Abstract:
A solar heat boiler is provided which is capable of avoiding damage to heat transfer tubes without increasing facility cost and construction cost. The solar heat boiler includes: a low-temperature heating device by which water supplied from a water supply pump is heated by heat of sunlight; a steam-water separation device by which two-phase fluid of water and steam generated in the low-temperature heating device is separated into water and steam; a high-temperature heating device by which the steam separated by the steam-water separation device is heated by the heat of sunlight; and a circulation pump by which the water separated by the steam-water separation device is supplied to the low-temperature heating device.

Description:
TECHNICAL FIELD 
     The present invention relates to a solar heat boiler for collecting heat from the sun and generating steam using the heat, and a solar heat electric power generation plant using the solar heat boiler. Particularly, it relates to a solar heat boiler which is inexpensive and capable of preventing thermal damage to a heat transfer tube, and a solar heat electric power generating plant using the solar heat boiler. 
     BACKGROUND ART 
     In some sites, the amount of collected heat in a solar heat boiler inevitably repeats sudden increase and decrease in accordance with the amount of solar radiation varying suddenly in a short time due to the sunlight blocked by cloud or the like. 
     On the other hand, solar heat boilers are often introduced into a region called the Sunbelt, that is, a region where annual Direct Normal Irradiance (DNI) is beyond 2,000 kWh/m 2 , in order to obtain as large the annular total amount of collected heat as possible. 
     It is usually sunny in the Sunbelt throughout the year, and the amount of solar radiation hardly changes suddenly due to the change in weather. Thus, the stable amount of collected heat over time prevents the aforementioned problem from coming to the surface. 
     In regions other than the Sunbelt, for example, in Japan, however, the amount of solar radiation frequently changes suddenly in a day due to the change in weather or the movement of clouds so that sudden increase or decrease in the amount of collected heat may appear repeatedly. It is therefore important to take measures against such a problem. 
     Concentrating solar power generation plants are roughly classified into stand-alone type electric power generation plants and integrated type electric power generation plants. In the stand-alone type electric power generation plants, heat may be secured mostly by solar heat and partially backed up with fossil fuel etc. On the other hand, in the integrated type electric power generation plants, heat is secured mostly by fossil fuel or nuclear fuel and partially backed up with solar heat. 
     In each type of the stand-alone type electric power generation plants and the integrated type electric power generation plants, heat from the sunlight is collected and used as a heating source, and both the types may use substantially common solar collectors. 
     Solar collectors used typically include trough type ones, Fresnel type ones, tower type ones, etc. Ina trough type solar collector, a heat transfer tube is disposed above an inner circumferential curved surface of a reflecting mirror extending like a trough so that the sunlight can be collected in the heat transfer tube by the mirror. Thus, water circulating in the heat transfer tube is heated to generate steam. In a Fresnel type solar collector, a several number of reflecting mirrors having flat surfaces or slightly curved surfaces are arranged side by side at angles differing bit by bit from one to another, and a several number of heat transfer tubes are disposed above the group of the reflecting so that the sunlight can be collected in the heat transfer tube by the group of the reflecting to generate steam. In a tower type solar collector, a heat transfer tube panel is disposed on a tower having a predetermined height and a large number of reflecting mirrors (heliostats) are disposed on the ground surface so that the sunlight can be collected in the heat transfer tube panel by the group of the reflecting mirrors (heliostats) to generate steam. 
     Among them, in the trough type and the Fresnel type, the focal length is so short that the concentration ratio of the sunlight (the heat density in a heat collecting portion) is low. On the other hand, the tower type has an advantage that the focal length is so long that the concentration ratio of the sunlight (the heat density in a heat collecting portion) is high. 
     High heat density in a heat collecting portion leads to increase in the amount of collected heat per unit heat transfer area, so that higher-temperature steam can be obtained. However, when the heat density is simply increased to make a phase change from a water state to superheated steam, there arises a problem that a high-temperature area is formed locally to thereby cause damage to transfer tubes or the like. 
     In a thermal power generation boiler or the like, the amount of fuel is managed properly to avoid such damage to any heat transfer tube. In the case of solar heat, however, the heat input amount fluctuates so largely that it is difficult to avoid thermal damage to the heat transfer tubes. 
     To solve such a problem in the tower type with high heat density, a solar heat boiler configured as shown in  FIG. 17  and  FIG. 18  has been proposed, for example, in Patent Literature 1, Patent Literature 2, etc. 
       FIG. 17  is a schematic configuration diagram of a solar heat boiler.  FIG. 18  is an enlarged schematic configuration diagram of a heat collecting device for use in the solar heat boiler. 
     In  FIGS. 17 and 18 , the reference numeral  1  represents a heat collecting device;  2 , an evaporator;  3 , a superheater;  4 , a steam-water separation device;  5 , a tower;  6 , a heliostat;  7 , the sun;  8 , a steam turbine;  9 , an electric power generator; and  11 , a water supply pump. 
     As shown in  FIG. 18 , the heat collecting device  1  is functionally divided into the evaporator  2  and the superheater  3 , and the steam-water separation device  4  is placed between the evaporator  2  and the superheater  3 . The heat collecting device  1  is placed on the tower  5  which is about 30 to 100 meters high. Light from the sun  7  is reflected by the heliostats  6  placed on the ground, and condensed on the heat collecting device  1  so as to heat the evaporator  2  and the superheater  3 . Superheated steam generated in the heat collecting device  1  is sent to the steam turbine  8  so as to rotate the electric power generator  9 . Electric power is generated in such a mechanism. 
     Further,  FIG. 19  is a schematic configuration diagram of a solar heat electric power generation system described in U.S. Pat. No. 7,296,410 (Patent Literature 3). In  FIG. 19 , the reference numeral  200  represents a solar heat electric power generation system;  201 , a fluid channel;  202 , a valve;  203 , a pump;  204 , a trough device;  205 , a heat collection tube;  206 , a solar heat collector;  207 , a tower;  208 , a low-temperature heat storage tank;  209 , an intermediate heat storage tank;  210 , a high-temperature heat storage tank;  211 , a high-output generation device;  212 , a turbine; and  213 , an electric power generator. 
     In the solar heat electric power generation system, a thermal fluid stored in the low-temperature heat storage tank  208  is supplied to the trough devices  204  by the pump  203 , and heated by heat derived from the condensed light of the sun  106 . The thermal fluid further heated in the tower  207  is then sent to the high-temperature heat storage tank  210 . The thermal fluid sent to the high-temperature heat storage tank  210  is sent to the high-output generation device  211  by the pump  203 . The thermal fluid whose temperature has decreased due to heat exchange is returned to the low-temperature heat storage tank  208 . 
     On the other hand, configuration is made in such a manner that steam generated by the high-output generation device  211  is sent to the turbine  212  so that electric power is generated by the electric power generator  213 . 
     Further,  FIG. 20  is a schematic configuration diagram of a solar heat/light collection plant described in U.S. Pat. No. 8,087,245 (Patent Literature 4). In  FIG. 20 , the reference numeral  301  represents a trough type collector;  302 , a tower with heliostats;  303 , a low-temperature heat storage;  304 . a high-temperature heat storage;  305 , an auxiliary device using fossil fuel;  306 , a turbine;  307 , an electric power generator;  308 , a condenser; and  309 , a pump. 
