JP2012106961A - Method and apparatus for separating methane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus which are suitable for removing an odorant from city gas and for concentrating and separating methane at a high purity.SOLUTION: A method for separating methane is provided which includes a pretreatment step and a pressure swing adsorption type gas separation step in which a cycle including an adsorption step and a desorption step is performed iteratively. In the pretreatment step, by a first adsorbent preferentially adsorbing the odorant in the city gas Gincluding methane, ethane, propane, butane and the odorant, the odorant is adsorbed and removed. In the adsorption step included in the gas separation step, a plurality of adsorption columns 5A, 5B, 5C each filled with a second adsorbent preferentially adsorbing hydrocarbon gas other than methane in the city gas Gisused and a gas Ghaving gone through the pretreatment step is introduced to the adsorption columns while pressure inside adsorption columns is relatively high, consequently hydrocarbon gas other than methane in the gas Gis adsorbed by second adsorbent and product gas Genriched in methane is led out from the adsorption columns. In the desorption step included in the gas separation step, hydrocarbon gas other than methane is desorbed from the second adsorbent by evacuating the inside of the adsorption columns, and the hydrocarbon gas other than methane is led out to the outside of the columns.

Description

  The present invention relates to a method and apparatus for concentrating and separating methane from city gas using a pressure fluctuation adsorption gas separation method (PSA method).

  The city gas is mainly obtained by adding an odorant (for example, a mixture of t-butyl mercaptan and dimethyl sulfide) to four types of hydrocarbon gases such as methane, ethane, propane, and butane. An example of the concentration of various gases in city gas is methane 88.9%, ethane 6.8%, propane 3.1%, butane 1.2%, and odorant less than 10 ppm. . In general, city gas is used as a combustion gas and does not require further processing or purification. On the other hand, methane purified from city gas that can be supplied stably can be used as a carbon source for coating carbide tools or as a carbon source for the production of silicon carbide films on photoreceptor drums and amorphous silicon carbide films on amorphous solar cells. There is a need to get.

  As a technique for separating a target gas from a mixed gas containing a plurality of component gases, there is a pressure fluctuation adsorption gas separation method (PSA method). This PSA method is a technique for concentrating and separating the target gas by utilizing the fact that the adsorption capacity for the adsorbent varies depending on the gas species. In gas separation by the PSA method, a pressure fluctuation adsorption gas separation device (PSA gas separation device) including an adsorption tower filled with an adsorbent for preferentially adsorbing a predetermined component is used. An adsorption process and a desorption process are performed. In the adsorption step, the mixed gas is introduced into the adsorption tower, the easily adsorbed component in the mixed gas is adsorbed on the adsorbent under high pressure conditions, and the non-adsorbed gas enriched with the hardly adsorbed component is led out from the adsorption tower. In the desorption step, the pressure in the tower is lowered to desorb the easily adsorbed component from the adsorbent, and the desorbed gas mainly containing the easily adsorbed component is led out from the adsorption tower.

  A technique for separating city gas by the PSA method is disclosed in Patent Document 1. According to this document, by changing the pressure of city gas having a methane number of 66 between 0.1 MPa and 0.5 MPa, the methane number of the non-adsorbed gas in the adsorption step is increased to about 70, and the desorption step is performed. The methane number of the desorption gas is as low as 60 to 64. This is a method of separating the gas into a high methane number gas and a low methane number gas by adjusting the composition of the city gas. However, in the conventional method for separating methane from city gas by the PSA method, high purity methane having a methane purity of 99% or more (methane value of 95 or more) cannot be obtained, and the odorant is significantly removed. I couldn't.

JP 2006-326545 A

  The present invention has been conceived under such circumstances, and provides a method and apparatus suitable for removing odorants from city gas and concentrating and separating methane with high purity. It is an issue.

  A method for separating methane provided by the first aspect of the present invention is a method for concentrating and separating methane from a city gas containing hydrocarbon gases methane, ethane, propane and butane and an odorant. A pretreatment step of adsorbing and removing the odorant with a first adsorbent that preferentially adsorbs the odorant in the city gas, and a first preferential adsorption of hydrocarbon gas other than methane in the city gas. 2 Using a plurality of adsorption towers filled with an adsorbent, in the state where the inside of the adsorption tower is at a relatively high pressure, the mixed gas having undergone the pretreatment step is introduced into the adsorption tower, An adsorption step of desorbing a hydrocarbon gas other than methane and deriving a methane-enriched gas enriched in methane from the adsorption tower, and depressurizing the inside of the adsorption tower to remove the methane-enriched gas from the second adsorbent Of hydrocarbon gas It is characterized in that it comprises a desorption step of deriving by wearing outside the tower, and the pressure swing adsorption-type gas separation step for repeating a cycle including, a.

