Study And Numerical Simulation On Erosion Degradation Characteristic Of Plate Denitration Catalysts

The catalytic reduction method of SCR system is the most widely used denitration method for coal-fired power stations,plate denitration catalyst is the core of SCR system.However,due to the influence of process layout,the excessive erosion of the catalyst has become increasingly prominent,which seriously threatens the safe and economic operation of the SCR system.In this paper,SCR plate catalyst for large thermal power unit was chosen as the research object,and the erosion degradation characteristic of plate catalyst was studied by combining experiment with numerical simulation,the main research contents include:Firstly,basing on experimental method,the effect of flue gas velocity and fly ash characteristic on catalyst erosion rate was studied.According to the experimental results,the correlation of catalyst erosion rate was obtained and applied as a catalyst erosion model to Fluent.The simulation results and experimental values were compared to verify the reliability of the erosion model.Results show that velocity exponent is 2.702,and impact angle exponent is 0.83.In the study of fly ash characteristic,the erosion rate of catalyst increases with the increase of particle size,concentration and hardness of fly ash.When the particle size and concentration of fly ash exceed 150?m and 100g/m~3 respectively,the erosion rate of catalyst slows down.The maximum relative error of the test results is 4.42%,and the reliability and adaptability of the erosion model under different working conditions are excellent.Secondly,basing on the numerical model,the single channel erosion of SCR catalyst in the period was studied,the effects of fly ash characteristic,pitch and arrangement spacing on the erosion rate of catalyst front and pore were analyzed.Results show that,when the impact angle of flue gas is zero,the erosion rate in the pore decreases rapidly at the entrance of0~30mm,then rises subsequently and decreases slowly to the exit of the pore.With the increase of the incidence angle of flue gas,the erosion rate of the front decreases,while the erosion rate of the pore rises firstly and then decreases,and the erosion rate of the pore is largest at incidence angle of 30 degrees.With the increase of the incidence angle of flue gas,the maximal erosion position gradually shifts to the inlet of the pore,while the minimal erosion position gradually shifts to the entrance of the pore on the reverse side of the incidence angle of flue gas,and the tail erosion is lighter.The pitch has less effects on the erosion rate of the front and greater effects on the erosion rate of the pore.The erosion rate of the pore reduces faster when pitch is 6.7~8.7mm,and the decline trend slows down when pitch is 8.7~10.7 mm.With the increase of arrangement spacing,erosion rates of the front and pore of the second layer catalyst increase,and the erosion rate of the front is larger than the pore.Erosion rates of the front and pore of the second layer catalyst are less than that of the first layer catalyst under the same inlet boundary condition.Finally,basing on the numerical model established in the previous paper,and taking into account the time factor,the trajectory of fly ash particle in the catalyst pore,the erosion loss(35)M,the erosion failure length l and the erosion profile deterioration characteristic of catalyst were studied by the dynamic grid technology.Results show that,with the increase of operation time,the impact angle of fly ash particle in the entrance region of catalyst increases,which causing the trajectory of fly ash particle changes significantly,while the change of the trajectory of fly ash particle in the tail of catalyst is not obvious.Under the condition of flue gas velocity is 5m/s,fly ash particle size is 50?m and fly ash concentration is 30g/m~3,when the catalyst has been eroded for three years,the(35)M is 22.43g and l is 79.6mm,which account for 23.88%and 13.26%of the total mass and length of catalyst past respectively.The erosion profile of the catalyst at the entrance section has corrugated characteristic,the vertical distance between peaks and troughs decreases continuously with time until the catalyst erodes through.With the same flue gas velocity,with the increase of fly ash particle size,the(35)M and l tend to be stable.With the same particle size of fly ash,with the increase of flue gas velocity,the(35)M tends to be stable and l increases exponentially.