Separation method

Abstract

The present invention relates to a method for separating a feed gas (30) by pressure swing adsorption, comprising: feeding the feed gas (30) to a separation unit (10) to produce a first gas fraction (31) enriched in a first component and a second gas fraction (32) enriched in a second component, the first component being more adsorbable than the second component, the separation unit (10) comprising a plurality of adsorbents, the adsorbents being subjected to pressure cycles characterized by high and low pressures, the pressure cycles comprising at least one adsorption step (101; 201) and a step of flowing a wash fluid enriched in the first component through the at least one adsorbent to adsorb the first component. and at least one washing step (102; 202) for flushing at least a portion of the second component from the adsorbent bodies, the pressure cycles having phase times corresponding to the duration of the pressure cycle divided by the number of adsorbents, the unit operates in a first mode in which the washing fluid flows at a first washing fluid flow rate value called the first washing flow rate value (Qri) and the phase times are determined by the first phase time duration (Tpi), the method comprising steps a), b), c) and d).

Description

[Technical field]

[0001] The present invention relates to a unit for separation by adsorption of a gas fed to said unit, known as feed gas or the gas to be treated, for the production of a first fraction enriched in highly adsorbable compounds of the feed gas and a second fraction enriched in poorly adsorbable compounds of the feed gas. The present invention also relates to a method of separation by adsorption. [Background technology]

[0002] Adsorption is widely used to purify or separate (fractionate) gases. Examples include fractionation of "n" and "iso" paraffins, xylene fractionation, alcohol fractionation, production of nitrogen or oxygen from air, and removal of CO2 from flue gases and from blast furnace gases. On the purification side are dryers, hydrogen or helium purging, methane-rich gas purging, adsorption of trace impurities in many streams (mercury, NOx, sulfur product termination, etc.).

[0003] The gas fed to the separation unit comprises a mixture of poorly and highly adsorbable compounds. In the method of separation by adsorption, firstly, one or more highly adsorbable gas compounds (hereinafter referred to as first or highly adsorbable components) and, secondly, one or more poorly adsorbable compounds (hereinafter referred to as second or poorly adsorbable components) must be extracted from the feed gas. The feed gas therefore comprises a mixture of two components. The highly adsorbable component is the more adsorbable of the two components and the poorly adsorbable component is the less adsorbable of the two components. Depending on the application, the usable gas (useful component) is either the poorly adsorbable component or, in contrast, the highly adsorbable component. This is then called the "product". The other component constitutes the residue or the "purge" (residual component).

[0004] In particular, a unit for separation by adsorption comprises a number of reservoirs for the circulation of the process gas, each reservoir containing an adsorbent material. These reservoirs, sometimes known as columns, serve to support the adsorbent material and ensure the circulation of the gas. These reservoirs are referred to below as "adsorbents".

[0005] Methods involving adsorption are of several types, depending on whether the adsorbent can be regenerated in situ or not: the adsorbent is said to be of the "spent charge" type, meaning that it needs to be regenerated when it becomes saturated with impurities (the term "back-up bed" is also used in this case to qualify such purification), or in other cases the term "adsorption cycle" is used.

[0006] Adsorption cycles differ primarily in the way the adsorbent is regenerated: if regeneration is essentially performed by increasing the temperature, it is a Temperature Swing Adsorption (TSA) process, whereas if regeneration is performed through a reduction in pressure, it is a Pressure Swing Adsorption (PSA) process, and the term PSA unit is used for the Pressure Swing Adsorption separation unit.

[0007] In general, the term PSA refers to any process for the purification or separation of gases using cyclic variations in pressure experienced by an adsorbent between a high pressure, called the adsorption pressure, and a low pressure (less than the high pressure), called the regeneration pressure. This is then called a purge process or a pressure swing adsorption separation process. This generic term PSA (Pressure Swing Adsorption) is therefore used indifferently to mean the following cyclic processes, which are also common to give more specific names depending on the pressure level used, or the time required for the adsorber to return to its starting point (cycle time): - a VSA process, in which the adsorption is carried out substantially at atmospheric pressure, preferably between 0.95 and 1.25 bar abs, and the desorption pressure is below atmospheric pressure, typically between 50 and 400 mbar abs; - MPSA or VPSA processes, in which the adsorption is carried out at high pressure above atmospheric pressure, typically between 1.35 and 6 bar abs, and the desorption is carried out at low pressure below atmospheric pressure, generally between 200 and 650 mbar abs; - a PSA process body, in which the high pressure is substantially greater than atmospheric pressure, typically between 3 and 50 bar abs, and the low pressure is substantially greater than atmospheric pressure, generally between 1 and 9 bar abs; - RPSA (rapid PSA) processes, where the duration of the pressure cycle is typically less than one minute; - URPSA (Ultra Rapid PSA) process, where the duration of the pressure cycle is of the order of a few seconds at most.

[0008] It should be noted that these various names are not standardized, and in particular that the limits stated may vary, Again, unless otherwise indicated, use of the term PSA covers all of these variations.

[0009] The adsorber starts a period of adsorption until it is full of one or more components to be captured at high pressure, then it is regenerated by depressurization and extraction of the adsorbed compounds, after which it is restored to start a new adsorption period again. The adsorber has now completed a pressure cycle, and the very principle of the PSA process is to string these cycles together in sequence. It is therefore a cyclical process. In principle, each adsorber follows the same cycle with a time shift known as phase time, or more simply phase.

[0010] Therefore, the following relationships exist: Phase time = (cycle time) / (number of adsorbents)

[0011] Each adsorbent sequentially passes through a series of phases that make up a PSA cycle, each phase being of equal duration.

[0012] Conventionally, the adsorber is subjected to a pressure cycle comprising the following steps, particularly in the following order: 1) adsorption at high pressure in a cycle with the production of a second fraction enriched in the less adsorbable component, in particular with the supply of a repressurized flow containing a portion of the second fraction produced; 2) reduction in pressure to a lower pressure with production of a first fraction; 3) Repressurization to high pressure, specifically with the repressurization flow provided in step 1.

[0013] It should be noted that in a cycle, a given step is distinguished from the preceding or succeeding step by one of the following reasons in particular: the presence or absence of inlet and / or outlet flows and their direction of circulation in the adsorber, the source of the inlet flows, the destination of the outlet flows. A phase may comprise multiple separate steps, conversely a step may last for more than one phase.

[0014] The adsorption separation unit operates with an extraction yield of the highly adsorbable component corresponding to the amount of the highly adsorbable component in the first fraction extracted at low pressure relative to the amount of the highly adsorbable component in the feed gas. The separation unit also operates with an extraction yield of the poorly adsorbable component corresponding to the amount of the poorly adsorbable component in the second fraction extracted at high pressure relative to the amount of the poorly adsorbable component in the feed gas. Depending on the application, the inventors use the terms "product extraction yield" for the extraction yield of the component suitable for use and "purge rate" for the extraction yield of the remaining component. More specifically, the invention relates to a method for separation by adsorption in which these extraction yields are not particularly high, neither for production nor for purging.

[0015] A standard separation unit with a given adsorbent charge and / or given dimensions operates on a feed gas fixed along the characteristic curve "extraction yield of highly adsorbable component" versus "extraction yield of poorly adsorbable component" or vice versa. FIG. 1 shows an exemplary curve (c) of "extraction yield of highly adsorbable component" on the ordinate and "extraction yield of poorly adsorbable component" on the ordinate. Optionally, the highly adsorbable component (first fraction) is selected as the yield product R and the poorly adsorbable component (second fraction) is therefore selected as the yield purge P. Very commonly, the phase time is used as an adjustment means to follow this curve. It is found that in the phase time Tp1, it is practically impossible for the highly adsorbable component to penetrate into the second fraction at high pressure. The highly adsorbable component therefore constitutes a very large proportion in the first fraction extracted at low pressure, resulting in a high extraction yield R1 of the more adsorbable component. Another consequence is that most of the poorly adsorbed component is left behind in the adsorber, at least a portion of which is extracted at low pressure, with a correspondingly reduced extraction yield of the poorly adsorbed component P1. Conversely, a longer phase time Tp2 results in a corresponding yield R2 less than R1, with P2 being greater than P1.

[0016] Generally, the main constraint for the product is to observe a certain purity (e.g. to produce hydrogen at 99.99% molar) and the separation unit is adjusted to operate at the best possible yield, which allows to limit the required feed gas flow and thus the cost of the raw material (natural gas in this example).

