Thermal cracking is a useful step in the petroleum refining which allows for the “seemingly useless” vacuum distillation residue (VDR) to be converted into distillate fuels and coke. In today’s petroleum refinery, thermal cracking is primarily used for the production of coke. The two processes used to create this coke are delayed coking and fluid coking. These processes are operated at relatively low pressures (just slightly above atmospheric) and at a temperatures just above 900 degrees Fahrenheit. Depending on the duration of these processes, petroleum coke can be made into fuel-grade coke or, after further processing, anode-grade coke which can be used in batteries. In 2012, coking exports accounted for 19% of our nation’s petroleum exports. [1]

However, thermal cracking of petroleum fuels wasn’t always primarily used for the production of coke. In 1913, thermal cracking was used for means of distillate fuel production. [2] Since the “gasoline boom” was occurring during this time, refineries had to find ways to compensate for the increasing demand of fuel. This thermal cracking process also utilized low pressures and high temperature to break apart heavy fuel, otherwise known as visbreaking, in order to make the smaller chained gasoline molecules. The problem facing thermal cracking in gasoline production is the resulting low octane number. In 1930, thermal cracking was replaced by catalytic cracking because of its higher gasoline yield and higher resulting octane numbers. [2]

Sources:
1. U.S. Energy Information Administration – EIA – Independent Statistics and Analysis. (n.d.). Coking is a refinery process that produces 19% of finished petroleum product exports. Retrieved June 28, 2014, from http://www.eia.gov/todayinenergy/detail.cfm?id=9731
2. Petroleum Refining Process. (n.d.). Petroleum Refining Process. Retrieved June 28, 2014, from http://www.ilo.org/oshenc/part-xii/oil-and-natural-gas/item/384-petroleum-refining-process