OCR Text |
Show INTRODUCTION Oxy-fuel combustion is considered to be one of the most effective methods to improve thermal efficiency and reduce NOx emission for high temperature processes such as glass melting furnaces. Oxy-fuel combustion, however, is not widely used in Japan due to the relatively high price of oxygen. The use of oxy-fuel combustion has been rather limited to largescale thermal plants, to which the cryogenic method is a suitable way to supply a large amount of oxygen at a reasonably low price. Recently, the PSA (pressure swing adsorption) method has become popular and produces a variable amount of oxygen at lower cost by the innovation of a new adsorbent and efficient operational process. The low cost of oxygen in the PSA method has extended the use of oxy-fuel combustion to a variety of high temperature industrial processes. In the oxy-fuel combustion, the combustion characteristics such as flame temperature and NOx emission are largely influenced by the process parameters such as the mixing between fuel gas and oxygen and the nitrogen content in the oxidant and fuel. However, concerning oxy-fuel combustion for high temperature furnaces, there is a lack of detailed information regarding the characteristics of oxy-fuel flames. For example, little is known about the effect of flame luminosity on heat transfer. Since the furnace atmosphere is filled with CO2 and H20, flame luminosity is thought to have less influence on radiative heat transfer in furnaces. The degree of the effect of flame luminosity, however, has not yet been investigated in detail. Theoretical adiabatic flame temperature exceeding 3000K favors to a large extent the formation of thermal NOx if the combustion process contains by some means a trace amount of N2• Few results have been reported regarding the relationship between radiative heat transfer and NOx emISSIon. EXPERIMENTAL SETUP Test flames |