NL2010576C2

NL2010576C2 - A system of membrane distillation and use therof.

Info

Publication number: NL2010576C2
Application number: NL2010576A
Authority: NL
Inventors: Hein Weijdema; Robertus Wilhelmus Jacobus Hollering
Original assignee: Aquaver B V
Priority date: 2013-04-05
Filing date: 2013-04-05
Publication date: 2014-10-08
Also published as: WO2014163507A1

Abstract

The membrane distillation apparatus comprises a membrane distillation unit comprising a plurality of membrane distillation modules, a heating channel transferring heat to a first one of said membrane distillation modules and a condenser. Furthermore, a fluid circuit is present, which extends to the heating channel so as to provide heat into the membrane distillation unit. The fluid circuit further comprises a heat exchanger for heating a fluid running in said fluid circuit, said heat exchanger comprising a second channel providing heat originating from the energy source. A generator generates heat and electricity, which heat is at least partially transferred to an intermediate cycle by means of a primary heat exchanger, the intermediate cycle extending to the second channel of the – secondary – heat exchanger. Moreover, a pump is present for pumping a fluid through the intermediate cycle.

Description

A system of membrane distillation and use thereof

Field of the invention

The invention relates to a system of a membrane distillation apparatus and an energy source therefore, which membrane distillation apparatus comprises a membrane distillation unit comprising a plurality of membrane distillation modules, a heating channel transferring heat to a first one of said membrane distillation modules and a condenser.

The invention also relates to the use of such a system for the provision of potable water. Background of the invention

Such a membrane distillation system is for instance known from W02007/054311 Al. The said system is a vacuum membrane distillation apparatus comprising a plurality of membrane distillation stages or modules. Each membrane distillation module comprises a liquid channel bound on one side by a wall and on the other side by a hydrophobic membrane. While liquid, particularly an aqueous solution, such as an aqueous salt solution is running through the liquid channel, heat is transferred through the wall, which leads to evaporation of water that disappears into a vapour channel located at the opposite side of the membrane. The vapour is transferred to a vapour space, where it condenses against a wall. This condensation process provides heat for evaporation in a liquid channel of a subsequent membrane distillation module. A polymer module suitable for this process is known from WO2009/127818A1. The distillation process will also be effective in the subsequent membrane distillation module, because the applied pressure in the subsequent module is lower than the pressure in the preceding module. Thereto, an underpressure is applied to the unit, particularly at the last distillation module or even more preferred at the condenser.

The membrane distillation process is thus dependent on the provision of heat to said wall with the first membrane distillation module and the application of an underpressure by means of a vacuum source. W02007/054311A1 discloses a process wherein the heat is provided to said wall by means of a closed circuit of with a heating medium, which is distilled water. The distilled water is heated and at least partially converted into steam in a steam raiser module preceding the first membrane distillation module. The steam then transfers the heat to the feed in the liquid channel, and thereby condenses. Thereafter, the resulting water is led away and heated again in a heat exchanger.

This system requires heat from a heat exchanger and electricity or another power source for the vacuum and liquid pumps. Sources of heat and electricity are known per se in the art, i.e. in the form of local electricity generators (f.i. diesel generator), cable network for supply of electricity, boilers and heaters based on gas, diesel/gasoline or other fuel, cokes, wood and/or solar energy.

The membrane distillation system is particularly needed for the generation of potable water, or even distilled water, at remote or industrial locations where tap water of sufficient quality is not available. There is a considerable chance that such locations do not have a decent provision of electricity either.

One known option for heat provision to a membrane distillation apparatus is known from WO2010/071605. The known membrane distillation apparatus includes a plurality of hollow fiber membranes that are fed by a feed solution. The known system also includes a heat source capable of heating the feed solution. The heat source is for instance a solar heat source, in which solar energy has been used to heat a heated fluid stream. The feed solution is heated in a heat exchanger via the heat fluid stream. Because the heat source is solar powered, the heat energy of the heat source may vary over time from day to day. Therefore the duty of each stage in the membrane distillation apparatus needs to be varied according to the particular energy load being imparted at a given time.

It is therefore desirable to provide a membrane distillation apparatus together with a local generator of energy needed for the heating of the feed or another heating medium running in a separate heating circuit, and also for the driving of any vacuum sources. Preferably, such local energy generator is sufficiently efficient, in order to obtain clean water at an affordable cost price. Moreover, the locally generated energy needs to be sufficient for heating the feed and/or said heating medium. The temperature of the heating medium is to be in the range of 70-100°C, and the flow rate of feed may well be in the order of 50-3000 liters/hour, for instance 1-3 liter/minute for a small system, or 5-30 liter/minute for a big system. This flow is maintained during operation, which may well be continuous over a plurality of hours. Moreover, the start-up time of the system is suitably limited. Even though the distilled water resulting may be stored in a tank, it is typically undesired to keep significant volumes of water in a tank, in view of development and growth of microbiological organisms therein.

Hence, there is a need for an appropriately efficient, local power generation for use for a water treatment system based on membrane distillation.

