Solar heat absorber with self-power-generation and heat-storage functions and operation method of solar heat absorber

Abstract

The invention relates to a solar heat absorber with self power generation and heat storage functions and an operation method thereof, and belongs to the technical field of solar heat absorbers. The heat absorber comprises heat absorbing pipes, an upper collecting box, a lower collecting box and heat storage systems, the multiple heat absorbing pipes are arranged between the upper collecting box and the lower collecting box side by side, and the upper collecting box and the lower collecting box are connected with the heat storage systems respectively; the pipe wall of the heat absorption pipe is of a multi-layer structure and sequentially comprises a hot electron anode, an electrode gap, a hot electron cathode and a heat transfer metal pipeline from outside to inside, a heat transfer working medium circulates in the heat transfer metal pipeline, and the hot electron anode and the hot electron cathode are connected with an external load through an anode wire and a cathode wire respectively. The heat absorber has a power generation function and can also store heat by utilizing light condensation energy, so that the efficiency and the stability of the whole power generation system are improved.

Description

Technical Field

[0001] The invention relates to a solar thermal absorber with self-generation and heat storage functions and an operation method thereof, belonging to the technical field of solar thermal absorbers. Background Art

[0002] Solar energy is a widely used renewable energy source. Currently, the main forms of solar power generation are photovoltaic power generation and solar thermal power generation. Photovoltaic power generation refers to the use of photovoltaic cells to directly convert solar energy into electrical energy through the photovoltaic effect, but it has inherent energy conversion limitations; solar thermal power generation refers to a power generation method that first converts solar energy into thermal energy and then converts thermal energy into electrical energy through other technologies. Solar thermal power generation coupled with a heat storage system can avoid the characteristics of photovoltaic power generation being affected by weather, but its process is complicated and the conversion efficiency is low, and it is still subject to many limitations in practical applications.

[0003] Thermionic emission power generation devices consist of a hot metal cathode and a cold anode, separated by a vacuum. By heating the metal with an energy source, the electrons in the metal can overcome the inter-electrode barrier and be emitted to the anode. When connected to an external load, a closed loop can be formed to generate electricity. The energy source of thermionic emission power generation devices comes from concentrated solar energy. Photon-enhanced thermal electron emission technology (PETE) can achieve both photovoltaic and photothermal effects in a single device. The difference between it and thermal electron power generation technology is that the cathode uses a semiconductor, and the rest of the devices are the same. Its working principle is that the semiconductor cathode absorbs concentrated solar radiation, and the electrons in the cathode can be excited from the valence band to the conduction band by the incident photons, while absorbing the heat of the cathode to overcome the inter-electrode barrier and be emitted to the anode. Since PETE uses both photon energy and photogenerated heat, it has a higher conversion efficiency and can operate at a lower temperature than thermal electron emission.

[0004] In a thermal electron emission power generation component, the cathode temperature is higher than the anode temperature, and the work function of the cathode is higher than the work function of the anode. During component operation, the anode temperature should not be too high. Since the anode has a lower work function, if the anode temperature is too high, the anode will easily emit electrons to the cathode, generating a larger anode reverse current. The total device current Jtotal = Jca - Ja. If the anode reverse current is too high, the total emission current of the device will be reduced, thereby affecting the power generation performance of the component. Therefore, controlling the anode temperature to be low is also a focus of research in this field.

[0005] In addition, both pure thermal electron emission technology and photon enhanced emission power generation technology are limited by the influence of space charge effect between electrodes. Limiting the electrode spacing to the micro-nano level can alleviate the space charge effect, but the near-field radiation heat transfer loss caused by the evanescent wave photon tunneling increases. At the same time, this micro-nano level spacing poses severe challenges to engineering applications. Introducing cesium vapor into the electrode gap is a common way to overcome the space charge effect, but the high-temperature thermal ionization of cesium requires a high temperature of more than 1200°C to achieve a transport effect, and it is difficult to achieve such a high temperature for conventional solar power generation. However, in addition to thermal ionization, resonant light can also excite cesium atoms to produce cesium ions, and the abundant resonant light sources in sunlight can be utilized. Based on this, the present invention designs a structure of a light-transmitting anode, in which solar photons first enter the electrode gap, and can preferentially excite cesium atoms to ionize them, thereby overcoming the space charge effect.

