CA2989100C

CA2989100C - Method for recovering oil by heating, stirring and centrifugation of a crude oil sludge

Info

Publication number: CA2989100C
Application number: CA2989100A
Authority: CA
Inventors: Shuichi Kobayashi; Taku Moriyama
Original assignee: Cosmo Oil Co Ltd
Current assignee: Cosmo Oil Co Ltd
Priority date: 2015-06-12
Filing date: 2016-06-03
Publication date: 2022-11-29
Anticipated expiration: 2036-06-03
Also published as: JPWO2016199692A1; CA2989100A1; JP6136042B2; WO2016199692A1; MX2017014228A; RU2676325C1

Abstract

A method for recovering an oil fraction in crude oil sludge, characterized in having: a first step (1) for mixing crude oil sludge (A) and crude oil (B), and subsequently heating and stirring the mixture of the crude oil sludge (A) and crude oil (B) to obtain a heated and stirred processed product composed of the crude oil sludge (A) and the crude oil (B); a second step (1) for centrifugally separating the heated and stirred processed product at 40-200°C to thereby separate light liquid from the heavy fraction and obtain a light liquid; and a third step (1) for bringing the temperature of the light liquid to the melting point temperature or greater and mixing the light liquid, which is equal to or greater than the melting point temperature, with crude oil (C) in a crude oil transfer tube, the temperature of the crude oil (C) being equal to or greater than the temperature of the light liquid, alternatively, the temperature of the crude oil (C) being less than that of the light liquid, and the difference between the temperature of the light liquid and the crude oil (C) being within 40°C. The present invention provides a method for recovering an oil fraction in crude oil sludge in which sludge is less likely to be generated even when the oil fraction recovered from the crude oil sludge is mixed with crude oil.

Description

METHOD FOR RECOVERING OIL BY HEATING, STIRRING AND
CENTRIFUGATION OF A CRUDE OIL SLUDGE
BACKGROUND OF THE INVENTION
Field of the Invention [0001]
The present invention relates to a method for recovering oil from in a crude oil sludge deposited in a crude oil tank in which a crude oil is stored.
Description of the Related Art

[0002]
A crude oil sludge deposited in crude oil tanks, after being taken out of the crude oil tanks, is generally processed as industrial waste, but its disposal needs a high cost. On the other hand, the crude oil sludge contains about 30 to 80% by volume of oil in many cases, and thus there is a large need to recover oil in the crude oil sludge.

[0003]
Then, attempts have conventionally been made to recover oil from a crude oil sludge by using a vacuum distillation method, a heat separation method, a centrifugal separation method or the like (for example, International Publication No. W02012/141024, Japanese Date recue / Date received 2021-11-02 cA029891002017-12-11 Patent Laid-Open No. 3-226481, Japanese Patent Laid-Open No.
2004-243300).
[0005]
However, oil recovered from a crude oil sludge is of a poor quality, and thus in the case where a good-quality fuel is produced by using the oil as a stock oil, the refining cost becomes high. Hence, oil recovered from a crude oil sludge is often used directly as an inexpensive fuel oil.
[0006]
Here, if oil recovered from a crude oil sludge is mixed with a stock oil, the mixture becomes allowed to be sold not as an inexpensive fuel oil but as a crude oil of a higher price. Studies by the present inventors, however, have revealed that oil recovered from a crude oil sludge is low in fluidity and poor in compatibility with a crude oil, and thus when the oil, as it is, is mixed with a crude oil, a sludge is easily generated again.
[0007]
Therefore, an object of the present invention is to provide a method for recovering oil in a crude oil sludge, wherein even if the oil recovered from the crude oil sludge is mixed with a crude oil, a sludge is unlikely to be generated again.

[0008]
The above-mentioned problem is solved by the following present inventions.
That is, the present invention (1) provides a method for recovering oil in a crude oil sludge, comprising:
a first step (1) of mixing a crude oil sludge (A) with a crude oil (B) so that the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) becomes 20 to 95% by mass, and then heating and stirring the mixture of the crude oil sludge (A) with the crude oil (B) at 40 to 200 C to thereby obtain a heated and stirred material of the crude oil sludge (A) and the crude oil (B);
a second step (1) of centrifugally separating the heated and stirred material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step (1) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the

- 4 temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.
[0009]
Further the present invention (2) provides a method for recovering oil in a crude oil sludge, comprising:
a first step (2) of heating a crude oil sludge (A) at 40 to 200 C to thereby obtain a heated material of the crude oil sludge (A);
a second step (2) of centrifugally separating the heated material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step (2) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.
[0010]

- 5 - Further the present invention (3) provides a crude oil (D), being obtained by carrying out:
a first step (1) of mixing a crude oil sludge (A) with a crude oil (B) so that the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) becomes 20 to 95% by mass, and then heating and stirring the mixture of the crude oil sludge (A) with the crude oil (B) at 40 to 200 C to thereby obtain a heated and stirred material of the crude oil sludge (A) and the crude oil (B);
a second step (1) of centrifugally separating the heated and stirred material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step (1) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.

- 6 - [0011]
Further the present invention (4) provides a crude oil (E), being obtained by carrying out:
a first step (2) of heating a crude oil sludge (A) at 40 to 200 C to thereby obtain a heated material of the crude oil sludge (A);
a second step (2) of centrifugally separating the heated material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step (2) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.
[0012]
The present invention can provide a method for recovering oil in a crude oil sludge, wherein even if the oil recovered from the crude oil sludge is mixed with a crude oil, a sludge is unlikely to be generated again.

