Patent Publication Number: US-2013228163-A1

Title: Thermal transfer apparatus and method therefor

Description:
BACKGROUND  
     This disclosure relates to a thermal transfer system and, more particularly, to thermal transfer between a concentrated solar receiver and a heat exchanger. 
     A variety of different industrial products and processes utilize thermal energy to process raw materials and produce an end product. For example, in the cement industry, quick-lime is produced in a process known as chemical disassociation. When heated to a sufficient temperature, the chemical disassociation of quick-lime generates a solid oxide and a gaseous carbon dioxide. More recently, solar heating has been utilized to heat the quick-lime. However, one challenge in utilizing solar energy, or other sources of thermal energy, is that the availability of the solar energy varies over time. 
     SUMMARY  
     An apparatus according to an exemplary aspect of the disclosure includes a closed loop circuit that has a concentrated solar receiver and a particulate thermal transfer media moveable through the closed loop circuit. The particulate thermal transfer media has a melting temperature of greater than 600° C./1112° F. A heat exchanger is in communication with the particulate thermal transfer media. 
     In a further embodiment, the apparatus includes a storage vessel within the closed loop circuit between an outlet from the concentrated solar receiver and an inlet into the heat exchanger. 
     In a further embodiment of any of the foregoing examples, the apparatus includes a storage vessel within the closed loop circuit between an outlet of the heat exchanger and an inlet of the concentrated solar receiver. 
     In a further embodiment of any of the foregoing examples, the apparatus includes reactor vessel in thermal communication with the heat exchanger. 
     In a further embodiment of any of the foregoing examples, the particulate thermal transfer media includes bauxite. 
     In a further embodiment of any of the foregoing examples, the particulate thermal transfer media includes silicon carbide. 
     In a further embodiment of any of the foregoing examples, the particulate thermal transfer media includes silica. 
     In a further embodiment of any of the foregoing examples, the particulate thermal transfer media includes first particles having a first composition and second, different particles, having a second, different composition. 
     In a further embodiment of any of the foregoing examples, the particulate thermal transfer media includes particles, the particles, on average, having a size of greater than 1 micrometer. 
     A method for operating an apparatus according to an exemplary aspect of the disclosure includes moving a particulate thermal transfer media through a closed loop circuit into a concentrated solar receiver to absorb thermal energy into the particulate thermal transfer media, moving the particulate thermal transfer media from the concentrated solar receiver into a heat exchanger and heating a working fluid using the thermal energy extracted from the particulate thermal transfer media in the heat exchanger. 
     In a further embodiment, the method includes storing the particulate thermal transfer media in a storage vessel after absorbing the thermal energy in the concentrated solar receiver and, at a later time, moving the particulate thermal transfer media into the heat exchanger in response to a demand to heat the working fluid. 
     In a further embodiment of any of the foregoing examples, the method includes storing the particulate thermal transfer media in a storage vessel after extraction of the thermal energy from the particulate thermal transfer media in the heat exchanger and, at a later time, moving the particulate thermal transfer media into the concentrated solar receiver in response to an availability of thermal energy in the concentrated solar receiver. 
     In a further embodiment of any of the foregoing examples, the particulate thermal transfer media is selected from the group consisting of bauxite, silicon carbide, silica and combinations thereof. 
     In a further embodiment of any of the foregoing examples, the particulate thermal transfer media includes first particles having a first composition and second, different particles having a second, different composition. 
     In a further embodiment of any of the foregoing examples, the method includes circulating the working fluid through the heat exchanger to extract the thermal energy from the particulate thermal transfer media and heating a reactant material using the thermal energy in the working fluid to chemically disassociate the reactant material into a solid material and a gas material. 
     A method for operating an apparatus according to an exemplary aspect of the disclosure includes moving a particulate thermal transfer media through a closed loop circuit into a concentrated solar receiver to receive solar energy and absorb thermal energy from the solar energy into the particulate thermal transfer media, moving the particulate thermal transfer media from the concentrated solar receiver into a heat exchanger, circulating a working fluid through the heat exchanger to extract the thermal energy from the particulate thermal transfer media and heating a reactant material using the thermal energy in the working fluid to chemically disassociate the reactant material into a solid material and a gas material. 
