GB2509894A

GB2509894A - Thermal energy storage and recovery

Info

Publication number: GB2509894A
Application number: GB1220188.5A
Authority: GB
Inventors: Jonathan Edward Ford; Graham Paul Ford
Original assignee: JEAN PIERRE DEWERPE; LUCIEN BASTIANELLI
Current assignee: JEAN-PIERRE DEWERPE; LUCIEN BASTIANELLI
Priority date: 2012-11-09
Filing date: 2012-11-09
Publication date: 2014-07-23
Also published as: GB201220188D0

Abstract

Storing and recovering energy in the form of heat by using energy to be stored to heat a heat transfer liquid, flowing the heat transfer liquid through a bed of particulate material 103 to transfer heat from the heat transfer liquid to the particulate matter to store the energy in the form of heat; and extracting the stored heat by flowing gas through the bed of particulate matter. The liquid preferably flows down the bed with the gas flowing up from inlet 107 to outlet 108. The particles may be rock or mineral and the liquid may be oil which is flowed onto the bed by means of an irrigator 105 and collected from the bed by sump 106 so that it can be reheated by a source of energy to be stored. The energy to be stored may be provided by heating the liquid with a solar concentrator.

Description

Energy Storage Systems

FIELD OF THE INVENTION

This invention relates to apparatus and methods for storing energy, in particular for use with renewable sources of energy such as solar thermal systems.

BACKGROUND TO THE INVENTION

Heat stores are used for storing thermal energy, generally at temperatures sufficiently high such that the heat can be used to boil waler or some other fluid in order to drive a turbine and produce power, or enable a chemical process to run more efficiently. Heat stores have frequently used molten salts, such as mixtures of nitrate and nitrite salts of sodium or potassium, as a pump-able medium in which heat is stored at temperatures in the range of 20000 up to 500 DC.

Processes that use these heat stores ideally fill and empty the store with heat several times a day, as both the media and the containment is quite costly. Frequently it is cheaper merely to modulate the supply of heat to suit the process. However, modulating solar energy is not possible when the supply is only available during the day and the demand is at night. The daily storage frequency makes such stores expensive and consequently their use has been limited to providing only a few hours, typically 6 hours, of storage each day.

The costs of a thermal store have three main components: the media, the vessel and the pumps. Of these the media is the most expensive and typically makes up 70% of the total cost.

A packed bed is a known type of alternative thermal storage device, in which granules or blocks of (usually) ceramic are arranged with gas ways in which a heat transfer gas can flow through the matrix of the bed to transfer heat into or back out from the store.

However, the use of gas as a heat transfer fluid, due to its low thermal capacity and low thermal conductivity compared to liquids, necessitates higher pumping power and much higher heat transfer areas in ancillary equipment in order to move the heat into or out of the gas stream, than compared to molten salt. However, they have found particular use as regenerative heat exchangers for reverberative furnaces such as are used for glass making.

In order to address these difficulties of high pumping powers and high heat exchange areas with the use of gas in packed bed heat stores, a packed bed may be filled with oil, the oil being circulated through the bed to transfer the heat. However, there are two difficulties with this approach. Firstly, all the spaces between the particles in the matrix are filled with oil, necessitating the use of a lot of oil, which is expensive. Secondly the thermal efficiency of the store is considerably reduced when the thermal capacity of both the fluid and the matrix in the store are comparable, which is the case when oil fills a packed bed composed of rock.

Embodiments of the present invention alleviate some of the problems described above and address the requirements of a cost effective thermal store.

SUMMARY OF THE INVENTION

According to the present invention there is therefore provided a method of storing and recovering energy in the form of heat and, the method comprising: using energy to be stored to heat a heat transfer liquid; flowing said heat transfer liquid through a bed of particulate material to transfer heat from said heat transfer liquid to said particulate matter to store said energy in the form of heat; and extracting said stored heat by flowing gas through said bed of particulate matter.

In some preferred embodiments droplets of the liquid are rained onto the bed, for example using an irrigator. The liquid egress from the bed is preferably collected and recalculated back to a source of the energy to bereheated. Preferred embodiments of the method extract the stored energy by flowing gas through the bed of particulate matter in an opposite direction to the flow of liquid, in particular allowing the liquid to flow down by gravity to store heat and blowing gas back up through the bed to extract the stored heat.

