JPH0155888B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating gas containing a relatively low concentration of organic solvent gas discharged from an organic solvent gas generation source such as a painting booth. The gas to be treated containing organic solvent gas discharged from painting booths, etc., as mentioned above, has a low concentration, so burning this gas by direct combustion requires a huge amount of fuel cost. , not practical. From the viewpoint of processing efficiency, it is desirable that such a gas to be treated is first adsorbed onto an adsorbent such as activated carbon, desorbed with a small amount of desorption gas, concentrated, and then treated. Regarding desorption, when steam is used as the desorption gas, the amount of heat required for heating is relatively large, and since a large amount of moisture is mixed into the concentrated gas after desorption, a large amount of water is required for the subsequent combustion process. of heat, resulting in a large overall thermal loss.Furthermore, if an inert gas is used as a desorption gas, not only is the gas itself expensive, but high-pressure gas storage equipment is required. In this case, the loss is also large from an economic standpoint. Instead of using steam or inert gas as mentioned above,
Techniques using combustion exhaust gas as a desorption gas have also been proposed (for example, Japanese Patent Application Laid-open No. 70819/1983,
Or Publication No. 51-38224). Using combustion exhaust gas as a desorption gas in this way is effective in eliminating the economic losses mentioned above when using steam or inert gas. Since exhaust gas is passed through as a desorption gas, the deterioration of the adsorbent is accelerated and its durability is reduced, which increases running costs. In all of the techniques proposed above, after adsorption (or desorption) is completed in one or more towers, the supply of the gas to be treated (or desorption gas) is stopped, and the desorption gas is stopped. Since the so-called batch treatment method is used, in which the supply of combustion exhaust gas (or gas to be treated) is switched, each time the switching is performed, the concentrated gas mixed with the solvent for desorption gas is discharged. There is a large fluctuation in the air volume on the side.
The operating efficiency of the post-processing device for processing the desorbed concentrated gas deteriorates, and in this respect it is not possible to carry out sufficiently economical processing. Therefore, in the past, when treating gases containing organic solvent components at low concentrations, an adsorbent made of a fibrous or finely divided adsorbent (activated carbon, etc.) was used to separate the adsorption area and desorption area. The adsorption zone and desorption zone are formed simultaneously on different sites, and the adsorption zone and desorption zone are switched on the adsorbent, and following the adsorption treatment, the adsorption body portion is subjected to the desorption treatment after the adsorption is completed. , using an adsorption/desorption device configured to carry out adsorption and desorption simultaneously and in equilibrium so that the adsorbent portion after the completion of desorption is adsorbed following the desorption process. (For example, Japanese Patent Publication No. 56-29576). In this adsorption/desorption device, for example, the adsorbent substance packed in the column adsorbs the adsorbed substance up to near the breakthrough point, and then desorbs it using steam with a large enthalpy. Compared to other methods, adsorption is much lower than the breakthrough point,
In addition, since the treatment is performed in a system with insufficient desorption to maintain an equilibrium between adsorption and desorption by performing insufficient desorption using relatively low-temperature heated air, relatively low-temperature gas is used as the desorption gas. (80 to 140°C) heated air can be used, requiring less energy, and since desorption can be performed at relatively low temperatures, losses due to deterioration of the adsorbent can be reduced. Due to the synergistic effect, this method is superior to the above-mentioned conventional techniques as a method for treating organic solvent gas. However, in this conventional technology, since the process is carried out continuously by balancing the amount of adsorption and the amount of desorption, it is not possible to arbitrarily change the desorption energy, which is a factor that causes fluctuations in the amount of desorption. In other words, if you try to increase the concentration of the desorbed gas by reducing the desorption air volume, the amount of desorption will also decrease, and by increasing the desorption amount by increasing the desorption gas temperature above the limit, the concentration of the desorbed gas will increase. If this were to be done, desorption would not be possible in the low-temperature range mentioned above, and the characteristics of this type of device would be impaired.In the end, the desorption temperature would be relatively low, requiring less energy for desorption. In addition, it is optimal to set the temperature at a constant temperature close to the limit that does not cause loss due to deterioration of the adsorbent, and also to set the desorption air volume so that the organic solvent in the gas to be treated continues to be adsorbed and removed at an appropriate removal rate. In order to obtain the amount of desorption commensurate with the amount of adsorption at the time, the air volume must be kept at an appropriate level, and therefore desorption can only be carried out at a relatively low temperature and using a fixed amount of air. Therefore, it has been difficult to increase the concentration ratio of the desorbed gas to the gas to be processed to a sufficiently satisfactory level. In general, the concentration ratio is defined as the organic solvent concentration C _A in the gas to be treated and the organic solvent concentration C A in the desorbed gas.
