WO2008094094A1

WO2008094094A1 - Arrangement and methods for generating and recovering heat of hydration

Info

Publication number: WO2008094094A1
Application number: PCT/SE2008/000040
Authority: WO
Inventors: Mats MÖLLERSTRÖM
Original assignee: Camiltek Ab
Priority date: 2007-01-31
Filing date: 2008-01-18
Publication date: 2008-08-07
Also published as: SE530811C2; SE0700223L

Abstract

The invention relates to an arrangement for generating heat by hydrating salt and for recovering heat from salt being hydrated, comprising: a first container for holding particulate dehydrated salt; a second container for holding particulate hydrated salt; a transport mechanism for transporting salt particles from one of said containers to the other of said containers; a nozzle, arranged in connection with the transport mechanism; and a heat exchanger being arranged in connection with the transport mechanism between the nozzle and the second container. The transport mechanism is arranged to function as a reactor using the heat exchanger to recover heat being generated when the dehydrated salt particles are hydrated. The invention also relates to a method for generating heat by hydrating salt, and to a method for dehydrating salt, which salt has previously been hydrated in order to generate heat.

Description

ARRANGEMENTAND METHODS FOR GENERATING AND RECOVERING

HEAT OF HYDRATION

Field of the Invention

The present invention relates to an arrangement for generating heat by hydrating salt and for recovering heat from salt being hydrated. The invention further relates to a method for generating heat by hydrating salt, as well as to a method for dehydrating salt, which salt has previously been hydrated in order to generate heat.

Background of the invention

Hydrates are solid crystalline compounds containing water molecules as an integral part of the crystal, water of crystallisation. Many salts are known to be able to form a hydrate by including water in their crystalline structures.

Many of these salts spontaneously take up water molecules to a specific ratio, generating heat in the process, called heat of hydration. Analogously heat needs to be added in order to dehydrate the salts. A particular salt, sodium sulphide (Na₂S), is known to form the hydrates Na₂S-2H₂O, Na₂S SH₂O and Na₂S-9H₂O while generating heat. US 4 291 755 mainly discloses methods and systems for storing energy in salts through dehydration. According to this document the salt is dehydrated by dispersing it in a moving stream of hot oil, whereby it is transported as a slurry to a container having low pressure, whereby water is removed as vapour. The slurry may then be transported through pipes to a point where it is desired to utilise heat, at which point water is admixed with the slurry and heat is released. The system and methods are intended for industrial scale dehydration of salt and is not easily downsized for consumer use. Advanced equipment and handling skills are required for handling e.g. hot oil and vacuum. Also, the document is silent on how to perform the hydration of the dehydrated salt and on how this hydration may be linked to the dehydration.

Summary of the Invention

An objective of the present invention is to provide an arrangement, for recovering stored heat of hydration in salt, mainly for consumer use. An other objective is to provide a compact such arrangement of a manageable size for use in e.g. a private home.

An other objective is to provide an arrangement for recovering stored heat of hydration based on the specific heat recovery demand at each specific point in time.

Yet an other objective is to provide an arrangement for recovering stored heat of hydration, whereby the arrangement is also adapted for dehydration, and thus for storing energy in salt.

Still an other objective of the invention is to provide an arrangement for recovering stored heat of hydration, which arrangement is reliable in running and is made up of non-complex parts which may be easily replaced and maintained.

An other objective of the invention is to provide an arrangement for recovering stored heat of hydration, which arrangement is relatively inexpensive to produce.

Another objective still is to provide an arrangement for recovering stored heat of hydration which may be automated for regulating indoor heat.

In line with these objectives a novel arrangement has now been developed for recovering heat from energy stored in dehydrated salt. Thus, one aspect of the present invention, achieving at least a part of the above objectives, relates to an arrangement for generating heat by hydrating salt and for recovering heat from salt being hydrated. The arrangement comprises: a first container for holding particulate dehydrated salt; a second container for holding particulate hydrated salt; a transport mechanism for transporting salt particles from one of said containers to the other of said containers; a nozzle, arranged in connection with the transport mechanism, for adding water to the salt particles when said salt particles are transported by said transport mechanism from said first container towards said second container; and a heat exchanger being arranged in connection with the transport mechanism between the nozzle and the second container.

