Fuels and Chemicals by Pyrolysis

27 Fuels and Chemicals by Pyrolysis JAMES R. LONGANBACH and FRED BAUER

Downloaded by CORNELL UNIV on October 24, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0032.ch027

Occidental Research Corp., 1855 Carrion Rd., LaVerne, Calif. 91750

The Occidental Research Company, a subsidiary of Occidental Petroleum Corporation, is developing a highly versatile flash pyrolysis process to produce gases, liquids and chars from a variety of organic materials. Flash pyrolysis has the potential of producing maximum yields of gases and liquids from coal and organic solid wastes such as municipal refuse, tree bark, cow manure, rice hulls and grass straw using simple process equipment. The main features of the process are near ambient pressure, no requirement for added chemicals, low capital investment, high feed throughput, flexibility of feedstock, variability of temperature, and minimum feed pretreatment. Process Description A diagram of the process is shown in Figure 1. The organic material is heated by contact with hot recycle char made in the process and carried in a gas stream through a reactor where pyrolysis occurs at very short residence times and high heat-up rates. This method maximizes the volatile yield and protects the products from further cracking. The char-tar-gas mixture is separated in a cyclone, and the char is heated by partial combustion with air in a second entrained bed, separated from the combustion gases and recycled. Excess char is removed and can constitute a sizeable by-product depending on the starting material used. The product gas and tar are separated and are then available for processing. This process maximizes the yields of high value products, both gaseous and liquid and produces a char which can be used as a fuel. The detailed nature of these products will be discussed along with the conditions used and yields obtained in the various modifications of the basic process.

476

Albright and Crynes; Industrial and Laboratory Pyrolyses ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

27.

LONGANBACH AND BAUER

Fuels and Chemicals

477

Coal G a s i f i c a t i o n Two c o a l p r o c e s s i n g m o d i f i c a t i o n s a r e b e i n g d e v e l o p e d . In the f i r s t , c o a l g a s i f i c a t i o n , subbituminous c o a l has been u s e d . An a n a l y s i s o f a t y p i c a l s u b b i t u m i n o u s c o a l i s shown i n T a b l e I TABLE

I

SUBBITUMINOUS COAL USED I N COAL GASIFICATION


Analysis

Weight % Dry As F e d

Moisture Ash V o l a t i l e Matter F i x e d Carbon C H Ν S 0 Heating Value, Btu/lb R e l a t i v e I g n i t i o n Temperature,

°F

Basis

15.1 10.3 31.1 43.5

0.0 12.1 31.1 56.8

55.3 5.3 0.7 1.3 27.1

65.1 4.3 0.8 1.5 16.2

9268 830

10913

The p r e f e r r e d t e m p e r a t u r e f o r c o a l g a s i f i c a t i o n h a s b e e n 1600°-1700°F. The r e s i d e n c e t i m e i s k e p t a s s h o r t as p o s s i b l e t o minimize secondary c r a c k i n g of the gas. The amount o f h y d r o g e n and c a r b o n m o n o x i d e w h i c h c a n b e s t r i p p e d f r o m t h e c o a l i n c r e a s e s w i t h t e m p e r a t u r e b u t t h e maximum g a s i f i c a t i o n t e m p e r a t u r e i s d e t e r m i n e d by t h e c h a r h e a t i n g s t e p . The c h a r must b e a t l e a s t 100°F h o t t e r than the d e s i r e d r e a c t o r temperature to provide d r i v i n g force f o r heat t r a n s f e r . The s o f t e n i n g p o i n t f o r c h a r ash from t y p i c a l American subbituminous c o a l s i s a p p r o x i m a t e l y 2000°F. T y p i c a l y i e l d s a t 1 7 0 0 F a r e 42% c h a r , 9% t a r , 37% gas and 12% w a t e r . A t y p i c a l a n a l y s i s o f gas p r o d u c e d a t 1 6 0 0 ° F i s shown i n Table I I . e


INDUSTRIAL AND LABORATORY PYROLYSES

COMBUSTION GAS CYCLONES


ENTRAINED

FLOW

REACTOR

COAL FEED

PYROLYSIS GAS PIPELINE GAS

CHAR BURNER GAS

AIR CYCLONES

PROCESSING

CHAR PRODUCT

Figure 1.

