JPH10174833A - Removing method of benzene vapor and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a benzene vapor removing method and the device remarkably economical in the view point of energy consumption and easy in the post- treatment of a desorbed gas after regeneration in adsorption and regeneration in an adsorption column. SOLUTION: In the method for removing benzene vapor from an air containing benzene vapor in a high concentration, the air containing benzene vapor is supplied to one of plural adsorption columns 21A, 21B packed with an adsorbent such as silica gel and kept at the normal temp. to adsorb benzene contained in the air and is exhausted as a purified gas. On the other hand, the adsorbent, on which benzene is adsorbed, in the adsorption columns 21A, 21B is indirectly heated to a temp. higher by 15-30 deg.C than the adsorption temp. with the pressure in the adsorption columns reduced to <=50Torr to desorb benzene from the adsorbent to be regenerated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for removing 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%).

Until now, the amount of vapor contained in the replacement air had only to be suppressed to 1000 ppm or less, but recently this has been severely restricted (currently undecided, but 30 pp in the future).
m or less).

[0004] Conventionally, a removal device by adsorption using activated carbon shown in FIG. 4 has been used.

[0005] In FIG. 4, a raw gas 10 containing benzene vapor is supplied to one of a pair of adsorption towers 11 A and 11 B, and benzene in the raw gas is adsorbed and removed through an activated carbon layer 12. 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 supplied to the decanter 16 through the reboiler 15 together with the steam. In the decanter 16, the upper benzene separated into two layers is recovered as the recovery solvent 17, and the lower condensed water is separated into the separated water tank 19. Is drained 18 through.

In this regeneration treatment, the activated carbon itself in the adsorption tower itself is flammable, so that in order to ensure safety during regeneration, steam 10, which is an inert gas, is directly blown into the adsorbent, and the temperature is not extremely increased. And heated to about 80 to 90 ° C. under reduced pressure.

[0008]

The problem with the system shown in FIG. 4 is that the steam used for heating at the time of benzene recovery and benzene are condensed while being mixed, so that benzene considerably dissolves in the condensed water, Draining this directly is problematic from the standpoint of environmental protection and requires further reprocessing.

Also, there is a problem that the treatment must be performed at a relatively high regeneration temperature of 80 to 90 ° C.

Therefore, an object of the present invention is to solve the above-mentioned problems, and it is very economical in terms of energy used in performing adsorption and regeneration in an adsorption tower, and benzene which is easy to post-process the desorbed gas after regeneration. It is an object of the present invention to provide a vapor removing method and an apparatus therefor.

[0011]

According to a first aspect of the present invention, there is provided a method for removing benzene vapor from air containing high-concentration benzene vapor, wherein the air containing benzene vapor is adsorbed on silica gel or the like. The benzene contained in the air is supplied to one of a plurality of adsorption towers maintained at approximately room temperature to adsorb benzene contained in the air and exhausted as a clean gas. This is a benzene vapor removing method in which indirect heating is performed so as to increase the temperature by 15 to 30 ° C., and benzene is desorbed from the adsorbent to regenerate the adsorbent by setting the pressure in the adsorption tower to about 50 Torr or less.

According to a second aspect of the present invention, there is provided an apparatus for removing benzene vapor from air containing high-concentration benzene vapor, comprising: a plurality of adsorption towers filled with an adsorbent such as silica gel; Air flow switching means for supplying to any of the adsorption towers and exhausting the clean gas from the adsorption tower, heating means for indirectly heating the adsorption tower after the benzene adsorption to 15 to 30 ° C. higher than the adsorption temperature, This is a benzene vapor removal apparatus provided with benzene recovery means for sucking the inside of the column at a pressure of about 50 Torr or less to desorb benzene from the adsorbent and recover desorbed gas.

[0013] The heating means of the invention according to claim 3 is the benzene vapor removing apparatus according to claim 2, further comprising benzene condensation heat recovery means for recovering heat of the desorbed benzene gas during regeneration of the adsorption tower.

[0014]

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 an adsorption apparatus 2 comprising a plurality of adsorption towers 21 for removing benzene from air containing benzene vapor.
1 shows a benzene vapor removal apparatus in which a benzene vapor removal apparatus is combined with a recovery tower 22 that collects benzene adsorbed and removed by the adsorption apparatus 20.

The adsorption apparatus 20 includes a plurality of adsorption towers 21A, 21A and 2A.
Each column 21 is filled with an adsorbent made of nonflammable, hydrophobically treated silica gel or the like.

The adsorber 21 has inlet-side flow switching valves 24A and 24B for switching and supplying replacement air containing benzene vapor from the supply line 23 to one of the adsorption towers 21A and 21B, and the adsorption towers. Outlet-side flow switching valves 26A and 26B for connecting the air introduced into 21A and 21B to the exhaust line 25 as clean gas are connected.

