GB2564662A

GB2564662A - Vacuum and degassing system

Info

Publication number: GB2564662A
Application number: GB1711513.0A
Authority: GB
Inventors: Olof Sonander Sven
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-07-18
Filing date: 2017-07-18
Publication date: 2019-01-23
Anticipated expiration: 2037-07-18
Also published as: GB201711513D0; GB2564662B

Abstract

An apparatus 1 for degassing water comprises: first and second degassing chambers 2, 4 each provided with a valved vent 6, 8 at the top of the respective chamber; at least one of the degassing chambers is/are provided with a valved inlet 40, 38 for incoming water; at least one of the degassing chambers is/are provided with a valved outlet for degassed water; and a transfer pipe 30 directly connects the degassing chambers to transfer water between the chambers. The transfer pipe includes a first pump 32 for transferring water from the first degassing chamber to the second, and a second pump 34 for transferring water from the second degassing chamber to the first. Each pump permits water flow therethrough when de-energised. The pumps can be centrifugal or turbine pumps. The apparatus may comprise a pressure sensor in each of the degassing chambers to measure pressure in the headspace above the water. Each of the degassing chambers may include a vacuum inlet 26, 27, for connection to a system to be evacuated. The apparatus may be provided as part of a desalination apparatus, used to degas salt water prior to a desalination process.

Description

Vacuum and Degassing System

Field of the Invention

The present invention relates to water degassing and vacuum pump apparatus for water purification processes, and more particularly to methods and apparatus for water desalination, with improved efficiency.

Background to the Invention

Many areas of the world do not have sufficient water to satisfy the population's needs to survive. If these areas suffer the consequences of drought then many people will die through lack of water or by drinking contaminated water:

Technology to purify salt or brackish water has been developed. Distillation techniques are well known.

In WO 2005/082784 the inventor, of the apparatus and methods described herein, describes methods and apparatus for desalinating salt water, including means for degassing salt water to allow efficient vaporization of salt water and the subsequent condensation of the vapour to produce fresh water. The entire content of WO 2005/082784 is incorporated herein by reference.

The desalination procedure of W02005/082784 can be described as isothermal gasfree water distillation, where salt-water is distilled to produce fresh water. For the purposes of convenience and conciseness, references to the term gas-free are intended to indicate water, or a volume of space, substantially free of gas other than water vapour and similar expressions are intended to be construed correspondingly.

Similarly It will be appreciated that the method and apparatus of the invention described herein may be used to assist in obtaining fresh-water from any convenient source of water containing dissolved solids, including, for example, sea-water, brackish water, water from salt-marshes, fresh-water contaminated with chemicals such as fertilisers, etc and all such sources are intended contemplated herein.

Although known apparatus and methods can provide means for desalinating water, there remains the desire to provide yet further improved apparatus and methods for water purification.

Description of the Invention

The present invention provides an apparatus for use in the degassing of water, which apparatus comprises:

first and second degassing chambers each provided with a valved vent at the top of the respective chamber;

at least one of said degassing chambers being provided with a valved inlet for connection to an incoming water supply;

at least one of said degassing chambers being provided with a valved outlet for degassed water;

a transfer pipe directly connecting between the two degassing chambers, configured for transfer of water there between and including:

a first pump configured for transferring water from the first degassing chamber to the second; and a second pump configured for transferring water from the second degassing chamber to the first, wherein the first and second pumps are each configured to permit flow of water there through when de-energised.

Both of the first and second pumps are configured to permit water to flow through them when de-energised i.e. when the pump is no longer being supplied with energy to power the pumping action. Typically this will be when electricity supply to a pump motor is turned off. As described in more detail hereafter, this allows the first and second pumps to be used in methods of degassing and vacuum pumping that have a reduced requirement for pipework and valve fittings in comparison with other arrangements.

A de-energised centrifugal pump can permit flow when de-energised, including in the direction contrary to its pumping action. Centrifugal pumps are generally robust and inexpensive. Other types of pump that may be employed include, for example turbine pumps that allow flow of water there through when de-energised. Centrifugal pumps also have the advantage that they only pump in one direction when energised. Other pumps that may be employed in the apparatus can be controlled to pump only in one desired direction when energised.