[0017] However, in certain industrial applications, it is necessary to observe strict specifications for both fractions produced by the PSA unit, even if there are changes in the composition of the feed gas. In contrast, for other applications where the feed remains unchanged, it is the product specifications that must change over time. A typical example that illustrates the latter case is the imposed increase in CO2 capture rates in the coming years due to environmental factors.

[0018] A so-called washing step may be added to the cycle involving the circulation of a gas rich in the highly adsorbable component, called washing fluid, through the adsorber, aiming at releasing the poorly adsorbable gas from the adsorber material and the dead volume. Such a step may increase the extraction yield of the poorly adsorbable component by recovering part of the poorly adsorbable gas compounds present in the adsorber at the end of the adsorption step. If the highly adsorbable component is a useful component, it is also possible to add such a washing step in order to limit the amount of poorly adsorbable component present therein.

[0019] It is known from the prior art to use such scrubbing processes to produce fractions enriched in poorly adsorbable gas compounds with high purity and yield. This is especially true when the aim is to produce methane for injection into the so-called natural gas network with the required methane purity, often exceeding 96%, and with an extraction yield of the order of 95% or more. To achieve high yields and purities, the scrubbing fluid flow rate may be higher than the production flow rate, resulting in a considerable overdimensioning in terms of the adsorption volume and the compression means. This has a significant impact on the price of the construction of the installation and the operating costs of this installation, since the energy consumption is higher. The installations known from the prior art are therefore mainly based on emissions and can only be justified economically by environmental factors (prohibition of the emission of large amounts of greenhouse gases) and the corresponding secondary costs. The installations known from the prior art which perform a scrubbing step are therefore not highly competitive. Moreover, an increase in the scrubbing fluid flow rate to achieve a high extraction yield of poorly adsorbable components leads to a decrease in the extraction yield of the more adsorbable components due to the characteristic curve (limit curve) of the operation of the unit.

[0020] These standard separation units, with or without a cleaning step, clearly do not meet the requirements if the aim is to go beyond these limiting curves, for example by increasing the product extraction yield while maintaining the purge rate, or by increasing the purge rate while maintaining the product extraction yield. Therefore, an adsorption separation unit with greater operational flexibility is needed. Summary of the Invention [Means for solving the problem]

[0021] An object of the invention is therefore a method for separating a feed gas by pressure swing adsorption, in which a separation unit is fed with the feed gas to produce a first gas fraction enriched in a first component and a second gas fraction enriched in a second component, the first component being more adsorbable than the second component. The separation unit comprises a number of adsorbents, said adsorbents being subjected to pressure cycles characterized by high and low pressures. The pressure cycles comprise a number of steps, including at least one adsorption step and at least one washing step. During the washing step, a washing fluid enriched in the first component is circulated through at least one adsorbent to release at least a portion of the second component from said adsorbent. The pressure cycles have a phase time corresponding to the duration of the pressure cycle divided by the number of adsorbents. The method comprises the following steps: a) determining a first component extraction yield value defined as the ratio of the amount of the first component in the produced first fraction to the amount of the first component in the feed gas fed to the separation unit; b) determining a second component extraction yield value defined as the ratio of the amount of the second component in the produced second fraction to the amount of the second component in the feed gas fed to the separation unit; c) determining a first difference between the first component extraction yield value determined in step a) and a first reference value related to the first component extraction yield and a second difference between the second component extraction yield value determined in step b) and a second reference value related to the second component extraction yield; d) if the first difference is greater than a first predetermined threshold and / or the second difference is greater than a second predetermined threshold, modifying the phase time and the flow rate of the cleaning fluid, referred to as the cleaning flow rate, to reduce the first difference and / or the second difference.

[0022] Acting on the phase time parameter and the wash flow rate parameter allows compensation for increases or decreases in extraction yield caused by modifications of one or the other of these parameters. For example, the phase time duration can be shortened and the wash flow rate value can be increased to increase the first component extraction yield while maintaining the second component extraction yield. Control of the two parameters, wash flow rate and phase time, therefore allows for greater operational flexibility in terms of the extraction yield of the first and second components compared to prior art separation units.

[0023] The first and second thresholds may be specifically defined to take into account normal variations in the yield of the separation method.

[0024] According to an embodiment of the method, the phase times and wash flow rates are modified such that the first difference is less than or equal to a first threshold and / or the second difference is less than or equal to a second threshold.

[0025] According to an embodiment of the method, the unit operates in a plurality of operational modes, and the cleaning fluid circulating at determined cleaning flow rate values ​​and phase times is defined by determined phase time durations in each of the operational modes.

[0026] According to an embodiment of the method, the wash flow rate and the phase time are jointly modified, in particular, the wash flow rate and the phase time are simultaneously modified.

[0027] The wash flow rate and phase time are specifically modified independently of each other.

[0028] According to an embodiment of the method, the wash flow rate is increased and the phase time is decreased to increase the determined first component extraction yield and maintain the determined second component extraction yield, which improves separation between the first and second components.

[0029] According to an embodiment of the method, the phase time and the cleaning flow rate are modified such that the determined first component extraction yield reaches a first reference value and / or the determined second component extraction yield reaches a second reference value.

[0030] According to an embodiment of the method, the first and / or second threshold values ​​are equal to 3%, preferably equal to 1.5%, preferably equal to 0.5% and possibly equal to zero. In the latter case, in the case of the difference between the determined first component extraction yield value and the first reference value and / or the difference between the determined second component extraction yield value and the second reference value, the phase time cleaning flow rate is corrected so that the determined first component extraction yield reaches the first reference value and / or the determined second component extraction yield reaches the second reference value. This gives a yield percentage on the scale 0-100%. For example, for a yield reference value of 65%, the various yield ranges over which the method is implemented are 62 / 68% for a threshold value of 3%, 63.5 / 66.5% for a threshold value of 1.5% and 64.5-65.5% for a threshold value of 0.5%. The choice of one of these ranges depends on the sensitivity of downstream units to the separation performance of the separation unit and the accuracy of the measurement to the yield of the separation unit.

[0031] According to an embodiment of the method, the first component extraction yield value and the second component extraction yield value are determined by analysis of the composition of the feed gas fed to the unit, the first fraction produced and the second fraction produced. In particular, an analyzer determines the content of the first and / or second component in the feed gas, the first fraction produced and the second fraction produced. The content of the first and / or second component is measured, for example, using one or more sensors. The analyzer is in particular able to deduce the content of the first and second component from the measured content of the other component. The flow rates of the feed gas, the first fraction and the second fraction can be taken into account in determining the yield values.

[0032] According to an embodiment of the method, the first reference value expressed as a yield percentage is between 25% and 90% and the second reference value expressed as a yield percentage is between 20% and 90%.

[0033] According to an embodiment of the method, the washing step immediately follows the adsorption step.

[0034] According to an embodiment of the method, the pressure cycle comprises at least the following steps, particularly in the following order: 1) adsorption at high pressure in a cycle with the production of a second fraction enriched in the second component, in particular with the supply of a repressurized flow comprising a portion of the second fraction produced; 2) Washing, 3) Reducing pressure to low pressure with production of a first fraction and supply of a wash flow; 4) Repressurization to high pressure, specifically with the repressurization flow provided in step 1.

[0035] According to an embodiment of the method, the pressure cycle comprises the following steps, particularly in the following order: 1) adsorption at high pressure in a cycle with the production of a second fraction enriched in the second component, in particular with the supply of a repressurized flow comprising a portion of the second fraction produced; 2) Washing, 3) providing at least one balancing step with a pressure drop and one or more balancing flows with a pressure increase; 4) Supply of elution gas; 5) Reducing pressure to a lower pressure with production of a first fraction; 6) supplying the elution gas to step 4, producing a first fraction and eluting with the supply of a wash flow through at least one of steps 5 and 6; 7) at least one balancing step with a pressure increase, with one or more balancing flows being fed to step 3; 8) Repressurization to high pressure, specifically with the repressurization flow provided in step 1.

[0036] Pressure cycles that include the preceding steps 1-8, but do not include the balancing steps with washing and pressure reduction (steps 3 and 7), can also be implemented as intermediate cycles between the cycles described above.

[0037] According to an embodiment of the method, after the step of depressurization to a pressure close to atmospheric pressure, the pressure cycle comprises a step of vacuum pumping, during which the first fraction is discharged. The elution step may coincide with the vacuum pumping step or may correspond to the final part of the vacuum pumping step. Depending on the flow rate, the low pressure of the cycle may be reached during or at the end of the vacuum pumping step.

