JP2018162425A - Method for recovering crude light oil component in gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering a crude light oil component in which the content of the crude light oil component in the gas after absorption can be made low by effectively absorbing the crude light oil component contained in the coke oven gas etc. into absorption oil, thereby capable of efficiently recovering the crude light oil component.SOLUTION: A method for recovering a crude light oil component in a gas of this invention includes: a cooling process 1, where a raw material gas containing the coke oven gas etc. is cooled by the cooling tower; a recycle process 1, where an organic compound component contained in the water and raw material gas discharged from the cooling tower are circulated through a heat exchanger to the cooling tower; an absorption process, where the crude light oil component contained in the gas is absorbed into the absorption oil from the raw material gas passed through the cooling process 1; a recovery process, where the crude light oil component is recovered by distilling the absorption oil having absorbed the crude light oil component in the cooling tower; a cooling process 2, where the absorption oil after recovery of the crude light oil component is cooled through the heat exchanger, then supplied again to the absorption process, in which the total contents of dibenzofuran and fluorene in the absorption oil introduced in the cooling tower are 35 wt% or below.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a method for recovering crude light oil components contained in coke oven gas or pyrolysis oven gas. More specifically, the present invention relates to a coke oven gas produced as a by-product in producing coke by dry distillation of coal in a coke oven, or a pyrolysis oven gas generated when coal is pyrolyzed in a pyrolysis oven. The present invention relates to a method for recovering the contained crude light oil component.

  Coke oven gas generated when coke is produced by carbonization in a coke oven, and pyrolysis oven gas generated when coal is pyrolyzed in a pyrolysis oven (hereinafter collectively referred to as “coke oven gas”) Etc.))) are the main components of hydrogen, methane, carbon monoxide, carbon dioxide, etc. In addition to these main components, tar content, ammonia, hydrogen sulfide, hydrocarbon gases other than methane, It contains crude light oil components, hydrogen cyanide and many other components. Since coke oven gas and the like are generated in a high temperature state from a coke oven and a coal pyrolysis furnace, the coke oven gas is first cooled and then separated and collected. Each component recovered from coke oven gas or the like is utilized as fuel or various raw materials. Among them, crude light oil components recovered from coke oven gas and the like contain a large amount of aromatic hydrocarbon compounds (aromatic components) such as benzene, toluene, and xylene as compared to petroleum-derived light oil components. Therefore, the utility value is high as various raw materials.

  Various methods are used to recover crude light oil components from coke oven gas, etc., but as a typical method, coke oven gas etc. are brought into contact with absorbing oil in an absorption tower and contained in coke oven gas etc. A method of absorbing the crude light oil component to be absorbed in the absorption oil, separating and recovering the crude light oil component from the absorption oil by distilling the absorption oil in the distillation tower, and circulating the absorbed oil after the separation and recovery to the absorption tower. (See FIG. 1).

  In the above method, in order to efficiently recover crude light oil components such as benzene, toluene, xylene from coke oven gas, etc., the absorption light tower absorbs a large amount of crude light oil components in the absorption oil, and efficiency in the distillation tower. It is preferable to separate well. For that purpose, it is necessary to lower the temperature of the absorption oil introduced to the absorption tower and the temperature of the raw material gas, and increase the amount of the crude light oil component absorbed in the unit absorption oil amount. On the other hand, as described above, since the absorption oil is circulated and used, the absorption oil discharged in a high temperature state in the distillation tower needs to be cooled using a cooler. Therefore, in order to efficiently recover the crude light oil component, it is preferable to cool the absorption oil discharged from the distillation tower to a lower temperature and supply it to the absorption tower, and further to lower the temperature of the raw material gas.

  However, if the temperature of the raw material gas is lowered, precipitation components (dibenzofuran and fluorene) are contained in the water used to lower the temperature of the raw material gas, and the heat exchanger that is being cooled will clog. There's a problem. Conventionally, two coolers are arranged in parallel and bypassed, and when one of the coolers is blocked, it is necessary to switch to the other cooler and open and clean the blocked cooler. It was. However, since much labor and cost are required to open and clean the cooler, a method for preventing precipitation of dissolved components while cooling the raw material gas to a lower temperature is desired.

As a means for preventing precipitation components in the liquid that is cooling the raw material gas from precipitating with a heat exchanger or the like, for example, a mist component contained in the raw material gas (included by being entrained from the previous step) In the component having the same composition as the absorbing oil), a method of reducing the composition of the precipitation component introduced into the heat exchanger can be mentioned. In order to reduce the composition of the precipitate from the absorbent oil, the composition of the absorbent oil in each part where the absorbent oil circulates is determined, and after calculating the precipitation start temperature of the absorbent oil from the composition,
A method is disclosed in which the operating condition of each part is set to be equal to or higher than the precipitation start temperature, or the composition of the absorbent oil is changed so as to lower the precipitation start temperature of the absorbent oil (see Patent Document 1).

JP 2005-194410 A

  As described above, conventionally, when recovering crude light oil components from coke oven gas, etc., as a means for preventing deposits in the liquid cooling the raw material gas from depositing on the cooler, etc., the temperature is raised. Only a method of washing away the precipitate or cooling in a temperature range in which the precipitate does not precipitate has been disclosed. However, the method described above requires a long period of time for cleaning or costs for the cleaning. Further, the raw material gas cannot be cooled during washing, and the original purpose of efficiently recovering the crude light oil component cannot be achieved.