Preferably, the second adsorbent has activated carbon having an average pore diameter of 1.5 to 2.0 nm and a specific surface area of 600 m ² / g or more, an average pore diameter of 2.5 to 12.0 nm and a specific surface area. 100-400 m < ² > / g activated alumina and 1 or more types selected from the zeolite whose pore diameter is 0.8-1.2 nm are included.

  Preferably, the first internal pressure of the adsorption tower in the adsorption step is in the range of atmospheric pressure to 4.0 MPaG.

  Preferably, the second internal pressure of the adsorption tower in the desorption step is in the range of −0.1 MPaG to 0.3 MPaG as long as it is lower than the first internal pressure.

  Preferably, the first adsorbent is an oxide of manganese, iron, cobalt, nickel, copper or zinc, or a mixture thereof.

  Preferably, water is added at a rate of 15 to 60 ppm to the city gas before being subjected to the pretreatment step.

  Preferably, the first adsorbent is activated carbon impregnated with a mixture of an oxide of manganese, iron, cobalt, nickel, copper or zinc and an alkali metal salt.

  The apparatus for separating methane provided by the second aspect of the present invention is an apparatus for concentrating and separating methane from city gas containing hydrocarbon gases methane, ethane, propane, and butane and an odorant. The first adsorbent that preferentially adsorbs the odorant in the city gas is filled, and before performing the pretreatment step of adsorbing and removing the odorant by the first adsorbent. A plurality of adsorption towers filled with a treatment tower and a second adsorbent that preferentially adsorbs a hydrocarbon gas other than methane in the city gas, and the inside of the adsorption tower is in a relatively high pressure state. The mixed gas that has undergone the pretreatment step is introduced into the adsorption tower to adsorb hydrocarbon gases other than the methane in the mixed gas, and the methane-enriched gas enriched in methane is derived from the adsorption tower. Adsorption process, and the adsorption tower A pressure fluctuation adsorption gas separation device configured to repeatedly perform a cycle including a desorption step of depressurizing and desorbing a hydrocarbon gas other than methane from the second adsorbent and deriving the hydrocarbon gas outside the tower, It is characterized by providing.

In the second aspect of the present invention, preferably, the second adsorbent is activated carbon having an average pore diameter of 1.5 to 2.0 nm and a specific surface area of 600 m ² / g or more, and an average pore diameter of 2. It includes one or more selected from activated alumina having a specific surface area of 5 to 12.0 nm and a specific surface area of 100 to 400 m ² / g, and zeolite having a pore diameter of 0.8 to 1.2 nm.

  In the second aspect of the present invention, preferably, the first adsorbent is an oxide of manganese, iron, cobalt, nickel, copper or zinc, or a mixture thereof.

  In the second aspect of the present invention, preferably, a water addition means for adding water to the city gas is provided.

  In the second aspect of the present invention, preferably, the first adsorbent is activated carbon impregnated with a mixture of an oxide of manganese, iron, cobalt, nickel, copper or zinc and an alkali metal salt.

  According to the methane separation method of the present invention, pretreatment and gas separation by pressure fluctuation adsorption gas separation method (PSA method) are performed to remove odorant from city gas and to separate methane with high purity. can do. In this method, since city gas is used as the source gas, the source gas can be stably supplied. In the gas separation by the PSA method performed using a plurality of adsorption towers, a methane-enriched gas can be obtained continuously. Therefore, according to this method, methane-enriched gas from which the odorant is significantly removed can be continuously obtained from the stably supplied city gas. The methane-enriched gas obtained in this way can be stably supplied to applications that require high-purity methane.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a whole schematic block diagram of the methane separation apparatus for implement | achieving the methane separation method which concerns on this invention. It is a figure which shows an example of the process (steps 1-9) performed by each adsorption tower in the PSA gas separation process performed with a PSA gas separation apparatus, and the open / close state of each valve in each step. It is a figure showing the gas flow state in steps 1-9 shown in FIG.

  Hereinafter, as a preferred embodiment of the present invention, a method for concentrating and separating methane from city gas will be specifically described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a methane separation apparatus that can be used to execute the methane separation method according to the present embodiment. The methane separation device X includes a water addition unit 1, a pretreatment tower 2, a compressor 3, a line 4, and a pressure fluctuation adsorption gas separation device (PSA gas separation device) 5, and is a city as a raw material gas. It is configured such that methane can be continuously concentrated and separated while supplying gas.

