Global Kinetic Constants Research Articles

Global kinetic constants for thermal oxidative degradation of a cellulosic paper

Values of global kinetic constants for pyrolysis, thermal oxidative degradation, and char oxidation of a cellulosic paper were determined by a derivative thermal gravimetric study. The study was conducted at heating rates of 0.5, 1, 1.5, 3, and 5°C/min in ambient atmospheres of nitrogen, 0.28%, 1.08%, 5.2% oxygen concentrations, and air. Sample weight loss rate, concentrations of CO, CO 2, and H 2O in the degradation products, and oxygen consumption were continuously measured during the experiment. Values of activation energy, pre-exponential factor, orders of reaction, and yields of CO, CO 2, H 2O, total hydrocarbons, and char for each degradation reaction were derived from the results. Heat of reaction for each reaction was determined by differential scanning calorimetry. A comparison of the calculated CO, CO 2, H 2O, total hydrocarbons, sample weight loss rate, and oxygen consumption was made with the measured results using the derived kinetic constants and accuracy of the values of kinetic constants was discussed.

Determination of global kinetics of coal volatiles combustion

Values of global kinetic constants for the combustion of coal volatiles have been determined for 14 coals ranging from 40 to 80% VM content (bituminous to lignite). The combustion rates of the volatiles from the different coals differed somewhat, but not markedly, and without any evident dependence on coal rank. Activation energies (E) were mostly in the range 9 to 14 kcal/mol, but higher and lower values were evidently the result of statistical scatter in the determinations, as shown by some double and triple repeats. In addition, the values of log(k0) and E in 22 pairs of measurements showed a high auto-correlation, supporting the conclusion that the variations between the different volatiles were not significant at the present level of measurement. The volatiles were pyrolysed from crushed coal pulled on trays through a muffle furnace, and were burned at the top of a vertical combustion tube in an intense back-mixed region treated theoretically as a stirred reactor using the usual equations. The total data base on which the kinetic determinations were based was in excess of 5000 measurements, yielding over 600 values of the velocity constants (k) from which the total of 22 paired values of activation energy and frequency factor were obtained for the 14 coals.