Abstract:
The invention relates to a facility for converting water power into mechanical or electrical energy, including at least one hydraulic turbine, a water reservoir (R), and a pipe ( 5 ) for supplying the turbine with water (E) from the water reservoir. The facility also includes a device ( 200 ) submerged in the water reservoir and suitable for imposing an ascending movement on a water flow (E 0 ) moving in the water reservoir (R) towards the opening ( 51 ) of the supply pipe ( 5 ), and a gas-collecting means ( 400 ), arranged above a portion (V 200 ) of the device ( 200 ) in which the ascending movement of the water flow (E 0 ) takes place.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an installation for converting hydraulic energy into mechanical or electrical energy, such an installation including a hydraulic turbine designed to have a forced flow of water pass through it coming from an impoundment of water such as a dam reservoir or the like. 
     2. Brief Description of the Related Art 
     Under certain conditions, a hydroelectric dam can be a greenhouse gas source. For example, in a tropical environment, decomposition of organic matter that is of plant origin or of geological origin and that is immersed in the impoundment of water can give rise to formation of methane (CH 4 ), of carbon dioxide (CO 2 ), or of other gases. Such a phenomenon takes place, in particular, in impoundments of water bordered with forests or when the impoundment of water was created over a preexisting forest. The methane forms mainly in the zones of the reservoir that are poor in oxygen, i.e. in the vicinities of the bottom and of the stagnant regions along the shore of the reservoir. Carbon dioxide forms mainly at the surface. Methane has a greater greenhouse effect than carbon dioxide. 
     The gases formed in this way can be discharged into the atmosphere via various routes. They are emitted by diffusion and by bubbling, those phenomena being distributed over the entire surface of the impoundment of water and, in practice, being impossible to avoid. Those gases are thus also emitted at the turbines of the dam insofar as, on passing through the turbine, the water undergoes a large pressure drop. Prior to passing through the turbine, the water is at a high pressure that depends on the depth of the water intake of the feed duct in the impoundment of water, so that a large quantity of each gas can have been dissolved in the water. At the outlet of the turbine, the water is at a relatively low pressure, i.e. at a pressure close to atmospheric pressure, so that the water is less likely to contain dissolved gas. A relatively large quantity of methane and of other gases dissolved in the water can thus be released by bubbling due to the lowering of the pressure of the water resulting from it passing through the turbine(s) of a dam. 
     In certain installations, such as those known from the article entitled “Mitigation and recovery of methane emissions from tropical hydroelectric dams” by L. Bambace, F. Ramos, I. Lima and R. Rosa, published in Energy (vol. 32, No. 6), it is known that metal boxes can be installed in an impoundment of water in order to prevent the water close to the bottom from entering a feed duct of a turbine. That avoids degassing in the turbine but it does not make it possible to treat the water charged with gas that remains at the bottom of the impoundment. Additional systems independent of the metal boxes, with pumps and spray rotors, must be used in order to degas the water, which consumes energy and is complex to put in place and to operate. 
     SUMMARY OF THE INVENTION 
     An object of the invention is, more particularly, to remedy that problem by limiting the emission of greenhouse gases in hydraulic installations, such as dams, without disrupting operation of such installations. 
     To this end, the invention provides an installation for converting hydraulic energy into mechanical or electrical energy, said installation comprising at least one hydraulic turbine, an impoundment of water, and a feed duct for feeding the turbine with water coming from the impoundment of water. Said installation is characterized in that it further comprises:
         a device immersed in the impoundment of water and suitable for constraining a flow of water advancing inside the impoundment of water towards the mouth of the feed duct to flow in an upward movement; and   gas collection means disposed over a portion of the device in which the upward movement of the flow of water takes place.       

     By means of the invention, the device makes it possible to cause the water flowing towards the feed duct to flow upwards, so that said water undergoes decompression conducive to releasing bubbles of the gases that it contains, such as methane. Those gases escape to the surface of the impoundment of water, in the vicinity of the device. The gas collection means then make it possible to recover the gases before they are dissipated into the atmosphere. The invention enables the water flowing towards the turbine(s) to have a dissolved gas content that is relatively small, so that the expansion that takes place when the forced flow passes through the turbine generates few gas bubbles at the outlet of the turbine. 
