Apparatus and method to transfer heat energy by means of phase change materials

Abstract

An apparatus for the extraction of heat energy from hot off-gases ( 2 ) from productive or service processes and for the transfer of the energy to an external user device ( 3 ) is positioned in contact with the off-gases ( 2 ), at least partly inside a containing chamber ( 22 ) or one or more pipes of a plant performing the productive or service processes. The apparatus comprises at least two sections ( 4 ), each of which is defined by at least a heat exchange module ( 5 ) having a container/exchanger ( 6 ), located at least partly in contact with the off-gases ( 2 ), in order to exchange heat energy with them. A first phase change material ( 7 ) having high heat diffusivity is located inside the container/exchanger ( 6 ). An extraction exchanger ( 8 ), disposed in contact with the first phase change material ( 7 ), has delivery and return pipes ( 9 ) in which a heat-carrying fluid ( 10 ) circulates, to extract and transfer the heat energy accumulated by the first phase change material ( 7 ). Furthermore, movement means ( 14, 15 ) move the heat-carrying fluid ( 10 ) and convey and manage the flow rate of the latter to selectively determine, for each section ( 4 ), a variation in the values of the heat flow extracted from the off-gases ( 2 ) and exchanged with said first phase change material ( 7 ).

1 . An apparatus for the extraction of heat energy from hot off-gases, with a temperature equal to or higher than 100° C., from productive or service processes and for the transfer of said energy to an external user device, said apparatus being positioned at least partly inside a containing chamber or one or more pipes of a plant performing said productive or service processes and in contact with said off-gases, wherein it comprises at least two sections, each of which is defined by at least a heat exchange module having:
 a container/exchanger, hollow in shape, made of metal material having a heat conductivity equal to or greater than 10 W/mK, located at least partly in contact with said off-gases, in order to exchange heat energy with them; 
 a first phase change material, having a heat diffusivity equal to or greater than 10 −7  m 2 /s, located inside said container/exchanger; 
 an extraction exchanger, disposed in contact with said first phase change material and having delivery and return pipes; 
 a heat-carrying fluid associated to said extraction exchanger and circulating in said pipes to extract and transfer the heat energy accumulated by the first phase change material; 
 movement means associated to said pipes in order to move the heat-carrying fluid which flows through them and to convey and manage the flow rate of said heat-carrying fluid to selectively determine, for each section, a variation in the values of the heat flow extracted from said off-gases and to achieve an at least partial phase change of said first phase change material of each section. 
 
     
     
         2 . The apparatus as in  claim 1 , wherein said movement means are configured to convey and manage the flow rate of said heat-carrying fluid to achieve an at least partial phase change of the first phase change material of each section in an alternate and complementary manner between the sections. 
     
     
         3 . The apparatus as in  claim 1 , wherein the extraction exchangers of the heat exchange modules of each section are connected by a single independent connection network of pipes and in that the single connection networks of each section with heat-carrying fluid at variable and independent flow rate are connected in parallel in a common circuit which feeds the external user device. 
     
     
         4 . The apparatus as in  claim 1 , wherein said heat-carrying fluid is gaseous and chosen from a group comprising at least air, steam, CO 2 , nitrogen or other similar or comparable gases, or mixtures thereof. 
     
     
         5 . The apparatus as in  claim 1 , wherein said heat-carrying fluid is a liquid chosen from a group comprising at least water, diathermic oil, molten salts, molten metals, molten metal alloys and other liquids with a high heat capacity. 
     
     
         6 . The apparatus as in  claim 1 , wherein it comprises at least one further container which contains a second phase change material, is at least partly immersed in said first phase change material, and has a separation surface which separates the second phase change material contained in said further container from the adjacent first phase change material and allows the heat exchange between said first and second phase change materials. 
     
     
         7 . The apparatus as in  claim 6 , wherein said second phase change material has a phase transition temperature lower than the melting temperature of the first phase change material, and a high latent phase-change heat, in order to contribute to the overall heat capacity of the apparatus. 
     
     
         8 . The apparatus as in  claim 6 , wherein said second phase change material is chosen from a group comprising at least molten salts for industrial use, such as NaNO3-KNO3, KCl—MgCl2, and other similar or comparable salts. 
     
