NO20220502A1

NO20220502A1 - A method and apparatus providing cooling of seawater surfaces comprising a bubble curtain

Info

Publication number: NO20220502A1
Application number: NO20220502A
Authority: NO
Inventors: Olav Hollingsæter
Original assignee: Oceantherm As
Priority date: 2022-05-02
Filing date: 2022-05-02
Publication date: 2023-11-03
Also published as: NO20230417A1

Description

A method and apparatus providing cooling of seawater surfaces comprising a bubble curtain

FIELD OF THE INVENTION

The present invention relates to a method and apparatus providing cooling of seawater surfaces comprising a bubble curtain creating a transport of colder seawater from below a seawater surface, wherein the colder seawater used for the cooling is a mix of different temperature layers of seawater, wherein the mix of seawater layers has a temperature close to or equal to a target temperature of the seawater surface.

BACKGROUND OF THE INVENTION

The ocean of the earth is an integral part of the weather system governing the climate we experience as humans as well as for animals. The climate change we may experience in the future will probably result in increased sea water temperatures.

An increase in seawater temperature may be beneficial for example for industrial fish farming in some northern sea water areas. However, there are also examples of problems related to marine wildlife due to increasing seawater temperatures. For example, a higher seawater surface temperature may provide thermal stress and for example coral bleaching and/or infectious diseases in coral reefs are known consequences.

Seawater surface temperatures may also influence weather systems. For example, tropical storms may increase its energy when the storm passes over warmer seawater surface areas. The most extreme case is a tropical storm turning into a hurricane. Research into hurricane development mechanisms has revealed that if the seawater surface temperature is above 26.5ºC a tropical storm may develop into a hurricane since the storm may gain more energy from the warmer sea surface water. If the seawater surface temperature is below 26.5ºC a tropical storm passing the seawater surface area cannot turn into a hurricane. The tropical storm will lose part of its energy when passing seawater surfaces below this temperature limit.

Therefore, there is an interest in developing techniques and systems that may be able to cool respective areas of seawater surfaces to be at a temperature below for example 26,5ºC, or at temperatures minimizing thermal stress for marine life.

A known technical solution enabling manipulation of seawater surface conditions is denoted bubble curtains. A pipe with an adapted plurality of holes is submerged to a certain depth in the seawater and compressed air is then applied to the submerged pipe. Compressed air will then flow out of the adapted holes in the pipe and then bubbles will move upwards towards the seawater surface. A water current of colder water will be generated on the sea water surface. The ascending bubbles will incorporate or entrain surrounding water generating a vertical flow of deeper water flowing upwards to the seawater surface. If the deeper water is colder than the seawater surface temperature a cooling of the sea water surfaces may be possible. The size of the area manipulated by a bubble curtain is a function of the length of the pipe and any natural water currents in the seawater surface area being mixed with water currents generated by the ascending bubbles.

An example of cooling a seawater surface area providing hurricane prevention is disclosed in the publication US 20090272817 which disclose a method and apparatus for reducing the intensity of hurricanes. A method may include positioning a fleet of submersibles in an area of ocean through which at least a portion of a hurricane's central core will pass within a predetermined amount of time. The submersibles are maneuvered to a depth greater than a depth of a thermocline in this area of the ocean. The submersibles maintain their station and depth for a finite amount of time, during which they may release a gas to form bubble plumes which rise toward the ocean's surface. The bubble plumes entrain and upwell cold sub-thermocline water toward the surface of the ocean, i.e., colder water from deep calm water below. The cooled ocean surface reduces the intensity of the hurricane whose portion of central core passes through the cooled area. An apparatus to generate a bubble plume may include a gas source, a gas manifold to releasably collect gas from the gas source, and a cover having perforations of a predetermined shape, size, and spacing to produce a predetermined rate of upwelling of seawater. The apparatus may further include a duct to receive at least a portion of the generated bubble plume and channel the cold upwelled seawater toward the surface of the ocean.

Another example is disclosed in US 3683627 disclosing an improved means and method for upwelling or raising sub-surface water to the surface of a body of water for manifold purposes. By dissolving air in the water and providing excess air, the water rises in a vertical current and is accelerated as the pressure on the water at various levels decreases toward the surface, causing the water to give off the dissolved air in a multitude of tiny bubbles which further accelerates the flow of water to the surface.

