Thermal Conversion of Solid Wastes and Biomass - ACS Publications

18 Biomass Gasification at the Focus of the Odeillo (France) 1-Mw (Thermal) Solar Furnace

Downloaded by EAST CAROLINA UNIV on September 28, 2015 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch018

M. J. ANTAL, JR. Princeton University, Princeton, NJ 08544 C. ROYERE and A. VIALARON C.N.R.S., Odeillo, France

Recently completed research at Princeton University (1-3) has shown biomass gasification to be a three step process: 1. Pyrolysis. At modest temperatures (300°C or more, depending upon heating rate) biomass materials lose between 70% and 90% of their weight by pyrolysis, forming gaseous volatile matter and solid char. As discussed in this paper, very high heating rates enhance volatile matter production at the expense of char formation. Recent Princeton publications review mechanistic and kinetic research on cellulose (4), lignin (5), and wood (6) pyrolysis in more detail. 2. Cracking/Reforming of the Volatile Matter. At somewhat higher temperatures (600°C or more) the volatile matter evolved by the pyrolysis reactions (step 1) reacts in the absence of oxygen to form a hydrocarbon rich synthesis gas. These gas phase reactions happen very rapidly (seconds or less) and can be manipulated to favor the formation of various hydrocarbons (such as ethylene). Rates and products of the cracking reactions for volatile matter derived from cellulose, lignin, and wood are now available in the literature (1, 3, 5, 6). 3. Char Gasification. At even higher temperatures char gasification occurs by the water gas and Boudouard reactions, and simple oxidation: (water gas) C + H20 -> CO + H 2 (Boudouard) C + C02 + 2C0 C + ^o 2 -> CO ) C + o 2 + co 2 )

(oxidation)

Because pyrolysis (step 1) produces less than 30% by weight char for most biomass materials, the char gasification reactions (step 3) play a less important role in biomass gasification than steps 1 and 2. 0-8412-0565-5/80/47-130-237$05.00/0 © 1980 American Chemical Society In Thermal Conversion of Solid Wastes and Biomass; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

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Figure 1 i l l u s t r a t e s the c r i t i c a l r o l e played by step 2 i n cellulose gasification. By i n c r e a s i n g the temperature achieved by the gas phase v o l a t i l e matter from 500°C to 750°C, the carbon con v e r s i o n e f f i c i e n c y η i s increased from η = 0.1 to n = 0.76. Here the carbon e f f i c i e n c y n i s defined by η = carbon i n perma nent gases ν carbon i n s o l i d feed. 0

0

c

c

0

The carbon conversion e f f i c i e n c y i s emphasized here because ( f o r non-oxidative conversion processes) η provides an e x c e l l e n t measure o f how w e l l the energy and chemical content of the s o l i d f u e l feedstock i s converted to gaseous f u e l s and chemicals. Because about 20% o f the carbon i n i t i a l l y i n the c e l l u l o s e i s c a r r i e d by the char product o f step 1, the data presented i n Figure 1 i n d i c a t e s that f o r gas phase temperatures above 750°C and residence times o f 2 sec o r more, permanent gases and char are e s s e n t i a l l y the only products o f c e l l u l o s e g a s i f i c a t i o n . Less than 4% o f the feedstock carbon i s c a r r i e d by the condensible f r a c t i o n of the r e a c t o r e f f l u e n t .


0

Because char commands a low market value, there i s some i n c e n t i v e to increase gas production at the expense o f char form a t i o n . The t r a d i t i o n a l approach i s to use the water gas, Boudouard, and combustion r e a c t i o n s (step 3) to g a s i f y the char produced by step 1. An a l t e r n a t i v e approach i s to r a p i d l y heat s o l i d biomass feed, modifying the p y r o l y s i s mechanism (step 1) and reducing the i n i t i a l formation o f char by the p y r o l y s i s r e a c t i o n s . The l a t t e r approach has been emphasized i n the research reported here. The work o f Broido (7), Shafizadeh (8), Lewellen (9) and others (10) has shown c e l l u l o s e p y r o l y s i s to be d e s c r i b a b l e i n terms o f a competitive mechanism: v o l a t i l e tars

