JPH10156127A - Benzene vapor recovery device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a benzene vapor recovery device in which post-treatment after regeneration in an adsorber is easy. SOLUTION: In a device for recovering benzene vapor form air containing benzene vapor of high concentration, there are provided a stripping column 20 in which replacement air containing benzene vapor of high concentration is contacted with precooled heavy oil or benzene to partly remove the benzene vapor, plural absorbers 27A, 27B packed with an adsorbent such as silica gel, an air flow passage switching means for feeding air discharged from the stripping column 20 to be fed to any one of the absorbers 27A 27B and also discharging purified air from the absorbers 27A, 27B, heating means 33A, 33B for indirectly heating the absorbers 27A, 27B after benzene adsorption, a regenerating recovery means for evacuating the absorbers 27A, 27B to desorb benzene from the absorbent under vacuum and also returning the desorbed gas to the stripping column 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recovering benzene vapor contained in air discharged from a container such as a storage tank when the container is filled with benzene.

[0002]

2. Description of the Related Art When benzene is charged into barges, lorries and storage tanks, air is released to the atmosphere by replacing the gas phase and liquid phase in those containers. The replacement air contains high-concentration vapor evaporated from the liquid (benzene concentration in summer; about 14 to 26%).

[0003] Until now, there was no emission regulation value for the amount of vapor contained in the displacement air, but recently it has been severely restricted (currently undecided, but 30 ppm or less in the future).
Is about to be.

Conventionally, a removal device by adsorption using activated carbon shown in FIG. 4 has been used.

In FIG. 4, a raw gas 10 containing benzene vapor is supplied to one of a pair of adsorption towers 11A and 11B, and benzene in the raw gas is adsorbed and removed through a fibrous activated carbon layer 12 to be cleaned. The gas 13 is exhausted into the atmosphere. In the adsorption towers 11A and 11B, one of them is adsorbed while the other is desorbed and regenerated. FIG. 4 shows that the adsorption tower 11A is performing adsorption and the adsorption tower 11B is performing regeneration.

For regeneration, the steam 14 is directly transferred to the adsorption tower 11B.
To remove the adsorbed benzene by heating.
The removed benzene is removed from the condenser 15 together with steam.
Is supplied to the decanter 16 through which the upper layer of benzene separated into two layers in the decanter 16 is recovered as a recovery solvent 17 and the lower layer of condensed water is drained 18.

In this regeneration treatment, the activated carbon itself in the adsorption tower itself is flammable. For safety of regeneration, steam 10 which is an inert gas is directly blown into the adsorbent and harmful substances are generated by the reaction of the adsorbed substance. In order to prevent the temperature, the temperature is reduced to 100 ° C. or less so that the temperature does not rise extremely.

[0008]

The problem with the system shown in FIG. 4 is that the steam used for heating at the time of benzene recovery and the benzene are condensed while being mixed, so that the benzene considerably dissolves in the condensed water, Since the amount of condensed water is relatively large, draining the water directly has a problem from the standpoint of environmental protection, and further increases the size of the apparatus for reprocessing.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a benzene vapor recovery apparatus in which post-treatment after regeneration in an adsorption tower is easy.

[0010]

According to a first aspect of the present invention, there is provided an apparatus for recovering benzene vapor from air containing high-concentration benzene vapor, wherein replacement air containing high-concentration benzene vapor is precooled. A recovery tower that partially removes benzene vapor by contacting with heavy oil or benzene, a plurality of adsorption towers filled with an adsorbent such as silica gel, and air discharged from the recovery tower is supplied to one of the adsorption towers. Air passage switching means for exhausting clean gas from the adsorption tower, heating means for indirectly heating the adsorption tower after benzene adsorption, and suction and desorption of benzene from the adsorbent under reduced pressure by sucking the inside of the adsorption tower. This is a benzene vapor recovery device provided with a regeneration recovery means for returning gas to the recovery tower.

