Patent Application
20110038674
This invention concerns a process and a device for the collection of undersea freshwater. It concerns, in particular, the collection of freshwater derived from undersea freshwater resurgences coming from karst networks.
The karst is a domain of calcareous rocks comprising many inter-communicating cavities, created by the calcium carbonate being dissolved by carbonic acid derived from rainwater loaded with carbon dioxide (CO2). All these cavities make up a karst network, the lower part of which constitutes significant reservoirs of freshwater.
For reasons connected to geological evolution, the karsts, especially those of the Mediterranean rim, have often been lowered by several tens of meters, or even hundreds of meters in places, and as a result their base level can now be located below sea level. It is known that freshwater springs coming from karst domains flow under the sea. Freshwater, with a lower density than seawater, rises towards the surface of the sea.
Attempts have been made to collect the freshwater from undersea karst resurgences, based on the use of a rigid barrier.
French patent no. FR 2 701 974 describes a submerged construction, comprising a concave part aimed downwards and covering the spring, the freshwater remaining trapped in the upper part of said cavity thanks to its density, which is less than that of the seawater. The lower part of this construction remains open so as to let the overflow, and in particular the seawater, escape, at the same time leaving the karst system unrestricted and removing the freshwater from the upper part of the construction by means of a variable-flow pumping system. The pumping device is subordinate to sensors, which enable a flow rate slightly less than the spring's flow rate to be maintained. This device allows freshwater to be removed without the existing equilibrium being disturbed and without introducing disruptions into the working of the karst system, facilitating the laminar flow, which obviates the mixing with seawater.
Document FR 2 785 001 describes a device whose purpose is an improvement enabling a significant simplification of the collection system by utilizing an impermeable surface, for preference flexible, which isolates the resurgence, anchored to the sea bottom and reaching the surface where it is held by a floating barrier, allowing the ventilation of the collection device. The device also comprises a system of valves in the lower part of the membrane, allowing the seawater to escape; the freshwater is removed by pumps installed on a floating device on the inside surface of the barrier.
Document WO 2007/017703 proposes to add, to the device of document FR 2 785 001, a current meter for each spring in order to control the pumps and thus maintain an equilibrium in the system. However, due to the existence of a large number of unpredictable springs and infiltrations, the current meters only give an imprecise measurement of the flow-rates available and the efficiency of this system is limited.
Document FR 2 795 109 proposes a flexible envelop forming a dome over an undersea freshwater spring. A salinity sensor is provided so that the pump opening draws in freshwater. However, as the spring of freshwater, which is lighter, is below the seawater, which is heavier, these two types of water mix. The water thus pumped therefore requires a desalination treatment practically as complex and expensive as the seawater desalination treatment.
The aim of the present invention is to respond to these drawbacks.
To this end, according to a first aspect, the present invention envisages a device for collecting water from at least one undersea freshwater spring, characterized in that it comprises:
Thanks to these provisions, according to the status of the interface, for example its depth or the turbulences causing a freshwater and seawater mixture there, more or less water is pumped. For example, the more the interface is subjected to turbulences, the more the interface's depth is increased, so that there is no risk of the freshwater coming from the springs being mixed with seawater as a result of this turbulence. In addition, apart from transitional phases during which the movement of the interface is commanded, the quantity of water pumped represents the quantity of freshwater coming from these springs, whatever the number, flow-rate, configuration of the springs and/or infiltrations.
In addition, as the freshwater coming from each of the freshwater spring openings is above the interface, there is little risk of the freshwater being mixed with seawater.
According to particular features, the sensor of the status of said interface comprises a depth sensor designed to determine the depth of said interface and the means of closed-loop control is designed to control the depth of said interface by controlling the flow-rate of at least one pump according to said depth.
According to particular features, the sensor of the status of said interface comprises a means of determining the agitation of said interface and the means of closed-loop control is designed to control the flow-rate of at least one pump according to said agitation.
According to particular features, the means of closed-loop control is designed to reduce the flow-rate of at least one said pump when said interface presents turbulences greater than a pre-defined value.
Thus, when the sea is agitated or the flow-rate of the springs increases to the point of causing turbulences, you can stop pumping freshwater in order to avoid pumping brackish water or spring water bearing earth or other impurities, or reduce the rate pumped so that the interface's depth is increased and is farther from the opening of each freshwater spring.
