JP2014073477A - Method for refining mixed gas and refining equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for refining a mixed gas and a refining equipment which can inhibit a concentration of a target gas in a refined gas from becoming less than a desired concentration while improving a recovery ratio of the target gas from the mixed gas.SOLUTION: Provided is a method for refining a mixed gas whereby a mixed gas is refined by a pressure swing adsorption method to obtain a refined gas by using a refining equipment provided with at least two adsorption towers packed with an adsorbent. While an adsorption process is performed with at least one adsorption tower, a desorption process is performed with at least one of the remaining adsorption towers and, at the same time, at least a portion of a desorbed gas is circulated as a recycled gas into the adsorbing tower which is performing an adsorption process and, at the end of the adsorption, concentrations of a target gas and/or an impurity gas in the mixed gas are measured, and, using the concentrations of the gases in the mixed gas, a maximum time is determined, during which the recycled gas can be circulated into the adsorbing tower when performing the next adsorption process. Also provided is a refining apparatus suitable for the refining process.

Description

  The present invention relates to a mixed gas purification method and purification apparatus, and more particularly to a mixed gas purification method and purification apparatus using a pressure swing adsorption method (PSA method).

  Conventionally, as a method of purifying a mixed gas and obtaining a purified gas containing a specific gas (hereinafter referred to as “target gas”) at a high concentration, a method of purifying the mixed gas using a pressure swing adsorption method has been used. .

  Here, the pressure swing adsorption method is a gas separation method utilizing the fact that the amount of gas adsorbed on the adsorbent varies depending on the gas species and the partial pressure of the gas. In the purification of the mixed gas using the pressure swing adsorption method, an adsorption process for supplying the mixed gas under pressure to an adsorption tower filled with an adsorbent to obtain a purified gas enriched in the target gas, and an adsorbent A desorption step of regenerating the adsorbent by desorbing the adsorbed gas under a pressure lower than that of the adsorption step is performed alternately.

  By the way, in the adsorption process of the pressure swing adsorption method, in addition to a gas other than the target gas contained in the mixed gas (hereinafter referred to as “impurity gas”), a part of the target gas is also adsorbed by the adsorbent. . Further, at the end of the adsorption step, the purified gas containing the target gas remains in the void portion in the adsorption tower. Therefore, in the initial stage of the desorption process, the desorption gas containing both the impurity gas and the target gas is discharged from the adsorption tower. Therefore, in the purification of mixed gas using the pressure swing adsorption method, if the entire amount of desorption gas generated in the desorption process is discharged out of the system, part of the target gas contained in the mixed gas is discharged out of the system. As a result, the recovery rate of the target gas from the mixed gas (= (amount of target gas in the obtained purified gas / amount of target gas in the supplied mixed gas) × 100%) is reduced.

Therefore, in recent years, a technique has been proposed in which the target gas is recovered from the desorption gas discharged in the initial stage of the desorption process, thereby improving the recovery rate of the target gas from the mixed gas.
Specifically, in Patent Document 1, for example, at least one of the remaining adsorption towers is prepared while two or more adsorption towers filled with an adsorbent are prepared and the adsorption step is performed in at least one adsorption tower. In addition, the desorption process is performed, and the first 20 to 40% of the total desorption gas discharged from the adsorption tower in the desorption process is circulated to the adsorption tower that is performing the adsorption process as a recycle gas. The recovery rate is increased.

International Publication No. 95/26804

  Here, in general, when a purified gas obtained by purifying a mixed gas is used as a city gas raw material or an automobile fuel, the purified gas to be used includes a target gas having a concentration according to the use of the purified gas. It is required to be out.

  However, the concentration of the target gas in the desorption gas discharged in the desorption process decreases with time. On the other hand, the concentration of the impurity gas in the desorption gas discharged in the desorption process increases with time. Therefore, as described in Patent Document 1, when the amount of the recycle gas to be circulated to the adsorption tower in which the adsorption step is being performed is defined as a ratio to the total amount of the desorption gas, the concentration of the impurity gas in the recycle gas gradually increases. However, the concentration of the target gas in the purified gas may be reduced. That is, in the above conventional technique, although the recovery rate of the target gas can be increased, the concentration of the target gas in the purified gas is reduced, and the purification containing the target gas having a desired concentration or more according to the use of the purified gas. There was a risk that gas could not be obtained. When the concentration of the target gas in the purified gas is lower than the desired concentration, the purified gas is mixed with another purified gas containing the target gas having a concentration higher than the desired concentration, or the purified gas is purified again. After the concentration of the target gas was increased to a desired concentration or more, it was necessary to use it as a city gas raw material or automobile fuel.

  Therefore, by appropriately controlling the amount of recycle gas that is circulated to the adsorption tower that is performing the adsorption process, the recovery rate of the target gas from the mixed gas is improved, and the concentration of the target gas in the purified gas is higher than the desired concentration. In addition, it has been demanded to achieve both suppression of lowering.

  Thus, the present invention is intended to improve the recovery rate of the target gas from the mixed gas by sufficiently recovering the target gas contained in the desorption gas, while the concentration of the target gas in the purified gas is higher than the desired concentration. It is an object of the present invention to provide a method for purifying a mixed gas and a purification apparatus capable of suppressing the lowering.

An object of the present invention is to advantageously solve the above-mentioned problems, and the method for purifying a mixed gas according to the present invention uses a purification apparatus including two or more adsorption towers packed with an adsorbent. A mixed gas purification method for purifying a mixed gas containing a gas and an impurity gas by a pressure swing adsorption method to obtain a purified gas enriched in the target gas. In each adsorption tower, the mixed gas is added to the adsorption tower. In the purification apparatus, and an adsorption process for regenerating the adsorbent by desorbing the gas adsorbed on the adsorbent in the adsorption process under reduced pressure. , While the adsorption process is being performed in at least one adsorption tower, the desorption process is performed in at least one of the remaining adsorption towers, and the desorption gas discharged from the adsorption tower in which the desorption process is being performed. At least A part of the gas is circulated as a recycle gas to the adsorption tower in which the adsorption process is being performed, and the concentration of the target gas and / or impurity gas in the purified gas is measured at the end of the adsorption process in the at least one adsorption tower. The recycle gas is adsorbed when the next adsorption step is performed in the at least one adsorption tower using the measured concentration of the target gas in the purified gas and / or the concentration of the impurity gas in the purified gas. Determining the maximum time that can be circulated through the tower, and when the measured concentration of the target gas in the purified gas exceeds a predetermined concentration and / or the concentration of the impurity gas in the purified gas is less than the predetermined concentration The maximum time is set to be longer than the time during which the recycled gas is circulated through the at least one adsorption tower in the adsorption step, and the measured precision is measured. When the concentration of the target gas in the gas is less than a predetermined concentration and / or when the concentration of the impurity gas in the purified gas exceeds a predetermined concentration, the maximum time is set as the at least one adsorption tower in the adsorption step. And when the concentration of the target gas in the measured purified gas is a predetermined concentration and / or the concentration of the impurity gas in the purified gas is a predetermined concentration. Is characterized in that the maximum time is equal to or less than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step. In this way, if at least a part of the desorption gas discharged from the adsorption tower that is performing the desorption process is recycled to the adsorption tower that is performing the adsorption process as a recycle gas, the target gas contained in the desorption gas And the recovery rate of the target gas from the mixed gas can be improved. In addition, the concentration of the target gas and / or impurity gas in the purified gas is used to determine the maximum time during which the recycle gas can be circulated to the adsorption tower when the next adsorption step is performed in at least one adsorption tower. For example, the concentration of the target gas in the purified gas may be lower than the desired concentration while sufficiently recovering the target gas contained in the desorption gas and improving the recovery rate of the target gas from the mixed gas. Can be suppressed.
In the present invention, the “predetermined concentration” can be determined in advance according to the performance of the adsorbent to be used, the required recovery rate of the target gas, and the allowable range of decrease in the concentration of the target gas in the purified gas. . The “desired concentration of the target gas in the purified gas” is a concentration determined in advance according to the use of the purified gas.

