Study on a High-efficiency Combustor using Rotary Heat-strage Regenerator

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Characteristics of a high-efficiency burner using a rotary regenerator have been investigated. The burner consists of a heat exchanger (regenerator) and a combustion chamber. The regenerator is a rotary heat-storage-type heat exchanger made by a ceramic honeycomb. The exit port of the regenerator is used as the burner port, and one-dimensional flame is formed close to the honeycomb surface. The burned gas flows out through the regenerator, and the exhaust heat is stored in the ceramics channel wall, which in turn preheats the inlet mixture of city gas and air. The temperature distribution and gas concentration in the combustor were measured. Experiments were made for various fuel-air ratios, and it was found that stable combustion is possible for 0.2<F<6, where F denotes the stoichiometric ratio of the inlet premixed gas, in contrast to the conventional flammable range of 0.5<F<1.8. The effectiveness of the regenerator for the heat reconvery from the exhaust gas was about 90%, which coincides well with the result of a numerical analysis. The temperature of the preheated unburned gas was higher than that of burned gas, which indicates that the heating of honeycomb core by the flame is significant. The measured flame temperature near the fuel-lean flammable limit was significantrly higher than the usual adiabatic flame temperature, which shows that the regenerative heat exchange successfully enlarges the flammable range. The NOx concentration has a maximum value, 8ppm, at F=1.3, and decreases below 1ppm for F<0.7 and F>1.5. Various heat transfer processes, such as the heat exchange in the regenerator, radiative heat transfer from the surface of honeycomb core, etc., were evaluated quantitatively to construct a predictive method for the present combustor. In addition, a thermo-electric module was attached to the combustor wall, and a electric power corresponding to the module performance was extracted.