JP4736268B2 - Gas processing apparatus and gas processing method - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a gas processing apparatus that uses an 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 recovers the adsorbed organic solvent, and a processing method using this apparatus. Is.
[0002]
[Prior art]
In recent years, emission concentration regulations for harmful air pollutants have been strengthened, and it is desirable to reduce the concentration of harmful air pollutants at the gas processing device outlet as much as possible when processing harmful air pollutants with a gas processing device. Yes.
[0003]
Conventionally, the above gas treatment apparatus has at least one pair of adsorption tanks for adsorbing a gas to be treated (that is, exhaust gas such as an organic solvent-containing gas) with activated carbon fiber material, and a gas supply means and a desorption means for each adsorption tank. Gas supply means is provided, 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 is provided.
[0004]
Conventionally, in the gas treatment apparatus, ACF or granular activated carbon is generally used as an adsorbent, but ACF has a large specific surface area of 1000 to 2000 m ² / g as compared with granular activated carbon. Since there are many effective micropores and an extremely high adsorption / desorption rate, it is known and used as the most general method in the field of organic solvent recovery. For example, Japanese Patent Application Laid-Open No. 51-38278 and Japanese Patent Application No. 64-11326 disclose an apparatus in which an ACF is fixed to a support or is formed in a cylindrical shape by self-supporting and arranged in a core in a core material. Proposed. In addition, a gas apparatus that performs similar adsorption and desorption is proposed in Japanese Utility Model Publication Nos. 7-2028, 2029, and 2030. In any of these, water vapor is ejected to the core material storing the ACF, and the organic solvent adsorbed on the ACF is desorbed and recovered.
[0005]
In general, the organic solvent adsorption ability of ACF is easily affected by moisture, and the adsorption ability is extremely lowered when the moisture content of ACF is increased. For this reason, in the proposal, various ideas have been devised, such as the direction of water vapor ejection to the core material, that is, the adsorption element, from above or below, or from the center internal direction. However, when the operation is started, there is a problem that the adsorbing element gets wet with moisture due to scattering of the drain of the water vapor to be ejected or the reverse flow of the condensate, thereby reducing the adsorption capacity of the ACF organic solvent.
[0006]
Furthermore, in the gas treatment apparatus using the gas adsorption element described above, it has been difficult to perform stable and continuous operation over a long period of time. In other words, when low-boiling solvents are used repeatedly and alternately, in which water vapor is spouted onto the element adsorbed with the organic solvent and the adsorbed organic solvent is desorbed, the solvent recovery unit is particularly affected by the temperature of the outside air. The condensate often flows backward from the pipe leading to (hereinafter referred to as a separator). Due to this reverse flow, there is a problem that the condensate comes into contact with the ACF in the gas treatment element and the adsorption capacity is greatly reduced, which also hinders continuous operation.
[0007]
[Problems to be solved by the invention]
The present invention relates to a gas processing apparatus capable of continuously performing adsorption / desorption of an organic solvent-containing gas, particularly a low boiling point solvent, using ACF with high efficiency.
[0008]
In the continuous operation of the gas treatment device using the adsorption element, in the desorption process state, the desorption gas water vapor and the desorbed desorption gas become condensate in the adsorption tank at the initial stage of the desorption gas supply, and the tank below the adsorption tank It is discharged to the separator through the drain line. On the other hand, uncondensed water vapor and organic solvent pass through the desorption gas line, condense in the cooling section (hereinafter referred to as condenser), join 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 (becomes a desorption tank when another tank is operating as an adsorption tank because of continuous operation) passes through the tank drain line 8 to form the separator 12. At this time, the condensate staying in the tank drain line 8 is heated by the condensate from the lower part of the adsorption tank 4 and converted into boiling gas and flows back. This tendency becomes remarkable when the outside air temperature is low and there is a large amount of condensate or when the gas to be treated contains a low-boiling solvent.
[0009]
[Means for Solving the Problems]
In the present invention, a baffle is installed at the outlet to the tank drain line of the adsorption tank to prevent wetting of the adsorption element due to the backflow of condensate into the tank. As shown in FIG. 2, the baffle is one in which a support is placed on a flat plate and is mounted on a discharge port. Between these columns, water vapor, gas to be treated and condensate can freely pass through, and the pressure balance in the tank and the gas flow are not affected. Even if the outside air temperature falls and the amount of condensate in the adsorption tank increases and flows backward and enters the adsorption tank, it is possible to prevent the condensate from splashing onto the adsorption element by hitting this baffle. Therefore, continuous operation is possible without wetting the adsorption element with the condensate.
