JPH06198119A - Method for recovering volatile matter - Google Patents

Abstract

PURPOSE:To prevent the frost accretion in a refrigerator for liquefaction and to improve the energy balance in an adsorptive recovery method of gaseous low boiling point materials, such as fluorocarbon. CONSTITUTION:When fluorocarbon adsorbed in an adsorption column A1 is desorbed and recovered by passing regenerating gas, the adsorption column A1 is connected to an air compression P, a heat exchanger E, a dehumidifier D taking a moisture content separation membrane as a diaphragm and a condenser to form a circulating passage for the regenerating gas. The regenerating gas leaving the adsorption column A1 is compressed by an gas compressor and then enters a heat exchanger E on the primary side where it exchanges heat with the low temperature regenerating gas passed through the condenser and then enters the dehumidifier D on the primary side to be dehumidified. And next, after an object material is separated from it in the condenser, it is circulated so as to pass through the heat exchanger E on the secondary side to return to the absorption column A1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering volatile substances represented by Freon (chlorofluorocarbon) and the like, and more particularly, a method for separating and recovering volatile substances existing as a component gas of a mixed gas. It is about.

[0002]

2. Description of the Related Art As one of the methods for separating a specific component gas from a mixed gas, the mixed gas is passed through one of a pair of adsorption towers filled with synthetic zeolite, activated carbon, etc. Gas is adsorbed and separated, and at the same time, the adsorption equilibrium condition is changed by passing the regeneration gas with different temperature and / or pressure to the other adsorption tower that adsorbs and captures the specific component gas in the previous step. Then, the specific component gas is desorbed, and the other adsorption tower is regenerated.

In order to separate and collect volatile substances in the mixed gas, the regeneration gas which desorbs the volatile substances from the adsorbent and carries them as a mixed gas is cooled to a temperature below the condensation temperature of the volatile substances and liquefied. Then, the method of collecting is performed. At that time, if the mixed gas contains water, the efficiency of capturing the target substance decreases. Also, if the adsorbent is not sufficiently regenerated in a short time, the capacity of the adsorption tower is reduced, and if the volatile substance to be recovered is a substance with a low condensation temperature such as CFC, it will be used as a condenser. Although it is necessary to use a refrigerating cooler, there is a possibility that the water content in the mixed gas may frost the cooling fins of the cooler and reduce its performance.

In order to improve the drawbacks of such a method,
As a method of separating water vapor from the mixed gas, a cooling method or an adsorption method is generally performed, but there is a drawback that the processing steps are congested such as a complicated apparatus or a new adsorbent regeneration processing step is required. . As a dehumidifier without such a disadvantage, for example, a high-humidity target gas is passed through one side (primary side) of a dehumidifier having a water separation membrane as a diaphragm as disclosed in JP-A-2-99113. There is known a device in which water vapor is diffused and transferred from the primary side to the secondary side by passing a dry gas through the other side (secondary side) across the diaphragm to separate the vapor.

However, a recovery device incorporating this dehumidifying device has a simple dehumidifying mechanism and does not require treatment such as regeneration of drain and adsorbent as in a conventional dehumidifier, but it is conventionally a primary dehumidifying device. On the side, the regeneration gas whose temperature has risen to a certain degree for heating and regeneration of the gas compressor and the adsorbent passes through, while as the gas passing through the secondary side, the dry exhaust gas that has passed through the adsorption tower in the separation process. Since it is used as it is, even if some heat exchange is performed through the diaphragm in the dehumidifier, it is not sufficient, and the refrigerating cooler is likely to be overloaded, and the regeneration gas Since water in the inside was not sufficiently removed, there was a risk of frost formation on the refrigerator, and frost formation on the cooling fins and defrosting management were essential.

