KR20070100714A - Solar energy collection apparatus and method - Google Patents

Abstract

An apparatus for collecting heat from a solar concentrator has an isothermal body defining an elongated cavity with a circular opening having a diameter equal to a diameter of a focus of the solar concentrator, the cavity having a reflective walls such that solar rays contacting the walls are substantially reflected. The circular opening is located at the focus of the solar concentrator and perpendicular to a principal axis of the solar concentrator, and the axis of the cavity is aligned with the principal axis of the solar concentrator. The heat generated in the isothermal body is absorbed by the heat sink. The length of the cavity is sufficient to absorb a desired proportion of the energy in the solar rays entering the cavity and is about 5 to 9 times the diameter of the opening of the cavity. Depending on material used, the isothermal body can be enclosed in a reducing atmosphere to maintain reflectivity of the cavity walls.

Description

Solar energy collection apparatus and method

The present invention belongs to the field of solar energy, and in particular relates to the collection of concentrated solar radiation energy for thermo-chemical, thermo-mechanical or other thermal processes.

There is a great deal of attention today for powering renewable solar energy for many thermal drive processes. These include thermo-mechanical applications such as sterling engines or steam turbine power generation systems, thermochemical reforming, thermal cracking, process heating, general heating, material processing, and the like. Solar collection systems are usually located in a location where the sun is sufficiently acceptable. In conventional system mirrors, flat-segmented or curved mirrors are disposed in a parabolic or trough to focus incident solar radiation on a predetermined target. . While the sun traverses the sky, tracking control systems or pre-programmed algorithms keep the optical shape required by moving the mirrors.

The target is usually shaped like a cavity or shallow dish, and a light cone focused on this target is induced. The cavity is typically arranged with a plurality of tubes into which coolant for carrying the absorbed heat flows into the working process. Certain cavity designs, such as in US Pat. No. 5,113,659, incorporate a series of hot shoes in the cavity to deliver thermal energy to a plurality of free piston sterling generators. In some thermo-chemical processes, image fireballs are used to directly heat the catalyst beds in the translucent process tube, which causes hotspots that cause catalyst sintering and poor process temperature control. Often causes

In all these collection structures the spot size and shape must be machined for heat exchange and cavity parameters. To prevent local overheating phenomena often skew a plurality of Fireball images to where process heat exchange tubes are located to defocus the fireball or provide a uniform heat zone. This is accompanied by an increase in the area of the high heat radiation plane due to the enlarged solar image size which is smaller than the optimal focal point on the target, increasing radiation loss.

Since the scale and cost of solar-intensive technology is highly related to the overall production conversion efficiency, the goal of any solar-intensive system is to produce the maximum yield at the lowest possible solar-intensive area. A key factor in achieving this goal is to minimize parasitic losses due to re-radiation.

을 따른다. 그리하여 열방사로 인한 손실은 공정 온도인 표적의 절대온도가 두 배가 되면 16 곱 상승하게 된다. 이는 가능한 파이어볼 이미지를 최소화하거나 흑점 면적이 집광된 태양 이미지와 같게 캐비티 수신기 구조를 최적화하는 것과 연동하여 태양 집광을 최대로 함으로써 최소 방사 손실을 실현할 수 있게 된다.The collecting means are related to the required process temperature, trough reflectors for low heat applications and parabolic condensers for higher temperatures. Steam systems can operate at weak temperatures below 800K Fahrenheit, but may require substantially higher temperatures in thermochemistry that strive to achieve high equilibrium coefficients. Unfortunately, as the process temperature rises, the parasitic radiation losses are Stefan's Law.

Follow. Thus, the loss due to thermal radiation rises 16 times when the absolute temperature of the target, which is the process temperature, is doubled. This can be achieved by minimizing the possible fireball image or by optimizing the cavity receiver structure, such as sun image condensed with sunspot area, to maximize solar condensation to achieve minimal radiation losses.

It is an object of the present invention to provide a solar collection device and method which overcomes the above problems of the prior art.