The ratio with C _B , that is, C _B /C _A = M (concentration ratio), and if the adsorption efficiency in the adsorption area is 100%,
The concentration ratio M is equal to the ratio of the supply amount Q _A of the gas to be treated and the supply amount Q _B of the desorption gas, and C _B /C _A = Q _A /Q _B = M. However, in general, adsorption Efficiency (=removal rate) is η
Then, M=C _B /C _A =η·Q _A /Q _B , and as the removal rate η increases, the concentration ratio increases. However, the above theoretical formula that the concentration ratio increases due to an increase in the removal rate η means that when the adsorption amount increases with an increase in the removal rate η, the air volume Q _B of the desorption gas increases. This equation holds true when the entire amount of the adsorbed organic solvent component is completely desorbed, and if the air volume Q _B of the desorption gas cannot be increased when the amount of organic solvent component to be desorbed increases. It is also true that the desorption energy cannot be increased unless the temperature of the desorption gas is increased, so the above theoretical formula is based on the air volume of the desorption gas.
Not only Q _B but also the temperature is constant, and
It cannot be applied to the treatment method using the aforementioned continuous adsorption/desorption type adsorption/desorption equipment, which balances adsorption and desorption by performing incomplete desorption, and desorption is performed using steam with high enthalpy or high-temperature exhaust gas, etc. It was recognized that this method could only be applied to a conventional batch-type adsorption/desorption device that performs the following steps. Furthermore, as means for improving the removal rate η, (a) lowering the absolute humidity of the gas to be treated using a dehumidifying device; (b) Lower the relative humidity of the gas to be treated using a heating device. The above methods (a) and (b) are possible, but when using the above method (a), the entire equipment tends to become complicated and large due to the installation of a dehumidifier (concentration type or absorption type). However, this method is not only a practical method, but also has the drawback that it requires a lot of effort to maintain and manage the dehumidification equipment, which deteriorates the operating efficiency of the equipment and, by extension, the productivity of the coating equipment itself. It's something that doesn't exist. Furthermore, although the method (b) above is effective in eliminating the disadvantages of the method (a), the adsorption efficiency of activated carbon generally decreases as the temperature of the gas to be adsorbed increases. Therefore, even if the rate of increase in adsorption efficiency due to a decrease in relative humidity exceeds the rate of decrease in adsorption efficiency due to a rise in temperature,
A sufficient improvement in adsorption efficiency cannot be expected unless there is a significant decrease in humidity, and experiments have shown that the relative humidity
When the adsorption efficiency is 92% at 65%, even if the relative humidity is reduced to 50%, the adsorption efficiency will only increase to 95%.
This slight improvement in adsorption efficiency is effective for the purpose of simply improving adsorption efficiency and increasing processing capacity, but if the purpose is to economically process the gas to be treated, it is necessary to increase the energy consumption of the heating device. Taking these factors into consideration, improving adsorption efficiency itself was not recognized as a very effective means. An object of the present invention is to break through the conventional technical common sense as described above, and to use an adsorption/desorption device that continuously performs adsorption and desorption by balancing the adsorption and desorption, to process a gas to be treated containing an organic solvent gas. The objective is to be able to carry out the concentration technically and economically advantageously, and to reduce the operating load on the entire processing device. The characteristic configuration of the present invention for achieving the above object is that an adsorption zone portion and a desorption zone portion are simultaneously and separately formed on an adsorbent using fibrous or finely powdered activated carbon as an adsorbent. Furthermore, the adsorption area and desorption area are transferred on the adsorbent, and following the adsorption process, the adsorbent area after the completion of adsorption is subjected to the desorption process, and following the desorption process, the part of the adsorbent after the completion of desorption is processed. At high relative humidity containing an organic solvent gas, an adsorption/desorption device configured to perform adsorption and desorption simultaneously and in equilibrium is used to adsorb the adsorbent part. A method for treating a gas to be treated at room temperature, comprising: [a] passing the gas to be treated through an adsorption zone of an adsorption/desorption device to adsorb and remove an organic solvent component from the gas to be treated, and [b] After that, a desorption gas is supplied to the desorption region of the adsorption/desorption device to desorb the organic solvent component adsorbed by the adsorption/desorption device, and [c] the desorbed organic solvent component and the desorption region are Supply the concentrated gas mixed with gas to the post-processing device. The gas to be treated is processed in the order of [A] to [C] above, and the amount of the desorption gas is smaller than the amount of the gas to be treated. Consists of heated air,
