ES2306628B2 - DEVICE AND PROCEDURE OF LOW ENTROPIA THERMAL STORAGE. - Google Patents

Abstract

Device and storage procedure Low entropy thermal.

Thermal storage device and method Low entropy based on the sensible heat they can absorb different compartments (1) of a calorific fluid, being said compartments (1) separated and thermally insulated from each other through internal walls (4) insulators, so that the fluid calorific flows through the compartments (1) in parallel circuits, establishing the flows from supply pipes (5) to the compartments (1), and from said compartments (1) to pipes of return (6) by opening and closing valves (7.8), transmitting heat-sensitive fluid heat sensitive to compartments (1), in which it is stored, so that subsequently said sensible heat is transmitted from the compartments to a fluid to be heated.

Description

Device and storage procedure Low entropy thermal.

Technical Field of the Invention

The present invention belongs to the technical field of devices and methods for energy storage, more specifically for heat-based thermal storage sensitive that can absorb a set of bodies, and more specifically when the set is of solid bodies, particularly ceramic, due to the high temperatures that These can reach. This thermal storage is low entropy, and therefore offers few losses, and a maximization of energy.

Background of the invention

When a heat source is available that does not can be used properly immediately, it must be resort to its storage, so as not to lose said energy. In the Currently, energy storage is a technical activity really difficult, since natural laws tend to increase entropy, favoring the elimination of gradients in intensive variables that are consubstantial with high energy densities such as temperature, pressure, or electric tension. Specifically, in the case of thermal energy, the high temperatures that would be necessary in a storage, regarding the temperature of the surrounding environment, they tend to decrease by heat transferred from storage to environment, by conduction, convection and radiation. Against this it fits fight with the appropriate thermal insulators, which greatly inhibit Measure the aforementioned thermal transfer mechanisms. Remains point out another property of thermal storage, and that is that in the sine of the material that constitutes them, be it in a fluid phase, in solid phase or plasma phase, it also tends to isothermalization In fact, in the absence of sources or sinks of heat acting on storage, the temperature tends to standardize This is an important effect, because energy Thermal available is not quantified only based on its quantity total, but also for its temperature, and in the case of a fluid, also for its pressure.

There are currently several methods designed for thermal storage, based on some cases in phase changes, which implies latent heat, and in others in heat sensitive, which implies an increase in temperature. In the document "Survey Thermal Energy Storage for Parabolic Trough Power Plants ", from Pilkington Solar International GmbH, NREL / SR-550-27925, (September 2000,  htpp: //www.ntis.gov/ordering.htm) there is a systematic description of the identified alternatives. It mentions the possibility of using solid or filled matrices, for example in the form of bed of balls, regular or labyrinth crosshairs, bed of rings and cylinders, etc., which are heated by a fluid, either liquid or gas, in the phase in which heat is supplied to the storage, and subsequently cooled by that same or another fluid when you want to extract heat to use it anywhere auspicious Other references are documents US 6374614 B2, US 2007/0220889 A1 and US 2008/0066736 A1; however, the solutions techniques described in all these documents differ markedly of those raised in the present invention.

The use of a bed of solid matrices, or filling, as energy storage is, in principle, simple and cheap, as estimated by the first document cited, although in these moments, in solar thermal energy, the most used alternative is the circuit of molten salts, therefore, fluids, with a tank of hot and other cold salts, and an exchanger in each of the circuit branches The heating is logically used in the branch that goes from the cold tank to the hot one, and that of extraction of heat, on the branch that goes from the hot tank to the cold one.

Although this is currently the method preferred, storage in a conveniently insulated tank, which is filled with appropriately arranged solid material, by for example, in channel forming reticles or in beds of rings, seems the most promising to lower costs, both of installation as operation and maintenance, which begin to be a problem in thermal storage in circuits of you go out.

The biggest problem with these storage of beds of solid matrices, or by filling, lies in the internal isothermalization that occurs when it has been provided heat, which results in the stored heat temperature it can be, and in general will be, much lower than the temperature of the fluid that has brought heat. This brings with it an important loss of energy, which is the relevant variable for the production of the useful good, as a result of the increase in entropy,  consubstantial with isothermalization.

This problem is represented in a series of State of the art documents. Specifically, it is very Representative patent application already cited, US2008 / 0066736 A1, in whose figure 4 a typical storage module can be seen of thermal energy through an aggregation of solids or filler, by  the sine from which the heating fluid flows, both in the phase of storage heating, as in the extraction phase of hot. This module can be used in various locations of a solar power plant, and eventually of a power plant multipurpose, as specified in the patent application US2007 / 0220889 Al. What is significant is that said modules of thermal storage involve redistribution, throughout the mass of the filling, of the thermal energy contributed by the gas, which It is the problem to solve.