According to a first embodiment of the present invention there is provided an apparatus for collecting heat from a solar energy concentrator and transferring the collected heat to a heat sink. The device comprises an isothermal body defined by an elongated cavity having a substantially circular opening and having a substantially circular opening having a diameter substantially the same as the focal diameter of the solar energy collector, the cavity The reflective walls have reflective walls such that the sun rays contacting the reflective walls are substantially reflected. The isotherm is aligned in a direction such that the circular opening is substantially at the focal point of the solar energy collector and is substantially perpendicular to the major axis of the solar energy collector, so that it is substantially aligned with the major axis of the solar energy collector. The isotherm is thermally coupled to the heat sink such that heat generated in the isotherm is absorbed by the heat sink. The length of the cavity has a length sufficient to absorb the desired rate of energy in the solar light entering the cavity.

According to a second embodiment of the present invention there is provided an apparatus for collecting heat from the sun and transferring the collected heat to a heat sink. The device comprises an isotherm defined as a substantially cylindrical cavity having a diameter opening having a diameter substantially equal to the diameter of the solar energy collector and the solar energy collector focal point, wherein the cavity has a Reflective walls are provided to reflect substantially. The isotherm is aligned in a direction such that the circular opening is substantially at the focal point of the solar energy collector and is substantially perpendicular to the major axis of the solar energy collector, so that it is substantially aligned with the major axis of the solar energy collector. The isothermal body is adapted to be thermally coupled such that heat generated in the isothermal body is absorbed by the heat sink, and the length of the cavity is 5 to 9 times the diameter of the circular opening.

According to a third embodiment of the present invention there is provided an apparatus for collecting heat from a solar energy concentrator for transfer to a heat sink. The apparatus includes providing an isotherm defined by an elongated cavity having a substantially circular opening of diameter substantially the same as the focal diameter of the solar energy collector. The cavity has reflective walls that allow the sun rays that hit the walls to be substantially reflected and direct the isotherm such that a circular opening is positioned substantially at the focal point of the solar energy collector and substantially perpendicular to the main axis of the solar energy collector. So that the axis of the solar energy collector and the axis of the cavity are substantially aligned, and some of the energy contained in each of the sun rays is absorbed until the desired magnification of the energy contained in the sun rays is absorbed by the reflecting wall. Reflects the sun's rays from the first contact point on the reflecting wall to the second contact point on the reflecting wall and the plurality of consecutive contact points on the reflecting wall so as to be absorbed by the reflecting wall at the contact point, and is generated by the sunlight energy absorbed in the isotherm The heat sink so that the heat is absorbed by the heat sink It is coupled to the body and a thermal.

Solar radiation is converted into heat by a plurality of internal reflections in a reflective cavity disposed within the isothermal body, the cavity receiver assembly being thermally coupled to the required thermal process or heat sink, and the isotherm incorporates thermal fluctuations. Sufficient mass to provide a combined process with a substantially constant temperature independent of minor thermal insulation or fireball image variations. The cavity opening is located at the focal point of the parabolic solar energy concentrator on the main optical axis such that the cone of cone is of minimum diameter at the cavity inlet.

The hierarchical configuration resembles a hollow walled cylinder clad with a thick-walled, chemically reducible material such as, but not limited to, copper as a whole.

The isotherm is thermally coupled to the thermal process with the open end of the cavity blocking the cone of light on the focal point from the solar energy concentrator. Solar flow enters the cavity, undergoes a number of internal reflections, spreads evenly and gradually decreases in radiant energy, absorbed therein by the receiver's isotherm, and transferred to the process. The reflectivity of the cavity walls remains constant in an inert atmosphere or in a reducing local atmosphere.

The above objects and effects, as well as additional objects and effects, will be more fully understood in the detailed description of the preferred embodiments, wherein like reference numerals designate like elements in the drawings.

1 and 2 show the structure of a prior art solar collection system adapted to drive a Stirling engine with an electrical transducer.

FIG. 3 shows a target survey of radially skewed solar energy collectors used in the prior art to reduce solar energy focus to an acceptable level.

4 is a graph showing the radial flow distribution in the prior art and the present invention.

FIG. 5 shows blackbody thermal radiation loss associated with target temperature and area. FIG.

6 is a side cross-sectional view showing an embodiment of the present invention applied in a Stirling engine driven generator system.

