JPH0738934B2 - Solvent recovery method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for recovering a solvent from a raw gas containing a highly reactive solvent and a solvent which is hard to be adsorbed by activated carbon.

[Conventional technology]

Conventional solvent recovery has been performed by the activated carbon adsorption method shown in FIG. The raw gas 101 is sucked by a gas blower 102, first enters a gas filter 103 to remove impurities (dust and the like), then flows to a gas cooler 104, and is cooled at a temperature (about 40 ° C.) suitable for adsorbing the activated carbon 106. Cooling in the gas cooler 104 is performed by indirect heat exchange between gas and cooling water (usually, cooling water is circulated and reused is water cooled by a cooling tower). Raw gas 101 cooled to a temperature suitable for adsorption is an adsorption tank 1
It is sent to 05 and the solvent component in the raw gas is adsorbed by the activated carbon 106 filled in the adsorption tank. The raw gas from which the solvent components have been removed is discharged from the upper part of the adsorption tank to the atmosphere. Immediately before the solvent adsorption amount of the activated carbon 106 approaches the limit and the solvent is discharged to the exhaust side, the adsorption operation is stopped and water vapor is introduced into the adsorption tank. Activated carbon 10
The solvent adsorbed on 6 is desorbed by steam 107,
After going through the slush tank 108 with 7, the condenser 109
It is cooled down and condensed. After that, it is sent to the separator 110 and separated into water and a solvent. Since water contains an equilibrium dissolved amount of solvent, it flows into the flush tank 108 and the adsorption tank 1
Simple steam distillation is performed with the steam and solvent vapor generated from 05 to remove most of the solvent in the water. After that, it is collected in a drainage tank 111 and sent to a drainage distillation column 112 to further remove solvent components.

On the other hand, the solvent separated by the separator 110 is sent to a distillation facility or the like because it is a mixed solvent containing an equilibrium dissolved amount of water, and is dehydrated and further separated into respective components for reuse.

[Problems to be solved by the invention]

In the conventional solvent recovery method, a highly reactive solvent such as cyclohexanone causes a polycondensation reaction in activated carbon,
Since the activated carbon deteriorates early due to this polymer and needs to be replaced, the running cost becomes enormous.

Further, for a solvent having a small adsorption amount on activated carbon, the equipment scale of the adsorption device is large and the running cost such as the vapor amount is high.

Further, in the case of an absorption method using an absorption liquid such as water, the efficiency of the absorption is low and the running cost cannot be reduced because the absorption rate of the solvent is low.

The present invention is intended to provide a solvent recovery method and apparatus that solve the drawbacks of conventional solvent recovery, have high recovery efficiency, and can reduce running costs.

[Means for Solving Problems] The present invention provides (1) solvent recovery having an absorption step of bringing a solvent-containing raw gas into gas-liquid contact with an absorption liquid, and an adsorption step of bringing an outflow gas from the absorption step into contact with activated carbon. In the method, the effluent absorption liquid from the absorption step is distilled with steam to recover the concentrated solvent gas, and steam is generated by the heat held by the concentrated solvent gas,
A method for recovering a solvent, characterized in that the water vapor is introduced into the activated carbon that has undergone the adsorption step to remove the solvent adsorbed on the activated carbon. (2) An absorption step of bringing a solvent-containing raw gas into gas-liquid contact with an absorption liquid; In a solvent recovery method having an adsorption step of contacting the effluent gas from the step with activated carbon, the effluent absorption solution from the absorption step is distilled with steam to recover the concentrated solvent gas, while the activated carbon that has undergone the adsorption step is treated with water vapor. The solvent adsorbed on the activated carbon is introduced, mixed with the concentrated solvent gas, and the heat of the mixed gas is used to operate the absorption refrigerator, and the refrigerator is used as a cooling source. Solvent recovery method characterized in that the gas and the absorption liquid are cooled and then introduced into the absorption step (3) The regenerated absorption liquid which is connected to the lower part of the absorption column through a gas cooler and is discharged from the bottom of the distillation column Suck the conduit It is connected to the upper part of the absorption tower via a liquid cooler, the top gas of the absorption tower is connected to one end of an activated carbon adsorption tank via a conduit, and the exhaust conduit is connected to the other end of the adsorption tank, while the above The absorption liquid conduit discharged from the bottom of the absorption tower is connected to the upper part of the distillation tower, the steam injection conduit is connected to the bottom of the distillation tower, and the concentrated solvent gas conduit which is the top gas of the distillation tower is connected. Connected to the solvent separator via the evaporator and hot water recovery heat exchanger,
Then, the steam conduit generated in the evaporator is connected to the adsorption tank, the recovered solvent-containing steam conduit from the adsorption tank is connected to the concentrated solvent gas conduit, and the hot water conduit of the hot water recovery heat exchanger is connected. The solvent recovery device is characterized in that it is connected to an absorption refrigerator and a cold water conduit cooled by the refrigerator is connected to the raw gas cooler and the absorption liquid cooler.

