NL2009614C2

NL2009614C2 - Membrane distillation system, method of starting such a system and use thereof.

Info

Publication number: NL2009614C2
Application number: NL2009614A
Authority: NL
Inventors: Peter Wardenier; Ralph Maessen; Hein Weijdema
Original assignee: Aquaver B V
Priority date: 2012-10-11
Filing date: 2012-10-11
Publication date: 2014-04-16

Description

Membrane distillation system, method of starting such a system and use thereof

FIELD OF THE INVENTION

5 The invention relates to a membrane distillation system comprising at least one membrane distillation module and a condenser module, in which, in use, a feed is converted into distillate and brine, which distillate is generated in the at least one membrane distillation modules and the condenser 10 modules, and which brine flows at least from a last membrane distillation module that precedes the condenser module into a brine collector vessel, wherein a brine pump is present for pumping liquid from the brine collector vessel to a higher pressure.

15 The invention also relates to a membrane distillation process comprising the steps of: - generating distillate from a feed by means of evaporation to vapour in at least one membrane distillation module and a condenser module to which vapour of a 20 preceding, last membrane distillation module is transferred, - removing non-evaporated, concentrated feed as brine at least from the last membrane distillation module to a brine collector vessel, and - pumping the liquid from the brine collector vessel to a 25 higher pressure,

The invention further relates to the use of such a membrane distillation system for water purification, for air conditioning and/or for other liquid purification applications, such as the removal of water from ethanol.

30

BACKGROUND OF THE INVENTION

The use of membrane distillation for desalination of water has already been investigated in the 1980s. EP0094543A2 2 discloses a membrane distillation system as defined hereabove, and discloses a series of graphs in its Figures 11 to 18, in which the volume of distillate is shown as a function of temperature and underpressure. While the primary 5 embodiment shows a single distillation module, it is clear from f.i. Fig. 2 that a plurality of membrane distillation modules may be put in series.

Further elaborations of said basic principles are known from WO-A 2005/089914, WO-A 2007/054311 and WO-A 2010/0127818.

10 WO-A-2005/089914 discloses in its Fig. 2 an embodiment of a series coupling of several distillation modules. The first of said distillation modules mere generates vapour, which is used as a heat source in the second distillation module for the needed evaporation from the feed liquid, and then 15 converted into distillate. The second distillation module again generates new vapour that is used as a heat source in the third distillation module and thus condensated into distillate. The vapour resulting from the third distillation module is condensated in a separate condenser module, 20 particularly a cooler in the form of a heat exchanger.

In the embodiment of WO-A-2005/089914, a plurality of liquid channels and vapor spaces is put in parallel within one distillation module, so as to increase the effective surface area. This is moreover an effective design for heat 25 exchange; a single vapour channel is present between two liquid channels, thus minimizing heat losses to the environmentIf the liquid channel is designed to be narrow, the feed liquid can easily fill the liquid channel, leading to maximation of the effective surface area.

30 An effective implementation providing such narrow liquid channels hereof is disclosed in WO-A 2010/0127818, in the form of a weldable and stackable frame, in which the required channels within one distillation module are 3 defined. If desired, fluid and/or vapour connections between subsequent distillation modules may be implemented into the stack of frames. Each frame may be provided with foils chosen from a.o. hydrophobic membranes and condensation 5 walls. Hence, a liquid channel is defined with a frame provided with a condensation wall foil on one side, and a hydrophobic membrane foil on the opposed side. As a result hereof, the system may have a membrane distillation module and a condenser that are integrated into one physical 10 system. Under pressure channels are moreover implemented herein for ensuring the setting of the intended underpressure through the complete system.

WO-A 2007/054311 discloses furthermore an arrangement for controlling the underpressure in the series of distillation 15 modules, and more particularly such that the full system runs at an underpressure. Thereto, an underpressure pipe system is shown extending to the vapour spaces of the membrane distllation modules, a condenser module as well as the preceding heat transfer module with a separate heat 20 generator. Moreover, several underpressure control means in the form of U-tubes (typically siphons) are present, i.e. in the feed line, in the system's distillate exit and in the brine exit, which further comprises a brine pump.

It has been observed that the brine pump constitutes a 25 vulnerable element within the system. The non-evaporated feed originating from the last distillation module is a concentrated, heated up fluid that is present at a low pressure, for instance the underpressure of the last membrane distillation module. This fluid is also called 30 brine. A typical pressure for the brine is 60-70 mbar and a typical temperature is 40°C. The pump is vulnerable, due to the generation of cavitation. As known per se, for instance from the field of marine engineering, cavitation is due to 4 the phenomenon that vapour bubbles are formed and grow locally due to acceleration in the water inlet. The thermodynamically instable bubbles collapse after a short time, causing shock waves to occur. This cavitation reduces 5 pump performance significantly and it reduces pump lifetime dramatically.

In order to reduce cavitation, a brine collector vessel and a brine pump may be applied in a position below a distillation assembly comprising the heat transfer module, 10 the at least one membrane distillation module and the condenser module. This positioning of the brine collector vessel and pump raises the brine's pressure at the brine pump inlet with a liquid column height between the pump inlet and the brine vessel outlet. However, the positioning 15 further increases the total height of the system. More particularly, the brine pump has turned out sensitive on variations in the level of the brine collector vessel, and as such, this proposal lacks the robustness required for a commercial machine.

20

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved membrane distillation system and a membrane distillation process of the type mentioned in the opening 25 paragraph, in which the issue of cavitation is suppressed significantly and any sensitivity of the brine pump is reduced.

According to a first aspect of the invention, the system comprises a brine collector vessel into which, in use, non-30 evaporated and concentrated feed from the liquid channel of a membrane distillation module flow. The brine pump is a frequency controlled pump for continuous pumping of the 5 liquid out of the brine collector vessel, when the pump is in a pumping mode.

According to a second aspect of the invention, the method comprises the steps of guiding non-evaporated feed from the 5 last module to a brine collector vessel, and pumping the liquid out of the brine collector vessel occurs continuously, when the pump is in a pumping mode. Frequency-controlled pumping allows continuous or semi-continuous pumping. This significantly reduces the effects 10 of cavitation, which most strongly occur upon switching on a pump. The frequency control is preferably coupled to a sensor detecting a volume in the brine vessel (which may be a tank or a tube). Upon a detection of a volume reduction, the frequency of pumping is reduced, and vice versa. It will 15 be understood that rather than detecting volume, use may be made of a system detecting a flow rate into the brine vessel. Sensors for volume detection, typically level detection, are known per se and suitably provide an electrical signal to a controller. Examples include 20 mechanical-electrical sensors, optical sensors, capacitive sensors, magnetic sensors.

Frequency-controlled pumping is moreover useful in the context of the present system, because a variation in the brine flow is expected: the brine flow during steady-state 25 production is likely to be significantly less than during start up. Typically, the reduction may be in the order of 30-70%.

