GB2037612A - Energy-transfer device for bleeding a stream of medium from a high pressure processor - Google Patents

Abstract

A device for bleeding a stream m1 of medium from a high pressure processor (1), in which medium m1 is under pressure pH, into a low pressure space (2 and/or 3) at pressure pN and returning a stream m2 of medium from low pressure space (2 and/or 3) to the processor (1), in which medium m2 undergoes a conversion to medium m1 and, if required, from which processor (1) a third medium is drawn off, e.g., for the desalinification of sea water by reverse osmosis, has a pressure exchanger (4) provided between the processor (1) and the low pressure space (2 and/or 3), having a continuously circulating set of power-driven cell compartments (5) interconnected for movement between the processor and the lower pressure space with which the cell compartments communicate, to release the medium m2 and take in the medium m1 at the processor, and to release the medium m1 and take in the medium m2. The cell compartments are preferably provided with means for separating one medium from the other and of a hydraulic, pneumatic and/or mechanical nature, and preferably incorporated in a rotor with inlets and outlets superimposed in the axial direction, preferably in four pairs at 90 DEG spacings with pairs of respective inlets and outlets diametrically opposed. <IMAGE>

Description

SPECIFICATION Device for bleeding a stream of medium from a high pressure processor This invention relates to a device for bleeding a stream mn of medium from a high pressure processor, in which the medium m1 is under a pressure PH, into a low pressure space at a pressure PN, and returning a stream m2 of medium from a low pressure space at a pressure PN to the high pressure processor, in which high pressure processor the medium m2 undergoes a conversion to the medium m7 and, if required from which high pressure processor a third medium is drawn off. The invention relates more particularly to a device for the desalinification of sea water on the principle of purification by reverse osmosis, medium m, being the concentrate (c.f.R6mpps Chemie-Lexikon, 1975, pp. 3733 and 3734). The process of reverse osmosis is particularly suitable for water treatment (e.g.

effluent purification), and is used on a large scale for the recovery of potable and technical water from sea water and brackish water (see Research Report K 72-27 of the Federal Ministry of Education and Science, Dec 1972, pp. 183 - 208). In general, and obviously in the case of reverse osmosis, the media m, and m2 are incompressible; m1 and m.2 denote their mass flow rates.

In the known practical devices of this type, the stream m2 of medium is returned from the low pressure space to the high pressure processor by means of a pump, while the medium m1 is bled into the low pressure space through a throttle or a turbine. If a turbine is used, it is normally coupled to the pump to ensure energy recovery. Typical efficiency levels for the turbines and the pumps suitable for this purpose lie between 70 and 80%. Thus the turbine-pump combinations function at an overall efficiency level between 49 and 64sub. In other words, more than a third of the energy released by depressurising a stream ml of medium is lost and must be made good by providing a motor.In fact, the static pressure PH of the stream of medium is converted in the turbine-pump system into dynamic pressure, i.e., kinetic energy, which is converted in the turbine into mechanical work and returned to the pump rotor, in which it is converted back to dynamic pressure initially and then converted to static pressure by means of a diffuser. The pumps used are of the centrifugal type. It is further known in principle that displacement pumps can be used for the same purpose, by operating one of them as a hydraulic motor. However, displacement pumps or hydraulic motors are not suitable for the large pressure differences and mass flow rates required.

The object of the invention is to provide a device of the type in question, in which the efficiency losses already referred to no longer arise.

According to the present invention a pressure exchanger is provided between the high pressure processor on the one hand and the low pressure space or spaces on the other hand, having a continuously circulating set of power-driven cell compartments interposed between the high pressure processor and the low pressure space or spaces, the cell compartments being connected as they pass round their circulation path inside a housing on the one hand between the low pressure space or spaces and the high pressure processor, with which the cell compartments communicate, there to release the medium m2 and take in the medium m1, and on the other hand between the high pressure processor and the low pressure space or spaces on the other hand, with which the cell compartments communicate, there to release the medium m1 and take in the medium m2.

