JP6540457B2 - Method of recovering crude gas oil component in gas - Google Patents

Description

The present invention relates to a method for recovering a crude gas oil component contained in coke oven gas or pyrolysis furnace gas.
More specifically, the present invention relates to coke oven gas by-produced during dry distillation of coal in a coke oven to produce coke, or in pyrolysis furnace gas generated during pyrolysis of coal in a pyrolysis furnace. The present invention relates to a method for recovering a crude gas oil component contained therein.

Coke oven gas generated during dry distillation of coal in a coke oven to produce coke, or pyrolysis furnace gas generated during pyrolysis of coal in a pyrolysis furnace (hereinafter referred to collectively as “coke oven gas The main components of “etc.” are hydrogen, methane, carbon monoxide, carbon dioxide, etc., but in addition to these main components, tar, ammonia, hydrogen sulfide, hydrocarbon gases other than methane, It contains crude gas oil, hydrogen cyanide and many other components.
Since coke oven gas and the like are generated at high temperature from coke ovens and coal pyrolysis furnaces, they are first cooled, and then the above components are separated and recovered. The components recovered from coke oven gas and the like are utilized as fuel and various raw materials. Among them, crude gas oil components recovered from coke oven gas etc. contain a large amount of aromatic hydrocarbon compounds (aromatic components) such as benzene, toluene, xylene and the like compared to petroleum oils of petroleum origin Therefore, it has high utility value as various raw materials.

  Although various methods are adopted for recovery of crude light oil components from coke oven gas etc., as a typical method, coke oven gas etc. is brought into contact with absorbent oil in an absorption tower and contained in coke oven gas etc. To absorb the crude light oil component to be absorbed into the absorbing oil and distilling the absorbing oil in the distillation column to separate and recover the crude light oil component from the absorbing oil and recycle the absorbing oil after separation and recovery to the absorber . (See Figure 1)

In the above method, in order to efficiently recover crude light oil components such as benzene, toluene and xylene from coke oven gas etc., a large amount of crude light oil components are absorbed in the absorbing oil in the absorption tower and the efficiency in the distillation tower Good separation is preferred. For this purpose, it is necessary to lower the temperature of the absorbing oil introduced to the absorption tower and to increase the amount of crude light oil component absorbed by the unit amount of absorbing oil.
On the other hand, as described above, since the absorbing oil is used in circulation, it is necessary to cool the absorbing oil discharged at high temperature in the distillation column using a cooler. Therefore, in order to recover the crude light oil efficiently, it is preferable to cool the absorbent oil discharged from the distillation column to a lower temperature and supply it to the absorber.

However, since various components are dissolved in the absorbent oil discharged from the distillation column, when the temperature of the absorbent oil is lowered excessively, these dissolved components are deposited on the inner wall of the cooler or the pipe. The precipitation of dissolved components from the absorbed oil on the inner wall of the cooler or pipe leads to a decrease in cooling capacity and an increase in flow and gas resistance, which in turn leads to blockage of the cooler and pipe. Because it was a problem.
Conventionally, it is necessary to arrange two units of coolers in parallel and bypass them, and when one cooler is clogged, it is necessary to switch to the other cooler and open the clogged cooler for open cleaning. The However, since a large amount of labor is required to open and clean the cooler, a method for preventing the precipitation of dissolved components while cooling the absorbent oil to a lower temperature is desired.

As a means for preventing the dissolved components in the absorbing oil from depositing in a cooler or the like, for example, a method of washing by flowing tar heated at 60 ° C. or higher at a predetermined interval in a pipe through which the absorbing oil flows is disclosed (See Patent Document 1).
In addition, as a method of efficiently recovering the crude light oil component from the absorbing oil, the composition of the absorbing oil at each site where the absorbing oil circulates is determined, the precipitation start temperature of the absorbing oil is calculated from the composition, and then the operation of each site is performed. There is disclosed a method of changing the composition of the absorbing oil so as to set the conditions above the precipitation start temperature or to lower the precipitation start temperature of the absorbing oil (see Patent Document 2).

JP 2004-138359 A JP, 2005-194410, A

As described above, conventionally, when crude gas oil components are recovered from coke oven gas or the like, precipitates are not washed away or deposited as a means for preventing precipitation of the dissolved components in the absorbent oil in the cooler or the like. Only the method of cooling in the temperature range was disclosed. However, the former method requires a long time for washing, and a sufficient precipitation suppression effect can not be seen. The latter method is not only complicated because it is necessary to analyze the composition of the absorbing oil at each facility, but it can not achieve the original purpose of efficiently recovering the crude gas oil component in the first place.
Also, as described above, although the method of changing the composition of the absorbing oil so as to lower the precipitation start temperature of the absorbing oil is disclosed, a study focusing on dissolved substances from the viewpoint of what kind of component precipitation should be suppressed Under the present circumstances, no sufficient effect has been obtained yet.

