Combustion characteristics of pulverized coal and mineral conversion under pressurized oxy-fuel condition

To better understand the combustion process of pulverized coal under pressurized oxy-fuel atmosphere, the influence of pressure on the combustion characteristics and mineral conversion during the pressurized oxy-fuel combustion was investigated by using the combination of pressurized thermogravimetric analyzer (PTGA) and X-ray diffractometer (XRD). The results indicate that the heterogeneous ignition at atmospheric pressure changes to the homogeneous ignition with the increase of pressure, but starts to change to the heterogeneous ignition gradually at 3 MPa, and becomes the heterogeneous ignition at 5 MPa. As a result of the transformation of ignition mechanism of pulverized coal, the combustibility index S increases firstly and then reduces with pressure. And the combustion temperatures may be different for different ignition mechanisms. Because of higher combustion temperature of the heterogeneous ignition at atmospheric pressure, some minerals, such as mullite, are generated in the ash, while some other minerals, such as illite, are found in the ash owing to lower combustion temperature of the homogeneous ignition at 1 MPa. As the pressure continues rising, the illite converts to mullite due to the homogeneous ignition transforming to the heterogeneous ignition.