MX2009014106A

MX2009014106A - Thermal tank of melted salts with nested vacuum.

Info

Publication number: MX2009014106A
Application number: MX2009014106A
Authority: MX
Inventors: Noel Leon Rovira; David Alejandro Contreras Garza; Jesus Omar Fernandez Gonzalez; Araceli Rivera Moreno; Beatriz Montoya Gomez
Original assignee: Monterrey Inst Tecnologico Y De Estudios Superiores De
Priority date: 2009-12-18
Filing date: 2009-12-18
Publication date: 2011-06-27

Abstract

The present invention refers to a tank for containing PCM (Phase Change Material) for storing thermal energy by means of one or a plurality of phase changes. Said PCM is contained into a tank with a reduced thermal conductivity, which is resistant to corrosion and leakage free. The PCM container tank is isolated by means of nested vacuums where the walls confining the vacuum, best known as "reflecting wall", have an arrangement of black surfaces for minimising the heat loss, and surfaces of a high reflecting index for avoiding leakages of heat caused by radiation, also the exterior tank has a similar finish for minimising losses by radiation. The vacuum is created by a valve located in an exterior tank made of an impact-resistant material. The thermal tank of melted salts is advantageous in that it has exchangeable parts that optimise the different heat transference steps. Said parts are exchanged by means of a snap-on mechanism. The first exchangeable part is a dome cap, which is int ended to transfer the heat towards the tank by means of solar radiation and avoid heat losses by means of convection. The second part is a stopper which main function is to avoid any heat transference when the tank is not in use.

Description

THERMAL TANK OF CASTED SALTS DESCRIPTION OBJECT OF THE INVENTION The present invention relates to a thermal tank of molten salts, which is presented as a "green" technology for sustainable development and at the same time as a possible substitute for electric batteries or portable power generating plants that use fuels for their operation.

The tank of the present patent application confines a phase change material (PCM), in the solid state; that due to the effect of the solar radiation that affects it, it changes phase, storing heat energy and therefore its temperature, and to avoid heat losses, the material is isolated from the environment through the formation of nested vacuum spaces, only access to the PCM is through a special conductive element that allows heat transfer in a controlled manner, the conductor can be interchanged by a dome that allows concentrating the solar radiation at a single point for transmission by convection to the PCM, or by a cover that helps to reduce the speed of thermal equilibrium between the PCM and the outside, to minimize the loss of heat energy of the PCM.

BACKGROUND The tanks of fiuid salts for solar thermal energy storage are currently used to store energy by means of solar concentrators that direct the light rays to strategic points and make them influence special mechanisms that conduct heat to the flux material. The PCM as a fluid is pumped from a tank to another tank of lower temperature that is later used to generate water vapor, which is injected into a turbine to generate electric current. Currently tanks with large insulation and complex systems of heat exchangers are used to flow the PCM. There are applications of molten salts to produce electricity, this due to their catalytic properties also have a high thermal capacity and can function as a fluid or as solvents. In order to corroborate that the object of this patent is subject to intellectual protection, a review of the state of the art related to thermal storage tanks is described below.

The patent application MX / a / 2008/015986 presents a device that stores thermal energy through the direct incidence of solar radiation through a lens, consists of two tanks one inside another separated by an insulating material. The energy is stored in molten sodium chloride whose temperature range is 600 ° C to 900 ° C, unlike the present invention, where in the separation of the tanks it is used to form nested voids that decrease the heat loss by radiation, and connection to the outside, in addition to the material where the heat energy is stored, is a phase change material (PCM) that once melted reaches temperature ranges higher than that reached by sodium chloride.

US patent 4,037,579 presents an energy storage system, which can be used during the day and when there is no sunlight. The tank is closed and comprises a set of layers of salt cans that are filled with the evaporated compound.

US Patent 4,088,183 discloses a thermal energy storage tank comprising: a container covered with an external thermal insulator wall; it includes a section in empty in the part superior and includes in his intermediate part a material that exchanges and stores thermal energy.

US 4,643,212 discloses a tank for storing liquid that is at a temperature above 400 ° C, comprising: a metal plate with a flat bottom wall of the same material; a cylindrical side wall and metal roof; a vertical cylinder essentially free of the internal wall supported by the base which, located axially in the tank, provides a space between the side of the tank and the inner wall.

