A geothermal district heating system

Abstract

The present disclosure is directed to a geothermal district heating system, comprising a primary circuit circulating a liquid through a plurality of geothermal wells, each geothermal well being separated from a subsequent geothermal well by an adjacent building and a cooler, such that the liquid is heated in each geothermal well and thermal energy from the heated liquid is communicated to the adjacent building to dissipate the thermal energy thereto cooling the heated liquid before communicating the liquid to a cooler where further thermal energy is dissipated from the liquid before being introduced into the subsequent geothermal well to be reheated, wherein the repeated heating and cooling of the liquid around the primary circuit generates a thermal syphoning effect to thereby drive the liquid around the primary circuit.

Description

[0001] A GEOTHERMAL DISTRICT HEATING SYSTEM

[0002] INCORPORATION BY REFERENCE

[0003] The present application claims priority from Australian provisional application no 2022900115, the entire contents of which are hereby incorporated by reference.

[0004] TECHNICAL FIELD

[0005] The invention is directed to a geothermal district heating system. The invention is further directed to a method of supplying a district heating system with thermal energy, the district heating system including a plurality of geothermal wells.

[0006] BACKGROUND

[0007] District heating (DH) is a widely used form of heating in densely-built areas of Northern Europe, the United States of America and most of Russia. District heating disperses heat from a centralised source to a district via a network of pipes to provide thermal energy to both residential and commercial properties within the district.

[0008] Utilising a centralised heating source eliminates the need for each property in the district to run a boiler or similar combustion devices thereby removing a multitude of smaller, less efficient heat sources, each of which may be drawing electrical energy and / or contributing to harmful emissions. A single centralised heat source is also typically configured to provide some form of flue cleaning, which many residential boilers do not have. Harmful emissions from boilers include, but are not limited to, carbon dioxide (CO2) and nitrogen dioxide (NO2).

[0009] In colder climates, for example Finland, it is estimated that more than half of Finnish inhabitants live in homes heated by district heating systems and that around 80% of the energy use of households is spent on heating these homes. Traditional district heating systems are configured to run on fossil fuels (coal, peat and oil) with others running on gas, wood and wood residues, bio and non-bio waste burning. In Finland alone, the total emissions from district heating systems in 2017 were estimated to be around 149g CO2 / kWh.

[0010] While wind and solar energy sources are being slowly integrated into some district heating systems, these alternative energy sources may be configured to generate electricity to contribute to the district heating system, which is a relatively inefficient use of the harvested energy. Further power requirements are also placed on existing district heating systems to distribute the heat or heated fluid to the commercial and residential properties in the district contributing to further power requirements and transmission losses. Additional draw backs to both wind and solar energy resources are: (i) the space required to install the solar array or wind farm; and (ii) the availability and location of the sun or wind natural resources in relation to the district network.

[0011] The present invention was conceived with these shortcomings in mind.

[0012] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, a limited number of the exemplary methods and materials are described herein.

[0013] SUMMARY OF THE INVENTION

[0014] The invention is broadly direct to a geothermal district heating system, comprising; a primary circuit circulating a liquid through a plurality of geothermal wells, each geothermal well being separated from a subsequent geothermal well by an adjacent building and a cooler, such that the liquid is heated in each geothermal well and thermal energy from the heated liquid is communicated to the adjacent building to dissipate the thermal energy thereto cooling the heated liquid before communicating the liquid to a cooler where further thermal energy is dissipated from the liquid before being introduced into the subsequent geothermal well to be reheated, wherein the repeated heating and cooling of the liquid around the primary circuit generates a thermal syphoning effect to thereby drive the liquid around the primary circuit.

[0015] Each geothermal well of the system is preferably capable of providing between 100-500 horsepower of pumping energy to drive the liquid around the primary circuit and thereby reducing, if not eliminating, the need for external pumping means to drive the system.

[0016] The geothermal district heating system of the invention uses natural geothermal heat to charge the system, potentially providing limitless, zero emission, baseload thermal energy 24 hours a day. Each geothermal well may be drilled to depths of 6,000 metres to 12,000 metres to access the natural thermal energy of the surrounding geology, while eliminating the need for fracking and other dangerous practices to access the energy source. The system preferably uses a plurality of single, vertical, closed-loop geothermal wells drilled to reach a bottom-hole temperature of about 200°C. In embodiments of the invention, the system can induce a thermal syphoning effect that will deliver super-heated liquid, for example water, to the surface under pressure, without pumping.

[0017] No fracking and no ground water extraction is required for thermal energy production using this system. It is contemplated that the system will be capable of producing thermal energy and fulfilling district heating system pumping requirements for hundreds of years.

[0018] It is calculated that thermal energy production and pumping from the geothermal district heating system according to the invention may cost as little as €0.005 per KW / h or less. Additionally, it is calculated that both capital expenditure costs and operating costs per MWth will be lower than conventional fossil fuel heating systems.

