WO2009030767A1

WO2009030767A1 - Method and system of producing gaseous components and condensable components

Info

Publication number: WO2009030767A1
Application number: PCT/EP2008/061821
Authority: WO
Inventors: Kazuo Kitsukawa; Naohiko 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: JP2009061420A

Abstract

A method of separating a feed gas containing multiple components, including a separation step using one or several selectively gas permeable membrane (s) and one or several steps consisting of a vapor-liquid separation using the differences in condensability of at least one component, said method generating: a permeable gas rich in a highly permeable and non-condensable component A; a byproduct liquid rich in a semi -permeable and condensable component B; and a byproduct gas lean in the component B obtained after the vapor-liquid separation, and being characterized in that it contains at least the following steps: (1) supplying the feed gas to the gas separation membrane (S2) (2) adjusting either the primary pressure of the gas separation membrane or the process values connected with said pressure (3) separating the feed gas into a permeable gas and a residual gas (R2) using the gas separation membrane (4) extracting the permeable gas rich in the aforementioned component A as product gas (5) extracting the residual, gas rich in semi-permeable gas (6) cooling the residual gas and performing a vapor-liquid separation (D2) into a byproduct liquid rich in the aforementioned component B and a byproduct gas lean in the component B (7) diverting part of the byproduct gas as added gas (8) adding part Of the added gas either to the secondary side (Sf) flow path of the gas separation membrane.

Description

Method and system of producing gaseous components and condensable components

The present invention relates to a method and a system of producing gaseous components and condensable components. More specifically the present invention relates to a method and a system of producing gaseous components and condensable components by separating and collecting specific gaseous components from multiple-component gas mixtures, using the separation property of a selectively permeable gas separation membrane and the vapor- liquid separation property based on the differences between the condensation temperatures of each component.

Conventionally, specific amounts of high purity gases are necessary as feed gases or processing gases in various processing stages in such plants as semiconductor producing plants or in various chemical processing plants; many such plants continually use these gases by separating them from easily accessible and low-cost materials. Specifically, for example, when obtaining either oxygen-enriched or nitrogen-enriched gas, or both, from air, such cases as separating and concentrating hydrogen (H2) from naphtha cracked gas, separating and recovering organic vapors from gas compounds that contain organic vapors, and separating hydrogen from water gas apply. In many of such processes, the method of obtaining permeable gases rich in highly permeable gas as products is used by supplying a gas mixture with varying permeability as feed gases to gas separation membranes with selective permeability and separating them into permeable gases and residual gases.

For such gas production method using gas separation membranes, various configurations have come to be used in response to the desired applications and specifications, based on the systems equipped with compressor 102, dryer

108, heater 109, gas separation unit 103 equipped with the gas separation membrane 101 , residual gas side pressure regulation valve 110, cooler 113, and permeable gas side pressure regulation valve 111 , as shown in Figure 9 (See for example the Japanese Patent Application No. 2000-33222).

For example, it is well-known that a cascade cycle as the one shown in Figure 10 is efficient in case it is necessary to produce comparatively high pressure hydrogen gas and comparatively low pressure hydrogen gas. In this example, a combination of two gas separation membranes 201 (the first gas separation membrane 201a and the second gas separation membrane 201 b) is used. In this structure, the feed gas g1 merges with the permeable gas g2aa from the second gas separation membrane 201 b, and it is supplied to the first gas separation membrane 201 a after compression. At this state, the permeable gas g2a is generated through the first gas separation membrane 201 a, and the residual gas g2b is fed to the second gas separation membrane 201 b as a feed gas. The residual gas is generated at this second gas separation membrane 201 b. The permeable gas g2aa is then reused by having it merge with the original feed gas (See for example the Japanese Patent Application No. 2002-35530). At this point, Figure 10 shows a structural example for cases in which the permeable gas g2aa from the second gas separation membrane 201 b is reused; however, it is possible to extract the permeable gas g2a as a high pressure product gas, and the permeable gas g2aa as a low pressure product gas.

Moreover, as shown in Figure 11 , a system for separating and collecting enriched nitrogen gas from air is given as an example parallel cycle. In Figure 11 , two hollow fiber separation membrane modules 312 and 313 are used in parallel, the supply gas is fed to modules 312 and 313 respectively after the pretreatment process had been completed, and the enriched nitrogen gases obtained from the hollow fiber separation membrane modules 312 and 313 respectively are merged and led towards the product gas exit 324. The air taken in from air intake port 301 is supplied to compressor 303 after such substances as suspended particles in the air are removed at dust filter 302. The air pressurized here is led from the gas supply port of hollow fiber separation membrane modules 312 and 313 to the supply side of the membranes. The permeated permeable gas flows through the permeation side of the membranes and is discharged to outside the system as permeable gas discharge flow via the permeable gas discharge port of the modules and after its flow rate is reduced at flow rate regulator valves 316 and 317 located midway through the piping (See for example the Japanese Patent Application No. 2002-35530). Here, although the system as shown in Figure 11 represents cases in which enriched nitrogen gas is collected as the product gas, the permeable gas discharge flow is enriched oxygen gas and therefore it is also possible to collect this as the product gas. At this time, it is possible to recover part of the permeable gas as high-pressure product gas and the other part of the permeable gas as low-pressure product gas by individually adjusting the pressure and flow rate of the air supplied to hollow fiber separation membrane modules 312 and 313 that are arranged in parallel. When gas is produced by using a gas separation membrane, the purity and the recovery rate of the product become major characteristics. Generally, depending on the intended use of the product gas, the required purity is determined, and a control method is determined, including an analysis process on the principle of maintaining the recovery rate in that range if possible, and an amount reduction process. However, several problems could occur when using the above-described system or method for feed gas containing multiple components including semi-permeable and condensable components.

(i) It is necessary to avoid the generation of mist in the gas on the primary side of the membrane because the membrane deteriorates by itself. More specifically, in case the feed gas contains condensable components, liquefaction can occur at ambient temperature; it was necessary to escape the danger of generation of liquefied mist on the gas separation membrane by cooling the feed gas to a temperature of, for example, 40 ⁰C (outdoor summertime conditions), then separating and heating the condensable liquefied components by means of a heating technique, because the condensable components in the gas on the primary side (the impermeable side) of the gas separation membrane may concentrate and liquefy with gas separation, when said condensable components are impermeable gas. (ii) However, the danger of liquefaction of the condensable components on the residual gas side of the gas separation membrane remains when attempting to raise the recovery rate of the desired components of permeable gas, because the heating temperature is limited from the point of view of characteristics such as the separation characteristics and high temperature resistance of the gas separation membrane. Consequently, countermeasures for avoiding liquefaction have been applied by decreasing the primary pressure of the gas separation membrane; however, there were cases when the recovery rate could not be guaranteed.