[0006]

The object of the present invention is that, in the conventional method for recovering volatile substances, the regenerating gas after the desired substance is condensed and separated is released to the outside of the system, such as being released into the atmosphere. Attention was paid to the fact that the heat loss was large, and in the regeneration process, by circulating and reusing the regeneration gas, the energy balance was improved, the dehumidification capacity of the moisture separation membrane dehumidifier was improved, and the refrigerator was used. The purpose is to prevent overload and frost formation.

[0007]

The first aspect of the present invention is to provide a separation step of introducing a gas to be treated containing a vaporized volatile substance to an adsorption tower having adsorption activity to adsorb and capture the volatile substance. A regeneration process in which a regeneration gas is passed through an adsorption tower that has captured volatile substances through a separation process to desorb volatile substances and regenerate the adsorption activity, and the regeneration gas that has passed through the adsorption tower is passed through a condenser for regeneration. In a method for recovering a volatile substance, which comprises liquefying and recovering a volatile substance in a working gas, a gas compressor, a heat exchanger, which feeds the regenerating gas to the adsorption tower in the regenerating process, A circulation channel for regeneration gas is formed by connecting with a dehumidifier having a water separation membrane as a diaphragm and a condenser, and the regeneration gas discharged from the adsorption tower in the regeneration step is pressurized by a gas compressor. To the primary side of the heat exchanger, where it passes through the condenser. Low temperature after regeneration gas and heat exchange with, dehumidified enters the primary side of the dehumidifier, then
In the method for recovering a volatile substance, the volatile substance is separated in a condenser and then circulated so as to pass through the secondary side of the heat exchanger and return to the adsorption tower.

A second aspect of the present invention is an adsorption tower having an adsorption activity among a plurality of adsorption towers connected in parallel to each other through a switching valve to a supply pipe of a gas to be treated containing a vaporized volatile substance. In the separation step of guiding the gas to be treated to adsorb and capture the volatile substance, the adsorption tower that has captured the volatile substance through the separation step in the previous stage passes a regeneration gas through the regeneration gas to desorb and adsorb the volatile substance. And a regeneration step of performing regeneration at the same time in parallel, and a recovery step of passing the regeneration gas that has passed through the adsorption tower through a condenser to liquefy and recover the volatile substances in the regeneration gas. In the method for recovering a volatile substance, the adsorption tower in the regeneration step is connected to a gas compressor for feeding the regeneration gas, a heat exchanger, a dehumidifier having a water separation membrane as a diaphragm, and a condenser for regeneration gas. To form a circulation flow path for Play for gas exiting from the adsorption tower,
After being pressurized with a gas compressor, the heat exchanger exchanges heat with the low-temperature regeneration gas that has passed through the condenser, then enters the primary side of the dehumidifier to be dehumidified, and then the volatile substances are separated in the condenser. A method for recovering volatile substances is characterized in that the volatile substances are circulated so as to return to the adsorption tower after the operation.

A third aspect of the present invention is the method for recovering a volatile substance defined in the first or second aspect, wherein the regeneration gas circulation passage extending from the condenser to the heat exchanger is heated by the regeneration gas. A volatilization device is provided to activate the regeneration gas heater when the temperature of the regeneration gas flowing through the regeneration gas circulation flow path from the heat exchanger to the dehumidifier falls below a predetermined temperature. The temperature of the regenerating gas that has passed through the condenser and is cooled and then enters the heat exchanger is lowered more than necessary due to the condensation temperature of the target substance and the ambient temperature surrounding the recovery device. Is to prevent.

In the method for recovering volatile substances defined in the first and second aspects, the regeneration gas is
When passing through the heat exchanger after the temperature has dropped through the condenser,
The recovery method is also designed to pass through the secondary side of the dehumidifier as dry regeneration gas whose relative humidity has decreased by exchanging heat with the regeneration gas pressurized by the gas compressor to raise the temperature. Included in the inventive method. Hereinafter, based on the examples,
The details will be described.

