JPH06312117A - Solvent recovery - Google Patents

Abstract

PURPOSE:To economize the supply of gas for desorption by installing at least, three adsorption towers side by side, and operating three steps in parallel such as a) adsorption of solvent gas, b) dry desorption by desorption gas, and c) purification of residual solvent gas after desorption recovery as well as using clean gas after the step c) again as gas for desorption in the step b). CONSTITUTION:At least, three desorption towers 1 to 3 are installed side by side, and each tower takes care of three sequential steps such as adsorption of solvent gas, b) dry desorption by desorption gas and c) adsorption of residual solvent gas after desorption recovery to repeat the continuous adsorption process of the solvent gas. In this solvent recovery method, clean gas after the step c) is repeatedly used as gas for desorption in the step b). In this case, inert gas such as nitrogen or carbon dioxide is preferred as gas for desorption. Consequently, it is possible to economize the external feed of inert gas and thereby minimize energy loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solvent recovery method, and more particularly to a solvent recovery method for continuously recovering a solvent component from a solvent-containing gas by using an adsorption tower filled with an adsorbent.

[0002]

2. Description of the Related Art The conventional technology is, for example, "pollution and measures vo
L.2, No. 12 (1990) P25 to P38 ", and will be explained while pulling out. There are three technologies for removing and recovering organic solvents from exhaust gas: cooling, compression, and adsorption / desorption. The cooling method is divided into 2 minutes depending on whether the cooling temperature is 0 ° C. or higher or 0 ° C. or lower. A device that cools at 5 ° C. or higher, which is commonly used, is relatively cheap, but the recovery rate of low boiling point compounds is low. The equipment that cools below 0 ° C has a high recovery rate, but since water freezes, in order to prevent this, a defrost method that melts ice intermittently or an air shower method that absorbs water with calcium chloride or lithium chloride is used. It is necessary to take measures.

As a compression method, there is a method of pressurizing the vapor of an organic solvent and increasing the partial pressure above the saturated vapor pressure of the solvent to liquefy it. However, since the temperature rises due to the heat of compression, it is necessary to increase the recovery rate. It requires heat dissipation and cooling. For example, if dichloromethane is compressed to 5 kg / cm ² and cooled to 5 ° C, 1
This is the same as when cooled to about -30 ° C at atmospheric pressure. That is, the recovery rate of dichloromethane or the like can be increased by using cooling together. However, it is not applicable to low-concentration exhaust gas, so there are not many examples of use so far.

The adsorption / desorption method is a method in which an organic solvent is adsorbed on activated carbon or the like, desorbed by steam or hot air, and the desorbed high-concentration organic solvent vapor is liquefied by a cooling method and recovered. The types and characteristics of this adsorption / desorption method are shown below. 1) Preconcentration method using honeycomb-type activated carbon drum In a general adsorption / desorption device, if a large amount of exhaust gas is treated at a low concentration of tens of ppm or less, the device becomes large, which is disadvantageous. Therefore, in such a case, pre-concentration is performed in advance by a simple adsorption / desorption device, and then a full-scale removal / recovery device is used. As a simple preconcentrating device, a device that rotates a honeycomb-type activated carbon drum to repeat adsorption and desorption in a short time is used.

2) Method using granular activated carbon For adsorption and desorption of organic solvent vapor, exhaust gas is sent to a large fixed bed filled with activated carbon formed into a cylindrical shape of 5 to 10 mm or crushed activated carbon for adsorption. A device has been widely used in which steam is desorbed every several hours to several days and the organic solvent in the desorbed gas is recovered by a cooling method.

3) Method using fibrous activated carbon A small fixed bed apparatus using fibrous activated carbon is one in which one or two cylinders of fibrous activated carbon molded into a hollow cylinder are attached and every 10 to 20 minutes. Adsorption and steam desorption are repeated alternately. Further, two stages of fibrous activated carbon formed into a mat shape are provided, and adsorption and desorption with steam or hot air are repeated every 10 to 20 minutes.

4) System using spherical activated carbon In a fluidized bed using spherical activated carbon, there is also a system in which an adsorption tower and a desorption tower are vertically connected to each other for continuous adsorption / desorption. In this apparatus, exhaust gas is passed from the lower part of the adsorption tower divided into several stages, activated carbon is made to flow, and it is adsorbed while being successively dropped to the lower stage, and the adsorbed activated carbon is desorbed by heating in the desorption tower. In this case, the steam is not directly blown in, but the activated carbon is heated through a heat exchanger, expelled with a small amount of air, and cooled and recovered in the condenser.

5) Method using honeycomb-like activated carbon An apparatus for adsorbing in a fixed bed using honeycomb-like activated carbon and desorbing by electrically heating while decompressing has a small ventilation resistance and a high adsorption rate, so that adsorption is performed at a high flow rate. It is possible to do so, and because steam is not used for desorption, there are features that water does not enter the collected liquid and wastewater treatment is easy. However, the adsorption capacity per volume is small, and desorption takes some time. There is also a type of this apparatus in which water vapor is directly introduced for desorption.