[0038] According to an embodiment of the method, the pressure cycle also includes one or more dead time steps during which the one or more adsorbents remain the same, in particular the adsorbents remain at the same pressure in the dead time steps.

[0039] According to an embodiment of the method, a portion of the first fraction is used as product gas and another portion is used as wash fluid.

[0040] According to an embodiment of the method, the wash flow rate divided by the sum of the wash flow rate and the flow rate of said product gas is between 0.05 and 0.65, preferably between 0.05 and 0.5.

[0041] According to an embodiment of the method, the product gas flow is compressed before being directed towards the downstream device.

[0042] According to an embodiment of the method, the washing fluid is also compressed before being introduced into the adsorber undergoing a washing step, in particular the washing fluid is compressed to a high pressure.

[0043] According to an embodiment of the method, the washing fluid circulates through at least one adsorber undergoing a washing step in the same circulation direction as the feed gas when said adsorber undergoes an adsorption step, the washing step then being described as co-current.

[0044] According to an embodiment of the method, the flow coming from the adsorber undergoing a washing step is introduced together with the feed gas into at least one adsorber undergoing an adsorption step.

[0045] According to an embodiment of the method, the cleaning step is performed for an integer multiple of the phase time, the cleaning step then being performed for at least one complete phase time.

[0046] According to an embodiment of the method, the phase time is modified by controlling at least one parameter of the gas flow supplied to the adsorber of the separation unit and / or at least one parameter of the gas flow produced by the adsorber of the separation unit, in particular at least one parameter of the gas flow transferred from one adsorber to another.

[0047] In particular, said parameters are selected from flow rate and / or flow duration.

[0048] According to an embodiment of the method, the phase time is modified via at least one of the following operations: - adding or removing steps in the pressure cycle, - Lengthening or shortening the steps.

[0049] According to an embodiment of the method, a dead time step is added to the pressure cycle during which one or more adsorbents remain in the same state as at the end of the preceding step, in particular by fluidically isolating the or said adsorbents remaining in the same state.

[0050] According to an embodiment of the method, the dead time step is lengthened or shortened.

[0051] According to an embodiment of the method, the phase time is modified at the phase start.

[0052] According to an embodiment of the method, the phase time is modified by changing the start and / or end times of the supply of gas flow to the at least one adsorber.

[0053] According to an embodiment of the method, the phase time is modified by changing the time of the beginning and / or end of the production of gas flow by at least one adsorbent.

[0054] According to an embodiment of the method, the phase time is modified by varying the time of the start and / or end of the supply of feed gas to one or more adsorbents in the adsorption step and / or by varying the time of the start and / or end of the production of the second fraction by said or said adsorbents.

[0055] According to an embodiment of the method, the flow rate of the gas flow transferred from one adsorbent to another is adjusted to accelerate or decelerate gas transport between said adsorbents.

[0056] In particular, the adsorbent supplying the gas flow is under reduced pressure and the adsorbent receiving the gas flow is under pressure, and gas transfer is accelerated or decelerated to speed up or slow down the depressurization and / or repressurization of said adsorbents. In particular, the transfer flow is a balance flow between at least one adsorbent in a balancing step with a pressure drop and at least one adsorbent in a balancing step with a pressure increase.

[0057] According to an embodiment, the method comprises the following steps: i) recording points of stabilization operation of the separation unit in a database, the operation points corresponding to pairs of phase time duration and wash flow rate values, each pair being associated with a first component extraction yield value and a second component extraction yield value of the separation unit; ii) if the first difference is greater than a first threshold and / or the second difference is greater than a second threshold, reading phase time durations and wash flow rate values ​​from the database, such that the first difference is less than or equal to the first threshold and / or the second difference is less than or equal to the second threshold, then allowing correction of the phase times to the phase time durations read from the database and correction of the wash flow rate to the wash flow rate values ​​read from the database.

[0058] According to an embodiment of the method, steps a), b), c) and d) defined above are repeated until the first difference is less than or equal to a first threshold value and / or the second difference is less than or equal to a second threshold value, with for step d) a modification of the last phase time duration to a new phase time duration and a modification of the last wash flow rate value to a new wash flow rate value.

[0059] According to an embodiment of the method, the phase time and wash fluid flow modification is performed by iterating through a phase time duration at a constant wash flow rate value at a first time, and then by iterating through a wash flow rate value at a constant phase time duration at a second time. Such a sequence may in particular be repeated.

[0060] According to an embodiment of the method, the phase time and wash fluid flow modifications are implemented by iterating through wash flow rate values ​​at a constant phase time duration at a first time, and then by iterating through phase time durations at a constant wash flow rate value at a second time, and such sequence may be repeated.

[0061] According to an embodiment of the method, steps a), b), c) and d) are repeated in addition to and in particular after the modification of the phase times and wash flow rates by reading from the database.

[0062] According to an embodiment of the method, instead of modifying the phase times and the wash flow rates by reading from the database, steps a), b), c) and d) are repeated.

[0063] According to an embodiment of the method, a useful component similar to the product and a residual component similar to the purge are extracted. In particular, the first component is the useful component and the second component is the residual component.

[0064] The method may be used in particular to capture carbon monoxide from blast furnace smoke and recycle it as a reducing agent into said blast furnace, the feed gas comprising a mixture of carbon monoxide and nitrogen, a first fraction being rich in carbon monoxide and a second fraction being rich in nitrogen, the carbon monoxide constituting the first component and the nitrogen constituting the second component.

[0065] The smoke is, for example, first treated in a carbon dioxide capture unit.

[0066] The method may be used to capture carbon dioxide, wherein the feed gas comprises a mixture of carbon dioxide and nitrogen, a first fraction being rich in carbon dioxide and a second fraction being rich in nitrogen, the carbon dioxide constituting the first component and the nitrogen constituting the second component.

[0067] The method may be used to purify a feed gas comprising a mixture of methane and nitrogen, according to this embodiment, a first fraction is rich in methane and a second fraction is rich in nitrogen, methane constituting the first component and nitrogen constituting the second component.

[0068] The invention also relates to a unit for separating a feed gas by pressure swing adsorption for the production of a first gas fraction enriched in a first component and a second gas fraction enriched in a second component, the first component being more adsorbable than the second component. The separation unit comprises a number of adsorbents configured to undergo pressure cycles characterized by high and low pressures. The pressure cycles comprise a number of steps including at least one adsorption step and a washing step. During the washing step, a washing fluid enriched in the first component is circulated through at least one adsorbent to release at least a portion of the second component from said adsorbent. The pressure cycles have a phase time corresponding to the duration of the pressure cycle divided by the number of adsorbents. The separation unit comprises: - a flow control system configured to modify the phase time by controlling at least one parameter of the gas flow, in particular supplied to the adsorber of the separation unit and / or at least one parameter of the gas flow produced by the adsorber of the separation unit, in particular at least one parameter of the gas flow transferred from one adsorber to another, - a flow regulation device configured to modify a cleaning fluid flow rate; a control unit and communication means between the control unit, the flow control system and the flow regulation device, the control unit being adapted to implement the method as described above; Includes.

[0069] According to an embodiment, the flow control system comprises: - adding or removing steps from a pressure cycle; - Extend or shorten a step The phase time is modified by:

[0070] According to an embodiment, the flow control system includes at least one supply valve configured to allow or prevent the supply of the feed gas to the one or more adsorbents during the adsorption step.

[0071] Additionally or alternatively, the flow control system comprises at least one production valve configured to allow or prevent production of a second fraction enriched in the second component by one or more adsorbents in the adsorption step, in particular by said or said adsorbents in the adsorption step.

[0072] According to an embodiment, the flow control system includes at least one switching valve configured to adjust a transfer flow rate between at least one adsorbent supplying the transfer flow and an adsorbent receiving the transfer flow.

[0073] The supply valves and / or the production valves may be shut-off valves. The switching valves are for example proportional valves.

[0074] According to an embodiment, the separation unit comprises a branching element configured to split the flow of the first fraction into a product flow and a wash fluid flow. In particular, the branching element comprises a circulation channel for the first gas fraction, a wash fluid circulation channel and a channel into which the product flow circulation channel branches. The branching element then has, for example, a T-shape. According to an example, the branching element comprises a three-way valve.

