; r o t a t i o n a l s p e e d o f t h e s u l p h u r - c o a t i n g d rum; a t o m i z i n g a i r f l o w r a t e ; p r o c e s s t e m p e r a t u r e s . T a b l e 2 .1 summar i zes t h e opt imum o p e r a t i n g t e m p e r a t u r e s f o r p n e u m a t i c and h y d r a u l i c a t o m i z a t i o n . As i n d i c a t e d by T a b l e 2 .1 S h i r l e y and M e l i n e were a b l e t o p r o d u c e an a c c e p t a b l e w a x - f r e e p r o d u c t . F i g u r e 2 .4 shows t h a t t h e e f f e c t o f s u b s t r a t e t e m p e r a t u r e on d i s s o l u t i o n r a t e i s v e r y p r o n o u n c e d . The d i s s o l u t i o n d e c r e a s e s w i t h s u b s t r a t e t e m p e r a t u r e up t o 95 .5 °C and t h e n i n c r e a s e s a g a i n . A t 70°C and 95 .5 °C t h e d i s s o l u t i o n v a l u e s were 40% and 5% Discharge Retaining Ring Discharge Retaining Ring Lifting Flights Spraying Distance 5 1/2" Deflector Plate Falling Curtain of Urea Granules (Curtain Height 17 " ) Spraying Height 2' Spraying Distance 5 1/2" (a) Pneumatic s p r a y i n g (b) H y d r a u l i c s p r a y i n g F i g u r e 2.2: I n t e r n a l s o f t h e C o a t i n g Drum, TVA P r o c e s s (900 kg/hour F a c i l i t y ) 14 (a) Pneumatic a t o m i z a t i o n <T ~> Flat Spray Pattern Retaining Cap Strainer Flange Nozzle Tip Aluminum Gaskets Strainer Assembly Nozzle Body "t" SULFUR (b) H y d r a u l i c a t o m i z a t i o n F i g u r e 2.3: S u l p h u r S p r a y Header System and Spr a y N o z z l e s D e t a i l TVA P r o c e s s 900 kg/hour P l a n t 15 Optimum O p e r a t i n g Temperatures f o r S u l p h u r C o a t i n g o f Urea i n t h e TVA 900 kg/hour P l a n t Pneumatic A t o m i z a t i o n H y d r a u l i c A t o m i z a t i o n W i t h S e a l a n t W i t h o u t S e a l a n t W i t h S e a l a n t W i t h o u t S e a l a n t 62.8-65.6°C 154.4°C 79.4-82.2°C 154.4°C 143.3-148.9°C 146.1-148.9°C 68.3-71.1°C Max. 95.5°C 51.7-79.4°C 154.4°C 148.9°C 93.3°C 60-73.9°C 154.4°C 148.9°C 93.3°C Max 73.9-76.7°C 76.7-110.0°C 90.6-93.3°C 73.9-90.6°C 73.9-85.0°C 76.7-110.0°C 68.3-71.1°C 15.6-37.8°C 40.6°C Max. 68.3-82.2°C 15.6-37.8°C 54.4°C Max 40.6°C Max 54.4°C Max T a b l e 2.1: P r e h e a t e d U r e a L i q u i d S u l p h u r A t o m i z i n g A i r S u l p h u r C o a t i n g Drum S u l p h u r C o a t i n g Drum E x i t L i q u i d Wax Wax Coat Drum e x i t C o o l i n g A i r C o o l e r E x i t 7 day D i s s o l u -t i o n R a te P r o d u c t w i t h 20% t o t a l c o a t i n g P r o d u c t i o n R ate 12.5% 907 k g s / h o u r 19.7% 454 k g s / h o u r 15.7% 3628 k g s / h o u r 31.2% 1814 k g s / h o u r 16 O 64 nr. Cooling to Ambient 160 190 200 210 220 230 Average Urea Temperature in Sulfur Coating Drum , ' F F i g u r e 2.4: E f f e c t o f S u b s t r a t e Temperature on D i s s o l u t i o n R a tes TVA P r o c e s s ( S h i r l e y and M e l i n e ) 1 3 r e s p e c t i v e l y . No c l e a r e x p l a n a t i o n o f t h i s b e h a v i o u r was g i v e n . A c o m p a r i s o n o f d i s s o l u t i o n r a t e s f o r pneumatic and h y d r a u l i c a t o m i z a t i o n p r o d u c t s w i t h and w i t h o u t s e a l a n t i s g i v e n on T a b l e 2.2. T a b l e 2.2 Summary o f D i s s o l u t i o n r a t e s f o r Pneumatic and h y d r a u l i c a t o m i z a t i o n ( w i t h and w i t h o u t s e a l a n t ) Pneumatic A t o m i z a t i o n H y d r a u l i c A t o m i z a t i o n With s e a l a n t W i t h o u t s e a l a n t With s e a l a n t W i t h o u t s e a l a n t T o t a l Coat w e i g h t % f o r a 20% 7 day D i s s o l u t i o n , % S u l p h u r , % 16 (11) 20 (20) 19.5 (14.5) 23 (23) 7 Day D i s s o l u t i o n Rate f o r 20% t o t a l c o a t i n g P r o d u c t Rates 12.5% 19.7% 15.7% 31.2% 907 k g / h r 454 k g / h r 3628 k g / h r 1814 k g / h r The p r o d u c t w i t h a s e a l a n t c o n t a i n e d 2% m i c r o c r y s t a l l i n e wax, 2% diatomaceous e a r t h and 1% B a r n e t c l a y , as u r e a p r e c o n d i t i o n e d t h e main c o a t i n g m a t e r i a l wats s u l p h u r and i t v a r i e d , between 11% and 15%. The u r e a p a r t i c l e s i z e was, i n terms o f T y l e r mesh: -6+7:9%, -7+8:70%, -8+9:19%j -9:2%. A l t h o u g h p n eumatic a t o m i z a t i o n gave good p r o d u c t q u a l i t y , TVA d e c i d e d t o l o o k f o r an a l t e r n a t i v e t o m i n i m i z e d u s t and s u l p h u r m i s t e l u t r i a t i o n f rom t h e c o a t i n g - d r u m . T y p i c a l d u s t l o a d i n g s i n t h e s u l p h u r c o a t i n g drum, when u s i n g p n e u m a t i c n o z z l e s , r a n g e d f r o m 0.150 t o 0.359 g/m 3/kg o f s u l p h u r s p r a y e d . The h y d r a u l i c n o z z l e s (see F i g . 2.3(b)) gave d u s t l o a d i n g s o f about 0.007 t o 18 0.018 g/m 3/kg o f s u l p h u r s p r a y e d . The l a r g e s t d u s t c o n c e n t r a t i o n measured was 3.2 g/m3, w e l l below t h e l o w e r e x p l o s i v i t y l i m i t o f s u l p h u r i n a i r which i s 35 g/m 3 ( 2 5 ). The h y d r a u l i c s y s t e m was q u i t e s i m i l a r t o t h e pn e u m a t i c one e x c e p t f o r t h e i n t e r n a l s o f t h e c o a t i n g drum (see F i g . 2.2 ( b ) ) . F u r t h e r m o r e , s u l p h u r was s p r a y e d i n a h o r i z o n t a l p a t t e r n a g a i n s t a f a l l i n g c u r t a i n o f u r e a g r a n u l e s . The s u l p h u r s y s t e m was steam h e a t e d and had 37 ym, 2 ym, and .74 ym i n l i n e f i l t e r s t o remove i m p u r i t i e s w h i c h were m a i n l y C a r s u l . A s t r a i n e r was i n s t a l l e d u p s t r e a m o f each n o z z l e . F i l t r a t i o n was more i m p o r t a n t due t o s m a l l e r n o z z l e openings (178 ym-381 ym) compared w i t h t h e op e n i n g s o f t h e pneumatic n o z z l e s (457 ym-711 ym). Due t o t h e s u c c e s s o b t a i n e d w i t h t h e p i l o t p l a n t s and t h e i n c r e a s i n g demand f o r s u l p h u r c o a t e d u r e a , TVA d e c i d e d t o d e s i g n and b u i l d a 9.070 t / h o u r d e m o n s t r a t i o n f a c i l i t y ^ * ^ . 2.1.2 Tl/A VzmoMthxvbion Scald Plant T h i s p l a n t was q u i t e s i m i l a r t o t h e 0,9 t / h o u r p l a n t (see F i g . 2,5) b u t i t d i f f e r e d from t h e p r e v i o u s p i l o t p l a n t s i n t h e f o l l o w i n g r e s p e c t s : a) F l u i d i z e d bed p r e h e a t e r f o r u r e a b) D i r e c t f e e d i n g f r o m t h e TVA p a n - g r a n u l a t o r t o e l i m i n a t e i n t e r m e d i a t e s t o r a g e and reduc e h e a t i n g c o s t s (The p r o d u c t l e a v e s t h e g r a n u l a t i n g p r o c e s s a t 115°C) c) New p o l l u t i o n c o n t r o l and abatement equipment; due t o s c a l e - u p more d u s t f o r m a t i o n was e x p e c t e d . d) Improved h i g h p r e s s u r e m o l t e n s u l p h u r f i l t r a t i o n . T h e o r e t i c a l l y (21) n o z z l e e f f i c i e n c y improves w i t h p r e s s u r e and d e c r e a s i n g n o z z l e s i z e O p e r a t i n g p r e s s u r e s were chosen between 6800-10400 kPa and n o z z l e o penings v a r i e d f r o m 178 ym t o 381 ym. e) H i g h degree o f i n s t r u m e n t a t i o n , t o p r o v i d e a b e t t e r c o n t r o l f o r a To Attn steam bright stock oil storage tank Sulfur Filter r-O primary sulfur filter steam  molten sulfur storage ft transfer pump Oversize mix tank urea from pan granulation ^JJ urea feed elevator process elevator heater F i g u r e 2.5: TVA D e m o n s t r a t i o n S c a l e P l a n t f o r S u l p h u r C o a t i n g o f U rea (9.07 m t o n / h o u r ) 20 Table 2.3: Main Process V a r i a b l e s and Product C h a r a c t e r i s t i c s of TVA Demonstration P l a n t (Capacity 9.07 t / h r ) T o t a l Coating, % 7 days D i s s o l u t i o n Test, % Substrate: Type S i z e ( T y l e r mesh) * • 7 -7*8 -8*9 -9 Urea Feed Rate, m e t r i c Ton/hour F l u i d i z e d Bed Preheater: E n t e r i n g A i r temp., °C Substrate e x i t temp., °C Retention time, min Sulphur Coating Drum: Sulphur feed r a t e : per Nozzle, kg/hour T o t a l , kg/hour Sulphur feed temp., °C Spray Nozzles Type: Number Spray T i p opening, um H y d r a u l i c press at Nozzle t i p s , kPa Revolutions per minute Retention time, min Temperature o f Sulphur-Coated urea l e a v i n g , "C Sealant Coating Drum Temperature o f coated product l e a v i n g "C 23 25-30 Pan Granulated Urea 6 21 43 30 7.S3 66.1 65.0 1.8 39.5 1733.3 154.4 H y d r a u l i c atomizing 44 330 7579 11.8 7 81.1 Type of sealant Temperature o f sealant at a p p l i c a t i o n , °C 2000 Mol wt. Polye t h y l e n e 30% wt B r i g h t s t o c k 79% wt 123.9 Revolutions per minute 11.5 Retention time, min 0.7 Sealant a p p l i e d , wt % of t o t a l prod. 2.1 F l u i d i z e d Bed Cooler Temperatures M a t e r i a l e n t e r i n g , °C 77.2 Cooler A i r e n t e r i n g , °C 13.9 M a t e r i a l l e a v i n g , "C 24.4 C o n d i t i o n i n g Drum Re v o l u t i o n per minute 10 Retention time, min 1.5 C o n d i t i o n i n g agent, wt % o f t o t a l prod. 2.4 21 smoother and s a f e r o p e r a t i o n and t o e n s u r e a more u n i f o r m t>roduct. f ) Improved b u l k h a n d l i n g f a c i l i t i e s f o r a l l raw m a t e r i a l s . g) Complete g r a v i t y f l o w t h r o u g h t h e whole p r o c e s s , from t h e p r e h e a t e r t o t h e f i n a l s c r e e n s . h) Hot sw e e p i n g a i r was p r o v i d e d t o b o t h s u l p h u r c o a t i n g and s e a l a n t drum. A i r i n t h e c o a t i n g drum r e d u c e d t h e s u l p h u r d u s t c o n c e n t r a t i o n and c a r r i e d d u s t away, t h e r e b y m i n i m i z i n g e x p l o s i o n p r o b l e m s . S i m i l a r l y , t h e a i r d i l u t e d any h y d r o c a r b o n v a p o r s p r e s e n t i n t h e s e a l a n t drum. The d e m o n s t r a t i o n p l a n t p r o v i d e s t h r e e c o a t i n g s t o t h e u r e a : s u l p h u r , s e a l a n t (70% b r i g h t s t o c k o i l p l u s 30% p o l y e t h y l e n e ) , c o n d i t i o n e r (diatomaceous e a r t h t o p r e v e n t s t i c k i n e s s and improve h a n d l i n g c h a r a c t e r i s t i c s ) . The main p r o c e s s v a r i a b l e s a r e summarized i n T a b l e 2.3. 2.2 The U n i v e r s i t y o f B r i t i s h C o l u m b i a (U.B.C) P r o c e s s I n i t i a l work was p e r f o r m e d by Mathur and M e i s e n ^ - ' i n 1975, who d e s i g n e d and o p e r a t e d a s p o u t e d bed c o a t i n g p r o c e s s (see F i g u r e 2.6). In t h i s b a t c h p r o c e s s , a bed o f u r e a was s p o u t e d w i t h warm a i r . S u l p h u r was m e l t e d i n an e l e c t r i c a l l y h e a t e d v e s s e l and f o r c e d by compressed n i t r o g e n t o an a i r a t o m i z e d n o z z l e . A l l l i n e s were e l e c t r i c a l l y h e a t e d and i n s u l a t e d . The n o z z l e arrangement c o n s i s t e d o f a c e r a m i c t u b e , i n t h e m i d d l e o f w h i c h two c o n c e n t r i c t u b e s were i n s t a l l e d . The i n s i d e t u b e was t h e s u l p h u r l i n e s u r r o u n d e d by t h e a t o m i z i n g a i r l i n e w hich was a l s o e l e c t r i c a l l y h e a t e d . Two c y c l o n e s were i n s t a l l e d t o r e c o v e r e l u t r i a t e d f i n e s from t h e bed. The s p o u t i n g and a t o m i z i n g a i r were h e a t e d by 3 kW and 0.75 kW e l e c t r i c a l h e a t e r s , r e s p e c t i v e l y . S e v e r a l problems were e n c o u n t e r e d w i t h t h i s equipment such as low s u l p h u r m e l t i n g r a t e s , i n a b i l i t y t o m a i n t a i n a c o n t i n u o u s s u l p h u r f l o w , p o o r a l i g n m e n t o f t h e a t o m i z i n g n o z z l e , s u l p h u r s o l i d i f i c a t i o n a t t h e NOZZLE I -Atomized Sulphur -Urea \ \ Air Flowt t —j—Ceramic Tube L— Heating Tape Sulphur Flow Spouting Air I 3 KW Heaters Atomizing Air Sulphur Melter Sulphur F i g u r e 2.6: UBC Spouted Bed f o r S u l p h u r C o a t i n g o f Urea ( I n i t i a l P r o t o t y p e d e s i g n e d by Mathur and Meisen) 23 n o z z l e t i p . Due t o t h e s e p r o b l e m s , m o d i f i c a t i o n s were made by Mathur, M e i s e n and Z e e ^ ^ d u r i n g t h e summer o f 1976 (see F i g u r e 2.7). M a j o r changes i n c l u d e d t h e d e s i g n o f a new m e l t e r , n o z z l e arrangement and s u l p h u r t r a n s f e r l i n e s . The m e l t e r was b a s i c a l l y a s h e l l and tube h e a t exchanger w i t h h o t a i r p a s s i n g t h r o u g h t h e t u b e s . A i r was e l e c t r i c a l l y h e a t e d and i t s t e m p e r a t u r e c o n t r o l l e d a u t o m a t i c a l l y . The m e l t e r had a c a p a c i t y o f 31 kg o f s u l p h u r . The m o l t e n s u l p h u r was pumped out o f t h e m e l t e r by a s t a i n l e s s s t e e l g e a r pump. To m a i n t a i n t h e d e s i r e d o p e r a t i n g t e m p e r a t u r e (130-158°C) t h e pump head was wrapped w i t h e l e c t r i c a l h e a t i n g t a p e and a s b e s t o s i n s u l a t i o n . A t h e r m o c o u p l e was f i t t e d i n t o t h e pump body t o m o n i t o r i t s t e m p e r a t u r e . The m o l t e n s u l p h u r was p a s s e d t h r o u g h an e l e c t r i c a l l y h e a t e d f i l t e r ( w i t h two c o n s e c u t i v e 80 mesh s t a i n l e s s s t e e l s c r e e n s ) . The n o z z l e assembly ( m o d i f i e d as shown i n F i g u r e 2.8) was h e a t e d by h o t a t o m i z i n g a i r f l o w i n g i n t o t h e gap between t h e n o z z l e and t h e cap. The n o z z l e was an " e x t e r n a l m i x i n g t y p e " w i t h an o p e n i n g o f 380 ym f o r t h e s u l p h u r f l o w . The s p o u t i n g v e s s e l was made from a 0.15 m I.D. m i l d s t e e l p i p e w i t h v i e w i n g g l a s s e s f i t t e d i n t o t h e f r o n t and back. S a m p l i n g p o r t s were l o c a t e d i n t h e c y l i n d r i c a l and c o n i c a l s e c t i o n s o f t h e bed. O r i f i c e p l a t e s w i t h d i f f e r e n t o p enings c o u l d be used. E x p e r i m e n t a l runs were p e r f o r m e d w i t h t h i s equipment by Z e e ^ ^ , H i s work was m a i n l y o r i e n t e d t o p r o d u c e b a t c h e s o f s u l p h u r c o a t e d u r e a and compare t h e i r d i s s o l u t i o n r a t e s w i t h t h o s e o f t h e c o m m e r c i a l C IL p r o d u c t . The p r o d u c t was t e s t e d by t h e TVA 7-days d i s s o l u t i o n t e s t ( u n a g i t a t e d ) w i t h s l i g h t m o d i f i c a t i o n s and by an a c c e l e r a t e d ( a g i t a t e d ) d i s s o l u t i o n t e s t d e v e l o p e d by Zee. The a c c e l e r a t e d t e s t i n v o l v e d t h e use o f a m e c h a n i c a l s h a k e r and a F i g u r e 2.7: UBC Spouted Bed f o r S u l p h u r C o a t i n g o f Urea ( M o d i f i c a t i o n d e s i g n e d by Mathur, M e i s e n and Zee) To Vent Atomizing Air Sulphur Flow = Air Flow Heating Tapes Asbestos Lagging F i g u r e 2.8: N o z z l e arrangement (Mathur, M e i s e n and Zee) - 2 1/4 d> 2 1/4 5/8" . 