As described above, various adsorption / desorption methods have been conventionally known, but in the case of performing steam desorption commonly used for activated carbon, cooling condensation is performed to separate the solvent and water. However, in reality, the solvent slightly dissolves in the separated water, and it is difficult to remove the solvent sufficiently with simple auxiliary equipment such as the aeration method, and the cost of wastewater treatment is high to comply with strict environmental regulations. It is expected to increase more and more. As a countermeasure for that, there is a dry method in which the temperature and pressure of the adsorbent are changed to desorb the adsorbed solvent.
However, the dry method has disadvantages that the initial cost is higher and the electric power cost is higher than that of the wet method. Besides,
If the solvent gas to be treated contains oxidizing or decomposable solvents such as ketones and esters, use inert solvent desorbed solvent as carrier gas or increase adsorbent to prevent ignition and deterioration. Since it is preferable to use it for warming,
A new inert gas generator is required.

As the inert gas generator, for example, in the case of N ₂ gas, a small-scale generator using N ₂ cylinder or liquid nitrogen, and a large-scale generator using N ₂ in the air as a raw material are used. However, for solvent recovery assuming continuous operation,
Since a large amount of inert gas is required for desorption, a generator for purifying nitrogen from air is inevitably adopted, which considerably increases the installation space and power consumption. By the way, when the desorption gas is air, a gas generator is not necessary, but the water content in the condensate is higher than in the case where a part of the processing gas is used for desorption. . In the desorption gas circulation method, all the water condensed and collected in the cooler is generated due to the desorption, which leads to a reduction in the amount of water generated in the collected liquid.

[0011]

The present invention, instead of installing the large-scale nitrogen gas refining apparatus as described above, suppresses energy loss as much as possible, and supplies inert gas from the outside in the desorption step. Only when replacing with gas,
An object of the present invention is to provide a solvent recovery method that can reduce power consumption and make the nitrogen gas generator itself small-scale.

[0012]

In order to solve the above-mentioned problems, in the present invention, three or more adsorption towers are installed in parallel, and each tower is sequentially installed (a) a solvent gas adsorption step and (b) desorption. In the solvent recovery method of continuously adsorbing a solvent gas by repeating three steps, a dry desorption step using a working gas and a (c) adsorption step of a residual solvent gas after desorption and recovery, after the (c) step The refining gas of No. 1 is repeatedly used as the desorption gas in the step (b) again. When the number of adsorption towers is 4 or more, it is possible to operate with an additional pause step.
Further, each step can be performed by a plurality of towers. In the above method, an inert gas such as nitrogen or carbon dioxide may be used as the desorption gas.

As described above, in the present invention, when three adsorption towers are installed, (a) a solvent gas adsorption step, (b) a dry desorption step using a desorption gas, and (c) a residual solvent after desorption recovery. One of the three towers takes charge of the three steps of gas purification in parallel, and each tower processes (a) adsorption step, → (b) desorption step, →
(C) Each step is repeated in the order of the step of purifying the residual solvent gas after desorption / recovery to continuously adsorb / desorb the solvent gas for treatment, and the refining gas obtained in the step (c) is again treated (b).
It is repeatedly used as a desorption gas for the process.

[0014]

As described above, when three adsorption towers of the present invention are used in parallel, one tower is used for adsorption and the other two towers are used for desorption.
One of them was used as an adsorption step for the residual solvent gas after desorption and recovery, the desorption gas was clarified, and the clarified desorption gas was circulated as the desorption gas in the desorption step in the other one column. Since the inert gas used as the desorption gas can be used only during the replacement in the first desorption step, the amount of the inert gas used can be greatly reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings, but the present invention is not limited to these embodiments. Example 1 FIG. 1 shows a flow chart for explaining a solvent recovery method when three adsorption towers of the present invention are installed. FIG. 2 shows an operation process chart of each adsorption tower in FIG. An example of a specific operation method of the present invention will be described with reference to FIG. 1, but here, for convenience, it is assumed that the process proceeds in the process of FIG. 2, and only the related valves to be opened are described.

(1) Adsorption The solvent gas is introduced into the adsorption tower 1 after being dehumidified by the raw gas mist separator 15 by the raw gas blower 7, and the solvent is removed by the adsorbent (activated carbon etc.). The processing gas is released to the atmosphere. (Valves 18 and 19 are opened) (2) Desorption and recovery of residual solvent gas after desorption Desorption is performed in the adsorption tower 3. The adsorption towers 2 and 3 are replaced with an inert gas. (A) The vacuum pump 9 is started to depressurize the adsorption towers 2 and 3. (Valve 26, valve 28, valve 32, valve 33, valve 34, valve 35, valve 40, valve 41, valve 43, valve 44, valve 45, valve 5
1. Open the valve 52) b. Stop the vacuum pump 9 and supply the inert gas from the inert gas generator 17 to the adsorption tower 2 and the adsorption tower 3 until the atmospheric pressure becomes almost normal pressure. (Valve 26, Valve 28, Valve 32, Valve 33, Valve 3
4, valve 35, valve 40, valve 41, valve 43, valve 44, valve 4
5. Open valve 48) Repeat steps a and b multiple times.

