WO2016174317A1

WO2016174317A1 - Production of helium from a gas stream containing hydrogen

Info

Publication number: WO2016174317A1
Application number: PCT/FR2015/052633
Authority: WO
Inventors: Bertrand DEMOLLIENS; Jean-Marc Tsevery
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2015-04-30
Filing date: 2015-10-01
Publication date: 2016-11-03
Also published as: US20180238618A1; FR3035656A1; EA201792303A1; FR3035656B1; EA035014B1

Abstract

The invention relates to a method for producing helium from a source gas stream (1) including at least helium, methane, nitrogen and hydrogen, comprising at least the following consecutive steps: step a): injecting said source gas stream (1) into at least one compressor (3); step b): eliminating the hydrogen and the methane by reacting the stream (4) obtained from step a) with oxygen; step c): eliminating at least the impurities from step b) by temperature swing adsorption (TSA); step d): partially condensing the stream (8) obtained from step c) in order to produce a stream (10) of liquid nitrogen and a gas stream (11) comprising mostly helium; step e): purifying the gas stream (11) obtained from step d) in order to increase the helium content by pressure swing adsorption (PSA) by eliminating the nitrogen and the impurities contained in the gas stream (11) obtained from step d).

Description

Helium production from a gaseous stream

The present invention relates to a process for producing helium from a source gas stream comprising at least helium, methane, nitrogen and hydrogen.

Helium is obtained commercially almost exclusively from a mixture of volatile components of natural gas, this mixture comprising, as well as helium, typically methane and nitrogen and traces of hydrogen, argon and other noble gases. During the production of mineral oil, helium is made available as a component of the gas that accompanies mineral oil, or as part of the production of natural gas. It is theoretically possible to obtain helium in the atmosphere, but it is not economical because of the low concentrations (typical concentration of helium in the air of the order of 5.2 ppmv).

In order to avoid unwanted freezing during a liquefaction process of helium, the concentration of impurities in the helium stream to be liquefied must not exceed a value of 1000 ppm by volume, preferably 10 ppmv.

For this reason, the liquefaction process of helium is connected downstream of a helium purification process. This is generally composed of a combination of cryogenic processes, generally based on partial condensation, and adsorption processes, the regeneration in the case of the latter being possible due to the variation of temperature and or pressure.

In many cases, it is advantageous to employ a process for purifying helium such that, in addition to the purified helium, nitrogen of requisite purity - in which the sum of the impurities is less than 1% by volume - can be obtained. In general, only a portion, typically from 5% to 70%, preferably from 10% to 50%, of the nitrogen present in the mixture to be purified is brought to the desired purity. The remaining nitrogen is released into the atmosphere along with methane as a low pressure gas, either directly or after an oxidation step, preferably carried out in a torch or incinerator.

A known example of a method of the state of the art for obtaining a pure helium fraction from a starting fraction comprising at least helium, methane and nitrogen is described in US Pat. patent application AU2013200075.

This process for obtaining a pure helium fraction from a starting fraction comprising at least helium, methane and nitrogen comprises the following successive stages:

a) the starting fraction is subjected to a methane and nitrogen removal,

(b) the fraction from (a) that consists essentially of helium and nitrogen is compressed,

c) the compressed fraction is subjected to nitrogen removal, and d) the helium-rich fraction obtained in step c) is subjected to adsorption purification to produce a fraction.

The early removal of the methane fraction contained in the initial gaseous stream to be treated requires the implementation of two independent cryogenic steps required, investment and operating costs are therefore important.

On the other hand, a part of the nitrogen contained in the initial gas stream to be treated is lost with the ethane removed in the first stage. However, nitrogen recycling for other applications is a key element on an industrial scale, since nitrogen, in particular liquid nitrogen, is highly valuable.

In addition, this method does not make it possible to treat gas streams containing a high hydrogen content, typically more than 6% by volume of hydrogen.