The apparatus may be provided as part of a desalination apparatus, used to degas salt water prior to a desalination process. In which case, the valved inlet connects to a supply of salt water. For example a desalination apparatus making use of an isothermal gas-free water distillation as described in W02005/082784. Alternatively degassed salt water may be prepared for supply to other desalination apparatus. For example, a multi-effect distillation apparatus such as is commonly used in desalination.

More generally the apparatus for degassing water may be used to degas any water supply that is going to be further processed, for example purified by a distillation procedure.

As described herein the apparatus may also be employed as a vacuum pump. In which case, at least one of the first and second degassing chambers further includes a vacuum inlet, for connection to a system to be evacuated. Each degassing chamber may have a vacuum inlet, for connection to a system to be evacuated.

Thus according to a second aspect the present invention provides an apparatus for use as a vacuum pump and/or in the degassing of water, which apparatus comprises:

at least one of said degassing chambers being provided with a vacuum inlet for connection to a system to be evacuated;

a first pump configured for transferring water from the first degassing chamber to the second; and a second pump configured for transferring water from the second degassing chamber to the first wherein the first and second pumps are each configured to permit flow of water there through when de-energised.

The first and second pumps can be centrifugal or turbine pumps or any other type of pump that permits water flow through when de-energised.

A vacuum inlet for connection to a system to be evacuated will typically be a valved inlet, to allow connection and disconnection, but the system, such as a desalination apparatus which makes use of the apparatus as a vacuum pump and/or a degassing apparatus, may itself have valve arrangements, fitted to apply and then disconnect from the vacuum provided.

In apparatus according to either of the above aspects of the invention the transfer pipe is configured for transfer of water there between. Therefore the connections to each of the degassing chambers are toward the bottom or even at the bottom of each degassing chamber, to allow emptying of the chambers to the extent desired. The transfer pipe connecting the two degassing chambers does so directly, i.e. the transfer pipe connects the two degassing chambers, with the first and second pumps in-line, without there being, in normal operation, any intervening openings to atmosphere such as tanks open to atmosphere or atmospheric pressure. The first and second pumps will typically be located lower than the bottoms of the degassing chambers to provide a head of water to the pumps at most times in normal operation.

There are two pumps for transferring water and fitted in the transfer pipe. These pump water in opposite directions; from the first degassing chamber to the second; and vice versa. For transfer of water from one degassing chamber to the other one pump will normally be in operation whilst the other is de-energised. This arrangement does not require piping to by-pass whichever pump is de-energised, as the de-energised pump can permit flow when de-energised, including in the direction contrary to its pumping action. Typically each of the first and second pumps is configured to pump water (when running) towards the other, however the opposite configuration, where each pumps water in the direction away from the other can also serve.

It is convenient that one valved inlet is provided for connection to an incoming water supply and it connects to both first and second degassing chambers. For example, by connecting to the two degassing chambers via the transfer pipe. Connection can conveniently be to the pipe at a location between the first and second pumps that direct water in either direction. Thus water can be directed to both degassing chambers, or optionally, to either, if suitable valves are provided to control flow and/or by use of the first or second pumps. It may be convenient to use a further pump or pumps to transfer water from the water supply into the degassing chambers.

Similarly it is convenient for the valved outlet for degassed water to be connected to the transfer pipe. More conveniently at a location between the first and second pumps that direct water in either direction. The degassed water can be pumped via the valved outlet from one or both of the degassing chambers by making use of the first and/or second pumps. Even when a degassing chamber is filled with degassed water, or contains a vacuum in the headspace above degassed water, pumping from the outlet, even to a location at atmospheric pressure can be achieved. A head of water of say about 1.2m or more above a pump such as a centrifugal or turbine pump can allow pumping against the resistance of the vacuum. Even more conveniently, where economy in construction cost and simplicity of operation is desired, the valved inlet for connection to an incoming water supply and the valved outlet for degassed water both connect to a single branch pipe that connects into the transfer pipe at a location between the first and second pumps.

