FR3120232A3 - Ultra-purification process of a fraction of hydrogen from a PSA H2 - Google Patents

Abstract

The invention relates to a process for the ultra-purification of a fraction of the hydrogen resulting from a PSA H2 (H) included in a hydrogen production unit (P) intended to mainly supply hydrogen at 99 + mole %, by means of a unit (A), characterized in that: the unit (A) is a unit for purification by adsorption at ambient temperature, the fraction purified by means of the unit (A) represents less of 50% of the production of unit (H), preferably a fraction of between 1% and 25%, the residual fraction enriched in impurities from said unit (A) returns to the hydrogen production unit ( P) to be fully recovered there without implementing any means of compression specific to this ultra-purification process. Abstract figure: Fig. 2

Description

Ultra-purification process of a fraction of hydrogen from a PSA H2

The present invention relates to a process for the ultra-purification of a dihydrogen fraction, which will be denoted hereinafter hydrogen or H2, resulting from a PSA H2 (PSA, for "Pressure Swing Adsorption") included in a unit hydrogen production intended to supply mainly hydrogen at a purity greater than or equal to 99% mole, a purity which will be noted below as 99+% mole.

The present invention relates more particularly to an arrangement of 2 gas purification units H and A making it possible to produce, from a feed gas, 2 fractions of different purity at lower cost. It is limited here to the case of hydrogen production, unit H being a PSA H2 and unit A a unit corresponding to an ultra-purification process by adsorption. Nevertheless, the principle described here could be applied to other separations provided that the purest fraction represents less than 50% of the total production, that the arrangement of unit H and unit A does not require no additional machinery and does not result in additional loss of product.

Hydrogen has become one of the main raw materials in chemistry or petrochemistry but is also used in many applications such as electronics, energy (fuel cell for example).

The sources of hydrogen are of varied origin, coming either from waste gases from industrial units (for example, ethylene or styrene production units, refinery off-gas, coke oven, chlorine electrolysis, etc. .), or units specifically made to produce this hydrogen (gas from hydrocarbon steam reforming, syngas production unit, cryogenic hydrogen-carbon monoxide separation units, ammonia cracking, reforming/ alcohol cracking…).

The hydrogen purity of these sources is generally insufficient for the applications envisaged and a PSA H2 unit is then generally used to obtain the required specification.

PSA H2 units, for their part, produce hydrogen at purities very generally greater than 99% mole and which can reach levels of 99.999% and more if necessary.

In general, a hydrogen production unit from an available residual gas will include, upstream of the PSA H2, equipment such as a separator, filter, compressor, specific purification unit intended to remove constituents such as oil and heavy hydrocarbons, mercury, possibly oxygen for safety reasons.

The units producing hydrogen from hydrocarbons or alcohols are for their part well known and include, upstream of the PSA H2, at least one furnace, one or more reactors, exchangers.

PSA H2, on the other hand, is made up of several adsorbers which follow a time lag in an operating cycle, which is uniformly distributed over as many phase times as there are adsorbers in operation, and which is made up of basic steps, namely the steps:

• adsorption at substantially high cycle pressure;
• co-current depressurization, generally from the high pressure of the cycle;
• counter-current depressurization, generally down to the low pressure of the cycle;
• elution at substantially the low pressure of the cycle; and
• of repressurization, from the low pressure of the cycle to the high pressure of the cycle.

A common point to all these PSA H2 cycles is that an increase in the purity required for hydrogen is paid for in terms of investment and/or operating costs.

For example, a PSA producing hydrogen at 99.999% mole (10ppm of residual impurities) will have an extraction yield of around 2 points lower than the same PSA producing at 99.9% (1000ppm of residual impurities).

To obtain the same production rate, it will be necessary for the highest purity to enlarge the upstream equipment, to consume more charge gas.

It may be preferable, if possible, to make the PSA itself more complex to recover the yield lost via the purity, but here too the additional cost of the PSA can be very high.

In the case of a hydrogen production unit intended for several applications corresponding to different purities, such an additional cost becomes all the more unacceptable as the highest purity required concerns only a fraction of the production, generally a minority.

This is particularly the case when the ultra-pure hydrogen is intended for a gas conditioning center in pressurized cylinders (each container contains only a few Nm3 of gas), for electronics or for powering batteries fuel.

These consumptions of a few hundred to a few thousand Nm3/h should be compared to industrial units of 50,000 to more than 150,000 Nm3/h intended to supply the hydrogen networks intended for industrial units in the petroleum, petrochemical and chemistry.

The content of impurities in hydrogen from a PSA is not perfectly constant during a cycle. In general, the content of an impurity drops to its minimum a few moments after the start of a new adsorption phase and then gradually rises until the end of the phase. The shape and amplitude of these fluctuations depend on the type of cycle used and the operating conditions.

Nevertheless, it is already difficult to recover a small fraction of the production which would have half as much impurity as the average and going beyond that does not seem realistic.

We were therefore led to study the possibility of adding purification downstream of a PSA H2 which would make it possible to improve the purity of the hydrogen produced by the PSA at a lower cost.

The optimization then consists in finding the PSA output content which leads to the best compromise of the PSA system with downstream purification.

A number of solutions have been studied and some used industrially.

For a majority of electronic applications, in particular in the manufacture of semiconductors, the residual impurities in hydrogen must be well below ppm.

