PETCOKE

Petroleum CokePetroleum coke is a byproduct of the oil refining process. As refineries worldwide seek to operate more efficiently and extract more gasoline and other high-value fuels from each barrel of crude oil, a solid carbon material known as petcoke is produced. The chemical and physical characteristics of petcoke are a function of the crude oil and refining technology used by the refinery. Petcoke can be hard or relatively soft. Physically, petcoke can resemble large sponges with numerous pores, or it can resemble small spheres, ranging in size from a grain of sand to a large marble. Chemically, petcoke can include a variety of elements and metals in a wide range of concentrations. Depending on these physical and chemical characteristics, petcoke is typically used in either an energy application, as a source of British Thermal Units (BTUs), or in an industrial application, as a source of carbon Fuel grade petcoke represents roughly 80 percent of worldwide pet-coke production, and Oxbow is the worldwide leader in fuel-grade petcoke sourcing and sales, handling more than 11 million tons per year. Oxbow sources petcoke from every major refining company in the world, including ExxonMobil, Valero, Chevron, British Petroleum, PBF Energy, Phillips 66, Tesoro, Essar, Reliance and Shell.

In petroleum coker units, residual oils from other distillation processes used in petroleum refining are treated at a high temperature and pressure leaving the petcoke after driving off-gases and volatiles and separating off remaining light and heavy oils. These processes are termed “coking processes”, and most typically employ chemical engineering plant operations for the specific process of delayed coking.

A delayed coking unit. A schematic flow diagram of such a unit, where residual oil enters the process at the lower leftproceeds via pumps to the main fractionator (tall column at right), the residue of which, shown in green, is pumped via a furnace into the coke drums (two columns left and center) where the final carbonization takes place, at high temperature and pressure, in the presence of steam.
This coke can either be fuel grade (high in sulfur and metals) or anode grade (low in sulfur and metals). The raw coke directly out of the coker is often referred to as green coke. In this context, “green” means unprocessed. The further processing of green coke by calcining in a rotary kiln removes residual volatile hydrocarbons from the coke. The calcined petroleum coke can be further processed in an anode baking oven to produce anode coke of the desired shape and physical properties. The anodes are mainly used in the aluminum and steel industry.
Petcoke is over 80% carbon and emits 5% to 10% more carbon dioxide (CO₂) than coal on a per-unit-of-energy basis when it is burned. As petcoke has a higher energy content, petcoke emits between 30 and 80 percent more CO₂ than coal per unit of weight. The difference between coal and coke in CO₂ production per unit of energy produced depends upon the moisture in the coal, which increases the CO₂ per unit of energy – the heat of combustion – and on the volatile hydrocarbons in coal and coke, which decrease the CO₂ per unit of energy.

Petcoke, altered through the process of calcined which it is heated or refined raw coke eliminates much of the component of the resource. Usually petcoke when refined does not release heavy metals as volatiles or emissions.
Depending on the petroleum feedstock used, the composition of petcoke may vary but the main thing is that it is primarily carbon. Petcoke is primarily made up of carbon, when in pure form petcoke can weigh 98-99% which creates a carbon-based compound with the hydrogen filling in. In raw form, hydrogen can have a weight range of 3.0- 4.0%. Petcoke in its raw(green coke) nitrogen at 0.1- 0.5% and sulfur 0.2- 6.0% become emissions after the coke calcined.