JP2008068205A - Method for cleaning large quantity of exhaust gas containing lean volatile hydrocarbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cleaning a large quantity of exhaust gas containing a lean concentration of volatile hydrocarbon discharging no carbon dioxide and very easily recovering volatile hydrocarbon contained as liquid, and for achieving no emission of the volatile hydrocarbon. <P>SOLUTION: In the method for cleaning a large quantity of exhaust gas containing a lean concentration of volatile hydrocarbon using an adsorption apparatus (adsorption tower) comprising adsorbent layers filled with pre-coated meso-pore activated carbon and/or hydrophobic silica gel, and is operated by alternately switching absorption and desorption, the lean volatile hydrocarbon contained in exhaust gas is condensed by common liquid cleaning or by supersaturated moisture in advance prior to the treatment in the adsorption apparatus, then is subjected to adsorption/desorption operation after being pressurized avoiding an explosion limit value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for purifying exhaust gas containing volatile hydrocarbons, and more particularly to a method for purifying a large amount of exhaust gas containing dilute volatile hydrocarbons that are diffused into the atmosphere, and combusts easily as in the past. In addition to the purpose of purifying the exhaust gas to zero emission, from the viewpoint of preventing global warming and preventing pollution, the carbon dioxide gas (CO ₂ ) is not diffused into the atmosphere. The present invention relates to a method for purifying a large amount of exhaust gas containing dilute volatile hydrocarbons according to an adsorption method for efficiently separating and reusing volatile hydrocarbons.

  Conventionally, many methods for treating exhaust gas containing volatile hydrocarbons have been proposed. In particular, a combustion method, an adsorption method, an absorption method, a membrane method, and the like are known as processing means that satisfy the legally required regulation value of volatile hydrocarbon emission concentration in order to prevent pollution.

Among these, the advantage of the combustion method is that the volatile hydrocarbons contained are extremely lean, and a large amount of exhaust gas, that is, the volatile hydrocarbons contained are on the order of several tens or several hundreds of PPM, and several thousand. As a method for treating a large amount of exhaust gas of m ³ / hour or tens of thousands of m ³ / hour, it can be said that it is the only method that can achieve zero emission. In addition, whether it is a regenerative combustion method or a catalytic combustion method capable of self-combustion, it is simpler than other adsorption methods, absorption methods, membrane methods, etc., and can be obtained at a very low cost.

However, the decisive disadvantage of such a combustion system is not only that volatile hydrocarbons cannot be reused, but also the extensive release of carbon dioxide gas accompanying combustion. With regard to this point, recently, the regulations on carbon dioxide, which is the cause of global warming, have been mandated by the Kyoto Protocol, and the question of whether or not the combustion law is appropriate is based on the fact that a carbon tax will be enacted in the near future. The situation has been reached.

On the other hand, in the case of an adsorption method that is widely used as an alternative to the combustion method, the concentration of volatile hydrocarbons contained is on the order of%, and the amount of exhaust gas to be treated is several thousand m ³ or less per hour. , Better than the combustion method. That is, this is because the processing apparatus is compact, and a large amount of volatile hydrocarbons can be recovered and reused without burning.

  However, when treating a large amount of exhaust gas containing the above-mentioned dilute volatile hydrocarbons, there are the following problems. That is, even if a conventional adsorbent, such as hydrophobic silica gel, synthetic zeolite, or microporous activated carbon is used, the time required for adsorption, that is, the contact time with the adsorbent, is determined in advance by the adsorbent used. ing. For example, it takes about 2 to 5 seconds for activated carbon and 10 to 15 seconds for hydrophobic silica gel. When this standard is exceeded, volatile hydrocarbons in the exhaust gas pass through the adsorbent layer before being adsorbed by the adsorbent. That is, when a large amount of exhaust gas is treated, an enormous amount of adsorbent is required more than necessary in order to increase the contact time necessary for adsorption. In addition, the adsorbents described above, particularly synthetic zeolite and microporous activated carbon, have excellent adsorption performance, but have poor desorption performance. Therefore, most of them are either heat desorption by steam or air heated to a high temperature. (Refer nonpatent literature 1).