The scrap rate of circuits or chips made from this hydrogen and other active compounds depends directly on the purity of these gases. A widely referenced process consists in treating the flow of hydrogen from the PSA in cryogenic purification at the level of liquid nitrogen (-196°C). It is an adsorption purification unit using silica gel, activated carbon or zeolite as adsorbents. Residual impurity levels of the order of one ppb are obtained.

Purification can include one or two adsorbers depending on the needs of the electronic manufacturing unit. These are complex installations, costly in terms of investment and operating costs (need for a supply of liquid nitrogen).

Other cryogenic processes use hopcalite type adsorbents, and zeolites exchanged with lithium or silver.

The addition of a permeation unit was considered since we are no longer looking for the ppb but for levels of the order of ppm.

The most immediate solution is the use of membranes that are selective for hydrogen with respect to nitrogen, CO, CH4. It is thus possible to extract from the flow of hydrogen leaving the PSA, a fraction having an improved purity. The permeators used for this purpose must be particularly well made in order to avoid any bypass between the high pressure supply and the purified gas recovered at low pressure as permeate.

A disadvantage of this process is that the pressure is lost on the purified fraction which must be recompressed for use under pressure. An example of hydrogen purification in argon is described in document FR 2 758 475.

A variant is to use a membrane with inverse hydrogen selectivity, i.e. impurities diffuse better through the membrane than hydrogen. In addition to the fact that this process is not very efficient due to lack of selectivity between the different constituents, it is the essential part of the production of PSA which would be found in low pressure and only the purified part which would remain in high pressure.

We can attach to this group the metallic membranes with hydrogen diffusion. One of the best known is the palladium membrane. The theoretical purity of hydrogen is in this case 100%, only this constituent being able to cross the barrier constituted by the membrane. The major defects result from the high levels of temperature required, the fragility of the membrane and the resulting risks of bypass and its high cost.

Another type of unit installed downstream of a hydrogen PSA is the catalytic reactor.

It is thus quite simple to reduce the oxygen content by reaction with hydrogen practically at room temperature.

Given the high hydrogen content and the high reactivity, the residual oxygen content can be very low, in the order of ppb.

To do this, reactors of sufficiently sophisticated geometry will be used to avoid any by-pass at the wall of the reactor and any preferential path. Thus, for example, the catalyst charge will be split into two or three beds separated by mixing zones. It is also recommended to increase the operating temperature to promote the reaction.

In addition to the cost of the catalyst, a disadvantage is of course the formation of water which may require the installation of a dryer which itself must be regenerated cyclically.

The fact remains that it is a process still used.

Since carbon monoxide is a poison for many processes, efforts have been made to remove it from hydrogen and replace it with a less harmful compound, methane.

This is also done by catalytic reaction in units called methanators.

Again, one of the disadvantages is the formation of another constituent instead of CO.

Some units have been designed to trap the compound formed in situ instead of it leaving in the hydrogen flow. For example, a reduced metal is used which will oxidize on contact with an impurity such as O2. Besides here again, the risk of direct reaction in the form of H2O and entrainment in the gas of this last constituent, it is advisable to reduce the metal cyclically and this requires a relatively complex procedure to avoid the risks of pollution, in particular on restarting.

When the quantity of hydrogen to be purified is particularly low, “getters” can be used, a type of chemical trap operating by chemisorption that must be replaced regularly.

A bed of nickel followed by a bed of an aluminum, vanadium, iron alloy at high temperature is supposed to produce ultra-pure hydrogen at the outlet.

Other processes use metals such as Nickel, Zirconium, Titanium, etc.

The cost is prohibitive for flow rates beyond a few tens of Nm3/h.

In summary, the purification processes intended to be placed downstream of an H2 PSA in order to increase the purity of a fraction of the hydrogen resulting from said PSA are costly in terms of investment (noble metals, complex units, etc.) and/or energy when, for example, it is necessary to compensate for the pressure drop caused by the process.

Often, they do not make it possible to obtain very high purity (insufficient selectivity of hydrogen membranes, appearance of other species in catalysis, etc.).

The represents the solutions most often used to produce purified hydrogen from 99+% mole 1 hydrogen from PSA H.

By purifying all or part of flow 2, we can thus obtain:

- ultra-pure hydrogen (H2) at high pressure 11 using a cryogenic unit at liquid nitrogen temperature 10,

- hydrogen (H2) at high purity but at medium or low pressure 21 via an H2-selective membrane 20,

- hydrogen (H2) purified into at least one constituent and at high pressure 31 via a previously reduced Deoxo or NiO2 type reactor or a methanator 30,

- ultra-pure, high-pressure hydrogen (H2) 41 using a high-temperature metallic membrane of the Pd 40 type or, in the event of a low flow rate of the order of a few tens of Nm3/h 51 via a getter 50.

It will be noted that the permeation unit 20 produces a residual under pressure 22 rich in hydrogen which can be recovered.

The cryogenic unit 10 is very generally an adsorption unit with long production times, of the order of several days or several weeks.

The hydrogen used for regeneration, loaded with impurities, is then usually sent to the torch.

Adsorption at cryogenic temperature, corresponding therefore to very high adsorption capacities, makes it possible to limit the frequency of regenerations and to make the loss of hydrogen acceptable.

The present invention consists in arranging downstream of the PSA H2, a second purification unit by adsorption at room temperature, treating only the flow rate necessary to obtain the production of ultra-pure H2 required with an arrangement such that the above drawback is totally removed.

