CA1098066A - Process for the production of a petroleum coke and coking crystallizer used therefor - Google Patents
Process for the production of a petroleum coke and coking crystallizer used thereforInfo
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- CA1098066A CA1098066A CA261,858A CA261858A CA1098066A CA 1098066 A CA1098066 A CA 1098066A CA 261858 A CA261858 A CA 261858A CA 1098066 A CA1098066 A CA 1098066A
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- coke
- coking
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Abstract
ABSTRACT
A process is described for the production of high purity, unusually high-crystalline texture petroleum coke from a low sulfur petroleum feedstock selected from the group consisting of virgin crude oil, distillation residuum, cracked residuum or mixtures. The process involves a preliminary heat treatment of the feedstock with removal of non-crystalline substances as pitch or coke, and the subsequent heating of a heavy oil fraction derived from the preliminary heating, following fractionation if necessary, to a coking temperature. The heated heavy oil fraction is then continuously introduced into a verticle, pressure coking-crystallizer which discharges gaseous light hydrocarbons through an upper outlet and progressively accumulates, in the lower portion of the coking-crystallizer, coke which is being formed. During operation the coking-crystallizer is treated with an upwardly passing, heated purging gas to prevent clogging. Once the crystallizer is full of coke crystals, the amount of purging gas injected is increased to expel remaining oily materials prior to removal of the coke from the crystallizer. The process permits production of a superior quality coke suitable for the production of graphite electrodes to be used in electric furnace steel-making under ultra high power operation.
kam
A process is described for the production of high purity, unusually high-crystalline texture petroleum coke from a low sulfur petroleum feedstock selected from the group consisting of virgin crude oil, distillation residuum, cracked residuum or mixtures. The process involves a preliminary heat treatment of the feedstock with removal of non-crystalline substances as pitch or coke, and the subsequent heating of a heavy oil fraction derived from the preliminary heating, following fractionation if necessary, to a coking temperature. The heated heavy oil fraction is then continuously introduced into a verticle, pressure coking-crystallizer which discharges gaseous light hydrocarbons through an upper outlet and progressively accumulates, in the lower portion of the coking-crystallizer, coke which is being formed. During operation the coking-crystallizer is treated with an upwardly passing, heated purging gas to prevent clogging. Once the crystallizer is full of coke crystals, the amount of purging gas injected is increased to expel remaining oily materials prior to removal of the coke from the crystallizer. The process permits production of a superior quality coke suitable for the production of graphite electrodes to be used in electric furnace steel-making under ultra high power operation.
kam
Description
6~ -This inventio~ relates to a process f'or the production of` petroleum coke of` unusually high-crystalline texture and of high purity from a petroleum material including a low~sulfur virgin crude oilg distillation residuum derived therefrom such as topped or vacuum residuum and a low-sulfur cracked residuum derived f'rom ca-talytic or thermal cracking of petroleum~
There are two types of coking process broadly classified, namely delayed coking and fluid coking, which have been utilized for large scale production of pet;roleum cokeg both of which would be developed firstly wit;h the intention o~ removing from topped or vacuum residua substances easily cokable by heating as coke thereby to provide liquid hyd.rocarbons~ thus the coke being so to speak a by-productO Such a petroleum coke, may, in most casesg be used as fue:L in power plants and others like coal. Howeverg certain of petroleum cokes of` a high quali.ty such as those produced ~rom low-sulfur petroleum residua under limited conditions may be utilized in place of pitch coke derived ~rom coal pitch.
Thus, such a high quality petroleum coke~ so called premium grade cokeg is now holding more and more a~
imporkant position as material for the production of graphite electrodes to be used in electric furnace sme:Lting of' aluminium and ironO
It is generally known that a coke suitable as material for the production of graphite electrodes to be usecL in electric furnace steel-making is characte,rized as Z! rule by having a low coefficient of' thermal expansion (CTE) and a low electric resistivity9 by showing diffraction bands due to the existence of crystals in X-ray diffraction and by having a crystalline texture well grown and oriented in one direction~ iOe, so-called needle-like structure~ in observation by naked eye or by microscopeO It is also known that in order to produce such a coke of needle~like structure~ the selection of starting petroleum heavy residue is most important~ that is the starting material should be one containing little or less amount of' non-crystalline carbon-forming substances (hereinafter referred to as non-crystalline substances) or one from which non-crystalline substances have been substantially removed by any appropriate treatment~
Recently, electric furnace steel-making has required ultra high power (UHP) operation in place of high power (HP) operation so far employed and this tendency has been more attractive 'in steel--making using iron pellets~ whereupon requirement for the performance of graphite electrodes has necessarily become more severe. The quality of graphite electrodes primarily depends upon the quality of coke from which the electrodes are produced and thus the improvement in the uuality of so-called premium grade coke is now æssential and eagerly desired in the art.
The ob~ect of this invention is to provide a process and apparatus f`or the production of a petroleum coke of higher quality than the premium grade one so~
called, with high reproducibility and stability on large scale, which is suitable as material for the production of graphite electrodes to be used in electric furnace steel-making under UHP operation.
There are various factors which have been considered as measures essential for evaluatlng the quality of coke to be suited for the production of graphite electrodes directed to the use in electric furnace steel-making under UHP operationO Thusg it is generally appreciated that the coke to be directed for such application should have a needle like structure~ a low coefficient of thermal expansion (CTE), a low electric resistivity and diffraction bands of crystals in X-ray diff'raction~ the value of CTE being the most important measure. Up to now, however, there is no testing method for determining each of the above-said factors which has bee:n established or authorized and the assessments or interpretations of respective values thus determined have not necessarily accorded with one anotherO It is therefore believed that the qualification of petroleum cokes on the basis of the above~mentioned ~actors only is not necessarily reasonable.
In view of the fact that it is important for a measure or criterion of the quality of coke to indicate sim~lltaneously not only the degree of thermal expansion but also the crushing strength of coke particles, crystal size~ degree of orientation and the like~ we have made many investigations to search for a new criterion by which the quality of coke to be directed to the produc-tion of electrodes may accurately be assessed and now found as such a criterion the value of maximum traversed magnetoresistance to be mos-t suitable in addition to or in place of the value of CTE. Thus~ the higher the value of maximum traversed magnetoresistance~ the better the crystal growîng3 the degree oi orientatlon and the layer stackingg all of which phenomena may decisively determine the quality of coke.
The maximum traversed magnetoresistance (~P/P) Tmax is defined as fo].lowso (~p/p) Tmax% = pHpo P x 100 where po is electric resistivlty free from a magnetic field and pH is electric resistivity under a magnetic field, Thc conditions of the measurement are as ~ollows:
Magnetic fîeld 10 Kgauss Temperature (liquid nitrogen) 77K
The magnetic field is applied in perpendicular direction to the sample~ The details of the measurement are based on the method reported by Yoshihiro Hishiyama et al in Japanese Journal of Applied Physicsg 109 lig 416~420 (1971)~
It is known that the value of maximum traversed magnetoresistance i.s the highest in case of a single crystal graph~te of æero defect with a constant magnetic fie].d and decreases considerabl.y with the increase in defect and that the value is independent of' the shape of sarnple~
We have studi.ed :l.n detail on relations of maximum traversed magn~toresistance with coefficient of thermal expansion (CTE)g coefficient, of cubic expansion (CCE) and electric resistivity9 al]. of which were mea.sured on samples in the form of' graphite artefactg and found that the lower the values of CTEg CCE and electric resistivity9 ~ :
the higher the value of maximum traversed magnetoresistanceO
Furtherg the observation of scanning electron photomicrographs and polarizing photomicrographs of' these samples has : . :
.
~8~i~6 shown that with the ircrease in the value of maximum traversed magnetoresistance~ the crystalline texture of coke is of higher groT~th3 of better orientation and of higher layer stacking~ Thus~ in view that the value of maximum traversed magnetoresistance has a good correspondence or correlativily with values of CTE~ CCE and electric resistivity and also with the crystalline texture 3 we now propose to use this as reasonable criterion to evaluate the coke to be used for the production of graphite electrodes.
The measurement of maximum traversed magne~o-resLstance of coke was made on a sample prepared by calcining a green coke at 1400C for 3 hours~ pulveriz-ing the calcined coke into particle s-lze fractions of 35-65 mesh and 100 mesh plus, blencling together llO parts Or 35-65 mesh fraction 9 60 parts of' 100 mesh plus fraction and 30 parts of coal tar pitch~ .kneading the mixture at 170C, extruding the kneaded mass i.nto a rod of 20 nun in diameter and 200 mm in length~ baking the rod at 1000C
for 3 hours and then at 2700C for 1 hour for graphitiza-tion and cutting samples of certain specific siæe and shapeO
We have found that petroleum coke obtained according to the present invention as defined hereinafter has a value of maximum traversed magnetoresistance of higher than 16.0% when measured as above~specified and of higher than 50% when measured in the form of a Kraphitized coke prepared by graphitizing the calcined coke as such at 2700C for 1 hour~ and is of unusually high-crystalline texture and has a silvery ~hite metallic luster in ~9~
appearance and that such a coXe is most suitable as material for the production of graphite electrodes to be used in electric furnace steel-making under UHP opera--tions. As far as we knowg such a high--crystalline petroleum coke is not commercially available as yetO I'he highest grade of petroleum coke commercially available which is so-called premium grade one has been found by our measurement to have a value of maximum traversed magneto res:i.stance of about 6~10%~ while the so-called regular grade petroleum coke has been found to have said value of about 3-6%, ~or convenience a the relation between the maximum traversed magnetoresistance and coefficient of thermal e~pansion in the direction parallel to the extrusion of these types of petroleum coke .~easured in the form of a graphite artefact is given as followsO
~laximum tra~ersed Coeff~cien-t of magnetoresistance thermal expansion (10 Kgaussa 77K) (o~er 100 400C) % 10"- 6/o C
Xi$h~crystalline coke Above 16 Below 1.
Premium grade coke 6 - 10 1.0 ~ 1.2 Regular grade coke 3 - 6 Abo~e 1.2 It is already known that in order to produce a high quality petroleum cokea that is so-~called premium grade one which ls suitable as material for the produc~
tion of high quallty graphite electrodes a the following are essentially required (1) Starting materi.al must be o~ a low sulfur content~
There are two types of coking process broadly classified, namely delayed coking and fluid coking, which have been utilized for large scale production of pet;roleum cokeg both of which would be developed firstly wit;h the intention o~ removing from topped or vacuum residua substances easily cokable by heating as coke thereby to provide liquid hyd.rocarbons~ thus the coke being so to speak a by-productO Such a petroleum coke, may, in most casesg be used as fue:L in power plants and others like coal. Howeverg certain of petroleum cokes of` a high quali.ty such as those produced ~rom low-sulfur petroleum residua under limited conditions may be utilized in place of pitch coke derived ~rom coal pitch.
