Development and Application of Direct Fired Regenerative Burner Heating System

Page 4

4 It has been commonly known that "highly preheated air combustion increases the NOx emission" and most combustion engineers believe that "it is impossible to achieve both ultimate heat recovery and low NOx combustion at the same time". 2. BACKGROUND OF THIS WORK In order to reduce fuel consumption in a reheating furnace, it is a good idea to utilize waste heat of flue gas for preheating combustion air. Fig.2 shows a calculated relation between preheated air temperature and normalized fuel consumption. A conventional shell and tube air preheater can raise preheated air temperature up to 920K, and the fuel saving is about 30% compared to a cold air system. If the preheated air temperature is raised as high as the furnace gas temperature, the fuel saving is about 50% compared to a cold air system. This means that a 30% energy saving is possible compared to a conventional air recuperator system. Although, the RCB needs improvements, the basic idea is reasonable. NKK Corporation and Nippon Furnace Kogyo Kaisha, LTD. (NFK) have recognized the high potential of the regenerative burner heating system, and started joint R&D work in 1990. The scope of R&D work was set as follows; (1) Development of a high performance regenerator Raise preheated air temperature as high as furnace gas temperature. Minimize weight and size of the regenerator. (2) Development of a low NOx burner Reduce NOx emission by 50% at preheated air temperature 1620K compared with a conventional low NOx burner (preheated air temperature 920K) . Research work set for achieving both "ultimate heat recovery" and "low NOx combustion" at the same time was a great challenge against "the common sense of a combustion engineer". 3. R&D WORK [5]