Delayed coker

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 with multiple parallel passes. This cracks the heavy, long chain hydrocarbon molecules of the residual oil into coker gas oil and petroleum coke.^[1][2][3] Delayed coking is one of the unit processes used in many oil refineries.

Description

Cracking begins in the furnace, continues in the transfer line, and finishes in the coke drum.

As cracking continues 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 only except for any liquid or solids entrainment, and is directed to a fractionation column where it is separated into the desirable boiling point fractions. Solid coke is deposited in the drum in a porous structure that allows flow through the pores. All solids and uncracked residual liquid produced from the vapor and liquid feed are intended to remain in the drum.

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 petroleum coke, and then water quenched 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.

Larger cokers have several pairs of tandem drums.

Typical schematic flow diagram

A typical schematic flow diagram of a delayed coking unit

Composition of coke

The table below illustrates the wide range of compositions for raw petroleum coke (referred to as green coke^[4]) produced in a delayed coker and the corresponding compositions after the green coke has been calcined at 2375 °F (1302 °C):

Composition Of Coke From A Delayed Coker

Component	Green coke as produced	Coke calcined at 2375 °F
Fixed carbon, wt %	80 − 95	98.0 − 99.5
Hydrogen, wt %	3.0 − 4.5	0.1
Nitrogen, wt %	0.1 − 0.5
Sulfur, wt %	0.2 − 6.0
Volatile matter, wt %	5 − 15	0.2 − 0.8
Moisture, wt %	0.5 − 10	0.1
Ash, wt %	0.1 − 1.0	0.02 − 0.7
Density, g/cc	1.2 − 1.6	1.9 − 2.1
Metals, ppm weight:
Aluminum	15 − 100	15 − 100
Boron	0.1 − 15	0.1 − 15
Calcium	25 − 500	25 − 500
Chromium	5 − 50	5 − 50
Cobalt	10 − 60	10 − 60
Iron	50 − 5000	50 − 5000
Manganese	2 − 100	2 − 100
Magnesium	10 − 250	10 − 250
Molybdenum	10 − 20	10 − 20
Nickel	10 − 500	10 − 500
Potassium	20 − 50	20 − 50
Silicon	50 − 600	50 − 600
Sodium	40 − 70	40 − 70
Titanium	2 − 60	2 − 60
Vanadium	5 − 500	5 − 500

See also

• Cracking (chemistry)
• Shukhov cracking process
• Burton process
• Coke (fuel)
• Visbreaker

References

1. ^ Gary, J.H. and Handwerk, G.E. (1984). Petroleum Refining Technology and Economics (2nd Edition ed.). Marcel Dekker, Inc. ISBN 0-8247-7150-8. 
2. ^ Leffler, W.L. (1985). Petroleum refining for the nontechnical person (2nd Edition ed.). PennWell Books. ISBN 0-87814-280-0. 
3. ^ Petroleum Coke Glossary
4. ^ Petroleum coke on the website of the IUPAC Compendium of Chemical Terminology

External links

• Detailed description of cokers and related topics
• Detailed description of delayed coker