For example, if a gas is supposed to provide a million Joules at 500 ° C, that the storage material was initially at 300 ° C, its specific heat is 100 Joules per degree Celsius and kilogram of mass, and that there were a thousand kilograms of material in total, by transferring heat to the material of the storage, once the transitional regime of heat transfer and reached equilibrium, the temperature of this would only have increased by 10 ° C, so the storage would be at 310 ° C, far from the initial 500 ° C at the ones that was the gas. Although in every phase of transfer of heat is lost temperature, in these cases it is lost too much

A device and a device were therefore desirable. method that achieved low entropy thermal storage based on sensible heat that can be absorbed by a set of bodies, avoiding the inconveniences and losses existing in the prior art systems.

Description of the invention

The present invention solves the problems existing in the state of the art by a procedure and a low entropy based thermal storage device in the sensible heat that a set of bodies can absorb solid geometric embedded in a bounded volume by which you can flow a fluid that carries heat.

The invention consists in compartmentalizing the storage so that heat transfer is not make the whole of the total mass available, but to a fraction from it, so as not to lose excess temperature, and therefore lose Lots of energy. The low thermal storage device entropy object of the present invention is based on heat sensitive that can absorb the aforementioned set of bodies solid geometric embedded in a bounded volume by which The heating fluid can flow.

The device consists of collecting pipes of discharge and return, and connecting pipes through which the calorific fluid, plus opening and closing valves located in the connecting pipes, also comprising compartments of energy storage with its fill, whose weight is supported by a bed base of support of the filling, and being also the compartments covered by an insulating material.

The energy storage device is divide into separate and thermally insulated compartments between yes, and with the stiffness of walls that require the differences of pressures of the case in question. In this way, the calorific fluid flows through the compartments in parallel circuits, but not in series, establishing the flows by opening or closing the valves of the connection pipes of the compartments with general collectors of fluid delivery and return calorific, having temperature recorders in both fluid collectors, as well as inside each compartment, to apply the procedure explained after.

In another configuration, the compartments of the Energy storage device, with its filling, will arranged in a concentric configuration, embedded one within another, each compartment having an interior wall and a exterior wall, except the first, which only has the exterior, of so that in general the outer wall of a compartment more interior makes interior wall of the next compartment Exterior.

The walls of the compartments of Energy storage consist of thermal insulator and have the thickness required depending on the pressures used. Every Energy storage compartment is attached to the supply and return manifolds of the heating fluid, at least for a pipe in each case, with its corresponding valves opening and closing of the fluid passage.

The effectiveness of the invention improves with increasing the number of energy storage compartments, but it It implies higher investment cost, for the connection pipes and the valves, which must be assessed against the improvement of thermal performance of the installation in a predictable scenario of loading and unloading transients. In any case, the invention it must consist of at least three compartments, the first of them destined to host the most common transients, the second to supplement the previous one for the transitory intermediate, and being the third to reach capacity Total calorific required by the major transitory, design. In definitively, the number of storage compartments of energy should be increased as better performance is required thermal storage, and must be at least equal to three.

The thermal storage procedure works with a load transient, a download transient, and the intermediate stationary period, except for leakage losses thermal and internal isothermalization.

In the transitory load, when host the heating fluid because its energy has to be stored thermal, it is identified which is the largest compartment temperature, below the temperature of the heating fluid, and They have to open their intake and exhaust valves. When said compartment is reaching a temperature close to that of fluid, between 10 and 20ºC below that of the fluid, must be open the valves of the next compartment, and close those of the had been charging with heat, repeating the operation so many times as necessary for the duration of the transitory.

In the thermal discharge operation of the storage is part of a fluid that must be heated, and start by opening the valves of the compartment that is at immediately higher temperature, at least 10 ° C above, that the fluid; operating like this until the fluid temperature is Approximately 10ºC below that of the compartment, and must be then open the one at an immediately higher temperature, closing the one that was open, and repeating the operation so many times as necessary while heating fluid is required, or until the storage can no longer give more heat, with the temperatures that are required.

Description of the figures

Then, to facilitate the understanding of the invention, by way of illustration but not limitation, will be described an embodiment of the invention that refers to a series of figures.

Figure 1 shows a device of low entropy thermal storage according to one embodiment particular of the invention, with four compartments of storage, attached to an upper and a lower pipe, by where the heating fluid that feeds the storage circulates and It is thermally nourished by it, as appropriate.