[0075] According to an embodiment, the separation unit comprises compression means, e.g. a compressor, configured to compress the wash fluid, in particular to a high pressure, before its introduction into the adsorber undergoing a wash step. In a method embodiment not shown, the compressor is also configured to compress the product gas flow, in particular to the pressure required for supply to downstream equipment.

[0076] According to an embodiment, the flow regulation device comprises at least one valve, for example a two-way valve, or two two-way valves. In particular, these may be proportional valves. In particular, the flow regulation device comprises a three-way valve. Alternatively or additionally, the flow regulation device comprises a compressor.

[0077] According to one embodiment, the separation unit includes at least one vacuum pump configured to facilitate desorption of the first component, the desorption being carried out at a pressure below atmospheric pressure.

[0078] According to an embodiment, the control unit comprises data matching software that enables the determination of the most likely values ​​of the determined extraction yields and their uncertainties from redundant measurements. [Brief description of the drawings]

[0079] [Figure 1] FIG. 1 shows a characteristic curve for a prior art separation unit in a graph showing product extraction yield versus purge rate. [Diagram 2] FIG. 2 illustrates the operating region of a unit according to the present invention in a graph of product extraction yield versus purge rate. [Diagram 3] FIG. 3 shows a separation unit according to the invention comprising four adsorbents. [Figure 4] FIG. 4 shows a separation unit according to the invention containing eight adsorbents. [Diagram 5] FIG. 5 is a block diagram illustrating the steps of the separation method according to the present invention and the adjustment of units by iteration. [Figure 6] FIG. 6 shows curves determined by simulation to determine the operating points of the separation unit for adjustment by reading from a database. [Figure 7] FIG. 7 shows an example of iterative refinement. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] A separation unit 10 implementing the method according to the invention is shown in Figure 3. In this embodiment, the unit comprises four adsorbents implementing steps 101, 102, 103 and 104 which are explained in detail below.

[0081] The unit 10 comprises a flow control system, which comprises a feed valve 6, which can enable or prevent the feed of the feed gas 30 to the adsorber in the adsorption step 101, and a production valve 7, which can enable or prevent the production of the second fraction 32 by the adsorber in the adsorption step 101. The feed valve 6 and the production valve 7 are here shut-off valves which enable or prevent the feed of the feed gas 30 or the production of the second fraction 32, respectively. Such a shut-off valve can therefore selectively enable or prevent the circulation of the corresponding gas flow. The flow control system comprises a switching valve, here a proportional pressurization valve 8, which allows the adjustment of the so-called transfer flow corresponding to the gas transfer between the two adsorber. This transfer flow is in this embodiment a pressurized flow 33 originating from the second fraction 32 between the adsorber producing the second fraction 32 in step 101 and the adsorber under pressurization or repressurization in step 104. Such a valve can progressively adjust the corresponding gas flow.

[0082] The flow regulation device, which here comprises the three-way valve 9 and the compressor 12, also allows the modification of the wash fluid flow rate (called "wash flow 34") during the wash steps 102; 202, which will be explained in more detail below. The compressor 12 also allows the compression of the wash flow 34, for example to the high pressure of a pressure cycle, before its introduction into the adsorber undergoing the wash step 102. The three-way valve 9 therefore also serves as a T-junction element to split the flow of the first fraction produced in step 103 into a useful product gas flow 35, which is sent to a subsequent step of the installation, including for example a separation unit, and the wash flow 34. This product gas flow is compressed, for example before being sent to downstream equipment. A buffer reservoir 15 allows the limitation of composition fluctuations and also facilitates the control of the compressor 12.

[0083] The separation unit also includes a vacuum pump 11 that facilitates desorption of the first component in step 103 at less than atmospheric pressure. During step 103, the low pressure of the cycle is reached.

[0084] The separation unit 10 comprises a control unit 13 and communication means 14 between the control unit 13, the flow control system and the flow regulation device. The control unit 13 is capable of implementing the separation method according to the invention. In particular, the control unit 13 comprises programmable electronic equipment programmed to implement the method according to the invention.

[0085] In the method according to the invention, the separation unit 10 is fed with a feed gas 30 comprising a mixture of one or more first poorly adsorbable compounds and one or more second highly adsorbable compounds. The separation unit 10 extracts from the feed gas 30 one or more highly adsorbable compounds constituting a first poorly adsorbable component. The separation unit 10 also extracts from the feed gas 30 one or more poorly adsorbable compounds constituting a second poorly adsorbable component. The "highly adsorbable component" is the most adsorbable component of the two components and the "poorly adsorbable component" is the least adsorbable component of the two components. In other words, the first component is more adsorbable than the second component. The separation unit 10 then produces a first gas fraction 31 enriched in the first component and a second gas fraction 32 enriched in the second component. In the applications described below, the useful component is the first component. It is then called the "product". The second component then constitutes the residue or purge. In certain applications, the second component comprises or is equal to the predominantly poorly adsorbable component, such as nitrogen, however, the second component may also comprise compounds such as argon, oxygen or hydrogen, especially when these are in minority amounts.

[0086] In an implementation of the method according to FIG. 3, the adsorbent of the unit is subjected to a pressure cycle comprising the following steps in the following order: Step 101: Adsorption at high pressure in a cycle with production of a second fraction 32 enriched in a second component, and extraction from the produced second fraction 32 of a pressurized or repressurized flow for the adsorber in step 104. The pressurized flow 33 is regulated by the pressurization valve 8. Step 102: Co-current washing. Step 103: Reducing pressure to low pressure with production of a first fraction 31 and providing a wash flow 34 for the adsorber in step 102. Step 104: Repressurizing to high pressure with repressurization flow 33 provided by adsorber 101.

[0087] The phase time is therefore equal to the duration of the pressure cycle, or cycle time, divided by the number of adsorbents, here four adsorbents.

[0088] In a second implementation of the method shown in Fig. 4, the separation unit 10 comprises eight adsorbents. For the sake of simplicity, only the differences with respect to the number and nature of the pressure cycle steps, gas flows and valves are shown compared to the embodiment in Fig. 3. The other elements of the unit can be implemented in an equivalent manner in this second embodiment.

[0089] The unit includes a flow control system including three switching valves, a pressurizing valve 8, a balancing valve 17 and an elution gas supply valve 18. These switching valves are valves for adjusting the gas transfer flow between the two adsorber bodies. These switching valves are proportional valves here.

[0090] The adsorber of the unit is subjected to a pressure cycle which includes the following steps in the following order: Step 201: Adsorption at high pressure in a cycle with production of a second fraction 32 enriched in a second component, and extraction of a pressurized or repressurized flow 33 for the adsorber from the produced second fraction 32 in step 208. The pressurized or repressurized flow 33 is regulated by a pressurization valve 8. Step 202: Co-current washing. The flow regulation device is now at least partially opened to allow circulation of the washing fluid. Step 203: Balancing with pressure drop and providing a balance flow 36 to balance the adsorber in step 207 with pressure increase. The balance flow 36 is regulated by the balance valve 17. Step 204: Supply of elution gas for elution of the adsorbent in step 206. The elution gas flow 37 is regulated by the elution gas supply valve 18. Step 205: Reducing pressure to low pressure with production of a first fraction 31 and providing a wash flow 34 for the adsorber in step 202. Step 206: Feeding of eluted gas to step 4, producing a first fraction 31 and eluting with feeding of the wash flow 34 to the adsorber in step 202. Step 207: Balancing the pressure rise with the balance flow 36 provided by the adsorber in step 203. Step 208: Repressurizing to high pressure with repressurization flow 33 provided by the adsorber in step 201.

[0091] In both of these implementations, the cleaning step 102;202 immediately follows the adsorption step 101;201. In other words, the adsorbent that has undergone the adsorption step 101;201 undergoes the cleaning step 102;202 as the next step once said adsorption step 101;201 is finished, with no intermediate steps between the adsorption step 101;201 and the cleaning step 102;202.

[0092] The phase time is therefore equal to the duration of the pressure cycle, or cycle time, divided by the number of adsorbents, here eight adsorbents.

[0093] In other embodiments, the pressure cycle includes multiple balancing steps with increasing pressure and multiple balancing steps with decreasing pressure. These may be successive balancing steps or balancing, and the gas flow rate or amount may vary from one balancing step to the next.

[0094] According to embodiments not shown, the pressure cycle may also include one or more dead time steps, e.g. at the same pressure, during which the adsorbent or adsorbents remain in the same state as at the end of the preceding step. The purpose may be, for example, to synchronize other steps between the adsorbents.

[0095] The following description applies to both the embodiment of FIG. 3 and the embodiment of FIG.

