EP0358700A1

EP0358700A1 - Process for extraction of helium

Info

Publication number: EP0358700A1
Application number: EP88904521A
Authority: EP
Inventors: Karl Knoblauch; Erwin Pilarczyk; Klaus Giessler; Hans Bukowski; Joseph S. D'amico; Herbert Reinhold
Original assignee: Bergwerksverband GmbH
Current assignee: Bergwerksverband GmbH
Priority date: 1987-05-20
Filing date: 1988-05-19
Publication date: 1990-03-21
Also published as: PL272593A1; AU604127B2; ES2023977B3; DD270124A5; JPH0577604B2; EP0291976B1; RU1816228C; WO1988009305A1; JPH02503552A; US5080694A; EP0291976A1; AU1781588A; DE3863585D1; PL160298B1; DE3716899C1

Abstract

Est décrite l'extraction d'hélium de pureté et de rendement élevés, sans enrichissement intermédiaire dans des installations frigorifiques, à partir de gaz contenant de très faibles concentrations d'hélium, au moyen d'un processus d'adsorption en pression alternée. Le gaz renfermant de l'hélium est acheminé cycliquement, au cours de chacune des trois étapes d'adsorption, dans quatre adsorbeurs reliés en parallèle. En premier lieu, des hydrocarbures supérieurs et d'autres impuretés sont piégés dans des adsorbeurs (J, K, L, M) remplis de charbon actif, au cours d'une phase préliminaire de filtration. Au cours de deux phases ultérieures d'adsorption, d'autres constituants gazeux, par exemple de l'azote et/ou du méthane sont piégés dans des adsorbeurs (A, B, C, D et E, F, G, H) remplis de tamis moléculaires au carbone. L'hélium est d'abord enrichi au cours de la phase (I) puis extrait au cours de la phase (II) sous forme d'hélium rafiné dont la teneur est de 99,9%. Le gaz utilisé est de préférence du gaz naturel dont la teneur en hélium est comprise entre 2 et 10%. L'hélium rafiné ainsi obtenu s'utilise par exemple comme gaz de couverture, gaz de respiration pour plongeurs, gaz pour ballons et gaz porteur en chromatographie.Described is the extraction of helium of high purity and yield, without intermediate enrichment in refrigeration plants, from gases containing very low concentrations of helium, by means of an alternating pressure adsorption process. The gas containing helium is routed cyclically, during each of the three adsorption stages, in four adsorbers connected in parallel. First, higher hydrocarbons and other impurities are trapped in adsorbers (J, K, L, M) filled with activated carbon, during a preliminary filtration phase. During two subsequent adsorption phases, other gaseous constituents, for example nitrogen and / or methane are trapped in filled adsorbers (A, B, C, D and E, F, G, H) carbon molecular sieves. The helium is first enriched during phase (I) and then extracted during phase (II) in the form of refined helium, the content of which is 99.9%. The gas used is preferably natural gas, the helium content of which is between 2 and 10%. The refined helium thus obtained is used for example as a covering gas, breathing gas for divers, gas for balloons and carrier gas in chromatography.

Description

Helium extraction process

The invention relates to a process for the production of helium by a pressure-swing adsorption process from gas mixtures which contain helium, nitrogen, methane and other gases and are passed through carbon molecular sieves which adsorb nitrogen, methane and the other gases, the gas mixture being cyclically four parallel adsorbers are abandoned, each of which successively goes through a pressure build-up phase, an adsorption phase and a pressure relief phase, pressure build-up and pressure relief being carried out in part by pressure equalization with another adsorber.

Such a pressure swing adsorption process for purifying helium is known from EP 00 92 695, in which helium is used from a starting gas mixture with helium and essentially nitrogen, argon and oxygen and also smaller proportions of carbon dioxide and methane using carbon molecular sieves a purity of over 99.9% by volume can be obtained. However, the starting gas mixture in this single-stage process already contains 50-95% by volume of helium. This method is not suitable for extracting helium from gas mixtures with up to 10% helium.

High purity helium is increasingly required for various applications, e.g. B. in refrigeration systems for refrigeration, as a protective gas during welding and in the chemical industry, in airspace technology as an inert gas, in diving work in the form of breathing gas, in chromatography as a carrier gas, in leak detection, as a balloon gas and for other purposes. Helium which has a high purity is required for these purposes. In order to achieve these high purities, several process steps are required for gas mixtures which have only low helium contents, in order first to enrich the gas mixture with helium and then finally to obtain helium of high purity from the gas mixture enriched with helium.

According to the state of the art, helium is, as is known from "Bureau of Mines, Preprint from Bulletin 675 - Helium -, 1985 Edition, United States of Interior", pp. 3 and 4, in multi-stage processes with a purity of Over 99.9 vol .-% obtained from helium-containing natural gases. The main constituents of helium-containing natural gases are nitrogen and methane and up to 10% by volume of helium in addition to smaller proportions of various higher hydrocarbons and carbon dioxide.