  However, the reason why these adsorbents with poor desorption performance are still widely used is that the concentration of lean hydrocarbons is reduced by passing the adsorbent compared to the above-mentioned combustion method in which dilute volatile hydrocarbons are burned as they are. This is because it has the advantage of being concentrated several tens of times. For this reason, even if it desorbs with steam, there is a merit that a small amount of hydrocarbons coexisting with water can be barely recovered.

  Typical examples are a fibrous activated carbon method and a honeycomb rotor method. In the case of the honeycomb rotor system, there is an advantage of increasing the concentration to a level at which self-combustion can be achieved by desorbing lean hydrocarbons concentrated below the explosion lower limit value with high-temperature air. This method uses a honeycomb-shaped (honeycomb-shaped, hexagonal-shaped) rotor specially formed of activated carbon or synthetic zeolite, and allows a large amount of exhaust gas containing dilute volatile hydrocarbons to pass through the rotor, thereby allowing volatile carbonization. Adsorb only hydrogen. On the other hand, the rotation of the rotor moves the adsorbing part to the desorbing part, where it is desorbed with air heated to about 200 ° C. and can be self-combusted, that is, taken out of the system as a concentrated gas of about 3000 to 4000 PPM, It burns by catalytic action. These series of steps can be continuously performed by the rotational movement of the honeycomb rotor.

  By the way, both the fibrous activated carbon method and the honeycomb rotor method are already known techniques, but the point that has been pointed out as a problem is that the concentration of the concentrated volatile hydrocarbon is 1000 to 5000 PPM at most. Therefore, it is not legally allowed to concentrate more than this because it exceeds the lower explosion limit. Therefore, volatile hydrocarbons of this level are almost impossible to recover, and it has been a common practice to burn them.

  The present inventors have attempted a new proposal to solve this difficulty. That is, in order to efficiently recover hydrocarbons from a large amount of exhaust gas containing lean hydrocarbons, the concentration of the lean hydrocarbons contained is concentrated about 5 to 10 times as necessary, and the gas By avoiding the explosion limit value in advance and pre-pressurizing, the amount to be processed in the subsequent adsorption device is reduced to about 1/5 to 1/10, and an effective means for interlocking with the subsequent adsorption / desorption device is found. It is a thing.

  By the way, regarding the latter-stage adsorption separation technique used in the present invention, as a method generally used in this field, activated carbon is used as an adsorbent, and desorption is performed using a heating medium such as steam (non-desorption) Patent Document 1), a method of alternately swinging an adsorption operation and a desorption operation using a nonflammable adsorbent such as hydrophobic silica gel pre-coated with a gaseous hydrocarbon (see Patent Document 2), mesopore activated carbon and / or A method of alternately swinging adsorption / desorption operations using hydrophobic silica gel (see Patent Document 4) is known. Further, from the viewpoint of preventing enormous heat generation due to heat of adsorption, means for incorporating a cooling coil in the adsorption tower has been widely used as common sense since ancient times. In addition, a method of circulating volatile hydrocarbons (liquid) obtained when cooling purged exhaust gas instead of cooling water in the adsorption tower has been proposed (see Patent Document 3).

"Separation Technology" Vol. 33, No. 4 (Vol. 174) Separation Technology Society, July 31, 2003, pp. 18-20 Japanese Patent Laying-Open No. 2004-42013 (Claim 1) JP 09-057060 A (Claim 1) Japanese Examined Patent Publication No. 59-50715 (Claim 1)

As seen in the above-mentioned Patent Document 2, the conventional adsorption method uses hydrophobic silica gel, synthetic zeolite, and mesopore activated carbon, and switches between the absorption and desorption operations by swinging in 1 to 15 minutes. It was a way of. Such an adsorption method includes conventional adsorption / desorption switching means, and is not particularly novel. However, each method is a small amount of exhaust gas of 1000 m ³ or less per hour, and the concentration of contained hydrocarbons is low. It can be said that it is an excellent method when treating a rich exhaust gas of 10,000 PPM or more.

