Closed loop geothermal and heat pump system

Abstract

A method includes determining a specified demand over time for thermal energy from a heat exchanger of a heat pump. The heat pump is configured to transfer thermal energy from a geothermal working fluid circulating in a closed loop geothermal well to the heat exchanger. The closed-loop geothermal well includes a first ground wellbore extending from a land surface to a geothermal subsurface; a second surface wellbore extending from the land surface to the geothermal subsurface; and a plurality of connection wellbores connecting the first surface wellbore to the second surface wellbore. The heat output of the heat exchanger is controlled by adjusting at least one of the flow or inlet temperature of geothermal working fluid in the closed loop geothermal well to meet specified requirements.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to geothermal systems and methods. BACKGROUND

[0002] Geothermal systems utilize heat within the Earth for surface heat distribution, power generation, or other applications. Some geothermal systems employ a geothermal working fluid that is injected into a closed loop of wellbores drilled into a subterranean region. The geothermal working fluid can be recovered after it has absorbed heat from the subterranean region.

[0003] Heat pump systems transfer heat from one location to another through a refrigerant fluid. For example, a typical mechanical heat pump system is composed of an evaporator, a compressor, a condenser, and an expansion valve. The refrigerant absorbs heat in the evaporator, is compressed by the compressor, releases heat in the condenser, and is decompressed at the expansion valve. This enables the heat pump to efficiently provide heating or cooling by moving heat rather than, for example, generating heat. SUMMARY

[0004] The present disclosure relates to geothermal energy production.

[0005] Certain aspects of the subject matter described herein can be implemented as a method. The method includes determining a specified demand for thermal energy from a heat exchanger of a heat pump over time. The heat pump is configured to transfer thermal energy from a geothermal working fluid circulating in a closed loop geothermal well to the heat exchanger. The closed loop geothermal well includes a first surface wellbore extending from a land mass surface to a geothermal subterranean region, a second surface wellbore extending from the land mass surface to the geothermal subterranean region, and a plurality of connecting wellbores connecting the first surface wellbore to the second surface wellbore. The method further includes controlling a thermal output of the heat exchanger to meet the specified demand. The controlling is achieved at least in part by adjusting at least one of a flow rate or an inlet temperature of the geothermal working fluid in the closed loop geothermal well.

[0006] One aspect, which can be combined with any other aspect, can include the following feature: the thermal energy from the heat exchanger can provide a first portion of thermal energy provided to a heat distribution system. The method can further include providing a second portion of thermal energy provided to the heat distribution system with thermal energy extracted directly from the geothermal working fluid, other than through the heat pump.

[0007] One aspect, which can be combined with any other aspect, can include the following feature: the thermal energy from the geothermal working fluid transferred by the heat pump can include a first portion of thermal energy from the geothermal working fluid, and the method further includes generating electrical power with a second portion of thermal energy from the geothermal working fluid.

[0008] One aspect, which can be combined with any other aspect, can include the following feature: flow of working fluid in the closed loop geothermal system can be achieved by thermosyphon.

[0009] One aspect, which can be combined with any other aspect, can include the following feature: flow of geothermal working fluid in the closed loop geothermal system can be driven at least in part by a circulation pump.

[0010] One aspect, which can be combined with any other aspect, can include the following feature: the heat pump can be a mechanical heat pump.

[0011] One aspect, which can be combined with any other aspect, can include the following feature: the heat pump can be an absorption or adsorption heat pump.

[0012] One aspect, which can be combined with any other aspect, can include the following feature: the specified demand is an annual peak demand, and is greater than 1 megawatt.

[0013] Certain aspects of the subject matter described herein can be implemented as a method that includes determining a specified target heat output provided to a district heat network based at least in part on a predicted electricity price or heat price. The method further includes controlling operation of a closed loop geothermal well by controlling a heat output of a heat exchanger of a heat pump to meet the target heat output. The closed loop geothermal well includes a first surface wellbore extending from a land surface to a geothermal subsurface region, a second surface wellbore extending from the land surface to the geothermal subsurface region, and a plurality of connecting wellbores connecting the first surface wellbore to the second surface wellbore. The heat pump is configured to transfer thermal energy from a geothermal working fluid circulating in the closed loop geothermal well to the heat exchanger. Controlling the heat pump is achieved at least in part by adjusting a flow rate and / or an inlet temperature of the geothermal working fluid in the closed loop geothermal well.

[0014] One aspect, which can be combined with any other aspect, can include the following feature: the target heat output can be based in part on at least one of a net cash flow and a predicted heat versus time varying electricity price.

[0015] One aspect, which can be combined with any other aspect, can include the following feature: flow of working fluid in the closed loop geothermal system can be achieved by thermosyphon.

[0016] One aspect, which can be combined with any other aspect, can include the following feature: flow of geothermal working fluid in the closed loop geothermal system can be supported in part by a circulation pump.

[0017] One aspect, which can be combined with any other aspect, can include the following feature: thermal energy from the heat exchanger can provide a first portion of thermal energy provided to a thermal distribution system. The method can further include providing a second portion of thermal energy provided to the thermal distribution system directly from geothermal working fluid extraction, other than through the heat pump.

[0018] One aspect, which can be combined with any other aspect, can include the following feature: the heat pump can be a mechanical heat pump.

[0019] One aspect, which can be combined with any other aspect, can include the following feature: the heat pump can be an absorption or adsorption heat pump.