The natural gas is first cooled in a refrigeration system to approx. -150 C, the hydrocarbons being mainly condensed out. The gas mixture produced in this way contains, apart from small amounts of other gases, more than 50% by volume of helium and nitrogen. This crude helium is further separated in a pressure change adsorption system, helium with a purity of over 99.9% by volume being obtained. The helium yield of the pressure swing system is about 60%, the remaining helium is highly contaminated in the desorption gas. The desorption gas is worked up further. In a second refrigeration system, the previously compressed desorption gas is cooled to approx. -185 C and. contaminants condense out. The remaining helium / nitrogen mixture is returned to the pressure change system and mixed with the raw helium from the first refrigeration system. The return makes it possible to recover a high proportion of helium. The disadvantage is that this method two refrigeration systems and also requires a pressure change system. It is also very energy intensive.

The invention is based on the object of avoiding the disadvantages of the known processes and of obtaining helium from natural gases with low helium contents solely by pressure swing adsorption without intermediate enrichment in refrigeration systems with high purity and at the same time with a high yield.

This object is achieved by the combination of several adsorption process stages, associated adsorption process step and adsorbents:

a) In a pre-filter stage (V), the adsorbers of which are filled with activated carbon, higher hydrocarbons and, if appropriate, further impurities are removed from the helium-containing gas mixture; b) The adsorbers of the prefilter stage ^' e (V) are operationally adsorbers of a first adsorption stage (I) _. assigned; c) The adsorbers of the first adsorption stage (I) are filled with carbon molecular sieves with an average adsorption pore diameter between 0.1 and 0.4 πm, preferably between 0.3 and 0.4 nm, and become helium enrichment - ^' pressed in several steps to adsorption pressure and relaxed after adsorption; d) In an adsorption stage (II) downstream of the first adsorption stage (I), the enriched helium is converted by means of four adsorbers, which are also made of carbon molecular sieves with an average adsorption pore diameter between 0.1 and 0.4 nm, preferably between 0 , 3 and 0.4 nm, are filled, helium with a purity of over 99.9% is obtained, the exhaust gas being returned to the feed gas of the upstream adsorption stage ( ^" I), and e) the adsorbers of the downstream adsorption stage (II) alternately pass through the phases of pressure build-up, adsorption and regeneration and the subsequent pressure build-up takes place first by pressure equalization with an adsorber to be regenerated and then with product gas, while the regeneration begins with pressure equalization, which is what the relaxation and purging with product gas follows.

Special carbon molecular sieves with an average adsorption pore diameter of between 0.1 and 0.4 nm, preferably 0.3 and 0.4 nm, are used as adsorbents for the process according to the invention, which extremely effectively separate nitrogen and methane from helium, so that helium of high purity can be obtained, an unexpectedly high yield of over 90% helium being achieved when using the proposed adsorption process steps and steps. According to the proposed enrichment process, this can be achieved by using the pressure swing technique alone from starting gas mixtures with a comparatively low helium content of about 2 to 10%, without the need for a refrigeration system. As a result, a product gas which has a helium purity of 99.9% and higher is generated with very low energy expenditure.

According to a further development, the individual phases in adsorption stage I proceed as follows:

ca) The pressure build-up phase consists of three steps:

1. pressure build-up step from a vacuum vacuum (P.) to a medium pressure level (P);

2. pressure build-up step from the medium pressure level (P ") to a higher pressure level (P.);

3. pressure build-up step from the higher pressure level (P _Λ ) to the highest pressure level (Pp-) - adsorption pressure; cb) The pressure relief phase comprises four steps:

1. pressure relief step from the highest pressure level (P ₅ ) to the higher pressure level (P.);

2nd pressure relief step from the higher pressure level (P ₄ ) to the medium pressure level (P ₃ );

3. Pressure relieving step from the middle pressure stage (P ") to the atmospheric pressure (P");

4th pressure relief step from atmospheric pressure {? > -) to the final vacuum pressure (P);

cc) The pressure equalization takes place in two stages, in the first stage from the outlet of a first adsorber, which

1. Relief step (from P - .. to P.) is carried out, the output of a second adsorber is relaxed, which carries out the second pressure build-up step (from P ₃ to P.), and in the second stage from the outlet of the first adsorber who the

2. Relief step (from P. to P) is carried out, the pressure is released at the inlet of a third adsorber, which carries out the 1st pressure build-up step (from P. to P "), and

cd) the 3rd relief step and the 4th relief step take place in countercurrent, a low-helium exhaust gas being produced, and the 3rd pressure build-up step is carried out with product gas.

The highest pressure level is (P - adsorption pressure - over 1 bar, preferably 10 - 30 bar, and the vacuum pressure is below 500 mbar, preferably 50 mbar. According to a special embodiment, the following pressure values are preferably assigned to the individual pressure stages:

^P l = 50 mbar

4 bar

11.7 bar

20 bar

The total cycle time is expediently 450 to 3600 s.

According to a preferred embodiment, a total cycle time of 720 s is used.

With a total cycle time of 720 s, the pressure relief phase can advantageously include the following time intervals:

1. Relief step from P-. on P. 55 s rest position 115 s

2. Relief step from P. to P “10 s

3rd relief step from P "to P _? 55 s

4. Relief step from P _? on P. 115 s

The pressure build-up phase with a total cycle time of 720 s is expediently divided into the following time intervals:

1.- Pressure build-up step from P. to P 10 s

2. Pressure build-up step from P to P. 55 s

3rd pressure build-up step from P 4.- to P._ 125 s With an overall cycle of 720 s it is advisable ^'to choose as Zeitiπtervall the product gas recovery 180 s.

