Abstract:
Said hydraulic turbine includes a wheel which is made to rotate about a rotational axis (X 2 ) by a main water stream (F 1 ) going from a penstock to a suction tube along a flow path that passes through the wheel. Said turbine also includes first means that are placed outside the flow path of the main water stream (F 1 ) and enable the mixing of a secondary water stream (F 2 ), taken from the flow path and located upstream from the wheel, and an oxygen-containing gas (A 2 ). Said turbine also includes second means for injection, downstream from the wheel of the turbine, a water/gas mixture (F 3 ) produced in the first means.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT/FR2013/050587 filed Mar. 19, 2013, which is hereby incorporated in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a hydraulic turbine and to an energy conversion installation comprising such a turbine. 
         [0003]    In the field of the conversion of hydraulic energy into electrical or mechanical energy, it is known to use a turbine, for example a Francis turbine, for driving in rotation a shaft bearing a runner of the turbine, this shaft being connected to an alternator. Such a turbine is integrated into an installation which comprises, inter alia, a water reservoir which is connected to a scroll casing supplying the turbine by means of a forced duct. 
         [0004]    In certain installations, in particular those used in relatively hot climates, and toward the end of summer, it is possible that the water coming from the water reservoir through the forced duct has a low level of dissolved oxygen, due to the fact that this water is drawn from a relatively great depth in the water reservoir, where the oxygen content is such that aquatic life cannot exist. In this case, in order to allow aquatic life to develop downstream of the installation, the water passing through the turbine must be enriched with oxygen. 
         [0005]    To that end, it is known to put in place, on the flow path of a water flow passing through the runner of the turbine, means for oxygenating this water flow, as set out in the article “ Methods for air admission in hydroturbines ” by B. Papillon, M. Couston, C. Deschenes, M. Sabourin, published in  Proceedings of the Hydraulic Machinery and Systems  21 st    AIHR symposium  (Sep. 9-12, 2002, Lausanne). Such systems disturb this water flow, which reduces the efficiency of the installation over the entire year, whereas the problem linked to supplying the turbine with air-depleted water arises only in certain circumstances. 
         [0006]    It is these drawbacks which the invention is to address more particularly, by proposing a novel hydraulic turbine which is able to operate with water having a low level of dissolved oxygen and whose efficiency is not markedly reduced as a consequence of the measures undertaken for increasing the level of dissolved oxygen in the water, when this is necessary. 
       SUMMARY 
       [0007]    To that end the invention relates to a hydraulic turbine comprising a runner rotating about an axis of rotation under the action of a main water flow traveling from a forced duct toward a draft tube along a flow path which passes through the runner of the turbine. According to the invention, this turbine comprises:
   first means which are arranged outside the flow path of the main water flow and by means of which it is possible to mix, on one hand, a secondary water flow drawn from the flow path, upstream of the runner of the turbine, and, on the other hand, a gas containing oxygen and   second means for injecting, downstream of the runner of the turbine, a water-gas mixture created in the first means.   
 
         [0010]    By virtue of the invention, the first means, which are arranged outside the flow path of the main water flow, do not disturb this main water flow which can therefore be used in optimal conditions for driving in rotation the runner of the turbine. When it is necessary to increase the oxygen content of the water leaving the turbine, the first means may be implemented, drawing the secondary water flow from the flow path, for example in the forced duct. When that is not necessary, in particular depending on climatic conditions, the secondary water flow is not drawn and the first and second means of the invention have no influence on the efficiency of the installation comprising the hydraulic turbine of the invention. 