However, the concentration of the contained hydrocarbon is 100,000 PPM or less, which is close to the upper limit of explosion, for example, several thousand PPM (specifically, less than 10 to 3000 PPM), and a large quantity that far exceeds 10,000 m ³ per hour. As a method of treating exhaust gas, it is not an appropriate method because it usually requires several adsorption towers with a diameter of 5 m or more and a height of more than 10 m. • Desorption methods have covered the requirements in this area. However, with any of these means, the recovery rate is less than 90%, so such a lean and large amount of exhaust gas cannot be dealt with, and the contained lean hydrocarbon (about several tens to several thousand PPM) The idea of burning after concentration to a self-combustible concentration (about 2000 to 5000 PPM) has come to the present day. Moreover, the adsorbent used in the conventional honeycomb rotor system is high silica zeolite, and high temperature purge air (air) of 150 to 200 ° C. is required for desorption.

  The combustion method is more economical than the above-described method of swinging the adsorption / desorption when treating an extremely lean and large amount of exhaust gas. However, this combustion method has a drawback that even if zero emission can be achieved, as described above, volatile hydrocarbons cannot be recovered, and carbon dioxide gas is released into the atmosphere in a wild manner. Therefore, the presently required technology is capable of treating a small amount of exhaust gas and recovering a small amount of volatile hydrocarbons contained therein, and does not release carbon dioxide gas. Development of an effective adsorption method.

The present invention has been made in view of the above points, and uses the activated carbon which does not require the use of air or steam heated to high temperature for desorption alone or in combination with hydrophobic silica gel or synthetic zeolite. By following the treatment method described in Patent Document 1 described above and combining with means for pressurizing a large amount of exhaust gas and concentrating volatile hydrocarbons contained in the pretreatment stage, the concentration becomes 10,000 PPM or less. The present invention provides an adsorption / desorption method suitable for processing a large amount of exhaust gas containing dilute volatile hydrocarbons and exceeding several thousand m ³ per hour.

  However, the pressure concentration of the exhaust gas containing volatile hydrocarbons has strict legal restrictions on explosion limit values. That is, although it depends on the chemical substance, the exhaust gas containing 5000 PPM or more and less than 100,000 PPM cannot be pressurized to 0.16 MPa or more. As a means of avoiding this limit value, it is a preferable method to pressurize the exhaust gas with a rich hydrocarbon (co-liquid) in advance to a pressure of 0.16 MPa or more. In addition, when a gas enriched several times in hydrocarbon is transferred to the adsorption / desorption operation, it is expected that the time required for the desorption will be several hours. In order to avoid this situation, the present inventors have invented a method of swinging three towers sequentially through a buffer tower for returning from high pressure to normal pressure during desorption, that is, a pressure equalizing tower. This method is suitable for hydrocarbons having a low boiling point such as gasoline vapor, but is not necessarily suitable for hydrocarbons such as benzene or ethyl acetate having a relatively high boiling point.

  As one of the means for solving this problem, the present inventors have improved the above-mentioned invention to pressurize a large amount of exhaust gas containing a relatively high boiling point lean hydrocarbon and send it to the adsorber at the subsequent stage. And a method for supersaturating the gas with moisture using a water ring pump. When it is supersaturated with moisture, at least not only explosion accidents due to static electricity can be prevented, but if the volatile hydrocarbons in the exhaust gas are 1000 to 10000 PPM or less, pressurizing to 1 MPa or less in a steam atmosphere reduces the explosion lower limit concentration. Can clear.

  More specifically, as an additional measure for the new VOC emission regulations to be implemented after April 2006 (April 2006), the target is to reduce VOC emissions by 30% from the FY2000 level by FY2010. This law was promulgated on June 1, 2005. According to this law, although it depends on the amount to be stored, it is not the voluntary regulation and delivery system of emission concentration that has been conventionally practiced, but individual concentration regulation for the discharge port, which is an oil factory, chemical factory, or Gases containing odors generated indoors, such as in laboratories and pharmaceutical factories, can no longer be released easily from ducts to the outdoors.