According to a second aspect of the present invention, there is provided an apparatus for recovering benzene vapor from air containing high-concentration benzene vapor, wherein the replacement air containing high-concentration benzene vapor is brought into contact with heavy oil or a precooled benzene liquid to partially convert the benzene vapor. A collection tower to be removed, a plurality of adsorption towers filled with an adsorbent such as silica gel, and an air flow for supplying air discharged from the collection tower to one of the adsorption towers and exhausting a clean gas from the adsorption tower. Path switching means, heating means for indirectly heating the adsorption tower after benzene adsorption, regeneration and recovery means for sucking the inside of the adsorption tower to desorb benzene from the adsorbent under reduced pressure and returning the desorbed gas to the recovery tower, The benzene collected from the bottom of the recovery tower is frozen and stored cold, and liquefied and supplied to the recovery tower as liquefied benzene for recovery. Benzene vapor recovery device that includes a vessel.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a recovery tower 20 using heavy oil (heavy oil A).
2 shows a recovery device in which a suction device and a suction device 21 are combined.

The recovery tower 20 includes upper and lower gas-liquid contact portions 22, 2
3 and a liquid reservoir 24, and upper and lower gas-liquid contact portions 22, 23.
In between, an air introduction line 25 for replacement air containing benzene vapor is connected, and an A fuel oil supply line 26 precooled (solidification temperature of benzene of 5.4 ° C. or higher) is connected to the upper part of the upper gas-liquid contact part 22. .

The adsorption device 21 includes a plurality of adsorption towers 27A, 2
Each column 27 is filled with an adsorbent made of nonflammable, hydrophobically treated silica gel or the like.

The recovery tower 20 and the adsorption device 21 are connected to the recovery tower 2
0 from any of the adsorption towers 27A and 27B.
And is connected by air flow switching means 28 for exhausting the clean gas from the adsorption towers 27A and 27B.

The air flow path switching means 28 includes an air line 29 connecting the top of the recovery tower 20 and the inlets of the adsorption towers 27A and 27B, and a clean gas exhaust line 30 connected to the outlets of the adsorption towers 27A and 27B. And inlet-side switching valves 31A, 31B connected to the inlets of the adsorption towers 27A, 27B and flowing air from the air line 29 to one of the adsorption towers 27A, 27B.
Are connected to the outlets of the adsorption towers 27A and 27B, and interlock with the inlet-side switching valves 31A and 31B to operate the adsorption towers 27A and 27B.
And outlet-side switching valves 32A and 32B that allow the air inside to flow through the clean gas exhaust line 30.

A heating means 3 for indirectly heating the adsorption towers 27A and 27B after benzene adsorption is provided in the adsorption towers 27A and 27B.
3A and 33B are provided, and the adsorption towers 27A and 27B are provided with regeneration / recovery means 34 for sucking the interior of the adsorption towers 27A and 27B after benzene adsorption to desorb benzene from the adsorbent and returning the desorbed gas to the recovery tower 20. Is connected.

The regenerating / recovering means 34 includes the adsorption towers 27A and 27A.
A desorption gas return line 35 connecting the inlet side of B to the lower part of the lower gas-liquid contact part 23 of the recovery tower 20, a vacuum pump 36 connected to the return line 35, switching valves 31A, 31B,
The desorption switching valve 37 which cooperates with the desorption gas in the adsorption towers 27A and 27B to flow into the desorption gas return line 35 in conjunction with the desorption gas 32A and 32B.
A and 37B, and purge gas supply lines 38A and 38B connected to the clean gas outlet side of the adsorption towers 27A and 27B and supplying a purge gas into the desorption adsorption towers 27A and 27B.

Reference numeral 39 denotes a pump connected to the liquid reservoir 24.

Next, the operation of the present embodiment will be described.

The replacement air discharged after filling a container such as a storage tank with benzene has a concentration of 2 in summer when the temperature is high.
About 6% of high-concentration benzene vapor is contained, and this replacement air is introduced from the air introduction line 25 below the upper gas-liquid contact part 22 of the recovery tower 20.
It is supplied from the heavy oil supply line 26 to the upper part of the upper gas-liquid contact part 22. The benzene vapor in the displacement air comes into contact with Fuel Oil A while being lifted up the upper gas-liquid contact portion 22 and is absorbed and removed by Fuel Oil A. The benzene concentration is about 1.5% while flowing from the recovery tower 20 to the air line 29. Down to

Thereafter, the replacement air is supplied to the adsorption towers 27A and 27A.
B, the benzene vapor in the displacement air is removed by being adsorbed by an adsorbent such as silica gel,
The benzene concentration is reduced to 30 ppm or less and exhausted as a clean gas from the clean gas exhaust line 30.

