JP6305938B2 - Gas purification equipment - Google Patents

Description

An adsorption tower filled with an adsorbent that adsorbs miscellaneous gases other than the gas to be purified from the source gas is provided.
A source gas supply path for supplying source gas to the adsorption tower is provided,
A product gas recovery path for discharging the gas to be purified that has not been adsorbed on the adsorbent as product gas is provided,
Provide a miscellaneous gas discharge path for desorbing and exhausting miscellaneous gas adsorbed on the adsorbent,
The adsorption tower, the raw material gas supply path, the product gas recovery path, and the exhaust gas,
An adsorption step of receiving a raw material gas from the raw material gas supply path, adsorbing a miscellaneous gas to the adsorbent, and collecting a product gas;
A desorption step of desorbing the miscellaneous gas adsorbed on the adsorbent and exhausting it from the miscellaneous gas discharge path;
The present invention relates to a gas purification apparatus connected so as to be capable of performing pressure fluctuation operation alternately.

  In order to effectively use the combustible gas, it is necessary to separate the gas such as air from the raw material gas containing the combustible gas and concentrate the combustible gas to an appropriate concentration range. Various devices and methods for concentrating such a combustible gas have been proposed. A gas generated from a coal mine containing methane as a combustible gas (so-called coal mine gas) is used as a raw material gas, and an adsorbent is obtained from the raw material gas. An invention has been proposed in which air (mainly containing nitrogen, oxygen and carbon dioxide) is separated using methane, and methane is concentrated for use.

That is, using natural zeolite as an adsorbent that adsorbs methane very slowly compared to nitrogen (in other words, using an adsorbent that preferentially adsorbs nitrogen, oxygen, and carbon dioxide to methane) The coal mine gas is introduced into the adsorption tower filled with the adsorbent by a compressor or the like until a predetermined pressure is reached. Thereby, oxygen, nitrogen, and carbon dioxide contained in the coal mine gas are first adsorbed to the front part (lower part) of the adsorption tower, and methane having a slow adsorption rate is adsorbed to the rear part (upper part) of the adsorption tower. Further, an invention of an apparatus and a method for concentrating methane by releasing the methane from the upper part of the adsorption tower to atmospheric pressure has been proposed.
Thereby, it is supposed that air can be separated from a coal mine gas as a raw material gas using an adsorbent, methane can be concentrated, and the concentrated methane can be used as a fuel or the like.

That is, an adsorption tower filled with an adsorbent that adsorbs miscellaneous gases other than the gas to be purified from the source gas is provided,
A source gas supply path for supplying source gas to the adsorption tower is provided,
A product gas recovery path for discharging the gas to be purified that has not been adsorbed on the adsorbent as product gas is provided,
A miscellaneous gas discharge path for exhausting the miscellaneous gas adsorbed on the adsorbent by desorbing under reduced pressure is provided,
The adsorption tower, the source gas supply path, the product gas recovery path, and the miscellaneous gas discharge path,
An adsorption step of receiving a raw material gas from the raw material gas supply path, adsorbing a miscellaneous gas to the adsorbent, and collecting a product gas;
A desorption step of desorbing the miscellaneous gas adsorbed on the adsorbent and exhausting it from the miscellaneous gas discharge path;
A configuration (hereinafter referred to as a PSA device) connected so as to be able to perform a pressure swing operation that alternately performs is assumed.

  Thereby, if source gas is supplied to an adsorption tower from a source gas supply path, the adsorption process which makes the adsorbent in the said adsorption tower adsorb the miscellaneous gas in source gas can be performed. The gas to be purified in the raw material gas that has not been adsorbed by the adsorbent is recovered from the product gas recovery path, and the adsorption tower that has adsorbed and saturated the miscellaneous gas desorbs the miscellaneous gas adsorbed by the adsorbent under reduced pressure. It can be regenerated by performing a desorption process. The exhaust gas generated at this time is mainly composed of miscellaneous gas and is exhausted from the miscellaneous gas discharge passage. A pressure swing operation in which the adsorption process and the desorption process are repeated can be performed.

  Here, in order to increase the purity of the product gas to be purified to a certain degree or more, it is necessary to suppress the amount of miscellaneous gas passing through the adsorption tower. Then, since the purification target gas remaining in the adsorption tower is discharged as exhaust gas, the recovery rate of the purification target gas is reduced. On the other hand, if an attempt is made to improve the recovery rate, the product gas purity is lowered. Therefore, it is desired to improve the recovery rate of the gas to be purified while maintaining the product gas purity.

  For the above purpose, the exhaust gas to be exhausted is further purified, and a configuration in which a membrane separation device is provided in the miscellaneous gas discharge path in order to improve the recovery rate of the gas to be purified (see Patent Document 1), The structure (refer patent document 2) which provides a membrane separation apparatus in the upstream is considered.

US Patent Application Publication No. 2004-099138 US Patent Application Publication No. 2011-094378

  However, in Patent Document 1, the gas to be purified in the exhaust gas is subjected to membrane separation, and the gas to be purified that has permeated through the separation membrane is returned to the raw material gas supply path. Therefore, the power for membrane separation of the gas to be purified is greatly increased. It is necessary to secure it, and the driving power of the entire apparatus is required. In addition, the final product gas purification target gas purity will be determined by the membrane separator, and in order to maintain high purity, it is necessary to increase the amount of separation membrane permeate gas in the membrane separator, and to improve the recovery rate. It has a configuration that must be reduced.

  Further, according to the technique of Patent Document 2, since the purity of the product gas can be determined by the PSA apparatus, the product gas can be set to a high purity, but the raw material gas supplied to the PSA apparatus As a result, the membrane separator used to improve the purity of the gas greatly reduces the recovery rate of the gas to be purified. As a result, the overall device is unlikely to contribute to the improvement of the recovery rate. It was.

  Accordingly, an object of the present invention is to improve the recovery rate of the gas to be purified from the gas purifier using the PSA device, and to achieve both the purity and the recovery rate with high power efficiency.

[Configuration 1]
The characteristic configuration of the gas purification apparatus of the present invention for achieving the above object is as follows:
An adsorption tower filled with an adsorbent that adsorbs miscellaneous gases other than the gas to be purified from the source gas is provided.
A source gas supply path for supplying source gas to the adsorption tower is provided,
A product gas recovery path for discharging the gas to be purified that has not been adsorbed on the adsorbent as product gas is provided,
Provide a miscellaneous gas discharge path for desorbing and exhausting miscellaneous gas adsorbed on the adsorbent,
The adsorption tower, the source gas supply path, the product gas recovery path, and the miscellaneous gas discharge path,
An adsorption step of receiving a raw material gas from the raw material gas supply path, adsorbing a miscellaneous gas to the adsorbent, and collecting a product gas;
A desorption step of desorbing the miscellaneous gas adsorbed on the adsorbent and exhausting it from the miscellaneous gas discharge path;
A gas purifier connected to perform pressure fluctuation operation alternately,
The miscellaneous gas discharge passage has a separation membrane that does not transmit the gas to be purified but permeates the miscellaneous gas, and a membrane separation device that separates the gas to be purified and the miscellaneous gas by the exhaust pressure of the adsorption tower,
A regeneration gas return path is provided for returning the regeneration gas whose concentration of the gas to be purified is increased by the separation membrane to the source gas supply path,
The regeneration gas return path is provided with a regeneration pressure control valve that controls the pressure by adjusting the opening so that the exhaust pressure of the adsorption tower gradually decreases during the desorption process, and the separation membrane is controlled by the regeneration pressure control valve. includes a reproduction control unit for controlling the membrane separation pressure is a membrane separation pressure of the membrane separation device in that a more controlled exhaust pressure of the adsorption tower with the regeneration pressure control valve.

[Function 1]
That is, a membrane separation device that has a separation membrane that does not allow the gas to be purified to permeate through the miscellaneous gas discharge path of the PSA device but permeates the gas to be purified, and that separates the gas to be purified and the gas by the exhaust pressure of the adsorption tower In the gas path for extracting the product gas from the raw material gas, although the PSA device contributes to the purification of the gas to be purified, the membrane separation device does not participate in the purification of the gas to be purified. The gas purity can be set high by the PSA apparatus. At this time, the purification target gas recovery rate from the PSA device tends to decrease, but the recovery rate of the purification target gas can be increased because the exhaust gas is recovered and returned to the source gas supply path. Even if the entire amount of exhaust gas is recovered, the concentration of miscellaneous gas in the gas supplied to the adsorption tower increases, so that the purity of the purification target gas in the product gas may be reduced. Therefore, if the true exhaust gas that does not contain the gas to be purified is removed from the exhaust gas that is returned by the membrane separator, it is possible to suppress an increase in the miscellaneous gas concentration in the gas supplied to the adsorption tower. Then, the recovery rate can be improved without reducing the purification target gas purity in the product gas and reducing the purification target gas purity in the PSA apparatus.

