Petroleum Coke Glossary


Anode grade coke

A grade of pet coke from a delayed coker (see same) low in metals such as vanadium, nickel and iron that is suitable for making graphite anodes for the aluminum smelting industry.  If the metals content does not qualify as anode grade coke, then the coke is generally known as fuel grade (see same).  The choice of whether a coke may qualify as anode or fuel grade is driven solely by the crude slate of the crude unit upstream of the coker and the metals contained therein.

Generally presence of any shot coke (see same) and Volatility (see same)> 10%  are unacceptable.  Sometimes anode grade is also referred to as calcineable coke  (see same)



The residue remaining when all of the coke is burned off.  It is mostly metals and silica.





Calcineable coke

Petroleum coke that qualifies to be calcined, i.e., generally non shot and low in metals that will qualify for anode grade.  Calcineable coke is generally referred to as the available supply to calciners. Also known a s green coke  (see same).


Calcined coke

Petroleum coke or green coke (see same) that has been processed in a calciner (see same)



A large rotary kiln (similar to a cement kiln) that drives off the moisture and volatility of green or calcineable coke (see each) so that the coke can be used for aluminum anodes, or titanium dioxide applications.  The kiln receives the coke at the higher end where the coke flows downhill as the kiln rotates.  At the same time heated air counterflows uphill from the lower end, driving off the moisture and volatile material


Carbon rejection

Crude oil contains a wide variety of hydrocarbon molecules, ranging from a single carbon atom (methane) to very long chain molecules.  The lighter molecules that make up gasoline, jet and diesel contain a lower ratio of carbon to hydrogen than the heavier molecules.  In order to convert the heavier molecules to lighter products, the heavier molecules must not only be cracked, but the excess carbon must be removed to reduce the carbon to hydrogen ratio of the cracked material.


Circulating Fluidized Bed (CFB) Boiler

A type of boiler where the solid fuel is fluidized in a vertical furnace.  The advantage for the pet coke industry is that 100% very high sulfur coke can be burned.  The sulfur is removed by addition of limestone in the bed which forms an easily removable calcium sulfate ash.  



A refinery processing unit that converts the residual oil from the crude unit vacuum or atmospheric column into gas oil that can be made into light products (gasoline, jet and diesel), weak (i.e., low energy content) fuel gas and pet coke.  There are 3 types:  Delayed, Fluid, and Flexi  (see each). These are all basically carbon rejection schemes  (see same).


Delayed coker

A type of coker whose process consists of heating the residual oil feed to its thermal cracking temperature in a multi parallel pass furnace.  This cracks the long chain heavy carbon and hydrogen molecules of the residual oil into coker gas oil and pet coke.  Both are in a liquefied form in the mixture as it leaves the furnace and enters the coke drum.

 In the drum, the coker gas oil vaporizes and separates from the mixture.  It is directed to a fractionation column where it is separated into the desirable boiling point fractions.  The liquid coke solidifies in the drum as it cools and the velocity slows down.

 After the drum is full of the solidified coke, the hot mixture from the furnace is switched to a second drum.  While the second drum is filling, the full drum is steamed to further reduce hydrocarbon content of the pet coke, and then water quenched to cool it.  The top and bottom heads of the full coke drum are removed, and the solid pet coke is then cut from the coke drum with a high pressure water nozzle, where it falls into a pit for reclamation to storage. 

 Larger cokers have several pairs of tandem drums.



Contracts for rail cars, trucks and marine ships always include a specified time limit that the respective vehicle or ship will take to unload or load.  The penalty for delaying beyond the time allowed is also specified in each contract.  Upon completion of the actual load or unload, the vehicle or ship owner presents the customer with a demurrage bill specifying the time delay beyond the allowance, reasons for it and the $ penalty. 


Dry metric or short ton

A unit of measure for billing pet coke weight, which refers to the gross coke weight adjusted for excluding the contained moisture content.  To get this measure, the coke must be tested for moisture content  (see same).  Calcineable coke (See same) is frequently measured in these units. Also see Wet metric ton.