[0006] At present, the commonly used heat collection forms of concentrated solar thermal power generation systems mainly include tower, dish, trough and linear Fresnel thermal power generation systems. In these heat collection forms, the concentrated energy can be absorbed by the absorber or heat absorbing tube, thereby heating the heat transfer medium to drive the heat engine to do work externally. Since the concentration ratio of these forms can reach a high degree, the absorber can work at a very high temperature. The absorber is a device that can convert high-power solar energy into thermal energy. According to different heat transfer methods, it can be divided into tubular and volumetric absorbers. The tubular absorber is currently the most commonly used form in tower solar power generation systems. Its main working principle is that the heat transfer medium enters the heat absorbing tube and exchanges heat with the tube wall, thereby absorbing heat. At present, the role of the absorber in the solar energy system is to absorb solar energy and convert it into thermal energy and transfer it to the medium in the tube. The role is relatively simple. Based on the above analysis, the present invention is proposed. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a solar thermal absorber with self-generating and heat storing functions. The thermal absorber itself has the function of generating electricity and can also utilize concentrated energy for heat storage, thereby improving the efficiency and stability of the entire power generation system.

[0008] The present invention also provides an operating method of the solar thermal absorber with self-generation and heat storage functions.

[0009] The technical solution of the present invention is as follows:

[0010] A solar thermal absorber with self-generating and heat storing functions, comprising a heat absorbing tube, an upper header, a lower header and a heat storage system, wherein a plurality of heat absorbing tubes are arranged side by side between the upper header and the lower header, the two ends of the heat absorbing tubes are connected to the upper header and the lower header respectively through connecting pipes, and the upper header and the lower header are connected to the heat storage system respectively through working fluid flow pipes;

[0011] The wall of the heat absorption tube is a multi-layer structure, which includes a thermal electron anode, an electrode gap, a thermal electron cathode and a heat transfer metal pipe from the outside to the inside. A heat transfer medium flows in the heat transfer metal pipe. The thermal electron anode and the thermal electron cathode are connected to an external load through an anode wire and a cathode wire respectively.

[0012] Preferably according to the present invention, a back insulating layer is provided between the thermionic cathode and the heat transfer metal pipe, and the back insulating layer is used to prevent the thermionic cathode and the heat transfer metal pipe from conducting electricity.

[0013] According to the preferred embodiment of the present invention, a plurality of electrode insulating layers are evenly arranged in the electrode gap, and the electrode insulating layers are used to prevent the thermal electron anode and the thermal electron cathode from conducting electricity at the fixed positions of the two electrodes, thereby affecting the thermal electron emission power generation performance. The electrode insulating layer and the back insulating layer should have good heat resistance and chemical stability, and can adopt phosphate-based inorganic binders, aluminum oxide and zirconium oxide, etc.;

[0014] Thermionic cathode, thermal electron anode, electrode gap and electrode insulation layer together constitute a thermal electron emission power generation component. For external power generation, the thermal electron anode adopts a light-transmitting anode. Most of the concentrated light energy is absorbed by the thermal electron cathode through the thermal electron anode. The temperature of the thermal electron cathode increases, and the kinetic energy of the electrons inside the cathode increases after absorbing energy. Some electrons can overcome the electronic potential barrier on the surface of the thermal electron cathode and then be emitted from the cathode surface. The emitted electrons pass through the electrode gap to reach the thermal electron anode, and then are connected to an external load through the anode wire and the cathode wire to realize power generation. The heat transfer metal pipe can absorb part of the heat from the thermal electron cathode, and the heat transfer medium absorbs the heat of the heat transfer metal pipe and enters the heat storage system for energy storage.

[0015] According to the preferred embodiment of the present invention, the hot electron anode is made of transparent conductive materials such as indium-tin oxide transparent conductive film glass, fluorine-doped SnO2 transparent conductive glass, quartz substrate or graphene;

[0016] Thermionic cathode materials are pure metals, metal oxides, semiconductors or graphene.

