| In the actual circulating fluidized bed boiler,SNCR denitration technology is widely used because it is easy to be implemented and applied and there is no need to make great changes to boiler equipment.However,due to the narrow temperature window of SNCR technology and the large temperature fluctuation in the boiler when the load changes,the denitration efficiency is still not high,which is not conducive to the effective use of this technology.In order to widen the reaction temperature window and ensure high denitrification efficiency,adding additives into SNCR denitrification process is one of the effective improvement methods at present.Through the analysis of experimental data,this study compares the effects of a variety of compound gas additives and a single gas additive.At the same time,an appropriate SNCR reaction kinetic mechanism model was studied to accurately reflect the effect of the mixed reducing agent composed of additives and ammonia,and the process of SNCR denitration was analyzed in detail from the mechanism.In this study,Glickmans modeling criterion was first adopted to conduct modeling calculation for a 75 t/h circulating fluidized bed boiler,and a small reaction experimental furnace was designed and built to ensure the geometric similarity and flow similarity between the reaction furnace and the 75t/h circulating fluidized bed boiler.Then,the denitrification performance test of the composite additive was carried out on the small reaction experimental furnace.Considering the presence of water vapor,the influence of the three components of the composite additive,H2,CO and CH4,on the denitrification reaction was analyzed.The results show that low temperature can effectively promote the denitrification reaction when water vapor is present,while high temperature has a certain inhibitory effect on the reaction.With the increase of water vapor concentration,the denitrification efficiency will decrease,but the decreasing extent will decrease gradually.H2,CO and CH4 can both widen the temperature window and move the temperature window towards low temperature,so as to improve the optimal denitrification efficiency and reduce the optimal denitrification temperature.In the low temperature area at 800℃or below,the combined action of the three components H2,CO and CH4 has a better effect of promoting denitrification reaction than the combined action of the two components or the separate action of the components.The combined action of H2,CO and CH4 can improve the denitrification efficiency.And the higher NSR is,the lower the minimum additive concentration is required,and NSR is negatively correlated with the ratio of additive concentration.Finally,based on the experimental data,the appropriate SNCR reaction kinetic mechanism model was studied,and the mechanism analysis of the denitrification process with mixed reducing agent was carried out.Studies have shown that,in the case of water vapor participating in denitrification reaction,there is a competitive relationship between the elementary reaction of NH2 reduction of NO and the elementary reaction of HNO conversion to NO,which is directly reflected in the temperature characteristics of denitrification reaction.When H2,CO and CH4 act alone or together,by changing the concentration of H,OH and O in the reaction system,the temperature window can be controlled to improve the optimal denitration efficiency.Changing the proportion of different components has different effects on temperature window size,optimal denitrification efficiency,optimal denitrification temperature and initial reaction temperature.Under the condition of oxygen,denitrification can inhibit the combustion reaction of H2 and CO. |
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