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: rohaniaa@ripi.ir).

Sharifi Kh. was with Research institute of petroleum Industry, National

Iranian Oil Company, Tehran, Iran. He is now with the Refining Division, (e-

mail: sharifikh@ripi.ir).

Golpasha R. is with the Refining Technology Development Division,

Research institute of petroleum Industry, National Iranian Oil Company,

Tehran, Iran. (e-mail: golpashar@ripi.ir).

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

[1] Bernie Vitchus, Frank Cannova , Howard Childs, Calcined Coke from

Crude Oil to Customer Silo Light Metals Carbon Technology 2001, p

589-596

[2] E. J. Swain, Oil & Gas Journal, Jan. 2, 1995, 33-39; Jan. 9, 1995, 37-42.

[3] N. P. Lieberman, Oil &Gas Journal, Mar. 27, 1989, 67-69.

[4] R E. Dymond and B. H. Spector, Light Metal Age, Feb., 1992, 34-38.

[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

paper title and editor),” in Plastics, 2nd ed. vol. 3, J. Peters, Ed. New

York: McGraw-Hill, 1964, pp. 15–64.

[7] W.-K. Chen, Linear Networks and Systems (Book style). Belmont, CA:

Wadsworth, 1993, pp. 123–135.

[8] H. Poor, an Introduction to Signal Detection and Estimation. New

York: Springer-Verlag, 1985, ch. 4.

[9] Schuetze, B. and Hofmann, H., Hydrocarbon Processing, 1984, 63(2),

75-82.

[10] Altgelt, K.H. and Boduszynski,. Compositional Analysis: Dream and

Reality. In: Composition and Analysis of Heavy Petroleum Fractions.

Marcel Dekker, Inc. New York, M. M. 1994

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