     In the solar heat/light collection plant, water is sent to the trough type collector  301  by the pump  309  and heated by the heat of the sun so as to generate saturated steam. The generated saturated steam is sent to the tower with heliostats  302 . The turbine  306  is driven by the superheated steam generated thus, so as to generate electric power in the electric power generator  307 . 
     The steam is returned to water in the condenser  308 , and the water is supplied again by the pump  309 . Further, the configuration includes a line in which the saturated steam from the trough type collector  301  is not circulated in the tower with heliostats  302  but is passed through the auxiliary device  305  using fossil fuel so as to generate superheated steam. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: WO 2009/129166A2 
         Patent Literature 2: WO 2010/048578A1 
         Patent Literature 3: U.S. Pat. No. 7,296,410 
         Patent Literature 4: U.S. Pat. No. 8,087,245 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the aforementioned background-art technique shown in  FIGS. 17 and 18 , it is, however, necessary to place not only the evaporator  2  and the superheater  3  but also the steam-water separation device  4  in an upper portion of the tower  5  which is 30 to 100 meters high. It is therefore necessary to build the tower  5  strong enough to withstand earthquakes etc. and to support not only the loads of the evaporator  2  and the superheater  3  which are assemblies of a large number of heat transfer tubes but also the load of the steam-water separation device  4  which holds saturated water internally. Therefore, there is a problem that the facility cost and the construction cost increase. 
     In addition, water must be pumped up to the steam-water separation device  4  at a high site by the water supply pump  11 . Therefore, the water supply pump  11  must be high in pumping-up capacity and expensive. Therefore, the facility cost and the running cost increase. 
     Further, the amount of collected heat in the heat collecting device  1  must be suppressed in order to avoid thermal damage to the heat transfer tubes constituting the evaporator  2  and the superheater  3 . Thus, there is another problem that the volume and temperature of steam supplied to the steam turbine  8  fluctuate, with the result that the amount of power generation is not constant. 
     In the background-art technique shown in  FIG. 19 , the high-output generation device  211  is required for heat exchange between the thermal fluid and the water-steam. Further, the low-temperature heat storage tank  208 , the intermediate heat storage tank  209  and the high-temperature heat storage tank  210 , etc. are required for suppressing the temperature change caused by the fluctuation of the solar radiation to thereby stabilize the output of the electric power generator  307 . Thus, there is a problem that the facility cost increases and the installation space increases. 
     On the other hand, in the background-art technique shown in  FIG. 20 , horizontal heat collecting tubes are placed in the trough type collector  301 . Therefore, the fluctuation of the solar radiation leads to a change in the fluid state of a two-phase flow of steam and water in the horizontal heat collecting tubes. Thus, the bottom portion of each tube is filled with water and the top portion of the tube is filled with steam. In the trough type collector  301  which is heated on one side, the temperature on the side (upper portion) where steam exists increases extraordinarily. It is therefore likely that the heat collecting tubes may be damaged. 
     Further, the auxiliary device  305  using fossil fuel must be placed for supporting the fluctuation of the solar radiation. There is a problem that the facility cost and the running cost increase thus. 
     To solve such disadvantages belonging to the background-art techniques, an object of the present invention is to provide a solar heat boiler capable of avoiding thermal damage to a heat transfer tube without increasing facility cost and construction cost, and capable of suppressing fluctuation in the amount of power generation in a steam turbine to thereby supply high-quality electricity, and an independent type or composite type solar heat electric power generation plant using the solar heat boiler. 
     Solution to Problem 
     In order to attain the foregoing object, according to a first configuration of the present invention, there is provided a solar heat boiler, including: 
     a low-temperature heating device including a heat transfer tube which is disposed horizontally so that water supplied from a water supply pump can circulate through the heat transfer tube, and a reflecting mirror which collects sunlight in the heat transfer tube, so that the low-temperature heating device can heat the water by heat of the sunlight; 
     a steam-water separation device by which two-phase fluid of water and steam generated in the low-temperature heating device is separated into water and steam; 
     a high-temperature heating device by which the steam separated by the steam-water separation device is superheated by heat of sunlight; and 
     a circulating pump by which the water separated by the steam-water separation device is supplied to the low-temperature heating device. 
     According to a second configuration of the invention, there is provided a solar heat boiler according to the first configuration, wherein: 
     the low-temperature heating device, the steam-water separation device and the circulating pump are placed on or near a ground surface, and the high-temperature heating device is placed in a higher site than the low-temperature heating device and the steam-water separation device; and 
     a water level gauge which measures a water level in the steam-water separation device, a water supply valve which adjusts a flow rate of water supplied to the low-temperature heating device, and a circulation flow rate control valve which adjusts the amount of water circulating between the low-temperature heating device and the steam-water separation device are provided so that the flow rate of the supplied water or the amount of the circulating water can be adjusted by the water supply valve or the circulation flow rate control valve with the water level in the steam-water separation device being set at a predetermined value. 
     According to a third configuration of the invention, there is provided a solar heat boiler according to the first or second configuration, wherein: 
     the low-temperature heating device includes a trough type 1 solar collector in which a heat transfer tube is disposed above an inner circumferential curved surface of a reflecting mirror extending like a trough so that the sunlight can be collected in the heat transfer tube by the reflecting mirror to heat water circulating through the heat transfer tube and generate steam, or a Fresnel type solar collector in which a several number of reflecting mirrors having substantially flat surfaces are arranged side by side and a heat transfer tube is disposed above the group of the reflecting mirrors so that the sunlight can be collected in the heat transfer tube by the group of the reflecting mirrors to heat water circulating through the heat transfer tube and generate steam; and 
     the high-temperature heating device includes a tower type solar collector in which a heat transfer tube panel is placed on a tower having a predetermined height and a large number of reflecting mirrors are disposed so that the sunlight can be collected in the heat transfer tube panel by the group of the reflecting mirrors to superheat steam circulating through the heat transfer tube panel. 
     According to a fourth configuration of the invention, there is provided a solar heat boiler according to any one of the first to third configurations, wherein: 
     a glass tube with a predetermined length is disposed on the periphery of the heat transfer tube with a predetermined length so as to form a double structure, and an airtight state or a vacuum state is kept between the heat transfer tube and the glass tube; 
     the heat transfer tube with the predetermined length is formed by a plurality of heat transfer tubes joined to each other by welding, and the glass tube with the predetermined length is formed by a plurality of glass tubes joined to each other through metal joint tubes which are disposed in joint portions between the glass tubes and which are welded with the glass tubes respectively; and 
     outlet fluid temperature in the low-temperature heating device is regulated to 300° C. or less. 
     According to a fifth configuration of the invention, there is provided a solar heat boiler according to the fourth configuration, wherein: 
     a thermometer and a flowmeter are placed in an outlet of the low-temperature heating device and a flow rate of water supplied to the low-temperature heating device is adjusted so that a temperature measured by the thermometer and a flow rate measured by the flowmeter can be set at predetermined values. 
