WO2009030766A1

WO2009030766A1 - Method and apparatus for gaseous mixture separation

Info

Publication number: WO2009030766A1
Application number: PCT/EP2008/061820
Authority: WO
Inventors: Kazuo Kitsukawa; Naoiko Yamashita
Original assignee: L'air Liquide, Société Anonyme pour l'Étude et l'Exploitation des Procédés Georges Claude
Priority date: 2007-09-07
Filing date: 2008-09-05
Publication date: 2009-03-12
Also published as: JP2009061422A; JP5406441B2

Abstract

To provide a production method and production device of gas components and condensable components that enable securing desired product gas and condensable components with the desired purity and yield ratio and preventing liquefaction of the condensable components in the primary side gas of the gas separation membrane even for high yield ratios, using an efficient and versatile method. It is a device having gas separation membrane S with selective permeability and primary and secondary vapor-liquid separation sections D1 and D2 based on the difference in condensability of each component to produce permeable gas rich in highly permeable and non-condensable components obtained from gas separation membrane S, by-product liquid rich in poorly permeable and condensable components obtained from primary and secondary vapor-liquid separation sections D1 and D2, and by-product gas with reduced poorly permeable and condensable components from a feed gas containing multiple components, and is characterized by having such compositional elements as recycle gas flow path Fa that circulates at least part of the secondary by-product gas and feed gas flow path UO.

Description

Method and apparatus for gaseous mixture separation

This invention pertains to a production method and production, apparatus for gaseous mixture separation, and specifically pertains to a production method and production apparatus for gaseous mixture separation by separating and collecting specific components from feed gas containing multiple components, using a separation function of gas separation membranes with selective permeability and a vapor-liquid separation function using the difference in condensation temperature of each component.

In such facilities as semiconductor production plants or various chemical processing plants, certain amounts of highly pure gases are required as feed gases or processing gases in various processing stages, and such gases have conventionally been separated from easily accessible low cost feeds and used continuously. More specifically, such cases, for example, as obtaining enriched oxygen gas or enriched nitrogen gas, or both from air, separating and concentrating hydrogen (H2) from naphtha cracking gas, separating and collecting organic vapor from gaseous mixtures that contain organic vapor, and separating H2 from water gas can be cited. For such processes, a method of supplying gaseous mixture with different permeability as the feed gases to gas separation membranes with selective permeability, separating them into permeable gases and residual gases, and collecting permeable gases containing highly permeable gases as products, is generally used since the device is compact and simple.

As shown in figure 9, in a gas production method using such gas separation membranes, various compositions catered to the desired objectives and specifications, based on a basic system equipped with compressor 102, dryer 108, heating device 109, separation unit 103 with gas separation membranes 101 , residual side pressure regulator 110, cooling device 113 and permeated side pressure regulator 111 , have been used (see Japanese patent application 2000- 33222 for example).

In case, for example, a relatively high-pressure hydrogen gas and relatively low- pressure hydrogen gas products are required, it is well known that a cascade cycle as shown in figure 10 is effective. In this example, two sets of gas separation membranes 201 (primary gas separation membrane 201 a and secondary gas separation membrane 201 b) are combined and used. In this composition, feed gas g1 merges with permeable gas g2aa of secondary gas separation membrane 201 b, and then is supplied to primary gas separation membrane 201 a after compression. At this state, permeable gas g2a from primary gas separation membrane 201a is produced and its residual gas g2b is supplied as feed gas to secondary gas separation membrane 201 b. Residual gas is produced at this secondary gas separation membrane 201b. Permeable gas g2aa from this merges with the original feed gas and reused (see Japanese patent application 2000-33222 for example). Here, while figure 10 shows a composition of reusing permeable gas g2aa from secondary gas separation membrane 201b, it is also possible to collect permeable gas g2a as the high- pressure product gas and permeable gas g2aa as the low-pressure product gas.

It is also possible to compose a system, as a parallel cycle, as shown in figure 11 , that separates and collects enriched nitrogen gas from air. In figure 11 , two hollow-fiber separation membrane modules 312 and 313 are used in parallel, the supply gas is diverged and supplied after pretreatment to each of hollow-fiber separation membrane modules 312 and 313, and the enriched nitrogen gas obtained from each of hollow-fiber separation membrane modules 312 and 313 is merged and led to product gas outlet 324. The air taken in from air inlet 301 is led to dust filter 302 to remove suspended particles in the air, and sent to compressor 303. The pressurized air is supplied from the gas supply port of hollow-fiber separation membrane modules 312 and 313 and sent to the supply side of the membranes. The permeable gas permeated flows through the permeated side of the membranes, forms a permeable gas discharge flow via the permeable gas discharge port, and is discharged out of the system after its flow rate is reduced at flow rate adjustment valves 316 and 317 at the middle of the piping (see Japanese patent application 2002-35530 for example). Here, while figure 11 shows a system in which enriched nitrogen gas is collected as the product gas and since the permeable gas discharge flow is enriched oxygen gas, it is also possible to collect this as the product gas. Here, by independently adjusting the pressure and flow rate of the air supplied to the parallel hollow-fiber separation membrane modules 312 and 313, it is possible to collect the permeable gas from one as the high-pressure product gas and collect the permeable gas from the other as the low-pressure product gas.

The purity and yield ratio of the product become the primary characteristics when using gas separation membranes to produce gas. In general, the desired purity is determined depending on the use of the product gas, and after investigation along the policy to secure the highest yield ratio within that purity range, the control method including the processes and turndown operations is determined. However, there have been problems with the system or method stated above when using feed gas that contains multiple components including non-permeable and condensable components.

(i) Since deterioration of the membrane itself may occur, it is necessary to avoid generation of mist in the gas at the primary side of the membrane. In more detail, when condensable components are contained in the feed gas, since there is a possibility of liquefaction at ambient temperature, and when these condensable components are non-permeable gases, there is a possibility of these condensable components in the gas condensing and liquefying at the primary side (non-permeable side) of the gas separation membrane as the gas separation progresses, it has been necessary to avoid generation of liquid mist at the gas separation membrane by cooling the feed gas to approximately 40⁰C (atmospheric condition in summer), for example, and then heating the condensable and liquefiable components using the heating means after their separation.

(ii) However, since there remains the possibility of re-liquefaction of the condensable components in the gas at the primary side of the gas separation membrane when attempting to raise the desired component yield ratio of the permeable gas (hereinafter referred to as "yield ratio") since there is limitation in the heating temperature due to such relationships as the gas separation membrane characteristics and its high-temperature tolerance, such measures as limiting the yield ratio or lowering the primary-side pressure of the gas separation membrane. This invention focuses on preventing liquefaction in the primary side gas of the gas separation membrane, accompanying concentration of the condensable components. As permeation progresses, concentration of the condensable components progresses, and hence the gas immediately near the residual gas outlet becomes most susceptible to liquefaction. Therefore, the under-pressure dew point of the gas at the residual gas outlet becomes important, and if the dew point is lower compared to the gas temperature at the gas separation membrane, liquefaction in the gas at the primary side of the gas separation membrane will not occur. In actuality, it is desirable to operate by setting the reference value of the aforementioned dew point at slightly lower (at 10⁰C for example) than the gas temperature of the gas separation membrane considering such factors as the feed gas composition and fluctuation in operational conditions. Hereafter, the pressure immediately after the residual gas outlet of the gas separation membrane is referred to as "residual gas pressure," the dew point under residual gas pressure immediately after the residual gas outlet of the gas separation membrane is referred to as "residual gas dew point," the flow rate of the residual gas of the gas separation membrane is referred to as "residual gas flow rate," and the pressure and flow rate of the permeable gas are referred to as "permeable gas pressure" and "permeable gas flow rate."

The objective of this invention is to provide a production method and production apparatus for gaseous mixture separation with the desired purity and yield ratio that securely produce the desired product gases and condensable components when collecting gas components and condensable components from feed gases that contain multiple components, and prevent liquefaction of condensable components in the primary side gas of the gas separation membrane even when using efficient and versatile methods to obtain high yield ratio. Its objective in particular is to gain even higher yield ratio when conducting the turndown operation. In this patent claim, simply "yield ratio" means the ratio of the total volume of the flow rate of the desired components (highly permeable gases) in the product gas to the flow rate of the desired components in the feed gas. Moreover, needless to say, this also includes cases in which the final residual gas is used as the by-product.