  In view of such a situation, the present inventors treated a large amount of exhaust gas containing a lean hydrocarbon, in combination with a novel adsorption / desorption method including a pretreatment stage different from the prior art, A proposition to recover volatile hydrocarbons as a liquid, together with a pollution prevention point of view that achieves zero emissions by removing all volatile hydrocarbons contained in it, and a point of view on carbon dioxide emission regulations In view of the above, the present invention has been completed.

That is, the problem to be solved by the present invention is that the upper limit of explosion, that is, a volatile hydrocarbon concentration of 100,000 PPM or less, and therefore, an exhaust gas of several thousand m ³ / hour or more, particularly a dilute of several thousand PPM or less. A large amount of exhaust gas containing volatile hydrocarbons at a high concentration and exceeding 3000 m ³ / hour (specifically, a large amount of exhaust gas containing extremely dilute volatile hydrocarbons of 5000 PPM or less and exceeding 3000 m ³ / hour) As one of the options in the process of complying with the above-mentioned pollution prevention regulations stipulated by law, it is not necessary to burn, ie, it does not release carbon dioxide and contains volatile carbonization. An object of the present invention is to provide a method for purifying exhaust gas containing volatile hydrocarbons capable of recovering hydrogen as a liquid. In addition, it is to provide the above method for achieving zero emissions for volatile hydrocarbons.

  In summary, the problem to be solved by the present invention is, firstly, to provide a purification method for reducing carbon dioxide gas to zero, which is a fatal drawback of the combustion methods conventionally used in this field. Second, by applying the adsorption method, volatile hydrocarbons are separated and recovered from a large amount of exhaust gas containing dilute volatile hydrocarbons, and reused as high-purity liquid hydrocarbons. Thirdly, it is a large amount of exhaust gas containing dilute volatile hydrocarbons, and the exhaust gas is previously contained in the gas while avoiding the explosion atmosphere in the pretreatment step. After concentrating dilute volatile hydrocarbons several or even ten times, a suitable purification method called zero emission is provided in combination with the adsorption / desorption method according to the invention of the present inventors.

  As a means for solving the above-mentioned problems, the purification method for a large amount of exhaust gas containing lean volatile hydrocarbons according to the present invention operates by alternately switching between adsorption and desorption as described in claim 1. In the exhaust gas purification method using the adsorption device comprising: before the treatment with the adsorption device, the exhaust gas is preliminarily saturated with water or liquid gasoline which is a co-liquid of contained volatile hydrocarbons. It is characterized by concentrating the dilute volatile hydrocarbons contained in the exhaust gas several times. In this way, by treating a large amount of exhaust gas containing dilute volatile hydrocarbons with the above-described means, the exhaust gas is purified to zero emission without using the combustion method that has been conventionally used. In addition, the volatile hydrocarbons in the exhaust gas can be efficiently separated and reused, and the above-mentioned problems, particularly the first, second and third objects can be achieved.

  Further, according to the method for purifying exhaust gas containing volatile hydrocarbons according to the present invention, as described in claim 2, when the adsorption device is desorbed, a vacuum pump and / or air or nitrogen is used together to switch between adsorption and desorption. The time is 5 to 60 minutes, and the purged exhaust gas obtained is cooled and taken out of the system, and the uncondensed gas at this time is returned to the inlet of the adsorption device before being pressurized.

  Furthermore, in the purification method of exhaust gas containing volatile hydrocarbons according to the present invention, as described in claim 3, the pressure of the pretreatment device is 1 MPa or less. This is because the danger of explosion can be avoided by washing with a hydrocarbon co-liquid, or in the case of extremely dilute, by sucking exhaust gas with a water-sealed pump and pressurizing to 1 MPa or less in a water supersaturated state.

  Also, by adopting such a treatment method, the hydrocarbons adsorbed under high pressure are returned to normal pressure to be desorbed, and then almost all hydrocarbons are obtained using a vacuum pump and / or an inert gas. In order to shorten the long cycle time of 1 hour or more, which is conventionally expected, to about 5 to 60 minutes, a pressure equalizing tower is provided in the desorption process.

