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Show Results of work at Brookhaven National Laboratory (7) using COM with ultrafine ground coal (mean size less than 2 micron). The COM was 20% coal - 73% #4 oil and 7% water. Virtually, no change was made to an existing 150 hp Cleaver- Brooks boiler to fire this fuel. Coal-ash had a fusion temperature of 2800°F, and constituted 8% of the total weight of the coal. Using this COM with 20% excess air, the maximum firing rate was achieved at half rated capacity of the boiler. It was reported that a very stable flame, similar to #4 oil, was observed. At this operating condition, it was possible to operate the boiler for 84 hours, and maintain a thermal efficiency equal to that when firing #4 oil. However, the most critical problem was slag build up in the combustion chamber. This was perhaps surprising since some investigators believe that the ultrafine grind coal would eliminate slag build up. In addition to this, the BNL investigators found that the grinding cost to obtain an ultrafine particle size was about 2 to 3 times more than that for normal pulverized coal. Having observed these facts, the program was discontinued until the economics of this fuel becomes competitive to #6 fuel oil. Finally, an assessment of the two extremes; i.e. COM with normal pulverized coal and COM with ultrafine pulverized coal reveals that the ash build up appears to be an unavoidable problem which may prohibit the use of COM in existing packaged firetube boilers. At least, this is true with existing technology and the current cost of COM. Conclusion: The results of analytical and experimental studies indicate that molten deposit build up imposes a major limitation on the use of COM in existing firetube boilers. Use of COM with ultrafine coal particles does not appear to ameliorate this limitation. 15-12 |