Other particular features of this first aspect of the present invention are presented following the third and fifth aspects of the present invention.
According to a second aspect, the present invention envisages a process for collecting water from at least one undersea freshwater spring, characterized in that it comprises:
As the advantages, aims and special features of this process that is the subject of the second aspect of the present invention are similar to those of the device that is the subject of first aspect of the present invention, as described in brief above, they are not repeated here.
According to a third aspect, the present invention envisages a device for collecting water from at least one undersea freshwater spring, characterized in that it comprises:
Thanks to these provisions, the quantity of water pumped represents the quantity of freshwater coming from these springs, whatever the number, flow-rate, configuration of the springs and/or infiltrations.
According to particular features, the depth sensor comprises a sensor of the difference in level between the surface of the freshwater inside the envelop collecting the freshwater and the surface of the seawater around said envelop.
Thanks to these provisions, the measurement can be accurate and maintenance easy.
According to particular features, the depth sensor comprises an equilibrium depth sensor for a float possessing a density half-way between the density of the freshwater and the density of the seawater.
Thanks to these provisions, the measurement can be especially stable and accurate.
According to particular features, the means of closed-loop control is designed to maintain said interface below the level of at least one spring.
According to particular features, the means of closed-loop control is designed to maintain said interface below the level of at least the spring with the greatest flow-rate.
According to particular features, the means of closed-loop control is designed to control the flow-rate of at least one pump according to the sea level during the tide.
Thanks to these provisions, the interface's absolute vertical position can remain noticeably stable even though the depth below the immediate level of the water inside and/or outside the envelop depends on the tidal phenomenon and varies cyclically.
According to particular features, said envelop comprises a flexible partition surrounding the vertical above at least one spring.
According to particular features, said flexible partition is kept in position by weights.
According to particular features, said flexible partition comprises, in its upper part, inflated booms.
According to particular features, the device as described in brief above comprises a means of determining the agitation of the water outside at least one source of water, the means of closed-loop control being designed to control the flow-rate of at least one pump according to the agitation of the water.
In this way it is possible to avoid pumping freshwater that has been too much mixed with seawater on output from the spring, because of the local agitation of the water.
According to particular features, the means of determining the agitation of the water comprises a radar or sonar doppler-effect sensor.
In this way the said agitation can be determined remotely without introducing a physical sensor into the spring water flow and thus you can avoid creating disturbances in this flow, which may lead to freshwater and seawater being mixed.
According to particular features, the means of determining the agitation of the water comprises at least one water agitation sensor positioned in the water and a means of measuring movements of each said sensor.
According to particular features, the means of determining the agitation of the water comprises a means of determining a density gradient of the water.
According to particular features, the device as described in brief above comprises a means of measuring the salinity of the water pumped or to be pumped and a means of stopping pumping when said salinity is greater than a pre-defined value.
Other particular features of this third aspect of the present invention are presented following the first and fifth aspects of the present invention.
According to a fourth aspect, the present invention envisages a process for collecting water from at least one undersea freshwater spring, retained by an envelop surrounded by seawater isolating a quantity of water above at least one freshwater spring, characterized in that it comprises:
As the advantages, aims and special features of this process that is the subject of the fourth aspect of the present invention are similar to those of the device that is the subject of third aspect of the present invention, as described in brief above, they are not repeated here.
According to a fifth aspect, the present invention envisages a device for collecting water from at least one undersea freshwater spring, characterized in that it comprises:
In this way it is possible to avoid pumping freshwater that has been too much mixed with seawater on output from the spring, because of the local agitation of the water.
According to particular features, the means of determining the agitation of the water comprises a radar or sonar doppler-effect sensor.
In this way the said agitation can be determined remotely without introducing a physical sensor into the spring water flow and thus you can avoid creating disturbances in this flow, which may lead to freshwater and seawater being mixed.
According to particular features, the means of determining the agitation of the water comprises at least one water agitation sensor positioned in the water and a means of measuring movements of each said sensor.
According to particular features, the means of determining the agitation of the water comprises a means of determining a density gradient of the water.
According to particular features, the means of determining the agitation of the water comprises a sensor of the difference in level between the surface of the freshwater inside an envelop collecting the freshwater and the surface of the seawater around said envelop.
