JPS63230789A - Method for improving density of coke - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a method for improving the density of coke.

BACKGROUND AND SUMMARY OF THE INVENTION There is an increasing demand for high quality premium coke for the production of large graphite electrodes used in electric arc furnaces used in the steel industry. A number of properties are important in characterizing the quality of graphite electrodes.

One such property is density. Generally, the higher the density, the better the electrode. Premium coke users are always looking for dense graphite materials. Even small changes in density have a substantial effect on large electrode properties.

Premium coke is produced by delayed coking, which converts heavy hydrocarbon feedstocks into coke and light hydrocarbon products. In this method, a heavy hydrocarbon feedstock is rapidly heated to crabbing temperature and fed to a coke drum. The heated feed permeates the drum with sufficient heat content to convert it to coke and cracked steam. The crabbed vapor is removed from the top and, if desired, rectified with the rectifier bottoms recycled to the feed. Coke is collected in the drum until the heated feed is sent to another coke drum, the coke is removed from the coke-filled drum, and the drum is filled with coke. After removal, the coke is calcined at elevated temperatures to remove volatiles and increase the carbon to hydrogen ratio of the coke.

To manufacture large graphite electrodes, calcined premium coke particles obtained from a delayed coking process are mixed with pitch and then baked at elevated temperatures to carbonize the pitch.

According to the present invention, calcined coke with increased density is produced by contacting the coke with a coker feed prior to calcining, followed by a calcining operation. In one embodiment, the method is used to obtain premium coke of increased density used in the manufacture of electrodes used in steel production.

BACKGROUND OF THE INVENTION U.S. Pat. No. 2,502,183 teaches high density carbon articles by mixing carbon aggregates, coke "flour" and pitch and hot molding the mixture. Disclosed is producing carbon. This patent also describes how carbon electrodes and other Discloses manufacturing an article. The only coke "flour" disclosed in this patent is calcined petroleum coke.

U.S. Pat. No. 4,105,501 discloses a method for producing metallurgically formed coke by carbonizing briquettes produced by forming an outer envelope of bituminous material on coal dust. Disclose.

The bituminous materials disclosed are coal tar, coal cool pitch, emulsified coal cool pitch, asphalt, modified asphalt, and heat treated asphalt.

U.S. Pat. No. 4,483,840 discloses a method in which pellets formed from agglomerated anthracite or coal dust with binders based on pitch and/or tar are oxidized at elevated temperatures and then calcined at elevated temperatures. Disclose. The resulting pellets can be used in all types of carbonaceous pastes, electrodes, and carbonaceous blocks for lining furnaces or electrolytic cells.

DETAILED DESCRIPTION OF THE INVENTION A new feedstock used in the preparation of premium coke is a heavy aromatic mineral oil fraction. These feedstocks are obtained from numerous sources including petroleum, shale oil, tar sands, coal, and the like. Particular feedstocks include decant oils, also known as slurry oils or product oils, obtained by rectifying the gaseous portion and/or the effluent from the residual oil. Another feedstock used is ethylene or pyrolysis tar. This is a heavily aromatic mineral oil obtained from the high temperature thermal cracking of mineral oils to produce olefins, such as ethylene. Another feedstock is vacuum residue, which is a heavy residue obtained from flashing or distilling residual oil under vacuum. Another feedstock is a vacuum body, which is a light material obtained from flashing or distillation under vacuum. Hot tar can also be used as feedstock. This is a heavy oil obtained from the rectification of materials produced by thermal cracking of gaseous parts or similar materials. The heavy premium coker gas portion is another feedstock, heavy oil obtained from the liquid product produced by coking oil into premium coke. The gaseous fraction from coking operations other than premium coking is also used as feedstock. Fresh atmospheric oil can also be used as a feedstock. This is the gaseous portion produced from the rectification of crude oil above atmospheric pressure. Another feedstock used is extracted coal tar pitch. Any of the above feedstocks may be used alone or in combination. Additionally, any of the feedstocks can be subjected to hydrotreating, hot soaking, thermal cracking, or a combination of these steps before being used to produce premium grade coke.

