JP4778403B2 - A method and apparatus for purifying exhaust gas by collecting and concentrating VOC from exhaust gas containing VOC. - Google Patents

Description

The present invention relates to water that is an absorption liquid in an exhaust gas containing VOC discharged from a hot air dryer of a chemical factory such as a factory for manufacturing electrical or electronic parts such as semiconductors, batteries, or a film or leather. By absorbing (recovering) the VOC, the exhaust gas is purified. Further, the VOC concentrating unit evaporates the water which is the absorption liquid (the absorption liquid described in the present specification means absorption water), and VOC is obtained. The present invention relates to a method and apparatus for recovering and concentrating VOCs from exhaust gas containing VOCs for purifying exhaust gas and purifying the exhaust gas. Note that “VOC” in the present invention means a volatile organic compound having a higher boiling point than water, being easily soluble in water, and having physical properties that do not have an azeotropic point with water.

  Conventionally, as a method of purifying exhaust gas containing VOC discharged from a hot air dryer, and further recovering / reusing VOC, (i) a cooling method and (ii) using a solid adsorbent such as activated carbon / zeolite (Iii) an absorption method using a liquid volatile solvent, and (iv) an absorption method using water. In April 2006, emission regulations for volatile organic compounds (VOC) based on the revised Air Pollution Control Law were enforced, and the emission standards for VOC contained in exhaust gas were determined. At the present time, it is almost always applied when the air volume of the blower or exhaust fan exceeds a certain level, but it is inevitable that voluntary reduction is required. In addition, reuse (recycling) that effectively uses limited resources is one of the major issues in future technology development.

  The cooling method (i) is a method in which exhaust gas is cooled with cooling water or the like by an indirect heat exchanger, the vapor pressure of VOC in the air is lowered, and the VOC is condensed and recovered using the difference. is there. As an example, a case where exhaust gas at a temperature of 100 ° C. containing 1000 ppm (v / v) of N, N-dimethylformamide (DMF) is cooled to 20 ° C. will be described. The vapor pressure of DMF at 100 ° C. is 19.5 kPa (maximum saturation at 100 ° C.) and that at 20 ° C. is 0.35 kPa. This vapor pressure difference (19.5-0.35 = 19.15) is condensed and can be recovered as a liquid. However, DMF has a vapor pressure of 0.35 kPa in 20 ° C. air discharged as purified gas, and the concentration of DMF at this time is ≈3500 ppm (v / v), so that the exhaust gas regulation value is cleared. I can't. When estimated from the relationship between temperature and vapor pressure, it can be said that it is practically difficult to remove VOC below this value. Vapor pressure varies depending on the type of VOC, but because there is a limit to the temperature that can be cooled (cooling water temperature, amount, etc.), the vapor pressure can only be lowered to a certain value, making it easy to clear the regulation value is not. In addition, since the moisture (water) in the exhaust gas condenses in the recovered VOC liquid at the same time, the recovered VOC recovered liquid concentration cannot be made constant and is not suitable for purification and recycling of recovered VOC. there were.

  The adsorption method using the solid adsorbent such as activated carbon / zeolite (ii) (refer to Patent Document 1) is cooled to about 40 ° C., which is a condition in which the exhaust gas can be adsorbed efficiently by the adsorbent in the previous stage, and the adsorbent The gas is purified by selectively adsorbing VOC / water. The adsorbed VOC is heated to a desorption condition of 140 to 150 ° C. and separated (desorbed). As described above, the method (ii) is a method of recovering VOC by repeating adsorption (cooling) and desorption (heating). Heating for cooling, heat for desorption, etc. are necessary, so running cost is high, VOC reacts due to overheating or catalytic action of adsorbent at high temperature to produce other substances (in the case of DMF, formic acid and dimethylamine are generated ) In addition, since the moisture (water) in the exhaust gas is simultaneously adsorbed and desorbed in the recovered VOC, the concentration of the VOC in the purified gas and the recovered liquid cannot be made constant, so it is not suitable for recycling. In addition, there is a problem that periodic replacement is required due to deterioration of the adsorbent over time.

  The absorption method using the liquid hardly volatile solvent (iii) (refer to Patent Document 2) is a method in which the solid adsorbent of [0004] is changed to a liquid hardly volatile solvent. That is, the VOC / water absorbed in the absorption tower is sent to a stripping tower (a column for separating VOC / water), and VOC / water is separated from the hardly volatile solvent and returned to the absorption tower again. It is a method to collect. In order to improve the absorption efficiency, the exhaust gas flowing into the absorption tower is cooled, and the running cost is high, such as heating to separate VOC / water. The recovered VOC absorbs and separates moisture (water) in the exhaust gas at the same time, so the VOC concentration cannot be kept constant, making it unsuitable for recycling. There are problems such as complicated equipment such as coolers and coolers.

  The absorption method using water (iv) (see Patent Document 3) is a gas absorption method using water as an absorbent, generally called a water scrubber type. Since the absorption efficiency of water with respect to VOC is better as the temperature is lower, the exhaust gas introduced into the absorption tower is cooled in advance, brought into gas-liquid contact with a large amount of water, and the gas is washed. Conventional gas absorbers using water as an absorbent have the purpose of separating the VOC concentration contained in the purified gas below the regulation value, and the VOC absorbed in the water is reduced to the VOC below the regulation value through activated sludge treatment and discharged. There were two purposes. For these two purposes, it is necessary to supply a large volume of water, and recycling of the absorbed VOC requires a recovery cost to separate it from the water. It was possible. With respect to VOCs having higher boiling point than water targeted by the present invention, hydrophilicity, and physical properties that do not have azeotropic point with water, the present inventors, when diverting existing equipment, There is a problem that the concentration of VOC which is as high as 50 ppm or higher and can be recovered from the bottom of the column considering recycling is 50% or less.

  In Patent Document 4 and Patent Document 5, a water absorption / concentration method as a VOC recovery method is described from Examples based on the material balance. Both are patents aimed at collecting and concentrating VOC, but one of the points of this apparatus is the concentration control of the collected concentrated liquid (collected liquid in Patent Documents 4 and 5). However, when considering application to an actual apparatus, in Patent Document 4, the VOC concentration in the VOC storage unit (in the lower part of the water displacement tower in Patent Document 4) is measured, and controlled by the amount of absorption liquid (make-up water in Patent Document 4). Proposed method to do. In Patent Document 5, the absorption liquid (supplementary water in Patent Document 5) is divided into two, and Control 1 controls the amount of the absorption liquid by the temperature difference between the exhaust gas and the purified gas (treated gas in Patent Document 5). In Control 2, a complicated method is proposed in which the amount of the absorbing liquid is controlled by the VOC concentration in the VOC storage section (lower part of the water displacement tower in Patent Document 5). Both methods are methods for controlling the amount of the absorbing liquid supplied to the uppermost part of the apparatus with the concentration of the VOC storage part located at the lowermost part, causing a time delay, and accurate control is difficult. Further, the VOC contained in the exhaust gas may be multi-component, and accurate VOC measurement is difficult with a normal densitometer. In addition, both documents deal only with high-temperature exhaust gas as an object of exhaust gas, and lack correspondence with low-temperature exhaust gas. Furthermore, since the actual VOC-containing exhaust gas is affected by disturbances due to concentration fluctuations, temperature fluctuations, and seasonal / weather changes, the composition of VOC and water in the gas does not always become constant. It is difficult to control the recovery rate and the concentration rate by the method of Patent Document 5.

