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 n
Introduction
I n the face of e n e r g y crisis and environmental pollution, t h e technology for coal
gasification 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 e
Ministry 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 hold
by 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 of
view 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 n
P 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 d
c 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 e
p 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 s
into 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 e
tar, 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 n
dioxide 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 is
shifted 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 the
p 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 shown
in 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 d
8 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 n
t 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 l
hopper 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 d
s 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 bed
height 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 e
p 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 is
r 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 l
h 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 s
p 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 the
c 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 gas
produced 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. 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 partial
oxidation 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, was
c 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 in
domestic 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 g
e 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 e
v 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 of
s 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 with
t 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 e
rises.
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 combustion
f 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. 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 the
f 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 h
a 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 and
exothermic 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 are
hydrogen, 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 are
supposedly 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 d
Kp’ 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 the
o 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 s
above 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 the
g 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, following
assumptions 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 of
p 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 e
mechanical and o p e r a t i o n a l p r o b l e m s .
162

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 it
w 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 of
MITI and is presented with their permission.
163

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 s
Coal
Cyclone Scrubber Quencher
Residual 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. , (a) P : 5 atm -
I
0.4 1 c
0.3
0.2
-
-
--w
0.1 -
,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

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I C + H20-
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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
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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
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