A Scientific investigation of the properties of a bubble curtain is disclosed in the article “Current Produced by an Air Curtain in Deep Water”. The Dock and Harbor Authority, Vol. 42, pp 15-22” by Bulson P.S. from 1961.

Bubble curtains are not only used for sea surface control of temperatures but also providing for example a water surface current moving floating objects away or lifting warmer water from below the seawater surface which may stop formation of ice in wintertime.

Cooling of a seawater surface is dependent on several factors. For example, mitigating a hurricane development or preventing thermal stress in coral reefs may require cooling of larger seawater surfaces. The assumption that bringing colder water from deeper seawater layers can cool a larger surface layer may be difficult due to an obvious observation that cold water has higher density and weight and hence the colder water will probably sink downwards again and cannot stay long enough to provide an effective cooling of a larger seawater surface area. Other factors as known in prior art influencing the effectivity of the cooling may for example be the salinity of respective water volumes that are mixed in the seawater surface layer and hence there is a difference in weight between the respective seawater volumes that are mixed. This influences the end temperature of the mixed water which may make it difficult to reach a target temperature of the mixed seawater volume.

Therefore, there is a need of an improved method and system when cooling a seawater surface area to a target temperature with a bubble curtain technique.

OBJECT OF THE INVENTION

It is an object of the present invention to provide an alternative to the prior art.

In particular, it may be seen as an object of the present invention to provide a control of a seawater surface temperature by upwelling water from below the seawater surface having an average temperature close to a target temperature of the seawater surface temperature.

SUMMARY OF THE INVENTION

Thus, the above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a bubble curtain uplifting water from below a seawater surface wherein a depth in the water wherein bubbles are created by the bubble curtain installation is given by a defined target temperature of the surface water.

The invention is particularly, but not exclusively, advantageous for obtaining a system comprising a bubble curtain configurable to manipulate a temperature of a seawater surface to be in an order of magnitude of a defined target temperature, wherein a pipe of the bubble curtain is positioned at a depth below the seawater surface wherein an average temperature of respective seawater layers between the position of the pipe and the seawater surface equals the defined target temperature and is upwelled and mixed by bubbles released through holes arranged in respective walls of the pipe, wherein the bubbles are ascending and entraining water from the respective seawater layers.

Respective aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be disclosed and elucidated with reference to the embodiments described herein.

DESCRIPTION OF THE FIGURES

Figure 1 illustrates an example of embodiment of the present invention.

Figure 2 illustrates further details of the example of embodiment illustrated in Figure 1.

Figure 3 illustrates further details of the example of embodiment illustrated in Figure 1.

Figure 4 illustrates another example of embodiment of the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

Although the present invention is disclosed in connection with specific examples of embodiments, it should not be construed as being in any way limited to the presented examples. The accompanying claim set defines the scope of protection of the present invention. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Further, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention.

Furthermore, combining individual features mentioned in different claims may possibly be advantageously, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Figure 1 illustrates an example of how a bubble curtain 10 is functioning. A pipe 10a with a perforated surface (holes in the pipe walls) is lowered down to a certain depth in the seawater. The pipe 10a should not rest on a seabed surface such that it is common to attach for example floats that are anchored to the seabed (not illustrated). Compressed air (not illustrated) is supplied in one end of the pipe 10a which is then released through the respective holes in the pipe wall of the pipe 10a. The bubbles are lighter than the water (due to the air inside the bubbles) and the bubbles will be ascending accelerated towards the seawater surface. The ascending of the bubbles is illustrated by the arrow 12 in Figure 1.

The ascending bubbles will entrain surrounding water 11a, 11b upwards on both sides of the bubble curtain 10 from the pipe 10a to the seawater surface 18. A natural seawater surface water current 17 is illustrated moving towards the bubble curtain 10. The natural water current 17 has a volume just below the seawater surface 18, which is defined by the depth 17a of the natural seawater surface water current 17.

When the ascending bubbles 12 interfere with the natural seawater surface water current 17 parts of the bubbles 12 are moving away from the bubble curtain 10 on both sides 13a, 13b of the bubble curtain 10. When the respective water currents 17, 14a, 14b meet like this the water of the meeting water currents will be mixed in a turbulent manner as illustrated by the reference numeral 15a, 15b and 16 for example.