At this time, the inlet-side switching valves 31A, 31B and the outlet-side switching valves 32A, 32B open and close in conjunction with each other, and when the adsorption tower 27A is adsorbing, the inlet-side and outlet-side switching valves. 31A and 32A are open and the other switching valves 31B and 3
When 2B is closed and the adsorption tower 27B side is adsorbing, the switching valves 31B and 32B are opened and the switching valves 31A and 32A are closed.

The adsorption in the adsorption tower 27A (or 27B)
Since most of the benzene vapor is removed in the recovery tower 20, the load can be reduced. In addition, since the adsorbent has been subjected to the hydrophobic treatment during the adsorption, the adsorption of moisture in the displacement air is extremely small. Here, the vapor outlet concentration is reduced to 30 ppm or less and released to the atmosphere.

The adsorbent saturates when adsorbing a few percent by weight of vapor.
7B (or 27A) and the replacement air is treated similarly.

In the desorption and regeneration of the adsorption tower 27A (or 27B) having adsorbed benzene, the adsorbent in the adsorption tower 27A is depressurized by the vacuum pump 36 and simultaneously heated by the heating means 33A (PTSA: Pressure). & Temperaturu Swing
Adsorption), the adsorbed benzene is desorbed and regenerated, the desorbed gas is returned to the recovery tower 20 via the desorbed gas return line 35, and the lower gas-liquid contact portion 23 The solution is brought into contact with the heavy fuel oil A and the benzene, and is collected in the liquid reservoir 24.

There is a correlation between the adsorption temperature in the absorption tower 22, the desorption temperature and the pressure, and the present inventors have clarified the relationship of the hydrophobically treated silica gel by experiments. In the experiment, when the adsorption was performed at room temperature (20 to 40 ° C.), the regeneration temperature was set to be lower than the adsorption temperature by 15 at a pressure of about 25 Torr.
It became clear that regeneration could be achieved by raising the temperature by -20 ° C.

In the case where the adsorption tower 27A (or 27B) is used for adsorption, if it is previously cooled with cooling water (30 ° C.), the heating means 33A provided inside the adsorption tower 27A will be used.
It can be about 35 ° C.

On the other hand, the replacement air flowing into the adsorption tower 27A (or 27B) is 20 to 25 even in summer due to precooling.
Since the temperature is low at 0 ° C., the bed temperature rises only a few degrees when the adsorption amount is several percent. Therefore, the regeneration temperature under these conditions is about 5
The temperature may be 5 to 60 ° C. If the temperature of the replacement air is low in other seasons, a lower temperature may be used. In any case, the desorption regeneration can be performed by heating to a temperature that is higher by 15 to 20 ° C. than the temperature at the time of adsorption, so that a very economical method in terms of energy consumption can be provided. In addition, since the desorption gas after the regeneration contains very little water, the post-treatment may be performed with a very small apparatus.

FIG. 2 shows another embodiment of the present invention, in which recovered benzene is used for recovering benzene vapor.
A cooling device 4 using a refrigerator 45 cools the recovered benzene.
6 are combined.

In the embodiment shown in FIG. 1, heavy fuel oil A is used for removing benzene vapor, but in the present embodiment, benzene collected in liquid reservoir 24 is used. In this case, since some water is mixed in the benzene, the recovered benzene in the liquid reservoir 24 is introduced into the decanter 47, where water w and benzene z are separated by a specific gravity difference, and the benzene z is pumped by the pump 4.
At 9, it is supplied to the cooling device 46, where it is precooled and supplied from the supply line 48 to the upper gas-liquid contact portion 22 of the recovery tower 20. The cooling device 46 includes a refrigerator 45 and a heat exchanger 50, and cools benzene with the refrigerant from the refrigerator 45.

