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(11) | EP 0 186 617 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Method for fractionating oil under methane atmosphere Verfahren zur Ölfraktionierung in einer Methanatmosphäre Méthode de fractionnement d'huile sous atmosphère de méthane |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to an improvement in a method for fractionating an oil. More specifically, it relates to a fractionation method which can be applied to fractionations of crude oils, coal tar, raffinates from apparatus for hydrogenolysis and hydrogenation refining, coal-liquefied oils, multi-component systems including inert gases, tar sand oils, shale oils and the like.
[0003] In Fig. 3, a crude oil 101 being fed through a line 1 is mixed with water vapor 102 fed through a line 2 and is then delivered to a furnace 3, in which the crude oil 101 is heated up to a temperature of 350 to 400°C. Afterward, the oil 101 is introduced into a distillation column 4 in which an operating pressure is in the vicinity of ordinary pressure. Water vapor 103 for stripping is introduced into the. distillation column 4 through its bottom and a line 5, and the crude oil 101 is then fractionated here into naphtha 104, kerosene 105, light gas oil 106, heavy gas oil 107 and residual oil 108. In general, the naphtha is taken out from a column top; the kerosene, the light gas oil and the heavy gas oil from a column side; and the residual oil from a column bottom of the distillation column.
[0004] The water vapor 103 introduced into the distillation column 4 through the bottom thereof is delivered through a column body and a column top to a condenser 6, in which the water vapor 103 is cooled, and is further delivered to a condensing tank 7, in which it is condensed to water. In this case, a fraction discharged from the column top of the distillation column 4 is heat-exchanged with a stream (not shown) above the condenser 6.
[0005] When a heat exchange temperature of the fraction from the column top of the distillation column 4 has reached a level near to a dew point of the water vapor 103, the latter is condensed at the column top prior to the above-mentioned condensation in the condensing tank 7. This condensed water will become a cause of the corrosion of materials constituting the column top, and thus the operation of the distillation column 4 is carried out so that the above-mentioned heat exchange temperature may be maintained at a higher level than the dew point.
[0006] Incidentally, the crude oil usually contains gases (hereinafter referred to as the methane-rich gas) such as methane and ethane, and the methane-rich gas is separated therefrom in the condensing tank 7 as an off-gas 110 which will be used as a fuel.
[0007] According to the conventional fractionation method described above, the heat exchange temperature at the top of the distillation column must be retained at a higher level than the dew point of the water vapor during operation so as to avoid the corrosion of the column top materials by the water condensed at the column top. Therefore, such a method involves the drawback that heat recovery is poor.
[0008] Additionally, since the water vapor for stripping has to be introduced into the distillation column from exterior, a drain treatment of its condensed water is required disadvantageously.
[0009] Thus, an object of the present invention is to provide an industrially useful fractionation method by which the above-mentioned drawbacks of the conventional method are overcome.
[0010] The present invention is directed to a method comprising the steps of separating a methane-rich gas included in a crude oil from the latter in a condensing tank, compressing the methane-rich gas, and recycling the same through a distillation column, instead of the use of water vapor, or alternatively a method further comprising an additional step of feeding a gas containing methane to a distillation column from exterior, whereby fractionation is carried out under a methane atmosphere to heighten an efficiency of the fractionation of a crude oil. That is to say, the present invention provides a method for fractionating an oil under a methane atmosphere which comprises the steps of delivering a methane-containing gas included in the oil from a distillation column through its top to a condenser, where the methane-containing gas is cooled and condensed and a methane-rich gas is then separated therefrom; increasing a pressure of the methane-rich gas; and introducing the methane-rich gas into the distillation column in order to recycle the methane-rich gas.
[0011] In the method of the present invention, a small amount of a gas containing methane may be further fed to the recycling methane-rich gas externally, and the gas may be fed to the distillation column and a stream above the furnace in order to obtain an identical effect. In general, the distillation column is operated at a temperature of 100 to 500°C at a pressure of 0 to 100 kg/cm2G (0 to 980 N/cm2 gauge).
[0012] Now, the present invention will be described in detail in reference to accompanying drawings, in which:
Fig. 1 is a flow sheet of an embodiment in which a method of the present invention is applied to the distillation of a crude oil;
Fig. 2 is a flow sheet of another embodiment of the present invention;
Fig. 3 is a flow sheet of the distillation of the crude oil in a conventional manner; and
Fig. 4 shows ASTM curves of components fractionated in the embodiment of the present invention.
