Abstract:
A heat collector of a dish-type solar thermal power generation system and the solar thermal power generation system having the heat collector. The heat collector of the dish-type solar thermal power generation system comprises a heat collecting cavity and at least one layer of heat absorbing coil. The heat collecting cavity is provided with an opening. The heat absorbing coil forms a cavity structure. The cavity structure is provided with a hole. The cavity structure is arranged within the heat collecting cavity. The hole and the opening are aligned. A low temperature inlet of the heat absorbing coil is arranged on the cavity structure at a location where incident light energy distribution density is at maximum. The heat collector is capable of preventing ablation of the heat absorbing coil due to localized overheating and burning of the heat collector due to abrupt drop in convective heat transfer coefficient caused by phase transition of working fluid.

Description:
[0001]    The present application claims priority to Chinese Patent Application No. 201110118565.6, filed with the Chinese Patent Office on May 9, 2011 and entitled “DISH-TYPE SOLAR THERMAL POWER GENERATION SYSTEM AND HEAT COLLECTOR THEREOF”, which is hereby incorporated by reference in its entirety. 
         [0002]    The present application claims priority to Chinese Patent Application No. 201120144531.X, filed with the Chinese Patent Office on May 9, 2011 and entitled “DISH-TYPE SOLAR THERMAL POWER GENERATION SYSTEM AND HEAT COLLECTOR THEREOF”, which is hereby incorporated by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0003]    The present application relates to the technical filed of solar thermal power generation system, and particularly to a heat collector for a dish solar thermal power generation system. The present invention further relates to a solar thermal power generation system having the above heat collector. 
       BACKGROUND OF THE INVENTION 
       [0004]    Energy source is an important foundation of development of economy and society. Since the industrial revolution, consumption of energy source in the world has significantly increased; traditional fossil energy sources are rapidly used; ecological environment has continuously deteriorated, particularly, greenhouse gas emissions result in a serious global climate change; and thus the sustainable development of human society is under serious threat. Due to some features including infinite reserves, wide distribution, clean and economy in use and so on, solar energy has gained positive outlook, and is considered to be one of new energies that has most potential development prospect and can most meet increasing energy demands of the future society development. 
         [0005]    Due to its characteristics such as relatively good adaptability to grid load, high photoelectric conversion efficiency, generating scale effect with ease, more environmental friendly producing processes of consumable materials, better electric adjustability, solar thermal power generation is considered to be an important development direction of utilization of solar power generation in the future. 
         [0006]    At present, depending on different condensing manners, there mainly are several technical ideas for solar thermal power generation such as groove typed idea, tower typed idea, dish typed idea and the like. Specifically, compared with other ideas, a dish solar thermal power generation system has the advantages of flexible arrangement ability, high concentration ratio, high total power generation efficiency, etc., and thus it gains more and more attention. 
         [0007]    A dish solar thermal power generation system generally includes a concentrating dish, a heat collector and a heat exchanger, a heat engine and so on. In the dish solar thermal power generation system, the heat engine based on different principles such as Rankine cycle (stream turbine), Bragton Cycle (gas turbine), stirling Cycle (Stirling engine) or the like may be adopted. However, no matter which heat engine is used, how to efficiently and reliability absorb light energy and convert it into heat energy and smoothly transfer the heat energy to heat absorbing medium is extremely important. In such process, energy loss directly affects on total power generation efficiency of the system. 
         [0008]    According to knowledge of radiation heat transfer, it is know that using a cavity structure with an opening portion facilitates improving a blackness system of a cross section of the opening. That is, once radiant energy radiates into the cavity structure through the opening portion, only a little part of the radiant energy is reflected from the opening portion. Thus, generally, a point-focusing heat collector of a thermal power generation system adopts a cavity structure. The cavity structure is usually formed by winding a heat absorbing coil which has a low-temperature inlet and a high-temperature outlet. Heat absorbing medium flows into the heat absorbing coil through the low-temperature inlet. Sunlight condensed by a condensing dish enters into a heat collecting chamber through the opening portion of the cavity structure and directly radiates onto the heat absorbing coil. After being absorbed by the heat absorbing coil, the sunlight is converted into heat energy and is transferred to the heat absorbing medium, and thus the heat absorbing medium with the higher temperature flows out from the high-temperature outlet and flows into a downstream energy utilization apparatus such as heat exchanger, heat engine and the like. 
         [0009]    According to principles of optics, it is known that, since energy of parallel light concentrated by a revolution paraboloid is not evenly distributed, and due to accuracy of manufacture of the condensing dish, the light energy directly irradiating on the heat absorbing coil is not evenly distributed, and it is prone to form a local high temperature area. Once the local temperature exceeds an allowable temperature of material of the heat absorbing coil, it is possible to induce ablation phenomenon of the heat absorbing coil, and to even burn the heat absorbing coil. 
