JPS6218207B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the adsorption/desorption method of a solvent recovery device using activated carbon. The present invention relates to an adsorption/desorption method that prevents white smoke and water droplets from scattering.

Many methods and devices are known for adsorbing a solvent in raw gas using a fixed-bed activated carbon adsorption tank consisting of two tanks or multiple tanks, and then desorbing and recovering the adsorbed solvent by passing water vapor into the activated carbon layer. These solvent recovery devices basically handle the adsorption process, desorption process,
It consists of a drying process, a cooling process, and a solvent purification process. In the above process, the drying and cooling equipment is a blower,
It consists of a heater, valves, and ducts, and after desorption is completed, a fairly large amount of heated air is passed through the adsorption tank to dry the moisture in the activated carbon layer, and then the activated carbon layer is cooled by switching to cold air.Because the processing air volume is large, it requires considerable equipment. This requires additional costs and operating costs, and the operation becomes complicated.

However, since omitting this drying/cooling step does not have a substantial adverse effect on the recovery rate of the solvent, it has recently become common practice to omit this drying/cooling step. However, in general solvent recovery equipment, the activated carbon adsorption layer immediately after the desorption process is desorbed by water vapor, so the inside of the adsorption tank is saturated with water vapor, contains about 40 to 50 wt% of water based on the amount of activated carbon used, and has a temperature of about 100°C. Because the drying and cooling process is carried out as in the conventional method, intense white smoke is generated for several minutes immediately after the start of the drying process, and water droplets from the condensation are scattered around the equipment. Ta. Furthermore, with the recent adsorption methods that omit drying and cooling, gas containing solvent enters the high-temperature adsorption tank, so in addition to white smoke and water droplets, breakthrough solvent concentration has been a major problem. There is a strong need to improve these negative effects, including the generation of white smoke, from a pollution standpoint.

The present invention solves the above-mentioned drawbacks caused by dehumidifying and cooling the activated carbon layer by passing the raw gas to the adsorption tank immediately after regeneration by adding a simple mechanism to the conventional solvent recovery device. The purpose is to provide an industrially advantageous adsorption method that solves all problems at once.

In the present invention, the time required for the desorption process is approximately 1/2 of the time required for a normal adsorption process, and there is sufficient time before the start of the next adsorption process, and when switching from desorption to adsorption, The generation time of heavy white smoke accompanied by highly concentrated solvents and water droplets is only the initial 3 to 4 minutes, and the fact that the water vapor that has completed the planned adsorption process halfway through the intended adsorption process is caused by the fact that the water vapor evaporates and the temperature decreases. The present invention was completed based on the knowledge that even if a small amount of solvent is introduced into another adsorption tank, the movement of the adsorption zone is slight and there is virtually no breakthrough of the solvent.

A feature of the present invention is that all of the raw gas introduced into the adsorption tank after the completion of the water vapor desorption process and into the other adsorption tank during the adsorption process or just before the completion of the adsorption process,
Or, by adjusting the opening degree of the valve, the exhaust gas after passing through the adsorption tank after the completion of the desorption process is passed as it is or after being cooled, and then passed through the adsorption tank during or just before the completion of another regular adsorption process, Discharge from the upper part, and then after a predetermined period of time, switch the valve to make the adsorption tank after the desorption process stand by for the start of the next adsorption process, or do not leave the adsorption tank after the desorption process on standby for the start of the next adsorption process. Subsequently, it consists of switching to an adsorption step. In this way, the raw gas is passed through the adsorption tank for a predetermined period of time at a predetermined air volume after the desorption process is completed, and the exhaust gas is discharged through another adsorption tank, thereby cooling and dehumidifying the high-temperature, moisture-rich adsorption tank. ,
The initial generation of white smoke and release of highly concentrated solvents at the time of switching the adsorption process are prevented.

Next, the configuration and operation of the present application will be explained using figures. FIG. 1 shows a principle embodiment in which the present invention is applied to a two-tank adsorption device. In Fig. 1, the raw gas containing the solvent to be recovered in a normal adsorption method is heated to 20 to 30°C after condensing and separating the moisture in the raw gas in the gas cooler 4 using the raw gas blower 3.
The exhaust gas enters the adsorption tank 1 through the valve 21 at a temperature of 22. After the solvent is adsorbed by the activated carbon layer in the adsorption tank 1, the exhaust gas is discharged from the valve 22 through the exhaust pipe 11 to the atmosphere. The time required for this adsorption step varies depending on the type of device, the type and amount of solvent to be adsorbed, etc., but is usually about 1 hour. When the adsorption tank 1 starts the adsorption process, the desorption process of the other adsorption tank 2, which has already completed the adsorption process, starts subsequently. The desorption process of adsorption tank 2
This is a process in which the solvent adsorbed on the activated carbon layer inside the tank is expelled by steam.