The invention differs from the various processes comprising two units in series for the successive stopping of different impurities or for the production of gases of notably different composition. One can cite for example to illustrate this type of process, a dehydration unit followed by a unit intended to stop VOCs or else a sequence of PSA intended to produce on the one hand a fraction enriched in methane and on the other hand a hydrogen-enriched fraction. There are also enrichment processes in a constituent present in low content in the feed gas comprising several units in cascade but in this case there is a single production flow (for example production of argon, helium, etc. ).

The solution recommended here consisting of adding purification in series immediately downstream of the PSA is not a priori used because, as we have just said, like any purification unit by adsorption, it requires a regeneration gas, here hydrogen, which is found at low or medium pressure and/or polluted by the impurities removed from the purified fraction. This flow, which can represent 10 to 50% of the ultra-pure product flow obtained, is a loss that quickly becomes economically unacceptable except for recycling. Hydrogen being produced downstream of the production unit, recycling will normally mean compression means, the cost of which will generally be very high compared to the purifier itself, especially since it will normally take avoid any oil pollution, and have extreme sealing vis-à-vis the outside to avoid any risk of ignition.

An important characteristic of the invention will consist in integrating this new adsorption unit into the overall hydrogen production unit in order to take advantage of the equipment or processes already in place and thus avoid:

• either any compression investment specific to this new unit which would be necessary, as we have just seen, to carry out a recycling of the streams enriched in impurities;
• or any loss of hydrogen to any fuel-gas network.

It should be noted that installing a final purification unit on hydrogen at more than 99 mol% does not constitute an innovation in itself, but when this unit exists, it is installed at the place of conditioning or use of the hydrogen and not on the production site which, in the case of pipeline distribution, can then be very far away. In this case, there is therefore no possible integration with the production unit.

The present invention aims to effectively remedy these drawbacks by proposing a process for the ultra-purification of a fraction of the hydrogen resulting from a PSA H2 included in a hydrogen production unit intended to supply mainly hydrogen at 99+% mole, by means of an A unit, characterized in that:

• the unit is a purification unit by adsorption at room temperature, also called hereafter "adsorption unit",
• the fraction purified by means of the unit represents less than 50% of the production of unit H, preferably a fraction between 1% and 25%,
• the residual fraction enriched in impurities from said unit returns to the hydrogen production unit to be fully recovered there without the use of any compression means specific to this ultra-purification process.

It is recalled that by hydrogen at 99+%, we mean hydrogen at a minimum purity of 99% mole and by ultra-purification process or unit, a process or a unit which makes it possible to improve the purity of the hydrogen from PSA. By hydrogen production unit, we mean a set of equipment making it possible to recover or produce flows containing hydrogen and then to purify them to obtain a fraction very rich in H2, here at least 99% mole. As opposed to the flow directly from the PSA, the purified fraction is the flow that has been treated by the ultra-purification unit. The other stream from the unit contains the impurities that have been stopped and the hydrogen needed for regeneration. By fully recovering this flow, we mean that no molecule of H2 is lost but that all of it is recycled in the hydrogen production unit. This recycling is done here without the need to install a compression machine. This means that the impure hydrogen is injected at an appropriate location in the hydrogen production unit depending on its pressure and composition. We therefore do not retain here the fact that the residual hydrogen can be burned to provide part of the calorific needs.

By purification unit at ambient temperature, it is meant that the supply of this unit is done, according to the local climatic conditions in the range going from approximately -10°C to +50°C, and this as opposed to cryogenic purifications (T < -40°C) or at high temperature (T > 150°C).

According to one embodiment, all the hydrogen molecules of the residual fraction of the unit are reinjected into the hydrogen production unit in order to ensure the required production.

According to one embodiment, the pressure of the purified hydrogen from the unit is substantially the same (except for pressure drops across the adsorption unit) as the pressure of the hydrogen from the PSA H2 supplying said unit.

According to one embodiment, the hydrogen-rich stream from the PSA H2 of the hydrogen production unit comprises at least one constituent X other than hydrogen at a content Y (mole) and that the content of X in the hydrogen purified product produced by the adsorption unit is then less than or equal to Y/5, preferably Y/10, even more preferably less than or equal to Y/50.

According to one embodiment, constituent X is part of the group consisting of CO, CH4, N2, Ar, O2, preferably constituent X being CO and/or N2.

According to one embodiment, the CO is present at a content equal to or greater than 10 ppm in the hydrogen resulting from and at a content less than or equal to 0.5 ppm in the purified hydrogen.

According to one embodiment, the production of purified hydrogen can be continuous or periodic depending on the demand or the purification process implemented.

According to one embodiment, the adsorption unit is a PSA type unit.

According to one embodiment, the elution and/or the repressurization of the unit is carried out at least in part by purified gas from said unit.

According to one embodiment, the waste gas from the unit is recycled in the PSA H2 as elution and/or repressurization gas.

According to one embodiment, the adsorption unit is a TSA type unit.

According to one embodiment, the gas used for the regeneration of the unit, for the cooling step and/or the heating step and/or a possible repressurization step is a fraction of the purified gas.

According to one embodiment, the gas for regeneration and any depressurization of the unit is recycled in the PSA H2 as elution and/or repressurization gas.

