JP2925522B2 - Method for recovering hydrocarbons in liquid form from waste gas containing gaseous hydrocarbons - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering hydrocarbons from waste gas containing gaseous hydrocarbons in a liquid state, and particularly to benzene and trichloroethylene which are carcinogenic and are one of substances causing air pollution. The present invention relates to the above-mentioned method for reducing the concentration of gaseous hydrocarbons such as the above to 100 ppm or less and discharging them to the atmosphere.

[0002]

2. Description of the Related Art For gaseous hydrocarbons such as benzene, trichloroethylene, and methyl ethyl ketone, which are one of the main causes of air pollution, in the United States, Europe, Japan, and other developed countries, the concentration that is released into the atmosphere is regulated by a method. Strictly regulated. Although the level of the regulation value varies depending on the circumstances of each country, in advanced countries other than Japan, for example, benzene is "5 ppm or less", and even in Japan, the Environment Agency Notification No. 5 (February 1997) 6th) "30ppm or less"
Came to be regulated.

[0003] By the way, as a source of such gaseous hydrocarbons, a particular problem is that a large amount generated from a printing plant, a cleaning plant, a painting plant, etc., and about 3000 p.
pm or less, which is a waste gas generated not only at factories but also at the time of unloading and unloading from tanks storing them.

As methods for treating and recovering such waste gases containing gaseous hydrocarbons, the following methods have been widely used: (1) gas separation membrane method + adsorption method (2) activated carbon, zeolite, hydrophobic For example, an adsorption method using silica gel or the like.

[0005] Of the above methods, the method (1) is a mainstream technology in Europe, and is mainly applied when a large amount of waste gas is used. The adsorption method is used as a post-treatment means by a gas separation membrane method. Things. In Japan,
As disclosed in Japanese Patent Application Publication No. 7-284623, a technique belonging to this field is disclosed. On the other hand, the method most widely adopted in the United States is the adsorption method (2), particularly the adsorption method using activated carbon. This method is disclosed in
JP-A-57-14687, JP-A-57-42319, JP-B-59-507
No. 15, JP-B-59-50716, and JP-B-2-46630.

In the current state of the art, in order to treat waste gas containing gaseous hydrocarbons to reduce the concentration of hydrocarbons in the clean gas released into the atmosphere to 100 ppm or less, the above-mentioned adsorption method using activated carbon is required. Is the best industrial tool.

In the method for treating and recovering waste gas containing gaseous hydrocarbons by the above-mentioned adsorption method, switching between adsorption and desorption is controlled by a time control via an electromagnetic valve. However, when switching is performed by time control, it is necessary to know in advance the time required for the adsorption tower to break through experiments and experiences. In addition, switching by time control is performed when the amount and concentration of gaseous hydrocarbons at the inlet of the adsorption tower are constantly fluctuating greatly.
It is necessary to fill the adsorbent more than necessary, and to switch over early. Therefore, there has been a problem that the adsorbent is not used effectively.

[0008] In order to solve the above-mentioned problems, a method of performing "detection of breakthrough" of an adsorption tower using various measuring instruments and switching to desorption when the concentration reaches a level at which breakthrough can be detected has been performed. Have been. Also, various proposals have been made for the above detection method since ancient times. For example, Japanese Patent Application Laid-Open No. 55-35996 discloses that "a two-column PSA purifying apparatus of adsorption and desorption is used,
Without using a vacuum pump, the adsorption tower is pressurized to 5 to 10 kg / cm ² to absorb the wet gas, and the dry gas is released from the top of the tower. In the dehumidification method in which the adsorbed gas is discharged and regenerated by returning to the above, the gas flow rate passing through the adsorption tower, the inlet and outlet temperatures of the adsorption tower, the inlet and outlet pressures of the adsorption tower, and the regeneration pressure of the desorption tower are changed every moment. The microcomputer stores the operating status of each part including the data as data, calculates the material balance and heat balance instantly, controls the desorption time based on the results, and indirectly determines the timing of switching between adsorption and desorption. How to control automatically. Is disclosed.

[0009]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 55-35996.
The method disclosed in the above publication is an epoch-making proposal in that the switching between adsorption and desorption is not controlled by time, but by an instruction from a microcomputer that stores the operation status of the apparatus. However, there was no excellent adsorption model as at present, so that the simulation method could not be used. That is, the idea of “predicting the breakthrough concentration by simulation of an adsorption model” was not reached.

After that, before the breakthrough, the concentration of the component to be adsorbed in the gas is detected from the measurement port embedded in the adsorbent layer quickly, and when the concentration reaches a certain level, the solenoid valve is automatically activated. Switching methods have been proposed. However, when the adsorbent has a pore diameter of 5 to 100 mm, such as granular activated carbon or silica gel, the concentration and the temperature fluctuate locally, so the adsorbent layer is not biased along the gas flow. There is no guarantee that it will rise toward the exit with a uniform width ", and therefore has the disadvantage that it is difficult to determine the position to be measured. (If the measurement port is inserted at a position that is too deep from the top, it is hard to say that it is superior to time control.)

