Abstract:
This power generation system is provided with a medium circuit, a circulation pump, an evaporator which evaporates a medium, an expander configured to be driven using the medium evaporated by the evaporator, a condenser configured to condense the medium discharged from the expander, a generator configured to be driven by the expander to generate power, a cooling system configured to cool the generator using the medium taken out from the medium circuit at a downstream side of the condenser, and a gas-liquid separator configured to separate the medium heated as a consequence of cooling the generator by the cooling system into gas and liquid phases, wherein the gas phase of the medium is flowed into the medium circuit at an upstream side of the condenser, and the liquid phase of the medium is flowed into the medium circuit at the downstream side of the condenser.

Description:
TECHNICAL FIELD 
     The present invention relates to a power generation system and method for performing power generation using waste heat from a ship, a plant, a gas turbine, and the like, terrestrial heat, solar heat, temperature difference between cooler deep and warmer shallow ocean waters, and the like as a heat source. 
     Priority is claimed on Japanese Patent Application No. 2012-288963, filed Dec. 28, 2012, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     In recent years, from the point of view of effective use of energy, environmental protection, and the like, as a system for performing power generation using waste heat from a ship, a plant, a gas turbine, and the like, terrestrial heat, solar heat, temperature difference between cooler deep and warmer shallow ocean waters, and the like as a heat source, a Rankine-type power generation system has been considered. In this case, if the heat source described above is used, as a medium, for example, a medium of which a boiling point is lower than that of water and more particularly, an organic fluid such as a Freon-based medium is used. 
     In such a power generation system  1 , as illustrated in  FIG. 5 , a medium is circulated by a circulation pump  6  in a cycle circuit  5  having an evaporator  2 , a turbine  3 , and a condenser  4 . Then, a heating medium recovered from the heat source as described above is fed to the evaporator  2 , is heat-exchanged with the medium, and is gasified by evaporating the medium. 
     The gasified medium drives a main shaft  3   a  to rotate by expansion in the turbine  3  and drives a generator  7 . The medium expanded by the turbine  3  is condensed by the condenser  4  and is circulated to the circulation pump  6 . 
     However, it is required to reduce a size of the turbine  3  or the generator  7  to reduce a size of the power generation system. If an amount of power equivalent to that of the related art is secured in the reduced generator  7 , it is required to accelerate a rotation of the turbine  3  and the generator  7 . 
     However, there is a concern that a temperature of each part of the generator  7  may increase and thereby cable coating, varnish, insulating paper, and the like forming the generator  7  may degrade and an insulation life be shortened by an increase in heat loss particularly due to acceleration of the rotation of the generator  7  or by a decrease in a heat radiation area due to the reduction of the size. Thus, it is preferable to cool the generator  7 . 
     Therefore, a configuration for cooling the generator by the medium passing through the turbine is disclosed in Patent Literature 1. 
     Furthermore, a configuration for cooling the generator by some of the medium taken out from an outlet of the circulation pump is disclosed in Patent Literature 2. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: United States Patent Application, Publication No. 2007/0063594 
     Patent Literature 2: Japanese Unexamined Patent Application, First Publication No. 2004-353571 
     SUMMARY OF INVENTION 
     Problem to be Solved by the Invention 
     However, if the medium has a low boiling point, the temperature of the medium is increased by cooling the generator  7  and some of the medium may be vaporized. 
     If the medium is fed to the circulation pump  6  while some of the medium is vaporized, medium delivery efficiency in the circulation pump  6  is greatly impaired. As a result, power generation efficiency in the generator  7  may be also reduced. 
     An object of the invention is to provide a power generation system in which a generator can be reliably cooled while a decrease in power generation efficiency is avoided and a power generation method. 
     Means for Solving the Problem 
     According to a first aspect of the present invention, a power generation system includes: a medium circuit through which a medium is circulated; a circulation pump configured to pressurize the medium so as to have the medium circulating through the medium circuit; an evaporator configured to evaporate the medium pressurized by the circulation pump, using heat from a heat source; an expander configured to be driven using the medium evaporated by the evaporator; a condenser configured to condense the medium discharged from the expander; a generator configured to be driven by the expander to generate power; a cooling system configured to cool the generator using the medium taken out from the medium circuit at a downstream side of the condenser; and a gas-liquid separator configured to separate the medium heated as a consequence of cooling the generator by the cooling system into gas and liquid phases, wherein the gas phase of the medium is flowed into the medium circuit at an upstream side of the condenser, and the liquid phase of the medium is flowed into the medium circuit at the downstream side of the condenser. 
