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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 1000) in reported kinetic rates for both overall weight loss and species evolution. The aim of this study was to usé data from three types of reactors, each with different heating characteristics, to develop a more accurate reactorindependent, heating-rate-independent, and coal-independent set of kinetic parameters. Toward this end, several steps were taken to obtain better measurements 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 oxygén-, 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. As the temperature increases above 1100 °C, secondary reactions, including soot formation and gasification, begin to play an important role. This léads to overprediction of olefins, CH4, H20, C02, and tar and underprediction of CO, H2, C2H2, 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 k = 4.28 X 1014 exp(-54570/fiT) s'1 11. This indicates that the rate of primary pyrolysis is much higher at elevated temperatures (>700 °C) than predicted by commonly used rate expressions.

The interest in utilizing biomass as a CO 2 neutral fuel by combustion, gasification, or pyrolysis processes is increasing due to concern about the emission of greenhouse gases from fossil fuel combustion. In thermal fuel conversion, pyrolysis is an important step which determines the split of products into char, tar, and gas. In this work, a combination of thermogravimetry and evolved gas analysis by Fourier transform infrared analysis (TG-FTIR) has been applied to study the influence of potassium chloride (KCl) on wheat straw pyrolysis. Raw straw, washed straw, and washed straw impregnated with KCl have been investigated. To facilitate interpretation of the results, pyrolysis of biopolymers (cellulose, xylan, lignin) in the presence and absence of KCl was investigated as well. The raw straw decomposed in a single broad featureless peak. By washing, two peaks appeared in the derivative weight loss curve, corresponding to the decomposition of hemicellulose and cellulose components in the straw. Washing reduced the char yield from 23 wt % (daf) to 12 wt % (daf), reduced the yields of gases, and increased the tar yield from 32 wt % (daf) to 66 wt % (daf). Adding 2 wt % (daf) KCl to the washed straw resulted in a char yield which was close to that of the raw straw, and the yields of tar and gases were between those from the raw and washed straw. Furthermore, the peaks corresponding to hemicellulose and cellulose decomposition moved to lower temperatures, from 670 to 633 K for the cellulose peak, but did not collapse to a single peak as in the raw straw. The influence of KCl on the peak temperature of hemicellulose and cellulose decomposition was not observed with the single biopolymers. This indicates that minerals in straw influence the interaction between the biopolymers in whole biomass. Combustion of the char remaining after pyrolysis showed that char combustion is catalyzed by the minerals present in wheat straw. Char from the washed straw with KCl added burned with two peaks in the derivative weight loss curve corresponding to a catalyzed and noncatalyzed part, indicating that the added salt did not behave in the same way as the inherent minerals in the straw.

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