JPH0938445A - Method for regenerating adsorption tower - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for regenerating an adsorption tower by which a decomposable solvent is completely recovered in dry desorption, and the equipment cost and running cost are reduced when an inert gas is used as the desorption gas. SOLUTION: A solvent adsorbed on the fixed adsorption bed in an adsorption tower 1A is dry-desorbed to regenerate the adsorption tower. In this case, the inside of the adsorption tower 1A is evacuated by a vacuum pump 6 and desorbed, a solvent is condensed 7 from the desorption gas and recovered 8, and the uncondensed gas is returned to the tower 1A in the circulating line. A clarified gas 24 is then supplied to the adsorption tower, the gas passed through the adsorption bed is discharged outside the circulating line to purify the adsorption bed. Accordingly, the bed is heated 2A in the desorption and recovery stages, and the inert gas 24 is preferably used as the circulating gas or clarifying gas in the desorption and recovery stages.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating an adsorption tower, and more particularly to a method for adsorbing a solvent-containing gas on a fixed adsorption layer and dry desorbing this solvent to regenerate the adsorption tower.

[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 described with reference to the drawings. 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 lower, which is commonly used, is relatively inexpensive, but the recovery rate of low-boiling substances 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. The compression method is a method of pressurizing the vapor of the 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 compression heat, heat dissipation and cooling are required to increase the recovery rate. Is required. For example, 5 kg / c of dichloromethane
If compressed to m ² and cooled to 5 ° C, it will be about -30 ° C at 1 atm.
It becomes the same as when cooled to. That is, the recovery rate of dichloromethane and 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 apparatus, if a large amount of exhaust gas is treated at a low concentration of several tens of ppm or less, the apparatus 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 molded into a cylindrical shape of 5 to 10 mm or crushed activated carbon to adsorb it, and from several hours A device that sends steam every few days to desorb it and recovers the organic solvent in the desorbed gas by a cooling method has been widely used.

3) Method using fibrous activated carbon A small fixed bed apparatus using fibrous activated carbon is one in which one or two fibrous activated carbons formed 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) Method using spherical activated carbon There is also a system in which an adsorption tower and a desorption tower are vertically connected to each other in a device for continuously adsorbing / desorbing in a fluidized bed using spherical activated carbon. 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 A device that adsorbs on a fixed bed using honeycomb-like activated carbon and desorbs it by heating it electrically while depressurizing it has a small ventilation resistance and a fast adsorption rate, so it can adsorb at a high flow rate. Since steam is not used for separation, there are features such as no water entering the recovered liquid and easy wastewater treatment. 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. Regarding desorption, there are a wet method using water vapor and a dry method using gas. Although the wet method is cheaper with the same treatment capacity, this system uses 2 to 8 times the amount of recovered solvent vapor, and waste water treatment becomes a problem. For example, even if water is separated, the solvent dissolves to some extent on the water side, and as seen in Table 1, the typical chlorine-based organic solvents, trichlorethylene and tetrachloroethylene, have a much lower drainage standard than the solubility in water. . Such water cannot be released directly, and the concentration must be further reduced by the aeration method or the like.

[Table 1]

Therefore, the wet method may be disadvantageous in consideration of water treatment. The problem with the dry method is when recovering decomposable solvents (ketones and esters). As a safety measure, replace the adsorption column with an inert gas (such as nitrogen) and desorb with an inert gas. It is desirable to do. But,
In order to supply the nitrogen gas, it is necessary to provide liquid nitrogen or a PSA method (pressure fluctuation adsorption / desorption method) nitrogen gas supply apparatus, which increases equipment costs and running costs. In order to solve this point, the present inventors have proposed a method in which a gas saturated with a solvent after desorption and condensation is clarified in another adsorption tower, sent again to the adsorption tower, and circulated as the desorption gas. No. 5-122114). This method has very good desorption efficiency because the downstream side of the adsorption layer (secondary side of aeration operation) constantly contacts the clear gas, but desorption efficiency is very good, but three or more adsorption towers are required, and control becomes rather complicated. .

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and, in the dry desorption process, safely recovers the decomposable solvent, and the equipment cost when an inert gas is used as the desorption gas, An object is to provide a method for regenerating an adsorption tower that can reduce running costs.