The inventors of this invention reached completion of this invention after accumulation of dedicated research to realize the aforementioned objective by the production method and production apparatus for gaseous mixture separation as described below. Here, as to the elements of the same function, the upstream side is referred to as the primary or first, and the downstream side is referred to as the secondary or second.

This invention relates to a separation method generating: - a permeable gas rich in highly permeable and non-condensable component A,

- a by-product liquid rich in a poorly permeable and condensable component B, and

- a by-product gas lean in the component B, from a feed gas containing multiple components including the components A and B, said method including a separation step using one or several selectively gas permeable membrane(s) and at least two steps consisting of a vapor-liquid separation using the differences in condensability of at least one component, one of these steps being performed before the aforementioned separation using membranes (primary vapor-liquid separation) and another one being performed after the aforementioned separation using membranes (secondary vapor-liquid separation), the method being characterized in that it also includes at least the following steps:

(I ) diverting part of the secondary by-product gas as a recycle gas, the secondary by-product gas being produced at the downstream side of the aforementioned secondary vapor-liquid separation and being lean in the component B (2) adjusting the flow rate and pressurizing the aforementioned recycle gas

(3) performing a primary cooling and/or a primary vapor-liquid separation of the aforementioned recycle gas

(4) extracting the primary by-product gas obtained by the aforementioned primary vapor-liquid separation, said primary by-product gas being lean in the component B

(5) extracting the primary by-product liquid obtained by the aforementioned primary vapor-liquid separation treatment and primarily composed of the aforementioned component B

(6) supplying the aforementioned primary by-product gas to the gas separation membrane after heating said primary by-product gas

(7) supplying the aforementioned feed gas and mixing it with the aforementioned recycle gas either before the aforementioned pressurizing process, before the primary cooling, before the primary vapor-liquid separation, after the primary vapor-liquid separation process or after the heating process (8) adjusting either the primary pressure of the aforementioned gas separation membrane or its correlated process values

(9) mixing the aforementioned feed gas with the aforementioned recycle gas either before the aforementioned pressure increase treatment, before the primary cooling treatment, before the primary vapor-liquid separation treatment, after the primary vapor-liquid separation step, or after the heating treatment

(10) separating the mix into a permeable gas and a residual gas at aforementioned gas separation membrane

(I I ) after performing the separation step using membrane(s), extracting the permeable gas rich in the aforementioned component A as a product and the residual gas rich in the aforementioned component B

(12) applying a secondary cooling treatment and a secondary vapor-liquid separation to the aforementioned residual gas (13) extracting the secondary by-product gas obtained from the aforementioned secondary vapor-liquid separation, said by-product gas being lean in the component B extracting the secondary by-product liquid obtained from the aforementioned secondary vapor-liquid separation step and primarily composed of the aforementioned component B.

This invention also relates to a device for obtaining gas components and condensable components using at least two vapor-liquid separation units and gas separation membranes with selective permeability and the difference in condensability of at least one component of the feed gas containing multiple components, characterized in that it produces a permeable gas rich in highly permeable and non-condensable component A obtained by the aforementioned gas separation membranes, a by-product liquid rich in poorly-permeable and condensable component B and a by-product gas lean in the component B and obtained by the aforementioned vapor-liquid separation sections, and it includes at least the following components:

(a) a recycle gas flow path diverting from the by-product gas flow path coming from the downstream side of the aforementioned vapor-liquid separation section

(b) a flow rate adjustment section and pressure booster section set up at the aforementioned recycle gas flow path

(c) a primary supply gas flow path connected to the aforementioned recycle gas flow path (d) a primary cooling section and primary vapor-liquid separation section set up at the aforementioned primary supply gas flow path (e) a primary by-product gas flow path from which the by-product gas is extracted from the gaseous section of the aforementioned primary vapor- liquid separation section (f) a primary by-product liquid flow path from which the by-product liquid is extracted from the liquid section of the aforementioned primary vapor-liquid separation section

(g) a heating section installed at the aforementioned primary by-product gas flow path (h) a feed gas flow path that supplies the feed gas containing multiple components, and joins the aforementioned recycle gas flow path or primary supply gas flow path at either the upstream side of the aforementioned pressure booster section, upstream side of primary cooling section, upstream side of primary vapor-liquid separation section, downstream side of primary vapor-liquid separation section or downstream side of the heating section

(j) gas separation membranes that is connected to the aforementioned primary by-product gas flow path and separates the gas into permeable gas and residual gas

(k) a permeable gas flow path to which the permeable gas is permeated from the aforementioned gas separation membranes (m) a residual gas flow path to which the residual gas is supplied from the aforementioned gas separation membranes

(n) a secondary cooling section and secondary vapor-liquid separation section installed at the aforementioned residual gas flow path (p) a secondary by-product gas flow path to which the by-product gas is supplied from the gaseous section of the aforementioned secondary vapor- liquid separation section

(q) a secondary by-product liquid flow path to which the by-product liquid is supplied from the liquid section of the aforementioned secondary vapor- liquid separation section (r) a secondary pressure adjustment section installed at the aforementioned secondary by-product liquid flow path after the aforementioned diverging point.

As methods of collecting highly permeable and non-condensable components (referred to as "components A" in this invention), and poorly permeable and condensable components (referred to as "components B" in this invention) from feed gases that contain multiple components, and securing production of desired product gases and condensable components of desired purity and yield ratio, such methods as a method of using a separation function with gas separation membranes with selective permeability, and a method of using a vapor-liquid separation function based on the difference in condensability of each component have been used, and in many cases, conventionally, these methods have been used independently. Even when combining these methods, there have been such methods as a method of using the latter as the pre-treatment and then using the former to treat the treated gas, or vice-versa, but in either case, one method is considered as the main and the other is considered as the supplementary. This invention is intended to prevent condensation of the aforementioned components in the primary side gas of the gas separation membrane and improve the yield ratio of the permeable gas and the condensable components by utilizing the fact components B concentrate in the residual gas of the gas separation membrane when components B are contained in the feed gas, and setting up a combination of a cooling unit and vapor-liquid separation unit before and after the gas separation membrane.

That is, it is possible to reduce the volume of components B that is transferred to the residual gas to prevent condensation in the gas at the primary side of the gas separation membrane, and improve the efficiency of permeable gas at the gas separation membrane. Moreover, by collecting components B concentrated in the residual gas at the cooling unit and vapor-liquid separation unit at the latter stage, in addition to the first stage collection, it is possible to secure an unprecedented yield ratio of components B. Furthermore, when the temperature of the feed gas is relatively low, it is possible to introduce it directly to the vapor-liquid separation unit without the need of the cooling unit.

Here, when components B are contained in the feed gas, it is necessary to leave components A that are supposed to be extracted as the permeable gas to a certain level and extract them as the residual gas with lowered dew point in order to prevent generation of mist since components B concentrate in the primary side of the gas separation membrane. Therefore, as a result, in actual operation, components A are included in the by-product gas and extracted. Hence, it is possible to collect and reuse components A corresponding to the flow rate if a part of them is diverted and mixed with the feed gas as the recycle gas. Especially when the feed gas contains poorly-permeable and non-condensable components, the effect of enabling lowering the aforementioned level of components A is added since the concentration of the aforementioned components in the residual gas increases due to the formation of the recycle system. Therefore, it is possible to provide a production method and production apparatus of gas components and condensable components with the desired purity, securely produce the desired product gases and condensable components, and prevent liquefaction of condensable components in the primary side gas of the gas separation membrane even when using efficient and versatile methods to obtain high yield ratio.