  The present invention efficiently absorbs the crude light oil component contained in the coke oven gas or pyrolysis furnace gas into the absorption oil, and can reduce the content ratio of the crude light oil component remaining in the gas after absorption. It aims at providing the collection method of a light oil component. Another object of the present invention is to provide a method for recovering crude light oil components that can efficiently recover crude light oil components and that can reduce energy consumption with a compact facility.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have reduced the concentration of precipitated components in the absorption oil introduced into the cooling tower for cooling the raw material gas, thereby reducing the mist contained in the raw material gas. The inventors have found that the concentration of precipitated components in the components can be reduced to solve the above problems, and the present invention has been completed. That is, the gist of the present invention is the following [1] to [4].

[1] Cooling step (1) of cooling a source gas containing at least one of coke oven gas and pyrolysis oven gas in a cooling tower, water discharged from the cooling tower, and organic contained in the source gas A circulation step (1) for circulating the compound component through the heat exchanger to the cooling tower, an absorption step for absorbing the crude light oil component contained in the gas into the absorption oil from the raw material gas after the cooling step (1), The recovery process for recovering the crude light oil component by distilling the absorbed oil that has absorbed the crude light oil component in the distillation tower, the absorbed oil after the recovery of the crude light oil component is cooled via a heat exchanger, and then absorbed again A method for recovering a crude light oil component in a gas, comprising a cooling step (2) to be supplied to the step, and introducing an absorbing oil having a total content of dibenzofuran and fluorene of 35% by weight or less into the cooling tower.

[2] A crude light oil component discharged from the distillation column is supplied to the de-pitch column with a part of the absorbed oil recovered, and after the removal step (1) for removing the pitch component, is circulated to the distillation column. The collection method according to [1].
[3] The raw material gas introduced into the cooling tower has been subjected to a removal step (2) in which naphthalene is removed by absorbing the absorbing gas in the denaphthalene tower, and described in [1] or [2]. Recovery method.
[4] The recovery method according to [3], including a circulation step (2) in which the absorbed oil after the recovery step is cooled by a heat exchanger and then circulated to the denaphthalene tower.

The crude light oil component recovery method of the present invention has the following effects 1) to 4).
1) According to the present invention, a method for efficiently recovering crude light oil components contained in coke oven gas or pyrolysis oven gas can be provided.
2) According to the present invention, when the crude light oil component contained in the gas is recovered with the absorption oil, even if the temperature of the raw material gas and the absorption oil is lowered in order to increase the absorption efficiency, it is deposited on the heat exchanger, piping, etc. And the like.
3) According to the present invention, since the crude light oil component contained in the coke oven gas or pyrolysis furnace gas can be efficiently absorbed into the absorption oil, the content ratio of the crude light oil component remaining in the absorbed gas Can be reduced, and the load on the refining equipment can be reduced.
4) According to the present invention, the crude light oil component can be efficiently recovered, so that the equipment can be made compact and the energy consumption can be reduced.

It is a schematic diagram which shows an example of the general method which collect | recovers crude light oil components from coke oven gas. It is a schematic diagram which shows an example of the recovery method of the crude light oil component of this invention. It is a schematic diagram which shows an example of the recovery method of the crude light oil component of this invention. It is a schematic diagram which shows an example of the recovery method of the crude light oil component of this invention. It is a schematic diagram which shows an example of the recovery method of the crude light oil component of this invention. It is a schematic diagram which shows an example of the recovery method of the crude light oil component of this invention. It is a schematic diagram which shows an example of the recovery method of the crude light oil component of this invention.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In the following, “mass%” and “wt%” and “part by mass” and “part by weight” have the same meaning.

  The method for recovering crude light oil components in the gas of the present invention includes a cooling step (1) in which a raw material gas containing at least one of a coke oven gas and a pyrolysis furnace gas is cooled in a cooling tower, and is discharged from the cooling tower. A circulation step (1) for circulating the organic compound component contained in the water and the raw material gas to the cooling tower through a heat exchanger, and a raw material gas that has undergone the cooling step (1), Absorption process of absorbing light oil components into the absorption oil, recovery process of recovering the crude light oil components by distilling the absorption oil that has absorbed the crude light oil components in a distillation tower, Having cooling step (2) to be supplied again to the absorption step after cooling through the exchanger, and introducing the absorption oil having a total content of dibenzofuran and fluorene of 35% by weight or less into the cooling tower Features (see Figure 2) . In the present invention, the coke oven gas and the pyrolysis oven gas may be collectively referred to as “coke oven gas”. The present invention is described in detail below.

[1. Raw material gas]
<Coke oven gas>
The coke oven gas means a gas generated from the coke oven when coke is produced from coal. Specifically, coke oven gas is a gas that is generated when coal is heated and distilled at a temperature of 600 ° C. or higher to produce coke. As a general composition, hydrogen is 10 to 70% by volume, methane 20 to 70. Volume%, hydrocarbons other than methane (olefins such as ethylene) 1 to 15 volume%, carbon monoxide 4 to 9 volume%, carbon dioxide 1 to 6 volume%, nitrogen 1 to 13 volume%, oxygen 0 to 0 0.5% by volume, sulfur compounds such as hydrogen sulfide 0.3 to 1.5%, nitrogen compounds such as ammonia 0.3 to 1.8%, benzoles 0.1 to 1.8% by volume, and other coals Contains trace components of origin.