  Here, since the membrane separation device is configured to obtain the membrane separation pressure in the separation membrane from the exhaust pressure of the back adsorption tower and separate the gas to be purified from the miscellaneous gas, the membrane separation device itself includes a gas such as a compressor. Membrane separation can be performed without providing a supply device. That is, the exhaust pressure from the adsorption tower is applied to the miscellaneous gas discharge passage while the desorption process is performed by the PSA device. By performing membrane separation using this exhaust pressure, the power required for gas supply can be reduced, and gas separation can be performed efficiently with low energy and power.

  Therefore, by effectively using the membrane separation apparatus, the recovery rate can be improved efficiently without reducing the purity of the gas to be purified.

In addition, the membrane separation device requires less equipment costs than the PSA device, so the gas purification is cheaper than the product gas purified by the PSA device and the gas to be purified in the exhaust gas are further purified by the PSA device. A device can be configured.
Further, according to the above configuration, the pressure applied to the separation membrane of the membrane separation device can be changed by the regeneration pressure control valve. This makes it possible to stably remove the miscellaneous gas from the exhaust gas in the membrane separation apparatus and balance the source gas supply pressure on the source gas supply path side, which makes the supply of the source gas unstable. It can be suppressed.
Further, if a regeneration control device that controls the membrane separation pressure of the separation membrane by the regeneration pressure control valve is provided, even if the regeneration gas pressure fluctuates during each process of the PSA device, This contributes to supplying the regeneration gas into the raw material gas.

[Configuration 2]
A regeneration gas recovery path may be provided for recovering the regeneration gas having a higher concentration of the gas to be purified by the separation membrane as product gas.
When exhaust gas with high product gas concentration is generated from a gas purification device, if the exhaust gas is passed through a membrane separation device, the product gas purity of the recycled gas flowing through the regeneration gas return path becomes extremely high and can be recovered as a product. It may become. It is considered that it is wasteful in terms of efficiency to mix such a gas with a regeneration gas whose product gas purity is only raised to the same level as that of the raw material gas and to re-purify it again as the raw material gas.

Therefore, even in such a case, if a regeneration gas recovery path is provided, the regeneration gas having a higher concentration of the purification target gas can be returned to the product gas recovery path. Gas can be efficiently recovered.

[Configuration 3 ]
A bypass path may be provided that guides the exhaust gas flowing through the miscellaneous gas discharge path to the regeneration gas return path by bypassing the membrane separation device.

[Effect 3 ]
Depending on the PSA process, an exhaust gas with a high product gas concentration may be generated from the gas purifier. If such an exhaust gas is supplied to a membrane separation device in the same manner as a miscellaneous gas having a low product gas purity, there is a risk that the loss of product gas in the membrane separation device may increase. Rather, it may be reused as a raw material gas as it is. It may be preferable.

  Therefore, in the above configuration, when the regeneration gas return path is provided, if the bypass path is provided, the exhaust gas is bypassed through the membrane separator and guided to the regeneration gas return path, so that the raw material gas is not lost. Can be reused as

[Configuration 4 ]
A buffer tank may be provided upstream of the membrane separation device in the miscellaneous gas discharge path.

[Effect 4 ]
The buffer tank can temporarily store the miscellaneous gas discharged in the desorption process before being supplied to the membrane separation device. At this time, high-pressure miscellaneous gas containing the gas to be purified having a relatively high concentration can be accumulated in the buffer tank by pressure equalization operation by the pressure difference between the adsorption tower and the buffer tank.

Thereafter, the miscellaneous gas in the buffer tank can be supplied to the membrane separation device, and the high-pressure miscellaneous gas discharged from the adsorption tower at an early stage can be relaxed and supplied to the membrane separation device. While performing a membrane separation operation with a high recovery rate using the pressure of high-pressure miscellaneous gas, the gas to be purified can be purified from the miscellaneous gas with high accuracy. In other words, the flow rate of high-pressure miscellaneous gas discharged from the adsorption tower at an early stage is too high, and the permeation of the miscellaneous gas through the separation membrane is not sufficiently performed, and a part of the miscellaneous gas is mixed into the regeneration gas side, thereby reducing the purification accuracy. You can avoid that.
[Configuration 5]
Further, a decompression pump may be provided in a state of steady operation on the miscellaneous gas permeation side of the membrane separation device in the miscellaneous gas discharge path.

[Effect 5 ]
If a vacuum pump is provided, the minimum necessary power can be supplied to continue the membrane separation of the gas to be purified when the membrane separation pressure of the membrane separation device is insufficient. Will be able to continue.

[Configuration 6 ]
A regeneration gas tank may be provided in the regeneration gas return path.

[Operation effect 6 ]
The gas after removing the miscellaneous gas from the exhaust gas from the PSA apparatus by the membrane separator has a higher concentration of the gas to be purified, and becomes a regeneration gas that can be used as a raw material gas. However, the concentration of the purification target gas in the regeneration gas varies during each process of the PSA apparatus. Thus, by temporarily storing the regeneration gas in the regeneration gas tank, the concentration fluctuation of the regeneration gas over time can be reduced, which contributes to the stable supply of the regeneration gas to the raw material gas.

[Configuration 7]
A product gas tank may be provided in the product gas recovery path.

[Operation effect 7]
If a product gas tank is also provided in the product gas recovery path, the concentration of the purification target gas in the product gas can be stabilized. In addition, if a product gas tank is provided in such a configuration, the product gas tank will have a pressure, so that the product gas can be used as a cleaning gas when desorbing miscellaneous gas from the adsorbent in the adsorption tower and regenerating it so that it can be resorbed. Can also be used.

[Configuration 8]
Furthermore, in the above-described configuration, a product gas cleaning path for flowing product gas from the product gas tank to the adsorption tower is provided, a product pressure control valve is provided between the product gas tank and the adsorption tower in the product gas cleaning path, and the product gas tank A cleaning control device may be provided for cleaning the adsorption tower by flowing product gas into the adsorption tower.

[Operation effect 8]
In addition to the product gas tank, if a cleaning path is provided for the product gas to flow from the product gas tank to the adsorption tower and a product pressure control valve is provided between the product gas tank and the adsorption tower in the cleaning path, the cleaning path from the product gas tank is The product gas can be supplied to the PSA apparatus via the PSA apparatus. As a result, the product gas can be used as it is as a cleaning gas when the miscellaneous gas is desorbed from the adsorbent in the adsorption tower and regenerated so as to be resorbable. The pressure at this time is also applied to the exhaust gas when the cleaning exhaust gas is discharged to the miscellaneous gas discharge passage. Therefore, the purification target gas contained in the cleaning exhaust gas is also operated so as to be recovered by the membrane separation device. In addition, since it is not necessary to separately supply a pressure to be applied, power supply to the membrane separation apparatus can be reduced.

  In addition, even when other gases are desorbed from the adsorbent in the adsorption tower and regenerated so that they can be adsorbed again, the membrane separation device can be operated continuously, so that it does not interfere with the operation of the membrane separation device. Stable operation is possible.

[Configuration 9]
The source gas may be a methane-containing gas, the purification target gas may be methane, and the miscellaneous gas may be a gas mainly composed of carbon dioxide.

[Effect 9]
For example, it is possible to supply methane having a purity that can be used as a fuel gas from a gas source having a low methane content to be used as a fuel gas, such as biogas, and to effectively use unused fuel gas. it can. In addition, when such raw material gas mainly contains carbon dioxide as a miscellaneous gas, separation by a membrane separation device is often suitable due to the difference in chemical properties between methane and carbon dioxide, which is particularly suitable. Available to:

[Configuration 10]
Furthermore, the source gas is a methane-containing gas containing 40% or more of methane as a gas to be purified, and a product gas containing 90% or more of methane can be obtained.

[Operation effect 10]
A typical biogas composition is about 40 to 60% methane and about 60 to 40% carbon dioxide. For such biogas, when a product gas containing 90% or more of methane is obtained using a conventional gas purification device, the recovery rate cannot be increased so much, and the methane contained in the exhaust gas cannot be increased. There was a fact that the concentration tends to be high.
However, if a product gas containing 90% or more of methane can be obtained as a gas purification device having a membrane separation device and an improved recovery rate, methane in biogas can be used effectively and the atmosphere It can contribute to environmental conservation by reducing methane as a global warming gas emitted into the environment.

