Patent Application
20120132398
The present disclosure is in the technical field of Thermal Energy Storage (TES).
In concentrated solar power (CSP) or similar energy systems, heat transfer fluid (HTF) is used to convey energy from the heat source to and/or from the energy conversion or use system. In CSP systems, the heat source is an array of concentrating solar collectors, and the energy conversion system is typically a heat engine such as a steam cycle or organic Rankine cycle. In CSP systems in particular, the functionality and, potentially, the economic worth of the system is enhanced by thermal energy storage (TES). The benefit of TES comes from extending the operating time of the energy conversion system or shifting the time of energy production to a more favorable time when energy is more valuable.
Various TES technologies have been developed, particularly for CSP applications, including the two-tank TES system and the single-tank thermocline, both of which have direct and indirect variations (referring to whether the HTF and thermal storage medium are the same or are segregated and interfaced through a heat exchanger). Each of these technologies has pros and cons related to system cost effectiveness, commercial history, and operational attributes. For example, a two-tank system using HTF with high vapor pressure requires plants at high temperature HTFs requires costly pressurized storage tanks. Systems with molten salt varieties as a HTF and/or thermal storage media require specialized tanks and heat exchanger designs. The single-tank thermocline can be a cheaper option due to reduced capital costs, yet must consider the same issues with the type of HTF used. In general, current TES technologies require heat transfer fluids and thermal storage mediums with significant cost and design implications.
The use of granular material such as sand would expand currently available thermal energy storage medium options. However, because sand is an abrasive solid, this requires new technical solutions to effectively utilize the material. Thus, there is a need for thermal energy storage systems and methods that can effectively use inexpensive granular materials as a storage medium and are compatible with a variety of heat transfer fluids.
Embodiments of the present disclosure provide alternatives to, and alleviate many of the disadvantages of TES systems by providing thermal energy storage devices, systems and methods which utilize granular materials as a thermal energy storage medium that is compatible with a variety of HTFs. Disclosed systems include combined heat exchange and conveyance systems in which thin layers of granular heat transfer material are cascaded down a network of ramps adjoined to heat transfer fluid channels such that heat transfer occurs between the heat transfer material and the heat transfer fluid. This thin flow is particularly advantageous because it boosts heat transfer effects by increasing the surface area of the heat transfer medium contacting the heat transfer fluid.
At least one heat transfer ramp is adjacent to at least one heat transfer fluid channel, and the heat transfer ramp is angled such that a granular material travels down assisted by force of gravity so heat exchange occurs between the granular material and a flow of heat transfer fluid traveling through the heat transfer fluid channels. Any number of ramps can be stacked in parallel or in a zig-zag configuration with heat transfer fluid channels in between the ramps or linked to the sides of the ramps to optimize heat transfer. Embodiments of the present disclosure effectively use sand, a relatively inexpensive and environmentally benign material, as a thermal storage medium while also providing heat transfer and heat exchange capabilities. Alternative granular materials would include any particles capable of acceptably handling the temperature parameters in a given application, whether it be a heating or cooling application.
Other advantages of the disclosed systems and methods include, but are not limited to: (1) use of sand or other inexpensive and inert granular material as the storage medium, which is environmentally benign, inexpensive, non-volatile, acceptable in thermal properties, (2) delivery of a constant temperature heat from the silos since a relatively constant temperature will be maintained in the bins irrespective of current sand volume, (3) compatibility with a variety of HTF fluids, as the design is adaptable to various HTFs and TES media, (4) achievement of high “round trip thermal efficiency” since energy loss is minimal, and (5) applicability to other CSP technology and other thermal systems.
Exemplary embodiments of a system of thermal energy storage and release comprise at least one storage vessel, at least one heat transfer ramp adjacent to the at least one storage vessel, and at least one heat transfer fluid channel adjacent to the heat transfer ramp such that heat exchange occurs between a heat transfer medium traveling down the heat transfer ramp and a heat transfer fluid traveling through the heat transfer channel. The heat transfer ramp is angled with respect to the storage vessel such that the heat transfer medium travels down the heat transfer ramp assisted by force of gravity. In exemplary embodiments, the heat transfer medium is a granular material. In exemplary embodiments, the storage vessel may be insulated to govern its contents' heat exchange with the surrounding environment.
In exemplary embodiments, the system may further comprise a distribution mechanism operatively connected to the heat transfer ramp to evenly spread the granular material. The at least one ramp could comprise at least two ramps in a substantially parallel layered configuration or at least two ramps in a cascading configuration. The at least one heat transfer fluid channel may be disposed between the two ramps. In exemplary embodiments, the at least one heat transfer channel is coupled to one or more of a side surface of the heat transfer ramp, a top surface of the heat transfer ramp, or a bottom surface of the heat transfer ramp. In exemplary embodiments, the at least one ramp defines a textured or channeled surface or defines at least one slot. The ramp could also vibrate to assist flow of the heat transfer medium.
