JP2003033619A - Gas treatment device and gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To utilize an adsorption power of activated carbon fiber material more effectively than that in the conventional technique and to improve recovery efficiency of organic solvent from gas to be treated. SOLUTION: In this gas treatment device of alternately switching an adsorption treatment state which uses the activated carbon fiber material as an adsorption element and a desorption state, a discharge pipe on the bottom part of an adsorption tank (tank drain line) and a piping which discharges coagulated liquid from a cooling part (recovered liquid line) are connected independently or joinedly to a solvent recovering part in such a manner that the drain which is coagulated on desorption does not flow backward and, thereby, the wetting of the activated carbon fiber material due to the backward flow of the coagulated liquid is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas treatment device which uses activated carbon fiber (hereinafter referred to as ACF) as an adsorbent to adsorb an organic solvent-containing gas and at the same time desorbs and collects the adsorbed organic solvent. The present invention relates to a processing method using an apparatus.

[0002]

2. Description of the Related Art In recent years, emission concentration regulations for harmful air pollutants have been strengthened, and when treating harmful air pollutants with a gas treatment device, the concentration of harmful air pollutants at the gas treatment device outlet is reduced as much as possible. Is desired.

Conventionally, the above-mentioned gas treatment device has one or more pairs of adsorption tanks for adsorbing a gas to be treated (that is, an exhaust gas such as a gas containing an organic solvent) with an activated carbon fiber material, and a means for supplying a gas to be treated to each adsorption tank. And a desorption gas supply means, and means for switching between an adsorption treatment state in which the gas to be treated is supplied to the adsorption tank and a desorption state in which the gas to be treated adsorbed by the desorption gas is desorbed. It was

Conventionally, the above-mentioned gas treatment device uses AC as the adsorbent.
Although F and granular activated carbon are generally used, ACF has a specific surface area of 1000 to 2000 m ² / m compared to granular activated carbon.
It has a large g and a large number of micropores effective for gas adsorption on the surface of the adsorbent and has an extremely high adsorption / desorption rate. Therefore, it is known and used as the most general method in the field of organic solvent recovery. For example, by fixing the ACF to a support,
Alternatively, a device in which it is formed into a cylindrical shape by self-support and arranged in a vertical mold in a core material is proposed in JP-A-51-38278 and JP-A-64-11326. Also, fairness 7
-2028, 2029, and 2030 have also proposed gas devices that perform similar adsorption and desorption. These are all A
The organic solvent adsorbed by the ACF is desorbed and collected by ejecting water vapor onto the core material containing the CF.

Generally, the ability of ACF to adsorb organic solvent is
It is easily affected by moisture, and when the water content of ACF is high, the adsorption capacity is extremely reduced. For this reason, in the above-mentioned proposal, various ideas have been devised such that the direction of jetting water vapor to the core material, that is, the adsorption element is from above or below, or from the center inside direction. However, at the time of starting operation, there is a problem that the adsorbing element becomes wet with water due to the scattering of the drain of the jetted water vapor and the reverse flow of the condensate, which lowers the ability of the ACF to adsorb the organic solvent.

Further, in the gas treatment device using the above-described gas adsorption element, it has been difficult to carry out stable continuous adsorption / desorption for a long period of time. That is,
When water vapor is jetted to the element to which the organic solvent is adsorbed and the adsorbed organic solvent is desorbed alternately and repeatedly, the low boiling point solvent is significantly affected by the temperature of the outside air, etc. (Separated)
Condensate often flows back from the pipe leading to. Due to this backflow, there is a problem that the condensate comes into contact with the ACF in the gas treatment element, greatly lowering the adsorption capacity, which has also hindered continuous operation.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to a gas treatment apparatus capable of continuously adsorbing and desorbing an organic solvent-containing gas, particularly a low boiling point solvent, using ACF with high efficiency. is there.