[0010]
In addition to the above, the baffle may have an umbrella shape or a hemispherical shape, and a conical shape or a divergent shape with respect to the discharge port is preferable. Moreover, it installs with a support | pillar so that it may be located in the upper part of a discharge port. Any material can be used as long as it does not dissolve in the organic solvent contained in the gas to be treated. Moreover, it installs so that it can remove from an adsorption tank with a support | pillar, and when cleaning etc., it can remove and can operate easily.
[0011]
In the case of a gas processing apparatus in which an organic solvent is continuously processed by desorption of water vapor using an adsorbing element, this effect is particularly remarkable in a low boiling point solvent. Usually, the organic solvent is discharged out of the adsorbing element together with water vapor. However, in the case of an organic solvent that is hardly soluble in water, the water layer and the solvent layer are separated by cooling outside the adsorbing element. In general, the specific gravity of the organic solvent is larger and the organic solvent is separated to the lower side of the two layers. Therefore, the organic solvent tends to be stored at the lowermost part of the tank drain line, and the backflow due to boiling becomes remarkable. Accordingly, when a backflow of the condensate is generated from the lower part of the adsorption tank, the adsorption element is wetted by the condensate, thereby reducing the adsorption capacity.
[0012]
The organic solvent here refers to an organic solvent such as methylene chloride, trichloroethane, trichloroethylene, carbon tetrachloride, chloroform, etc., and in the present invention, in particular, a solvent having a boiling point lower than water and a specific gravity heavier than water. Is suitable.
By installing this baffle, the adsorption element is not wetted by the condensate, and the temperature and relative humidity in the adsorption / desorption tank can be easily controlled, further improving the adsorption efficiency.
[0013]
Furthermore, since the adsorption element is no longer in contact with moisture and the adsorption capacity is maintained, it can be continuously switched as an adsorption tank or a desorption tank. As a result, the apparatus of the present invention can continuously adsorb and desorb the organic solvent-containing gas as well as smooth operation during operation and stop, so that it has excellent operability and can be operated over a long period of time.
[0014]
The ACF used in the present invention is a specific surface area of 1000 to 2000 m ² obtained by treating raw materials such as acrylonitrile (PAN) fiber, rayon fiber, coal pitch resin, phenol resin resin and petroleum pitch resin by an existing method. / G, fiber diameter of about 2 to 30 μm, fiber length of about 0.5 to 10 mm, and pore radius of about 5 to 20 mm may be used.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, an example of an embodiment of the present invention will be described with reference to FIG. Organic solvent-containing gas (treated gas) X is prefilter 1 (gases * 3, * 4 staying in condenser 10 and separator 12 are returned to prefilter 1 again through return gas line 13). As described above, the blower 2 sucks the adsorption tank 3 (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, water vapor is already blown out, The gas adsorbed by the adsorption element 5 is in a state of being desorbed), gas adsorption is performed by the adsorption element 5, and the purified air Y is discharged out of the system from the exhaust port 14 of the adsorption tank 3. . The condensate is sent to the separator 12 through the tank drain line 8 below the adsorption tank 4. Uncondensed water vapor and organic solvent are sent to the condenser 10 through the desorption gas line 9. From the condenser 10, the condensate containing a high concentration organic solvent passes through the recovery liquid line 11, joins the tank drain line 8, and is sent to the separator 12.
[0016]
At this time, in the case of a mixed gas mixed with a low-boiling solvent, the amount of flow into the tank drain line 8 increases as the external temperature decreases, so that the backflow of the condensate to the adsorption tank becomes remarkable. As a result, it is ejected to the adsorption tank 4 and wets the adsorption element.
[0017]
FIG. 2 shows an enlarged baffle in the adsorption tank (desorption tank) and the upper part of the tank drain line. In particular, even if the outside air temperature decreases and the amount of condensate in the adsorption tank increases and flows backward into the adsorption tank, it is possible to prevent the condensate from splashing onto the adsorption element by hitting this baffle. Therefore, continuous operation is possible without wetting the adsorption element with the condensate.
[0018]
As a result, even if the adsorption tanks 3 and 4 are switched and continuously operated, the concentration of the organic solvent gas discharged out of the system can be kept low and constant.
[0019]
The organic solvent adsorbed by the adsorption element 5 is ejected from the water vapor W1 to the adsorption element in the adsorption tank through the automatic valve 7 in the adsorption tank 4 to desorb the organic solvent. The amount of water vapor is controlled by the automatic steam control valve 7. Further, the water vapor is jetted into the tank from the upper part or the lower part (dotted line in FIG. 1) of the adsorption tank 4.