         [0010]    Furthermore, due to the accuracy of manufacturing of the condensing dish and wind load and so on, a focal spot condensed by the condensing dish usually has a shape and a size that deviate from design values, and it cannot ensure that all of the light reflected by the condensing dish can enter into the heat collecting chamber. Thus, there is always a part of the light projecting onto the external of the heat collector, which may increase surface temperature of the heat collector and even burn it. 
         [0011]    Therefore, the technical problems to be solved by those skilled in the art is how to improve matching performance between the heat collector and the condensing dish, optimize temperature distribution of the heat absorbing coil and improve working stability and reliability of the heat collector. 
       SUMMARY OF THE INVENTION 
       [0012]    A first object of the present invention is to provide a heat collector. The heat collector can prevent ablation phenomenon on a heat absorbing coil caused by an over-high local temperature. A second object of the present invention is to provide a solar thermal power generation system having the above heat collector. 
         [0013]    In order to achieve the first object, the present application provides a heat collector for a dish solar thermal power generation system including a heat collecting chamber and at least one layer of heat absorbing coil. Specifically, the heat collecting chamber has an opening portion. The heat absorbing coil forms a cavity structure with a hole, the cavity structure being placed inside the heat collecting chamber such that the hole is aligned with the opening portion. The heat absorbing coil has a low-temperature inlet provided on a part with a maximum solar radiation energy density of the cavity structure that has the maximum solar radiation density. 
         [0014]    Preferably, at least two layers of the heat absorbing coil are provided. 
         [0015]    Preferably, there is a preset clearance between adjacent layers of the heat absorbing coil. 
         [0016]    Preferably, a heat absorbing rib is provided on an outer wall of the heat absorbing coil. 
         [0017]    Preferably, the heat absorbing rib is a straight rib or a helical rib. 
         [0018]    Preferably, the heat collecting chamber includes an inner shell, an outer shell and a front covering plate. The inner shell has an inner wall defining the inner wall of the heat collecting chamber. The outer shell is disposed outside of the inner shell. The front covering plate forms the opening portion of the heat collecting chamber. The inner shell and the outer shell are fixed relative to the front covering plate, and a thermal insulation layer is provided between the inner shell, the outer shell and the front covering plate 
         [0019]    Preferably, a transparent covering plate is provided at the opening portion. 
         [0020]    Preferably, the front covering plate is provided thereon with a cooling sheath for circulation of cooling medium. 
         [0021]    Preferably, the cooling sheath has a cooling-medium outlet in communication with the low-temperature inlet of the heat absorbing coil 
         [0022]    Preferably, the inner wall of the heat collecting chamber is provided with a reflective coating. 
         [0023]    Preferably, the inner shell and the outer shell each are formed by a plurality of segments, and the plurality of segments are connected by a flange or a fastener to form an integral structure. 
         [0024]    Preferably, the cavity structure is of a spherical crown shape, or an inverted conical frustum shape. 
         [0025]    The heat collector according to the present application includes a heat collecting chamber and a heat absorbing coil. The heat collecting chamber has an opening portion. The heat absorbing coil forms a cavity structure having a hole. The hole of the cavity structure is aligned with the opening portion of the heat collecting chamber. The heat absorbing coil has a low-temperature inlet and a high-temperature outlet, with the low-temperature inlet being provided at the location of the cavity structure irradiated by incident light. 
         [0026]    In the heat collector with such structure, the low-temperature inlet is provided at the location of the cavity structure irradiated by the incident light. The energy at the location irradiated by incident light has a highest energy density, and the heat absorbing medium at the low-temperature inlet has the lowest temperature, so that the heat absorbing medium with a low temperature may quickly absorb energy from incident light, thereby preventing ablation phenomenon due to a local temperature at that location of the heat absorbing coil exceeding an allowable temperature. Furthermore, the location of less energy density corresponds to the heat absorbing coil containing the heat absorbing medium with a higher temperature. As a result, the temperature of the heat absorbing coil is more uniform, and a collecting temperature of the heat collector is higher, thus broadening range of application of the heat collector. 
         [0027]    For achieving the second object, the present application further provides a dish solar thermal power generation system. The dish solar thermal power generation system includes a condensing dish, a heat exchanger and the heat collector described above. Since the above heat collector provides the above technical effects, the dish solar thermal power generation system having such heat collector also provides the corresponding technical effects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a structural schematic view of a specific embodiment of a heat collector according to the present invention; 
           [0029]      FIG. 2  is a schematic view showing an outer structure of the heat collector in  FIG. 1 ; 
           [0030]      FIG. 3  is a structural schematic view of a heat absorbing coil in  FIG. 1 ; 
           [0031]      FIG. 4  is a structural schematic view of another heat absorbing coil of the heat collector according to the present invention; 
           [0032]      FIG. 5  is a structural schematic view of a heat absorbing rib of the heat collector according to the present invention; 
           [0033]      FIG. 6  is a structural schematic view of another heat absorbing rib of the heat collector according to the present invention; 
           [0034]      FIG. 7  is a structural schematic view of a third heat absorbing rib of the heat collector according to the present invention. 
       