[0017] Preferably according to the present invention, the electron receiving surface of the thermionic anode is provided with a thermionic anode coating, the light receiving surface of the thermionic cathode is provided with a thermionic cathode coating, the light receiving surface of the thermionic cathode is also the electron emitting surface, both the thermionic anode coating and the thermionic cathode coating achieve low surface work function, and the thermionic anode coating should have good light transmittance, and the materials of the thermionic cathode coating and thermionic anode coating can be selected from nitrogen-doped diamond, phosphorus-doped diamond, lanthanum hexaboride, barium fluoride or other materials with low work function characteristics.

[0018] Preferably according to the present invention, the electrode gap is a vacuum or filled with cesium vapor maintained at a specified temperature, and the cesium atoms can be ionized into cesium ions by light / thermal excitation. The cesium vapor can not only mitigate the space charge effect, but also further reduce the work function of the surface of the hot electron cathode and the hot electron anode. The cesium atoms can be directly ionized under the radiation of light of a specific wavelength, and can also be thermally ionized to form cesium ions. The cesium ions can neutralize the electrons accumulated in the electrode gap, thereby mitigating the space charge effect; at the same time, a portion of the cesium atoms adsorbed on the electrode can form a surface dipole to effectively reduce the work function, so that more electrons from the cathode are emitted to the inter-electrode gap, thereby increasing the output current.

[0019] Preferably according to the present invention, a focusing system is arranged outside the heat absorber, and the focusing system is of tower type, dish type, trough type, linear Fresnel type, tower-trough coupling type, tower-dish coupling type or dish-trough coupling type.

[0020] Preferably according to the present invention, the heat transfer medium is one or more fluids such as molten salt, water vapor, water, air, carbon dioxide, etc.

[0021] When the heat transfer medium is air, the inner wall of the heat transfer metal pipe is coated with a thermochemical heat storage coating. The material system of the thermochemical heat storage coating includes but is not limited to one or more of the systems such as BaO2 / BaO, Co3O4 / CoO, Mn2O3 / Mn3O4 and CuO / Cu2O. The thermochemical heat storage coating has the function of stabilizing the air temperature, absorbing heat through reduction reaction to achieve heat storage, and releasing heat to heat the air through oxidation reaction, thereby reducing the temperature fluctuation of the air.

[0022] Preferably, according to the present invention, the heat storage system includes a heat storage tank and a pump, the upper header, the heat storage tank, the pump and the lower header are connected in sequence by pipelines, and valves are provided on each connecting pipeline. The heat storage tank can adopt a double tank form of a high-temperature molten salt storage tank and a low-temperature molten salt storage tank, a single tank heat storage form of a molten salt inclined temperature layer, a thermochemical heat storage tank of a metal hydroxide system, a thermochemical heat storage tank of a carbonate system, a porous medium heat storage tank with phase change heat storage effect of a phase change material, and other types of heat storage devices.

[0023] The operating method of the above-mentioned solar thermal absorber with self-generation and heat storage functions comprises the following steps:

[0024] (1) When there is sufficient sunlight, the concentrated energy is absorbed by the thermionic cathode through the thermionic anode. After absorbing the energy, the temperature of the thermionic cathode rises. After being excited, some electrons inside the thermionic cathode overcome the surface potential barrier and are emitted to the thermionic anode through the electrode gap. The thermionic anode receives the electrons emitted from the thermionic cathode. The electrons are led to the external load through the anode wire and then returned to the thermionic cathode through the cathode wire, forming a closed loop, thereby realizing power generation;

[0025] During the power generation process, the heat transfer medium in the heat transfer metal pipe absorbs the heat from the back of the hot electron cathode and becomes a high-temperature medium. After that, it enters the heat storage system to store heat.

[0026] (2) When the sunlight is insufficient, the heat transfer medium absorbs the heat of the high-temperature medium in the heat storage tank and becomes a high-temperature heat transfer medium. The heat transfer medium enters the heat absorption tube, and the thermionic cathode absorbs the heat energy of the heat transfer medium, causing the temperature of the thermionic cathode to rise, thereby realizing thermionic emission power generation.

[0027] The beneficial effects of the present invention are:

[0028] The photon incident surface of the thermal electron emission power generation component in the present invention is the electron emission surface, and the concentrated energy is incident on the thermal electron cathode through the transparent thermal electron anode. Compared with the traditional thermal electron emission power generation component that concentrates light on the back side of the thermal electron cathode, the photon incident surface of the component is the electron emission surface, which reduces the electron recombination in the diffusion process and increases the emission current, thereby improving the power generation efficiency of the entire component. In addition, by filling cesium vapor into the electrode gap to overcome the space charge effect, the rich resonant light source in the sunlight can preferentially excite cesium atoms through the transparent anode. At the same time, the heat transfer medium in the present invention combined with the heat storage system can greatly improve the power generation efficiency of the heat absorber.

