Determination of pyrolysis kinetic parameters of San Miguel (Texas) lignite

The kinetics of San Miguel (Texas) lignite pyrolysis was investigated in range of 650 to 800°C at atmospheric pressure. An experimental system which facilitated the monitoring of the actual sample temperature, collection of gas and tar, and measurement of sample weight loss as a function of time was used. It is found that, in the range investigated, lignite decomposition into gas, tar, and char can be described by three parallel first order reactions. Examination of experimental data indicated that, in the range investigated, the rate of pyrolysis is controlled by intraparticle heat transfer. A simplified kinetic-transport model was used to estimate the individual reaction rate constants and the activation energies. The amount and composition of the pyrolysis gas products were also analyzed. The gas produced consisted mainly of carbon dioxide, carbon monoxide, hydrogen, and some low hydrocarbons. The hydrocarbon products consisted mainly of methane, ethane, ethylene, and trace amounts of C+3 compounds.