Thus, such a high quality petroleum coke~ so called premium grade cokeg is now holding more and more a~
imporkant position as material for the production of graphite electrodes to be used in electric furnace sme:Lting of' aluminium and ironO
It is generally known that a coke suitable as material for the production of graphite electrodes to be usecL in electric furnace steel-making is characte,rized as Z! rule by having a low coefficient of' thermal expansion (CTE) and a low electric resistivity9 by showing diffraction bands due to the existence of crystals in X-ray diffraction and by having a crystalline texture well grown and oriented in one direction~ iOe, so-called needle-like structure~ in observation by naked eye or by microscopeO It is also known that in order to produce such a coke of needle~like structure~ the selection of starting petroleum heavy residue is most important~ that is the starting material should be one containing little or less amount of' non-crystalline carbon-forming substances (hereinafter referred to as non-crystalline substances) or one from which non-crystalline substances have been substantially removed by any appropriate treatment~
Recently, electric furnace steel-making has required ultra high power (UHP) operation in place of high power (HP) operation so far employed and this tendency has been more attractive 'in steel--making using iron pellets~ whereupon requirement for the performance of graphite electrodes has necessarily become more severe. The quality of graphite electrodes primarily depends upon the quality of coke from which the electrodes are produced and thus the improvement in the uuality of so-called premium grade coke is now æssential and eagerly desired in the art.
The ob~ect of this invention is to provide a process and apparatus f`or the production of a petroleum coke of higher quality than the premium grade one so~
called, with high reproducibility and stability on large scale, which is suitable as material for the production of graphite electrodes to be used in electric furnace steel-making under UHP operation.
There are various factors which have been considered as measures essential for evaluatlng the quality of coke to be suited for the production of graphite electrodes directed to the use in electric furnace steel-making under UHP operationO Thusg it is generally appreciated that the coke to be directed for such application should have a needle like structure~ a low coefficient of thermal expansion (CTE), a low electric resistivity and diffraction bands of crystals in X-ray diff'raction~ the value of CTE being the most important measure. Up to now, however, there is no testing method for determining each of the above-said factors which has bee:n established or authorized and the assessments or interpretations of respective values thus determined have not necessarily accorded with one anotherO It is therefore believed that the qualification of petroleum cokes on the basis of the above~mentioned ~actors only is not necessarily reasonable.
In view of the fact that it is important for a measure or criterion of the quality of coke to indicate sim~lltaneously not only the degree of thermal expansion but also the crushing strength of coke particles, crystal size~ degree of orientation and the like~ we have made many investigations to search for a new criterion by which the quality of coke to be directed to the produc-tion of electrodes may accurately be assessed and now found as such a criterion the value of maximum traversed magnetoresistance to be mos-t suitable in addition to or in place of the value of CTE. Thus~ the higher the value of maximum traversed magnetoresistance~ the better the crystal growîng3 the degree oi orientatlon and the layer stackingg all of which phenomena may decisively determine the quality of coke.
The maximum traversed magnetoresistance (~P/P) Tmax is defined as fo].lowso (~p/p) Tmax% = pHpo P x 100 where po is electric resistivlty free from a magnetic field and pH is electric resistivity under a magnetic field, Thc conditions of the measurement are as ~ollows:
Magnetic fîeld 10 Kgauss Temperature (liquid nitrogen) 77K
The magnetic field is applied in perpendicular direction to the sample~ The details of the measurement are based on the method reported by Yoshihiro Hishiyama et al in Japanese Journal of Applied Physicsg 109 lig 416~420 (1971)~
It is known that the value of maximum traversed magnetoresistance i.s the highest in case of a single crystal graph~te of æero defect with a constant magnetic fie].d and decreases considerabl.y with the increase in defect and that the value is independent of' the shape of sarnple~
We have studi.ed :l.n detail on relations of maximum traversed magn~toresistance with coefficient of thermal expansion (CTE)g coefficient, of cubic expansion (CCE) and electric resistivity9 al]. of which were mea.sured on samples in the form of' graphite artefactg and found that the lower the values of CTEg CCE and electric resistivity9 ~ :
the higher the value of maximum traversed magnetoresistanceO
Furtherg the observation of scanning electron photomicrographs and polarizing photomicrographs of' these samples has : . :
.
~8~i~6 shown that with the ircrease in the value of maximum traversed magnetoresistance~ the crystalline texture of coke is of higher groT~th3 of better orientation and of higher layer stacking~ Thus~ in view that the value of maximum traversed magnetoresistance has a good correspondence or correlativily with values of CTE~ CCE and electric resistivity and also with the crystalline texture 3 we now propose to use this as reasonable criterion to evaluate the coke to be used for the production of graphite electrodes.
The measurement of maximum traversed magne~o-resLstance of coke was made on a sample prepared by calcining a green coke at 1400C for 3 hours~ pulveriz-ing the calcined coke into particle s-lze fractions of 35-65 mesh and 100 mesh plus, blencling together llO parts Or 35-65 mesh fraction 9 60 parts of' 100 mesh plus fraction and 30 parts of coal tar pitch~ .kneading the mixture at 170C, extruding the kneaded mass i.nto a rod of 20 nun in diameter and 200 mm in length~ baking the rod at 1000C
for 3 hours and then at 2700C for 1 hour for graphitiza-tion and cutting samples of certain specific siæe and shapeO
We have found that petroleum coke obtained according to the present invention as defined hereinafter has a value of maximum traversed magnetoresistance of higher than 16.0% when measured as above~specified and of higher than 50% when measured in the form of a Kraphitized coke prepared by graphitizing the calcined coke as such at 2700C for 1 hour~ and is of unusually high-crystalline texture and has a silvery ~hite metallic luster in ~9~
appearance and that such a coXe is most suitable as material for the production of graphite electrodes to be used in electric furnace steel-making under UHP opera--tions. As far as we knowg such a high--crystalline petroleum coke is not commercially available as yetO I'he highest grade of petroleum coke commercially available which is so-called premium grade one has been found by our measurement to have a value of maximum traversed magneto res:i.stance of about 6~10%~ while the so-called regular grade petroleum coke has been found to have said value of about 3-6%, ~or convenience a the relation between the maximum traversed magnetoresistance and coefficient of thermal e~pansion in the direction parallel to the extrusion of these types of petroleum coke .~easured in the form of a graphite artefact is given as followsO
~laximum tra~ersed Coeff~cien-t of magnetoresistance thermal expansion (10 Kgaussa 77K) (o~er 100 400C) % 10"- 6/o C
Xi$h~crystalline coke Above 16 Below 1.
Premium grade coke 6 - 10 1.0 ~ 1.2 Regular grade coke 3 - 6 Abo~e 1.2 It is already known that in order to produce a high quality petroleum cokea that is so-~called premium grade one which ls suitable as material for the produc~
tion of high quallty graphite electrodes a the following are essentially required (1) Starting materi.al must be o~ a low sulfur content~
(2) The content of light oil fractions and the amount o~ steam or inert vapour to be blown into coking drum for dilution of material should be as low as possible so that excessive agitation of the reaction mass is prevented dur:ing the reaction of delayed coking;
(3) Starting material should be one containing little or less amount of non~crystalline substances or one from which non-crystalline substances have been substantially removed by any appropriate treatment.
As a result of many investigations on important fact;ors of petroleurn coke for being suited as material for the production of high quality graphite electrodes, we have found that the most important~ ~undamental requisite ~or petroleum coke in question is to have a crystalline teY~ture highly grown and oriented in one direction with a minimum content of non~crystalline substances and of foreign matters and that to produce such a high-crystalline coke it, is most important to carry out thc coke-forming reaction under such conditions that the formation and growth of coke crystals are conducted with a minimum agitation or disturbance of the reaction system whereby the growth and orientation of coke crystals formed are promoted~
~ here have already been proposed various processes for the remo~al o~ non-crystalline substances from petroleum materials with the intention of producing a prem:ium grade or higher grade petroleum coke~ for example a process wherein the petroleum material is preheat--treated in the presence or absence of a catalyst followed by removing a part o~ the materi.al before coking and a process wherein the petroleum material is subjected ~ 3~
to delayed coking in two states~ but as far as we know SUC]l a high quality coke as one obtained by the present invention, named a high-crystalline coke, has never been obtained as yet, possibly due to the difficulty of ach:ieving compl.ete and efficient removal of non~
crystalline substances before coking, We have further paid attention to disadvantages o~ delayed coking rnethod itself for the pt~pose o~
proclucing such a high-crystalline coke. As is well-known, according to delayed coking method, a petroleumfeecLstock which has been heated to a temperature required for the coking is fed in a-t the bottom of a heali~in~ulated coking drum and maintained therein to e*~ec-t the ~ormation o~ coke. In this method, the coking reaction involving cracking, polymeri~ation and concLensation is e~fected under such condition~ that pitch-li`ke~ heavy oil being ~ormed thereirl is stirred, diluted and contaminated by .reohly charged material and by light oil formed by the cracking of heavy oil during the coking~
namely under -the conditions of notable agitation or distrubance occurring in the drum, thus dif~iculties are brought in achieving the growth and orientation o~
coke crystals formed~ Furthermore, the quality oP coke ~ormed varies with its position in the coking drum because the freshly charged ma-terial is passed upwardly through the coke already formed in the coking drum, during which pass the fresh charge is coked to some extent and thus the concentration of coke is higher at the lower part o~ the drum and lower at the higher part of the drum ~hus, we came to a conclusion that the delayed coking system is not suitable for the purpose of producing a high crystalline petroleum coke even when a well-se]ected starting material is used owing to difficult-ies in the prosecution o-f coking reaction under ideal condition~.
Under the circumstance~, we have intended to provide a new method for the removal of non-crys-talline substances from starting materials and a new type of coking drum which makes it possible ^to carry out the coking reaction involving the formation9 growth and orientation of coke crystals under the conditions of a high concentration of coke-forming substances and of a min:imum agi-tation of the reaction system~ ~or the remo~al of non~crys-talline substances 9 we have in~estigated in detail on influences of nature of starting materials and coking reaction condition3 including temperature, pre~3sure and time on the yield and properties of coke obtained and, ~or the structure of coking drum, o~ the elimînation of agitation or disturbance of the reaction system due to the i~troduc-tion of ~resh feed and con~ec-tio~ ~low which would result in the prevention o~ the grow-th and orientation of coke crystals. This in~ention is the combination of the results of these in~estigatLons.
