WO2000048713A1

WO2000048713A1 - Method for treating dilute gaseous hydrogen carbide contained in waste gas and device for performing the method

Info

Publication number: WO2000048713A1
Application number: PCT/JP2000/000513
Authority: WO
Inventors: Hiroshi Tahara; Hiroshi Nochi; Hideki Sakuma
Original assignee: System Eng Service Co., Ltd.; Shinko Plantech Co., Ltd.; Tsuru, Yoshiko
Priority date: 1999-02-17
Filing date: 2000-01-31
Publication date: 2000-08-24
Also published as: JP3133988B2; JP2000300955A; KR20010114209A; AU2323300A

Abstract

A method for treating waste gas and a device for performing the method, which can treat a large amount of waste gas containing dilute gaseous hydrogen carbide for separation of the dilute gaseous hydrogen carbide safely, easily and efficiently, and can reduce, after the treating, a gaseous hydrogen carbide concentration remaining in the waste gas to be exhausted into the air to up to 100 ppm. The method comprises the steps of (1) using as an adsorption device an adsorbent layer and adsorption columns (1a, 1b) for cooling the layer, (2) filling into the adsorption columns active carbon and Y-type synthetic zeolite over the active carbon, (3) switching between adsorption and desorption alternately at a switching timing determined by operating automatically adsorption/desorption switching valves (d) according to an instruction of 'an estimated concentration at which the absorbent layer breaks through' by a data logger, (4) using 'water' at adsorption and sucking it by a water-sealed vacuum pump (14), and (5) returning the entire amount of purged exhaust gas into a waste gas feed pipe (11) while (6) treating liquid from a gas/liquid separator (16) at an industrial waste treating device (17).

Description

Description: A method for treating a lean gaseous hydrocarbon contained in waste gas and an apparatus for performing the method. Technical field

The present invention relates to a method and an apparatus for treating lean gaseous hydrocarbons contained in waste gas, and more particularly to efficiently separating hydrocarbons from waste gas containing harmful gaseous hydrocarbons that cause air pollution. And a detoxifying method and apparatus.

Specifically, as harmful gaseous hydrocarbons, for example, gaseous substances such as benzene, toluene, methylethylketone, trichloroethylene, and chlorofluorocarbon, which are carcinogenic and are one of the three substances causing air pollution The present invention relates to the treatment of waste gas containing hydrocarbons, and relates to the treatment method and apparatus for reducing the concentration of hydrocarbons to 100 ppm or less (preferably 10 ppm or less) and discharging the hydrocarbons to the atmosphere. Background art

Gaseous hydrocarbons, such as benzene, toluene, methyl ethyl ketone, trichloroethylene, and chlorofluorocarbon, which are one of the main causes of air pollution, are released into the atmosphere in the United States, Europe, Japan, and other developed countries. Concentrations are strictly regulated by law. 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 in Japan, the Environment Agency Notification No. 5 (February 6, 1997) According to the Japanese government, the regulation was restricted to “30 ppm or less”.

By the way, a particularly problematic source of such gaseous hydrocarbons is, for example, a large amount of diluted waste gas of about 500 ppm or less generated in a printing factory, a cleaning factory, a painting factory, and the like. Yes, it is waste gas generated not only at factories but also at the time of unloading and unloading from tanks storing them.

<Conventional technology related to waste gas treatment method> As a method for detoxifying waste gas containing gaseous hydrocarbons as described above, methods that have been widely used in the past include:

(1) Gas separation membrane method + adsorption method

(2) Adsorption method using activated carbon zeolite, hydrophobic silica gel, etc.

And so on.

Of the above methods, the method (1) is a mainstream technology in Europe. If the amount of waste gas is large, the adsorption method is used as a polishing step in the treatment after the gas separation membrane method (pressurized membrane method). It is used. In Japan, as disclosed in Japanese Patent Publication No. 4-235658 / Japanese Patent Publication No. Hei 7-2846423, technologies belonging to this field are disclosed.

On the other hand, the most widely used method in the United States is the adsorption method (2), particularly the adsorption method using activated carbon. This method is disclosed in Japanese Patent Application Laid-Open No. 57-146687, Japanese Patent Application Laid-Open No. 57-42319, Japanese Patent Publication No. 59-50715, Japanese Patent Publication No. — It is disclosed in Japanese Patent Publication No. 507716 and Japanese Patent Publication No. 2-46663. With the current state of the art, the above-mentioned methods for processing large amounts of waste gas containing dilute gaseous hydrocarbons to reduce the hydrocarbon concentration in clean gas released to the atmosphere to less than 100 ppm are as described above. The adsorption method using activated carbon is the best 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. Strong.)

However, in the conventional adsorption method using activated carbon, "steam" is usually used as a purge gas at the time of desorption. The amount of steam required for desorption is about three times the amount of adsorbent used, requiring a large amount. In addition, hydrocarbons are entrained and mixed in when this steam condenses into water, so that clear water quality standards require a considerable burden on wastewater treatment facilities such as the activated sludge process. There were drawbacks.

For this reason, it has been proposed to use "heated nitrogen" instead of steam as the purge gas for desorption, and to recycle it. Separation of lean gaseous hydrocarbons requires a large refrigerator and must be cooled to a low temperature of less than o ° c, which is rather uneconomical.

As a means for solving the above-mentioned problems, as disclosed in Japanese Patent No. 28323835, prior to recovering gaseous hydrocarbons from the purged exhaust gas, a power scale method is used. One of the solutions is to concentrate the dilute gaseous hydrocarbons in the purged exhaust gas through a concentration adsorption tower (adapter) and remove it from this concentrated adsorption tower (adapter).

In addition, when the adsorption tower is switched to the desorption tower and suction is performed by the vacuum pump, the gas is discharged in a state where gaseous hydrocarbons in the purged exhaust gas have been concentrated by applying a displacement purging means to the desorption tower in advance. A method for cooling and liquefying the purged exhaust gas is one of the solutions.

In any of the above-mentioned means, liquefaction of gaseous hydrocarbons in the purged exhaust gas is possible only by cooling the purged exhaust gas, but involves means for concentrating the gaseous hydrocarbons in the purged exhaust gas, Moreover, it can be said that the enrichment means itself is complicated.

In addition, in the case of hydrocarbons having a low boiling point, any of the above-mentioned means is not easily cooled and requires a powerful refrigerator, so that it is complicated to concentrate lean gaseous hydrocarbons. It is.

Therefore, in order to overcome the above drawbacks, Oite activated carbon adsorption method has been widely used conventionally, when processing a large amount of gas that per minute hundred m ^3, are used primarily fibrous active carbon, On the other hand, as an apparatus, there has been used an “adsorption apparatus in which a large number of cylinders or boxes are arranged inside” in which the adsorbent layer made of the fibrous activated carbon is thinly surrounded by a thickness of several cm to several hours. "K-filter (trade name, manufactured by Nitto Bo)" or "Pyromex (trade name, manufactured by Toho Rayon Co., Ltd.)" is used. In this method, a dilute hydrocarbon is adsorbed over a long period of time of several tens of minutes to several hours without being concentrated as in the present invention which will be described later, and then desorbed by steam.