     In advantageous but non-essential aspects of the invention taken in any technically feasible combination, the installation may incorporate one or more of the following characteristics:
         The device comprises at least two panels disposed in the impoundment of water and co-operating to define between them a volume in which the upward movement of the flow of water takes place.   A first panel chosen from among the two panels is situated upstream from the second panel, in the general direction of flow of the water inside the impoundment of water, and the first panel extends at some distance from the bottom of the impoundment of water, an inlet passage via which the flow of water can enter the upward-movement volume being provided between a bottom edge of the first panel and the bottom of the impoundment of water. Advantageously, the first panel projects from the surface of the water in the impoundment.   The second panel extends to the bottom of the impoundment of water, and an outlet passage via which the flow of water can exit from the upward-movement volume is provided between a top edge of the second panel and the surface of the impoundment of water.   The panels are stationary. In a variant, the panels are mounted to be vertically movable, at least in part, thereby making it possible to adapt operation of said panels to accommodate the height of water that can vary depending on the seasons.   The gas collection means comprise a chamber formed by a concave structure that has its concave side facing towards a portion of the device, and that is open downwards.   The concave structure is a structure floating on the surface of the impoundment of water; it may be disposed substantially over the upward-flow volume and over the top edge of the second panel.   A discharge duct is provided for removing a flow of water downstream from the turbine, and at least one gas collection chamber is in fluid communication with the internal volume of said duct.   At least one gas collection chamber is in fluid communication with a top zone of the internal volume of the duct in a substantially horizontal portion of the duct, while the chamber(s) is/are connected to the internal volume of the duct via one or more openings that are distributed parallel to a longitudinal axis of the substantially horizontal portion of the duct, and while the chamber is defined by a shell that is mounted on the top portion of a wall of the duct and that is connected thereto in leaktight manner.   The chamber is a single chamber and is connected to the internal volume of the duct via a plurality of openings.   A plurality of chambers are distributed over the length of the substantially horizontal portion of the duct, and each of them is connected via at least one opening to the internal volume of the duct.   A first ratio between firstly the distance, measured parallel to a central axis of the horizontal portion of the duct, between the axis of rotation of the wheel of the hydraulic turbine and the upstream edge of the upstream-most opening of the gas collection chamber, and secondly the diameter of the wheel is greater than 1, and in particular equal to 2, and a second ratio between firstly the distance, measured parallel to a central axis, between the axis of rotation of the wheel and the downstream edge of the downstream-most opening of the gas collection chamber, and secondly the diameter of the wheel is greater than 2, and in particular equal to 3, when the first ratio is equal to 1.   The chamber is connected via a duct to an optionally removable gas accumulation tank or to a treatment unit for treating the gases collected in the chamber.   The chamber is connected to means for removing or for treating the collected gas(es).       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood and other advantages of the invention appear more clearly from the following description of embodiments of an installation that complies with the principle of the invention, the description being given merely by way of example and with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic view in axial section along the axis of rotation of the wheel of a turbine, showing the principle of an installation of the invention; 
         FIG. 2  is a view on a larger scale of the detail II of  FIG. 1 ; 
         FIG. 3  is a view on a larger scale of the detail III of  FIG. 1 ; 
         FIG. 4  is a section view on line IV-IV of  FIG. 3 ; 
         FIG. 5  is a view analogous to  FIG. 2  for a second embodiment of an installation of the invention; and 
         FIG. 6  is a view analogous to  FIG. 3  for a third embodiment of an installation of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The installation I shown in  FIGS. 1 and 2  includes a Francis turbine  1  having its wheel or “runner”  2  designed to be rotated about a vertical axis X 2  by a forced flow E coming from an impoundment of water R defined by a dam D. A shaft  3  mounted to rotate with the wheel  2  is coupled to an alternator  4  that delivers AC current to a network or grid (not shown) as a function of the rotation of the wheel  2 . The installation I thus makes it possible to convert hydraulic energy from the flow E into electrical energy. 
     The installation I may include a plurality of turbines  1  fed from the impoundment of water R. 
     In a variant, the shaft  3  may be coupled to a mechanical assembly, in which case the installation I converts hydraulic energy from the flow E into mechanical energy. 
     A feed duct  5  makes it possible to bring the flow E to the wheel  2  and extends between the impoundment of water R and a casing  6  equipped with wicket gates  61  that make it possible to regulate the flow E. 
     A discharge duct  8  is provided downstream from the turbine  1  so as to remove the flow E and so as to return it to a river channel from which the impoundment R is formed. 
     A control unit  10  is provided for controlling the turbine  1  as a function, in particular, of the electricity needs of the network fed from the alternator  4 . The unit  10  is capable of defining a plurality of points of operation of the installation I and of sending control signals S 1  and S 2  respectively to the alternator  4  and to the wicket gates  61 . 
     A device  200  is immersed in the impoundment of water R so as to constrain the water flowing towards the mouth  51  of the duct  5  to flow in an upward movement. The flow of water in the impoundment of water R towards the mouth  51  is referenced E 0 . This flow substantially takes place towards the dam D. 