(levoglucosan)

c e l l u l o s e -==CCII^I3L ~2

char + low molecular weight volatiles

Two p y r o l y s i s r e a c t i o n s compete to consume the c e l l u l o s e ; however only one r e a c t i o n produces char. The f i r s t r e a c t i o n i s favored by high temperatures and r a p i d heating, producing combustible v o l a t i l e matter at the expense of char formation. The second r e a c t i o n i s favored by low temperatures and slow heating o f the c e l l u l o s e . Thus chemical r e a c t o r s designed to provide very r a p i d heating ("flash p y r o l y s i s " ) o f s o l i d c e l l u l o s i c feedstocks can minimize char form a t i o n with the p o t e n t i a l o f s i g n i f i c a n t l y i n c r e a s i n g gas y i e l d s . With but one exception, past s t u d i e s o f the f l a s h p y r o l y s i s o f c e l l u l o s e using l a b o r a t o r y equipment have r e l i e d on r a d i a t i o n to achieve the high heating r a t e s r e q u i r e d . L i n c o l n (11) used pulsed carbon arcs and xenon f l a s h tubes to achieve the complete v o l a t i l i z a t i o n of c e l l u l o s e by p y r o l y s i s r e a c t i o n s . Berkowitz-Mattuck

In Thermal Conversion of Solid Wastes and Biomass; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


ANTAL ET AL.

239

Biomass Gasification

1 .0 CARBON EFFICIENCY

0.8

Χ

-

O W

υ Π3^ Μ

0.2

Ο Δ

•

•

• 4

5

6

7

R e s i d e n c e Time ( s e c )

Figure 1.

Cellulose carbon conversion efficiency as a function of gas-phase residence time for various gas-phase temperatures Vc


240


and Noguchi (12) used carbon arc and s o l a r furnace r a d i a t i o n sources to achieve f l a s h p y r o l y s i s o f cotton c e l l u l o s e . They p r o j e c t no char formation f o r r a d i a n t f l u x e s i n excess of 120 w/cm . Martin (13) used a high current carbon arc r a d i a t i o n source f o r h i s experiments, and noted that char formation was reduced to 4% o f the o r i g i n a l c e l l u l o s e weight with a r a d i a n t f l u x l e v e l o f 49 w/cm . Martin speculates that no char formation should occur f o r r a d i a t i o n f l u x e s exceeding 400 to 4000 w/cm . E x p l o r a t o r y research a t P r i n c e t o n has r e c e n t l y achieved 99% v o l a t i l i z a t i o n o f c e l l u l o s e with a f l u x l e v e l o f 30 w/cm . Other researchers (14-15) have also employed r a d i a t i o n sources to achieve very r a p i d heating o f c e l l u l o s i c m a t e r i a l s ; however t h e i r r e s u l t s are not p e r t i n e n t to t h i s research. 2