In the continuous operation of the gas treatment apparatus using the adsorption element, in the desorption process, the desorption gas, steam, and the desorbed desorption gas become a condensate in the adsorption tank at the initial stage of supplying the desorption gas. It is discharged to the separator through the tank drain line at the bottom. On the other hand, the uncondensed water vapor and the organic solvent pass through the desorption gas line, condense in the cooling unit (hereinafter referred to as a condenser), merge with the tank drain line, and are discharged to the separator. For example, the condensate from the lower part of the adsorption tank 4 in FIG. 1 (because of continuous operation, it becomes a desorption tank when another tank is operating as an adsorption tank) passes through the tank drain line 8 and the separator 12 However, the condensate retained in the tank drain line 8 at this time is heated by the condensate from the lower part of the adsorption tank 4 to be boiled gas and flow backward. This tendency becomes remarkable when the outside air temperature is low, the condensate is large, and the gas to be treated contains a low boiling point solvent.

[0009]

According to the present invention, in order to eliminate the reverse flow of the condensate, the condensate containing a high concentration of the organic solvent discharged from the condenser flows through the recovery liquid line and into the tank drain line. This is to prevent the condensate from flowing back into the tank by making some measures. In the conventional recovery liquid line, the tank drain line of each tank was connected at the lowermost end for the purpose of liquid sealing, and then it rose upward and was connected to the separator. Also, the recovery liquid line was connected to the above-mentioned tank drain line at the lowermost part and was similarly liquid-sealed and connected to the separator. Furthermore, by mixing the condensate of the high temperature tank drain line and the condensate of the relatively low temperature recovery liquid line cooled by the condenser, the temperature of the condensate flowing into the separator is lowered as a whole, and the solvent in the separator is reduced. The recovery liquid line and the tank drain line were joined to connect to the separator for the purpose of suppressing the volatilization of. However, in the above method, when the organic solvent to be recovered has a lower boiling point than water, the organic solvent flowing from the recovery line into the tank drain line is heated by the high-temperature condensate condensed in the adsorption tank and boils,
It was made to flow back into the adsorption tank from the gasification tank drain line. Therefore, as shown in FIG. 2, the recovery liquid line and the tank drain line were independent of each other, liquid sealing was performed, and the back flow of the condensate was eliminated by connecting to the separator.

When the condensate in the tank drain line becomes hot and the temperature of the recovered liquid in the separator rises and the concentration of the gas returned to the process gas inlet increases, as shown in FIG. By connecting the tank drain line to the recovery liquid line at a position higher than the connection position of the recovery liquid line with the separator after rising, the concentration of the return gas was reduced and the reverse flow of the condensate was eliminated. By changing these piping routes, wetting of the adsorption element did not hinder continuous operation of the gas treatment device.

In the case of a gas treatment apparatus in which an organic solvent is continuously treated by desorption of water vapor using an adsorption element, this effect is remarkable especially in a low boiling point solvent. Usually, these gases are discharged together with water vapor to the outside of the adsorption element, but in the case of an organic solvent which is difficult to dissolve in water, cooling outside the adsorption element causes separation into a water layer and a solvent layer. Generally, the specific gravity of the organic solvent is large, and the organic solvent is separated into the lower layers of the two layers, so that the organic solvent easily accumulates at the bottom of the drain line of the tank, and the reverse flow due to boiling becomes remarkable. Therefore, when a backflow of the condensate is generated from the lower part of the adsorption tank, the condensate wets the adsorbing element, thereby lowering the adsorption capacity.

The organic solvent referred to here is methylene chloride,
Trichloroethane, trichlorethylene, carbon tetrachloride,
It refers to an organic solvent such as chloroform, and in particular, a solvent such as methylene chloride having a lower boiling point than water and a specific gravity heavier than water is suitable in the present invention.

By changing the recovery liquid line, wetting of the adsorption element by the condensate is eliminated, the temperature and relative humidity in the adsorption / desorption tank are easily controlled, and the adsorption efficiency is further improved.

