Study of the high heating rate devolatilization of a pulverized bituminous coal under oxygen-containing atmospheres

•The high heating rate devolatilization of a pulverized bituminous coal is analyzed.•Devolatilization kinetics are faster under oxygen enriched environments.•Experimental devolatilization profiles are compared with modeled ones.•Devolatilization is only controlled by the thermal history of the fuel particles.•SO2 emissions and fuel-NO production increase with the oxygen enrichment.

This study deals with the analysis of pulverized coal devolatilization in oxygen-containing atmospheres. To do so, a newly developed flat flame reactor allowing coal jet flames to be stabilized with fuel heating rates of the order of 106 K s−1 has been used to mimic operating conditions close to those met in practical combustors. A high volatile bituminous coal milled in an industrial grinder has been fluidized by carrier gases containing various amounts of oxygen (air and pure oxygen) and then injected in hot gases (temperatures ranging up to ∼1240 K) generated by propane/air flat flames. The thermal history of coal particles has been monitored by coupling particle image velocimetry (PIV) and pyrometric measurements to be integrated in constant-rate, single-kinetic-rate, two-competing-rate and DAEM devolatilization models. Devolatilization profiles derived from the analysis of the char collected at different residence times have then been compared with simulated data and a simplified fitting procedure has been implemented to find kinetic parameters leading to reproduce experimental data so as to evaluate the relative influence of the surrounding atmosphere on the devolatilization kinetics. Obtained results confirm that devolatilization is faster and more complete under oxygen enriched environments which has been related to an enhanced combustion of volatiles inducing a rise of the temperature of fuel particles. On the other hand, apparent devolatilization rates appeared to be only indirectly affected by the surrounding atmosphere through the way this one influences the heating of the coal. Furthermore, results obtained in this work tend to indicate the absence of overlapping between devolatilization and char oxidation stages. Measurements of gaseous species released during or formed after the devolatilization process finally confirm that the combustion of volatiles is more complete under oxygen enriched combustion (OEC). More CO2 is thus produced while CO concentrations significantly decrease. An enhanced fuel-N conversion has moreover been related to the higher temperatures and oxygen partial pressures met under OEC while SO2 concentrations ∼50% higher have been measured due the higher quantities of fuel-sulfur and oxygen available in the medium.