Investigations of the PERC Process for Biomass Liquefaction at the

19 Investigations of the PERC Process for Biomass Liquefaction at the Department of Energy, A l b a n y , O r e g o n Experimental Facility

Downloaded by UNIV OF ARIZONA on January 22, 2013 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0076.ch019

T. E. LINDEMUTH Research and Engineering, Bechtel National, Inc., 50 Beale Street, San Francisco, CA 94119 Background of the Project Earliest efforts in the liquefaction of biomass as i t is currently practiced at the Albany experimental facility took place during the late 1960's and early 1970's at the U.S. Bureau of Mines Pittsburgh Energy Research Center (PERC). The study there showed that a wide variety of biomass materials, including wood municipal solid waste and cattle manure, could be turned into an oil-like material by reaction with carbon monoxide in the presence of an alkaline catalyst under conditions of moderate temperature and high pressure.1-3 This work was an outgrowth from earlier experiments of coal liquefaction using a similar reaction scheme. On the basis of the PERC results, the flow scheme for both a commercial size plant and what was to eventually become the Albany facility was developed in 1973.4 Figure 1 shows the process portion of the Albany experimental facility. Detailed engineering specifications were prepared in 19745 and construction of the facility proceeded soon thereafter. In late 1976 Bechtel National, Inc. was contracted to monitor the completion of construction and then to commission the facility. The following paper describes some of the activities involved with commissioning of the facility as well as the initial results and preliminary economic assessments of the process. Objectives The major objectives in the first year's activities at Albany were to verify, as well as possible, the original process data, to evaluate the process equipment involved, and to develop a preliminary conceptual design and economic assessment. The plant itself is located within the city limits of Albany, Oregon immediately adjacent to the U.S. Bureau of Mines Metallurgical Research Center. This facility is set in the middle of a residential area instead of the more isolated setting that one might expect. The location has created a special concern for new adverse environmental effects. In addition to the PDU shown in Figure 1, the site has a modern control room, an office building for technical and administrative staff, a repair and maintenance shop, a small process 0-8412-0434-9/78/47-076-371$05.25/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


SOLID

Figure 1.

WASTES

AND

Albany, Oregon biomass liquefaction PDU

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES


19.

LiNDEMUTH

Biomass Liquefaction

373

c o n t r o l l a b o r a t o r y , and simple p o l l u t i o n c o n t r o l f a c i l i t i e s . Figure 2 i s a s i m p l i f i e d flow scheme f o r the Albany f a c i l i t y as i t was o r i g i n a l l y b u i l t . In the o r i g i n a l process scheme, wood i n the form of wood c h i p s , such as are used i n the manufacture of pulp and paper, are brought to the p l a n t and conveyed i n t o a storage hopper. F i r s t , moist wood chips are d r i e d i n a r o t a r y drum d r i e r . Here, the moisture content i s reduced from 50 percent down to 3 percent or 4 percent. A f t e r d r y i n g , the wood i s ground i n a hammer m i l l to approximately 50 mesh. T h i s gives the m a t e r i a l the consistency of ordinary f l o u r . In order to b r i n g the wood i n t o the r e a c t i o n system, i t i s f i r s t blended with p l a n t r e c y c l e d o i l i n a multibladed continuous blender, s i m i l a r to those used i n making bread dough or compounding rubber. The wood/oil s l u r r y , c o n t a i n i n g approximately 25 percent wood f l o u r i s then pumped up to the r e a c t i o n system pressure which i s i n the range of 100 to 250 atmospheres. The s l u r r y i s then routed to a scraped s u r f a c e heat exchanger where i t i s heated to approximately 350°C. At that point a c a t a l y s t s o l u t i o n of aqueous sodium carbonate i s added and the mixture i s routed to a 375 L. s t i r r e d autoclave. In the autoclave the mixture i s f u r t h e r heated to 370°C and contacted with carbon monoxide gas. T h i s gas i s prov i d e d from storage tanks and d e l i v e r e d by multistage diaphragm comp r e s s o r s . Both the preheater and s t i r r e d tank r e a c t o r are e l e c t r i c a l l y heated. Offgases from the r e a c t o r c o n t a i n i n g carbon monoxide, carbon d i o x i d e , and hydrogen are cooled, condensed, and combusted in a flare. The l i q u i d mixture that remains from the CSTR i s f i r s t cooled and then depressurized f o r removal of water and noncondensible gases. These gases are also routed to the f l a r e system. L i q u i d from the f l a s h tank i s sent to a c e n t r i f u g e f o r the removal of water and s o l i d sludge. From the c e n t r i f u g e , p a r t of the o i l i s r e c y c l e d to the wood/oil blender, thus completing the process loop. The remaining o i l i s removed as product. Plant Commissioning Before any process t e s t i n g could begin, the e n t i r e f a c i l i t y had to be checked out and each i n d i v i d u a l p i e c e of equipment commissioned. To give you an i d e a of the o v e r a l l complexity of the p l a n t , Table 1 l i s t s the number of major process items i n the p l a n t , each of which r e q u i r e d some s o r t of check-out. To f u r t h e r i l l u s t r a t e the complexi t y of the f a c i l i t y , Figure 3 shows the c e n t r a l c o n t r o l panel. During the commissioning of the p l a n t a number of d i f f i c u l t i e s were encountered with the process equipment i t s e l f . This i s not unusual f o r the f i r s t development u n i t i n a new process. Table 2 highl i g h t s the areas where most d i f f i c u l t i e s were encountered. Of part i c u l a r importance were pump and a g i t a t o r shaft s e a l s on high pressure equipment. In order to use t h i s equipment, many m o d i f i c a t i o n s had to be made i n t h i s area. In a d d i t i o n , problems showed up with the gas compressors, wood handling equipment, and the preheater scraper. To i l l u s t r a t e the magnitude of some of the problems, F i g u r e 4


