MULTI-STAGE MEMBRANE FILTRATION SYSTEM AND METHOD, CARBON CAPTURE SYSTEM AND METHOD USING MULTI-STAGE MEMBRANE FILTRATION FOR WATER MANAGEMENT

Description

DESCRIPTION TECHNICAL FIELD

[0001] This description refers in general to technologies for the removal of water from highly concentrated salt solutions, such as solvent solutions used 10 used in carbon capture systems. The description also refers to carbon capture plants. carbon capture, which removes carbon dioxide from a flue gas containing no humidity. The embodiments described herein relate to systems and methods of ammonia-based carbon capture. STATE OF THE ART 15

[0002] Carbon dioxide (CO2) is a greenhouse gas that is considered one of the main culprits of global warming and climate change. The ani- Carbon dioxide is generated by various industrial processes in which energy is generated thermal energy from the combustion of fossil fuels, such as natural gas and oil.

[0003] Carbon capture and storage (CCS for short) 20 Storage) is an effective technology to drastically reduce greenhouse gas emissions. Post-combustion capture (PCC for short) is a process which uses an aqueous absorption solution (here also referred to as solvent) containing compounds such as ammonia, potassium salts and the like, to capture carbon dioxide carbon from the flue gas generated by the combustion of fossil fuels. 25

[0004] The solvent comes into contact with the CO2-rich flue gas in an absorber and causes carbon dioxide to remain trapped in the solvent. The solvent is rich in CO2 is then transferred to a regenerator, where the carbon dioxide is removed. and fed to a carbon dioxide recovery line for further processing, -1- while the CO2-poor solvent is obtained by removing carbon dioxide from it is recirculated to the absorber.

[0005] The flue gas usually contains water in the form of humidity. Part moisture can condense in a direct contact cooler, placed upstream 5 of the absorber. However, a certain amount of water remains in the flue gas which flows through the absorber and condenses in the solvent. The percentage of water in the solvent therefore tends to increase due to condensation in the solvent of the humidity contained in the flue gas.

[0006] To maintain the correct solvent concentration, it is necessary to remove 10 water from the solvent cycle. This is typically achieved by evaporating the water in the re- blacker using the heat of a reboiler. However, this process consumes a significant amount of energy, thereby negatively impacting efficiency of the carbon capture process.

[0007] It is therefore an objective of what is described here to be a system capable of removing 15 water from a highly concentrated salt solution, as a solvent in a system carbon capture, and which can be used, for example, to remove water from the solvent cycle in a carbon capture plant more efficiently and with lower energy consumption. SUMMARY 20

[0008] In one aspect, a system for the removal of water is described herein. by membrane filtration from a concentrated saline solution, the system com- taking a plurality of membrane filtration units in series. Each unit of Membrane filtration involves a filtration membrane that separates one side of the concentrated on one side of the permeate of the respective membrane filtration unit. 25 Each membrane filtration unit also includes a discharge duct for the concentrate, in fluid coupling with the respective side of the concentrate, to re- move from it a concentrate, and a permeate discharge duct, in coupling fluid with the respective side of the permeate, to remove a permeate from it. A first fluid inlet for each membrane filtration unit is coupled 30 fluid flow with the concentrate side of the membrane filtration unit. -2- Additionally, each membrane filtration unit, except the most downstream one, includes also a second fluid inlet, in fluid coupling with the side of the per- membrane filtration unit meatus.

[0009] As will be evident from the following detailed description, the structure so- 5 pra delineata allows the removal of water from a highly con- saline solution centered using an arrangement of membrane and differential filtration units of acceptable pressure on the filtration membranes of the filtration units arranged in sequence. The second fluid inlet in fluid coupling with the side of the permeate from each membrane filtration unit, except the most downstream one, with- 10 feels the delivery of saline solution which maintains the correct salt concentration on the permeate side of each membrane filtration unit.

[0010] The system can be used in a carbon capture plant, where gas combustible material having a high degree of humidity is processed to remove the ani- carbon dioxide. In this system, a highly concentrated saline solution can be 15 evenings treated in membrane filtration units to remove water from it. The water removed compensates for the increase in water in the system caused by the moisture content of the treated flue gas.

[0011] According to a further aspect, therefore, a system is described herein carbon capture, such as a carbon capture plant using am- 20 mines, comprising an absorber, comprising: a flue gas inlet; a CO2-poor solvent inlet and CO2-rich solvent outlet. The system It also includes a regenerator, which in turn includes: a solvent inlet CO2-rich, in fluid coupling with the CO2-rich solvent outlet of the as- 2 2 absorber; a CO2-poor solvent outlet, in fluid coupling with the in- 25 CO2-poor solvent input from the absorber; and a CO2 output. The plant carbon capture also includes a membrane filtration unit for removing water from the solvent, between the absorber and the regenerator. The membrane filtration unit brana can be configured as outlined above.

