Multi-stage filtration system and method of operation thereof

Abstract

A multi-stage filtration system for filtering a feed is described. The system comprises a plurality of filtration units and one or more concentrate lines. A first filtration unit is arranged to be connected to a feed line for feeding the feed to the filtration unit. The concentrate line is connected to the first filtration unit for collecting a concentrate filtered out of the feed by the first filtration unit. A second filtration unit is connected to the concentrate line for feeding the concentrate to the second filtration unit. The system is configured for selectively switching at least one further filtration unit between a first operation mode, in which the filtration unit is arranged to filter the feed or concentrate from one of the lines, and a second operation mode in which the filtration unit is arranged to filter the concentrate from another of the lines.

Description

[0001] MULTI-STAGE FILTRATION SYSTEM AND METHOD OF OPERATION THEREOF

[0002] The present invention relates to a multi-stage filtration system for filtering a feed. The present invention further relates to methods of operating such a multi-stage filtration system.

[0003] Known filtration systems comprise a plurality of filtration units. Each filtration unit of the known system can filter a feed by separating the feed into two or more output streams. The feed is typically a mixture, such as a solution. For example, membrane filtration technologies are widely used for separating various substances from a liquid feed, including solid particles, bacteria, viruses, dissolved molecules, and ions. Depending on the type of membrane, such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) or reverse osmosis (RO), different levels of filtration can be achieved. During the filtration process, the feed stream is divided into two distinct output streams: a purified stream known as permeate and a residual stream containing the separated components, referred to as concentrate.

[0004] The efficiency of a filtration system is often measured by its recovery rate, which is the ratio of permeate produced to the total feed volume. Depending on conditions like the composition of the feed, the configuration of the system, and operating conditions, filtration systems can achieve recovery rates of, e.g., about 80 percent, meaning that 80 percent of the feed is converted to permeate, while the remaining 20 percent exits as concentrate. To further improve recovery rates, the concentrate can be passed through a second filtration stage to extract additional permeate. This process can be repeated in one or more further stages, thus incrementally increasing the overall yield of the system.

[0005] One approach to maximising recovery in filtration systems is the so-called “X-mas (or Christmas) tree configuration”. In this setup, as described above, the concentrate from the first stage serves as the feed for the second stage, and, depending on the desired level of recovery, one or more further stages may also be incorporated to further process the concentrate. The distribution of filtration units across these stages forms a hierarchical structure, wherein the number of filtration units decreases from the first to the subsequent stages, creating a layout that resembles a Christmas tree, hence the name.

[0006] In the X-mas tree configuration, each filtration unit in the system is dedicated to a specific stage. When a filtration unit in a particular stage becomes unavailable, the capacity of the whole system is affected. For example, if one of the units in the second stage is offline, the first stage can no longer operate at full capacity, leading to an overall reduction in throughput. To address this, discharge arrangements can be employed on the concentrate lines between stages, allowing the feed from an earlier stage to be redirected, thus maintaining partial operation. While this solution preserves some of the capacity of the system, it results in reduced recovery, as less concentrate is processed for permeate extraction. In addition, such arrangement substantially increases the capital cost of the system. An alternative approach to ensuring reliability is to provide additional filtration units as spares. That is, for continuous operation, spare filtration units are available to maintain capacity when others are offline for cleaning or maintenance. In the X-mas tree configuration, spare filtration units are provided separately for each stage. However, this increases the complexity and cost of the system. For instance, a relatively complex tube system for transporting the mixtures between the units may be required.

[0007] It is an object of the present invention, amongst other objects, to provide an improved filtration system wherein the aforesaid drawbacks are at least partially alleviated.

[0008] Hereto, a multi-stage filtration system for filtering a feed is provided, the system comprising a plurality of filtration units and one or more concentrate lines, wherein at least a first filtration unit is arranged to be connected to a feed line for feeding the feed to the first filtration unit, wherein a first concentrate line is connected to at least the first filtration unit for collecting a first concentrate filtered out of the feed by the first filtration unit, wherein at least a second filtration unit of the plurality of filtration units is connected to the first concentrate line for feeding the first concentrate to the second filtration unit, wherein the system is configured for selectively switching at least one further filtration unit between a first operation mode, in which the respective filtration unit is arranged to filter the feed or concentrate from one of the lines, and a second operation mode in which the respective filtration unit is arranged to filter the concentrate from another of the lines.