In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978. Figure 2. Albany PD U schematic (as built)

HOT GASES



LiNDEMUTH


Figure 3. Albany PDU control panel

Figure 4. Reactor head seal



376

SOLID

WASTES

AND

RESIDUES

shows m o d i f i c a t i o n work on the head to s h e l l c l o s u r e of the s t i r r e d tank r e a c t o r . This v e s s e l i s approximately 600 m i l l i m e t e r s i n diameter, and designed f o r pressures of up to 300 atomospheres. The problems uncovered r e q u i r e d complete removal of the o r i g i n a l s e a l mechanism, replacement of the v e s s e l l i n i n g , and remachining f o r a new s e a l r i n g . A l l of the work was done i n p l a c e , i n c l u d i n g the machining of the r e a c t o r head, which weighs over 1,000 kilograms and was l o cated 15 meters above the ground. The i n i t i a l operation of the preheater uncovered d i f f i c u l t i e s w i t h i n t e r n a l coking and eventual damage to the scraper blades themselves. Figure 5 i l l u s t r a t e s the before and a f t e r c o n d i t i o n of some of the 50 scraper blades that are used i n t h i s heat exchanger. Degradation of polymeric m a t e r i a l s caused numerous problems i n the p l a n t . The product o i l or the anthracene v e h i c l e o i l which was used f o r startup r a p i d l y attacked gaskets, s e a l p a r t s , and 0-rings, as i l l u s t r a t e d i n Figure 6. Replacement of those p a r t s was r e q u i r e d i n almost every s e a l and pressure boundary part i n the p l a n t . On the b a s i s of information acquired during the commissioning, a number of equipment and process m o d i f i c a t i o n s were made. Figure 7 i l l u s t r a t e s the changes that were made i n the flow scheme as f o l l o w s : •

The s t i r r e d tank r e a c t o r was bypassed due to cont i n u i n g problems with the a g i t a t o r shaft s e a l

•

The preheater v e s s e l alone was ing and r e a c t i o n

•

Carbon monoxide and c a t a l y s t s o l u t i o n were i n t r o duced ahead of the preheater

•

L i q u i d e f f l u e n t bypassed the c e n t r i f u g e s i n c e the c e n t r i f u g e was unable to handle the r e a c t o r e f f l u e n t

Process

then used f o r heat-

Results

In s p i t e of o b s t a c l e s that were encountered, v a l u a b l e operating time has been logged - r e c e n t l y , exceeding 50 percent — and important process r e s u l t s are being accumulated. The f i r s t area studied was r e a c t i o n c h a r a c t e r i s t i c s which included the e f f e c t s of system temperature, pressure, carbon monoxide concentration, residence time, and c a t a l y s t use. These have been evaluated f o r t h e i r e f f e c t on wood conversion, o v e r a l l y i e l d , and product q u a l i t y . Figure 8 i l l u s t r a t e s p r e l i m i n a r y r e s u l t s on the r a t e of wood conversion per pass through the preheater v e s s e l .



19. L i N D E M U T H


Figure 5.. Reheater scraper blades

Figure 6. Decomposed reactor rubber seal material


377

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978. Figure 7. Albany PD U schematic (modified)


19.