2

2


2

Lewellen e t a l . (9) at M.I.T. studied f l a s h p y r o l y s i s of c e l l u l o s e using a bench s c a l e , e l e c t r i c a l l y heated screen. They found that f o r heating r a t e s ranging between 400 and 10,000°C/sec i n an i n e r t helium atmosphere the c e l l u l o s e completely vaporized by p y r o l y s i s reactions, leaving no char r e s i d u e . Only by extended heating o f the c e l l u l o s e at 250°C was the M.I.T. group able to produce some char (2% by weight o f the i n i t i a l c e l l u l o s e ) . Only l i m i t e d data i s a v a i l a b l e on the f l a s h p y r o l y s i s of l i g n o c e l l u l o s i c m a t e r i a l s . R e n s f e l t et a l . have reported a s i g n i f i c a n t r e d u c t i o n i n char y i e l d s f o l l o w i n g the f l a s h p y r o l y s i s o f various biomass m a t e r i a l s (17) . D i e b o l t has obtained high gas y i e l d s from Eco Fuel II by f l a s h p y r o l y s i s (18) . These r e s u l t s suggest that f l a s h p y r o l y s i s may be the p r e f e r r e d thermochemical method f o r o b t a i n i n g gaseous f u e l s and chemicals from a l l biomass m a t e r i a l s . The f a c t that most f l a s h p y r o l y s i s studies have used r a d i a n t heating suggests s o l a r heat as a n a t u r a l means f o r e f f e c t ing f l a s h p y r o l y s i s o f biomass f e e d s t o c k s . Since s o l a r r a d i a t i o n has a c h a r a c t e r i s t i c temperature o f almost 6000°K, i t can be used to achieve very r a p i d heating of opaque, s o l i d p a r t i c l e s . E a r l i e r s t u d i e s (2) have shown that the q u a n t i t y o f heat required f o r biomass g a s i f i c a t i o n i s small: l e s s than 1 Gj per Mg o f dry s o l i d feed. Consequently, small amounts o f s o l a r heat can be used to process large q u a n t i t i e s o f biomass. F i n a l l y , a recent study f o r the P r e s i d e n t s C o u n c i l on Environmental Q u a l i t y (19) concluded that the use o f s o l a r heat f o r f l a s h p y r o l y s i s o f biomass appears to be more economical than conventional g a s i f i c a t i o n processes. References 19-24 d i s c u s s i n greater d e t a i l these and other reasons f o r using s o l a r heat to g a s i f y biomass. Experiments described i n t h i s paper were undertaken to explore the use o f concentrated s o l a r r a d i a t i o n f o r the f l a s h p y r o l y s i s o f biomass. APPARATUS AND PROCEDURE The O d e i l l o 1000 kw ^ s o l a r furnace has been described i n d e t a i l by Royere (25); consequently only a summary w i l l be given t


18.

ANTAL

ET A L .


241

here. The furnace c o n s i s t s o f s i x t y - t h r e e 6 χ 7.5 m h e l i o s t a t s which track the sun and r e d i r e c t the s o l a r r a d i a t i o n onto a 2000 m p a r a b o l i c concentrator which focuses the r a d i a t i o n w i t h i n a c i r c l e of about 20 cm r a d i u s . The h e l i o s t a t s are composed o f eleven thousand three hundred f o r t y 50 χ 50 cm f l a t , back surfaced mirrors and the parabola c o n s i s t s o f over 9000 mechanically warped m i r r o r s . Radiant f l u x l e v e l s o f 1600 w/cm are a v a i l a b l e a t the f o c a l point, and temperatures i n excess o f 3800°C can be obtained. 2


2

The biomass f l a s h p y r o l y s i s r e a c t o r s , designed and f a b r i c a t e d at Princeton, followed i n part a c o a l g a s i f i c a t i o n r e a c t o r design described by Badzioch and Hawksley (26), and Howard (27). A v i b r a t i n g feeder with a c a p a c i t y o f about 1 g f e d about 0.01 g/s of powdered biomass m a t e r i a l i n t o a flow s t r a i g h t e n e r (see Figure 2). A small flow (40-100 ml/min) o f He was used as à c a r r i e r gas, and p a r t i a l l y f l u i d i z e d the bed o f biomass m a t e r i a l i n the feeder. E x i t i n g the flow s t r a i g h t e n e r , the biomass m a t e r i a l was entrained by flowing superheated steam (about 3 g/min) and c a r r i e d i n t o the s o l a r f l u x passing through the wall o f the r e a c t o r . Char residue was c o l l e c t e d i n a bucket and weighed. E x i t i n g the quartz r e a c t o r , the steam was condensed i n a t a r trap/condenser and permanent gases were c o l l e c t e d i n 1.2 1 t e f l o n bags f o r a n a l y s i s by gas chromatography. Following an experiment, the volume o f the i n f l a t e d bags was measured by water displacement and the volume o f gas produced during the experiment was c a l c u l a t e d . Two o f the f l a s h p y r o l y s i s r e a c t o r s used f o r the experiments were f a b r i c a t e d from Amersil T08 commercial grade 50 mm OD quartz tube, and one from 25 mm OD vycor tube (Corning Glass Co.). The flow straightener/female j o i n t was made o f quartz f o r one o f the 50 mm OD r e a c t o r s , and pyrex f o r the other two r e a c t o r s . The feeder was made p r i m a r i l y from p l e x i g l a s . T e f l o n tube (6 mm ID) was used to connect the r e a c t o r to the pyrex t a r t r a p . Biomass samples taken to France f o r use with the r e a c t o r included A v i c e l ® PH 101 and 102 powdered m i c r o c r y s t a l l i n e c e l l u l o s e , ground corn cob m a t e r i a l , hardwood and softwood sawdust, K r a f t l i g n i n , and Eco Fuel I I . The corn cob and softwood m a t e r i a l was sieved and samples with p a r t i c l e s i z e s 0.004 0.12 0.13 0.01 0.01 0.002