〔Example〕

FIG. 1 shows an example of the solvent recovery process of the present invention. Here, the raw gas 1 is air containing toluene and MEK in addition to cyclohexanone which is a reactive solvent. The process is explained below.

The raw gas 1 is sucked by a gas blower 2, first enters a gas filter 3 and impurities (dust and the like) are removed, then flows to a gas cooler 4, and is cooled to about 15 ° C. to 25 ° C. to improve absorption efficiency. The raw gas 1 cooled by the gas cooler 4 enters the lower part of the absorption tower 5. Here, raw gas 1 is 15 ° C from the top
Most of the cyclohexanone in the raw gas is absorbed by water by making gas-liquid contact with water cooled to about -25 ° C.

The water (absorption liquid) that has absorbed cyclohexanone is sent to the upper part of the cyclohexanone recovery distillation column 8 by the recovery column feed pump 6 via the absorption liquid heat exchanger 7. Cyclohexanone is separated from the absorbing liquid by the water vapor J blown into the lower portion. The separated cyclohexanone vapor flows into the evaporator 9 together with the steam. Here, latent heat is applied to the soft water by the indirect heat exchanger to generate steam. The generated water vapor is compressed by the vapor compressor 10, and the adsorption tank 11
And is used to desorb the solvent from the activated carbon 12 that has adsorbed the remaining solvent that has not been absorbed in the absorption tower 5.

In addition, the solvent-containing steam that comes out of the adsorption tank 11 in this desorption process flows to the evaporator 9 together with the cyclohexanone vapor that is the top gas of the distillation column, and heat recovery is performed.

The remaining steam that has given latent heat in the evaporator 9 flows to the hot water recovery heat exchanger 14 via the flash tank 13 together with the solvent vapor. Here, the latent heat is used to raise the warm water by indirect heat exchange. The hot water flows into the absorption refrigerator 15 to give heat, and then returns to the hot water recovery heat exchanger 14 again.

In the absorption refrigerator 15, the gas cooler 4 and the absorption liquid cooler 16
The cold water that has been heated up and returned from is cooled and sent again to the gas cooler 4 and the absorption liquid cooler 16 by the cold water pump 17.

The water vapor and solvent vapor emitted from the hot water recovery heat exchanger 14 flow into the condenser 18, are condensed and cooled, and then flow into the separator 19, where they are separated into solvent and water. Water is flush tank 13,
Drainage distillation tower 22 by drainage pump 21 via drainage tank 20
To reduce the concentration of solvent in the wastewater sent to.

Since the solvent separated by the separator is a mixed solvent containing water of equilibrium dissolved content, it is preferable to send it to a distillation facility or the like for dehydration and further to separate it into respective components for reuse, rather than recover and reuse as it is.

On the other hand, the absorption liquid from which cyclohexanone has been removed in the cyclohexanone recovery distillation column 8 flows to the absorption liquid heat exchanger 7 and undergoes indirect heat exchange with the absorption liquid that has absorbed cyclohexanone from the absorption tower 5 and is cooled to about 40 ° C. It flows to the absorbent cooler 16. Here, the absorption liquid is further heated to 15 ° C by heat exchange with cold water.
After being cooled to about -25 ° C, it is sent to the absorption tower 5 to absorb cyclohexanone again by the absorption liquid pump 23.

A solvent recovery test was conducted using the apparatus shown in FIG. A raw gas containing 1800 ppm of cyclohexanone, 800 ppm of MEK, and 650 ppm of toluene was introduced into the absorption tower at 10000 Nm ³ / Hr, and it was operated at 6000 Hr so that the solvent concentration in the exhaust gas discharged from the activated carbon adsorption tank was suppressed to an average of 100 ppm or less.