[0029] For thermionic emission power generation components, the temperature of thermionic cathode is usually much higher than the temperature of thermionic anode, the cathode work function is higher than the anode work function, and in the power generation process, since thermionic anode has a lower work function, when the temperature rises to a certain value, it will emit electrons to thermionic cathode, thereby generating a reverse current, which affects the power generation efficiency of the component. Therefore, the temperature of thermionic anode should not be too high. This leads to a low working fluid temperature when absorbing heat from the thermal electron anode side to drive the power cycle to do work, which will affect the efficiency of the entire system. Compared with the related inventions in which the working fluid directly absorbs the heat of the anode, the heat transfer working fluid of the present invention absorbs the heat from the back side of thermionic cathode, the temperature of thermionic cathode is higher, and the heat transfer working fluid can absorb more heat. At the same time, the heat transfer working fluid reversely transfers heat to the cathode at night to achieve nighttime power generation, and the power generation efficiency of the entire system is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the cross-sectional structure of the heat absorption tube of the present invention.

[0031] Figure 2 It is a schematic diagram of the structure of the heat absorber of the present invention.

[0032] Figure 3 This is a schematic diagram of the thermal electron emission power generation principle in the present invention.

[0033] Figure 4 Schematic diagram of the working system of Example 2 of the present invention.

[0034] Figure 5 Schematic diagram of the working system of Example 3 of the present invention.

[0035] Figure 6 This is a schematic diagram of the working system of Example 4 of the present invention.

[0036] Figure 7 Schematic diagram of the trough type solar concentrating system in Example 5 of the present invention.

[0037] Figure 8 This is a schematic diagram of the thermal electron emission power generation principle when the electrode gap is filled with cesium vapor in the present invention.

[0038] Reference numerals:

[0039] 1. Thermionic emission power generation assembly; 2. Back insulation layer; 3. Heat transfer metal pipe; 4. Heat transfer medium; 5. Anode wire; 6. Cathode wire; 7. Heat absorber; 8. Concentrator system; 9. Heat storage system; 10. Power cycle system; 11. Valve A; 12. Valve B; 13. Valve C; 14. Valve D; 15. Transmission pump; 16. Valve E; 17. Tower; 18. Heliostat; 19. Turbine; 20. Regenerator; 21. Compressor; 22. Steam generator; 23. Steam turbine; 24. Condenser; 25. Circulation pump; 26. Trough concentrator;

[0040] 101, hot electron anode; 102, electrode gap; 103, hot electron cathode; 104, electrode insulation layer;

[0041] 701, heat absorption pipe; 702, connecting pipe; 703, upper header; 704, lower header; 705, working fluid flow pipe. DETAILED DESCRIPTION

[0042] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0043] Embodiment 1:

[0044] like Figure 1-3 As shown, this embodiment provides a solar thermal absorber with self-generation and heat storage functions, including a heat absorption tube 701, an upper header 703, a lower header 704 and a heat storage system, wherein a plurality of heat absorption tubes 701 are arranged side by side between the upper header 703 and the lower header 704, and both ends of the heat absorption tube 701 are connected to the upper header 703 and the lower header 704 through a connecting pipe 702, respectively, and the upper header 703 and the lower header 704 are connected to the heat storage system through a working fluid flow pipe 705;

[0045] The wall of the heat absorbing tube 701 is a multi-layer structure, which includes, from the outside to the inside, a thermionic anode 101, an electrode gap 102, a thermionic cathode 103 and a heat transfer metal pipe 3. A heat transfer medium 4 flows in the heat transfer metal pipe 3. Thermionic anode 101 and thermionic cathode 103 are connected to external loads through anode wire 5 and cathode wire 6 respectively.

[0046] A back insulating layer 2 is provided between the thermionic cathode 103 and the heat transfer metal pipe 3 , and the back insulating layer is used to prevent the thermionic cathode and the heat transfer metal pipe from conducting electricity.

