Advancement of Furnace Technology by Highly Preheated Air Combustion and Its Future Evolution

Recent advancement in industrial furnaces brought by highly preheated air combustion is reviewed. A large amount of waste heat can be recovered by alternating flow regenerators, and the temperature level of preheated air has reached within 100 K of the furnace temperature by an well-designed regenerator, which has resulted higher thermal efficiency of furnaces, hence the reduction of carbon dioxide emission. Adding this fact, it is noted that combustion in low oxygen atmosphere, produced by dilution of preheated air with a plenty of burned gas in the furnace, generates lower flame temperatures even with the use of highly preheated air, which contributes to reduce nitric oxide emission. As a result, energy saving and reduction of nitric oxide emission are compatible in the new technology using highly preheated air. This is the most important and attractive character of highly preheated air combustion. Further, a high quality heating process can be realized by use of regenerative burners, in which uniform heating of materials, higher heat transfer rate, and better controlabity of operation are expected. Optimum design procedure should be taken into account in the application of the technology to new fields.