- 7 - BRIEF DESCRIPTION OF THE DRAWING
[0013]
FIG. 1 is a view illustrating a mixing system of a light liquid with a crude oil, used in Examples and Comparative Examples.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014]
A method for recovering oil in a crude oil sludge according to a first aspect of the present invention is a method for recovering oil in a crude oil sludge, comprising:
a first step (1) of mixing a crude oil sludge (A) with a crude oil (B) so that the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) becomes 20 to 95% by mass, and then heating and stirring the mixture of the crude oil sludge (A) with the crude oil (B) at 40 to 200 C to thereby obtain a heated and stirred material of the crude oil sludge (A) and the crude oil (B);
a second step (1) of centrifugally separating the heated and stirred material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and

- 8 - a third step (1) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.
[0015]
The first step (1) in the method for recovering oil in a crude oil sludge according to the first aspect of the present invention is a step of mixing a crude oil sludge (A) with a crude oil (B), and then heating and stirring the mixture of the crude oil sludge (A) with the crude oil (B) at 40 to 200 C to thereby obtain a heated and stirred material of the crude oil sludge (A) and the crude oil (B).
[0016]
The crude oil sludge (A) in the first step (1) is a sludge generated from in a stored crude oil and deposited on the bottom of a crude oil tank. The crude oil sludge (A) includes a crude oil sludge which is generated from a crude oil cleared of solid contents, moisture and the like cA029891002017-12-11

- 9 -after crude oil mining, and stored in a crude oil tank, and before being shipped to oil production plants, and is deposited on the bottom of the crude oil tank; a crude oil sludge deposited on the bottom of a crude oil tank in a crude oil tanker; and a crude oil sludge which is generated from a crude oil in a crude oil tank for storage before being refined in an oil production plant, and is deposited on the bottom of the crude oil tank. The crude oil sludge (A) may be generated from one crude oil, or may be generated from a plurality of crude oils.
[0017]
The crude oil sludge (A) contains oil, asphaltene, iron, sand, water and the like. The oil in the crude oil sludge (A) is mainly paraffins and aromatic hydrocarbons having 40 or more carbon atoms. Then, the oil in the crude oil sludge (A) is a component to be recovered from in the crude oil sludge (A) by the method for recovering oil in a crude oil sludge according to the present invention.
[0018]
A method of taking out a crude oil sludge (A) deposited in a crude oil tank outside the crude oil tank is not especially limited, and examples thereof include a method (COW: crude oil washing) in which after a crude oil in the crude oil tank is extracted outside the crude oil tank, a high-pressure crude oil is jetted against the crude c.A029891002017-12-11

- 10 -oil sludge (A) deposited in the crude oil tank to crush or partially dissolve the crude oil sludge (A), which is then extruded outside the crude oil tank with the crude oil, and a method in which after the crude oil in the crude oil tank is extracted outside the crude oil tank, the crude oil sludge (A) deposited in the crude oil tank is taken out by manpower.
[0019]
The crude oil (B) to be mixed with the crude oil sludge (A) is not especially limited, and may be a crude oil before being cleared of solid contents, moisture and the like after crude oil mining, and being stored in a crude oil tank, may be a crude oil shortly after being cleared of solid contents, moisture and the like after crude oil mining, and starting to be stored in a crude oil tank, and before generating a crude oil sludge, or may be a supernatant crude oil in a crude oil tank after a crude oil sludge is generated on the bottom of the crude oil tank during a certain-period storage of the crude oil in the crude oil tank. The crude oil (B) may be the same crude oil as a crude oil as a generation source of the crude oil sludge (A), or may be a crude oil different therefrom.
[0020]
When a crude oil sludge (A) is taken out of a crude oil tank, and in the case where the crude oil sludge (A) is c.A029891002017-12-11

- 11 -taken out by extruding the crude oil sludge (A) with a crude oil outside the crude oil tank (for example, COW), a material taken out of the crude oil tank is a mixture of the crude oil sludge (A) with the crude oil used for taking out the crude oil sludge (A), but in this case, the crude oil used for taking out the crude oil sludge (A) is included in the crude oil (B).
[0021]
The first step (1) first mixes a crude oil sludge (A) with a crude oil (B) so that the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) becomes 20 to 95% by mass, preferably 40 to 90% by mass, and more preferably 60 to 90% by mass. If the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) is less than the above range, the amount to be processed in the second step (1) increases and the economic efficiency decreases;
and if the proportion exceeds the above range, the recovery of oil from the crude oil sludge (A) becomes insufficient.
[0022]
Further when a crude oil sludge (A) is taken out of a crude oil tank, in the case where the crude oil sludge (A) is taken out by extruding the crude oil sludge (A) with a crude oil outside the crude oil tank (for example, COW
washing), the crude oil used for taking out the crude oil c.A029891002017-12-11

- 12 -sludge (A) is included in the crude oil (B), and the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) is calculated.
Hence, in this case, by using the crude oil in an amount such that the proportion of the crude oil sludge (A) deposited on the bottom of the crude oil tank to the sum of the crude oil sludge (A) and the crude oil to be used for taking out the crude oil sludge (A) is a predetermined mixing proportion, that is, the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) is 20 to 95% by mass, preferably 40 to 90% by mass, and more preferably 60 to 90% by mass, the crude oil sludge (A) may be taken out outside the crude oil tank to provide a mixture, as it is, of the taken-out crude oil sludge (A) with the crude oil as a mixture of a crude oil sludge (A) and a crude oil (B) to be used for the heating and stirring. Alternatively, by using a small amount of a crude oil, a crude oil sludge (A) deposited on the bottom of a crude oil tank may be taken out outside the crude oil tank to further mix, into a mixture of the taken-out crude oil sludge (A) with the crude oil, the same crude oil as the crude oil used for taking out the crude oil sludge (A) or a crude oil different therefrom to make a predetermined mixing proportion, that is, bring the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A)

