A solar energy collection and heat storage device based on a secondary reflection concentrator system

Abstract

The present invention relates to a solar energy collection and storage device based on a secondary reflection concentrator system. The device includes a cylindrical cavity filled with liquid molten salt and a cold salt storage tank outside the cylindrical cavity. The cylindrical cavity is provided with a cold salt convection device and a hot salt circulation device. The bottom of the cold salt storage tank and the cold salt convection device are connected by a pipeline, and a cold salt pump is installed on the pipeline. The hot salt circulation device includes a hot salt inlet branch pipe, a hot salt pump and a hot salt outlet pipe installed in the cylindrical cavity. The hot salt inlet branch pipe is vertically and circumferentially distributed along the inner wall of the cylindrical cavity, and its lower end is connected to the hot salt outlet pipe. The hot salt outlet pipe is installed at the bottom of the cylindrical cavity, and part of the hot salt outlet pipe is located outside the cylindrical cavity, and a hot salt pump is provided thereon. A filter screen is provided at the bottom of the cylindrical cavity. This device not only has a high heat absorption efficiency, but also the temperature of the heat transfer working medium can be precisely controlled, operates under normal pressure, is easy to operate, has no adverse impact on the surrounding ecological environment, and integrates heat absorption and storage.

Description

Technical Field

[0001] The present invention relates to a solar energy collection and storage device, and particularly to a direct absorption type solar energy collection and storage device based on a secondary reflection concentrating system. Background Art

[0002] Solar energy, as a new type of clean energy, has great promise to be an important part of the basic energy in the future. The secondary reflection concentrating system consists of a secondary reflector with a height of about 100 meters, heliostats, and a heat collection device. The solar rays concentrated by the heliostats and the secondary reflector form an angle of 70 - 90° with the horizontal plane, and the concentrated solar rays enter the heat collection device to heat the molten salt inside the heat collection device.

[0003] The characteristics of the secondary reflection solar light spot are that the energy flux density is large in the central region and small in the edge region. Different from the bottom heating of a common boiler that relies on natural convection heat transfer, for a direct absorption type heat absorber, the molten salt liquid surface receives a large amount of radiation and cannot convect, which will cause problems such as high temperature in the top central region, a large amount of evaporation of the molten salt, low temperature at the bottom, and a large overall temperature difference. Summary of the Invention

[0004] The purpose of the present invention is to provide, in view of the defects and deficiencies of the prior art, a safe, reliable, high - efficiency, environment - friendly, and low - cost direct absorption type solar energy collection and storage device based on a secondary reflection concentrating system. This device not only has a high heat absorption efficiency, but also the temperature of the heat transfer medium can be accurately controlled, operates at normal pressure, is easy to operate, has no adverse impact on the surrounding ecological environment, and integrates heat absorption and storage.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A solar energy collection and storage device based on a secondary reflection concentrating system, which includes a cylindrical cavity filled with liquid molten salt and a cold salt storage tank outside the cylindrical cavity. The cylindrical cavity is provided with a cold salt convection device and a hot salt circulation device. The bottom of the cold salt storage tank and the cold salt convection device are connected by a pipeline, and a cold salt pump is installed on the pipeline; the hot salt circulation device includes a hot salt inlet branch pipe, a hot salt pump, and a hot salt outlet pipe installed inside the cylindrical cavity. The hot salt inlet branch pipe is vertically and circumferentially distributed along the inner wall of the cylindrical cavity, and its lower end communicates with the hot salt outlet pipe. The hot salt outlet pipe is installed at the bottom of the cylindrical cavity; a part of the hot salt outlet pipe is located outside the cylindrical cavity, and a hot salt pump is provided on it; a filter screen is provided at the bottom of the cylindrical cavity.

[0007] The cold salt convection device consists of multiple cylinders with different radii and heights arranged from top to bottom in a manner where the radius gradually increases, and is welded in the middle of the cylindrical cavity. It is provided with internal flow channels. From bottom to top, the diameter of the internal flow channels gradually decreases. Cold salt enters the internal flow channels from the bottom, and the wall surface of the internal flow channels is cooled through convective heat transfer. The cold salt overflows from the top and, under the action of gravity, flows along each surface of the outer wall of the device. Multiple annular grooves are formed on the outer wall surface at each step, and the depth in each layer of the grooves remains at about 0.5 m, which can directly absorb most of the high-density radiation in the central area. The remaining radiation irradiating on the wall surface is reflected by the wall surface or transferred to the nearby molten salt through heat conduction. The molten salt continuously reverses the flow direction from downward to upward in each annular groove. The molten salt always flows along the wall surface, and the flowing molten salt is used to maintain a relatively low temperature of the wall surface. Each annular groove can significantly improve the uniformity of the downward circumferential flow of the cold molten salt.