7 is a side cross-sectional view showing another embodiment in an overheating application.

8 and 9 are side cross-sectional views of one embodiment of the present invention applied to a thermo-chemical reaction system.

10 is an isometric perspective view of the isotherm of the present invention, defined as a coaxial cavity, illustrating a single light path and the principle of cavity operation.

FIG. 11 is an end view of the thermal conductor of FIG. 10 showing an inner ray path. FIG.

1 and 2 schematically show a conventional solar collection system for driving a heat engine and an electricity generating coupling structure. Solar heat collection systems are used to supply heat for a wide variety of purposes, and the collected heat is in principle transferred to a heat sink such as the illustrated heat engine that consumes heat therein. The process temperature varies with the purpose, and the system is designed such that all collected heat is once dropped by the heat sink to the desired temperature from about 100 ° C to 1400 ° C or more.

In this example the solar energy radiation 1 in the sun beam 7 of the sun beam is reflected by the solar energy concentrator and onto the target 8 located on the focal point of the parabolic concentrator 2 in the cavity 11. Focused. The target 8 consists of a plurality of metal tubes 3 arranged so as to be symmetrical about the main axis 9 so that the main axis 9 of the parabolic solar energy collector 2 blocks the light cone. The quartz window 5 covers the target 8 to reduce heat transfer loss. Coolant flows along the tubes 3 to remove heat generated by radiation absorption on the tubes and transfers this heat to the heat engine 4 by conduction. In this example, the mechanical energy converted by the heat engine is communicated to the generator 6 by the shaft 10, which is converted into electrical energy.

In an effort to reduce the solar fluidity strength level to the heat exchange design limit in this example, the flow distribution towards the target 8 is shown in FIG. 3 by skewing a plurality of Fireball images onto a tubular heat exchange structure. Appears as an annular ring, such as Curves W in FIG. 4 diagrammatically show the resulting radial flow distribution at the target 8 caused by the skewed Fireball images of FIG. 3. As shown in FIG. 3, approximately circular portions within the target are substantially not exposed to the sun's rays 7. Thus the focusing of the sun beam 7 on the target 8 is reduced by increasing the irradiated target area.

Solar energy focusing is usually measured in units of "suns". One sun represents the energy irradiated on a unit area perpendicular to the sun, which is approximately 1000 watts per square meter (W / m ² ). Continuing, for example, the possible solar energy focus at the focal point would be approximately 5500 suns so that the heat exchange tube 3 would not withstand the heat generated at that focus. Given the heat capacity of the heat exchange and the volumetric flow of coolant, the maximum safe solar focus is limited to approximately 877 suns or 877000 W / m ² . By skewing the parabolic concentrator 2 to reduce the solar focusing mechanism, a larger area is irradiated and the solar focus is reduced, thus affecting the required heat transfer while maintaining the temperature of the exchanger within the design limits. do.

Vaporizing the target size increases radiation loss at a given temperature and reduces the efficiency of the solar energy collector. As shown in FIG. 5, the magnitude of energy loss due to target re-radiation at an emissivity of 1.0 substantially affects the process temperature and the radiation area of the target. In the example above from FIGS. 1 and 2, the diameter of the target 8 is 15 inches in diameter and includes a target area of approximately 177 square inches (the circular portion of the center portion of the target that is not substantially exposed to the sun's rays 7). At) the solar energy concentration can be 877 suns.

By repositioning the parabolic solar energy concentrator 2 to focus a single fireball at the focal point, the target can have a diameter of approximately 6 inches, whereby the solar energy focus is at 5500 suns at the focal point on the target area of approximately 28 square inches. Becomes In other words, the target area can be reduced at a rate of approximately 6.25 and thus the focusing is increased at a rate of 6.25.

By reducing the target size from 15 inches to 6 inches as shown in FIG. 5, the radiation loss can be reduced from 13% to 2% at a process temperature of 850 ° C. As shown in FIG. 5, radiation losses at larger targets increase rapidly as the process temperature increases, while radiation losses increase even less for smaller targets.

