PROCESSES AND MEDIA FOR HIGH TEMPERATURE HEAT TRANSFER, TRANSPORT AND/OR STORAGE

Abstract

A thermal energy conveyance process involving at least one of transferring heat to a first heat transfer fluid and recovering heat from a second heat transfer fluid, wherein the first and the second heat transfer fluids include a gaseous carrier containing a quantity of micron sized solid particles and wherein the at least one of transferring heat and recovering heat is conducted to involve at least one of a) a temperature in excess of 1000° F. and b) a dilute-to-dense phase of the micron sized solid particles. Also provided is a media adapted for such heat conveyance operation.

Claims

1. A thermal energy conveyance process, said process comprising at least one of: a. transferring heat to a first heat transfer fluid; and b. recovering heat from a second heat transfer fluid; wherein the first and the second heat transfer fluids comprise a gaseous carrier containing a quantity of micron sized solid particles and wherein the at least one of transferring heat and recovering heat is conducted to involve at least one of a) a temperature in excess of 1000° F. and b) a dilute-to-dense phase of the micron sized solid particles.

2. The process of claim 1 wherein the at least one of transferring heat and recovering heat is conducted to involve a temperature in excess of 1000° F.

3. The process of claim 1 wherein the at least one of transferring heat and recovering heat is conducted to involve a temperature in excess of 1050° F.

4. The process of claim 1 wherein the at least one of transferring heat and recovering heat is conducted to involve a temperature in excess of 1100° F.

5. The process of claim 1 wherein the at least one of transferring heat and recovering heat is conducted to involve a dilute-to-dense phase of the micron sized solid particles.

6. The process of claim 5 wherein the dilute-to-dense phase of the micron sized solid particles comprises a solids loading ratio of at least 2.

7. The process of claim 5 wherein the dilute-to-dense phase of the micron sized solid particles comprises a solids loading ratio of at least 2.5.

8. The process of claim 5 wherein the dilute-to-dense phase of the micron sized solid particles comprises a solids loading ratio of greater than 10.

9. The process of claim 5 wherein the dilute-to-dense phase of the micron sized solid particles comprises a solids loading ratio of greater than 20.

10. The process of claim 5 wherein the dilute-to-dense phase of the micron sized solid particles comprises a solids loading ratio of at least 30.

11. The process of claim 5 wherein the dilute-to-dense phase of the micron sized solid particles comprises a solids loading ratio of at least 100.

12. The process of claim 1 wherein the gaseous carrier is selected from the group consisting of air, nitrogen, carbon dioxide, inert gases and combinations thereof.

13. The process of claim 1 wherein the micron sized particles are in a particle size range of 30 to 250 microns.

14. The process of claim 1 wherein the micron sized particles comprise a material selected from the group consisting of carbon, composite material, alumina, sand, minerals, corundum, silicon carbide, metals, metal oxides, glass, graphite, graphene, talc, refractory material, iron, iron oxide and combinations, either as multi-component or layered particles, thereof.

15. The process of claim 1 wherein: the first and the second heat transfer fluids comprise a gaseous carrier selected from the group consisting of air, nitrogen, carbon dioxide, inert gases and combinations thereof and containing a quantity of micron sized solid particles in a particle size range of 30 to 250 microns and wherein the at least one of transferring heat and recovering heat is conducted to involve at least one of a) a temperature in excess of 1100° F. and b) a dilute-to-dense phase of the micron sized solid particles having a solids loading ratio of at least 2.

16. A thermal energy conveyance process, said process comprising at least one of: a. transferring heat to a first heat transfer fluid; and b. recovering heat from a second heat transfer fluid; wherein the first and the second heat transfer fluids comprise a gaseous carrier comprising air and containing a quantity of micron sized solid particles comprising carbon or alumina and wherein the at least one of transferring heat and recovering heat is conducted to involve at least one of a) a temperature in excess of 1050° F. and b) a dilute-to-dense phase of the micron sized solid particles having a solids loading ratio of at least 2.