[0012] Further details, embodiments and features of the filtration system 30 membrane treatment and carbon capture plant are described below and set out in the attached claims. -3-

[0013] According to a further aspect, a method for the re- motion of water by membrane filtration from a concentrated salt solution treat. According to one embodiment, the method comprises the following steps: feed a concentrated salt solution from a solution feeder 5 concentrated saline on one side of the concentrate of a first membrane filtration unit brane comprising a first filtration membrane separating one side of the con- centered on one side of the permeate of the first membrane filtration unit; remove a concentrate from the concentrate side of the first filter unit membrane ction; 10 remove a permeate from the permeate side of the first filtration unit a membrane and dispense the permeate removed from the first membrane filtration unit brane to one side of the concentrate of a second membrane filtration unit, the second membrane filtration unit comprising a second membrane filtration that separates the concentrate side from one side of the permeate of the second 15 membrane filtration units; remove a concentrate from the concentrate side of the second filter unit membrane ction; remove a permeate from the permeate side of the second filtration unit membrane and deliver the permeate removed from the second membrane filtration unit 20 brane to one side of the concentrate of a third membrane filtration unit, the third membrane filtration unit comprising a third filtration membrane which separates the concentrate side from the permeate side of the third filtration unit membrane; and feed a saline solution to the permeate side of all filtration units 25 membrane filtration unit, except the downstream membrane filtration unit.

[0014] According to another aspect, a method for the removal of water by membrane filtration from a concentrated salt solution, in which the method uses a system comprising a plurality of membrane filtration units series brane; wherein each membrane filtration unit comprises: a mem- 30 filtration brane that separates one side of the concentrate from one side of the permeate of the respective membrane filtration unit; a concentrate discharge duct, in coupling of fluid with the respective side of the concentrate, to remove from it -4- a concentrate; a permeate discharge duct, in fluid coupling with the respective side of the permeate, to remove the permeate from it; a first inlet of fluid, in fluid coupling with the concentrate side of the filtration unit membrane; where each membrane filtration unit, except the most downstream one, 5 further comprises a second fluid inlet, in fluid coupling with the side of the permeate of the membrane filtration unit. The method comprises the following phases: generate a pressure difference on each filtration membrane; flow a saline solution through each filtration membrane from the 10 respective concentrate side to the permeate side of each filtration unit; remove concentrate from the concentrate side of each filtration unit membrane; transfer the permeate from the permeate side of each filtration unit to membrane on the concentrate side of the next membrane filtration unit; 15 maintain a correct salt concentration in the permeate side of each membrane filtration unit, except the most downstream membrane filtration unit, feeding a saline solution through the second fluid inlet in the side of the permeated.

[0015] Also described here is a method for removing carbon dioxide from 20 a combusted gas containing carbon dioxide and moisture; the method comprising the phase of condensing the humidity contained in the combustion gas forming water; remove remove water from the flue gas through an absorber; remove water from the absorber filter through a membrane filtration process.

[0016] Further features and embodiments of the methods of this de- 25 The registrations are described below, with reference to the attached drawings, and are outlined in the attached claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Reference is now made briefly to the attached drawings, in which: Fig. 1 illustrates a schematic of a multi-stage reverse osmosis system se- 30 according to this description; Fig. 2 illustrates in more detail a multi-stage reverse osmosis system. -5- stage according to this description; Figs. 3 and 5 illustrate two embodiments of a capture system carbon based on a mixed salt process and including a reverse osmosis system for water management in the carbon capture system; and 5 Fig. 5 illustrates a carbon capture plant based on the process of refrigerated ammonia and including a reverse osmosis system for management of water in the carbon capture system. DETAILED DESCRIPTION

[0018] In the following description, reference is made in particular to a system and 10 a membrane filtration method that uses reverse osmosis technology. It is understood, however, that other embodiments may use different types of filtration membranes, in particular nanofiltration membranes.

[0019] Fig. 1 illustrates a simplified schematic of a reverse osmosis system. multi-stage 1 according to the present description. In the embodiment represented 15 As shown in Fig. 1, the reverse osmosis system 1 comprises four osmosis units reverse, marked 3A, 3B, 3C, 3D. However, it should be noted that the number of reverse osmosis unit shown in Fig. 1 is provided as an example only, and that it is possible to use a greater or lesser number of reverse osmosis units. reference number 3 is used to indicate a generic reverse osmosis unit. 20

[0020] Each reverse osmosis unit 3 comprises a semipermeable membrane bile, also referred to here as reverse osmosis membrane. Semi-permeable membranes meables or membranes for reverse osmosis of reverse osmosis units 3A, 3B, 3C, 3D are marked 5A, 5B, 5C, 5D respectively. The reference number 5 indicates a generic semipermeable membrane. Each semipermeable membrane 25 5 separates the internal volume of the respective reverse osmosis unit 3 into one side of the con- center 7 and one side of the permeate 9. The sides of the concentrate of the reverse osmosis units 3A, 3B, 3C, 3D are marked 7A, 7B, 7C, 7D respectively. The sides of the permeate of reverse osmosis units 3A, 3B, 3C, 3D are marked respectively- mind with 9A, 9B, 9C, 9D. The reference numbers 7 and 9 indicate respectively a 30 generic side of the concentrate and a generic side of the permeate. -6-

[0021] Each reverse osmosis unit 3 comprises a condenser discharge duct. centered 11, marked 11A, 11B, 11C, 11D for the four osmosis units reverse 3A-3D shown in Fig. 1. The concentrate discharge ducts 11A-11D are in fluid coupling with the respective sides of the concentrate 7A-7D of the re- 5 prospective reverse osmosis units 3A-3D. Concentrate discharge lines 11A-11D. are in fluid coupling with, through a manifold or a manifold tube 12, a concentrate removal line 13.

[0022] Each reverse osmosis unit 3 further comprises a respective conduit permeate discharge 15. The permeate discharge ducts are marked re- 10 respectively with 15A, 15B, 15C, 15D.