     The device  200  includes a first panel  202  that extends over substantially the entire width of the impoundment of water R, i.e. the dimension of said impoundment of water that is parallel to the dam D. The device  200  also includes a second panel  204  that is substantially parallel to the first panel  202  and that also extends over substantially the entire width of the impoundment of water R. 
     Relative to the direction of flow of water in the impoundment of water R, the panel  202  is upstream from the panel  204 . 
     When the impoundment of water R is of large width, each of the panels  202  and  204  may extend over a fraction only of the width of the impoundment of water, so long as all of the water that is to enter the duct  5  flows between said panels. To this end, partitions perpendicular to the dam D may be provided in order to isolate the mouth  51  from a portion of the impoundment of water R. 
     The panel  202  is supported by legs  206  that are uniformly spaced apart along the panel, so that the bottom edge  208  of the panel  202  extends at a non-zero height H 1  relative to the bottom F of the impoundment of water R. The heights of the legs  206  and of the panel  202  are chosen such that said panel projects from the surface S E  of the water in the impoundment of water R. 
     The panel  204  stands on the bottom F and its top edge  210  is immersed in the impoundment of water R, at a depth P 1  that depends on the level of water in the impoundment R. 
     Bracing rods  212  are installed between the panels  202  and  204 , thereby imparting good stability to the device  200 . 
     The volume defined between the panels  202  and  204  is referenced V 200 . 
     Since the panel  204  is in abutment against the bottom F of the impoundment of water R, the flow E 0  that is directed towards the mouth  51  of the duct  5  necessarily passes over the top edge  210  of the panel  204 . To do so the flow E 0  necessarily has an upward movement in the volume V 200 . 
     Since the panel  202  projects from the surface S E , the flow E 0  necessarily passes under this panel and enters the volume V 200 , where it necessarily has the above-mentioned upward movement. 
     The flow E 0  penetrates between the panels  202  and  204  by passing through a first passage  214  defined, in the height direction, between the edge  208  and the bottom F, and, in the width direction, between at least two of the legs  206 . From the passage  214 , the flow E 0  flows in an upward movement, inside the volume V 200 , until it flows over into the downstream portion of the impoundment R, between the panel  204  and the dam D, so as to flow into the duct  5 . This flow-over of the flow E 0  takes place through a passage  216  defined between the top edge  210  of the panel  204  and the surface S E . 
     This upward movement of the flow E 0 , inside the volume V 200  and towards the passage  216 , is obtained without using a pump or any other equipment for causing water to move. It results from the natural flow of the water in the impoundment (R). 
     Due to the upward movement of the flow E 0  inside the volume V 200 , the water constituting said flow is subjected to decreasing pressure. The water pressure is large in the vicinity of the bottom F, whereas it decreases considerably in the vicinity of the surface S E , since said pressure is proportional to the depth of the water. Thus, the effect of the upward movement of the flow E 0  inside the volume V 200  is to decrease the pressure to which the flow E 0  is subjected, to the extent that bubbles B of methane or of other gases form in the flow E 0 , in the vicinity of the surface S E . In other words, the effect of forcing the flow E 0  to flow in a vertically upward movement inside the volume V 200  before entering the mouth  51  of the duct  5  is to release, by bubbling, the methane and the other gases present in said flow. 
     Means for collecting and recovering the bubbles of methane that are released in this way are provided in the form of a raft  400  floating on the surface S E  and held stationary over the volume V 200  and over the panel  204 . This raft  400  includes both a tube  402  for keeping it afloat, and a concave cover  404  having its concave side facing towards the surface S E . Thus, bubbles B of methane and/or other gases that reach the surface of the impoundment of water R, within the zone bounded by the tube  402 , can be recovered by a collection chamber  412  formed by the cover  404 . 
     The cover  404  is connected via a flexible duct  406  to a tank  420  supported by the dam D and in which the gases recovered in the chamber  412  are stored. The tank  420  may be removable, so that it can be replaced when it is full. 
     In practice, the flow E 0  may include various gases and the bubbles B can be mixtures of different gases, these different gases being collected by the raft  400  and being brought to the tank  420 . 
     The panels  202  and  204  may be made of metal, of concrete, or of a composite or synthetic material. They are held stationary inside of the impoundment of water R by means that are not shown, such as, for example, anchor blocks and/or struts bearing against the dam D. 