However, a feature of this method is that it has a sorbent layer so that it can process large quantities of gas. However, it is difficult to reduce the hydrocarbon concentration in the gas discharged into the atmosphere to "100 ppm or less".

Conventional technology relating to means for switching between absorption and desorption>

On the other hand, in the method for treating waste gas containing gaseous hydrocarbons by the adsorption method, switching between adsorption and desorption is controlled by a time control via a solenoid valve. However, when switching by time control, it is necessary to know in advance the time required for the adsorption tower to break through experiments and experiences.

Switching by time control is straightforward, but if the amount and concentration of gaseous hydrocarbon at the inlet of the adsorption tower constantly fluctuates greatly, the adsorbent should be filled more than required and then switched earlier. Is forced. Therefore, there was a problem that the adsorbent was not used effectively.

In order to solve the above problems, a method of detecting the breakthrough of the adsorption tower using various measuring instruments and switching to desorption when the concentration reaches a level at which breakthrough can be detected has been used for some time.

However, the concentration at the time of breakthrough is a trace concentration of several 10 ppm or less according to the recent severe air pollution control law, and the concentration that requires detection before that is 1-2 ppm. The order is as follows, and requires a very dog-based and precise measuring device.

In addition, various proposals have been made for the above detection method since ancient times. For example, Japanese Patent Publication No. 55-39996 describes

"Adsorption, using a twin tower PSA purifier desorption performs adsorption wet gas in a state where pressurized adsorption tower 5 ~ 1 O kg Z cm ² without using a vacuum pump, dry from the top In the dehumidification method in which the gas is released and the adsorption gas is discharged and regenerated by returning the pressure of the tower to normal pressure, the gas flow rate through the adsorption tower that changes every moment, the inlet and outlet of the adsorption tower The microcomputer stores the operating conditions of each part, including temperature, inlet and outlet pressures of the adsorption tower, and regeneration pressure of the desorption tower, as data, and calculates the material balance and heat balance instantaneously. A method that controls the desorption time and indirectly automatically controls the timing of switching between adsorption and desorption. " Is disclosed.

The method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-35996 is a method in which switching between adsorption and desorption is performed not by time control but by a microcomputer in which the operating state of the device is stored. It was an epoch-making proposal in that it was left to the public, but at the time, there was no superior adsorption model as at present, so 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 adsorbed component in the gas is quickly detected from the measurement port embedded in the adsorbent layer, and the solenoid valve is automatically switched when the concentration reaches a certain level. Proposed.

However, when the adsorbent has a pore size of 10 OA from 5 people, such as granular activated carbon or silica gel, the concentration and temperature fluctuate locally. There is no guarantee that it will rise toward the exit with a uniform width without deviation. Therefore, it is difficult to specify the position to be measured. If the measurement port is inserted too deep from the top, it is hard to say that it is better than time control. For this reason, at present, the mainstream technology for switching between absorption and desorption is simple time control.

The present invention has been made in view of the problems and disadvantages of the prior art described in the above section <Prior art related to waste gas treatment method> and <Prior art related to absorption / desorption switching means>. This is an attempt to further improve the prior art.

And, the present invention concentrates the dilute gaseous hydrocarbons contained in a large amount of waste gas, extracts it as an extremely small amount of gas as a whole, and incurs an economic burden in incineration, industrial waste treatment, or liquefaction. The objective (technical issue) is to reduce significantly.

The present invention also provides a method and an apparatus for detoxifying a large amount of waste gas containing a dilute gaseous hydrocarbon, wherein the waste gas is treated using a solid adsorbent such as hydrophobic silica gel, activated carbon, or synthetic zeolite. Safe, easy and efficient separation of harmful hydrocarbons from gas, and residual gas in waste gas released into the atmosphere after treatment An object of the present invention is to provide a "method for treating a lean gaseous hydrocarbon contained in waste gas and an apparatus for performing the method", which can make the concentration of gaseous hydrocarbon less than 100 ppm.

Still another object of the present invention is to provide a method and apparatus which 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. Disclosure of the invention

The method according to the present invention (the method for treating a lean gaseous hydrocarbon contained in waste gas) is as follows:

(1) alternately performs adsorption and desorption using an "adsorption unit having an adsorbent layer", [especially when dealing with large volumes of waste gas hundreds m ³ per minute, multi internal adsorbent layer Using a double-placed adsorption device (see (9) to (12) below)

The waste gas containing gaseous hydrocarbons is passed through one of the adsorbers, the gaseous hydrocarbons are adsorbed by the adsorbent layer in the adsorber, and the waste gas containing substantially no gaseous hydrocarbons is discharged into the atmosphere. Release to

In the meantime, the other adsorber is switched to desorption, and the gaseous hydrocarbon adsorbed on the adsorbent layer in the adsorber is desorbed by suction with a vacuum pump, and is converted into waste gas, which is transferred to purged exhaust gas. In the method of treating lean gaseous hydrocarbons contained,

Returning all or most of the purge exhaust gas to the waste gas to be treated, thereby increasing the hydrocarbon concentration in the adsorbent layer and switching to desorption before the adsorbent layer breaks through;

(Characterizing the invention).

And according to the method of the present invention, as described above,

• Return all or most of the purged exhaust gas to waste gas to increase the concentration of hydrocarbons in the adsorbent layer (first feature).

• Switch to desorption before the adsorbent layer breaks through (second feature), This makes it possible to safely, easily, and efficiently treat hydrocarbons from waste gas, and reduce the concentration of residual hydrocarbons in the gas released into the atmosphere after treatment to 100 ppm or less. In particular, it can be "less than 20 ppm".

Also, the method according to the present invention comprises:

(2) When a part of the gaseous hydrocarbons in the purged exhaust gas is liquefied, the liquid hydrocarbons are burned or detoxified as industrial waste, whereby the gaseous carbon Complex means associated with the recovery of hydrogen can be avoided.

Further, in the method according to the present invention,

(3) The adsorbent layer is composed of a layer of activated carbon and Z or hydrophobic silica gel, and a synthetic zeolite layer is disposed on top of the layer.

By combining such an adsorbent, the temperature in the adsorbent layer can be easily and promptly kept constant at around room temperature, and the performance of the adsorbent can be fully exhibited without waste.

In the method according to the present invention,

(4) A gaseous hydrocarbon is pre-coated on the adsorbent or the adsorbent layer filled in the adsorption device,

As a result, it is possible to prevent the adsorption of nitrogen gas and oxygen gas in the waste gas, which is originally preferentially adsorbed, as well as the adsorption of water, and to effectively adsorb gaseous hydrocarbons in the waste gas. Can be utilized very effectively.

Further, in the method according to the present invention,

(5) Air or liquid "water" heated above the boiling point of the hydrocarbon to be adsorbed is used as a means for releasing gaseous hydrocarbons adsorbed on the adsorbent layer in the adsorption device. .

However, when heated air is used, an adsorbent other than activated carbon is used. When using nonflammable hydrophobic silica gel other than activated carbon, for example, air having a high temperature of up to 250 ° C can be used as a purge gas.