[0047] Several electrode insulating layers 104 are evenly distributed in the electrode gap 102. The electrode insulating layers are used to prevent the thermal electron anode and the thermal electron cathode from conducting electricity at the fixed positions of the two electrodes, which affects the thermal electron emission power generation performance. The electrode insulating layer and the back insulating layer should have good heat resistance and chemical stability, and can use phosphate-based inorganic binders, aluminum oxide and zirconium oxide, etc.;

[0048] Thermionic cathode 103, thermal electron anode 101, electrode gap 102 and electrode insulating layer 104 together constitute a thermal electron emission power generation component 1. For external power generation, the thermal electron anode adopts a light-transmitting anode. Most of the concentrated light energy is absorbed by the thermal electron cathode through the thermal electron anode. The temperature of the thermal electron cathode increases, and the kinetic energy of the electrons inside the cathode increases after absorbing energy. Some electrons can overcome the electronic potential barrier on the surface of the thermal electron cathode and then be emitted from the cathode surface. The emitted electrons pass through the electrode gap to reach the thermal electron anode, and then are connected to an external load through the anode wire and the cathode wire to realize power generation. The heat transfer metal pipe can absorb part of the heat from the thermal electron cathode, and the heat transfer medium absorbs the heat of the heat transfer metal pipe and enters the heat storage system for energy storage.

[0049] Thermionic anode 101 is made of indium-tin oxide transparent conductive film glass; thermionic cathode 103 is made of pure metal, and the metal material is tungsten.

[0050] The electron receiving surface of the thermionic anode 101 is provided with a thermionic anode coating, and the light receiving surface of the thermionic cathode is provided with a thermionic cathode coating. The light receiving surface of the thermionic cathode is also an electron emitting surface. Both the thermionic anode coating and the thermionic cathode coating achieve low surface work function, and the thermionic anode coating should have good light transmittance. The materials of the thermionic cathode coating and the thermionic anode coating can be selected from nitrogen-doped diamond, phosphorus-doped diamond, lanthanum hexaboride, barium fluoride or other materials with low work function characteristics.

[0051] The electrode gap 102 is a vacuum.

[0052] A light concentrating system 8 is arranged outside the heat absorber 7, and the light concentrating system is a dish-type concentrating solar energy system.

[0053] The heat transfer medium 4 is one or more fluids such as molten salt, water vapor, water, air, carbon dioxide, etc.

[0054] When the heat transfer medium is air, the inner wall of the heat transfer metal pipe is coated with a thermochemical heat storage coating. The material system of the thermochemical heat storage coating includes but is not limited to one or more of the systems such as BaO2 / BaO, Co3O4 / CoO, Mn2O3 / Mn3O4 and CuO / Cu2O. The thermochemical heat storage coating has the function of stabilizing the air temperature, absorbing heat through reduction reaction to achieve heat storage, and releasing heat to heat the air through oxidation reaction, thereby reducing the temperature fluctuation of the air.

[0055] Embodiment 2:

[0056] like Figure 4 As shown, this embodiment provides a working system of the solar thermal absorber with self-generation and heat storage functions described in Example 1, including a thermal absorber and a power circulation system 10, the upper header 703 is connected to a heat storage tank through a valve A11, the upper header 703 is connected to the power circulation system 10 through a valve B12, the power circulation system 10 is connected to a lower header 704 through a valve C13, the power circulation system 10 is connected to the heat storage tank through a valve D14, and a valve E16 is provided on the connecting pipe between the heat storage tank and the transmission pump 15.

[0057] The heat storage system 9 in the solar thermal absorber with self-generation and heat storage functions includes a heat storage tank and a transmission pump 15. The upper header 703, the heat storage tank, the transmission pump 15 and the lower header 704 are connected in sequence through pipelines. The heat storage tank can adopt a double tank form of a high-temperature molten salt storage tank and a low-temperature molten salt storage tank, a molten salt thermocline single tank heat storage form, a thermochemical heat storage tank of a metal hydroxide system, a thermochemical heat storage tank of a carbonate system, a porous medium heat storage tank with phase change material phase change heat storage effect, and other types of heat storage devices.