When the conventional apparatus of FIG. 2 was used and operated under the same conditions, the running cost of the apparatus of FIG. 1 was significantly reduced to 63% of that of FIG.

〔The invention's effect〕

The present invention, by installing a low-temperature absorption tower in front of the activated carbon adsorption device, allows the highly reactive solvent component in the raw gas and the solvent component difficult to be adsorbed by activated carbon to be absorbed by water at low temperature (15 to 25 ° C). The remaining solvent in the raw gas is completely separated by activated carbon and can be released into the atmosphere, at which time the activated carbon is prevented from deteriorating due to the highly reactive solvent. Also, the solvent absorbed in water is separated by steam in the distillation column, but it is used for desorption of activated carbon by generating steam using the heat of the solvent-containing steam, which is the top gas, and is absorbed by the heat of storage. The raw gas and the absorption liquid introduced into the absorption tower are cooled by operating the type refrigerator, and the absorption efficiency is greatly improved. In this way, the efficiency of the absorption tower can be increased by the waste heat of the distillation tower, and the desorption steam of the adsorption tank can be provided, so that the efficiency of solvent recovery can be greatly improved, and the running cost of the entire solvent recovery process can be improved. It has become possible to greatly reduce.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of the solvent recovery process of the present invention, and FIG. 2 is a flow chart of a conventional solvent recovery process.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location B01D 53/34 ZAB 53/77 53/81 B01D 53/34 ZAB (72) Inventor Hayami Nagano Hyogo prefecture 2-1-1, Niihama, Arai-cho, Takasago-shi Takasago Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Shigekazu Hatano 2-1-1, Niihama, Niihama, Arai-cho, Takasago-shi, Hyogo (56) References Special Kai 62-244423 (JP, A) JP-A-50-63031 (JP, A)

Claims (3)

[Claims] 1. A solvent recovery method comprising: an absorption step of bringing a solvent-containing raw gas into gas-liquid contact with an absorption liquid; and an adsorption step of bringing the outflow gas from the absorption step into contact with activated carbon. Distilling with steam to recover the concentrated solvent gas, heat generated by the concentrated solvent gas is used to generate steam, and this steam is introduced into the activated carbon that has undergone the adsorption step to separate the solvent adsorbed on the activated carbon. Characteristic solvent recovery method. 2. A solvent recovery method comprising: an absorption step of bringing a solvent-containing raw gas into gas-liquid contact with an absorption liquid; and an adsorption step of bringing the outflow gas from the absorption step into contact with activated carbon. The concentrated solvent gas is recovered by distillation with steam, while steam is introduced into the activated carbon that has undergone the adsorption step to separate the solvent adsorbed on the activated carbon, mix with the concentrated solvent gas, and retain the mixed gas. A method for recovering a solvent, characterized in that an absorption refrigerating machine is operated by utilizing heat, the raw gas and the absorbing liquid are cooled using the refrigerating machine as a cooling source, and then introduced into an absorbing step. 3. A raw gas conduit is connected to the lower part of the absorption tower via a gas cooler, and a regenerated absorption liquid conduit discharged from the bottom of the distillation tower is connected to the upper part of the absorption tower via an absorption liquid cooler, and the absorption tower is described above. Is connected to one end of an activated carbon adsorption tank via a conduit, and an exhaust conduit is connected to the other end of the adsorption tank, while an absorption liquid conduit discharged from the bottom of the absorption tower is connected to the distillation tower. Connected to the upper part, connected to the bottom of the distillation column with a steam blowing conduit, and connected the concentrated solvent gas conduit, which is the top gas of the distillation tower, to the solvent separator via the evaporator and the hot water recovery heat exchanger. Then, the steam conduit generated in the evaporator is connected to the adsorption tank, the recovered solvent-containing steam conduit from the adsorption tank is connected to the concentrated solvent gas conduit, and the hot water of the hot water recovery heat exchanger is further connected. Cold water cooled by the refrigerator by connecting the conduit to an absorption refrigerator. Solvent recovery apparatus characterized by connecting a pipe to said initial gas cooler and the absorption liquid cooler.