These data are thermodynamic realities consistent with the blackbody solar receiver design at the temperatures shown. However, if the solar energy concentration is too high, problems actually arise when making such a smaller diameter collector.

FIG. 6 illustrates an apparatus for collecting heat from a solar energy collector and transferring the collected heat to a heat sink according to an embodiment of the present invention. The heat sink in the illustrated embodiment is a Stirling engine generator similar to that of FIGS. 1 and 2.

The solar energy radiation 1 focused here by the parabolic collector 2 instead of the skew collector is sharply focused in a single fireball at the opening inlet of the elongated cavity 13. Here, the solar energy focus is maximized and the diameter of the target and the diameter of the opening inlet of the cavity 13 are minimum. Curve S in FIG. 4 shows the resulting radial flow at target 8 for a single Fireball image.

The opening of the cavity 13 has a diameter substantially the same as the focal diameter of the solar energy collector 2. The cavity 13 has a circular opening at the focal point of the solar energy collector 2 and is substantially perpendicular to the main axis 9 of the solar energy collector 2 and the axis of the cavity 13 is substantially parallel to the main axis 9. Oriented to be aligned.

The cavity 13 is confined within an isotherm 12 made of stainless steel or similar material. The cavity 13 is treated with a metal liner 32, such as copper, which exhibits good reflectivity and excellent thermal conductivity in a chemically reduced state. Alternatively, the isotherm 12 may be made of copper, which is chemically reduced and thermally conductive as a whole, but is not limited thereto. In any case, the cavity 13 has reflective walls that allow the sun beam 7 in contact with the walls to be substantially reflected. The multiple order reflection of light rays in the cavity 13 converts the sun's rays into heat at the walls in the cavity 13, which is transferred to the isotherm 12 by conduction, raising its temperature to heat this heat energy. It can be used in sink processes.

The effective area of the receiver is reflected by the sun rays 7 in contact with the reflecting wall from the first contact point on the reflecting wall to the second contact point on the reflecting wall and the plurality of continuous contact points on the reflecting wall. Increased to area Because the cavity is elongated relative to the opening of the cavity, there is a small percentage of the sun's rays exiting through the opening before it is reflected from the wall to the wall and thus absorbed.

The proportion of solar energy absorbed can be increased by increasing the length of the cavity. The total absorption of the rays is impractical, but if the length of the reflective cavity 13 is 5 to 9 times the diameter of the opening of the cavity inlet, the length of the cavity is generally sufficient to absorb the desired significant proportion of the sun's rays entering the cavity. Experiments have shown that the length of the reflective cavity 13 achieves a very good approximation of blackbody absorption at approximately seven times the diameter of the cavity inlet opening. In such a structure, 95% of the solar energy is absorbed.

Increasing the length of the cavity 13 will increase the proportion of sun light absorbed, but the length of the isotherm 12 will also increase. Increasing the size of the isotherm 12 also increases the conductive heat loss from the isotherm and limits the gain in radiation reduction by conduction loss through the expanded surface area of the isotherm 12. The reduction of the cavity 13 length results in a decrease in the energy ratio of the sun rays 7 absorbed by the larger light ratio being reflected off the cavity 13 and lost.

When oxidized, the reflectance is reduced and the cavity 13 is preserved in the local reducing atmosphere because of the chemical deformation of the exposed metallic parts, thereby reducing the efficiency of the device.

10 and 11 show an isotherm 12 and a cavity 13 of the present invention excluding all heat extraction means, where a single light path of the solar light beam 7 is followed by an inlet ( It passes through 20 and hits the reflective wall of the cavity 13.

In this example, the sun's rays 7 or photons undergo a lot of reflection until they are finally absorbed by the cavity wall, and their energy is transferred to the isotherm 12 to raise its internal energy or temperature.

The path followed by the photons shown in FIGS. 10 and 11 is shown for illustrative purposes only and is one of countless possible paths. Condensed light energy with a Gaussian beam profile directed to the cavity inlet will follow all possible paths within the cavity and evenly distribute heat therein.