The transport mechanism is arranged to function as a reactor using the heat exchanger to recover heat being generated when the dehydrated salt particles are transported by the transport mechanism from the first container towards the second container while water is added by the nozzle to the dehydrated salt particles for hydrating the same. Thus, since the salt is being hydrated during transport, only the amount of salt needed for heat generation at a specific time may be hydrated, and the rest of the dehydrated salt may remain in its container for later use. In other words, the dehydrated salt does not have to get hydrated all at once, i.e. batch-wise. As the nozzle and heat exchanger are integrated with the transport mechanism, allowing the hydration and heat recovery processes to take place at it, the arrangement may have a compact and less bulky design.

The heat exchanger is arranged in connection with the transport mechanism downstream of the nozzle which allows it to recover heat of hydration as the salt particles are passing the heat exchanger after water having been added to the salt particles by the nozzle. Dehydrated salt particles may e.g. be obtained from an industry which dehydrates the salt using excess heat from its regular processes.

The transport mechanism of the above arrangement may be arranged to be activated upon receiving an activation signal after which it is continuously active until receiving a deactivation signal. Thus, the amount of salt being hydrated may be regulated in an automated fashion with the help of a control unit known to those skilled in the art. If the arrangement is e.g. used for regulating the indoor temperature of a house, the transport mechanism, as well as the nozzle and heat exchanger etc., may be activated based on the temperature dropping below a preset value, and may be deactivated e.g. based on the amount of salt that has been hydrated or based on the indoor temperature climbing above another preset value.

Alternatively, the arrangement may be designed to also be able to dehydrate the salt.

Thus, an embodiment of the inventive arrangement may further comprise a heater in connection with the transport mechanism. Said heater is arranged to heat salt particles being transported by the transport mechanism when hydrated salt particles are transported from the container holding hydrated salt towards the container holding dehydrated salt, dehydrating the salt during said transport. Thus, the flow of salt within the arrangement may be reversed, whereby the salt is hydrated and heat recovered when the salt is transported in one direction, and the salt is dehydrated/regenerated when the salt is transported in the opposite direction. Thus, the salt particles may be regenerated and may later once again be transported from the container holding dehydrated salt to the container holding hydrated salt while once again being hydrated and generating heat during the transport.

In accordance with this embodiment, the arrangement may function as a closed system with regard to the salt. When it is desired to obtain generated heat from the arrangement, dehydrated salt particles may be transported from the container holding them, be hydrated through addition of water, and be delivered to the container for hydrated salt. At times when such heat generation is not desired, or less desired, hydrated salt particles may instead be transported from the container holding them, be dehydrated by supplied heat, and be delivered to the container for dehydrated salt. The arrangement may thus be a convenient way of storing energy (from e.g. a solar or wind power station) when energy is available in excess, for use at a later time (e.g. for the heating of a house). As the transport mechanism is also used as the reactor for hydrating and dehydrating the salt, the salt present in the containers is not affected by whichever reaction, hydration or dehydration, that takes place. There is thus no need, in accordance with this embodiment, to first hydrate all of the salt of the container holding the dehydrated salt, and thereafter dehydrating all the salt in order to regenerate it. Instead it is possible to, as the need arises, hydrate only a part of the dehydrated salt. Later, when e.g. excess energy is available, a part of the hydrated salt may in an analogous manner be dehydrated.

The nozzle may be arranged to add water to the salt particles by spraying water onto said salt particles as they are being transported through a specific section of the transport mechanism towards the second container, i.e. the container for holding hydrated salt. By using a spray nozzle the water may be evenly dispersed over the salt being transported through the section of the transport mechanism where the nozzle is arranged, allowing for efficient uptake of the water molecules by the salt crystals. Evenly dispersing the water also minimises the risk of adding too much water to parts of the salt, possibly even dissolving this salt, while other parts of the salt receives too little water to be completely hydrated, not releasing all its stored hydration heat. Thus, using a spray nozzle provides for a high power economy. The transport mechanism may be any suitable transport mechanism, such as a conveyor belt, but conveniently the transport mechanism comprises a transport screw surrounded by a casing. A rotating screw within a casing is a convenient way of transporting particulate material. The screw may also facilitate mixing of the particulate salt in order for e.g. the water from the nozzle being intimately intermixed with the salt, providing good heat transfer from the salt to the heat exchanger and, analogously, providing good heat transfer from the heater to the salt. A screw also has the advantage of being able to transport the particulate salt in a non-horizontal direction, e.g. vertically upwards, implying that the transport screw may e.g. transport salt from the lower part, specifically the bottom, of the first container to the upper part, specifically the top, of the second container, and vice versa, without taking up much horizontal space, allowing the containers to be placed close together, compacting the arrangement further. It is thus preferred that the transport mechanism is non-horizontal.

