KR20120083220A - Methane recovering method and methane recovering apparatus - Google Patents

Abstract

PURPOSE: A method and apparatus for recovering methane are provided to control oxygen under predetermined content and collect methane from biogas. CONSTITUTION: A method for recovering methane comprises the following steps: absorbing siloxane among the biogas and removing thereof(S1); reacting hydrogen sulfide among the biogas with metal oxide and removing as metal sulfide(S2); reacting oxygen among the biogas with copper-zinc and capturing as cupric oxide(S3); and separating carbon dioxide among the biogas and concentrating methane using a pressure swing absorbing method(S4).

Description

Methane Recovery Method and Methane Recovery System {METHANE RECOVERING METHOD AND METHANE RECOVERING APPARATUS}

The present invention relates to a methane recovery method for recovering methane contained in the biogas, and more particularly, to a methane recovery method and a methane recovery apparatus for recovering methane at a high recovery rate by removing impurities from the biogas.

Biogas is produced by anaerobic fermentation of organic resources and the like, and its composition is generally composed of methane and contains carbon dioxide and other traces of oxygen, nitrogen, hydrogen sulfide, siloxane, and the like, and is harmful to hydrogen sulfide, siloxane, and the like. It removes impurities and is used for heat sources of boilers and fuels of generators.

Conventionally, impurities contained in biogas are dissolved by dissolving CO ₂ and sulfur-based impurities in water by high pressure water absorption (for example, see Japanese Patent Application Laid-Open No. 2006-95512), or by adsorbing on an adsorbent (e.g., For example, see Japanese Patent Application Laid-Open No. 2002-60767), remove it as a reaction product (see, for example, Japanese Patent Application Laid-Open No. 2003-277779), or separate by a multistage separation membrane (for example, Japanese Patent Application Laid-Open No. 2009-242773). Removal method).

Further, as described in Japanese Patent Application Laid-Open No. 2006-16439, an X-type zeolite using Li and Ca as an exchange cation was charged into a adsorption tower as a carbon dioxide adsorbent, and carbon dioxide and water were removed by pressure swing adsorption to concentrate methane. Doing.

Gases mainly composed of combustible gases such as methane are used for combustion purposes, so the gas obtained from the biogas may not contain harmful substances such as hydrogen sulfide, and there is no problem even if it contains oxygen. Therefore, conventionally, oxygen contained in biogas containing methane as a main component has not been subjected to removal.

If the oxygen content in the biogas is attempted for some reason, the reaction of oxygen and methane using a catalyst is considered, but the reaction between methane and oxygen using the catalyst does not occur sufficiently unless it is about 380 ° C or higher. Enormous energy is required to heat the gas.

Further, it has been proposed to purify biogas to remove carbon dioxide and to use methane as a main component and to use it as fuel gas for fuel cells such as automobiles and household generators. In view of the effective use of biogas, it is preferable to mix the purified biogas with city gas mainly composed of natural gas.

However, when used as a fuel gas for a fuel cell, since oxygen promotes deterioration of the catalyst for steam reforming natural gas, it is necessary to limit the oxygen content of the city gas used as fuel for domestic generators. Therefore, when the purified biogas is mixed with the city gas, it is necessary to reduce the oxygen content of the biogas to less than 100 mol ppm in order to secure the quality of the fuel gas.

Since oxygen has a low solubility in water even at high pressures, separation with methane is difficult in principle by a high pressure water absorption method such as Japanese Patent Laid-Open No. 2006-95512. In addition, when oxygen is separated by separation techniques such as Japanese Patent Application Laid-Open No. 2002-60767, Japanese Patent Application Laid-Open No. 2003-277779, Japanese Patent Publication No. 2009-242773, and Japanese Patent Application Laid-Open No. 2006-16439 The recovery of methane is lowered.

It is an object of the present invention to provide a methane recovery method and a methane recovery apparatus capable of restraining oxygen below a predetermined content and recovering methane from biogas at a high recovery rate.

The present invention relates to a methane recovery method for recovering methane from a biogas containing methane as a main component and at least oxygen as an impurity.

