A system, method and prediction method for obtaining the pH of a solution of saturated acidic gas under high temperature and high pressure conditions

Abstract

A system, method and prediction method for obtaining the pH of a solution of saturated acidic gas under high temperature and high pressure conditions, comprising a gas extraction tank which contains a liquid-phase soluble acidic gas; an injection pump for pressurizing the liquid-phase soluble acidic gas supplied to the gas extraction tank through a pipeline; a pre-saturation container which contains a brine solution, and the pressurized liquid-phase soluble acidic gas supplied by the injection pump through the pipeline is mixed with the brine solution in the pre-saturation container to form an acidic gas pre-saturated solution; a reaction container including a housing and a containing space; a temperature control device arranged in the containing space; a stirring device arranged in the containing space; a pH detection electrode arranged in the containing space, and the pH detection electrode includes at least two different types of electrodes for detecting the pH of the saturated acidic gas solution in the reaction container under different environmental temperature ranges. The present invention can accurately measure the pH value of a brine solution or a pure solution of saturated acidic gas under high temperature and high pressure conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of pH value measurement of brine or pure solution saturated with acidic gas at high temperature and high pressure, and relates to a system and method for obtaining the pH of saturated soluble acidic gas brine or pure solution based on the electrical measurement method.

[0002] Background Introduction

[0003] Under the background of the "dual carbon goal", the CO2 capture and storage technology can effectively reduce the amount of CO2. Usually, the captured CO2 is injected into underground reservoirs for storage. During the storage process, CO2 will react with the brine in the underground reservoir, which will cause the pH of the reservoir brine to change, and then change the chemical interaction and reactive transport phenomenon between the brine and the reservoir rock, thus changing the geological conditions of the reservoir area. Therefore, in the processes of simulating production increase, seal leakage and injection for projects such as CO2 capture, storage and utilization, the measurement of pH value change is crucial. The traditional electrical measurement method for pH value is mainly used for measuring the pH value of brine at normal temperature and pressure. For the high temperature and high pressure conditions in the reservoir, this method loses its due accuracy. Therefore, how to obtain the pH value of brine solution with high accuracy under the high temperature and high pressure conditions in the reservoir is crucial. In view of the above existing problems, a new system and method for obtaining the pH of saturated soluble acidic gas brine or pure solution based on the electrical measurement method are studied and designed to solve the pH value change situation after CO2 is injected into the reservoir. At the same time, the device and method can be extended to the measurement of the pH value of other soluble acidic gas saturated brine solutions, such as the pH value of SO2, H2S and other acidic gas saturated brine solutions under high temperature and high pressure conditions. At the same time, under high temperature and high pressure conditions, the pH problem of pure brine solution can also be obtained through this device and method. In addition, for the measurement of the pH of domestic wastewater or the pH of mine water discharged during mining with high ion concentration, this device and method are also applicable. Summary of the Invention

[0004] In order to solve the problem of inaccurate pH value measurement in the existing pH value measurement technology in the reservoir, the present invention proposes a system, method and prediction method for obtaining the pH of a solution saturated with acidic gas under high temperature and high pressure conditions, which can accurately detect the pH value of a saturated acidic gas brine solution under high temperature and high pressure conditions, and can also accurately measure the pH value of a pure solution under high temperature and high pressure conditions, and can accurately predict the pH value. To achieve the above object, the present invention adopts the following technical solutions:

[0005] In a first aspect, a system for obtaining the pH of a solution saturated with acidic gas under high temperature and high pressure conditions based on the electrical measurement method according to some embodiments of the present application includes:

[0006] A gas extraction tank, which contains a liquid-phase soluble acidic gas;

[0007] An injection pump for pressurizing a liquid-soluble acidic gas supplied to the injection pump through a pipeline from the gas extraction tank;

[0008] A pre-saturation container filled with a brine solution, and the pressurized liquid-soluble acidic gas supplied by the injection pump through a pipeline is mixed with the brine solution in the pre-saturation container to form an acidic gas pre-saturated solution;

[0009] A reaction container, including

[0010] A housing including a receiving space formed inside the housing;

[0011] A temperature control device disposed in the receiving space for forming a temperature-controlled environment of the reaction container;

[0012] A stirring device disposed in the receiving space for stirring the acidic gas pre-saturated solution supplied from the pre-saturation container to the reaction container through a pipeline to form an acidic gas saturated solution;

[0013] pH detection electrodes disposed in the receiving space, the pH detection electrodes including at least two different types of electrodes, and different types of electrodes respectively detect the pH of the acidic gas saturated solution in the reaction container at different ambient temperature ranges of the reaction container.

[0014] A system for obtaining the pH of a solution saturated with an acidic gas under high temperature and high pressure conditions according to some embodiments of the present application, the gas extraction tank is connected to the injection pump, a first three-way valve is provided between the gas extraction tank and the injection pump, the gas extraction tank is connected to a first port of the first three-way valve through a first pipeline, a first needle valve and a check valve are sequentially provided between the gas extraction tank and the first three-way valve, a second port of the first three-way valve is connected to one end of the injection pump through a second pipeline, the first needle valve has an open state and a closed state for liquid acidic gas, when the first needle valve is in the open state for liquid acidic gas, the liquid acidic gas in the gas extraction tank flows into the injection pump through the first pipeline, the first three-way valve and the second pipeline;

[0015] The other end of the injection pump is connected to one end of the pre-saturation container through a fourth pipeline, and a third needle valve, an indicating pressure relief valve and a pressure sensor are provided on the fourth pipeline;

[0016] The other end of the pre-saturation container is connected to the water inlet / outlet through a fifth pipeline. The third end of the pre-saturation container is connected to the reaction container through a sixth pipeline. A fourth needle valve is provided between the pre-saturation container and the water inlet / outlet. The fourth needle valve has a brine open and closed state. When the fourth needle valve is in the brine open state, brine enters the pre-saturation container through the fifth pipeline. The pre-saturation container is used to mix the injected brine with the pressurized liquid acidic gas supplied by the injection pump through the fifth pipeline to form an acidic gas pre-saturated solution.

[0017] A fifth needle valve is provided between the pre-saturation container and the reaction container. When the fifth needle valve is opened, the pre-saturation container and the reaction container are in communication, and the acidic gas pre-saturated solution in the pre-saturation container is injected into the reaction container through the sixth pipeline.

[0018] For the solution pH acquisition system for saturating acidic gas under high temperature and high pressure conditions according to some embodiments of the present application, the third port of the first three-way valve is connected to the exhaust water inlet through a third pipeline, and a second needle valve is provided between the first three-way valve and the exhaust water inlet.

[0019] For the solution pH acquisition system for saturating acidic gas under high temperature and high pressure conditions according to some embodiments of the present application, a discharge vacuum branch line is further provided on the fourth pipeline. The discharge vacuum branch line includes a second three-way valve, a drain port, an indicating pressure relief valve, and a vacuum pump. The first port of the second three-way valve is connected to the fourth pipeline through a first three-way pipeline. The second port of the second three-way valve is connected to the drain port. The second port of the second three-way valve is connected to the first port of a second three-way pipeline. The second port of the second three-way pipeline is connected to the vacuum pump. The third port of the second three-way pipeline is connected to the indicating pressure relief valve. When the third needle valve is opened, the injection pump and the pre-saturation container are in communication with each other. A purification branch line is further provided on the fourth pipeline. The purification branch line is connected to the fourth pipeline through a third three-way valve.

[0020] For the solution pH acquisition system for saturating acidic gas under high temperature and high pressure conditions according to some embodiments of the present application, a first shut-off check valve is provided between the first three-way valve and the injection pump. The first shut-off check valve is used to prevent the backflow of liquid acidic gas.

[0021] In a second aspect, for the solution pH acquisition system for saturating acidic gas under high temperature and high pressure conditions according to some embodiments of the present application, using the above acquisition system, includes the following steps:

[0022] S1. Electrode calibration and calibration stage;

[0023] S2. Preparation stage;

[0024] S3. Seal inspection and cleaning stage;

[0025] S4. Premixing preparation stage: pressurizing the liquid-soluble acid gas supplied from the gas extraction tank to the injection pump through a pipeline;

[0026] S5. Premixing stage: the pressurized liquid-phase soluble acid gas and the brine solution are mixed in the presaturation container to form an acid gas presaturated solution;

[0027] S6. Saturated solution formation stage: stirring the acid gas pre-saturated solution in the reaction vessel to form an acid gas saturated solution;

[0028] S7. pH value measurement stage: using different types of electrodes to detect the pH of the acid gas saturated solution in the reaction container under different ambient temperature ranges;

[0029] S8. Cleaning phase.

