Petroleum coke, or petcoke, is the solid carbonaceous residue produced from thermal processing of petroleum residua (the delayed coking process). Coke has a very low volatile content, high carbon content, and can contain significant amounts of sulfur and nitrogen. The acicular structure of petroleum coke produces excellent electrical conductivity and thermal conductivity, making it an attractive fuel for the forging industry.
Fuel grade petcoke can be used to produce electricity in cyclone and fluidized bed power plants. It has a very low ash content and is an excellent substitute for coal in these systems. Fuel grade petcoke is also used in cement production and as a raw material for the manufacture of graphite electrodes for aluminium smelting.
Graphite fossil oil coke (also known as green or raw petcoke) is a solid with a distinctive acicular texture that can be ground to a very fine particle size for use in the forging industry. This material has the advantages of low sulfur, nitrogen and ash content; it is very thermally conductive, which improves metal-to-metal adhesion. Typical application include pre-baked anode for electrolytic aluminum, carbon addictive used in steel production and graphite electrodes in the aluminium smelting process.
The sulphur and heavy metal contents of petroleum coke are dependent on the type and production process. The chemical formula of petroleum coke is CxHgOsNt and it consists mainly of carbon, with small quantities of hydrogen, oxygen, sulfur and other elements.
Due to its lower sulphur and heavy metal content, high quality calcined petcoke or graphite fossil oil coke can be used as anode material for aluminium smelting. Graphite petcoke has an excellent chemical stability in the strong corrosive environment of the aluminium electrolytic cell, and it can help to reduce power loss and increase electrolytic efficiency.
A very important factor when determining whether or not to use petroleum coke in a smelter is the concentration of vanadium and nickel, which are detrimental to smelting. Concentrations of these deleterious elements are determined by the source crude oil from which the coke is made. Generally, "sweet" crude oils result in lower concentrations of these contaminants.
The gasification of petroleum coke and other refinery non-volatile waste streams (atmospheric residuum, vacuum residuum, visbreaker tar, deasphalter pitch) results in production of power, steam and hydrogen for cleaner transportation fuels. Gasification is a relatively energy-intensive process that requires a high degree of control to maintain furnace efficiencies and availability.
A key issue in deciding whether or not to gasify petroleum coke is the ability of the fuel to generate sufficient power to justify the capital investment required for the gasification equipment. Several important factors must be considered in this analysis, including the level of coke ash in the resulting gas, and the ability to manage ash chemistry for optimized slagging performance and air emissions control. The sulphur content of the feed is also a factor, since high levels can produce significant quantities of sulphur dioxide and other pollutants in combustion.
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