[0019] Maintenance and running costs will be extremely low, in typical embodiments, as there are no moving parts in the geothermal wells or coolers. The system can further be configured such that no mechanical pumps are required, and therefore no mechanical pump maintenance. Embodiments of the system of the present invention may use no power-lines to be maintained, and suffer from no power losses through long distance transmission. This is to be contrasted with alternative energy sources such as solar, where locations for solar arrays invariably dictate the location of the power source and transmission losses significantly reduce the usable energy obtained. Furthermore, as the system does not require fossil fuels or oil for its power, there is no reliance on fuel or oil providers, making the system independent once installed and commissioned.

[0020] The system according to embodiments of the invention requires no electricity, and no pumps for the liquid circulation within the geothermal wells or for the overall district heating system to flow. The geothermal district heating system according to embodiments of the invention requires no heat plant buildings and as such produces no CO2 or NO2 emissions with no toxic waste. Aside from the environmental benefits, the geothermal district heating system of the invention offers prospects of a major reduction in heating costs. Furthermore, the piping network of the geothermal district heating system of the invention can be buried in the ground presenting minimal disruption to the environment around the system with no requirement for clearing of trees or deforestation. It is contemplated that in colder climes the granite geology will be capable of delivering a thermal gradient of about 24°C / 1000 metres; thus reaching bottom-hole well temperatures of about 200°C at around 10,000 metres. These temperatures are to be contrasted with ambient air temperatures averaging between 4°C in winter and 20°C in summer (in Finland), each of which provide a sufficient temperature differential to maintain the system.

[0021] Each geothermal well (5) of the system (100) may be individually adjusted by means of a first valving set on the injection bore inlet and a secondary valving set on the production bore outlet, to thereby vary the flow volumes into and out of each geothermal well of the system. The primary and secondary valving sets additionally allow control over the flow created by thermal syphoning volumes of each well, wherein each valving set may be configured for remote operation to allow remote well head flow control within the system.

[0022] In some embodiments, the geothermal district heating system is driven solely by the thermal syphoning effect. As such, no additional pumping equipment is incorporated within the primary circuit for maintaining circulation of the liquid.

[0023] In some embodiments, the liquid of the primary liquid circuit may be introduced into the adjacent building to communicate thermal energy to the adjacent building. Alternatively, in some embodiments, the liquid of the primary liquid circuit may be communicated to a heat exchanger to transfer thermal energy to the adjacent building.

[0024] The thermal energy received by the adjacent building from the liquid of the primary liquid circuit may be additionally used to power an internal building pump, or internal pumping system. For example, the thermal energy from the liquid may be communicated to a secondary heat transfer medium by virtue of a heat exchanger: the heat transfer medium circulating within a secondary circuit internal to the building. The heat within the secondary transfer medium may be used to drive a turbine or pump, either directly or indirectly, to circulate the heated heat transfer medium within the building's internal system. Alternatively, the heated liquid of the primary liquid circuit may be directly communicated to drive a turbine or pump located within the internal building system to thereby circulate the thermal energy within the building's internal system. The internal building system may require a screw expander, heat pump or low-pressure steam engine to convert thermal energy into mechanical energy for the purposes of pumping, driving motors, compressors etc. A flow pressure of the heated liquid exiting each geothermal well of the primary circuit may encourage circulation of the liquid around the primary circuit. The cooled liquid exiting each cooler may be drawn into each respective geothermal well of the primary circuit by the heated, pressurised liquid exiting the geothermal well.

[0025] Each geothermal well may comprise an injection bore and a production bore, the injection bore receiving cooled liquid and the production bore exhausting heated, pressurised liquid. In some embodiments, the injection bore and the production bore may be coaxially aligned. In some embodiments, the injection bore may circumferential bound and insulate the production bore therein, while in other embodiments the production bore may circumferentially bound and insulate the injection bore therein.

[0026] In some embodiments, the cooler may dissipate heat directly to atmospheric air. In some embodiments, the cooler may comprise a conduit. The conduit of the primary circuit may comprise a pipe having minimal insulation. The cooler may comprise an atmospherically cooled heat exchanger.

[0027] In some embodiments, the geothermal district heating system may comprise a plurality of buildings arranged in series to receive thermal energy from the heated liquid from the primary liquid circuit before discharging the cooled liquid to the cooler.

[0028] In some embodiments, the geothermal district heating system may comprise a plurality of buildings arranged in parallel to receive thermal energy from the heated liquid from the primary liquid circuit before discharging the cooled liquid to the cooler.

[0029] In some embodiments, the primary liquid circuit may be configured to fluidly communicate with internal heating and / or cooling systems within each building. In some embodiments, the primary liquid circuit may be configured to communicate thermal energy only and not liquid with internal heating and / or cooling systems within each building. The thermal energy transfer may be effected via a heat exchanger.

[0030] The heated liquid may be drawn from each of the plurality of geothermal wells at a temperature in excess of 100°C. The heated liquid may be drawn from each of the plurality of geothermal wells at a pressure of about 100bar. The heated liquid may be drawn from each of the plurality of geothermal wells at a flow rate of about 10kg / second. The cooled liquid may be directed to a respective cooler at a temperature of about 70°C. The cooled liquid from a cooler may enter each geothermal well at a temperature of about 50°C.

[0031] In some embodiments, each geothermal well is a closed loop preventing contact between the liquid of the primary liquid circuit and geology surrounding the geothermal well.