The process according to the invention is particularly suitable for feed gases whose helium content is up to 10% by volume, preferably 2 to 8% by volume. The proportion of helium in the product gas of the first adsorption stage (I) should expediently reach up to 95% by volume. The helium content in the end product gas of the second adsorption stage (II) is expediently 99.9% by volume and higher.

The process according to the invention is preferably used in the extraction of helium from natural gases which, after prior separation of higher hydrocarbons and trace impurities, e.g. B. in known adsorption prefilters, can have the following composition (in% by volume):

N ₂ . , 40-80

He 2-10 CH 10-40 co, <0.1-10

Further advantages and refinements of the method result from the following description of exemplary embodiment with reference to the accompanying drawings. The drawings show:

1 shows a single-stage adsorption system with four parallel adsorbers for enriching helium up to 95% by volume;

2 shows a pressure-time diagram of an adsorber of the system according to FIG. 1 ; 3 shows a pressure-Zεi diagram with an assigned partial step sequence table for the four adsorbers of the system according to FIG. 1;

4 shows a circuit diagram for the four adsorbers of the plant according to FIG. 1;

5 shows a diagram of the dependence of the helium yield on the helium purity in a system according to FIG. 1;

6 shows a two-stage adsorption system with four parallel adsorbers per stage for the production of helium with a pure purity of over 99.9 vol.

FIG. 7 shows a pressure-time diagram with an assigned partial step sequence table for the four adsorbers of stage II of the plant according to FIG. 6;

8 shows a valve circuit diagram for the four adsorbers of stage II of the system according to FIG. 6.

1 consists of four adsorbers A to D filled with a carbon molecular sieve with an average adsorptive diameter between 0.1 and 0.4 nm, preferably between 0.3 and 0.4 nm, in parallel and ge optionally from four pre-filters J, K, L, M filled with activated carbon, in which, if necessary, higher hydrocarbons and trace impurities present in the feed gas can be removed before entering adsorbers A to D. Each adsorber cycles through the following eight sub-steps cyclically, with a time lag to the other three adsorbers: Tl adsorption

T2 pressure relief through pressure equalization (Da 1)

T3 pressure relief through pressure equalization (Da 2)

T4 countercurrent relaxation (GEE)

T5 evacuation (Ev)

T6 pressure build-up through pressure equalization (DA 1)

T7 pressure build-up through pressure equalization (DA 2)

T8 pressure build-up with product gas (DA 3)

Before FIG. 1 is explained in detail, the sequence of the eight sub-steps T1 to T8 is first clarified using the pressure-time profiles shown in FIGS. 2 and 3.

Fig. 2 shows an example of an adsorption pressure of 20 bar and a total cycle time of 720 s, the pressure-time profile that occurs in each of the four adsorbers, staggered from the other adsorbers. Five pressure values Pl to P5 are marked on the pressure axis, between which the pressure build-up and pressure relief steps take place in the present example.

3 shows the time-shifted pressure-time profiles in the four adsorbers A to D. The procedure for adsorber A is described below by way of example. Corresponding procedures apply to the other three adsorbers B, C and D.

The adsorption (sub-step T1) takes place at a constant increased pressure, for example at 20 bar. The adsorber A is flowed through at this pressure with the feed gas, nitrogen, methane and other gas components being adsorbed by the carbon molecular sieve, so that helium which is not adsorbed flows out at the adsorber outlet in high purity. After adsorption, the loaded adsorber A is regenerated by several pressure relief steps (sub-steps T2 to T5).

First, there is a first pressure equalization Da 1 (sub-step T2), the gas under adsorption pressure from adsorber A being expanded in cocurrent from the adsorption pressure P _ς into the adsorber C, which is at a lower pressure P. The gas release from adsorber A (T2) to adsorber C (T7) is illustrated by an arrow in the partial step sequence table in FIG. 3.

During the first pressure equalization (Da 1), the pressure in the adsorber A is released to a pressure P., for example to 11.7 bar, while at the same time the pressure in the adsorber C increases from the pressure P to the pressure P. (pressure build-up DA 2 ) -.

After a short standstill (stand by), a second pressure equalization takes place in the adsorber A (Da 2, substep T3), the gas under pressure P. from adsorber A - again in cocurrent - into the adsorber D at the final vacuum pressure P is relaxed. The pressure in the adsorber A drops from the pressure P. to a pressure P_, which is, for example, 4 bar. During both pressure equalization steps, a helium-enriched gas mixture flows from adsorber A into adsorber C or into adsorber D.

After the two pressure equalization steps (Da 1 and Da 2), adsorber A is further expanded in countercurrent from the pressure P ^ to atmospheric pressure P_ (GEE, substep T4). This results in a low helium gas mixture in which the components desorbing during counter-relaxation (GEE) such as nitrogen and methane are enriched and which is discarded as exhaust gas. Adsorber A is then evacuated to vacuum P, for example 50 mbar, using a vacuum pump 80 (Ev, substep T5). This leads to an increased desorption of nitrogen and methane as well as the other gas components previously adsorbed in the sub-step Tl. The extracted gas is extremely low in helium and is also discarded as waste gas.