[0023] For each pair of upstream reverse osmosis units and respective reverse osmosis 3 downstream arranged in sequence, the permeate discharge duct 15 of the upstream reverse osmosis unit is in fluid coupling with the con- side center 7 of the respective downstream reverse osmosis unit 3. Therefore, for example, the 15 permeate discharge duct 15A is in fluid coupling with the con- side center 7B of reverse osmosis unit 3B, permeate discharge pipe 15B is in fluid coupling with the 7C concentrate side of the reverse osmosis unit 3C, the permeate discharge duct 15C is in fluid coupling with the side of the 7D concentrate of the 3D reverse osmosis unit. The permeate discharge pipe 20 15D of the downstream reverse osmosis unit 3D is in fluid coupling with a water discharge line 17, which removes nearly pure water (i.e. water with a low or negligible salt concentration) from the reverse osmosis system 1.

[0024] A pump, or other pressure-increasing device, marked with 16 is positioned along each permeate discharge duct 15 which places in 25 fluid coupling the permeate side 9 of a reverse osmosis unit 3 upstream with the concentrate side 7 of the respective downstream reverse osmosis unit 3. The pumps arranged along the permeate discharge ducts 15A, 15B, 15C are marked respectively with 16A, 16B, 16C.

[0025] Each reverse osmosis unit 3 comprises a first fluid inlet 30 19, in fluid coupling with the concentrate side 7 of the respective unit reverse osmosis 3. The first fluid inlets are marked 19A, 19B, 19C, -7- 19D for reverse osmosis units 3A, 3B, 3C, 3D.

[0026] In addition, each reverse osmosis unit 3A, 3B, 3C, except the most downstream 3D, includes a second fluid inlet 21A, 21B, 21C, in coupling of fluid with the permeate side 9A, 9B, 9C of the reverse osmosis unit 3A, 3B, 3C. 5

[0027] In the embodiment of Fig. 1, the first fluid inlet 19B, 19C, 19D of each reverse osmosis unit 3B, 3C, 3D, except the upstream one (unit of reverse osmosis 3A), is in fluid coupling with the discharge pipe of the permeate 15A, 15B, 15C of reverse osmosis unit 3A, 3B, 3C directly to upstream. In addition, the second fluid inlet 21A, 21B, 21C of each osmosis unit 10 reverse 3A, 3B, 3C (i.e. all reverse osmosis units except the highest one) downstream 3D) and the first fluid inlet 19A of the upstream reverse osmosis unit 3A are in fluid coupling with a common saline supply concentrated 25. A pump or other pressure-increasing device 18 is po- located between the common concentrated saline solution feeder 25 and the first in- 15 fluid inlet 19A of the upstream reverse osmosis unit 3A.

[0028] In some embodiments, between each pair of osmosis units in- pours arranged in sequence, except between the first and second reverse osmosis units 3A, 3B further upstream, a recirculation line 27 places the con- in fluid coupling concentrate discharge duct 11 of reverse osmosis unit 3 downstream with the second 20 fluid inlet 21 of the reverse osmosis unit 3 directly upstream of the same. Therefore, in the embodiment of Fig. 1, for example, a first line of re- circle 27.1 is arranged between the concentrate exhaust duct 11C of the third unit of reverse osmosis 3C and the second fluid inlet 21B of the second osmosis unit reverse 3B. Similarly, a second recirculation line 27.2 is arranged between the con- 25 concentrate discharge duct 11D of the downstream reverse osmosis unit 3D and the second 21C fluid inlet of the third (penultimate) 3C reverse osmosis unit.

[0029] The reverse osmosis system 1 of Fig. 1 described so far works as follows. An aqueous solution containing a high salt concentration, such as solvent from a carbon capture plant, is fed into the reverse osmosis system 30 reverse 1 through the common feeder of concentrated saline solution 25. The objective The main purpose of this system is to extract water from the solution while preserving the -8- most of the chemical compounds present, thus obtaining substantially less water at the output. pure mind. This would not be possible with a reverse osmosis system of the technique anterior because, due to the high salt concentration in the saline solution con- centered, the osmotic pressure that would have to be overcome would be beyond the limits at- 5 tuable.

[0030] Typical salt concentrations in concentrated saline solution can vary, for example, between 50 and 100 g / l.

[0031] To overcome this limitation, the multi-stage reverse osmosis system 1 described here ensures that in each stage, i.e. in each osmosis unit 10 inverse 3A, 3B, 3C, 3D, the difference in salt concentration between the concentrate side and the permeate side is low enough to allow the water to pass through through the semipermeable membrane 5A, 5B, 5D, 5E from the concentrate side 7A, 7B, 7C, 7D at the permeate side 9A, 9B, 9C, 9D with operating pressures (i.e., pressure differences between the two faces of the semipermeable membrane 5A, 5B, 5C, 15 5D) of acceptable size. These values ​​are illustrative, but not limiting, of the difference of pressure between the concentrate side 7A, 7B, 7C, 7D and the permeate side 9A, 9B, 9C, 9D can vary, for example, between 30 bar and 90 bar, preferably between 40 bar and 80 bars.

[0032] Using an adequate number of stages, the permeate side (9D) of the unit 20 of reverse osmosis further downstream (3D) will accumulate almost pure water, coming from the highly concentrated saline solution fed through the common inlet of so- concentrated saline solution (25).

