US20110146939A1

US20110146939A1 - Energy absorption and release devices and systems

Info

Publication number: US20110146939A1
Application number: US12/926,883
Authority: US
Inventors: Damian Joseph Peter Bond; Douglas Nangle
Original assignee: Carbon Zero Ltd
Current assignee: Carbon Zero Ltd
Priority date: 2008-06-16
Filing date: 2010-12-15
Publication date: 2011-06-23

Abstract

A thermal storage device comprising a container containing a body of zeolite comprising a zeolite sieve and thermally conducting fins extending substantially into the body of zeolite in which said thermally conducting fins are thermally connected to a heat source.

Description

This invention relates to systems and devices for absorbing and releasing thermal energy. The invention can be used in a number of ways, examples include systems and devices:

- to absorb thermal energy produced, for example by an electrical heater, solar panel or a wind turbine and subsequently to make energy available when is required by a consumer;
- to absorb energy from a cooling system and to dissipate it externally to the cooling system;
- to purify or sterilize water.

One particular aspect of the invention describes a device for converting rotational energy to thermal energy, absorbing it, subsequently releasing thermal energy.
Energy storage means are well known, for example normal electrical rechargeable batteries, ceramic materials used in storage heaters and hot water cylinders. But all are relatively inefficient. The systems and devices described in this invention can operate efficiently directly using energy generated from so called green sources, such as wind generators and solar power. In both cases peak energy generation does not usually match peak demand and a relatively efficient means of absorbing and subsequently releasing energy is needed.
JP 2004003832 A (DENSO CORP) 18/01/2004 proposes a thermal storage system comprising a material which releases heat when water is supplied and absorb heat by ejecting water when heated. The material can be a hydrate of calcium chloride, caldium bromide, lithium bromide, or zeolite. This device requires the material to be sprayed with water droplets on top of the material and absorption of water by the material is poor.
U.S. Pat. No. 4,741,028 B (ALEFELD) 18/10/1983 describes a system for storing and upgrading heat in which a zeolite is used to absorb relatively warm water under pressure and requires significant energy supply and is not an energy storage system of the kind being addressed here.
U.S. Pat. No. 4,742,868 B (MITANI) 18/05/1988 describes a thermal energy storage system using, inter-glia, a zeolite medium for storage. But the system does not ensure widespread distribution of heat within the zeolite during discharge or efficient distribution of water vapour within the zeolite on recharge, thus the system is relative inefficient.
EP 1666140 A (TOSOH CORPORATION) Jul. 6, 2006 describes a zeolite-water heat pump system and an open cycle moisture adsorption-desorption system. Total efficiency is still relatively poor as heat and water vapour is not distributed widely and quickly within the zeolite, and a separate pump is needed to evacuate the zeolite.
In this invention a device for absorbing and releasing thermal energy comprises a container containing a body of zeolite characterised in that thermally conducting fins extending substantially into the body of zeolite and in that said conducting fins are thermally connected to a heat source. Although very useful for use with alternative energy generation, the invention can also be used with conventional energy sources. The invention can also be used as a sink for unwanted energy, say as part of an air conditioning system for a closed room or building; and subsequent discharge of that energy externally.
Issues with associated with distribution and removal of water vapour can be improved when a device of the kind described herein has one or more ducts to conduct water vapour into and out of the container wherein said ducts have a plurality of apertures allowing water vapour into and out of the zeolite molecular sieve.
In one embodiment the said one or more ducts may be in a central core disposed generally around a central axis of the container. In another embodiment the one or more ducts may be disposed on an inner wall of the container, and preferably be part of said wall.
Greater efficiency is obtained when heat is conducted to the zeolite molecular sieve through a plurality of fins extending into the body of zeolite, with the optional addition of spines extending laterally from the fins.
In one configuration of such a device the container has with at least one electrical heating element at the core of the container thermally connected to the zeolite molecular sieve by radiating fins and spines extending laterally there from. In such a configuration the core may also contain the ducts. If the cylinder is cylindrical greater efficiency is obtained as heat and water vapour are distributed evenly throughout the device.
In another configuration of such a device the heat energy source is a solar panel. In further device according to the invention the heat energy source is provided by magnetic fields generating a magnetic flux in the device. In both these cases the ducts are conveniently formed on the inside wall of the container.
In this invention the means to allow expulsion of water vapour may be connected to a condenser and means is provided to recover heat from the condenser.
Further the device of this invention may incorporate a switchable valve at any one time to allow expulsion of water vapour to a condenser or entry of water vapour from an evaporator.
Conveniently in a device according to the invention the means to admit water is coupled an evaporator to evaporate water at low pressure and temperature, which evaporator is connected to a low grade heat source.
In one possible application of the device to water purification in which expulsion of water vapour is to a condenser, the heat recovered from the condenser may be used to provide low grade heat to an evaporator and/or to a de-aerator. In this device the means to admit water vapour is connected to the evaporator, which in turn is connectable to a source of impure water. Conveniently a de-aerator is connected between the source of impure water and the evaporator.
In water purification system using a device according to the invention and having a condenser to condense water vapour expelled from the zeolite molecular sieve, means is provided to collect water from this condenser.
In cooling system having a device according to the invention, the means to admit water vapour is connected to an evaporator and the evaporator has a heat exchanger to take heat from a cooling system to vaporise water in the evaporator.
A number of devices of this invention may be linked with the means to allow expulsion of water vapour from each container being connected to a single condenser and the means to admit water vapour is connected to a single evaporator. In such a situation a control system can be provided such that the zeolite in different containers may be at different stages of their charging and or discharging.
By passing a heat transfer medium in a conduit going through the container, the heat generated by the exothermic reaction can be removed from the system. It will be seen that the device is thus a thermal storage thermal storage device charged when water vapour is driven from the zeolite absorbing thermal energy from the heat source, and discharged by releasing thermal energy when water vapour is admitted to the zeolite molecular sieve. The expression “charge” herein describes the action of driving water vapour from the zeolite molecular sieve in the container, the expression “discharge” herein describes the action of allowing water vapour into the zeolite molecular sieve creating heat by water vapour rejoining the zeolite structure and releasing heat exothermically.
The expression “zeolite molecular sieve” herein describes a presentation of zeolite with pore sizes similar to the molecular size of a water molecule in which when water vapour is able to react with and be absorbed into the pores or be driven from the pores of the zeolite structure.
