Petroleum coke or generally referred as petcoke is one of many valued products produced during the oil refining process. In petroleum refining world crude oil is processed into gasoline, diesel fuel, jet fuel, lubricating oils and waxes, leaving some residual crude that usually undergoes additional processing. The crude residue may be further refined (depending from refinery configuration) by a process known as Coking to produce incremental transportation fuels as well as petroleum coke, which has a variety of uses as an alternative, cost-effective fuel. Although petroleum coke is in many cases considerate a refinery by-product and not a well-liked material, it is nevertheless an important industrial product which finds wide acceptance in many metallurgical and chemical process. It’s most important use is in the aluminum industry where this product after a calcination process is used in the manufacture of anodes for the aluminum’s refining potlines.
Uses of Petroleum Coke
Worldwide petroleum refinery production of petroleum coke is typically divided in two types – Fuel Grade and Anode grade (generally referred as Green Coke) and its used as a source of energy or as a source of carbon for
industrial applications. Fuel grade petcoke represents nearly 75-80 percent of the global refinery petcoke production is used as a source of fuel for cement kilns and electric power plants and other niche markets. The remaining 20-25 percent is generally considerate as Anode Grade and its typically processed into Calcined petroleum coke grade which has the highest carbon purity and is used to manufacture energy, as well as in the aluminum, graphite electrode, titanium dioxide and other carbon consuming industries. The steel industry also uses calcined coke as carbon raisers.
Quality of Petroleum coke
In petroleum refinery’s world, there are three types of Coking processes during normal commercial operation. Generally, they are referred as Delayed Coking, Fluid Coking and Flexicoking.
The cokes from each process differ significantly with respect to their end products and with the advent of Coker technology the source of petcoke produced is widely used for a variety of applications.
The most common types of coke produced are called Sponge coke, Needle coke, Fluid coke and Shot coke.
Sponge coke – is produced in a delayed Coker where residuum such as atmospheric reduced crude or vacuum residue is rapidly heated in a furnace and confined in a reaction zone or coke drum under specific operating temperature and coked drum pressure condition until the feed is converted into gas, oil stream and Petcoke. The petcoke formed under normal process and typical residue feed has a sponge structure, hence the name Sponge Coke.
Depending on the impurity level, typically metals and Sulfur contents Sponge Coke is used for fuel or other industrial processes.
Needle Coke- is a special application on the delayed coking process using special feedstocks which are highly aromatic, and have low levels of asphaltene and impurities. Due to a specific molecule structure, needle coke
has a more crystalline structure and less cross-linking. Needle Coke is typically used in the production of carbon and graphite electrodes as well other specialty niche products.
Shot Coke – is another result of a product from delayed coke operation. It is typically a hard pebble-like material and is produced when the Coker unit and sponge coke is operated in such way as to maximize the quality and the quantity of liquid products or non-coke products. When processing high asphaltene and high Sulphur feeds, the refineries goal is to maximize production of liquid products and to minimize the quantity of coke produced.
Under these conditions, shot coke may be formed and the percentage of shot will vary depending of numbers of factors like recycle ratio, operating pressure, temperature and feedstock composition and general Coker operating
conditions. As the name indicates, shot coke is spheroid in shape, it is a hard product with low HGI index, and ranges in sizes form a small pebble size to a basketball size.