17. A media adapted for at least one heat conveyance operation selected from the group consisting of heat transport, heat transfer and heat storage, the media comprising: a gaseous carrier fluid containing a quantity of micron sized solid particles and wherein the at least one heat conveyance operation is conducted to involve at least one of a) a temperature in excess of 1000° F. and b) a dilute-to-dense phase of the micron sized solid particles.

18. The media of claim 17 wherein the at least one heat conveyance operation is conducted to involve a temperature in excess of 1050° F.

19. The media of claim 17 wherein the at least one heat conveyance operation is conducted to involve a dilute-to-dense phase of the micron sized solid particles having a solids loading ratio of at least 2.5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 is a simplified flow diagram illustrating one embodiment of the subject development in the context of a thermal energy conveyance process in a heat storage cycle application.

[0042] FIG. 2 is a simplified flow diagram illustrating one embodiment of the subject development in the context of a thermal energy conveyance process in a heat recovery cycle application.

[0043] FIG. 3 is a graphical presentation of baseline heat transfer increase versus solids loading ratio showing the effect of particle loading on heat transfer realized in the subject examples.

[0044] FIG. 4 is a graphical presentation of heat transfer increase enhancement factor versus particle loading showing heat transfer enhancement with particle loading ratio.

DETAILED DESCRIPTION OF THE INVENTION

[0045] As described in greater detail below, there is provided a thermal energy conveyance process, such as involving at least one of transferring heat to a first heat transfer fluid and/or recovering heat from a second heat transfer fluid, wherein the first and the second heat transfer fluids include a gaseous carrier containing a quantity of micron sized solid particles and wherein at least one of transferring heat and recovering heat is conducted to involve operation at a high temperature, a dilute-to-dense phase loading of the micron sized solid particles. More particularly, such high temperature operation may involve a temperature in excess of 1000° F., in excess of 1050° F., or in excess of 1100° F. Operation with such or under such dilute-to-dense phase loading may involve micron sized solids particle loading level of at least 2.0, micron sized solids particle loading level of at least 2.5, micron sized solids particle loading level of greater than 10, micron sized solids particle loading level of greater than 20, or micron sized solids particle loading level of at least 30.

[0046] Those skilled in the art and guided by the teachings herein provided will understand and appreciate that heat transfer fluids as herein provided for process heating and other thermal transfer applications can potentially operate at temperatures of up to 2100° F. or even higher, without an associated pressure increase, while providing wide ranging flexibility in energy absorption, heat capacity and thermal conductivity for direct thermal transfer applications up to 2100° F. or even higher.

[0047] In accordance with one aspect of the invention, suitable heat transfer fluids involve mixing fine (10's to 100's of micron mean diameter) particles (e.g., carbon, sand, minerals, refractory, metals, composite, glass, multi-component, or layered) with suitable one or more characteristics of service temperature, melting point, thermal conductivity and absorptivity (useful if directly exposed to radiation in a transmissive flow conduit) in an inert gas (e.g., N.sub.2, CO.sub.2 etc.) to create the heat transfer fluid. Compared with gas only heat transfer fluids, particle laden heat transfer fluids as herein provided enable or allow one or more of: a) an increase in the radiation absorption (if directly exposed to the radiation); b) operation up to the working temperature of the solid particles; and c) a simultaneous increase in the thermal conductivity and heat transfer coefficient of the carrying gas. With proper selection of the gas and particles, the heat transfer fluid can be used to transfer and store thermal energy at up to 2100° F. or higher depending on the process needs and heat source availability. The hot fluid may go through a supplementary fired heater if needed, to increase its temperature to the desired levels, for example in solar applications when the solar radiation levels are insufficient to generate the required process temperatures. The hot fluid then flows to a heat exchanger, transfers heat to the work load (e.g., food processing, mineral processing, water heating, steam generation, air heating, organic fluid heating or boiling) and the cooler fluid returns for reheating.

