CA1127988A - Inhibition of coke puffing - Google Patents
Inhibition of coke puffingInfo
- Publication number
- CA1127988A CA1127988A CA320,986A CA320986A CA1127988A CA 1127988 A CA1127988 A CA 1127988A CA 320986 A CA320986 A CA 320986A CA 1127988 A CA1127988 A CA 1127988A
- Authority
- CA
- Canada
- Prior art keywords
- puffing
- coke
- inhibitor
- iron
- feedstock
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
Case No. 6071 Inhibition of Coke Puffing Abstract of the Disclosure Puffing of electrode grade coke during graphi-tization is reduced or eliminated by addition of a puf-fing inhibitor to the coker feedstock prior to formation of the coke.
Description
~ .lZ79~8 ~
Background of the Invention 1. Field of the Invention This invention relates to the manufacture of graphite electrodes ~rom petroleum coke, and more parti-cularly to the inhibition of "puffing" of coke during graphitization of premium coke electrodes. These elec-trodes, primarily used in the electric furnace steel making process, must meet rigid specifications. Much of the petroleum coke presently available commercially has a tendency to expand rapidly and irreversibly during the heat treatment required as part of the electrode manufacturing process. This expansion is commonly re-ferred to as "puffing". When the puffing phenomenon oc-curs to too great an extent, the electrode is ren-dered useless.
Background of the Invention 1. Field of the Invention This invention relates to the manufacture of graphite electrodes ~rom petroleum coke, and more parti-cularly to the inhibition of "puffing" of coke during graphitization of premium coke electrodes. These elec-trodes, primarily used in the electric furnace steel making process, must meet rigid specifications. Much of the petroleum coke presently available commercially has a tendency to expand rapidly and irreversibly during the heat treatment required as part of the electrode manufacturing process. This expansion is commonly re-ferred to as "puffing". When the puffing phenomenon oc-curs to too great an extent, the electrode is ren-dered useless.
2. Prior Art The reduction or elimination of the puffing phenomenon has been accomplished in the past by adding a puffing inhibitor to a blend of calcincd petroleum coke and binder pitch prior to extruding and baking the electrode.
A method of controlling puffinq comprising adding sodium carbonate prior to extruding the elec-trode is descxibed in U.S. Patent No. 2,814,076.
A method of con-trolliny puffin~ by addition of iron oxide prior to extruding and baking an electrode is descri~ed in U.S Patents Nos. 3,5~"745 and
A method of controlling puffinq comprising adding sodium carbonate prior to extruding the elec-trode is descxibed in U.S. Patent No. 2,814,076.
A method of con-trolliny puffin~ by addition of iron oxide prior to extruding and baking an electrode is descri~ed in U.S Patents Nos. 3,5~"745 and
3,624,231.
- ~1~98B
A method of blending petroleum coke with an oxygen-containing compound of iron, calcium, aluminum or manganese to inhibit puffing during graphitization is described in U.S. Patent No. 3,842,165.
The addition of a titanium or zirconium com-pound with conventional puffing inhibitors is described in U.S. Patent No. 3,563,705; and the addition of calcium cyanamid as a puffiny inhibitor is disclosed in U.S.
Patent No. 3,642,962.
A method of producing a low sulfur coke com-prising addition of an iron compound and a metal chloride, either to a coker feedstoc~ or subsequent to the coking operation, is described in U.S. Patent No. 3,873,427. The process described in that patent contemplates addition of a large amount, such as from 3 to 25 weight percent, of an iron compound along with a metal chloride, and the resulting low sulfur coke is not suitable for electrode manufacture because of the high level of impurities in-troduced during the desulfurization step.
Conventional commercial yraphite electrode manufacture presently utilizes the addition of from 0.5 to 3.0 percent iron oxide mixed with co~e and binder pitch prior to extrusion and baking of the electrode.
This proce~ure has been ~uite effective in controlling puffing of the electrode during the graphitization step.
It is an object of the present invention to pxo~ide an improved process for reducing or eliminating puffiny during manufacture of gra~hite electrodes.