[0013] In Fig. 1, a crude oil 101 is introduced into a furnace 3 together with a mixture of a small amount of a methane-including gas fed through a line 28 and a methane-rich gas 113 which has been separated in a condensing tank 7 and a pressure of which has been heightened by a compressor 8. Afterward, the crude oil 101 is then heated up to 350 to 400°C in the furnace 3 and is afterward introduced into a distillation column 4. An operating pressure in the distillation column 4 is in the vicinity of ordinary pressure.
[0014] Through the bottom of the distillation column 4, a methane-rich gas 112 is introduced thereinto as a stripping material. In the distillation column 4, the crude oil 101 is fractionated into light naphtha 115, heavy naphtha 114, kerosene 105, light gas oil 106, heavy gas oil 107 and residual oil 108.
[0015] A column top fraction 118 containing methane and the light naphtha is discharged from the top of the distillation column 4, and after heat-exchanged with a stream (not shown), the fraction 118 is then delivered to a condenser 6, in which it is cooled and condensed. Afterward, the thus condensed fraction 118 is further delivered to a condensing tank 7, in which it is separated into a methane-rich gas 111 and the light naphtha 115.
[0016] The separated methane-rich gas 111 is increased in pressure by means of the compressor 8, and a part of the gas 111 is fed to the bottom of the distillation column 4 as the methane-rich gas 112 and another part of the gas 111 is fed to the stream above the furnace 3 as the methane-rich gas 113 and is then recycled. Further, the remaining part of the gas 111 is taken out from the system as an off-gas 116 which will be used as a fuel. During the operation, the heavy naphtha 114, the kerosene 105, the light gas oil 106 and the heavy gas oil 107 are recovered through the column side of the distillation column 4, and the residual oil 108 is taken out through the column bottom.
[0017] As described above, the methane-rich gas is used for stripping, and a dew point of the column top fraction in the distillation column can be lowered, because the latter is operated under the methane atmosphere. In consequence, the operation of the distillation column can be carried out at a lowered heat exchange temperature at the column top thereof without any problem of corrosion.
[0018] Moreover, Fig. 2 shows an embodiment in which an Arabian light crude oil is employed as a crude oil.
[0019] The crude oil is delivered through a crude oil duct 11 to the distillation column 4 via the furnace 3. On the other hand, the methane-rich gas is introduced into the crude oil duct 11 through a methane-rich gas duct 10 and into the distillation column 4 through the bottom thereof and a methane-rich gas duct 9 in a rate of 24 Nm3/m3 of the crude oil (10% of the methane-rich gas are fed to the stream above the furnace 3 and 90% thereof to the distillation column) in order to fractionate the crude oil. An outlet temperature of the furnace 3 is 346°C and an operating pressure of the distillation column is 0.8 kg/cm3G (7,8 N/cm2 gauge).
[0020] Components fractionated in this distillation column 4 (having 42 steps) are set forth in Table 1.
[0021] The above-mentioned separation state of the respective components is shown with ASTM curves in Fig. 4. The results of this embodiment indicate that the dew point of the water vapor in the column top fraction is 50°C in contrast with 95°C in the case of the conventional technique, and if a load of the condenser in the conventional case is regarded as 100, that of the condenser in the present invention is 56, which fact elucidates that the load of the condenser can be reduced remarkably. That is to say, in the distillation of the crude oil in accordance with the present invention, the fractionation can be accomplished without introducing any water vapor, and the load of the condenser is a small as 56% of the conventional one. In addition thereto, the corrosion of the column top materials can be inhibitied. Therefore, it becomes clear that usual carbon steel can be used as such materials.
[0022] According to the methods of the present invention, the following effects can be obtained:
(1) Since the fractionation is carried out under the methane atmosphere, the corrosion at the top of the distillation column can be restrained, and since the operation can be accomplished at the lowered column top temperature, the heat recovery can be improved.
(2) In the conventional method, water vapor introduced into the distillation column through its bottom is condensed at the top thereof, and thus the load of the condenser is large. On the contrary, in the method of the present invention, the removal of sensible heat alone from the methane-rich gas suffices, and thus the load of the condenser can be reduced remarkably.
