Advanced low NOx combustion using highly preheated air

Flameless combustion or invisible flame in regenerative furnaces using high ly preheated air has recently received much attention for its accomplishmen t not only in energy saving, but also for low nitric oxide emission. The ch aracteristics of combustion with highly preheated air were studied to under stand the change of combustion regime and the reason for the compatibility between high performance and low nitric oxide emission. It was found that c ombustion was sustained even in an extremely low concentration of oxygen, i f the combustion air were preheated higher than the auto-ignition temperatu re of the fuel. As an application of the principle, we can reduce nitric ox ide emission by dilution of the combustion air with plenty of recirculated burned gas in the furnace. Dilution makes the oxygen content of the oxidize r low, which decreases temperature fluctuations in the flame as well as the mean temperature, hence, low nitric oxide emission. Finally, the applicabi lity of highly preheated air combustion to other fields than industrial fur naces has been discussed. (C) 2000 Elsevier Science Ltd. All rights reserve d.