[0033] More specifically, the first reverse osmosis unit 3A receives a first flow of concentrated saline solution through the first fluid inlet 19A in its side 25 of the 7A concentrate. A second flow of concentrated saline solution is delivered to the side of the permeate 9A through the second fluid inlet 21A. Since both the first fluid inlet 19A and the second fluid inlet 21A receive the solution concentrated saline from the common concentrated saline feeder 25, the con- The salt concentration is the same in both flows. Therefore, the difference in osmotic pressure 30 between the permeate side and the concentrate side is 0 bar. In some embodiments tion, most of the concentrated saline solution delivered through -9- the common feeder of concentrated saline solution 25 is delivered to the side of the con- center 7A of the first reverse osmosis unit 3A, for example 70% of the flow of concentrated saline solution is delivered through the first inlet of fluid 19A of the first reverse osmosis unit 3A, i.e. the most upstream one. A 5 substantially lower flow rate, e.g. 25% of the total solution flow rate concentrated saline, is fed to the permeate side 9A of the first osmosis unit reverse 3A.

[0034] Pump 18 ensures a differential pressure between the concentrate side 7A and the permeate side 9A of the first reverse osmosis unit 3A, so that 10 the water flows through the reverse osmosis membrane (i.e. the membrane semipermeable) 5A of the first reverse osmosis unit 3A. The remaining solution, i.e. the total incoming concentrated salt solution minus the permeating water through the semipermeable membrane 5A, exits from the first reverse osmosis unit 3A through the first concentrate discharge duct 11A. 15

[0035] Due to the pressure difference across the first membrane for reverse osmosis 5A, the salt concentration of the solution contained in the per- side meatus 9A of the first reverse osmosis unit 3A is lower than the salt concentration of the solution exiting the first reverse osmosis unit 3A, and lower than the con- salt concentration of the incoming concentrated saline solution delivered through 20 the common feeder of concentrated saline solution 25, while the concentration saline solution exiting from the concentrate side 7A of the first osmosis unit reverse 3A through the concentrate exhaust duct 11A is higher. For example- pio, if the concentrated saline solution is in the input, delivered through the feeder common concentrated saline solution 25, has a salt load SF equal to 1 (SF = 1), the 25 salt load of the solution exiting from the concentrate side 7A through the first 11A concentrate exhaust duct can be SF=1.01.

[0036] The liquid with lower salt concentration collected on the permeate side 9A of the first reverse osmosis unit 3A is gradually transferred through the permeate discharge duct 15A to the concentrate side 7B of the second unit 30 reverse osmosis 3B. A small flow rate, for example about 4%, of the salt solution concentrated in total input, which enters system 1 through the common power supply -10- of concentrated saline solution 25, is fed to the permeate side 9B of the se- second reverse osmosis unit 3B. Pump 16A increases the pressure of the liquid which flows from the permeate side 9A of the first reverse osmosis unit 3A to the side of the concentrate 7A of the second reverse osmosis unit 3B. In this way, it is established 5 a pressure difference across the semipermeable membrane 5B of the second reverse osmosis unit 3B. The recirculation line 27.1 is intended to return the concen- drawn from the downstream reverse osmosis unit 3C to the permeate inlet 9B. To ensure the correct functioning of the reverse osmosis unit 5B, the salt concentration on the its side of the permeate 9B will be kept lower than the salt concentration in its 10 side of concentrate 7B increasing the salt concentration in the recirculated fluid through the first recirculation line 27.1. This is achieved by using the solvent from the feed saline solution dispenser 25 via the respective second fluid inlet 21B and by discharging the fluid with too low a salt concentration through the duct discharge of concentrate 11C towards collector pipe 12. 15

[0037] The pressure difference causes the water to flow through the semi-permeable membrane. meable 5B, thus reducing the salt concentration in the permeate side 9B of the second reverse osmosis unit 3B. The flow rate of liquid pumped along the conduit permeate discharge 15A, minus the water flowing through the semi-membrane permeable 9B, is removed by the second reverse osmosis unit 3B through the 20 respective concentrate discharge duct 11B and is collected, together with the solution concentrated salt ion exiting from the concentrate side 7A of the first unit of reverse osmosis 3A, in the concentrate removal line 13, from which the solution concentrated salt is removed by reverse osmosis system 1.

[0038] Since the liquid that collects in the concentrate side 7B of the second 25 units of reverse osmosis 3B has a lower salt concentration than that coming from the permeate side 9A of the first reverse osmosis unit 3A, the solution saline ion exiting the second reverse osmosis unit 3B has a saline load less than 1, for example about 0.75 (SF=0.75).

[0039] The permeate side 9B of the second reverse osmosis unit 3B receives the ac- 30 here which passes through the semipermeable membrane 5B, which combines with the flow recirculation (first recirculation line 27.1) from the concentrate side 7C of the unit -11- downstream reverse osmosis 3C. Under ideal conditions, the flow of water through the mem- The composition of the different reverse osmosis modules 3A, 3B, 3C, and 3D is the same. Otherwise, It is necessary to adjust the salt concentrations of the different stages to regulate the pressure osmotic. This is achieved by using the small flow of high concentration saline solution 5 centering from the common feeder of concentrated saline solution 25 (in this example, as mentioned, about 4% of the total flow rate fed through the feed common dispenser of concentrated saline solution 25). In case the passage of water in the downstream reverse osmosis unit 3C is less than the flow in the unit upstream reverse osmosis 3B, the diluted recycling is disposed of using the pipes 10 concentrate discharge (drain connections) 11C or 11D. Commercial projects aim- will achieve a reduction in water permeation capacity from one stage to the next one to obtain an easy control of the salt concentration by adding a portion of the concentrated saline solution feeder 25 and disposing of the rest in the concentrate removal line (effluent side) 13. 15