The patent US 5,685,151 presents a solar energy system comprising a concentrator with parabolic geometry whose movement is relative to the movement of the sun, this in order to optimize the absorption of energy. This apparatus also serves to store heat and includes a heat energy exchange system. The energy concentrated in the collector is transported by means of sodium vapor which is then stored in sodium chloride, the work produced activates the turbine of a boiler, which, by means of steam, transports the sodium in a liquid state to the solar collector.

Patent US 6,272,856 Bl presents a method for operating (driving) vehicles not connected by systems, by means of a high temperature accumulator. The system comprises a body provided with graphite (which can also be beryllium, boron, lithium, silicon) reinforced with carbon fiber.

Due to the high working temperatures, the material sublimates from a solid state to a gas, without going through the liquid state. This phase change releases energy. The protection system consists of a set of gas layers around the tank. The loading and unloading of energy is automated. The capacity of the accumulator is from 10 to 50 kW / h per liter. The accumulator works with a thermionic generator or a Stirling engine to extract the stored energy and use it for the operation of a vehicle.

The patent US 6,343,647 presents the description of a thermal connection that facilitates the transfer of heat between two components. This joint is formed of an alloy of at least two elements. Said alloy has a temperature for the liquid state and a temperature for the solid state. The alloy consists of a liquid phase which is in substantial equilibrium with at least one solid phase.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1. Assembly view of the device showing its internal components.

Figure 2. External isometric view of the thermal tank of molten salt with plug to avoid energy losses.

Figure 3. External isometric view of the thermal tank of molten salts with the dome to receive the radiation.

Figure 4. External isometric view of the thermal tank of molten salts that is the subject of this invention.

Figure 5. Axial section of the device with a dome to receive radiation, showing its internal components.

Figure 6. Isolated isometric view of the exterior tank.

Figure 7. Isolated isometric view of the lower cover.

Figure 8. Isolated isometric view of the upper support.

Figure 9. Isolated isometric view of the lower support.

Figure 10. Isolated isometric view of the PCM container tank.

Figure 11. Isometric view of the reflecting wall with which the nested vacuum is made.

Figure 12. Isolated isometric view of the driver.

Figure 13. Isolated isometric view of the security cover.

Figure 14. Isolated isometric view of the top cover.

Figure 15. Isolated isometric view of the nut.

Figure 16. Isolated isometric view of the valve.

Figure 17. Exploded isometric view of the dome.

Figure 18. Side view of the dome.

Figure 19. Cutting the dome, showing its internal components.

Figure 20. Isolated isometric view of the cap.

Figure 21. Cutting the stopper.

DETAILED DESCRIPTION OF THE INVENTION The thermal tank of molten salts reason for this patent application, allows the phase change of the material it contains, an unlimited number of times, taking advantage of the heat energy of each discharge, because it has interchangeable parts, which allow it: - charging, ie receiving solar radiation, -store the heat energy, with the minimum of losses, and -transfer the heat energy stored by a conductor.

Given that the thermal tank of molten salts can store the heat energy, it is possible that the "discharged" thermal tanks are exchanged, by thermal tanks "loaded"; providing practicality in their employment.

In general, the present patent application consists of a thermal tank that confines a phase change material (PCM for its acronym in English of Phase Change Material) surrounded by an arrangement of vacuum chambers (nested voids, taking advantage of the vacuum as a thermal insulator, to avoid heat losses by conduction and convection) with bright surfaces (reflective wall) for a high reflection index and black body surfaces for a high rate of radiation absorption, to minimize heat losses by convection and radiation, which allows us to keep PCM stored at extreme temperatures with a small heat loss ratio.

The PCM changes its physical state from solid to liquid, when it absorbs the solar radiation that hits the dome. When the PCM is in liquid physical state, it maintains a high calorific energy and the loss of it must be avoided. Since the PCM has a high capacity to absorb solar radiation, it also has a high capacity to transfer it, so the thermal tank that is the subject of this invention provides the necessary elements to capture and store solar radiation, allowing it to subsequently be transferred in a controlled manner as heat energy to other devices.