The city gas G ₀ can be continuously and stably supplied from, for example, a gas supply company via a gas supply line (not shown), and is introduced into the line 4 through the gas introduction end E1. The city gas G ₀ includes four types of hydrocarbon gases, methane, ethane, propane and butane, and an odorant. Examples of the odorant include a sulfide-type odorant (a mixture of t-butyl mercaptan and dimethyl sulfide). An example of the concentration of various gases in the city gas G ₀ is 88.9% methane, 6.8% ethane, 3.1% propane, 1.2% butane, The odorant is less than 10 ppm.

The water addition unit 1, the pretreatment tower 2, and the compressor 3 are arranged in series in the line 4. The water addition unit 1 is for adding water to the city gas G ₀ as necessary, and is connected to the line 4. The water addition unit 1 includes, for example, a water storage unit and a valve capable of controlling the opening degree and the like, and the amount of water added from the water storage unit to the line 4 is controlled by the valve. Although details will be described later, a small amount of water (for example, at a rate of 15 to 60 ppm) is added to the city gas G ₀ as necessary.

The pretreatment tower 2 is for adsorbing and removing the odorant in the city gas G ₀ and is configured to allow gas to pass therethrough. The pretreatment tower 2 is filled with an adsorbent (first adsorbent) that preferentially adsorbs the odorant. The adsorbent is preferably a chemical substance that selectively adsorbs a sulfur compound or a mixture or mixture thereof, such as manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide or zinc oxide, or Mixtures of these are used. When the above oxide is used as the adsorbent, water is added to the city gas G ₀ by the water addition unit 1. By adding water to the city gas G ₀ , the adsorption rate by the adsorbent is increased, and the effect of removing the odorant can be enhanced. In addition to the above, the adsorbent that preferentially adsorbs the odorant includes, for example, activated carbon with a mixture of manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide or zinc oxide and an alkali metal salt ( For example, granular white birch NCC) is used.

When the city gas G ₀ is introduced into the pretreatment tower 2, the odorant in the city gas G ₀ is significantly adsorbed and removed by the adsorbent in the tower, and the gas G ₁ (mixed gas) is removed from the pretreatment tower 2. Is derived from

The compressor 3 is for sending the gas G ₁ flowing through the line 4 toward the PSA gas separation device 5 at the subsequent stage while pressurizing the gas G ₁ .

  The PSA gas separation device 5 includes three adsorption towers 5A, 5B and 5C, a mixed gas line 51, a product gas line 52, a gas extraction line 53 in the tower, a gas introduction line 54, a product backflow line 55, and An off-gas line 56 is provided.

Each of the adsorption towers 5A, 5B, 5C has gas passages 5a, 5b at both ends, and hydrocarbons other than methane among the hydrocarbon gases contained in the city gas G ₀ between the gas passages 5a, 5b. An adsorbent (second adsorbent) that preferentially adsorbs gas (that is, ethane, propane, and butane) is packed. As the adsorbent, activated carbon such as coconut shell or coal can be used. For example, the average pore diameter is 1.5 to 2.0 nm and the specific surface area is 600 m ² / g or more. Is used. Moreover, activated alumina can be adopted as the adsorbent, and for example, those having an average pore diameter of 2.5 to 12.0 nm and a specific surface area of 100 to 400 m ² / g are used. Furthermore, as said adsorbent, a zeolite can be employ | adopted and a pore diameter is 0.8-1.2 nm.

Mixed gas line 51 is for introducing a gas G ₁ adsorption tower 5A, 5B, in 5C, in communication with each of the adsorption columns 5A, 5B, the gas passage holes 5a of 5C through a branch passage . The product gas line 52, the gas extraction line 53 in the tower, and the gas introduction line 54 are in communication with the gas passage ports 5b of the adsorption towers 5A, 5B, and 5C, respectively, via branch paths. The off-gas line 56 communicates with the gas passage ports 5a of the adsorption towers 5A, 5B, and 5C through branch paths.

  Automatic valves a to q are provided in the respective lines 51 to 56, and flow rate adjusting valves 57 and 58 are provided in the column gas extraction line 53, the gas introduction line 54, and the product backflow line 55, respectively.