Of course in some applications, such as if the first container is placed higher than the second container and salt is only transported from the first container to the second container, it may be more convenient to use a horizontal transport mechanism, such as a conveyor belt or a horizontal screw.

Also, if the first container is placed above the second container and salt is only transported from the first container to the second container, i.e. the arrangement is only arranged to hydrate salt and not to dehydrate salt, salt may be transported with the aid of gravity, e.g. through a pipe from the lower part of the first container to the upper part of the second container, where the transportation rate is regulated e.g. by adjusting the size of the opening allowing salt through the pipe. If transportation of salt from the second container to the first container is then desired, the relative positions of the two containers may be changed such that the second container is higher than the first container, e.g. by placing the first container where the second container was and vice versa. Since salt expands when it is hydrated, the transport mechanism needs to be able to accommodate a larger volume after water has been added to the salt than before said water addition. Thus, the transport mechanism may be designed for transporting a smaller volume per unit of time upstream of the section where the nozzle is arranged, and a larger volume per unit of time downstream of the nozzle, when dehydrated salt is transported towards the container for holding hydrated salt, allowing the salt to expand. When a transport screw is used different alternatives for accommodating this expansion may be used. The outer core diameter of the transport screw may vary longitudinally along the screw. The screw may thus be designed with a core having a larger outer diameter on the upstream side of the nozzle and a smaller outer diameter on the downstream side of the same, the thread diameter and the inner diameter of the surrounding casing, respectively, being essentially constant. Alternatively, the thread pitch or the thread diameter of the transport screw may vary longitudinally along the screw. The outer core diameter may then be the same both sides of the nozzle, but, in the case of a variable thread diameter, the casing inner diameter may be smaller upstream of the nozzle than downstream of the same.

The heater may be in the form of a longitudinal through hole within the core of the transport screw, which through hole is arranged to have a heating medium flowing there through. In this way the heating may take place along the whole of the transport mechanism, optimising the heat transfer to the salt. The heater is by this design also integrated with the transport mechanism, reducing the number of parts, and the size of the novel arrangement.

By arranging the heat exchanger around the outer periphery of the casing of the transport screw, the heat transfer from the salt is optimised while the heat exchanger is made easily accessible from outside the transport mechanism.

The casing of the transport screw may be rotatably arranged around its longitudinal axis. This facilitates that the casing may interact with different feeding and discharge mechanisms connected to the transport mechanism depending on whether salt is transported towards the second container or the first container, as the casing may be put in different positions by rotating the same. Again, this facilitates using the same transport mechanism for transporting the salt in both directions, while maintaining the size of the arrangement at a minimum. The feeding of, and discharging from, the transport mechanism may also, or alternatively, be controlled by other types of feeding and discharge mechanisms or valves, such as by a plurality of ball valves arranged in connection to the transport mechanism.

It may be desirable that one of or both of the containers of the inventive arrangement are removable and replaceable, in order to facilitate e.g. exchanging an empty container for holding dehydrated salt with a new filled such container, especially when the salt is dehydrated elsewhere e.g. in industrial scale at a power plant. The container holding the hydrated salt may, when all the dehydrated salt has been used, be removed and sent to e.g. such a plant for regeneration, and a container holding regenerated/dehydrated salt may be obtained in its stead. Depending on the design of the arrangement the new container holding dehydrated salt may replace the removed container holding hydrated salt, or replace the old, empty, container that held dehydrated salt. The possibility of dehydrating salt elsewhere is of course most important when the arrangement is not adapted to also dehydrate/regenerate the salt, but may also be a useful complement to arrangements being able to dehydrate the salt, when e.g. too little excess energy is available for the arrangement to use for dehydration. Removable containers may also be desirable in order to e.g. rinse the containers or replace damaged containers.

Provided that the inventive arrangement is designed to both hydrate and dehydrate salt, it may be desirable to arrange the arrangement such that the first and second containers together with the transport mechanism and feeding/discharging pipes form a closed system with regard to the particulate salt. Thus the salt never needs to leave the arrangement, but may be hydrated and dehydrated indefinitely, which keeps down the work hours for maintaining the arrangement as well as the cost, since the salt does not need to be exchanged and transported between the arrangement and e.g. a power plant for dehydration. This also reduces the risk of salt spill around the arrangement, thus reducing the cleaning needed and reducing the risk of salt particles jamming, corroding or otherwise interfering with any components outside of the closed system.

