CA1072476A - Process for producing high-crystalline petroleum coke - Google Patents
Process for producing high-crystalline petroleum cokeInfo
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- CA1072476A CA1072476A CA261,855A CA261855A CA1072476A CA 1072476 A CA1072476 A CA 1072476A CA 261855 A CA261855 A CA 261855A CA 1072476 A CA1072476 A CA 1072476A
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Abstract
ABSTRACT
A novel process is described for preparation of high-crystalline petroleum coke from a variety of petroleum feedstocks, including feedstocks from which a premium grade coke could not heretofore have been obtained. The process involves the removal of non-crystalline carbon-forming substances from petroleum feedstocks by subjecting the feedstocks to preliminary heat-treatment to effect cracking and soaking, and subsequently by subjecting the materials to high-temperature flash distillation so as to remove the non-crystalline substances in the form of pitch. The overhead distillate of the flash distillation is then fractionated into cracked gas, gasoline, gas oil and a heavy residue, with subsequent coking of the heavy residue to yield high-crystalline petroleum coke.
A novel process is described for preparation of high-crystalline petroleum coke from a variety of petroleum feedstocks, including feedstocks from which a premium grade coke could not heretofore have been obtained. The process involves the removal of non-crystalline carbon-forming substances from petroleum feedstocks by subjecting the feedstocks to preliminary heat-treatment to effect cracking and soaking, and subsequently by subjecting the materials to high-temperature flash distillation so as to remove the non-crystalline substances in the form of pitch. The overhead distillate of the flash distillation is then fractionated into cracked gas, gasoline, gas oil and a heavy residue, with subsequent coking of the heavy residue to yield high-crystalline petroleum coke.
Description
~7Z~7~
This invention relates to a process for the pro~uction of a high-crystalline petroleum coke by treating in a delayed coking manner a feedstock of petroleum orig~n including a low-sulfur, virgin crude oil, a low-sulfur distillation or cracke~ residuum, a hydrodesulfurized residuum of distillation or cracking and a mixture thereof.
There have already been proposed various processes for producing a premium grade coke from a virgin crude oil, topped residue or vacuum residue and the cokes thus obtained have, in principle, been suited for the purpose of the production of graphite electrodes. At present, however, with the rapid progress of electric furnace smelting, requirement for the quality of premium grade coke is becoming more severe. Further-more, the progress of steel-making technique using iron pellets and of electric furnace method essentially I requires higher quality synthetic graphite electrodes suited for ultra-high power electric furnace steel-making, for which purpose such a higher quality of petroleum coke will be most suitable as material. Therefore, the development of new techniques for producing a petroleum coke of higher quality than that of commercially available premium grade coke, which are suited for large-scale operation in a simple manner with high reproducibility at reasonable costs, has been eagerly desired in the art.
For convenience sake, such a higher quality coke than the premium grade one is called hereinafter as high-crystalline coke in view of its textural appearance being more highly crystalline than premium grade one.
~i7~
It is the pr:imary object o~ this invention to provide a new, simple process for producing a petroleum coke of high-crystalline grade in a high yield at reasonable cost ~rom a wide variety o~ petroleum materials including those from which a premium grade coke could never been obtained in the prior art. To achieve the said object, the present invention provides a new method for efficient removal of non~crystalline carbon-forming substances (hereinarter re~erred to as non-cryskalline substances) from petroleum materials to be directed for the production of coke by sub;ecting such petroleum materials to previous heat-treatment ~or e~ecting cracking and soaking thereo~ rollowed by subjecting the materials to high-temperature flash distillation to remove the non-crystalline substances contained therein as pitch~ the pitch being utilized for various appli-cations.
It is apparent that in order to obtain a high-crystalline coke from a petroleum feedstock containing a substantial amount o~ non-crystalline substances~
complete and e~ficien~ removal of the non-crystalline substances is necessary, but no economical success has been achieved as yet for this purpose. Thus, a heat-treatment of the starting feedstock or recycling of a thermal tar to the feedstock was ineffective for the removal of non-crystalline substances. Incorporation of an oil or tar containing no such non-crystalline substances into the feedstock would really resul'c in lowering the concentration of non-crystalline substances, but no appreciable improvement in the crystallinity o~
~6~72~'7~
coke wa~ obtained. A process wherein a heavy petroleum residuum is heat-treated in the presence or absence of a catalyst, then a part of the residuum thus heat-treated is removed by filtration, distillation, centri-fugation, extraction and the like and thereafter the residuum remained is sub;ected to delayed coking was effective to a certain extent, but still insu~ficient for the complete removal of non-crystalline substances, thus resulting in the formation of not a premium grade but a regular grade coke at most and in a low yield if the feedstock used contains a substantial amount of non-crystalline substances. A variant of the last-mentioned process wherein the heat-treatment of the starting petroleum residuum is effected by a delayed coking operation was also still insufficient, when applied to a petroleum residuum containing a substantial amount of non-crystalline substances, for the selective removal of the non-crystalline substances in the said first coking stage, possibly due to the coprecipitation of crystalline carbon-forming substances with non-crystalline ones in the form of a coke occurring in the first coking stage and also due to the contamination, with non-crystal]ine substances, of uncoked product in that stage which is to be coked in the second stage to form a premium grade coke 7 thus inevitably bringing the lowering in both the yield and quality of the coke obtained in the second coking stage. Similar dis-advantages were more or less unavoidable in other two stage delayed coking processes such as one wherein three coking drums are alternately used for the production ~1~7;~ 7~
of two types o:f coke and one wherein a petroleum starting material is subjected to a se.rial two-stage delayed coking when the starting material contains a substantial amount of non-crystalline substances.
We have made many studles on the removal of non-crystalline substances from petroleum feedstocks for the production of premium grade or higher grade coke and now successfully established a new process for the produckion of a high-crystalline coke by taking such steps before delayed coking that the feedstock is first heated in a tube heater and made to stay therein under certain limited conditions thereby to effect cracking and soaking of the feedstock and then subJected to a flash-dis-tillation under certain limited conditions thereby to remove selectively non-crystalline substances contained in the feedstock as pitch to provide a refined oil fraction satisfactorily suited as material for the delayed coking intended.
According to one aspect of this invention, therefore, we provide a process for producing a high-crystalline petroleum coke from a petroleum feedstock selected from the group consisting of a virgin crude oil having a sulfur content of 0.4% by weight or less, a distillation residue derived from the crude oil, a cracked residue having a sulfur content of o.8% by weight or less, a hydrodesulfurized product having a sulfur content of o.8%
by weight or less of any residue from a distillation or cracking of petroleum and a mixture thereof, which comprises the steps of:
(1) heating the petroleum feedstock in a tube heater ~t97Z~7tj to a temperature of 430-520C under a pressure o~ 20 Kg/cm2G;
This invention relates to a process for the pro~uction of a high-crystalline petroleum coke by treating in a delayed coking manner a feedstock of petroleum orig~n including a low-sulfur, virgin crude oil, a low-sulfur distillation or cracke~ residuum, a hydrodesulfurized residuum of distillation or cracking and a mixture thereof.
There have already been proposed various processes for producing a premium grade coke from a virgin crude oil, topped residue or vacuum residue and the cokes thus obtained have, in principle, been suited for the purpose of the production of graphite electrodes. At present, however, with the rapid progress of electric furnace smelting, requirement for the quality of premium grade coke is becoming more severe. Further-more, the progress of steel-making technique using iron pellets and of electric furnace method essentially I requires higher quality synthetic graphite electrodes suited for ultra-high power electric furnace steel-making, for which purpose such a higher quality of petroleum coke will be most suitable as material. Therefore, the development of new techniques for producing a petroleum coke of higher quality than that of commercially available premium grade coke, which are suited for large-scale operation in a simple manner with high reproducibility at reasonable costs, has been eagerly desired in the art.
For convenience sake, such a higher quality coke than the premium grade one is called hereinafter as high-crystalline coke in view of its textural appearance being more highly crystalline than premium grade one.
~i7~
It is the pr:imary object o~ this invention to provide a new, simple process for producing a petroleum coke of high-crystalline grade in a high yield at reasonable cost ~rom a wide variety o~ petroleum materials including those from which a premium grade coke could never been obtained in the prior art. To achieve the said object, the present invention provides a new method for efficient removal of non~crystalline carbon-forming substances (hereinarter re~erred to as non-cryskalline substances) from petroleum materials to be directed for the production of coke by sub;ecting such petroleum materials to previous heat-treatment ~or e~ecting cracking and soaking thereo~ rollowed by subjecting the materials to high-temperature flash distillation to remove the non-crystalline substances contained therein as pitch~ the pitch being utilized for various appli-cations.