The at least one heat transfer fluid channel may comprise a system of tubes or parallel plates linked to the ramps. In exemplary embodiments, the system further comprises at least one height adjustment mechanism operatively connected to at least one of the at least one ramp(s) to change the flow direction of and/or regulate the rate of flow of the heat transfer medium. The at least one storage vessel may comprise a first and second storage vessel and the at least one ramp comprises a first ramp removing the granular heat transfer medium from the first storage vessel and a second ramp delivering the heat transfer medium to the second storage vessel. In exemplary embodiments, energy is stored as heat gathered by, or discharged to, a concentrating solar thermal power plant.
Exemplary embodiments include methods of storing thermal energy comprising providing a granular material and a heat transfer fluid. The methods include conveying the granular material through at least one ramp angled with respect to a storage vessel such that granular material travels down the heat transfer ramp assisted by force of gravity and conveying the heat transfer fluid through at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. The granular material may travel in overall counterflow to a flow of heat transfer fluid, or flow could be generally concurrent or cross-current. In exemplary embodiments, the granular material is sand. Exemplary methods may further comprise evenly distributing the granular material in the ramp.
In exemplary embodiments, methods further comprise adjusting the height of at least one of the at least one ramp(s) to change the flow direction and/or speed of the granular material. Exemplary methods also include providing a first and second storage vessel, removing the granular material from the first storage vessel, and delivering the granular material to the second storage vessel. Exemplary methods may also include releasing stored thermal energy comprising providing a granular material and a heat transfer fluid. The granular material is conveyed through at least one ramp angled with respect to a storage vessel such that granular material travels down the heat transfer ramp assisted by force of gravity. The heat transfer fluid is conveyed through at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid.
Exemplary embodiments include a combined heat exchange and conveyance system comprising a bundled heat transfer assembly including at least two stacked heat transfer ramps and at least one heat transfer fluid channel adjacent to the at least two stacked heat transfer ramps. A heat transfer medium is conveyed through the heat transfer ramps such that the heat transfer medium travels down the heat transfer ramps assisted by force of gravity, and a heat transfer fluid is conveyed through the at least one heat transfer fluid channel such that heat exchange occurs in the bundled heat transfer assembly between the heat transfer medium and the heat transfer fluid.
The heat transfer medium may be a granular material. The heat transfer medium travels in overall counterflow to a flow of heat transfer fluid or in overall co-current flow to a flow of heat transfer fluid. In exemplary embodiments, the heat transfer ramps define at least one slot such that the heat transfer medium falls through the at least one slot in a first heat transfer ramp to a second heat transfer ramp below the first heat transfer ramp. The system may further comprise at least one storage vessel, wherein the heat transfer ramps are angled with respect to the storage vessel. The at least one heat transfer fluid channel may be disposed between the two stacked heat transfer ramps. In exemplary embodiments, the at least one heat transfer channel is coupled to one or more of a side surface of the heat transfer ramp, a top surface of the heat transfer ramp, and/or a bottom surface of the heat transfer ramp.
In exemplary embodiments, a thermal heat transfer device is provided comprising a combined heat exchanger and conveyor including at least one heat transfer ramp and at least one heat transfer fluid channel adjacent to the heat transfer ramp. A granular material is conveyed through the at least one heat transfer ramp such that the granular material travels down the heat transfer ramp assisted by force of gravity, and a heat transfer fluid is conveyed through the at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. In exemplary embodiments, the granular material is sand.
The heat transfer channel may be angled in relation to the at least one heat transfer ramp. In exemplary embodiments, the ramp comprises at least two ramps in a substantially parallel layered configuration, and the at least one heat transfer fluid channel may be disposed between the two ramps. The ramps may define at least one slot such that the heat transfer medium falls through the at least one slot in a first ramp to a second ramp below the first ramp. In exemplary embodiments, the ramp comprises at least two ramps in a cascading configuration. In exemplary embodiments, the at least one heat transfer channel is coupled to one or more of a side surface of the heat transfer ramp, a top surface of the heat transfer ramp, and/or a bottom surface of the heat transfer ramp.