The rate at which water vapour enters the zeolite molecular sieve can be used to control the rate of heat generation and thus the rate of discharge. When such a thermal storage device is used as a thermal storage battery, heat is transferred from the device to the place at which it is to be used by a heat transfer fluid passing through ducts. The ducts can be heated by the heat being released from the zeolite molecular sieve during discharge. The heat transfer fluid can be liquid or gas. Water, however, is cheap and is suitable for most applications.
When the thermal storage device is seen as a thermal battery the thermal energy generated by the exothermic reaction during full discharge of the thermal storage device is only a little less than the thermal energy absorbed during charging, and the device is very efficient. Thermal efficiency is improved even further by condensing the water vapour driven off from the zeolite molecular sieve during charging and using the latent heat released by condensation and also by using heat released from the device as it cools after charging, and before discharge starts. Efficiency is improved further if the container is surrounded with a conventional thermal insulator, which can be spaced apart from the container itself to provide an additional insulating air gap.
In one embodiment of such a thermal storage system the body of zeolite is supported in a metal matrix, comprising thermally conducting fins extending substantially into the zeolite molecular sieve, with spines extending laterally from the spines into the body of the zeolite molecular to ensure excellent thermal connection between the source of heat and the zeolite molecular sieve. Such a structure is called a “zeolite matrix”. Aluminium is particularly suited for use at the spines and fins and for the container itself as it has good thermal conductivity and is light. The container itself can be of modular construction using extruded aluminium sections.
If electrical heating is used as the heat energy source it can be mains supplied, more economically. More economically, however, the electrical heating can come from a wind turbine or wave generator.
Solar heating from a solar panel is also a very economic form of heat, and the heat energy from such a source is very conveniently stored in the device of this invention by linking the panel to the device by a high thermal conductivity material.
When the device is part of a cooling system, for example, an air conditioning system, power can be drawn from solar energy or from more normal conventional sources. Such device is discharged by drawing water vapour from an evaporator which has a heat exchanger with circulating fluid being the part of a conventional air conditioning system which evaporates water vapour. In the charging cycle, energy, say, from a solar panel is used to heat the zeolite molecular sieve and drive off water vapour absorbed by the zeolite into a condenser. When the device cools, a vacuum is created in the zeolite container which in turn draws water vapour from the evaporator, repeating the cycle cooling the circulating fluid in the air conditioning system. In this configuration the device provides a low energy air-conditioning system particularly for use in hot sunny climates, where the power consumption of conventional air conditioning systems is very high.
The invention can be used as part of a water purification system, for example a desalination plant. The device can draw power from solar energy or from more normal conventional sources. The device is discharged by drawing water vapour from an evaporator which is fed by impure water. When the thermal storage device is discharged and charging begins the water vapour driven out is pure and can be collected in a condenser for use. Latent heat released from condensation, and heat released from the device while cooling and discharging can be recycled to the evaporator to improve efficiency. Such heat can also be used in a de-aeration stage for de-aerating the impure water before it enters the evaporator. A system of this kind can be used for emergency sterilization.
A number of devices according to the invention can be connected to the heat energy source to ensure constant operation, for example in a desalination plant.
In other applications the input shaft can be driven form other rotatable outputs, the output shafts of wave energy devices would be one possibility.
It should be noted too that in a particularly interesting embodiment of the invention the device can be heated inductively by a magnetic field rotating about permanent magnets at the core of the device. This is particularly useful in thermal storage applications and in water purification. The rotatable magnetic field is coupled directly to an input shaft coupled to a wind turbine which can be used to charge the device when wind conditions are suitable.
One issue is that under normal conditions, heating a zeolite to drive off water vapour as part of a thermal store requires temperature within the store to be raised to 200° C. and this cannot be achieved easily or cheaply from environmental heat sources such as solar or geothermal in cooler climates such as those found in Northern Europe or in the northern part of North America.
In a further embodiment of the invention therefore this invention a thermal storage system comprising a zeolite molecular sieve in a container coupled to a thermal collector wherein water vapour is desorbed from the zeolite molecular sieve by heating the sieve at a pressure below that of atmospheric pressure.
In such a thermal storage system the zeolite molecular sieve is at a higher pressure after any re-sorption step than during any de-sorption step.
The storage system of this invention is particularly useful with a thermal collector that is a solar collector and desorption occurs under reduced pressure (compared to atmospheric pressure) to allow desorption of zeolite to occur at temperatures achievable by solar thermal collectors. In such a system desorption can be at about 80° C.
In such a system the pressure in the various parts of the system can be cycled between low and high pressures to allow desorption of water vapour from the zeolite to occur at temperatures achievable by solar thermal collectors and adsorption of water vapour from the zeolite to occur at higher pressure to liberate heat at a higher temperature than that at which desorption occurs. At least 150° C. is achievable during the adsorption stage.
Ideally the pressure in the evaporator is reduced to allow water to boil at low temperatures less than 50° C. and low grade heat energy is supplied to the evaporator. By reducing the pressure in the evaporator to allow water to boil at low temperatures (say 5-50° C.) and supplying low grade heat energy to the evaporator from an environmental source, such as external air outside a building in which the storage system is installed, the overall efficiency of the system can be improved, increasing the co-efficient of performance up to 2 times. The thermal collector may, for example, be a geothermal heat collector or solar panel source.
In another embodiment of the invention a thermal storage and release system comprises:

- a. at least one thermal collector having first ducts therein for the transport of a heat collecting fluid;
- b. a thermal storage device having a container with a zeolite molecular sieve therein, the device incorporating a means to provide for unidirectional flow of water vapour on its expulsion from the zeolite molecular sieve and means to admit water vapour to the zeolite molecular sieve;
- c. one or more second fluid ducts in or around the container connected to the first ducts to provide a thermal path from the collector to the zeolite molecular sieve;
- d. a condenser to receive water vapour driven from the zeolite molecular sieve;
- e. an evaporator to supply water vapour to the zeolite molecular sieve under reduced pressure when heat is demanded of the system.

