| OCR Text |
Show 3 2.2 Method on reducing NOx The greatest problem encountered in developing the PAX-R burner was how to achieve low NOx when using pre-heated air of 1000°C while satisfying the above mentioned concepts. As a method to realize low NOx, "the auxiliary-burner flame retaining two-stage combustion" was devised. Details are described below. First, the relation between the flame temperature of the conventional type two-stage combustion low N O x burner made by our company and N O x was examined. Fig. 2 shows the flame temperature distribution made visible and N O x values. With the increase in ratio of the injection air flow rating inside the furnace (secondary air), the flame retaining area, namely the high temperature area of the flame center contracts, the flame temperature distribution becomes uniform and N O x emission is restrained. On the other hand, the flame shape becomes extremely large and stable combustion becomes difficult when the furnace temperature is low. From this, it can be said that flame retention is a main factor for emission of N O x but on the other hand, it plays an important role in deciding the flame shape and continuing of combustion reaction at low temperatures. Of these, a problem was seen in that with regard to flame shape in the conventional combustion system, the flue gas temperature rose with an extreme long flame and exhaust loss became great. However with the regenerative burner system, exhaust heat is recovered by the regenerator element and therefore it is thought that the increase of exhaust loss and adverse effect by a long flame are both small. Consequently, as shown in Fig. 3, it is thought that increasing the ratio of the injection air into the furnace as much as possible within a range which enables stable combustion at low temperature and narrowing the flame retaining area are effective in lowering N O x with the regenerative burner. To implement this, the PAX-R burner is structured with an auxiliary-burner of the nozzle-mixing type, bearing a very small combustion rating for flame retention, incorporated in the main burner which is without a flame retention structure with 1 0 0 % injection of main air into the furnace. |