[Configuration 11]
The adsorbent may be mainly composed of at least one material selected from activated carbon, molecular sieve carbon, zeolite, and a porous metal complex.

[Operation effect 11]
Adsorbents mainly composed of at least one material selected from activated carbon, molecular sieve carbon, zeolite, and porous metal complexes are widely used as adsorbents for PSA equipment, and those with high gas adsorption separation efficiency are known. ing. In particular, activated carbon and molecular sieve carbon have excellent separation characteristics between methane gas and carbon dioxide, and can efficiently adsorb and separate carbon dioxide when concentrating biogas and coal mine gas. Molecular sieve carbon, zeolite, and a porous metal complex are suitable for separating a gas having a small molecular diameter, and are also suitably used for concentrating methane from a gas containing hydrogen, helium, or the like.

[Configuration 12]
When the adsorbent has a pore diameter of 0.38 nm or more measured by the MP method, the pore volume (V _0.40 ) at the pore diameter does not exceed 0.01 cm ³ / g, and the pore diameter is 0.34 nm. Molecular sieve carbon having a volume (V _0.34 ) of 0.20 cm ³ / g or more may be used.

[Operation effect 12]
Such molecular sieve carbon has extremely high methane and air separation performance, and can be in a form suitable for concentrating methane as a gas to be purified from a raw material gas such as biogas.

[Configuration 13]
The separation membrane is at least selected from cellulose acetate, polyamide, polyimide, polysulfone, polytetrafluoroethylene, polyethersulfone, carbon membrane, microporous glass composite membrane, DDR type zeolite, multi-branched polyimide silica, and polydimethylsiloxane. One kind of material can be the main component.

[Operation effect 13]
When a membrane separation apparatus includes these separation membranes, it is known that membrane separation can be performed efficiently and durability is high, which is useful. In addition, these materials have a high separation factor between methane and carbon dioxide, and are effective when concentrating methane from biogas.

[Configuration 14]
The source gas supply path may be provided with a booster pump, and the supply pressure of the source gas to the adsorption tower by the booster pump may be 0.5 MPaG to 2 MPaG.
Note that “PaG” used in the present application represents the gauge pressure in terms of Pa, and indicates a relative pressure with respect to the atmospheric pressure.

[Operation effect 14]
Such a pressure is preferable because the raw material gas supplied at normal pressure can be supplied to the adsorption tower of the PSA apparatus with relatively little power, and the PSA apparatus can easily exhibit sufficient adsorption separation performance. In addition, if the pressure is increased too much, there is a problem that the recovery rate of methane decreases.
Therefore, by setting the pressure to 0.5 MPaG or more, the gas separation capability in the PSA apparatus is maintained high, and by setting the pressure to 2 MPaG or less, the apparatus as a whole can be set to energy-efficient power, and the methane recovery rate can also be maintained high.

  Note that the exhaust pressure of the PSA apparatus varies according to the gas desorption pressure in the desorption process and the gas cleaning pressure when cleaning the adsorbent. In addition, the maximum membrane separation pressure is a differential pressure from the normal pressure (or the degree of pressure reduction when a decompression pump is provided on the miscellaneous gas permeation side of the membrane separation device). Therefore, the exhaust pressure varies to some extent depending on the progress of the process in the PSA apparatus, and the membrane separation pressure also varies accordingly. Further, if a decompression pump is provided on the miscellaneous gas permeation side of the membrane separation apparatus, the driving power of the decompression pump can be maintained and set within a range where efficient membrane separation is possible.

  Accordingly, it is possible to recover methane of higher purity, and it is possible to effectively use biogas and the like that have been difficult to reuse in the past with a high methane recovery rate.

Schematic diagram of gas purification equipment Process diagram showing methane concentration method Explanatory diagram of gas flow when performing the methane concentration method of FIG. The figure which shows transition of the pressure in the adsorption tower when performing the methane concentration method of FIG. Schematic of the gas purification device of another embodiment (2) Schematic of the gas purification device of another embodiment (5) Schematic of the gas purification device of another embodiment (6) Process drawing which shows the methane concentration method by the gas purification apparatus of another embodiment (7) Schematic of the gas purification apparatus of another embodiment (10) Process drawing which shows the methane concentration method of another embodiment (11) Explanatory diagram of gas flow operation when performing methane concentration method of FIG. The figure which shows transition of the pressure in an adsorption tower in the case of performing the methane concentration method of FIG. Schematic of still another gas purification device of another embodiment (5)

  Below, the gas purification apparatus of this invention is demonstrated. Preferred embodiments will be described below, but these embodiments are described in order to more specifically illustrate the present invention, and various modifications can be made without departing from the spirit of the present invention. The present invention is not limited to the following description.

[Gas purification equipment]
As shown in FIG. 1, the gas purification apparatus includes adsorption towers A1 to A4 filled with adsorbents A11 to A14. In each adsorption tower, for example, a raw material gas supply path L1 for supplying biogas as a raw material from a raw material gas tank T1, and a product gas recovery path for recovering methane as a purification target gas that has not been adsorbed by the adsorbents A11 to A14 as a product gas. L2 and product gas tank T2, and miscellaneous gas discharge passage L3 for desorbing and exhausting carbon dioxide as miscellaneous gas adsorbed on adsorbents A11 to A41 are provided. In this Embodiment, it was set as the structure provided with 4 towers of adsorption tower A1-A4, However, if the number of towers is two or more, it will not be limited, 3 towers, 5 towers, etc. can be suitably selected as needed. Is possible.

  Gas supply from the source gas tank T1 to the source gas supply path L1 is performed using the supply pump P1, and when the pressure control valve Vc1 is provided in the bypass path L10 that bypasses the supply pump P1, the adsorption towers A1 to A4 are pressurized. The pressure can be controlled stably. The source gas supplied to the source gas supply path L1 is supplied to the adsorption towers A1 to A4 via supply paths L11 to L41 provided with switching valves V11 to V41.

  The product gas discharged from the adsorption towers A1 to A4 flows into the product gas recovery path L2 through the recovery paths L12 to L42 having switching valves V12 to V42. A pressure control valve Vc2 is provided in the product gas recovery path L2. By controlling the pressure of the product gas recovered from the adsorption towers A1 to A4 to the product gas tank T2 by the pressure control valve Vc2, the adsorption tower A1 is related to the supply pressure of the raw material gas in the adsorption towers A1 to A4. The product gas recovery pressure from ~ A4 can be controlled.

  The miscellaneous gas adsorbed in the adsorption towers A1 to A4 is desorbed from the adsorbents A11 to A14 by being depressurized, and is discharged from the miscellaneous gas discharge path L3 through the exhaust gas paths L13 to L43 having switching valves V13 to V43. Is done. The miscellaneous gas discharge path L3 has a separation membrane M1 that does not transmit methane as the gas to be purified but transmits carbon dioxide as the miscellaneous gas. Further, a membrane separation device M for separating the purification target gas and the miscellaneous gas by the exhaust pressure of the adsorption towers A1 to A4 is provided, and the regeneration gas whose concentration of the purification target gas is increased by the separation membrane M1 is supplied to the raw material gas supply path L1. A regeneration gas return path L5 for return is provided, and an exhaust path L6 is provided on the miscellaneous gas permeation side of the membrane separation apparatus M in the miscellaneous gas discharge path L3.

  The product gas recovery path L2 has a product gas cleaning path L4 through which product gas as a cleaning gas flows from the product gas tank T2 into the adsorption towers A1 to A4 on the upstream side of the pressure control valve Vc2 (adsorption tower). (A1-A4 side). That is, the cleaning gas flows from the product gas tank T2 to the product gas cleaning path L4, and is supplied to each adsorption tower through the cleaning paths L14 to L44 having switching valves V14 to V44, and the gas in the adsorption towers A1 to A4. Is replaced with product gas and discharged as miscellaneous gas from the miscellaneous gas discharge path L3 through exhaust gas paths L13 to L43 provided with switching valves V13 to V43. Further, a pressure reducing valve Vr4, an on-off valve Vo, and a needle valve Vn4 are provided between the product gas recovery path L2 and the adsorption towers A1 to A4 in the product gas cleaning path L4. As a result, the product gas from the product gas tank T2 is flowed into the adsorption towers A1 to A4 through the washing paths L14 to L44 having the switching valves V14 to V44 from the product gas washing path L4 as the cleaning gas. A1 to A4 can be cleaned. Therefore, the washing pressures of the adsorption towers A1 to A4 are controlled by the pressure reducing valve Vr4, adjusted so as not to cause a rapid pressure change by the needle valve Vn4, and easily switched by the on-off valve Vo4.