Occidentalflashpyrolysis process schematic

C H 2

5

C MOLECULAR AROMATIC

WEIGHT

2 3

H

l 9

N0 3 2 5 q/mole

CARBON

8 3 %

A L I P H A T I C CARBON

I 7 %

AROMATIC HYDROGEN

53 %

A L I P H A T I C HYDROGEN

4 2 %

PHENOLIC

HYDROGEN

AROMATIC

SULFUR

5 %

AROMATIC NITROGEN PHENOLIC

OXYGEN

Figure 2.

Typical tar molecule from coal gasification


27.

479

Fuels and Chemicals


TABLE

II


GAS ANALYSIS FROM COAL GASIFICATION AT 1 6 0 0 ° F Gas

Mole %

H

26.8

2

CO

30.0

co

8.5

2

22.4

CH,

0.7

2 2

C

( a )

H

C H 2

8.9 4

C

2 6

C

3 6

1.0

H

1.2

H

0.3

c + 4

2 0 . 0 g/Mole 626 B t u / S C F

M o l e c u l a r Weight (b) Heat o f Combustion (a)

Dry,

N »Free,

(b)

C a l c u l a t e d , 25°C,

2

H S-Free 2

HHV

The e t h y l e n e y i e l d i s 8 . 9 % . O p t i m i z a t i o n o f t h e e t h y l e n e y i e l d f o r p o s s i b l e s e p a r a t e s a l e i s one o f t h e g o a l s o f t h e c o a l c o n v e r s i o n program. The gas i s medium B t u g a s , 620 B t u / S C F , a n d may b e p r o c e s s e d t o o b t a i n h i g h B t u p i p e l i n e gas u s i n g e x i s t i n g technology. T a r i s p r o d u c e d as a b y - p r o d u c t d u r i n g c o a l g a s i f i c a t i o n . The t a r y i e l d i s ^ 5 % a t 1 7 0 0 ° F and i n c r e a s e s t o >15% a t 1 2 0 0 F . A s t r u c t u r e o f a t y p i c a l t a r m o l e c u l e made a t 1 6 5 0 ° F i s shown i n Figure 2. The t y p i c a l t a r m o l e c u l e c o n t a i n s 3 - 4 c o n d e n s e d aromatic rings with a l i p h a t i c side chains. The c a r b o n c o n t e n t i s 83% a r o m a t i c and 17% a l i p h a t i c . The h y d r o g e n d i s t r i b u t i o n i s 53% a r o m a t i c , 42% a l i p h a t i c and 5% p h e n o l i c . The t a r a l s o c o n t a i n s a r o m a t i c n i t r o g e n and s u l f u r and p h e n o l i c o x y g e n . Typical t a r p r o p e r t i e s a r e shown i n T a b l e I I I . Because o f the h i g h h e a t o f c o m b u s t i o n ( 1 5 , 6 6 6 B t u / l b ) and l o w s u l f u r content ,(0.7%), t h e t a r c o u l d b e u s e d d i r e c t l y as a f u e l . The h i g h a r o m a t i c s c o n t e n t makes t h e t a r a t t r a c t i v e f o r u s e as a p e t r o c h e m i c a l f e e d stock. The t a r m i g h t a l s o b e c r a c k e d f u r t h e r t o y i e l d a d d i t i o n a l e



TABLE I I I TAR FROM COAL GASIFICATION AT 1650°F

Analysis

Weight % 0.0 0.0 86.5 5.7 1.0 0.7 6.0

Moisture Ash C H Downloaded by CORNELL UNIV on October 24, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0032.ch027

Ν S

Ο 1.14g/ml Density,

( a t 100°C) 33 cps

Viscosity,

( a t 100°C) 15,666 B t u / l b

Heating Value M o l e c u l a r Weight, Boiling

(Number Average) 315g/mole

Range

Percent

Distilled

IBP 13 % 20.5% 30 % 10.5% Residue (16%)

Distillate,

% by Volume

Temperature °C 100 100-200 200-300 300-400 400-600 >600 (100-180°C F r a c t i o n )

Acids

20.4

Bases

0.7

Neutral O i l

78.9


27.

