SOLAR ENERGY RECEIVER
A solar energy receiver comprises a panel, having a graphite core, a substantially gas tight housing encasing the graphite core, a heat exchanger comprising heat exchanger tubing, a heat exchanger inlet and a heat exchanger outlet. The heat exchanger tubing is at least partially embedded in the graphite core, and the heat exchanger inlet and the heat exchanger outlet extend through the housing. The housing is sealed around the heat exchanger inlet and the heat exchanger outlet. A method of manufacturing a solar energy receiver comprises: a) fabricating the heat exchanger in a serpentine coil shape; b) inserting grooved planks of graphite between individual coils of the heat exchanger to form the graphite core such that the coils are encompassed in the grooves; c) inserting the graphite and heat exchanger into the housing; and d) sealing the housing and sealing openings around the inlet and outlet where they pass through the housing.
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The present invention relates to the fields of solar energy conversion and in particular to devices for collecting solar energy as heat and storing heat whereby its use is not directly linked to the availability of sunlight.
BACKGROUND OF THE INVENTIONWorldwide there is an increasing awareness of the need to reduce reliance on fossil fuels and increase the use of renewable energy sources. One major renewable energy source that is effectively unlimited in the foreseeable future is solar energy, however solar energy has the disadvantage that it is not available at night and during cloudy periods and so conversion systems need to include some form of energy storage if they are to become a viable replacement for fossil fuel as a source of energy.
Existing solar energy conversion systems fall into several categories:—
1) Photovoltaic (PV) systems, in which solar energy is absorbed into materials that convert the solar energy directly into electricity;
2) Concentrating Solar Power (CSP), in which solar energy is used to heat a fluid and that heated fluid is used to directly or indirectly drive a mechanical device (such as a turbine) to convert the heat energy into electrical energy.
To enable solar radiation to be used as heat for a thermodynamic cycle to produce process steam or electricity, it must be first concentrated to achieve higher temperatures, as solar radiation reaches the earth at a density too low to directly produce such temperatures. A variety of technologies are being developed for use in CSP Systems including:—
Trough and “Fresnel” type linear collector systems, which comprise an elongate reflector, and one collector tube or assembly of tubes running along the focal point of the reflector. The tube(s) contains a fluid which is heated and then pumped to a heat engine (e.g. a turbine);
Tower systems which collect solar energy concentrated to a target from a large number of mirrors which track the sun and focus the large number of images at one collection point (heliostats), where the high temperatures achieved are used to heat a fluid which is transmitted to a heat engine (e.g. a turbine). Tower systems may include single towers and multiple tower arrangements;
Dish/Engine systems, where a small heat engine is placed at the focal point of a parabolic dish and driven directly by the concentrated solar energy.
Within the category of tower systems one arrangement that has shown promise is the use of a graphite body as a solar receiver in which heat exchanger tubes are embedded where the heat exchange fluid used to drive an engine such as a turbine is directly heated by heat energy stored in the graphite body. Such systems are in their infancy and existing configurations have a variety of disadvantages typical of early stage technologies including high cost of manufacture and structural integrity problems. In particular, present designs (or at least those which have been shown to be practical) comprise a gas tight containment housing which encompasses most of the remainder of the assembly and this design places constraints on the manufacture of the receiver such as:—
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- If receivers are to be of a size that achieves reasonable efficiency and cost effectiveness, they must be fully assembled and tested at or near site, typically from outsourced sub-assemblies. Due to the gas tight nature of the housing this assembly operation is not trivial and adds considerably to the expense of manufacture;
- If assembly were to be contemplated at a site remote from the installation site, overall dimensions of receivers are constrained by road transport limitations and even with onsite assembly there is a limitation on the size of subassemblies that can be readily transported;
- Graphite and heat exchanger piping costs amount to only 45% of total cost of the receiver. Other major costs relate to the containment housing and other structural items 16%, insulation 10% (of which 7% is for the shield protecting the base structure);
- The design requires many sub-assemblies and the resultant supply chain has many vendors;
- The need to ship unassembled parts and to assemble the parts on site makes it expensive. Alternatively, shipping assembled units would be difficult, if not impossible and prohibitive in cost;
- The present receiver designs have limited scalability options without total redesign and so the external dimensions, graphite mass and potential power handling capacity are effectively fixed;
- Preparation of the receiver at site before installation on the tower is time consuming;
- Dimensional constraints imposed on the receiver design by transport limitations restrict utilization of graphite in previous designs to at best 70% to 75% because the constraints on the design do not allow maximized usage of the standard manufactured sizes of graphite block.
Throughout this specification, unless otherwise specified, panels of solar receivers will be described in a vertical orientation with vertical side walls at least one of which is a solar energy receiving wall. The panels and their components will be described as having a top and a bottom and two ends relative to the vertical side walls, and will include a top and bottom walls, and end walls, however the panels may be used in other orientations in which, for example a horizontal orientation in which the side wall may be at the top and a top wall may be at the side.