     According to a sixth configuration of the invention, there is provided a solar heat boiler according to the fourth configuration, wherein: 
     a thermometer and a flowmeter are placed in an outlet of the low-temperature heating device and the amount of collected heat in the low-temperature heating device is adjusted so that a temperature measured by the thermometer and a flow rate measured by the flowmeter can be set at predetermined values. 
     According to a seventh configuration of the invention, there is a provided a solar heat boiler according to any one of the first to third configurations, wherein: 
     a thermometer and a flowmeter are placed in an outlet of the low-temperature heating device and the amount of collected heat in the high-temperature heating device is adjusted in accordance with a value of a temperature measured by the thermometer and a value of a flow rate measured by the flowmeter. 
     According to an eighth configuration of the invention, there is provided a solar heat boiler, including: 
     a solar collector including a thermal channel in which a thermal such as diphenyl, biphenyl, 1,1-diphenylethane, etc. circulates, a thermal fluid circulating pump which is provided in the middle of the thermal fluid channel, a heat transfer tube which is provided in the middle of the thermal fluid channel and which is disposed horizontally so that the thermal fluid can circulate through the heat transfer tube, and a reflecting mirror which collects sunlight in the heat transfer tube, so that heat generated by collection of the sunlight can be transferred to the thermal fluid circulating through the heat transfer tube; 
     a heat exchanger-including low-temperature heating device in which a part of the thermal fluid channel of the solar collector is placed internally as a heat exchanger; 
     a water supply pump which supplies water to the heat exchanger-including low-temperature heating device; 
     a steam-water separation device by which two-phase fluid of water and steam generated by transferring the heat collected by the solar collector through the thermal fluid to water in the heat exchanger-including low-temperature heating device is separated into water and steam; 
     a high-temperature heating device by which the steam separated by the steam-water separation device is superheated by heat of sunlight; and 
     a circulating pump by which the water separated in the steam-water separation device is supplied to the heat exchanger-including low-temperature heating device. 
     According to a ninth configuration of the invention, there is provided a solar heat boiler according to any one of the first to eighth configurations, wherein: 
     the circulating pump is placed on a channel extending from the steam-water separation device to the low-temperature heating device. 
     According to a tenth configuration of the invention, there is provided a solar heat electric power generation plant, including: 
     a solar heat boiler according to any one of the first to ninth configurations; 
     a steam turbine which is driven by steam generated by the solar heat boiler; and 
     an electric power generator which is driven by the steam turbine. 
     According to an eleventh configuration of the invention, there is provided a solar heat electric power generation plant, including: 
     a boiler which generates steam by burning fuel or generating heat therefrom; 
     a water supply pump which supplies water to the boiler; 
     a steam turbine which is driven by steam generated by the boiler; 
     an electric power generator which is driven by the steam turbine; 
     a water supply heater which heats the water supplied from the water supply pump using steam extracted from the steam turbine; 
     a low-temperature heating device including a heat transfer tube which is disposed horizontally so that water supplied from the water supply pump can circulate through the heat transfer tube, and a reflecting mirror which collects sunlight in the heat transfer tube, so that the low-temperature heating device can heat a part of the water by heat of the sunlight; 
     a steam-water separation device by which two-phase fluid of water and steam generated in the low-temperature heating device is separated into water and steam; 
     a high-temperature heating device by which the steam separated by the steam-water separation device is heated by heat of sunlight; and 
     a circulating pump by which the water separated by the steam-water separation device is supplied to the low-temperature heating device. 
     According to a twelfth configuration of the invention, there is provided a solar heat electric power generation plant according to the eleventh configuration, wherein: 
     the low-temperature heating device, the steam-water separation device and the circulating pump are placed on or near a ground surface, and the high-temperature heating device is placed in a higher site than the low-temperature heating device and the steam-water separation device; and 
     a water level gauge which measures a water level in the steam-water separation device, a water supply valve which adjusts a flow rate of water supplied to the low-temperature heating device, and a circulation flow rate control valve which adjusts the amount of water circulating between the low-temperature heating device and the steam-water separation device are provided so that the flow rate of the supplied water or the amount of the circulating water can be adjusted by the water supply valve or the circulation flow rate control valve with the water level in the steam-water separation device being set at a predetermined value. 
     According to a thirteenth configuration of the invention, there is provided a solar heat electric power generation plant according to the eleventh or twelfth configuration, wherein: 
     the low-temperature heating device includes a trough type solar collector in which a heat transfer tube is disposed above an inner circumferential curved surface of a reflecting mirror extending like a trough so that the sunlight can be collected in the heat transfer tube by the reflecting mirror to heat water circulating through the heat transfer tube and generate steam, or a Fresnel type solar collector in which a several number of reflecting mirrors having substantially flat surfaces are arranged side by side and a heat transfer tube is disposed above the group of the reflecting mirrors so that the sunlight can be collected in the heat transfer tube by the group of the reflecting mirrors to heat water circulating through the heat transfer tube and generate steam; and 
     the high-temperature heating device includes a tower type solar collector in which a heat transfer tube panel is placed on a tower having a predetermined height and a large number of reflecting mirrors are disposed so that the sunlight can be collected in the heat transfer tube panel by the group of the reflecting mirrors to heat water circulating through the heat transfer tube panel and generate steam. 
     According to a fourteenth configuration of the invention, there is provided a solar heat electric power generation plant according to any one of the eleventh to thirteenth configurations, wherein: 
     a glass tube with a predetermined length is disposed on the periphery of the heat transfer tube with a predetermined length so as to form a double structure, and an airtight state or a vacuum state is kept between the heat transfer tube and the glass tube; 
     the heat transfer tube with the predetermined length is formed by a plurality of heat transfer tubes joined to each other by welding, and the glass tube with the predetermined length is formed by a plurality of glass tubes joined to each other through metal joint tubes which are disposed in joint portions between the glass tubes and which are welded with the glass tubes respectively; and 
     outlet fluid temperature in the low-temperature heating device is regulated to 300° C. or less. 
     According to a fifteenth configuration of the invention, there is provided a solar heat electric power generation plant according to the fourteenth configuration, wherein: 
     a thermometer and a flowmeter are placed in an outlet of the low-temperature heating device and a flow rate of water supplied to the low-temperature heating device is adjusted so that a temperature measured by the thermometer and a flow rate measured by the flowmeter can be set at predetermined values. 
     According to a sixteenth configuration of the invention, there is provided a solar heat electric power generation plant according to the fourteenth configuration, wherein: 
     a thermometer and a flowmeter are placed in an outlet of the low-temperature heating device and the amount of collected heat in the low-temperature heating device is adjusted so that a temperature measured by the thermometer and a flow rate measured by the flowmeter can be set at predetermined values. 
     According to a seventeenth configuration of the invention, there is provided a solar heat electric power generation plant according to any one of the eleventh to thirteenth configurations, wherein: 
     a thermometer and a flowmeter are placed in an outlet of the low-temperature heating device and the amount of collected heat in the high-temperature heating device is adjusted in accordance with a value of a temperature measured by the thermometer and a value of a flow rate measured by the flowmeter. 