It is a further object of the invention to llZ7988 pro~desuch a process which results in an electrode having a lower level of impurities than results from conventional methods of manufacture.
The present invention provides a method of produ-cing premium delayed petroleum coke wherein a coking feed-stock having a sulfur content high enough to produce a puf-fing coke is heated in a coking furnace and then charged to a coking drum maintained at premium coking conditions to produce premium coke, the improvement wherein an effective amount of a puffing inhibitor is added to said feedstock prior to charging the feedstock to the coking drum.
In accordance with the present invention, electrode puffing is controlled by addition of a small amount of a puf-fing inhibitor to a coker feedstock prior to introducing the feedstock to a coking drum. The addition of from 0.005 to 1.0 percent by weight based on weight of coker feedstock, of an inhibitor such as iron oxide to a coker feedstock has been found to inhibit puffing as effectively as does the addition of a much larger amount of puffing inhibitor to a blend of calcined coke and binder pitch in accordance with conventional procedure.
As used herein, the term "premium coke" is used to described delayed petroleum coke which is suitable for manufacture of large graphite electric arc steel furnace electrodes.
~ n order for coke to be marketa~le as premium coke, it must meet certain specifications as to composition and physical properties. An important specification is the linear coefficient of thermal expansion (CTE). One method of determining the CTE of a coke is the optical lever method in which the expansion of a bar formed of graphitized coke is measured over a temperature range of 30 to g8C. The CTE
measured in this manner should be less than 7.0 x 10 /C, and in many cases .................. ~
~Z79~
must be less than 5.0 x 10 7/oC in order to meet customer requirements. The CTE of an actual large electrode made from such coke is normally slightly higher than that of the graphite test rod.
The conventional process for making premium coke comprises introducing a premium coker feedstock or feedstocks such as thermal tar, decant oil from a fluid catalytic cracking unit, pyrolysis tar or the like to a coker furnace where the feedstock is heated to coking temperature, generally from 425 to 540C, Eollowed by introduction of the heated feedstock to a delayed coking drum maintained at typical premium coking conditions of from 440 to 470C and 2.5 to 7 kg/cm2. The coke product is removed from the coking drum, and is typically cal-cined in a rotary kiln at a temperature of from 1100 to 1500C to remove Yolatile material therefrom. The cal-cined coke is then sizc~ to a desired size distribution such as from 200 mesh material to about 3 or 4 mesh mate-rial, blended with a binder pitch and extruded into the desired electrode configuration. The thus-formed material is then baked at a temperature of from 800 to 1200C to car~onize the binder pitch and to give the extruded electrode strength. Finally, the baked electrode is graphitized by heating to a temperature oE from 2500 to 2S 3000C to produce thc graphitizod clectrodc. The graphi-tized electrode is then machined to specifications for use in an electric arc steel furnace.
~ccording to present co~nercial practice, pre-mium coke having an amount of sulfur insufficient to 1~,2 7988 .~
cause puffing can be graphitized as described above with-out addition of a puffing inhibitor. Premium coke ha~ing an amount of sulfur high enough to cause puffing generally is treated with from 0.5 to 3.~ weight percent iron oxide, depending on the amount of sulfur and the degree of puf-fing, added to a mixture of calcined coke and binder pitch prior to extrusion and baking. Premium coke having less than 0.25 weight percent sulfur normally does not require a puffing inhibitor. Premium co~e having up to about 0.7 weight percent sulfur may require an inhibitor, and prem-ium coke having more than that amount almost always needs an inhibitor.
According to the present invention, the above procedure is modified by adding the puffing inhibitor to lS the coker feedstock prior to introduction of the feed-stock to the coking drum, and by utilizing a much lower amount of the inhibitor. The exact operation of the inhibitor is not clearly unders~ood, b~t it is apparent that when the inhibitor is added directly to the coker feedstock prior to formation of the coke particles, the inhibitor is distributed throughout the coke particles more or less uniformly, whereas according to con~entional techniques for adding the inhibitor, the inhihitor can only contact the outer surface of the previously formed 2~ co~e particles.