1/4$ — 2 " * --2 1/8"$ 2 3/8 $ - 4 > -1/4 NPT Jl/4" « 0.700 i /7T&T7 1/2" A Nozzle B Nozzle Cap C Locking Ring D Nozzle Base E Nozzle Housing F Orifice Plate a Atomizing Air Inlet b Atomizing Air Distribution Well c Atomizing Air Passage d Atomizing Air Gap e Sulphur Inlet f Sulphur Passage 26 r e f r a c t o m e t e r a n a l y s i s o f t h e d i s s o l v e d u r e a . Two t y p e s o f u r e a were c o n s i d e r e d as raw m a t e r i a l , f o r e s t and a g r i c u l t u r a l g rade. H i g h p u r i t y s u l p h u r s l a t e was used. The i n f l u e n c e o f t h e f o l l o w i n g v a r i a b l e s on p r o d u c t q u a l i t y (as d e t e r m i n e d by t h e d i s s o l u t i o n t e s t ) was s t u d i e d : s i z e o f t h e u r e a g r a n u l e s , c o a t i n g t i m e , c o o l i n g t i m e and t y p e o f c o o l i n g . The e f f e c t o f bed t e m p e r a t u r e and s u l p h u r f l o w r a t e on d i s s o l u t i o n r a t e s was n o t i n v e s t i g a t e d . A l l e x p e r i m e n t s were p e r f o r m e d a t h i g h bed t e m p e r a t u r e s ('v 90°C) and the s u l p h u r f l o w r a t e used was n o t d e t e r m i n e d d i r e c t l y . S u l p h u r c o a t e d g r a n u l a r u r e a w i t h 28% s u l p h u r c o n t e n t had a 7-day d i s s o l u t i o n v a l u e o f 89% w h i l e SCU from C IL w i t h 39% s u l p h u r c o a t i n g and 2% wax gave t h e same d i s s o l u t i o n v a l u e . From t h e a f o r e m e n t i o n e d r e s u l t s Zee c o n c l u d e d t h a t t h e o r o d u c t o b t a i n e d bv t h e s n o u t e d bed p r o c e s s was o f s u p e r i o r q u a l i t y t o t h e one p r o d u c e d by C I L . A c o a t i n g t i m e o f 11 mi n u t e s was r e q u i r e d t o a c h i e v e 28% s u l p h u r i n t h e s p o u t e d bed f o r g r a n u l a r u r e a . I t was a l s o f o u n d t h a t c o o l i n g t h e p r o d u c t i n a s p o u t e d bed had l i t t l e i n f l u e n c e on d i s s o l u t i o n r a t e s . The 24 h o u r a c c e l e r a t e d d i s s o l u t i o n t e s t appeared t o g i v e r e s u l t s w h i c h c o r r e l a t e d b e s t w i t h t h e 7-day t e s t . No a t t e m p t was made t o e s t a b l i s h a c o r r e l a t i o n o f t h e 5, 24, and 48 h r t e s t and t h e 7-day d i s s o l u t i o n t e s t . A l t h o u g h t h e i n v e s t i g a t i o n c a r r i e d out by Zee d i d n o t p r o v i d e e x t e n s i v e q u a n t i t a t i v e i n f o r m a t i o n i t s e r v e d as a s t e p p i n g s t o n e f o r t h e d e s i g n o f an improved c o a t i n g f a c i l i t y . The main o p e r a t i o n a l problems e n c o u n t e r e d by Zee w i t h h i s equipment were s o l i f i c a t i o n o f s u l p h u r a t t h e n o z z l e t i p ; s u l p h u r f l o w o b s t r u c t i o n s due t o s o l i d i f i c a t i o n i n t h e p i p i n g s y s t e m ; problems w i t h t e m p e r a t u r e c o n t r o l ; an 27 i n a d e q u a t e s u l p h u r m e l t i n g s y s tem; t h e need f o r l a r g e amounts o f h o t a i r t o m e l t t h e s u l p h u r . To overcome t h e s e p r o b l e m s a new p l a n t was d e s i g n e d by Ma t h u r , M e i s e n and L i m ^ ^ . T h i s p l a n t (see F i g u r e 2.9) was s i m i l a r t o t h e p r e v i o u s one b u t w i t h s e v e r a l major changes such as a new s u l p h u r m e l t e r ; steam j a c k e t e d p i p i n g f o r a l l s u l p h u r l i n e s ; steam h e a t e d m e t e r i n g pump f o r s u l p h u r ; improved steam h e a t e d n o z z l e arrangement; h e a t i n g o f a t o m i z i n g a i r by e l e c t r i c a l t a p e s ; a g l a s s s p o u t e d bed column; a v a r i a b l e o r i f i c e ; a s c r u b b e r f o r p o l l u t i o n c o n t r o l . The new m e l t e r (see F i g u r e 2.10) was a p y r e x g l a s s v e s s e l e q u i p p e d w i t h a s t a i n l e s s s t e e l steam c o i l . The m e l t e r c a p a c i t y was 27.2 kg o f m o l t e n s u l p h u r . The m o l t e n s u l p h u r was pumped from t h e m e l t e r by a steam h e a t e d m e t e r i n g pump (Lewa: Model HKI) t h r o u g h steam j a c k e t e d t r a n s f e r l i n e s . The steam h e a t e d n o z z l e assembly i s shown i n F i g u r e 2.11. The a i r a t o m i z i n g n o z z l e was an " i n t e r n a l m i x i n g " - t y p e ( S p r a y i n g Systems I n c . : F l u i d Cap 2050, A i r Cap 67147). The s p o u t i n g v e s s e l c o n s i s t e d o f a 0.15 m I.D., 0.91 m l o n g , p y r e x g l a s s column (see F i g u r e 3.2) w i t h a s t a i n l e s s s t e e l c o n i c a l base (60°.Angle). Temperatures were m o n i t o r e d by t h r e e i r o n - c o n s t a n t a n t h e r m o c o u p l e s a t d i f f e r e n t bed l e v e l s . A s a m p l i n g p o r t was p r o v i d e d a t t h e s i d e o f t h e c o n i c a l bottom. A w a t e r s c r u b b e r was added downstream from t h e c y c l o n e , t o remove v e r y f i n e p a r t i c l e s and e l i m i n a t e odour p r o b l e m s . I n t h e t e s t s p e r f o r m e d by L i m ^ ^ t h e main v a r i a b l e s i n v e s t i g a t e d were c o a t i n g t e m p e r a t u r e , s p o u t i n g a i r f l o w r a t e , a t o m i z i n g a i r f l o w r a t e , s u l p h u r f l o w r a t e , bed d e p t h , e f f e c t o f a d d i t i v e s (such as C O 2 , ammonia, n i t r o g e n , D i c y c l o p e n t a d i e n e ) , t y p e o f u r e a ( i . e . g r a n u l a r and p r i l l e d ) . The TVA 7-day d i s s o l u t i o n t e s t w i t h s l i g h t m o d i f i c a t i o n s was us e d t o check p r o d u c t q u a l i t y i n a l l c a s e s . The bed t e m p e r a t u r e was f o u n d t o have a s t r o n g e f f e c t on t h e d i s s o l u t i o n : F i g u r e 2.9: UBC Spouted Bed f o r S u l p h u r C o a t i n g o f Urea ( M o d i f i c a t i o n d e s i g n e d by Mathur, M e i s e n and Lim) Rotameters 1 J L X Air-Water-TTTT • — — * — * [Stirrer * 1 I Sulphur Pot Steam Supply—» From Main ( - 7 5 psig) ROTAMETERS 1. Cooling Air 2. Spouting Air 3. Atomizing Air 4 . Water I Main LHeater Cyclonej —JfD Cooling Column Spouting Column t Ly Spouting Air Drain Atomizing Air Line r Steaml Trap To Drain w Steam Heated Pump Steam Traps Shutter Orifice To Drain To Drain Asbestos Lagging Heating Tape +-+-+-+-+ Sulphur Flow Dust Free Exhaust i Scrubber To Drain CO F i g u r e 2.10: Steam Heated S u l p h u r M e l t e r (Mathur, Meisen and Lim) Motor and Stirrer 1 Stainless Steel Plate-(14" square) Pyrex Glass Cyl inder-(9"diameter x 12" high) To Steam Trap and Drain Inlet for Solid Sulphur Drain Molten Sulphur Outlet Steam Coil (1/2" diameter Stainless Steel Tube) Steam Inlet (75 psig ) 30 1 0.5' T W777Z7, 0.25 c D 0.25 + 1 ^ 0.25 $ T | ^ - ^ ' 0.75" 1 i A Nozzle B Nozzle Cap C Nozzle Cap Retainer Ring D Nozzle Base E Nozzle Housing F. Plug a Sulphur Passage b Atomizing Air Passage c Atomizing Air Distribution Well d Steam Inlet e Sulphur Inlet f Steam Outlet g Atomizing Air Inlet F i g u r e 2.11: N o z z l e Arrangement (Mathur, M e i s e n and Lim) 31 i t d e c r e a s e d w i t h i n c r e a s i n g t e m p e r a t u r e up t o about 80°C and t h e n i n c r e a s e d f 171 a g a i n . Lim gave no e x p l a n a t i o n f o r t h i s b u t a p a p e r by M e i s e n and Mathur c o n t a i n e d t h e f o l l o w i n g s t a t e m e n t s : " F i r s t , a t e l e v a t e d t e m p e r a t u r e s t h e u r e a - s u l p h u r bond i s i m p r o v e d , p o s s i b l y due t o t h e i n c r e a s e d p r e s e n c e o f t h e 8 and p o l y m e r i c s u l p h u r a l l o t r o p e s . The p r o d u c t i s b r i g h t - y e l l o w and s h i n y whereas low t e m p e r a t u r e o p e r a t i o n r e s u l t s i n a w h i t i s h - y e l l o w , mat c o a t s u g g e s t -i n g a - s u l p h u r . I t i s n o t e w o r t h y t h a t t h e h i g h t e m p e r a t u r e p r o d u c t l o o s e s i t s b r i g h t c o l o u r o v e r a p e r i o d o f about 25 h o u r s w i t h o u t , however, s u f f e r i n g n o t i c e a b l y i n d i s s o l u t i o n c h a r a c t e r i s t i c s . The s econd r e a s o n may be t h a t s p r a y i n g m o l t e n s u l p h u r i n t o a c o o l bed causes t h e d r o p l e t s t o s o l i d i f y p a r t i a l l y b e f o r e t h e y c o l l i d e w i t h t h e u r e a p a r t i c l e s g i v i n g a p o o r e r bond. T h i s e x p l a n a t i o n i s s u p p o r t e d by t h e o b s e r v a t i o n t h a t i n c r e a s i n g s u l p h u r f l o w r a t e and hence d r o p l e t s i z e improves p r o d u c t q u a l i t y " . The s p o u t i n g a i r f l o w r a t e was f ound t o have l i t t l e e f f e c t on p r o d u c t d i s s o l u t i o n r a t e s i n t h e range t e s t e d (0.34 t o 1,28 m 3/min), The a t o m i z i n g a i r f l o w r a t e had a c l e a r i n f l u e n c e on d i s s o l u t i o n i . e . a t 0.83 and 0.39 m 3/hr t h e D 2 5 v a l u e s were 90.5 and 46.6%, r e s p e c t i v e l y . Hence i n c r e a s i n g t h e a t o m i z i n g a i r f l o w d e c r e a s e s p r o d u c t q u a l i t y . No c l e a r e x p l a n a t i o n was g i v e n . The s u l p h u r f l o w r a t e a l s o i n f l u e n c e d t h e v a l u e s , w h i c h were 61.6 and 25.5% a t s u l p h u r f l o w r a t e s o f 54.4 and 86 g/min, r e s p e c t i v e l y . T h e r e f o r e , i n c r e a s i n g t h e s u l p h u r f l o w r a t e improved p r o d u c t q u a l i t y . T h i s e f f e c t was s a i d t o be due t o : " C o a r s e r s u l p h u r d r o p l e t s p r o d u c e d by t h e i n c r e a s e d f l o w " . The e f f e c t o f bed depth on was a l s o i n v e s t i g a t e d and i t was f o u n d t h a t s h a l l o w e r bed depths gave a somewhat b e t t e r p r o d u c t q u a l i t y . "The p a r t i c l e s a r e r e c y c l e d more r a p i d l y and hence have a b e t t e r chance o f r e c e i v i n g a u n i f o r m c o a t " . 32 Gaseous ( C 0 2 , Ammonia, N i t r o g e n ) and l i q u i d ( D i c y c l o p e n t a d i e n e ) a d d i t i v e s were t r i e d w i t h o u t p o s i t i v e r e s u l t s . Lim was a b l e t o p r o d u c e a s u l p h u r c o a t e d u r e a w i t h a 7-day d i s s o l u t i o n t e s t o f l e s s t h a n 20%, p r o v i d e d t h e u r e a was p r e h e a t e d t o about 80°C and an a p p r o p r i a t e c o m b i n a t i o n o f s u l p h u r and a t o m i z i n g a i r f l o w r a t e s was m a i n t a i n e d ( i . e . 18.1 kg s u l p h u r / m 3 o f a t o m i z i n g a i r ) . A l t h o u g h p r o d u c t q u a l i t y was f a i r l y good and t h e p i l o t p l a n t was p e r f o r m i n g r e a s o n a b l y w e l l , some o p e r a t i o n a l problems were e n c o u n t e r e d ; i . e . s u l p h u r p l u g g i n g i n t h e l i n e s , v e r y l o n g p r e h e a t i n g t i m e s , c o l d s p o t s i n t h e s u l p h u r pump. Hence a new d e s i g n (see F i g u r e 3.1) was made by M e i s e n and Weiss as d e s c r i b e d l a t e r i n t h i s t h e s i s . 2.3 S e l e c t e d P h y s i c a l P r o p e r t i e s o f S u l p h u r (18) S u l p h u r o c c u r s i n a number o f d i f f e r e n t a l l o t r o p i c f o r m s : ' o r t h o r h o m b i c , m o n o c l i n i c , p o l y m e r i c and o t h e r s . The o r t h o r h o m b i c ( a l s o c a l l e d r hombic) form i s t h e most common t y p e o f s u l p h u r . Each a l l o t r o p i c form d i f f e r s i n s o l u b i l i t y , s p e c i f i c g r a v i t y , c r y s t a l l i n e arrangement and o t h e r p h y s i c a l p r o p e r t i e s ( S e e T a b l e s 2.4 and 2.5). At a t m o s p h e r i c p r e s s u r e and t e m p e r a t u r e s l e s s t h a n 95.5°C, rhombic s u l p h u r , S a , i s t h e s t a b l e form. Between 95.5°C and 119°C ( t h e s u l p h u r m e l t i n g p o i n t ) t h e m o n o c l i n i c c r y s t a l l i n e s t r u c t u r e S 0 i s dominant. p At t h e m e l t i n g p o i n t , c y c l o o c t a s u l p h u r (S-j.) i s i n e q u i l i b r i u m w i t h c a t e n a o c t a s u l p h u r (S^) w h i c h t h e n p o l y m e r i z e s w i t h S^ i n t o unbranched c h a i n s ( S y ) . At 159°C t h e p o l y m e r i z a t i o n i n c r e a s e s s h a r p l y and S , w h i c h had been a s o l v a t e , s u d d e n l y becomes t h e s o l v e n t . Most p h y s i c a l p r o p e r t i e s o f m o l t e n s u l p h u r e x h i b i t a s t r o n g d i s c o n t i n u i t y a t t h i s t e m p e r a t u r e . V i s c o s i t y , h e a t c a p a c i t y , t h e r m a l c o n d u c t i v i t y and d e n s i t y have been measured by s e v e r a l (24) r e s e a r c h e r s and t a b l e s a r e a v a i l a b l e . 33 Table 2.4: Physical and Chemical Properties of Sulphur (25) Physical State (21°C-1 atm) Bulk density, kg/m3 B o i l i n g point, °C Melting point, °C Odour Flash Point, °C COC Autoignition Temperature (Dust i n a i r , °C) Vapor pressure, 20°C, mm Hg Explosive l i m i t s (Dust i n A i r ) g/m3 Solid 1200-1394 Lumps 560-960 Powder 444°C 119°C None 188°C 190°C Less than 0.0001 35 (Lower) 1400 (Upper) 34 T a b l e 2.5: P r o p e r t i e s o f Common S u l p h u r A l l o t r o p e s ^ ' 2 7 - ' P r o p e r t y Common Name Recommended Name M o l e c u l a r F o r m u l a C r y s t a l l i n e Form U n i t C e l l S t a b i l i t y C o l o r D e n s i t y , g/cm 3 Shore B-2 Hardness T e n s i l e S t r e n g t h , p s i a O r t h o r h o m b i c S u l p h u r O r t h o r h o m b i c (a) S u l p h u r S 1 2 8 O r t h o r h o m b i c 16 M o l e c u l e s o f S, ( S J A 8 < 95.5°C Opaque Y e l l o w a t 24°C 2.07 90 48 M o n o c l i n i c S u l p h u r M o n o c l i n i c (8) S u l p h u r S 4 8 M o n o c l i n i c 6 M o l e c u l e s o f S , ( S D ) A 8 95.5°C t o 119°C Between Y e l l o w and Orange 1.96 95 60 35 F i g u r e 2.12 shows t h e s u l p h u r v i s c o s i t y as a f u n c t i o n o f t e m p e r a t u r e . 0.06 — Supercooled Sulphur — Normal Liquid Sulphur O Extrapolated X Calc. Farr 8t MacLeod Data o Determined, R. Fanelli — Det., R. Fanelli & R.F. Bacon 0.05 o a T 0.04 003 u> o o in 0 0 2 001 o I I o \ \ Q 0.00' 80 _l 120 200 240 280 320 160 Temperature ° F F i g u r e 2.12: V i s c o s i t y o f S u l p h u r , Low Temperature Range 3. EXPERIMENTAL APPARATUS AND PROCEDURE 3.1 A p p a r a t u s The main components o f t h e a p p a r a t u s a r e t h e s p o u t e d bed, t h e s u l p h u r s u p p l y system, t h e n o z z l e a s s e m b l y , t h e d u s t c o l l e c t o r s , a i r and o t h e r s u p p l y systems (see F i g u r e 3.1). 