The thermal tank advertised here is made up of the following elements: An outer tank (8), closed at its lower end by a lower cover (7); inside it houses a pair of supports (5 and 6) that provide stability to the container tank (1) that confines PCM, besides giving resistance to changes of position and make safer the transport of the tank in question and is surrounded by a reflective wall (16). A conductor (2) that receives the solar radiation is inserted through the upper end of the container tank and conveys it by convection to the PCM; This container tank is closed by a safety cover (3). And the upper end of the outer tank (8), is closed by a top cover (9), to the center of the top cover is placed a nut that holds the container tank, safety cover and top cover in a single assembly to form a seal and airtight seal. A plug (11) or a dome plug (10) is optionally inserted into the nut. In such a way that when the PCM is melted and the calorific energy it contains is stored, the plug (11) is placed, in this way it is transported or stored; and when the plug-dome (10) is placed is when the tank will receive solar radiation.

In particular, the thermal tank of molten salts is made up of: An exterior tank (8), of cylindrical geometry, with hollow interior to house: -A container tank (1) of cylindrical geometry, of dimensions (length and diameter) smaller than those of the outer tank (8).

The container tank (1) is made of a material with a high degree of resistance to corrosion of the PCM that will contain, and with little thermal conductivity, such as ceramic material. The container tank (1) is closed by the lower and upper end, forming a single piece, but at its upper end has a central hole (1.1), which allows the deposit of the PCM and the coupling with a conductor (2), ( see figure 1).

-A conductor (2) manufactured from copper to achieve greater heat transfer; This piece has the function of capturing the solar radiation and, by conduction, transferring it uniformly to the PCM, contained inside the container tank (1). The conductive body is a single piece formed by a first and second section. The first section is a hollow cylindrical body (2.2), which forms a cavity in its interior, in the shape of a truncated cone (2.4), where the largest diameter is the upper face, and the smaller diameter (2.2) extends a second section (2.3), cylindrical of smaller diameter than the smaller diameter of the first section, this second section, extends to the base of the container (2), and of the body of the second section, fins (2.1) extend longitudinally and equidistantly, avoiding that these are in contact with the container (2), The dimension of the fin (2.1) in radial direction is equal to the radius of the hollow cylindrical body (2.2) and the dimension of the fins (2.1) is equal to the length of the axial axis of the second section. The conductor (2) is introduced into the interior of the container tank (1) through a central circular hole (1.1) from which slots extend as guide for the fins, so that they coincide in number, (see figure 12). .) The container tank (1), see figure 6, has a safety cover (3, see figure 1, 5 and 13) which is the same refractory material as the container tank (1). The diameter of the safety cap (3) is greater than the upper diameter of the first section (2.2) and has a circular perforation (3.1), which is concentric to the first section cavity of the conductor (2). The cover (3) has teeth (3.2), equidistantly spaced apart, the teeth extend forming a right angle with the diameter of the cover and its function is to close the slots in the central hole of the container tank, through which the conductor (2), see figure 13.

A nut (4), whose function is to hold the container tank (1), the safety cover (3) and the upper cover (9) in a single assembly in such a way that an airtight seal is formed, see figure 15.

The nut is a single circular body, on the outside is surrounded by a projection that is located at half of its height and forms a right angle with the body; the projection allows to visualize in the nut, an upper section and a lower section, characterized as described below: In the lower section of the nut, and on the inside, lower flanges (4.1) are located, which consist of slots in the shape of "L", equidistant from each other, parallel to the outer projection, with which the driver is fastened (2), making a small turn and hold the whole assembly, see figure 15.

In the upper section of the nut, and on the inside, are located upper flanges (4.3) consisting of slots in the shape of "L", equidistant from each other, shorter than the lower lashes, which allow insertion and removal of the stopper (11) and the dome plug (10), with the aim of making a rapid transition for the charge and discharge phase of heat energy; and on the outside, there are located fasteners (4.2) distributed equidistantly and consisting of projections of length equal to the length of the projection. The function of the fasteners is to serve as a support to turn with more force, see figure 15.

