Learn about petroleum coke-２ (classification based on shape)

There are at least four basic types of petroleum coke:

needle coke, honeycomb coke, sponge coke and shot coke.

Different types of petroleum coke have different microstructures due to differences in operating variables and nature of feedstock. Significant differences are also to be observed in the properties of the different types of coke, particularly ash and volatile matter contents.

1,Needle coke, also called acicular coke, is a highly crystalline petroleum coke used in the production of electrodes for the steel and aluminium industries and is particularly valuable because the electrodes must be replaced regularly. Needle coke is produced exclusively from either fluid catalytic cracking (FCC) decant oil or coal tar pitch.

2,Honeycomb coke is an intermediate coke, with ellipsoidal pores that are uniformly distributed. Compared to needle coke, honeycomb coke has a lower coefficient of thermal expansion and a lower electrical conductivity.

3,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.

4,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.

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