As the coke oven gas used in the present invention, the gas having the above composition discharged from the coke oven can be used as it is, but it is preferable to use a pretreated coke oven gas. Specifically, it is preferable to use a coke oven gas that has been subjected to a purification treatment for reducing sulfur compounds such as hydrogen sulfide, nitrogen compounds such as ammonia, and benzols among the above components.

  The pretreatment can be performed using, for example, a catalyst for deoxygenation reaction having a function as a desulfurization catalyst, such as a Ni—Mo series or a Co—Mo series. When these catalysts are used, deoxygenation and desulfurization are performed by hydrogenation with hydrogen in coke oven gas. The pretreatment may be performed according to a conventional method. For example, the treatment may be performed under conditions of a reactor inlet temperature of about 200 to 350 ° C., a reactor internal pressure of about 0.5 to 5.0 MPaG, and a reactor outlet temperature of about 100 to 450 ° C. That's fine. Further, for example, coke oven gas may be sent to an adsorption desulfurizer to perform adsorption desulfurization with ZnO. The concentration of each component of the pretreated coke oven gas is generally 0.001 to 0.2% of a sulfur compound such as hydrogen sulfide, 0.01 to 0.2% of a nitrogen compound such as ammonia, and benzols 0 0.02 to 0.3%, and the concentration of components other than these is substantially unchanged before and after the purification treatment.

  The composition of the coke oven gas used in the present invention is not limited, but usually contains hydrogen, carbon dioxide, carbon monoxide, methane, nitrogen and the like as main components and a crude light oil component. Although the content rate of the crude light oil component in the coke oven gas used for this invention is not limited, Usually, it is 1-5000 volume ppm. When the content ratio of the crude light oil component in the coke oven gas is within the above range, it is preferable because the crude light oil component tends to be efficiently absorbed by the absorbent oil in the absorption step. For the same reason as described above, the lower limit of the content ratio of the crude light oil component in the coke oven gas is preferably 10 ppm by volume or more, more preferably 100 ppm by volume or more, still more preferably 500 ppm by volume or more, particularly preferably 1000 volumes. ppm or more. Moreover, the upper limit of the content ratio of the crude light oil component in the coke oven gas is preferably 4000 ppm by volume or less, more preferably 3000 ppm by volume or less, for the same reason as described above.

  In particular, from the viewpoint of recovering useful components more efficiently, the total content of benzene, toluene and xylene contained in the coke oven gas is preferably 1 to 4000 ppm by volume. Further, the lower limit of the total content is preferably 10 volume ppm or more, more preferably 100 volume ppm or more, still more preferably 500 volume ppm or more, particularly preferably 1000 volume ppm or more, and the upper limit is preferably 3000. Volume ppm or less.

  The raw material gas used in the present invention may be any one of coke oven gas and pyrolysis oven gas, but preferably contains at least coke oven gas. The content ratio of the coke oven gas in the raw material gas is not limited, but is usually 1% by volume or more, preferably 10% by volume or more, more preferably 50% by volume or more, still more preferably 70% by volume or more, and particularly preferably 85% by volume. That's it. The upper limit of the content ratio of the coke oven gas is not limited, and may be 100% by volume.

<Pyrolysis furnace gas>
The pyrolysis furnace gas means a gas generated when coal is pyrolyzed in the pyrolysis furnace. The composition of the pyrolysis furnace gas used in the present invention is not limited, but usually contains hydrogen, carbon dioxide, carbon monoxide, methane, nitrogen and the like.

  Although the content rate of the crude light oil component in the pyrolysis furnace gas used for this invention is not limited, Usually, it is 1-5000 volume ppm. It is preferable that the content ratio of the crude light oil component in the pyrolysis furnace gas is in the above range because the crude light oil component tends to be efficiently absorbed by the absorbent oil in the absorption step. Moreover, the minimum and upper limit of a preferable content rate are the same as that of coke oven gas mentioned above. In particular, from the viewpoint of recovering useful components more efficiently, the total content of benzene, toluene and xylene contained in the pyrolysis furnace gas is preferably 1 to 4000 ppm by volume. Moreover, the minimum and upper limit of a preferable total content rate are the same as that of coke oven gas mentioned above.

  In the present invention, coke oven gas and pyrolysis oven gas may be used in combination as the raw material gas. Even when the coke oven gas and the pyrolysis oven gas are used in combination, the content ratio of the crude light oil component in the raw material gas obtained by mixing both is preferably 1 to 5000 ppm by volume. The coke oven gas and pyrolysis oven gas in the present invention are not necessarily formed in a complete gas state, and may be aerosols such as dust, fume, smoke, mist, etc. The thing of a state may be contained. Furthermore, a liquid or solid form formed by agglomeration or solidification of a gas is also included.

  Both the gas composition in the coke oven gas and the pyrolysis furnace gas and the content ratio of the crude light oil component can be measured by a gas chromatography apparatus.

<Other raw materials>
In the method for recovering crude light oil components of the present invention, any raw material can be used in combination with coke oven gas and / or pyrolysis furnace gas (hereinafter, raw materials other than coke oven gas and pyrolysis furnace gas are referred to as “other raw materials”. ”). The other raw material may be a gas, a solid or a liquid, but is preferably a gas in a state mixed with a coke oven gas and / or a pyrolysis oven gas (including the state described above). .