[0020]
As a result, the organic solvent-containing gas X is released out of the system as clean air Y, and the desorbed uncondensed organic solvent gas and water vapor are cooled by the condenser 10, condensed and recovered by the separator 12. Liquids that are hardly soluble in water are recovered as heavy specific gravity liquid Z and light specific gravity liquid W2 by specific gravity. For example, when the organic solvent gas is methylene chloride having a specific gravity of 1.3 (20/4 ° C.), the heavy specific gravity liquid Z is recovered as methylene chloride, and the light specific gravity liquid W2 is recovered as steam condensed water.
[0021]
[Example 1]
Using the gas treatment apparatus shown in FIG. 1 provided with the baffle of the present invention, 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 an air flow rate of 70 Nm ³ / min. Desorption was performed for 8 minutes in the adsorption tank 4, and then the air blown to the adsorption tank 3 was blocked by the automatic damper 6, and then water vapor was jetted into the adsorption element 5 of the adsorption tank 3. Simultaneously with this treatment, the automatic damper 6 of the adsorption tank 4 was opened, and gas adsorption was performed in this adsorption tank 4 this time. This adsorption and desorption operation was repeated 10 times or more. An enlarged view of the baffle is shown in FIG.
The concentration of the gas discharged out of the system was measured at the confluence of the outlet of the blower 2 and the adsorption tanks 3 and 4 using a measuring instrument of a total hydrocarbon meter HCM-1B manufactured by Shimadzu Corporation. FIG. 3 shows the gas concentrations at the inlet and outlet of the gas processing apparatus when continuously operated.
[0022]
[Comparative Example 1]
The same conditions were applied to the case where an apparatus equivalent to that in FIG. 1 was used except that the baffle of the present invention was not installed. The gas concentration when continuously operated is shown in FIG.
[0023]
As can be seen by comparing the graphs of FIGS. 3 and 4, the concentration of the gas discharged out of the system by using the method of the invention of the embodiment is stable and low in the switching operation of the adsorption tanks 3 and 4 alternately. It is clear that Even in continuous operation, there is almost no fluctuation in gas concentration.
[0024]
【The invention's effect】
As explained above, by installing a baffle so that the condensate in the recovered liquid line does not flow into the tank drain line, the adsorption and desorption of the organic solvent-containing gas containing the low boiling point solvent can be performed continuously and stably with high efficiency. It will be possible to contribute to the industry.
[Brief description of the drawings]
1 is an example of a basic process flow diagram of a gas adsorption processing apparatus. FIG. 2 is an enlarged view of an example of a baffle. FIG. 3 is an exhaust gas concentration when a baffle is provided (Example).
FIG. 4 Exhaust gas concentration when no baffle 16 is provided (comparative example)
[Explanation of symbols]
1: Prefilter 2: Blower 3: Adsorption tank (When 4 functions as an adsorption tank, desorption tank)
4: Desorption tank (when 3 functions as a desorption tank, adsorption tank)
5: Adsorption element 6: Automatic damper 7: Steam adjustment automatic 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 16: Baffle (generic name for 17 and 18)
17: Prop 18: Backflow prevention plate X: Gas containing organic solvent (treated gas)
Y: Clean air Z: Heavy specific gravity liquid W1: Water vapor W2: Light specific gravity liquid W3: Cooling water

Claims (6)

An activated carbon fiber material adsorbing element for adsorbing the gas to be treated is provided in the adsorption tank, and a gas to be treated supply means and a desorption gas supply means for the adsorption tank are provided and desorption is performed by the desorption gas supply means. In the gas processing apparatus provided with a means for cooling and recovering the gas, a baffle comprising a column and a backflow prevention plate is provided above the discharge port from the adsorption tank of the tank drain line which is a pipe connecting from the lower part of the adsorption tank to the solvent recovery unit. gas processing apparatus, characterized in that the provided. The gas adsorption processing apparatus according to claim 1, wherein the backflow prevention plate of the baffle has a flat plate shape, an umbrella shape, a hemispherical shape, a conical shape, or a divergent shape. The adsorption vessel comprises two or more tanks, and the adsorption process conditions for adsorbing the gas to be treated, according to claim 1 or 2 provided with sequentially switching means and a desorption process conditions to desorb the gas to be treated is adsorbed in the desorption gas Gas processing equipment. The gas processing apparatus according to any one of claims 1 to 3, wherein the desorption gas supply means is disposed at an upper part, a lower part, or a central part of the core of the adsorption element in the adsorption tank. The method to process organic solvent containing gas using the gas processing apparatus in any one of Claims 1-4 . The method for treating an organic solvent-containing gas according to claim 5, wherein the organic solvent is an organic solvent having a boiling point lower than that of water and a specific gravity heavier than that of water.

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