Direct coking

After hot water extraction, crude bitumen is upgraded into synthetic oil fractions by either delayed coking or fluidized coking. A representative product yield from direct coking of Athabasca oil sand bitumen is provided in TABLE 12-7. 

TABLE 12-7. Product Yield from Direct Coking of Athabasca Bitumen... 

In this way the useful petroleum fractions are recovered from the surface or near surface exposures of tar sand by the two currently operating hot water process extraction plants in Alberta. The production of synthetic crude oil by Alberta tar sand processors has risen from 28 million barrels (ca. 4 million tonnes) in 1978, to 77.3 million barrels (ca. 10.5 million tonnes) in 2003, which now supplies about 13% of Canada s current crude oil requirements [48]. Other processes for bitumen recovery from minable sands, such as preliminary partial sand removal with the help of cold water, followed by direct coking of the whole of the bitumen/solid residue, and solvent extraction methods have both been tested but are apparently not attractive for commercial development [49]. 

Two basic methods of approach can be undertaken to determine the suitability of a coal or coking blend (1) indirect coking pressure measurements at laboratory scale and (2) direct coking pressure measurements by larger-scale tests, using a few hundreds of kilograms of coal while trying to reproduce industrial conditions. 

Intermediate feedstock preparation processes such as direct hydroconversion of vacuum residues, solvent deasphalting, improved coking will also make their appearance. 

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. 

Acetylene traditionally has been made from coal (coke) via the calcium carbide process. However, laboratory and bench-scale experiments have demonstrated the technical feasibiUty of producing the acetylene by the direct pyrolysis of coal. Researchers in Great Britain (24,28), India (25), and Japan (27) reported appreciable yields of acetylene from the pyrolysis of coal in a hydrogen-enhanced argon plasma. In subsequent work (29), it was shown that the yields could be dramatically increased through the use of a pure hydrogen plasma. 

When magnesium oxide is chlorinated in the presence of powdered coke or coal (qv), anhydrous magnesium chloride is formed. In the production of magnesium metal, briquettes containing CaCl2, KCl, NaCl, MgO, and carbon are chlorinated at a temperature such that the electrolyte or cell melt collects at the bottom of the chlorinator, enabling the Hquid to be transferred directly to the electrolytic cells. 

Direct ammonolysis involving dehydratioa catalysts is geaerahy ma at higher temperatures (300—500°C) and at about the same pressure as reductive ammonolysis. Many catalysts are active, including aluminas, siUca, titanium dioxide [13463-67-7], and aluminum phosphate [7784-30-7] (41—43). Yields are acceptable (>80%), and coking and nitrile formation are negligible. However, Htfle control is possible over the composition of the mixture of primary and secondary amines that can be obtained. 

Manufacture. An extensive technology was developed initially ia the 1930s for isolation of ammonium thiocyanate from coke-oven gases, but this technology is no longer practiced ia the United States (372). However, such thiocyanate recovery processes are used iadustrially ia Europe. Likewise, the direct sulfurization of cyanides to thiocyanates is not practiced commercially ia the United States. The principal route used ia the United States is the reaction of carbon disulfide with aqueous ammonia, which proceeds by way of ammonium dithiocarbamate [513-74-6]. Upon heatiag, the ammonium dithiocarbamate decomposes to ammonium thiocyanate and hydrogen sulfide. 

Bitumen is a hydrogen-deficient oil that is upgraded by carbon removal (coking) or hydrogen addition (hydrocrackiag) (2,4). There are two methods by which bitumen conversion can be achieved by direct heating of mined tar sand and by thermal decomposition of separated bitumen. The latter is the method used commercially, but the former has potential for commercialisation (see Fuels, SYNTHETIC). 

Thus the amount of heat that must be produced by burning coke ia the regenerator is set by the heat balance requirements and not directly set by the coke-making tendencies of the catalyst used ia the catalytic cracker or by the coking tendencies of the feed. Indirectly, these tendencies may cause the cracker operator to change some of the heat-balance elements, such as the amount of heat removed by a catalyst cooler or the amount put iato the system with the feed, which would then change the amount of heat needed from coke burning. 

Coke on the catalyst is often referred to as delta coke (AC), the coke content of the spent catalyst minus the coke content of the regenerated catalyst. Delta coke directly influences the regenerator temperature and controls the catalyst circulation rate in the FCCU, thereby controlling the ratio of catalyst hydrocarbon feed (cat-to-od ratio, or C/O). The coke yield as a fraction of feed Cpis related to delta coke through the C/O ratio as ... 

Fig. 7. Primary functions of coke in a blast furnace showing the various furnace zones where arrows indicate direction of gas flow. The term size consist...

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