     The duct  8  has an upstream portion  81  that is substantially vertical, frustoconical, and centered on the axis of rotation X 2  of the wheel  2 . The duct  8  also has a downstream portion  82  centered on a substantially horizon axis X 82 . In the meaning of the present application, the axis X 82  is substantially horizontal in that it forms an angle with a horizontal plane that is less than 20°. In practice, the axis X 82  may be inclined slightly upwards in the direction of the flow E. A 90° bend  83  interconnects the portions  81  and  82  of the duct  8 . The magnitude of the angle formed by the bend  83  may be less than 90°. The internal volume of the duct  8  is referenced V 8 . 
     A chamber  12  is provided over the portion  82  of the duct  8 , and said chamber communicates with the volume V 8  by means of a plurality of openings  14  provided in the wall  16  of the duct  8 , in the top portion of said wall. The openings  14  are distributed over the length of the portion  82 , along the axis X 82 . 
     Thus, when bubbles B of methane are formed in the flow E, at the outlet of the turbine  1 , due to the pressure of said flow E decreasing resulting from the flow passing through the wheel  2 , said bubbles migrate towards the top portion S 8  of the volume V 8  in its downstream portion  82 , and pass through the openings  14 , as indicated by the arrows F 1  in  FIGS. 2 and 3 , so that the chamber  12  collects a fraction of the gas present in the flow E. 
     The chamber  12  thus makes it possible to recover a substantial fraction of the methane released by the flow E, thereby preventing said methane from propagating to the atmosphere. 
     The chamber  12  is connected via a pipe  18  to a tank  20  in which the methane can be accumulated. A valve  22  makes it possible to control the flow of the methane from the chamber  12  towards the tank  20 . The unit  10  controls the valve  22  by a signal S 3 . 
     In practice, the chamber  12  makes it possible to collect the various different gases that are released due to the drop in pressure of the flow E in the turbine  1  and, whenever methane is mentioned below, it is to be understood also to include the other gases. 
     The tank  20  may be removable so that it can be replaced when it is full. 
     In place of a storage tank  20  for storing the gas(es) collected in the chamber  12 , it is possible to provide a treatment unit for treating said gases, in order to make them less harmful relative to the ambient atmosphere. This unit may comprise a burner that makes it possible to generate heat energy. 
     Reference d 1  designates the distance, measured parallel to the axis X 82 , between the axis X 2  and the upstream edge  121  of the chamber  12 . Reference d 2  designates the distance, measured parallel to the axis X 82 , between the axis X 2  and the downstream edge  122  of the chamber  12 . The edges  121  and  122  respectively form the upstream edge of the opening  14  that is furthest upstream, and the downstream edge of the opening  14  that is furthest downstream. For an installation in which the wheel  2  has a diameter D 2  of about 5 meters, the distance d 1  is greater than 5 meters, and is preferably equal to about 10 meters, while the distance d 2  is greater than 10 meters, and is preferably equal to about 15 meters. It can be considered that the ratio d 1 /D 2  is greater than 1, e.g. equal to 2, while the ratio d 2 /D 2  is greater than 2, e.g. equal to 3 when d 1 /D 2  is equal to 2. These values are given by way of indication and may be adapted to accommodate the configuration of the duct  8 , in particular in the event of renovation of an existing dam. 
     The chamber  12  is defined be a shell  24  made of steel that is mounted on the top portion o 161  of the wall  16  and is connected thereto in leaktight manner, e.g. by welding. The welds “W” are shown in  FIGS. 3 and 4 . The shell may be made of a material different from steel, in particular, of a synthetic material or of concrete. 
     The relatively simple construction of the assembly formed by the parts  18  to  24  makes it possible to consider altering existing installations in order to recover greenhouse gases, such as methane. Naturally, the installation may also be implemented with new installations. 
     In an embodiment of the invention that is not shown, the chamber  12  may be replaced with a plurality of individual chambers distributed along the portion  82  of the duct  8 , each of which chambers is connected via one or more openings to the internal volume V 8  of the duct  8 . 
     The chamber(s)  12  supplement(s) the action of the device  200  and of the raft  400  so as to recover the bubbles of gas that form in the installation I. However, it is not essential to use such chambers  12 . 
     In the second embodiment of the invention shown in  FIG. 5 , the elements analogous to the elements of the first embodiment bear identical references. 
     In this embodiment, the downstream panel  204  is formed of a stationary portion  2042  held stationary in the impoundment of water R and of a moving portion  2044  controlled by an actuator  2046  mounted on the stationary portion  2042 . The moving portion  2044  is mounted to be movable vertically relative to the stationary portion, as indicated by the double-headed arrow F 1 , thereby making it possible to adjust the position of the top edge  210  of the panel  204  relative to the surface of the water S E , so that a pre-established height can be maintained for the outlet passage  216  of the volume V 200 . In other words, the depth P 1  at which the edge  210  is situated can be adjusted by means of the actuator  2046 . 
