Numerical Analysis Of NO_x Control Process In Oxy-fuel Combustion Furnace Coupled With Oxygen-fuel Staging And SNCR

Oxy-fuel combustion is a potential large-scale carbon capture combustion technology.Compared with conventional air,the emission of nitrogen oxide（NO_x）is reduced by 50～70%,but the emission concentration is slightly higher.In this paper,by means of numerical simulation,the combination of"oxygen-fuel bidirectional staging oxy-fuel combustion technology"and selective non-catalytic reduction technology（SNCR）is discussed,and the process parameter optimization research in response is carried out,so as to provide a low-cost solution for the realization of NO_x emission control in the oxy-fuel combustion furnace.In this paper,35 MW oxy-fuel pulverized coal boiler is taken as the research object,and a high-precision numerical prediction model for NO_x generation in oxy-fuel combustion is established.Combined with CPD model,the detailed volatile emission characteristics were considered.The self-optimized 35-component and 259-step PG2018 skeleton mechanism was used to simulate the gas reaction mechanism,and the self-developed WSGG model was used to calculate the radiation characteristics of the medium.The accuracy and reliability of the numerical model are verified by the good agreement between the simulated values of the basic air and oxy-fuel conditions and the experimental values.On the basis of the above method,considering the measures of fuel staging,oxygen（air）staging and increasing recirculation rate,the NO_x generation characteristics under air combustion and oxy-fuel combustion conditions were further simulated and analyzed.The results show that the NO emission in the basic air case is 92 mg/MJ,and the NO emission in the basic oxy-fuel condition is 38 mg/MJ.The NO emission in the optimal staged oxy-fuel condition is 31 mg/MJ,which is reduced by 66%compared with the basic Air condition.Staged oxy-fuel combustion inhibits the oxidation of HCN and NH₃,promoting the reduction of NO to HCN by CH₂.Finally,the staged oxy-fuel combustion and SNCR technology were combined to explore the potential of NO_x deep reduction.The results show that under the condition of staged oxy-fuel combustion,the optimal ammonia nitrogen ratio of SNCR is 1.0-1.5,the optimal temperature range is 1275-1300 K.The optimal temperature range and ammonia nitrogen ratio of oxy-fuel combustion are respectively higher and lower,and higher O₂ concentration increases the optimum ammonia nitrogen ratio.The combination of staged oxy-fuel combustion and SNCR resulted in a final NO_x emission of 6 mg/MJ,which reduced NO emission by 84%,compared with the basic oxy-fuel conditions.