Application of Low NOx Combustion Technique for Regenerative System

As we have reported in the AFRC/ JFRC Conference in 1991, FDI (Fuel Direct Injection) combustion technique for high temperature furnaces is quite effective for NOx reduction. In the FDI combustion, gas and air is directly injected into the furnace with a high velocity. Both gas and air entrain substantial amount of recirculated in-furnace gas before ignition so that a self-induced flue gas recirculation effect is created, resulting low NOx combustion. While the regenerative systems have remarkable characteristics in energy saving by means of waste heat recovery, but due to use the high temperature pre-heated air, this systems has a defect of high NOx emission level. In conforming with the severe NOx regulation of Japan, the commercialization of this system was difficult, where a NOx reduction technology better than the conventional methods has been required. We applied FDI combustion to the regenerative system, by which a series of characteristic tests were made. The result was that the NOx emission level was reduced into 1/5 to 1/10, by the FDI combustion. Now, we are in stage of application of the subject system to the actual furnace such as forge furnace, aluminum melting and holding furnace, and so on. In these application, NOx emission level was reduced from approx., 1000 ppm (02=0% base) to 200 ppm.