[0008] The cold salt is pumped out of the cold salt storage tank by a cold salt pump, flows along the internal flow channels of the cold salt convection device, overflows from the top, then flows downward step by step along the outer wall surface, and absorbs the strong radiation in the central area. After heating up, it flows to the bottom of the cylindrical cavity. Along the flow direction of the cold salt, the diameter of the internal flow channels of the cold salt convection device gradually becomes smaller. Subsequently, during the natural downward flow of the cold salt along the outer wall surface, the diameter of the annular grooves on the outer wall surface gradually increases. Looking from the center outwards, as the diameter of the outer wall surface gradually increases, the temperature of the cold salt near the outer wall surface gradually increases as it absorbs heat during the flow, but the radiation power absorbed per unit area gradually decreases, and the heating rate gradually decreases.

[0009] The hot salt inlet branch pipe is located near the side wall of the cylindrical cavity and is a corrugated hose or a variable-diameter telescopic pipe similar to an umbrella rod. There is a traction rope at the upper part to make the height of the inlet surface increase as the liquid level rises, and the inlet surface is always about 0.1 m lower than the liquid level, reducing the air content in the pipe.

[0010] The upper part of the hot salt outlet pipe is provided with a filter screen, and the porosity of the filter screen is between 10% and 30%, which can prevent excessive radiation penetrating the molten salt from irradiating on the bottom surface. The hot salt naturally convects upward through the voids and mixes with the cold salt flowing evenly down through each annular groove nearby. The filter screen completely covers the bottom area of the cylindrical cavity, about 0.1 m away from the lower hot salt outlet pipe. The hot salt convects upward along the voids of the filter screen, and the cold salt convects downward above the filter screen, and the two mix near the filter screen.

[0011] The cold salt rapidly heats up along the top center high-radiation area, then mixes with the hot salt downward for further heating, then slowly heats up and convects upward, and finally flows out from the hot salt inlet branch pipes around. There is cold molten salt flowing along the wall for heat exchange on both the inner and outer surfaces of the cold salt convection device in the fluid center area. The energy absorbed by the device can be promptly conducted into the molten salt, and it can adapt to the distribution characteristics of the spot center focus of the secondary reflection concentrator system. Through the precise control of the cold and hot salt flow rates by the molten salt pumps, the outlet temperature of the hot salt in the cavity can be precisely controlled within 30°C. The focusing energy flux density received by the cylindrical cavity is 500 kW / m 2 ~1500 kW / m 2 .

[0012] The temperature range for the molten salt to remain liquid under normal pressure is 250°C to 650°C, and the operating temperature is 280°C to 580°C. The temperature of the molten salt in the cold salt storage tank is 280°C to 320°C, and the inlet temperature of the high-temperature molten salt is 560°C to 580°C. The cold and hot salt pump flow regulating valves are both high-temperature solenoid valves, and the materials in the device that come into contact with the molten salt are all nickel-based alloy steels.

[0013] The top of the cylindrical cavity has a thermal insulation cover, which can reduce the heat loss of the solar heat collection device at night and during shutdown conditions after being closed, and can prevent the adverse effects caused by rainwater to the solar heat collection device on rainy days. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, but do not constitute an improper limitation to the present invention. In the drawings:

[0015] Figure 1 is a schematic structural diagram of the present invention;

[0016] Figure 2 is a schematic structural diagram of the cold salt convection device in the present invention;

[0017] Figure 3 is a schematic structural diagram of the hot salt circulation system in the present invention.

[0018] Figures 1 - 3 In [the drawings]: 1 - cold salt storage tank; 2 - cold salt pump; 3 - cold salt convection device; 4 - hot salt inlet branch pipe; 5 - hot salt pump; 6 - hot salt outlet pipe; 7 - filter screen; 8 - highest liquid level; 9 - cylindrical cavity wall. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The present invention will be described in detail below in conjunction with the drawings and specific embodiments, where the illustrative embodiments and descriptions are only used to explain the present invention, but do not constitute a limitation to the present invention. Embodiment