[0020] One aspect, which can be combined with any other aspect, can include the following feature: thermal energy from the resistive heater can provide a portion of the thermal energy to a thermal distribution system. The method can further include providing a second portion of thermal energy to the thermal distribution system with thermal energy directly extracted from geothermal working fluid of the closed loop geothermal system and transferred through the heat pump, wherein an allocation of thermal energy provided between the systems can be determined based in part on forecasted electricity and heat prices.

[0021] One aspect, which can be combined with any other aspect, can include the following feature: the prediction time horizon can be less than 72 hours.

[0022] One aspect, which can be combined with any other aspect, can include the following feature: the closed loop geothermal system can be operated in a dispatchable manner through a charge-discharge cycle.

[0023] One aspect, which can be combined with any other aspect, can include the following feature: thermal energy from the geothermal working fluid transferred by the heat pump can include a first portion of thermal energy from the geothermal working fluid. The method can further include generating electricity with a second portion of thermal energy from the geothermal working fluid.

[0024] One aspect, which can be combined with any other aspect, can include the following feature: the specified demand is an annual peak demand, and is greater than 1 megawatt. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a graphical illustration of heat demand on a city scale over a one year period, in accordance with the concepts described herein.

[0026] Figure 2A is a schematic side cross-sectional view of another exemplary closed loop geothermal system, in accordance with the concepts described herein.

[0027] Figure 2B is a schematic side cross-sectional view of another exemplary closed loop geothermal system, in accordance with the concepts described herein.

[0028] Figure 2C This is a schematic lateral cross-sectional view of another exemplary closed-loop geothermal system conceived in this paper.

[0029] Figure 3 This is a schematic diagram of a heat pump system conceived in this paper, supplied by geothermal working fluid circulating in a closed-loop geothermal system.

[0030] Figure 4 It is a graphical diagram illustrating how the coefficient of performance varies with the required thermal temperature, based on the concept conceived in this paper.

[0031] Figure 5 This is a graphical diagram illustrating the change in heat output with the flow rate of the geothermal working fluid circulating in a closed-loop geothermal system, based on the concept conceived in this paper.

[0032] Figure 6 It is a graphical diagram illustrating how the coefficient of performance varies with the required thermal temperature, based on the concept conceived in this paper.

[0033] Figure 7 This is a graphical diagram illustrating the optimal capacity of a closed-loop geothermal and heat pump system under three different electricity prices and a constant heat price.

[0034] Figure 8 This is a graphical diagram illustrating the variation of the coefficient of performance (COP) with heat output at the condenser of different systems, based on the concept conceived in this paper.

[0035] Figure 9 This is a graphical representation of heat demand under conditions where intraday electricity prices are variable.

[0036] Figure 10 It is a schematic diagram illustrating the parallel operation of a resistance heater, a combined heat pump, and a closed-loop geothermal system.

[0037] Figure 11 An example of a “cascaded configuration” is illustrated in which the geothermal working fluid of the closed-loop geothermal system is preheated before the heat distribution fluid enters the heat pump evaporator.

[0038] Figure 12 It shows the relationship with Figure 11 A similar cascaded configuration, but in the opposite direction.

[0039] Figure 13 This is a schematic diagram of a combined closed-loop geothermal system with a heat pump, which can be configured to include a combined heat and power (CHP) mode, prioritizing the sale of heat while surplus heat is directed to an organic Rankine cycle unit to generate electricity.

[0040] Figure 14 It shows in Figure 10The example shown illustrates how heat from the geothermal working fluid can be distributed in the configuration depicted. Detailed Implementation

[0041] The production of intermediate-temperature heat and steam (considered here to be between 100–400°C) may present challenges in terms of decarbonization. Current heat pump systems suffer from low theoretical maximum thermal efficiency and engineering difficulties, which may limit the application of producing this level of heat using ambient temperature heat sources via heat pump systems.

[0042] In a closed-loop geothermal system, the geothermal working fluid circulates within a closed loop comprising an underground well and a surface facility. The geothermal working fluid is heated by the soil (rock) surrounding the well and then circulates to the surface, where the surface facility extracts heat from the geothermal working fluid. In some cases, the facility includes a heat exchanger for extracting heat and transferring it to an associated process, such as a Rankine cycle (e.g., an organic Rankine cycle) or other thermal cycles for power generation, district heating plants, steam generation processes, or other processes. In some cases, the process directly uses the heated geothermal working fluid, for example, by passing it through an expander (e.g., a turbine) to drive a generator, or by directly using the heat from the geothermal working fluid for industrial, agricultural, or residential applications. In a closed-loop system, the primary heat transfer is conduction between the geothermal working fluid and the soil (rock) surrounding the well. Therefore, the well is sealed to prevent (complete or substantially) contact between the geothermal working fluid and natural fluids in the formation, such as groundwater.

[0043] In some cases, heat production in a closed-loop geothermal system may be limited by underground temperatures. If the rock temperature exceeds the required process temperature, methods to bring these high temperatures to the surface include increasing the inlet temperature and / or reducing the circulation rate of the geothermal working fluid. The disadvantage of both methods is that they both reduce the heat output of the closed loop and thus reduce the potential revenue gained from heat sales for a given closed-loop system. In other words, the same capital expenditure can be used to build the closed loop, but the heat output is reduced at higher production temperatures. For example, if the required process heat is provided in the form of steam (rather than pressurized liquid water), a high outlet temperature may be required to provide the latent heat needed to convert the liquid water into steam (which will further reduce the system's heat output).