In the adsorption towers 21A and 21B, the adsorption towers 21A and 21B after benzene adsorption are placed in the adsorption towers 15 to 3 from the adsorption temperature.
Heating means 27A and 27B for indirect heating to increase the temperature by 0 ° C
Is provided in the adsorption towers 21A and 21B.
A, 21B is pressurized to a pressure of about 50 Torr or less, and benzene recovery means 30 for desorbing benzene from the adsorbent and supplying the desorption gas to the recovery tower 22 is connected.

The benzene recovery means 30 includes an adsorption tower 21A,
A desorption gas line 32 connecting the inlet side of 21B and the lower part of the gas-liquid contact part 31 of the recovery tower 22, and a vacuum pump 33, a heat exchanger 34, and a cooler 35 connected to the desorption gas line 32.
And interlock with the switching valves 24A, 24B, 26A, 26B,
The desorbed gas in the adsorption towers 21A and 21B is transferred to the desorbed gas line 3
2, the desorption switching valves 36A and 36B flowing to the adsorption tower 21A,
Adsorption tower 2 connected to the clean gas outlet side of 21B and being desorbed
Purge gas supply lines 37A and 37B for supplying a purge gas into 1A and 21B.

In the upper part of the gas-liquid contact part 31 of the recovery tower 22, precooled heavy oil or benzene is supplied through a line 7.
The gas desorbed from the desorption gas line 32 is gas-liquid contacted in the gas-liquid contact part 31 to condense benzene in the desorption gas and accumulate at the bottom of the recovery tower 22, and the air in the gas is recovered. The supply line 23 from the line 38 at the top of the tower 22
Is returned to. The benzene liquid collected at the bottom of the recovery tower 22 is recovered by a recovery pump 39.

The heating means 27A and 27B are
A, 21B, heating coils 40A, 40B, hot water supply means 41 for supplying hot water to the heating coils 40A, 40B,
0A, 40B, inlet-side switching valves 42A, 42B, and outlet-side switching valves 43A, 43B, 44.
A, 44B.

The hot water supply means 41 includes a hot water tank 45, a hot water supply line 47 for supplying hot water in the hot water tank 45 to the heating coils 40 A and 40 B via a pump 46, and a hot water from the hot water supply line 47. , Heating coil 40A, 4
0B to supply any of the inlet side switching valves 48A, 48B
And switching valves 43A, 43B, 44A, 44B connected to the outlet side of the heating coils 40A, 40B, and hot water heated from one of the outlet side switching valves 43A, 43B via a mixer 48 into a hot water tank. And a hot water return line 49 for returning to 44.

Steam is supplied to the hot water tank 45 from a line 55 through a control valve 56 and a mixer 49.
The hot water 50 condensed in the pump 5 passes through one of the inlet-side switching valves 42A and 42B from the pump 46 to the corresponding heating coil 40.
A, 40B, where the adsorbent in the adsorption towers 21A, 21B is heated, and the outlet side switching valves 43A, 43B, 44A, 4
4B, a part is drained from the drain line 58 through the outlet side switching valves 43A and 43B, and the rest is the outlet side switching valve 44.
A, 44B, the heat exchanger 34 as the benzene condensation heat recovery means 71 and the hot water return line 49, and the mixer 4
8 and is returned to the hot water tank 45.

A cooling water supply line 60 is connected to the hot water tank 45, and the temperature of the hot water in the hot water tank 45 is adjusted by the steam from the mixer 48, the circulating water, and the cooling water from the supply line 60.

That is, the temperature detector 61 is provided in the hot water tank 45.
On the other hand, temperature detectors 62A and 62B are provided in the adsorption towers 21A and 21B, and the detected temperature values are input to the controller 63. The control device 63 sets the temperature in the adsorption towers 21A and 21B at the time of regeneration to 15 to 30 below the adsorption temperature.
The control valve 56 is adjusted to control the amount of steam so that the temperature in the hot water tank 45 is maintained at an appropriate value so that the temperature in the tower is about 55 to 60 ° C.

In addition, the adsorption towers 21A, which have completed the desorption and regeneration,
Since the adsorbent in 21B is higher than room temperature immediately after the hot water flows in the heating coils 40A and 40B, the cooling water is switched from the cooling water supply line 60 by appropriately switching the switching valves 65A and 65B to the heating coil 40A. , 40B to be cooled and drained to the drain line 58 from the outlet side switching valves 43A, 43B.

Next, a method for removing benzene vapor will be described.