<Coarse light oil component>
In the present invention, the crude light oil component broadly includes what is generally called light oil (light oil). Specifically, it means a component that can be absorbed from the raw material gas into the absorption oil, and includes at least benzene, It preferably contains any component selected from toluene and xylene. Usually, the crude light oil component further contains styrene, benzofuran, indene, naphthalene, methylnaphthalene, biphenylene, acenaphthene, biphenyl, ethylnaphthalene, dimethylnaphthalene, fluorene, dibenzofuran, phenanthrene, anthracene, fluoranthene, pyrene and the like. The crude light oil component may be a single compound, but is usually a mixture of a plurality of compounds.

  As the raw material gas introduced into the absorption step described later, the total content of benzene, toluene and xylene in the total crude light oil component contained in the raw material gas is preferably 10% by volume or more, and 30% by volume or more. More preferably, it is more preferably 50% by volume or more. The upper limit of the total content of benzene, toluene and xylene in the total crude light oil component is not limited, and may be 100% by volume, but is usually 90% by volume or less.

[2. Cooling step (1)]
The “cooling step (1)” in the present invention is a step of cooling the raw material gas containing at least one of the coke oven gas and the pyrolysis furnace gas (see FIG. 2). More specifically, the source gas is supplied to the cooling tower, the source gas is brought into contact with water, and the temperature of the source gas is cooled. At this time, it is preferable to cool the temperature of the source gas by spraying water in the cooling tower.

  The temperature of the raw material gas charged into the cooling tower is not limited, but is usually 26 to 50 ° C. Although the temperature of the absorption oil charged into the absorption tower is not limited, it is necessary to control the temperature so as not to cause the blockage of the heat exchanger in the cooling step (2) to be described later. It is. The lower these temperatures, the higher the absorption efficiency of the crude light oil component in the raw material gas. In the present invention, in order to lower the temperature of the raw material gas, the temperature of the raw material gas charged into the absorption tower is controlled to 25 ° C. or lower, further 22 ° C. by controlling the ratio of the components dissolved in the absorption oil. In particular, the temperature can be set to 20 ° C. or less.

  In this invention, the absorption oil whose total content of dibenzofuran and fluorene is 35 weight% or less is introduce | transduced into the cooling tower of a cooling process (1). Hereinafter, the total content of dibenzofuran and fluorene referred to herein is referred to as “content of specific substance”. If the content of the specific substance in the absorption oil introduced into the cooling tower is 35% by weight or less, even if the cooling temperature in the heat exchanger is lowered in the circulation step (1), it is dissolved in the absorption oil. It can suppress that a substance precipitates. On the other hand, when the content of the specific substance exceeds 35% by weight, even if the content ratio of other components (components other than dibenzofuran and fluorene) in the absorption oil is reduced, precipitation of dissolved components is sufficiently suppressed. Can not do it. For example, even if acenaphthene (melting point: 92 ° C.), which has a higher melting point than dibenzofuran (melting point: 81 ° C.), is contained in a large amount in the absorption oil, even if its content is significantly reduced, When the content of the specific substance is not within the above range, the precipitation of dissolved components cannot be sufficiently suppressed. The content of the specific substance in the absorption oil introduced into the cooling tower is preferably 32% by weight or less, more preferably 30% by weight or less, and still more preferably 28% by weight or less for the same reason as described above.

  In the present invention, by setting the total content of dibenzofuran and fluorene in the absorption oil within the above range, the cooling temperature of the absorption oil by the heat exchanger in the circulation step (1) described later is 30 ° C. or less, and further 20 ° C. In the following, it is possible to suppress the absorption oil from solidifying and precipitating on the surface of the heat exchanger, particularly even at 15 ° C. or lower. Furthermore, since the precipitation component is contained in the cooling water in the cooling of the raw material gas, the concentration of the precipitation component in the moisture is reduced by reducing the composition of the precipitation component in the absorption oil, and heat exchange is performed. When cooled by a vessel, it is possible to lower the temperature of the raw material gas without depositing deposits inside the heat exchanger.

  Conventionally, it has been known that a substance that solidifies and precipitates upon cooling is dissolved in the absorption oil after the crude light oil component is recovered by distillation in the recovery process. Moreover, the idea of changing the composition of the absorbing oil so as to lower the precipitation start temperature of the absorbing oil was also observed. However, no investigation has been made focusing on dissolved substances from the viewpoint of what kind of components should be suppressed in order to prevent solidification / precipitation.

  Usually, it is considered that reducing the most dissolved substance as much as possible or reducing the substance having a lower melting point is effective as a measure for suppressing precipitation, but the present inventors have examined As a result, the inventors have found that the above-described idea cannot exhibit a sufficient precipitation suppressing effect, and have reached the present invention. That is, it has been found that if the content of the specific substance is not more than a predetermined value, precipitation can be suppressed even if a compound having a higher melting point is dissolved. Further, it has been found that even if a specific substance is present in the absorbent oil, precipitation can be suppressed even if the absorbent oil is cooled if the content ratio is equal to or less than a predetermined value. Furthermore, the same effect was obtained not only for cooling the absorption oil but also for cooling the raw material gas.