The amount of salt being hydrated or dehydrated is determined by the capacity of the transport mechanism in combination with the length of the time period when it is active. When the transport mechanism is active, it will create an essentially continuous flow of salt particles from one container to the other, of course provided that the container from which the transport mechanism is arranged to transport salt actually contains salt.

The reversible arrangement including a transport screw thus may comprise only two moving parts, the rotatable screw and the rotatable casing, improving the reliability of the arrangement and minimising the maintenance need as well as reducing the need for especially skilled or professional maintenance.

Additionally, the arrangement may be constructed of relatively few and conventional parts, making the arrangement less costly to produce and repair, and making spare parts readily available. Further, a novel method for recovering heat from energy stored in dehydrated salt has been developed. Thus, another aspect of the present invention relates to a method for generating heat by hydrating salt, and for recovering heat from salt being hydrated. Said method comprises: transporting dehydrated salt particles from a first container for holding particulate dehydrated salt towards a second container for holding particulate hydrated salt, using a transport mechanism; spraying the dehydrated salt particles with water during said transport, thus hydrating the dehydrated salt particles; and recovering heat generated by the hydration of said dehydrated salt particles.

Also, a novel method for dehydrating hydrated salt has been developed.

Thus, another aspect of the present invention relates to a method for dehydrating salt, which salt has previously been hydrated in order to generate heat. Said method comprises: activating a transport mechanism; using said activated transport mechanism for transporting hydrated salt particles from a second container, for holding particulate hydrated salt, towards a first container, for holding particulate dehydrated salt, the transport mechanism being continuously active until it is deactivated; heating the hydrated salt particles during said transport, thus dehydrating the hydrated salt particles; and deactivating the transport mechanism.

Brief Description of the Drawings

Fig. 1 is a perspective view of an arrangement according to the invention.

Fig. 2 is a front view of a pipe system of the arrangement of Fig. 1 allowing the containers to communicate.

Fig. 3 is a front view, partially cross-sectional, of a screw of the transport mechanism in the pipe system of Fig. 2, the view displaying three magnified details, wherein one shows a cross-section of the top of the screw, one shows a front view of a section of the screw where a spray nozzle is intended to be arranged, and one shows a cross-section of the bottom of the screw.

Fig. 4 is a front view of a casing around the transport screw of Fig. 3. Fig. 5 is a partial cross-sectional front view of an alternative screw and casing of the transport mechanism in the pipe system of Fig. 2. Fig. 6 is a front view of a pipe system of an alternative design according to the invention. Detailed Description of a Preferred Embodiment of the Invention

The invention will now be discussed in more detail and a specific preferred embodiment, as well as variations of the same, will be discussed by reference to the accompanying drawings. It should be noted that these discussions are merely intended for illustrative purposes and should not be construed as limiting the invention in any way.