SUMMARY OF THE INVENTION The present invention seeks to further improve the prior art. It is an object of the present invention to provide a method for treating waste gas containing gaseous hydrocarbons and recovering and recycling gaseous hydrocarbons. Using a solid adsorbent such as activated carbon, synthetic zeolite, or the like, safely, easily, and efficiently recovering hydrocarbons from the gas in liquid form, and after treatment, the remaining hydrocarbons in the gas released into the atmosphere Concentration
An object of the present invention is to provide a "method of recovering hydrocarbons from waste gas containing gaseous hydrocarbons" which can be reduced to 100 ppm or less. Another object of the present invention is to provide a method that can be made portable so that the system can be integrated and mounted on a skid when the above method is implemented as an apparatus.

[0012]

According to the present invention, there is provided a method comprising:
Using an "adsorption device with an adsorbent layer" that alternately performs adsorption and desorption, let the waste gas containing gaseous hydrocarbons pass through the adsorption device on one side, and apply gaseous gas to the adsorbent layer in the adsorption device. The hydrocarbons were adsorbed, and the waste gas substantially free of gaseous hydrocarbons was released into the atmosphere, during which time the other adsorber was switched to desorption and adsorbed on the adsorbent layer in the adsorber. A method in which gaseous hydrocarbons are sucked and released with a vacuum pump while using a purge gas together, and the separated purged exhaust gas is cooled to recover gaseous hydrocarbons as a liquid. Returning the entire amount of the purged exhaust gas containing condensed hydrocarbons to the adsorption device that allows the waste gas to pass, increasing the hydrocarbon concentration in the adsorbent layer, and switching to desorption before the adsorbent layer breaks through. Feature How to recover from a waste gas containing a scan-like hydrocarbon hydrocarbons in liquid form. "The a gist (claim 1).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. Prior to this, the present invention will be described in more detail in comparison with the prior art.

[0014] As described in the above-mentioned "Prior Art" section, in the current state of the art, the waste gas containing gaseous hydrocarbons is treated to reduce the hydrocarbon concentration in the clean gas released to the atmosphere. In order to reduce the concentration to 100 ppm or less, the adsorption method using activated carbon is the most excellent industrial means. (Note that the catalytic combustion method is also a simple and effective means, but depending on the concentration of gaseous hydrocarbons in the waste gas, there is a danger of an explosion. .)

However, in the conventional adsorption method using activated carbon, since "steam" is usually used as a purge gas at the time of desorption, there is a drawback that a considerable burden is imposed on wastewater treatment equipment in order to clear strict water quality standards. Was. For this reason, a method of using nitrogen as a purge gas and circulating it has been proposed, but a large refrigerator is required to separate the dilute gaseous hydrocarbons accumulated in the circulating nitrogen, and a low temperature of 0 ° C. or lower is required. There is a problem that it has to be cooled.

As a means for solving this problem, before recovering gaseous hydrocarbons from the purged exhaust gas, the lean gaseous hydrocarbons in the purged exhaust gas are concentrated through a cascade-type concentration adsorption tower (adapter). However, this method has a problem that an adapter must be separately prepared.

A first feature of the present invention is to solve the above-mentioned problems. The following features are provided. The entire amount of the purged exhaust gas including the uncondensed hydrocarbon after the cooling treatment is transferred to the adsorption device for treating the waste gas. Return, to increase the hydrocarbon concentration in the adsorbent layer in the adsorption device,
As a result, the hydrocarbon concentration in the purge exhaust gas is increased, and the hydrocarbon can be easily recovered as a liquid only by cooling the hydrocarbon exhaust gas to about room temperature, and the treatment of the purge exhaust gas after the cooling process is facilitated. Things.

Next, the second feature of the present invention, that is, "switching to desorption before the adsorbing device breaks through" will be described. It is due to the circuit chip incorporated in the
In order to use an ultra-small chip that has been remarkably advanced recently, a large-scale microprocessor for the purpose of calculation as described in the above-mentioned known technology (the technology disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-35996) is used. do not need. In addition, the present invention picks up data obtained during driving,
This is completely different from the above-described prior art in that the breakthrough concentration is predicted by simulation of an adsorption model, instead of only calculating the material balance and heat balance. That is,
This is clearly different from the idea of “predicting breakthrough concentration by simulation of an adsorption model” which is a preferred embodiment of the present invention.

In addition to the above-mentioned prior art, a method for detecting breakthrough of the adsorbent layer using various measuring instruments and switching to desorption when the concentration reaches a level at which breakthrough can be detected has been carried out for some time. Have been However, according to the recent severe air pollution control law, the concentration at the time of breakthrough is several tens of p.
Since a trace concentration of less than pm is a problem, the concentration that needs to be detected before that is on the order of 1 to 2 ppm or less, requiring a considerably large and precise measuring instrument. On the other hand, in the preferred embodiment of the present invention, as described above, the use of a very small chip, which has been remarkably advanced recently, has an advantage that a large and precise measuring instrument is not required.

The second feature of the present invention will be described in more detail including preferred embodiments thereof. The present inventors have developed a means for treating a large amount of waste gas containing gaseous hydrocarbons. In this system, the hardware technology of "data logger signal", which is a means to capture data, is skillfully incorporated into this system, and the suction device is simulated with "adsorption model". As a result, the temperature in the adsorbent layer could be easily and promptly kept constant at around room temperature regardless of the change in the hydrocarbon concentration in the waste gas every moment.

