Numerical Simulation On Blended Coal Combustion Based On Chemical Reaction Kinetics

With the development of green energy,energy consumption structure is transformed.The steady growth of green power sources such as wind power,hydropower,nuclear power and solar energy,the transformation of power supply structure is the only way to transform energy consumption structure.However,limited by technology and geography,green energy cannot be stably supplied.what's worse,it's costs are high.During the transition period,the main power source is still thermal power.After ensured the safe operation of the boiler,the main purpose of the power plant is to improve the combustion characteristics and economy of the boiler.In this paper,a 350MW four-wall tangential supercritical boiler of a power plant is taken as the research object.The combustion properties of coal is studied by thermogravimetric analysis.The mathematical model of combustion reaction kinetics is established to analyze the relationship between kinetic parameters of coal combustion and ignition temperature.The one-dimensional reaction network model and chemical kinetics model of boiler combustion are established to analyze the emission characteristics of boiler based on chemical kinetics.In order to improve the economy of power plant operation,the mathematical model of blending ratio optimization is established to optimize the blending ratio of blended coal.The combustion characteristic parameters of Inner Mongolia coal,Hesgwula coal,Automobile coal,Train coal and their blends are analyzed by HS-TGA-101thermogravimetric analyzer.The results have shown that the ignition temperature of train coal blended with Hesgwula coal is lower than that of Train coal blended with Inner Mongolia coal and Train coal blended with Automobile coal.The ignition temperature and burnout temperature of blended coal are between the temperature of component coal,so blended combustion can improve combustion performance.The mathematical model of combustion reaction kinetics is established to analyze the relationship between kinetic parameters of coal combustion and ignition temperature.The results have shown that the activation energy and frequency factor of train coal are higher than those of three kinds of lignite.The activation energy and frequency factor of Hesgwula coal are the lowest.When bituminous coal is blended with lignite,the higher the proportion of lignite is,the lower the activation energy is.The activation energy of blended coal is between the activation energy of component coal and slightly larger than the weighted average value of component coal.The ignition temperature is proportional to the activation energy.The higher the activation energy is,the higher the energy required for combustion reaction is,the higher the ignition temperature is.The one-dimensional reaction network model and chemical kinetics model of boiler combustion are established based on the chemical kinetics software CHEMKIN.The main elementary reactions that promote and inhibit NO and SO₂ production are analyzed,and the effects of coal quality and CO₂ volume concentration on boiler emission characteristics are studied.The results have shown that NH and NH₂ promote the formation of NO in oxidizing atmosphere and inhibit the formation of NO in reducing atmosphere.SO is an important intermediate product in the process of SO₂ formation.The production of NO increases with the increase of nitrogen content.The amount of NO produced by the blended coal is basically equal to the linear addition value of component coal.The production of SO₂ increases with the increase of sulfur content.The amount of SO₂ produced by the blended coal is slightly higher than the linear addition value of component coal.Blended combustion can improve boiler emission characteristics.With the increase of the volume concentration of CO₂ in the inlet,the production of CO increases,while the production of NO and SO₂ decreases.A three-dimensional calculation model of boiler combustion is established.The coke heterogeneous reaction includes the reaction of coke with oxygen?carbon dioxide and water vapor in the combustion model.The two-step reaction mechanism of volatile combustion is selected.The numerical calculation and test are carried out under BMCR conditions.The errors between the numerical calculation results and the measured values of temperature and NO concentration are within the controllable range.The reliability of the calculation model is verified.The results have shown that the temperature gradually decreases from the main combustion zone to the outlet of the furnace.The NO concentration increases in the main combustion zone and the burnout zone.The NO concentration is high on both sides of the furnace,what's more,there is an obvious concentration ring in the center of the furnace.The NO concentration decreases along the edge of the tangential circle to the center.The mathematical model of blending ratio optimization is established.The genetic algorithm is used to solve the mathematical model.The blending ratio optimization system is developed based on MATLAB.In scheme 1,the blending ratio of Hesgwula coal,Inner Mongolia coal and Train coal is 3:5:2,in scheme 2,the blending ratio of Hesgwula coal,Automobile coal and Train coal is 3:4:3,in scheme 3,the blending ratio of Inner Mongolia coal,Automobile coal and Train coal is 2:2:1.The combustion performance and emission characteristics of coal blending schemes are analyzed by numerical calculation.The average temperature at the furnace outlet of the three schemes is lower than that of the designed coal.The maximum error between the three schemes and the designed coal is 4%.The NO concentration at the furnace outlet is higher than that of the designed coal.The maximum error between the three schemes and the designed coal is 9%.The numerical calculation results have shown the reliability of the blending ratio optimization model.