After the evacuation, the regeneration of the adsorber A has ended. In adsorber A, the pressure in sub-steps 16 to T8 is then increased successively to the adsorption pressure P.

First, there is pressure compensation (sub-step 16) between adsorber A and adsorber B, which has previously passed through sub-step T2 and is at a higher intermediate pressure P. at the end of the evacuation of adsorber A. During the pressure equalization, a helium-enriched gas mixture flows from adsorber B into adsorber A, the gas mixture preferably being drawn off from adsorber B in cocurrent and introduced into adsorber A in cocurrent (head-to-floor pressure equalization). The pressure in the adsorber A (pressure build-up DA 1) rises from the final vacuum pressure P to an intermediate pressure P,, ^', for example 4 bar, while at the same time the pressure in the adsorber B drops from the intermediate pressure P to the intermediate pressure P - ,.

The pressure in adsorber A (pressure build-up DA 2) is increased further by a further pressure equalization (sub-step T7) with adsorber C. Adsorber C has previously passed through the sub-step T1, adsorption, and is located before the pressure equalization with adsorber A at the adsorption pressure P, .. The pressure equalization is carried out in the example in such a way that the helium-enriched gas mixture is drawn off in a cocurrent from the adsorber C and in Countercurrent is relaxed in the adsorber A (head-to-head pressure compensation). The pressure in the adsorber A increases from the intermediate pressure P to the intermediate pressure P, for example 11.7 bar, while at the same time the pressure in the adsorber C drops from the adsorption pressure P to the intermediate pressure P.

After the pressure has been equalized twice, the pressure in the adsorber A is finally increased from the higher intermediate pressure P. to the adsorption pressure P_, for example 20 bar, using product gas (pressure build-up DA 3, substep T8). A new adsorption step then begins in adsorber A (sub-step T1).

The four adsorbers A to D are, as shown in FIG. 1, connected via a series of valves in such a way that one of the four adsorbers is constantly on adsorption and produces high-purity helium as product gas. The circuit of the valves is shown in Fig. 4. The gas supply and discharge in the pressure change system shown in FIG. 1 is explained below with reference to FIGS. 4 and 1, as an example for adsorber A. Before the adsorbers A to D, prefilters 3, K, L, M can be provided, which are state of the art and in which strongly adsorbing gas components such as, for. B. higher hydrocarbons from Bohrloch¬ gases can be pre-separated. As shown in the example, their mode of operation is generally the same as that of the main adsorbers A to D arranged in series, so that there is no need to go into them in detail below.

After the pressure build-up with product gas (DA 3, substep T8), adsorber A is at the adsorption pressure P _ς . During the subsequent adsorption (sub-step T1) feed gas flows through a line 1 at a pressure which is used to overcome the Pressure loss in the system is slightly above the adsorption pressure, with the valves 10 and 13 open, which are arranged in the flow direction upstream or downstream of the adsorber A, through the adsorber A. Apart from helium, all other components of the feed gas, such as nitrogen and methane, are adsorbed on the carbon molecular sieve, so that a helium rich gas flows out at the top of the adsorber A via a line 4 into a product gas line 91, in which a needle valve 71 is arranged. According to the valve circuit diagram in FIG. 4, the adsorption is divided into three time steps ZI, Z2 and Z3. In time step ZI, a valve 50 contained in a line 5 is closed, so that the entire product gas flows via line 4 into the product gas line 91. In time steps Z2 and Z3, valve 50 is opened, so that part of the product gas flows into adsorber B via a downstream throttle valve 72 and via line 5 and an open valve 25, which is connected upstream of adsorber B, which is pressed from the intermediate pressure P to the adsorption pressure P with the product gas in substep T8. The duration of the three time steps ZI, Z2 and Z3 can be, for example, 55 s for time step ZI, 115 s for time step Z2 and 10 s for time step Z3 with a total cycle time of 720 s.

After the adsorption, adsorber A is expanded to a higher intermediate pressure P 1 in sub-step T2 (Da 1), the gas flowing out of the adsorber A when the valve 15 is open (head-to-head pressure compensation via a throttle valve) 73 in line 5 with the valve open

35 flows into adsorber C, which in partial step T7 from an intermediate pressure P .. to an intermediate pressure P, aufqed

3 4 ^y will. According to the valve circuit diagram in FIG. 4, a time step ZI is required for this pressure compensation (Da 1) in the example with a total cycle time of 720 s has a duration of 55 s.

After this first pressure equalization and a standstill (stand by), which has a duration of 115 s, for example with a total cycle time of 720 s, adsorber A is increased in sub-step T3 (Da 2) via a further pressure equalization with adsorber D from the higher intermediate pressure P. a lower intermediate pressure P.- further relaxed. For this purpose, gas is released from the adsorber A via a ring line 3 (valve 60 in line 92 is closed) and a throttle valve 74 is expanded into the adsorber D when the valves 14 and 42 are open, which in the sub-step 16 changes from the final vacuum pressure P to the intermediate pressure P. , is pressed. The pressure equalization takes place in the example, as described, as head-to-floor pressure equalization. According to the valve circuit diagram in FIG. 4, a time step Z3 is required for the pressure compensation Da 2, which in the example has a duration of 10 s with a total cycle time of 720 s.