  In the PSA gas separation device 5 configured as described above, the gas flow direction and pressure in the adsorption towers 5A, 5B, and 5C are adjusted by appropriately switching the open / close states of the automatic valves a to q. In the pressure fluctuation adsorption type gas separation step performed using the PSA gas separation device 5, a cycle including, for example, an adsorption step, a desorption step, and a cleaning step is repeated in each of the adsorption towers 5A, 5B, and 5C. .

  In the adsorption step, the mixed gas is introduced into any of the adsorption towers in a predetermined high pressure state, and hydrocarbon gases other than methane (ethane, propane, and butane) in the mixed gas are adsorbed on the adsorbent, It is a process for deriving a non-adsorbed gas (methane-enriched gas) enriched with methane from the adsorption tower. For example, the desorption process is a process for depressurizing any of the adsorption towers after the adsorption process to desorb hydrocarbon gas other than methane from the adsorbent, and leading the gas in the tower out of the tower as an off-gas. The cleaning step is a step for introducing the gas in the tower as an off-gas to the outside of the tower while introducing a gas having a relatively high methane concentration derived from another adsorption tower as the cleaning gas.

In the methane separation method according to the present embodiment, a methane-enriched gas (product) in which methane is enriched from the gas G ₁ (the gas from which the odorant is removed from the city gas G ₀ ) using the PSA gas separation device 5. Gas) is separated. Specifically, by switching the automatic valves a to q in the mode shown in FIG. 2, a desired gas flow state can be realized in the apparatus, and for example, one cycle consisting of the following steps 1 to 9 can be repeated. In FIG. 2, the open state of each automatic valve is represented by ◯ and the closed state is represented by ×. In one cycle of this method, in each of the adsorption towers 5A, 5B, 5C, an adsorption step, a pressure reduction step (first pressure reduction step and a second pressure reduction step), a desorption step, a washing step, and a pressure increase step (first pressure increase) Step and second step-up step) are performed. FIG. 3 schematically shows a gas flow state in the PSA gas separation device 5 in steps 1 to 9.

  In step 1, the open / close state of each automatic valve is selected as shown in FIG. 2, and the gas flow state as shown in FIG. 3 (a) is achieved, and the adsorption process is performed in the adsorption tower 5A. The cleaning step is performed in the first depressurization step in the adsorption tower 5C.

As can be understood with reference to FIG. 2 and FIG. 3 (a), in step 1, on the gas passage 5a side of the adsorption tower 5A in a predetermined high pressure state, the mixed gas line 51 and the automatic valve a are provided. Gas G ₁ (mixed gas) is introduced. Here, ethane, propane and butane in the gas G ₁ are adsorbed by the adsorbent in the adsorption tower 5A, and the product gas G ₂ having a high methane gas concentration is led out from the gas passage port 5b side of the adsorption tower 5A. The product gas G ₂ is recovered through the automatic valve i and the product gas line 52.

For the adsorption tower 5B, the gas in the tower (cleaning gas) derived from the gas passage 5b of the adsorption tower 5C is the automatic valve n, the gas extraction line 53 in the tower, the flow rate adjusting valve 57, the automatic valve p, and the gas introduction. The gas is introduced into the gas passage 5b through the service line 54 and the automatic valve j. Since the adsorption tower 5C has previously performed the adsorption process, the adsorption tower 5B has previously performed the desorption process (see step 9 shown in FIG. 3 (i)), so that the internal pressure of the adsorption tower 5C is absorbed. The pressure is higher than the internal pressure of the tower 5B. Therefore, by introducing the gas in the adsorption tower 5C into the adsorption tower 5B, the pressure in the tower of the adsorption tower 5C is reduced to the first intermediate pressure, and the gas remaining in the tower from the gas passage port 5a of the adsorption tower 5B. Is derived. This gas is discharged out of the apparatus as an off gas G ₃ through an automatic valve d and an off gas line 56. The off gas G ₃ has a lower methane concentration than the city gas, while the concentration of hydrocarbon gas other than methane is substantially higher. Therefore, the off gas G ₃ is suitable for use as a combustion gas.

  In step 2, the open / close state of each automatic valve is selected as shown in FIG. 2, and the gas flow state as shown in FIG. 3B is achieved, and the adsorption process is performed in the adsorption tower 5A. The first pressure increasing step is performed in the adsorption tower 5C.

As can be understood with reference to FIG. 2 and FIG. 3B, in step 2, the adsorption process is continued from step 1 in the adsorption tower 5A, and the product gas G ₂ is led out of the tower. Product gas G ₂ is recovered in the same manner as in Step 1.

