WO2002100510A1

WO2002100510A1 - Improvements relating to degassing liquids

Info

Publication number: WO2002100510A1
Application number: PCT/GB2002/002447
Authority: WO
Inventors: Paul Whitehead; Richard Vines; Lee Underwood
Original assignee: Vivendi Water Systems Limited
Priority date: 2001-06-12
Filing date: 2002-06-12
Publication date: 2002-12-19
Also published as: GB0114227D0

Abstract

A method of degassing a liquid. Comprising the steps of: (a) drawing liquid from the reservoir/volume to form a degassing stream (4B); (b) using a vacuum to degas the degassing stream; and (c) wholly, substantially or partly returning the vacuum-forming stream A to the reservoir/volume. The effect of the present invention is to provide a system in dynamic equilibrium, in which a stream of liquid is degassed, made available for use and, if not required, re-mixed with a second stream. Thus, a volume of degassed liquid such as water is immediately available on demand; water savings are created compared with operating a separate water as a vacuum-forming (a) supply to power the ejector (6).

Description

IMPROVEMENTS RELATING TO DEGASSING LIQUIDS

The present invention relates to methods and apparatus, f_or_d.e ass.ing liquids, particularly but not exclusively water.

For certain uses, it is necessary or desired to reduce the dissplyed gas content of liquids where the presence of reactive gases such as oxygen or carbon dioxide might interfere with a chemical reaction or physical properties, or where the release of gas bubbles into a liquid stream might affect volumes and flows. For example, clinical analysers .

Dissolved gases can be removed by exposing large surface areas of the liquid to a vapour phase deficient in the gases to be removed. This is conveniently done by flowing the liquid past a suitable membrane with a vacuum applied to the other side. One method for doing this is shown in EP0535607A2, which describes a system for degasifying water. A high pressure waste water stream is passed through an ejector to produce a vacuum, which vacuum is used to degasify a pure water stream. The waste water is discarded and the degasified water is provided as a constant stream.

It is an object of the present invention to improve the degassing system.

Thus, according to one aspect of the present invention, there is provided a method of degassing a volume of liquid comprising the steps of: (a) drawing liquid from the volume to form a ..de.gas_s_ixι.g.__stream; (b) using a vacuum to degas the degassing stream; and (c) wholly, substantially or partly returning the degassing stream to the volume.

Preferably, the vacuum to degas the degassing stream is generated by a vacuum-forming stream, which is also drawn from the volume.

The liquid can be drawn from the volume and/or circulated through the system using any suitable means, generally one or more pump means. The vacuum-forming stream and degassing stream could be separately drawn from the volume, or divided from one stream. _. . After degassing, the degassed stream could be made immediately available for use, possibly through one or more valves. Alternatively, the degassed stream could undergo further treatment or purification, if required, by one or more means known in the art such as deionisation, UV irradiation or filtration.

The volume preferably is or at least includes a reservoir or other liquid holding means. The degassed stream is preferably wholly, substantially or partly returned to any such reservoir.

The method could include a path for some or all of the vacuum-forming stream to return to the volume as a recirculation loop.

The method could be operated continuously or intermittently.

The r_at_e_ of flow of each stream, including _.any_ . recirculation loops, depends upon the desired rate of takeoff of the degassed stream, and/or any rate of intermittent use, and the degree of degassing required.

The method preferably includes one or more locations or arrays able to hold a volume of degassed liquid ready for immediate use, e.g. 5 or 10 litres. Thus, a certain volume of liquid is available On demand' . Such locations or arrays include purification units or other tanks, etc, generally being closed to atmosphere or similar. 1 The pump(s) are preferably used to maintain a

2 certain level of degassed liquid in a recirculating

3 flow, and/or in a location immediately available for

4 use . Liquid to make up for that removed may be

5 added at any part of the volume or circuit, but is

6 preferably added to any reservoir or pump. 7

8 The part of any vacuum-forming stream being

9 returning to the volume will be super-saturated with

10 the removed gases (from the degassing stream) . Upon

11 its return to the volume, time will provide the

12 possibility of equilibration with the surrounding

13 atmosphere to lose some or all of the excess gas. 14. _0_ther_ gas-removal methods could .als_o_be__used,

15 including catalytic nucleation, membranes, thermal

16 effects, or contact with inert gases. If there is a

17 requirement for greater degassing, the returning 18_ __vacuum-forming stream could be who_lly_Dr partly