Energy content

The energy content of coal and coke is usually specified in either BTU/lb or Kcal/kg.  It is measured in a calorimeter that literally ignites the test sample and measures the temperature rise of the water bath surrounding it.


Flexi coker

The flexicoker adds a third vessel, a gasifier, to the fluid coker to gasify the purge coke into a weak fuel gas.  Coke is made in 3 areas: purge coke from the heater, and both larger and smaller recovered coke fines from the weak gas scrubbers.  It is a “flexible” coker in that the gasifier can be run to make either more coke or more weak fuel gas.


Fluid Coker

A fluid coker produces more light product yield and less coke but the coke is higher in metals and harder than a delayed coker.  The process is a continuous fluidized bed consisting of a reactor and a burner vessel.  Feed is sprayed onto seed pellets of coke in the reactor where it is coked.  Purge coke is drawn off the burner vessel.


Fuel grade coke

Pet coke that competes with steam coal as fuel for a furnace, boiler  or cement kiln.  If the coke contains low metals, it may qualify as anode grade  (see same).  The choice of whether a coker makes fuel grade vs anode grade is dictated solely by the crude slate and the metals content therein.


Green coke

Usually refers to calcineable coke, i.e, potential anode quality coke that still contains moisture and volatile material, i.e, before calcining.


Hargrove Grindability Index  (HGI)

A measure of the relative hardness of the coke in terms of resistance to grinding.  An HGI below 35 usually means a very hard coke requiring considerable grinding before it can be properly sized  to meet burner nozzle specifications for the pulverized feed to the furnace where the coke will be burned.  An HGI above 65 is usually recognized as a soft coke that will grind very easily.











Loss on Ignition (LOI)

Coke that is added to coal in a furnace originally designed for coal, may not fully burn in the furnace.  Some coke particles escape the flame envelope and are caught by the precipitators or bag houses. This LOI results in reduced furnace efficiency and some carbon contamination of the flue gas ash recovered.


Metals content

The distillation processes of the atmospheric and vacuum columns result in almost all of the metals content of the crude to concentrate in the residual oil (the coker feed), and then further concentrated in the coker.  Generally metals are not a problem to fuel grade coke buyers, other than vanadium to some.  However anode grade coke buyers prefer low metals as the metals tend to reduce the efficiency of the anode in the aluminum smelting process


Moisture content

Pet coke as cut from a coker contains roughly from 7-10% moisture which the coke picked up from the steaming and quench operations.  It is measured by heating a 100g sample of ground coke, until the moisture is gone, and then re weighing.  See Wet metric tons and Dry Metric tons.


Needle Coke

A special quality coke produced from aromatic feed stocks.  It has a crystalline structure with more unidirectional pores.  It is used for high quality graphite anodes such as for electric arc furnaces in the steel industry.














Shot coke

Due to mechanisms not well understood, the coke from some crudes forms into small, tight, non attached clusters that look like pellets, marbles or BB’s.  It usually is a very hard coke , i.e., low HGI  (see same).  Such coke is less desirable to the end users because of difficulties in handling and grinding.  It is also less desirable for calcineable coke because the shot tends to “pop” in the kiln reducing the thermal stability.


Sponge coke

Most delayed coke is in a form that resembles a sponge, i.e, sort of bubbly looking.


Sulfur content

Sulfur in crude naturally distributes itself throughout the range of the crude’s hydrocarbon molecules.  However, the residual oil and coke usually attract a disproportionately higher Sulfur percent.  Also, as most low sulfur crudes become extinct, refineries will run higher sulfur crudes thereby increasing the coke sulfur. 








Volatility or VCM

Pet coke from a coker contains a small amount (<10%) of light hydrocarbons trapped in the pores of the coke.  The amount of such volatility is generally related to the how hard the coker furnace is driven:  hotter furnace outlet temperatures result in more hydrocarbons driven off and therefore lower volatility.


Wet metric ton

Fuel grade coke is typically sold in these billing units which is at a standard 8% moisture.  If the coke tests for a higher %, the billing weight is adjusted accordingly.











Copyright 2003 - 2016 Phillip H Fisher Web Site Design and Hosting by
Focused Web, Inc.