JPH02202989A - Manufacture of premium coke - Google Patents

Abstract

PURPOSE: To produce premium coke having a low thermal expansion coefficient and excellent characteristics by conducting soaking at the same temp. as that of the coking step for a specified time in the process for producing premium coke from a heavy arom. mineral oil material by delayed coking.

CONSTITUTION: An arom. mineral oil material (e.g. a decant oil, a high-temp. cracking tar, a vacuum residue oil, or a distilled coal tar pitch) is heated to about 850-950°F, introduced continuously into a coke drum, and coked at about 800-925°F under a pressure of about 15-200 psi to give a cracking vapor and coke. The coke in the drum is subjected to hot soaking to give premium coke. The soaking is conducted at the same temp. as that of the step of coke formation and for a time (TS) given by the formulas: TS≥TSM and TSM=e×p(0.050×fa-42.8) (wherein fa is the carbon content (%) in arom compds. measured by C¹³NMR).

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing premium coke using a delayed premium coking process.

There is an increasing demand for high quality aluminum/mium coke for the production of large graphite electrodes used in electric arc furnaces employed in the steel industry. The quality of premium coke used in graphite electrodes is often determined by its coefficient of thermal expansion, whose value ranges from -5 to +8 am/am/”CX
It is in the range of 10-7. Premium coke users are constantly looking for graphite materials with low CTE. C.T.E.
Even small changes in can substantially affect the properties of large electrodes. The density of the graphite electrode is also important in characterizing its properties. Generally, the higher the density, the more
The quality of the electrodes is good.

Premium coke is produced by delayed loking, which converts heavy hydrocarbon feedstocks into coke and lighter hydrocarbon products. In this process, a heavy hydrocarbon feedstock is rapidly heated to crabbing temperature and continuously fed to a coke drum. The heated feed is soaked in the drum with sufficient heat, i.e., the heat contained in the feed, to convert the heated feed into coke and cracked steam. The crabbed steam is taken out at the top of the tower and fractionated,
If necessary, the bottom material is recycled into raw materials. Coke is accumulated in the drum until the drum is full of coke, and when the drum is full, the heated raw material is transferred to another coke drum, and the coke is removed from the full drum. Remove. After removing
The coke is calcined in the cavity to remove volatiles and increase the carbon to hydrogen ratio of the coke.

For the production of large graphite electrodes, calcined premium coke particles obtained from the delayed drawing process are mixed with pitch and then heated at high temperatures to carbonize the pitch.

According to the present invention, premium coke having excellent properties is obtained by subjecting coke to heat soaking performed at substantially the same temperature as the temperature in the coking step. Coke properties are also improved by coking at temperatures lower than those in normal coking processes.

U.S. Pat. No. 4,547,284 discloses that coking is carried out at a temperature below normal temperatures and the resulting coke is heated at a temperature above the coking temperature, preferably at least 18
``Discloses a premium coking process that involves heat soaking at high temperatures.

European Patent Application No. 155.163 discloses temperatures for soaking or drying coke and describes three processes: (1) When making coke, the temperature of the drum is raised especially after the coke making stage; (2)
After stopping the fresh feed of feedstock to the coke drum and forming coke by turning the coker product, or a portion thereof, into heated steam and passing this steam through the already formed coke, (3) discharging the formed coke; 750@F
Maintain temperatures above .

The new feedstock used in this invention is a heavy aromatic mineral oil fraction. These raw materials can be obtained from many coke sources including petroleum, rock oil, tar sand, coal, and the like. A particular raw material is decant oil, also known as slurry oil or clear oil, which is obtained from the effluent fraction from catalytic cracking of gas oils and/or residual oils. Another raw material used in the present invention is ethylene or high temperature cracking tar. This feedstock is a heavy aromatic mineral oil derived from high temperature thermal clubbing of mineral oil to produce olefins such as ethylene. Another raw material is vacuum residue oil, which is a heavy residual oil obtained by flashing or distilling the residue under vacuum. Yet another raw material is vacuum gas oil, a light material obtained by flashing or distilling residual oil under vacuum. Hot tar is also used as a raw material. This thermal tar is a heavy oil and is obtained from the fractionation of a material produced by thermal cracking of gas oil or its WA-like material. Heavy premium coker gas oil is also another feedstock and is an ffi oil obtained from the liquid product produced in coking which turns oil etc. into premium coke. Light oils obtained from coking operations other than premium coking can also be used as raw materials. Straight-run atmospheric gas oil can also be used as a feedstock. This light oil is produced by distilling raw sake at atmospheric pressure or higher pressure. Another raw material that can be used in the present invention is solvent extracted coal tar pitch.