     According to the above-mentioned power generation system, the generator is cooled by the medium taken out from downstream of the condenser in the cooling system. When the medium is heated by cooling the generator, some of the medium evaporates. Then, the medium is separated into the gas phase and the liquid phase in the gas-liquid separator, the gas phase of the medium is made to flow into the medium circuit upstream of the condenser and the liquid phase is made to flow into the medium circuit downstream of the condenser. Thereby it is possible to prevent lowering of the power generation efficiency caused by the reason such that the medium in which gas and liquid are mixed flows into the circulation pump. 
     Furthermore, the cooling system may include a flow rate-adjusting valve configured to adjust a flow rate of the medium supplied to the generator such that the medium is evaporated in the generator. 
     When the medium is evaporated in the generator, it is possible to further efficiently cool the generator by the heat of vaporization. 
     Furthermore, the circulation pump may be coaxially installed on a rotation shaft of the generator. 
     Thus, a motor for driving the circulation pump is not required and power loss of the circulation pump is reduced. 
     Here, the cooling system is operated using the medium may take out from the medium circuit at a downstream side of the circulation pump. For example, the cooling system may take the medium out from the downstream side of the circulation pump. 
     Furthermore, the cooling system is operated using the medium may take out from the medium circuit at an upstream side of the circulation pump. The cooling system may include a pump configured to pressurize the medium taken out from the medium circuit at the upstream side of the circulation pump. 
     Thus, even if the medium is taken out from the upstream side of the circulation pump, that is, from a position in which a pressure of the medium is the lowest in the medium circuit, it is possible to secure the flow of the medium in the cooling system by boosting the pressure by the pump. 
     Furthermore, the gas phase of the medium separated from the liquid phase of the medium by the gas-liquid separator may be flowed into the medium circuit at a downstream side of the evaporator. 
     According to a second aspect of the present invention, a power generation method includes the steps of: generating power by a generator, in which a medium is pressurized to have the medium circulating through a medium circuit, the pressurized medium is evaporated using heat of a heat source, an expander is rotated using the evaporated medium, and then the generator is driven using the rotation of the expander; cooling the generator using the medium taken out from the medium circuit at a downstream side of the condenser; and separating the medium heated as a consequence of cooling the generator into gas and liquid phases, wherein the gas phase of the medium is flowed into the medium circuit at an upstream side of the condenser, and the liquid phase of the medium is flowed into the medium circuit at the downstream side of the condenser. 
     Advantageous Effects of the Invention 
     According to the power generation system and the power generation method described above, it is possible to reliably cool the generator while avoiding a decrease in power generation efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of a power generation system according to a first embodiment of the present invention. 
         FIG. 2  is a diagram illustrating a configuration of a modified example of the power generation system according to the first embodiment of the present invention. 
         FIG. 3  is a diagram illustrating a configuration of a power generation system according to a second embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a configuration of another example of a power generation system. 
         FIG. 5  is a diagram illustrating a configuration of a power generation system of the related art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of a power generation system according to the present invention will be described with reference to the accompanying drawings. However, the invention is not limited to only the embodiments. 
     (First Embodiment) 
     As illustrated in  FIG. 1 , a power generation system  20 A includes a heating medium circuit  21  into which a heating medium is fed from a heat source such as waste heat from a ship, a plant, a gas turbine, and the like, terrestrial heat, solar heat, and temperature difference between cooler deep and warmer shallow ocean waters, and a medium circuit  22  which circulates a medium (medium) capable of obtaining thermal energy by heat exchange with the heating medium of the heating medium circuit  21 . 
     Here, as the medium of the medium circuit  22 , for example, it is possible to use a medium of which a boiling point is low and which is easily vaporized, more particularly, a medium having a boiling point lower than that of water, a Freon-based medium such as HFC-134a, HFC-245fa, HFO-1234yf, and HFO-1234ze, and the like, and, a medium of Freon-based media having a boiling point lower than that of water. 
     The heating medium circuit  21  supplies the heating medium such as steam and water (hot water) obtained by recovering heat from the heat source. 
     The medium circuit  22  is provided with a circulation pump  23 , an evaporator  25 , a turbine (expander)  26 , and a condenser  27 . 
     The circulation pump  23  compresses the medium and sends out the medium, and thereby circulates the medium in the medium circuit  22  such that the medium sequentially passes through the evaporator  25 , the turbine  26 , and the condenser  27 . 
