Combustion of coal particles in H2O/O2 supercritical fluid

Combustion of single coal particles of 1-5 mm diameter in H2O/O-2 supercritical fluid with a mass share of oxygen of 0-6.6%, pressure of 30 MPa, and temperature of 400-750 degrees C was studied in the semi-batch reactor. A decrease in coal mass was observed in two parallel processes: gasification by water and oxidation by oxygen. With an assumption of zero order in H2O concentration and Arrhenius dependence for the rate of gasification by water, the activation energy was estimated as 19 kJ/mol and the pre-exponential factor was determined as 1.02 x 10(-2) s(-1). It was found out that oxidation by oxygen under the temperature of above 500 degrees C is limited by the rate of O-2 diffusion to combustible coal residue. Below 500 degrees C the rate of heterogeneous oxidation by oxygen is described by the first-order reaction in concentration of O-2 and zero-order reaction in concentration of H2O with activation energy of 166 kJ/mol and pre-exponent of 1.5 x 10(8) cm(3)/(g.s).