OCR Text |
Show 5 3-1. Regenerator a) Choice of regenerator material A regenerator has to withstand not only high temperature but also chemical attacks by dust in the furnace gas. For this reason, ceramics, such as Al203/Si02, are chosen as a material. b) Optimization of the shape of a regenerator The shape of a regenerator should be designed so as to increase the heat exchange efficiency. Therefore, a regenerator should have a large heat exchange surface area per unit volume, as well as a large gas passage opening area per unit cross sectional area, so as to minimize the pressure drop of the gas and to avoid clogging by dust. In addition, the weight and the volume of a regenerator should not be too large. Ceramic balls/nuggets have been used as heat storage medium in conventional regenerative burners. In this work, a ceramic honeycomb regenerator was developed. The honeycomb regenerator has a larger heat exchange surface area per unit volume, as well as a larger gas passage opening area per unit cross sectional area. Therefore, the honeycomb regenerator is thermally efficient and its pressure loss is less compared to a ball regenerator. Also, temperature response is faster than the ball regenerator as the honeycomb wall is thin. c) Optimization of the mass of a regenerator Assuming that the temperature of a heat storage medium is equal to the temperature of the passing gas, the mass of a honeycomb regenerator can be calculated by equition (1). Mh = (Tao-Tai)*Ca*B*Ao*m*6/{q*[(Tgi+Tgo-Tao-Tai)/2]*Ch} (1) Fig.3 shows the calculated results. In the figure, solid circle (•) show design value [2], and stars(*[3],ft[4]) shows an example use of a conventional ball regenerator. In case of star ("ft [4]) , 850kg of balls (diameter :13mm) are used for 3873kW regenerative burner. Only 170kg of honeycomb is nesessary when balls are replaced with honeycomb. This clearly demonstrates the advantage of a honeycomb regenerator. |