In addition, in the method according to the present invention, particularly when liquid “water” is used, this water is vaporized inside the desorption device in combination with the vacuum pump, and works in the same manner as the purge gas. In addition to the use of steam, the amount of vaporized gas has the remarkable effect of being able to be purged with a gas amount as small as "several tenths" when using conventional steam.

The “means for switching to desorption before the adsorbent layer breaks through” that is the second feature of the present invention includes:

(6) A temperature detection port is provided at the top of the adsorbent layer, and the solenoid valve is automatically switched when the temperature from the temperature detection port stops rising.

(7) The “inlet gas flow rate”, “hydrocarbon concentration in the inlet gas”, and “desired hydrocarbon concentration in the outlet gas (assumed value)” of the adsorption device obtained during the adsorption operation are written as numerical data on the chip. The switching time is set in advance by using a simulation model for control incorporated in the chip.

By employing these means, it is possible to automatically detect the breakthrough point of the adsorbent layer and automatically switch between adsorption and desorption.

And according to the method of the present invention,

(8) The hydrocarbon concentration in the clean gas discharged from the adsorption device into the atmosphere can be reduced to 100 ppm or less.

On the other hand, the device according to the present invention

(9) An apparatus for performing the processing method according to any one of (1) to (8),

The "adsorption device having an adsorbent layer" in the device is composed of a component including an adsorbent layer, and the component is composed of a container that can be sealed but cannot be closed, that is, a container for containing the adsorbent. Regardless of the shape, the filled adsorbent does not leak from the container, and the container is provided with a large number of fine holes through which gas can flow in and out. Container,

Is a feature (items that specify the invention),

(10) The “adsorption device having an adsorbent layer” is an adsorption device that surrounds the adsorbent layer and has multiple built-in cylinders through which waste gas can be passed in the circumferential direction. (11) The enclosure of the adsorbent layer is a box-type component or a honeycomb-type component, and an adsorber that incorporates the component in a multiplex manner.

(1 2) The adsorbent layer is a layer filled with fine adsorbent having a diameter of 0.1 to 1 mm,

This makes it possible to provide a device suitable for treating a large amount of waste gas of several hundred m ³ per minute. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flow sheet diagram for explaining “a method for treating a lean gaseous hydrocarbon in a waste gas” which is one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a “control panel for grasping and controlling an operating condition” in the flow sheet shown in FIG.

FIG. 3 is a longitudinal sectional view of an adsorption tower used in Example 1 of the present invention.

FIG. 4 is a longitudinal sectional view of the adsorption tower used in Embodiment 2 of the present invention.

FIG. 5 is a diagram further illustrating the adsorption tower of FIG. 4, wherein FIG. 5 (A) is a sectional view taken along line AA of FIG. 4, and FIG. 5 (B) is a diagram of FIG. It is the elements on larger scale of the figure. FIG. 6 is a diagram showing a “water adsorption isotherm of activated carbon”.

The symbols in the figure are 1a and 1b for the adsorption tower, 2a and 2b for the outer cylinder, 3a and 3b for the adsorbent layer, 3-la and 3-lb for activated carbon, 3-2a and 3-lb. 3-2b is a Y-type synthetic zeolite, 4a and 4b are inner cylinders, 5 is cooling water, 10 is a waste gas generation source, 11 is a waste gas air pipe, 12 is a discharge pipe, and 13 is a discharge pipe. Water pipe, 14 is a water ring vacuum pump, 15 is a purge exhaust gas pipe, 16 is a gas-liquid separator, 17 is an industrial waste treatment device, 18 is a return gas air pipe, 20 is a control Board, 21 is memory, 22 is CPU (calculation), 23 is memory (adsorption model), 41a (41b) is adsorption tower, 42a (42b), 42a ' (4 2 b ') is the outer cylinder, 4 3 a (4 3 b) is the adsorbent layer, 4 3-1 a (43 -lb) is crushed activated carbon, and 4 3 -2 a (43-2b) is Y-type synthetic zeolite. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a method and an apparatus according to the present invention (hereinafter, simply referred to as “the present invention”) will be described, and the present invention will be described in more detail.

As described above, the first feature of the present invention lies in "returning all or most of the purged exhaust gas to the waste gas to be treated and increasing the hydrocarbon concentration in the adsorbent layer". Is to switch to desorption before the adsorbent layer breaks through, thereby safely, easily and efficiently treating hydrocarbons from waste gas, and after treatment, to the atmosphere. The residual hydrocarbon concentration in the released gas can be less than 100 ppm, especially "less than 20 ppm".

First, the first feature of the present invention will be described. In one embodiment of the method according to the present invention, the entire amount of the purged exhaust gas is returned to the waste gas to be treated, but the hydrocarbon concentration in the purge exhaust gas is reduced. At extremely high levels, the adsorbent layer will break through in a very short time, which will adversely affect the treatment of waste gas. Therefore, as another embodiment of the present invention, when the hydrocarbon concentration is extremely high, a part of the purged exhaust gas is taken out, detoxified, for example, subjected to a combustion process, and the remaining (most) It is desirable to return the purge exhaust gas to the waste gas to be treated.

Further, when a part of the gaseous hydrocarbons in the purged exhaust gas is liquefied, the liquid hydrocarbons can be separated and burned, or detoxified as industrial waste.

Next, the second feature of the present invention, that is, "switching to desorption before the adsorption device breaks through" will be described. The breakthrough detecting means of the present invention basically includes a device. Although it is based on a built-in circuit chip, it uses an ultra-small chip, which has recently made remarkable progress, so that the above-mentioned known technology (the technology disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-35996) is used. It does not require a large microphone processor for the purpose of calculation as described in (1).

In addition, according to a preferred embodiment of the present invention, instead of picking up data obtained during operation and calculating only the material balance and heat balance, the adsorption model is entered into R〇M, while By reading the operation data that changes during the operation as a logger signal into a computer and simulating it, the breakthrough concentration is preferably reduced. This is completely different from the prior art in that it attempts to control the adsorption system by predicting in seconds. In other words, 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.

By the way, various types of "adsorption model" have been proposed. Among them, the physical properties of the adsorbent, that is, "adsorption isotherm and adsorption pressure inside adsorption tower, vacuum degree of vacuum pump, gas flow rate in tower" , The height of the adsorbent layer and the purge coefficient are fixed, and the variable “inlet gas flow rate and concentration” is used as the switching time or the outlet of the adsorbent layer. The so-called "Frozen Model", in which the concentration (breakthrough concentration) is input to the chip as an assumed value and calculated, is famous.

In addition, an "equilibrium model", which takes time but is excellent in accuracy, is also known, but the "adsorption model" used in the present invention is not particularly limited to these.

