GB2025604A - A power supply system - Google Patents

Abstract

In a power supply system connected to a source of energy (11), e.g. a solar collector, and adapted to operate at a predetermined mean power load, a latent heat storage unit (13) is used to absorb excess energy when the power demand is less than the mean load. The latent heat storage unit which is preferably connected in parallel with the consumer or power sink, (12), e.g. a power station, may comprise spherical storage elements suspended in a flowpath for a heat carrier or contained in a heat exchanger, the storage elements consisting of spheres filled with a latent heat storage medium. <IMAGE>

Description

SPECIFICATION A power supply system This invention relates to a power supply system.

The problem commonly associated with power supply systems, of whatever kind whether in electrical or thermal engineering, is that consumption varies with time. Because the demand is irregular, supply systems are normally designed to suit the peak load, so being very much larger and more costly than is necessary for normal operation.

It has also been shown that the power consumption and wear is increased by the irregular operation of a machine as compared with a machine running at constant load.

In thermal or electrical power stations for example, the peak load occurs rarely and, if it does, only intermittently, while in normal operation the load fluctuates about a mean value.

In order to save energy, therefore, attempts are made to utilize the surplus energy arising from part-load operation, in some other manner, using a secondary power sink, e.g. by drinking water or hot water. But even in this case there will be much unused energy owing to the equally limited capacity of the secondary power sink and because of the often considerable difference between the occasion ai peak load and the mean load.

It is an object of this invention to enable utilisation of energy with greater economy than in known systems.

According to this invention we propose a power supply system connected to a source of energy and adapted to operate at a predetermined mean power load and comprising a latent heat storage unit for absorbing excess energy from the source when the power demand is less than the mean load and supplies energy when the demand rises above the mean load.

Designing the system for operation at a mean powder load cuts the capital running costs, extends the life of the system components and facilitates control of the system.

Various latent heat storage units are known, these essentially comprising a vessel filled at least in part with storage elements or storage materials which depending on their physical state will absorb or yield latent heat. The storage media are selected to suit the specific application. When the storage unit is used for cooling purposes, for example, water or salt with constitutional water may be used. For making hot water, on the other hand, a nitrate hydrate melting at about 80"C is used. An important consideration here is that the transition temperature of the medium lies in the operating temperature range of the storage unit.

In conventional storage units the storage medium is contained in a vessel fitted with internal pipes for the flow of the gaseous or liquid heat carrier, heat transfer between the heat carrier and the storage medium being across the walls of the pipes.

Special advantage accrues, however, from the use of modular latent heat storage units wherein the storage medium is enclosed in a plurality of spheres or simiiar containers wetted by the heat carrier. In this arrangement, the exchange of heat between the storage media and the heat carrier is effected via the walls of the container. Subdividing the storage medium into small portions considerably enlarges and relieves the thermal transmission areas. Further, down-time needed for the repair of defective pipes is eliminated since the containers can be replaced continually and individually.

The heat storage unit may have stationary storage elements ranging from 10 mm to 100 mm in diameter to ensure adequate heat exchange. Further, the exchange of heat between the storage medium and the heat carrier may be promoted by suspending storage elements in the heat carrier, the elements preferably being from 1 mm to 10 mm in diameter. This arrangement of stationary storage elements has another advantage in that charging and discharging of the elements may be effected concurrently, where a collector vessel and a separate heat exchanger may be provided. Also, stationary storage elements may serve as heat carriers in that they are charged at one point in the circulating flow, which may be the storage heat exchanger, and discharged at another point, which may be a heat exchanger. Discharging and charging may here be alternative but also continuous and concurrent.

Preferably, the latent heat storage unit is connected in parallel with the power sink and provisions are made for effecting partial reversal of the circu lating flow for charging or discharging the heat storage unit.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings: Figures 1 and2 are block diagrams each illustrating a power supply system according to the invention, and Figure 3 shows a heat exchanger.

With reference now to Figure 1, a power supply system 10 is fitted connected to a power source 11, and supplies a load such as a power station, represented by a power sink 12. A latent heat storage unit 13 is connected in parallel with the power sink 12. The source 11 may perhaps be a solar array absorbing solar energy 14 and routing it, after its conversion into thermal energy, to a heat carrier flowing to the power sink 12, in the directon of arrow 15.