     According to an eighteenth configuration of the invention, there is provided a solar heat electric power generation plant according to any one of the eleventh to thirteenth configurations, wherein: 
     a water level gauge which measures a water level in the steam-water separation device, a water supply valve which adjusts a flow rate of water supplied to the low-temperature heating device, and a circulation flow rate control valve which adjusts the amount of water circulating between the low-temperature heating device and the steam-water separation device are provided so that the flow rate of the supplied water or the amount of the circulating water can be adjusted by the water supply valve or the circulation flow rate control valve with the water level in the steam-water separation device being set at a predetermined value. 
     According to a nineteenth configuration of the invention, there is provided a solar heat electric power generation plant according to any one of the eleventh to thirteenth configurations, wherein: 
     a steam extraction valve is provided on the outlet side of the steam turbine; and 
     the steam extraction valve is operated in accordance with the amount of steam supplied from the high-temperature heating device, so that a steam extraction_flow in the steam turbine can be adjusted. 
     Advantageous Effects of Invention 
     According to the invention configured as described above, it is possible to provide a solar heat boiler capable of avoiding thermal damage to a heat transfer tube without increasing facility cost and construction cost, and capable of suppressing fluctuation in the amount of power generation in a steam turbine to thereby supply high-quality electricity, and an independent type or composite_type solar heat electric power generation plant using the solar heat boiler. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A schematic configuration diagram of a stand-alone type solar electric power generation plant according to a first embodiment of the invention. 
         FIG. 2  A view showing principles for explaining the configuration and so on of a tower type solar collector where a high-temperature heating device is placed. 
         FIG. 3  An enlarged schematic configuration diagram of a heat transfer tube panel for use in the high-temperature heating device. 
         FIG. 4  A schematic configuration diagram of a stand-alone type solar electric power generation plant according to a second embodiment of the invention. 
         FIG. 5  A view showing principles for explaining the configuration and so on of a trough type solar collector. 
         FIG. 6  A view showing principles for explaining the configuration and so on of a Fresnel type solar collector. 
         FIG. 7  A schematic configuration diagram of a stand-alone type solar electric power generation plant according to a third embodiment of the invention. 
         FIG. 8  A partially enlarged sectional view showing the vicinities of a heat transfer tube for use in a trough type (or Fresnel type) solar collector. 
         FIG. 9  A schematic configuration diagram of a solar heat integrated type electric power generation plant according to a fourth embodiment of the invention. 
         FIG. 10  A diagram showing an example in which the opening degree of a steam extraction valve provided on the outlet side of a steam turbine is adjusted in accordance with a change in the amount of steam passing through a steam valve provided on the outlet side of a high-temperature heating device according to the fourth embodiment. 
         FIG. 11  A schematic configuration diagram of a solar heat integrated type electric power generation plant according to a fifth embodiment of the invention. 
         FIG. 12  A schematic configuration diagram of a solar heat integrated type electric power generation plant according to a sixth embodiment of the invention. 
         FIG. 13  A schematic configuration diagram of a stand-alone type solar electric power generation plant according to a seventh embodiment of the invention. 
         FIG. 14  A characteristic graph showing the relationship between a water level L in a steam-water separation device and an outlet steam quality X in a low-temperature heating device. 
         FIG. 15  (a) is a view showing classification of fluid states in a two-phase flow of water and steam in a horizontal heat transfer tube of a low-temperature heating device, and (b) is a schematic view showing each fluid state of the two-phase flow of water and steam in the horizontal heat transfer tube. 
         FIG. 16  A schematic configuration diagram of a solar heat integrated type electric power generation plant according to an eighth embodiment of the invention. 
         FIG. 17  A schematic configuration diagram of a solar heat boiler according to the background art. 
         FIG. 18  An enlarged schematic configuration diagram of a heat collecting device for use in the solar heat boiler. 
         FIG. 19  A schematic configuration diagram of a solar heat electric power generation system proposed in Patent Literature 3. 
         FIG. 20  A schematic configuration diagram of a solar heat/light collecting plant proposed in Patent Literature 4. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (First Embodiment) 
     Next, embodiments of the invention will be described with reference to the drawings.  FIG. 1  is a schematic configuration diagram of a stand-alone type solar electric power generation plant according to a first embodiment of the invention. 
     In this solar heat electric power generation plant, as shown in  FIG. 1 , water supplied from a water supply pump  11  is sent to a water supply heater  12  through a water supply valve  19 . The water heated thus by the water supply heater  12  is introduced into a low-temperature heating device  13  through a steam-water separation device  4 . In the low-temperature heating device  13 , the supplied water is heated by light  32  from the sun  7 . The water is circulated between the steam-water separation device  4  and the low-temperature heating device  13  by a circulating pump  15 . 
     Two-phase fluid of water and steam generated in the low-temperature heating device  13  is separated into saturated water and saturated steam by the steam-water separation device  4 . The separated steam is sent to a high-temperature heating device  14  placed on a tower  16 . The steam introduced into the high-temperature heating device  14  is further superheated by solar heat reflected by heliostats  6  and introduced into the high-temperature heating device  14 . 
     The superheated steam generated in the high-temperature heating device  14  is designed to rotate a steam turbine  8  so that electric power can be generated by an electric power generator  9  due to the rotation of the steam turbine  8 . In order to adjust the amount of steam supplied to the steam turbine  8 , the water supply valve  19  is placed between the water supply pump  11  and the water supply heater  12 , and a steam valve  18  is placed between the high-temperature heating device  14  and the steam turbine  8 . 
       FIG. 2  is a view showing principles for explaining the configuration and so on of a tower type solar collector where the high-temperature heating device  14  is placed. 
     In the tower type solar collector, as shown in  FIG. 2 , the high-temperature heating device  14  (heat transfer tube panel  27 ) is placed on the tower  16  having a predetermined height (about 30 to 100 meters). On the other hand, a large number of heliostats  6  are disposed on the ground surface so as to face in various directions. The heliostats  6  are designed to follow the movement of the sun  7  so that light can be collected in the high-temperature heating device  14  (heat transfer tube panel  27 ) by the group of the heliostats  6  so as to generate superheated steam. 
     The tower type solar collector can generate steam at a higher temperature than a trough type solar collector. Thus, the tower type solar collector has a merit that the turbine efficiency can be increased to obtain higher electric power. 
       FIG. 3  is an enlarged schematic configuration diagram of the heat transfer tube panel  27  for use in the high-temperature heating device  14 . The heat transfer tube panel  27  is constituted by a superheater lower header  22 , a large number of superheater heat transfer tubes  21 , and a superheater upper header  23 . The superheater lower header  22  distributes steam from the steam-water separation device  4  evenly. The superheater heat transfer tubes  21  are disposed in parallel so that the steam distributed by the superheater lower header  22  can be circulated through the superheater heat transfer tubes  21 . The superheater upper header  23  collects superheated steam flowing out from the superheater heat transfer tubes  21 . The superheated steam outputted from the superheater upper header  23  is supplied to the steam turbine  8 . 