According -to one aspect of this in~ention~
therefore, there is provided a process for the production oP a petrole~m coke of unusually high-crystalline te~ture and of a high purity ~rom a petroleum starting ma-terial ha~:Lng a low ~ulfur content selected from the group consisting of a low-sulfur, virgin crude oil~ distilla-tion residuum~ cracked residuumg their mi~ture and their 109 !3C~66 equivalent which comprises the steps of:subjecting the starting material to heat treatment to remove non-crystalline substances contained therein as pitch or coke;
heating a heavy oil fraction o~ the starting material derived *rom the preceding stage, if nece~sary after removing a lighter fraction or fraction~ there~rom9 to a temperature required ~or the subsequent coking;
continuou~ly introducing the preheated oil with downward in~ection into a vertical, pre~sure coking-cryotallizer, which is provided with a heating ~acket surrounding the body thereof, an injection nozzle pipe at the upper part thereo~ for downwardly injecting the pre-heated oil and an in~ection nozzle at the lower part ther00~ ~or upwardly injecting a purging ga~, where gase-OU8 light hydrocarbons formed either by evaporation or by reactione o~ the oil introduced are discharged through an outlet positioned at the upper part o~ tho cry~tallizer and the remaining pltoh-llke heavy oil downw~rdly ~lows and i~ progressi.vely accumulated ~nd coked under the given conditions o~ temperature and pre~ure, while a small amount o~ a heated purging gas ~elected ~rom steam, ga~eou~ hydrocarbon~ and other inert gase~ is introduced therein with upward injection at a ~low rate capable of preventing the clogging of the ga~ injection nozzle, thereby conducting the coking with a high growth and high orientat-ion of coke crystals ~ormed lmtil the crystallizer is full; and increa~ing the amolmt of the purging gas injected to expe~l the remaining oily materials and discharging the coke from the cry~tallizer.
'- , , ; ' By the term "unusuallJ high-crys-talline texture"
used with respec-t to the petroleum coke obtained according to -thls in~ention is meant for the coke to have a higher crystalline texture than that of so-called premium grade or needle-like coke, both in the growth and in the orientation of coke cry?tals1 and by the term "high pur:ity" is rneant that the contents of foreign matters and of non-crystalline substances are minimized.
The pe-trole~ starting material should be one having a low sulfur content. ~or a virgin crude oil9 usually9 the sulfur content should be 0.4% by weight or less, preferably 0.25~o or less. Distillation residuum should be one derived from a low-sulfur virgin crude oil as above~
mentioned. ~or a cracked residuum, the sul-fur cont~.nt should preferably be 0~8% or less. :Distillation and crac?ked residua containing a higher amount of sulfur may if cLesi.red be used after they are subJected to hydro-deslllfuriza1iion to lower the sulfur conten1i-to a required level. ~ny other refinery residuum e~ui~alent to those men1iioned above may be used, if desired~
~ he heat treatment which constitutes the Pir~t stagte o~ -the process of this invention may be e~fected by any desired method capable of separating ~ld removing non--crystalline substances contained in the starting ma-terial as pitch or coke~ One method particularl~
ef~ective for this purpose is to heat and maintain the starting material in a tube hea-ter under certain controlled condi-tion~ for an appropriate -time thereby to cau~e cracking and soaking of the material and then to subject ~0 the material to flash distillation or coking to remove . . .
selectively non-crystalline substances therefrom as pitch or coke~ The conditions of such a heat treatment depend primarily upon the nature cf starting materialO
Our experiments have shown that in most cases desired results can be obtained by heating the starting material in a tube heater to a temperature of 430-520C under a pressure of 4~20 Kg/cm2G followed by maintaining the same therein at this temperature for 30-~00 secondsO
We have further found that the presence of a small amount 9 preferably 0.5-10% by weightg of a hydroxide and or a carbonate o~ an alkali or alkaline-earth metal in the starting material much more improves the efficiency of the separation of non--crystal].ine substances f'rom the material in the heat-treatment stage according to this invention parti.cularly when the starting material is a heav~ oil or residuum and as a result the coke obtained has a value of maximum traversed magnetoresistance higher than 21% in the form of graphite artefact~and a value higher than 60% in the form of graphitized cokeO
~ccording to another aspect of the present inven tion!, there is provided a coking-cr~stallizer comprising a body in which a petroleum material is coked9 a heating jacket surrounding the body through which a heating medium is ci.rculated to provide a heat required ~or the body in a controlled manner9 an injection nozzle pipe introduced into the body at the upper part thereof to downwardly inject a petroleum material to be coked9 a purging gas injection nozzle introduced into the body at the lower part thereof to upwardly inject a purging gàs~ an outlet for discharging gaseous hydrocarbons formed and the , purKing gas at the upper part of the body and out]ets for discharging coke formed at the top and bottorn of the body.
We named the coking drum of this lnvention as coking~crystallizer because it makes possible to achieve unusually high growth and orientation of coke crystals~
In operation9 of the heavy oil fraction introduced into the coking~crystallizer9 gaseous hydrocarbons may be dlscharged at the upper part through an outlet 1~ therefor with a minimum agitation inside of the bodyg named coking zone~ and the remaining heavy hydrocarbons downwardly flow in the coking zone and are progressively accumulated and coked therein in a high concentration~
Thus, the agitation and disturbance whiGh may occur owîng ko the release of cracked light hydrocarbons during the coke~forming reactions and to the introducti.on of th material may be minimizecl~ and the coklng reactions are conducted under well~controlled3 optimum conditi.ons so that the formakion and growth of coke crystals regularly and progressively proceed in upward direction along the vertical axis of the crystallizerO As a result 9 the variation in quality o~ coke with the variation in positions khereof in the crystallizer can be minimizedO
The inside temperature of coking~crystallizer may be well-controlled to a desired level by circulating a heating medium through the heating jacket of the crystallizer as requiredO ~ purging gas injection nozzle is inserted at the lower part of crystallizer3 as above-described5 to e~pel uncoked oil and cracked light oil fractions from the crystallizer after the completion o~
the coking reactions~ In order to prevent the ~aid injection no~zle from being clogged during the coking reactions, it is necessary to pass continuously there-through a smal.l amount of a heated purging gas such as steamS gaseou~ hydrocarbons and other inert gas at such a slow rate that the agitation of coking zone is minimi~ed but the clogging of said no~zle is avoided, '~he coke obtained according to the process of this invention is of significantly higher quality than that of any of petroleum cokes hitherto publicly reported as above-mentioned, and is particularly characterized by its values of maximum -traversed magnetoresistance of higher than 16.0% measured at 10 Kgauss and 77 K in the ~orm of graphite artefact and o~ higrher than 50% measured at the same conditions in the form of graphitized coke.
The observati.on o~ the crystalline te~ture of ..
cok:e obtained according to this invention in the form of a graphitized coke by a scanning electron microscope and a polariæing microscope has confirmed such a bett~r ~uality.
In the drawings attached herewith.
~ igure la is a reproduction o~ a polarizing photomicrograph taken at 250 time~ magni~ication o~ a graphitized coke obtained by this invention;
Figure lb is a reproduction of a scanning electron photomicrograph taken at 1000 times ma~nification of the sam.e coke as that o~ ~igure la;
Figure 2a is a reproduction of a polariæing photomicrograph taken at 250 times magnification of a graphiti~ed coke o~ a typical premium grade petroleum ~Q~
eoke commercially available, Figure 2b is a reproduetion of a scanning eleetron photomierograph talcen at 1000 times magnification o~ the same eoke as that of Figure 2a 3 Figure 3 is a sketeh of a longitudinal seetion of one typieal embodiment of the coking-erystallizer aeeording to this invention; and ~ igure 4 i3 a representative flow diagram of one spee_fic embodiment of the process aecording to this inventionO
Typical properties of coke obtained by the process of this invention are shown in Table 1 and by way of eomparison properties of a typieal premium grade eoke commereially available are shown in Table 2 Table Properties of eoke obtained by this invention . . _ . .
Graphite artefaet Graphitization eondition 2700~C x 1 hr Coeffieient of thermal expansion i.n the direetion parallel to the extrusion (CTE) 25-125C 0O25 x ~.0 6/oC
100-400C oO83 "
Coef'fieient of eubie expansion (CCE) 130-300C 6.63 "
Maximum traversed magnetoresistanee 18~0%
Caleined eoke Calcination eonclition 1400C x 3 hr ~ 6 ~
Real density 2 0170 g/cc Crushin~ strength 51.8%
Water content 0,05 wt%
Ash content 0O05 "
Volatile matter content Or 43 ;~
Fixed carbon content 9~, L~7 Sulfur content 0O45 Metal content Fe 6 wt ppm Ni 3 7~
V 4 ~7 Cll 6 ~ . . _ . _ _ .. . .. _ Table 2 ties of a pr mium grade coke _ _ . . . .
Graphlte artefact ~raphitization condition 2700C x 1 hr Coefflcient of thermal expansion in the direction parallel to the extrusion ~CTE) 25-125C 0065 ~ 1~~6/C :
100-400C lo 20 "
Coefficient of cubic expansion (CCE) 130-300C lOo 7 ~t Maximum traversed magnetoresistance 6O4%
Calcined coke CalcinatiQn condition 1400C x 3 hr Real density 2~124 g/cc - 16 ~
Crushing strength 5~.2%
Water content 0007 wt%
Ash content .7 i7 Volatile matter content 0044 91 Fixed carbon content 99~42 !1 Sulfur content 0.23 "
Metal content Fe 15 wt ppm Ni ll 1' V 4 '~
Cu 10 '~
.
The crushing strength was determined by the following procedure-About 30 g of calcined coke grist of 5 to 12 meshs:Lze were put tnto a cylindrical mold made of stainless steel~ 30 mm IoD~ by 100 mm long. After setting a cylindrical piston head to contact with the top surface of the coke grist~ a load up to a pressure of 100 Kg~cm2G
was applied thereto for 30 seconds and the load was kept for further 30 seconds. The coke grist was khen taken out of mold and sieved out 12 mesh minus. The remaining coke grist was weighed. The ratio of the remaining coke grist to the original one is expressed as crushing strength in per cent by weight.