[0044] In addition to providing baseload heat, a solution is needed to provide flexible / schedulable heat production to meet daily and seasonal variations in heat demand throughout the year. Closed-loop geothermal systems may not be economically viable for storing underground thermal energy on seasonal timescales, and dispatchable operation may only be efficient on intraday cycles. Since a large portion of the cost of a closed-loop geothermal system may be capital expenditure, and marginal production costs are low, it may be necessary to operate the system at close to 100% capacity factor to achieve economic viability.

[0045] Compared to closed-loop geothermal systems, heat pump systems likely represent a large portion of their total cost in operating expenses, primarily due to electricity expenditures. For example, if the electricity price is €100 / MWh and the heat pump's COP is 2.5, the heat cost (ignoring the heat pump's capital cost and other operating costs) would be approximately €100 / MWh ÷ 2.5 = €40 / MWh. This makes the unit economics of heat pump use extremely sensitive to electricity prices. Due to the high marginal production costs, heat pumps may operate with a low capacity factor (typically less than 50%), thus providing flexible / schedulable heat production.

[0046] Besides efficiency challenges, heat pump system design may also present engineering limitations, primarily around the compressor. Some off-the-shelf heat pumps are limited to a temperature rise of <100°C. Generally, higher temperature rises require higher compression ratios, leading to multi-stage compressor designs, complex engineering structures, and high costs due to extreme operating conditions (high compressor pressure ratios). Therefore, heat pumps are rarely able to deliver heat above 120°C (using ambient temperature heat sources). To provide even higher temperatures (for industrial applications and / or steam generation), even higher temperature heat sources are required (which are often unavailable or difficult to obtain).

[0047] The demand curve for a heat distribution network (such as a district heating network) can be correlated with ambient temperature. Throughout the year, the hours with the lowest daytime ambient temperatures correspond to the hours with the highest heat demand. Most networks have a base load heat demand for hot water heating and other uses. Figure 1 This is a graphical representation of the regional heat demand (30 MWth base load demand and 210 MWth peak demand) of an exemplary medium-sized European city. Providing flexible / schedulable heat production throughout the year to meet heat demand can be challenging.

[0048] Compared to applications using small heat pumps for individual residential or commercial buildings (e.g., small ground-source heat pumps), large heat distribution networks designed to provide heat on a regional scale or for industrial use (typically with annual peak demand > 1 MW(heat)) may require significantly higher input temperatures when ambient temperatures are at their lowest (peak heat demand coincides with peak temperature rise). If the heat pump is powered by a heat source that is affected by environmental conditions (such as water, air, etc.), this can result in the system efficiency being at its lowest during peak demand periods.

[0049] Figure 2AAn exemplary closed-loop geothermal system 100 conceived herein is illustrated in a schematic lateral cross-section. In some cases, this closed-loop geothermal well system may be, for example, a system developed by Eavor Technologies Inc. of Calgary, Alberta, Canada, comprising a network of sealed lateral wells for heat exchange with underground areas. Figures 2A to 2C The illustrated closed-loop system (including multiple lateral wells connecting the inlet and outlet surface wells) offers a larger surface area for heat transfer from geothermal zone 204 compared to other closed-loop systems (e.g., pipe-in-pipe systems). The multi-lateral closed-loop system design improves the capital efficiency of the closed-loop system because the majority of the wells are free of casing, lining, and / or cement, eliminating the use of large amounts of consumable materials during well construction. When combined with a heat pump system, the multi-lateral closed-loop system offers a wider range of inlet temperature and flow rate selection due to a stronger thermosiphon effect, significantly reducing or even completely eliminating the parasitic load on the circulating pump compared to other closed-loop systems. Furthermore, the multi-lateral closed-loop system can have a larger underground volume and residence time for the geothermal working fluid, thereby enhancing the system's energy storage capacity, which is beneficial for dispatchable operation.

[0050] System 200 includes a geothermal well 202 that drills into the earth through a geothermal subsurface region 204 of interest. In some cases, this subsurface region is a stratum, part of a stratum, or multiple strata in which naturally occurring fluids are minimal or nonexistent. In some cases, the stratum may be impermeable or substantially impermeable (e.g., 0.1 millidarcy or less). In some cases, the subsurface region is located within a basement stratum. In some cases, the rock in the subsurface region is granite. In the illustrated example, well 202 includes an inlet surface wellbore 220 and an outlet surface wellbore 230 that are close to each other, each extending between the surface of the landmass and the subsurface region 204. The inlet surface wellbore 220 and the outlet surface wellbore 230 are connected within the subsurface region 204 by one or more connecting wellbores 240. In the example shown, the connecting shaft 240 defines a multi-lateral configuration of the shaft, including multiple pairs of lateral shafts 250, a subset of which branches off from the inlet shaft 220, and another subset of which branches off from the outlet shaft 230. Each pair of lateral shafts 250 intersects at or near its toe at a corresponding junction. Therefore, the inlet shaft 220, the outlet shaft 230, and the connecting shaft 240 together define a closed loop.

[0051] The inlet wellbore 220 and outlet wellbore 230 can be drilled from the same drilling platform and / or located at the same well site. In some cases, wellbores 220 and 230 are drilled within 10 meters, 25 meters, 50 meters, or 100 meters of each other. In other cases, the inlet surface wellbore 220 and the outlet surface wellbore 230 can be separated by a longer distance. For example, as will be discussed in more detail below. Figure 2B One configuration is shown in which surface wellbores 220, 230 and connecting wellbore 240 define a U-shaped configuration. In some cases, when the geothermal well 202 is configured in a U-shape, the inlet surface wellbore 220 and the outlet surface wellbore 230 are drilled to be 3,000 meters or more apart.

