Fuel grade petcoke is used as an energy source to produce steam in refinery boilers. It is also used to make carbon products like graphite electrodes and carbon brushes.
The quality of petroleum coke is largely determined by its microstructure, which can be assessed using X-ray diffraction analysis (the ratio between the average height Lc and the average diameter La) and scanning electron microscopy. With increasing concentration of polystyrene up to 15%, the structure shifts from a circular area anisotropy to a string approach.
There are two primary methods of processing petroleum coke: delayed and fluid. Delayed coking involves heating the coke to high temperatures over an extended period of time, while fluid coking uses a fluidized bed to suspend the coke particles in a hot gas stream. Both processes produce coke that can be used for energy production and in the production of various metals.
Calcined petroleum coke is a solid carbon material that has a low ash content and is often used in the production of aluminum and steel. It is also used as a fuel for power plants and in other industrial applications that require a low-sulfur, low-ash fuel source.
Regular testing of calcined petcoke is important to ensure its safety and usefulness. Tests include proximate analysis (moisture, ash volatile matter and fixed carbon) as well as ultimate analyses of sulfur, nitrogen, oxygen and trace metals. Graphitic analysis is also carried out to determine the microstrength of the calcined coke.
Petroleum coke, or petcoke, is a carbonaceous solid produced during the refining of crude oil. It is typically thermally treated into a crystalline, or calcined, form used in the manufacture of electrodes for steel and aluminum extraction. It has a high heat value and low ash content making it an excellent fuel for conventional cyclone, PC, or fluidized bed boilers. However, it is also highly sulfurous and volatile and can cause environmental and technical problems.
In a chemical engineering process called coking, heavy fractions of crude oil are heated in a reactor to break down long hydrocarbon chains into smaller ones. The result is the formation of coke. This process takes place in units called coker units. Delayed coking produces a variety of different grades of petroleum needle coke. The quality of these grades depends on the amount of polystyrene present in the feedstock. It has been shown that if the decanted heavy gasoil of catalytic cracking is mixed with polystyrene in a certain concentration range, it can be converted to a highly refined needle coke having an improved string-base anisotropic structure and a microstructure point of 6.2 corresponding to super-premium grade.
Petroleum coke is a solid byproduct of the refining process that has many uses. It is used to produce carbon anodes for the aluminum industry, graphite electrodes for steel production, and as fuel in power generation and cement kilns. It has a high carbon content and low ash content, which makes it an important raw material for producing metals and chemicals. It is also used as a substitute for coal in furnaces and boilers.
It is an energy source that produces less pollution than other fossil fuels and emits fewer greenhouse gases. However, it has some disadvantages, including the sulfur and heavy metal content of low grade petcoke and its dusty storage conditions.
The use of polystyrene in delayed coking can significantly improve the quality of calcined needle coke, reducing the particle size and improving the texture. X-ray diffraction analysis shows that as the concentration of polystyrene increases, the ratio of the height Lc to the diameter La decreases, moving further away from 1. This indicates a more elongated structure and improved pore size in the microstructure of the coke.
As crude oil gravities decrease and sulfur content increases the coke production rate of refiners is increasing. This is prompting more coking units to come on line.
The delayed coking process operates at elevated temperatures and is divided into a reactor fluidized bed section and a combustion section. In the reactor fluidized bed section the coke is thermally cracked to a range of gas and liquid products, including light ends.
In the combustion section steam enters the reaction chamber and mixes with the coke particles to initiate oxidation and carbonization reactions. The kneading/mixing action exposes new surfaces of the residuum mass to the vapor phase, accelerating the transfer of volatiles into the gas phase and resulting in more rapid carbonization. The combustion reaction also results in a lower coefficient of thermal expansion for the coke (see temperature chart). This improves quality indices and the potential to use the needle coke as boiler fuel. This is especially important because of the current focus on environmental compliance and the need to meet particulate and water specifications on naphtha and diesel streams heading for hydrotreaters.
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