[0009] The second filtration unit can thus function as a second-stage filtration unit while said at least one further filtration unit can function as, e.g., a first-stage filtration unit in its first operation mode and as, e.g., a second-stage filtration unit in its second operation mode. By enabling one or more filtration units to selectively filter the different mixtures, the filtration unit can be selectively deployed in the desired stage. As the filtration units can be flexibly allocated across different stages, it is no longer necessary to provide spare filtration units separately for each stage. Likewise, a filtration unit initially designated for one stage can be switched to another operation mode to be used in another stage for optimising operation of the system. As the filtration units are made stageindependent, spare filtration units can be assigned to any stage, which reduces the overall need to install spare filtration units to provide the same security of supply. As fewer filtration units are needed over the entire system, costs can be minimised. The system can thus offer greater flexibility in filtration unit allocation, reduce the need for stage-specific redundancy, and / or enhance overall system efficiency. Furthermore, a relatively simple tube system can be enabled, that may facilitate cleaning and maintenance of the system. It is to be understood that herein the terms “tube”, “pipe” and “piping” can be used interchangeably.

[0010] Moreover, the ratios between the numbers of filtration units in the different stages can now be freely selected. Additionally, as the filtration units can be used freely for any stage, the operator of the system has more options in the event of partial unavailability of the system. Furthermore, the modularity and scalability of the system can be enhanced. In contrast, in the classical used X-mas tree configuration, the system is not as easily adaptable to other processes with different requirements.

[0011] Preferably, said at least one further filtration unit is arranged to selectively filter the feed from the feed line in a first operation mode and the first concentrate from the first concentrate line in a second operation mode. Furthermore, preferably also the second filtration unit is connected to a feed line for feeding the feed thereto, and is switchable between the first and second operation modes. More preferably, the plurality of filtration units includes further filtration units connected to a feed line and switchable between said operation modes. The filtration units may be connected to the same feed line. Preferably, the system further comprises at least a second concentrate line as described further below, more preferably also a third concentrate line.

[0012] A preferred embodiment of the multi-stage filtration system comprises a selectively controllable valve system arranged to switch said at least one further filtration unit between its operation modes. By means of the valve system, the one or more filtration units can be made stageindependent. For example, the valve system may comprise at least one feed line valve respectively provided to said at least one further filtration unit for operably connecting the feed line to the respective filtration unit. This way, the connection to the feed line can be closed to switch the filtration unit to its second operation mode in which the filtration unit filters, e.g., the first concentrate from the first concentrate line instead of the feed from the feed line. It is further preferred if said one or more filtration units are provided with respective concentrate valves of the valve system, to be opened when closing the feed line valve, such that the one or more filtration units can discharge a second concentrate filtered out of the first concentrate. Inversely, to switch the filtration unit to its first operation mode, the concentrate valve is closed and the feed line valve is opened, such that the feed can be fed to the filtration unit and the concentrate can be discharged into the first concentrate line. A further preferred embodiment of the multi-stage filtration system comprises a second concentrate line, connected to the second filtration unit for collecting a second concentrate filtered out of the first concentrate by the second filtration unit.

[0013] Preferably, the valve system comprises at least one concentrate line valve respectively arranged between the second concentrate line and said at least one further filtration unit for operably connecting the respective filtration unit to the second concentrate line. The concentrate line valve can function as the aforesaid concentrate valve. That is, to switch the respective filtration unit to its first operation mode, the concentrate line valve is closed and the feed line valve is opened, whereas the concentrate line valve is opened and the feed line valve is closed to switch the filtration unit to its second operation mode.