2

0.11 0.13

0.04 0.37

0.03

0.01

>0.27

The very low char y i e l d s f o r the low f l u x experiments (Tables I - I I I ) , and the high y i e l d f o r the high f l u x experiment (Table IV) are a s u b j e c t o f i n t e r e s t . The r e a c t o r used i n the low f l u x experiments bent s l i g h t l y under exposure to the intense s o l a r f l u x ; consequently some o f the char may not have f a l l e n i n t o the bucket. However, very l i t t l e char was observed w i t h i n the r e a c t o r o u t s i d e o f the bucket f o l l o w i n g the experiments. On the other hand, copious amounts o f soot were p r e s e n t . More char was obtained i n the high f l u x experiment (using a l a r g e r bucket p r o p e r l y o r i e n t e d below the flow s t r a i g h t e n e r ) , and very l i t t l e soot was formed. The i n c r e a s e d formation o f char may have been the r e s u l t o f premature i n i t i a t i o n o f the p y r o l y s i s r e a c t i o n s by (lower i n t e n s i t y ) s c a t t e r e d r a d i a t i o n contained between the s h i e l d and the backplate surrounding the r e a c t o r . The c a v i t y c o n t a i n i n g the r e a c t o r acted as a conduit f o r the r a d i a t i o n , c a r r y i n g i t up and down the length of the r e a c t o r . T h i s unfortunate a r t i f a c t o f the experimental design could not be avoided because o f necessary s a f e t y precautions i n using the l a r g e s o l a r furnace.