An adsorption removal step of adsorbing and removing the siloxane in the biogas by adsorbent, a reaction removal step of removing hydrogen sulfide in the biogas with a metal oxide to remove it as a metal sulfide,

A capture step of capturing oxygen in the biogas with copper-zinc oxide to capture copper oxide;

Methane recovery, characterized in that the methane is recovered from the biogas by separating the carbon dioxide in the biogas by the pressure swing adsorption method and concentrating the methane, and performing the adsorption removal step, the reaction removal step, the capture step, and the concentration step. It is a way.

According to the present invention, the siloxane in the biogas is removed by adsorbing the adsorbent in the adsorption removal step, and the hydrogen sulfide in the biogas is reacted with the metal oxide in the reaction removal step to remove the metal sulfide. In the capturing step, oxygen in the biogas is reacted with copper-zinc oxide and captured as copper oxide. In the concentration process, carbon dioxide in biogas is separated by pressure swing adsorption to concentrate methane.

By performing each of these steps, oxygen can be suppressed to a predetermined content or less, for example, 10 ppm or less, and methane can be recovered from the biogas at a high recovery rate.

Moreover, in this invention, it is preferable to contact a to-be-processed gas with copper- zinc oxide in the said capture process under the temperature conditions of 200 degreeC-300 degreeC.

According to the present invention, in the capturing step, the gas to be treated is brought into contact with copper-zinc oxide under a temperature condition of 200 ° C to 300 ° C.

This makes it possible to remove oxygen from the biogas at a lower temperature than the method of reacting oxygen with methane.

In the present invention, in the concentration step, it is preferable to adsorb carbon dioxide in the biogas to the adsorbent by pressurizing, and to release the carbon dioxide from the adsorbent by setting it to atmospheric pressure.

According to the present invention, in the concentration step, carbon dioxide in biogas is adsorbed to the adsorbent by pressurization, and carbon dioxide is separated from the adsorbent by setting it to atmospheric pressure, so that carbon dioxide can be efficiently separated.

Moreover, in this invention, it is preferable that the said capture process is performed after the said reaction removal process.

According to the present invention, since the biosulfide from which hydrogen sulfide has been removed is introduced in the capturing step, hydrogen sulfide does not react with copper-zinc oxide, and the reaction between oxygen and copper-zinc oxide is not inhibited.

Moreover, this invention is a recovery apparatus which collect | recovers methane from the biogas which has methane as a main component and contains oxygen at least as an impurity,

An adsorption tower for adsorbing and removing siloxane in the biogas by adsorbent,

A hydrogen sulfide reaction tower for reacting hydrogen sulfide in the biogas with a metal oxide to remove it as a metal sulfide,

A deoxygenation reaction tower which reacts oxygen in the biogas with copper-zinc oxide and captures it as copper oxide,

It has a pressure swing adsorption system for concentrating methane by separating carbon dioxide in biogas by pressure swing adsorption method, and recovering methane from biogas by operating adsorption tower, hydrogen sulfide reaction tower, deoxygenation reaction tower and pressure swing adsorption system. It is a methane recovery apparatus.

According to the present invention, the siloxane in the biogas is adsorbed and removed in the adsorption column in the adsorption column, and the hydrogen sulfide in the biogas is reacted with the metal oxide in the hydrogen sulfide reaction column to remove the metal sulfide. Oxygen in the biogas is reacted with copper-zinc oxide in the deoxygenation column to capture it as copper oxide. In the pressure swing adsorption system, carbon dioxide in biogas is separated by pressure swing adsorption to concentrate methane.

By operating each of these towers and devices, oxygen can be suppressed to a predetermined content or less, for example, 10 ppm or less, and methane can be recovered from the biogas at a high recovery rate.

Moreover, in this invention, it is preferable to further have a hydrogen introduction apparatus which introduces hydrogen into a deoxidation reaction tower and reduces the copper oxide produced by reaction.

According to the present invention, since the hydrogen introduction device introduces hydrogen into the deoxygenation reaction column and reduces the copper oxide produced by the reaction, the copper oxide-zinc oxide can be recycled to copper-zinc oxide.

In addition, in the present invention, it is preferable that a biogas from which hydrogen sulfide has been removed from the hydrogen sulfide reaction tower is introduced into the deoxidation reaction tower.

According to the present invention, since the biogas from which hydrogen sulfide has been removed from the hydrogen sulfide reaction tower is introduced into the deoxygenation reaction column, hydrogen sulfide does not react with copper-zinc oxide in the deoxygenation reaction tower, and oxygen and copper-zinc oxide are used. Reaction is not inhibited.

