Separate effects of pressure and some other variables on char combustion under fixed bed conditions

Abstract

The effects of pressure, oxygen partial pressure, oxygen flow rate, total gas flow rate and temperature on the combustion rates of chars from three different coals were measured by means of a small fixed bed, linked to a high pressure thermobalance at initial sample temperatures of 450–750 °C and total pressures of 0.1–2.1 MPa. The combustion rate was estimated with the help of three different functions: the time required for total oxidation ( t r ), the maximum sample temperature Ts max , and the maximum mass loss rate (dm dt) max . The results were interpreted with statistical models, using factor analysis combined with a partial least square method. This allowed determination of the separate influence of each variable. These models indicated that combustion rate increased strongly with oxygen partial pressure and oxygen flow rate. The char type also influenced the combustion rate. The effect of initial temperature was weaker, and that of total flow rate was the weakest of the variables. These data can be used when developing pressurized fixed bed gasifiers and combustors for combined cycles.