Adsorber A is then further expanded in partial step T4 (GEE) with open valves 12 and 60 via throttle valve 75 in countercurrent from intermediate pressure P ^ to aspherical pressure P. The gas flowing out is fed into an exhaust pipe 92. With a total cycle time of 720 s, the countercurrent relaxation in the example has a duration of 55 s.

After the countercurrent relaxation, adsorber A is evacuated in sub-step T5 (Ev) with the valve 11 open using the vacuum pump 80 from the atmospheric pressure P to the final vacuum pressure P, for example to 50 mbar. The low-helium gas mixture extracted in the process is fed into an exhaust line 93. With a total cycle time of 720 s, the evacuation in the example has a duration of 115 s. The evacuated adsorber A is then pressed in partial step T6 (DA 1) in a pressure equalization with adsorber B, which is preferably carried out as head-to-floor pressure equalization, from the end vacuum pressure P to the intermediate pressure P. A helium-enriched gas mixture is expanded from the outlet end of adsorber B when valves 24 and 12 are open (valve 60 is closed) via ring line 3 and throttle valve 74 into the inlet end of adsorber A. Adsorber B passes through sub-step T3. During pressure equalization, the pressure in adsorber B drops from intermediate pressure P. to intermediate pressure P ... With a total cycle time of 720 s, pressure equalization DA 1 in the example takes 10 s.

Adsorber A, which is partially pressed onto intermediate pressure P, is then further pressed onto intermediate pressure P. in partial step T7 (DA 2) by a further pressure equalization with adsorber C. This pressure equalization is preferably carried out as head-to-head pressure equalization in such a way that a gas mixture enriched with hydrogen is expanded from the outlet end of the adsorber C with valves 35 and 15 open via throttle valve 73 in line 5 into the outlet end of the adsorber A. Adsorber C passes through sub-step T2, the pressure in adsorber C dropping from adsorption pressure P, _ to intermediate pressure P. The time for pressure equalization DA 2 is 55 s in the example with a total cycle time of 720 s.

Finally, in partial step T8 (DA 3), adsorber A is converted with product gas from the intermediate pressure P to the adsorption pressure P -. pressed on. For this purpose, part of the product gas is passed into the adsorber A via the throttle valve 72 with the valves 50 and 15 open. According to the valve circuit diagram in FIG. 4, the pressure build-up DA 3 is composed of the two time steps Z2 and Z3 together, which have a duration of 115 or 10 s with a total cycle time of 720 s in the example.

After the pressure build-up DA 3 with product gas, a new pressure change cycle begins in adsorber A, which begins again with the adsorption step. The pressure change cycle in adsorbers B, C and D takes place accordingly, but with a time shift, as can be seen from FIG. 3.

The regeneration of the adsorbent is, as described, achieved by an evacuation step. The gas components to be removed from the helium-containing feed gas, such as nitrogen and methane, could also be desorbed according to the prior art by flushing with product gas. Such a rinsing desorption would, however, in the extraction of helium from earth and borehole gases with a helium content of max. 8 vol .-? Ό lead to extremely high yield losses for helium, because due to the low helium content in the feed gas, only a small amount of helium rich gas is produced as product gas and at the same time large amounts of gas have to be desorbed, because the gas components to be removed and desorbed by adsorption have in the feed gas a proportion of at least 92 vol .-? o '.

Examples

1 (but without pre-filter 3, K, L, M), at an adsorption pressure of 20 bar, a vacuum end pressure of 50 mbar and a total cycle time of 720 s, corresponding to 5 cycles / h, separation tests with a Gas mixture carried out in which no contamination conditions such. B. higher hydrocarbons were contained and that only helium (about 5 mol.%), Methane (about 29 Vo1. -Jό) and nitrogen (about 66 vol .-? Ά) contained. The four adsorbers A to D were filled with a carbon molecular sieve with an average adsorption pore diameter of 0.35 nm and had a filling volume of 2 l / adsorber. In the experiments, the amount of product gas generated was changed by adjusting the needle valve 71 and the helium purity in the product gas was thereby varied. The test results listed in Tables 1 to 4 below demonstrate that with the process according to the invention helium from a feed gas with a helium content of <8% by volume to a helium purity of 75-95% by volume in the product gas the first adsorption stage (I) can be enriched, depending on the helium purity in the product gas of the first adsorption stage (I) a helium yield of 90 - 99.9? ό is achieved. The test results are shown below in the form of a complete mass balance.

Table 1

Concentration amount (Vol .-? Ό) (Nl / h) He CH,

Feed gas 5.1 28.9 66.0 602.2

Exhaust gas from evacuation 0.7 23.1 76.2 191.3

Exhaust gas from counter-flow relaxation 0.5 34.0 65.5 381.7

Product gas 95.0 5.0 29.2

From this, a He yield of 90.3 is calculated Table 2

Concentration quantity (Vol. -58) (Nl / h)

Hey CH ,.