[0030] According to some embodiments of the present application, the pH of a solution of saturated acidic gas under high temperature and high pressure conditions is obtained: S1. Electrode calibration and calibration stage: Before the experiment begins, the glass electrode and zirconium oxide electrode for pH measurement and the Ag / AgCl reference electrode are calibrated and calibrated using low pH and high pH calibration solutions, respectively. When the glass electrode and zirconium oxide electrode are calibrated and calibrated using the low pH calibration solution, the seventh needle valve is opened, and the low pH calibration solution is introduced through the seventh pipeline to calibrate and calibrate the glass electrode and zirconium oxide electrode for pH measurement. After the calibration and calibration are completed, the eighth needle valve is opened, the low pH calibration solution is discharged through the eighth pipeline, and the high pH calibration solution is introduced through the eighth pipeline. When calibrating and calibrating the glass electrode and the zirconium oxide electrode, open the seventh needle valve, and introduce the high pH calibration solution through the seventh pipeline to calibrate and calibrate the glass electrode and the zirconium oxide electrode for pH measurement. After the calibration and calibration are completed, open the eighth needle valve and discharge the high pH calibration solution through the eighth pipeline. Among them, the calibration solution can be a professional pH calibration solution, or a calibration solution can be prepared according to your own needs. When calibrating, the N2 pressure can be slightly higher than the boiling point of the liquid. Use N2 as the pressurized medium, measure the low pH and high pH calibration solutions at ambient temperature and a pressure of 16MPa, and then calibrate the glass electrode under low pressure conditions;

[0031] S2. Preparation stage: After the calibration and calibration are completed, close the second needle valve, the fourth needle valve, the sixth needle valve, the seventh needle valve and the eighth needle valve to seal the entire system, set the indicated pressure of the indicating pressure relief valve to 0.35MPa, and the indicated pressure of the indicating pressure relief valve to 18.6MPa;

[0032] S3. Sealing inspection and cleaning stage: Open the seventh needle valve and the eighth needle valve, close the fifth needle valve to form an independent sealed space for the reaction vessel, remove the remaining other gases in the reaction vessel, and then close the seventh needle valve and the eighth needle valve; then open the second needle valve to introduce He gas, use the He gas to inspect the airtightness of the overall system. After the airtightness inspection is completed, turn on the vacuum pump to suck out the He gas. After the He gas is sucked out, turn off the vacuum pump and introduce ultrapure water through the second needle valve. Use the ultrapure water to clean the second pipeline, the third pipeline, the syringe pump, the fourth pipeline, the pre-saturation container, the sixth pipeline and the reaction vessel of the device. After the cleaning is completed, open the eighth needle valve to discharge the ultrapure water. After discharging the ultrapure water, open the purification branch line, so that nitrogen gas passes through the third three-way valve into the system from the purification branch line, and use N2 to purge and dry each part of the system. After the purging is completed, close the eighth needle valve and the second needle valve;

[0033] S4. Pre-mixing preparation stage: Close the third needle valve, open the first needle valve, and use the syringe pump to suck the liquid acidic gas in the gas extraction tank, and pressurize the acidic gas with the syringe pump; thus, the closing of the second needle valve and the third needle valve forms an independent sealed space for the gas extraction tank and the syringe pump; while pressurizing the acidic gas with the syringe pump, open the fourth needle valve and close the fifth needle valve. At this time, the third needle valve is in the closed state, thus forming an independent sealed space for the pre-saturation container, and the saline solution is injected into the pre-saturation container through the fourth needle valve;

[0034] S5. Pre-mixing stage: After the pressurization of the acidic gas in the syringe pump is completed and the injection of the saline solution into the pre-saturation container is completed, open the third needle valve and close the fourth needle valve, stop supplying the saline solution to the pre-saturation container, connect the syringe pump and the pre-saturation container, and form a common independent sealed space for the connection of the syringe pump and the pre-saturation container, so that the pressurized liquid acidic gas enters the pre-saturation container and is mixed with the saline solution in the pre-saturation container to form an acidic gas pre-saturated solution. During the pre-mixing process, continuously monitor the reading of the pressure sensor. When the reading of the pressure sensor is less than 4.5 MPa, manually adjust the pressure to ensure that the acidic gas and the solution to be tested are in full contact and dissolve in each other;

[0035] S6. Saturated solution formation stage: Open the fifth needle valve to inject the acidic gas pre-saturated solution in the pre-saturation container into the reaction vessel, and use a magnetic stirrer to stir the solution in the reaction vessel to further mix the acidic gas and the saline solution, maintain the saturated state of the acidic gas salt solution, and at the same time observe the pressure of the syringe pump and the reading of the pressure sensor to ensure that the acidic gas is fully dissolved in the solution to be tested, and finally make the salt solution a solution of saturated acidic gas; among them, when using the magnetic stirrer to stir, when the pressure of the pressure sensor is less than 10 MPa, it needs to be stirred for at least 4 hours, and when the pressure of the pressure sensor is greater than 10 MPa, it needs to be stirred for at least 24 hours;

[0036] S7. pH Measurement Stage: After stirring is completed, turn on the electric heater to heat the reaction vessel to form different temperature ranges. At different temperature ranges, use the insulation layer to keep it insulated. When the temperature and pressure are stable and the system reaches phase equilibrium, use a pH meter to measure the pH value of the acidic gas saturated solution. When measuring the pH value of the acidic gas saturated solution, continuously monitor the reading of the thermometer in the reaction vessel. When the thermometer reading is less than 90 °C, use a glass electrode to measure the pH value. When the thermometer reading is greater than 90 °C, use a zirconia electrode to measure the pH value;

[0037] S8. Cleaning Stage: After completing one measurement, first open the sixth needle valve and the back pressure regulating device to slowly reduce the pressure of the reaction vessel. When the pressure in the reaction vessel is normal pressure, then open the second needle valve, the fourth needle valve, the seventh needle valve, the eighth needle valve and the vacuum pump to exhaust and drain the device.

[0038] In a third aspect, a method for predicting the pH of a saturated acidic gas solution under high temperature and high pressure conditions according to some embodiments of the present application includes the following steps:

[0039] According to the prediction method, obtain the predicted pH value of the CO2 saturated CaCl2 aqueous solution under the set parameter conditions;

[0040] According to the above acquisition system, under the same parameter conditions as those in the implementation of the prediction method, obtain the measured pH value of the CO2 saturated CaCl2 aqueous solution, and verify the accuracy of the predicted pH value according to the measured pH value;

[0041] The prediction method includes:

[0042] Step 1: Analyze the influencing factors of the pH of the CO2 saturated CaCl2 aqueous solution, and establish a Pitzer calculation model according to the empirical formula;

[0043] Step 2: According to the Pitzer calculation model, obtain the partial pressure data of CO2 by obtaining the pressure data and relevant empirical formulas with temperature as variables. The empirical formula is as follows;

[0044]

[0045] P is the applied pressure, with the unit of MPa, the value of T1 is 647.096, with the unit of K, the temperature T ranges from 2298.15 K to 425.15 K, and the applied pressure P ranges from 0.2 to 15 MPa;

[0046] Step 3: Convert the obtained partial pressure data of CO2 into a CO2 pressure coefficient that can be imported into PHREEQC. The formula is as follows;

[0047]

[0048] wherein is the partial pressure data of CO2, and P0 is the standard atmospheric pressure, with a value of 0.010325 MPa;

[0049] Step 4: Optimize the interaction parameters of the Pitzer calculation model based on relevant data, and use the optimized Pitzer calculation model to obtain the predicted data of the CO2-saturated CaCl2 solution;

[0050] Step 5: Set relevant parameters in PHREEQC, including temperature, solution type, and CO2 partial pressure coefficient;

[0051] Step 6: Reset the relevant parameters and predict the pH of the CO2-saturated CaCl2 solution under the next parameter condition.

[0052] According to the method for predicting the pH of a solution saturated with an acidic gas under high temperature and high pressure conditions of some embodiments of the present application, the influencing factors of the pH of the CO2-saturated CaCl2 aqueous solution in Step 1 include temperature factor, pressure factor, and ionic factor. The temperature factor is the temperature of the CO2-saturated CaCl2 aqueous solution, the pressure factor is the CO2 partial pressure, and the ionic factor is the concentration of the CaCl2 aqueous solution;

[0053] Regarding the optimization of the interaction parameters of the Pitzer model in Step 4, for the B0 and B3 terms in β MX (0) and β MX (1) and the B0 term in Ψ ijk are modified and optimized. In PHREEQC, the Pitzer coefficient P is related to the function of temperature, and the general form is as follows:

[0054]

[0055] The optimization of the interaction parameters includes:

[0056] First, consider the β MX (0) and β MX (1) β MX (2) parameters fitted from single-salt data. By optimizing β MX (0) and β MX (1) β MX (2)The modification of the empirical parameters B0, B1, B2, B3, B4, and B5 makes the prediction results close to the experimental data. Through multiple attempts by the trial-and-error method, the relevant empirical coefficients B0, B1, B2, B3, B4, and B5 are modified multiple times. The results obtained by running the program using the modified database are compared, and the prediction results are gradually approximated to the experimental results:

[0057] Secondly, considering the CO2 dissolution, according to for θ ij , Ψ ijk the relevant empirical coefficients B0, B1, B2, B3, B4, and B5 are modified. Through multiple trial-and-error attempts and the comparison of the results after multiple runs, it shows that the optimization effect of Ψ ijk is better. Subsequently, only Ψ ijk is optimized, and the final results are compared with the results of the initial database.

[0058] Beneficial effects: The pH acquisition system, method, and prediction method for a saturated acidic gas solution under high temperature and high pressure according to the present invention can measure the pH value of a saturated acidic salt solution or a pure solution under high temperature and high pressure conditions. By using different pH meter measuring electrodes to measure the pH value of the solution at different temperatures, the measured pH value can still have high accuracy under high temperature and high pressure conditions. Further, the exhaust process of the reaction vessel is automatically controlled by a programmable backpressure regulating device, reducing the damage to the pH meter electrode. By setting a pre-saturation container, the time for the acidic gas to mix with the salt solution to reach the saturated state in the container is reduced, improving the accuracy of the device when measuring the pH value. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a block diagram of the pH acquisition system for a saturated soluble acidic gas brine or pure solution based on the electrical measurement method of the present invention.