         [0011]    According to advantageous but non-essential aspects of the invention, such a turbine may incorporate one or more of the following features, in any technically permissible combination:
   The first means comprise a mixing chamber which is supplied, on one hand, with water via a first line connected to the flow path and, on the other hand, with gas via a second line which is supplied with gas containing oxygen.   The mixing chamber comprises a Venturi effect hydro-injector, a system excited by a piezoelectric element, a cavitating vortex system, a porous mesh or a combination of these means.   The first means are provided to mix the secondary water flow with air. In this case, the second line can be connected to the atmosphere.   As a variant, the second line is connected to a reservoir of gas containing oxygen, preferably under pressure.   The turbine comprises means, for controlling the flow rate of the secondary water flow, between the flow path and the first means.   The means for controlling the flow rate of the secondary water flow comprise at least one first valve arranged on the first line.   The turbine comprises means for controlling the flow rate of gas supplied to the first means.   The means for controlling the flow rate of gas comprise at least one second valve arranged on the second line.   The means for controlling the flow rate of the secondary water flow and/or the means for controlling the flow rate of gas comprise a control unit for the first valve and/or for the second valve.   The second means comprise a distributor equipped with one or more nozzles arranged on a wall of the draft tube and oriented toward a central axis of this tube.   When the injector comprises multiple nozzles, these nozzles are preferably distributed regularly about the central axis of the draft tube.   When the injector comprises multiple nozzles, the distributor advantageously comprises a chamber, between the nozzles, for distributing the water-gas mixture coming from the first means, this chamber being arranged radially around the nozzles.   The distributor comprises a deflector arranged in the draft tube, downstream of the nozzles.   The secondary water flow is drawn from the forced duct. As a variant, it is drawn from a scroll casing for distributing the main water flow or from a water reservoir supplying the turbine.   
 
         [0026]    The turbine of the invention may be a Francis turbine or a turbine of the propeller, bulb or Kaplan type. 
         [0027]    The invention also relates to an installation for converting hydraulic energy into electrical or mechanical energy, which comprises a turbine as mentioned hereinabove, and also a forced duct for supplying this turbine with a main water flow and a draft tube for evacuating the main water flow leaving the turbine, whereas the first means are selectively supplied with a secondary water flow drawn from the flow path, upstream of the runner of the turbine, and with a flow of gas containing oxygen at atmospheric pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The invention will be better understood and other advantages thereof will become clearer in light of the following description of two embodiments of a turbine and of an installation in accordance with the principle thereof, which description is given purely by way of example and with reference to the appended drawings, in which: 
           [0029]      FIG. 1  is a diagrammatic representation, in axial section, of an installation in accordance with the invention, 
           [0030]      FIG. 2  is an enlarged view of detail II of  FIG. 1  and 
           [0031]      FIG. 3  is a detail section corresponding to the plane of  FIG. 2 , for a second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The installation  100  shown in  FIG. 1  comprises a Francis-type turbine  1  whose runner  2  is designed to be set in rotation about a vertical axis X 2  by means of a main water flow shown by arrows F 1 . This main water flow F 1  comes from a water reservoir which is not shown. In  FIG. 1 , for the sake of clarity, the runner  2  is shown in external view. A shaft  3  supports the runner  2  and is coupled to an alternator  4  which provides an alternating current to an electrical grid (not shown). The installation  100  thus makes it possible to convert the hydraulic energy of the main water flow F 1  into electrical energy. 
         [0033]    The installation  100  may comprise multiple turbines  1  supplied from the same water reservoir. 
         [0034]    As a variant, the shaft  3  may be coupled to a mechanical assembly, in which case the installation  100  converts the hydraulic energy of the main water flow F 1  into mechanical energy. 
         [0035]    A forced duct  5  brings the main water flow F 1  to the runner  2  and extends between the water reservoir and a scroll casing  6  for distributing the flow F 1 , equipped with wicket gates  7  which orient the main water flow F 1 . A draft duct  8  is provided downstream of the turbine  1 , in the direction of the main water flow F 1 , for evacuating this water flow and returning it toward the bed of a river, or toward a downstream reservoir when the turbine  1  is a pump-turbine. 
         [0036]    The duct  8  comprises a first segment  82  which is generally frustoconical, is centered on an axis X 82  which coincides with the axis X 2 , and is diverging downwards. The duct  8  also comprises a second segment  83  in the form of an approximately 90° bend, and a third generally horizontal segment  84 . Leaving the runner  2 , the water leaving the turbine  1  passes in succession through the segments  82 ,  83  and  84  of the duct  8 . 