It is apparent that in order to obtain a high-crystalline coke from a petroleum feedstock containing a substantial amount o~ non-crystalline substances~
complete and e~ficien~ removal of the non-crystalline substances is necessary, but no economical success has been achieved as yet for this purpose. Thus, a heat-treatment of the starting feedstock or recycling of a thermal tar to the feedstock was ineffective for the removal of non-crystalline substances. Incorporation of an oil or tar containing no such non-crystalline substances into the feedstock would really resul'c in lowering the concentration of non-crystalline substances, but no appreciable improvement in the crystallinity o~
~6~72~'7~
coke wa~ obtained. A process wherein a heavy petroleum residuum is heat-treated in the presence or absence of a catalyst, then a part of the residuum thus heat-treated is removed by filtration, distillation, centri-fugation, extraction and the like and thereafter the residuum remained is sub;ected to delayed coking was effective to a certain extent, but still insu~ficient for the complete removal of non-crystalline substances, thus resulting in the formation of not a premium grade but a regular grade coke at most and in a low yield if the feedstock used contains a substantial amount of non-crystalline substances. A variant of the last-mentioned process wherein the heat-treatment of the starting petroleum residuum is effected by a delayed coking operation was also still insufficient, when applied to a petroleum residuum containing a substantial amount of non-crystalline substances, for the selective removal of the non-crystalline substances in the said first coking stage, possibly due to the coprecipitation of crystalline carbon-forming substances with non-crystalline ones in the form of a coke occurring in the first coking stage and also due to the contamination, with non-crystal]ine substances, of uncoked product in that stage which is to be coked in the second stage to form a premium grade coke 7 thus inevitably bringing the lowering in both the yield and quality of the coke obtained in the second coking stage. Similar dis-advantages were more or less unavoidable in other two stage delayed coking processes such as one wherein three coking drums are alternately used for the production ~1~7;~ 7~
of two types o:f coke and one wherein a petroleum starting material is subjected to a se.rial two-stage delayed coking when the starting material contains a substantial amount of non-crystalline substances.
We have made many studles on the removal of non-crystalline substances from petroleum feedstocks for the production of premium grade or higher grade coke and now successfully established a new process for the produckion of a high-crystalline coke by taking such steps before delayed coking that the feedstock is first heated in a tube heater and made to stay therein under certain limited conditions thereby to effect cracking and soaking of the feedstock and then subJected to a flash-dis-tillation under certain limited conditions thereby to remove selectively non-crystalline substances contained in the feedstock as pitch to provide a refined oil fraction satisfactorily suited as material for the delayed coking intended.
According to one aspect of this invention, therefore, we provide a process for producing a high-crystalline petroleum coke from a petroleum feedstock selected from the group consisting of a virgin crude oil having a sulfur content of 0.4% by weight or less, a distillation residue derived from the crude oil, a cracked residue having a sulfur content of o.8% by weight or less, a hydrodesulfurized product having a sulfur content of o.8%
by weight or less of any residue from a distillation or cracking of petroleum and a mixture thereof, which comprises the steps of:
(1) heating the petroleum feedstock in a tube heater ~t97Z~7tj to a temperature of 430-520C under a pressure o~ 20 Kg/cm2G;
(2) maintaining the feedstock in the tube heater at that temperature for 30-500 seconds to e~fect cracking and soaking thereof;
(3 ? introducing the feedstock thus heat-treated into a high-temperature flashing column, where a ~lash-distillation is e~ected at a temperature o~ 380-520C
under a pressure of 0-2 Kg/cm2G;
(4) continuously removing non-crystalline substances contained in the ~eedstock as pitch from the bottom of the flashing column; and (5) introducing the overhead distillate of the ~lashing column or a heavy fraction thereo~, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subjected to delayed coking at a temperature of 430-460C under a pressure of 4-20 Kg/cm G ~or at least 20 hours, preferably at least 30 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less ~han 1.0 x 10 6/oC over 100-400C when measured in the form of a graphite artefact thereof.
In this process, the steps (1) to (4) are o~ a pre-treatment of the ~eedstock to be subjected to a delayed coking in the step (5) and therefore re~erred to hereina~ter as the ~irst stage o~ the process as a whole, the s~ep (5) being the second stage of the process.
The first stage of the process of this invention was arranged as a result of our minute study on the 1~7'~
relation in cok:Lng reactioll between (1) feedstock and reaction condltions including temperature, pressure and time and (2) yield and properties o~ coke ~ormed, rrom which was derlved such discovery that non-crystal:Line substances contained in the petroleum feedstocks can be efficiently removed as pitch by taking a previous treatment comprising heating a petroleum feedstock containing a~substant,ial amount of non~crystalline substances in a tube heater to a temperature o~ ~30-520C
under a pressure of 4-20 Kg/cm2G, maintaining the feedstock therein at that temperature for 30-500 seconds to effect cracking and soaking thereof and then subjecting the feedstock thus heat-treated to a flash distillation at a temperature of 380-520C under a pressure of 0-2 Kg/cm2G. The pitch removed from the flash-distillation step may, if desired, be subjected to a delayed coking operated at a temperature of 410-430C under a pressure of 2-10 Kg/cm2G to produce another coke. The coke thus obtained in a high yield (50-70% by weight) has appearance and texture like or close to amorphous carbon such as charcoal and activated carbon particularly when the feedstock contains a large amount of non-crystalline substances. This clearly suggests that the removal or separation of the non-crystalline substances from the petroleum feedstock was achieved very efficiently and economically by the adoption of the first stage of the process of this invention. The overhead distillate thus obtained from the high temperature flash distillation is substantially free from such non-crystalline substances as a result of the selective and efficient removal, ~37Z~7~
thereof. Thererore, the sald dist:lllate or a heavy ~raction thereo~ is satisractorlly sulted as ~eedstock for the productlon of a high-quali~y coke. Thus, when subjected to a delayed coking at a temperature of 430-1160C under a pressure of 4-20 Kg/cm2G, it gives a high-crystalline coke which has a degree of crystallinity significantly higher than that of premium grade coke so-called and which is in higher yield.
In large-scale operations, it will be always advantageous to use as coking feedstock a heavier part of the overhead distillate of the flashing column from the economical point of view.
Thus, according to a preferred aspect of this invention, there is provided a process for producing a high-crystalline petroleum coke from a feedstock selected from the group consisting of a virgin crude oil havin~ a sulfur content of 0.4% by weight or less, a distillation residue derived from the crude oil, a cracked residue having a sulfur content of 0.8% by weight or less, a hydrodesulfurized product having a sulfur content of 0.8%
by weight or less of any residue from a distillation or cracking of petroleum and a mixture thereof, which comprises the steps of:
heating the petroleum feedstock in a tube heater to a temperature of 430-520C under a pressure of 4-20 Kg/cm2G;
maintaining the feedstock in the tube heater at that temperature for 30-500 seconds to effect cracking and soaking thereof;
introducing the feedstock thus heat-treated into ~(3724t7~
a high-temperature flashing column, where a flash distillation is effected at a temperature of 380-520C
under a pressure of 0-2 K~/cm2G;
~ continuously removing non~crystalline substances contained in the feedstock as pltch from the bottom o~
the flashing column;
fractionating in a fractionating column the overhead distillate from the flashing column into cracked ~as, gasoline, gas oil and heavy residue; and introducing the heavy residue, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subJected ko delayed coking at a temperature of ll30-460C under a pressure of 4-20 Kg/cm2G for at least 20 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less than 1.0 x 10 6/oC over 100-400C
when measured in the form of a graphite artefact thereof.
We have further found as a result of a study on the influence of alkali or alkaline~earth metal salts on the coking reaction of hydrocarbon oils, particularly of heavy oils and residua that among those salts hydro-xides and carbonates have a retarding action for pitch-forming and coking reactions of various heavy oils and residua in addition to an accelerating action for the so-called water gas forming reactions including reactions of heavy oil, pitch and coke ~ith water.
We already found when we proposed a two-stage delayed coking mekhod for producing a high-crystalline coke together with a non-crystalline coke that non-1~7Z~'7~
crystalline substances to be re~oved from ~eedstock in the rirst coking stage may be coked at a somewhat higher reaction rate than that of high-crystalline substances and this has in fact suggested the possibility of producing a premium grade coke by a two-stage delayed coking process. Since, however~ the difference in the reaction rate between non-crystalline and high-crystalline substances was slight in usual processes, the selective separation of the non-crystalline substances was not necessarily easy. The success achieved in the present invention is believed to be principally the result of the removal of non-crystalline substances in the ~orm of pitch by adopting the first stage of the process.
Then, we tried to apply to the process of this invention the retarding action above-mentioned of hydroxides or carbonates of alkali or alkaline-earth metals on the pitch-~orming and coking reactions of heavy oils and residua with the intention of improving the selectivity of the separation of non-crystalline substances as pitch from the feedstock~ and have now found that the addition of said basic compound in an amount of 0.5-10% by weight to the feedstock to be used for the process of this invention further improves the quality of the coke with an additional advantage that the yield of pitch being non-crystalline substances is lowered. For example, when a cracked residue derived from the thermal cracking of gas oil for the production of ethylene was used as feed-stock for the process of khis invention, the coefficient of thermal expansion over 100-400C of the resulting coke when such a basic compound was added to the ~eed~
.