Here, in the method for purifying a mixed gas of the present invention, when the concentration of the target gas and / or the impurity gas in the desorption gas is measured and the next adsorption step is performed, the next adsorption step is performed. The timing for stopping the circulation of the recycle gas to the adsorption tower that is performing the next adsorption step so that the concentration of the target gas in the recycle gas to be circulated to the adsorption tower that is being performed is equal to or higher than a predetermined concentration. It is preferable to determine. If the concentration of the target gas in the desorption gas and / or the concentration of the impurity gas is also used to determine the timing for stopping the circulation of the recycle gas so that the concentration of the target gas in the recycle gas exceeds the predetermined concentration, This is because it is possible to effectively improve the recovery rate of the target gas from the mixed gas by suppressing the desorption gas having a low gas concentration from flowing into the adsorption tower as a recycle gas.
In the present invention, the “predetermined concentration of the target gas in the recycle gas” refers to the performance of the adsorbent used, the required recovery rate of the target gas, and the allowable range for reducing the concentration of the target gas in the purified gas. It can be set accordingly.

In the mixed gas purification method of the present invention, in the next adsorption step, when the concentration of the target gas in the desorption gas is equal to or lower than a predetermined value and / or the concentration of the impurity gas in the desorption gas is predetermined. When the value exceeds the value, it is preferable to stop the circulation of the recycle gas to the adsorption tower that is performing the next adsorption step even before the maximum time has elapsed. If the circulation of the recycle gas is stopped when the concentration of the target gas in the desorption gas becomes lower than the predetermined value and / or when the concentration of the impurity gas in the desorption gas becomes higher than the predetermined value, the concentration of the target gas is reduced. This is because it is possible to sufficiently effectively improve the recovery rate of the target gas from the mixed gas by suppressing the low desorption gas from flowing into the adsorption tower as the recycled gas.
In the present invention, the “predetermined value of the concentration of the target gas in the desorption gas” and the “predetermined value of the concentration of the impurity gas in the desorption gas” are the performance of the adsorbent used and the required recovery rate of the target gas. Or it can set suitably according to the tolerance | permissible_range of the density | concentration fall of the target gas in refined gas.

Further, the present invention aims to advantageously solve the above-mentioned problems, and the mixed gas purifying apparatus of the present invention comprises two or more adsorption towers filled with an adsorbent, and contains the target gas and impurities. A gas purification apparatus for producing a purified gas enriched with the target gas by purifying a mixed gas containing a gas by a pressure swing adsorption method, wherein each of the adsorption towers supplies the mixed gas to the adsorption tower Repeatedly performing an adsorption step for obtaining the purified gas, and a desorption step for regenerating the adsorbent by desorbing the gas adsorbed on the adsorbent in the adsorption step under reduced pressure. While the mixed gas is supplied to produce purified gas, at least one of the remaining adsorption towers is configured to desorb the gas adsorbed on the adsorbent by depressurizing the inside of the adsorption tower, Of the remaining adsorption tower A recycle gas supply line for supplying at least a part of the desorption gas discharged from at least one of the above to the at least one adsorption tower as a recycle gas, and recycling to the at least one adsorption tower via the recycle gas supply line A supply shut-off mechanism for shutting off gas supply, a purified gas concentration meter for measuring the concentration of a target gas and / or impurity gas in the purified gas, and an operation of the supply shut-off mechanism to control the recycled gas And a control device for controlling the time during which the gas flows through the at least one adsorption tower, the control device uses the measured concentration of the target gas in the purified gas and / or the concentration of the impurity gas in the purified gas. When the next adsorption step is performed in the at least one adsorption tower, the recycled gas is supplied to the adsorption tower. Determining the maximum time that can be circulated, and the concentration of the target gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower exceeds a predetermined concentration and / or When the concentration of the impurity gas in the purified gas is less than a predetermined concentration, the supply shut-off mechanism is configured such that the maximum time is longer than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step. The concentration of the target gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower is less than a predetermined concentration and / or in the purified gas When the concentration of the impurity gas exceeds a predetermined concentration, the maximum time is recycled to the at least one adsorption tower in the adsorption step. The operation of the supply shut-off mechanism is controlled so as to be shorter than the time when the gas is circulated, and the target gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower When the concentration is a predetermined concentration and / or when the concentration of the impurity gas in the purified gas is a predetermined concentration, the maximum time is the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step. The operation of the supply cutoff mechanism is controlled so as to be as follows. Thus, if a recycle gas supply line is provided, at least a part of the desorption gas is circulated through the adsorption tower as a recycle gas, the target gas contained in the desorption gas is recovered, and the target gas from the mixed gas is recovered. The recovery rate can be improved. In addition, the control device uses the measured value measured with the purified gas concentration meter at the end of the adsorption process, and when the next adsorption process is performed in at least one adsorption tower, the maximum time during which the recycle gas can be circulated to the adsorption tower The target gas concentration in the purified gas is lower than the desired concentration while sufficiently recovering the target gas contained in the desorption gas and improving the recovery rate of the target gas from the mixed gas. It can be suppressed.
In the present invention, the “predetermined concentration” can be determined in advance according to the performance of the adsorbent to be used, the required recovery rate of the target gas, and the allowable range of decrease in the concentration of the target gas in the purified gas. . The “desired concentration of the target gas in the purified gas” is a concentration determined in advance according to the use of the purified gas.

Here, the mixed gas purification apparatus of the present invention further includes a desorption gas concentration meter for measuring the concentration of the target gas and / or the impurity gas in the desorption gas, and the control device includes the desorption gas concentration meter. The operation of the supply shut-off mechanism is controlled using the concentration of the target gas in the desorption gas and / or the concentration of the impurity gas in the desorption gas measured in step 1, and when performing the next adsorption step, the at least It is preferable to shut off the supply of the recycle gas to the at least one adsorption tower so that the concentration of the target gas in the recycle gas to be circulated to one adsorption tower is equal to or higher than a predetermined concentration. The control device also uses the concentration of the target gas in the desorption gas and / or the impurity gas concentration measured by the desorption gas concentration meter, so that the concentration of the target gas in the recycle gas is equal to or higher than the predetermined concentration. By controlling the operation, it is possible to effectively improve the recovery rate of the target gas from the mixed gas by suppressing the desorption gas having a low concentration of the target gas from being supplied to the adsorption tower as a recycle gas. It is.
In the present invention, the “predetermined concentration of the target gas in the recycle gas” refers to the performance of the adsorbent used, the required recovery rate of the target gas, and the allowable range for reducing the concentration of the target gas in the purified gas. It can be set accordingly.