JP 2001-137646 A JP 2000-157834 A JP-A-10-118440 Japanese Patent Laid-Open No. 2004-230265 JP 2005-246218 A

The first object of the present invention is to purify by absorbing (recovering) VOC with water having a higher boiling point than water contained in the VOC-containing exhaust gas, hydrophilicity, and further having no physical boiling point with water. As a gas, the emission control value (ppmC) of volatile organic compounds (VOC) based on the revised Air Pollution Control Law is greatly cleared.
The second problem of the present invention is that the VOC recovery liquid concentration to be recovered is recovered at a high concentration necessary for reducing the recycling load and reused.
The third object of the present invention is to utilize the temperature (energy) of the VOC-containing exhaust gas as much as possible and to use it as the VOC concentration energy.
The fourth problem of the present invention is that the VOC concentration contained in the VOC-containing exhaust gas always fluctuates with time. Therefore, the VOC concentration of the purifying gas is constantly cleared to less than the required emission regulation value. The purpose of this is to provide a VOC recovery and concentration device that enables continuous unmanned operation.
The fifth problem of the present invention is that the water used as the absorption water is preferably distilled water, pure water or soft water in order to prevent the precipitation of inorganic substances. The load is large. In order to overcome this problem, in order to reduce the release of distilled water, pure water, and soft water as the moisture content of the purified gas, a cooler is installed at the purified gas outlet and condensed to supply the absorption liquid. It is in the point which provides the apparatus which reduces this. Furthermore, it is provided with a dehumidifier and provides a closed system for dehumidified gas.
The sixth problem of the present invention is that the VOC-containing exhaust gas discharged from a normal hot air dryer is often at a high temperature. However, when the low-temperature VOC-containing exhaust gas is sometimes targeted, the low-temperature VOC-containing exhaust gas is heated directly with a heater, or the circulating fluid from the VOC storage part is heated to supplement the energy to supplement the low-temperature VOC-containing exhaust gas. The object is to provide an apparatus applicable to exhaust gas.
A seventh problem of the present invention is that the gas discharged from a normal hot air dryer often uses air taken from the atmosphere, and the humidity (moisture) contained in the gas with seasonal changes and weather changes Often fluctuate. In an adsorption-type VOC treatment facility, it is difficult to control the VOC recovery rate and concentration rate to a certain level due to the influence of moisture in the gas. An object of the present invention is to provide an apparatus capable of constantly controlling the VOC recovery rate and the concentration rate regardless of the moisture in the gas accompanying the change in season and weather to overcome this problem.
An eighth object of the present invention is to provide an apparatus for reducing the height of the entire apparatus by separating the VOC concentrating part and the VOC recovery part.
A ninth object of the present invention is to provide equipment capable of adopting various shapes such as a vertical square type, a horizontal square type, and a cylindrical type, regardless of the cylindrical shape, in order to reduce the installation area. It is in.

A first aspect of the present invention is a method for recovering and concentrating VOC contained in exhaust gas and purifying the exhaust gas. A VOC enrichment unit having a one-block gas-liquid contact mechanism and a gas downstream side of the VOC enrichment unit (gas outlet in the apparatus) In the VOC recovery unit, an absorption liquid supplied from the gas downstream side of the VOC recovery unit is used, using a VOC recovery and concentration device composed of a VOC recovery unit having a gas-liquid contact mechanism of one to several blocks on the side) While absorbing the VOC contained in the exhaust gas, the inside of the VOC concentrating part is allowed to flow down, while the VOC-containing exhaust gas is introduced from the upstream side of the VOC concentrating part gas, and the water as the absorbing liquid is evaporated in the VOC concentrating part, and the VOC recovery part The VOC concentrated liquid discharged through the system and discharged from the system and concentrated in the VOC concentration unit is stored in the VOC storage unit provided at the lower end of the VOC concentration unit and / or the VOC recovery unit. The VOC storage liquid collected in the VOC storage section is circulated and supplied to the gas downstream side of the VOC concentration section, the VOC is concentrated by evaporation of water in the circulation liquid, and the VOC stored in the VOC storage section is concentrated. The circulating fluid relates to a method of recovering and concentrating VOC from VOC-containing exhaust gas, wherein the circulating fluid is discharged out of the system as a recovered concentrated solution when the concentration reaches a certain concentration.
In the second aspect of the present invention, a main absorbent for recovering VOC having an amount of “a range not exceeding the amount of evaporation of water calculated from the energy brought in by exhaust gas” is sprayed from the gas downstream side of the VOC recovery unit, 2. The method of recovering and concentrating VOC from exhaust gas containing VOC according to claim 1, wherein an auxiliary amount of auxiliary absorption liquid for adjusting the concentration of the VOC recovery liquid is supplied into the apparatus. .
The third aspect of the present invention is that a cooling means is provided at the outlet of the purified gas discharged out of the system through the VOC recovery section, and the condensed water is reused as an absorbing solution. The present invention relates to a method for recovering and concentrating VOC from exhaust gas containing VOC and purifying exhaust gas.
The fourth aspect of the present invention is that the recovered concentrated liquid is discharged out of the system when a temperature rise mutation point occurs in the temperature curve representing the temperature change of the VOC storage section in the VOC storage section. The present invention relates to a method for recovering and concentrating VOC from the VOC-containing exhaust gas described above to purify the exhaust gas.
5th of this invention cools the said purification | cleaning gas, condenses the water vapor | steam in purification | cleaning gas, and recycles it as an absorption liquid, collect | recovers and concentrates VOC from the VOC containing exhaust gas in any one of Claims 1-4. The present invention relates to a method for purifying exhaust gas.
According to the sixth aspect of the present invention, when the temperature of the exhaust gas is insufficient for water evaporation, (b) heating the exhaust gas at a stage before introducing the exhaust gas into the VOC concentrating unit, and (b) heating the VOC storage unit. From the VOC-containing exhaust gas according to any one of claims 1 to 5, wherein the heating is performed by at least one heating method of (c) heating the VOC storage liquid at a stage of circulating the VOC storage liquid to the gas downstream side of the VOC concentration unit. The present invention relates to a method for recovering and concentrating VOC and purifying exhaust gas.
The seventh aspect of the present invention is a VOC concentrator having a one-block gas-liquid contact mechanism and a VOC recovery unit having one to several blocks of gas-liquid contact mechanism on the gas downstream side (gas outlet side in the apparatus) of the VOC concentrator. VOC-containing gas introduction means for introducing VOC-containing exhaust gas from the gas upstream side (gas inlet side in the device) of the VOC concentrating section in a device for collecting and concentrating VOC contained in the exhaust gas composed of Means for supplying absorption liquid from the gas downstream side of the recovery unit, VOC recovery means for recovering VOC in the exhaust gas and purifying the gas, purified gas discharge means in the VOC recovery unit, the VOC concentration unit And the VOC storage section for storing the VOC-containing processing liquid sent from the VOC recovery section, and the storage liquid remaining in the VOC storage section is circulated to the gas downstream side of the VOC concentration section. Means for supplying and concentrating VOC by evaporation of absorbed water in the circulating liquid, means for measuring the VOC concentration of the stored liquid provided in the VOC storage section, and when the VOC concentration in the stored liquid reaches a predetermined concentration, The present invention relates to an exhaust gas purification / VOC recovery and concentration apparatus, characterized by comprising discharge means for discharging the stored liquid as a recovered concentrated liquid to the outside of the system.
The eighth aspect of the present invention relates to an exhaust gas purification / VOC recovery and concentration apparatus according to claim 7, wherein a gas cooling heat exchanger is attached to the purified gas discharge means.
According to a ninth aspect of the present invention, a purified gas cooling heat exchanger is provided at a purified gas outlet provided further above the absorbing liquid spraying means above the VOC recovery unit, and the purified gas discharged from the heat exchanger is transferred to a carrier gas. 9. To recover and concentrate VOC from the VOC-containing exhaust gas according to claim 7 or 8, which is provided with a carrier gas recycle / closed system, wherein the exhaust gas is returned to the dryer and reused. Relating to the device.
The tenth aspect of the present invention is
(A) a stage before introducing exhaust gas into the VOC enrichment section;
(B) VOC storage part,
(C) circulating the VOC storage liquid to the gas downstream side of the VOC concentrator,
The present invention relates to an apparatus for recovering and concentrating VOC from exhaust gas containing VOC according to any one of claims 7 to 9, wherein a heating means is provided at at least one location.

As a main means for solving the problems of the present invention, in the process in which the VOC-containing exhaust gas passes through one block of the VOC concentrating unit and one to several blocks of the VOC recovery unit, Concentrates and absorbs VOC contained in VOC-containing exhaust gas, removes VOC in VOC-containing exhaust gas, discharges purified gas below the standard value to the outside of the system, and absorbs (recovers) VOC to a recyclable concentration It is a means to concentrate and discharge out of the system.
A basic block flow of this means is shown in FIG. The absorption water supplied from the gas downstream side of the VOC recovery unit absorbs VOC contained in the VOC-containing exhaust gas in the VOC recovery unit and flows down to the VOC concentration unit. The exhaust gas introduced from the upstream side of the VOC concentrating part gas evaporates the water that is the absorbing liquid in the VOC concentrating part, discharges it as a purified gas outside the system through the VOC recovering part, and reaches the top of the VOC concentrating part and / or the VOC collecting part. The liquid in the VOC storage section provided at the lower end is circulated and supplied to the gas downstream side of the VOC concentrating section by a pump, etc., and the VOC is concentrated by evaporation of water in the circulating liquid. This is a basic flow to discharge out of the system as a recovered concentrated liquid when a certain concentration is reached by measurement.