Figure 2 illustrates a cross section of a water volume wherein a pipe 10a is located at a specified depth below the seawater surface 18. Between the pipe 10a and the seawater surface 18 there is a vertical cross sectional view of a vertical water column 19 from which the bubbles 12 entrain water. The ascending water bubbles 12 and entrained water is mixed in the upper surface volume below the seawater surface 18 with a natural water current 17 moving towards a first side of the bubble curtain 10. Due to the natural water current 17 mixed water as discussed with reference to Figure 1 moves to a second side of the bubble curtain 10 opposite the first side of the bubble curtain 10. The line 21 illustrate the extent of the affected seawater surface area from the bubble curtain on the first side and second side of the bubble curtain 10. The length of the line 21 illustrates how far the upwelled seawater from below the seawater surface can reach due to the induced surface current away from the bubble curtain 10.

Figure 2 illustrates a possibility to arrange a temperature sensor 20 that may be floating and for example anchored to the seabed (not illustrated). The temperature sensor may be configured with a wireless transmitter that can send temperature measurements to a control center or to a ship configured with a compressor feeding compressed air to the submerged pipe 10a. A possibility can then be to increase for example the volume of air flowing through the pipe 10a thereby increasing the bubble curtain effect if the temperature is above a defined target temperature of the seawater surface.

It is within the scope of the present invention that several temperature sensors 20 may be deployed in the seawater area of interest and for example an average temperature of the respective measured temperatures may be used when assessing if a target temperature is achieved.

Figure 3 illustrates an example of a ship 22 configured to deploy a pipe 10a. For example, floats 10b, 10c or trawl doors may be arranged on respective ends of the pipe 10a to keep the pipe 10a fixed to a certain depth in the water. It is also within the scope of the present invention that a buoyancy of the respective floats can be adjusted, for example by filling a chamber of the float with water of blowing filled water in the chamber out with compressed air. Trawl doors can also be used to control the position in the water of the pipe 10a.

The ship 22 is further arranged with a compressor feeding compressed air through a pipe 22b connected in a center position of the pipe 10a.

It also within the scope of the present invention that a bubble curtain 10 according to the present invention can be located stationary on a selected position, or for example the boat 22 can move a bubble curtain 10 across a seawater surface. The bubble curtain can be positioned in the seawater with for example with the same technique used for trawls.

The compressor arranged for example onboard a ship 22 can be of any conventional compressor type delivering the necessary flux of air with for example a required overpressure (depending on the actual installation depth). Some of the largest commercial compressors have capacities of approximately 6-7 000 Nm3/min of air (N denotes normal air) with working pressure of 16-20 bar and power consumption of some 35 MW. Connecting compressors in parallel will multiply the output capacity to even higher flux rates.

As discussed above, just upwelling cold water may not be enough to achieve a desired temperature of a larger seawater surface. The problem of difference of weight of colder water and warmer water that is mixed can be solved according to an aspect of the present invention. With reference to Figure 2, the water column 19 between the pipe 10a and the seawater surface 18 comprises layers of seawater having different temperatures. Therefore, dependent on which depth the pipe 10a is placed in the seawater a mix of upwelled water will be mixed to a temperature from respective water layers of the water column 19 that is a function of the depth the pipe 10a of a bubble curtain 10 is located relative to the water column 19. This is an observation that is different from prior art wherein the depth of a corresponding pip 10a of a bubble curtain is located below a thermocline in the water.

Therefore, increasing the efficiency when cooling a larger seawater area can be achieved by lowering a pipe 10a of a bubble curtain 10 to a depth below the seawater surface 18 defining a seawater column 19 which the bubbles 12 entrain water from respective seawater layers having a combined average temperature equal to a defined target temperature, or a temperature just below or just above the target temperature. An aspect of the present invention is that if too cold water is collected by the bubble curtain 10 the efficiency of the cooling will be less.

Therefore, determining the depth of the location wherein the pipe 10a is to be located is of importance for the efficiency of the operation.

With reference to Figure 2, if a temperature sensor 20 measures a temperature above a target temperature it is possible to lower the pipe 10a to a depth providing a more efficient average temperature of the upwelled water. If the temperature sensor measures a temperature below a target temperature the pipe 10a may be lifted upwards.

Therefore, changing a vertical position of a pipe 10a relative to a seawater surface can be used to achieve an efficient temperature control of a larger seawater surface.