In the mixed gas purification apparatus of the present invention, the concentration of the target gas in the desorption gas measured by the desorption gas concentration meter is equal to or less than a predetermined value during the next adsorption step. And / or when the concentration of the impurity gas in the desorption gas exceeds a predetermined value, the supply of the recycle gas to the at least one adsorption tower is shut off even before the maximum time has elapsed. It is preferable. When the concentration of the target gas in the desorption gas becomes a predetermined value or less and / or when the concentration of the impurity gas in the desorption gas becomes a predetermined value or more, the control device operates the supply cutoff mechanism to supply the recycle gas. Since the desorption gas having a low concentration of the target gas is prevented from being supplied to the adsorption tower as a recycle gas, the recovery rate of the target gas from the mixed gas can be improved sufficiently effectively. It is.
In the present invention, the “predetermined value of the concentration of the target gas in the desorption gas” and the “predetermined value of the concentration of the impurity gas in the desorption gas” are the performance of the adsorbent used and the required recovery rate of the target gas. Or it can set suitably according to the tolerance | permissible_range of the density | concentration fall of the target gas in refined gas.

  According to the method and apparatus for purifying a mixed gas of the present invention, the concentration of the target gas in the purified gas is suppressed from being lower than the desired concentration while improving the recovery rate of the target gas from the mixed gas. Can do.

It is a figure which shows schematic structure of the purification apparatus of the typical mixed gas according to this invention. (A) shows the operation process table | surface of the refiner | purifier shown in FIG. 1, (b) shows the operation process table | surface of the refiner | purifier of a modification. It is a figure which shows the gas flow in the process 1 of the stage 1 of the driving | operation process table | surface shown to Fig.2 (a). It is a figure which shows the gas flow in the process 2 of the stage 1 of the driving | operation process table | surface shown to Fig.2 (a). It is a figure which shows the gas flow in the process 3 of the stage 1 of the driving | operation process table | surface shown to Fig.2 (a). It is a figure which shows the gas flow in the process 4 of the stage 1 of the driving | operation process table | surface shown to Fig.2 (a).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, what attached | subjected the same code | symbol in each figure shall show the same component.

Here, the purification apparatus for a mixed gas of the present invention can be used when producing a purified gas enriched in a target gas by purifying a mixed gas containing the target gas and an impurity gas by a pressure swing adsorption method. .
In addition, below, although the methane fermentation gas (mixed gas containing methane gas and a carbon dioxide gas) obtained by the methane fermentation process of organic waste is refine | purified, the case where the refined gas which contains methane gas in high concentration is manufactured is demonstrated. The mixed gas purification apparatus of the present invention can also be used to purify mixed gases other than methane fermentation gas.

<Purified gas purification equipment>
The mixed gas purification apparatus 100 shown in FIG. 1 includes two or more (three in the illustrated example) adsorption towers 10, 20, and 30 filled with an adsorbent. And in the refiner | purifier 100, the methane fermentation gas (mixed gas) containing the methane gas as target gas and the carbon dioxide gas as impurity gas is refine | purified using a pressure swing adsorption method, The refined gas enriched in methane gas is obtained. Manufactured. Specifically, in the purification apparatus 100, methane gas was enriched by supplying methane fermentation gas to the adsorption tower and adsorbing most of the carbon dioxide and part of the methane gas with the adsorbent in the adsorption tower. Purified gas is produced. The adsorbent that adsorbs carbon dioxide gas and methane gas is appropriately regenerated by desorbing the gas adsorbed on the adsorbent under reduced pressure (pressure lower than the pressure during adsorption).

  Here, as shown in FIG. 1, the purification apparatus 100 includes a first adsorption tower 10, a second adsorption tower 20, and a third adsorption tower 30 that are connected in parallel to each other. Each of the adsorption towers 10, 20, and 30 is filled with a known adsorbent that can be used for purification of methane fermentation gas using the pressure swing adsorption method, such as activated carbon, molecular sieve charcoal, zeolite, and the like. ing.

Moreover, the refiner | purifier 100 is common with the 1st methane fermentation gas line 11 which connects the common methane fermentation gas line 40 into which methane fermentation gas flows in from the outside of the apparatus, the common methane fermentation gas line 40, and the 1st adsorption tower 10, and. A second methane fermentation gas line 21 connecting the methane fermentation gas line 40 and the second adsorption tower 20; and a third methane fermentation gas line 31 connecting the common methane fermentation gas line 40 and the third adsorption tower 30. ing.
The first methane fermentation gas line 11 is provided with a first methane fermentation gas valve 12, the second methane fermentation gas line 21 is provided with a second methane fermentation gas valve 22, and a third methane fermentation gas valve 21 is provided. The gas line 31 is provided with a third methane fermentation gas valve 32.

Furthermore, the purification apparatus 100 includes a common purification gas line 50 that flows the purified gas flowing out from each adsorption tower to the outside of the apparatus, and a first purification gas line 13 that connects the first adsorption tower 10 and the common purification gas line 50. The second purification gas line 23 that connects the second adsorption tower 20 and the common purification gas line 50 and the third purification gas line 33 that connects the third adsorption tower 30 and the common purification gas line 50 are provided. . The common purified gas line 50 is provided with a first carbon dioxide gas sensor 51 as a purified gas concentration meter that measures the concentration of carbon dioxide in the purified gas flowing out from the purification apparatus 100.
The first purified gas line 13 is provided with a first purified gas valve 14, the second purified gas line 23 is provided with a second purified gas valve 24, and the third purified gas line 33 is provided with A third purified gas valve 34 is provided.

The purifier 100 also includes a first pressure equalizing line 15 extending from the first purified gas line 13, a second pressure equalizing line 25 extending from the second purified gas line 23, and a third purification. And a third pressure equalizing line 35 extending from the gas line 33. The first pressure equalizing line 15, the second pressure equalizing line 25, and the third pressure equalizing line 35 are connected to each other via a common pressure equalizing line 60.
The first pressure equalizing line 15 branches from the first purified gas line 13 between the first adsorption tower 10 and the first purified gas valve 14, and the second pressure equalizing line 25 is the second pressure equalizing line 25. The second purification gas line 23 is branched between the adsorption tower 20 and the second purification gas valve 24, and the third pressure equalizing line 35 is provided between the third adsorption tower 30 and the third purification gas valve 34. Branches from the third purified gas line 33. The first pressure equalizing line 15 is provided with a first pressure equalizing valve 16, the second pressure equalizing line 25 is provided with a second pressure equalizing valve 26, and the third The pressure equalization line 35 is provided with a third pressure equalization valve 36.

Further, the purification apparatus 100 has a common desorption gas line 70 for flowing the desorption gas generated when the adsorbent in each adsorption tower is desorbed under reduced pressure to regenerate the adsorbent. doing. The common desorption gas line 70 includes a first desorption gas line 17 extending from the first methane fermentation gas line 11, a second desorption gas line 27 extending from the second methane fermentation gas line 21, and a third methane. A third desorption gas line 37 extending from the fermentation gas line 31 is connected.
The first desorption gas line 17 branches from the first methane fermentation gas line 11 between the first methane fermentation gas valve 12 and the first adsorption tower 10, and the second desorption gas line 27 is the second desorption gas line 27. The methane fermentation gas valve 22 and the second adsorption tower 20 branch from the second methane fermentation gas line 21, and the third desorption gas line 37 includes a third methane fermentation gas valve 32, a third adsorption tower 30, and the like. Is branched from the third methane fermentation gas line 31. The first desorption gas line 17 is provided with a first desorption gas valve 18, the second desorption gas line 27 is provided with a second desorption gas valve 28, and a third desorption gas line 37 is provided. Is provided with a third desorption gas valve 38.

  Here, the common desorption gas line 70 includes a vacuum pump 71 as a depressurization device used for depressurization in each adsorption tower from the connection side with the third desorption gas line 37 toward the outside of the apparatus, and a desorption gas. A second carbon dioxide gas sensor 72 as a desorption gas concentration meter for measuring the carbon dioxide gas concentration and a common desorption gas valve 73 are sequentially arranged.