Summary of the invention

According to a first aspect of the invention, a system of a membrane distillation apparatus and an energy source therefore is provided. The membrane distillation apparatus comprises a plurality of membrane distillation modules, a heating channel transferring heat to a first one of said membrane distillation modules and a condenser. The system further comprises a fluid circuit extending to said heating channel so as to provide heat for the membrane distillation, said fluid circuit further comprising a heat exchanger for heating a fluid running in said fluid circuit, said heat exchanger comprising a second channel providing heat originating from the energy source. The system also comprises a generator generating heat and electricity, which heat is at least partially transferred to an intermediate cycle by means of a primary heat exchanger, the intermediate cycle extending to the second channel of the - secondary - heat exchanger. The intermediate cycle further comprises heat storage means and preferably also additional heating means that may be switched on and off, dependent on the amount of heat transferred from the generator, and preferably rather instantaneously. The system of the invention is further provided with temperature control means for controlling the provision of heat into the intermediate cycle.

According to a second aspect of the invention, use of the system is provided for the provision of potable water.

According to a third aspect of the invention, a method of operating a membrane distillation apparatus is provided, using the system of the invention and comprising the steps of:

Generating heat in a generator, which heat is transferred to an intermediate cycle, in which a fluid is pumped;

Controlling the temperature of the fluid running in the intermediate cycle, and

Transmitting heat from the fluid at the controlled temperature to a fluid circuit extending to a heating channel of the membrane distillation apparatus.

The invention provides an efficient local power generation for use with a water treatment system based on membrane distillation. An intermediate cycle is applied between the heating medium of the membrane distillation apparatus, and the power generator with any cooling circuits.

The intermediate cycle has an important function for the stability and performance of the system.

As seen from the side of the power generator, the intermediate cycle may absorb heat that needs to be dissipated in order that the engine of the generator continues running in the desired temperature operation window. If an engine is cooled to an extent that is not sufficient, the engine will be damaged. However, even when an engine is switched down, it will continue to produce heat that needs to be dissipated. The intermediate cycle can absorb such heat, and even store in temporarily in the form of a tank with heated water. Moreover, the intermediate cycle is provided with additional heating means that may be switched on and off, dependent on the amount of heat transferred from the generator, and preferably rather instantaneously.

Moreover, as known per se, an engine will only generate heat under a sufficient load, i.e. when it needs to produce sufficient electricity. If there is no external load or not sufficient external load, any available heating means, such as a boiler may be used as the load for the generator.

As seen from the side of the membrane distillation apparatus, the intermediate cycle has the function to provide a sufficient amount of heat so as to heat the heating medium to a temperature at which membrane distillation is effective. Typically, membrane distillation does not lead to a significant amount of distillate, if the temperature of the heating medium is below a minimum temperature. The minimum temperature is for instance in the range of 55°C to 70°C. A significantly larger flow of distillate is obtained when the heating medium is heated so as to contain both a liquid phase and a vapour phase, particularly in a pulsated form. This requires a higher temperature of the heating medium.

Hence, preferably, the supplied heat is sufficient to maintain the temperature of the heating medium at a predefined value of at least said minimum temperature, and suitably at an optimum temperature to cause generation of a two-phase mixture, particularly in a pulsated form.

Thereto, the system is provided with temperature control means for controlling the provision of heat into the intermediate cycle. One or more temperature sensors will be available for sensing the temperature, typically within the intermediate cycle, but suitably also in the heating medium of the membrane distillation apparatus, and/or in the generator.

Preferably, temperature control means are available, which allow to vary the temperature of the fluid of the intermediate cycle. Therewith the temperature of the heating medium can be varied, so as to adjust, particularly to maximize or rather to significantly decrease the distillate flow rate.

The control means may achieve temperature control by means of driving one or more elements within the intermediate cycle. The pump speed of the pump of the intermediate cycle may be set and adjusted through the temperature control means. A valve defining a diameter at a location within the intermediate cycle, and therewith a (maximum) flow rate at a given pump speed, may be adjustable by means of said control means. The additional heating means may be switched on and off through said temperature control means. More suitably such control means are also able to control operation of the power generator.

With a generator of a suitable size relative to the membrane distillation apparatus, the amount of heat of the generator may not be sufficient for a steady-state operation of the distillation apparatus, let alone for a start up or volume increase of the membrane distillation apparatus. The combined heating of the medium of the intermediate cycle by means of the heat exchanger with the generator and the boiler and a storage tank allows the provision of the required amount of heat.

Accordingly, in a preferred embodiment, the medium in the intermediate cycle is heated by means of at least two sources: heat from the power generator, supplied by means of a heat exchanger, and heat from a second source, which is more particularly a boost heating means. Specifically, the heat of the power generator is used, which conventionally is dissipated as needed for appropriate cooling of the engine of the power generator. The electricity generated by the power generator may be applied to heat up the second source, but could alternatively be used externally, i.e. as a source of electricity for lamps, electrical equipment, phones and the like. The boiler could be warmed up -entirely or partially - by means of solar cells. Most preferably, there is thus a double use of the power generator, which improves the efficiency of the process.

Particularly, the intermediate cycle is provided with a boost heating means. Such a boost heating means are intended for additional heating of the fluid in the intermediate cycle.

Particularly, this additional heating may be started up and stopped more rapidly that the provision of heat via the primary heat exchanger from the generator. Therefore, the boost heating means can be used in several situations, such as during a start-up of the generator, when the heat supplied via the primary heat exchanger is insufficient; as an additional heating means, for instance in a design wherein the maximum heat supply from the generator is less than needed for the heating of the fluid for the membrane distillation apparatus; and/or as a temporary boost for the operation of the membrane distillation apparatus, so as to bring the fluid thereof to a higher temperature. The latter may be occurring at start up of the membrane distillation apparatus, but also in the course of operation, to increase the temperature and therewith the distillate production rate.

