Separation method

Abstract

The invention relates to a method for separating a feedstock gas (30) by pressure swing adsorption in which a separation unit (10) is supplied with the feedstock gas (30) and produces a first gaseous fraction (31) enriched in a first component and a second gaseous 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 adsorbers, the adsorbers being subjected to a pressure cycle featuring a high pressure and a low pressure, the pressure cycle comprising a plurality of steps (101;...; 104; 201;...; 208) including at least one adsorption step (101; 201) and at least one rinsing step (102; 202) in which a rinsing fluid enriched in a first component flows through at least one adsorber so as to flush at least some of the second component out of the adsorber, the pressure cycle having a phase time corresponding to the duration of the pressure cycle divided by the number of adsorbers, the unit operating in a first mode in which the rinsing fluid flows with a first rinsing fluid flow rate value, which value is referred to as the first rinsing flow rate value (Qri), and in which the phase time is defined according to a first phase time duration (Tpi), the method comprising the steps a), b), c) and d).

Description

Separation process

[0001] The present invention relates to a unit for the adsorption separation of a feed gas of said unit, called feed gas or gas to be treated, for the production of a first fraction of the feed gas enriched in highly adsorbable compounds and a second fraction of the feed gas enriched in weakly adsorbable compounds. The invention also relates to a method of adsorption separation.

[0002] Adsorption is widely used to purify or separate (fractionate) gases. Examples include the fractionation of "n" and "iso" paraffins, the fractionation of xylenes and alcohols, the production of nitrogen or oxygen from atmospheric air, and the deballasting of CO2 from combustion gases and blast furnace gases. On the purification side, there are dryers, hydrogen or helium purification, methane-rich gas purification, and the adsorption of trace impurities in many fluids (mercury, NOx, and sulfur products, etc.).

[0003] A feed gas to the separation unit comprises a mixture of weakly adsorbable compounds and strongly adsorbable compounds. In an adsorption separation process, one or more strongly adsorbable gaseous compounds (hereinafter the first component or strongly adsorbable component) and one or more weakly adsorbable gaseous compounds (hereinafter the second component or weakly adsorbable component) are extracted from the feed gas. The feed gas therefore comprises a mixture of these two components. The strongly adsorbable component is the most adsorbable of the two components and the weakly adsorbable component is the least adsorbable of the two components. Depending on the application, the recoverable gas (recoverable component) is the weakly adsorbable component or, on the contrary, the strongly adsorbable component. This is then referred to as the "product".The other component then constitutes the residual or the “purge” (residual component).

[0004] In particular, an adsorption separation unit comprises several tanks for circulating the treated gases, each of the tanks comprising an adsorbent material. These tanks, sometimes also called columns, serve as a support for the adsorbent material and ensure the circulation of the gases. These tanks are subsequently referred to as "adsorbers".

[0005] The processes using adsorption are of several types depending on whether the adsorbent can be regenerated in situ or not. We therefore speak of "lost charge" adsorption, i.e. to be renewed when the adsorbent is saturated with impurities (in this case we also use the term "guard bed" to describe such purification) or adsorption cycles in the other case.

[0006] Adsorption cycles differ primarily in the way the adsorbent is regenerated. If regeneration is primarily achieved by increasing the temperature, it is a TSA (Temperature Swing Adsorption) process. If, on the other hand, regeneration is achieved by lowering the pressure, it is a PSA (Pressure Swing Adsorption) process, and pressure swing adsorption separation units are referred to as a PSA unit.

[0007] In general, the term PSA refers to any gas purification or separation process that involves a cyclical variation in the pressure experienced by the adsorbent between a high pressure, called the adsorption pressure, and a low pressure (lower than the high pressure), called the regeneration pressure. This is then referred to as a pressure swing adsorption purification or separation process. Thus, this generic term PSA (from the English "Pressure swing adsorption") is used interchangeably to designate the following cyclic processes, which are also commonly given more specific names depending on the pressure levels involved or the time required for an adsorber to return to its initial point (cycle time): - VSA processes in which adsorption takes place substantially at atmospheric pressure, preferably between 0.95 and 1.25 bar abs and the desorption pressure is lower than atmospheric pressure, typically 50 to 400 mbar abs;- MPSA or VPSA processes in which adsorption takes place at a high pressure higher than atmospheric pressure, typically between 1.35 and 6 bar abs, and desorption at a low pressure lower than atmospheric pressure, generally between 200 and 650 mbar abs;- PSA processes proper in which the high pressure is significantly higher than atmospheric pressure, typically between 3 and 50 bar abs and the low pressure is substantially equal to or higher than atmospheric pressure, generally between 1 and 9 bar abs;- RPSA (Rapid PSA) processes for which the pressure cycle time is typically less than a minute;- URPSA (Ultra Rapid PSA) processes for which the pressure cycle time is of the order of a few seconds maximum.

[0008] It should be noted that these various names are not standardized and that in particular the limits indicated are subject to variation. It should be noted that, unless otherwise stated, the use of the term PSA here covers all these variants.

[0009] An adsorber will begin an adsorption period until it is loaded with the constituent(s) to be stopped at high pressure and will then be regenerated by depressurization and extraction of the adsorbed compounds before being restored to begin a new adsorption period. The adsorber has then completed a pressure cycle and the very principle of the PSA process is to chain these cycles one after the other. It is therefore a cyclic process. In principle, each adsorber follows the same cycle with a time lag which is called phase time or more simply phase.

[0010] We therefore have the relationship: Phase time = (cycle time) / (number of adsorbers)Each of the adsorbers successively passes through the series of phases constituting the PSA cycle, each of the phases being of equal duration.

[0011] An adsorber is, conventionally, subjected to the pressure cycle comprising the following steps and in particular in the following order: 1) adsorption at the high pressure of the cycle with production of the second fraction enriched in weakly adsorbable component, in particular with supply of a re-pressurization flow consisting of a part of the second fraction produced; 2) depressurization to low pressure with production of the first fraction; 3) re-pressurization to high pressure, in particular with the re-pressurization flow provided in step 1.

[0012] It should be noted that in a cycle, a given stage is distinguished from the preceding or following stage by one of the following reasons: the existence or not of inlet and / or outlet flows and by their direction of circulation in the adsorber, by the origin of an inlet flow, by the destination of an outlet flow. A phase can comprise several distinct stages and conversely a stage can take place over more than one phase.

[0013] An adsorption separation unit operates with an extraction efficiency of highly adsorbable components corresponding to the ratio of the quantity of highly adsorbable components in the first fraction extracted at low pressure to the quantity of highly adsorbable components in the feed gas. The separation unit also operates with an extraction efficiency of weakly adsorbable components corresponding to the ratio of the quantity of weakly adsorbable components in the second fraction extracted at high pressure to the quantity of weakly adsorbable components in the feed gas. Depending on the applications, the extraction efficiency of the recoverable components is referred to as "product extraction efficiency" and the extraction efficiency of the residual components is referred to as "purge rate".The invention relates more particularly to adsorption separation processes in which these extraction yields are not particularly high, either for the product or for the purge.

[0014] A standard separation unit comprising a given adsorbent load and / or a given dimension operates for a feed gas fixed according to a characteristic curve "extraction yield in strongly adsorbable component" versus "extraction yield in weakly adsorbable component" or vice versa. La shows an example of curve (c) with here, the "extraction yield in strongly adsorbable component" on the ordinate and the "extraction yield in weakly adsorbable component" on the abscissa. The product of yield R was arbitrarily chosen to be the strongly adsorbable component (first fraction) and therefore the purge (second fraction) of yield P to be the weakly adsorbable component. Very generally, the phase time is used as a means of adjustment to run through this curve.It is understood that with a short phase time Tp1, the highly adsorbable component is practically not allowed to penetrate into the second fraction at high pressure. The highly adsorbable component is then found in very large majority in the first fraction extracted at low pressure, leading to a high extraction yield of the more adsorbable component R1. The other consequence is that a significant part of the weakly adsorbable component is left in the adsorber, that this component comes out at least in part at low pressure and that the extraction yield of the weakly adsorbable component P1 is reduced. A longer phase time Tp2 leads to the opposite reasoning with the corresponding yields R2 lower than R1 and P2 higher than P1.

[0015] Typically, the main constraint for the product is to meet the specified purity (e.g., produce 99.99 mol% hydrogen) and the separation unit is set to operate at the highest possible efficiency, thereby limiting the feed gas flow rate required and thereby the cost of the raw material (natural gas in the same example).