SUMMARYAccording to one aspect, the present invention consists in a solar energy receiver comprising a panel, the panel comprising a graphite core, a substantially gas tight housing encasing the graphite core, a heat exchanger comprising heat exchanger tubing including a heat exchanger inlet and a heat exchanger outlet, the heat exchanger tubing at least partially embedded in the graphite core, the heat exchanger inlet and the heat exchanger outlet extending through the housing and the housing sealed around the heat exchanger inlet and the heat exchanger outlet.
According to a second aspect, the present invention consists in method of manufacturing a solar energy receiver comprising a panel, the panel comprising a graphite core, a substantially gas tight housing encasing the graphite core, a heat exchanger comprising heat exchanger tubing including a heat exchanger inlet and a heat exchanger outlet the heat exchanger tubing at least partially embedded in the graphite core, the heat exchanger inlet and the heat exchanger outlet extending through the housing and the housing sealed around the heat exchanger inlet and the heat exchanger outlet, the method comprising:
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- a) fabricating the heat exchanger in a serpentine coil shape;
- b) inserting grooved planks of graphite between individual coils of the heat exchanger to form the graphite core such that the coils are encompassed in the grooves;
- c) inserting the graphite and heat exchanger into the housing; and
- d) sealing the housing.
The heat exchanger may further comprise a heat exchanger drain which also extends through the housing and the housing is sealed around the heat exchanger drain.
The heat exchanger drain may also act as an inlet/outlet such that only one other inlet/outlet is required to pass through the housing wall. The working fluid may pass between the inlet/outlets in either direction depending on the location of the panel in the solar receiver installation:
The drain may be configured to also be used as the inlet to the heat exchanger and the outlet will be located at the top of the receiver panel such that flow of working fluid through the panel is from bottom to top through the panel.
The housing may have two spaced apart side walls joined together about their periphery by one or more additional walls to form a closed container. One of, or a portion of the one or more additional walls is a bottom wall forming a base of the housing and in one embodiment the graphite core will be located in thermal communication with the base and at least one of the two side walls of the housing. At least 2 walls of the housing may be in thermal communication with the graphite core. The bottom wall of the housing may also be formed by bending a single piece of wall material into a “U” shape having curved bends in which the bottom wall transitions into each of the side walls to which it is connected via one of the curved bends. The curved bends at the edges of the bottom wall will reduce stresses in the housing wall allowing the use of lighter wall construction and eliminating the need for further structural support in the base wall. The walls of the housing may be fabricated from 253MA austenitic stainless steel or any other high temperature thermally conductive material (e.g. 800H or Inconel alloys) finished to mill finish class 2B. Depending upon the location of the surfaces within the final receiver configuration and the geographic location of the installation, some surfaces may be provided with a specific thermal emittance while others may be provided with a specific thermal absorptance to enhance performance. Surface treatments or surface coatings may be applied to achieve specific emissivity in the range of 0.2-1.0. For example, if some surfaces are required to be emittive they may be left natural (specific emissivity 0.7) may be polished (specific emissivity 0.2-0.3), or may be coated with or surface treated to achieve a specific emissivity in the range of 0.3-0.8 while other surfaces which are required to be highly thermally absorptive may be coated with or surface treated to achieve a highly heat absorbing surface (such as a black surface with a specific absorptivity of 0.8-1.0, preferably 0.9-1.0).
The other walls of the housing may also comprise a top wall opposite the bottom wall, and two end walls. The housing may also include a plurality of mounting flanges extending from the housing and capable of suspending and supporting the weight of the receiver element. The mounting flanges may extend from joins between adjoining walls of housing and may include holes for attachment to a mounting frame. For example the flanges may extend from joins between the side walls and the end walls of the housing. Each mounting flange may comprise an extension of one of the end walls beyond the respective side wall to which it is joined. Alternatively each mounting flange may comprise an extension of one of the end walls beyond the top wall. The mounting flanges may extend from an end wall that in use is typically oriented vertically. By suspending the receiver element rather than supporting it from below, the resulting tension in the side walls due to gravity of the graphite core acting on the housing allows them to resist buckling to maintain good thermal communication with the graphite core. The shape of the housing also tends to keep the metal walls pressed against the graphite core. In addition, by suspending the receiver from above, the base of the housing is exposed to, and can absorb, solar irradiation which would otherwise be reflected by shielding tiles used in prior art designs to protect the base structure from overheating.
The graphite core may be shaped to conform to the internal shape of the housing and in particular has a portion shaped to conform to the shape of the curved bends of the bottom wall of the housing. The graphite core may comprise a plurality of stacked graphite planks, at least a lower one of which is profiled to match the shape of the curved transitions between the base and the lower portions of the side walls.