  In the method of the present invention, VOC is absorbed by water, and the recovered liquid is concentrated by evaporating the water in the aqueous solution absorbed by heat energy. Therefore, VOC applied to the method of the present invention has a larger boiling point (smaller vapor pressure) than water and does not have an azeotropic point, that is, does not form an azeotropic mixture. Since pure water is continuously supplied from the top of the column (on the downstream side of the VOC gas), the VOC recovery unit creates a concentration gradient of the recovered liquid in which the VOC concentration in the absorbent gradually approaches 0 from the upstream side to the downstream side of the recovery unit. When the gas is discharged, the VOC is hardly included. Since the absorption liquid that has passed through the recovery section contains VOC, the amount of absorbed water can be increased in order to improve the VOC recovery performance of the recovery section. The problem of increased capacity arises. Therefore, the above-mentioned problem is solved by providing a concentrating part in front of the recovery part and evaporating and concentrating the moisture in the absorbing liquid using the thermal energy of the VOC-containing exhaust gas.

Looking at the specific relationship between VOC and the absorbing water, (a) Since VOC has a higher boiling point than water, the vapor pressure of water is greater than that of VOC, that is, water is more likely to evaporate than VOC. (B) VOC is hydrophilic, ie VOC is readily soluble in water, (c) VOC has no azeotropic point with water, in other words, VOC does not form an azeotrope with water, ie VOC Can be said to be a substance having the property of forming a low boiling azeotrope with water and not evaporating with water. The VOC applied to the present invention is a VOC having physical properties with the above three conditions (a), (b), and (c).
Examples of VOCs that meet the above conditions include NMP (N-methylpyrrolidone), DMF (N, N-dimethylformamide), DMAC (N, N-dimethylacetamide), DMSO (dimethylsulfoxide), EG (ethylene glycol), Examples include DEG (diethylene glycol), TEG (triethylene glycol), PG (propylene glycol), 1,4-BD (1,4-butanediol), MEA (monoethanolamine), and DGME (diethylene glycol monomethyl ether). it can.

When the concentration of the first absorption liquid (main absorption liquid) or VOC supplied from the gas downstream side of the VOC recovery section reaches or exceeds the specified level and is discharged out of the system as a recovery concentrated liquid or by evaporation of water, the VOC storage section The second absorbing liquid (sub-absorbing liquid) to be supplied when the liquid level decreases is water. Most of these waters evaporate in the VOC concentrating part by the energy brought into the VOC-containing exhaust gas (when the exhaust gas is high temperature) or the energy supplied from the outside (when the exhaust gas is low temperature). When inorganic substances such as calcium salt and magnesium salt are mixed into the first and second absorbed water (hard water or the like), these inorganic substances are not evaporated and concentrated, and when the solubility is exceeded, inorganic crystals are precipitated. If this crystal adheres to the gas-liquid contact mechanism of the VOC concentrating part or the VOC recovery part, the efficiency of the function may be reduced. In addition, in order to recycle the recovered concentrated liquid remaining in the circulating liquid in the VOC storage section, it is necessary to purify with a separate device. At this time, the inorganic substance remaining in the recovered concentrated liquid adversely affects the purification yield of VOCs due to wall adhesion or the like. give. In order to avoid this phenomenon, it is preferable to use distilled water, soft water, or pure water that has been treated in advance so that the water that is the absorption liquid to be supplied does not contain inorganic substances.

  The gas-liquid contact mechanism that constitutes the VOC concentrating unit is a normally used gas-liquid contact means such as shelves, irregular packing, regular packing, sprinkling spray, etc., and new packing of Japanese Patent Application No. 2006-045996 of the present applicant. However, if the gas superficial velocity is increased, flooding (the liquid that should flow down at the gas-liquid contact section will not fall off and stay in the liquid-liquid contact means may be used. The phenomenon that the contact mechanism collapses (which is affected by the liquid-gas ratio) is likely to occur, so the adaptation conditions of the device are narrowed, and since the pressure increases, the power of the blower increases, which affects the running cost. Those with small loss are preferred. The flow direction of the liquid circulated from the VOC-containing exhaust gas and the VOC reservoir can be countercurrent or cocurrent, but cocurrent that reduces pressure loss is preferred.

The main function of the VOC concentrating unit is to use the energy of the VOC-containing exhaust gas when the temperature of the VOC-containing exhaust gas to be introduced is high, or when the temperature of the VOC-containing exhaust gas is low, with the energy heated by the gas, or the circulating circulation This is a function of concentrating VOC by evaporating both the absorbed water that has absorbed the VOC flowing down from the VOC recovery section and the water in the circulating liquid in the VOC storage section with the energy of heating the liquid.

The gas-liquid contact mechanism that constitutes the VOC recovery unit includes normally used gas-liquid contact means such as shelves, irregular packing, and regular packing, and new packing according to Japanese Patent Application No. 2006-045996 of the present applicant. Although no problem with gas-liquid contact means such as the amount of absorbed water supplied in the present invention, a small amount of approximately 1 / 2-1 / 100 in comparison with the absorption of water of normal water scrubber type gas absorber It is preferable to use a high-performance gas-liquid contact mechanism with a precise liquid disperser. Also, if the pressure loss is large, the same as the reason described in [0013], if the gas superficial velocity is increased, flooding (the liquid that should flow down at the gas-liquid contact part does not fall and stays, causing the gas-liquid contact mechanism to collapse. Phenomenon (which is affected by the liquid-gas ratio) is likely to occur, so the adaptation conditions of the device are narrowed, and since the pressure increases, the running cost such as the power of the blower increases, so the pressure loss is small Those are preferred.

The main function of the VOC recovery unit is to absorb the VOC contained in the VOC-containing exhaust gas flowing into the VOC recovery unit through the VOC concentrating unit into the absorption water supplied from the VOC recovery unit gas downstream side, and to absorb the VOC-containing exhaust gas. It is to purify. Since the flow of the exhaust gas and the absorption water involves mass transfer (VOC in the exhaust gas moves to the absorption liquid), it must be an efficient countercurrent flow.

  The gas-liquid contact mechanism described in [0017] calculates the VOC concentration sent to the recovery unit from the concentration and temperature of the concentrate from the simulation and test data, and obtains the VOC concentration obtained from the calculation result and the required regulations. From the VOC concentration below the value, the VOC transfer amount absorbed in the water in the recovery unit is determined, and the design is made from that value. In the case of shelves, in the case of the number of stages necessary for the mass transfer amount, irregular packing, ordered packing, and new packing of Japanese Patent Application No. 2006-045996, the filling height corresponding to the number of stages is required. .

VOC-containing exhaust gas discharged from a hot air dryer or the like is often at a high temperature (80 ° C. ± 10 ° C.). In the case of high-temperature VOC-containing exhaust gas, the liquid in the VOC storage unit is pump-circulated on the upper surface of the VOC concentration unit, and water in the circulating liquid is evaporated (concentration of VOC) by gas-liquid contact to cool the high-temperature VOC-containing exhaust gas. However, there are cases where the VOC-containing exhaust gas temperature is low (45 ° C. or lower) such that the VOC-containing exhaust gas temperature is low in the gas generation source, or because the distance between the generation source and the exhaust location is long and the gas is cooled. In this case, since the energy flowing into the VOC concentrating part is small, in other words, the amount of water contained in the circulating fluid is small, the circulating fluid concentration cannot be increased. In order to compensate for this energy shortage, a method of heating the circulating liquid by providing a heat exchanger for heating in the middle of the pump circulation line can be mentioned. The heating method is not limited to the circulation line, and any method may be used as long as it is a means for supplementing heat, such as heating the low-temperature exhaust gas or heating the liquid in the VOC storage unit.
In the present invention, a VOC-containing exhaust gas having a temperature of about 45 ° C. or less is described as a low-temperature VOC-containing exhaust gas, and a VOC-containing exhaust gas having a temperature higher than about 45 ° C. is described as a high-temperature VOC-containing exhaust gas.

