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Home , Petroleum coke

3rd International Conference on Chemical, Ecology and Environmental Sciences (ICEES'2014) March 19-20, 2014 Abu Dhabi (UAE)

Calcinations of

Aliasghar Rohani, Khashayar Sharifi, and Rahmatollah Golpasha

quality results in much more consistent finished Abstract—Petroleum coke is a process that involves steps such as carbon product to the end user/smelter as opposed to trying to thermal decomposition, polymerizationion and condensation. blend solids (green and/or calcined) to spec. "after the fact". The Petroleum Coke category consists of two substances; green coke World calcinations coke demand in 2016 is shown in figure 1. 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 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 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. 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 Fig. 1 World calcinations coke demand in 2016(CRU) required for calcined product, only low sulfur green cokes are calcined. Proper in the Vacuum Unit is critical to reside (Coker feed) quality control. Specifically, the amount of Keywords—Calcination, green coke, petroleum coke, rotary kiln vacuum gas oil sent to the Coker with the vacuum residuum (determined by the efficiency of the fractionation in the I. INTRODUCTION Vacuum tower itself) must be carefully monitored and RUDE oil is a complex mixture of hydrocarbons, controlled to insure adequate hardness of the green coke C sometimes characterized as "a useless mixture of useful produced by the Coker. An "optimal" reside yield for a refiner products." Petroleum coke is, essentially, the "bottom of the more concerned about downstream catalytic units may not crude barrel" - the carbon in the crude charge that cannot be necessarily be optimal for eventual calcined coke properties recovered in normal refining processes - comprising about 5-7 [1]. Petroleum cokes are produced at using three wt% of each barrel of crude. A refiner must carefully balance different types of coking processes: delayed, hid, and flexi crude characteristics against refining unit capacities and coking. The is mostly used at forty-nine U.S. product slates. If the facility produces anode-grade carbon, refineries processing [2]. The other fliud coker and flexicoker other impacts must be considered. Consistent quality coke are less utilized at a relatively smaller capacity. Coke products begins with consistent quality crudes; "trim" crudes introduced from a delayed coker are classified as shot, sponge, at the "front end" of the refining process to control eventual (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 Rohani A. A. is with the Refining Division, Research institute of physically produced through precipitating asphaltenes; sponge petroleum Industry, National Iranian Oil Company, Tehran, Iran, (phone: +98 (21)48255019; fax: +98 (21) 44739738; e-mail: [email protected]). coke (mostly used for anode-grade) is dull and black, having Sharifi Kh. was with Research institute of petroleum Industry, National porous, amorphous structure, and is considered as a mixture of Iranian Oil Company, Tehran, Iran. He is now with the Refining Division, (e- shot and needle cokes; and needle coke (not used in anode mail: [email protected]). Golpasha R. is with the Refining Technology Development Division, production) is silver-gray, having crystalline broken needle Research institute of petroleum Industry, National Iranian Oil Company, structure, and chemically produced through cross linking of Tehran, Iran. (e-mail: [email protected]).

100 3rd International Conference on Chemical, Ecology and Environmental Sciences (ICEES'2014) March 19-20, 2014 Abu Dhabi (UAE) 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. and Nickel are the most common metals in crude oil. These metals usually exist in solution in the oil and residual 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 Fig. 2 calcined petroleum coke years and don't have environmental pollution. But these methods have not yet been industrialized [6-9] . The green coke must have sufficiently low metals content in order to be used as anode material. Green coke with this low II. PETROLEUM COKE metals content is referred to as anode grade coke. The green coke with too high metals content will not be calcined and is A. Desulphurization of petcoke used for burning. Some property of calcined petroleum coke is Petroleum coke is no longer a left-over by-product of shown in table 1. “bottom-of-the-barrel” operations whose chief aims TABLE I TYPICAL PROPERTIES OF CALCINED PETROLEUM COKE 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 Specification UOM Aluminium Industry Industry with high sulphur content is being produced, and means Moisture % 0.3 whereby such sulphur content is reduced to an acceptable level or eliminated altogether are called for, in particular with the Volatile Matter 0.3 0.5 ever-tightening restrictions on sulphur oxides emissions for % environmental considerations. The desulphurization of petcoke Ash 0.5 0.5 involves in general desorption of the inorganic sulphur present % in the coke pores or on the coke surface, and the partition and Si % 0.04 removal of the organic sulphur attached to the aromatic carbon Fe % 0.06 skeleton. The desulphurization techniques proposed fall Nickel % 0.025 generally under these headings - Solvent extraction. Vanadium % 0.025 - Chemical treatment. S ( Sulphur ) % 3 0.1 - Thermal desulphurization. - Desulphurization in an oxidizing atmosphere. Real Density gm/cc 2.050 - 2.085 - Desulphurization in an atmosphere of sulphur-bearing gas. HGI 36 - 42

- Desulphurization in an atmosphere of hydrocarbon gases. - Hydrodesulphurization. III. ELECTRODE PRODUCTION B. Calcined petroleum coke Depending on its physical form, coke may also be classified Calcined petroleum coke (CPC) is the product from as shot, sponge or needle coke. Shot coke occurs as hard calcining petroleum coke. This coke is the product of the spheres and is produced from high asphaltene precursors. in a crude . The calcined petroleum coke Needle coke appears as silver-gray crystalline needles and is is used to make anodes for the aluminum, steel and derived from feedstocks with high aromatic hydrocarbon smelting industry. Calcined petroleum coke is shown in figure content. Sponge coke is dull black with a macroscopically 2. amorphous appearance but is a mixture of shot and needle

coke structures.

101 3rd International Conference on Chemical, Ecology and Environmental Sciences (ICEES'2014) March 19-20, 2014 Abu Dhabi (UAE)

In the calcining process, the green coke feed is heated to a REFERENCES sufficiently high temperature to drive off any residual [1] Bernie Vitchus, Frank Cannova , Howard Childs, Calcined Coke from moisture, and to drive off and combust any residual Crude Oil to Customer Silo Light Metals Carbon Technology 2001, p hydrocarbons (the combustion of the evolved volatile materials 589-596 provides the necessary heat for the calcination process) in the [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. green coke feed. [4] R E. Dymond and B. H. Spector, Light Metal Age, Feb., 1992, 34-38. The production of electrodes is closely controlled process. [5] w,Jam es J. Baker, JefI?ey G. Rolle, Robert Llerena,, A. J. Edmond Co, Flow scheme of general electrode production shown in figure Characterization of green and calcined coke properties used for 3. 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

Fig. 3 diagram for manufacturing of 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.

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