The objects, features, and advantages of the present invention will become more apparent from the following detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS The process chart which shows the methane collection method of one Embodiment of this invention.
2 is a schematic view showing the configuration of a recovery apparatus of one embodiment of the present invention.
3 is a schematic view showing an example of a pressure swing adsorption device.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described in detail with reference to drawings.

The present invention is a recovery method for recovering methane from biogas. Biogas is, for example, a gas generated from sludge or the like in a sewage treatment plant, and contains about 60 mol% of methane and about 40 mol% of carbon dioxide as main components, and in addition, oxygen, nitrogen, hydrogen sulfide, siloxane and the like. Contains trace amounts.

When biogas is used for automobile or city gas, the methane concentration is preferably 95 mol% or more. When used for automobiles, since it is compressed and used, carbonic acid gas, which is an impurity of main biogas, must be avoided by compression and liquefaction, and therefore 95 mol% or more is required. In addition, when used for city gas, the heat content is lowered when the concentration is low, so 95 mol% or more is required as in the case of automobiles.

Biogas has been used as a fuel gas for combustion until now, but oxygen is not removed as an impurity. However, in the use of a fuel cell, the oxygen contained in the biogas deteriorates the catalyst for steam reforming. It is necessary to remove oxygen. According to the present invention, methane can be recovered at a high recovery rate, for example, a recovery rate of 80% or more, while suppressing oxygen to a predetermined content or less, for example, 10 ppm or less.

BRIEF DESCRIPTION OF THE DRAWINGS The process chart which shows the methane collection method of one Embodiment of this invention. In the methane recovery method of the present invention, in order to remove impurities from biogas and recover methane at a high recovery rate, the adsorption removal step of removing siloxane (step S1), the reaction removal step of removing hydrogen sulfide (step S3), and (step S3) ) Is a capture step of trapping oxygen and a concentration step of concentrating methane.

(Step S1) Adsorption Removal Step

In the adsorption removal step, an adsorbent is filled in the adsorption column, and biogas is introduced into the adsorption column to adsorb siloxane, which is an impurity contained in the biogas, to the adsorbent to remove the siloxane from the biogas. The adsorbent may be one that is easy to adsorb siloxane, and one that is difficult to adsorb methane. For example, activated carbon is used. Activated carbon may be natural activated carbon such as palm shell and charcoal, mineral activated carbon such as pitch and petroleum coke, but the activated carbon is not recycled and exchanged with a new agent. Palm husk activated carbon is preferred.

It is preferable to make content of siloxane in biogas into 2 mg / Nm <^3> or less by adsorption removal process, More preferably, you may be 1 mg / Nm <^3> or less.

(Step S2) Reaction Removal Step

In the reaction removal step, a metal oxide is charged into the reaction column, and biogas is introduced into the adsorption column, whereby sulfur-based compounds such as hydrogen sulfide and mercaptan, which are impurities contained in the biogas, are fixed as metal sulfides in the reaction column. Iron oxide, copper oxide, zinc oxide, etc. can be used as a metal oxide. For example, when these metal oxides and hydrogen sulfide chemically react, they form metal sulfides, such as iron sulfide, copper sulfide, and zinc sulfide, respectively.

It is preferable to make content of hydrogen sulfide in a biogas into 3 mol ppm or less by reaction removal process, More preferably, it is 1 mol ppm or less.

As described above, the siloxane and the hydrogen sulfide in the biogas can be removed by performing the adsorption removal step and the reaction removal step.

In addition, an adsorption removal process and a reaction removal process may perform any process first, and a process order in particular is not limited.

Moreover, you may perform the compression process which compresses a biogas, and the dehumidification process which removes the water in biogas before an adsorption removal process and a reaction removal process. In the dehumidification step, for example, the biogas is cooled to around 0 ° C and dewatered. In addition, moisture may be adsorbed and dehydrated with an alumina ball, zeolite (MS-3A), or the like, and a water adsorption agent such as alumina ball or zeolite may be filled in the adsorption column, and biogas may be introduced. The adsorption tower for adsorption removal of the siloxane may also be filled with water adsorption such as alumina balls, zeolites, or the like to dehumidify simultaneously in the adsorption removal step.