The heat collecting fluid may be any suitable fluid, including gases. Water is the cheapest most convenient fluid, but refrigerants, and gases such as nitrogen are easily used.
In the above embodiment, the zeolite molecular sieve may be heated by the thermal collecting fluid passing through said second ducts to drive water vapour from the zeolite molecular sieve and out of the container and wherein water vapour is admitted into the zeolite molecular sieve when heat is demanded. The thermal collector having first ducts may be a conventional water circulating solar collector such as the TUBO 12™ CPC tube collectors or PLANO 26™ flat plate collectors both marketed by Corisolar GmbH of Frankfurt. However there are may other similar solar collectors on the market which using water as the thermal transport means in the same way. Alternatively, a parabolic mirror collector may be used focussing solar energy onto first ducts at the centre of the mirror, in some situations such a collector my raise the temperature of the heat collecting fluid considerably.
Conventionally such thermal collectors are coupled to a thermal store comprising a conventional insulated hot water cylinder connected to provide hot water to, say, a building. Although cheap and simple to install such thermal collectors were not previously generally thought to be suitable for supplying heat to buildings.
Although conveniently water is used as the thermal transport fluid, other fluids, such as conventional refrigerants may be used instead.
To achieve the desired desorption temperature the pressure in the container should be 0.2 bar or less.
In a further variant after re-sorption the pressure within the store is higher than that at which desorption occurs and is normally atmospheric pressure.
In one embodiment the zeolite store, condenser, and ducting and valves there between are a hermetically sealed unit pressurised initially at 0.2 Bar or less.
In a variant on this latter embodiment a pump is disposed between the zeolite store and condenser to reduce pressure in the store on starting desorption and in addition means (such as an air valve) is provided to restore the pressure in the store to atmospheric pressure when re-sorption is complete.
Such a thermal storage system described above is designed to be a constituent of a heating system, but its use is not so limited and in particular it may at least be part of a Rankine cycle to generate electricity. As part of a Rankine cycle the zeolite heat storage cell would also contain sealed passageways for a refrigerant liquid to be heated by zeolite adsorption and be boiled to a high pressure gas. This gas refrigerant would then drive an expander such as a scroll or turbine. Once the gas has passed through the expander (driving an electrical generator) it would be cooled and condensed back into a liquid. The efficiency of such a heat engine is improved by extending the temperature range between the hot gas expansion and the cold gas compression regions. Combining the Zeolite system with the Rankine cycle system provides two advantages. The evaporator unit in the zeolite system provides a cool source as the liquid boil and draws energy of evaporation from the liquid. Linking this to the condenser unit of the Rankine cycle improves the efficiency of the heat cycle is supplied to the evaporator of the zeolite system, recycling the energy and improving the co-efficient of performance.

In this specification “adsorb” refers to the adsorption of water vapour into the zeolite molecular sieve, “desorption” refers to the release of water vapour from the zeolite molecular sieve, during the adsorption phase heat is released from the zeolite molecular store and during the desorption phase the heat is taken into the zeolite providing the energy to expel the water and the energy is effectively stored until the next adsorption phase occurs.

FIG. 1A shows a partial section through a device according to the invention forming a thermal storage battery;

FIG. 1B is an end on view of the section shown in FIG. 1A;

FIG. 2 shows schematically a thermal storage system comprising a number of thermal batteries of the kind shown in FIG. 1.

FIG. 3 shows a section through a thermal storage device according to the invention in which the heat source is a solar panel.

FIG. 4A shows a number of thermal storage batteries according to the invention mounted in an insulating container;

FIG. 4B is a plan view of the thermal storage batteries of FIG. 4A;

FIG. 4C is a section on the line A-A′ of FIG. 4B;

FIG. 4D is a detail view of the area B in FIG. 4C;

FIG. 5A shows a partial section of a device according to the invention similar to that of FIGS. 3A and 3B but used as part of a cooling system;

FIG. 5B is an end on view of the section of FIG. 5A;

FIG. 6 is a schematic diagram of such a cooling system;

FIG. 7 is a schematic diagram illustrating the use of a device according to the invention as part of a desalination system;

FIG. 8 shows device according to the invention used in a desalination system and charged by a rotating magnetic field;

FIG. 9 shows a schematic installation for a heating system according to in which desorption takes place under reduced pressure invention; and

FIG. 10 is a cross section showing in more detail inside of zeolite thermal store of FIG. 9.

