TWI625460B - Enhanced geothermal system and method for building such system - Google Patents

Abstract

The invention relates to an enhanced geothermal optimal heat extraction system and a method for establishing the same, the method comprising: establishing a numerical model for simulating heat extraction. Using the numerical model, a simulated data is obtained after the simulation takes heat. The correctness of the numerical model was verified by a heat extraction experiment. An experimental data is obtained by using the heat extraction experiment, and the simulation data is compared to verify the correctness of the numerical model. One of the best operating conditions in the simulation data is obtained in an optimized manner. An optimum geothermal heat recovery system is established using the optimal operating conditions. By means of the average particle size and pressure available for inputting geological pore conditions, the mass flow rate corresponding to the maximum calorific value is inquired.

Description

Optimal heat extraction system for enhanced geothermal heat and method for establishing same

The present invention relates to a method of establishing an optimal heat extraction system that can be used to establish enhanced geothermal heat to provide optimal heat extraction parameters that can reduce actual operating costs.

Due to the current shortage of energy on the earth, the search for a renewable energy system has become a top priority. Renewable energy is a kind of restorative energy that can be continuously replenished and reused. The most representative ones are solar energy, wind energy, ocean energy, biomass energy and geothermal energy. As the development technology becomes more and more mature, the geothermal energy is not as good as other energy sources in cost recovery, power generation efficiency and storage capacity, and has to overcome the limitations of many terrain rock layers, but it can be recycled more continuously than other energy sources. It can reduce carbon emissions and create many geothermal industry opportunities.

Therefore, there is a patent case No. 201402943 of the Republic of China on January 16, 103, "Single Well, Self-Flowing Geothermal System for Exploitation of Energy", which discloses: providing a renewable energy, single well, primary gravity, geothermal A heat/power generation system that uses a heat exchanger or turbine/generator to obtain naturally generated underground geothermal heat to heat water and/or generate mechanical force/electricity. Vacuum insulation can be used, for example, to insulate the subterranean structure defining the working fluid flow path to increase system efficiency and ensure substantially self-generated working fluid flow.

This patent pending is available for use in a system known as Enhanced Geothermal System (EGS). The so-called enhanced geothermal system development technology utilizes a natural heat source to heat up in the high temperature and high pressure reservoir to create artificial fractures plus injection of working fluid. The principle is to inject high-pressure working fluid through the wellbore into the deep underground rock formation of three kilometers or more underground, and use the working fluid to flow through the high-temperature rock gap. The seam is returned to the surface while the working fluid is heated. The recirculating high-temperature working fluid is further exchanged with the heat exchanger and another closed low-temperature circulation system for heat exchange. After the working fluid is heated and pressurized once again, the turbine can be gasified and promoted to generate mechanical energy by thermal energy and then converted into electric energy. . The cryogenic working fluid that completes the heat exchange can be re-injected into the ground to form a closed loop. Therefore, it has high utilization efficiency and good system stability, and is a clean energy source. As long as the formation of the appropriate temperature can be found, the permeability of the rock layer can be amplified by engineering methods and then introduced into the heat-removing fluid, which is almost free from any geographical restrictions and is a global emerging energy industry.

Since the enhanced geothermal system initially uses water as the working fluid for heat extraction, the viscosity and density of the water are found in the long run, and more pumping work is required in the application, resulting in more power consumption. At the same time, because the physical properties of water easily react with minerals, when the main minerals are gradually dissolved, the pipeline will be fouled, the working fluid flow path will be blocked, and finally the electricity production rate will be lowered, and the maintenance is not easy. Therefore, research began to replace carbon dioxide with water as a working fluid. Because carbon dioxide brings more advantages and benefits, it can even be stored in geology to reduce carbon emissions. Therefore, many research experts have explored the heat transfer between carbon dioxide pipes through numerical simulation and experimental systems to better understand the variability of carbon dioxide. However, whether water or carbon dioxide is used as the working fluid during construction, in the application of geothermal heat, actual mining is still required to obtain geothermal heat for supply. Geothermal heat is often not fully utilized because the heat extraction efficiency after mining geothermal heat is not as good as expected.

