Patent Application
20240024821
The invention refers to a control method for or used in a membrane filter system and to a membrane filter system.
Membrane filter systems are for example used as reverse osmosis systems or nanofiltration systems. In these systems a clogging or fouling of the membrane may occur. Therefore, from time to time a cleaning is required which may be a flushing, physical cleaning and/or chemical cleaning in place. Thus, the system is operated in iterative filtration cycles, which cycles each comprise a production period and a following flushing. For economic reasons it is intended to minimize the cleaning and/or flushing time and to prolong the production period.
It is the object of the present invention to provide a control method for a membrane filter system and a respective membrane filter system allowing a maximized output at minimum costs.
This object is achieved by a control method having control method features according to the invention and a membrane filter system having membrane filter system features according to the invention. Preferred embodiments are disclosed in the following description and the accompanying drawings.
The control method according to the invention is a control method for a membrane filter system, i.e. used in a membrane filter system. The membrane filter system is a system which is operated in iterative filtration cycles which each comprise a production period and a following flushing. The respective control of the filtration cycle may also be part of the control method according to the invention. During the production cycles there is a feed applied to an entrance side of the membrane and a permeate flow leaving the membrane on the opposite outlet side of the membrane. Furthermore, there is a retentate or concentrate flow along the entrance side out of a concentrate outlet. This concentrate flow is a crossflow along one side of the membrane, i.e. the entrance side, and a flow not passing the membrane. Either this concentrate or the permeate or both may form the desired output of the filter system. At the end of the production period the feed flow is stopped and instead a flushing is carried out, preferably on the entrance side or along the entrance side of the membrane to clean the membrane, in particular to remove fouling or clogging from the membrane.
During the production period according to the invention there is provided a crossflow on the entrance side or along the entrance side of the membrane, in particular a crossflow along the membrane surface. This crossflow according to the invention is defined as the flow at the concentrate outlet or outlets. This crossflow preferably is a flow from the feed inlet towards the concentrate or retentate outlet. However, there may be provided at least one additional inlet and/or outlet to provide a crossflow. This means, the crossflow is not passing the membrane but flowing along the entrance side or entrance surface of the membrane. A part of the flow is passing the membrane towards the permeate outlet. The essential idea of the invention is a control or setting of the described crossflow at the concentrate outlet of at least one membrane during the production period, i.e. to set or tune the volume flow rate of this cross flow. According to the invention this setting is controlled or adjusted such that the energy consumption per entire filtration cycle reaches an optimum. Thus, it is not just the maximum output of the filter system, which is considered to find the optimum crossflow, but an optimization of the energy consumption per filtration cycle is carried out. Thereby, the total energy consumption during the production period and the energy consumption for the flushing are considered or accumulated. For example, an increased fouling of the membrane will require a more extensive flushing resulting in an increased energy consumption and/or a longer interruption of the production. On the other hand, an increased crossflow may further reduce or prevent fouling, but results in an increased energy consumption for providing the crossflow. If an increased fouling would be allowed, this may result in reduced energy consumption for the crossflow, however then more energy would be required to maintain a necessary entrance pressure on the entrance or feed side of the membrane. This shows there are conflicts in control since an improvement of one cost component may result in a worsening of another cost component. According to the invention the optimum is found by considering the total energy consumption of the filtration cycle which represents the costs for producing a certain amount of output of the filter system.
Preferably said optimum of the energy consumption is a minimum energy consumption. According to this the crossflow setting is optimized or changed until the minimum energy consumption for operation under given conditions is found. Further preferred said optimum energy consumption is the smallest or minimum energy consumption which can substantially be kept constant over time or several filtration cycles.
Preferably, the cost optimum or optimum of energy consumption is a long-term optimum representing a stable condition. Thus, it may be that for a certain shorter period of time a further reduction of costs or energy consumption could be achieved but resulting in higher energy consumption later. This preferably should be avoided. Especially, the costs for a longer period may be considered which may implicate higher costs for a shorter period at the beginning. Preferably, the optimum of the energy consumption may be a constant energy consumption over time, in particular a minimum of costs which is constant over time or several filtration cycles. By this, an increase of the energy consumption after several production cycles can be avoided. Such an increase in the end would not be the optimum of energy consumption, in particular the overall minimum energy consumption.