LINDEMUTH


379

Wood conversion, K, i s d e f i n e d as: Κ = where

Cf - Co χ 100 Cf

Κ i s wood conversion i n % Cf i s the undissolved s o l i d s i n the feed


Co i s the undissolved s o l i d s i n the o u t l e t . I t should be noted that conversion does not n e c e s s a r i l y mean o i l production but simply the disappearance o f wood. Residence time i s the o v e r a l l residence time i n the preheater and not time a t temp e r a t u r e . I t should be noted t h a t the temperature range i n the pre heater i s from 100° t o approximately 350°C. As F i g u r e 8 i l l u s t r a t e s , at approximately 25 minutes residence time, 70 percent conversion per pass i s u s u a l . Since the s l u r r y i s r e c y c l e d on an approximate 5 p a r t s r e c y c l e to one p a r t product r a t i o , o v e r a l l wood conversion i s over 90 percent. Under the c o n d i t i o n s t e s t e d so f a r , the approx imate c a p a c i t y o f the p l a n t i s 1,000 kilograms a day o f wet wood feed w i t h 400 to 500 kilograms of o i l produced. This i s shown s c h e m a t i c a l l y i n F i g u r e 9, which i l l u s t r a t e s the o v e r a l l p l a n t mass balance. As shown, the main r e a c t a n t s are carbon monoxide and wood w h i l e the main products are o i l and f l u e gases. I n a commercial s i z e d p l a n t , as w i l l be i l l u s t r a t e d l a t e r , only wood would be used as a r e a c t a n t . To date, the product o i l that has been produced has been q u i t e viscous and resembles heavy h e a t i n g o i l i n i t s c o n s i s t e n c y . Table 3 i l l u s t r a t e s a few of the more important p r o p e r t i e s of the product o i l i t s e l f . At times, i n c r e a s i n g v i s c o s i t y of the product o i l has n e c e s s i t a t e d t e r m i n a t i o n o f t e s t runs. Methods t o c o n t r o l t h i s phenomenon are now being examined and w i l l have h i g h p r i o r i t y i n f u t u r e experiments. As can be seen, the h e a t i n g value i s s i m i l a r to a bunker f u e l o i l . The elemental a n a l y s i s shows that the oxygen content i s approximately 8 percent as compared t o the wood f l o u r used t o feed which has over 40 percent oxygen. The net e f f e c t o f conversion i s that the h e a t i n g value i s approximately twice as high as wood on a weight b a s i s and over f o u r times as high on a volume b a s i s . Commercial P l a n t Concepts With the i n f o r m a t i o n learned a t Albany, a p r e l i m i n a r y conceptual design has been developed. Some o f the c r i t e r i a that have been i n corporated i n t o t h i s conceptual design are the amount of carbon monoxide consumed, the use o f the s l u r r y r e c y c l e o p e r a t i o n , the technique of CO a d d i t i o n ahead o f the preheater, and a knowledge of the s l u r r y and o f f - g a s c h a r a c t e r i s t i c s . Figure 10 i l l u s t r a t e s the main f e a t u r e s o f a commercial flow scheme. While the carbon monoxide gas i s brought i n t r u c k s t o the A l bany p l a n t , a commercial f a c i l i t y w i l l use a s y n t h e s i s gas c o n t a i n -


SOLID WASTES AND RESIDUES

Table I . •

Equipment Commissioning and Proof T e s t i n g PRESSURE VESSELS

7

PUMPS

•

15

HEAT EXCHANGERS

WOOD HANDLING


•

UNITS

ELECTRIC MOTORS

40

CONTROLS

60

Table I I .

Mechanical D i f f i c u l t i e s

PUMP A N D A G I T A T O R S H A F T S E A L S GAS

COMPRESSORS

E L E C T R I C A L PROCESS HEATING WOOD HANDLING

EQUIPMENT

REACTOR HEAD SEAL PREHEATER SCRAPER

Table I I I .

BLADES

Product O i l P r o p e r t i e s

VISCOSITY

200-1000 cp

SPECIFIC G R A V I T Y

1.05-1.10

B O I L I N G POINT

280OC

HEATING V A L U E

15,000 Btu/lb

ELEMENTAL

%C

ANALYSIS

77.2

% H

6.5

% Ν

0.4

%0

8.4


LiNDEMUTH


100


381

h

0

5

10

15

20

25

O V E R A L L RESIDENCE TIME, MINUTES

Figure 8.

Rate of wood conversion




382

Figure 10. Biomass liquefaction conceptual commercial process



19.