  On the other hand, the gas in the column (cleaning gas) led out from the gas passage port 5b of the adsorption tower 5C is an automatic valve n, a gas extraction line 53 in the tower, a flow rate adjustment valve 57, an automatic valve p, a gas introduction line 54, And it introduce | transduces into the gas passage 5b side of the adsorption tower 5B through the automatic valve j. In Step 1, the adsorption tower 5B has led out the residual gas through the automatic valve d and the off-gas line 56, but in Step 2, the automatic valve d is closed to close the space between the adsorption tower 5B and the adsorption tower 5C. The pressure equalization can be achieved. As a result, the inside of the adsorption tower 5C is further depressurized to a second intermediate pressure lower than the first intermediate pressure, and the adsorption tower 5B is boosted.

  In step 3, the open / close state of each automatic valve is selected as shown in FIG. 2, and the gas flow state as shown in FIG. 3C is achieved, and the adsorption process is performed in the adsorption tower 5A. Thus, the second pressurization step is performed in the adsorption tower 5C.

As well understood with reference to FIGS. 2 and FIG. 3 (c), the step 3, the adsorption tower 5A, subsequently adsorption step is carried out from step 2, the product gas G ₂ is derived to the outside of the tower. The product gas G ₂ is recovered in the same manner as in Step 1, but a part of the product gas G ₂ passes through the product backflow line 55, the automatic valve q, the flow rate adjustment valve 58, the gas introduction line 54, and the automatic valve j. The gas is introduced into the gas passage 5b of the adsorption tower 5B, and the pressure in the tower of the adsorption tower 5B is increased.

On the other hand, in the adsorption tower 5C, the inside of the tower is depressurized in steps 1 and 2, the automatic valves e, m, n, o are closed, and the automatic valve f is opened, so that the internal pressure ( The lowest pressure) is between 0.05 MPaG and atmospheric pressure (0 MpaG). Therefore, unnecessary gas is desorbed from the adsorbent inside the adsorption tower 5C, and this gas is led out from the gas passage port 5a together with the gas remaining in the adsorption tower 5C. This gas is discharged out of the apparatus as off-gas G ₃ through the automatic valve f and off-gas line 56. The off gas G ₃ is suitable for use as a combustion gas, as in step 1.

  In Steps 1 to 3, the internal pressure (first internal pressure) of the adsorption tower 5A in the adsorption process is, for example, in the range of atmospheric pressure to 4.0 MPaG. In step 3, the internal pressure (second internal pressure) of the adsorption tower 5C in the desorption process is, for example, in the range of atmospheric pressure to 0.3 MPaG as long as it is lower than the internal pressure of the adsorption tower 5A in the adsorption process.

  In steps 4 to 6, as shown in FIGS. 3D to 3F, in the adsorption tower 5A, the first decompression process, the second decompression process, and the desorption process are performed in the same manner as the adsorption tower 5C in steps 1-3. In the adsorption tower 5B, the adsorption process is performed in the same manner as the adsorption tower 5A in steps 1-3, and in the adsorption tower 5C, the washing process, the first pressure increase, in the same manner as the adsorption tower 5B in steps 1-3. A process and a second boosting process are performed.

  In steps 7 to 9, as shown in FIGS. 3G to 3I, the adsorption tower 5A is the same as the adsorption tower 5B in steps 1 to 3 in the cleaning process, the first pressure increasing process, and the second pressure increasing process. In the adsorption tower 5B, the first depressurization process, the second depressurization process and the desorption process are performed in the same manner as the adsorption tower 5C in steps 1-3. In the adsorption tower 5C, the same as the adsorption tower 5A in steps 1-3. Thus, the adsorption step is performed.

Then, each of the adsorption towers 5A steps 1-9 described above, 5B, by repeating in 5C, unnecessary gas is removed, high product gas G ₂ of methane gas concentration can be continuously obtained.

In the methane separation method of the present embodiment, by performing gas separation by pretreatment and pressure fluctuation adsorption type gas separation method (PSA method), odorant is removed from city gas G ₀ and methane is separated with high purity. can do. In this method, since city gas is used as the source gas, the source gas can be stably supplied. In the gas separation by the PSA method performed using a plurality of adsorption towers 5A, 5B, and 5C, a methane-enriched gas (product gas G ₂ ) can be obtained continuously. Therefore, according to this method, the methane-enriched gas from which the odorant is significantly removed can be continuously obtained from the stably supplied city gas G ₀ . The methane-enriched gas (product gas G ₂ ) obtained in this way can be stably supplied to applications that require high-purity methane.