The second feature of the present invention, that is, "switching to desorption before the adsorption device breaks through" is an essential component, because the first feature of the present invention, "purge exhaust gas" Is returned to the waste gas to be treated to increase the hydrocarbon concentration in the adsorbent layer. "

In other words, when the amount of waste gas to be treated and the concentration of gaseous hydrocarbons contained therein are not constant and change every moment, and it is difficult to predict in advance the time until breakthrough, By mixing the uncondensed purge exhaust gas with the waste gas (by adopting the first feature point), the hydrocarbon concentration in the adsorber inlet gas and the hydrocarbon concentration in the adsorbent layer in the adsorber are reduced. Both of them change even more, and it becomes even more difficult to predict the time until breakthrough. Therefore, in order to solve this problem, the above-mentioned second characteristic point is set as an essential component.

However, the present invention does not eliminate 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 tower (waste gas / the above-mentioned uncondensed page exhaust gas) is almost constant over time, the operation of the adsorption tower is started and the destruction occurs. This is because it is one of the expedients to determine the time until the time is spent in advance, and to switch using this time as a guide in the next suction operation. You. In addition, in the adsorption apparatus developed by the present inventors, it is one of the options to adopt a “switching means by time control” by predicting the time when desorption is completed from the operation of the desorption tower. is there. That is, contrary to the above-described example (switching the adsorption tower to the desorption tower), the means for switching the desorption tower to the adsorption tower can be time-controlled. If this means is described in detail, the operation shifts to the desorption operation, the vacuum pump starts operating, and after detecting the point when a predetermined degree of vacuum is reached, purge gas is introduced into the desorption tower, and this introduction time is set in advance. This is a method that automatically switches to the suction operation when the time is up.

As described above, in the case where the flow rate and the concentration of the inlet gas fluctuate, according to a preferred embodiment of the present invention, the concentration of the gaseous hydrocarbon adsorbed on the adsorbent layer is automatically reduced to just before the breakthrough. It can be concentrated to a high concentration.

Then, after taking out this as a small amount of purge exhaust gas, as described above, a part of this purge exhaust gas can be taken out and subjected to, for example, a combustion treatment, and gaseous hydrocarbons in the purge exhaust gas can be removed. It can be separated as liquid hydrocarbons and burned, or detoxified as industrial waste.

However, while having such advantages, the disadvantage is that if the time required for adsorption and the time required for desorption are too different, for example, it takes several days before adsorption and just before breakthrough, If the desorption process takes only a few hours, it is not necessarily the preferred method from the perspective of the person managing the work.

Therefore, 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, which is generated. The amount of heat absorbed is extremely reduced, and more heat is radiated outside from the cooling water and the wall of the adsorption tower. As a result, the signal from the measurement port inserted near the top to capture data into the chip, ie, the indicated temperature, stops, and the temperature gradually decreases over time. If the means for automatically switching the intake / desorption switching valve (solenoid valve) at this time is used together, the above-mentioned disadvantages can be solved, and this is also included in the present invention.

“Appropriate adsorbent” means that the adsorption pore diameter is controlled to a certain size, Adsorbents that are unlikely to cause unevenness in the amount of adsorption and that do not easily adsorb moisture even in areas where the relative humidity in the waste gas is as high as about 50% or more.For example, an adsorbent such as synthetic zeolite is optimal. .

Therefore, as an example of a preferred embodiment of the present invention, a synthetic zeolite layer is provided on the top of the adsorbent layer, and a temperature detection port is provided in the adsorbent layer made of the synthetic zeolite. However, means for automatically switching the solenoid valve when the temperature from the temperature detection port stops increasing its temperature is adopted. As the adsorbent to be filled in the lower part of the adsorbent layer composed of the synthetic zeolite, pre-coated activated carbon or similarly pre-coated hydrophobic silica gel is preferable.

Here, the technical significance of the above-mentioned “precoat”, which is a preferred embodiment of the present invention, will be described.

The degree to which gaseous hydrocarbons are concentrated in the adsorbent layer is, theoretically, "760725" if only hydrocarbons are adsorbed when the degree of vacuum is 25 mm Hg, That is, the density is about 25 times higher, but usually a large amount of air coexists, and the molecular diameter of nitrogen gas or oxygen gas in this air is larger than that of hydrocarbons. Therefore, nitrogen gas and oxygen gas are adsorbed in preference to hydrocarbon gas. As a result, it is empirically known that it can only be concentrated to four times the concentration of hydrocarbons at the inlet.

In addition, 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 target concentration.

When the gas to be adsorbed is moist air, almost no water is adsorbed when the relevant temperature is less than about 40%, but water is rapidly adsorbed when the temperature exceeds 50% (see Fig. 6). Fig. 6 shows the water adsorption isotherm of activated carbon, but the same can be said for other hydrophobic adsorbents.

Therefore, it is desirable to pre-coat the adsorbent layer in order to prevent the adsorption of nitrogen gas, oxygen gas, and moisture in waste gas which is originally preferentially adsorbed. As a pre-coating method, for example, the adsorbent layer is pre-coated by dripping liquid hydrocarbons into the waste gas to be treated, specifically, by spraying the liquid hydrocarbons into the conduit of the waste gas to be treated. can do. As the pre-coating agent, in addition to the above liquid hydrocarbons, for example, substances such as hydrocarbons having an affinity for water and having a higher boiling point than water can be used.

As described above, the present inventor developed a system for processing a large amount of waste gas containing gaseous hydrocarbons, using the elemental technology on the hard surface called “loga signal”, which is a means for capturing data, in this system. By using a new technique on the so-called soft surface, that is, a “simulation of a ROMized adsorption model” that has been cleverly incorporated into the control system, it is possible to shorten the time regardless of the change of the hydrocarbon concentration at the inlet. By easily estimating the breakthrough concentration in time and selecting an appropriate adsorbent, the temperature in the adsorbent layer was easily and promptly kept constant at around room temperature.

As a result, the timing of switching from adsorption to desorption is not simply set by a cycle of time, but is left to the discretion of a personal computer (software) that incorporates an "adsorption model", thereby reducing the performance of the adsorbent without waste. It is now possible to make full use of it. For this reason, it became possible to concentrate the lean hydrocarbons in the purge exhaust gas to just before breakthrough, and to extract it as an extremely rich hydrocarbon with a very small amount of purge exhaust gas.

(About adsorbent)

As the adsorbent used in the present invention, any solid adsorbent having an affinity for the hydrocarbon gas in the waste gas can be used regardless of whether the material is flammable or nonflammable.

However, when the concentration of hydrocarbons in the waste gas is as low as about 500 ppm, hydrophobic silica gel which is inexpensive and easy to handle is desirable. The reason is no. —Because the temperature of the digas can be raised to about 250 ° C for use.

When using non-combustible silica gel, if it is hydrophobized with a silane coupling agent such as trimethylchlorosilane or treated at high temperature for a long time, it will be hydrophobic and lipophilic. Preferred are adsorbents or adsorbents precoated with high boiling hydrocarbons such as ethylene glycol heptane. But the best adsorbent is

It is a solid adsorbent that absorbs only a few% of water, even if R H is 50% or more.

In the first place, solid adsorbents such as activated carbon, synthetic zeolite, silica gel, and activated alumina used as adsorbents have strong affinity for gaseous hydrocarbons, but are also widely used as heat insulators. Apart from synthetic zeolite, the other adsorbents have a wide distribution of adsorption pore diameters, so that the concentration at the adsorption site is not uniform and mouth-to-mouth heating tends to occur.

