Process for treating a gas containing a contaminant

Abstract

The present invention relates to a method for removing at least one contaminant from a gas to be treated by means of a temperature-modulated adsorption treatment unit with regeneration. The treatment unit comprises at least a first adsorber, a second adsorber, and a third adsorber, each containing, respectively, a first set of regenerated adsorbent beds, a second set of regenerated adsorbent beds, and a third set of contaminant-loaded adsorbent beds. The method allows for improved energy integration and enhanced purification. The invention also relates to an associated gas treatment unit. Figure 2 to be published

Description

Title of the invention: Method for treating a gas containing a contaminant Technical field

[0001] The present invention relates to a method for treating a gas containing at least one contaminant with a view to purifying it by means of a temperature modulation treatment unit using adsorbents.

[0002] In the context of the invention, the gas to be treated is in particular natural gas, CO2 or hydrogen, preferably hydrogen, and the contaminant to be eliminated is preferably water. The method according to the invention is characterized by the fact that it does not use a recirculation compressor (also called a "recycle compressor") to carry out the adsorbent regeneration step and meets the energy optimization objectives. The method is in particular suitable for drying hydrogen extensively, for example for specifications below 1 ppmv (parts per million by volume) for liquefaction, or up to 5 ppmv, in particular for hydrogen used for mobility.

[0003] Throughout this text, the following terms are understood to mean:

[0004] TSA (“Temperature Swing Adsorption”) an adsorber implementing adsorption by thermal modulation.

[0005] PSA (“Pressure Swing Adsorption”) an adsorber implementing pressure swing adsorption. Prior art

[0006] A known method for the advanced drying of water-saturated gas in the natural gas industry but applicable to hydrogen and CO2 consists of using a TSA (thermal switch adsorption) process with an adsorbent (for example, of the 3A, 4A or other molecular sieve type, zeolites, or for less stringent specifications, alumina or silica gel) in order to obtain residual water contents less than or equal to 500 ppmv, 100 ppmv, 5 ppmv or even 1 ppmv. The treatment scheme most often comprises two adsorbers: an adsorber in the adsorption phase and an adsorber in the regeneration phase (which requires a heating step, then cooling of the adsorbent bed).Regeneration of the adsorbent is essential in this case and in order to achieve the required specifications, it is customary to regenerate the water-saturated sieves at the end of the adsorption cycle using a dry regeneration gas when seeking to achieve a water content of less than or equal to 10 ppmv.

[0007] While the adsorption of components contained in a gas mixture by ad- While the desorption of solid sorbents is an exothermic process, the desorption process is endothermic. This process of desorption of the component is achieved by applying heat to the adsorbent and the adsorbed phase. Thus, when the applied heat is sufficient, the adsorbed components desorb from the adsorbent. To complete the regeneration, the adsorbent must be cooled to a temperature close to its initial temperature. These steps of heating and cooling the solid adsorbent constitute the step called "regeneration".

[0008] The standby phase which is an integral part of the end of regeneration is not described for the sake of simplification, but it must be added to the heating and cooling steps to meet the criterion that the regeneration time is equal to the adsorption time.

[0009] Figure 1a shows a schematic diagram of a drying process using the TSA process with regeneration by dry gas using a recirculation compressor. In this case, a percentage of the dried gas flow from the adsorption phase in adsorber B1 is used to regenerate the second adsorber B2 in the regeneration phase and requires the use of a compressor to send the dried gas into adsorber B2. However, this flow must then be recycled to the inlet of the sieve in the adsorption phase.

[0010] This prior art method has the disadvantages of increasing the capacitive cost (CAPEX) of the unit: - the implementation of a recirculation compressor implies that the volume of adsorbent required is increased proportionally to the regeneration gas flow rate. - The process requires the installation of at least one recirculation compressor, often with a second compressor as backup.

[0011] The use of a compressor also has an impact on the operating cost (OPEX): - an additional volume of adsorbent per adsorber means more calories to be supplied in the regeneration-heating phase; - the energy consumption to operate the compressor.

[0012] This therefore increases the overall carbon footprint of the process.

[0013] According to another method known from document EP 2809752, which implements a treatment unit comprising three adsorption adsorbers, the adsorption step is carried out in a first adsorber and concomitantly the regeneration step of the second and third adsorbers is carried out in which one of them is in the desorption phase by passing a stream of treated gas heated to a required temperature so that the adsorbed contaminants are eliminated from the bed, while the other adsorber which has already undergone the desorption phase is in the cooling phase by passing a portion of the cold untreated gas.

[0014] With reference to Figure 1b, the natural gas treatment process implements a TSA unit with three adsorbers (first adsorber in adsorption (14), a second adsorber (18) in regeneration / cooling mode (“cooling”) and third adsorber (16) in regeneration / heating mode (“heating”). A portion (“slip stream”) of gas to be treated (13) is used to cool the adsorber (18) from which the treated effluent (20) is withdrawn, which is heated and sent to regenerate the adsorber (16). The gaseous effluent (26) from the adsorber (16) in regeneration is cooled and treated in a PSA unit (40). Summary of the invention

[0015] The present invention makes it possible to improve the processes according to the prior art in terms of capacity and operating costs (CAPEX and OPEX) by proposing an alternative method of regenerating the adsorbent beds in a thermal modulation adsorption process while ensuring thorough decontamination of the gas to be treated during the adsorption phase.

