Recuperative and regenerative burners have thus been developed for direct waste heat recovery through combustion air preheating. A recuperator is a heat exchanger that extracts heat from the furnace waste gases to preheat the incoming combustion air. Compared with cold air combustion systems, recuperators can be expected to achieve energy savings of around 30 %. They will, however, normally only preheat the air to a maximum of 550−600 °C. Recuperative burners can be used in high temperature processes (700−1100 °C).
Regenerative burners operate in pairs and work on the principle of short term heat storage using ceramic heat regenerators, see Figure 3.3. They recover between 85−90 % of the heat from the furnace waste gases; therefore, the incoming combustion air can be preheated to very high temperatures of up to 100− 50 °C below the furnace operating temperature. Application temperatures range from 800 up to 1500 °C. Fuel consumption can be reduced by up to 60 %.
Recuperative and regenerative burners (HiTAC technology) are being implemented in a novel combustion mode with homogeneous flame temperature (flameless combustion, see Section 5.1), without the temperature peaks of a conventional flame, in a substantially extended combustion zone. Figure 3.4 shows the different regions of combustion at varying oxygen concentrations and air temperature.
和一般冷空氣進氣燃燒比較，同流換熱器可節省約30%的熱能，但正常情況下，預熱空氣最多只能到550−600 °C，同流換熱器可用在700−1100 °C的高溫製程。
The important constraint of state-of-the-art recuperative/regenerative burner technology is the conflict between technologies designed to reduce emissions and to focus on energy efficiency. The N Ox formation, for fuels not containing nitrogen, is basically a function of temperature, oxygen concentration, and residence time. Due to high temperatures of the preheated air, and the residence time, conventional flames have high peak temperature which leads to strongly increase NOx emissions.
A drawback with these burners is the investment cost. The decreased costs for energy can rather seldom alone compensate the higher investment cost. Therefore, higher productivity in the furnace and lower emissions of nitrogen oxides are important factors to be included in the cost benefit analysis.
Energy Efficiency (2009) 3.1.2