     The low-temperature heating device  13  and the steam-water separation device  4  hold a large amount of water internally and therefore each device is heavy as a whole. Thus, the low-temperature heating device  13  and the steam-water separation device  4  are placed on the ground surface or near the ground surface by use of a low foundation which is, for example, about 1 to 2 meters high. Since the low-temperature heating device  13  and the steam-water separation device  4  are thus placed on or near the ground surface, it is not necessary to pump up water to a site which is, for example, 30 to 100 meters high as in the background art. Therefore, the water supply pump  11  which is low in pumping-up capacity and low in price can be used. 
     On the other hand, light  32  from the heliostats  6  is collected with high optical density in the high-temperature heating device  14 . Therefore, the high-temperature heating device  14  is placed in a site which is 10 or more meters (for example, 30 to 100 meters) high from the ground surface. Since fluid flowing inside the high-temperature heating device  14  is only steam, the high-temperature heating device  14  is much lighter in weight and much smaller in size than the background-art heat collecting device  1  (see  FIG. 18 ) which is constituted by the evaporator  2 , the superheater  3  and the steam-water separation device  4 . Incidentally, the ratio in the amount of collected heat between the low-temperature heating device  13  and the high-temperature heating device  14  is generally 9:1 to 7:3. The amount of collected heat in the high-temperature heating device  14  is much smaller than that of the low-temperature heating device  13 . 
     In the embodiment shown in  FIG. 1 , the circulating pump  15  is placed on a channel from the steam-water separation device  4  to the low-temperature heating device  13 . The use temperature of the circulating pump  15  can be decreased as compared with that in the case where the circulating pump  15  is placed on a channel from the low-temperature heating device  13  to the steam-water separation device  4 . Thus, it is not necessary to use a pump which is high in heat resistance and high in price, but it is possible to reduce the cost and improve the reliability. This effect can be also obtained in each embodiment on and after a second embodiment in the same manner. 
     (Second Embodiment) 
       FIG. 4  is a schematic configuration diagram of a stand-alone type solar electric power generation plant according to a second embodiment of the invention. 
     In the embodiment, a low-temperature heating device  24  consisting of a trough type solar collector is used. The other configuration, the mechanism of electric power generation, etc. are similar to those in the aforementioned first embodiment, and redundant description thereof will be omitted. 
       FIG. 5  is a view showing principles for explaining the configuration and so on of a trough type solar collector. 
     The trough type solar collector has the following mechanism, as shown in  FIG. 5 . That is, a heat transfer tube  31  is disposed horizontally in a focal position above the inner circumferential curved surface of each reflecting mirror  30  extending like a trough, so that sunlight  32  can be collected in the heat transfer tube  31  by the reflecting mirror  30 . Water  33  circulates through each heat transfer tube  31 . The water  33  is heated by heat collected in the heat transfer tube  31  so that two-phase fluid  34  of water and steam can be obtained from the heat transfer tube  31 . 
     The trough type solar collector has a merit that it does not require any advanced light condensing technique but the structure is comparatively simple. 
     Although the low-temperature heating device  24  consisting of a trough type solar collector is used in the embodiment, a low-temperature heating device consisting of a Fresnel type solar collector may be used. 
       FIG. 6  is a view showing principles for explaining the configuration and so on of a Fresnel type solar collector. 
     The Fresnel type solar collector has the following mechanism, as shown in  FIG. 6 . That is, a several number of reflecting mirrors  35  having flat surfaces or slightly curved surfaces are arranged side and side at angles differing bit by bit from one to another, and a group of heat transfer tubes  31  formed like a panel are disposed horizontally several meters above the group of the reflecting mirrors  35 . 
     The mechanism works as follows. Sunlight  32  is collected in the group of the heat transfer tubes  31  by the group of the reflecting mirrors  35  so that water  33  circulating through each heat transfer tube  31  can be heated. Thus, two-phase fluid  34  of water and steam can be obtained from the heat transfer tube  31 . 
     The Fresnel type solar collector can be manufactured more easily and more inexpensively than the aforementioned trough type curved reflecting mirrors  30 . The Fresnel type solar collector has another merit that the reflecting mirrors  35  are rarely affected by wind pressure. 
     (Third Embodiment) 
       FIG. 7  is a schematic configuration diagram of a stand-alone type solar electric power generation plant according to a third embodiment of the invention. 
     In the embodiment, as shown in  FIG. 7 , a thermometer  25  and a flowmeter  28  for measuring the temperature and flow rate of fluid are provided on the outlet side of a low-temperature heating device  24 . Measurement signals of the thermometer  25  and the flowmeter  28  are supplied to an arithmetic unit  26 . In the arithmetic unit  26 , a control signal for controlling the opening degree of a water supply valve  19 , that is, the flow rate of water supply is outputted to the water supply valve  19  so as to make the outlet fluid temperature of the low-temperature heating device  24  always not higher than 300° C. 
     When the outlet fluid temperature of the low-temperature heating device  24  is limited to 300° C. or less in this manner, there is a merit that the structure of the low-temperature heating device  24  consisting of a trough type (or Fresnel type) solar collector can be simplified while the lowering of the heat transfer efficiency can be suppressed. Specifically, it is impossible to suppress cracking in a peripheral glass tube caused by a difference in thermal expansion between the heat transfer tube and the peripheral glass tube and radiative cooling caused by increase in surface temperature of the heat transfer tube, which are problems to be solved when a trough type (or Fresnel type) solar collector is used under high temperature. 
       FIG. 8  is a partially enlarged sectional view showing the vicinities of a heat transfer tube for use in a trough type (or Fresnel type) solar collector. As shown in  FIG. 8 , a peripheral glass tube  42  is disposed on the periphery of a horizontal heat transfer tube  38  so as to form a double structure. The peripheral glass tube  42  is provided to make an airtight state or a vacuum state between the horizontal heat transfer tube  38  and the peripheral glass tube  42  so that heat radiation from the horizontal heat transfer tube  38  to the outside air can be suppressed. 
     A plurality of heat transfer tubes  38  are joined together as one long heat transfer tube  38 . The heat transfer tubes  38  are made of metal such as carbon stainless steel. Therefore, the heat transfer tubes  38  may be formed into a predetermined length by welding  43  with each other as shown in  FIG. 8 . 
     On the other hand, peripheral glass tubes  42  cannot be welded with each other directly. As shown in  FIG. 8 , joint tubes  44  made of metal are disposed on the inner and outer sides of a joint portion between peripheral glass tubes  42 , and the peripheral glass tubes  42  are welded with the joint tubes  44  so as to form a structure in which the peripheral glass tubes  42  are joined to each other through the joint tubes  44  to have a predetermined length. 
     The heat transfer tube  38  jointed into a predetermined length is inserted inside the peripheral glass tube  42  joined into a predetermined length in this manner, and attached into the solar collector. Thus, when the difference in thermal expansion between the heat transfer tube  38  and the peripheral glass tube  42  increases, cracking may occur near the joint portion between the peripheral glass tube  42  and the joint tube  44 . 
     In addition, there is another problem that heat radiation to the outside air may increase due to a radiative cooling phenomenon (movement of heat in the fourth power of a temperature difference) when the difference in temperature between the surface temperature of the heat transfer tube  38  and the outside air increases due to increase in the surface temperature of the heat transfer tube  38 . 