An important factor is also the speed of an induced surface water current on the seawater surface. The speed is directly related to how much air is water currenting through a pipe 10a of a bubble curtain 10 and the induced surface speed should be in the same order as a natural water current speed at the location of the bubble curtain 10.

The pipe diameter of a pipe can be found from practical engineering diagrams based on the working pressure, permissible pressure drop, air flux, and pipe length etc.

The diameter of the holes in the surface of the pipe 10a can be defined from common knowledge of distributed flow systems. For example, according to the practices with manifolds the total area of the holes should be less than the crosssectional area of pipe 10a of the bubble curtain 10.

Here follows some examples, wherein a target temperature of 26.5ºC is to be achieved in areas of the Gulf of Mexico. A typical depth of the location of a pipe 10a below the seawater surface in these areas is estimated from known temperature date to be 150 meters.

The depth of 150 meters is decided on knowledge of a temperature profile of respective layers of a water column 19 between a possible position of a pipe 10a and the seawater surface. By adjusting the depth position of the pipe 10a different average temperatures of the water column 19 can be calculated.

It is also within the scope of the present invention to use more than one pipe 10a in a bubble curtain 10, for example in a parallel configuration.

Table 1a. Bubble-induced surface water current speed when 30 000 Nm3/min of air is led down to 150 m.

Table 1 b. Bubble-induced surface water current speed when 10 000 Nm3/min of air is led down to 150 m.

Table 1 c. Bubble-induced surface current speed when 5 000 Nm3/min of air is led down to 150 m.

Respective calculations show that a 'harsh' environment with a natural surface current of 1.5 m/s requires a two pipe solution each with five compressors delivering 30 000 Nm3/min over maximum 1 km length. At the other end of the scale: a single 5 km pipe will be able to homogenize the upper 150 m below 26.5 in a current of up to 35 cm/s.

A complicating factor in some applications of an example of embodiment of the present invention is for example the fact that when trying to stop a development of a hurricane it is necessary to identify a trajectory the center of the hurricane will follow over the seawater surface. Further, the depth of the water needs to be deep enough to enable establishment of a seawater column 19 having an average temperature of the respective seawater layers that is close to the target temperature of 26,5ºC. The examples above disclose that a depth of 150m can achieve this average temperature in the Gulf of Mexico. This necessary depth need not always be available dependent on the trajectory of a specific tropical storm that is approaching. Respective meteorologic authorities have the capability to estimate a trajectory of a tropical storm, but the trajectory can change. Therefore, deployment of a bubble curtain system or systems according to the present invention needs to be somewhat dynamical. Therefore, a small fleet of ships 22 illustrated in Figure 3 may be stand by at certain areas of a possible trajectory of a tropical storm, and when the trajectory is more certain one or more of the respective ships 22 may deploy a bubble curtain 10 at a calculated depth of the location for the deployment.

A further possible problem can be that the depth at the location is not deep enough to satisfy the necessary average temperature of a seawater column 19 as disclosed in Figure 2. According to an aspect of the present invention a pipe 10a of a bubble curtain 10 may be arranged with cooling as disclosed in Figure 4. The pipe 10a comprises in this example of an inner tube 10d surrounded by an outer tube 10f defining a space 10g in between the outer and inner tubing 10f and 10d.

The inner tubing 10d receives compressed air from an external compressor as discussed in connection with Figure 3. The compressed air flow out of openings 10e arranged as a pipe through the space 10g between the inner and outer tubing 10d, 10f. There are several such openings but only one is illustrated as an example in Figure 4. The space in between respective pipes 10e and the inner and outer tubing 10d, 10f can be connected to a cooling machine that circulates a cooling agent in this space. A cooling machine as known in prior art can be operated and located at a same location as a compressor, for example onboard a ship 22.

Monitoring surface temperatures with a temperature sensor as discussed in connection with Figure 2 makes it possible to regulate the cooling such that a target temperature of for example 26.5 ºC is achieved even though the water is not deep enough at a specific location a system according to the present invention is located.

According to an example of embodiment of the present invention a system comprising a bubble curtain 10 is configurable to manipulate a temperature of a sweater surface 18 to be in an order of magnitude of a defined target temperature, wherein a pipe 10a of the bubble curtain 10 is positioned at a depth below the seawater surface 18 wherein an average temperature of respective seawater layers between the position of the pipe 10a and the seawater surface 18 equals the defined target temperature and is upwelled and mixed by bubbles released through holes arranged in respective walls of the pipe 10a), wherein the bubbles are ascending and entraining water from the respective seawater layers.