In a preferred embodiment, a brine collector vessel is present into which, in use, non-evaporated and concentrated 30 feed from the liquid channel of a membrane distillation module flows. Piping means are present for transporting at least part of the warmed-up cooling liquid after passing the condenser module to the brine collector vessel, so as to 6 thin the non-evaporated and concentrated feed. In other words, non-evaporated feed from the last module is combined with at least part of warmed-up cooling liquid after passing the condenser module into the brine collector vessel.

5 The addition of cooling liquid reduces temperature and concentration of the brine. As a result, the liquid in the brine collector vessel may be pumped more easily. Moreover, this reduces a risk of corrosion and of crystallization of salts in the course of pumping, or particularly, when some 10 brine is left behind in the pump after pumping. Furthermore, in view of reduced temperature, the vapour pressure of the brine may be increased, therewith reducing the possibility of cavitation effects in the brine flow.

A further advantage hereof is an increase of the flow rate. 15 This helps to use a continuous or semi-continuous pumping rather than a batch-wise pumping. For instance, for a system with an output of 0.5m3 per hour, the brine flow is around 20 liters per minute in the start-up phase. However, after start-up, at a steady-state production, the brine flow 20 decreases significantly, for instance with 30-70%. Such reduction would likely lead to a repeated on- and off-switching of the pump, while cavitation is particularly to occur at switching the pump on. Adding warmed-up cooling liquid therefore reduces differences in flow (at least 25 relatively) through the brine pump between start-up phase and steady-state production. Moreover, it increases the flow anyhow. The frequency-controlled brine pump can thus more easily be operated continuously or semi-continuously.

It will therefore be understood that the present invention 30 is particularly suitable for systems with a relatively small distillate output of less than 1 m3 per hour, such as 0.1, 0.3 or 0.5 m3 per hour. Such systems are deemed suitable for a single household, or a couple of households. Use of 7 drinking water of a single average household in the Netherlands was, in 2008, nearly 0.4 m3 drinking water per day. Such a capacity may be easily generated with a system having an output of 0.1 m3 per hour.

5 The pumping in accordance with the invention is more preferably carried out in one of at least three modes; in a first mode, the pump is off. In a second mode, the pump operation is frequency controlled. In a third mode, the pump operates at maximum frequency.

10 For specifying the pumping mode, and an appropriate pumping frequency in the second mode, suitably the level or the inflow of the brine collector vessel is sensed with one or more sensors. Suitable sensors are level sensors, and alternatively flow sensors. Most suitably, use is made of 15 sensors for sensing a minimum level and an upper limiting level. The upper limiting level need not be the absolute maximum, but a limiting value above which another operation, for instance at maximum flow speed, is obtained.

Rather than relying on sensors only, the control may be 20 operated via an algorithm in a controller, wherein a flow into the brine collector vessel is estimated on the basis of input parameters, such as the feed flow and optionally flow of cooling liquid.

The use of a brine collector vessel moreover has the 25 advantage of buffering, and, in case of combining cooling liquid and brine, to obtain adequate mixing. Particularly, in one suitable embodiment, the brine originates from the last distillation module, whereas the pressure in the brine collector vessel is taken from the condenser. The brine flow 30 will thus be at a higher pressure than the inflow of warmed-up cooling liquid. Experiments have shown that artefacts occur, in this embodiment, when a brine collector vessel is left out.

8

In a most suitable embodiment, the brine flow is injected into the brine collector vessel at a position lower than the inflow of warmed-up cooling liquid, and more preferably below a usual upper level of the liquid in the brine 5 collector vessel. Due to a tendency of warm liquid to rise, as since the brine is warmer than the cooling liquid, a tendency to countercurrent flow between the brine and the cooling liquid inside the brine collector vessel may occur. Such flow behaviour is very good for mixing of the two 10 flows. Moreover, the brine has a tendency to evaporate, particularly in view of the lower pressure in the brine collector vessel. By injecting it below the cooling liquid, evaporation of brine is suppressed. Too much evaporation of brine might cause problems in the vacuum lines of the 15 system.

Preferably, the underpressure in the brine collector vessel is derived from the underpressure in one of the modules of the system, more preferably in vapour channel of the condenser module, by means of pressure communication means. 20 In a further embodiment, a protection device is present for preventing overflow of the brine collector vessel in case of current interruption. An overflow of the brine collector vessel would result in flow of brine into the vapour channel through the pressure communication means. Such entrance of 25 brine in the vapour channel inevitably leads to contamination of the distillate, and of a contamination of the vapour channel that is difficult to remove. A first embodiment of the protection device is an electric normally closed valve (V2). Another embodiment of the protection 30 device is is a hydrophobic means installed in the pressure communication means (i.e. pressure line) between brine vessel and condenser. Examples of such hydrophobic means are for instance filters, membranes, but also coatings. Suitable 9 results were obtained with a filter with a pore size of 0.ΙΟ. 4 microns turned out suitable.

The cooling liquid of the present invention may be operated in any desired manner. For instance, the cooling liquid may 5 flow in a substantially closed system, with an outlet into the brine collector vessel. The cooling liquid may flow in an open system, driven by a separate pump, and part of the cooling liquid may be used as a feed source, such as in W02007/054311A1. The cooling liquid may further be flowing 10 on the basis of a pressure difference, for instance relative to the pressure in the brine collector vessel. The latter embodiment appears suitable for the present invention, but is not essential. Suitably, in an embodiment wherein the condenser module comprises a foil-based condensation wall, a 15 protection device is present for limiting a pressure difference over the foil-based condensation wall.

The brine collector vessel may be considered as a waste storage. Alternatively, at least part of the brine collector vessel may be recirculated, for instance as a feed source.

20 Suitably, the membrane distillation system comprises a heat transfer means for the transfer heat into a heating channel, that is separated by a wall from an adjacent liquid channel of a membrane distillation module.

More suitably, the membrane distillation system also 25 comprises a first membrane distillation module comprising the heating channel, the wall and the liquid channel, further comprising a feed entry and a feed exit and a substantially fluid-impermeable, vapor permeable membrane, wherein in use feed enters the liquid channel through the 30 feed entry and is heated by means of the transferred heat transmitted from the heating channel so as to evaporate feed liquid to vapour that may pass through the membrane into a vapor space coupled to a subsequent vapour channel for 10 condensation at a condensation wall, so as to generate distillate and transfer heat to an adjacent liquid channel of a subsequent module.

Advantageously, a condenser module is present in combination 5 with the heat transfer means and the first membrane distillation module for generating of distillate from vapour from a preceding, last membrane distillation module, comprising a vapour channel for receiving said vapour, a condensation wall, and a cooling channel through which, in 10 use, a cooling liquid flows.

Suitably means for applying an underpressure to one of the modules, preferably the condenser module, is present. This allows to set the underpressure and therewith define and control system operation. The underpressure in one module 15 will be communicated to other modules and/or elements of the system by means of pressure communication. As will be understood by the skilled person, such pressure communication does not imply that all pressures are the same. Rather, the pressure will adapt to local conditions 20 The heat transfer means of the present invention could be provided with a heat generator, such as known from W02007/054311A1. Herein a separate circuit is provided with which steam is generated that is condensed in the heating channel and then recirculated. The feed then enters the 25 assembly of the heat transfer module, the membrane distillation modules and the condenser module in the first membrane distillation modules. It is not excluded, when using such a separate circuit that the heat exchanging fluid is a fluid different from water.