For example, as shown in FIGS. 2 and 3, the absorption water is preferably supplied from at least two locations of the main absorption liquid inlet and the sub absorption liquid inlet. The amount of water supplied from the main absorption liquid inlet (1) is adjusted by the energy (calculated from the temperature and amount) brought in by the exhaust gas and the amount not exceeding the amount of water evaporation calculated from this energy (for example, 90% of the calculated amount) This is a specific method for adjusting the VOC concentration.

  The amount of water supplied from the auxiliary absorbent inlet (2) is utilized to adjust the VOC concentration of the VOC circulating liquid. That is, the amount of water supplied from the main absorbent inlet (1) is set to be smaller than the calculated amount. In this case, the amount of water in the VOC storage unit (or the entire apparatus) decreases, and VOC is constantly concentrated. The amount of heat brought into the VOC-containing exhaust gas is unsteady, such as the concentration of VOC contained in the VOC-containing exhaust gas always changes, so the condensation heat of the VOC naturally also changes, and the VOC concentration in the VOC storage part always changes. . The water supplied from the secondary absorbent inlet (2) serves as a buffer for these fluctuations, and it is easy to adjust the VOC concentration in the VOC storage unit to be constant by detecting the VOC concentration in the VOC storage unit. Sensing and adjusting these variations at one location only at the main absorbent inlet (1) is too unsteady and cannot be adjusted. The secondary absorption liquid inlet (2) is (f) the gas downstream side of the VOC recovery unit [same position as the main absorption liquid inlet (1)], (g) the VOC storage unit, or (v) the VOC recovery unit and the VOC concentration unit. However, considering that the main fluctuation factor is the VOC-containing exhaust gas, it is most suitable to supply it to the VOC storage section.

  In the present invention, an absorption liquid necessary for absorption obtained from calculation is referred to as a main absorption liquid, and an absorption liquid used as a concentration adjustment necessary for actual operation is referred to as a secondary absorption liquid. Both the main absorption liquid and the sub absorption liquid use water, but the main absorption liquid collects VOC, so the sub absorption liquid is for adjusting the concentration of the VOC collection concentrated liquid, and performs different control. Therefore, even if the main absorption liquid and the auxiliary absorption liquid are supplied from the same position, they are supplied by different control systems of different systems in the preceding stage. In other words, the supply ports of the main absorption liquid and the sub absorption liquid to the apparatus may be the same position or different positions, but the system for controlling the supply amount is different.

  The liquid in the VOC storage part is discharged out of the system when it reaches a certain concentration. The circulating fluid concentration can be measured with a general concentration meter such as specific gravity, ultrasonic wave, specific resistance value, refractive index, etc. if the VOC brought into the exhaust gas is one component (VOC1 component and water). However, when the VOC is two or more components (VOC two or more components and water) and the ratio of the components is constantly fluctuating, it is often impossible to measure with a general densitometer. When two or more VOC components coexist, the liquid temperature in the VOC storage portion decreases rapidly (due to water evaporation), and when the concentration proceeds from a certain concentration, the temperature suddenly increases. The concentration of the VOC reservoir can be estimated from this temperature rise mutation point. When the concentration reaches a certain concentration, the recovered concentrated liquid is discharged out of the system by operating a bypass valve provided in the discharge pipe of the circulation pump.

The water that is the absorption liquid is preferably pure water or distilled water, but since pure water requires a purification process with an ion exchange resin or reverse osmosis membrane, it depends on the quality of the water before the purification process. According to this, a running cost of ¥ 500 / m ³ or more is required. In the present invention, most of the water in the absorbing solution evaporates in the VOC concentrating part and is scattered outside the system along with the purified gas. The scattered purified gas has a relative humidity of almost 100% at that temperature. If water is condensed by cooling, it can be reused as an absorbing solution. If the water is further condensed here, the purified gas having a humidity of 100% can be obtained. It is also possible to prevent the phenomenon of falling droplets by diffusing and cooling to the atmosphere.

  The VOC concentrating unit, the VOC storing unit, and the VOC collecting unit may be any one of a cylindrical vertical vertical installation shape, a rectangular tube vertical vertical installation shape, a rectangular tube horizontal vertical installation shape, and the like.

  As described in [0025], in order to produce pure water, the running cost is heavy. When the temperature of the VOC-containing exhaust gas is too high (always 80 ° C. or higher), the required amount of pure water increases in this apparatus in which the amount of water supplied is determined from the thermal energy of the VOC-containing exhaust gas. In addition, the temperature of the concentrated liquid in the VOC storage unit rises accordingly, increasing the mass transfer amount of the VOC described in [0018] and [0019], and the number of stages or filling of the gas-liquid contact mechanism necessary for the recovery unit It is necessary to increase the height. At that time, it is possible to reduce the supply amount of pure water by lowering the temperature of the VOC-containing exhaust gas to a certain temperature that is necessary for the apparatus at the previous stage before being sent to the apparatus, and the temperature of the concentrate. Therefore, the amount of mass transfer through the VOC recovery unit can be reduced, and the required number of stages or filling height of the gas-liquid contact mechanism can be reduced.

  When the method of the present invention is applied to an actual apparatus, the apparatus must be adaptable to fluctuations in VOC-containing exhaust gas conditions (VOC concentration, gas flow rate, gas temperature, moisture in exhaust gas). A control method for providing a device in which the concentration of the recovered VOC solution is made substantially constant while adapting to this change, and the concentration of the purified gas is largely cleared of the regulation value will be described.

The supply amount of the absorbing liquid is determined from the thermal energy (calculated from the gas flow rate and gas temperature) brought into the VOC-containing exhaust gas. Even if the flow rate and temperature of the gas fluctuate, the thermal energy brought into the VOC-containing exhaust gas can be obtained by calculating from the flow rate and temperature, and the amount of water is determined accordingly.
The most problematic factor is the fluctuation of the VOC concentration. However, the VOC concentration changes every minute and every second, and it is impossible to constantly supply water corresponding to the VOC concentration. Therefore, in order to simplify the control, the control can be performed in the following flow.
1. A predetermined amount of water is previously placed in the VOC storage unit.
2. Calculate the required amount of absorbed water from the flow rate and temperature of the VOC-containing exhaust gas.
3. The amount of water required is 2. An amount smaller than the amount determined in step (for example, 90% of the calculated amount) is set as the actual absorbed water supply amount.
By controlling from 4.2 to 3, the liquid level decreases in the VOC reservoir due to water evaporation. However, the amount of VOC absorbed in the exhaust gas increases.
5. Ultimately, it will be concentrated to the required concentration in the reservoir,
When this concentration is reached, the liquid is extracted and transported to the tank. When extracting
The amount necessary for the circulation of the concentrating part is left in the storage part. Then add water again for the extracted amount.
6). Return to “2.”.
This control makes it possible to adapt to changes in gas concentration, temperature, and flow rate.

FIG. 2 shows a basic flow in which a VOC enrichment unit and a VOC recovery unit that process the high-temperature VOC-containing exhaust gas that embodies the block flow diagram of FIG. 1 are placed in the vertical direction. The high-temperature VOC-containing exhaust gas introduced to the upstream side of the VOC enrichment part gas makes gas-liquid contact in the VOC enrichment part and the VOC recovery part, and is exhausted out of the system as a purified gas. During this time, in the VOC concentrating unit, the circulating fluid in the VOC storing unit is circulated by the pump downstream of the VOC concentrating unit gas, brought into contact with the high-temperature VOC-containing exhaust gas, and the VOC-containing exhaust gas temperature itself is evaporated by evaporating the water contained in the circulating fluid. Will be reduced. The VOC concentration in the VOC-containing exhaust gas after the gas-liquid contact in the VOC concentrating part is the concentration in the vapor-liquid equilibrium relationship with the concentration of the recovered liquid concentrated to a high concentration by evaporation (the difference in vapor pressure between VOC and water). The VOC-containing exhaust gas is introduced into the VOC recovery unit. This is a basic flow in which the VOC recovery unit absorbs (dissolves) the unremovable VOC in the absorption water and separates the VOC in the exhaust gas.