The invention arises from the realisation that, when transferring energy from the stream rhi of medium taken from the high pressure processor to the stream m2 of medium, it is disadvantageous or unnecessary to convert the static pressure to dynamic pressure and vice versa orto apply volumetric constraints, provided the two streams rng and tri72 are or can be made of substantially the same magnitude.

If provision must be made to prevent the media m, and m2 from mixing inside the pressure exchanger, this can be effected simply by constructing the cell compartments as separation compartments by fitting them with separating means of a hydraulic, pneumatic and/or mechanical nature. The details of this procedure will emerge when the accompanying drawings are described. The continuously circulating set of power-driven cell compartments interposed between the high pressure processor and the low pressure space or spaces can be connected to a suitably adapted traction system. However, in one preferred embodiment of the invention the continuously circulating set of cell compartments is disposed in a cellular rotor and rotates therewith.

Within the scope of the invention, the cellular rotor can be constructed in various ways. One embodiment of outstanding simplicity and functional reliability has the housing of the cellular rotor provided with inlet and outlet apertures superimposed in the axial direction for connection to the high pressure processor and the low pressure space or spaces. In the simplest case, two parts of inlet and outlet apertures are provided in a diametrically opposed array.In the case of devices in which a substantial pressure difference must be overcome, a preferred embodiment of the invention has four pairs of inlet and outlet apertures distributed round the periphery of the cellular rotor housing, superimposed in the axial di#rection of the cellular rotor and spaced 900 apart, the two pairs of apertures connecting to the high pressure processor and to the low pressure space or spaces respectively being diametrically opposed. This relieves the rotor shaft almost entirely from transverse loads arising from the ruling pressure difference.

The accruing advantages are to be seen in that the devices of the invention are substantially more efficient than the known devices of the type in question. As already indicated, higher efficiency arises from the fact that the devices of the invention no longer require the inefficient conversion of static to dynamic pressure and vice versa. The cellular rotor requires a power drive, but energy is only consumed in overcoming the frictional losses inhe rent in all rotating machinery, and they can be minimised by suitably supporting the rotating parts.

The detailed advantages, the efficiency relationships and the functioning of devices of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a plan of a device in accordance with the invention having cell compartments joined together by traction means; Figure2 is a plan partly in section of a device in accordance with the invention having a cellular rotor; Figure 3 is a fragmentary section taken on the line A-A of Figure 2; Figure 4 shows another embodiment of the invention, in a view similar to Figure 2; Figure 5 is a section taken on the line B-B of Figure 4; Figure 6 shows in full section yet another embodiment of the invention, in a view similar to Figure 2; Figure 7 is a section taken on the line X-X of Figure 6;; Figure 8 is a developed fragmentary section of a device in accordance with the invention having pneumatic separating means to separate the media m1 and m2 in the cell compartments; Figure 9 is a developed fragmentary section of a device in accordance with the invention having mechanical separating means in the cell compartments; Figure 10 is a view similar to Figure 2, with a part broken away, of a device in accordance with the invention having mechanical separating means in the cell compartments:: Figure 11 is a section taken on the line C-C of Figure 10; Figure 12 is a fragmentary view on a larger scale of the portion D of Figure 11; Figure 13 is a similar view to Figure 12 of yet another embodiment of device in accordance with the invention; Figure 14 is a similar view to Figure 2, partly in section, of a device in accordance with the invention integrated with an electric driving motor; and Figure 15 is a section taken on the line E-E of Figure 14.

The devices shown in the Figures are intended for bleeding a stream mi of medium from a high pressure processor 1, in which the medium m1 is under a pressure PH, into a low pressure space 2 at a pressure PN At the same time, the devices are intended for returning a stream m2 of medium from a low pressure space 3 at a pressure PN to the high pressure processor 1. Inside the high pressure processor 1 itself, the medium m2 undergoes a conversion to the medium m1. If required a third medium may be drawn off from the high pressure processor. All the devices may operate on the principle of reverse osmosis, e.g., for the desalinification of seawater, m1 being the concentrate, m2 the untreated water and the third medium to be drawn off being the permeate.For clarity, the drawing off of a third medium is not indicated in any of the Figures.