    
    
       [0035]    In  FIGS. 1 to 7 , 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
             
             
               
                  1 high-temperature outlet, 
                  2 heat absorbing medium, 
                  3 low-temperature inlet, 
               
               
                  4 thermal insulation layer, 
                  5 upper outer shell, 
                  6 upper inner shell, 
               
               
                  7 heat absorbing coil, 
                  8 thermal insulation layer, 
                  9 lower inner shell, 
               
               
                 10 lower outer shell, 
                 11 cooling medium inlet, 
                 12 cooling medium outlet, 
               
               
                 13 cooling sheath, 
                 14 sunlight, 
                 15 transparent covering plate, 
               
               
                 16 front covering plate, 
                 17 cooling medium flowing cavity, 
               
               
                 18 cooling medium, 
                 19 heat absorbing rib. 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    For those skilled in the art to understand better the technical solutions of the present invention, the present invention will be further explained in detail in conjunction with the accompanying drawings and specific embodiments. 
         [0037]    Referring to  FIGS. 1 ,  2  and  3 ,  FIG. 1  is a structural schematic view of a specific embodiment of a heat collector according to the present invention;  FIG. 2  is a schematic view showing an outer structure of the heat collector in  FIG. 1 ; and  FIG. 3  is a structural schematic view of a heat absorbing coil in  FIG. 1 . 
         [0038]    As shown in  FIGS. 1 and 2 , a heat collector for a dish solar thermal power generation system according to the present application includes a heat collecting chamber and a heat absorbing coil  7 . At least one layer of the heat absorbing coil  7  is provided. The heat collecting chamber has an opening portion for allowing sunlight  14  to enter in the heat collecting chamber. Each layer of the heat absorbing coil  7  is wound into a substantially helical structure to form a cavity structure. The cavity structure has a hole having a certain dimension. The cavity structure is placed inside the heat collecting chamber. The hole is aligned with the opening portion of the heat collecting portion. The heat absorbing coil  7  has a low-temperature inlet  3  and a high-temperature outlet  1 . In a specific solution, the low-temperature inlet  3  and the high-temperature outlet  1  may each be provided with a connecting flange or a dedicated connector for connecting to the outside. Heat absorbing medium  2  flows into the heat absorbing coil  7  through the low-temperature inlet  3  and flows out from the high-temperature outlet  1 . The low-temperature inlet  3  of the heat absorbing coil  7  is provided at a part of the cavity structure having the maximum solar radiation energy density. The part of the cavity structure having the maximum solar radiation energy density may be a part of the heat absorbing coil  7  irradiated by sunlight. As shown in  FIG. 1 , when sunlight irradiates vertically through the opening portion, the location illuminated by sunlight may be specifically located at the bottom of the cavity structure. 
         [0039]    After flowing into the heat collecting cavity through the opening portion of the heat collecting cavity, firstly, the sunlight condensed by a condensing dish directly radiates to the inside of the heat absorbing coil  7 , with a part of the sunlight being absorbed directly by the heat absorbing coil  7  to be converted into heat energy and the other part being diffusely reflected. Since the opening portion of the heat collecting cavity has a smaller area than the effective heat absorbing area of the heat collector, and the radiation heat transfer angle coefficient of the opening portion is smaller relative to a total heat absorbing surface, only a little part of the diffusely reflected light runs out from the opening portion, and most of the diffusely reflected light may project onto other part of the heat absorbing coil  7  or an inner wall of the heat collecting chamber again. The heat absorbing medium  2  passes through the heat absorbing coil  7  which absorbs energy and transfers it to the heat absorbing medium  2 , so as to increase internal energy of the heat absorbing medium  2 . The heat absorbing medium  2  with higher internal energy flows out of the heat collector through the high-temperature outlet  1  and flows into a downstream energy utilization apparatus, for example, a heat exchanger, a heat engine and so on. Thus, the light energy is converted into heat energy and the heat energy is output. 