The purification apparatus 100 also has a recycle gas line 80 having one end connected to the common methane fermentation gas line 40 and the other end connected to the common desorption gas line 70.
Here, one end of the recycle gas line 80 is a common methane fermentation gas between the inlet of the methane fermentation gas to the refining device 100 and the connection portion between the common methane fermentation gas line 40 and the first methane fermentation gas line 11. Connected to line 40. The other end of the recycle gas line 80 is connected to the common desorption gas line 70 between the second carbon dioxide gas sensor 72 and the common desorption gas valve 73.
The recycle gas line 80 includes a recycle gas valve 81 as a supply shut-off mechanism that blocks the flow of the recycle gas from the other end side to the one end side, and a recycle gas pump 82 that pressurizes and sends the recycle gas. They are arranged sequentially.

And in the refiner | purifier 100 which has the structure mentioned above, the common methane fermentation gas line 40, the 1st methane fermentation gas line 11, the 2nd methane fermentation gas line 21, and the 3rd methane fermentation gas line 31 are each adsorption towers 10. , 20, 30 can function as a mixed gas supply line for supplying methane fermentation gas as a mixed gas.
Moreover, the 1st refinement gas line 13, the 2nd refinement gas line 23, the 3rd refinement gas line 33, and the common refinement gas line 50 carry out the refinement gas which flowed out from each adsorption tower 10,20,30 out of an apparatus. It can function as a flowing purified gas line.
Further, a part of the first purified gas line 13 (from the first adsorption tower 10 to a portion where the first pressure equalizing line 15 branches), the first pressure equalizing line 15, and one of the second purified gas lines 23. Part (from the second adsorption tower 20 to the portion where the second pressure equalization line 25 branches), the second pressure equalization line 25, and a part of the third purified gas line 33 (from the third adsorption tower 30 to the third The pressure equalization line 35, the third pressure equalization line 35, and the common pressure equalization line 60 communicate with each other to equalize the pressure in the adsorption tower. It can function as a conversion line.
Further, a part of the first methane fermentation gas line 11 (from the first adsorption tower 10 to a part where the first desorption gas line 17 branches), a part of the first desorption gas line 17 and the second methane fermentation gas line 21 ( From the second adsorption tower 20 to the portion where the second desorption gas line 27 branches), the second desorption gas line 27, and a part of the third methane fermentation gas line 31 (from the third adsorption tower 30 to the third desorption gas line). 37) and the third desorption gas line 37 and the common desorption gas line 70 can function as a desorption gas line for flowing the desorption gas flowing out from each of the adsorption towers 10, 20, 30 to the outside of the apparatus. .
Furthermore, the recycle gas line 80, the common methane fermentation gas line 40, the first methane fermentation gas line 11, the second methane fermentation gas line 21, and the third methane fermentation gas line 31 are adsorption towers that are regenerating the adsorbent. It can function as a recycle gas supply line for supplying at least a part of the desorption gas flowing out from the recycle gas to other adsorption towers. In the recycle gas supply line of the refining apparatus 100, the recycle gas is supplied to the adsorption towers 10, 20, and 30 in a state of being mixed with the methane fermentation gas. You may supply directly to an adsorption tower.

  In addition, while the refinement | purification apparatus 100 supplies the methane fermentation gas to at least 1 adsorption tower, and manufactures refined gas so that it may demonstrate in detail below about the purification method of the methane fermentation gas using the refinement | purification apparatus 100, In addition, at least one of the remaining adsorption towers is operated to depressurize the inside of the adsorption tower and desorb the gas adsorbed on the adsorbent. The operation of the refining apparatus 100 may be performed manually or automatically using a control panel (not shown).

  In the refining device 100, at least a part of the desorption gas discharged from at least one of the remaining adsorption towers is supplied to the at least one adsorption tower as a recycle gas. Incidentally, the amount of the desorption gas supplied to the adsorption tower as a recycle gas can be controlled using the control device 90 that controls the operations of the common desorption gas valve 73, the recycle gas valve 81 and the recycle gas pump 82. Here, the control device 90 of the purification apparatus 100 uses the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 and the concentration of carbon dioxide in the desorption gas measured by the second carbon dioxide sensor 72, As will be described in detail later, this device controls the operation of the common desorption gas valve 73, the recycle gas valve 81, and the recycle gas pump 82.

<Purification method of mixed gas>
Purification of methane fermentation gas using the purification apparatus 100 shown in FIG. 1 can be performed according to an operation process chart as shown in FIG. 2 (a) using an example of the method for purifying mixed gas of the present invention. Specifically, in the refiner 100, the stages 1 to 3 shown in FIG. 2 (a) are sequentially repeated to continuously purify the methane fermentation gas and to produce a purified gas containing a high concentration of methane gas. Can be obtained.
In addition, it is preferable that the density | concentration of the methane gas in refined gas is more than desired density | concentration. Here, the “desired concentration” is a concentration determined in advance according to the use of the purified gas. For example, when the purified gas is used as a city gas raw material, the concentration is 99.5% by volume. When used as an industrial fuel, it is 95% by volume.

  Here, as shown in FIG. 2 (a), in this example purification method, in each of the first adsorption tower 10, the second adsorption tower 20, and the third adsorption tower 30, methane fermentation gas is supplied to the adsorption tower. The adsorption process for obtaining the purified gas and the desorption process for regenerating the adsorbent by desorbing the gas adsorbed by the adsorbent in the adsorption process under reduced pressure (lower pressure than the adsorption process) are repeatedly performed. In this example of the purification method, as shown in FIG. 2 (a), while the adsorption process is performed in one adsorption tower, the desorption process is performed in one of the remaining adsorption towers.

  As is clear from FIG. 2A, in this example of the purification method, the methane fermentation gas is continuously purified by sequentially switching the adsorption tower for performing the adsorption step for each stage. Accordingly, those skilled in the art can understand that stage 2 and stage 3 can be implemented in the same manner as stage 1. Therefore, in the following, using FIG. 3A to FIG. 3D, the operation content of the purification apparatus 100 in the stage 1 after the second start from the start of the purification of the methane fermentation gas (that is, after performing the stages 1 to 3 at least once). And the description of the operation of the purification apparatus 100 in stages 2 and 3 is omitted. In FIG. 3A to FIG. 3D, the gas flow is displayed using thick arrows.

Here, at the start of stage 1 for the second and subsequent times after the start of purification of methane fermentation gas, each adsorption tower 10, 20, 30 is in a state where step 4 of stage 3 has been completed. Therefore, as apparent from FIG. 2A, the third adsorption tower 30 is in a state where carbon dioxide gas or the like is adsorbed on the adsorbent.
And in the stage 1, the following processes 1-4 are implemented sequentially.

(Process 1)
As shown in FIG. 3A, in the process 1 of the stage 1, only the first methane fermentation gas valve 12, the first purified gas valve 14, the second pressure equalizing valve 26, and the third pressure equalizing valve 36 are opened. The valve is closed and the vacuum pump 71 and the recycle gas pump 82 are stopped.

  And in the process 1 of the stage 1, methane fermentation gas is supplied to the 1st adsorption tower 10 via a part of common methane fermentation gas line 40 and the 1st methane fermentation gas line 11. FIG. Here, in the first adsorption tower 10, most of the carbon dioxide gas contained in the supplied methane fermentation gas and a part of the methane gas are adsorbed by the adsorbent. As a result, the purified gas enriched with methane gas flows out from the first adsorption tower 10, and the purified gas that flows out from the first adsorption tower 10 passes through the first purified gas line 13 and the common purified gas line 50 to be a device. It flows out.

