Numerical Simulation Of Low-nitrogen Combustion Combined With Desulfurization In 300MW Unit CFB Boiler

In order to solve the increasingly serious energy and environmental problems and resource depletion caused by the rapid development of the electric power industry,CFB boiler has been more and more applied to thermal power units due to its advantages of wide fuel adaptability and low pollutant discharge.However,with the introduction of the new pollutant emission standards,the concentration of SO₂ and NO_x emission from the original CFB boiler can no longer meet the new emission standards,so the flue gas must be denitrified and desulfurized.Due to its easy implementation and low cost,air fractional combustion nitration reduction technology has been deeply studied and successfully applied in industrial furnaces.However,the application research in CFB boilers is at the initial stage,and the research on de-calcification in collaborative composite furnaces is rarely involved.Therefore,with the help of numerical simulation method,this paper carries out in-depth research on high efficiency nitrogen reduction and high efficiency desulfurization of limestone by fractional combustion in CFB boiler,providing technical support for its application in CFB boiler.The main research contents are as follows:?1?The CFB boiler combustion model of 300 MW unit is established and simulated and verified.The three-dimensional physical model of CFB boiler is established.Then the geometric model is established according to the actual size of the boiler and grid division is carried out.Finally,the model is numerically simulated by Fluent software.The temperature field,gas-solid flow distribution and each component distribution in the CFB boiler are obtained through simulation calculation.Then the actual boiler temperature and gas composition are measured,and the simulation results are compared with the actual measured values to verify the reliability of the model.?2?Analysis and technical improvement of CFB boiler air graded combustion.The influence of the ratio of primary and secondary air distribution,the ratio of upper and lower secondary air distribution and the angle of inlet of secondary air on the NO concentration at the furnace outlet is analyzed,and the operation parameters are improved.The results show that the operation parameters of primary and secondary air can affect the reduction zone in the furnace,and the larger the reduction zone is,the lower the concentration of NO at the furnace outlet will be.It is finally determined that when the ratio of primary and secondary air is 1:2,the ratio of upper and lower secondary air is 2:1,the upper secondary air is incident horizontally upwards at 30°and the lower secondary air is incident horizontally downwards at 30°,the NO concentration at the furnace outlet is relatively lowest.?3?The influence of burnout air system on reducing furnace outlet SO₂ is analyzed.Based on the improved air fractional combustion model,a burning-out air system is added on the upper part of the secondary air,and the contact time between limestone and flue gas is increased by disturbing the flow field in the furnace,so as to reduce SO₂.The results showed that the concentration of SO₂ at the outlet of the furnace is 1689 mg/m³,which decrease by 21.7%compared with the original condition.?4?The influences of calcium-sulfur ratio,limestone inlet location and limestone particle size on NO and SO₂ discharge at furnace outlet are analyzed.The results show that:The concentration of SO₂ at the furnace outlet will decrease with the increase of the ratio of calcium to sulfur,but the concentration of NO will increase slightly.When the level of the limestone entrance fell,the furnace outlet SO₂concentration fell,but it could cause NO concentration to rise.The average size of the limestone is too large or too small,which can lead to the increase of SO2concentration in furnace outlet,but it has little influence on NO concentration.In the end,the calcium sulfur ratio is 2.4,the limestone entrance is located in fluidized air inlet,and the limestone size is 0.5 mm,and the total discharge of the furnace is the lowest.