[0060] Figure 2 is a flowchart of the prediction method of the present invention.

[0061] Figure 3 is a prediction result diagram in an embodiment of the present invention.

[0062] In the figure: 1. Gas extraction tank, 2. First needle valve, 3. Check valve, 4. Second needle valve, 5. First three-way valve, 6. First shut-off check valve, 7. Injection pump, 8. Second shut-off check valve, 9. Indicating pressure relief valve, 10. Vacuum pump, 11. Second three-way valve, 12. Third needle valve, 13. Pressure sensor, 14. Indicating pressure relief valve, 15. Third three-way valve, 16. Pre-saturation container, 17. Fourth needle valve, 18. Fifth needle valve, 19. Reaction vessel, 20. Backpressure regulating device, 21. Sixth needle valve, 22. Seventh needle valve, 23. Eighth needle valve. DETAILED DESCRIPTION OF THE INVENTION

[0063] The following further describes in detail the embodiments of the present invention in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0064] Example 1: A method for obtaining the pH of a solution of saturated acidic gas under high temperature and high pressure conditions in this example is as Figure 1 shown, including a gas extraction tank 1, an injection pump 7, a pre-saturation container 16, a reaction container 19, and an electrode for pH detection.

[0065] The gas extraction tank 1 is internally loaded with liquid acidic gas. The gas extraction tank 1 is connected to the injection pump 7. The injection pump 7 is used to pressurize the liquid acidic gas provided by the gas extraction tank 1. A first three-way valve 5 is provided between the gas extraction tank 1 and the injection pump 7. The gas extraction tank 1 is connected to the first port of the first three-way valve 5 through a first pipeline. A first needle valve 2 and a check valve 3 are sequentially provided between the gas extraction tank 1 and the first three-way valve 5. The check valve 3 is used to prevent the reverse flow of liquid acidic gas. The second port of the first three-way valve 5 is connected to one end of the injection pump 7 through a second pipeline. The first needle valve 2 has an open state and a closed state for liquid acidic gas. When the first needle valve 2 is in the open state for liquid acidic gas, the liquid acidic gas in the gas extraction tank 1 flows into the injection pump 7 through the first pipeline, the first three-way valve 5, and the second pipeline. The third port of the first three-way valve 5 is connected to an exhaust water inlet through a third pipeline. A second needle valve 4 is provided between the first three-way valve 5 and the exhaust water inlet.

[0066] The other end of the injection pump 7 is connected to one end of the pre-saturation container 16 through a fourth pipeline. On the fourth pipeline in the direction from the injection pump 7 to the pre-saturation container 16, a second shut-off check valve 8, a discharge vacuum branch line, a third needle valve 12, a pressure sensor 13, an indicating pressure relief valve 14, and a purification branch line are sequentially provided. The second shut-off check valve 8 is used to prevent the reverse flow of liquid acidic gas. The discharge vacuum branch line includes a second three-way valve 11, a drain port, an indicating relief valve 9, and a vacuum pump 10. The first port of the second three-way valve 11 can be connected to the fourth pipeline through a first three-way pipe. The second port of the second three-way valve 11 is connected to the drain port. The second port of the second three-way valve 11 is connected to the first port of a second three-way pipe. The second port of the second three-way pipe is connected to the vacuum pump 10. The third port of the second three-way pipe is connected to the indicating relief valve 9. When the third needle valve 12 is opened, the injection pump 7 and the pre-saturation container 16 are in communication with each other. The purification branch line is connected to the fourth pipeline through a third three-way valve 15.

[0067] The other end of the pre-saturation container 16 is connected to the water inlet / outlet through the fifth pipeline. The other end of the pre-saturation container 16 is also connected to the reaction container 19 through the sixth pipeline. A fourth needle valve 17 is provided between the pre-saturation container 16 and the water inlet / outlet. The fourth needle valve 17 has a brine open and closed state. When the fourth needle valve 17 is in the brine open state, brine enters the pre-saturation container 16 through the fifth pipeline. The pre-saturation container 16 is used to mix the injected brine with the pressurized liquid acidic gas supplied by the injection pump 7 through the fifth pipeline to form an acidic gas pre-saturated solution. A fifth needle valve 18 is provided between the pre-saturation container 16 and the reaction container 19. When the fifth needle valve 18 is opened, the pre-saturation container 16 and the reaction container 19 are in communication, and the acidic gas pre-saturated solution in the pre-saturation container 16 is injected into the reaction container 19 through the sixth pipeline.

[0068] The other end of the reaction container 19 is connected to the feed inlet through the seventh pipeline. The other end of the reaction container 19 is also connected to the discharge outlet through the eighth pipeline. A seventh needle valve 22 is provided between the reaction container 19 and the feed inlet. The seventh needle valve 22 has an open state for calibrating solution or acidic gas and a closed state. When the seventh needle valve 22 is in the open state for calibrating solution or acidic gas, the calibrating solution or acidic gas is supplied to the reaction container 19 through the seventh pipeline.

[0069] The reaction container 19 includes a housing, a temperature control device, and a stirring device. The housing includes a receiving space formed inside the housing. The temperature control device is disposed in the receiving space for forming a temperature controllable environment of the reaction container 19. The stirring device is disposed in the receiving space for stirring the acidic gas pre-saturated solution supplied from the pre-saturation container 16 to the reaction container 19 through the sixth pipeline to form an acidic gas saturated solution.

[0070] The electrodes for pH measurement are disposed in the receiving space of the reaction container 19. The electrodes for pH measurement include at least two different types of electrodes. Different types of electrodes respectively detect the pH value of the acidic gas saturated solution in the reaction container 19 at different ambient temperature ranges of the reaction container 19.

[0071] A particle filter may be provided at the outlet of the gas extraction tank 1. The aperture of the particle filter may be 0.5 μm. A first shut-off check valve 6 is provided between the first three-way valve 5 and the injection pump 7. The first shut-off check valve 6 is used to prevent the reverse flow of the liquid acidic gas.

[0072] The temperature control device includes a thermometer and an electric heater. There are blind holes on the wall of the reaction vessel 19. The thermometer and the electric heater pass through the blind holes and are arranged inside the reaction vessel 19. The thermometer can be a Pt100 thermometer, and there can be multiple electric heaters. An insulating layer is provided on the outer surface of the reaction vessel 19. By setting the insulating layer, better heat preservation can be achieved for the interior of the reaction vessel 19. The insulating layer material can be silicone rubber foam. A backpressure regulating device 20 is provided outside the reaction vessel 19. The electrode of the pH meter is inserted into the reaction vessel 19 through the backpressure regulating device 20. The backpressure regulating device 20 is connected to the reaction vessel 19 through a sixth needle valve 21. The other end of the backpressure regulating device 20 is an exhaust port. The backpressure regulating device 20 is a programmable backpressure regulating device. The backpressure regulating device 20 can adopt PID control to ensure that the pressure reduction and air release process will not damage the pH electrode. The reaction vessel 19 is a high-temperature and high-pressure reaction vessel, and the high-temperature and high-pressure reaction vessel adopts a surface sealing method to achieve sealing. The electrode of the pH meter includes a glass electrode and a zirconia electrode. The glass electrode can be used to measure the pH value in the low-temperature range of 0 - 90 °C, and the zirconia electrode can be used to measure the pH value in the high-temperature range of 80 - 150 °C.

[0073] The gas extraction tank 1, the injection pump 7, the pre-saturation container 16, the reaction vessel 19, various connecting pipelines and valves of the device can all be made of corrosion-resistant titanium or Hastelloy C276.

[0074] This system can measure the pH value of a soluble saturated acidic salt solution and the pH value of a pure solution. By using different pH meter measuring electrodes to measure the pH value of the solution at different temperatures, the measured pH value can still have high accuracy under high-temperature and high-pressure conditions.

[0075] A method for obtaining the pH value of a saturated acidic gas solution under high-temperature and high-pressure conditions in this embodiment includes the following steps:

[0076] Electrode calibration and standardization stage: Before the experiment, the glass electrode, zirconia electrode and Ag / AgCl reference electrode of the pH meter are calibrated and standardized using two calibration solutions with low pH and high pH respectively. When calibrating and standardizing the glass electrode and zirconia electrode with the low pH calibration solution, open the seventh needle valve 22, and introduce the low pH calibration solution through the seventh pipeline to calibrate and standardize the glass electrode and zirconia electrode of the pH meter. After the calibration and standardization are completed, open the eighth needle valve 23 and discharge the low pH calibration solution through the eighth pipeline. When calibrating and standardizing the glass electrode and zirconia electrode with the high pH calibration solution, open the seventh needle valve 22, and introduce the high pH calibration solution through the seventh pipeline to calibrate and standardize the glass electrode and zirconia electrode of the pH meter. After the calibration and standardization are completed, open the eighth needle valve 23 and discharge the high pH calibration solution through the eighth pipeline. Among them, the calibration solution can be a professional pH calibration solution, or a calibration solution can be prepared according to your own needs. When calibrating, the N2 pressure is slightly higher than the liquid boiling point. Use N2 as the pressurizing medium. At ambient temperature, measure the two calibration solutions with low pH and high pH at a pressure of 16 MPa, and then calibrate the glass electrode under low pressure conditions.

