138 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Energy zyxwvuts & Fuels zyxwvut 1987,1,138-152 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Kinetics of Volatile Product Evolution in Coal Pyrolysis: Experiment and Theory Michael A. Serio,* David G. Hamblen, James R. Markham, and Peter R. Solomon Advanced Fuel Research, Inc., East Hartford, Connecticut zyxw 06108 Received September 15, 1986. Revised Manuscript Received October 29, 1986 Relatively few studies have addressed the kinetics of individual volatile species evolution, particularly at high-temperature, high-heating-rate conditions. In addition to the sparsity of species evolution data, substantial controversy surrounds the wide variation (factors of 1OOO) in reported kinetic rates for both overall weight loss and species evolution. The aim of this study was to use data from three types of reactors, each with different heating characteristics, to develop a more accurate reactor- independent, heating-rate-independent, and coal-independent set of kinetic parameters. Toward this end, several steps were taken to obtain better measurementa of the pyrolysis rates and heat-transfer rates for coal. In addition to improvements to the experiments, improvements were also made to a previously described functional group (FG) model for coal pyrolysis. Two submodels were added to describe (a) the cracking of hydrocarbon species released in primary pyrolysis and (b) the equilibration of oxygen-, hydrogen-,and carbon-containing species at high temperatures. Comparisons of data obtained in the three reactors with the predictions of the improved FG model are presented for six coals. In general, the agreement of the FG model and the data is quite good for all the pyrolysis products at temperatures below 1100 “C. zyxwvu As the temperature increases above 1100 “C, secondary reactions, including soot formation and gasification, begin to play an important role. This leads to overprediction of olefins, CH4,HzO, COz, and zyxwvu tar and underprediction of CO, Hz, CzHz, and benzene. The results for weight loss during primary pyrolysis are in reasonable agreement with predictions of a single first-order model for primary pyrolysis weight loss that uses a rate constant It = 4.28 X 1014 exp(-54570/RT) s-l. This indicates that the rate of primary pyrolysis is much higher at elevated temperatures (>700 “C) than predicted by commonly used rate expressions. Introduction Coal devolatilization is important because it is the initial step in a coal conversion process, accounting far up to 70% weight loss of the coal. It is also the process that is most dependent on the organic properties of the coal. Knowl- edge of the individual species evolution is important for a number of reasons. The composition of the species must be known to model the energy released by oxidation of the volatiles in combustion or gasification. For example, up to 30% of the volatiles weight can consist of C02 and pyrolytic HzO. Knowledge of the amounts and rates of the individual species is important in gasification or mild ga- sification where product composition is of concern. It is also important in pollution control by staged combustion or sorbent addition. Finally, knowledge of the species evolution provides added understanding of pyrolysis mechanisms and their relation to coal structure. Recent re~iewsl-~ of the coal pyrolysis literature have identified numerous studies on the kinetics and amount of total volatile yield. Some of these studies have ad- dressed the individual volatile species“30 and measured the kinetics of species evolution.k‘20v29a Only a few studies have been performed at high temperatures (>600 “C) and high heating rates (> lo3 K/s),”12~14~16~20~2”30 even though these are the conditions of interest in most coal conversion processes. In addition to the sparsity of species evolution data, substantial controversy surrounds the wide variation (factors of 1000) in reported kinetic rates for both overall weight loss and species evolution. The reasons for the wide variations have been examined in several recent publica- tion~,&~~,~~,~~ and it appears that there are several causes *To whom correspondence is to be addressed. 0887-0624/87/2501-0138$01.50/0 for the discrepancies. A major contributor has been in- accurate knowledge of particle temperatures, which has (1) Anthony, D. B.; Howard, J. B. AIChE J. 1976,22, 625-656. (2) Howard, J. B.; Peters, W. A.; Serio, M. A. “Coal Devolatilization Information for Reactor Modeling”; Final Report, EPRI Project No. 986-5, 1981. (3) Howard, J. B. Chemistry of Coal Utilization; Elliott, M. A,, Ed.; Wiley: New York, 1981; Chapter 12, pp 665-784. (4) Gavalas, G. R. Coal Science and Technology 4: Coal Pyrolysis; Elsevier Scientific: Amsterdam, The Netherlands, 1982. (5) Solomon, P. R.; Colket, M. B. Symp. zyxwv (Int.) Combust., [Proc.] 1978, (6) Solomon, P. R.; Hamblen, D. G.; Carangelo, R. M.; Krause; J. L. (7) Solomon, P. R.; Hamblen, D. G. EPRI Final Report No. 1654-8, (8) Solomon, P. R.; Hamblen, D. G. B o g . Energy Combust. Sci. 1983, (9) Solomon, P. R.; Hamblen, D. G. Chemistry of Coal Conversion; Schlosberg,R. H., Ed.; Plenum: New York, 1985; Chapter 5, pp 121-251. (10) Solomon, P. R.; Serio, M. A.; Carangelo, R. M.; Markham, J. R Fuel 1986,65,182-194. (11) Suuberg, E. M.; Peters, W. A.; Howard, J. B. Ind. Eng. Chem. Process Des. Deu. 1978,17,37-46. (12) Suuberg, E. M.; Peters, W. A.; Howard, J. B. Symp. (Int.) Com- (13) Campbell, J. H. Fuel, 1978,57, 217-223. (14) Juntgen, H.; van Heek, K. H. Fuel, 1968,47, 103-117. (15) Juntgen, H.; van Heek, K. H. Fuel Process. Technol. 1979,2, (16) Juntgen, H. Fuel 1984,63,731-737. (17) Weimer, R. F.; Ngan, D. Y. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1979,24(3),129-140. (18) Fitzgerald, D.; van Krevelen, D. W. Fuel 1959, 38, 17-37. (19) Serio, M. A,; Peters, W. A.; Sawada, K.; Howard, J. B. Prepr. Pap.-Am. Chem. SOC., Diu. Fuel Chem. €984,29(2), 65-76. (20) Doolan, K. R.; Mackie, J. C.; Mulcahy, M. F. R.; Tyler, R. J. Symp. (Int.) Combust. [Proc.] 1982,19th,1131-1138. (21) Morris, J. P.; Keaims, D. L. Fuel, 1979, 58, 465. (22) Tyler, R. J. Fuel, 1980,59,218-226. (23) Suuberg, E. M.; Scelza, S. T. Fuel, 1982,61,198-199. (24) Loison, R.; Chauvin, F. Chem. Ind. (London) 1964,91, 269-275. 17th,131-143. Symp. (Int.) Combust., [Proc.] 1982,19th 1139-1149. 1983. 9, 323-361. bust., [P~oc.] 1978, zyxwv 17th, 117-130. 261-293. 0 1987 American Chemical Society