In Figure 1 a pressure exchanger 4 is provided between the high pressure processor 1 on the one hand and the low pressure spaces 2 and 3 on the other hand. It has a set of power-driven cell compartments 5 continuously circulating between the high pressure processor 1 and the low pressure spaces 2 and 3. The cell compartments 5 are connected as they pass round their circulation path 7 inside a housing 6 between the low pressure spaces 2 and 3 and the high pressure processor 1, with which the cell compartments communicate, on the one hand, there to release the medium m2 and take up the medium m1. Moreover, the cell compartments also communicate with, on the other hand, the low pressure spaces 2 and 3, there to release the medium m1 and take up the medium m2. In the embodiments shown in Figures 1 to 3, no special provision is made to prevent the media m1 and m2 from mixing.In the embodiments shown in Figures 4 to 15, on the other hand, the cell compartments are constructed as separation compartments 5 by fitting them with hydraulic or pneumatic separating means 8a (Figures 4to 8) or mechanical separating means 8b (Figures 9 to 15). The function of these hydraulic or pneumatic separating means 8a and mechanical separating means 8b in the cell compartments 5 will be described in detail later. For the moment, Figure 1 shows that the cell compartments 5, continuously circulating in the manner described, can be joined together by a traction system 9. In the remaining Figures, which show only the equivalents of the pressure exchanger 4 of Figure 1, the continuously circulating cell compartments 5 are disposed in a cellular rotor 10.

In the embodiments having a cellular rotor 10 the housing 6 has inlet and outlet apertures 11, 12 and 13, 14 (see Figure 5) superimposed in the axial direction for connection to the high pressure processor 1 and the low pressure spaces 2 and 3 respectively. The inlet and outlet apertures leading to the high pressure processor are numbered 11 and 12 throughout the Figures. The inlet and outlet apertures leading to the low pressure spaces 2 and 3 are numbered 13 and 14 th roug hout the Figures. Provided the pressure difference between the high pressure processor 1 and the low pressure spaces 2 and 3 is not excessive, the pairs 11,12 and 13, 14 of inlet and outlet apertures can be disposed diametrically opposite each other. However, in this case the shaft 15 of the cellular rotor 10 must take a corresponding radial pressure load. If this must be avoided, the arrangement shown in Figures 6 and 7 should be adopted. It will be seen that four pairs 11, 12 and 13, 14 of inlet and outlet apertures are distributed round the periphery ofthe cellular rotor housing 6, each inlet aperture 11 or 13 being axially adjacent to an outlet aperture 12 or 14. The pairs of apertures 11,12, 13 and 14 are spaced 90" apart, the two pairs 11, 12 of apertures connecting to the high pressure processor 1 and the two pairs 13, 14 of apertures connecting to the low pressure spaces 2 and 3 being diametrically opposed.

The detailed construction and functioning of the devices and parts thereof shown in the Figures can be described as follows.

Figure 1 illustrates the basic principle. It will be seen that the spaces at pressures PH and PN are connected to each other by two cylinders of the same cylindrical diameter, which form the housing 6 and in which move a plurality of pistons 17 connected together by the aforementioned traction means 9. The cell compartments 5 are formed between successive pistons 17. The pressure difference (PH - PN) over all the pistons 17 in each cylinder 16 is the same. Hence the torque on the rollers 18 in the traction system 9, round which the pistons 17 rotate, is zero.Hence a driving torque sufficient to overcome the friction forces alone will suffice to exchange the streams rh1 and m2 between PH and PN A simpler arrangement is obtained by using a cellular rotor 10, various forms of which are illustrated in Figures 2 to 15. The cellular rotor 10 is simply a rotor fitted with blades 19 and mounted to rotate in a housing 6 so that the blades 19 form a plurality of cell compartments 5 with minimum sealing gaps.When the rotor is driven as described, the streams rhi and rh2 are interchanged between the spaces at pressures PH and PN without having to convert the static pressure or its equivalent energy into any other form of energy. Leakages between the successive cell compartments 5, assuming equal sealing gaps, allow the pressures to vary linearly, decreasing from PH to PN in tri71 and increasing from PN to PH in m2. Under these conditions, assuming equal blade areas, the force on each blade in the path of m1 is balanced by an equal force on a blade in the path of m2.