The boost heating means may be embodied in several ways. In a preferred embodiment, the boost heating means may be a boiler. This boiler may be an electrical boiler, or alternatively another type of boiler, such as a solar boiler. Preferably, the boiler - particularly the electrical boiler, but also the solar boiler if needed - are loaded from the generator. Most suitably, the temperature control means are integrated into the boiler. In an alternative embodiment, the boost heating means comprises a heat exchanger means, wherein the exhaust gases from the fuel generator are heat exchanged with the intermediate cycle. These are also known as waste heat recovery systems.

Hence, the intermediate cycle enables temporarily boosting the membrane distillation apparatus by means of increasing the temperature of its medium. Such a boosting may be desired to increase the speed at which distillate is produced, but also in view of a temperature decrease of the fluid in the fluid circuit extending to the heating channel.

In one embodiment, the generator is a fuel generator provided with an engine with an internal cooling circuit, and a further cooling circuit extending through the primary heat exchanger and through heat dissipation means, such as a radiator. The heat dissipation means are additional means for ensuring that the engine temperature does not rise too much. Suitably, ventilation means, such as a fan, are present, particularly in combination with a radiator as a heat dissipation means. The ventilation means will therewith ensure that heated air around the radiator is quickly dispersed. Evidently, there are more options of heat dissipation means than only a radiator, including the dissipation of heat to either a gaseous medium, a liquid medium (such as a water bath) or a solid medium (such as ice). In a further implementation hereof, the further cooling circuit may be provided with a heat regulation means, such as for instance a thermostat. This heat regulation means will then set the flow of the cooling medium of said further cooling circuit through said heat dissipation means, and relatively thereto, a flow directly back into the engine from the primary heat exchanger with the intermediate cycle. Therefore, the original cooling circuit remains operative, with the effect that the engine can be cooled anyhow and at any time, also in case that the membrane distillation apparatus is inactive.

The fuel of the fuel generator is suitably diesel. However, alternative fuels such as natural gas, coke, charcoal, wood, alcohols, gasoline, crude oil distillates and the like could be used alternatively. Optionally, the fuel generator is designed to work with one or more fuel sources. Suitably, diesel fuel is used for ignition.

One suitable further embodiment resides therein that the cooling medium of the cooling circuit is an oil. The generator is thus an oil-cooled generator, more preferably an oil-cooled diesel generator. The use of an oil as a cooling medium is advantageous in that its temperature typically lies above 100°C, for instance between 110°C and 125°C. This allows, without too much complications, to transfer sufficient heat from the generator via the primary and the secondary heat exchangers to the fluid of the fluid circuit at a desired temperature in the range of 85°C-95°C. The boiler may be primarily used for start-up and for boosting in this embodiment. However, clearly the size of the generator may be limited.

An alternative further embodiment resides therein that the cooling medium of the cooling circuit of the generator is aqueous, such as water or a water-glycol mixture. This further embodiment allows making use of an installed base of diesel generators, since a liquid-cooled diesel generator is very common and in use in many service and office locations worldwide, such as hotels, hospitals, offices. The boiler is in this embodiment required for preheating the medium of the intermediate cycle after that it has been cooled in the secondary heat exchanger. The boiler and/or a hot water storage tank is therefore, most preferably, located stream upwards from the primary heat exchanger. The reason thereof is a prevention of a so-called cold motor effect, meaning that if the temperature of the cooling medium of the generator falls down below a minimum temperature, the generator will shut off its cooling circuit, relying only on its internal circuit. Such minimum temperature is for instance 78°C. However, for some types of membrane distillation apparatus, the temperature of the medium of the intermediate cycle after passing the secondary is lower, for instance 70-72°C. In other words, unless said medium is preheated, there is no viable steady-state operation of the system.

The membrane distillation modules, the heating channel and the condenser are suitably arranged into a unit that preferably is of modular design. The membrane distillation apparatus furthermore comprises pumps, pipe and other auxiliary means, as needed for proper operation.

The membrane distillation apparatus coupled to the intermediate cycle may contain a single membrane distillation unit. Alternatively, a plurality of membrane distillation units may be present. Suitably, in such as a case, all of the membrane distillation units may be heated from the same heat source, i.e. the generator and the intermediate cycle with the said boiler.

In a further embodiment, the fluid circuit may also be provided with a boiler and/or a storage tank for hot water. This however appears less advantageous for temperature regulation, in the sense that it requires control of sources on even more locations.

Suitably, the vacuum source or vacuum sources of the membrane distillation apparatus are driven on the basis of the generator. This also applies for any vacuum pumps and other pumps required.

In again a further embodiment, the generator may load a cooling circuit used to cool cooling liquid of the condenser. This use is suitable at locations where no sufficient cooling water is available.

In one suitable embodiment, the invention provides a mobile system for the provision of electricity and clean water, for instance present on a truck. In a further embodiment, the invention provides a system for the provision of clean water and electricity for catastrophes.