According to the example of embodiment disclosed above a temperature profile of a water column 19 is established by measuring respective temperatures of seawater layers of the column 19 and iterating different combinations of temperatures of the respective sweater layers until an average temperature of the column 19 is in the order of magnitude of the defined target temperature.

According to the example of embodiment disclosed above the bubble curtain 10 comprises at least two pipes 10a arranged in parallel in a distance from each other.

According to the example of embodiment disclosed above wherein the pipe 10a comprises a plurality of holes, in the respective walls of the pipe 10a, wherein the number of holes is limited to form a total summed hole area opening surface being less than a cross sectional area of the pipe 10a.

According to the example of embodiment disclosed above, wherein the pipe 10a is arranged with means for controlling a position of a submerged pipe 10a to be located above a seabed surface with a defined distance from the seabed surface.

According to the example of embodiment disclosed above, wherein the means for controlling the position is a float arranged with an adjustable bouncy enabling a shift of position of the pipe 10a upwards or downwards relative to a seawater surface (18), or the means are trawl doors.

According to the example of embodiment disclosed above, wherein the pipe (10a) comprises an inner tubing (10d) surrounded by an outer tubing (10f), wherein the inner tubing (10d) receives compressed air from an external located compressor while a space 10g in between the first and second tubing 10d, 10f receives a cooling agent from a cooling machine.

According to the example of embodiment disclosed above, wherein a ship 22 is configured to deploy a bubble curtain 10 at a position defined by a meteorological institution.

According to the example of embodiment disclosed above, wherein at least one temperature sensor is configured to be deployed in an induced water surface water current from the bubble curtain 10.

According to the example of embodiment disclosed above, wherein a measured temperature from at least one temperature sensor is used to modify a pressure of a compressor feeding compressed air to the pipe 10a) or the location wherein the pipe 10a is located is adjusted upwards or downwards relative to the sea surface 18.

Claims

1. A system comprising a bubble curtain (10) configurable to manipulate a temperature of a seawater surface (18) to be in an order of magnitude of a defined target temperature, wherein a pipe (10a) of the bubble curtain (10) is positioned at a depth below the seawater surface (18), wherein an average temperature of respective seawater layers between the position of the pipe (10a) and the sweater surface (18) equals the defined target temperature and is upwelled and mixed by bubbles released through holes arranged in respective walls of the pipe (10a), wherein the bubbles are ascending and entraining water from the respective seawater layers.

2. The system of claim 1, wherein a temperature profile of a water column (19) is established by measuring respective temperatures of seawater layers of the column (19) and iterating different combinations of temperatures of the respective sweater layers until an average temperature of the column (19) is in the order of magnitude of the defined target temperature.

3. The system if claim 1, wherein the bubble curtain (10) comprises at least two pipes (10a) arranged in parallel in a distance from each other.

4. The system of claim 1 wherein the pipe (10a) comprises a plurality of holes in respective walls of the pipe (10a), wherein the number of holes is limited to form a total summed hole area opening surface being less than a cross sectional area of the pipe (10a).

5. The system of claim 1, wherein the pipe (10a) is arranged with means for controlling a position of a submerged pipe (10a) to be located above a seabed surface with a defined distance from the seabed surface.

6. The system of claim 5, wherein the means for controlling the position is a float arranged with an adjustable bouncy enabling a shift of position of the pipe (10a) upwards or downwards relative to a seawater surface (18), or the means are trawl doors.

7. The system of claim 1, wherein the pipe (10a) comprises an inner tubing (10d) surrounded by an outer tubing (10f), wherein the inner tubing (10d) receives compressed air from an external located compressor while a space 10g in between the first and second tubing (10d, 10f) receives a cooling agent from a cooling machine.

8. The system of claim 1, wherein a ship (22) is configured to deploy a bubble curtain (10) at a position defined by a meteorological institution.

9. The system of claim 1, wherein at least one temperature sensor is configured to be deployed in an induced water surface current from the bubble curtain (10).

10.The system of claim 9, wherein a measured temperature from the at least one temperature sensor is used to modify a pressure of a compressor feeding compressed air to the pipe (10a), or the location wherein the pipe (10a) is located is adjusted upwards or downwards relative to the sea surface (18).

11.The system of claim 1, wherein the target temperature is 26,5ºC.