This operation first opens the valve 19, then the steam valve 1.
6 opens to introduce water vapor into the adsorption tank 2 from the water vapor conduit 6. Although the steam pressure varies depending on the type of solvent to be desorbed and the size of the apparatus, steam at a gauge pressure of 2 to 8 kg/cm ² is usually used. When water vapor is introduced into the adsorption tank 2, the solvent adsorbed on the activated carbon layer is driven out by heat and displacement by the water vapor, condenses together with the water vapor in a condensing cooler, is cooled, and reaches a decanter 9, where it is The water that dissolves the solvent in the upper layer and the trace amount of solvent in the lower layer is sent to the next purification step and treated separately.

The time required for this desorption step is approximately that of the adsorption step.
1/2, and the time required for desorption is 30 minutes compared to the usual 1 hour adsorption. Therefore, there is a downtime of about 30 minutes before the adsorption tank 2 starts the next adsorption. In a normal solvent recovery device consisting of two or more adsorption tanks,
The adsorption and desorption steps as described above are repeated alternately or sequentially.

Previously, the adsorption tank 2, which had completed the desorption process as described above, was used to dry and cool down during the downtime before starting the next desorption process. Since there is no substantial adverse effect on the phenomenon itself, recent solvent recovery apparatuses omit the drying and cooling steps due to cost considerations. The drying and cooling process requires a blower gas heater, duct, and valve to be installed separately from the adsorption system, and the diameter of the duct is large, so the construction and maintenance costs account for a large proportion of the overall equipment cost. . Furthermore, even when this drying and cooling process is carried out, intense white smoke is emitted for the first 2 to 3 minutes after the start of the drying process. This is because the adsorption tank is filled with water vapor immediately after the adsorption process is completed, and the activated carbon layer inside contains a large amount of water, so the hot air introduced for drying drives out the water vapor and water. It is.

On the other hand, if the drying and cooling steps are omitted, the next adsorption step will be started after a pause of about 30 minutes after the desorption step is completed, but the adsorption tank has a fairly large volume and will hardly be cooled if left for 30 minutes. Naturally, therefore, heavy white smoke is generated at the beginning of the adsorption process.

The white smoke at this time is different in quantity and quality from the white smoke at the start of the drying process described above. The hot air for drying has a relatively high temperature and does not contain any solvent, but if the drying and cooling steps are omitted and adsorption is performed, the raw gas introduced is close to room temperature, so the amount of white smoke is quite large, and the adsorption tank The solvent contained in the raw gas is not adsorbed until it cools down, and tends to break through the activated carbon layer and be released into the atmosphere, and momentarily the solvent concentration in the raw gas and the solvent concentration in the exhaust gas are almost the same. It becomes equal. As described above, the time and concentration of the solvent in the exhaust gas are approximately proportional to the time and concentration of white smoke generation. The white smoke generation time is 3 to 4 minutes, and as time passes, the adsorption tank cools down and returns to normal adsorption. Since such exhaust gases have a very short time to discharge solvent close to the concentration of solvent in the raw gas, the impact on the overall solvent recovery rate is substantially small.

The steps described above are performed in conventional general solvent recovery equipment. However, the generation of white smoke containing solvents and water droplets is undesirable from the standpoint of pollution prevention, and recently, even a slight improvement in the recovery rate has been considered, especially when recovering expensive solvents such as ketones and THF. . In this case, the present invention solves the above problem by adding simple equipment. That is, the first
In the figure, it is assumed that 30 minutes have passed since adsorption tank 1 started the adsorption process and adsorption tank 2 started the desorption process at the same time. If the set adsorption time is 60 minutes, adsorption tank 1
has halfway completed the adsorption process and has cooled considerably due to water evaporation, and the adsorption tank 2 has just completed the desorption process. The amount of activated carbon in the adsorption tank 1 is designed to have enough adsorption margin to be about three times the amount required to adsorb a given solvent. The thin tip is adsorption tank 1
The activated carbon layer only reaches the bottom 1/3 of the layer, and the remaining top 2/3 is hardly used for adsorption. In this way, adsorption tank 1 has halfway completed the adsorption process, and adsorption tank 2
30 minutes after starting the desorption process, the valve states are raw gas 21, exhaust valve 22 open, and steam valve 1.
6 and desorption steam valves 19 are open, and all other valves are closed. Next, the adsorption tank 2 completes the desorption process while the state of the adsorption tank 1 remains the same. That is, the steam valve 16 and the desorption steam valve 19 are closed in sequence. Next, the adsorption tank 2 is subjected to the cooling process of the present invention.