Another type of helium purification process known from the prior art is illustrated in FIG. A gaseous stream 1 'comprising nitrogen, methane, helium and hydrogen, for example originating from the outlet of a nitrogen rejection unit (NRU) 15 following the treatment of a stream of natural gas to remove nitrogen from this natural gas, is introduced into a compressor 2 '. Once this gas is compressed, it is introduced into a 3 'helium concentrator device.

At the outlet of this device 3 ', the hydrogen contained in the gas stream is removed by means of a system 4' in which hydrogen and oxygen react.

At the end of this step, the gas stream is then purified by means of an alternating pressure adsorption (PSA) process. A gas stream 6 'from PSA 6' containing predominantly helium is then liquefied in a helium liquefaction device 7 '. The liquefied helium is sent to an 8 'helium storage system. Said storage system 8 'being cooled by liquid nitrogen 9' from a liquid nitrogen storage device 10 'fed by an air separation unit 11'.

In addition, the liquid nitrogen stored in the device 10 'is used to feed the helium concentrator device 3'.

The gaseous stream 12 'containing a majority of nitrogen and a small amount of helium is purified by means of a purification means 13' eliminating the impurities contained in the gas stream 12 'in order to produce a gaseous stream 14' of recycling sent to the compressor 2 'after having been mixed with the gas mixture the initial to be treated.

When the hydrogen content is high, typically more than 4% by volume or even 6%, the addition of air at the hydrogen removal system 4 'in which hydrogen and oxygen react is important. A large amount of nitrogen and argon is then introduced at this level, which sizes the 5 'PSA system.

A purge implemented at the 3 'helium concentrator contains methane. It must then be treated using a methane oxidation device to meet environmental requirements. It is necessary to have an air separation unit 11 '(in English ASU) which produces the liquid nitrogen to the specification compatible with the 8' helium storage (of the order of ppm of methane).

The inventors of the present invention have then bridged a solution to solve the problems raised above.

The subject of the present invention is a process for producing helium from a source gas stream comprising at least helium, methane, nitrogen and hydrogen, comprising at least the following successive stages:

Step a): introducing said source gas stream into at least one compressor;

Step b): elimination of hydrogen and methane by reacting the stream from step a) with oxygen;

Step c): removal of at least impurities from step b) by alternating-temperature adsorption (TSA);

Step d): partial condensation of the stream resulting from stage c) in order to produce a stream of liquid nitrogen and a gas stream mainly comprising helium;

Step e): purification of the gas stream from step d) in order to increase the helium content by pressure swing adsorption (PSA) by eliminating the nitrogen and the impurities contained in the gas stream from step d ).

According to other embodiments, the subject of the present invention is: A process as defined above characterized in that the source gas stream comprises from 40% to 95% by volume of nitrogen, from 0.05% to 40% by volume of helium, from 50 ppmv to 5% by volume of methane and from 1% to 10% by volume of hydrogen, preferably from 5% by volume to 10% by volume of hydrogen.

A process as defined above characterized in that the source gas stream comprises from 40% to 60% by volume of nitrogen, from 30% to 50% by volume of helium, from 50 ppm to 5% by volume of methane and from 1% to 10% by volume of hydrogen, preferably from 5% by volume to 10% by volume of hydrogen. A process as defined above comprising a step prior to step a) of producing the source gas stream to be treated by means of a nitrogen extraction unit or a natural gas liquefaction unit, said unit producing a stream of liquid nitrogen implemented in step d) allowing the partial condensation of the stream from step c) to produce a stream of liquid nitrogen and a gas stream comprising predominantly helium.

A process as defined above characterized in that the pressure at the end of step a) is between Bara and Bara, preferably between Bara and Bara.

A process as defined above characterized in that the gaseous stream from step b) comprises less than 1 ppm by volume of hydrogen and less than 1 ppm by volume of methane.

A process as defined above characterized in that said impurities contained in the gas stream from step b) mainly comprise carbon dioxide and water.

A process as defined above characterized in that the stream of liquid nitrogen from step d) comprises more than 98.5% by volume of nitrogen.