7;~:~i7~
stock was a value 0.1-0.2 x 10 6/oC lower than that Or the coke obtained without said addition. The effect of the addition of sald basic compound will be detailed in Examples 5 and 7 hereina~ter given, It is well-known that the quality or per~ormance of synthetic graphite electrodes depends largely upon the graphitizabilîty of coke from which the electrodes are made. Thus, the higher the crystallinity of coke, the higher the graphitizability thereof and there are several factors~ such as coefficient of thermal expansion (CTE), degree of graphitization (h/w), real density~
electric resistivity and others, as measures of evalu-ating the quality o~ coke. In general~ the better the quality of coke, the lower the value of CTE, the higher the value of h/w, the higher the real density and the lower the electric resistivity thereof.
Typical properties of various grades of coke are ! shown in Table 1.
~7~'7~
~ABLE 1 . _ . . .
Coefficient Coefficient o~
of thermal Degree Real den- cub:ic expan-expansion (1) o~ gra- sity (3) sion (4) (CTE) over phiti- at 2500C over 130-100-40QC zation (2) 300C
__ (x 10-~/C) h/w (~ lo-6/oc) e-crystalline Above 5.0 Below ~ 1 w Above 15 ~egular grade ~eneral 1;8-3.0 4.1-4.4 2.10 ?urposes ) ~_ ._ ~egular grade ~oke (for 1.2-1.8 4.4-4.8 A2bl5Ve 9.5-12 ~lectrodes) .
._ _ .... __ Premium grade 1.0-1.2 4.5-5.0 2.15 8-9~5 . ._ _ _ . .. _ .. _ __ ~igh-crystalline Below Around Above Below oke 1.0 _~ 2.15 _ (1) measured on a graphite artefact and in the ~- direction parallel to the extrusion.
(2) measured on a calcined coke.
(3 ? introducing the feedstock thus heat-treated into a high-temperature flashing column, where a ~lash-distillation is e~ected at a temperature o~ 380-520C
under a pressure of 0-2 Kg/cm2G;
(4) continuously removing non-crystalline substances contained in the ~eedstock as pitch from the bottom of the flashing column; and (5) introducing the overhead distillate of the ~lashing column or a heavy fraction thereo~, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subjected to delayed coking at a temperature of 430-460C under a pressure of 4-20 Kg/cm G ~or at least 20 hours, preferably at least 30 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less ~han 1.0 x 10 6/oC over 100-400C when measured in the form of a graphite artefact thereof.
In this process, the steps (1) to (4) are o~ a pre-treatment of the ~eedstock to be subjected to a delayed coking in the step (5) and therefore re~erred to hereina~ter as the ~irst stage o~ the process as a whole, the s~ep (5) being the second stage of the process.
The first stage of the process of this invention was arranged as a result of our minute study on the 1~7'~
relation in cok:Lng reactioll between (1) feedstock and reaction condltions including temperature, pressure and time and (2) yield and properties o~ coke ~ormed, rrom which was derlved such discovery that non-crystal:Line substances contained in the petroleum feedstocks can be efficiently removed as pitch by taking a previous treatment comprising heating a petroleum feedstock containing a~substant,ial amount of non~crystalline substances in a tube heater to a temperature o~ ~30-520C
under a pressure of 4-20 Kg/cm2G, maintaining the feedstock therein at that temperature for 30-500 seconds to effect cracking and soaking thereof and then subjecting the feedstock thus heat-treated to a flash distillation at a temperature of 380-520C under a pressure of 0-2 Kg/cm2G. The pitch removed from the flash-distillation step may, if desired, be subjected to a delayed coking operated at a temperature of 410-430C under a pressure of 2-10 Kg/cm2G to produce another coke. The coke thus obtained in a high yield (50-70% by weight) has appearance and texture like or close to amorphous carbon such as charcoal and activated carbon particularly when the feedstock contains a large amount of non-crystalline substances. This clearly suggests that the removal or separation of the non-crystalline substances from the petroleum feedstock was achieved very efficiently and economically by the adoption of the first stage of the process of this invention. The overhead distillate thus obtained from the high temperature flash distillation is substantially free from such non-crystalline substances as a result of the selective and efficient removal, ~37Z~7~
thereof. Thererore, the sald dist:lllate or a heavy ~raction thereo~ is satisractorlly sulted as ~eedstock for the productlon of a high-quali~y coke. Thus, when subjected to a delayed coking at a temperature of 430-1160C under a pressure of 4-20 Kg/cm2G, it gives a high-crystalline coke which has a degree of crystallinity significantly higher than that of premium grade coke so-called and which is in higher yield.
In large-scale operations, it will be always advantageous to use as coking feedstock a heavier part of the overhead distillate of the flashing column from the economical point of view.
Thus, according to a preferred aspect of this invention, there is provided a process for producing a high-crystalline petroleum coke from a feedstock selected from the group consisting of a virgin crude oil havin~ a sulfur content of 0.4% by weight or less, a distillation residue derived from the crude oil, a cracked residue having a sulfur content of 0.8% by weight or less, a hydrodesulfurized product having a sulfur content of 0.8%
by weight or less of any residue from a distillation or cracking of petroleum and a mixture thereof, which comprises the steps of:
heating the petroleum feedstock in a tube heater to a temperature of 430-520C under a pressure of 4-20 Kg/cm2G;
maintaining the feedstock in the tube heater at that temperature for 30-500 seconds to effect cracking and soaking thereof;
introducing the feedstock thus heat-treated into ~(3724t7~
a high-temperature flashing column, where a flash distillation is effected at a temperature of 380-520C
under a pressure of 0-2 K~/cm2G;
~ continuously removing non~crystalline substances contained in the feedstock as pltch from the bottom o~
the flashing column;
fractionating in a fractionating column the overhead distillate from the flashing column into cracked ~as, gasoline, gas oil and heavy residue; and introducing the heavy residue, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subJected ko delayed coking at a temperature of ll30-460C under a pressure of 4-20 Kg/cm2G for at least 20 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less than 1.0 x 10 6/oC over 100-400C
when measured in the form of a graphite artefact thereof.
We have further found as a result of a study on the influence of alkali or alkaline~earth metal salts on the coking reaction of hydrocarbon oils, particularly of heavy oils and residua that among those salts hydro-xides and carbonates have a retarding action for pitch-forming and coking reactions of various heavy oils and residua in addition to an accelerating action for the so-called water gas forming reactions including reactions of heavy oil, pitch and coke ~ith water.
We already found when we proposed a two-stage delayed coking mekhod for producing a high-crystalline coke together with a non-crystalline coke that non-1~7Z~'7~
crystalline substances to be re~oved from ~eedstock in the rirst coking stage may be coked at a somewhat higher reaction rate than that of high-crystalline substances and this has in fact suggested the possibility of producing a premium grade coke by a two-stage delayed coking process. Since, however~ the difference in the reaction rate between non-crystalline and high-crystalline substances was slight in usual processes, the selective separation of the non-crystalline substances was not necessarily easy. The success achieved in the present invention is believed to be principally the result of the removal of non-crystalline substances in the ~orm of pitch by adopting the first stage of the process.
Then, we tried to apply to the process of this invention the retarding action above-mentioned of hydroxides or carbonates of alkali or alkaline-earth metals on the pitch-~orming and coking reactions of heavy oils and residua with the intention of improving the selectivity of the separation of non-crystalline substances as pitch from the feedstock~ and have now found that the addition of said basic compound in an amount of 0.5-10% by weight to the feedstock to be used for the process of this invention further improves the quality of the coke with an additional advantage that the yield of pitch being non-crystalline substances is lowered. For example, when a cracked residue derived from the thermal cracking of gas oil for the production of ethylene was used as feed-stock for the process of khis invention, the coefficient of thermal expansion over 100-400C of the resulting coke when such a basic compound was added to the ~eed~
.
7;~:~i7~
stock was a value 0.1-0.2 x 10 6/oC lower than that Or the coke obtained without said addition. The effect of the addition of sald basic compound will be detailed in Examples 5 and 7 hereina~ter given, It is well-known that the quality or per~ormance of synthetic graphite electrodes depends largely upon the graphitizabilîty of coke from which the electrodes are made. Thus, the higher the crystallinity of coke, the higher the graphitizability thereof and there are several factors~ such as coefficient of thermal expansion (CTE), degree of graphitization (h/w), real density~
electric resistivity and others, as measures of evalu-ating the quality o~ coke. In general~ the better the quality of coke, the lower the value of CTE, the higher the value of h/w, the higher the real density and the lower the electric resistivity thereof.
Typical properties of various grades of coke are ! shown in Table 1.
~7~'7~
~ABLE 1 . _ . . .
Coefficient Coefficient o~
of thermal Degree Real den- cub:ic expan-expansion (1) o~ gra- sity (3) sion (4) (CTE) over phiti- at 2500C over 130-100-40QC zation (2) 300C
__ (x 10-~/C) h/w (~ lo-6/oc) e-crystalline Above 5.0 Below ~ 1 w Above 15 ~egular grade ~eneral 1;8-3.0 4.1-4.4 2.10 ?urposes ) ~_ ._ ~egular grade ~oke (for 1.2-1.8 4.4-4.8 A2bl5Ve 9.5-12 ~lectrodes) .
