Study On Stable Combustion Of Low Concentration Gas With Low Pollution

The application amount of gas in coal mine(also called coal bed gas)increases greatly,which has multiplied 10 times in recent years.With the increase of national coal mining,the hidden problems of gas use also increase.At present,the utilization rate of low-concentration gas is less than 40%in China.Especially for the low-concentration gas with the concentration of 3%to 8%,the utilization technology is few and the method is not mature enough,so that most of the low-concentration gas is discharged into the atmosphere,causing waste and pollution.The development of low-concentration gas power generation utilization technology,the use of gas turbine generator set can increase about 20 percentage points,can not only make full use of energy,but also solve the problem of low-concentration gas explosion in use,can largely eliminate hidden problems in coal mine production and use,so as to achieve the goal of maximizing the comprehensive utilization rate of low-concentration gas.Based on the development of low-emission dilute premixed combustion technology for industrial gas turbines,the combustion performance of a new type of countercurrent combustion chamber is simulated in this article.The model combustor draws on the flame stability mechanism of flameless combustion,and the high nozzle exit velocity can induce the flue gas to realize recirculation,so that the high temperature flue gas and fuel can be mixed to realize spontaneous combustion.In order to eliminate the influence of air and fuel mixture on the stability characteristics of the model burner,complete premix of air and fuel is used in the calculation.In this article,methane is used to replace low-concentration gas gas to veri fy the stability mechanism of the model burner.The main work is as follows:(1)The PSR model and 0-dimensional reactor are used to calculate the 0-dimensional chemical reaction of low-concentration gas and air premixed gas.The GRI3.0 methane combustion mechanism and the soft combustion method are adopted to complete the spontaneous combustion reaction process of low-concentration gas and air premixed gas mixed with flue gas at high temperature.The reflux ratio under different working conditions is calculated.The effect of ignition delay time on each other is that the spontaneous combustion reaction between fuel and flue gas can occur well if the reflux ratio is 1.2 or above.The combustion chamber model with large model size and relatively high reflux should be selected in the subsequent design of the combustion chamber.The optimal preheating temperature of inlet flue gas is 797K.the mass flow rate is 25kg/s,the optimal inlet pressure is 7atm,and the equivalent ratio of inlet is 0.22 or above can complete the stable combustion in the subsequent combustion chamber.The inlet gas and air mixtures are more conducive to the stable combustion reaction in the combustion chamber under this condition.(2)The calculation of the four-nozzle countercurrent combustor model shows that the countercurrent combustor can fulfill the requirements of high reflux ratio and low ignition delay time required by the fuel,and two reflux areas are formed in the combustion chamber to make the flue gas reheat internal circulation,and achieve a better mixing effect with the fuel.The maximum reflux ratio is close to 1:5,which can achieve a good spontaneous combustion effect at high temperature.Through the simulation calculation under different working conditions,it is concluded that the fuel equivalent ratio is 0.23(methane concentration is 0.013%)and above.the adiabatic flame temperature is above 1340K,the optimal mass flow rate is 25kg/s,the mass flow rate is too large,it is easy to cause flameout phenomenon,the optimal pressure is 7atm,When the preheating temperature is 650K or above,the spontaneous combustion reaction between the flue gas and the fuel in the combustion chamber can be completed.The optimal preheating temperature is 797K.Under this condition,the combustion is more stable and the emission of pollutants at the export is low.(3)Through the simulation of the single-nozzle countercurrent combustor,it is concluded that compared with the four-nozzle combustor,the internal space utilization rate of the combustor is relatively higher,and a larger reflux area is formed around the combustor.The maximum reflux ratio is 1:Above 4.the combustion research under different working conditions shows that the fuel can be fully burned when the equivalent ratio is 0.22(methane concentration 0.012%)or above,the adiabatic flame temperature is above 1320K,the optimal mass flow rate is 25kg/s,and the large inlet flow rate reduces the residence time of the fuel,which is not conducive to the full combustion of the fuel.When the preheating temperature is 650K or above,the stable combustion in the combustion chamber can be completed.When the preheating temperature is 797K,the combustion effect is the best.The change of the length and diameter of the combustion chamber will affect the distribution trend of the reflux ratio in the combustion chamber.The best combustion effect is when the width to diameter ratio is between 1-2.When the length of the combustion chamber is too short or the diameter is too small,it is easy to cause the flameout phenomenon and excessive pollutants(such as CO,NO.etc.).Through the above research,this article has a good application of low-concentration gas with a concentration of 3%-8%.For a given amount of low-concentration gas,the zero-dimensional chemical reaction calculation and CFD numerical simulation can be carried out to calculate appropriate premixed gas state parameters and countercurrent burner model,so as to carry out stable and low-pollution combustion reaction.Make this part of the gas to get a good application.