The aforementioned raw materials can be used alone or in combination. In addition, each feedstock may be subjected to hydrotreating and/or thermal cracking prior to use in producing premium grade coke.

As shown in FIG. 1, raw materials are introduced into the coking process via line 1. The raw material, for example, hot tar, is heated in the furnace 3 at a temperature of usually about 800 to 1050 @F, preferably 850 to 950
Heating at a temperature in the range of F. Usually a furnace, such as a vibe still, is used that can rapidly heat the hot tar to said temperature. Take it out of the furnace and pass it through line 4, about 15~
It is introduced into the bottom of coke drum 5 which is maintained at a pressure of about 200 psig. About 780 to about 100 coke drums
Temperatures in the range of 0°F, preferably about 800 to about 925”F
Operate with. In the coke drum, heavy hydrocarbons in the hot tar are cracked to produce cracked steam and premium coke.

Steam is continuously removed from the top of the drum through line 6. The supply of raw material to the drum 5 is interrupted when a predetermined level is reached, and the supply is switched to the second coke drum 5a. Coke has accumulated in drum 5 up to this point. In addition, the same operation as in the drum 5 is performed in the second drum a. This switching removes drum 5 from the feed system, opening it and removing the accumulated coke therefrom using conventional techniques. This caulking cycle lasts from about 16 to about 60 hours, preferably from about 24 to about 48 hours.
It takes time.

Before removing coke from coke drum 5,
The coke within is subjected to a heat soak at substantially the same temperature at which the coking operation was performed. Heat soaking is performed using a non-coking fluid. This non-coking fluid is introduced into the apparatus through line 16, heated in a heat soak oven 17, and passed as steam from the heat soak oven through line 18 to the bottom of the coke drum.

The heat soaked material leaves the top of the coke drum through line 19 and is introduced into the heat soaked fractionator 20.

The vapor stream entering fractionation column 20 contains not only heat soaking material, but also light or heavy material released from the coke during the heat coking operation. This vapor is fractionated in fractionator 20 into a c,-C3 product stream 21, a gasoline stream 22, a heavy gas oil stream 23, and a heavier gas oil which is removed from the fractionator through line 24. If desired, some of the materials may be combined with the coke feedstock.

Any material that is not coked and does not affect the premium coke properties can be used as the heat soaking material. For example, heat soaking materials are
Liquid hydrocarbon fractions or gaseous hydrocarbons such as light hydrocarbons, nitrogen, steam, etc. Usually distillates or light gas oils are applied because these materials are readily available and are not affected by heat soaking temperatures. In this case, light gas oil is used as the heat soaking material. If desired, this heat soak material may be recovered from the heat soak fractionator and recycled through line 26 to heat soak furnace 26.

When heat soaking is performed at the same temperature as the coking operation, the coke drum is operated at a lower temperature than normal coking temperatures, while at the same time producing a product with excellent physical properties, ie, very low CTE. Surprisingly, as the coking (and heat soaking temperature) is lowered, the CTE of the coke improves as indicated by the TSN as defined herein. The CTE is as low as possible and the VBD is as high as possible.

Referring again to FIG. 1, the vapor obtained from the top of the coke drum in a coking operation is conveyed by line 6 to coker fractionation column 7. As shown in FIG.
and fractionated into premium coker heavy gas oil which is taken out from fractionator 7 through line 11.

As mentioned above, the premium coker heavy gas oil removed from fractionator 7 can be recycled through line 12 to coker furnace 3 in a desired proportion. The excess bottoms material can be subjected to numerical residue purification techniques, if desired.