._ _ .... __ Premium grade 1.0-1.2 4.5-5.0 2.15 8-9~5 . ._ _ _ . .. _ .. _ __ ~igh-crystalline Below Around Above Below oke 1.0 _~ 2.15 _ (1) measured on a graphite artefact and in the ~- direction parallel to the extrusion.
(2) measured on a calcined coke.
(3) measured on a graphitized coke.
(4) measured on a graphibe artefact.
.
' ' ' - ' ' ' 1~7Z~7tj The degree of graphitizatiorl, h/w, i~ calculated by the followlng f'ormula:
h/w = height Or [002~ peak / [002] peak width at ~ half intensity The [002] peak was measured on a sample of coke which was prepared by calclning the green coke at 1450C by X-ray analysis under the following conditions:
Target: CuKa (Filter: Nickel) Voltage and Current: 30 KVP; 20 mA
Current Voltage: Proportional Counter, 1450 V
Count Full Scale: lO000 c/s to 20000 c/s Time Constant: 2 sec.
Slit: Divergence 1, Receiving Slit: 0.15 mm Scanning Speed: 1/min.
Chart Scanning Speed: 2 cm/min.
The sample for the measurement of X-ray diffraction was t prepared by the following procedure: The calcined coke was pulverized and sieved out 350 mesh plus. A certain amount of this coke flour was put into an aluminium mount (15 mm in length x 20 mm in width x 1.5 mm in thickness), pressed under a given pressure and then used for the measurement.
The coefficient of thermal expansion was measured on a graphite arkefact prepared from the coke by the following procedure: The calcined green coke was pulverized into particle size fractions of 35-65 mesh and 100 mesh plus. The coke grist used in making the test artefact contained 40 parts of the f'ormer fraction and 60 parts Or the latter fraction. Seventy (70) parts ~L~7;~7tj of the coke composite and 30 parts of coal tar pitch were well mixed and the mixture was extruded through a hydraulic extruder to forrn a green extruded rod of 20 mm in diameter. The green extrudate was packed in earbon powder and slowly baked to form a baked artefact.
The baking schedule consisted of increasing the tem-perature in linear fashion to 1000C over a period of 8 hours and keeping that temperature for 3 hours.
Graphitization of the artefact was carried out in a graphite tube resistance furnace at 2600C for 1 hour.
The non-crystalline coke corresponds to "hard earbon" so-ealled~ sueh as ehareoal and activated earbon and as far as we know such a type of eoke has not been obtained from a petroleum origin. Most of petroleum eokes and pitch cokes which are generally called as "soft earbon" fall within the class of regular grade ones and the premium grade eoke is rather a special class for petroleum eokes and the high-erystalline coke is much more rare. Even in the production of premium grade eoke from a feedstoek of petroleum origin, it was neeessary to solve various diffieulties involving the purifieation of feedstock and coke-forming conditions.
This will evidence the process of this invention to be quite unique and advantageous over the prior art processes in such point that it gives not only premium grade but also higher grade, namely high-crystalline eoke having a value of CTE (in the direetion parallel to the extrusion) of less than 1.0 x 10 6/oC over 100-400C in economical and effieient way, details of whieh will be illustrated later.
~LC9724'~;
The essence of this invention can be more readily unders~ood by reference to the attached drawing wh~ch displa~s a representatlve flow diagram of one preferred embodiment of this invention. Referring now to the diagram, a petroleum feedstock is introduced into tube preheater 2 through line 1 as it is or when desired after a small amoun~ of an alkali or alkaline earth metal hydroxide or~carbonate is added through line 30 thereto.
In the preheater, the feedstock is heated to a temperature of 430-520C under a pressure of 4-20 Kg/cm2G and main-tained at that temperature for 30-500 seconds during which time cracking and soaking of the feedstock are effected. The feedstock thus heat treated is introduced into ~lashing column 3 where it is subjected to flash distillation. At the bottom of the flashing column 3 a heating medium 4 is circulated to keep the bottom temperature at 410-520C, thereby 410-520C heavy fraction of the heat-treated feedstock is discharged from line 6 through valve 5 as pitch. The distillate free from the pitch in the flashing column 3 is introduced through line 7 into main column 12. If the operating conditions of the preheater 2 become so severe that one-through pass of the feedstock to the preheater 2 is insufficient for effecting the intended heat-treatment or otherwise that the blockage of the tube heater is unavoidable, the operation of the preheat-treatment may be modified in such a manner that a gas-liquid separator 8 is provided between the flashing column 3 and the main column 12 as shown in the drawing to effect the condensation of a part of the pre-heated feedstock from which pitch has been removed and to, _ ll~ _ ~L07~Z~'7~
recycle the co~densate through l:in~ 9 to the inlet of the preheater 2 as comb.lned f'eed, thus makin~ the intended preheat-treatment complete under reasonable operating conditlons of the preheater 2. The flash:Lng column 3 is provided with a demister 29 to avoid the introduction into the main column of foreign and un-desirable substances by entrainment wlth the distillate.
The feedstock, introduced into the main column 12 through lines 10 and 11 is fractionated into gas, gasoline, gas oil fractions, leaving a heavy residue which is withdrawn from the bottom of the column 12 as combined feed which is a mixture with a recycle oil derived from coking drum 17 or 18 through line 20 and i~ desired with a thermal tar derived from a thermal cracker 22 through line 23 and then passed through line 13 to coking preheater 14. The pre-hea~ed feedstock is charged through switch valve 16 into a delayed coking drum 17 or 18 where it is coked at 430-ll60C
under 4-20 Kg/cm2G. The coke drum overhead discharged through switch valve 19 is returned to the main column 12 through line 20, where it is fractionated into gas, gasoline, gas oil and recycle oil. The gas is discharged at the top of column 12 through line 28, gasoline through line 27 and recycle oil is withdrawn through line 13 as combined :~eed which is a mixture with the fresh feed and if desired with the thermal tar as above-mentioned.
The coking drums 17 and 18 are alternately used for the delayed coking operation by switching over every 36 hours. While one is in operation, another is under discharging the coke formed and then under standing by l~Z~7~
The gas oil fraction derived from the coking drum through the main column 12 may be charged lnto thermal cracker 22 through line 21 where it is thermally cracked at 510-550C under 35-65 Kg/cm2~ into gas, gasoline and thermal tar which are all recycled through line 23 to the main column 12. The thermal tar is thus mixed at the bottom of the column 12 with the ~resh ~eedstock and recycle oil to increase the yield of coke. Alternatively, the gas oil ~raction may directly be introduced through line 24 into stripper 25 to remove lighter oil and recovered through ]ine 26 for any desire application. In the latter case, the yield of coke based on the starting feedstock is lowered, but the quality of coke is not affected thereby.
The following Examples further illustrate, but not limit, this invention, in which percentages are by weight unless otherwise stated.
Example 1 A thermal tar named as tar-boktom obtained as by-product in a conventional thermal cracking of gas oil for the purpose of producing ethylene which has sulfur content of o.76% (the properties of which being shown in Table 2) was used as feedstock for this Example.
The feedstock was introduced into a stainless steel tube heater having 4 mm inside diameter, 6 mm outside diameter and 20 m length which was externally heated by a heating medium, heated under a pressure o~
4 Kg/cm2G to 450C and maintained at this temperature for about 260 seconds. The feedskock was then introduced at the middle part of a high temperature flashing column having 100 mm diameter and 1000 mm height which was 3l~7~9~7~
externally heated by electric wire heater, where the flash dis~illation o~ ~he feedstock was effected at 450C
under 0 Kg/cm G to recover distillate as overhead and to withdraw pitch at the bottom o~ column in an amount o~
24.6% based on the feedstock~ with a retention time of about 10 minutes at the bottom of column, together with gas generated in an amount of 5% on the same basis.
The distillate was then passed through a tube heater having inside and outside diameters of 4 mm and 6 mm, respectively~ to preheat to the temperature required ror the subsequent coking and charged into a coking drum, where it was subjected to delayed coking at 435C under 9.0 Kg/cm2G ~or 38 hours, yielding ?8 . 5% of coke based on the charge (20.0% based on the feedstock). By-products of the coking were 11. 5% gas ( 8 .1% ) ~ 25~ L~%
gasoline boiling up to 200C (17.9%), 28.9% gas oil boiling in the range 200-300C (20.3%) and 5.7% heavy oil boiling 300C+ (4.01%).
The properties of coke obtained abo~e are shown in Table 3. The coke was clearly classified under high-crystalline grade.
Example 2 A thermal tar named as ethylene-bottom obtained as by-product in a conventional thermal cracking o~
naphtha ~or the purpose o~ producing ethylene, having sulfur content of 0.02% (the properties of which being shown in Table 2) was used as ~eedstock for this ~xample.