Furthermore, the gas to be treated is heated to a temperature that maintains the concentration ratio of the concentrated gas after desorption at approximately the maximum value while maintaining a predetermined adsorption efficiency. be effective. In other words, the unique advantages of an adsorption/desorption device that performs continuous adsorption and desorption by balancing adsorption and desorption are that it can operate at a relatively low temperature with minimal loss due to deterioration of the adsorbent, and requires less energy. Although heated air can be used as a desorption gas, we have changed the perspective of technology for reducing relative humidity, which was previously only considered to be for improving the adsorption efficiency of solvents, etc., to reduce relative humidity. By doing this, we focused on the fact that even though the amount of organic solvent adsorption increases, the amount of water adsorption decreases.Moreover, under the condition that the heating temperature range for lowering relative humidity maintains a predetermined adsorption efficiency, , if the temperature is raised within the range of 2 to 15℃ from room temperature to maintain the concentration ratio of the concentrated gas after desorption at almost the maximum value, the desorption energy will be significantly reduced due to the reduction in the amount of water adsorption. Based on the experimental results, we found that there is a region in which the relative humidity can be reduced, and we have made it possible to incorporate the above-mentioned relative humidity reduction technology into this type of adsorption/desorption device, thereby significantly improving the concentration ratio. This was possible. In other words, if the amount of organic solvent adsorbed increases by lowering the relative humidity, the amount of organic solvent desorbed must also increase, and the desorption energy for this must also inevitably increase. In this type of adsorption/desorption equipment, where the flow rate of the desorption gas at a constant temperature must be kept below a certain level in order to avoid a reduction in the concentration ratio, it seems impossible to increase the desorption energy itself. However, when the relative humidity is lowered within the temperature range mentioned above, even if the amount of organic solvent adsorbed increases, the amount of water adsorbed decreases significantly, and moreover, the amount of organic solvent adsorbed increases. The rate of decrease in the required desorption energy due to the decrease in water content is far greater than the rate of increase in the required desorption energy due to the increase in the rate of increase in the required desorption energy due to the increase in the rate of increase in the required desorption energy. Therefore, the flow rate of heated air for desorption at a constant temperature that is low enough not to cause loss due to deterioration of the adsorbent is reduced, and the concentration of the organic solvent component mixed in the heated air for desorption is increased. This enabled processing at a concentrated ratio to be carried out economically. This can be understood more clearly from the experimental results shown in Tables 1 and 2 below. In other words, the relationship between the relative humidity RH, the equilibrium adsorption amount of an organic solvent (toluene is shown here as an example), and the equilibrium adsorption amount of water is as follows.

[Table] As shown in Table 1 above, it can be seen that as the relative humidity RH decreases, the amount of toluene adsorbed increases and the amount of water adsorbed decreases.

[Table] As shown in Table 2 above, it can be seen that lowering the relative humidity RH is extremely effective in reducing desorption energy. In other words, as the relative humidity RH decreases, the amount of toluene adsorbed increases as shown in Table 1 above, and the energy for desorption of the increased toluene also increases. The energy required for desorption of this water is greatly reduced, and the total desorption energy can be greatly reduced. Embodiments of the present invention will be described below along with devices used therein. First Embodiment (See Figure 1) Reference numeral 1 denotes a painting booth, and a water washing device 2 is provided at the bottom of the booth 1 to wash the air inside the booth 1 with water to remove paint mist. 2
The gas to be treated A containing organic solvent gas discharged from the coating booth 1 through which it is discharged has a relative humidity of approximately 75 to 95% and a temperature of 28 to 32 degrees Celsius in summer and 18 to 23 degrees Celsius in winter. It is becoming. Reference numeral 3 denotes a preheater, which heats the gas A to be treated so as to raise the temperature in the range of about 2 to 15°C, and this preheater 3 is generally used for heating air. Use a steam heater or hot water heater. A filter 4 is provided upstream of the preheater 3 to remove fine mist remaining in the gas A to be treated. 5 is an adsorption/desorption device for continuously performing adsorption/desorption processing by balancing adsorption and desorption, and is made by mixing activated carbon fibers or activated carbon powder with other fibers to form paper. The rotor 6 is assembled into a cylindrical honeycomb rotor 6, and a drive device 7 is provided to rotate the rotor 6 in a fixed direction around its center line.