3.1.1 Trie Spouted Hud T h i s i s t h e v e s s e l i n w h i c h t h e c o a t i n g o p e r a t i o n as w e l l as h e a t i n g and c o o l i n g were p e r f o r m e d . E x i s t i n g equipment from t h e p i l o t p l a n t d e s i g n e d by Lim and M e i s e n was u s e d . The v e s s e l c o n s i s t e d o f a 0.152 m I.D., 0.91 m l o n g , 6.35 mm t h i c k p y r e x g l a s s column; a s t a i n l e s s s t e e l c o n i c a l b o t t o m , and an o r i f i c e p l a t e w i t h a s h u t t e r t y p e mechanism (see F i g u r e 3.2). Three i r o n -c o n s t a n t a n t h e r m o c o u p l e s were used t o m o n i t o r t h e bed t e m p e r a t u r e a t d i f f e r e n t l e v e l s . The s h u t t e r s e r v e d as a v a r i a b l e - s i z e o r i f i c e f o r t h e s p o u t i n g a i r i n l e t . As shown i n F i g . 3.3, i t c o n s i s t e d o f f i v e S - s h a p e d , - o v e r l a p p i n g s t a i n l e s s s t e e l l e a v e s a r r a n g e d i n a c i r c l e . The o r i f i c e o p e n i n g and c l o s i n g was a c h i e v e d w i t h a l e v e r . (Minimum and maximum o p e n i n g s were 3.2 mm and 40 mm, r e s p e c t i v e l y ) . 3.1.2 The. Sutphun. Supply System T h i s system c o n s i s t e d o f t h e s u l p h u r m e l t e r , f i l t e r , r o t a m e t e r , s u l p h u r l i n e s and n i t r o g e n s u p p l y . (a) The s u l p h u r m e l t e r : As shown i n F i g . 3.4, t h e m e l t e r was a steam j a c k e t e d , 0.203 m I.D., 0.457 m h i g h s t a i n l e s s s t e e l c y l i n d e r . I t s c a p a c i t y was a p p r o x i m a t e l y 25 kg w h i c h was s u f f i c i e n t f o r s e v e r a l r u n s . To e n s u r e u n i f o r m t e m p e r a t u r e s an e l e c t r i c a l , v a r i a b l e speed s t i r r e r was p r o v i d e d . (Model GT 60-10, M a n u f a c t u r e d by S a r g e n t W e l c h ) . F i g u r e 3.1: S i m p l i f i e d Diagram o f UBC Spouted Bed F a c i l i t y Used In t h i s Work (Designed by Meisen and Weiss) Water Additives Line Sulfur Melter ROTAMETERS I. Cooling Air 2 Spouting Air 3 Atomizing Air 4 Sulfur Steam Heated Electrical Tape Dust Free Exhaust to Fume Hood Scrubber 38 3' Long Iron-Constontin Thermocouple VA VS To Cyclone Sampling Port — Top Plote H t _ T l O " d i a . xl l /4" S.S.) - C D 6" dia. x3 'x 1/4" Pyrex Glass Vessel Conical Base Shutter Assembly F i g u r e 3.2: Spouted Bed Column (Mathur, M e i s e n , and Lim) 39 F i g u r e 3.3: S h u t t e r Assembly (Mathur, M e i s e n , and Lim) 40 Steam Inlet " 18' I r7 r r ^ r Mixer Shaft Seal Housing Sulphur Fitting Port I 3 / 8 1/4 I *1 Viton 0 Ring I.D. 8 1/2 1 3 / 8 O.D. 8 3/4 1/2 " T Sulphur Outlet Sulphur Melter 10 3/4-5^ 6^ CI±E2ZZZZZZZZZZ ( /2 __ Em n ^ 3/8 JZ r / / / / t Steam Inlet Condensate Outlet Bottom Plate / / / i Drainage Plug Condensate Outlet F i g u r e 3 . 4 ( a ) : S e c t i o n a l View o f S u l p h u r M e l t e r F i g u r e 5 / l 6 > S u l p h u r M e l t e r Top View b) The F i l t e r : To p r e v e n t n o z z l e p l u g g i n g due t o p a r t i c u l a t e s , a 316 SS c a r t r i d g e f i l t e r ( R i g i m e s h , m a n u f a c t u r e d by P a l l Canada L t d . ) s c r e e n s i z e 100 (149 ym), was u s e d . A steam h e a t e d j a c k e t e d c a s i n g h e l d t h e f i l t e r e lement (see F i g u r e 3.5). c) S u l p h u r Rotameter: A s t a n d a r d r o t a m e t e r t u b e ( B r o o k s , Model R-6M-25-A) was encased i n a steam-heated b r a s s b l o c k as shown i n F i g . 3.6. The t u b e was h e l d i n p o s i t i o n by two 316 SS p i e c e s l o c a t e d a t t h e t o p and bottom o f t h e b r a s s c a s i n g ; v i t o n "0" r i n g s were used t o s e a l t h e ends. Two p o l y c a r b o n a t e windows w i t h h e a t r e s i s t a n t g a s k e t s , a l l o w e d a c l e a r v i e w o f t h e r o t a m e t e r t u b e . A p y r e x f l o a t (6.35 mm d i a . ) was used i n most e x p e r i m e n t s ; i t was exchanged l a t e r f o r a s e t o f s a p h i r e and s t a i n l e s s s t e e l f l o a t s . d) S u l p h u r L i n e s : ( F i g . 3.10). The main s u l p h u r l i n e was 1/4", 316 s t a i n l e s s s t e e l t u b i n g j a c k e t e d by a 3/8" steam h e a t e d t u b e . A l l f i t t i n g s were s u p p l i e d by Swagelock. e) N i t r o g e n S u p p l y : S u l p h u r was f o r c e d out o f t h e m e l t e r by p r e s s u r i z e d n i t r o g e n . A p r e s s u r e r e l e a s e v a l v e was i n s t a l l e d on t o p o f t h e s u l p h u r m e l t e r . 3.1.3 The. Hozzle. ki>i>embly The assembly c o n s i s t e d o f a p e r f o r a t e d p l a t e , t h e " b a y o n e t " and t h e n o z z l e as shown i n F i g . 3.7. a) The p e r f o r a t e d p l a t e : The p e r f o r a t e d p l a t e i s used as a f l o w s t r a i g h t e n e r f o r t h e s p o u t i n g a i r . As shown i n F i g . 3.8, i t a l s o p o s i t i o n e d t h e n o z z l e and b a y o n e t . b) The b a y o n e t : The bayonet was b a s i c a l l y a 1" I.D. steam h e a t e d s t a i n l e s s s t e e l t u b e , w h i c h c o n t a i n e d t h e s u l p h u r , a t o m i z i n g a i r and steam l i n e s (see F i g . 3.7). T h i s t u b e was f l a r e d a t t h e bottom t o p r o v i d e a d d i t i o n a l s p a c e f o r a t h e r m o c o u p l e and c o n d e n s a t e o u t l e t . Thermal e x p a n s i o n problems were overcome by l e t t i n g t h e b o t t o m o f t h e bayonet expand f r e e l y . F i g u r e 3 . 5 ( a ) : S e c t i o n a l View o f S u l p h u r F i l t e r Sulphur Outlet Steom Inlet I Condensate vOutlet • Vtf j -q—----« i ^4 Steam Inlet 1/8 3 = i JJL 11/2 'i 2 ^ F Condensate Outlet -Filter Casing -Filter Element Sulphur Inlet Axis Line 5 1/2 "0 F i g u r e 3 . 5 ( b ) : Top P l a t e o f S u l p h u r F i l t e r F i g u r e 3 . 6 ( a ) : S e c t i o n a l View o f S u l p h u r Rotameter Back Front I Steam Inlet 1/8 MPT x 1/4 Tubing 2 ,3 ,4 = Sealed Plugs 1/8" MPT Scale h i Back Front Front Back 4 Condensate Outlet 1/8 MPT x 1/4 Tubing 1,2,3 : Sealed Plugs 1/8 " M P T Scale I I F i g u r e 3 . 6 ( b ) : V a r i o u s V i e w s o f Rotameter Ends 47 B Sulphur Outlet Steam Inlet 3/8" Tubing -3/8" Pipethread 1/16 Bolts B Polycarbonate Window Plug 1/8" MPT Hole 3/8" Sulphur Inlet F i g u r e 3 . 6 ( c ) : G e n e r a l View o f S u l p h u r Rotameter 48 Nozzle I y/m/h -Top Flange -Gasket Spouting Air Line 3" ID. Copper Tubing 24" Bayonet I 1/8" O.D. SS. Tubing Spouting Air Inlet Steom Inlet Atomizing Air Line Sulphur Line F i g u r e 3.7: S e c t i o n a l View o f N o z z l e Arrangement and G e n e r a l Assembly 49 A i r C a p - R e t a i n e r R i n g - F l u i d C a p 3/16 0545 T 0 . 4 5 5 J — P e r f o r a t e d Plate i * - l 5 Holes 1/4"* . A x i s L i n e 2 5 / 8 * 1—15 Holes 1/4 > . A x i s L ine 2 3/8d> 15 Holes i / 4 > . A x i s L ine 2 * — 1 5 Holes 1/4"d> . A x i s Line I 1/2* Atomizing Air L ine 1/4 > T u b e -Su lphur L i n e 1/4 "0 T u b e - S t e a m 1/4" <f> T u b e F i g u r e 3.8: P e r f o r a t e d P l a t e , Upper F l a n g e and N o z z l e S e c t i o n a l View 50 c ) The n o z z l e : The p n e u m a t i c n o z z l e was s u p p l i e d b y S p r a y i n g S y s t e m s C o . ( F l u i d Cap 2 0 5 0 , A i r Cap 67147) and was o f t h e " i n t e r n a l - m i x i n g " t y p e . I t c o n s i s t e d o f t h r e e p a r t s : t h e f l u i d c a p , t h e a i r cap and t h e r e t a i n e r r i n g . The f l u i d cap ends i n a f i n e t i p (640 ym I . D . ) t h r o u g h w h i c h t h e m o l t e n s u l p h u r f l o w e d . A i r e n t e r e d t h r o u g h t h r e e h o l e s ( p l a c e d 120° a p a r t ) i n t o t h e s p a c e be tween t h e f l u i d and a i r c a p . The a i r and s u l p h u r c o n v e r g e d j u s t above t h e n o z z l e t i p t h u s f o r m i n g s u l p h u r d r o p l e t s . 3 . 1 . 4 Vtut CoU.e.c£oAA As shown i n F i g . 3 . 9 , any u r e a and s u l p h u r d u s t e l u t r i a t e d f r o m t h e s p o u t e d bed p a s s e d t h r o u g h a f l e x i b l e h o s e i n t o t h e c y c l o n e . Any r e m a i n i n g d u s t was removed b y t h e s c r u b b e r . The t r e a t e d a i r was f i n a l l y d i s c h a r g e d i n t o t h e l a b o r a t o r y e x h a u s t s y s t e m . 3 . 1 . 5 kiA and SupptL&i As shown i n F i g u r e 3 . 1 0 , a l l a i r l i n e s were t a k e n f rom a common m a n i f o l d c o n n e c t e d t o t h e ma in c o m p r e s s e d a i r l i n e i n t h e l a b o r a t o r y (Max. P r e s s u r e a p p r o x . 240 k P a ) . The a i r f l o w f o r t h e d i f f e r e n t s e r v i c e s was measu red b y r o t a m e t e r s . The s p o u t i n g a i r was h e a t e d by a 3 kW e l e c t r i c h e a t e r c o n t r o l l e d by a p r o p o r t i o n a l - i n t e g r a l c o n t r o l l e r s u p p l i e d by Omega E n g i n e e r i n g I n c . (Mode l No . 4 9 J , r a n g e 0 - 2 0 0 ° C ) . The a t o m i z i n g a i r was h e a t e d e l e c t r i c a l l y . I t s t e m p e r a t u r e was m o n i t o r e d by a t h e r m o c o u p l e and c o n t r o l l e d by a p r o p o r t i o n a l - i n t e g r a l c o n t r o l l e r (Omega E n g i n e e r i n g I n c . , M o d e l 4 9 J , Range 0 - 2 0 0 ° C ) . The c e n t r a l l a b o r a t o r y s team s u p p l y was u s e d w h i c h had a p r e s s u r e o f a p p r o x . , 550 k P a . A p r e s s u r e r e g u l a t o r was i n s t a l l e d t o s e t t h e p r e s s u r e t o t h e d e s i r e d v a l u e ( u s u a l l y 480 k P a ) . The l a y o u t o f t h e s team and c o n d e n s a t e From Water Supply F i g u r e 3.9: Dust C o l l e c t i o n System 52 IS) C u 3 X. PH 1—1 3 CO c rt • H 3 • H Q . Q . 3 C O < —eo ^ Cooling Position J^^J l i n e s i s shown i n F i g . 3.11. A l l steam t r a p s d i s c h a r g e d i n t o a common a t m o s p h e r i c h e a d e r w h i c h d r a i n e d i n t o t h e main sewer system. 3.2 E x p e r i m e n t a l P r o c e d u r e s The e x p e r i m e n t a l p r o c e d u r e s f o l l o w e d i n t h i s s t u d y a r e d e s c r i b e d below. 3.2.1 Stout Up P r i o r t o t h e c o a t i n g e x p e r i m e n t s , t h e f o l l o w i n g s t e p s have t o be p e r f o r m e d : a) F i l l up t h e m e l t e r w i t h g r a n u l a r o r sl-ated s u l p h u r . Open up t h e main a i r and steam v a l v e s . S e t t h e steam p r e s s u r e r e g u l a t o r a t t h e d e s i r e d v a l u e ( u s u a l l y 480 k P a ) . b) S l o w l y open t h e steam s u p p l y v a l v e u n t i l t h e p r e s s u r e r e a c h e s t h e d e s i r e d v a l u e ( t h i s has t o be done s l o w l y t o p r e v e n t "hammering"). c) S t a r t t h e w a t e r f l o w t o t h e s c r u b b e r . d) S w i t c h on t h e main power s u p p l y and d i g i t a l t e m p e r a t u r e r e a d o u t ; check t h e t e m p e r a t u r e s a t d i f f e r e n t p o i n t s o f t h e equipment. e) A f t e r a p p r o x i m a t e l y 1 hour o f p r e h e a t i n g , s w i t c h on t h e s t i r r e r . I f i t does n o t t u r n due t o i n c o m p l e t e m e l t i n g , w a i t f o r a w h i l e and t r y a g a i n . Once t h e s t i r r e r s t a r t s , s e t i t t o t h e mid p o i n t o f t h e low v e l o c i t y r ange (Approx. 100 R.P.M.) f ) M o n i t o r t h e t e m p e r a t u r e s t h r o u g h o u t t h e equipment and, once a l l t h e s u l p h u r i s m e l t e d ( t y p i c a l l y one t o two h o u r s ) , p r o c e e d w i t h t h e c o a t i n g e x p e r i m e n t s . 3.2.2 Coating Vh.oczduA.0. a) Weigh a u r e a c h a r g e ( t y p i c a l l y about 4.5 kg) and t r a n s f e r i t t o t h e s p o u t i n g column. Make s u r e t h e s a m p l i n g v a l v e and t h e bottom s h u t t e r a r e c l o s e d , and t h e column i s i n t h e " r e s t " p o s i t i o n (which means t o move t h e column away from t h e s u l p h u r n o z z l e , t o t h e l e f t s i d e o f t h e e q u i p m e n t ) . F i g u r e 3.11: Steam ;ind Condensate System Layout 55 b) Connect t h e a i r exhaust t r u n k t o t h e column t o p . E n sure t h a t t h e c y c l o n e d u s t h o p per i s c l e a n and i n p l a c e . c) Crack open t h e a t o m i z i n g a i r v a l v e ( a p p r o x . 0.35 m 3 / h r ) and t u r n on t h e a t o m i z i n g a i r h e a t e r . T h i s i s done t o p r e v e n t p a r t i c l e s f r o m f a l l i n g o n t o t h e n o z z l e once t h e s p o u t e d bed column i s i n t h e " c o a t i n g " p o s i t i o n . d) S e t t h e t e m p e r a t u r e c o n t r o l l e r f o r t h e a t o m i z i n g a i r t o 150°C. e) Move t h e s p o u t i n g column t o t h e " c o a t i n g " p o s i t i o n and s e c u r e i t by t i g h t e n i n g t h e b o l t s i n t h e bo t t o m f l a n g e . f ) S i m u l t a n e o u s l y open t h e s p o u t i n g a i r v a l v e and t h e s h u t t e r ( t o t h e d e s i r e d s e t t i n g ) t i l l t h e s p o u t i n g s t a r t s ; l e t s p o u t i n g c o n t i n u e f o r approx. 5 min. t o e x p e l f i n e s from t h e bed. S w i t c h on t h e s p o u t i n g a i r h e a t e r . g) Reduce t h e f l o w o f a i r u n t i l s p o u t i n g s t o p s and s e t t h e s p o u t i n g a i r t e m p e r a t u r e c o n t r o l l e r t o a p p r o x i m a t e l y h a l f o f t h e d e s i r e d bed t e m p e r a t u r e ; p r e h e a t t h e bed i n t h e q u a s i s t a t i c c o n d i t i o n t o m i n i m i z e u r e a a t t r i t i o n . h) M o n i t o r t h e s p o u t i n g a i r t e m p e r a t u r e b e f o r e i t e n t e r s t h e bed and ens u r e t h a t i t does n o t exceed 100°C, t o p r e v e n t u r e a a g g l o m e r a t i o n a t t h e bottom o f t h e cone. i ) A f t e r 10 min. r e s e t t h e s p o u t i n g a i r t e m p e r a t u r e c o n t r o l l e r t o a h i g h e r t e m p e r a t u r e and r e p e a t t h e p r e v i o u s s t e p s . C o n t i n u e t h i s p r o c e d u r e t i l l t h e d e s i r e d t e m p e r a t u r e i s r e a c h e d . The p r e h e a t i n g o p e r a t i o n t a k e s a p p r o x i m a t e l y 30 m i n u t e s . j ) I f t h e a t o m i z i n g a i r t e m p e r a t u r e i s i n c r e a s i n g t o o s l o w l y , r a i s e t h e a t o m i z i n g a i r f l o w r a t e . However, when t h i s f l o w i s e x c e s s i v e (approx. 