Petroleum coke, or petcoke, is the common name for this valuable carbon-rich byproduct of oil refining. With a high carbon content and high heating value, petroleum coke contains lower moisture and is an effective fuel as well as an industrial material in many sectors. It can be used as fuel in the generation of power and cement industries aluminum production and other metallurgical processes. For a better understanding of this industrial material join Advanced Management in Oil and Gas Industry training course offered by British Academy for Training and Development.
Petroleum coke is a solid, carbon-rich by-product of the coking units in oil refining. It is the residue left during the thermal decomposition process used to convert heavy residues into lighter, more valuable products from crude oil. It is said to have a very high carbon content with relatively low ash compared to traditional fuels; it can be said that it is efficient and cheap compared to other traditional fuels, such as coal, mainly in energy-intensive industries or where it serves as an input for various production processes.
The manufacture of coke is delayed coking, fluid coking, and flexi-coking. All the above-mentioned processes are utilized with the prime objective of cracking heavy residues of oil with thermal cracking at a high temperature in a gaseous as well as liquid condition along with some solid coke of production. In each process, different forms of petcoke with structure, properties, and different applications are attained.
It is one of the most significant applications used for the preparation of pet coke. In this process, heavy oil residues are pumped into a coking drum where they are heated to very high temperatures, about 500°C or higher, for a considerable period. The thermal cracking in the drum breaks the heavy hydrocarbons and produces solid coke at the bottom of the drum while the lighter hydrocarbons come out as gases or liquids from the drum. The petroleum coke calcination has a porous structure and is normally used in fuel-grade applications.
Fluid and flexi-coking are more advanced processes using a fluidized bed reactor. In this process, oil residues are fed into the presence of fluidized hot coke particles. They are generally faster than delayed coking and produce fluid coke, which has a uniform particle size compared to sponge coke. Flexi-coking also includes a gasification stage, which may convert the by-product gases into valuable hydrogen or low-Btu fuel gases. Delayed and fluid coking are two essential steps towards maximizing yield from heavy oil residues, which are usually considered waste and is changed into usable fuel and industrial products.
Coke types can be broadly classified into a variety of categories based on the types, characteristics, and applications in the industry. There are some major classifications in petcoke as well, such as fuel-grade coke, calcined petroleum coke (CPC), needle coke, sponge coke, and shot coke.
The most common and affordable is the fuel grade. Fuel-grade petcoke is mainly used in combustion as fuel for generation, cement kilns, and any industries that consume high energies.
Generally, since fuel-grade coke contains a lot of sulfur and metal impurities, it is not used much in applications where there are requirements to achieve purity. However, features: extremely high in impurities especially on metals; extremely high level of metals impurities but sulfur and moderate. Cement and power industries furnaces are used; however, most other applications such as anode for smelter for primary steel.
Calcined petroleum coke, abbreviated as CPC, is produced by baking raw petroleum coke, called green coke, to remove of volatile compounds and moisture present. This baking increases the carbon content in the coke, and as such, CPC finds an application in the aluminum smelting industry, and the steel production industry, that requires a high-purity carbon material.
Needle coke has a needle-like structure crystalline, with little or no sulfur and more electrical conductivity. Such petcoke is the necessary one to be used to manufacture graphite electrodes used by steel companies in the manufacture of electric arc furnaces.
Characteristic: Low-sulfur, highly conducting electrically, needle coke.
Use Graphite electrode of arc furnaces on which it is applied as electric furnaces to process steel products.
Sponge coke. It is produced through delayed coking, with a very porous structure. It can be used in fuel grade or as feedstock to manufacture calcined coke.
Properties: Moderate amount of sulfur. Sponge texture
Products: Fuel grades and feedstocks for manufacturing calcined coke
Shot coke is produced in the process as small, hard spherical pellets. It is less favored because it is harder to handle. It is also used in applications wherein its hard nature and high sulfur content are not a problem.
Characteristics: High sulfur, spherical shape, hard structure
Applications: Not much industrial use as fuel, mostly in specific applications because of the handling problems
The utility and coke processing are directly related to its specific chemical composition and physical properties, which differ considerably with the type and process of production. Some of the common specifications and quality parameters used for making coke material are as follows:
Carbon Content: Carbon content in petcoke may range between 80 and 99%, depending upon the type. Calcined coke and needle coke tend to have the highest carbon content, which is significant for the aluminum and steel industries.
Sulfur Content: Sulfur in petcoke is quite variable, ranging from under 1% for such high-grade types as needle coke to greater than 6% for fuel-grade coke. Sulfur is an important consideration since sulfur when burned creates greater emissions.
Volatile Matter: Fuel-grade coke typically contains volatile matter, while calcined coke is processed further to minimize volatility. These lower volatiles are important for high-purity uses.
Moisture Content: Petcoke has a relatively low moisture content, which is less than 10%, and hence, contributes to its high heating value and stability as a fuel.
Ash Content: The ash content must be kept low for its use in aluminum and steel production processes, where impurities can interfere with the quality of the final product.
The different forms and grades of petcoke can be applied to various types of industries. Some of the major industries that use petcoke are as follows:
Power Generation and Cement Manufacturing: Fuel-grade petcoke is usually used as a primary fuel source in cement kilns and power plants because it contains a lot of carbon, is cheap, and can be relied upon as a fuel.
Aluminum Production: Calcined petroleum coke is a crucial part of the production of aluminum smelting anodes. High carbon purity with low sulfur content makes it suitable for this process.
Steel Production: Needle coke is used to manufacture graphite electrodes, which are needed for electric arc furnaces in steel production due to high conductivity and resistance to very high temperatures.
Petroleum coke, though valuable both economically and functionally, poses significant environmental problems because of the high levels of sulfur and carbon content:
The high sulfur content of fuel-grade petcoke: in combustion, it is passed into SO2 and creates air and acid rain pollution. Industry frequently mixes such fuels with lesser sulfurous fuels or utilizes desulfurization techniques.
Greenhouse Gas Emissions: Petcoke combustion passes into the atmosphere CO2 as a powerful greenhouse gas. More and more regulatory bodies set stringent CO2 emission limits that encourage industries to opt for less polluting combustion technology.
Heavy Metal Contamination: Some petcoke contains heavy metals like nickel and vanadium, which pose complications in handling and final disposal. Ash residue in burning petcoke requires hazardous waste treatment, more so when heavy metals exist.
Minimization strategies for the harmful impact on the environment include clean-burning technologies, fuel blending, and strict environmental policies. For the most part, businesses using pet coke are committed to utilizing systems controlling emissions and the removal of air pollutants to achieve sustainability and diminish their ecological footprint.
Petroleum coke is an oil refinery byproduct with many applications in various industries. Petroleum coke has emerged as a preferred option because of its economic fuel and raw material characteristics in power generation, cement manufacturing, aluminum production, and steel making. Make sure to join training courses in Washington by British Academy for Training and Development to learn more about the production and uses of petroleum coke.