Any of the above feedstocks may be used to contact the green (unfired) premium coke in carrying out the process of the present invention. Preferred are feedstocks that provide high yields of coke, including hot tar, decant oil, pyrolysis tar, and various types of pitch. The raw coke can be contacted with some of the same feedstock used in coke preparation, or if desired, a different feedstock can be used for this purpose.

All types of untreated premium coke are applicable to the process of the present invention. That is, untreated coke prepared from any of the conventional coke feedstocks can be used. VBD (Vibration Bulk Density) of Calcined Coke
The greatest improvement in coke density is achieved when the coke density is less than or equal to about 0.77 g/cc (3×6 particles). However, the method is applicable to coke of somewhat greater or lesser density.

The figure shows that the feedstock is introduced into the coking process via line 2. The feedstock, in this case hot tar, is heated in furnace 3, typically from about 850°F to about 1100°F.
in the temperature range of 900°F to about 97°F, preferably about 900°F to about 97°F.
Heat to 5°F. A furnace such as a vibe still is used which rapidly heats the hot tar to the temperature. The hot tar exits the furnace at substantially the same temperature and is introduced via line 4 into the bottom of a coke drum 5, which is maintained at a pressure of about 15 to about 200 psig. Coke drum is about 800
°F to about 1000'F, usually about 820°F to about 9
Operate at temperatures in the 50°F range. Inside the drum,
The heavy hydrocarbons in the hot tar are cracked to form cracking steam and premium coke. Cracking steam is continuously removed from the top of the coke drum 5 via line 6. Coke accumulates in the drum until it reaches a predetermined level at which the feed to the drum is closed and switched to a second coke drum 5a where the same operation is carried out. This switching allows the drum 5 to be deactivated, opened and the accumulated coke removed using conventional techniques. A caulking cycle requires about 1615 to about 60 hours, but typically about 2
Complete in 4 to about 48 hours.

The steam extracted from the top of the coke drum is in line 6.
is sent to the rectifier 7. In the rectifier, the steam is C1
-C5 product stream 8, gasoline boiling range product stream 9, light gas fraction product stream 1O1 and premium coker heavy gas oil removed from the rectifier via line 11. As previously mentioned, the premium coker heavy gas oil from the rectifier is recycled via line 12 at the desired ratio to the coker furnace. Excess netting can be subjected to conventional residue purification techniques if desired.

Untreated coke is removed from the coke drums 5 and 5a via outlets 13 and 13a, respectively, and introduced via 14 into a coke soaker 16. The coke soaker is a tank or container 17 of liquid hot tar feedstock;
and a continuous flexible belt 15 partially immersed in a tank of feedstock.

The raw coke is introduced onto the flexible belt 15 and passes downwardly through the feedstock bath. The feedstock soaked coke then passes upwardly through the belt, exits the soaker, and is introduced into calciner 191; Excess feedstock of coke leaving the soaker flows down the belt and back to tank 17.

Once the feedstock has been consumed in the coke soaker, additional material is introduced via line 18 in an amount sufficient to maintain the level of feedstock in tank 17.

The amount of feedstock removed by the coke will vary depending on the particular coke and feedstock used. Typically feedstock consumption is about 2 to 20 weight percent based on raw coke.

In addition to the disclosed method, other conventional methods may be used to contact the coke with the feedstock.

For example, a liquid feedstock is sprayed onto the coke, or if the feedstock is solid at ambient temperature, the coke is passed through a finely divided feedstock powder.

Coke is typically removed from the coke drum with high velocity water jets. As a result, the coke cooled rapidly and reached a relatively low temperature by the time it entered the coke soaker 16. This is important because contacting hot coke in a bath of liquid feedstock will result in boiling and volatilization of the liquid which will interfere with the objectives of this invention. However, there is no need to cool the coke to room temperature. Somewhat heated coke can be advantageous in wet processes.