Therefore, there is a patent for the invention of CN310743580, "Enhanced Geothermal System Development Test Device" published by the Chinese mainland on April 23, 2014, which discloses: including carbon dioxide cylinders, carbon dioxide supercritical conveying devices, and simulated dry hot rocks. Reactor, carbon dioxide turbine, high pressure variable frequency piston pump, PLC data acquisition system, carbon dioxide carbon dioxide cylinder carbon dioxide through carbon dioxide flow control valve and pressure regulating valve into carbon dioxide supercritical conveying device increased to high pressure into simulated dry hot rock reactor for heating The heated high temperature and high pressure carbon dioxide CO ₂ flow enters the carbon dioxide turbine, the carbon dioxide turbine drives the generator or the power machine for energy conversion; the lower grade carbon dioxide from the carbon dioxide turbine enters the heat exchanger, after heat exchange The carbon dioxide is sent back to the simulated dry hot rock reactor for recycling by a high pressure variable frequency piston pump. The utility model provides a geothermal energy development simulation system with high utilization rate of heat energy, low energy consumption and good treatment effect.

However, the structure of the patent is complicated, the test accuracy is insufficient, and it is difficult to simulate the true heat transfer behavior in the underground rock layer. Therefore, there are many defects in use.

Therefore, in view of the fact that geothermal energy development is actually carried out on the spot, it is necessary to survey the appropriate strata, such as whether the rock formation is easy to manufacture artificial fissures, and whether the underground heat is abundant. In addition, it is necessary to select a suitable geothermal wellbore and related system equipment. For example, which design of the wellbore is more cost-effective in drilling and how many standards the unit should meet in order to meet the development cost. Therefore, in order to save time, cost and other unnecessary expenses, the main advantages of increasing the working speed, reducing the time consumption and saving the cost are achieved. Therefore, the present invention provides a method for establishing an optimal heat extraction system for enhanced geothermal heat, comprising: establishing a numerical model for simulating heat extraction, and using the numerical model to simulate the heat extraction efficiency of a carbon dioxide flowing through a reservoir, the reservoir The layer obtains a simulation data after the simulation takes heat, and the parameter of the simulation data includes at least one of temperature, average particle diameter, inlet mass flow rate or pressure. Through a heat extraction experiment to verify the correctness of the numerical model, using carbon dioxide as a working fluid, the heat extraction experiment was performed, and one of the heat taken from the heat extraction experiment and a system inlet and outlet temperature difference were compared with the simulation. The data is compared to verify the correctness of the numerical model. One of the best operating conditions in the simulation data is obtained by an optimization method, which is a Nelder-Mead optimization search method, a genetic algorithm optimization search method or a simple conjugate gradient method. One of them is to know the pressure of the geological conditions in a particular reservoir under the optimized operating conditions and the optimum inlet mass flow rate under the average particle size to obtain a maximum calorific value. Using the optimal operating conditions to establish an enhanced geothermal optimal heat extraction system, by which the average particle size and pressure can be input, and the corresponding optimal inlet mass flow rate can be queried to obtain the maximum calorific value. Mass flow rate.

The above is a circular tube to simulate an impermeable dense rock formation in the outer environment of the reservoir, a permeable porous rock layer in the internal environment, the outer wall surface of the circular tube is a pipe wall, the inner wall surface is a porous medium, and one side is an inlet, and the other side is an inlet. One side is the outlet, and the energy equation of the outer wall surface of the circular tube is to adjust the heating wattage by setting a constant heat flux.

The above-mentioned tube is used as a test section, and the heat extraction experiment is performed with a syringe type high-pressure apparatus, which comprises a carbon dioxide cylinder through which a carbon dioxide injection and supply of carbon dioxide are supplied and outputted. Inside the pipeline, a data capture system uses a T-type thermocouple as a signal measurement, and is sent back to the computer for processing through the capture system. A constant temperature water tank is used to keep the carbon dioxide before the heat test constant in a supercritical state, and a cooling The water tank condenses the carbon dioxide after absorption to the liquefied state, and a syringe high-pressure pump system establishes a high-pressure environment of carbon dioxide, precisely controls the inlet pressure and the flow rate, and stabilizes the flow rate of the output constant pressure, supercritical carbon dioxide in the circle The heat taken in the tube is calculated by using the input mass flow rate and the inlet and outlet enthalpy values. The calculation formula is as follows: Where h _in is the entry threshold and h _out is the exit threshold.

The operating conditions and experimental parameters of the above heat extraction experiments were as follows: wall heat flux 1473.66 W/m ² , inlet fluid temperature 313.15 K, porous medium average particle diameter 1.54 mm and 2.03 mm, inlet mass flow rate 0.00027 kg/s, 0.00054 Kg/s, 0.00082 kg/s and 0.00109 kg/s, operating pressures 7.5 MPa, 9 MPa, 10 MPa, 11 MPa and 12.5 MPa.

