OCR Text |
Show examined experimentally. Furthermore, an example of its applicability to the practical burner is introduced. 2. General discussion of scaling law Table 1. shows influential factors for emission of NOx, soot, and CO those are representative pollutants were summarized on the basis of past studies. 2)-6) In this Table, a gas phase soot means the soot which is formed through gas phase reaction followed by nucleation in the gas fuel or light oil combustion process and a residual coke soot means the unburnt char or residual coke which is formed in the coal or residual oil combustion process. In Table 1, the Key 0 indicates the influential factor and the Key 0 indicates the strong influential factor. For example, the distribution of air ratio and mixing rate are strong influential factors for an emission of CO. Next, influential factors are divided into several basic factors in Table 2. where macro mixing time means the time constant of diffusion of fuel in the combustor and micro mixing time means the time constant of the molecular level mixing between fuel and air. In Table 2, the Key. indicates the basic factors of each influential factor. For example, the residence time distribution is determined by three basic factors those are residence time, flow pattern and macro mixing time. In these factors, air preheating temperature, heat release rate, mean residence time and overall air ratio can be determined a priori regardless of scale. Especially, both heat release rate and residence time can be determined by the ratio of combustor volume to fuel flow rate only. Hence, it is easy for these factors to be coincident each other between a model and a prototype. On the other hand, as heat loss , flow pattern , macro mixing time and micro mixing time are influenced by the combustor scale in complex manner, it is difficult to keep analogy between a model and a prototype unless the scale effect is not quantitatively clarified. In these factors, heat loss is increased with a decrease of scale 8S heat loss is proportional to the specific area. Hence, in order to realize the same level 2 |