Graphite cores in prior art receivers were surrounded by insulation (except for the energy receiving surfaces) and the core and insulation were housed in an inert gas environment to prevent chemical reaction of the core. The inert gas was generally maintained at a positive pressure to prevent leakage of air into the complex housing structure. In contrast, embodiments of the present receiver have a simplified housing which has greater structural integrity. There is also no internal insulation within the housing and the graphite core conforms to the inner shape of the housing. Therefore the amount of space left in the housing is quite small after the graphite and heat exchanger are inserted and the housing is sealed, and it is possible to leave this remaining space filled with air. On the first heating of the receiver element a small amount of graphite will oxidize until the oxygen in the air is consumed, leaving the spaces substantially filled with nitrogen and carbon dioxide protecting the graphite from further oxidation when exposed to high temperatures in subsequent thermal cycles. However if the operating temperature of the panel is to exceed 700° C. a reduction reaction may occur causing the carbon dioxide to reduce to carbon monoxide with further carbon being consumed by the liberated oxygen. Subsequent cooling can lead to some of the carbon monoxide decomposing to carbon and oxygen which again forms carbon dioxide. This can lead to deterioration of the physical structure of the graphite over time. Therefore if the operating temperature of the panels is expected to exceed 700° C. in a particular installation, it will be desirable at manufacture to replace the air filling the spaces in the panel between the graphite and the walls with an inert gas such as argon or helium. Alternatively the spaces in the panel may be filled with thermally conductive material that exists in a solid, liquid or gaseous state at least in the working temperature range of the panel, such as tin, zinc, mercury, or a molten salt such as potassium nitrate, potassium nitrite, sodium nitrate, sodium nitrite, other nitrate, nitrite, chloride or fluoride salts or a mixture of such salts or graphite powder. A reservoir containing graphite powder may be located in communication with the interior of the housing, whereby graphite powder is supplied from the reservoir to the interior of the housing to fill additional void space created by expansion of the housing.
The points where the heat exchanger inlet and heat exchange outlet pass through the housing may be in close proximity and may be at one end of the top wall of the housing, to assist with mounting and manifolding the pipes with other receivers. Alternatively, the drain, which is located at the lowest point of the heat exchanger, may double as one of the inlet/outlets, in which case only one inlet/outlet is required to be provided at the top of the heat exchanger.
At least some of the heat exchanger tubes may be fabricated in a coiled or serpentine form suitable for compression (like a spring) during assembly, such that when the container expands due to thermal expansion, the resulting stresses from the movement of the pipe configuration do not exceed the mechanical properties of the pipe material.
The heat exchanger coils may comprise a plurality of straight tube portions arranged to be parallel to each other and connected at their ends to form one or more serpentine or coil shapes. In some embodiments the straight tube portions are arranged in parallel planes forming rows of straight tube portions. The straight tube portions may be arranged in coils where rows of straight tube portions are interconnected at their ends and each row is connected to the row above and below to form a single coil structure. Alternatively the straight tube portions may each be connected at respective ends to a straight tube portion above and below to form parallel serpentine constructions. Where the straight tube portions form parts of coils there may be an even number of straight tube portions (such as two straight tube portions) in each row. The straight tube portions in each row may be aligned with the straight tube portions in adjacent rows such that they also form planes perpendicular to the first mentioned parallel planes. At a first end of the heat exchanger (which will become the insertion end for subsequent insertion of graphite planks) the straight tube portions in each row may be connected in pairs by first U-shaped connecting tube portions. At a second end of the heat exchanger (the non-insertion end), the straight tube portions in each row may be connected to straight tube portions in each of the two adjacent rows by second U-shaped connecting tube portions. In the case where there are two straight tube portions per row, the two straight tube portions in each row may therefore be connected together at the first (insertion) end and each of the two straight tube portions in each row are respectively connected to straight tube portions of each of two adjacent rows at their second (non-insertion) end. A heat exchanger inlet tube and a heat exchanger outlet tube may be connected to one of the straight tubes in each of top row of straight tube portions and bottom row of straight tube portions via interconnecting tube portions.
Where the straight tube portions form serpentine constructions, there may be an even number or an odd number of straight tube portions (such as two or three straight tube portions) in each row. The straight tube portions in each row may be aligned with the straight tube portions in adjacent rows such that they also form planes perpendicular to the first mentioned parallel planes. At a first end of the heat exchanger each of the straight tube portions in each row may be connected by first U-shaped connecting tube portions to straight tube portions in the row below. At a second end of the heat exchanger, each of the straight tube portions in each row may be connected to straight tube portions in row above by second U-shaped connecting tube portions. In this arrangement the graphite planks are inserted from alternate ends of the serpentine structure such that the planks are always inserted between two rows of straight tube portions at an end opposite the end at which those two rows are interconnected.