30 Alternatively, heat is added to the feed. Feed then enters the heat transfer means, and produces sufficient steam in the heating channel so as to enable heat transfer to the adjacent liquid channel of first distillation module. The 11 architecture of the present invention already supports this embodiment, in that the cooling liquid is both warmed up and decreased in pressure. It therewith can easily be pretreated for use as a feed. More preferably, feed is pretreated such 5 that a two-phase feed is obtained. This has turned out to increase the system's efficiency significantly. Moreover, the distillate from this heating channel in the first distillation module may be added to the distillate output. Preferably, the heat transfer means are embodied as a heat 10 transfer module. Such a heat transfer module may be

integrated with the one or more distillation modules into an assembly. The heat transfer module more suitably operates as a distillation module, in that steam is separated from liquid feed and transferred to a vapour channel adjacent to 15 the liquid channel of the first distillation module. A

condensation wall is present between said vapour channel and said liquid channel for optimum heat transfer.

Alternatives to the use of a heat transfer module are by no means excluded. Steam could be injected directly into the 20 vapour channel adjacent to the liquid channel, i.e. as supplied via a steam inlet. Furthermore, the heat transfer means could be embodied as a unit combined with a heat exchanger and to be located adjacent - either above, below or laterally adjacent- to one or more of the distillation 25 modules. Preferably such unit is located substantially below one or more distillation modules, such that steam resulting therefrom is easily coupled into the said vapour channel. Rather than, or in addition to, taking the flow through the above mentioned second connection as the feed source, the 30 liquid in the brine collector vessel could be used as a feed source. The advantage of using the liquid from the brine collector vessel is its lower pressure and higher 12 temperature. However, the concentration of salts may be somewhat higher.

Further alternatives for generating heat to the heat transfer module are not excluded. A combination of both 5 mentioned embodiments is not excluded either, for instance in that the cooling liquid is used as a feed source, and is optionally pretreated, but that additional steam is injected into the feed prior to and/or upon entry of the heat transfer module.

10 The membrane distillation system of the invention most suitably comprises a physically integrated modular assembly of the membrane distillation modules and the condenser module, and optionally any heat transfer module. More preferably, use is made of a single frame that defines the 15 various channels. The functions or condensation wall and membrane are therein defined by means of application of dedicated foils. Such a modular frame defining various channels, including a liquid channel, a pressure connection, an inert gas channel, a distillate channel is for instance 20 known from WO-A 2010/127818, which is herein included by reference .

Rather than a single physically integrated modular assembly, a plurality of such assemblies may be present. This is particularly feasible in the context of the invention, as 25 several voluminous supplementary components such as vacuum pumps, recirculation lines of a steam riser circuit, siphons are no longer necessary. Instead, a plurality (for instance two or three or four) physically integrated modular assemblies may be stacked on top of each other. It will be 30 understood that further components such as a pretreatment module and means for setting the underpressure may be common to a plurality of such assemblies.

13

The means for applying an underpressure to the condenser in the present invention suitably comprise a vacuum pump as well as any connections between such vacuum pump and the condenser module. The connections may extend to both the 5 vapour channel and the cooling channel in the condenser module. Alternatives are envisagable, such as a connection to a pipe to or from the cooling channel rather than the cooling channel itself; a single connection to the condenser module with an appropriate pressure equilibration connection 10 between vapour channel and cooling channel.

Rather than a single distillate output, more than one output could be present, allowing different portions of the distillate to be collected separately. In a single distillate output, all distillate exits in the vapour 15 channels are typically coupled to one distillate channel leading to a single distillate collector. In a system with a plurality of distillate output, more than one of such distillate channel and such distillate collector is present. Most suitably, a vapour channel has a single distillate exit 20 to one of the distillate channels.

The system suitably comprises rather conventional supplementary elements, such as vessels for storage, pumps for throughout of brine and distillate and filters and/or sieves for removal of particulates, biological organisms and 25 the like.

Most suitably, the generated distillate is stored at reduced pressure, particularly a pressure lower than atmospheric pressure. The advantage of storage at reduced pressure is that risk of contamination of the distillate with bacteria 30 and/or other microbiological contamination is reduced. Furthermore, such a system is preferably provided with reservoirs at different temperatures, so as to provide hot water for f.i. cooking, cold water for f.i. drinking and 14 medium temperature water for f.i. washing, cleaning and the like. Such reservoirs with different temperatures are not merely beneficial for a user, but also, particularly in a hot and sunny environment, it tends to cost time to cool the 5 distillate to a desired temperature. Hence, means and flows may be designed so as to ensure that water of a desired temperature is generated in a sufficient quantity. Thermostats for setting and controlling the desired temperature in a reservoir may be present.

10

BRIEF INTRODUCTION OF THE FIGURES

These and other aspects of the invention will be further elucidated with reference to theFigures, which are purely diagrammatical and not drawn to scale, and wherein: 15 Fig .1 shows diagrammatically a general architecture in accordance with the prior art as shown in W02005/089914 A1 Fig. 2 shows a schematical view according to one embodiment of the invention;

Fig. 3 shows a view corresponding to that of Fig. 2, but 20 indicating the pressure operation of the system;

Fig. 4 shows a more detailed schematical view specifying sensors and valves for one embodiment,

Fig. 5 shows a more detailed schematical view specifying sensors and valves for an alternative embodiment, and 25 Fig. 6 shows a more detailed schematical view for a third embodiment.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS The Figures are not drawn to scale and are intended purely 30 for illustrative purposes. Equal reference numerals in different figures refer to equal or corresponding parts.

Fig .1 shows diagrammatically a general architecture in accordance with the prior art as shown in W02005/089914 A1.

15

As shown herein, the membrane distillation system 100 comprises a heat transfer module 40, a first membrane distillation module 14, a second membrane distillation module 16 and a separate condenser 42 in the form of a heat 5 exchanger, particularly so as to preheat the feed. As is indicated in the Fig. 4, 5 and 6, the said modules 40, 14, 16, 42 are suitably physically integrated in a modular assembly 10. Cross-connections for pressure, distillate and connections between vapour channel and vapour spaces as well 10 as between the liquid channels may be implemented herein. This integration is deemed beneficial so as to keep heat within the unit and to reduce pressure leakages as much as possible .

Rather than a heat transfer module 40 suitable for 15 integration into the modular system, any other heat transfer means could be used for the provision of heat in the form of condensable vapour. More particularly, the heat transfer means constitute a steam generator for generating steam. Source of the steam may be a separate source, for instance a 20 circulating hot water circuit, but alternatively the feed itself. The heat transfer means is further also referred to as a vapor generator module.