[0016] The invention relates to a method for removing at least one contaminant contained in a gas to be treated by means of a treatment unit by adsorption by temperature modulation and regeneration, the treatment unit comprising at least a first adsorber, a second adsorber and a third adsorber respectively containing a first set of regenerated adsorbent beds, a second set of regenerated adsorbent beds and a third set of adsorbent beds loaded with contaminant, the method comprising the following steps carried out concomitantly: a) a first flow of gas to be treated is brought into contact in the first adsorber with the first set of regenerated adsorbent beds adapted to capture said contaminant and obtain a first flow of purified gas; b) a second flow of gas to be treated is brought into contact in the second adsorber with the second set of regenerated adsorbent beds so as to cool the second set of regenerated absorbent beds and obtain a second flow of purified gas; c) heating said second purified gas stream to a temperature sufficient to achieve desorption of the contaminant; d) bringing into contact, in the third adsorber, the second flow of purified gas heated in step c) with the third set of adsorbent beds loaded with contaminant so as to desorb the contaminant adsorbed by the third set of adsorbent beds and obtain a third flow of gas containing the contaminant; e) upstream of step c), a heat transfer is carried out between the third gas flow and the second purified gas flow from step b),

[0017] the pressure in the second adsorber (P3) being higher than the pressure in the first adsorber (PI) and the pressure in the first adsorber (PI) being lower than the pressure in the third adsorber (P2).

[0018] For a specific duration during the regeneration step, the second adsorber (in cooling) can be isolated and steps b), c), d), e) can be replaced by steps b'), c'), d') and: a) a first flow of gas to be treated is brought into contact in the first adsorber with the first set of adsorbent beds to capture the contaminant and obtain a purified gas; b') a second flow of gas to be treated is heated to a temperature sufficient to achieve desorption of the contaminant; c') the second flow of gas to be treated, heated, is brought into contact in the third adsorber with the third set of adsorbent beds loaded with contaminant so as to desorb the contaminant adsorbed by the third set of adsorbent beds and obtain a second flow of gas containing the contaminant; d') upstream of step b') a heat transfer is carried out between the second gas flow containing the contaminant and the second gas flow to be treated.

[0019] The specific duration advantageously corresponds to the heating duration necessary to desorb the contaminant in the third adsorber.

[0020] The second adsorber can be put back online at the end of said specific duration and steps a), b), c), d), e) can be carried out again.

[0021] In one embodiment, when the temperature of the second purified gas stream from the second adsorber is greater than or equal to the temperature of the third gas stream containing the contaminant from the third adsorber, all or part of the second purified gas stream can be sent to the third adsorber without carrying out a heat transfer with the third gas stream.

[0022] The third gas flow from step d) can be returned to the first adsorber.

[0023] The direction of circulation of the first gas flow to be treated in the first adsorber in adsorption and of the second gas flow to be treated in the second adsorber in cooling can advantageously be co-current.

[0024] Advantageously, the direction of circulation can be from the top to the bottom of the adsorbers in adsorption and in cooling.

[0025] The gas to be treated can be chosen from CO2, natural gas, hydrogen produced by electrolysis of water or by treatment of natural gas by steam reforming.

[0026] The contaminant may be water.

[0027] Heat exchange step e) can be carried out directly or indirectly.

[0028] The adsorbent may comprise at least one material selected from silica, silica gel, alumina, silica-alumina and zeolite.

[0029] The invention also relates to a unit for treating a gas by adsorption by temperature modulation for implementing the method according to any one of the variants described, comprising: - at least a first absorber, a second absorber and a third adsorber respectively containing a first set, a second set and a third set of adsorbent beds, each set containing one or more beds of an adsorbent of the same nature or several beds of adsorbents of a different nature; - a first supply line for a gas to be treated connected to the first adsorber to supply the first absorber with gas to be treated; - a first discharge line connected to the first adsorber to discharge a purified gas; - a second gas supply line to be treated connected to the second adsorber to supply the second absorber with gas to be treated; - a second discharge line connected to the second adsorber for discharging a purified gas from said second adsorber, said second discharge line being connected to the third adsorber for supplying said third adsorber; - a heating device for heating the gas contained in the second discharge line before supplying the third adsorber; - a third discharge line for discharging a hot gas from the third adsorber - a heat exchange device capable of transferring heat from the gas contained in the third discharge line to the purified gas contained in the second discharge line, - a pressure relief valve for the gas to be treated upstream of the unit and configured to lower the pressure of the gas to be treated in the first supply line relative to the pressure of the gas to be treated in the second supply line.

[0030] The third discharge line can be connected, downstream of the heat exchange device, to the first supply line.

[0031] The unit may comprise a bypass line from the second adsorber (in cooling), said bypass line being arranged upstream of the expansion valve and connected to the heat exchange device so as to allow heat transfer from the gas contained in the third discharge line to the gas contained in said bypass line.

[0032] The unit may comprise a bypass line of the heat exchange device, said bypass line being arranged upstream of said heat exchange device and fluidically connected to the second adsorber and to the second discharge line which feeds the third adsorber. List of figures [Fig 1]

[0033] [Fig.l] shows the process diagrams according to the prior art:

[0034] Figure 1: schematic diagram of drying by TSA process with regeneration by dry gas using a recirculation compressor.

[0035] Figure 1b: Natural gas treatment process diagram using a three-adsorber TSA unit from document EP 2809752. [Fig 2]

[0036] [Fig.2] represents the principle diagram of the process according to the invention with regeneration by dry gas without compressor and with double energy integration in two sequenced stages.