Feed from the water supply, such as a salt water supply, may be by a further pump, for example a centrifugal pump. Discharge via the valved outlet for degassed water may make use of one or both of the first and second pumps of the transfer pipe. Alternatively another separate pump may be provided, for example a centrifugal pump. As a yet further alternative transfer via the valved outlet may be achieved, at least partially, by vacuum applied from a downstream apparatus such as a desalination apparatus that operated under vacuum.

The two degassing chambers may be located at different heights and may be of different sizes, but for convenience in manufacture and operation they are generally located at the same level in a side by side relationship (have bases at substantially the same vertical height) and are of the same size and construction.

The first and second degassing chambers are each provided with a valved vent at the top of the respective chamber. These vents allow the discharge of gas (air) as the respective degassing chamber is being filled with water and also to allow discharge of gas evolved from water during the degassing procedures described hereafter. The valves employed may be non-return valves operating, typically automatically, to discharge gas but not to allow the ingress of air from atmosphere. The non-return valve arrangements may be of any suitable known type.

In one arrangement the apparatus may make use of a non-return system making use of gravity atmospheric pressure. A vent pipe from the top of each degassing chamber connects, openly into a reservoir of water located at a height lower than the bottoms of the degassing chambers. For example at about 10m lower, the approximate height of a water column supported by atmospheric pressure. The first and second pumps may advantageously be located at about 10m or lower below he bottoms of the degassing chambers. This provides a head pressure of water within the pump, convenient where a leak occurs, as it prevents ingress of air. This liquid trap arrangement can act as a non-return valve to allow gasses to bubble through the water in the reservoir but at the same time act as a barrier against air returning from atmosphere. However more conventional non-return valves can allow the use of an apparatus of relatively low height, convenient where construction at a height is expensive.

It may also be convenient to employ at least one, or even both, of the valved vents as a connection for a vacuum inlet when the apparatus is to be employed as a vacuum pump according to the second aspect of the invention.

Although the degassing apparatus may also include further valves and pipe connections in addition to those described above, advantageously the apparatus includes the minimum number of such items i.e. as far as valves and pipe connections are concerned the apparatus only has those described in the paragraph above.

Although more than two degassing chambers could be employed, it is preferred that only two are provided for use in the degassing and vacuum pump methods described hereafter.

As far as the pipes fitted are concerned, it is preferred that they have the minimum number of connecting joints and/or joints are welded, as far as practicable.

Operation of the apparatus according to the first or second aspects of the invention may be essentially manual. The provision of various sensors can enable more efficient manual operation or even semi-automatic or automatic operation if desired. Semiautomatic or automatic operation can make use of a control system connecting between sensors, valves and pumps.

A flow meter may be fitted to the transfer pipe to determine direction and amount of flow. Additional flow meters may be fitted elsewhere if desired.

Conveniently both degassing chambers may each have pressure sensors to measure pressure (vacuum) in the headspace above water within. Similarly both degassing chambers may each have pressure sensors to measure water pressure within, typically located near the bottom of the respective chamber. These can be used to determine water loading in the degassing chambers. The pressure differential between top (headspace) and bottom (water pressure) sensors in the chambers can serve to provide data to a control system, confirming the depth of water. Other means such as load cells may be employed. Temperature sensors may detect water temperature in the degassing chambers.

Conveniently a water detector may be provided at the valved vent of each degassing chamber, to detect when the respective degassing chamber is filled with water. A simple sight glass can be employed to show the presence of liquid water, but an electronic system can be more convenient, especially if an automatic or semi-automatic control system is employed. The first and second pumps may have sensors to detect loading on their motors.

Valves may be motorised and/or be provided with visual or electronic indicators of status (open or closed).

The apparatus described above according to either of the first two aspects of the invention is particularly useful in producing degassed salt water for use in the desalination procedures described in the inventor’s previous application W02005/082784 (patents US7811420 and EP1716082 ) as it contains few valves and pipe connections, reducing the possibility of leakage when the degassing chambers are “under vacuum” i.e. contain degassed salt water with substantially all gases removed, apart from water vapour, in any space above the body of degassed salt water. However any use of degassed water, can be contemplated.

