Numerical Simulation Of Coal-fired Grate Boilers

Coal-fired grate boilers,as one of the most widely used industrial boilers,still faces problems such as low combustion efficiency and high NO_x emissions.Partial decoupling combustion of coal was realized in a traditional grate boiler only by installing a pre-combustion equipment on the boiler,thus facilitating burning bituminous briquette in grate boilers to achieve high combustion efficiency and low NO_x emissions simultaneously.Compared with other NO_x emission reduction measures,upgrading the grate boiler by utilizing the decoupling pre-combustion technology has the advantages of low cost,convenient modification,and obvious energy conservation and pollution reduction effects.In order to prove the advantages of decoupling coal-fired grate boiler in increasing combustion efficiency and decreasing NO_x emissions and to explore the reduction mechanism of NO_x in the furnace,a grate boiler combustion model was established in this study.Firstly,a steady model of coal combustion in grate boilers was established by using DPM method,and was verified by simulating a 6t/h coal-fired grate boiler and comparing with the experimental data.The proposed model was further used to simulate a 20t/h pre-combustion coal-fired grate boiler.By comparing the temperature field and concentration distribution of O₂ as well as NO in the furnace,it can be shown that the pre-combustion equipment plays an important role in improving combustion efficiency and reducing pollutant emissions.By optimizing air distribution,NO emission can be reduced further.The reducing effects of methane(CH₄),carbon monoxide(CO)and high-temperature char and their combination on NO were also investigated by numerical simulation,showing that the reduction effect of high-temperature char is much more significant than those of CO and CH₄.An unsteady model of coal combustion in coal-fired grate boilers was also established to realize the moving combustion of coal bed on the grate and to eliminate the influence of initial conditions.A User Defined Function was programmed to simulate the moving grate and to ensure the introduction of air,which was verified by error analyses.Combining this model with the aforementioned model,an unsteady cold-state simulation of the 20t/h coal-fired grate boiler was also implemented,and further the whole process from introducing coal to discharging ash and slag in the 6t/h traditional coal-fired grate boiler was realized in this study.