0.6 m 3/hr) some s u l n h u r mav be a t o m i z e d due t o a s u c t i o n e f f e c t . (Note t h a t t h e s u l p h u r l i n e does n o t have a v a l v e ) . k) Once t h e bed and a t o m i z i n g a i r t e m p e r a t u r e s have r e a c h e d t h e d e s i r e d v a l u e s ( u s u a l l y 80 and 150°C, r e s p e c t i v e l y ) , open t h e s p o u t i n g a i r v a l v e u n t i l t h e f o u n t a i n r e a c h e s a h e i g h t o f about 0,20 m above t h e bed. T h i s h e i g h t i s i n d i c a t i v e o f good p a r t i c l e c i r c u l a t i o n and improves e l u t r i a t i o n o f f i n e s from 56 t h e bed b e f o r e c o a t i n g s t a r t s . H i g h e r s p o u t i n g a i r f l o w r a t e s c o u l d cause u n n e c e s s a r y p a r t i c l e a t t r i t i o n . 1) When t h e bed t e m p e r a t u r e has r e a c h e d a s t e a d y v a l u e , c l o s e t h e n i t r o g e n r e l e a s e v a l v e l o c a t e d on t h e m e l t e r and ensure t h a t t h e s u l p h u r f i l l i n g p o r t i s c l o s e d . I n c r e a s e t h e a t o m i z i n g a i r f l o w t o t h e d e s i r e d v a l u e ; open t h e n i t r o g e n s u p p l y v a l v e t o g i v e t h e d e s i r e d s u l p h u r f l o w r a t e as i n d i c a t e d by t h e r o t a m e t e r . m) A d j u s t t h e s p o u t i n g a i r f l o w r a t e as needed t o m a i n t a i n a f o u n t a i n h e i g h t o f about 0.20 m above t h e bed. As t h e c o a t i n g c o n t i n u e s , t h e u r e a g r a n u l e s become l a r g e r and h e a v i e r w h i c h r e q u i r e s more s p o u t i n g a i r . n) M o n i t o r a l l o p e r a t i n g c o n d i t i o n s , t a k e u r e a samples when r e q u i r e d ( t y p i c a l l y e v e r y 5 min) , always e n s u r i n g t h a t a d d i t i o n a l s p o u t i n g a i r i s s u p p l i e d t o p r e v e n t t h e sp o u t from c o l l a p s i n g . o) When t h e c o a t i n g i s c o m p l e t e d , c l o s e t h e n i t r o g e n s u p p l y v a l v e , and open t h e p r e s s u r e r e l e a s e v a l v e on t h e m e l t e r . Reduce t h e a t o m i z i n g a i r f l o w t o a minimum v a l u e . Once t h e n i t r o g e n p r e s s u r e i s r e l e a s e d , t h e s u l p h u r r o t a m e t e r u s u a l l y empties due t o t h e back p r e s s u r e i n t h e column. p) S i m u l t a n e o u s l y c l o s e t h e s p o u t i n g a i r v a l v e and s h u t t e r . Turn o f f t h e s p o u t i n g and a t o m i z i n g a i r h e a t e r s . U n b o l t t h e column and s w i n g out t h e column f o r u n l o a d i n g . Open t h e s h u t t e r and empty c o a t e d p r o d u c t i n t o a b u c k e t . When f i n i s h e d , move t h e column t o t h e " r e s t i n g " p o s i t i o n . Shut o f f t h e a t o m i z -i n g a i r f l o w c o m p l e t e l y . q) Weigh t h e p r o d u c t and d u s t c o l l e c t e d i n t h e c y c l o n e hopper, r ) The equipment i s now re a d y f o r a n o t h e r b a t c h r u n . s) I t i s i m p o r t a n t t o check t h e s u l p h u r m e l t e r a f t e r s e v e r a l r u n s t o ensure that, s u f f i c i e n t s u l p h u r r e m a i n s . I f n o t , more s o l i d s u l p h u r has t o be added t o t h e m e l t e r . A good p r a c t i c e i s t o f i l l t h e m e l t e r w i t h s u l p h u r a t t h e end o f t h e day and keep t h e steam s u p p l y on o v e r n i g h t ; t h i s r e d u c e s t h e s t a r t - u p t i m e on t h e n e x t day. 57 t ) The equipment can be l e f t w i t h t h e steam on o v e r n i g h t b u t t h e e l e c t r i c power has t o be t u r n e d o f f f o r s a f e t y r e a s o n s . 3.2.3 Shutdown a) Remove t h e n o z z l e and i n s t a l l f i t t i n g s f o r n i t r o g e n blow-back t o remove s u l p h u r from t h e r o t a m e t e r and l i n e s . Open t h e p r e s s u r e r e l i e f v a l v e and t h e s u l p h u r f i l l i n g p o r t . Do n o t blow-back w i t h more t h a n 70 kPa n i t r o g e n p r e s s u r e ( t h i s o p e r a t i o n t a k e s from 3 t o 6 m i n u t e s ) . b) A f t e r t h e s u l p h u r l i n e s a r e e m p t i e d , d i s c o n n e c t t h e blow-back s y s t e m , c o v e r t h e n o z z l e s e a t w i t h a screw cap and s h u t - o f f t h e steam s u p p l y v a l v e . c) T u r n o f f t h e s t i r r e r and main power s o u r c e . d) Stop t h e w a t e r s u p p l y and main power s o u r c e . e) C l o s e t h e a i r and steam v a l v e s a t p l a n t l i m i t s . f ) I f r e q u i r e d , c l e a n up column and c y c l o n e d u s t c o l l e c t o r . 3.2.4 Special. 0p£Aatlom> S m a l l q u a n t i t i e s o f c h e m i c a l l y and t h e r m a l l y s t a b l e a d d i t i v e s , l i q u i d s o r g a s e s , can be i n j e c t e d d i r e c t l y downstream o f t h e a t o m i z i n g a i r r o t a m e t e r by means o f a s y r i n g e pump and an i n j e c t i o n n o z z l e . The main a d d i t i v e t r i e d i n t h i s study.was s i l i c o n e (Dow C o r n i n g 200) wh i c h had a v i s c o s i t y o f 20 cs @ 25°C. S i l i c o n e i s a t r a d e name f o r D i m e t h y l S i l o x a n e P o l y m e r s . 3.2.5 MeaAuAzmmt ol Operating VasujxbZeA a) F l u i d Flow Measurements: A l l f l o w r a t e s were measured by c a l i b r a t e d f u l l v i e w r o t a m e t e r s . P a r t i c u l a r s o f t h e f l o w m e t e r i n g equipment a r e p r e s e n t e d i n T a b l e 3.1. A l l gas f l o w s a r e r e p o r t e d a t s t a n d a r d c o n d i t i o n s o f 20°C and 101.3 k P a . b) Temperature measurement: A l l t e m p e r a t u r e s were measured w i t h c a l i b r a t e d i r o n - c o n s t a n t an t h e r m o c o u p l e s c o n n e c t e d t o a d i g i t a l d i s p l a y 58 Stream A t o m i z i n g A i r S p o u t i n g A i r C o o l i n g A i r S u l p h u r T a b l e 3.1: F l u i d Flow Measurement Equipment R o t a m e t e r s Type Range 0-1.572 m 3/hr 0-1.434 m 3/min 0-2.538 0-100 g/min Brooks Tube S i z e R-7M-25-1 F l o a t G l a s s Brooks Tube S i z e R-12M-25-4 F l o a t S i z e 12-RS-221 Brooks Tube S i z e R-12M-127-3 F l o a t S i z e 12-RS-221 Brooks Tube S i z e R-6M-25-1 F l o a t G l a s s S a p h i r e S t a i n l e s s S t e e l T a b l e 3.2: Cominco Urea S c r e e n A n a l y s i s T y l e r mm wt,g X. l d . P 1 x./d i p: 6 3.36 - - - --6+7 -3.36+2.83 2.20 0.044 3.095 0.014 -7+8 -2.83+2.38 18.40 0.372 2.605 0.143 -8+10 -2.38+2.00 22.54 0.455 2.190 0.208 -10+12 -2.00+1.68 4.61 0.093 1.840 0.051 -12+14 -1.68+1.41 1.34 0.027 1.545 0.017 -14+16 -1.41+1.19 0.31 0.006 1.300 0.005 -16+18 -1.19+1.00 0.10 0.002 1.095 0.002 E = 0.439 4 = 1/(E x./d .) = 1/0.439 = 2.277 mm p ^ l p i / P a r t i c l e s below 1 mm amounted t o l e s s t h a n 0.05 g 59 ( F l u k e , Model 2160 A ) . Temperatures i n t h e s p o u t e d bed were measured a t t h r e e d i f f e r e n t l e v e l s (see F i g . 3.2) a p p r o x i m a t e l y 30 mm from t h e column w a l l . Thermocouples were a l s o used t o measure t e m p e r a t u r e s a t d i f f e r e n t p o i n t s i n t h e a p p a r a t u s (see F i g . 3.12). c) S o l i d s _ e l u t r i a t i o n r a t e : S o l i d s e l u t r i a t e d from t h e s p o u t e d bed were measured a f t e r each r u n by e m p t y i n g and w e i g h i n g t h e c o n t e n t s o f t h e c y c l o n e d u s t hopper. S u l p h u r c o n t e n t was d e t e r m i n e d by d i s s o l v i n g t h e u r e a i n w a t e r and w e i g h i n g t h e r e s i d u e a f t e r f i l t r a t i o n and d r y i n g . The u r e a c o n t e n t was d e t e r m i n e d by d i f f e r e n c e . d) The w e i g h t o f u r e a and s u l p h u r c o a t e d u r e a were d e t e r m i n e d w i t h a p l a t f o r m s c a l e b e f o r e and a f t e r each t e s t . e) The s p o u t h e i g h t and bed l e v e l were measured w i t h a m e a s u r i n g t a p e a t t a c h e d t o t h e o u t s i d e o f t h e g l a s s column. 3.2.6 AnaZytXA and quatiXy control a) Raw M a t e r i a l s : The o n l y t e s t p e r f o r m e d w i t h t h e u r e a b e f o r e c o a t i n g , was s c r e e n i n g t o d e t e r m i n e t h e p a r t i c l e s i z e d i s t r i b u t i o n . S t a n d a r d s i e v e s were u s e d and t h e a v e r a g e s i z e was d e t e r m i n e d by: d = 1/Z ( x./d .) p l p i where x. denotes t h e mass f r a c t i o n o f p a r t i c l e s w i t h d i a m e t e r d .. T a b l e l ^ p i 3.2 shows t h e i n d i v i d u a l s i z e f r a c t i o n s and t h e average p a r t i c l e s i z e f o r a t y p i c a l u r e a sample (Cominco). S u l p h u r was not a n a l y z e d f o r i m p u r i t i e s . C l e a n p r i l l e d s u l p h u r from A l b e r t a was used i n a l l e x p e r i m e n t s . S u l p h u r and u r e a were s u p p l i e d by "Green V a l l e y F e r t i l i z e r and C h e m i c a l Co. L t d . " . Ammonium Phosphate was used i n some runs t o d e t e r m i n e s u b s t r a t e i n f l u e n c e on s u l p h u r c o a t i n g q u a l i t y . A s c r e e n a n a l y s i s was p e r f o r m e d and gave t h e r e s u l t s shown i n T a b l e 3.3. b) P r o d u c t A n a l y s i s : S u l p h u r c o a t e d u r e a was a n a l y z e d f o r s u l p h u r c o n t e n t and d i s s o l u t i o n i n w a t e r . F i g u r e 3.12: Thermocouple l o c a t i o n 0 Ambient Temperature 1 Column # I 2 Atomizing Air 3 Sulfur Pot 4 Nozzle Arrang. Temp. 5 Spout Air Heater Exit 6 Column # 2 7 Column * 3 8 Scrubber Liquid Exiting 9 Spouting Air before entering Column 10 Sulfur Filter 11 Sulfur Rotameter CONTROL # I To Spouting Air Temperature Controller #2 To Atomizing Air Temperature Controller ON o 61 T a b l e 3.3: Cominco Ammonium Phosphate S c r e e n A n a l y s i s T y l e r mm wt,g x. l d . x./d i I 6 3.36 - - - --6+7 -3.36+2.83 4.3 0.089 3.095 0.029 -7+8 -2.83+2.38 19.0 0.392 2.605 0.150 -8+10 -2.38+2.00 20.0 0.412 2.190 0.188 -10+12 -2.00+1.68 3.7 0.076 1.840 0.041 -12+14 -1.68+1.41 0.7 0.014 1.545 0.009 -14+16 -1.41+1.19 0.4 0.008 1.300 0.006 -16+18 -1.19+1.00 0.3 0.006 1.095 0.006 -18+20 -1.00+0.841 0.1 0.002 0.921 0.002 2 = 0.432 d = 1/CEx.j/d ,.) = 1/0.432 = 2.313 mm P a r t i c l e s below 0.841 mm amounted t o l e s s t h a n 0.05 g. p b u l k = 9 8 6 ^ 62 b . l D i s s o l u t i o n t e s t : A known w e i g h t ( a p p r o x i m a t e l y lOg) o f s u l p h u r c o a t e d u r e a were p l a c e d i n t o a 100 ml capped t e s t tube t o g e t h e r w i t h ^0 ml o f w a t e r . The t e s t tube was t h e n k e p t i n a c o n s t a n t t e m p e r a t u r e b a t h a t 37.8°C f o r 7 days. P r i o r t o a n a l y s i s t h e tube was shaken t w i c e g e n t l y and t h e d i s s o l v e d u r e a c o n c e n t r a t i o n was d e t e r m i n e d by r e f r a c t i v e i n d e x . The p r o c e d u r e was t h e n r e p e a t e d . When s u c c e s s i v e measurements o f r e f r a c t i v e i n d e x d i f f e r e d by more t h a n 10%, i t i n d i c a t e d t h a t t h e c o a t was v e r y f r a g i l e and u n a b l e t o w i t h s t a n d even g e n t l e s h a k i n g ( t h e r e f r a c t o m e t e r was c a l i b r a t e d as o u t l i n e d i n Appendix I I ) . b.2 T o t a l S u l p h u r C o n tent A p p r o x i m a t e l y lOg o f s u l p h u r c o a t e d u r e a were weighed a c c u r a t e l y and p l a c e d i n t o a c r u c i b l e . 40 ml o f w a t e r were added and t h e c o a t e d u r e a c r u s h e d i n t o a f i n e s l u r r y . The c r u c i b l e was p l a c e d on a m a g n e t i c s t i r r e r f o r 20 min. A f t e r s e t t l i n g f o r 1 min, a sample o f t h e c l e a r s o l u t i o n was a n a l y z e d f o r i t s u r e a c o n t e n t by r e f r a c t o m e t e r . The s u l p h u r c o n t e n t was d e t e r m i n e d by d i f f e r e n c e and i s denoted by S^. As an i n d e p e n d e n t c h e c k , t h e i n s o l u b l e s u l p h u r was f i l t e r e d and d r i e d i n an oven a t 66°C t o a c o n s t a n t w e i g h t . The w e i g h t o f s u l p h u r i s denoted by S^. The p e r c e n t a g e o f s u l p h u r i n t h e c o a t e d u r e a was t h e n c a l c u l a t e d from: C = SOCSj+S^/w where w denotes t h e sample w e i g h t o f t h e c o a t e d f e r t i l i z e r . b.3 D i s s o l u t i o n r a t e , D^^ The 7 day d i s s o l u t i o n i s g i v e n by: 100 ( w e i g h t o f u r e a d i s s o l v e d ) T o t a l w e i g h t o f u r e a i n sample By p l o t t i n g D v e r s u s t h e s u l p h u r c o n t e n t i n t h e sample, t h e d i s s o l u t i o n c o r r e s p o n d i n g t o 25% s u l p h u r , i . e . D^^, may be found. The p r o c e d u r e i s i l l u s t r a t e d i n F i g . 3.13. 80 F i g u r e 3.13: D „ D e t e r m i n a t i o n 4. RESULTS AND DISCUSSION The r e d e s i g n o f t h e s p o u t e d bed c o a t i n g f a c i l i t y overcame t h e major d i f f i c u l t i e s e x p e r i e n c e d by e a r l i e r w o r k e r s . I n p a r t i c u l a r , b l o c k a g e s i n t h e s u l p h u r l i n e s due t o i m p u r i t i e s o r uneven h e a t i n g were s u c c e s s f u l l y e l i m i n a t e d by t h e f i l t r a t i o n and steam t r a c i n g s y s t e m s , r e s p e c t i v e l y . The t e m p e r a t u r e c o n t r o l s f o r t h e a t o m i z i n g a i r and s p o u t e d bed a l s o o p e r a t e d s a t i s f a c t o r i l y , w i t h t e m p e r a t u r e s s t a y i n g w i t h i n 2 o r 3°C o f t h e d e s i r e d v a l u e s . I t was t h e r e f o r e r a t h e r s u r p r i s i n g t h a t t h e q u a l i t y o f t h e p r o d u c t ( e x p r e s s e d i n terms o f D^^ v a l u e s ) p r e p a r e d under a p p a r e n t l y i d e n t i c a l c o n d i -t i o n s was n o t t h e same. S i m i l a r l y , t h e r e was no c l e a r r e l a t i o n s h i p between and bed t e m p e r a t u r e ( w h i l e h o l d i n g a l l o t h e r e x p e r i m e n t a l c o n d i t i o n s a p p a r e n t l y c o n s t a n t ) even though such a r e l a t i o n s h i p had been r e p o r t e d on s e v e r a l o c c a s i o n s i n t h e p a s t ( ' 1 3 ' ; t h e D 2 5 v a l u e s e x h i b i t e d a g r e a t d e a l o f s c a t t e r . The cause o f t h e p r o b l e m was f o u n d t o be t h e s u l p h u r r o t a -meter w h i c h p r o v i d e d e r r o n e o u s r e a d i n g s . S i n c e t h e f l o a t and t h e t u b e were n o t p r o p e r l y matched, even m i n o r v a r i a t i o n s i n v i s c o s i t y ( w hich a r e a l m o s t u n a v o i d a b l e w i t h s u l p h u r between about 150°C and 160°C), gave f a u l t y i n d i c a t i o n s o f s u l p h u r f l o w r a t e . However, t h e r o t a m e t e r s t i l l s e r v e d as a f l o w i n d i c a t o r , i . e . i t was a r e l i a b l e i n s t r u m e n t f o r showing whether t h e r e was any s u l p h u r f l o w o r n o t . F o r t u n a t e l y , i t was p o s s i b l e t o overcome t h e d e f i c i e n c i e s o f t h e r o t a m e t e r w i t h o u t r e p e a t i n g t h e r u n s by c a l c u l a t i n g t h e s u l p h u r f l o w r a t e from t h e samples w h i c h were w i t h d r a w n from t h e s p o u t e d bed p e r i o d i c a l l y . 