[0037] Fig. 2a: drying by TSA process with regeneration by dry gas without compressor and with energy integration - regeneration step 1

[0038] Fig. 2b: drying by TSA process with regeneration by dry gas without compressor and with energy integration - regeneration step 2 [Fig 3]

[0039] [Fig. 3] shows a variant of the process diagram according to the invention with hybrid regeneration broken down into three sequenced stages: - Fig. 3a: drying by TSA process with hybrid regeneration by wet gas with double thermal integration - regeneration step 1. - Fig. 3b: drying by TSA process with hybrid regeneration by dry gas without compressor and double energy integration - regeneration stage 2. - [Fig.3]c: drying by TSA process with hybrid regeneration by dry gas without compressor and double energy integration - regeneration step 3. [Fig 4]

[0040] [Fig.4] shows a variant of the process diagram according to the invention with regeneration and cooling with the gas to be treated (for example a wet gas): Fig. 4a: Drying by TSA process without compressor with regeneration by heating a wet gas with simple thermal integration - regeneration step 1 [Fig.4]b: drying by TSA process with wet gas cooling without compressor and simple energy integration - regeneration step 2 Description of the embodiments

[0041] Figures 2, 3 and 4 show a gas drying unit according to the invention, in the case where the contaminant is water. However, it should be noted that the method according to the invention can be applied to remove any contaminant other than water.

[0042] The present invention makes it possible to improve the processes according to the prior art in terms of capacity and operating costs (CAPEX and OPEX) with a thermal modulation adsorption process making it possible to ensure thorough drying of the gas to be treated during the adsorption phase and energetically optimized.

[0043] [Fig.2] shows the principle diagram of drying by TSA process with regeneration by dry gas without compressor and with double energy integration according to the invention.

[0044] The recirculation compressor is eliminated by adding a pressure relief valve VI upstream of the drying unit. Upstream of the valve is drawn a flow which is used to carry out the cooling of the adsorbent already regenerated by heating during a previous step. This cooling flow can therefore be saturated or undersaturated with water (wet gas).

[0045] An additional adsorber (B3) is added to the regeneration circuit in series with the previous one. Thus, an adsorber B1 is in the adsorption phase while, concomitantly, two adsorbers are in the regeneration phase, one of which is in the heating (desorption) phase (B2) and the second in the cooling phase (B3). Adsorbers B2 and B3 are in series in the regeneration circuit. The objective of the additional adsorber B3 is to dry the wet regeneration gas coming from upstream of the expansion valve V1 to be used as dry regeneration gas for adsorber B2.

[0046] The circulation of the wet gas in the bed during the cooling phase is carried out concurrently with the direction of circulation of the gas to be treated during the adsorption in order not to prematurely saturate the adsorbent at the outlet of the bed, which would lead to a water leak during the subsequent adsorption phase (i.e. the next time the adsorber is put into service after it has cooled).

[0047] The circulation of the gas in the adsorption bed is preferably done from top to bottom and the circulation of the dry gas in the bed in the desorption phase (heating) is done from bottom to top to limit hydrothermal aging.

[0048] The invention allows double energy recovery which makes it possible to improve operating costs.

[0049] Initially, at the start of the cooling phase of adsorber B3 and at the start of regeneration / heating of adsorber B2, the hot gas leaving the cooling bed can be used to preheat the bed in the regeneration phase via a bypass line of the heat exchanger (gas / gas) equipped with a valve (V3). A pressure restriction member or equivalent can be installed on this bypass line to force part of the flow into the heat exchanger in order to adjust the temperature of the gas entering the heating device and then into the bed in the heating phase. A person skilled in the art can thus configure the bypass line in order to guarantee a gradual rise in temperature in the bed of the adsorbent in regeneration. This is an “indirect” recovery of the calories stored in the adsorber which has just undergone a previous regeneration step by heating: this energy integration is made possible only by the presence of three adsorbers (one adsorption adsorber, one heating adsorber and one cooling adsorber). It should be noted that during this operational phase, the gas / gas heat exchanger can also be used to transfer part of the calories from the gas leaving the cooling adsorber to the gas from the heating adsorber, i.e. to cool the hot gas from the cooling adsorber to control the heating of the adsorber (B2).

[0050] In a second stage, when the gas leaving the adsorber during cooling is colder than the gas leaving the bed during heating, the bypass is stopped and the valve (V3) is closed in order to thermally integrate the cold gas leaving the absorber B3 with the hot gas coming from the absorber B2 through only the heat exchange device. The gas thus preheated is then sent to a heating device. During this operating phase, the heat recovery exchanger is used to recover calories from the flow leaving the adsorber during the heating phase, that is to say to preheat this time the cold gas coming from the adsorber during cooling.

[0051] The invention provides that this energy integration, of the direct type, can be carried out using a shell and tube (S&T) or compact type (PHE, PCHE) or other exchanger according to those skilled in the art, but that it can also be indirect via, for example, ceramic beds.

[0052] When the heat exchange is carried out indirectly using two ceramic beds, one of the ceramic beds releases the calories captured during a previous desorption step (e.g. B3), the other ceramic bed recovers the calories from the current cycle coming from the adsorber in the desorption phase (heating) via the regeneration gas (e.g. B2).

[0053] The invention thus allows drying to be carried out using the TSA process with regeneration by dry gas without a recirculation compressor and with double energy integration.

[0054] According to the invention, the operating pressure PI of the adsorber in adsorption is lower than that of the adsorber in regeneration in the cooling phase P3 which is itself higher than the operating pressure P2 of the adsorber in the heating phase so that the following relationship is obtained: P1 <P2<P3.

[0055] In one embodiment (see [Fig.3]), taking into account that the cooling phase is shorter than the heating phase, it is possible according to the invention to implement a bypass of the adsorber in the cooling phase B3, thanks to a line (bypass line) equipped with a bypass valve (V2), for a specific duration during the regeneration of the bed of the adsorber B2 in heating and this in order to potentially reduce the volume required by adsorbing by ad- sorbers (CAPEX savings) or to extend the adsorption phases of each ht (OPEX savings)). When the bypass is implemented temporarily, it is then a drying process by a TSA process with hybrid regeneration (i.e. first with a wet gas, then with a dry gas) without a recirculation compressor and with double thermal integration.

