The CFD software was adopted to simulate and optimize the flow field and NH3 concentration field for a subcritical 600 MW coal-fired unit.The gas mixture component and the turbulent flow equation were coupled to solve

and the flow field and component concentration distribution of the flue gas were ascertained.The results show that

under the BMCR condition

adding converging circular guiding plate at the quarter turn of three flue ducts and installing cascade grid in front of the first layer of catalyst

can decrease the non-uniformity of velocity from 47.42%to 12.18%

but the that of the NH3 concentration is not satisfied.When the inclination angle of the cascade grid reaches 30°and 3pieces of 1/4circular guiding plates is arranged in the reactor inlet corner spacing

the non-uniformity of velocity and mole fraction of NH3are8.27% and 9.53%

respectively

which satisfies the technical requirements.The scheme is suitable for varying load operation of thermal power unit.