The above is to establish the numerical model with multiple physical quantity software, verify the correctness of the numerical model and obtain the optimal operating conditions.

The present invention can also be an optimal heat extraction system for enhanced geothermal heat, which is established by the above-mentioned method for establishing an optimal heat extraction system for enhanced geothermal heat.

According to the above technical features, the following advantages are obtained:

1. The optimal heat extraction operating conditions are obtained through an optimization procedure, and the correctness of the experimental equipment and the simulation model can be used to verify the correctness, and then the optimal heating method can be used to find the optimal heat extraction operating conditions. Forecast for geothermal energy development work in actual use.

2. It takes a long time to improve the conventional computing data, and can greatly shorten the actual mining time, in order to save costs and other unnecessary expenses. First, research, analysis and comparison through laboratory-scale experiments and simulations. Verification, after repeated repeated testing, correction and improvement, and finally enlarge the model to the actual scale of geothermal development, so as to make proper use of numerical analysis to achieve the advantages of improving work speed, reducing time consumption and saving cost.

3. The enhanced geothermal optimal heat extraction system established for the enhanced system geothermal power plant technicians to query the average formation particle size and pressure in the geothermal reservoir, and the corresponding maximum heat extraction mass flow rate In order to reduce the relevant actual operating costs, and to evaluate the development cost, and further provide a recommended value and an estimated value, as a reference for the mass flow rate to obtain the maximum calorific value.

(1) ‧‧‧ round tube

(11) ‧‧‧ outer wall

(12) ‧ ‧ inner wall

(13)‧‧‧ Entrance

(14) ‧‧‧Export

(15)‧‧‧ Sidewall

(1A)‧‧‧Test section

(2) ‧‧‧CO2 cylinder

(3) ‧ ‧ constant temperature water tank

(4) ‧‧‧Cooling trough

(5)‧‧‧Syringe type high pressure pumping system

[First figure] is a flow chart of the present invention.

[Second diagram] is a schematic view of the appearance of a round tube (test section) for conducting experiments of the present invention.

[Third image] is a three-phase diagram of carbon dioxide of the present invention.

[Fourth figure] is a supercritical carbon dioxide density distribution map of the present invention under different pressures and temperatures.

[Fifth diagram] is a graph showing the specific heat distribution of supercritical carbon dioxide at different pressures and temperatures of the present invention.

[Sixth image] is a distribution map of supercritical carbon dioxide heat conduction coefficient of the present invention under different pressures and temperatures.

[Seventh] is a distribution map of supercritical carbon dioxide viscous coefficient of the present invention under different pressures and temperatures.

[Eighth image] is a distribution ratio of supercritical carbon dioxide specific heat ratio at different pressures and temperatures of the present invention.

[Ninth Diagram] is a schematic diagram of a miniature high-voltage apparatus for performing a heat extraction experiment of the present invention.

[Tenth] is the comparison of the outlet temperature of the experimental heat extraction and the simulated heat extraction in the case 1 of the present invention.

[11th] is the comparison of the outlet temperature of the experimental heat extraction and the simulated heat extraction in the case 2 of the present invention.

[Twelfth image] is a comparison chart of the heat taken by the experimental heat extraction and the simulated heat extraction in the case 1 of the present invention.

[Thirteenth image] is a comparison chart of the heat taken by the experimental heat extraction and the simulated heat extraction in the case 2 of the present invention.

[Fourteenth] is a distribution diagram of the longitudinal thermal diffusivity of Case 1 of the present invention under different pressures and flows.

[Fifteenth Figure] is a distribution diagram of the longitudinal thermal diffusivity of Case 2 of the present invention under different pressures and flows.

[16] is a distribution diagram of the transverse thermal diffusivity of Case 1 of the present invention under different pressures and flows.

[Fig. 17] is a distribution diagram of the lateral thermal diffusion coefficient of Case 2 of the present invention under different pressures and flows.

[18th] is a distribution diagram of the transverse vertical thermal diffusion coefficient of Case 1 of the present invention under different pressures and flows.

[19th] is a distribution diagram of the transverse vertical thermal diffusion coefficient of Case 2 of the present invention under different pressures and flows.

[Twentyth] is the heat extraction map of Case 1 of the present invention under different pressures and flows.