[0008]

In order to solve the above-mentioned problems, in the present invention, in a method for regenerating an adsorption tower by dry desorbing a solvent adsorbed in a fixed adsorption bed of the adsorption tower, A step of desorbing and decompressing with a vacuum pump, condensing and recovering the solvent from the desorbed gas and returning the uncondensed gas to the adsorption tower to desorb and recover the solvent with a circulation system, and then supplying a refining gas to the adsorption tower and passing through the adsorption layer This is a method for regenerating an adsorption tower, characterized in that it is treated in a step of purifying the adsorption layer by releasing the gas thereafter to the outside of the circulation system. In the method for regenerating the adsorption tower, the desorption recovery step is performed while heating the adsorption layer, and using an inert gas as the circulating gas or the refining gas during desorption recovers the decomposable solvent, which is a safety measure. Good from a perspective.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a regeneration flow chart for explaining a regeneration method for an adsorption tower of the present invention. FIG. 1 is an example of a method of desorbing while heating the adsorption layer of the present invention with a heater, which is applied to a temperature-pressure fluctuation adsorption / desorption method (TPSA method) and is a flow for continuously treating exhaust gas.
In FIG. 1, 1A and 1B are adsorption towers, 2A and 2B are heaters, 3 is an exhaust gas cooler, 4 is an exhaust gas blower, 5 is a circulation blower, 6 is a vacuum pump, 7 is a condenser, 8 is a recovery tank, and 9 is a solvent. Transfer pumps, and 10 and 11 are filters. And these devices are 12-21, respectively.
It is connected by a pipe having a valve.

Next, the operation method according to the flow of FIG. 1 will be described. (1) The gas 22 containing the solvent is discharged by the exhaust gas blower 4.
20 to 25 ° C through the exhaust gas cooler 3 and the filter 10
After cooling to remove the dust, the solvent is removed in the adsorption layer of the adsorption tower 1A, and the processing gas 23 is released into the atmosphere. (The open valves are the exhaust gas inlet valve 12A and the exhaust gas outlet valve 13A) (2) The process is completed and the passing gas is switched to the adsorption tower 1B. (The valves 12A and 13A are closed and the valves 12B and 13B are opened.) The switching is determined by whether the solvent concentration in the processing gas exceeds a reference value, by a timer, or by using both of them.
The adsorption tower 1A is isolated from the ventilation line.

(3) Using the circulation blower 5, the heater 2A
By utilizing the above, the temperature of the adsorption layer of the adsorption tower 1A is raised. (Circulation heating step) At this time, there are a method of circulating heating the adsorption layer temperature up to a reference value (around 100 ° C) and a method of circulating heating up to the reference value (60 to 80 ° C). (The open valve is the circulation blower outlet valve 1
4A, circulating blower inlet valve 15A) When the decomposability of the target solvent is particularly high, it is possible to replace the air in the circulating heating system with an inert gas. That is, the vacuum pump 6 is used (valves 17 and 16A are opened) to reduce the pressure in the system, then the valve 17 is closed and the inert gas 24 is introduced into the system from 20A. (Valve 21A is always constant opening).

(4) Stop circulation. When the inert gas is replaced in (3), the process proceeds to step (5). If the gas is not replaced, the gas in the adsorption tower 1A is exhausted to the gas to be processed side by the vacuum pump 6. (The open valves are the vacuum pump inlet valve 16A and the vacuum pump outlet valve 17) When the desorption of the adsorption tower progresses, the vacuum pump 6 is stopped,
The inert gas 24 is supplied until the pressure inside the adsorption tower 1A becomes almost normal pressure. (Inert gas replacement step. Open valves are vacuum pump inlet valve 16A, vacuum pump outlet valve 17, desorption gas inlet valve 20A, desorption gas pressure reducing valve 21A (always constant opening)) (5) Desorption gas inlet The valve 20A is closed, and the inside of the adsorption tower 1A is adjusted by the vacuum pump 6 to 0.1 to 0.5 kg / cm ²
The pressure is reduced to about bs, and the gas is exhausted to the side of the gas to be processed during aeration. (Decompression step. Open valves are vacuum pump inlet valve 16A and vacuum pump outlet valve 17).