[0016] In some industrial applications, however, it is necessary to comply with precise specifications for the two fractions produced by PSA units even if the composition of the feed gas changes. For other applications, on the contrary, with unchanged feed, the specifications of these productions will have to evolve over time. A current example illustrating this last case is the imposed increase in the CO2 capture rate in the coming years for environmental reasons.

[0017] A so-called rinse step can be added to the cycle, which consists of circulating a gas enriched in the highly adsorbable component, called the rinse fluid, through an adsorber, with the aim of removing the gases of the weakly adsorbable component from the adsorbent material and the dead volumes. Such a step makes it possible to increase the extraction yield of the weakly adsorbable component by recovering a portion of the weakly adsorbable gaseous compounds found in the adsorber at the end of the adsorption step. It is also possible to add such a rinse step when the highly adsorbable component is the recoverable component in order to limit the quantity of the weakly adsorbable component in the latter.

[0018] It is known from the prior art to use such a rinsing step in order to produce a fraction enriched in weakly adsorbable gaseous compounds with high purity and yield. This is particularly the case when it is desired to produce methane for injection into a so-called natural gas network with a required methane purity often greater than 96% and with an extraction yield of the order of 95% and more. In order to achieve high yield and purity, the rinsing fluid flow rate may be higher than the production flow rate, resulting in significant oversizing in terms of adsorbent volume and compression means. This has significant repercussions on the construction price of the installation and on the operating price of this installation, due to higher energy consumption.Thus, these known installations of the prior art are mainly located on landfill gas and are only economically justified by environmental reasons (bans on venting large quantities of greenhouse gases) and the corresponding subsidies. The known installations of the prior art operating a rinsing step are therefore not competitive. In addition, an increase in the rinsing fluid flow rate to achieve a high extraction efficiency in weakly adsorbable components leads to a reduction in the extraction efficiency in strongly adsorbable components, due to the characteristic curve (limit curve) of operation of the unit.

[0019] These standard separation units, with or without a rinsing step, obviously do not meet the requirements for exceeding these limit 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. There is therefore a need for an adsorption separation unit with increased operational flexibility.

[0020] The invention thus relates to a method for separating a feed gas by pressure swing adsorption in which a separation unit is supplied with the feed gas and produces a first gaseous fraction enriched in a first component and a second gaseous fraction enriched in a second component, the first component being more adsorbable than the second component. The separation unit comprises a plurality of adsorbers, said adsorbers being subjected to a pressure cycle having a high pressure and a low pressure. The pressure cycle comprises a plurality of steps including at least one adsorption step and at least one rinsing step. During the rinsing step,a rinsing fluid enriched in the first component circulates in at least one adsorber so as to expel at least a portion of the second component from said adsorber. The pressure cycle has a phase time corresponding to a duration of the pressure cycle divided by the number of adsorbers. The method comprises the following steps:a) determining a first component extraction efficiency value defined by the ratio of the quantity of first component in the first fraction produced to the quantity of first component in the feed gas feeding the separation unit,b) determining a second component extraction efficiency value defined by the ratio of the quantity of second component in the second fraction produced to the quantity of second component in the feed gas feeding the separation unit,c) determining a first deviation between the extraction efficiency value in the first component determined in step a) and a first setpoint value relating to the extraction efficiency in the first component and a second deviation between the extraction efficiency value in the second component determined in step b) and a second setpoint value relating to the extraction efficiency in the second component,d) if the first deviation is greater than a first predetermined threshold and / or the second deviation is greater than a second predetermined threshold, modifying the phase time and modifying a flow rate of the rinsing fluid, called the rinsing flow rate, so as to reduce the first deviation and / or the second deviation.,

[0021] Acting on the phase time parameter and the rinsing flow rate parameter makes it possible to compensate for the increase or decrease in extraction efficiency experienced due to the modification of one or the other of these parameters. For example, to increase the extraction efficiency in the first component while maintaining the extraction efficiency in the second component, the duration of the phase time can be shortened and the value of the rinsing flow rate can be increased. Controlling both the rinsing flow rate and phase time parameters therefore allows increased operational flexibility on the extraction efficiencies in the first component and in the second component compared to the separation units of the prior art.

[0022] The first threshold and the second threshold may in particular be defined to take into account the usual fluctuations in the efficiency of the separation process.

[0023] According to one implementation of the method, the phase time and the rinsing flow rate are modified so as to make the first deviation less than or equal to the first threshold and / or to make the second deviation less than or equal to the second threshold.

[0024] According to one implementation of the method, the unit operates according to a plurality of operating modes, the rinsing fluid circulating according to a determined rinsing flow rate value and the phase time being defined according to a phase time duration determined in each of the operating modes.

[0025] According to one implementation of the method, the rinsing flow rate and the phase time are modified jointly. In particular, the rinsing flow rate and the phase time are modified simultaneously.

[0026] In particular, the rinsing flow rate and the phase time are modified independently of each other.

[0027] According to one implementation of the method, the rinsing flow rate is increased and the phase time is shortened so as to increase the determined first component extraction yield and maintain the determined second component extraction yield. This improves the separation between the first component and the second component.

[0028] According to one implementation of the method, the phase time and the rinsing flow rate are modified, so that the determined first component extraction efficiency reaches the first set value and / or the determined second component extraction efficiency reaches the second set value.

[0029] According to one implementation of the method, the first threshold and / or the second threshold is equal to 3%, preferably equal to 1.5%, preferably equal to 0.5%, possibly equal to zero. In the latter case, in the event of a difference between the determined first component extraction efficiency value and the first setpoint value and / or a difference between the determined second component extraction efficiency value and the second setpoint value, the phase time and the rinsing flow rate are modified so that the determined first component extraction efficiency reaches the first setpoint value and / or the determined second component extraction efficiency reaches the second setpoint value. The above are percentages relative to the 0-100% scale of the efficiencies.Thus, for an efficiency setpoint of 65%, for example, the different efficiency ranges beyond which the process would be implemented would be for the 3% threshold: 62 / 68%, for the 1.5% threshold: 63.5 / 66.5%, for the 0.5% threshold: 64.5-65.5%. The choice of one of these ranges will depend on the sensitivity of the downstream units to the separation performance of the separation unit as well as the measurement accuracy of the separation unit's efficiencies.

[0030] According to one implementation of the method, the first component extraction efficiency value and the second component extraction efficiency value are determined by analyzing the composition of the feed gas feeding the unit, the first fraction produced and the second fraction produced. In particular, an analyzer determines the first component and / or second component content in the feed gas, the first fraction and the second fraction. The first and / or second component content is, for example, measured using one or more probes. The analyzer can in particular deduce the first component or second component content 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 efficiency values.

[0031] According to one implementation of the method, the first setpoint value expressed as a percentage of efficiency is between 25 and 90% and the second setpoint value expressed as a percentage of efficiency is between 20 and 90%.

[0032] According to one implementation of the process, the rinsing step immediately follows an adsorption step.

[0033] According to one implementation of the method, the pressure cycle comprises at least the following steps and in particular in the following order: 1) adsorption at the high pressure of the cycle with production of the second fraction enriched in the second component, in particular with supply of a re-pressurization flow consisting of a part of the second fraction produced; 2) rinsing; 3) depressurization to the low pressure, with production of the first fraction and supply of the rinsing flow; 4) re-pressurization to the high pressure, in particular with the re-pressurization flow supplied in step 1.

[0034] According to one implementation of the method, the pressure cycle comprises the following steps and in particular in the following order: 1) adsorption at the high pressure of the cycle with production of the second fraction enriched in the second component, in particular with supply of a re-pressurization flow consisting of a part of the second fraction produced; 2) rinsing; 3) at least one step of balancing in descending pressure and supply of one or more balancing flows in ascending pressure; 4) supply of elution gas; 5) depressurization to the low pressure, with production of the first fraction; 6) elution with the elution gas supplied in step 4, production of the first fraction and supply of the rinsing flow in at least one of steps 5 and 6; 7) at least one step of balancing in ascending pressure with the balancing flow(s) supplied in step 3;8) re-pressurization to high pressure, in particular with the re-pressurization flow provided in step 1.;

[0035] A pressure cycle comprising the preceding steps 1 to 8 but without the rising and falling pressure balancing steps (steps 3 and 7) can also be implemented as an intermediate cycle between the cycles described previously.