In addition, methane fermentation gas can be supplied to the 1st adsorption tower 10 in the state pressurized to 0.1-1.0 MPa (gauge pressure) arbitrarily. This is because if methane fermentation gas is supplied under pressure, the adsorption of carbon dioxide gas as an impurity gas to the adsorbent can be promoted. Incidentally, when supplying the methane fermentation gas at a low pressure, for example, 3 to 100 kPa (gauge pressure), the amount of the adsorbent packed in the adsorption tower is increased, and the space velocity SV is decreased, so that the carbon dioxide gas is used as the adsorbent. It can be sufficiently adsorbed. Specifically, when molecular sieve charcoal is used as the adsorbent, the carbon dioxide gas can be sufficiently adsorbed by the adsorbent by setting the space velocity SV to 300 h ⁻¹ or less. Here, the space velocity SV can be calculated using the following equation (1).
SV = (Methane fermentation gas supply rate [m ³ / h] / adsorbent volume [m ³ ]) × 100% (1)

  Moreover, in the process 1 of the stage 1, the 2nd adsorption tower 20 and the 3rd adsorption tower 30 are connected via the 2nd pressure equalization line 25, the common pressure equalization line 60, and the 3rd pressure equalization line 35. And by equalizing the pressure in the second adsorption tower 20 and the pressure in the third adsorption tower 30, the pressure in the second adsorption tower can be increased in the subsequent process, Reduce the energy required to reduce pressure.

That is, in the process 1 of the stage 1, in the first adsorption tower 10, an adsorption process is performed in which the methane fermentation gas is supplied to the adsorption tower to obtain purified gas, and in the second adsorption tower 20 and the third adsorption tower 30, the adsorption is performed. A pressure equalization step is performed to equalize the pressure between the columns.
In addition, the implementation time of the process 1 can be sufficient time to make the pressure of the 2nd adsorption tower 20 and the 3rd adsorption tower 30 uniform.

(Process 2)
In step 2 performed after step 1, as shown in FIG. 3B, the first methane fermentation gas valve 12 and the first purified gas valve 14 remain open, while the second pressure equalizing valve 26 and the second pressure equalizing valve 26 are maintained. The three pressure equalizing valve 36 is closed. In step 2, the third desorption gas valve 38 and the recycle gas valve 81 are opened, and the vacuum pump 71 and the recycle gas pump 82 are operated. The other valves remain closed.

  Here, in step 2 of stage 1, the inside of the third adsorption tower 30 is decompressed using the vacuum pump 71, and the gas adsorbed by the adsorbent in the third adsorption tower is desorbed to regenerate the adsorbent. Further, the desorption gas flowing out from the third adsorption tower 30 is recycled using a recycle gas pump 82, a part of the third methane fermentation gas line 31, the third desorption gas line 37, a part of the common desorption gas line 70 and the recycle gas. It flows into the common methane fermentation gas line 40 via the line 80. That is, in step 2, the desorption gas flowing out from the third adsorption tower 30 is supplied to the first adsorption tower 10 together with the methane fermentation gas as a recycle gas.

  And in the process 2 of the stage 1, the mixed gas of methane fermentation gas and recycle gas supplied to the 1st adsorption tower 10 via a part of common methane fermentation gas line 40 and the 1st methane fermentation gas line 11 is obtained. And purified in the first adsorption tower 10. That is, in the first adsorption tower 10, most of the carbon dioxide gas contained in the mixed gas of methane fermentation gas and recycle gas and a part of the methane gas are adsorbed by the adsorbent and the methane gas is enriched. Gas flows out. Note that the purified gas flowing out of the first adsorption tower 10 flows out of the apparatus through the first purified gas line 13 and the common purified gas line 50.

  That is, in the process 2 of the stage 1, in the 1st adsorption tower 10, the adsorption process which supplies methane fermentation gas and recycle gas to an adsorption tower, and obtains purified gas is implemented. Further, in the third adsorption tower 30, a desorption process for regenerating the adsorbent by desorbing the gas adsorbed by the adsorbent is performed, and the desorption gas generated in the desorption process is performed by the adsorption process. A recycling process for supplying the 1 adsorption tower 10 as a recycled gas is performed. In addition, in the 2nd adsorption tower 20, the holding process which maintains the state after completion | finish of the process 1 is implemented.

  Here, in the adsorption step, most of the carbon dioxide gas contained in the methane fermentation gas and a part of the methane gas are adsorbed by the adsorbent. In addition, at the end of the adsorption step, purified gas containing high-concentration methane gas remains in the voids in the adsorption tower. Therefore, the gas (desorption gas) discharged from the adsorption tower in the desorption step contains both carbon dioxide gas and methane gas. Therefore, when the desorption gas is supplied to the first adsorption tower 10 as a recycle gas, the methane gas in the desorption gas can be effectively recovered as a purified gas, so that the entire amount of the desorption gas is exhausted outside the apparatus. The methane gas recovery rate can be improved.

However, here, the concentration of methane gas contained in the desorption gas is low (for example, about 20% by volume at maximum), and the desorption gas contains a relatively high concentration of carbon dioxide gas.
In addition, the adsorbent used in the pressure swing adsorption method usually adsorbs carbon dioxide more easily than methane gas, but more easily desorbs methane gas than carbon dioxide. Further, the purified gas remaining in the adsorption tower at the end of the adsorption process is discharged immediately after the start of the desorption process. Therefore, the concentration of methane gas contained in the desorption gas becomes maximum immediately after the start of the desorption process, and then gradually decreases.
Therefore, when the desorption gas is continuously supplied to the first adsorption tower 10 as the recycle gas, the amount of carbon dioxide flowing into the first adsorption tower 10 increases. When the amount of carbon dioxide gas flowing into the first adsorption tower 10 increases, the amount of gas adsorbed by the adsorbent approaches the saturated adsorption amount, and in the purified gas during the adsorption process, particularly at the end of the adsorption process. There is a risk that the concentration of carbon dioxide gas increases (that is, the concentration of methane gas decreases). When the concentration of carbon dioxide in the refined gas increases, it becomes impossible to obtain a purified gas having a methane gas concentration higher than the desired concentration.

Therefore, in the purification apparatus 100, the process 2 is ended as follows, and the supply of the recycled gas to the first adsorption tower 10 is stopped.
That is, in the refining apparatus 100, the stage 1 (hereinafter, referred to as “previous stage 1”) performed one time before the stage 1 (hereinafter, sometimes referred to as “current stage 1”) currently being performed may be referred to. .)) At the end of the adsorption step (that is, at the end of step 4), using the carbon dioxide gas concentration in the purified gas measured using the first carbon dioxide sensor 51, step 2 of the current stage 1 is performed. The maximum time to be obtained is determined, and the process 2 is completed between the start of the process 2 and the elapse of the maximum time. Specifically, in the refining device 100, when a predetermined maximum time has elapsed from the start of step 2, the control device 90 closes the recycle gas valve 81 and stops the operation of the recycle gas pump 82, so that the first adsorption tower The supply of the recycle gas to 10 is cut off, and the process 2 is finished.

Here, the maximum time during which step 2 can be performed is the following (I) to (I) using the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 at the end of step 4 of the previous stage 1. It can be determined as in III).
(I) When the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 is less than a predetermined concentration, the time during which the recycle gas is circulated through the first adsorption tower 10 in the adsorption process of the previous stage 1 ( That is, the time is longer than the previous execution time of step 2.
(II) When the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 exceeds a predetermined concentration, the time during which the recycle gas is circulated through the first adsorption tower 10 in the adsorption process of the previous stage 1 ( That is, the time is shorter than the previous execution time of step 2).
(III) When the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 is equal to the predetermined concentration, the time during which the recycle gas is circulated through the first adsorption tower 10 in the adsorption process of the previous stage 1 ( In other words, the time is equal to or less than the previous execution time of the step 2, preferably the same time as the previous execution time of the step 2.

