OCR Text |
Show the extent of this influence is affected by many other factors. The relationship between NOx generation and air ratio"can not be generalized as the mixing characteristic differs depending on respective combustion equipment. Referring to the result of the test by the same equipment, however, it will be known that the peak point moves to the side of lower air ration with larger quantity of combustion, and that the influence of air ratio is higher with higher heating temperature. It also .seems that shorter flame is more susceptible to the influence of air ratio than long flame as the increase of flame temperature is more abrupt. Fig-7 shown the relationship between air ration and NOx generation, from which it is known that the NOx exhaust peak point of complexed combustion•system with low mixing effeciency such as large and medium sized boilers is at an excessive air side. With - . M J Fig.7 Relationship .between air ratio and small sized boilers, the jjOx quantity of 18 T/hr water tube boiler peak point moves to the side of logical air ratio. With low NOx burner like exhaust gas re-circulation burner, the peak point also seems to be moved to the side of high air ratio. Air ratio exterts influence not only over thermal NOx but over fuel NOx, and fuel NOx is of problem with solid and liquid fuel. Described in this text is the result of the investigation with liquid fuel. As fig-8 indicates, the rate of convertion of N content in fuel into NOx by combustion(rate of Combustion l/h 5 C o I I I 1 \ ^ o 1-0 1-5 2.02.5 8.0 Air ratio n irt i i I I I I Combustion Jim]/h Jt",u *j .1.0 1.2 1.4 1.5 1.8 2.0 2.2 Air ratio Fig.-8 O2 concentration^) (from "Investigation report on combustion technology" by Combustion Technology Committee, Japan Industrial Furnace Association) a w e o «« 8 - 12- |