Abstract—Petroleum coke is a process that involves steps such as
thermal decomposition, polymerizationion and condensation.
The Petroleum Coke category consists of two substances; green coke
and calcined coke. These two substances are grouped together in a
category based on their similarity of manufacturing processes which
results in similar physical chemical characteristics and chemical
composition. The principal difference is the amount of residual
hydrocarbon (also termed volatile matter) in the two products.
Petroleum coke (both green and calcined) is a black-colored solid
produced by the high pressure thermal decomposition of heavy (high
boiling) petroleum process streams and residues. Green coke is the
initial product from the cracking and carbonization of the feedstock's
to produce a substance with a high carbon-to-hydrogen ratio. Green
coke undergoes additional thermal processing to produce calcined
coke. The additional processing removes volatile matter and
increases the percentage of elemental carbon, which results in a lower
potential for toxicity for calcined coke.
Calcinations of coke are usually done in a rotary kiln at about
1300°C to 1500°C. During the process the coke is further
decomposed, increasing in the carbon to hydrogen ratio from 20 of
green coke to 1000 for calcined coke. Along with increasing in the
fixed carbon of the coke to over 95%, electrical conductivity
improved and real density increase when coke is calcined. Sulfur
content of the calcined coke is dependent on the sulfur in the green
coke as feed of process. Typically, since low sulfur content is usually
required for calcined product, only low sulfur green cokes are
calcined.
Keywords—Calcination, green coke, petroleum coke, rotary kiln
I. INTRODUCTION
RUDE oil is a complex mixture of hydrocarbons,
sometimes characterized as "a useless mixture of useful
products." Petroleum coke is, essentially, the "bottom of the
crude barrel" - the carbon in the crude charge that cannot be
recovered in normal refining processes - comprising about 5-7
wt% of each barrel of crude. A refiner must carefully balance
crude characteristics against refining unit capacities and
product slates. If the facility produces anode-grade carbon,
other impacts must be considered. Consistent quality coke
begins with consistent quality crudes; "trim" crudes introduced
at the "front end" of the refining process to control eventual
Rohani A. A. is with the Refining Division, Research institute of
petroleum Industry, National Iranian Oil Company, Tehran, Iran, (phone: +98
(21)48255019; fax: +98 (21) 44739738; e-mail: [email protected]).
Sharifi Kh. was with Research institute of petroleum Industry, National
Iranian Oil Company, Tehran, Iran. He is now with the Refining Division, (e-
mail: [email protected]).
Golpasha R. is with the Refining Technology Development Division,
Research institute of petroleum Industry, National Iranian Oil Company,
Tehran, Iran. (e-mail: [email protected]).
Carbon quality results in much more consistent finished
carbon product to the end user/smelter as opposed to trying to
blend solids (green and/or calcined) to spec. "after the fact".
World calcinations coke demand in 2016 is shown in figure 1.
Fig. 1 World calcinations coke demand in 2016(CRU)
Proper distillation in the Vacuum Unit is critical to reside
(Coker feed) quality control. Specifically, the amount of
vacuum gas oil sent to the Coker with the vacuum residuum
(determined by the efficiency of the fractionation in the
Vacuum tower itself) must be carefully monitored and
controlled to insure adequate hardness of the green coke
produced by the Coker. An "optimal" reside yield for a refiner
more concerned about downstream catalytic units may not
necessarily be optimal for eventual calcined coke properties
[1]. Petroleum cokes are produced at refineries using three
different types of coking processes: delayed, hid, and flexi
coking. The delayed coker is mostly used at forty-nine U.S.
refineries processing [2]. The other fliud coker and flexicoker
are less utilized at a relatively smaller capacity. Coke products
from a delayed coker are classified as shot, sponge,
(sometimes honeycomb), or needle coke depending on their
chemical and physical characteristics. Shot coke (almost
always sold as fuel) is hard, having spherical form, and
physically produced through precipitating asphaltenes; sponge
coke (mostly used for anode-grade) is dull and black, having
porous, amorphous structure, and is considered as a mixture of
shot and needle cokes; and needle coke (not used in anode
production) is silver-gray, having crystalline broken needle
structure, and chemically produced through cross linking of
Calcinations of Petroleum coke
Aliasghar Rohani, Khashayar Sharifi, and Rahmatollah Golpasha
C
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condensed aromatic hydrocarbons during coking reactions
[3,4]. Most of fluid coke does not enter the anode pool and
flexi coke has never been used in aluminum smelting.[5]
Crude oil contains of various compound of hydrocarbons but
low concentrations of inorganic compounds or metals found in
crude oil. Vanadium and Nickel are the most common metals
in crude oil. These metals usually exist in solution in the oil
and residual fuel oil in the refining process is condensed.
Deleterious effects of metals in petroleum have been known
for some time. These metals not only contaminate the product
but also cause intoxication and loss of catalyst and corrosion to
equipment. In this study removal heavy metals and petroleum
residues were investigated. These methods include physical
and chemical and biological treatment processes. For example,
Processes such as solvent extraction and hydro-catalytic and
catalytic methods are effective and practical methods, but
typically often have high costs and environmental pollution.