According to one embodiment, the gas used for the heating step of the unit is a fraction of the gas from the PSA H2 and in that it is then reinjected into the production line from the PSA H2 downstream of the tapping powering the unit.

The invention also relates to a hydrogen production installation comprising in series a PSA H2 and an ultra-purification unit by adsorption at ambient temperature, characterized in that:

• the unit treats a minority fraction of less than 50% and preferably 1% to 25% of the H2 flow from the PSA,
• at least one of the constituents present in the flow from the PSA H2 has its content divided by at least a factor of 5 at the purification outlet,
• the residual gas loaded with impurities from said purification is fully recovered in the hydrogen production unit, without requiring its own compression means.

The invention will be better understood on reading the following description and on examining the accompanying figures. These figures are given only by way of illustration but in no way limit the invention.

The is a schematic representation of solutions for producing purified hydrogen from 99+% mole 1 hydrogen from a PSA;

The is a schematic representation of a hydrogen production unit according to the invention;

The is a schematic representation of a first embodiment of a unit according to the invention;

The is a schematic representation of a variant of the unit of the ;

The is a schematic representation of a second embodiment of a unit according to the invention;

The is a schematic representation of a third embodiment of a unit according to the invention;

The is a schematic representation of a fourth embodiment of a unit according to the invention;

The is a schematic representation of a final purification unit of the PSA type of the unit of the ; and

The is a schematic representation of a variant of the final purification unit of the .

We have seen that the ultra-purification unit makes it possible to increase the purity of a fraction of the hydrogen from the PSA. It is possible, for example, to have respectively contents of 99.9% and 99.995 or respective contents of 99.995 and 99.999 or even 99.999 and 99.9999.

The increase in purity can also relate to a single constituent, for example obtaining hydrogen with less than 50 ppm of nitrogen from a main production containing 1000.

The principle of the invention is represented on the .

The feed 1 of the hydrogen production unit P can be a source containing hydrogen, such as a waste gas from a petrochemical unit, compressed and/or pretreated in the unit S or a hydrocarbon for example reformed with steam in the unit S to give a synthesis gas (“syngas” in English) rich in hydrogen, or even for example methanol also giving by reaction in the unit S a stream containing hydrogen.

The residual 30 from the final purification unit A contains, in addition to the hydrogen, the impurities contained in the fraction 21 of the gas from the PSA H sent to the unit A with a content depending on the concentration factor linked to the operation of said unit. .

This diagram shows the different possibilities for injecting and recovering this waste 30: in supply 1 of unit P via line 35, at the level of the pre-treatment unit via line 34, upstream of PSA H via line 33 if there is already a compression means, in PSA H via line 32, in the main production of hydrogen at 99+% mole via line 31.

We can also, if there is interest, reinject this fraction in 2 separate places depending on its composition or pressure.

The hydrogen contained in the fraction 30 enriched in impurities from unit A therefore returns in full to the hydrogen production unit P to be recovered there without the use of any compression means which would be specific to this recycling.

As described, this then means that the impurity-enriched gas will:

• either be used in one of the equipment of the hydrogen production unit (P) at the availability pressure instead of or in addition to another process stream, in particular in the PSA (H);
• either be injected at the suction or at an intermediate stage of a compression means already existing in the hydrogen production unit P (three potential compressors have thus been represented which could be used for this purpose, the compressors being represented in the form of a triangle on the ); it is recalled that the flow of purified hydrogen is generally low, often of the order of 5 to 10% of the total production of hydrogen and that under these conditions, the flow to be recycled represents only a few percent of this production and even less relative to the supply gas;
• or be produced under pressure and constitute all or a fraction of the least pure hydrogen production.

As for the purified hydrogen from unit A, its pressure will be substantially the same (to the pressure drops through the adsorption unit A near) as the pressure of the hydrogen from the PSA H2 H supplying said unit A. The pressure difference between the 2 H2 streams can be reduced to less than 50 mbar for example.

The hydrogen-rich stream from the PSA H2 H of the hydrogen production unit P comprises at least one constituent X other than hydrogen at a content Y (mole) and the content of X in the purified hydrogen produced by adsorption unit A is then less than or equal to Y/5, preferably Y/10, even more preferably less than or equal to Y/50. The PSA will therefore have been optimized to produce, for example, hydrogen with 50 ppm of constituent X, which corresponds to the Customer's request for the major part of the flow, whereas the specification for a fraction of the hydrogen production could be 10ppm, 5PPM, or even less than 1 ppm. The yield of a PSA sized to produce hydrogen with an impurity content X of 50ppm is significantly higher (one to two points for example) than that of a PSA sized for a content lower than one ppm.

Constituent X is part of the group consisting of CO, CH4, N2, Ar, O2, preferably constituent X being nitrogen and especially CO often present at a content equal to or greater than 10 ppm in the hydrogen from H and at a content less than or equal to 0.5 ppm in the purified hydrogen.

CO is often incompatible with certain hydrogen-using processes and for these applications, the specifications concerning it are therefore generally the most restrictive. It is therefore this constituent which is often the "dimensioning" constituent for the PSA. Relaxing its specification saves money on the H2H production unit.

The fraction of purified hydrogen from the adsorption unit A represents less than 50% of the quantity of hydrogen from the PSA H2 H of the hydrogen production unit P, preferably less than 25%, even more preferably less than 10%. The majority of potential applications will be in the 1% to 25% range.