The present invention focuses on the avoidance of liquefaction accompanying the concentration of condensable components in the gas on the primary side of the gas separation membrane. The gas in the (nearest) residual gas port is the most liquefiable because the concentration of the condensable components passes together with the permeability. Consequently, the dew-point temperature under the pressure of the gas in the residual gas port becomes important, and liquefaction does not occur in the gas on the primary side of the gas separation membrane provided the dew-point temperature is low in comparison with the temperature of the gas at the gas separation membrane. Actually, taking into consideration such aspects as the fluctuation of the feed gas mixture and of the operation conditions, it is preferable to set slightly lower gas temperature (for example, 10 ⁰C) at the gas separation membrane, and standard values for the dew-point temperature. The pressure shortly after the residual gas port of the gas separation membrane is referred to hereafter as "residual gas pressure", the dew-point temperature under the residual port pressure shortly after the residual gas port of the gas separation membrane is referred to as "residual gas flow rate", and the pressure and the flow rate of the permeable gas are referred to as "permeable gas pressure" and "permeable gas flow rate" respectively.

The aim of the present invention is to provide a method and a system of producing gaseous components and condensable components that guarantee the desired gas product having the desired purity and condensable components by collecting gaseous components and condensable components from feed gas containing multiple components, and a high recovery rate while avoiding the liquefaction of the condensable components in the primary side gas of the gas separation membrane through an efficient multipurpose method. The aim of the present invention is particularly to yield an even higher recovery rate through the amount reduction process. When the phrase "recovery rate" is used in the present invention, it means the rate of the total desired components (highly permeable gas) flow rate in the product gas as against the desired components flow rate in the feed gas; moreover, it includes cases when final residual gas is used as byproduct. In view of the above-described problems, the present inventors conducted intensive research and discovered that the aim of the present invention can be reached by means of the method and the system of gaseous mixture separation presented hereafter. The invention is based on this discovery. Elements of similar functions are called first or primary for upstream path and second or secondary for downstream path.

The present invention relates to a method of separating a feed gas containing multiple components, including a separation step using one or several selectively gas permeable membrane(s) and one or several steps consisting of a vapor-liquid separation using the differences in condensability of at least one component, said method generating:

- a permeable gas rich in a highly permeable and non-condensable component A,

- a byproduct liquid rich in a semi-permeable and condensable component B, and

- a byproduct gas lean in the component B obtained after the vapor-liquid separation, and being characterized in that it contains at least the following steps:

(1 ) supplying the feed gas to the gas separation membrane

(2) adjusting either the primary pressure of the gas separation membrane or the process values connected with said pressure (3) separating the feed gas into a permeable gas and a residual gas using the gas separation membrane

(4) extracting the permeable gas rich in the aforementioned component A as product gas

(5) extracting the residual gas rich in semi-permeable gas (6) cooling the residual gas and performing a vapor-liquid separation into a byproduct liquid rich in the aforementioned component B and a byproduct gas lean in the component B

(7) diverting part of the byproduct gas as added gas

(8) adding part of the added gas either to the secondary side flow path of the gas separation membrane, and

(9) as an option, mixing the some of the added gas with the permeable gas to obtain more product gas

Highly permeable and non-condensable components (referred to hereinafter as "component A") and semi-permeable and condensable components (referred to hereinafter as "component B") or semi-permeable and non-condensable components (or components containing a reduced amount of the component

B) are collected from a feed gas containing multiple components, including component A and B. Component A consists of one or several highly permeable gases, such as, but not limited to, hydrogen, oxygen and/or nitrogen.

Component B consists of one or several less permeable, condensable gases, such as, but not limited to, water and/or organic compounds. "Highly permeable", "semi permeable" and "condensable" can have a relative meaning, in the sense that component A is more permeable than component B through the membranes that are considered and chosen for the purpose of the invention and component B is more easily condensed than component A in an industrial vapor-liquid separation.

A method using the separation property by means of a selectively gas permeable separation membrane, and a method using the vapor-liquid separation property based on the differences between the condensability of each component are methods for securing the desired purity and recovery rate, that were previously often used separately. Moreover, even when these methods are combined, the method of processing the gas processed by using the vapor-liquid separation property as preprocessing by using the separation property of the gas separation membrane, or the reverse method thereof are used; however, any one of them was considered as the main method, while the other one was considered as an auxiliary method. In case the feed gas contains the component B, the present invention aims at increasing the recovery rate of the condensable and semi-permeable components by using the fact that the component B in the residual gas on the gas separation membrane concentrates, and by installing the assembly consisting of the cooling unit and the vapor-liquid separation unit before or after the gas separation membrane. Moreover, the present invention limits the residual gas dew-point temperature, has the component A left to some degree in the residual gas concentrated in the byproduct gas by the cooling and vapor-liquid separation of the residual gas in order to avoid the liquefaction on the primary side of the gas separation membrane, and aims at increasing the recovery rate of the permeable gas components by adding part of the byproduct gas to the secondary side flow path of the gas separation membrane. Namely, when the purity of the permeable gas at the gas separation membrane can be afforded from the point of view of the basic values, by efficiently using part of the byproduct gas as the added gas, liquefaction on the primary side of the gas separation membrane is prevented, and high recovery rate of the permeable gas components can be secured. Moreover, "gas separation membrane" does not refer only to each inflow and outflow of supply gas, permeable gas and residual gas using one membrane module, but also to the combined inflow and outflow of each supplied gas, permeable gas and residual gas provided by using the necessary number of multiple membrane modules arranged in parallel lines. Moreover, "secondary side flow path of the gas separation membrane" includes any of the following flow paths: the flow path and the space between the permeable side of the gas separation membrane inner membrane element, as well as the permeable gas discharge flow channel. "Condensable components" are those components which possess condensability properties as against condensation management and are not restricted to easy or difficult permeability as against gas separation membrane. "Highly permeable and non-condensable component A" is that component which is highly permeable as against gas separation membrane and is non-condensable as against condensability management, more specifically, in the embodiments below, it refers to, for example, the hydrogen wherein a mixture of hydrogen, methane, butane and pentane is present in the feed gas. "Semi-permeable and condensable component B" is that component which is semi-permeable as against gas separation membrane and is condensable as against condensability management, namely the above- mentioned butane and pentane. Moreover, in the present invention, even when the source gas contains permeable and condensable components in small quantities (for example, the feed gas moisture content in the embodiments below), the result is essentially the same. Consequently, the present invention will make annotations on such cases. Moreover, "pressure and connected process values" refer to the process value changes following the pressure changes, being possible to raise either the quantity of the residual gas as against primary pressure or the distribution of the permeable gas as against secondary pressure. The same applies hereinafter.

