CO emission reduction of a HRSG duct burner

A heat-recovery steam generator was erected after a gas-turbine with a duct burner into the district heat centre. After commissioning, the CO emissions were found to be above the acceptable level specified in the initial contract. The Department of Energy Engineering of the BME was asked for their expert contribution in solving the problem of reducing these CO emissions. This team investigated the factors that cause incomplete combustion: the flue-gas outlet of the gas-turbine has significant swirl and rotation, the diffuser in between the gas-turbine and heat-recovery steam generator is too short and has a large cone angle, the velocity of flue-gas entering the duct burner is greater than expected, and the outlet direction of the flammable mixture from the injector of the duct burner was not optimal. After reducing the flow swirl of flue-gas and modifying the nozzle of the duct burner as suggested by the Department of Energy Engineering of the BME, CO emissions have been reduced to an acceptable level. The method involves the application of CFD modeling and studying images of the flames which proved to be very informative.