As a result, according to the present invention, the timing of switching from adsorption to desorption is not simply set in a time cycle, but is left to the judgment of the installed software, so that the performance of the adsorbent can be fully and without waste. Therefore, it is possible to recover the gaseous hydrocarbon in a liquid state only by cooling the purge exhaust gas to a temperature near room temperature of about 10 to 30 ° C. If the detection time of breakthrough is wrong, gaseous hydrocarbons leak into the clean exhaust gas discharged from the adsorbent layer, and the object of the present invention is lost.

Various "adsorption models" have been proposed. Among them, the physical properties of the adsorbent, that is, "adsorption isotherm curve and adsorption pressure inside the adsorption tower, vacuum degree of vacuum pump, gas flow rate in the tower" , The height of the adsorbent layer, the purge coefficient ”is fixed (Frozen), and the“ inlet gas flow rate and concentration ”that changes from moment to moment are used as variables to determine the switching time or the outlet concentration of the adsorbent layer ( A so-called “Frozen Model”, which is input to a chip as a hypothetical value as a hypothetical value and is operated, is famous. The “adsorption model” used in the present invention is a “Frozen Model”
Is preferred, but not particularly limited thereto.

The second characteristic feature of the present invention, namely, "switching to desorption before the adsorbing device breaks through" is an essential component, and the reason why the "purge" is the first feature feature of the present invention is as follows. To increase the concentration of hydrocarbons in the exhaust gas and cool it down to about room temperature, hydrocarbons can be easily recovered as a liquid, and the processing of the purged exhaust gas after cooling is facilitated. The entire amount of (purged exhaust gas containing uncondensed hydrocarbons after the cooling process) is returned to the adsorption device that processes the waste gas. That is, by mixing the uncondensed purge exhaust gas with the waste gas supplied to the adsorption device, the hydrocarbon concentration of the adsorption device inlet gas further changes, and the hydrocarbon concentration in the adsorbent layer in the adsorption device is reduced. Because it changes every moment, it is difficult to estimate in advance the time until breakthrough.

Therefore, in the present invention, in order to make the above-mentioned first feature point an essential component, the second feature point of “switching to desorption before the suction device breaks through” is an essential component. It is necessary to However, the present invention does not exclude the switching means based on time control that has been performed conventionally. If the concentration of gaseous hydrocarbons contained in the gas at the inlet of the adsorption device (waste gas + the uncondensed purge exhaust gas) is substantially constant over time,
This is because it is one of the convenient methods to determine in advance the time from the start of the operation of the suction device to the breakthrough, and to use the time as a guide in the next suction operation.

As described above, when the flow rate and the concentration of the inlet gas fluctuate every moment, according to the preferred embodiment of the present invention, the concentration of the gaseous hydrocarbon adsorbed on the adsorbent layer is reduced to just before the breakthrough. Can be automatically concentrated to a high concentration.As a result, it is possible to condense and remove (collect) gaseous hydrocarbons as a liquid simply by cooling the purged exhaust gas to around room temperature. . However, despite these advantages, the disadvantage is that if the time required for adsorption and the time required for desorption are alternately too different, from the perspective of the person managing the work, the switching between adsorption and desorption is automated. If not, it is not always preferable.

When the appropriate adsorbent is properly filled, the amount of gaseous hydrocarbons to be adsorbed is extremely small near the top of the adsorbent layer. The amount of heat of adsorption is extremely reduced, and the amount of heat exceeding that amount is released from the adsorption device to the atmosphere. As a result, the signal from the measurement port inserted near the top to take in the chip, ie, the indicated temperature, stops and gradually falls. If the means for automatically switching the suction / removal switching valve (electromagnetic valve) at this time is used in combination, the above-mentioned disadvantage can be solved, and this is also included in the present invention.

The term "appropriate adsorbent" refers to an adsorbent such as synthetic zeolite in which the diameter of the adsorption hole is controlled to a certain size and the amount of adsorption is hardly locally localized. Therefore, as an example of a preferred embodiment of the present invention, as described later in detail, a synthetic zeolite layer is disposed on the top of the adsorbent layer, and a temperature detection port is provided in the adsorbent layer made of the synthetic zeolite. And means for automatically switching the solenoid valve when the temperature from the temperature detection port stops its rise.

The adsorbent used in the present invention includes:
Regardless of whether the material is flammable or non-flammable, any solid adsorbent that is compatible with the waste gas can be used. However, if the concentration of hydrocarbons in the waste gas is as low as about 2000 ppm, it is desirable. It is desirable to use granular activated carbon which is inexpensive and easily available. Non-combustible silica gel other than the above-mentioned granular activated carbon can be used. In this case, silica gel hydrophobized with a silane coupling agent such as trimethylchlorosilane or treated at high temperature for a long time to impart hydrophobicity and lipophilicity. Silica gel is preferred.

Incidentally, solid adsorbents such as activated carbon, synthetic zeolite, silica gel and activated alumina used as adsorbents have strong affinity for gaseous hydrocarbons,
It is also heavily used as a heat insulator. In addition, apart from synthetic zeolite, other adsorbents have a wide distribution of adsorption pore diameters, so that the concentration at adsorption sites is not uniform, and local heating is likely to occur.