In FIGS. 1A and 1B, a device according to the invention used as a thermal storage device comprises a cylindrical container 1 having an inner wall 2 made of extruded aluminium sections. The ends (not shown) of the cylinder are closed by aluminium caps. The container 1 is separated by a gap 3 from an insulating outer wall 4. The gap 3 is filled with insulating material such as rock wool. An extruded aluminium central core 5 has a plurality of radial aluminium fins 6 extruding to the inner wall 2. Each fin 6 has a number of aluminium spines 7 extending the length of the cylinder and formed as arcs around the central core 5. The region between the inner wall 2 and the central core 5 is filled with a zeolite forming a zeolite molecular sieve 8. The zeolite known as X13 is particularly efficient in this application. The configuration of the fins 6, spines 7 makes for good heat transfer to the central core 5 and the zeolite 8, the spines 7 forming a fine mesh to contact the zeolite molecular sieve 8. It will be seen that the combination of zeolite 8, fins 6 and spines 7 forms a zeolite matrix.
The central core itself has a number of slots 9 on its periphery in which the fins 6 are mounted. Close to the surface of the core are a number of ducts 10 for water vapour. The ducts 10 have slots 11 to the zeolite molecular sieve 8, through which water vapour may pass.
A series of heat transfer pipes 12 run the length of the central core 5. For a system used in a domestic or light industrial situation, water would often be used as the heat transfer medium. In this situation the heat transfer pipes would connect to a hot water supply and/or a heat exchanger that is part of a central heating system. But there is no reason why other heat transfer media should not be used, including steam or air as part of the warm air supply in an air conditioning system.
Along the axis of the central core is disposed an electrical heater 13 connected to a source of electricity. In practice the ducts 10 are connected through the end caps of the cylinder, on one side via a non-return valve to a condenser and on the other side to a low-pressure evaporator. Initially, the zeolite molecular sieve 8 is fully charged with water molecules.
The electric heater is connected to its supply. This heats the zeolite molecular sieve 8 forcing the chemically absorbed water in the zeolite out as water vapour, through the slots 11 and ducts 10 out of the cylinder. This water vapour passes through a non-return valve to a condenser (not shown). This charges the battery. After charging, water is passed through the heat transfer pipes 12, cooling the interior of the cylinder. Any water vapour remaining in the cylinder is reabsorbed into the zeolite molecular sieve 8, creating a vacuum. This vacuum draws low-pressure water vapour through the ducts 10 and slots 11 into the zeolite molecular sieve 8. As the water vapour is absorbed into the zeolite molecular sieve it combines in an exothermic reaction with the zeolite releasing heat, this heat release gradually discharges the thermal storage device until no more water vapour can be taken back into the zeolite, at which point discharge is complete. The heat thus released is transferred via the spines 7 and fingers 6 to the central core 5 where it heats water passing through the heat transfer pipes 12. It can be seen that heat taken from the thermal storage device both during cooling and discharge is available for use.
In a full system, it is unlikely that a single device as described would be entirely satisfactory, as it can only be charging or discharging at any one time. Thus in FIG. 2 shows a schematic heating system that is more likely to be adopted in practice. In FIG. 2 a plurality of thermal batteries 20 of the kind shown in FIG. 1 is shown. The vapour duct 10 of each of the batteries 20 is connected to the combined condenser and evaporation unit 16, with low pressure vapour capable of being drawn from the evaporator, and vapour forced out of the cylinders being passed through a non-return valve to the condensing side of the unit. The heat transfer pipes of each thermal storage device are connected through a common duct 17 to the system output. Electrical energy is passed through a control system 18 to be directed to the batteries being charged. At the same time charged batteries can be discharged to provide heat output to the duct 17.
Latent heat from the condensation of water vapour can be used for heating purposes.
It can be seen that if this system is used with a variable and unpredictable energy source such as a wind turbine, continuous output can be obtained, whilst the control system switches a number of batteries to charge when input is available.
This system is an economic solution to thermal energy. It may also be more reliable than existing systems over long periods of time. In contrast to conventional storage heaters, which discharge as soon as they are warm, the thermal storage device would only need to be discharged when there is a need for thermal energy in contrast to conventional storage heaters, which discharge as soon as they are warm. The input to such a system could be from a variety of sources, solar or a wind turbine driven heat operating device. With large enough storage cylinders, substantial amounts of thermal energy could be stored (up to 275 KW per cubic meter). One option would be to convert the output to electricity. Such converting devices do exist, such as heat engines coupled to generators. Steam turbines and Stirling engines are particularly suitable.
In FIGS. 3A and 3B a thermal storage device 21 comprises a container 22 filled with a zeolite molecular sieve 23. Fins 24 extend from the wall of container 22 into a zeolite molecular sieve 23 to help transmit heat into and out of the zeolite molecular sieve. A tube 25 runs within the container and through the container's end caps (not shown). A slot 26 through the wall of the tube 25 allows passage of water vapour into and out of the zeolite molecular sieve 23 via the tube 25. Ducts 27 thermally connected to the container allow the flow of a heat transfer medium. For many applications, water is perfectly satisfactory as the heat transfer medium. Thermally coupled to the container is a thermal collector 28. In this example, it is a large surface planer collector. The thermal collector has a thermally absorbing coating 29 which in its simplest for is matt black paint, but commercially available solar absorbing paints would be preferred.
The solar collector is further supported on the container by spars 30, which also provide the thermal coupling to the container. In this construction, the container 22, fins 24, ducts 25 and 27, collector 28 and spars 29 are manufactured in extruded aluminium. Aluminium has high thermal conductivity, is robust and easily fabricated, however, other high thermal conductivity materials such as copper could be used. The container 22 is oval in cross section to allow for maximum transmission of heat from the panel 28 to the entire zeolite molecular sieve 23. The assembly is mounted in an open topped box (not shown) which is made of insulating material, and the volume between the box and the assembly filled with conventional insulating material. In this configuration the solar panel is exposed to the sun beneath a solar glass plate closing the top of the box.
Operation is similar to the electrically heated thermal storage device of FIGS. 1A and 1B, however, the source of heat is the solar panel 28. Heat from the panel is transmitted through the container 22 and fins 24 to the zeolite. This drives water vapour from the zeolite molecular sieve 23 through slots 26 and ducts 25, out of the thermal storage device 21 through a non-return valve. When the solar panel is not exposed to the sun, the container and zeolite cool and any remaining water vapour in the container recombines with the zeolite creating a vacuum within the container 22. Low-pressure low temperature water vapour is admitted to duct 25 through slot 26 into the zeolite molecular sieve. This combines with the zeolite in an exothermic reaction releasing heat. This heat is taken from the thermal storage device by water flowing through ducts 27. This heat can be used for hot water systems, central heating systems or converted into electricity.
A series of such thermal storage batteries can be controlled such that some may be charging and others discharging at the same time, providing a continuous source of energy. The devices can be charged at times when plenty of thermal energy is available and maintained in a charged condition until energy is needed. Typically a single thermal storage device would have a solar collector 28 which is 200 mm wide by 1000 mm long. The speed of charging will vary depending on location and weather conditions.