Fuels and Chemicals


481

gas. H o w e v e r , t h e t a r y i e l d and t h e amount o f p o t e n t i a l gas a v a i l a b l e by f u r t h e r c r a c k i n g decrease as the c o a l g a s i f i c a t i o n temperature i s i n c r e a s e d . Options a v a i l a b l e f o r use of the t a r are presently being studied. The c h a r f r o m g a s i f i c a t i o n o f s u b b i t u m i n o u s c o a l i s a n i d e a l pulverized fuel. A t y p i c a l a n a l y s i s i s shown i n T a b l e I V f o r a c h a r w h i c h h a s b e e n d e v o l a t i l i z e d a t 1 6 0 0 F b u t h a s not b e e n p a r t i a l l y b u r n e d t o p r o c e s s h e a t , and f o r c h a r w h i c h h a s b e e n p a r t i a l l y burned a t 1900 F. e

e


TABLE

IV

CHAR FROM GASIFICATION OF STOBITUMINOUS COAL Analysis

Weight % Devolatilized 1600°F

Partially Combusted 1900 F e

Moisture Ash V o l a t i l e Matter F i x e d Carbon

0.0 19.5 17.2 63.3

0.0 21.6 6.7 71.7

C H Ν S 0

69.1 2.5 0.9 1.2 6.7

73.5 0.8 1.0 0.6 2.5

Heating Value, Btu/lb R e l a t i v e I g n i t i o n Temp., °F S u r f a c e A r e a , m2/g Pore Volume, ml/g

11,111 740 123 0.12

10,994 870 312 0.17

To p r o v i d e t h e p r o c e s s h e a t a b o u t 12% o f t h e c h a r i s b u r n e d . The h e a t i n g v a l u e o f t h e c h a r changes o n l y s l i g h t l y , the s u r f a c e a r e a i s i n c r e a s e d and t h e s u l f u r c o n t e n t i s d e c r e a s e d b y p a r t i a l c o m bustion. The r e l a t i v e i g n i t i o n t e m p e r a t u r e s o f t h e c h a r s w e r e d e t e r m i n e d b y d i s p e r s i n g them i n o x y g e n i n a h o t t u b e a t s h o r t residence time to s i m u l a t e i g n i t i o n of p u l v e r i z e d f u e l . The r e l a t i v e i g n i t i o n temperature of the unoxidized char i s lower than the parant subbituminous c o a l ( 8 3 0 ° F ) . The p a r t i a l l y o x i d i z e d c h a r i g n i t e s a t a, t e m p e r a t u r e s l i g h t l y h i g h e r b u t c o m p a r able to the i g n i t i o n temperature of the c o a l . Full scale c o m b u s t i o n t e s t s h a v e b e e n made o n t h e s e c h a r s b y an o u t s i d e c o n tractor.


482


Most Western s u b b i t u m i n o u s c o a l s w i l l y i e l d a c h a r w i t h a s u f f i c i e n t l y l o w l e v e l o f s u l f u r t o meet e m i s s i o n s t a n d a r d s a s a p u l v e r i z e d f u e l s o no e f f o r t h a s b e e n made t o d e s u l f u r i z e t h e s e chars.


Coal-to-Liquids The s e c o n d p r o c e s s u t i l i z i n g c o a l i s t h e c o n v e r s i o n o f coal-to-liquids. The c o a l t o l i q u i d s p r o c e s s was o r i g i n a l l y developed to convert hvc bituminous c o a l from the Western K e n tucky Hamilton Mines of I s l a n d Creek C o a l C o . , a l s o a s u b s i d i a r y of Occidental Petroleum Corporation, i n t o l i q u i d f u e l s . A typi c a l a n a l y s i s o f t h e c o a l i s shown i n T a b l e V . TABLE V HAMILTON BITUMINOUS

hvc

COAL

Analysis As F e d Moisture Ash V o l a t i l e Matter F i x e d Carbon C H Ν S 0

2.6 9.7 37.6 50.2 70.7 5.2 1.5 2.7 10.3

Heating Value, Btu/lb R e l a t i v e I g n i t i o n T e m p . , °F Fischer Assay, Char Tar Water Light O i l Gas