  Here, the “predetermined concentration” when determining the maximum time during which the step 2 can be performed is the permissible range of the performance of the adsorbent used, the required recovery rate of methane gas, and the decrease in the concentration of methane gas in the purified gas. The concentration is determined according to Specifically, the “predetermined concentration” can be determined experimentally, for example, within a range in which the concentration of methane gas in the purified gas does not become less than a desired concentration until the end of stage 1. In the purification of methane fermentation gas, the total of the methane gas concentration and the carbon dioxide gas concentration in each gas can be approximated to 100% by volume. Therefore, the “predetermined concentration” is more specifically 0, for example, than the concentration of carbon dioxide when the concentration of methane gas in the purified gas is a desired concentration (hereinafter referred to as “limit carbon dioxide concentration”). The concentration may be lower by 2 to 2.0% by volume. If the predetermined concentration is lower than the limit carbon dioxide concentration by 0.2% by volume or more, the concentration of methane gas in the refined gas becomes less than the desired concentration when the maximum time is set longer than the previous execution time of step 2. This is because it can be sufficiently suppressed. If the predetermined concentration is lower than the limit carbon dioxide concentration within a range of 2.0% by volume or less, the probability that the maximum time is set shorter than the execution time of the previous step 2 is reduced, and methane gas It is because it can suppress that a recovery rate falls.

  It should be noted that how long (or short) the maximum time with respect to the execution time of the previous step 2 is determined using a known method such as proportional control, differential control, integral control, PID control. Can do. Specifically, how long (or shorter) the maximum time is accumulated using PID control or the like by accumulating data on the past execution time of step 2 and carbon dioxide concentration at the end of step 4 Can be determined.

Here, as described above, the concentration of methane gas contained in the desorption gas becomes maximum immediately after the start of the desorption process, and then gradually decreases. Therefore, when ending the process 2 at the elapse of the maximum time determined by using the carbon dioxide gas concentration in the refined gas at the end of the process 4 of the previous stage 1, the concentration of methane gas particularly in the latter half of the process 2 There is a possibility that a desorption gas having a very low value will be supplied to the first adsorption tower 10 as a recycle gas.
Therefore, in this purification apparatus 100, from the viewpoint of suppressing the supply of the desorption gas containing almost no methane gas to the first adsorption tower 10 as the recycle gas, the concentration of the carbon dioxide gas contained in the desorption gas is also reduced. It is preferable to use and determine the timing to end the process 2 of the current stage 1.
That is, in the purification apparatus 100, the carbon dioxide concentration in the desorption gas is continuously measured using the second carbon dioxide sensor 72 in the process 2 of the present stage 1 and the measured carbon dioxide concentration in the desorption gas is used. It is preferable to determine the timing for ending step 2. Specifically, the carbon dioxide concentration in the desorption gas is continuously measured during the step 2, and only the desorption gas having a methane gas concentration equal to or higher than a predetermined concentration is supplied to the first adsorption tower 10 as a recycle gas. In addition, it is preferable to determine the timing for ending step 2.

  More specifically, in the refining device 100, even before the maximum time elapses, if the concentration of carbon dioxide in the desorption gas measured by the second carbon dioxide sensor 72 becomes a predetermined value or more, the control is performed. It is preferable that the apparatus 90 closes the recycle gas valve 81 and stops the operation of the recycle gas pump 82 to shut off the supply of the recycle gas to the first adsorption tower 10 and end the step 2. If the concentration of the carbon dioxide gas in the desorption gas does not become a predetermined value or more before the maximum time elapses, the process 2 is terminated when the maximum time elapses.

Here, the “predetermined value of the concentration of carbon dioxide in the desorption gas” for ending Step 2 can be appropriately set according to the performance of the adsorbent used and the required recovery rate of methane gas.
Specifically, the “predetermined value of the concentration of carbon dioxide in the desorption gas” can be set, for example, within a range of 40% by volume to 80% by volume. This is because if the predetermined value is 40% by volume or more, the recovery rate of methane gas can be sufficiently increased. Further, if the predetermined value is 80% by volume or less, the desorption gas containing almost no methane gas is suppressed from being supplied to the first adsorption tower 10 as a recycle gas while sufficiently increasing the methane gas recovery rate. Because you can.

In the above example, the process 2 is ended when the maximum time has elapsed from the start of the process 2 or when the concentration of carbon dioxide in the desorption gas is equal to or higher than a predetermined value, but the process 2 is ended. The timing may be determined by a method other than the above example.
Specifically, the timing for ending Step 2 is when the maximum time has elapsed since the start of Step 2 and when the predetermined time has elapsed since the concentration of carbon dioxide in the desorption gas has reached a predetermined value. It may be any earlier timing. The “predetermined time” can be determined by conducting an experiment in advance.

(Process 3)
In step 3 performed after step 2, as shown in FIG. 3C, the first methane fermentation gas valve 12, the first purified gas valve 14, and the third desorption gas valve 38 are kept open, and the vacuum pump 71 is Continue driving. On the other hand, the control device 90 closes the recycle gas valve 81. In step 3, the control device 90 opens the common desorption gas valve 73 and stops the operation of the recycle gas pump 82. The other valves remain closed.

  Here, in the process 3 of the stage 1, the pressure reduction in the third adsorption tower 30 using the vacuum pump 71 is continued. In the third adsorption tower, the gas adsorbed on the adsorbent is desorbed to regenerate the adsorbent. On the other hand, the desorption gas that has been desorbed from the adsorbent and has flowed out of the third adsorption tower 30 is not supplied to the first adsorption tower 10 as a recycle gas, but a part of the third methane fermentation gas line 31, the third desorption. The gas is discharged outside the apparatus through the gas line 37 and a part of the common desorption gas line 70.

  And in the process 3 of the stage 1, like the process 1, the methane fermentation gas supplied to the 1st adsorption tower 10 via the part of the common methane fermentation gas line 40 and the 1st methane fermentation gas line 11 is 1st. Purification is performed in one adsorption tower 10. Note that the purified gas flowing out of the first adsorption tower 10 flows out of the apparatus through the first purified gas line 13 and the common purified gas line 50.

That is, in the process 3 of the stage 1, in the 1st adsorption tower 10, the adsorption process which supplies methane fermentation gas to an adsorption tower and obtains refined gas is implemented. Further, in the third adsorption tower 30, a desorption process for regenerating the adsorbent by desorbing the gas adsorbed by the adsorbent is performed, and an exhaust process for discharging the desorbed gas generated in the desorption process to the outside of the apparatus. carry out. In the second adsorption tower 20, the holding process is continued.
In addition, the timing which complete | finishes the process 3 can be made into the timing from which gas is fully desorbed from the adsorbent in the 3rd adsorption tower 30 (namely, adsorbent fully reproduce | regenerates). Specifically, the timing at which the pressure in the third adsorption tower 30 becomes, for example, −80 kPa (gauge pressure) can be set.

(Process 4)
In step 4 performed after step 3, as shown in FIG. 3D, the first methane fermentation gas valve 12, the first purified gas valve 14, and the third desorption gas valve 38 are kept open, and the vacuum pump 71 is Continue driving. On the other hand, the common desorption gas valve 73 is closed. In step 4, the second purified gas valve 24, the third purified gas valve 34, and the recycled gas valve 81 are opened, and the recycled gas pump 82 is operated. The other valves remain closed.

