FR2733698A1 - LIQUID-OPERATING PRESSURE DEVICE FOR A DESALINATION PLANT OF SEA WATER OR BRINE WATER - Google Patents

Abstract

A fluid-actuated pressurisation device particularly for a sea water or briny water desalination plant using reverse osmosis is described, as well as a sea water desalination plant using reverse osmosis and provided with at least one such device. A water pressurisation device for a water treatment plant has at least one pressurisation chamber (12 or 32) in which a pressurising piston (13 or 33) slides, and an actuating chamber (14 or 34) in which an actuating piston (15 or 35), coupled to the pressurising piston (13 or 33), slides. The piston assembly (13, 15 or 33, 35) is capable of sliding between a position where the pressurisation chamber (12 or 32) is emptied, and a position where said chamber (12 or 32) is filled, the actuating chamber (14 or 34) having a larger base area than that of the pressurisation chamber (12 or 32). The device is characterised in that the actuating piston is ballast-loaded so that a pressure is exerted on the actuating piston to move the piston assembly to the position where the pressurisation chamber (12 or 32) is emptied, and in that it has a controllable return means to urge back the piston assembly to the position where the pressurisation chamber (12 or 32) is filled.

Description

 The invention relates to a pressurizing device with liquid actuation for a seawater or brackish water desalination installation by reverse osmosis, as well as a seawater desalination installation by reverse osmosis comprising at least such a device.

 Desalination of seawater or brackish water is conventionally carried out by two types of process. distillation processes and membrane processes.

 In all cases, these processes consume a lot of energy.

 In particular, in reverse osmosis desalination plants, a volume of salt water is subjected to high pressure in a filtration chamber equipped with a semi-permeable membrane. The salts are retained by the membrane, so that the water passing through the membrane is purified. Below the membrane remains a concentrated salt solution, which is intended to be rejected.

 To ensure operation, it is necessary to bring the water to be desalinated to a high pressure upstream of the membrane. This high pressure is generally obtained by means of a high pressure pump whose energy consumption is high.

 One of the aims of the invention is to propose a device for pressurizing seawater or brackish water for a seawater desalination installation, which makes it possible to reduce the energy consumption necessary for operation. of the installation.

 To this end, the pressurizing device according to the invention for a seawater desalination installation by reverse osmosis, installation comprising a pre-treated seawater or brackish water reservoir to be desalinated supplying by a leads a reverse osmosis desalination filter assembly connected to a fresh water storage tank and a supersalted water storage tank, is characterized in that it comprises a pressurizing chamber of cylindrical shape of revolution or another, one end of which opens onto a section of the supply duct controlled by two valves, and in which slides a pressurizing piston, and a cylindrical or other actuating chamber communicating at one end with the atmosphere, and in which slides an actuating piston, the actuating piston being integral with the pressurizing piston, this set of pistons being capable of sliding between a position emptying the ch amber pressurizing and a position filling the pressurizing chamber, the actuating chamber having a base surface greater than that of the pressurizing chamber, and by the fact that the actuating chamber is surmounted by '' a column of liquid so that a liquid pressure is permanently exerted on the actuating piston in order to bring all the pistons to their position emptying the pressurization chamber, the actuating piston comprising a return means which can be controlled to return all of the pistons to the position filling the pressurization chamber.

 Preferably, the entire installation is immersed in a liquid, and preferably also, the actuation chamber, the pressurization chamber and the part of the conduit connecting the pressurization chamber to the filter assembly. by reverse osmosis are placed vertically in line with one another.

 The return means of the actuating piston is advantageously an air tank called "ballast" with variable pressure connected to the actuating piston and immersed.

 For example, the ballast can be connected by a first conduit to a source of compressed air or gas and by a second conduit to the external atmosphere, these conduits being controlled by filling and expansion valves.

 The opening and closing of the upstream and downstream valves of the supply conduit and of the ballast filling and expansion valves are advantageously controlled by a programmable controller.

 The device also makes it possible to recover part of the energy used by placing an expansion turbine on the conduit connecting the desalination filter assembly and the reservoir of brine, so as to improve the yield.

 A seawater or brackish water desalination installation according to the invention advantageously comprises at least one pressurizing device according to the invention.

 Advantageously, the installation comprises several filtration modules each equipped with a filter assembly and with a pressurization device according to the invention, the ballasts being supplied in series by the same source of air or compressed gas for a successive operation of the devices.

The invention will be better understood on reading the following description of an exemplary embodiment made with reference to the accompanying drawings among which
Figure 1 is a schematic view of a seawater or brackish water desalination plant comprising a pressurizing device according to the invention, in an intermediate position of a set of pistons being filled d '' a pressurization chamber
Figure 2 is a view similar to Figure 1 in a position of the piston assembly filling the pressurization chamber; and
Figure 3 is a view similar to Figure 1 in a position of the piston assembly emptying the pressurization chamber.