Here "gas separation membrane" is not limited to cases in which one membrane module is used with inlet ports and outlet ports of supply gas, permeable gas and residual gas, but also includes compositions using a necessary number of multiple membrane modules lined in parallel and each module having inlet ports and outlet ports of supply gas, permeable gas and residual gas. Moreover, "condensable components" refer to components with condensability to the condensation treatment, and are not limited to high or poor permeability to the gas separation membrane. "Highly permeable and non-condensable components" refer to components with high permeability to the gas separation membrane and non-condensability to the condensation treatment, and more specifically refer, in the implementation example below, to hydrogen when, for example, hydrogen, methane, butane and pentane are mixed in the feed gas. "Poorly permeable and non-condensable components" refer to components with poor permeability to the gas separation membrane and non-condensability to the condensation treatment, and in the above example, refer to methane. "Poorly permeable and condensable components" refer to components with poor permeability to the gas separation membrane and condensability to the condensation treatment, and in the above example, refer to butane and pentane. Furthermore, this invention essentially has the same effect in cases where small amounts of permeable and condensable components (such, for example, as water in the feed gas in the implementation example below) are contained in the feed gas. Therefore, it is noted here that this invention also includes such cases. "Process value connected with the pressure" refers to a process value that changes with the pressure change, and such values as the residual gas flow rate to the primary pressure and the permeable gas flow rate to the secondary pressure can be cited. The same applies to the following.

According to another embodiment of the invention the abovementioned method, is characterized in that, especially for turndown operation, the flow-rate of aforementioned recycle gas is adjusted according to the degree of turndown.

When poorly permeable and condensable components are contained in the feed gas, it is required to maintain the dew point of the residual gas at a low level to prevent liquefaction of the condensable components in the gas at the primary side of the gas separation membrane, and by forming a recycle system in which a part of the by-product gas is diverted and mixed with the feed gas as the recycle gas, it is possible to prevent liquefaction of the condensable components in the gas at the primary side of the gas separation membrane. However, when turndown operation of the feed gas occurs, the concentration of the permeable gas at the residual gas outlet port lowers and the condensable components become susceptible to liquefaction if the primary side pressure of the gas separation membrane is kept at constant. At this time, by increasing the flow rate of the recycle gas, the concentration of the non-condensable components in the residual gas increases, and hence it is possible to prevent liquefaction of the condensable components. In this manner, by adjusting the flow rate of the recycle gas in accordance with the level of turndown, it is possible to secure the desired product gas with the desired purity and yield ratio and prevent liquefaction of the condensable components in the primary side gas of the gas separation membrane even with a high yield ratio. Especially when a pressure booster unit is necessary, it is possible to use the pressure booster unit of the recycle gas for this purpose, and make use of the excess capacity of this unit even during turndown operation.

According to another embodiment of the invention, the above mentioned methods are characterized by adjusting the primary pressure, the secondary pressure of the aforementioned gas separation membrane, or a process value connected with said pressure levels, according to the degree of turndown.

When turndown operation of the feed gas occurs, by lowering primary pressure P1 in accordance with the reduction in the flow rate of the feed gas, in addition to the effect of recycle part of the secondary by-product gas, it is possible to prevent liquefaction of the condensable components in the primary side gas of the primary gas separation membrane since the partial pressure of the condensable gas lowers. Moreover, a similar effect can also be obtained by adjusting the residual gas flow rate to increase instead of primary pressure P1. Furthermore, it is also possible to prevent liquefaction of the condensable components in the primary side gas of the primary gas separation membrane by adjusting secondary pressure P2 to increase or permeable gas flow rate to decrease, and suppressing the increase in the yield ratio of the permeable gas.

According to another embodiment of the invention, the above mentioned methods are characterized by:

- preventing liquefaction within the gas at the primary side of the aforementioned gas separation membrane by expressing the flow rate ratio r defined as the aforementioned recycle gas flow rate divided by feed gas flow rate, - pre-analyzing the aforementioned flow rate ratio r as a parameter regarding the correlation function between the residual gas pressure and the concentration of the aforementioned component A in the residual gas of the aforementioned gas separation membrane by setting a reference value Za of the dew point Z under the pressure at the flow path immediately after the residual gas outlet of the aforementioned gas separation membrane based on the characteristics of the feed gas composition and the aforementioned gas separation membrane,

- monitoring the aforementioned dew point Z so that it is below the aforementioned reference value Za from the measured values of the aforementioned flow rate ratio r and the concentration of the aforementioned component A in the residual gas using the aforementioned correlation function during the operation, and

- adjusting either the aforementioned recycle gas flow rate, the residual gas pressure of the aforementioned gas separation membrane, the permeable gas pressure or their connected process value, in order to keep the aforementioned dew point Z below the aforementioned reference value Za.

When the composition of the feed gas supplied to the gas separation membrane and the residual gas dew point are fixed, there is a correlation between residual gas pressure Pr and concentration X of components A in the residual gas, that is the correlation of 1/Pr and X to be linear, and since this correlation can be expanded in a form that includes various other parameters, it can be used to prevent liquefaction of the condensable components at the primary side of the gas separation membrane in specific cases (see Japanese patent application 2007-232918). This invention is an expansion to including flow rate ratio r between the recycle gas flow rate and the feed gas flow rate using the dew point under the pressure at immediately after the outlet port of the residual gas flow path as the reference, and its effectiveness was also confirmed by the numerical analysis in the implementation example stated later. This correlation function provides for the judgment of preventing liquefaction at the primary side of the gas separation membrane, and if necessary, it is possible to adjust any of the recycle gas flow rate, residual gas pressure of the gas separation membrane, permeable gas pressure or the process values that are connected with these. Hereinafter, the dew point under the pressure immediately after the residual gas flow path outlet port is referred to as "residual gas dew point Z, and it is possible to prevent liquefaction of condensable components in the gas at the primary side of the gas separation membrane, secure the desired purity, and provide a production method of gas components and condensable components with the highest possible yield ratio using a versatile and cost efficient method.

According to another embodiment of the invention the abovementioned apparatus is characterized by forming a cascade connection by using multiple layers of the aforementioned gas separation membranes and supplying the residual gas from the first layers of the gas separation membranes to the subsequent layers of the gas separation membranes.

According to another embodiment of the invention, the above mentioned methods are characterized in that the gas separation membrane consists of several stages of gas separation membranes forming a cascade, the residual gas of one separation membrane being sent to the following gas separation membrane in the cascade.

Generally, the cascade cycle is used to secure the desired product purity and yield ratio even with relatively small membrane area in such cases as producing multiple product gases with different purity, by using multiple stages of gas separation membranes and making the permeable gas from each membrane as the product gas. According to this invention that circulates part of the secondary by-product in addition to this cascade cycle, it is possible to secure an even higher yield ratio while preventing liquefaction of the condensable components in the primary side gas of the gas separation membrane. Moreover, it is possible to further improve the yield ratio of the permeable gas since a relatively large amount of permeable gas is contained in the residual gas from the early stages of gas separation membranes, the dew point of the residual gas is relatively low and the possibility of the condensable components liquefying is low, and by sequentially controlling the primary pressure of each stage of the gas separation membrane, it is possible to prevent liquefaction as the gas is supplied sequentially to the latter gas separation membranes even if the condensable components are concentrated. Therefore, it is possible to provide a method for gaseous mixture separation and its apparatus that secure the desired product gases and condensable components with the desired purity and yield ratio, and prevent liquefaction of the condensable components in the primary side gas of the gas separation membrane, using an efficient and versatile method even for high yield ratios.

As stated above, by applying the method for gaseous mixture separation and the apparatus pertaining to this invention, it is possible to provide a method for gaseous mixture separation and its apparatus that secure the desired product gases and condensable components with the desired purity and yield ratio, and prevent liquefaction of the condensable components in the primary side gas of the gas separation membrane, using an efficient and versatile method even for high yield ratios. It has become possible to realize an even higher yield ratio especially when conducting a turndown operation.

The configuration of implementing this invention is described below with figures. The basic objective is to produce permeable gases with the desired purity and secure the desired yield ratio also for the condensable components by applying primary cooling treatment and primary vapor-liquid separation process to the feed gas before and after the selective separation process using the gas separation membranes, secondary cooling treatment and secondary vapor-liquid separation treatment to the residual gas, and diverting and recycle part of the secondary byproduct gas and merging it with the feed gas in the process of producing permeable gas rich in highly permeable and non-condensable component A obtained by the separation function, by-product liquid rich in poorly-permeable and non-condensable component B obtained by at least two vapor-liquid separation functions located at the upstream and downstream of the gas separation membranes, and lean component B by-product gas, by subjecting the feed gas containing multiple components to a separation function of gas separation membranes with selective permeability and a vapor-liquid separation function based on the difference in condensability of each component. Since the conditions required for this process vary diversely depending on the upstream and downstream process compositions and the purpose of the product gas, and the operational conditions and control methods vary according to them, a typical example is described here. This invention is not limited to the compositional examples stated below, and many variations and expansions are possible by combining the above characteristics to general gas separation membrane processes.

