Enhanced geothermal system parameter coupling design method

Abstract

The application provides an enhanced geothermal system parameter coupling design method, and a computer storing a computer program is connected with a memory through at least one processor to realize design calculation. The application takes the maximum power generation in the whole life cycle of the enhanced geothermal system as a design target, takes the evaporation temperature of an evaporator, the flow of geothermal fluid, the number of evaporators, the expansion ratio of an expander and the like as optimization variables, adopts a programming language to call REFPROP thermophysical property parameters to realize system simulation, and can rapidly and accurately obtain an optimization result. The enhanced geothermal system parameter coupling design method provided by the application can realize the optimal operation of the enhanced geothermal system in the whole life cycle under the condition of variable heat source working conditions by considering the mutual influence of multiple optimization parameters.

Description

Technical Field

[0001] This application belongs to the field of renewable energy power generation, specifically involving an enhanced geothermal system parameter coupling design method. Background Technology

[0002] Renewable energy sources such as wind and solar power suffer from unstable power supply and high volatility, which contradicts the stability required for grid-connected operation. In contrast, hot dry rock reserves are vast and offer a stable power supply, meeting both grid-connected operation requirements and power demand. Enhanced geothermal systems, as one form of hot dry rock development and utilization, offer advantages such as long system lifespan, less pollution, and stable power supply, making them the most promising and potential hot dry rock utilization technology.

[0003] Enhanced geothermal systems inject geothermal fluids through injection wells. After exchanging heat with dry hot rock in the fractures, the high-temperature geothermal fluids are extracted from the production wells as a heat source. Subsequently, the organic working fluid undergoes Rankine cycle thermodynamic processes such as evaporation, expansion, and condensation, using the high-temperature geothermal fluids as a heat source. The system has complex components and numerous operating parameters. Among them, the geothermal fluid parameters and the organic Rankine cycle operating parameters are mutually influential and closely related, which increases the difficulty and complexity of system design. Therefore, an efficient, reasonable, and orderly parameter design method is required.

[0004] However, current research on enhanced geothermal systems is still incomplete. Most designs fail to consider the interactions between different operating parameters within the overall system, and there is a lack of an efficient coupled design method for enhanced geothermal systems that optimizes multiple parameters and objectives. On the other hand, during the long-term operation of dry hot rock geothermal reservoirs, there is a problem of the reservoir temperature decreasing year by year, which leads to a year-by-year decrease in the temperature of the geothermal fluid at the wellhead of the produced well. In other words, the heat source of the organic Rankine cycle power generation system is in a dynamic process of change.

[0005] Therefore, existing technologies urgently need coupled design methods for multi-parameter optimization of enhanced geothermal systems under variable heat source conditions. Summary of the Invention

[0006] The purpose of this application is to provide a multi-parameter optimization design method for enhanced geothermal systems under variable heat source conditions.

[0007] To achieve the above objectives, the liquefied air energy storage system parameter coupling design method provided in this application includes the following steps:

[0008] Step S1: Set the initial temperature and initial pressure of the deep geothermal reservoir based on the temperature and pressure distribution of the deep geothermal target area;

[0009] Step S2: Assuming the enhanced geothermal system scheme, calculate the geothermal fluid temperature and pressure at the wellhead of the produced well throughout the entire life cycle of the enhanced geothermal system based on the condensation temperature of the organic Rankine cycle condenser, and preliminarily determine the installed capacity of the enhanced geothermal system.

[0010] Step S3: Calculate the full life cycle evaluation index of the enhanced geothermal system based on the calculation results of step S2, and determine whether it meets the design requirements. If not, return to step S2 to modify the enhanced geothermal system scheme and the geothermal reservoir exploitation scheme. If yes, determine the optimal evaporation temperature and geothermal fluid flow rate according to the following steps S4, S5 and S6 in sequence.

[0011] Step S4: Based on the geothermal fluid temperature at the wellhead of the enhanced geothermal system throughout its entire life cycle and the annual surface temperature of the area where the enhanced geothermal system is located, as calculated in Step S2, set the evaporator evaporation temperature range and the condenser condensation temperature range, calculate the performance parameters of the enhanced geothermal system under different evaporation temperature conditions and different condensation temperature conditions, and select the evaporation temperature with the optimal performance parameters as the optimal evaporation temperature.