Figure 2 shows an alternative embodiment of the thermal storage device object of the present invention where different storage compartments go embedded inside each other, concentrically, the higher temperature in the innermost compartment, and decreasing outward, in such a way that losses are minimized net of heat.

Figure 3 represents a function of Statistical distribution, thermal energy being recorded in abscissa carried in a transitory, and in ordinates the frequency integrated.

This function is used to guide the compartment sizing, and choose their number.

In these figures reference is made to a set of elements that are:

one.

storage compartments of Energy

2.

filling the inside of the compartments

3.

support bed base

Four.

internal walls of the compartments

5.

fluid supply pipe to compartments

6.

fluid return pipe

7.

inlet valves

8.

outlet valves

9.

inlet connection pipes

10.

outlet connection pipes

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Description of preferred embodiments of the invention

As can be seen in Figure 1, the thermal storage device object of the present invention consists of a conduit pipe 5 which, in the mode of heat input, conducts the calorific fluid to the 1 energy storage compartments with a padding 2. Connecting pipes 9 and valves 7 complete the circuit fluid inlet The circuit is complemented with the pipe bottom 6, the connection pipes 10 to the bottom manifold, and the valves 8 of the lower manifold.

The storage compartments 1 of energy are provided with a filling material 2, being supported its weight by a base 3 of support of the filling 2. The compartments 1 are separated and thermally insulated from each other by the inner walls 4, and with the stiffness of said walls that require pressure differences of the case in question.

The calorific fluid flows through the 1 compartments in parallel circuits, but not in series, establishing the flows by opening or closing the valves 7, 8 of the compartments with the general collectors of supply and return of the heating fluid. In each of the compartments 1 as well as in the fluid manifolds there are temperature recording devices to know the status thermal fluid at each point of the installation; knowledge of this thermal map is basic to see how the loading or unloading procedure, as will be seen later.

Figure 2 illustrates another geometric arrangement preference of the invention, according to which the various compartments 1, energy storage, with its filling 2 They can be `configured as pressure tanks when conditions of the fluid as required, embedding the tanks one inside another, as an optimal solution to reduce the entropy generated by Store heat Note that this provision is similar to the structure of an onion with its different layers. In this layout each compartment has an interior wall and a wall exterior, except the first, which lacks interior wall. In the embodiment of figure 2 only three have been represented compartments 1, but extrapolation can be done for a invention of n compartments (n> 3); it is easily appreciated that the outer wall of an innermost compartment 1 acts as a wall inside of the next outer compartment 1. The walls of the different 1 energy storage compartments they have the appropriate thermal insulator to minimize leaks thermal and have the necessary thickness to withstand the pressures used in each application. Each compartment 1 is attached to the collectors of impulsion and return of the heating fluid, to the less, for a pipe in each case, 9, 10, and each one has its own corresponding valves 7, 8 opening and closing the passage of the fluid.

The invention is optimized by compartmentalizing the storage with appropriate size tanks thermal of the installation and the transients that are foreseen in this one, to prevent the energy of many of these transients from lose by temperature reduction. The compartmentalization must be done with volumes arranged in parallel, never in series, regarding fluid flow, and with the relevant valves to guide said flow exclusively where appropriate.

The thermal storage procedure works with a load transient, a download transient, and the intermediate stationary period, except for leakage losses thermal and internal isothermalization.

The transitory load is indicated by the black arrows in the figures, and the arrows without padding point the direction of the fluid in the thermal discharge of the storage.

All storage compartments 1 They must have their temperature recorder. When to welcome to the heating fluid because its thermal energy has to be stored, It is necessary to identify which compartment 1 is the largest temperature, below the temperature of the heating fluid, and their intake and exhaust valves must be opened. When said compartment 1 is reaching a temperature close to that of fluid, between 10 and 20ºC below that of the fluid, must be open the valves of the next compartment, and close those of the He had been charging heat. The operation is repeated so many times as necessary while the transitory lasts.

In the thermal discharge operation of the storage is part of a fluid that must be heated, and start by opening the valves of compartment 1 that is at higher temperature, at least 10 ° C above, than the fluid. When the temperature of the fluid approaches those 10ºC below from that of compartment 1, the one at temperature must be opened immediately superior, closing the one that was open. Thus repeat the operation while it is required to heat the fluid, or until that the storage can no longer give more heat, with the temperatures that are required. The invention must be sized agreement with the thermal transients to be done front in the installation. These must be determined by specifications of the overall design of the installation, or by hypothesis of its operation.