     In a further embodiment of any of the foregoing examples, the method includes circulating the gas material from the chemical disassociation of the reactant material as the working fluid. 
     In a further embodiment of any of the foregoing examples, the reactant material includes a metal carbonate and the gas material is carbon dioxide. 
     In a further embodiment of any of the foregoing examples, the method includes removing the gas material to establish a steady state gas pressure. 
     In a further embodiment of any of the foregoing examples, the method includes heating the reactant material within a sealed volume. 
     In a further embodiment of any of the foregoing examples, the method includes storing the particulate thermal transfer media in a storage vessel after absorbing the thermal energy in the concentrated solar receiver and, at a later time, moving the particulate thermal transfer media into the heat exchanger in response to a demand to heat the working fluid. 
     In a further embodiment of any of the foregoing examples, the method includes storing the particulate thermal transfer media in a storage vessel after extraction of the thermal energy from the particulate thermal transfer media in the heat exchanger and, at a later time, moving the particulate thermal transfer media into the concentrated solar receiver in response to an availability of the solar energy in the concentrated solar receiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  is a schematic illustration of a thermal transfer apparatus. 
         FIG. 2  illustrates particles of a particulate thermal transfer media. 
         FIG. 3  is a schematic illustration of another example thermal transfer apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 1  schematically illustrates an apparatus  20 . As will be described herein, the apparatus  20  utilizes a particulate thermal transfer media  22  for thermal exchange and, optionally, thermal storage. The ability to store thermal energy allows time-shifting of the utilization of the thermal energy to overcome periods when a source of thermal energy, such as solar energy, is weak or unavailable. The particulate thermal transfer media  22  also permits tailoring thermal properties to enhance efficiency. 
     In this example, the apparatus  20  includes a closed loop circuit  24  through which the particulate thermal transfer media  22  circulates. A pump, conveyor, gravity or combinations thereof may be used to move the particulate thermal transfer media  22  in the closed loop circuit  24 . The term “closed loop” as used herein refers to the particulate thermal transfer media  22  being contained, with the exception of unintentional escape, within the closed loop circuit  24  for recirculation rather than consumption. 
     The closed loop circuit  24  includes a concentrated solar receiver  26  and is arranged such that the particulate thermal transfer media  22  is in communication with a heat exchanger  28 . The particulate thermal transfer media  22  is thus movable through the closed loop circuit  24  between the concentrated solar receiver  26  and the heat exchanger  28 . In this regard, the concentrated solar receiver  26  includes an inlet  26   a  through which the particulate thermal transfer media  22  is received and an outlet  26   b  through which the particulate thermal transfer media  22  is discharged from the concentrated solar receiver  26 . Similarly, the heat exchanger  28  includes an inlet  28   a  through which the thermal transfer media  22  is received and an outlet  28   b  through which the particulate thermal transfer media  22  is discharged. As an example, the heat exchanger  28  has a tube/plate configuration. 
     Referring also to  FIG. 2 , the particulate thermal transfer media  22  has a melting temperature of greater than 600° C./1112° F. and includes particles  30  that are selected for good thermal absorbance and transfer. In one example, the particles  30  are made of inorganic material, such as ceramic material, that is chemically stable at elevated temperatures of approximately 900° C./1652° F. or higher in the environmental gas that the particulate thermal transfer media  22  is exposed to. For instance, the particulate thermal transfer media  22  may be exposed to air within the closed loop circuit  24  and/or in the concentrated solar receiver  26 , if the concentrated solar receiver  26  is open to the surrounding atmosphere. Additionally, the particles  30  have a relatively high thermal capacity and thermal absorbance for effective thermal storage and transfer within the apparatus  20 . 
