OCR Text |
Show effect of energy saving by the reduction of exhaust 553 ' loss of boiler, besides the reduction of NOx, and the reduction of NOx discharge is multiplied as the result. In most cases, air ratio is discussed from the point of the ratio between the air quantity supplied to burner and logi^ cal air quantity. In practice, however, all the air going into combustion chamber shall be regarded to extert infl-ence over NOx. For example, air to an ignition burner or the cooling air for flame eye or for the sight hole of combustion chamber may often cause problems, and for the boiler of blance draft, the total air ratio including the air comming into the combustion chamber from all the other routes shall be considered. Reduction of combustion chamber thermal load(lowering of output) 1 This is the technic to reduce the thermal load of combustion chamber, i.e. to lower the boiler load which means lowering of the output. In most cases, however, substantial reducing of output is difficult due to the type and purpose of application of each boiler. Speaking totally on experience, the relationship between NOx and load is close to a logarithmic linear relation, and can be shown by the following expression including the width. Exhaust gas NOx«/Load x (l±l/2) This means the reduction of NOx is only up to about 3 0% even when the load is cut into a half so the counter-measure may not be quite effective. The problem is that the rate down is resulted for the exisiting furnaces and designing in larger size (for allowance) is necessary for newly installed furnaces. NOx reduction by lowering thermal load of combustion chamber is rather hard to generalize and the effect differs greatly depending on the thermal load on the combustion chamber at the rating of the boiler itself or on the characteristic of the burner. Further description is given in 8 - 14 - |