An object of the present invention is to provide a method for efficiently recovering crude gas oil components contained in coke oven gas or pyrolysis furnace gas.
Further, according to the present invention, in recovering crude light oil components contained in the gas using the absorbing oil, even if the temperature of the absorbing oil is lowered to increase the absorption efficiency, precipitation and the like does not occur in the heat exchangers and pipes. An object of the present invention is to provide a method for recovering crude gas oil components.
The present invention is a crude that is capable of efficiently absorbing the crude light oil component contained in coke oven gas or thermal decomposition furnace gas into the absorbent oil and reducing the content ratio of the crude light oil component remaining in the gas after absorption. An object is to provide a method for recovering a light oil component.
An object of the present invention is to provide a method for recovering crude gas oil component that can efficiently recover crude gas oil component and can reduce energy consumption with compact equipment.

  The inventors of the present invention conducted intensive studies to solve the above problems, and as a result, among the various compounds dissolved in the absorbing oil, the content ratio of the specific compound is reduced to a specific value or less. The inventors have found that the problems can be solved and completed the present invention.

That is, the present invention is summarized as the following [1] to [7].
[1] From the raw material gas containing at least one of coke oven gas and thermal decomposition furnace gas, the “absorbing step” for absorbing the crude gas oil component contained in the raw material gas into the absorbing oil, the crude gas oil component was absorbed A “recovery step” of recovering the crude light oil component by distilling the absorbent oil in a distillation column, the absorbent oil after recovery of the crude light oil component is cooled through a heat exchanger, and then supplied again to the absorption step A method for recovering a crude gas oil component in gas, comprising a "cooling step", wherein the total content of dibenzofuran and fluorene in the absorbing oil introduced into the heat exchanger in the cooling step is 35% by weight or less. [2] The method for recovering a crude gas oil component according to [1], wherein the crude gas oil component contains at least any component selected from benzene, toluene and xylene.
[3] or [2] having a "removal step" of removing at least a portion of dibenzofuran and / or fluorene contained in the absorbing oil from the absorbing oil after recovering the crude light oil component in the collecting step [1] or [2] The recovery method of the crude light oil component as described in 4.
[4] The method for recovering crude light oil component according to [3], wherein at least a part of the absorbent oil subjected to the removal step is returned to the distillation column in the recovery step.
[5] The method for recovering crude light oil component according to [3] or [4], wherein the absorbent oil subjected to the recovery step is distributed and supplied to the cooling step and the removal step.
[6] The heat exchanger according to any one of [1] to [5], including a heat exchanger using water as a refrigerant and a heat exchanger using absorbing oil having the crude gas oil component absorbed as a refrigerant. Recovery method of crude gas oil component. [7] In the recovery method according to any one of [3] to [6], the dibenzofuran and / or fluorene removed in the removal step is mixed with tar to form a pitch coke raw material, which is coked A method of producing pitch coke characterized by

ADVANTAGE OF THE INVENTION According to this invention, the method of collect | recovering efficiently the crude light oil component contained in coke-oven gas or thermal decomposition furnace gas can be provided.
According to the present invention, when crude gas oil components contained in gas are recovered using an absorbing oil, precipitation occurs in a heat exchanger, piping, etc. even if the temperature of the absorbing oil is lowered to increase absorption efficiency. It is possible to provide a method for recovering crude crude oil components that do not exist.
According to the present invention, since the crude light oil component contained in coke oven gas or pyrolysis furnace gas can be efficiently absorbed into the absorbing oil, the content ratio of the crude light oil component remaining in the gas after absorption is low. It is possible to reduce the burden of purification.
According to the present invention, since crude crude oil components can be recovered efficiently, the equipment can be made compact, and energy consumption can be reduced.

It is a schematic diagram which shows an example of the general method of collect | recovering crude gas oil components from coke-oven gas. It is a schematic diagram which shows an example of the collection | recovery method of the crude gas oil component of this invention. It is a schematic diagram which shows an example of the collection | recovery method of the crude gas oil component of this invention. It is a schematic diagram which shows an example of the collection | recovery method of the crude gas oil component of this invention. It is a schematic diagram which shows an example of the collection | recovery method of the crude gas oil component of this invention. It is a schematic diagram which shows an example of the collection | recovery method of the crude gas 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 scope of the present invention. In the following, "mass%" and "wt%", and "mass part" and "part by weight" are respectively synonymous.