LiNDEMUTH

383


ing both hydrogen and oxygen. A synthesis gas plant and a product separation system have been added to the commercial f a c i l i t y design. The synthesis gas i s produced i n an oxygen blown g a s i f i e r and i s t r e a t e d f o r removal o f water and carbon d i o x i d e . The synthesis gas a l s o t r e a t s the c a t a l y s t s o l u t i o n f o r recovery of the a l k a l i . In a commercial p l a n t about h a l f the wood that i s introduced as feed goes f o r synthesis gas production. The other h a l f of the wood i s t r e a t e d by drying and g r i n d i n g and then blending with r e c y c l e d o i l p r i o r to pumping i n t o the r e a c t o r system as i n the Albany p l a n t . A h e l i c a l c o i l preheater followed by a holdup tank i s a l s o c u r r e n t l y part of the design. The preheater i s heated by combustion of system o f f g a s e s . A f t e r pressure letdown from the r e a c t o r hold tank, some of the s l u r r y i s r e c y c l e d to the blender while the product p o r t i o n i s routed f o r p u r i f i c a t i o n . Here the product, c o n t a i n i n g some unreacted wood as w e l l as water and c a t a l y s t , i s f i r s t d i l u t e d with a l i g h t s o l v e n t . A f t e r d i l u t i o n , the mixture i s f i l t e r e d f o r the removal of s o l i d s . The l i q u i d stream i s then f u r t h e r d i l u t e d w i t h water to wash out any remaining c a t a l y s t . Both the s o l i d s and the aqueous waste stream are routed to the synthesis gas r e a c t o r f o r treatment. The organic stream i s sent to a f r a c t i o n a l column f o r recovery of the s o l v e n t . At t h i s point the s t i l l bottom becomes the product. Figure 11 i s an a r t i s t ' s rendering o f a commercial plant env i s i o n e d i n a P a c i f i c Coast s e t t i n g . In the foreground a l a r g e p i l e o f wood chips i s shown. These are assumed to be prepared i n the f o r e s t . From the p i l e , the wood i s d i s t r i b u t e d by conveyors to the synthesis gas r e a c t o r s and to the d r i e r - g r i n d e r apparatus. In a d d i t i o n to the major f a c i l i t i e s f o r o i l production, administrat i o n b u i l d i n g r e p a i r shops, c o o l i n g towers and wastewater f a c i l i t i e s are a l s o i l l u s t r a t e d . I t i s important to note that the l i q u e f a c t i o n p l a n t should be an environmentally good neighbor. Some of the h i g h l i g h t s of the design w i l l serve to i l l u s t r a t e : •

Biomass and a i r are the only raw m a t e r i a l s

•

O i l i s the only product

•

The e f f l u e n t s c o n s i s t of only water, clean f l u e gases, and i n e r t ash

•

The process i s e f f i c i e n t from an energy

standpoint

C a l c u l a t i o n s to date show that o v e r a l l y i e l d f o r a commercial plant should be approximately 35 percent wood to o i l , while energy balance would i n d i c a t e approximately 54 percent, as i l l u s t r a t e d i n Figures 12 and 13. Economic A n a l y s i s In order to develop operating and c a p i t a l c o s t s , s e v e r a l p l a n t s i z e s were costed out. Figure 14 i l l u s t r a t e s the e f f e c t of p l a n t



384

SOLID

Figure 11.

WASTES

AND

RESIDUES

Artist's rendering of a commercial biomass liquefaction plant

TRACE

Figure 12.

Biomass liquefaction mass balance



LiNDEMUTH


TRACE

Figure 13.

Biomass liquefaction energy balance



386

SOLID

20

h

10

h

0 I Ο

1

L_

0.5

1.0*

WASTES AND

I

I

1.5

2.0

PLANT CAPACITY, THOUSAND TONS/DAY

Figure 14.

Effect of plant size on production cost


RESIDUES

Ι

2.5


19.