The most recent hydrogen production units generally supply very large H2 flows either for petrochemical units where generally a content of 99.5 or 99.9 mol% is sufficient, or for a network with contents of the order of 99.99% and a constraint on CO, generally between 50 and 10ppm.

The higher contents, 99.999 or even 99.9999+, or presenting a particular constraint for a particular constituent, such as CO, are rather due to particular units requiring a few hundred or a few thousand Nm 3/h; It can also be a question of supplying a packaging center (gas in bottles or cylinders) and here too the flow rates involved are of the same order.

Fuel cells are also very sensitive to CO and this constituent must be lower than the ppm to ensure sufficient operation.

Compared to units producing more than 100,000 Nm3/h, the production of pure gas may only represent a few percent. It is then all the more interesting to use a final purification unit on a small flow and to produce most of the gas just to the required specification.

It should be noted that the production of high-purity hydrogen can be continuous or periodic depending on the request or the purification process implemented, the quantity of hydrogen from the PSA H2 H available then varying accordingly. This will be the case in particular if this hydrogen supplies a packaging center or is used to fill rolling tanks intended for private customers.

According to one of the most frequent variants, the hydrogen production unit P comprises at least one synthesis gas production unit, preferably a hydrocarbon steam reforming unit, and a PSA H2 unit and in that the fraction enriched in impurities from unit A is sent as fuel to the syngas production unit, thus replacing natural gas, and/or as complementary gas to the suction (or to an intermediate stage) of a gas recycling compressor to the pressurized process gas line upstream of the PSA H2 H.

This last solution will for example correspond to the case where part of the PSA residual is recycled in the PSA feed gas to increase the production of hydrogen, this recycling being done directly or via a permeation unit. .

According to another variant, the preceding hydrogen production unit P also comprises a unit for at least partial capture of the co-produced CO2 and the fraction enriched in impurities from unit A is then recycled by means of a compressor used in the frame of this capture.

When the production unit P is supplied from a source of gas already containing hydrogen available in sufficient quantity but at a pressure P1 lower than the pressure P2 required for the main production of hydrogen, it comprises among other equipment, a compressor compressing the gas from said source at least up to the supply pressure of the PSA H2 H and the fraction enriched in impurities from unit A, at a pressure equal to or greater than P1, can be sent as complementary gas to the suction (or to an intermediate stage) of the compressor.

This will generally be the case when the raw source of hydrogen is the waste gas from an electrolysis unit intended to produce chlorine.

We then have at a pressure P1 close to atmospheric pressure a flow very rich in H2 but containing traces of mercury, chlorine, oxygen (and nitrogen) due to air ingress, micro salt dust. A part of these impurities is stopped in a pretreatment located before and/or after compression. The compression is done in several stages up to the pressure P2 and the waste gas from purification A is then injected at the suction or at an inter-stage of this compressor.

As described previously, the ultra-purification unit A proposed here is a gas separation unit by adsorption. Adsorption makes it possible to obtain an almost total stoppage of the residual impurities of hydrogen. Two processes are likely to be used: unit A can be either a PSA-type unit or a TSA-type unit.

Those skilled in the art will choose the best solution depending on the flow to be treated, the impurities to be stopped, the periodic or continuous operation of the ultra-purification unit A, the possibilities of recycling the impure H2 fraction in the unit production p.

A TSA will probably be the best solution in the event of a low flow to be purified, for example only a few percent of the flow from the PSA H, in discontinuous operation. Conversely, a PSA will be used instead in the event of a higher flow rate, continuous operation, a substantial quantity of impurities to be stopped, for example if the content of an impurity must be divided by 50.

The operation of a PSA type unit has already been described.

As for a unit of the TSA (Temperature Swing Adsorption) type, it is characterized by an adsorption stage at the pressure of the feed gas to be purified and a more or less complex regeneration stage but calling for an increase in temperature to desorb the impurities previously stopped by the adsorbent generally at room temperature.

The heating can be done at any pressure, in particular at a pressure close to the adsorption pressure (within pressure drops) or at low pressure, which facilitates regeneration. In the latter case, the TSA cycle then includes a depressurization sub-step (from the adsorption pressure to the regeneration pressure) and at the end of the cycle a repressurization sub-step. There is also usually a cooling sub-step following the heating.

The waste gas from PSA-type unit A or the gas for regeneration- and possible depressurization- of TSA-type unit A is preferentially recycled in the H2H PSA, i.e. uses the fact that the PSA H2 has stages at various pressures between the high and the low pressure of the cycle to inject the gas loaded with impurities from the purification unit A.

Preferably, the waste gas from unit A of the PSA type or the gas for regeneration and possible depressurization of the unit A of the TSA type is used at least in part as the elution gas of the PSA H2H.

The waste gas from PSA-type unit A or the regeneration (and possible depressurization) gas from TSA-type unit A can also be used, at least in part, as repressurization gas for the PSA H2H.

By repressurization, we mean here the so-called repressurization steps themselves but also possibly the balancing steps.

When choosing a PSA type unit for purification unit A, it is preferable to choose a simple cycle, favoring investment. Given that the waste from said unit A is reused and recovered in one way or another, the performance of this latter unit is secondary.

In this way, the elution of unit A of the PSA type is carried out at least in part by purified gas from said unit A.

Similarly, the repressurization of unit A of the PSA type is done at least in part by purified gas.