The present invention absorbs the crude gas oil component contained in the raw material gas from the raw material gas containing at least one of the coke oven gas and the thermal decomposition furnace gas in the absorbing oil, and absorbs the crude gas oil component. The recovered oil is distilled in a distillation column to recover the crude gas oil component, and after the crude oil component is recovered, the absorbed oil is cooled via a heat exchanger and then supplied to the absorption step again. A crude gas oil component in gas comprising a “cooling step” and having a total content of dibenzofuran and fluorene in the absorbing oil introduced into the heat exchanger in the cooling step at 35% by weight or less It is a recovery method.
In the present invention, coke oven gas and pyrolysis furnace gas may be collectively referred to as "coke oven gas etc."
Hereinafter, the present invention will be described in detail.

[1. Raw material gas]
<Coke oven gas>
The coke oven gas means a gas generated from the inside of the coke oven when producing coke from coal. Specifically, coke oven gas is a gas generated when heating and distilling coal at a temperature of 600 ° C. or more to produce coke, and as a general composition, 10 to 70% by volume of hydrogen and 20 to 70 of methane. % By volume, hydrocarbons other than methane (olefins such as ethylene etc.) 1 to 15% by volume, carbon monoxide 4 to 9% by volume, carbon dioxide 1 to 6% by volume, nitrogen 1 to 13% by volume, oxygen 0 to 0 .5% by volume, 0.3 to 1.5% of sulfur compounds such as hydrogen sulfide, 0.3 to 1.8% of nitrogen compounds such as ammonia, 0.1 to 1.8% by volume of benzols, and other coals It contains trace constituents derived from it.

  As the coke oven gas used in the present invention, the gas of 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 which 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, for example, using a catalyst such as a Ni-Mo-based catalyst or a Co-Mo-based catalyst that is a catalyst for deoxygenation reaction that also has an action as a desulfurization catalyst. When these catalysts are used, deoxygenation and desulfurization are carried out by hydrogen addition with hydrogen in coke oven gas. The pretreatment may be performed according to a conventional method, for example, the reactor inlet temperature is about 200 to 350 ° C., the pressure in the reactor is about 0.5 to 5.0 MPaG, and the reactor outlet temperature is about 100 to 450 ° C. Just do it. Also, for example, coke oven gas may be sent to an adsorption desulfurizer to perform adsorption desulfurization by ZnO.
Generally, the concentration of each component of the coke oven gas subjected to the pretreatment is 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 The concentration of the other components is substantially unchanged before and after the purification treatment.

Although the composition of the coke oven gas used in the present invention is not limited, it usually contains hydrogen, carbon dioxide, carbon monoxide, methane, nitrogen and the like as main components, and also contains crude light oil components.
Although the content rate of the crude gas oil component in the coke oven gas used in the present invention is not limited, it is usually 1 to 5000 ppm by volume. If the content ratio of the crude gas oil component in the coke oven gas is within the above range, the crude gas oil component tends to be efficiently absorbed by the absorbing oil in the absorption step, which is preferable. The lower limit of the content of the crude gas 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 vol. It is more than ppm. Further, 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 the feature of the present invention that the useful components are recovered more efficiently, the total content ratio of benzene, toluene and xylene contained in coke oven gas is preferably 1 to 4000 ppm by volume. The lower limit of the total content ratio 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 3,000. It is less than volume ppm.

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

<Pyrolytic furnace gas>
Pyrolysis furnace gas means the gas generated when pyrolyzing coal in a pyrolysis furnace. Although the composition of the pyrolysis furnace gas used in the present invention is not limited, it usually contains hydrogen, carbon dioxide, carbon monoxide, methane, nitrogen and the like.
Although the content rate of the crude gas oil component in the pyrolysis furnace gas used in the present invention is not limited, it is usually 1 to 5000 ppm by volume. If the content ratio of the crude gas oil component in the pyrolysis furnace gas is within the above range, the crude gas oil component tends to be efficiently absorbed by the absorbing oil in the absorption step, which is preferable. Further, the lower limit and the upper limit of the preferable content ratio are the same as those of the coke oven gas described above.
In particular, from the viewpoint of the feature of the present invention that the useful components are recovered more efficiently, the total content ratio of benzene, toluene and xylene contained in the pyrolysis furnace gas is preferably 1 to 4000 ppm by volume. Further, the lower limit and the upper limit of the preferable total content ratio are the same as those of the coke oven gas described above.

In the present invention, coke oven gas and pyrolysis furnace gas may be used in combination as the source gas. Also when using coke oven gas and thermal decomposition furnace gas together, it is preferable that the content rate of the crude light oil component in the raw material gas which mixed both is 1-5000 volume ppm.
In the present invention, the coke oven gas and the thermal decomposition furnace gas do not necessarily have to be formed completely in a gas state, and may be aerosols such as dust, fume, smoke, mist, etc. You may contain the thing of a state. Furthermore, it also includes liquid or solid substances formed by gas aggregation or coagulation.
The gas composition in the coke oven gas and the pyrolysis furnace gas and the content ratio of the crude gas 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 In some cases). The other raw materials may be gaseous or solid or liquid, but are preferably gaseous in a state of being mixed with coke oven gas and / or pyrolysis furnace gas (including the states described above) .