The upper (5) and lower (6) supports go under the container tank of the PCM (1). Its objective is to provide an extra grip on the bottom and sides of the container tank of the PCM (1). Each support consists of a single body with peculiar characteristics that are described below. First, we will describe the upper support (see figure 8), which consists of a straight piece (called the base), with a fold at each end (called a bra) in the same direction, each fold forms a 90 ° angle, and is rounded for its interior and exterior. The outer length of each support, which refers to the length of the straight line, coincides with the internal diameter of the outer tank, where it is located. Its internal length, which refers to the distance between the separators, coincides with the diameter of the container tank (1). Each lateral fastener, in its upper base, has a groove transverse to the base of the support, and in these a reflective wall is placed that surrounds the container tank. The wall of the separators that adjoins the exterior tank, adopts its geometry, that is to say if it presents folds in a manner coinciding with the exterior tank.

The upper support, present at the middle of its base and on the opposite side to the lifting of the separators, a notch, of equal length as the width of the lower separator. And the lower support (see figure 9), presents half of its base, and on the side to the lifting of the spacers, a notch, of equal length that the width of the upper separator; and in this way they are assembled, forming a crosshead ("+"). The assembly of the supports, supports the base of the container tank, and provides stability, decreasing the changes of position of the container tank, during the transport of the thermal tank, in addition to allowing a constant separation between the container tank and the exterior tank.

The reflective wall (16), which surrounds the container tank, is made of rock wool, which allows to obtain sufficient flexibility, with a low coefficient of thermal expansion and a good thermal insulation. The reflecting wall (16) on the side that coincides with the container tank, is reflective; and the side that coincides with the external tank, is opaque; this in order to reduce energy losses by radiation. With the reflective wall, the creation of nested voids is favored, the reflecting wall is represented in figure 11, and its upper end, has a central opening (16.2) through which the conductor (2) enters and has rectangular cuts (16.1) with which they rest on the grooves of the upper (5) and lower (6) supports.

The outer tank (8), is closed at the lower end with a lower cover (7, see figure 7) of stainless steel, which has concentric folds (7.1) in order to withstand high pressures, in addition to the wall of the outer tank (8) presents two sets of folds (8.1) transverse to its axis, which increase its rigidity, to allow it to resist higher pressures, in the same way the material of said tank is stainless steel.

Its upper end is closed by an upper cover (9) of stainless steel with folds (9.1) concentric to its central hole (9.2), whose purpose is that the tank will resist exposure to high pressures, see figure 14. The central hole presents a slight inclination, giving a semi-conical appearance (9.3) in the center, space in which the nut (4) will be supported.

The lid also has a second eccentric hole (9.4), with a smaller diameter, the central hole, and its function is to allow the coupling of a valve (13) see figure 16. Assembled to the nut, a base-dome is located ( 12) of fireclay. The geometry of the base-dome is circular with a first, second and third diameter concentric to each other, forming two external steps, having in its interior the same opening diameter, to allow the assembly with a plug-dome (14), see figures 18 and 19.

The plug-dome consists of a circular piece made of silicon carbide since its main function is to conduct the heat, since it receives the energy by radiation and transfers it by convection to the conductor (2), see figure 17 .. The first diameter is greater and in its upper contour it presents a channel to insert in it, the dome. In the contour of the second diameter, has stops (12.2) equidistant to mount to the nut, can assemble and disassemble the nut (4). The last section that presents the third and smaller diameter has a slight conicity that coincides with the conicity of the cap and nut.

A dome (10) concentrator of solar radiation. Inside contains vacuum to prevent losses by convection, is made of quartz in order to withstand high temperatures and is mounted on a base dome (12) whose material is fireclay and serves to assemble and disassemble the dome (10) of the outer tank (8), see figure 17. To avoid loss of heat when transported, the molten salt thermal tank has a plug (11) which inside is vacuum (11.3), said plug (11) is fireclay to avoid heat loss, this has some stops (1.1) that serve to attach to the nut (4), likewise has a notches (11.2) in the upper part in order to grab it from here and that it is easy to place or remove the plug (11), see figures 20 and 21.

The vacuum valve (13) allows to extract the air inside the external tank (8) and generate a sufficient vacuum to avoid losses due to conduction and convection. This valve withstands temperatures above 200 ° C which is higher than the temperature in the outer tank (8). This allows us to keep the heat stored for much longer and reduce the temperature in the outer tank (8).