Unit A of the PSA type can comprise from 1 to 6 adsorbers, preferably from 1 to 4 adsorbers.

As a variant, unit A can comprise as many adsorbers as the main PSA H2 unit. This can facilitate its integration into the control-command system or even its physical integration into the main adsorber. This point will be detailed in the examples.

The PSA type unit A contains an adsorbent material comprising at least one of the adsorbents of the activated alumina, silica gel, charcoal, zeolite group and among the zeolites preferentially the exchanged zeolites of type A or X such as CaX, CaLSX, LiX, LilSX, BaX, BaLSX as well as silver and/or copper exchanged zeolites.

The gas used for the regeneration of the TSA type unit A, for the cooling step and/or the heating step is generally a fraction of the purified gas but alternatively, the gas used for the heating step of the TSA type unit A can be a fraction of the gas from the PSA H2 H which is then reinjected into the production line from the PSA H2 H.

The heating then takes place under pressure.

The gas used for possible repressurization of unit A of the TSA type is a fraction of the purified gas.

Unit A of the TSA type comprises 1 to 3 adsorbers, preferably 2 adsorbers.

Unit A of the TSA type contains an adsorbent material comprising at least one of the adsorbents of the activated alumina group, silica gel, carbon, zeolite A and/or X and among the zeolites, preferentially the exchanged zeolites CaX, CaLSX, LiX, LilSX , BaX, BaLSX as well as silver and/or copper exchanged zeolites.

The method according to the invention will now be explained in detail based on the following examples.

The describes a first example and the describes variants of this first example.

The hydrogen production unit P comprises a source S of pressurized impure hydrogen 1 which can be a unit for the production of synthesis gas or for the pretreatment and compression of a waste gas from a petrochemical unit which supplies the gas supply 10 to the PSA H2 H,2 unit which produces hydrogen 20 of 99+% purity, which after possible filtration to a threshold below 50 microns through filter 3 will supply 27, 28 the hydrogen network 90. This flow 28 here represents 90% of the flow from the PSA H and corresponds to a first specification of the hydrogen with a CO content less than or equal to 10 ppm allowing an H2 extraction yield from the PSA H of 89.5% very close to the maximum yield attainable.

Unit P also produces 10% hydrogen with a second specification corresponding to a maximum CO content of 0.5ppm and injected via 24 into the ultra-pure network 100.

This secondary purification A is carried out by a TSA 4 unit comprising, in this example, three adsorbers: 41 in the purification phase, 42 in the regeneration-heating phase and 43 in the cooling phase.

A flow corresponding to 13% of the total flow of hydrogen from PSA H is withdrawn via line 21. The majority of this flow (10% of the flow from PSA H) is directed via line 22 to adsorber 41 at through which it is purified so that the residual CO content is less than 0.5 ppm.

This flow passes through line 23 and cools the previously regenerated adsorber 43. At the output, this flow constitutes ultra-pure hydrogen and via line 24 joins the High Purity 100 customer network.

The remaining 3% of hydrogen taken from the production of PSA H passes via line 25 through heater 5 then regenerates at a temperature of the order of 80/120°C adsorber 42 previously saturated during the phase time previous. The gas loaded with impurities, mainly CO in this example, is reinjected, via line 26, into most of the PSA H production and the whole constitutes the main production of hydrogen (90% of the PSA flow) which joins the H2 90 hydrogen network. The pressure drop of the regeneration/heating circuit is very low and the reinjection into the main flow will generally be energetically free. This is all the more true as normally the hydrogen from the PSA H is filtered (to 50 μ or less) and this filter 3 causes pressure drops on the direct production line 27 greater than those of the regeneration circuit allowing the required flow rate to flow through adsorption unit A.

The diverted flow is filtered in the filters integrated into the adsorbers 44, 45, 46.

The regeneration flow representing only 30% of the adsorption (and cooling) flow, it is understandable that the pressure drops are negligible.

To produce 1000 Nm3/h of ultra-pure hydrogen, it was estimated that in this case it would be necessary to install three adsorbers of about 3 m ³ , for a phase time of 150 minutes. The investment and energy consumption are significantly lower than those of cryogenic purification, a metal membrane and more generally any system requiring the addition of a compressor.

A number of remarks should also be made:

• If the PSA H produced hydrogen at a content of exactly 10 ppm, the main production would have a content of around 11 ppm due to the additional purification; in this case, therefore, the PSA must produce with a CO content of 9 ppm to meet the purity specification. In practice, this does not change the gain that can be expected from purification by additional adsorption compared to production at 0.5 ppm for the entire flow; the calculation of the purity required at the PSA H outlet according to the respective purities and flow rates of 99+% hydrogen and ultra-pure hydrogen is obvious and will not be further detailed here;
• The and the are particularly schematic: all the circuits (piping and valves) allowing continuous operation are not shown for the sake of clarity but it should be remembered that TSA type operation is cyclical and that each adsorber passes successively through the different phases : adsorption, heating, cooling; similarly, the transient or secondary steps have not been described, contributing nothing to the understanding of the process; for the record, these are, for example, steps of the paralleling type (to avoid any cut in the flow rate), sweeping between heating and cooling (to eliminate the CO from the interstitial zones of the adsorber);
• There may be discontinuous cycles with a single adsorber successively linking the different phases, cycles with 2 adsorbers with an adsorption phase and a heating/cooling phase; similarly, the cooling can be carried out with only part of the purified flow; if the pressure drops allow it, the regeneration flow can successively cool an adsorber then heat the last one; in practice, any of the TSA cycles known in the literature can be used.