[0052] In the example shown, the inlet surface wellbore 220 and the outlet surface wellbore 230 are vertical wellbores, drilled substantially in a straight line (i.e., without the use of directional drilling methods or equipment). In other cases, one or both of these surface wellbores are non-vertical (e.g., inclined), and / or can be drilled using directional drilling techniques. The connecting wellbore 240 is drilled through the surface wellbores 220 and 230 using directional drilling techniques, and includes a bend in its trajectory starting at the kickoff point 248 at the surface wellbores 220 and 230. Although shown inclined downwards, in some cases, some or all of these connecting wellbores can be horizontal. In some cases, the connecting wellbore 240 follows the geological dip of the strata in the subsurface area. In some cases, the length of the lateral wellbore 250 can be between 2,000 meters and 10,000 meters or longer, and its depth (measured from the surface) can be between 1,000 meters and 8,000 meters or deeper. Typical wells can be more than 3,000 meters deep.

[0053] Figure 2A Each pair of lateral shafts 250 is shown parallel to each other and extends from their respective surface shafts 220, 230 in the same direction (azimuth). The lateral shaft 250 extending from the inlet surface shaft 220 is shown above the lateral shaft 250 extending from the outlet surface shaft 230. In some cases, the upper lateral shaft 250 is located directly above the lower lateral shaft 250 (in some cases, directly above the corresponding one of the lower lateral shafts 250). Figure 2AIn this configuration, the upper lateral shafts 250 each turn to intersect with their adjacent lower lateral shafts 250 at a junction 254, thereby connecting the surface shafts 220 and 230. In other cases, one or more of the lower lateral shafts 250 may intersect with the upper lateral shaft 250. Regardless, this stacked configuration of the connecting shafts 240 defines a stacked shaft configuration, with one sub-configuration shaft located above and one sub-configuration shaft located below. In some cases, one or more additional sets of stacked configurations can be drilled from the surface shafts 220 and 230 at different depths (i.e., using different build-up points 248). Figure 2A In the middle section, the lower lateral wellbore 250 extends beyond and lies below the junction 254 to form a sump 252. This sump 252 provides a location for debris to accumulate outside the flow path through the wellbore. In other cases, one or more of the upper lateral wellbores 250 may extend beyond the junction to define the sump 252.

[0054] Figure 2A The connecting shafts 240 are inclined downwards; that is, they have an inclination angle 270 relative to the vertical. In some cases, some or all of the connecting shafts may be horizontal (i.e., the inclination angle 270 is approximately ninety degrees) or substantially horizontal. In some cases, such as... Figure 2B As shown, the connecting shaft 240 can have a steeper inclination; that is, the inclination angle 270 can be less than... Figure 2A As shown, the shaft 240 is either vertical (with an inclination angle of 270° being zero) or substantially vertical. In some cases, the connecting shaft 240 follows the geological dip of the strata in the underground area. In some cases, the lateral shaft 250 can be 2,000 meters to 10,000 meters or longer in length and 1,000 meters to 8,000 meters or deeper in depth.

[0055] Figure 2C This is another embodiment of a geothermal well system 200 with lateral wellbores 250, wherein the lateral wellbores 250 extend toward each other from the inlet surface wellbore 220 and the outlet surface wellbore 230, respectively. Once the pairs of lateral wellbores 250 intersect, they together with the inlet wellbore 220 and the outlet wellbore 230 define a generally U-shaped shape. In some cases, the configuration of the connecting wellbores 240 defines a wellbore configuration in the same plane. In some cases, one or more additional connecting wellbores may be drilled between the surface wellbores 220 and 230 at different depths (i.e., using different build-up points 248).

[0056] See also Figure 2A , 2BIn cases involving 2C, surface wellbores 220 and 230 are casingd (at least partially or completely), while connecting wellbore 240 (including the junction at build-up point 248) is open hole (i.e., without casing, liner, or junction liner). In some cases, connecting wellbore 240 may be at least partially linerred (e.g., in sections where subsurface area 204 is fractured, prone to collapse, unconsolidated, or otherwise requires liner). Connecting wellbore 240 (including the junction with inlet surface wellbore 220 and outlet surface wellbore 230) is sealed (completely or substantially sealed) with a sealant to prevent fluid exchange with the surrounding subsurface area 204. In some cases, the sealant may be in the form of a fluid sealant (e.g., an alkaline silicate fluid) flowing through the wellbore. The sealant is designed so that all or substantially all of the geothermal working fluid circulating through well 202 during operation is recovered to the surface, and naturally occurring fluids from subsurface region 204 are not recovered or are minimally recovered. In other words, the resulting well 202 is a closed loop. In some cases, the sealant may be applied to the wellbore during drilling into the connecting wellbore 240, for example, contained in the drilling fluid, and / or supplied as a fluid slug separate from the drilling fluid. Alternatively or additionally, the sealant may be applied post-drilling and / or during well operation. In some cases, the sealant may be contained in the geothermal working fluid, and / or supplied as a fluid slug separate from the geothermal working fluid.

