Numerical Simulation For SCR System Optimization

In this paper the optimization for the flow field of a preliminary design of SCR device was studied of a cement plant production line with Fluent,which mainly aims to solve the problem of uneven distribution of velocity field.The design target of numerical simulation was the velocity distribution uniformity index value（γ₁）of catalyst inlet plane was more 0.9000.The CV value of catalyst inlet plane in physical model experiment was less than 15%and the maximum airflow deflection angle was under 10°.Firstly,the structure of SCR equipment was reconstructed.The top member of the originalπ-type SCR device was transformed into a wedge shape,and the internal flow field distribution situation of the two types of SCR devices was compared without installing internal flow field optimization components.As the results showed,when the vertical height value（ΔH）of SCR reactor wedge-shaped top chamfering was 650 mm,the uniformity of gas velocity distribution at the inlet section of the catalyst in the wedge SCR reactor was the best,theγ₁ value was increased from 0.6882 in theπ-type SCR device to 0.7389,the optimization effect was obvious.The flow field at the first bend of?H=650 mm-wedge-type SCR device was optimized using the method of installing deflectors.The shape of the deflector was designed with geometrical similarity,the best baffle plate number and arrangement were determined by equidistant layout.Then by changing the distance between each two deflectors,a better design to make gas flow rate more uniform was explored.Through simulation,the design of using the methed of uniformly debided the airflow flux to put three straight-arc-straight shape deflector in"flat-style"arrangement（Plane P）could get the largest prompt value ofγ₁,the catalyst entrance section uniformity index value reached 0.7862.Due to the guiding effect of the SCR top wedge member,the need to install deflectors inside the top of the SCR was reduced.On the basis of scheme P,the research of rectifier arrangement was studied priority.The research shows that the installation of the rectifier is the most direct and effective optimization method for the airflow distribution at the entrance section of the catalyst.When the rectifier is in the"oblique-type"arrangement,the rectifier can eliminate eddy currents when the top line of the rectifying grid is collinear with the external chamfering end of the wedge member（?l=0 mm）.Theγ₁ of“oblique-type”rectifying grid of?l=0 mm,the effective rectifying length is 300mm,the spacing between the plates was 100 mm and the same shape of grid hole was 100 mm×100 mm“oblique top”type rectifier grille was 0.9226 and0.9310,both had reached the design goal of numerical simulation.After physical model verification,it could be determined that the design scheme of the rectification grille could reach the engineering goal that the CV value of the gas velocity distribution at the catalyst inlet plane is lower than 15%.Using the streamer experiment to analyze the airflow direction below the rectifying grid,the reslut can be seen that the maximum airflow bias is lower than 10°,achieving the overall design goal.The design of the rectifying grid,which reached the numerical simulation design goal,had not reached the engineering design standard in the verification of the physical model.This result showed the necessity of physical model verification experiment.