Generally speaking, in the case of hydrophobic silica gel or granular activated carbon, depending on the particle size and temperature rise, if the thickness is about 4 inches or more, the heat of adsorption is transferred to the cooling water layer in a short time. It is said that it cannot be done. Therefore, 4
For thicknesses greater than an inch, heat transfer in the circumferential direction is not so much expected, but relies on heat transfer carried out by the gas flowing in the vertical direction. For this reason, there is a problem whether the adsorption layer having a certain width moves uniformly and uniformly toward the outlet of the adsorption device, affected by the temperature distribution in the adsorption device. That is, there is no problem when the concentration at the time of breakthrough is detected at the outlet of the adsorption device, but there is a problem when the detection port is disposed at a position embedded in the adsorbent layer.

To avoid this, a preferred embodiment of the present invention is to place the synthetic zeolite at the top of the adsorbent layer, ie, at the position closest to the waste gas outlet.
As the synthetic zeolite, for example, “Y-type zeolite“ 3
60HUD "" (product name manufactured by Tosoh Corporation) is preferred. The reason is that, unlike hydrophobic silica gel and granular activated carbon, the Y-type zeolite has a strictly controlled pore size to a certain size, and, depending on the material selected, the generation of gaseous hydrocarbons in waste gas. Varieties covering almost the entire molecular diameter are also commercially available. Moreover, the ratio of adsorbing gaseous hydrocarbons is 15 to 20% by weight. For this reason, no offset occurs in the adsorption band having a certain width moving in this layer. In the present invention, the synthetic zeolite has an SiO ₂ / Al ₂ O ₃ of 20 or more,
Those having a pore size of about 8 mm are desirable.

In a preferred embodiment of the present invention, it is desirable that the port for detecting the concentration and temperature taken in as a data logger signal be arranged at the center of the synthetic zeolite layer. In this case, in addition to the above-described means for detecting the breakthrough point, the temperature of the portion is indicated by the temperature instruction (the temperature instruction at the time when the temperature increase due to the heat of adsorption is stopped).
It can be used as a guide for switching between desorption.

In a preferred embodiment of the present invention,
In order to locally homogenize the temperature of the adsorbent layer and the concentration of the adsorbed hydrocarbon, the heat of adsorption generated in the adsorbent layer is quickly moved laterally from the adsorbent layer to remove it. It is preferable to use a double-cylindrical or multi-cylindrical adsorption tower in which the agent layer and the cooling water layer for cooling the adsorbent layer are adjacent to each other. And, taking into account the tendency of static electricity generated in the adsorbent layer to gather at the center of the layer,
In order to release static electricity for cooling, an adsorption tower having a metal cylinder at the center is desirable.

In the present invention, the vacuum pump used at the time of desorption is preferably a completely dry type. For example, a “high vacuum (final vacuum degree: 7 mmHg), large capacity (50 m ³ / min) completely dry type vacuum pump” manufactured by Hori Engineering Co., Ltd. is particularly suitable. In a liquid ring vacuum pump, when the sealing liquid is, for example, water, the degree of vacuum cannot be reduced to a value higher than the vapor pressure of water, and the limit is about 60 mmHg commercially. For this purpose, a combined use of a gas ejector is required.

In a liquid ring vacuum pump using a liquid such as ethylene glycol which has no affinity for gaseous hydrocarbons and has a very low vapor pressure as a sealing liquid,
When the seal liquid is mixed into the purge gas and the hydrocarbons in the purge gas are separated from the seal liquid, there is a concern that an emulsion may be formed at the interface. The reason is,
This is because the separated seal liquid must be cooled and circulated.

In the present invention, it is preferable to use a part of the clean gas discharged into the atmosphere from the adsorbent layer as the purge gas used when desorbing using a vacuum pump. As a result, the gaseous hydrocarbon concentration in the purge exhaust gas becomes leaner than a predetermined level, and liquefaction occurs unless the gas is cooled to a considerably low temperature of room temperature or lower. That is, such a rare gas is
It is self-evident that the dew point does not easily reach. For example, if the purge exhaust gas containing 12.95 VOL% of n-pentane is to be cooled and liquefied, the dew point of the component in the purge exhaust gas is about -15 ° C, and below this temperature, the component will not form dew (condensate). (The rate of condensation depends on the cooling temperature.)

As a means for solving this problem, the pressure of the gas discharged from the vacuum pump is increased from normal pressure to 2 atm and discharged, and the same hydrocarbon liquid is evaporated in a separately provided container. The problem can be solved by returning the hydrocarbon vapor to the outlet pipe directly connected to the desorption layer, or by injecting the same liquid hydrocarbon into the outlet pipe and performing a so-called displacement purge. As described above, a method of increasing the hydrocarbon concentration in the purge exhaust gas and promoting the condensation and liquefaction by performing the displacement purge has already been proposed.

In the above-mentioned proposed method, when the pressure of the purge exhaust gas is increased to 2 atm, the above-mentioned n-pentane is reduced by one.
Taking a purge gas containing 2.95 VOL% as an example, the concentration of the component is increased to 25 VOL%, and the dew point of the component is about 18 ° C. This gas cooling to 18 ° C. is a temperature level which can be achieved very easily. However, this already proposed method has a problem that it is cumbersome in terms of equipment and construction of a sequence system.