Liquid, i.e. particularly an aqueous solution or a fluid mixture, enters the system via a liquid line 7. It is 25 optionally preheated in a heat exchanger 34, but still at atmospheric pressure. Thereafter, it enters the vapor generator module 40 at the fluid entry 8. Here the fluid runs in a liquid channel 12 and evaporates under the influence of the available heat, and subsequently leaves 30 this vapor generator module 40 at the fluid exit 9 as a concentrated fluid. The fluid is thereafter led via a liquid connection 19 to the first membrane distillation module 14, which it enters at the fluid entry 8, runs through in liquid 16 channel 12 and leaves at the fluid exit 9 as a further concentrated fluid. In order to ensure that distillation occurs, the pressure in the first membrane distillation module 14 is lower than that in the vapor generator module 5 40. Subsequently, the fluid is led through a liquid connection 19 to the second membrane distillation module 16, which it enters at the fluid entry 8, passes through liquid channel 12 and leaves through the fluid exit 9 as an even further concentrated fluid. This fluid is also known as 10 brine and removed via brine exit 39. The brine is in fact present at atmospheric pressure, rather than at an underpressure.

Vapor is generated by means of distillation of the fluid. The vapor enters a vapor space 23 that is separated 15 from the liquid channel 12 by means of substantially fluid-impermeable membranes 20. The substantially fluid-impermeable membranes 20 are particularly hydrophobic membranes. Evidently, if the fluid is non-aqueous but rather an organic liquid, the fluid-impermeable membranes will be 20 chosen to be impermeable for said organic fluid. The generated vapor is led from the vapor space 23 to the vapour chamber of a subsequent module - in casu the first distillation module 14 - via vapour connection 29 and arrives in the vapour channel 21. The vapour channel 21 is 25 provided with at least one condensation wall 24. The vapour will condensate at this condensation wall 24 and be converted into distillate. Simultaneously, heat generated in the condensation process is transferred to the liquid channel 12, which is located adjacent to the condensation 30 wall 24. In the present embodiment, the vapour channel 21 is bound by two condensation walls 24 on opposite sides. While being advantageous, this is not strictly necessary.

17

Liquid evaporating from the liquid channel 12 in the first membrane distillation module 14 enters the vapor space 23 through said hydrophobic membranes 20, and flows through vapour connection 29 into the vapour channel 21 of the 5 second membrane distillation module 16. Liquid evaporating from the liquid channel 12 in the last membrane distillation module - in this embodiment the second membrane distillation module 16 - enters the vapor space 23 through hydrophobic membranes 20, and flows through vapour connection 29 into 10 the condenser unit 42. It is therein converted into liquid and thereafter brought to a desired pressure (typically a higher pressure) by means of pump 38 (typically a vacuum pump) . Instead of being led away as a separate liquid stream, the condensate from the condenser 42 may be added to 15 a distillate collector. Distillate is collected in a distillate collector 54, from which it is pumped to a higher pressure using a vacuum pump 36. The distillate collector 54 is coupled to the distillate exits 52 of the first and second membrane distillation modules 12, 14 via a 20 (distillate) connection 53.

It is observed for sake of clarity, that the number of fluid channels 12 in parallel within one module 40, 14, 16 may be specified on the basis of the intended distillate volume. While the number of fluid channels 12 is the same in each 25 module 40, 14, 16 of the present embodiment, this is not necessary. While the present embodiment shows a design wherein the vapour space 23 and the vapour channel 21 are mutually coupled through an external vapour connection 29, this is not necessary. Alternative embodiments are 30 envisageable wherein the vapour space 23 and the vapour channel 21 are merged into a "vapour channel space". In such case, the vapour channel space is suitably bounded on one 18 side by a membrane 20 and on the opposite side by a condensation wall 24.

Fig. 2 and 3 show the general architecture in accordance with one embodiment of the present invention. Fig. 2 shows 5 schematically the flows of liquid and vapour. Fig. 3 shows schematically the pressures in the system. For sake of clarity, details within the modules 40, 14, 16 are not shown, but are suitably corresponding to those shown in Figure 1. As shown in Fig 2, the system comprises a heat 10 transfer module 40, distillation modules 14, 16 and a condenser 42. All these modules are suitably physically integrated into a single assembly. The drawn lines 7, 19, 39, 47, 49 indicate substantially liquid flows. The liquid feed 7 goes through the modules 40, 14, 16 and liquid 15 connections 19. It is finally converted into brine 39. The cooling liquid 47 passes the condenser 42 and is obtained as warmed up cooling liquid 49. This warmed up cooling liquid 49 is suitably divided into a first stream 49a that is merged with the brine 39, and a second stream 49b for other 20 purposes, for instance use as a feed 7.

The dotted line 52, 53 indicate distillate flows. In this example architecture, the distillate flow 52 from the first distillation module 14 is merged with the distillate flow 53 from the second distillation module 16 and the condenser to 25 arrive at a distillate collector 54. However, as shown in

Fig. 4-6, the distillate flow (pipe) 52 may be integrated in the modular assembly, such that merely a single distillate exit 53 is present.

Furthermore vapour lines 107, 29 are shown. In accordance 30 with the present invention, the feed 7 is pretreated in a pretreatment module 134 to obtain a multi-phase feed, i.e. a two-phase feed comprising a feed vapour 107 and a liquid feed 7. The feed vapour 107 and the liquid feed 7 are 19 indicated separately in this Figure 2 for sake of clarity, but may physically be provided in a single pipe.

The architecture shown in Fig. 3 corresponds to that of Fig.2. For sake of clarity, the distillate channels 52, 53 5 are omitted. Fig. 3 intends to represent the pressure balance in one embodiment according to the invention. Particularly, the system 100 operates at underpressure. The pressure is defined with a limited number of pumps 35, 38. The pressures within the system 10 will be set during use.

10 The pressure build-up is controlled through a vacuum pump 38. This pump sets an underpressure F which is communicated through the system via lines 101-104. Line 101 communicates the pressure to a condenser channel of the condenser 42 (i.e. the vapour channel coupled to a preceding module). .

15 Line 102 indicates the clamping vacuum (Dutch: klemvacuüm) of the system. This line 102 is a branch of the main line 101, wherein vacuum pressure is brought between the individual modules for clamping them together. Line 103 communicates the pressure from the condenser 42 to a brine 20 collector vessel 37. A further pump 35 is coupled thereto as an output valve. A similar pump, not shown, will be coupled a distillate collector vessel. Line 104 communicates the pressure from the condenser 42 to other modules 40, 14, 16. This communications do not imply that the underpressure is 25 identical everywhere in the system 100. An actual pressure is obtained as a dynamic equilibrium on the basis of temperature, actual amount of vapour in dependence of flow rate and evaporation rate plus condensation rate.

The membrane distillation processes resulting in evaporation 30 of feed 7, 19 result in a pressure difference between each module 40, 14, 16. The pressure E at the entrance of the second distillation module 16 is thus higher than the pressure F in the brine collector vessel 37. The pressure D

20 at the entrance of the first distillation module 14 is again higher than the pressure E. The pressure C at the entrance of the heat transfer module 40 is again higher. For instance, the pressure C is 0.4 bar, pressure D is 0.3 bar, 5 pressure E is 0.2 bar and pressure F is 0.1 bar. In accordance with the invention, the feed is pretreated in a pretreatment module, so as to obtain a two-phase feed 7, 107. During this pretreatment, the feed is suitably reduced in pressure from pressure B to pressure C. Pressure B is for 10 instance 0.7 bar. This pressure B is also available at the warmed up cooling liquid 49, notwithstanding the communicated low pressure F. In fact, atmospheric pressure A may exist at the inlet 47 of cooling liquid. The cooling liquid is then driven through the condenser on the basis of 15 the existing pressure difference, in which process the pressure is significantly lowered relative to the inlet pressure A.