[0014] According to a further preferred embodiment of the multi-stage filtration system, a third filtration unit of the plurality of filtration units is connected to the second concentrate line for feeding the second concentrate to the third filtration unit. The third filtration unit can thus function as a third- stage filtration unit. Preferably, the plurality of filtration units includes further filtration units connected to the second concentrate line. Preferably, said at least one further filtration unit is arranged to selectively filter the feed in its first operation mode, the first concentrate in its second operation mode, and the second concentrate from the second concentrate line in a third operation mode. This way, it can also function as a third-stage filtration unit. Thereto, a first concentrate line valve of the valve system may be arranged between the first concentrate line and said at least one filtration unit for operably connecting the respective filtration unit to the first concentrate line. To switch the respective filtration unit to its third operation mode, the feed line valve and the first concentrate line valve are closed and the second concentrate line valve, arranged between the second concentrate line and the respective filtration unit, is opened for feeding the second concentrate to the filtration unit.

[0015] It is to be understood that in the same manner as described above, further stages can be added by adding further filtration units and concentrate lines. Similarly, further filtration units can be added to existing stages. Moreover, further filtration units of the system can be made switchable between two or more operation modes to be selectively deployed in respective stages as described above, for example by means of valves arranged between the filtration units and the respective lines for operably connecting the filtration units to these lines.

[0016] According to a further preferred embodiment of the multi-stage filtration system, each filtration unit of the plurality of filtration units is arranged to be connected to the feed line and the one or more concentrate lines, and the filtration units are arranged to selectively operate in said operation modes. More in general, any number of filtration units of the system may be arranged switchable between any number of operation modes, as desired.

[0017] Each filtration unit may be a (membrane) filtration unit, preferably an RO unit, an MF unit, a UF unit or an NF unit. The membrane filtration unit can be a membrane, a membrane module, a membrane rack, or a membrane skid.

[0018] Preferably, the filtration units are identical or at least of the same type. This way, the filtration units can be flexibly allocated to different stages without the need to take account of differences between the filtration units.

[0019] According to a further preferred embodiment of the multi-stage filtration system, at least one of the one or more concentrate lines comprises a drainage port provided with a control valve. This provides further possibilities to optimise the operation of the system. Depending on its purpose, such a drainage port can be used as, e.g., a purge port or blowdown port. It is to be appreciated that the feature of the drainage port can also be implemented in other multi-stage filtration systems, including systems that are not configured for selectively switching a filtration unit between said operation modes.

[0020] According to a further preferred embodiment of the multi-stage filtration system, wherein at least one of the one or more concentrate lines is provided with a booster pump arranged to pump the respective concentrate through the respective concentrate line. It is then preferred if the valve system includes a further arrangement of valves, for ensuring proper directionality of flow in the concentrate lines provided with a booster pump.

[0021] Each filtration unit preferably comprises a filtrate outlet for discharging filtrate from the filtered by the filtration unit. This filtrate can also be referred to as permeate.

[0022] Furthermore, each filtration unit preferably comprises at least two connection ports for connecting the filtration unit to a respective line and for feeding a feed to the respective filtration unit or discharging a concentrate filtered out by the respective filtration unit.

[0023] According to a further aspect, a method of operating a multi-stage filtration system, preferably a multi-stage filtration system as described above, is provided, wherein the method comprises the steps of feeding a feed to the first filtration unit, collecting, in the first concentrate line, a first concentrate filtered out of the feed by the first filtration unit, feeding the first concentrate from the first concentrate line to said at least one further filtration unit, and filtering the first concentrate using said at least one further filtration unit. Alternatively, the first concentrate may be fed to, and filtered using, the second filtration unit.

[0024] The method may further comprise the step of disconnecting the second filtration unit from the first concentrate line, for instance by closing a valve arranged between the second filtration unit and the first concentrate line. This way, the second filtration unit can get offline for cleaning or maintenance, while allowing the system to continue the multi-stage filtration operation, as said further filtration unit now forms part of the second stage. Alternatively, if the first concentrate is filtered using the second filtration unit, said further filtration unit may be disconnected. Thus, as a filtration unit can be isolated from participation in the filtration operation, the filtration units can be cleaned individually instead of at the level of a stage or of the entire system. As a result, the equipment used for, e.g., cleaning, such as tanks, piping and (dosing) pumps, can be made smaller and therefore cheaper. To illustrate, in the known X-mas tree configurations wherein filtration units cannot be isolated individually, large tanks are required to be able to extract the amount of rinse water needed for backwashing the filtration units together and / or for a forward flush thereof. Likewise, large piping for the supply and discharge of flushing water is required, as well as high- capacity pumps.