[0096] During the washing step 102;202, a so-called washing fluid rich in the first component circulates, moving rapidly from one end to the other through at least one adsorber in order to release at least a portion of the second component from the adsorber. The flow originating from the adsorber in the washing step 102;202 is injected into the adsorber undergoing the adsorption step together with the feed gas 30 in step 101;201. This recycling of the flow from the adsorber undergoing the washing step (the so-called recycled gas flow 38) allows an increase in the yield of the first component. "Flow rich in the first component" means that the first component is the quantitatively predominant component of the first and second components.

[0097] It is possible to define the cleaning ratio RR by the equation:

number

[0098] The three-way valve 9 and the compressor 12 of the flow regulation device allow the modification of the wash flow 34 and thus the wash ratio RR.

[0099] The cleaning steps 102;202 may be carried out over an integer number of phase times, i.e. over at least one complete phase time, which results in a continuous and constant cleaning flow 34 and thus recycled gas flow 38.

[0100] In the context of the method according to the invention, the separation unit 10 can therefore operate in a number of operating modes 1; 2; 3; 4 (see FIG. 2 ). In each of said operating modes the washing fluid circulates at a determined washing flow rate value 34 and the phase times are defined by determined phase time durations.

[0101] 5, the unit operates in a first mode in which the cleaning fluid circulates at a first cleaning flow rate value Qri and the phase time is equal to a first duration Tpi. In particular, this may be the first nominal operating mode of the separation unit 10 after start-up.

[0102] FIG. 5 also shows steps 301-304 of the separation process:

[0103] In step 301, a yield value of the separation unit 10 for the extraction of the first component of the raw gas 30 is determined. This first component extraction yield corresponds to the ratio of the amount of the first component in the first fraction 31 produced by the separation unit 10 to the amount of the first component in the raw gas 30 fed to the unit. In particular, the first component extraction yield corresponds to the content of the first component in the first fraction 31 to the content of the first component in the raw gas 30. This yield is determined, for example, by analysis of the composition of the raw gas 30 fed to the unit and the first fraction 31 produced. In particular, an analyzer determines the content of the first component in the raw gas 30 and in the first fraction 31. The content of the first component is measured, for example, using one or more sensors. This is therefore a mass ratio. Since the first component is here a useful component, the first component extraction yield is called "product yield" for the yield of the useful component or product. In the initial state, the separation unit 10 therefore operates with a product yield value Ri.

[0104] Instrumentation including analyzers, flow meters, pressure and temperature sensors are not shown in FIGS.

[0105] In step 302, a yield value of the separation unit 10 for the extraction of the second component from the feed gas 30 is determined. This second component extraction yield corresponds to the ratio of the amount of the second component in the produced second fraction 32 to the amount of the second component in the feed gas 30 fed to the unit. In particular, the second component extraction yield value corresponds to the content of the second component in the produced second fraction 32 to the content of the second component in the feed gas 30. This yield is determined, for example, by analysis of the composition of the feed gas 30 fed to the unit and the produced second fraction 32. In particular, an analyzer determines the content of the second component in the feed gas 30 and in the second fraction 32. The content of the second component is measured, for example, using one or more sensors. It is therefore a mass ratio. Since the first component is a useful component, the second component extraction yield is called the "purge rate". In the initial state, the separation unit 10 operates with a purge rate Pi.

[0106] The analyzer can in particular deduce the contents of the first and second components from the measured contents of the other components. The flow rates of the feed gas 30, the first fraction 31 and the second fraction 32 can be taken into account in determining the yield value. Data collation software, for example integrated in the control unit 13, allows the determination of the most likely values ​​for the yield and the uncertainty of these values ​​in case of redundant data. Such software takes into account the uncertainty of all measurements used in the determination of the parameter or parameters whose values ​​are sought, and of the evaluation, here the necessary repetition of the material evaluation, in order to maximize the probability of the result.

[0107] Steps 301 and 302 may be performed simultaneously. Step 301 may also be performed before step 302, or step 302 may be performed before step 301.

[0108] The control unit receives, for example from an operator, a first reference value C1 for the product extraction yield and a second reference value C2 for the purge rate. If there is a change in the specifications of the composition of the first fraction 31 produced and / or the second fraction 32 produced, the product yield value Ri and the purge rate Pi must change. This can also happen if the flow rate of the feed gas 30 changes. The first reference value is typically 25-90% and the second reference value is typically 20-90%. These are the yield percentages for the operation of the separation unit. In contrast to the findings in the prior art where high extraction yields and purity levels are achieved, it has been found that the use of a cleaning step is competitive as soon as the desired extraction yield is of the order of magnitude of that corresponding to a standard separation unit, but with increased flexibility between the product extraction yield and the purge rate.

[0109] In step 303, a first difference is calculated between the product yield value Ri determined in step 301 and a first reference value C1 related to the first component extraction yield. Similarly, a second difference is calculated between the purge rate Pi determined in step 302 and a second reference value C2 related to the second component extraction yield.

[0110] The first threshold value S1 and the second threshold value S2 are predetermined and recorded in the control unit. The threshold values ​​correspond to the allowed differences between the determined extraction yields (product yields and purge rates) and the reference values ​​C1;C2 associated with these extraction yields. The selected threshold values ​​may therefore depend on the allowed extraction yield uncertainty. In other words, in this case, there may be an agreed residual difference between the determined extraction yields (product yields and purge rates) and the reference values ​​C1;C2, as long as these residual differences remain below the corresponding threshold values ​​S1;S2 in absolute value.

[0111] The first difference is compared to a first threshold S1 and the second difference is compared to a second threshold S2. If the first difference is less than or equal to the first threshold S1, then the second difference is less than or equal to the second threshold S2 and the method ends.

[0112] If at least one of the first and second differences is greater in absolute value than the corresponding threshold value S1 or S2, the method proceeds to step 304, which consists in modifying the first phase time duration Tpi to a second phase time duration Tpi+1 different from the first, and modifying the first wash flow rate value Qri to a second wash flow rate value Qri+1 different from the first, in order to reduce the first difference and / or reduce the second difference. In other words, both phase time wash flow rates at which the unit operates in step 300 are modified simultaneously. The phase time durations may be extended or shortened, and the wash flow rate values ​​may be increased or decreased. It is therefore possible that the first difference or the second difference, and also both, may exceed the corresponding threshold value S1 or S2, which is insufficient to proceed to step 304 of the method.

[0113] The phase time may be modified first, then the cleaning flow rate. Conversely, the cleaning flow rate may be modified first, then the phase time may be modified second. The cleaning flow rate and the phase time may be modified together in order to reach the required yield value more quickly. In particular, the cleaning flow rate and the phase time are modified simultaneously. The control of the separation method is then faster. In fact, before making a new change, the operation of the separation unit should be allowed to stabilize, i.e. the measured yields should move towards their new values ​​in a sufficiently asymptotic manner to allow the evaluation of the residual differences between the measured values ​​and the reference values. Such stabilization requires several cycles, and the simultaneous modification of the two parameters, the phase time and the cleaning flow rate, achieves stabilization more quickly than if this modification is performed in two successive steps, with the second modification being performed only after the initial stabilization of the separation unit 10.

[0114] The cleaning flow rate and the phase time are in particular modified independently of each other. In other words, the actuators 6;7;8;9;12;17;18 act on the two parameters of the phase time and the cleaning flow rate, changing the value of each of the two parameters independently of the modification of the value of the other parameter, in particular modifying each of these parameters above any modification caused by the modification of the other parameter. In particular, the flow control system acts on the first parameter of the phase time, in particular the duration of the cleaning phase, and the flow regulation device acts on the parameter of the cleaning flow rate. In a particular implementation of the method, the cleaning flow rate is modified independently of the feed gas flow rate.

[0115] It is understood that the flow control system includes all actuators that allow the modification of the phase times (and thus the change of the cycle time of the separation unit 10) by one or more of the methods described below.

[0116] The separation unit 10 is then operated at the new product yield and the new purge rate, e.g., the wash flow rate value 34 is increased and the phase time is decreased to increase the determined first component extraction yield and maintain the determined second component extraction yield.

[0117] The selected threshold for the difference is a function of the uncertainties in the product yield R and the purge rate P, so that a correction only occurs if the measured difference between the measured yield and the reference yield is equal to or greater than the yield uncertainty. This also allows the method to be stopped as soon as the difference between the measured value and the reference value is equal to or less than the calculated uncertainty. Without redundant data and matching software, the process for triggering and / or stopping the correction of the operating parameters may be the same, but with a larger uncertainty, and logically so too for the difference threshold.