The present invention also relates to a gas separation system including a selectively gas permeable membrane and a vapor-liquid separating unit based on the differences in condensability of each component, and generating a permeable gas rich in highly permeable and non-condensable component A obtained from the gas separation membrane, a byproduct liquid rich in semipermeable and condensable component B obtained from the vapor-liquid separation unit, and byproduct gas lean in the component B, and a system for producing gaseous components and condensable components characterized in that it contains at least the following elements:

(a) a feed gas flow path for supplying the feed gas (b) a gas separation membrane for separating the permeable gas and the residual gas

(c) a permeable gas flow path for extracting the permeable gas from the gas separation membrane (d) a residual gas flow path for delivering the residual gas from the gas separation membrane

(e) a cooling unit and a vapor-liquid separation unit located on the residual gas flow path

(f) a byproduct gas flow path for delivering the byproduct gas from the gas phase unit of the vapor-liquid separation unit

(g) a byproduct liquid flow path for eliminating the byproduct liquid from the liquid phase unit of the vapor-liquid separation unit

(h) an added gas flow path for separating and making the byproduct gas flow path (j) a pressure adjustment unit or a flow rate regulating unit located on the byproduct gas flow path after the separation process

(k) a flow rate regulating unit located on the added gas flow path

(m) a product gas flow path for connecting and making the added gas flow path and the permeable gas flow path A producing system which embodies the above-described producing method necessarily includes a gas separation membrane and the elements (a) - (k¹) constituted of a cooling unit and a vapor-liquid separation unit, as well as an element for adding the added gas to the secondary side flow path of the gas separation membrane. In the present invention, component (m), "a product gas flow path for connecting and making the added gas flow path and the permeable gas flow path", is provided as such an element; component A, present in the residual gas to a certain level, is condensed in the byproduct gas by residual gas cooling and vapor-liquid separation, thus being possible to measure the increase in the permeable gaseous components recovery rate by adding part of the byproduct gas to the permeable gas. Namely, when the purity of permeable gas at separation membrane exceeds the standard value, the high recovery rate of the permeable gaseous components can be preserved by efficiently using part of the byproduct gas as permeable gas, while avoiding the liquefaction on the gas separation membrane primary side. Moreover, when a pressure rising means is available to increase the permeable gas pressure on the gas separation membrane at a subsequent phase, it is desirable that the loss of pressure energy of the byproduct gas should be reduced by adjusting either the added gas confluence point to an intermediary phase of pressure increasing or a suitable exit point.

The present invention also relates to a gas separation system including a selectively gas permeable membrane and a vapor-liquid separating unit based on the differences in condensability of at least one component, generating a permeable gas rich in highly permeable and non-condensable component A obtained from the gas separation membrane, a byproduct liquid rich in semipermeable and condensable component B obtained from the vapor-liquid separation unit, and a byproduct gas containing a reduced amount of component B, said system being characterized in that it contains at least the following elements:

(a) a feed gas flow path for supplying the feed gas

(b) a gas separation membrane for separating the permeable gas and the residual gas

(c) a permeable gas flow path for eliminating the permeable gas from the gas separation membrane

(d) a residual gas flow path for delivering the residual gas from the gas separation membrane

(e) a cooling unit and a vapor-liquid separation unit located on the residual gas flow path (f) a byproduct gas flow path for delivering the byproduct gas from the gas phase unit of the vapor-liquid separation unit

(h) an added gas flow path for separating and making the byproduct gas flow path

(j) a pressure adjustment unit or a flow rate adjustment unit located on the byproduct gas flow path after the separation process (k) a flow path adjustment unit located on the added gas flow path, or a flow rate adjustment unit and a heating unit

(n) an added gas installation unit connected to the added gas flow path on the secondary side of the gas separation membrane The manufacturing system which embodies the above-described producing method necessarily includes a gas separation membrane and the elements (a) - (k¹) constituted of a cooling unit and a vapor-liquid separation unit, as well as an element for adding the added gas to the secondary side flow path of the gas separation membrane. The present invention provides (n) "the added gas entry that connects to the added gas flow path on the secondary side of the gas separation membrane" as such a component. In addition to the regulating property of the purity and recovery rate of the added gas obtained by adding the byproduct gas, by mixing the low concentration added gas of component A inside the gas separation membrane and the permeable gas, the pressure of component A on the permeable side of the gas separation membrane decreases, and the permeability property of the component A can be increased.

According to another embodiment of the present invention the abovementioned method is characterized in that the aforementioned feed gas is fed to the gas separation membrane after undergoing one or a combination of the following steps:

(1 a) a primary cooling of the feed gas

(1 b) a primary vapor-liquid separation into a first byproduct gas lean in the component B and a first byproduct gas (1 c) a heating of the first byproduct gas in order to obtain a new feed gas to be sent to the gas separation membrane.

Moreover, according to another embodiment of the present invention the abovementioned systems, are characterized in that the following elements are located on the feed gas flow path: (aa) a first cooling unit

(ab) a first vapor-liquid separation unit

(ac) a first byproduct gas flow path for eliminating the byproduct gas from the gas phase unit of the first vapor-liquid separation unit (ad) a first byproduct liquid flow path for eliminating the byproduct liquid from the gas phase unit of the first vapor-liquid separation unit

(ae) a heating unit located on the feed gas flow path or on the first byproduct gas flow path

In concrete terms, within the above-described system, the cooling means and the vapor-liquid separation means are located after the gas separation membrane, and byproduct gas is added to the permeable gas; however, it is preferable for the functions and results obtained by means of such a configuration to preprocess the feed gas according to its properties. In concrete terms, in case of source gas containing highly concentrated component B, the first cooling unit and the first vapor-liquid separation unit for collecting the component B, or the heating unit aiming at preventing the liquefaction due to the raise in concentration of the component B in the residual gas, are installed on the upstream path side of the gas separation membrane, making it possible to aim at increasing the recovery rate of the permeable gas and of the condensable components.

In another embodiment of the present invention the abovementioned methods are characterized in that, especially for turndown operation, either the primary pressure of the aforementioned membrane, the secondary pressure of the aforementioned membrane or the process values connected with said pressure is adjusted according to the degree of turndown, and wherein the flowrate of the added gas is also adjusted according to the degree of turndown.

In case the amount reduction process was applied to the feed gas, if the primary pressure and the secondary pressure of the gas separation membrane are kept at a constant value, the recovery rate increases on the one hand, and on the other hand the concentration of the permeable gas in the permeable gas decreases, while the component B in the gas on the primary side of the gas separation membrane becomes easily liquefiable. The present invention aims at preventing the liquefaction of the condensable components, and at maintaining the desired product gas purity and recovery rate by adjusting either the primary pressure and the secondary pressure of the gas separation membrane or the process values connected with said pressures according to the degree of amount reduction to preserve the purity of the product gas, and by controlling the added gas flow rate according to the degree of amount reduction.

In another embodiment of the present invention, the abovementioned 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.

Moreover, In another embodiment of the present invention the abovementioned systems are characterized in that gas separation membrane 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.

