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Show - 1 - PAPER NO. 26 NOx REDUCTION AND HEAT TRANSFER CHARACTERISTICS IN GAS FIRED GLASS MELTING FURNACES W L van de KAMP, J P SMART, T NAKAMURA and M E MORGAN International Flame Research Foundation IJmuiden, The Netherlands SUMMARY This paper describes the results of a series of experiments executed in 1988 at the IFRF for a consortium of gas companies . The main objective of the experimental programme was t o investigate practical NOx reduction methods and their impact on the heat transfer characteristics for natural gas fired glas s melting furnaces. In the research programme, a semi-industrial scale (0 . 75 MWt) compartment of an underport fired glass melting furnace was simulated. In total, 130 differe n t flames were studied with NOx emissions varying from 80 to 4200 ppm. The most promising results with respect to NOx reduction were obtained by optimisation of the air-fuel mixing characteristics. Reduction in NOx emissions by up to 75% were achievable in some cases, while corresponding heat transfer was maintained at an acceptable level. Resul ts are also reported on the effect of: excess air I air preheat temperature, water injection, fuel cracking and thermal input variation. BACKGROUND The main pollutant from natural gas fired glass melting furnaces is NOx. Process requirements typically demand high levels of air preheat ( >800 °C) and consequently flame temperatures are usually above 1800 °C for a significant fraction of the furnace residence time. As a result, NOx emissions are high, typically in the range 1000-3500 ppm (0% 02), dependent on air preheat level. Currentl y, governments throughout the world are considering or enact ing legislation to decrease the NOx emissions from glass melting furnaces. As a consequence, practical methods of reducing NOx without compromising the heat transfer requirements of the glass melting process to an unacceptable level needed to be determined. The NOx formed in gas fired glass furnaces is mainly thermal NOx produced via the Zeldovich Mechanism [1 ] . Therefore, the formation rate is controlled by flame temperature and oxygen availabili ty; the absolute level being determined by the residence time of the flame gases at high temperature. Air preheat temperatures in gas fired glass melting furnaces commonly vary from 800 to 1300 o C. Consequently, flame temperatures are above 1800 °C. Above this temperature, thermal NOx is known to form extremely rapidly [2]. OBJECTIVES The principle objective of the experimental programme was to investigate practical techniques for minimizing NOx while maintaining acceptable heat transfer characteristics in natural |