     In the embodiment, therefore, the outlet fluid temperature of the low-temperature heating device  24  is limited to 300° C. or less, specifically within a range of from 250° C. to 300° C., so as to suppress cracking in the peripheral glass tube  42  caused by the difference in thermal expansion between the heat transfer tube  38  and the peripheral glass tube  42  and the radiative cooling caused by increase in surface temperature of the heat transfer tube  38 . 
     The amount of collected heat in the high-temperature heating device  14  can be adjusted based on the measurement signals of the thermometer  25  and the flowmeter  28  so as to make the outlet fluid temperature of the high-temperature heating device  14  not lower than 300° C. The opening degree of the water supply valve  19  is adjusted to change the flow rate of water supply to thereby adjust the amount of the collected heat. 
     The other configuration, the mechanism of electric power generation, etc. are similar to those in the aforementioned second embodiment, and redundant description thereof will be omitted. 
     Although the thermometer  25  and the flowmeter  28  are placed on the outlet side of the low-temperature heating device  24  and the flow rate of water supply to the low-temperature heating device  24  is adjusted to set the measured temperature and flow rate at predetermined values in the embodiment, the amount of collected heat in the low-temperature heating device  24  may be adjusted so that the temperature and flow rate measured by the thermometer  25  and the flowmeter  28  placed on the outlet side of the low-temperature heating device  24  can be set at predetermined values. 
     (Fourth Embodiment) 
       FIG. 9  is a schematic configuration diagram of a solar heat integrated type electric power generation plant according to a fourth embodiment of the invention, in which a boiler plant and a solar heat electric power generation plant are combined so that steam can be generated by burning of fuel, heat generated therefrom (for example, in the case of nuclear fuel), or heat recovered from exhaust gas. 
     The solar heat integrated type electric power generation plant includes a boiler plant  10 , a water supply pump  11 , a steam turbine  8 , a water supply heater  12 , etc. in addition to the solar heat electric power generation plant shown in  FIG. 1 . In the boiler plant  10 , steam is generated by burning of fuel, heat generated therefrom, or heat recovered from exhaust gas. The water supply pump  11  supplies water to the boiler plant  10 . The steam turbine  8  is driven by superheated steam generated by the boiler plant  10 . In the water supply heater  12 , the water supplied from the water supply pump  11  is heated using steam extracted from the steam turbine  8 . 
     In the solar heat integrated type electric power generation plant, a major part of the water supplied from the water supply pump  11  is supplied to the boiler plant  10 , and the water is finally converted into superheated steam by burning of not-shown fuel or heat generated therefrom. The superheated steam is sent to the steam turbine  8  to operate an electric power generator  9 , which generates electric power. 
     On the other hand, a part of the steam is extracted from the steam turbine  8  and sent to the water supply heater  12  through an steam extraction valve  17  so as to heat the supplied water. 
     Of the water supplied from the water supply pump  11 , the water excluding the water supplied to the boiler plant  10  is supplied to a low-temperature heating device  13  through a water supply valve  20 . The water is heated by light  32  of the sun  7  and made into two-phase fluid of water and steam, in which a part of the water has been converted into steam. The two-phased fluid of water and steam flows into a steam-water separation device  4 . The two-phased fluid of water and steam is separated into saturated steam and saturated water by the steam-water separation device  4 . The saturated water is supplied again to the low-temperature heating device  13  by a circulating pump  15 . The saturated steam separated by the steam-water separation device  4  is heated by a high-temperature heating device  14  and formed into high-temperature steam. The high-temperature steam is sent to the water supply heater  12  (from A to A in  FIG. 9 ). 
     In addition, as shown in  FIG. 9 , the high-temperature steam heated by the high-temperature heating device  14  may be supplied to the boiler plant  10  (from A to A′ in  FIG. 9 ) or may be supplied to the steam turbine  8  together with the superheated steam outputted from the boiler plant  10  (from A to A″ in  FIG. 9 ). 
       FIG. 10  is a diagram showing an example in which the opening degree of the steam extraction valve  17  provided on the outlet side of the steam turbine  8  is adjusted (see  FIG. 10( b ) ) in accordance with a change in the amount of steam passing through a steam valve  18  provided on the outlet side of the high-temperature heating device  14  (see  FIG. 10( a ) ) as shown in  FIG. 9 . 
     As shown in  FIG. 10 , the opening degree of the steam extraction valve  17  is reduced with the increase in the amount of steam passing through the steam valve  18 , and on the contrary, the opening degree of the steam extraction valve  17  is increased with the decrease in the amount of steam passing through the steam valve  18 . In this manner, the steam extraction valve  17  is operated in accordance with the amount of steam supplied from the high-temperature heating device  14 , so as to increase/decrease (adjust) the amount of extracted steam in the steam turbine  8 . Thus, large fluctuation in the output of electric power generation can be avoided. 
     The adjustment of the amount of extracted steam in the steam turbine  8  in accordance with the amount of steam supplied from the high-temperature heating device  14  may be also applied to the following embodiments. 
     (Fifth Embodiment) 
       FIG. 11  is a schematic configuration diagram of a solar heat integrated type electric power generation plant according to a fifth embodiment of the invention. 
     The embodiment is different from the aforementioned fourth embodiment in that a low-temperature heating device  24  consisting of a trough type or Fresnel type solar collector is used. 
     The other configuration, the mechanism of electric power generation, etc. are similar to those in the aforementioned fourth embodiment, and redundant description thereof will be omitted. 
     (Sixth Embodiment) 
       FIG. 12  is a schematic configuration diagram of a solar heat integrated type electric power generation plant according to a sixth embodiment of the invention. 
     In the embodiment, as shown in  FIG. 12 , a thermometer  25  for measuring the temperature of fluid and a flowmeter  28  are provided on the outlet side of a low-temperature heating device  24 . Measurement signals of the thermometer  25  and the flowmeter  28  are supplied to an arithmetic unit  26 . In the arithmetic unit  26 , a control signal for controlling the opening degree of a water supply valve  20 , that is, the flow rate of water supply is outputted to the water supply valve  20  so as to make the outlet fluid temperature of the low-temperature heating device  24  always not higher than 300° C. 
     The reason why the outlet fluid temperature of the low-temperature heating device  24  is limited thus to 300° or less is similar to that in the aforementioned third embodiment, and redundant description thereof will be omitted. 
     (Seventh Embodiment) 
     In any of the aforementioned embodiments, the low-temperature heating device  13  ( 24 ) and the high-temperature heating device  14  serve as Solar collectors by which fluid consisting of steam (water) for finally driving the steam turbine  8  is used as a thermal fluid which is heated directly by the light  32  of the sun  7 . 
     Accordingly, the solar heat boiler will use no other heat exchanger but the low-temperature heating device  13  ( 24 ) and the high-temperature heating device  14 . Thus, there is an advantage that the configuration of the boiler as a whole is simple enough to thereby achieve reduction in the size and cost or the like. 