The structure and method of operation of one typical embodiment of the ccking-crystallizer according to this invention are now explained by referring to Figure 3. A heavy oil for coking which has been heated to 450-550C is continuously introduced through line 9 and valve 10 at the upper part of coking-crystalli~.er 1 provided wi-th heating jacket 4 by means of injection nozzle pipe 117 the coking-crystalli7.er being maintained at 410-500~ and 4 20 kg/cm2~ In the coking~crystallizer~
gaseous light hydrocarbon -.Eraction is dischargad -through ].ine 14 and valve 15 and pitch-like heavy oil fraction downwardly flows and progressively accumulates therein with the proceeding of coking reaction. The lower part o the crystallizer is provided with purging steam line ]2 with ~alve 13 through which a small amount of steam, gaseous hydrocarbon or an inert gas such as nitrogen heated to 400-500C is introduced i.nto the crystalli~er to prevent the clogging o-E line 12. When the level Of the accumulated coke reaches near t;he noz~le 119 the introduction oE the heavy oil through line 9 is stopped ancl the amoun-t of high temperature ste~m through line 12 is increased -to e~pel the remaining oily hydrocarbons Erom the crystalli~er. On completion oE the egpulsion, ~lange~
2 and 3 are opened, through which coke Eormed is dis-charged. Any heating medium may be used provided it can maintain the temperature o-E-the interior of crys-tallizer to 410~500C9 for e~ample molten 3alt~ s-team and hydro-carbons such as gaseous hydrocarbons discharged from the cr~rstallizer~ The heating medium is introduced through line 5 with valve 6 into -tb.e jacket 4 and discharged through line 7 with valve 8 thereErom. As a mat-ter of course 9 the heating jacket 4 is covered with a heat-insulating material to minimi~e the radiation of heat.
One embodi.me~t o:E the process according to this invention is illustrated by referring to Fi~ure 4. The starting petroleum material is p~mped by means of pump 17 and introduced through line 16 into heater 18 for preheat~treating the same, where'it is heated to 430-520C
under 4-20 kg~cm2G and then maintained therein at that temperature for 30-500 seconds thereby to e-~fect crack-ing and heat-soaking of the same. The material thus heat-treated is passed through transfer line 19 into high-temperature flashing column 20 of which upper trays have been packed wi-th wire mesh blanket and the like to prevent pitch ~eing entrained with distillate during the flash distillation. ~he pitch having a softening point of 100-240DC is discharged from the bottom of column through line 21 by means of pump in a mol-ten state while the 'bottom temperature being maintained at 380 480 C under a pressure of 2-10 kg/cm2G~ At the same time, the flash-distillate is discharged at the head of col~unn through line 22 and passed through cooler 2~ into drum 24 wherein condensed oil is held while non-condensed gaseous h~Jdrocarbon fraction is passed through line 25 into main fractionating column 31 at the middle part thereof. Alternatively, all the flash-distilla-te may be directly introduced through lines 50 and 25 into main column 31~ ~he conde~ed oil i~ then pumped through line 26 into coking preheater 27 were it is heated to 450-550 C and injected through line 28 into coking-crystallizer 29a at the head thereo:E.
In the cokingYcrystallizer~ gaseous light hydrocarbons ~ormed ei-ther by evaporation or by cracking and poly-condensation of pitch-like heavy oil as well as a small amoun-t of ~team (or gaseous hydrocarbons or iner-t gas) are discharged at the head of crystallizer through line 30 and introduced in-to the main fractlonating column 31 at a lower position than that of line 25. Heating medi~ is co:ntinuously circulated through the outer jacket o~ the crystallizers 29a and 29b to keep the inside tamperature of crystallizers to 410 500~C by passing the heating medium from line 37 through dru~ 32, line 33, heater 34 9 li:ne 35 and line 36 back to drum 32. This circulation iæ
fo:r a molten sa]t as heating mediumO If æuper heated steam is us~d as heating medium, more simple system may be used. Alternativelyg gaseous light hydrocarbons coming from line 22 (450-550C) or ~rom line 30 (430-520C) may be used as heating medium for coking crystalli~er. When -the col~ing-crystallizer 29a is ~illed with coke formed, the in1kroduction of the heavy oll charge is swi-tched over into the crys-tal.llzer 29b and the green coke acc~ulated in the crvstalli~er 29a is discharged, .A d:istillate boiling above 20() C taken ~rom the middle part o-f main column ~1 as side~
cut is passed through line 38 into heater ~9 where a heat treatment at 500-550 C under pressure is ef~ected to form a 1;ar and then re-turned -through line ~0 to the main column at lower part than that of line 38. At t;he bottom of main colu~n 31~ the bottom residue rich in tar is dis-charged by pump 49 and introduced through line 48 into coking preheater 27 in combination with the condensate o-~
flash~distillate coming from line 26~ Gas and gasoline ~ractions discharged at the top of main column 31. are passed through line 41 and cooler 42 into receiver 43 ~here the separation o-f gas and liquid is ef~ected, the gas being cllscharged through line 45 and the liquid being 20 ~
discharged through lines 44 and 46 as reflux of the mai.n co:Lumn and as product9 respectively. In some cases~ a part of side~cut 38 f:rom the main column may be combined through line 51 with the sucti.on si.de of pump 17 for -the dilution of starting materialO
l'he fo]lowing Ex.~mples f~ther illustra-te9 but not limit~ thi.s inventlon, in which percentages are by wei.ght unless otherwlse specified.
Ex~ le 1 A cracked residue containing 0~76~ of sulfur named as ta.r-bottom l~hlch was obtalned as by-product in a conventional thermal cracXing o.f gas oil for the production of ethylene and which has properti.es shown in Table 3 ~as used as feedstock ~or this ~xample.
~ he ~e~dstock was introduced into a tube heater having 4 mm i.nside diamete:r, 6 mm olltsi.de dlameter and 20 m length, heated under Q press~e of 4 kg/cm2G
to 490~ and maintained therein at this tempera-ture for a~out 260 seconds~ T'he feedstock was then introduced into æ high-temperatllre flashing colllmn maintained at 490-~, where ~lash distillation of the feedstocX is effected to recover distilla-te at the head of column and to w-lthdraw pitch at the bo-t-tom of column in an amount of 20% based on the ~eedstock~ with a retention time of about 10 minutes at the bottom of colu~n~
together with gas generated in an amount o~ 5~0~o on the same basise ~he distillate ~Jas then passed through a tube heater having 4 mm inside diametere 6 mm out~ide diameter and 4 m length to preheat it to 4S0 C a.nd then injected under a pressl~e o~ 9.0 kg/cm2~ into a jacketed coking-crystallizer as shol~n in ~igo 3 at the rop thereof.
wherein pitch~like heavy oil was progressively accumulated and coked while lightg uncoked hydrocarbons were dis--charged at the head of crystallizerO
The yield of coke was 46~ 2% based on the charge of crystallizer (34O9% based on the starting feedstock)O
By-products of the coking stage were 18.1~ (1306%) of cracked gas~ 1~1% (o.&%) of gasoline boiling up to 200C 9 28O9% (21~6%) of gas oil boiling in the range 200-300C
and 5~7% (4O3%) of heavy oil boiling 300C~o The properties of coke obtained are shown in Tab:le 4. Particularly noticeable were CTE of o.83 x 10 fi/oC over 100~400Cg C'CE o:t' 6~63 x lO 6/oC over 130-300C and maximum traversed magnetoresistance of' 18~0%
measured all in the form o~ a graphite artefactO The coke was o~ unusually high-crystallirle texture an~l apparently superlor to premiurn gracle one~
Example 2 A hydrodesulfurized product containing 0 3% of sulf'ur (named as desulfurized tar) o~ a cracked residue containing 1.05% of sulfur which was obtained as by product ln a ~onventional thermal cracking of gas oil for the production of ethylene was used as feedstock for this Example. The properties of the desulfurized tar are shown in Table 3O
The feedstock was treated in the same apparatus~
in the same manner and under the same conclitions as those used in Example 1. At the flash distillation stage9 pitch was rernoved in an amount of 7.8% based on the feedstock together with gas generated in an amount of 0O~% on the s~me basisO
The yield of coke was 22.~% based on the charge of crystallizer (2009% based on the starting feedstock).
By-products of the coking stage were 13 1% (1200%) of cracked gas~ 1.9% (1.7%) of gasoline boiling up to 200C~
53.2% (48.6%) of gas oil boiling in the range 200-300C
and 9O0% (8.2%) of heavy oil boiling 300C-~, The properties of coke obtained are shown in Table 4. The coke was of unusually high~crystalline texture and apparently superior to premium grade one.
Example 3 The gas oil (200 300C fraction) named as coker gas oil which was obtained ~s by-product in the cok:ing stage of Example 2 and which has properties shown in Tab:Le 3 was introduced at a rate of' 1 kg/hr into a tube heater having 4 mm inside diameter~ 6 l~l outside diameter and 40 m length and thermally crackecl therein under the conditions of 530C and 65 kg/cm2~r; the heavy residue boiling 300C+ being taken out as thermal tar and the unreacted oil being recycled to the thermal cracking. Thus~ there were obtained 33O5% of cracked gas~ 29.9% of gasoline boiling up to 200C and 36.6% of thermal tar boiling 300C+~ based on the starting gas oilO
The thermal tar thus obtained was introduced into the coking-crystallizer as used in Example 1 and coked mder the same conditions as those of Example 1~ yielding 47.3% of coke and as by-products 2301% of cracked gas and 29.6% of cracked oil based on the therm21 tarO
l'he properties of coice obtained are shown in 6~i Table 4~ The coke was o-e unusually high-cry3talline texture and superlor to premium grade one~
EY~a~L
The procedure of Exarnple 1 was repeated except that 005% based on the feedstock of sodium hydroxide were mixed with the feedstock before treatment in -the *orm of an aqueous solution. At`the flash distilla-tion stage, pi-tch ~Jas removed in an amount of 29.0% together with ~ o of gas. ~he coking stage gave a coke in a yield of 34.5% based on the charge of crystallizer (24~2~o based on -the starting feedstock) and as by~products 15.2% (10. 6~o) of cracked gas and 50~3~ (35.1~) of cracked oil.
The proper-ties of coke obta-ined are shown in Tab:le 4~ ~he coXe was of unusually high-crystalline tex-ture and superior to premium grade one.