Exemplary embodiments include a heat exchanger that is comprised of an Archimedes screw conveyor design to transport sand over an internal HTF tube bundle, which contains heat transfer fluid used to store and remove heat from the sand. In exemplary embodiments a system of energy storage and release comprises at least one storage vessel and a combined conveyor and heat transfer device linked to the at least one storage vessel by at least one discharge device. The combined conveyor and heat transfer device includes a rotatable conveyor drum and at least one heat transfer fluid channel within the rotatable conveyor drum. A granular material travels from the at least one storage vessel to the combined conveyor and heat transfer device via the at least one discharge device. The rotatable conveyor drum moves the granular material therethrough in counterflow to a flow of heat transfer fluid traveling through the heat transfer fluid channel. In exemplary embodiments the granular material is sand.
In exemplary embodiments, the rotatable conveyor drum may be an Archimedes screw and may comprise one or more vanes fixed to an inner surface of the drum. The one or more vanes may be spiral shaped, longitudinally straight, substantially T-shaped or substantially V-shaped in cross-section to distribute the granular material over the heat transfer fluid channels. The at least one heat transfer fluid channel may comprise a plurality of tubes arranged in a bundle. In exemplary embodiments, when the rotatable conveyor drum rotates the granular material pours over the at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. The one or more vanes may pick up and rain the granular material over the at least one heat transfer fluid channel.
In exemplary embodiments, the at least one storage vessel comprises a first and second storage vessel, and the first storage vessel has a higher temperature than the second storage vessel. The at least one storage vessel may be located above or below ground level and may have at least one angled wall. In exemplary embodiments, the stored energy is heat gathered by, or discharged to, a concentrating solar thermal power plant.
Exemplary embodiments include methods of storing thermal energy. Exemplary methods comprise providing a granular material and a heat transfer fluid. The heat transfer fluid has a temperature relatively higher than a temperature of the granular material. The granular material and the heat transfer fluid are conveyed such that the granular material continually pours over a tube carrying the heat transfer fluid such that heat exchange occurs between the granular material and the heat transfer fluid. A set of vanes may direct the pouring of the conveyed granular material, and the granular material may be sand. The granular material may travel in overall counterflow to a flow of heat transfer fluid or in overall cocurrent flow to the flow of heat transfer fluid.
Exemplary methods may further include methods of releasing stored thermal energy comprising providing a granular material and a heat transfer fluid. The granular material has a temperature relatively higher than a temperature of the heat transfer fluid. The granular material and the heat transfer fluid are conveyed such that the granular material pours over a tube carrying the heat transfer fluid such that heat exchange occurs between the granular material and the heat transfer fluid. The result of this exchange is that the granular material is cooled and the HTF is heated.
In exemplary embodiments, a combined conveyor and heat transfer device comprises a rotatable conveyor drum and at least one heat transfer fluid channel within the rotatable conveyor drum. The rotatable conveyor drum moves a granular material therethrough in counterflow to a flow of heat transfer fluid traveling through the heat transfer fluid channel. The rotatable conveyor drum may be an Archimedes screw. When the rotatable conveyor drum rotates, the granular material pours over the at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. The rotatable conveyor drum may be capable of rotating at one or more speeds.
Accordingly, it is seen that thermal energy storage devices, systems and methods are provided which effectively use granular materials as a thermal storage media while also providing heat transfer and heat exchange capabilities. These and other features and advantages will be appreciated from review of the following detailed description, along with the accompanying figures in which like reference numbers refer to like parts throughout.
In the following paragraphs, embodiments will be described in detail by way of example with reference to the accompanying drawings, which are not drawn to scale, and the illustrated components are not necessarily drawn proportionately to one another. Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than as limitations of the present disclosure. As used herein, the “present disclosure” refers to any one of the embodiments described herein, and any equivalents. Furthermore, reference to various aspects of the disclosure throughout this document does not mean that all claimed embodiments or methods must include the referenced aspects.
With reference to
The system 110 further comprises a combined heat exchanger and conveyor 111, which includes one or more heat transfer ramps 114 located adjacent to the storage vessels 112, or linked thereto, and extending into each storage vessel 112. The ramps 114 may be mechanically linked to the storage vessels 112 either indirectly through attachment to one or more vertical conveyors 116 connecting a pair of storage vessels 112 or directly through attachment of a first end 118 of the ramp 114 to the interior bottom 120 of a storage vessel 112. Supporting structures 119 of various sizes may be provided to support the ramp 114 and achieve the desired angle of the ramp 114. Additional linkages could be provided as well, and it should be understood that any linking of the ramps 114 to the storage vessels 112 could be used so long as the granular material 115 can pass freely between the ramps and the storage vessels.