[0058] The operating method of the working system of the solar thermal absorber with self-generation and heat storage functions described in the above-mentioned application embodiment 1 comprises the following steps:

[0059] When the sunlight is sufficient, the absorber 7 absorbs the concentrated energy from the focusing system 8, and most of the concentrated energy is absorbed by the thermoelectron cathode 103. After absorbing heat, the kinetic energy of some electrons inside the thermoelectron cathode 103 is increased, and they overcome the surface potential barrier and are emitted to the thermoelectron anode 101. The electrons can flow into the load through the wire to do work, and return to the thermoelectron cathode 103, thereby realizing the power generation function of the device; the heat transfer metal pipe 3 can absorb most of the heat of the thermoelectron cathode 103, and the heat transfer medium 4 flows into the absorber 7 through the medium flow pipe 705, absorbs the heat of the heat transfer metal pipe 3 and becomes a high-temperature medium, and then part of the heat transfer medium 4 enters the heat storage system 9 for heat storage, and the other part of the heat transfer medium 4 enters the power cycle system 10 to drive the heat engine to do work externally. Under this working condition, valve A11, valve B12 and valve C13 are opened, valve D14, valve E16 and transmission pump 15 are closed, and the flow ratio of the medium can be adjusted by the opening of valve A11 and valve B12;

[0060] When the sunlight is insufficient, the absorber 7 can also generate electricity externally. The heat transfer medium 4 first enters the heat storage system 9, absorbs the heat of the high-temperature heat storage medium and becomes a high-temperature medium. After that, part of the heat transfer medium 4 can enter the heat absorption tube 701 to heat the thermoelectron cathode 103. The thermoelectron cathode 103 absorbs heat and emits electrons to the thermoelectron anode 101 to generate electricity. Part of the heat transfer medium 4 enters the power cycle system 10 to drive the heat engine to do work externally. The heat distribution of the thermoelectron emission power generation component and the power cycle system can be adjusted by controlling the opening of the valve. Under this working condition, valve A11, valve D14, valve E16, valve B12 and transmission pump 15 are opened, and valve C13 is closed.

[0061] Embodiment 3:

[0062] like Figure 5 As shown, this embodiment provides a working system of a solar thermal absorber with self-generation and heat storage functions as described in Example 2, except that the concentrating system adopts a tower solar concentrating system, the power circulation system adopts an air Brayton circulation system, and the heat transfer medium is air;

[0063] The operating method of the working system of the solar thermal absorber with self-generation and heat storage functions is as follows:

[0064] When the sunlight is sufficient, the heliostat 18 can reflect the sunlight to the absorber 7 through its focusing and tracking functions. The absorber 7 is located on the tower 17. The temperature of the thermionic cathode 103 on the absorber tube 701 rises after absorbing most of the concentrated energy. After absorbing the energy, some electrons inside the thermionic cathode 103 overcome the surface potential barrier and are emitted to the thermionic anode 101. The electrons are transported to the load through the wire to generate electricity externally. In this embodiment, the air enters the Brayton cycle system through the compressor 21, and enters the absorber 7 after passing through the regenerator 20. The air can flow into the absorber tube 701 through the working fluid flow pipe 705 to absorb the heat on the back side of the cathode. After that, part of the air enters the heat storage system 9 for heat storage, and part of the air enters the turbine 19 to perform work externally. Under this working condition, valve A11, valve B12 and valve C13 are opened, valve D14, valve E16 and transmission pump 15 are closed, and the flow ratio of the air is adjusted by the opening of valve A11 and valve B12;

[0065] When the sunlight is insufficient, after the heat transfer medium 4 air comes out of the regenerator 20, it first enters the heat storage system 9, absorbs the heat of the high-temperature heat storage medium and becomes high-temperature air. After that, part of the air can enter the heat absorption tube 701 to heat the thermal electron cathode 103. The thermal electron cathode 103 absorbs the heat of the high-temperature heat transfer medium and the concentrated energy, and its temperature rises, and emits electrons to the thermal electron anode 101 to generate electricity. Part of the air enters the turbine 19 to drive the heat engine to do external work. The heat distribution of the thermal electron emission power generation component and the power cycle system can be adjusted by controlling the valve opening. Under this working condition, valve A11, valve D14, valve E16, valve B12 and transmission pump 15 are opened, and valve C13 is closed.