[0025] The method may further comprise the step of cleaning the second filtration unit. This cleaning step may include, e.g., a backwash programme, a forward flush programme, a drain, and / or a chemically enhanced forward flush or clean-in-place (CIP) programme.

[0026] According to yet another aspect, a further method of operating a multi-stage filtration system, preferably a multi-stage filtration system as described above, is provided, wherein the method comprises the steps of selecting a number of filtration units to filter the feed and / or a number of filtration units to filter the first concentrate, and setting the selected number by switching said at least one further filtration unit to one of its operation modes.

[0027] According to a further aspect, the multi-stage filtration system may be used for filtering a fluid. The fluid may be a liquid, preferably water, in particular to obtain drinking water. Said permeate is then the drinking water. The fluid may for example be wastewater or a beverage that needs further filtration.

[0028] Thus, the feed may comprise a liquid, preferably water to be filtered. In the following, preferred embodiments of the present invention are illustrated with reference to the accompanying drawings, wherein:

[0029] Figure 1 schematically represents a multi-stage filtration system known in the art;

[0030] Figure 2 schematically represents a filtration system according to the present disclosure; Figures 3A-C represent different scenarios of operation of the filtration system. Figure 4 schematically represents a further embodiment of the filtration system.

[0031] Throughout the drawings, like elements are indicated by means of like reference signs.

[0032] In Figure 1, a known multi-stage filtration system 100’ with an X-mas tree configuration is schematically shown. The system 100’ comprises a plurality of membrane filtration units 1, 2, 3, 4, 5, 6, 7, hereafter referred to as “membranes”. The first stage includes four membranes 1, 2, 3, 4, the second stage includes two membranes 5, 6, and the third stage includes one membrane 7. Together, the three stages form a so-called “train”. A filtration system can comprise a plurality of such trains. A feed mixture Fi is fed to the first stage. Throughout the drawings, the direction of flow in pipelines is indicated by arrows. The concentrate Ci from the first stage is collected in a first concentrate line 21 and fed to the second stage as feed F2. The concentrate C2 from the second stage is collected in a second concentrate line 22 and fed to the third stage as feed F3. Each of the membranes 1, 2, 3, 4, 5, 6, 7 comprises an outlet for permeate P. At the outlet for concentrate C3 of this final stage, a control valve 43 is installed to be used to control the permeate-to-concentrate ratio of the system 100’. The control valve 43 is connected to a flow sensor 53. Adjusting this valve 43 allows for fine-tuning of the permeate-to-concentrate ratio to optimise the operation of the entire system 100’. As this valve 43 is closed more, more water from the feed Fi is pushed through the membranes 1, 2, 3, 4, 5, 6, 7 to the permeate side.

[0033] It can be seen that the membranes 5, 6 of the second stage cannot serve in the first or third stage, nor vice versa. If one of the membranes in, for example, the second stage is not available for filtration, the capacity of the entire system 100’ is reduced.

[0034] In Figure 2, a multi-stage membrane filtration system 100 in accordance with the present disclosure is shown. The system 100 comprises eight membranes 1, 2, 3, 4, 5, 6, 7, 8, a feed line 10 and three concentrate lines 21, 22, 23. Each membrane 1, 2, 3, 4, 5, 6, 7, 8 is connected to the feed line 10 via a feed line valve 30, to the first concentrate line 21 via a first concentrate valve 31, to the second concentrate line 22 via a second concentrate valve 32, and to the third concentrate line 23 via a third concentrate valve 33. Each membrane 1, 2, 3, 4, 5, 6, 7, 8 comprises an outlet for permeate P, a first connection port la, 2a, 3a, 4a, 5a, 6a, 7a, 8a for connecting the membrane to the feed line 10 and the second concentrate line 22, and a second connection port lb, 2b, 3b, 4b, 5b, 6b, 7b, 8b for connecting the membrane to the first concentrate line 21 and the third concentrate line 23. Each concentrate line 21, 22, 23 comprises a drainage port 210, 220, 230 provided with a control valve 41, 42, 43 connected to a flow sensor 51, 52, 53. The control valve 43 of the last concentrate line 23 serves to control the permeate-to-concentrate ratio of the system 100. The other drainage ports 210, 220 function as purge or blowdown.

