Study On The Influence Law Of Different Thermal Coals On Mixed Firing Of Ventilation Air Methane Boiler

The greenhouse effect of gas(methane)is 21 times that of carbon dioxide,and it is the main "contributor" to global warming.As the main source of gas emissions from coal mines,the global annual emissions are about 67.15 billion m3,of which the total amount of methane emissions contained in the ventilation air methane from mines ranks the highest in the world.However,due to its low concentration,coal mines cannot make reasonable and effective use of ventilation air methane at all,and can only discharge it ineffectively.By passing the gas as auxiliary fuel into the coal-fired boilers of the pit-head power plant for oxidative co-combustion and heat increase,the purpose of reducing emissions and increasing economic benefits can be achieved at the same time.Meanwhile,as a country with large coal resources,the thermal coal used in coal-fired power plants covers a variety of types from lignite,bituminous coal to anthracite.In this case,it is necessary to study the combustion characteristics of different types of coal and ventilation air methane in power station boilers,and the research results can lay a solid foundation for the industrial application of mixed combustion of exhaust air and coal in mines for oxidative heat increase.Based on the experimental requirements and objectives,this paper built an experimental system for co-combustion of ventilation air methane and coal.First,the effect of the change of methane concentration in ventilation air methane in the absence of pulverized coal on the ignition temperature of ventilation air methane,methane conversion rate,on this basis,the effects of pulverized coal types on the ignition temperature,methane conversion and flue gas emission characteristics of the coupling system were further studied.Finally,the stability and thermochemical properties of pulverized coal and gas combustion were simulated,analyzed and calculated by means of quantum chemical simulation methods,the relevant phenomena of the experiment are explained from the microscopic point of view.The results show that:when ventilation air methane is burned alone in the furnace,with the increasing concentration of methane,the ignition temperature is decreasing.When the methane concentration is 0.25%,the ignition temperature of ventilation air methane is 748℃;When the methane concentration is 1%,the ignition temperature of ventilation air methane is 725℃.The change of methane concentration in ventilation air methane has no effect on the conversion of methane in the furnace.The furnace temperature is the main reason for the change of methane conversion rate,the higher the temperature,the higher the methane conversion rate,and the conversion of methane can reach 98%in the combustion process.For the co-combustion of pulverized coal and ventilation air methane,the addition of different types of power coal can reduce the ignition temperature of ventilation air methane.Among them,when the methane concentration is 1%,the ignition temperature of the coupling system composed of lignite is 442℃,and the ignition temperature of the coupling system composed of anthracite coal is 536℃.The addition of lignite reduces the ignition temperature of ventilation air methane most significantly,about 39%;The addition of anthracite makes the ignition temperature of ventilation air methane reduce the least significantly,by about 26%.For the influence of different coal combustion on methane conversion,it is mainly related to the heat generated after different coal combustion.The higher the heat generated,the stronger the promotion effect on methane conversion.When different kinds of coal and ventilation air methane with different methane concentration are burned together,the concentration peak value of NO emission is in the following order:lignite>long flame coal>anthracite,that is,the higher the degree of coalification,the more NO concentration peak value.However,the addition of ventilation air methane will reduce the concentration of NO,and with the increase of methane concentration in ventilation air methane,its reduction effect on NO will increase,and the emission concentration of NO will continue to decrease.Under different methane concentrations,the concentration peak value of SO2 emission from co-combustion of different coal types and ventilation air methane at a certain temperature always has the following order:long flame coal>anthracite>lignite,different sulfur content is the main reason for the above phenomenon and methane in ventilation air methane also has the reduction effect on SO2.Based on the quantized simulation calculation results of the co-firing of coal and gas,it can be seen that the order of the bond dissociation energy(BDE)values of lignite,long-flame coal,anthracite and methane is:anthracite>long flame coal>lignite>methane,i.e.In the coupling system of pulverized coal and gas,pulverized coal ignites before methane,and lignite has the lowest BDE value and is the easiest to ignite,and anthracite has the highest BDE value and is the most difficult to ignite.Calculating the heat released by the combustion of the three types of coals,the following results are obtained:anthracite>long-flame coal>lignite.The absolute value of the required energy shows that all three kinds of coals can promote the combustion of methane,and the promotion effect of anthracite is the strongest,and the promotion effect of lignite is the weakest.