Generally speaking, in the case of hydrophobic silica gel or granular activated carbon, depending on the particle size and the temperature rise, for a thickness of about 4 inches or more, the heat of adsorption can be transferred to the cooling water layer in a short time. It is not possible.

Therefore, with a thickness of 4 inches or more, heat transfer in the circumferential direction cannot be expected so much, and it depends on heat transfer carried out by gas flowing in the vertical direction. For this reason, it is a problem whether or not the adsorption zone having a certain width moves uniformly and uniformly toward the outlet of the adsorption tower, affected by the temperature distribution in the adsorption tower. That is, there is no problem when the concentration at the time of breakthrough is detected at the outlet of the adsorption tower, but it is a problem when viewed at the detection port disposed at the position embedded in the adsorbent.

The recommended way to avoid this is to place the synthetic zeolite at the top of the adsorbent layer, ie, near the outlet. For example, Y-type zeolite “360 HUD (product name of Tosoh Corporation)” or the like.

Synthetic zeolite, unlike hydrophobic silica gel or granular activated carbon, has a strictly controlled pore size to a certain size.Depending on the material selected, some varieties cover almost the entire molecular diameter of gaseous hydrocarbons. is there. In addition, despite the fact that the ratio of adsorbing gaseous hydrocarbons is 15% to 20% by weight, the amount of water adsorbed is 10% even for gases with RH of 50% or more. % Or less. For this reason, there is no deviation in the adsorption band having a certain width moving in this layer.

In addition, the port for detecting the concentration and temperature to be taken in as a data logger signal must be located at the center of the synthetic zeolite layer. In this way, the breakthrough point is detected. In addition to the above-mentioned means, the point at which the temperature indication at the central portion stops the temperature rise due to the heat of adsorption can be used as a guide for switching. Such synthetic Zeorai DOO, the ratio of S i 0 _2, A 1 ₂ 0 ₃ is 2 0 or more, those having a pore size of about 8 angstroms Ichimu is desirable.

(About the adsorption device)

Next, embodiments (first and second embodiments) of the “adsorption device having an adsorbent layer” used in the present invention will be described.

(First embodiment of the adsorption device)

In the first embodiment of the "adsorption device having an adsorbent layer" used in the present invention, in order to locally uniform the temperature and concentration of the adsorbent layer, the heat of adsorption generated in the adsorbent layer is used. As a means for quickly moving and removing the adsorbent layer in the lateral direction, an adsorbent layer for adsorbing gaseous hydrocarbons and a cooling water layer for cooling the adsorbent layer are adjacent to each other. It is preferable to use a “double cylinder or multiple cylinder type adsorption tower” configured. In consideration of the tendency of static electricity generated in the adsorbent layer to gather at the center of the layer, use of an adsorption tower with a structure in which a metal cylinder is arranged at the center to release static electricity while also cooling. Is desirable.

The specific adsorption tower of the first embodiment used in the present invention will be described with reference to FIG. 3. The adsorption tower 1a (1b) comprises an outer cylinder 2a (2b) and an adsorbent. Layer 3 a (3 b), inner cylinder 4 a (4 b), and cooling water 5.

The adsorption tower 1a (1b) is an adsorption tower used in Example 1 of the present invention described later, and 3-la (3-lb) in the figure is activated carbon, and 3-2a ( 3-2b) is a Y-type synthetic zeolite.

One of the points to be noted as the adsorption tower 1a (1b) of the present invention is that if the pressure inside the adsorption tower is increased, the effective adsorption amount of hydrocarbons adsorbed by the adsorbent is remarkably increased. since the pressure is a matter of course to say from the theory of PSA process, even in the practice of the present invention, the gauge pressure "1 kg / cm ² or less that does not conflict with the internal pressure of the adsorption tower la (lb) to the" high pressure regulations " Working with "is highly desirable.

(Second embodiment of the adsorption device) In the present invention, a conventionally used “tower-type, adsorption device that is densely packed with an adsorbent” can also be used, but when the amount of waste gas to be treated is large, In this case, a problem arises with this conventional type.

To explain this problem in detail, for example, when processing 36,000 m ³ of waste gas per hour, the conventional type requires a tower diameter of about 1 Om.

The reason is that there is a limitation on the passage speed of waste gas passing through the adsorbent layer [that is, the time of contact with the adsorbent (SV value)] in terms of adsorption efficiency. Generally, this speed is set to a value below which the adsorbent particles do not flow, and is usually "10 to 20 cmZ seconds". Calculating the average value of this gas passage velocity "15 cmZ seconds (0.15 m / sec)" results in "1 Om" as shown in the following equation.

'Formula: TTR ² XO. 15 = 3 6, 0 0 0/3, 6 0 0 = 1 0

In the present invention, it is not practical to use an adsorption tower having such a diameter.

On the other hand, adsorption efficiency is closely related to the size of the adsorbent particles. For example, when comparing the case where a large particle size adsorbent and a small particle size adsorbent are packed in an adsorbent layer of the same capacity, it is natural that the smaller the particle size, the higher the efficiency, but the higher the flow rate. There is a problem even if it is too small. For this reason, the diameter of the conventionally used adsorbent depends on the type and shape of the adsorbent, but 2-3 mm is appropriate.

The adsorber, which avoids the flow of the adsorbent and is densely packed, has a structure in which the cross of fibrous activated carbon is coordinated inside the adsorber and the waste gas flows in the direction across the cloth. There are specific examples of the above-mentioned "K-filter (trade name, manufactured by Toyobo)" and "Pyromex (trade name, manufactured by Toho Rayon Co., Ltd.)". The adsorber with the above structure has the advantage that a large gas passage area can be obtained, but has the disadvantage that the adsorbent layer is thin, so that the contact time is short and dilute hydrocarbons in waste gas cannot be collected sufficiently. are doing.

In addition, the desorption means of this device cannot be considered other than the use of steam, and cannot be used together with a vacuum pump.

In terms of adsorption theory, the adsorption efficiency is "Kfav", that is, "overall mass transfer capacity" The value of the coefficient (1 / sec) is shown in the following table. From the experiments conducted by the present inventor and the analysis of the operation results with the industrial equipment constructed by the present inventor, the value of K fav When the adsorbent is used, it is almost in the range of "3 to 6", depending on the properties of the gaseous hydrocarbon.

On the other hand, when fibrous activated carbon is used, the adsorption performance is several times better in the range of "15 to 25". Specifically, the contact time between the gas and the adsorbent is "about 1 Z5".

By paying attention to this point, the present inventor has developed a novel and economical adsorption apparatus that can be applied even when the amount of waste gas to be treated is large [adsorption apparatus having an adsorbent layer used in the present invention] 2nd Embodiment] was developed.

