Boiler Plant in Power Stations

Abstract

To the electrical engineer a knowledge of the thermal efficiency, operating costs, and trustworthiness of the boiler plant in his power station is almost as important as a knowledge of his electrical machines. J. Brace read a lengthy paper on this subject on March 10 to the Institution of Electrical Engineers. He had, however, to omit the discussion of flue gas, dust, and sulphurous fume extraction, as the Chimney Emissions Committee has not yet reported. He pointed out that a study of present-day American conditions leads to the general conclusion that the best American generating stations have a higher thermal efficiency than those representative of the best average British practice. A number of American generating stations produce a kilowatt hour for a heat expenditure of less than 14,000 B.Th.U. This is due to better boiler plant and to the higher grade of employee used in operating it. The Detroit Edison Company, for example, has a boiler-house efficiency of 87 per cent. In the United States, when a station uses high steam pressure, it either uses a pressure of about 600 Ib. per square inch or one of about 1300 Ib. per square inch. At the present time, there are 15 boiler units operating successfully and with no serious troubles in the neighbourhood of the higher pressure. Large boiler units capable of evaporating one million pounds of water per hour are being successfully operated. The capital cost of the boiler plant required increases rapidly with the pressure when it is above 600 Ib. per square inch. Consequently, when coal is cheap the interest on the increased capital cost may more than offset the gain in the heat efficiency. America has the advantage over Great Britain that combustion equipment can be developed for a particular quality of coal owing to the geological characteristics of the coal being uniform over wide areas. British practice, although not obtaining such excellent thermal results, has yet made good progress of recent years.