[0066] Embodiment 4:

[0067] like Figure 6 As shown, this embodiment provides a working system of a solar thermal absorber with self-generation and heat storage functions as described in Example 3, except that the power cycle system adopts a steam Rankine cycle, and the heat transfer medium is a heat storage medium molten salt;

[0068] The operating method of the working system of the solar thermal absorber with self-generation and heat storage functions is as follows:

[0069] When the sunlight is sufficient, the thermal electron emission power generation component 1 generates electricity externally. In this embodiment, the molten salt enters the heat absorption tube 701 after passing through the low-temperature storage tank in the heat storage system 9. After absorbing the heat from the back of the cathode, the molten salt becomes high-temperature molten salt and enters the high-temperature storage tank for heat storage. Part of the molten salt in the storage tank enters the steam generator 22 to heat the water vapor, so that the water vapor becomes a high-temperature and high-pressure working medium and enters the steam turbine 23 to perform work externally. After the water vapor performs work, part of the heat is discharged through the condenser 24, and then returned to the steam generator 22 through the circulation pump 25 for a new power cycle. After passing through the steam generator 22, the high-temperature molten salt loses part of the heat and becomes low-temperature molten salt. The low-temperature molten salt enters the low-temperature storage tank, and part of the molten salt is stored in the low-temperature storage tank, and part of the molten salt flows to the heat absorber to absorb heat and enter the high-temperature storage tank for a new heat storage cycle. The flow distribution of the molten salt can be adjusted by controlling the opening of the valve. Under this working condition, valve A11, valve D14, valve E16 and transmission pump 15 are opened, and valve C13 and valve B12 are closed;

[0070] When the sunlight is insufficient, part of the high-temperature molten salt can flow from the high-temperature storage tank through valve B12 to the absorber 7 to heat the thermionic cathode 103. Thermionic emission power generation assembly 1 absorbs the concentrated light energy and the energy of the high-temperature molten salt to generate electricity externally. After that, the molten salt returns to the low-temperature storage tank through valve C13 and valve D14. Another part of the high-temperature molten salt enters the steam generator 22 to heat the water vapor, pushing the water vapor into the steam turbine 23 to perform external work, and the low-temperature molten salt returns to the low-temperature storage tank through valve D14. The heat distributed to the thermionic emission power generation assembly and the power cycle system can be adjusted by controlling the opening of the relevant valves. In this working condition, valve B12, valve C13 and valve D14 are opened, and valve A11, transmission pump 15 and valve E16 are closed.

[0071] Embodiment 5:

[0072] This embodiment provides a solar thermal absorber work system with self-generation and heat storage functions as described in Embodiment 3, except that the concentrating system adopts a trough solar concentrating system, such as Figure 7 As shown, a heat absorber 7 is installed on the trough-type focusing mirror 26 .

[0073] Embodiment 6:

[0074] This embodiment provides a working system of a solar thermal absorber with self-generation and heat storage functions as described in Example 3, except that the thermal electron cathode 103 adopts a semiconductor thermal electron cathode, and the thermal electron emission power generation component 1 can produce photon-enhanced thermal electron emission. Some electrons in the valence band of the thermal electron cathode 103 can be excited to the conduction band by photons, and then the heat of the thermal electron cathode 103 can overcome the surface potential barrier and be emitted to the thermal electron anode 101. Compared with thermal electron emission power generation that can only use heat to excite internal electrons, photon-enhanced thermal electron emission power generation can have a stronger output current at a lower temperature. At the same temperature, photon-enhanced thermal electron emission power generation has a higher conversion efficiency.

[0075] The photon incident surface of this embodiment, that is, the electron emission surface, greatly reduces the loss of free electrons in the process of diffusion to the emission surface compared to ordinary photon enhanced thermal electron emission cathodes, has a higher electron emission rate and higher efficiency.

[0076] Embodiment 7:

[0077] This embodiment provides a work system of a solar thermal absorber with self-generation and heat storage functions as described in Example 3, except that the electrode gap 102 is filled with cesium vapor maintained at a specified temperature. The filling of cesium vapor can not only reduce the work function of the surface of the thermal electron anode 101 and the thermal electron cathode 103, but also slow down the space charge effect between the electrodes.