The apparatus can be used in a method of degassing water comprising: introducing water into both of the first and second degassing chambers with a volume of gas above the water; isolating one said chamber from the atmosphere; transferring water from said one chamber to the other so as to reduce the pressure in said one chamber thereby inducing the release of dissolved gas therefrom, and expelling gas above the water in said other chamber out of said other chamber; isolating the other said chamber from the atmosphere, and reversing the direction of water transfer so as to induce the release of dissolved gas from the water in said other chamber and expelling gas above the water in said one chamber.

These steps can be accomplished by using the apparatus of the invention even where only the minimum number of valves and pipe connections are provided, as described above.

Water (e.g., salt water) is introduced via the valved inlet into at least one of the two degassing chambers, which has its valved vent open to allow corresponding escape of air as the water fills the chamber. The other chamber of the two can also be filled to a desired level with incoming water at the same time, either by making use of the transfer pipe and appropriate one of the first and second pumps or directly where one valved inlet is provided for connection to an incoming water supply and it connects to both first and second degassing chambers. When being filled the valved vent on the second chamber is opened to allow displacement of air.

Once the desired level of water in the two chambers is reached the salt water inlet valve is closed. Transfer of salt water between the chambers using one of the first and second pumps is instigated (in either direction), with the valved vent at the top of the degassing chamber being emptied set to closed, inducing release of dissolved gas. At the same time the valved vent on the chamber being filled is open to allow expulsion of gas by the incoming water. The vent valve of the chamber being filled will be opened at the point when the pressure above the water exceeds atmospheric pressure. When the water in the chamber being filled reaches a desired level e.g. up to the valve of its valved vent, that vent valve is closed. Transfer back in the opposite direction is commenced by reversing the pumping direction, making use of the other pump of the two, and the valved vent on the chamber now being filled is opened to allow expulsion of gas from the system. The space formed above the water in the chamber being emptied is then filled with gas and water vapour released from the salt water.

It will be appreciated that the water transfer steps may be repeated as many times as required, in order to achieve a desired degree of degassing. Typically though, the water in each chamber would be subjected to at least two degassing steps, preferably from 2 to 4 steps. The process may continue to provide gas-free water, and a gas-free headspace above the water, as defined in the section above headed Background to the Invention.

In general the desired water level in the degassing chambers, when both are equally filled, will be such that a substantial amount of water inside the chambers can be effectively degassed, there being a sufficient volume above the desired level to accommodate gas released from the water.

Typically the desired water level would correspond to from 50 to 90% of the chamber volume, preferably from 60 to 80% of the chamber volume. Lower or higher fill levels can be employed but may be less efficient at achieving the desired results.

After degassing the water to the desired extent it can be transferred via the valved outlet for degassed water for further processing, e.g. to a desalination plant.

When provided with a vacuum inlet in accordance with an apparatus according to the second aspect of the invention, the apparatus can still operate to degas water. Alternatively or additionally the apparatus can operate to create or increase a vacuum in another apparatus, such as an isothermal gas-free water distillation apparatus or other desalination apparatus that makes use of reduced (below atmospheric) pressures.

As described above, water can be introduced into the degassing chambers via the valved inlet. As the transfer back and forth between the two degassing chambers proceeds the chambers have a headspace above the liquid water that is at increasingly reduced pressure i.e. the apparatus produces a vacuum as water is transferred from one degassing chamber to the other.

Connection of a system to a vacuum inlet of one of the degassing chambers when it has a vacuum within, will result in a vacuum being applied to that system. A vacuum will be present in a degassing chamber when water is being transferred from it, or after completion of a degassing operation and the degassing chamber has a headspace above the degassed water. When the degassing chamber is being filled with water again the vacuum inlet can be closed. If both degassing chambers have a vacuum inlet then connection to the system to be evacuated can alternate: from one inlet to the other as dictated by the direction of water transfer.