[0012] Step S5: Repeat step S4 to calculate the optimal evaporation temperature corresponding to different wellhead geothermal fluid temperatures of the produced wells.

[0013] Step S6: Assuming the range of geothermal fluid flow rate, call the current optimal evaporation temperature, calculate the full life cycle evaluation index of the enhanced geothermal system, and select the optimal geothermal fluid flow rate that simultaneously meets all evaluation indexes.

[0014] Step S7: Input the optimal geothermal fluid flow rate and the optimal evaporation temperature into step S4 to calculate the full life cycle evaluation index of the enhanced geothermal system. Determine whether the evaluation index has reached the optimal level. If yes, the system optimization is complete. If not, repeat step S6 to reselect the optimal geothermal fluid flow rate.

[0015] In step S1, based on the temperature T and pressure P of the deep geothermal target area, the initial temperature T0 and initial pressure P0 of the deep geothermal reservoir are set, and it is stipulated that the initial temperature T0 and initial pressure P0 satisfy the following conditions: T0 = T, P0 = P;

[0016] In step S2, the enhanced geothermal system scheme is an organic Rankine cycle power generation or cogeneration scheme. Its design scheme includes the number of evaporator stages and the number of expander stages on the heat source side. The number of evaporator and expander stages on the heat source side is set according to the geothermal fluid temperature at the wellhead of the produced well. When the geothermal fluid temperature at the wellhead of the produced well is lower than or equal to 130°C, a single-stage evaporation and single-stage expansion scheme is selected. When the geothermal fluid temperature at the wellhead of the produced well is higher than 130°C, a two-stage evaporation and multi-stage expansion scheme is selected, and the number of stages is determined according to the optimal flow rate, optimal evaporation temperature and expansion ratio.

[0017] In step S2, the single-stage evaporation scheme uses an evaporator to cool the high-temperature geothermal fluid at the wellhead of the produced well to the reinjection temperature T. in T in The parameter values ​​range from 20 to 50℃; the two-stage evaporation scheme uses one evaporator to cool the high-temperature geothermal fluid at the wellhead of the produced well to the reinjection temperature T. in T in The parameter values ​​range from 20 to 50°C; the organic Rankine cycle uses an organic working fluid to realize the Rankine cycle process; the geothermal fluid is water.

[0018] In step S4, the optimal evaporation temperature T eva The following conditions must be met:

[0019] T eva +ΔT≤T pro

[0020] In the formula, ΔT is the heat exchange temperature difference between the geothermal fluid and the organic working medium in the evaporator; T pro The temperature of the geothermal fluid at the wellhead of the extracted well.

[0021] Steps S4, S5, and S6: Optimal evaporation temperature T eva and optimal geothermal fluid flow rate m optimum The following conditions must be met:

[0022] W optimum =m optimum (h in -h out )

[0023] In the formula W optimum For optimal power generation, h in Specific enthalpy at the expander inlet; h out The specific enthalpy at the expander outlet.

[0024] P max =W optimum ·t

[0025] In the formula P max t represents the maximum power generation of the enhanced geothermal system; t represents the design operating time of the enhanced geothermal system.

[0026] The most important evaluation metrics include: optimal flow rate and optimal evaporation temperature.

[0027] Steps S1 to S7 use programming software to call the REFPROP thermophysical parameter library for simulation calculations.

[0028] An enhanced geothermal system coupling design device, comprising:

[0029] At least one processor, and a memory communicatively connected to the at least one processor;

[0030] The memory contains instructions that can be executed by at least one processor;

[0031] An enhanced geothermal system coupling design method in which instructions are executed by at least one processor to enable at least one processor to perform.

[0032] The beneficial effects of this application are:

[0033] (1) This application provides a multi-parameter design method to overcome the shortcomings of single-parameter optimization design of enhanced geothermal systems. The multi-parameter design method provided in this application designs multiple important parameters of the enhanced geothermal system at the same time.