[0020] As Figures 1 - 3As shown in the figure, a solar energy collection and heat storage device based on a secondary reflection concentrator system. The device is a cylindrical cavity with molten salt inside. The cylindrical cavity is provided with a cold salt convection device and a hot salt circulation device. The cold salt convection device includes a cold salt storage tank 1 outside the cylindrical cavity and a cold salt convection device 3 installed inside the cylindrical cavity. The bottom of the cold salt storage tank 1 and the cold salt convection device 3 are connected by a pipeline, and a cold salt pump 2 is installed on the pipeline. The hot salt circulation device includes a hot salt inlet branch pipe 4, a hot salt pump 5 and a hot salt outlet pipe 6 installed inside the cylindrical cavity. The hot salt inlet branch pipe 4 is vertically and circumferentially distributed along the inner wall of the cylindrical cavity, and its lower end is connected to the hot salt outlet pipe 6. The hot salt outlet pipe 6 is installed at the bottom of the cylindrical cavity, and part of the hot salt outlet pipe is located outside the cylindrical cavity, and a hot salt pump 5 is provided thereon. A filter screen 7 is provided at the bottom of the cylindrical cavity.

[0021] Part of the hot salt outlet pipe at the bottom of the cylindrical cavity is arranged in a circular pattern.

[0022] The temperature of the cold salt in the cold salt storage tank 1 is 280°C to 320°C, and the temperature of the high-temperature molten salt is 560°C to 580°C.

[0023] The cold salt pump 2 pumps out the cold salt in the cold salt storage tank 1, flows through the inside of the cold salt convection device 3, overflows at the top, and then flows along the outer wall surface of the cold salt convection device 3. The flow direction changes continuously along the wall surface in the annular groove, and absorbs the radiation energy focused in the center. Finally, it converges with the hot salt at the bottom near the filter screen. Under the suction of the hot salt pump 5, the hot salt that naturally convects from the bottom to the top converges at the hot salt pump 5 through multiple hot salt inlet branch pipes 4 and flows out through the hot salt outlet pipe 6. The hot salt naturally convects upward due to its low density, penetrates through the filter screen gaps and mixes with the cold salt. The filter screen with a smaller porosity can significantly improve the uniformity of the circumferential flow of the hot salt and enhance the mixing effect. As the cold salt continuously flows in, the liquid level in the cylindrical cavity continuously rises, and the top surface of the hot salt inlet branch pipe 4 also rises continuously with the liquid level, sucking in the hottest hot salt near the liquid level. As the cold salt is continuously injected, the liquid level gradually approaches the highest liquid level.

[0024] As Figure 2As shown, the cold salt convection device 3 is arranged from top to bottom by a plurality of cylinders with different radii and heights in a manner that the radius gradually increases, and is welded in the middle of the cylindrical cavity. It is provided with a flow channel inside. From bottom to top, the diameter of the internal flow channel gradually decreases, and from top to bottom, a plurality of annular grooves are formed on the outer wall surface at each step. When the heat storage device is full, the liquid level is the highest liquid level 8. The top surface of the uppermost cylinder of the cold salt convection device 3 exceeds the highest liquid level by about 0.1 m, and the cold salt overflows from this outlet. The depth of the molten salt in each layer of the groove is about 0.5 m, which can directly absorb most of the radiation energy. After the remaining energy is absorbed and reflected by the wall surface, it is indirectly absorbed by the molten salt. The low-temperature molten salt continuously flows reversely along the wall surface, making the flow velocity of each circle relatively uniform, which can effectively reduce the temperature at the wall surface of the device and ensure that the device temperature does not exceed the boiling point of the molten salt. The low-temperature molten salt continuously absorbs the radiation energy focused in the center along the cold salt convection device 3, and after being buffered by each circle of annular grooves, it continuously flows downward evenly, and finally flows to the vicinity of the filter screen 7 at the bottom of the cylindrical cavity and mixes with the hot salt at the bottom. The cold salt flows downward from the center of the top with the largest radiation, absorbs the energy with a high radiation density in the central part, and can effectively reduce the temperature of the molten salt in the central high-radiation area. This device relies on the forced convection of the cold and hot salt pumps to form a distribution characteristic that the unheated cold salt is on the top and the heated hot salt is on the bottom, which is opposite to the natural convection of cold and heat. The forced convection and natural convection interact with each other to reduce the temperature difference caused by the height difference inside the cylindrical cavity.

[0025] As Figure 3 shown, after the mixed salt is heated by radiation, it naturally convects to the vicinity of the liquid level, and then is pumped in from each hot salt inlet branch pipe 4 at the top under the pumping force of the hot salt pump 5. After convergence, it is discharged from the bottom hot salt outlet pipe 6. The flow of the hot salt in the pipe and the natural convection of the mixed salt together form a hot salt circulation loop.

