Combustion performance and NOx emissions in a 330 MW tangentially fired boiler retrofitted with preheating combustion devices

A preheating combustion device was designed and implemented in a 330 MW tangentially fired boiler to enhance combustion efficiency and reduce emissions. The device was placed between the primary combustion and burnout zones of the furnace. It pre-treated the fuel (bituminous coal) to generate high-temperature combustible gas and char under the excess air ratio range of 0.35–0.7, effectively lowering the nitrogen oxide (NOx) emissions in the primary combustion zone. Experimental investigations were carried out to analyze the composition of the preheated combustion products under varying pulverized coal concentrations and coal feed rates. The main combustible gases produced were CO, CH4, and H2. Additionally, numerical simulations were performed to evaluate the combustion characteristics and NOx emissions of the boiler with and without the preheating combustion device. The composition, temperature, and mass flow rate of gas and char measured from the experimental tests were used as input for the numerical simulations in the reduction zone. The study focused on the impact of pulverized coal concentration and coal feed rates on boiler performance. The results showed that retrofitting the boiler with the preheating combustion device led to a significant reduction in NOx emissions and improved combustion efficiency. As the pulverized coal concentration increased, the retrofitted boiler efficiency improved with minimal variation in NOx emissions. Moreover, increasing the preheating coal feed rate from 10 t/h to 40 t/h resulted in a rise in combustion efficiency, while the NOx emissions decreased from 167.6 mg/Nm3 to 121.1 mg/Nm3 (at 6 % O2), promoting cleaner and more efficient boiler combustion.