SEPARATE EFFECTS OF PRESSURE AND SOME OTHER VARIABLES ON CHAR COMBUSTION UNDER FIXED-BED CONDITIONS

The effects of pressure, oxygen partial pressure, oxygen flow rate, to tal gas flow rate and temperature on the combustion rates of chars fro m three different coals were measured by means of a small fixed bed, l inked to a high pressure thermobalance at initial sample temperatures of 450-750-degrees-C and total pressures of 0.1-2.1 MPa. The combustio n rate was estimated with the help of three different functions: the t ime required for total oxidation (t(r)), the maximum sample temperatur e Ts(max), and the maximum mass loss rate (dm/dt)max. The results were interpreted with statistical models, using factor analysis combined w ith a partial least square method. This allowed determination of the s eparate influence of each variable. These models indicated that combus tion rate increased strongly with oxygen partial pressure and oxygen f low rate. The char type also influenced the combustion rate. The effec t of initial temperature was weaker, and that of total flow rate was t he weakest of the variables. These data can be used when developing pr essurized fixed bed gasifiers and combustors for combined cycles.