OCR Text |
Show local temperature rises. However, the NOx concentration in this test was not significantly lower than the average NOx concentration (MK-AVE) for constant operation of each pair of burners, i.e. A and B (MK-A, B), Band C (MK-B, C), and C and A (MK-C, A). Based on these experiments, we believe that maximum NOx concentration reduction in this cylindrical furnace type is possible with the following measures: (1) Burner type Use LC type burners with as high a flow speed as possible. We are now developing an LC-vh burner - an LC-h burner modified by closing the end of its combustion pipe even more tightly to attain the gas ejection velocity of an MK burner. (2) Excess air ratio Increase the excess air ratio as far as energy consumption permits with LC type burners. (3) Position of burners Keep burners as far away from the inner case and the furnace wall as possible. (4) Diameter of inner case Reduce the firing volume, by increasing the diameter as much as possible to avoid flame contact. (5) Combustion load of burners Operate burners at a constant load. Use a method such as ON-OFF combustion to maintain constant furnace temperature. (6) Chimney position We were unable to obtain a clear answer for the ideal chimney position in relation to the burners. With no practical examples available, it is not possible to assume that NOx reduction can be achieved in every furnace by off-stoichiometric combustion. These experiments have produced some interesting results regarding this type of combustion, and so we are considering further tests in this area. Conclusion Furnace shape, burner type and combustion conditions were investigated in cylindrical type furnaces, to achieve reduced NOx concentration in industrial furnaces. As a consequence, - 5 - . |