The preferred inhibitors in accordance with the in~ention are oxygen-containing cc,mpounds o~ iron, calcium, aluminum and manyanese. Of these, iron oxide is the preferred matelial. Inhihitors il~ so~id particle form can be added to the coker feedstock by forming a slurry of the inhibitor particles with a portion of the feedstock and injecting it at the discharge of the fur-nace charge pump Any conventional puffing inhibitor S can be used in the invention, including oxygen-containing compounds of iron, calcium, aluminum and manganese, with or without a titanium or zirconium compound. The oxides, hydroxides and carbonates of these elements all have utility as puffing inhibitors. Ferric oxide is widely used because of its availability and low price. ~inely divided iron powder may also be used.
In accordance with one embodiment of the in-vention, the puffing inhibitors are added in hydrocarbon-soluble form. Acetyl acetonates of metals are soluble in hydrocarbons and can be used as a source of the in-hibiting metal. Another soluble iron compound which is suitable is ferrocene. The use of soluble compounds as a source of the inhibitor assures maximurn uniformity of dispersion, and also ~liminates the problems associated with presence of particulate material in the piping.
The in~ention is applicable in the formation of graphitized electrodes fro~l coke containin~ an amount of sulfur sufficient to cause an undesirable amount of puffing. The amount of inhibitor needed is dependent to some extent upon the sulfur leve} in the feedstock, and varies from about 50 parts pex million to about 1.0 percent by weight of the inhibiting metal in the coker feedstock. The level of inhibitor in the coke is de-pendent on the coke yield. For example, if a feedstock 1~7988 makes 30 weight percent coke, the metal inhibitor in the coke would be expected to be about three times as much as the level in the feedstock, as the inhibitor tends to concentrate in the coke rather than in the volatile material going from the coke drum as vapor.
The impro~ed results obtained by operation in accordance with the invention are illustrated in the following example.
Example I
In this example, various amounts of iron oxide were added to a blend of binder pitch and previously formed coke particles. The amount of expansion of the resulting material during heat treatment is shown in Table l below.
_able 1 i ppm Iron Added ~egree of Puffing as Ferric Oxide (Percent of 1ength) 0 7.0 300 7.0 700 6~2 In another run where the conditions were the same as for the experiments listed in Table l, a coker feedstock to which iron oxide had been added was coked, and the resulting coke with the iron distributed there-through was ~lended with binder pitch and tested in the same manner as the samples to which the iron oxide had been added later. The resulting coke contained 1260 parts per million of iron and showed an expansion of only 2.4 percent, whereas, as can be seen from Table l above, addition of 2500 parts per million iron after the coke was formed produced an electrode which exhi-bited 4.4 percent expansion. Thus, it can be seen from the above example that operation in accordance with this invention provides reduced puffing compared to operation with a larger amount of inhibitor added after the coke has been formed.
To meet most specifications, it is generally required that the expansion during graphitization be of the order of l.0 percent or less, and preferably an expansion of near zero is obtained. The required re-duction or elimination of puffing can be obtained according to this invention utilizing a much lower amount of inhibitor than is required according to con-ventional practice.
The process accordin~ to this invention in-volves addition of from 50 parts per million to l.0 percent by weight of a puffing inhibitor to a coker feedstock. Preferably, from 500 to 5000 parts per million of the puffing inhibitor, based on the amount of metal in the inhibitor compound, is added to the feedstock.
The point of addition of the inhibitor may be anywhere upstream from the coking drum, but preferably is at the discharge of the coker furnace charge pump to mini-mize materials handling problems, particularly when a particulate inhibitor is utilized.
It is essential in accordance with the invention l~Z7988 that an effective amount of a puffing inhibitor be added to a coking feedstock prior to forming coke in the coke drum. When this is done, reduction or elimination of puf-fing is obtained with a smaller amount of inhibitor than is required according to conventional practice, The fore-going detailed description of the preferred embodiments of the invention is intended to be exemplary, rather than limiting, and numerous variations and modifications will be apparent to those skilled in the art upon consideration of the foregoing disclosure.