<Crude light oil component>
In the present invention, crude gas oil components include, in a broad sense, those generally called light oils (light oils), but specifically mean components capable of being absorbed from raw material gas into absorbing oil, at least benzene, It is preferable to contain any component selected from toluene and xylene. Usually, the crude light oil component further contains styrene, benzofuran, indene, naphthalene, methyl naphthalene, biphenylene, acenaphthene, biphenyl, ethyl naphthalene, dimethyl naphthalene, 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 a raw material gas to be introduced into the absorption step described later, the total content of benzene, toluene and xylene in the total crude gas oil component contained in the raw material gas is preferably 10% by volume or more, and 30% by volume or more It is more preferable that the content be 50% by volume or more. The upper limit of the total content ratio of benzene, toluene, and xylene in the total crude gas oil component is not limited and may be 100% by volume, but is usually 90% by volume or less.

[2. Absorption process]
The “absorption step” in the present invention is a step of absorbing crude gas oil components contained in the gas from the raw material gas containing at least one of coke oven gas and thermal decomposition furnace gas into the absorbing oil. is there. More specifically, the raw material gas is supplied to the absorption tower, the raw material gas and the absorbing oil are brought into contact, and the crude light oil component in the raw material gas is absorbed into the absorbing oil.

Absorbed oil
Although the absorbent oil used in the present invention is not limited, specific examples thereof include coal tar distilled fractionated oil, diesel oil, B heavy oil and the like. Among these, coal tar distilled fractionated oil is preferable in view of the convenience available from the coke plant.
The coal tar distilled fractionated oil is an oil obtained by distilling coal tar, and is an oil obtained from other than the bottom of the distillation column. Specific examples thereof include carbol oil, naphthalene oil, anthracene oil, creosote oil and the like.

  In the present invention, since the absorbing oil is used in circulation, the absorbing oil in the system is present in a state in which the substance derived from the crude light oil component is dissolved in the above absorbing oil. In other words, even if the absorbing oil is derived from the oil exemplified above, it is configured substantially as a mixture of the compounds listed above as the crude light oil component. That is, as each process such as the absorption process and the recovery process is circulated as in the present invention, the crude light oil component itself substantially becomes an absorbent oil, and the composition ratio is changed and circulated.

<Absorption method>
The method for absorbing the crude gas oil component from the raw material gas into the absorbing oil is not limited, but is usually performed in an absorption tower.
In the absorption tower, the absorbent oil is charged from the top to the bottom in the tower, and the source gas is charged from the bottom to the top, and the absorbent oil and the source gas contact in the tower, It is an apparatus in which the crude light oil component contained in the raw material gas is phase shifted in the absorbing oil. Although the method of charging the absorbing oil in the absorption tower is not limited, it is preferable to use spray spraying.

The temperature of the raw material gas charged to the absorption tower is not limited, but is usually 20 to 50 ° C.
The temperature of the absorbing oil charged into the absorption tower is not limited, but is usually about 30 to 50 ° C. because it is necessary to control the temperature to such an extent that the heat exchanger does not clog in the cooling step described later. As the temperature is lower, the absorption efficiency of the crude gas oil component in the raw material gas is enhanced. In the present invention, by controlling the proportion of components dissolved in the absorbing oil, the temperature of the absorbing oil charged to the absorption tower is made 30 ° C. or less, further 25 ° C. or less, particularly 20 ° C. or less be able to.
The total content of benzene, toluene and xylene contained in the absorbing oil which absorbs the crude gas oil component and is discharged from the absorber is usually about 1% by weight, but in the present invention, the crude gas oil component is Since it can collect | recover efficiently, it can be made into 1.1 weight% or more, and also 1.2 weight% or more.

[3. Recovery process]
The "recovery step" in the present invention is a step of recovering the crude light oil component by distilling the absorbing oil having absorbed the crude light oil component in a distillation column.

Although the distillation method in the recovery step is not limited, steam distillation is preferable from the viewpoint of removing the inorganic salt. That is, the absorbing oil having the crude gas oil component absorbed therein is supplied to a steam distillation column for steam distillation, the crude gas oil component and water are distilled from the column top, and the absorbing oil is recovered from the column bottom.
Hereinafter, although the case of steam distillation is made into an example and details are explained, when changing distillation methods other than steam distillation, it can change suitably and can carry out.
Although the temperature of the absorption oil which absorbed the crude gas oil component charged into a steam distillation column is not limited, it is usually 100 to 200 ° C. In addition, although the temperature of the absorption oil which absorbed crude light oil components and was discharged from the absorption tower is usually 15 to 50 ° C, if this is charged into the steam distillation column as it is, the thermal energy required for distillation becomes large, It is preferable that the temperature is raised beforehand to the above temperature and charged into the steam distillation column.

