Clean Coke Process

The liquid products from both the carbonization and hydrogenation stages of the process are combined for further processing to yield synthetic liquid fuels and a variety of other coal products. The gases are treated for sulfur and ammonia removal and are also capable of acting as a source of valuable materials other than the usual fuel gas. 

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A combination of coal beneficiation and relatively high-temperature roasting of the char is required for production of low-sulfur char from high-sulfur coal. When an equilibrium recycle gas composition (at about 70 psi H2) is used, char must be roasted at about 1400°F for periods of about 1 hr, as in the U.S. Steel Clean Coke process. Alternatively, the use of low-sulfur coal permits production of low-sulfur char under a wider range of hydrocarbonization conditions so that higher liquid yields, for example, may be obtained. 

The clean coke process (Figure 19.6) involves feeding oxidized clean coal into a fluidized bed reactor at temperatures up to 800°C (1470°F) whereupon the coal reacts to produce tar, gas, and low-sulfur char. Alternatively, the coal may be processed by noncatalytic hydrogenation at455°C-480°C (850°F-900°F) and pressures of up to 5000 psi hydrogen. 

Medium temperature 700-900 Lower tar yield compared to that obtained in low-temperature operation. Clean Coke Process oxidized clean coal (in fluid bed). 

Clean Coke A process for making coke and chemicals from high-sulfur coals. Developed by the United States Steel Corporation with support from the U.S. Department of Energy. See also carbonization. 

Reinluft A flue-gas desulfurization process using coke. The carbon acts as a catalyst for the oxidation of the sulfur dioxide to sulfur trioxide in the presence of water, and the sulfur trioxide is retained on the coke. The coke is regenerated in another vessel by heating with a hot gas stream, which reduces the sulfur trioxide back to sulfur dioxide and expels it for use in sulfuric acid manufacture. The key to this process is the inexpensive adsorbent. Developed by Reinluft GmbH and Chemiebau Dr. A. Zieren GmbH, and marketed as the Reinluft (Clean Air) Process. Four plants had been built by 1985. 

Flexicoking a modification of the fluid coking process insofar as the process also includes a gasifier adjoining the burner/regenerator to convert excess coke to a clean fuel gas. 

The final step is desulfurization. A number of processes have been developed which are suitable for removing H2S from coke-oven gas. These include using solutions of potassium carbonate, monoethanolamine (MEA), or ammonia to absorb the H2S. If ammonia solution is used as the absorbent, desulfurization is frequently combined with the ammonia removal step. Recovered H2S can be converted to elemental sulfur or sulftiric acid. The product remaining after all the above steps is cleaned coke-oven gas, some of which is used to heat the coke ovens and produce more coke with the rest going to the boiler house and/or the blast furnace for direct injection. 

Cracked residue is not solid coke but pitch. It makes the operation site clean and compact compared to other Coking processes, because pitch is handled as liquid in the process. 

To solve these problems, the development of an innovative coke-making process has been underway during the period 1994 to 2001 (SCOPE 21 project).96 The following technical items have been developed to realize more economical and clean coke plants.97... 

Abrasive cleaning Chemical processing Coal and coke handling... 

The carbon black (soot) produced in the partial combustion and electrical discharge processes is of rather small particle si2e and contains substantial amounts of higher (mostly aromatic) hydrocarbons which may render it hydrophobic, sticky, and difficult to remove by filtration. Electrostatic units, combined with water scmbbers, moving coke beds, and bag filters, are used for the removal of soot. The recovery is illustrated by the BASF separation and purification system (23). The bulk of the carbon in the reactor effluent is removed by a water scmbber (quencher). Residual carbon clean-up is by electrostatic filtering in the case of methane feedstock, and by coke particles if the feed is naphtha. Carbon in the quench water is concentrated by flotation, then burned. 

The passing of the Clean Air Act in the United Kingdom in 1956 resulted in a revival of interest in low temperature carbonization to produce a very reactive coke suitable for open fires. In the CoaUte process, the coal is heated at 600—650°C for 4 h in small retorts each hoi ding 6—7 metric tons (5). The Rexco process employed large internally heated retorts in which charges of 34 metric tons were heated to 700—750°C for 6 h, but is no longer in operation in the United Kingdom (6). 

Product separation for main fractionators is also often called black oil separation. Main fractionators are typically used for such operations as preflash separation, atmospheric crude, gas oil crude, vacuum preflash crude, vacuum crude, visbreaking, coking, and fluid catalytic cracking. In all these services the object is to recover clean, boiling range components from a black multicomponent mixture. But main fractionators are also used in hydrocracker downstream processing. This operation has a clean feed. Nevertheless, whenever you hear the term black oil, understand that what is really meant is main fractionator processing. 

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