     Since the evaporator  25  allows heat exchange between the heating medium of the heating medium circuit  21  and the medium of the medium circuit  22 , the evaporator  25  heats and evaporates a pressurized medium by heat exchange with the heating medium (external heat source) supplied by the heating medium circuit  21 . 
     The medium is expanded within a turbine chamber and thereby the turbine  26  drives a main shaft  26   a  around an axis thereof to rotate. The main shaft  26   a  is connected to a rotor (not illustrated) of a generator  28  and the rotor is driven to rotate with facing a stator (not illustrated) of the generator  28 . Thus, an AC current is output from the generator  28 . 
     In the power generation system  20 A described above, a conduit (cooling system)  30  branching from the medium circuit  22  is provided at the downstream side of the condenser  27  and the downstream side (between the circulation pump  23  and the condenser  27 ) of the circulation pump  23 . The conduit  30  is connected to a gas-liquid separator  31  through the generator  28 . 
     In the generator  28 , a medium flow path (not illustrated) through which the medium fed by the conduit  30  passes is formed in a housing and the like. 
     The gas-liquid separator  31  separates the medium into a gas phase and a liquid phase, a gas pipe  33  communicating with the gas phase inside the gas-liquid separator  31  is connected to the medium circuit  22  at an outlet side of the turbine  26 , a liquid pipe  34  communicating with the liquid phase inside the gas-liquid separator  31  is connected to the medium circuit  22  at an outlet side of the condenser  27 . 
     In the power generation system  20 A having such a configuration, some part of the medium which passed through the circulation pump  23  is taken out from the medium circuit  22  by the conduit  30  and is fed into the generator  28 . The fed medium passes through the medium flow path (not illustrated) of the generator  28  and thereby the generator  28  is cooled. Here, since the medium is heated by cooling the generator  28 , some medium is gasified. 
     The medium cooling the generator  28  is separated into the gas phase and the liquid phase in the gas-liquid separator  31 . 
     The gas phase of the medium flows into the medium circuit  22  at the upstream side of the condenser  27  through the gas pipe  33  and joins the gasified medium passing through an expansion process in the turbine  26 . Furthermore, the liquid phase of the medium is fed into the medium circuit  22  on the downstream side of the condenser  27  through the liquid pipe  34  and joins a liquefied medium in the condenser  27 . 
     In the manner described above, it is possible to cool the generator  28  by some medium circulating in the medium circuit  22 . Furthermore, in this case, even if the medium is gasified in the generator  28 , the gas phase joins the medium that is gasified in the medium circuit  22  and a remaining liquid phase joins the liquefied medium in the medium circuit  22 . Thus, the medium of which some is gasified in the generator  28  is fed in the circulation pump  23  after being liquefied in the condenser  27 . As a result, it is possible to prevent power generation efficiency from being lowered in the generator  28  and to also reliably cool the generator  28  without impairing medium delivery efficiency in the circulation pump  23 . 
     (Modified Example of First Embodiment) 
     In the power generation system  20 A having the configuration illustrated in the first embodiment described above, the conduit  30  may be provided with a flow rate adjusting valve  40  which adjusts a flow rate of the medium fed into the generator  28 . 
     In this case, it is preferable that an opening degree of the flow rate adjusting valve  40  is adjusted under control of a control unit  50  such that the medium is gasified when cooling the generator  28 . As the adjusting of an opening degree of the flow rate adjusting valve  40 , for example, a temperature or a pressure of the medium at the outlet side of the generator  28  or a temperature of the generator  28  itself is measured, and the control unit  50  refers to correlation data between the temperature or the pressure which is predetermined, and the opening degree of the flow rate adjusting valve  40 . Thereby it is possible to determine the opening degree of the flow rate adjusting valve  40 . 
     Thus, it is also possible to use heat of evaporation for cooling the generator  28 , along with the evaporation of the medium in the generator  28  and to cool the generator  28  more efficiently. 
     Furthermore, in the control unit  50 , it is possible to control to monitor an amount of the medium fed into the evaporator  25 , to throttle the flow rate adjusting valve  40  when the amount of the medium becomes small, and to increase the amount of the medium fed into the evaporator  25 . 
     Furthermore, in the embodiment described above, the conduit  30  branches from the medium circuit  22  at the downstream side of the circulation pump  23 , but, alternatively, as in a power generation system  20 A′ illustrated in  FIG. 2 , the medium may be taken out through the conduit  30  which branches from the medium circuit  22  at the downstream side of the condenser  27  and the upstream side of the circulation pump  23 . 