- ~1~98B
A method of blending petroleum coke with an oxygen-containing compound of iron, calcium, aluminum or manganese to inhibit puffing during graphitization is described in U.S. Patent No. 3,842,165.
The addition of a titanium or zirconium com-pound with conventional puffing inhibitors is described in U.S. Patent No. 3,563,705; and the addition of calcium cyanamid as a puffiny inhibitor is disclosed in U.S.
Patent No. 3,642,962.
A method of producing a low sulfur coke com-prising addition of an iron compound and a metal chloride, either to a coker feedstoc~ or subsequent to the coking operation, is described in U.S. Patent No. 3,873,427. The process described in that patent contemplates addition of a large amount, such as from 3 to 25 weight percent, of an iron compound along with a metal chloride, and the resulting low sulfur coke is not suitable for electrode manufacture because of the high level of impurities in-troduced during the desulfurization step.
Conventional commercial yraphite electrode manufacture presently utilizes the addition of from 0.5 to 3.0 percent iron oxide mixed with co~e and binder pitch prior to extrusion and baking of the electrode.
This proce~ure has been ~uite effective in controlling puffing of the electrode during the graphitization step.
It is an object of the present invention to pxo~ide an improved process for reducing or eliminating puffiny during manufacture of gra~hite electrodes.
It is a further object of the invention to llZ7988 pro~desuch a process which results in an electrode having a lower level of impurities than results from conventional methods of manufacture.
The present invention provides a method of produ-cing premium delayed petroleum coke wherein a coking feed-stock having a sulfur content high enough to produce a puf-fing coke is heated in a coking furnace and then charged to a coking drum maintained at premium coking conditions to produce premium coke, the improvement wherein an effective amount of a puffing inhibitor is added to said feedstock prior to charging the feedstock to the coking drum.
In accordance with the present invention, electrode puffing is controlled by addition of a small amount of a puf-fing inhibitor to a coker feedstock prior to introducing the feedstock to a coking drum. The addition of from 0.005 to 1.0 percent by weight based on weight of coker feedstock, of an inhibitor such as iron oxide to a coker feedstock has been found to inhibit puffing as effectively as does the addition of a much larger amount of puffing inhibitor to a blend of calcined coke and binder pitch in accordance with conventional procedure.
As used herein, the term "premium coke" is used to described delayed petroleum coke which is suitable for manufacture of large graphite electric arc steel furnace electrodes.
~ n order for coke to be marketa~le as premium coke, it must meet certain specifications as to composition and physical properties. An important specification is the linear coefficient of thermal expansion (CTE). One method of determining the CTE of a coke is the optical lever method in which the expansion of a bar formed of graphitized coke is measured over a temperature range of 30 to g8C. The CTE
measured in this manner should be less than 7.0 x 10 /C, and in many cases .................. ~
~Z79~
must be less than 5.0 x 10 7/oC in order to meet customer requirements. The CTE of an actual large electrode made from such coke is normally slightly higher than that of the graphite test rod.
The conventional process for making premium coke comprises introducing a premium coker feedstock or feedstocks such as thermal tar, decant oil from a fluid catalytic cracking unit, pyrolysis tar or the like to a coker furnace where the feedstock is heated to coking temperature, generally from 425 to 540C, Eollowed by introduction of the heated feedstock to a delayed coking drum maintained at typical premium coking conditions of from 440 to 470C and 2.5 to 7 kg/cm2. The coke product is removed from the coking drum, and is typically cal-cined in a rotary kiln at a temperature of from 1100 to 1500C to remove Yolatile material therefrom. The cal-cined coke is then sizc~ to a desired size distribution such as from 200 mesh material to about 3 or 4 mesh mate-rial, blended with a binder pitch and extruded into the desired electrode configuration. The thus-formed material is then baked at a temperature of from 800 to 1200C to car~onize the binder pitch and to give the extruded electrode strength. Finally, the baked electrode is graphitized by heating to a temperature oE from 2500 to 2S 3000C to produce thc graphitizod clectrodc. The graphi-tized electrode is then machined to specifications for use in an electric arc steel furnace.