  FIG. 3 is a flow diagram including a heating method for supplementing heat necessary for processing the low-temperature VOC-containing exhaust gas in the basic flow of FIG. 2 (when the temperature is lower than about 45 ° C.). As for the control point of the heating medium to be heated, the VOC reservoir liquid temperature or VOC concentrator upper part temperature is optimal in (a) and (b) in the figure, and in the case of (c) in the figure, the outlet temperature of the gas heater is Is optimal.

In the method of the present invention, concentration is promoted by evaporation of water, but all of the evaporated water is discharged out of the system as vapor. By providing a dehumidifier before the release, the condensed water obtained by dehumidification can be reused again as an absorbing liquid, and the gas is humidity-controlled, so it should be returned again as a carrier gas for the dryer. Is possible.
The method of the present invention has a mechanism for evaporating water using the thermal energy of the VOC-containing exhaust gas and concentrating the VOC aqueous solution. However, when the gas temperature is low, there is a case where the thermal energy necessary for water evaporation is insufficient. is there. In this case, as described in [0031], the heater is installed in the concentrated liquid circulation section, the concentrated liquid storage section, or before the exhaust gas enters the apparatus, thereby assisting the insufficient heat energy. Can be operated without problems.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 4 is a mass balance diagram of the VOC recovery and concentration apparatus according to the present invention. F is a VOC-containing exhaust gas composed of air: G ₁ [kg / h], moisture: H ₁ [kg / h], and VOC: S ₁ [kg / h] to be introduced into the VOC recovery and concentration apparatus. Moisture: H ₁ [kg / h] is the sum of the moisture in the air introduced into the drying chamber (determined from the relative humidity of the air taken in) and the moisture evaporated from the material to be dried.

D is a recovered concentrated liquid recovered by a VOC recovery and concentration apparatus and concentrated to an easily recyclable concentration, and has a composition of moisture: H ₃ [kg / h] and VOC: S ₃ [kg / h].

F ′ is a purified gas processed by the VOC recovery and concentration device, and its composition is air: G ₂ [kg / h], moisture: H ₂ [kg / h], and VOC: S ₂ [kg / h]. .

M (kg / h) is an absorbed water flow rate at which VOC is absorbed (recovered) by the VOC recovery unit.

The relationship between these F, D, F ', and M (material balance) is INPUT = OUTPUT.
G ₁ = G ₂ [in the case of capacity (VOL), it depends on temperature] (1)
About moisture
M = H ₂ + H ₃ −H ₁ (2)
About VOC
S ₂ = S ₁ -S ₃ (3)
The relationship is established. Here, H ₂ is the moisture carried away by the purified gas, which is the amount of moisture with a relative humidity of 100% at the temperature of the purified gas, and H ₃ is the moisture contained in the recovered concentrate, which is determined by the concentration of the concentrate. The S ₂ at a concentration of VOC which is set below the emission standard of VOC contained in the exhaust gas based on the revised Air Pollution Control Law, necessary from the absorption rate of the VOC recovery unit [vapor-liquid equilibrium of water and VOC (absorption equilibrium) The processing time (height) is determined].

FIG. 5 is a heat balance diagram of the VOC recovery and concentration apparatus according to the present invention. In the material balance diagram of FIG. 4, the temperatures of the respective locations are F = t ₁ , F ′ = t ₂ , D = t ₃ , M = t ₄ , the relative humidity Ψ _{2 at} F ′ and the air necessary for the heat balance calculation, The specific heat of water and VOC and the latent heat of water and VOC are displayed. Here, the temperature of the VOC-containing exhaust gas shown in FIG. 2 is a high-temperature VOC-containing exhaust gas, and t ₁ > t ₃ > t ₂ > t ₄ .

Here, the relative humidity Ψ ₂ in F ′ is the relative humidity of the purified gas because sufficient gas-liquid contact is made between the VOC-containing exhaust gas (air) and the absorbed water in the VOC concentration unit and the VOC recovery unit. Is almost 100% saturated. Moreover, since water is a polar substance, the relationship between temperature and latent heat of vaporization cannot be ignored in calculation. (The specific heat of water and VOC and the latent heat of VOC are constant). Furthermore, the temperature reference is set to 0 ° C. to simplify the calculation.

The heat balance of the entire VOC recovery and concentration device is as follows.
(I) The amount of heat Q _F brought into the exhaust gas F can be expressed by the following formula (4).
Q _F = (G ₁ × C _pa + H ₁ × C _pw + S ₁ × C _pvoc ) × t ₁
+ H ₁ × λ _{wt 1} + S ₁ × λ _voct1 (4)
Here, λ _wt1 and λ _voct1 are the latent heat of vaporization of water and VOC at the temperature t ₁ .
(II) The amount of heat Q _M brought into the absorbing liquid M can be expressed by the following formula (5).
The temperature of M (t ₄ ) is a room temperature equivalent to the atmosphere.
Q _M = M × C _pw × t ₄ (5)
(III) The amount of heat Q _{D taken} out of the recovered concentrated liquid _D is as follows.
The temperature (t ₃ ) of D is t ₁ > t ₃ > t ₂ , but water evaporation (heat exchange) by the exhaust gas is performed in the VOC concentration unit. Water and air in direct contact, opposite water evaporates instantaneously relative humidity of 100% of the air at the temperature t _3. The final balance of air, moisture and temperature is F '. Accordingly, the temperature of t ₃ is assuming 90% efficiency of VOC concentration portion (t ₃ varies depending on the performance and contact time of the gas-liquid contact mechanism in the enrichment section), the amount of heat Q _D to bring the recovered concentrate D is represented by the following It can be shown by equation (7).
t ₃ ≈ (t ₁ −t ₂ ) × (1−0.9) + t ₂ (6)
Q _D = (H ₃ × C _pw + S ₃ × C _pvoc ) × t ₃ (7)
(IV) The amount of heat Q _{F ′} carried out by the purified gas F ′ can be expressed by the following formula (8).
Q _{F ′} = (G ₂ × C _pa + H ₂ × C _pw + S ₂ × C _pvoc ) × t ₂ + H ₂
× λ _wt2 + S ₂ × _λvoct2 (8)
Here lambda _wt2 and lambda _Voct2 is latent heat of vaporization of water and VOC at a temperature _{t 2.}
Further, H ₂ is an amount in which the air G ₂ is equal to the relative humidity Ψ = 100% at the temperature t ₂ .

The amount of heat (INPUT) brought into the VOC recovery and concentration device is the sum of Q _F and Q _M , and can be expressed by the following formula (9).
INPUT = Q _F + Q _M = {(G ₁ × C _pa + H ₁ × C _pw + S ₁ × C _pvoc )
× t ₁ + H ₁ × λ _{wt 1} + S ₁ × λ _voct1 } + {M × C _pw
× t ₄ } (9)
In this equation, values other than the absorbed water M are initial conditions and are known numerical values.

Heat bring the VOC recovery system (OUTPUT) is the sum of 'heat _{Q F} to bring _the' with heat _{Q D} to bring the recovered concentrate D purifying gases F, can be represented by the following formula (10).
OUTPUT = Q _D + Q _{F ′} = {(H ₃ × C _pw + S ₃ × C _pvoc ) × t ₃ }
+ {(G ₂ × C _pa + H ₂ × C _pw + S ₂ × C _pvoc ) × t ₂
+ H ₂ × λ _{wt 2} + S ₂ × λ _voct2 } (10)
From mass balance, _{S 3} is the _{value S 2} has been determined in the following VOC regulation value _is calculated by S _{3 =} S 1 -S _2. H ₃ is determined from the concentration of S ₂ concentrate. G ₂ is equal to _{G 1.} Although unknown values in this formula is _{H 2} and _{t 2 H 2} has saturated humidity [psi = 100% of the relationships included in the _{G 2} at _{t 2,} can be determined assuming a _{t 2.} (Λ _wt2 and _λ voct2 also can be determined once the _{t 2).}

Like the mass balance, INPUT = OUTPUT holds in the case of the heat balance, so the unknown of INPUT is M. M is from mass balance M = H ₂ + H ₃ −H ₁
Is related to H ₂ as given by That is,
H ₂ −H ₁ = M−H ₃ = M ′
Then, M ′ is the amount of water evaporated in the VOC concentrating part.
M ′ × λ _wt2
Is the amount of heat of water evaporation, most of which evaporates in the VOC concentrator.
OUTPUT unknowns is a lambda _Voct2 and _{t 2} and _{H 2} and lambda _{wt2, H 2} and lambda _wt2 the lambda _Voct2 Assuming _{t 2} is obtained.