[0036] According to one implementation of the method, the pressure cycle comprises, after a depressurization step to a pressure close to atmospheric pressure, a vacuum pumping step during which the first fraction is evacuated. The elution step may coincide with the vacuum pumping step or may correspond to a final part of the vacuum pumping step. The low pressure of the cycle may then be reached during the vacuum pumping step or at the end of said step, depending on the flow rates.

[0037] According to one implementation of the method, the pressure cycle also includes one or more dead time steps, during which one or more adsorbers remain in the same state. In particular, the adsorbers in the dead time step remain at the same pressure.

[0038] According to one implementation of the process, part of the first fraction is recovered as product gas and another part is used as rinsing fluid.

[0039] According to one implementation of the method, the rinsing flow rate divided by the sum of the rinsing flow rate and a flow rate of said produced gas is between 0.05 and 0.65, preferably between 0.05 and 0.5.

[0040] According to one implementation of the process, the flow of gas produced is compressed before being directed to downstream equipment.

[0041] According to one implementation of the method, the rinsing fluid is also compressed before being introduced into the adsorber which undergoes the rinsing step. In particular, the rinsing fluid is compressed to high pressure.

[0042] According to one implementation of the method, the rinsing fluid circulates in the at least one adsorber undergoing the rinsing step in the same direction of circulation as that of the feed gas when said adsorber undergoes the adsorption step. The rinsing step is then said to be co-current.

[0043] According to one implementation of the method, a stream from the adsorber which undergoes the rinsing step is introduced, with the feed gas, into at least one adsorber which undergoes the adsorption step.

[0044] According to one implementation of the method, the rinsing step is carried out over an integer number of phase times. The rinsing step is then carried out over at least one complete phase time.

[0045] According to one implementation of the method, the phase time is modified by controlling at least one parameter of a gas flow supplying an adsorber of the separation unit and / or at least one parameter of a gas flow produced by an adsorber of the separation unit, in particular at least one parameter of a gas flow transferred from one adsorber to another.

[0046] In particular, said parameter is chosen from the flow rate and / or the flow duration.

[0047] According to one implementation of the method, the phase time is modified via at least one of the following actions: - adding or removing a step from the pressure cycle; - lengthening or shortening a step.

[0048] According to one implementation of the method, a dead time step during which one or more adsorbers remain in the same state as at the end of the previous step is added to the pressure cycle. In particular, the dead time step is added by fluidically isolating the adsorber(s) remaining in the same state.

[0049] Depending on an implementation of the method, a dead time step is lengthened or shortened.

[0050] According to one implementation of the method, the modification of the phase time is carried out at the start of the phase.

[0051] According to one implementation of the method, the phase time is modified by shifting in time a start and / or an end of supply by the gas flow of at least one adsorber.

[0052] According to one implementation of the method, the phase time is modified by shifting in time a start and / or an end of production of the gas flow by at least one adsorber.

[0053] According to one implementation of the method, the phase time is modified by shifting in time a start and / or an end of feed gas supply to one or more adsorbers in the adsorption stage and / or by shifting in time a start and / or an end of production of the second fraction by said adsorber(s).

[0054] According to one implementation of the method, a flow rate of a gas stream transferred from one adsorber to another, called the transfer flow rate, is regulated so as to accelerate or slow down a gas transfer between said adsorbers.

[0055] In particular, the adsorber supplying the gas flow is in depressurization and the adsorber receiving the gas flow is in pressurization and the gas transfer is accelerated or slowed down so as to increase or decrease a depressurization and / or pressurization speed of said adsorbers. In particular, the transfer flow rate is a balancing flow rate between at least one adsorber in balancing in descending pressure and at least one adsorber in balancing in ascending pressure.

[0056] According to one implementation, the method comprises the following steps:i) recording in a database of stabilized operating points of the separation unit, the operating points corresponding to pairs of phase time duration and rinsing flow rate value, each pair being associated with a first component extraction efficiency value and a second component extraction efficiency value of the separation unit,ii) if the first deviation is greater than the first threshold and / or the second deviation is greater than the second threshold, reading from the database a phase time duration and a rinsing flow rate value making it possible to make the first deviation less than or equal to the first threshold and / or to make the second deviation less than or equal to the second threshold,then changing the phase time to the phase time duration read from the database and changing the flushing flow rate to the flushing fluid flow rate value read from the database.,

[0057] According to one implementation of the method, steps a), b), c) and d) as defined above are repeated until the first deviation is less than or equal to the first threshold and / or the second deviation is less than or equal to the second threshold, with for step d) a modification of the last duration of the phase time into a new duration of the phase time and a modification of the last rinsing flow rate value into a new rinsing flow rate value.

[0058] According to one implementation of the method, the modification of the phase time and the rinsing fluid flow rate is implemented initially by iterations over the phase time duration, at a constant rinsing flow rate value, then in a second step by iterations over the rinsing flow rate value, at a constant phase time duration. Such a sequence can in particular be repeated.

[0059] According to one implementation of the method, the modification of the phase time and the rinsing flow rate is implemented initially by iterations on the rinsing flow rate value, at constant phase time duration, then in a second stage by iterations on the phase time duration, at constant rinsing flow rate value. Such a sequence can also be repeated.

[0060] According to one implementation of the method, steps a), b), c) and d) are repeated in addition to the modification of the phase time and the rinsing flow rate by reading from a database, in particular after this modification by reading from a database.

[0061] According to one implementation of the method, steps a), b), c) and d) are repeated as an alternative to modifying the phase time and the rinsing flow rate by reading from a database.

[0062] According to one implementation of the method, a recoverable component similar to a product and a residual component similar to a purge are extracted. In particular, the first component is the recoverable component and the second component is the residual component.

[0063] The method can be implemented to capture carbon monoxide, in particular from the fumes of a blast furnace in order to recycle it as a reducing agent in said blast furnace, the charge gas comprising a mixture of carbon monoxide and nitrogen, the first fraction being enriched in carbon monoxide and the second fraction being enriched in nitrogen, the carbon monoxide constituting the first component and the nitrogen constituting the second component.

[0064] For example, the fumes are first treated in a carbon dioxide capture unit.

[0065] The method can be implemented for the capture of carbon dioxide, the feed gas comprises a mixture of carbon dioxide and nitrogen and the first fraction is enriched in carbon dioxide, the second fraction being enriched in nitrogen, carbon dioxide constituting the first component and nitrogen constituting the second component.

[0066] The method can be implemented for the purification of a feed gas comprising a mixture of methane and nitrogen. According to this implementation, the first fraction is enriched in methane, the second fraction is enriched in nitrogen, the methane constituting the first component and the nitrogen constituting the second component.

[0067] The invention also relates to a unit for separating a feed gas by pressure swing adsorption for the production of a first gaseous fraction enriched in a first component and the production of a second gaseous fraction enriched in a second component, the first component being more adsorbable than the second component. The separation unit comprises a plurality of adsorbers configured to be subjected to a pressure cycle having a high pressure and a low pressure. The pressure cycle comprises a plurality of steps including at least one adsorption step and a rinsing step. During the rinsing step, a rinsing fluid enriched in the first component circulates in at least one adsorber so as to expel at least a portion of the second component from said adsorber. The pressure cycle has a phase time corresponding to the duration of the pressure cycle divided by the number of adsorbers.The separation unit comprises:- a flow control system configured to modify the phase time, in particular by controlling at least one parameter of a gas flow feeding an adsorber of the separation unit and / or at least one parameter of a gas flow produced by an adsorber of the separation unit, in particular at least one parameter of a gas flow transferred from one adsorber to another,- a flow adjustment device configured to modify a flow rate of the rinsing fluid,- a control unit and means of communication between the control unit, the flow control system and the flow adjustment device, the control unit being configured to implement the method as described above.

[0068] According to one embodiment, the flow control system is configured to modify the phase time by:- adding a step to the pressure cycle or removing a step from the pressure cycle;- lengthening or shortening a step.

[0069] According to one embodiment, the flow control system comprises at least one feed valve configured to allow or prevent the feed of feed gas to one or more adsorbers in the adsorption stage.

[0070] Additionally or alternatively, the flow control system comprises at least one production valve configured to authorize or prevent the production of the second fraction enriched in the second component by one or more adsorbers in the adsorption stage, in particular said adsorber(s) in the adsorption stage.

[0071] According to one embodiment, the flow control system comprises at least one transfer valve configured to regulate a transfer flow rate between at least one adsorber providing the transfer flow rate and an adsorber receiving the transfer flow rate.

