The embodiments disclosed herein relate generally to concentrating solar thermal technology and more particularly to methods and apparatus for remelting recycled metal with concentrated solar power and optionally using the melted recycled metal as a heat transfer material for electrical generation.
Primary metal production and recycling are well known industrial activities requiring vast amounts of energy. Particularly in metal recycling, a large fraction of the required energy usage is simply to provide heat to melt scrap metal prior to reprocessing the scrap into billets or other useful forms. The melting steps required for metal recycling are commonly performed with coal-burning reverberatory furnaces (in the case of aluminum recycling) or electric-arc furnaces (in the case of steel recycling). These processes can be inefficient. For example, reverberatory furnaces cause conversion of aluminum into slag and dross and electric-arc furnaces produce heat from electricity which is a relatively inefficient heat production method.
The embodiments disclosed herein are directed toward overcoming one or more technical limitations including but not limited to the problems discussed above.
One embodiment disclosed herein is a concentrated solar thermal system for re-melting recycled or scrap metal. The system includes a source of recycled (or scrap) metal. As defined herein, recycled or scrap metal is any metal of any type which has previously been manufactured into a product, or which is an otherwise unused by-product of a metal manufacturing process. The system includes a solar receiver configured to receive concentrated solar flux reflected from one or many reflecting surfaces to heat a quantity of the recycled metal and cause at least a portion of the recycled metal to melt. The system also includes a solidification stage receiving molten recycled metal and providing for the molten metal to be cast into any type of solid form useful for sale or the subsequent production metal products. The solidified metal may then be sold or otherwise removed from the system.
In certain embodiments, the system also includes at least one heat exchanger in fluid communication with the solar receiver which receives molten metal from the receiver and provides for heat exchange between the molten metal and the working fluid of an electrical power generation cycle. The system may include fluid or solid material conduits which provide for recycling some or all of the molten metal between the solar receiver, an optional molten metal storage system or the solidification stage. In embodiments which include an electrical power generation cycle, the system may be configured as an open-ended system where substantially all of the recycled or scrap metal input to the solar receiver is cast into a useful solid form either directly after melting, after storage or after optional heat exchange with an electrical power generation cycle.
Alternatively, certain embodiments may be operated as a periodically closed-loop system where the molten metal is passed through the solar receiver and any heat exchanger elements multiple times before being cast into a useful form and removed from the system.
Certain embodiments include preprocessing of the recycled or scrap metal prior to input to a solar receiver. For example, recycled scrap metal may be shredded prior to input to the receiver or shredded and then compressed into a billet of desirable shape before input to the receiver.
Other embodiments include methods of remelting metal. Remelting method embodiments utilize a source of recycled or scrap metal as defined above, which may be shredded or compressed into a suitable shape. The metal is then loaded into a solar receiver configured to receive concentrated solar flux causing at least a portion of the metal to melt. The molten metal is then cast into a solid form with a casting machine or other solidification stage. The solid form may be of any shape including but not limited to ingots, billets, sheets, wire, grains or other forms. The solid may then be removed from the system, sold or remanufactured into a useful product.
Other embodiments comprise a method of generating electricity. Electricity generation methods also utilize a source of recycled or scrap metal which may be loaded into a solar receiver and melted as described above. The melted metal functions as a heat transfer material and after heating is caused to undergo heat exchange with the working fluid of a electricity generation cycle. Energy transferred to the working fluid may then be used to drive one or more turbines to generate electrical power. The melted metal heat transfer material may be solidified into a useful solid form and removed from the system as described above or recirculated to the solar receiver for additional heating. In certain embodiments, additional heat exchange between the working fluid and metal heat transfer material occurs during or after the solidification process.
Unless otherwise indicated, all numbers expressing quantities of ingredients, dimensions, reaction conditions and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”.
In this application and the claims, the use of the singular includes the plural unless specifically stated otherwise. In addition, use of “or” means “and/or” unless stated otherwise. Moreover, the use of the term “including”, as well as other forms, such as “includes” and “included”, is not limiting. Also, terms such as “element” or “component” encompass both elements and components comprising one unit and elements and components that comprise more than one unit unless specifically stated otherwise.
The embodiments disclosed herein include concentrated solar thermal systems and methods for remelting metal including but not limited to recycled or scrap metal. In addition, concentrated solar power (CSP) systems and methods are disclosed which feature the use of recycled metal as a heat transfer material (HTM) which undergoes a solid-liquid phase change. The term “heat transfer material” is used herein instead of the more commonly used “heat transfer fluid” because in certain stages of the described systems, the recycled or scrap metal HTM is moved, stored and utilized as a non-fluid solid. In certain embodiments detailed below, the system is open-ended. Therefore, metal is input to a solar receiver to be melted and then later solidified into a useful form for sale, remanufacturing or otherwise taken away from the solar recycling system. In other embodiments, the system is operated in partially or periodically closed-loop manner with scrap metal being input to the system and moved through a heat transfer cycle more than once before being cast into a useful form and removed from the solar thermal facility.
In the
At the solar receiver 106, the recycled metal billets are subject to illumination with concentrated solar flux which causes some or all of the metal to melt into a liquid. The molten recycled metal may then flow, for example in conduit 116, to a casting machine 118 for casting into an ingot, bar, billet, sheet or other form which may be sold were used to manufacture products. Prior to casting, the molten recycled metal may be stored in a hot storage tank 120 which may provide thermal storage useful for electricity generation as described in detail below.
