Patent Description:
Such a reverse osmosis arrangement is known, for example, from <CIT>. The first port of the first chamber is connected to a feed pump and the second port of the first chamber is connected to a pump portion of a booster.

Such a reverse osmosis arrangement is used, for example, to treat wastewater or sea water in order to remove unwanted ingredients. For example, such a reverse osmosis arrangement can be used for desalinating of sea water.

The following explanation is made with the desalination of sea water as an example. However, the reverse osmosis arrangement is not limited to the use in combination with sea water.

When sea water is desalinated, the sea water is supplied to the first chamber via the first port. The first pump produces a rather high pressure in the magnitude of several tens of bar. The membrane in the housing is a semi-permeable membrane. Part of the sea water penetrates the membrane without the salt and leaves the second chamber via the permeate outlet. The remaining water having a higher concentration of salt leaves the chamber via the second port. This fluid is also called brine.

It is known to increase the lifetime of the membrane by reversing the flow through the membrane unit from time to time. To this end the sea water is supplied to the second port and the brine leaves the first chamber via the first port. The permeate is still leaving the second chamber via the permeate outlet.

The brine has still a rather high pressure. Without additional measures this high pressure is lost leading to a waste of energy.

<CIT> describes an integrated reverse osmosis module with energy recovery for desalination. The module comprises a single reverse osmosis membrane module which is adapted to reversibly receive a feed flow through one of the first and second fluid inlet/outlet channels and produce a brine outflow through the other of the first and second inlet/outlet channels. To this end it has two pressure exchanger chambers of opposite flow directions, thereby allowing oscillatory feed flow reversal in the reverse osmosis module.

<CIT> describes a power recovery pump turbine the inlet of which is connected to a second port of the first chamber of a reverse osmosis module. The outlet of the pump turbine is connected to the first port of the first chamber. The pump turbine comprises a turbine section and a pump section each having an impeller, wherein the impellers are connected by a common shaft.

The object underlying the invention is to operate a reverse osmosis arrangement with high efficiency.

This object is solved with a reverse osmosis arrangement as described at the outset in that the second port is connected to a second pump.

In this way reverse of the flow through the membrane unit is performed by using the first pump to generate a flow through the membrane unit in a first direction and by using the second pump to create a flow through the membrane unit in the opposite direction.

The first pump is operatively connected to a first reversible electric machine which can be operated in a motor mode and in a generator mode and the second pump is connected to a second reversible electric machine which can be operated in a motor mode and in a generator mode, wherein the first pump can be operated as hydraulic motor driving the first electric machine and the second pump can be operated as hydraulic motor driving the second electric machine. This embodiment has the advantage that the high pressure of the brine can be used to operate the pump arranged at the side of the membrane unit at which the brine leaves the first chamber. The energy of the brine with the high pressure and thus with the high energy is transformed by the pump in electric energy, since the brine drives the hydraulic motor and the hydraulic motor in turn drives the electric machine. The electric machine can be, for example, a variable frequency device comprising an electric motor/generator controlled by a frequency converter. Thus, the hydraulic energy of the brine is converted into electric energy. The electric energy can be used at another location.

In an embodiment of the invention at least one of first pump and second pump is an axial piston machine. An axial piston machine comprises, for example, a cylinder drum in which a plurality of cylinders is arranged. Each cylinder comprises a piston which rests with one end against a swash plate. When the cylinder drum is rotated, a swash plate drives the pistons in the cylinder to perform a pumping action. When, on the other hand, hydraulic fluid under high pressure is supplied to the cylinders, this high pressure moves the pistons and produces a rotating movement of the cylinder drum due to the cooperation of the pistons with the swash plate. Thus, an axial piston machine is in particular useful to be operated as pump and as motor.

In an embodiment of the invention the first electric machine and the second electric machine are connected by an electric line transferring electric power between the first electric machine and the second electric machine. Thus, the electric power produced by the electric machine which is driven by the pump, when the pump is operated as motor, can directly be supplied to the other electric machine driving the pump. Since the distance between the two electric machines is short, the electric losses are low.