A benzene concentration detector 51 is connected to the replacement air introduction line 25, and when the benzene concentration reaches a predetermined concentration, the refrigerator 45 is started to supply benzene to the recovery tower 20. The temperature of the replacement air is controlled by controlling the flow rate control valve 41 connected to the supply line 48 with the cooling / absorption benzene flow rate by the outlet temperature control instrument 40 connected to the air line 29 of the recovery tower 20.

The temperature at which the precooling is performed is controlled at a temperature higher than the benzene solidification temperature (5.4 ° C.). When the benzene concentration is high such as in summer, the temperature is controlled to be lowered to about 10 ° C. That is, the temperature of the benzene liquid is detected by the temperature control instrument 42 connected to the supply line 48, and the control valve 43 for controlling the amount of the refrigerant from the refrigerator 45 to the heat exchanger 50 is controlled, thereby controlling the temperature of the benzene liquid. Control.

In the present embodiment, benzene vapor contained in the displacement air is recovered by absorption in the recovery tower 20 and regeneration in the adsorption device 21 and can be reused.

FIG. 3 shows still another embodiment of the present invention.

As described above, in the embodiment of FIG. 2, since a large amount of vapor is contained in the replacement air in summer, a large capacity refrigeration capacity is required.

Normally, when filling a lorry, barge or tank, the time during which the replacement air having a high gas concentration flows is not so long in a day's operation. Therefore, it is uneconomical to install a large-capacity refrigerator 45 at the time of the highest concentration.

To solve this problem, a regenerator 55 is provided as shown in FIG. 3, and the refrigerator 56 is operated by operating the refrigerator 56 at a time when electricity rates are low at night or when no cooling is required. Then, cooling is performed using this cold storage. Thus, the capacity of the refrigerator 56 can be reduced.

In FIG. 3, the cold storage container 57 of the cold storage 55
A spray pipe 58 is provided at the upper part of the tube, a heat exchanger 59 cooled by a refrigerator 56 is provided below the spray pipe 58, and a circulating suction line 60 is connected to the cold storage container 59, and the circulating suction line 60 is connected to a pump 49. Is connected to the suction side.

The regenerative operation is performed when the benzene vapor removal operation is not performed from the replacement air or when nighttime power can be used, such as at midnight.

The regenerator container 57 is filled with the benzene liquid by the pump 49 from the decanter 47 or a lorry so that the liquid level is lower than the lower portion of the heat exchanger 59 in the upper portion of the regenerator container 57. After the filling is completed, the valve 61 of the suction line 60 of the pump 49 is opened, the benzene liquid 62 is sucked from the regenerator 57, and the benzene liquid is sprayed from the spray pipe 58 to the heat exchanger 59. Next, the refrigerator 56 is started. The refrigerant enters the tube side of the heat exchanger 59 and cools the benzene liquid sprayed on the outer surface of the heat exchanger 59.

Since the evaporating temperature of the refrigerant is controlled at about -5 to 0 ° C., the benzene liquid flowing on the outer surface of the heat exchanger 59 is cooled. Since benzene solidifies at about 5.4 ° C. under atmospheric pressure, a part of the benzene liquid cooled by the heat exchanger 59 solidifies. Since the release agent is applied to the surface of the heat exchanger 59, the solidified benzene falls to the benzene liquid surface due to gravity (the heat exchange tube may be vibrated by a vibrator to separate the benzene solid).

Since the solid dropped on the liquid surface has a higher specific gravity than the liquid, it is deposited below the liquid. A baffle plate 64 is provided near the suction port of the suction line 60 so that the sedimented benzene solid 63 is not sucked into the pump 49. Baffle board 64
Protrudes above the liquid surface, and covers the liquid surface on the wall side of the regenerator 57 so that a mixture of benzene solid and benzene liquid falling from the heat exchanger 59 does not enter.