Embodiments of this method are advantageous because, after storing the energy, the bed of particulate matter includes a forni of liquid over the particles but not completely filling the interstitial spaces between the particles. For example, a packed bed might typically have 10%-50% pore volume and thus, in some embodiments, the gas occupied greater than 10%, 20%, 30% 40% or 50% of the total volume of the bed.

Operating the bed with gas in the pores is helpful as this facilitates extracting heat from the bed by blowing gas through the bed. Another significant advantage of embodiments of the invention is that a reduced volume of liquid is employed: This is because in some preferred embodiments the liquid comprises oil, which is relatively expensive.

In some preferred embodiments the particulate matter comprises rock or mineral matter. Preferably rock that is resistant to high temperature thermal cycling is employed, for example basalt which has a relatively uniform composition (as opposed to, say, granite where there can be differential thermal expansion between grains, or limestone, which tends to decompose).

Preferred embodiments of the method can be employed with a renewable energy source; embodiments of the method are particularly useful with a solar thermal source which can be employed to heat the liquid using a solar concentrator.

In a related aspect the invention provides apparatus for storing energy, the apparatus comprising: a liquid input to receive hot heat transfer liquid bearing energy for storing; a bed of particulate matter; an irrigator, coupled to said liquid input, to rain droplets of said hot heat transfer liquid onto said bed of particulate matter; and a liquid collection system to collect said liquid from said bed of particulate mailer after heating.

Preferably the irrigation system is arranged to provide a relatively uniform distribution of oil over the upper surface of the particulate bed.

In embodiments the apparatus may include one or more temperature sensors to sense the temperature of one or more depth levels of the bed of particulate matter. Such a temperature sensors may be configured to sense temperatures greater than 100°C, that is suitable for the relatively high temperatures at which the heat is stored.

Embodiments of the apparatus may be coupled to a source of renewable energy via one or more liquid conduits, to provide hot heat transfer liquid from the source of renewable energy and to deliver the liquid back after it has passed through the bed.

Preferred embodiments of the apparatus include a system to blow gas through the bed, in particular from an opposite side of the bed to that onto which the liquid is rained. A system may also be provided to collect the heated gas from the bed, and to provide this to a heat exchanger to extract the heat from the heated gas.

Use of heated gas to extract the stored heat from the bed is not essential, but provides some advantages.

Thus In a further aspect the invention there is provided apparatus for storing energy, the apparatus comprising: a bed of particulate matter; a heat input system to pass hot liquid through said bed, to heat said bed to store energy; and a heat extraction system to pass gas through said bed, for heating said gas to extract stored energy from said bed.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 shows a thermal store according to an embodiment of the invention; and Figure 2 shows the store of Figure 1 with the top cover removed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

We will describe a heat store to store heat at moderately high temperatures, for example such as can be endured by petroleum oil without chemical breakdown. This is for use with devices that either produce or consume heat intermittently, such as concentrating solar collectors (producers of heat) or chemical or food processing plants (consumers of heat).

In embodiments of the invention we provide a packed bed heat store in which oil is allowed to trickle down over the surface of the stones, being spread over the upper surface of the packed bed by a means of distributing a rain of oil droplets evenly over the upper surface of the packed bed. Conveniently this may be carried out by a centre-pivot irrigator, similar in principle to those typically used in sewerage works for distributing foul water over a packed bed of granules.

The oil is hot and so as it flows down over and between the stones as a film, the oil gives up its heat to the stones. The stones in the uppermost layer of the bed would be heated first, and then as they near the temperature of the oil the zone in which the stones are being heated slowly moves down through the bed until all of the stones are up to the oil temperature and no more heat can be delivered into the stones. At this point the store is full of heat.

Oil that drips off the bottom layer of the bed is collected, filtered and pumped back to the system that heated the oil, such as a concentrating solar collector or a fuel-fired oil heater.

When heat needs to be extracted from the bed, and (inert) gas, such as nitrogen, is blown up through the bed. As it flows up through the bed, heat is transferred to the gas from the stones. This time, the bottom-most layer of stones are cooled first, and then the layer in which heat transfer takes place moves up through the bed until all the bed has been cooled and all the heat has been extracted. The gas flows from the bed to whatever device requires the use of the heat.