Thanks to these provisions, the measurement can be accurate and maintenance easy.
According to particular features, the means of determining the agitation of the water comprises an equilibrium depth sensor for a float possessing a density half-way between the density of the freshwater and the density of the seawater.
Thanks to these provisions, the measurement can be especially stable and accurate.
According to particular features, the means of closed-loop control is designed to control the flow-rate of at least one pump according to the sea level during the tide.
Thanks to these provisions, the interface's absolute vertical position can remain noticeably stable even though the depth below the immediate level of the water inside and/or outside the envelop depends on the tidal phenomenon and varies cyclically.
According to particular features, said envelop comprises a flexible partition surrounding the vertical above at least one spring.
According to particular features, said flexible partition is kept in position by weights.
According to particular features, said flexible partition comprises, in its upper part, inflated booms.
Other particular features of this fifth aspect of the present invention are presented following the first and third aspects of the present invention.
According to a sixth aspect, the present invention envisages a process for collecting water from at least one undersea freshwater spring, retained by an envelop surrounded by seawater isolating a quantity of water above at least one freshwater spring, characterized in that it comprises:
As the advantages, aims and special features of this process that is the subject of the sixth aspect of the present invention are similar to those of the device that is the subject of fifth aspect of the present invention, as described in brief above, they are not repeated here.
Other advantages, aims and characteristics of this invention will become apparent from the description that will follow, made, as an example that is in no way limiting, with reference to the drawings included in an appendix, in which:
Throughout the description the term “float” relates to an element with a density less than at least one of the liquids utilized, generally saline seawater, and which, as result, rises to the interface between this liquid and a less-dense liquid, generally water that is less salty, or the air.
At the immediate outlet of the freshwater from at least one spring, a system of deflectors imposes a forced route on the flowing freshwater, in order to reduce turbulences and to induce a laminar flow of freshwater.
A pump 125, borne by a raft 130, is linked by pipes 135 to a purification unit 140. The pump 125 is controlled by a control unit 145 linked to sensors 150, 151, 152 and 155. The flexible envelop 110 is surrounded, in its upper part, by compressed air booms 160 and is retained, in its lower part, by weights or lines attached to the ocean floor and/or the edges of the fissure.
In a variant, the pump 125 is replaced by a plurality of pumps.
At least one sensor 150 is designed to measure the average difference of level between the surface of the water inside the flexible envelop 110 and the surface of the water outside the flexible envelop 110. This difference is averaged over a long period, compared to the wave period on the sea surface, for example over two minutes, and represents, as a consequence of buoyancy, the depth at which the interface 170 is found between the seawater, which is more dense, and the spring water, which is less dense. This sensor 150 is, for example, comprised of two level sensors, one positioned close to the envelop 110 on the inner side, and the other positioned close to the envelop 110 on the outer side.
At least one sensor 151 is designed to measure the salinity of the water close to the inlet or in the water circuit of the pump 125. The measurement is performed, for example, by measuring an electrical characteristic (resistance or capacitance) of a strip of water with a known thickness, saline water being more conductive than pure water.
At least one sensor 152 is designed to measure the average level, under the surface inside the envelop, at which water with a pre-defined density is found. This sensor is, for example, comprised of a radar, a sonar or a “float” the density of which is half-way between the density of the freshwater and the density of the seawater, “float” of which the depth under the surface is measured. It can also be comprised of a Doppler-effect sensor measuring the speed of the interface based on the partial reflection of sound waves on this interface.
At least one sensor 155 is designed to measure the agitation of the water at the location of at least one freshwater resurgence. This sensor 155 is, for example, comprised of a radar, a sonar or a plurality of “floats” the density of which is half-way between the density of the freshwater and the density of the seawater, and possibly different, “floats” whose respective movements are measured. As is understood, the sensors 152 and 155 can be coupled in order to provide the two measurements in question.
The agitation sensor 155 can also be comprised of a turbulence sensor, for example acquiring the infrasounds emitted in the turbulences. The agitation sensor can also be comprised of a sensor of the intensity of the sound waves partially reflected on the interface. The agitation sensor can also be comprised of a Doppler-effect sensor measuring the turbulences on the interface based on the partial reflection of sound waves on this interface.
