OCR Text |
Show improve buring times and combustion efficiency. In particular, the flexibility of dual fuel firing should eliminate all derating and turn-down problems. A potential disadvantage is that natural gas is a premium, and somewhat high-priced fuel (with price partly the result of step changes in regulatory decisions). Offsetting that, however, the use of air preheat as the commonly proposed alternative for improving CWS flame stability, though common in some boilers, can be an expensive undertaking for many smaller boilers or for industrial furnaces. At the very least, gas atomization is a good interim solution even when added heat exchangers are thought to be more cost-effective for CWS firing; air atomization would also require use or addition of an appropriate pump or compressor where, by contrast, the gas compression costs are, in effect, already included in the price of the gas. Possibly the greatest advantage of gas atomization, however, lies in the added value in pollution control, particularly using a high organic sulfur coal where the CWS by itself might not be in compliance but, by appropriately ratioing the two fuels, a compliance mixture could be obtained. There would be a particular market here for small boilers or industrial furnaces where addition of stack gas cleaning for S02 control is prohibitively expensive or impractical (for space reasons, for example). The furnace used in the experiments described in this paper is a hot-wall furnace with thermal loading by water-cooled tubes on the furnace floor that typically extracts 1/5 to 1/3 of the heat released. This furnace was preferred at this time to using a boiler because of the design of thermal loading that provides a profile of the thermal flux down the furnace; this has been found in past experiments (11, 12) to be usefully sensitive to both |