The regeneration gas return path L5 is provided with a regeneration gas tank T5 and a regeneration pressure control valve Vc5. That is, the miscellaneous gas that has not permeated through the separation membrane M1 in the membrane separation device M is collected and stored in T5 through L5, and is re-supplied from the regeneration gas tank T5 to L1. As a result, the membrane separation pressure of the membrane separation apparatus M is controlled based on the exhaust pressure of each adsorption tower A1 to A4, and the regeneration gas stored in the regeneration gas tank T5 and returned to the regeneration gas return path L5 is a constant pressure. It is returned to the raw material gas supply path L1 and reused.

Further, a bypass passage L30 that bypasses the miscellaneous gas from the miscellaneous gas discharge passage L3 to the downstream side (regeneration gas tank T5 side) from the regeneration pressure control valve Vc5 of the regeneration gas return passage L5 without passing through the membrane separation device M. Is provided. On-off valves Vo3 and Vo5 are provided on the bypass passage L30 and the miscellaneous gas discharge passage L3 on the side of the membrane separator M from the bypass passage L30, so that miscellaneous gases having high methane purity can be directly regenerated without passing through the membrane separator M. Recoverable at T5.

  A decompression pump P6 is provided in the exhaust passage L6 on the miscellaneous gas permeation side of the membrane separator M. The decompression pump P6 is operated in a steady state and plays a role of maintaining the membrane separation pressure at a predetermined pressure or higher based on the miscellaneous gas discharge path L3 side pressure of the adsorption towers A1 to A4.

  Each adsorption tower A1 to A4 is provided with an inter-column pressure equalization path L7, and the gas discharged from the upper part of the adsorption towers A1 to A4 in each pressure equalization (pressure reduction) step is supplied to each pressure equalization (pressure increase) via L4. ) It can be transferred to the upper part of the adsorption towers A1 to A4 where the process is performed. That is, the gas discharged from the upper part of the adsorption towers A1 to A4 in the pressure equalization (step-down) step flows into the inter-column pressure equalization path L7 via the pressure equalization paths L17 to L47 provided with the switching valves V17 to V47. It flows into the adsorption towers A1 to A4 where each pressure equalization (pressure increase) process is performed through washing paths L14 to L44 including valves V14 to V44. At this time, the inter-column pressure equalizing path L7 is provided with a needle valve Vn7 and an on-off valve Vo7, whereby the gas discharged from the upper part of the adsorption tower through each pressure equalizing path is gradually moved by the needle valve Vn7. It is transferred and flows into different adsorption towers A1 to A4 through the product gas cleaning path L4. In the present embodiment, as shown in FIG. 1, the pressure equalizing path is configured to connect the upper parts of the adsorption towers to equalize the pressure, but the present invention is not limited to this. For example, the upper and lower parts of the adsorption towers The connecting structure, the structure connecting the lower part and the lower part, the structure connecting the intermediate part, and the like can be changed as appropriate.

  Each of the adsorption towers A1 to A4 is provided with a product gas pressure increase path L8 for supplying a product gas as a pressure-increasing gas inside the adsorption towers A1 to A4. That is, in the pressure increasing process, the product gas supplied from T2 flows into the respective adsorption towers from the product gas pressure increasing path L8 via pressure increasing paths L18 to L48 including switching valves V18 to V48. At this time, the product gas pressurization path L8 is provided with an on-off valve Vo8 and a pressure control valve Vc8, and the product gas can be boosted by advancing the product gas into the adsorption towers A1 to A4 based on the pressure held in the product gas tank T2. It is configured.

Moreover, the control apparatus C is provided in the gas purification apparatus. The controller C includes the adsorption towers A1 to A4, the raw material gas supply path L1, the product gas recovery path L2, the miscellaneous gas discharge path L3, the product gas cleaning path L4, the L5, the L6, and the L7. The switching valves V11 to V48 and the like provided in the pipes of L8 are controlled to open and close. Thus, the regeneration control device that functions as an adsorption / desorption control device that performs each adsorption step in each adsorption tower A1 to A4 using P1 and P6, and controls the membrane separation pressure of the separation membrane M1 by the regeneration pressure control valve Vc5. Alternatively, it also functions as a cleaning control device that cleans the adsorption towers A1 to A4 by flowing product gas from the product gas tank T2 into the adsorption towers A1 to A4.

Here, as the adsorbents A11 to A41, adsorbents A11 to A14 capable of selectively adsorbing miscellaneous gases mainly composed of carbon dioxide in biogas are preferably used. As such adsorbents A11 to A41, those mainly composed of at least one material selected from activated carbon, molecular sieve carbon, zeolite, and porous metal complex are used. Specifically, for example, the MP method The pore volume (V _0.40 ) at the pore diameter does not exceed 0.01 cm ³ / g and the pore volume (V _0.34 ) at the pore diameter of 0.34 nm is measured. A molecular sieve carbon having an A of 0.20 cm ³ / g or more is used.

  As the separation membrane M1, a material that transmits a miscellaneous gas mainly composed of carbon dioxide in the exhaust gas and does not transmit methane as a purification target gas is preferably used. Such a separation membrane is selected from cellulose acetate, polyamide, polyimide, polysulfone, polytetrafluoroethylene, polyethersulfone, carbon membrane, microporous glass composite membrane, DDR type zeolite, multi-branched polyimide silica, and polydimethylsiloxane. The main component is at least one kind of material.

  The biogas as the raw material gas used here is mainly for methane and carbon dioxide with a methane content rate of about 60%, to obtain a product gas containing 98% or more of methane. Perform gas purification.

[Adsorption tower]
The adsorption towers A1 to A4 are filled with adsorbents A11 to A14, respectively. Under the respective adsorption towers A1 to A4, supply paths L11 to L41 for supplying biogas from the source gas tank T1 by the supply pump P1 are provided to constitute the source gas supply path L1. Further, recovery paths L12 to L42 for recovering methane as a purification target gas that has not been adsorbed to the adsorbents A11 to A41 among the biogas supplied to the adsorption towers A1 to A4 are provided above the adsorption towers A1 to A4. A product gas recovery path L2 is provided. Thus, the biogas is supplied from the raw material gas supply path L1 to the adsorption towers A1 to A4, and the methane that has not been adsorbed by the adsorbents A11 to A14 is discharged from the product gas recovery path L2, thereby causing the adsorbents A11 to A14. It can be separated from methane by adsorbing miscellaneous gas. Further, in the adsorption towers A1 to A4, exhaust gas passages L13 to L43 for discharging the miscellaneous gases adsorbed by the adsorbents A11 to A14 are provided below the adsorption towers A1 to A4 to constitute the miscellaneous gas discharge passage L3. In addition, the biogas supplied from the raw material gas supply path L1 is adsorbed by the adsorbents A11 to A41, and is configured to be able to take out high-concentration carbon dioxide after concentration.

  The gas passages L11 to L48 are provided with switching valves V11 to 48, and the operation of the pumps P1 and P6 controls the switching of gas supply, discharge, and stop to the adsorption towers A1 to A4. The apparatus C can be controlled collectively.

[Membrane separator]
The membrane separation apparatus M includes a separation membrane M1 as a module, and is configured to be capable of recovering a purification target gas contained in the miscellaneous gas by performing membrane separation on the miscellaneous gas supplied via the miscellaneous gas discharge path L3. Specifically, when purifying methane as a gas to be purified using biogas as a raw material gas, carbon dioxide is the main component as miscellaneous gas, and a gas containing methane is supplied to the membrane separator M. The miscellaneous gas supplied to the membrane separator M comes into contact with the separation membrane M1 in the membrane separator M, and carbon dioxide permeates and is removed through the separation membrane M1 due to the membrane separation characteristics of the separation membrane M1. As the gas, a regenerated gas in which methane is more concentrated than the supplied miscellaneous gas is obtained. The regeneration gas is discharged to the regeneration gas return path L5 and returned to the raw material gas supply path L1, while the gas mainly composed of carbon dioxide that has permeated through the membrane is discharged to the outside through the exhaust path L6.

  The regeneration gas return path L5 is provided with a regeneration gas tank T5. The regeneration gas separated from the membrane is stored in the regeneration gas tank T5 and then returned to the raw material gas supply path L1 at a predetermined pressure.

[Methane enrichment method]
As shown in FIG. 3, the control device C controls the switching valves V11 to V47 and the pumps P1 and P6, and in accordance with FIG.
An adsorbing step of receiving a raw material gas from the raw material gas supply path L1, adsorbing a miscellaneous gas to the adsorbents A11 to A14, and collecting a product gas;
A pressure fluctuation operation is performed in which the desorption step of desorbing the miscellaneous gas mainly composed of carbon dioxide adsorbed on the adsorbents A11 to A14 and exhausting it from the miscellaneous gas discharge path L3 is performed alternately.