Brief introduction of the figures

These and other aspects of the invention will be further elucidated with reference to the figures, in which:

Fig. 1 shows diagrammatically the system of the invention according to a first embodiment;

Fig. 2 shows diagrammatically a general architecture of the membrane distillation apparatus in accordance with the prior art as shown in W02005/089914 Al;

Fig. 3 shows a schematical view of the membrane distillation apparatus according to one embodiment of the invention;

Fig. 4 shows a view corresponding to that of Fig. 3, but indicating the pressure operation of the system;

Fig. 5 shows a more detailed schematical view specifying sensors and valves for one embodiment, and

Fig. 6A shows one application of the system of the invention;

Fig. 6B shows a block diagram corresponding to the application of Fig. 6A.

Detailed description of illustrated embodiments

The figures are not drawn to scale and equal reference numerals in different figures refer to same or corresponding elements.

Fig. 1 shows diagrammatically the system of the invention in accordance with a first embodiment. Broadly speaking, the system comprises a generator GE that is coupled via a primary heat exchanger 24 to an intermediate cycle IC. Fleat running in the intermediate cycle IC is then coupled to a stream 1 via a secondary heat exchanger 34, which heated up stream 7 transfers the heat into the membrane distillation apparatus 100, with a distillate 5 and a concentrated stream 3 -also referred to as brine - as outputs. By virtue of the intermediate cycle IC, the generator GE and the membrane distillation apparatus 100 are held independent with respect to their thermal management; i.e. the heat transferred into the membrane distillation apparatus 100 from the intermediate cycle IC during a period of time tl does not need to be identical to the heat transferred into the intermediate cycle IC during the same period tl. This is particularly relevant since the heat from the generator GE is dependent on the generation of electricity, which again depends on its load. As a rule of thumb, a generator running under electric load, will produce at least as much electric power as thermal, so 1 kW electric = 1 kW thermal. When the electric load is reduced, the heat also reduces. Moreover, the generator GE cannot be switched off or be increased in power instantaneously, whereas such instantaneous increase may be needed due to variations in the flow through the membrane distillation apparatus 100; the temperature of the incoming fluid, typically an aqueous liquid, may vary. Moreover, the needed water volume depends on users, and behavior of users will typically vary in the course of time during a day and from one day to another. Hence, there may well be periods in which settings of the membrane distillation apparatus 100 should be changed from normal to maximum distillate production and back to minimum distillate production. Thereto, the intermediate cycle is provided, and the temperature of the fluid running therein is controlled by means of temperature control means. In accordance with the first embodiment, the intermediate cycle IC comprises at least two sources of energy; heat enters this intermediate cycle IC not only from the primary heat exchanger 24, but also from a boost heating means, in this example a boiler 190. The boiler may be any type of boiler, and is suitably fed with electricity, at least partially, from the generator GE. In this embodiment, the intermediate cycle moreover comprises heat storage means 180, 181, more particularly, vessel for containing water of a predefined temperature. The vessel 180 is intended to contain a surplus of heat, and is preferably located in the stream 191 between the primary and the secondary heat exchanger. The stored heat may put back into the intermediate cycle IC at a later moment, for instance for boosting the transfer of heat into the membrane distillation apparatus 100. The stored heat could also be removed, if thus needed. The vessel 181 is intended to contain an additional volume of water that has been cooled in passing the secondary heat exchanger 34. It is thus suitably coupled to the stream 192 from secondary to primary heat exchanger 34, 24.

The intermediate cycle IC is further provided with a manual valve V19 in this embodiment. However, this manual valve V19 may be replaced for a valve that is controlled by control means. The valve may further be present as a protection device, so as to set a maximum to the flow, and/or to ensure that the medium in the intermediate cycle IC will flow in a well-organized, preferably laminar flow. Furthermore, an expansion vessel may be present, as known to persons skilled in the art. The temperature control means suitably also drive the boiler. Such temperature control means are for instance embodied in the form of a microcontroller integrated circuit, as known per se to the skilled person.

However, neither the hot water storage vessel 180, nor the cold water storage vessel 181 is necessary. Moreover, merely one of those could be foreseen rather than both (or none). The cold water storage vessel 181 could for instance be replaced with any inlet and outlet of water. In again an alternative implementation, the cold water storage vessel 181 could be left out, and its role being replaced by a well-defined control means, which monitors temperature changes by means of sensors, and as a result may adjust settings of a pump speed 195, the boiler 190, and inflow and outflow of any other available vessel 180 within the intermediate cycle IC. The storage vessels 180, 181 are for instance embodied as thermally isolated vessels, of the type known as Dewar vessels. If desired, the hot water storage vessel may be a storage under pressure, resulting in an additional liberation of energy in the form of heat, when hot water is released from said storage vessel 180. The storage vessels 180, 181 could further be coupled to the boiler 190, so as to allow increase of temperature of the stored liquid.

The membrane distillation apparatus 100 of the embodiment that is shown in Fig. 1, operates on the basis of an incoming stream 1, more particularly feed. The feed 1 is heated up in the secondary heat exchanger 34 and enters the membrane distillation apparatus as a preheated feed 7. Preferably, the feed is heated up to a temperature above 65°C, for instance between 70 and 95°C, such as from 75 to 85°C in the secondary heat exchanger 34. More suitably, the feed is heated up so as to contain a two-phase mixture of vapour and liquid. This simultaneous provision of vapour and liquid speeds up flow and has been found to increase the production of distilled water, as has been set out in the non-prepublished application NL2009615, which is included herein by reference. However, for other applications, for instance a concentration of a waste stream as shown in Fig. 6B, it may be better that the stream 1 is part of a preferably closed heating circuit running through a heating channel of a membrane distillation unit in the apparatus 100.