- 13 -and the crude oil (B) to 20 to 95% by mass, preferably 40 to 90% by mass, and more preferably 60 to 90% by mass to provide the obtained mixture as a mixture of a crude oil sludge (A) with a crude oil (B) to be used for the heating and stirring.
[0023]
The first step (1) then heats and stirs the mixture of the crude oil sludge (A) with the crude oil (B) at 40 to 200 C, preferably 50 to 150 C, and more preferably 60 to 100 C to thereby obtain a heated and stirred material of the crude oil sludge (A) and the crude oil (B). If the heating and stirring temperature is lower than the above range, the recovery of oil from the crude oil sludge (A) becomes insufficient; and if the temperature exceeds the above range, a demerit due to a loss of light fractions is generated. A method for heating and stirring the mixture of the crude oil sludge (A) with the crude oil (B) is not especially limited, and examples thereof include a method in which the mixture of the crude oil sludge (A) with the crude oil (B) is heated and stirred in a tank where the crude oil sludge (A) taken out of a crude oil tank is stored. The heating and stirring time is not especially limited, and is selected according to the stirring conditions so as to make a homogeneously mixed state.
[0024]

- 14 -=
The content of oil in the crude oil sludge (A) is not especially limited, but is usually 30 to 80% by mass. Then, the oil in the crude oil sludge (A) is dissolved in the crude oil (B) in the first step by heating and stirring the mixture of the crude oil sludge (A) with the crude oil (B) at 40 to 200 C, preferably 50 to 150 C, and more preferably 60 to 100 C.
[0025]
The second step (1) in the method for recovering oil in a crude oil sludge according to the first aspect of the present invention is a step of centrifugally separating the heated and stirred material of the crude oil sludge (A) and the crude oil (B) obtained by carrying out the first step (1), at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid.
[0026]
In the second step (1), the temperature when the heated and stirred material of the crude oil sludge (A) and the crude oil (B) is centrifugally separated is 40 to 200 C, preferably 50 to 150 C, and more preferably 60 to 100 C. If the centrifugal separation temperature is lower than the above range, then part of the heated and stirred material of the crude oil sludge (A) and the crude oil (B) freezes and the fluidity of the heated and stirred material greatly decreases during the centrifugal separation, and thus the c.A029891002017-12-11

- 15 -centrifugal separation cannot be carried out; and if the temperature exceeds the above range, a demerit due to a loss of light fractions is generated. Further in the second step (1), the temperature when the heated and stirred material of the crude oil sludge (A) and the crude oil (B) are centrifugally separated is preferably made equal to or higher than the heating and stirring temperature of the mixture of the crude oil sludge (A) with the crude oil (B) in the first step (1).
[0027]
The heated and stirred material of the crude oil sludge (A) and the crude oil (B) obtained by carrying out the first step (1) is a mixture of a light liquid having a low specific gravity and a heavy fraction having a higher specific gravity than the light liquid; and in the second step (1), the light liquid and the heavy fraction are separated by the difference in specific gravity. Then, the light liquid is a liquid obtained by that the oil in the crude oil sludge (A) is dissolved in the crude oil (B) in the first step (1). That is, the light liquid is basically composed of the crude oil (B) and the oil in the crude oil sludge (A) dissolved in the crude oil (B). The heavy fraction is components in the crude oil sludge (A) which have not been dissolved in the crude oil (B) in the first step (1), and mainly asphaltene, moisture, iron, sand, oil

- 16 -being carried in these components and being in a hard-to-separate state, and the like.
[0028]
A centrifugal separation apparatus to centrifugally separate the heated and stirred material in the second step (1) is not especially limited, and suffices if being one capable of continuously separating the light liquid and the heavy fraction by the difference in specific gravity with the above centrifugal separation temperature being held.
Examples thereof include a decanter-type centrifugal separator, a disc separator-type centrifugal separator, and a centrifugal separator in a combination of these.
[0029]
The physical properties of the light liquid obtained by carrying out the second step (1) are not especially limited; but its density is preferably 0.80 to 0.95 g/cm3, and more preferably 0.80 to 0.88 g/cm3; its melting point is preferably 40 to 150 C, more preferably 40 to 110 C, and still more preferably 40 to 90 C; its freezing point is preferably 30 to 140 C, more preferably 30 to 100 C, and still more preferably 30 to 80 C; and its oil content is 60% by mass or higher.
[0030]
The third step (1) in the method for recovering oil in a crude oil sludge according to the first aspect of the

- 17 -present invention is a step of bringing the temperature of the light liquid obtained by carrying out the second step (1) to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe. If the temperature of the light liquid is lower than the melting point, it becomes difficult to mix the light liquid into the crude oil (C) in the crude oil transfer pipe.
[0031]
In the third step (1), the crude oil (C) to be mixed with the light liquid is not especially limited, and may be a crude oil before being cleared of solid contents, moisture and the like after crude oil mining, and being stored in a crude oil tank, may be a crude oil shortly after being cleared of solid contents, moisture and the like after crude oil mining, and starting to be stored in a crude oil tank, and before generating a crude oil sludge, or may be a supernatant crude oil in a crude oil tank after a crude oil sludge is generated on the bottom of the crude oil tank during a certain-period storage of the crude oil in the crude oil tank. The crude oil (C) may be the same crude oil as a crude oil as a generation source of the crude oil sludge (A), may be a crude oil different