[0118] To modify a phase time, in particular an adsorption phase time, the control unit 10 can for example send a control signal to the feed valve 6 commanding a full opening or full closing of the feed valve 6. One possible action is for example to vary the time of the start of the feed of the feed gas 30 to the adsorber in the adsorption step 101;201 at the beginning of a phase. Similarly, it is also possible to vary the time of the end of the feed of the feed gas 30 to said adsorber.

[0119] Additionally or alternatively, the control unit 10 may send a control signal to the production valve 7, for example commanding a full opening or a full closing of the production valve 7. One possible action is to vary the time of the start of the production of the second fraction 32 by the adsorber in the adsorption step 101;201, for example at the beginning of the phase. Similarly, it is also possible to vary the time of the end of the production of the second fraction 32 by the adsorber.

[0120] Varying the supply of gas flow to the adsorbent in the adsorption step 101;201 and / or the production of gas flow by this adsorbent in this manner is equivalent to lengthening or shortening said adsorption step 101;201 in the embodiments of figures 3 and 4.

[0121] Another additional or alternative solution for extending or shortening the pressure cycle duration by acting on the duration of the cycle steps is to modify one or more phases including the pressurization or repressurization step 104;208, the balancing step 203 with pressure drop and the balancing step 207 with pressure increase, as well as the elution gas supply step 204 and the elution step 206. In this case, the control unit 13 sends a control signal to one of the switching valves 8;17;18 in order to regulate the so-called transfer flow 33;36;37 between one of the adsorbents supplying a gas flow in steps 101;201;203;204 and one of the adsorbents receiving said corresponding gas flow in steps 104;206;207;208. Then, by adjusting the transfer flow, it is possible to increase or decrease the speed of pressurization, repressurization, balancing or elution of the adsorbents in steps 104;206;207 and 208. In the case of an adsorber in a repressurization or pressurization step 208, the transfer flow is the pressurization flow 33 and the changeover valve allowing the adjustment is the pressurization valve 8. In the case of an adsorber in a balancing step 203;207, the transfer flow is the balance flow 36 and the changeover valve allowing the adjustment is the balance valve 17. In the case of an adsorber in an elution gas supply or elution step 204;206, the transfer flow is the elution gas supply flow 37 and the changeover valve allowing the adjustment is the elution gas supply valve 18. In the embodiment of figures 3 and 4, this is equivalent to lengthening or shortening the pressurization or repressurization steps 104;208, the balancing step 203 with pressure drop and the balancing step 207 with pressure increase, and / or the elution gas supply step 204 and the elution step 206.

[0122] By these actions, the duration of the pressure cycle is shortened or lengthened. Since the number of adsorber in the separation unit 10 is constant in this method, the phase time is lengthened or shortened. This means that each of the pressure cycle phases is lengthened or shortened in the same manner.

[0123] As an alternative to lengthening or shortening the phase time by acting on the cycle step duration, dead time steps may be added to the pressure cycle during which the adsorbent or adsorbents remain the same, for example by fluidically isolating the adsorbent or adsorbents, or such steps may be deleted from the pressure cycle. Such steps are not shown in Figures 3 and 4. However, such methods may also be used in addition to modifying the pressure cycle duration by acting on the cycle step duration.

[0124] It is understood that the phase time of the separation unit 10 can be modified by controlling at least one parameter of the gas flow fed to the adsorber of the separation unit and / or by controlling at least one parameter of the gas flow produced by the adsorber of the separation unit. At least one parameter of the gas flow transferred from one adsorber to another can be specifically controlled for this purpose. In the described embodiment, the or said parameter of the gas flow is selected from the flow rate of said gas flow and / or the flow duration of said flow, i.e., lengthening or shortening the flow over time. This can cause the incorporation of a step in a pressure cycle or the removal of a step from a cycle. The step is considered to have zero duration or zero gas flow rate, for example before its incorporation in the cycle. The added step can be a dead-time step.

[0125] To modify the wash flow rate, the control unit 13 may send a control signal to the flow rate adjusting device to increase or decrease the wash flow rate. The control unit 13 may, for example, command the three-way valve 9 to adjust a portion of the first fraction between the product gas flow 35 and the wash flow 34.

[0126] For example, for compliance with specifications given for product yield R and purge rate P, the phase time and the cleaning flow rate can be modified such that the first difference is less than or equal to a first threshold value S1 and / or the second difference is less than or equal to a second threshold value S2. It is then possible to arrive at a pair of values ​​of the parameters phase time TpX and cleaning flow rate QrX that allows reaching or at least sufficiently close to both the reference value C1 for the product yield and the reference value C2 for the purge rate.

[0127] Various methods are proposed for determining this pair of values ​​of phase time TpX and wash flow rate QrX.

[0128] A first preferred method for determining the variations to be made to the phase times and the washing fluid flow rates is used by the control unit from a database containing a number of operating points 1;2;...;N of the separation unit, each point 1;2;...;N including the feed conditions (flow rate, composition, pressure, temperature) and in particular the phase times Tp1;Tp2;...;TpN, the washing flow rates Qr1;Qr2;...;QrN, the first component extraction yields (here product yields R1;R2;...;RN) and the second component extraction yields (here purge rates P1;P2;...;PN).

[0129] Thus, the separation method may include a step 400 of recording in a database the points 1;2;...;N of stable operation of the separation unit 10, the operating points in particular corresponding to pairs of phase time duration and wash flow rate values ​​Tp1, Qr1;Tp2, Qr2,...;TpN, QrN, each pair being associated with a product yield value R1;R2;...;RN and a purge rate value P1;P2;...;PN of the separation unit 10. This recording step may be performed continuously or periodically. In particular, the operating points 1;2;...;N are determined by simulating the operation of the separation unit 10 and are then recorded in the database. The simulation software performs a series of digital calculations until a stable converged solution is found for a given set of input parameters. By simulation software is meant software that dynamically simulates the adsorption process. Such a procedure allows the provision of a large database from the first use of the separation unit 10.

[0130] The simulation is performed by fixing a set of input parameters including, for example, a nominal flow rate for the supply of the source gas 30, a nominal composition of the source gas 30, a step of the pressure cycle, a nominal phase time and / or a pressure at the end of the step.

[0131] 6 shows an example of the determination of a stabilized operating point: the simulation includes a first calculation step during which a phase time duration Tp1 is fixed and the wash flow rate value is modified so as to obtain a correlation between the first component extraction yield (particularly the product yield) and the second component extraction yield (particularly the purge rate) as a function of the wash flow rate for said fixed phase time duration Tp1. The first calculation step can be repeated for new fixed phase time durations Tp2;Tp3 different from the previous one so as to obtain a new correlation. In particular, the fixed phase time durations Tp1;Tp2;Tp3 are calculated as percentages of the nominal phase time. The simulation also includes a second calculation step, in which the cleaning flow rate value Qr1 is fixed and the phase time duration is modified so as to obtain, for said fixed cleaning flow rate value Qr1, a correlation between the first component extraction yield (particularly the product yield) and the second component extraction yield (particularly the purge rate) as a function of the phase time duration. The second calculation step is repeated for new fixed cleaning flow rate values ​​Qr2;Qr3 different from the previous one so as to obtain a new correlation.

[0132] The second calculation step may also be performed before the first calculation step. The first and / or second calculation steps may use an interpolation method to determine the correlation.

[0133] With each correlation, a corresponding curve can be traced in FIG. 6. The intersection between the curves at iso-phase time duration Tp1;Tp2;Tp3 and the curves at iso-values ​​of the wash flow rates Qr1;Qr2;Qr3 corresponds to the operating point 1;2;3 "first component extraction yield" versus "second component extraction yield". For each recorded operating point 1;2;3 at a fixed phase time duration and fixed wash flow rate, this thus results in a pair of "phase time duration" and "wash flow rate value" Tp1, Qr1;Tp2, Qr2;Tp3, Qr3 that allows the achievement of the required product yield R1;R2;R3 and purge rate P1;P2;P3 for the separation unit 10. The simulation thus allows the determination of a predetermined number of operating points to be recorded in a database.

[0134] Operating points 1;2;...;N are specifically within a predetermined performance range of the unit. In particular, the phase time durations Tp1;Tp2;...;TpN and wash flow rate values ​​Qr1;Qr2;...;QrN correspond to operating points that are within the range of phase time durations and wash flow rates defined by the dimensions of the unit.