[0057] In the illustrated example, system 200 further includes facility 210 located between inlet surface wellbore 220 and outlet surface wellbore 230. Well 202 may be sealed, and geothermal working fluid is added to this closed loop and circulates in the system, causing it to absorb heat from underground region 204. In some cases, facility 210 includes: valves and pumps for controlling the flow of geothermal working fluid through well 202; and a heat exchanger for extracting heat from the geothermal working fluid and delivering it to an associated process, such as a Rankine cycle (e.g., an organic Rankine cycle) or other thermal cycles for power generation, a steam generation process for industrial, agricultural, or residential use, or other processes. In some cases, instead of or outside of a heat exchanger, facility 210 directly uses the heated geothermal working fluid, for example, by passing it through an expander (e.g., a turbine) to drive a generator, or directly uses the heat of the geothermal working fluid for industrial, agricultural, or residential processes. In some cases, facility 210 is located at or near the Earth's surface; in others, facility 210 may be partially or completely located in an underground site. Facility 210 does not need to be located in a single location. For example, in some cases, it can be located between one or more discrete locations connected by pipes.

[0058] In the example shown, facility 210 includes a heat pump system 260 configured to extract heat from the geothermal working fluid as it circulates through a closed-loop system. Figure 3 As shown, the heat pump system 260 may include an evaporator 302, a compressor 304, a condenser 306 (driven by mechanical energy, such as from an electrical source), and an expansion valve 308 through which the heat pump working fluid circulates. The heat pump system includes a heat exchanger 310 for achieving heat exchange from the geothermal working fluid to the heat pump working fluid; and a heat exchanger 312 for achieving heat exchange from the heat pump working fluid to a heat distribution system (e.g., a district heating network). As those skilled in the art will understand, a closed-loop geothermal system provides thermal energy that is mechanically raised to the temperature (Q) required for the heat demand. 冷凝器 In other words, the heat pump is the interface between heat demand and the closed-loop geothermal system. The advantage of this configuration is that it eliminates the interaction between the closed-loop geothermal system and heat demand (and the temperature constraints resulting from this interaction), thereby providing maximum flexibility and optimization opportunities to improve system output.

[0059] The efficiency of a heat pump system 260 is represented by its coefficient of performance (COP), which is defined by the following formula: COP = Q 冷凝器 / Q 电 (1) Among them, Q 冷凝器 For the heat output of the heat pump, and Q 电 This is the electrical input to the compressor. The energy balance of this system can be expressed as follows: Q 冷凝器 = Q 电 + Q 蒸发器 (2) Among them, Q 蒸发器 The heat absorbed by the evaporator. A heat pump COP greater than 1 means that the heat energy exchanged is greater than the electrical energy supplied to the system. The second law of thermodynamics limits the maximum COP of a heat pump as follows: COP 卡诺 = T 热 / (T 热 – T 冷 ) = T 热 / T 温升 (3) Alternatively, the Lorenz method can be used to evaluate the COP with temperature glide. Commercial heat pump systems typically achieve a COP that is 50% to 60% of the maximum Lorenz / Carnot COP. 热 – T 冷 This is called the lift temperature required by the system: the greater the lift temperature, the lower the efficiency of the heat pump.

[0060] Figure 4 This is a graphical diagram illustrating how the COP changes with the heat demand of a heat pump system, based on the concept conceived in this paper. More specifically, Figure 4 This example illustrates how the COP varies with different required heat temperature levels, assuming a COP of 55% of the Carnot COP. The COP is approximately 2.8 when generating 80°C of heat from a constant 10°C heat source; however, the COP is below 2 when generating 120°C of heat. Many heat distribution networks, especially older and less efficient district heating networks, require peak demand temperatures ≥120°C. This variation in COP with required temperature also affects the carbon intensity of these systems, depending on the power grid structure supplying the heat pump.

[0061] Figure 5 This is a graphical representation of the heat output as a function of the flow rate of the geothermal working fluid circulating in a closed-loop geothermal system, based on the concept described in this paper. Two main variables can be manipulated: the geothermal working fluid circulation rate and the inlet temperature. Each variable corresponds to heat output (plotted on the vertical axis) and outlet temperature (not shown). A higher circulation rate and a lower inlet temperature maximize the temperature difference between the geothermal working fluid and the rock (and thus maximize heat output), but will decrease the outlet temperature.

[0062] This interdependence between flow rate and inlet temperature and outlet temperature is often unique to closed-loop systems, so changing the operating point of the loop will hardly or not increase costs at all (unless the flow rate exceeds the maximum thermosiphon rate and a circulating pump is required). Figure 5As shown, the heat output of the loop can be increased by two times or more simply by changing the operating point (e.g., a heat output of 14 MWth corresponds to an inlet temperature of 60°C and a flow rate of 60 kg / s, while a heat output of 28 MWth corresponds to an inlet temperature of 20°C and a flow rate of 150 kg / s). In systems containing only a closed-loop geothermal system, the loop operating point can be fixed based on the required heat distribution system temperature (i.e., the inlet temperature is set by the heat distribution system return water temperature (plus a small margin), and the outlet temperature is set by the required heat distribution system inlet temperature (plus a small margin)). This constraint does not apply to combined closed-loop geothermal and heat pump systems, thus increasing system flexibility and providing additional optimization opportunities. In many cases, using a circulating pump to maximize heat extraction may be optimal for the combined system, while the lower-temperature heat generated by the closed-loop geothermal system can be raised to the required temperature by the heat pump.