Feed gas 5.3 28.9 65.8 593.6

Exhaust gas from evacuation 0.2 23.8 76.0 188.5

Exhaust gas from countercurrent relaxation 0.2 34.1 65.7 371.5

Product gas 90.0 10.0 33.6

From this, a He yield of 96.1 is calculated

Table 3

Concentration quantity (vol.-Ä) (Nl / h)

Hey CH,

Feed gas 5.1 28.6 66.3 604.1

Exhaust gas from evacuation - 24.5 75.5 190.4

Exhaust gas from countercurrent relaxation <0.1 33.7 66.2 375.2

Product gas 80.0 - 20.0 38.5

From this, a He yield of 99.9 is calculated Table 4

Concentration quantity (vol.-Ä) (Nl / h)

Hey CH,

Feed gas 5.4 28.5 66, 1 609, 4

Exhaust gas from evacuation 26.0 74, 0 194, 1

Exhaust gas from countercurrent relaxation <0.1 33.1 66, 8 372, 4

Product gas 76.4 23, 6 42, 9

From this, a He yield of 99.6 is calculated

With increasing helium purity, the helium yield decreases and vice versa. The relationship between helium purity and helium yield is shown in FIG. 5.

A higher helium purity of up to> 99.9 Vo1. With a high helium yield at the same time, it can be generated if the rich helium gas generated in a pressure swing system I according to FIG. 1 has a helium concentration of up to 95% by volume. -? ό further separated in a downstream pressure change system II and the hot exhaust gas from the pressure change system II is returned to the pressure change system I and mixed there with the feed gas of the pressure change system I and jointly separated in the pressure change system I. The process flow diagram of the series connection of two pressure change systems I and II with exhaust gas recirculation is shown in FIG. 6.

The pressure change system II, like the upstream pressure Exchange system I, which is equipped with four adsorbers A to D, four adsorbers E to H, which are filled with a carbon molecular sieve with an average adsorption pore diameter of 0.35 nm. The process sequence in the downstream pressure swing system II is composed of six sub-steps Tl.2 to T 6.2, which each adsorber E to H cycles through in succession to the other three adsorbers:

Part 2 adsorption

T2.2 Pressure relief through pressure equalization (Da 1)

T3.2 counter current voltage (GEE)

T4.2 Purge with product gas

T5.2 pressure build-up by

Pressure equalization (DA 1)

T6.2 Pressure build-up with product gas (DA 2)

The cyclical, time-delayed sequence of this six step steps Tl.2 to T6.2 in the four adsorbers E to H is illustrated with the aid of the pressure-time profile shown in FIG. The sub-steps Tl.2 to T6.2 take place in such a way that an adsorber is always on adsorption and produces high-purity helium as product gas. This ensures continuous production of high-purity helium. The corresponding switching sequence of the valves is shown in FIG. 8.

6 and 8, the gas flow in the pressure swing system II is explained using the example of the adsorber E. The product gas of pressure swing system I, which is fed as feed gas into pressure swing system II, is used as rich helium gas (helium content up to 95% by volume) and the product gas of pressure swing system II as end product gas (high-purity helium with a helium content of over 99, 9 vol .-? Ό). After a pressure build-up with the end product gas, adsorber E is located at an increased pressure P, “, the adsorption pressure, in the downstream pressure change system II, which can be higher, lower or the same as the adsorption pressure P_ in the upstream pressure change system I. In the first case, the helium rich gas can be supplied with an intermediate compressor (not shown) from P ,. to P, "in the second case, the helium rich gas can be expanded, for example, from P_ to P," with an intermediate pressure reducer, also not shown here. Fig. 6 shows a plant in which the adsorption pressures P and P, "are equal. After the pressure build-up, during the subsequent adsorption in partial step T1.2, rich helium gas flows through a line 94 with valves 110 and 115 open at a pressure P, through the adsorber E. Here, the residual contaminants, in the essential nitrogen, removed from the helium rich gas by adsorption, so that high-purity helium with a purity of over 99.9 Vo1. -? ό as the end product gas via a line 97 and a needle valve 76 (control valve) leaves the system at a pressure which, owing to the pressure losses, is slightly below the pressure P ". Depending on the intended use, the high-purity helium can either be used directly, compressed for storage and / or further transport in containers or gas bottles and stored in gaseous form at high pressure, fed into pipelines - possibly after post-compression - or liquefied in refrigeration systems.

After the adsorption, adsorber E is expanded to an intermediate pressure P "in partial step T2.2 by pressure equalization (Da 1) with the adsorber G. For this purpose, the adsorbers E and G are gaseously connected to one another by opening valves 114 and 134 (valve 150 is closed), with helium-rich gas from the adsorber E via εinε line 98 and εin throttle valve 78 is released into the previously rinsed adsorber G, which is pressed from the rinsing pressure P "to the intermediate pressure P"". The pressure equalization is preferably carried out as head-to-head pressure equalization.