The flexible belt 15 becomes contaminated with liquid feedstock and coke particles over a period of time. Feedstocks that have been cleaned or heated by washing or spraying with light hydrocarbon fractions can be used for this purpose.

In the calciner 19, the raw coke impregnated with feedstock is subjected to elevated temperatures to remove volatiles and increase the carbon to hydrogen ratio of the coke. Firing is approximately 2000"
F to about 3000 degrees F1, preferably about 2400 to about 2
It is carried out at temperatures in the range of 600'F. Coke is about 1
The firing conditions are maintained for a period of 30 minutes to about 10 hours, preferably about 1 to about 3 hours. Calcining temperature and time will vary depending on the desired coke properties. Calcined premium coke of increased density suitable for the manufacture of large graphite electrodes is withdrawn from the calciner via outlet 20.

[Example code] The following examples illustrate the results obtained in practicing the invention.

Example 1 A mixture of hot tar and decant oil was coked in a retarded coker at 28 psig and 878°F. The caulking cycle was 44 hours. A sample of the produced untreated coke was placed in a beaker for 15 minutes in chloroform and
00°F and coated with solvent soluble coal tar pitch (2 parts chloroform: 1 part pitch). The chloroform/pitch mixture was decanted from the coke. The chloroform was then evaporated by leaving the coke and liquid mixture in the pan for 3 hours. The pan was positioned at an angle so that excess liquid flowed away from the coke. Calcining is accomplished by placing the coke in an oven and increasing the temperature to 2.600°F for approximately 2.5 hours, followed by 2 hours.
A temperature of 2600'F was maintained.

Example 2 Another sample of the same untreated coke was coated with a 720°F + heat cool heated to 200°F for 15 minutes. After decanting the hot tar, the coke was placed in a tilted pan for 3 hours to remove excess liquid. Firing was carried out as in Example 1.

Example 3 Another sample of the same untreated coke was heated to approximately 330"F and placed in a beaker with -60 mesh particles of 900F + solvent-soluble coal tar pitch. Pitch particles were removed by gently shaking the mixture. It was adhered to coke. Calcining was carried out again as in Example 1.

The physical properties of the coker feedstock used in the examples are shown in Table 1. The VBD and CTE of the coke produced in Examples 1-3 and the base case without added coker feed are shown in Table 2.

Table 1 Characteristics of feedstock Feedstock 720°
F heat tower gravity, 60/60Dcg, F
1.133API specific gravity
-6,58 Conradson Carbon Residue, wt% 8.03 Molecular Weight
272C13NM
R, 96 aromatic C atoms 83.3 specific gravity, 60/80Deg, F
1.297API Gravity
-22,4 sulfur, wt%
0.61 Conradson carbon residue, weight % 56.0 Pentane insolubles, weight % 89.2
molecular weight
649 metal, PPM V<2. O N i
<2. OF e
IB, 8 Elements by Perkin-Elmer, wt% C91,8 H4,8 N1.2 01.5 Total hydrogen by NMR, wt%
4.77 Hydrogen type Rel by NMR, % methyl 1.0
methylene
1.5 Naphthene
2.2 Alpha H14,5 Olefin
1.5 aromatic
79.3C13NMR, % aromatic C atoms
89.9 Table 2 Characteristics of calcined coke Feed material consumption Coker supply/Coke basic case 0.794 0.723 5 2.
72 - -Example 1 0.809 0.746 2
3.32 * 0.070 Example 2 0.790 0
．． 748 2 3.290.071 0.101 Example 3
0.802 0.732 2 3.50 * *
*Infiltrating the coker feedstock with raw coke increases the density of calcined coke, as evidenced by coke loss data that interfered with measurements. However, the CTE of the calcined coke increased somewhat during the process. The amount of coker feed consumed in the process varied from about 7 to about 10 percent based on raw coke.