 The figures schematically represent an example of an installation for desalinating seawater or brackish water by reverse osmosis equipped with a pressurizing device with liquid actuation according to the invention.

 This installation includes a reservoir 1 of seawater or brackish water pre-treated to desalinate, which is connected by a supply duct 2 to a filtering assembly for reverse osmosis desalination 3, itself connected by a duct 4 to a fresh water storage tank 5 and via a conduit 6 to a supersalted water storage tank 7.

 On a section 8 of the supply conduit between two valves called upstream control valve 9 and downstream control valve 10 is connected a pressurizing device 11 according to the invention.

 This pressurizing device 11 comprises a pressurizing chamber 12 of cylindrical shape of revolution or other, arranged vertically, which opens by one end on the section 8 of the supply conduit 2 between the valves 9 and 10, and in which a pressurizing piston 13 is capable of sliding between a low position emptying the chamber 12 and a high position filling the chamber 12.

 The pressurizing device 11 also comprises a second chamber called the actuating chamber 14, also of cylindrical shape of revolution or the like, of the same height as the pressurizing chamber 12, arranged vertically above the pressurizing chamber. 12 and in the extension of the latter, and in which an actuating piston 15 is capable of sliding between a low position against lower stops 16 near the bottom of the actuating chamber 14 and a high position against upper stops 17.

 The actuating chamber 14 communicates by its bottom with the external atmosphere by means of a connecting duct 18.

 The pressurizing piston 13 and the actuating piston 15 are rigidly secured to one another by a connecting rod 19, which passes through the bottom of the actuating chamber through an orifice 20.

 Furthermore, as mentioned above, the pressurization chamber 12 and the actuation chamber 14 are of the same height.

 Thus, the set of pistons 13,15 formed by the two pistons connected by the rod 19 is movable between two extreme positions, a high position filling the pressurizing chamber 12 and a low position emptying the pressurizing chamber 12 .

 The part of the supply duct 2 connecting the pressurization chamber 12 to the reverse osmosis filter assembly 3, the pressurization chamber 12 itself and the actuation chamber 14 are placed in the extension l one from the other and vertically, so as to limit as much as possible the pressure drops and the lateral forces during operation.

The surface of the actuating piston 15 is greater than the surface of the pressurizing piston 13. More precisely, the ratio of the base surfaces of the pressurizing 1 and actuating chambers 14, and therefore of the corresponding pistons respectively 13 and 15, is calculated such that when a given pressure is exerted on the actuating piston 15, this pressure is multiplied by the pressurizing piston 13 according to the formula
P2 = P1 x (S2 / S1) where S1 is the surface of the actuating piston 15,
P1 is the pressure exerted on this piston,
S2 is the surface of the pressurizing piston 13,
P2 is the pressure exerted by this piston on the salt water to be desalted in the pressurization chamber 12, so as to obtain the desired salt water pressure in the pressurization chamber 12 and at the inlet of the reverse osmosis filter assembly 3.

 For example, when the chambers 12 and 14 are cylinders of revolution, the pressure ratio is proportional to the square of the diameter ratio.

 The reverse osmosis filter assembly 3 and the pressurizing device 11 are, in the example shown, immersed in a volume of liquid 21, for example water, so that pressure is exerted in permanently by the liquid on the actuating piston 15, this pressure tending to bring the piston 15 against the bottom 16 of the actuating chamber 14, and therefore to actuate the pressurizing piston 13 downwards so as to empty the pressurization chamber 12.

 Alternatively, the actuating piston 15 could be surmounted by a column of water or liquid.

 The value of the pressure exerted by the liquid on the actuating piston 15 is a function of the height of the column of liquid above the actuating piston 15.

 The actuating piston 15 further comprises a return means constituted by an air tank called ballast 22 at variable pressure fixed to the piston 15 for example by cables 23 while also being submerged. The ballast 22 is connected by a filling conduit 24 to a source of compressed air 25 and by an expansion conduit 26 to the external atmosphere, the conduits 24 and 26 being controlled by filling 27 and expansion valves 28.

The operation of the device is as follows (we can follow an operating cycle in Figures 1 to 3, the open valves being colored in black)
In a first step, the downstream valve 10 of the supply conduit 2 is closed, and the upstream valve 9 open. The filling valve 27 is opened so as to fill the ballast 22 with pressurized air. This rises, driving the set of pistons 13,15, which causes the progressive filling of the pressurization chamber 12 with salt water to be desalted coming from the salt water tank 1 (FIG. 1 ).

 This step continues until reaching the upper end position of the piston assembly 13,15, which corresponds to the maximum filling of the pressurization chamber 12. The upstream valve 9 of the supply conduit is then closed. 2, as well as the filling valve 27 of the ballast 22 (Figure 2).

