Abstract
It has elapsed about thirty years since the inauguration of power generation using low-grade coal in Japan.In this duration, many improvements both in boiler and combustion techniques have been achieved through the resolution of the problem encountered.From the aspect of combustion, Johan and Ube Oha coals are most suitable followed by the low-grade coal of Kyushu district for the present purpose.On the other hand, Ube anthracite of high ash content induces an increase of unburned carbon in the cinder.The problem in the operation of the plant is rather the troubles in the handling of high-moisture coal than the fluctuation of heat value of coal.Recently, the use of vapor of high temperature and high pressure is dominant in the power generation including the power station using low-grade coal.The change of the design of plant, as the result, in which the velocity of gas is increased as far as possible in order to increase the heat transfer coefficient and to decrease the heat area, induces a new problem of erosion of heat tube by fly-ash in gas. The increase of dust collecting efficiency, at the same time, is required from the viewpoint of the abatement of air pollution. However, when the coal of high ash content is used the improvement of dust collecting efficiency, for instance from 97% to 98%, is by far difficult than the elevation of heat efficiency by 1%.Furthermore, the fact that the cost for model change of the plant will be expensive provides another problem.