- 18 -therefrom, or may be the same crude oil as the crude oil (B) or a crude oil different therefrom.
[0032]
The oil in the crude oil sludge (A) is mainly hydrocarbons having large molecular weights having 40 or more carbon atoms, and thus if the temperature of the light liquid becomes too low compared to the temperature when the heating and stirring is carried out in the first step (1), the light liquid freezes or the fluidity of the light liquid remarkably decreases; therefore, in the third step (1), the temperature of the light liquid is brought to a temperature equal to or higher than the melting point thereof and then the light liquid is mixed into the crude oil (C). The temperature of the light liquid is preferably equal to or higher than the melting point, and in the range of 40 to 200 C, more preferably 50 to 150 C, and still more preferably 60 to 100 C.
[0033]
In the third step (1), with respect to the relation between the temperatures of the crude oil (C) and the light liquid when the light liquid is mixed into the crude oil (C), the temperature of the crude oil (C) is equal to or higher than that of the light liquid, or the temperature of the crude oil (C) is lower than that of the light liquid and the difference between the temperature of the light

- 19 -liquid and the temperature of the crude oil (C) is 40 C or lower. In the case where the temperature of the crude oil (C) is lower than that of the light liquid, with a smaller difference between the temperature of the light liquid and the temperature of the crude oil (C), when the light liquid is mixed into the crude oil (C), the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is more suppressed or even if the oil deposits, more of the oil deposits finely, more unlikely causing a sludge, and thus a difference between the temperature of the light liquid and the temperature of the crude oil (C) that is 40 C or lower has the following effect: the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge. Further in the case where the temperature of the crude oil (C) is lower than that of the light liquid, a difference between the temperature of the light liquid and the temperature of the crude oil (C) that is preferably 30 C or lower, more preferably 20 C or lower, and still more preferably 10 C or lower enhances the following effect: the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge. Further in the case where the temperature of the crude oil (C) is equal to or higher than

- 20 -that of the light liquid, when the light liquid is mixed into the crude oil (C), the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge, and thus a temperature of the crude oil (C) equal to or higher than that of the light liquid has the following effect: when the light liquid is mixed into the crude oil (C), the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge. Further in the case where the temperature of the crude oil (C) is equal to or higher than that of the light liquid, the difference between the temperature of the crude oil (C) and the temperature of the light liquid is preferably 10 C or lower, and more preferably 5 C or lower.
[0034]
In the third step (1), the temperature of the crude oil (C) flowing in a crude oil transfer pipe meets the above relation between the temperature of the crude oil (C) and the temperature of the light liquid; however when the temperature of the crude oil (C) is too high, a demerit due to a loss of light fractions is generated, and thus the temperature of the crude oil (C) is preferably 60 C or lower, and more preferably 50 C or lower.

cA0m9100201711

- 21 -[0035]
In the third step (1), by mixing the light liquid into the crude oil (C) in the crude oil transfer pipe, the light liquid is mixed into the crude oil (C). The crude oil transfer pipe is a transfer pipe to transfer the crude oil (C), and the crude oil (C) flows therein, and thus mixing of the light liquid in the crude oil (C) into the crude oil transfer pipe refers to mixing the light liquid into the crude oil (C) in the state of flowing in the crude oil transfer pipe. Then, in the third step (1), by mixing the light liquid into the crude oil (C) in the flowing state, the depositing oil of the crude oil sludge (A) can be dispersed in the crude oil (C) quickly before the depositing oil of the crude oil sludge (A) aggregates in the crude oil (C), and thus a sludge can be made unlikely to be generated in the crude oil (C). By contrast, when the light liquid is added directly to and mixed with a not-flowing crude oil, for example, a crude oil in a crude oil tank, the depositing oil of the crude oil sludge (A) in the crude oil (C) is unlikely to be dispersed in the crude oil (C), and thus even if the oil of the crude oil sludge (A) becomes a fine deposit unlikely forming a sludge, a sludge becomes likely to be generated in the crude oil (C) because the depositing oil ends in aggregating immediately after the mixing.

c.A029891002017-12-11

- 22 -[0036]
A method of mixing the light liquid into the crude oil (C) in the crude oil transfer pipe includes mixing by line mixing, a static mixer, an injection nozzle, a mixing valve or the like.
[0037]
In the third step (1), the amount of the light liquid to be mixed into the crude oil (C) is, with respect to 100 parts by volume of the crude oil (C), preferably 45 parts by volume or smaller, and more preferably 2 to 15 parts by volume. When the amount of the light liquid to be mixed into the crude oil (C) is in the above range, a sludge is unlikely to be generated in the crude oil (C).
[0038]
In the third step (1), the linear velocity of the crude oil (C) flowing in the crude oil transfer pipe is preferably 1 cm/sec or higher, more preferably 4 cm/sec or higher, and still more preferably 6 cm/sec or higher. When the linear velocity of the crude oil (C) flowing in the crude oil transfer pipe is in the above range, the depositing oil of the crude oil sludge (A) in the crude oil (C) easily becomes dispersed, and thus a sludge becomes unlikely to be generated in the crude oil (C). Here, although there is no upper limit value of the linear velocity of the crude oil (C) flowing in the crude oil

- 23 -transfer pipe, the usual linear velocity of the crude oil in the crude oil transfer pipe is 500 cm/sec or lower in many cases.
[0039]
Then, by carrying out the third step (1), there is obtained a crude oil (D) in which the light liquid is mixed into the crude oil (C).
[0040]
The crude oil (D) according to the present invention is a crude oil obtained by carrying out:
a first step (1) of mixing a crude oil sludge (A) with a crude oil (B) so that the proportion of the crude oil sludge (A) to the sum of the crude oil sludge (A) and the crude oil (B) becomes 20 to 95% by mass, and then heating and stirring the mixture of the crude oil sludge (A) with the crude oil (B) at 40 to 200 C to thereby obtain a heated and stirred material of the crude oil sludge (A) and the crude oil (B);
a second step (1) of centrifugally separating the heated and stirred material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step (1) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having

