Numerical Simulation And Analysis Of NO_x Reduction In Gas-fired Boilers Based On Flue Gas Recirculation Technology

With the adjustment of the national energy structure,although the coal-based energy structure will not change in the short term.However,with the use of coal,the emission of greenhouse gases and NO_x gases has increased,so more and more companies have begun to convert coal-fired boilers into gas-fired boilers.In industrial production applications,gas-fired boilers are mainly used to burn natural gas.Gas-fired boilers currently have the same high emission problem as coal-fired boilers,and with the formulation and promulgation of a series of emission restriction documents by the state,the state is increasingly restricting NO_xemissions from gas-fired boilers.At present,the mainstream flue gas low-nitrogen emission technologies are mainly divided into three categories:pre-combustion treatment,in-combustion treatment and post-combustion treatment.This paper mainly focuses on the flue gas recirculation technology in the combustion processing technology.Among them,the flue gas recycling has less investment,simple design and high denitrification efficiency.This paper starts from reducing the NO_x emission of gas boilers,and takes a certain type of 1 ton heavy natural gas steam boiler as a prototype.A three-dimensional simplified model was established,and the simplified gas boiler was numerically analyzed by using the commercial software Fluent.Firstly,the flue gas recirculation technology is used to control the flue gas recirculation rate within the range of 0%,5%,10%and 15%,respectively,and simulate the temperature field,flow rate and flow rate in the furnace under different flue gas recirculation rate conditions.Field composition and NO_x emissions.With the improvement of the flue gas recirculation rate,preliminary conclusions are drawn:It is most appropriate to control the flue gas recirculation rate within the range of 10%-15%.By modeling the two-dimensional cross-section of the gas boiler,and then using CFD software,by loading standard wall surfaces（SWF）and using Realizable k-ε,non-premixed combustion models and using stable flamelet diffusion combustion components,adding Chemkin chemical kinetics combustion mechanism,Simulated the effect of four groups of spacing D on the flow field,temperature and various components in the furnace under the conditions of 0m,0.01m,0.1m and 0.2m spacing of the gas inlet of the gas boiler.The flame temperature field,flame size and O₂,CO₂ and other components in the combustion process of the gas boiler are analyzed.The simulation conclusion preliminarily shows that the D between the flue gas inlets should be controlled within the range of 0.01～0.1m.Finally,in this paper,a certain proportion of biomass gas-natural gas is mixed into the furnace for simulated combustion.The Realizable turbulence model,the non-premixed combustion model and the P1 radiation model are used for specific simulation.The accuracy is controlled at the second order,and the simple algorithm is used for specific analysis.The model,the mixing ratio of the doping ratio is 0%,5%,10%,15%,and the numerical simulation is carried out.The preliminary conclusion of the simulation is that doping a certain proportion of biomass gas can reduce the combustion heat in the furnace.value.The role of biomass gas is to reduce the combustion temperature by changing the content of combustion components,thereby reducing NO_x emissions.It is best to control the ratio within 10%-15%.If the ratio is too high,the required biomass gas content will increase,which is not conducive to cost control.