| A kinetic study of coal devolatilization and hydropyrolysis is conducted using 15-20 mg of coal, at 1500 psig pressure. Batch experiments are performed at (LESSTHEQ) 625(DEGREES)C/sec heating rates by passing electric current through stainless steel screens containing known weights of dry pulverized North Dakota lignite (53-149 micron). Kinetic data is obtained from the weight loss of coal and from the concentrations of the evolved products, measured by a gas chromatograph.;A general model for the coal hydropyrolysis, based on a single coal particle surrounded by H(,2) gas, is developed. A single object function was formulated for three dependent variables. It was defined as:;(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI).;where the weighting factor W(,i) of a given dependent variable Y(,ij) is inversely proportional to the variance of that variable and N is number of data points. Simpson's rule was used to evaluate the effect of temperature variation with time on the rate of conversion of coal. The object function was minimized using a library program MINUIT, which contains Monte Carlo, Simplex and Variable Metric options. For order of reaction n = 6, a reasonably good fit was found for 21 data points with overall correlation coefficient 0.62, having 95% confidence limits of 0.26 and 0.83. The activation energy was estimated to be about 48,900 cal/gmole which is consistent with the assumption that chemical reaction is the rate controlling step. The preexponential factors of the rate constants based on dimensionless concentration variations with time are:;Yields on a carbon converted basis of (LESSTHEQ) 11.5% CO, 5% CO(,2), 40% CH(,4), 4% C(,2)H(,6) and 3% C(,6)H(,6) were obtained from coal hydropyrolysis experiments in the range of 538(DEGREES)-910(DEGREES)C, 500-1500 psig, 20-625(DEGREES)C/sec and 0.1-25 seconds at reaction temperature. Yields on a carbon converted basis of (LESSTHEQ) 4% CO(,2), 4% CH(,4) and 0.5% C(,6)H(,6) were obtained from coal devolatilization experiments in the range of 720-84(DEGREES)C, 100-1500 psig, in the presence of helium alone, at a heat up rate of about 20(DEGREES)C/sec and time at reaction temperature of about 25 seconds. At 1500 psig, no significant amounts of hydrocarbons were obtained from coal devolatilization.;for conversion of carbon, k(,o) = 9.95 x 10('9) sec('-1).;for formation of hydrocarbon gases, k(,10) = 2.72 x 10('9) sec('-1).;for formation of benzene, k(,20) = 0.18 x 10('9) sec('-1). |