Pipes connected to the ducts 25 to carrying water vapour should be sealed and evacuated of air. These pipes are connected to a small vessel, which would act as a condenser and evaporator of water vapour during use. Control of a panel to release its heat energy would be in the form of a simple solenoid valve between evaporator and the thermal storage battery, controlled by a straightforward end user clock/timer system to call for heat as in a typical heating system control.
During energy storage phase solar energy heats the collector surface to a temperature of between 200 and 300° C. As the solar panel is manufactured from aluminium, heat conducts rapidly through the internal fins 24 into the zeolite molecular sieve 23. As the zeolite molecular sieve 23 is heated, water vapour that was previously combined with the zeolite is driven out, this effectively charges the battery. The water vapour thus form has a much larger volume than when it is trapped within the molecular sieve of the zeolite. Pressure in the container 22 rises as vapour leaves the sieve, this forces the vapour through a non return value, into the condenser where it is introduced to a lower temperature and readily condenses. During the process of condensation heat energy is given off, this heat energy could be used to heat end user hot water or is simply discharged, it is a by-product of the charging process. As the device cools naturally after the charging cycle any residual water vapour in the container is absorbed back into the chemical causing a vacuum to occur. This system is now in a fully charged state as the vapour that passed through the non-return valve into the condenser cannot return.
To activate heat discharge water vapour at low temperature and pressure is reintroduced. The end users control system calls for heat, a pump starts to circulate water around a system in a conventional manner to heat a water tank, water passes through each solar collector to take heat away. The control signal that calls for heat, in turn, opens the solenoid valve separating the interior of the container from the water in the condenser which now becomes an evaporator, and the vacuum within the container so reduces the pressure in the condenser that water therein boils and vaporizes. Water vapour fills the system and is rapidly drawn into the molecular sieve of the zeolite. The vapour is absorbed into the sieve, maintaining the low pressure until the molecular sieve can absorb no more vapour. During absorption an exothermic reaction takes place within the molecular sieve, and heat energy is generated, approximately 275 watts per litre of molecular sieve of type X13 zeolite. The rate of energy release is a function of volume of water vapour allowed into the container area and also the rate at which heat energy is taken away. If no heat energy is taken from the system the temperature of the sieve during discharge could rise above 200° C. and reach an upper limit.
Care is required in designing the condenser/evaporator. In the evaporation phase, if insufficient energy is provided to the evaporating water, it will freeze halting the process and similarly if the water vapour during charging is not condensed the pressure in the system would rise excessively and also halting the process.
FIGS. 4A to 4D illustrate a large thermal system storage device suitable for mounting as a panel on a roof. A box 34 has mounted within it a plurality of individual thermal storage batteries 31 of the kind described in FIG. 3. The thermal collectors 28 are visible mounted below a glass plate 33, which insulates the contents of the box. Each of the batteries has water vapour ducts and ducts for heat transfer medium, water in this example, as in FIGS. 3A and 3B. The water vapour ducts, are connected together and to a condenser and evaporator, now shown. The heat transfer ducts are connected to a hot water circulating system, again not shown. Control valves are mounted below a panel 32. A 3 m²panel of this kind could collect and store 12 KWhs of thermal energy a day, and be available for use long after collection. Such a panel can provide the basis for space heating and hot water for a house.
In FIGS. 5A and 5B, a device 41 according to the invention for absorption and subsequent release of energy comprises a container 42 within which is a zeolite molecular sieve 43. Fins 44 extend down into the zeolite molecular sieve 43. A water vapour duct 45 runs through the container with slots 46 connecting duct 45 to the zeolite molecular sieve 43. At the top of the container 42 a solar panel 48 is mounted with a solar energy absorbing surface 49 of matt black paint, or special solar absorbing paint. Spars 50 help support the solar panel on the container 42. Mounted below the container, but thermally connected thereto, are cooling fins 47.
FIG. 6 is a schematic diagram of a cooling system using the device of FIG. 5. The water vapour duct 45 is connected to a condenser 51 having external cooling fins. Water vapour leaving the thermal storage device 41 condenses in the condenser 51. The condenser 51 is connected to an evaporator 53 via a capillary tube 52. Within the evaporator 53 is a heat exchanger 56 through which fluid flows. The fluid can be water or another heat transfer fluid. Warm fluid is pumped through pipe 54 into the heat exchanger 56, wherein it gives up its heat to evaporate low pressure water arriving through the capillary 52 into evaporator 53. The container 42, fins 44 and 47, solar collector 48 and spars 50 are all made from extruded aluminium, which has good thermal conductivity. Heat falling on the solar collector 48 is thus transmitted easily to the zeolite molecular sieve 43.
In use, heat energy falling on solar panel 48 is transmitted to the molecular sieve 43 causing water vapour in the sieve to be driven off, through slots 46 to the duct 45 and a non-return valve 57 (FIG. 6) into the condenser 51. Heat in the water vapour is lost through external fins 58 as the water vapour cools and condenses. If the source of solar energy is now cut off, the thermal storage device cools creating a vacuum in the container 42 as any remaining water vapour in the container recombines with the zeolite molecular sieve 43. This vacuum in turn transmits to the evaporator 53 via the duct 45, causing water in the evaporator to boil and taking heat from the heat exchanger 56 in the process, cooling circulating fluid entering through pipe 54 and leaving through pipe 55.
The water vapour thus created enters the zeolite molecular sieve 43 via duct 45 and slots 46 and combines with the zeolite, releasing heat in the process as a result of the exothermic reaction that occurs. This heat is conducted from the thermal storage battery, through the walls of the container and fins 47. Once the process of discharging all the heat energy in the water vapour is complete in this way, the cycle can be repeated. A number of thermal storage batteries can be used in this way each a different phase of the charging discharging cycle, so that continuous cooling of the heat transfer fluid circulating in pipes 54 and 55 can be achieved.
Although this device is shown with a solar collector for heating purposes, it is also possible to construct it with an electrical heating system as in FIG. 1; the solar panel should thus be seen as just one example of a heat source. Nevertheless, the advantages of the solar heating system are particularly obvious in countries where cooling systems, such as in air conditioners, are most used. The more solar energy that is available the more effectively will the device work.
Although for schematic purposes the duct 45 is shown as two separate ducts in FIG. 6, in reality the evaporator and condenser can be connected through the opposite ends of container 42 through end covers, or a single entry point over to container 42 is provided with a solenoid control valve controlling whether duct 45 is connected to the condenser 51 or the evaporator 53.
In FIG. 7, a device for absorption and subsequent release according to the invention similar to that shown in FIGS. 3A and 3B is used as part of a desalination system. Water vapour duct 25 of the thermal storage device 21 is connected through a solenoid switch valve 71 to ducts 67 and 68. Duct 67 is the water vapour outlet of an evaporator 64, and duct 68 is the water vapour inlet of a condenser 66. The heat transfer fluid duct 27 of the thermal storage device is connected to the heat exchanger 72 of the evaporator 66. Sea water (or other water needing purification) is admitted through a pipe 61 to a de-aerator holding vessel 62. The air outlet low down the holding vessel connects through a further pipe 63 to the evaporator 64. Sea water can thus be drawn from the holding vessel 62 to the evaporator 64.
Water vapour that is condensed in the condenser 66 can be drained through pipe 69. A conventional heat exchange system 70 connects the heat exchanger 73 of the condenser 66 with the heat exchanger 72, to the evaporator 64. Waste heat from the condenser 66 can then be used to assist evaporation in the evaporator.