Exa3~
A topped residue o~ ~inas crude oil which has propertieæ shown in ~able 3 was used as feedstock for this E~ample~
The feedstock was introduced into a tubo heater having 4 mm inside diameter, 6 mm outside di.ameter and 40 m lengtll and heated under 20 kg/cm2G to 480C and maintained therein at this temperature for about 190 seconds. The feedstock -thus heat-treated was introduced into a high-temperature :.lashing column and subjected to flash distillation under conditions of 400C and 0 kg/cm2G to recover distillate at the top of colwnn and to withdraw pitch at the bottom of col~unn i~ an amount of 10.7~o based on the feedstock, with a retention time of about 15 min~ltes at that bottom, toget.her with gas - 24 - .
generated in a.n amount of 21~0~ on the same basis. The distillate ~68.3% based on tne feedstock) was passed through a tube heater same as that used in Example 1 to preheat it to 450C and then in~ected under a pressure of 9 kg/cm2G into a Jacketed colcîng--crystallizer as used in :Example 1 at the top thereof3 wherein pitch like heavy oil was gradually and increasingly accumulated and coked~ while light~ uncoked hydrocarbons were discharged at the head of crystallizerO
I`he yield of coke was 5O9~o~ based on the charge of crystallizer (401% based on the starting feedstock)O
By-products of the coking stage were 1802% (120 4~) of cracked gas~ 20,0% (130 6%) of gasoline boll:ing up to 200"C~ 34O5% (2306%) o~ gas oil boiling in the range 200-~300C and 21.4% (14~6%) of heavy oîl boiling 300C+, The properties of coke obtained are shown in Table 4~ The coke was Or unusually hi~h-crystalli.ne text,ure and superior to premium grade oneO
_ample 6 Djatibarang virgin crude oil which has properties shown in Table 3 was used as feedstock for this Example.
The feedstock was introduced into a tube heater having 4 mm inside diameter~ 6 mm outsîde dlameter and 40 m length and heated under 18 kg/cm~G to 480C and maintained therein at, this temperature for about 300 secondsO The feedstock thus heat-tre2ted was introduced into a coking drum haviIlg 100 mm diameter and 1000 mm height which was externally heated by electric wire heater and coked therein at 415C under 3 kg/cm2~ to remove non~crystalli.ne substances contained in the ~9~
feedstock as cokeO The amount of coke formed at this stage was 11~0% by weight based on the .feedstock and simultaneously cracked gases were generated in an amount of 10,8~ on the same basis, The distillate from this coking stage (7802%
based on the feedstock) was introduced into a tube heal;er having 4 mm inside diamete~r~ 6 mm outside diameter and 4 m length to heat it to 440C at the outlet thereof and then inJected under a pressure of 10 kg/cm2G into a ~acketed coking crystallizer as used in Example 1 at the top thereof, wherein pitch~like heavy oil was gradually and increasingly accumulated and coked, whil.e light, mcoked hydrocarbons were discharged at the head of crystallizer.
The yield of coke formed i.n the crystallizer was 11~2% based on the charge of crystallizer (808% based on the f'eedstoclc)~ The properties of coke thus obtained are shown in Table 40 llhe coke was of unusually high-crystalline texture and superior to premium grade oneO
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This Example illustrates the superiority of -the coking-crystallizer system of' this invention to the delayed coking systemO
The same charge as that introduced into the coking~-crystallizer in Example 2 was used for the comparative runs of' this Example~
In the first run, the chargeg iOeO the distillate from the flash distillation stage of Example 2~ was preheated to 450C in a tube heater having 4 mm inside d.iameter3 6 mm outside diameter and 4 m length and then injected under a pressure of 9 kg/cm2G into a ,jacketed colcing--crystallizer as used in Exarnple 1 at the top thereoI' 3 wherein pitch~llke heavy oil was gradually and increasingly accumulated and coked 3 while li.ght~ ~mcoked hydrocarbons wer~ discharged at the head of crystalli~erO
In the second run, the charge was preheakecl in the same manner as that of the first run and was introduced into a conventlonal delayed coking drum and coked therein.
The results of the two runs are shown in Table 5O
The comparison of the results clearly shows`2 ..
significant improvement in properties of coke of the first run (accorcling to this invention) over the second run (according to the delayed coking ~rocess), particularly with respect to CTE~ CCE and maximum traversed magneto resistanceO
Table 5 ~ Coking~ ' ¦ crystallizer ¦ Delayed system of ~ coking this ! system invention j (Run 2) (Run 1) l ¦
ield of coke (wt.%) 20.9 ¦ 18.9 ield of cracked oil (wt.%~5805 ¦ 70.7 roperties of coke Graphite artefact CTE (x 10 6/oC~ l 25-125C Ool9 ¦ 0O34 100-400C 0.76 1 l.o6 CCE (X'LO~6/C) I
130-300C 6,55 1 7O66 Maximum traversed 19.9 12.1 magnetoresistance (%) Calcined coke Crushing tren~ Q ¦ 56.3 ¦
Example 8 This Example illustrates a further comparison between the coking-crystallizer system of this invention and the delayed cok.ing system particularly to assess the variation in quality of coke with its position along the ..
height of coking drumO
The procedures of the flrst and second runs of Example 7 were repeated using the same charge, The properties of cokes obtained in the two runs were determined for each of test items on coke samples 5;6 taken from the upper~ middle and lower parts o~ coking drums~ Results are shown in Table 6~
The results clearly show that the variation in quality o~ coke with the variation in positions thereof in coking drum is much less in the coking~crystallizer system of this invention than in the delayed coking system. Thus~ for CTE over lOn-400C the former shows a dispersion o~ only 0. os--o 0 o6 x lo 6/oCg whereas the latter of 0.11 0.17 x lO 6/oC. ~or maximum traversed magnetoresistance 3 the former has a dispersion of' only Ool-0~4%~ whereas the latter of 1.3~2.2~, ~o~i~
Table _6 . . _ Coking~crystallizer Delayed I system of this coking ¦ invention system ! (Run 1) (Run 2) Posîtion of sampling Upper Middle , Lower Upper Middle Lower _ . _ ____ _ . _ _ Gr~phite artefact CTE (x 10 6/oC) 25-125C 0 ~ 19 0~ 19 0 ~ lg 0O 50 0~ 34 0~ 33 100 400C 0 O 76 0O 71 0.71 lo 17 1.06 lo 00 CCE (x 10 6/oC) 130 - 300 C 6 O 85 6 ~ 66 6 a 52 8~ 32 8 ~ 00 7 ~ 75 j Maximum traver.sed 19.9 19. 8 19~ 9 11~ 2 12~ 1 13.4 I magneto-¦ resistance t%) ~Calcined coke ! c~ ushin~ strength 62.7 63.3 63.2 40.3 56.3 60.5 ----- --32 ~ ~
As a result of many investigations on important fact;ors of petroleurn coke for being suited as material for the production of high quality graphite electrodes, we have found that the most important~ ~undamental requisite ~or petroleum coke in question is to have a crystalline teY~ture highly grown and oriented in one direction with a minimum content of non~crystalline substances and of foreign matters and that to produce such a high-crystalline coke it, is most important to carry out thc coke-forming reaction under such conditions that the formation and growth of coke crystals are conducted with a minimum agitation or disturbance of the reaction system whereby the growth and orientation of coke crystals formed are promoted~
~ here have already been proposed various processes for the remo~al o~ non-crystalline substances from petroleum materials with the intention of producing a prem:ium grade or higher grade petroleum coke~ for example a process wherein the petroleum material is preheat--treated in the presence or absence of a catalyst followed by removing a part o~ the materi.al before coking and a process wherein the petroleum material is subjected ~ 3~
to delayed coking in two states~ but as far as we know SUC]l a high quality coke as one obtained by the present invention, named a high-crystalline coke, has never been obtained as yet, possibly due to the difficulty of ach:ieving compl.ete and efficient removal of non~
crystalline substances before coking, We have further paid attention to disadvantages o~ delayed coking rnethod itself for the pt~pose o~
proclucing such a high-crystalline coke. As is well-known, according to delayed coking method, a petroleumfeecLstock which has been heated to a temperature required for the coking is fed in a-t the bottom of a heali~in~ulated coking drum and maintained therein to e*~ec-t the ~ormation o~ coke. In this method, the coking reaction involving cracking, polymeri~ation and concLensation is e~fected under such condition~ that pitch-li`ke~ heavy oil being ~ormed thereirl is stirred, diluted and contaminated by .reohly charged material and by light oil formed by the cracking of heavy oil during the coking~
namely under -the conditions of notable agitation or distrubance occurring in the drum, thus dif~iculties are brought in achieving the growth and orientation o~
coke crystals formed~ Furthermore, the quality oP coke ~ormed varies with its position in the coking drum because the freshly charged ma-terial is passed upwardly through the coke already formed in the coking drum, during which pass the fresh charge is coked to some extent and thus the concentration of coke is higher at the lower part o~ the drum and lower at the higher part of the drum ~hus, we came to a conclusion that the delayed coking system is not suitable for the purpose of producing a high crystalline petroleum coke even when a well-se]ected starting material is used owing to difficult-ies in the prosecution o-f coking reaction under ideal condition~.
Under the circumstance~, we have intended to provide a new method for the removal of non-crys-talline substances from starting materials and a new type of coking drum which makes it possible ^to carry out the coking reaction involving the formation9 growth and orientation of coke crystals under the conditions of a high concentration of coke-forming substances and of a min:imum agi-tation of the reaction system~ ~or the remo~al of non~crys-talline substances 9 we have in~estigated in detail on influences of nature of starting materials and coking reaction condition3 including temperature, pre~3sure and time on the yield and properties of coke obtained and, ~or the structure of coking drum, o~ the elimînation of agitation or disturbance of the reaction system due to the i~troduc-tion of ~resh feed and con~ec-tio~ ~low which would result in the prevention o~ the grow-th and orientation of coke crystals. This in~ention is the combination of the results of these in~estigatLons.
According -to one aspect of this in~ention~
therefore, there is provided a process for the production oP a petrole~m coke of unusually high-crystalline te~ture and of a high purity ~rom a petroleum starting ma-terial ha~:Lng a low ~ulfur content selected from the group consisting of a low-sulfur, virgin crude oil~ distilla-tion residuum~ cracked residuumg their mi~ture and their 109 !3C~66 equivalent which comprises the steps of:subjecting the starting material to heat treatment to remove non-crystalline substances contained therein as pitch or coke;
heating a heavy oil fraction o~ the starting material derived *rom the preceding stage, if nece~sary after removing a lighter fraction or fraction~ there~rom9 to a temperature required ~or the subsequent coking;
continuou~ly introducing the preheated oil with downward in~ection into a vertical, pre~sure coking-cryotallizer, which is provided with a heating ~acket surrounding the body thereof, an injection nozzle pipe at the upper part thereo~ for downwardly injecting the pre-heated oil and an in~ection nozzle at the lower part ther00~ ~or upwardly injecting a purging ga~, where gase-OU8 light hydrocarbons formed either by evaporation or by reactione o~ the oil introduced are discharged through an outlet positioned at the upper part o~ tho cry~tallizer and the remaining pltoh-llke heavy oil downw~rdly ~lows and i~ progressi.vely accumulated ~nd coked under the given conditions o~ temperature and pre~ure, while a small amount o~ a heated purging gas ~elected ~rom steam, ga~eou~ hydrocarbon~ and other inert gase~ is introduced therein with upward injection at a ~low rate capable of preventing the clogging of the ga~ injection nozzle, thereby conducting the coking with a high growth and high orientat-ion of coke crystals ~ormed lmtil the crystallizer is full; and increa~ing the amolmt of the purging gas injected to expe~l the remaining oily materials and discharging the coke from the cry~tallizer.