[0077] Preparation stage: After the calibration and standardization are completed, close the second needle valve 4, the fourth needle valve 17, the sixth needle valve 21, the seventh needle valve 22 and the eighth needle valve 23 to seal the entire device, and set the indication pressure of the indication relief valve 9 to 0.35 MPa and the indication pressure of the indication pressure relief valve 14 to 18.6 MPa.

[0078] Sealing inspection and cleaning stage: Open the seventh needle valve 22 and the eighth needle valve 23, close the fifth needle valve 18, form an independent sealed space for the reaction vessel 19, remove the remaining other gases in the reaction vessel 19, and then close the seventh needle valve 22 and the eighth needle valve 23. Then open the second needle valve 4 to introduce He gas, and use the He gas to inspect the tightness of the overall system. After the airtightness inspection is completed, turn on the vacuum pump 10 to suck out the He gas. After the He gas is sucked out, turn off the vacuum pump and introduce ultrapure water through the second needle valve 4. Use the ultrapure water to clean the second pipeline, the third pipeline, the injection pump 7, the fourth pipeline, the pre-saturation container 16, the sixth pipeline and the reaction vessel 19 of the device. After the cleaning is completed, open the eighth needle valve 23 to discharge the ultrapure water. After discharging the ultrapure water, open the valve of the purification branch line, so that nitrogen gas passes through the third three-way valve 15 from the purification branch line into the system, and use N2 gas to purge and dry each part of the device. After the purging is completed, close the eighth needle valve 23 and the second needle valve 4. It can be understood that the pipeline for supplying nitrogen gas connected to the inlet of the third three-way valve 15 is provided with a valve (not shown) for coordinating the intake control.

[0079] Pre-mixing preparation stage: Close the third needle valve 12, open the first needle valve 2, and use the injection pump 7 to suck the liquid acidic gas in the gas extraction tank 1. Pressurize the acidic gas using the injection pump 7. Thus, the closing of the second and third needle valves 12 forms an independent sealed space for the gas extraction tank 1 and the injection pump 7. While pressurizing the acidic gas using the injection pump 7, open the fourth needle valve 17 and close the fifth needle valve 18. At this time, the third needle valve 12 is in the closed state, thereby forming an independent sealed space for the pre-saturation container 16. The brine solution is injected into the pre-saturation container 16 through the fourth needle valve 17.

[0080] Pre-mixing stage: After the pressurization of the acidic gas in the injection pump 7 is completed and the injection of the brine solution into the pre-saturation container 16 is completed, open the third needle valve 12, close the fourth needle valve 17, and preferably close the first needle valve 2, that is, stop supplying the brine solution to the pre-saturation container 16, connect the injection pump 7 and the pre-saturation container 16, and form a common independent sealed space where the injection pump 7 and the pre-saturation container 16 are connected. It can be understood that a check valve is installed on the pipeline of the gas extraction tank to prevent the reflux of the acidic gas. Therefore, it is preferred to close the first needle valve 2 to further ensure that the gas extraction tank is isolated during the current stage or subsequent stages when gas supply is not required, so that the pressurized liquid acidic gas enters the pre-saturation container 16 and mixes with the brine solution in the pre-saturation container 16 to form an acidic gas pre-saturated solution. During the pre-mixing process, continuously monitor the reading of the pressure sensor 13. When the reading of the pressure sensor 13 is less than 4.5 MPa, manually adjust the pressure to ensure the continuous inhalation of the acidic gas.

[0081] Saturated solution formation stage: Open the fifth needle valve 18 to inject the acidic gas pre-saturated solution in the pre-saturation container 16 into the reaction container 19. Use a magnetic stirrer to stir the solution in the reaction container 19 to further mix the acidic gas with the brine solution, maintain the saturated state of the acidic gas brine solution, and at the same time observe the pressure of the injection pump 7 and the reading of the pressure sensor 13 to ensure that the acidic gas saturated solution is always in a saturated state.

[0082] Among them, when using a magnetic stirrer for stirring, it is necessary to stir for at least 4 hours when the pressure of the pressure sensor 13 is less than 10 MPa, and it is necessary to stir for at least 24 hours when the pressure of the pressure sensor 13 is greater than 10 MPa.

[0083] pH value measurement stage: after the stirring is completed, the electric heater is turned on to heat the reaction vessel 19 to form different temperature ranges. In different temperature ranges, it is kept warm by an insulation layer. When the temperature and pressure stability system reaches phase equilibrium, the pH value of the salt solution saturated with acidic gas is measured using a pH meter. When measuring the pH value of the saturated salt solution of acidic gas, it is necessary to monitor the reading of the thermometer in the reaction vessel 19 at all times. When the thermometer reading is less than 80°C, the pH value is measured using a glass electrode. When the thermometer reading is greater than 80°C, the pH value is measured using a zirconium oxide electrode.

[0084] Device cleaning stage: After completing a measurement, first open the sixth needle valve 21 and the back pressure regulating device 20 to slowly reduce the pressure of the reaction container 19. When the pressure in the reaction container 19 is normal pressure, open the second needle valve 4, the fourth needle valve 17, the seventh needle valve 22, the eighth needle valve 23 and the vacuum pump 10 to exhaust and drain the device to prevent the internal residue of the device from corroding the device. Among them, the slow reduction of the pressure of the reaction container 19 is to prevent the reaction container 19 from quickly returning to normal pressure from high pressure, which may cause damage to the electrodes in the shell.

[0085] The above-mentioned time-sharing method selectively seals the space of the equipment used at different stages of the process, so that the process at each stage maintains the environment required for the reaction without affecting the upstream and downstream equipment, and forms a stable process supply after completing the initial reaction at each stage, and supplies the reactor with a continuous pre-saturated solution throughout the process.

[0086] The inventors found in the process of studying interfacial tension that the time to reach the saturated state can be reduced by using a pre-saturated container, so that the pressurized and continuously supplied acidic gas and brine solution are first mixed in the pre-saturated container 16, in order to pre-saturate the carbon dioxide and the brine. The pre-saturation mainly changes the state of the material into a brine solution saturated with carbon dioxide and a carbon dioxide saturated with brine. The whole process lasts for 4-5 hours. In some experimental examples, the volume of the pre-saturated container is 60 ml. During the experiment, 1 / 3 of the volume is injected into the test liquid, and 2 / 3 is the acidic gas. The subsequent stirring time in the container is shortened to about 10 hours, which, together with the pre-saturation time, is less than 20 hours without the pre-saturated container.

[0087] The pre-saturation container changes the state of the material into a brine solution saturated with carbon dioxide and a brine solution saturated with carbon dioxide, thereby reducing the time for the acid gas and the brine solution to be mixed to a saturated state in the reaction container 19. The maximum pressure of the measurement of this method is 15MPa and the minimum pressure is 0.1MPa. This method is also applicable to the measurement of pH value of pure solution under high temperature and high pressure conditions.

[0088] Example 2: A system for obtaining the pH of a solution of saturated acidic gas under high temperature and high pressure conditions, including a fluid circulation device and a measuring device. The circulation device includes an injection pump 7 for gas injection, a purification pipeline, a pre-saturation container 16, a vacuum pipeline, a discharge pipeline, and several valves. The measuring device includes a glass electrode, a zirconia electrode, a pressure sensor 13, a digital voltmeter, and a Pt100 thermometer. The system realizes the measurement of the pH of a soluble gas saturated brine solution under high temperature and high pressure conditions.

[0089] In a preferred solution of the acquisition system, the circulation device is made of corrosion-resistant titanium or Hastelloy C276.

[0090] In a preferred solution of the acquisition system, the glass electrode is used to measure the pH in the low temperature range of 0 - 90 °C, and the zirconia electrode is used to measure the pH in the high temperature range of 90 - 150 °C.

[0091] In a preferred solution of the acquisition system, a back pressure regulating device 20 is designed outside the reaction vessel. The pH electrode is inserted into the reaction vessel through the back pressure regulating device 20. The back pressure regulating device 20 uses PID control to ensure that the pressure reduction and air release process will not damage the pH electrode. The reaction vessel is provided with several electric heaters, and at the same time, the outermost layer is covered with a heat insulation layer.

[0092] In a preferred solution of the acquisition system, a pre-saturation container 16 is installed in front of the reaction container 19. The soluble acidic gas and the brine solution are mixed in the pre-saturation container and then enter the reaction container 19.

[0093] A method for measuring the pH of a solution of saturated acidic gas under high temperature and high pressure conditions, including the following steps:

[0094] Before use, each part of the circulation device is cleaned with deionized water, and each part of the circulation device is purged and dried with N2 gas through the purification pipeline.

[0095] The soluble acidic gas in the liquid phase is sucked out from the extraction tank 1, and a 0.5 μm pore size particle filter is installed at the tank mouth to make it enter the injection pump 7 through the first three-way valve 5.

[0096] Use the injection pump 7 to pressurize it. A cooling jacket is arranged outside the injection pump 7 to cool the injection pump to ensure that the solubility always remains in the liquid phase.

[0097] The pressurized gas enters the pre-saturation container 16 and is pre-saturated by mixing with the brine in the container.

[0098] The pre-saturated mixed liquid enters the reaction container. A magnetic stirrer bar is arranged in the reaction container 19 to ensure sufficient dissolution and mixing. At the same time, observe the pressure of the injection pump 7 and the reading of the digital voltmeter to ensure that it is a saturated gas solution.