With reference to Fig. 1 , the arrangement according to the invention includes a supporting frame 1 holding one container 2 for holding dehydrated salt, one container 3 for holding hydrated salt, and a pipe system 4 there between for allowing the containers to communicate with each other. At least two containers 2 and 3 for holding salt, one for holding dehydrated salt and one for holding hydrated salt, are needed. The size and shape of these containers are not critical, but their convenient holding capacities are dependent on their intended use. If, e.g., the arrangement is intended for heating a private detached house, the individual holding capacity of each of the containers is conveniently 100-5000 litres. Since dehydrated salt expands in volume, up to double size, as it is hydrated, it may be convenient to use a container 3 for holding hydrated salt which is larger than the corresponding container 2 for holding dehydrated salt. Thus, the container 2 for holding dehydrated salt may typically have a capacity of 200-1000 litres, preferably 300-800 litres, whereas the container 3 for holding hydrated salt may typically have a capacity of 500-2000 litres, preferably 700-1500 litres. If, on the other hand, the arrangement is intended for industrial applications, the containers 2 and 3 may be considerably larger. Now, with reference to Fig. 2 the pipe system 4 includes a central pipe arrangement 5 and four feeding/discharging pipes 6-9 communicating the central pipe arrangement 5 with the containers 2 and 3, as well as a condensation pipe 10. The central pipe arrangement 5 contains a transport mechanism (not shown). Outside of the central pipe arrangement 5 there are three separate heat exchangers 12 surrounding the central pipe arrangement 5. Below the lower-most heat exchanger 12 there is mounted a spray nozzle 13 arranged to, through a hole in the central pipe arrangement 5, spray water onto salt being transported by said transport mechanism. Below the spray nozzle 13, ends of two feeding/discharging pipes 8 and 9, one end of each pipe, are connected to the central pipe arrangement 5. The other ends of these two pipes 8 and 9 are arranged to be connected to respective bottom walls of the two containers 2 and 3 (Fig. 1). These two pipes 8 and 9 are arranged to feed salt from respective container 2 or 3 (Fig. 1) to the transport mechanism in the central pipe arrangement 5. Above the top-most heat exchanger 12, ends of two other feeding/discharging pipes 6 and 7, one end of each pipe, are connected to the central pipe arrangement 5. The other ends of these two pipes 6 and 7 are arranged to be connected to respective top walls of the two containers 2 and 3 (Fig. 1). These two pipes 6 and 7 are arranged to feed salt to respective container 2 or 3 (Fig. 1) via the transport mechanism in the central pipe arrangement 5.

At either ends of the central pipe arrangement 5 there are respective connections 16 and 17 for connecting a flow of heating medium, which will be explained below, forming a heater 11 of the arrangement.

The transport mechanism may be any transport mechanism capable of transporting particulate salt from one container to another, such as a conveying belt or a transport screw. In this preferred embodiment of the arrangement, the transport mechanism is a transport screw 18 (see Fig. 3). The transport mechanism might be horizontal, but it may be more practical if it is non-horizontal, e.g. vertical, such that it may transport salt from the bottom of one container to the top of the other if the containers are level with each other. Thus the salt may be fed to the transport mechanism via a pipe 8 or 9 by act of gravity alone.

The nozzle 13 for adding water to the salt may be arranged in direct connection with the transport mechanism, such that it may add water to salt being transported by the transport mechanism as the salt passes the section of the transport mechanism at which section the nozzle 13 is connected. This section is preferably close to where the dehydrated salt enters the transport mechanism. The nozzle 13 is preferably a spray nozzle. The amount of water added to the salt passing by the nozzle is preferably balanced with the amount of salt such that enough water is added for essentially hydrating the salt completely, but not more, since too much water would dissolve the salt rather than hydrating it and would unnecessarily add to the volume of the hydrated salt. In case of using sodium sulphide as the salt, 9HbO is preferably added per Na₂S.

The heat exchangers 12 of the arrangement are arranged in connection with the transport mechanism (not shown) downstream of the nozzle 13, i.e. above the nozzle in the disclosed embodiment, if salt is transported from the container 2 for holding dehydrated salt towards the container 3 for holding hydrated salt. The heat exchangers 12 are intended to recover heat generated as salt being transported by the transport mechanism is hydrated with water added by the nozzle 13. The salt transported by the transport mechanism is thus contacted with water and generates heat as it is essentially continuously transported towards the container 3 for holding hydrated salt, the heat being recovered between the nozzle 13 and the container 3 by the heat exchangers 12. Due to practical and/or technical considerations, it may be convenient to use a plurality of heat exchangers as disclosed, but the skilled man would find it obvious that only one heat exchanger may also be used. The heat exchangers 12 are preferably in direct contact with the transport mechanism or its casing 22 (see Fig. 4). The heat exchangers 12 may be arranged around the casing 22 of the transport mechanism, partly or completely encasing the same along a longitudinal section of said casing. As medium in the heat exchanger, any conventional medium may be used, such as water and/or glycol. With reference to Fig. 3, the transport screw 18 of this preferred embodiment will now be described. The transport screw 18 comprises a core 19 and an external thread 20. The core 19 of the screw 18 has a longitudinal through hole 21 , making the core 19 hollow. This through hole 21 is at either end connected to the connectors 16 and 17 (Fig. 2), respectively, for flowing heating medium through said through hole 21.