[0040] The liquid flowing into the permeate side 9B of the second osmosis unit reverse 3B flows through the respective permeate discharge duct 15B towards the 7C concentrate side of the third 3C reverse osmosis unit. The 16B pump au- mint the pressure of the solution flowing through said discharge duct of the permeate 15B, so that the pressure in the concentrate side 7C of the third 20 units of 3C reverse osmosis is higher than the pressure in the respective permeate side 9C, which is in fluid coupling with the common saline supply concentrated 25 through the second fluid inlet 21C.

[0041] Similarly to the second reverse osmosis unit 3B, the per- side also meatus 9C of the third unit of reverse osmosis 3C in fluid coupling with in 25 correspondence of 21C the common feeder of concentrated saline solution 25, from to which a highly concentrated solution can be added to the permeate, while the concentrate from the fourth 3D reverse osmosis unit recirculates to the side of the permeate of the third 3C reverse osmosis unit through the recirculation line 27.1. The small flow rate (in the example 1% of the concentrated saline solution in the inlet 30 total entering the system 1) of concentrated saline solution from the co-feeder mune of concentrated saline solution 25 increases the concentration in the fluid made recirculate from the recirculation line 27.2, while the fluid with too much salt concentration -12- low is discharged through the fourth concentrate discharge duct 11D. It is thus maintaining the correct salt concentration in the 9C permeate side of the third 3C reverse osmosis unit.

[0042] The pressure difference across the 5C reverse osmosis membrane per- 5 meabile causes water to permeate through it, so that the concentration saline in the 9C permeate side of the third 3C reverse osmosis unit decreases. salt load of the liquid exiting from the 7C concentrate side of the third osmosis unit reverse 3C through the concentrate exhaust duct can be about 0.5 (SF=0.5), which is a value lower than the salt loading (SF=1) of the saline solution in 10 inlet delivered to the permeate sides 9A, 9B, 9C, 9D of all reverse osmosis units 3A, 3B, 3C, 3D through the common feeder of concentrated saline solution 25.

[0043] By recycling, through the recycling line 27.2, a fraction of solution a low concentration from the fourth exhaust duct of the 11D concentrate to the second 21C fluid inlet of the third 3C reverse osmosis unit, the salt concentration 15 in the 9C permeate side of the third 3C reverse osmosis unit is kept co- consistently lower than the salt concentration in the 7C concentrate side of the itself, so that water can continue to permeate through the membrane se- 5C permeable under the effect of the pressure difference across the said mem- permeable brane. 20

[0044] The liquid that collects in the 9C permeate side of the third osmosis unit reverse 3C is transferred through the respective permeate discharge duct 15C towards the 7D concentrate side of the fourth 3D reverse osmosis unit. The pump 16C increases the pressure of the fluid flowing through the exhaust duct of the permeate 15C, so as to maintain a pressure difference across the mem- 25 semipermeable 5D brane of the fourth 3D reverse osmosis unit. The difference of pressure can be, similarly to the previous reverse osmosis units 3A, 3B, 3C, between 30 bar and 90 bar, preferably between 40 bar and 80 bar, values ​​given as examples general and not limiting.

[0045] The last 3D RO unit is preferably of conventional type, i.e. 30 comprises only a first fluid inlet 19D on the concentrate side, a conduit 11D concentrate discharge and a fluid outlet (permeate discharge duct -13- 15D) on the permeate side.

[0046] Pushed by the pressure difference across the semi-permeable membrane 5D, water flows through the 5D semipermeable membrane from the concentrate side 7D to the permeate side 9D of the fourth 3D reverse osmosis unit. The solution con- 5 centered exits from the concentrate side 7D through the concentrate exhaust duct section 11D. The salt loading of this saline solution can be about 0.1 (SF=0.1), while essentially pure water collects in the 9D permeate side of the fourth 3D reverse osmosis unit and is removed from the reverse osmosis system 1 through the water drain line 17. 10

[0047] As mentioned, a fraction of the low concentration solution that flows through the concentrate exhaust duct 11D is recycled to the side of the 9C permeate of the third 3C reverse osmosis unit to maintain a difference of concentration between the 7C concentrate side and the 9C permeate side, so that water continues to flow through the semipermeable membrane 5C, pushed by the dif- 15 pressure difference through it.

[0048] From it a flow of almost pure water is extracted, which represents app- approximately 5% of the total flow rate of concentrated saline solution, fed to the reverse osmosis system 1 through the common saline solution feeder concentrated 25. The remaining 95% of the total flow is collected in the collector or pipe 20 collector 12 and fed to the concentrate removal line 13.