(Step S3) Capture Process

In the capturing process, a mixture of copper-zinc oxide is charged into the reaction tower as an oxygen supplement, and oxygen, which is an impurity contained in the biogas, is captured as copper oxide by introducing a biogas from which siloxane and hydrogen sulfide have been removed into the adsorption column.

When the copper-zinc oxide mixture is brought into contact with the biogas, oxygen in the biogas reacts with copper to form copper oxide, which is captured in the reaction column as the copper oxide-zinc oxide mixture.

In the capture process, the treated gas from which siloxane and hydrogen sulfide are removed is contacted with copper-zinc oxide under a temperature condition of 200 ° C to 300 ° C. In this case, even if 30 to 40% of carbon dioxide coexists in the gas to be treated, it is possible to generate a copper oxide reaction, so that energy for heating the gas to be treated can be reduced as compared with the case where oxygen is reacted with methane to reduce the oxygen content. have.

The copper-zinc oxide mixture may be granulated and filled into the reaction column as it is, but in order to improve the contact efficiency with the biogas introduced into the column, a copper-zinc oxide mixture having a particulate shape is supported on a support such as alumina or diatomaceous earth. It is preferable to make it to the reaction tower.

The copper-zinc oxide mixture used in the capture process of the present invention is an oxygen supplement obtained by reducing what is used as a methanol steam reforming catalyst with hydrogen gas diluted with an inert gas. For example, since a methanol steam reforming catalyst is commercially available in which a copper oxide-zinc oxide is supported on alumina, a hydrogen gas obtained by diluting it to 1 to 5% by an inert gas such as argon or nitrogen, and a temperature of 230 to 260 ° C. By contacting under conditions, the copper oxide is reduced to become copper, which is obtained as a copper-zinc oxide mixture supported on alumina.

It is preferable to make content of oxygen in a biogas into 10 ppm or less by the capture | acquisition process, More preferably, it is 1 ppm or less.

Here, the effect of performing the reaction removal process for removing hydrogen sulfide will be described including the relationship with the capture process for trapping oxygen.

Since sulfur-based compounds such as hydrogen sulfide are adsorbed on activated carbon, when activated carbon is used as an adsorbent in the adsorption removal step for removing siloxane, hydrogen sulfide can also be removed to some extent, but this is not sufficient. When the reaction removal process by reaction of hydrogen sulfide and a metal oxide is abbreviate | omitted, hydrogen sulfide will be contained in the to-be-processed gas in a capture process. When copper-zinc oxide is in contact with hydrogen sulfide, hydrogen sulfide is reduced to generate sulfur, and further reacts with oxygen to generate sulfur dioxide. In addition, zinc sulfide is produced by reaction between zinc oxide and hydrogen sulfide. When hydrogen sulfide is contained in the gas to be treated in the capturing step as described above, hydrogen sulfide reacts with copper-zinc oxide, and thus the reaction between oxygen and copper-zinc oxide is inhibited and oxygen cannot be sufficiently captured.

In order to sufficiently react the oxygen in the trapping process with copper-zinc oxide so that the oxygen content is 10 ppm or less, it is insufficient to adsorb and remove hydrogen sulfide in the adsorption removal step, and a reaction removal step by reaction with a metal oxide is necessary. Do.

(Step S4) concentration step

The siloxane, hydrogen sulfide and oxygen which are impurities in the biogas are sufficiently removed by the adsorption removal process, the reaction removal process and the capture process, and the gas to be treated in the concentration process only includes methane and carbon dioxide. In the concentration step, carbon dioxide is adsorbed to the adsorbent by the pressure swing adsorption method to obtain concentrated high-purity methane.

In the pressure swing adsorption method, for example, in order to concentrate and obtain one gas from a mixed gas of two substances, an adsorbent having a high adsorption capacity to one substance and a low adsorption capacity to the other substance is used, The material is adsorbed onto the adsorbent. Subsequently, one of the substances adsorbed under low pressure is released from the adsorbent to regenerate the adsorbent.

In the concentration process, a plurality of adsorption towers are adsorbed with a relatively high adsorption capacity for adsorbing carbon dioxide and a relatively low adsorption capacity for methane, and the pressure in the tower is changed, and the adsorption tower used is appropriately switched. And methane are separated and high purity methane is recovered.

