By taking the waste heat boiler in an E class gas-steam combined cycle unit with low position arrangement as the example

numerical simulation was carried out for the selective catalytic reduction(SCR) denitration technology. The flow field of the deNO_x system was obtained and the installation position of the ammonia injection grid(AIG) inside the heat recovery boiler was determined. The results show that

guide plates are necessary in inlet flue duct of the heat recovery boiler when the gas turbine is arranged at a lower position. A bin type guide plate

which is suitable for the inlet gas duct of heat recovery boiler

is proposed. Using a multicomponent ammonia injection mixer with adjustable partition can strengthen the mixing of ammonia and NO_x in short distance. The square root deviation of NH_3 distribution on the catalyst inlet plane is 2.05% if the AIG are installed in front of module 2. Optimization test of the AIG should be carried out to obtain the best uniform of NO_x distribution and less ammonia slip on the exit section of heat recovery boiler.