In an embodiment of the invention a first dump valve is arranged in parallel to the first pump and a second dump valve is arranged in parallel to the second pump. When the flow through the membrane unit is reversed, there is a risk of unwanted particles being flushed out of the first chamber. These particles could damage the respective machine arranged at the outlet side of the first chamber. Thus, the dump valve can be opened to avoid the entrance of unwanted particles into the respective pump. The dump valve connects the membrane unit to a brine line.

In an embodiment of the invention a first flow restriction is arranged between the first dump valve and a brine line and a second flow restriction is arranged between the second dump valve and the brine line. The flow restrictions can be, for example, in form of an orifice. This has the advantage that the pressure drops over the dump valve can be kept small, so that the dump valves do not produce too high costs.

In an embodiment of the invention at least a second parallel membrane unit is arranged in parallel to the membrane unit. Thus, two or more membrane units can be arranged in parallel to allow a large flow through the reverse osmosis arrangement and correspondingly a high production of permeate.

In an embodiment of the invention at least a second serial membrane unit is arranged in series with the membrane unit. The brine leaving the first chamber has still a rather high pressure. This pressure can be used in a following step of desalination or treatment of water. It is possible to gain permeate also from the brine. Thus, a multistage reverse osmosis arrangement can be used. It is also possible to use in each stage a number of membrane units arranged in parallel.

In an embodiment of the invention an interstage pump is arranged between the membrane unit and the first serial membrane unit. If more than two stages are used, such an interstage pump can be arranged between each stage. The interstage pump can increase the pressure of the brine leaving the membrane unit. Thus, the following membrane unit can be supplied with sea water under the desired elevated pressure.

In an embodiment of the invention the interstage pump is a bi-directional pump. Thus, even a sequence of two or more membrane units can be operated in two directions.

In an embodiment of the invention a third dump valve connects a point between the membrane unit and the interstage pump with the brine line and a fourth dump valve connects a point between the serial membrane unit and the interstage pump with the brine line. In this case also the interstage pump can be protected from unwanted particles which can be flushed out of the first chamber of each membrane unit when the flow direction is reversed.

In an embodiment of the invention a third flow restriction is arranged between the third dump valve and the brine line and a fourth flow restriction is arranged between the fourth dump valve and the brine line. Again, the flow restrictions can be realized by an orifice or the like. In this way it is possible to keep the pressure drop over the dump valves low, so that the dump valves do not produce too much costs.

Preferred embodiments of the invention will now be described with reference to the drawing, in which:.

Same elements are denoted with same reference numbers in all Fig..

<FIG> shows a reverse osmosis arrangement <NUM> comprising a membrane unit <NUM> having a housing <NUM> and a membrane <NUM> separating a first chamber <NUM> and a second chamber <NUM> in the housing <NUM>. The first chamber <NUM> has a first port <NUM> and a second port <NUM> and the second chamber <NUM> is connected to a permeate outlet <NUM>.

Water to be purified, for example sea water <NUM> having a low pressure is pumped by means of a boost pump <NUM> into a piping system <NUM>. The piping system <NUM> connects the boost pump to a first pump <NUM> and to a second pump <NUM>. The first pump <NUM> is operatively connected to a first reversible electric machine <NUM> and the second pump <NUM> is operatively connected to a second reversible electric machine <NUM>. The first pump <NUM> and the first reversible electric machine <NUM> form together a bidirectional drive <NUM>. The second pump <NUM> and the second reversible electric machine <NUM> form together a second bidirectional drive <NUM>.

The first pump <NUM> and the second pump <NUM> can be, for example, in form of an axial piston machine. An axial piston machine comprises a cylinder drum which can be rotated. The cylinder drum comprises a number of cylinders. A piston is arranged in each cylinder. The piston rests against a swash plate which is tilted with respect to an axis of rotation of the cylinder drum. When the cylinder drum is rotated, the swash plate produces a reciprocating movement of the pistons in the cylinder and thus a pumping action, so that the axial piston machine can be operated as pump in this case. However, the axial piston machine can also be operated as motor. In this case, hydraulic fluid under pressure is supplied to the cylinder pressing the pistons against the swash plate. Since the swash plate is tilted with respect to the axis of rotation of the cylinder drum, this pressure produces a rotating movement of the cylinder drum, so that in this case the axial piston machine is operated as motor.