The concentration step is carried out by repeating the adsorption operation and the detachment operation based on the pressure swing adsorption method. The adsorption operation makes the pressure in the adsorption tower packed with the adsorbent relatively higher than during the desorption operation and introduces biogas from which siloxane, hydrogen sulfide and oxygen are removed under high pressure conditions. Under high pressure conditions, carbon dioxide is adsorbed to the adsorbent but methane is hardly adsorbed to the adsorbent, so that carbon dioxide and methane are separated in the adsorption column, and concentrated methane is obtained. The continuous introduction of biogas into one adsorption column increases the carbon dioxide adsorbed on the adsorbent and decreases the adsorption capacity, thereby regenerating the adsorbent by the separation operation.

The removal operation stops the introduction of the biogas and makes the pressure in the adsorption column relatively lower than during the adsorption operation to release carbon dioxide adsorbed on the adsorbent from the adsorbent. The released carbon dioxide is discharged out of the adsorption tower.

When two adsorption towers are used, the other adsorption tower performs the adsorption operation in the period during which the separation operation is performed in one adsorption tower, and the adsorption operation and the removal operation are simultaneously performed in each tower. After the predetermined amount is processed, the adsorption operation and the detachment operation are switched. Thereby, since the adsorption operation is always performed in either column, it is possible to continuously separate methane while regenerating the adsorbent.

As the adsorbent having a high adsorption capacity of carbon dioxide and a low adsorption capacity of methane, a carbon-based adsorbent can be used, and preferably carbon molecular sieve. In addition, depending on the desired product gas composition, for example, when nitrogen concentration of the product gas is desired to be low, when nitrogen concentration is required, such as when the nitrogen concentration of the source gas is relatively high, it is added to the carbon molecular sieve. The zeolite may be laminated.

As pressure P1 in a column in an adsorption operation, they are atmospheric pressure (0.10 lMPa)-4.0 MPa, for example. As pressure P2 in the column in the detachment operation, it is 0.001-0.3 Mpa (however, P1> P2).

The gas obtained through each process as mentioned above has an oxygen content of 10 ppm or less, and the purity of methane is obtained as methane enriched gas of 98 mol% or more, for example.

Next, a recovery apparatus for recovering methane from the biogas of the present invention will be described. The recovery apparatus of the present invention may have any configuration as long as it is an apparatus capable of carrying out the above recovery method.

2 is a schematic view showing the configuration of a recovery apparatus 100 which is one embodiment of the present invention. The recovery device 100 includes a compressor 1, a dehumidifier 2, a siloxane adsorption tower 3, a hydrogen sulfide reaction tower 4, a deoxygenation reaction tower 5 and a pressure swing adsorption device 6. The biogas supplied from the source 7 is processed. The gas supply source 7 is a generation source for generating biogas, for example, a sewage treatment plant.

The biogas containing impurities supplied from the gas supply source 7 is compressed by the compressor 1 and sent to the dehumidifying apparatus 2 for removing moisture. As a dehumidifier, for example, a cooling dehydrator, a pressure adsorption dehydrator, a heating regeneration dehydrator and the like are used, but a cooling dehydrator for cooling and dehydrating the biogas to around 0 ° C is preferable. In addition, instead of using a dehydrator, an adsorption tower packed with a moisture adsorbent such as alumina balls or zeolite (MS-3A) may be used as the dehumidifier 2. In addition, depending on the amount of water, a water adsorbent such as alumina balls or zeolite may be laminated and filled in each column after the siloxane adsorption tower 3 for adsorbing the siloxane.

The siloxane adsorption tower 3 which adsorbs and removes the siloxane is an adsorbent for adsorbing the siloxane, as described in the adsorption removal step, and is filled with, for example, activated carbon in the adsorption tower. The hydrogen sulfide reaction tower 4 for reacting and removing hydrogen sulfide fills the reaction column with a metal oxide that reacts with hydrogen sulfide to produce metal sulfides as described in the reaction removal step.

Biogas from which siloxane and hydrogen sulfide are removed is introduced into the deoxygenation reaction column (5). As described in the capturing step, the deoxygenation reaction column 5 is filled with a copper-zinc oxide mixture in a form supported on a carrier such as alumina. Oxygen contained in the introduced biogas reacts with copper in the copper-zinc oxide mixture and is captured as copper oxide. At this time, the deoxygenation reaction column 5 is heated to 200-300 degreeC by the heating heater not shown.