[0135] A product yield value Ri is thus determined in step 301 and a purge rate value Pi is determined in step 302. A first difference between the product yield Ri and a first reference value C1 and a second difference between the purge rate Pi and a second reference value C2 are calculated in step 303. The first difference is compared to a first threshold value S1 and the second difference is compared to a second threshold value S2.

[0136] If the first difference is less than or equal to a first threshold S1 and the second difference is less than or equal to a second threshold S2, the method ends.

[0137] If the first difference is greater than the first threshold value S1 and / or if the second difference is greater than the second threshold value S2, proceed to step 401 of reading from the database, from the recorded pairs of phase time durations and wash flow rate values ​​TP1, Qr1; Tp2, Qr2, ..., TpN, QrN, those phase time durations TpX and wash flow rate values ​​QrX that enable the first difference to be less than the first threshold value S1 or the value of the first threshold value S1 and / or the second difference to be less than the value of the second threshold value S2 or the value of the second threshold value S2.

[0138] Once the pair of values ​​of phase time TpX and wash flow rate QrX has been determined, the method proceeds to step 304: the phase time duration Tpi is changed to the phase time duration TpX read from the database, and the wash flow rate value Qri is changed to the wash flow rate value QrX read from the database. The separation unit 10 is then operated at a product yield and purge rate such that the first difference is less than or equal to a first threshold value S1 and the second difference is less than or equal to a second threshold value S2.

[0139] Values ​​of the phase time and cleaning flow rate parameters that allow reaching, or at least reaching sufficiently close, both the criterion value C1 for product yield and the criterion value C2 for purge rate can thus be determined iteratively.

[0140] According to this second method, steps 301; 302; 303 and 304 are repeated, with step 304 involving modification of the last phase time duration Tpn reached by the separation unit 10 during the previous iteration to a new phase time duration Tpn+1 and modification of the last washing flow rate value Qrn reached by the separation unit 10 during the previous iteration to a new washing flow rate value Qrn+1, until the first difference is less than or equal to the first threshold value S1 and / or the second difference is less than or equal to the second threshold value S2.

[0141] As shown in Fig. 7, phase time and wash fluid flow rate modifications may be implemented at a first time by iteration through phase time durations at a constant wash flow rate value, and then at a second time by iteration through wash flow rate values ​​at a constant phase time duration. Such a sequence may be specifically repeated. In a reverse implementation (not shown), phase time and wash fluid flow rate modifications may also be implemented at a first time by iteration through wash flow rate values ​​at a constant phase time duration, and then at a second time by iteration through phase time durations at a constant wash flow rate value. Such a sequence may be repeated.

[0142] Steps 301; 302; 303 and 304 are repeated in addition to the modification of the phase time durations and the washing fluid flow rate values ​​by reading from the database in step 401, and in particular after this modification by reading from the database. The last phase time duration Tpn may be reached by the separation unit 10 using, for example, a method of reading from the database, as may the first washing fluid flow rate value Qrn. The iterative method may also be implemented as an alternative to the method of reading from the database. The modification of the phase time durations and the washing fluid flow rate by the iterative method is particularly advantageous when a certain threshold of difference is not exceeded. The modification of the phase time durations and the washing fluid flow rate values ​​by the iterative method is particularly advantageous for more finely adjusting the extraction yield following the modification of the phase time durations and the washing fluid flow rate values ​​by reading from the database. The switching from the method of reading from the database to the iterative method (or vice versa) may be performed depending on the first difference value and / or the second difference value.

[0143] Steps 301; 302; 303 and 304 may also be repeated via a cause / effect learning process in which the results of initial modifications of the phase time durations and wash flow rate values ​​are determined and then stored in memory, said results being taken into account in subsequent modifications of the phase time durations and wash flow rate values.

[0144] Such a learning process also makes it possible to determine the sequence of phase time / wash flow rate corrections such that, when corrections are performed successively, the yield remains above an initial yield, considered to be the minimum, when the reference value is changed. For example, in operation according to the curve in Figure 7, in order to increase the purge rate P while preserving the product yield R and never letting it go below its initial value during the transition phase, the method first provides for a reduction in the phase time and then an increase in the wash flow rate.

[0145] If the uncertainty is negligible, the phase time and the cleaning flow rate are corrected so that the determined product yield R reaches the first reference value C1 and / or the determined purge rate P reaches the second reference value C2. In this case, a zero value can be assigned to the first threshold value S1 and the second threshold value S2. Thus, if there is a difference between the determined product yield R and the first reference value C and / or a difference between the determined purge rate P and the second reference value C2, the phase time and the cleaning flow rate are corrected so that the determined product yield R reaches the first reference value C1 and / or the determined purge rate P reaches the second reference value C2.

[0146] Controlling the two parameters of the wash flow rate and the phase time therefore causes the variation of the extraction yield (product yield R and purge rate P) and therefore allows a greater operational flexibility for the first and second component extraction yields compared to prior art separation units. This flexibility can be shown not by a curve as in Figure 1, but diagrammatically by a band or more generally by an operating area S(R,P) in the diagram "product extraction yield" versus "purge rate", at least part of which lies beyond the limit curve that can be achieved by standard PSA. An example is shown in Figure 2.

[0147] For example, if the feed flow rate of the feed gas 30 is varied as a first approximation, the phase time must be varied inversely to the feed flow rate and the wash flow rate must be varied proportionally to this same flow rate in order to maintain the same performance. If necessary, this can be refined by simulations that can take into account the generally very secondary effects associated with the adsorption kinetics and the load losses of the unit.

[0148] 2 shows, next to a conventional curve L1 of the PSA yield, an operating region S(R,P) including operating points 1, 2, 3, 4 that the separation unit 10 can achieve during its operation, taking into account expected variations. Except for point 1, all other points are unreachable by a standard PSA.

[0149] A set of target operating points 1-N is determined at the time of definition of the separation unit 10 depending on expected changes in supply conditions (e.g., it is known how the composition of the exhaust gas or natural gas source varies over time), the required performance (e.g., reduced air emissions, increased capacity of downstream units, need for periodic purging of the recycle circuit). The separation unit 10 is then dimensioned such that an operating domain S of possible points (R, P) includes the selected operating points 1-N. In practice, all points in the domain correspond to possible operations.

[0150] More precisely, in the case of FIG. 2, the operating region S is limited by the curve L1 corresponding to the operation of the unit at zero wash fluid flow rate, i.e. with a standard PS cycle, and, in contrast, by the curve L2 corresponding to the maximum wash fluid flow rate selected at design time. This maximum flow rate is decisive for the dimensions of the bulk of the device (adsorbent, adsorbent mass, machinery, etc.). The upper limit of this unit, here similar to the slope d3, corresponds to the selected minimum phase time duration. This minimum value is generally fixed from the design time, taking into account features such as the adsorption kinetics, durations of elementary steps, dimensions of valves, velocities of fluids, and especially the risk of exhaustion of the adsorbent. Finally, the lower limit - here similar to the slope d4 - is fixed by the minimum acceptable extraction yield threshold Rm (for economic reasons or for example to ensure satisfactory operation of downstream units).

[0151] Among the points selected for determining the operating region S, and therefore the dimensioning of the unit, we distinguish point 1, which corresponds to a first nominal operating mode of the separation unit 10. According to another embodiment, point 1 corresponds to the limit point acceptable in case of an inoperative cleaning (for example a compressor repair management). This point corresponds to the operation of the unit with a product yield value R1 and a purge rate P1. We can distinguish point 2, which tends to favor a useful product yield, against point 3, which favors a loss of the purge rate, or conversely, a purge. These two cases can also be extreme operations leading to a recycle loop in which the content of inert gases (here poorly adsorbable fractions) varies as a function of time for reasons external to the separation unit. Points 4 and 5 correspond to performance targets expected in the future. In fact, all points of the region S can be reached by the separation unit and correspond to a single pair of "phase time, cleaning flow rate" (not shown in FIG. 2).

[0152] The wash ratio in the process according to the invention is typically between 0.05 and 0.65, or even between 0.05 and 0.5. The process according to the invention allows for the operational flexibility of low wash ratios so that the unit 10 remains effective and competitive, as opposed to processes that require high yields and high purity levels.

[0153] The method according to the present invention has several applications.