252

THERMAL

CONVERSION

OF

SOLID W A S T E S

AND

BIOMASS

CONCLUSIONS


Biomass m a t e r i a l s (powdered, m i c r o c r y s t a l l i n e c e l l u l o s e and ground corn cob m a t e r i a l ) have been s u c c e s s f u l l y g a s i f i e d i n a windowed chemical r e a c t o r operating at the focus o f the O d e i l l o 1 Mw-th s o l a r furnace. The quartz window survived r a d i a n t f l u x l e v e l s i n excess of 1000 w/cm2; however i m p u r i t i e s c a r r i e d by the steam flow i n t o the r e a c t o r u l t i m a t e l y clouded the window. Some d e v i t r i f i c a t i o n may a l s o have occured. Future experiments should be designed to i n s u r e that no mineral matter i s deposited on the chemical r e a c t o r ' s windowed area. P y r o l y t i c char y i e l d s o f the O d e i l l o experiments were q u i t e low: ranging between one and f o u r percent. Gas y i e l d s were a l s o r e l a t i v e l y low, but condensible y i e l d s were h i g h . These r e s u l t s r e f l e c t the important r o l e played by the gas phase chemistry ( l a r g e l y u n a f f e c t e d by the high s o l a r f l u x ) i n the production of permanent gases from biomass. The O d e i l l o r e s u l t s are i n good agreement with e a r l i e r f l a s h tube and arc image furnace work a s s o c i a t e d with the s i m u l a t i o n of thermonuclear weapons e f f e c t s . They are also i n concord with e a r l i e r P r i n c e t o n work on biomass g a s i f i c a t i o n . A c o n s i d e r a t i o n of the c h a r a c t e r i s t i c times f o r chemical k i n e t i c and heat t r a n s f e r phenomenon w i t h i n a r a p i d l y p y r o l y z i n g p a r t i c l e i n d i c a t e that heat t r a n s f e r (not chemical k i n e t i c s ) i s the r a t e l i m i t i n g s t e p . However, the thermochemical and o p t i c a l p r o p e r t i e s o f biomass m a t e r i a l s are p o o r l y understood and much more experimental work must be completed before d e f i n i t i v e conclusions i n t h i s important area can be made. Because the use of concentrated s o l a r r a d i a t i o n f o r d i r e c t g a s i f i c a t i o n of biomass m a t e r i a l s r e s u l t s i n the formation o f l i t t l e or no char without r e l i a n c e on the water gas or Boudouard r e a c t i o n s , s o l a r f l a s h p y r o l y s i s of biomass holds unusual promise f o r the economical production of l i q u i d and gaseous f u e l s from renewable resources. ACKNOWLEDGMENTS At P r i n c e t o n , much of the p r e l i m i n a r y experimental work was done by Mr. W. Edwards and Mr. F. Conner. The p l e x i g l a s feeder was f a b r i c a t e d by Mr. B. Reavis and the quartz r e a c t o r s by Mr. H. Olson. P r o f e s s o r W. Russel o f f e r e d h e l p f u l i n s i g h t s i n t o the r o l e of c h a r a c t e r i s t i c times discussed i n t h i s paper. In France, the gas a n a l y s i s was a b l y performed by Dr. Rivot. Dr. Tuhault, Mr. R i b e i l l and Mr. Peroy were of great a s s i s t a n c e i n operating the experiment. H e l p f u l information on the o p t i c a l p r o p e r t i e s o f quartz


was

18. ANTAL ET AL.


253

obtained from Mr. H. Hoover (Corning Glass), andAmersil Corporation. The Avicel microcrystalline cellulose was obtained from Dr. L.Jones with the FMC Corporation, and the ground corn cob material from Mr. S. Bosdick with DeKalb AgResearch. Support for this work was obtained jointly from the Solar Thermal Test Facilities Users Association and Centre National De La Recherche Scientifique. The authors also wish to thank F.Smith and M. Gutstein for their interest in this work.


LITERATURE CITED 1.

Antal, M. J. "The Effects of Residence Time, Temperature and Pressure on the Steam Gasification of Biomass", American Chemical Society Division of Petroleum Chemistry, Honolulu, 1979.

2.

Antal, M. J. "Synthesis Gas Production from Organic Wastes by Pyrolysis/Steam Reforming", IGT Conference on Energy from Biomass and Wastes, Washington, D. C., 1978.

3.

Antal, M. J.; Friedman, H. L.; Rogers, F. E.; "A Study of the Steam Gasification of Organic Wastes", (Final Progress Report, U.S.Ε.P.A.)", Princeton University, Princeton, N. J., 1979.

4.

Antal, M. J.; Friedman, H. L.; Rogers, F. E. "Kinetic Rates of Cellulose Pyrolysis in Nitrogen and Steam", to appear in Combustion Science and Technology, 1979.

5.

Kothari, V. S.; Antal, M. J.; Reed, T. B. "A Comparison of the Gasification Properties of Cellulose and Lignin in Steam", to appear.

6.

Mattocks, T. N. J., 1979.

7.

Broido, A. "Kinetics of Solid Phase Cellulose Pyrolysis" in "Thermal Uses and Properties of Carbohydrates and Lignins", Shafizadeh, F. et al. (ed.), Academic Press, New York, 1976.