[0072] The supply valve and / or the production valve can be a shut-off valve. The transfer valve is, for example, a proportional valve.

[0073] According to one embodiment, the separation unit comprises a divergence member configured to distribute the flow rate of the first fraction between the production flow rate and the rinsing fluid flow rate. In particular, the divergence member comprises a pipe for circulating the first gaseous fraction produced, from which pipe diverges a pipe for circulating the rinsing fluid and a pipe for circulating the production flow rate. The divergence member then takes the form of a "T" for example. According to one example, the divergence member comprises a three-way valve.

[0074] According to one embodiment, the separation unit comprises a compression means, for example a compressor, configured to compress the rinsing fluid, in particular to high pressure, before introduction into the adsorber which undergoes the rinsing step. In an implementation of the method not shown, the compressor is also configured to compress the flow of gas produced, in particular to a pressure required for provision for downstream equipment.

[0075] According to one embodiment, the flow control device comprises at least one valve, such as a two-way valve, two two-way valves. These may in particular be proportional valves. In particular, the flow control device comprises the three-way valve. Alternatively or additionally, the flow control device comprises the compressor.

[0076] According to one embodiment, the separation unit comprises at least one vacuum pump configured to facilitate the desorption of the first component. The desorption then takes place at a low pressure below atmospheric pressure.

[0077] According to one embodiment, the control unit comprises data reconciliation software making it possible to determine from redundant measurements the most probable value of the determined extraction yields as well as their uncertainty.

[0078] Lrepresents the characteristic curve of a separation unit according to the prior art on a diagram of product extraction yield vs. purge rate;Lrepresents the operating range of a unit according to the invention on the diagram of product extraction yield vs. purge rate;Lrepresents a separation unit according to the invention comprising four adsorbers;Lrepresents a separation unit according to the invention comprising eight adsorbers;Lis a block diagram illustrating the steps of the separation method according to the invention and a regulation of the unit by iterations;Lrepresents curves determined by simulation for the determination of operating points of the separation unit for regulation by reading from a database;Lrepresents an example of regulation by iterations.

[0079] A separation unit 10 implementing the method according to the invention is shown in. In this embodiment, the unit comprises four adsorbers implementing steps 101, 102, 103 and 104 which will be detailed below.

[0080] The unit 10 comprises a flow control system which comprises a supply valve 6 capable of authorizing or preventing the supply of feed gas 30 to an adsorber in the adsorption stage 101, a production valve 7 capable of authorizing or preventing the production of the second fraction 32 by the adsorbers in the adsorption stage 101. The supply valves 6 and production valves 7 are here stop valves which respectively authorize or prevent a supply of feed gas 30 or a production of a second fraction 32. Such stop valves can therefore selectively authorize or prohibit the circulation of a corresponding gas flow. The flow control system comprises a transfer valve which is here a proportional pressurization valve 8 which makes it possible to regulate a so-called transfer flow rate which corresponds to a gas transfer between two adsorbers.This transfer flow rate is, in this embodiment, a pressurization flow rate 33 from the second fraction 32, between the adsorber producing the second fraction 32 in step 101 and the adsorber in pressurization or re-pressurization in step 104. Such a valve can progressively regulate a corresponding gas flow rate.

[0081] Furthermore, a flow rate adjustment device, which here comprises a three-way valve 9 and a compressor 12, makes it possible to modify a flow rate of a rinsing fluid (called “rinsing flow rate 34”) during a rinsing step 102; 202 which will be described in more detail below. The compressor 12 also makes it possible to compress the rinsing flow rate 34, for example to the high pressure of the pressure cycle, before introduction into the adsorber which undergoes the rinsing step 102. The three-way valve 9 here also acts as a “T”-shaped divergence member to distribute the flow rate of the first fraction produced in step 103 between a flow rate of recoverable product gas 35, for example sent to a following step of an installation comprising the separation unit, and the rinsing flow rate 34. This flow rate of product gas is for example compressed before being sent to downstream equipment.A buffer tank 15 makes it possible to limit pressure and composition fluctuations and also facilitates the regulation of the compressor 12.

[0082] The separation unit additionally comprises a vacuum pump 11 which facilitates the desorption of the first component in step 103, at a pressure below atmospheric pressure. A low cycle pressure is reached during step 103.

[0083] 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 adjustment device. The control unit 13 is capable of implementing the separation method according to the invention. In particular, the control unit 13 comprises programmable electronics programmed to implement the method according to the invention.

[0084] In the method according to the invention, the separation unit 10 is supplied with a feed gas 30 which comprises a mixture of one or more weakly adsorbable compounds on the one hand and one or more strongly adsorbable compounds on the other hand. The separation unit 10 extracts from the feed gas 30 the strongly adsorbable compound(s) which constitute a first strongly adsorbable component. The separation unit 10 also extracts from the feed gas 30 the weakly adsorbable compound(s) which constitute in turn a second weakly adsorbable component. By "strongly adsorbable component" is meant the most adsorbable component among said two components and by "weakly adsorbable component" is meant the least adsorbable component among said two components. In other words, the first component is more adsorbable than the second.The separation unit 10 then produces a first gaseous fraction 31 enriched in a first component and a second gaseous fraction 32 enriched in a second component. In the applications described below, the recoverable component is the first component. This is then referred to as the “product”. The second component then constitutes the waste or the purge. In certain applications, the second component comprises the weakly adsorbable compound which is in the majority, such as nitrogen, or the second component is even assimilated to this weakly adsorbable compound in the majority. The second component may however also comprise compounds such as argon, oxygen or hydrogen, in particular when these are in the minority.

[0085] In implementing the method according to the, the adsorbers of the unit are subjected to a pressure cycle comprising the following steps and in the following order:Step 101: adsorption at the high pressure of the cycle with production of the second fraction 32 enriched in the second component and extraction of the second fraction 32 produced from a pressurization flow or re-pressurization for the adsorber in step 104. The pressurization flow 33 is regulated by the pressurization valve 8.Step 102: co-current rinsing.Step 103: depressurization to the low pressure, with production of the first fraction 31 and supply of the rinsing flow 34 for the adsorber in step 102.Step 104: re-pressurization to the high pressure with the re-pressurization flow 33 supplied by the adsorber 101.

[0086] The phase time is therefore equal to the duration of the pressure cycle, or cycle time, divided by the number of adsorbers, here four adsorbers.

[0087] In a second implementation of the method shown in , the separation unit 10 comprises eight adsorbers. For the sake of simplicity, compared to the embodiment of , only the differences concerning the number and nature of the stages of the pressure cycle, the gas flows as well as the valves are shown. The other elements of the unit can be implemented in an equivalent manner in this second embodiment.

[0088] The unit includes a flow control system that includes three transfer valves, including a pressurization valve 8, a balancing valve 17 and an elution gas supply valve 18. These transfer valves are valves for regulating a gas transfer flow rate between two adsorbers. These transfer valves are proportional valves here.

[0089] The adsorbers of the unit are subjected to a pressure cycle comprising the following steps and in the following order:Step 201: adsorption at the high pressure of the cycle with production of the second fraction 32 enriched in the second component and extraction of the second fraction 32 produced from a pressurization or re-pressurization flow 33 for the adsorber in step 208. The pressurization or re-pressurization flow 33 is regulated by the pressurization valve 8.Step 202: co-current rinsing. The flow control device is then at least partially open to allow the rinsing fluid to circulate.Step 203: balancing in descending pressure and supplying a balancing flow 36 to balance the adsorber in step 207 in ascending pressure. The balancing flow 36 is regulated by the balancing valve 17. Step 204: supply of elution gas to elute the adsorber in step 206.The elution gas flow rate 37 is regulated by the elution gas supply valve 18. Step 205: depressurization to low pressure, with production of the first fraction 31 and supply of the rinsing flow rate 34 for the adsorber in step 202. Step 206: elution with the elution gas supplied in step 4, production of the first fraction 31 and supply of the rinsing flow rate 34 for the adsorber in step 202. Step 207: rising pressure balancing with the balancing flow rate 36 supplied by the adsorber in step 203. Step 208: re-pressurization to high pressure with the re-pressurization flow rate 33 supplied by the adsorber in step 201.