[0099] According to the temperature and pressure range, the zirconia electrode and the glass electrode are used in sequence to detect the pH value of the solution.

[0100] In a preferred embodiment, the calibration solution can be a professional pH calibration solution or can be prepared according to one's own needs. When performing calibration, it is required to be above the boiling point under the pressure of N2.

[0101] The maximum pressure measured by this method is 15 MPa, and the minimum pressure is 0.1 MPa.

[0102] When using a magnetic stir bar for stirring, it takes at least 4 hours when less than 10 MPa and 24 hours when greater than 10 MPa.

[0103] A system and method for obtaining the pH of a solution saturated with acidic gas under high temperature and high pressure conditions, including a high temperature and high pressure reaction vessel 19, an injection pump 7, a pre-saturation vessel 16, and a gas extraction tank 1. There is a magnetic stir bar in the high temperature and high pressure reaction vessel 19. There are vertical blind holes on the wall of the high temperature and high pressure reaction vessel, and a Pt100 thermometer and four electric heaters are placed. The outer shell of the high temperature and high pressure reaction vessel 19 uses a silicone rubber foam sheath as the heat insulation layer. A pH meter is provided at the top of the high temperature and high pressure reaction vessel, and the pH meter is equipped with a back pressure regulating device 20. The high temperature and high pressure reaction vessel 19 is sealed by a face seal method.

[0104] The gas extraction tank 1 contains liquid acidic gas. A 0.5 μm pore size particle filter is installed at the top of the gas extraction tank 1. The filter is connected to a first needle valve 2, and the other end of the first needle valve 2 is connected to a check valve 3. The check valve 3 is connected to the first port of the first three-way valve 5 through a connecting pipe.

[0105] In a preferred embodiment of the measuring device, the second port of the first three-way valve 5 is connected to a second needle valve 4. The other end of the second needle valve 4 is connected to an exhaust port and a water inlet. The third port of the first three-way valve 5 is connected to a first stop check valve 6, and the other end of the first stop check valve 6 is connected to an injection pump 7.

[0106] In a preferred embodiment of the measuring device, the other end of the injection pump 7 is connected to a second stop check valve 8. The other end of the second stop check valve 8 is connected to a three-way pipe. The second interface of the three-way pipe is connected to a second three-way valve 11, and the third port of the three-way pipe is connected to a third needle valve 12.

[0107] In a preferred embodiment of the measuring device, the second port of the second three-way valve 11 is connected to a drain port. The third port of the second three-way valve 11 is connected to a three-way pipe. The second port of the three-way pipe is connected to a vacuum pump 10, and the third port of the three-way pipe is connected to an indicating pressure relief valve 9, with an indicated pressure of 0.35 MPa.

[0108] In a preferred embodiment of the measuring device, the other end of the third needle valve 12 is connected to a tee pipe. The second port of the tee pipe is connected to a pressure sensor 13, and the third port of the tee pipe is connected to a third three-way valve 15. An indicating pressure relief valve 14 is provided in the middle of the connecting pipe, and the indicating pressure is 18.6 MPa.

[0109] In a preferred embodiment of the measuring device, the second port of the third three-way valve 15 is connected to an N2 purification pipeline, and the third port of the third three-way valve is connected to a pre-saturation container 16.

[0110] In a preferred embodiment of the measuring device, the other end of the pre-saturation container 16 is respectively connected to a fourth needle valve 17 and a fifth needle valve 18. The other end of the fourth needle valve 17 is connected to a water inlet / outlet, and the other end of the fifth needle valve 18 is connected to a high-temperature and high-pressure reaction vessel 19.

[0111] In a preferred embodiment of the measuring device, a programmable backpressure regulating device 20 is installed on the top of the reaction vessel 19. The glass electrode and the zirconia electrode are inserted into the reaction vessel 19 through this device. The backpressure regulating device 20 is connected to the container through a sixth needle valve 21, and the other end of the backpressure regulating device 20 is an exhaust port.

[0112] In a preferred embodiment of the acquisition system, there is a branch pipeline between the sixth needle valve 21 and the container, which is connected to a seventh needle valve 22, and the other end of the seventh needle valve 22 is connected to an exhaust port.

[0113] In a preferred embodiment of the acquisition system, the bottom end of the container is connected to an eighth needle valve 23, and the other end of the eighth needle valve 23 is connected to a drain port.

[0114] Through this system and method, the pH value of the soluble saturated acidic salt solution and the pH value of the pure solution can be measured.

[0115] The calibration solution of the pH electrode can use a professional pH calibration solution or be prepared by oneself according to the detection requirements.

[0116] The pH values of the saturated acidic salt solution and the pure solution measured by this system and method have high accuracy under high-temperature and high-pressure conditions.

[0117] The process of exhausting gas from the reaction vessel is controlled by the PID control method to reduce the damage to the pH electrode.

[0118] A pre-saturation container is designed to reduce the time for acidic gas to mix with the salt solution to reach the saturated state in the container.

[0119] Before the experiment, the glass electrode, zirconia electrode, and Ag / AgCl reference electrode were calibrated separately using two calibration solutions with low pH and high pH. N2 was used as the pressurizing medium, and all calibration solutions were measured at pressures up to 16 MPa at ambient temperature, and then the glass electrode was calibrated under low-pressure conditions.

[0120] After calibration and calibration were completed, the entire system was sealed, and the airtightness of the overall system was inspected using He gas. After the airtightness inspection was completed, each part of the experimental device was cleaned with ultrapure water, and then the third three-way valve 15 was opened to purge and dry each part with N2 gas. Before sealing and pressurizing, the remaining other gases in the high-temperature and high-pressure reaction vessel 19 were removed.

[0121] Close the second needle valve 4, the third needle valve 12, the seventh needle valve 22, and the eighth needle valve 23 to seal the system. Open the first needle valve 2 and the first three-way valve 5 to suck in the acidic gas through the injection pump 7. The acidic gas is obtained from the gas extraction tank 1, and the injection pump 7 is used to pressurize the acidic gas.

[0122] Monitor the reading of the pressure sensor 13. When it is less than 4.5 MPa, manually adjust the pressure to ensure the inhalation of the acidic gas. The stirrer in the container stirs the system at a frequency of 0.8 s for at least 4 hours. If the pressure is higher, it needs to be stirred for 24 hours. To ensure the safety of the system, set the indicated pressure of the pressure relief valve 9 to 0.35 MPa and the indicated pressure of the pressure relief valve 14 to 18.6 MPa.

[0123] Open the fourth needle valve 17 and inject brine into the pre-saturation container through the fourth needle valve 17 while closing the fifth needle valve 18.

[0124] Open the third needle valve 12 and close the fourth needle valve 17. The pressurized acidic gas enters the pre-saturation container 16 and is mixed with the brine solution.

[0125] Open the fifth needle valve 18. The pre-saturated acidic gas salt solution enters the high-temperature and high-pressure reaction vessel 19, and the magnetic stirrer is used in the reaction vessel 19 to further mix the gas with the brine solution to achieve a saturated state.

[0126] Turn on the electric heater for heating, monitor the reading of the Pt1000 thermometer, and use the glass electrode for measurement when it is less than 90 °C, and use the zirconia electrode for measurement when it is above 90 °C.

[0127] After completing one measurement, open the second needle valve 4, the third needle valve 12, the fourth needle valve 17, the sixth needle valve 21, the seventh needle valve 22, and the eighth needle valve 23, and at the same time turn on the back pressure regulating device 20 to exhaust and drain water and reduce the pressure of the device.

[0128] Repeat the cleaning steps in 2 before the next experiment.

[0129] Example 3: With the increasing severity of the greenhouse effect, CO2 is considered the main gas causing the greenhouse effect. Therefore, relevant research has been carried out in various countries to reduce the CO2 content in the atmosphere. Currently, carbon capture and storage technology is one of the effective technologies to reduce the CO2 content in the atmosphere. The captured CO2 is stored in underground aquifers. A large amount of CO2 will react with underground brine, thus changing its physical and chemical properties. The change in the pH of the brine may cause pipeline corrosion and the precipitation of a large amount of mineral substances, further changing the properties of the surrounding rocks, leading to a series of safety problems. Therefore, a large amount of research has been carried out on the pH after CO2 injection into underground aquifers. Among them, both the electrical measurement method and the spectroscopic method have high accuracy, but they require a large amount of equipment time and high economic costs. CaCl2 is one of the main ions existing in underground brine. Its precipitation of CaCO3 due to a large amount of CO2 gas poses a threat to the safety of the entire transportation pipeline. Therefore, this method proposes a prediction method for the pH value of CO2-saturated CaCl2 solution based on the Pitzer model. This method can achieve small-error prediction within the temperature range of (25 - 150 °C) and pressure range of (0.1 - 15.3 MPa). This method can effectively save time and economic costs and provide prediction data when designing relevant carbon capture and storage projects to improve the safety and feasibility analysis of the projects.

[0130] In this example, a prediction method for the pH value of CO2-saturated CaCl2 solution based on the Pitzer model is proposed. This method can predict the pH value of CO2-saturated CaCl2 solution under high temperature and high pressure conditions to solve problems such as high cost, time-consuming, and space occupation caused by actual measurement. It can be understood that the prediction method described in this example can be verified by the systems in Examples 1 and 2. The verification results show that the prediction method described in this example has high prediction accuracy.