Since the skirt of the baffle plate 64 covers the liquid below the suction port of the suction line 60 in the liquid, it prevents solids settling by gravity from floating and mixing. Solid 6
When the deposited layer No. 3 reaches a predetermined level, the pump 49 and the refrigerator 56 are stopped to stop the cool storage operation.

The level gauge 65 is provided with a nozzle for blowing air or other gas to a depth from a predetermined liquid level, and detects a change in gas blowing pressure. That is, when the solid 63 is deposited up to the position of the nozzle, the viscosity is higher than that of the liquid. In another detection method, a benzene liquid feed nozzle is provided in the same manner as gas blowing with a thin tube from a pump, and when the resistance increases due to solid deposition, the flow rate decreases.

When the deposition position of the solid 63 reaches a predetermined position, the refrigerator 56 and the pump 49 are automatically stopped, and the valve 66 between the decanter 47 and the pump 49, the valve 61 of the suction line 60, and the spray pipe 58 Valve 67
Close.

The benzene vapor removal operation is performed as follows.

The replacement air passes through a heat exchanger 68 connected to the replacement air introduction line 25, where it exchanges heat with the replacement air at the outlet of the air line 29 and is introduced into the recovery tower 20. The flow rate of the replacement air flowing through the replacement air introduction line 25 is detected by the flow rate detector 70 and the concentration of the benzene vapor by the benzene concentration detector 51. When the concentration becomes 5% or more, the control device 69 communicates with the pump 49 and the refrigeration unit. The device 56 is started.

The benzene liquid (normal temperature) stored in the decanter 47 is sucked by the pump 49 and is supplied to the blowing line 7.
The benzene liquid is fed into the regenerator 57 by the steps 2 and 73.
The blowing lines 72 and 73 are arranged vertically, and the upper blowing line 72 is provided with a nozzle at a slightly higher position of the layer of the benzene solid 13 deposited in the regenerator 57 so as to blow downward. Connected to the header, and squirt the benzene solution. The liquid ejected from the nozzle is cooled by stirring and mixing the benzene solid 13. The cooled liquid is sent to the recovery tower 20 via the supply line 48 from the top of the cold storage container 57 through the supply line 48 while being further cooled by the heat exchanger 59 connected to the refrigerator 45 at the top of the cold storage container 57, and is used for lashing and the like. In the upper gas-liquid contact part 22 filled with the material, the replacement air is cooled to absorb the benzene vapor in the replacement air and reduce its content to 5% or less.

The benzene liquid flowing out of the regenerator 57 is
The amount of the refrigerant supplied to the heat exchanger 59 is controlled at the outlet temperature so that the heat exchanger 59 does not become extremely cooled and become solid.

The amount of the cooled benzene liquid fed into the recovery tower 20 is determined by detecting the replacement air in the air line 29 connected to the recovery tower 20 with a temperature sensor 74, and detecting the temperature at the outlet of the replacement air.
The controller 76 controls the opening degree of the flow control valve 75 connected to the supply line 48 so as to lower the temperature to ° C. When the vapor concentration in the replacement air reaches 5%, the supply of the liquid to the recovery tower 20 is stopped according to the detection value of the temperature sensor 74.

On the other hand, the liquid recovered in the liquid reservoir 24 of the recovery tower 20 is recovered by a decanter 47 and then continuously transferred to a predetermined storage tank (not shown) through a line 77 by a pump 49 or The volume of the decanter 47 is set such that one day's worth of collected liquid can be stored, and transported to a predetermined tank by a lorry or the like. The water w of the decanter 47 is drained through a treatment device 78 made of a fixed adsorption tower.

The replacement air exiting the recovery tower 20 is supplied to the heat exchanger 6
At 8, the replacement air introduced into the recovery tower 20 is precooled to recover cold energy, and then sent to the adsorption device 21.

In the embodiment shown in FIG. 3, the capacity of the refrigerator 56 can be reduced, the cost of electricity can be reduced by storing cold at night, and the size of the adsorption device for extremely lowering the concentration can be reduced. It is intended to provide a device which is excellent in terms of quality.

Next, the details of the heating means 33A and 33B at the time of desorption and regeneration of the adsorption device 21 will be described.