The generator GE is suitably a fuel generator, although other types of generators are not excluded. A fuel generator however may be better regulated. In order to dissipate heat generated in the course of electricity generation, the engine 200 is provided with three layers of heat dissipation means 210, 220, 224. A first layer is the internal cooling circuit 210, which is anyhow present in a conventional engine 200. The internal cooling circuit 210 is provided with a pump 211, which furthermore defines the pumping speed also in the further cooling circuit 220.. A flow regulation means 212 is present to define the relative transfer of heat from the internal cooling circuit 210 to the further cooling circuit 220. This flow regulation means 212 is suitably a thermostat. The internal cooling circuit 210 and the further cooling circuit 220 may alternatively be connected directly, such that cooling liquid from the internal cooling circuit 210 partially flows into the further cooling circuit 220. This is a matter of design of the generator GE, as known per se to the skilled person in the art thereof.

The further cooling circuit 220 contains the second layer of heat dissipation means in the generator GE. Its heat dissipation is effectively the primary heat exchanger 24. The further cooling circuit be operated and designed on the basis of oil as a medium, or alternatively an aqueous medium, such as a mixture of water and glycol. Since the temperature of the oil is significantly higher than the aqueous medium, the operation of the system of generator and intermediate cycle, and suitably also the design of the generator GE, will be different dependent on the type of medium. If the transfer of heat in the primary heat exchanger 24 is sufficient to cool down the medium to a predefined temperature, as sensed and controlled by means of regulation means 222, the medium will flow back through by-pass 226.

A third, suitable layer of heat dissipation means is defined by the additional circuit 225, in which heat is actively dissipated in heat dissipation means 224. This heat dissipation means 224 are suitably embodied as a radiator. A fan or the like 223 is preferably present for air convection and therewith efficient heat dissipation from the radiator 224. The fan 223 may be driven directly from the engine 200.

Operational process:

The system as shown in Fig. 1 is suitably operated in following manner. The example is given for an oil-based cooling medium. When the engine 200 is started, and still cold, the regulation means 212 remains closed, circulating the oil inside the engine 200 to warm up. Subsequently, upon reaching an engine nominal operating oil temperature, regulation means 212 opens and let oil pass to the primary heat exchanger 24. Here, heat will be transferred to the intermediate cycle IC. The amount of heat transfer is clearly dependent on the temperature and flow rate of the medium of the intermediate cycle IC. This again depends on the activity of the membrane distillation apparatus 100. If the heat transfer through the primary heat exchanger 24 is sufficient, the regulation means 222 will remain closed, returning the oil flow to the engine oil circuit 211. If however the membrane distillation apparatus 100 is not or only partly active, the oil temperature coming out of the primary heat exchanger 24 will still be too high. This will open up regulation means 222, letting oil run through the additional circuit 225 and the radiator 224 for cooling. From the radiator 224, the cooled oil runs back to the engine oil circuit 211. The radiator enables sufficient cooling for the engine, for the period that the primary heat exchanger does not lead to sufficient cooling. The primary heat exchanger 24 will give heat to the intermediate cycle IC, wherein the flow rate is set through pump 195 and manual valve V19, in this example. The intermediate cycle will transfer the heat via the secondary heat exchanger 34 to the membrane distillation apparatus 100. Depending on the flow in this circuit, a certain temperature difference AT over each heat exchanger 24, 34 can be set, making possible the tuning the diesel oil circuit 211, 221 to the water circuit 7 of the membrane distillation apparatus 100.

In order for the system regulation and control a plurality of operational conditions may be defined. A number of those are specified in the following. It will be apparent that these conditions may be optimized in more detail, and may be modified for the operation of additional elements in the intermediate cycle IC, such as the boiler 190 and the storage vessels 180, 181.

I. The diesel generator GE runs under normal or high electric load and the membrane distillation apparatus 100 is active. Then the cooling of the engine 200 is primarily achieved by the membrane distillation apparatus 100 alone. The additional circuit 225 with the fan 223 and the radiator 224 is not active.

II. The diesel generator GE runs under normal or high electric load and the membrane distillation apparatus 100 is not active. Then the cooling of the engine 200 is done by the the fan/radiator circuit 225.

III. The diesel generator GE runs under normal or high electric load and the membrane distillation apparatus 100 is partly active (low feed flow, high vacuum). Then the cooling is done partly done by the fan/radiator circuit 225, and partly done by the membrane distillation apparatus 100.

IV. The diesel generator GE runs under low/no electric load & the membrane distillation apparatus 100 is active: the engine 200 runs (close to) idle. Then the cooling is done by the membrane distillation apparatus 100, if the engine 200 is too hot (Thermostat 212 open), or there is no cooling, if the diesel generator 200 is below nominal temperature (Thermostat 212 closed). The heat supply to the membrane distillation apparatus 200 will be primarily provided by means of boiler 190 and/or hot water from the hot water storage vessel 180 if present. If no extra heating means 190, 180 are present, the module 100 will just work with the heat taken from the heat exchanger, and lower its distillate output accordingly. This occurs preferably in a passive way, for which no active controlling is necessary.