~ccording to present co~nercial practice, pre-mium coke having an amount of sulfur insufficient to 1~,2 7988 .~
cause puffing can be graphitized as described above with-out addition of a puffing inhibitor. Premium coke ha~ing an amount of sulfur high enough to cause puffing generally is treated with from 0.5 to 3.~ weight percent iron oxide, depending on the amount of sulfur and the degree of puf-fing, added to a mixture of calcined coke and binder pitch prior to extrusion and baking. Premium coke having less than 0.25 weight percent sulfur normally does not require a puffing inhibitor. Premium co~e having up to about 0.7 weight percent sulfur may require an inhibitor, and prem-ium coke having more than that amount almost always needs an inhibitor.
According to the present invention, the above procedure is modified by adding the puffing inhibitor to lS the coker feedstock prior to introduction of the feed-stock to the coking drum, and by utilizing a much lower amount of the inhibitor. The exact operation of the inhibitor is not clearly unders~ood, b~t it is apparent that when the inhibitor is added directly to the coker feedstock prior to formation of the coke particles, the inhibitor is distributed throughout the coke particles more or less uniformly, whereas according to con~entional techniques for adding the inhibitor, the inhihitor can only contact the outer surface of the previously formed 2~ co~e particles.
The preferred inhibitors in accordance with the in~ention are oxygen-containing cc,mpounds o~ iron, calcium, aluminum and manyanese. Of these, iron oxide is the preferred matelial. Inhihitors il~ so~id particle form can be added to the coker feedstock by forming a slurry of the inhibitor particles with a portion of the feedstock and injecting it at the discharge of the fur-nace charge pump Any conventional puffing inhibitor S can be used in the invention, including oxygen-containing compounds of iron, calcium, aluminum and manganese, with or without a titanium or zirconium compound. The oxides, hydroxides and carbonates of these elements all have utility as puffing inhibitors. Ferric oxide is widely used because of its availability and low price. ~inely divided iron powder may also be used.
In accordance with one embodiment of the in-vention, the puffing inhibitors are added in hydrocarbon-soluble form. Acetyl acetonates of metals are soluble in hydrocarbons and can be used as a source of the in-hibiting metal. Another soluble iron compound which is suitable is ferrocene. The use of soluble compounds as a source of the inhibitor assures maximurn uniformity of dispersion, and also ~liminates the problems associated with presence of particulate material in the piping.
The in~ention is applicable in the formation of graphitized electrodes fro~l coke containin~ an amount of sulfur sufficient to cause an undesirable amount of puffing. The amount of inhibitor needed is dependent to some extent upon the sulfur leve} in the feedstock, and varies from about 50 parts pex million to about 1.0 percent by weight of the inhibiting metal in the coker feedstock. The level of inhibitor in the coke is de-pendent on the coke yield. For example, if a feedstock 1~7988 makes 30 weight percent coke, the metal inhibitor in the coke would be expected to be about three times as much as the level in the feedstock, as the inhibitor tends to concentrate in the coke rather than in the volatile material going from the coke drum as vapor.
The impro~ed results obtained by operation in accordance with the invention are illustrated in the following example.
Example I
In this example, various amounts of iron oxide were added to a blend of binder pitch and previously formed coke particles. The amount of expansion of the resulting material during heat treatment is shown in Table l below.
_able 1 i ppm Iron Added ~egree of Puffing as Ferric Oxide (Percent of 1ength) 0 7.0 300 7.0 700 6~2 In another run where the conditions were the same as for the experiments listed in Table l, a coker feedstock to which iron oxide had been added was coked, and the resulting coke with the iron distributed there-through was ~lended with binder pitch and tested in the same manner as the samples to which the iron oxide had been added later. The resulting coke contained 1260 parts per million of iron and showed an expansion of only 2.4 percent, whereas, as can be seen from Table l above, addition of 2500 parts per million iron after the coke was formed produced an electrode which exhi-bited 4.4 percent expansion. Thus, it can be seen from the above example that operation in accordance with this invention provides reduced puffing compared to operation with a larger amount of inhibitor added after the coke has been formed.