Preferably, the regarded energy consumption is a relative energy consumption per volume of produced permeate or concentrate, depending on the required output of the filtration system. By considering the relative energy consumption it is possible to optimize the costs in relation to the output of the filtration system, i.e., to find an optimum in view of output and energy consumption.
Said crossflow along the entrance side of the membrane is defined as a flow, i.e. a volume flow rate, at or out of a concentrate outlet, wherein according to a further preferred embodiment the crossflow is at least partly recirculated, for example by use of a crossflow pump. The crossflow is the retentate or concentrate flow resulting from a feed flow towards the membrane minus the permeate flow passing the membrane. In a possible embodiment a part of this crossflow may be recirculated, i.e. a part of the retentate flow is recirculated towards the feed side so that a circulating flow along the entrance side or surface of the membrane is provided as a crossflow. There may be additional in- and outlets for such a circulating crossflow on the entrance side of the membrane, i.e., on a space or conduit containing the entrance side of the membrane.
In a preferred embodiment according to the method the crossflow is set by adjusting the flow, i.e. volume flow rate, or speed of a crossflow pump, which crossflow pump at least partly recirculates the crossflow. There may be a circulation line connecting the concentrate outlet and the feed inlet of the membrane arrangement or unit, providing a loop. In this circulation line according to this preferred embodiment there is arranged the circulation or crossflow pump recirculating a part of the concentrate flow back to the feed side of the membrane. The crossflow pump provides an adjustable flow, for example by adjusting the speed of the pump. Thus, the crossflow can be set by adjusting the flow provided by the crossflow pump, in particular by changing the speed of the pump.
The crossflow may have an influence on the ratio of the permeate flow to the feed or entrance flow, i.e., the flow entering the entrance side of the filtration system. This means, the crossflow or a part of the crossflow defines the recovery level, which is the ratio of permeate flow to entrance flow. At a constant feed, by reducing such crossflow which is defined by a concentrate or retentate outlet flow the permeate flow will change. The recovery level, furthermore, may be changed by changing the feed flow at a constant retentate outlet flow. The crossflow optimized may be a crossflow partly or fully circulating on the entrance side of the membrane and/or may be a crossflow defined by the retentate outlet flow. The part of the crossflow which is not recirculated influences the recovery level as defined before. Thus, an optimization of the recovery level is possible by setting the crossflow in form of a retentate outlet flow as explained above. The setting of the crossflow may include a setting of a ratio of two flows, for example the feed flow and the retentate flow and/or the ratio of the retentate flow to the permeate flow. When changing the recovery level either the feed and/or the retentate flow may be changed, thus, there is a change in the crossflow settings, namely in the relation between feed and retentate flow.
According to a further preferred embodiment said membrane filter system for which the control method is used comprises at least one membrane having a pore size smaller than 10 nm, further preferred smaller than 5 nm, which preferably is defined as the axis of maximum extension of the pore. Preferably, the filter system may be a nano filtration system (NF system), reverse-osmosis system (RO system), an electrodialysis-system (ED system) or a forward-osmosis system (FO system). These all are systems having a small pore size of the membrane. For those membrane systems of small pore size, the optimization of the crossflow may be of particular benefit.
As described before, the crossflow may be defined as a recovery level defining the ratio of permeate flow to feed flow. This means, in the meaning of the present invention an optimization or setting of the crossflow includes a setting of the recovery level, i.e. an optimization of the recovery level according to which the energy consumption per filtration cycle reaches an optimum or minimum as discussed above. The recovery level may be changed or adjusted for example by adjusting the opening degree of a valve, in particular a valve at a concentrate outlet. Without a recirculation this valve would directly influence the crossflow. However, with a recirculation line and a crossflow pump as described above the crossflow can be set or adjusted independently of the recovery rate. A valve as mentioned before may be provided in addition to the recirculation line, preferably in a concentrate outlet downstream the branch of the recirculation line, such that the valve recirculated crossflow is not flowing through said valve.