[0131] The technical problem to be solved by this method is to provide a prediction method for the pH value of CO2-saturated CaCl2 solution based on the Pitzer model, aiming at the relatively high measurement cost of the pH of CO2-saturated CaCl2 solution under the above high temperature and high pressure conditions. The method steps are simple, reasonably designed, easy to implement, can be effectively applied to the prediction of the pH of CO2-saturated CaCl2 solution under high temperature and high pressure conditions, have high prediction accuracy, good use effect, and are convenient for popularization and use.

[0132] The specific steps of the prediction method are as follows:

[0133] Step 1: Analyze the influencing factors of the pH of CO2-saturated CaCl2 aqueous solution and establish a relevant calculation model;

[0134] Step 2: According to the calculation model, obtain the partial pressure data of CO2 by acquiring pressure data and relevant empirical formulas with temperature as a variable.

[0135] Step 3: Convert the obtained partial pressure data of CO2 into a CO2 pressure coefficient that can be imported into PHREEQC.

[0136] Step 4: Optimize the interaction parameters of the Pitzer model based on relevant data, and use the optimized Pitzer model to obtain the prediction data of CO2-saturated CaCl2 solution.

[0137] Step 5: Set relevant parameters in PHREEQC, including temperature, solution type, CO2 partial pressure coefficient and other relevant data.

[0138] Step 6: Reset relevant parameters to predict the pH of CO2-saturated CaCl2 solution under the next condition.

[0139] In the above method for predicting the pH value of CO2-saturated CaCl2 solution based on the Pitzer model, the influencing factors of the pH of the CO2-saturated CaCl2 aqueous solution in Step 1 include temperature factor, pressure factor and ionic factor. The temperature factor is the temperature of the CO2-saturated CaCl2 aqueous solution, the pressure factor is the partial pressure of CO2; the ionic factor is the concentration of the CaCl2 aqueous solution. The prediction model aims to predict the pH of the CO2-saturated CaCl2 solution under controlled temperature and pressure conditions.

[0140] In the above method for predicting the pH value of CO2-saturated CaCl2 solution based on the Pitzer model, the empirical formula of the partial pressure of CO2 in Step 2 is as follows, where P is the applied pressure, with the unit of MPa; the value of T1 is 647.096, with the unit of K, the temperature range is 2298.15K - 425.15K, and the pressure range is 0.2 - 15MPa:

[0141]

[0142] In the above method for predicting the pH value of CO2-saturated CaCl2 solution based on the Pitzer model, the partial pressure data of CO2 in Step 3 is converted into a CO2 pressure coefficient that can be imported into PHREEQC according to the empirical formula, and its empirical formula is as follows:

[0143]

[0144] where is the partial pressure data of CO2 obtained in Step 2, and P0 is the standard atmospheric pressure, with a value of 0.010325MPa.

[0145] The above-mentioned prediction method for the pH value of a CO2-saturated CaCl2 solution based on the Pitzer model. In step four, regarding the optimization of the interaction parameters of the Pitzer model, for β MX (0) and β MX (1) in the B0 and B3 terms, and for the B0 term in Ψ ijk in the Pitzer coefficient P in PHREEQC is related to the function of temperature. The general form is as follows:

[0146]

[0147] The above-mentioned prediction method for the pH value of a CO2-saturated CaCl2 solution based on the Pitzer model. In step five, according to the conditions, relevant parameter data in PHREEQC are set, such as temperature, ion species, etc. The unit of temperature in this simulator is °C.

[0148] In the empirical formula in step two, the partial pressure of CO2 is converted into a function with pressure and temperature as variables. The partial pressure of CO2 can be obtained through the empirical formula, and it has a wide applicable range: temperature range 25 - 150 °C; pressure range 0.2 - 15 MPa.

[0149] In step four, for the optimization of the interaction parameters of CaCl2 in the Pitzer model, through the modification and optimization of these β MX (0) , β MX (1) and Ψ ijk terms in the Pitzer model for CaCl2 solution, the high-concentration prediction results are more in line with the experimental data.

[0150] The PHREEQC simulator mentioned in step five rewrites all chemical equations according to the main species and calculates the fugacity coefficient from the Peng-Robinson equation of state using the classical Van der Waals one-fluid mixing rule. The temperature scale in the simulator is °C, and the solution concentration is in molality (mol / kgw).

[0151] This method has the following advantages: 1. It is easy to operate. Only one computer is needed to carry out the experiment, without the support of a large amount of financial and material resources. 2. The overall time consumption is short, the result output speed is fast, and the applicable environment range is wide. 3. Modify and optimize the Pitzer parameters to improve the prediction accuracy of high-concentration solutions. 4. It can be effectively applied to the prediction of the pH value of a CO2-saturated CaCl2 solution, with high prediction accuracy, good use effect, and is convenient for popularization and use.

[0152] In summary, the method has simple steps, reasonable design, and convenient implementation. It can be effectively applied to the prediction of the pH value of CO2-saturated CaCl2 solution, with high prediction accuracy, good use effect, and is convenient for popularization and use.

[0153] Next, through the attached Figures 2-3 , the technical solution of the method of this embodiment will be further described in detail.

[0154] As Figure 2 shown, the CO2-saturated CaCl2 solution pH prediction method of the present invention includes:

[0155] Step 1: Analyze the influencing factors of the pH of CO2-saturated CaCl2 aqueous solution and establish a relevant calculation model;

[0156] In the implementation of this case, the influencing factors of the pH of CO2-saturated CaCl2 aqueous solution include temperature factor and pressure factor. The temperature factor is the temperature of CO2-saturated CaCl2 aqueous solution, and the pressure factor is the partial pressure of CO2.

[0157] Specifically, set the temperature parameter and pressure parameter according to the conditions

[0158] pH = A(px) + B

[0159] Step 2: According to the calculation model, obtain the partial pressure data of CO2 by obtaining pressure data and relevant empirical formulas with temperature as a variable.

[0160] Calculate the partial pressure data of CO2 according to the empirical formula. P is the applied pressure value (MPa), and T1 takes the value of 647.096K. The specific formula is as follows:

[0161]

[0162] Among them, for the partial pressure calculation formula, the overall pressure, and C0, C1, C2, C3, C4 are all empirical coefficients.

[0163] Table 1: Values of the empirical formula coefficients C0, C1, C2, C3, C4

[0164]

[0165]

[0166] Step 3: Convert the obtained partial pressure data of CO2 into a CO2 pressure coefficient that can be imported into PHREEQC. The empirical formula is as follows, is the partial pressure of CO2 obtained in Step 2, and P0 is the standard atmospheric pressure with a value of 0.010325MPa

[0167]

[0168] In specific implementation, based on the data calculated in Step 2, perform a one-step calculation through a formula to convert it into the data required by the EQUILIBRIUM_PHASES module in PHREEQC.

[0169] Step 4: Optimize the interaction parameters of the Pitzer model according to relevant data, and use the optimized Pitzer model to obtain the predicted data of the CO2-saturated CaCl2 solution;

[0170] In specific implementation, in PHREEQC, the Pitzer coefficient P is related to the function of temperature, and the general form is as follows:

[0171]

[0172] where T R takes the value of 298.15K, K is the temperature-dependent equilibrium constant, and the relevant calculations are obtained according to empirical formulas; the values of B0, B1, B2, B3, B4, and B5 are as shown in the parameters used in the Pitzer database of PHREEQC.

[0173] Table 2: Parameters used in the Pitzer database of PHREEQC (parameters not listed are zero)

[0174]

[0175]

[0176] [1]L.N.Plummer, D.L.Parkhurst, G.W.Fleming, S.A.Dunkle, A Computer Program Incorporating Pitzer's Equations for Calculation of Geochemical Reactions in Brines, in: Water-Resources Investigations Report, 1988.

[0177] [2]C.A.J. Appelo, Principles, caveats and improvements in databases for calculating HydrogeocHemical reactions in saline waters from 0 to 200 degrees C and 1 to 1000 atm, Appl. GeocHem., 55(2015)62 - 71.

[0178] Modify and optimize some of the parameters according to the results of multiple runs. After analyzing the results of multiple runs, it is found that modifying β MX (0) and β MX (1) in B0, B3, Ψ ijk gives the most ideal results for high - concentration salt solutions in terms of the B0 term in Ψ

[0179] Specifically, elaborate on the meanings of each symbol in the Pitzer parameter table: The parameter β MX (0) and β MX (1) β MX (2) and C MX (φ) are obtained by fitting the experimental data of single salts; θ ij is defined by each pair of cations and each pair of anions; λ Nj is defined by the interaction between neutral substances and cations or anions; Ψ ijk is determined from the same two - salt mixture used when defining θ ij and is consistent with the value of θ ij and the single - salt interaction parameters internally.

[0180] The Pitzer coefficient P is related to the function of temperature and is generally in the following form:

[0181]

[0182] where B0, B1, B2, B3, B4, B5 are all empirical coefficients obtained by fitting relevant data; T R = 298.15 K.