The configuration of the heat exchanger tubing and drain may be arranged to allow drainage of liquid from top to bottom of the heat exchanger both when the heat exchanger is in a vertical orientation (i.e. where the are coils stacked vertically above one another) and when the heat exchanger is angled from the vertical orientation (with the mounting points on the upper side) as when the panels are configured in an inverted “V” configuration. In one embodiment where the straight tube portions form a coil structure, the heat exchange may be angled at an angle of up to 21°, however this angle is dictated by the angle of the second “U” shaped connecting tube portions which interconnect straight tube portions of different rows of straight tube portions and may be varied depending on the angle of interconnection of adjacent rows of straight tube portions. The angle by which the heat exchanger deviates from the vertical orientation should not exceed the angle of the second “U” shaped connecting tube portions (with respect to the plane of a row of straight tube portions), such that condensed liquid in the heat exchanger is not required to flow up hill to reach the drain. In the serpentine structure the heat exchanger may be readily angled at angles of up to 45° and possibly even approaching 90° to the vertical.
After the heat exchanger, is fabricated, pre-shaped planks of graphite are positioned to be located between each row of tubes and capping planks are placed over the inlet end rows of straight tube portions and the outlet end row of straight tube portions. The abutting surfaces of the graphite planks may have a surface finish which is N8 or better (ISO 1302). The graphite planks (excluding the capping planks) each include two grooved surfaces, on opposite surfaces thereof, where the grooves may be semi-circular in cross-section conforming to the shape and radius of the straight tube portions and interconnecting tube portions at the first (insertion) end of the heat exchanger when the tube portions and the surrounding graphite are at their working temperature such that when assembled between rows of straight tube portions adjacent pairs of the planks encompass and closely conform to the respective straight tube portions and first connecting tube portions. To achieve close conformity of the heat exchanger tubes with the grooves in the graphite at the internal working temperature of the panel, which is up to 800° C., the grooves are made approximately 1.6% bigger than the nominal outside diameter of the tubes to allow for the radial expansion of the tube at working temperature with a tolerance of approximately +0.00/−1.00%. For example, when the heat exchanger tubes (made for example from 253MA austenitic stainless steel, or any other suitable high temperature thermally conductive material like 800H austenitic steel or alloys such as Inconel) have a nominal outside diameter of 26.67 mm the grooves will be 27.1 mm (+0.00/−0.25 mm) in diameter. Alternatively when the heat exchanger tubes made from the same or a similar material have a nominal outside diameter of 42.16 mm the grooves will be 42.9 mm (+0.00/−0.25 mm) in diameter. The smoothness of the surface of the grooves will have a bearing on heat transfer with smooth surfaced grooves having a higher contact surface than rough surface grooves, however the smoother the surface the more expensive the cost of finishing the grooves.
The surface within the grooves may have a surface finish which is N7 or better (ISO 1302). Rather than being semicircular, the grooves may also be a half obround shape with a radius which is slightly greater (by about 1.6% with a straight section about 1.6% of the radius in the direction perpendicular to (i.e. across) the parallel groove, to accommodate lateral movement of the tube when the coils expand. However this has the disadvantage that the tubes will not be as closely encompassed in the grooves and in some cases it may be preferable to accommodate expansion of the coils by other means such as by allowing them to expand into the cavity which accommodates the second connecting portions.
At the second (non-insertion) end of the heat exchanger, ends of the graphite planks are recessed to accommodate the second connecting tube portions joining straight tube portions from adjacent rows of straight tube portions.
Capping planks are provided at either end of the stack of graphite planks. A lower capping plank is grooved on one surface facing an adjacent graphite plank the grooves conforming to the shape and radius of the straight tube portions and interconnecting tube portions at the first (insertion) end of the heat exchanger. Edges of the lower capping plank between the face opposite the adjacent graphite plank and the sides of the lower capping plank are radiused. An upper capping plank is preferably recessed on a surface facing an adjacent graphite plank to accommodate inlet and outlet tubing without constraining thermal expansion thereof. As an inlet and outlet of the heat exchanger are fixed to the top wall of the housing where they pass through the housing, the recess in the upper capping plank accommodates longitudinal expansion of the tubes as well as allowing the coils, to separate or compress with differential movement between the graphite and the housing as the housing expands and contracts with heating and cooling between ambient and its upper working temperature, which can be as high as 1000° C. In the present embodiment the volume of void spaces within the housing not occupied by graphite or tubing is generally in the range of 4-10% and typically 5-7% of the internal volume of the housing (at the working temperature). Correspondingly the side panel of the housing, which is the irradiated surface of the panel when in use, is generally backed by the graphite core over all but 1-5% of its area and typically 2-3% (at the working temperature) in the preferred embodiment.