(1) According to the present invention, an area that cannot be reached by the conventional VOC-containing exhaust gas treatment technology [(i) Removal to a concentration that is further lower than the VOC regulation value in the purified gas. (B) Concentrate the collected VOCs to a concentration that facilitates purification and recycling. (C) Energy saving is achieved by using the energy of exhaust gas containing VOC for enrichment], and industry environmental conservation, process simplification, and energy saving were achieved.
(2) Volatile organic compounds that have higher boiling point than water, are hydrophilic, and have physical properties that do not azeotrope with water, but these substances (solvents) are used in recent electricity, electronics, batteries, and films.・ The frequency of use of leather and other technological innovations is increasing. Conventionally, measures such as air pollution and waste liquid treatment of these new solvents have been delayed, but the present invention has recovered them.
(3) As in Example 6, four items of (A) exhaust gas treatment, (B) recovery of VOC, (C) recovery of absorbent, (D) recycling of air sent to the dryer, centering on the present invention It was possible to establish a flue gas treatment apparatus that can prevent air pollution and does not require waste liquid treatment.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in detail, this invention is not limited at all by this.

Example 1
FIG. 6 is an example of an embodiment of the present invention for treating an exhaust gas containing N, N-dimethylformamide (DMF) generated in a hot air drying process in a dry manufacturing method of a certain synthetic leather. In the figure, LC is a liquid level controller, and FIC is a flow rate indicator / controller. Drying air is taken from outside air but introduced through a dehumidifier. The condition is
Air amount G ₀ = 1000 kg / h,
Temperature t ₀ = 20 ° C.,
Relative humidity ψ ₀ = 30%,
Moisture contained in air H ₀ = 1000 × 0.0045 = 4.5 kg / h
(0.0045 is an estimate of the amount of water contained in 1.0 kg of dry air at a temperature of 20 ° C. and a relative humidity of 30%). This air is heated, a solution obtained by dissolving a resin composition (synthetic leather material) in DMF is applied to the core material, and this is dried using several dryers.
The exhaust gas discharged from the dryer is about 80 ° C. (this temperature varies from 70 to 120 ° C.) and averages 1500 ppm (w / w) (S ₁ ≈1000 × 0.0015 = 1.5 kg / h). DMF vapor is included (actually, there is a variation of 0 to 3000 ppm (w / w)). It is assumed that no water is generated from the heartwood during drying. The material balance when this DMF-containing exhaust gas is treated with the VOC recovery and concentration apparatus of the present invention (purified gas concentration is removed to 20 ppm (w / w)) is shown below. The DMF concentration of the collected concentrated liquid is 80%, and the temperature of the absorbing liquid is 25 ° C.

In the calculation, the specifications of each substance are as follows.
Specific heat of air: C _pa = 0.24 kcal / kg · ° C.
Specific heat of water: C _pw = 1.0 kcal / kg · ° C
Evaporation latent heat of water: λ _w30 = 579 kcal / kg · 30 ° C
λ _w28 = 580 kcal / kg · 28 ° C
λ _w80 = 551 kcal / kg · 80 ° C
λ _w25 = 582 kcal / kg · 25 ° C
Saturated water: X = 0.028 kg water / kg dry air, 30 ° C
X = 0.026 kg water / kg dry air, 28 ° C
Specific heat of DMF: _CpDMF = 0.485 kcal / kg · ° C.
DMF latent heat: λ _DMF = 138.6 kcal / kg

First, calculate the mass balance.
About DMF
Since DMF in the purified gas is 20 ppm (w / w),
S ₂ ≈1000 × 0.00002 = 0.02 kg / h
Therefore, the recovered concentrated DMF is
S ₃ = 1.5−0.02 = 1.48 kg / h,
Therefore, the recovered concentrated water is
H ₃ = (1.48 ÷ 0.8) −1.48 = 0.37 kg / h
Indicated by

Therefore, when INPUT is calculated by the above equation (9), INPUT = {(1000 × 0.24 + 4.5 × 1.0 + 1.5 × 0.485)
× 80 + 4.5 × 551 + 1.5 × 138.6} + (M = H ₂ + H ₃
−H ₁ ) × 25
= 22306+ (1000 × 0.028 + 0.37−4.5) × 25
= 22903 kcal / h
According to the equation (10), OUTPUT is calculated when t ₂ = 30 ° C. and the relative humidity ψ = 100%.
t ₃ = (80-30) × (1-0.9) + 30 = 35 ° C.
OUTPUT = {(0.37 × 1.0 + 1.48 × 0.485) × 35}
+ {(1000 × 0.24 + 0.028 × 1000 × 1.0
+ 0.02 × 0.485) × 30 + 0.028 × 1000 × 579
+ 0.02 × 138.6}
= 24293 kcal / h
INPUT (= 22903) <OUTPUT (= 24293).
According to the equation (10), OUTPUT is calculated assuming that t ₂ = 28 ° C. and the relative humidity ψ = 100%.
t ₃ = (80−28) × (1−0.9) + 28 = 33.2 ° C.
OUTPUT = {(0.37 × 1.0 + 1.48 × 0.485) × 33.2}
+ {(1000 × 0.24 + 0.026 × 1000 × 1.0
+ 0.02 × 0.485) × 28 + 0.026 × 1000
× 580 + 0.02 × 138.6}
= 22566 kcal / h
At t ₂ = 28 ° C
INPUT (= 22903)> OUTPUT (= 22566).
In this trial calculation, the temperature t ₂ at which INPUT = OUTPUT is
At t ₂ = 30 ° C.
INPUT (= 22903) <OUTPUT (= 24293)
From this relationship, it can be seen that it is between 28-30 ° C.
When the absorbed water M is calculated with t ₂ = 29 ° C., M = 1000 × 0.029 + 0.028−4.5 = 24.5 kg / h
It turns out that it is almost balanced.
Actual M is about 90% of M determined by calculation with the absorption liquid M _1, the absorption liquid required for density adjustment of the recovering solution becomes possible density control by taking the material balance of the overall M ₂ ( M = M ₁ + M ₂ ).
Based on these calculations, the first embodiment shown in FIG. 6 proved that the temperatures t ₂ and t ₃ accompanying the fluctuation of the temperature t ₁ had an error of several percent, but the VOC concentration in the purified gas, the recovery concentration Predetermined ability such as liquid concentration could be obtained.

Example 2
FIG. 7 is an example of an embodiment of the present invention for treating an exhaust gas containing N, N-dimethylformamide (DMF) generated in a hot air drying step in the same synthetic leather dry manufacturing method as FIG. The drying air is taken from outside air, but the condition is
Air amount G ₀ = 1000 kg / h,
Temperature t ₀ = 30 ° C.,
Relative humidity ψ = 50%,
Moisture contained in air H ₀ = 1000 × 0.0133 = 13.3 kg / h
(0.0133 is the amount of water contained in 1.0 kg of dry air at a temperature of 30 ° C. and a relative humidity of 50%). The air is heated, a solution obtained by dissolving a resin composition (synthetic leather material) in DMF is applied to the core material, and this is dried using several types of dryers. In this drying process, if temperature is applied to the core material, the physical properties of the product are adversely affected, so that it cannot be dried with high-temperature hot air. DMF-containing exhaust gas discharged from the dryer is about 30 ° C. (this temperature varies between 20 and 40 ° C.) and average 500 ppm (w / w) (S ₁ ≈1000 × 0.0005 = 0.5 kg / h) Of DMF vapor (which actually varies from 0 to 1000 ppm (w / w)). It is assumed that no water is generated from the heartwood during drying. The material balance when this DMF-containing exhaust gas is treated with the VOC recovery concentration apparatus of the present invention (purified gas concentration is removed to 20 ppm (w / w)) is shown. The DMF concentration of the collected concentrated liquid is 80%, and the temperature of the absorbing liquid is 25 ° C.