As the temperature of the isotherm 12 increases, the exposed surface 14 emits energy that contributes to the total parasitic loss, depending on its emissivity and area. Similar to copper, covering all exposed surfaces of the isotherm 12 between the exposed surface or cavity opening and the outer edge of the isotherm as shown in FIGS. 6-9 in an effort to reduce thermal radiation loss by reducing surface emissivity. It is advantageous to construct the shield 30 of the reducing material. Chemically reducible and similar shields can be used to cover all exposed parts at the process temperature.

Figure 7 shows the superheated heating arrangement used for the working fluid of the steam or heating process. The solar energy described as described above is absorbed by a number of internal cavity reflections and absorption mechanisms, which heat the isotherm 12 to the required process temperature. The working fluid enters the receiver of reference 18 and periodically circulates along path 17 located symmetrically within isothermal body 12, absorbing energy from the body and exiting to the required process of reference 19.

In the embodiment of FIGS. 6-9 a shielded enclosure 16 is provided which provides for storing the reducing atmosphere 15 with all the desired insulation.

The window 5 allows the entry of solar radiation into the reflective cavity 13 and provides a gas seal for the enclosure 16.

Enclosure 16 is filled with a reducing atmosphere such as 5% hydrogen and a balance a filler gas that is reducing at operating temperature. Nitrogen is a good choice because it is inexpensive and reducible at high operating temperatures. Other reducing gases include argon, which may be used as well.

The reducing atmosphere keeps reducing metals such as oxygen free high conductivity (OFHC) copper or similar metal compounds in the desired metal state.

In this state, the reflective surfaces of the liner 32 of the reflective cavity 13 and the shield 30 maintain their low emissivity to meet their function in the present invention.

In order to reduce heat loss, the enclosure 16 storing the reducing gas is insulated. In FIGS. 6-9, thermal expansion of the metal cavity liner 32, which forms the metal walls of the cavity 13 as the solar radiation heats the cavity 13, results in a high compressive force against the inner walls of the isotherm 12. . Intimate contact between these components reduces the thermal resistance of the metal boundary between the liner 32 and the isotherm 12 to improve heat transfer to the isotherm 12 receiving heat and substantially isothermal the cavity liner and receiver assembly. By making the state increase the maximum rated flux density of the cavity.

8 and 9 show a thermo-chemical reactor, where the focused solar light beam 7 enters the gas sealed enclosure 16 through a quartz window 5 and passes through a plurality of cavity reflections. The energy of 7) is absorbed by the isotherm 12 and converted into heat.

The reactant gas is injected into the feed line 22 and the preheat channel 24. The hot reactant exiting the preheat channels 24 enters the reaction beds 25 in the isotherm where the catalytic endothermic reaction takes place.

In these examples, the outputs exit the isotherm in the tube 23. Other embodiments shown in FIGS. 6-9 can include a solid isotherm made of a reducing metal or ceramic to eliminate the need for a reflective cavity liner or shield. It would be conceivable within the scope of the present invention to change the concentrations of the aforementioned gases or other means of preventing the oxidation of key components, such as other reducing gases.

The apparatus of the present invention is suitable for use at higher process temperatures where radiation losses represent an important part of the collected solar energy. At low process temperatures, radiation losses are less important and typically do not provide a significant benefit in using the device.

In other words, the above description will be understood for the purpose of illustrating the principles of the invention. It is also not intended to limit the invention to the configurations and effects shown and described per se, as many changes and modifications may occur at any time by those skilled in the art, and therefore, all such suitable changes and modifications are to be considered the scope of the claimed invention. It should be divided into what belongs to.

Claims (20)