In the system embodiment 100 of
The system 100 of
As shown in
The recuperated heat stream 302 may use any suitable heat transfer fluid, water steam or heat transfer oil for example, to move heat from the casting machine to the recuperative preheater 304. Accordingly, the casting machine 118 will typically be provided with suitable heat exchanger elements which facilitate heat exchange between the molten or solidified recycled metal in the casting machine 118 and the heat transfer fluid in the recuperated heat stream 302. The transfer of heat from the casting machine 118 to the recuperated heat stream 302 can accelerate the casting process by cooling the molten or solidified metal and also accelerate the initial melting process by preheating the input metal prior to the solar receiver. Therefore, use of a recuperated heat stream 302 and recuperative preheater 304 can provide for relatively enhanced throughput.
As noted above, heat from the molten or solidifying recycled metal may be utilized to improve system throughput or efficiency. Alternatively, as shown in
System 400 is therefore substantially open-ended and does not include significant thermal storage. System 500 of
Alternatively, the system 500 may be operated periodically in a closed loop fashion. For example, molten recycled metal may undergo primary heat exchange with the working fluid of the electric power generation cycle 401 in the primary heat exchanger 402 and then re-circulated to the receiver in return conduit 502 for additional heating. Electricity may thus be generated for a period of time without removing billets 410 from the system, increasing the efficiency of electrical power generation operations. The optional hot buffer and storage tank 120 may be used to allow the system to generate electricity for a period of time after sufficient solar flux is unavailable to melt metal flowing through the receiver, at night for example. System 500 therefore provides an operator with the opportunity to favor power generation, or metal recycling operations or a combination of both, based upon the needs of the power grid, energy prices, recycled metal prices and other considerations which may change on an hourly, daily, weekly or other periodic or random basis.
As noted above, systems 400 and 500 may be used to re-melt recycled or scrap metal and/or to generate electricity. When used to generate electricity the recycled metal functions as a HTM which is a solid-liquid phase change material (PCM). Certain CSP systems and methods featuring the use of solid-liquid phase change material (PCM) as a heat transfer material (HTM) are described in co-owned and co-pending PCT patent application PCT/US2012/045425 entitled; “Concentrating Solar Power Methods and Systems with Liquid-Solid Phase Change Material for Heat Transfer” the content of which application is incorporated herein for all matters disclosed therein. Other related CSP systems and methods are described in a United States provisional patent application entitled “Flow Control Systems and Methods for a Phase Change Material Solar Receiver” and “Apparatus and Methods for Recovering heat Expelled During Metal Casting” which applications are incorporated herein for all matters disclosed therein.
As defined herein a solid-liquid phase change material is a material which exists in a solid phase at cooler operating temperatures but melts to a liquid phase at hotter operating temperatures. One benefit of utilizing a phase change material as the HTM of a CSP system is the high energy density realized by exploiting the latent heat as well as the sensible heat of a suitable HTM. The energy storage density of a suitable HTM can typically be doubled by exploiting the latent heat storage of a phase change transition.
The foregoing systems may be implemented with various alternative receiver designs. In any embodiment, the solar receiver is configured to heat the recycled or scrap metal HTM and cause at least some solid HTM to melt. The disclosed systems also include one or more heat exchangers in fluid and thermal communication with the solar receiver and receiving liquid HTM directly or indirectly from the receiver. The heat exchanger(s) may be of any type or any level of sophistication needed to provide for heat exchange between the liquid HTM and an electrical power generation cycle working fluid. The heat exchanger(s) also provide for the cooling and solidification of liquid HTM in conjunction with heating the working fluid.
The heat exchanger elements and other subsystems are, for technical convenience described and shown in the figures as simple schematic elements. All elements of a commercial system would be implemented with more complex apparatus.
The disclosed systems also include material transport systems providing for the transportation of solid HTM from the outlet of the heat exchanger to the solar receiver for reheating. Thus, some or all of the HTM undergoes a thermal cycle including a solid to liquid phase change as solar energy is applied to the HTM and a liquid to solid phase change as energy is exchanged with a working fluid.
The embodiments disclosed herein are not limited to any specific type of heat exchanger, power generation block or any specific working fluid. The high operating temperatures achievable with certain types of metal HTM facilitate use with higher temperature thermodynamic power production cycles for example a supercritical CO2 (s-CO2) Brayton cycle. All types of power block will include one or more turbines which are caused to rotate by the heated working fluid to generate electricity. The power block 416 typically include some or all of the following power block elements: turbines, compressors, condensers, expansion stages, recuperators, heat exchangers and associated pipes, ducts, valves and controls.
The heat exchanger elements described herein may include separate HTM and working fluid conduits such that heat is exchanged between the HTM and working fluid without physical mixing of the HTM and working fluid streams. Alternatively, a direct contact heat exchanger may be utilized where liquid metal HTM interacts directly into the working fluid of the power cycle. In a direct contact heat exchanger, direct physical contact between the HTM and the working fluid heats the working fluid as the liquid metal HTM is solidified.
Appendices A, B and C attached hereto contain additional disclosure supporting the disclosed embodiments and directed to additional and supplemental embodiments.
Various embodiments of the disclosure could also include permutations of the various elements recited in the claims as if each dependent claim was a multiple dependent claim incorporating the limitations of each of the preceding dependent claims as well as the independent claims. Such permutations are expressly within the scope of this disclosure.
While the invention has been particularly shown and described with reference to a number of embodiments, it would be understood by those skilled in the art that changes in the form and details may be made to the various embodiments disclosed herein without departing from the spirit and scope of the invention and that the various embodiments disclosed herein are not intended to act as limitations on the scope of the claims. All references cited herein are incorporated in their entirety by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/US2013/077002 | 12/20/2013 | WO | 00 |
Number | Date | Country | |
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61746950 | Dec 2012 | US |