         [0037]    The runner  2  comprises a crown  202 , a band  204  and multiple blades  206  distributed about the axis X 2  which is an axis of symmetry for the crown  202  and the band  204 . The blades  206  define, between them and between the crown  202  and the band  204 , flow ducts for the main water flow F 1  within the runner  2 , between the scroll casing  6  and the draft duct  8 . 
         [0038]    The duct  5 , the scroll casing  6 , the wicket gates  7 , the runner  2  and the duct  8  together define a flow path for the main water flow F 1 . 
         [0039]    In order to take account of the case in which the level of dissolved oxygen in the water provided to the runner  2  is low, in particular when this water is drawn from a great depth in the water reservoir, toward the end of summer and when the installation  100  is used in a relatively hot climate, a mixing chamber  102  is provided close to segment  82  of the draft duct  8 . This mixing chamber  102  is supplied with water, from the forced duct  5 , by means of a first line  104  which connects the forced duct  5  to the mixing chamber  102 . The mixing chamber  102  is also supplied with air by means of a second line  106  whose opening  107  is in communication with the atmosphere. Thus, the second line  106  makes it possible to supply the mixing chamber  102  with air at atmospheric pressure. The mixing chamber  102  comprises baffles (not shown) placed on the flow path of the water inside this chamber, as well as orifices, distributed within this chamber, out of which flows the air from the second line  106 . Thus, a two-phase mixture of water and air is created in the chamber  102 . 
         [0040]    The structure of the mixing chamber  102  depends on a design choice. It comprises a Venturi effect hydro-injector. As a variant, the mixing chamber  102  comprises a system excited with a piezoelectric element, a cavitating vortex system or a porous mesh or a combination of these different means. Other types of mixing chamber are conceivable. 
         [0041]    A first valve  114  is mounted on the line  104 , while a second valve  116  is mounted on the line  106 . The valves  114  and  116  are solenoid valves controlled by an electronic unit  120  by means of two electronic signals S 114  and S 116 . They make it possible to selectively prevent or allow water and air to flow respectively in lines  104  and  106 . The unit  120  is thus able, as a function of an electronic signal S 120  received from an external measuring means or from an operator, to control the valves  114  and  116  so as to allow or prevent the supply of, respectively, water from the forced duct  5  and air from the atmosphere, to the mixing chamber  102 . 
         [0042]    The valves  114  and  116  may be “all or nothing” valves. In this case they make it possible to control the values of the flow rates of water F 2  and air A 2  between a zero value and a maximum value. As a variant, these valves are proportional valves, which makes it possible to adjust these flow rates, in particular as a function of the flow rate in the forced duct  5  or of the atmospheric pressure. When the first valve  114  is open, a secondary water flow F 2  flows, from the forced duct  5  and through the line  104 , into the mixing chamber  102 . When the second valve  116  is open, air flows in the line  106  into the mixing chamber  102 , as shown by the arrows A 2 . The secondary water flow F 2  and the airflow A 2  then combine in the mixing chamber  102  and flow thence, in the form of a flow F 3  of a two-phase mixture of water and air, into the distributor  110 , whence this flow re-emerges into the segment  82  in the form of individual flows F′ 3  of water-air mixture. These individual flows F′ 3  open into the draft duct  8  through nozzles  1102  belonging to the distributor  110  and distributed over the periphery of the segment  82 , about the axis X 82 . The distributor  110  comprises a distribution chamber  1104  which extends at least partially around the segment  82  and by means of which it is possible to regularly distribute the flow of mixture F 3  which is split into multiple flows F′ 3  at the various nozzles  1102 . The nozzles  1102  consist of orifices created in the wall  822 . The nozzles or orifices  1102  are oriented toward the axis X 82 . 
         [0043]    In practice, the respective water and air supply pressures to the mixing chamber  102  are such that air bubbles of several tenths of a millimeter in size are created in the flow F 3 . These bubbles are stable at least until the individual flows F′ 3  discharge into the segment  82 , downstream of the runner  2 . 