[0056] The implementation of this bypass allows the regeneration phase to be carried out in two stages: • initially, regeneration by heating is carried out with a humid gas (Fig. 3a): during this first stage, adsorber B3 (cooling phase) is put on standby, i.e. it is not crossed by a gas then; • in a second step, regeneration by heating is carried out with a dry gas from the adsorber regenerated in the cooling phase (Fig. 3b): during this second step, adsorbers B3 and B2 are in series as explained previously. This second step can be carried out by implementing the thermal integration described above, namely: - the start of this second stage may include bypassing the heat exchanger with all or part of the dry gas from the cooling adsorber, then; - when the gas leaving the adsorber during cooling is colder than the gas leaving the bed during heating, the bypass of the heat exchanger is stopped in order to thermally integrate the cold gas leaving absorber B3 with the hot gas from absorber B2 through the heat exchanger only.

[0057] It is up to the person skilled in the art to determine the maximum possible duration of the bed bypass in the cooling phase in the sequence in order to comply with the following constraints: • at the end of the sequence, the cooling bed must have reached the temperature of the inlet load, with possibly a few more residual degrees. • the bed in the heating phase must have been regenerated for a dry gas over a minimum duration which is set by the person skilled in the art, taking into account in particular the fact that the drying of the wet gas through the bed in the cooling phase will vary during the sequence; the adsorption capacity of the regenerated adsorbent in the cooling phase is initially low when the temperature of the adsorbent bed is still high, but increases as the temperature of the bed drops during cooling.

[0058] In a variant of this embodiment, a bypass of the bed adsorbent in the cooling phase B3 can be set up for several cycles, thus allowing an operating mode with regeneration (heating and cooling) by wet gas when the contaminant specifications for the treated gas are less strict (for example, change of purified gas production campaign). This embodiment with bypass of one of the adsorbers thus offers additional operating flexibility allowing to switch from an operating mode with three adsorbers: one adsorber in adsorption, one adsorber in regeneration / heating and one adsorber in regeneration / cooling, to a mode with three adsorbers: one adsorber in adsorption, one adsorber in regeneration (heating then cooling) and one adsorber stopped at any time. In this configuration, adsorption times are increased and operating costs reduced.

[0059] The modularity of the purification unit according to the invention makes it possible to temporarily or permanently implement one or more operating modes of the unit in order to adapt the operation of the unit with regard to the desired purification specifications.

[0060] In the various embodiments of the invention, the sequencing of the valves is advantageously carried out by servocontrol: the authorizations to open or close the valves are given according to one or more position indicators and as a function of the programmed duration of the sequence. This makes it possible in particular to avoid the risks of cross-contamination.

[0061] A variety of adsorbents can be used in the process according to the invention.

[0062] Suitable adsorbents may include, without limitation, one or more amorphous silica adsorbents (optionally with other components such as adsorbed cations), an amorphous silica-alumina adsorbent (optionally with other components such as adsorbed cations), a high silica zeolite adsorbent (such as zeolite beta, ZSM-5, zeolite Y, or combinations thereof), zeolite A (e.g., zeolite 3A, zeolite 4A, zeolite 5A, or a combination thereof), zeolite X (e.g., zeolite 13X, which is zeolite X that has been exchanged with sodium ions), zeolite Y, alumina, or a combination thereof. In some cases, the zeolite is exchanged with any element from columns I and II of the periodic table, such as Li, Na, K, Mg, Ca, Sr or Ba.As used herein, the term "high silica zeolite" means a material having a silica / alumina ratio, on a molar basis, of at least 5, at least 10, at least 20, at least 30, at least 50, at least 100, at least 150, at least 200, at least 250, at least 300, at least 350, at least 400, at least 450 or at least 500.

[0063] It should also be noted that the adsorbers used in the method according to the invention may comprise one or more beds of adsorbents, for example one, two, three or four adsorbent beds, of the same or different nature depending on the contaminant(s) to be eliminated and depending on the severity of the desired output specification for the purified gas.

[0064] For example, the temperature used for the regeneration of the adsorbent (desorption by heating) is advantageously between approximately 100°C and approximately 300°C. In certain embodiments, the adsorption is carried out at an adsorption temperature between ambient temperature and approximately 50°C, the temperature being of course chosen in accordance with the nature of the adsorbent envisaged and the technical and economic optimization.

[0065] In the event of co-adsorption of a contaminant (other than water) contained in the gas to be treated, and which would accumulate in the regeneration loop, purification, for example by trapping or washing, can be implemented on the gas supply line to be treated or on the regeneration circuit (before or after cooling).

[0066] Description of the figures in the case of the treatment of a gas containing water (drying)

[0067] Figures 2, 3 and 4 illustrate the implementation of the gas treatment method in the case of drying, the contaminant being water, according to different embodiments of the invention (2a, 2b, 3a, 3b, 3c, 4a and 4b). The valves for supplying or stopping supplying the various pipes including the expansion valve VI and the bypass valves V2 and V3 are shown, depending on the configuration chosen, open (white background) or closed (blackened).

[0068] In Fig. 2a, a flow of gas to be treated is supplied via line 1 (for example H2, CO2, natural gas or other gas) saturated or undersaturated with water coming for example from a separation tank where the liquid water has been previously mechanically separated, and enters the purification unit according to the invention.