[0049] As can be understood from the above description of the schematic system- as shown in Fig. 1, the cascade of reverse osmosis units arranged in sequence is capable of removing a controlled amount of nearly pure water from a solution highly concentrated saline with a salt content that can reach 50-100 g / l 25 with a pressure difference achievable across the reverse osmosis membranes arranged in sequence 5A, 5B, 5C, 5D. As will be explained later with reference In Figs. 3, 4 and 5, the multi-pass or cascade reverse osmosis system can be used in a carbon capture system to manage the water content at its internal. 30

[0050] Continuing to refer to Fig. 1, Fig. 2 shows a form of -14- More detailed realization of 1 second multi-pass reverse osmosis system this description. In Fig. 2 identical reference numbers indicate identical parts tical or corresponding to those illustrated in Fig. 1 and described above. Such parts do not will be described again. 5

[0051] In the embodiment of Fig. 2, the reverse osmosis system 1 com- takes five reverse osmosis units, instead of four as in Fig. 1. The unit of The downstream reverse osmosis unit is labeled 3E. The downstream reverse osmosis unit is labeled 3E. It has the same structure and fluid connections as the 3D reverse osmosis unit of the Fig. 1, while the reverse osmosis units 3B, 3C and 3D in Fig. 2 have the same 10 structure of the reverse osmosis units 3B or 3C in Fig. 1.

[0052] In Fig. 2 the reference numbers 41A, 41B, 41C, 41D and 41E refer to to flow control valves that control the flow of concentrated saline solution from the common feeder of concentrated saline solution 25 to the permeate side 9A, 9B, 9C, 9D of each reverse osmosis unit 3, except the downstream one 9E. 15

[0053] Reference numbers 51A, 51B, 51C, 51D indicate respective li- liquid / gas arranged along the permeate discharge ducts 15A, 15B, 15C, 15D which connect each pair of reverse osmosis units 3A, 3B, 3C, 3D arranged in sequence. Liquid / gas separators 51A, 51B, 51C, 51D, if present, remove spe- gaseous particles from the permeate flow upstream of the respective pumps 16A, 16B, 16C, 16D, 20 to avoid possible damage to the pumps. The gaseous species removed by the li- liquid-gas 51A-51D are collected in a gas removal manifold 52 and pos- they can be recycled, for example.

[0054] In addition, in the diagram of Fig. 2, the reference number 61.1 indicates a flow control valve arranged on the first recirculation line 27.1 which connects 25 the 11C concentrate discharge pipe of the 3C reverse osmosis unit with the se- second fluid inlet 21B of the reverse osmosis unit 3B. The reference number 61.2 indicates a flow control valve located on the second recirculation line 27.2 Connecting the 11D concentrate discharge pipe of the reverse osmosis unit 3D with the second fluid inlet 21C of the 3C reverse osmosis unit. The number of 30 reference 61.3 indicates a flow control valve arranged on a recirculation line colo 27.3 connecting the 11D concentrate discharge pipe of the osmosis unit -15- 3D reverse with the second 21C fluid inlet of the 3C reverse osmosis unit.

[0055] Flow control valves 71A, 71B, 71C, 71D, 71E are arranged along the respective concentrate discharge ducts 11A, 11B, 11C, 11D, 11E of the five reverse osmosis units 3A, 3B, 3C, 3D, 3E. 5

[0056] A multi-stage reverse osmosis system 1 as described above may be used, for example and in particular, in a carbon capture plant to con- control the amount of water in the saline solution processed through the system. Fig. 3 illustrates a 100 carbon capture plant based on a mixed salt process, known in the art, which will not be described in detail. Here only the components will be mentioned. 10 main components of the 100% carbon capture plant.

[0057] In short, the carbon capture system 100 comprises an inlet 101 CO2-rich flue gas, a direct contact cooler 103, a heater direct contact 105, an absorber section 107, comprising a first absorber tore 107A and a second absorber 107B, as well as a water washing column 15 107C. The carbon capture plant 100 further includes a regenerator 109, comprising a carbon dioxide removal line 111 and a reboiler 113

[0058] A stream of cooled CO2-rich flue gas flows through the line 115 in the absorber section 107, where carbon dioxide is removed from the gas CO2-rich combustion gas and is absorbed into the saline solution circulating in the first 20 absorber 107A and in the second absorber 107B. The CO2-poor flue gas cools resulting cooled air exits the absorber section 107 along a discharge line of the burned gas 117 and is heated in the direct contact heater 105 before be discharged into the environment through a chimney 119.

[0059] Flows of CO2-rich saline solution, loaded with removed carbon dioxide 25 from the burnt gas, are fed through lines 121A and 121B, which start from the bottom of the first absorber 107A and the second absorber 107B, towards the regenerator 109.

[0060] In the regenerator 109 the carbon dioxide is separated from the saline solution. and collected in the carbon dioxide removal line 111, and the saline solution 30 CO2-poor line is returned from regenerator 109 to the absorber section -16- 107. In particular, two streams of 2-poor saline solution are recycled by the re- blacker 109 through lines 123A and 123B respectively to the first absorber 107A and the second absorber 107B, to absorb carbon dioxide from the combustible gas. This CO2-rich refrigerated tank is fed by the direct contact chiller 103. 5

[0061] The moisture contained in the CO2-rich flue gas is partially im- placed in the saline solution removed through lines 121A, 121B from the section of absorber 107. This continuous addition of water into the circulating salt solution in the absorber section 107 and in the regenerator 109 must be continuously re- move, to maintain the correct balance of water and other species in the saline solution. 10 lina.

[0062] This is achieved through the reverse osmosis system 1 positioned along a of the lines that place the absorber section 107 in fluid coupling with the regenerator 109. In the exemplary embodiment of Fig. 3, the system of reverse osmosis 1 is positioned along line 123B. Some or all of the flow 15 of CO2-poor saline solution flowing through line 123B can be processed borate through the reverse osmosis system 1 to remove from it a quantity controlled water flow, which corresponds to the amount of water that is transferred from the gas combusted to the salt solution in absorber section 107.