The control unit 145 operates as a means of closed-loop control of the depth of the interface 170 between the freshwater and the seawater. The control unit 145 controls, the flow-rate of at least one pump 125 pumping freshwater above said interface, according to said interface depth. When the interface depth goes over a certain threshold, or limit value, the control unit 145 increases the flow-rate of the pumped water. Conversely, when the interface depth is less than another threshold, or limit value, the control unit 145 decreases the flow-rate of the pumped water. For preference, the flow-rate is a continuous function of the depth, the control loop transfer function, in counter-reaction, is calculated to avoid interface depth oscillations, in a way known to people in the closed-loop control field.
For preference the control unit 145 takes account of the tide and is designed to maintain the interface below the level of at least one spring and, for preference, below the level of at least the spring with the greatest flow-rate. In other words, by compensation, the depth is replaced by the altitude of the interface with regard to a fixed point and the control unit 145 controls the flow-rate of at least one pump according to the sea level during the tide.
The control unit 145 thus constitutes a means of determining the agitation of the water outside at least one water source and inside the envelop 110, and is designed to control the flow-rate of at least one pump according to the agitation of the water. In particular, when the turbulences exceed a pre-defined limit value, the control unit stops the operation of the pump 125 or reduces it as described in a variant of steps 315 and 325 (see description of
The control unit is also designed to stop the operation of the pump 125 when the salinity measurement of the water pumped or to be pumped is greater than a pre-defined value, which depends on the desalination capacities of the purification unit 140.
In a general way, the control unit 145 comprises a means 145 of closed-loop control designed to control the flow-rate of at least one pump 125 designed to pump freshwater above the interface between the freshwater and the seawater, according to the status of said interface, especially its depth with respect to at least one or, if possible, all the springs and/or turbulences of this interface in order to maintain the depth of said interface below the opening of at least one said freshwater spring and, possibly, so that the highly saline water generated by these turbulences is not pumped.
As can be seen in
If, during the step 310, it is determined that the salinity measured is below the first pre-defined value, during a step 320, the magnitude of the turbulences at the interface between the seawater and the freshwater is determined. Then, during a step 325, it is determined whether the magnitude and/or speed of the turbulences is greater than a second pre-defined value. If it is, then during step 315, the operation of the pump 125 is stopped and a restart command, either manual or automatic, for example after a pre-defined length of time (for example five minutes), is waited for. Then you go back to step 305.
If during a step 325 it is determined that the magnitude and/or speed of the turbulences is less than the second pre-defined value, then during a step 330, pumping is resumed, if it was stopped, or continued and the depth of the interface between the seawater and the freshwater is determined.
In a variant, depending on the measurement of the turbulences of the interface 170, the reduction in the flow-rate of the pumped water is induced (for example, by the control unit 145) such that the depth of the interface 170 increases and the mixed water coming from the turbulences does not come in front of at least one, preferably all, freshwater spring opening(s). In this variant, if during a step 325, it is determined that the amplitude and/or speed of the turbulences is greater than a second pre-defined value, the flow-rate of the pump 125 is reduced and a command to resume the normal flow-rate of the pump is waited for, which occurs when the interface is at a depth which is an increasing function of the amplitude and/or speed of the turbulences.
During a step 335, the depth measurement is compensated for according to the tide in order to obtain an absolute altitude value.
During a step 340, according to the depth of the interface and/or its altitude and according to the depth of at least the main freshwater spring, or its altitude, and possibly the amplitude or speed of the turbulences, the water flow-rate that the pump 125 must provide is determined. The closed-loop control transfer function, which supplies this flow-rate according to the depths and/or altitudes, depends on the flow-rate of the springs in the envelop 110 and speeds of variation in this flow-rate noted prior to the installation of the device or obtained during a learning phase or operational phase of the device. For preference, by means of the flow-rate of the pump 125, the interface depth is maintained below the opening of at least one freshwater spring and, for preference, of all the freshwater springs.
During a step 345, the pump 125 is controlled so that it provides the flow-rate defined during the step 340. Then you go back to step 305.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0800358 | Jan 2008 | FR | national |
| 0800359 | Jan 2008 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2009/000076 | 1/23/2009 | WO | 00 | 10/4/2010 |