[21] is the heat extraction profile of Case 2 of the present invention under different pressures and flows.

[22] is the temperature distribution diagram of the outlet of the invention 1 under different pressures and flows.

[Twenty-third figure] is the temperature distribution diagram of the outlet of the invention case 2 under different pressures and flows.

[Twenty-fourth] is a comparison of the heat extraction of the case 1 optimization experiment and the simulation of the present invention.

[Twenty-fifth] is a comparison of the heat extraction of the case 2 optimization experiment and simulation of the present invention.

[Table 1] is a table of the properties of the properties of stainless steel and cerium oxide of the present invention.

[Attachment] is a schematic diagram of the operation interface of the optimal heat extraction system for enhanced geothermal energy established by the present invention.

Referring to the first figure, the present invention is a method for establishing an optimal heat extraction system for enhanced geothermal heat, comprising:

A. Establishing a numerical model for simulating heat: using the numerical model to simulate heat extraction, thereby simulating the heat extraction efficiency of a working fluid flowing through a reservoir, the reservoir obtaining a simulation data after simulated heat extraction, The parameters of the simulation data include: a temperature of 200 ° C, an average particle diameter of 1.54 mm to 2.03 mm, an inlet mass flow rate of 0.00027 to 0.00109 kg / s, and a pressure of 7.5 to 12.5 MPa. The workflow system can be a carbon dioxide.

In this embodiment, a multi-physical software is used to establish a numerical model of the Brinkmann pore flow, and a heat transfer module is coupled to simulate the heat extraction efficiency of the working fluid flowing through the geothermal reservoir. Through the simulation of the numerical model, the heat of supercritical carbon dioxide under different rock formation characteristics can be observed. performance. The study parameters include reservoir operating pressure, inlet mass flow rate, wall heat flux, and porosity (ie, particle size). Knowing the specific heat and viscosity of supercritical carbon dioxide at different temperatures, the flow rate changes, significantly affecting the heat taken. The geothermal gradient will vary with different geological formations. And by changing the wall heat flux, we can observe the different heat transfer behavior of supercritical carbon dioxide at different ground temperatures. The structural composition of the underground rock layers is different, and it varies with age and depth. The porosity represents the space of the fluid flow channel, and the different porosity is more significant for fluid viscosity, and the different inlet flow rates most significantly affect the heat extraction. .

Therefore, in order to describe the heat extraction efficiency of supercritical carbon dioxide in the reservoir of enhanced geothermal system, the numerical model of the simulation analysis is set as the coupling of the two models of flow field and temperature field, and the following basic assumptions are used to simplify the problem.

(1) The system condition is steady state heat transfer.

(2) The fluid is a compressible fluid.

(3) Ignore radiant heat transfer and gravity effect.

(4) The porous medium is homogeneous.

In this embodiment, a numerical model for understanding the thermal simulation of supercritical carbon dioxide in the reservoir of the enhanced geothermal system is established, so data of the flow field and the temperature field are required. Therefore, the Navier-Stokes equation and the Brinkmann equation are used to describe the laminar flow field and the pore flow field respectively. The continuous equation and the momentum balance equation are combined to calculate the flow velocity and pressure of the flow field.

Therefore, when establishing a numerical model, this embodiment uses a circular tube (1) to simulate an impermeable dense rock formation in the external environment of the reservoir, and a permeable pore rock formation in the internal environment. As shown in the second figure, one of the outer wall surfaces (11) of the circular tube is a tube wall, and an inner wall surface (12) is a porous medium, the fluid flow direction is along the X axis, the left side is an inlet (13), and the right side is An exit (14).

Since supercritical refers to the state when the fluid exceeds the critical temperature and pressure, the fluid has both gas and liquid properties in this state, but the fluid is near the critical point pressure or temperature. At the time, it will make a large change in its density, as shown in the third figure. Therefore, when supercritical carbon dioxide is established, it is necessary to ensure that the fluid is above the minimum temperature and pressure at supercritical conditions to ensure that the fluid is in a supercritical state. Secondly, the physical properties of the fluid, such as density, atmospheric specific heat, heat transfer coefficient, viscosity coefficient, specific heat ratio, are different due to the temperature and pressure of the fluid. Because of the change of temperature and pressure, the fluid must change with temperature and pressure. The nature of the measurement is a factor to determine its accuracy.