[0063] Figure 6 This is a graphical representation of the coefficient of performance (COP) of a closed-loop geothermal system, illustrating how the COP varies with the required heat temperature, based on the concept presented in this paper. The blue area in the figure represents a "pure heat pump" system that relies solely on ambient temperature heat, as well as two simplified closed-loop geothermal scenarios (modeled as isothermal heat sources), one producing 60°C of heat and the other producing 100°C. Higher heat source temperatures result in higher system efficiency and lower power consumption. Closed-loop geothermal operation and heat pump design can be synergistically optimized based on required heat demand, loop / heat pump capital costs, and electricity prices (operating expenses). For a given required temperature, the COP of a closed-loop geothermal heat pump system can be twice or more than that of an equivalent pure heat pump system (thus halving CO2 emissions and power consumption). Figure 6 The three production temperatures shown (120°C, 150°C, and 200°C) represent peak heat distribution network temperature, low-temperature / low-pressure steam generation, and high-temperature / high-pressure steam generation, respectively. Optimal capacity and system design are partly influenced by predicted electricity and heat prices.

[0064] Figure 7The optimal capacity of closed-loop geothermal and heat pump systems is shown for three different electricity prices and a constant heat price. In all cases, the structure and geometry of the closed-loop geothermal system are identical, and its heat output is regulated by varying the inlet temperature and flow rate. Each operating point of the closed-loop geothermal system corresponds to a specific heat input and temperature input to the heat pump's evaporator, which also determines the system's total heat output and COP. The dashed vertical lines in the figure represent the optimal system capacity that maximizes project cash flow after deducting electricity costs. This simplified example shows that the optimal system capacity increases to 48 MWth at lower electricity prices ($50 / MWh) and decreases to 23 MWth at higher electricity prices ($150 / MWh). For a given system design, reducing the power consumption of the heat pump system by adjusting the operating point (closed-loop geothermal inlet temperature and circulation flow rate) is often unique to closed-loop systems and provides system flexibility for implementation in regions with varying heat and electricity prices.

[0065] Compared to traditional geothermal systems and traditional enhanced geothermal systems (EGS), for closed-loop geothermal systems (such as...) Figure 2A and 2B The ability to control the outlet temperature and heat output (as shown) can affect the dispatchability when combined with a heat pump system. Such systems may have weak (or no) control over the outlet temperature and flow rate, and therefore cannot achieve the desired performance. Figure 2A and 2B The system shown achieves the same level of efficiency. Using the systems and methods disclosed herein, after designing to meet maximum heat demand specifications, system efficiency can be improved in off-design conditions through coordinated control of the operating points of the heat pump and geothermal working fluid circulation. The temperature of the geothermal working fluid at the ground can be adjusted to match heat demand and improve system efficiency. Reducing heat output (by decreasing the circulation rate or increasing the inlet temperature) leads to an increase in the working fluid outlet temperature, thus reducing temperature rise, increasing COP, and reducing power consumption.

[0066] Figure 8 This is a graphical representation of the coefficient of performance (COP) as a function of heat output at the condenser in different systems, based on the concept conceived in this paper. When matched to the temperature profile of the heat source, a closed-loop geothermal system can provide, for example, approximately 15 MWth. For any production exceeding this rated capacity, the operating point of the geothermal working fluid is adjusted (to increase the circulation rate and / or decrease the temperature of the geothermal working fluid at the loop inlet), thereby increasing the heat output of the geothermal system but reducing the outlet temperature. The heat generated from the closed-loop geothermal system is boosted by a heat pump to meet the temperature requirements of the heat demand. Figure 8 The maximum design capacity of the closed-loop geothermal heating pump system shown is 36 MWth (Q 冷凝器This requires maximum temperature rise. This flexibility is particularly useful in applications where heat demand fluctuates on seasonal timescales. For example, for a district heating network in winter, the system can deliver 36 MWth, while in summer, it can provide approximately 15 MWth of baseload from a closed-loop geothermal system alone, and can also efficiently generate heat when demand falls between those two extremes. Conventional pure heat pump systems lack the ability to regulate the temperature of the heat source (according to changing demand), thus the COP is flat (ignoring inefficiencies in the compressor and heat exchanger under off-design conditions). Furthermore, closed-loop geothermal systems can operate in a dispatchable manner to generate higher temperatures for certain intermittent processes or varying demands within the daily cycle, thereby reducing the heat pump's temperature rise requirement (which would be desirable for reducing electricity consumption when electricity prices are predicted to be high). Many industrial processes experience significant daily fluctuations in heat demand, and according to the concepts disclosed herein, thermal energy can be stored underground to reduce the heat pump's power consumption during peak periods.

[0067] exist Figure 9 In the example shown, under varying intraday electricity prices, heat demand is flat (20 MWth) and is determined by... Figures 2A to 2C The system described herein satisfies this requirement. It should be noted that the combined closed-loop geothermal and heat pump system can be configured to deliver heat under a wide range of intraday fluctuations in electricity prices, heat prices, and heat demand. “Heat demand” refers to the heat output of the heat pump at the condenser, while “closed-loop geothermal system heat output” refers to the input of the heat pump evaporator. According to the energy balance in Equation (2), the remaining energy is provided through the electrical input to the heat pump. Changes in electricity prices (due to a significant imbalance between electricity supply and demand trends) are often characterized by the term “duck curve,” especially as the penetration rate of intermittent renewable energy generation increases, leading to significant intraday variations in electricity prices. The dispatchability of the closed-loop geothermal system can reduce the system’s electricity expenditure and take advantage of intraday variations in electricity prices. The closed-loop geothermal system achieves dispatchability through underground energy storage, i.e., by slowing down or stopping the circulation of the geothermal working fluid through automated ground valve control, thereby extending the fluid residence time and increasing its heat absorption, thus essentially “charging” the system. When needed, the preheated fluid is rapidly displaced to the ground by increasing the circulation rate to release the energy. When electricity prices are low, the closed-loop geothermal system can be reheated, with the increase in total heat output consisting of electricity. During periods of high electricity prices, the preheated fluid can be lifted to the ground, thereby reducing the amount of electricity required to meet specific heat demands.

