In gritty northwest Indiana, oil refineries and steel mills still loom large over working-class neighborhoods. Freight trains rumble by. Smokestacks spew pollution into the air.
Petroleum coke is a byproduct of the oil refining process. It is used as a cost-effective fuel in industrial processes, including making carbon products such as graphite electrodes.
During this stage, petroleum coke is tested to make sure it doesn’t contain any contaminants. This testing includes determining its metal, sulfur and carbon content. It’s important to know how much of each is in petcoke because these contaminants can damage industrial equipment and lead to higher emissions of greenhouse gases.
It is generally known that raw petroleum coke has a limited adsorption capacity because it has a tight crystal structure and high crystalline density. However, a new method has been developed to purify it and enhance its adsorption properties. The process involves sodium carbonate roasting, adding alkaline matter (such as potassium hydroxide or a mixture of them), and treating it for a specified time.
Afterward, the adsorption capacity of the resulting activated petroleum coke has been significantly enhanced. The specific surface area of the sample reached 59.0 m2 g-1, and the tar and hydrocarbons covering or blocking the micropores of the material were removed.
The calcination of petroleum coke is an essential step to remove any contaminants. It is particularly important to avoid any volatile constituents such as polycyclic aromatic hydrocarbons (PAHs) and leachable metals like nickel and vanadium.
This is typically done in a fluidized bed calciner with electrodes and a gas cleaning system. Most of these units are also integrated with a waste heat energy recovery system to improve project economics.
After being calcined, the resulting petcoke slurry is pumped through a pipeline where it adsorbs any dissolved organics. The resulting treated water can then be recycled for operations needs or can be evaluated for release into the environment.
This is often accompanied by further processing steps to produce a variety of high-purity carbon products such as graphite, metal carburizers and others. This can be accomplished by a variety of methods including but not limited to extrusion, granulation and agglomeration. The resultant compacts, which may be in the form of pellets, extrusions, briquettes, cylinders or structural blocks, have a variety of useful applications.
A petroleum coke refining process known as delayed coking converts heavy residual oil streams and coke residues such as vacuum resid, visbreaker tar and deasphalter pitch to lighter products used for transportation fuels. The process requires filtering and quenching to separate the coke from contaminants.
Refineries may use a steam-injection method to strip the light oils from the coke. A steam-injection system also helps to cool the coke before it is shipped to a storage area where it can be burned in boilers and furnaces.
As a solid fuel, petcoke burns very slowly and produces less air pollution than coal when burned. However, the high levels of sulfur and heavy metals present in some petcokes raise concerns about how they affect the environment when burned or stored during storage. Testing petcoke is important to make sure that metal and sulfur concentrations are low enough to protect industrial equipment and the environment from damage. Evoqua Water Technologies was recently contacted by a California business that accumulated, stored and shipped petcoke. Their stored petcoke contaminated rainwater with nickel and vanadium at levels above discharge limits.
Petroleum coke is a solid carbon-rich byproduct of oil refining. It is used in a variety of industrial applications including power generation, cement production and metal smelting. It is also used to produce liquid fuels, such as jet and diesel fuel. In order to be used in these industrial applications, the petcoke must undergo additional steps to remove any contaminants.
To prepare petroleum coke for use as a solid fuel, it must be mixed with an agglutinating carbonaceous binder. The binder is typically asphalt, coal tar, gilsonite or pitch. Compaction can be accomplished under pressures ranging from 10 psi to 24,000 psi depending on the type of binder and desired physical properties.
Mixing is especially important for smelters that use both shaft and rotary cokes as the different porosity and bulk density profiles can cause large variations in fraction preparation, anode density and pitch level. The blending process can minimize these issues and improve overall quality and performance of the smelter operation.
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