Effects of Flue Gas Recirculation on NOx Emissions from Gas-Fired Utility Boilers

Abstract

Gas-fired utility boilers are most common in the district heating system in the city of Belgrade. Thus, they are an important stationary source of NOx emissions, which are particularly harmful for people and environment. In this paper the effectiveness of the flue gas recirculation (FGR) system that is applied to reduce NOx emissions of the utility hot water and steam boilers in district heating plant is experimentally investigated. Two types of systems are analysed; the first with the application of flue gas recirculation fan at hot water boilers; and the second without the application of flue gas recirculation fan at steam boilers. In both cases the rate of flue gas recirculation was 10%. The results of measurements showed that applied FGR systems efficiently reduced NOx emissions from utility boilers by 20 to 50% and below the reference values defined by legislative regulations. Emissions are higher at steam boiler which is expected because of the higher flue gas temperature at boiler furnace. Since the measured values for hot water boilers are close to the reference values, it was concluded that there is a potential for further improvements by increasing the flue gas recirculation rate.