19 diverted, e.g. to a drain, to reduce the level of

20 gas returning into the volume. 21 2 Preferably, the part of the degassed stream being

23 recirculated to a reservoir enters the reservoir at 4 or near the base of the reservoir, and/or near the 5 degassing stream outflow. Thus, the degassing stream

26 outflow should at least partly include some of the

27 incoming degassed stream, thereby using an already

28 partly degassed flow. 29

30 Similarly, the part of any vacuum-forming stream

31 being recirculated to the volume preferably enters 2 the volume at a point distal to the outflow of the 1 liquid drawn to form the degassing stream, such as

2 at or near the top of the reservoir, so as to lessen

3 the use of this stream, being super-saturated, in

4 the degassing stream outflow. 5

6 The vacuum-forming stream may be directly or

7 indirectly circulated to the volume. Indirect

8 circulation may include one or more degassing or

9 ^λ de-supersaturation' treatment steps as previously 10 discussed.

11

12 According to a second aspect of the present 3 invention, there is provided apparatus for degassing L4 a liquid comprising a means_t_o__hold a volume of 5 liquid, means for drawing liquid from the volume, 6 means to provide a degassing-stream from said drawn 7 liquid, means for providing a vacuum, means for 8 degassing the degassing stream using the vacuum, 9 wherein the apparatus includes means able to wholly, 0 substantially or partly return the degassed stream 1 to the volume. 2 3 Preferably, the apparatus includes means for drawing 4 liquid to provide a vacuum-forming stream, which 5 vacuum-forming stream generates the vacuum to degas 6 the degassing stream, and possibly includes means 7 able to wholly, substantially or partly return the 8 vacuum-forming stream to the volume means. The 9 volume means may be a reservoir or similar liquid ,0 holding means, and the means for drawing liquid may 1 be one or more pumps . 2 In particular, the apparatus of the present invention for degassing water comprises a reservoir to hold the water, a pump to draw the water from the reservoir, a first water circuit providing a degassing stream from the pump, a second water circuit providing a vacuum-generating stream from the pump, wherein the first circuit includes a degassing module for degassing the water, a degassed water take-off point, a water take off point and a return to the reservoir, and the second circuit includes an ejector to generate the vacuum for the degassing module.

The present invention is usable with any suitable liquid, including high and low-temperature liquids and solvents. One liquid is water.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawing and graphs in which;

Figure 1 shows a scheme for the system of the present invention; and

Figures 2 to 7 are graphs illustrating aspects of the invention.

Referring to the drawing, Figure 1 shows a reservoir 2 holding a volume of water to be degassed. The water may already have undergone one or more purification operations. The reservoir 2 has an out-flow 4 to a pump 5. The outflow from the pump 5 is then divided between a vacuum-forming stream A and a degassing stream B. The vacuum-forming stream A provides the motive power for an ejector 6. The ejector 6 is used to produce a vacuum, which vacuum is directed through a vacuum line 8, having at its other end, a degassing module 10.

The degassing stream B passes through the degassing module 10, and the vacuum on the degassing module 10 reduces the dissolved gas content of the stream B to form a degassed stream C.

The operation of the pump 5, ejector 6 and degassing module 10 are known in the art.

The flow__of__the vacuum-forming stream A after- the..... ejector 6 is returned to the reservoir 2. The return stream A is supersaturated with the removed gasses, and is preferably given the possibility of equilibrating with the surrounding atmosphere to lose some of the excess gas. If necessary, some or all of the returning vacuum-forming stream could be taken through line 12 to a separate location or to a drain to reduce the returning level of gassified water into the reservoir 2. This assists the provision of higher than 'normal' degassed-water if desired or necessary. Other degassing of the super- saturated stream is possible. Meanwhile, the degassed steam C is available for use through a means such as a solenoid valve 14. Stream C may also undergo further treatment of purification (16) , if desired or necessary.

Stream C may also be wholly or partly recirculated back into the reservoir 2 via line 18. Stream C is preferably returned to the bottom of the reservoir 2 to minimise re-solution of gasses from the atmosphere. In practice, it has been found that with water as the fluid, the dissolved oxygen content of the re-circulated water from stream C is decreased.

