| The NOx from coal combustion is one of the air pollution sources,its substantial emission seriously harms human health and the environment,so it's of great urgency to reduce its emission.Advanced reburning with natural gas has many advantages such as high denitration efficiency,little impact on combustion of boiler,low cost of boiler transformation and so on,so it has been becoming a research hotspot.In this paper,chemical dynamics simulation and experimental methods are used to study the effects of different factors on natural gas reburning and advanced reburning for NOx reduction, and analysis the corresponding reaction mechanism which can be used to provide some reference on the development and application of natural gas advanced reburning.Firstly,GRI3.0 mechanism was selected to simulate the effects of different factors on natural gas reburning for NOx reduction after setting up physical model,and the NOx reduction mechanism of natural gas reburning was also analyzed.The results indicate that natural gas reburning can achieve 50%～70%NOx reduction efficiency,and some factors which affect NOx reduction efficiency have optimum value range.With the reaction temperature increasing,the NOx reduction efficiency by reburning with CH4 firstly increases and then decreases slightly.The optimum temperature window is from 1050℃to 1100℃.Low reburn stoichiometric(SR) is useful to NO reduction,but when SR＜0.3 the NOx reduction efficiency will decrease,and the optimum SR is 0.7～0.8 under this experimental condition.With the molar ratio of natural gas and NO(NG/NO) increasing,the NOx reduction efficiency firstly increases and then becomes gently,the optimum value of NG/NO is 3～4. The initial concentration of NO has little effect on NOx reduction efficiency. However,when some C2H6 is added into natural gas as the reburning fuel,the NOx reduction efficiency increases with the initial concentration of NO increasing.The longer the residence time is,the higher the NOx reduction efficiency is.But the increased rate would fall if the residence time exceeds 0.3s.Through the sensitivity analysis it has been found that CHi and NHi are the major reducing agents of natural gas reburning which all come from the reburning fuel,and the primary intermediates which affect the reduction of NO are HCN and HCCO.Secondly,the mechanism of advanced reburning with natural gas was based on the mechanism of reburning and SNCR,and it was used to simulate the effect law of different factors on natural gas reburning to reduce NOx,and those laws were also used to analysis the mechanism of advanced reburning with natural gas.The results indicate that the NOx ruduction efficiency of advanced reburning with natural gas is about 20～30 percents higher than that of reburning.Some factors which affect NOx reduction efficiency all have a suitable range.Compared with natural gas reburning,the temperature,SR and NG/NO of advanced reburning all decrease,which are about 1050℃,0.7 and 2～3.However,the optimum residence time hardly change.The higher the initial concentration of NO is,The higher NOx reduction efficiency of advanced reburning with CH4 is,but when its concentration exceeds 800×10-6, the NOx reduction efficiency changes gently.The most suitable molar ratio of NH3 and NO is about 1 at 1050℃,and the consumption of NH3 increases when the temperature is lower than 1050℃to achieve the same NOx reduction efficiency.The reaction can be promoted and the NOx removal efficiency can be increased by adding C2H6 into the reburning fuel.The more the C2H6 is,the higher the NOx removal efficiency is.In addition,the most suitable temperature decrease for about 50℃and the suitable temperature window can be expanded at the same SR by adding some C2H6 into the reburning fuel. Besides,it can save the reburning fuel and expand the suitable SR range. Through the sensitivity analysis it has been found that the NHi originated from the oxidation of NH3 and the conversion of CHi plays an important role on reducing NO during the advanced reburning with natural gas.In addition, the O and OH which are generated by the consecutive reaction can decrease the consumption of O2,so the residual O2 can promote the process of CHi→CH2O→HCO→HCCO→NHi which is propitious of increasing the NOx reduction efficiency.Finally,thermal denitration equipment was used to study advanced reburning with natural gas,and the results were used to validate the rationality of the mechanism of advanced reburning with natural gas which has been set up previously.The results indicate that the mechanism of advanced reburning with natural gas which was extended on the basic of GRI3.0 can predict the effect laws of different factors on natural gas reburning,and the optimum parameters can be used to guide the practical application of natural gas advanced reburning.
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