The upper part of the evaporator is connected to a pump 65, to create low pressure in the evaporator. In use, sea water enters the holding vessel 62 which acts as a de-aerator. This water is at ambient temperature and pressure. The de-aeration can be achieved by raising the water's temperature or reducing the pressure. Most economically this can be done by using heat from the condenser 66 or from the thermal storage device 21 by connecting the heat transfer fluid duct 27 through the holding vessel 62 (this connection is not shown). The de-aerated salt water is fed at a controlled rate through pipe 63 to the evaporator 64. As some water is boiled in the evaporator 64, salt and/or other impurities will build up and concentrate in the remaining water, which can be drained away from time to time through duct 74 at the bottom of the evaporator.
The system is primed by reducing pressure in the evaporator using pump 65. As a result water in the condenser will boil. For maximum efficiency the heat to assist this can be supplied from the condenser heat exchanger 73 and/or from the heat exchange fluid in duct 27.
In the thermal storage device 21, solar energy drives water vapour from the zeolite molecular sieve (23 in FIG. 3) through ducts 25 and 68 into the condenser 66. Here the water vapour condenses to pure water and can be taken for use through pipe 69. If now the thermal storage device 21 is isolated from the source of energy, the thermal storage device cools and any remaining water vapour will combine with the zeolite in the zeolite molecular sieve as described before. This in turn creates a vacuum in the thermal storage device 21. The valve 71 is switched to allow water vapour from evaporator 64 to enter the thermal storage device 21 and combined with the zeolite, drawing in more water vapour and generating heat as a result of this exothermic reaction. This heat is transported from the thermal storage device 21 using the heat transfer fluid in duct 27. In turn this heat can be used as described to aid evaporation in the evaporator and de-aeration in holding vessel 62.
Once the zeolite absorbed all the water vapour that it can, the cycle is repeated by exposing the thermal storage device once again to the source of energy. But this time the water collected in condenser 66 will have originally entered the system through pipe 61. It can be seen therefore that an energy efficient desalination system is created.
A water purification system of this kind can be used for emergency sterilization. If wished water can be prevented from entering the evaporator until it had reached a suitable temperature at which bacteria and viruses would have been substantially killed or deactivated. This can be achieved through the preheating of water in the de-aerator holding vessel 62 before it enters the evaporator 64, with a flow control valve (not shown) in pipe 63 which only opens when the required temperature had been reached, preventing unsterilized water from getting into the evaporator. Such a flow control valve could be constructed in many different ways, but one possibility would be from single piece of memory metal another is to use a conventional bimetal combination that will change shape with temperature. This modification is not essential for safe operation as only water vapour is able to travel to the zeolite and the condenser and the temperature that the zeolite reaches in operation would be more than enough to destroy any bacteria and viruses that reached the container.
As in the other embodiments, a number of batteries each connected to the evaporator and condenser can be used be used, the individual batteries will be at different stages of the cycle to ensure continuous operation. The desalination system can also be used with electrically heated thermal storage batteries of the kind shown in FIG. 1.
Other forms of energy creation can also be used. FIG. 8 illustrates a particularly novel approach to providing a heat source in a thermal storage device of the kind described in the previous examples. Here a thermal storage device 81 is shown having a cylindrical container 82 with end caps (not shown). A hollow core 85 is disposed around the central axis of the cylinder. Within the hollow 83 formed by the core, a shaft (not shown) is free to rotate. The shaft would be driven by the output shaft of a wind turbine, or a wave energy device. Around the inside of the hollow core and parallel to its axis, permanent magnets 84 are disposed. An insulating layer 89 covers the inside of the core 85 thermally isolating the shaft on the shaft. Fins 86 extend radially from the core 85 to the wall of the container 82, with spines 87 extending laterally from the fins forming arcs around the axis of the container. The volume between the hollow core, the container wall, and the end caps is filled with a zeolite molecular sieve 88. The combination of zeolite molecular sieve 88, fins 86 and spines 87 make a zeolite matrix. The container 82, fins 86, and spines 87 are all constructed of a good electrically conducting material. Extruded aluminium was used in this case. Ducts and openings to transport water vapour to and from the zeolite molecular sieve have not been shown in FIG. 8 for clarity, but they are formed at the inner wall of the container, in a similar way to ducts 45 and slots 46 in FIGS. 5 and 5B. If this device is being used as thermal storage battery, the duct for heat transfer fluid would also be placed along the container wall in a similar way to the ducts 27 in FIGS. 3A and 3B. The thermal storage device is externally insulated.
In operation the thermal storage device is charged by coupling the shaft to a rotary power source. The output shaft of a wind turbine is particularly appropriate. The magnetic field created by the permanent magnets, rotates though the core 85, fins 86 and spines 87, heating these parts by induction. With good insulation this heat builds causing water vapour to be driven from the zeolite as described with the other examples. This water can be condensed in a condenser. When the magnetic field stops rotating the thermal storage device cools and any remaining water vapour is reabsorbed into the zeolite creating a vacuum as before. Water vapour is then allowed into the zeolite molecular sieve to recombine with the zeolite and create heat by an exothermal reaction as described before.
The thermal storage device shown in FIG. 8 is particularly suitable for use in the water purification system of FIG. 7. With the source of water vapour being the evaporator 64 of FIG. 7 and with expelled water vapour going to the condenser 66.
Performance of the thermal storage device shown in FIG. 8 can be improved further by embedding annular steel or iron rings in the body of the battery, coaxial with the core 85. In practice for continuous operation, several devices of the kind shown in FIG. 8 will be needed, each at different stages of the charge/discharge cycle. This can be achieved, either by using a number of devices operating from separate inputs, or operating a number of devices from a single shaft coupled to, for example, a wind turbine, by mounting the permanent magnets on a slip ring around the shaft, and coupling or decoupling the slip rings from the shaft as desired. The invention will now be described with reference to the accompanying drawings in which.
In FIG. 9 a zeolite thermal store 101, in a building 131, has a coil 109 wrapped around it through which a thermal transport fluid, water in this case, may flow. One end of the coil 109 is connected to a pump 104, whose operation may be controlled by a control means 111, depending on the circumstances this may be a timer, light sensor or a thermostat. The exit of the pump is connected via duct 105 to entry of a water circulating solar collector 106 on the roof 132 of the building. The exit of the solar collector 6 is connected via duct 107 to the other end of coil 109. Water circulating though the water circuit described by coil 109, duct 103, pump 104, duct 105, solar collector 106 duct 107 back to coil 109, will be heated by solar energy impinging on solar collector 6 and will release its energy to the zeolite thermal store 101. When the external temperature drops pump 104 can be stopped by thermostat 111.
To prevent heat loss externally to the coil 109 the thermal store 101 and coil 109 have thick lagging 102.
The interior of zeolite thermal store 101 is connected through a one way valve 113 through pipe 115 to condenser/evaporator 117. The condenser/evaporator 117 is connected back to the zeolite thermal store by duct 119 and expansion valve 123. The circuit of thermal store 101, valve 113, duct 115, condenser/evaporator 117, duct 119 and expansion valve 123 back to the thermal store 101 is hermetically sealed. Water, more than sufficient fully to be absorbed in the zeolite in the thermal store 101 is contained within the circuit. The pressure within the system, with the zeolite fully charged, is reduced to 0.2 Bar prior to final sealing. By so doing so the temperature at which the zeolite desorbs water can be reduced to from 200° C. to as low as 80° C., within reason for the temperature likely to be present in coil 109 when operating with the kind of a solar collector described.