  Usually, the content of the specific substance in the absorption oil is over 35% by weight. On the other hand, the content of the specific substance in the present invention is as described above, and the difference is only a few weight% in a small case. In general, in order to prevent solidification and precipitation, it is considered that the prevention effect is not exhibited unless the causative substances are significantly reduced. For this reason, if it is only a reduction in the content ratio as described above, it seems that it is difficult to significantly reduce the precipitation start temperature from the absorption oil, but in the present invention, the target substance is specified. As a result, it was found that an unexpected improvement effect was exhibited.

GC-MS (gas chromatograph mass spectrometer) is mentioned as a method of measuring content of the specific substance in absorption oil. Usually, chloroform or the like is used as a solvent, and a solution obtained by dissolving and dispersing absorption oil in this solvent is used as a sample. In the obtained data, the peak of the substance dissolved in the absorbing oil is detected together with the peak of the standard substance and the solvent. In the present invention, the content of the specific substance is calculated based on the total amount of the absorption oil. The means for confirming (monitoring) the content of the specific substance in the absorption oil introduced into the cooling tower is not limited, but examples include a method of sampling the absorption oil from the bottom of the cooling tower and analyzing the composition.

[3. Circulation process (1)]
The “circulation step” in the present invention refers to the water discharged from the cooling tower and the organic compound component contained in the raw material gas (organic compound component that is mainly an aromatic compound derived from the raw material gas) through a heat exchanger. This is a step of circulating through the cooling tower (see FIG. 2). More specifically, in the cooling step (1), it is preferable that the spray liquid or the like used for cooling the raw material gas is cooled with a heat exchanger and circulated again to the cooling tower.

  The cooling method by the heat exchanger is not limited, and a method using a refrigerant or a method not using a refrigerant may be used. From the viewpoint of cooling efficiency, a heat exchange system using a refrigerant is preferable. In addition, as a cooling method which does not use a refrigerant | coolant, the method etc. which cool the said metal block etc. using the metal block etc. which penetrated the flow path are mentioned, for example.

  The refrigerant used in the heat exchanger is not limited, and may be a gas, a liquid, or a mixture thereof, but is usually a liquid. Examples of the liquid refrigerant include water, oil (vegetable oil, animal oil, mineral oil, chemically synthesized oil, etc.), liquid nitrogen, acetone, ethylene glycol, and the like. As described above, absorbed oil can also be used as the refrigerant. . Among these, water or oil is preferable as the refrigerant. In addition, when using water as a refrigerant | coolant, seawater can also be used other than tap water or industrial water. Use of seawater as the refrigerant is preferable because the supply thereof is abundant and the temperature fluctuation is relatively small. Examples of the refrigerant of gas (including vapor and mist) include air, carbon dioxide (including dry ice), nitrogen, water vapor, chlorofluorocarbon, and ammonia. As the refrigerant, one of the above may be used, or two or more may be used in combination.

[4. Absorption process]
The “absorption process” in the present invention is a raw gas containing at least one of the coke oven gas and the pyrolysis furnace gas that has passed through the cooling process, and the crude light oil component contained in the gas is converted into the absorption oil. This is a process of absorbing (see FIG. 2). More specifically, the raw material gas is supplied to the absorption tower, the raw material gas and the absorbing oil are brought into contact with each other, and the crude light oil component in the raw material gas is absorbed by the absorbing oil.

<Absorbing oil>
Although the absorption oil used for this invention is not limited, Specifically, coal tar distillation fractionation oil, diesel oil, B heavy oil, etc. are mentioned. Among these, coal tar distillate fraction is preferable because of its simplicity available from a coke plant. The “coal tar distillation fraction oil” is an oil obtained by distilling coal tar and obtained from other than the bottom of the distillation column. Specific examples include carbol oil, naphthalene oil, anthracene oil, creosote oil, and the like.

  The total content of benzene, toluene and xylene contained in the absorption oil that absorbs the crude light oil component and is discharged from the absorption tower is usually about 1% by weight, but in the present invention, the crude light oil component is used as described above. Since it can collect | recover efficiently, it can be 1.1 weight% or more, Furthermore, it can be 1.2 weight% or more.

  In the present invention, since the absorption oil is used in a circulating manner, the absorption oil in the system exists in a state where the substance derived from the crude light oil component is dissolved in the absorption oil. In other words, even if the absorbing oil is derived from the oil exemplified above, it is substantially constituted as a mixture of the compounds mentioned as the crude light oil component. That is, as each process of the absorption process, the recovery process, and the like is circulated as in the present invention, the crude light oil component itself becomes the absorption oil, and circulates with its composition ratio varied.

<Absorption method>
The method for absorbing the crude light oil component from the raw material gas into the absorbing oil is not limited, but is usually performed in an absorption tower. “Absorption tower” means that absorption oil is charged from the upper part to the lower part of the tower and that the raw material gas is charged from the lower part to the upper part, and the absorption oil and the raw material gas are in contact with each other in the tower. Thus, the crude light oil component contained in the raw material gas is phase-shifted into the absorption oil. The method of charging the absorbing oil in the absorption tower is not limited, but it is preferable to use a spraying method.

[5. Collection process]
The “recovery step” in the present invention is a step of recovering the crude light oil component by distilling the absorbed oil that has absorbed the crude light oil component in a distillation tower (see FIG. 2).