[0090] In these two implementations, the rinsing step 102; 202 immediately follows the adsorption step 101; 201. In other words, an adsorber having undergone the adsorption step 101; 201 undergoes, once said adsorption step 101; 201 is finished, as the next step, a rinsing step 102; 202, without an intermediate step between the adsorption step 101; 201 and the rinsing step 102; 202.

[0091] The phase time is therefore equal to the duration of the pressure cycle, or cycle time, divided by the number of adsorbers, here eight adsorbers.

[0092] In other embodiments, the pressure cycle comprises several upward pressure balancing steps and several downward pressure balancing steps. These may be successive balancing steps or successive balancings, the flow rates or quantities of gas being able to vary from one balancing step to the next.

[0093] In an implementation not shown, the pressure cycle may additionally include one or more dead time steps, during which one or more adsorbers remain in the same state as at the end of the previous step, for example at the same pressure. The objective may be, for example, to synchronize the other steps between the adsorbers.

[0094] The following description applies to both the embodiment of the and the embodiment of the.

[0095] During the rinsing step 102; 202, a so-called rinsing fluid, enriched in the first component, circulates in at least one adsorber, sweeping it from one end to the other, so as to expel at least a portion of the second component from said adsorber. A flow from the adsorber in the rinsing step 102; 202 is injected with the feed gas 30 into the adsorber in the step 101; 201 which undergoes the adsorption step. Thus recycling the flow from the adsorber undergoing the rinsing step (so-called recycled gas flow 38) makes it possible to increase the yield of the first component. By “flow enriched in the first component”, it is to be understood that the first component is the predominant component in quantity among the first and second components.

[0096] It is possible to define a RR rinse ratio according to the relationship:

[0097] Qr being the flushing flow rate and Qp a flow rate of the produced gas. Typically the value of the flushing ratio RR is between 0.05 and 0.65, preferably between 0.05 and 0.5.

[0098] The three-way valve 9 and the compressor 12 of the flow control device make it possible to modify the rinsing flow rate 34 and therefore the rinsing ratio RR.

[0099] The rinsing step 102; 202 can be carried out over an integer number of phase times, i.e. at least over one complete phase time, which makes it possible to have a rinsing flow rate 34 and therefore a continuous and constant flow rate of recycled gases 38.

[0100] In the context of the method according to the invention, the separation unit 10 can therefore operate according to a plurality of operating modes 1; 2; 3; 4 (see). In each of said operating modes, the rinsing fluid circulates according to a determined rinsing flow rate value 34 and the phase time is defined according to a determined phase time duration.

[0101] In an initial state shown in step 300, the unit thus operates according to a first mode in which the rinsing fluid circulates with a first rinsing flow rate value Qri, and in which the phase time is equal to a first duration Tpi. This may in particular be a first nominal operating regime of the separation unit 10, after its start-up.

[0102] Also shown are steps 301 to 304 of the separation process:

[0103] In step 301, an efficiency value of the separation unit 10 for extracting the first component from the feed gas 30 is determined. This first component extraction efficiency corresponds to the ratio of the quantity of first component in the first fraction 31 produced by the separation unit 10 to the quantity of first component in the feed gas 30 feeding the unit. In particular, the first component extraction efficiency corresponds to the first component content in the first fraction 31 to the first component content in the feed gas 30. This efficiency is, for example, determined by analyzing the composition of the feed gas 30 feeding the unit and the first fraction 31 produced. In particular, an analyzer determines the first component content in the feed gas 30 and in the first fraction 31. The first component content is, for example, measured using one or more probes.This is in particular a mass ratio. As the first component here is the recoverable component, the extraction yield in the first component is called "product yield", for the yield in recoverable component or product. In the initial state, the separation unit 10 therefore operates with a product yield value Ri.

[0104] The instrumentation including analyzers, flow meters, pressure and temperature sensors have not been shown in Figures 3 and 4.

[0105] In a step 302, a yield value of the separation unit 10 for extracting the second component from the feed gas 30 is determined. This second component extraction yield corresponds to the ratio of the quantity of second component in the second fraction 32 produced to the quantity of second component in the feed gas 30 feeding the unit. In particular, the second component extraction yield corresponds to the content of second component in the second fraction 32 to the content of second component in the feed gas 30. This yield is, for example, determined by analyzing the composition of the feed gas 30 feeding the unit and the second fraction 32 produced. In particular, the analyzer determines the content of second component in the feed gas 30 and in the second fraction 32. The content of second component is, for example, measured using one or more probes. This is in particular a mass ratio.The first component being the recoverable component, the extraction yield in the second component is called the “purge rate”. In the initial state, the separation unit 10 therefore operates with a purge rate Pi.

[0106] The analyzer can in particular deduce the content of the first component or the second component from the measured content of the other component. The flow rates of the feed gas 30, of the first fraction 31 and of the second fraction 32 can be taken into account in determining the yield values. Data reconciliation software, for example integrated into the control unit 13, makes it possible to find the most probable values ​​of the yields as well as the uncertainty on these values ​​in the case of redundant data. Such software takes into account the uncertainties of all the measurements involved in determining the parameter(s) whose value is sought as well as the necessary looping of the balances, here the material balances 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 before step 301.

[0108] The control unit receives, for example from an operator, a first setpoint C1 for the product extraction efficiency and a second setpoint C2 for the purge rate. In the event of a change in the specifications in the composition of the first fraction 31 produced and / or the second fraction 32 produced, the product efficiency value Ri and the purge rate Pi are caused to change. This can also occur in the event of a variation in the feed gas feed rate 30. The first setpoint is typically between 25 and 90% and the second setpoint is between 20 and 90%. These are percentage efficiencies with which the separation unit operates.Contrary to what was established in the prior art when high extraction yields and purity levels had to be achieved, it turns out that the implementation of a rinsing step is competitive when the desired extraction yields are of the order of magnitude of those corresponding to standard separation units, but with increased flexibility between product extraction yield and purge rate.

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

[0110] A first threshold S1 and a second threshold S2 are predetermined and recorded in the control unit. The thresholds correspond to an admissible deviation between the extraction efficiencies (product yield and purge rate) determined and the setpoint values ​​C1; C2 relating to these extraction efficiencies. The thresholds retained may be a function of the uncertainties on the extraction efficiencies admitted. That is to say that in this case there may remain an agreed residual deviation between the extraction efficiencies determined (product yield and purge rate) and the setpoint values ​​C1; C2, as long as these residual deviations remain lower in absolute value than the corresponding threshold S1; S2.

[0111] The first deviation is compared to the first threshold S1 and the second deviation is compared to the second threshold S2. If the first deviation is less than or equal to the first threshold S1 and the second deviation is less than or equal to the second threshold S2, the process is terminated.

[0112] If at least one of the first and second deviations is greater in absolute value than the corresponding threshold S1 or S2, the method proceeds to step 304 which consists of modifying the first phase time duration Tpi into a second phase time duration Tpi+1 different from the first and modifying the first flushing flow rate value Qri into a second flushing flow rate value Qri+1 different from the first, so as to reduce the first deviation and / or reduce the second deviation. In other words, both the phase time and the flushing flow rate with which the unit operates in step 300 are modified. The phase time duration can be lengthened or shortened and the flushing flow rate value increased or decreased. It may therefore happen that either the first deviation or the second deviation, but also both of them exceed the corresponding threshold S1 or S2, which is sufficient to proceed to step 304 of the method.

[0113] The phase time can be changed first, then the rinsing flow rate is changed. Conversely, the rinsing flow rate can be changed first and then the phase time second. In order to converge more quickly towards the desired efficiency values, the rinsing flow rate and the phase time can be changed together. In particular, the rinsing flow rate and the phase time are changed simultaneously. Control of the separation process is then faster. Indeed, before making a new change, the operation of the separation unit should stabilize, i.e. here the measured efficiencies should tend towards their new value sufficiently asymptotically to be able to judge the residual deviations between measurements and setpoints.Such stabilization will take several cycles and a simultaneous modification of the two parameters phase time and rinsing flow rate will be stabilized more quickly than if this modification is carried out in two successive stages, the second modification being made only after an initial stabilization of the separation unit 10.

[0114] The rinsing flow rate and the phase time duration are notably modified independently of each other. In other words, actuators 6; 7; 8; 9; 12; 17; 18 act on the two parameters phase time and rinsing flow rate to change the value of each of these two parameters independently of the modification of the value of the other parameter, notably to modify each of these parameters beyond a possible modification induced by the modification of the other parameter. In particular, the flow control system acts on the phase time parameter, therefore notably on the duration of the rinsing phase and the flow adjustment device on the rinsing flow rate parameter. In a particular implementation of the method, the rinsing flow rate is modified independently of the flow rate of the feed gas.