[0183] Specifically, elaborate on the optimization method:

[0184] Optimize the Pitzer parameters using the trial - and - error method. This scheme mainly focuses on the accuracy of high - concentration prediction results, so mainly optimize and compare the data in terms of high - concentration. The specific idea is as follows:

[0185] For the optimization of the CaCl2 solution, referring to the KCl solution, where both CaCl2 and KCl are single-salt solutions, first consider the β MX (0) and β MX (1) β MX (2) parameters. By modifying the empirical parameters B0, B1, B2, B3, B4, B5 in β MX (0) and β MX (1) β MX (2) to make the prediction results close to the experimental data. Through multiple attempts by the trial-and-error method, modify the relevant empirical coefficients B0, B1, B2, B3, B4, B5 multiple times, run the program using the modified database to obtain the results for comparison, and gradually approach the prediction results to the experimental results. Further consider the dissolution of CO2

[0186]

[0187] Modify the relevant empirical coefficients B0, B1, B2, B3, B4, B5 for θ ij and Ψ ijk . Through multiple trial-and-error and result comparison after multiple runs, it shows that the optimization effect of Ψ ijk is better. Therefore, only Ψ ijk was optimized subsequently.

[0188] Compare the final results with the results of the initial database. The prediction effect of the optimized database is better than that before modification in terms of high concentration.

[0189] Step 5: Set relevant parameters in PHREEQC, including temperature, solution type, CO2 partial pressure coefficient and other relevant data. For specific details, see Table 3: Example Table of State Parameters in PHREEQC.

[0190] Table 3 Examples of State Parameters in PHREEQC

[0191]

[0192] where p CO2 is the partial pressure of CO2 and p0 = 0.010325 MPa is the standard atmospheric pressure.

[0193] During specific implementation, establish a new solution in PHREEQC and select the initial ion species: Ca 2+ and Cl -, Set the ion concentration (mol / kgw) according to the conditions; set the temperature, set the temperature (°C) according to the conditions to be predicted, and the temperature setting range is (25 - 150 °C); set pe to 4 and the charge to pH; insert the EQUILIBRIUM_PHASES working module. When the phases in this module come into contact with the aqueous solution, each phase will dissolve or precipitate to reach equilibrium or complete dissolution. The parameters set in this module are the CO2 pressure coefficients obtained in step three; insert the Pitzer module.

[0194] Step 6: Reset the relevant parameters and predict the pH of the CO2-saturated CaCl2 solution under the next condition.

[0195] During specific implementation, the prediction results obtained according to the conditions are as Figure 3 shown. According to the prediction results, guidance for engineering practical applications can be provided. Please refer to Table 4 for the comparison results of the experimental values and predicted values of pH measurement. Table 4 shows that the prediction method of the present invention has relatively accurate predicted values, and after optimization, there is an obvious improvement in the prediction accuracy for high-concentration solutions.

[0196] Table 4: Comparison Results of Experimental Values and Predicted Values of pH Measurement for CO2-Saturated KCl Solution

[0197]

[0198]

[0199] The embodiments of the present invention are given for purposes of illustration and description, and are not exhaustive or limit the invention to the disclosed form. Many modifications and variations are obvious to those of ordinary skill in the art. The embodiments are chosen and described in order to better explain the principles of the invention and its practical application, and to enable those of ordinary skill in the art to understand the invention and design various embodiments with various modifications suitable for specific purposes.

Claims

1. A method for predicting the pH of a solution of saturated acidic gas under high temperature and high pressure conditions, characterized in that, Including the following steps: According to the prediction method, obtain the predicted pH value of CO2-saturated CaCl2 aqueous solution under the set parameter conditions; According to the acquisition system, under the same parameter conditions as those implemented in the prediction method, obtain the measured pH value of the CO2-saturated CaCl2 aqueous solution, and verify the accuracy of the predicted pH value according to the measured pH value; The prediction method includes: Step 1: Analyze the influencing factors of the pH of CO2-saturated CaCl2 aqueous solution, and establish a Pitzer calculation model according to the empirical formula; Step 2: According to the Pitzer calculation model, obtain the partial pressure data of CO2 by obtaining pressure data and relevant empirical formulas with temperature as a variable. The empirical formula is as follows: P is the applied pressure in MPa, the T1 value is 647.096 in K, the temperature ranges from 2298.15 K to 425.15 K, and the range of the applied pressure P is from 0.2 to 15 MPa; Step 3: Convert the obtained partial pressure data of CO2 into a CO2 pressure coefficient that can be imported into PHREEQC. The formula is as follows: Among them is the partial pressure data of CO2, and P0 is the standard atmospheric pressure with a value of 0.010325 MPa; Step 4: Optimize the interaction parameters of the Pitzer calculation model according to relevant data, and use the optimized Pitzer calculation model to obtain the prediction data of the CO2-saturated CaCl2 solution; Step 5: Set relevant parameters in PHREEQC, including temperature, solution type, and CO2 partial pressure coefficient; Step 6: Reset relevant parameters to predict the pH of the CO2-saturated CaCl2 solution under the next parameter condition; Among them, the influencing factors of the pH of the CO2-saturated CaCl2 aqueous solution in Step 1 include temperature factor, pressure factor, and ion factor. The temperature factor is the temperature of the CO2-saturated CaCl2 aqueous solution, the pressure factor is the partial pressure of CO2, and the ion factor is the concentration of the CaCl2 aqueous solution; For the optimization of the interaction parameters of the Pitzer model described in Step 4, for β MX (0) and β MX (1) in terms of the B0 and B3 terms, and for Ψ ijk in terms of the B0 term, modification and optimization are carried out. In PHREEQC, the Pitzer coefficient P is related to the function of temperature, and the general form is as follows: The optimization of the interaction parameters includes: First, consider β fitted from single-salt data MX (0) , β MX (1) β MX (2) parameters. By modifying the empirical parameters B0, B1, B2, B3, B4, B5 in β MX (0) , β MX (1) β MX (2) , the prediction results are made to approach the experimental data. Through multiple attempts by the trial-and-error method, the relevant empirical coefficients B0, B1, B2, B3, B4, B5 are modified multiple times. The results are obtained by running the program using the modified database for comparison, and the prediction results are gradually approximated to the experimental results; Secondly, considering CO2 dissolution, according to , modify the relevant empirical coefficients B0, B1, B2, B3, B4, B5 for θ ij , Ψ ijk . Through multiple trials and errors and comparison of the results after multiple runs, it shows that the optimization effect of Ψ ijk is better. Subsequently, only optimize Ψ ijk and compare the final result with the initial database result; Among them, the acquisition system is a solution pH acquisition system for saturated acid gas under high temperature and high pressure conditions, including A gas extraction tank (1) filled with a liquid-phase soluble acid gas; An injection pump (7) for pressurizing the liquid-phase soluble acid gas supplied to the injection pump (7) from the gas extraction tank (1) through a pipeline; A pre-saturation container (16) filled with a brine solution, and the pressurized liquid-phase soluble acid gas supplied by the injection pump (7) through a pipeline is mixed with the brine solution in the pre-saturation container (16) to form an acid gas pre-saturated solution; A reaction container (19), including A housing including an accommodation space formed inside the housing; A temperature control device arranged in the accommodation space for forming a temperature-controlled environment of the reaction container; A stirring device arranged in the accommodation space for stirring the acid gas pre-saturated solution supplied to the reaction container from the pre-saturation container through a pipeline to form an acid gas saturated solution; An electrode for pH detection arranged in the accommodation space. The electrode for pH detection includes at least two different types of electrodes, and different types of electrodes respectively detect the pH of the acid gas saturated solution in the reaction container under different ambient temperature ranges of the reaction container.

2. The method for predicting the pH of a solution of saturated acidic gas under high temperature and high pressure conditions according to claim 1, characterized in that The gas extraction tank (1) of the solution pH acquisition system for saturated acidic gas under high temperature and high pressure conditions is connected to the injection pump (7). A first three-way valve (5) is provided between the gas extraction tank (1) and the injection pump (7). The gas extraction tank (1) is connected to the first port of the first three-way valve (5) through a first pipeline. A first needle valve (2) and a check valve (3) are successively provided between the gas extraction tank (1) and the first three-way valve (5). The second port of the first three-way valve (5) is connected to one end of the injection pump (7) through a second pipeline. The first needle valve (2) has an open state and a closed state for passing liquid acidic gas. When the first needle valve (2) is in the open state for liquid acidic gas, the liquid acidic gas in the gas extraction tank (1) flows into the injection pump (7) through the first pipeline, the first three-way valve (5) and the second pipeline; The other end of the injection pump (7) is connected to one end of the pre-saturation container (16) through a fourth pipeline. A third needle valve (12), an indicating pressure relief valve (14), and a pressure sensor (13) are provided on the fourth pipeline; The other end of the pre-saturation container (16) is connected to the water inlet and outlet through a fifth pipeline. The third end of the pre-saturation container (16) is connected to the reaction container (19) through a sixth pipeline. A fourth needle valve (17) is provided between the pre-saturation container (16) and the water inlet and outlet. The fourth needle valve (17) has an open and closed state for brine. When the fourth needle valve (17) is in the open state for brine, brine enters the pre-saturation container (16) through the fifth pipeline. The pre-saturation container (16) is used to mix the injected brine with the pressurized liquid acidic gas supplied by the injection pump (7) through the fifth pipeline into an acidic gas pre-saturated solution; A fifth needle valve (18) is provided between the pre-saturation container (16) and the reaction container (19). When the fifth needle valve (18) is opened, the pre-saturation container (16) and the reaction container (19) are connected. The acidic gas pre-saturated solution in the pre-saturation container (16) is injected into the reaction container (19) through the sixth pipeline.