Specifically, in this pressure fluctuation operation, as shown in FIG.
A supply of biogas in the vicinity of atmospheric pressure from the lower part of the adsorption towers A1 to A4 is supplied to the adsorbents A11 to A41 by the supply pump P1, adsorbing miscellaneous gas mainly composed of carbon dioxide, and as a gas to be purified. Before and after the adsorption step of releasing the product gas mainly composed of methane from the upper part of the adsorption towers A1 to A4, a parallel adsorption process is performed in which the adsorption process proceeds simultaneously to the two adsorption towers A1 to A4. Adsorption process, adsorption process, and post-parallel adsorption process are performed in order)
After the post-parallel adsorption step, the gas having a relatively low concentration in the high-pressure adsorption towers A1 to A4 is transferred to other adsorption towers A1 to A4 in an intermediate pressure state lower than the adsorption towers A1 to A4. The first-stage pressure equalization (pressure reduction) step for setting the pressure in the adsorption towers A1 to A4 to an intermediate pressure state on the high-pressure side,
A standby step in which the operation of the adsorption towers A1 to A4 is not performed,
A gas having a slightly higher methane concentration than the first-stage pressure equalization (pressure reduction) process in the adsorption towers A1 to A4 in the intermediate pressure state higher than the low pressure state is transferred to the other adsorption towers A1 to A4 in the low pressure state. A final pressure equalization (pressure reduction) step in which the pressure in the adsorption towers A1 to A4 is set to an intermediate pressure state on the low pressure side,
After the pressure in the tower is lowered by the pressure equalization (pressure reduction) step, the adsorbents A11 to A41 are further depressurized to a low pressure state, and the miscellaneous gases adsorbed on the adsorbents A11 to A41 are desorbed to adsorb the towers A1 to A1. Desorption process to recover from the bottom of A4,
A cleaning process in which the miscellaneous gas remaining in the adsorption towers A1 to A4 regenerated of the adsorbents A11 to A14 by the desorption process is replaced with a product gas. First-stage pressure equalization (pressure increase) step of receiving the gas in the adsorption towers A1 to A4 and setting the pressure in the adsorption towers A1 to A4 to an intermediate pressure state on the low pressure side;
Waiting process;
The gas in the other adsorption towers A1 to A4 in the high pressure state is received into the adsorption towers A1 to A4 in the intermediate pressure state on the low pressure side, and the pressure in the adsorption towers A1 to A4 is changed to the intermediate pressure state on the high pressure side. Pressure equalization (pressure increase) process;
After increasing the pressure in the tower by the pressure equalization (pressure increase) step, pressurization air is further supplied from above the adsorption towers A1 to A4 into the adsorption towers A1 to A4, and methane is selected as the adsorbents A11 to A41. Boosting process to restore the high-pressure state that can be adsorbed automatically,
The operation is controlled in such a way as to perform in order.

  Moreover, the internal pressure of each adsorption tower A1-A4 changes like FIG. 4 by such control. That is, by sequentially reducing the pressure in the tower through each pressure equalization process, the desorption process can be performed from a state where the pressure in the tower is greatly reduced, and adsorption is performed by desorbing the miscellaneous gas adsorbed on the adsorbent with less power. The material can be easily regenerated.

  More specifically, the adsorption tower A1 is controlled according to the following steps. The same operation is performed by shifting the phases of the other adsorption towers A2 to A4. However, since the description is duplicated, the detailed description is omitted with the description of FIGS. The adsorption towers A1 to A4 are referred to as first to fourth adsorption towers A1 to A4 in this order. 2 and 3 show the operating state of the on-off valve and the like in each step. Further, <number> in the following description indicates a step number in FIGS. The operating conditions specifically shown below are examples, and the present invention is not limited to the following specific examples.

<1> Pre-parallel adsorption process As shown in FIGS. 2 and 3, biogas as a raw material gas is introduced into the first adsorption tower A1 from the raw material gas tank T1. At this time, the pressure in the first adsorption tower A1 is increased by the supply pressure of the raw material gas. Further, carbon dioxide as a miscellaneous gas in the biogas supplied from the raw material gas tank T1 through the switching valve V11 of the supply path L11 is adsorbed to the adsorbent A11, and methane as a product gas that has not been adsorbed is recovered. It collects in the product gas tank T2 via the switching valve V12 of the path L12.
Here, in the initial stage of the adsorption process, in order to gradually increase the internal pressure of the first adsorption tower A1, the internal pressure of the fourth adsorption tower A4 is gradually decreased at the end of the adsorption process of the fourth adsorption tower A4. The adsorption process of the first adsorption tower A1 is started. That is, prior to the start of the adsorption process of the first adsorption tower A1, the pre-parallel adsorption process is performed together with the post-parallel adsorption process of the fourth adsorption tower A4.

  At this time, the second adsorption tower A2 becomes a standby process, and the third adsorption tower A3 starts the desorption process.

  This pre-parallel adsorption step is performed for about 5 seconds, and adsorption separation of methane and carbon dioxide in the raw material gas is started in the first adsorption tower A1.

<2-4> Adsorption process As shown in FIGS. 2 and 3, biogas is introduced into the first adsorption tower A1 from the raw gas tank T1 following the preceding parallel adsorption process. At this time, the pressure in the first adsorption tower A1 is further increased by the supply pressure of the raw material gas. Further, methane is recovered in the product gas tank T2 while carbon dioxide is adsorbed on the adsorbent A11 via the switching valve V11 of the supply path L11.

At this time, in the second adsorption tower A2, the <1> final pressure equalization (pressure increase) step is performed and the process proceeds to the <2-3> pressure increase step.
In the third adsorption tower A3, after the <1> desorption step, a <2> cleaning step and a <3> first-stage pressure equalization (pressure increase) step are performed.
Further, in the fourth adsorption tower A4, the <1> first-stage pressure equalization (step-down) process is performed, and the <2> standby step is interposed, and the process proceeds to the <3> final pressure-equalization (step-down) process.

Further, the methane purity in the product gas at this time can be set by setting the time of the adsorption process, and can be 90% or more.
For example, a cylindrical type (inner diameter 54 mm, volume 4.597 L) adsorption tower A1 is used,
As the adsorbent A11, when the pore size distribution is measured by the MP method and the pore size is 0.38 nm or more, the pore volume (V _0.40 ) at the pore size is 0.05 cm ³ / g. Using molecular sieve carbon having a pore volume (V _0.34 ) of 0.20 to 0.23 cm ³ / g at a pore diameter of 0.34 nm,
When a biogas of about 60% methane and about 40% carbon dioxide was processed at 10 L / min,
When the adsorption process is performed for 90 seconds with the supply pressure of the supply pump P1 being about 0.8 MPaG, a product gas tank with a product gas tank with a methane concentration of 96 to 98%, a carbon dioxide concentration of 2% and a pressure of about 0.7 to 0.75 MPaG is used. It was possible to recover at T2.

<5> Post-parallel adsorption process At the end of the adsorption process of the first adsorption tower A1, a post-parallel adsorption process is performed in which the adsorption process is performed in parallel with the second adsorption tower A2 at the beginning of the adsorption process. That is, since the biogas supply amount in the adsorption step and the sum of the biogas supply amounts to the first and second adsorption towers A1 and A2 in this step are the same, in this step, the first and second adsorption towers A1 are used. , A2 is set to be smaller than the biogas supply amount in the adsorption process. Therefore, as shown in FIGS. 2 and 3, in this process, by reducing the adsorption flow rate at the end of the adsorption process, the environmental change in the adsorption tower can be suppressed so as to proceed gently, and the adsorption tower A1. It is possible to stabilize the internal biogas flow, suppress the generation of turbulent flow in the adsorption tower A1, and allow the adsorbent A11 to act stably.

  At this time, a standby process is performed in the third adsorption tower A3, and a desorption process is performed in the fourth adsorption tower A4.

  Further, the subsequent parallel adsorption step is performed for 5 seconds immediately after the adsorption step.

<6> First-stage pressure equalization (pressure reduction) process In the first adsorption tower A1 after the adsorption process, the first-stage pressure equalization (pressure reduction) process is performed with the third adsorption tower A3 that performs the final pressure equalization (pressure increase) process. That is, as shown in FIGS. 2 and 3, the non-adsorbed gas in the tower is discharged via the switching valve V17 of the pressure equalizing path L17 and transferred to the third adsorption tower A3 via the switching valve V34 of the cleaning path L34. It is the composition to do. As a result, as shown in FIG. 3, the first adsorption tower A1 is pressure balanced with the third adsorption tower A3 in the intermediate pressure state on the low pressure side.