  The distillation method in the recovery step is not particularly limited as long as it is based on a distillation tower, but steam distillation is preferable from the viewpoint of removing inorganic salts. That is, the absorption oil having absorbed the crude light oil component is supplied to the steam distillation tower and subjected to steam distillation, the crude light oil component and water are distilled from the top of the tower, and the absorption oil is recovered from the bottom of the tower. Hereinafter, the case of steam distillation will be described as an example in detail. However, when a distillation method other than steam distillation is employed, it can be implemented with appropriate modifications.

  Although the temperature of the absorption oil which absorbed the crude light oil component charged into a steam distillation tower is not limited, it is usually 100 to 200 ° C. In addition, although the temperature of the absorption oil which absorbed the crude light oil component and was discharged | emitted from the absorption tower is 15-50 degreeC normally, when this is directly charged into a steam distillation tower, the thermal energy required for distillation will become large, It is preferable that the temperature is raised to the above-mentioned temperature in advance and charged into the steam distillation column.

  As will be described later, the heat energy required to raise the temperature of the absorption oil that has absorbed the crude light oil component is heat using the heat of the high-temperature absorption oil that is discharged from the steam distillation tower and recycled to the absorption tower. It is preferable to exchange (see FIG. 2). In other words, it is preferable that the absorbed oil that has absorbed the crude light oil component and discharged from the absorption tower is used as a refrigerant in the cooling step described later. When heating is insufficient only by this heat exchange, another heating method such as a heater may be used in combination.

  The top temperature of the steam distillation column is set according to the composition of the crude light oil component to be recovered, but is preferably 50 to 107 ° C, more preferably 70 to 105 ° C, and 90 to 100 ° C. Is more preferable. By appropriately controlling the tower top temperature, the contents of dibenzofuran and fluorene in the absorption oil introduced into the cooling tower can be reduced.

  Since steam containing a crude light oil component and water usually flows out from the top of the steam distillation column, after condensing the steam, the crude light oil component and water are separated by a difference in specific gravity to recover the crude light oil. Since the steam distillation tower consumes a large amount of water vapor, the energy consumption is large. For this reason, it is preferable to make the equipment as compact as possible. In order to reduce the energy consumed in steam distillation at a constant feed gas throughput or a constant crude light oil component recovery amount, the content ratio (concentration) of the crude light oil component absorbed in the absorption oil in the absorption process is set. Need to be high. In this invention, since it can be set as the absorption oil which contains the crude light oil component in higher concentration, the quantity of the absorption oil which circulates in the system can be reduced. For this reason, since it becomes possible to reduce the usage-amount of the water vapor | steam in a collection | recovery process, it also becomes possible to make an installation compact.

Crude light oil components discharged together with water vapor from the top of the steam distillation tower and separated from water are mainly composed of benzene, toluene and xylene, but the total content of benzene, toluene and xylene in the crude light oil components The proportion is usually 70 to 100% by weight. After recovering the crude light oil component, the total content of benzene, toluene and xylene contained in the absorption oil discharged from the steam distillation tower is usually 1 to 5000 ppm by weight.

[6. Cooling step (2)]
The “cooling step (2)” in the present invention is a step of cooling the absorbed oil after recovering the crude light oil component through a heat exchanger and then supplying it again to the absorption tower (see FIG. 2). Although the temperature of the absorption oil discharged | emitted from a distillation tower is not limited, Usually, it is 150-190 degreeC. Even if the absorption oil at this temperature is recycled to the absorption tower as it is, the absorption of the crude light oil component from the raw material gas is negligible, so it is necessary to cool it to the above temperature with a heat exchanger.

  The cooling method by the heat exchanger is not limited, and a method using a refrigerant or a method not using a refrigerant may be used. From the viewpoint of cooling efficiency, a heat exchange system using a refrigerant is preferable. In addition, as a cooling method which does not use a refrigerant | coolant, the method etc. which cool the said metal block etc. using the metal block etc. which penetrated the flow path are mentioned, for example.

  The refrigerant used in the heat exchanger is not limited, and may be a gas, a liquid, or a mixture thereof, but is usually a liquid. Examples of the liquid refrigerant include water, oil (vegetable oil, animal oil, mineral oil, chemically synthesized oil, etc.), liquid nitrogen, acetone, ethylene glycol, and the like. As described above, absorbed oil can also be used as the refrigerant. . Among these, water or oil is preferable as the refrigerant. In addition, when using water as a refrigerant | coolant, seawater can also be used other than tap water or industrial water. Use of seawater as the refrigerant is preferable because the supply thereof is abundant and the temperature fluctuation is relatively small. Examples of the refrigerant of gas (including vapor and mist) include air, carbon dioxide (including dry ice), nitrogen, water vapor, chlorofluorocarbon, and ammonia. As the refrigerant, one of the above may be used, or two or more may be used in combination.

  One heat exchanger may be provided, but two or more heat exchangers may be provided. When two or more heat exchangers are used, they may be arranged in series or in parallel. Moreover, the heat exchanger using a different refrigerant | coolant can also be used together. As an aspect in which two or more heat exchangers are provided, a method using a heat exchanger that uses water as a refrigerant and a heat exchanger that uses absorbed oil discharged from the absorption tower after absorbing crude gas oil components as a refrigerant is preferable. It is. In this case, a heat exchanger using water as a refrigerant is provided on the downstream side (side near the absorption tower), and a heat exchanger using absorption oil as a refrigerant is provided on the upstream side (side near the distillation tower). It is preferable to arrange (see FIG. 2). By disposing in this way, energy loss in the system can be reduced and cooling to a lower temperature is possible, which is preferable.