It is preferable to further include a hydrogen introducing apparatus 5a for introducing hydrogen into the tower of the deoxidation reaction column 5 and reducing copper oxide-zinc oxide to regenerate copper-zinc oxide. The hydrogen introduction device 5a includes, for example, a rotation blower for nitrogen gas by a circulation path returning from the outlet of the deoxygenation reaction tower 5 to the inlet, and adding hydrogen to the nitrogen gas to deoxidize the reaction tower 5. ) Hydrogen gas for regeneration can be supplied.

The pressure swing adsorption apparatus 6 can use a well-known PSA (Pressure Swing Absorption) apparatus, for example, uses a two tower PSA apparatus.

3 is a schematic view showing an example of the pressure swing adsorption device 6. The pressure swing adsorption apparatus 6 has the 1st adsorption tower 12 and the 2nd adsorption tower 13, and each of the adsorption towers 12 and 13 is filled with carbon molecular sieve which is a carbon type adsorption agent.

The raw material pipe 13f is connected to the inlet 12a, 13a of each adsorption tower 12, 13 via switching valve 12b, 13b. Each of the inlet 12a, 13a of the adsorption tower 13 is comprised so that switching valve 12c, 13c and the silencer 13e are connected, and can open | release in air | atmosphere. In addition, the suction tower lower equalizing pipe 13g is connected to each of the inlets 12a and 13a of the suction tower 13 through the switching valve 13d.

The outlets 12k and 13k of the adsorption towers 12 and 13 are connected to the outlet pipe 13o through the switching valves 12l and 13l and to the cleaning pipe 13p through the switching valves 12m and 13m. It is connected to the adsorption tower upper equalization piping 13q via the switching valve 13n.

The outflow pipe 13o is connected to the equalization tank 14 through the check valve 13r and the manual valve 13s. The pressure equalizing tank 14 is connected to the product tank 15 via the pressure regulating valve 14a. The product tank 15 is connected to the outlet pipe 15a of the pressure swing adsorption device 6. The adsorption pressure of the pressure swing adsorption device 6 is controlled by the pressure regulating valve 14a.

The cleaning pipe 13t is connected to the cleaning pipe 13p via the flow control valve 13u and the flow rate indicating controller 13v, and the gas flow rate of the cleaning pipe 13p is adjusted to adjust the flow of the adsorption towers 12 and 13. The filler is constantly washed.

In each of the 1st adsorption tower 12 and the 2nd adsorption tower 13 of the pressure swing adsorption apparatus 6, adsorption operation, equalization operation, detachment operation, washing operation, and equalization operation are performed in order.

The biogas supplied by opening the switching valve 12b is introduced into the first adsorption tower 12, and in the first adsorption tower 12, only the switching valve 12l is simultaneously opened with the switching valve 12b. As a result, at least carbon dioxide in the biogas introduced into the first adsorption tower 12 is adsorbed to the adsorbent, so that the adsorption operation is performed, and methane not adsorbed to the adsorbent is separated from the carbon dioxide, and the outflow pipe 13o is released from the first adsorption tower 12. Is derived from At this time, a part of the methane sent to the outflow pipe 13o is sent to the second adsorption tower 13 through the cleaning pipes 13p and 13t and the flow control valve 13u to perform the cleaning operation in the second adsorption tower 13. All.

Subsequently, a pressure equalization operation is performed in which the switching valves 12b and 12l are closed, and the switching valves 13n and 13d are opened to equalize the pressure in the tower of the first adsorption tower 12 and the second adsorption tower 13.

Subsequently, by closing the switching valves 13n and 13d and opening the switching valve 12c, a detachment operation for removing impurities including carbon dioxide from the adsorbent of the first adsorption tower 12 is performed. Together with the silencer 13e.

At this time, while opening the switching valve 13b and opening the manual valve 13s, the methane gas whose carbon dioxide content is reduced from the pressure equalizing tank 14 through the outflow pipe 13o is supplied to the second adsorption tower 13. It is introduced and the pressure raising operation and the suction operation are performed. Each subsequent operation is performed in the same manner as the operation for the first adsorption tower 12.

Each of these operations is repeated in each of the first adsorption tower 12 and the second adsorption tower 13 to obtain methane gas in which the content of impurities containing carbon dioxide is reduced.