The raw coke is removed from the coke drums 5 and 5a through outlets 13 and 13a, respectively, and introduced into a calciner 14 in which it is exposed to high temperatures to remove volatile substances and increase the carbon number relative to the hydrogen number of the coke. . Firing takes approximately 2
000 to about 3000"F, preferably about 2400"
to about 2600"F. The coke is heated under calcination conditions for about 0.5 to about 10 hours, preferably about 1 to about
Maintain for about 3 hours. The calcination temperature and time will vary depending on the desired properties of the final coke product. Calcined premium coke suitable for the production of large graphite electrodes is recovered from the calciner through outlet 15.

Although the present invention has been described as utilizing both a coker fractionator and a heat soaking fractionator, it is within the scope of the invention to perform both operations in a single fractionator, in which case the coking The distillate from the coke drum during both the heat soaking and heat soaking operations is fed to this single fractionation column. Also, the streams that are normally regenerated from two fractionators are all obtained from one fractionator. Only TSN conditions are necessary to obtain coke with predetermined properties.

The heat soaking operation typically ranges from about 4 to about 60, preferably about 8
~32 hours. The appropriate operating time depends on the raw materials used in the coking operation, the coking time, and the coking temperature;
SN is obtained.

TSN is the CTE and VB of premium coke range.
Represents the amount of heat soaking required to make coke with D. The sum of the temperature and time combination during the heat soaking and the temperature and time combination during the coking stage of the coke produced according to the invention is given by the following equation:

TS, - or yr + T S v- or da ≧TSN
...(1) However, in equation (1), TS, -◆2 Thermal intensity during the mite coking stage, TS
y-4y,: thermal intensity during the soaking stage, and TSN: indicates the thermal intensity required to produce premium coke from all feedstock entering the coke drum during one cycle.

Thermal severity (TS) is defined by the following equation:

TS-[exp(-58273/T [@R1)] X
1: RX time 1 hour] - (2) However, RX time is the time for coking and/or heat soaking of raw materials, and T: temperature of coke or a liquid forming coke.

In commercial coke drums, - T in the membrane is about 5"F to about 60@F above the drum steam temperature. More commonly, TS ranges from about 15" to about 60@F above the drum steam temperature.
The temperature is about 30'F higher.

TSN is determined by the following equation.

T S N -exp (0,050X f a -39
, 8) -<3) fa: percentage of carbon atoms in aromatic form, determined by C1C13N analysis; often the part of the feedstock that undergoes the least intensity of reaction, i.e. the last drop of feedstock entering the coke drum It is economically appropriate to select coking and thermal coking conditions that satisfy equation (1). If extremely low cracking temperatures are used in combination with relatively aromatic feedstocks, ensuring that the final feedstock entering a conventional drum satisfies equation (1) may require excessively long heat soak times. do. In such a case, the actual heat soaking time required is as follows.

T S ,,-Yuda ≧ 'r S M
=, (4) TS, the minimum thermal intensity during the soaking stage required to obtain acceptable CTE and acceptable VBD based on single drum average values for coke produced across two drums.

TS is determined from the following equation.

T S M -exp (0,050X f a -42
, 8) - (5) In a preferred embodiment of the present invention, the soaking time is such that the equation (1) is equal to choose to be satisfied. Since the TS of the last drop of feedstock placed in a standard ordinary coke drum is 0, the value of equation (1) decreases to: for standard ordinary coking.

T.S.-. (6) Due to the wide range of thermal severities, the average coke properties of the entire ordinary coke drum are those of premium coke even in the case of heat soaking with low thermal severities. This range is defined by equation (4) and equation (5).

The examples presented below illustrate the results obtained by practicing the invention. Table 1 shows the physical properties of the raw materials used in the invention.

Example 1 A hot tar exhibiting the physical properties shown in Table 1 was prepared on a laboratory scale in a batch coke drum for 825.850 s 8
75 and 900' FM) im and 1100 psi pressure for 8 hours.

Similar hot tars were also coked under identical conditions except that the 8 hour, 24 hour and 56 hour heat soak treatments were conducted at coking temperatures.