Figure 1 shows compositional example 1 (compositional example 1 , Apparatus 1 ) of the gaseous mixture separation apparatus pertaining to this invention (hereinafter referred to as "this Apparatus"). Specifically, it is composed of feed gas flow path UO, primary supply gas flow path U1 , primary by-product gas flow path G1 , primary by-product liquid flow path L1 , gas separation membranes S, permeable gas flow path T1 , residual gas flow path R1 , secondary by-product gas flow path G2, secondary by-product liquid flow path L2, recyclegas flow path Fa, primary cooling unit C1 and primary vapor-liquid separation unit D1 installed in primary supply gas flow path U1 , heating unit H installed in primary by-product gas flow path G1 , primary liquid surface detection unit LC1 and primary control valve LCV1 installed in primary by-product liquid flow path L1 , secondary cooling unit C2 and secondary vapor-liquid separation unit D2 installed in residual gas flow path R1 , pressure control means PCrI (pressure control valve PCV1 and pressure controller PC1 ) installed in secondary by-product gas flow path G2, secondary liquid surface detection unit LC2 and secondary control valve LCV2 installed in secondary by-product liquid flow path L2, flow rate control means FCM (flow rate control valve FCV1 and flow rate controller FC1 ) installed in recycle gas flow path Fa, and pressure booster unit E and control unit (not shown in figure). Here recycle gas flow path Fa is formed with its original feeding point at the diverging point setup in secondary by-product gas flow path G2, and connected to primary supply gas flow path U1 (connects to feed gas flow path UO) via flow rate control means FCrI and pressure booster unit E. Moreover, feed gas analysis port APo and permeable gas analysis port AP1 (used for batch analysis by such instruments as a gas chromatography mass spectrometer) are installed. In addition to the analysis ports, it is also possible to install concentration measuring means. Details will be discussed later.

When a relatively large amount of components B is contained in the feed gas, this Apparatus 1 is used for primary cooling treatment and primary vapor-liquid separation process, and selective separation process by the gas separation membranes of the feed gas, and load reduction of secondary cooling treatment and secondary vapor-liquid separation process of the residual gas, by diverting part of secondary by-product gas with low condensable components after the secondary vapor-liquid separation process and mixing it as the recycle gas with the feed gas so that it is possible to collect and reuse components A (e.g. hydrogen) depending on its flow rate. That is, by forming such a circulatory system, there is no need to forcibly raise the hydrogen concentration remaining in the residual gas, and the effect of being able to set the condition suited to the characteristics of gas separation membranes S is added.

Here, the mixing point of the feed gas and recycle gas is not limited to the point immediately before pressure booster unit E as shown in figure 1 , but it is also possible to set it at a ~ d shown in dotted lines depending on such factors as the feed gas pressure, temperature and dew point, where a: is a mid-point between pressure booster unit E and primary cooling unit C1 , b: is a mid-point between primary cooling unit C1 and primary vapor-liquid separation unit D1 , c: is between primary vapor-liquid separation unit D1 and heating unit H, and d: is between heating unit H and gas separation membranes S. Moreover, these compositions can also be applied to the compositional examples below. In a: above, it is enough to only supplement the pressure loss of the circulation loop in cases pressure booster unit E is used only for increasing the pressure of the recycle gas, and it is possible to use a method of suck-drawing the recycle gas using the flow of the feed gas and an ejector.

In this Apparatus 1 , a composition in which primary pressure P1 that supplies the feed gas is controlled by pressure control means PCrI installed in secondary byproduct gas flow path G2 is shown as an example, but needless to say, it is not limited to this and such compositions as installing pressure control means PCrI in feed gas flow path UO, supply gas flow path U1 , primary by-product gas flow path G1 , primary residual gas flow path R1 , or in a separately added bypass flow path, are also possible. Since a high-pressure state is generally more effective for condensation at secondary vapor-liquid separation unit D2, it is desirable to locate pressure control valve PCV1 after the recycle gas diversion point on secondary by-product gas flow path G2. It is also possible to control the residual gas flow rate using the process value that changes according to the change in the primary pressure instead of the control by primary pressure P1. The same applies to the following.

As the feed gas, it is desirable to supply refined gas or refinement-treated crude gas, and specifically such gases as refined air, refined naphtha cracking gas, refined reformed gas, refined water gas, and refined natural gas can be considered. As to the supply condition of the feed gas, the above gases are used generally at ambient temperature, and a flow rate of 1 ,000 ~ 100,000 [Nm³/h]. The pressure condition varies depending on the purpose of the permeable gas, but it should be pressurized to approximately 1 ~ 50 [bar (abs)].

As to gas separation membranes S, those with the optimal material, capacity (surface area) and form shall be selected depending on the type of the feed gas or permeable gas. As to the material of gas separation membranes S, such materials, for example, as polyethylene (PE), polypropylene (PP), silicone rubber, polysulfone, cellulose acetate, polyaramid (PA), and polyimide (Pl) can be considered. This Apparatus 1 is not limited to the above materials.

Here, it is desirable to set up a heating means (heating unit H) at primary byproduct gas flow path G1 that supplies the feed gas to gas separation membranes S. It is desirable that gas separation is performed at an adequate temperature depending on the characteristics and purpose of the gas separation membranes, and it is necessary to heat the feed gas to a certain adequate temperature. If liquid mist is contained in the feed gas, there is a risk of causing deterioration of the gas separation membrane depending on its material. In more detail, if the feed gas contains high-boiling point components, liquefaction may occur at ambient temperature, and when this high-boiling point component is poorly-permeable gas, there is a risk of concentration and liquefaction of the high-boiling point component in the gas at the primary side of the gas separation membrane. Therefore, by cooling the feed gas to, for example, 40⁰C (summer condition) with primary cooling unit C1 installed in primary supply gas flow path U1 , and then heating it with heating unit H after separating the condensable and liquefiable components at primary vapor-liquid separation unit D1 , it is possible to avoid the risk of generating liquid mist at gas separation membrane S. However, in case the amount of the high-boiling point components contained in the feed gas is small, it is possible to omit primary cooling unit C1 (that is the supply of feed gas to primary supply gas flow path U1 ), and further omit primary vapor- liquid separation unit D1 (that is the supply of feed gas to primary by-product gas flow path G 1 ).

The gases sampled from analysis ports APo and AP1 are batch-analyzed using such devices as the gas chromatography, so that it is possible to adopt a method of correcting the coefficient of the calculation equation from regular periodic analysis results. It is also possible to use the concentration measuring means described later for control instead of this. As to the concentration measuring means, it is desirable to use an analyzer that is highly selective to the desired components, that is the product gas components, and highly reliable for continuous analysis. For example, in case the component is hydrogen, such analyzers as the thermal conductivity type analyzer, or in case the component is methane, an infrared ray absorption type analyzer can be considered. It is also possible to adopt a method of combining the batch analysis and continuous analysis. It is possible to provide for judging fine adjustments while checking the deviation of the continuous analysis instrument from the results of the more reliable batch analysis.

Example control method using this Apparatus 1 :

In the process from the feed gas supplied to gas separation membranes S of this Apparatus 1 to production of the final product gas and condensable components, in case the permeable gas from gas separation membranes S is the product gas, the composition includes at least the following steps.

