Numerical Simulation And Engineering Application Of Selective Non-catalytic Reduction Denitration In Circulating Fluidized Bed Boiler

Nitric oxide is one of the major air pollutants, and control of nitric oxide needs to be started from the electric power industry. The NOx control technology includes low NOx combustion technology and flue gas denitration technology. The SNCR technology, shorted for selective non-catalytic reduction, is suitable for circulating fluidized bed boiler, and there are some engineering applications at home and abroad. But theoretical research about SNCR in CFB boilers is relatively rare. The main purpose of this paper is to study the SNCR process in CFB boilers through FLUENT, and to design a workable SNCR system for one 130t/h CFB boiler.First, the mass balance calculation and heat loss analysis for the SNCR system were put forward in order to obtain some key parameters, such as the consumption of reductant, dilution water, and atomizing air, and to validate the feasibility of the system.In addition, the numerical simulation of one air-blast atomizer in SNCR system was performed by FLUENT. The simulation contains two parts, one of which is the process of compressed air mixing with liquid inside the nozzle and the other is the process of jet breakup and atomization outside the nozzle. The laws of flow characteristics and atomizing effect were given, and they were in good agreement with the experimental results.Based on the results of mass balance calculation, by comparing distribution of reductant in the cyclone under six different arrangements of atomizers with the help of FLUENT, an optimized arrangement was presented. Using appropriate SNCR reaction mechanism, the effects of temperature, NSR, arrangement of atomizers, injection parameters, oxygen and circulating ash on SNCR performance were studied. The results indicate that, with the increase of temperature, the denitration efficiency first increases, then decreases and will reach a maximum at about 925℃, while the ammonia slip continues to decline. Increasing reductant quantity can expand the temperature window, but will also promote the ammonia slip. The injection parameters have little effect on the denitration efficiency. Increasing the oxygen concentration can help the temperature window move towards lower temperature, and lower the ammonia slip, but the denitration efficiency will decline at the same time. The circulating ash may lower the optimum reaction temperature to about 900℃, promote the denitration efficiency and significantly reduce the ammonia slip.Finally, according to the design requirements and actual condition of the CFB boiler, an ammonia SNCR system was selected and designed. The SNCR system consists of six subsystems, namely ammonia storage system, water storage system, mixing and pressurization system, spray system, wastewater treatment system and automatic control system.