This vacuum pumping action can be applied as art of the start-up procedure for an apparatus, such as a distillation apparatus for desalination. Alternatively initial vacuum may be obtained by conventional pump and the apparatus of the invention used for maintenance of vacuum during distillation. When used at start up the pumping action can continue until the desired vacuum is reached and then be used as required to maintain the desired vacuum (within the desired operational range).

For example when used with an isothermal gas-free water distillation apparatus the vacuum pump function may be applied intermittently, as and when the pressure within the isothermal gas-free water distillation apparatus rises towards an undesired level.

There are advantages in use of the apparatus as a vacuum pump when connected to a distillation system for water. When connected as a vacuum pump to a mixture of water vapour and other gases (e.g. air) the water vapour will tend to condense in the low pressure (vacuum) that is present in the headspace of the degassing chamber, leaving the non-condensable gases in the headspace above the water. The extent of condensation will be dependent on temperature and pressure conditions.

The condensation effect can be particularly effective when used to reduce pressure in an environment containing warmer water vapour than the temperature of the degassing chambers, such as may be found vacuum distillation equipment. The higher vapour pressure over the warmer water in the distillation equipment drives water vapour and non-condensable gases into a degassing chamber having a vacuum in the headspace, even when water is not being transferred from one chamber to the other. Condensation can occur, lowering the pressure and tending to maintain the flow from the distillation equipment. This process results in a collection and concentration of non-condensable gases in the degassing chamber,

It is possible to remove non-condensable gasses from vacuum distillation equipment a number of times by this effect alone, without operating the first and second pumps to transfer water between degassing chambers to restore the vacuum.

As the pressure due to non-condensable gasses in the headspace rises further, water transfer operations between the degassing chambers can be resumed so that the accumulated non-condensable gas can be vented to atmosphere. Only at this point in the procedure is the further use of the first and second pumps required, to restore vacuum in the degassing chambers.

This intermittent use of the first and second pumps provides an advantage over the use of conventional vacuum pump arrangements in vacuum distillations. Conventional operations have vacuum pumps running continually throughout a distillation procedure.

A more detailed description of procedures with reference to specific embodiments is given below under the heading Detailed Description of the Invention with Reference to Some Embodiments.

Brief Description of the Drawings

Figure 1 shows an apparatus for degassing water and providing a vacuum; and Figure 2 shows an alternative apparatus for degassing water and providing a vacuum.

Detailed Description of the Invention with Reference to Some Embodiments

Figure 1 shows a schematic of a water degassing apparatus 1 including a vacuum pumping capability. The apparatus 1 includes first and second degassing chambers (cylindrical in this example) 2, 4 each having a respective valved vent 6, 8. In this example the valved vents 6, 8 include a non-return valve 10, 12 which vents the top of chambers 2, 4 to atmosphere via pipe 13. Also included in the venting arrangements at the top of chambers 2, 4 are pressure transducers 14, 16, water detectors 18, 20 and optional further valves 22, 24 which in this example operate selectively to connect to pipes 26, 27 leading to a system to be evacuated, such as a desalination plant that makes use of vacuum. Thus pipe 26 is a vacuum inlet to chambers 2 and 4.

Connecting the bottom of chambers 2, 4 is a transfer pipe 30 with first and second pumps 32, 34 which pump towards each other as suggested by arrows P1 and P2. In this example the pumps 32, 34 are centrifugal pumps. Between the pumps 32, 34 is a bidirectional flow meter 36. Also between pumps 32 and 34 is pipe branch 38 which connects to feed and discharge pipe 40 and includes valves 42, 44 and centrifugal pump 46 for pumping in direction P3. Feed and discharge pipe 40 connects to a source of salt water 48, which may be the sea itself.

In this example chambers 2, 4 are also provided with pressure transducers 50, 52 for determining the load of water 54 in the respective chamber and temperature sensors 56, 58 for determining the temperature of water 54.