[0048] Use and processing of heat transfer fluids such as herein described will be further described herein below making specific mention to solar energy related thermal energy conveyance process, those skilled in the art and guided by the teachings herein provided will understand and appreciate that these heat transfer fluids can be used in a wide variety of applications including those involving transport and storage of energy from radiative, conductive and/or convective heat sources, including in heat recovery applications.

[0049] FIG. 1 is a simplified flow diagram illustrating one embodiment of the subject development in the context of a thermal energy conveyance process, generally designated by the numeral 10, in a heat storage cycle application. More specifically, the thermal energy conveyance process 10 integrates hot and cold storage, 12 and 14, respectively, as applied to or used in conjunction with a concentrated solar power farm 16 using parabolic reflectors. The concept will also be applicable to other solar collector designs including Fresnel, Dish and Power Tower types, for example.

[0050] During the heat storage cycle, solid particles from the cold separation and storage vessel(s) 14 are mixed with a carrier fluid, such as air such as supplied or provided via an air blower or compressor 20, and transported via a line 22 to and through a heating zone, generally designated 24, such as a through concentrated solar energy absorbers in the solar farm 16. The fluid-particle mixture is heated in the absorbers to an elevated temperature and the heated mixture is then transported via a line 26 to the hot separation and storage vessels(s) 12, where the particles are separated from the carrier fluid (such as with the separated carrier fluid forming an exhaust air stream 30).

[0051] FIG. 2 is a simplified flow diagram illustrating one embodiment of the subject development in the context of a thermal energy conveyance process, generally designated by the reference numeral 50, in a heat recovery cycle application and such as may be used in conjunction or in association with the heat storage cycle thermal energy conveyance process 10 shown in FIG. 1 and described above. While the heat recovery cycle thermal energy conveyance process 50 is described further below making reference to such a process used in conjunction or in association with the heat storage cycle thermal energy conveyance process 10 shown in FIG. 1, those skilled in the art and guided by the teaching herein provided will understand and appreciate that the broader practice and application of the processing herein described is not necessarily so limited and such conjunctive or associated use or practice is not necessarily so required.

[0052] In the heat recovery cycle thermal energy conveyance process 50 shown in FIG. 2, solid particles from the hot separation and storage vessel(s) 12 are mixed with a carrier fluid, such as air such as supplied or provided via an air blower or compressor 52, and transported via a line 54 through a cooling zone 56, such as a particle-fluid mixture to a fluid heat exchanger or a process heating equipment, for example. In the cooling zone 56, the fluid-particle mixture transfers a portion of its thermal energy to the fluid being heated or to the process and as a result is cooled to a lower temperature. As shown, such cooling can be by means of air such as supplied or provided via a line 60 from a power block and such as resulting in a stream of hot air such as returned to the power block via a line 62. The resulting cooler particle-fluid mixture is then transported such as via a line 64 to the cold separation and storage vessels(s) 14, where the particles are separated from the carrier fluid and stored for use during the heating cycle, such as shown in FIG. 1.

[0053] Moreover, while aspects of the invention have been described making reference to a specific or particular configuration, a wide range of other configurations are possible. Further, the development herein described can, if desired, be used or employed in a continuous heating-cooling configuration such as where both heating and cooling are carried out continuously and simultaneously. Further, the subject development can be used or employed without one of the hot and cold storage vessels or in a closed loop such as using an in line particle-gas mixture pump.

[0054] It is to be understood and appreciated that transport and/or storage systems employed in the practice of the processing herein described can be operated under pressure or under vacuum, as may be desired for particular applications.

[0055] While not required in the broader practice of the developments herein described, in particular applications the incorporation and use of thermally insulated transport and storage components may be preferred to reduce or minimize heat losses.