(3) It is not required to feed water vapor for stripping externally, and the drain treatment of condensed water can also be eased.
(4) A recycling rate of the methane-rich gas can be optionally and conveniently selected by compressing, with the aid of the compressor, the methane-rich gas which will be introduced into the distillation column through its bottom, and recycling the same.
(5) In the case that the method of the present invention is applied to the distillation of the crude oil, the methane-rich gas is separated and compressed at the column top, and is then introduced into the distillation- column through_ its-bottom. Therefore, the recycling rate of the methane-rich gas can be optionally selected, and heavy naptha, kerosene, light gas oil, heavy gas oil and residual oil can be fractionated by the use of the one distillation column, and light naphtha can be recovered in the condensing tank.
1. A method for fractionating an oil under a methane atmosphere which comprises the
steps of delivering a methane-containing gas included in the oil from a distillation
column through its top to a condenser, where the methane-containing gas is cooled
and condensed and a methane-rich gas is then separated therefrom; increasing a pressure
of the methane-rich gas; and introducing the methane-rich gas into the distillation
column in order to recycle the methane rich gas.
2. A method according to Claim 1 wherein a suitable amount of a gas containing methane
is additionally fed to the recycling methane-rich gas from exterior.
3. A method according to Claim 1 where the gas containing methane is additionally
fed to the distillation column or a stream above a furnace.
4. A method according to Claim 1, wherein the oil is at least one selected from the
group consisting of crude oils, coal tar, raffinates from apparatus for hydrogenolysis
and hydrogenation refining, coal-liquefied oils, multi-component systems including
inert gases, tar sand oils and shale oils.
1. Verfahren zum Fraktionieren eines Öls unter Methangasatmosphäre, gekennzeichnet
durch die Verfahrensschritte des Zuführens eines methanhaltigen Gases einschließlich
des Öls aus einer Destillationskolonne durch dessen oberen Teil an einen Kondensator,
wo das methanhaltige Gas gekühlt und kondensiert wird und ein methanangereichertes
Gas dann davon abgetrennt wird, des Erhöhen des Drucks des methanangereicherten Gases
und des Einführens des methanangereicherten Gases in die Destillationskolonne zur
Rückleitung des methanangereicherten Gases.
2. Verfahren nach Asnpruch 1, dadurch gekennzeichnet, daß eine angemessene Menge eines
Methan enthaltenden Gases zusätzlich von außen dem rückfließenden methanangereicherten
Gas zugefürht wird.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Methan enthaltende Gas
zusätzlich der Destillations-kolonne oder einem Strom über einem Ofen zugeführt wird.
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet daß als Öl ein Öl aus der Gruppe
verwendet wird, der Rohöle, Kohlenteer, Raffinate aus Hydrogenolyse- und Hydrierungs-Raffinationsvorrichtungen,
kohleverflüssigte Öle, Mehrkomponentensystem einschließlich Edelgase, Teersandöle
und Schieferöle zuzurechnen sind.
1. Procédé de fractionnement d'une huile sous une atmosphère de méthane, qui comprend
les étapes consistant à amener un gaz contenant du méthane inclus dans l'huile à partir
d'une colonne de distillation, par son extrémité supérieure, à un condenseur, où le
gaz contenant du méthane est refroidi et condensé, et un gaz riche en méthane en est
alors séparé; à augmenter la pression du gaz riche en méthane; et à introduire le
gas riche en méthane dans la colonne de distillation de façon à recycler le gaz riche
en méthane.
2. Procédé selon la revendication 1, dans lequel une quantité appropriée d'un gaz
contenant du méthane est de plus ajoutée au gaz riche en méthane de recyclage, de
l'extérieur.
3. Procédé selon la revendication 1, dans lequel le gaz contenant de méthane est de
plus amené à la colonne de distillation ou en amont d'un four.
4. Procédé selon la revendication 1, dans lequel l'huile est au moins une huile choisis
dans le groupe constitué des huiles brutes, du goudron de charbon, de produits de
raffinage d'un appareil pour hydrogénolyse et raffinage par hydrogénation, d'huile
de charbon liquéfié, de systèmes à plusieurs composants comportant des gaz inertes,
des huiles de sable bitumineux et des huiles de schiste.