  At this time, the adsorption process is performed in the second adsorption tower A2, and the desorption process is performed in the fourth adsorption tower A4.

  In addition, this first-stage pressure equalization (step-down) step is performed for 5 seconds, and shifts to an intermediate pressure state on the high pressure side of about 0.5 MPaG.

<7> Standby process Next, 1st adsorption tower A1 will be in a standby state, and the intermediate pressure state of a high voltage | pressure side is maintained.

  At this time, the second adsorption tower A2 performs the adsorption process, the third adsorption tower A3 shifts to the pressure increasing process, and the fourth adsorption tower A4 shifts to the washing process.

  The standby process is performed for 90 seconds, and the intermediate pressure state on the high pressure side is maintained.

<8> Final pressure equalization (pressure reduction) step Next, as shown in FIGS. 2 and 3, the first adsorption tower A <b> 1 finishes the desorption process and performs the first-stage pressure equalization (pressure increase) process with the fourth adsorption tower A <b> 4. The final pressure equalization (pressure reduction) process is performed in between. That is, the non-adsorbed gas in the tower and the miscellaneous gas that starts to be desorbed from the adsorbent A11 are discharged through the switching valve V17 in the pressure equalizing path L17, and the fourth adsorbing tower through the switching valve V44 in the cleaning path L44. It is configured to transfer to A4. Thereby, the first adsorption tower A1 finishes the desorption process, and the pressure is balanced with the fourth adsorption tower A4 in the low pressure state.

  At this time, the second adsorption tower A2 is performing an adsorption process, and the third adsorption tower A3 is performing a pressure increasing process.

  Further, this final pressure equalization (pressure reduction) step is performed for 5 seconds, and shifts to an intermediate pressure state on the low pressure side of about 0.25 MPaG.

<9-10> Desorption Step As shown in FIGS. 2 and 3, the first adsorption tower A1 that has reached the intermediate pressure state on the low pressure side is adsorbing a high-concentration miscellaneous gas to the adsorbent A11 in the tower. The high concentration miscellaneous gas adsorbed by the adsorbent A11 is recovered by performing a desorption process in which the inside of the tower is depressurized from an intermediate pressure state on the low pressure side to a low pressure state. That is, the miscellaneous gas concentrated through the switching valve V13 of the exhaust gas passage L13 is supplied to the membrane separation device M by the internal pressure of the first adsorption tower A1.
The operation state of the membrane separation apparatus M at this time will be described later.

At this time, the second adsorption tower A2 performs the <8> post-parallel adsorption process in parallel with the third adsorption tower A3, and then the <9> first-stage pressure equalization (pressure reduction) process with the fourth adsorption tower A4. Is done.
In the third adsorption tower A3, the <9> pre-adsorption process is performed in parallel with the second adsorption tower A2, and then the <9> adsorption process is performed.
In the fourth adsorption tower A4, after the <8> standby process, a <9> final pressure equalization (pressure increase) process is sequentially performed with the second adsorption tower A2.

  Further, this desorption step is performed for 365 seconds, and the first adsorption tower A1 shifts from the intermediate pressure state on the low pressure side to the low pressure state of almost atmospheric pressure as shown in FIG.

<11> Cleaning step As shown in FIGS. 2 and 3, the first adsorption tower A1 that has shifted to a low pressure state replaces the gas in the tower with a gas mainly composed of methane by flowing the product gas into the tower. Wash. That is, the on-off valve Vo4 of the product gas cleaning path L4 is opened, the needle valve Vn4 is adjusted, and the product gas is allowed to flow from the product gas tank T2 to the first adsorption tower A1 through the switching valve V14 of the cleaning path L14. Is gently applied to the adsorption tower A1, the atmosphere in the first adsorption tower A1 is replaced with methane, and the gas exhaust gas remaining in the first adsorption tower A1 is passed through the switching valve V13 of the exhaust gas passage L13. It supplies to discharge to the miscellaneous gas discharge path L3.
At this time, the on-off valve Vo5 is opened, the on-off valve Vo3 is closed, and the cleaning gas containing the product gas as a main component is transferred to the regeneration gas return path L5, bypassing the membrane separation device M, and directly into the regeneration gas tank. It is set as the structure collect | recovered at T5.

  At this time, the second adsorption tower A2 becomes a standby process, and the third adsorption tower A3 continues the adsorption process. In the fourth adsorption tower A4, a pressure increasing process is performed.

  This washing step is performed for about 90 seconds, and the inside of the first adsorption tower A1 is shifted to a low pressure state of almost atmospheric pressure.

<12> First-stage pressure equalization (pressure increase) step As shown in FIGS. 2 and 3, in the first adsorption tower A1 in which the adsorbent A11 is regenerated by releasing the adsorbed methane by releasing the adsorbed methane, the second adsorption tower By performing the first-stage pressure equalization (pressure increase) step with A2, the pressure in the tower is recovered, and the initial pressure from the adsorbent A11 discharged in the final pressure equalization (pressure decrease) step in the second adsorption tower A2 The desorbed gas receives exhaust gas containing a relatively high concentration of methane. That is, in the inter-column pressure equalizing path L7, the gas in the column discharged from the second adsorption tower A2 in the intermediate pressure state on the high pressure side via the switching valve V27 in the pressure equalizing path L27 is transferred from the switching valve V14 in the cleaning path L14. accept. As a result, the first adsorption tower A1 recovers the pressure from the low pressure state to the intermediate pressure state on the low pressure side, as shown in FIG.

  At this time, the third adsorption tower A3 continues the adsorption process, and the fourth adsorption tower A4 performs the pressure increasing process.

  This first-stage pressure equalization (pressure increase) step is performed for about 10 seconds, and the first adsorption tower A1 recovers the pressure to about 0.25 MPaG.

<13> Standby Step Next, as shown in FIGS. 2 and 3, the first adsorption tower A1 is in a standby state, and the intermediate pressure state on the high pressure side is maintained.

  At this time, the second adsorption tower A2 is performing the desorption process, and the third adsorption tower A3 and the fourth adsorption tower A4 are shifted to the post-parallel adsorption process and the pre-parallel adsorption process.

  This standby process is performed for about 5 seconds, and the first adsorption tower A1 is maintained at about 0.25 MPaG.

<14> Final pressure equalization (pressure increase) step As shown in FIGS. 2 and 3, the first adsorption tower A <b> 1 that has recovered the pressure to the intermediate pressure state on the low pressure side immediately after the adsorption step is finished, The pressure in the column is further recovered by performing a final pressure equalization (pressure increase) step with the third adsorption tower A3 that performs the (pressure decrease) step. That is, in the pressure equalization paths L17 to L37 of the inter-column pressure equalization path L7, the gas in the tower discharged from the high-pressure third adsorption tower A3 is received via the switching valves V17 and V37. Thereby, as shown in FIG. 3, the first adsorption tower A1 recovers the pressure from the low pressure side intermediate pressure state to the high pressure side intermediate pressure state.

  At this time, the desorption process is performed in the second adsorption tower A2, and the adsorption process is performed in the fourth adsorption tower A4.

  This final pressure equalization (pressure increase) step is performed for about 10 seconds, and the pressure in the first adsorption tower A1 is increased to about 0.5 MPaG.

<15-16> Boosting Step As shown in FIG. 3, the first adsorption tower A <b> 1 that has recovered the pressure to the intermediate pressure state on the high pressure side is restored to the high pressure state by injecting the product gas. That is, the product gas is caused to flow into the first adsorption tower A1 via the switching valve V14 of the product gas cleaning path L4. Thereby, the inside of the first adsorption tower A1 is restored to a high pressure state, and is regenerated to a high pressure state capable of adsorbing carbon dioxide in the biogas by supplying the biogas.

  At this time, in the second adsorption tower A2, after the <14> washing process, a <15> first-stage pressure equalization (pressure increase) process is performed with the third adsorption tower A3. In the third adsorption tower A3, after the <14> standby process, a <15> final pressure equalization (pressure reduction) process is performed with the second adsorption tower A2. Further, an adsorption step is performed in the fourth adsorption tower A4.

  This pressurization step is performed for about 50 seconds, and the pressure in the first adsorption tower A1 is increased to 0.8 MPaG that can separate methane and carbon dioxide in the biogas.

[Operation status of membrane separator]
The miscellaneous gas discharge path L3 is provided with a membrane separation device M having a separation membrane M1, and separates methane by permeating carbon dioxide from miscellaneous gas mainly composed of carbon dioxide discharged from the miscellaneous gas discharge path L3. Connected as possible. A gas that does not permeate the separation membrane M1 and has an increased methane concentration is discharged as a regeneration gas to the regeneration gas return path L5, and a gas mainly containing carbon dioxide that permeates the separation membrane M1 and passes through the separation membrane M1. Thus, it can be discharged into the exhaust path L6.