[0011]

1 and 2 show an example of an apparatus for carrying out the method according to the invention. In the figure, reference numeral 1 is a suction port for the gas to be treated which is opened at the upper edge of the cleaning tank using a volatile solvent such as CFC or at the upper side, and is a blower B through a duct
Connected to. A pair of main adsorption towers A ₁ and A ₂ are connected to a supply pipe 2 for the gas to be treated, which is an outlet pipe line of the blower, via an electric three-way switching valve V _0. Each of them is provided with an auxiliary adsorption tower A ₃ which can be selectively connected by operating the on-off valve, and forms an adsorption separation section for volatile substances. H _{1 to} H ₃ are gas heaters each having an electric heater housed in a duct connected in series with these adsorption towers.

The adsorption tower is filled with an appropriate gas adsorbent such as activated carbon, synthetic zeolite or silica gel depending on the properties of the target substance to be separated and recovered. A condensation recovery unit is connected to each of these adsorption towers via a pipe line provided with a switching valve. The condensing / recovering section sucks the regeneration gas after desorption / regeneration of the adsorption tower and the air supplemented from the air introduction port 6 as necessary through the suction pipe 5, and supplies it to the aftercooler C ₃ as a pressurized regeneration gas. The gas compressor P, the air filter F, the heat exchanger E, the gas-liquid separator S ₁ , the moisture separation membrane type dehumidifier D, the refrigeration condenser G, and the gas-liquid separator S ₂ which are discharged toward them are combined in this order. The adsorption towers A _{1 to} A ₃ are connected to form a gas circulation flow path by a conduit provided with an opening / closing valve as appropriate.

V _{1 to} V ₆ , V _{8 to} V ₁₁ , and V _{13 to} V ₁₆ are electric on-off valves for switching the above-mentioned pipelines, and V ₇ and V ₁₂ are both pressure reducing valves. Further, 3 is a purge port, 4
Is a recovery tank, 7 is a drain tank, 8 is a check valve, and C _{1 to} C ₄ are fan type coolers. As the moisture separation membrane type dehumidifier E, a hollow fiber type moisture separation membrane composed of a perfluorosulfone-based ion exchange membrane as disclosed in JP-A-2-99113 is used, and heat exchange is performed inside the hollow fiber membrane. As the primary side flow path of the vessel, the one surrounding the container was used as the secondary side flow path, but as the water separation membrane, other known water separation membranes were used, including the polyimide water separation membrane. Can be done. The shape of these separation membranes is not limited to the hollow fiber type, and a known type such as a flat membrane type can be adopted.

As an example of the recovery method of the present invention using the recovery device as described above, the case of recovering CFCs will be described.
By undergoing regeneration steps in the previous stage, the adsorption tower A ₂ adsorption activity is being played through the switching valve V _0, the process air is guided containing chlorofluorocarbon, in passing through the adsorption tower A _2, The chlorofluorocarbon gas is trapped by the adsorbent, so that the air that has passed through the adsorption tower A ₂ is discharged to the atmosphere from the purge port 3 through the opening / closing valve V ₁₆ in a state that the fluorocarbon gas is substantially free of chlorofluorocarbon. It goes without saying that the open / close valves V ₉ , V ₁₄ and V ₁₅ are closed at this time. Therefore,
In the following description, in order to avoid complexity, the gas flow path will be mainly described, and the opening / closing valve will be opened / closed so as to realize the flow by a preset control program.

As a part of the regeneration step, first, the desorption regeneration of the auxiliary adsorption column A ₃ and the adsorption concentration step of the desorption CFC in the adsorption column A ₁ are performed in parallel with the above-mentioned CFC separation step. The temperature of the regeneration gas (regeneration air) discharged from the compressor P is slightly lowered by the cooler C ₃ (the outside air temperature is set to 2
When the temperature is around 0 ° C., the temperature is about 60 ° C.), the fine particles such as the adsorbent are removed by the filter F, and the particles enter the primary side of the heat exchanger E. Here, it is cooled (for example, 10 ° C. or less) by a regeneration gas cooled to a temperature equal to or lower than the condensation temperature under pressure (eg, 7 kg / cm ² ) of the CFCs to be recovered that has passed through the condenser G.
Then, the drain is separated and enters the primary side of the dehumidifier D in a state where the relative humidity is close to 100%.