     This makes it possible to take account of the height of water in the impoundment R, which height can vary as a function of precipitation. The shallower the depth P 1 , the closer to the surface S E  the flow E 0  must pass, and the more accentuated the formation of bubbles B becomes. However, the value P 1  is maintained greater than a minimum value so as not to cause turbulence that could adversely affect the efficiency of the installation. 
     The upstream panel  202  is stationary, and its top edge projects from the surface of the water S E . It co-operates with the downstream panel  204  to define a volume V 200  in which a flow E 0  that is to enter the mouth  51  of the forced-flow duct  5  is constrained by the device  200  to flow in an upward movement, thereby causing bubbles of gas B to form, as in the first embodiment. 
     The raft  400  used in this embodiment is held stationary over the volume V 200  and is equipped with a flare stack  418  mounted on its cover  404 , thereby making it possible to burn off the gases, such as methane, that migrate in the form of bubbles B towards the chamber  412  defined by the cover  404 . Said gases are then destroyed by combustion and the gases resulting from said combustion (essentially CO 2 ) have less influence on the greenhouse effect than methane. 
     In a variant of the invention (not shown), the panel  202  may also be mounted to be vertically movable, at least in part. For example, the legs  206  may be telescopic or the panel  202  may be a floating panel that is guided vertically by a frame fastened to the bottom F. Its top edge nevertheless still projects from the surface S E . 
     In the two embodiments described, means (not shown), such as mooring lines fastened to the panel  202 , are provided to retain the raft  400  over the volume  200  and over the passage  216 . 
     In a variant of the invention (not shown) means for collecting the gas bubbles generated by the upward movement of the flow E 0  inside the device  200  may be supported by the top portion of the panel  202 , so that it is not necessary to use a raft. 
     In the third embodiment of the invention shown in  FIG. 6 , elements analogous to the elements of the first embodiment bear like references. 
     Only that which distinguishes this embodiment from the preceding embodiment is described below. 
     In this embodiment, three chambers  12 ,  12 ′, and  12 ″ are distributed over the length of the downstream portion  82  of the duct  8 , along the axis X 82 . Each of these chambers is connected via an opening  14 ,  14 ′,  14 ″ to the top portion S 8  of the internal volume V 8  of the discharge duct  8  of the installation, so that they make it possible to collect the bubbles B of methane or of other greenhouse gases that are formed in said duct. 
     Each chamber  12  is defined by a steel shell  24  that is mounted in leaktight manner on the top portion  161  of the wall  16  of the duct  8 . 
     The various chambers are interconnected via portions of a duct  18  that connects them collectively to a tank, such as the tank  20  of the first embodiment or to a treatment unit for treating the collected gases. 
     As in the first embodiment, references d 1  and d 2  designate the distances measured parallel to the axis X 82  between the axis of rotation of the wheel of the turbine and, respectively, the upstream edge  121  of the chamber  12  and the downstream edge  122  of the chamber  12 . With the same references as for the first embodiment, the ratio d 1 /D 2  is greater than 1, while the ratio d 2 /D 2  is greater than 2 and greater than d 1 /D 2 . 
     In an embodiment (not shown), each of the chambers  12   1 ,  12 ′ or  12 ″ may be connected to the internal volume V 8  of the duct  8  via a plurality of openings that are themselves distributed along the axis X 82 . 
     Regardless of the embodiment in question, the structure comprising the device  200  and the raft  400  is relatively simple to implement, so that it can be used not only for new installations, but also for renovating existing installations. 
     The invention is not limited to installations including Francis turbines. It may be implemented in any installation including a turbine of some other type, e.g. a Kaplan turbine, or a bulb turbine, in which one or more gases dissolved in the water can be released due to a flow of water being forced through the turbine. 
     Other variants are also possible. Thus, the chamber  412  may be supported by a floating raft, while being immersed in the impoundment of water, thereby making it less sensitive to wind and waves than the chamber of  FIG. 2 . To this end, it suffices to place the floats  402  on top of the cover  404 . In addition, when the invention is implemented for renovating an installation, the existing discharge duct may be extended to enable the gas collection chamber to be put into place. In a variant, the gas collection chamber may be formed by a bell-type device disposed at the outlet of the discharge duct, e.g. on a raft floating on the surface of the river, downstream from the installation, or fastened to the downstream end of the discharge duct. 
     The technical feature of the various variant embodiments considered may be combined without going beyond the ambit of the invention.