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

ABSTRACT

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 (O₂/H₂O/N₂) 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%O₂/5%H₂O/80%N₂ 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%O₂/30%H₂O/49%N₂ atmosphere and the residence time of 0.4 s.

KEYWORDS:

• H₂O gasification
• thermal effect
• char combustion
• carbon conversion

Declaration of interest statement

The authors declare no competing financial interest.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51776161]; Fundamental Research Funds for the Central Universities [xtr042019007]; Foundation of Key Laboratory of Low-grade Energy Utilization Technologies and Systems (Chongqing University) [LLEUTS-201911].