The feedstock was introduced into the stainless steel tube heater same as that used in Example 1 and heated under a pressure of 4 Kg/cm2G to 430C and .
~.~7'æ4~'7~
maintained at this temperature for about 260 seconds.
The feedstock thus heat-treated was introduced at the middle part of the high-temperature flashing column same as that used in Example 1 and subjected to flash distilla-tion under conditions of ll00C and 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 17.7% based on the feedstock, with a retention time of about 10 minutes at that bottom, together with gas generated in an amount of 2.6% on the same basis. The distillate was passed through the tube heater same as that used in Example 1 to preheat to the temperature required for the subsequent coking and charged into a coking drum where it was subjected to delayed coking at 435C under 9.0 Kg/cm2G
for 38 hours, yielding 21.0% of coke based on the charge (16.7% based on the feedskock). By-products of the coking were 7.3% gas ( 5.8% ), 25.1% gasoline boiling up to 200c (20.1%), 32.3% gas oil boiling in the range 200-300C (25.7%) and 14.3% heavy oil boiling 300C~
(11.4%) .
The properties of coke thus obtained are shown in Table 3. The coke was similarly classified under high-crystalline grade.
E mple 3 The same thermal tar as that used in Example 2, named "ethylene bottom", was used as feedstock for this Example and subjected ko the preheat treatment and the subsequent flash distillation in the same manner and under the same conditions as those in Example 2, giving pitch as bottom product in an amount of 18.2% based on ~ 18 -~7~'76 ~he feed~tock.
The overhead from the flashing column was fraction-ated in a fractionator to give 2.8% gas, 1.8% gasoline, 17 . 6% gas oil and 59 . 6% heavy residue based on the feedstock.
The heavy residue was passed through the tube heater into the coking drum same as those used in Example 2 and coked therein in the same manner and under the same conditions as those in Example 2, yielding 28.7% 0~ coke based on the coker charge (17.1/o based on the feedstock). By-products of the coking were 7.4% gas (11.4%), 21.8% gasoline boiling up to 200C
(13.0%), 27.9% gas oil boiling in the range 200 - 300C
(16.6%) and 14.3% heavy oil boiling 300C ~ (8.5%).
The properties of coke thus obtained are shown in Table 3. The coke was evaluated as high-crystalline coke comparable to that obtained in Example 2.
Example 4 :r A topped residue of Minas crude oil (the properties of which being shown in Table 2) was used as feedstock for this Example.
The feedstock was introduced into a stainless steel tube heater having 4 mm inside diameter, 6 mm outside diameter and 40 m length which was externally heated by a heating medium and heated under 20 Kg/cm2G to 480C and maintained at this temperature for about 190 seconds. The feedstoc~
thus heat-treated was introduced at the middle part of a high-temperature flashing column and subjected to flash distillation under conditions of 400C and 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 10.7% based on the feedstock, with a retention time of about 15 minutes at that bottom, together with gas ~7~
generated :in an amount Or 21. 0% on the same basls.
The distillate was passed through the tube heater same as that used in Example 1 to preheat to the temperature required f`or the subsequent coking and charged into a coking drum where it was subjected to ~elayed coking at 435C under 9.0 Kg/cm G ~or 38 hours, yield.ing 5.9%
of coke based on the charge (4 .1% based on the starting feedstock). By-products of the coking were 18.2% gas (12.4%), 20.0% gasoline boiling up to 200C (13.6%), 34.5% gas oil boiling in the range 200-300C (23.6%) and 21.4% heavy oil boiling 300C~ (14.6%).
The properties of coke thus obtained are shown in Table 3. The coke was similarly classified under high-crystalline grade.
Example 5 The procedure of Example 1 was repeated except khat 0.5% based on the feedstock of sodium hydroxide were pre~
mixed with the ~eedstock in the form of an aqueous solution.
At the flash distillation stage, pitch was removed in an amount of 17.0% together with 5.0% of gas. The coking stage gave a coke in a yield of 34.5% based on the charge (26.9% based on the feedstock) and as by-products 15.2%
gas (11.9%) and 50.3% cracked oil (39.2%).
The properties of coke thus obtained are shown in Table 3. The comparison of Example 1 with Example 5 clearly demons~rates significant improvements in both the yield and quality of coke of Example 5 over Example 1.
Example 6 DJatibarang virgin crude oil (the properties of which being shown in Table 2) was used as ~eedstock for fs~ 7~ .
this Example.
The ~eedstock was introduced into a stainless steel tube heater having l~ mm inside diameter, 6 mm outside diameter and 40 m length which was externally heated by a heating medium~ heated under 20 Kg/cm2G to 480C and maintained at this temperature for about 230 seconds. The feedstock thus heat-treated was introduced at the middle part o~ a high-temperature ~lashing column having 100 mm diameter and 1000 mm height which was externally heated by electric wire heater, where the flash distillation of the feedstock was effected at 400C under 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 12.0% based on the feedstock~ with a retention time of about 5 minutes at that bottom, together with gas generated in an amount of 10.0% on the same basis.`
The distillate was then passed through a tube heater !- having 4 mm inside diameter and 6 mm outside diameter to preheat to the temperature required for the subsequent coking and charged into a coking drum, where it was subjected to delayed coking at 435C under 9.0 Kg/cm2G
for 24 hours, yielding 10.1% of coke based on the charge (7.9% based on the feedstock). By-products of the coking were 9.8% gas (7.6%), 22.4% gasoline boiling up to 200C
(17.5%), 48.1% gas oil (37.5%) and 9.6% heavy oil boiling 300C-~ (7.5%).
The properties of coke obtained above are shown in Table 3. The coke was simllarly classified under high-crystalline grade.
Example 7 ~1~724'~
(1) A hydro~esulfurized product containing 0.3% of sulfur from a cracked residue named as desul~urized tar ~hich was obtaine~ by hydrodesulfurizing the latter o~tained as by-product in a conventional thermal cracking of gas oil for the purpose of producing ethylene (the properties of which being shown in Table 2) was used as feedstock for this Example.
The feedstock was introduced into a stainless steel tube heater having ll mm inside diameter, 6 mm outside diameter and 30 m length which was externally heated by a heating medium, heated under 20 Kg/cm2G to 490C and maintained at this temperature for about 250 seconds. The feedstock was then introduced at the middle part of a high-temperature flashing column having 100 mm diameter and 1000 mm height which was externally heated by electric wire heater, where the flash - distillation of the feedstock was effected at 400C
under 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 7.9% based on the feedstock, with a retention time of about 10 minutes at that bottom, together with gas generated in an amount of 1.5% on the same basis. The distillate was then passed through a tube heater having 4 mm inside diameter and 6 mm outside diameter to preheat to the temperature required for the subsequent coking and charged into a coking drum, where it was sub~ected to delayed coking at 435C under 9.0 Kg/cm2G for 38 hours, yielding 10.9% of coke based on the charge (9.9%
based on the feedstock). By-products of the coking were 8.6% gas (7.8%), 5.0% gasoline boiling up to 200C
~7;~'76à
(4.5%), 50.11% gas oil (45.7%) and 25.1% heavy oil boiling 300C~ (22.7%).
The properties of coke thus obtained are shown ~in Table 3, which clearly show that the coke is of high-crystalline grade.
(2) The same procedure as above was repeated except that 1.0% based on the ~eedstock of sodium carbonate was premixed with the ~eedstock in the form o~ an aqueous solution. The yield of coke thus obtained was increased to 11.5% based on the feedstock as well as the properties of coke being further improved as shown in Table 3.
Example 8 (1) A hydrodesulfurized product containing 0.16% of sulfur from a topped residue of Kuwait crude oil (the properties of which being shown in Table 2) was used as feedstock ~or this run.
The feedstock was introduced into the tube heater same as that used in Example 1 and heated under a pressure of 4 Kg/cm2G to 500C and maintained at this temperature for about 230 seconds. The feedstock thus heat-treated was introduced at the middle part of the flashing column same as that used in Example 1 and subjected to flash distillation under conditions of 500C and 0 Kg/cm2G to withdraw pitch at the bottom of ~he column in an amount o~
4.9% based on the feedstock. The overhead of the ~lashing column was sub~ected to fractional distillation to recover lighter fractions and to provide a bottom residue boiling 300C~ in an amount of 60.1% based on the feedstock.
The residue was passed through the tube heater into 7Z~7~
the coking drum same as those used in Example 1 and coked therein in the same manner and under the same conditions as those used in Example 1, yielding 11.6% of coke based on the coker charge (7.0% based on the feedstock).
The proper~ies of coke thus obtained are shown in Table 3. The coke was similarly classified under high-crystalline grade.
(2) A mixture of 6 parts by weight of the hydrodesulfurized residue same as that used in the run (1) above and 1 part by lG weight of the "ethylene bottom" thermal tar same as that used in Example 2 was used as feedstock for this run.
The feedstock was subjected to heat treatment and flash distillation in the same manner and under the same conditions as those used in the run (1~ above with the removal of 1.3% pitch based on the feedstock.