A state in which the adsorption region 6a is located in the passage path of the gas to be processed A that has passed through the preheater 3, and the desorption region 6b is located in the passage path of the desorption gas B made of heated air at a relatively low temperature. The device is placed at a position where it continuously performs adsorption and desorption operations as it rotates at that position. The specific structure of this adsorption/desorption device 5 is generally well known to those skilled in the art, as shown in Japanese Patent Publication No. 56-29576, and therefore further detailed explanation will be omitted. Reference numeral 10 denotes a post-treatment device for treating the organic solvent component mixed in the desorption gas, and has the following configuration. The desorption gas B that has passed through the desorption zone 6b of the adsorption/desorption device 5 is heated through the heating side of the first heat exchanger 9, and this heated desorption gas is sent to the catalytic oxidation device 8 which also serves as a heating device. The solvent gas is catalytically combusted and deodorized in the catalytic oxidizer 8. The exhaust gas after the deodorization process passes through the heated side of the first heat exchanger 9 and is used as a preheating source for the desorption gas B. And this first
The exhaust gas that has passed through the heat exchanger 9 is transferred to the second heat exchanger 11
is discharged to the outside air through the heat dissipation side of the The desorption gas B heading for the adsorption device 5 passes through the heating side of the second heat exchanger 11 and is heated here.
The desorption gas B to be heated is outside air that has been purified through the filter 12. A bypass passage 13 bypasses the second heat exchanger 11, and is used to adjust the temperature to a temperature suitable for desorption by the heating action of the second heat exchanger 11. 14 is a preheating burner provided in the catalytic oxidation device 8. 15 is a catalyst. In this way,
The deodorizing gas B is deodorized by combustion, and the heat generated by the combustion deodorizing is used to heat the desorbing gas B. Note that since the specific structure of each of the above parts is well known, further detailed explanation will be omitted. The experimental results using the apparatus of this example are shown in FIG. In the graph of FIG. 5, the vertical axis indicates the ratio of the organic solvent gas concentration C _A in the gas to be treated (air) to the organic solvent gas concentration C _B in the desorption type gas, that is, the concentration ratio M. C _B /C _A =M The horizontal axis shows the change in temperature T (°C) of the gas to be processed heated by the preheater 3. Assuming that the adsorption efficiency in the adsorption zone 6a is 100%, the concentration target M is equal to the supply amount Q _A of the gas to be treated and the desorption zone 6
It is equal to the ratio of the supply amount Q _B of the desorption gas B passing through b, and C _B /C _A =Q _A /Q _B =M. In general, adsorption efficiency (=removal rate) is defined as η
(%), M=C _B /C _A = η・Q _A /Q _B. The middle line a in the graph shows the experimental results under the following condition settings. Q _A = 1200m ³ /h t _O = 32℃ (temperature before heating) Concentration of gas to be treated before adsorption = 100ppm Concentration of gas to be treated after adsorption = 4.5ppm Adsorption efficiency η = 95.5% Relative humidity before preheater heating = 80% Desorption zone supply temperature of desorption gas = 120°C The organic solvent gas contained in the gas to be treated is mainly toluene. The middle line b in the graph shows the experimental results under the following condition settings. Q _A = 1200m ³ /h t _O = 31℃ x = 23g/Kg' [absolute temperature] Concentration of gas to be treated before adsorption = 175ppm Concentration of gas to be treated after adsorption = 10.0ppm Adsorption efficiency η = 90% Preheater Relative humidity before heating = 80% Desorption zone supply temperature of desorption gas = 120℃ Organic solvent gas contained in the gas to be treated is 1PA
and xylene in a 1:1 mixing ratio. The middle line c in the graph shows the experimental results under the following condition settings. Q _A = 1200m ³ /h t _O = 30°C =75.5% Desorption zone supply temperature of desorption gas = 120℃ Organic solvent gas contained in the gas to be treated is 1PA
The main component is Next, the relationship between the outlet concentration of adsorbed substances (including water) during desorption and relative humidity is shown in the graph shown in FIG. 6. However, the conditions for attachment and detachment are the same.