This embodiment corresponds to the low-temperature VOC-containing exhaust gas VOC recovery concentration apparatus shown in FIG. In this case, INPUT exhaust gas is heat to bring the formula (9) is small, it is necessary to supplement the heat (and Q _S) from the outside due to the lack amount of heat required for the evaporation of water in the VOC concentration of the [0038] . In the case of high-temperature exhaust gas, the amount of absorbed water is determined by the amount of heat brought in, but in the case of low-temperature exhaust gas, the efficiency of the gas-liquid contact mechanism (including the performance of the liquid distributor) of the VOC recovery unit is involved. That is, the ratio (L / G) of the liquid (L) that descends the gas-liquid contact mechanism and the gas (G) that rises has a lower limit, and L when the lower limit of L / G is L = 50 to 200 L / m ² · h (m ² is the cross-sectional area of the VOC recovery unit, and the amount of liquid varies depending on the type and performance of the gas-liquid contact mechanism). If the cross-sectional area of the VOC recovery unit is determined from the gas flow rate, the minimum liquid amount M is inevitably determined from the product of L and the cross-sectional area of the recovery unit. Heat Q _S compensate the temperature and external t ₂ when calculated back calculation formula of the hot gas to the M based on is determined.

The conditions of t ₁ and S _{1 in} the _first embodiment are changed to the conditions in the second embodiment shown in FIG. 7, and M, t ₂ , and Q _S are obtained.
If the cross-sectional area of the VOC absorber is 0.16 m ² (gas superficial velocity ≈ 2.0 m / s), M = 0.16 m ² × 50 L / m ² · h = 8 L / h = 8 kg / h
[0037] Equation (9) is
INPUT = Q _F + Q _M = {(G ₁ × C _pa + H ₁ × C _pw + S ₁ × C _pvoc )
× t ₁ + H ₁ × λ _{wt 1} + S ₁ × λ _voct1 } + {M × t ₄ }
+ Q _S
INPUT = {(1000 × 0.24 + 13.3 × 1.0 + 0.5 × 0.485)
× 30 + 13.3 × 579 + 0.5 × 138.6} + 8 × 25 + Q _S
= (15576 + Q _S ) kcal / h
H ₃ is based on the mass balance.
S ₁ −S ₂ = 0.5−0.02 = 0.48 to H ₃ = (0.48 / 0.8)
-0.48 = 0.12
H ₂ is M = H ₂ + H ₃ −H ₁ , H ₂ = 8 + 13.3−0.12 = 21.18 kg / h
The saturation temperature when H ₂ = 21.18 kg / h of water in 1000 kg / h of air is obtained from the humidity chart as t ₂ ≈26.0 ° C.
If OUTPUT is calculated based on this,
t ₃ = (30−26) × (1−0.9) + 26 = 26.4 ° C.
OUTPUT = {(0.12 × 1.0 + 0.48 × 0.485) × 26.4}
+ {(1000 × 0.24 + 21.18 × 1.0 + 0.02
× 0.485) × 26 + 21.18 × 581.5 + 0.02
× 138.6}
= 19120 kcal / h
(581.5 is the latent heat of vaporization of water at 26 ° C)
From INPUT = OUTPUT,
Q _S = 19120-15576 = 3544 kcal / h
This heat quantity is externally heated in one place among the circulating fluid of case 1 shown in FIG. 3, the VOC storage part of case 2, and the VOC-containing exhaust gas of case 3 shown in FIG. Based on these calculations were demonstrated in Example 2 shown in FIG. 7, the temperature t _2, t ₃ due to variations in the temperature t ₁ there was a few percent error, VOC concentration in the purified gas, recovered concentrated Predetermined ability such as liquid concentration could be obtained. If the concentration is excessive, the VOC reservoir may be replenished with an absorbing solution to adjust the concentration.

Example 3
FIG. 8 according to the third embodiment is an embodiment relating to the absorption liquid supply method, in other words, the concentration adjustment of the recovered concentrated liquid. In the figure, XC is a concentration controller, FIC is a temperature indicator / controller, and LC is an upper / lower liquid level controller. In the embodiment shown in FIG. 6, the supply amount of the absorbing liquid is M = 24.5 kg / h. Among these, the water used for adjusting the concentration of the VOC storage section is H = 0.37 kg / h (in this case, the exhaust gas to be introduced) Always 1500 ppm (w / w) VOC). If the VOC concentration in the VOC-containing exhaust gas varies from 0 to 3000 ppm (w / w), it is necessary to adjust H = 0 to 0.74 kg / h in order to adjust the concentration of the recovered concentrate to a constant level. Yes, this amount requires a fine adjustment of -1.5% to + 1.5% with M = 24.5. Furthermore, it is impossible to cope with the unsteady VOC concentration change or exhaust gas temperature change by using an inexpensive adjustment mechanism for the water supply amount at one place (on the VOC recovery unit). Explaining based on FIG. 8, as the absorbent supply means, a main supply port is provided at the upper part of the VOC absorption section, and 90% of the supply amount {L / G) exceeds the minimum value of the liquid gas ratio (L / G) described in [0047]. }, And the remainder is supplied intermittently between the upper and lower liquid levels of the VOC storage part from the auxiliary absorption liquid supply port, and when the VOC concentration reaches the upper limit by the concentration sensor, the recovered concentrated liquid is discharged to the lower limit. The sub-absorption liquid is supplied up to the upper limit (of course, if the absorption liquid is supplied, the VOC concentration decreases). The sub-absorption liquid port may be at the same position as the main supply port and between the VOC recovery unit and the VOC concentrating unit. However, in order to prevent a time lag or the like, it is desirable to supply it to the VOC storage unit. In this embodiment, the upper and lower limits of ON / OFF are used, but continuous control is also possible. It was confirmed from Example 1 and Example 2 that this method is an optimal adjustment method for unsteady fluctuations in the VOC concentration in the exhaust gas.

Example 4
When VOC contained in the VOC-containing exhaust gas is one component and is a mixture with water, it is easy to measure with a commercially available densitometer such as a specific gravity, a refractometer, or an ultrasonic wave. However, when the VOC has two or more components and is a mixture with water, it is not easy to measure the water concentration. Further, the exhaust gas component introduced into the VOC recovery and concentration apparatus according to the present invention is the VOC-containing exhaust gas from the drying apparatus in the previous step, and has a lot of low boiling point VOC in the initial stage and a lot of high boiling point VOC in the final stage. It is impossible to predict the proportion. FIG. 9 shows an example of detecting the concentration of the collected concentrated liquid. The liquid concentrated in the VOC reservoir is a mixture of two or more VOCs and water, and each of the two or more components has a different boiling point. When the recovered concentrated liquid is sufficiently concentrated by evaporation of water in the VOC concentration unit, the water content in the VOC storage unit is reduced. When this liquid is circulated to the upper part of the VOC concentrating part, the amount of water in the VOC concentrating part is reduced, so that the amount of water to be evaporated is insufficient, and the VOC concentrating part is sufficiently evaporated (heat exchange with exhaust gas). Not done. As a result, the temperature of the VOC storage unit rises. FIG. 10 shows a temperature curve of the VOC storage part when exhaust gas containing DMF, NMP, and other multi-component VOCs is processed by the VOC recovery and concentration apparatus according to the present invention. From this figure, it can be seen that when the VOC concentration in the reservoir reaches a certain concentration or more, a rapid temperature rise occurs, and the concentration at which moisture is insufficient is reached. By measuring this temperature and discharging the recovered concentrated solution out of the system, a concentrated solution having a certain concentration or more can be obtained.

Example 5
In [0013], it is described that the water of the absorbing solution is preferably distilled water or pure water not containing inorganic substances. In [0024], removing inorganic substances such as distilled water and pure water requires investment in equipment for purifying water and running costs, and the supplied water diffuses due to atmospheric discharge, which may increase the investment. Said.
FIG. 11 shows an embodiment in which the purified gas is indirectly cooled with cooling tower water or chiller water, and water vapor in the purified gas is condensed and reused as an absorbing liquid. FIG. 11 is a diagram in which incidental equipment is provided at the purified gas outlet of FIG.
When the outside air temperature is 20 ° C. (relevant humidity ψ = 30%, the dew point temperature is 11 ° C.), the cooling water in the cooling tower can be cooled to ≈12 ° C. The purified gas at 29 ° C. of Example 1 was cooled to 22 ° C. with this cooling water. The amount of water to condense (W) is W = 1000 × (0.027−0.0167) = 10.3 kg / h
Since the water used was 24.5 kg / h, about 42% (10.3 / 24.5 × 100 = 42%) of distilled water or pure water could be recovered and reused.