- 24 -the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.
[0041]
The crude oil sludge (A), the crude oil (B), the mixture of the crude oil sludge (A) with the crude oil (B), the heated and stirred material of the crude oil sludge (A) and the crude oil (B), the first step (1), the centrifugal separation, the light liquid, the heavy fraction, the second step (1), the crude oil (C) and the third step (1) relevant to the crude oil (D) according to the present invention are the same as the crude oil sludge (A), the crude oil (B), the mixture of the crude oil sludge (A) with the crude oil (B), the heated and stirred material of the crude oil sludge (A) and the crude oil (B), the first step (1), the centrifugal separation, the light liquid, the heavy fraction, the second step (1), the crude oil (C) and the third step (1) relevant to the method for recovering oil in a crude oil sludge according to the first aspect of the present invention.

- 25 -[0042]
A method for recovering oil in a crude oil sludge according to a second aspect of the present invention is a method for recovering oil in a crude oil sludge, comprising:
a first step (2) of heating a crude oil sludge (A) at 40 to 200 C to thereby obtain a heated material of the crude oil sludge (A);
a second step (2) of centrifugally separating the heated material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step (2) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.
[0043]
The first step (2) in the method for recovering oil in a crude oil sludge according to the second aspect of the = - 26 -present invention is a step of heating a crude oil sludge (A) at 40 to 200 C to thereby obtain a heated material of the crude oil sludge (A).
[0044]
The crude oil sludge (A) in the first step (2) is the same as that in the first step (1).
[0045]
The first step (2) heats the crude oil sludge (A) at 40 to 200 C, preferably 50 to 150 C, and more preferably 60 to 100 C to thereby obtain a heated material of the crude oil sludge (A). If the heating temperature is lower than the above range, the recovery of oil from the crude oil sludge (A) becomes insufficient; and if the temperature exceeds the above range, the heating cost rises and the economic efficiency is lost. A method of heating the crude oil sludge (A) is not especially limited, and examples thereof include a method in which the crude oil sludge (A) is heated in a tank where the crude oil sludge (A) taken out of a crude oil tank is stored.
[0046]
The second step (2) in the method for recovering oil in a crude oil sludge according to the second aspect of the present invention is a step of centrifugally separating the heated material of the crude oil sludge (A) obtained by carrying out the first step (2), at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid.
[0047]
In the second step (2), the temperature when the heated material of the crude oil sludge (A) is centrifugally separated is 40 to 200 C, preferably 50 to 150 C, and more preferably 60 to 100 C. If the centrifugal separation temperature is lower than the above range, then part of the heated material of the crude oil sludge (A) freezes and the fluidity of the heated material greatly decreases during the centrifugal separation, and thus the centrifugal separation cannot be carried out; and if the temperature exceeds the above range, the heating cost rises and the economic efficiency is lost. Further in the second step (2), the temperature when the heated material of the crude oil sludge (A) is centrifugally separated is preferably made equal to or higher than the heating temperature of the crude oil sludge (A) in the first step (2).
[0048]
The heated material of the crude oil sludge (A) obtained by carrying out the first step (2) is a mixture of a light liquid having a low specific gravity and a heavy fraction having a higher specific gravity than the light liquid; and in the second step (2), the light liquid and - 28 - the heavy fraction are separated by the difference in specific gravity. Then, the light liquid is oil in the crude oil sludge (A). That is, the light liquid is basically composed of oil in the crude oil sludge (A). The heavy fraction is components in the crude oil sludge (A) which have higher specific gravities than the oil, mainly such as asphaltene, moisture, iron, sand, oil being carried in these components and being in a hard-to-separate state by the heating in the first step (2).
[0049]
A centrifugal separation apparatus to centrifugally separate the heated material in the second step (2) is not especially limited, and suffices if being one capable of continuously separating the light liquid and the heavy fraction by the difference in specific gravity with the above centrifugal separation temperature being held.
Examples thereof include a decanter-type centrifugal separator, a disc separator-type centrifugal separator, and a centrifugal separator in a combination of these.
[0050]
The physical properties of the light liquid obtained by carrying out the second step (2) are not especially limited; but its density is preferably 0.80 to 0.95 g/cm3, and more preferably 0.80 to 0.88 g/cm3; its melting point is preferably 40 to 150 C, more preferably 40 to 110 C, and still more preferably 40 to 90 C; its freezing point is preferably 30 to 140 C, more preferably 30 to 100 C, and still more preferably 30 to 80 C; and its oil content is 60% by mass or higher.
[0051]
The third step (2) in the method for recovering oil in a crude oil sludge according to the second aspect of the present invention is a step of bringing the temperature of the light liquid obtained by carrying out the second step (2) to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe. If the temperature of the light liquid is lower than the melting point, it becomes difficult to mix the light liquid into the crude oil (C) in the crude oil transfer pipe. The third step (2) is the same as the third step (1), except that in the third step (2), the light liquid to be mixed into the crude oil (C) is a light liquid obtained by carrying out the first step (2) and the second step (2) whereas in the third step (1), the light liquid to be mixed into the crude oil (C) is a light liquid obtained by carrying out the first step (1) and the second step (1).
[0052]