The reversible electric machines <NUM>, <NUM> can be operated in motor mode and in generator mode. Since they can be operated in both modes in both directions (clockwise and counter clockwise) they allow an operation in four quadrants (motor clockwise and counter clockwise and generator clockwise and counter clockwise).

When the first reversible electric machine <NUM> is operated as motor, it drives the first pump <NUM>. The first pump <NUM> drives the sea water through the membrane unit <NUM>. The brine leaving the second port <NUM> is supplied to the second pump <NUM>, which in this case is operated as motor and drives the second reversible electric drive <NUM>. In this mode of operation the second reversible electric drive <NUM> is operated as generator producing electric energy which can be transferred to the first reversible electric drive <NUM> by means of an electric line <NUM> transferring the electric power between the second reversible electric machine <NUM> and the first reversible electric machine <NUM>.

When the flow through the membrane unit <NUM> is reversed, the second pump <NUM> is used to drive the sea water through the membrane unit <NUM> and the first pump <NUM> is used as motor. In this case the second reversible electric machine <NUM> is working in motor mode. The brine leaving the first port of the chamber <NUM> drives the first pump <NUM> in motor mode. The first reversible electric machine <NUM> is then operated as generator producing electric energy which is transferred via the electric line <NUM> to the second reversible electric machine <NUM>.

In order to control the flow between the boost pump <NUM> and the first pump <NUM> or the second pump <NUM>, respectively, a first input valve <NUM> is arranged between the boost pump <NUM>, more precisely between a feed line <NUM> into which the boost pump <NUM> supplies the sea water, and the first pump <NUM>. A first outlet valve <NUM> is arranged between the first pump <NUM> and a brine line <NUM>. A second input valve <NUM> is arranged between the feed line <NUM> and the second pump <NUM> and a second outlet valve <NUM> is arranged between the second pump <NUM> and the brine line <NUM>. All valves <NUM>, <NUM>, <NUM>, <NUM> can be in form of motor valves.

The permeate outlet <NUM> of the membrane unit <NUM> is connected to a permeate line <NUM>.

The use of the two pumps <NUM>, <NUM> has a number of advantages. The feed flow direction through the membrane unit <NUM> can be frequently changed reducing fowling and scaling. The reversal of the flow can be automatic initiated with measuring values from different sensors which can measure for example the salinity in the system at different points. Thus, lower chemical consumption for cleaning and descaling is required. A reduction in downtime for cleaning is achieved. The service life of the membrane <NUM> is increased. Thus, less downtime for membrane replacement is required. Furthermore, costs for membrane module replacement are reduced. There is an increase recovery rate of the energy of the brine recovered directly after leaving the membrane unit <NUM>, so that piping required for high pressure flow can be kept short. This reduces costs for piping. The use of two pumps <NUM>, <NUM> on both sides of the membrane unit <NUM> enables a variable and individual control of the recovery rate of the membrane <NUM>. A variable control of i.e., the recovery rate can increase the service life of the membrane <NUM>, optimize the energy consumption needed for the reverse osmosis process and adjust the system to operate with different kind of fluids. This can be of benefit when there are changes in the composition of the sea water entering the membrane unit <NUM>, for wastewater treatment systems and other industrial reverses osmosis processes.

The drive units <NUM>, <NUM> convert the hydraulic energy to electrical energy. The electrical energy can either be fed directly to the electrical grid or to other drive units.

<FIG> shows a second embodiment of the invention, in which the same elements are denoted with the same reference numerals.

The boost pump <NUM> is not shown. Only shown is the feed line <NUM> and the brine line <NUM>. A first difference is that not only one membrane unit <NUM> is used, but two more membrane units <NUM>, <NUM>. All membrane units <NUM>, <NUM>, <NUM> are arranged in parallel, i.e. the membrane unit <NUM> and a first parallel membrane unit <NUM> and a second parallel membrane unit <NUM> are arranged in parallel. All membrane units <NUM>, <NUM>, <NUM> are connected with their first ports <NUM> to the first pump <NUM> and with their second ports <NUM> to the second pump <NUM>. The permeate outlets <NUM> of the membrane units <NUM>, <NUM>, <NUM> are connected to the permeate line <NUM>.