The secondary side of the dehumidifier passes through the secondary side of the heat exchanger to increase the temperature (around 40 ° C.), and further passes through the pressure reducing valve V ₁₂ to reduce the pressure to near normal pressure. By doing so, the regenerating gas with a reduced relative humidity is V ₁₁ , cooler C
After going through ₄ in this order, it is flowing. Thus, the regeneration gas flowing through the primary side of the dehumidifier D is dehumidified and dried with extremely high efficiency (for example, the atmospheric pressure dew point is −35 ° C. or lower), so that the condensation temperature of the Freon to be recovered under pressure in the condenser G is increased. Even if it is cooled to a lower temperature,
Enter the refrigeration condenser with no risk of frost on the cooling fins of the refrigerator.

Next, the regeneration gas is heated from the condenser G through the heat exchanger E, the secondary side of the dehumidifier D, the on-off valve V ₈ and the gas heater H ₃ as described above. After that, the auxiliary adsorption tower is entered, the tower A ₃ is desorbed and regenerated, and then the on-off valve V ₃
After passing through the column, it enters the main adsorption tower A ₁ , and the desorbed CFC is adsorbed on the main adsorption tower and concentrated. The CFC desorbed from the auxiliary adsorption tower was adsorbed and captured by the pressure adsorption of CFC which could not be completely condensed and separated in the condenser during the regeneration process of the main adsorption tower A _{1 in} the preceding stage and was refluxed together with the regeneration gas. Is. The regeneration gas passing through the main adsorption tower A ₁ returns to the compressor through the on-off valve V ₁₃ , and circulates in the same flow path again.

When the desorption / regeneration of the auxiliary adsorption tower is completed, the on-off valve is switched, the gas heater H ₃ is stopped, and the gas heater H ₁ is operated instead. The regeneration gas is, as shown by the thick line in FIG. 2, the compressor P → the primary side of the heat exchanger E → the primary side of the dehumidifier D → the condenser G → the secondary side of the heat exchanger E → the open / close valve V. ₄ → auxiliary adsorption tower A ₃ → cooler C ₁ → pressure reducing valve V ₇ → open / close valve V ₆ → secondary side of dehumidifier D → open / close valve V ₁₀ → gas heater H ₁ → adsorption tower A ₁ → open / close valve V ₁ → Cooler C ₂ → Circulates in the circulation passage of the compressor P.

The regeneration gas near atmospheric pressure heated by the gas heater H ₁ heats the adsorption tower H ₁ to desorb the fluorocarbon gas concentrated in the adsorbent, and the desorption regeneration step of the auxiliary adsorption tower. As described in detail in 1., this is pressurized by a compressor, then cooled by a heat exchanger, enters a dehumidifier in a low temperature and high humidity state, diffuses and releases water vapor to a secondary side through a moisture separation membrane, Acquire the required low temperature and low humidity conditions. This requirement is that the temperature of the regeneration gas that has passed through the dehumidifier is the condensation temperature of the steam contained in the regeneration gas (air) at the same pressure, rather than the condensation temperature of CFCs under pressure, which is the volatile substance to be separated and recovered. Is to be dried so that it is lower.

In the gas that has passed through the condenser G, it is inevitable that a small amount of CFCs remain unseparated. For this reason, the regeneration gas that has passed through the heat exchanger is guided to the auxiliary adsorption tower A ₃ while maintaining a high pressure state, and is passed through the adsorbent layer that has already been regenerated, so that the partial pressure of the dilute Freon gas component is reduced. It is raised and adsorbed on an adsorbent to be removed. Thus, the partial pressure of the Freon of the regeneration gas that has passed through the auxiliary adsorption column becomes almost equal to zero. The regeneration gas is also dried by adsorbing moisture in the auxiliary adsorption tower, and is further depressurized by the decompression valve V ₇ to near normal pressure, so that the dehumidifier D is in a state where the relative humidity is extremely reduced. Of the gas heater H ₁ and then again,
The adsorption tower A ₁ is desorbed and regenerated. By repeating this circulation for a predetermined time, the desorption / regeneration step of the adsorption tower A ₁ is completed.