To meet most specifications, it is generally required that the expansion during graphitization be of the order of l.0 percent or less, and preferably an expansion of near zero is obtained. The required re-duction or elimination of puffing can be obtained according to this invention utilizing a much lower amount of inhibitor than is required according to con-ventional practice.
The process accordin~ to this invention in-volves addition of from 50 parts per million to l.0 percent by weight of a puffing inhibitor to a coker feedstock. Preferably, from 500 to 5000 parts per million of the puffing inhibitor, based on the amount of metal in the inhibitor compound, is added to the feedstock.
The point of addition of the inhibitor may be anywhere upstream from the coking drum, but preferably is at the discharge of the coker furnace charge pump to mini-mize materials handling problems, particularly when a particulate inhibitor is utilized.
It is essential in accordance with the invention l~Z7988 that an effective amount of a puffing inhibitor be added to a coking feedstock prior to forming coke in the coke drum. When this is done, reduction or elimination of puf-fing is obtained with a smaller amount of inhibitor than is required according to conventional practice, The fore-going detailed description of the preferred embodiments of the invention is intended to be exemplary, rather than limiting, and numerous variations and modifications will be apparent to those skilled in the art upon consideration of the foregoing disclosure.
Claims (10)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method of producing premium delayed petroleum coke wherein a coking feedstock having a sulfur content high enough to produce a puffing coke is heated in a coking furnace and then charged to a coking drum maintained at premium coking conditions to produce premium coke, the improvement comprising an amount of a puffing inhibitor being added to the feedstock prior to charging the feedstock to the coking drum sufficient to provide an iron level of from 0.005 to 1.0% by weight of the feedstock.
2. The method of claim 1 wherein the puffing inhibitor is selected from the group consisting of oxygen-containing compounds of iron, calcium, aluminum and manganese.
3. The method of claim 1 wherein the puffing inhibitor is iron oxide.
4. The method of claim 3 wherein the puffing inhibitor is ferric oxide and is added in an amount to provide an iron level of from 0.05 to 0.5 percent by weight of the coker feedstock.
5. The method of claim 1 wherein the puffing inhibitor is a hydrocarbon soluble compound containing a metal selected from the group consisting of iron, calcium, aluminum and manganese.
6. The method of claim 1 wherein the puffing inhibitor is an acetyl acetonate of a metal selected from the group consisting of iron, calcium, aluminum and manganese.
7. The method of claim 5 wherein the puffing inhibitor is ferrous acetyl acetonate.
8. The method of claim 1 wherein the puffing inhibitor is ferrocene.
9. The method of claim 1 wherein the puffing inhibitor is a hydrocarbon-soluble iron compound and is added in an amount to provide an iron level of from 0.05 to 0.5 percent by weight in the coker feedstock.
10. The method of claim 1 wherein the puffing inhibitor is iron powder.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320,986A CA1127988A (en) | 1979-02-05 | 1979-02-05 | Inhibition of coke puffing |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320,986A CA1127988A (en) | 1979-02-05 | 1979-02-05 | Inhibition of coke puffing |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1127988A true CA1127988A (en) | 1982-07-20 |
Family
ID=4113479
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA320,986A Expired CA1127988A (en) | 1979-02-05 | 1979-02-05 | Inhibition of coke puffing |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1127988A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114621792A (en) * | 2022-03-30 | 2022-06-14 | 西安交通大学 | By using KMnO4System and method for removing gasified tar by modified biomass coke |
-
1979
- 1979-02-05 CA CA320,986A patent/CA1127988A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114621792A (en) * | 2022-03-30 | 2022-06-14 | 西安交通大学 | By using KMnO4System and method for removing gasified tar by modified biomass coke |
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