Metallurgical coke

Most coal-tar chemicals are recovered from coproduct coke ovens. Since the primary product of the ovens is metallurgical coke, production of coal chemicals from this source is highly dependent on the level of activity in the steel industry. In past years most large coke producers operated thein own coproduct recovery processes. Because of the decline in the domestic steel industry, the recent trend is for independent refiners to coUect cmde coal tars and light oils from several producers and then separate the marketable products. 

In 1990, U.S. coke plants consumed 3.61 x 10 t of coal, or 4.4% of the total U.S. consumption of 8.12 x ICf t (6). Worldwide, roughly 400 coke oven batteries were in operation in 1988, consuming about 4.5 x 10 t of coal and producing 3.5 x 10 t metallurgical coke. Coke production is in a period of decline because of reduced demand for steel and increa sing use of technology for direct injection of coal into blast furnaces (7). The decline in coke production and trend away from recovery of coproducts is reflected in a 70—80% decline in volume of coal-tar chemicals since the 1970s. 

Coal carbonization to produce metallurgical coke involves much the same chemistry as pyrolysis. 

Purification of Carbide Acetylene. The purity of carbide acetylene depends largely on the quaUty of carbide employed and, to a much lesser degree, on the type of generator and its operation. Carbide quahty in turn is affected by the impurities in the raw materials used in carbide production, specifically, the purity of the metallurgical coke and the limestone from which the lime is produced. The nature and amounts of impurities in carbide acetylene are shown in Table 4. 

The furnace charge consists of 2iac—lead siater, metallurgical coke, and recirculating metallic drosses and flux. The charge cycle is fully automatic. Hoist... 

The demand for electrode binder pitch has grown as aluminium output has expanded and the requirement for aluminium smelting is now between 1.5 and 2 x 10 t /yr. In Japan pitch is used for mixing with coal for carbonization in coke ovens to make metallurgical coke. 

Metallurgical coke gives rise to ferrosiHcon, which in the Hquid phase is more dense than calcium carbide and tends to setde and penetrate the bottom of the furnace. After a lengthy operating period it may extend 30 cm or more below the taphole, eventually reaching the furnace shell where it causes hot spots requiring repair and replacement of the furnace refractory. 

The principal binder material, coal-tar pitch, is produced by the distillation of coal tar. Coal tar is obtained primarily as a by-product of the destmctive distillation of bituminous coal in coke ovens during the production of metallurgical coke. Petroleum pitch is used to a much lesser extent as a binder in carbon and graphite manufacture. Because of its low sohds content, petroleum pitch is used as an impregnant to strengthen carbon artifacts prior to graphitization. 

Coking coal is cleaned so that the coke ash content is not over 10%. An upper limit of 1—2 wt % sulfur is recommended for blast furnace coke. A high sulfur content causes steel (qv) to be brittle and difficult to roU. Some coal seams have coking properties suitable for metallurgical coke, but the high sulfur prevents that appHcation. Small amounts of phosphoms also make steel brittle, thus low phosphoms coals are needed for coke production, especially if the iron (qv) ore contains phosphoms. 

Material dried Ammonium sulfate Foundry sand Metallurgical coke... 

A U.S. Bureau of Mines suivev of 12 blast-furnace coke plants, whose capacity is 30 percent of the total production in the United States, provides an excellent picture of the acceptable chemical and physical properties of metallurgical coke. The ranges of properties are given in Table 27-2. 

Coal-based pitches are predommantly byproducts of metallurgical coke operations in recovery-type coke ovens. The volatile products from the coke oven are recovered and processed, in simplest terms, into gas, light oils, and tar. The quantity and character of the materials are influenced by the type of coal charge, the design of the cokmg equipment, and the temperature and time profile of carboni2ation. Table 1 shows a typical yield of products from the... 

This subsection provides an overview of the production of metallurgical coke and the associated by-products using intermittent horizontal retorts, as well as the pollution prevention practices. Coke and coke by-products, including coke oven... 