As best seen in
In some embodiments, the heat transfer channels 122 are adjacent the ramps 114 or in direct contact with the ramps 114. The heat transfer channels 122 could be enclosed tubes, open plates or ramps, or spaces created in between the ramps 114 when the ramps are in a stacked configuration. For high pressure HTF applications (e.g., steam) the heat transfer channel 122 would likely be in the form of an enclosed pipe. For lower pressure HTF applications, the heat transfer channel 122 would likely be open, such as a thin, flat channel, perhaps located parallel to the ramps 114. While rounded pipes handle higher pressures better since there are no uneven pressures that create deformities, either form of channel could be used in either circumstance. As shown in
As illustrated in
In exemplary embodiments, multiple heat transfer ramps 114 are joined together in various configurations to form a network of ramps and heat transfer channels 122. Turning to
Two or more parallel heat transfer ramps 114 could also be linked in a cascading, or zig-zag, configuration. As shown in
As described in more detail herein, heat transfer from the energy storage medium to the HTF is achieved by gravity assisted flow of the granular material functioning as the storage medium down or along the surface of the ramps. To effectively utilize gravity to move the granular material, the ramps are deployed at various angles relative to the ground and relative to the storage vessels. The ramp angle could be anywhere from 0° to 90°, or perpendicular to the ground, i.e., vertically oriented. It should also be understood that the ramps could be fixed or could have a height adjustment mechanism 132 to elevate or lower the respective ends of the ramp and change the flow direction of the energy storage medium. Height adjustment mechanisms could be any known mechanical or electronic system including motors, etc. An example of a combined heat exchange and conveyance system 111 at a relatively steep angle is depicted in
Turning to
In operation, high temperature HTF 128 is pumped to the site of the energy storage and release system 110, having been heated, for example, by a renewable energy facility such as a concentrating solar thermal power plant 105. Meanwhile, vertical conveyor 116, best seen in
As discussed above, additional ramp features such as channels, a textured surface, or vibrations 117, could also aid the flow of the granular material 115. It should also be noted that the operator of the energy storage and release system 110 could change the orientation and angle of the heat transfer ramp 114 to optimize flow of the granular material 115. Any ramp angle, including a 90° vertical orientation could be employed. Significant advantages of the systems described, especially the various ramp structures, features, and layouts, are that the conveyed granular material 15, 115 is retarded so it moves in a soft flow, reducing abrasiveness, and as the conveyed granular material 15, 115 falls slowly in a thin layer, it provides increased time and surface area contact to improve heat transfer to or from the granular material.
In exemplary embodiments, the HTF 128 flows through one or more of the heat transfer channels 122 in counterflow, co-current flow, or cross-current flow to the granular material 115. As discussed above, the HTF 128 could flow through heat transfer channels 122 which are internal tubes 130 within the ramps 114 or externally linked tubes 132. In this way, the HTF 128 adsorbs or gives up heat, which is transferred to the granular material 15 functioning as a thermal energy storage medium. The granular material 115, now hot from the heat transfer, exits the heat transfer ramp 114 into the second storage vessel 112b, where it is stored until the thermal energy is needed.
The thermal energy storage process would be similar when employed using other exemplary embodiments described above, such as parallel stacked or layered configuration of heat transfer ramps 114 or a cascading configuration of shorter ramps or plates. It may be advantageous for the granular material 115 to travel in cocurrent flow relative to the flow of HTF 128. In such embodiments, the HTF 128 may flow downward through the heat transfer channels 122 as the granular material 115 flows down the heat transfer ramps 114, as illustrated in
To release the thermal energy stored in the storage medium, the hot granular material 115 is lifted by the vertical conveyor 116 from the second storage vessel 112b up to a top entry point of a heat transfer ramp 114. The granular material 115 is then loaded into the heat transfer ramp 114 and flows down the ramp toward a second storage vessel 112b, with the aid of gravity. At the same time, HTF 128 having a temperature cooler than that of the granular material 115 is distributed through heat transfer channels 122 and flows in counterflow to the hot granular material 115. Thus, the granular material 115 exchanges heat with the HTF 128 as they flow adjacent each other. The now cooler granular material 115 reaches the lower end point of the heat transfer ramp 114 and exits into storage vessel 112a where it awaits another round of thermal energy storage. The now hot HTF 128 may be used to produce usable energy by known methods such as providing steam for a turbine. It should be noted that any of the variations discussed above could be employed in the energy release mode, including different relative flow directions of the granular material 115 and HTF 128, different ramp angles and configurations, and different heat transfer channel arrangements.
It also should be noted that thermal energy storage and release are not the only functions provided by disclosed systems and methods. Heat exchange could be conducted for non-energy storage purposes such as use of the heated granular material 115 or HTF 128 for industrial heat or cooling or to directly provide power in various energy generation applications.