  Here, in step 4 of stage 1, a part of the purified gas flowing out from the first adsorption tower 10 is supplied to the second adsorption tower 20 via the second purification gas line 23, and the inside of the second adsorption tower 20 Pressurize. And the pressure in the 2nd adsorption tower 20 is raised to the pressure substantially equal to the pressure of refined gas, and it prepares for implementation of the adsorption process in the 2nd adsorption tower 20 in process 1 of stage 2.

  In step 4 of stage 1, a part of the purified gas flowing out from the first adsorption tower 10 is supplied to the third adsorption tower 30 via the third purification gas line 33, and the inside of the third adsorption tower 30 is The atmosphere is replaced with purified gas, and the desorption gas remaining in the third adsorption tower 30 is caused to flow out of the third adsorption tower 30. The gas flowing out from the third adsorption tower 30 (hereinafter referred to as “substitution gas”) has almost the same composition as the purified gas, and contains methane gas at a high concentration. Therefore, the replacement gas is not exhausted, and the common methane fermentation gas line passes through a part of the third methane fermentation gas line 31, the third desorption gas line 37, a part of the common desorption gas line 70, and the recycle gas line 80. 40 is supplied to the first adsorption tower 10.

  And in the process 4 of the stage 1, the mixed gas of the methane fermentation gas and the replacement gas supplied to the first adsorption tower 10 via the part of the common methane fermentation gas line 40 and the first methane fermentation gas line 11 is Purification is performed in the first adsorption tower 10. That is, in the first adsorption tower 10, most of the carbon dioxide gas contained in the mixed gas of the methane fermentation gas and the replacement gas and a part of the methane gas are adsorbed by the adsorbent and the methane gas is enriched. Gas flows out.

That is, in the process 4 of the stage 1, in the 1st adsorption tower 10, the adsorption process which supplies methane fermentation gas and substitution gas to an adsorption tower, and obtains purified gas is implemented. Moreover, in the 2nd adsorption tower 20, the pressurization process with which the adsorption process implemented next is implemented by pressurizing the inside of an adsorption tower previously is implemented. Further, in the third adsorption tower 30, a substitution step is performed in which the inside of the adsorption tower is substituted with a purified gas and the adsorbent is sufficiently regenerated.
It should be noted that the timing at which the step 4 is completed, that is, the timing at which the stage 1 is terminated can be a timing at which a predetermined time has elapsed from the start of the stage 1.
Incidentally, at the end of the step 4, the first carbon dioxide sensor 51 measures the concentration of carbon dioxide in the purified gas. The measured concentration of carbon dioxide gas is used to determine the maximum time during which the process 2 can be performed in the next stage 1 (that is, the stage 1 after performing the stages 2 and 3).

  Then, according to the purification method of the above example using the purification apparatus 100, in the step 2 of each stage, the adsorption step is performed using at least a part of the desorption gas discharged from the adsorption tower performing the desorption step as a recycle gas. Since it is made to distribute | circulate to the inside adsorption tower, the methane gas contained in desorption gas can be collect | recovered as refined gas. Therefore, the recovery rate of methane gas from methane fermentation gas can be improved.

In the purification method of the above example, the maximum time during which the process 2 of each stage can be performed is determined by using the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 at the end of the process 4 of the previous stage. Has been decided. Therefore, the methane gas contained in the desorption gas is sufficiently recovered to improve the recovery rate of the methane gas from the methane fermentation gas, and the concentration of the methane gas in the refined gas is suppressed from being lower than the desired concentration. be able to.
Specifically, when the concentration of carbon dioxide gas in the purified gas measured by the first carbon dioxide sensor 51 is less than a predetermined concentration, that is, at the end of the previous step 4, there is a sufficient margin for adsorbing carbon dioxide gas to the adsorption tower. In the case where it remains, the recovery time of methane gas can be further improved by setting the maximum time to be longer than the previous execution time of step 2.
Further, when the concentration of carbon dioxide in the purified gas measured by the first carbon dioxide sensor 51 exceeds a predetermined concentration, that is, when there is not enough room to adsorb carbon dioxide in the adsorption tower at the end of the previous step 4. In this case, the maximum time is set to be shorter than the previous execution time of step 2, and the concentration of methane gas in the purified gas can be suppressed from becoming lower than the desired concentration.
Furthermore, when the concentration of carbon dioxide gas in the purified gas measured by the first carbon dioxide sensor 51 is a predetermined concentration, the maximum time is set to be less than the execution time of the previous step 2 and the purification rate of methane gas is improved while improving the recovery rate. It can suppress that the density | concentration of the methane gas in gas becomes lower than a desired density | concentration.

  In the purification method of the above example, if the circulation of the recycle gas is also stopped using the concentration of the carbon dioxide gas in the desorption gas, the desorption gas having a low concentration of methane gas is suppressed from flowing to the adsorption tower as the recycle gas. Thus, the recovery rate of methane gas from methane fermentation gas can be effectively improved.

As mentioned above, although the refiner | purifier and purification method of the mixed gas of this invention were demonstrated using an example, the refiner | purifier and purification method of this invention are not limited to the said example, The refiner | purifier and purification method of this invention Can be appropriately modified.
Specifically, in the above example, a carbon dioxide gas sensor is provided and control is performed by measuring a carbon dioxide concentration that is easier to measure than the methane gas concentration. However, in the purification apparatus and method of the present invention, the carbon dioxide sensor is used instead. Alternatively (or in addition), a methane gas sensor may be provided, and control may be performed by measuring the methane gas concentration instead of (or in addition to) the carbon dioxide gas concentration. More specifically, the maximum time during which Step 2 of the above example can be performed may be determined by measuring the concentration of methane gas in the purified gas in Step 4 of the previous stage and using the measured methane gas concentration. In addition, when using the methane gas concentration in the refined gas measured in the step 4, the maximum time can be determined as follows (IV) to (VI).
(IV) When the concentration of methane gas in the purified gas measured by the methane gas sensor exceeds a predetermined concentration, the time during which the recycle gas is circulated through the adsorption tower in the adsorption process of the previous stage (ie, implementation of the previous process 2) Time).
(V) When the concentration of the methane gas in the purified gas measured by the methane gas sensor is less than the predetermined concentration, the time during which the recycle gas is circulated through the adsorption tower in the adsorption process of the previous stage (that is, the execution of the previous process 2) Time).
(VI) When the concentration of methane gas in the purified gas measured by the methane gas sensor is equal to the predetermined concentration, the time during which the recycle gas is circulated through the adsorption tower in the adsorption process of the previous stage (ie, implementation of the previous process 2) Time) The following time, preferably the same time as the previous execution time of step 2.
Further, step 2 in the above example may be terminated when the concentration of methane gas in the desorption gas is measured in step 2 and the concentration of methane gas in the desorption gas becomes a predetermined value or less. In the above example, the sum of the methane gas concentration and the carbon dioxide gas concentration can be approximated to 100% by volume. Therefore, when the control is performed using the methane gas concentration, the above approximation is used to indicate “methane gas in purified gas”. And the “predetermined value of the concentration of methane gas in the desorption gas” can be determined.
Further, in the purification method of the present invention, step 1 and step 3 in the operation step table of the above example may not be performed.
Furthermore, in the purification method of the present invention, the execution time of step 1, the total execution time of step 2 and step 3, and the execution time of step 4 are determined in advance, and the execution time of step 2 is the same as that of step 2 and step 3 above. You may change within the range of total implementation time.
Furthermore, in the purification method of the present invention, when purification is performed using two adsorption towers, the purification can be performed according to an operation process chart as shown in FIG.