In operation starting from the position where degassing chambers 2, 4 are empty, valve 42 is opened and valve 44 is shut. Pump 46 delivers seawater from supply 48 via pipes 40, 38 and transfer pipe 30 to chambers 2, 4 until a desired fill level is reached, typically the total water volume in chambers 2, 4 will be about 1.3 times the volume of one of the chambers.

During this operation air displaced will vent through non-return valves 10,12 (valves 22, 24 being closed). Flow of water through transfer pipe 30 will pass through pumps 32, 34 as they are centrifugal pumps.

Pump 46 can then be de-energised and valve 42 closed. Pump 32 can be started to transfer water from chamber 2 to chamber 4. As the water transfers reduced pressure develops in the headspace 60 of chamber 2, causing evolution of dissolved gas from the water 54. Transfer can be monitored by flow meter 36 and can be stopped when water reaches water detector 20 in chamber 4, or when pump 32 can no longer pump effectively, for example if an ‘airlock’ (space filled with gas and/or vapour) develops in the pump. Pumping may also become ineffective if headspace 60 has too high a vacuum. The loss of effective pumping can be determined by the flow meter 36.

The flow from a centrifugal pump will tend to slow or even stop when resistance to flow increases. Initially when water being pumped contains significant quantities of dissolved gas, the gas (air) may be evolved within the pump or associated piping, further interfering with flow. Even when the dissolved gas level is low the centrifugal pump may tend to cavitate when pumping out from a chamber with low pressure in the headspace above the water.

In any event, water transfer using pump 32 can be stopped when flow is reduced or when chamber 4 is filled. Pump 34 is then used to transfer water from chamber 4 into chamber 2, evolving dissolved gases in headspace 62. Monitoring of flow by meter 36 and/or liquid water presence at sensor 18 can be used to determine when to stop pump

34. The back and forth transfer of water via transfer pipe 30 can continue until degassing is completed to the desired extent.

The extent of degassing can be determined by readings from pressure transducers 14, 16 with accuracy improved if desired by considering temperature e.g. from sensors 56, 58. Alternatively experience of the required number of water transfer cycles back and forth between the chambers 2, 4 to achieve satisfactory results can be used as a guide to when degassing should be complete.

Once degassing is complete valve 44 can be opened and at least one, typically both of pumps 32, 34 activated to discharge degassed water through transfer pipe 30, branch pipe 38, and feed and discharge pipe 40. Pumping out of the degassing chambers 2, 4 can continue, even against the vacuum in headspaces 60, 62 and to atmospheric pressure if desired; provided there is sufficient head of water above the pumps 32, 34 (typically about 1.2m or more).

The process can be repeated by replenishing chambers 2,4 from supply 48 as discussed above.

The apparatus depicted in figure 1 can also serve to provide vacuum via valves 22, 24 when transfers of water from chamber 2 to chamber 4, and vice versa, are being carried out. Operating valve 22 to connect pipe 26 to chamber 2 as water is transferred out of chamber 2 provides a vacuum. When water transfer from chamber 4 to chamber 2 is being carried out valve 22 is closed and valve 24 operated to connect pipe 27 to chamber 4 again providing a vacuum. Thus a vacuum pump action is provided via pipes 26, 27.

Thus for example pipes 26, 27 may be connected to a vacuum distillation system such as those of W02005/082784 (not shown in any detail, indicated by box 64 in the drawing). When the distillation of salt water is proceeding, but the pressure in the system is higher than desired, pipes 26, 27 can be used to provide a means of removing non-condensable gases and restoring or maintaining the desired conditions for distillation. Non-condensable gases collected in headspaces 60, 62 can be displaced by transferring water 54 back and forth through transfer pipe 30 so as to send the gases out through non-return valves 10, 12 as described above for degassing procedures.

In addition, at start-up of distillation the apparatus of figure 1 can be used to evacuate, or aid in evacuating, a vacuum distillation system 64 by making use of the vacuum generated in the headspaces 60, 62.

