Measurements and Modeling of Flue Height Influence on Air Pollution Emissions and Thermal Efficiency of Natural-draught Gas Fired Boilers

This paper presents and analyses results from experimental and CFD work undertaken on a 24 kW domestic natural-draught gas fired boiler. The effect of chimney height on boiler flue gases is being considered to address the need for increasing concern over environmental safety as well as saving of energy. A multi-component analysis computer (DELTA 2000 CD) is used to analyze the flue gases. 3D numerical simulations are performed using the CFD-code Fluent. The theoretical results of partially premixed combustion incorporating the prompt NOx model compare well with measurements. The results show that the pollutant emissions and thermal behavior of natural-draught burners are sensitive to draught produced by the chimney and there is an optimum chimney height, which corresponds to the minimum air pollution emissions. The results also show that the level of NO exits the natural-draught boiler is lower than Environmental Protection Agency (EPA) standard for gas fired boilers and small-scale boilers are environmentally cleaner than large central heating boilers.