3. The method for predicting the pH of a solution of saturated acidic gas under high temperature and high pressure conditions according to claim 2, wherein, The other end of the reaction container (19) of the solution pH acquisition system for saturated acidic gas under high temperature and high pressure conditions is connected to the feed port through a seventh pipeline. The other end of the reaction container (19) is also connected to the discharge port through an eighth pipeline. A seventh needle valve (22) is provided between the reaction container (19) and the feed port. The seventh needle valve (22) has an open and closed state for passing calibration solution or acidic gas. When the seventh needle valve (22) is in the open state for calibration solution or acidic gas, the calibration solution or acidic gas provides the calibration solution or acidic gas to the reaction container (19) through the seventh pipeline.

4. The method for predicting the pH of a solution of saturated acidic gas under high temperature and high pressure conditions according to claim 3, characterized in that, The third port of the first three-way valve (5) of the solution pH acquisition system for saturated acidic gas under high temperature and high pressure conditions is connected to the exhaust water inlet through a third pipeline. A second needle valve (4) is provided between the first three-way valve (5) and the exhaust water inlet.

5. The method for predicting the pH of a solution saturated with acid gas under high temperature and high pressure conditions according to claim 4, characterized in that A discharge vacuum branch line is also provided on the fourth pipeline of the system for obtaining the pH value of a solution of saturated acidic gas under high temperature and high pressure conditions. The discharge vacuum branch line comprises a second three-way valve (11), a drain port, an indicating pressure relief valve (9) and a vacuum pump (10). The first port of the second three-way valve (11) is connected to the fourth pipeline via a first three-way pipeline, the second port of the second three-way valve (11) is connected to the drain port, the second port of the second three-way valve (11) is connected to the first port of the second three-way pipeline, the second port of the second three-way pipeline is connected to the vacuum pump (10), and the third port of the second three-way pipeline is connected to the indicating pressure relief valve (9). When the third needle valve (12) is opened, the injection pump (7) and the pre-saturation container (16) are connected to each other. A purification branch line is also provided on the fourth pipeline, and the purification branch line is connected to the fourth pipeline via a third three-way valve (15).

6. The method for predicting the pH of a solution of saturated acidic gas under high temperature and high pressure conditions according to claim 5, characterized in that, A first stop check valve (6) is provided between the first three-way valve (5) and the injection pump (7) of the system for obtaining pH of a solution of saturated acidic gas under high temperature and high pressure conditions. The first stop check valve (6) is used to prevent the backflow of liquid acidic gas.

7. The method for predicting the pH of a solution saturated with acidic gas under high temperature and high pressure conditions according to claim 6, characterized in that, The method for obtaining the pH measurement value of the CO2 saturated CaCl2 aqueous solution by the acquisition system includes: The steps include: S1. Electrode calibration and calibration phase; S2. Preparation stage; S3. Seal inspection and cleaning stage; S4. Premixing preparation stage: pressurizing the liquid-soluble acid gas supplied from the gas extraction tank (1) to the injection pump (7) through a pipeline; S5. Premixing stage: the pressurized liquid-phase soluble acid gas and the brine solution are mixed in the presaturation container (16) to form an acid gas presaturated solution; S6. Saturated solution formation stage: stirring the acid gas pre-saturated solution in the reaction vessel (19) to form an acid gas saturated solution; S7. pH value measurement stage: using different types of electrodes to detect the pH of the acid gas saturated solution in the reaction container (19) under different ambient temperature ranges; S8. Cleaning phase.

8. The method for predicting pH of a saturated acidic gas solution under high temperature and high pressure conditions according to claim 7, characterized in that: S1. Electrode Calibration and Calibration Phase: Before the experiment starts, the glass electrode, zirconia electrode for pH measurement, and Ag / AgCl reference electrode are calibrated and calibrated using two calibration solutions with low pH and high pH respectively. When calibrating and calibrating the glass electrode and zirconia electrode with the low pH calibration solution, open the seventh needle valve (22), and introduce the low pH calibration solution through the seventh pipeline to calibrate and calibrate the glass electrode and zirconia electrode for pH measurement. After the calibration and calibration are completed, open the eighth needle valve (23) and discharge the low pH calibration solution through the eighth pipeline. When calibrating and calibrating the glass electrode and zirconia electrode with the high pH calibration solution, open the seventh needle valve (22), and introduce the high pH calibration solution through the seventh pipeline to calibrate and calibrate the glass electrode and zirconia electrode for pH measurement. After the calibration and calibration are completed, open the eighth needle valve (23) and discharge the high pH calibration solution through the eighth pipeline; among them, the calibration solution can be a professional pH calibration solution or can be prepared according to your own needs. When calibrating, the N2 pressure is slightly higher than the liquid boiling point. Use N2 as the pressurizing medium. At ambient temperature, measure the two calibration solutions with low pH and high pH at a pressure of 16 MPa, and then calibrate the glass electrode under low pressure conditions; S2. Preparation Phase: After the calibration and calibration are completed, close the second needle valve (4), the fourth needle valve (17), the sixth needle valve (21), the seventh needle valve (22), and the eighth needle valve (23) to seal the entire system, and set the indicated pressure of the indicating pressure relief valve (9) to 0.35 MPa and the indicated pressure of the indicating pressure relief valve (14) to 18.6 MPa; S3. Sealing Inspection and Cleaning Phase: Open the seventh needle valve (22) and the eighth needle valve (23), close the fifth needle valve (18), form an independent sealed space for the reaction vessel (19), remove the remaining other gases in the reaction vessel (19), and then close the seventh needle valve (22) and the eighth needle valve (23); then open the second needle valve (4) to introduce He gas, use He gas to check the airtightness of the overall system. After the airtightness inspection is completed, turn on the vacuum pump (10) to suck out the He gas. After the He gas is sucked out, turn off the vacuum pump and introduce ultrapure water through the second needle valve (4). Use ultrapure water to clean the second pipeline, the third pipeline, the syringe pump (7), the fourth pipeline, the pre-saturation container (16), the sixth pipeline, and the reaction vessel (19) of the device. After the cleaning is completed, open the eighth needle valve (23) to discharge the ultrapure water. After discharging the ultrapure water, open the purification branch line, and make nitrogen pass through the third three-way valve (15) into the system through the purification branch line. Use N2 to purge and dry each part of the system. After the purging is completed, close the eighth needle valve (23) and the second needle valve (4); S4. Pre-mixing preparation stage: Close the third needle valve (12), open the first needle valve (2), and use the injection pump (7) to suck the liquid acidic gas in the gas extraction tank (1). Pressurize the acidic gas using the injection pump (7). Thus, the closing of the second needle valve (4) and the third needle valve (12) forms an independent sealed space for the gas extraction tank (1) and the injection pump (7). While pressurizing the acidic gas using the injection pump (7), open the fourth needle valve (17) and close the fifth needle valve (18). At this time, the third needle valve (12) is in the closed state, thereby forming an independent sealed space for the pre-saturation container (16). The brine solution is injected into the pre-saturation container (16) through the fourth needle valve (17). S5. Pre-mixing stage: After the pressurization of the acidic gas in the injection pump (7) is completed and the injection of the brine solution into the pre-saturation container (16) is completed, open the third needle valve (12), close the fourth needle valve (17), stop supplying the brine solution to the pre-saturation container (16), and connect the injection pump (7) and the pre-saturation container (16), and form a common independent sealed space where the injection pump (7) and the pre-saturation container (16) are connected, so that the pressurized liquid acidic gas enters the pre-saturation container (16) and is mixed with the brine solution in the pre-saturation container (16) to form an acidic gas pre-saturated solution. During the pre-mixing process, constantly monitor the reading of the pressure sensor (13). When the reading of the pressure sensor (13) is less than 4.5 MPa, manually adjust the pressure to ensure that the acidic gas and the solution to be tested are in full contact and dissolve in each other. S6. Saturated solution formation stage: Open the fifth needle valve (18) to inject the acidic gas pre-saturated solution in the pre-saturation container (16) into the reaction container (19). Use a magnetic stirrer to stir the solution in the reaction container (19) to further mix the acidic gas and the brine solution to maintain the saturated state of the acidic gas brine solution. At the same time, observe the pressure of the injection pump (7) and the reading of the pressure sensor (13) to ensure that the acidic gas is fully dissolved in the solution to be tested, and finally make the brine solution a solution of saturated acidic gas. Among them, when using the magnetic stirrer to stir, it needs to be stirred for at least 4 hours when the pressure of the pressure sensor (13) is less than 10 MPa, and it needs to be stirred for at least 24 hours when the pressure of the pressure sensor (13) is greater than 10 MPa. S7. pH value measurement stage: After the stirring is completed, turn on the electric heater to heat the reaction container (19) to form different temperature ranges. Insulate it with a heat insulation layer at different temperature ranges. When the temperature and pressure are stable and the system reaches phase equilibrium, use a pH meter to measure the pH value of the acidic gas saturated solution. When measuring the pH value of the acidic gas saturated solution, constantly monitor the reading of the thermometer in the reaction container (19). When the thermometer reading is less than 90 °C, use a glass electrode to measure the pH value, and when the thermometer reading is greater than 90 °C, use a zirconia electrode to measure the pH value. S8. Cleaning stage: After completing one measurement, first open the sixth needle valve (21) and the back pressure regulating device (20) to slowly reduce the pressure of the reaction vessel (19). After the pressure in the reaction vessel (19) reaches atmospheric pressure, then open the second needle valve (4), the fourth needle valve (17), the seventh needle valve (22), the eighth needle valve (23) and the vacuum pump (10) to exhaust and drain the device.

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