In addition, the pressure swing adsorption apparatus 6 is not limited to the structure shown in FIG. 3, The number of towers may be three towers or four towers other than two, for example, and usually nine towers or less.

According to such a recovery apparatus 100, after removing water, siloxane and hydrogen sulfide from the supplied biogas, oxygen in the biogas is reacted with copper-zinc oxide to capture copper oxide, and finally carbon dioxide is captured by a pressure swing adsorption method. Separation can yield concentrated high-purity methane.

This invention is not limited to the said structure, For example, the hydrogen sulfide reaction tower 4 may be provided after the compressor 1, and it arrange | positions reverse the arrangement order of the siloxane adsorption tower 3 and the hydrogen sulfide reaction tower 4. Alternatively, the deoxygenation reaction tower 5 and the pressure swing adsorption device 6 may be arranged in reverse order.

(Example 1)

Assuming the biogas generated from the sludge at a sewage treatment plant, and 60.0 mol% methane, carbon dioxide, 38.7 mol%, nitrogen 0.5 mol%, a mixture of 0.3 mol% water, oxygen 0.3 mole%, hydrogen sulfide 0.2 mol%, a siloxane 50mg / Nm ³ The gas was supplied at a flow rate of 450 NL / hr as the gas to be treated.

0.2 kg of alumina ball (KHD-24 manufactured by SUMITOMO CHEMICAL Co., Ltd.) as a dehydrating agent inside a cylindrical adsorption column having a diameter of 37 mm, and coconut shell activated carbon (GG manufactured by KURARAY CHEMICAL Co., Ltd.) as an adsorbent of siloxane. The object gas was introduced at 25 ° C into the siloxane adsorption tower 3 in which kg was stacked. Subsequently, the biogas derived from the siloxane adsorption tower 3 was subjected to 2.0 kg of zinc oxide (JIS standard type 1 assembly manufactured by HakusuiTech Co., Ltd.) in a reactor having the same dimensions as the siloxane adsorption tower 3. The hydrogen sulfide reaction tower 4 was charged at 25 ° C.

Subsequently, 1.2 kg of a copper oxide-zinc oxide catalyst (MDC-3 manufactured by SUD-CHEMIE CATALYSTS JAPAN, Inc.) was charged into the deoxidation reaction tower 5 having the same dimensions as the siloxane adsorption tower 3, and the deoxygenation reaction tower 5. Hydrogen was introduced by the hydrogen introduction device 5a to reduce the copper oxide-zinc oxide catalyst to obtain a copper-zinc oxide mixture. The inside temperature of the deoxidation reaction tower 5 was heated up to 260 degreeC, and the biogas derived from the hydrogen sulfide reaction tower 4 was introduce | transduced.

Subsequently, pressure swing adsorption with 0.6 kg of carbon molecular weight (GN-UC-H manufactured by KURARAY CHEMICAL Co., Ltd.) having a micropore diameter of 3 mm was carried out inside the adsorption tower having the same dimensions as the siloxane adsorption tower 3. The biogas derived from the deoxidation reaction column 5 was introduced into the apparatus 6. Operation of the pressure swing adsorption apparatus 6 was carried out similarly to the above operation, methane was separated from carbon dioxide and concentrated by setting the maximum pressure in the adsorption operation to 0.8 MPa and the minimum pressure in the detachment operation to atmospheric pressure.

The concentration of carbon dioxide and nitrogen in biogas was measured using GC-TCD (gas chromatography with thermal conductivity detector) manufactured by SHIMADZU CORPORATION, the moisture was measured by a dew point meter, and the oxygen concentration was measured by DELTA F. Measured by (Form DF-150E), the siloxane concentration was measured using GC / MS (Gas Chromatography Mass Spectrometer) made by SHIMADZU CORPORATION, and the hydrogen sulfide concentration was measured by GC-FPD (Gas Chromatograph with SHIMADZU CORPORATION) Graphy).

The composition of the gas derived from the deoxygenation reaction column 5 was 62.5 mol% of methane, 37 mol% of carbon dioxide, 0.5 mol% of nitrogen, water, oxygen, hydrogen sulfide and siloxane of less than 1 mol ppm.