By adopting such a processing method, as described in claim 5, it has become possible to purify volatile hydrocarbons in the emitted gas to almost zero PPM. The amount of exhaust gas to be treated in the present invention is preferably 3000 m ³ or more per hour, and the concentration of volatile hydrocarbons contained is preferably 10,000 PPM or less. Thereby, an above-described subject can be achieved.

  Hereinabove, the present invention will be specifically described in detail including the embodiment of the present invention. (In the following description, volatile hydrocarbons in exhaust gas targeted by the present invention may be referred to as HC gas.)

  In the embodiment of the present invention, when a large amount of exhaust gas containing dilute volatile hydrocarbons is treated, the pretreatment is performed by concentrating the dilute volatile hydrocarbons contained therein several times to about 10 times. An adsorption / desorption device including the device.

(Exhaust gas targeted by the present invention)
Exhaust gas targeted by the present invention is 1,000 m ^{3 to} tens of thousands m ³ or more discharged from petroleum bases, gasoline vapor discharged from tankers, painting plants, cleaning shops, manufacturing processes handling chemical products, etc. A large amount of exhaust gas and dilute HC gas (for example, olefin hydrocarbons such as ethylene and propylene, alcohols such as methanol, aromatic hydrocarbons such as benzene and toluene, butadiene, hexene, and styrene. Diene polymerized substances such as trichrene, carcinogenic substances such as methylene chloride and ethyl acetate). Moreover, the exhaust gas is a large amount of exhaust gas preferably exceeding 3000 m ³ / hour, and is preferably a dilute HC gas having an HC gas concentration of 100,000 PPM or less contained in the exhaust gas, and several thousand m ³ The target is a large amount of exhaust gas exceeding / hour, but is not limited to this.

(Embodiment using adsorption apparatus and pretreatment apparatus in the present invention)
The activated carbon used in the conventional adsorption method using activated carbon is as described in catalogs issued by activated carbon manufacturers such as Osaka Gas Chemical Co., Ltd., Kuraray Chemical Co., Ltd., and Tsurumi Coal Co., Ltd. Innumerable pores are composed of microbore. The volatile hydrocarbon and the carbon wall that have penetrated deeply into the pores and diffused form a strong C—C bond by strong van der Waals force. However, the affinity is strong, but so-called capillary condensation occurs. Therefore, enormous heat of adsorption exceeding the heat of condensation has been generated, and there has been a concern about the risk of fire for easy use. In addition, in order to remove volatile hydrocarbons causing capillary condensation from the microbore, a heating means such as steam is necessary (see Non-Patent Document 1 mentioned above), and desorption is performed by a simple means such as a vacuum pump or purge. It is also known not to.

  In addition, when the mixed HC gas is a diene, olefin, etc., it is inspired by a large number of active sites present in the activated carbon, such components easily polymerize, and the heat of polymerization reduces the risk of ignition and explosion. The problem that accompanies occurs. For this reason, when using such activated carbon, desorption by steam is indispensable, and HC gas dissolves in a large amount of water generated by condensation of steam, and the water quality standards in Japan that are the most stringent in water quality regulations in the world. To clear it, expensive wastewater treatment equipment is required.

  In order to solve the above problems, the present inventors have replaced the activated carbon that has been widely used in the past with flame retardant activated carbon (hereinafter referred to as MPC) consisting of mesopores mainly having a pore size of 10 to 100 mm. Or other known non-flammable solid adsorbents, specifically hydrophobic silica gel and / or synthetic zeolite in multilayer with MPC, and the above-mentioned dangers when adsorbing volatile hydrocarbons I found that I can avoid sex. In addition, by changing the ratio of mesopores and micropores, new knowledge has also been obtained about the adsorbent that does not absorb moisture but absorbs volatile hydrocarbons well. This point has already been proposed by the present inventors as described in the above-mentioned Patent Document 1, and has been demonstrated in a swing method of a small amount of exhaust gas containing rich HC gas.

