Characteristics of coal purification combustion and wide-load NO_x emissions on a 200 kW platform

A purification-combustion coal utilization method has been proposed in this study to align with China’s energy structure and reduce pollution emissions in coal power station. This method transforms the traditional coal combustion pathways into two steps: purification and mild combustion. Purification involves medium temperature activation (enhance coal activation) and high temperature reduction (remove impurities at high temperature), ultimately achieving coal purification, directional transformation of N and low NO_x emissions in subsequent reactions. Experimental tests are conducted on a 200 kW purification-combustion platform aimed to explore purification and combustion characteristics and transmutation of N under wide-load conditions. The results indicate that the stable operation of the platform at loads ranging from 53%-89%, with uniform distribution across the system that increases with load. The peak temperature of the purification unit which locates at the bottom of the high-temperature reduction unit reaches a maximum of 1378 ℃, while the mild combustion unit peaks at a distance of 3700 mm from the top. At the purification outlet, the proportion of CO, H₂ and CH₄ can reach 23.28%, 4.97% and 1.52% at 89% loads. The conversion rates of C, H and N at the high temperature reduction outlet increase with load and are significantly higher than those at medium temperature activation unit, with maximum values of 88.63%, 96.83% and 93.91%. The majority of N is transformed into N₂ during the process, with only 1.27% converts into NO_x at 53% loads. The minimum NO_x emissions are 47.38 mg/m³ with the combustion efficiency of 99.01%. Moreover, the research on the migration pathway of N transformation demonstrates the absence of HCN detection along the process, while NH₃ is found to be abundant above the third-stage tertiary air nozzle. NO_x is observed to distribute along the mild combustion unit initially in the form of N₂O and NO₂, and converts to NO after the injection of the fourth-stage tertiary air.