In this embodiment, the carbon dioxide value table is established by using the database of the NIST American National Standards Agency, and obtains the density and temperature density, atmospheric specific heat, heat transfer coefficient, viscosity coefficient and specific heat of carbon dioxide at critical point pressures and temperatures. Instead, type the material library of the multiple physical quantity software one by one by segmentation interpolation. Since the supercritical point is above the temperature of 304.2K and the pressure of 7.38MPa, in order to obtain the heat transfer variation accuracy, the density is obtained when the temperature is 304K to 474K and the pressure is 7.5MPa to 12.5MPa respectively (as shown in the fourth figure), Normal pressure specific heat (as shown in Figure 5), heat transfer coefficient (as shown in Figure 6), viscosity coefficient (as shown in Figure 7) and specific heat ratio [as shown in Figure 8].

B. Verifying the correctness of the numerical model through a heat extraction experiment: using carbon dioxide as the working fluid, performing the heat extraction experiment, comparing one experimental data obtained by the heat extraction experiment with the simulation data, thereby Verifying the correctness of the numerical model, using the thermal diffusion coefficient of the comparison result, obtaining a thermal diffusion coefficient under different pressure and mass flow rates by interpolation, adjusting the thermal diffusion coefficient to make the simulated data approach the Experimental data. The experimental data includes a calorific value and a system inlet and outlet temperature difference.

In order to simulate the heat transfer phenomenon when operating in the heat test, the outer wall surface (11) of the round pipe (1) is made of stainless steel (AISI 316) as a heat transfer medium to simulate an impermeable dense rock formation. The inner wall surface (12) of the round pipe (1) is widely used in nature and the applied cerium oxide (SiO2) as a porous medium to simulate a permeable pore rock formation. The density, thermal conductivity, and atmospheric specific heat at normal temperature and pressure are obtained (as shown in the following list), and the material library of the multiple physical quantity software is entered.

Table I

As shown in the ninth figure, the tube in the step A is actually manufactured as a test section (1A), and is tested with a micro high-voltage device for the heat extraction experiment. The micro high pressure apparatus comprises a carbon dioxide cylinder (2) for supplying carbon dioxide into the pipeline of the test section (1A) through a high pressure pipeline system. A data capture system uses a T-type thermocouple as a signal measurement and is transmitted back to the computer for processing via the capture system. A constant temperature water tank (3) keeps the carbon dioxide before the heat extraction experiment in a supercritical state. A cooling water tank (4) is used to condense the heat-absorbing carbon dioxide to a liquefied state. A syringe type high-pressure pumping system (5) establishes a high-pressure environment of carbon dioxide, precisely controls the inlet pressure and flow rate, and stabilizes the flow rate of the output constant pressure. The test section (1A) made of stainless steel establishes a thermal reservoir condition that can withstand temperatures up to 350 °C. In the data conversion part, the calorific value of supercritical carbon dioxide in the test section (1A) is calculated by using the input mass flow rate and the inlet and outlet enthalpy values, and the calculation formula is as follows: Where h _in is the entrance threshold and h _out is the exit threshold. Thereby, the mild heat extraction of the outlet of the steady state result in the subsequent program verification can be made more accurate.

This embodiment is a heat extraction experiment performed by a supercritical carbon dioxide heat extraction experimental apparatus for verifying the correctness of the simulation data of the numerical model. The operating conditions and experimental parameters are: wall heat flux 1473.66W/m ² ; inlet fluid temperature 313.15K; porous media average particle size 1.54mm and 2.03mm; inlet mass flow rate 0.00027, 0.00054, 0.00082 and 0.00109kg/s Operating pressures 7.5, 9, 10, 11 and 12.5 MPa. The average particle size of the porous medium is 1.54mm and 2.03mm, which are abbreviated as Case 1 and Case 2. The effect of mild heat extraction on the outlet at different flow rates in different cases is discussed. The thermal diffusion coefficient is adjusted in the comparison check to approximate the experimental data. The exit temperature check results are shown in the tenth and eleventh figures, and the average error value is less than 7.5%. The heat efficiency results are shown in Figures 12 and 13, and the average error value is less than 2.3%. Through these results, it is found that the present embodiment is quite accurate in comparison and verification, and the thermal diffusion coefficients of different cases under different pressures and flow rates can be obtained as an important basic parameter for subsequent optimization.