The overhead of the flashing column was fractionally distilled to provide a bottom residue boiling 300C~ in an amount of 70.6% based on the feedstock.
The residue was then coked in the same manner and under the same conditions as those used in Example 1, yielding 13.5% of coke based on the coker charge (9.5%
based on the feedstock).
The properties of coke are shown in Table 3. The coke was similarly classified under high-crystalline coke.
Example 9 A mixture of ~ parts by weight of a topped residue containing 0.25% sulfur from Taching crude oil (khe pro-perties of which being shown in ~able 2) and 1 part by weight of the "ethylene bottom" thermal tar same as that used in Example 2 was used as feedstock for this Example.
~t72~7~ ~
The ~eedstock was lntroduced into the tube heater same as that used in Example 1 and heated under a pressure of Ll l~g/cm2G to 510C and maintalned at this temperature ~or about 230 seconds. The feedstock thus heat-treated was introduced at the middle part of the flashing column same as that used in Example 1 and subjecked to ~lash distillation under conditions o~ 510C and 0 Kg/cm2G to withdraw pitch at the bottom of the column in an amount of 0.7% ~ased on the feedstock. The overhead of the flashing column was subjected to fractional distillation to recover lighter fractions and to provide a bottom residue boiling 300C+ in an amount of 67.0%
based on the feedstock.
The residue was passed through the tube heater into the coking drum same as those used in Example 1 and coked therein in the same manner and under the same conditions as those used in Example 1, yielding 11.4% of coke based on the coker charge (7.6% based on the feedstock).
The properties of coke are shown in Table 3. The coke was classified under high-crystalline coke.
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' ' ' - ' ' ' 1~7Z~7tj The degree of graphitizatiorl, h/w, i~ calculated by the followlng f'ormula:
h/w = height Or [002~ peak / [002] peak width at ~ half intensity The [002] peak was measured on a sample of coke which was prepared by calclning the green coke at 1450C by X-ray analysis under the following conditions:
Target: CuKa (Filter: Nickel) Voltage and Current: 30 KVP; 20 mA
Current Voltage: Proportional Counter, 1450 V
Count Full Scale: lO000 c/s to 20000 c/s Time Constant: 2 sec.
Slit: Divergence 1, Receiving Slit: 0.15 mm Scanning Speed: 1/min.
Chart Scanning Speed: 2 cm/min.
The sample for the measurement of X-ray diffraction was t prepared by the following procedure: The calcined coke was pulverized and sieved out 350 mesh plus. A certain amount of this coke flour was put into an aluminium mount (15 mm in length x 20 mm in width x 1.5 mm in thickness), pressed under a given pressure and then used for the measurement.
The coefficient of thermal expansion was measured on a graphite arkefact prepared from the coke by the following procedure: The calcined green coke was pulverized into particle size fractions of 35-65 mesh and 100 mesh plus. The coke grist used in making the test artefact contained 40 parts of the f'ormer fraction and 60 parts Or the latter fraction. Seventy (70) parts ~L~7;~7tj of the coke composite and 30 parts of coal tar pitch were well mixed and the mixture was extruded through a hydraulic extruder to forrn a green extruded rod of 20 mm in diameter. The green extrudate was packed in earbon powder and slowly baked to form a baked artefact.
The baking schedule consisted of increasing the tem-perature in linear fashion to 1000C over a period of 8 hours and keeping that temperature for 3 hours.
Graphitization of the artefact was carried out in a graphite tube resistance furnace at 2600C for 1 hour.
The non-crystalline coke corresponds to "hard earbon" so-ealled~ sueh as ehareoal and activated earbon and as far as we know such a type of eoke has not been obtained from a petroleum origin. Most of petroleum eokes and pitch cokes which are generally called as "soft earbon" fall within the class of regular grade ones and the premium grade eoke is rather a special class for petroleum eokes and the high-erystalline coke is much more rare. Even in the production of premium grade eoke from a feedstoek of petroleum origin, it was neeessary to solve various diffieulties involving the purifieation of feedstock and coke-forming conditions.
This will evidence the process of this invention to be quite unique and advantageous over the prior art processes in such point that it gives not only premium grade but also higher grade, namely high-crystalline eoke having a value of CTE (in the direetion parallel to the extrusion) of less than 1.0 x 10 6/oC over 100-400C in economical and effieient way, details of whieh will be illustrated later.
~LC9724'~;
The essence of this invention can be more readily unders~ood by reference to the attached drawing wh~ch displa~s a representatlve flow diagram of one preferred embodiment of this invention. Referring now to the diagram, a petroleum feedstock is introduced into tube preheater 2 through line 1 as it is or when desired after a small amoun~ of an alkali or alkaline earth metal hydroxide or~carbonate is added through line 30 thereto.
In the preheater, the feedstock is heated to a temperature of 430-520C under a pressure of 4-20 Kg/cm2G and main-tained at that temperature for 30-500 seconds during which time cracking and soaking of the feedstock are effected. The feedstock thus heat treated is introduced into ~lashing column 3 where it is subjected to flash distillation. At the bottom of the flashing column 3 a heating medium 4 is circulated to keep the bottom temperature at 410-520C, thereby 410-520C heavy fraction of the heat-treated feedstock is discharged from line 6 through valve 5 as pitch. The distillate free from the pitch in the flashing column 3 is introduced through line 7 into main column 12. If the operating conditions of the preheater 2 become so severe that one-through pass of the feedstock to the preheater 2 is insufficient for effecting the intended heat-treatment or otherwise that the blockage of the tube heater is unavoidable, the operation of the preheat-treatment may be modified in such a manner that a gas-liquid separator 8 is provided between the flashing column 3 and the main column 12 as shown in the drawing to effect the condensation of a part of the pre-heated feedstock from which pitch has been removed and to, _ ll~ _ ~L07~Z~'7~
recycle the co~densate through l:in~ 9 to the inlet of the preheater 2 as comb.lned f'eed, thus makin~ the intended preheat-treatment complete under reasonable operating conditlons of the preheater 2. The flash:Lng column 3 is provided with a demister 29 to avoid the introduction into the main column of foreign and un-desirable substances by entrainment wlth the distillate.
The feedstock, introduced into the main column 12 through lines 10 and 11 is fractionated into gas, gasoline, gas oil fractions, leaving a heavy residue which is withdrawn from the bottom of the column 12 as combined feed which is a mixture with a recycle oil derived from coking drum 17 or 18 through line 20 and i~ desired with a thermal tar derived from a thermal cracker 22 through line 23 and then passed through line 13 to coking preheater 14. The pre-hea~ed feedstock is charged through switch valve 16 into a delayed coking drum 17 or 18 where it is coked at 430-ll60C
under 4-20 Kg/cm2G. The coke drum overhead discharged through switch valve 19 is returned to the main column 12 through line 20, where it is fractionated into gas, gasoline, gas oil and recycle oil. The gas is discharged at the top of column 12 through line 28, gasoline through line 27 and recycle oil is withdrawn through line 13 as combined :~eed which is a mixture with the fresh feed and if desired with the thermal tar as above-mentioned.
The coking drums 17 and 18 are alternately used for the delayed coking operation by switching over every 36 hours. While one is in operation, another is under discharging the coke formed and then under standing by l~Z~7~
The gas oil fraction derived from the coking drum through the main column 12 may be charged lnto thermal cracker 22 through line 21 where it is thermally cracked at 510-550C under 35-65 Kg/cm2~ into gas, gasoline and thermal tar which are all recycled through line 23 to the main column 12. The thermal tar is thus mixed at the bottom of the column 12 with the ~resh ~eedstock and recycle oil to increase the yield of coke. Alternatively, the gas oil ~raction may directly be introduced through line 24 into stripper 25 to remove lighter oil and recovered through ]ine 26 for any desire application. In the latter case, the yield of coke based on the starting feedstock is lowered, but the quality of coke is not affected thereby.
The following Examples further illustrate, but not limit, this invention, in which percentages are by weight unless otherwise stated.
Example 1 A thermal tar named as tar-boktom obtained as by-product in a conventional thermal cracking of gas oil for the purpose of producing ethylene which has sulfur content of o.76% (the properties of which being shown in Table 2) was used as feedstock for this Example.
The feedstock was introduced into a stainless steel tube heater having 4 mm inside diameter, 6 mm outside diameter and 20 m length which was externally heated by a heating medium, heated under a pressure o~
4 Kg/cm2G to 450C and maintained at this temperature for about 260 seconds. The feedskock was then introduced at the middle part of a high temperature flashing column having 100 mm diameter and 1000 mm height which was 3l~7~9~7~
externally heated by electric wire heater, where the flash dis~illation o~ ~he feedstock was effected at 450C
under 0 Kg/cm G to recover distillate as overhead and to withdraw pitch at the bottom o~ column in an amount o~
24.6% based on the feedstock~ with a retention time of about 10 minutes at the bottom of column, together with gas generated in an amount of 5% on the same basis.
