Optimization of the Combustion Organization in a 1000 MW_e Opposed Wall-Fired Utility Boiler by Wall Air Injection

When low NOx combustion technology is employed in an opposed wall-fired utility boiler, problems of high temperature corrosion and slagging often occurs on the side water wall, especially when burning low-quality coal. In this study, the wall air injection technology was proposed to be developed in a 1000 MWe opposed wall-fired utility boiler for alleviating these problems. Four rows of nozzles for wall air injection were set on the side wall, with three nozzles in each row. The multiphase flow, coal combustion, and heat transfer in the furnace were numerically simulated to obtain the distributions of gas velocity, temperature, and components. Results show that when burning low-quality coal without wall air injection, the gas velocity, temperature, and CO concentration near the side wall is particularly high, where ash tends to melt to cause slagging, and corrosive H2S gas is easily formed to damage the water wall tube. By injecting wall air, which provides oxygen for coal combustion and prevents flue gas from approaching the wall, the gas velocity and temperature near the side wall are both decreased, and the stability of coal combustion in the primary combustion zone gets improved. The CO concentration is significantly decreased near the wall and increased near the furnace center, which helps strengthen the air-staged combustion to benefit the low NOx emission. At the outlet of the furnace, the NO concentration in the flue gas is reduced by 38 mg/Nm(3) by wall air injection.