A function of Statistical distribution, thermal energy being recorded in abscissa carried in a transitory, and in ordinates the frequency integrated. In this function, the curve gives, for each energy E, a probability value, which is precisely the probability that the transitory one carries an Energy equal or inferior to the chosen one. In that sense, there is a maximum energy carried, E_ {M}, which is the  top of the function, and limit of the transients, and that serves to dimension the total storage, which is characterized by the mass M of the total filling 2, of all compartments 1. For determine this one needs to know the specific heat C of the material, and the temperature values between which the storage, which we will call T_ {m} to the minimum, and T_ {M} to maximum. These values are logically given by the design of the installation to be taken care of with storage. Specified all this, the mass M is the one that meets the equation next

E_ {M} = C M (T_ {M} - T_ {m})

The number of compartments 1 can be chosen at will, under the thermodynamic principle that, how many more 1 compartments are used, less energy is lost, less Entropy is generated.

In figure 3, by way of example, considers that there are four compartments 1. In this case, they are defined four tranches of probability, bounded by 25%, 50%, 75% and 100%, that through the distribution function give the values corresponding as indicated below:

E_ {1} = thermal sizing of the first compartment

E_ {2} = dimensioning of the sum of the two first

E_ {3} = dimensioning of the sum of the three first

E_ {M} = total dimensioning, already specified by the previous equation.

For the first compartment, its mass M_ {1} would be given by

E_ {1} = C M_ {1} (T_ {M} - T_ {m})

And for the second, of mass M_ {2}

E_ {2} = C (M_ {1} + M_ {2}) (T_ {M} - T_ {m})

And so on.

It remains to be clarified that this method of sizing is not required for the invention to work, which it will also be useful if another criterion is chosen, such as mass Filling equals in all compartments. However, of know the incidence of thermal transients at which attend, this is the recommended method.

The configurations should not be confused. described in this invention with the storage cascade thermal by phase change from various substances to various temperatures, such as those described for example in the document NREUSR-550-27925, already cited, and in which each storage is independent, and all are in series them with respect to the fluid that heats or cools them (depending on the phase of loading or unloading in which they are).

Nor can they be confused with sensible heat storage, independent of each other, which they do in some cogeneration and polygeneration facilities, in order to dedicate thermal energy, at various temperatures, to  different purposes, such as steam generation, production of cold by absorption, desalination and others, because in that case, as appreciate in the patent application US 2007/0220889 A1, where the storages are independent of each other, not compartmentalized internally, and located in different parts of the circuits of General installation energy. For each of these modules storage can and should be applied the presented invention, in order to reduce the entropy generated by heat transfer of the heating fluid to the filling.

Once the invention has been clearly described, notes that the particular realizations above described are subject to modifications of detail provided that do not alter the fundamental principle and the essence of the invention.

Claims (1)

1. Procedure for thermal storage low entropy, which includes - a first transitory stage of thermal load in a low entropy thermal storage device that comprises at least three compartments (1) with padding (2) that It comprises a set of solid geometric bodies, which absorb sensible heat from a calorific fluid, - a second stage substantially stationary, thermal storage in compartments (one), - and a third transitory stage of discharge thermal over a fluid to be heated by the filling (2) of the compartments (1), said process for thermal storage of low entropy characterized in that - the first transitory stage of thermal load in turn includes the sub-stages of

-

compartment identification (1) of higher temperature, below the fluid temperature heater

-

inlet valve opening (7) and the outlet valve (8) of the highest temperature compartment (1) for the passage of the fluid through it,

-

closing of the inlet valve (7) and the outlet valve (8) of said compartment (1) when it reaches a temperature between 10 and 20 ° C below the temperature of the heating fluid, and opening of the inlet valve (7) and the outlet valve (8) of the next compartment (1), repeating this sub-stage as many times as compartments (1) exist,

- and because the third transitory stage of thermal discharge includes the sub-stages from

-

compartment identification (1) of lower temperature, which is at least 10 ° C above the temperature of the fluid to be heated,

-

inlet valve opening (7) and the outlet valve (8) of the lower temperature compartment (1) that is at least 10 ° C above the temperature of the fluid at heating, for the passage of said fluid through it,

-

closing of the inlet valve (7) and the outlet valve (8) of the compartment (1) when the fluid reaches a temperature of 10 ° C less than said compartment (1), and opening of the valve inlet (7) and outlet valve (8) of the next compartment (1), which is at a higher temperature, repeating this sub-stage as many times as necessary to heat the fluid, or until the storage device thermal cannot transmit more heat to the fluid.