         [0040]    In the heat collector with such structure, the low-temperature inlet  3  is provided at the part of the cavity structure having the maximum solar radiation energy density. Since the highest energy density occurs at the position irradiated by sunlight  14 , and the heat absorbing medium  2  at the low-temperature inlet  3  has the lowest temperature, the heat absorbing medium  2  with a low temperature may quickly absorb energy from incident light, thus preventing ablation phenomenon due to a local temperature at that position of the heat absorbing coil  7  exceeding an allowable temperature. Furthermore, the location of less energy density corresponds to the heat absorbing coil  7  containing the heat absorbing medium  2  with a higher temperature. As a result, the temperature of the heat absorbing coil  7  is more uniform, and a collecting temperature of the heat collector is higher, thus broadening range of application of the heat collector. 
         [0041]    In a specific solution, the heat collecting chamber specifically may include an inner shell, an outer shell and a front covering plate  16 . The inner wall of the inner shell defines the inner wall of the heat collecting chamber. The outer shell is disposed outside of the inner shell. The front covering plate  16  is provided therein with an opening which defines the opening portion of the heat collecting chamber. The inner shell and the outer shell are fixed relative to the front covering plate  16 . A thermal insulation layer is provided between the inner shell, the outer shell and the front covering plate  16 . Particularly, the thermal insulation layer between the inner shell and the outer shell may reduce lose of heat absorbed by the inner wall of the inner shell to the outside, so as to increase the temperature of the inner shell and reduce effective radiant heat transfer between the heat absorbing coil land the inner shell, thereby reducing heat loss of the heat collector. 
         [0042]    In a further solution, the heat absorbing coil  7  can be fixed onto the inner wall of the inner shell by an elastic clip seat or a pinch tube or the like. 
         [0043]    In a preferred solution, the inner wall of the inner shell is provided with a reflective coating with a high reflection coefficient, such as a metallic silver coating. After projecting onto the reflective coating on the inner wall of the inner shell, the diffusely reflected light is reflected onto the heat absorbing coil  7  again, thus reducing the heat absorbed by the inner wall of the inner shell, and reducing the heat lose of the heat collector. 
         [0044]    In a preferred solution, a transparent covering plate  15  is provided at the open portion of the heat collector. In a specific solution, a transparent covering plate  15  is provided at the opening of the front covering plate  16 . The transparent covering plate  15  may block air flow between the inside and the outside of the heat collecting chamber, which may thus not only reduce convection heat loss in the heat collecting cavity, but also prevent foreign matters such as insects, dust or the like from entering the heat collecting chamber to otherwise negatively affect working reliability of the heat collector. In a specific solution, the transparent covering plate  15  may be a glass covering plate. However, the present invention is not limited to the glass covering plate, and the transparent covering plate  15  can be a resin covering plate, a plastic covering plate or the like. All of transparent sheet can be used as the transparent covering plate  15  in the present invention. 
         [0045]    In a preferred solution, for simplifying the manufacturing process of the heat collector, both the inner shell and the outer shell can be formed by multiple segments, with the segments being connected by a flange or a fastener to form an integral structure. As shown in  FIGS. 1 and 2 , the inner shell may include an upper inner shell  6  and a lower inner shell  9 , and the outer shell may include an upper outer shell  5  and a lower outer shell  10 . A thermal insulation layer  4  is provided between the upper inner shell  6  and the upper outer shell  5 , and a thermal insulation layer  8  is provided between the lower inner shell  9  and the lower outer shell  10 . 