According to a possible embodiment of the control method, said setting of the crossflow may be varied stepwise for different filtration cycles and the energy consumption for the different filtration cycles is compared to find an optimum, preferably the relative energy consumption for the different filtration cycles is compared. Thus, the optimization of the crossflow may take several filtration cycles with changes of the setting between the filtration cycles to compare the impact of the change in setting on the energy consumption. Thus, the control of the crossflow setting may be carried out in an iterative manner to find the desired optimum.
According to the method, in a further possible embodiment when stepwise varying the setting, said setting is kept constant for a few filtration cycles. This means, the setting is not changed for every filtration cycle, but after a certain number of filtration cycles, for example three or five filtration cycles. However, any possible number of filtration cycles may be taken. With the constant setting of the crossflow a trajectory for the energy consumption over time is generated for the number of filtration cycles. Then, the optimum for the energy consumption is found for the obtainable limit crossflow or flow ratio, as discussed above, with a gradient of the trajectory below a predefined limit. Preferably the energy consumption is constant over the number of filtration cycles, i.e., the gradient of the trajectory is substantially zero. By this, the optimum for the energy consumption with a stability over time can be found. With a too high crossflow, for example, the fouling can be prevented, however, the energy consumption is not at a minimum. With a too low crossflow an increase of fouling likely will occur after several filtration cycles resulting in an increase of energy consumption. Thus, it is desired to find the crossflow with a minimum stable energy consumption.
Preferably, beginning with a starting level a crossflow is reduced in an iterative manner after a number of filtration cycles as long as the gradient of the trajectory of the energy consumption remains below the predefined limit, preferably, the gradient is substantially zero, i.e., the energy consumption maintains stable over several filtration cycles. This method is preferred for optimizing the crossflow setting.
In case that the crossflow is defined by a recovery level defining the ratio of permeate flow to feed flow, as explained above, according to a further possible embodiment of the method, the recovery level may be increased beginning with a starting level in an iterative manner after a number of filtration cycles as long as the gradient of the trajectory of the energy consumption remains below a predefined minimum, preferably substantially zero, such that the energy consumption remains constant over the number of filtration cycles. Thus, also when controlling the setting of a recovery level the optimum for the energy consumption is found as a constant minimum energy consumption.
According to a further preferred embodiment the energy consumption per filtration cycle includes the total energy consumption for production, flushing and cleaning of the filter system. This, preferably, is the overall energy consumption required for producing a certain output volume, which may be the concentrate and/or the permeate of the membrane system. As described above, preferably the regarded energy consumption is the total relative energy consumption per volume of produced permeate or concentrate. Preferably, further costs in addition to the energy consumption may be considered as an energy equivalent in the control method. For example, the costs for brine or retentate treatment and/or for cleaning agents or similar may be regarded as an energy equivalent, so that at the end a cost optimization is achieved, the crossflow setting is controlled to achieve stable minimum costs.
For the control the energy consumption and possible energy equivalents may be recorded by suitable energy recording means. Furthermore, the necessary hydraulic values may be recorded by suitable recording or sensing means, for example flow sensors for detecting the volume flow of feed, crossflow, permeate flow and/or retentate flow. Instead of flow sensors the respective volume flows may be evaluated or output by the control means of pumps providing the respective flows.
Apart from the described control method a membrane filter system is subject of the present invention. Preferred embodiments of the control method as described above may be regarded as preferred embodiments of the membrane filter system and preferred embodiments described in relation to the membrane filter system may be regarded as preferred embodiments of the method, too.