[0069] An expansion valve (or pressure regulator or pressure controller) V1 divides the flow into a first flow which is sent (lines 2 and 4) to the adsorber B3 in the cooling phase, which has just been regenerated (whose adsorbent bed is still hot) and a second flow which is directed (line 3) to the adsorber B1 in the adsorption phase in order to treat (here dry) said second flow. The adsorption step in the adsorber B1 is carried out from top to bottom. The pressure is reduced at the inlet of the bed in the adsorption phase so that the resulting flow rate of the flow (line 2) is equal to the regeneration gas flow rate determined during the sizing of the unit. The pressure difference or pressure drop in the valve V1 is equal to the pressure drop in the regeneration circuit and is proportional to the square of the regeneration gas flow rate.

[0070] The first flow (line 4) is directed towards the adsorber B3 (previously regenerated and therefore at the end of the desorption phase) to carry out the cooling phase of said adsorber B3. This first flow, saturated or undersaturated with water, is furthermore dried in the through adsorber B3. The flow withdrawn at the outlet of adsorber B3 in the cooling phase (via line 5), which is a gas whose water content will decrease during the cooling of the bed, thus serves as regeneration gas after heating in the heating device (6) for the adsorbent bed of adsorber B2, thus following a thermal regeneration scheme using dry gas.

[0071] The cooling step is advantageously carried out from top to bottom in order to avoid saturating the bottom of the bed with water by the wet gas used while the regeneration step with the heated dry gas is advantageously carried out from bottom to top in order to limit hydrothermal aging of the bed.

[0072] According to an operating mode of the invention, in a first stage of the cooling phase of the adsorber B3 (Fig. 2a) and when the temperature of the gas coming from the adsorber in cooling B3 is higher than that of the gas withdrawn from the adsorber B2 in heating, at least a part of the hot gas (line 5) coming from the absorber B3 in cooling can bypass the heat exchanger used to carry out a heat exchange (described below). In order to control the temperature of the gas flow entering the adsorber B2 in the heating phase, a part of the hot gas is sent to the adsorber B2 via a bypass line of the heat exchange device (20) (equipped with an open valve V3), the heating equipment (6), lines (11), (12) and (13), while the complementary part of hot gas is sent (via line 8) to the heat exchanger (7) equipped with a valve (V4, open) and then mixed with the hot gas of the bypass line (20).The mixture is heated by the heating device (6). According to the invention, a pressure restriction member or equivalent can be placed on the bypass pipe (20) to modulate as desired the temperature of the flow directed towards the heating device (6) then towards the adsorber in the heating phase. During this operating phase, the heating device (6) is: . - either switched off if the resulting temperature of the mixture is higher than the set temperature defined by the heating ramp of adsorber B2 in heating. In this case, over this period the power required by the heating device is zero (saving in operating costs). - either in operation if the resulting temperature of the mixture is lower than the set temperature defined by the heating ramp of the tank in regeneration / heating. However, in this case, the temperature of the mixture at the inlet of the heating device is higher than that expected if valve V3 were closed and therefore makes it possible to reduce the power required by the heating device (6) over this period (saving in operating costs).

[0073] According to the invention and in a second stage of the cooling phase of the adsorber B3 (Fig. 2b) when the temperature of the gas coming from the adsorber in cooling B3 is lower than that of the gas withdrawn from the adsorber B2 in heating, stops the bypass of the heat exchanger (7) (valve V3 is closed) and the entire flow (5) is thus sent (via line 8) to a gas / gas heat recovery exchanger (7) (for example of the shell and tube type or of the compact type (PHE, PCHE)) in order to maximize the recovery of the calories contained in the regeneration gas leaving the adsorber B2 via line (9) which feeds said exchanger.

[0074] The regeneration gas preheated through the exchanger (7) is directed (line 10) to the main heating equipment (6) which can be an electric exchanger powered by green / clean electricity or other technology. The heated flow (line 11), having a temperature compatible with the type of adsorbent (alumina or molecular sieve or silica gel) and with the defined temperature ramp, is then directed (via lines 11, 12) to the bottom of the adsorber B2 in the regeneration phase in order to desorb the water captured during the adsorption phase.

[0075] At the outlet of the adsorber B2, the gas flow (9) loaded with water and whose temperature may be less than or equal to the inlet temperature of the bed in the heating phase, feeds the heat exchanger (7). The flow which leaves it (14) passes through a cooling system (15) which is for example of the ambient air fan type or cooling water exchanger or refrigerant exchanger. The cooled flow containing liquid water passes through a gas / liquid separator tank (16) with or without a mist eliminator mattress where the water is separated from the gas phase. The gas / liquid separation tank (16) can also be placed on the pipe of line 3.

[0076] The head flow of the water-saturated tank is then returned (line 17) downstream of the expansion valve V1 to be mixed with the flow of gas to be treated (3) to finally be dried through the adsorber B1 in the adsorption phase. The flow of dry gas evacuated from the adsorber B1 via the line (18) can then supply a downstream system, for example for particulate filtration and / or recompression or other.

[0077] In another embodiment of the method according to the invention shown in [Fig.3] (3a), the implementation of the invention is identical to that described in Fig. 2a (the flows, pipes and units are identical), with the difference that at the start of the sequence a bypass of the bed in the cooling phase is implemented in the regeneration circuit.

[0078] In the first hours of the regeneration phase, the flow of wet gas (2) is directed towards the adsorber B2 in the regeneration phase (heating / desorption) following a regeneration scheme by wet gas thanks to the installation of a bypass pipe (21) equipped with a valve V2 (open, in white) making it possible to bypass the adsorber B3 which is put on standby for a subsequent cooling phase.