For this purpose, as shown in FIG. 1, a cooling exhaust gas introduction path consisting of cooling exhaust gas conduits 12, 13 and cooling exhaust gas valves 17, 18 is provided. A cooling exhaust gas valve 17 for cooling the adsorption tank 2 after the desorption process is completed;
18 and raw gas valve 20 are sequentially opened. When the raw gas is passed through the adsorption tank 2 in this manner, the solvent in the raw gas is adsorbed, and the cooled exhaust gas removes moisture from the activated carbon layer in the adsorption tank 2, and the adsorption tank 2 is gradually cooled by this evaporation. The amount of raw gas flowing into the adsorption tank 2 is approximately 1/15 of the amount of raw gas from the time when white smoke is generated, which is sufficient to achieve the purpose. To perform this operation, the raw gas valve 21 of the adsorption tank 1 is fully closed, the raw gas is passed into the adsorption tank 2 for about 4 minutes, and the adsorption tank 2 adsorbs and cools the gas, which has moisture and heat. It is discharged to the atmosphere through the exhaust pipe 11.

At this time, a gas cooler (not shown) may be provided in the middle of the cooled exhaust gas conduit 13 to condense and separate moisture in the cooled exhaust gas, thereby performing gas cooling.
After passing the entire amount of raw gas to the adsorption tank 2 for a predetermined time in this way, instead of exhausting the cooled exhaust gas through the adsorption tank 1 and from the exhaust pipe 11, the raw gas valve 21 is opened to an appropriate opening degree without fully closing. The raw gas valve 20 is fully opened or adjusted to an appropriate opening so that both the adsorption tank 1 and the adsorption tank 2 have a raw gas flow rate ratio of about 15:2, for example.
At the same time, the cooled exhaust gas that has cooled the adsorption tank 2 through the raw gas is adsorbed in the adsorption tank 1 together with the raw gas that enters from the raw gas valve 21 through the cooled exhaust gas conduits 12, 13, and 14, and is released into the atmosphere from the exhaust valve 11. You can also do that. In this case as well, a gas cooler (not shown) can be provided in the middle of the cooling exhaust gas conduit 13 in the same manner as described above.

Of the above two methods, the latter, that is, simultaneously passing the raw gas in parallel to the two adsorption tanks 1 and 2, is particularly advantageous because the cooling exhaust gas pipes 12 to 14, the valves 17 and 18, and the cooler (not shown) are smaller. advantageous;
The ratio of raw gas amounts can be minimized when the above ratio is achieved. In both of the above two methods, about 1/1/2 of the specified total amount of raw gas that should enter the adsorption layer 1 in one cycle.
After passing 15 of the raw gas through the adsorption tank 2, the adsorption tank 1 returns to the normal adsorption process, and the adsorption tank 2 waits for switching to the next adsorption process. Even if this cooling step is carried out, the initially set adsorption and desorption time schedule will not be disrupted, and no white smoke will be generated in the exhaust gas or solvent will break through.

FIG. 2 shows another embodiment of the invention. The exhaust gas containing water vapor and water droplets from the raw gas that has passed through the adsorption tank 2 that has completed the desorption process and is divided into the adsorption tanks 1 and 2 in proportion is transferred from the end of the cooling exhaust gas conduits 12 and 13 to the raw gas blower 3. It is sent to the suction side, combined with other raw gas, passed through the raw gas cooler 4 to condense moisture, and after being cooled, it is proportionally distributed again and sent to both the adsorption tank 1 and the adsorption tank 2 at the same time. configured. The rest is the same as the embodiment shown in FIG. In this case as well, it is advantageous to provide a gas cooler (not shown) in the middle of the cooling gas conduit 13. Using the process shown in FIG. 2 simplifies the cooling exhaust gas conduit after passing through the adsorption tank 2.