Referring now to additional embodiments of the invention in more detail,
As shown in
It is understood that alternatively the granular material might be moved between the top and the bottom of a single vessel. It is also understood that the heat transfer tube bundle may employ finned tubes to promote heat transfer and distribution of the sand.
As shown in
An exemplary conveyor used to move the sand is a variation of an Archimedes screw. The Archimedes screw is normally used as a type of lift pump. In this case, it is used as a sand conveyor and heat exchanger. As more specifically shown in FIGS. 2 and 3A-3B, the Archimedes screw conveyor 1 is a rotating sand conveyor drum 11 with one or more spiral vanes 12 fixed to the inner surface of the drum. As the drum turns, the spiral vane 12 pushes the sand 15 along the bottom of the rotating drum 11. The Archimedes screw has no close sliding fits to achieve this pushing motion; indeed, there is no sliding metal-to-metal contact at all. As the sand 15 is conveyed by the spiral vane 12, a set of longitudinal straight vanes 13 acts to simultaneously lift and convey the sand 15 over the heat transfer tube bundle 8 containing the heat transfer fluid (HTF) 28. By this action the HTF 28 flowing in the tubes 8 is made to either adsorb or give up heat. As shown in
The Archimedes screw sand conveyor 1 has the great advantage that switching the direction of rotation changes the direction of the motion of the sand. This feature makes it is easy to change the direction of the motion of the sand as the system is switched between the heat storage function and the heat recovery function.
Details of the Archimedes screw conveyor 1 are shown in
Various types of extended surfaces such as longitudinal, latitudinal, and/or corrugated fins may be used to increase the heat transfer surface on the sand side. Furthermore, the fins may have additional features to improve the contact between the flowing sand and the base tubes. In addition the tubes may have elongated or elliptical shapes to improve the contact and heat transfer with the sand. Indeed, the preferred “tube” cross section may be more plate like or similar to an elongated rectangular passage than a generally circular “tube”. These additional features enhance the contact between tube and fins with the sand and heat transfer to or from the sand may be included.
Various additional features to enhance heat transfer to or from the sand or from the tube to the internal heat transfer fluid may be included. In some situations, for example, it may be advantageous for the granular material to travel in overall cocurrent flow to the flow of internal heat transfer fluid.
An overhead view of the supply and return piping, including the heat transfer tube bundle 8 is shown in
It may be further understood that the option exists for the sand-shifter system to employ in ground storage vessels or pits as the storage volume as opposed to above ground storage vessels.
Embodiments of charging processes to store thermal energy in the sand are shown by a side view in
Embodiments of Discharging Processes to release stored thermal energy and heat the HTF are shown by a side view in
Turning to
In concentrator solar thermal power, embodiments of the disclosed systems and methods are used to store heat gathered during the day that is not needed for power generation or that is in excess of the heat needed for power generation at some time. This heat will be stored and used to generate power when needed, such as during afternoon peaking periods, or during the evening and nighttime. The basic concept of the sand shifter may be applicable in other applications in power generation cycles, in materials processing, or in other heating, cooling, and/or mass transfer applications.
It should be understood that good heat transfer performance is obtained by raining the sand 15 over a heat transfer tube bundle 8 carrying the HTF used to convey heat alternatively from the collector field or to a power conversion plant. Ideally, heat transfer coefficients moderately approximating the performance seen in similarly-agitated fluidized beds will be achieved. Good heat exchange effectiveness means close approach of the thermal storage medium to the inlet temperature of the HTF during charging of the storage and close approach of the HTF temperature to the maximum temperature of the storage medium during discharge. This good effectiveness will be obtained by heating sand or alternatively removing heat from the sand while moving the sand to or from a higher temperature above ground storage vessel 2 in a novel conveyor that doubles as a counter flow heat exchanger. The counter flow arrangement promotes high effectiveness. The sand storage containers will be simple and inexpensive insulated silos or bins above ground or buried pits.
Thus, it is seen that systems and methods of storing and releasing thermal energy are provided. It should be understood that any of the foregoing configurations and specialized components or chemical compounds may be interchangeably used with any of the systems of the preceding embodiments. Although illustrative embodiments of the present invention are described hereinabove, it will be evident to one skilled in the art that various changes and modifications may be made therein without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.
This application is a continuation-in-part of U.S. patent application Ser. No. 12/881,102, filed Sep. 13, 2010, which is hereby incorporated by reference in its entirety, which claims priority to U.S. Provisional Patent Application Ser. No. 61/241,909, filed Sep. 13, 2009, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61241909 | Sep 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12881102 | Sep 2010 | US |
| Child | 13305542 | US |