However, the devices shown in both Figure 1 and Figures 2 and 3 still have one disadvantage. The fluids m1 and m2 undergo mixing in the two spaces at pressures PH and PN Although this disadvantage does not entirely preclude the bleeding of fluid m1 and its replacement by fluid m2, mixing can lead to intolerable problems in many technical processes.

Accordingly, the invention further teaches that the fluids m1 and m2 can be kept separate.

Figures 4 and 5 show one possibility. The cell compartments 5 are made long and slender. The admission and removal of tri71 and m2 take place at fourapertures, 11,12 and 13,14(2 each at p# and pin), as nearly as possible at right angles to the rotary movement of the cell compartments 5. The slender form minimises mixing between ml and m2, provided the two fluids are admitted and removed simultaneously as the cell compartments 5 pass through the apertures 11, 12 and 13, 14. Mixing can be further reduced by mounting honeycomb partitions in the cell compartments 5 to form numerous slender parallel channels.The motor speed must be matched to the entry and exit velocity so that each cell compartment 5 reaches the limits of the inlet and outlet apertures 11. 12 and 13, 14 exactly when the plane of separation between m, and m2 reaches the blade end.

In the embodiment shown in Figure 5, each pair of apertures 11, 12 at pressure PH is set opposite a pair of apertures 13, 14 at pressure PN This places very high bearing forces on the rotor mounting, at right angles to the axis of rotation. The bearing forces can be reduced to zero by providing two opposing pairs of apertures 13, 14 at PN and two opposing pairs of apertures 11, 12 at PH In this case, the pressure of m for example falls from PH to PN over 90O rather than over 180 .

Figures 6 and 7 show this arrangement, together with a preferred form of the cell compartments 5 as long, slender, tubular spaces with the inlet and outlet apertures side by side.

Figure 8 shows another possible way of keeping m1 and m2 separate, using air or some other suitable substance as the separating medium.

In Figure 9, a bladed ring 20 rotates past the outlet and inlet apertures 11, 12 and 13, 14, synchronously with the rotor carrying the cell compartments 5. The blades 20 keep m1 and m2 separate.

A preferred embodiment of the device is shown in Figures 10 and 11. For clarity, only two pairs of outlet and inlet apertures 11, 12 and 13, 14 are shown. Each cell compartment 5 contains a piston or a membrane 21 or a similar known separator, free to move easily from one end of the cell compartment 5 to the other.

When the cell compartment 5 passes across the indicated apertures 11, 12, for example, tri7, is fed into the compartment under a small pressure difference (set up by a pump in the tri71 delivery line), and m2 is displaced until the separator 21 (the sealing piston for example) reaches a stop 22 at the end of the cell compartment 5. With this preferred arrangement, there is virtually no mixing between the medium streams ml and m2. Sealing between the cell compartments 5 is improved by mounting the cell compartments 5 between two concentric rings 23 in which labyrinth seals or the like are machined.The blades 19 between the cell compartments 5 are broadened in the two sealing planes, so that efficient sealing members can also be accommodated there. The residual leakage currents only lead to a reduction in the efficiency of the pressure exchanger, without causing the two streams to mix. For the same reason, the cell compartments 5 must not empty completely. If for example (referring to Figures 10 and 11) a residue of m2 remains in a cell compartment 5, because the separating piston 21 does not travel to the end of the cell compartment 5, this residue of m2 is merely retracted at a different pressure, without mixing with m1.