[0068] In some cases, such as Figure 10As shown, the heat demand can be met by system 1000, which combines a parallel-operating resistance heater 1002 with a heat pump system 260. The resistance heater 1002 converts electricity into heat with a COP of approximately 1, while the combined heat pump and closed-loop geothermal system has a COP exceeding 1. During periods of low electricity prices, the closed-loop geothermal system can be "shut down," or its heat output can be reduced to charge the system, with the resistance heater providing most or all of the heat demand. When electricity prices rise, the closed-loop geothermal system can release heat, and the heat output of the resistance heater can be reduced or eliminated entirely.

[0069] Figure 11 An example of a "cascaded configuration" 1100 is illustrated, in which the geothermal working fluid of the closed-loop geothermal system is preheated at a preheater heat exchanger 1102 before the heat pump fluid (refrigerant) enters the heat pump evaporator. The evaporator lowers the inlet temperature of the geothermal working fluid, and this energy is used to raise the inlet temperature of the heat distribution network. The advantage of this configuration is that it lowers the inlet temperature of the geothermal working fluid, thereby increasing the temperature difference between the rock and the geothermal working fluid, and improving the heat output of the closed-loop geothermal system. It should be noted that this configuration may result in a decrease in COP due to the larger temperature rise between the inlet temperature of the geothermal working fluid and the required heat demand temperature.

[0070] Figure 12 A cascaded configuration 1200 is shown, which is related to Figure 11 The configuration 1100 is similar but in the opposite direction. The higher-temperature geothermal working fluid outlet is first used by the heat pump system, resulting in a higher heat pump COP due to a smaller temperature rise. The remaining heat is used to preheat the heat pump return water fluid at the preheater 1202. This configuration has a higher heat pump COP, but relative to... Figure 8 The configuration has reduced system heat output.

[0071] like Figure 13As shown, the combined closed-loop geothermal heating pump plus Organic Rankine Cycle (ORC) configuration 1300 can include a combined heat and power (CHP) mode, prioritizing the sale of heat energy and diverting surplus heat to the ORC unit to generate electricity through a simple ORC and heat distribution heat exchanger system 1302. In this embodiment, the ORC includes one or more turbines, evaporators, regenerators, pumps, and air coolers to generate electricity from the closed-loop geothermal heat source when the heat demand is less than the base load capacity of the closed-loop geothermal system. The ORC can include a Rankine cycle or other thermodynamic cycles for power generation. The heat exchanger in system 1302 transfers heat from the closed-loop geothermal working fluid to the heat distribution network without the need for a heat pump. In some cases, the heat for the heat distribution network can be drawn from the ORC working fluid rather than directly from the closed-loop geothermal working fluid. The cooled geothermal working fluid is returned to the closed-loop geothermal well. The advantage of this operating mode is that it prioritizes the sale of heat energy, and due to minimal or no conversion losses, it can be highly economical. When the rated capacity of the closed-loop geothermal working fluid loop (without using a heat pump) exceeds the annual base load or minimum heat demand, ORC can be used to fully utilize the available heat from the geothermal working fluid and convert it into electrical energy.

[0072] Figure 14 Is Figure 10 The diagram illustrates a process flow of an example method 1400 for how heat from the geothermal working fluid can be distributed in the configuration shown. For example, it can be assumed that there is a 10 MW baseload geothermal working fluid output capable of generating the temperature profile required by the heat demand. The method begins at step 1402, where it is determined whether the heat demand of the heat distribution system is greater than or less than the baseload (e.g., 10 MW). If the demand is greater than the baseload by 10 MW, then at step 1404, the heat pump can be started (and the operating point of the geothermal working fluid adjusted) so that all heat flow from the geothermal working fluid is directed to the heat pump. If it is determined at step 1402 that the demand is not greater than the baseload, and further determined at step 1406 that the demand is exactly equal to the baseload (e.g., 10 MW), then at step 1408, all heat flow from the geothermal working fluid can be directed to the heat distribution heat exchanger. If it is determined at step 1406 that the demand is less than the baseload (e.g., less than 10 MW), then at step 1410, a portion of the heat flow can be transferred from the geothermal working fluid to the heat distribution heat exchanger, while the remaining heat flows to the ORC for power generation. (Note: The heat pump can be shut down if the heat demand is less than or equal to the base load (e.g., ≤10 MW). In some cases using this configuration, there is no situation where both the heat pump and ORC can operate simultaneously. This configuration including a heat pump and ORC is only suitable when the base load heat demand is less than the rated capacity of the closed-loop geothermal loop; otherwise, a separate geothermal working fluid loop or a geothermal working fluid loop plus a heat pump can be used economically.