(1 ) diverting part of a secondary by-product gas as the recycle gas

(2) adjusting the flow rate: of the recycle gas and pressurizing said recycle gas: the flow rate here is the subject of control (3) performing a primary cooling treatment and primary vapor-liquid separation process, or only the primary vapor-liquid separation process of recycle gas

(4) extracting the primary by-product gas

(5) extracting the primary by-product liquid

(6) supplying the aforementioned primary by-product gas to gas separation membrane after applying heat treatment to it

(7) supplying the feed gas, and mix it with the recycle gas before the pressure increase process: the point of mixing can be before primary cooling treatment, before primary vapor-liquid separation process, after primary vapor-liquid separation process or after heating treatment depending on the characteristics of the feed gas

(8) adjusting either the primary pressure of gas separation membrane S or its connected process value: the pressure here is the subject of control

(9) separating the gas into permeable gas and residual gas at gas separation membrane S (10) extracting the permeable gas as the product

(11 ) extracting the residual gas

(12) to applying secondary cooling treatment and secondary vapor-liquid separation process to the residual gas

(13) extracting the secondary by-product gas (14) extracting the secondary by-product liquid

Here, it is desirable to control primary pressure P1 and, at the same time, recycle gas flow rate F1 to adjust the concentration and yield ratio of the product gas within the desired range. More specifically, based on the desired component concentration sampled from analysis ports APo and AP1 , they are controlled using pressure control means PCrI (pressure control valve PCV1 and pressure controller PC1 ) installed in secondary by-product gas flow path G2 and flow rate control means FCrI (flow rate control valve FCV1 and flow rate controller FC1 ) installed in recycle gas flow path Fa.

Furthermore, during the turndown operation, as stated above, it is also possible to use (i) a method of adjusting primary pressure P1 or secondary pressure P2 of gas separation membrane S according to the degree of turndown, (ii) a method of adjusting recycle gas flow rate F1 according to the degree of reduction, and (iii) a method of adjustment using a combination of (i) and (ii) according to the degree of turndown.

(i) The method of adjusting primary pressure P1 or secondary pressure P2 of gas separation membrane S according to the degree of turndown In cases the feed gas contains poorly-permeable and condensable components, there is a risk of liquefaction of the condensable components in the primary side gas of gas separation membrane S as stated above when conducting a turndown operation of the feed gas if primary pressure P1 of gas separation membrane S is kept at constant. By lowering primary pressure P1 according to the decrease in the feed gas flow rate in addition to the effect of circulating part of the secondary by-product gas, it is possible to prevent liquefaction of the condensable components in the primary side gas of gas separation membrane S since the partial pressure of the condensable gas lowers. At this time, it is possible to secure stable yield ratio when conducting the turndown operation since the flow rates of the permeable gas and residual gas also change according to the flow rate of the feed gas.

However, depending on the required specifications of the product, there are cases in which setting the value at a constant is desirable since decrease in the concentration of the permeable gas and liquefaction of the condensable components in the primary side gas of gas separation membranes S during the turndown operation may not be a problem. Also depending on the required specifications of the product, there are cases in which it is desirable to set the value by calculating using a function (such as a primary expression) of the feed gas flow rate or permeable gas flow rate to gas separation membrane S. Moreover, there are cases in which it is desirable to adopt a method of calculating using a broken-line function of the turndown ratio, for example, not lowering primary pressure P1 to a certain turndown ratio, and lowering primary pressure P1 according to the turndown ratio after that certain level. That is, by applying the composition or method stated above, it has become possible to secure stability of the desired product gas purity and yield ratio with a simple method without having to change the module number even when the feed gas flow rate is reduced. Moreover, when performing turndown, the yield ratio increases if primary pressure P1 and secondary pressure P2 are set at constant, but a method of raising secondary pressure P2 and regulate increase in the yield ratio to prevent liquefaction is also possible. Moreover, if secondary pressure P2 can be reduced, a method of reducing both primary pressure P1 and secondary pressure P2 simultaneously is also possible.

(ii) The method of adjusting recycle gas flow rate F1 according to the degree of turndown

The recycle gas is composed of gas with reduced component B since it is a part of the secondary by-product gas that has been diverged. Therefore, it is possible to reduce the effect of the turndown operation and, at the same time, reduce the risk of liquefaction of the condensable components in the primary side gas of gas separation membranes S by the control through incrementally mixing the recycle gas flow rate corresponding to the turndown volume to the feed gas without lowering primary pressure P1 , and produce the product gas and condensable components while securing stable product purity and yield ratio.

(iii)The method of adjustment using a combination of (i) and (ii) according to the degree of turndown

In the turndown operation, while the control content varies depending on the required specifications such as a control for the purpose of maintaining the product gas flow rate, or a control for the purpose of maintaining the yield ratio of the desired components, the characteristics and the risk of condensation also change depending on the turndown ratio. Therefore, by utilizing the different technological effects of the methods (i) and (ii) as stated above, and combining and adjusting them it is possible to reduce the effect of the turndown operation and produce the product gas and condensable components while securing stable product purity and yield ratio. Specifically, by the control through incrementally mixing the recycle gas flow rate corresponding to the turndown to the feed gas without lowering primary pressure P1 up to a certain turndown ratio, and then lowering primary pressure P1 corresponding to the reduction ratio after that certain turndown level, it is possible to prevent the risk of liquefaction while securing stable product purity and yield ratio.

Furthermore, as stated above, it is also effective by setting the flow rate ratio between the aforementioned recycle gas flow rate and feed gas flow rate as r, pre-analyzing flow rate ratio r as a parameter regarding the correlation function between the residual gas pressure and the concentration of component A in the residual gas at the gas separation membranes by setting reference value Za of dew point Z based on the characteristics of the feed gas composition and the aforementioned gas separation membrane, and controlling above stated (i) and (ii) so that residual gas dew point Z is below reference value Za from the measured values of flow rate ratio r and concentration of component A in the residual gas using the correlation function during the operation. The same applies to the other compositional examples described below.

Modified example 1 of this Apparatus 1 is shown in figure 2. While the basic composition is the same as compositional example 1 , pressure control means PCro (pressure control valve PCVo) is further installed in primary by-product gas flow path G1. It is possible to independently control primary vapor-liquid separation unit D1 from primary pressure P1 of gas separation membranes S, and at the same time, control it to a higher pressure even during turndown operation. The mixing (merging) point of the feed gas and the recycle gas, as shown in dotted lines a ~ c, can be set up a: midway between pressure booster unit E and primary cooling unit C1 , b: midway between primary cooling unit C1 and primary vapor-liquid separation unit D1 , or c: midway between primary vapor- liquid separation unit D1 and pressure control means PCro.

Modified example 2 of this Apparatus 1 is shown in figure 3. While the basic composition is the same as compositional example 1 , a diverging point is set up in secondary by-product gas flow path G2, and additive gas flow path Fc is formed connected to permeable gas flow path T1 via flow rate control means FCr3 (flow rate control valve FCV3 and flow rate controller FC3). Analysis port AP3 for assessing the performance is set up at product gas flow path A1 from which the permeable gas and additive gas are collected. This is to improve the yield ratio of the permeable gas and condensable components by adding the highly permeable and non-condensable components concentrated in secondary by-product gas by vapor-liquid separation of the residual gas to the permeable gas. Moreover, by limiting the dew point of the residual gas, it is possible to prevent liquefaction at the primary side of gas separation membrane and secure high yield ratio by effectively using the by-product gas produced by subjecting the residual gas to vapor-liquid separation unit D2.

Specifically, primary pressure P1 is controlled at pressure control means PCrI installed at by-product gas flow path G2 of gas separation membranes S based on the concentration of the desired components sampled from analysis ports APo and AP1 , and recycle gas flow rate F1 is controlled at flow rate control means FCbI . Then, additive gas flow rate F3 is controlled at flow rate control means FCb3. At this time, it is also possible to control additive gas flow rate F3 based on the concentration of the desired components sampled from analysis port AP3. Moreover, even during turndown operation, it is possible to produce the product gas and condensable components while securing stable product purity and yield ratio by controlling additive gas flow rate F3 after controlling primary pressure P1 and recycle gas flow rate F1 by mixing them incrementally to the feed gas corresponding to the degree of turndown so that the effect of turndown is reduced considerably. This compositional example is an example of combining with the method of improving the permeable gas yield ratio of the gas separation membrane (see patent application 2007-233029) by adding part of the by-product gas obtained from the vapor-liquid separation process to secondary side flow path of the gas separation membrane, but combinations with other compositional examples of this invention stated above are also similarly effective.

Figure 4 shows compositional example 2 of the gaseous mixture separation apparatus pertaining to this invention. While the basic composition is the same as compositional example 1 , it uses multiple stages of gas separation membranes, connects the residual gas flow path of the earlier stages of the gas separation membranes to the supply gas flow path of the latter layers of the gas separation membranes to compose an apparatus (hereinafter referred to as "this Apparatus 2") in which a cascade connection is formed. That is, by connecting primary residual gas flow path R1 of primary gas separation membrane S1 to the supply gas flow path of secondary gas separation membrane S2, it is possible to collect the primary permeable gas from primary permeable gas flow path T1 and the secondary permeable gas from secondary permeable gas flow path T2.