     In a further example, the particles  30  are substantially spherical to facilitate flow through the closed loop circulation passage  24  and are made of at least one material having good high temperature chemical stability, good thermal capacity and good thermal absorbance. For example, the particles  30  are made of at least one of bauxite, silicon carbide and silica, which may be provided as sand. 
     In a further example, the particles  30 , on average, have a size of greater than 1 micrometer to facilitate flow through the closed loop circulation passage  24 . Additionally, the disclosed size of the particles  30  also facilitates flow through the concentrated solar receiver  26 . For example, if the concentrated solar receiver  26  is open to the surrounding environment, such as to enable solar energy to be received, gusts of wind may alter flow of the particles  30  in the thermal receiver  26 . To prevent or limit undesired escape of the particles  30 , the particles  30  are provided with the disclosed size to reduce the effects of the wind gusts. 
     In a further example, the particles  30  include first particles  30   a  and second, different particles  30   b.  The first particles  30   a  have a first composition and the second particles  30   b  have a second, different composition. As an example, the first particles  30   a  include one of bauxite, silicon carbide and silica, and the second particles  30   b  include a different one of bauxite, silicon carbide and silica. It is to be understood, however, that additional particles of other, different compositions may also be used. 
     The use of a hetero-compositional mix in the particulate thermal transfer media  22  allows the properties of the particulate thermal transfer media  22  to be tailored to meet design goals for thermal capacity, thermal absorbance, thermal transfer and flow of the particulate thermal transfer media  22  in the closed loop circuit  24 . For example, the first particles  30   a  are silicon carbide and the second particles  30   b  are bauxite. In a mixture in the particulate thermal transfer media  22 , the combination of silicon carbide and bauxite enhances bulk thermal capacity and bulk thermal transfer of the particulate thermal transfer media  22 . The bauxite has a relatively higher heat capacity than silicon carbide and the silicon carbide has a relatively higher thermal conductivity than the bauxite. Thus, in the mixture, the bauxite enhances thermal capacitance and the silicon carbide enhances heat transfer. In further examples, the compositions of the first particles  30   a  and the second particles  30   b  can also be selected to reduce expense of the particulate thermal transfer media  22  or tailor other properties, such as color, to enhance solar or thermal absorbance. 
     In this example, the apparatus  20  is a solar-based system with regard to the source of thermal energy. The apparatus  20  therefore enables the elimination of the use of fossil fuel as a thermal energy source. The concentrated solar receiver  26  is thus a receiver that is arranged to receive solar energy  32  directed from a solar concentrator  34 , such as one or more heliostats. The solar energy  32  is received into the concentrated solar receiver  26  through an opening or a window, and heats the particulate thermal transfer media  22 . In one example, the solar energy  32  directly impinges upon the particulate thermal transfer media  22  to heat the particulate thermal transfer media  22 . 
     Turning to the operation of the apparatus  20 , the particulate thermal transfer media  22  circulates through the closed loop circuit  24  between the concentrated solar receiver  26  and the heat exchanger  28 . The particulate thermal transfer media  22  is heated in the concentrated solar receiver  26  and then circulated into the heat exchanger  28  through the inlet  28   a.  The particulate thermal transfer media  22  may be continuously moved through the heat exchanger  28  or delivered as a “charge” that is held statically in the heat exchanger  28  for a period of time. 
     In this example, the heat exchanger  28  is in communication with a sub-system  36 . Within the sub-system  36 , a working fluid  38  circulates through the heat exchanger  28  to thereby absorb thermal energy from the heated particulate thermal transfer media  22 . By way of example, the sub-system  36  may be a reactor system that utilizes the thermal energy to drive a chemical reaction, a system based upon a super-critical carbon dioxide cycle, a Rankine steam cycle or a Brayton cycle. It is to be understood, however, that the sub-system  36  is not limited to any particular type of system. 