     Moreover, in such a configuration, since the medium flowing through the conduit  30  has the lowest pressure immediately before the circulation pump  23  in the medium circuit  22 , it is preferable that the conduit  30  is provided with a pump  41  and the medium is supplied to the generator  28  after the medium is pressurized by the pump  41 . 
     (Second Embodiment) 
     Next, a second embodiment of a power generation system according to the present invention will be described. In the following second embodiment, the same reference numerals are given in the drawings to the configurations shared by the first embodiment described above and description thereof will be omitted. 
     As illustrated in  FIG. 3 , a basic configuration of machinery included in a power generation system  20 B according to the embodiment, is shared by the power generation system  20 A according to the first embodiment described above. In the power generation system  20 B, a circulation pump  23  is provided coaxially with a rotation shaft  28   a  of a generator  28  and is driven by the rotation of the rotation shaft  28   a.    
     In this case, the circulation pump  23  may be connected to the rotation shaft  28   a  of the generator  28  through a transmission. 
     Also in the power generation system  20 B having such a configuration, similar to the power generation system  20 A of the first embodiment described above, it is possible to prevent power generation efficiency from being lowered in the generator  28  and to also reliably cool the generator  28  without impairing medium delivery efficiency in the circulation pump  23 . 
     Furthermore, the circulation pump  23  is provided coaxially with the rotation shaft  28   a  of the generator  28  and thereby a motor for driving the circulation pump  23  and the like are not required. Thus, it is possible to decrease power loss in the circulation pump  23  and to increase the power generation efficiency in the generator  28 . 
     In addition, the circulation pump  23  is connected to the rotation shaft  28   a  of the generator  28  through the transmission and thereby it is possible to handle a turbine  26  and the generator  28  which are rotated at high speed. 
     Moreover, as illustrated in  FIG. 2 , also in the configuration illustrated in the second embodiment described above, it is possible to take out the medium through a conduit  30  which branches from the medium circuit  22  at a downstream side of a condenser  27  and an upstream side of the circulation pump  23 . 
     (Another Modified Example) 
     Moreover, the power generation system of the invention is not limited to each of the embodiments described above with reference to the drawings and various modifications may be applied within the technical scope of the present invention. 
     For example, in the above described embodiments, the gas phase of the medium separated in the separator  31  flows into the medium circuit  22  at the upstream side of the condenser  27  However, the present invention is not limited to this configuration. The gas phase of the medium at the downstream side of the evaporator  25  may flow into the medium circuit  22 . 
     Furthermore, as a power generation system  20 C illustrated in  FIG. 4 , the medium circuit  22  can be configured to reach the evaporator  25  through the generator  28  after passing through the circulation pump  23 . 
     Thus, all amount of the medium delivered from the circulation pump  23  is fed to the medium flow path (not illustrated) of the generator  28  and cools the generator  28 . 
     Also in such a configuration, it is possible to reliably cool the generator  28 . 
     For example, in each of the power generation systems  20 A,  20 A′,  20 B, and  20 C of the embodiments described above, waste heat from a ship, a plant, a gas turbine, and the like, terrestrial heat, solar heat, and temperature difference between cooler deep and warmer shallow ocean waters are used as the heat source for generating power; however a type of heat source is arbitrary. 
     Furthermore, in each of the embodiments described above, the turbine  26  is exemplified as the expander; however, it is possible to employ a scroll type expander instead of the turbine  26 . 
     In addition, it is possible to choose the configurations mentioned in each of the embodiments described above and to appropriately change the configurations to other configurations without departing from the spirit of the invention. 
     INDUSTRIAL APPLICABILITY 
     According to the power generation system and the power generation method described above, it is possible to reliably cool the generator while avoiding a decrease in power generation efficiency. 
     REFERENCE SIGNS LIST 
       20 A,  20 A′,  20 B,  20 C POWER GENERATION SYSTEM 
       21  HEATING MEDIUM CIRCUIT 
       22  MEDIUM CIRCUIT 
       23  CIRCULATION PUMP 
       25  EVAPORATOR 
       26  TURBINE (EXPANDER) 
       26 A MAIN SHAFT 
       27  CONDENSER 
       28  GENERATOR 
       30  CONDUIT (COOLING SYSTEM) 
       31  GAS-LIQUID SEPARATOR 
       33  GAS PIPE 
       34  LIQUID PIPE 
       40  FLOW RATE ADJUSTING VALVE 
       41  PUMP 
       50  CONTROL UNIT