As a novel and economical adsorption device (adsorption tower according to the second embodiment) of the present invention, an adsorption device having an adsorbent layer is composed of a component including an adsorbent layer, and the component can be hermetically sealed. It consists of a container that cannot be closed, that is, regardless of the shape of the container containing the adsorbent, the filled (contained) adsorbent does not leak out of the container, and It is a container that has a configuration with many micropores that allow gas inflow and outflow.Specifically,

The adsorbing device having an adsorbent layer is an adsorbing device that surrounds the adsorbent layer and has multiple built-in cylinders through which the waste gas can be passed in the circumferential direction;

The enclosure of the adsorbent layer is a box-type component or a honeycomb-type component, and is an adsorption device in which the component is multiplexed;

It is characterized by.

As the adsorbent to be filled (contained), fine particles of 0.1 to 1 mm (preferably fine particles of 0.2 to 0.5 mm) are used, thereby shortening the contact time with the gas, In addition, the configuration of the adsorbent layer in the adsorber is multiplexed to increase the gas passage area.

As described above, the use of fine particles of 0.1 to 1 mm as the adsorbent has an excellent effect that the contact time can be reduced to "about 1/5" as compared with the conventional means. And to say that it can be reduced to "about 1 Z5" This means that the thickness of the adsorbent layer will also be "about 1 Z5".

Conventional commercial plants are all single towers, and the thickness (layer height) is “l to 2 m”. However, in the adsorption apparatus of the present invention, the thickness of the adsorbent layer is “about 1 Z5”. From that point, the thickness is "20 cm to 40 cm", and as a result, there is an excellent effect that the adsorbent layer does not need to be cooled in principle.

The reason is that the hydrocarbon gas contained in the large amount of waste gas passing through the adsorbent layer is extremely dilute, and most of it is air, so the amount of heat absorbed exceeds the amount of heat carried out by the air and remains in the adsorbent layer Because there is nothing.

Moreover, in the conventional adsorption apparatus using the fibrous activated carbon layer described above, the concentration of the adsorbed hydrocarbon is extremely low because the waste gas ends up in one pass through this adsorbent layer, and the means for desorption is other than steam. I could not imagine. In the above-described adsorption apparatus of the present invention, since the entire or most of the purged exhaust gas is returned to the waste gas to be treated, the hydrocarbon concentration in the adsorbent layer can be increased. This makes it possible to use a vacuum pump that could not be achieved by using a vacuum pump.

By using a vacuum pump, water can be used as a purge medium for desorption. (For details on "Using vacuum pump" and "Using water as purge medium", see below.)

Regarding a specific adsorption tower of a novel and economical adsorption apparatus [the second embodiment of the “adsorption apparatus having an adsorbent layer” used in the present invention], which exhibits the above-mentioned remarkable effects of the present invention, Referring to Fig. 4 and Figs. 5 (A) and 5 (B), the adsorption tower 41a (41b) is filled with the adsorbent layer 43a (43b). The outer cylinder is composed of a double cylinder of 42a (42b) and 42a '(42b'). Then, the waste gas passes through the adsorbent layer 43a (43b) as shown by the arrow line in Fig. 5 (B), thus increasing the gas passage area. It is.

This adsorption tower 4 la (41b) is an adsorption tower used in Example 2 of the present invention described later, and 43-1a (43 -lb) in the figure indicates crushed activated carbon, 43 -2a (43-2b) is a Y-type synthetic zeolite.

(About system integration) Furthermore, the inventor of the present invention has made the present invention as a result of intensive studies to integrate the apparatus proposed in the present invention as a system and to make the apparatus portable so that it can be mounted on a skid. .

That is, the adapter-type system disclosed in Japanese Patent Nos. 2,840,563, 2,766,793, and 2,382,335, which have already been obtained by the present inventors. Instead of using the purging method and the purging method, the gaseous hydrocarbons in the purged exhaust gas are recovered without using a method of washing with the same type of hydrocarbon liquid, and the desorbed gas is recycled. Instead of using a complicated cooling means to recover gaseous hydrocarbons from the gas as a liquid after enriching the hydrocarbon concentration in the adsorption tower, a simple and economical method in which the recovery means is omitted is provided. Provided.

(About desorption means)

In the present invention, air or water heated above the boiling point of the hydrocarbon to be adsorbed can be used as a means for releasing gaseous hydrocarbons adsorbed on the adsorbent layer. Of these, the use of "water" is particularly preferred (see below).

(Note that as this air, a part of the clean gas discharged into the atmosphere from the adsorbent layer can be used.)

Conventionally, in the field of application of the present invention, "the means for detoxifying dilute hydrocarbons contained in a large amount of waste gas", the adsorption method has been used exclusively. The adsorbent used is, with exceptions, granular activated carbon or fibrous activated carbon.

This type of activated carbon has excellent adsorption capacity compared to other adsorbents, but has the drawback that it is extremely difficult to desorb. For this reason, at the time of desorption as described above, at present, a large amount of steam, which is about three times the amount of filled activated carbon, is used. In addition, the hydrocarbons entrained in the steam are detoxified together with water by wastewater treatment means such as activated sludge treatment equipment.

Desorption using a large amount of heated air as a purge gas instead of steam may cause the activated carbon to burn, and the use of activated carbon other than room temperature air or non-combustible nitrogen is permitted by the Fire Service Law. Not _c

However, when non-combustible hydrophobic silica gel is used as the adsorbent, There is no danger. This has made it possible to use high-temperature air, up to 250 ° C, as the purge gas. (Note that the concentration of gaseous hydrocarbons is specified below the lower explosive limit. Therefore, it should be preferably less than about 500 ppm.)

In the present invention, the gaseous hydrocarbon desorbed along with the heated purge gas is a gas suitable for burning as it is as a purge exhaust gas.

Furthermore, when a vacuum pump is used as an auxiliary means for desorption, the larger the amount of heated air, that is, the purge coefficient, the more the load on the vacuum pump is reduced, and the more desorption is carried out. The degree of vacuum to be sucked is "60 to 15 OT orr". Since the vacuum pump is expensive, it can be said that this is a remarkable effect of the application of the present invention.

On the other hand, when activated carbon is used as the adsorbent, as described above, there has conventionally been no choice except for a large amount of steam (or nitrogen gas) as the purge gas at the time of desorption. "Has been found.

By injecting water into the desorption tower, not only can it be vaporized inside the desorption tower with the help of a vacuum pump and exert the same effect as the purge gas, but also the amount of vaporized gas can be reduced by the conventional steam use. In this case, the gas can be purged with a small gas amount of "several tenths".

When "water" is used in the present invention, a water-sealed vacuum pump is preferable as the vacuum pump used at that time. The reason is that the concentrated hydrocarbon gas is mixed with the water in the water seal to obtain wastewater and wastewater suitable for industrial waste treatment.

The embodiment according to the present invention is as described in detail above. However, the method according to the present invention can employ a publicly known PSA method or PTSA method. In addition, VSA method, VTSA method, etc. And these applications are also included in the present invention.