LiNDEMUTH


387

s i z e on product c o s t . As can be seen, due to the p l a n t complexity, the economies o f s c a l e a r e q u i t e strong. I t would appear that only l i q u e f a c t i o n p l a n t s of l a r g e production ( i n excess of 1,000 tons per day) w i l l be a t t r a c t i v e . F i g u r e 14 i l l u s t r a t e s the r e l a t i v e p o r t i o n o f p l a n t c a p i t a l a t t r i b u t a b l e to the major process s e c t i o n s of a commercial p l a n t . This breakdown was based on a plant of approximately 1,000 metric tons of oven-dried wood a day. The costs of the wood handling and synthesis gas p l a n t are the l a r g e s t s i n g l e items i n the p l a n t . The p o r t i o n of the p l a n t cost f o r the high pressure r e a c t i o n equipment i s only 16 percent of the t o t a l . This would tend to i n d i cate that f u t u r e development work should center on r e d u c t i o n i n the s i z e of the s y n t h e s i s gas p l a n t and a s i m p l i f i c a t i o n of wood handling. Based on a p l a n t of t h i s s i z e , Figure 15 shows the r e l a t i v e cost p o r t i o n s of the product that can be a l l o c a t e d to a m o r t i z a t i o n of c a p i t a l , feed stock, e l e c t r i c power, taxes and insurance, labor and consumables. Amortization of c a p i t a l i s by f a r the l a r g e s t f a c tor followed by the cost of feed stock. In t h i s instance, wood i s assumed to c a r r y a value o f $20 per oven-dried ton. O v e r a l l , t h i s r e s u l t s i n a breakeven production cost of j u s t under $35 per b a r r e l . Future A c t i v i t i e s 1

The past y e a r s e f f o r t s and the development of the f i r s t conc e p t u a l designs have shown a number of areas of f r u i t f u l continued e f f o r t s as i l l u s t r a t e d i n Figure 16. The o v e r a l l production costs are very s e n s i t i v e to p l a n t y i e l d and c a p i t a l cost. In the f o l l o w i n g program s u b s t a n t i a l e f f o r t s w i l l be aimed a t reducing the amount of s y n t h e s i s gas r e q u i r e d , r a i s i n g o v e r a l l y i e l d and e f f i c i e n c y , and reducing energy input. F i g u r e 17 i s a p r o j e c t i o n of the e f f e c t of f u t u r e a c t i v i t i e s on the o v e r a l l cost of biomass produced o i l . It i s expected that continued developments at the Albany f a c i l i t y w i l l y i e l d improvements that should show a r e d u c t i o n i n p r o j e c t ed product p r i c e to approximately $25 a b a r r e l . T h i s should take place over the next 2-1/2 years. At t h i s point i t i s suggested that a p i l o t p l a n t of approximately 100 to 300 tons per day c a p a c i t y be b u i l t and operated. This p i l o t p l a n t would have a l l the f a c i l i t i e s now envisioned f o r a commercial p l a n t but o f much smaller s i z e . I n formation gained by the o p e r a t i o n of t h i s p l a n t should reduce the product cost as expressed i n constant 1978 d o l l a r s to $20 per b a r r e l . T h i s would take approximately f i v e years. The f i n a l step i n the development would be the design and c o n s t r u c t i o n of a demonstration plant u t i l i z i n g f u l l - s i z e process t r a i n s . Information gained here should provide the means to be commercially competitive by approximately 1990.



388


Figure 15. Capital cost breakdown—commercial biomass liquefaction plant



LiNDEMUTH


Figure 16. Oil production (break-even) costs—commercial biomass liquefaction plant


SOLID

390


40

WASTES

AND

h

1980

1985

1990

YEAR

Figure 17.

Projected process economics


RESIDUES

19. LiNDEMUTH


391

Summary Investigations to date have led the authors to be optimistic about the possibilities of oil production from biomass. While difficulties in bringing the current facilities on-stream have somewhat limited information to date, i t is felt that a vigorous activity in the future can eventually provide a new source of energy for the country in the form of o i l from biomass.


References 1.

Appell, H.R., Wender, I., and Miller, R.D., Chem & Ind.(London) Vol. 47, 1703 (1969).

2.

Appell, H.R., Fu, Y.C., Friedman, S., Yavorsky, P.M., and Wender, I., "Converting Organic Wastes to Oil," U.S. Bureau of Mines, RI 7560, 1971.

3.

Appell, H. R., Fu, Y.C., I l l i g , E.G., Steffgen, F.W., and Miller, R.D., "Conversion of Cellulosic Wastes to Oil," U.S. Bureau of Mines, RI 8013, 1975.

4.

Dravo Corporation, Blaw-Knox Chemical Plants Division, "Economic Feasibility Study for Conversion of Wood Wastes to Oil," prepared for U.S. Bureau of Mines, June 1973.

5.

The Rust Engineering Co., "U.S. Bureau of Mines Wood-to-Oil Pilot Plant — Final Design Report," prepared for U.S. Bureau of Mines, February 1974.

MARCH 15, 1978.


Investigations of the PERC Process for Biomass Liquefaction at the

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