V. The diesel generator GE runs under low/no electric load & the membrane distillation apparatus 100 is not active: the engine 200 runs (close to) idle. Then the cooling is done by the fan/radiator circuit 225 if the engine 200 gets too hot (Thermostats 212 and 222 open), or there is no cooling when the engine 200 is below nominal temperature (Thermostat 212 closed). Furthermore, some energy may be used for heating up the medium in the intermediate cycle IC, and or filling the hot water storage vessel 180 with hot water, in case such a vessel 180 is available. The terms low electric load, normal electric load and high electric load are to be understood relative to each other and broadly, as different operation modi. A high load may even be a full electric load. An example of a normal electric load for a generator is an air conditioning system as a load. The skilled person will understand this schematic classification and will be able to specify it on the basis of common general knowledge.

Figures 2-5 show in more detail a preferred embodiment of the membrane distillation apparatus 100.

Fig. 2 shows diagrammatically a general architecture in accordance with the prior art as shown in W02005/089914 Al. As shown herein, the membrane distillation system 100 comprises a heat transmitter 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 exchanger, particularly so as to preheat the feed. As is indicated in the Fig. 4 and 5, 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 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 integration into the modular system, any other heat transfer means could be used for the provision of heat in the form of condensable vapour, particularly steam.

Liquid, i.e. particularly an aqueous solution or a fluid mixture, enters the system via a liquid line 7. It is optionally preheated in a heat exchanger 34, but still at atmospheric pressure. Thereafter, it enters the heat transmitter 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 this heat transmitter 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 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 heat transmitter module 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 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 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 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 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 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.

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 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 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 liquid pump). Instead of being led away as a separate liquid stream, the condensate from the condenser 42 may be added to a distillate collector. Distillate is collected in a distillate collector 54, from which it is pumped to a higher pressure using a liquid 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 (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 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 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 side by a membrane 20 and on the opposite side by a condensation wall 24.

Fig. 3 and 4 show the general architecture in accordance with one embodiment of the present invention. Fig. 3 shows 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 transmitter module 40, distillation modules 14, 16 and a condenser 42. All these modules are suitably physically integrated into a single assembly. The heat transmitter module transmits heat that is supplied in the form of a flow of vapour and/or liquid to the adjacent distillation module, from which this module is separated with a condensation wall, at which vapour will condensate. The vapour and/or liquid are suitably water, such as distilled water, but could be another medium. The vapour, i.e. steam, may be generated locally, i.e. from hot liquid by means of pressure reduction and/or temperature increase. The vapour may alternatively be flowing into the heat transmitter module 40, and be generated in advance. Moreover, a combination of local steam generation and supply of steam is also feasible.

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 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 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 arrive at a distillate collector 54. However, as shown in Fig. 4-5, the distillate flow (pipe) 52 may be integrated into the modular assembly, such that merely a single distillate exit 53 is present.

Furthermore vapour lines 107, 29 are shown. In accordance 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 indicated separately in this Figure 2 for sake of clarity, but may physically be provided in a single pipe.

The architecture shown in Fig. 4 corresponds to that of Fig. 3. For sake of clarity, the distillate channels 52, 53 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. 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 the condenser 42, and particularly to the vapour channel 29 therein. Line 102 indicates the clamping vacuum (Dutch: klemvacuiim) 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 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 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 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 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 transmitter module 40 is again higher. For instance, the pressure C is 0.4 bar, pressure D is 0.3 bar, 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 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 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 V1 is present, which lowers the Pressure B to a 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 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 condensation wall were made of steel, aluminum, or a heat-conducting ceramic, the provision of a predefined maximum is not deemed necessary.

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 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 condensation wall in the first membrane distillation module 14.

Fig. 5 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. According to this system, the 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 cooling liquid 49 is pretreated by means of valve V4 and a heat exchanger 34 to become a two-phase feed 7. The heat exchanger 34 is provided with a separate heating liquid inlet 191 and a heating liquid outlet 192. The heat exchanger 34 has a suitable total surface for heat transfer into the feed flow. If the total surface area is too low, it turns out difficult, if not impossible to generate a multiphase feed. If the total surface is too high, the effectiveness of the heat transmitter 40, and therewith the system performance is reduced.

Suitably the heat exchanger is connected to the heat transmitter with any pipe, such that the multiphase feed can be transported in a stable manner, i.e. without reconversion into a liquid feed. Such stable transport is suitably achieved with a line of sufficient diameter, preferably isolated and without sudden curves that have an impact on flow. In a preferred embodiment, the heat exchanger 34 is designed for an updraft feed flow. Herein the heat exchanger is installed in a vertical manner, at least substantially, such that the feed entry point is lower than the multiphase feed exit point. Preferably, such feed entry point is at or near the bottom, whereas the feed exit point is at or near the top. It is believed that the updraft flow has a positive effect on creation of the multiphase feed mixture, in that gravity counteracts the pressure gradient in the heat exchanger feed flow.

The feed then passes the membrane distillation unit 10, comprising the heat transmitter 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. 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 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 increase and transport. The resulting brine 3 is thereafter recirculated back into cooling water vessel 202 via recirculation line 205. It will be understood that alternatives are envisageable. In the preferable embodiment that use is made of an assembly of modules made of polymer material, such as polyethylene or polypropylene, and more suitably modules with foils attached to module frames, for instance by means of welding, it has been found beneficial to subdivide the two phase feed into a primarily liquid stream 7 and a primarily vapour stream 107 prior to entry of the heat transmitter module 40. This appears to increase lifetime of the frames and foils. The liquid stream 7 would then go directly into the first membrane distillation module 14 without passing the heat transmitter module 40. However, it has been found that the yield is also enhanced in this version as a consequence of the two phase feed. The two-phase mixture 7, 107 has a very turbulent flow, even considered wild. Even when applying a pre-separation step before entering the heat transmitter module 40, it was found that the steam is feasible to suck the water and therewith to accelerate the mixture. Moreover, there is sufficient water in the steam portion to ensure a very good heat transfer, and there is sufficient steam in the water left to accelerate the evaporation process in each of the membrane distillation modules.

