Basic Knowledge Of Petroleum Coke
Petroleum coke (often abbreviated pet coke or petcoke) is a carbonaceous solid delivered petroleum refinery china website from oil refinery coker units or other cracking processes. Coking processes that may be employed for making petcoke include contact coking, fluid coking, flexicoking and delayed coking. Other coke has traditionally been delivered from coal.
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 might be further processed in an anode baking oven in order to provide anode coke of the desired shape and physical properties. The anodes are mainly used in the aluminium and steel industry.
Petcoke is over 90 percent carbon and emits 5 to 10 percent more carbon dioxide (CO2) than coal on a per-unit-of-energy basis when it is burned. As petcoke has the next 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 energy produced depends upon the moisture within the coal (increases the CO2 per unit energy – heat of combustion) and volatile hydrocarbon in coal and coke (decrease the CO2 per unit energy).
Sorts of petroleum coke
There are not less than four basic kinds of petroleum coke, namely, needle coke, honeycomb coke, sponge coke and shot coke. Various kinds of petroleum coke have different microstructures on account of differences in operating variables and nature of feedstock. Significant differences are also to be observed within the properties of the various kinds of coke, particularly ash and volatile matter contents.
Needle coke, also called acicular coke, is a highly crystalline petroleum coke used within the production of electrodes for the steel and aluminium industries and is especially valuable because the electrodes must be replaced regularly. Needle coke is produced exclusively from either FCC decant oil or coal tar pitch.
Honeycomb coke is an intermediate coke, with ellipsoidal pores which can be uniformly distributed. Compared to needle coke, honeycomb coke has a lower coefficient of thermal expansion and a lower electrical conductivity.
Fuel grade coke
Fuel grade coke is classified as either sponge coke or shot coke morphology. While oil refiners have been producing coke for well over 100 years, the mechanisms that cause sponge coke or shot coke to form usually are not well understood and can’t be accurately predicted. Generally, lower temperatures and better pressures promote sponge coke formation. Additionally, the amount of heptane insolubles present, and fraction of light components in the coker feed contribute.
While its high heat and low ash content make it an honest fuel for power generation in coal fired boilers, petroleum coke is high in sulfur and low in volatile content, and this poses environmental (and technical) problems with its combustion. To fulfill current North American emissions standards, some type of sulfur capture is required, a typical choice of sulfur recovering unit for burning petroleum coke is the SNOX Flue gas desulfurisation technology, which is based on the well-known WSA Process. Fluidized bed combustion is commonly used to burn petroleum coke. Gasification is increasingly used with this feedstock (often using gasifiers placed in the refineries themselves).
Calcined petroleum coke
Calcined petroleum coke (CPC) is the product from calcining petroleum coke. This coke is the product of the coker unit in a crude oil refinery. The calcined petroleum coke is used to make anodes for the aluminium, steel and titanium smelting industry. The green coke will need to have sufficiently low metals content in order to be used as anode material. Green coke with this low metals content is known as anode grade coke. The green coke with too high metals content is not going to be calcined and is used for burning. This green coke is known as fuel grade coke.
Desulfurization of petroleum refinery china website petcoke
A high sulfur content in petcoke reduces its market value and may prevent its use as fuel attributable to restrictions on sulfur oxides emissions for environmental reasons. Methods have thus been proposed to cut back or eliminate the sulfur content of petcoke. Most of them involve the desorption of the inorganic sulfur present in the pores or surface of the coke, and the partition and removal of the organic sulfur attached to the aromatic carbon skeleton.
Potential petcoke desulfurization techniques might be classified as follows:
- Solvent extraction
Desulfurization in an oxidizing atmosphere
Desulfurization in an atmosphere of sulfur-bearing gas
Desulfurization in an atmosphere of hydrocarbon gases
As of 2011 there was no commercial process available to desulfurize petcoke.
Storage, disposal, and sale
Nearly pure carbon, petcoke is a potent source of carbon dioxide if burned.
Petroleum coke could also be stored in a pile near an oil refinery pending sale. One example, as of 2013, was the large stockpile owned by Koch Carbon near the Detroit River which was produced by a Marathon Petroleum refinery in Detroit which began refining bitumen from the oil sands of Alberta in November 2012. Large stockpiles of petcoke also existed in Canada as of 2013. China and Mexico were markets for petcoke exported from California for use as fuel. As of 2013 the EPA was declining permits to make use of petcoke as fuel within petroleum refinery china website the United States but markets existed in India and Latin America where it was used to fuel cement manufacture. As of 2013 Oxbow Corporation, owned by William I. Koch, was a serious dealer in petcoke, selling 11 million tons annually.
Petroleum coke is sometimes a source of fine dust, which might get through the filtering technique of the human airway and lodge within the lungs. Once these small dust particles lodge within the lungs they may cause serious health problems.
Petroleum coke can contain vanadium, a toxic metal, in sufficient quantities to poison people. Vanadium was found in the dust, collected in occupied dwellings near the petroleum coke stored next to the Detroit River. Vanadium is toxic in tiny quantities, 0.8 micrograms per cubic meter of air, according to the EPA.