A process as defined above characterized in that said gaseous stream from step d) comprises between 80% by volume and 95% by volume of helium.

A process as defined above characterized in that said gaseous stream from step e) comprises at least 99.9% by volume of helium.

A process as defined above characterized in that step b) consists in bringing the gas stream coming from step a) into contact with oxygen and a catalytic bed comprising particles of at least one selected metal. among copper, platinum, palladium, osmium, iridium, ruthenium and rhodium, supported by a chemically inert carrier with respect to carbon dioxide and water so as to react with methane and hydrogen with oxygen. A process as defined above characterized in that it comprises an additional step f) liquefaction of the helium from step e).

A process as defined above characterized in that the liquid nitrogen from step d) cools the liquefied helium in step f).

A plant for producing helium from a source gas mixture comprising methane, helium, hydrogen and nitrogen comprising at least one compressor directly receiving the source gas mixture, at least one means for removing hydrogen and methane, at least one nitrogen removal and helium concentration device, and at least one helium purification means located downstream of the nitrogen removal and helium concentration, characterized in that the means for removing hydrogen and methane is located downstream of said at least one compressor and upstream of the nitrogen removal device and helium concentration.

An installation as defined above characterized in that it further comprises a helium liquefaction device downstream of the helium purification means.

The invention will be described in more detail with reference to FIG. 2 which illustrates an embodiment of a method according to the invention.

A source gas stream 1 containing at least helium, nitrogen, hydrogen and methane is treated by a process of the present invention to produce a pure helium stream, typically containing more than 99.9% % by volume of helium. The source stream 1 comes for example from a unit 2 of nitrogen extraction (in English, nitrogen rejection unit, NRU) located downstream of a cryogenic unit for treating natural gas.

The source current 1 is introduced into a compressor 3 making it possible to compress the gas stream 4 at a pressure of between 15 bara (absolute bar) and 35 bara, preferably between 20 bara and 25 bara. The temperature is the ambient temperature where the installation is located.

The gas stream 4 is introduced into a unit 5 for eliminating hydrogen and methane. This unit 5 consists for example of one to several reactors in series containing a catalyst between grids. This catalyst is typically Pd / Al ₂ O 3. A catalytic oxidation between oxygen and oxidants (hydrogen / methane) is created.

Hydrogen reacts with oxygen to form water. This reaction being exothermic, the temperature rises.

To oxidize methane also, higher temperatures are required. A high hydrogen content at the inlet makes it possible to operate at a high temperature and to co-oxidize the methane (for example, with 2% of hydorgene, the temperature rises to about 200 ° C. which is not sufficient not to oxidize methane).

Thus, the hydrogen and methane contained in the initial source stream 1 to be treated are oxidized by the oxygen of unit 5.

Impurities such as water and carbon dioxide are therefore produced in the gas stream 6 at the outlet of the unit 5. This gas stream 6 comprises mainly nitrogen and helium.

The outgoing gas (against ambient air or cooling water) is cooled before being sent to the adsorption unit 7. Part of the water then condenses directly in a condensate recuperator. Part of the heat produced can be recovered for use in another process

The gaseous stream 6 is then treated in an adsorption unit 7, such as an alternating-temperature adsorption unit (TSA), in order to eliminate water and carbon dioxide from the gaseous stream 6. this results in a gaseous stream 8 essentially comprising nitrogen and helium (that is to say comprising less than 5 ppm by volume of methane, less than 1 ppm by volume of hydrogen, less than 0.1 ppm by volume of carbon dioxide and less than 0.1 ppm by volume of water). The gaseous stream 8 is treated in a unit 9 for purifying nitrogen and concentrating helium.

This unit 9 comprises at least one heat exchanger in which the gas stream is cooled from ambient temperature (0 ° C - 40 ° C for example) to a temperature between -180 ° C and -195 ° C. At the outlet of this heat exchanger, the gaseous flow is for example introduced into a phase separator pot generating a liquid flow 10 and a gaseous stream 11. The liquid stream contains 98.8% by volume of nitrogen. This liquid flow 10 is sent to a storage device 12 of liquid nitrogen. It does not contain methane.

