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coke and metallurgical coal

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coke and metallurgical coal

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coke and metallurgical coal

  1. 1. Coke Introduction Coke is a hard gray fuel, it bears the same relation to coal as charcoal to wood. Coke is made in brick furnaces with bituminous coal as the source. Coke is the most vital raw material fed in a blast furnace operation and hot metal quality. A high quality coke should be able to support a smooth origin of the blast furnace burden with as little degradation as possible while providing the lowest amount of impurities, highest thermal energy, highest metal reduction, and optimum absorptivity for the flow of gaseous and molten products. Metallurgical Coke Coke is a solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. The volatile constituents of the coal including water, coal-gas and coal-tar are driven off by baking in an airless oven at temperatures as high 1000° C. Metallurgical coke is produced by carbonization of coal at high temperatures to produce a macro-porous carbon material of high strength and relatively large lump size. Metallurgical cokes must have a high strength to support heavy loads in the blast furnace without disintegration. Metallurgical Coal Metallurgical coal is a special type of coal used to make metallurgical coke. There are two types of metallurgical coal used to make coke;  Hard Coking Coal  Semisoft Coking Coal These types of coal are ideal for coke because they melt, swell and re-solidify when placed into a superheated furnace. These types of coal also have low levels of impurities. A third type of metallurgical coal, PCI (Pulverized Coal Injection) is sometimes used in steel or iron making to replace more-expensive coke. The coking coal must have the following;  Low ash content  Low Sulphur content  Porosity factor  Abrasive strength and hardness Coke Manufacturing Coke is created by heating metallurgical coal to around 2,000 degrees Fahrenheit. The coking process takes about 12 to 36 hours in the oven to complete. After being taken out of the oven, the coke is cooled with water or air to before it is either placed into storage or is put directly to the blast furnace. The finished product is about two-thirds the weight of the original raw material. Metallurgical Coke Manufacturing Metallurgical coke is made from low ash, low sulfur bituminous coal, with special coking properties, which is inserted into ovens and heated to 1000F to fuse fixed carbon and inherent ash and drive off most of the volatile matter. The final product is a nearly pure carbon source with sizes ranging from basketballs (foundry coke) to a fine powder (coke breeze).
  2. 2. Factors Affecting Quality High quality coke is normally made from high quality coking coals. An excellence coal should not generate high pressure on the coke oven wall and should shrink enough to allow easy removal from the coking oven. The properties of coke and its performance in the process are influenced by moisture content, density, weathering of coal, and several other factors. Application of Metallurgical Coke  Coke is mainly used to make iron, which in turn used as the main ingredient in steel. In iron making procedure iron ore, coke and small quantities of minerals used to collect impurities are placed into a blast furnace. Superheated air is then blown into the furnace, making the coke burn. The burning produces carbon monoxide which reacts with the iron ore and heat to melt the iron. A tap at the bottom of the furnace allows molten iron, as well as impurities, to flow out of the furnace.  Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. The carbon monoxide produced by its combustion reduces iron oxide (hematite) in the production of the iron product. Blast Furnace Construction and Working Blast furnace consists of a vertical steel shell, 100 ft. high & 21 ft. diameter and lined with refractory material. It has a charging arrangement (Bell & Cone) at the top. Raw material is charged by a skip car through this charging mechanism into the blast furnace. It has a means of running off Pig iron & Slag at the bottom. Air is blown in near the bottom of the furnace. This forced draught increases the speed of combustion & maintains the necessary high temperature. Cooling water is circulated around the Bosh area in order to protect the furnace from high temp. Figure 2 Sketch of Blast Furnace
  3. 3. Chemical Reactions Occurring In Blast Furnace Using Coke In the blast furnace there are several chemical reactions taking place that eventually result in the desired product (iron) being extracted; The coke (carbon) burns with oxygen to produce carbon dioxide. This reaction is exothermic. The CO2 then reacts with more coke to give carbon monoxide. C + O2  CO2 CO2 + C  2CO Carbon Monoxide (CO) acts as a reducing agent and reacts with the iron ore to give molten iron, which trickles to the bottom of the furnace where it is collected. Fe2O3 + 3CO  2Fe + 3CO2 The limestone in the furnace decomposes, forming calcium oxide. This is a fluxing agent and combines with impurities to make slag, which floats on top of the molten iron and can be removed. CaO + SiO2  CaSiO3 Figure 1 Blast Furnace
  4. 4. Low Ash Metallurgical (LAM), hard coke is used in blast furnace for production of pig iron & in the production of cast iron. Low ash coke and low ash coal are widely used as a primary fuel where a uniform and high temperature is required. Widely used in the manufacture of Silico Manganese, Pig Iron. Composition: Fixed Carbon 83% Volatile Matter 2% Sulphur 1% Moisture 8-10% Ash Content 13-15% Size Greater than 60mm

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