A heat collecting device for collecting heat from a solar energy collector and transferring the collected heat to a heat sink, An elongated cavity having a substantially circular opening and having a substantially circular opening having a diameter substantially the same as the focal diameter of the solar energy collector is defined as an elongated cavity, wherein the cavity is configured to substantially reflect the sunlight that contacts the reflective wall. An isotherm having reflective walls; The isotherm is oriented in a direction such that the circular opening is substantially at the focal point of the solar energy collector and is substantially perpendicular to the main axis of the solar energy collector, so that the isotherm is substantially aligned with the main axis of the solar energy collector, The isotherm is thermally coupled to the heat sink so that heat generated in the isotherm is absorbed by the heat sink, And the length of the cavity has a length sufficient to absorb a desired rate of energy in the solar light entering the cavity. The method of claim 1, And increasing the percentage of energy in the sun's rays that enters and is absorbed by the cavity with an increase in cavity length. The method according to claim 1 or 2, And the length of the cavity is 5 to 9 times the diameter of the circular opening. The method of claim 3, And the length of the cavity is 6.5 to 7.5 times the diameter of the circular opening. The method according to any one of claims 1 to 4, And the cavity is substantially cylindrical. The method according to any one of claims 1 to 5, And the isotherm is made of a reflective material such that the walls of the cavity are reflective. The method according to any one of claims 1 to 5, And a liner made of a reflective material between the isotherm and the cavity, the liner operative to provide a reflective wall of the cavity. The method of claim 7, wherein And a low emissivity shield covering the end of the isotherm between the opening of the cavity and the outer edge of the isotherm. The method according to any one of claims 1 to 8, An enclosure that shields the isotherm, And the interior of the enclosure includes a reducing atmosphere to act to substantially prevent oxidation of the cavity reflecting wall and thereby maintain reflectivity of the reflecting walls. The method of claim 9, And the reflective walls comprise OFHC copper and the reducing atmosphere comprises hydrogen and filler gas. The method of claim 9 or 10, And heat insulation in the walls of the enclosure. An apparatus for collecting heat from the sun and transferring the collected heat to a heat sink, Solar energy collector; And An isotherm defined as a substantially cylindrical cavity having a circular opening having a diameter substantially the same as the diameter of the solar energy concentrator focal point, the cavity having reflective walls such that the sun rays in contact with the reflective wall are substantially reflected; Including, The isotherm is aligned in a direction such that the circular opening is substantially at the focal point of the solar energy collector and is substantially perpendicular to the major axis of the solar energy collector, so that it is substantially aligned with the major axis of the solar energy collector, The isothermal body is adapted to be thermally coupled such that heat generated in the isothermal body is absorbed by the heat sink, And the length of the cavity is 5 to 9 times the diameter of the circular opening. The method of claim 12, And a low emissivity shield covering the isothermal end between the opening of the cavity and the outer edge of the isotherm. The method according to claim 12 or 13, An enclosure that shields the isotherm, And the interior of the enclosure includes a reducing atmosphere to act to substantially prevent oxidation of the cavity reflecting wall and thereby maintain reflectivity of the reflecting walls. The method of claim 14, And the reflective walls comprise OFHC copper and the reducing atmosphere comprises hydrogen and filler gas. A device for collecting heat from a solar energy concentrator for transfer to a heat sink, An isotherm defined and provided as an elongated cavity having a substantially circular opening of a diameter substantially the same as the focal diameter of the solar energy collector, the cavity comprising reflective walls that allow the sun rays that strike the walls to be substantially reflected; Including, Directing the isothermal body substantially circularly positioned at the focal point of the solar energy collector and substantially perpendicular to the major axis of the solar energy collector so that the axis of the solar energy collector and the axis of the cavity are substantially aligned, From the first contact point on the reflecting wall so that a portion of the energy contained in each sun ray is absorbed by the reflecting wall at each contact point until the desired magnification of the energy contained in the sun's rays is absorbed by the reflecting wall. 2 reflects the sun's rays into contact points and a plurality of consecutive contact points on the reflecting wall, And a heat sink thermally coupled to the isotherm such that heat generated by solar energy absorbed in the isotherm is absorbed by the heat sink. The method of claim 16, And increasing the percentage of energy in the sun's rays that enters and is absorbed by the cavity with an increase in cavity length. The method according to claim 16 or 17, The cavity is substantially cylindrical, And the length of the cavity is 5 to 9 times the cavity opening diameter. The method according to any one of claims 16 to 18, An enclosure that shields the isotherm, And the interior of the enclosure includes a reducing atmosphere to act to substantially prevent oxidation of the cavity reflecting wall and thereby maintain reflectivity of the reflecting walls. The method of claim 19, And the reflective walls comprise OFHC copper and the reducing atmosphere comprises hydrogen and filler gas.

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