OCR Text |
Show recirculation temperature to the combustion air temperature, as near as practicably possible. (See Illustrations 6, 6a and 7, 7a). Gas recirculation is not a new technique but we required to put inert gas in zones of the burner to affect zones of the flame without destroying its stability. It was also our intention to maintain the same flexibility of load, with flue gas recirculation, without uprating the forced draught fan system. In other words, working with the same draught loss with gas recirculation as the low oxygen axial flow burners operated without gas recirculation. It was also, of course, necessary to work within the confines of the combustion chamber and not sacrifice any other combustion condition for the low NOx results. Modelling The necessity for complete flame control under all conditions is, in our mind, paramount. Thus, air/fuel ratios are not only quantitative but also positional. Therefore, if the flame is to be starved in any one position of its formation, it must be a known position and likewise to complete combustion air must also be applied in a known position. This quantitative and positional air control becomes extremely important in multi burner furnaces. The windbox was supplied by a typical forced draught system through an air heater into a common plenum chamber and our experiences told us that the air distribution to the burners was inadequate for controlled, low oxygen burning. We, therefore, applied the technique this Company has developed over the years of modelling the air supply ductings, the windbox and furnace and applying various baffles to even the distribution 5-11 |