Petrol coke or petcoke is a black, solid carbon material produced as a by-product in the oil refining process. Its unique physical and chemical properties make it an essential raw material in the metallurgical, graphite, and cement industries. Although it contains a high amount of carbon, the material is also rich with other elements, such as oxygen, nitrogen and trace metals. In order to maintain consistency in performance and ensure compliance with environmental laws, it is essential that testing and quality controls are performed.
Distillation and cracking in oil refineries are used to produce a range of petroleum derivatives. Most well-known is gasoline. But the petroleum refinery industry produces a wide range of other fuels and petrochemicals like jet fuel, asphaltenes and paraffin waxes.
The process of refining petroleum is extremely complex. Crude petroleum is subjected to a series distillation and cracking reaction to separate heavy components like residual crude oil and vacuum hydrocarbons. Asphaltenes and tars are also separated. These heavy crude oils are then subjected a delayed coking reaction (typically at temperatures between 480°C and 550°C). This delayed coking process produces a product rich in carbon called petroleum coke.
This solid black material is high in carbon and also contains metals, such as iron, nickel, vanadium, as well other chemicals. Depending on the type of crude oil and production process, petcoke can vary in composition with different levels of volatile matter, volatiles, ash, and fixed carbon as well as particle size, Hardgrove Grindability Index, and density.
Until recently, much of the petroleum coke available in the US was used for power generation and in cement kilns. Its high sulfur and volatile content necessitates blending with coal in order to maintain ignition stability and combustion stability. However, it's low gross calorific values result in lower heating value compared to fossils fuels like bituminous coke.
Anode materials in integrated steel plants are made from high-quality calcined coke. The anode is better able to resist corrosion in the electrolytic environment because of its uniform size and low impurities. The quality of calcined carbon is also very important, since its high content of carbon increases the efficiency of the plant. Lower volatiles reduce emissions and costs.
Testing for sulphur in petroleum coke and trace metals are common and crucial. High levels of metals or sulphur can cause damage to equipment or the environment. For determining the elemental content in petcoke and coal, there are several ASTM and ISO tests. However, all of them require extensive sample preparation using specialist gases. This can increase the time between sample preparation and results, as well as reduce the sensitivity.
Petroleum coke's macroporosity can also be determined. It is also possible to test for its microporosity and isotropy. These parameters are crucial in determining mechanical properties which can have an impact on handling, storage and combustion efficiency.
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