[0063] Continuing to refer to Fig. 3, Fig. 4 illustrates embodiments 20 alternative carbon capture plant options 100 including a system of reverse osmosis 1 according to this description. Reference numbers same as those used in Figs. 3 and 4 designate equal parts, which will not be described again. mind. Fig. 4 illustrates two alternative exemplary positions of the osmosis system reverse 1, which can be positioned along the 121A line (1X position) or along the 25 line 121B (position 1Y).

[0064] The reverse osmosis system 1 can be used in any type of im- carbon capture plant, particularly in am-based CO2 capture plants moniaca. Still referring to Figs. 3 and 4, Fig. 5 illustrates a scheme of a 200-year CO2 capture plant based on a refrigerated ammonia process 30 (CAP, Chilled Ammonia Process), known in the art and which will not be described in detail cut. -17-

[0065] In brief, the carbon capture system 200 comprises a gas inlet CO2-rich combustion 201, a direct contact cooler 203, a heater direct contact 205, an absorber section 207, comprising an absorber 107A and a 207C water scrubber. The carbon capture plant 5 200 also includes a regenerator 209, which includes a removal line of carbon dioxide 211 and a reboiler 213

[0066] A stream of cooled, CO2-rich flue gas flows through the line 215 in absorber section 207, where carbon dioxide is removed from the gas CO2-rich combustion gas and is absorbed into the salt solution circulating in the absorber. 10 bitore 207A. The resulting cooled CO2-poor flue gas exits the section of absorber 207 along a flue gas exhaust line 217 and is heated in the direct contact heater 205 before being discharged into the environment through towards a fireplace 219.

[0067] A flow of CO2-rich saline solution, loaded with carbon dioxide re- 15 driven by the combustion gas, is fed through line 221, which starts from the bottom of the absorber 207A, towards the regenerator 209.

[0068] In the regenerator 209 the carbon dioxide is separated from the saline solution. and collected in the carbon dioxide removal line 211, and the saline solution CO2-poor line is returned from regenerator 209 to the absorber section 20 207A. More precisely, a CO2-poor saline solution flow is recycled from regenerator 209 through line 223 to the top of the absorber 207, to absorb carbon dioxide from the cooled CO2-rich flue gas fed cooled by direct contact cooler 203.

[0069] The moisture contained in the CO2-rich flue gas is partially absorbed 25 put in the saline solution removed through line 221 from the absorber section 207. To maintain the correct balance of water and other species in the saline solution, a reverse osmosis system 1 is located in one of the lines 212, 223 which connect the absorber 207A and the regenerator 209. In the embodiment of Fig. 5, the reverse osmosis system 1 is arranged along line 221. 30

[0070] Exemplary embodiments have been disclosed above and illustrated -18- in the attached drawings. Those skilled in the art will understand that changes may be made various changes, omissions and additions to those expressly disclosed herein, without departing from the scope of the invention as defined in the following claims. tions. -19-

Claims

1. A system for removing water by membrane filtration from a concentrated salt solution, the system comprising a plurality of membrane filtration units in series, wherein each membrane filtration unit comprises: a filtration membrane separating a concentrate side from a permeate side of the respective membrane filtration unit; a concentrate discharge conduit, in fluid coupling with the respective concentrate side, for removing a concentrate therefrom; a permeate discharge conduit, in fluid coupling with the respective permeate side, for removing a permeate therefrom; a first fluid inlet, in fluid coupling with the concentrate side of the membrane filtration unit;wherein each membrane filtration unit, except the most downstream one, further includes a second fluid inlet, in fluid coupling with the permeate side of the membrane filtration unit.; 2. The system of claim 1, wherein for each pair of sequentially arranged membrane filtration units, comprising an upstream membrane filtration unit and a downstream membrane filtration unit of said plurality of membrane filtration units, the permeate discharge conduit of the upstream membrane filtration unit is in fluid coupling with the first fluid inlet of the respective downstream membrane filtration unit.

3. The system of claim 2, further comprising a pressure boosting device along each permeate discharge conduit that fluidly connects the permeate side of the upstream membrane filtration unit -20Ufficio Mannucci srl and the concentrate side of the downstream membrane filtration unit.

4. The system of any preceding claim, wherein the permeate side of the most downstream membrane filtration unit is in fluid coupling with a water discharge line.

5. The system of any preceding claim, wherein the second fluid inlet of each membrane filtration unit and the first fluid inlet of the most upstream membrane filtration unit are in fluid coupling with a common feeder of concentrated brine.

6. The system of claim 5, including a flow control valve adapted to deliver a controlled flow rate of concentrated brine from the common concentrated brine feeder to the respective membrane filtration unit, the controlled flow rate decreasing from the most upstream to the most downstream membrane filtration unit.

7. The system of claims 5 or 6, wherein a pressure booster device is positioned between the common concentrated brine feeder and the first fluid inlet of the most upstream membrane filtration unit.

8. The system of any preceding claim, wherein for each pair of sequentially arranged membrane filtration units, comprising an upstream membrane filtration unit and a downstream membrane filtration unit of said plurality of membrane filtration units, except between the first most upstream membrane filtration unit and the second most upstream membrane filtration unit, a recirculation line is arranged, which places in fluid coupling the concentrate discharge duct of the downstream membrane filtration unit to the second fluid inlet of the upstream filtration unit.