[0078] Specifically, cesium vapor can be directly ionized into cesium ions by absorbing photons of a specific spectrum, or it can be ionized into cesium ions by heat. Cesium ions can neutralize space charges in the electrode gap 102, reducing the inter-electrode potential barrier, thereby playing a role in transporting electrons and increasing the power generation current; at the same time, a portion of cesium atoms adsorbed on the electrodes can form surface dipoles, thereby effectively reducing the work function of the thermal electron anode 101 and the thermal electron cathode 103, increasing the output current and output voltage of the thermal electron emission power generation component 1, and improving the power generation capacity of the thermal electron emission power generation component 1.

[0079] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A solar thermal absorber with self-generating and heat storing functions, characterized in that: It includes a heat absorbing tube, an upper header, a lower header and a heat storage system, wherein a plurality of heat absorbing tubes are arranged side by side between the upper header and the lower header, and the upper header and the lower header are respectively connected to the heat storage system; The wall of the heat absorption tube is a multi-layer structure, which includes a thermal electron anode, an electrode gap, a thermal electron cathode and a heat transfer metal pipe from the outside to the inside. A heat transfer medium flows in the heat transfer metal pipe. The thermal electron anode and the thermal electron cathode are connected to an external load through an anode wire and a cathode wire respectively.

2. The solar thermal absorber with self-generation and heat storage functions as claimed in claim 1, characterized in that: A back-side insulating layer is provided between the thermionic cathode and the heat transfer metal pipe.

3. The solar thermal absorber with self-generating and heat storing functions as claimed in claim 2, characterized in that: A plurality of electrode insulating layers are evenly distributed in the electrode gap.

4. The solar thermal absorber with self-generating and heat storing functions as claimed in claim 1, characterized in that: The hot electron anode uses indium tin oxide transparent conductive film glass, fluorine-doped SnO2 transparent conductive glass, quartz substrate or graphene; The hot electron cathode material is pure metal, metal oxide, semiconductor or graphene.

5. The solar thermal absorber with self-generating and heat storing functions as claimed in claim 1, characterized in that: The electron receiving surface of the thermionic anode is provided with a thermionic anode coating, the light receiving surface of the thermionic cathode is provided with a thermionic cathode coating, and the light receiving surface of the thermionic cathode is also an electron emitting surface.

6. The solar thermal absorber with self-generating and heat storing functions as claimed in claim 1, characterized in that: The electrode gap is either vacuum or filled with cesium vapor.

7. The solar thermal absorber with self-generating and heat storing functions as claimed in claim 1, characterized in that: A focusing system is arranged outside the heat absorber, and the focusing system is of tower type, dish type, trough type, linear Fresnel type, tower-trough coupling type, tower-dish coupling type or dish-trough coupling type.

8. The solar thermal absorber with self-generating and heat storing functions as claimed in claim 1, characterized in that: The heat transfer medium is one or more of molten salt, water vapor, water, air and carbon dioxide.

9. The solar thermal absorber with self-generating and heat storing functions as claimed in claim 3, characterized in that: The heat storage system includes a heat storage tank and a pump, and the upper header, the heat storage tank, the pump and the lower header are connected in sequence through pipelines.

10. The method for operating a solar thermal absorber with self-generation and heat storage functions according to claim 9, characterized in that: Here are the steps: (1) When there is sufficient sunlight, the concentrated energy is absorbed by the thermionic cathode through the thermionic anode. After absorbing the energy, the temperature of the thermionic cathode rises. After being excited, some electrons inside the thermionic cathode overcome the surface potential barrier and are emitted to the thermionic anode through the electrode gap. The thermionic anode receives the electrons emitted from the thermionic cathode. The electrons are led to the external load through the anode wire and then returned to the thermionic cathode through the cathode wire, forming a closed loop, thereby realizing power generation; During the power generation process, the heat transfer medium in the heat transfer metal pipe absorbs the heat from the back of the hot electron cathode and becomes a high-temperature medium. After that, it enters the heat storage system to store heat. (2) When the sunlight is insufficient, the heat transfer medium absorbs the heat of the high-temperature medium in the heat storage tank and becomes a high-temperature heat transfer medium. The heat transfer medium enters the heat absorption tube, and the thermionic cathode absorbs the heat energy of the heat transfer medium, causing the temperature of the thermionic cathode to rise, thereby realizing thermionic emission power generation.

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