In this graph, when the air volume is constant, the temperature of desorption gas B is
The temperature was 120℃. _{Figure A} shows _the concentration _of moisture They are respectively expressed in . Similarly, the figure B shows the relative humidity when RH=65%, and the figure C shows the relative humidity.
The case where RH=50% is shown. As shown in this graph, as the relative humidity RH decreases, the outlet concentration of water X ₁ decreases, indicating that desorption energy is effectively acting on _the organic solvent It can be seen that when is high, water X ₁ is desorbed before organic solvent X ₂ , and the desorption energy for this is wasted. Second embodiment (see Figure 2) The preheater 3 is an indirect heat exchanger, and a part of the desorption gas between the first heat exchanger 9 and the second heat exchanger 11 is supplied to the heating side. The amount of heat generated by combustion deodorization of the desorption gas is used for combustion deodorization of the gas to be treated. The rest of the structure is the same as that of the first embodiment. Note that the second heat exchanger 11
A part of the desorption gas that has passed through is transferred to the preheater 3.
It is also good to pass it through the heating side of a heat exchanger. Third Embodiment (See FIG. 3) The heating device 8 of the post-processing device 10 is configured as follows. The rest of the structure is the same as that of the first embodiment. The outside air that has passed through the filter 16 is transferred to the indirect heat exchanger 17
, then passes through the heater 18 and the desorption zone 6b of the adsorption/desorption device 5, then passes through the endothermic side of the indirect heat exchanger 17, enters the cooler 19, and then enters the solvent recovery device 20. The system is configured to liquefy and separate and recover solvent gas, etc. The configurations of each of the above parts are well known,
Further detailed explanation will be omitted. Fourth Embodiment (See Figure 4) In the third embodiment, the preheater 3 is an indirect heat exchanger, and on the heat absorption side there is a connection between the heat exchanger 17 and the cooler 19 of the heating device 8. Bypassing a portion of the gas for use. The rest is the same as the third embodiment. In each of the embodiments described above, one or more of the following combinations may be used. The direction in which the gas to be treated or the gas for desorption passes through the rotor 6 is the radial direction. The preheater 3 is of a burner heating type. Regarding the combustion deodorization of the after-treatment device 10,
Burner combustion should be used instead of catalytic combustion.

[Brief explanation of drawings]

The drawings show an example of the method for treating organic solvent gas according to the present invention, FIG. 1 is a flowchart showing the first embodiment, FIG. 2 is a flowchart showing the second embodiment, and FIG. 3 is a flowchart showing the third embodiment. Flowchart showing the embodiment, FIG. 4 is a flowchart showing the fourth embodiment,
FIGS. 5 and 6 are graphs showing experimental results. 5...Adsorption/desorption device, 6a...Adsorption area, 6b...
Desorption area, A... gas to be treated, B... gas for desorption.

Claims (1)

[Scope of Claims] 1. An adsorption region 6a portion and a desorption region 6b portion are formed simultaneously and in separate parts in an adsorbent using activated carbon in the form of fibers or fine particles as an adsorbent,
Furthermore, the adsorption zone 6a and the desorption zone 6b are switched on the adsorbent, and following the adsorption treatment, the adsorption body portion after the completion of adsorption is subjected to the desorption treatment, and following the desorption treatment, the adsorption body portion after the completion of desorption is An adsorption/desorption device 5 configured to perform adsorption and desorption simultaneously and in equilibrium is used to absorb an organic solvent gas under high relative humidity and room temperature. A method for treating gas A to be treated, comprising: (a) passing the gas to be treated A through an adsorption zone 6a of an adsorption/desorption device 5 to adsorb and remove an organic solvent component from the gas to be treated A; (b) After that, the desorption area 6b of the adsorption/desorption device 5
, a desorption gas B is supplied to desorb the organic solvent component adsorbed on the adsorption/desorption device 5, and [c] the desorbed organic solvent component and the desorption gas B are mixed to form a concentrated mixture. Gas post-processing device 1
The gas to be treated A is treated in the order of [A] to [C] above, and the desorption gas B is composed of heated air in a smaller amount than the amount of the gas to be treated A, Furthermore, the to-be-treated gas A is heated to a temperature that maintains the concentration ratio of the concentrated gas after desorption to a substantially maximum value while maintaining a predetermined adsorption efficiency. Processing method.