A delayed coker is a type of
coker whose process consists of heating a residual oil feed to its
thermal cracking temperature in a
furnace
A furnace is a structure in which heat is produced with the help of combustion.
Furnace may also refer to:
Appliances Buildings
* Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings
* Boiler, used t ...
with multiple parallel passes. This cracks the heavy, long chain
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
molecules of the residual oil into coker
gas oil and
petroleum coke
Petroleum coke, abbreviated coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracki ...
.
Delayed coking is one of the
unit processes A ''unit process'' is one or more grouped operations in a manufacturing system that can be defined and separated from others.
In life-cycle assessment (LCA) and ISO 14040, a unit process is defined as "smallest element considered in the life cycle ...
used in many
oil refineries
An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefie ...
. The adjacent photograph depicts a delayed coking unit with 4 drums. However, larger units have tandem pairs of drums, some with as many as 8 drums, each of which may have diameters of up to 10
meters and overall heights of up to 43 meters.
The yield of coke from the delayed coking process ranges from about 18 to 30 percent by weight of the feedstock residual oil, depending on the composition of the feedstock and the operating variables. Many refineries worldwide produce as much as 2,000 to 3,000 tons per day of petroleum coke and some produce even more.
Schematic flow diagram and description
The
flow diagram and description in this section are based on a delayed coking unit with a single pair of coke drums and one feedstock furnace. However, as mentioned above, larger units may have as many as 4 pairs of drums (8 drums in total) as well as a furnace for each pair of coke drums.
Residual oil from the
vacuum distillation
Vacuum distillation is distillation performed under reduced pressure, which allows the purification of compounds not readily distilled at ambient pressures or simply to save time or energy. This technique separates compounds based on differences i ...
unit (sometimes including high-boiling oils from other sources within the refinery) is pumped into the bottom of the distillation column called the main fractionator. From there, it is pumped, along with some injected steam, into the fuel-fired furnace and heated to its thermal cracking temperature of about 480 °C. Thermal cracking begins in the pipe between the furnace and the first coke drums, and finishes in the coke drum that is on-stream. The injected steam helps to minimize the deposition of coke within the furnace tubes.
Pumping the incoming residual oil into the bottom of the main fractionator, rather than directly into the furnace, preheats the residual oil by having it contact the hot vapors in the bottom of the fractionator. At the same time, some of the hot vapors condense into a high-boiling liquid which recycles back into the furnace along with the hot residual oil.
As cracking takes place in the drum, gas oil and lighter components are generated in vapor phase and separate from the liquid and solids. The drum effluent is vapor except for any liquid or solids entrainment, and is directed to main fractionator where it is separated into the desired boiling point fractions.
The solid coke is deposited and remains in the coke drum in a porous structure that allows flow through the pores. Depending upon the overall coke drum cycle being used, a coke drum may fill in 16 to 24 hours.
After the first drum is full of the solidified coke, the hot mixture from the furnace is switched to the second drum. While the second drum is filling, the filled first drum is steamed out to reduce the hydrocarbon content of the petroleum coke, and then quenched with water to cool it. The top and bottom heads of the full coke drum are removed, and the solid petroleum coke is then cut from the coke drum with a high pressure water nozzle, where it falls into a pit, pad, or sluiceway for reclamation to storage.
Composition of coke
The table below illustrates the wide range of compositions for raw petroleum coke (referred to as
green coke) produced in a delayed coker and the corresponding compositions after the green coke has been calcined at 2375 °F (1302 °C):
History
Petroleum coke was first made in the 1860s in the early oil refineries in Pennsylvania which boiled oil in small, iron
distillation
Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...
stills to recover
kerosene
Kerosene, paraffin, or lamp oil is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regi ...
, a much needed lamp oil. The stills were heated by wood or coal fires built underneath them, which over-heated and coked the oil near the bottom. After the distillation was completed, the still was allowed to cool and workmen could then dig out the coke and tar.
[
*In 1913, William Merriam Burton, working as a chemist for the ]Standard Oil of Indiana
Amoco () is a brand of filling station, fuel stations operating in the United States, and owned by BP since 1998. The Amoco Corporation was an American chemical and petroleum, oil company, founded by Standard Oil Company in 1889 around a oil re ...
refinery at Whiting, Indiana
Whiting is a city located in the Chicago Metropolitan Area in Lake County, Indiana, which was founded in 1889. The city is located on the southern shore of Lake Michigan. It is roughly 16 miles from the Chicago Loop and two miles from Chicago's ...
, was granted a patent for the Burton thermal cracking process that he had developed. He was later to become the president of Standard Oil of Indiana before he retired.
*In 1929, based on the Burton thermal cracking process, Standard Oil of Indiana built the first delayed coker. It required very arduous manual decoking.[
*In the late 1930s, Shell oil developed hydraulic decoking using high-pressure water at their refinery in ]Wood River, Illinois
Wood River is a city in Madison County, Illinois. The population was 10,657 according to the 2010 census.
Geography
Wood River is located at (38.863047, -90.088527).
According to the 2010 census, Wood River has a total area of , of which (or 9 ...
. That made it possible, by having two coke drums, for delayed decoking to become a semi-continuous process.[
*From 1955 onwards, the growth in the use of delayed coking increased.
*As of 2002, there were 130 petroleum refineries worldwide producing 172,000 tons per day of petroleum coke.] Included in those worldwide data, about 59 coking units were operating in the United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
and producing 114,000 tons per day of coke.[
]
Uses of petroleum coke
The product coke from a delayed coker has many commercial uses and applications.[Tutorial: Delayed Coking Fundamentals]
(written by Paul Ellis and Christopher Paul of the Great Lakes Carbon Corporation) The largest use is as a fuel.
The uses for green coke are:
* As fuel for space heater
A space heater is a device used to heat a single, small to medium sized area.
Operation
Electric space heaters fall into four main categories: fan heaters, ceramic, infrared, and oil-filled.
* Fan heaters are the cheapest, but are often the ...
s, large industrial steam generators, fluidized bed combustions, Integrated Gasification Combined Cycle
integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas ( syngas). It can then remove impurities from the syngas prior to the elect ...
(IGCC) units and cement
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mix ...
kilns
A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay int ...
* In silicon carbide foundries
* For producing blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric ...
coke
The uses for calcined coke are:
* As anodes
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
in the production of aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
* In the production of titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
* As a carbon raiser in cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
and steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
making
* Producing graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
s and other graphite products such as graphite brushes used in electrical equipment
* In carbon structural materials
Other processes for producing petroleum coke
There are other petroleum refining processes for producing petroleum coke, namely the Fluid Coking and Flexicoking processes both of which were developed and are licensed by ExxonMobil Research and Engineering. The first commercial unit went into operation in 1955. Forty-three years later, as of 1998, there were 18 of these units operating worldwide of which 6 were in the United States.
There are other similar coking processes, but they do not produce petroleum coke. For example, the Lurgi-VZK Flash Coker which produces coke by the pyrolysis of biomass.Lurgi's Biomass-To-Liquid (BTL) Strategy
Dr. Ludolf Plass, Dr. Armin Günther and Pietro Di Zanno, Biomass-To-Liquid (BTL) Congress, Berlin (Scroll down to pdf page 9 of 21 pdf pages)
References
External links
{{Commons, Oil refinery
Petroleum production
Chemical equipment
Oil refineries