[0035] In the situation illustrated in Figure 2, membranes 2 to 5 of the multi-stage filtration system 100 are allocated to the first stage, as their feed line valves 30 and first concentrate valves 31 are opened and their second and third concentrate valves 32, 33 are closed. Membranes 6 and 7 are allocated to the second stage, as their first and second concentrate valves 31, 32 are opened and their feed line valves 30 and third concentrate valves 33 are closed. Membrane 8 is allocated to the third stage, as its second and third concentrate valves 32, 33 are opened and its feed line valve 30 and first concentrate valve 31 is closed. Membrane 1 is not allocated to any stage, as all its valves 30, 31, 32, 33 are closed. It can be envisaged that the membranes 1, 2, 3, 4, 5, 6, 7, 8 can be freely allocated to any selected stage by selectively opening and closing its respective valves 30, 31 , 32, 33 as described above. In Figure 2, membrane 1 thus functions as a spare unit that can be used in any stage.

[0036] Thus, the problem of the installation of spare membranes, as experienced with the “X-mas tree” configuration, is solved with this system 100. That is, additional membranes can be provided, without having to assign them in advance to a particular stage, as the membranes can be made stage-independent.

[0037] Figures 3A and 3B represent two example scenarios, illustrating how membranes 1, 2, 3, 4, 5, 6, 7 can be assigned to any stage by means of the valves 30, 31, 32, 33. In Figure 3 A, membranes 1 to 4 are assigned to the first stage, membranes 5 and 6 are assigned to the second stage, and membrane 7 is assigned to the third stage. In the situation illustrated in Figure 3B, membranes 2, 4, 5 and 7 are switched to another operation mode. Specifically, membrane 4 is assigned to the second stage by closing its feed line valve 30 and opening its second concentrate valve 32. Inversely, membrane 5 is assigned to the first stage by opening its feed line valve 30 and closing its second concentrate valve 32. Further, membranes 2 and 7 are assigned to respectively the third stage and the first stage by switching all their valves 30, 31, 32, 33. Figure 3C represents a further example scenario, illustrating how the number of filtration units per stage can be changed. In Figure 3C, the first and second stage are each assigned three filtration units, while the rightmost unit is again assigned to the third stage.

[0038] Depending on the desired pressure per stage, it may be desirable to use booster pumps, as illustrated in Figure 4, which shows a further embodiment of the multi-stage membrane filtration system 100 in accordance with the present disclosure. The system 100 comprises eight membranes 1, 2, 3, 4, 5, 6, 7, 8, a feed line 10 and three concentrate lines 21, 22, 23. The first and second concentrate lines 21, 22 are each provided with a respective pair of a booster pump 61, 62 and a connected pressure sensor 71, 72, dividing the concentrate lines 21, 22 into an inlet segment 21a, 22a, connected to the inlet of the booster pump 61, 62, and an outlet segment 21b, 22b connected to the outlet of the booster pump 61, 62. To ensure proper directionality of flow in the first and second concentrate lines 21, 22, each membrane 1, 2, 3, 4, 5, 6, 7, 8 is connected to the inlet segment 21a of the first concentrate line 21 via a first concentrate line inlet valve 31a, to the outlet segment 21b of the first concentrate line 21 via a first concentrate line outlet valve 31b, to the inlet segment 22a of the second concentrate line 22 via a second concentrate line inlet valve 32a, and to the outlet segment 22b of the second concentrate line 22 via a second concentrate line outlet valve 32b. Furthermore, each membrane 1, 2, 3, 4, 5, 6, 7, 8 is connected to the feed line 10 via a feed line valve 30, and to the third concentrate line 23 via a third concentrate valve 33. Each membrane 1, 2, 3, 4, 5, 6, 7, 8 comprises an outlet for permeate P. Each concentrate line 21, 22, 23 comprises a drainage port 210, 220, 230 provided with a control valve 41, 42, 43 connected to a flow sensor 51, 52, 53.

[0039] The drawings and the above description serve to illustrate specific embodiments of the invention and do not limit the scope of protection defined by the appended claims.