Because the salt expands in volume when it is hydrated by the water sprayed onto it by the nozzle 13 (Fig. 2), the screw 18, in combination with its casing, is adapted to accommodate this expansion. In this disclosed embodiment this is achieved by the core 19 having different outer diameters below and above the nozzle 13 respectively. Consequently the core 19 is divided into two sections, core section 19a with a first specific outer diameter below the nozzle 13 and core section 19b with a second specific outer diameter, smaller than the first outer diameter of core section 19a, above the nozzle 13. The outer diameter of the thread 20, as well as the inner diameter of the screw casing, is the same below and above the nozzle 13.

The heater 11 in accordance with the invention may be any heater capable of conferring enough energy to the salt being transported by the transport mechanism such that the salt is dehydrated. The heater 11 may e.g. be in the form of a heat exchanger using a heating medium, but microwave, gas or electrical heating may also be used. Specifically, the heat exchangers 12 used for recovering heat of hydration may also be used in the reversed manner, for conferring heat to the salt, when hydrated salt is dehydrated and transported towards the container 2 for holding dehydrated salt. In this way the inventive arrangement may also be used for cooling, and not only for heating, e.g. a house. In this preferred embodiment, when the transport mechanism is in the form of a transport screw 18, the heater 11 is preferably in the form of a longitudinal through hole 21 within the core 19 of the transport screw 18, through which hole 21 heating medium may flow, heating the screw 18 as well as the salt transported thereby. The heating medium may be any conventional heating medium, such as water and/or glycol. Additional heaters may also be used. To further assist in the dehydration, a vacuum or lowering of pressure may be applied such that the water more easily departs from the salt. While the hydrated salt is dehydrated by heating medium flowing through the through hole 21 during the transport from the container 3 (Fig. 1) to the container 2 (Fig. 1), the thus released water vapour rises along the screw 18 to condense when it reaches the condensation pipe 10 (Fig. 2), through which pipe 10 the condensate is removed from the transport mechanism.

Now, with reference also to Fig. 4, the casing 22 of the transport mechanism of this preferred arrangement will be discussed. When a transport screw 18 is used, as in this described preferred embodiment, the casing 22 is essentially an open ended hollow circular cylinder surrounding the transport screw 18. The casing 22 has three holes 23-25 in its wall. The nozzle 13 (Fig. 2) is mounted through the hole 23 for spraying water onto salt transported by the transport mechanism. The other two holes 24 and 25 are intended for admitting and discharging salt into or from the transport mechanism. In the disclosed embodiment, the screw 18 and its casing 22 are essentially vertical. In this embodiment, salt may be admitted through hole 24 in the casing 22 at the bottom of the screw 18, transported upwards, and discharged through hole 25 in the casing 22 at the top of the screw 18.

When dehydrated salt is transported towards the container 3 for holding hydrated salt, dehydrated salt from the bottom of the container 2 holding it may be fed to the screw 18 through pipe 9 by act of gravity and admitted through the hole 24 in the casing 22 at the bottom part of the screw 18. The dehydrated salt may then be transported by the rotating screw 18, the salt being hydrated and generating heat along the way, to the top part of the screw 18, where after the now hydrated salt is discharged through the hole 25 in the casing 22 at the top part of the screw 18, allowing it to enter through the top wall of the container 3 for holding hydrated salt via the pipe 6 by act of gravity. The salt transport direction when salt is hydrated is indicated by the arrows denoted "A" in Fig. 2. During this process there is no communication between pipes 8 and 7 and the transport mechanism, since the wall of the casing 22 is cutting off such communication.

When it is required that hydrated salt is to be dehydrated, i.e. the salt is transported from the container 3 for holding hydrated salt to the container 2 for holding dehydrated salt, the casing 22 may be rotated around its longitudinal axis such that the holes 24 and 25 in the wall of the casing 22, at the top and bottom parts of the screw 18, may connect with corresponding other pipes 8 and 7 allowing hydrated salt to be fed to the screw 18 by act of gravity and admitted through the hole 24 in the casing 22 at the bottom of the screw 18 and allowing the dehydrated salt to be discharged through the hole 25 in the casing 22 at the top of the screw 18, after being transported upwards by the rotating screw 18 and being dehydrated along the way, to enter the container 2 for holding dehydrated salt by act of gravity. The salt transport direction when salt is dehydrated is indicated by the arrows denoted "B" in Fig. 2. Accordingly, during this process there is no communication between pipes 6 and 9 and the transport mechanism, since the wall of the casing 22 is cutting off such communication.