After the pressure equalization (Da 1), adsorber E is relaxed in partial step T3.2 in countercurrent to a lowest pressure P .. “(GEE), which is preferably at atmospheric pressure. For this purpose, a valve 112 is opened. The gas mixture flowing out of the adsorber E has a helium content which is substantially higher than the helium content of the feed gas flowing in upstream of the pressure change system I and is therefore returned via line 96 and a throttle valve 70 to the input of the upstream pressure growth system I. In this case, the expansion gas, the composition and volume flow of which changes during the expansion, is first passed into a buffer 81 arranged in line 100 for the purpose of comparison, where it is mixed with the purge gas generated in partial step T4.2 and, if necessary, recycled and subsequently transferred Circulation compressor 82 to the adsorption pressure P ,. the upstream pressure change system I is compressed and pressed into a mixing container 83 in which the return gas from pressure change system II is mixed with the feed gas for the pressure change system I.

Adsorber E is then flushed in sub-step T4.2 for the purpose of regeneration of the loaded adsorbent with the end product gas at the end pressure of the counter current voltage P ₁ . For this purpose, a partial stream of the end product gas is passed through εinε line 99 and εin throttle valve 79 with open valves 113 and 111 through the adsorbent E. When purging the contaminants previously removed from the helium rich gas, essentially nitrogen. That too at the bottom The outflowing purging gas in the adsorber has a helium content which is substantially above the helium content of the feed gas. The purge waste gas is therefore also returned to the inlet of the upstream pressure change system I, in the same way as was previously described for the countercurrent expansion gas.

After the rinsing, adsorber E is pressed onto its intermediate pressure P "in partial step T5.2 by pressure equalization with adsorber G, which has previously ended the adsorption. For this purpose, valves 114 and 134 are opened (valve 150 is closed) and helium-rich gas from the adsorber G is expanded via line 98 and throttle valve 78 into the adsorber E. The pressure in the adsorber G drops from the adsorption pressure P "to the intermediate pressure P _? from.

Finally, in the last partial step T6.2, adsorbent E is pressed with the end product gas onto the adsorption pressure P, _. For this purpose, a partial stream of the end product gas is passed via line 98 with valves 150 and 114 open via throttle valves 77 and 78 into the adsorber E. Thereafter, a new pressure change cycle in adsorber E begins with the adsorption. The pressure change cycle in adsorbers F, G and H runs accordingly, but is shifted in time, as can be seen from FIG. 7.

The total cycle time in the downstream pressure change system II can be selected independently of the total cycle time in the upstream pressure change system I. It can be longer, shorter or the same length, depending on the purity of the rich helium gas and the selected adsorption pressures P - or. P-. ". Depending on the total cycle time for sub-steps Tl.2 to T6.2 required different times. For a total cycle time of, for example, 1600 s, a high helium purity with a high helium yield was achieved with the following time division:

Adsorption 400 s

Pressure equalization Da 1.2 200 s countercurrent relaxation 200 s flushing 400 s

Pressure compensation DA 1.2 200 s pressure build-up DA 2.2 200 s,

Other time divisions are possible.

example

In addition, the laboratory pressure growth system I (4 adsorbers A to D with a filling volume of 2 1 / adsorber), which has already been described and used in experiments 1 to 4, became two smaller laboratory pressure growth system II (4 adsorbents with a 0.1 filling volume of 0.1) / Adsorber) in which the helium rich gas produced in the upstream pressure swing system I was further separated. The entire system had a structure according to FIG. 6 (but without a prefilter in system I). The gas mixture occurring in the downstream pressure change system II during the counter current voltage and purging was returned to the input of the upstream pressure change system I as shown in FIG. 6. The adsorbers in both systems were filled with a carbon molecular sieve with an average adsorption pore diameter of 0.35 nm. The upstream pressure swing system I was operated as in experiments 1 to 4 at an adsorption pressure of 20 bar, an end vacuum pressure of 50 mbar and a total cycle time of 720 s. The Adsorption pressure in the downstream pressure swing system

II was also 20 bar, the total cycle time was 1600 s

A helium rich gas with a helium concentration of 79.5 vol. -? ≤ ersεugt that in the downstream pressure change system II further to pure helium with a helium content of over 99.9 Vo1. -? was processed. The amounts and the compositions of the various partial gas flows are listed below.

Table 5

Concentration amount (Vol.-S) (1 / h (i.N.))

Hey CH, N,

Level I

Feed gas 5.4 28.5 66.1 592.3

Recycle gas from 2nd stage 41.5 - 58.5 17.1

Product gas 79.5 - 20.5 48.9

Exhaust gas from counter current voltage 0.1 32.6 67.4 368.1

Exhaust gas from evacuation - 25.5 74.5 192.4

5th level II

Feed gas 79.5 20.5 48.9

End product gas> 99.9 <0.1 31.7

Gas from countercurrent relaxation 1) 43.6 56.4 14.0

Purge gas 32.2 67.8 3.1

1) Recycle gas to stage I From 592.3 l / h (i.N.) feed gas with a helium content of 5.4% by volume, 31.7 l / h (i.N.) became pure theslium with a purity of over 99.9 Vαl .-? Ό won. From this, a helium yield of 99.1 is calculated for the two-stage enrichment of helium by means of pressure swing adsorption and integrated exhaust gas recirculation.

