OCR Text |
Show temperature while keeping the calorific value at the same level. As a principle of NOx reduction for oil fuel, carbon particle suppression by water gas chemical reaction is also conceivable. Practical methods reported so far are as follows: •Water addition • Steam addition Wet air Added to fuel Ejected together with fuel. Added to furnace. Added to combustion air. Elected into flame. The effect differs depending on the conditions of combustion but in each case, the effect of NOx reduction is comparatively substantial. While the introduction of such incombustible air into the thermal plant will naturally reduce the thermal efficiency, and, moreover, corrosion of gas routa, or increase in smoke concentration depending on the condition may possibly derive. For practical purpose, therefore, it is necessary to find out the optimum condition from both sides of NOx reduction rate and these disadvantages. From the point of boiler efficiency, this method is somewhat advantageous for low air ratio operation because of the good combustion, and the thermal transmission is also increased even if the flame temperature is lowered and the absorbed heat quantity at the furnace becomes .smaller/ because of the increased flow velocity at the convection due to increase of combustion gas, and of the increased conductivity of radiation heat due to increased H20 partial pressure. Practically, however, the steam is lost by the Fig. 17 NOx reduction rate by steam ejection and addition for city gas combustion boiler Steam ejection 100 Boiler capacity (Dead rate 30~80Z) '0 19T/hlCity gas A 38T/hJ(Natural gas) • 10 " |City gas A 30 " (Natural gas) x!5 " ) 0.2 0.4 0.6 0.8 St"" i>HHition 8 xr/"ioq KC^L F^ - 22 ^ |