The liquid in the evaporator will boil under low temp at low pressure, but needs to draw energy of evaporation from somewhere. Using energy from an air source (e.g. fan driven air flow taken from a source external to the building in which the any building in which the store is installed across the surface of the evaporator) provides this energy and prevents the water in the evaporator from freezing and this improves the co-efficient of performance (COP) of the thermal store up to a maximum of 2 times. Therefore the system can be designed to maximise the uptake of low grade heat (e.g. solar thermal to desorb under low pressure, with latent heat of evaporation supplied by air source around 8-10° C.) and output heat at higher temperatures for domestic use (60° C. for heating/water, 150° C. for electricity via a Rankine cycle).
Alternatively valve 113 can be replaced by a pump/one way valve combination which will have the effect of reducing vapour pressure within the system when it is turned on such that the desorption temperature is reduced to 80° C. In this embodiment an air entry valve 121, closed at this stage of the cycle, is also provided in the duct 119 back to the zeolite store 101. An, air vent 125 is also required in the condenser/evaporator to relieve excess pressure in the condenser evaporator when the pump is operating. When heat is being supplied from the solar panel 106, pump 113 will be turned on reducing the vapour pressure within the thermal store 101 to allow zeolite within the thermal store to desorb water vapour at a lower temperature than usually the case. In effect this reaction stores heat within the thermal store.
Useful heat can be extracted by the condensing of water vapour in the condenser. However the main heat extraction from the system is as a result of water vapour being admitted to the system from the evaporator as a result of the significantly reduced pressure in the thermal store as a result of original water vapour having been desorbed when coil 109 is providing heat. As coil 109 cools as will happen, as it becomes darker outside and the collector 106 ceases to provide heat, cold water is circulated through pipes 133 and 135 into and out of ducts in the thermal store 101 as described with reference to FIG. 10 (below) the temperature in the thermal store drops and any remaining water vapour therein is re-adsorbed by the zeolite creating a reduced pressure drawing low pressure/low temperature from the condenser/evaporator 117 though one way expansion valve 123.
As water vapour is drawn from condenser/evaporator 117 into the store 101, adsorption within the zeolite takes place, liberating heat causing the store to heat. At reduced pressure in a hermetically sealed unit this adsorption takes place at about 60° C. and the temperature within the store stabilises to that. This heat is extracted to circulating water in, for example, a central heating system. This circulating water enters and leaves the store by piped 133 and 135 which are coupled to ducts within the store itself as described below in FIG. 10.
However, if the valve 113 has been replaced by a pump/one way valve and air entry valve 121 is opened and the pump is turned off the pressure within the system will rise to atmospheric pressure and the temperature within the store on re-sorption will rise to 150° C.
In FIG. 10, the thermal store 101 is similar to that of FIGS. 1A, 1B and 3 and comprises cylindrical container made up of an inner wall 142 made of extruded aluminium sections. The ends (not shown) of the cylinder are closed by aluminium caps. The wall 142 is separated by a gap 143 from an insulating outer wall 144. Coil 109 is wrapped around the inner wall 142 and any remaining spaces between the inner wall and insulating outer wall 144 filled with insulating material such as rock wool. The outer wall 144 may be surrounded by further insulating materials. An extruded aluminium central core 145 has a plurality of radial aluminium fins 46 extruding to the inner wall 142. Each fin 6 has a number of aluminium spines 147 extending the length of the cylinder and formed as arcs around the central core 145. The region between the inner wall 142 and the central core 145 is filled with a zeolite molecular sieve 148. The zeolite known as X13 is particularly efficient in this application. The configuration of the fins 146 and spines 147 makes for good heat transfer to the central core 145 and the zeolite 148, the spines 147 forming a fine mesh to contact the zeolite molecular sieve 148. It will be seen that the combination of zeolite 148, fins 146 and spines 147 forms a zeolite matrix.
The central core itself has a number of slots 149 on its periphery in which the fins 146 are mounted. Close to the surface of the core are a number of ducts 150 for water vapour. The ducts 150 have slots 151 to the zeolite molecular sieve 148, through which water vapour may pass. The ducts 110 are connected through the end caps of the zeolite store 101 on one side via a non-return valve 113 (FIG. 9) to a condenser 115 (FIG. 9) and on the other side via valve 123 (FIG. 9) to low-pressure evaporator 119 (FIG. 9).
A series of heat transfer pipes 152 run the length of the central core 145. Water is used as the heat transfer medium in this case. In this example the heat transfer pipes would connect to a hot water supply or central heating system via the ducts 133 and 135 shown in FIG. 9. But there is no reason why another heat transfer media should not be used.
During the day circulating water in coil 109, which has absorbed solar energy when passing through collector 106 (FIG. 9) heats the zeolite molecular sieve 148 forcing the adsorbed water in the zeolite out as water vapour (i.e. desorbs), through the slots 151 and ducts 150 out of the cylinder. This water vapour passes through a non-return valve to a condenser (not shown). Cool water is passed through the heat transfer pipes 152, cooling the interior of the cylinder. Any water vapour remaining in the cylinder is re-adsorbed into the zeolite molecular sieve 148, creating a reduced pressure, even a vacuum. This low pressure draws water vapour through the ducts 150 and slots 151 into the zeolite molecular sieve 48. As the water vapour is adsorbed into the zeolite molecular sieve with the zeolite releasing heat, the heat release gradually charges the zeolite with water until no more can be adsorbed, at which point all possible heat has been released from the zeolite. The heat thus released is transferred via the spines 147 and fingers 146 to the central core 145 where it heats water passing through the heat transfer pipes 152. It can be seen that heat taken from the thermal storage device both during cooling and discharge is available for use.
In the system described, when heat is demanded, circulation of warm thermal fluid in coil 109 is discontinued and water to be heated is passed into and out of the internal ducts 152 (FIG. 10) though pipes 133 and 135.
Although in this example the output is to a central heating system and or/hot water cylinder, the heated output from the zeolite store can be used to drive a scroll compressor to create rotational energy driving an electricity generator. It is calculated that in this configuration described 10 m²of solar collector would provide to 5 KWh of hot water and then a Rankine cycle device of the kind described in this paragraph would further convert that to 1 KWh of electricity with 4 KWh of hot water remaining for heating applications.
The system as described in FIGS. 9 and 10 may be used in conjunction with a conventional solar collector supplying hot water to heat a hot water cylinder directly.
Other ways of implementing the device shown in FIGS. 9 and 10 by use of alternative fluids and of varying the construction of the thermal store will be readily apparent to those of normal skill in the field. In the latter case, for example, the coil 109 around the store can be replaced by ducts or coils within the store to allow transfer of heat to the zeolite, the ducts 112 to allow heat to be collected from the system can be within the wall 142 for example, as can the ducts 110 and slots 111. Water has been described as the heat transfer fluid passing through the first ducts in the thermal collector, fluids such as refrigerants can be used and gases such as N₂are also suitable.
Water has been described as the liquid that is adsorbed and desorbed from the zeolite matrix, but the system is not limited to water. Zeolites will operate in the same manner with any polar gas, such as H₂O, N₂, CO₂etc as well as fluoro-, chloro- and hydrocarbons.
The embodiment described in FIGS. 9 and 10, by using low pressure to adsorb the water vapour into the zeolite molecular sieve, enables use an environmental source of low grade heat to maximise efficiency of storage of solar thermal energy and to effectively to liberate it as higher grade heat for heating or electrical generation.