As a result of the pre-separation step, the primarily liquid stream is a first two-phase mixture with suitably at least 80vol%, preferably at least 90vol%, more preferably about 95vol% water. This mixture will be led directly to the first membrane distillation module 14. The primarily vapour stream is a second two-phase mixture with suitably less than 10vol% liquid, more preferably at most 5vol% liquid or even at most lvol% liquid. The liquid is more suitably an aqueous solution. The vapour will be substantially water or a mixture of water and a further low-boiling compound such as an alcohol. The pre-separation is suitably achieved on the basis of density, more particularly by means of gravity. This is for instance carried out by means of a Y-shape connector part, with an inlet for the two-phase mixture and a first upper outlet for the vapour stream and a second lower outlet for the liquid stream. The first upper outlet is coupled to the heat transmitter module, the second lower outlet is coupled to the first membrane distillation module. It will be understood that other connector parts could be used; however the Y-shape does not have the disadvantage of a sharp corner for at least one of the streams. This could have an impact on flow rate, pressure, heat dissipation.

For an appropriate operation, a plurality of valves is suitably 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.

Valve V1 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 the like. Valve VI is for instance embodied as a restriction device.

Valve V2 is a further and optional 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 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 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 so as to prevent, at least substantially, the backwards flow of warmed up cooling liquid after turning the apparatus off. Rather than as a valve, this protection device may further be embodied differently, for instance in the form of a hydrophobic filter present in a vacuum line 103 between the brine collector vessel 37 and the condenser.

Valve V3 serves a similar function for the feed line 7.

Valve V4 is a device for setting the underpressure in the 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 obtained. Alternatively, use may be made of a manual one-time setting, so that the system always reaches the twophase state if sufficient heat is available. The setting of this valve is not in need of further change after its initial setting. A reset of this valve is envisaged for the event that the system suffers from scaling or fouling, affecting the total feed inflow, and/or when less or more heat is available, and the system settings need to be different.

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 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.

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

Valve V7 is a further optional 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 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.

Fig. 5 moreover indicates sensors in the system, more particularly 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.

Fig. 5 furthermore shows post treatment means. Herein, the distilled water is treated to obtain potable water 5. A carbon dioxide vessel 53 is present, from which carbon dioxide may be inserted in the system using valves V9, V10. Furthermore, a marble filter 151 and a UV lamp 152 are 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 present in the system, which are known per se and have been left out for sake of clarity.

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, 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 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 of both potable water and sea water for test purposes, which led to virtually identical results with respect to stability and product output.

While all of the Figures 2-5 show embodiments wherein the cooling liquid is driven through the condenser 42 on the basis of a pressure difference, this is a preferred feature that is not considered essential for the 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 or sucked through the condenser actively, rather than passively on the basis of an existing pressure difference. Furthermore, while the embodiments show that the cooling liquid and the brine are merged to end up in the brine collector vessel, this is not deemed necessary. Two separate streams could be used alternatively. Moreover, 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.

Fig. 6A shows a diagrammatical view of an application of the system according to the invention. Fig. 7B shows a diagram for this application. The application is a movable unit, such as a truck, that comprises the generator GE and the membrane distillation apparatus 100, as well as the intermediate cycle IC in between thereof. This movable unit may be brought to a location, where concentration of a fluid is desired, for instance to reduce a volume of waste to be disposed, and/or to increase its concentration to such an extent that the volume may be transported or that ingredients can be obtained more easily. Moreover, the distillate may be reused locally.

One suitable post-treatment is for instance crystallization, for which the fluid needs to be concentrated so as saturated or near to saturation. When the fluid is cooled down after the membrane distillation process, the degree of saturation will cross the border at which crystallization will start, or can be made to be started by addition of nucleating elements of by addition of a suitable reagent. An alternative application may be the reduction of a volume of contaminated water. It is apparent that such applications could even be carried out if the system is not embodied in a movable manner. However, the movability provides an additional advantage, also business-wise: different clients may be served with a single apparatus. And if individual units would not be useable anymore, the foils constituting walls and membranes may be replaced and the frames could be cleaned.

Fig. 6B shows a diagram of this application 1000. A feed 1 is provided from a tank, container or basin 300. The feed 1 is heated in the secondary heat exchanger 34 and enters the membrane distillation module 100 as two-phase feed 7. It is observed that the feed 1 may be too corrosive, viscous or would adhere too quickly, such that a separate, preferably closed fluid circuit may be used. The membrane distillation module 100 is further provided with cooling liquid 47 that leaves the condenser as stream 49. The cooling liquid 47 originates in this example from an active cooling device 240, with any fluid, particularly a liquid 2 as input. That takes away the need of water availability, such as a lake or a river, for cooling purposes. The membrane distillation process results in a brine 3 and a distillate 5 as outputs. The generator GE herein not merely provides heat to the membrane distillation apparatus 200 via the intermediate cycle IC, but further uses the devices in the system as its loads. Thereto, the active cooling device 240 is connected to the generator GE by means of power connection 231. The pumps and vacuum source in the membrane distillation apparatus 100 are connected to the generator GE by means of power connection 232. The boiler in the intermediate cycle IC is connected to the generator GE by means of power connection 233. Though not shown in Fig.7B, it is feasible that a diesel generator is provided with diesel fuel directly from the fuel tank of the truck.