Further, the present invention provides a treatment method for concentrating and separating a dilute gaseous hydrocarbon contained in a waste gas and an apparatus for performing the method, wherein a dilute hydrocarbon generated at the time of coating is provided. Not only multi-component hydrocarbon gas, but also benzene, toluene, It is widely applied to dilute single-component gases such as trichloroethylene, methylethylketone, and even freon. Example

Next, the present invention will be specifically described with reference to examples of the present invention. However, the present invention is not limited to Examples 1 and 2 below.

(Example 1)

FIG. 1 is a flow sheet diagram for explaining “a method for treating a lean gaseous hydrocarbon in a waste gas” which is one embodiment of the present invention. FIG. 2 is a flow sheet diagram shown in FIG. It is a figure which shows an example of the "control panel for grasping and controlling an operating condition" in a flow sheet. FIG. 3 is a longitudinal sectional view showing one example (Example 1) of the structure of the adsorption tower used in the flow sheet shown in FIG.

In the first embodiment, as shown in FIG. 3, the inner cylinder 4a (4b) through which the cooling water 5 circulates and the outer cylinder 2a (2b) filled with the adsorbent layer 3a (3b) outside The adsorption column la (lb) composed of the double cylinder of b) was used. The cooling water 5 flowing through the inner cylinder 4a (4b) is turbulent so that it flows countercurrently to the waste gas flowing through the adsorbent layer 3a (3b).

In addition, granular activated carbon (granular Shirasagi No .: trade name, manufactured by Takeda Pharmaceutical Co., Ltd.) and Y-type synthetic zeolite (360 HUD: trade name, manufactured by Tosoh Corporation) were used as adsorbents. Then, as shown in Fig. 3, the Y-type synthetic zeolite 3-2a (3-2b) was filled in the upper part of the granular activated carbon 3-la (3-lb) into the adsorption tower 1a (1b), This was used as an adsorbent layer 3a (3b). The granular activated carbon used was pre-coated with benzene vapor in advance.

Hereinafter, Example 1 will be described in detail with reference to FIG. 1. A waste gas generated from a waste gas generation source (not shown) (a waste gas containing about 500 ppm benzene: 20 liters) (Amount of gas in Torr Z) is blown to the adsorption tower 1a by a blower (not shown) that compresses the gauge pressure to 1 kg / cm or less or the waste gas air pipe 11 by its own pressure. At this time, the gas velocity passing through the adsorbent layer 3a (3b) was "about 10 cm / sec". The treated waste gas after the adsorption process contains 20 ppm or less of benzene vapor from the top of the adsorption tower la (adsorption tower 1b after switching to the desorption step) via the discharge pipe 12. Released into the atmosphere as air (clean gas).

In addition, the adsorption towers 1a and 1b are operated while alternately switching between the above adsorption step and the desorption step described later, but at this switching point, the adsorbent layer in the adsorption towers 1a and 1 lb is broken. This is done before passing through, and by automatically opening and closing valves (2) and (2) shown in Fig. 1.

That is, the valves (e) and (e) for switching between suction and desorption are opened and closed

'Read the "inlet gas flow rate" "J" and the "inlet gas concentration" "H" of the adsorption towers la and 1b into the memory 1 shown in Fig. 2 and fill in the memory (adsorption model) 23 in advance. The CPU (calculation) of the selected adsorption model 22 The “expected breakthrough time,” which indicates the result of the calculation, and the temperature detection board (not shown) placed above the adsorbent layer allows the Y-type synthetic zeolite 3-2 a (3-2 b) [See Fig. 3 above] The time when the "temperatures" "F" and "G" in the adsorbent layer stopped rising,

Automatically switches using.

On the other hand, to the adsorption tower 1a after the completion of the adsorption step (the adsorption tower 1b after switching to the desorption step), water is supplied via the water pipe 13 to the adsorption tower 1a (the tower switched to desorption). And a water ring vacuum pump 14 (Nash Pump: trade name, manufactured by Kurimura Seisakusho), and then detached by suction.

In the first embodiment, the water ring vacuum pump 14 is operated at about 60 T 0 rr, and the pressure in the adsorption tower 1 a (the tower switched to desorption) is reduced to a low pressure (vacuum). As a result, the supplied water turns into steam in the adsorption tower 1a to become a purge gas. Then, the gas is extracted as purged exhaust gas from the purge gas air supply pipe 15 through the water ring vacuum pump 14. Room temperature industrial water was used to cool the purged exhaust gas sucked by the water ring vacuum pump 14. That is, the purge exhaust gas is sent to the gas-liquid separator 16. The gas-liquid separator 16 is cooled by industrial water flowing through a cooling pipe (not shown) arranged inside. At this time, the benzene vapor in the purged exhaust gas is condensed and liquefied in the water-sealed water in the gas-liquid separator 16 connected to the lower part, and is separated from uncondensed gas. Accumulated water And benzene are taken out of the system and are subjected to industrial waste treatment with an industrial waste treatment unit 17.

Since benzene vapor remains in the exhaust gas not condensed in the gas-liquid separator 16, the benzene vapor is returned to the waste gas air pipe 11 again via the return gas air pipe 18, and is returned together with the waste gas. To perform the adsorption process.

The uncondensed gas contains a high concentration of residual benzene, and by returning the entire amount to the waste gas supply pipe 11, the benzene concentration in the adsorption tower is further increased. Then, by using the above-described means, the switching time of the valve (e) is set by predicting the time at which the adsorbent layer in the adsorption tower breaks through, and the operation is automatically switched to the desorption operation.

In addition, A to J shown in Fig. 1 indicate the positions of the instruments provided to grasp the operation status. On the other hand, (a) to (2) indicate the This shows the position of the provided valve.

FIG. 2 shows a control panel 20 for grasping and controlling the operation status in the flow shown in FIG. 1, and includes a memory 21, a memory (adsorption model) 23, and a CPU ( Arithmetic) 22. In FIG. 2, as the data signals to be read into the memory 21, only those necessary at the time of switching between absorption and desorption are indicated as “X”. (Reading of other data signals was omitted.) In the first embodiment, as described above, switching between adsorption and desorption is performed by detecting a data logger signal before the adsorption tower breaks through, so that gaseous hydrocarbons are used. When the concentration is low, the concentration can be concentrated several times in the adsorption tower, and by devising cooling means to remove the heat generated in the adsorbent layer (see Fig. 3 above), local heating is avoided. The temperature of the adsorbent layer during the operation period was almost room temperature.

The benzene concentration in the gas released into the atmosphere from the discharge pipe 12 was substantially less than 20 ppm.

(Example 2)

FIG. 4 is a longitudinal sectional view of an adsorption tower used in Example 2. FIG. 5 is a diagram further explaining the adsorption tower of FIG. 4, wherein FIG. 5 (A) is a cross-sectional view taken along the line A-A of FIG. 4, and FIG. 5 (B) is a diagram of FIG. It is the elements on larger scale of the figure.

In Embodiment 2, as shown in FIGS. 4 and 5 (A) and (B), the adsorbent layer Adsorption tower 4 1a (4 1 b) consisting of a double cylinder of outer cylinder 4 2 b (4 2 b) and 4 2 a '(4 2 b') filled with 4 3 a (4 3 b) ) Was used.