Commonly, when several gas products with different purity are produced, the cascade cycle can preserve the given product purity and the recovery rate by using a multiple phase gas separation membrane and by making each permeable gas a product gas, even when the membrane area is comparatively small. Namely, because permeable gas is found in relatively large quantities in the residual gas of the former gas separation membrane and is provided in a gas separation membrane, it is possible to efficiently recover the condensable components which condense. Beside this general benefit of the cascade cycle, the present invention makes it possible to obtain product gas by adding the condensed gas obtained as above to permeable gas and to obtain a high- recovery rate desired component purity in the product gas even as against small quantities. In such cases, the addition can be done as against any of the permeable gas multiple phases. Moreover, by using the cascade method, with decreasing control on gas separation membrane primary pressure in each phase, it is possible to suppress the liquefaction of component B in the gas separation membrane primary side gas, to supply on the gas separation membrane in subsequent phases and to recover permeable components to a maximum extent in each phase. Consequently, together with preserving the gas product having the desired purity and condensable components, it is possible to provide a system and a method of producing condensable components and gas components that has a high recovery rate while avoiding the liquefaction of the condensable components in the primary side gas of the gas separation membrane through an efficient multipurpose method. By applying the inventive method of producing gaseous components and condensable components and the producing system as shown above, it becomes possible to provide a method of producing gaseous components and condensable components and a producing system that guarantee the desired gas product having the desired purity and condensable components, and a high recovery rate while avoiding the liquefaction of the condensable components in the primary side gas of the gas separation membrane through an efficient multipurpose method. It has become possible to yield an even higher recovery rate through the amount reduction process.

Hereinafter, the embodiments of the present invention will be explained with reference to the drawings. Here, in a production process applied to source gas containing multiple components, that uses the separation property of a selectively permeable gas separation membrane, and the vapor-liquid separation property based on the differences in condensability of each component, and that generates permeable gas rich in highly permeable and non-condensable component A obtained through the separation property of the gas separation membrane, byproduct liquid rich in semi-permeable and condensable component B obtained through the vapor-liquid separation function, and byproduct gas containing a reduced amount of the component B, after the selective separation process by gas separation membrane, a residual gas cooling process and vapor-liquid separation take place. Moreover, a part of the residual gas generated in the vapor-liquid separation process is added on the secondary side flow path of the gas separation membrane, leading to the production of permeable gas with the desired purity and ensuring the desired recovery rate for the condensable components. Furthermore, the conditions required in the process using gas separation membrane suffer various changes depending on whether the upstream path or downstream path process structure or gas product is applied and because the operational conditions or the control method are selected according to that, here typical examples are provided. Moreover, the present invention is not restricted to the configuration examples mentioned below, a large number of deformations or dilatations being possible as a result of the combination of the gas separation membrane above-mentioned general characteristics.

Figure 1 shows the basic configuration example of the inventive gaseous mixture separation system (the first configuration example is referred to as "the inventive system 1"). In concrete terms, this systems consists of the feed gas flow path Uo, the gas separation membrane S, permeable gas flow path T1 , residual gas flow path R1 , byproduct gas flow path G2, byproduct liquid flow path L2, added gas flow path Fa, product gas flow path A1 , cooling unit C2 and vapor-liquid separation unit D2 installed on the residual gas flow path G1 , pressure adjustment means PCrI (pressure control valve PCV1 and pressure regulator PC1 ) installed on the byproduct gas flow path G2, liquid surface detection unit LC2 and control valve LCV2 installed on the byproduct liquid flow path L2, flow path adjustment means FCbI (flow path control valve FCV1 and flow path controller FC1 ) installed on the added gas flow path Fa, and control unit (not illustrated). Moreover, the analysis port APo of the feed gas, the analysis port AP1 of the added gas, and the analysis port AP3 of the product gas (used for batch analysis by means of a gas chromatography spectrometer, for example) are provided to confirm performance of the gas producing process. It is also possible to install a concentration measurement means instead of the analysis ports. See details below.

Connecting the added gas flow path Fa to the permeable gas flow path T1 and mixing the added gas with the permeable gas is used as a method of adding the added gas to the secondary side flow path of the gas separation membrane S in the inventive system 1. The structure illustrated here shows a structure wherein the primary pressure P1 supplying the feed gas is controlled by means of the pressure adjustment means PCrI installed on the byproduct gas flow path G2; however, the feed gas flow path Uo, the residual gas flow path R1 , or another by-pass flow path can be added to the pressure adjustment means PCrI ; the present invention is in no way limited to these structures. It is preferred to set the pressure control valve PCV1 after the circulating gas ramification point of the byproduct gas flow path G2, because the condensation at the vapor-liquid separation unit D2 is generally more efficient in high- pressure state. Moreover, it is possible to control the flow rate of the residual gas as the process value that changes together with the primary pressure, instead of controlling the primary pressure P1.

Purified gas or crude gas that has undergone a purification treatment is preferably supplied as the feed gas; in concrete terms, purified air, purified naphtha cracked gas, purified reformed gas, purified water gas, or purified natural gas is applicable. The supply conditions for the feed gas are usually ambient temperature and the flow rate of these gases ranges from 1 ,000 to 100,000 [Nm³/h]. Moreover, the pressure conditions are different depending on the intended use of the permeable gas; however, a pressure up to 1-50 [bar(abs)] can be applied.

The optimal raw material and capacity (surface area) of the gas separation membrane S is chosen depending on the types of feed gas or permeable gas. The raw materials that can be used for the gas separation membrane S include, for example, polyethylene (PE), polypropylene (PP), silicon gum, polysulfone, cellulose acetate, polyaramide (PA), and polyimide (Pl). The present invention is in now way limited to these materials.

The gas collected from the analysis port APo, AP1 , and AP3 is subjected to a batch analysis using for example gas chromatography, and a method of modifying the coefficient of the calculation formula based on regular assay results can be applied. Moreover, instead of this, concentration measurement means can also be used for control, as described below. Concentration measurement means having highly selective analyzer are preferred for the desired components, namely for the product gas components, and a device that can be relied upon for continuous analysis is preferred. Moreover, an analyzer that does not cause chemical modifications of the product gas is preferred. For example, a thermal conductivity analyzer can be used in case the components are hydrogen, and an infrared absorption spectrophotometer can be used in case of methane. Moreover, it is also possible to use batch analysis and continuous analysis together. The adjustment can be decided while verifying error of the continuous analysis as compared to the more reliable results of the batch analysis.