The distillate was then passed through a tube heater having inside and outside diameters of 4 mm and 6 mm, respectively~ to preheat to the temperature required ror the subsequent coking and charged into a coking drum, where it was subjected to delayed coking at 435C under 9.0 Kg/cm2G ~or 38 hours, yielding ?8 . 5% of coke based on the charge (20.0% based on the feedstock). By-products of the coking were 11. 5% gas ( 8 .1% ) ~ 25~ L~%
gasoline boiling up to 200C (17.9%), 28.9% gas oil boiling in the range 200-300C (20.3%) and 5.7% heavy oil boiling 300C+ (4.01%).
The properties of coke obtained abo~e are shown in Table 3. The coke was clearly classified under high-crystalline grade.
Example 2 A thermal tar named as ethylene-bottom obtained as by-product in a conventional thermal cracking o~
naphtha ~or the purpose o~ producing ethylene, having sulfur content of 0.02% (the properties of which being shown in Table 2) was used as ~eedstock for this ~xample.
The feedstock was introduced into the stainless steel tube heater same as that used in Example 1 and heated under a pressure of 4 Kg/cm2G to 430C and .
~.~7'æ4~'7~
maintained at this temperature for about 260 seconds.
The feedstock thus heat-treated was introduced at the middle part of the high-temperature flashing column same as that used in Example 1 and subjected to flash distilla-tion under conditions of ll00C and 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 17.7% based on the feedstock, with a retention time of about 10 minutes at that bottom, together with gas generated in an amount of 2.6% on the same basis. The distillate was passed through the tube heater same as that used in Example 1 to preheat to the temperature required for the subsequent coking and charged into a coking drum where it was subjected to delayed coking at 435C under 9.0 Kg/cm2G
for 38 hours, yielding 21.0% of coke based on the charge (16.7% based on the feedskock). By-products of the coking were 7.3% gas ( 5.8% ), 25.1% gasoline boiling up to 200c (20.1%), 32.3% gas oil boiling in the range 200-300C (25.7%) and 14.3% heavy oil boiling 300C~
(11.4%) .
The properties of coke thus obtained are shown in Table 3. The coke was similarly classified under high-crystalline grade.
E mple 3 The same thermal tar as that used in Example 2, named "ethylene bottom", was used as feedstock for this Example and subjected ko the preheat treatment and the subsequent flash distillation in the same manner and under the same conditions as those in Example 2, giving pitch as bottom product in an amount of 18.2% based on ~ 18 -~7~'76 ~he feed~tock.
The overhead from the flashing column was fraction-ated in a fractionator to give 2.8% gas, 1.8% gasoline, 17 . 6% gas oil and 59 . 6% heavy residue based on the feedstock.
The heavy residue was passed through the tube heater into the coking drum same as those used in Example 2 and coked therein in the same manner and under the same conditions as those in Example 2, yielding 28.7% 0~ coke based on the coker charge (17.1/o based on the feedstock). By-products of the coking were 7.4% gas (11.4%), 21.8% gasoline boiling up to 200C
(13.0%), 27.9% gas oil boiling in the range 200 - 300C
(16.6%) and 14.3% heavy oil boiling 300C ~ (8.5%).
The properties of coke thus obtained are shown in Table 3. The coke was evaluated as high-crystalline coke comparable to that obtained in Example 2.
Example 4 :r A topped residue of Minas crude oil (the properties of which being shown in Table 2) was used as feedstock for this Example.
The feedstock was introduced into a stainless steel tube heater having 4 mm inside diameter, 6 mm outside diameter and 40 m length which was externally heated by a heating medium and heated under 20 Kg/cm2G to 480C and maintained at this temperature for about 190 seconds. The feedstoc~
thus heat-treated was introduced at the middle part of a high-temperature flashing column and subjected to flash distillation under conditions of 400C and 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 10.7% based on the feedstock, with a retention time of about 15 minutes at that bottom, together with gas ~7~
generated :in an amount Or 21. 0% on the same basls.
The distillate was passed through the tube heater same as that used in Example 1 to preheat to the temperature required f`or the subsequent coking and charged into a coking drum where it was subjected to ~elayed coking at 435C under 9.0 Kg/cm G ~or 38 hours, yield.ing 5.9%
of coke based on the charge (4 .1% based on the starting feedstock). By-products of the coking were 18.2% gas (12.4%), 20.0% gasoline boiling up to 200C (13.6%), 34.5% gas oil boiling in the range 200-300C (23.6%) and 21.4% heavy oil boiling 300C~ (14.6%).
The properties of coke thus obtained are shown in Table 3. The coke was similarly classified under high-crystalline grade.
Example 5 The procedure of Example 1 was repeated except khat 0.5% based on the feedstock of sodium hydroxide were pre~
mixed with the ~eedstock in the form of an aqueous solution.
At the flash distillation stage, pitch was removed in an amount of 17.0% together with 5.0% of gas. The coking stage gave a coke in a yield of 34.5% based on the charge (26.9% based on the feedstock) and as by-products 15.2%
gas (11.9%) and 50.3% cracked oil (39.2%).
The properties of coke thus obtained are shown in Table 3. The comparison of Example 1 with Example 5 clearly demons~rates significant improvements in both the yield and quality of coke of Example 5 over Example 1.
Example 6 DJatibarang virgin crude oil (the properties of which being shown in Table 2) was used as ~eedstock for fs~ 7~ .
this Example.
The ~eedstock was introduced into a stainless steel tube heater having l~ mm inside diameter, 6 mm outside diameter and 40 m length which was externally heated by a heating medium~ heated under 20 Kg/cm2G to 480C and maintained at this temperature for about 230 seconds. The feedstock thus heat-treated was introduced at the middle part o~ a high-temperature ~lashing column having 100 mm diameter and 1000 mm height which was externally heated by electric wire heater, where the flash distillation of the feedstock was effected at 400C under 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 12.0% based on the feedstock~ with a retention time of about 5 minutes at that bottom, together with gas generated in an amount of 10.0% on the same basis.`
The distillate was then passed through a tube heater !- having 4 mm inside diameter and 6 mm outside diameter to preheat to the temperature required for the subsequent coking and charged into a coking drum, where it was subjected to delayed coking at 435C under 9.0 Kg/cm2G
for 24 hours, yielding 10.1% of coke based on the charge (7.9% based on the feedstock). By-products of the coking were 9.8% gas (7.6%), 22.4% gasoline boiling up to 200C
(17.5%), 48.1% gas oil (37.5%) and 9.6% heavy oil boiling 300C-~ (7.5%).
The properties of coke obtained above are shown in Table 3. The coke was simllarly classified under high-crystalline grade.
Example 7 ~1~724'~
(1) A hydro~esulfurized product containing 0.3% of sulfur from a cracked residue named as desul~urized tar ~hich was obtaine~ by hydrodesulfurizing the latter o~tained as by-product in a conventional thermal cracking of gas oil for the purpose of producing ethylene (the properties of which being shown in Table 2) was used as feedstock for this Example.
The feedstock was introduced into a stainless steel tube heater having ll mm inside diameter, 6 mm outside diameter and 30 m length which was externally heated by a heating medium, heated under 20 Kg/cm2G to 490C and maintained at this temperature for about 250 seconds. The feedstock was then introduced at the middle part of a high-temperature flashing column having 100 mm diameter and 1000 mm height which was externally heated by electric wire heater, where the flash - distillation of the feedstock was effected at 400C
under 0 Kg/cm2G to recover distillate as overhead and to withdraw pitch at the bottom of column in an amount of 7.9% based on the feedstock, with a retention time of about 10 minutes at that bottom, together with gas generated in an amount of 1.5% on the same basis. The distillate was then passed through a tube heater having 4 mm inside diameter and 6 mm outside diameter to preheat to the temperature required for the subsequent coking and charged into a coking drum, where it was sub~ected to delayed coking at 435C under 9.0 Kg/cm2G for 38 hours, yielding 10.9% of coke based on the charge (9.9%
based on the feedstock). By-products of the coking were 8.6% gas (7.8%), 5.0% gasoline boiling up to 200C
~7;~'76à
(4.5%), 50.11% gas oil (45.7%) and 25.1% heavy oil boiling 300C~ (22.7%).
The properties of coke thus obtained are shown ~in Table 3, which clearly show that the coke is of high-crystalline grade.
(2) The same procedure as above was repeated except that 1.0% based on the ~eedstock of sodium carbonate was premixed with the ~eedstock in the form o~ an aqueous solution. The yield of coke thus obtained was increased to 11.5% based on the feedstock as well as the properties of coke being further improved as shown in Table 3.
Example 8 (1) A hydrodesulfurized product containing 0.16% of sulfur from a topped residue of Kuwait crude oil (the properties of which being shown in Table 2) was used as feedstock ~or this run.