[7. Removal step (1)]
In the present invention, the “removal step (1)” can be optionally provided. The “removal step (1)” in the present invention refers to supplying a part of the absorption oil after recovering the crude light oil component discharged from the distillation tower to the de-pitch tower, and dibenzofuran and / or contained in the absorption oil. Or it is the process of removing at least one part of a fluorene (refer FIG. 3). Thus, after absorption oil is supplied to a depitch tower and after a removal process (1), it is preferable to be supplied to the said distillation tower. By providing such a pitch removing tower, the contents of dibenzofuran and fluorene in the absorption oil introduced into the cooling tower can be further reduced.

  The method for removing dibenzofuran and / or fluorene from the absorbing oil in the removing step (1) is not particularly limited as long as it is a depitch tower, but it is preferably removed by steam distillation. Absorbed oil discharged from the steam distillation column in the recovery process contains a heavy component (pitch component) such as dibenzofuran, fluorene, acenaphthene, and phenanthrene while the content of benzene, toluene, and xylene is reduced. . In the depitch tower, these pitch components can be separated and removed from the absorbed oil.

  As described above, the absorption oil after the crude light oil component is recovered from the distillation tower in the recovery step is introduced into the removal step (1). Specifically, part of the absorbed oil discharged in the recovery step can be introduced into the removal step (1), and the remaining portion can be introduced into the cooling step (2).

  Hereinafter, detailed conditions for removing dibenzofuran and / or fluorene by a depitch column will be described. However, when other methods are adopted, the method can be appropriately changed and implemented. Although the temperature of the absorption oil discharged | emitted from a collection | recovery process and charged into a depitch tower is not limited, Usually, it is 150-180 degreeC. The tower top temperature of the pitch removing tower is not limited and is appropriately set depending on the composition of the pitch component to be removed, etc., but is usually 150 to 195 ° C. The content ratio of the crude light oil component in the absorption oil from which the pitch component has been removed discharged from the pitch removal tower is usually 37 to 32% by weight.

  The pitch component discharged from the pitch removal tower in the removal step (1) includes dibenzofuran and fluorene, and the total content of dibenzofuran and fluorene in the total pitch component is usually 30 to 70% by weight, 50 It is preferable that it is weight% or more.

  Although the pitch component discharged | emitted by the removal process (1) can also be used as a fuel, it can be utilized as various raw materials. Specifically, it can be used as pitch coke, creosote oil or the like.

[8. Removal step (2)]
In the present invention, the “removal step (2)” can be optionally provided. The “removal step (2)” in the present invention is a step of removing naphthalene by allowing the raw material gas introduced into the cooling step to be absorbed by the absorption oil in the denaphthalene tower (see FIG. 4). Further, it is preferable to provide the removal step (2) in combination with the removal step (1) (see FIG. 5).

  When providing a removal process (2), absorption oil is normally supplied to a denaphthalene tower, and is introduce | transduced into the said cooling tower through a denaphthalene tower. At this time, it is preferable that the absorption oil is introduced into the cooling tower by being entrained together with the raw material gas.

[9. Circulation process (2)]
In the present invention, the “circulation step (2)” can be optionally provided. The “circulation step (2)” in the present invention is a step in which the oil absorbed after the recovery step is cooled by a heat exchanger and then circulated to the denaphthalene tower (FIG. 6). The circulation step (2) is provided in combination with the removal step (2), but is preferably provided in combination with the removal step (1) (see FIG. 7).

  In the cooling step (2), it is preferable that the absorbing oil used in the denaphthalene tower is branched and introduced from the cooling step (2) after being cooled by the heat exchanger. In this case, the contents of dibenzofuran and fluorene in the cooling step (2) and their contents introduced into the denaphthalene tower are usually the same.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded.

<Analysis of coke oven gas composition>
The gas to be analyzed was analyzed using gas chromatography (2000-EX-2, manufactured by Toa DKK Corporation).

<Analysis of organic compound component composition in absorbing oil and drain>
The liquid to be analyzed was dissolved in chloroform and analyzed using GC-MS (manufactured by Agilent, 7890GC-5975 MSD & Shimadzu GC 2014). In the analysis, a fixed volume was injected into the GC-MS apparatus with a syringe, and the composition of each component was calculated from a calibration curve from the obtained component and the peak area of the internal standard (ethylphenol).

[Example 1]
Coke was produced by dry distillation of coal (“coking coal A” in which a plurality of types of coal and a binder were mixed) in a chamber-type coke oven. From the coke oven gas discharged at the time of coke production, a purification treatment for reducing sulfur compounds, nitrogen compounds, benzoles and the like was performed, and the purified gas was used as a raw material gas. The results of analyzing the composition of the source gas are shown in Table-1. In addition to the gas composition shown in Table 1, the raw material gas contained 200 mg / m ³ of tar dust as a solid content.