In the shown implementation, a throttle valve VI is present, as shown in Fig.4 , which lowers the Pressure B to a 20 predefined maximum, for instance between 650 and 900 mbar, suitably in the range of 750-800 mbar. This maximum setting of the Pressure B reduces a risk of damage to any foils in the condenser, more particularly any polymer foils in the condenser that are used as a condensation wall. This 25 damaging is a risk, since the unexpected pressure differences over the foils may arise in the course of starting up and/or in case of system interruptions or failures. It will be understood that the predefined maximum may depend on the foil type in use. Furthermore, if the 30 condensation wall were made of steel, aluminium, or a heat-conducting ceramic, the provision of a predefined maximum is not deemed necessary.

21

Hence, the system of the shown embodiment of the present invention may be operated with a minimum number of pumps 35, 38. Surprisingly, the stability in the system can be properly controlled, and a high distillate output may be 5 obtained. This high distillate output is deemed due to the combination of the underpressure in the system together with the provision of a two-phase feed 7, 107 that more effectively results in the creation of a vapour flow of sufficient magnitude through vapour connection 29 to the 10 condensation wall in the first membrane distillation module 14.

Fig. 4 shows schematically a more detailed view of a system 100 according to one embodiment of the invention, with an emphasis on all valves and sensors. The shown embodiment 15 relates to a system with a hot water vessel 201 and a cooling water vessel 202 that are external to the system. Such a situation is for instance foreseen for use in industrial environments, or in combination with cooling or heating facilities, such as solar panels and/or caves for 20 water disposal.

According to the shown embodiment, the feed 7 is herein pretreated to lower its pressure by means of valve V4. Heating means may be added for bringing the feed 7 to the desired temperature. The feed then passes the membrane 25 destination assembly 10, comprising the heat transfer module 40, the condenser 42 as well as a series of membrane distillation modules 14, 16, 114, 116. The number of membrane distillation modules 14, 16, 114, 116 is open for design and typically ranges from 1 to 8, preferably 3 to 6. 30 The distillate is thereafter removed via distillate channel 53 into a distillate collector vessel 54. The brine is removed via brine channel 39 to brine collector vessel 37. The brine 39 is merged with warmed up cooling liquid 49 that 22 has passed the condenser 42 and was fed into the system from cooling water vessel 202 via cooling liquid line 47. The brine collector vessel 37 and the distillate collector vessel 54 are each coupled to a pump 35, 55 for pressure 5 increase and transport. The brine is thereafter recirculated back into cooling water vessel 202 via recirculation line 205. It will be understood that alternatives are envisageable.

For an appropriate operation, a plurality of valves is 10 provided. Valve VO is a manual valve added for inspection purposes, in case of any leakage of vacuum (so that the desired underpressure is not reached). With this valve VO, on may find out easily, whether the leakage occurs in the assembly 10 or is related to the vacuum pump 38.

15 Valve VI is a protection valve. It is defined so as to set a maximum to a pressure difference over the condenser 42. Therewith, polymer foils in the condenser 42 acting as condensation walls between a vapour channel and a cooling channel are protected, so as to prevent tearing, aging and 20 the like. Valve VI is for instance embodied as a restriction device .

Valve V2 is a further protection device for the event of any current interruption. The valve V2 prevents inflow of brine into the condenser via vacuum line 103, when for instance 25 pump 35 does not work and hence an overflow of the brine collector vessel 37 occurs. In such case of current interruption, valve V2 will close automatically, therewith preventing any overflow of the brine collector vessel 37. This valve V2 is arranged in the line for the warmed up 30 cooling liquid, since the cooling liquid flow tends to be larger than the brine flow. Evidently, a similar valve may be arranged in the brine line 39, if necessary for the prevention of any overflow. A further valve may be arranged 23 so as to prevent, at least substantially, the backwards flow of warmed up cooling liquid after turning the apparatus off. Valve V3 serves a similar function for the feed line 7.

Valve V4 is a device for setting the underpressure in the 5 feed line 7 and therewith creating a two-phase feed 7 + 107. Suitably, this valve V4 is implemented as a throttle valve, but alternatives such as a tap or valve are not excluded.

The setting of valve V4 is suitably controlled through a controller (not shown), on the basis of the sensor signals 10 obtained. Alternatively, the setting may be carried manually, so as to ensuring sufficient heat. The setting does not need to be modified thereafter. A reset may however be done if the system suffers from scaling and/or fouling, affecting the total feed inflow, or when less heat 15 is available.

The flow sensor F is in a highly preferred implementation arranged upwards from the means for providing an underpressure, such as valve V4. If the flow sensor were placed downwards from the valve V4, vapour bubbles tend to 20 make the sensing more complex, or could result in an inappropriate sensing result. The latter is caused in that the creation of steam in the feed flow accelerates the mixture. Hence, a mass or volume measurement is no longer representative .

25 Valves V5 and V6 are used for preventing backwards flow due to the pressure difference, particularly after turning off the apparatus .

Fig. 5 shows a schematical view of another embodiment of the system 100 of the invention. According to this system, the 30 part 49a of the warmed up cooling liquid 49 is recirculated into the feed 7. A further part 49b of the warmed-up cooling liquid 49 is combined with the brine 39 to the brine collector vessel 37. In this embodiment, the warmed up 24 cooling liquid 49 is pretreated by means of valve V4 and a heat exchanger 34 to become a two-phase feed 7+107. The heat exchanger 34 is provided with a separate inlet 191 and an outlet 192 for the heat flow.

5 This configuration suitably includes two further valves. Valve V7 is a protection device so as to prevent backwards flow of warmed-up cooling liquid 49a after turning off the system, and/or in case of any current interruption.

Valve V8 is a device with which the flow rate ratio between 10 the flows 49a and 49b can be set. This device is suitably controlled by a system controller on the basis of the sensor measurements in the course of operation. Evidently, a manual control may be used alternatively, wherein corrections are likely to be made only subsequent to an operation run.

15 Fig. 4 and 5 moreover both indicate sensors in the system, more particuarly a flow sensor F, a temperature sensor T, a pressure sensor P, level sensors L and a salinity sensor S. These sensors allow investigation of appropriate product quality and control of system stability and operation.

20 Fig. 5 furthermore shows post treatment means. Herein, the distilled water is treated to obtain potable water. A carbondioxide vessel 53 is present, from which carbondioxide may be inserted in the system using valves V9, V10. Furthermore, a marble filter 151 and a UV lamp 152 are 25 provided so as to obtain water that meets all quality standards. It will be understood that the shown post treatment is merely an example and may be left out or replaced with alternative post treatments. It is furthermore indicated that additional filters and check valves may be 30 present in the system, which are known per se and have been left out for sake of clarity.