[0079] The flow from the bypass pipe (21) is sent to the heat exchange device (7) in order to recover the calories from the flow leaving via the discharge line (9) of adsorber B2 in regeneration / heating. The regeneration gas preheated through the exchanger (7) is directed to the main heating device (6). The resulting heated flow having a temperature compatible with the type of adsorbent and with the defined temperature ramp, is then directed to the bottom of the adsorber bed B2 (via lines 11, 12 and 13) in order to desorb the water captured during the adsorption phase of adsorber B2.

[0080] In the last hours of the regeneration phase, the bypass valve V2 is closed (in black, in Figures 3b and 3c) and the unit is operated as described previously (Figs. 3b and 3c correspond to Figs. 2a and 2b). The gas flow to be treated (1), taken upstream of valve VI, is directed (via lines 2 and 4) to adsorber B3 (previously regenerated and therefore at the end of the desorption phase) to cool it. The wet flow is therefore dried by passing through adsorber B3. At the outlet of adsorber B3, a gas is obtained from absorber B3 (line 5), the water content of which will decrease during the cooling of the bed, which will serve as regeneration gas for adsorber B2.

[0081] The gas flow from the cooling adsorber B3 is sent at least in part via line (5) to the gas / gas heat exchanger (7), in order to maximize the recovery of calories from the regeneration gas (drawn via line 9) leaving the adsorber B2 in the heating phase. The regeneration gas preheated through the exchanger is directed (line 10) to the main heating device (6). The resulting outgoing flow (line 11) having a temperature compatible with the type of adsorbent is then directed to the bottom of the adsorber B2 in order to desorb the water captured during the adsorption phase.

[0082] In the context of the invention, the isolation ("bypass") via the valve V2 and the bypass pipe (21) of the adsorbent bed in the cooling phase B3 can take place for several cycles, thus allowing an operating mode with regeneration (heating and cooling) by wet gas when the contaminant specifications are less strict (for example between 30 and 50 ppmv). This mode of implementation is described in [Fig.4] (Fig. 4a and 4b).

[0083] With reference to Fig. 4a, the gas to be treated (1) is sent to adsorber B1 from which a treated gaseous effluent is withdrawn from adsorber B1 via line (18). Adsorber B2 is in the regeneration (heating) phase while adsorber B3 is isolated, said to be in "standby" or emergency mode. In order to carry out the regeneration of adsorber B2, a portion of the gas to be treated is sent via line (2), bypass line (21) (valve V2 being open), and lines (8) and (10) into the main heating device (6) in order to bring the gas to a suitable temperature to desorb the water captured in adsorber B2. The hot gas flow is conveyed through lines (11), (12) and (13) into adsorber B2. At the outlet of adsorber B2, the flow loaded with contaminant (water) and whose temperature may be lower than or equal to the inlet temperature of the bed in the heating phase, feeds (line 9) the exchanger (7) in order to provide its heat to the regeneration gas. The cooled flow which leaves the exchanger is sent (via line 14) to a cooling system (15). The cooled flow containing liquid water leaving the cooling system (15) passes through a gas / liquid separator tank (16) where the water is separated from the gas phase. The head flow of the water-saturated tank is then returned (via line 17) downstream of the expansion valve V1 to be mixed with the flow of gas to be treated (3) to be dried through the adsorber B1 in the adsorption phase.

[0084] Once adsorber B2 is regenerated, it is cooled with a wet gas for use in adsorption. This step is shown in Fig. 4b in which adsorber B1 continues to operate in adsorption to treat the gas supplied by line (3). As shown in Fig. 4a, the wet gas taken (line 2) upstream of expansion valve VI is sent to adsorber B2 via line (22), valve V6 being open. Valve V2 of bypass line (21) is closed. As shown in Fig. 4b, the gaseous effluent (line 13) is returned to adsorber B1 bypassing gas / gas exchanger (7). Thus the valve upstream of the exchanger (V4, line 8) is closed and the valve (V5) of the bypass line (19) is open so that the gas flow passes through this bypass line to join the flow exiting via line (14).

[0085] It should be noted that in figures 2a, 2b, 3a, 3b, 3c, 4a and 4b, the adsorption is carried out by injecting the gas to be treated into the adsorber counter-current to the direction of injection of the gas into the adsorber in regeneration / heating while the injection of the gas into the absorber in cooling is done co-currently with the adsorption. Examples

[0086] The objective of this example of a method for treating a gas, here dihydrogen, comprising a contaminant, water, is to compare the diagram of the prior art (case 1 called reference (figure 1a)) with that of the invention (case 2 ([Fig.2])) qualitatively concerning the capacitive cost of the unit (CAPEX) and quantitatively concerning the operating cost of the unit (OPEX).

[0087] For both cases the number of equipment, the required mass of adsorbent (molecular sieve 4A in this example) and the energy required for regeneration are estimated.

[0088] The required energy is taken as the sum of the following terms: - A, the desorption energy of water from the adsorbent - B', the energy transmitted to the adsorber enclosure during the heating phase (increase in the temperature of the mass of the metal in the enclosure

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] the adsorber and the mass of the adsorbent) -B”, the energy lost by thermal transfers to the outside during the heating phase (energy loss) - C, the residual energy lost, i.e. the calories contained in the regeneration gas at the bed outlet which will be lost through the cooler - E, the energy supplied by the heating device (calories supplied to the regeneration gas) [Math.l] E = A + B' * B"* C Parameter B” is essentially fixed by the type and thickness of insulation installed and therefore does not depend on the scheme. Concerning the total mass of adsorbent contained per bed in each case, this is defined as follows: [Math.2] Total M = ml + fh2 - ml is the mass required to dry the given gas flow rate without taking into account recirculations, ml is therefore independent of the scheme considered. - m2 is the additional mass required to process the recirculation of the regeneration gas - Q (gas to be treated) is the flow rate of gas to be treated - Q (regeneration gas) is the regeneration gas flow rate. [Math.3] mi = adsorption time * water content * Q'fgas to be treated] / adsorption capacity [Math.4] = recirculation time * water content * Q (regeneration gas] / adsorption capacity The characteristics of the gas to be treated and the operating conditions of the unit are given in Table 1 below: [Table 1]: Gas Type Hydrogen Unit Dihydrogen (H2) Content Mol% 99.78 (wet basis) Water Content ppmv 2200 Feed Gas Flow Nm3 / h 52,000 Regeneration Flow Nm3 / h 16,000 Adsorption temperature °C 42 Regeneration temperature °C 280 Pressure barg 44 Target water specification ppmv < 1