The first (insertion) ends of the straight tube portions may be sprung apart slightly to allow the planks to be easily inserted into the fabricated heat exchanger tubing past the first connecting tube portions and between adjacent rows of coils. Alternatively during fabrication of the heat exchanger coils, they may be spaced by a spacing greater than or equal to a plank thickness of the graphite planks between which they are located in the final assembly (or at least the first (non-insertion) ends may be so spaced), such that the planks may be easily inserted into the fabricated heat exchanger tubing between adjacent rows of coils and the coils of the tubing may then be compressed into contact with the graphite after insertion of the graphite planks between the coils.
A solar energy receiver may comprise two or more receiver panels configured and mounted to form a downward opening cavity. The cavity may be formed with a combination of receiver panels and insulation panels. Outside surfaces of the receiver panels forming the solar energy receiver may also be covered by insulation.
The solar energy receiver may comprise a plurality of receiver panels arranged to form an opening, which is in a shape of a rectangular prism. The top of the rectangular prism opening may be closed by one or more additional receiver panels or may be closed by insulation on transparent panels such as fused quartz. An underside of the insulation closing the top of the rectangular prism shaped opening may have a high emissivity surface facing into the opening.
Alternatively the solar energy receiver may comprise a plurality of receiver panels arranged in an inverted “V” configuration to form an opening which is in a shape of a triangular prism (with the lower parallelogram side horizontal). The ends of the triangular prism shaped opening may be closed by further receiver panels or may be closed by insulation panels or panels of optically transparent material such as fused quartz which can pass solar energy directed from the heliostats to the skies of the receiver while confining convection within the opening and can withstand the high temperatures created by absorption Of the solar energy. Again, an inside surface of the insulation closing the ends of the triangular prism shaped opening may be a high emissivity surface facing into the opening.
Outer surfaces of the receiver panels of the solar energy receiver are preferably covered with insulation, which may comprise prefabricated insulation panels, to prevent heat loss from the outer surfaces by radiation or conduction.
The rectangular or “V” shaped openings in the bottom of panel assemblies may be partially closed by insulating tiles or fused quartz panels (not illustrated) to restrict heat loss by convection while leaving smaller apertures through which solar energy may be directed from the heliostats.
The solar energy receiver may be mounted suspended from a tower and energy is directed at the openings in the receiver by heliostats located around a base of the tower. The solar energy receiver may be mounted on a side of the tower facing away from the equator and the heliostats may be located predominantly on the opposite side of the tower to the equator although an East-West orientation is also possible.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:
Referring to
In
The bottom wall 14 of the housing may be integrally formed with the two side walls 12, 13 by bending a single piece of wall material into a “U” shape in which the base transitions into each of the side walls via a curved bend of radius R which in the present example is in the range of 50 to 180 mm and nominally 80 mm. The wall material is preferably a sheet steel material capable of retaining structural integrity to support the enclosed graphite core, the heat exchanger and any heat exchange fluid contained therein at elevated temperatures of at least 1000° C.
Mounting flanges 21 are provided extending from the end walls 15, 16 and include respective upper and lower mounting holes 23, 24. The flanges 21 are used to suspend the panel from a mounting frame (not shown) by bolting them to the frame via the mounting holes 23, 24. Each flange may comprise an extension of one of the end walls 15, 16 beyond the respective side wall 13 to which it is joined (i.e. the flange may be cut from the same piece of sheet material as the end walls 15, 16 from which they extend). By suspending the receiver panel from the flanges 21 rather than supporting it from below, the resulting tension in the side walls due to gravity of the graphite core acting on the housing allows them to resist buckling to maintain good thermal communication with the graphite core. The curved shape of the housing where the side walls 15, 16 join the bottom wall 14 through a bend also tends to keep the metal walls pressed against the graphite core. In addition, suspending the receiver from above leaves the base of the receiver free of supporting structure and associated protective insulation such that it may be exposed to and can absorb solar radiation from which it would otherwise be protected, allowing more of the surface of the receiver panel 111 to be used for energy absorption.
Vents 51 are provided in the top wall 17 of the housing to allow venting during welding together of the housing walls. These holes may be plugged (e.g. by welding after the panel walls are joined, or they may be used to accommodate sealed cable ports through the wall to pass instrumentation cables such as thermocouple wires into the housing, as fill ports to provide an Argon blanket to the graphite core, to accommodate a filling nozzle to fill the void space and/or an internal reservoir with graphite powder or other thermally conductive media, or to accommodate a connection to an external reservoir to maintain the level of such materials, when the graphite core and housing expand and contract during thermal cycling.