Reference numeral 10 is an electric heater provided in the regeneration gas flow path from the condenser G to the secondary side flow path of the heat exchanger E, a hot gas heat exchanger bypassed from the refrigeration condenser G, and the like. A temperature detector 1 for detecting the temperature of the regeneration gas, which is directed to the dehumidifier D through the primary side flow path of the heat exchanger, in the gas heater 1.
On the basis of the detection signal of No. 1, when the temperature of the regeneration gas falls below a predetermined set temperature, the temperature of the regeneration gas entering the secondary side of the heat exchanger rises, Prevents material from condensing and separating. Therefore, this set temperature is determined by the condensation temperature of the volatile substance to be recovered. The gas heater 10 is effective when the ambient temperature surrounding the device is low, such as when the device of the present application is operated in winter.

When the regeneration step of the adsorption tower A ₁ is completed, the switching valve V ₀ is switched, and the adsorption tower A ₂ which has been subjected to the separation step until then, together with the auxiliary adsorption tower A ₃ , is regenerated in exactly the same manner as described above. In the process, the air to be treated is introduced into the adsorption tower A ₁ and subjected to the separation process. By continuing the exchange between the main adsorption towers A ₁ and A ₂ , the vaporized solvent can be continuously recovered.

In the above-mentioned embodiment, the method of continuously separating and recovering the volatile substance is exemplified. This is because the adsorption separation section of the above-mentioned apparatus is used for a certain period of time (for example, the working hours of the day). It is also possible to perform only the separation step and operate the condensation recovery section to perform regeneration of the adsorption tower and condensation recovery of the target substance during a time period such as nighttime when the separation step is unnecessary.

[0024]

[Effect] In the method for recovering volatile substances according to the present invention, the amount of gas newly replenished from outside the system as regeneration gas is
Very little, and most of them circulate in the system for reuse, so there is very little energy loss, and therefore, there is little opportunity for water vapor in the outside air to newly enter the system. Therefore, the load on the adsorption tower and the dehumidifier is reduced. Furthermore, the heat exchanger E achieves the pre-cooling of the regeneration gas toward the condenser and the significant improvement of the dehumidification performance of the moisture separation membrane type dehumidifier, so that the defrosting control of the refrigerator of the refrigeration type condenser can be performed. It is not necessary at all, and a maintenance-free recovery device can be provided.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of an apparatus for carrying out a recovery method according to the present invention, and a flow path indicated by a thick line shows a circulation flow path of a regeneration gas in a regeneration process of an auxiliary adsorption tower. .

FIG. 2 shows a flow path in the regeneration process of the main adsorption tower by a thick line in the conceptual diagram of FIG.

[Explanation of symbols]

A _{1 to} A ₂ main adsorption tower A ₃ auxiliary adsorption tower B blower C _{1 to} C ₄ fan type cooler H _{1 to} H ₃ gas heater V ₀ switching valve V _{2 to} V ₆ , V _{8 to} V ₁₁ , V ₁₂ to V ₁₆ Open / close valve P Compressor E Heat exchanger D Moisture separation membrane type dehumidifier G Refrigerating condenser 1 Treated gas inlet 6 Atmosphere inlet 4 Recovery tank

Claims (6)

