32. Investigation on NO_x Formation Characteristics During Semi-coke Air-Staged Combustion

Semi-coke is the product of low-rank coal by pyrolysis at low temperature. If semi-coke could be used as fuel of industrial pulverized coal boilers, it will widen the fuel range of the industrial pulverized coal boilers and effectively promote the coal staged utilization. As the semi-coke need higher temperature than bituminous coal for its ignition and combustion process, the NO_x emission will rapidly increase with the rising of temperature. So, decreasing the NO_x is an important task in its utilization. In this paper, the NO_x emission rules at the higher fuel-rich zone temperature and properties of semi-coke air-staged combustion were explored by two-stage drop-tube furnace. In the air-staged combustion experiments, the influence of fuel-rich zone temperature and the ratio of air on NO_x emission and combustion behavior were investigated. The results indicate that the NO_xemission concentration of non-staged combustion rises with fuel-rich zone temperature and the excess air coefficient in its combustion process. The air-staged combustion could visibly reduce the NO_x emission in the combustion process. As the Fig. 32.1 shows, the optimum ratio of secondary air is 0.56, at which NO_x emission concentration is under 120 mg/m3 and the burn-out rates were above 90%. The conclusions of the burn-out rate and the decrease rate of NO_x can be used to guide the industry enlargement experiment in running conditions.