Referring to
The heat exchanger tubes may be made, for example, from 253MA austenitic stainless steel (or any suitable high temperature thermally conductive material such as 800H austenitic steel or alloys such as Inconel), and may have a nominal outside diameter of for example 42.16 mm in the present embodiment but the outside diameter may vary to be greater or smaller than this depending on the particular circumstances of the application. For example, in other embodiments the heat exchanger tubes may be made from the same or a similar material and may have a nominal outside diameter of 26.67 mm. The heat exchanger tubing 25, 26, 27, 28, 39, 40, the drain 29 and associated inlet/outlet tubes 18, 19 are preferably formed with at least some of the tube assembly taking a coiled or serpentine form suitable for compression (like a spring) during assembly, such that when the housing 111 expands due to thermal expansion, the resulting stresses from the movement of the pipe configuration does not exceed the mechanical properties of the pipe material.
In an alternative arrangement, the drain 29 may also act as an inlet or outlet in which case the inlet/outlet 18 will be redundant and might be removed along with its connecting tubes 25 and 40 and passage of fluid through the heat exchanger will be (in either direction) between the drain 29 and the inlet/outlet 19.
The heat exchanger tubing (as seen in
Referring to
The housing is sealed around the first and second heat exchanger inlet/outlets 18, 19, and the end 38 of the drain 29 where they exit the housing such that air cannot enter the housing after it is sealed. The plurality of openings 51 in the top wall 17 of the housing (as seen in
The points where the first and second heat exchanger inlet/outlet 18, 19 pass through the housing 111 are preferably in close proximity and preferably exit through the top wall 17 of the housing, to assist with mounting and manifolding the pipes with other receivers.
The heat exchanger coils comprise a plurality of straight tube portions 26 arranged in parallel and connected at their ends by connecting portions 27, 28 to form a serpentine coil. Preferably the straight tube portions 26 are arranged in parallel planes forming rows of pairs of straight tube portions. The straight tube portions 26 in each row are aligned with the straight tube portions in adjacent rows such that they also exist in vertical planes perpendicular to the first mentioned parallel planes.
In the example illustrated in
After the heat exchanger is fabricated, pre-shaped planks of graphite 31, 32 & 52 are positioned to encompass most of the heat exchanger tubes. Referring to
Referring to
Referring to
The heat exchanger tubes may again be made, for example, from 253MA austenitic stainless steel (or any suitable high temperature thermally conductive material such as 800H austenitic steel or alloys such as Inconel), and may have a nominal outside diameter of for example 42.16 mm in this embodiment but the outside diameter may vary to be greater or smaller than this depending on the particular circumstances of the application.
The heat exchanger tubing 678, 682, 683, 684, 685, 686, 687 & 688 are formed with at least some of the tube assembly taking a coiled or serpentine form suitable for compression (like a spring) during assembly, such that when the housing 111 expands due to thermal expansion, the resulting stresses from the movement of the pipe configuration does not exceed the mechanical properties of the pipe material.
The heat exchanger tubing (as seen in
The housing is sealed around the heat exchanger inlet tubes 686, 687, 688 where they exit the housing such that air cannot enter the housing after it is sealed. The plurality of openings 51 in the top wall 17 of the housing (as seen in
After the heat exchanger is fabricated, pre-shaped planks of graphite 689, 692, 701 are positioned to encompass most of the heat exchanger tubes. Referring to
Referring to
Preferably the abutting surfaces of the graphite planks of
Embodiments may also be manufactured in which the grooves 35, 36 (
Because, in the embodiment of
The panel described with reference to
Once the graphite planks 31, 32, 52 are assembled to encompass the heat exchanger 20, (or planks 689, 692, 701 are assembled to encompass the heat exchanger 670) the assembly is inserted into the housing, locating tubes are inserted into the holes 41 (or 702) extending through all of the planks to maintain alignment. At least one of the locating tubes will engage a locating pin projecting from the base of the housing (not shown) to locate the graphite core 31, 32, 52 within the housing. The housing is then welded closed, including sealing the openings through which the inlet/outlet tubes 18, 19 (or 686, 687, 688, 683, 684, 685) and the drain 29 (or 686, 687, 688) pass through the housing to form the finished panel 111 (see
In the alternative arrangement shown in
Referring to
Preferably a solar energy receiver will comprise two or more receiver panels configured to form a downward opening cavity. The cavity may be formed with a combination of receiver panels and insulation panels. Outside surfaces of the receiver panels forming the solar energy receiver will preferably be covered by insulation to minimize unwanted heat loss.