The feedstock was introduced into the tube heater same as that used in Example 1 and heated under a pressure of 4 Kg/cm2G to 500C and maintained at this temperature for about 230 seconds. The feedstock thus heat-treated was introduced at the middle part of the flashing column same as that used in Example 1 and subjected to flash distillation under conditions of 500C and 0 Kg/cm2G to withdraw pitch at the bottom of ~he column in an amount o~
4.9% based on the feedstock. The overhead of the ~lashing column was sub~ected to fractional distillation to recover lighter fractions and to provide a bottom residue boiling 300C~ in an amount of 60.1% based on the feedstock.
The residue was passed through the tube heater into 7Z~7~
the coking drum same as those used in Example 1 and coked therein in the same manner and under the same conditions as those used in Example 1, yielding 11.6% of coke based on the coker charge (7.0% based on the feedstock).
The proper~ies of coke thus obtained are shown in Table 3. The coke was similarly classified under high-crystalline grade.
(2) A mixture of 6 parts by weight of the hydrodesulfurized residue same as that used in the run (1) above and 1 part by lG weight of the "ethylene bottom" thermal tar same as that used in Example 2 was used as feedstock for this run.
The feedstock was subjected to heat treatment and flash distillation in the same manner and under the same conditions as those used in the run (1~ above with the removal of 1.3% pitch based on the feedstock.
The overhead of the flashing column was fractionally distilled to provide a bottom residue boiling 300C~ in an amount of 70.6% based on the feedstock.
The residue was then coked in the same manner and under the same conditions as those used in Example 1, yielding 13.5% of coke based on the coker charge (9.5%
based on the feedstock).
The properties of coke are shown in Table 3. The coke was similarly classified under high-crystalline coke.
Example 9 A mixture of ~ parts by weight of a topped residue containing 0.25% sulfur from Taching crude oil (khe pro-perties of which being shown in ~able 2) and 1 part by weight of the "ethylene bottom" thermal tar same as that used in Example 2 was used as feedstock for this Example.
~t72~7~ ~
The ~eedstock was lntroduced into the tube heater same as that used in Example 1 and heated under a pressure of Ll l~g/cm2G to 510C and maintalned at this temperature ~or about 230 seconds. The feedstock thus heat-treated was introduced at the middle part of the flashing column same as that used in Example 1 and subjecked to ~lash distillation under conditions o~ 510C and 0 Kg/cm2G to withdraw pitch at the bottom of the column in an amount of 0.7% ~ased on the feedstock. The overhead of the flashing column was subjected to fractional distillation to recover lighter fractions and to provide a bottom residue boiling 300C+ in an amount of 67.0%
based on the feedstock.
The residue was passed through the tube heater into the coking drum same as those used in Example 1 and coked therein in the same manner and under the same conditions as those used in Example 1, yielding 11.4% of coke based on the coker charge (7.6% based on the feedstock).
The properties of coke are shown in Table 3. The coke was classified under high-crystalline coke.
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Claims (10)
1. A process for producing a high-crystalline petroleum coke from a petroleum feedstock selected from the group consisting of a virgin crude oil having a sulfur content of 0.4% by weight or less, a dustily tion residue derived from the crude oil, a cracked residue having a sulfur content of 0.8% by weight or less, a hydrodesulfurized product having a sulfur content of 0.8% by weight or less of any residue from a distillation or cracking Or petroleum and a mixture thereof, which comprises the steps of:
heating the petroleum feedstock in a tube heater to a temperature of 430-520°C under a pressure of 4-20 Kg/cm2G;
maintaining the feedstock in the tube heater at that temperature for 30-500 seconds to effect cracking and soaking thereof;
introducing the feedstock thus heat-treated into a high temperature flashing column, where a flash distillation is effected at a temperature of 380-520°C
under a pressure of 0-2 Kg/cm2G;
continuously removing non-crystalline substances contained in the feedstock as pitch from the bottom of the flashing column; and introducing the overhead distillate of the flashing column or a heavy fraction thereof, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subjected to delayed coking at a temperature of 430-460°C under a pressure of 4-20 Kg/cm2G for at least 20 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less than 1.0 x 10-6/°C over 100°-400°C
when measured in the form of a graphite artefact thereof.
heating the petroleum feedstock in a tube heater to a temperature of 430-520°C under a pressure of 4-20 Kg/cm2G;
maintaining the feedstock in the tube heater at that temperature for 30-500 seconds to effect cracking and soaking thereof;
introducing the feedstock thus heat-treated into a high temperature flashing column, where a flash distillation is effected at a temperature of 380-520°C
under a pressure of 0-2 Kg/cm2G;
continuously removing non-crystalline substances contained in the feedstock as pitch from the bottom of the flashing column; and introducing the overhead distillate of the flashing column or a heavy fraction thereof, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subjected to delayed coking at a temperature of 430-460°C under a pressure of 4-20 Kg/cm2G for at least 20 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less than 1.0 x 10-6/°C over 100°-400°C
when measured in the form of a graphite artefact thereof.
2. A process for producing a high-crystalline petroleum coke from a petroleum feedstock selected from the group consisting of a virgin crude oil having a sulfur content of 0.4% by weight or less, a distilla-tion residue derived from the crude oil, a cracked residue having a sulfur content of 0.8% by weight or less, a hydrodesulfurized product having a sulfur content of 0.8% by weight or less of any residue from a distillation or cracking of petroleum and a mixture thereof, which comprises the steps of:
heating the petroleum feedstock in a tube heater to a temperature of 430-520°C under a pressure of 4-20 Kg/cm2G
maintaining the feedstock in the tube heater at that temperature for 30-500 seconds to effect cracking and soaking thereof;
introducing the feedstock thus heat-treated into a high-temperature flashing column, where a flash distillation is effected at a temperature of 380-520°C
under a pressure of 0-2 Kg/cm2G;
continuously removing non-crystalline substances contained in the feedstock as pitch from the bottom of the flashing column;
fractionating in a fractionating column the overhead distillate from the flashing column into cracked gas, gasoline, gas oil and heavy residue; and introducing the heavy residue, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subjected to delayed coking at a temperature of 430-460°C under a pressure of 4-20 Kg/cm2G for at least 20 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less than 1.0 x 10-6/°C over 100°-400°C
when measured in the form of a graphite artefact thereof.
heating the petroleum feedstock in a tube heater to a temperature of 430-520°C under a pressure of 4-20 Kg/cm2G
maintaining the feedstock in the tube heater at that temperature for 30-500 seconds to effect cracking and soaking thereof;
introducing the feedstock thus heat-treated into a high-temperature flashing column, where a flash distillation is effected at a temperature of 380-520°C
under a pressure of 0-2 Kg/cm2G;
continuously removing non-crystalline substances contained in the feedstock as pitch from the bottom of the flashing column;
fractionating in a fractionating column the overhead distillate from the flashing column into cracked gas, gasoline, gas oil and heavy residue; and introducing the heavy residue, after heating to a temperature required for the subsequent delayed coking, into a coking drum, where it is subjected to delayed coking at a temperature of 430-460°C under a pressure of 4-20 Kg/cm2G for at least 20 hours, thereby forming a high-crystalline petroleum coke having a coefficient of thermal expansion in the direction parallel to the extrusion of less than 1.0 x 10-6/°C over 100°-400°C
when measured in the form of a graphite artefact thereof.
3. A process as claimed in Claim 1 wherein the first heating step of the petroleum feedstock in a tube heater is effected in the presence of a small proportion of a basic compound selected from the group consisting of hydroxides and carbonates of alkali and alkaline-earth metals.
4. A process as claimed in Claim 3 wherein the basic compound is selected from the group consisting of sodium hydroxide and sodium carbonate.
5. A process as claimed in Claim 3 or 4 wherein the basic compound is present in an amount of 0.5-10% by weight based on the feedstock.
6. A process as claimed in Claim 1 or 2 wherein the time for which the temperature of the feedstock in a tube heater is maintained at 430-520°C is 200-500 seconds.
7. A process as claimed in Claim 1 or 2 wherein the time for which the delayed coking is carried out is at least 30 hours.
8. A process as claimed in Claim 2 wherein the first heating step of the petroleum feedstock in a tube heater is effected in the presence of a small proportion of a basic compound selected from the group consisting of hydroxides and carbonates of alkali and alkaline-earth metals.
9. A process as claimed in Claim 8 wherein the basic compound is selected from the group consisting of sodium hydroxide and sodium carbonate.
10. A process as claimed in Claim 8 or 9 wherein the basic compound is present in an amount of 0.5-10% by weight based on the feedstock.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA261,855A CA1072476A (en) | 1976-09-23 | 1976-09-23 | Process for producing high-crystalline petroleum coke |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA261,855A CA1072476A (en) | 1976-09-23 | 1976-09-23 | Process for producing high-crystalline petroleum coke |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072476A true CA1072476A (en) | 1980-02-26 |
Family
ID=4106915
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA261,855A Expired CA1072476A (en) | 1976-09-23 | 1976-09-23 | Process for producing high-crystalline petroleum coke |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1072476A (en) |
-
1976
- 1976-09-23 CA CA261,855A patent/CA1072476A/en not_active Expired
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