Example of Control Method Using the Inventive System 1 :

In case the permeable gas of the gas membrane S was the product gas, the process from the feed gas supplied to the gas separation membrane S of the inventive system 1 to the producing of final product gas and condensable component includes at least the following processes:

(1 ) a process of feeding the multiple-component feed gas to the gas separation membrane S

(2) a process of adjusting either the primary pressure of the gas separation membrane or the primary pressure of the gas separation membrane and the connected process values

(3) a process of separating permeable gas from residual gas using the gas separation membrane S

(4) a process of extracting the permeable gas rich in component A using the gas separation membrane S, as product gas

(5) a method of extracting residual gas rich in semi-permeable gas using the gas separation membrane S

(6) a process of cooling and vapor-liquid separation of the residual gas (7) a process of extracting byproduct gas rich in component B obtained through the vapor-liquid separation process

(8) a process of extracting byproduct liquid containing obtained mainly from component B obtained through the vapor-liquid separation process

(9) a process of separating part of the byproduct gases as added gas (10) a process of adding the added gas to the permeable gas and making it into the product gas

At this point, the primary pressure P1 is controlled, the permeable gas pressure and recovery rate are adjusted, and at the same time the dew-point temperature is adjusted; in addition, the added gas flow rate F1 is adjusted, and the product gas concentration and recovery rate are adjusted within the desired range. In concrete terms, first, based on the desired components concentration extracted from the analysis ports APo and AP1 , the primary pressure P1 of the gas separation membrane S is controlled using the pressure control means PCrI installed on the byproduct gas flow rate G2; next, the added gas flow rate F1 is controlled using the flow path control means FCbI . It is also possible to control the added gas flow rate F1 based on the desired components concentration extracted from the analysis port AP3.

Moreover, during the amount reduction process, as above, (i) the primary pressure P1 or the secondary pressure P2 of the gas separation membrane S are adjusted according to the degree of amount reduction, and (ii) the added gas flow rate F1 is adjusted according to the degree of amount reduction. Each adjustment method is described hereafter.

(i) Method of adjusting the primary pressure P1 or the secondary pressure P2 of the gas separation membrane S according to the degree of amount reduction

In case the feed gas contains the component B, during the amount reduction process of the feed gas, if the primary pressure P1 of the gas separation membrane S was kept at a constant level, on the one hand the recovery rate rises as above, and on the other hand the concentration of the permeable gas in the permeable gas decreases, while the component B in the gas on the primary side of the gas separation membrane S is concentrated and liquefaction may occur. When the primary pressure P1 was reduced according to the decrease of feed gas flow rate, the liquefaction of the component B in the gas on the primary side of the gas separation membrane S can be prevented because the pressure of the component B drops. At this point, constant recovery rate can be maintained in the amount reduction process because the flow rates of the permeable gas and the residual gas respectively also change according to the flow rate of the feed gas.

However, there are situations when, depending on the required specifications, the decrease in concentration of the permeable gas and the possible liquefaction of the component B in the gas on the primary side of the gas separation membrane S during the amount reduction do not constitute problems, and there are also situations when making the set values constant is preferred. Moreover, depending on the required specifications regarding the product, there are also situations when a method of calculating the set values by a function (for example, the primary equation) of the feed gas flow rate or the permeable gas flow rate to the gas separation membrane is preferred. In addition, the calculation of the amount reduction rate using the diode function, for example, the primary pressure does not drop, until the predetermined amount reduction rate, and for the amount reduction rate beyond this value, there are cases when a method of decreasing the primary pressure P1 according to the amount reduction rate is preferred. Namely, by using a configuration or a method as the one described above, the size of the membrane module does not change even when the feed gas flow rate decreases, and it has become possible to stabilize the purity and the recovery rate of the desired product gas by means of a simple method. The recovery rate increases when the primary pressure P1 and the secondary pressure P2 are kept at a constant value upon amount reduction; however, it is also possible to prevent liquefaction by controlling the increase of recovery rate by increasing the secondary pressure P2.

(ii) Method of adjusting the added gas flow rate F1 according to the degree of amount reduction The residual gas dew-point temperature is limited and a certain level of the component A is left in the residual gas, in order to avoid the liquefaction on the primary side of the gas separation membrane S. The components in the byproduct gas increase through the cooling and vapor-liquid separation of the residual gas. When the purity of the permeable gas of the gas separation membrane S can be afforded from the standard values, part of the byproduct gas can be added. The component A can be recovered efficiently. High recovery rate can also be obtained in the amount reduction, by adjusting the added gas flow rate F1 according to the changes in the concentration of the permeable gas as a result of controlling the primary pressure P1.

In concrete terms, in case a trustworthy analyzer is used, the analyzer is placed in the location of AP3, and the added gas flow rate F1 can be controlled so that the product purity after merging becomes the defined value. Moreover, the added gas flow arte F1 can also be controlled by the function of the degree of reduction (for example, the primary function or the polygonal line function). Details are not provided, however, in addition, using the concentration of the component A in the residual gas and the correlation function of the residual gas pressure, the method of avoiding the liquefaction on the primary side of the gas separation membrane (See patent Citation 2007-232918 A VERIFIER) is also efficient. The same applies to the other configuration examples below.

The second configuration example of the inventive gaseous mixture separation system (referred to hereafter as the inventive system 2) is shown in Figure 2 The method of adding part of the byproduct gas into the secondary side flow path of the gas separation membrane S consists from connecting the added gas flow path Fa to the added gas installation unit located on the permeable side (secondary side) of the gas separation membrane S, and mixing the added gas inside the gas separation membrane S with the permeable gas. While mixing with the permeable gas, the mixture of added gas and permeable gas is extracted from the permeable gas flow path T1 passing though the secondary side. The concentration of the component A is generally lower in the added gas than in the permeable gas; therefore, the component A becomes highly permeable when the added gas is introduced into the secondary side of the gas separation membrane S, because the pressure of the component A on the secondary side decreases. Namely, the recovery rate of the ingredient A gained, and the surface area of the gas separation membrane S can be reduced. At this point, the primary side flow (feed gas flow path Uo - regeneration gas flow path G1 ) and the secondary side flow (added gas flow path Fa - permeable gas flow path T1 ) are passing via the membrane module (not shown) from opposite sides; however, cases of both flows passing orthogonally, as counter-flows, or co-current flows are possible. In practice, it is uncommon to use the co-current flows because of the separation efficiency rate. Counter-flows are preferably used for the inventive system 2. For the primary side flow, it is difficult to maintain the driving force of the permeation, because the concentration of the ingredient A decreases as the flow comes closer to the outlet. From the perspective of redressing this situation, if the counter-flow style is used, it is preferable to introduce the added gas having a low concentration of component A from this position, because the inlet on the secondary side flow is placed on the opposite side of the outlet of the primary side flow.

At this point, the heating means (heating unit H) is preferably installed on the flow path supplying the added gas to the gas separation membrane S. the added gas is not mixed directly with the permeable gas, but introduced into the added gas entry Sf of the gas separation membrane S after heating with the heating unit H. the byproduct gas forming the added gas is cooled in the second cooling unit C2 and the second vapor-liquid separation unit D2, and heating is preferable for the gas separation membrane S to function at the adequate temperature. Moreover, in case the added gas contains liquefied mist, the gas separation membrane S deteriorates by itself. In addition, in case the added gas contains condensable components, maximum vapor pressure is obtained at cooled temperature in the second cooling unit C2; therefore, liquefaction can occur at ambient temperature, danger can be avoided by heating, and gas separation can be carried out under safe conditions.