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

[0116] The separation unit 10 then operates according to a new product yield and a new purge rate. For example, the value of the rinse flow rate 34 is increased and the duration of the phase time is shortened so as to increase the determined first component extraction yield and maintain the determined second component extraction yield.

[0117] The thresholds chosen for the deviations mentioned above being a function of the uncertainties in the product yield R and the purge rate P, a modification will only take place if the measured difference between the measured yield and the setpoint yield is greater than or equal to the uncertainty in the yield. Similarly, this can make it possible to stop the process as soon as the measurement-setpoint difference is equal to or less than the calculated uncertainty. In the absence of redundant data and reconciliation software, the approach to trigger and / or stop the modification of the operating parameters can be equivalent, knowing that the uncertainties will be higher and logically the thresholds of the deviations as well.

[0118] To modify the phase time, in particular the time of the adsorption phase, the control unit 10 can for example send a control signal to the supply valve 6 to control its total opening or its total closing. A possible action is for example to shift in time a start of supply of feed gas 30 to the adsorber in adsorption step 101; 201, at the start of the phase. In an equivalent manner, it is also possible to shift in time an end of supply of feed gas 30 to said adsorber.

[0119] In a complementary or alternative manner, the control unit 10 can for example send a control signal to the production valve 7 to control its total opening or its total closing. A possible action is for example to shift in time a start of production of the second fraction 32 by the adsorber in adsorption step 101; 201, at the start of the phase. In an equivalent manner, it is also possible to shift in time an end of production of the second fraction 32 by said adsorber.

[0120] Shifting the supply of gas flow from the adsorber to the adsorption step 101; 201 and / or the production of a gas flow by this adsorber in this way amounts to lengthening or shortening said adsorption step 101; 201 in the embodiments of FIGS. 3 and 4.

[0121] Another complementary or alternative solution for lengthening or shortening the duration of the pressure cycle, by varying the duration of a step of the cycle, is to modify the phase(s) comprising the pressurization or re-pressurization step 104; 208, the steps of balancing in descending pressure 203 and balancing in ascending pressure 207 and the steps of supplying elution gas 204 and elution 206. In this case, the control unit 13 sends a control signal to one of the transfer valves 8; 17; 18 in order to regulate a so-called transfer flow rate 33; 36; 37 between one of the adsorbers supplying a gas flow in steps 101; 201; 203; 204 and one of the adsorbers receiving said gas flow corresponding to steps 104; 206; 207; 208. It is then possible, by regulating the transfer flow rate, to increase or decrease the speed of pressurization, re-pressurization, balancing or elution of the adsorbers in steps 104; 206; 207 and 208.In the case of the adsorber in the re-pressurization or pressurization step 208, the transfer flow rate is a pressurization flow rate 33 and a transfer valve allowing regulation is the pressurization valve 8. In the case of the adsorbers in the balancing steps 203; 207, the transfer flow rate is a balancing flow rate 36 and a transfer valve allowing regulation is the balancing valve 17. In the case of the adsorbers in the elution gas supply and elution steps 204; 206, the transfer flow rate is an elution gas supply flow rate 37 and a transfer valve allowing regulation is the elution gas supply valve 18. In the embodiments of FIGS. 3 and 4, this amounts to lengthening or shortening the pressurization or re-pressurization step 104; 208, the steps of downward pressure balancing 203 and upward pressure balancing 207 and / or the steps of providing elution gas 204 and elution 206.

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

[0123] An alternative to lengthening or shortening the phase time by varying the duration of a cycle step is to add a dead time step to the pressure cycle during which one or more adsorbers remain in the same state, for example by fluidly isolating said adsorber(s), or to remove such a step from the pressure cycle. Such a step is not shown in Figures 3 and 4. However, such a method can also be implemented in a complementary manner to modifying the duration of the pressure cycle by varying the duration of a cycle step.

[0124] It is therefore understood that the phase time of the separation unit 10 can be modified by controlling at least one parameter of a gas flow feeding an adsorber of the separation unit and / or by controlling at least one parameter of a gas flow produced by an adsorber of the separation unit. At least one parameter of a gas flow transferred from one adsorber to another can in particular be controlled for this. In the implementations described, said gas flow parameter(s) are chosen from a flow rate of said gas flow and / or the flow duration of said flow, i.e. the lengthening or shortening of the flow of said flow over time. This can result in the integration into the pressure cycle of a step or the elimination of the cycle of a step. Said step would, for example before its integration into the cycle, be considered as having a zero duration and a zero gas flow rate. The added step may be a dead time step.

[0125] To change the flushing flow rate, the control unit 13 can send a control signal to the flow control device to increase or decrease the flushing flow rate. The control unit 13 can, for example, control the three-way valve 9 to regulate the distribution of the first fraction between the product gas flow rate 35 and the flushing flow rate 34.

[0126] In order to adapt, for example, to the specifications imposed on the product yield R and the purge rate P, the phase time and the rinsing flow rate can be modified so as to make the first difference less than or equal to the first threshold S1 and / or to make the second difference less than or equal to the second threshold S2. It is then possible to reach the pair of values ​​of the parameters phase time TpX and rinsing flow rate QrX which will make it possible to reach or get sufficiently close to both the set value C1 in product yield and the set value C2 in purge rate.

[0127] Different methods are proposed to determine this pair of phase time values ​​TpX and rinsing flow rate QrX.

[0128] A first method applicable for determining the variations to be made to the phase time and the rinsing fluid flow rate is the use by the control unit of a database comprising a plurality of operating points 1; 2; …; N of the separation unit, each point 1; 2; …; N grouping the supply conditions (flow rate, composition, pressure, temperature) and in particular the phase time Tp1; Tp2; …; TpN, the rinsing flow rate Qr1; Qr2; …; QrN, the extraction efficiency in the first component (here the product efficiency R1; R2; …; RN) and the extraction efficiency in the second component (here the purge rate P1; P2; …; PN).

[0129] Thus, the separation method may comprise a step 400 of recording in a database of points 1; 2; …; N of stabilized operation of the separation unit 10, the operating points corresponding in particular to pairs of phase time duration and rinsing flow rate value Tp1, Qr1; Tp2, Qr2; …; TpN, QrN, each pair being associated with a product yield value R1; R2; …; RN and with a purge rate value P1; P2; …; PN of the separation unit 10. This recording step may be done continuously or periodically. In particular, the operating points 1; 2; …; N are determined by simulating the operation of the separation unit 10 and then recorded in the database. Simulation software performs series of numerical calculations until the stable converged solution is found for a given series of input parameters.Simulation software means software for dynamic simulation of adsorption processes. Such a procedure makes it possible to have a large library of data available as soon as the separation unit 10 is put into operation.

[0130] The simulation is for example carried out by fixing a series of input parameters including a nominal feed rate of feed gas 30, a nominal composition of the feed gas 30, stages of the pressure cycle, a nominal phase time and / or end-of-stage pressures.

[0131] This represents an example of determining the stabilized operating points: the simulation comprises a first calculation step during which a phase time duration Tp1 is fixed and a flushing flow rate value is modified so as to obtain a correlation between the extraction efficiency in the first component (in particular the product efficiency) and the extraction efficiency in the second component (in particular the purge rate), as a function of the flushing flow rate, for said fixed phase time duration Tp1. The first calculation step can be repeated for a new fixed phase time duration Tp2; Tp3 different from the previous one so as to obtain a new correlation. In particular, the fixed phase time duration Tp1; Tp2; Tp3 is calculated as a percentage of the nominal phase time.The simulation also comprises a second calculation step during which a flushing flow rate value Qr1 is fixed and a duration of the phase time is modified so as to obtain a correlation between the extraction efficiency in the first component (in particular the product yield) and the extraction efficiency in the second component (in particular the purge rate), as a function of the duration of the phase time, for said fixed flushing flow rate value Qr1. The second calculation step is repeated for a new flushing flow rate value Qr2; Qr3 fixed different from the previous one so as to obtain a new correlation.

[0132] The second calculation step can also take place before the first calculation step. The first and / or second calculation steps may involve an interpolation method for determining correlations.