         [0046]    In a preferred solution, the front covering plate  16  is provided thereon with a cooling sheath  13  for circulation of cooling medium  18 . The cooling sheath  13  is provided with a cooling medium inlet  11 , a cooling medium outlet  12  and a cooling medium flowing cavity  17 . The cooling medium  18  flows into the cooling medium flowing cavity  17  through the cooling medium inlet  11 , and flows out from the cooling medium outlet  11  after circulating in the cooling medium flowing cavity  17 . When the light reflected by the condensing dish partly projects onto a front end of the heat collector, the cooling medium  18  in the cooling sheath  13  may bring away the heat generated by the light projected onto the front end of the heat collector, which may avoid the front end of the heat collector from burning out, thus effectively protecting the heat collector and ensuring reliability of the heat collector. 
         [0047]    In a more preferred solution, if the cooling medium  18  in the cooling sheath  13  is identical to the heat absorbing medium  2  in the heat absorbing coil  7 , the outlet  12  of the cooling sheath  13  for the cooling medium  18  may be in communication with the low-temperature inlet  3  of the heat absorbing coil  7 . Thus, the cooling medium  18  flowing out of the cooling sheath  13  may be converged into the low-temperature inlet  3  of the heat absorbing coil  7  through a pipeline so as to increase the temperature of the medium flowing into the heat absorbing coil  7 , thereby increasing the heat exchange efficiency of the heat collector. 
         [0048]    In a preferred solution, there are at least two layers of heat absorbing coil  7 . As shown in  FIG. 3 , two or more layers of heat absorbing coil  7  can be arranged concentrically. With such structure, temperature gradient inside the wall of the heat absorbing coil  7  can be improved, and the flowing path of the heat absorbing medium  2  heated in the heat absorbing coil  7  is lengthened, thereby ensuring that the heat absorbing medium  2  can be heated continuously and smoothly. 
         [0049]    In a more preferred solution, there is a preset clearance between adjacent layers of the heat absorbing coil  7 . The preset clearance between different layers of the heat absorbing coil  7  may ensure that the surface of each layer of the heat absorbing coil  7  can suitably absorb heat. Therefore, flowing path of the heat absorbing medium  2  heated in the heat absorbing coil  7  can be further prolonged and the heat absorbing medium  2  can be heated continuously and smoothly. 
         [0050]    In a further solution, the heat absorbing coil  7  in the same layer can be arranged with a preset clearance. With such structure, it can be ensured that the entire surface of the heat absorbing coil  7  in the same layer can suitably absorb heat. 
         [0051]    In a preferred solution, for enhancing heat absorbing capacity of the heat absorbing coil  7 , in particular heat absorbing capacity of the part with higher energy density of the heat absorbing coil  7 , a heat absorbing rib  19  may be provided on an outer wall of the heat absorbing coil  7 . As shown in  FIGS. 5 ,  6  and  7 , the heat absorbing rib  19  may be a straight rib or a helical rib. 
         [0052]    In the present application, the shape of the cavity structure formed by the heat absorbing coil  7  is not limited. The cavity structure can be a structure of spherical crown as shown in  FIG. 3 , or a structure of inverted conical frustum as shown in  FIG. 4 . If the cavity structure is of the spherical crown shape, the layers of the heat absorbing coil  7  can be concentrically arranged. If the cavity structure is of the inverted conical frustum shape, the layers of the heat absorbing coil  7  can be coaxially arranged. 
         [0053]    The present invention further provides a dish solar thermal power generation system. The dish solar thermal power generation system includes a condensing dish, a heat exchanger and the heat collector described above. Since the above heat collector produces the above technical effects, the dish solar thermal power generation system having such heat collector also produces the corresponding technical effects, which will not be introduced in detail herein. 
         [0054]    The foregoing only relates to the preferred embodiments of the present application. It should be noted that, due to limitation of literal expression, and since there are unlimited specific structures objectively, various improvements and modifications can be made by those skilled in the art without departing from the principle of the present application, and these improvements and modifications should also be deemed to fall within the scope of protection of the present application.