         [0044]    The segment  82  is a region of relatively low pressure in the main water flow F 1 , which promotes mixing between the flows F 1  and F′ 3 , in particular since the flow F 1  leaving the runner  2  is very turbulent. Thus, elements  102  to  120  make it possible, when necessary, to inject the flow F 3  of water-air mixture downstream of the runner  2 , that is to say into a region of the installation  100  in which the pressure of the water is relatively low, in particular lower than in the forced duct  5 . This flow F 3  of water-air mixture then combines with the main water flow F 1 , which makes it possible to increase the air content in the flow of water leaving the turbine  1 , this flow being the sum of the flows F 1  and F 3 . 
         [0045]    In these conditions, the total water flow F 0 , drawn from the water reservoir and flowing in the forced duct  5 , is split into the main water flow F 1  and the secondary water flow F 2 , whereas the total flow F′ 0  leaving the turbine is the sum of flows F 1  and F 3 . 
         [0046]    When, taking into account the signal S 120 , the unit  120  determines that it is not necessary to increase the level of dissolved oxygen in the main water flow F 1  passing through the runner  2 , the valves  114  and  116  are closed and the elements  102  to  116  have no influence on the operation of the turbine  1 . In particular, they do not reduce the overall efficiency of the installation  100 . This is in particular due to the fact that the elements  102  to  116  are installed outside the flow path of the flow F 1 . 
         [0047]    In these conditions, the water flows F 0 , F′ 0  and F 1  have the same flow rate and the flow rate of the secondary water flow is zero. 
         [0048]    It is also noted that, as these elements  102  to  116  are located outside the path of the flow F 1 , the elements  2 ,  3  and  5  to  8  may be standard elements, which is advantageous in terms of design and maintenance. 
         [0049]    In the second embodiment of the invention, shown in  FIG. 3 , the elements which are similar to those of the first embodiment bear the same references. In what follows, the description focuses on the differences between this first embodiment and the preceding embodiment. 
         [0050]    The distributor  110  of this embodiment also comprises a distribution chamber  1104  which supplies various orifices or nozzles  1102  created in the wall  822  of a segment  82  of the draft tube. An annular deflector  1106  is arranged, within the segment  82 , level with the nozzles  1102 . This deflector is secured to the wall  822  above the nozzles  1102  and makes it possible to create, close to these nozzles and under the effect of the main water flow F 1 , a region of low pressure, which sucks in the individual flows F′ 3  of the two-phase mixture of water and air into the draft duct  8 . 
         [0051]    The present invention can be the subject of various arrangements and modifications. 
         [0052]    In particular, it can be implemented with turbines other than a Francis turbine, in particular with a turbine of the propeller, bulb or Kaplan type. The invention may also be implemented with a pump-turbine. 
         [0053]    Instead of a distributor  110  comprising multiple nozzles or orifices and a distribution chamber, other types of distributors may be envisaged. For example, the nozzles may be replaced by a continuous or discontinuous groove on the periphery of the suction unit, or by a single injection nozzle. 
         [0054]    As a variant, the air flow F 3  may be injected into another part of the turbine  1 , as long as this is a region of relatively low pressure in the main water flow F 1 , downstream of the runner of the turbine. 
         [0055]    According to another variant, the secondary water flow F 2  may be drawn from another part of the path of the main water flow F 1 . This can in particular be the case at the scroll casing  6  or in the water reservoir. 
         [0056]    According to another variant, a gas other than air and containing oxygen may be supplied to the mixing chamber  102 . This gas may be supplied from a dedicated reservoir, preferably under pressure and installed close to the turbine  1 . 
         [0057]    According to another variant, pumps and/or compressors may be installed on the lines  104  and  106  in order to ensure that the mixing chamber  102  is supplied with water and with oxygen-containing gas, respectively, at sufficient pressure. 
         [0058]    The technical features of the embodiments and variants set forth hereinabove may be combined with one another to give rise to novel embodiments.