The method of the invention has been described when applied to premium coke. However, other grades of coke can also be used. For example, large amounts of coke are produced for use in electrodes consumed in aluminum production. This “aluminum grade” coke is distinguished from premium coke in that it does not have the needle-like structure common in premium coke. Although CTE is not a factor in the properties of conventional or aluminum grade coke, dense coke is desirable for such coke when used in electrode manufacturing.

Aluminum grade coke is also prepared by delayed coking and calcination under the same conditions for use in premium coking. Highly aromatic feedstocks are not required and such coke is usually prepared from residues or other heavy hydrocarbon fractions. Also, when aluminum grade coke is used in carrying out the present invention, the feedstock used to contact the untreated coke may be the same feedstock used to make the coke; or a different feedstock.

[Brief explanation of drawings]

The figure is a schematic flow diagram of a premium delay coker illustrating one embodiment of the present invention. 3... Furnace, 5... Coke drum, 7... Rectifier, 9... Product stream, 17... Tank, 19... Calciner, 20... Outlet.

Claims (19)

[Claims] (1) A method of increasing the density of calcined coke comprising contacting untreated (uncalcined) coke with a coker feedstock and then calcining the coke. (2) The method according to claim 1, wherein the coke is aluminum class coke. (3) A process in which the coker feedstock is a different feedstock than that used to prepare the green coke. 4. The method of claim 1, wherein the untreated coke is passed through a bath of liquid coker feedstock. (5) A method of increasing the density of calcined premium coke comprising contacting untreated (uncalcined) premium coke with a coker feedstock and then calcining the coke. 6. The method of claim 5, wherein the coker feedstock is part of the same feedstock used to prepare the green coke. 7. The method of claim 5, wherein the coker feedstock is a different feedstock than that used to prepare the green coke. 8. The method of claim 5, wherein the untreated coke is passed through a bath of liquid coker feedstock. 9. The method of claim 5, wherein the untreated coke is atomized with a liquid coker feed. 10. The method of claim 5, wherein the untreated coke is passed through a finely divided feedstock powder. (11) for a period of time under delayed coking conditions in which an aromatic mineral oil feedstock is heated to an elevated temperature and the heat contained in the heated feedstock penetrates and converts the feedstock into crack vapor and premium coke; introducing the heated feedstock into a coking drum, removing coke from the coke drum upon completion of delayed coking, cooling the coke, contacting the cooled coke with a portion of the aromatic mineral oil feedstock, and calcining the contacted coke. A premium coking method comprising obtaining calcined premium coke with increased density. 12. The method of claim 11, wherein the removed coke is passed through a liquid bath of aromatic mineral oil feedstock. 13. The method of claim 11, wherein the removed coke is atomized with a liquid aromatic mineral oil feedstock. (14) the aromatic mineral oil feedstock is solid at the contact temperature;
12. A process according to claim 11, wherein the coke withdrawn is passed through a finely divided powder of such feedstock. (15) Aromatic mineral oil feedstock from about 850°F to about 11
00°F and the heated feedstock is at a temperature of about 800°F to about 1000°F and a pressure of about 15 psig to about 200 psig sufficient to convert the feedstock to crack vapor and premium coke. The coke is removed from the coke drum upon completion of coking with a portion of the high velocity water jet and the removed coke is contacted with a portion of the aromatic mineral oil feedstock at a temperature of about 2000°F to about 3000°C. A premium coking method comprising calcining the contacted coke at a temperature of F for about 30 minutes to about 10 hours to obtain calcined premium coke with increased density. 16. The method of claim 15, wherein the removed coke is passed through a liquid bath of aromatic mineral oil feedstock. 17. The method of claim 15, wherein the removed coke is atomized with a liquid aromatic mineral oil feedstock. (18) the aromatic mineral oil feedstock is solid at the contact temperature;
16. A process according to claim 15, wherein the coke withdrawn is passed through a finely divided powder of such feedstock. 19. The method of claim 15, wherein the aromatic mineral oil feedstock is selected from the group consisting of hot tar, decant oil, pyrrolytic tar, and pitch.