  At the time of the desorption process, the primary side pressure of the separation membrane M1 by the membrane separation apparatus M becomes the exhaust pressure of the adsorption towers A1 to A4, and thus varies to about 0.25 MPaG to 0 MPaG. -0.1 MPaG (equivalent to vacuum), the membrane separation pressure of 0.35 MPaG to 0.1 MPaG is maintained, and a continuous membrane separation operation can be performed.

  In the cleaning process, the primary pressure of the membrane separation by the membrane separation device M becomes the cleaning pressure of the adsorption towers A1 to A4 and is constant at about 0 MPaG, so the membrane separation pressure of 0.1 MPaG is maintained. Although continuous membrane separation operation can be performed, basically, when product gas is used as a cleaning gas, the gas supplied to the membrane separator M does not contain much carbon dioxide gas. Sufficient gas separation is continued.

  With such a configuration, the exhaust gas discharged from the exhaust path L6 can be an exhaust gas of about 2 to 6% methane and 94 to 98% carbon dioxide. The gas composition returned to the regeneration gas return path L5 is a methane-containing gas of about 60% methane and about 40% carbon dioxide.

Further, provided with the regeneration pressure control valve Vc5 the regeneration gas return path L5, between the membrane separation device M and the regeneration pressure control valve Vc5, is provided with a regeneration gas tank T5, the regeneration gas return passage L5 is raw material Since it is connected to the upstream side of the supply pump P1 in the gas supply path L1, the regeneration gas can be mixed with the raw material gas and separated and purified again.

In the methane concentration method of the above embodiment, when a biogas of 60% methane is treated at 10 L / min, a product gas of 96 to 98% methane and an exhaust gas of 2 to 5% methane are obtained, and the methane recovery rate Was 95%. Further, even if the flow rate is increased to 17 L / min, a product gas of 96 to 98% methane and an exhaust gas of 2 to 5% methane are obtained, and the methane recovery rate is 95%, with the same concentration efficiency and recovery rate. It was confirmed that concentration was possible.
On the other hand, when the adsorption tower was operated with pressure fluctuation and the methane concentration was performed without using the membrane separator, methane 96 was obtained when 60% methane biogas was processed at 10 L / min. When ˜98% product gas was obtained, the exhaust gas was 15-20% methane, and the methane recovery was 83%.
That is, according to the methane concentration method of the present invention, it was experimentally clarified that both high concentration efficiency and high recovery rate can be achieved.

[Another embodiment]
(1)
The gas purification apparatus can be appropriately provided with a pressure sensor, a temperature sensor, and the like. Specifically, a pressure sensor or a gas sensor for monitoring the supply pressure of the raw material gas or the methane concentration of the product gas is usually provided, but detailed description is omitted in the above-described embodiment. .

(2)
Further, the supply pump P1 and the decompression pump P6 for allowing the gas to flow through each pipe are not limited to the above arrangement, and can be variously modified as long as the gas can flow. Specifically, in the above-described gas refining apparatus, it is constituted of a necessary minimum, raw material supply pump to the upstream side (raw gas tank T1 side) than the connection portion between the regeneration gas return passage L5 in the gas supply passage L1 P1 For example, the supply pump P1 may be omitted, and the compression pump P5 that applies the supply pressure of the source gas to the source gas supply path L1 may be provided in the regeneration gas return path L5. In such a case, for example, the supply pressure to the raw material gas supply path L1 is appropriately maintained by the pressure control valve Vc51 configured as shown in FIG. 5 and provided in the bypass path bypassed to the compression pump P5.

(3)
Further, according to the description of the above-described embodiment, it is clear that the exhaust passage L6 can be operated without providing the pressure reducing pump P6, and the pressure reducing pump P6 is omitted from the viewpoint of simplifying the equipment. It is preferable to provide a decompression pump P6 from the viewpoint of stabilizing the membrane separation pressure. In the case of providing the decompression pump P6, it is desirable to operate the decompression pump P6 in a steady manner from the viewpoint of stable operation. However, Steps 3, 7, 11, 15 in which the cleaning process in FIG. In steps 4, 8, 12, and 16 until the desorption process is started, the decompression pump P6 can be operated at a low load or stopped. In such a case, the regeneration pressure control valve Vc5 can be fixed in a state where the opening degree is reduced or in a closed state.

  That is, in the desorption process, the gas in the miscellaneous gas discharge path L3 needs to be membrane-separated to obtain a regenerated gas. Therefore, it is necessary to sufficiently apply the membrane separation pressure. When a product gas is used at the time of a process that does not flow out or at the time of a cleaning process, it is less necessary to perform membrane separation. In the first place, the gas supply pressure to the membrane separation apparatus M is low in the cleaning process. Therefore, the output of the decompression pump P6 can be lowered during a time period when the membrane separation pressure is not required. When the output of the pressure reducing pump P6 is reduced according to the required membrane separation pressure, the pressure reducing pump P6 can be inverter-controlled.

(4)
In the above embodiment, in the regeneration gas return path L5, it is assumed that the amount of gas recovered from the membrane separator M exceeds the amount of gas re-supplied to the raw material gas supply path L1 in order to balance the gas composition. . In such a case, since the gas stored in the regeneration gas tank T5 continues to increase, a waste path for discarding excess regeneration gas can be provided in the regeneration gas tank T5.

(5)
As described above, since the product gas is the main component of the gas flowing through the miscellaneous gas discharge passage L3 during the cleaning process, it may be recovered directly as the product gas after the membrane separation process. It can be purity. Moreover, even if it is the regeneration gas in a normal desorption process, it may have sufficient purity similarly. In such a case, as shown in FIG. 6, the regeneration gas return path L5 is provided with a regeneration gas recovery path L9 for recovering the regeneration gas as product gas, and the product gas recovery path L2 is connected via the press-fit pump P9. It can also be bypassed. In such a case, depending on the composition of the gas flowing through the miscellaneous gas discharge path L3, the regeneration gas distribution destination is the regeneration gas return path L5 → the raw material gas supply path L1, or the regeneration gas recovery path L9 → the product gas tank T2. Or branch control. That is, when the product gas purity of the regeneration gas is high, the regeneration gas is recovered to the product gas tank T2 via the regeneration gas recovery path L9, and when the product gas purity of the regeneration gas is low, the raw material is returned via the regeneration gas return path L5. It can be set as the form which returns to the gas supply path L1.
In addition, as another embodiment of reference, for example, (1) When the regeneration gas can always be maintained at the product gas purity that can be recovered as the product gas, or (2) The regeneration gas has a higher purity than the source gas. Or (3) the regeneration gas return path L5 is omitted if it has a purity that can be sufficiently used as a fuel for power generation by adding an appropriate amount of source gas to the regeneration gas. Thus, only the regeneration gas recovery path L9 can be provided (see FIG. 13).

(6)
In the above embodiment, the gas purification apparatus includes four adsorption towers A1 to A4. However, the gas purification apparatus is not limited to this, and may be a system that alternately processes two or three towers. Any configuration that can perform typical PSA is acceptable. For example, three towers can be configured as shown in FIG.

(7)
The PSA cycle is not limited to the above-described configuration as long as each adsorption tower can be effectively used continuously, and various modifications can be made. For example, if the gas purification apparatus has the configuration shown in FIG. 7, the operation method according to FIG. 8 is possible.

(8)
In the previous embodiment, the product gas was supplied at a static pressure (no pressure applied) to the adsorption tower during the cleaning step, but the cleaning step can be performed in a pressurized state. In this case, the cleaning efficiency can be improved.

(9)
The gas purification apparatus of the present invention has shown an example used for biogas purification, but in addition to biogas, for example, coal mine gas, etc. It can be used for the purpose of purification by adsorbing miscellaneous gases other than the gas to be purified from the raw material gas. Can be changed.

(10)
In addition to the configuration of the previous embodiment, as shown in FIG. 9, a buffer tank T3 can be provided in the upstream portion of the membrane separation device M in the miscellaneous gas discharge path L3. Vc52 is a pressure control valve for appropriately maintaining the pressure in the buffer tank T3 lower than the internal pressure of the adsorption towers A1 to A4. In addition, L9 in FIG. 9 is similar to the regeneration gas recovery path L9 in FIG. 6 and is denoted by the same reference numeral as being a conduit for recovering the regeneration gas to the product gas recovery path L2 via the press-in pump P9. It is shown.

