OCR Text |
Show - 4 - Figure 3 shows the effect of the straddle angle f) of combustion ai r on NOx reduction. The vertical axis represents the rate of decrease of NOx formation relative to the amount of NOx which forms when the combustion air takes a uniform flow pattern of f)=360° (the concentration of NOx in the case of a uniform flow pattern being 108ppm (11% O2 ) for the straight type burner, 80ppm (11~ 02) for the a =15 0 inc I i ned type, and 56ppm (11 % O2 ) for the a =30 0 inc I i ned type). As is apparent from the figure, the reduction percentage of NOx inc reases as the st radd I e ang I e () of the combust i on air injection opening section is decreased to increase the amount of deviation. Above al I, The reduction percentage of NOx for a straddle angle of 120° is 60-80%. The incl ined type burner has the function of al lowing fuel-air mixing to proceed slowly, in the early stages of combustion lowering the maximum flame temperature and al lowing the combustion to proceed at a constant temperature, thereby decreasing the amount of formation of thermal NOx and fuel NOx. This effect of the incl ined type burner cooperates with the effect brought about by the control led deviation of flow of air for combustion to contribute to a further decrease in the amount of NOx formation. The incl ined angle a of the incl ined type burner for effectively developing the aforementioned function may be selected within the range of about 10- 30° . Figure 4 shows the effect of fuel/air injection velocity ratio on NOx emission. The air velocity for the shaded marks is about twice that for the unshaded marks. It wi II be seen that, by intensifying the deviation of fuel flow and increasing the fuel/air injection velocity ratio, excel lent results can be obtained within a definite range of fuel/air injection velocity ratio. The mixing characteristics of the KOBELCO Low-NO x burner were investigated by measuring flow velocity distributions of fuel and air us i ng butane gas as the fue I. F i gu re 5 shows the d i st r i but ion ac ross a section of the furnace at a position of 200 mm from the burner quarl. With the conventional burner, the streams of fuel and air are rapidly mixed as shown in Figure 5 (a) , but they are separated when the |