Furthermore, since the adsorption element does not always come into contact with moisture and the adsorption ability is maintained,
The adsorption tank and desorption tank can be continuously switched. As a result, the device of the present invention is capable of adsorbing and desorbing the organic solvent-containing gas continuously along with smooth operation at the time of operation and stoppage, and is excellent in operability, and can be operated for a long period of time.

The ACF used in the present invention means a specific surface area of 1000 obtained by treating raw fibers such as acrylonitrile (PAN) fiber, rayon fiber, coal pitch fiber, phenol resin fiber and petroleum pitch fiber by an existing method. ~ 2000m
² / g, the fiber diameter is about ² to 30 μm, and the fiber length is 0.
Any may be used as long as it has a pore radius of 5 to 10 mm and a pore radius of 5 to 20 Å.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an example of an embodiment of the present invention will be described with reference to FIG. Organic solvent-containing gas (process gas)
X passes through the pre-filter 1 (gas * 3, * 4 staying in the condenser 10 and the separator 12 is returned to the pre-filter 1 again through the return gas line 13), and the adsorption tank 3 is blown by the blower 2. (At this time, the organic solvent-containing gas is not sent to the adsorption tank 4 and is blocked by the automatic damper 6. In the adsorption tank 4, steam is jetted to remove the gas already adsorbed by the adsorption element 5. (In a desorbed state), the adsorption element 5 adsorbs the gas, and is discharged as clean air Y from the exhaust port 14 of the adsorption tank 3 to the outside of the system. The condensate is sent to the separator 12 through the tank drain line 8 below the adsorption tank 4. The uncondensed water vapor and the organic solvent are sent to the condenser 10 through the desorption gas line 9. A condensate containing a high-concentration organic solvent flows from the condenser 10 through the recovery liquid line 11 to the tank drain line 8 and is sent to the separator 12.

At this time, in the case of a mixed gas in which a low-boiling-point solvent is mixed, as the external temperature lowers, the amount flowing into the tank drain line 8 increases, so that the condensate flows back into the adsorption tank. Becomes noticeable and jets out into the adsorption tank 4,
Wet the adsorption element. Therefore, in the present invention, the recovery liquid line 11 is separated from the tank drain line 8 and independently connected to the separator 12 to prevent the condensate from flowing back to the lower portions of the adsorption tanks 3 and 4.

2 and 3 show enlarged piping diagrams of the condenser and the separator portion.

As a result, even when the adsorption tanks 3 and 4 are switched and continuously operated, the concentration of the organic solvent gas discharged outside the system can be kept low and constant.

The organic solvent adsorbed by the adsorption element 5 is ejected from the water vapor W1 in the adsorption tank 4 through the automatic valve 7 to the adsorption element in the adsorption tank to desorb the organic solvent. The amount of water vapor is controlled by the vapor adjustment automatic valve 7.
In addition, this water vapor is either above or below the adsorption tank 4 (see FIG.
It is ejected from the inside (dotted line).

As a result, the organic solvent-containing gas X is discharged outside the system as clean air Y, and the desorbed uncondensed organic solvent gas and water vapor are cooled by the condenser 10 and condensed to be collected in the separator 12. To be done. The liquid that is difficult to dissolve in water is collected as the heavy specific gravity liquid Z and the light specific gravity liquid W2 due to the specific gravity.