Claims

Patent claim: Process for the extraction of helium by a pressure-changing adsorption process from gas mixtures which contain helium, nitrogen and methane and possibly other gases and are dissolved by carbon molecular sieves which adsorb nitrogen and methane and possibly the other gases, the gas mixture is fed cyclically to four adsorbers connected in parallel, each of which successively goes through a pressure build-up phase, an adsorption phase and a pressure relief phase, and pressure build-up and pressure relief are partly achieved by pressure equalization with another adsorber, characterized by the combination of the following process stages: a) in one Pre-filter stage (V), whose adsorbers (J, K, L, M) are filled with activated carbon, higher hydrocarbons and possibly other impurities are removed from the helium-containing gas mixture; b) the adsorbers (J, K, L, M) of the pre-filter stage (V) are operationally assigned to adsorbers (A, B, C, D) of a first adsorption stage (I); c) the adsorbers (A, B, C, D) of the first adsorption stage (I) are with carbon molecular sieves with an average adsorption pore diameter between 0.1 and 0.4 nm, preferably between 0.3 and 0.4 nm , filled and are pressed to adsorption pressure in several steps for helium enrichment and relaxed after adsorption; d) in an adsorption stage (II) downstream of the first adsorption stage (I), the enriched helium is extracted using four adsorbers (E, F, G, H), which are also equipped with carbon molecular sieves with an average adsorption pore diameter between 0.1 and 0, 4 nm, preferably between 0.3 and 0.4 nm, helium with a purity of over 99.9% is obtained, the exhaust gas being recycled into the feed gas of the upstream adsorption stage (I), and e) the adsorber (E, F, G, H) alternately go through the phases of pressure build-up, adsorption and regeneration and the pressure build-up takes place first through pressure equalization with an adsorber to be regenerated and then with product gas, while the regeneration with pressure equalization begins, which is what happens Expansion and flushing with product gas follows. 2. Process according to claim 1, characterized in that the individual phases in the adsorption stage I proceed as follows: ca) The pressure build-up phase comprises three steps:

1. Pressure build-up step from a final vacuum pressure (P-,) to a medium pressure level (P-,);

2. Pressure build-up step from the medium pressure level (P- _∑ ) to a higher pressure level (P,);

3. Pressure build-up step from the higher pressure level (P, ) to the highest pressure level (P ) - adsorption pressure; cb) The pressure relief phase includes four steps:

1. Pressure relief step from the highest pressure level (P _r ) to the higher pressure level (P, );

2. Pressure relief step from the higher pressure level (P. ) to the medium pressure level (P-,);

3. Pressure relief step from medium pressure stage (P,) to atmospheric pressure (P~);

4. Pressure relief step from atmospheric pressure to final vacuum pressure (P _χ );

cc) The pressure equalization takes place in two stages, whereby in the first stage the output of a first adsorber, which carries out the 1st relief step (from P to P.), is relaxed to the output of a second adsorber, which carries out the 2nd pressure build-up step (from P, to P. ), and in the second stage from the output of the first adsorber, which carries out the 2nd relief step (from P. to P^), is relaxed to the entrance of a third adsorber, which carries out the 1st. Pressure build-up step (from P. to P,) is carried out, and

cd) the 3rd relief step and the 4th relief step take place in countercurrent, producing a low-helium exhaust gas, and the 3rd pressure build-up step is carried out with product gas.

3. Process according to claim 2, characterized in that the The highest pressure level (P,-) - adsorption pressure - is over 1 bar, preferably 10 - 30 bar, and the final vacuum pressure is under 500 mbar, preferably 50 mbar.

4. The method according to claim 3, characterized in that the following pressure values are preferably assigned to the individual pressure levels:

^P l = 50 mbar ^P 2 ^« - 1 bar ^P 3 = 4 bar * = 11.7 bar

5. Method according to one of claims 2 to 4, characterized in that the total cycle time is 450 to 3600 s, preferably 720 s.

6. The method according to claim 5, characterized in that the pressure relief phase preferably comprises the following time intervals with a total cycle time of 720 s:

1. Relief step from P.b- to P4. 55s

Rest position 115 s

2._ Relief step from P. to -P„ 10 s

3. Relief step from P„ to P _? 55s

4. Relief step from P >~ to P ₁ 115 s

7. The method according to claim 5, characterized in that the pressure build-up phase preferably comprises the following time intervals with a total cycle time of 720 s:

1. Pressure build-up step from P. to Po 10 s

2. Pressure build-up step from P~ to P. 55 s

3. Pressure build-up step from P. to P- 125 s

8. The method according to claim 5, characterized in that the product gas extraction includes a time interval of 180 s with a total cycle time of 720 s.

9. The method according to claim 1, characterized in that the helium content in the feed gas is <10% by volume, preferably 2 - 8% by volume and the helium content in the product gas of the first adsorption stage (I) is up to 95% by volume. is and the helium content in the end product gas of the second adsorption stage (II) is 99.9% by volume and greater.

10. The method according to any one of the preceding claims, characterized in that helium-containing natural gases are used as the feed gas mixture.