  However, it is dangerous to easily apply this swing method as a means for treating a large amount of exhaust gas containing dilute HC gas. That is, as described above, when using activated carbon with a small pore diameter, which is normally used, apart from the extremely diluted HC gas below PPM (PPB order), due to heat generation due to capillary condensation into the pores, The temperature in the adsorption tower far exceeds 100 ° C. As a countermeasure, means for incorporating a cooling coil in the adsorption tower has been widely used for a long time. Also, as described in the above-mentioned Patent Document 3, a method of cooling the adsorption tower by circulating liquid HC obtained when the purge exhaust gas is cooled in the adsorption tower and utilizing the latent heat of evaporation thereof Has also been proposed.

  In the present invention, an adsorbent that easily condenses HC gas in the meso region easily, that is, mesopore activated carbon (adsorption pore diameter is in the range of 10 to 100 mm), although it is difficult to condense the capillaries in combination with such a known method. This is solved by using activated carbon). (Note that this activated carbon is called “canister” as described above, and in the developed countries of Europe and the United States except Japan, it adsorbs gasoline vapor that leaks while the vehicle is running due to legal regulations. (It is used in a system that is desorbed and burned in the engine room. Cars that do not have this system even if they are produced in Japan cannot be exported.)

  That is, the fact that it can be detached only by purging (air) means that it is more complete if a vacuum pump is used in combination, and the capacity of the vacuum pump in this case can be small. Selection of the mesopore activated carbon, which has been proven to be safe in the operation of adsorption / desorption, is a decisive factor for the adsorption / desorption method, which is a combination of the pretreatment device (pretreatment concentrating device) which is a component of the present invention. It can be said that.

  As an example of a pretreatment apparatus that is an essential condition of the configuration of the present invention, after washing a dilute hydrocarbon with a rich hydrocarbon (co-liquid), it is compressed to a high pressure of 1 MPa or less, and is post-treated to avoid an explosion limit value. Although the method has been widely used conventionally, the post-treatment at this time is exclusively a membrane separation method. However, with the currently widely used membrane separation technology, it is extremely difficult to keep the hydrocarbon concentration released after the treatment to 1% or less. As a means to solve this, when the volatile hydrocarbons contained in the treated exhaust gas are as thin as several hundred to several thousand PPM, the purpose of adding the hydrocarbons to a rich state is the membrane separation used in the post-treatment. This is because pressurization is an indispensable condition in order to improve the performance. Similarly, the same can be said for the adsorption / desorption operation. It is desirable that the exhaust gas to be treated is compressed to a small amount and the HC gas is rich, but it is a dilute gaseous hydrocarbon. Pressurizing the pressure exceeding 0.16 MPa is always a dangerous operation accompanied by an explosion, and is a prohibited clause strictly regulated by law. In order to solve the above problem, the present inventors use a water-sealed pump as a means before pressurization when the contained volatile hydrocarbon is thinner than%, and pressurize when it is thicker than%. This was solved by using co-liquid washing as a previous measure.

(Embodiment of the present invention)
The purification method according to the present invention is a method comprising a combination of a pre-stage pressure concentration apparatus (pretreatment apparatus) and a post-stage adsorber, and the post-stage adsorbent has an adsorption pore diameter of 10 to 100 mm. It is characterized by using activated carbon and / or hydrophobic silica gel in the range. Moreover, when the water | moisture content near saturation is contained in waste gas, it is preferable to use together the hydrophobic silica gel which has a macropore, and / or activated carbon which has a macropore, ie, the adsorption agent which does not co-adsorb | suck moisture.

  In the purification method according to the present invention, the desorption operation in the adsorption apparatus is more completely desorbed by using a purge gas in combination with a purge gas under a vacuum lower than atmospheric pressure after the operating pressure is returned from the high pressure of 1 MPa or less to the pressure equalization state. It takes the form of performing. As the purge gas, it is preferable to use a part of the diffused gas from the adsorption device, dry air and / or nitrogen, or homogeneous volatile hydrocarbons. The purge exhaust gas taken out by this desorption operation is preferably cooled, and the uncondensed gas at this time is preferably returned to the exhaust gas before being pressurized.