As a variant, we will indicate ( ), the case where the pressure of the hydrogen produced by the PSA H is lower than the pressure of the H2 network 90. In this case, it will be necessary to compress the hydrogen from P1 to P2 via the compressor 6.

The additional purification can in this case be done at the pressure P2 and the regeneration flow 26 be injected at the suction of the compressor at the pressure P1 (or possibly at an inter-stage pressure), or even at the inlet of the PSA H respectively via the dotted lines 60 or 61.

The common point of the example and the variants quoted is:

• that the PSA H is sized on the least restrictive purity, possibly taking into account the presence of impurities removed from the purified flow, that is to say with the best possible performance, for example 89.5% extraction yield, instead of a yield of the order of 87% or less if the hydrogen were to be produced at 0.5 ppm of CO; and
• that the hydrogen used for the regeneration of the TSA is fully used, leading to zero losses.

The describes a second example.

The hydrogen production unit P comprises a synthesis gas production unit 1 which supplies the feed gas 10 to the PSA H2 H unit which produces the hydrogen 20 which, after optional filtration, at a threshold below 50 microns will feed the 90 grid with 99+% hydrogen via stream 28.

This flow represents 90% of the flow from the PSA H and corresponds to a first specification of the hydrogen with a CO content less than or equal to 10 ppm allowing an H2 extraction yield from the H PSA of 89.5% (the extraction yield is called , or more simply efficiency, the ratio of the quantity of pure counted hydrogen contained in the production to the quantity of hydrogen contained in the feed gas).

Unit P also produces 10% hydrogen with a second specification corresponding to a maximum CO content of 0.5ppm and injected via 24 into the ultra-pure network 100.

This additional purification is carried out by a TSA 4 unit comprising two adsorbers: 47 in the purification phase and 48 in the regeneration phase, the operation of which will not be detailed here.

The waste from this treatment is produced at low pressure via line 26.

The recycling of this stream in the syngas unit 1 can be done in different ways.

In a preferred variant, the residual flow is recycled in the main gas flow (also called "process gas") between the supply of the SMR 11 and the inlet of the PSA H by taking advantage of an existing compression means.

The effectively represents the case where the PSA H residual (line 70) is compressed by compressor 7 and sent to permeator 8 via line 71.

The hydrogen-enriched 80 permeate is reinjected at the PSAH inlet, increasing hydrogen production. In this case, the residual from the adsorption unit 4, the stream 26 is injected at the suction of the compressor 7.

Via the permeate 80 of the membrane, it then joins the inlet of the PSA H.

It will be noted that this PSAH residual recycling process also exists without using the permeator 8.

In this case, only a fraction of the residual is recycled in this way, the remainder constituting the purge. This type of process is described for example in the documents FR 2682611 B1 or EP 1023934 B1.

The important point is that there is then a compressor and that the latter can be used to recycle the residual hydrogen from the complementary purification A.

It will be noted in the second example that the final purification unit by adsorption can also be a unit of the PSA type, the stream 26 then corresponding to the residual of this PSA and that the PSA H comprising the direct recycling of a fraction of the residual or recycles it via a permeation unit are particularly favorable for the reinjection of the residual from the additional purification A, the same product at low pressure and therefore for the production of an ultra-pure H2 fraction alongside the main production of hydrogen.

The describes a third example.

In this third example, the hydrogen production unit P includes a CO2 capture unit.

Among the large number of diagrams proposed, to describe the integration of the adsorption unit 4 according to the invention, the one corresponding to patent EP 2 432 732 B1 has been retained. The residual PSA H is compressed via the compressor 11 before being sent to the inlet of the PSA CO2 12. The CO2-depleted gas 15 passes through the membrane 18; the hydrogen-enriched gas, on the permeate side, is sent to the second compressor 26 and is injected upstream of the PSA H.

With this CO2 capture scheme, the residual from the adsorption unit 4 can be injected preferentially at low or medium pressure according to the ultra-purification process at the suction of the compressor 26 via the line 30 or possibly by low pressure at the suction of compressor 11 via line 31. In the latter case, the reinjected hydrogen will pass through the PSA CO2 while being unadsorbed and then will permeate into the membrane 18.

In another variant, said residual from the complementary adsorption unit A is injected into the suction of the compressor 21 via line 32 and then joins the supply of the steam reforming unit producing the rich synthesis gas in hydrogen.

In general, the CO2 capture units comprise at least one of the units of the group: cryogenic cold box, PSA, H2-selective membrane, CO2-selective membrane, and most often at least two of these units.

Whatever the diagram, there is a compressor making it possible to recycle the residual material from the adsorption unit 4 in a useful way, even if it is available at low pressure.

It may be noted that in some cases, the CO2 capture unit is placed upstream of the PSA H as described for example in document US 8746009 B2.

In these cases too, there is a compressor allowing the recycling of the residual from the final purification 4.

The describes a fourth example.

We limited ourselves to representing on the an adsorber of the PSA H unit in the elution phase, the adsorber marked 2i as well as the adsorber 2k providing if necessary part of the elution flow rate of 2i.

Unit 4, assumed here to be of the PSA type, comprises an adsorber marked 4j itself in the elution phase.