Thus, regardless of if the salt is transported from the container 2 for holding dehydrated salt to the container 3 for holding hydrated salt or from the container 3 for holding hydrated salt to the container 2 for holding dehydrated salt, the transport screw 18 transports the salt essentially vertically upwards, and from which container to which container the salt is transported is merely dependent on how the casing 22 is rotated and which pipes 6-9 the casing holes 24 and 25 connect with. Preferably the respective pipes 6-9 are positioned such that a casing rotation of about 180 degrees is performed in order to change the salt transport direction.

Alternatively, the feeding of, and discharging from, the transport mechanism is not controlled by rotating the casing, but rather by e.g. four ball valves, one in each of respective pipes 6, 7, 8 and 9.

With reference to Fig. 2 again, the rotations of the transport screw 18 and its casing 22 respectively may be run by two separate motors, preferably electrical motors and preferably the motors are engaged with the screw and casing through respective belts 14 and 15. The screw 18 may e.g. be rotated by a belt 15 driven by a motor at the bottom of the central pipe arrangement 5, below the pipes 8 and 9 for feeding salt to the screw 18, whereas the casing 22 e.g. may be rotated by a belt 14 driven by a motor at the top of the central pipe arrangement 5, above the pipes 6 and 7 for feeding the containers 2 and 3 with salt.

An alternative design of the transport screw for accommodating the expansion of salt as it is being hydrated is illustrated by Fig.5, wherein the screw core 19' has a constant outer diameter longitudinally along the screw, but the outer diameter of the thread 20' as well as the internal diameter of the casing 22' is smaller below the nozzle 13 (Fig. 2) than above said nozzle 13. It is to be understood that accommodating the expansion of salt may also be achieved by providing the screw with a pitch varying along the longitudinal axis of the screw.

Fig. 6 discloses an alternative design of the pipe system 4', which is adapted to accommodate a horizontal transport mechanism within its central pipe arrangement 5'. This design may e.g. be used if the inventive arrangement is only used for hydrating salt, not for dehydrating salt, whereby the first container is placed higher than the second container and salt is only transported from the first container to the second container. Dehydrated salt may be introduced, from the first container, to the central pipe arrangement 5' via the pipe 9', e.g. by act of gravity, after which the salt is transported by means of a transport mechanism within the arrangement 5' to the pipe 6', through which pipe 6' the salt is introduced into the second container. During said transport, water is added via the nozzle 13' and the salt is hydrated, generating heat. The transport mechanism within the central pipe arrangement 5' may e.g. be a horizontal transport screw or conveyor belt.

The inventive arrangement may be controlled either manually, such as by activating and deactivating it by the press of a button, or in an automated fashion. For the automated fashion the arrangement may be controlled through a control unit (not shown) which activates and deactivates the arrangement based on pre-programmed parameters. If the arrangement is used for the heating of a house, the control unit may e.g. detect the room temperature and may send an activation signal to the arrangement when the temperature needs to be raised, and will send a deactivation signal when enough heat has been generated from the salt. If the arrangement is also able to dehydrate salt, the control unit may also activate the arrangement in reverse in an analogous manner, based e.g. on when excess heat is available or if no dehydrated salt remains. When the arrangement is activated by an activation signal, the transport mechanism starts to transport salt from one container to the other in an essentially continuous manner, heat exchange medium or heating medium starts to flow, the nozzle starts to add water, etc, depending on if salt is hydrated or dehydrated.

Sodium sulphide, Na₂S, is a preferred salt for use in the invention, but many other salts may also be utilised, such as aluminium chloride, AICI₃; aluminium sulphate, Al2(SO₄)₃; barium hydroxide, Ba(OH)₂; chromium(lll) sulphate, Cr₂(SO₄)₃; iron(lll) nitrate, Fe(NO₃)₃; iron(lll) chloride, FeCI₃; iron(ll) sulphate, FeSO₄; iron(lll) sulphate, Fe₂(SO₄)₃; potassium hexa-cyano ferrate(ll), K₄Fe(CN)₆; cobalt(ll) chloride, CoCI₂; magnesium chloride, MgCI₂; magnesium nitrate, Mg(NO₃)₂; magnesium sulphate, MgSO₄; manganese(ll) chloride, MnCI₂; sodium tetra-borate, borax, Na₂B₄O₇; sodium carbonate, Na₂CO₃; sodium di-hydrogen phosphate, NaH₂PO₄; sodium hydrogen phosphate, Na₂HPO₄; sodium phosphate, Na₃PO₄; nickel(ll) chloride, NiCI₂; tin(ll) chloride, SnCI₂; and zinc nitrate, Zn(NO₃)₂.