c.A029891002017-12-11 In the third step (2), the crude oil (C) to be mixed with the light liquid is not especially limited, and may be a crude oil before being cleared of solid contents, moisture and the like after crude oil mining, and being stored in a crude oil tank, may be a crude oil shortly after being cleared of solid contents, moisture and the like after crude oil mining, and starting to be stored in a crude oil tank, and before generating a crude oil sludge, or may be a supernatant crude oil in a crude oil tank after a crude oil sludge is generated on the bottom of the crude oil tank during a certain-period storage of the crude oil in the crude oil tank. The crude oil (C) may be the same crude oil as a crude oil as a generation source of the crude oil sludge (A), or may be a crude oil different therefrom.
[0053]
The oil in the crude oil sludge (A) is mainly hydrocarbons having large molecular weights having 40 or more carbon atoms, and thus if the temperature of the light liquid becomes too low compared to the temperature when the heating is carried out in the first step (2), the light liquid freezes or the fluidity of the light liquid remarkably decreases; therefore, in the third step (2), the temperature of the light liquid is brought to a temperature equal to or higher than the melting point thereof, and then, the light liquid is mixed into the crude oil (C). The temperature of the light liquid is preferably equal to or higher than the melting point, and in the range of 40 to 200 C, more preferably 50 to 150 C, and still more preferably 60 to 100 C.
[0054]
In the third step (2), with respect to the relation between the temperatures of the crude oil (C) and the light liquid when the light liquid is mixed into the crude oil (C), the temperature of the crude oil (C) is equal to or higher than that of the light liquid, or the temperature of the crude oil (C) is lower than that of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower. In the case where the temperature of the crude oil (C) is lower than that of the light liquid, with a smaller difference between the temperature of the light liquid and the temperature of the crude oil (C), when the light liquid is mixed into the crude oil (C), the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is more suppressed or even if the oil deposits, more of the oil deposits finely, more unlikely causing a sludge, and thus a difference between the temperature of the light liquid and the temperature of the crude oil (C) that is 40 C or lower has the following effect: the deposition of the oil of the =
crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge. Further in the case where the temperature of the crude oil (C) is lower than that of the light liquid, a difference between the temperature of the light liquid and the temperature of the crude oil (C) that is preferably 30 C or lower, more preferably 20 C or lower, and still more preferably 10 C or lower enhances the following effect: the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge. Further in the case where the temperature of the crude oil (C) is equal to or higher than that of the light liquid, when the light liquid is mixed into the crude oil (C), the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge, and thus a temperature of the crude oil (C) that is equal to or higher than that of the light liquid has the following effect: when the light liquid is mixed into the crude oil (C), the deposition of the oil of the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, unlikely causing a sludge. Further in the case where the temperature of the crude oil (C) is equal to or higher than that of the light liquid, the difference between the temperature of the crude oil (C) and the temperature of the light liquid is preferably 10 C or lower, and more preferably 5 C or lower.
[0055]
In the third step (2), the temperature of the crude oil (C) flowing in a crude oil transfer pipe meets the above relation between the temperature of the crude oil (C) and the temperature of the light liquid; however when the temperature of the crude oil (C) is too high, a demerit due to a loss of light fractions is generated, and thus the temperature of the crude oil (C) is preferably 60 C or lower, and more preferably 50 C or lower.
[0056]
In the third step (2), by mixing the light liquid in the crude oil (C) into the crude oil transfer pipe, the light liquid is mixed into the crude oil (C). That is, the light liquid is mixed into the crude oil (C) in the state of flowing in the crude oil transfer pipe. Further in the third step (2), by mixing the light liquid into the crude oil (C) in the flowing state, the depositing oil of the crude oil sludge (A) can be dispersed in the crude oil (C) quickly before the depositing oil of the crude oil sludge (A) aggregates in the crude oil (C), and thus a sludge can be made unlikely to be generated in the crude oil (C). By cA029891002017-12-11 contrast, when the light liquid is added directly to and mixed with a not-flowing crude oil, for example, a crude oil in a crude oil tank, the depositing oil of the crude oil sludge (A) in the crude oil (C) is unlikely to be dispersed in the crude oil (C), and thus even if the oil of the crude oil sludge (A) becomes a fine deposit unlikely forming a sludge, a sludge becomes likely to be generated in the crude oil (C) because the depositing oil ends in aggregating immediately after the mixing.
[0057]
A method of mixing the light liquid into the crude oil (C) in the crude oil transfer pipe includes mixing by line mixing, a static mixer, an injection nozzle, a mixing valve or the like.
[0058]
In the third step (2), the amount of the light liquid to be mixed into the crude oil (C) is, with respect to 100 parts by volume of the crude oil (C), preferably 45 parts by volume or smaller, and more preferably 2 to 15 parts by volume. When the amount of the light liquid to be mixed into the crude oil (C) is in the above range, a sludge becomes unlikely to be generated in the crude oil (C).
[0059]
In the third step (2), the linear velocity of the crude oil (C) flowing in the crude oil transfer pipe is preferably 1 cm/sec or higher, more preferably 4 cm/sec or higher, and still more preferably 6 cm/sec or higher. When the linear velocity of the crude oil (C) flowing in the crude oil transfer pipe is in the above range, the depositing oil of the crude oil sludge (A) in the crude oil (C) easily becomes dispersed, and thus a sludge becomes unlikely to be generated in the crude oil (C). Here, although there is no upper limit value of the linear velocity of the crude oil (C) flowing in the crude oil transfer pipe, the usual linear velocity of the crude oil in the crude oil transfer pipe is 500 cm/sec or lower in many cases.
[0060]
Then, by carrying out the third step (2), there is obtained a crude oil (E) in which the light liquid is mixed into the crude oil (C).
[0061]
The crude oil (E) according to the present invention is a crude oil obtained by carrying out:
a first step (2) of heating a crude oil sludge (A) at 40 to 200 C to thereby obtain a heated material of the crude oil sludge (A);
a second step (2) of centrifugally separating the heated material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step (2) of bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a crude oil (C) in a crude oil transfer pipe, wherein the temperature of the crude oil (C) is equal to or higher than the temperature of the light liquid, or the temperature of the crude oil (C) is lower than the temperature of the light liquid and the difference between the temperature of the light liquid and the temperature of the crude oil (C) is 40 C or lower.
[0062]
The crude oil sludge (A), the heated material of the crude oil sludge (A), the first step (2), the centrifugal separation, the light liquid, the heavy fraction, the second step (2) and the third step (2) relevant to the crude oil (E) according to the present invention are the same as the crude oil sludge (A), the heated material of the crude oil sludge (A), the first step (2), the centrifugal separation, the light liquid, the heavy fraction, the second step (2) and the third step (2) relevant to the method for recovering oil in a crude oil sludge according to the second aspect of the present invention.
[0063]