[0032] Each geothermal well may be drilled to a sufficient depth to access a bottom-hole temperature of above 180°C. Each geothermal well may be drilled to a depth between 6,000 metres and 12,000 metres.

[0033] In some embodiments, a start-up pump may be incorporated into the primary circuit to initiate movement of the liquid within the primary circuit. In some embodiments, a liquid storage tank may be incorporated within the primary liquid circuit, to store a volume of liquid at ambient temperature, the liquid storage tank configured to release the stored volume of liquid into at least one of the geothermal wells to thereby initiate circulation of the liquid within the primary liquid circuit on start-up. A plurality of liquid storage tanks may be incorporated into the primary liquid circuit to supply one or more of the geothermal wells of the system.

[0034] In some embodiments the primary liquid in the primary liquid circuit may be water. In some embodiments the primary liquid in the primary liquid circuit may be distilled water. In some embodiments, the distilled water may additionally contain additives to prevent corrosion of piping within the system, and piping and components within the building's heating systems.

[0035] A start-up pump may be incorporated into the primary circuit to initiate circulation of the liquid of the primary circuit. The start-up pump may be deactivated once the primary liquid circuit is flowing totally under the thermal syphoning affect. Circulation of the liquid in the primary liquid circuit, once initiated by the start-up pump, is sustained by a thermal syphoning effect drawing liquid into a first of the plurality of geothermal wells at a first temperature as heated liquid is forced out of the well head at a second temperature, greater than the first temperature.

[0036] Thermal syphoning is a mode of passive heat exchange sustained by convection to circulate the liquid within the primary liquid circuit without the requirement for mechanical pumps. Once a heat transfer is initiated to a first part of the circuit, the change in heat will give rise to a change in density, urging the hotter, less dense liquid in one part of the circuit to rise, as cooler, denser liquid in the circuit sinks: using natural convection to draw the liquid around the circuit to and from the heat source. For example, liquid, or fresh water at a temperature of approximately 50°C is drawn down an injection annulus or injection bore of the geothermal well to be heated by the hot geology surrounding the well. The thermal syphoning effect will then push the heated water back to the surface of the well at temperatures of around 100°C, such that the delivery of thermal energy to the surface requires no energy input to maintain the thermal energy flow. As the heated, pressurised water is drawn to the surface via the production annulus or production bore of the well, more cool water is drawn into the closed loop well from the primary liquid circuit to maintain the thermal syphon, thus eliminating the need for electrical or mechanical pumps to drive circulation around the district heating network. The invention thereby provides a low-cost renewable thermal energy source reducing operating costs as compared to typical district heating systems or networks where the liquid (or similar performing heat transfer medium) is circulated by pumps driven by electricity.

[0037] The heated liquid exhausted from each of the geothermal wells will be at elevated pressures of around 50 bar.

[0038] A pump can be used to initiate circulation of the liquid through the geothermal wells of the primary circuit, and facilitate the start-up of the thermal syphoning effect.

[0039] Each geothermal well of the system may have a surface foot print of approximately 10 square metres, each well capable of producing up to 2.5MWth at 100°C. Comparisons with both wind and solar power shows geothermal energy to have a very small physical footprint, thus leaving surrounding land untouched, and available for alternative use. Additionally, this greatly reduces the environmental impact of district heating system as there is no requirement for power lines, clearing of trees, no emissions and no toxic waste produced and the land above and around the geothermal bore can be rehabilitated after installation.

[0040] The present invention can provide additional advantages over known district heating systems, in that there is minimal well maintenance required and no power line maintenance or power losses through long distance transmission. In comparison to other alternative energy sources like solar and wind, there are no turbines or solar panels to clean and maintain.

[0041] Once drilled and installed each geothermal well will produce for hundreds of years while the well head flow can be controlled remotely by a valving set to adjust the pumping volumes achieved to meet heating demand. In addition the district heating system can be configured to have additional redundant geothermal well, so allow for increased capacity or the ability to take a given geothermal well off line from the primary liquid circuit for maintenance or repair.

[0042] The above advantages provide for significant reductions in typical district heating system costs and significant reductions, if not elimination, in CO2 and NO2 emissions.

[0043] In a second aspect, the invention provides a method of supplying a district heating system with thermal energy, the district heating system including a plurality of geothermal wells, the method comprising the steps of: (a) circulating a liquid within a primary liquid circuit into each of the plurality of geothermal wells and extracting the liquid at an elevated temperature from each of the plurality of geothermal wells, wherein the geothermal wells are spaced around the primary liquid circuit having at least one adjacent building and at least one cooler disposed between each subsequent geothermal well of the circuit; (b) communicating the liquid at the elevated temperature from each geothermal well to each respective adjacent building to dissipate thermal energy thereto; (c) subsequently routing the liquid to each respective cooler to further dissipate thermal energy therefrom and reduce the temperature of the liquid; and (d) introducing the reduced temperature liquid into a subsequent geothermal well of the plurality of geothermal wells to be reheated, wherein the repeated heating and cooling of the liquid within the primary liquid circuit creates a thermal syphoning effect to thereby drive the liquid around the circuit.

