A Quantitative Method for Determining the Primary Air Ratio in Coal-Fired Power Plant

Abstract

In a long-term time, the primary air ratio (PAR) is determined based on the empirical data in coal-fired power plants and lack of theory. With the TG-DSC experiment of three different rank coals, a new method is proposed for quantitatively determining the PAR in coal-fired power plant in terms of the theory of intensive ignition at the initial stage of coal combustion, at which only the rate of heat released from coal oxidation is not less than that of heat loss in combustion system; the fuel is initially ignited (ignition temperature, T _i), until the heat flow is accelerated to the value of inflection point; i.e., the intensive ignition temperature of T _ig by the combustion of active components; the chars are fully ignited, the corresponding conversion ratio is determined at temperature T _ig, and PAR can be calculated. The results of TG-DSC test showed the conversion ratio at the intensive ignition temperature of JWY anthracite which is 22 %, higher than the volatile matter content (12.3 %) of parent coal; it is further stated that the homogeneous and heterogeneous ignition of anthracite simultaneously takes place; however, the conversion ratios of ZCY bituminous coal and SLH lignite at T _ig were 24 and 43 %, respectively, and were close to or less than the volatile matter content of parent coals; it indicates that the ignition is attributed to parts of volatile matter burning homogeneously with air. The PAR calculated based on TG-DSC experiment data is in the range of the proposal value of handbook and close to the less value, but is slightly greater than that of coal-fired power plant for anthracite and bituminous coal combustion and has a more wider adjustable range for lignite combustion in initial stage for the requirement of controlling slagging and NO_x production, so it provides a upper limit of PAR for the coal-fired boiler.