Example 6
There is a demand for minimizing the release of VOC-containing exhaust gas (purified gas) into the atmosphere from the idea of complying with environmental conservation, and FIG. 12 shows an embodiment of the closed system of the VOC recovery and concentration apparatus of the present invention. In this example, the processing amount of VOC containing exhaust gas at 80 ° C. (VOC contained in exhaust gas is NMP) was large (1000 kg / min), so the shape of the VOC concentrating part and the VOC recovery part was rectangular, and the VOC concentration The gas-liquid contact mechanism of the part was a spray system. In addition, the height of the apparatus was limited, and the VOC concentrating part and the VOC recovery part were juxtaposed as shown in FIG. 12 and connected at the bottom. The air intake conditions of the dryer were 25 ° C. and the relative humidity was 40%, and the air to be recycled was required to be returned under the same conditions.
The VOC-containing exhaust gas from the dryer makes gas-liquid contact with the circulating fluid sprayed by the VOC concentrating unit, and VOC is recovered by gas-liquid contact with water in the VOC recovery unit. The gas exiting the VOC recovery unit is cooled to 10 ° C. (25 ° C., dew point of absolute humidity at a relative humidity of 40%) or less in a water recovery unit equipped with a mist separator and recycled to the dryer. In the water recovery unit, heat exchange was performed by direct contact with distilled water, and the distilled water was cooled with a cooling tower and chiller water via a water cooling heat exchanger. This embodiment is based on the basic flow of VOC treatment of high-temperature exhaust gas shown in FIG. 2, using the calculation method of FIG. 6 and the absorption liquid supply method of FIG. 8, and in addition to the water recovery method of FIG. This is an example in which the steps are taken.

It is a block flow figure showing the basic idea of the present invention. FIG. 2 is a specific flow diagram of one embodiment of the present invention for treating a high temperature VOC-containing exhaust gas embodying FIG. 1. FIG. 2 is a specific flow diagram of one embodiment of the present invention for treating a low temperature VOC containing exhaust gas embodying FIG. 1. 1 is a mass balance diagram of the method and apparatus of the present invention. 2 is a heat balance diagram of the method and apparatus of the present invention. It is a flowchart which shows the high temperature VOC containing exhaust gas purification of this invention used in Example 1, and a VOC collection | recovery concentration system. It is a flowchart which shows the low-temperature VOC containing waste gas purification of this invention used in Example 2, and a VOC collection | recovery concentration system. FIG. 6 is a flowchart showing an absorbing liquid supply method used in Example 3. FIG. 10 is a flowchart showing a VOC concentration adjustment system used in Example 4; In Example 4, the temperature curve of a VOC storage part when processing the VOC containing exhaust gas containing multi-component VOC is shown. It is a flowchart which shows the distilled water used in Example 5, and a pure water collection | recovery system. FIG. 10 is a flowchart showing a closed VOC recovery and concentration system used in Example 6.

Claims (10)

In a method of recovering and concentrating VOC contained in exhaust gas and purifying exhaust gas, a VOC concentrator having a one-block gas-liquid contact mechanism and a gas-liquid contact mechanism of one to several blocks on the gas downstream side of the VOC concentrator Using the VOC recovery / concentration device configured from the exhaust gas composed of the VOC recovery unit, the VOC recovery unit absorbs the VOC contained in the exhaust gas in the VOC recovery unit by absorbing water supplied from the gas downstream side of the VOC recovery unit. On the other hand, the VOC-containing exhaust gas is introduced from the upstream side of the VOC concentrating part gas, the water as the absorbing liquid is evaporated in the VOC concentrating part, and the purified gas is discharged out of the system through the VOC collecting part, and the VOC concentrating part The VOC concentrated solution concentrated in the step is sent to the VOC storage unit provided at the lower end of the VOC concentration unit and / or the VOC recovery unit, and the VO collected in the VOC storage unit The stored liquid is circulated and supplied to the gas downstream side of the VOC concentrating unit, the VOC is concentrated by evaporation of the water in the circulating liquid, and the VOC-concentrated circulating liquid accumulated in the VOC storing unit is kept at a constant concentration by concentration measurement. A method for purifying exhaust gas by recovering and concentrating VOC from exhaust gas containing VOC, wherein the exhaust gas is discharged out of the system as a recovered concentrated liquid.   Sprinkle the main absorption liquid for recovering VOC with the amount of “the range of water evaporation calculated from the energy brought in by the exhaust gas” from the gas downstream side of the VOC recovery section, and adjust the concentration of the VOC recovery liquid 2. A method for purifying exhaust gas by recovering and concentrating VOC from the VOC-containing exhaust gas according to claim 1, wherein an auxiliary amount of auxiliary absorption liquid is supplied into the apparatus.   The cooling means is provided at the outlet of the purified gas discharged out of the system through the VOC recovery section, and the condensed water is reused as an absorbing solution from the VOC-containing exhaust gas according to claim 1 or 2. A method of collecting and concentrating and purifying exhaust gas.   The VOC-containing exhaust gas according to any one of claims 1 to 3, wherein the recovered concentrated liquid is discharged out of the system when a temperature rise mutation point occurs in a temperature curve representing a temperature change of the VOC storage part in the VOC storage part. Recovering and concentrating VOCs from wastewater and purifying exhaust gas.   The method for purifying exhaust gas by recovering and concentrating VOC from the VOC-containing exhaust gas according to any one of claims 1 to 4, wherein the purified gas is cooled, water vapor in the purified gas is condensed and reused as an absorbing solution.   When the temperature of the exhaust gas is insufficient for water evaporation, (b) heating the exhaust gas in the stage before introducing the exhaust gas into the VOC concentrating part, (b) heating the VOC storage part, (c) the VOC storage liquid The VOC is exhausted from the VOC-containing exhaust gas according to any one of claims 1 to 5, and heated by at least one heating method of heating at a stage where the gas is circulated downstream of the VOC concentrating portion. How to purify. Collect and concentrate and purify VOCs contained in exhaust gas, which consists of a VOC concentrating unit with a one-block gas-liquid contact mechanism and a VOC recovery unit with one to several blocks of gas-liquid contact mechanism downstream of the VOC concentrating unit The VOC-containing gas introduction means for introducing the VOC-containing exhaust gas from the gas upstream side of the VOC enrichment section, the means for supplying the absorbing liquid from the gas downstream side of the VOC recovery section, and the VOC in the exhaust gas is recovered, Absorbing liquid spraying means in the VOC recovery section for purifying gas, purified gas discharging means in the VOC recovery section, the VOC concentrating section, and a VOC storing section for storing the VOC-containing processing liquid sent from the VOC recovery section , Means for circulatingly supplying the stored liquid remaining in the VOC storage section to the gas downstream side of the VOC concentration section, and concentrating the VOC by evaporation of absorbed water in the circulating liquid, V The VOC concentration measuring means for the stored liquid provided in the C storage section, and the discharging means for discharging the stored liquid as a recovered concentrated liquid outside the system when the VOC concentration in the stored liquid reaches a predetermined concentration. An apparatus for recovering and concentrating VOC from exhaust gas containing VOC and purifying exhaust gas.   The apparatus for purifying exhaust gas by collecting and concentrating VOC from exhaust gas containing VOC according to claim 7, wherein a heat exchanger for gas cooling is attached to the purifying gas discharge means. A purified gas cooling heat exchanger is provided at the purified gas outlet provided further above the absorbing liquid spraying means above the VOC recovery unit, and the purified gas emitted from the heat exchanger is used as a carrier gas for the dryer. The apparatus for recovering and concentrating VOC from the VOC-containing exhaust gas according to claim 7 or 8, which is provided with a carrier gas recycle / closed system that is returned and reused . (A) a stage before introducing exhaust gas into the VOC enrichment section;
(B) VOC storage part,
(C) circulating the VOC storage liquid to the gas downstream side of the VOC concentrator,
The apparatus for recovering and concentrating VOC from the VOC-containing exhaust gas according to any one of claims 7 to 9, wherein a heating means is provided at at least one location of the exhaust gas.

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