[0034] (2) Compared with the prior art, this enhanced geothermal system design method considers the mutual influence between system components and parameters, parameters and parameters and components, and provides an enhanced geothermal system multi-parameter coupling design method.

[0035] (3) Existing technologies fail to consider the power generation performance of enhanced geothermal systems under varying heat source conditions. This application combines the temperature range and attenuation characteristics of geothermal reservoirs, and by changing the system structure and matching the optimal evaporation temperature and geothermal fluid flow rate, it is possible to achieve optimal performance of the enhanced geothermal system throughout its entire life cycle under varying heat source conditions. Attached Figure Description

[0036] Figure 1 This is a flowchart of this application.

[0037] Figure 2 This is a schematic diagram of the enhanced geothermal system in Embodiment 1 of this application.

[0038] Figure 3 This is a schematic diagram of the enhanced geothermal system in Embodiment 2 of this application. Detailed Implementation

[0039] The specific implementation methods of this application will be further described in detail below with reference to the embodiments. The scope of protection of this application is not limited to the scope of the embodiments.

[0040] The enhanced geothermal system operates as follows: During system operation, low-temperature geothermal fluid is transported to the hot dry rock geothermal reservoir via injection wells. It exchanges heat with the hot dry rock in the internal fissures of the reservoir, heating from low temperature to high temperature. This high-temperature fluid is then transported to the surface via production wells to serve as the heat source for the organic Rankine cycle power generation system. After heating the organic working fluid in the evaporator of the organic Rankine cycle power generation system, it flows back into the geothermal reservoir via injection wells to complete the heat exchange cycle. During the organic Rankine cycle, the organic working fluid, after being heated by the high-temperature geothermal fluid, enters the expander to perform work and generate electricity. In a combined heat and power (CHP) system, the organic working fluid flows out of the expander and indirectly exchanges heat with the heating system to supply heat to users. In a power generation system, the organic working fluid, after performing work in the expander, directly enters the condenser for condensation and then re-enters the evaporator for heating to complete the organic Rankine cycle power generation process.

[0041] Example 1:

[0042] Figure 2 This is a schematic diagram of a single-stage evaporation enhanced geothermal system according to a specific embodiment of this application. As shown in the figure: This system includes an expander 1, an evaporator 2, a condenser 3, a working fluid pump 4, an injection well 5, a production well 6, a cooling water system, and a geothermal reservoir. The geothermal reservoir has been operated using artificial fracturing technology and contains a hydraulically interconnected network of artificial fractures. The cooling water system is connected to an external cold source to cool the condenser. The specific working process is as follows:

[0043] When the organic Rankine cycle is working, the organic working fluid flows through the evaporator, is heated by the high-temperature geothermal fluid and becomes superheated and saturated, and then enters the expander to do work to complete the power generation process. Subsequently, the exhaust steam from the expander outlet enters the condenser and is cooled to a subcooled state by cooling water. Driven by the working fluid pump, it enters the evaporator again to be heated, completing a complete organic Rankine cycle.

[0044] During the geothermal reservoir circulation operation, the geothermal fluid flows out through the organic Rankine cycle evaporator and then into the injection well, flowing into the geothermal reservoir. It completes the heat exchange process with the dry hot rock within the artificial fracture network of the geothermal reservoir, and then flows into the production well and out to the surface. It then enters the evaporator as an organic Rankine cycle heat source to heat the organic working fluid, completing one injection well-geothermal reservoir-production well cycle.

[0045] Preferably, the enhanced geothermal system parameter coupling design method uses a programming language to call REFPROP to carry out system simulation calculations.

[0046] like Figure 1 As shown, the steps of the above-mentioned enhanced geothermal system parameter coupling design method are as follows:

[0047] Step S1: Based on the temperature T and pressure distribution P of the geothermal target area, set the initial temperature T0 and initial pressure P0 of the deep geothermal reservoir.

[0048] Step S2: Assuming the enhanced geothermal system power generation scheme is a single-stage evaporation enhanced geothermal system, calculate the geothermal fluid temperature and pressure at the wellhead of the produced well throughout the entire life cycle of the enhanced geothermal system based on the condenser condensing temperature of the power generation system. The geothermal fluid temperature at the wellhead of the produced well is below 130℃, and the installed capacity of the enhanced geothermal system is initially determined.