The inventive system 2 comprises the aforementioned processes (1 )-(9) and the processes below into the process of producing gaseous components and condensable components. (10a) a process of adding added gas into the secondary side flow path of the gas separation membrane

(11 a) a process using the permeable gas, or a mixture of the permeable gas and the added gas as the product gas

At this point, the flow rate F1 of the added gas is controlled, and the product gas concentration and recovery rate are adjusted within the desired range, in a way similar to that of the above-described first configuration example. .

Figure 3 shows the third configuration example of the inventive gaseous mixture separation system (referred to hereafter as "the inventive system 3"). In concrete terms, this system is similar to the first configuration example; however, in order to enable primary processing of the feed gas, this system also comprises any of the following units located between the feed gas flow path Uo and the gas separation membrane S: first cooling unit C1 , the first vapor-liquid separation unit D1 , the first byproduct gas flow path G1 , the heating unit H, the first byproduct liquid flow path L1 , the first byproduct gas flow path G1 , and the first liquid surface liquid surface detection unit LC1 and the first control valve LCV1 installed on the first byproduct liquid flow path L1. The byproduct gas flow path G2, the byproduct liquid flow path L2, the cooling unit C2 and the vapor-liquid separation unit D2, the liquid surface detection unit LC2 and the control valve LCV2 of the first configuration example are hereafter each preceded by "the second, as for example the second byproduct gas flow path G2 and so on.

The inventive system 3 is preferably used in order to prevent occurrence of mist in case the feed gas contains an even larger amount of component B. The concentration of the ingredient A in the gas supplied to the gas separation membrane S can be increased and the concentration of the component B can be decreased through the primary cooling process of the feed gas and the primary vapor-liquid separation process, and the load of the selective separation process through the gas separation membrane S, the secondary cooling process of the residual gas, and the secondary vapor-liquid separation process can be reduced. Moreover, because the concentration of the ingredient A in the permeable gas also increases, part of the second byproduct gas containing a smaller amount of the component B after the secondary vapor-liquid separation process is diverged and mixed with the permeable gas as added gas, yielding higher recovery rate of the ingredient A. At this point, the point of the primary processing of the feed gas is that it is in no way restricted directly in front of the primary cooling unit C1 as shown in Figure 3, but depending on the temperature of the feed gas or on the dew-point temperature thereof, it can be placed in the locations marked by the broken lines a - c, namely, a: between the first cooling unit C1 and the first vapor-liquid separation D1 , b: between the first vapor-liquid separation unit D1 and the heating unit H, or c: between the heating unit H and the gas separation membrane S. Another processor (no representation) can be used in cases such as difficult maintenance of the desired supply pressure combined with the properties of the gas separation membrane S.

At this point, the heating means (heating unit H) are preferably installed on the flow path supplying the feed gas to the gas separation membrane S. Gas separation must be carried out according to the characteristics and use of the gas separation membrane, and at the adequate temperature. Moreover, in case the feed gas comprises liquid mist, the gas separation membrane S may deteriorate by itself. Moreover, in case the feed gas comprises condensable components, liquefaction can occur at ambient temperature; when these condensable components are semi-permeable (component B), the component B in the gas on the primary side (impermeable side) of the gas separation membrane concentrate and liquefaction can occur. Therefore, it was possible to escape the danger of generation of liquefied mist on the gas separation membrane S by cooling the feed gas to a temperature of, for example, 40 ⁰C (outdoor summertime conditions) using the first cooling unit C1 installed on the feed gas flow path Uo, then separating the condensable liquefied components by means of the first vapor-liquid separation unit D1 , and heating them by means of the heating unit H. However, in case the feed gas comprises a small amount of high boiling components, it is also possible to skip the first cooling u it C1 ; in addition, it is possible to also skip the first vapor-liquid separation unit D1 (namely, supplying the feed gas to the first byproduct gas flow path G1 ).

Beside the aforementioned processes (1 )-(10), the inventive system 3 comprises either one or a combination of the processes below, as part of the process of producing gaseous components and condensable components.

(1 a) a process of primary cooling of the feed gas

(1 b) a process of primary vapor-liquid separation of the feed gas

(1 c) a process of extracting the first byproduct gas containing a reduced amount of the component B obtained through the primary vapor-liquid separation process

(1d) a process of extracting the first byproduct liquid obtained mainly from the component B obtained through the primary vapor-liquid separation process

(1e) a process of heating the feed gas or the first byproduct gas

At this point, the added gas flow rate F1 is adjusted, and the product gas concentration and recovery rate are adjusted within the desired range, in a way similar to that described for the first configuration example.

The alternative embodiment of the third configuration example is shown in Figure 4. Namely, the specific configuration is similar to the third configuration example; however, in addition to said configuration example, the pressure adjustment means PCro (the pressure control valve PCVo and the pressure regulator PCO) are installed on the first byproduct gas flow path G1. In the reduction of amount of feed gas, it becomes possible to control the pressure of the first vapor-liquid separation unit D1 independently of the primary pressure of the gas separation membrane S, and it also become possible to control the even higher pressure. Moreover, this type of configuration comprising the third configuration example can also be applied to the second configuration example, yielding similar effects and functions.

Figure 5 shows the forth configuration example of the inventive gaseous mixture separation system (referred to hereafter as "the inventive system 4"). In concrete terms, this system is similar to the first configuration example; however, multiple stage gas separation membrane is used, the first residual gas flow path R1 of the former stage of the first gas separation membrane S1 is connected to the upper flow path side of the latter stage of the second gas separation membrane S2, and a cascade connection forms. Namely, by connecting the first residual gas flow path R1 of the first gas separation membrane S1 to the supply gas flow path of the second gas separation membrane S2, the first permeable gas is extracted from the first permeable gas flow path T1 , and it becomes possible to extract the second permeable gas is extracted from the second permeable gas flow path T2. Moreover, the configuration in Figure 5 allows the unification of the added gas flow path Fa, separated from the byproduct gas flow path G2, with the first permeable gas flow path T1 , so as to mix the added gas with the first permeable gas.

The cascade cycle is often used because it has the advantage of yielding raised recovery rate in case multiple-purity permeable gas is obtained by changing permeable gas pressure of each stage and the material of the membrane in the gas separation membrane. At this point, the concentration of the component B in the second residual gas is controlled and it is possible to efficiently prevent liquefaction, by selecting the surface are of the first gas separation membrane S1 and the second gas separation membrane S2.

In addition to the functions of the cascade cycle, concentrated gas is added to the permeable gas, and it can be extracted as the product gas; also, in the amount reduction process, it becomes possible to form the desired component concentration in the product gas with a high recovery rate. Moreover, it becomes possible to react flexibly to the modifications in process conditions during amount reduction.

At this point, Figure 5 illustrates the case wherein the permeable gas of the first gas separation membrane S1 is mixed with the added gas; however, the mixture of the permeable gas and the added gas is in no way limited to this situation; addition is possible to any of the permeable gases of the multiple stages. Moreover, using the cascade system, by controlling the primary pressure of the gas separation membrane of each stage to a sequentially lower value, it becomes possible to raise the recovery rate of the permeable gas.