  The apparatus shown in FIG. 7 was provided and operated as an apparatus for recovering crude light oil components from the raw material gas. The coke oven gas was supplied to the denaphthalene tower and absorbed by the absorbing oil in the denaphthalene tower to remove naphthalene, and then the gas was cooled by the cooling tower. The cooled gas was transported to the absorption tower and absorbed by the absorption oil in the absorption tower. At this time, the temperature of the raw material gas charged into the absorption tower was 30 ° C., and the temperature of the absorption oil was 35 ° C. The temperature of the absorption oil (referred to as “RO liquid”) discharged from the absorption tower was 33 ° C. This was subjected to heat exchange with a high-temperature absorbing oil circulated from the distillation tower to the absorption tower, heated to 180 ° C., and charged into the distillation tower.

  In the distillation column, the temperature at the top of the column was 98 ° C., the crude light oil component (referred to as “BTX solution”) was recovered from the top of the column, and the absorbed oil (referred to as “AO solution”) was discharged from the bottom. The AO liquid was 180 ° C. at the time of discharge from the distillation column, but after cooling by first exchanging heat with the above-mentioned RO liquid, it was further cooled to 35 ° C. by a heat exchanger using water as a refrigerant. Circulated to the absorption tower. In addition, the AO liquid was transported to the denaphthalene tower from a line branched between the two heat exchangers. Further, a part of the AO liquid before being transferred to the heat exchanger was supplied to the pitch removal tower, and the pitch component was extracted. The gas distilled from the top of the depitch tower was circulated to the distillation tower.

  The AO liquid circulated to the denaphthalene tower was entrained in the cooling tower together with the coke oven gas, and the AO liquid was discharged from the bottom of the cooling tower and circulated to the cooling tower after passing through the heat exchanger.

  Table 2 shows the results of sampling the AO solution and analyzing the composition of the precipitated components in AO when the above operation is in a steady state.

  As shown in Table 2, the total content of dibenzofuran and fluorene in the absorption oil (AO liquid) discharged from the distillation tower and introduced into the denaphthalene tower was 31% by weight.

[Example 2]
The apparatus shown in FIG. 7 was provided and operated as an apparatus for recovering crude light oil components from the raw material gas. It implemented like Example 1 except having transferred the whole quantity of AO liquid to the heat exchanger, without using a depitch tower.

  Table 2 shows the results of sampling the AO solution and analyzing its composition when the above operation reaches a steady state. As shown in Table 2, the total content of dibenzofuran and fluorene in the absorption oil (AO liquid) discharged from the distillation column and introduced into the heat exchanger was 35% by weight.

[Comparative Example 1]
The apparatus shown in FIG. 7 was provided and operated as an apparatus for recovering crude light oil components from the raw material gas. The same operation as in Example 1 was performed except that the top temperature of the distillation column was 108 ° C.

  Table 2 shows the results of sampling the AO solution and analyzing its composition when the above operation reaches a steady state. As shown in Table 2, the total content of dibenzofuran and fluorene in the absorption oil (AO liquid) discharged from the distillation tower and introduced into the denaphthalene tower was 41% by weight.

  As for the AO liquids at the bottoms of the distillation towers of Examples 1 and 2 and Comparative Example 1, the state of precipitation when cooled was confirmed. The AO liquid of Comparative Example 1 was a liquid that started to precipitate at about 16 to 20 ° C. However, the AO liquids of Examples 1 and 2 could be liquids that did not precipitate even when cooled to 16 ° C. or lower.

  When the liquid entrained from denaphthalene and discharged from the bottom of the cooling tower was analyzed, the contents of dibenzofuran and fluorene were 19% by weight in Example 1 and 25% by weight in Example 2. . Thereby, in Example 1 using the depitch tower, the contents of dibenzofuran and fluorene are less than in Example 2 where the depitch tower was not used, and it is possible to lower the cooling by the heat exchanger. I know that there is. Therefore, the coke oven gas in the cooling tower can be cooled to a lower temperature.

Claims (4)

A cooling step (1) for cooling the raw material gas containing at least one of the coke oven gas and the pyrolysis furnace gas in a cooling tower;
A circulation step (1) for circulating water discharged from the cooling tower and organic compound components contained in the raw material gas to the cooling tower via a heat exchanger;
An absorption step in which the crude gas oil component contained in the gas is absorbed into the absorption oil from the raw material gas that has undergone the cooling step (1),
A recovery step of recovering the crude light oil component by distilling the absorbed oil that has absorbed the crude light oil component in a distillation tower;
It has a cooling step (2) in which the absorption oil after the crude light oil component is recovered is cooled through a heat exchanger and then supplied to the absorption step again, and the total content of dibenzofuran and fluorene is 35 in the cooling tower. A method for recovering crude light oil components in a gas, wherein absorbing oil that is not more than% by weight is introduced.   The crude light oil component discharged from the distillation column is supplied to the de-pitch column after a part of the recovered oil oil is recovered, passed through the removal step (1) for removing the pitch component, and then circulated to the distillation column. The recovery method described in 1.   The recovery method according to claim 1 or 2, wherein the raw material gas introduced into the cooling tower is subjected to a removing step (2) in which naphthalene is removed by absorbing oil in a denaphthalene tower.   The recovery method according to claim 3, further comprising a circulation step (2) in which the absorption oil after the recovery step is cooled by a heat exchanger and then circulated to the denaphthalene tower.

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