[0056] It is to be understood and appreciated that the broader practice of the subject development is not necessarily limited to use or practice with specific or particular separators or separation techniques or, correspondingly, specific or particular mixers or mixing techniques, relative to the heat transfer fluids herein described. For example, a wide range of devices or techniques can be used to separate particles from gas (e.g. cyclone separator, cartridge filters, baghouse, etc.) and to feed particles into the carrier fluid (e.g. rotary valve, venturi mixer, etc.). These and other techniques and devices are well known, established and/or commonly practiced such as in the petrochemical and other industries, for example.

[0057] It is to be further understood and appreciated that features or components such as the filtering and/or feeding component(s) can suitably be incorporated and, if desired, integrated such as with or in a storage vessel or built into a separate housing and connected to the vessel, such as may be desired for particular applications.

[0058] A wide range of gaseous fluids are useable as the carrier fluid. Suitable gaseous carriers can include air, nitrogen, carbon dioxide, inert gases and combinations thereof. In accordance with one embodiment, air is a preferred carrier fluid such as for use in an open loop, for example.

[0059] A wide range of naturally occurring and synthetic materials or solids can be used as or to provide solid particles employed in a heat transfer fluid as herein provided and such as depending on their thermal, mechanical and/or flow properties and the specific or particular use or application. Examples of suitable materials can include carbon, sand, minerals, alumina, corundum, silicon carbide, metals, metal oxides, glass, graphite, graphene, talc, refractory material, iron, iron oxide and combinations thereof, with combinations including multi-component, layered, or coated particles engineered to optimize desired properties or to minimize undesired properties, for example.

[0060] While the broader practice of the development herein described is not necessarily limited to employment with specific or particularly sized particles as a wide range of particle sizes ranging from submicron to millimeter in diameter can, if desired, be employed, a preferred particle size for use in selected embodiments is in the range of 30 to 250 micron.

[0061] The subject development is suitably applicable to dilute-to-dense phase transport of particle-gas mixture. In one embodiment, a preferred approach is to use or employ a dilute-to-dense phase transport, e.g., a dilute-to-dense phase loading of the micron sized solid particles, to maximize heat transfer rates and minimize transport velocity, particle attrition and transport component erosion. In specific or particular embodiments, suitable dilute-to-dense phase loading of the micron sized solid particles can refer to a micron sized solids particle loading level of at least 2.0, micron sized solids particle a loading level of at least 2.5, a micron sized solids particle loading level of greater than 10, a micron sized solids particle loading level of greater than 20, a micron sized solids particle loading level of at least 30 or a micron sized solids particle loading level of at least 100.

[0062] If desired, suitable flow loop designs can incorporate single or multiple branches separating and combining as appropriate, and one or more storage vessels can be used for either or both cold and hot storage of particles.

[0063] The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.

EXAMPLES

Examples 1-5

[0064] Tests were carried out to assess the heat transfer impacts of adding solid powder to a gas, the ability to maintain flow, and the ability to separate the particles from gas.

[0065] In these tests, expanded graphite in air was used to demonstrate significant increases in heat transfer rates compared with particle-free air.

[0066] The test stand was constructed from ½ inch stainless steel tubing running through two high temperature electric tube heaters for heating the material under investigation. Air flow through the test stand was measured using a variable area flow meter installed upstream of the powder feed. The powder was added through a small hopper/funnel attached to a piping tee installed in the main tubing run by opening a small gate valve located above the feed port. The motive force to move both the gas and the test material was a HEPA vacuum attached at the outlet of the tubing, run after a fan cooled coil. The use of the HEPA vacuum allowed for the efficient collection, post-test measurement, and reuse of the test material. The test stand was configured with four thermocouples to measure the temperature of the gas/powder mixture: before the first heater; between the heaters; and after the second heater.