The thermal diffusivity in this example is the difference between the thermal diffusion coefficients of the comparison of the different operating pressures of 7.5, 9, 10, 11 and 12.5 MPa through the known case 1 and case 2, and the difference between the pressures of 7.5 and 9 by interpolation. Between 9 to 10, 10 to 11, and 11 to 12.5 MPa, including longitudinal thermal diffusion coefficients, as shown in Figures 14 and 15; lateral horizontal thermal diffusion coefficients, such as sixteenth and tenth Figure 7 shows the horizontal vertical thermal diffusivity as shown in Fig. 18 and Fig. 19. Finally, these values are entered into the pressures of Cases 1 and 2, 7.5 to 12.5 MPa, respectively, as key variables for optimizing the search to obtain the maximum heat extraction operating conditions.

C. obtaining an optimal operating condition in the simulation data by an optimization method: obtaining the optimal operating condition in the simulation data by the optimization method, the optimal operating condition is pressure 9.0 MPa and mass flow rate of 0.00109 kg / s. Therefore, it can be known that the thermal diffusivity has different average particle diameters, inlet mass flow rate and pressure changes in the reservoir, and the maximum target heat gain is the maximum objective function, the inlet mass flow rate is used as the variable, and the pressure is determined. Value, in order to obtain the mass flow rate of the maximum calorific value.

The data of the geothermal reservoir heat extraction simulation is obtained by using the numerical model through the above step A. The analysis of the average particle size, inlet mass flow rate and operating pressure of different porous media was carried out to obtain a mild heat extraction at the steady state. And performing a comparison check via step B. The coupled Brinkman pore flow model and the heat transfer module are used to establish an enhanced geothermal system reservoir in the simulation. The thermal diffusion coefficient description in the heat transfer behavior of the porous medium is defined as vertical, horizontal and horizontal vertical, and the value is adjusted. In order to meet the data of the heat test. And using interpolation method, by numerical model under certain reliability To reduce the cost of analysis. The thermal diffusion coefficients at different pressure and mass flow rates are obtained by interpolation using a known thermal diffusion coefficient of the operating pressure comparison result.

In this embodiment, the multiple physical quantity software is used to find the operating condition of the maximum heat extraction under different pressures, so that the accurate result can be quickly obtained in the optimization process, so it is simpler and more accurate than other optimization methods. The high Nelder-Mead optimization search method is used as an optimization method, or other best methods such as genetic algorithm optimization search method or simple conjugate gradient method. In the process of optimizing the search method to obtain the maximum heat extraction operating conditions, Case 1 and Case 2 were searched between pressures of 7.5 to 12.5 MPa, respectively, wherein the total pressure number was 51 groups (the pitch range was 0.1 MPa). The optimization process takes the maximum calorific value as the objective function, and the inlet mass flow rate is between 0.00027 and 0.00109 kg/s as the variable range to obtain the mass flow rate when the maximum calorific value occurs, and the relevant variable result of the search process can be recorded. Therefore, the data of the heat extraction result of the detailed relevant operating conditions will be available after the system is established and learned through the system query.

As shown in the twentieth figure, it is the heat extraction map of Case 1 under different pressures and flows. It can be observed from the figure that the heat extraction increases with the increase of the mass flow rate, and the maximum calorific value of 38.53 can be found. W occurs when the pressure is 9 MPa and the mass flow rate is 0.00109 kg/s, which is better than the pressures of 7.5 and 12.5 MPa. Further, it can be observed that the change of heat extraction at a mass flow rate of 0.00109 kg/s and pressure increases by 42.95% at a pressure of 7.5 to 9 MPa, by 9.54% at 9 to 10 MPa, and then by 12.78% at 10 to 11 MPa. Decrease by 4.58% at 11 to 12.5 MPa. The main reason is because the supercritical carbon dioxide is caused by the different outlet temperature at steady state. As shown in Figure 22, the change of the outlet temperature at the mass flow rate of 0.00109 kg/s and the pressure is also observed. It decreases by 13.45% from 7.5 to 9MPa, increases by 2.79% from 9 to 10MPa, increases by 2.66% from 10 to 11MPa, and increases by 3.08% from 11 to 12.5MPa.