  While specific embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention. For example, a configuration different from that of the above-described embodiment may be adopted for the configuration of the line forming the gas flow path of the PSA gas separation device. The number of adsorption towers of the PSA gas separation apparatus is not limited to the three-column type shown in the above embodiment, and the same effect can be expected even in the case of two towers or a plurality of towers of four or more towers. In addition, a cycle composed of a plurality of steps executed in the PSA gas separation apparatus can be set to a mode different from the above embodiment.

  For example, the pressure in the tower (minimum pressure) in the desorption process is not limited to the above-described range of 0.05 MPaG to atmospheric pressure, and the pressure in the tower in the desorption process is reduced from atmospheric pressure to -0.1 MPaG. May be. In this case, for example, a vacuum pump may be provided in the off-gas line 56.

  Next, the usefulness of the present invention will be described with reference to examples and comparative examples.

[Example 1]
In this example, methane was separated from the city gas G ₀ using the methane separation device X described above with reference to the drawings.

As the pretreatment tower 2, a cylindrical one having a diameter of 37 mm is used, and activated carbon (manufactured by Nippon Enviro Chemicals, Inc.) impregnated with a mixture of nickel oxide and an alkali metal salt as an adsorbent (first adsorbent) is used. A total of 0.5 liters of granular white birch NCC) was filled. The city gas G ₀ is 88.9% methane, 5.3% ethane, 3.0% propane, 1.9% butane and 10 ppm odorant (mixture of t-butyl mercaptan and dimethyl sulfide) on a volume basis. And was supplied to the pretreatment tower 2 at a flow rate of 180 L / hr in a standard state. The pressure in the pretreatment tower 2 was 350 kPaG, and the odorant was adsorbed and removed from the city gas G ₀ .

Next, the PSA gas separation process was performed by the PSA gas separation device 5 using the gas G ₁ from which the odorant was removed. As the adsorption towers 5A, 5B, and 5C, cylindrical ones having a diameter of 37 mm are used, and the inside thereof has an average pore diameter of 1.6 to 1.7 nm and a specific surface area of 1000 to 1200 m ² / g as an adsorbent. A total of 1.08 liters of coconut shell activated carbon (manufactured by Nippon Enviro Chemicals Co., Ltd .: granular white cocoon G2X) was filled. The adsorption pressure (maximum pressure) in the adsorption process was 350 kPaG, the end pressure (first intermediate pressure) in the first decompression process was 250 kPaG, and the pressure difference between these was 100 kPa. The end pressure (second intermediate pressure) in the second decompression step was 130 kPaG, and the minimum pressure in the desorption step was 20 kPaG. A product gas G ₂ was obtained through gas separation in the PSA gas separation device 5. The results are shown in Table 1.

  In addition, for the measurement of the average pore diameter and specific surface area described in the present Example etc., a specific surface area / pore distribution measuring device (manufactured by Nippon Bell Co., Ltd .: BELSORP-max) is used, and the adsorption temperature is −196 ° C. It was calculated by the BET method from the nitrogen adsorption isotherm.

[Example 2]
Methane was separated from the city gas G ₀ in the same manner as in Example 1 except that zinc oxide was used as the adsorbent packed in the pretreatment tower 2. The results are shown in Table 1.

Example 3
Methanol was separated in the same manner as in Example 2 except that 50 ppm of water was added to the city gas G ₀ by the water addition unit 1. The results are shown in Table 1.

Example 4
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, a coconut shell activated carbon having an average pore diameter of 1.7 to 1.8 nm and a specific surface area of 900 to 1100 m ² / g (manufactured by Nippon Enviro Chemicals: Granular white birch NCC) Was used, and methane was separated from the city gas G ₀ in the same manner as in Example 1. The results are shown in Table 1.

Example 5
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, activated alumina (manufactured by Sumitomo Chemical Co., Ltd .: NKHD-24HD) having an average pore diameter of 3.0 to 4.0 nm and a specific surface area of 250 to 350 m ² / g is used. Otherwise, methane was separated from city gas G ₀ in the same manner as in Example 1. The results are shown in Table 1.

Example 6
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, activated alumina (Sumitomo Chemical Co., Ltd .: KHO-24) having an average pore diameter of 8.5 to 9.5 nm and a specific surface area of 150 to 250 m ² / g is used. Otherwise, methane was separated from city gas G ₀ in the same manner as in Example 1. The results are shown in Table 1.