The membrane filter system according to the invention comprises at least one membrane, at least one flow regulating device and a control device for controlling the flow regulating device to set a crossflow at a concentrate outlet of the membrane during a production period of the membrane filter system. The control device of the membrane filter system may be configured to control the filter system such that the filtration is carried out in filtration cycles each consisting of a production period and a following flushing. The crossflow may be fully or partly recirculated on the entrance side or for example a concentrate or retentate outlet flow, i.e. not recirculated. This not recirculated crossflow may define a recovery level being the ratio of a permeate flow to a feed flow. The flow regulating device may influence the crossflow directly or indirectly. The at least one flow regulating device may regulate a feed flow, a permeate flow, a retentate flow and/or a recirculated part of the crossflow. By the regulating device a ratio of two flows may be changed, for example the ratio of permeate flow to feed flow.
According to the invention said control device is configured such that the crossflow, i.e. the volume flow of the crossflow, in the production period is regulated in a manner that the energy consumption per filtration cycle reaches an optimum. This optimum preferably is a minimum or a stable minimum, i.e., the minimum of the energy consumption which maintains stable over several filtration cycles. For further details and aspects, it is referred to the afore-mentioned description of the control method.
The at least one membrane preferably has a pore size smaller than 10 nm, further preferred smaller than 5 nm, which preferably is defined as the axis of maximum extension of the pore. Especially, the membrane filter system may be a nano-filtration system, a reverse-osmosis system, an electrodialysis system or a forward-osmosis system. These are filter systems comprising at least one membrane having a small pore size. The control of the crossflow or setting of the crossflow particularly is of advantage for those filter systems.
The at least one flow regulating device may be a valve or a pump, preferably a pump with variable speed. The valve may have a variable opening degree for adjusting a flow, for example an outlet flow of concentrate not being recirculated. A flow can be regulated or adjusted by changing an opening degree of a valve or changing the speed of a pump, for example in a pump driven by an electric motor with frequency converter. According to a possible embodiment of the invention such pump may be a crossflow pump recirculating at least a part of the crossflow along the entrance side of the at least one membrane. For example, the crossflow pump may circulate a part of the retentate back from the concentrate outlet to an entrance or feed side so that a circulating flow on the entrance side of the membrane is provided. In a further possible embodiment, a pump acting as a flow regulating device may be a feed pump providing a feed flow to said at least one membrane, i.e., towards the entrance side of the membrane filter system. The feed pump is feeding an entrance flow to and through the membrane filter. By adjusting the feed flow for example, the recovery level may be influenced. Furthermore, it is possible to influence a crossflow directly or indirectly, particularly a flow through a concentrate or retentate outlet. The flow regulating device is connected to the control device such that the control device can change the crossflow by controlling or adjusting the flow regulating device, for example setting the speed of a pump and/or the opening degree of a valve. For setting or controlling the cross flow, several pumps and/or valves may be controlled by the control device in combination. This may be preferred for example to adjust a flow ratio as discussed above.
According to a further possible embodiment of the invention, said control device comprises energy recording means or receives data from such energy recording means. The energy recording means are configured for recording the energy consumption of the filter system. Further preferably the energy recording means and/or the control device are configured to record or calculate a relative energy consumption per volume of produced permeate or concentrate. For detecting the volume of produced permeate or concentrate respective flow sensors may be provided and connected to the control device to deliver the necessary data. Instead of flow sensors, pumps providing the respective flows may be used to output flow values for the control device.
Furthermore, flow sensors may be used to provide a feedback control of a crossflow set by the control device to ensure that the crossflow is kept on the desired level. Furthermore, the control device may be configured to allow the input of energy equivalents representing further costs occurring during the filtration and/or cleaning process of the filter system. This allows to not just carry out an optimization in view of energy consumption but in view of the overall costs, in particular the overall costs per volume produced by the filter device. Such additional costs for example may be costs for cleaning agents. The costs may be manually input into the control device having respective input means allowing to input such values. Furthermore, it may be possible that the control device has an interface to receive respective data from an external or connected control means.
According to a further preferred embodiment the control device of the membrane filter system is configured such that it controls the flow regulating device to adjust the setting of a crossflow by a control method as described above. In view of this it is referred to the foregoing description of the method.