4.1 C a l c u l a t i o n o f t h e A verage S u l p h u r Flow Rate The a v e r a g e s u l p h u r f l o w r a t e f o r a r u n was c a l c u l a t e d f r o m a s u l p h u r b a l a n c e , i . e . 64 S u l p h u r I n j e c t e d 65 ' S u l p h u r \ / S u l p h u r \ [ S u l p h u r on u r e a i n [ w i t h d r a w n J I c o l l e c t e d i n } bed / \ i n samples/ \ c y c l o n e o r , i n m a t h e m a t i c a l t e r m s : N N DO C C ^-^ S , l 1 •=y, S , l 1 N + W X (4.1) c c • v ' where: Q = s u l p h u r i n j e c t i o n r a t e (g/min) t = t o t a l t i m e o f e x p e r i m e n t (min) WgQ = i n i t i a l bed w e i g h t o f u r e a (g) W£ = w e i g h t o f d u s t c o l l e c t e d i n c y c l o n e (g) X £ = w e i g h t f r a c t i o n o f s u l p h u r i n c y c l o n e d u s t W . = w e i g h t o f i t h sample w i t h d r a w n from s p o u t e d bed, (g) s, 1 X^  = w e i g h t f r a c t i o n o f s u l p h u r i n i t h sample N = t o t a l number o f samples w i t h d r a w n from bed X^ = w e i g h t f r a c t i o n o f s u l p h u r i n Nth ( i . e . f i n a l ) sample w i t h -drawn from bed The f i r s t terms on t h e r i g h t hand s i d e o f Eq. 4.1 a l l o w s f o r t h e f a c t t h a t some u r e a i s e l u t r i a t e d i n t h e form o f d u s t ( e s p e c i a l l y d u r i n g p r e h e a t i n g ) and u r e a i s w i t h d r a w n w i t h t h e samples. T h i s t e r m i s s i m p l i f i e d i f t h e f i n a l bed w e i g h t i s d e t e r m i n e d d i r e c t l y ; t h i s was done i n some, b u t n o t a l l c a s e s . 4.2 E f f e c t o f S u l p h u r Flow Rate on D i s s o l u t i o n V a l u e , D 2 5 A l o g a r i t h m i c p l o t o f vs 1/Q a t c o n s t a n t bed t e m p e r a t u r e s gave a f a m i l y o f s t r a i g h t l i n e s w i t h u n i t s l o p e (see F i g . 4.1). I n o t h e r words, t h e v a l u e i s i n v e r s e l y p r o p o r t i o n a l t o t h e s u l p h u r f l o w r a t e a t c o n s t a n t bed t e m p e r a t u r e s . E x p e r i m e n t a l v a l u e s o b t a i n e d by L i m ^ ^ were a l s o p l o t t e d i n F i g . 4.1 and showed t h e same b e h a v i o u r . F i g u r e 4 . 1 : E f f e c t o f S u l p h u r Flow Rate on D7C. 67 The r e a s o n why p r o d u c t q u a l i t y ( e x p r e s s e d i n terms o f d i s s o l u t i o n , D2<.) improves w i t h s u l p h u r f l o w r a t e i s n o t c l e a r a t t h i s s t a g e . However, a c c o r d i n g t o t h e Nukiyama-Tanasawa e q u a t i o n , t h e a v e r a g e d r o p l e t d i a m e t e r (6) p r o d u c e d by p n e u m a t i c a t o m i z i n g n o z z l e s i n c r e a s e s w i t h l i q u i d f l o w r a t e , i . e . 1.5 > 585 o = 2] * 597| P 0.45 /1000 x Q£ x (4.2) Hence, t h e p r o d u c t q u a l i t y i mproves as t h e s i z e o f t h e s u l p h u r d r o p l e t s i n c r e a s e s . T h i s o b s e r v a t i o n w i l l be used s u b s e q u e n t l y (see S e c t i o n 4.7) t o d e v e l o p a q u a l i t a t i v e model f o r t h e c o a t i n g p r o c e s s . 4.3 C o r r e c t e d D i s s o l u t i o n V a l u e , D ^ As m e n t i o n e d p r e v i o u s l y , t h e e x p e r i m e n t a l D^^ v a l u e s c o u l d n o t be used d i r e c t l y f o r f u r t h e r a n a l y s i s , due t o t h e f a c t t h a t a l l r u n s were n o t p e r f o r m e d a t t h e same s u l p h u r f l o w r a t e s and t h e d i s s o l u t i o n showed s t r o n g dependence on s u l p h u r f l o w r a t e . To overcome t h i s p r o b l e m i t was n e c e s s a r y t o d e f i n e a new v a r i a b l e , T h i s v a r i a b l e d e n o t e s t h e d i s s o l u t i o n o f a p r o d u c t c o n t a i n i n g 25% s u l p h u r h a v i n g been p r o d u c e d a t a s p e c i f i e d , r e f e r e n c e s u l p h u r f l o w r a t e . S i n c e t h e s l o p e s o f t h e l i n e s i n F i g . 4.1 a r e a p p r o x i m a t e l y u n i t y , i t f o l l o w s t h a t : D 2 5 X Q S = °25 X %R where: ~ The e x p e r i m e n t a l l y d e t e r m i n e d d i s s o l u t i o n v a l u e a t f l o w r a t e Qs Q = R e f e r e n c e s u l p h u r f l o w r a t e (60 g/min) DLC = D i s s o l u t i o n c o r r e s p o n d i n g t o t h e r e f e r e n c e f l o w r a t e Q C D D 2 5 v a l u e s i n s t e a d o f D 2 5 w i l l be used h e n c e f o r t h t o c o r r e l a t e and i n t e r p r e t t h e e x p e r i m e n t a l d a t a . 68 4.4 E f f e c t o f A t o m i z i n g A i r F l o w R a t e on F i g u r e 4.2 and T a b l e 4.1 show t h a t t h e v a l u e s i n c r e a s e d l i n e a r l y w i t h i n c r e a s i n g a i r f l o w r a t e i n t h e range o f 0.402 t o 0.785 m 3/hr p r o v i d e d a l l o t h e r v a r i a b l e s were k e p t c o n s t a n t . A c c o r d i n g t o E q u a t i o n 4.2 t h e d r o p l e t > s i z e (6) d e c r e a s e s w i t h a t o m i z i n g a i r f l o w r a t e and t h e p r o d u c t q u a l i t y ( i n terms o f D^) t h e r e f o r e i s seen t o improve w i t h d r o p l e t d i a m e t e r . 4.5 E f f e c t o f Bed Temperature on T a b l e 4.2 summarizes t h e and v a l u e s as f u n c t i o n s o f bed t e m p e r a t u r e f o r s e v e r a l e x p e r i m e n t a l r u n s , u s i n g u r e a as a s u b s t r a t e . The d a t a a r e p l o t t e d i n F i g . 4.3 as a f u n c t i o n o f bed t e m p e r a t u r e f o r a r e f e r e n c e s u l p h u r f l o w r a t e o f 60 g/min. The i n i t i a l d e c r e a s e i n w i t h t e m p e r a t u r e , f o l l o w e d by an i n c r e a s e w i t h a minimum a t about 80°C, i s i n agreement w i t h F i g . 4.1. Some o f Lim's d a t a , w h i c h a r e a l s o shown i n F i g . 4.3 a l s o a g r e e g e n e r a l l y w i t h t h e p r e s e n t r e s u l t s . Some s c a t t e r i n t h e d a t a i s i n e v i t a b l e due t o measurement e r r o r s , uneven u r e a q u a l i t y and u r e a p a r t i c l e s i z e . The minimum i n t h e c u r v e shown i n F i g . 4.3 i s a p p r o x i m a t e l y 15°C below t h e phase t r a n s i t i o n o f S^ t o S^ (which i s 95.5°C). When a t h e r m o c o u p l e was i n s e r t e d i n t o t h e c e n t e r o f t h e spout a p p r o x i m a t e l y 0.10 m above t h e n o z z l e , a t e m p e r a t u r e o f 87°C was measured compared t o a mean bed t e m p e r a t u r e o f 78°C. The r e a s o n f o r t h e v a r i a t i o n o f w i t h t e m p e r a t u r e w i l l be d i s c u s s e d more f u l l y l a t e r . 4.6 E l e c t r o n m i c r o g r a p h s o f S u l p h u r C o a t e d U r e a The s c a n n i n g - e l e c t r o n m i c r o s c o p e was u s e d t o examine t h e s u l p h u r c o a t s p r o d u c e d u n d e r d i f f e r e n t c o n d i t i o n s i n an a t t e m p t t o r e l a t e c o a t appearance t o F i g . 4.2: E f f e c t o f A t o m i z i n g A i r Flow Rate on N o r m a l i z e d D i s s o l u t i o n R a t e , D' 70 T a b l e 4.1: D i s s o l u t i o n v s A t o m i z i n g A i r Flow Rate ( S u l p h u r Coated Urea) Bed Weight: 4,535 g RUN BED DISSOLUTION NO. TEMPERATURE D.c, % °c Zb ER 87 50.0 ES 87 50.0 ET 86 40.0 EU 86 40.0 EV 87 35.0 EW 87 35.0 EX 86.5 34.0 EY 86.0 21.0 EE 86.0 35.5 EF 86.0 32.1 EN 86.0 45.0 EO 86.0 25.0 SULPHUR FLOW CORRECTED ATOMIZ. AIR gr/ m i n DISSOLUTION FLOW RATE D 2 5 > % mVhour 63.3 52.8 0.785 68.9 57.4 0.785 67.9 45.3 0.658 69.8 46.5 0.658 68.5 40.0 0.530 68.9 40.2 0.530 86.9 49.2 0.402 86.9 30.4 0.402 66.3 39.2 0.594 62.6 33.5 0.594 43.4 32.6 0.594 82.3 34.3 0.594 * D' i s t h e d i s s o l u t i o n v a l u e n o r m a l i z e d f o r a s u l p h u r f l o w r a t e o f 60 g/min. F i g u r e 4.3: E f f e c t o f Bed Temperature on D' 72 T a b l e 4.2: D i s s o l u t i o n v s Bed Temperature ( S u l p h u r C o ated Urea) I n i t i a l Bed Weight: 4,535 g RUN BED DISSOLUTION SULPHUR CORRECTED ATOMIZING COMMENTS [SSC TEMPERATURE D 2 5, % FLOW RATE DI SOLUTION AIR FLOW °C g/min D' % RATE m 3/hr EA 76 32.0 61.7 32.9 0.594 T h i s work EB 76 29.5 61.7 30.3 0.594 T h i s work EC 83 25.0 72.1 30.0 0.594 T h i s work ED 82 39.0 62.6 40.7 0.594 T h i s work EE 86 35.5 66.3 39.2 0.594 T h i s work EF 86 32.1 62.6 33.5 0.594 T h i s work EG 67 56.0 52.6 49.1 0.594 T h i s work EH 67 59.0 52.6 51.7 0.594 T h i s work EI 58 56.0 60.3 56.3 0.594 T h i s work E J 58 37.1 86.9 53.7 0.594 T h i s work FA 85 66.0 34.4 37.8 0.594 T h i s work FB 85 64.0 34.4 37.8 0.594 T h i s work BF 51 41.0 122.1 83.4 0.490 Lim's Data BG 59 32.3 109.2 58.8 0.510 Lim's Data BH 68.5 27.3 117.9 53.6 0.544 Lim's Data BI 79 17.5 120.9 35.3 0.459 Lim's D a t a CA 67.5 73.2 37.6 45.9 0.204 Lim's Data CB 78.0 49.5 36.4 30.0 0.136 Lim's Data * D 2 5 i s t h e d i s s o l u t i o n v a l u e n o r m a l i z e d f o r a s u l p h u r f l o w r a t e o f 60 g/min. 73 p r o d u c t q u a l i t y ( D ^ ) • Uncoated u r e a p a r t i c l e s were a l s o s t u d i e d t o d i s t i n g u i s h u n c o a t e d s u r f a c e s . P l a t e s 4.1, 4.2 and 4.3 show t h e s u r f a c e o f u n c o a t e d g r a n u l a r u r e a a t m a g n i f i c a t i o n s o f 100, 400 and 2000, r e s p e c t i v e l y . I n P l a t e 4.1 t h e u r e a s u r f a c e a p p ears q u i t e smooth whereas, a t l a r g e r m a g n i f i c a t i o n s ( e . g . P l a t e 4 . 3 ) , rou g h c r y s t a l l i n e r e g i o n s a r e n o t i c e a b l e . 4.6.1 E ^ z c t ol Bed TmpeAatu/ie. on Coat AppzaAance. P l a t e s 4.4 and 4.5 show s u l p h u r c o a t e d u r e a p r o d u c e d a t bed t e m p e r a t u r e s o f 76 and 86°C, r e s p e c t i v e l y . The sample c o a t e d a t 86°C shows c r a c k s w h i c h p r o b a b l y r e s u l t from t h e i n i t i a l p r e s e n c e o f i n t h e c o a t . As t h e p r o d u c t i s c o o l e d , S Q changes i n t o t h e more s t a b l e S . S i n c e S i s d e n s e r t h a n S 0 , p ct ot p c r a c k s d e v e l o p . The sample c o a t e d a t 76°C d i d n o t show c r a c k s , w h i c h s u g g e s t s t h a t t h e r m a l c o n t r a c t i o n d i d n o t p l a y an i m p o r t a n t r o l e and S^ was p r o b a b l y a b s e n t from t h e c o a t . P l a t e s 4.6, 4.7, and 4.8 show t h e c o a t s u r f a c e f o r samples c o n t a i n i n g 10% s u l p h u r and p r o d u c e d a t bed t e m p e r a t u r e s o f 58, 67 and 76°C, r e s p e c t i v e l y . A t 58°C t h e s i z e o f t h e s u l p h u r p a r t i c l e s i s q u i t e l a r g e , s u g g e s t i n g t h a t t h e s u l p h u r d r o p l e t s d i d n o t have t i m e t o s p r e a d s i g n i f i c a n t l y . The d r o p l e t s s o l i d i f y r a p i d l y ( p o s s i b l y even b e f o r e r e a c h i n g t h e u r e a s u r f a c e ) t h e r e b y l e a v i n g gaps between t h e s u l p h u r p a r t i c l e s . T h i s e x p l a i n s t h e h i g h d i s s o l u t i o n v a l u e s f o r samples c o a t e d a t low t e m p e r a t u r e s . A t 67°C t h e s u r f a c e appears more u n i f o r m and t h e s u l p h u r p a r t i c l e s a r e s m a l l e r . However, t h e c o a t i s s t i l l q u i t e p o r o u s . A t 76°C i t i s seen t h a t t h e s i z e o f t h e s u l p h u r p a r t i c l e s i s s m a l l and 74 P l a t e 4.1: Uncoated Urea S u r f a c e ( M a g n i f i c a t i o n : 100 x) 75 P l a t e 4.2: Uncoated Urea S u r f a c e ( M a g n i f i c a t i o n : 400 x) P l a t e 4.3: Uncoated Urea S u r f a c e ( M a g n i f i c a t i o n : 2000 x) P l a t e 4.5: S u l p h u r Coated Urea ( M a g n i f i c a t i o n : 20 x) Bed Temperature: 86°C S u l p h u r C o n t e n t : 30% P l a t e 4.7: S u l p h u r Coated Urea ( M a g n i f i c a t i o n : 1000 x) Bed Temperature: 67°C S u l p h u r C o n t e n t : 10% 78 P l a t e 4.8: S u l p h u r Coated Urea ( M a g n i f i c a t i o n : 1000 x) Bed Temp.: 76°C S u l p h u r C o n t e n t : 10% 79 u n c o a t e d a r e a s between s u l p h u r p a r t i c l e s a r e r e d u c e d . As a r e s u l t , t h e p r o d u c t q u a l i t y i m p r o v e s . P l a t e s 4.9 and 4.10 show v e r y s l i g h t l y c o a t e d u r e a p a r t i c l e s p r o d u c e d a t bed t e m p e r a t u r e s o f 67 and 76°C, r e s p e c t i v e l y . A g a i n c o a r s e r c r y s t a l s a r e seen a t t h e l o w e r t e m p e r a t u r e . 4 . 6 . 2 EHe.ct ol Sulphuh. F£ow Rate, on Coat Appearance P l a t e s 4.10, 4.11 and 4.12 show s l i g h t l y c o a t e d samples p r o d u c e d a t d i f f e r e n t s u l p h u r f l o w r a t e s . The s u l p h u r p a r t i c l e s a r e l a r g e r - a t h i g h e r -s u l p h u r f l o w r a t e s , and s m a l l e r a t l o w e r s u l p h u r f l o w r a t e s ; t h i s a g a i n c o n f i r m s t h e r e l e v a n c e o f Eq. 4.2 w h i c h s u g g e s t s t h a t d r o p l e t - s i z e . (6) i s p r o p o r t i o n a l t o s u l p h u r f l o w r a t e . P r o d u c t q u a l i t y i m p r o v e d w i t h an i n c r e a s e i n s u l p h u r f l o w r a t e p r o b a b l y due t o a l a r g e r and more f r e q u e n t d r o p l e t s i m p i n g i n g on t h e u r e a s u r f a c e . I t gave a b e t t e r a r e a c o v e r a g e and a b e t t e r f u s i n g - t o g e t h e r o f p a r t i c l e s t h e r e b y i m p r o v i n g c o a t q u a l i t y . 4.7 Q u a l i t a t i v e model o f C o a t i n g P r o c e s s 4.7.1 Vtwplet Size. A t t e m p t s were made t o measure t h e d r o p l e t s i z e p r o d u c e d by t h e s p r a y b u t no r e l i a b l e r e s u l t s would be o b t a i n e d . However t h e d r o p l e t s i z e can be i n f e r r e d f r o m P l a t e s 4.10, 4.11 and 4.12. The s u l p h u r p a r t i c l e s i n c r e a s e w i t h s u l p h u r f l o w r a t e and d e c r e a s e w i t h a t o m i z i n g a i r f l o w r a t e ; t h e s e b e h a v i o u r p a t t e r n s a r e i n g e n e r a l agreement w i t h t h e Nukiyaiiia-Tanasawa e q u a t i o n (Eq. 4 . 2 ) . 4 . 7 . 