By this means, the gas heat exchanger is limited to one side of the he, compared to a situation where gas was both charging as well as discharging the thermal store with heat.. The amount of oil needed in the store is limited to only that required to form the film of oil over the stones in the packed bed, leaving the spaces between the stones filled only with gas.

By this means the store is able to operate efficiently, is able to use a low cost storage media, the stone, uses a minimum quantity of oil and minimises the gas heat exchange required.

An example of a thermal store embodying the invention will now be described with reference to the accompanying drawing Figure 1 showing a section through the store, and Figure 2, a plan view of the store.

A thermal store is shown in the Figure 1 which is a container (100), thermally insulated (101) and lined with an impervious (liquid/gas tight) liner (102). The stone forms a packed bed (103) over a grill (104) so that oil, distributed by a rotating irrigator (105) is able to rain out the bottom into a sump (106) and nitrogen may be fed in (107) and rise up through the bed (103) and out through its outlet (108). The rotating irrigator is driven by a motor (109) whenever oil is required to be circulated through the bed.

The same store shown in Figure 2 shows the top of the bed with the cover removed, showing the bed (103) and the rotating irrigator (105).

No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

CLAIMS: 1. A method of storing and recovering energy in the form of heat, the method comprising: using energy to be stored to heat a heat transfer liquid; flowing said heat transfer liquid through a bed of particulate material to transfer heat from said heat transfer liquid to said particulate matter to store said energy in the form of heat; and extracting said stored heat by flowing gas through said bed of particulate matter.
2. A method as claimed in claim 1 comprising flowing said gas in an opposite direction to a direction of flow of said liquid.
3. A method as claimed in claim 2 comprising flowing said liquid down through said bed and flowing said gas up through said bed.
4. A method as claimed in claim 1, 2 or 3 wherein said flowing of said liquid comprises raining droplets of said liquid onto said bed.
5. A method as claimed in claim 4 comprising using an irrigator to rain said droplets of liquid onto an upper surface of said bed.
6. A method as claimed in any preceding claim further comprising collecting liquid egressing from said bed and providing said collected liquid back to a source of said energy to be stored.
7. A method as claimed in any preceding claim wherein, after storing said energy, said bed of particulate matter includes a film of said liquid over particles of said particulate matter and gas in spaces between particles of said particulate matter.
8. A method as claimed in any preceding claim wherein said particulate matter comprises rock or mineral matter and wherein said liquid comprises oil.
9. A method as claimed in any preceding claim further comprising providing said energy for storing as heat.
10. A method as claimed in claim 9 comprising providing said energy for storing as heat from a solar thermal source, the method comprising heating said liquid using a solar concentrator.
11. Apparatus for storing energy, the apparatus comprising: a liquid input to receive hot heat transfer liquid bearing energy for storing; a bed of particulate matter; an irrigator, coupled to said liquid input, to rain droplets of said hot heat transfer liquid onto said bed of particulate matter; and a liquid collection system to collect said liquid from said bed of particulate matter after heating.
12. Apparatus as claimed in claim 11 further comprising one or more temperature sensors to sense a temperature at one or more depth levels of said bed of particulate matter.
13. Apparatus as claimed in claim 12 wherein a said temperature sensor is configured to sense temperatures greater than 100°C.
14. Apparatus as claimed in claim 11, 12 or 13 further comprising a source of renewable energy, and one or more liquid conduits to collect said hot heat transfer liquid from said source of renewable energy and to deliver said heat transfer liquid from said bed of particulate matter to said source of renewable energy.
15. Apparatus as claimed in claim 14 wherein said source of renewable energy comprises a concentrating solar collector.
16. Apparatus as claimed in any one of claims 11 to 15 wherein said heat transfer liquid comprises oil and wherein said particulate matter comprises rock and/or mineral matter.
17. Apparatus as claimed in any one of claims 11 to 16 further comprising a system to blow gas through said bed to extract heat from said bed.
18. Apparatus as claimed in claim 17 wherein said system to blow gas through said bed is configured to blow said gas up through said bed.
19. Apparatus as claimed in claim 17 or 18 further comprising a system to collect heated gas from said bed, coupled to a heat exchanger to extract heat from said heated gas.
20. Apparatus for storing energy, the apparatus comprising: a bed of particulate matter; a heat input system to pass hot liquid through said bed, to heat said bed to store energy; and a heat extraction system to pass gas through said bed, for heating said gas to extract stored energy from said bed.