  In this case, the buffer tank can temporarily store the miscellaneous gas discharged in the desorption process before being supplied to the membrane separation device. At this time, high-pressure miscellaneous gas containing the gas to be purified having a relatively high concentration can be accumulated in the buffer tank by pressure equalization operation by the pressure difference between the adsorption tower and the buffer tank. Among miscellaneous gases, miscellaneous gases having a relatively low pressure can be supplied to the regeneration gas tank via Vo5, and the miscellaneous gases in the buffer tank and the regeneration gas tank are not subjected to the desorption process in the adsorption tower. Even if it exists, it can supply to a membrane separator as needed.

  After that, when the miscellaneous gas in the buffer tank is supplied to the membrane separation device, the high-pressure miscellaneous gas discharged from the adsorption tower in the initial stage can be relaxed and supplied to the membrane separation device. While performing a membrane separation operation with a high recovery rate using the pressure of the miscellaneous gas, the gas to be purified can be purified from the miscellaneous gas with high accuracy.

Also in the configuration of FIG. 9, as in the configuration of FIG. 6, the regeneration gas distribution destination is changed from the regeneration gas return path L5 to the source gas supply path L1 in accordance with the composition of the gas flowing in the miscellaneous gas discharge path L3. Alternatively, branch control can be performed such that the regeneration gas recovery path L9 is changed to the product gas tank T2, or the regeneration gas recovery path L9 is directly used as the product gas. That is, when the product gas purity of the regeneration gas is high, the regeneration gas is recovered in the product gas tank T2 via the regeneration gas recovery path L9, or the product gas in the product gas tank T2 without being recovered in the product gas tank T2. The product gas can be used as another product gas for other purposes, and when the product gas purity of the regeneration gas is low, it can be returned to the raw material gas supply path L1 via the regeneration gas return path L5.
As another embodiment of reference, when it is possible to always maintain the product gas purity so that the regeneration gas can be recovered as the product gas, the regeneration gas return path L5 may be omitted and only the regeneration gas recovery path L9 may be provided. it can.

(11)
The operation method according to FIGS. 10 to 12 can be performed by simplifying the piping and valve configuration in the gas purification apparatus having the configuration of FIGS.
That is, according to the configuration of FIGS. 10 to 12, the pressure of the adsorption tower by the product gas is omitted, and the pressure by the raw material gas is eliminated, so that the product gas pressure increasing path L <b> 8 is unnecessary and the cleaning process is unnecessary. The gas cleaning path L4 is unnecessary. At this time, loss of product gas due to pressure increase can be saved, so that the product gas recovery rate can be improved. Further, by providing a standby process after the post-parallel adsorption process, the pressure fluctuation is temporarily interrupted, so that the pressure changes in three stages from the maximum pressure to the minimum pressure in FIG. 4, but becomes slower in four stages in FIG. As a result, there is no sudden pressure fluctuation in the adsorption tower, which contributes to a more stable operation of the gas purification apparatus.

  The gas purification apparatus of the present invention can recover higher-purity methane, and can be used as a gas purification apparatus that can effectively utilize biogas and the like that have been difficult to reuse in the past with a high methane recovery rate. be able to.

A1 to A4: (first to fourth) adsorption towers A11 to A41: adsorbent C: control device L1: raw material gas supply path L2: product gas recovery path L3: miscellaneous gas discharge path L4: product gas cleaning path L5: regeneration Gas return path L6: Exhaust path L7: Inter-column pressure equalization path L8: Product gas pressure increase path L9: Regeneration gas recovery path L10, L30: Bypass paths L11-L41: Supply paths L12-L42: Recovery paths L13-L43: Exhaust path L14 to L44: Washing paths L17 to L47: Pressure equalizing paths L18 to L48: Boosting path M: Membrane separation device M1: Separation membrane P1: Supply pump P5: Compression pump P6: Pressure reducing pump P9: Pressurizing pump T1: Feed gas tank T2: Product gas tank T5: Regeneration gas tanks V11 to V44: Switching valves Vc1 to Vc8: Pressure control valves Vn4, Vn7: Needle valves Vo3 to Vo8: On-off valves Vr4: Pressure reducing valves

Claims (14)

An adsorption tower filled with an adsorbent that adsorbs miscellaneous gases other than the gas to be purified from the source gas is provided.
A source gas supply path for supplying source gas to the adsorption tower is provided,
A product gas recovery path for discharging the gas to be purified that has not been adsorbed on the adsorbent as product gas is provided,
Provide a miscellaneous gas discharge path for desorbing and exhausting miscellaneous gas adsorbed on the adsorbent,
The adsorption tower, the source gas supply path, the product gas recovery path, and the miscellaneous gas discharge path,
An adsorption step of receiving a raw material gas from the raw material gas supply path, adsorbing a miscellaneous gas to the adsorbent, and collecting a product gas;
A desorption step of desorbing the miscellaneous gas adsorbed on the adsorbent and depressurizing the miscellaneous gas discharge path;
A gas purifier connected to perform pressure fluctuation operation alternately,
The miscellaneous gas discharge path has a separation membrane that does not transmit the gas to be purified and transmits the miscellaneous gas, and a membrane separation device that separates the gas to be purified and the miscellaneous gas by the exhaust pressure of the adsorption tower,
A regeneration gas return path is provided for returning the regeneration gas whose concentration of the gas to be purified is increased by the separation membrane to the source gas supply path,
The regeneration gas return path is provided with a regeneration pressure control valve that controls the pressure by adjusting the opening so that the exhaust pressure of the adsorption tower gradually decreases during the desorption process, and the separation membrane is controlled by the regeneration pressure control valve. of includes a reproduction control unit for controlling the membrane separation pressure, the gas purification system further controls the membrane separation pressure of the membrane separation device using the regeneration pressure control valve to exhaust pressure of the adsorption tower.   The gas purification apparatus according to claim 1, further comprising a regeneration gas recovery path that recovers a regeneration gas having a concentration of a purification target gas increased by the separation membrane as a product gas.   The gas purification apparatus according to claim 1 or 2, further comprising a bypass path for bypassing the miscellaneous gas flowing through the miscellaneous gas discharge path to the regeneration gas return path by bypassing the membrane separation device.   The gas purification apparatus according to any one of claims 1 to 3, wherein a buffer tank is provided upstream of the membrane separation apparatus in the miscellaneous gas discharge path.   The gas purification apparatus as described in any one of Claims 1-4 provided in the state which carries out the steady operation of the decompression pump in the miscellaneous gas permeation | transmission side of the said membrane separator in the said miscellaneous gas discharge path.   The gas purification apparatus according to any one of claims 1 to 5, wherein a regeneration gas tank is provided in the regeneration gas return path.   The gas purification apparatus according to any one of claims 1 to 6, wherein a product gas tank is provided in the product gas recovery path.   A product gas cleaning path for flowing product gas from the product gas tank to the adsorption tower is provided, a product pressure control valve is provided between the product gas tank and the adsorption tower in the product gas cleaning path, and product gas is supplied from the product gas tank. The gas purification apparatus according to claim 7, further comprising a cleaning control device that flows into the adsorption tower to wash the adsorption tower.   The gas purification apparatus according to any one of claims 1 to 8, wherein the source gas is a methane-containing gas, the gas to be purified is methane, and the miscellaneous gas is a gas mainly containing carbon dioxide.   The gas purification apparatus according to any one of claims 1 to 9, wherein the raw material gas is a methane-containing gas containing 40% or more of methane as a gas to be purified, and a product gas containing 90% or more of methane is obtained.   The gas purification apparatus according to any one of claims 1 to 10, wherein the adsorbent is mainly composed of at least one material selected from activated carbon, molecular sieve carbon, zeolite, and a porous metal complex. When the adsorbent has a pore diameter of 0.38 nm or more measured by the MP method, the pore volume (V _0.40 ) at the pore diameter does not exceed 0.01 cm ³ / g, and the pore diameter is 0.34 nm. The gas purifier according to claim 11, which is a molecular sieve carbon having a pore volume (V _0.34 ) of 0.20 cm ³ / g or more.   The separation membrane is at least one selected from cellulose acetate, polyamide, polyimide, polysulfone, polytetrafluoroethylene, polyethersulfone, carbon membrane, microporous glass composite membrane, DDR type zeolite, multi-branched polyimide silica, and polydimethylsiloxane. The gas purification apparatus according to any one of claims 1 to 12, wherein the gas purification apparatus is composed mainly of a material.   The gas purification apparatus according to any one of claims 1 to 13, wherein a pressure pump is provided in the source gas supply path, and a supply pressure of the source gas by the pressure pump to the adsorption tower is 0.5 MPaG to 2 MPaG.

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