2 Spreading ol Sulphun VKopLeM, L e t us c o n s i d e r a s u l p h u r d r o p l e t i m p i n g i n g on t h e u r e a s u r f a c e a t two P l a t e 4.9 S u l p h u r Coated Urea ( M a g n i f i c a t i o n : 800 x) Bed Temp.: 67°C S u l p h u r Flow R a t e : 94 g/min A t o m i z i n g A i r Flow R a t e : 0.594 m 3/hr P l a t e 4.10: S u l p h u r Coated Urea ( M a g n i f i c a t i o n : 800 x) Bed Temp.: 76°C S u l p h u r Flow R a t e : 94 g/min A t o m i z i n g A i r Flow R a t e : 0.594 m 3/hr 81 P l a t e 4.11: S u l p h u r Coated Urea ( M a g n i f i c a t i o n : 800 x) Bed Temperature: 77°C S u l p h u r Flow R a t e : 187.9 g/min A t o m i z i n g A i r Flow R a t e : 0.278 m 3/hr P l a t e 4.12: S u l p h u r Coated Urea ( M a g n i f i c a t i o n : 800 x) Bed Temperature: 77°C S u l p h u r Flow R a t e : 223.4 g/min A t o m i z i n g A i r Flow R a t e : 0.278 m / h r 82 d i f f e r e n t t e m p e r a t u r e s . A t low t e m p e r a t u r e s , t h e d r o p l e t s o l i d i f i e s q u i c k l y (due t o r a p i d h e a t t r a n s f e r ) and does n o t s p r e a d s i g n i f i c a n t l y . T h i s b e h a v i o u r i s shown s c h e m a t i c a l l y i n F i g s . 4.4a, b and c. At h i g h e r t e m p e r a t u r e s , t h e h e a t t r a n s f e r i s r e d u c e d and t h e s u l p h u r d r o p l e t s p r e a d s t h e r e b y c o v e r i n g more o f t h e u r e a s u r f a c e b e f o r e s o l i d i f y i n g ; t h i s i s shown i n F i g s . 4.5a, b and c. F i g s . 4.4c and 4.5c i n d i c a t e t h e f o r m a t i o n o f s u l p h u r c r y s t a l s . When a second l a y e r (see F i g s . 4.6a, b and c) i s formed by s u l p h u r d r o p l e t s i m p i n g i n g on t h e p r e v i o u s l a y e r , h i g h t e m p e r a t u r e s a s s i s t t h e s u l p h u r t o f l o w i n t o t h e c r a c k s between t h e s u l p h u r c r y s t a l s . F u r t h e r m o r e , t h e i n i t i a l l a y e r may mel t p a r t i a l l y w h i c h a l s o r e d u c e s i t s p o r o s i t y . Con-s e q u e n t l y , 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 improve t h e p r o d u c t q u a l i t y w h i c h was i n d e e d f o u n d e x p e r i m e n t a l l y up t o bed t e m p e r a t u r e s o f 80°C. Beyond t h a t t e m p e r a t u r e , s i g n i f i c a n t q u a n t i t i e s o f a r e formed w h i c h c r a c k upon c o o l i n g t o room t e m p e r a t u r e s . ( T h i s phenomenon was a l r e a d y d i s c u s s e d i n s e c t i o n 4.5). 4.7.3 SZCULLYIQ O{, VOUU, P o r e s i n t h e u r e a g r a n u l e s a r e d i f f i c u l t t o s e a l w i t h s u l p h u r d r o p l e t s because t h e d r o p l e t s may n o t be a b l e t o p e n e t r a t e d e e p l y . I n s t e a d , t h e y have a t e n d e n c y t o c o l l i d e w i t h t h e w a l l s o f t h e p o r e s (see P l a t e 4.13) w h i l e s t i l l l e a v i n g an ea s y p a t h f o r w a t e r t o p e n e t r a t e and l e a c h o u t t h e u r e a . C o n s e q u e n t l y , i t i s p r e f e r a b l e t o use g r a n u l a r r a t h e r t h a n p r i l l e d u r e a ; t h e l a t t e r t y p e u s u a l l y c o n t a i n s some p o r e s and/or d i m p l e s . 4.8 E f f e c t o f Bed Weight on F i g u r e 4.7 and T a b l e 4.3 show t h e r e s u l t s f o r r u n s p e r f o r m e d a t d i f f e r e n t bed w e i g h t s r a n g i n g f r o m 2,721 g t o 4,535 g. Lower w e i g h t s l e d t o 83 V (a) (a) /////////// / xxxxxxxxxx (b) /7777T77T77T7T7 (b) ///7//f//7/7// (c) F i g u r e 4 . 4 (Low Temperature) F i g u r e 4 . 5 (High Temperature) D e p o s i t i o n o f F i r s t Layer o f S u l p h u r onto Urea S u r f a c e Figure 4.6: Deposition of Second Layer of Sulphur Plate 4.13: Pore i n a Sulphur Coating (Magnification: 400 x) N 86 u n s t a b l e s p o u t i n g w h i l e i n s u f f i c i e n t a i r was a v a i l a b l e t o s p o u t h e a v i e r b e d s . F i g u r e 4 . 7 shows t h a t bed w e i g h t had l i t t l e i n f l u e n c e on t h e D' v a l u e s 25 i n t h e r a n g e s t u d i e d . A l t h o u g h an i n c r e a s e i n bed w e i g h t gave h i g h e r s o l i d s (19) c i r c u l a t i o n i n t o t h e s p o u t and r e s u l t e d i n l e s s . s u l p h u r d e p o s i t i o n p e r g r a n u l e p e r p a s s ( s e e T a b l e 4 . 4 ) , t h e p r o d u c t q u a l i t y was n o t s i g n i f i c a n t l y a l t e r e d . T a b l e 4 . 3 : E f f e c t o f Bed We igh t on ( S u l p h u r C o a t e d U r e a ) A t o m i z i n g A i r F l o w R a t e : 0 .594 m 3 / h r RUN TEMP °C BED WT. kg D 2 5 % SULPHUR FLOW g r / m i n D 2 5 EP 83 2 .721 2 7 . 0 7 8 . 8 3 5 . 5 EQ 85 2 .721 4 0 . 0 5 8 . 7 39 .1 EN 86 3 .628 4 5 . 0 4 3 . 4 3 2 . 6 EO 86 3 .628 2 5 . 0 8 2 . 3 3 4 . 3 EE 86 4 . 5 3 5 3 5 . 5 6 6 . 3 3 9 . 2 EF 86 4 . 5 3 5 3 2 . 1 6 2 . 6 3 3 . 5 4 . 9 E f f e c t o f S i l i c o n e A d d i t i v e on D!,^ T a b l e 4 . 5 shows t h e r e s u l t s o b t a i n e d when i n j e c t i n g s i l i c o n e t h r o u g h t h e a t o m i z i n g a i r l i n e . The s i l i c o n e was e i t h e r added t o t h e bed b e f o r e c o a t i n g , o r i n j e c t e d t o g e t h e r w i t h t h e s u l p h u r d u r i n g c o a t i n g . The r e s u l t s d i d show t h a t s i l i c o n e i m p r o v e s p r o d u c t q u a l i t y . S i n c e s i l i c o n e i s w a t e r r e p e l l e n t , s p r a y i n g i t o n t o t h e u r e a s u r f a c e m i g h t , b y i t s e l f , c a u s e a d e c r e a s e i n d i s s o l u t i o n . Howeve r , u r e a s p r a y e d w i t h s i l i c o n e o n l y , d i s s o l v e d c o m p l e t e l y and v e r y q u i c k l y . 60 50 o 40 30 20 o o o o 2.725 3.628 B E D WEIGHT , kg 4.535 F i g u r e 4.7: E f f e c t o f Bed Weight on D 2 5 D c = 0.152 m; = 0.208 m Bed Temperature = 80°C 88 T a b l e 4.4: S o l i d s c i r c u l a t i o n i n a Spouted Bed f o r S u l p h u r C o a t i n g o f U r e a D = 0.1524 m c d = 2.1 u n P D. = 0.02083 m l Bed Temperature: 80°C Bed Weight, g Bed H e i g h t , m Minimum S p o u t i n g V e l o c i t y , Urns, m/sec. V e l o c i t y 1, v (28) w P a r t i c l e V e l o c i ta t WalJ m/sec. C y c l e Time, s e c . S o l i d s C i r c u l a t i o n , g/sec. S u l p h u r i n j e c t i o n g/sec S u l p h u r % p e r 1 s t P a s s . 2721 0.2805 0.5924 0.0186 15.08 180.4 3.8 2.06 3628 4535 5442 0.3446 0.4088 0.4729 0.6566 0.0214 16.18 225.3 3.8 1.66 0.7151 0.0242 16.89 268.5 3.8 1.40 0.7691 0.0271 17.45 311.9 3.8 1.20 89 T a b l e 4.5: E f f e c t o f S i l i c o n e A d d i t i v e on D' Bed Weight: 4,535 g • A t o m i z i n g A i r Flow R a t e : 0.594 m 3/hr RUN T D Op 2i> L % GG 76 13.0 GH 76 15.0 GM 77 12.0 GN 77 12.0 EA 76 32.0 EB 76 29.5 GI 42-56 34.0 GJ 42-53 39.0 GK 41-52 46.0 GL 42-54 46.0 S u l p h u r Flow D^g gr/min . 94 20.4 94 23.5 93.4 18.7 94.6 18.9 61.7 32.9 61.7 30.3 260.7 47.2 223.4 46.4 187.9 46.0 187.9 46.0 Comments 3 c c . S i l i c o n e b e f o r e c o a t i n g Idem 3 c c . c o n t i n u o u s S i l i c o n e I n j e c t i o n w h i l e c o a t i n g Idem No S i l i c o n e I n j e c t i o n Idem No S i l i c o n e I n j e c t i o n Idem S i l i c o n e I n j e c t i o n b e f o r e C o a t i n g S i l i c o n e I n j e c t i o n b e f o r e C o a t i n g 90 When u r e a was s p r a y e d w i t h s i l i c o n e p r i o r t o s u l p h u r c o a t i n g , a s i g n i f i c a n t d e c r e a s e i n d i s s o l u t i o n r e s u l t e d ; f u r t h e r t e s t s w i t h a c o n t i n u o u s i n j e c t i o n o f s i l i c o n e w h i l e c o a t i n g gave s l i g h t l y b e t t e r r e s u l t s . The r e a s o n s why s i l i c o n e has a b e n e f i c i a l e f f e c t a r e n o t c l e a r a t p r e s e n t . S i l i c o n e may i m p r o v e t h e b o n d i n g o f s u l p h u r t o u r e a and i m p r o v e t h e m e c h a n i c a l p r o p e r t i e s o f s u l p h u r . The l a t t e r had a l r e a d y been n o t e d by E l l i o t ^ 2 0 - ' . E v i d e n c e o f i m p r o v e d m e c h a n i c a l s t r e n g t h was a l s o f o u n d i n t h i s work s i n c e t h e s u l p h u r c o a t e d u r e a c o n t a i n i n g s i l i c o n e was l e s s s u s c e p t i b l e t o b r e a k a g e d u r i n g t h e d i s s o l u t i o n t e s t t h a n a s i m i l a r p r o d u c t w i t h o u t s i l i c o n e . 4 . 1 0 E f f e c t o f t i m e on S e v e r a l s a m p l e s were s u b j e c t e d t o t h e s t a n d a r d d i s s o l u t i o n t e s t 6 and 10 months a f t e r b e i n g p r o d u c e d ( s e e T a b l e 4 . 6 ) . I t i s c l e a r t h a t s i l i c o n e may a l s o r e t a r d p r o d u c t d e t e r i o r a t i o n due t o a g i n g . T a b l e 4 . 6 : E f f e c t o f t i m e on D 2 5 ( S u l p h u r C o a t e d U r e a ) DISSOLUTION, D, 6 Months RUN EA EB GG GN 0 Month 3 2 . 0 3 0 . 0 1 3 . 0 1 2 . 0 ' 25 10 Mon ths 1 7 . 0 1 2 . 0 3 5 . 0 3 5 . 0 TREATMENT NONE NONE S i l i c o n e added t o u r e a b e f o r e s u l p h u r c o a t i n g S i l i c o n e and S u l p h u r i n j e c t e d t o g e t h e r d u r i n g c o a t i n g 4 . 1 1 E f f e c t o f S u b s t r a t e ( F e r t i l i z e r M a t e r i a l ) on D l F i g u r e 4 . 8 and T a b l e 4 . 7 show t h e dependence on bed t e m p e r a t u r e f o r ammonium p h o s p h a t e . These r u n s were p e r f o r m e d t o d e t e r m i n e w h e t h e r t h e f e r t i l i z e r m a t e r i a l , i . e . t h e c o a t i n g s u b s t r a t e , has a s i g n i f i c a n t e f f e c t on p r o d u c t q u a l i t y . As i n t h e c a s e o f u r e a , t h e V' v a l u e s d e c r e a s e d w i t h bed t e m p e r a t u r e s up t o 86° A change i n s u b s t r a t e d i d n o t i n f l u e n c e t h e t e m p e r a t u r e dependence o f c o a t q u a l i t y (as d e t e r m i n e d by D ' 25) and i t a p p e a r s t o be c h a r a c t e r i s t i c o f t h e c o a t i n g m a t e r i a l i . e . , s u l p h u r . T a b l e 4 . 7 : E f f e c t o f T e m p e r a t u r e on S u b s t r a t e : Ammonium P h o s p h a t e Bed W e i g h t : 4 , 5 3 5 g A t o m i z i n g A i r F l o w R a t e : 0 .594 m 3 / h r RUN TEMP. °C ° 2 5 % SULPHUR FLOW g r / m i n . D 2 5 % F I 81 2 1 . 0 7 5 . 7 2 6 . 5 F J 82 2 0 . 0 7 5 . 7 2 5 . 2 FK 86 1 9 . 0 5 6 . 5 1 7 . 9 F L 86 1 9 . 0 5 6 . 5 1 7 . 9 FR 77 2 2 . 0 1 1 5 . 4 4 2 . 3 FS 68 2 5 . 0 1 1 5 . 4 4 8 . 1 FT 68 2 4 . 0 1 1 5 . 4 4 6 . 2 FU 5 9 . 5 2 8 . 0 1 0 4 . 2 4 8 . 6 FV 5 8 . 0 2 8 . 0 1 0 4 . 2 4 8 . 6 92 60 F i g u r e 4.8: E f f e c t o f Bed Temperature on o f S u l p h u r - C o a t e d Ammonium Phosphate 5. CONCEPTUAL DESIGN OF A SEMICOMMERCIAL COATING FACILITY T h i s c h a p t e r i n c l u d e s b a s i c c r i t e r i a f o r t h e d e s i g n o f b a t c h w i s e , s p o u t e d bed p l a n t s f o r p r o d u c i n g s u l p h u r c o a t e d u r e a . P r e l i m i n a r y economic d a t a a r e a l s o p r o v i d e d . Two p l a n t s c a p a b l e o f p r o d u c i n g 196 and 315 t / y e a r o f p r o d u c t a r e c o n s i d e r e d . Both p l a n t s a r e assumed t o o p e r a t e 250 days p e r y e a r and 8 h r / d a y . The r e a s o n s f o r c h o o s i n g such s m a l l p l a n t s a r e : ( i ) Green V a l l e y F e r t i l i z e r and C h e m i c a l Co. s e l l s a p p r o x i m a t e l y 90 t / y e a r o f s u l p h u r c o a t e d u r e a b u t t h i s i s e x p e c t e d t o r i s e , e s p e c i a l l y i f t h e p r i c e can be r e d u c e d from t h e p r e s e n t v a l u e o f $540/t; ( i i ) m i n i m i z e s c a l e - u p problems from t h e l a b o r a t o r y f a c i l i t y . B a t c h p r o c e s s e s were chosen s i n c e t h e y a r e s i m p l e t o d e s i g n and e n s u r e u n i f o r m p r o d u c t q u a l i t y . The l a t t e r f o l l o w s f r o m t h e f a c t t h a t a l l u r e a g r a n u l e s have a p p r o x i m a t e l y t h e same r e s i d e n c e t i m e . 5.1 T e c h n i c a l D e s i g n o f a Semi-commercial C o a t i n g F a c i l i t i e s The f l o w s h e e t i s b a s i c a l l y t h e same as t h e one used f o r t h e p r e s e n t p i l o t p l a n t (see F i g . 3.1) but a l l u n i t s a r e l a r g e r . A 0.60 m column i s recommended as a s p o u t i n g v e s s e l and p r e h e a t i n g and c o o l i n g a r e p e r f o r m e d i n t h e same v e s s e l . The s u l p h u r s u p p l y s y s t e m , a t o m i z i n g and s p o u t i n g a i r , a r e h e a t e d by low p r e s s u r e (415 k P a ) , s a t u r a t e d steam. E l e c t r i c h e a t i n g i s p o s s i b l e b u t g r e a t c a r e must be t a k e n t o a v o i d l o c a l h ot s p o t s s i n c e t h e v i s c o s i t y o f s u l p h u r i s v e r y t e m p e r a t u r e dependent. 5.1.1 Vulgn ComldzMuLLoYii, a) Spouted Bed: The s p o u t e d bed s i z e chosen i s a 0.60 m d i a m e t e r , 93 94 2.40 m h i g h c y l i n d r i c a l column w i t h a c o n i c a l base (60° i n c l u d e d a n g l e ) . The main r e a s o n s f o r t h i s d e v i c e a r e t h a t t h e b e h a v i o u r o f t h e bed can be p r e d i c t e d w i t h a h i g h degree o f a c c u r a c y and t h a t t h e p r o d u c t i o n c a p a c i t y i s adequate. b) Minimum S p o u t i n g V e l o c i t y : The minimum v e l o c i t y , U M S , a t w h i c h t h e bed r e m a i n s i n t h e s p o u t e d s t a t e ( U ) was c a l c u l a t e d from t h e M a t h u r - G i s h i e r ms «.• (19) E q u a t i o n J , U ms 2 g H ,1/2 C ps - p f ) P f , (5.1) Where, d^, D . , T>c> H, p g and denote t h e p a r t i c l e d i a m e t e r , t h e column i n l e t d i a m e t e r , column d i a m e t e r , bed h e i g h t , s o l i d d e n s i t y and f l u i d d e n s i t y , r e s p e c t i v e l y . T a b l e s 5.1 and 5.2 show t h e c a l c u l a t e d v a l u e s o f t h e minimum s p o u t i n g v e l o c i t y a t d i f f e r e n t s t a g e s i n t h e p r o c e s s . c) S p o u t i n g A i r and Flow Rate R e q u i r e m e n t s : To e n s u r e good p a r t i c l e c i r c u l a t i o n and t o p r e v e n t a g g l o m e r a t i o n o f f r e s h l y c o a t e d p a r t i c l e s , t h e a i r f l o w r a t e s h o u l d exceed U . A spout number (N = U / U ) o f 1.1 was chosen ms r s ms and t h e v o l u m e t r i c a i r f l o w r a t e was c a l c u l a t e d as f o l l o w s : Q = U x 1.1 x TTD 2/4 ms c The b l o w e r c a p a c i t i e s f o r t h e two s e m i - c o m m e r c i a l p l a n t s a r e t h e r e f o r e 8 and 12 m 3/min, r e s p e c t i v e l y . The p r e s s u r e d rop a c r o s s t h e bed a t U M S was f 19) f o u n d by Mathur and G i s h l e r J t o be a p p r o x i m a t e l y 2/3 o f t h e s t a t i c bed p r e s s u r e . R o t a r y b l o w e r s w i t h a maximum d i s c h a r g e p r e s s u r e o f 7;0 kPa a r e adequate f o r t h i s s e r v i c e . However, i f a p r e h e a t e r i s p r e s e n t , a h i g h e r b l o w e r d i s c h a r g e p r e s s u r e s h o u l d be s p e c i f i e d . Table 5.1: Specifications for a Batch-wise Plant Producing 196.3 t/year of Sulphur Coated Urea (D = 0.6096 m, D. = 0.0762 m, 28=60°, v * 0.013 m/s, C = 0.25)c 1 P VARIABLE PREHEATING START FINISH COATING START FINISH COOLING START FINISH Time, t(hr) Bed Weight, W(kg) Bed Height, H(m) Mean Particle diameter, dp (mm) 196.2 1.219 2.1 Bulk Density, 7 7 E. P B (kg/m3) Bed Tempera-ture, T(°C) Inlet Air Temp., T. (°C) i Minimum Spouting Velocity 8 20"C Urns(m/sec) Spout Number, N s « U/ms Inlet Air Flow 8 20°C, Q (mVoin) Pressure Drop AP(kPa) Atomizing Air Flow 6 20°C Q ( m V h r ) Atom. Air Temp, T ( C) 20 110 0.306 1.10 5.891 7.39 0.730 196.2 1.219 2.1 775 75 0.294 1.10 5.665 0.730 1.323 196.2 261.6 1.219 1.388 2.1 2.245 775 75 75 847 75 75 0.301 0.359 1.10 1.10 5.805 6.916 7.39 9.20 5.20 5.20 1.323 1.956 261.6 261.6 1.388 1.388 2.245 2.245 847 847 20 20 0.374 0.385 1.10 1.10 7.207 7.412 9.20 9.20 150 150 Sulphur Flow, (kg/hr) 110.25 110.25 Note: Allowing 15' for unloading and loading. The total production time/batch = 1.956 + 0.250 • 2.206 hours. Table S.2: Specifications for Batch Wise-Plant Producing 314.8 t/year of Sulphur Coated Urea (D c • 0.6096 m, D. - 0.0762 m, 26=60°, v • 0.023 m/s, C • 0.25). 