     As indicated above, the particulate thermal transfer media  22  can be tailored to enhance thermal transfer. As an example, the particulate thermal transfer media  22  includes the first particles  30   a  and the second particles  30   b  of different compositions, such as silicon carbide and bauxite, respectively. The first particles  30   a,  which have better thermal transfer properties, not only facilitate thermal exchange with the working fluid  38  but also facilitate thermal transfer from the second particles  30   b  by being in close proximity to the second particles  30   b  to remove thermal energy from the second particles  30   b  and provide a path of thermal transfer. 
       FIG. 3  schematically illustrates another example apparatus  120 . In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred designate modified elements that are understood to incorporate the same features and benefits of the corresponding elements. In this example, the apparatus  120  includes a first storage vessel  150  and a second storage vessel  152 . 
     The first storage vessel  150  is located within a closed loop circuit  124  between the outlet  26   b  of the concentrated solar receiver  26  and the inlet  28   a  of the heat exchanger  28 . Thus, the storage vessel  150  receives heated particulate thermal transfer media  22  from the concentrated solar receiver  26 . 
     The second storage vessel  152  is located within the closed loop circuit  124  between the outlet  28   b  of the heat exchanger  28  and the inlet  26   a  of the concentrated solar receiver  26 . Thus, the second storage vessel  152  receives relatively cool particulate thermal transfer media  22  from the heat exchanger  28 . 
     The apparatus  120  further includes a sub-system  136 . In this example, the sub-system  36  is a reactor system for utilizing the thermal energy from the particulate thermal transfer media  22  to drive a chemical reaction. The sub-system  136  includes a reactor vessel  154  that is in communication with the heat exchanger  28 . The reactor vessel  154  includes an inlet  154   a  in fluid-receiving communication with regard to the heat exchanger  28  and an outlet  154   b  in fluid-discharge communication with regard to the heat exchanger  28 . The heat exchanger  28  includes a second inlet  28   c  connected to the outlet  154   b  of the reactor vessel  154  and a second outlet  28   d  in communication with the inlet  154   a  of the reactor vessel  154 . 
     The reactor vessel  154  further includes a feed  158  for delivery of a reactant material into the reactor vessel  154 . Product lines  160   a  and  160   b  serve to transport reaction product materials, such as solid material and gaseous materials, respectively. 
     Turning to the operation of the apparatus  120 , the particulate thermal transfer media  22  circulates through the closed loop circuit  124  in a manner described above with reference to  FIG. 1 . The heated particulate thermal transfer media  22  discharged from the concentrated solar receiver  26  is received into the first storage vessel  150 . If there is an immediate demand for thermal energy within the sub-system  136 , the particulate thermal transfer media  22  is responsively moved into the heat exchanger  28  for thermal transfer to a working fluid  138  circulating through a circulation loop  156 . Alternatively, if there is no immediate demand for thermal energy within the sub-system  136 , the heated particulate thermal transfer media  22  is stored in the storage vessel  150  until a later time at which there is a demand. 
     Because of the relatively high heat capacity of the particulate thermal transfer media  22 , the particulate thermal transfer media  22  retains the thermal energy absorbed from the thermal receiver  26 . Thus, the apparatus  120  permits a time-shifting of utilization of thermal solar energy with regard to the collection of the solar energy. That is, solar energy can be collected, as thermal energy, when available, such as when adequate sunshine is available, and immediately used or alternatively stored for a later time when there is a demand for such thermal energy. 
     After thermal exchange within the heat exchanger  28 , the particulate thermal transfer media  22  circulates to the second storage vessel  152 . If there is continued demand for thermal energy within the sub-system  136  and solar energy is available, the particulate thermal transfer media  22  is circulated from the second storage vessel  152  to the concentrated solar receiver  26  for another cycle of thermal absorbance and transfer. Alternatively, if there is no demand or if the solar energy is weak or unavailable, the particulate thermal transfer media  22  is stored within the second storage vessel  152  until a later time when there is demand and/or adequate solar energy availability. 