As the thermal energy required to raise the temperature of the absorbing oil having absorbed the crude gas oil component, as described later, heat is utilized by utilizing the heat of the high-temperature absorbing oil which is discharged from the steam distillation column and recycled to the absorber. It is preferable to replace (see FIG. 2). In other words, it is preferable to utilize the absorption oil which absorbed the crude light oil component and was discharged from the absorption tower as a refrigerant in the cooling step described later. If heating is insufficient only by this heat exchange, other heating methods such as a heater may be used in combination.
The temperature at the top of the steam distillation column is not limited and is set depending on the composition of the crude light oil component to be recovered, but is usually 95 to 110 ° C.

Since a crude gas oil component and a steam containing water usually flow out from the top of the steam distillation column, the crude gas oil component and water are separated at a specific gravity difference to recover the crude gas oil after condensation thereof.
The steam distillation column consumes a large amount of steam, so 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 processing amount of raw material gas or a constant recovery amount of crude light oil components, the content ratio (concentration) of crude light oil components absorbed by the absorbing oil in the absorption step You need to raise it. In the present invention, since the absorbing oil containing the crude gas oil component at a higher concentration can be obtained, the amount of absorbing oil circulating in the system can be reduced. As a result, the amount of water vapor used in the recovery step can be reduced, and the equipment can be made compact.

The crude gas oil component discharged from the top of the steam distillation column with steam and separated from water is mainly composed of benzene, toluene and xylene, but the total content of benzene, toluene and xylene in the crude gas oil component The proportion is usually 70 to 100% by weight.
The total content of benzene, toluene, and xylene contained in the absorbent oil discharged from the steam distillation column after recovering the crude gas oil component is usually 1 to 5000 ppm by weight.

[4. Cooling process]
The “cooling step” in the present invention is a step of supplying the absorbing oil after the crude light oil component is recovered to the absorption step after it is cooled through a heat exchanger.
The temperature of the absorbing oil discharged from the steam distillation column is not limited, but is usually 150 to 190 ° C. 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 slight, so it is necessary to cool it by the heat exchanger to the above temperature.
The method of cooling by the heat exchanger is not limited, and a method using a refrigerant may be used, or a method not using a refrigerant may be used. From the viewpoint of the cooling efficiency, it is preferable to use a heat exchange method with a refrigerant. In addition, as a cooling method which does not use a refrigerant | coolant, the method of cooling the said metal block etc. are mentioned, for example using the metal block etc. which penetrated the flow path.

The refrigerant used for the heat exchanger is not limited, and may be gas or liquid, or a mixture thereof, but is usually liquid.
Examples of the liquid refrigerant include water, oil (vegetable oil, animal oil, mineral oil, chemically synthesized oil, etc.), liquid nitrogen, acetone, ethylene glycol, etc. As described above, absorbing oil can also be used as a refrigerant. . Among them, water or oil is preferable as the refrigerant. In addition, when using water as a refrigerant | coolant, sea water can also be used other than drinking water and industrial water. It is preferable to use seawater as the refrigerant because the supply is abundant and the temperature fluctuation is relatively small.
Examples of gas (including vapor and mist) refrigerants include air, carbon dioxide (including dry ice), nitrogen, water vapor, fluorocarbons, and ammonia.
As a refrigerant | coolant, 1 type in the above may be used and 2 or more types may be used together.

The heat exchanger may be a single heat exchanger, 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. Also, heat exchangers using different refrigerants can be used in combination.
As an embodiment in which two or more heat exchangers are provided, a system using a heat exchanger using water as a refrigerant and a heat exchanger using crude oil as a refrigerant and absorbing oil discharged from the absorption tower as a refrigerant is preferable. It is. In this case, a heat exchanger using water as a refrigerant is provided downstream (side closer to the absorption tower), and a heat exchanger using an absorbing oil as refrigerant is provided upstream (side near the steam distillation column), and these are connected in series. It is preferable to arrange in (refer FIG. 2). By arranging in this manner, energy loss in the system can be reduced, and cooling to a lower temperature is possible, which is preferable.

In the present invention, the total content of dibenzofuran and fluorene in the absorbing oil introduced into the heat exchanger in the cooling step is 35% by weight or less. Hereinafter, the total content of dibenzofuran and fluorene is referred to as “content ratio of specific substance”.
If the content ratio of the specific substance in the absorbing oil introduced into the heat exchanger is 35% by weight or less, the substance dissolved in the absorbing oil will precipitate even if the cooling temperature in the heat exchanger is lowered. Can be suppressed.
On the other hand, when the content ratio of the specific substance exceeds 35% by weight, even if the content ratio of other components (components other than dibenzofuran and fluorene) in the absorbing oil is reduced, precipitation of dissolved components is sufficiently suppressed. I can not do it. For example, acenaphthene (melting point: 92 ° C), which has a melting point higher than that of dibenzofuran (melting point: 81 ° C), is significantly reduced even though it is contained in a large amount in the absorbing oil. If the content ratio of the specific substance is not within the above range, precipitation of the dissolved component can not be sufficiently suppressed.