The gaseous stream 11 contains from 80% by volume to 95% by volume of helium and from 5% by volume to 20% by volume of nitrogen. Stream 11 is sent to a helium purification unit 13.

This purification unit 13 is for example an alternating pressure adsorption unit (in English PSA) and produces two streams. One 14, containing 99.9% by volume of helium and another containing the remainder of the elements (essentially nitrogen). The gas stream 15 is introduced into a compressor 16 and then mixed with the source gas stream 1 to be treated, this is a regeneration loop of the unit 13.

The helium rich stream 14 may be supplied to a helium liquefaction unit 17 producing a liquid helium stream 18 directed to a storage device 19. The pure liquid nitrogen stored in the nitrogen storage device 12 can be used to maintain the temperature of the helium storage device 19.

According to a preferred embodiment, a stream of liquid nitrogen produced by the nitrogen extraction unit 2 is introduced into the unit 9 for purifying nitrogen and concentrating helium. This makes it possible to obtain the necessary cooling capacity and thereby avoid the investment of a dedicated air separation unit contrary to the process illustrated in FIG.

Another refrigerant present at the site (for example LNG) can also be used or a high pressure fluid can be used (by Thomson expansion or turbines) to create the necessary cold.

Advantages of a method as illustrated in Figure 2 object of the present invention compared to the method illustrated in Figure 1 are described below.

The simultaneous oxidation of hydrogen and methane occurs before the helium concentration. The TSA 7 then operates under pressure which guarantees a better efficiency (a reduction of the necessary volume of adsorbents as well as a reduction of the heat consumption at the level of the regeneration heater). The purge from the cryogenic helium concentration unit 9 no longer contains methane (which has been oxidized beforehand).

Liquid nitrogen without methane can therefore be produced from unit 9. It is sufficient to integrate this unit 9 with the Helium concentration unit 2 (NRU or natural gas liquefaction unit) to obtain the cooling capacity required. This avoids the investment of a dedicated air separation unit (ASU).

According to one particular embodiment of the invention, a stream 21 previously expanded in the unit 9 containing nitrogen and helium is extracted from said unit 9 and then sent to a compressor 3 and / or 16. Thus, Helium from the expansion of the liquid nitrogen unit 9 is recycled to increase the percentage of helium produced.

For example, the stream 21 comprises between 40% and 50% by volume of helium and between 50% and 60% by volume of nitrogen.

The performance of the PSA unit 13 and its size are also greatly improved. Helium 1 1 is preconcentrated at about 90% to PSA 13 (rather than

70% in the process of Figure 1 and with a high hydrogen content. Argon and oxygen impurities are also much lower

(since argon and oxygen condense together with nitrogen).

There is also no more carbon dioxide or water to be treated in the incoming gas. The waste gas pressure (in English (offgas) of the PSA 13 can also be reduced compared with that of the process illustrated in FIG. 1 since they can return directly to the compressor 16 without first going through a drying unit.

All these points make it possible to improve the efficiency of the PSA 13 which dimensions the return line and the compressor 3 of the current 1 to be treated (the energy consumption of the compressor is reduced.)

The table below summarizes the compositions of the gas streams entering the helium purification unit (element numbered 13 of FIG. 2 and 5 'of FIG. 1). Current

Figure 1 Figure 2 Gaseous

Composition

He mol% 69.48% 89.9697%

N2 mol% 29.94% 9.9979%

CH4 ppm v 1 1

Ar ppm v 2,658,181

H2 ppm v <0.5 <0.5

Do not ppm v 300 300

CO ppm v 0 0

02 ppm to 2 703 143

H2O saturated 0

CO2 ppmv 355 <0.1

Total mol% 100% 100%

Flow rate (sec) Nm3 / h 4806 3713

Pressure bars at 23.55 23.45

Temperature ° C 47 47

Table: Composition of the incoming gases in the PSA

Claims

claims

1. A process for producing helium from a source gas stream (1) comprising at least helium, methane, nitrogen and hydrogen, comprising at least the following successive stages:

Step a): introducing said source gas stream (1) into at least one compressor (3);

Step b): elimination of hydrogen and methane by reacting the stream (4) from step a) with oxygen;

Step d): partial condensation of the stream (8) from step c) to produce a stream (10) of liquid nitrogen and a stream (1 1) gas comprising predominantly helium;

Step e): purification of the gas stream (1 1) from step d) in order to increase the helium content by pressure swing adsorption (PSA) by eliminating the nitrogen and the impurities contained in the gas stream (1 1) from step d).

2. Method according to the preceding claim characterized in that the source gas stream (1) comprises from 40% to 95% by volume of nitrogen, from 0.05% to 40% by volume of helium, from 50 ppmv to 5% by volume. % by volume of methane and from 1% to 10% by volume of hydrogen, preferably from 5% by volume to 10% by volume of hydrogen.

3. Process according to claim 2, characterized in that the source gas stream (1) comprises from 40% to 60% by volume of nitrogen, from 30% to 50% by volume of helium, from 50 ppm to 5% by weight. volume of methane and 1% to 10% by volume of hydrogen, preferably 5% by volume to 10% by volume of hydrogen.

4. Method according to one of the preceding claims comprising a step prior to step a) of producing the source gas stream (1) to be treated by means of a nitrogen extraction unit (2) or a natural gas liquefaction unit, said unit (2) producing a stream (20) of liquid nitrogen implemented in stage d) allowing partial condensation of the stream (8) resulting from stage c) in order to produce a stream of liquid nitrogen (10) and a gaseous stream (1 1) comprising mainly helium.

5. Method according to the preceding claim characterized in that the pressure at the end of step a) is between Bara and Bara, preferably between Bara and Bara.

6. Method according to the preceding claim characterized in that the gas stream (6) from step b) comprises less than 1 ppm by volume of hydrogen and less than 1 ppm by volume of methane.

7. Method according to any one of the preceding claims characterized in that said impurities contained in the gas stream (6) from step b) mainly comprise carbon dioxide and water.

8. Method according to any one of the preceding claims, characterized in that the liquid nitrogen stream from step d) comprises more than 98.5% by volume of nitrogen.

9. Method according to any one of the preceding claims characterized in that said gaseous stream from step d) comprises between 80% by volume and 95% by volume of helium.

10. Method according to any one of the preceding claims characterized in that said gaseous stream from step e) comprises at least 99.9% by volume of helium.

1 1. Process according to any one of the preceding claims, characterized in that step b) consists in bringing the gas stream coming from step a) into contact with oxygen and a catalytic bed comprising particles of at least a metal chosen from copper, platinum, palladium, osmium, iridium, ruthenium and rhodium, supported by a carrier that is chemically inert with respect to carbon dioxide and water so that react methane and hydrogen with oxygen.

12. Method according to any one of the preceding claims characterized in that it comprises an additional step f) liquefaction of the helium from step e).

13. Method according to the preceding claim characterized in that the liquid nitrogen from step d) cools the liquefied helium in step f).

14. Installation for producing helium from a mixture of source gas (1) comprising methane, helium, hydrogen and nitrogen comprising at least one compressor (3) directly receiving the mixture of source gas (1), at least one means (5) for removing hydrogen and methane, at least one device (9) for eliminating nitrogen and helium concentration, and at least one means for purification (13) in helium located downstream of the device (9) for removing nitrogen and helium concentration, characterized in that the means (5) for removing hydrogen and methane is located downstream of said at least one compressor (3) and upstream of the device (9) for removing nitrogen and concentrating helium.

15. Installation according to the preceding claim characterized in that it further comprises a device (17) for liquefying helium downstream of the purification means (13) in helium.