Optimization Control Technology Research Of SCR-DeNO_x System Flow Field By Numerical Simulation

In recent years,China is intensifying efforts to reduce NOx emissions from coal-fired power plants.As the mainstream technology in the application of flue gas denitrification in thermal power plants,SCR-DeNOx system has great research value and significance for a long time in the future.In order to ensure the stable and efficient operation of SCR-DeNOx system,flow field optimization control technology is necessary.In this context,combined with the engineering practice,the paper researches ammonia injection mixing technology and flue gas bypass modification technology.The research work of ammonia injection mixing technology includes three parts.Firstly,according to the SCR-DeNOx system flow field simulation and cold model test method,scaling down CFD model and cold physical model of a SCR-DeNOx system project are established.The results show CFD simulation results are in good agreement with model test results,indicating simulation method is reliable.Secondly,proposing two structural characteristic numbers — cover number and cut-off ratio.Cover number is used to analyze mixing performance,which shows that increasing cover number is beneficial to improving mixing performance.Cut-off ratio is used to analyze resistance performance,which shows that the greater cut-off ratio,the greater resistance.Thirdly,considering the structural characteristic,mixing characteristic and resistance characteristic of ammonia injection mixing technology,applicable situations of the four technologies are as follows: technology A is suitable for denitrification projects with small flue section size and long mixing distance;Technology B is suitable for denitrification projects with medium flue section size and medium mixing distance;Technology C and D is suitable for denitrification projects with medium or large flue section size and short mixing distance,but technology D need to pay attention to the system resistance index and economy.The research work of flue gas bypass flue modification technology is as follows:taking three SCR-DeNOx projects with different sizes of bypass flue modification space as examples,to study the optimal arrangement of bypass flue.The results show the key point of flue gas bypass flue is that the interface between main flue and bypass flue should be equal in depth.For the SCR-DeNOx project with large bypass flue reconstruction space,measures are as follows: arrange bypass flue at the upstream of ammonia spray grille,and,arrange two groups of mixers in depth direction and width direction in the main flue,to enhance mixing effect between the high and low temperature flue gas;for the SCR-DeNOx project with middle size bypass flue reconstruction space,measures are as follows: the interface between main flue and bypass flue is in the form of multiple small passages,set drainage plates at the interface,and set static mixers at downstream of the interface,so that flue gas of high and low temperature can be mixed evenly and in corresponding zones.for the SCR-DeNOx project with small bypass flue reconstruction space,measures are as follows: similar to middle size bypass flue reconstruction space,main flue needs to be separated into a section as a bypass flue,which will increase additional system resistance,and needs to pay attention to re-check distribution of flow field when the load is full.The above research results can provide effective reference for the design of bypass flue in the wide load SCR-DeNOx project.