23 3 miami beach_09-78_0160

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23 3 miami beach_09-78_0160

  1. 1. E f f e c t s o R e a c t i o n Conditions on Gasification f of Coal-Residual Oil S l u r r y H i r o s h i Miyadera, Mizuho H i r a t o , S h u n t a r o Koyama, Kenichi Gomi H i t a c h i R e s e r a c h L a b o r a t o r y , H i t a c h i L t d . , Ibaraki-ken, J a p a nIntroduction I n the face of e n e r g y crisis and environmental pollution, t h e technology for coalgasification is b e i n g developed as a p a r t of "Sunshine P r o j e c t " promoted by t h eMinistry of I n t e r n a t i o n a l T r a d e a n d I n d u s t r y (MITI). P e t r o l e u m , h o w e v e r , w i l l holdby f a r the l a r g e s t s h a r e in J a p a n s p r i m a r y e n e r g y supply f o r t h e n e x t d e c a d e s .While the utilization of heavy oil s u c h as vacuum r e s i d u e is limited f r o m a point ofview of the air pollution because of difficult d e s u l f u r i z a t i o n . T h e r e f o r e , in 1974 we h a v e s t a r t e d t h e development of " H y b r i d G a s i f i c a t i o nP r o c e s s 1 in which c o a l a n d r e s i d u a l oil are simultaneously g a s i f i e d to c l e a n f u e l g a s .T h i s r e p o r t b r i e f l y d e s c r i b e s the p r o c e s s and e x p e r i m e n t a l r e s u l t s .P r o c e s s Description A flow d i a g r a m of H y b r i d G a s i f i c a t i o n P r o c e s s is shown i n F i g u r e 1. P u l v e r i z e dc o a l is mixed and s t i r r e d with r e s i d u a l oil to form a s l u r r y , which is pumped to t h ep r e s s u r i z e d fluidized b e d gasifier with atomizing s t e a m . T h e slurry i c o n v e r t e d sinto gas and char by t h e r m a l c r a c k i n g r e a c t i o n s in t h e upper z o n e of t h e f l u i d i z e d b e d .The c h a r produced is f u r t h e r g a s i f i e d with s t e a m a n d oxygen. The gas leaving the gasifier is s c r u b b e d i n o i l and then i n w a t e r quench to r e m o v etar, d u s t and steam. A conventional gas c l e a n up s y s t e m is u s e d to a b s o r b c a r b o ndioxide and hydrogen s u l f i d e from the gas. If SNG is r e q u i r e d , the p r o d u c t gas isshifted and methanated. The advantages of the p r o c e s s are(1) Almost all g r a d e s of c o a l a n d r e s i d u a l oil c a n b e simultaneously c o n v e r t e d to c l e a n fuel gas.(2) Raw m a t e r i a l s are t r a n s p o r t e d a n d fed to t h e p r e s s u r i z e d gasifier without difficulty by means of s l u r r y .(3) T h e gasifier c o n s i s t s of a s i n g l e fluidized bed a n d the g a s i f i c a t i o n r e a c t i o n s p r o c e e d i n two s t a g e s- s l u r r y thermal c r a c k i n g a n d c h a r p a r t i a l oxidation. T h i s simple s t r u c t u r e of t h e g a s i f i e r a c h i e v e s e a s y c o n t r o l a n d h i g h t h e r m a l efficiency.Experimental I n o r d e r to i n v e s t i g a t e t h e gasification c h a r a c t e r i s t i c s and to i m p r o v e thep r o c e s s , experiments were conducted in t h e p r e s s u r i z e d g a s i f i c a t i o n a p p a r a t u s shownin F i g u r e 2. T h e g a s i f i e r h a s the i n n e r diameter of 120mm i n t h e u p p e r zone a n d8 0 m m in the l o w e r zone. T h e height of e a c h zone is 2000mm. The temperatures i nt h e g a s i f i e r a r e c o n t r o l l e d by t h e s u r r o u n d i n g e l e c t r i c h e a t e r s . A t the