Experimental Studies on Thermal Effect of H2O on the Combustion of Pulverized Coal Char

The differences in the gas thermophysical properties (including heat capacity, thermal conductivity and diffusivity) between char combustion in wet and dry environments have remarkable influences on the combustion process. We conducted a detailed experimental study on the thermal effects of H2O on the coal char combustion at 1773 K in a high-temperature drop tube furnace (HTDTF). An appropriate portion of Ar was introduced into the bulk gas (O-2/H2O/N-2) during combustion to eliminate the opposed thermal effect of H2O. Results indicate that the H2O thermal effect initially increased with higher H2O concentrations from 0 to 10 vol.%, but it declined with a further increase in H2O concentrations in the bulk gas. Meanwhile, its effect was dominant in the preliminary and middle stages of char burning at low H2O concentrations. The increased H2O concentration and residence time promoted the gasification reaction and the water-gas shift reaction so as to weaken the negative thermal effect of H2O and improve the carbon conversion. In the 15%O-2/5%H2O/80%N-2 environment, the relative contribution of thermal effects to carbon conversion ratios ranked up to -36% at the residence time of 0.3 s, but it decreased to -0.3% at 21%O-2/30%H2O/49%N-2 atmosphere and the residence time of 0.4 s.