[0049] Step S3: Calculate the total life-cycle power generation and economic efficiency of the single-stage evaporation-enhanced geothermal system, and determine whether it meets the design requirements. If not, return to step S2 to modify the power generation scheme and geothermal reservoir exploitation scheme of the enhanced geothermal system. If yes, determine the optimal evaporation temperature and geothermal fluid flow rate according to the following steps S4, S5 and S6 in sequence.

[0050] Step S4: Based on the geothermal fluid temperature at the wellhead of the enhanced geothermal system throughout its entire life cycle and the annual surface temperature of the area where the enhanced geothermal system is located, as calculated in Step S2, set the evaporator evaporation temperature range and the condenser condensation temperature range, calculate the power generation of the enhanced geothermal system under different evaporation temperature conditions and different condensation temperature conditions, and select the evaporation temperature at which the maximum power generation is achieved as the optimal evaporation temperature.

[0051] Step S5: Repeat step S4 to calculate the optimal evaporation temperature T corresponding to different wellhead geothermal fluid temperatures in the production wells. eva It meets the following conditions:

[0052] T eva +ΔT≤T pro ;

[0053] Step S6: Assuming the geothermal fluid flow rate range, call the current optimal evaporation temperature, calculate the power generation and economic efficiency of the enhanced geothermal system throughout its entire life cycle, and select the geothermal fluid flow rate m that simultaneously satisfies the optimal power generation and economic efficiency. optimum The following conditions must be met:

[0054] W optimum =m optimum (h in -h out );

[0055] P max =W optimum ·t;

[0056] Step S7: Input the optimal geothermal fluid flow rate and optimal evaporation temperature into step S4 to calculate the power generation of the enhanced geothermal system. Determine whether the maximum power generation has been reached. If yes, the system optimization is complete. If no, repeat step S6 to reselect the optimal geothermal fluid flow rate.

[0057] The coupling design device of the above-mentioned enhanced geothermal system parameter coupling design method includes: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory contains instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the above-mentioned enhanced geothermal system parameter coupling design method.

[0058] Furthermore, the geothermal fluid is liquid water.

[0059] Example 2:

[0060] Figure 3 This is a schematic diagram of an enhanced geothermal system cogeneration according to a specific embodiment of this application. The system includes: an expander 1, an evaporator 2, a condenser 3, a working fluid pump 4, an injection well 5, a production well 6, a cooling water system, a heating system, and a geothermal reservoir. The geothermal reservoir has been operated using artificial fracturing technology and contains a hydraulically interconnected network of artificial fractures. The cooling water system is connected to an external cold source to cool the condenser. The heating system includes a heat exchanger 7, which indirectly supplies heat to users using water as the heat transfer fluid. The specific working process is as follows:

[0061] When the organic Rankine cycle is working, the organic working fluid flows through the evaporator 2 and is heated by the geothermal fluid. The temperature of the organic working fluid rises, and then it flows into the evaporator. After being heated by the high-temperature geothermal fluid, it becomes superheated and saturated. Then it enters the expander to do work and complete the power generation process. Afterward, the organic working fluid flows out of the expander outlet and enters the heat exchanger 7 of the heating system to heat the water, realizing indirect heating to the heat users. Finally, it flows out of the heat exchanger of the heating system and enters the condenser 3 to be cooled to a subcooled state by the cooling water. Driven by the working fluid pump, it enters the evaporator 2 again to be heated, completing one organic Rankine cycle cogeneration process.

[0062] During the geothermal reservoir circulation operation, the geothermal fluid passes through evaporator 2 in sequence, is cooled by the organic working medium, and then flows into the injection well to be transported to the geothermal reservoir. It completes the heat exchange process with the dry hot rock in the artificial fracture network of the geothermal reservoir, and then flows into the production well to flow out of the surface. It enters the evaporator as an organic Rankine cycle heat source to heat the organic working medium, thus completing one injection well-geothermal reservoir-production well cycle.