A second difference is that a first dump valve <NUM> is arranged in parallel to the first pump <NUM> and a second dump valve <NUM> is arranged in parallel to the second pump <NUM>. A first flow restriction <NUM> is arranged between the first dump valve <NUM> and the brine line <NUM> and a second flow restriction <NUM> is arranged between the second dump valve <NUM> and the brine line <NUM>. The flow restrictions <NUM>, <NUM> can be in form of an orifice, for example. They lower a pressure drop over the respective dump valve <NUM>, <NUM>.

It should be noted that these dump valves <NUM>, <NUM> can also be used in connection with the embodiment shown in <FIG>.

When the first pump <NUM> is used to pump the sea water through the membrane units <NUM>, <NUM>, <NUM> and the flow through the membrane units <NUM>, <NUM>, <NUM> is then reversed, there is a risk that unwanted particles are flushed out of the first chamber <NUM>. These particles could damage the first pump <NUM>. Thus, the first dump valve <NUM> is opened for a predetermined time or as long as such particles are detected in the flow out of the membrane units <NUM>, <NUM>, <NUM>. When all dirt is removed from the membrane units <NUM>, <NUM>, <NUM>, the first dump valve <NUM> is closed and the first pump <NUM> is operated again as motor.

In the same way, when the flow through the membrane units <NUM>, <NUM>, <NUM> is again reversed and the sea water is driven through the membrane units <NUM>, <NUM>, <NUM> by means of the first pump <NUM>, the second dump valve <NUM> is opened to allow the unwanted particles which are flushed out of the first chamber <NUM> to flow directly to the brine line <NUM>. When there are no particles or other dirt in the fluid coming out of the membrane units <NUM>, <NUM>, <NUM>, the second dump valve <NUM> is closed and the second pump <NUM> is again operated as motor driving the second reversible electric machine <NUM> to produce electric energy. The electric line <NUM> between the two drives <NUM>, <NUM> is not shown. However, it can be provided.

<FIG> shows a third embodiment in which elements corresponding to elements of <FIG> are denoted with the same reference numerals.

The embodiment of <FIG> is a multistage arrangement having a first stage <NUM> of membrane units <NUM>, <NUM>, <NUM> and a second stage <NUM> of membrane units <NUM>, <NUM>, <NUM>. The membrane units of the second stage <NUM> are termed "serial membrane units". Thus, at least a second serial membrane unit <NUM> is arranged in series with the membrane unit <NUM> or with the arrangement of two or more membrane units <NUM>, <NUM>, <NUM> arranged in parallel.

An interstage pump <NUM> is arranged between the two stages <NUM>, <NUM>. The interstage pump <NUM> is a bidirectional pump, i.e. it can pump liquid from the first stage <NUM> to the second stage <NUM> or from the second stage <NUM> to the first stage <NUM>.

If more than the two stages <NUM>, <NUM> are used, an interstage pump <NUM> in form of a bidirectional pump can be arranged between each stage <NUM>, <NUM>.

A third dump valve <NUM> connects a point <NUM> between the membrane unites <NUM>, <NUM>, <NUM> and the interstage pump <NUM> with the brine line <NUM> and a fourth dump valve <NUM> connects a point <NUM> between the serial membrane units <NUM>, <NUM>, <NUM> and the interstage pump <NUM> with the brine line <NUM>.

A third flow restriction <NUM> is arranged between the third dump valve <NUM> and the brine line <NUM> and a fourth flow restriction <NUM> is arranged between the fourth dump valve <NUM> and the brine line <NUM>. The flow restrictions <NUM>, <NUM> can be, for example, in form of orifices.