As shown in Table 1, the TSN of this hot tar is calculated by the formula (3
), it is 9.8×10 −17 hours.

The results of the caulking experiment are shown in Table 2. This result clearly shows that heat soaking dramatically improves the properties of coke. The increase in heat soaking time is 9.8X1 for TS that combines caulking and heat soaking.
When less than 0"" time - numerically very beneficial. The best coke properties, i.e. low CTE and high VBD, are achieved when the combined TS is approximately 9.8X10-17
When equal to or more than the time, obtained at lower coking and heat soaking temperatures.

CTE is determined by X-ray diffraction using a 3/4-inch graphitized electrode rod or from the intensity of the 002 peak of graphite.
ll can be determined. The two methods have certain determinable relationships, as shown in FIG. CTE obtained from either method can be correlated with results obtained using the other method.

Example 2 Pyrolysis decant oil having the physical properties shown in Table 1 was
Temperature 825.8 in a laboratory scale batch coke drum
50.875 and 900"F and 60 psig pressure for 8 hours. The same decanted oil was also co-kinked for 8 hours.
Coking was done under similar conditions except that the 24 hour, 56 hour, and 88 hour heat soaks were conducted at coking temperatures.

As shown in Table 1, TSN of decant oil is 20.3X1
0-17 hours.

The caulking experiment results are shown in Table 3. Similar to Example 1, heat soaking dramatically improved the CTE of the coke. In this case, the length of heat soaking time is 20.3X10-1
When less than 7 hours - the numerical benefit is clear.

The best CTE is also obtained when coking and heat soaking temperatures are low, when the combined TS is approximately equal to or greater than TSN.

Example 3 The pyrolysis decant oil shown in Table 1 was coked at a pressure of 55 psig in a continuously fed pilot plant similar to conventional coking operations. Experimental conditions and d
The caulking results are shown in Table 4. The TSN and TSM of this raw material were calculated from equations (3) and (4), and were
20.4><IQ-17 and 1.0X10-17, respectively. Alphabet groups B to E shown in Table 4
is a heat soak at a constant temperature as opposed to a heat soak at an elevated temperature.

The experimental results without heat soaking are shown in Group A of Table 4. Group A experiments number 1 and 2 were conducted under conditions such that the feedstock placed in the drum (ie, the feedstock that was in the drum for an extended period of time) did not initially have a TS equal to TSN. In run numbers 3 and 4, the initial feedstock TS entering the coke drum was 65.7X1
0-17, which was higher than TSN. however,
In these experiments as well, approximately 31% by weight of the final feedstock placed in the coke drum ([(20,4X10
'''l〕hour/65゜7×10-17 hours)×100]
) was not subjected to the same thermal intensity as TSN.

Groups B, C, and D shown in Table 4 show the effect of heat soaking under the coking conditions substantially shown in Group A. In each case, heat soaking
Shows general benefits to coke properties. Experiment 5 of Group B shows that a lower CTE is obtained by using a thermal intensity of 2,8 x 10'7 hours, which is a slightly more intense condition of 1.0 x 10-17 hours.

Looking at the results obtained from experiment numbers 8 (Group B), 9 (Group C) and 7 (Group D), the coke with the best properties (low CTE and high VBD) reduces coking and heat soaking temperatures. It shows what can be obtained according to the method.

Group E of Table 4 substantially simulates the effect of heat soaking (Experiment No. 8) on coke forming temperatures at temperatures above the coke forming temperature as described in U.S. Pat. No. 4,547,284 as a conventional example. A comparison is shown with the effect of heat soaking (experiment numbers 10 and 11). In experiment number 8, a coke with clearly superior properties is obtained. Also, clearly coke with superior properties can be obtained by soaking at temperatures close to the coke forming temperature.

Example 4 Thermal tar and pyrolysis decant oil having the properties and TSN shown in Table 1 were coked in a laboratory scale batch coke drum under Loops ig pressure and temperatures of 825 and 850°C.

The coke drum was then subjected to a heat soak at the same pressure and either the coke forming temperature or a temperature of 775'F.

Table 5 shows the results of these experiments.