The cascade cycle is often used for its advantage of enabling improved yield ratio when obtaining permeable gases with multiple different purity conditions by altering such factors as the permeable gas pressure and membrane materials of the gas separation membranes in each stage. Here, since the residual gas from the earlier stages of the gas separation membranes contains a relatively large amount of non-condensable gas, the dew point of the residual gas is relatively low and the possibility of liquefaction of its condensable components is low, and as it is sequentially supplied subsequently to the latter stages of the gas separation membranes, the condensable components are concentrated, and it is possible to efficiently collect them. At this time, by selecting the membrane surface areas of primary gas separation membrane S1 and secondary gas separation membrane S2, it is possible to control the concentration of the condensable components in the secondary residual gas and efficiently prevent liquefaction.

In addition to the function based on the cascade cycle, the concentration of the non-condensable components in the primary supply gas rises due to having the cyclic system, and hence it is possible to flexibly cope with the changes in process conditions during turndown operations.

Modified examples of this Apparatus 2 are shown in figures 5 and 6. The basic composition is the same as compositional example 2, but in figure 5, it is equipped with pressure control means PCr2 (pressure control valve PCV2 and pressure controller PC2) in primary residual gas flow path R1. It is possible to independently control the pressure of primary vapor-liquid separation unit D1 and primary pressure P1 i of gas separation membranes S1 from primary pressure P12 of secondary gas separation membranes S2. Moreover, in figure 6, in addition to pressure control means PCr2 (pressure control valve PCV2 and pressure controller PC2) in primary residual gas flow path R1 , it is further equipped with pressure control means PCro (pressure control valve PCVo and pressure controller PCo) in primary by-product gas flow path G1. Even during turndown operation of the feed gas, it is possible to independently control the pressure of primary vapor-liquid separation unit D1 from the primary pressure of primary and secondary gas separation membranes S1 and S2, and further enables highly versatile control such as controlling the pressure even higher. The mixing (merging) point of the feed gas and the recycle gas, as shown in dotted lines a ~ c, can be set up a: midway between pressure booster unit E and primary cooling unit C1 , b: midway between primary cooling section C1 and primary vapor-liquid separation unit D1 , or c: midway between primary vapor- liquid separation unit D1 and pressure control means PCrO.

While this Apparatus 2 described above has 2 stages of the gas separation membranes connected in cascade, it is also possible to use 3 or more stages of gas separation membranes to make use of their functions and compose a highly versatile gas production device. For example, it is also possible to compose multiple groups of gas separation membranes connected in parallel as the primary gas separation membranes so that product gases of different conditions can be obtained, and merge the residual gas from each group and supply it to the secondary gas separation membranes.

Furthermore, it is also possible to set up a third gas separation membrane in secondary residual gas flow path R2 of the latter stage secondary gas separation membrane S2, and apply the composition or functions of this invention. It is also possible to serially arrange these compositions formed by sequentially setting more gas separation membranes (fourth, fifth...) to secure purity of each gas product complying to individual specifications and secure a high yield ratio of this composition pertaining to this invention as a whole. Moreover, it is possible to further improve the yield ratio of the permeable gas by controlling the primary pressure of each stage of the gas separation membrane low.

Moreover, when setting up two gas separation membranes S1 and S2, it is possible to separately collect product gas 1 from primary gas separation membrane S1 and product gas 2 from secondary gas separation membrane S, but it is also possible to mix at least part of these to produce a single gas product, and furthermore, it is also possible to serially arrange multiple stages of gas separation membranes sequentially to secure purity of each gas product complying to individual specifications and secure a high yield ratio of this Apparatus 2 as a whole.

Figure 7 shows compositional example 3 (hereinafter referred to as "this Apparatus 3") of the gaseous mixture separation apparatus pertaining to this invention. While the basic composition is the same as compositional example 1 shown in figure 1 , it is characterized by the addition of recycle gas flow path Fb and flow rate control means FCr2 (flow rate control valve FCV2 and flow rate controller FC2) in recycle gas flow path Fb. Here, recycle gas flow path Fb, having its starting point at a diversion point set up at primary permeable gas flow path T1 , is connected via flow rate control means FCr2 to recycle gas flow path

Fa at the downstream side of flow rate control means FCrI .

By having the recycle gas composed of the primary permeable gas in addition to the recycle gas composed of part of the secondary by-product gas, the concentration of the non-condensable components in the primary supply gas that contains highly permeable components becomes high, and it is possible to easily prevent liquefaction in the primary side gas of the gas separation membrane, and prevent lowering of the purity of the permeable gas during the turndown operation.

As to the compositional examples stated above, a hydrogen gas production process was assumed and the results of numerical analysis of the permeable gas purity and yield ratio are provided below.

(1 ) Analysis condition

(1-1 ) Table 1 shows the feed gas composition.

[Table 1

(1-2) The material of the gas separation membranes used, both the primary and secondary gas membranes, were polyamide. (1-3) The entry temperature of the feed gas to the gas separation membranes was set at 90⁰C.

(1-4) The reference for residual gas dew point was set at 80⁰C or below. (1-5) Water cooled type cooling means was used as primary and secondary cooling units to cool to 40°C. (1-6) The maximum feed gas flow rate was 10,000 Nm³/h and hereafter the "flow rate" is expressed in percentage (%) to this maximum flow rate. (1-7) The permeable gas pressure at the exit of the gas separation membranes was set at 15bar (abs). (1-8) Pressure loss of this Apparatus (i) When the feed gas flow rate is maximum (100%): The pressure loss of the secondary cooler and secondary vapor-liquid separation unit was assumed to be 0.2bar.

(ii) Pressure loss during turndown: The pressure loss of this Apparatus was assessed by assuming that it changes proportionally to pV2 with the case of 100% as stated above as the reference. Here, p(kg/ m³) is the gas density, and V (m³/h) is the volume flow rate. (1-9) Pressure reference point of this Apparatus

(i) When the feed gas flow rate is maximum (100%): The reference of the pressure of the primary by-product gas at the primary vapor-liquid separation unit was set at 38bar (abs).

(ii) During turndown: This depends on the control method. Here, when the gas separation membrane is one stage, the reference was set at the pressure (represented by the pressure of the secondary by-product gas from the secondary vapor-liquid unit) of the residual gas flow path, and in cases of using the cascade cycle with two stages of the gas separation membranes, the reference was set at the primary residual gas flow path pressure (represented by the pressure immediately near the primary gas separation membrane of the primary residual gas flow path) or the secondary residual gas flow path pressure (represented by the secondary residual gas flow path pressure from the secondary vapor-liquid separation unit). The figures represented by Pr in table 5 and table 6, and the figures in parentheses in table 7 are pressure values of immediately near the primary gas separation membrane of the primary residual gas flow path.

Analysis was made using the device (compositional example 1 ) shown in figure 1 , setting the membrane area, setting the flow rate of the feed gas composed of Case 1 at maximum, and setting the recycle gas flow rate at 0. The yield ratio was 85.84% and the hydrogen purity in the permeable gas was 99.7%. However, residual gas dew point Z was approximately 91.3⁰C, and hence did not satisfy the above-stated dew point reference value.

If the recycle gas flow rate is increased from the state in verification 1 stated above,

(i) Residual gas dew point Z lowers uniformly. (ii)The hydrogen purity in the permeable gas lowers gently. (iii)The yield ratio increases gradually until a certain maximum point of 86.7% and then lowers gradually.

(iv)The permeable gas flow rate changes in connection with the yield ratio fluctuation stated above.

It was revealed that by adjusting the recycle gas flow rate from the state in verification 2 stated above, residual dew point Z becomes 80⁰C when the recycle gas flow rate is approximately 11.8%. At this time the yield ratio was 86.61 % and the hydrogen purity was 99.69%.

For comparison, the following was conducted with the recycle gas flow rate set at 0.