Alternative embodiments of the forth configuration example are shown in Figure 6 and Figure 7. Namely, this system is similar to the forth configuration example; however, a system comprising the pressure adjustment means PCr2 (pressure control valve PCV2 and pressure controller PC2) installed on the first residual gas flow path R1 is shown in Figure 6. In the amount reduction of the feed gas, the pressure of the first vapor-liquid separation unit D1 and the primary pressure P1 of the first gas separation membrane S1 can be controlled independently of the secondary pressure P2 of the second gas separation membrane S2. Moreover, a system comprising the pressure adjustment means PCr2 installed on the first residual gas flow path R1 , together with the pressure adjustment means PCro (pressure control valve PCVo and pressure controller PCO) installed on the first byproduct gas flow path G1 is shown in Figure 7. In the amount reduction of the feed gas, the pressure of the first vapor-liquid separation unit D1 can be controlled independently of the primary pressure of the first and second gas separation membranes S1 and S2, and in addition it become possible to control the even higher pressure. The mixing point of the feed gas and the circulating gas in Fig, 7 is that as shown can be placed in the locations marked by the broken lines a - b, namely, (a) between the first cooling unit C1 and the first vapor-liquid separation D1 , (b) between the first vapor-liquid separation unit D1 and the pressure adjustment means PCro.

Figure 8 shows the fifth configuration example of the inventive gaseous mixture separation system (referred to hereafter as "the inventive system 5"). This system is similar to the second configuration example; however, the configuration in Figure 8, allows the unification of the added gas flow path Fa with the added gas installation unit Sf located on the permeable side (secondary side) of the second gas separation membrane S2, so as to mix the added gas with the first permeable gas inside the second gas separation membrane S2. In addition to the functions based on the cascade cycle, higher purity and recovery rate of the ingredient A can be secured by introducing part of the byproduct gas as added gas into the secondary side of the second gas separation membrane S2. Moreover, it becomes possible to react flexibly to the modifications in process conditions during amount reduction.

At this point, Figure 8 illustrates the case wherein the permeable gas and the added gas of the second gas separation membrane S2 are mixed; however, the mixture of the permeable gas and the added gas is in no way limited to this situation; gas can be added against permeable gas at any stage. Moreover, using the cascade style, by controlling the primary pressure of the gas separation membrane in each stage to a lower value, it becomes possible to raise the recovery rate of the permeable gas. In addition, the effects and functions disclosed in the above-described "alternative embodiment of the inventive system 4" can be applied to the inventive system 5, yielding similar technical results.

The hydrogen gas producing process is set with respect to the above- described configuration examples, and the results of the numerical analysis for the purity and recovery rate of the permeable gas are shown hereafter.

(1 ) Analysis conditions

(1 -1 ) The composition of the feed gas is shown in Table 1. [Table 1]

(1-2) The gas separation membranes used for analysis, both the first and the second, were polyaramide type membranes.

(1-3) The temperature of the feed gas at the entrance of the gas separation membrane was 90 ⁰C. (1-4) The dew-point temperature of the residual gas at the exit of the gas separation membrane was < 80 ⁰C as a general rule.

(1-5) The temperature was reduced to 40 ⁰C using the water cooling method as the first and second cooling units. (1 -6) The pressure of the permeable gas was 10 bar (abs) at the exit of the gas separation membrane. The pressure of the permeable gas in the first and second gas separation membranes was equal, also in case of the cascade system.

(1-7) The maximum value of the flow rate of the feed gas was 10,000 Nm³/h; the "flow rate" shown below is the rate (%) as against this maximum value.

(1-8) The pressure loss of the inventive system

(i) When the value of the flow rate of the feed gas was maximum (100%): the pressure loss of the second cooler and the second vapor-liquid separation unit was presumed to be 0.2 bar. (ii) Pressure loss during amount reduction: the above situation of 100% was taken as the standard, and the pressure loss of the inventive system was presumed to change proportionally to pV², and was analyzed, p (kg/ m³) is gas density, and V² (m³/h) is sample flow rate.

(1-9) The pressure standards of the inventive system (i) When the value of the flow rate of the feed gas was maximum: the standard supply pressure of the gas separation membrane was set at 30.8 bar (abs).

(ii) During amount reduction: depending on the control method. Here, when one stage gas separation membrane is applied, the pressure of the residual gas flow path (represented by the pressure of the second byproduct gas from the second vapor-liquid separation unit) was chosen as the standard; in case of cascade cycle using two stages of gas separation membranes, the pressure of the first residual gas flow path (represented by the pressure nearest to the first gas separation membrane on the first residual gas path flow), or the pressure of the second residual gas flow path (represented by the pressure of the second byproduct gas from the second vapor-liquid separation unit) was chosen as the standard.

(1-10) 95 mor/o of the purity of the permeable gas or the product gas was chosen as the standard. (2) Analysis results

The analysis results are shown in the Embodiments 1 to 3. Embodiment 1 :

(i) Analysis conditions

A case was analyzed with the system using the one stage gas separation membrane as shown in Figure 1 , wherein the flow path of added gas (simulating the case wherein the hydrogen concentration of the product was determined with an analyzer) was controlled so that the product purity was near 95% of the standard value. The residual gas pressure of the gas separation membrane of the feed gas in Table 1 was modified by means of the primary equation of the degree of amount reduction, and reduction of the amount was attempted. Moreover, the surface area of the gas separation membrane was set so that the dew-point temperature at the residual gas exhaust port was approximately 80 ⁰C when the feed gas flow rate was 100%.

(ii) Analysis results

As shown in Table 2, the recovery rate increased in an outstanding way with the amount reduction. For the sake of comparison, the recovery rate decreased to 79.39% in case the added gas flow rate was set to 0 when the feed gas flow rate was 100%. At this pressure level, condensation did not occur even when the feed gas was cooled to a temperature of 40 ⁰C.

[Table 2]

Embodiment 2:

(i) Analysis conditions A case was analyzed with the system using the one stage gas separation membrane as shown in Figure 1 , wherein the residual gas pressure of the gas separation membrane of the feed gas in Table 1 and the added gas flow rate was modified by means of the primary equation of the degree of amount reduction, and the amount was reduced. The surface area of the gas separation membrane was adjusted as in Embodiment 1.

(ii) Analysis results

As a result, the desired recovery rate and purity of hydrogen were obtained, as shown in Table 3.

[Table 3]

Embodiment 3:

(i) Analysis conditions

A case was analyzed with the cascade system using the two stage gas separation membrane as shown in Figure 5, wherein the residual gas pressure of the gas separation membrane of each stage of the feed gas in Table 1 and the added gas flow rate was modified by means of the primary equation of the degree of amount reduction, and the amount was reduced. The surface areas of the first and second gas separation membranes were adjusted to 100% and 50% of Embodiment 1 respectively.