As adsorbents, crushed activated carbon with a particle size of 0.4 mm (HC42: trade name of Tsurumi Coal) and Y-type synthetic zeolite with a particle size of 1.0 mm (360 HUD: East (Trade name, manufactured by Soviet Union).

Then, as shown in Fig. 4 and Fig. 5 (B), the Y-type synthetic zeolite 43-2a (43-2b) is adsorbed on the top of the broken activated carbon 43-la (43-lb). The column 41a (41b) was packed and used as an adsorbent layer 43a (43b). The crushed activated carbon used was previously pre-coated with benzene vapor.

In Example 2, the above-mentioned crushed activated carbon and Y-type synthetic zeolite were used using the adsorption towers 41a (41b) shown in FIGS. 4 and 5 (A) and (B) described above. Except for the above, waste gas (waste gas containing about 50,000 ppm of benzene: gas amount of 300 liters Z) was treated under the same conditions and means as in Example 1. At this time, the gas velocity passing in the circumferential direction through the adsorbent layer 43a (43b) was "1.5 cmZ seconds".

In Example 2, the benzene concentration in the gas released into the atmosphere from the discharge pipe 12 (see Fig. 1) was such that it could not be detected with a commercially available HC concentration detection pipe (isobutane conversion). It was a trace amount.

In Example 1 described above, the benzene concentration in the gas released into the atmosphere is 20 ppm or less, whereas in Example 2, as described above, a trace amount It can be understood that the amount is superior to that of Example 1.

Further, in the second embodiment, it can be understood that a large amount of waste gas of "300 liters / minute (18 m ³ / hour)" can be effectively treated.

As described above, the double-cylinder adsorption towers 1a and 1b shown in FIG. 3 are used as the first embodiment of the present invention. However, the present invention is not limited to such a double cylinder. Instead, for example, it is also possible to use a double-cylinder or multi-cylinder 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.

In addition, as Embodiment 2 of the present invention, the suction of the multiple cylinders shown in FIGS. Although a landing tower was used, the present invention is not limited to such a multi-cylinder, and for example, an adsorbent configured by filling an adsorbent into a honeycomb-shaped core and bundling the same, or It is also possible to use an adsorption device or the like constituted by packing adsorbents in a box and stacking them.

The other requirements are not limited to the above embodiments, and various embodiments are possible within the scope of the features of the present invention (items limiting the invention). Industrial applicability

The present invention, as described in detail above,

· Return all or most of the purged exhaust gas containing the released gaseous hydrocarbons to the waste gas to be treated, thereby increasing the hydrocarbon concentration in the adsorbent layer (first feature point). • This adsorbent Switch to desorption before the layer breaks through (second feature)

This makes it possible to safely, easily and efficiently treat hydrocarbons from waste gas, and to reduce the residual hydrocarbon concentration in the gas released into the atmosphere after treatment to 100 ppm. In particular, it can be set to “20 ppm or less”.

Therefore, according to the present invention, in the removal treatment of gaseous hydrocarbons as 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 even if this figure becomes less than half strict, it can sufficiently cope with it.

Further, the present invention can be configured to be 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.

Claims

The scope of the claims

1. Using an "adsorption device having an adsorbent layer" that alternately performs adsorption and desorption, let waste gas containing gaseous hydrocarbons pass through one of the adsorption devices, and apply gaseous gas to the adsorbent layer in the adsorption device. The hydrocarbons are adsorbed and the waste gas substantially free of gaseous hydrocarbons is released into the atmosphere, during which time the other adsorber is switched to desorption and adsorbed on the adsorbent layer in the adsorber A method for treating lean gaseous hydrocarbons contained in waste gas, comprising removing gaseous hydrocarbons with a vacuum pump to remove the gaseous hydrocarbons and transferring the gaseous gas to a purged exhaust gas.

All or most of the purged exhaust gas is returned to the waste gas to be treated, thereby increasing the hydrocarbon concentration in the adsorbent layer and switching to desorption before the adsorbent layer breaks through. A method for treating a lean gaseous hydrocarbon contained in waste gas.

2. When part of the gaseous hydrocarbons in the purge exhaust gas is liquefied, the liquid hydrocarbons are burned or detoxified as industrial waste. For the treatment of dilute gaseous hydrocarbons contained in the waste gases mentioned

3. The waste gas according to claim 1, wherein the adsorbent layer comprises a layer of activated carbon and Z or a hydrophobic silicic acid gel, and a synthetic zeolite layer is disposed on top of the layer. A method for treating a lean gaseous hydrocarbon contained.

4. The method according to any one of claims 1 to 3, wherein the adsorbent or the adsorbent layer filled in the adsorber is pre-coated with gaseous hydrocarbon. A method for treating lean gaseous hydrocarbons contained in waste gas.

5. As means for releasing gaseous hydrocarbons adsorbed on the adsorbent layer in the adsorber, use is made of air or water heated above the boiling point of the hydrocarbons to be adsorbed. The method for treating a lean gaseous hydrocarbon contained in a waste gas according to any one of claims 1 to 4, characterized in that:

6. As a means for switching to desorption before the adsorbent layer breaks through, a temperature detection port is provided at the top of the adsorbent layer, and when the temperature from the temperature detection port stops its rise 6. The method for treating a lean gaseous hydrocarbon contained in waste gas according to any one of claims 1 to 5, wherein the solenoid valve is automatically switched with the method.

7. As means for switching to desorption before the adsorbent layer breaks through, the "gas flow rate at the inlet", the "hydrocarbon concentration in the inlet gas" of the adsorber obtained during the adsorption operation, and

Read the "desired hydrocarbon concentration in the outlet gas (assumed value)" into the chip as numerical data, and set the switching time in advance using a simulation model for control incorporated in the chip. The method for treating a lean gaseous hydrocarbon contained in waste gas according to any one of claims 1 to 5, characterized in that:

8. The waste gas according to any one of claims 1 to 7, wherein the hydrocarbon concentration in the clean gas discharged to the atmosphere from the adsorption device is set to 100 pm or less. For treating rare gaseous hydrocarbons contained therein.

9. An apparatus for carrying out the treatment method according to any one of claims 1 to 8, comprising an "adsorption apparatus having an adsorbent layer" in the apparatus. An apparatus for treating a dilute gaseous hydrocarbon contained in waste gas, comprising a component, wherein the component is a container that can be sealed but cannot be closed.

10. The "adsorbing device having an adsorbent layer" force The adsorbing device includes a plurality of cylinders that surround the adsorbent layer and are capable of circulating waste gas in the circumferential direction. Equipment for treating lean gaseous hydrocarbons contained in waste gas according to paragraph

11. The enclosure according to claim 10, wherein the enclosure of the adsorbent layer is a box-type component or a honeycomb-type component, and is an adsorption device in which the components are multiplexed. An apparatus for treating lean gaseous hydrocarbons contained in the waste gas described in the item.

12. The adsorbent layer according to any one of claims 9 to 11, wherein the adsorbent layer is a layer filled with fine adsorbent having a diameter of 0.1 to 1 mm. Equipment for treating lean gaseous hydrocarbons contained in waste gas.