[Claims] 1. A gas to be treated containing a vaporized volatile substance,
A separation step of guiding to an adsorption tower having adsorption activity to adsorb and capture a volatile substance, and a regeneration gas is passed through the adsorption tower capturing the volatile substance through the separation step to desorb the volatile substance and In a method for recovering a volatile substance, which includes a recovery process for performing a regeneration process, a recovery gas passing through an adsorption tower through a condenser, and a recovery process for liquefying and recovering a volatile substance in the recovery gas, The adsorption tower in the regeneration step is connected to a gas compressor for feeding the regeneration gas, a heat exchanger, a dehumidifier having a water separation membrane as a diaphragm, and a condenser to form a circulation channel for the regeneration gas. , The regeneration gas discharged from the adsorption tower in the regeneration step enters the primary side of the heat exchanger after being pressurized by the gas compressor, and in the heat exchanger, the low-temperature regeneration gas that has passed through the condenser After exchanging heat with, it enters the primary side of the dehumidifier and is dehumidified, Ide, method for recovering volatile substances, characterized in that to circulate back to the adsorption tower through the secondary side of the heat exchanger of volatiles is separated in the condenser. 2. The gas to be treated is introduced into an adsorption tower having adsorption activity among a plurality of adsorption towers connected in parallel to each other through a switching valve to a supply pipe for the gas to be treated containing a vaporized volatile substance. A separation step of adsorbing and capturing a volatile substance by a gas, and a regeneration step of desorbing the volatile substance and regenerating the adsorption activity through a regeneration gas through the adsorption tower that has captured the volatile substance through the separation step in the previous stage. In parallel with the above, the regeneration gas that has passed through the adsorption tower is passed through a condenser, and in a recovery method for volatile substances, including a recovery step of liquefying and recovering volatile substances in the regeneration gas, A gas compressor, a heat exchanger, for feeding a regeneration gas to the adsorption tower in the regeneration step.
A circulation channel for regeneration gas is formed by connecting with a dehumidifier having a water separation membrane as a diaphragm and a condenser, and the regeneration gas discharged from the adsorption tower in the regeneration step is pressurized by a gas compressor. To the primary side of the heat exchanger, and after heat exchange with the low temperature regeneration gas that has passed through the condenser in the heat exchanger, enters the primary side of the dehumidifier to be dehumidified, and then to remove volatile substances in the condenser. A method for recovering a volatile substance, characterized in that the volatile substance is circulated through the secondary side of the heat exchanger and back to the adsorption tower after the separation. 3. A regeneration gas heater is provided in the regeneration gas circulation passage from the condenser to the heat exchanger, and the temperature of the regeneration gas flowing through the regeneration gas circulation passage from the heat exchanger to the dehumidifier is ,
The recovery method according to claim 1 or 2, wherein the regeneration gas heater is operated when the temperature becomes equal to or lower than a predetermined temperature. 4. A plurality of adsorption towers comprises a pair of adsorption towers and an auxiliary adsorption tower that can selectively communicate with each of the pair of main adsorption towers, and the regeneration gas is used in the regeneration step. The auxiliary adsorption tower is connected to the main adsorption tower so that it enters the main adsorption tower after passing through.First, the auxiliary adsorption tower is desorbed and regenerated, and the regeneration gas is passed through the main adsorption tower to remove the desorbed components from the main adsorption tower. At the time of desorption regeneration of the main adsorption tower, which is performed after desorption regeneration of the auxiliary adsorption tower, the residual components of the volatile substances in the circulation regeneration gas that could not be liquefied and separated by the condenser were added to the auxiliary adsorption tower. The recovery method according to any one of claims 1 to 3, wherein after the pressure adsorption, the regeneration gas is decompressed and allowed to flow in the main adsorption tower. 5. The regeneration gas whose relative humidity has been lowered by exchanging heat with the regeneration gas pressurized by the gas compressor in the heat exchanger in the regeneration step is passed through the secondary side of the dehumidifier. The recovery method according to any one of to 4. 6. In the regeneration step of the main adsorption tower, the regeneration gas whose relative humidity is lowered by exchanging heat with the regeneration gas pressurized by the gas compressor in the heat exchanger is further dried by passing through the auxiliary adsorption tower. 5. After making it pass, the secondary side of a dehumidifier is passed.
Recovery method.