Abstract
The cootrol of a supply of coals, such as the storage of surplus coals and the release of it by a lack of coals, is necessary to both coal producers and consumers for maintaining the normal market of coals.
When a unit of 500, 000 tons coal fines of the moisture from 6 to 15 percent and of the size under 25-mm is stored away nearby a place of coal consumption in about two years, it is considered that (1) the compact storage in the field, (2) the storage in water, (3) the underground storage and (4) the storage in a structure which is suitable to the coal storage method.
The compact storage in the field has a danger of weathering and spontaneous combustion of coals. From the above reason the enough caution is necessary to execute this method. The storage in water has not a danger of weathering and spontaneous combustion, but the transportation and the dewatering of it may be difficult in case of containing pulveriged coals. In the underground storage it is apt to make bridgings in a coal pocket and the find of the suitable place for it is very difficult. Also in the storage in a structure it is apt to make bridgings in a coal pocket as well as the underground storage and has a problem of the side pressure of a coal pocket, especially in case of earthquake.
From a commercial standpoint the compact storage in the field is cheapest. The storage in water, the underground storage and the storage in a structure are in order of cost. Because the seal by nitrogen gas is necessary to carry out two methods of the storage in an nderground and in a structure, these methods may become cheaper when the oxygen n which is a by-product in a process of nitrogen production is sold in markets.