The content ratio of the specific substance in the absorbing oil introduced into the heat exchanger 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 absorbing oil to the above range, the cooling temperature of the absorbing oil by the heat exchanger is 30 ° C. or less, further 20 ° C. or less, particularly 15 ° C. or less Also, it can be suppressed that the absorbing oil solidifies and precipitates on the heat exchanger surface.
Although the lower limit of the content ratio of the specific substance in the absorbing oil introduced into the heat exchanger is not limited, it requires a large amount of energy to reduce the content ratio excessively, so it is usually at least 1% by weight, Preferably it is 5 weight% or more.

Heretofore, it has been known that a substance which solidifies and precipitates upon cooling is dissolved in the absorbent oil after crude gas oil components are recovered by distillation in the recovery step. In addition, the idea of changing the composition of the absorbing oil so as to lower the precipitation onset temperature of the absorbing oil was also seen. However, no consideration has been given to dissolved substances in terms of what kind of component precipitation should be suppressed in order to prevent solidification and precipitation.
Under normal circumstances, it is thought that reducing the most dissolved substances as much as possible or reducing the substance with a lower melting point is effective as a measure to suppress precipitation, but the inventors examined As a result, it has unexpectedly been found that the above-described idea can not exert a sufficient precipitation suppressing effect, and the present invention has been achieved.

That is, it was found that if the content ratio of the specific substance is set to a predetermined value or less, precipitation can be suppressed even if a compound having a higher melting point is dissolved. In addition, 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.
Usually, the content of the specific substance in the absorbing oil introduced into the heat exchanger is 36% by weight or more. On the other hand, the content ratio of the specific substance in the present invention is as described above, and the difference is only a few weight% in small cases. Generally, in order to prevent solidification and precipitation, it is considered that the prevention effect can not be exhibited unless the substance causing the reduction is significantly reduced. For this reason, it is thought that it is difficult to significantly lower the precipitation start temperature from the absorbing oil if it is only the reduction of the content ratio as described above, but in the present invention, the target substance is identified. It could be found that unexpected reduction effects are produced by reducing it.

  GC-MS (gas chromatograph mass spectrometer) is mentioned as a method of measuring the content rate of the specific substance in absorption oil. Usually, chloroform or the like is used as a solvent, and a solution obtained by dissolving or dispersing the absorbing oil in this solvent is used as a sample. In the obtained data, peaks of substances dissolved in the absorbing oil are detected together with peaks of the standard substance and the solvent. In the present invention, the content ratio of the specific substance is calculated based on the total amount of the absorbing oil.

Although the means to confirm (monitor) the content rate of the specific substance in absorption oil introduced into a heat exchanger at a cooling process is not limited, For example, the following methods are mentioned.
(1) From the distillation column in the recovery step, the absorbent oil is sampled from the piping of the heat exchanger tank and composition analysis is performed.
(2) In the piping of the heat exchanger from the distillation tower in the recovery step, the composition analysis of the absorbing oil is performed online.
(3) The steady operation is performed by setting the composition of the absorbing oil in advance in the process design stage.

  The means for setting the content ratio of the specific substance in the absorbing oil introduced into the heat exchanger within the range specified above is not limited, and is achieved by appropriately using distillation, absorption, adsorption, filtration separation, etc. In particular, it is preferable to achieve this by providing a removal step described later.

[5. Removal process]
In the present invention, an optional "removal step" can be provided. The “removing step” in the present invention is a step of removing at least a part of dibenzofuran and / or fluorene contained in the absorbing oil from the absorbing oil after the crude light oil component is recovered in the recovering step.
The method for removing dibenzofuran and / or fluorene from the absorbing oil in the removal step is not limited, but it is preferable to remove by steam distillation using an apparatus called a depitching column (see FIG. 3). The absorbing oil discharged from the steam distillation column in the recovery step contains heavy components such as dibenzofuran, fluorene, acenaphthene and phenanthrene, while the content of benzene, toluene and xylene is reduced. In the depitching tower, these components can be separated and removed from the absorbing oil.

As described above, in the "removal process", the absorbent oil after the crude gas oil component is recovered in the recovery process is introduced, but it is not necessary to introduce all of the absorbent oil discharged in the recovery process into the removal process. Specifically, part of the absorbent oil discharged in the recovery step can be introduced into the removal step, and the remaining part can be introduced into the cooling step (see FIG. 4).
In addition, the absorbent oil discharged from the “removal process” is (1) introducing the whole amount into the cooling process, (2) recycling the whole amount into the recovery process, (3) introducing a part into the cooling process, and Methods such as recycling in the recovery step may be mentioned (see FIGS. 4 and 5).