1 P VARIABLE PREHEATING START FINISH COATING START FINISH COOLING START FINISH Time, t(hr) 1.242 1.242 1.933 2.988 Bed weight, W(kg) 472.0 472.0 472.0 629.3 629.3 629.3 Bed Height, H(m) 2.438 2.438 2.438 2.897 2.897 2.897 Mean Particle diameter, dp (mm) 2.1 2.1 2.1 2.245 2.245 2.245 Bulk den-sity, (tg/m3) 775 775 775 847 847 847 Bed Temp-erature, T(°C) 20 75 75 75 75 40 Minimum Spouting Velocity 6 20°C, Urns (m/s) 0.432 0.416 0.426 0.541 Spout Number N s • U/Ums Inlet Air Flow e 20°C Q(m3/min) 1.1 8.328 1.1 8.010 1.1 8.210 1.1 9.992 1.1 10.410 1.1 10.710 Pressure Drop, iP(kPa) 14.94 14.94 14.94 19.92 19.92 19.92 Atomizing Air Flow § 20°C, Q(m3/hr) Atomizing Air Tempera-ture, Ta(°C) 10.74 150 10.74 150 Sulphur Flow, G- (kg/hr) 227.7 227.7 Note: Allowing 25' for unloading and loading, the total time/batch » 2.988 + 0.417 » 3.405 hr. 97 d) E s t i m a t i o n o f H e a t i n g and C o o l i n g Times: P r e h e a t i n g and c o o l i n g a r e p e r f o r m e d i n t h e same u n i t f o r s i m p l i c i t y and economy. The h e a t i n g and c o o l i n g f 17) t i m e s may be e s t i m a t e d from a s i m p l e h e a t b a l a n c e , i . e . fM C T 1 = Q p C (T. - T ) (5.2) d i [ P PP Pj P i P ^ J o r , i f t h e p h y s i c a l p r o p e r t i e s a r e r e g a r d e d as c o n s t a n t , M C -T = QV^ £ n { < T i " T b o ) / ( T i " T b f » <5-3> P where: M , C , T , Q, p, C , T., T, , T, _ denote t h e mass o f p a r t i c l e s , P PP P p I bo b f r s p e c i f i c h e a t o f p a r t i c l e s , p a r t i c l e t e m p e r a t u r e , v o l u m e t r i c a i r f l o w r a t e , a i r d e n s i t y , s p e c i f i c h eat o f a i r , i n l e t a i r t e m p e r a t u r e , i n i t i a l p a r t i c l e t e m p e r a t u r e and f i n a l p a r t i c l e t e m p e r a t u r e , r e s p e c t i v e l y . The s i m p l e h e a t b a l a n c e , w h i c h i s based on t h e a s s u m p t i o n t h a t t h e gas l e a v e s t h e bed i n t h e r m a l e q u i l i b r i u m w i t h t h e p a r t i c l e s , i s f a i r l y a c c u r a t e (22) as shown by B e r q u i n f o r a s p o u t e d bed s u l p h u r g r a n u l a t o r . e) E s t i m a t i o n o f C o a t i n g Time: The number o f p a s s a g e s w h i c h t h e u r e a g r a n u l e s must make t h r o u g h t h e s p r a y zone can be c a l c u l a t e d f r o m , c = t v p / H ' (5.4) where t i s t h e t i m e s p e n t by t h e p a r t i c l e s i n t h e bed t o r e a c h a s u l p h u r c o n t e n t o f 25% wt, v ^ i s t h e ave r a g e g r a n u l e v e l o c i t y and H i s t h e bed h e i g h t . The a v e r a g e g r a n u l e v e l o c i t y can be e s t i m a t e d from t h e movement a l o n g t h e bed w a l l . I n t h e p i l o t p l a n t t e s t s i t was found t o be a p p r o x i m a t e l y 0.023 m/s. (F o r bed w e i g h t s o f 4.535 kg and N g = 1.1). The c o r r e s p o n d i n g v a l u e s o f t and H a r e 400 s e c o n d s , and 0.48 m r e s p e c t i v e l y . T h e r e f o r e , t h e ave r a g e number o f p a s s a g e s t h r o u g h t h e s p r a y zone was about 20 and t h i s number i s used as t h e s c a l e - u p c r i t e r i o n . The c o a t i n g t i m e f o r a l a r g e , b a t c h - w i s e u n i t can be e s t i m a t e d once c, 98 H and v- a r e s p e c i f i e d . Based on t h e e q u a t i o n d e v e l o p e d by T h o r l e y e t a l J f o r 0.60 d i a m e t e r columns, t h e v e l o c i t y a l o n g t h e bed w a l l i s about 0.013 m/s and 0.018 m/s f o r bed h e i g h t s o f 1.388 m and 2.154 m, r e s p e c t i v e l y . P r e h e a t i n g , c o o l i n g and c o a t i n g t i m e s f o r t h e two c a s e s c o n s i d e r e d a r e summarized i n T a b l e s 5.1 and 5.2. 5.2 E n v i r o n m e n t a l and S a f e t y F e a t u r e s A l t h o u g h m i n i m a l p a r t i c l e a t t r i t i o n was o b s e r v e d i n t h e l a b o r a t o r y u n i t , s m a l l q u a n t i t i e s o f u r e a and s u l p h u r d u s t l e a v e t h e s p o u t e d bed; i n t h e l a r g e r s i z e equipment t h i s p r o b l e m i s e x p e c t e d t o r e c u r and, i n o r d e r t o comply w i t h a i r p o l l u t i o n r e g u l a t i o n s , t h e e l u t r i a t e d s o l i d s s h o u l d be c o l l e c t e d i n a h i g h e f f i c i e n c y d o u b l e s t a g e c y c l o n e . I t i s a l s o a d v i s a b l e t o i n s t a l l a s c r u b b e r a f t e r t h e c y c l o n e t o e l i m i n a t e t h e e m i s s i o n o f malodorous s u l p h u r compounds. A l l equipment has t o be e l e c t r i c a l l y grounded t o p r e v e n t e x p l o s i o n h a z a r d s due t o s u l p h u r d u s t . 5.3 Economics T a b l e 5.3 summarizes t h e economic d a t a o f t h e two s e m i - c o m m e r c i a l f a c i l i t i e s . A l l o w a n c e s f o r l a n d and b u i l d i n g have n o t been made s i n c e t h e c o a t i n g p l a n t s a r e supposed t o be a d j u n c t s t o e x i s t i n g f a c i l i t i e s . Based on a 20% r e t u r n on i n v e s t m e n t , t h e p r o d u c t c o s t p e r t o n o f s u l p h u r c o a t e d u r e a a r e e s t i m a t e d t o be $523 and $448 f o r t h e two p l a n t s . The p r e s e n t V a n c o u v e r w h o l e s a l e p r i c e f o r s u l p h u r c o a t e d u r e a ( i n b u l k ) i s a p p r o x i m a t e l y $540 p e r m e t r i c t o n . T h i s s u g g e s t s t h a t t h e s m a l l c o m m e r c i a l u n i t s a r e c o m p e t i t i v e . T a b l e 5.4 a l s o shows t h e raw m a t e r i a l s r e q u i r e m e n t s and t h e i r c o s t . I t s h o u l d be n o t e d t h a t one o f t h e main c o s t s o f s u l p h u r c o a t e d u r e a 99 T a b l e 5.3: P r e l i m i n a r y Economics o f Semicommercial F a c i l i t i e s f o r S u l p h u r C o a t i n g o f Urea. Based on one 8 hour s h i f t / d a y and 250 d a y s / y e a r . ITEM 3 B a t c h e s / d a y 196.3 t / y e a r 2 B a t c h e s / d a y 314.8 t / y e a r C a p i t a l I n v e s t m e n t , $: Equipment I n s t a l l a t i o n E n g i n e e r i n g Raw M a t e r i a l s (1 mo. s u p p l y ) S i l i c o n e (1 mo. s u p p l y ) P r o d u c t i n S t o r a g e (2 mo. pro d ) T o t a l P r o d u c t C o s t , $/Year: I n t e r e s t ( 1 2% o f C a p i t a l I n v e s t m e n t ) D e p r e c i a t i o n ( 10% o f C a p i t a l I n v e s t m e n t ) R e t u r n o f Investment (20% o f s u l p h u r ) M a i n t e n a n c e ( 5 % o f C a p i t a l C o s t ) S u l p h u r @ (@ $104/t) Urea (@ $209.5/t) S i l i c o n e (@ $6.6/kg) Labour (1 o p e r a t o r ) U t i l i t i e s S e l l i n g Expenses P r o d u c t C o s t T o t a l 26,000 34,000 22,750 29,750 16,250 21,250 3,060 4,799 68 108 17,126 23,501 85,254 113,408 10,230 13,609 8,525 11,341 17,051 22,682 3,250 4,250 5,084 8,152 30,828 49,436 811 1,304 21,600 21,600 3,000 4,800 100,379 137,174 2,356 3,800 102,735 140,974 Co s t p e r m e t r i c t o n o f p r o d u c t 523.35 447.82 100 by t h e s p o u t e d bed i s l a b o r . I n t h e two c a s e s c o n s i d e r e d , l a b o u r c o s t s a r e 110 and 69 $ p e r m e t r i c t o n . ( t ) o r 21 and 15% o f t h e f i n a l p r o d u c t v a l u e . A l l p r i c e s a r e g i v e n i n C a n a d i a n d o l l a r s and t h e c o s t e s t i m a t e s a r e v a l i d f o r J u n e , 1980. T a b l e 5.4: Raw M a t e r i a l Requirements and C o s t s Based on J u n e , 1980 P r i c e s . ITEM 3 B a t c h e s / d a y , Weight 196.3 t / Y e a r C o s t 2 B a t c h e s / d a y , Weight 314.8 • C o s t k g / y e a r $/year k g / y e a r $/year Urea 147,150 30,828 235,970 49,436 S u l p h u r 49,050 5,084 78,657 8,152 S i l i c o n e 123 811 197 1,304 T o t a l 196,323 36,723 314,824 58,892 5.4 C o n t i n u o u s O p e r a t i o n As shown i n t h e p r e v i o u s s e c t i o n , l a b o u r a c c o u n t s f o r a major f r a c t i o n o f f i n a l p r o d u c t v a l u e . One way o f r e d u c i n g t h i s c o s t i s t o o p e r a t e t h e p l a n t c o n t i n u o u s l y t h e r e b y p r o v i d i n g a h i g h e r t h r o u g h p u t . W i t h m i n o r changes, ( i . e . c o n t i n u o u s u r e a f e e d e r , s l i d e f o r p r o d u c t c o o l i n g ) t h e p r e v i o u s f a c i l i t i e s c o u l d be adap t e d t o o p e r a t e c o n t i n u o u s l y . T a b l e 5.5 shows t h e e s t i m a t e d c a p a c i t i e s f o r t h e b a t c h w i s e and c o n t i n u o u s o p e r a t i o n o f t h e f a c i l i t i e s . I t i s n o t i c e d t h a t t h e p l a n t c a p a c i t y has been i n c r e a s e d more t h a n 5 t i m e s . A major p r o b l e m w h i c h c o u l d a r i s e i s t h e p r o d u c t q u a l i t y , because i t may be d i f f i c u l t t o e n s u r e a u n i f o r m p r o d u c t . To overcome t h i s , some o f t h e p r o d u c t may have t o be r e c y c l e d . T a b l e 5.5: Comparison o f B a t c h w i s e and C o n t i n u o u s O p e r a t i o n o f S u l p h u r C o a t i n g F a c i l i t i e s ( S u l p h u r Coat 25% w t ) . D e s c r i p t i o n B a t c h w i s e C o n t i n u o u s O p e r a t i o n O p e r a t i o n T o t a l C o a t i n g t i m e , h r 3.40 0.69 Bed h o l d up, kg u r e a 472 472 Flow o f u r e a t o bed, k g / h r - 684 Number o f b a t c h e s / d a y 2 D a i l y P r o d u c t i o n , kg/day 1259 7297 Y e a r l y P r o d u c t i o n , t / y e a r (250 d a y s , 8 h r / d a y ) 315 1824 6. CONCLUSIONS AND RECOMMENDATIONS 6.1 L a b o r a t o r y T e s t s B a t c h w i s e l a b o r a t o r y t e s t s have shown t h a t i t i s p o s s i b l e t o o b t a i n h i g h q u a l i t y s u l p h u r c o a t e d u r e a (D 25 ^ e s s t h a n 25%) p r o v i d e d t h e u r e a i s p r e h e a t e d t o t e m p e r a t u r e s between 75-80°C and t h e s u l p h u r i s i n j e c t e d a t an adequate f l o w r a t e (90-190 g/min); t h e p r o d u c t q u a l i t y i s a f u n c t i o n o f s u l p h u r f l o w r a t e , bed t e m p e r a t u r e , a t o m i z i n g a i r f l o w r a t e and u r e a s i z e ; from t h e a f o r e -m e n t i o n e d i t i s p o s s i b l e t o i n f e r t h a t p r o d u c t q u a l i t y depends on t h e s i z e o f d r o p l e t g e n e r a t e d by t h e s p r a y i n g n o z z l e . V e r y s m a l l a d d i t i o n s o f s i l i c o n e (0.25% wt o f s u l p h u r ) appear t o improve t h e p r o d u c t q u a l i t y s u b s t a n t i a l l y . 6. 2 Semi-commercial U n i t E n g i n e e r i n g and c o s t e s t i m a t e s i n d i c a t e t h a t i t i s p o s s i b l e t o b u i l d s e m i - c o m m e r c i a l spouted beds p r o d u c i n g 196 and 315 m e t r i c t o n p e r y e a r o f s u l p h u r c o a t e d u r e a a t a p r i c e o f $524 and $448 p e r t o n r e s p e c t i v e l y , compared t o t h e w h o l e s a l e p r i c e o f $540/t. 6.3 Recommendations . F u r t h e r work on s u l p h u r c o a t i n g o f u r e a w i t h t h e sp o u t e d bed s h o u l d be p e r f o r m e d w i t h a 0.6 m bed. Such a bed w i l l f a c i l i t a t e t h e a c c u r a t e d e s i g n o f s e m i - c o m m e r c i a l u n i t s . 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Food Chem. 1 9 ( 5 ) , (1971). 4. R i n d t , D.W., B l o u i n , G.M. and G e t s i n g e r , J.G., J . A g r . Food Chem. 1 6 ( 5 ) , ( 1 9 6 8 ) . — 5. Anonymous, S u l p h u r No. 142, (May-June, 1979). 6. A l l e n , E.R. and Mays, D.A., J . A g r . Food Chem. 1_9, (1971). 7. L i e g e l , E.A. and Walsh, L.M., J . A g r . Food Chem. 68, (1976). 8. Sharma, G.C., P a t e l , A . J . and Mays, D.A. J . Am. Soc. H o r t i c , S c i . 1 0 1 ( 2 ) , (1976). 9. J a r a m i l l o C e l i s , R. and Bazan, R., T u r r i a l b a 2 6 ( 1 ) , (1976). 10. M a t h u r , K.B. and M e i s e n , A., P r i v a t e communication. 11. Zee, C . J . , B.A. Sc. T h e s i s , U.B.C, (1977). 12. Anonymous, S u l p h u r I n s t . J . 8_(4), (1972). 13. S h i r l e y , A.R. J r . , and M e l i n e , R.S., New Uses o f S u l p h u r , Advances i n C h e m i s t r y S e r i e s v. 140, AChS, Washington, D.C. (1975). 14. Anonymous, S u l p h u r I n s t . J . , 8_(4), 1974. 15. TVA B u l l e t i n , TVA DEMONSTRATION SCALE PLANT. 16. J e f f r e y L i m , B.A.Sc. T h e s i s , U.B.C, (1978). 17. M e i s e n , A., and Ma t h u r , K.B., Paper p r e s e n t e d a t t h e 2nd I n t e r n a t i o n a l C o n f e r e n c e on F e r t i l i z e r s . P r o c e e d i n g s o f t h e B r i t i s h S u l p h u r C o r p o r a t i o n - P a r t I , December 3-6 (1 9 7 8 ) . 18. Meyer, B., Chem. Rev. 64, 429, (1964). 19. M a t h u r , K.B., E p s t e i n , N. Spouted Beds , Academic P r e s s , New York ( 1 9 7 4 ) . 20. E l l i o t , H.J., B r i t i s h P a t e n t 1 536 694 (Dec. 20, 1978). 21. Nukiyama, S., and Y. Tanasawa, T r a n s . Soc. Mech. E n g r s . ( J a p a n ) , 4-6, R e p o r t s 1-6 (1938-40). T r a n s l a t e d by E. Hooc f o r Defense R e s e a r c h Board, Dept. o f N a t i o n a l D e f e n s e , Canada, 10 M-9-47(393), H.Q. 2-0-264-1 (March 18, 1950). 22. B e r q u i n , Y.F., 4 t h J o i n t Chem. Eng. Conf. (AIChE-CSChE), Paper No. 38e, 104 105 V a n c o u v e r , B.C., 1973. 23. T h o r l e y , B., M athur, K.B., K l a s s e n , J . and G i s h l e r , P.E. R e p o r t N a t i o n a l R e s e a r c h C o u n c i l o f Canada, Ottawa, 1955. 24. F r e e p o r t S u l p h u r Co., S u l p h u r Data Book, M c G r a w - H i l l (1954). 25. S t a u f f e r C h e m i c a l Co., B u l l e t i n . 26. Donahue, J . and Meyer, B., The Naming o f S u l p h u r A l l o t r o p e s , E l e m e n t a l S u l p h u r , B. Meyer, @ by John W i l l e y and Sons I n c . (1965). 27. D a l e , J.M. and Ludwig, A . C , M e c h a n i c a l P r o p e r t i e s o f S u l p h u r A l l o t r o p e s . Mat. Res. £ S t a n d . , (Aug. 1965). 