[0044] In some embodiments, the method may further comprise the step of activating a start-up pump to initiate circulation of the liquid in the primary circuit. The method may further comprise the step of deactivating the start-up pump once the liquid of the primary circuit is circulating.

[0045] In some embodiments, the liquid of the primary liquid circuit may be selected from: water; distilled water; and water containing a corrosion inhibitor.

[0046] Various features, aspects, and advantages of the invention will become more apparent from the following description of embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the invention are illustrated by way of example, and not by way of limitation, with reference to the accompanying drawings, of which: Figure 1 is a schematic view of a geothermal district heating system, according to one embodiment of the invention, comprising five geothermal wells arranged in series around a primary liquid circuit of the district heating system;

[0049] Figure 2 is a cross-sectional view of a geothermal well of Figure 1 , illustrating a plurality of casings supporting the geothermal well extending from ground level into the surrounding geology;

[0050] Figure 3 is a cross-sectional view of a head of a geothermal well of Figure 1 , illustrating the internal liquid flow into and out of the well; and

[0051] Figure 4 is a flow chart illustrating the steps of a method for delivering thermal energy to a district heating system.

[0052] Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which various embodiments, although not the only possible embodiments, of the invention are shown. The invention may be embodied in many different forms and should not be construed as being limited to the embodiments described below.

[0053] DETAILED DESCRIPTION OF EMBODIMENTS

[0054] The term "liquid" has been used herein to refer to the heat transfer medium of the primary liquid circuit. It is understood that the liquid could, in some embodiments, be water or distilled water, thereby incurring minimal impact to the surrounding environment in the event of any leakage.

[0055] With reference to Figure 1 there is illustrated a geothermal district heating system (100) according to an embodiment of the invention, comprising; a primary circuit (1) circulating a liquid (4) through a plurality of geothermal wells (5), each geothermal well (5) being separated from a subsequent geothermal well (5') by an adjacent building (10) and a cooler (15), such that the liquid (4) is heated in each geothermal well (5,5') and thermal energy from the heated liquid (4) is communicated to the adjacent building to dissipate the thermal energy thereto, cooling the heated liquid (4) before communicating the liquid (4) to a cooler (15) where further thermal energy is dissipated from the liquid (4) before being introduced into the subsequent geothermal well (5') to be reheated, wherein the repeated heating and cooling of the liquid (4) around the primary liquid circuit (1) generates a thermal syphoning effect to thereby drive the liquid (4) around the primary liquid circuit (1). The district heating system (100) can comprise two or more geothermal wells, depending on the scale of the network to be serviced, and installed at known cold locations where large residential and / or industry growth requires heat. The surface foot print for each geothermal well head (7, 7') will be approximately 10 square metres, with a capacity to produce up to 5MWth at 100°C. This allows each of the geothermal wells (5, 5') to be located in the areas where the heating is required with minimal environmental impact to the surroundings.

[0056] Each well (5) comprises an injection bore (25) for receiving liquid (4) from the primary circuit (1) at a temperature of about 50°C (4c), and a production bore (26) for returning the heated liquid (4) to the well head (7) at a temperature of about 100°C (4a). It will be appreciated by those skilled in the art, that different arrangements of the system (100) can be tailored to service more or fewer buildings (10) depending on the temperature of the liquid (4) exiting the well head (7). Additionally, the depth of the geothermal well (5) can be tailored to further increase or decrease the temperature (thermal energy) of the liquid (4) received at the well head (7) depending on the thermal requirements of the system (100).

[0057] The injection bore (25) and production bore (26) are ideally coaxially located to minimise the footprint of the well (5); however, they need not be. As shown in Figure 2, each production bore (26) is encased by an insulated casing (27) and located centrally of the injection bore (25). It is contemplated that in some arrangements, the production bore (26) and injection bore (25) can be reversed. The heated liquid (4) from the well head (7) exits via an outlet pipe (8) to be communicated to the adjacent building (10). Once the thermal energy has been released from the liquid (4) to building (10) and cooler (15) the liquid (4) is injected into the well (5') via inlet pipe (9) to be re-energised.

[0058] Returning to Figure 1 , between each of the plurality of wells (5, 5') is the adjacent building (10) requiring heat from the system (100), and the cooler (15). The building (10) can be arranged in a series with one or more additional buildings (11 , 12). The number of buildings that can be serviced between each geothermal well (5) will be a function of the temperature of the liquid (4) at the well head (7) within the primary circuit (1) and the size of the building (10) to be serviced.

[0059] As heat or thermal energy from the heated liquid (4) of the primary liquid circuit (1) is communicated to each building the temperature of the liquid in the primary liquid circuit (1) is reduced. The heat from the liquid (4) of the primary liquid circuit (1) can be communicated to each building (10, 11 , 12) of the system (100) in two manners:

[0060] (a) communicating the heated liquid of the system directly into the buildings and through a boiler system or individual radiators of each building; or

[0061] (b) installing a heat exchanger in co-operation with each building to interface with the system (100), to thereby transfer heat and not liquid into each building.