As shown in Figure 21, it is the heat extraction map of Case 2 under different pressures and flows. It can be observed from the figure that the heat extraction increases with the increase of the mass flow rate, and the maximum heat gain can be found. 38.92W occurs at a pressure of 9 MPa and a mass flow rate of 0.00109 kg/s, compared to a pressure of 7.5 and 12.5 MPa is preferred. We can observe the change of heat taken at the mass flow rate of 0.00109kg/s and the pressure, increase by 49.46% at 7.5 to 9MPa, 6.37% at 9 to 10MPa, and then decrease by 13.68% at 10 to 11MPa. Decrease by 7.66% at 11 to 12.5 MPa. The main reason is that the supercritical carbon dioxide is caused by the different outlet temperature at steady state. As shown in the twenty-third figure, the change of the outlet temperature at the mass flow rate of 0.00109 kg/s and the pressure is also observed. Decrease by 12.27% from 7.5 to 9MPa, increase by 3% from 9 to 10MPa, increase by 2.62% from 10 to 11MPa, and increase by 2.58% from 11 to 12.5MPa.

Therefore, it can be known that the optimal heat extraction of supercritical carbon dioxide in Case 1 and Case 2 is 38.53 W and 38.92 W, respectively. The amount of change in calorific value increased by 1% between Case 1 and Case 2. It can be known that the average particle size of porous media has the effect on heat extraction. The main thermal performance of supercritical carbon dioxide depends on pressure and quality. The flow rate changes, so proper operating pressure and mass flow rate are necessary.

After optimizing the heat extraction simulation in this embodiment, it can be confirmed that the maximum heat is generated at a pressure of 9.0 MPa. In order to find the operating conditions that are closer to the true maximum heat extraction, the pressure is 9.0 MPa through the heat test equipment. The analysis was carried out again at a pressure of 8.9, 8.95, 9.05, 9.1 and 9.15 MPa and a mass flow rate of 0.00109 kg/s. As shown in the twenty-fourth figure, it is a comparison chart of the heat comparison between the optimization experiment and the simulation (case 1). It can be observed from the figure that the optimal heat extraction of the experiment 39.46W occurs at a pressure of 9 MPa. It is better than other adjacent pressures. Further, it can be observed that the optimum heat extraction of the experiment increases by 3.92% at a pressure of 8.9 to 8.95 MPa, by 3.52% at 8.95 to 9 MPa, then by 0.35% at 9 to 9.05 MPa, and finally at 9.05 to 9.1 MPa. It is also decremented by 0.31%. Therefore, it can be known that the pressure of approaching the true maximum heat is occurring at 9 MPa.

As shown in the twenty-fifth figure, it is a comparison chart of the heat comparison between the optimization experiment and the simulation (case 2). It can be observed from the figure that the optimal heat extraction of the experiment is 40.83W at a pressure of 9.05 MPa. It is better than other adjacent pressures. Further observation can be made to optimize the heat gain of the experiment. The increase is 1% at a pressure of 8.9 to 8.95 MPa, 4.46% at 8.95 to 9 MPa, then 4.93% at 9 to 9.05 MPa, and a decrease of 0.05% at 9.05 to 9.1 MPa. Therefore, it can be known that the pressure of approaching the true maximum heat is occurring at 9.05 MPa.

Therefore, the comparison of the optimal heat extraction between the experiment and the simulation can be known. The heat loss errors of Cases 1 and 2 are less than 2.4% and 4.91%, respectively, and the pressure error is less than 0.56%. From this, it can be confirmed that the simulation data optimized in this embodiment is quite accurate with the result of the finally optimized experimental data.

D. Using the optimal operating conditions to establish an enhanced geothermal optimal heat extraction system: by inputting the average particle size and pressure, the corresponding optimal mass flow rate can be queried to obtain the maximum calorific value. The mass flow rate is used to evaluate development costs.

In the present embodiment, the heat transfer phenomenon of the supercritical carbon dioxide flowing through the test section (1A) [ie, the round tube (1)] is analyzed by the above-mentioned steps, and the average particle diameter of the porous medium is 1.54 mm and 2.03 mm at the inlet. The mass flow rate is between 0.00027 and 0.00109 kg/s, the operating pressure is between 7.5 and 12.5 MPa, and the inlet fluid temperature is 313.15 K to understand the different heat transfer phenomena and to find the operating conditions for maximum heat extraction.

In this embodiment, data such as the heat extraction result of the relevant operation parameters are obtained from the simulation data, and the optimal heating system of the enhanced geothermal system is developed by the programming software, and the operation interface is as shown in the attached file, thereby being enhanced. The geothermal power plant inputs the average particle size and pressure of the formation, and can query the corresponding optimal inlet mass flow rate to obtain the mass flow rate of the maximum calorific value.

