Experimental study and kinetic modeling of pulverized coal devolatilization under air and oxycombustion conditions at a high heating rate

摘要

This work aims to study the devolatilization of pulverized coal particles under air and oxycombustion conditions. To do so, a newly developed experimental test bench has been used to stabilize coal jet flames with fuel heating rates similar to those found in industrial cbmbustors. The thermal history of coal particles has been experimentally monitored by coupling pyrometric and particle image velocimetry (PIV) measurements. Char samples have been collected at different residence times to obtain devolatilization profiles that have been compared with data issued from 4 empirical models. New sets of kinetic parameters have been proposed to simulate coal devolatilization under high heating rate (>10~6 K/s) with N2- and CO2-based atmospheres. The composition of the burnt gases has also been characterized at various heights above the burner (HAB). The analysis of the obtained results confirmed that an oxygen enrichment of the combustion atmosphere enhances the devolatilization process by favoring an increase of the coal particle temperature. From the comparison between measured and modeled data, it has been observed that apparent devolatilization rates and kinetics were influenced only by the thermal history of the fuel particles with no char-CO2 gasification or CO2-cross linking reaction at the surface of the char in the conditions investigated here. CO releases were found to depend on the devolatilization rates and on the temperatures of the flames. An increase of the SO2 emissions has been strongly correlated to the oxygen concentration in the medium for a given devolatilization yield. NO emissions were not significantly reduced during experiments conducted under oxycombustion conditions compared to those performed under air which is due to the fact that NO emissions have been mainly related to the formation of fuel-NO in this work.