Utilizing the heater 6 and the gas heater 12,
The circulation blower 8 is started to raise the temperature of the adsorption tower 3 (60 ° C to 80 ° C).
℃) by circulation. (Valve 28, valve 35, valve 45
Open) When the temperature of the adsorption tower 3 reaches a predetermined temperature (90 to 100 ° C.), the operation of the circulation blower 8 is stopped, the vacuum pump 9 is activated, and the pressure of the adsorption tower 3 is reduced (at a level of 0.1 ata). The heater 6 and the gas heater 12 are still alive. The desorption gas is mixed with the solvent gas through the desorption gas cooler 13.
(Valve 34, valve 35, valve 41, valve 44, valve 49, valve 50,
(Valve 52, valve 53 open)

A circulation operation is performed between the adsorption tower 3 and the adsorption tower 2 by a vacuum pump 9 via a desorption gas cooler 13. The heater 6 and the gas heater 12 are kept alive, and desorption is performed at about 0.1 ata in the adsorption tower 3. The desorbed gas is recovered by the desorbed gas cooler 13, the residual organic solvent gas is adsorbed by the adsorption tower 2, and the purified gas after adsorption is reused for desorption of the adsorption tower 3. At this time, the adsorption tower 3 is operated under reduced pressure, and the adsorption tower 2 is operated under normal pressure, so that it is necessary to interpose the desorption gas recovery valve 27, which is a pressure reduction valve. (Valve 34, valve 3
5, valve 37, valve 43, valve 49, valve 50, valve 53 open)

After a predetermined time, the heater 6 and the gas heater 1
After turning off 2, carry out the operation of and cool. The process is repeated until the temperature of the adsorption tower 3 drops to about 60 ° to 80 ° C. (Valve 3
4, valve 37, valve 41, valve 43, valve 44, valve 49, valve 5
0, open valve 53) After stopping the vacuum pump 3 and the recovered gas cooler 13, the pressure in the adsorption tower 3 is released (vacuum break). (Valve 23, valve 34, valve 41, valve 44 open) Part of the gas to be treated is sucked using the circulation blower 8,
It is cooled until the temperature of the adsorption tower 3 reaches about 30 to 50 ° C. The gas after the cooling gas is mixed with the solvent gas. (Valve 2
3, valve 28, valve 46 open) The above operation is sequentially performed in each tower according to the process of FIG.

[0020]

The present invention has the following effects due to the above-mentioned configuration. The inert gas generator is used only for replacing the adsorption tower with the inert gas, and is circulated for desorption, which reduces the running cost. Especially when the adsorption cycle is long, the effect is great. The inert gas generator itself can be downsized.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining an example of a solvent recovery method of the present invention.

FIG. 2 is an operation process diagram of the adsorption tower in FIG.

[Explanation of symbols]

1, 2, 3 ... Adsorption tower, 4, 5, 6 ... Heater, 7 ... Raw gas blower (fan), 8 ... Circulation blower (fan), 9 ... Vacuum pump, 10, 11, 12 ... Gas heater, 13 ... Desorption gas Cooler, 14 ... Recovery tank, 15 ... Raw gas mist separator, 16 ... Recovery gas mist separator, 17 ... Inert gas generator, 18, 20, 22 ... Raw gas inlet valve,
19, 21, 23 ... Process gas outlet valve, 24, 26, 28
Adsorption tower outlet heating / cooling valve, 25, 27, 29 ... Desorption gas recovery valve (pressure reducing valve) 30, 32, 34 ... Adsorption tower outlet desorption valve, 31, 33, 35 ... Adsorption tower inlet heating / cooling valve, 36,
37, 38 ... Desorption gas return valve, 39, 40, 41 ... Vacuum release valve, 42, 43, 44 ... Purified gas source valve, 45 ... Circulation blower outlet circulation valve, 46 ... Circulation blower outlet return valve, 47
… Inert gas flow control valve, 48… Inert gas source valve, 49
... Vacuum pump source valve, 50 ... Desorption gas cooler outlet valve, 51
Desorption gas cooler bypass valve, 52 ... Return valve, 53 ... Recovery tank source valve, 54 ... Desorption gas cooler circulation valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirofumi Inagawa 11-1 Haneda-Asahicho, Ota-ku, Tokyo Inside EBARA CORPORATION

Claims (3)

[Claims] 1. Three or more adsorption towers are installed in parallel, and each tower has a (a) solvent gas adsorption step, (b) a desorption gas dry desorption step, and (c) residual solvent after desorption recovery. In a solvent recovery method in which three steps of gas adsorption step are repeated and solvent gas is continuously adsorbed and treated, the refining gas after step (c) is repeatedly used as the desorption gas in step (b). A method for recovering a solvent, comprising: 2. When the number of adsorption towers is 4 or more, (a),
The solvent recovery method according to claim 1, wherein a rest step is added to the three steps (b) and (c). 3. The solvent recovery method according to claim 1, wherein the desorption gas in the step (b) is an inert gas.