The replacement air discharged after filling a container such as a storage tank with benzene contains high-concentration benzene vapor. This replacement air is supplied from the supply line 23 to the inlet side switching valves 24A, 24B. Through the adsorption tower 21
A and 21B, 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 the benzene vapor is exhausted as a clean gas from the clean gas exhaust line 25. You.

At this time, the inlet-side switching valves 24A, 24B and the outlet-side switching valves 26A, 26B open and close in conjunction with each other, and when the adsorption tower 21A is adsorbing, the inlet-side and outlet-side switching valves 24A, 24B. , 26A are open and the other switching valves 24B, 26A
When B is closed and the adsorption tower 21B side is adsorbing, the switching valves 24B and 26B are opened and the switching valves 24A and 26A are closed.

The adsorption in the adsorption tower 21A (or 21B)
The adsorption is performed at room temperature, and the adsorbent is nonflammable and has been subjected to a hydrophobic treatment. Therefore, the adsorption of moisture is extremely small, and the adsorption of moisture in the displacement air is extremely small, which is 1/10 or less of the amount of vapor adsorbed. In this adsorption tower 21A, the vapor outlet concentration is 3
It is reduced to 0 ppm or less and released to the atmosphere.

At the time of adsorption, in order to prevent the temperature of the adsorption tower 21A from rising due to heat of adsorption and to reduce the amount of adsorption, cooling water from the cooling water line 60 is supplied to the heating coil 40A (or 40B). Cooling.

The adsorbent saturates when adsorbing a few percent by weight of vapor.
Switch to 1B (or 21A) and treat the replacement air similarly.

In the desorption regeneration of the adsorption tower 21A (or 21B) adsorbing benzene, the adsorbent in the adsorption tower 21A is depressurized by the vacuum pump 33 and simultaneously heated by the heating means 27A (PTSA: Pressure). & Temperaturu Swing
Adsorption) to desorb and regenerate the adsorbed benzene.

In this case, there is a correlation between the adsorption temperature, the desorption temperature and the pressure, and the present inventors have clarified the relationship of the hydrophobically treated silica gel by experiments. In experiments, it was found that when adsorbed at room temperature (20-40 ° C), about 25
It was found that the regeneration can be performed by increasing the regeneration temperature by 15 to 30 ° C. under the pressure of Torr above the adsorption temperature.

This experimental example will be described with reference to FIGS.

FIG. 2 shows that the adsorption tower 21 is adsorbed at 40.degree.
It shows the change over time in the temperature of the adsorption tower and the outlet concentration of benzene when performed under the conditions of desorption, and after performing desorption for about 40 minutes, cooling is performed for about 50 minutes, and adsorption is performed at 40 ° C. The adsorbing capacity of the adsorbent for about 50 minutes is determined by the outlet concentration of 30 pp.
m could be maintained. This indicates that a sufficient adsorptivity can be obtained even if the regeneration is performed at a temperature 20 ° C. higher than the adsorption temperature.

FIG. 3 also shows that the adsorption tower 21 is adsorbed at 40 ° C.
The graph shows the change over time in the temperature in the adsorption tower and the outlet concentration of benzene when the desorption was performed at 70 ° C. After desorption for about 60 minutes, cooling was performed for about 50 minutes. In this case,
When the adsorption is performed at 40 ° C., the adsorbing ability of the adsorbent is good for about 80 minutes, during which the outlet concentration can be kept at 30 ppm or less.

As described above, when the regeneration temperature is high, the adsorptivity is also increased. However, when the regeneration temperature is increased, the energy consumption is increased. Therefore, the regeneration is preferably performed at a temperature higher by 15 to 30 ° C. than the adsorption temperature. .

In the experimental examples shown in FIGS. 2 and 3, the adsorption time is shorter than the desorption / cooling time. This is an example for explaining the relationship between the regeneration and the adsorption temperature. When performing adsorption, three or more adsorption towers 21 may be installed.
When two units are used, the pressure in the tower and the temperature of the cooling water may be adjusted so as to shorten the desorption / cooling time.

When the adsorption tower 21A (or 21B) is used for adsorption, cooling water (30 ° C.) is previously supplied to the adsorption tower 21A.
The temperature can be set to about 35 ° C. by flowing the heat through the heating coil 40 </ b> A provided inside.

On the other hand, if the replacement air flowing into the adsorption tower 21A (or 21B) is at 20 to 25 ° C., the adsorption amount is several%.
Then the bed temperature rises only a few degrees. Therefore, the regeneration temperature under this condition may be set to about 55 to 60 ° C. If the temperature of the replacement air is low in other seasons, a lower temperature may be used. In any case, desorption regeneration can be performed by heating to a temperature 15 to 30 ° C. higher than the temperature at the time of adsorption,
This provides a very economical method in terms of energy use as compared to conventional devices.