The split of water between streams A and B is designed such that the flow in stream A is sufficiently great to provide a high and sufficient level._-θf-_degasification. If necessary, this—f-low can be reduced when water is being dispensed or otherwise taken off.

Suitable-sized vessels could be included in the circuit to provide the required volume of degassed water. This can be conveniently and economically achieved by positioning some or all of any other purification technologies (16) between the degassing module and the take-off point (D) .

As degassed stream C is removed from the system, it may be replaced in the reservoir 2 by water with a higher level of dissolved gas. The present invention uses the release of excess gas from the returning stream A, as described above, to maintain the overall gas content at levels consistent with producing an adequately degassed product stream C. If there is a higher liquid purity requirement, returning stream A could periodically be diverted to drain as described above .

The overall system could be operated on an intermittent basis such as for five minutes every 30 minutes, to minimise energy consumption. The design will permit the maintenance of sufficient volumes of degassed water available for use with no additional delays over the time necessary to restart the pump.

In general, the overall effect of the present invention is to provide a system in dynamic equilibrium, in which a stream of liquid is __degassed, made available for use, and, i.f_not required, remixed with a second stream which contains some or all of the gasses which have been removed from the first stream. The general advantages of this arrangement are, firstly, a volume of degassed liquid such as water, is immediately available on demand. Secondly, a vacuum ump is not required, creating savings in energy, noise, cost- and reliability. Thirdly, no external processes, such as a reverse osmosis step, need to be operating. Fourthly, water savings are created compared with operating a separate water supply to power the ejector. 1 Example 1 2

3 Using the arrangement shown in Figure 1, the

4 following system was followed. 5

6 RESERVOIR R (2) 25 litre

7 EJECTOR (6) 1.0mm orifice

8 DEGASSING MODULE (10) Minntech LV-C-030-A

9 VOLUME (16B) 1.4 litre

10 VOLUME (16A) 0 litre

11 Dissolved oxygen content of feed is 9.0 ppm 12

13 There are two states of operation, recirculation and

1_4_ .dispense. Flow rates are dif£erent—ln.-the two

15 conditions.

16

17 In recirculation (valve 14 closed)

1.8,

19 Flow A is 1.2 litre/ in

20 Flow B is 0.5 litre/min

21 Flow C (line 18) is 0.5 litre/min

22 Vacuum (line 8) is -0.90 Bar gauge (0.1 Bar

23 absolute)

24 Dissolved oxygen content of C is 1.1 to 2.0 ppm 25

26 In dispense (valve 14 open) 27

28 Flow A is 0.7 litre/min

29 Flow B is 1.0 litre/min

30 Flow C (line 18) is 0 litre/min

31 Vacuum (line 8) is -0.65 Bar gauge (0.1 Bar

32 absolute) Dissolved oxygen content of C is 2.0 to 5.0 ppm Dispense flow (D) is Ϊ . O litre/min.

Figures 2 to 7 provide graphic information of test data using the arrangement in Figure 1. Figures 2, 4 and 6 show one cycle of the system with water being dispensed at a regular interval. Figures 3, 5 and 7 show several cycles for these conditions.

Figures 2 and 3 show the performance of a system as in example 1 where 1.5 litres of water were taken off every 7.5 minutes . Water was added to the reservoir R (2) to make up for that removed. The dissolved oxygen content of the water varied between a minimum of approximately 0.8 ppm and a maximum of 1.6 ppm through the dispense cycle .

Figures 4 and 5 show the same system with the same dispense but with a longer time between dispenses of 20 minutes. The extra time for recalculation and degassing prior to dispense resulted in the dissolved oxygen content being reduced to 0.35 ppm. Further recalculation could result in even lower dissolved oxygen values.

Figures 6 and 7 show data from the same system with a similar time between dispenses but with significantly larger dispense volumes. Initially the dissolved oxygen levels are low, but once the volume of the purification volume (16B) has been exceeded dissolved oxygen levels increase but remain at a level below that of the feed water. Figures 2 to 7 confirm the benefits of the present invention, in that a volume of a liquid such as water can be provided ^yon tap' with a reduced dissolved gas content, irrespective of any prior withdrawal or a static output situation. The present invention provides a simple and elegant arrangement able to always provide reduced dissolved gas content liquid in situations where demand can be variable.