     On the other hand, when the fluid consisting of water and steam is heated directly by the light  32  of the sun  7 , a change of phase from water to steam may occur within a heat transfer tube in a Fresnel type or trough type solar collector particularly for use in the low-temperature heating device  13  ( 24 ). When a two-phase flow is generated, there is a possibility that the heat transfer tube may be thermally damaged locally. 
     That is, particularly in the Fresnel type or trough type solar collector, of the peripheral surface of the heat transfer tube disposed horizontally, a region where light is collected receives heat. Therefore, the Fresnel type or trough type solar collector has a structure in which an uneven distribution of heat flux may be generated easily over the periphery of the heat transfer tube. 
     For this reason, when the internal fluid forms a two-phase flow, there is a possibility that abnormality in heat transfer may occur due to an instant change in the amount of collected light and heat, so as to cause thermal damage to that portion of the heat transfer tube. 
     In the Fresnel type or trough type solar collector, a long heat transfer tube is disposed substantially horizontally and placed in a wide area. The amount of collected heat derived from the sunlight fluctuates largely in a day, or changes suddenly depending on the weather. It is therefore difficult to beforehand specify the region where two-phase fluid may flow. 
     As a result, there is a problem that the heat transfer tube must be entirely made of a high-performance material, that is, an expensive material that hardly suffers thermal damage, thereby causing the increase in cost. 
     The seventh embodiment of the invention is a solution to such a problem.  FIG. 13  is a schematic configuration diagram of a solar heat independent type electric power generation plant according to the seventh embodiment. 
     In the embodiment, as shown in  FIG. 13 , a water supply circulating flow rate control valve  37  and a flowmeter  28  for adjusting the circulating flow rate are provided on the inlet side of a low-temperature heating device  13 , and a water level gauge  29  for detecting the water level of a steam-water separation device  4  is provided. 
     A flow rate measurement signal of the flowmeter  28  and a water level measurement signal of the water level gauge  29  are supplied to an arithmetic unit  26 , which outputs a control signal to a water supply valve  19  for adjusting the flow rate of water supply and (or) the water supply circulating flow rate control valve  37  for adjusting the circulating flow rate, so that the water level of the steam-water separation device  4  can be set at an intended value. 
     When the water level of the steam-water separation device  4  is controlled as in this embodiment, operation can be made to prevent phase separation from occurring in the heat transfer tube of the low-temperature heating device  13 . This principle will be described with reference to  FIG. 14  and  FIG. 15 . 
       FIG. 14  is a characteristic graph showing the relationship between a water level L (abscissa) in the steam-water separation device  4  and an outlet steam quality (ratio of steam mass flow rate to total mass flow rate) X (ordinate) in the low-temperature heating device  13 . A total mass flow rate G of the steam-water separation device  4  is used as a parameter for showing the relationship between the water level L and the outlet steam quality X. 
     The outlet steam quality X of the low-temperature heating device  13  corresponds to the ratio of the mass flow rate of steam to the total mass flow rate G. In addition, the total mass flow rate G of the steam-water separation device  4  corresponds to the flow rate of fluid circulating in the low-temperature heating device  13  through the steam-water separation device  4 . 
       FIG. 15( a )  is a view showing respective regions of classified fluid states in a two-phase flow of water and steam in the horizontal heat transfer tube  38  of the low-temperature heating device  13 , with the outlet steam quality X of the low-temperature heating device  13  in the abscissa and the total mass flow rate G of the steam-water separation device  4  in the ordinate. The classified fluid states include a spray flow, an annular flow, a bubble flow, a slug flow and a stratified flow. 
       FIG. 15( b )  is a schematic view showing each fluid state of the two-phase flow of water and steam in the horizontal heat transfer tube  38 . In  FIG. 15( b ) , the states of a spray flow, an annular flow, a bubble flow, a slug flow and a stratified flow are depicted. 
     In the  FIG. 15( b ) , in the state where the two-phase flow of water and steam is a spray flow, a major part of the two-phase flow in the tube is steam, and very small water drops accompanied by the steam flow in the steam. In the state of the annular flow, a very thin water film is formed on the tube wall, and a spray flow chiefly consisting of steam is located inside the water film. In the state of the bubble flow, a major part of the tube is filled with water, and small bubbles are present in the water. In the state of the slug flow, bubbles are much larger in size than in the aforementioned bubble flow, showing an intermediate state between the bubble flow and the stratified flow. In the state of the stratified flow, a vapor phase and a liquid phase are vertically separated by the effect of gravity. 
     Therefore, a preferred flow state for the two-phase flow of water and steam in the horizontal heat transfer tube  38  is the spray flow or the annular flow. 
     As apparent from the aforementioned result of  FIG. 14 , it is known that there is a correlation between the water level L of the steam-water separation device  4  and the outlet steam quality (the ratio of the steam flow rate to the total mass flow rate) X of the low-temperature heating device  13 . Accordingly, for example, an outlet steam quality X 1  of the low-temperature heating device  13  can be obtained by measurement of a water level L 1  of the steam-water separation device  4  in a mass flow rate G 1  of the steam-water separation device  4 . 
     Next, as shown in  FIG. 15( a ) , the flow state of the two-phase flow of water and steam in the low-temperature heating device  13  can be grasped if the outlet steam quality X of the low-temperature heating device  13  and the total mass flow rate G of the steam-water separation device  4  are known. When description is made along the example shown in  FIG. 14 , it is understood that the outlet steam quality is X 1  when the water level of the steam-water separation device  4  is L 1  in the condition that the mass flow rate is G 1 . 
     From  FIG. 15( a ) , it is understood that the flow state of the two-phase flow of water and steam in the horizontal heat transfer tube  38  of the low-temperature heating device  13  is a spray flow because the outlet steam quality is X 1  when the mass flow rate is G 1 . 
     In order to prevent phase separation from being generated in the horizontal heat transfer tube of the low-temperature heating device  13 , the flow state of the bubble flow, the annular flow or the spray flow is preferred in any operation conditions. When a thermal load on the low-temperature heating device  13  is high, it is particularly desired to set the flow state in the annular flow or the spray flow. 
     In the tube of the low-temperature heating device  13  which is heated on one side as shown in  FIG. 13 , the horizontal heat transfer tube  38  is superheated locally when the flow is separated into two phases of water and steam as in the slug flow or the stratified flow shown in  FIG. 15( b ) . As a result, there occurs an undesired event, such as high-temperature creep or tube deformation, for stable operation of the electric power generation plant. It is therefore extremely important on stable operation of the electric power generation plant to properly manage the flow state of the two-phase flow of water and steam in the low-temperature heating device  13 . 
     Accordingly, in the embodiment, an intended value of the water level in the steam-water separation device  4  corresponding to each value of the outlet steam quality X to make a desired flow state as described above is stored in the arithmetic unit  26  in advance. Measurement signals of the flow rate of the flowmeter  28  and the water level of the water level gauge  29  are supplied to the arithmetic unit  26 . The arithmetic unit  26  is designed to output a control signal to the water supply valve  19  for adjusting the flow rate of water supply and (or) the water supply circulating flow rate control valve  37  for adjusting the circulating flow rate, so that the water level of the steam-water separation device  4  can be set at the intended value. Thus, the electric power generation plant can be operated stably. 
