Simulation Research Of Denitration In A450t/h Boiler By Combining Air Classification And SNCR Technology

Nitrogen oxides NO_x emissions is one of the major coal-fired power plantpollutants, in recent years, NO_x emission standards become more stringent with thegrowing awareness of environmental protection. As the older furnace did not considerthe application of denitration technology, facing a very severe pressure on reducingNO_x emissions and a field condition limit of the power plant, air classificationtechnology and selective non-catalytic reduction (SNCR) technology are idealdenitration transformations for the units in use. The two technologies are difficult tomeet the current emission standards when applied separately as the denitrificationefficiency is too low. So the application researches of the combination of these twotechnologies have important economic and environmental values.In this paper, a450t/h furnace boiler with air classification and SNCR process werenumerically researched. ICEM was employed as the meshing code. Through theanalysis of the full load flow field, the grid structure can be determined effectively tosimulate the flow process inside the furnace. With the application of the airclassification technology, furnace temperature distribution and composition distributionare consistent with the actual operation situations. When primary combustion zone is ina strong reducing atmosphere, the combustion intensity is declined and the formation ofNO_x in the combustion process is effectively inhibited. NO emissions of75%load andfull load were130.8and151.6μmol/mol respectively.Based on the detailed analysis of the combustion results, the gun layout programsof SNCR system at100%and75%load were proposed respectively, and the simulationof SNCR process was conducted. By comparison we conclude that: with the gun layoutin the layer of24.5m and26m at full load, the denitrification efficiency of the system isabout38%; with the gun layout in the layer of23.5m and25m at75%load, thedenitrification efficiency of the system is about43.7%; the NO_x emissions are lowerthan200mg/m3at the two kinds of loads and the amount of ammonia slipped is at areasonable range of5.7μmol/mol and10μmol/mol. Then the influence of differentammonia/nitrogen ratios and particle sizes of the reducing agent on the denitrificationprocess were simulated, which provides reference for the devising of SNCR system.Air classification system has a great effect on the generation of NO_x and SNCRprocess. In order to improve the overall efficiency of the combination of these twotechniques, the influence of different air-staging conditions on NO_x formation andSNCR process were studied in this paper. The results of different forms of airclassification show that: the highest operating efficiency of the entire system occurswhen the main combustion zone air volume is70%of the total amount of air, when theup two over-fire airs (OFA) are put into operation and when primary and secondary airsare coaxial tangential and the tangential circles of over-fire air and secondary air are reduced. Considering the three factors above, the best solution of combination of SNCRsystem and air classification system is obtained, which provides a reference forengineering applications.