c.A029891002017-12-11 The crude oil (D) according to the present invention is obtained by carrying out the first step (1), the second step (1) and the third step (1), and thus when the crude oil (D) is stored in a crude oil tank, a crude oil sludge is unlikely to be generated. Further the crude oil (E) according to the present invention is obtained by carrying out the first step (2), the second step (2) and the third step (2), when the crude oil (E) is stored in a crude oil tank, a crude oil sludge is unlikely to be generated.
[0064]
In the method for recovering oil in a crude oil sludge according to the first aspect of the present invention, oil can be recovered from in a crude oil sludge (A) by dissolving oil in the crude oil sludge (A) in a crude oil (B) and centrifugally separating a light liquid, that is, a crude oil (B) containing the oil in the crude oil sludge (A) dissolved therein from a heavy fraction, that is, components excluding the oil in the crude oil sludge (A), by carrying out the first step (1) and the second step (1).
Further in the method for recovering oil in a crude oil sludge according to the second aspect of the present invention, oil can be recovered from in a crude oil sludge (A) by centrifugally separating oil in the crude oil sludge (A) as a light liquid from a heavy fraction, that is, components excluding the oil in the crude oil sludge (A), by carrying out the first step (2) and the second step (2).
[0065]
Here, the oil in the crude oil sludge (A) cannot be dissolved in the crude oil (B) at the crude oil storage temperature (usually 20 to 40 C), and thus when the light liquid obtained by carrying out the second step (1) or the second step (2) is returned directly to a crude oil tank, simultaneously with contacting of the light liquid with the crude oil in the crude oil tank, the oil in the crude oil sludge (A) dissolved in the light liquid is deposited as a large solid and generates a large deposit, which thus again forms into a sludge.
[0066]
Then, in the method for recovering oil in a crude oil sludge according to the present invention, by carrying out the third step (1) or the third step (2), that is, by bringing the temperature of the light liquid to a temperature equal to or higher than the melting point thereof, and mixing the light liquid into the crude oil (C) whose temperature is equal to or higher than the temperature of the light liquid, or whose temperature is lower than the temperature of the light liquid wherein the temperature difference between the crude oil (C) and the light liquid is 40 C or lower, the deposition of the oil of c.A029891002017-12-11 the crude oil sludge (A) in the crude oil (C) is suppressed or even if the oil deposits, the oil deposits finely, making it possible to unlikely cause a sludge; and by mixing the light liquid into the crude oil (C) in the flowing state, the oil in the crude oil sludge (A) can be dispersed in the crude oil (C) before the depositing oil of the crude oil sludge (A) aggregates in the crude oil (C);
thus, the oil in the crude oil (C) can be made unlikely to form into a sludge in the crude oil (C).
Examples [0067]
Hereinafter, the present invention will be described more specifically by way of Examples, but the present invention is not limited thereto.
[0068]
<The crude oil sludge (A)>
A crude oil sludge a recovered from a crude oil tank Analysis values: oil content: 75.1% by mass, asphaltene content: 10.3% by mass, moisture content: 11.0%
by mass, sediment content: 3.6% by mass <The crude oil (B)>
A crude oil b having the following analysis values API: 30.3 , water and sediment content: 0% by volume <The crude oil (C)>
The above crude oil b was used as the crude oil (C).

[0069]
(Examples 1 to 4) The crude oil sludge a and the crude oil b were added to a stirring vessel so that the proportion of the crude oil sludge a to the sum of the both became 70% by mass; and the mixture was heated and stirred at 80 C.
Then, with the temperature being held at 80 C, the heated and stirred material was put in a centrifugal separator set at 80 C, and centrifugally separated under the conditions of 80 C, 1,000 G and 1 min.
Then, a light liquid was separated by decantation to thereby obtain the light liquid. The analysis values of the obtained light liquid are shown in Table 1.
Then, the light liquid heated to 80 C was mixed in a corresponding proportion indicated in Table 1 into the crude oil b of 50 C flowing at a corresponding linear velocity indicated in Table 1 to thereby obtain a mixture (mixed sample). The mixing method is as shown in FIG. 1.
Then, the obtained mixture was allowed to stand still at 35 C for 5 days, and there were measured the amount of deposited sludge, and API and the water and sediment content of the crude oil cleared of the sludge. The results are shown in Table 1.
[0070]
<The measuring method of the amount of deposited sludge>