[0133] Each correlation allows a corresponding curve to be plotted on the. The intersection between a curve with iso-phase time duration Tp1; Tp2; Tp3 and a curve with iso-value of rinsing flow rate Qr1; Qr2; Qr3 corresponds to an operating point 1; 2; 3 “extraction efficiency in first component” versus “extraction efficiency in second component”. For each operating point 1; 2; 3 recorded, we thus have, with the fixed phase time durations and rinsing flow rates, a pair of values ​​“phase time duration” and “rinsing flow rate value” Tp1, Qr1; Tp2, Qr2; Tp3, Qr3 allowing the desired product efficiency R1; R2; R3 and purge rate P1; P2; P3 to be achieved for the separation unit 10. The simulation thus allows the determination of a given number of operating points which are recorded in the database.

[0134] The operating points 1; 2; …; N are in particular within a predetermined unit performance range. In particular, the phase time durations Tp1; Tp2; …; TpN and the flushing flow rate values ​​Qr1; Qr2; …; QrN correspond to the operating points within the phase time duration and flushing flow rate ranges defined by the unit design.

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

[0136] If the first deviation is less than or equal to the first threshold S1 and the second deviation is less than or equal to the second threshold S2, the process is terminated.

[0137] If the first deviation is greater than the first threshold S1 and / or if the second deviation is greater than the second threshold S2, the method proceeds to step 401 of reading in the database, among the pairs of recorded phase time durations and rinsing flow rate values ​​Tp1, Qr1; Tp2, Qr2; …; TpN, QrN of a phase time duration TpX and a rinsing flow rate value QrX making it possible to bring the first deviation below the first threshold S1 or to the value of the first threshold S1 and / or to bring the second deviation below the second threshold S2 or to the value of the second threshold S2.

[0138] Once the pair of phase time values ​​TpX and rinsing 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 rinsing flow rate value Qri is changed to the rinsing flow rate value QrX read from the database. The separation unit 10 then operates with a product yield and a purge rate such that the first deviation is less than or equal to the first threshold S1 and the second deviation is less than or equal to the second threshold S2.

[0139] The values ​​of the phase time and rinse flow rate parameters which will make it possible to reach or get sufficiently close to both the set value C1 in product yield and the set value C2 in purge rate can also be determined by iterations.

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

[0141] As can be seen in the, the modification of the phase time and the rinsing fluid flow rate can be implemented initially by iterations on the phase time duration, at a constant rinsing flow rate value, then in a second step by iterations on the rinsing flow rate value, at a constant phase time duration. Such a sequence can in particular be repeated. In a reverse implementation not shown, the modification of the phase time duration and the rinsing flow rate value can also be implemented initially by iterations on the rinsing flow rate value, at a constant phase time duration, then in a second step by iterations on the phase time duration, at a constant rinsing flow rate value. Such a sequence can also be repeated.

[0142] Steps 301; 302; 303 and 304 are repeated in addition to the modification of the phase time duration and the value of the rinsing flow rate by reading from a database in step 401, in particular after this modification by reading from a database. Said last phase time duration Tpn may for example have been reached by the separation unit 10 using the method by reading from a database and said last rinsing flow rate value Qrn also. The iteration method may also be implemented as an alternative to the method by reading from a database. The modification of the phase time and the rinsing fluid flow rate by the iteration method is particularly advantageous when a certain threshold on the deviations is not exceeded.Changing the phase time duration and the flushing fluid flow rate value by iterations is particularly advantageous for fine-tuning extraction yields following a change in the phase time duration and the flushing fluid flow rate value by reading from the database. Switching from the database reading method to the iteration method (or vice versa) can be done based on the value of the first deviation and / or the value of the second deviation.

[0143] Steps 301; 302; 303 and 304 may also be repeated via a cause / effect learning process in which the effects of an initial modification of the phase time duration and the flushing flow rate value are determined and then stored in a memory, said effects being taken into account during a subsequent modification of the phase time duration and the flushing flow rate value.

[0144] Such a learning process also makes it possible to determine the order of phase time / rinsing flow rate modifications, in the case where these modifications are made one after the other, to remain, during a change of setpoints, always above an initial efficiency considered as a minimum. For example, in an operation according to the curves of the, to increase the purge rate P while maintaining the product efficiency R and never allowing it to fall below its initial value during the transient phases, the process would lead to first shortening the phase time and then increasing the rinsing flow rate.

[0145] When the uncertainties are negligible, the phase time and the flushing flow rate are modified so that the determined product yield R reaches the first setpoint C1 and / or the determined purge rate P reaches the second setpoint C2. In this case, a zero value can be assigned to the first threshold S1 and to the second threshold S2. Thus, in the event of a deviation between the determined product yield value R and the first setpoint C and / or a deviation between the determined purge rate P and the second setpoint C2, the phase time and the flushing flow rate are modified so that the determined product yield R reaches the first setpoint C1 and / or the determined purge rate P reaches the second setpoint C2.

[0146] Controlling the two parameters of rinsing flow rate and phase time therefore varies the extraction efficiencies (product yield R and purge rate P) and thus allows increased operational flexibility on the extraction efficiencies in the first component and in the second component compared to the separation units of the prior art. This flexibility can be represented schematically, no longer by a curve as in the figure, but by a band or more generally by an operating surface S (R, P) in the diagram "product extraction yield" vs "purge rate" of which at least a part will be beyond the limit curve achievable by a standard PSA. An example is shown in the figure.

[0147] For example, in the case where the feed gas flow rate 30 varies, it is appropriate as a first approximation to vary the phase time inversely proportional to the feed flow rate and the rinsing flow rate proportionally to this same flow rate in order to maintain the same performance. It is possible, if necessary, to refine by means of simulations which can take into account generally very secondary effects linked to the adsorption kinetics and the unit's pressure losses.

[0148] Lamontre, next to the classic curve L1 of the yields of a PSA, the operating surface S (R, P) contains the operating points 1, 2, 3, 4 that the separation unit 10 can reach during its operation taking into account the expected developments. With the exception of point 1, all the other points cannot be reached by a standard PSA.

[0149] The series of objective operating points 1 to N is determined when defining the separation unit 10 according to the foreseeable changes in the supply conditions (for example, we know how the composition of a landfill gas or a natural gas well varies over time), the required performances (for example, reduction of atmospheric emissions, increase in capacity of a downstream unit, need to periodically purge a recycling circuit). The separation unit 10 is then dimensioned so that the operating surface S of the possible points (R, P) contains the selected operating points 1 to N. In practice, all the points of the surface correspond to a possible operation.

[0150] More precisely, in the case of the, the operating surface S is limited by the curve L1 which corresponds to the operation of the unit with a zero rinsing fluid flow rate, therefore with a standard PSA cycle and by the curve L2 which on the contrary corresponds to the maximum rinsing fluid flow rate retained during the design. This maximum flow rate is dimensioning for the majority of equipment (adsorbers, adsorbent mass, machines, etc.). The upper limit, here assimilated to the line d3, corresponds for this unit to the minimum phase time duration retained. This minimum value is fixed by taking into consideration, generally from the design stage, characteristics such as the adsorption kinetics, the duration of the elementary stages, the sizing of the valves, the speed of the fluids and in particular the risks of attrition of the adsorbent.Finally, the lower limit, here assimilated to the line d4, was fixed by the threshold of minimum extraction efficiency Rm acceptable (for economic reasons or for example to ensure the satisfactory operation of a downstream unit).

[0151] Among the points retained to determine the operating surface S and thus the dimensioning of the unit, we can distinguish point 1 corresponding to the first nominal operating regime of the separation unit 10 after start-up. According to another implementation, point 1 corresponds to the acceptable limit point in the event of non-operational rinsing (maintenance of a compressor for example). This point corresponds to the operation of the unit with the product efficiency value R1 and the purge rate P1. We can also distinguish point 2 which tends to favor the yield of the recoverable product to the detriment of the purge rate or conversely point 3 which favors the purge. These two cases can be the extreme operations linked to a recycling loop whose inert gas content (here, the weakly adsorbable fraction) varies as a function of time for reasons external to the separation unit.Points 4 and 5 correspond to the performance objectives planned for the future. In practice, all points on the surface S can be reached by the separation unit and correspond to a single pair "phase time, rinsing flow rate" (not shown).

[0152] A rinsing ratio in the process according to the invention is typically between 0.05 and 0.65, or even between 0.05 and 0.5. Thanks to the process according to the invention, it is possible to obtain operational flexibility with low rinsing ratios so that the separation unit 10 remains efficient and competitive unlike processes in which high yields and high purities are sought.