(6) Subsequently, the adsorption tower 1A is heated to the heater 2
A and vacuum pump 6 are used to perform depressurization by heating and decompression, and the condenser 7 collects uncondensed gas after recovery by vacuum pump return valve 18
A, returning to the adsorption tower 1A through a line including the vacuum pump return pressure reducing valve 19A, and performing heating, pressure reduction and desorption while circulating.
(Heating / decompression / desorption process. Open valve is vacuum pump inlet valve 16
A, vacuum pump return valve 18A, vacuum pump return pressure reducing valve 1
9A (always constant opening)) (7) Stop heating by the heater 2A, continuously supply the inert gas 24, purify and cool the adsorption tower 1A, and exhaust to the side of the gas being aerated by the vacuum pump 6 To do.
(Purification step: open valves are vacuum pump inlet valve 16A, vacuum pump outlet valve 17, desorption gas inlet valve 20A, desorption gas pressure reducing valve 21A (always constant opening))

Since the supply gas in this step is not circulated,
Air (such as partial use of process gas) can be used from the perspective of utility cost savings, but with the addition of some piping valves. (8) The vacuum pump is stopped, and the inside of the adsorption tower is returned to normal pressure with an inert gas. (Pressure return step. Opening valves are the desorption gas inlet valve 20A and the desorption gas pressure reducing valve 21A (always constant opening)). When returning to normal pressure, it is possible to use air (partial use of the gas to be treated, etc.) instead of the inert gas, but if the waiting time until the next ventilation is long, decompose in the adsorption layer. The use of an inert gas is desirable to eliminate the risk of ignition due to the heat of decomposition of the organic solvent. (9) Wait until the aeration process of the 1B tower is completed. In this flow, the adsorption tower 1A is cooled in the steps (7), (8), and (9), but it is not sufficient, and when the aeration is transferred to the A side again, cooling is promoted by the gas to be treated itself. Become. During desorption, inert gas is supplied to the adsorption tower until atmospheric pressure is reached, and after heating and circulating again, heating and decompression desorption are performed while circulating (to reduce oxygen partial pressure and improve desorption efficiency). However, these are within the scope of the present invention because the point is to recycle the uncondensed gas during desorption.

[0015]

According to the present invention, the following effects can be obtained. (A) Since the gas is circulated and reused, this leads to a reduction in running cost, especially when an inert gas (nitrogen) is used as a desorption gas as a measure against a decomposable solvent. (B) Since the uncondensed gas in the condenser is circulated, even if the capacity of the condenser is slightly reduced, the solvent concentration at the condenser inlet will eventually increase and the condensation will be possible. That is, it is possible to reduce the condensation capacity of the condenser, that is, the equipment cost. (C) After desorption by heating under reduced pressure, the adsorbent layer can be purified by passing it through a cleaning gas to remove the organic solvent content remaining in the adsorption layer that has been circulated and desorbed under reduced pressure by heating. Resolved. (D) By desorbing the adsorption layer while heating, the desorption efficiency is improved as compared with the case where the adsorption layer is not heated. In fact, this operation is important, and it is difficult to expect sufficient desorption by only reducing the pressure.

[Brief description of drawings]

FIG. 1 is a regeneration flow chart for explaining an example of a regeneration method for an adsorption tower of the present invention.

[Explanation of symbols]

1A, 1B: adsorption tower, 2A, 2B: heater, 3: exhaust gas cooler, 4: exhaust gas blower, 5: circulation blower, 6:
Vacuum pump, 7: condenser, 8: recovery tank, 9: solvent transfer pump, 10: filter, 11: filter, 12A to
18B, 20A, 20B: switching valve, 19A, 19B, 2
1A, 21B: Pressure reducing valve

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

Claims (3)

[Claims] 1. A method of regenerating an adsorption tower by dry desorption of a solvent adsorbed on a fixed adsorption layer of an adsorption tower, wherein the adsorption tower is depressurized and desorbed by a vacuum pump, and the solvent is condensed and recovered from the desorbed gas. A step of desorbing and collecting the solvent in a circulation system for returning the uncondensed gas to the adsorption tower, and then supplying a refining gas to the adsorption tower to release the gas after passing through the adsorption layer to the outside of the circulation system to purify the adsorption layer. A method for regenerating an adsorption tower, characterized in that treatment is carried out in steps. 2. The method for regenerating an adsorption tower according to claim 1, wherein the desorption recovery step is performed while heating the adsorption layer. 3. The method for regenerating an adsorption tower according to claim 1, wherein the circulating gas in the desorption / recovery step is an inert gas.