     
         9 . The apparatus as in  claim 1 , wherein it comprises at least two first phase change materials and at least two second phase change materials, positioned in respective containers/exchangers and further containers having corresponding internal separation surfaces disposed in a substantially concentric development, and in that the extraction exchanger of each of said modules is located in contact with one of said second phase change materials or with one of the first phase change materials, different from the more external first phase change material. 
     
     
         10 . The apparatus as in  claim 1 , wherein said first phase change material is aluminum, either pure or an alloy, with a melting temperature comprised between 500° C. and 700° C. 
     
     
         11 . The apparatus as in  claim 9 , wherein between the more external first phase change material and the more external second phase change material a further first phase change material is interposed, different from said more external first phase change material, having a melting temperature lower than that of the more external first phase change material, and higher than that of the more external second phase change material, in order to maintain the operating temperatures of the latter below a value, about equal to the melting temperature of said more external first phase change material, harmful for the structural resistance of the respective separation surface. 
     
     
         12 . The apparatus as in  claim 11 , wherein it comprises a thermocouple, located in contact with said further first phase change material in order to measure its temperature and to manage, on the basis of said value, the extraction power of the extraction exchanger. 
     
     
         13 . The apparatus as in  claim 1 , wherein it is configured to increase the heat energy of the first phase change material of at least most of said sections and to selectively extract, in series, heat energy from the first phase change material of at least most of the sections, in the presence, respectively, of phases of said productive or service processes in which said off-gases are provided with high temperature and high thermal power, and of phases of said productive or service processes subsequent to said phases in which said off-gases are provided with high temperature and high thermal power. 
     
     
         14 . A method for the extraction of heat energy from off-gases from productive or service processes and for the transfer of said energy to an external user device, using an apparatus, comprising at least two sections, wherein:
 it provides to thermally force each of said at least two sections by managing the flow of a heat-carrying fluid circulating in delivery and return pipes of each of said at least two sections, in order to selectively determine a thermal flow extracted from a first phase change material above or below the thermal flow yielded by said off-gases, so as to respectively determine thermo-physical states of at least partial melting or solidification, and vice versa, in the first phase change material of each of said sections, said thermo-physical states being alternated in each section and complementary between the sections;   it provides that a relatively high flow rate of said heat-carrying fluid determines an overall and progressive cooling of the first phase change material of the section in which said heat-carrying fluid circulates, in order to take said first phase change material to progressive solidification, if initially molten;   it provides that a relatively low or non-existent flow rate of said heat-carrying fluid determines an overall and progressive heating of the first phase change material of the section in which said heat-carrying fluid circulates, in order to take said first phase change material to melt, if initially in the solid state;   it provides to alternate solidification phases with melting phases of the first phase change material of each section, to determine a continuous state of phase transition of said first phase change material and to transfer a substantially constant, or in any case manageable, overall power to a user device downstream of said apparatus.   
     
     
         15 . The method as in  claim 14 , wherein it provides to thermally force each of said at least two sections in an alternate and complementary manner. 
     
     
         16 . The method as in  claim 14 , wherein it provides to increase the heat energy of the first phase change material of at least most of said sections during phases of said productive or service processes in which the off-gases are provided with high temperature and high thermal power, and to extract heat energy from the first phase change material of at least most of the sections during phases of said productive or service processes subsequent to said phases in which said off-gases are provided with high temperature and high thermal power. 
     
     
         17 . The method as in  claim 14 , wherein it provides to effect a connection in parallel of connection networks of delivery and return pipes of said sections, in order to obtain the overall power extracted as a sum of the thermal powers extracted by the individual sections, and in that it provides to extract an overall thermal power almost constant over time, or at least manageable, setting alternate solidification and melting cycles inside the individual sections, forcing them to a reciprocally complementary functioning. 
     
     
         18 . The method as in  claim 14 , wherein each section comprises at least one heat exchange module, wherein, for every heat exchange module of each section, it provides to take the first phase change material, in the solidification phase, to a temperature lower than the solidification temperature of a second phase change material positioned inside said first phase change material, and in the melting phase, to a temperature higher than the melting temperature of said second phase change material. 
     
     
         19 . The method as in  claim 14 , wherein it provides both to force the individual sections of the apparatus, to determine in the first phase change material temperatures that are lower than the melting temperatures of said second phase change material, in order to obtain the phase transition thereof, and to use the corresponding latent heat for subsequent heat exchanges.