Embodiments pertain to solar thermal receivers with concentric tube modules for converting concentrated sunlight into heat.
Solar-Thermal Receivers convert concentrated sunlight, e.g., as coming from a heliostat field, into heat and are cooled by a heat transfer fluid (HTF) such as molten salt, oil, or water. In the prior art one example includes, a receiver having one or more panels of parallel absorber tubes. Fluid flow through said panels may be parallel or in an alternate/serpentine fashion. This may result in an additional part count, e.g., valves, manifolds; complex drainage procedures; added costs; and a significant pressure drop within the receiver.
Embodiments include an assembly comprising: an inner wall of a cylindrical vessel and an outer wall of a toroidal shell forming a first HTF conduit configured to conduct HTF in an elevating direction; a distal portion of the inner wall of the cylindrical vessel and a distal portion of the outer wall of the toroidal shell configured to conduct the HTF toward a volume defined by the inner wall of the toroidal shell; the inner wall of the toroidal shell forming a second HTF conduit configured to conduct HTF in a descending direction; and a proximal portion of the cylindrical vessel and a proximal portion of toroidal shell forming a manifold configured to conduct HTF into the first HTF conduit and out of the second HTF conduit. Additional exemplary embodiments include the first HTF conduit further comprising a helical structure having an angle of ascent and configured to conduct HTF along the first HTF conduit.
Additional exemplary embodiments include a solar-thermal receiver comprising: a first tube; a second tube where the diameter of the first tube is greater than the diameter of the second tube; and a third tube where the diameter of the second tube is greater than the diameter of the third tube. The first tube, the second tube, and the third tube are mutually concentric. The second tube is disposed within the first tube, providing an annular gap between the outer surface of the second tube and the inner surface of the first tube for an input flow of a heat transfer fluid (HTF). The third tube is disposed within the second tube, where the third tube is separated from the second tube by an internal volume, and where the inside of the third tube is a conduit providing for an output flow of the HTF. In other exemplary embodiments, the first tube, the second tube, and the third tube are connected to a header at only one end. In additional exemplary embodiments, the internal volume between the second tube and the third tube further comprises at least one of: thermocouples, heating elements, heat absorbing materials, and insulation. In additional exemplary embodiments, the annular gap between the outer surface of the second tube and the inner surface of the first tube further comprises a helical structure having an angle of ascent and configured to conduct an input flow of the HTF. In additional embodiments, the helical structure may further comprise a pitch that varies along the length of the tube or a pitch that remains constant along the length of the tube. In some exemplary embodiments, the first tube may comprise an array of convex indentations disposed interstitial with an array of concave indentations on the second tube. Other exemplary embodiments may comprise at least one baffle in the annular gap between the outer surface of the second tube and the inner surface of the first tube. Other exemplary embodiments may further comprise at least one angular flange comprising at least one hole in the at least one angular flange in the gap between the outer surface of the second tube and the inner surface of the first tube. Additional exemplary embodiments may further comprise a throttle poppet valve, where the throttle poppet valve is further configured to adjust the flow rate of the HTF.
Exemplary method embodiments may comprise a method of monitoring the flow and thermal state of a HTF in a solar thermal receiver comprising: providing a temperature measurement device proximate to an input flow of HTF; providing a heater proximate to the input flow of HTF; measuring a temperature of the input flow of HTF by the temperature measurement device proximate to the input flow of HTF; determining, by a processor having addressable memory, whether the measured temperature of the input flow of HTF is below a set point; if the temperature of the input flow of HTF is below the set point, then generating a command for the heater proximate to the input flow of HTF to turn on; and, otherwise, if the temperature of the input flow of HTF is not below the set point, then generating a command for the heater proximate to the input flow of HTF to turn off. In additional exemplary embodiments, the provided temperature measurement device proximate to an input flow of HTF may be a thermocouple.
Exemplary solar-thermal receiver embodiments comprise: at least one receiver module; and a bell-shaped cap, where the bell-shaped cap is affixed to the top of the at least one receiver module, and is coextensive with a top portion of the at least one receiver module. In some exemplary embodiments, the bell-shaped cavity may be supported by a structural beam extending from a header. In additional exemplary embodiments, an inner portion of the bell-shaped cavity may have a ceramic coating.
This design may allow for fewer tubes than previous receivers, as a relatively greater volume of HTF may be passed through the modules while maintaining adequate receiver characteristics such as a good heat transfer coefficient and low pressure drop. The reduced supports required by this receiver design may allow for thermal deflection. The reduced supports may also allow for the addition of more tube modules, and greater HTF flow, at the same weight as other solar thermal receivers. Alternatively, the reduced supports may allow for the creation of a lighter solar thermal receiver, which may also reduce tower costs. In embodiments where the tube modules and/or headers are manufactured separately, the number of tube module welds required may decrease. Additionally, the solar thermal receiver may be broken up into parts for greater shipping efficiency.
One exemplary embodiment may include drain valves located in the bottom of the receiver modules. In the exemplary bottom-supported module, the number of drain valves may be reduced compared to prior art solar thermal receivers as the design does not include a flow path that includes several up and down serpentine passes of HTF where freeze points may be created at the low point of any U-bend created. In an exemplary embodiment, the receiver modules may contain no bottom-connected U-bends.
Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, and in which:
The HTF flows upwards, i.e., opposite the local gravity vector, through the annular gap 104 as it is heated by incident sunlight, i.e., from a heliostat array directed towards the surface of the first outer tube 101. The HTF may flow directly upwards through the annular gap 104 or may be guided upwards along a spiral path 106, i.e., a spiral helix having a first pitch 107, positioned within the annular gap 104. This spiral path 106 increases the overall heat transfer flow length while allowing for a short overall axial length of the receiver module. The spiral flow may also result in a gradually increasing temperature gradient from the bottom of the receiver module to the top of the receiver module. The use of a spiral path may be used to achieve the desired temperature rise of the HTF in a single pass from the bottom to the top of the receiver module, where the overall flow length is greater than the minimum required to achieve the desired temperature rise.
Upon reaching the top of the receiver module, the heated HTF is directed down and out of the solar thermal receiver through the third concentric tube 103 located within the second concentric tube 102. The outlet flow 108 may be isolated from the inlet flow 109 by the internal volume 105, which may or may not contain insulation. The concentric tubes may be made of steel, high temperature alloys, silicon carbide, graphite, ceramics, or other suitable materials known in the art.
The receiver module may be exposed to incident flux on more than one side of the tube. In embodiments with a spiral flow path 106, the flow of heated HTF may reduce any temperature differential between different surface areas in the first tube circumference. The flow of HTF up a spiral path 106 may also reduce any temperature differential around the entire tube perimeter. In a case where one section of the receiver module is exposed to a zone of higher flux, the HTF may flow from the zone of higher flux to the other sections of the module, which may add heat to those other sections more effectively than by conduction through the tube surface. The exemplary receiver module design may therefore mitigate undesirable stresses and bowing of the tubes resulting from a thermal expansion differential between various sections of the module.
The spiral flow path of the HTF in the annular gap 104 gives rise to a velocity differential between the HTF which flows adjacent to the inner surface of the first tube 101, i.e., the outer wall of the annular gap 104, versus the HTF which flows adjacent to the outer surface of the second tube 102, i.e., the inner wall of the annular gap 104. This type of differential promotes high flow turbulence, which increases the overall heat transfer coefficient between the HTF and the heat absorbing surface. In addition, flow disturbances may be used to increase flow turbulence. In an exemplary embodiment with a spiral flow in the annular gap 104, the created turbulence may self-clean the receiver module and remove any sediments accumulating in the annular gap 104 that would otherwise reduce the cross-sectional area. The turbulence created by the spiral flow embodiment may be great enough to remove accumulated sedimentations in a single pass.
The internal volume 105 between the second tube 102 and the third tube 103 may contain a plurality of thermocouples or other instrumentation to measure the temperature profile and the flow rate of the HTF. This internal volume 105 may also contain heating elements capable of pre-heating the receiver or melting HTF freezes, e.g., in a molten salt application. This internal volume 105 may also be filled with heat-absorbing materials such as alumina, graphite, some metals, or other materials known in the art to provide additional thermal mass to mitigate cloud transients, i.e., short-term storage or buffering. Additionally, a layer of insulation may be present in the internal volume 105 to insulate the outlet flow 108 of hot HTF from the inlet flow 109 of cold HTF to be heated by concentrated sunlight. The addition of measurement devices and/or heaters may allow for the direct monitoring and control of temperatures and flow rates in real-time or near real-time. This monitoring and control may be used to identify and prevent the freezing of molten salt or other HTFs. It may also be used to adjust the heat transfer fluid flow rate for the optimization of receiver efficiency.
The receiver module may be connected at the bottom to a header, which may provide structural support for the module. This header may comprise an inlet flow header 111 and an outlet flow header 112. In some exemplary embodiments, the outlet flow header 112 may comprise additional insulation 113 to prevent heat loss of the outlet flow 108 of the HTF.
In one exemplary embodiment shown in
In one exemplary embodiment shown in
As shown in
As shown in
Embodiments of a solar thermal receiver are presented comprising a plurality of tube in tube modules.
The receiver modules may be replaced and/or repaired independent of the remaining receiver modules, as they may be independently attached to the header at only one end. In one exemplary embodiment, the receiver modules may be detachably attached to the bottom manifold assembly. In embodiments where the receiver modules are detachably attached by means other than welding, the receiver modules may be readily assembled and/or repaired on-site. The use of detachably attached receiver modules may also allow for mass production on an assembly line rather than requiring that the entire solar thermal receiver be built and assembled in one place. By accomplishing a significant portion of the assembly off-site, the assembly time on-site could be significantly reduced and the overall process could be accomplished more efficiently. In other exemplary embodiments, the receiver modules and inlet flow header may be pre-manufactured. The header may be manufactured to have slots in the inlet flow header which set the receiver modules in the correct orientation relative to the header. Accordingly, any final assembly and welding to this configuration may be done on-site.
The use of a bottom-supported module in a solar thermal receiver may simplify reflector pointing strategies allowing for the addition of a bell-shaped cavity cap. The bell-shaped cavity cap may reduce radiation and convection losses from the hottest portion of the solar thermal receiver. The bell-shaped cap may be supported by a structural beam positioned in the middle of the receiver modules, i.e., in the middle of the X in the X-receiver embodiment shown in
It is contemplated that various combinations and/or sub-combinations of the specific features and aspects of the above embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments may be combined with or substituted for one another in order to form varying modes of the disclosed invention. Further it is intended that the scope of the present invention herein disclosed by way of examples should not be limited by the particular disclosed embodiments described above.
This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/406,384, filed Oct. 25, 2010, which is hereby incorporated herein by reference in its entirety for all purposes.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/US11/57708 | 10/25/2011 | WO | 00 | 3/7/2013 |
Number | Date | Country | |
---|---|---|---|
61406384 | Oct 2010 | US |