(ii) Analysis results

As shown in Table 4, the recovery rate increased in an outstanding way in accordance with the amount reduction. . Moreover, high recovery rate was obtained in comparison with Embodiment 1 and Embodiment 2. For the sake of comparison, the recovery rate decreased to 86.49% in case the added gas flow rate was set to 0 when the feed gas flow rate was 100%. [Table 4]

As shown by the results above, in any of Embodiments 1-3, highly stable product gas purity and high recovery rate can be guaranteed. [Figure 1] is an explanatory drawing illustrating the basic configuration example of the inventive producing system.

[Figure 2] is an explanatory drawing illustrating the second configuration example of the inventive producing system.

[Figure 3] is an explanatory drawing illustrating the third configuration example of the inventive producing system.

[Figure 4] is an explanatory drawing illustrating the alternative embodiment of the third configuration example of the inventive producing system.

[Figure 5] is an explanatory drawing illustrating the forth configuration example of the inventive producing system. [Figure 6] is an explanatory drawing illustrating the alternative embodiment of the fourth configuration example of the inventive producing system.

[Figure 7] is an explanatory drawing illustrating the alternative embodiment of the fourth configuration example of the inventive producing system.

[Figure 8] is an explanatory drawing illustrating the fifth configuration example of the inventive producing system.

[Figure 9] is an explanatory drawing illustrating the basic configuration example of the conventional producing system.

[Figure 10] is an explanatory drawing illustrating another configuration example of the conventional producing system. [Figure 11] is an explanatory drawing illustrating yet another configuration example of the conventional producing system.

Explanation of codes:

APo, AP1 , AP2, AP3 analysis ports

C1, C2 (first, second) cooling units

D1, D2 (first, second) vapor-liquid separation units

Fa added gas flow path

FC1 flow rate regulator

FCbI flow rate adjustment means

FCV1 flow rate control valve

G1, G2 (first, second) byproduct gas flow path

H heating unit

L1, L2 (first, second) byproduct liquid flow paths

LC1, LC2 (first, second) liquid surface detection units

LCV1, LCV2 (first, second) control valves

P1 primary pressure of the (first) gas separation membrane

PCo, PC1, PC2 pressure regulators

PCro, PCM, PCr2 pressure adjustment means

PCVo, PCV1, PCV2 pressure control valves

R1, R2 (first, second) residual gas flow path

S, S1, S2 (first, second) gas separation membranes

Sf added gas installation unit

T1 , T2 (first, second) permeable gas flow paths

Uo feed gas flow path

Claims

1. A method of separating a feed gas containing multiple components, including a separation step using one or several selectively gas permeable membrane(s) and one or several steps consisting of a vapor-liquid separation using the differences in condensability of at least one component, said method generating:

- a permeable gas rich in a highly permeable and non-condensable component A,

- a byproduct liquid rich in a semi-permeable and condensable component B, and

- a byproduct gas lean in the component B obtained after the vapor-liquid separation, and being characterized in that it contains at least the following steps: (1 ) supplying the feed gas to the gas separation membrane (2) adjusting either the primary pressure of the gas separation membrane or the process values connected with said pressure

(3) separating the feed gas into a permeable gas and a residual gas using the gas separation membrane

(5) extracting the residual gas rich in semi-permeable gas

(6) cooling the residual gas and performing a vapor-liquid separation into a byproduct liquid rich in the aforementioned component B and a byproduct gas lean in the component B (7) diverting part of the byproduct gas as added gas

(9) as an option, mixing the some of the added gas with the permeable gas to obtain more product gas.

2. A method in accordance with Claim 1 , characterized in that the aforementioned feed gas is fed to the gas separation membrane after undergoing one or a combination of the following steps:

(1 a) a primary cooling of the feed gas

(1 b) a primary vapor-liquid separation into a first byproduct gas lean in the component B and a first byproduct gas

(1 c) a heating of the first byproduct gas in order to obtain a new feed gas to be sent to the gas separation membrane.

3. A method in accordance with either Claim 1 or 2, wherein, especially for turndown operation: either the primary pressure of the aforementioned membrane, the secondary pressure of the aforementioned membrane or the process values connected with said pressure is adjusted according to the degree of turndown, and wherein the flowrate of the added gas is also adjusted according to the degree of turndown.

4. A method in accordance with any of Claims 1 to 3 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.

5. A gas separation system including a selectively gas permeable membrane and a vapor-liquid separating unit based on the differences in condensability of each component, and generating a permeable gas rich in highly permeable and non-condensable component A obtained from the gas separation membrane, a byproduct liquid rich in semi-permeable and condensable component B obtained from the vapor-liquid separation unit, and byproduct gas lean in the component B, and a system for producing gaseous components and condensable components characterized in that it contains at least the following elements: (a) a feed gas flow path for supplying the feed gas

(b) a gas separation membrane for separating the permeable gas and the residual gas (c) a permeable gas flow path for extracting the permeable gas from the gas separation membrane

(d) a residual gas flow path for delivering the residual gas from the gas separation membrane (e) a cooling unit and a vapor-liquid separation unit located on the residual gas flow path

(j) a pressure adjustment unit or a flow rate regulating unit located on the byproduct gas flow path after the separation process (k) a flow rate regulating unit located on the added gas flow path

(m) a product gas flow path for connecting and making the added gas flow path and the permeable gas flow path.

6. A gas separation system including a selectively gas permeable membrane and a vapor-liquid separating unit based on the differences in condensability of at least one component, generating a permeable gas rich in highly permeable and non-condensable component A obtained from the gas separation membrane, a byproduct liquid rich in semi-permeable and condensable component B obtained from the vapor-liquid separation unit, and a byproduct gas containing a reduced amount of component B, said system being characterized in that it contains at least the following elements:

(a) a feed gas flow path for supplying the feed gas

(b) a gas separation membrane for separating the permeable gas and the residual gas (c) a permeable gas flow path for eliminating the permeable gas from the gas separation membrane (d) a residual gas flow path for delivering the residual gas from the gas separation membrane

(j) a pressure adjustment unit or a flow rate adjustment unit located on the byproduct gas flow path after the separation process

(k) a flow path adjustment unit located on the added gas flow path, or a flow rate adjustment unit and a heating unit (n) an added gas installation unit connected to the added gas flow path on the secondary side of the gas separation membrane.

7. A system in accordance with either Claim 5 or 6, characterized in that the following elements are located on the feed gas flow path: (aa) a first cooling unit

(ab) a first vapor-liquid separation unit

(ac) a first byproduct gas flow path for eliminating the byproduct gas from the gas phase unit of the first vapor-liquid separation unit

(ad) a first byproduct liquid flow path for eliminating the byproduct liquid from the gas phase unit of the first vapor-liquid separation unit

(ae) a heating unit located on the feed gas flow path or on the first byproduct gas flow path.

8. A system in accordance with any of Claims 5 to 7, characterized in that gas separation membrane 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.