'- , , ; ' By the term "unusuallJ high-crys-talline texture"
used with respec-t to the petroleum coke obtained according to -thls in~ention is meant for the coke to have a higher crystalline texture than that of so-called premium grade or needle-like coke, both in the growth and in the orientation of coke cry?tals1 and by the term "high pur:ity" is rneant that the contents of foreign matters and of non-crystalline substances are minimized.
The pe-trole~ starting material should be one having a low sulfur content. ~or a virgin crude oil9 usually9 the sulfur content should be 0.4% by weight or less, preferably 0.25~o or less. Distillation residuum should be one derived from a low-sulfur virgin crude oil as above~
mentioned. ~or a cracked residuum, the sul-fur cont~.nt should preferably be 0~8% or less. :Distillation and crac?ked residua containing a higher amount of sulfur may if cLesi.red be used after they are subJected to hydro-deslllfuriza1iion to lower the sulfur conten1i-to a required level. ~ny other refinery residuum e~ui~alent to those men1iioned above may be used, if desired~
~ he heat treatment which constitutes the Pir~t stagte o~ -the process of this invention may be e~fected by any desired method capable of separating ~ld removing non--crystalline substances contained in the starting ma-terial as pitch or coke~ One method particularl~
ef~ective for this purpose is to heat and maintain the starting material in a tube hea-ter under certain controlled condi-tion~ for an appropriate -time thereby to cau~e cracking and soaking of the material and then to subject ~0 the material to flash distillation or coking to remove . . .
selectively non-crystalline substances therefrom as pitch or coke~ The conditions of such a heat treatment depend primarily upon the nature cf starting materialO
Our experiments have shown that in most cases desired results can be obtained by heating the starting material in a tube heater to a temperature of 430-520C under a pressure of 4~20 Kg/cm2G followed by maintaining the same therein at this temperature for 30-~00 secondsO
We have further found that the presence of a small amount 9 preferably 0.5-10% by weightg of a hydroxide and or a carbonate o~ an alkali or alkaline-earth metal in the starting material much more improves the efficiency of the separation of non--crystal].ine substances f'rom the material in the heat-treatment stage according to this invention parti.cularly when the starting material is a heav~ oil or residuum and as a result the coke obtained has a value of maximum traversed magnetoresistance higher than 21% in the form of graphite artefact~and a value higher than 60% in the form of graphitized cokeO
~ccording to another aspect of the present inven tion!, there is provided a coking-cr~stallizer comprising a body in which a petroleum material is coked9 a heating jacket surrounding the body through which a heating medium is ci.rculated to provide a heat required ~or the body in a controlled manner9 an injection nozzle pipe introduced into the body at the upper part thereof to downwardly inject a petroleum material to be coked9 a purging gas injection nozzle introduced into the body at the lower part thereof to upwardly inject a purging gàs~ an outlet for discharging gaseous hydrocarbons formed and the , purKing gas at the upper part of the body and out]ets for discharging coke formed at the top and bottorn of the body.
We named the coking drum of this lnvention as coking~crystallizer because it makes possible to achieve unusually high growth and orientation of coke crystals~
In operation9 of the heavy oil fraction introduced into the coking~crystallizer9 gaseous hydrocarbons may be dlscharged at the upper part through an outlet 1~ therefor with a minimum agitation inside of the bodyg named coking zone~ and the remaining heavy hydrocarbons downwardly flow in the coking zone and are progressively accumulated and coked therein in a high concentration~
Thus, the agitation and disturbance whiGh may occur owîng ko the release of cracked light hydrocarbons during the coke~forming reactions and to the introducti.on of th material may be minimizecl~ and the coklng reactions are conducted under well~controlled3 optimum conditi.ons so that the formakion and growth of coke crystals regularly and progressively proceed in upward direction along the vertical axis of the crystallizerO As a result 9 the variation in quality o~ coke with the variation in positions khereof in the crystallizer can be minimizedO
The inside temperature of coking~crystallizer may be well-controlled to a desired level by circulating a heating medium through the heating jacket of the crystallizer as requiredO ~ purging gas injection nozzle is inserted at the lower part of crystallizer3 as above-described5 to e~pel uncoked oil and cracked light oil fractions from the crystallizer after the completion o~
the coking reactions~ In order to prevent the ~aid injection no~zle from being clogged during the coking reactions, it is necessary to pass continuously there-through a smal.l amount of a heated purging gas such as steamS gaseou~ hydrocarbons and other inert gas at such a slow rate that the agitation of coking zone is minimi~ed but the clogging of said no~zle is avoided, '~he coke obtained according to the process of this invention is of significantly higher quality than that of any of petroleum cokes hitherto publicly reported as above-mentioned, and is particularly characterized by its values of maximum -traversed magnetoresistance of higher than 16.0% measured at 10 Kgauss and 77 K in the ~orm of graphite artefact and o~ higrher than 50% measured at the same conditions in the form of graphitized coke.
The observati.on o~ the crystalline te~ture of ..
cok:e obtained according to this invention in the form of a graphitized coke by a scanning electron microscope and a polariæing microscope has confirmed such a bett~r ~uality.
In the drawings attached herewith.
~ igure la is a reproduction o~ a polarizing photomicrograph taken at 250 time~ magni~ication o~ a graphitized coke obtained by this invention;
Figure lb is a reproduction of a scanning electron photomicrograph taken at 1000 times ma~nification of the sam.e coke as that o~ ~igure la;
Figure 2a is a reproduction of a polariæing photomicrograph taken at 250 times magnification of a graphiti~ed coke o~ a typical premium grade petroleum ~Q~
eoke commercially available, Figure 2b is a reproduetion of a scanning eleetron photomierograph talcen at 1000 times magnification o~ the same eoke as that of Figure 2a 3 Figure 3 is a sketeh of a longitudinal seetion of one typieal embodiment of the coking-erystallizer aeeording to this invention; and ~ igure 4 i3 a representative flow diagram of one spee_fic embodiment of the process aecording to this inventionO
Typical properties of coke obtained by the process of this invention are shown in Table 1 and by way of eomparison properties of a typieal premium grade eoke commereially available are shown in Table 2 Table Properties of eoke obtained by this invention . . _ . .
Graphite artefaet Graphitization eondition 2700~C x 1 hr Coeffieient of thermal expansion i.n the direetion parallel to the extrusion (CTE) 25-125C 0O25 x ~.0 6/oC
100-400C oO83 "
Coef'fieient of eubie expansion (CCE) 130-300C 6.63 "
Maximum traversed magnetoresistanee 18~0%
Caleined eoke Calcination eonclition 1400C x 3 hr ~ 6 ~
Real density 2 0170 g/cc Crushin~ strength 51.8%
Water content 0,05 wt%
Ash content 0O05 "
Volatile matter content Or 43 ;~
Fixed carbon content 9~, L~7 Sulfur content 0O45 Metal content Fe 6 wt ppm Ni 3 7~
V 4 ~7 Cll 6 ~ . . _ . _ _ .. . .. _ Table 2 ties of a pr mium grade coke _ _ . . . .
Graphlte artefact ~raphitization condition 2700C x 1 hr Coefflcient of thermal expansion in the direction parallel to the extrusion ~CTE) 25-125C 0065 ~ 1~~6/C :
100-400C lo 20 "
Coefficient of cubic expansion (CCE) 130-300C lOo 7 ~t Maximum traversed magnetoresistance 6O4%
Calcined coke CalcinatiQn condition 1400C x 3 hr Real density 2~124 g/cc - 16 ~
Crushing strength 5~.2%
Water content 0007 wt%
Ash content .7 i7 Volatile matter content 0044 91 Fixed carbon content 99~42 !1 Sulfur content 0.23 "
Metal content Fe 15 wt ppm Ni ll 1' V 4 '~
Cu 10 '~
.
The crushing strength was determined by the following procedure-About 30 g of calcined coke grist of 5 to 12 meshs:Lze were put tnto a cylindrical mold made of stainless steel~ 30 mm IoD~ by 100 mm long. After setting a cylindrical piston head to contact with the top surface of the coke grist~ a load up to a pressure of 100 Kg~cm2G
was applied thereto for 30 seconds and the load was kept for further 30 seconds. The coke grist was khen taken out of mold and sieved out 12 mesh minus. The remaining coke grist was weighed. The ratio of the remaining coke grist to the original one is expressed as crushing strength in per cent by weight.
The structure and method of operation of one typical embodiment of the ccking-crystallizer according to this invention are now explained by referring to Figure 3. A heavy oil for coking which has been heated to 450-550C is continuously introduced through line 9 and valve 10 at the upper part of coking-crystalli~.er 1 provided wi-th heating jacket 4 by means of injection nozzle pipe 117 the coking-crystalli7.er being maintained at 410-500~ and 4 20 kg/cm2~ In the coking~crystallizer~
gaseous light hydrocarbon -.Eraction is dischargad -through ].ine 14 and valve 15 and pitch-like heavy oil fraction downwardly flows and progressively accumulates therein with the proceeding of coking reaction. The lower part o the crystallizer is provided with purging steam line ]2 with ~alve 13 through which a small amount of steam, gaseous hydrocarbon or an inert gas such as nitrogen heated to 400-500C is introduced i.nto the crystalli~er to prevent the clogging o-E line 12. When the level Of the accumulated coke reaches near t;he noz~le 119 the introduction oE the heavy oil through line 9 is stopped ancl the amoun-t of high temperature ste~m through line 12 is increased -to e~pel the remaining oily hydrocarbons Erom the crystalli~er. On completion oE the egpulsion, ~lange~
2 and 3 are opened, through which coke Eormed is dis-charged. Any heating medium may be used provided it can maintain the temperature o-E-the interior of crys-tallizer to 410~500C9 for e~ample molten 3alt~ s-team and hydro-carbons such as gaseous hydrocarbons discharged from the cr~rstallizer~ The heating medium is introduced through line 5 with valve 6 into -tb.e jacket 4 and discharged through line 7 with valve 8 thereErom. As a mat-ter of course 9 the heating jacket 4 is covered with a heat-insulating material to minimi~e the radiation of heat.