Claims

A system of a membrane distillation device (100) and an energy source (200) therefor, said membrane distillation device (100) a plurality of distillation modules (14, 16, 114, 116), a heating channel (40) transferring heat to a first (14) of said distillation modules (14, 16, 114, 116) and a condenser (42), which system further comprises: - a liquid circuit (7) extending to the heating channel (40) in order to heat up feeding the membrane distillation, which liquid circuit (7) comprises a heat exchanger (34) for heating up and optionally partially evaporating a liquid flowing into the liquid circuit (7), which heat exchanger (34) comprises a second channel for supplying heat originating from the energy source (200), an intermediate circuit (IC) extending from a first heat exchanger (24) to the second channel of the - secondary - heat exchanger (34), a generator (GE) for generating heat and electricity , which heat is at least partially transferred to the intermediate circuit (IC) by means of the primary heat exchanger (24), and a pump for circulating a fluid in the intermediate circuit, wherein the intermediate circuit (IC) is further provided with: means for temperature control, and a means (180, 181) for storing heat.

A system according to claim 1, wherein the intermediate circuit is provided with a heating means (190) for additional heating, which is controlled by the temperature control means.

3. System as claimed in claim 1 or 2, wherein the intermediate circuit comprises a temperature sensor, which is connected to the means for temperature control.

A system according to claim 1 or 2 or 3, wherein the pump is driven by said temperature control means.

A system according to any one of the preceding claims, characterized in that the temperature control means are adapted to vary the temperature of the fluid in the intermediate circuit in order to adjust a flow rate of the distillate from the membrane distillation apparatus.

The system of claim 2, wherein the heating means (190) is a boiler.

The system of claim 2, wherein the heating means (190) is a heat exchange means for heat exchange between exhaust gases from the generator (GE) and the intermediate circuit (IC).

A system according to any one of the preceding claims, wherein the heating means (190) is upstream of the primary heat exchanger (24), so that a liquid cooled in the secondary heat exchanger (34) is first heated by the heating means (190) .

The system of claim 6, wherein the boiler (190) is driven at least partially with electricity from the generator (GE).

The system of claim 1, wherein the heat storage means is a heated water tank.

A system according to any one of the preceding claims, wherein the means for temperature control are coupled to the generator (GE) in order to change settings of the generator (GE).

12. System as claimed in any of the foregoing claims, wherein a sensor for determining a distillate outflow is present, which sensor is connected to the means for temperature control, so as to set and adjust an operating speed of the membrane distillation device.

A system according to any one of the preceding claims, wherein the generator (GE) is fuel-fired and comprises an engine (200) with an internal cooling circuit (210) and a further cooling circuit (220) passing through the primary heat exchanger ( 24) and through a heat dissipation means (224), such as a radiator.

The system of claim 13, wherein the further cooling circuit is further provided with switching means (222) between the primary heat exchanger (24) and the heat dissipating means (224), so that a cooling medium returns from the further cooling circuit (220) to the motor (200) can turn without passing through the heat dissipation means (224).

The system of claim 14, wherein the switching means (224) is formed by a thermostat.

The system of any one of claims 13 to 15, wherein the generator (GE) is an oil-cooled generator, wherein a lubricating oil is used as cooling medium of the further cooling circuit (200).

The system of any one of claims 13 to 15, wherein the generator (GE) is a liquid-cooled generator, wherein an aqueous liquid is used as cooling medium of the further cooling circuit (200).

A system according to any one of the preceding claims, wherein the liquid flowing into the liquid circuit (7) is an aqueous feed, which feed at least partially enters the first membrane distillation module (14).

The system of claim 18, wherein the aqueous feed in the secondary heat exchanger (34) is heated such that a two-phase mixture of liquid and vapor is obtained.

A system according to any one of the preceding claims, wherein the membrane distillation device (100) is a vacuum membrane distillation device, and wherein a vacuum source imposes a vacuum on the condenser (42) and / or one of the membrane distillation modules (14, 16 , 114, 116).

A portable unit (1000) for providing drinking water containing the system according to any of the preceding claims.

Use of a system according to any of claims 1-20 and / or the movable unit (1000) according to claim 21 for providing drinking water.

The use of claim 22, wherein the system is further used for supplying electricity.

Use of a system according to any of claims 1-20 and / or the movable unit according to claim 21 for concentration of a water-based residual or waste water stream.

A method of operating a membrane distillation apparatus (100) comprising the steps of: Generating heat in a generator (GE), which heat is transferred to an intermediate circuit (IC), in which liquid is pumped around; Controlling the temperature of the fluid circulating in the intermediate circuit (IC), and Passing heat from the fluid at the controlled temperature to a fluid circuit (7) that extends to a heating channel (40) of the membrane distillation apparatus ( 100), wherein the system according to any of claims 1-20 or the movable unit according to claim 21 is used.

The method of claim 25, wherein a rate of distillate production is controlled by adjusting the temperature of the liquid in the intermediate circuit.

The method of claim 25 or 26, wherein the generator is operated such that a generator motor continues to run in a desired temperature range.