[0022]

COMPARATIVE EXAMPLE 1 An organic solvent-containing gas containing 9000 ppm of methylene chloride and having a temperature of 40 ° C. was blown from the blower 2 to the adsorption tank 3 at a flow rate of 70 Nm ³ / min using a gas treatment apparatus equivalent to that shown in FIG. Desorption was performed in the adsorption tank 4 for 8 minutes, and then the air blow to the adsorption tank 3 was blocked by the automatic damper 6, and then steam was jetted into the adsorption element 5 of the adsorption tank 3. At the same time as this treatment, the automatic damper 6 of the adsorption tank 4 was opened, and this time, gas adsorption was performed in this adsorption tank 4. This operation of adsorption and desorption was repeated 10 times or more. The concentration of the gas discharged to the outside of the system was measured at the confluence of the outlet of the blower 2 and the outlets of the adsorption tanks 3 and 4 using a measuring instrument of total hydrocarbon meter HCM-1B manufactured by Shimadzu Corporation. The gas concentrations at the inlet and outlet of the gas treatment device during continuous operation are shown in FIG.

[0023]

Example 1 The same conditions were also applied to the case of FIG. 2 in which the recovery liquid line was connected to the bottom end of the tank drain line. The gas concentration during continuous operation is shown in FIG.

As can be seen by comparing the graphs of FIGS. 4 and 5, the gas concentration discharged to the outside of the system by using the method of the invention of the embodiment is stable even in the alternate switching operation of the adsorption tanks 3, 4. And it is clear that the concentration is low. There is almost no change in gas concentration even during continuous operation. It was also found that backflow of drain could be prevented.

[0025]

As described above, by changing the piping route of the recovery liquid line so that the condensate of the recovery liquid line does not flow into the tank drain line, the adsorption / desorption of the organic solvent-containing gas containing the low boiling point solvent can be performed. It will be possible to continuously and stably perform with high efficiency, which will greatly contribute to the industrial world.

[Brief description of drawings]

FIG. 1 Example of basic processing flow diagram of gas adsorption processing device

FIG. 2 shows an example of independent connection of the recovery liquid line 11.

FIG. 3 is an example of confluent connection of the recovery liquid line 11.

FIG. 4 is an exhaust gas concentration when the recovery liquid line 11 is conventionally connected (comparative example).

FIG. 5: Exhaust gas concentration when collecting liquid line 11 is independently connected (Example)

[Explanation of symbols]

1: Pre-filter 2: Blower 3: Adsorption tank (desorption tank when 4 functions as an adsorption tank) 4: Desorption tank (adsorption tank when 3 functions as a desorption tank) 5: Adsorption element 6: Automatic Damper 7: Automatic vapor control valve 8: Tank drain line 9: Desorption gas line 10: Condenser 11: Recovery liquid line 12: Separator 13: Return gas line 14: Exhaust port 15: Water vapor line X: Organic solvent-containing gas (processing target) Gas) Y: Clean air Z: Heavy specific gravity liquid W1: Water vapor W2: Light specific gravity liquid W3: Cooling water

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D002 AA00 AB03 BA04 BA13 CA07                       DA44 EA08 FA01 GA01 GB12                       HA10                 4D012 CA11 CB16 CD02 CG04 CG05                       CH06 CK10

Claims (4)

[Claims] 1. An adsorption element made of an activated carbon fiber material for adsorbing a gas to be treated is provided in an adsorption tank, and means for supplying a gas to be treated and a desorption gas supply means for said adsorption tank are provided by a desorption gas supply means. In a gas treatment device provided with means for cooling and recovering the desorbed desorbed gas, a pipe (tank drain line) for discharging the condensate from the lower part of the adsorption tank and a pipe (recovered liquid line) for discharging the condensate from the cooling part. A gas adsorption treatment device, wherein the gas adsorption treatment device is connected to the solvent recovery unit independently or by joining. 2. A means for switching between an adsorption treatment state for adsorbing a gas to be treated and a desorption treatment state for desorbing a gas to be treated adsorbed by a desorption gas, wherein two or more adsorption tanks are provided. 1. The gas processing device according to 1. 3. The gas treatment apparatus according to claim 1, wherein the desorption gas supply means is arranged at the upper part, the lower part or the central part of the core of the adsorption element in the adsorption tank. 4. A method for treating an organic solvent-containing gas using the gas treatment apparatus according to claim 1.