Hereinafter, although the detailed conditions in the case of removing dibenzofuran and / or fluorene by a pitch removal column are explained, also when changing other methods, it can change suitably and can carry out.
Although the temperature of the absorption oil discharged | emitted from a collection | recovery process and charged to a de-pitching tower is not limited, it is 150-180 degreeC normally.
The top temperature of the depitching column 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 gas oil component in the absorbing oil from which the pitch component has been discharged, which is discharged from the depitching tower, is usually 37 to 32% by weight.

  Although dibenzofuran and fluorene are contained in the pitch component discharged from the depitching column in the removal step, the total content of dibenzofuran and fluorene in all pitch components is usually 30 to 70% by weight, and 50% by weight or more. Is preferred.

  Although the pitch component discharged | emitted by the removal process 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 and the like.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

<Analysis of coke oven gas composition>
The gas to be analyzed was analyzed using gas chromatography (manufactured by Toa DK Co., Ltd., 2000-EX-2).
<Analysis of Absorbent Composition>
The liquid to be analyzed was dissolved in chloroform and analyzed using GC-MS (manufactured by Agilent, 7890 GC-5975 MSD).
In the analysis, a constant volume was injected into a 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).

[Reference Example 1]
Coke was produced by dry-distilling coal ("raw material coal A" in which a plurality of types of coal and binder are mixed) in a chamber-type coke oven. The coke oven gas discharged during coke production was subjected to a purification treatment for reducing sulfur compounds, nitrogen compounds, benzols and the like, and the purified gas was used as a source gas. The results of analyzing the composition of the source gas are shown in Table 1. In addition to the gas compositions 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. 6 was provided and operated as an apparatus for recovering the crude gas oil component from the raw material gas.
The temperature of the feed gas charged to the absorption tower was 30 ° C., and the temperature of the absorbing oil was 35 ° C. The temperature of the absorbent oil (referred to as “RO liquid”) discharged from the absorber was 33 ° C. The resultant was subjected to heat exchange with a high temperature absorbing oil circulated from the distillation column to the absorption tower, heated to 180 ° C., and charged to the distillation column.
In the distillation column, the crude gas oil component (referred to as "BTX solution") was recovered from the column top at a tower top temperature of 98 ° C, and the absorbent oil (referred to as "AO solution") was discharged from the lower part. The AO liquid was at 180 ° C. at the time of discharge from the distillation column, but it was first cooled by heat exchange with the above-mentioned RO liquid and then further cooled to 35 ° C. by a heat exchanger using water as a refrigerant It circulated to the absorption tower. In addition, in this examination, the de-pitching tower | column shown in FIG. 6 was not used, but AO liquid transferred the whole quantity to the heat exchanger.
When the above operation reaches a steady state, RO solution, BTX solution, and AO solution are collected, and the composition was analyzed. The results are shown in Table 2.

As shown in Table 2, the total content ratio of benzene, toluene and xylene contained in the absorption liquid (RO liquid) in which crude gas oil components were absorbed from coke gas in the absorption tower was 0.68% by weight, but the distillation column The total content in the BTX liquid discharged from the mixture was 80.12% by weight, and the total content in the absorption liquid (AO liquid) recycled to the absorber was 0.04% by weight.
Further, the total content of dibenzofuran and fluorene in the absorbing oil (AO liquid) discharged from the distillation column and introduced into the heat exchanger was 35.76% by weight.

As described above, the AO liquid is introduced into the heat exchanger, cooled to 35 ° C., and circulated for a long period of time to the absorption tower. As a result, water is used as a refrigerant from the AO liquid to the inner wall of the heat exchanger No precipitation was observed.
Next, the temperature of the AO liquid charged into the absorption tower was lowered to 12 ° C. by lowering the water temperature of the refrigerant, and the same circulation operation was continued. As a result, since the precipitation from the AO liquid on the inner wall of the heat exchanger using water as a refrigerant was observed, continuous circulation operation was difficult.

