Study On Reducing Nitrogen Oxide Emissions Of Fluidized Bed With The Associated Flue Gas Recirculation And SNCR

In Emission Standards of Air Pollutants for Thermal Power Plants(GB13223-2011),the coal-fired power plants'nitrogen oxide(NO_x)emissions was strictly limited to 100mg/Nm~3,even 50 mg/Nm~3 in the key regions.However,a part of the Circulating Fluidized Bed(CFB)are failed to meet the limit.Therefore,how to reduce the nitrogen oxides of CFB is a necessary research direction.This paper,taking a 75t/h CFB boiler as the research object,researches denitrification of the method of combing flue gas recirculation and SNCR using the method of engineering experiment and numerical simulation.Firstly,changing the flue gas recirculation rate?under the load of 55t/h and 68t/h,the variation law of the temperature field,the oxygen content,the flue gas temperature and the carbon content of the fly ash were studied.The denitrification efficiency was emphatically studied.The results show that the flue gas recirculation can effectively optimize the combustion.Using this mothed,the temperature of the layer,the transition zone and the outlet of the furnace are all obviously reduced.The temperature of the dilute phase is essentially constant.But the flue gas temperature and the carbon content of fly ash are increased.Meanwhile,it will reduce the NO_x emission effectively,when boiler load is 55t/h and?is 23%,the denitrification efficiency is 27.9%.And when boiler load is 68t/h and?is 21.2%,the value can also reach 25.1%.Secondly,when the load was 50~60t/h and the flue gas recirculation fan frequency conversion was set as 85%,SNCR was run to investigate the influence of boiler load,ammonia nitrogen ratio and jet flow rate to denitrification efficiency.The result shows that NOx emission less than 100mg/Nm~3 by using flue gas recirculation and SNCR,total denitrification efficiency is 79.4%~81.5%,SNCR denitrification efficiency can reach 74.3%.When using the same NSR,decreasing boiler load or increasing the jet flow rate,the denitrification effect will be improved.Compared with4 spray guns of two layers,using 6 spray guns of the three layers were more efficient.Finally,based on the test boiler,the model was estabilished and cold flow simulation and thermal simulation were studied.From the simulation,the furnace temperature field,velocity field,species concentration field and the discrete phase distribution were realized.On the basic of the thermal numerical simulation,flue gas recirculation were token in two cases:?is 6.7%and 14.2%.This work verified that the effects of flue gas recirculationto the combustion in the furnace and the emission rule of the nitrogen oxides emission:when the?is 14.2%,the maximum temperature of cross section decreases 76?and the denitrification efficiency is 14%.