A study of combustion characteristics of gasified coal fuel

The development of integrated, coal-gasification combined cycle (IGCC) syst ems provides cost-effective and environmentally sound options for meeting f uture coal-utilizing power generation needs in the world. The Japanese gove rnment and the Electric Power Industries in Japan promoted research and dev elopment of art IGCC system. We have being working on developing a low-NOx combustion technology used in gas turbine combustors for IGCC. Each gaseous fuel produced from some raw materials contained CO and H-2 as the main com bustible components, and a small amount of CH,. Compositions and calorific values of gasified coal fuels varied widely depending on raw materials and gasifier types. Gaseous fuel, produced in various gasifiers, has a calorifi c value of 4-13 MJ/m(3), which is about one-tenth to one-third that of natu ral gas. The flame temperatures of fuels increase as the fuel calorific val ue rises. When the fuel calorific value rises 8 MJ/m(3) or higher; the flam e temperature is higher than that of natural gas, and so NOx production fro m nitrogen fixation is expected to increase significantly. Also, some gasif ied coal fuels contain fuel nitrogen, such as ammonia, if the hot/dry type gas clearing system is employed. These factors affect the combustion charac teristics of the gasified coal fuel. lit this paper, we clarified the influ ence of gasified coal fuel properties on NOx arzd CO emissions through expe riments rising a small diffusion burner and through numerical analysis base d on reaction kinetics. The main results were as follows: 1 NH3 conversion to NOx increases with increasing CH4 concentration in gaseous fuel. 2 If ga seous fuel contains CH4, there will be some specific equivalence ratio in t he primary combustion zone for the minimum NH3 conversion to NOx in the two -staged combustion. 3 Its specific equivalence ratio in the primary combust ion zone increases with decreasing CH4 concentration in gaseous fuel. 4 If the fuel contains a small percent of CH4, there is no influence of the CO/H -2 molar ratio in the fuel on the conversion rate of NH3 to NOx while there is an influence in the case where fuel contains no CH4. The conversion rat e increases with rises in the CO/H-2 molar ratio. 5 As the pressure increas es, the conversion rate of NH3 to NOx slightly decreases and the CO emissio n declines significantly.