beginning of e a c h experiment, p u l v e r i z e d and s i e v e d c o a l in t h e c o a lhopper is c h a r g e d a n d Fluidized with steam a n d oxygen. T h e n t h e 2OO0C p r e - h e a t e ds l u r r y with atomizing s t e a m is fed to the middle p a r t of the f l u i d i z e d b e d . The bedheight above t h e s l u r r y f e e d i n g point is 700mm. A f t e r d u s t , tar and s t e a m i n t h ep r o d u c t gas are removed i n c y c l o n e s , s c r u b b e r and quencher, the gas p r e s s u r e isr e d u c e d and its composition and its flow rate are m e a s u r e d . Since a p a r t of t h e gas is p r o d u c e d by t h e h e a t supplied f r o m t h e e x t e r n a lh e a t e r s , the gas y e i l d s of t h e s e e x p e r i m e n t s are somewhat d i f f e r e n t f r o m t h e o n e sp r o d u c e d in t h e p u r e l y i n t e r n a l l y f i r e d gasifier. T h e r e f o r e , w e h a v e examined thec h a r a c t e r i s t i c s of thermal c r a c k i n g a n d p a r t i a l oxidation s e p a r a t e l y . T h e gasproduced in t h e thermal c r a c k i n g z o n e is c o n s i d e r e d as follows. 160
  2. 2. GS= GT-CC 1)w h e r e GS : gas production r a t e i n t h e s l u r r y thermal c r a c k i n g z o n e , C c : g a s production r a t e i n t h e c h a r p a r t i a l oxidation zone, CT : total g a s production r a t e i n the g a s i f i e r when s l u r r y t h e r m a l c r a c k i n g a n d c h a r p a r t i a l oxidation o c c u r simultaneously.G c c a n b e measured when s l u r r y feeding is stopped a n d only t h e c h a r partialoxidation r e a c t i o n t a k e s p l a c e . F e e d i n g m a t e r i a l s are shown i n T a b l e I. Taiheiyo coal, mined in Hokkaido, wasc h o s e n f o r this study b e c a u s e i t is t h e most p r a c t i c a b l e for g a s i f i c a t i o n u s e indomestic coals. T a b l e I. Raw m a t e r i a l s Taiheiyo coal Gach S a r a n Vacuum R e s i d u e P r o x i m a t e analysis (wt5) B o i l i n g point (OC) 7550 Moisture 5.3 A s p h a l t e n e (wt$) 10.4 Ash 14.4 C o n r a d s o n c a r b o n (wt%) 21 -8 Fixed carbon V 318 .37.7 Metal content (pprn) Volatile matter 42.5 Ni 112 Ultimate a n a l y s i s (wt%,daf) Ultimate a n a l y s i s ( w t 5 ) C 76.6 C 85.0 H 6.5 H 10.8 N 1 .o N 0.1 0 15.3 0 - S 0.6 S 35 . Heating value (kcal/kg) 6580 H e a t i n g value (kcal/kg) 10090 (Note) F e e d s l u r r y ; Coal/Residual oil : 30/70 (wt. r a t i o ) Coal s i z e : 40-140 mesh (0.105-0.42 mm) Initially c h a r g e d coal s i z e : 25-40 mesh (0.42-0.71 mrn) G a s i f i e r t e m p e r a t u r e s w e r e c o n t r o l l e d by oxygen feed r a t e a n d t h e s u r r o u n d i n ge l e c t r i c h e a t e r s between 800 a n d 95OoC i n t h e l o w e r p a r t i a l oxidation z o n e and bet-ween 700 a n d 800°C i n t h e u p p e r thermal c r a c k i n g zone. Reaction p r e s s u r e s w e r ev a r i e d from 5 to 20 atm.Results and Discussion(1) C h a r a c t e r i s t i c s of S l u r r y T h e r m a l C r a c k i n g Reaction. F i g u r e 3 s h o w s t h e e f f e c t s of t e m p e r a t u r e and p r e s s u r e o n t h e p r o d u c t yield ofs l u r r y thermal c r a c k i n g . T h e main components p r o d u c e d are h y d r o g e n , methane,c a r b o n monoxide a n d c a r b o n dioxide. T h e y i e l d s of t h e s e gases i n c r e a s e witht e m p e r a t u r e (Ts)a n d p r e s s u r e , while yield of by-product tar d e c r e a s e s as p r e s s u r erises. In t h i s zone, following r e a c t i o n s t a k e place.O v e r a l l h e a t of r e a c t i o n AH, c a n b e estimated by t h e next equation.w h e r e the f i r s t t e r m o n the r i g h t s i d e r e f e r s to t h e summation of h e a t s of combustionf o r the r e a c t a n t s a n d t h e second t e r m f o r the p r o d u c t s . T h e o v e r a l l h e a t of r e a c t i o n estimated by t h e m e a s u r e d - h e a t s of combustion for 161