Figure 2 shows a generally similar apparatus to that of figure 1, with like parts numbered the same. In this example non-return venting from tanks 2, 4 can be via reservoir 66 of water. Pipes 68, 70 leading from the top of chambers 2, 4 are open into the water held in reservoir 66 which acts as a bubble trap, allowing exit of noncondensable gases from headspace 60 or 62 when water is being transferred into the respective chamber 2, 4. At the same time water in reservoir 66 acts as a liquid seal, preventing ingress of air into a headspace 60 or 62 when water is being transferred out of the respective chamber 2, 4. Reservoir 66 and first and second (centrifugal pumps) 32, 34 are at least 10 m below the bottom of chambers 2, 4. This height differential acts to prevent water from reservoir 66 being drawn into headspaces 60 or 62 when they are at reduced pressure.

Claims

CLAIMS:

1. An apparatus for use in the degassing of water, which apparatus comprises: first and second degassing chambers each provided with a valved vent at the top of the respective chamber;

2. The apparatus of claim 1 wherein the first and second pumps are each independently selected from the group consisting of: centrifugal pumps and turbine pumps.

3. The apparatus of claim 2 wherein both the first and second pumps are centrifugal pumps.

4. The apparatus of any one of claims 1 to 3 wherein at least one of the first and second degassing chambers further includes a vacuum inlet, for connection to a system to be evacuated.

5. The apparatus of claim 4 wherein each of the first and second degassing chambers further includes a vacuum inlet, for connection to a system to be evacuated.

6. The apparatus of any preceding claim wherein both the first and second pumps are located lower than the bottoms of the degassing chambers.

7. The apparatus of any preceding claim wherein the first and second pumps are configured to pump water towards each other.

8. The apparatus of any one of claims 1 to 7 wherein the first and second pumps are configured to pump water away from each other.

9. The apparatus of any preceding claim wherein one valved inlet is provided for connection to an incoming water supply and the valved inlet connects to both first and second degassing chambers.

10. The apparatus of claim 9 wherein the one valved inlet provided for connection to an incoming water supply connects to the first and second degassing chambers via the transfer pipe.

11. The apparatus of claim 10 wherein the one valved inlet connects to the transfer pipe at a location between the first and second centrifugal pumps.

12. The apparatus of any preceding claim wherein one valved outlet for degassed water is provided and connects to both the first and second degassing chambers.

13. The apparatus of claim 12 wherein the one valved outlet for degassed water connects to both the first and second degassing chambers via the transfer pipe.

14. The apparatus of claim 13 wherein the one valved outlet for degassed water connects to the transfer pipe at a location between the first and second centrifugal pumps.

15. The apparatus of any one of claims 1 to 8 wherein the valved inlet for connection to an incoming water supply and the valved outlet for degassed water both connect to a single branch pipe that connects into the transfer pipe at a location between the first and second centrifugal pumps.

16. The apparatus of any preceding claim wherein feed from a water supply, such as a salt water supply, is by a pump.

17. The apparatus of any preceding claim configured for discharge via the valved outlet for degassed water by use of one or both of the first and second pumps of the transfer pipe.

18. The apparatus of any one of claims 1 to 16 further comprising an additional pump for effecting discharge of degassed water via the valved outlet.

19. The apparatus of any preceding claim wherein the valved vents each include a non-return valve for discharge of gas.

20. The apparatus of any one of claims 1 to 19 wherein a vent pipe from the top of each degassing chamber connects openly into a reservoir of water located at a height lower than the bottoms of the degassing chambers, the reservoir of water acting as a non-return valve for gases.

21. The apparatus of claim 4 wherein at least one of the valved vents is a connection for a vacuum inlet.

22. The apparatus of any preceding claim further comprising a water detector at the valved vent of each degassing chamber, to detect liquid water.

23. The apparatus of any preceding claim further comprising a flow meter fitted to the transfer pipe.

24. The apparatus of any preceding claim further comprising a pressure sensor in each of the first and second degassing chambers to measure pressure in the headspace above water.

25. The apparatus of any preceding claim further comprising one of a pressure sensor, a depth gauge or a load cell for each of the first and second degassing chambers to measure water loading within.

26. The apparatus of any preceding claim further comprising a temperature sensor in each of the first and second degassing chambers to measure water temperature.