Example 7
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, activated alumina (Sumitomo Chemical Co., Ltd .: FO-35) having an average pore diameter of 10.0 to 11.0 nm and a specific surface area of 100 to 200 m ² / g is used. Otherwise, methane was separated from city gas G ₀ in the same manner as in Example 1. The results are shown in Table 1.

Example 8
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, a zeolite gas having a pore diameter of 0.9 to 1.0 nm (manufactured by Tosoh Corporation: F9HA) is used. Methane was separated from _zero . The results are shown in Table 1.

Example 9
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, a coconut shell activated carbon having an average pore diameter of 1.7 to 1.8 nm and a specific surface area of 900 to 1100 m ² / g (manufactured by Nippon Enviro Chemicals: Granular white birch NCC) And activated alumina having an average pore diameter of 3.0 to 4.0 nm and a specific surface area of 250 to 350 m ² / g (Sumitomo Chemical Co., Ltd .: NKHD-24HD), 0.54 liters of these layers are stacked and filled. did. Otherwise, methane was separated from city gas G ₀ in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, a coconut shell activated carbon having an average pore diameter of 1.75 to 1.85 nm and a specific surface area of 400 to 500 m ² / g (manufactured by Nippon Enviro Chemicals: Molecular Sieve 4A) Was used, and methane was separated from the city gas G ₀ in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, zeolite having a pore diameter of 0.3 to 0.4 nm (Union Showa Co., Ltd .: 4A-1.6) was used, and other than that, the same as in Example 1. Thus, methane was separated from the city gas G ₀ . The results are shown in Table 1.

[Comparative Example 3]
As an adsorbent packed in the adsorption towers 5A, 5B, and 5C, zeolite having a pore diameter of 0.4 to 0.5 nm (made by Union Showa Co., Ltd .: 5A-HP) was used, and the others were performed in the same manner as in Example 1. It was separated methane from natural gas G _0. The results are shown in Table 1.

As is apparent from Table 1, by using activated carbon (granular white birch NCC) impregnated with a mixture of nickel oxide and an alkali metal salt as a filler to be packed in the pretreatment tower 2, the sulfide-based odorant is reduced to 0. 0. It can be removed to less than 1 ppm. In addition, as is clear from Examples 2 and 3, metal oxides such as zinc oxide that selectively adsorb sulfur compounds increase the adsorption rate by adding water, and have the effect of removing odorants. Although it increases, the odorant can be significantly removed without adding water. Then, using a gas G ₁ to remove the sulfide odorant were gas separation by pressure swing adsorption gas separation method (PSA method). Thus, by going through the gas separation in the pretreatment and PSA gas separation apparatus 5 in the pretreatment tower 2, as shown in each example, the city gas G ₀ being stable supply, high purity methane gas (product gas G ₂ ) could be obtained continuously with a methane gas recovery rate of 40% or more. The product gas G ₂ of the above-described embodiment has a high methane purity of 99% or more, the odorant is almost completely removed, and can be stably supplied to applications where high-purity methane is required. .

As the adsorbent (second adsorbent) filled in the adsorption towers 5A, 5B, 5C, activated carbon can be used, and the average pore diameter is 1.5 according to Examples 1, 4 and Comparative Example 1. Activated carbon having a surface area of ˜2.0 nm and a specific surface area of 600 m ² / g or more is preferably used. Moreover, activated alumina can be used as the adsorbent packed in the adsorption towers 5A, 5B, and 5C. From Examples 5 to 7 and the like, the average pore diameter is 2.5 to 12.0 nm and the specific surface area is. A general activated alumina of 100 to 400 m ² / g can be used. Further, zeolite can be used as the adsorbent packed in the adsorption towers 5A, 5B, and 5C. According to Example 8, Comparative Examples 2 and 3, etc., the zeolite having a pore diameter of 0.8 to 1.2 nm. Are preferably used. From Example 9, it can be seen that a plurality of types of adsorbents may be stacked and filled.

As described above, according to each example, it is possible to obtain 40% or more of high-purity methane gas (product gas G ₂ ) having a purity of 99% or more from the city gas G ₀ with a methane gas recovery rate. On the other hand, the off gas G ₃ discharged through the off gas line 56 of the PSA gas separation device 5 can be used for combustion, so there is no waste even if the methane gas recovery rate in the product gas G ₂ is about 40%. High purity methane can be obtained. Further, when off gas is used for combustion, the higher the methane gas recovery rate in the product gas, the higher the proportion of hydrocarbon gas (ethane, propane and butane) other than methane in the off gas, and the amount of heat of the off gas increases. If it does so, since calorie | heat amount adjustment is needed when burning off-gas, it is preferable that the methane gas recovery rate at the time of obtaining high purity methane is about 40 to 60%.