  3. 3. s l u r r y , t a r a n d c h a r are shown in t h e upper columns of F i g u r e 3 . A s shown i n thef u g u r e , I i n c r e a s e s with i n c r e a s i n g t e m p e r a t u r e s and d e c r e a s e s with i n c r e a s i n g &pressures. T h e c h a r a c t e r i s t i c s s t a t e d above definitely show that endothermic r e a c t i o n s s u c ha s thermal c r a c k i n g a n d steam r e f o r m i n g are dominant a t higher t e m p e r a t u r e s andexothermic hydrogasification t a k e s p l a c e a t higher p r e s s u r e s . II’(2) C h a r a c t e r i s t i c s of C h a r Partial Oxidation Reaction. T h e main components i n the g a s produced in t h e p a r t i a l oxidation zone arehydrogen, c a r b o n monoxide and c a r b o n dioxide. T h e r e f o r e , t h e main r e a c t i o n s aresupposedly as follows. I : C (char) + 02 = C02 6) C (char) + C02 = 2CO 7) C ( c h a r ) + H20 = CO+H2 8) CO + N20 = C 0 2 + H2 9)T h e approach of t h e s e r e a c t i o n s toward equilibrium is indicated i n F i g u r e 4. Kp a n dKp’ are the equilibrium c o n s t a n t a n d the o b s e r v e d p a r t i a l p r e s s u r e r a t i o r e s p e c t i v e l y .It is a p p a r e n t from F i g u r e 4 that t h e c a r b o n - c a r b o n dioxide r e a c t i o n a n d the carbon-s t e a m r e a c t i o n a r e far f r o m equilibrium f o r all of t h e r u n conditions t e s t e d , while theo b s e r v e d r a t i o s f o r the shift r e a c t i o n a p g r o a c h t h e equilibrium c o n s t a n t at p r e s s u r e sabove 1 0 atm. i n t h e r a n g e of 800 to 950 C .(3) H e a t and Material B a l a n c e i n G a s i f i e r . B a s e d o n the r e s u l t s d e s c r i b e d above, t h e h e a t a n d m a t e r i a l b a l a n c e i n theg a s i f i e r without e x t e r n a l heating w a s investigated. A s shown i n F i g u r e 5, followingassumptions are made. (i) Qs, the heat r e q u i r e d i n t h e s l u r r y thermal c r a c k i n g zone, is r e p r e s e n t e d by E e Equation A , w h e r e A H is t h e h e a t r e q u i r e d to w a r m t h e r e a c t a n t s from t h e inlet t e m p e r a t u r e t o t h e r e a c t i o n t e m p e r a t u r e Ts. (ii) I n the c h a r p a r t i a l oxidation zone, Reaction 6 - 9 t a k e p l a c e , R e a c t i o n 9 b e i n g i n equilibrium. O v e r a l l h e a t of r e a c t i o n i n t h i s zone raises the t e m p e r a t u r e of fluidizing c h a r a n d gas, and t h i s h e a t is r e l e a s e d i n the t h e r m a l c r a c k i n g zone. T h e r e f o r e , in t h e s t e a d y s t a t e , h e a t balance i n t h e g a s i f i e r c a n b e r e p r e s e n t e d by Equation B , w h e r e QRC a n d Q G r~ p r e s e n t t h e quantities of h e a t t r a n s f e r r e d e by c h a r and g a s , r e s p e c t i v e l y . (iii) I n the steady s t a t e , t h e amount of c h a r produced i n the thermal c r a c k i n g zone is equal to the amount of c h a r g a s i f i e d i n the p a r t i a l oxidation z o