[0062] Each of manners (a) and (b) has advantages and disadvantages. For example, allowing the liquid (4) to directly enter each building can provide ease of metering thermal demand / use for each customer. Alternatively, keeping the liquid (4) of the system (100) distinctly separated from any internal fluid system of each building (10, 11 , 12) can prevent corrosion and any particle impurities within the liquid from older buildings entering and damaging any internal fluid system of a newer building in the network. Where each building of the district cooling network merely interfaces with the primary circuit (1) and does not form a part of the primary liquid circuit (1) the buildings (10,11 ,12) may require additional pumping means for circulating the received thermal energy within an internal heat transfer medium, independently of the district heating system (100). In some embodiments of the system (100) buildings utilising manner (a) and buildings utilising manner (b) can be contemporaneously supplied with thermal energy from the primary liquid circuit (1).

[0063] Whether the heated liquid (4) physically enters the building (10,11 ,12) or dissipates heat via a heat exchanger in co-operation with each of the buildings (10,11 ,12), thermal energy is removed from the liquid (4) reducing the temperature thereof. After thermal energy is dissipated to the building (10) the temperature of the liquid (4) reduces from about 100°C to about 90°C (4b). Each building (10, 11 , 12) connected to the district heating system will require either: (i) an inlet and an outlet; or (ii) an interface, to receive thermal energy from the heated liquid (4) of the primary liquid circuit (1). The internal systems of each building (10, 11 , 12) can be independently configured in numerous ways to allow the thermal energy from the liquid (4) to be utilised by the internal building systems.

[0064] Multi-storey buildings represent a particularly efficient use of the district heating system (100) as minimal connections / interfaces to and from the primary liquid circuit (1) are required; however, individual residences can also be integrated into the district heating system (100), although not represented in Figure 1. There may be competing interests in relation to market suppliers wanting to supply heat to an existing district heating system generated from solar, fossil, or wind energy sources, until geothermal energy takes its market position. However, the thermal syphoning district heating system described herein solves or at least reduces existing problems with system maintenance down time as there are no mechanical pumps within the system (100) that can fail, and minimal well maintenance required.

[0065] A further advantage of the system (100) is the ability to solve cold spots. Existing fossil fuel heating plants and wood chip heating plants are typically situated more than 20km away from residential and business areas (customers). As new buildings are erected, generally in areas where people want to live, cold spots can be created. This presents a problem for existing district heating companies. Unlike the very large fossil fuel heating plants, a single closed loop geothermal well (5) can be drilled in the residential areas to provide a circulatory boost to the system (100) in the cold spot. The lower the temperature of the liquid (4) going into the geothermal well (5), the higher the levels of thermal energy that can be harvested from this well (5). For example, in a warmer portion of the system (100), the temperature of the liquid in the system might be 80°C and the production temperature from the well would be about 100°C; providing a delta T of about 20°C. This is contrasted to a cold portion of the system, where the injection temp might be about 60°C and this would provide a Delta T of 40°C; thereby doubling the return.

[0066] In some embodiments of the system (100), the heat within circulating liquid (4) can be further utilised within the building (10) to at least partially fulfil the building's pumping requirements and thereby circulate internal heating fluids, rather than depending on an external power source. For example, where a heat exchanger is utilised to transfer thermal energy from the heated liquid (4) to the adjacent building (10), the corporate body or building owner can elect to draw a portion of the transferred thermal energy to drive a pump to circulate the thermal energy around the building. As such, the energy source for the building's pumping requirements can also be drawn from the building side of the system, and metered accordingly. The meters can measure heat and liquid flow volume into, and out of, the heat exchanger. Each individual building (10) or customer of the district heating system (100) can then use this thermal energy for supplementary purposes, such as pumping, heating water, heating building, processing facilities, air conditioning etc. It is envisioned that each customer will simply pay for the heat that they extract from the district heating system (100). As the liquid (4) releases heat to the first building (10) an average temperature drop of 10°C is anticipated in the primary circuit (1). The liquid (4) is then at a temperature of about 90°C (4b) and is communicated by means of insulated piping (2) to a secondary building (11). Again delivering thermal energy to the secondary building (11), the liquid (4) of the primary liquid circuit experiences a further 10°C drop in temperature, dropping the temperature of the liquid (4) to a temperature of about 80°C. The liquid (4) is then communicated between the secondary building (11) and the tertiary building (12), where a further anticipated 10°C drop in temperature will occur on losing thermal energy to the tertiary building (12). In some embodiments of the system (100) the number of buildings (10, 11 , 12, xx) can be designed such that the cooler (15) is no longer required, as a sufficient temperature drop can be achieved to bring the liquid (4) down to a temperature of about 50°C for reinjection into the well (5').

[0067] In Figure 1 , the liquid (4) communicated from the tertiary building (12) is at a temperature of about 70°C and is piped directed to the cooler (15) to reduce the temperature of the liquid (4) further. The cooler (15) can be configured as a condenser or heat exchanger. The heat exchanger is cooled by exposure to ambient air, which can be below 0°C in the northern hemisphere during the winter months. Alternatively, cooler (15) can be configured as an extension of the insulated piping (2) of the primary liquid circuit (1) where insulation is removed to provide non-insulated piping (3) to better facilitate heat exchange with cold ambient air.