25

It is observed that the above mentioned valves are suitable for use for protection and control of the system, and are claimed as separate features of the present invention.

In preliminary experiments with a system as shown in Fig 5, 5 a cooling liquid input of 15 liter per minute was used at atmospheric pressure. After passing the condenser, 20% thereof was recirculated to become feed 7. This feed was heated to 70 °C and its pressure was lowered to approximately 0.3 bar. As a result, 0,8 liter per minute of distillate was 10 obtained. The system pressure applied through the vacuum pump was 75 mbar. A further increase of the distillate output to 70 liter per hour (1,2 liter per minute) was obtained by means of optimization of the temperature and underpressure of the two-phase feed 7+107. Use was made both 15 potable water and sea water for test purposes, which led to virtually identical results with respect to stability and product output.

A third embodiment is shown in Fig. 6. This embodiment is deemed beneficial for water treatment systems particularly 20 suitable for the production of a larger distillate production, for instance a distillate production of at least 250 liter output per hour and more preferably at least 400 liter output per hour. In accordance with this embodiment, the cooling liquid 47 passes the cooling channel of the 25 condenser 42 to become a warmed-up cooling liquid flow 49. Part 49a of this flow 49 is transmitted to heat exchanger 34, so as to become feed 7. Another part 49b of the warmed-up cooling liquid flow 49 is pumped away to an output by means of pump 45. A protection valve Vll is present so as to 30 prevent flow in an opposite direction. The pump is suitably a pump suitable for a liquid medium.

The pressure defined on the cooling liquid flow part is 100-500 mbar, suitably 200-400 bar and preferably in the range 26 of 250-350 mbar, for instance 300 mbar. This pressure on part 49b results, in combination with an appropriate setting for valve or restriction VI to a pressure of 600-900 mbar, suitably 700-800 mbar, for instance 750 mbar.

5 No cooling liquid flows in this embodiment into the brine vessel 37. The low pressure applied by vacuum pump 38 to the condenser channel of the condenser 42 is also in this embodiment transmitted to the brine vessel 37. The resulting pressure difference between the last stage 116 and the brine 10 vessel ensures that brine will flow into the brine vessel 37. The brine vessel 37 is herein dimensioned such that the frequency controlled brine pump 35 will operate appropriately, either continuously, or in intervals. In order to operate in intervals, a valve could be added at the 15 bottom of the brine vessel 37. Alternatively, the pump 35 could work as a valve or a valve could be coupled thereto.

A line 105 is added between the vacuum line 101 and the outlet pipe 109 from the brine vessel. This line has a double function. First, it ensures that the low pressure 20 applied to the condenser channel of the condenser 42 is not only applied to a top side of the brine vessel, but also to the outlet pipe 109. This leads to better pressure equilibration, and therewith increases the stability of the overall system. Secondly, the brine vessel and also the 25 condenser itself can generate vapour that is sucked out by the vacuum lines connected to the brine vessel and condenser. This vapour tends to condense in the vacuumlines, forming water droplets that can hinder the operation of the vacuum pump. Line 105 with valve V12 acts as a trap for 30 these droplets, releasing them into the brinestream when the brinepump is pumping. With this installation only condensed vapour can be removed; any vapour in the vacuumlines that does not condense is taken out by the vacuumpump. Valve V12 27 will only open when there is a water column on top of it (condens) that is higher than the water column on top of the lower level sensor inside the brine vessel. So the condens-trapping system needs to collect a certain amount of condens 5 before it can be pumped out of the system by the brine pump. While all of the Figures 2-6 show embodiments wherein the feed is pretreated and used for the heat generation to the heat transfer module, this is not essential for the present invention, and alternatives or variations may be envisaged. 10 For instance, use can be made of a separate heat generator. While all of the Figures 2-6 show embodiments wherein the cooling liquid is driven through the condenser 42 on the basis of a pressure difference between feed and condenser, this preferred feature is not considered essential for the 15 operation of the present invention. Alternatively, use could be made of a closed system with cooling liquid, and/or a separate pump could be added so that the cooling liquid is pushed through the condensor actively, rather than passively on the basis of an existing pressure difference. Moreover, 20 while the distillate of any distillation module and the condenser is shown to be guided to a single distillate collector, two separate distillate collectors may be applied.

Rather than as constructing the invention as using a 25 frequency-controlled pump for pumping the brine, the invention may be construed, in its broadest sense, as a method and a system as mentioned in the opening paragraph, in which thinning of the brine with warmed-up cooling liquid is carried out, particularly within a brine collector 30 vessel. Any embodiment as discussed before can be combined with said principle as defined in its broadest sense.

Claims

1. Membraandestillatiesysteem dat tenminste een membraandestillatiemodule en een condensormodule omvat, en verder voorzien is van middelen voor het aanleggen van een 5 onderdruk op één van de modules aanwezig is, en waarbij het systeem zo ingericht is dat in bedrijf een onderdruk in één module aan andere modules wordt doorgegeven via drukuitwisseling, waarin, in bedrijf, een voeding omgevormd wordt tot destillaat en brijn, welk destillaat gevormd wordt in de ten minste ene membraandestillatiemodule en de condensormodule, en welke brijn in een brijnopvangvat stroomt ten minste uit een laatste 10 membraandestillatiemodule die aan de condensormodule voorafgaat, waarbij een brijnpomp aanwezig is voor het oppompen van vloeistof uit het brijnopvangvat naar een hogere druk, Waarin de brijnpomp een frequentie-gecontroleerde pomp is, welke het in continu bedrijf pompen van de vloeistof uit het brijnopvangvat toestaat, wanneer de pomp zich in een pompmodus bevindt. 15A membrane distillation system comprising at least one membrane distillation module and a condenser module, and further comprising means for applying an underpressure to one of the modules, and wherein the system is arranged such that in operation an underpressure in one module is applied to others modules is passed on via pressure exchange, in which, during operation, a feed is transformed into distillate and brine, which distillate is formed in the at least one membrane distillation module and the condenser module, and which brine in a brine collection vessel flows at least from a last 10 membrane distillation module which precedes the condenser module, wherein a brine pump is present for pumping up liquid from the brine collection vessel to a higher pressure, wherein the brine pump is a frequency-controlled pump which allows the liquid to be pumped out of the brine collection vessel in continuous operation when the pump is in a pump mode. 15

2. Membraandestillatiesysteem volgens conclusie 1, omvattend: Een warmte-overdrachtsmiddel voor het overdragen van warmte naar een verwarmingskanaal, dat van een naburig vloeistofkanaal van een membraandestillatiemodule gescheiden is door een wand;A membrane distillation system according to claim 1, comprising: A heat transfer means for transferring heat to a heating channel separated from a neighboring fluid channel of a membrane distillation module by a wall;

3. Systeem volgens conclusie 2, met het kenmerk dat pijpmiddelen aanwezig zijn voor het transporteren van ten minste een deel van de opgewarmde koelvloeistof die door de condensormodule heengegaan is, naar het brijnopvangvat, teneinde de niet-verdampte en geconcentreerde voeding te verdunnen. 53. System as claimed in claim 2, characterized in that pipe means are provided for transporting at least a part of the heated cooling liquid that has passed through the condenser module to the brine receiving vessel, in order to dilute the non-evaporated and concentrated feed. 5

4. Membraandestillatiesysteem volgens één van de conclusies 1-3, waarin de genoemde koelvloeistof in het brijnopvangvat stroomt op basis van een drukverschil.A membrane distillation system according to any one of claims 1-3, wherein said cooling fluid flows into the brine collection vessel based on a pressure difference.