The solar array 11 is designed to generate just sufficient energy to satisfy the normal power de mandforthe power station 12. In this case the by-pass circuit 16 leading through the latent heat storage unit 13 remains closed. When the power demand falls, however, the surplus energy from the continuously flowing heat carrier 15 is routed to the heat storage unit 13. For the purpose, a pump 17 in the circuit 16 starts and maintains the flow in the direction of the arrow-head (unbroken line). This energy is stored as the latent heat of a storage medium contained in the storage unit 13.Then when the power demand rises above the normal, the pump 17 reverses the flow in the circuit 16, now in the direction of the dotted arrowhead, so that the latent heat is recovered from the storage unit 13 and routed to the power sink 12 so supplementing the energy 15 whereby the power sink (e.g. station) 12 can deliver the extra power without drawing additional energy from the source 11.

Figure 2 illustrates a power supply system 20 having a heat exchanger 21 and a storage vessel 22 connected to a circuit 23 for the flow of the storage medium. As in the system of Figure 1, the storage medium is again charged during part-load operation and is discharged during high-load or peak-load conditions. The charging or discharging process, however, is here effected in a heat exchanger 21 through which the storage medium from the collector vessel 22 flows through the circuit 23 to absorb or yield heat.

In the two embodiments described above the charging and discharging processes are alternating.

It is nevertheless practicable also tp use the latent heat exchanger for concurrent charging and discharging operation. For this purpose, use can be made, e.g. of a second heat exchanger 25 supplied with energy from a same 11 or a separate source and communicating with the storage vessel 22 through a storage medium circuit 26. The two circuits 23 and 26, here shown as separate loops, can naturally be integrated to form a single circuit leading through the vessel 22.

The additional heat circuit is shown dotted in Figure 2, and the associated second heat exchanger 25 can be connected either to the power sink 12 or to another sink 27. A system of this kind can be used, e.g. wherever waste heat as from motors or engines, is produced. This waste is stored in the vessel 22 and routed when needed to the power sink 12, which affords a considerable advantage especially for systems burdened by extended peak-load or heavily fluctuating load conditions.

Figure 3 is a diagram of a latent heat exchanger 13 having stationary storage elements 30 which com prise spheres filled with a storage medium, the spheres nearly completely filling the storage vessel 13. The storage medium is selected to have a transformation temperature (normally solid to liquid physical state) ranging between the temperatures of the heat carrier or of the source of energy 11 and the temperature of the power sink 12. The heat carrier proper is routed through the heat storage vessel 13 along pipe-lines 31.

The pipe-line 31 can if necessary be replaced by separate lines 31,32 respectively for discharging and charging. In this arrangement the heat carrier is in thermal contact with the spheres 30 to impart to or extract from them sensible as well as latent heat.

With the circuit illustrated in Figure 1 warmer carrier medium flows to the heat storage unit in the direction of the arrowhead 18 so that the storage substance in the spheres 30 gains heat and is melted. Then when the flow of the carrier medium in the circuit is reversed, the medium reaches the heat storage unit 13 at a temperature below the point of transition and hence extracts both sensible and latent heat, causing the storage medium to solidify.

In the case of the heat storage unit 21, 22 the storage elements are not permanently retained in the vessel. They are suspended in a heat carrier to flow through the circuit 23 when they gain or lose heat, depending on the operating condition, at the heat exchanger 21. In a system shown dotted in Figure 2 the storage elements are charged on the one side, i.e. in the heat exchanger 25, and they discharge when they pass the heat exchanger 21,so effecting continuous charging and discharging.

Claims (9)

1. A power supply system connected to a source of energy and adapted to operate at a predetermined mean power load and comprises a latent heat storage unit for absorbing excess energy from the source when the power demand is less than the mean load and supplies energy when the demand rises above the mean load.

2. A system according to Claim 1, wherein the latent heat storage unit has stationary storage elements ranging in diameter from 10 mm to 100 mm.

3. A system according to Claim 1, wherein the latent heat storage unit has storage elements which are suspended in a heat carrier flowing through the storage unit and which range in diameter from 1 mm to 10 mm.

4. A system according to Claim 2 wherein the latent heat storage unit comprises a storage vessel and a heat exchanger connected to it.

5. A system according to Claim 3 or Claim 4, wherein the storage elements are charged at one point of the circuit and discharged at another, so functioning as heat carriers.

6. A system according to any one of the preceding Claims, wherein the latent heat storage unit is connected in the circulating flow of the system in parallel to the consumer.

7. A system according to Claim 4, wherein the vessel and the heat exchanger of the latent heat storage unit are connected into a closed-loop heat carrier circuit and in that the heat exchanger is additionally connected in parallel to the consumer.

8. Asystem according to any one of the preceding Claims, wherein the latent heat storage unit is connected to two separate sources of energy.

9. A power supply system constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accom panying drawings.