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

[0154] The separation method is for example implemented in a recycling loop, to capture carbon monoxide from the flue gases of a blast furnace and recycle it as a reducing agent in said blast furnace. The flue gases constitute the feed gas 30 and comprise a mixture of carbon monoxide and nitrogen and the first fraction 31 is enriched in carbon monoxide and the second fraction 32 is enriched in nitrogen. The flue gases are, for example, pretreated in a carbon dioxide capture unit. Carbon monoxide is a recoverable gas, comparable to a product and is extracted from the flue gases by the separation unit 10 with an adjustable product yield R. Nitrogen is a residual gas, comparable to a purge and is extracted from the flue gases by the separation unit 10 with a purge rate P that is also adjustable. Thanks to the method according to the invention, it is possible to obtain the desired carbon monoxide extraction yield and nitrogen purge rate.Thus, precise specifications such as the proportion of nitrogen and carbon monoxide can be met for the first gaseous fraction 31 recycled to the blast furnace. In steelmaking processes, reducing the amount of nitrogen in a stream from the flue gases and recycled to a blast furnace allows less carbon dioxide to be emitted at the blast furnace outlet and therefore reduces the size of the carbon dioxide capture unit.

[0155] The separation method can also be implemented for the capture of carbon dioxide. The feed gas 30 comprises a mixture of carbon dioxide and nitrogen and the first fraction 31 is enriched in carbon dioxide, the second fraction 32 being enriched in nitrogen, the carbon dioxide constituting the first component and the nitrogen constituting the second component. It may indeed be necessary, for environmental reasons, to increase the CO2 capture rate over time with a feed gas 30 supply that is constant in flow rate and composition. It may for example be necessary to go from an extraction efficiency of 50% to 55% then 60% while still purging the same quantity of nitrogen.

[0156] The separation method can also be implemented for the purification of a feed gas 30 comprising a mixture of methane and nitrogen. The first fraction 31 is enriched in methane, the second fraction 32 is enriched in nitrogen, the methane constituting the product and the nitrogen constituting the purge. It is then possible to separate the nitrogen from a biogas as a step in a biogas treatment in order to make it compatible with the specifications of a natural gas distribution network. More generally, any gas stream containing methane and compounds less adsorbable than methane can be treated in this way.

Claims

A process for separating a feed gas (30) by pressure-modulated adsorption, wherein a separation unit (10) is fed with the feed gas (30) and produces a first gaseous fraction (31) enriched in a first component and a second gaseous 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 adsorbers, said adsorbers being subjected to a pressure cycle having a high pressure and a low pressure, the pressure cycle comprising a plurality of steps (101; …; 104; 201; …; 208) of which at least one adsorption step (101; 201) and at least one rinsing step (102; 202) during which a rinsing fluid enriched in the first component circulates in at least one adsorber so as to expel at least a part of the second component of said adsorber,the pressure cycle having a phase time corresponding to a duration of the pressure cycle divided by the number of adsorbers, the process comprising the following steps: a) determination of a first component extraction yield value defined by the ratio of the quantity of first component in the first fraction (31) produced to the quantity of first component in the feed gas (30) supplying the separation unit (10), b) determination of a second component extraction yield value defined by the ratio of the quantity of second component in the second fraction (32) produced to the quantity of second component in the feed gas (30) supplying the separation unit (10),c) determination of a first deviation between the extraction efficiency value in the first component determined in step a) and a first setpoint value (C1) relating to the extraction efficiency in the first component and of a second deviation between the extraction efficiency value in the second component determined in step b) and a second setpoint value (C2) relating to the extraction efficiency in the second component, d) if the first deviation is greater than a first predetermined threshold (S1) and / or the second deviation is greater than a second predetermined threshold (S2), modification of the phase time and modification of a flow rate of the rinsing fluid, called the rinsing flow rate (34), so as to reduce the first deviation and / or the second deviation. Method according to the preceding claim, wherein the first setpoint value (C1) expressed as a percentage of yield is between 25 and 90% and the second setpoint value (C2) expressed as a percentage of yield is between 20 and 90%. A process according to any one of the preceding claims, wherein a part of the first fraction (31) is recovered as a produced gas and another part is used as a rinsing fluid, the ratio of the rinsing flow rate (34) to the sum of the rinsing flow rate (34) and a produced gas flow rate (35) being between 0.05 and 0.65, preferably between 0.05 and 0.

5. A method according to any one of the preceding claims, wherein the phase time is modified by controlling at least one parameter of a gas stream feeding an adsorber of the separation unit (10) and / or at least one parameter of a gas stream produced by an adsorber of the separation unit (10), in particular at least one parameter of a gas stream transferred from one adsorber to another. Method according to the preceding claim, wherein said parameter is chosen from the flow rate and / or the flow duration. A method according to any one of claims 4 or 5, wherein the phase time is modified by shifting in time a start and / or an end of feeding by the gas flow of at least one adsorber. A method according to any one of claims 4 to 6, wherein the phase time is modified by shifting in time a start and / or an end of production of the gaseous stream by at least one adsorber. A method according to any one of claims 4 to 7, wherein a flow rate of a gas stream transferred from one adsorber to another is regulated so as to accelerate or slow down a gas transfer between said adsorbers. A method according to any one of the preceding claims, the method further comprising the following steps: i) recording in a database of stabilized operating points (1; 2; …; N) of the separation unit (10), the operating points (1; 2; …; N) corresponding to pairs of phase time duration and rinsing flow rate value (Tp1, Qr1; Tp2, Qr2; …;TpN, QrN), each pair being associated with an extraction yield value in the first component and an extraction yield value in the second component of the separation unit (10),ii) if the first deviation is greater than the first threshold (S1) and / or the second deviation is greater than the second threshold (S2), reading from the database a phase time duration (TpX) and a rinsing flow rate value (QrX) enabling the first deviation to be less than or equal to the first threshold (S1) and / or the second deviation to be less than or equal to the second threshold (S2), then modification of the phase time to the phase time duration (TpX) read from the database and modification of the rinsing flow rate to the rinsing fluid flow rate value (QrX) read from the database.; A method according to any one of the preceding claims, wherein steps a), b), c) and d) are repeated until the first deviation is less than or equal to the first threshold (S1) and / or the second deviation is less than or equal to the second threshold (S2), with for step d) a modification of the last duration of the phase time to a new duration of the phase time (Tpn+1) and a modification of the last value of the rinsing flow rate to a new value of the rinsing flow rate (Qrn+1). A method according to any one of the preceding claims for capturing carbon monoxide, in particular from blast furnace fumes in order to recycle it as a reducing agent in said blast furnace, wherein the feed gas (30) comprises a mixture of carbon monoxide and nitrogen, the first fraction (31) being enriched in carbon monoxide and the second fraction (32) being enriched in nitrogen, carbon monoxide constituting the first component and nitrogen constituting the second component. A method according to any one of claims 1 to 10 for capturing carbon dioxide, wherein the feed gas (30) comprises a mixture of carbon dioxide and nitrogen, the first fraction (31) being enriched in carbon dioxide, the second fraction (32) being enriched in nitrogen, carbon dioxide constituting the first component and nitrogen constituting the second component. 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 enriched in methane, the second fraction (32) being enriched in nitrogen, methane constituting the first component and nitrogen constituting the second component. A separation unit (10) of a feed gas (30) by pressure-modulated adsorption for the production of a first gaseous fraction (31) enriched in a first component and a second gaseous 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 adsorbers configured to be subjected to a pressure cycle having a high pressure and a low pressure, the cycle comprising a plurality of steps (101; …; 104; 201; …; 208) of which at least one adsorption step (101; 201) and a rinsing step (102; 202) during which a rinsing fluid enriched in the first component circulates in at least one adsorber so as to expel at least a part of the second component of said adsorber, the pressure cycle having a phase time corresponding to the duration of the pressure cycle divided by the number of adsorbers,characterized in that the separation unit (10) comprises: - a flow control system configured to modify the phase time, in particular by controlling at least one parameter of a gas feed flow to an adsorber of the separation unit and / or at least one parameter of a gas flow produced by an adsorber of the separation unit, in particular at least one parameter of a gas flow transferred from one adsorber to another, - a flow control device configured to modify a flow rate of the rinsing fluid (34), - a control unit (13) and communication means (14) between the control unit, the flow control system and the flow control device, the control unit (13) being configured to implement the process according to any one of the preceding claims.

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