9. The system of any preceding claim, wherein each membrane filtration unit is a reverse osmosis unit, and wherein each filtration membrane is a reverse osmosis membrane.

10. A carbon capture system comprising: an absorber, comprising: a flue gas inlet; a CO2-poor solvent inlet and a CO2-rich solvent outlet; a regenerator, comprising: a CO2-rich solvent inlet, fluidly coupled to the CO2-rich solvent outlet of the absorber; a CO2-poor solvent outlet, fluidly coupled to the CO2-poor solvent inlet of the absorber; and a CO2 outlet; a membrane filtration system for removing water from the solvent, between the absorber and the regenerator.

11. The carbon capture system of claim 10, wherein the membrane filtration system is positioned along a line that fluidly couples the CO2-lean solvent outlet of the regenerator with the CO2-lean solvent inlet of the absorber.

12. The carbon capture plant of claim 10 or 11, wherein the carbon capture plant is selected from the group comprising: an ammonia-based treatment plant; a mixed salt treatment plant; or a refrigerated ammonia treatment plant.

13. The carbon capture system of any of claims 10 to 12, wherein the membrane filtration system is positioned along a line that fluidly couples the CO2-rich solvent outlet of the absorber with the CO2-rich solvent inlet of the regenerator.

14. The carbon capture system of any of claims 10 to 13, wherein the membrane filtration system comprises a system according to any of claims 1 to 9.

15. A method for removing water by membrane filtration from a concentrated salt solution, comprising the following steps: feeding a concentrated salt solution from a concentrated salt solution feeder to a concentrate side of a first membrane filtration unit comprising a first filtration membrane separating a concentrate side from a permeate side of the first membrane filtration unit; removing a concentrate from the concentrate side of the first membrane filtration unit;-22Mannucci srl Office remove a permeate from the permeate side of the first membrane filtration unit and deliver the removed permeate from the first membrane filtration unit to a concentrate side of a second membrane filtration unit, the second membrane filtration unit comprising a second filtration membrane that separates the concentrate side from a permeate side of the second membrane filtration unit; remove a concentrate from the concentrate side of the second membrane filtration unit;removing a permeate from the permeate side of the second membrane filtration unit and supplying the removed permeate from the second membrane filtration unit to a concentrate side of a third membrane filtration unit, the third membrane filtration unit comprising a third filtration membrane separating the concentrate side from a permeate side of the third membrane filtration unit, and supplying a brine solution to the permeate side of all membrane filtration units except the most downstream membrane filtration unit.; 16. The method of claim 15, wherein the filtration units are reverse osmosis units and the filtration membranes are reverse osmosis membranes.

17. The method of claim 15 or 16, wherein the step of feeding a brine solution to the permeate side of all membrane filtration units, except the most downstream membrane filtration unit, comprises the step of feeding a concentrated brine solution from the concentrated brine solution feeder to said membrane filtration units.

18. The method of any of claims 15 to 17, further comprising the step of recycling the concentrate from the concentrate side of the third membrane filtration unit to the permeate side of the second membrane filtration unit.

19. The method of any of claims 15 to 18, further comprising the following steps: increasing the pressure of the concentrated brine solution fed to the concentrate side of the first membrane filtration unit; and -23Ufficio Mannucci srl increasing the pressure of the permeate removed from the permeate side of each first and second membrane filtration unit prior to delivering the permeate to the second and third membrane filtration units, respectively.

20. A method for removing water by membrane filtration from a concentrated salt solution, with a system comprising a plurality of membrane filtration units in series; wherein each membrane filtration unit comprises: a filtration membrane separating a concentrate side from a permeate side of the respective membrane filtration unit; a concentrate discharge conduit, in fluid coupling with the respective concentrate side, for removing a concentrate therefrom; a permeate discharge conduit, in fluid coupling with the respective permeate side, for removing permeate therefrom; a first fluid inlet, in fluid coupling with the concentrate side of the membrane filtration unit;wherein each membrane filtration unit, except the most downstream one, further comprises a second fluid inlet, fluidly coupled to the permeate side of the membrane filtration unit; the method comprising the following steps: generating a pressure difference across each filtration membrane; flowing a salt solution through each filtration membrane from the respective concentrate side to the permeate side of each filtration unit; removing the concentrate from the concentrate side of each membrane filtration unit; transferring the permeate from the permeate side of each membrane filtration unit to the concentrate side of the next membrane filtration unit;maintain proper salt concentration in the permeate side of each membrane filtration unit, except the most downstream membrane filtration unit, by feeding a salt solution through the second fluid inlet on the permeate side.; 21. The method of claim 20, wherein the saline solution fed through the second fluid inlet comprises a saline solution -24Ufficio Mannucci srl concentrated from a common concentrated saline solution feeder.

22. The method of claim 20 or 21, wherein the brine supplied through the second fluid inlet comprises concentrate discharged from the concentrate side of the subsequent membrane filtration unit. 5 23. A method of removing carbon dioxide from a flue gas containing carbon dioxide and moisture; the method comprising the step of condensing the moisture contained in the flue gas to form water; removing water from the flue gas through an absorber; removing water from the absorber by a membrane filtration process. 10 24. The method of claim 23, wherein the membrane filtration process comprises the steps of any one of claims 15 to 23