  According to the method and apparatus for purifying a mixed gas of the present invention, the concentration of the target gas in the purified gas is suppressed from being lower than the desired concentration while improving the recovery rate of the target gas from the mixed gas. Can do.

DESCRIPTION OF SYMBOLS 10 1st adsorption tower 11 1st methane fermentation gas line 12 1st methane fermentation gas valve 13 1st refinement gas line 14 1st refinement gas valve 15 1st pressure equalization line 16 1st pressure equalization valve 17 1st desorption gas Line 18 First desorption gas valve 20 Second adsorption tower 21 Second methane fermentation gas line 22 Second methane fermentation gas valve 23 Second purification gas line 24 Second purification gas valve 25 Second pressure equalization line 26 Second pressure equalization Valve 27 second desorption gas line 28 second desorption gas valve
30 Third adsorption tower 31 Third methane fermentation gas line 32 Third methane fermentation gas valve 33 Third purification gas line 34 Third purification gas valve 35 Third pressure equalization line 36 Third pressure equalization valve 37 Third desorption gas Line 38 Third desorption gas valve 40 Common methane fermentation gas line 50 Common refining gas line 51 First carbon dioxide sensor 60 Common pressure equalization line 70 Common desorption gas line 71 Vacuum pump 72 Second carbon dioxide sensor 73 Common desorption gas valve 80 Recycle gas Line 81 Recycle gas valve 82 Recycle gas pump 90 Controller 100 Purifier

Claims (6)

Using a purification apparatus including two or more adsorption towers packed with an adsorbent, a mixed gas containing a target gas and an impurity gas is purified by a pressure swing adsorption method to obtain a purified gas enriched in the target gas. A method for purifying a mixed gas comprising:
In each adsorption tower, an adsorption step of supplying the mixed gas to the adsorption tower to obtain the purified gas, and a desorption for regenerating the adsorbent by desorbing the gas adsorbed on the adsorbent in the adsorption step under reduced pressure Repeat the process,
In the purification apparatus,
While the adsorption process is being performed in at least one adsorption tower, the desorption process is performed in at least one of the remaining adsorption towers, and at least the desorption gas discharged from the adsorption tower in which the desorption process is being performed Distribute a part of the adsorption process to the adsorption tower as a recycle gas,
Measuring the concentration of the target gas and / or the impurity gas in the purified gas at the end of the adsorption step in the at least one adsorption tower;
Using the measured concentration of the target gas in the purified gas and / or the concentration of the impurity gas in the purified gas, when the next adsorption step is performed in the at least one adsorption tower, the recycled gas is supplied to the adsorption tower. Determine the maximum time that can be distributed to
When the measured concentration of the target gas in the purified gas exceeds a predetermined concentration and / or when the concentration of the impurity gas in the purified gas is less than a predetermined concentration, the maximum time is set in the adsorption step. When the recycle gas is circulated through at least one adsorption tower for a longer time, the measured concentration of the target gas in the purified gas is less than a predetermined concentration and / or the concentration of the impurity gas in the purified gas is When the concentration exceeds a predetermined concentration, the maximum time is made shorter than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step, and the concentration of the target gas in the measured purified gas is predetermined. And / or when the concentration of the impurity gas in the purified gas is a predetermined concentration, the maximum time is set to the at least the adsorption step. One of the at most times that circulating recycle gas to the adsorption tower,
A method for purifying a mixed gas, characterized in that Measuring the concentration of the target gas and / or the concentration of the impurity gas in the desorption gas;
When carrying out the next adsorption step, the next adsorption step is carried out so that the concentration of the target gas in the recycled gas that is circulated to the adsorption tower that is carrying out the next adsorption step is equal to or higher than a predetermined concentration. The method for purifying a mixed gas according to claim 1, wherein the timing for stopping the circulation of the recycle gas to the adsorption tower is being determined.   In the next adsorption step, when the concentration of the target gas in the desorption gas becomes a predetermined value or less and / or when the concentration of the impurity gas in the desorption gas becomes a predetermined value or more, the maximum time is reached. The method for purifying a mixed gas according to claim 2, wherein the flow of the recycle gas to the adsorption tower that is performing the next adsorption step is stopped even before the progress. Purification of a mixed gas comprising two or more adsorption towers filled with an adsorbent and purifying a mixed gas containing a target gas and an impurity gas by a pressure swing adsorption method to produce a purified gas enriched in the target gas A device,
In each adsorption tower, an adsorption step of supplying the mixed gas to the adsorption tower to obtain the purified gas, and a desorption for regenerating the adsorbent by desorbing the gas adsorbed on the adsorbent in the adsorption step under reduced pressure Repeat the process,
While supplying the mixed gas to at least one adsorption tower and producing purified gas, at least one of the remaining adsorption towers depressurizes the adsorption tower to desorb the gas adsorbed on the adsorbent. Configured to let
A recycle gas supply line for supplying at least a part of the desorption gas discharged from at least one of the remaining adsorption towers to the at least one adsorption tower as a recycle gas;
A supply shut-off mechanism for shutting off the supply of the recycle gas to the at least one adsorption tower via the recycle gas supply line;
A purified gas concentration meter for measuring the concentration of the target gas and / or impurity gas in the purified gas;
A control device for controlling the operation of the supply shut-off mechanism to control the time for circulating the recycle gas to the at least one adsorption tower;
With
The control device includes:
Using the measured concentration of the target gas in the purified gas and / or the concentration of the impurity gas in the purified gas, when the next adsorption step is performed in the at least one adsorption tower, the recycled gas is supplied to the adsorption tower. Determine the maximum time that can be distributed to
When the concentration of the target gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower exceeds a predetermined concentration and / or the concentration of the impurity gas in the purified gas is If the concentration is less than a predetermined concentration, the operation of the supply shut-off mechanism is controlled so that the maximum time is longer than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step.
When the concentration of the target gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower is less than a predetermined concentration and / or the concentration of the impurity gas in the purified gas is If the concentration exceeds a predetermined concentration, the operation of the supply cutoff mechanism is controlled so that the maximum time is shorter than the time during which the recycle gas is circulated through the at least one adsorption tower in the adsorption step.
When the concentration of the target gas in the purified gas measured by the purified gas concentration meter at the end of the adsorption step in the at least one adsorption tower is a predetermined concentration and / or the concentration of the impurity gas in the purified gas is predetermined. In the case of the concentration, the operation of the supply shut-off mechanism is controlled so that the maximum time is equal to or less than the time during which the recycled gas is circulated through the at least one adsorption tower in the adsorption step.
An apparatus for purifying a mixed gas, characterized in that A desorption gas concentration meter for measuring the concentration of the target gas and / or the impurity gas in the desorption gas;
The control device controls the operation of the supply shut-off mechanism using the concentration of the target gas in the desorption gas and / or the concentration of the impurity gas in the desorption gas measured by the desorption gas concentration meter;
Recycle gas to the at least one adsorption tower so that the concentration of the target gas in the recycle gas to be circulated to the at least one adsorption tower is not less than a predetermined concentration when performing the next adsorption step. The mixed gas purifier according to claim 4, wherein the supply of gas is cut off. During execution of the next adsorption step, when the control device has a concentration of the target gas in the desorption gas measured by the desorption gas concentration meter below a predetermined value and / or impurity gas in the desorption gas The supply of the recycle gas to the at least one adsorption tower is shut off even before the elapse of the maximum time when the concentration of the gas reaches a predetermined value or more. A device for purifying mixed gas.

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