The invention can be an optimal heat extraction system for enhanced geothermal heat, which is established by the above-mentioned method for establishing an optimal heat extraction system for enhanced geothermal heat. By means of the average particle size and pressure available for input into the formation, it is possible to query the corresponding optimal inlet mass flow rate to obtain the mass flow rate of the maximum calorific value for evaluation and development of the geothermal reservoir to be mined. Use. A recommended value and an estimated value may be further provided as a reference for obtaining the mass flow rate of the maximum calorific value.

However, the above description is only one of the embodiments of the present invention. When the scope of the patent application of the present invention is not limited thereto, the simple equivalent changes and substitutions made by the scope of the patent application and the contents of the specification of the present invention are It is still within the scope of the protection covered by the scope of the invention.

Claims (6)

A method for establishing an optimal heat extraction system for enhanced geothermal heat includes: establishing a numerical model for simulating heat extraction, and using the numerical model to simulate the heat extraction efficiency of a carbon dioxide flowing through a reservoir, the reservoir being simulated After taking heat, obtaining a simulation data, the parameters of the simulation data including at least one of temperature, average particle diameter, inlet mass flow rate or pressure; verifying the correctness of the numerical model through a heat extraction experiment, using carbon dioxide as a Working fluid, and performing the heat extraction experiment, and taking the heat taken by one of the heat extraction experiments and the temperature difference of a system inlet and outlet, and comparing with the simulation data, thereby verifying the correctness of the numerical model; The method obtains one of the optimal operating conditions in the simulation data, and the optimization method is one of a Nelder-Mead optimization search method, a genetic algorithm optimization search method or a simple conjugate gradient method. Knowing the pressure of the geological conditions in a particular reservoir under the optimized operating conditions and the optimal inlet mass flow rate under the average particle size to obtain a maximum take Using the optimal operating conditions to establish an enhanced geothermal optimal heat extraction system, by which the average particle size and pressure can be input, and the corresponding optimal inlet mass flow rate can be queried to obtain the maximum take-up The mass flow rate of heat. The method for establishing an optimal heat extraction system for enhanced geothermal heat according to claim 1, wherein a circular tube is used to simulate an impermeable dense rock formation of the outer environment of the reservoir, and a permeable pore rock layer of the internal environment. The outer wall surface of the round pipe is a pipe wall, the inner wall surface is a porous medium, one side is an inlet, and the other side is an outlet. The energy equation of the outer wall surface of the circular pipe is to adjust the heating wattage by setting a constant heat flux. The method for establishing an optimal heat extraction system for enhanced geothermal heat as described in claim 2, wherein the circular tube is used as a test section, and the heat extraction experiment is performed with a syringe type high pressure device, the syringe The high-pressure equipment consists of a carbon dioxide cylinder that supplies carbon dioxide into the pipeline through a high-pressure pipeline system, and a data extraction system that uses a T-type thermocouple as a signal measurement and transmits it back to the computer via the capture system. The treatment is carried out, a constant temperature water tank is used to keep the carbon dioxide before the heat extraction experiment in a supercritical state, a cooling water tank is used to condense the carbon dioxide after absorption to a liquefied state, and a high pressure pumping system of a syringe type establishes a high pressure environment of carbon dioxide, and is precisely controlled. The inlet pressure and the flow rate are such that the flow rate of the constant output constant pressure is stabilized, and the heat taken by the supercritical carbon dioxide in the round pipe is calculated by using the input mass flow rate and the inlet and outlet enthalpy values, and the calculation formula is as follows: Where h _in is the entrance threshold and h _out is the exit threshold. The method for establishing an optimal heat extraction system for enhanced geothermal heat as described in claim 3, wherein the operating conditions and experimental parameters of the heat extraction experiment are: wall heat flux 1473.66 W/m ² , inlet fluid temperature 313.15 K, average particle size of porous media is 1.54mm and 2.03mm, inlet mass flow rate is 0.00027kg/s, 0.00054kg/s, 0.00082kg/s and 0.00109kg/s, operating pressure is 7.5MPa, 9MPa, 10MPa, 11MPa and 12.5MPa . For example, the method for establishing an optimal heat extraction system for enhanced geothermal heat according to claim 1 is to establish the numerical model by using multiple physical quantity software, verify the correctness of the numerical model, and obtain the optimal operating condition. An optimal heat extraction system for enhanced geothermal heat is established by the method for establishing an optimal heat extraction system for enhanced geothermal heat according to any one of claims 1 to 5.