Claims

1. A thermal storage device comprising a container containing a body of zeolite comprising a zeolite sieve and thermally conducting fins extending substantially into the body of zeolite in which said thermally conducting fins are thermally connected to a heat source.

2. A thermal storage device according to claim 1 characterised in that the fins have lateral spines extending into the bulk zeolite.

3. A thermal storage device according to claim 1 having one or more ducts to conduct water vapour into and out of the container wherein said ducts have a plurality of apertures allowing water vapour into and out of the body of zeolite.

4. A thermal storage device according to claim 3 in which the said one or more ducts are in a central core of the container.

5. A thermal storage device according to claim 3 in which the one or more ducts are disposed on an inner wall of the container.

6. A thermal storage device according to claim 5 in which the said ducts are part of said wall.

7. A thermal storage device according to claim 1 in which the heat source is a solar panel.

8. A thermal storage device according to claim 1 in which the heat source comprises at least one magnetic field generating a magnetic flux within the device.

9. A thermal storage device according to claim 1 in which the zeolite container and associated condenser and ducting and valves there between are a hermetically sealed unit pressurised initially at 0.2 Bar or less.

10. A thermal storage device according to claim 1 wherein water vapour is desorbed from the zeolite molecular sieve by heating the sieve at a pressure below that of atmospheric pressure.

11. A thermal storage device according to claim 9 wherein the pressure in the container is 0.2 bar or less during desorption.

12. A thermal storage device according to claim 9 wherein the zeolite molecular sieve is at a higher pressure after any adsorption step than during any desorption step.

13. A thermal storage device according to claim 9 in which adsorption is at about 80° C.

14. A thermal storage device according to claim 9 cycleable between low and high pressures to allow desorption of water vapour from the zeolite to occur at temperatures to can be achieve by solar thermal collectors and adsorption of water vapour from the zeolite to occur at higher pressure to liberate heat at a higher temperature than that at which desorption occurs.

15. A thermal storage system according to claim 13 in which said higher temperature is at least 150° C.

16. A thermal storage device according to claim 9 wherein the heat source is a thermal collector coupled to the wall of the container by a fluid transfer duct, which duct is wrapped around the wall of the container.

17. A thermal storage device according to claim 1 in which the container comprises aluminium.

18. A thermal storage device according to claim 16 in which the container comprises a plurality of extruded aluminium panels.

19. A thermal storage device according to claim 16 in which the fins and any spines comprise aluminium.

20. A thermal storage device comprising:

At least one thermal collector having first ducts therein for the transport of a heat collecting fluid;

a container with a zeolite molecular sieve therein, the container having a means to provide for unidirectional flow of water vapour on its expulsion from the zeolite molecular sieve and means to admit water vapour to the zeolite molecular sieve;

one or more second fluid ducts in or around the container connected to the first ducts to provide a thermal path from the collector to the zeolite molecular sieve;

at least one condenser to receive water vapour driven from the zeolite molecular sieve;

at least one evaporator to supply water vapour to the zeolite molecular sieve under reduced pressure when heat is demanded of the system.

wherein the:

the zeolite molecular sieve is heated by the thermal collecting fluid passing through said second ducts to drive water vapour from the zeolite molecular sieve and out of the container;

and wherein water vapour is admitted to into the zeolite molecular sieve when heat is demanded.