Furthermore, biological methods have been discussed in recent
years and don't have environmental pollution. But these
methods have not yet been industrialized [6-9] .
II. PETROLEUM COKE
A. Desulphurization of petcoke
Petroleum coke is no longer a left-over by-product of
“bottom-of-the-barrel” refinery operations whose chief aims
are the production of other materials. Petcoke has become a
valuable product in its own right, and the demand for high-
quality low-sulphur coke is increasing. However, more coke
with high sulphur content is being produced, and means
whereby such sulphur content is reduced to an acceptable level
or eliminated altogether are called for, in particular with the
ever-tightening restrictions on sulphur oxides emissions for
environmental considerations. The desulphurization of petcoke
involves in general desorption of the inorganic sulphur present
in the coke pores or on the coke surface, and the partition and
removal of the organic sulphur attached to the aromatic carbon
skeleton. The desulphurization techniques proposed fall
generally under these headings
- Solvent extraction.
- Chemical treatment.
- Thermal desulphurization.
- Desulphurization in an oxidizing atmosphere.
- Desulphurization in an atmosphere of sulphur-bearing
gas.
- Desulphurization in an atmosphere of hydrocarbon
gases.
- Hydrodesulphurization.
B. 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 aluminum, steel and titanium
smelting industry. Calcined petroleum coke is shown in figure
2.
Fig. 2 calcined petroleum coke
The green coke must have sufficiently low metals content in
order to be used as anode material. Green coke with this low
metals content is referred to as anode grade coke. The green
coke with too high metals content will not be calcined and is
used for burning. Some property of calcined petroleum coke is
shown in table 1. TABLE I
TYPICAL PROPERTIES OF CALCINED PETROLEUM COKE
Specification UOM Aluminium Industry Steel Industry
Moisture % 0.3
Volatile Matter %
0.3 0.5
Ash 0.5 0.5 %
Si % 0.04
Fe % 0.06
Nickel % 0.025
Vanadium % 0.025
S ( Sulphur ) % 3 0.1
Real Density gm/cc 2.050 - 2.085
HGI
36 - 42
III. ELECTRODE PRODUCTION
Depending on its physical form, coke may also be classified
as shot, sponge or needle coke. Shot coke occurs as hard
spheres and is produced from high asphaltene precursors.
Needle coke appears as silver-gray crystalline needles and is
derived from feedstocks with high aromatic hydrocarbon
content. Sponge coke is dull black with a macroscopically
amorphous appearance but is a mixture of shot and needle
coke structures.
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In the calcining process, the green coke feed is heated to a
sufficiently high temperature to drive off any residual
moisture, and to drive off and combust any residual
hydrocarbons (the combustion of the evolved volatile materials
provides the necessary heat for the calcination process) in the
green coke feed.
The production of electrodes is closely controlled process.
Flow scheme of general electrode production shown in figure
3.
Fig. 3 diagram for manufacturing of graphite electrodes
IV. CONCLUSION
Petroleum coke calcining is taking green coke or anode
grade green coke from the refining process and convert this
coke to different structures of carbon. The calcined coke is
used to produce carbon anodes for the aluminum industry. To
obtain the calcined coke properties required by the carbon and
graphite industries, the temperature of coke must be reached to
1200-1450°C or higher to refine its crystalline structure.
Calcined coke is a very dusty material, and without adequate
provision for containing the dust a calcining plant can be a
very dirty operation, with excessive atmospheric discharge.
calcination processes is a process whereby green or raw
petroleum coke is upgraded with high temperature to remove
associated moisture and volatile combustion matter and to
otherwise improve in critical physical properties, electrical
conductivity, real density and oxidation characteristics. It is
known that at the temperature of calcining some sulfur
oxidation also take place. the average rate of desulfurization of
delayed coke is 2 to 3 times higher than that of coke from fluid
or contact cokers. The calcining process is essentially a time-
temperature function with the most important control variables
being heating rate, VCM/air ratio and final calcinations
temperature. The final quality of the calcined coke is directly
related to the specific characteristics and quality of the green
coke fed to the calciner. The demand for low sulfur coke for
electrode manufacture is hardly satisfied from feedstock.
REFERENCES
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Crude Oil to Customer Silo Light Metals Carbon Technology 2001, p
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[3] N. P. Lieberman, Oil &Gas Journal, Mar. 27, 1989, 67-69.
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[5] w,Jam es J. Baker, JefI?ey G. Rolle, Robert Llerena,, A. J. Edmond Co,
Characterization of green and calcined coke properties used for
aluminum anode-grade carbon, 2001
[6] G. O. Young, “Synthetic structure of industrial plastics (Book style with
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[7] W.-K. Chen, Linear Networks and Systems (Book style). Belmont, CA:
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