Claims

1. A method of degassing a volume of liquid comprising the steps of: (a) drawing liquid from the volume to form a degassing stream; (b) using a vacuum to degas the degassing stream; and (c) wholly, substantially or partly returning the degassing stream to the volume.

2. A method as claimed in Claim 1 further comprising the steps of drawing liquid from the volume to form a vacuum-forming stream, and using the vacuum-forming stream to generate the vacuum to degas the degassing stream.

3. A method as claimed in Claim 2 which further comprises the step of returning at least some of the vacuum-forming stream to the volume after degassing.

. A method as claimed in any one of Claims 1 to 3 wherein the liquid is drawn from the volume using a pump.

5. A method as claimed in any one of Claims 2 to 4 wherein the vacuum-forming stream and degassing stream are drawn separately from the volume.

6. A method as claimed in any one of Claims 2 to 4 wherein the vacuum-forming stream and degassing stream are drawn together from the volume and then divided into the two streams .

7. A method as claimed in any one of the preceding Claims wherein after degassing, the degassed stream undergoes further treatment or purification.

8. A method as claimed in any one of the preceding Claims wherein the volume includes a reservoir.

9. A method as claimed in Claim 8 wherein the degassed stream is wholly, substantially or partly returned to the reservoir.

10. A method as claimed in Claim 9 wherein the degassed stream being returned to the reservoir enters the reservoir at or near its base.

11. XTnethod as claimed in any one^""oϊ^__the preceding Claims wherein the degassed stream being returned to the volume enters the volume at or near the outflow of the liquid drawn to form the degassing stream.

12. A method as claimed in any one of the preceding Claims wherein the liquid drawn from the volume for the degassing stream is at least partly some of the incoming degassed stream.

13. A method as claimed in any one of Claims 3 to 12 wherein the vacuum-forming stream being returned to the volume is wholly or partly degassed, de-supersaturated or both before being returned to the volume .

14. A method as claimed in any one of Claims 3 to 13 wherein the vacuum-forming stream being returned to the volume enters the volume at a point distal to the outflow of the liquid drawn to form the degassing stream.

15. A method as claimed in any one of the preceding Claims wherein at least some of the degassed stream flows through or is held by a separate reservoir so as to be available on demand.

_.___!_?_•_. ^A method as claimed in any one of Claims 2 to 15 wherein at least some of the returning vacuum-forming stream is diverted to a drain.

17. A method as claimed in any one of the preceding Claims wherein the method is continuous.

18. A method as claimed in any one of Claims 1 to 16 wherein the method is intermittent.

19. A method as claimed in any one of the preceding Claims wherein the liquid to be degassed is water.

20. Apparatus for degassing a liquid comprising a means to hold a volume of liquid, means for drawing liquid from the volume, means to provide a degassing-stream from said drawn liquid, means for providing a vacuum, means for degassing the degassing stream using the vacuum, wherein the apparatus includes means able to wholly, substantially or partly return the degassed stream to the volume.

21. Apparatus as claimed in Claim 20 wherein the means for drawing liquid also provides a vacuum-forming stream, which vacuum-forming stream generates the vacuum to degas the degassing stream.

22. Apparatus as claimed in Claim 21 which includes' means able to wholly, _s_ubstantially or partly return the vacuum-forming stream to the volume means.

23. Apparatus as claimed in any one of Claims 20 to 22 wherein the volume means is a reservoir.

24. Apparatus as claimed in any one of Claims 20 to 23 wherein the means for drawing liquid from the volume is one or more pumps.

25. Apparatus as claimed in any one of Claims 20 to 24 further comprising one or more means for separately holding at least some of the degassed liquid.

26. Apparatus as claimed in Claim 25, wherein at least one said means is a purification means.

27. Apparatus as claimed in any of Claims 20 to 26, wherein the means for providing a vacuum is an ejector.

28. Apparatus as claimed in any one of Claims 20 to 27 for degassing water comprising a reservoir to hold water, a pump to draw water from the reservoir, a first water circuit providing a degassing stream from the pump, a second water circuit providing a vacuum-generating stream from the pump, wherein the first circuit includes a degassing module for degassing the water, a degassed water take-off point, and a return to the reservoir, and the second circuit includes an ejector to generate the vacuum for the degassing module.

29. A method of degassing a liquid substantially as hereinbefore defined with reference to Figure 1.

30. Apparatus for degassing a liquid substantially as hereinbefore defined with reference to Figure 1.