[0063] Preferably, the enhanced geothermal system parameter coupling design method uses a programming language to call REFPROP to carry out system simulation calculations.

[0064] Similar to Example 1, the steps of the above-described enhanced geothermal system parameter coupling design method are as follows:

[0065] Step S1: Based on the temperature T and pressure distribution P of the geothermal target area, set the initial temperature T0 and initial pressure P0 of the deep geothermal reservoir.

[0066] Step S2: Assuming the enhanced geothermal system power generation scheme is a single-stage evaporation enhanced geothermal system, calculate the geothermal fluid temperature and pressure at the wellhead of the produced well throughout the entire life cycle of the enhanced geothermal system based on the condenser condensing temperature of the power generation system. The geothermal fluid temperature at the wellhead of the produced well is below 130℃. The cogeneration capacity of the enhanced geothermal system is preliminarily determined.

[0067] Step S3: Calculate the power generation, heat supply and economic efficiency of the single-stage evaporation-enhanced geothermal system throughout its entire life cycle, and determine whether it meets the design requirements. If not, return to step S2 to modify the cogeneration scheme and geothermal reservoir exploitation scheme of the enhanced geothermal system. If yes, determine the optimal evaporation temperature and geothermal fluid flow rate according to the following steps S4, S5 and S6 in sequence.

[0068] Step S4: Based on the geothermal fluid temperature at the wellhead of the enhanced geothermal system throughout its entire life cycle and the annual surface temperature of the area where the enhanced geothermal system is located, as calculated in Step S2, set the evaporator evaporation temperature range and the condenser condensation temperature range, calculate the power generation and heating power of the enhanced geothermal system under different evaporation temperature conditions and different condensation temperature conditions, and select the evaporation temperature at which the maximum power generation is achieved under the condition of meeting the heating demand as the optimal evaporation temperature;

[0069] Step S5: Repeat step S4 to calculate the optimal evaporation temperature T corresponding to different wellhead geothermal fluid temperatures in the production wells. eva It meets the following conditions:

[0070] T eva +ΔT≤T pro ;

[0071] Step S6: Assuming the geothermal fluid flow rate range, call the current optimal evaporation temperature, calculate the power generation and economic efficiency of the enhanced geothermal system throughout its entire life cycle, and select the geothermal fluid flow rate m that simultaneously satisfies the optimal heating load, optimal power generation, and optimal economic efficiency. optimum The following conditions must be met:

[0072] W optimum =m optimum (h in -h out );

[0073] Q optimum =m optimum (h Q_in -h Q_out );

[0074] In the formula Q optimum For optimal heating power; h Q_in h is the inlet temperature of the organic working fluid in the heat exchanger of the heating system. Q_outThis refers to the outlet temperature of the organic working fluid in the heat exchanger of the heating system.

[0075] P max =W optimum ·t;

[0076] Step S7: Input the optimal geothermal fluid flow rate and optimal evaporation temperature into step S4 to calculate the power generation of the enhanced geothermal system. Determine whether the maximum power generation has been reached. If yes, the system optimization is complete. If no, repeat step S6 to reselect the optimal geothermal fluid flow rate.

[0077] The coupling design device of the above-mentioned enhanced geothermal system parameter coupling design method includes: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory contains instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the above-mentioned enhanced geothermal system parameter coupling design method.

[0078] Furthermore, the geothermal fluid used is liquid water.

[0079] The above are merely preferred embodiments of this application, but this application is not limited to the specific embodiments described above. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of this application, and these all fall within the protection scope of this application.