The elution gas from adsorber 4j comes from another adsorber 4k in the phase of supplying elution gas during its co-current depressurization.

According to the principle of the invention, the gas at the outlet of the adsorber 4j will be used to ensure at least in part the elution of the adsorber 2i and thus return to the normal cycle of the PSA H.

It should be noted that a very simple cycle can be chosen for the PSA 4 because the yield does not matter in this case. The hydrogen lost at the level of unit 4 is used in the upstream unit H. The PSA corresponding to the final purification unit 4 may thus have from 2 to 4 adsorber, or even a single adsorber if the production of ultra-pure hydrogen can be discontinuous. The elution can be done, in the simplest cycles, with a fraction of ultra-pure hydrogen. Depending on the complexity of the PSA (and therefore its cost), ultra-pure gas extraction yields of 90 to around 50% can be obtained.

We will also note:

• that we can reinject in the same way the waste from a final purification which would be of the TSA type;
• that depending on the pressure of this residual (from the final purification unit of the PSA or TSA type), it can be made to participate at least in part in the repressurization of at least one adsorber of the PSA H unit , together or in lieu of forming eluting gas;
• that the extraction yield of the complementary unit A not being fundamental since all the hydrogen lost at this level is recycled, rapid PSA cycles (RPSA), that is to say with cycle times of the order of a minute or ultra-rapid PSAs (VRPSAs) with cycle times of a few seconds, in particular rotary PSAs can advantageously be envisaged;
• that for the same reason, in the case of TSA, one could afford higher regeneration flow rates than usual, for example flow rates of the order of 50% of the supply gas of said unit and therefore use short cycles, for example cycle times (purification + regeneration) of less than one hour.

The advantage of the last two points mentioned is obviously a reduction in the size of the additional adsorption unit A and therefore in the corresponding investment.

As already explained, the common point of these examples and the variants cited is:

• that the PSA H is sized on the least restrictive purity, taking into account if necessary the presence of impurities removed from the purified stream and possibly reinjected into the main stream, that is to say with the best possible performance, for example at least 89.5% extraction yield, instead of a yield of the order of 87% and less if the hydrogen were to be produced at 0.5 ppm of CO;
• that the hydrogen used for the regeneration of TSA 4 or the hydrogen constituting the residue of PSA 4 is entirely used in the hydrogen production unit, leading to zero losses;
• that in the event of recycling requiring an increase in the pressure of the residual from the ultra-purification unit A, this is carried out using an existing compression means, thus avoiding a significant investment. This will be the case in particular in units where part of the residual PSA H2 is recycled at the inlet of said PSA H2, directly or via a permeation unit, in the case where this residual is recycled to the very supply of the hydrogen production unit; this is also the case for hydrogen production units with even partial capture of the co-produced CO2.

Figures 7a and 7b represent a particular integration of the final purification unit A of the PSA type corresponding to the fourth example.

The adsorbent material of said purification (for example bed 40i) is placed at the upper part of the PSA H2H adsorbers (for example above bed 20i).

The main streams enter and leave via the intermediate output s1.

Ultra-pure hydrogen is produced at the top via s2.

This tubing is also used to perform elution and repressurization by ultra-pure hydrogen of the head zone.

Such a configuration avoids the need for a second adsorption unit, but the overall operation is a little more complex. In practice, only part of the PSA H adsorbers could be modified in this way.

The simplest regulation consists of installing an additional bed per main adsorber, drawing off the ultra-pure gas from the adsorbers in production, letting the depressurization stages take place naturally and injecting a flow of ultra-pure gas during the rise in pressure in order to prevent gas coming from s1 or the main adsorber from rising in the additional part.

The coupling of two PSAs is known to those skilled in the art and the various means and/or processes that can be implemented to produce the two required fractions will not be further detailed here.

As the flow rate of ultra-pure hydrogen is generally lower than the flow rate at 99+%, the head section can be reduced as shown in .

The adsorbent 40i can be in the form of a contactor (monolith, wheel, etc.).

It is recalled in conclusion that the principle of the invention is limited here to the production of hydrogen but that it could be applied to other gases, in particular for the supply of an ultra-pure fraction of argon, helium or various gases when the fraction to be purified represents only a small fraction of the total production, in particular of the order of 1 to 25%.

Claims (2)

Process for the ultra-purification of a fraction of the hydrogen resulting from a PSA H2 (H) included in a hydrogen production unit (P) intended to supply mainly hydrogen at 99 +% mol, at the means of a unit (A), characterized in that:

• unit (A) is a room temperature adsorption purification unit,
• the fraction purified by means of unit (A) represents less than 50% of the production of unit (H), preferably a fraction of between 1% and 25%,
• the residual fraction enriched in impurities from said unit (A) returns to the hydrogen production unit (P) to be fully recovered there without the use of any compression means specific to this ultra -purification.

Hydrogen production installation comprising in series a PSA H2 (H) and an ultra-purification unit by adsorption (A) at ambient temperature, characterized in that:

• unit (A) processes a minority fraction of less than 50% and preferably 1% to 25% of the H2 stream from the PSA (H),
• at least one of the constituents present in the flow from the PSA H2 (H) has its content divided by at least a factor of 5 at the purification outlet (A),
• the residual gas charged with impurity from said purification (A) is fully recovered in the hydrogen production unit, without requiring a compression means of its own.