(Specific application example of the present invention)
Hereinafter, a specific application example of the present invention will be described with reference to FIG. 1 by taking up a case where an exhaust gas of 5000 m ³ per hour including about 10% of gasoline vapor is treated. FIG. 1 is a flowchart showing one embodiment of the purification method according to the present invention.

As described above, this embodiment is a case where an exhaust gas of 5000 m ³ per hour containing 10% gasoline vapor is treated, and an example in which a gasoline washing tower is used as a pretreatment stage concentrating device (pretreatment device). Exhaust gas in which the gasoline concentration is included in a saturated state is further pressurized, cooled, and post-treated, that is, recovered, is a method already developed by the present inventors (pre-brown patent document 1). See). The apparatus is composed of adsorption towers (pressure equalization tower, desorption tower) 7a, 7b, 7c filled with an adsorbent, vacuum pump 4, gas-liquid separator 5, exhaust gas supply line 10, uncondensed gas return line 6, air ( Purging gas) This device comprising supply lines 8a, 8b, 8c and gas line 9 that diffuses to the atmosphere, and a pretreatment device for this device, a gasoline washing tower 13 for pre-cleaning the exhaust gas with liquid gasoline, washing is completed A compressor 14 for pressurizing the gas, and a cooler 15 for cooling the gas, and 2a, 2b, 2c, 3a, 3b, 3c, 9a, 9b, and 9c in the figure are all switched. It is a solenoid valve at the time of.

  That is, as shown in FIG. 1, as a pretreatment stage, the gasoline vapor-containing exhaust gas is supplied from the top 11 to another tank through the exhaust gas supply line 10, and the liquid that returns from the bottom 12 to another tank is supplied. The gas is sent to a counter-current type gasoline washing tower 13 using gasoline, where the concentration of gasoline vapor is saturated at room temperature. Thus, the gas exceeding the upper limit of the explosion limit value is sent to the compressor 14 and pressurized to a pressure of 1 MPa or less. The pressurized gas whose temperature has been increased by being pressurized is cooled to room temperature by the cooler 15 and then the gasoline vapor is recovered by the adsorption / desorption device at the subsequent stage.

  That is, the concentrated gas is sent to the adsorption towers 7a, 7b, and 7c through the exhaust gas supply line 16, where gasoline vapor is adsorbed and then diffused into the atmosphere from the gas line 9 that diffuses into the atmosphere. . On the other hand, the air vapor (purge gas) supply lines 8a, 8b and 8c are supplied to the adsorption towers 7a, 7b and 7c after the adsorption process, and the vacuum vapor 4 is sucked to remove the gasoline vapor. Let This operation will be described in more detail. Exhaust gas pressurized to 1 Mpa or less is adsorbed by the adsorption tower 7a for 5 minutes, and after 5 minutes, it is switched to the adsorption tower 7b. Meanwhile, the adsorption tower 7c completes the desorption operation with the purge gas using the vacuum pump together from the pressure equalized state for 5 minutes, and is in a standby state for the next adsorption. That is, the adsorption, pressure equalization, and desorption operations are sequentially performed in three towers. However, in the case of pressure equalization operation, without using a vacuum pump or purge gas, it is cooled as it is to condense the gasoline vapor, and the uncondensed gas is returned to the exhaust gas supply line 10 through the return line 6.

  As described above, the reason for dividing into adsorption, pressure equalization, and desorption is to reduce the capacity of the adsorbent by reducing the adsorption time as much as possible and to reduce the capacity of the adsorption tower. is there. In the absence of a pressure equalizing tower, the swing time required for adsorption / desorption usually depends on the amount of adsorption, but usually exceeds one hour. In this example, the adsorbent used in the adsorption towers 7a, 7b, and 7c is mesopore activated carbon (activated carbon having an adsorption pore diameter in the range of about 10 to 100 mm, specifically, Caterer's product name GC-1). Was pre-coated with gasoline vapor.

In this example, the amount of exhaust gas is 5000 m ³ per hour and the gasoline vapor contained is 10%, but this gas is added to 0.8 Mpa after submerging the liquid gasoline washing tower. By the pressure, the amount processed in the latter adsorption / desorption device becomes about 1/8, that is, 600 m ³ / Hr, which is extremely easy to handle, and the gasoline vapor concentration is concentrated several times. There is an advantage that when it is cooled by the vessel 5, it is easily condensed and liquefied.