The heating coils 8 are provided in the adsorption towers 27A and 27B.
0A and 80B are provided, and the heating coils 80A and 80B are provided.
B is connected to a drum 82 via a pump 81, and switching valve groups 82A, 82 are provided at the entrances and exits of the heating coils 80A, 80B.
2B, 83A and 83B are connected.

Steam is supplied to the drum 82 from a line 84 via a control valve 85 and a mixer 86.
The condensed water 88 condensed in 2 flows from the pump 81 to the corresponding heating coils 80A, 80B through one of the inlet-side switching valve groups 82A, 82B, where it heats the adsorbent of the adsorption towers 27A, 27B, and the outlet side. Part of the water passes through the switching valve groups 83A and 83B and is drained from the drain line 89, and the rest is returned to the drum 82 via the circulation line 90 and the mixer 86.
Reference numeral 91 denotes a cooling water supply line.

The temperature of the condensed water supplied to the heating coils 80A and 80B is detected by a temperature sensor 92 provided on the drum 82, and the opening of the control valve 85 is controlled so that the temperature becomes a set value. To control the amount of steam introduced.
The heating source may be heated by an electric heater when there is no steam.

In addition, the adsorption tower 27A after the desorption regeneration is completed,
Since the adsorbent in 27B has a high temperature immediately after the condensed water flows in the heating coils 80A and 80B, the cooling water is supplied from the cooling water supply line 91 to the switching valve groups 82A, 82B and 83.
A and 83B are appropriately switched to heat coils 80A and 80B.
And cool.

As described above, in the embodiment of FIG. 3, the refrigerating machine is constituted by the regenerative operation, the concentration reducing operation by precooling using the regenerator and the refrigerating machine, and the operation for ultimately removing benzene vapor by adsorption. Capacity can be reduced, and cold storage can be made economically superior because late-night power can be used.

[0062]

In summary, according to the present invention, the benzene vapor in the displacement air is partially recovered by the recovery tower and then adsorbed by the adsorption tower, so that benzene can be removed to near the limit and the adsorption tower can be miniaturized. In addition, post-processing after reproduction becomes easy.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

FIG. 3 is a diagram showing an embodiment in which FIG. 2 is further improved.

[Explanation of symbols]

 Reference Signs List 20 recovery tower 27A, 27B adsorption tower 28 air flow path switching means 33A, 33B heating means

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[Procedure amendment]

[Submission date] January 20, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Fig. 4

[Correction method] Added

[Correction contents]

FIG. 4 is a diagram showing a conventional example.

Claims (2)

[Claims] An apparatus for recovering benzene vapor from air containing high-concentration benzene vapor, comprising: a recovery tower for removing replacement benzene vapor by contacting replacement air containing high-concentration benzene vapor with precooled heavy oil or benzene; A plurality of adsorption towers filled with an adsorbent such as silica gel, air flow switching means for supplying air discharged from the recovery tower to any one of the adsorption towers and exhausting a clean gas from the adsorption tower; Heating means for indirectly heating the adsorption tower after adsorption, and regeneration and recovery means for sucking the inside of the adsorption tower to desorb benzene from the adsorbent under reduced pressure and returning the desorbed gas to the recovery tower, Benzene vapor recovery equipment. 2. An apparatus for recovering benzene vapor from air containing high-concentration benzene vapor, comprising: a collection tower for removing a portion of benzene vapor by contacting replacement air containing high-concentration benzene vapor with heavy oil or precooled benzene. A plurality of adsorption towers filled with an adsorbent such as silica gel, air flow switching means for supplying air discharged from the recovery tower to any one of the adsorption towers and exhausting a clean gas from the adsorption tower, Heating means for indirectly heating the adsorption tower after benzene adsorption, regeneration and recovery means for sucking the inside of the adsorption tower to desorb benzene from the adsorbent under reduced pressure and returning the desorbed gas to the recovery tower, and from the bottom of the recovery tower A regenerator that freezes the collected benzene, cools and stores it, liquefies it, and supplies it to the collection tower as liquefied benzene for recovery. A benzene vapor recovery device.