Claims

CLAIMS1. A multi-stage filtration system for filtering a feed, the system comprising a plurality of filtration units and one or more concentrate lines, wherein at least a first filtration unit is arranged to be connected to a feed line for feeding the feed to the first filtration unit, wherein a first concentrate line is connected to at least the first filtration unit for collecting a first concentrate filtered out of the feed by the first filtration unit, wherein at least a second filtration unit of the plurality of filtration units is connected to the first concentrate line for feeding the first concentrate to the second filtration unit, wherein the system is configured for selectively switching at least one further filtration unit between a first operation mode, in which the respective filtration unit is arranged to filter the feed or concentrate from one of the lines, and a second operation mode in which the respective filtration unit is arranged to filter the concentrate from another of the lines.

2. Multi-stage filtration system according to claim 1 , further comprising a selectively controllable valve system arranged to switch said at least one further filtration unit between its operation modes.

3. Multi-stage filtration system according to claim 2, wherein the valve system comprises at least one feed line valve respectively provided to said at least one further filtration unit for operably connecting the feed line to the respective filtration unit.

4. Multi-stage filtration system according to claim 1, 2 or 3, further comprising a second concentrate line, connected to the second filtration unit for collecting a second concentrate filtered out of the first concentrate by the second filtration unit.

5. Multi-stage filtration system according to claim 2 or 3 and claim 4, wherein the valve system comprises at least one concentrate line valve respectively arranged between the second concentrate line and said at least one further filtration unit for operably connecting the respective filtration unit to the second concentrate line.

6. Multi-stage filtration system according to claim 4 or 5, wherein a third filtration unit of the plurality of filtration units is connected to the second concentrate line for feeding the second concentrate to the third filtration unit, wherein said at least one further filtration unit is arranged to selectively filter the feed in its first operation mode, the first concentrate in itssecond operation mode, and the second concentrate from the second concentrate line in a third operation mode.

7. Multi-stage filtration system according to any of the preceding claims, wherein each filtration unit of the plurality of filtration units is arranged to be connected to the feed line and the one or more concentrate lines, and the filtration units are arranged to selectively operate in said operation modes.

8. Multi-stage filtration system according to any of the preceding claims, wherein each filtration unit is a membrane filtration unit, preferably a nano- or ultrafiltration unit.

9. Multi-stage filtration system according to any of the preceding claims, wherein at least one of the one or more concentrate lines comprises a drainage port provided with a control valve.

10. Multi-stage filtration system according to any of the preceding claims, wherein at least one of the one or more concentrate lines is provided with a booster pump arranged to pump the respective concentrate through the respective concentrate line.

11. Multi-stage filtration system according to any of the preceding claims, wherein each filtration unit comprises a filtrate outlet for discharging filtrate from the feed filtered by the filtration unit.

12. Multi-stage filtration system according to any of the preceding claims, wherein each filtration unit comprises at least two connection ports for connecting the filtration unit to a respective line and for feeding a feed to the respective filtration unit or discharging a concentrate filtered out by the respective filtration unit.

13. Multi-stage filtration system according to any of the preceding claims, wherein the filtration units are identical.

14. A method of operating a multi-stage filtration system according to any of the preceding claims, wherein the method comprises the following steps:- feeding a feed to the first filtration unit;- collecting, in the first concentrate line, a first concentrate filtered out of the feed by the first filtration unit;- feeding the first concentrate from the first concentrate line to said at least one further filtration unit;- filtering the first concentrate using said at least one further filtration unit.

15. The method according to claim 14, further comprising the step of disconnecting the second filtration unit from the first concentrate line.

16. The method according to claim 14 or 15, further comprising the step of cleaning the second filtration unit.

17. A method of operating a multi-stage filtration system according to any of the preceding claims 1-13, wherein the method comprises the steps of selecting a number of filtration units to filter the feed and / or a number of filtration units to filter the first concentrate, and setting the selected number by switching said at least one further filtration unit to one of its operation modes.

18. Use of a multi-stage filtration system according to any of the preceding claims 1-13 for filtering a fluid.

19. Use according to claim 18, wherein the fluid is a liquid, preferably water to obtain drinking water.

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