By the way, the degree to which gaseous hydrocarbons are concentrated in the adsorbent layer is, theoretically, when the degree of vacuum is 25 mmHg.
If only hydrocarbons are adsorbed, the concentration will be "760/25", that is, "about 25 times", but usually a large amount of air coexists, and nitrogen gas and oxygen in this air The molecular diameter of the gas is much smaller than the molecular diameter of the hydrocarbon, so that nitrogen gas or oxygen gas is adsorbed preferentially to hydrocarbon gas. As a result, it is empirically known that the concentration can be reduced to only four times the hydrocarbon concentration at the inlet.

Therefore, the inventors of the present invention dropped the liquid hydrocarbon onto the waste gas to be treated (specifically, sprayed the liquid hydrocarbon on the conduit of the waste gas to be treated) to thereby form the adsorbent. By pre-coating the layer and continuously returning the entire amount of uncondensed purge exhaust gas (purged exhaust gas containing uncondensed hydrocarbons after cooling treatment) to the adsorption device, the concentration of hydrocarbons is successively increased to an integral multiple of 4 I found the fact that I could do that. For example, when the hydrocarbon concentration in the waste gas is initially 2000 ppm, the concentration ratio in the adsorption device is 8000 ppm, and 8000 ppm is 32 in the next circulation.
000 ppm, ie 3.2%.
This is because, by pre-coating the adsorbent layer with the liquid hydrocarbon or the uncondensed hydrocarbon, the adsorption of nitrogen gas or oxygen gas in air that is originally preferentially adsorbed is prevented.

Further, the solid adsorbent such as activated carbon, synthetic zeolite, and hydrophobic silica gel used in the present invention is not an adsorbent that does not adsorb moisture at all, but as shown in FIG. The water absorption varies greatly depending on the relative concentration. When the gas to be adsorbed is moist air, almost no moisture is adsorbed when the relative humidity is about 40% or less,
If it exceeds 0%, water will be rapidly adsorbed (see FIG. 4). Although FIG. 4 shows the water adsorption isotherm of activated carbon, the same can be said for other hydrophobic adsorbents.

The case where the above-mentioned phenomenon becomes a practical problem is a case where a hydrocarbon gas and moisture coexist in the gas to be adsorbed, and the relative concentration of the moisture in the gas exceeds 40%. In the adsorbent layer, a "co-adsorption phenomenon" occurs between hydrocarbons and water.

As a specific example of the embodiment of the present invention, particularly when the hydrocarbon concentration in the gas to be adsorbed is as low as about 5000 ppm or less, the water concentration (related humidity) becomes relatively high. "Is easy to occur. This “co-adsorption phenomenon” is closely related to the “precoat” described above,
If the component to be precoated is water instead of hydrocarbon gas, the adsorption of hydrocarbon gas is significantly inhibited. Moreover, at the time of desorption, it is pushed out first (by suction of a vacuum pump using a purge gas together), resulting in a large amount of water contained in the liquid component taken out.

However, the problem is that the adsorption of hydrocarbon gas is hindered during the adsorption, and in the experimental example conducted by the present inventors, about 3000 ppm of dilute ethyl acetate was adsorbed on hydrophobic silica gel. Even when the operation of returning the entire amount of the purged exhaust gas after desorption to the inlet of the adsorption tower was repeated, the outlet concentration did not become 1500 ppm or less. (This value is 1
It is no exaggeration to say that almost no adsorption was observed for the expected value of 00 ppm or less. This fact does not detract from the fact that ethyl acetate is not concentrated in the adsorption tower and passed through. )

As means for avoiding such "co-adsorption phenomenon", the following methods (1) to (3) can be considered. (1) The adsorbent that has passed through the adsorbed moisture
(Vacuum state) A method of performing normal adsorption and desorption operations after sufficient desorption and regeneration over time. (At this time, the water remaining without being desorbed can be regarded as a “precoat agent”.) (2) Hydrocarbons having an affinity for water and having a higher boiling point than water, such as ethylene glycol A method in which a substance is used as a "precoat agent" prior to an adsorption operation. (3) A method of pre-adsorbing a high-concentration hydrocarbon before adsorbing a high-humidity gas to be adsorbed that contains a low-concentration hydrocarbon. (This high concentration of hydrocarbons is also used as a "precoat agent".)

The above three methods can be considered. Among them, according to the methods (1) and (2), even if the amount of hydrocarbons in the gas discharged to the atmosphere can be suppressed to about 100 ppm or less. However, there are difficulties in recovering the components to be adsorbed. However, since it is insoluble in aromatic compounds such as benzene and toluene, it does not mix with the recovered liquid, thus providing an effective precoat means.

In the present invention, a substance such as a hydrocarbon having an affinity for water and having a higher boiling point than water is used as a “precoat agent” as in the method (2), although not particularly limited. It is preferred to use As described above, the fact that the precoat agent is water-based is effective not only for the generation of sparks due to the concern about the charging of the hydrophobic silica gel, but also as a measure against the deterioration of the adsorbent due to the polymerization of the precoat agent. A contributing effect is obtained.

For the above reasons, the present invention includes any of the above methods (1) to (3) in order to avoid the above “co-adsorption phenomenon”. The method of 3) can be carried out by appropriately selecting or using together.