Claims

1. An arrangement for generating heat by hydrating salt and for recovering heat from salt being hydrated, comprising: a first container (2) for holding particulate dehydrated salt; a second container (3) for holding particulate hydrated salt; a transport mechanism for transporting salt particles from one of said containers (2,3) to the other of said containers (2,3); a nozzle (13; 13'), arranged in connection with the transport mechanism, for adding water to the salt particles when said salt particles are transported by said transport mechanism from said first container (2) towards said second container (3); and a heat exchanger (12) being arranged in connection with the transport mechanism between the nozzle (13; 13') and the second container (3); the transport mechanism being arranged to function as a reactor using the heat exchanger (12) to recover heat being generated when the dehydrated salt particles are transported by the transport mechanism from the first container (2) towards the second container (3) while water is added by the nozzle (13; 13') to the dehydrated salt particles for hydrating the same.

2. The arrangement according to claim 1 , whereby the transport mechanism is arranged to be activated upon receiving an activation signal after which it is continuously active until receiving a deactivation signal.

3. The arrangement according to any one of the preceding claims, whereby the nozzle (13; 13') is arranged to add water to the salt particles by spraying water onto the salt particles as they are being transported through a section of the transport mechanism towards the second container (3).

4. The arrangement according to any one of the preceding claims, further comprising a heater (11) in connection with the transport mechanism, said heater (11) being arranged to heat salt particles being transported by the transport mechanism when hydrated salt particles are transported from the second container (3) towards the first container (2), thus dehydrating the salt.

5. The arrangement according to any one of the preceding claims, whereby the transport mechanism comprises a transport screw (18) surrounded by a casing (22;22').

6. The arrangement according to any one of the claims 1-3, whereby the arrangement further comprises a heater (11) in connection with the transport mechanism, said heater (11) being arranged to heat salt particles being transported by the transport mechanism when hydrated salt particles are transported from the second container (3) towards the first container (2), thus dehydrating the salt; and whereby the transport mechanism comprises a transport screw (18) surrounded by a casing (22;22'), the heater (11) being in the form of a longitudinal through hole (21) within the core of the transport screw (18), which through hole (21) is arranged to have a heating medium flowing there through.

7. The arrangement according to any one of the claims 5-6, whereby the transport screw (18) is non-horizontal.

8. The arrangement according to any one of the claims 5-7, whereby the outer core diameter of the transport screw (18) varies longitudinally along the screw.

9. The arrangement according to any one of the claims 5-7, whereby the thread pitch of the transport screw (18) varies longitudinally along the screw.

10. The arrangement according to any one of the claims 5-7, whereby the thread diameter of the transport screw (18) varies longitudinally along the screw.

11. The arrangement according to any one of claims 5-10, whereby the heat exchanger (12) is arranged around the outer periphery of the casing

(22;22') of the transport screw (18).

12. The arrangement according to any one of claims 5-11 , whereby the casing (22;22^J) of the transport screw (18) is rotatably arranged around its longitudinal axis.

13. The arrangement according to any one of the preceding claims, whereby the first container (2) and/or the second container (3) is removable and replaceable.

14. The arrangement according to any one of claims 4-13, whereby the first and second containers (2,3) together with the transport mechanism and feeding/discharging pipes (6-9) are arranged to form a closed system with regard to the particulate salt.

15. A method for generating heat by hydrating salt, and for recovering heat from salt being hydrated, said method comprising: transporting dehydrated salt particles from a first container (2) for holding particulate dehydrated salt towards a second container (3) for holding particulate hydrated salt, using a transport mechanism; spraying the dehydrated salt particles with water during said transporting, thus hydrating the dehydrated salt particles; and recovering heat generated by the hydration of said dehydrated salt particles.

16. A method for dehydrating salt, which salt has previously been hydrated in order to generate heat, said method comprising: activating a transport mechanism; using said activated transport mechanism for transporting hydrated salt particles from a second container (3) for holding particulate hydrated salt towards a first container (2) for holding particulate dehydrated salt, the transport mechanism being continuously active until it is deactivated; heating the hydrated salt particles during said transporting, thus dehydrating the hydrated salt particles; and deactivating the transport mechanism.