[0068] As the liquid (4) exits from the cooler (15) the temperature has dropped to around 50°C at which temperature the liquid (4) is reinjected to the subsequent geothermal well (5'). A sufficient temperature differential is required between the liquid (4) entering the injection bore (25) of the well (5) and the liquid (4) exiting the production bore (26) of the well (5) to maintain the thermal syphoning effect that drives the liquid (4) around the primary circuit (1).

[0069] At each geothermal well (5, 5') of the system (100) the liquid (4) is reheated and exhausted from the well (5) at around 100°C and 100bar of pressure. A calculated flow rate of liquid (4) from the well head (7) will be a volume of about 10kg / second. As the heated liquid (4) is exhausted from each well (5, 5'), the cooler liquid (4) from the respective coolers (15, 15') is drawn into the injection bore (25) to replace the exhausted heated liquid (4) effectively pumping the liquid (4) around the circuit (1) independently of any mechanical or electrically driven pump / s. In this manner extraneous power sources are eliminated from the district heating system (100) thereby reducing the environmental impact of the system (100) and significantly reducing the running costs thereof. The geothermal wells (5) require bottom-hole geology temperatures of about 200°C to heat the liquid (4). In this description, the liquid is water; however, it is contemplated that other liquids can be used in the primary circuit (1). Water is a low risk liquid, as any leaks or damage to the system (100) will release nothing more than water into the surrounding environment.

[0070] The system (100) uses the thermal syphoning effect to force the geothermally heated liquid (4) to the surface (G) as the cooler liquid (4) is drawn into the well (5) to heat. However, in some embodiments, the primary circuit can also comprise a start-up pump to initiate liquid circulation of a new well or a well that has been isolated for service or maintenance before the thermal syphoning affect provides all of the flow at the required temperature. At such time as the thermal syphoning process begins, there is no further requirement for pumping (eg. zero external energy input to keep the system running).

[0071] In the summer months, the district heating system (100) can be shut down allowing time for any required maintenance of piping (2, 3, 8, 9) and coolers (15). When the geothermal wells (5) have been sitting without flow or thermal energy production, the temperature of the liquid (4) inside of the production bore (26) will equalise with the temperature of the liquid in the injection bore (25). The total volume of liquid (4) in the well (5) is then heated according to thermal gradients of the surrounding geology. As such, the residual liquid (4) in each geothermal well (5) will be warmer than the liquid (4) in the non-insulated piping (3), which can then be used to re-initialise the system (100).

[0072] To start the thermal syphoning effect in the system (100), a small amount of liquid (4) movement is required. This can be achieved with a start-up pump within the primary circuit, for example a small 10kW pump. Alternatively, a store of ambient temperature water held in an elevated storage tank can be delivered into each injection bore (25) of each well (5, 5') by gravity and water head pressure which would avoid the requirement for additional energy. As soon as a volume of cooler liquid (4) is added to the well head (7), the weight of the newly added liquid (4) which will be heavier than the weight of the hotter liquid (4) inside of the well (5), and a flow from the well head (7) will increase as the cooler liquid (4) continues to be added and drawn into the injection bore (25) of the well (5). Within a few minutes, the start-up pump or supply of stored ambient temperature water can be discontinued as the thermal syphoning effect will generate the flow within the primary liquid circuit (1). Geothermal well

[0073] The geothermal well (5) and well head (7) are further described in relation to Figures 2 and 3.

[0074] One of the plurality of geothermal wells (5) is illustrated in Figure 2 to provide a means for circulating liquid (4) into the injection bore (25) and out of the insulated production bore (26) thereby supplying heated liquid (4) to the well head (7). The bores (25, 26) are arranged coaxially in tubing strings within the wellbore (5). Shown in Figures 2 and 3, the well (5) includes a well inlet (20), and a well outlet (21), both arranged within a dual-flow well head. The well head (7) can further comprise a pair of valves (not illustrated) for adjusting the inlet flow volume to or outlet flow volume from the well (5)

[0075] The injection bore (25) receives liquid from the well inlet (20) and is defined between a noninsulated casing (28) and an insulated casing (27). The production bore (26) is defined by the insulated casing (27) positioned within the non-insulated casing (28). The production bore (26) provides the heated liquid (4) to the well outlet (21).

[0076] Additional casings can be nested to extend the well downwards with a decreasing diameter. For example, a primary outer casing (22) extends from the well head (7) and geological surface (G) into the ground. In some embodiments, the primary outer casing (22) extends axially into the ground to a depth of approximately 100 metres. The primary outer casing (22) may have a diameter of 30 inches.

[0077] A secondary outer casing (23) is positioned within, and may abut, the primary outer casing (22) and extends from the well head and geological surface (G) into the ground at a depth greater than the primary outer casing (22). In some embodiments, the secondary outer casing (23) extends axially into the ground to a depth of approximately 1500 metres. The secondary outer casing (23) may have a diameter of 18 5 / 8 to 20 inches.

