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Show PAPER NO. 28 LOW NOx COMBUSTION TECHNIQUE FOR mGH TEMPERATURE FURNACE EijiSmGETA Hitoshi KANAZA WA Takeshi KOIZUMI Industrial Customers Development and Service Section Takahiro NAGATA Research & Development Institute Tokyo Gas Company, Limited SUMMARY With the advent of strict NOx legislation in Japan, further development for low NOx combustion technique has been strongly required. Tokyo Gas has developed a novel gas fIred combustion system, called FOI, which accomplishes a substantially low NOx level compared with conventional low NOx burners. FOI can be applied to high temperature furnaces such as steal reheating and glass melting furnaces which use high temperature preheated air. Extensive experimental study along with mathematical modeling of flames has been conducted and promising results have been obtained in evaluation of the performance of the FDI system. By applying this combustion technique, NOx emission level has been reduced more than 50% compared with conventional low NOx burners . In fact, low NOx emission level of below 40 ppm (02=11 % conversion) has been obtained at furnace temperature 1300 °C and preheated air temperature 650°C. INTRODUCTION In gas fIred high temperature industrial processes such as steel heating, metal melting, glass melting etc., preheated air has been quite commonly used and its temperature has been increased to improve thermal effIciency. One serious problem with higher preheated air temperature is thermal NOx. Since the flame temperature becomes higher as preheated air temperature is increased, higher NOx emission is often observed in high effIciency combustion systems. With the advent of the severe NOx legislation imposed in Japan, research and development on low NOx combustion techniques has become intense. Tokyo Gas has developed a novel low NOx combustion technique named FOI (Fuel Direct Injection) for high temperature furnaces. This technique is based on a unique idea to reduce peak flame temperature and oxygen availability in a flame. Gas and combustion air are separately and directly injected into the furnace to create slow mixing between the gas and the air. Combustion takes place slowly in the furnace. A sharp peak of flame temperature is thus eliminated, resulting in very low NOx emission. Another important feature of the FDI is that gas and air which are separately injected entrain substantial amounts of flue gas before ignition. Self induced in-furnace combustion products recirculation is successfully created which contributes to NOx reduction. Furthermore, FDI creates luminous flames with high emissivity due to thermal cracking of 1 |