Further, when the methane concentration of the product gas derived from the pressure swing adsorption device 6 was 98 mol%, the methane recovery rate was 85.1%, and the oxygen concentration in the product gas was less than 1 mol ppm.

(Example 2)

Methane was concentrated from the gas to be treated in the same manner as in Example 1 except that the siloxane adsorption tower 3 and the hydrogen sulfide reaction tower 4 were replaced, that is, the order of the siloxane adsorption process and the desulfurization process was reversed.

When the methane concentration of the product gas derived from the pressure swing adsorption device 6 was 98 mol%, the methane gas recovery rate was 84.9%, and the oxygen concentration in the product gas was less than 1 mol ppm.

(Comparative Example 1)

Methane was concentrated from the gas to be treated in the same manner as in Example 1 except that the deoxygenation reaction column was not passed through, i.e., no oxygen trapping step was performed.

When the methane concentration of the product gas derived from the pressure swing adsorption device 6 was 98 mol%, the methane gas recovery rate was 84.0%, and the oxygen concentration in the product gas was 90 mol ppm.

(Comparative Example 2)

Methane was removed from the gas to be treated in the same manner as in Example 1 except that the raw material flow rate was reduced to 370 NL / hr without passing through a deoxygenation reaction column, i.e., no oxygen capturing step was performed. Concentrated.

When the oxygen concentration in the product gas derived from the pressure swing adsorption apparatus 6 was 1 mol ppm, the methane concentration of the product gas was 99 mol% or more, and the recovery rate of methane gas was 72.4%.

If it is desired to obtain a high recovery rate as in Comparative Example 1, the oxygen concentration in the product gas will not be reduced. If the oxygen concentration in the product gas is reduced as in Comparative Example 2, the recovery rate of methane gas will be lowered. On the other hand, in Examples 1 and 2, the oxygen concentration in the product gas is less than 1 mol ppm, and methane can be recovered from the biogas at a high recovery rate.

This invention can be implemented in other various forms, without deviating from the mind or main character. Therefore, embodiment mentioned above is only a mere illustration at all points, the scope of the present invention is shown by a claim, and is not restrained in the specification body at all. In addition, all the modifications and changes which belong to a claim are within the scope of the present invention.

Claims (7)

As a methane recovery method for recovering methane from a biogas containing methane as a main component and at least oxygen as an impurity:
An adsorption removal step of adsorbing and removing the siloxane in the biogas by adsorbent,
A reaction removal step of reacting hydrogen sulfide in the biogas with a metal oxide to remove it as a metal sulfide;
A capturing step of reacting oxygen in the biogas with copper-zinc oxide to capture copper oxide;
Having a concentration step of concentrating methane by separating carbon dioxide in biogas by a pressure swing adsorption method;
Methane recovery method from the biogas by performing the adsorption removal step, reaction removal step, capture step and concentration step. The method of claim 1,
In the capture step, the gas to be treated is brought into contact with copper-zinc oxide under a temperature condition of 200 ° C to 300 ° C. The method of claim 1,
In the concentration step, the carbon dioxide in the biogas is adsorbed to the adsorbent by pressurization, and the carbon dioxide is removed from the adsorbent by setting it to atmospheric pressure. The method of claim 1,
The capture process is carried out after the reaction removal step, methane recovery method. A recovery apparatus for recovering methane from biogas containing methane as a main component and at least oxygen as an impurity:
An adsorption tower for adsorbing and removing the siloxane in the biogas by adsorbent;
A hydrogen sulfide reaction tower for reacting hydrogen sulfide in the biogas with a metal oxide to remove it as a metal sulfide,
A deoxygenation reaction tower for reacting oxygen in the biogas with copper-zinc oxide to capture copper oxide;
A pressure swing adsorption device for separating carbon dioxide in biogas by pressure swing adsorption and concentrating methane;
Methane recovery apparatus for recovering methane from biogas by operating the adsorption tower, hydrogen sulfide reaction tower, deoxygenation reaction tower and pressure swing adsorption device. The method of claim 5, wherein
Methane recovery apparatus further comprises a hydrogen introduction device for introducing hydrogen into the deoxygenation reaction tower, reducing the copper oxide produced by the reaction. The method of claim 5, wherein
The methane recovery apparatus is characterized in that the deoxygenation reaction column is introduced with a biogas from which the hydrogen sulfide is removed from the hydrogen sulfide reaction column in advance.

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