At present, the widely used carburizing agent -- petroleum coke

Petroleum coke is a widely used carburizer at present.

Petroleum coke is a by-product of refined crude oil, and the residual oil and petroleum asphalt obtained by pressure distillation or vacuum distillation of crude oil can be used as raw materials for the production of petroleum coke, and then the raw petroleum coke is obtained after coking. The production of raw petroleum coke is about less than 5 percent of the crude oil used. The annual production of raw petroleum coke in the United States is about 30 million tons. The impurity content in raw petroleum coke is high, can not be directly used as a carburizer, must be calcined first.

There are many kinds of raw petroleum coke, such as spongy, acicular, granular and fluid.

Spongy petroleum coke is produced by delayed coking process, because of the high content of sulfur and metal, it is usually used as a calcined fuel, but also as a raw material for calcined petroleum coke. Calcined sponge coke is mainly used for aluminum production and as a carburizer.

Needle petroleum coke is produced by delayed coking process with high aromatic hydrocarbon content and low impurity content. This coke has a needle-like structure that is easy to break, sometimes called graphite coke, which is mainly used to make graphite electrodes after calcination.

Granular petroleum coke is hard granular, is made from raw materials with high content of sulfur and asphaltene by delayed coking process, and is mainly used as fuel.

Fluid petroleum coke, which is produced by continuous coking in a fluid bed, has fine granular shape, non-directional structure, high sulfur content and low volatile content.

Petroleum coke is calcined to remove sulfur, moisture, and volatiles. Calcination of raw petroleum coke at 1200 ~ 1350℃ can make it become basically pure carbon.

The largest user of calcined petroleum coke is aluminum, 70% of which is used to make the anode for the reduction of bauxite. About 6% of the calcined petroleum coke produced in the United States is used as a cast iron carburizer.