Metallurgical Coal

Metallurgical Coal Metallurgical coal is also called ‘met coal’ or ‘coking coal. It is a bituminous coal which allows the production of a coke suitable to support a blast furnace (BF) charge. It is distinguished by the strong low-density coke produced when the coal is heated in a low oxygen (O2) environment or in absence of air to reduce mineral impurities (e.g. less sulphur, phosphorus). On heating, the coal softens, and volatile components evaporate and escape through pores in the mass. On cooling, the resultant coke has swollen, becoming a larger volume. The strength and density of coke is particularly important when it is used in a BF, as the coke supports part of the ore and flux burden inside the BF. Metallurgical coal possesses the ability to soften and re-solidify into a coherent, porous mass, when heated from 300 deg C to 550 deg C in the absence of air in a confined space. The conversion from coal to coke occurs in chambers called coke ovens where the volatiles from the coal escape, leaving behind what is referred to as metallurgical coke, which reaches a temperature of around 1,000 deg C to 1200 deg C before being removed from the ovens. The coking cycle is normally dependent on several parameters. Coke is used primarily as a fuel and a reducing agent in a BF. The gross calorific value (CV) of the metallurgical coal is greater than 5700 kcal/kg on an ash?free but moist basis. It presents unique plastic properties during carbonization which in turn produces a porous solid, high in carbon (C) coke. Metallurgical coals, when heated at a moderate rate in the absence of air, undergo complex and continuous changes in chemical composition and physical character. During carbonization, most bituminous coals, except those bordering...

Coking coals

Coking coals  Coking coals because of their special characteristics are suitable for carbonizing to produce blast furnace (BF) coke. Coking coal is also known as metallurgical coal. Fig 1 shows coking coal.  Fig 1 Coking or Metallurgical coal  Important properties required technically to produce good coke are Good coking and caking properties such as fluidity, dilatation and crucible swelling number etc. Appropriate rank indicated by reflectance value (MMR) Properties important for commercial as well as BF operation such as total moisture, ash etc. Properties which affects the properties of hot metal and steel such as percentage of sulphur and phosphorus. Modern coke making practice involves carbonization of a blend of coking coals. Coking coals in blended form are carbonized in a coke oven battery to produce metallurgical grade coke which is suitable for the operation of a blast furnace. Each plant uses its own blend based on the facilities available. In some of the Japanese plants coal blends consists of up to 20 different coals ranging in quality from coals with very high coking properties to coals with almost zero coking properties. The blended coking coal should have desirable coking properties for producing coke of required properties for BF operation. Quality requirement of coking coals Total moisture – It is limited to 10% maximum in as received condition. High moisture creates handling problem and lowers available carbon. Ash – It is limited to 10% maximum in air dried condition. High ash content reduces BF productivity and increases coke rate in the furnace. Volatile matter (VM) – The volatile matter in coking coals ranges from 20% to 35% in air dried sample. High volatile matter reduces the yield of metallurgical coke in coke oven battery but improves the coke oven gas generation. Sulphur – In coking coals sulphur is...