[0154] The separation method is used, for example, in a recycling loop to capture carbon monoxide from the smoke of a blast furnace and to recycle them as a reducing agent to said furnace. The smoke constitutes the raw gas 30 and contains a mixture of carbon monoxide and nitrogen, a first fraction 31 being rich in carbon monoxide and a second fraction 32 being rich in nitrogen. The smoke is first treated, for example, in a carbon dioxide capture unit. Carbon monoxide is a useful gas similar to a product and is extracted from the smoke by a separation unit 10 with an adjustable product yield R. Nitrogen is a remaining gas similar to a purge and is extracted from the smoke by a separation unit 10 with an adjustable purge rate P as well. Thanks to the method according to the invention, it is possible to obtain a desired carbon monoxide extraction yield and a desired nitrogen purge rate. Thus, precise specifications, for example the proportions of nitrogen and carbon monoxide, can be observed for the first gas fraction 31 recycled into the blast furnace. In the steel making process, reducing the amount of nitrogen in the flow that originates from the smoke and is recycled into the blast furnace makes it possible to emit less carbon dioxide at the outlet from the blast furnace and therefore to reduce the size of the carbon dioxide capture unit.

[0155] The separation method may also be used to capture carbon dioxide. The feed gas 30 comprises a mixture of carbon dioxide and nitrogen, with a first fraction 31 being rich in carbon dioxide and a second fraction 32 being rich in nitrogen, with carbon dioxide constituting the first component and nitrogen constituting the second component. In practice, environmental factors may require increasing the CO2 capture rate over time for a feed gas 30 supply at a constant flow rate and composition. For example, a change from an extraction yield of 50%-55% and then 60% while always purging the same amount of nitrogen may be required.

[0156] The separation method is also used for the purification of a feed gas 30 comprising a mixture of methane and nitrogen. A first fraction 31 is rich in methane and a second fraction 32 is rich in nitrogen, the methane constituting the product and the nitrogen constituting the purge. It is then possible to separate the nitrogen from the biogas as a step in the processing of the biogas in order to meet the specifications of the natural gas distribution network. More generally, any gas flow containing methane and compounds less adsorbable than methane can be similarly processed.

Claims

1. A method for separating a feed gas (30) by pressure swing adsorption, comprising: a separation unit (10) receiving the feed gas (30) and producing a first gas fraction (31) enriched in a first component and a second gas fraction (32) enriched in a second component, said first component being more adsorptive than said second component, said separation unit (10) comprising a plurality of adsorbents, said adsorbents being subjected to pressure cycles characterized by high and low pressures, said pressure cycles comprising a plurality of steps (101; ...; 104; 201; ...; 208) including at least one adsorption step (101; 201) and at least one wash step (102; 202) in which a wash fluid enriched in said first component is circulated through at least one adsorbent to release at least a portion of said second component from said adsorbent, said pressure cycles having a phase time corresponding to the duration of said pressure cycle divided by the number of adsorbents, said method comprising the following steps: a) determining a first component extraction yield value defined as the ratio of the amount of the first component in the produced first fraction (31) to the amount of the first component in the feed gas (30) fed to the separation unit (10); b) determining a second component extraction yield value defined as the ratio of the amount of the second component in the produced second fraction (32) to the amount of the second component in the feed gas (30) fed to the separation unit (10); c) determining a first difference between the first component extraction yield value determined in step a) and a first reference value (C1) associated with the first component extraction yield, and a second difference between the second component extraction yield value determined in step b) and a second reference value (C2) associated with the second component extraction yield; d) modification of the phase times and of the wash fluid flow rate, referred to as wash flow rate (34), to reduce the first difference and / or the second difference if the first difference is greater than a first predetermined threshold (S1) and / or the second difference is greater than a second predetermined threshold (S2). A method comprising:

2. 2. The method of claim 1, wherein the first reference value (C1) expressed as a yield percentage is between 25 and 90% and the second reference value (C2) expressed as a yield percentage is between 20 and 90%.

3. 3. The method according to claim 1 or 2, wherein a part of the first fraction (31) is used as product gas and another part is used as scrubbing fluid, the ratio of the scrubbing flow rate (34) to the sum of the scrubbing flow rate (34) and the product gas flow rate (35) being between 0.05 and 0.65, preferably between 0.05 and 0.

5.

4. 4. The method according to claim 1, wherein said phase time is modified by controlling at least one parameter of a gas flow supplying the adsorbent of the separation unit (10) and / or at least one parameter of a gas flow produced by the adsorbent of the separation unit (10), in particular at least one parameter of a gas flow transferred from one adsorbent to another.

5. The method according to any one of claims 1 to 4, wherein said parameters are selected from said flow rate and / or said flow duration.

6. 6. The method according to claim 4 or 5, wherein the phase time is modified by varying the start and / or end times of the supply of the gas flow to at least one adsorber.

7. A method according to any one of claims 4 to 6, wherein the phase time is modified by varying the time of the start and / or end of the production of the gas flow by at least one adsorbent.

8. 8. The method of claim 4, wherein the flow rate of the gas flow transferred from one adsorbent to another is adjusted to accelerate or decelerate gas transfer between the adsorbents.

9. The method also comprises the steps of: i) recording in a database points (1; 2; ...; N) of stabilization operation of the separation unit (10), said operation points (1; 2; ...; N) corresponding to pairs of phase time duration and wash flow rate values ​​(Tp1, Qr1; Tp2, Qr2; ...; TpN, QrN), each pair being associated with a first component extraction yield value and a second component extraction yield value of the separation unit (10); ii) if the first difference is greater than the first threshold (S1) and / or the second difference is greater than the second threshold (S2), reading a phase time duration (TpX) and a wash flow rate value (QrX) from the database, whereby the first difference is less than or equal to the first threshold (S1) and / or the second difference is less than or equal to the second threshold (S2), then allowing a correction of the phase time to the phase time duration (TpX) read from the database, and a correction of the wash flow rate to the wash flow rate value (QrX) read from the database; The method according to any one of claims 1 to 8, comprising:

10. 10. The method according to any one of claims 1 to 9, wherein steps a), b), c) and d) are repeated until the first difference is less than or equal to the first threshold value (S1) and / or the second difference is less than or equal to the second threshold value (S2), with for step d) a modification of the last phase time duration to a new phase time duration (Tpn+1) and a modification of the last wash flow rate value to a new wash flow rate value (Qrn+1).

11. 11. The method according to any one of claims 1 to 10, wherein the feed gas (30) comprises a mixture of carbon monoxide and nitrogen, the first fraction (31) being rich in carbon monoxide and the second fraction (32) being rich in nitrogen, carbon monoxide constituting the first component and nitrogen constituting the second component, in particular for capturing carbon monoxide from blast furnace smoke and recycling it as reducing agent in the blast furnace.

12. 11. The method for capturing carbon dioxide according to any one of claims 1 to 10, wherein the feed gas (30) comprises a mixture of carbon dioxide and nitrogen, the first fraction (31) being rich in carbon dioxide and the second fraction (32) being rich in nitrogen, carbon dioxide constituting the first component and nitrogen constituting the second component.

13. 11. A method according to any one of claims 1 to 10 for the purification of a feed gas (30), wherein the feed gas (30) comprises a mixture of methane and nitrogen, the first fraction (31) being rich in methane and the second fraction (32) being rich in nitrogen, methane constituting the first component and nitrogen constituting the second component.

14. A unit (10) for separating a feed gas (30) by pressure swing adsorption for the production of a first gas fraction (31) enriched in a first component and a second gas fraction (32) enriched in a second component, the first component being more adsorptive than the second component, the separation unit (10) comprising a plurality of adsorbents configured to be subjected to pressure cycles characterized by high and low pressures, the cycles comprising a plurality of steps (101; ...; 104; 201; ...; 208) including at least one adsorption step (101; 201) and a wash step (102; 202) in which a wash fluid enriched in the first component is circulated through at least one adsorber to release at least a portion of the second component from the adsorber, the pressure cycles having a phase time corresponding to the duration of the pressure cycle divided by the number of adsorber, the separation unit (10) comprising: a flow control system adapted to modify said phase times by controlling at least one parameter of the gas flow supplied to the adsorber of said separation unit and / or at least one parameter of the gas flow produced by the adsorber of said separation unit, in particular at least one parameter of the gas flow transferred from one adsorber to another, a flow regulation device configured to modify the washing fluid flow rate (34); a control unit (13) and communication means (14) between said control unit, said flow control system and said flow regulation device, said control unit (13) being adapted to implement the method according to any one of claims 1 to 13; A unit (10), comprising:

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