The fact that the concentration of hydrocarbons in the adsorption device is high means that the concentration of hydrocarbons in the purge exhaust gas is high, which results in a favorable result for the condensation of hydrocarbons in the purge exhaust gas. . That is,
Cooling to around room temperature brings about the effect of easy liquefaction. However, apart from the case where this means is performed only at the start of operation, if it is performed continuously, since the inlet concentration and gas amount (note) fluctuate every moment, the breakthrough concentration is detected in advance, or It is an essential requirement that the above-mentioned synthetic zeolite is arranged at the uppermost stage of the adsorption apparatus, and that the operation is performed after confirming that the temperature rise in the substantially central portion has stopped. (Note): Total hydrocarbon concentration of hydrocarbon concentration in waste gas supplied to adsorption device and concentration of uncondensed hydrocarbon in the purge exhaust gas, total gas amount of waste gas and purge exhaust gas

Therefore, as a simpler and more preferable method,
Before taking out the liquid hydrocarbon obtained by cooling the purge exhaust gas to the outside of the system, the present inventors refluxed it again to the cooler of the purge exhaust gas, brought it into countercurrent contact with the original gas, and A method was developed to promote the liquefaction by absorbing light components that are hardly condensed in the purged exhaust gas into the relatively heavy condensed liquid.

The present inventors have conducted intensive studies to integrate the device proposed in the present invention as a system and to make the device portable so that it can be mounted on a skid.
This has led to the present invention. That is, instead of using the adapter method or the displacement purging method disclosed in Japanese Patent Application Nos. 7-270754 and 8-86878 filed by the present inventors, gaseous carbonization of purge exhaust gas is performed. In recovering hydrogen, a means for recovering gaseous hydrocarbons from the gas in a liquid state by simply cooling the purged exhaust gas to a temperature near normal temperature without using a method of washing with a homogeneous hydrocarbon liquid was provided. This makes it possible to provide a portable device.

Although the embodiments of the present invention have been specifically described above, the preferred embodiments of the present invention will be summarized. In this case, the solid adsorbent is filled and the adsorption and desorption are alternately performed. Using a device, ・ Clean gas substantially free of gaseous hydrocarbons by passing waste gas containing dilute gaseous hydrocarbons through the adsorber on one side to adsorb gaseous hydrocarbons on the adsorbent layer. The waste gas is released into the atmosphere. ・ The point of switching between adsorption and desorption is performed before the adsorber breaks through. At this time, the means for detecting the breakthrough include: ・ Simulation of operating numerical values taken into the personal computer. In accordance with the result, the solenoid valve is switched when the indication of the thermometer arranged near the top of the adsorbent layer (the adsorbent layer made of synthetic zeolite) is stopped. Suction is performed using a pump (completely dry vacuum pump), and the sucked purge exhaust gas is cooled to a temperature around room temperature to condense and liquefy gaseous hydrocarbons. To increase the hydrocarbon concentration in the adsorption device, and if necessary, a small amount of liquid hydrocarbon is dropped or sprayed into the waste gas to be treated, thereby increasing the hydrocarbon concentration in the waste gas and The adsorbent layer is pre-coated with hydrocarbons. ・ Condensation and liquefaction of purged exhaust gas by returning non-condensed gas by returning the liquefied hydrocarbon to the cooler of the purged exhaust gas and bringing it into countercurrent contact with the gas. Enhance the effect of
Is the way.

Although the embodiment according to the present invention is as described in detail above, the method according to the present invention can employ a known PSA method or PTSA method.
The present invention can be applied to the SA method, the VTSA method, and the like, and these applications are also included in the present invention. The present invention also provides a method of recovering hydrocarbons from waste gas containing gaseous hydrocarbons in a liquid state, and is not limited to dilute multi-component gases generated at the time of coating, such as benzene and toluene. It is widely applied to single-component lean gases such as trichloroethylene and methyl ethyl ketone.

[0054]

Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the processing and processing of waste gas containing a dilute gaseous hydrocarbon according to an embodiment of the present invention.
FIG. 2 is a view showing a flow sheet of a recovery method, and FIG.
FIG. 4 is a diagram showing a “control panel for grasping and controlling the operating state” in the flow sheet shown in FIG. FIG. 3 is similar to FIG.
FIG. 3 is a longitudinal sectional view showing an example of the structure of an adsorption tower used in the flow sheet shown in FIG.

In this embodiment, as shown in FIG. 3, the inner cylinder 4a (4b) through which the cooling water 5 circulates and the adsorbent layer 3
An adsorption tower 1a (1b) composed of a double cylinder of an outer cylinder 2a (2b) filled with a (3b) was used. The inner cylinder 4a (4b)
Of the cooling water 5 flowing through the adsorbent layer 3a (3b) is made to flow in a countercurrent to the waste gas flowing through the adsorbent layer 3a (3b). As the adsorbent, granular activated carbon ("Granular Shirasagi No. 1" manufactured by Takeda Pharmaceutical Co., Ltd.) and Y-type synthetic zeolite ("360 HU" manufactured by Tosoh Corporation)
D ″) was used. As shown in FIG. 3, a Y-type synthetic zeolite 3-2a (3-b) was placed on top of the granular activated carbon 3-1a (3-1b).
2b) is packed in the adsorption tower 1a (1b), and the adsorbent layer 3a (3b)
It was provided for implementation.

