Experimental Study On Combustion And NO_X Emission Of High Temperature Preheated Coal-Based Fuel

High efficiency and stable combustion, low emissions and good adaptability to various ranks of coal are required to boilers, especially intensifying combustion and flame stability at low boiler load.A new technique of pulverized coal combustion after highly preheated to 800℃is presented. Pulverized coal is preheated in a circulating fluidized bed with partial combustion under low ratio of fuel-air. The combustible matters after the cyclone located at the exit of the circulating fluidized bed is named high temperature preheated coal-based fuel, which is mainly composed of N₂, CO₂, CO, H₂, CH₄, carbon residual and ash.The test rig includes a circulating fluidized bed to product high temperature preheated coal-based fuel and a down-fired combustor for high temperature preheated coal-based fuel combustion.High temperature preheated coal-based fuel can be achieved steadily and continuously by combustion in a low fuel-air ratio in the circulating fluidized bed. The combustion characteristics of the high temperature preheated coal-based fuel are fast ignition, good flame stability and a uniform temperature profile along the axis of the down-fired combustor with the maximum temperature difference less than 200℃. Combustion efficiency is up to 99%. NO_x emission of high temperature preheated coal-based fuel is low and the most is from char nitrogen. NO_x emission is effected by the coal particle size and air supplying of the down-fired combustor. NO_x emission is about 201 mg/m³ (@ 6% O₂), 50% lower than that with larger coal particle size and uneven air distribution.Based on the experiments energy and mass balance analysis were carried out to provide theory reference to engineering application.