5. Membraandestillatiesysteem volgens conclusie 4, dat voorts een regelende klep omvat voor het 10 instellen van een stroomsnelheid van de koelvloeistof naar het brijnopvangvat toe.5. A membrane distillation system according to claim 4, further comprising a control valve for adjusting a flow rate of the cooling liquid to the brine collection vessel.

6. Membraandestillatiesysteem volgens één van de voorgaande conclusies, dat verder drukuitwisselingsmiddelen omvat tussen het brijnopvangvat en het dampkanaal van de condensormodule, teneinde het drukniveau in het brijnopvangvat te bepalen waarheen de 15 koelvloeistof aangezogen wordt.6. A membrane distillation system according to any one of the preceding claims, further comprising pressure exchange means between the brine collection vessel and the vapor channel of the condenser module, in order to determine the pressure level in the brine collection vessel to which the cooling liquid is drawn.

7. Membraandestillatiesysteem volgens één van de conclusies 4 tot 6, dat verder een protectie-inrichting omvat voor het voorkomen van een overstroom van het brijnopvangvat gedurende of na een stroomonderbreking en daarmee het voorkomen van het stromen van vloeistof uit het 20 brijnopvangvat naar het dampkanaal van de condensormodule via de drukuitwisselingsmiddelen.7. A membrane distillation system according to any one of claims 4 to 6, further comprising a protection device for preventing an overflow of the brine collection vessel during or after a power interruption and thereby preventing the flow of liquid from the brine collection vessel to the vapor channel of the condenser module via the pressure exchange means.

8. Membraandestillatiesysteem volgens één van de voorgaande conclusies, dat verder een niveausensor omvat voor het meten van het vloeistofniveau in het brijnopvangvat, en waarin 25 de frequentie van de pomp wordt ingesteld op basis van variaties in het vloeistofniveau in het brijnopvangvat zoals gemeten met de niveausensor.8. A membrane distillation system according to any one of the preceding claims, further comprising a level sensor for measuring the liquid level in the brine receiving vessel, and wherein the frequency of the pump is adjusted based on variations in the liquid level in the brine receiving vessel as measured with the level sensor .

9. Membraandestillatiesysteem volgens conclusie 1, 2 of 8, dat verder een sensor omvat voor het bepalen of een feitelijke instroom in het brijnopvangvat boven een minimumwaarde ligt, en 30 waarin het bedrijven van de pomp omgezet wordt van een pompmodus naar een uit-modus of vice versa bij het waarnemen dat de feitelijke instroom de minimumwaarde passeert.9. A membrane distillation system according to claim 1, 2 or 8, further comprising a sensor for determining whether an actual inflow into the brine collection vessel is above a minimum value, and wherein the operation of the pump is converted from a pump mode to an off mode or vice versa when observing that the actual inflow passes the minimum value.

10. Membraandestillatiesysteem volgens een van de voorgaande conclusies, dat verder een sensor omvat voor het bepalen of een feitelijke instroom in het brijnopvangvat boven een maximale 35 waarde ligt, en waarin het bedrijven van de pomp omgezet wordt van een frequentie- gecontroleerde modus naar een maximale frequency modus of vice versa bij het waarnemen dat de feitelijke instroom de maximale waarde passeert.10. A membrane distillation system according to any one of the preceding claims, further comprising a sensor for determining whether an actual inflow into the brine collection vessel is above a maximum value, and wherein the operation of the pump is converted from a frequency-controlled mode to a maximum frequency mode or vice versa when observing that the actual inflow passes the maximum value.

11. Membraandestillatiesysteem volgens een van de voorgaande conclusies, waarin ten minste de 5 destillatiemodules en de condensor van een modulair ontwerp zijn en fysiek geïntegreerd zijn in een destillatiesamenstel.11. A membrane distillation system according to any one of the preceding claims, wherein at least the distillation modules and the condenser are of a modular design and are physically integrated in a distillation assembly.

12. Membraandestillatiesysteem volgens conclusie 11, waarin de warmte-overdrachtsmiddelen vormgegeven zijn als een warmte-overdrachtsmodule van modulair ontwerp die geïntegreerd is 10 in het destillatiesamenstel.12. A membrane distillation system as claimed in claim 11, wherein the heat transfer means are designed as a heat transfer module of modular design that is integrated in the distillation assembly.

13. Membraandestillatiesysteem volgens conclusie 11 of 12, waarin de genoemde modules elk een folie tussen naburige kanalen bevatten, en waarbij het type folie bepaalt of het folie dienst doet als membraan danwel als condensatiewand. 15A membrane distillation system according to claim 11 or 12, wherein said modules each contain a film between adjacent channels, and wherein the type of film determines whether the film serves as a membrane or as a condensation wall. 15

14. Membraandestillatieproces dat de stappen omvat van: het aanleggen van een onderdruk op een module in een gebruikt membraandestillatiesysteem aanwezig is, en waarbij het systeem zo ingericht is dat in bedrijf een onderdruk in één module aan andere modules wordt doorgegeven via 20 drukuitwisseling; Het vormen van destillaat uit een voeding door middel van verdamping tot damp in ten minste één membraandestillatiemodule en een condensormodule, waarheen damp uit een voorafgaande, laatste membraandestillatiemodule overgebracht wordt; Het verwijderen van niet-verdampte, geconcentreerde voeding als brijn ten minste uit 25 de laatste membraandestillatiemodule naar een brijnopvangvat, en Het oppompen van de vloeistof uit het brijnopvangvat naar een hogere druk, Waarin het pompen van de vloeistof uit het brijnopvangvat continu plaats heeft, wanneer de pomp zich in een pomp-module bevindt.14. A membrane distillation process comprising the steps of: applying a negative pressure to a module in a used membrane distillation system, and wherein the system is arranged such that in operation a negative pressure in one module is passed on to other modules via pressure exchange; Forming distillate from a feed by evaporation to vapor in at least one membrane distillation module and a condenser module, to which vapor is transferred from a previous, last membrane distillation module; Removing non-evaporated, concentrated feed as brine at least from the last membrane distillation module to a brine collection vessel, and Inflating the liquid from the brine collection vessel to a higher pressure, wherein the pumping of the liquid from the brine collection vessel takes place continuously when the pump is in a pump module.