Hereinafter, the present embodiment will be described in detail with reference to FIG. 1. A waste gas (a waste gas containing about 2,000 ppm of benzene) generated from a waste gas generation source (not shown) is blower (not shown). ) Or the gas is sent to the adsorption tower 1a from the waste gas air pipe 11 at its own pressure. The treated waste gas that has completed the adsorption step is supplied to the adsorption tower 1a (after switching to the desorption step, the adsorption
From the top of b), the air is discharged into the atmosphere via the discharge pipe 12 as air (clean gas) containing 20 ppm or less of benzene vapor.

The adsorption towers 1a and 1b are operated while alternately switching between the adsorption step and the desorption step described later. At the time of this switching, the adsorbent layers in the adsorption towers 1a and 1b break through. Before, and the valve (e) shown in FIG.
This is done by automatically opening and closing (e). That is, the valves (e) and (e) for switching between suction and desorption are opened and closed. The "inlet gas flow rate""I" and the "inlet gas concentration""J" of the adsorption towers 1a and 1b are shown in FIG. "Estimated breakthrough time" indicating the result of calculation by the CPU (calculation) 22 of the adsorption model read in the memory 21 and previously written in the memory (adsorption model) 23; and a temperature detection button disposed above the adsorbent layer. (Not shown), the "temperature""F" in the adsorbent layer taken out of the Y-type synthetic zeolite 3-2a (3-2b) [see FIG.
When “G” stops its rise, it is automatically switched using together.

On the other hand, the adsorption tower 1a after the completion of the adsorption step
(After switching to the desorption step, the adsorption tower 1b), the purge gas is supplied to the adsorption tower 1a via the purge gas air pipe 13.
(Tower which has been switched to desorption), and is also desorbed by suction using a completely dry vacuum pump 14 (“oscillating type” manufactured by Hori Giken Kogyo Co., Ltd.). In this embodiment, a part of the clean gas discharged from the top during the adsorption operation was used as the purge gas, and the completely dry vacuum pump 14 was operated at about 25 Torr.

The purge exhaust gas is supplied to the purge exhaust gas supply pipe 15.
From the gas-liquid separator 1 through a completely dry vacuum pump 14
Air is sent to 6. The gas-liquid separator 16 is cooled by water (10-35 ° C. water) flowing in a cooling water flexible tube 16a provided therein. At this time, the benzene vapor is supplied to the gas-liquid separator 1
The condensed liquid is condensed and liquefied in the recovery unit 17 connected to the lower part of the tube 6, and is separated from uncondensed gas. The condensed and liquefied benzene is returned to the original gas-liquid separator 16 via the benzene feed pipe 18, where it is brought into countercurrent contact with the uncondensed purge exhaust gas, and then accumulates in the recovery unit 17. The accumulated benzene is taken out of the system by the pump P by controlling the level of the liquid in the recovery unit 17.

Since benzene vapor remains in the exhaust gas not condensed in the recovery unit 17, the entire amount thereof is
The waste gas is returned to the waste gas supply pipe 11 again via the return gas supply pipe 19, and the adsorption process is performed together with the waste gas. As described above, the purge exhaust gas after the cooling treatment contains a high concentration of residual benzene, and the benzene concentration in the adsorption tower is further increased by repeatedly returning the entire amount to the adsorption tower. Then, by using the above-mentioned means, the time when the adsorbent layer in the adsorption tower breaks through is predicted, the switching time of the valve (e) is set, and the operation is automatically switched to the desorption operation.

A to J shown in FIG. 1 indicate the positions of instruments provided for grasping the operation status, while (A) to (G) indicate the operation control. 2 shows the position of the valve provided in the first embodiment. FIG. 2 shows a control panel 20 for grasping and controlling the operating state in the flow shown in FIG. 1 and comprises a memory 21, a memory (suction model) 23 and a CPU (calculation) 22. Is what is being done. In FIG. 2, only data necessary for switching between absorption and desorption are shown as "X" as data signals to be read into the memory 21. (Reading of other data signals was omitted.)

In the present embodiment, as described above, the switching between adsorption and desorption is performed by detecting the data logger signal before the adsorption tower breaks through. By devising a cooling means that can concentrate several times in the tower and remove heat generated in the adsorbent layer
(Refer to FIG. 3 described above), local heating was avoided, and the temperature of the adsorbent layer during the operation period was almost room temperature. Further, the concentration of benzene in the gas released into the atmosphere from the discharge pipe 12 was substantially 20 ppm or less.

As described above, the embodiment of the present invention is shown in FIG.
Are used, the present invention is not limited to such a double cylinder, but the present invention is not limited to such a double cylinder.
For example, it is also possible to use a double-cylinder or multi-cylindrical adsorption tower in which an adsorbent is filled in an inner cylinder and water for cooling the adsorbent layer is circulated outside the inner cylinder. With respect to other requirements, the present invention is not limited to the above-described embodiment, and various embodiments are possible within the scope of the present invention.