Claims

1. An enhanced geothermal system parameter coupling design method, characterized in that, Includes the following steps: S1, based on the temperature and pressure distribution of the deep geothermal target area, set the initial temperature and initial pressure of the deep geothermal reservoir; S2, based on the condensation temperature of the condenser, calculate the geothermal fluid temperature and pressure at the wellhead of the production well throughout the entire life cycle of the enhanced geothermal system, and determine the installed capacity of the enhanced geothermal system. S3. Calculate the full life cycle evaluation index of the enhanced geothermal system based on the calculation results of step S2 to determine whether it meets the design requirements: If not, return to step S2 to modify the enhanced geothermal system scheme and the geothermal reservoir exploitation scheme; If so, proceed to step S4; S4. Based on the geothermal fluid temperature at the wellhead of the production well during the entire life cycle of the enhanced geothermal system and the annual surface temperature of the area where the enhanced geothermal system is located, as calculated in step S2, set the evaporator evaporation temperature range and the condenser condensation temperature range, calculate the performance parameters of the enhanced geothermal system under different evaporation temperature conditions and different condensation temperature conditions, and select the evaporation temperature with the optimal performance parameters as the optimal evaporation temperature. S5. Repeat step S4 to calculate the optimal evaporation temperature corresponding to the geothermal fluid temperature at the wellhead of different production wells. S6, set the geothermal fluid flow range, call the current optimal evaporation temperature, calculate the full life cycle evaluation index of the enhanced geothermal system, and select the geothermal fluid flow rate that simultaneously meets all the optimal evaluation indexes; as well as S7, Substitute the optimal geothermal fluid flow rate and optimal evaporation temperature into step S4 to calculate the performance parameters of the enhanced geothermal system and determine whether the performance parameters have reached the optimal level. If so, the system optimization is complete; If not, repeat step S6 to reselect the optimal geothermal fluid flow rate. Wherein, step S2 adopts organic Rankine cycle power generation or cogeneration, and step S2 also includes driving the number of evaporator stages and expander stages on the heat source side; The number of evaporator and expander stages on the heat source side is set according to the geothermal fluid temperature at the wellhead of the produced well. When the geothermal fluid temperature at the wellhead of the produced well is lower than or equal to 130°C, a single-stage evaporation-single-stage expansion scheme is selected; when the geothermal fluid temperature at the wellhead of the produced well is higher than 130°C, a two-stage evaporation-multi-stage expansion scheme is selected, and the number of evaporator stages and expander stages are determined according to the optimal flow rate, optimal evaporation temperature, and expansion ratio. The optimal evaporation temperature in steps S4, S5, and S6 T eva and optimal geothermal fluid flow rate m optimum The following conditions must be met: in, W optimum To achieve optimal power generation, h in Specific enthalpy at the expander inlet; h out Specific enthalpy at the expander outlet; in, P max t represents the maximum power generation of the enhanced geothermal system; t represents the design operating time of the enhanced geothermal system.

2. The enhanced geothermal system parameter coupling design method according to claim 1, characterized in that: In step S1: based on the temperature of the deep geothermal target area T and pressure P Set the initial temperature of deep geothermal reservoirs T 0 and initial pressure P 0, while specifying the initial temperature T 0 and initial pressure P 0 satisfies the following conditions: T 0= T , P 0= P .

3. The enhanced geothermal system parameter coupling design method according to claim 1, characterized in that, In the single-stage evaporation-single-stage expansion scheme, a single evaporator cools the high-temperature geothermal fluid at the wellhead of the produced well to the reinjection temperature T. in , among which, T in The value range is 20~50℃; in the two-stage evaporation-two-stage expansion scheme, the high-temperature geothermal fluid at the wellhead of the produced well is cooled to the reinjection temperature T by two evaporators. in , among which, T in The value range is 20~50℃.

4. The enhanced geothermal system parameter coupling design method according to claim 1, characterized in that: The optimal evaporation temperature T eva satisfy: Where, Δ T The heat exchange temperature difference between the geothermal fluid and the organic working medium in the evaporator; T pro The temperature of the geothermal fluid at the wellhead of the extracted well.

5. The enhanced geothermal system parameter coupling design method according to claim 1, characterized in that, In step S2, organic Rankine cycle power generation is used, with organic working fluid in the Rankine cycle process and water as the geothermal fluid.

6. The enhanced geothermal system parameter coupling design method according to claim 1, characterized in that, The optimal evaluation indicators include: optimal flow rate and optimal evaporation temperature.

7. An enhanced geothermal system parameter coupling design device, characterized in that, include: At least one processor, and a memory communicatively connected to the at least one processor, wherein the memory has instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the enhanced geothermal system parameter coupling design method as described in any one of claims 1 to 6.

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