OCR Text |
Show d) Prevention methods to avoid thermal crack of honeycomb It was reported that the honeycomb regenerator is easily cracked due to thermal stress. This was true, when the design was falty. Fig.4 shows the mechanism of thermal stress occurrence, as well as thermal crack prevention method. Thermal stress occurs when non-linear temperature distribution exists in a honeycomb. The magnitude of the stress is proportional to the temperature difference (Ts) between linearlized temperature and non-linear temperature. Smaller honeycomb has smaller Ts, and it can withstand thermal stress. Based on the unsteady temperature distribution analysis in a honeycomb, the newly developed honeycomb regenerator is designed so that the thermal stress which occurs in each honeycomb is minimized. e) Control of preheated air temperature and exhaust gas temperature The newly developed honeycomb regenerator is applied to a pair of regenerative burner systems, and preheated air temperature was measured. The results are shown in Fig.5. In the test, the mass flow rate of flue gas passing through the regenerator was calculated by equation (2) and controlled. Note that equation (2) is an energy balance equation, and the heat exchange efficiency of a well designed regenerator is easily evaluated by equation (2). Gg = Cpa*Ga*(Tao-Tai)/Cpg*(Tgi-Tgo) (2) A honeycomb regenerator can raise preheated air temperature up to Furnace gas temperature - 40 [K] which is about 130K higher than a ball regenerator. And temperature fluctuation was less than 50K. f) Manufacturing Honeycomb is manufactured by NGK Insulators,LTD. and assembled by NFK. 3-2. Development of a low NOx burner A schematic diagram of a newly developed fuel-staged low NOx burner is shown |