The retrofitting scheme for selective catalytic reduction(SCR) deNO_x system of heat recovery boiler are designed for a 9F gas-steam combined cycle unit. The ammonia evaporation system is designed to provide enough ammonia using the heat of flue gas from heat recovery boiler. The parameters and position of catalyst layer are designed based on the operation parameters and actual dimensions of the heat recovery boiler. Moreover

numerical simulations are carried out to study the flow field of the deNO_x system after the retrofitting. The results show that

guide plates are not necessary in inlet flue duct of the heat recovery boiler if the outlet duct of gas turbine is placed in the central axis of the heat recovery boiler. An integral ammonia injection mixer is applied in this project

which can adjust the ammonia flow rates of different zones. Specially

the structure of the integral ammonia injection mixer can realize effective mixing of ammonia and NO_x in short distance. At last

optimization test of the integral ammonia injection mixer was carried out

and the result shows that the distribution of NO_x mass concentration in the outlet cross section was improved

and the ammonia escape amount reduced.