Experimental study on the influence of O2/CO2 ratios on NO conversion and emission during combustion and gasification of high-temperature coal char

NO is one of the major pollutants generated in the process of coal thermal conversion, and shall be controlled in order to fulfil the requirements of industrial production and environmental protection. The ratio of oxygen concentration to carbon dioxide concentration (O2/CO2 ratio) is one of the key factors that affect the thermal coal-N transformation and nitrogen oxide generation. However, there are few related research in this field at present and the conclusion needs to be refined. This study adopted the coal self-preheating combustion technology to obtain the high-temperature coal char on a bench-sale test rig, and combustion and gasification experiments of this modified fuel were carried out on TG-MS combined analyzer. The sum of the percentage content of O-2 and CO2 was always 21% and Ar percentage content was 79% to simulate actual combustion. With the advanced equivalent characteristic spectrum analysis (ECSA) method, a quantitative analysis was conducted on the release rate and generative rules of gas products with temperature change during combustion and gasification of graphite and high-temperature coal char under different O-2/CO2 ratios. As per the results, O-2/CO2 ratio was the main factor affecting combustion characteristics of fuel and NO emission. In the atmosphere of 11% CO2 + 10% O-2 + 79% Ar, NO emission reached the highest level. NO, HCN and N-2 release time of the high temperature char of Shenmu bituminous coal was earlier than that of the high-temperature coal char of Shenmu semi-coke, with wider temperature range corresponding to the period of evolved gas. Reaction (NO + CO -> 1/2N(2) + CO2) was the most cardinal reaction that affected the release of NO during coal thermal conversion progress.