8.

Shafizadeh, F.; Groot, W. F. "Combustion Characteristics of Cellulosic Fuels" in "Thermal Uses and Properties of Carbo hydrates and Lignins", Shafizadeh, F. et a l . (ed.), Academic Press, New York, 1976.

9.

Lewellen, P.C.; Peters, W. Α.; Howard, J. B. "Cellulose Pyrolysis Kinetics and Char Formation Mechanism", 16th International Symposium on Combustion, Cambridge, 1976.

MSE Thesis, Princeton University, Princeton,



254


10.

Arseneau, D. F.

Can. J. Chem., 1971, 49, 632.

11.

Lincoln, K. A. Pyrodynamics, 1965, 2, 133.

12.

Berkowitz-Mattuck, J. B.; Noguchi, J. B. Polymer Science, 1963, 7, 709.

13.

Martin, S. "Diffusion Controlled Ignition of Cellulosic Materials by Intense Radiation", 10th International Symposium on Combustion, Cambridge, Mass. 1964.

14.

Shivadev, U.; Emmons, Η. W. Combustion and Flame, 1974, 22, 223.

15.

Hottel, H. C.; Williams, G. C. Chemistry, 1955, 47, 1136.

Industrial Engineering and

16.

Nelson, L. S.; Lundberg, J. L.

J. Phys. Chem., 63, 434.

17.

Rensfelt, Ε . ; Blomkvist, G; Ekstrom, C.; Engstrom, S.: Espenas, B-G.; Liinanki, L. "Basic Gasification Studies for Develop ment of Biomass Medium Btu Gasification Process", IGT Conference on Energy from Biomass and Wastes, Washington, D.C., 1978.

18.

Diebolt, J.; Smith, G. "Conversion of Trash to Gasoline", NWC Tech. Pub. 6022, Naval Weapons Center, 1978.

19.

Antal, M. J. "Biomass Energy Enhancement, A Report to the Presidents Council on Environmental Quality", Princeton University, Princeton, N. J. 1978.

20.

Antal, M. J.; Rodot, M.; Royere, C.; Vialaron, A. "Solar Flash Pyrolysis of Biomass" in Proceedings of the ISES Silver Jubilee International Congress, Atlanta, Ga., 1979.

21.

Antal, M. J. "Tower Power: Producing Fuels from Solar Energy" in Towards a Solar Civilization, Williams, R. (ed.), M.I.T. Press, Cambridge, Mass. 1978.

22.

Antal, M. J. "The Conversion of Urban Wastes" in Energy Sources and Development, Barcelona, Spain, 1978.

23.

Antal, M. J.; Feber, R. C.; Tinkle, M. C. "Synthetic Fuels From Solid Wastes and Solar Energy" in Proceedings of the World Hydrogen Energy Conference, Miami, Fla., 1976.

24.

Feber, R. C.; Antal, M. J. "Synthetic Fuel Production from Solid Wastes", EPA-600/2-77-147, Cincinnati, 1977.

Journal of Applied



18. ANTAL ET AL.


255

25.

Royere, C. "CNRS Solar Furnace" in Proceedings of Annual Meeting Technical Sessions, Solar Thermal Test Facilities Users Association, Golden, Colorado, 1978.

26.

Badzioch, S.; Hawksley, P. G. W. Ind. Eng. Chem. Process. Des. Develop., 1970, 9, 521.

27.

Kobayashi, H.; Howard, J. B.; Sarofim, A. F. "Coal Devolatilization at High Temperatures", 16th International Symposium on Combustion, Cambridge, Mass., 1976.

28.

"Avicel PH Microcrystalline Cellulose", Bulletin PH-6, FMC Corporation.

29.

Carlslaw, H. S.; Jaeger, F. C. "Conduction of Heat in Solids", Clarendon Press, Oxford, 1959.

RECEIVED November 20,

1979.


Thermal Conversion of Solid Wastes and Biomass - ACS Publications

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