[0026] At a position about 0.1 m above the bottom hot salt outlet pipe 6 at the bottom of the cylindrical cavity, a layer of stainless steel filter screen with a porosity of about 10% - 30% is laid to equalize the distribution of the hot salt at the bottom. This structure can significantly increase the temperature in the bottom area and improve the uniformity of the mixing of cold and hot salts. The focused radiation energy flux density received by the cylindrical cavity is 500 kW / m 2 ~1500 kW / m 2 ; the cold salt flow rate is mainly related to the focused radiation intensity at each moment of the day, and the hot salt flow rate is based on controlling the temperature near the hot salt inlet branch pipe at 560 °C - 580 °C; the temperature range in which the molten salt is in a liquid state is 250 °C - 650 °C, and the designed highest liquid level of the cylindrical cavity is 10 - 20 m.

[0027] At the initial moment when the molten salt runs in the cylindrical cavity, the reserved depth of the molten salt in the cylindrical cavity is more than 2 m, the temperature is above 280 °C, and the radiation intensity and the flow rate adjustment switches of the cold and hot salt pumps both increase uniformly at the same ratio and reach the set value within 2 minutes. Subsequently, the flow rates of the cold and hot salt pumps are adjusted according to the temperature of the hot salt outlet to keep the outlet temperature at about 570 °C. As time increases, more and more cold salt flows into the device, the liquid level continuously rises and approaches the highest liquid level. 10 minutes before the end of the endothermic process, the cold salt flow rate and the radiation intensity gradually decrease, and the hot salt circulation flow rate gradually increases to improve the overall temperature and temperature uniformity of the molten salt. After 10 minutes, the molten salt pumps are all stopped, and then the heat preservation cover is closed to complete all the procedures of endothermic. Subsequently, the upper hot salt is pumped away for use, and 2 m deep molten salt with a relatively low temperature is left at the bottom. The low-temperature molten salt in the internal and external annular grooves of the cold molten salt convection device 3 remains full. The cold salt formed after the use of the hot salt inside the cylindrical cavity is injected into the cold salt storage tank 1.

[0028] The above is only the preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made according to the structure, characteristics and principles described in the scope of the present invention patent application are included in the scope of the present invention patent application.

Claims

1. A solar energy collection and heat storage device based on a secondary reflection concentrator system, characterized in that, The solar energy collection and heat storage device includes a cylindrical cavity filled with liquid molten salt and a cold salt storage tank (1) outside the cylindrical cavity. The cylindrical cavity is provided with a cold salt convection device (3) and a hot salt circulation device. The bottom of the cold salt storage tank and the cold salt convection device are connected by a pipeline, and a cold salt pump (2) is installed on the pipeline. The hot salt circulation device includes a hot salt inlet branch pipe (4), a hot salt pump (5) and a hot salt outlet pipe (6) installed in the cylindrical cavity. The hot salt inlet branch pipe (4) is vertically and circumferentially distributed along the inner wall of the cylindrical cavity, and its lower end communicates with the hot salt outlet pipe (6). The hot salt outlet pipe (6) is installed at the bottom of the cylindrical cavity, and part of the hot salt outlet pipe is located outside the cylindrical cavity, on which a hot salt pump (5) is provided. A filter screen (7) is provided at the bottom of the cylindrical cavity. The top surface of the cold salt convection device is 0.1 m higher than the highest designed liquid level in the cylindrical cavity. The porosity of the filter screen is between 10% and 30%.

2. The solar energy collection and heat storage device based on the secondary reflection concentrator system according to claim 1, wherein: The cold salt convection device is composed of a plurality of cylinders with different radii and heights, arranged from top to bottom in a manner that the radius gradually increases, and welded in the middle of the cylindrical cavity. From bottom to top, the diameter of the internal flow channel gradually decreases. From top to bottom, a plurality of annular grooves are formed on the outer wall surface at each step.

3. The solar energy collecting and heat storage device based on the secondary reflection concentrating system according to claim 1, characterized in that: The hot salt inlet branch pipe (4) is a corrugated hose or a variable-diameter telescopic pipe similar to an umbrella rod, and is towed by a towing rope at the upper part, so that the height of the inlet surface increases with the rise of the liquid level, and the inlet surface is always 0.1 m lower than the liquid level.

4. The solar energy collection and heat storage device based on the secondary reflection concentrator system according to claim 1, characterized in that: The filter screen completely covers the bottom area of the cylindrical cavity and is 0.1 m away from the lower hot salt outlet pipe.

5. The solar energy collection and heat storage device based on the secondary reflection concentrator system according to claim 1, wherein: A heat preservation cover is installed on the top of the cylindrical cavity.

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