One embodi.me~t o:E the process according to this invention is illustrated by referring to Fi~ure 4. The starting petroleum material is p~mped by means of pump 17 and introduced through line 16 into heater 18 for preheat~treating the same, where'it is heated to 430-520C
under 4-20 kg~cm2G and then maintained therein at that temperature for 30-500 seconds thereby to e-~fect crack-ing and heat-soaking of the same. The material thus heat-treated is passed through transfer line 19 into high-temperature flashing column 20 of which upper trays have been packed wi-th wire mesh blanket and the like to prevent pitch ~eing entrained with distillate during the flash distillation. ~he pitch having a softening point of 100-240DC is discharged from the bottom of column through line 21 by means of pump in a mol-ten state while the 'bottom temperature being maintained at 380 480 C under a pressure of 2-10 kg/cm2G~ At the same time, the flash-distillate is discharged at the head of col~unn through line 22 and passed through cooler 2~ into drum 24 wherein condensed oil is held while non-condensed gaseous h~Jdrocarbon fraction is passed through line 25 into main fractionating column 31 at the middle part thereof. Alternatively, all the flash-distilla-te may be directly introduced through lines 50 and 25 into main column 31~ ~he conde~ed oil i~ then pumped through line 26 into coking preheater 27 were it is heated to 450-550 C and injected through line 28 into coking-crystallizer 29a at the head thereo:E.
In the cokingYcrystallizer~ gaseous light hydrocarbons ~ormed ei-ther by evaporation or by cracking and poly-condensation of pitch-like heavy oil as well as a small amoun-t of ~team (or gaseous hydrocarbons or iner-t gas) are discharged at the head of crystallizer through line 30 and introduced in-to the main fractlonating column 31 at a lower position than that of line 25. Heating medi~ is co:ntinuously circulated through the outer jacket o~ the crystallizers 29a and 29b to keep the inside tamperature of crystallizers to 410 500~C by passing the heating medium from line 37 through dru~ 32, line 33, heater 34 9 li:ne 35 and line 36 back to drum 32. This circulation iæ
fo:r a molten sa]t as heating mediumO If æuper heated steam is us~d as heating medium, more simple system may be used. Alternativelyg gaseous light hydrocarbons coming from line 22 (450-550C) or ~rom line 30 (430-520C) may be used as heating medium for coking crystalli~er. When -the col~ing-crystallizer 29a is ~illed with coke formed, the in1kroduction of the heavy oll charge is swi-tched over into the crys-tal.llzer 29b and the green coke acc~ulated in the crvstalli~er 29a is discharged, .A d:istillate boiling above 20() C taken ~rom the middle part o-f main column ~1 as side~
cut is passed through line 38 into heater ~9 where a heat treatment at 500-550 C under pressure is ef~ected to form a 1;ar and then re-turned -through line ~0 to the main column at lower part than that of line 38. At t;he bottom of main colu~n 31~ the bottom residue rich in tar is dis-charged by pump 49 and introduced through line 48 into coking preheater 27 in combination with the condensate o-~
flash~distillate coming from line 26~ Gas and gasoline ~ractions discharged at the top of main column 31. are passed through line 41 and cooler 42 into receiver 43 ~here the separation o-f gas and liquid is ef~ected, the gas being cllscharged through line 45 and the liquid being 20 ~
discharged through lines 44 and 46 as reflux of the mai.n co:Lumn and as product9 respectively. In some cases~ a part of side~cut 38 f:rom the main column may be combined through line 51 with the sucti.on si.de of pump 17 for -the dilution of starting materialO
l'he fo]lowing Ex.~mples f~ther illustra-te9 but not limit~ thi.s inventlon, in which percentages are by wei.ght unless otherwlse specified.
Ex~ le 1 A cracked residue containing 0~76~ of sulfur named as ta.r-bottom l~hlch was obtalned as by-product in a conventional thermal cracXing o.f gas oil for the production of ethylene and which has properti.es shown in Table 3 ~as used as feedstock ~or this ~xample.
~ he ~e~dstock was introduced into a tube heater having 4 mm i.nside diamete:r, 6 mm olltsi.de dlameter and 20 m length, heated under Q press~e of 4 kg/cm2G
to 490~ and maintained therein at this tempera-ture for a~out 260 seconds~ T'he feedstock was then introduced into æ high-temperatllre flashing colllmn maintained at 490-~, where ~lash distillation of the feedstocX is effected to recover distilla-te at the head of column and to w-lthdraw pitch at the bo-t-tom of column in an amount of 20% based on the ~eedstock~ with a retention time of about 10 minutes at the bottom of colu~n~
together with gas generated in an amount o~ 5~0~o on the same basise ~he distillate ~Jas then passed through a tube heater having 4 mm inside diametere 6 mm out~ide diameter and 4 m length to preheat it to 4S0 C a.nd then injected under a pressl~e o~ 9.0 kg/cm2~ into a jacketed coking-crystallizer as shol~n in ~igo 3 at the rop thereof.
wherein pitch~like heavy oil was progressively accumulated and coked while lightg uncoked hydrocarbons were dis--charged at the head of crystallizerO
The yield of coke was 46~ 2% based on the charge of crystallizer (34O9% based on the starting feedstock)O
By-products of the coking stage were 18.1~ (1306%) of cracked gas~ 1~1% (o.&%) of gasoline boiling up to 200C 9 28O9% (21~6%) of gas oil boiling in the range 200-300C
and 5~7% (4O3%) of heavy oil boiling 300C~o The properties of coke obtained are shown in Tab:le 4. Particularly noticeable were CTE of o.83 x 10 fi/oC over 100~400Cg C'CE o:t' 6~63 x lO 6/oC over 130-300C and maximum traversed magnetoresistance of' 18~0%
measured all in the form o~ a graphite artefactO The coke was o~ unusually high-crystallirle texture an~l apparently superlor to premiurn gracle one~
Example 2 A hydrodesulfurized product containing 0 3% of sulf'ur (named as desulfurized tar) o~ a cracked residue containing 1.05% of sulfur which was obtained as by product ln a ~onventional thermal cracking of gas oil for the production of ethylene was used as feedstock for this Example. The properties of the desulfurized tar are shown in Table 3O
The feedstock was treated in the same apparatus~
in the same manner and under the same conclitions as those used in Example 1. At the flash distillation stage9 pitch was rernoved in an amount of 7.8% based on the feedstock together with gas generated in an amount of 0O~% on the s~me basisO
The yield of coke was 22.~% based on the charge of crystallizer (2009% based on the starting feedstock).
By-products of the coking stage were 13 1% (1200%) of cracked gas~ 1.9% (1.7%) of gasoline boiling up to 200C~
53.2% (48.6%) of gas oil boiling in the range 200-300C
and 9O0% (8.2%) of heavy oil boiling 300C-~, The properties of coke obtained are shown in Table 4. The coke was of unusually high~crystalline texture and apparently superior to premium grade one.
Example 3 The gas oil (200 300C fraction) named as coker gas oil which was obtained ~s by-product in the cok:ing stage of Example 2 and which has properties shown in Tab:Le 3 was introduced at a rate of' 1 kg/hr into a tube heater having 4 mm inside diameter~ 6 l~l outside diameter and 40 m length and thermally crackecl therein under the conditions of 530C and 65 kg/cm2~r; the heavy residue boiling 300C+ being taken out as thermal tar and the unreacted oil being recycled to the thermal cracking. Thus~ there were obtained 33O5% of cracked gas~ 29.9% of gasoline boiling up to 200C and 36.6% of thermal tar boiling 300C+~ based on the starting gas oilO
The thermal tar thus obtained was introduced into the coking-crystallizer as used in Example 1 and coked mder the same conditions as those of Example 1~ yielding 47.3% of coke and as by-products 2301% of cracked gas and 29.6% of cracked oil based on the therm21 tarO
l'he properties of coice obtained are shown in 6~i Table 4~ The coke was o-e unusually high-cry3talline texture and superlor to premium grade one~
EY~a~L
The procedure of Exarnple 1 was repeated except that 005% based on the feedstock of sodium hydroxide were mixed with the feedstock before treatment in -the *orm of an aqueous solution. At`the flash distilla-tion stage, pi-tch ~Jas removed in an amount of 29.0% together with ~ o of gas. ~he coking stage gave a coke in a yield of 34.5% based on the charge of crystallizer (24~2~o based on -the starting feedstock) and as by~products 15.2% (10. 6~o) of cracked gas and 50~3~ (35.1~) of cracked oil.
The proper-ties of coke obta-ined are shown in Tab:le 4~ ~he coXe was of unusually high-crystalline tex-ture and superior to premium grade one.
Exa3~
A topped residue o~ ~inas crude oil which has propertieæ shown in ~able 3 was used as feedstock for this E~ample~
The feedstock was introduced into a tubo heater having 4 mm inside diameter, 6 mm outside di.ameter and 40 m lengtll and heated under 20 kg/cm2G to 480C and maintained therein at this temperature for about 190 seconds. The feedstock -thus heat-treated was introduced into a high-temperature :.lashing column and subjected to flash distillation under conditions of 400C and 0 kg/cm2G to recover distillate at the top of colwnn and to withdraw pitch at the bottom of col~unn i~ an amount of 10.7~o based on the feedstock, with a retention time of about 15 min~ltes at that bottom, toget.her with gas - 24 - .
generated in a.n amount of 21~0~ on the same basis. The distillate ~68.3% based on tne feedstock) was passed through a tube heater same as that used in Example 1 to preheat it to 450C and then in~ected under a pressure of 9 kg/cm2G into a Jacketed colcîng--crystallizer as used in :Example 1 at the top thereof3 wherein pitch like heavy oil was gradually and increasingly accumulated and coked~ while light~ uncoked hydrocarbons were discharged at the head of crystallizerO
I`he yield of coke was 5O9~o~ based on the charge of crystallizer (401% based on the starting feedstock)O
By-products of the coking stage were 1802% (120 4~) of cracked gas~ 20,0% (130 6%) of gasoline boll:ing up to 200"C~ 34O5% (2306%) o~ gas oil boiling in the range 200-~300C and 21.4% (14~6%) of heavy oîl boiling 300C+, The properties of coke obtained are shown in Table 4~ The coke was Or unusually hi~h-crystalli.ne text,ure and superior to premium grade oneO
_ample 6 Djatibarang virgin crude oil which has properties shown in Table 3 was used as feedstock for this Example.