Referring to
The configurations of solar energy receivers 102 shown in
A particularly advantageous configuration of a solar energy receiver 102 is illustrated in sectional end elevation in
The walls of each housing are preferably fabricated from 253MA austenitic stainless steel (or any suitable high temperature thermally conductive material such as 800H austenitic steel or alloys such as Inconel) finished to mill finish class 2B. The surfaces 191 of panels 111 which face inwardly of the opening 486 and are forward facing with respect to the heliostat field 106, have a natural class 2B mill finish to the stainless steel material to provide a degree of emissivity which causes a portion of the incident solar energy to be re-radiated onto the surface 192 of the opposing panel 111, which is a rearward facing surface with respect to the heliostat field 106. The rearward facing surface 192 on the other hand will preferably be coated with a robust high temperature heat absorbing (black—specific absorptivity 0.80-1.0) paint, surface treatment or other suitable coating. Inwardly facing surfaces of the side receiver panels 491 also have a natural class 2B mill finish (specific emissivity 0.7) or polished surface (emissivity 0.2) or may be provided with a further surface treatment or coating to achieve a medium emissivity surface (specific emissivity in the range of 0.3-0.8) such that some of the solar energy falling on these panels is re-radiated to other internal surfaces within the opening 162.
The sides and top of the solar energy receiver 102 are surrounded with insulating panels as with the earlier described arrangements. In particular the top of the openings 486 are closed with insulating panels 485 which include high emissivity surfaces 487 facing into the opening 486 to reflect any solar energy reaching the top of the openings 486 back towards the heat absorbing surfaces of the fins 481. Insulating panels 483 are also located over the front (heliostat facing) surface of the front fin 481 and further insulating panels 483 are located over the rear (non heliostat facing) surface of the rear fin 481. Insulating panels 492 also cover the outside surfaces of the side closure heat absorbing panels 491.
Referring to
In the
The walls of the housing are preferably fabricated from 253MA austenitic stainless steel (or any suitable high temperature thermally conductive material such as 800H austenitic steel or alloys such as Inconel) finished to mill finish class 2B. The surfaces 191 of panels 111 which face inwardly of the opening 162 and are forward facing with respect to the heliostat field 106, have a natural class 2B finish to the stainless steel material to provide a degree of emissivity which causes a portion of the incident solar energy to be re-radiated onto the surface 192, which is a rearward facing surface with respect to the heliostat field 106. The rearward facing surface on the other hand will preferably be coated with a robust high temperature heat absorbing (black—specific absorptivity 0.80-1.0) paint, surface treatment or other suitable coating. Inward facing surfaces of the additional receiver panels 111 which form end closures 401 have a natural class 2B mill finish (specific emissivity 0.7) to the stainless steel material, or may be polished (specific emissivity 0.2) or polished surface (emissivity 0.2) or may be provided with a further surface treatment or coating to achieve a medium emissivity surface (in the range of 0.3-0.8) which causes a portion of the incident solar energy to be re-radiated onto other internal surfaces of the opening 162.
As illustrated in
Referring to
In the
The walls of the housings in
A further embodiment is illustrated in
The openings 62, 162, 486 in the bottom of panel assemblies 102, 641,642 may be fully or partially closed by insulating tiles or fused quartz panels (not illustrated) to restrict heat loss by convection while leaving smaller apertures through which solar energy may be directed from the heliostats.
The walls of the housings in
The outside surfaces of the sides fronts, backs and top of the inverted “V” shaped panel assemblies of the solar energy receiver 102 will be surrounded with insulating panels similar to those previously described, for example in the description of the
Referring to
By using modular receiver panels that can be assembled into a variety of solar energy receiver configurations, simple and fast site installation can be achieved with minimal on site preparation requirements. The receiver panels can be shipped to site assembled and fully tested for simple mounting on a tower along with associated insulation panels in a preferred one of a variety of optional configurations.
Reduced cost is achieved by simplification of design, having only 1 basic panel design and a single basic configuration which is scalable by adding panels in a repeating pattern, thereby maximizing utilization of key materials and maximise graphite and heat exchanger piping costs as a percentage of the overall cost of installation.
In the preferred embodiment the receiver panel can be manufactured at a single (off site) location from prefabricated parts supplied by perhaps 2 to 4 suppliers. After assembly the panels may be sealed and QC tested at the manufactured site. Hence no further assembly or testing of the panels is required on site. The panel design also optimizes usage of graphite and high pressure tubing which is manufactured in a very small number of standard dimensions. Assembly of the panels into a solar energy receiver on site is achieved by hanging the panels and the arrangement can be configured to suit different applications with varying heat storage capacities by using multiples of the panel combined to increase the size of the total assembly. Because the arrangement is suspended the lower surfaces 14 of the panels may be exposed to solar radiation and is no supporting base structure under the solar energy receiver or heat shields to protect the base. Thus additional heat is captured by the hung panel through its base.
By using the planks of graphite stacked one on top of the other and hung within a clad ‘skin’ of the housing, the skin will be tensioned due to gravity acting on the graphite core such that when the ‘skin’ expands at temperature, skin buckling which would otherwise reduce the transfer of heat to the graphite is eliminated or at least minimized.