100 mL of the sample was put in a 100-mL centrifuging tube, and allowed to stand still at 35 C for 5 days. Then, the centrifuging tube was tilted and the supernatant was thrown away over 15 sec; and the centrifuging tube was then turned upside down, and allowed to stand still for 30 sec.
Then, the centrifuging tube was restored to its original position, and allowed to stand still at 80 C for 60 min;
and the amount of sludge remaining in the centrifuging tube was measured.
[0071]
(Comparative Examples 1 and 2) A light liquid heated to 80 C was mixed in a corresponding proportion indicated in Table 1 into the crude oil b of 30 C flowing at a corresponding linear velocity indicated in Table 1 to thereby obtain a mixture (mixed sample). Here, the light liquid was prepared by the same method as in the Examples.
Then, the obtained mixture was allowed to stand still at 35 C for 5 days, and there were measured the amount of deposited sludge, and API and the water and sediment content of the crude oil cleared of the sludge. The results are shown in Table 1.
[0072]
(Comparative Example 3) A light liquid heated to 80 C was added and mixed, without being stirred, in a proportion indicated in Table 1 to the crude oil b of 30 C allowed to stand still in a vessel. Here, the light liquid was prepared by the same method as in the Examples.
Then, the obtained mixture was allowed to stand still at 35 C for 5 days, and there were measured the amount of deposited sludge, and API and the water and sediment content of the crude oil cleared of the sludge. The results are shown in Table 1.
[0073]

..
, [Table 1]
Example Example Example Example Comparative Comparative Comparative 1 2 3 4 Example 1 Example 2 Example 3 <First Step> , Mixing Proportion (% by mass) Crude Oil Sludge a 70 70 70 70 70 70 70 Crude Oil b 30 30 30 30 30 30 30 <Second Step>
_ Light Liquid (% by mass) 72.5 72.5 72.5 72.5 72.5 72.5 72.5 Heavy Fraction (% by 27.5 27.5 27.5 27.5 27_5 27.5 27.5 mass) Melting Point of Light 78.8 78.8 78.8 78.8 78.8 78.8 78.8 Liquid ( C) Freezing Point of Light 69.1 69.1 69.1 69.1 69.1 69.1 69.1 Liquid ( C) Density at I5 C of Light 0.869 0.869 0.869 0.869 0.869 0.869 0.869 Liquid (g/mL) Oil [% by mass]
Asphaltene [%
4.0 4.0 4.0 4.0 4.0 4.0 4.0 Light Liquid by mass]
Composition Sediment [%
<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 by mass]
Moisture [%
0.16 0.16 0.16 0.16 0.16 0.16 0.16 by mass]
<Third Step>
Crude Oil b (parts by volume) Light Liquid (parts by 7.5 7.5 7.5 7.5 7.5 7.5 7.5 volume) Temperature of Light Liquid ( C) Temperature of Crude Oil 50 b ( C) Linear Velocity of Crude 40 32 20 6.0 32 20 -Oil b (cm/sec) <Evaluation Results>
Amount of Deposited 0.9 1.1 1.3 1.0 5.0 5.5 12 Sludge (% by volume) API ( ) 30.7 30.7 30.7 30.6 30.7 30.7 30.4 , Water And Sediment 0.05 0.05 0.05 0.10 0.05 0.05 0 Content (% by mass) , ' -

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for recovering oil in a crude oil sludge, comprising:
a first step of mixing a crude oil sludge with a first crude oil so that a proportion of the crude oil sludge to a sum of the crude oil sludge and the first crude oil becomes 20 to 95% by mass, and then heating and stirring the mixture of the crude oil sludge with the first crude oil at 40 to 200°C
to thereby obtain a heated and stirred material of the crude oil sludge and the first crude oil;
a second step of centrifugally separating the heated and stirred material at 40 to 200°C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step of bringing a temperature of the light liquid to a temperature equal to or higher than a melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a second crude oil in a crude oil transfer pipe, wherein a temperature of the second crude oil is equal to or higher than the temperature of the light liquid, or the temperature of the second crude oil is lower than the temperature of the light liquid and a difference between the temperature of the light liquid and the temperature of the second crude oil is 40°C or lower.

2. The method for recovering oil in a crude oil sludge according to claim 1, wherein in the third step, the t emp e r a tur e of the light liquid when the light liquid is mixed into the second crude oil is 50 to 150 C.

3. The method for recovering oil in a crude oil sludge according to claim 1 or 2, wherein in the third step, an amount of the light liquid mixed based on 100 parts by volume of the second crude oil is 45 parts by volume or smaller.

4. The method for recovering oil in a crude oil sludge according to any one of claims 1 to 3, wherein in the third step, a linear velocity of the second crude oil flowing in the crude oil transfer pipe is 1 cm/sec or higher.

5. A crude oil, being obtained by carrying out:
a first step of mixing a crude oil sludge with a first crude oil so that a proportion of the crude oil sludge to a sum of the crude oil sludge and the first crude oil becomes 20 to 95% by mass, and then heating and stirring the mixture of the crude oil sludge with the first crude oil at 40 to 200 C
to thereby obtain a heated and stirred material of the crude oil sludge and the first crude oil;
a second step of centrifugally separating the heated and stirred material at 40 to 200 C into a light liquid and a heavy fraction to thereby obtain the light liquid; and a third step of bringing a temperature of the light liquid to a temperature equal to or higher than a melting point thereof, and mixing the light liquid having the temperature equal to or higher than the melting point into a second crude oil in a crude oil transfer pipe, wherein a temperature of the second crude oil is equal to or higher than Date Recue/Date Received 2022-04-12 the temperature of the light liquid, or the temperature of the second crude oil is lower than the temperature of the light liquid and a difference between the temperature of the light liquid and the temperature of the second crude oil is 40 C or lower.
Date Recue/Date Received 2022-04-12