Weight % Dry

(As

Basis

0.0 10.0 37.6 52.4 72.6 5.0 1.5 2.8 8.1

12,754 940

13,082

Fed) 73.4 14.5 8.2 0.0 3.9

The optimum y i e l d o f l i q u i d p r o d u c t i s o b t a i n e d i n t h e c o a l - t o - l i q u i d s process at approximately 1075°F. A typical pro duct d i s t r i b u t i o n f o r c o a l - t o - l i q u i d s p r o c e s s i n g using t h i s c o a l i s 56% c h a r , 35% t a r , 7% g a s , and 2% w a t e r . The r e s i d e n c e t i m e f o r t h i s p r o c e s s i s a l s o k e p t as s h o r t as p o s s i b l e w h i c h m a x i m i z e s t h e y i e l d and p r e v e n t s f u r t h e r c r a c k i n g o f t h e l i q u i d p r o duct. The e f f e c t o f f l a s h p y r o l y s i s on t h e l i q u i d y i e l d i s shown by t h e f a c t t h a t t h e t a r and l i g h t o i l y i e l d f o r t h i s c o a l from


27.


Fuels and

483

Chemicab

s l o w , f i x e d bed h e a t i n g i n the F i s c h e r Assay i s 14.5% w h i l e the l i q u i d y i e l d f r o m f l a s h p y r o l y s i s i s ^ 3 5 % . The l i q u i d p r o d u c t f r o m h v c b i t u m i n o u s c o a l h a s t h e a n a l y s i s shown i n T a b l e V I . TABLE

VI

TAR FROM THE COAL-TO-LIQUIDS PROCESS AT 1 0 0 0 ° F


Analysis

Weight %

Moisture Ash C H Ν S 0

0.0 0.0 80.3 7.0 1.4 2.1 9.2

D e n s i t y ( a t 100°C) V i s c o s i t y ( a t 100°C) Heating Value

1.04g/ml 127 c p s 15342 B t u / l b

B o i l i n g Range Percent D i s t i l l e d IB Ρ 20% 25 22.5 Residue (32.5%)

T e m p e r a t u r e , °C 75 75-200 200-350 350-520 >520

D i s t i l l a t e , % b y Volume ( 7 5 - 3 5 0 ° C Acids Bases Neutral Oils

Fraction) 25% — 75%

T h e r e i s a l a r g e amount o f o x y g e n a t e d m a t e r i a l w h i c h i s primarily tar acids. Work w i l l b e done t o t r y t o i s o l a t e t h e s e as a s e p a r a t e p r o d u c t f r a c t i o n . The p r i m a r y i n t e n t o f t h e p r o c e s s i s t o h y d r o g e n a t e t h e t a r l i q u i d to produce a low s u l f u r f u e l o i l or p o s s i b l y a s y n t h e t i c crude o i l . C o n v e r s i o n o f the t a r t o c h e m i c a l s by a second s t a g e p y r o l y s i s o f t h e t a r - g a s s t r e a m b e f o r e t a r c o n d e n s a t i o n has a l s o been i n v e s t i g a t e d . The g o a l o f t h i s w o r k i s an e c o n o m i c a l l y v i a b l e y i e l d o f BTX o r l o w m o l e c u l a r w e i g h t g a s e s s u c h a s e t h y l e n e o r methane. T y p i c a l char analyses from the c o a l - t o - l i q u i d s process a r e shown i n T a b l e V I I .



~

8 WT.

%

TO

DISPOSAL

SOLIDS

UNRECOVERED

φ.

PRIMARY SHREDDER

xsz

REFUSE

AS-RECEIVED

METALS

GLASS

'9000BTU/LB

CHAR

TO

AND

DISPOSAL

PURIFICATION

WATER

GAS Τ Ο PURIFICATION AND RECYCLE

'4.8 M M BTU/BBI

OIL

Figure 3. Recycling of solid wastes via pyrolysis

MAGNETIC

CLEAN

INORGANIC PROCESSING SUBSYSTEM

> α: ο.

(Τ UJ

ο
I— oc

y. yj

oc

MOLECULAR WEIGHTS NUMBER AVERAGE - 3 6 5

Fuels and Chemicals by Pyrolysis

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