15. Membraandestillatieproces volgens conclusie 14, waarin de stap van het vormen van destillaat volgende stappen omvat: Het verschaffen van voeding aan een fluïdum ingang van de eerste membraandestillatiemodule, welke voeding het vloeistofkanaal binnenkomt en verwarmd wordt teneinde te voedingsvloeistof om te zetten in damp die door een in 35 hoofdzaak vloeistof-ondoorlaatbare, dampdoorlaatbare membraan heen kan gaan naar een dampruimte die gekoppeld is aan een volgend dampkanaal voor condensatie voor de vorming van destillaat en het overdragen van warmte aan een naburig vloeistofkanaal, en Het herhaaldelijk overdragen van niet-verdampte voeding van de voorafgaande 5 membraandestillatiemodule naar een volgende membraandestillatiemodule teneinde destillaat te vormen en warmte over te dragen naar een volgend vloeistofkanaal, waarbij het aantal keren afhangt van het aantal gebruikte destillatiemodules, en waarin het destillaat van de laatste module gevormd wordt in een condensormodule tegen een koelvloeistof die in een koelkanaal stroomt. 10A membrane distillation process according to claim 14, wherein the distillate forming step comprises the following steps: Providing feed to a fluid inlet of the first membrane distillation module, which feed enters the fluid channel and is heated to convert the feed fluid to vapor passing through a substantially liquid-impermeable, vapor-permeable membrane can go to a vapor space that is coupled to a subsequent vapor channel for condensation to form distillate and transfer heat to an adjacent liquid channel, and to repeatedly transfer non-vaporized feed from the preceding membrane distillation module to a next membrane distillation module to form distillate and transfer heat to a subsequent liquid channel, the number of times depending on the number of distillation modules used, and in which the distillate of the last module is formed in a condenser module t against a coolant that flows into a cooling channel. 10

16. Membraandestillatieproces volgens conclusie 15, waarin de voeding in het vloeistofkanaal van de eerste membraandestillatiemodule verwarmd wordt vanuit een verwarmingskanaal, dat door een wand gescheiden is van het vloeistofkanaal, en waarin warmte in het verwarmingskanaal verschaft is in de vorm van damp die in het verwarmingskanaal condenseert. 15A membrane distillation process according to claim 15, wherein the feed in the fluid channel of the first membrane distillation module is heated from a heating channel separated from the fluid channel by a wall, and wherein heat is provided in the heating channel in the form of vapor contained in the heating channel condenses. 15

17. Membraandestillatieproces volgens één van de conclusies 14 tot 16, dat verder de stap omvat van het aanbrengen van een onderdruk op ten minste één van de modules in het systeem, welke onderdruk aan andere modules verder geleid wordt door uitwisseling van druk.The membrane distillation process according to any of claims 14 to 16, further comprising the step of applying an underpressure to at least one of the modules in the system, which underpressure is further directed to other modules through exchange of pressure.

18. Proces volgens één van de conclusies 14-17, waarin het pompen frequentie-gecontroleerd is in de pomp-modus.The process of any one of claims 14-17, wherein the pumping is frequency controlled in the pumping mode.

19. Proces volgens conclusie 14 of 18, dat verder de stappen omvat van het meten van een niveau in of een stroomsnelheid naar het brijnopvangvat toe en van het beheersen van de 25 pompfrequentie op basis van het gemeten niveau of de gemeten stroomsnelheid of een variatie daarvan.19. Process as claimed in claim 14 or 18, further comprising the steps of measuring a level in or a flow rate towards the brine collection vessel and of controlling the pumping frequency based on the measured level or the measured flow rate or a variation thereof .

20. Proces volgens één van de conclusies 14-19, dat verder het meten van een minimumniveau omvat, waarbij het bedrijven van de pomp wordt omgezet van een pomp-modus naar een uit- 30 modus of vice versa bij het waarnemen dat de feitelijke instroom de minimumwaarde passeert.20. Process as claimed in any of the claims 14-19, further comprising measuring a minimum level, wherein the operation of the pump is converted from a pump mode to an off mode or vice versa upon observing that the actual inflow the minimum value passes.

20. Een eerste membraandestillatiemodule die het verwarmingskanaal, de wand en het vloeistofkanaal omvat, en voorts een voedingsingang en een voedingsuitgang en een in hoofdzaak vloeistof-ondoorlaatbare, dampdoorlaatbare membraan, waarbij in bedrijf voeding het vloeistofkanaal binnenkomt door de voedingsingang en verwarmd wordt door middel van de overdragen warmte die doorgegeven is vanuit het 25 verwarmingskanaal ten einde voedingsvloeistof te verdampen tot damp die door het membraan heen kan gaan naar een dampruimte die gekoppeld is aan een volgende dampkanaal voor condensatie tegen een condensatiewand, om zo destillaat te vormen en warmte over te dragen aan een naburig vloeistofkanaal van een volgende module, en20. A first membrane distillation module comprising the heating channel, the wall and the liquid channel, and furthermore a feed inlet and a feed outlet and a substantially liquid-impermeable, vapor-permeable membrane, wherein in operation feed enters the liquid channel through the feed inlet and is heated by means of the transferred heat transferred from the heating channel in order to evaporate feed liquid into vapor that can pass through the membrane to a vapor space that is coupled to a subsequent vapor channel for condensation against a condensation wall, so as to form distillate and transfer heat to a neighboring fluid channel of a subsequent module, and

30. Een condensormodule voor het vormen van destillaat uit damp van een voorafgaande, laatste membraandestillatiemodule, welke condensormodule een dampkanaal voor het ontvangen van de genoemde damp, een condensatiewand en een koelkanaal omvat, door welk koelkanaal in bedrijf een koelvloeistof stroomt.A condenser module for forming distillate from vapor of a preceding, last membrane distillation module, which condenser module comprises a vapor channel for receiving said vapor, a condensation wall and a cooling channel, through which cooling channel a cooling liquid flows in operation.

21. Proces volgens één van de conclusies 14 tot 20, dat verder het meten omvat, of een feitelijke instroom in het brijnopvangvat boven een maximale waarde ligt, waarbij het bedrijven van de pomp wordt omgezet van een frequentie-gecontroleerde pomp-modus naar een pomp-modus op maximale frequentie of vice versa bij het waarnemen dat de feitelijke instroom de maximale waarde passeert.The process of any one of claims 14 to 20, further comprising measuring whether an actual inflow into the brine collection vessel is above a maximum value, the operation of the pump being converted from a frequency-controlled pump mode to a pump mode at maximum frequency or vice versa when observing that the actual inflow passes the maximum value.

22. Proces volgens één van de conclusies 14-21, dat verder de stap omvat van het verdunnen van 5 de niet-verdampte voeding die uit een laatste membraandestillatiemodule het brij nop vang vat instroomt.A process according to any of claims 14-21, further comprising the step of diluting the non-vaporized feed that flows into the slurry tank from a final membrane distillation module.

23. Proces volgens conclusie 22, waarin de niet-verdampte voeding verdund wordt met ten minste een gedeelte van de opgewarmde koelvloeistof die door de condensormodule is heengegaan. 10The process of claim 22, wherein the non-vaporized feed is diluted with at least a portion of the warmed-up cooling fluid that has passed through the condenser module. 10

24. Proces volgens conclusie 22 of 23, waarin de genoemde samenvoegingsstap plaats in het brijnopvangvat plaats heeft.The process according to claim 22 or 23, wherein said merging step takes place in the brine collection vessel.