Systematic Effects of Coal Rank and Type on the Kinetics of Coal Pyrolysis M. J. G. Alonso, D. Alvarez, A. G. Borrego, R. Mene ´ndez, and G. Marba ´n* Instituto Nacional del Carbo ´ n (CSIC), Apartado 73, 33080-Oviedo, Spain In this work, the global pyrolysis kinetics of a broad range of coals was studied by means of thermogravimetric experiments (heating rate ) 25 °C/min). An Arrhenius-based deconvolution model was applied to the experimental DTG curves in order to obtain reliable kinetic parameters for the different DTG peaks. The model assumes that the weight loss rate ascribed to volatile release during primary and secondary pyrolysis is a result of the parallel occurrence of three pseudo-unimolecular nth-order reactions (peaks 1, 2, and 3). The kinetic results were expressed as a function of coal rank (0.43 e R r e 1.14%) and maceral composition in order to obtain reliable kinetic trends. By error minimization, an average apparent reaction order of 1.67 was found. The mass fractions corresponding to peaks 1, 2, and 3 were found to follow definite trends with rank and maceral composition. The temperature of maximum reactivity for peak 1 was almost coincident with that of the maximum overall reactivity and followed clear trends with coal rank and type. The activation energies of peaks 2 and 3 were found to be independent of coal type and clearly related to coal rank. The kinetic parameters (activation energy and preexponential factor) of the three peaks exhibited clear isokinetic effects. It is thought that the deviations of the obtained activation energies from those calculated by the isokinetic effect trends are a consequence of a narrow distribution of activation energies within each peak. Introduction Coal pyrolysis has been the object of numerous studies as a consequence of its paramount relevance in the processes of coal combustion and gasification. Thus, several reviews produced in the nineties 1-3 remark the influence of coal pyrolysis on softening, swelling, particle agglomeration, char reactivity, and char physical struc- ture during combustion or gasification of coal. Addition- ally, tar produced during the pyrolysis stage is normally the volatile product of highest initial yield and not only controls ignition and flame stability but is also a precursor of soot, which affects the radiative heat transfer in the boiler. Pyrolysis of coal is also the basic process of cokemaking and it is a process in its own right for producing liquid and gaseous products from coal. All these points clearly justify the extensive amount of kinetic studies undergone in the past few years with the objective of obtaining reliable kinetic parameters to be used in complex models (i.e., functional group models 4-6 ) that allow pyrolysis yields of various chemi- cal species to be predicted with relative success for different heating rates, reactors, and coal types. On the other hand, these kinetic studies have also permitted us to attain a deeper knowledge on the relations existing between certain characteristics of given coals and their pyrolysis behavior, although a systematic description of coal pyrolysis is to date difficult to carry out due to the inherent heterogeneity of coal. Thus, certain at- tempts were performed in order to establish systematic trends of pyrolysis yields and kinetic parameters with coal variables such as rank, 7 carbon content, 8,15,16 vit- rinite reflectance, 9-11,25 degree of artificial matura- tion, 10,12 and maceral composition 11-16,20 of coals and * Author to whom correspondence should be addressed. Tel.: +34 985280800. Fax: +34 985297662. E-mail: greca@incar.csic.es. (1) Saxena, S. C. Devolatilization and combustion characteristics of coal particles. Prog. Energy Combust. Sci. 1990, 16, 55-94. (2) Solomon, P. R.; Serio, M. A.; Suuberg, E. M. Coal pyrolysis experiments. Kinetic rates and mechanisms. Prog. Energy Combust. Sci. 1992, 18, 133-220. (3) Solomon, P. R.; Fletcher, T. H.; Pugmire, R. J. Progress in coal pyrolysis. Fuel 1993, 72 (5), 587-597. (4) Serio, M. A.; Hamblen, D. G.; Markham, J. R.; Solomon, P. R. Kinetics of volatile product evolution in coal pyrolysis: Experiment and theory. Energy Fuels 1987, 1 (2), 138-152. 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