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] Tables 2 and 3 below present the sequences considered for this example for each of the cases. It should be noted that in the reference case with two adsorbers (Table 2), regeneration must be carried out over the adsorption time. In other words, over a cycle, the adsorption time in adsorber B1 must be equal to the heating time plus the cooling time for the regeneration process of adsorber B2, i.e.: Adsorption time = Heating time + Cooling time = Regeneration time For Tables 2 to 3, the standby time is considered to be zero for simplification in this example. Table 2 shows a regeneration sequence in case 1 with two adsorbers based on 12 hours of adsorption. Reference (comparison) Adsorber 1 Adsorber 2 Sequence 1 0-6h Adsorption Heating Sequence 2 6-12h Adsorption Cooling Sequence 3 12-18h Heating Adsorption Sequence 4 18-24h Cooling Adsorption In case 2, scheme according to the invention; the addition of a third bed modifies the sequence described in the reference case. In the new scheme proposed, two regenerating beds being in series, but one being in cooling and the other in heating, on the same stage, the adsorption time is greater than or equal to the time of a heating phase and a cooling phase. Table 3 presents a regeneration sequence in case 2 with three adsorbers based on 12 hours of adsorption. In the sequence of Table 3 below, the adsorption time is equal to the heating time and the cooling time. For both cases, the adsorption time is set at 12 hours.

[0105] [Tables3] Reference case Adsorber 1 Adsorber 2 Adsorber 3 Sequence 1 0-12h Adsorption Heating Cooling Sequence 2 12-24h Heating Cooling Adsorption Sequence 3 24-36h Cooling Adsorption Heating

[0106] The implementation of the sequence according to the invention has the following consequences: 1- The respective cooling and heating stages of adsorbers B3 and B2 are simultaneous; 2- The duration of the regeneration sequence is therefore doubled compared to the basic scheme (with 2 adsorbers, reference case) thus making it possible to reduce the regeneration flow rate.

[0107] In this example, we will consider that the mass m2 is unchanged between the reference case 1 and case 2, according to the invention. However, it should be noted that an optimization of the mass m2 is possible when sizing the unit.

[0108] Table 4 gives for a drying diagram with recirculation compressor (figure 1a) and for a drying diagram according to the invention (Fig. 2a): - The list of main equipment required (CAPACITIES) - The main design parameters of the adsorbent beds and associated energy consumption over a cycle (OPERATING COSTS)

[0109] [Tables4] Gas type REFERENCE DIAGRAM ACCORDING TO THE INVENTION DIAGRAM Dry gas regeneration with recirculation compressor Fig. 1 Dry gas regeneration without recirculation compressor Fig. 2a CAPACITIES Separation drum (KO drum) 1 1 Heating / cooling device (heat exchanger) 1 / 1 1 / 1 Compressor 1 + (1 spare) - Compressor (auxiliary) 1 - Number of adsorbers 2 3 Sequence valves 4 / adsorber 6 / adsorber Heat integrator na 1 Bed design parameters Number of cycles / year 365 247 Adsorption time h 12 12 Regeneration time Heating h 6 11 Regeneration time Cooling h 6 11 Standby time h 0 1 Adsorbent Molecular sieve 4A Molecular sieve 4A Mass of adsorbent Unit mass in base 100 per adsorber 124 124 Mass required to dry the feed Unit mass in base 100 per adsorber 100 100 Additional mass to dry the recycled regeneration gas Unit mass in base 100 per adsorber 24 24 OPERATING COSTS Energy supplied to the regeneration gas, E Unit heat in base 100 100 60 A 18% of the energy supplied E 36% of the energy supplied E B' 18% of the energy supplied E 35% of the energy supplied EB” 1% of the energy supplied E 1% of the energy supplied EC 63% of the energy supplied E 28% of the energy supplied E

[0110] The energy supplied to the regeneration gas between the reference case and the scheme according to the invention was reduced by a third. The energy integration made it possible to recover almost three-quarters of the calories contained in the regeneration gas at the bed outlet. during heating. Furthermore, in this example, only the calories recovered by the Gas / Gas recovery heat exchanger (7), as described in the different operating modes of the invention Fig. 2a-2 / 3b-2 have been quantified. The use of calories leaving the bed in cooling as described in the different operating modes of the invention Fig. 2a / 3b to directly preheat bed B2 at the start of the regeneration phase from the calories stored in bed B3 makes it possible to reduce the consumption of the heating device from 60 (base 100 case 1 / reference) to almost 45 for this example. The energy consumed during the regeneration sequence between the reference case and according to the invention could ultimately be reduced by more than half.

[0111] The increase in the volume of adsorbent to be installed (linked to the change from two to three adsorbers), which has a negative impact on capacity costs (CAPEX), is offset by the reduction in the number of cycles per year carried out, thus delaying the adsorbent replacement campaign (positive annual impact on OPEX operating costs).

[0112] Compared to the schemes with recirculation compressor, the invention makes it possible to eliminate the compressor and possibly a backup compressor, but adds an adsorber with its associated sequencing valves.