 The downstream valve 10 of the supply conduit 2 is then opened, and simultaneously, the expansion valve 28 is opened so as to empty the ballast 22. The pressure exerted by the liquid on the actuating piston 15 causes the lowering of the '' set of pistons 13,15. Due to the ratio of the surfaces of the pistons 13 and 15, this pressure is multiplied, so that the pressure exerted by the pressurizing piston 13 on the seawater to be desalted at the inlet of the filter assembly reverse osmosis 3 reaches the desired level suitable for the proper functioning of this filter assembly 3. The descent of the piston assembly 13,15 continues until the low position emptying the pressurization chamber (Figure 3).

 The device is then ready for a new operating cycle.

 Of course, the different stages of the operating cycle are preferably controlled by a programmable controller (not shown in the figures).

 At the outlet of the reverse osmosis filter assembly 3, fresh water at a low pressure reaches the fresh water storage tank 5 and supersalted water at a high pressure reaches the storage tank d supersalted water 7.

 Advantageously, a turbine 29 can be placed on the pipe 6 of oversalted water, so as to recover part of the energy used and improve the yield.

 A recovery pump 30 can be connected to one and the other of the reservoirs 5, 7 so as to reject the oversalted water by a nozzle 31, and direct the fresh water to a main fresh water tank 32.

 We can also compensate for the pressure increase due to the variation in liquid height above the actuating piston 15 during its movement by having a balancing valve (not shown) between the pressurizing chamber 12 and the reverse osmosis filter assembly 3.

 As a variant, the installation could be composed of several filtration modules each comprising a filter assembly and a pressurization device according to the invention, the ballasts being supplied in series by the same source of air or gas under pressure. Thus, by operating the modules successively, the same volume of air or gas under pressure can effect the recall of the pressurizing device on several modules in succession.

Claims (9)

1. Liquid actuation pressurization device for a seawater or brackish water desalination installation by reverse osmosis, installation comprising a seawater or brackish water reservoir to be desalinated (1) connected by a supply duct (2) to a reverse osmosis desalination filter assembly (3) itself connected to a fresh water storage tank (5) and a supersalted water storage tank (7), characterized by the fact that it comprises a pressurizing chamber (12) of cylindrical shape, one end of which opens onto a section (8) of the supply duct (2) disposed between an upstream valve (9) and a downstream valve (10) and in which slides a pressurizing piston (13) and a cylindrical actuation chamber (14) communicating at one end with the atmosphere, and in which slides an actuation piston (15), the piston actuator (15) being integral with the pressurizing piston (13), this assembly pistons (13,15) being able to slide between a position emptying the pressurization chamber (12) and a position filling the pressurization chamber (12), the actuation chamber (14) being of surface area base higher than that of the pressurizing chamber (12), and by the fact that the actuating chamber (14) is surmounted by a column of liquid so that a liquid pressure is permanently exerted on the actuating piston (15) in order to bring the piston assembly (13,15) to the position emptying the pressurization chamber (12), the actuating piston (15) comprising a return means which can be ordered to return the piston assembly (13,15) to the position filling the pressurization chamber (12). 2. Device according to claim 1, characterized in that it is immersed in a liquid. 3. Device according to any one of claims 1 or 2, characterized in that the actuating chamber (14), the pressurizing chamber (12) and the part of the supply conduit (2) connecting the pressurization chamber (12) to the reverse osmosis filter assembly (3) are placed vertically in line with one another. 4. Device according to any one of claims 1 to 3, characterized in that the return means of the actuating piston is an air tank called ballast (22) with variable pressure fixed to the actuating piston (15 ) and submerged. 5. Device according to claim 4, characterized in that the ballast (22) is connected by a filling duct (24) to a source of pressurized air (25) and by an expansion duct (26) to the exterior atmosphere, these conduits (24, 26) being controlled respectively by a filling valve (27) and an expansion valve (28). 6. Device according to claim 5, characterized in that the opening and closing of the upstream (9) and downstream (10) valves of the supply duct (2) and of the filling (27) and expansion valves ( 28) of the ballast (22) are controlled by a programmable controller. 7. Device according to one of the preceding claims, characterized in that a pressure reduction turbine (29) is arranged on the duct (6) connecting the desalination filter assembly (3) and the reservoir of oversalted water ( 7). 8. Seawater desalination installation characterized in that it comprises at least one reverse osmosis module equipped with a pressurization device according to any one of claims 1 to 7. 9. Installation according to claim 8, characterized in that it comprises several reverse osmosis modules each equipped with a filter assembly and a pressurizing device according to any one of claims 1 to 7, the ballasts being supplied in series by the same source of compressed air or gas.