Claims
1. A solar energy receiver comprising a panel, the panel comprising a graphite core, a substantially gas tight housing encasing the graphite core, a heat exchanger comprising heat exchanger tubing including a heat exchanger inlet and a heat exchanger outlet, the heat exchanger tubing at least partially embedded in the graphite core, the heat exchanger inlet and the heat exchanger outlet extending through the housing and the housing sealed around the heat exchanger inlet and the heat exchanger outlet.
2. The solar energy receiver of claim 1 wherein one of the heat exchanger inlet and the heat exchanger outlet comprises a heat exchanger drain.
3. (canceled)
4. The solar energy receiver of claim 1, wherein the housing has two spaced apart side walls joined together about their periphery by one or more further walls to form a closed container.
5. The solar energy receiver of claim 4 wherein one of, or a portion of the one or more further walls is a bottom wall forming a base of the housing and the graphite core is located in thermal communication with the base and at least one of the two side walls of the housing.
6. The solar energy receiver of claim 5 wherein at least two sides of the receiver element are in thermal communication with the graphite core.
7. (canceled)
8. The solar energy receiver as claimed in claim 5 wherein the graphite core has a shape to conforming to an internal shape of the housing and has a portion shaped to conform to an internal shape of the bottom wall of the housing.
9. The solar energy receiver of claim 1, wherein the housing includes a plurality of. mounting flanges extending from the housing and capable of suspending and supporting the weight of the receiver element, the mounting flanges extending including mounting holes therein.
10-11. (canceled)
12. The solar energy receiver of claim 9 wherein each mounting flange comprises an extension of one of the end walls beyond the respective side wall to which it is joined.
13. The solar energy receiver as claimed in claim 1 wherein the graphite core comprises a plurality of stacked graphite planks, at least a lower one of which is profiled to match the shape of the transition between the base and the lower portions of the side walls of the housing.
14. The solar energy receiver as claimed in claim 1 wherein at least some the heat exchanger tubes are in a coiled or serpentine form which is compressed when the heat exchanger is at ambient temperature, such that when the container expands due to thermal expansion under exposure to solar energy, the compression of the compressed coiled or serpentine tubes is released.
15-16. (canceled)
17. The solar energy receiver as claimed in claim 14 wherein there are two or more coils in each panel.
18. (canceled)
19. The solar energy receiver as claimed in claim 2 wherein the heat exchanger tubing and drain are arranged to allow drainage of liquid from top of the heat exchanger to the bottom of the heat exchanger when the panel is angled from the vertical orientation by up to 21° to one side whereby none of the connecting tube portions present an uphill course for liquid draining from the top of the heat exchanger to the bottom.
20-25. (canceled)
26. The solar energy receiver as claimed in claim 2 wherein the heat exchanger tubing is arranged to allow drainage of liquid from the top of the heat exchanger to the bottom of the heat exchanger and the heat exchanger inlet located at the bottom of a heat exchanger is also the drain outlet.
27. The solar energy receiver as claimed in claim 1 wherein shaped planks of graphite are located between each row of tubes and capping planks are placed over the inlet end rows of straight tube portions and the outlet end row of straight tube portions to encase a majority of the heat exchanger tubes.
28. The solar energy receiver as claimed in claim 27 wherein the graphite planks, other than the capping planks, each, include two opposed surfaces, having grooves conforming to the shape and radius of the straight tube portions such that adjacent pairs of the planks encompass the respective straight tube portions.
29-37. (canceled)
38. The solar energy receiver as claimed in claim 1 wherein void spaces within the housing are filled with an inert gas.
39. The solar energy receiver as claimed in claim 1 wherein void spaces within the housing are filled with graphite powder.
40. (canceled)
41. The solar energy receiver as claimed in claim 1 wherein the solar energy receiver comprises two or more receiver panels configured and mounted to form a downward opening cavity.
42. The solar energy receiver as claimed in claim 41 wherein the cavity is formed with a combination of receiver panels and insulation panels.
43. The solar energy receiver as claimed in claim 41 wherein the solar energy receiver comprises a plurality of receiver panels arranged to form an opening which is in a shape of a rectangular prism.
44-114. (canceled)
Type: Application
Filed: Jun 7, 2013
Publication Date: May 7, 2015
Applicant: GRAPHITE ENERGY N.V. (Amersterdam)
Inventors: Nicholas Jordan Bain (Sydney), Garry James Baddock (Mount Colah), Paul Soo-Hock Khoo (Castle Hill), David John Reynolds (Randwick), Alexander McKechran Handie McNeil (Gladsville), Adam Timothy Laws (East Ryde), Jun Chao (North Ryde)
Application Number: 14/405,128
International Classification: F24J 2/04 (20060101); F24J 2/46 (20060101);