In general, coal used in a steel mill is largely classified into coal for manufacturing coke, coal for pulverized coal injection (PCI) into a furnace, and coal for sintering.
In case of the coal for manufacturing the coke, the coal has a property in which the coal changes into a very stiff liquid state when coal is indirectly heated. The powder coal may be manufactured into coke having a lump shape by using the above-described phase change phenomenon. All coal may not have the above-described property, but a portion of coal may have the above-described property. That is, coal having a liquid state such as bitumen may be called bituminous coal. Since the bituminous coal has finite resources, and a ratio of supply to demand is less, the bituminous may be expensive.
Coke together with iron ore may be sequentially inserted through an upper portion of a furnace to generate heat, thereby melting the iron ore. Then, the coke may be disposed in the form of slag through a lower portion of the furnace. Here, a method for supplying heat into the furnace may include a method for putting coke through the upper portion of the furnace and a method for injecting pulverized coal together with hot wind through the lower portion of the furnace. The pulverized coal that is used in the method for injecting the pulverized coal together with the hot wind through the lower portion of the furnace may be called “coal for pulverized coal injection (PCI)”. Since the coal for the PCI had to be sufficiently well burnt for a shot time, a pulverized degree of the coal or heat quantity of the coal may be very important. Since a waste gas generated while heat is released is not radiated to the atmosphere, but is collected as a heating source having a gas shape, various kinds of coal may be used.
The coal for sintering may be used for supplying heat to the pulverized coal while the heat is applied to the pulverized coal such as iron ore to generate sintered ore. In the sintering process, the coal for sintering may be directly burnt, and the waste gas generated when the combustion may be discharged to the outside through a chimney. Thus, anthracite coal having a high heat generation rate and low nitrogen content to reduce emission of nitrogen oxide (NOx) may be used as the coal for sintering.
Studies for removing minerals constituting ash and sulfur (S) components from coal are being systematically carried out for a long time. However, development of a dry sorting technology having high sorting efficiency and economic feasibility are treated as problems to be ironed out.
A wet treating process such as specific gravity sorting using spiral, jig, and heavy liquid and flotation sorting using a collecting agent and foaming agent are mainly used for the general coal sorting process. In case of the wet treating process, an incidental process for recycling used water and treating waste water and a dehydrating and drying process for removing moisture of the sorted coal concentration are necessary. Thus, the wet treating process may be complicated, and costs required for the sorting may increase. However, since coal is an inexpensive mineral, it may be necessary to develop a technology in which the coal is dry-treated to economically sort the coal.
Effects that are expected by removing the ash and sulfur from the coal may include an increase in heat generation rate of coal, stabilization in combustion, an increase in thermal efficiency of a power plant due to reduction of coal ash, and improvement in production efficiency of a furnace for manufacturing iron due to reduction of slag. Also, abrasion and corrosion within a boiler and furnace due to the ash and sulfur may decrease to reduce a time that is taken to repair and maintain equipment, thereby improving working efficiency.
Also, since an additionally installing process and operation cost of dust collection equipment or desulfurization facility for removing coal ash and sulfurous acid gas that are generated when the coal is burnt is necessary, a technology for minimizing contents of the ash and sulfur in the coal before the combustion is very important. Also, it is necessary to develop a technology for effectively sorting the ash and sulfur components of the coal to deal with environmental pollution problems that are being enhanced at home and abroad.