When the embodiment shown in <FIG> is operated, the first pump <NUM> pumps sea water from the feed line <NUM> through the first stage <NUM> of membrane units <NUM>, <NUM>, <NUM>. The brine leaving this stage <NUM> is combined at point <NUM> and supplied to the interstage pump <NUM>. The interstage pump <NUM> can increase the pressure again, so that the pressure loss of the first stage <NUM> can be compensated or overcompensated. In some cases, this is necessary, since the brine leaving the first stage <NUM> has a higher salt concentration so that a higher pressure is required in the second stage <NUM> of serial membrane units <NUM>, <NUM>, <NUM>. The brine which is supplied to the second stage <NUM> of serial membrane units <NUM>, <NUM>, <NUM> produces again permeate which is fed to the permeate line <NUM>. The brine leaving the serial membrane units <NUM>, <NUM>, <NUM> having an even higher salt concentrate is again used to operate the second pump <NUM> as motor. The second pump <NUM> drives the second reversible electric machine <NUM> which is in this case used as generator producing electric energy which can be transferred to the first reversible electric machine <NUM>. The electric line <NUM> is not shown.

When the flow direction is reversed by operating the valves <NUM>, <NUM>, <NUM>, <NUM>, there is a risk that unwanted particles which are flushed out of the serial membrane units <NUM>, <NUM>, <NUM> of the second stage <NUM> damage the interstage pump <NUM>. To avoid such damage the fourth dump valve <NUM> is opened to allow this polluted liquid to enter directly the brine line <NUM>. After a predetermined time, or, when a corresponding sensor is provided, after detection that the fluid leaving the membrane units <NUM>, <NUM>, <NUM> of the second stage <NUM> is "clean" enough, the fourth dump valve <NUM> is closed an the liquid can be pumped by the interstage pump <NUM> into the membrane units <NUM>, <NUM>, <NUM> of the first stage <NUM>. Since again dirt or particles are flushed out of the membrane units <NUM>, <NUM>, <NUM> of the first stage <NUM>, the first dump valve <NUM> is opened until the liquid leaving the membrane units <NUM>, <NUM>, <NUM> of the first stage <NUM> is clean enough. Thereafter, the first dump valve <NUM> is closed and the first pump <NUM> is operated as motor driving the first reversible electric machine <NUM>.

The same operation is performed when the flow direction is reversed again. After reversing the flow direction, the first dump valve <NUM> is opened to allow particles or dirt flushed out of the membrane units <NUM>, <NUM>, <NUM> of the first stage <NUM> to flow directly to the brine line <NUM>. When the liquid is clean enough, the third dump valve <NUM> is closed and the interstage pump <NUM> can pump the liquid through the serial membrane units <NUM>, <NUM>, <NUM> of the second stage <NUM>. At this time the second dump valve <NUM> is opened to allow the particles or dirt from the serial membrane units <NUM>, <NUM>, <NUM> of the second stage <NUM> to flow directly to the brine line <NUM>. Only, when the liquid leaving the membrane units <NUM>, <NUM>, <NUM> of the second stage <NUM> is clean enough, the fourth dump valve <NUM> is closed and the liquid is used to operate the second pump <NUM> as motor.

Claim 1:
Reverse osmosis arrangement (<NUM>) comprising a membrane unit (<NUM>) having a housing (<NUM>) and a membrane (<NUM>) separating a first chamber (<NUM>) and a second chamber (<NUM>) in the housing (<NUM>), the first chamber (<NUM>) having a first port (<NUM>) and a second port (<NUM>) and the second chamber (<NUM>) being connected to a permeate outlet (<NUM>), wherein the first port (<NUM>) is connected to a first pump (<NUM> and the second port (<NUM>) is connected to a second pump (<NUM>), characterized in that the first pump (<NUM>) is operatively connected to a first reversible electric machine (<NUM>) which can be operated in a motor mode and in a generator mode and the second pump (<NUM>) is connected to a second reversible electric machine (<NUM>) which can be operated in a motor mode and in a generator mode, wherein the first pump (<NUM>) can be operated as hydraulic motor driving the first electric machine (<NUM>) and the second pump (<NUM>) can be operated as hydraulic motor driving the second electric machine (<NUM>).