Hochofen, m. blast furnace, -anlage, /. blastfurnace plant, -betrieb, m. blast-furnace operation. gas, n. blast-furnace gas. -guss, m. blastfurnace cast iron, -koks, m. blastfurnace coke, metallurgical coke, -schlacke, /, blast-furnace slag, -schmelze, /, blastfurnace smelting, -verfahren, n. blastfurnace process. 

In practice resistivities between 0-08 and 0-29 ohm m have been recorded on coke breeze samples used in typical groundbeds. The effect of pressure on the measured value for resistivity of different coke samples has also been reported elsewhere ". The resistivity of bulk metallurgical coke is given as 0-024 ohm m with a slightly lower value of 0-020 ohm m at a pressure of 0-43 Nm whilst in calcined fluid petroleum coke at zero applied pressure the resistivity was 0 - 02 ohm m, which decreased to 0 - 002 ohm m when tested at an applied pressure of 1-31 MNm... 

The production of coke involves the heating of coal in the absence of air, called the carbonization or destructive distillation of coal. Carbonization, besides its main purpose of production of coke, also results in a coproduct called coke oven gas from which various liquid products such as tar, benzol, naphthalene, phenol, and anthracene are separated. There are two main types of carbonization based on the temperature to which the coal is heated in the absence of air. One type is low-temperature carbonization (LTC) the other is high-temperature carbonisation (HTC). Some features of LTC and HTC are listed in Table 1.28. The LTC Process is mainly carried out to manufacture domestic smokeless fuel. This presentation, however, concentrates on the HTC process by which metallurgical coke is produced. 

The production of coke from coal is an important activity in the ferrous metallurgical industries. While coal serves as the principal source for coke, a second source, namely, heavy petroleum fractions, is especially important for countries which have large petroleum resources and lack coal deposits. The properties of metallurgical coke are listed in Table 1.29. 

Fusinite macerals are generally held to be inert in coking, and in liquefaction, as will be seen below. In the production of metallurgical coke, they do not become fluid on heating, and... 

A notable feature of the Western Canadian coals is their low sulphur content (usually <0.5%) which tends, however, to be partly offset by higher mineral matter contents than are associated with the Eastern coals. As well, bituminous coals in the mountain belts are typically deficient in vitrinite, which often represents less than 50% of the coal "substance" and only occasionally reaches 70-75%, but this is compensated by the fact that their micrinites and semifusinites tend to be "reactive" constituents when the coals are carbonized. Notwithstanding their low fluidity (rarely >1000 dd/min), Western mvb coals therefore make excellent metallurgical cokes when carbonized in suitably proportioned blends. 

Coke. Metallurgical coke is obtained by high-temperature carbonization of coal. It is a poorly graphitized form of carbon it is mainly used in blast furnace for steel manufacture (see Iron, 5.10). 

Hi i-Temperature Coke (1173 to 1423 K or 1652 to 2102°F.) Essentially all coal-derived coke produced in the United States is high-temperature coke for metallurgical applications its production comprises nearly 5 percent of the total bituminous coal consumed in the United States. About 90 percent of this type of coke is made in slot-type by-product recovery ovens, and the rest is made in heat recovery ovens. Blast furnaces use about 90 percent of the production, the rest going mainly to foundries and gas plants. The ranges of chemical and physical properties of metallurgical coke used in the United States are given in TAle 24-3. Blast furnaces use about 90 percent of the production, the rest going mainly to foundries and gas plants. 

TABLE 24-3 Chemical and Physical Properties of Metallurgical Cokes Used in the United States... 

Pyrolysis In pyrolysis, coal is heated in the absence of oxygen to drive off volatile components, leaving behind a solid residue enriched in carbon and known as char or coke. Most coal pyrolysis operations are for the purpose of producing metallurgical coke, with the liquids... 

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