Example 1, Comparative Example 1
The circulation operation was performed in the same manner as in Reference Example 1 except that “raw material carbon B”, which was blended differently from this, was dry-distilled in place of the raw material carbon A to produce coke. The AO liquid (AO liquid-1) obtained here was extract | collected, and the result of having analyzed the composition is shown in Table-3.
The AO solution 1 was cooled to 12 ° C., and the solid content was separated by filtration to obtain AO solution 2. The result of having analyzed the composition of solid content (pitch ingredient) obtained by AO liquid 2 and filtration separation is shown in Table-3.
The total content of dibenzofuran and fluorene in the AO solution was 39.66% by weight in AO solution-1, but was 32.07% by weight in AO solution-2.
With regard to AO solution-1 and AO solution-2, when the precipitation state upon cooling was confirmed, AO solution-1 was a solution in which precipitation started at about 20 ° C, but AO solution-2 was not more than 12 ° C. Even if it cooled, it could be set as the liquid which does not precipitate.
In addition, although this examination did not perform confirmation of precipitation generation in the apparatus shown in FIG. 6 directly for safety of the apparatus, it changes to the above filtration operation, and by operating the de-pitching tower in FIG. By making the composition of the AO liquid the same as in Example 1 and introducing it into the heat exchanger, the precipitation preventing effect can be exhibited as described above.

When the compositions of AO solution-1 and AO solution-2 were compared, both of dibenzofuran and fluorene decreased in AO solution-2, and were recovered as pitch components. On the other hand, with regard to acenaphthene, it was confirmed that the amount recovered as the pitch component was small despite being contained in a large amount in the absorbing solution, and was concentrated and remained in AO solution-2.
Although the melting point of dibenzofuran is 81 ° C and the melting point of acenaphthene is 92 ° C, precipitation does not occur based solely on the melting point because precipitation does not occur despite the fact that acenaphthene has a higher melting point. Can be seen.

[Examples 2 to 5, Comparative Example 2]
The circulation operation was carried out in the same manner as in Reference Example 1 except that “raw material carbon C” which was blended differently from the raw material coal A was dry-distilled to produce coke. The AO liquid (AO liquid-3) obtained here was extract | collected, and the result of having analyzed the composition is shown in Table-4.
The AO solution 3 was cooled at any temperature of 16 ° C., 12 ° C., 8 ° C., 5 ° C., and the solid content was separated by filtration to obtain AO solutions 4 to 7. The results of analyzing the compositions of AO solutions 4 to 7 are shown in Table 4.
The total content of dibenzofuran and fluorene in the AO solution was 35.76 wt% in AO solution-3, 34.58 wt% in AO solution-4, 31.00 wt% in AO solution-5, In AO solution-6, it was 28.51% by weight, and in AO solution-7, it was 26.75% by weight.
With regard to the AO liquids 3 to 7, when the deposition state upon cooling was confirmed, AO liquid 3 was a liquid whose precipitation started at about 20 ° C., but AO liquid 4 was 16 ° C. or less, AO liquid − It was possible to obtain a liquid that does not precipitate even if it is cooled to 5 ° C. or lower, AO liquid-6 to 8 ° C. or lower, and AO liquid-7 to 5 ° C. or lower.
In addition, although this examination did not perform confirmation of precipitation generation in the apparatus shown in FIG. 6 directly for safety of the apparatus, it changes to the above filtration operation, and by operating the de-pitching tower in FIG. By making the composition of the AO liquid similar to that of Examples 2 to 5 and introducing it into the heat exchanger, the precipitation preventing effect can be exhibited in the same manner as described above.

Claims (7)

“Absorption process” which absorbs crude light oil components contained in the raw material gas from the raw material gas containing at least one of coke oven gas and thermal decomposition furnace gas in an absorbing oil,
"Recovery step" of recovering the crude light oil component by distilling the absorbing oil having absorbed the crude light oil component in a distillation column;
After cooling the absorbing oil after recovering the crude light oil component through a heat exchanger, it has a “cooling step” to supply it again to the absorption step,
The collection | recovery method of the crude light oil component in gas which makes the sum total content of dibenzofuran and fluorene in absorption oil introduce | transduced into a heat exchanger at a cooling process 35 wt% or less.   The method for recovering a crude gas oil component according to claim 1, wherein the crude gas oil component contains at least any component selected from benzene, toluene and xylene.   The crude light oil according to claim 1 or 2, further comprising a "removal step" of removing at least a portion of dibenzofuran and / or fluorene contained in the absorbing oil from the absorbing oil after recovering the crude gas oil component in the recovery step. Method of recovery of ingredients.   The method for recovering crude light oil components according to claim 3, wherein at least a part of the absorbed oil that has undergone the removal step is returned to the distillation column of the recovery step.   The method for recovering crude light oil components according to claim 3 or 4, wherein the absorbent oil subjected to the recovery step is distributed and supplied to the cooling step and the removal step.   The crude light oil component according to any one of claims 1 to 5, wherein the heat exchanger comprises a heat exchanger using water as a refrigerant and a heat exchanger using an absorbing oil having the crude gas oil component absorbed as a refrigerant. Recovery method. The method according to any one of claims 3 to 6, characterized in that the dibenzofuran and / or fluorene removed in the removing step and / or fluorene are mixed with tar to make a pitch coke raw material, which is coked. How to make pitch coke.

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