     Although the embodiment has been described in the case of a stand-alone type solar electric power generation plant, the invention can be also applied to the case of a solar heat composite type electric power generation plant. 
     (Eighth Embodiment) 
     An eighth embodiment of the invention is to solve the same problem as the problem the aforementioned seventh embodiment is to solve.  FIG. 16  is a schematic configuration diagram of a solar heat integrated type electric power generation plant according to the eighth embodiment. 
     As shown in  FIG. 16 , a low-temperature heating device  51  and a solar collector  52  are formed separately, and a thermal fluid channel  53  is added to the solar collector  52 . A thermal fluid circulating pump  55  is provided in the middle of the thermal fluid channel  53 . A part of the thermal fluid channel  53  is disposed as a heat exchanger in the low-temperature heating device  51 , which serves thus as a heat exchanger-including low-temperature heating device. A thermal fluid  54  is designed to circulate from the solar collector  52  into the thermal fluid channel  53 . 
     Heat collected in the solar collector  52  is transferred to the low-temperature heating device  51  through the thermal fluid  54  circulating through the thermal fluid channel  53 , so as to heat fluid consisting of water and steam in the low-temperature heating device  51 . 
     The heat exchanger in the low-temperature heating device  51  (in this embodiment, a part of the thermal fluid channel  53 ) does not have to be limited especially as long as it is a noncontact type in which the thermal fluid  54  is not in direct touch with the fluid consisting of water and steam in the low-temperature heating device  51 . 
     In the embodiment, a solar collector such as a Fresnel type or trough type solar collector in which a light collecting unit and a heat collecting unit can be placed in a low position close to the ground surface is preferable as the solar collector  52 . 
     A thermal fluid whose phase does not change within an operating temperature range is used as the thermal fluid  54 . The thermal fluid  54  circulates from the solar collector  52  into the thermal fluid channel  53  by the thermal fluid circulating pump  55 . A chemical synthesis oil of diphenyl oxide, biphenyl, 1,1-diphenylethane, etc. alone or blended may be used as the thermal fluid  54 . 
     The maximum operating temperature of the thermal fluid  54  represented above is about 400° C. Beyond the maximum operating temperature, remarkable deterioration or loss in performance may occur. It is therefore necessary to manage the temperature strictly. However, a thermal fluid thermometer  56  may be added to the thermal fluid channel  53  as shown in  FIG. 16 , in order to monitor the outlet thermal fluid temperature of the solar collector  52 . When the temperature of the thermal fluid  54  is limited to be lower than the maximum operating temperature, for example, to be not higher than 300° C., it is not necessary to take special measures within the operation range. 
     In this manner, there is no fear that the phase of the thermal fluid  54  changes into a two-phase flow in the solar collector  52 . Therefore, there is no fear that abnormality in heat transfer may occur due to an instant change in the amount of collected light or collected heat. Accordingly, there is no fear that thermal damage to the heat transfer tube may occur even under the condition of an uneven distribution of heat flux, but it is possible to improve the reliability and reduce the material cost. 
     The following configuration may be further provided. 
     As shown in  FIG. 16 , a thermal fluid thermometer  56  and a thermal fluid flowmeter  57  for measuring the temperature and flow rate of the thermal fluid  54  are provided on the outlet side of the solar collector  52 , and measurement signals of the thermal fluid thermometer  56  and the thermal fluid flowmeter  57  are supplied to the arithmetic unit  26 . 
     In the arithmetic unit  26 , a control signal for controlling the opening degree of a water supply valve  20 , that is, the flow rate of water supply is outputted to the water supply valve  20  so as to make the outlet side thermal fluid temperature of the low-temperature heating device  52  not higher than 300° C. 
     The reason why the outlet fluid temperature of the low-temperature heating device  52  is thus limited to 300° C. or less is similar to that in the aforementioned third embodiment, and redundant description thereof will be omitted. In addition, the other configuration is the same as that in each of the aforementioned embodiments, and redundant description thereof will be omitted likewise. 
     In the eighth embodiment, solar heat is used in the low-temperature heating device  51  for generating and heating steam indirectly through a thermal fluid heated by the solar collector  52  formed separately. In the high-temperature heating device  14 , steam is heated directly by the solar heat collected in the same manner as in each of the aforementioned embodiments. The eighth embodiment may be referred to as a so-called hybrid heating type. 
     According to the eighth embodiment, the problem described in the beginning of the description of the seventh embodiment can be suppressed surely while suppressing and necessarily minimizing the configuration and scale of sections relating to a circulating system of the thermal fluid, such as the heat exchanger, the thermal fluid circulating pump  55 , etc. which complicate the configuration of the boiler device. Thus, the eighth embodiment is effective. 
     Although a configuration for heating supplied water with a thermal fluid such as steam is used as the water supply heater  12  in each of the aforementioned embodiments, the water supply heater  12  may be also designed to heat the supplied water using the solar heat. 
     According to the invention, as described above, the low-temperature heating device and the steam-water separation device are placed on the ground surface or near the ground surface. A structure (for example, a supporting base) for supporting a heavy substance holding saturated water is not necessary, or the structure can be placed to be low enough to easily install and maintain the low-temperature heating device and the steam-water separation device. In addition, it is possible to simplify a structure by which the high-temperature heating device which holds only steam and is comparatively light in weight can be installed in a high site. 
     Further, when the low-temperature heating device and the high-temperature heating device are separated functionally and the steam-water separation device is placed therebetween, the risk of damage to the heat transfer tube can be reduced. 
     Furthermore, when the high-temperature heating device is installed in a high site, heat exchange can be performed with high thermal density, so that high-temperature steam can be obtained efficiently. 
     In addition, when the amount of extracted steam on the steam turbine side is adjusted in accordance with a fluctuation in the steam temperature or the steam flow rate when the amount of collected heat in the high-temperature heating device is controlled, the output of the steam turbine can be kept constant. 
     Although this embodiment has been described in the case of a solar heat integrated type electric power generation plant, the invention can be also applied to a solar heat stand-alone type electric power generation plant. 
     REFERENCE SIGNS LIST 
     
         
           4 : steam-water separation device 
           6 : heliostat 
           7 : sun 
           8 : steam turbine 
           9 : electric power generator 
           10 : boiler plant 
           11 : water supply pump 
           12 : water supply heater 
           13 : low-temperature heating device 
           14 : high-temperature heating device 
           15 : circulating pump 
           16 : tower 
           17 : steam extraction valve 
           18 : steam valve 
           21 : superheater heat transfer tube 
           24 : trough type low-temperature heating device 
           25 : thermometer 
           26 : arithmetic unit 
           27 : heat transfer tube panel 
           28 : flowmeter 
           30 , 35 : reflecting mirror 
           31 : heat transfer tube 
           32 : light of the sun 
           33 : water 
           34 : two-phase flow of water and steam 
           37 : circulating flow rate control valve 
           38 : horizontal heat transfer tube 
           51 : low-temperature heating device 
           52 : solar collector 
           53 : thermal fluid channel 
           54 : thermal fluid 
           55 : thermal fluid circulating pump 
           56 : thermal fluid thermometer 
           57 : thermal fluid flowmeter