X Methane separator 1 Water addition section 2 Pretreatment tower 3 Compressor 4 Line 5 PSA gas separator 5A, 5B, 5C Adsorption tower 5a, 5b Gas passage 51 Line for mixed gas 52 Line for product gas 53 Gas extraction in tower Line 54 Gas introduction line 55 Product backflow line 56 Off-gas line 57, 58 Flow control valves a to q Automatic valves

Claims (12)

A method for concentrating and separating methane from a city gas containing hydrocarbon gas methane, ethane, propane and butane and an odorant,
A pretreatment step of adsorbing and removing the odorant with a first adsorbent that preferentially adsorbs the odorant in the city gas;
A plurality of adsorption towers filled with a second adsorbent that preferentially adsorbs hydrocarbon gases other than methane in the city gas are used, and the adsorption tower has a relatively high pressure in the adsorption tower. An adsorption step of introducing the mixed gas that has undergone the pretreatment step to adsorb a hydrocarbon gas other than the methane in the mixed gas and deriving a methane-enriched gas enriched in methane from the adsorption tower; and A pressure fluctuation adsorption type gas separation step of repeatedly performing a cycle including a desorption step of depressurizing the inside of the adsorption tower and desorbing a hydrocarbon gas other than the methane from the second adsorbent to lead out of the tower. A methane separation method characterized by the above. The second adsorbent is activated carbon having an average pore diameter of 1.5 to 2.0 nm and a specific surface area of 600 m ² / g or more, an average pore diameter of 2.5 to 12.0 nm and a specific surface area of 100 to 400 m. The methane separation method according to claim 1, comprising at least one selected from ² / g activated alumina and zeolite having a pore diameter of 0.8 to 1.2 nm.   The methane separation method according to claim 1 or 2, wherein the first internal pressure of the adsorption tower in the adsorption step is in the range of atmospheric pressure to 4.0 MPaG.   The methane separation method according to claim 3, wherein the second internal pressure of the adsorption tower in the desorption step is in the range of -0.1 MPaG to 0.3 MPaG as long as it is lower than the first internal pressure.   The methane separation method according to any one of claims 1 to 4, wherein the first adsorbent is an oxide of manganese, iron, cobalt, nickel, copper or zinc, or a mixture thereof.   The methane separation according to any one of claims 1 to 4, wherein the first adsorbent is activated carbon impregnated with a mixture of an oxide of manganese, iron, cobalt, nickel, copper or zinc and an alkali metal salt. Method.   The methane separation method according to claim 5, wherein water is added to the city gas before being subjected to the pretreatment step at a rate of 15 to 60 ppm. An apparatus for concentrating and separating methane from city gas containing hydrocarbon gases methane, ethane, propane, and butane and an odorant,
A first adsorbent that preferentially adsorbs the odorant in the city gas, and a pretreatment tower for performing a pretreatment step of adsorbing and removing the odorant by the first adsorbent;
The adsorption tower has a plurality of adsorption towers filled with a second adsorbent that preferentially adsorbs hydrocarbon gas other than methane in the city gas, and the adsorption tower has a relatively high pressure in the adsorption tower. An adsorption step for introducing a mixed gas that has undergone the pretreatment step to adsorb a hydrocarbon gas other than the methane in the mixed gas and deriving a methane-enriched gas enriched in methane from the adsorption tower; And a desorption step in which the inside of the adsorption tower is depressurized and a hydrocarbon gas other than the methane is desorbed from the second adsorbent and led out to the outside of the tower, and the pressure fluctuation adsorption type gas is configured to be repeated. A methane separator. The second adsorbent is activated carbon having an average pore diameter of 1.5 to 2.0 nm and a specific surface area of 600 m ² / g or more, an average pore diameter of 2.5 to 12.0 nm and a specific surface area of 100 to 400 m. The methane separation device according to claim 8, comprising at least one selected from ² / g activated alumina and zeolite having a pore diameter of 0.8 to 1.2 nm.   The methane separation device according to claim 8 or 9, wherein the first adsorbent is an oxide of manganese, iron, cobalt, nickel, copper or zinc, or a mixture thereof.   The methane separation apparatus according to claim 8 or 9, wherein the first adsorbent is activated carbon impregnated with a mixture of an oxide of manganese, iron, cobalt, nickel, copper, or zinc and an alkali metal salt.   The methane separation apparatus according to claim 10, further comprising water addition means for adding water to the city gas.

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