[0073] In some cases, it is not the case that... Figures 2A to 2C , Figure 3 as well as Figures 8 to 10 Instead of a conventional heat pump with a compressor, the diagram shows an absorption / adsorption cycle heat pump. Essentially, an absorption / adsorption heat pump extracts medium-temperature heat from the geothermal working fluid and splits it into two streams, one for high temperature and the other for low temperature. No mechanical compression is required in such systems, which can mean significantly lower operating / electricity costs for these cycles; however, system efficiency can be lower. The COP of these cycles can be defined as: (Useful heat output (high temperature)) / (Heat input (medium temperature)). The COP of these systems can be around 50%, meaning that 0.5 MW of high-temperature heat is generated per MW of geothermal working fluid heat input. Due to this lower thermal efficiency, the benefits of these systems may be limited in some cases, and their technological maturity may be lower than that of conventional heat pumps. Furthermore, absorption / adsorption systems can also be reverse-configured when combined with closed-loop geothermal systems to produce chilled fluid suitable for district cooling networks, where the geothermal working fluid acts as a heat sink.

Claims

1. A method comprising: Determine a specified time-varying demand for thermal energy from a heat pump's heat exchanger, the heat pump being configured to transfer thermal energy from a geothermal working fluid circulating in a closed-loop geothermal well to the heat exchanger, the closed-loop geothermal well comprising: The first surface wellbore extends from the surface of the land parcel to the geothermal underground area; A second surface wellbore, extending from the surface of the land parcel to the geothermal underground region; and Multiple connecting shafts, the multiple connecting shafts connecting the first surface shaft to the second surface shaft; and The heat output of the heat exchanger is controlled to meet the specified requirements, and the control is achieved at least in part by adjusting at least one of the flow rate or the inlet temperature of the geothermal working fluid in the closed-loop geothermal well.

2. The method of claim 1, wherein the thermal energy from the heat exchanger provides a first portion of the thermal energy supplied to the heat distribution system, and the method further comprises: The second portion of the heat energy supplied to the heat distribution system is provided by heat energy extracted directly from the geothermal working fluid rather than obtained through the heat pump.

3. The method according to claim 1 or 2, wherein the thermal energy transferred by the heat pump from the geothermal working fluid includes a first portion of the thermal energy from the geothermal working fluid, and the method further comprises: Electricity is generated using a second portion of the thermal energy from the geothermal working fluid.

4. The method according to any one of claims 1 to 3, wherein the flow of the working fluid in the closed-loop geothermal system is achieved by thermosiphon.

5. The method according to any one of claims 1 to 4, wherein the flow of the geothermal working fluid in the closed-loop geothermal system is at least partially driven by a circulation pump.

6. The method according to any one of claims 1 to 5, wherein the heat pump is a mechanical heat pump.

7. The method according to any one of claims 1 to 6, wherein the heat pump is an absorption or adsorption heat pump.

8. The method according to any one of claims 1 to 7, wherein the specified demand is an annual peak demand and is at least 1 megawatt of heat.

9. A method comprising: The specified target heat output for the heat distribution system is determined, at least in part, based on the predicted electricity or heat price. as well as The operation of a closed-loop geothermal well is controlled by controlling the heat output of a heat pump's heat exchanger to meet the target heat output. The heat pump is configured to transfer thermal energy from a geothermal working fluid circulating in the closed-loop geothermal well to the heat exchanger. The closed-loop geothermal well comprises: The first surface wellbore extends from the surface of the land parcel to the geothermal underground area; A second surface wellbore, extending from the surface of the land parcel to the geothermal underground region; and Multiple connecting wells connect the first surface well to the second surface well, wherein the heat output is controlled at least in part by adjusting the flow rate and / or inlet temperature of the geothermal working fluid in the closed-loop geothermal well.

10. The method of claim 9, wherein the target heat output is based in part on at least one of net cash flow and predicted heat and electricity price changing over time.

11. The method according to claim 9 or 10, wherein the flow of the working fluid in the closed-loop geothermal system is achieved by thermosiphon.

12. The method according to any one of claims 9 to 11, wherein the flow of the geothermal working fluid in the closed-loop geothermal system is partially supported by a circulation pump.

13. The method according to any one of claims 9 to 12, wherein the thermal energy from the heat exchanger provides a first portion of the thermal energy supplied to the heat distribution system, and the method further comprises: The second portion of the heat energy supplied to the heat distribution system is provided by heat energy extracted directly from the geothermal working fluid rather than obtained through the heat pump.

14. The method according to any one of claims 9 to 13, wherein the heat pump is a mechanical heat pump.

15. The method according to any one of claims 9 to 14, wherein the heat pump is an absorption or adsorption heat pump.

16. The method according to any one of claims 9 to 15, wherein a portion of the thermal energy from the resistance heater is provided to the heat distribution system, and the method further comprises: The second portion of the heat energy is provided to the heat distribution system by heat energy extracted directly from the geothermal working fluid of the closed-loop geothermal system and transferred through the heat pump, wherein the distribution of the heat energy provided between these systems is determined in part based on predicted electricity and heat prices.

17. The method of claim 16, wherein the prediction time domain is less than 72 hours.

18. The method of claim 17, further comprising: The closed-loop geothermal system can be operated in a schedulable manner through a heat charge and discharge cycle.

19. The method according to any one of claims 9 to 15, wherein the thermal energy transferred by the heat pump from the geothermal working fluid includes a first portion of the thermal energy from the geothermal working fluid, and the method further comprises: Electricity is generated using a second portion of the thermal energy from the geothermal working fluid.

20. The method according to any one of claims 9 to 15, wherein the specified demand is an annual peak demand and is at least 1 megawatt of heat.

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