FIG. 3 shows an embodiment in which the cooled exhaust gas passing through the adsorption tank 2 is circulated through the cooled exhaust gas conduits 12 and 13, the existing desorption vapor conduit 7, the condensing cooler 8 and the decanter 9 to the raw gas blower 3. be. In this case, the gas flow rate is regulated by the existing desorption steam conduit 7, condensing cooler 8, etc., and it is not possible to pass the entire amount of raw gas. The cutoff valve 24 is connected to the adsorption tank 1
Alternatively, it may be opened only during the cooling step 2 and closed at other times. Other general explanations are the same as those in FIGS. 1 and 2.

In the above explanation, in principle, the entire amount of raw gas for cooling to be passed through the adsorption tank 2 after regeneration and desorption can be passed through, but for the purpose of cooling, approximately 1/12 of the total amount of raw gas is required. Since the objective is achieved by passing ~1/15, it is advantageous to use a small flow rate that allows cooling to be completed within the above-mentioned margin time until the start of the next adsorption. This gas flow rate is, for example, when recovering 50 kg/H of toluene, and if the raw gas concentration is 0.5 Vol%, the total amount of raw gas is 2620 m ³ (20°C)/H, and the air excluding toluene vapor is 2600 m ³ (20°C)/H. H, so in this case, 180 to 200 m ³ is used as the raw gas for cooling.
(20℃) for about 30 minutes. In this way, the diameter of the conduit and the valve can be reduced to reduce the cost of the equipment and eliminate the need for a gas cooler for the cooled exhaust gas exiting the adsorption tank 2. The load on the condensing cooler 8 can be reduced. Also valves 17, 17'
Alternatively, 18 and 18' can be combined into one switching valve.

As described above, according to the present invention, it is possible to prevent the breakthrough of highly concentrated solvent and the release of white smoke and water droplets into the atmosphere that occur when the solvent recovery device starts adsorption by installing simple equipment and with easy operation. This is extremely beneficial from an industrial and environmental standpoint.

[Brief explanation of the drawing]

Figure 1 shows an embodiment showing the main points of the present invention, and Figure 2 shows the cooled exhaust gas that has passed through the adsorption tank after the desorption process is completed, is guided to the suction side of the raw gas blower, cooled by suction, and then transferred to another adsorption tank. Another embodiment is shown in which the cooled exhaust gas that has passed through the adsorption tank after the desorption step is guided to the suction side of the raw gas blower through the existing condensing cooler and decanter. This is another embodiment in which the adsorbent is cooled by suction and then passed through another adsorption tank and exhausted to the atmosphere. 1... Adsorption tank, 2... Adsorption tank, 3... Raw gas blower, 4... Raw gas cooler, 5... Raw gas conduit, 6... Steam conduit, 7... Desorption vapor conduit, 8... Condensing cooler,
9...Decanter, 10...Exhaust pipe, 11...Exhaust pipe,
12...Cooled exhaust gas conduit, 13...Cooled exhaust gas conduit,
14... Cooled exhaust gas conduit, 15... Exhaust valve, 16... Steam valve, 17... Cooled exhaust gas valve, 18... Cooled exhaust gas valve, 19... Desorption steam valve, 20... Raw gas valve, 21...
Raw gas valve, 22...Exhaust valve, 23...Cooled exhaust gas conduit, 24...Shutoff valve.

Claims (1)

[Scope of Claims] 1. Desorption and regeneration in a method that repeats an operation of adsorbing a solvent in a gas phase, which is a raw gas, using a plurality of activated carbon adsorption tanks in turn, and then desorbing the adsorbed solvent using water vapor. All or part of the exhaust gas obtained by passing at least a portion of the raw gas through one adsorption tank is passed through another adsorption tank as it is or after cooling, and is then dissipated into the atmosphere, and then switched to pass the normal amount of exhaust gas into the atmosphere. Well, it is an adsorption/desorption method characterized by dissipation into the atmosphere. 2. The adsorption/desorption method according to claim 1, wherein all of the exhaust gas obtained by passing at least a portion of the raw gas through the desorption and regenerated adsorption tank is sent to another adsorption tank. 3. The adsorption/desorption method according to claim 1, wherein the exhaust gas obtained by passing a part of the raw gas through the desorption and regenerated adsorption tank is sent to the suction side of the raw gas blower and mixed with the raw gas.