Coking at 825"F for 24 hours and 850"'F for 16 hours each reduced the feedstock in batch coke drums to 3.
Subjected to thermal intensity of 2 x 10-17 hours and 4.7 x 10-17 hours.

These thermal intensities are relatively close to and greater than 4.5 x 10" hours, which is the thermal intensity required to produce coke of the best properties from the particular hot tar studied. This result would indicate that additional heat soaking would not be expected to substantially lower the CTE of coke from this feedstock. The results shown in the table confirm the expectations based on TSN. Heat soaking of hot tar at widely different thermal intensities (24 hours at 825"F and 24 hours at 775"F) results in approximately 1.
gives a coke with a CTE of 6X10-''/'C. However, for the pyrolysis decant oil in Table 5,
TSN is 20.9XIQ - 17 hours, which is 82
The thermal intensity is significantly greater than that achieved by coking at 5@F for 24 hours or 850@F for 16 hours.

For this feedstock, heat soaking under more severe conditions at the coke forming temperature would be expected to yield coke with better properties than heat soaking at 775"F. This result is confirmed by the data. ing.

Based on the standard deviations shown in the table, the differences in CTH obtained by coking temperature and heat soaking at 775'F are statistically significant with 99% confidence.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic flow sheet explaining the present invention, and FIG. 2 is a diagram showing the relationship between two general methods for determining the coefficient of thermal expansion of coke O1.

Claims (1)

[Scope of Claims] (1) Heating an aromatic mineral oil feedstock to a high temperature, introducing it into a coke drum under delayed stirring conditions, and soaking the heated feedstock in the drum with the heat contained in the feedstock, the contents of the drum in a method in which the feedstock is converted to cracked steam and premium coke at a temperature below normal coking temperatures and the introduction of feedstock into the drum is interrupted when the drum is filled to a predetermined volume; Delayed premium comprising obtaining premium coke by subjecting a product to heat soaking at substantially the same temperature as forming coke, and characterized in that the time of the heat soaking is expressed by the following formula: A method for producing premium coke using a coking process. TS_SO_KING_G≧TS_M TS_M=exp(0.050×fa-42.8) (where fa is the percentage of carbon in the aromatic compound measured by C^1^3 NMR analysis method (2) The aromatic mineral oil raw material is decant oil, high temperature decomposition tar, vacuum residue, vacuum light oil, hot tar, heavy premium coker light oil,
2. The method of claim 1, wherein the gas oil is selected from the group consisting of straight-run atmospheric gas oil and distilled coal tar pitch. (3) The soaking time is defined by TS soaking, and TS_so_king_g ≧TS_N and TS_N
3. The method of claim 2, wherein =exp(0.050*fa-39.8). 4. The method of claim 2, wherein the heat soaking is performed for about 4 to about 6 hours. (5) Claim 2, wherein the heat soaking is performed for about 8 to about 32 hours.
The method described in. (6) heating an aromatic mineral oil to about 850 to about 950°F;
Continuously introduced into the coke drum, the heated raw material is heated to approx.
00 to about 925°F, about 15 to about 200 psig
and soaking in the heat contained in the heated feedstock in the drum at a pressure of A method in which the introduction of feedstock into a drum is interrupted when the drum is filled to a predetermined volume, the contents of the coke drum being subjected to a heat soak at a temperature substantially the same as the temperature of the coke drum during the coking operation. 1. A method for producing premium coke using a delayed premium coking process, the method comprising obtaining premium coke by subjecting the coke to water, and characterized in that the heat soaking time is expressed by the following formula. TS_SO_KING_G≧TS_M TS_M=exp(0.050×fa-42.8) (where fa is the percentage of carbon in the aromatic compound measured by C^1^3 NMR analysis method ) (7) The aromatic mineral oil raw material is decant oil, high temperature decomposition tar, vacuum residue, vacuum gas oil hot tar, heavy premium coker gas oil,
7. The method of claim 6, wherein the method is selected from the group consisting of straight-run atmospheric gas oil and distilled coal tar pitch. (8) Claim 7, wherein the heat soaking is performed for about 8 to about 32 hours.
The method described in. (9) The soaking time is TS_so_kin_
defined as
The method according to claim 6.