[0078] A tertiary outer casing (24) can be positioned within, and may abut, the secondary outer casing

[0079] (23) and extends from the well head and geological surface (G) into the ground) at a depth greater than the secondary outer casing (23). In some embodiments, the tertiary outer casing

[0080] (24) extends axially into the ground to a depth of approximately 3000 metres. The tertiary outer casing (24) may have a diameter of 13 3 / 8 to 16 inches. A non-insulated casing (28) is positioned with the tertiary outer casing (24) and extends past the tertiary outer casing (24) and defines a bottom of the well (5). The non-insulated casing (28) extends from about 3000 metres to a depth between 6,000 metres - 12,000 metres. The noninsulated casing (28) can have a diameter of 12 to 14.5 inches.

[0081] The insulated casing (27) is positioned within the non-insulated casing (28) and is configured to receive the flow of liquid (4) from the injection bore (25) at an end of the insulated casing (27). The liquid (4) is heated as it passes through the lower layers of geology. The slower the liquid flows down the injection bore (25), the more the heat will be transferred from the geology into the injected liquid (4).

[0082] An expanded view of the well head (7) is shown in Figure 3. The well head (7) includes a plurality of seals (29) and an exterior support member (30) to support the inlet (20) and outlet (21) of the well (5).

[0083] Thermal syphoning moves the liquid (4) within the well (5) once the system begins flowing. In some embodiments, 50°C liquid (from the cooler 15) is drawn down the well (5) where the liquid (4) is heated on its journey to the bottom of the well (5) and then pushed to the surface at the well head (7). The increased temperature and the pressure of liquid (4) created from the hot geology forces the heated liquid (4) up the insulated production casing (27) to the surface (G).

[0084] The insulated casing (27) can have an outer diameter of about 6 inches and an inner diameter of about 4 inches. The insulated casing (27) can be made from an insulated or ceramic casing.

[0085] Each geothermal well (5) can be bored to a depth of a few thousand metres up to about 12,000m into almost any geology including granite. The geothermal heat is exchanged at depth via the closed-loop system rather than bringing deep geothermal brine to the surface. The term "closed- loop" refers to the liquid (4) remaining closed within the well and not being exposed directly to the surrounding geology. Where the liquid of the well is exposed to the surrounding geology, the term "open-loop" is used to distinguish between the two types of well.

[0086] This form of closed-loop geothermal well (5) has a production life of 100+ years, with relatively low maintenance costs. The well (5) has a small physical footprint and has minimal impact on surface ground water systems, as the layers of casings around the well (5) provide protection. In some embodiments the liquid (4) of the primary circuit (1) can also contain corrosion inhibitors to reduce corrosion to the piping of the district heating system (100). The addition of corrosion inhibitors into the liquid of the primary circuit (1) will also assist in reducing corrosion around the piping of the buildings of the system (100).

[0087] In a further embodiments, the invention provides a method of supplying a district heating system (100) with thermal energy, the district heating system (100) including a plurality of geothermal wells (5), the method comprising the steps of: (a) circulating a liquid (4) within a primary liquid circuit (1) into each of the plurality of geothermal wells (5,5') and extracting the liquid (4) at an elevated temperature from each of the plurality of geothermal wells (5,5'), wherein the geothermal wells are spaced around the primary liquid circuit (1) having at least one adjacent building (10) and at least one cooler (15) disposed between each subsequent geothermal well of the circuit (1); (b) communicating the liquid (4) at the elevated temperature from each geothermal well to each respective adjacent building (10) to dissipate thermal energy thereto; (c) subsequently routing the liquid (4) to each respective cooler (15) to further dissipate thermal energy therefrom and reduce the temperature of the liquid; and (d) introducing the liquid (4) at the reduced temperature into a subsequent geothermal well (5') of the plurality of geothermal wells to be reheated, wherein the repeated heating and cooling of the liquid (4) within the primary liquid circuit (1) creates a thermal syphoning effect to thereby drive the liquid (4) around the circuit (1).

[0088] The method can further comprise a step of initiating the circulation of the liquid (4) within the primary circuit (1) by activating a start-up pump for a predetermined duration. The start-up pump can be deactivated once the thermal syphoning effect is initiated, at which time the thermal syphoning effect will maintain the circulation of liquid (4) within the primary circuit (1).

[0089] It will be appreciated by persons skilled in the art that numerous variations and modifications may be made to the above-described embodiments, without departing from the scope of the following claims. The present embodiments are, therefore, to be considered in all respects as illustrative of the scope of protection, and not restrictively.

[0090] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, a limited number of the exemplary methods and materials are described herein.

[0091] As used herein and in the appended claims, the singular form of a word includes the plural, unless the context clearly dictates otherwise. Thus, the references "a," "an" and "the" are generally inclusive of the plurals of the respective terms. For example, reference to "a feature" includes a plurality of such "features." The term "and / or" used in the context of "X and / or Y" should be interpreted as "X," or "Y," or "X and Y.