[0064]

According to the present invention, as described in detail above, the whole amount of the purge exhaust gas containing uncondensed hydrocarbons after the cooling treatment is returned to the adsorber through which the waste gas is passed, and the hydrocarbons in the adsorbent layer are returned. Increase the concentration (first feature point) ・ Switch to desorption before this adsorbent layer breaks through (second feature point)
This feature allows safe, easy, and efficient recovery of hydrocarbons from waste gas in liquid form, and the concentration of residual hydrocarbons in the gas released into the atmosphere after treatment. 100 ppm or less, especially "20pp
m or less. "

Therefore, according to the present invention, in the removal treatment of gaseous hydrocarbons, which are air pollutants, the benzene concentration specified in the Amendment of the Air Pollution Control Law (publicly announced on February 6, 1997). Not only can the emission standard "30 ppm or less" be completely cleared, but it is also possible to sufficiently cope with the case where the numerical value is less than half as severe. Also, the present invention can be made portable so that the system can be integrated and mounted on a skid when the method according to the present invention is implemented as an apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow sheet of a method for treating and recovering waste gas containing dilute gaseous hydrocarbons according to one embodiment of the present invention.

FIG. 2 is a diagram showing a “control panel for grasping and controlling an operating state” in the flow sheet shown in FIG. 1;

FIG. 3 is a longitudinal sectional view showing an example of a structure of an adsorption tower used in the flow sheet shown in FIG.

FIG. 4 is a graph showing “water adsorption isotherm of activated carbon”.

[Explanation of symbols]

 1a, 1b Adsorption tower 2a, 2b Outer cylinder 3a, 3b Adsorbent layer 3-1a, 3-1b Activated carbon 3-2a, 3-2b Y-type synthetic zeolite 4a, 4b Inner cylinder 5 Cooling water 10 Waste gas generation source 11 Disposal Gas supply pipe 12 Discharge pipe 13 Purging gas supply pipe 14 Completely dry vacuum pump 15 Purged exhaust gas supply pipe 16 Gas-liquid separator 16a Cooling water serpentine pipe 17 Recovery unit 18 Benzene supply pipe 19 Return gas supply pipe 20 Control panel 21 Memory 22 CPU (calculation) 23 Memory (suction model)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C10G 5/02 B01D 53/34

Claims (9)

(57) [Claims] 1. An adsorber having an adsorbent layer that alternately performs adsorption and desorption is used, and waste gas containing gaseous hydrocarbons is passed through one adsorber, and the adsorbent in the adsorber is removed. The bed adsorbs gaseous hydrocarbons and releases waste gas substantially free of gaseous hydrocarbons into the atmosphere, during which time the adsorber on the other side is switched to desorption and the adsorbent in the adsorber The method of recovering gaseous hydrocarbons adsorbed on a layer by suctioning with a vacuum pump while using a purge gas together with a purge gas, cooling the separated purged exhaust gas, and recovering gaseous hydrocarbons as a liquid. The entire amount of the purged exhaust gas containing the uncondensed hydrocarbons is returned to the adsorption device that allows the waste gas to pass therethrough, the hydrocarbon concentration in the adsorbent layer is increased, and the desorption is switched before the adsorbent layer breaks through. Features Of recovering hydrocarbons in liquid form from waste gas containing gaseous hydrocarbons. 2. The method according to claim 1, wherein the “adsorption device having an adsorbent layer” is
The method for recovering hydrocarbons from a waste gas containing gaseous hydrocarbons according to claim 1, wherein a synthetic zeolite layer is disposed on top of the adsorbent layer. 3. As a means for switching to desorption before the adsorbent layer breaks through, a temperature detection port is disposed at the top of the adsorbent layer, and the temperature from the temperature detection port stops rising. The method for recovering hydrocarbons in liquid form from waste gas containing gaseous hydrocarbons according to claim 1, wherein the solenoid valve is automatically switched at a point in time. 4. The method according to claim 3, wherein a top portion of the adsorbent layer is a synthetic zeolite layer, and a hydrocarbon is recovered in a liquid form from a waste gas containing a gaseous hydrocarbon. 5. As means for switching to desorption before the adsorbent layer breaks through, the "gas flow rate at the inlet", "hydrocarbon concentration in the inlet gas", and "concentration in the outlet gas" of the adsorber obtained during the adsorption operation. The desired hydrocarbon concentration (assumed value) "is read into a chip as numerical data, and the switching time is set in advance using a simulation model incorporated in the chip. A method for recovering hydrocarbons in liquid form from waste gas containing hydrocarbons. 6. A liquefied hydrocarbon obtained by recovering the gaseous hydrocarbon as a liquid is returned to a purge exhaust gas cooler,
The method for recovering a hydrocarbon from a waste gas containing a gaseous hydrocarbon according to claim 1, wherein the hydrocarbon is brought into contact with an uncondensed gas in a purge exhaust gas. 7. A liquid hydrocarbon is dropped into the waste gas,
Or spraying to increase the concentration of hydrocarbons in the waste gas, and pre-coating the adsorbent layer with hydrocarbons to remove hydrocarbons from the waste gas containing gaseous hydrocarbons according to claim 1. Method to recover in liquid form. 8. The waste gas containing a gaseous hydrocarbon according to claim 1, wherein the waste gas is a waste gas containing 3000 ppm or less of a lean gaseous hydrocarbon. A method for recovering hydrocarbons in liquid form. 9. The gaseous hydrocarbon according to claim 1, wherein the hydrocarbon concentration in the clean gas discharged from the adsorption device to the atmosphere is 100 ppm or less. A method for recovering hydrocarbons from waste gas in liquid form.