In the following a preferred embodiment of the invention is described by way of example with reference to the figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
In the drawings:
Referring to the drawings, the membrane filter system as schematically shown in
In this example there is arranged a recirculation line 16 connecting the concentrate outlet 14 and the feed line 10 downwards the feed pump 12. In the recirculation line 16 there is arranged a recirculation or crossflow pump 18. This crossflow pump 18 is recirculating a part c1 of the crossflow c, i.e. a part of the flow of the concentrate or brine leaving the entrance side through the concentrate outlet 14. Thus, the crossflow pump 18 provides an additional partial crossflow c1 along the entrance side 4 in addition to the part c2 of the crossflow produced by the feed pump and flowing out of a concentrate drain 15. Downstream the branch of the recirculation line 16 there is arranged a valve 20 controlling the partial crossflow c2 defining the concentrate flow through said concentrate drain 15. The valve 20 may adjust the opening degree of the line towards the concentrate drain 15 and may allow to completely close the concentrate drain 15. If the valve 20 completely closes the concentrate drain 15, the crossflow c would be provided via the recirculation line 16 only since the entire feed flow from the feed line 20 would have to pass the membrane 2 towards the permeate outlet 8.
The filter system comprises a control device 22 connected to the feed pump 12, the crossflow pump 18 and the valve 20 for controlling the pumps 12 and 18 and the valve 20, i.e., to adjust the opening degree of the valve 20 and the speed of the pumps 12 and 18. It must be understood that the control device 22 may control the valve 20 or one of the pumps 12, 18 only, or control the valve 20 and just one of the two pumps 12 and 18. Furthermore, the crossflow pump 18 or the valve 20 may be omitted. Instead of a valve 20 having an adjustable opening degree, for example, there may be provided a fixed flow restriction. However, in all embodiments the control device 22 can control the setting of a crossflow c along the entrance side 4 of the membrane 2, i.e. a concentrate flow at the concentrate outlet 14 by controlling at least one pump 12, 18 and/or at least one valve 20.
Furthermore, the system may comprise one or more sensors. In this example the feed flow may be detected by or output from the feed pump 12 and the respective information is transferred to the control device 22 via a data connection between the feed pump 12 and the control device 22. However, there may be an additional flow sensor to detect the feed flow. Furthermore, in this example there is shown a flow sensor 24 on the permeate outlet 8 for detecting the volume flow of filtrate or permeate leaving the filter device. The flow sensor 24 is connected to the control device 22 for transmitting data representing the volume flow in the permeate outlet 8 to the control device 22. Depending on the desired setting of the crossflow c the flow sensor 24 may not be necessary and may be omitted. Instead, it would be possible to arrange further flow sensors, for example on the recirculation line 16 and/or the concentrate outlet 14, in particular downwards the branch of the circulation line 16, i.e. for detecting the flow through the concentrate drain 15. Furthermore, it would be possible to detect or provide the recirculation flow c1 by the control of the crossflow pump 18. The control device 22 may have an interface for communication with external or further devices.
According to the invention the control device 22 is configured to control a crossflow c or a setting of a crossflow c along the entrance side 4.
To find the optimum crossflow the control device 22 carries out a control method for setting the crossflow as explained with reference to
In
In the embodiment discussed with reference to
Furthermore, according to the invention a recovery level may define the crossflow c. The recovery level or recovery rate is defined as a ratio of the permeate flow in the permeate outlet 8 to the feed flow, i.e., the volume flow in the inlet line 10. As can be seen in
The setting of the recovery level is explained with reference to
As can be seen in the examples according to
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20216211.1 | Dec 2020 | EP | regional |
This application is a United States National Phase Application of International Application PCT/EP2021/086781, filed Dec. 20, 2021, and claims the benefit of priority under 35 U.S.C. § 119 of European Application 20216211.1, filed Dec. 21, 2020, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/086781 | 12/20/2021 | WO |