Since the frictional forces and leakage streams in devices of the invention are virtually independent of the constructional height of the compartments, such residues can be simply compensated by a slight increase in the constructional height.

Figure 12 shows an enlarged view of a piston 21 used as the sealing means in a cell compartment 5, at the top end position. The same Figure shows the labyrinthine sealing face 24 of a blade 19.

Figure 13 shows, in schematic outline, the use of a sealing membrane 21 of resilient material, again at the top end position. To support it, the end covey of the cell compartment is constructed as a perforated plate 25.

Figures 14 and 15 show the passage of the cell compartments 5 through an emptying/filling station.

The fluid m2 is admitted and m, removed (or vice versa). Another special form for the pressure exchanger is also depicted. The angle of admission and removal is determined in conformity with the rotary speed of the cell compartments 5 and the filling speed of stream m2 (by the addition of velocity vectors).

The preferred embodiment shown in Figure 15 completely avoids external moving seals. The rotor set with the blades 19 is contained in a housing 6 which is closed on all sides. The preferred method of driving the rotor to overcome the frictional force is by means of an electromagnetic system. The rotor set with the blades 19 forms the motor rotor; the statorwindings 26 are disposed on the outside of the housing 6.

When the pressure difference (pH - PN) is very high, major constructional difficulties may arise from the large number of blades (large number of sealing gaps) which are required, and the correspondingly large rotor diameter. In this connection, it is within the scope of the invention to provide two or more pressure exchangers connected in series, each operating over a fraction of the difference (pH - p#). The rotors of these pressure exchangers are preferably mounted on a common shaft 15. The transfers of streams, and m2 are preferably effected with the aid of an additional pump in each stage. When there are two or more pressure exchangers on a common shaft 15, it is no longer necessary to provide four pairs of apertures to relieve the rotor bearings of the loads, since the bearing forces in the individual rotors cancel each other out.

It is also within the scope of the invention to mount two or more pressure exchangers on a common shaft 15 but to operate them in parallel so that each takes a fraction of the required medium flow rate.

Claims (6)

1. A device for bleeding a streams1 of medium from a high pressure processor, in which the medium m1 is under a pressure PH, into a low pressure space at a pressure PN and returning a streams of medium from a low pressure space at a pressure PN to the high pressure processor, in which high pressure processor the medium m2 undergoes a conversion to the medium m1 and, if required, from which high pressure processor a third medium is drawn off, a pressure exchanger being provided between the high pressure processor on the one hand and the low pressure space or spaces on the other hand, having a continuously circulating set of power-driven cell compartments interposed between the high pressure processor and the low pressure space or spaces, the cell compartments being connected as they pass round their circulation path inside a housing, on the one hand between the low pressure space or spaces and the high pressure processor, with which the cell compartments communicate, there to release the medium m2 and take in the medium m1, and on the other hand between the high pressure processor and the low pressure space or spaces, with which the cell compartments communicate, there to release the medium m, and take in the medium m2.

2. A device as in Claim 1, wherein the cell compartments are constructed as separation compartments by providing them with separating means of a hydraulic, pneumatic and/or mechanical nature.

3. A device as in either of Claims 1 and 2, wherein the continuously circulating set of cell compartments is disposed in a cellular rotor.

4. A device as in Claim 3, wherein the housing of the cellular rotor has inlet and outlet apertures superimposed in the axial direction for connection to the hiah pressure processor and the low pressure space or spaces.

5. A device as in Claim 4, wherein four pairs of inlet and outlet apertures are distributed round the periphery of the cellular rotor housing, at 90 spacings, the two pairs of apertures connecting to the high pressure processor and to the low pressure space or spaces respectively being diametrically opposed.

6. A device for bleeding a stream of medium from a high pressure processor substantially as hereinbefore described with reference to any of Figures 1; 2and3; 4and 5; 6 and7; 10 and 11; 14 and 15; oras modified in accordance with Figures8 and 9 or Figures 12 and 13 of the accompanying drawings.