28. A b d e l r a z e k , J . , Ph. D. T h e s i s , U n i v e r s i t y o f Tennessee, K n o x v i l l e , (1969). APPENDIX I 1.1 D i s s o l u t i o n T e s t R e s u l t s 1.2 O p e r a t i n g C o n d i t i o n s 106 107 RUN NO. T a b l e 1.1 D i s s o l u t i o n T e s t R e s u l t s SAMPLE NUMBER 1 D 2 5 D 3 0 t , M i n 10 15 20 , 25 30 EOR EA D,% 62.6 53.7 45.6 33.4 26.5 25.5 32.0 25 C , % 10.5 15.8 20.0 24.5 29.0 29.4 l EB 71.5 58.2 43.9 29.8 26.1 24.7 29.5 25 10.5 15.8 20.3 24.5 29.0 29.4 EC 43.9 35.9 25.0 19.7 21.1 21.2 25.0 21 12.3 17.8 22.0 27.5 32.3 32.5 ED 77.4 58.0 44.9 38.4 36.5 31.2 39.0 33 12.8 15.8 21.3 25.8 29.3 29.5 EE 82.5 57.2 45.5 34.8 25.9 25.0 35.5 25 12.0 16.3 21.3 25.8 30.5 29.0 EF 66.3 54.0 45.7 31.5 30.0 27.0 32.1 27 12.0 15.8 21.3 25.3 29.3 29.3 EG 68.4 69.5 57.5 57.8 53.5 57.2 56.0 52 10.8 15.8 20.0 23.7 25.8 29.0 EH 77.0 73.1 64.8 62.0 55.9 57.1 59.0 50 10.8 15.5 19.5 23.7 25.8 27.0 E I 78.1 71.6 66.0 57.1 49.7 50.6 56.0 49 12.0 16.2 21.5 24.7 28.5 29.3 108 SAMPLE NUMBER RUN NO ~ 2 5 " 3 0 U 1 2 3 4 5 6 t , M i n 10 15 20 25 30 EOR E J D,% 62.0 42.7 27.6 21.9 17.3 15.5 37.1 27 C i > % 15.8 23.7 29.3 33.0 36.5 38.2 EK 94.6 92.5 7.3 13.5 -EL 92.1 - 72.9 75.4 61.5 63.4 9.2 _ 15.8 19.5 22.0 22.0 EM 91.9 87.5 81.6 74.5 69.6 66.0 8.0 12.0 15.8 19.5 22.0 22.0 EN 93.1 77.1 62.8 44.7 28.5 26.9 44.7 27 11.0 17.0 22.0 25.0 26.4 30.2 EO 41.1 21.1 13.0 9.5 7.7 5.6 25.0 17 18.5 27.4 33.0 36.5 40.5 41.5 EP 33.0 19.8 10.2 7.7 4.1 2.8 27.0 19 22.7 29.3 35.3 42.5 46.5 46.7 EQ 73.4 48.6 29.8 20.2 10.9 9.6 40.0 29 15.3 24.2 29.5 36.5 39.3 39.3 ER 82.8 N / s 56.7 40.4 40.0 50.0 40 12.3 22.4 29.5 29.5 109 SAMPLE NUMBER RUN NO. D 2 5 °30 t.min 10 15 20 25 30 EOR ES D, % 84.6 66.7 53.9 44.9 37.9 35.2 50.0 40 C±, % 12.6 17.3 23.5 27.4 31.3 31.3 ET 76.1 61.1 44.9 39.0 33.3 34.9 40.0 35 12.0 17.3 21.5 27.0 31.0 31.3 EU 72.4 57.0 43.9 35.8 27.8 28.8 40.0 31 12.3 18.8 23.7 27.4 31.6 31.6 EV 80.2 57.8 46.5 26.9 - 21.8 35.0 25 14.0 18.2 23.7 27.4 - 31.3 EW 79.3 57.8 40.4 31.2 25.6 21.4 35.0 25 13.0 18.2 23.7 27.9 31.3 31.3 EX 70.4 46.1 28.4 14.9 9.9 9.0 34.0 19 14.0 22.0 26.1 31.3 36.5 35.3 EY 62.3 29.5 13.7 8.9 7.9 5.2 21.0 11 14.5 22.0 27.0 32.5 36.5 36.5 EZ 99.0 89.3 86.3 79.6 75.5 81.8 7.3 10.4 14.0 15.8 18.5 18.5 t,min 20 30 40 50 60 EOR FA D, % 83.5 72.9 67.3 69.2 70.6 69.9 66.0 65 C , % 13.0 17.0 22.4 27.0 31.3 31.3 l SAMPLE NUMBER RUN D D NO. , 25 U 3 0 t,min 20 30 40 50 60 EOR FB D, % 77.7 68.7 65.6 63.4 61.9 62.6 64.0 62 C , % 13.8 17.3 22.7 27.0 31.3 31.3 t,min 10 15 20 25 30 EOR FD D, % 90.9 86.0 81.8 77.1 76.0 73.8 78.0 C., % 12.0 17.8 22.0 25.8 31.3 31.6 l FE 87.1 84.0 79.4 73.2 60.2 58.3 73.0 10.4 15.8 20.0 25.8 28.2 29.3 FF 86.7 79.7 80.1 70.4 61.1 58.4 71.0 12.0 17.8 22.0 25.8 29.3 29.5 FG 83.8 81.8 60.0 48.0 27.7 27.8 75.0 20.0 25.8 31.3 36.5 41.5 41.7 FH 81.6 78.6 64.2 47.2 27.7 27.8 75.0 15.8 25.8 31.3 36.5 41.5 41.7 F I 35.0 16.3 9.8 6.7 7.3 7.3 21.0 14 21.5 29.5 33.7 40.8 45.5 45.5 A Phos p h a t e F J 27.5 13.5 10.3 9.1 7.3 7.3 20.0 14 A.P. 21.5 29.5 33.7 40.8 45.5 45.5 FK 47.1 22.9 16.3 14.3 13.8 9.9 19.0 16 A.P. 15.0 21.5 29.5 33.7 38.4 45.5 RUN SAMPLE NUMBER N 0 - 1 2 3 4 5 6 ° 2 5 t , m i n 10 15 20 25 30 EOR FL D, % 43.2 21.7 15.9 8.6 7.3 9.5 19.0 15 A P *C* 9. 15.0 23.0 27.7 33.7 38.4 43.3 i * ° t , m i n 5 10 15 20 25 EOR FM D, % - 26.2 8.4 4.7 - 2.0 1 8 - ° 1 0 C., % 20.0 31.3 36.5 - 40.0 FN 70.5 18.4 4.8 3.6 - 3.6 16.0 10 12.3 23.7 31.3 38.2 - 38.2 FO 41.0 13.0 14.9 4.0 30.0 20 22.0 34.5 44.8 - - 45.2 FP 38.1 20.0 6.4 - - 6.5 30.0 20 20.0 34.4 43.5 " " 44.4 FQ 76.7 31.8 8.4 5.1 - 5.3 21.0 10 10.4 22.0 31.0 35.3 - 38.2 t , m i n 10 15 20 25 30 EOR FR D, % 37.7 21.4 10.6 10.9 7.1 7.1 22.0 15 A P. 'C., % 17.2 27.4 31.8 37.4 43.3 43.3 AP 1 FS 45.3 23.0 12.5 9.7 6.2 6.2 25.0 15 A.P. 19.0 27.4 31.8 38.4 43.3 43.3 FT 45.3 16.5 12.6 8.8 9.5 9.5 24.0 15 A.P- 19.0 27.4 32.3 38.4 43.3 43.3 112 RUN NO. SAMPLE NUMBER 3 4 5 '25 '30 t , m i n 10 15 20 41.0 24.8 12.5 25 30 EOR 8.4 6.8 6.8 FU D, % C , % 19.0 27.4 31.8 35.8 40.8 40.8 28.0 17 FV A.P. 46.3 26.4 14.7 8.4 6.8 6.8 17.2 26.5 31.8 35.8 40.8 40.8 28.0 17 t , m i n GA D, % C.., % 10 15 20 25 EOR 45.1 19.8 12.7 - 17.2 15.8 25.8 33.0 - 33.0 20.0 16 GB 37.1 7.4 5.0 17.8 25.8 33.0 5.0 33.0 10.0 GC 75.4 15.8 31.8 29.3 14.9 33.0 32.0 20 GD 22.0 20.0 3.3 33.0 3.5 37.9 12.0 GE 49.3 15.8 14.9 33.0 3.6 38.2 25.0 16 GF 38.5 20.0 5.5 34.5 3.6 39.3 20.0 11 GG 47.4 17.0 14.4 23.7 7.8 29.3 6.7 31.3 13.0 113 SAMPLE NUMBER RUN N 0 - °25 °30 t , m i n 10 15 20 25 GH D, % 52.4 19.2 10.3 7.0 7.2 15.0 10 % 15.8 22.0 29.3 34.5 36.5 t , m i n 5 10 15 20 25 EOR GI D, % 55.5 24.4 - 12.5 34.0 26 C i , % 20.5 36.5 - 41.5 GJ 53.8 16.4 - 17.1 39.0 26 20.0 33.0 - - - 4.1.5 GK 72.4 34.0 - - - 24.7 46.0 33 17.8 29.3 - 34.5 GL 66.7 31.8 - - - 18.1 46.0 31 17.8 29.3 - 36.5 t , m i n 10 15 20 25 30 EOR GM D, % 38.7 14.8 6.5 5.5 5.3 5.4 12.0 6 C , % 15.8 22.4 29.3 34.5 38.2 39.0 l GN 43.1 17.0 6.8 5.5 5.4 5.6 12.0 6 17.0 22.7 29.3 34.4 38.5 40.5 BED RUN wt. kg EA 4. 535 EB 4.535 EC 4.535 ED 4.535 EE 4.535 EF 4.535 EG 4.535 EH 4.535 EI 4.535 EJ 4.535 EM 5.442 EN 3.628 il Final Temp. wt. °C kg 76 5.952 76 5.726 83 5.896 82 5.896 86 5.641 86 5.896 67 5.839 . 67 5.584 58 6.066 58 6.944 86 6.661 86 4.677 Temp. Flow °C m V m i n 76 1.265 76 1.230 83 1.375 82 1. 360 86 1.375 86 1.338 67 1.410 67 1.375 58 1.370 58 1.381 86 1 . 365 86 1.291 touting Air Temp. Press °C cm Hg 74 4 73 3.8 82 4.4 81 4.3 88 5.0 87 4.5 67 4.1 64 4.1 54 50 88 86 AVERAGE OPERATING CONDITIONS Atomizing Air Sulphur Column Temp. Flow Temp. Press Average Jet T Pot T Tj T 2 T 3 m3/hr °C kPa Flow °C °C °C °C °C g/min COMMENTS 0 .594 146 117. .0 61. .7 160 156 76 75 73 0. .594 148 96. .5 61. .7 160 156 76 76 73 0. .594 148 103. .4 72. . 1 160 159 83 82 79 0. .594 148 103. .4 62. .6 160 158 82 81 78 0. .594 148 106. .8 66. . 3 160 156 86 86 84 Slight sulphur deposition on column wall 0. .594 148 99. 9 62. .6 160 156 86 85 82 Slight sulphur deposition on column wall 0. .594 148 96. 5 52. .6 159 156 67 67 65 Coat loose and fragile and Sulphur depos-ition on column wall 0. S94 154 99. .9 52. .6 160 156 67 67 65 Coat loose and fragile and Sulphur depos-ition on column wall 0. .594 148 no. .2 60. .3 159 158 58 58 57 Same as previous 0. 594 148 130. 9 86. .9 159 158 58 58 S7. .5 Same as previous 0. 594 148 110. 2 51 . 2 160 156 86 86 84. .5 Spouting a i r insuficient to reach 25"& Sulphur content 0. 594 148 110. 2 43. 4 160 157 86 84 81. .0 I n i t i a l Final Spouting Air Atomizing Air Sulphur Temp""" RUN wt. Temp, wt. Temp. Flow Temp. Press. Flow Temp. Press. Average Jet T Pot Temp. T T T k g C k « c " V m i n "C cmHg. m V h r °C kPa Flow °c °C ^ .* gr/min. EO 3.628 86 5 .668 86 1 .315 84 0.594 148 110.2 82 .3 159 156 86 85 81 EP 2.721 83 4 .762 83 1 .210 80 0.594 148 110 .2 78 .8 159 156 , 83 80 78 EQ 2.721 85 4 .025 85 1 .165 83 0.594 147 107 .2 58 .7 160 156 85 81 78 ER 4.535 87 6 .037 87 1 .291 86 0.785 148 237 .7 67 .9 160 159 87 84.5 80 ES 4.535 87 6 .037 87 1 .250 84 0.785 148 237 .7 69 .8 160 159 87 85 81 ET 4.S35 86 6. .236 86 1 .320 86 0.658 148 144 .7 63 .3 160 159 86 85 81 EU 4.535 86 6. . 122 86 1, .270 88 0.658 154 144. .7 68. .9 160 159 86 86 81 EV 4,535 87 6. 293 87 1. .320 86 0.530 148 82, ,7 68. S 159 156 87 86 82 EW 4.535 87 6. 349 87 1. 320 87 0.530 148 86. .1 68. .9 160 156 87 86 83 EX 4.535 86. 5 6. 548 86.5 1. 338 87.5 0.402 148 51. 7 86. 9 159 155 86.5 85 81 EY 4.535 86. 5 6. 638 86.5 1. 330 85.0 0.402 148 49. 6 86. 9 159 15S 86 85 82 EZ 4.535 86. 0 5. 102 86.0 1. 150 90.5 0.594 148 106. 8 34. 4 159 158 86 85 81 BED AVERAGE OPERATIONS CONDITIONS In i t i a l Final Spouting Air Atomizing Air Sulphur Column Temp. COMMENTS wt. Temp. wt. Temp. Flow Temp. Press Flow Temp. Press Average Jet T Pot T T[ T 2 T3 kg °C kg °C m3/min "C cm Hg m3/hr °C kPa Flow °C °C °C °C °C g/min 4.535 85 5.924 85 1.315 89 0.594 148 103.4 34.4 159 158 85 85 82 4.535 85 6.122 85 1.260 89 0.594 148 106.8 34.4 159 158 85 85 82 4-535 82 6.122 82 1.200 84 0.402 148 46.0 68.9 159 156 82 82 79 Very dirty area and coats loose and improper sample cooling 4.535 82 5.952 82 1.338 84 0.402 148 82.7 59.4 159 4.535 81 6.009 81 1.338 82 0.402 148 51.7 62.7 159 2.721 82 4.308 82 1.158 81 0.402 148 44.8 64.3 159 2.721 82 3.997 82 1.165 81 0.402 148 44.8 64.3 159 4.535 81 6.576 81 1.400 75 0.594 148 55.12 75.7 158 155 82 82 77 Same as previous one 156 SI 81 77 Same as previous one 156 82 78 73 Same as previous one 156 82 79 73.5 Same as previous one 157 81 79 75.0 Substrate: Ammonium Phosphate 4 - 5 3 5 8 2 7 - 2 8 5 8 2 1 ' 4 3 9 7 7 0.594 148 124.0 75.7 157.5 157 82 79.5 75.0 Same as previous one 4 - 5 3 5 8 6 7 2 5 6 8 6 »-320 84 — - Q 56.5 158 157 86 83.0 78.0 Same as previous one 4 - 5 3 5 7 8 7.370 78 1.360 72 0.402 147 55.1 78.2 159 158 78 77 75 4 - 5 3 5 7 7 7-086 77 1.284 68 0.402 147 55.1 84.1 159 158 77 76 72 BED I n i t i a l AVERAGE OPERATING CONDITIONS Final Spouting Air Atomizing Air Sulphur Column Temp. COMMENTS RUN wt. Temp. wt. Temp. Flow Temp. Press Flow Temp. Press Average Jet T Pot T T[ T 2 T 3 kg °C kg °C mVmin °C cm Hg m3/hr °C kPa Flow °C °C °C °C °C g/min FO 2.721 80 4.705 80 1.210 68 0.402 148 55.1 147.2 159 158 80 75 72 FP 2.721 78 4.535 78 1.221 69.5 0.402 148 48.2 139.7 159 155 78 75.5 72 FQ 4.535 76 6.803 76 1.410 70 0.402 148 55.1 123.7 159 155 76 76 73 FR 4.535 77 6.888 77 1.308 70 0.594 147 124.0 115.4 157 157 77 74 71 Substrate: Ammonium FS 4.535 68 7.001 68 1.241 59.5 0.594 FT 4.535 68 7.143 68 1.220 59 FU 4.53S 59.5 7.143 59.5 1.250 48 FV 4.535 58 7.143 58 1.188 47 Phosphate 1 4 7 124.0 115.4 157.5 156.5 68 66.5 63.5 Same as previous one 0 594 147 124.0 11S.4 157 153 68 67 63 Same as previous one 0.594 147 132.8 104.2 157 153 59.5 58.5 56 Same as previous one 0 594 132 132.8 104.2 157 153 58 57 55 Same as previous one GA 4.535 78 6.576 78 1.439 69 0.203 136 24.1 111.7 158 157 78 77 73 Probe inserted in spout to measure temp, at lOcms above nozzle GB 4.535 74 7.143 74 1.265 67 0.278 132 33.3 111.7 158 157 74 72 69 GC 4.535 80 6.604 80 1.439 63 0.278 147 17.2 187.9 158 154 80 77 73 CD 4.535 77 6.689 77 1.284 73 0.278 143 34.5 223.4 157 157 77 74 69 BED AVERAGE OPERATING CONDITIONS Spouting Air Atomizing Air Sulphur Column Temp. COMMENTS RUN wt. kg Temp. °C wt. kg Temp. °C Flow mVmin Temp. °C Press cm Hg Flow m3/hr Temp. °C Press kPa Average Flow g/min Jet T °C Pot T °C "C T 2 °C T 3 °C GE 4.535 79 7.. 256 79 1.158 72 0.278 143 48.2 223.4 157 156 79 75 70 GF 4.535 78 7. 256 78 1.439 57 0.278 147 41.3 238.9 157 153 78 77 73 GG 4.535 . 76 6..349 76 1.420 71 0.594 148 124.0 94.0 158 155 76 76 73 Gil 4. 535 76 6. 122 76 1.300 69 0.594 148 127.5 94.0 159 155 76 75 72 GI 4.535 42 7.596 56 1.338 36 0.594 148 89.6 260. 7 158 157 48 48 46 GJ 4.535 42 7.483 53 1.360 37 0.594 148 137.8 223.4 158 157 47. 5 46. 5 44. GK 4.535 41 6.859 52 1.270 36 0.594 148 182.6 187.9 158 154 48 47 45 GL 4.535 42 7.256 54 1.215 37 0.594 148 156.2 187.9 157 154 48 48 47 GM 4.535 77 6.973 77 1.260 73 0.594 148 87.5 93.4 158 157 77 75 73 GN 4.535 77 7.029 77 1.200 72 0.594 148 81.0 94.6 158 157 77 76 72 00 4.535 59 4.505 59 0.970 67 59 58 S6 01 4.535 88 4.535 88 0.822 102 88 86 81 02 4.535 88 4.535 88 0.890 102 88 87 83 Silicone injected for 5 minutes through atomize a i r line before coating app. 4 ml. Slight sulphur deposition on column walls Silicone injected for 5 minutes through atomize a i r line before coating app. 4 ml Silicone injected for 20 minutes while coating app. 4ml OO APPENDIX I I CALIBRATION CURVES FOR ROTAMETERS AND REFRACTOMETER 119 120 140 10 2.0 3.0 AIR FLOW RATE , m 3 / m i n F i g u r e I I . 1 : C a l i b r a t i o n Curve f o r C o o l i n g A i r Rotameter (Temp.: 20°C P r e s s . : 101.28 kPa) 121 F i g u r e I I . 2 : C a l i b r a t i o n C urve f o r S p o u t i n g A i r Rotameter (Temp.: 20 C P r e s s : 101.28 kPa) 122 F i g u r e I I . 4 : C a l i b r a t i o n C urve f o r S u l p h u r Rotameter. Temp: 148 ( G l a s s F l o a t . ) 124 F i g u r e I I . 5 : Abbe R e f r a c t o m e t e r C a l i b r a t i o n Curve f o r Aqueous S o l u t i o n s o f U r ea. 125 1.330 1.340 1.350 1.360 REFRACTIVE INDEX TEMP = 2 5 ° C F i g u r e I I . 6 : Abbe R e f r a c t o m e t e r C a l i b r a t i o n Curve f o r Aqueous S o l u t i o n s o f Ammonium Phosphate. 126 NOMENCLATURE A A r e a A c C r o s s - s e c t i o n a l a r e a o f column Aj[ C r o s s - s e c t i o n a l a r e a o f f l u i d i n l e t o r i f i c e C S u l p h u r p e r c e n t a g e i n c o a t e d u r e a Cp S p e c i f i c h e a t o f a i r Cpp S p e c i f i c h e a t o f p a r t i c l e s c Number o f passages w h i c h t h e u r e a g r a n u l e s must make t h r o u g h t h e s p r a y zone i n a s p o u t e d bed c o a t i n g f a c i l i t y D 7 d a y - d i s s o l u t i o n p e r c e n t a g e o f s u l p h u r c o a t e d u r e a D25 7 d a y - d i s s o l u t i o n p e r c e n t a g e o f s u l p h u r c o a t e d u r e a w i t h a s u l p h u r c o a t o f 25% wt D'25 N o r m a l i z e d d i s s o l u t i o n r a t e dp P a r t i c l e d i a m e t e r d . P a r t i c l e d i a m e t e r o f s i z e f r a c t i o n x. p i 1 F V o l u m e t r i c f e e d r a t e g A c c e l e r a t i o n o f g r a v i t y H Bed de p t h M Mass o f p a r t i c l e s P N T o t a l number o f samples w i t h d r a w n from bed N s Spout number AP P r e s s u r e drop Q S u l p h u r i n j e c t i o n r a t e (Eq. 4.1) Q V o l u m e t r i c a i r f l o w r a t e (Eq. 5.3) Q Gas f l o w r a t e x a Qg . L i q u i d f l o w r a t e Q R e f e r e n c e s u l p h u r i n j e c t i o n r a t e SR 127 S u l p h u r c o n t e n t i n s u l p h u r c o a t e d u r e a Temperature F i n a l p a r t i c l e t e m p e r a t u r e I n i t i a l p a r t i c l e t e m p e r a t u r e I n l e t a i r t e m p e r a t u r e P a r t i c l e t e m p e r a t u r e T o t a l t i m e o f e x p e r i m e n t (Eq. 4.1) H e a t i n g and c o o l i n g t i m e s (Eq. 5.3) Time s p e n t by t h e p a r t i c l e s i n t h e bed t o r e a c h a s u l p h u r c o n t e n t o f 25% (Eq. 5.4) Minimum s u p e r f i c i a l v e l o c i t y f o r s p o u t i n g Approach v e l o c i t y Average g r a n u l e v e l o c i t y Downward p a r t i c l e v e l o c i t y a t column w a l l I n i t i a l bed w e i g h t o f u r e a Weight o f d u s t c o l l e c t e d i n c y c l o n e Weight o f i t h sample w i t h d r a w n from s p o u t e d bed Weight f r a c t i o n o f s u l p h u r i n c y c l o n e d u s t Weight f r a c t i o n o f s u l p h u r i n i t h sample Weight f r a c t i o n o f s u l p h u r i n Nth sample w i t h d r a w n from bed Mass f r a c t i o n o f p a r t i c l e s o f s i z e a~ . p i I n c l u d e d a n g l e o f cone S u r f a c e t e n s i o n F l u i d v i s c o s i t y S o l i d s b u l k d e n s i t y F l u i d d e n s i t y Gas d e n s i t y P a r t i c l e d e n s i t y 

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