In order to perform this regeneration rationally (energy saving), the adsorption temperature is detected by a temperature detector 62A (or 62B) installed in the adsorption tower 21A (or 21B), and the hot water tank 4
5 The temperature of the hot water for regeneration is 15 to 30 from the adsorption temperature.
The temperature of the hot water 50 in the hot water tank 45 is detected by the temperature detector 61 so as to increase the temperature by a degree, and the control temperature is set.

The setting of the temperature of the hot water tank 45 is not necessarily automatic, and the control value may be manually set higher by about 15 to 30 ° C. depending on the temperature of the four seasons or each month.
This can prevent the use of excessive energy.

When the adsorption tower 21A (or 21B) is regenerated, the benzene vapor (partially mixed with air) sucked and desorbed by the vacuum pump 33 is heated to about 79 ° C. (352 K) under a pressure of 0.1 to 0.15 MPa. ) To condense. Since the heat of condensation is about 94 Kcal / kg, the gas discharged from the vacuum pump 33 is supplied to the heat exchanger 3 as the benzene condensation heat recovery means 71.
By exchanging heat with circulating hot water in 4 and the hot water return line 49, heat can be recovered. As a result, about 40% of the heat required for desorption can be recovered. When the temperature is low, the regeneration temperature is also low, so that the rate of the recovered heat becomes even higher. This is also based on experimental data, showing that the regeneration temperature is 15 to 3
It was confirmed that it was possible at 0 ° C.

In this embodiment, the vacuum pump 33
Since the regeneration is performed under reduced pressure and by indirect heating, the amount of water coexisting with the recovered benzene vapor is extremely small as compared with the conventional method. A small one is acceptable.

As described above, the adsorption tower 21A (or 21B)
, The desorbed gas discharged by the vacuum pump 33 is recovered from the desorbed gas line 32 through the heat exchanger 34, is further cooled and condensed by the cooler 35, and is condensed by the gas-liquid separation unit 31 of the recovery tower 22. It flows into the lower part, where the benzene liquid is recovered, and the air is returned to the supply line 23 via the line 38 and finally exhausted from the exhaust line 25.

The benzene liquid recovered in the recovery tower 22 is
The liquid is continuously transferred to a predetermined storage tank by the recovery pump 39 by controlling the liquid level of the recovery tower 22, or the volume of the liquid in the recovery tower 22 is set so that the recovered liquid for one day can be stored. Transport to designated tank.

[0048]

In summary, according to the present invention, the benzene vapor in the displacement air is adsorbed at room temperature, and the regeneration is performed by keeping the regeneration temperature 15 to 30 ° C. higher than the adsorption temperature and at a pressure of about 50 Torr or less. In addition, benzene can be removed to near the limit and the size of the adsorption tower can be reduced, and post-treatment after regeneration 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 experimental results of a change over time in an adsorption tower temperature and a benzene outlet concentration at a desorption temperature and an adsorption temperature in the present invention.

FIG. 3 is a graph showing experimental results of changes over time in the adsorption tower temperature and the benzene outlet concentration at the desorption temperature and the adsorption temperature in the present invention.

FIG. 4 is a view showing a conventional removing device.

[Explanation of symbols]

 21A, 21B adsorption tower 23 replacement air supply line 27A, 27B heating means 30 benzene recovery means

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B01D 53/81

Claims (3)

[Claims] 1. A method for removing benzene vapor from air containing high-concentration benzene vapor, wherein the air containing benzene vapor is filled with an adsorbent such as silica gel in one of a plurality of adsorption towers maintained at approximately normal temperature. Benzene contained in the air is adsorbed and exhausted as a clean gas. On the other hand, the inside of the adsorption tower adsorbing benzene is heated indirectly to 15 to 30 ° C. higher than the adsorption temperature, and the inside of the adsorption tower is A method for removing benzene vapor, comprising regenerating the adsorbent by desorbing benzene from the adsorbent at a pressure of 50 Torr or less. 2. An apparatus for removing benzene vapor from air containing high-concentration benzene vapor, comprising: a plurality of adsorption towers filled with an adsorbent such as silica gel; Air flow switching means for supplying clean air to the adsorption tower and exhausting clean gas from the adsorption tower;
A benzene vapor removing apparatus comprising: a heating means for indirectly heating the temperature of the adsorbent so as to increase the temperature by ℃; 3. The benzene vapor removing apparatus according to claim 2, wherein the heating means has a benzene condensation heat recovery means for recovering heat of the desorbed benzene gas during regeneration of the adsorption tower.