The feedstock was introduced into a tube heater having 4 mm inside diameter~ 6 mm outsîde dlameter and 40 m length and heated under 18 kg/cm~G to 480C and maintained therein at, this temperature for about 300 secondsO The feedstock thus heat-tre2ted was introduced into a coking drum haviIlg 100 mm diameter and 1000 mm height which was externally heated by electric wire heater and coked therein at 415C under 3 kg/cm2~ to remove non~crystalli.ne substances contained in the ~9~
feedstock as cokeO The amount of coke formed at this stage was 11~0% by weight based on the .feedstock and simultaneously cracked gases were generated in an amount of 10,8~ on the same basis, The distillate from this coking stage (7802%
based on the feedstock) was introduced into a tube heal;er having 4 mm inside diamete~r~ 6 mm outside diameter and 4 m length to heat it to 440C at the outlet thereof and then inJected under a pressure of 10 kg/cm2G into a ~acketed coking crystallizer as used in Example 1 at the top thereof, wherein pitch~like heavy oil was gradually and increasingly accumulated and coked, whil.e light, mcoked hydrocarbons were discharged at the head of crystallizer.
The yield of coke formed i.n the crystallizer was 11~2% based on the charge of crystallizer (808% based on the f'eedstoclc)~ The properties of coke thus obtained are shown in Table 40 llhe coke was of unusually high-crystalline texture and superior to premium grade oneO
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This Example illustrates the superiority of -the coking-crystallizer system of' this invention to the delayed coking systemO
The same charge as that introduced into the coking~-crystallizer in Example 2 was used for the comparative runs of' this Example~
In the first run, the chargeg iOeO the distillate from the flash distillation stage of Example 2~ was preheated to 450C in a tube heater having 4 mm inside d.iameter3 6 mm outside diameter and 4 m length and then injected under a pressure of 9 kg/cm2G into a ,jacketed colcing--crystallizer as used in Exarnple 1 at the top thereoI' 3 wherein pitch~llke heavy oil was gradually and increasingly accumulated and coked 3 while li.ght~ ~mcoked hydrocarbons wer~ discharged at the head of crystalli~erO
In the second run, the charge was preheakecl in the same manner as that of the first run and was introduced into a conventlonal delayed coking drum and coked therein.
The results of the two runs are shown in Table 5O
The comparison of the results clearly shows`2 ..
significant improvement in properties of coke of the first run (accorcling to this invention) over the second run (according to the delayed coking ~rocess), particularly with respect to CTE~ CCE and maximum traversed magneto resistanceO
Table 5 ~ Coking~ ' ¦ crystallizer ¦ Delayed system of ~ coking this ! system invention j (Run 2) (Run 1) l ¦
ield of coke (wt.%) 20.9 ¦ 18.9 ield of cracked oil (wt.%~5805 ¦ 70.7 roperties of coke Graphite artefact CTE (x 10 6/oC~ l 25-125C Ool9 ¦ 0O34 100-400C 0.76 1 l.o6 CCE (X'LO~6/C) I
130-300C 6,55 1 7O66 Maximum traversed 19.9 12.1 magnetoresistance (%) Calcined coke Crushing tren~ Q ¦ 56.3 ¦
Example 8 This Example illustrates a further comparison between the coking-crystallizer system of this invention and the delayed cok.ing system particularly to assess the variation in quality of coke with its position along the ..
height of coking drumO
The procedures of the flrst and second runs of Example 7 were repeated using the same charge, The properties of cokes obtained in the two runs were determined for each of test items on coke samples 5;6 taken from the upper~ middle and lower parts o~ coking drums~ Results are shown in Table 6~
The results clearly show that the variation in quality o~ coke with the variation in positions thereof in coking drum is much less in the coking~crystallizer system of this invention than in the delayed coking system. Thus~ for CTE over lOn-400C the former shows a dispersion o~ only 0. os--o 0 o6 x lo 6/oCg whereas the latter of 0.11 0.17 x lO 6/oC. ~or maximum traversed magnetoresistance 3 the former has a dispersion of' only Ool-0~4%~ whereas the latter of 1.3~2.2~, ~o~i~
Table _6 . . _ Coking~crystallizer Delayed I system of this coking ¦ invention system ! (Run 1) (Run 2) Posîtion of sampling Upper Middle , Lower Upper Middle Lower _ . _ ____ _ . _ _ Gr~phite artefact CTE (x 10 6/oC) 25-125C 0 ~ 19 0~ 19 0 ~ lg 0O 50 0~ 34 0~ 33 100 400C 0 O 76 0O 71 0.71 lo 17 1.06 lo 00 CCE (x 10 6/oC) 130 - 300 C 6 O 85 6 ~ 66 6 a 52 8~ 32 8 ~ 00 7 ~ 75 j Maximum traver.sed 19.9 19. 8 19~ 9 11~ 2 12~ 1 13.4 I magneto-¦ resistance t%) ~Calcined coke ! c~ ushin~ strength 62.7 63.3 63.2 40.3 56.3 60.5 ----- --32 ~ ~
Claims (10)
1. A process for the production of a petroleum coke of unusually high-crystalline texture and of a high purity from a petroleum starting material having a low sulfur content selected from the group consisting of a low-sulfur, virgin crude oil, distillation residuum, cracked residuum, their mixture and their equivalent which com-prises the steps of:
subjecting the starting material to heat treatment to remove non-crystalline substances contained therein as pitch or coke;
heating a heavy oil fraction of the starting material derived from the preceding stage, if necessary after removing a lighter fraction or fractions therefrom, to a temperature required for the subsequent coking;
continuously introducing the preheated oil with downward injection into a vertical, pressure coking-crystallier, which is provided with a heating jacket surrounding the body thereof, an injection nozzle pipe at the upper part thereof for downwardly injecting the preheated oil and an injection nozzle at the lower part thereof for upwardly injecting a purging gas, where gaseous light hydrocarbons formed either by evaporation or by reactions of the oil introduced are discharged through an outlet positioned at the upper part of the crytallizer and the remaining pitch like heavy oil downwardly flows and is progressively accumulated and coked under the given conditions of temperature and pressure, while a small amount of a heated purging gas selected from steam, gaseous hydrocarbons and other inert gases is introduced therein with upward injection at a slow rate capable of preventing the clogging of the gas injection nozzle, thereby conducting the coking with a high growth and high orientation of coke crystals formed until the crystallizer is full; and increasing the amount of the purging gas injected to expel the remaining oily materials and finally dis-charging the coke from the crystallizer.
subjecting the starting material to heat treatment to remove non-crystalline substances contained therein as pitch or coke;
heating a heavy oil fraction of the starting material derived from the preceding stage, if necessary after removing a lighter fraction or fractions therefrom, to a temperature required for the subsequent coking;
continuously introducing the preheated oil with downward injection into a vertical, pressure coking-crystallier, which is provided with a heating jacket surrounding the body thereof, an injection nozzle pipe at the upper part thereof for downwardly injecting the preheated oil and an injection nozzle at the lower part thereof for upwardly injecting a purging gas, where gaseous light hydrocarbons formed either by evaporation or by reactions of the oil introduced are discharged through an outlet positioned at the upper part of the crytallizer and the remaining pitch like heavy oil downwardly flows and is progressively accumulated and coked under the given conditions of temperature and pressure, while a small amount of a heated purging gas selected from steam, gaseous hydrocarbons and other inert gases is introduced therein with upward injection at a slow rate capable of preventing the clogging of the gas injection nozzle, thereby conducting the coking with a high growth and high orientation of coke crystals formed until the crystallizer is full; and increasing the amount of the purging gas injected to expel the remaining oily materials and finally dis-charging the coke from the crystallizer.
2. A process as claimed in Claim 1 wherein the heat treatment of the starting material is carried out in the presence of a small amount of a basic compound selected from the group consisting of hydroxides and carbonates of alkali and alkaline-earth metals.
3. A process as claimed in Claim 2 wherein the basic compound is selected from the group consisting of sodium hydroxide and sodium carbonate.
4. A process as claimed in Claim 2 wherein the basic compound is present in an amount of 0.5-10% by weight based on the starting material.
5. A process as claimed in Claim 1 wherein the heat treatment is carried out by heating the starting material in a tube heater at a temperature of 430 to 520°C under a pressure of 4 to 20 kg/cm2G for 30 to 500 seconds followed by subjecting the material to flash distillation to remove non-crystalline substances contained therein as pitch.
6. A process as claimed in Claim 1 wherein the heat treatment is carried out by heating the starting material in a tube heater at a temperature of 430 to 520°C under a pressure of 4 to 20 kg/cm2G for 30 to 500 seconds followed by subjecting the material to a delayed coking to remove non-crystalline substances contained therein as coke.
7. A process as claimed in Claim 1 wherein the coking in the coking crystallizer is carried out at a temperature of 410 to 500°C under a pressure of 4 to 20 kg/cm2G.
8. A process as claimed in Claim 1 wherein a gas oil fraction derived as by-product from a coking process is used as the starting material and is heat treated so as to effect a thermal cracking thereof to give a heavy residue which is served as charge for the coking crystallizer.
9. A process as claimed in Claim 8 wherein the gas oil fraction is one derived from the coking stage of the process of Claim 1.
10. Petroleum coke having a maximum traversed magnetro-resistance of at least 16% when measured in a magnetic field of 10 Kgauss at a temperature of 77°K and when measured in the form of an extruded graphite artefact made by calcining green petroleum coke at 1400°C for 3 hours, pulverizing the calcined coke into particle size fractions of 35-65 mesh and 100 mesh plus, blending together 40 parts of the 35-65 mesh fraction, 60 parts of the 100 mesh fraction, and 30 parts of coal tar pitch, kneading the mixture at 170°C, extruding the kneaded mass into a rod of 20 mm in diameter and 200 mm in length, baking the rod at 1000°C for 3 hours, and then graphitizing at 2700°C for 1 hour, and having a coefficient of thermal expansion over the temperature range 100°C to 400°C of less than 1.0 x 10-6/°C when measured in the form of said extruded graphite artefact in a direction parallel to the direction of extrusion of said artefact.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA261,858A CA1098066A (en) | 1976-09-23 | 1976-09-23 | Process for the production of a petroleum coke and coking crystallizer used therefor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA261,858A CA1098066A (en) | 1976-09-23 | 1976-09-23 | Process for the production of a petroleum coke and coking crystallizer used therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1098066A true CA1098066A (en) | 1981-03-24 |
Family
ID=4106916
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA261,858A Expired CA1098066A (en) | 1976-09-23 | 1976-09-23 | Process for the production of a petroleum coke and coking crystallizer used therefor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1098066A (en) |
-
1976
- 1976-09-23 CA CA261,858A patent/CA1098066A/en not_active Expired
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