[0067] These tests were carried out at an air flow rate of 2.5 scfm and a temperature of approximately 400° F./200° C. using expanded graphite as the particles. The graphite has a density of 16.63 ft.sup.3/lbm, specific heat of 0.242 Btu/lbm*° F. and thermal conductivity of 150 W/(k.Math.m) at 400° F./200° C.

[0068] FIG. 3 shows the relationship between heat transfer increases over particle-free air as a function of particle loading.

[0069] As shown, heat transfer increased linearly with particle loading reaching 2.5 times at a particle loading of 2.5. This increase is much greater than the increase for larger glass particles tested by Farber and Depew, referred to above, suggesting very high heat transfer rates could potentially be achieved using properly sized expanded graphite such as at proposed 10-20 to 1 loading ratios. No issues with maintaining flows were observed and the HEPA filter equipped vacuum was able to effectively capture the particles, with no visible dust observed either during or after the tests on or around the vacuum.

Examples—with 70 μm Alumina

[0070] Further testing was conducted employing 70 μm alumina particles in air at particle to air loading ratios up to 50:1 and temperatures up to 1202° F./650° C.

[0071] These tests employed a particle-air mixture flow loop that had several cross sectional non-uniformities and obstructions, such as bends, fittings, pressure gauges, inserted thermocouples, and inline circulation pump. The particle-gas media was heated up to 1202° F./650° C. using electric heaters and then cooled in a water-cooled heat exchanger.

[0072] FIG. 4 is a graphical presentation of heat transfer increase enhancement factor versus particle loading results obtained and showing heat transfer enhancement with particle loading ratio.

[0073] The results further showed or demonstrated no clogging, no particle degradation, and no heat transfer and pressure drop changes for over 4,000 heating cooling cycles (212° F./100° C. to 1202° F./650° C.). The flow was stopped and started many times during the tests without cleaning the loop.

[0074] The heat transfer coefficient for particle-gas media at a particle to air weight ratio of 30 reached 15 times the value measured with air alone, as shown in FIG. 4. Also, the heat transfer coefficient enhancement levels at different particle to air weight ratios were similar for 752° F./400° C., 932° F./500° C., and 1202° F./650° C.

[0075] Those skilled in the art and guided by the teachings herein provided will understand and appreciate that the subject approach of using a particle laden gas as a combined heat transfer and storage media provides or offers a number of advantages or benefits over current technologies employed in high temperature thermal transfer and storage applications, for example, including one or more of the following:

[0076] a. Allows direct absorption of solar energy by or into solid particles such as when using a receiver made from materials that are substantially transparent to solar radiation (e.g. borosilicate glass).

[0077] b. Provides direct contact heat transfer between particles and the carrier fluid such as to eliminate heat exchanger surface and dramatically increase heat transfer rates during both energy storage and energy recovery.

[0078] c. Allows use of a single closed loop combining both energy transfer and storage. d. A wide range of useful and useable materials area available offering, providing or resulting in a desirable possible performance costs tradeoffs.

[0079] e. No direct link between temperature and pressure of the fluid resulting from increased vapor pressures at higher temperatures.

[0080] f. Potential to achieve temperatures of greater than 2100° F., limited only by the ability of transport and storage equipment to handle the hot media.

[0081] g. Potential for direct contact storage and recovery of heat for higher efficiencies and fewer exchange surfaces.

[0082] h. Improved or increased costs control such as through choice of materials.

[0083] i. Advantages over the use of molten salts can include one or more of: less sensitivity of viscosity to temperature, no need to maintain temperatures above melting point to avoid solidification/freezing, no side reactions, noncorrosive, elimination of the minimal vapor pressure of molten salts, elimination of salt reactions, and potential for much higher temperatures.

[0084] j. Advantages over the use of thermal oils can include one or more of: more efficient storage, no need to maintain temperatures above a certain limit to maintain flow properties, ability to create a non flammable gas particle mixture and ability to operate at low pressures.

[0085] The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.

[0086] The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.

[0087] While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.