(i) With the same membrane area, when the gas separation membrane is controlled to lower the primary pressure, residual gas dew point became 80°C when the pressure of the primary vapor-liquid separation device was approximately 34.8bar (abs). At this time, the yield ratio lowered to 77.87% and the hydrogen purity was 99.73%. (ii) With a reduced membrane area (approximately 79% of the original area), residual dew point Z was 80⁰C. At this time, the yield ratio dropped to 77.45% and the hydrogen purity was 99.78%. From the above, the effect of adjusting residual gas dew point Z using the recycle gas was proven.

(2) Analysis result

(3-1 ) Embodiment example 1

With the device shown in figure 1 , the membrane area was set as the same as the preliminary analysis, the primary pressure of the gas separation membrane was set at constant, and the turndown characteristics were examined. The recycle gas flow rate was adjusted so that residual gas dew point would be approximately 80⁰C.

The verification results are shown in table 2.

It was revealed that the yield ratio increases significantly as the volume is reduced. This demonstrates that in applications that allow the hydrogen purity levels as shown in table 2, this method can be adopted.

[Table 2]

(3-2) Embodiment example 2

As a modified version of embodiment example 1 , the membrane area was set as the same as the preliminary analysis, the residual gas pressure of the gas separation membrane was changed using a primary expression of the degree of turndown, and analysis was made during turndown operation with a prerequisite of hydrogen purity to be 99.0% or higher. The recycle gas flow rate during the turndown operation was set at constant. The verification results are shown in table 3.

It was revealed also in this operation that the yield ratio increases significantly as the volume is reduced. [Table 3]

(3-3) Embodiment example 3

As a modified version of embodiment example 2, the membrane area was set as the same as the preliminary analysis, and embodiment examples 1 and 2, the pressure of the primary vapor-liquid separation unit was maintained at a constant as shown in figure 2 (corresponds to the modified version of compositional example 1), and the turndown operation was analyzed when the residual gas pressure of gas separation membrane S was changed using a primary expression of the degree of turndown. The differential pressure of the pressure maintaining valve (PCVo) of the primary vapor-liquid separation unit was assumed to be 0.2bar at maximum flow rate. The recycle gas flow rate was set at constant during the turndown operation. The verification results are shown in table 4.

It was revealed that at maximum rated state, the yield ratio lowers slightly due to the differential pressure of the pressure maintaining valve (PCVo), but the yield ratio is larger compared to embodiment example 2 during turndown operation.

[Table 4]

3-4) Embodiment example 4

As shown in figure 2, as in embodiment example 3, a case in which the pressure of the primary vapor-liquid separation unit is maintained at constant was examined. However, as to the correlation function between the residual gas pressure and the hydrogen concentration (component A) in the residual gas, a case in which pre-analysis is made by including flow rate ratio r as a parameter and using the turndown operation was analyzed. For that reason, the correlation function was derived as follows.

(i) The condition for adjusting the residual gas pressure so that residual gas dew point becomes 80⁰C was sought when setting flow rate ratio r at 0.11 , and when the turndown degree is 100%, 70% and 40%. The results are shown in table 5. Here, the figures represented by residual gas pressure Pr in table 5 and subsequent table 6 are pressure values immediately near the residual gas flow path of the gas separation membrane.

[Table 5]

(ii) Similarly, the condition for adjusting the residual gas pressure so that residual gas dew point becomes 80⁰C was sought when setting flow rate ratio r at 0.18, and when the turndown degree is 80%, 60% and 40%. The results are shown in table 6.

[Table 6]

(iii) By plotting reciprocals 1/Pr of the residual gas pressure and hydrogen concentration X in the residual gas, as shown in figure 8, an almost linear correlation was confirmed in each of the cases when r=0.11 and r=0.18. At this time, the following equations 1 and 2 were obtained as the correlation functions.

X = ar - br / Pe — (equation 1 )

Pe = br / (ar - X) - - - (equation 2)

Here, Pe represents the residual gas pressure of component A to concentration X, expected from the correlation functions. Moreover, ar = [(0.18 - r) ^* ai + (r - 0.11 ) ^* a2] / 0.07 br = [(0.18 - r) ^* bi + (r - 0.11 ) ^* b2] / 0.07 here, ai and bi are coefficients when r = 0.11 and a2 and b2 are coefficients when r = 0.18

With the preparation stated above, the recycle gas flow rate was changed by the primary expression of the turndown degree, and the turndown operation was analyzed according to the correlation functions shown in equations 1 and 2 above, when the residual gas pressure of the gas separation membrane was lowered corresponding to the degree of turndown. The analysis results are shown in figure 7. As to the residual gas pressure, both the secondary vapor-liquid separation unit pressure and pressure Pr immediately near the residual gas flow path are shown (the latter is shown in parentheses). When the turndown degrees are 100% and 40%, residual gas dew point became 80⁰C since each of the flow rate ratios r is 0.11 and 0.18. When the turndown degrees is 70%, while there is a slight deviation accompanying, it was confirmed that the above correlation functions have sufficient accuracy for practical application. Moreover, high yield ratios were secured while maintaining the prerequisite for the hydrogen concentration in the permeable gas of 99mo1 %. [Table 7]

(3-5) Embodiment example 5

A similar verification was made as to the feed gas with the composition of Case 2. The similar effect was seen with the recycle gas. However, when conducting the turndown operation with the method of maintaining the primary pressure of the gas separation membrane at constant, it was revealed that residual gas dew point becomes higher than 80⁰C as the secondary by-product gas flow rate becomes the limit even when attempting to increase the recycle gas flow rate even when the full amount is circulated. Moreover, when gradually lowering the primary pressure of the gas separation membrane, the secondary by-product gas flow rate increases, and it becomes possible to adjust residual gas dew point stated above.

Therefore, as in the case with embodiment example 3, as shown in figure 2, the turndown operation was analyzed when the residual gas pressure of gas separation membrane was changed using a primary expression of the degree of reduction while maintaining the pressure of the primary vapor-liquid separation unit. The recycle gas flow rate was also changed according to the primary expression. The differential pressure of the pressure maintaining valve (PCVo) of the primary vapor-liquid separation sunit was assumed to be 0.2bar at maximum flow rate.

The verification results are shown in table 8.

It was revealed that the yield ratio increases significantly according to the degree of turndown.

[Table 8]

(3-6) Embodiment example 6

A similar analysis was made using the cascade cycle (corresponds to modified example of device 2 in figure 5). Each of the membrane areas of the primary gas separation membrane and secondary gas separation membrane was set at 100% and 50% of the membrane area of the gas separation membrane used in the preliminary verification, and embodiment examples 1 and 2. The permeable gas pressures of the primary gas separation membrane and secondary gas separation membrane were set to be the same, and the product gas was assumed to be obtained by merging these permeable gases. The pressure of the primary vapor-liquid separation unit was maintained at constant, the residual gas pressure of the primary gas separation membrane and secondary gas separation membrane was changed according to the primary expression of the degree of turndown, and the flow rate of the recycle gas was set to be proportional to the degree of turndown. Residual gas dew point Z of both the primary gas separation membrane and secondary gas separation membrane was restricted to be 80⁰C or lower, and the hydrogen purity of the permeable gas was set to be 99mol% or higher. The differential pressure of the pressure maintaining valve (PCVo) of the primary vapor-liquid separation unit was assumed to be 0.2bar at maximum flow rate.

The verification results are shown in table 9. The yield ratio was 90% or higher in every case. Table 9

(3-7) Embodiment example 7

As the device (corresponds to compositional example 3) shown in figure 7, a case of adding a part of the secondary by-product gas to the recycle gas and supplying part of the permeable gas was examined. Using the feed gas with the composition of Case 1 , the membrane area was set as the same as verifications 1 ~ 3, the setting value of the recycle gas flow rate from the permeable gas was changed according to the primary expression of the feed gas flow rate, and the recycle gas flow rate from the secondary by-product gas and the pressure of the residual gas were set at constant. Within a broad turndown range of 100% ~ 40%, it was possible to gain high yield ratios while setting the hydrogen purity to be 99mol% or higher.

The verification results are shown in table 10.

It was revealed that the purity of the permeable gas during turndown can be raised and higher yield ratios compared to embodiment examples 2 and 3 can be obtained by adding at least a part of the permeable gas to the recycle gas.

(3) Conclusion of verification

As stated above, it was possible to maintain high stability in the permeable gas purity and high yield ratio in each and every embodiment example 1 ~ 7.