     The particulate thermal transfer media  22  that is discharged from the heat exchanger into the second storage vessel  152  may still include thermal energy that was not fully transferred to the working fluid  138  of the sub-system  136 . Optionally, the apparatus  120  includes an additional heat exchanger  162  through which the particulate thermal transfer media  22  can be circulated. The thermal energy absorbed from the particulate thermal transfer media  22  in the heat exchanger  162  may be utilized in another sub-system or within the apparatus  120 . As an example, the thermal energy absorbed from the particulate thermal transfer media  22  in the heat exchanger  162  may be used to preheat a reactant material before feeding the reactant material into the reactor vessel  154 . Alternatively, the thermal energy may be used in another process, such as a cement-producing process. Thus, the use and ability to store the particulate thermal transfer media  22  enables recovery of the thermal energy for other uses, which increases overall efficiency and reduces costs. 
     In a further example, the reactant material fed into the reactor vessel  154  is metal carbonate. The metal carbonate is either preheated using the thermal energy from the heat exchanger  162  or fed without preheating into the reactor vessel  154 . The reactor vessel  154  is used to chemically disassociate the metal carbonate into a constituent solid material and gas material. For metal carbonates, the gas material is carbon dioxide and the solid material is metal oxide. 
     As an example, an initial charge of the working fluid  138 , such as carbon dioxide, may be provided within the reactor vessel  154 . The working fluid  138  circulates in the circulation loop  156  through the heat exchanger  28  to receive thermal energy from the particulate thermal transfer media  22 . The heated working fluid  138  circulates back into the reactor vessel  154  and heats the metal carbonate material therein. The heat transfer that occurs in the apparatus  120  is thus double-indirect in that the thermal energy is transferred in two working materials, the particulate thermal transfer media  22  and the working fluid  138 , before being delivered to a target, reactant material. 
     The heating of the metal carbonate drives the disassociation reaction to thereby generate additional carbon dioxide. The generated carbon dioxide is then used as additional working fluid  138  and circulates in the circulation loop  156  to the heat exchanger  28  for further heating to further drive the chemical disassociation reaction. As more carbon dioxide is produced in the chemical disassociation, carbon dioxide may be removed through product line  160   b  to establish a steady state carbon dioxide partial pressure within the reactor vessel  154 . The solid metal oxide produced may be removed from the reactor vessel  154  during or after the process through product line  160   a.    
     The use of the particulate thermal transfer media  22  allows time-shifting between thermal solar energy collection and use in the reaction process within the sub-system  136 . That is, the apparatus  120  can be utilized to collect thermal energy in response to availability of solar energy and store the thermal energy within the first storage vessel  150  until a time at which there is a demand for the thermal energy within the sub-system  136 . Thus, even at times when solar energy is weak or unavailable, the heated particulate thermal transfer media  22  may be circulated from the first storage vessel  150  through the heat exchanger  28  to thereby heat the working fluid  138  and drive the reaction within the reactor vessel  154 . 
     Further, the use of the particulate thermal transfer media  22  enables indirect heating of the metal carbonate in the sub-system  136 , which limits exposure of tars or other impurity substances present in the metal carbonate to the sub-system  136  without fouling other components in the apparatus  120 . Additionally, the indirect heating enables the particulate thermal transfer media  22  to be tailored for efficient thermal capacitance and absorbance of solar energy. In comparison, the efficiency for direct heating of metal carbonate or other reactant material is limited by the thermal capacitance and absorbance properties inherent in the reactant material. 
     In a further example, the reactor vessel  154  and circulation loop  156  are sealed such that the generated gas remains within the volume of these components. The generated gas is thus sequestered and may be selectively removed through product line  160   b  for further use in a downstream process or for economic purposes. The sequestering of the generated gas, such as carbon dioxide, also prevents discharge into the atmosphere which, in the cement industry, represents a substantial reduction in carbon dioxide emissions and potentially avoids penalties for such emissions. Further, the sealing of the reactor vessel  154  and circulation loop  156  also limits or prevents contamination of the product solid materials and gas materials, which adds economic value. In another example, the gas that is removed from the reactor vessel  154  has a relatively high temperature and is used to preheat the reactant material that is fed into the reactor vessel  154 . 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.