n e . The conclusions from this investigation a r e summarized i n F i g u r e 6. It is indi- cated i n F i g u r e 6-a that the thermal efficiency, i.e., the r a t i o of the heating value ofp r o d u c t gas to that of r a w m a t e r i a l s , h a s the maximum value a t about 75OoC. T h i s is b e c a u s e the h e a t r e q u i r e d i n the thermal c r a c k i n g zone is so l a r g e a t h i g h e r tempera- t u r e s that the amount of c a r b o n dioxide i n c r e a s e s . When p r e s s u r e s i n c r e a s e a t c o n s t a n t t e m p e r a t u r e , as shown i n F i g u r e 6-b, both the product g a s heating v a l u e and t h e thermal e f f i c i e n c y i n c r e a s e and oxygen f e e d r a t e d e c r e a s e s . T h i s is b e c a u s e hydrogasification r e a c t i o n s play a m o r e important r o l e a t higher p r e s s u r e s . I T h e typical h e a t and m a t e r i a l balance is shown in F i g u r e 7. T h e heating value of the r a w gas is 4070 kcal/Nm3(460 Btu/scf), a n d 5970 kcal/Nm3(670 Btu/scf) a f t e r r e m o v a l of c a r b o n dioxide a n d hydrogen sulfide on the b a s i s of d r y gas. The thermal efficiency is about 75%. The by-product t a r y i e l d is r a t h e r high (13-15 wt%) i n this p r o c e s s . T h e t a r c a n be either r e c y c l e d to the g a s i f i e r or utilized as f u e l o i l , b i n d e r , r a w m a t e r i a l s f o r chemical i n d u s t r i e s a n d so on. I n addition t o t h e study mentioned above, r e c e n t l y a low p r e s s u r e (max. 3 a t m )i n t e r n a l l y f i r e d g a s i f i e r with a 300mm diameter h a s b e e n o p e r a t e d t o s o l v e t h e p o s s i b l emechanical and o p e r a t i o n a l p r o b l e m s . 162
  4. 4. On the b a s i s of these r e s e a r c h e s , a 12 t/D pilot plant is being designed, and itw i l l be constructed in 1980.A c kflowledgement This work w a s sponsored by the Agency of Industrial S c i e n c e and Technology ofMITI and is presented with their permission. 163
  5. 5. Purification I I I I I Slurry Slurry Thermal F e e d System Cracking Steam Char Partial Oxidation P r e s s u r i z e d fluidized bed gasifier Figure 1 . Coal-Residual O i l Hybrid Gasification P r o c e s sCoal Cyclone Scrubber QuencherResidual O i l A s h Receiver Figure 2 . P r e s s u r i z e d fluidized bed gasification apparatus 164
  6. 6. , (a) P : 5 atm - I 0.4 1 c0.30.2 - - --w0.1 - ,o - 700 750 800 0- io 20 Temperature TS ( O C ) P r e s s u r e (atrn) Figure 3 . Effects of temperature and pressure o n s l u r r y thermal cracking 4 -a 0.1 Y Reaction 7 0.01 0 10 20 P r e s s u r e (atm)Figure 4 . Comparison of observed partial p r e s s u r e ratio of partial oxidation gas with equilibrium constant 165
  7. 7. I - & Partial c + co2- IS t e a m (300 "C) J Oxidation I I C + H20- 2co CO + H 2oxy@n(250C) TCOC I 1 co + ~ ~ C 0 2 0 H2 + s F i g u r e 5. R e a c t i o n model in H y b r i d G a s i f i e r S t e a m F e e d R a t e : 1.6 kg/kg s l u r r y x c: (a) P : 5 atm (b) TS : 750 "c . I ? 80 0 .- .I c b W g 70 ;- E $ 60 s: 50 3 a, 5000 k t I I I I u 700 750 800 0 10 20 T e m p e r a t u r e TS (OC) P r e s s u r e (atm) F i g u r e 6. Effects of t e m p e r a t u r e a n d p r e s s u r e o n H y b r i d Gasification P r o c e s s 166
  8. 8. 5 2: 5" aW0 v) v)d3 Wm E.$ a CW4 1 .r(2 .Y LI .r( u : .- 5 h P h N 2 .-. ." C W 2 d 2 P l d 4 .r( W c E 5 d 4 W X I- 5 .r( G4 167

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