[0113] Compared to the schemes with recycling of the regenerated gas to a compressor on the main line, the invention makes it possible to reduce the power consumed by this compressor and therefore to obtain a gain on operating costs (OPEX).

Claims

Claims

1. Method for removing at least one contaminant contained in a gas to be treated by means of a treatment unit by adsorption by temperature modulation and regeneration, the treatment unit comprising at least a first adsorber, a second adsorber and a third adsorber respectively containing a first set of regenerated adsorbent beds, a second set of regenerated adsorbent beds and a third set of adsorbent beds loaded with contaminant, the method comprising the following steps carried out concomitantly: a) a first gas flow to be treated is brought into contact in the first adsorber with the first set of regenerated adsorbent beds adapted to capture said contaminant and obtain a first purified gas flow; b) a second gas flow to be treated is brought into contact in the second adsorber with the second set of regenerated adsorbent beds so as to cool the second set of regenerated absorbent beds and obtain a second purified gas flow; c) heating said second purified gas stream to a temperature sufficient to achieve desorption of the contaminant; d) bringing into contact, in the third adsorber, the second flow of purified gas heated in step c) with the third set of adsorbent beds loaded with contaminant so as to desorb the contaminant adsorbed by the third set of adsorbent beds and obtain a third flow of gas containing the contaminant; e) upstream of step c), a heat transfer is carried out between the third gas flow and the second purified gas flow from step b), the pressure in the second adsorber (P3) being higher than the pressure in the first adsorber (PI) and the pressure in the first adsorber (PI) being lower than the pressure in the third adsorber (P2).

2. Method according to claim 1, in which for a specific duration during a regeneration step, the second adsorber is isolated (in cooling) and steps b), c), d), e) are replaced by steps b'), c'), d') and in which: a) a first flow of gas to be treated is brought into contact in the first adsorber with the first set of adsorbent beds to capture the contaminant and obtain a purified gas; b') a second gas flow to be treated is heated to a temperature sufficient to carry out desorption of the contaminant; c') the second gas flow to be treated, heated, is brought into contact in the third adsorber with the third set of adsorbent beds loaded with contaminant so as to desorb the contaminant adsorbed by the third set of adsorbent beds and obtain a second gas flow containing the contaminant; d') a heat transfer is carried out upstream of step b') between the second gas flow containing the contaminant and the second gas flow to be treated.

3. The method of claim 2, wherein the specific time corresponds to the heating time required to desorb the contaminant in the third adsorber.

4. Method according to one of claims 2 or 3, in which the second adsorber is put back online at the end of said specific duration and steps a), b), c), d), e) are carried out.

5. Method according to one of claims 1 or 4, in which when the temperature of the second purified gas flow from the second adsorber is greater than or equal to the temperature of the third gas flow containing the contaminant from the third adsorber, all or part of the second purified gas flow is sent to the third adsorber without carrying out a heat transfer with the third gas flow.

6. Method according to one of claims 1 and 4 to 5, in which the third gas flow from step d) is returned to the first adsorber.

7. Method according to one of claims 1 and 4 to 6, in which the direction of circulation of the first gas flow to be treated in the first adsorber in adsorption and of the second gas flow to be treated in the second adsorber in cooling is co-current.

8. A method according to claim 7, wherein the direction of circulation is from the top to the bottom of the adsorbers in adsorption and cooling.

9. Method according to one of the preceding claims, in which the gas to be treated is chosen from CO2, natural gas, hydrogen produced by electrolysis of water or by treatment of natural gas by steam reforming.

10. A method according to any preceding claim, wherein the contaminant is water.

11. Method according to one of the preceding claims, in which step e) of heat exchange is carried out directly or indirectly.

12. A method according to any preceding claim, wherein the adsorbent comprises at least one material selected from silica, silica gel, alumina, silica-alumina and zeolite.

13. Unit for treating a gas by temperature modulation adsorption for implementing the method according to any one of claims 1 to 12, comprising: - at least a first absorber, a second absorber and a third adsorber respectively containing a first set, a second set and a third set of adsorbent beds, each set containing one or more beds of an adsorbent of the same nature or several beds of adsorbents of a different nature; - a first supply line for a gas to be treated connected to the first adsorber to supply the first absorber with gas to be treated; - a first discharge line connected to the first adsorber to discharge a purified gas; - a second supply line for gas to be treated connected to the second adsorber to supply the second absorber with gas to be treated;- a second discharge line connected to the second adsorber for discharging a purified gas from said second adsorber, said second discharge line being connected to the third adsorber for supplying said third adsorber; - a heating device for heating the gas contained in the second discharge line before supplying the third adsorber; - a third discharge line for discharging a hot gas from the third adsorber - a heat exchange device capable of carrying out a heat transfer from the gas contained in the third discharge line to the purified gas contained in the second discharge line, - a valve for expanding the gas to be treated upstream of the unit and configured to lower the pressure of the gas to be treated in the first supply line relative to the pressure of the gas to be treated in the second supply line.;

14. A unit according to claim 13, wherein the third discharge line is connected, downstream of the heat exchange device, to the first supply line.

15. Unit according to one of claims 13 or 14 comprising a bypass pipe of the second adsorber (in cooling), said bypass pipe being arranged upstream of the expansion valve and connected to the heat exchange device so as to allow a transfer of heat from the gas contained in the third discharge line to the gas contained in said bypass pipe.

16. Unit according to one of claims 13 to 15, comprising a bypass line of the heat exchange device, said bypass line being arranged upstream of said heat exchange device and fluidically connected to the second adsorber and to the second discharge line which feeds the third adsorber.

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