  This embodiment is an example suitable for processing a large amount of gasoline vapor discharged from a large tanker entering and leaving an oil base. For this exhaust gas regulation measure, measures should be taken by FY2010. Is required. With this method, a large amount of gasoline vapor that has been diffused into the atmosphere until now has been recovered as a liquid, and a large amount of exhaust gas is burned in that it has opened the way for the emission concentration to be zero emission. Compared to this combustion method, not only is it more economical, but it has become possible to eliminate the release of carbon dioxide, which is a fatal drawback of the combustion method.

  As described above, the method for purifying a large amount of exhaust gas containing dilute volatile hydrocarbons according to the present invention is an adsorption apparatus (adsorption tower) comprising an adsorbent layer filled with mesopore activated carbon and / or hydrophobic silica gel pre-coated as an adsorbent. In the exhaust gas purification method using the above, before processing with the adsorption device, the dilute volatile hydrocarbons contained in the exhaust gas are concentrated in advance by co-liquid washing, and after the upper limit of explosion is avoided, pressurization is performed. By the epoch-making method that the adsorption / desorption device in the latter stage is remarkably miniaturized, and a large amount of gasoline vapor contained in the exhaust gas is recovered as a liquid, and the exhaust gas can be purified to zero emission, Its industrial applicability is very remarkable.

It is a flow sheet figure showing one embodiment of the purification method concerning the present invention.

Explanation of symbols

2a to 2c Electromagnetic valve 3a to 3c Electromagnetic valve 4 Vacuum pump 5 Gas-liquid separator 6 Return line 7a to 7c Adsorption tower 8a to 8c Air (purge gas) supply line 9a to 9c Electromagnetic valve 10 Exhaust gas supply line 11 Top 12 Bottom 13 Gasoline Washing tower 14 Compressor 15 Cooler 16 Exhaust gas supply line

Claims (5)

It consists of a layer filled with pre-coated mesoporous activated carbon and / or hydrophobic silica gel as an adsorbent, and uses an adsorber that alternately performs adsorption and desorption. One adsorber allows exhaust gas containing volatile hydrocarbons to pass through the adsorbent. Adsorb volatile hydrocarbons to the adsorbent layer in the device, discharge exhaust gas substantially free of volatile hydrocarbons from the outlet of the adsorption device, switch the other adsorption device to desorption before breaking through, In the processing method of exhaust gas containing volatile hydrocarbons, which comprises taking out previously adsorbed volatile hydrocarbons out of the system,
Exhaust gas to be treated is a gas containing a large amount of dilute volatile hydrocarbons. Before treating the gas with the adsorption device, the gas is saturated with water or volatile hydrocarbons contained in the gas before explosion. A large amount of exhaust gas containing dilute volatile hydrocarbons, characterized by providing a pretreatment device to pressurize after avoiding the limit value and concentrate the dilute volatile hydrocarbons contained in the exhaust gas several times. Purification method.   The adsorption device uses a vacuum pump and / or an inert gas at the time of desorption, the adsorption / desorption switching time is 5 to 60 minutes, and the purged exhaust gas obtained is cooled and taken out of the system. 2. The method for purifying a large amount of exhaust gas containing lean volatile hydrocarbons according to claim 1, wherein the uncondensed gas at this time is returned to the inlet of the adsorption device before being pressurized.   The method for purifying a large amount of exhaust gas containing lean volatile hydrocarbons according to claim 1 or 2, wherein the pressure of the pretreatment device is 1 MPa or less.   The exhaust gas purification method containing a lean volatile hydrocarbon according to any one of claims 1 to 3, wherein the adsorption device has a pressure equalizing tower in the desorption step.   The method for purifying a large amount of exhaust gas containing lean volatile hydrocarbons according to any one of claims 1 to 4, wherein the concentration of volatile hydrocarbons in the exhaust gas is substantially zero PPM.

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