[Figure 1] Explanatory diagram showing the basic compositional example of production apparatus (compositional example 1 ) pertaining to this invention [Figure 2] Explanatory diagram showing modified example 1 of compositional example 1 of production apparatus pertaining to this invention [Figure 3] Explanatory diagram showing modified example 2 of compositional example 1 of production apparatus pertaining to this invention [Figure 4] Explanatory diagram showing compositional example 2 of production apparatus pertaining to this invention [Figure 5] Explanatory diagram showing modified example of compositional example 2 of production apparatus pertaining to this invention [Figure 6] Explanatory diagram showing modified example of compositional example 2 of production apparatus pertaining to this invention

[Figure 7] Explanatory diagram showing compositional example 3 of production apparatus pertaining to this invention [Figure 8] Explanatory diagram showing analysis results in production apparatus pertaining to this invention [Figure 9] Explanatory diagram showing basic composition of production apparatus pertaining to conventional technology [Figure 10] Explanatory diagram showing another composition 1 of production apparatus pertaining to conventional technology

[Figure 11] Explanatory diagram showing another composition 2 of production apparatus pertaining to conventional technology

Explanation of codes:

APo, AP1 , AP2, AP3 Analysis ports C1 , C2 (Primary, secondary) cooling units

D1 D2 (Primary, secondary) vapor-liquid separation units

E Pressure booster unit

Fa, Fb Recycle gas flow paths

FC1 , FC2 Flow rate controllers FCrI , FCr2 Flow rate control means

FCV1 , FCV2 Flow rate control valves

G1 , G2 (Primary, secondary) by-product gas flow paths

H Heating unit

L1 , L2 (Primary, secondary) by-product liquid flow paths LC1 , LC2 (Primary, secondary) liquid surface detection units

LCV1 , LCV2 (Primary, secondary) control valves

Pr Residual gas pressure

PCo, PC1 , PC2 Pressure controllers PCro, PCM , PCr2 Pressure control means

PCVo, PCV1 , PCV2 Pressure control valves

R1 , R2 (Primary, secondary) residual gas flow paths

S, S1 , S2 (Primary, secondary) gas separation membranes

T1 , T2 (Primary, secondary) permeable gas flow paths

Uo feed gas flow path

U1 , U2 (Primary, secondary) supply gas flow paths

X Hydrogen concentration

Claims

1. A separation method generating:

- a permeable gas rich in highly permeable and non-condensable component A, - a by-product liquid rich in a poorly permeable and condensable component B, and

(14) diverting part of the secondary by-product gas as a recycle gas, the secondary by-product gas being produced at the downstream side of the aforementioned secondary vapor-liquid separation and being lean in the component B (15) adjusting the flow rate and pressurizing the aforementioned recycle gas

(16) performing a primary cooling and/or a primary vapor-liquid separation of the aforementioned recycle gas

(17) extracting the primary by-product gas obtained by the aforementioned primary vapor-liquid separation, said primary by-product gas being lean in the component B

(18) extracting the primary by-product liquid obtained by the aforementioned primary vapor-liquid separation treatment and primarily composed of the aforementioned component B

(19) supplying the aforementioned primary by-product gas to the gas separation membrane after heating said primary by-product gas

(20) supplying the aforementioned feed gas and mixing it with the aforementioned recycle gas either before the aforementioned pressurizing process, before the primary cooling, before the primary vapor-liquid separation, after the primary vapor-liquid separation process or after the heating process (21 ) adjusting either the primary pressure of the aforementioned gas separation membrane or its correlated process values

(22) mixing the aforementioned feed gas with the aforementioned recycle gas either before the aforementioned pressure increase treatment, before the primary cooling treatment, before the primary vapor-liquid separation treatment, after the primary vapor-liquid separation step, or after the heating treatment (23) separating the mix into a permeable gas and a residual gas at aforementioned gas separation membrane (24) after performing the separation step using membrane(s), extracting the permeable gas rich in the aforementioned component A as a product and the residual gas rich in the aforementioned component B (25) applying a secondary cooling treatment and a secondary vapor-liquid separation to the aforementioned residual gas (26) extracting the secondary by-product gas obtained from the aforementioned secondary vapor-liquid separation, said by-product gas being lean in the component B

(27) extracting the secondary by-product liquid obtained from the aforementioned secondary vapor-liquid separation step and primarily composed of the aforementioned component B.

2. The method stated in claim 1 , wherein, especially for turndown operation, the flow- rate of aforementioned recycle gas is adjusted according to the degree of turndown.

3. The method stated in claim 1 or 2, characterized by adjusting the primary pressure, the secondary pressure of the aforementioned gas separation membrane, or a process value connected with said pressure levels, according to the degree of turndown.

4. The method stated in either claim 1 , 2 or 3, characterized by:

- preventing liquefaction within the gas at the primary side of the aforementioned gas separation membrane by expressing the flow rate ratio r defined as the aforementioned recycle gas flow rate divided by feed gas flow rate,

- pre-analyzing the aforementioned flow rate ratio r as a parameter regarding the correlation function between the residual gas pressure and the concentration of the aforementioned component A in the residual gas of the aforementioned gas separation membrane by setting a reference value Za of the dew point Z under the pressure at the flow path immediately after the residual gas outlet of the aforementioned gas separation membrane based on the characteristics of the feed gas composition and the aforementioned gas separation membrane,

- monitoring the aforementioned dew point Z so that it is below the aforementioned reference value Za from the measured values of the aforementioned flow rate ratio r and the concentration of the aforementioned component A in the residual gas using the aforementioned correlation function during the operation, and - adjusting either the aforementioned recycle gas flow rate, the residual gas pressure of the aforementioned gas separation membrane, the permeable gas pressure or their connected process value, in order to keep the aforementioned dew point Z below the aforementioned reference value Za.

5. The method stated in either claim 1 , 2, 3 or 4, characterized in that the gas separation membrane consists of several stages of gas separation membranes forming a cascade, the residual gas of one separation membrane being sent to the following gas separation membrane in the cascade.

6. A device for obtaining gas components and condensable components using at least two vapor-liquid separation units and gas separation membranes with selective permeability and the difference in condensability of at least one component of the feed gas containing multiple components, characterized in that it produces a permeable gas rich in highly permeable and non-condensable component A obtained by the aforementioned gas separation membranes, a by-product liquid rich in poorly- permeable and condensable component B and a by-product gas lean in the component B and obtained by the aforementioned vapor-liquid separation sections, and it includes at least the following components:

(b) a flow rate adjustment section and pressure booster section set up at the aforementioned recycle gas flow path (c) a primary supply gas flow path connected to the aforementioned recycle gas flow path

(d) a primary cooling section and primary vapor-liquid separation section set up at the aforementioned primary supply gas flow path

(e) a primary by-product gas flow path from which the by-product gas is extracted from the gaseous section of the aforementioned primary vapor-liquid separation section

(f) a primary by-product liquid flow path from which the by-product liquid is extracted from the liquid section of the aforementioned primary vapor-liquid separation section (g) a heating section installed at the aforementioned primary by-product gas flow path

(h) a feed gas flow path that supplies the feed gas containing multiple components, and joins the aforementioned recycle gas flow path or primary supply gas flow path at either the upstream side of the aforementioned pressure booster section, upstream side of primary cooling section, upstream side of primary vapor-liquid separation section, downstream side of primary vapor-liquid separation section or downstream side of the heating section (j) gas separation membranes that is connected to the aforementioned primary by-product gas flow path and separates the gas into permeable gas and residual gas

(n) a secondary cooling section and secondary vapor-liquid separation section installed at the aforementioned residual gas flow path

(p) a secondary by-product gas flow path to which the by-product gas is supplied from the gaseous section of the aforementioned secondary vapor-liquid separation section

(q) a secondary by-product liquid flow path to which the by-product liquid is supplied from the liquid section of the aforementioned secondary vapor-liquid separation section (r) a secondary pressure adjustment section installed at the aforementioned secondary by-product liquid flow path after the aforementioned diverging point.

7. The device stated in claim 6, characterized in that gas separation membranes includes several stages of gas separation membrane forming a cascade, the residual gas flow path of one gas separation membrane being connected to the feed gas flow path of the next gas separation membrane.