[0092] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

[0093] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[0094] LEGEND

Claims

CLAIMS A geothermal district heating system, comprising a primary circuit circulating a liquid through a plurality of geothermal wells, each geothermal well being separated from a subsequent geothermal well by an adjacent building and a cooler, such that the liquid is heated in each geothermal well and thermal energy from the heated liquid is communicated to the adjacent building to dissipate the thermal energy thereto cooling the heated liquid before communicating the liquid to a cooler where further thermal energy is dissipated from the liquid before being introduced into the subsequent geothermal well to be reheated, wherein the repeated heating and cooling of the liquid around the primary circuit generates a thermal syphoning effect to thereby drive the liquid around the primary circuit. The geothermal district heating system of claim 1 , wherein no additional pumping equipment is incorporated within the primary circuit for maintaining circulation of the liquid. The geothermal district heating system of claim 1 , wherein the liquid of the primary liquid circuit is introduced into the adjacent building to communicate thermal energy to the adjacent building. The geothermal district heating system of claim 1 , wherein the liquid of the primary liquid circuit is communicated to a heat exchanger to thereby transfer thermal energy to the adjacent building. The geothermal district heating system of claim 1 , wherein a flow pressure of the heated liquid exiting each geothermal well of the primary circuit encourages circulation of the liquid around the primary circuit. The geothermal district heating system of claim 1 , wherein the liquid of the primary circuit exiting each cooler is drawn into each respective geothermal well of the primary circuit by a temperature differential and / or a pressure differential between the liquid on entering the geothermal well and the liquid on exiting the geothermal well.The geothermal district heating system of claim 1, wherein each geothermal well comprises an injection bore and a production bore, the injection bore receiving cooled liquid and the production bore exhausting heated, pressurised liquid. The geothermal district heating system of claim 8, wherein the injection bore and the production bore are coaxially aligned, the injection bore circumferentially bounding and insulating the production bore therein. The geothermal district heating system of claim 1, wherein the cooler dissipates heat directly to atmospheric air. The geothermal district heating system of claim 1, wherein the cooler comprises a conduit or pipe. The geothermal district heating system of claim 1, wherein the cooler comprises a conduit or pipe of the primary circuit having minimal insulation. The geothermal district heating system of claim 1 , wherein the cooler comprises an atmospherically cooled heat exchanger. The geothermal district heating system of claim 1 , wherein a plurality of buildings are arranged in series to receive thermal energy from the heated liquid from the primary liquid circuit before discharging the cooled liquid to the cooler. The geothermal district heating system of claim 1 , wherein a plurality of buildings are arranged in parallel to receive thermal energy from the heated liquid from the primary liquid circuit before discharging the cooled liquid to the cooler. The geothermal district heating system of claim 1 , wherein the primary liquid circuit is configured to fluidly communicate with internal heating and / or cooling systems within each building. The geothermal district heating system of claim 1 , wherein the heated liquid is drawn from each of the plurality of geothermal wells at a temperature in excess of 100°C.The geothermal district heating system of claim 1 , wherein the heated liquid is drawn from each of the plurality of geothermal wells at a pressure of about 100bar. The geothermal district heating system of claim 1 , wherein the heated liquid is drawn from each of the plurality of geothermal wells at a flow rate of about 10kg / second. The geothermal district heating system of claim 1 , wherein the cooled liquid is directed to a respective cooler at a temperature of about 70°C. The geothermal district heating system of claim 1 , wherein the cooled liquid from a cooler enters each geothermal well at a temperature of about 50°C. The geothermal district heating system of claim 1 , wherein each geothermal well is a closed loop preventing contact between the liquid of the primary liquid circuit and geology surrounding the geothermal well. The geothermal district heating system of claim 1 , wherein each geothermal well is drilled to a sufficient depth to access a bottom-hole temperature of above 180°C. The geothermal district heating system of claim 1 , wherein each geothermal well is drilled to a depth between 6,000 metres and 12,000 metres. The geothermal district heating system of claim 1 , wherein a start-up pump is incorporated into the primary circuit to initiate movement of the liquid within the primary circuit. The geothermal district heating system of claim 1 , wherein a liquid storage tank is incorporated within the primary liquid circuit, to store a volume of liquid at ambient temperature, the liquid storage tank configured to release the stored volume of liquid into at least one of the geothermal wells to thereby initiate circulation of the liquid within the primary liquid circuit on start-up. A method of supplying a district heating system with thermal energy, the district heating system including a plurality of geothermal wells, the method comprising the steps of:(a) circulating a liquid within a primary liquid circuit into each of the plurality of geothermal wells and extracting the liquid at an elevated temperature from each of the plurality of geothermal wells, wherein the geothermal wells are spaced around the primary liquid circuit having at least one adjacent building and at least one cooler disposed between each subsequent geothermal well of the circuit;(b) communicating the liquid at the elevated temperature from each geothermal well to each respective adjacent building to dissipate thermal energy thereto;(c) subsequently routing the liquid to each respective cooler to further dissipate thermal energy therefrom and reduce the temperature of the liquid; and(d) introducing the liquid at the reduced temperature into a subsequent geothermal well of the plurality of geothermal wells to be reheated, wherein the repeated heating and cooling of the liquid within the primary liquid circuit creates a thermal syphoning effect to thereby drive the liquid around the circuit. The method of claim 26, comprising the step of activating a start-up pump to initiate circulation of the liquid in the primary circuit. The method of claim 27, comprising the step of deactivating the start-up pump once the liquid of the primary circuit is circulating. The geothermal district heating system of any one of claims 1 to 25 or the method of any one of claims 26 to 28, wherein the liquid of the primary liquid circuit is selected from: water; distilled water; and water containing a corrosion inhibitor.

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