Metallurgical coke, also known as “Met” coke, is a carbon material manufactured by the “destructive distillation” of various blends of bituminous coal. Bituminous coal is a soft, medium grade coal that contains a high percentage of volatile components. Destructive distillation is performed in “coke batteries” which are banks of large enclosed kilns. Once the kilns are loaded, they are heated to approximately 1000 C in the absence of air. During the heat cycle the volatile components of the coal are released and the solid coal goes through a partial melt and subsequent re-solidification to a non-melting carbon. Volatile components include coal tar, ammonia, and literally dozens of other “products of decomposition”. Most volatile components are reclaimed or recycled.
Petroleum coke is a manufactured carbon product produced at a limited number of oil refineries. Petroleum coke results from the thermal processing of residual oil, which has been cracked or otherwise processed to remove low boiling fractions. Coke is made by heat-treating the residual oil (more accurately described as tar) to a temperature high enough to result in its polymerization to form a non-melting solid carbon. The process is performed to maximize the yield of lower molecular weight compounds derived from crude oil feedstocks.
Coke, as it is removed from the coking process, is referred to as “green coke”. Green petroleum coke contains approximately 15-20% residual hydrocarbon materials. These hydrocarbons are those compounds that do not polymerize in the coking process and cannot be removed from the coke substrate due to process limitations. Calcined petroleum coke (CPC) is manufactured by heating green coke to approximately 1300-1400 C in a rotary kiln. This effects the removal of virtually all residual hydrocarbons and moisture. The final calcined product contains only a trace of volatile matter, and from 0.3 to 6% sulfur depending on the petroleum base used to make the coke.