The thermal tank starts its operation when the tank containing the PCM in solid state is connected to the solar collector by means of a conductive interface. The solar energy that is concentrated melts the PCM, in this way the energy absorbed inside the tank is stored. Thanks to the phase change that the PCM undergoes, the stored energy is released. It has the ability to operate at night as well as the supply of 300 kW / h.

Claims

CLAIMS According to the detailed description previously given about our invention, we claim as exclusive property contained in the following clauses:

1. A thermal tank of molten salts with capacity for recharging, storing and transferring heat energy, characterized in that it is formed by an exterior tank, with cylindrical geometry, with hollow interior, closing its base with a lower cover, forming a single piece, the external tank presents in its lower cover and in its body folds to provide support at high pressures, and inside are located, a pair of supports, similar characteristics, are called as upper support and lower support, which are coupled together forming a cross and have at each end a fold that forms an angle of 90 °, each fold has at its base, a slot transverse to the base of the support, it is important to note that the distance between the folds of the same support coincide with the diameter of a container tank, which is placed there; The container tank is cylindrical closed at both ends forming a single piece of hollow interior, at its upper end, has a central hole, through which phase exchange material (PCM) is introduced, which is confined there and the insertion of a conductor that consists of a piece whose function is to capture the solar radiation and by conduction transfer it in a uniform way to the PCM, confined in the container tank; due to this the conductive body is a single piece formed by a first and second section; where the first section is a hollow cylindrical body, which forms in its interior a cavity in the shape of a truncated cone, where the largest diameter is the upper one, and of the smaller diameter, the second section extends, which is cylindrical of smaller diameter than the second. smaller diameter of the first section, this second section extends to the base of the container, and of the body of the second section, longitudinally and equidistantly extends a fins, whose width is equal to the radius of the hollow cylindrical body; this conductor is introduced inside the container tank through the central circular hole, from which grooves extend as a guide for the fins, so that they coincide in number; the container tank also has a safety cap, with a diameter greater than the upper diameter of the first section of the conductor; has a circular perforation, which is concentric to the cavity of the first section of the conductor, and forming a right angle with the diameter of the lid, teeth are spread equidistantly apart, whose function is to close the slots of the central orifice of the container tank, by which the driver is previously introduced; holding the container tank, the security lid and the top cover and forming a single assembly presents a nut, which is a single circular body, on the outside is surrounded by a projection that is located at half its height and forms a right angle to the body; the projection allows to visualize in the nut, an upper section and a lower section; inside the lower section, lower tabs are located, consisting of slots in the shape of "L", equidistant from each other, parallel to the outer projection, with which the driver is held; Inside the upper section of the nut, upper flanges are located, which consist of slots in the shape of "L", equidistant from each other, shorter than the lower flanges, which allow the insertion and removal of the cap and the dome plug; and on the outside, there are located fasteners (4.2) distributed equidistantly and consisting of projections of length equal to the length of the projection. The function of the fasteners, is to serve as support to turn with more force; surrounding, to the container tank, and the assembly of the nut, is located a reflective, rock wool wall; the reflective wall is assembled in the groove of the folds of the supports, taking that on the side that coincides with the container tank the wall is reflective, and on the side that coincides with the external tank is opaque, this in order to decrease the energy losses by radiation, and creates nested vacuum that is used as a thermal insulator, decreasing heat loss; the upper end of the outer tank is closed by an upper cover that also presents concentric folds to its central orifice that presents a slight inclination, giving a semi-conical appearance in the center, space in which the nut is located; a hole more eccentrically located, to allow the coupling of a valve to generate vacuum; at the upper end of the nut, optionally a plug or a plug-dome is assembled, the plug hermetically closes the hole that is located at the upper end of the thermal tank and the vacuum inside it serves as an insulator; storing the heat energy of the PCM; the plug-dome, is for the reception of solar radiation. The molten salt thermal tank with capacity for recharging, storing and transferring heat energy, according to claim 1, characterized in that the dome contains a vacuum to prevent heat loss by convection. The molten salt thermal tank with capacity for recharging, storing and transferring heat energy, according to claim 1, characterized in that when the tank closes with the plug it can be transported and stored, with minimum energy losses.