Carbon dioxide fracturing flowback carbon capture recovery method

Abstract

The application provides a carbon dioxide fracturing flowback carbon capture and recovery method, and belongs to the technical field of carbon dioxide recovery, and the specific steps are as follows: a wellhead high-pressure flowback mixed gas is subjected to primary filtration treatment through a carbon dioxide fracturing flowback carbon capture and recovery device, and a primary filtered high-pressure mixed gas is obtained; the pressure of the primary filtered high-pressure mixed gas is reduced to a set value, and a reduced-pressure mixed gas is obtained; the obtained reduced-pressure mixed gas is subjected to secondary filtration, drying and tertiary filtration treatment in sequence, and a dried mixed gas is obtained; the dried mixed gas is subjected to pressure balance treatment, and a pressure-stabilized mixed gas is obtained; the pressure-stabilized mixed gas is subjected to cooling treatment, and condensed liquid carbon dioxide and non-condensed gas are obtained respectively; and the purified gas is obtained after temperature increase and pressure reduction flash evaporation. The application can efficiently and at low cost realize mixed gas treatment, separation and carbon dioxide liquefaction recovery under the condition that the mixed gas contains water and impurities and the inlet gas quantity fluctuates greatly.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide recovery technology, specifically relating to a method for capturing and recovering carbon from carbon dioxide fracturing backflow. Background Technology

[0002] Carbon dioxide fracturing has been rapidly deployed across major oilfields due to its advantages in carbon utilization and carbon emission reduction. Currently, due to its technical advantages such as carbon reduction, emission assistance, viscosity reduction, energy enhancement, and water reduction, the scale of carbon dioxide fracturing operations is expanding rapidly, and it has been widely used in oil and gas reservoir stimulation.

[0003] After fracturing operations are completed, a large amount of carbon dioxide released into the ground is transported to the surface along with the flowback liquid and directly emitted into the air, causing carbon dioxide waste and environmental pollution. This also hinders the closed-loop management of carbon emissions from fracturing operations. With the increasing scale of carbon dioxide fracturing, the problem of flowback carbon emissions is becoming increasingly acute. To reduce carbon emissions, achieve the recovery and reuse of flowback carbon dioxide, and reduce the cost of carbon dioxide fracturing operations, this study investigates methods for capturing and recovering flowback carbon from fracturing operations.

[0004] Most existing carbon capture and recovery (CCR) devices recover high-purity carbon dioxide emitted from upstream chemical plants and power plants, while a few obtain it directly from air analysis. These systems are all built in fixed locations, are large in size, have high investment and operating costs, and are complex to install, making them unsuitable for mobile field operations. Furthermore, existing methods cannot handle, separate, or liquefy carbon dioxide from mixed gases containing water and impurities, even under conditions of fluctuating intake volumes. Summary of the Invention

[0005] To overcome the problem that existing methods cannot handle, separate, and liquefy carbon dioxide from mixed gases containing water and impurities under conditions of large fluctuations in intake volume, this invention provides a carbon dioxide fracturing flowback carbon capture and recovery method. This invention can efficiently and cost-effectively handle, separate, and liquefy carbon dioxide from mixed gases containing water and impurities under conditions of large fluctuations in intake volume. It is also suitable for harsh working conditions in oilfields, with an operating temperature range of -20℃ to 35℃ and a humidity of ≤90% (+20℃), making it suitable for all-weather outdoor operations.

[0006] The technical solution adopted in this invention is as follows: A method for capturing and recovering carbon from carbon dioxide fracturing flowback, comprising the following steps: Step 1: The high-pressure flowback mixed gas at the wellhead is filtered once using a carbon dioxide fracturing flowback carbon capture and recovery device to obtain a high-pressure mixed gas after primary filtration. Step 2: Reduce the pressure of the high-pressure mixed gas after the first filtration in Step 1 to the set value, and control the temperature of the high-pressure mixed gas at the set value to obtain the depressurized mixed gas; Step 3: The depressurized mixed gas obtained in Step 2 is subjected to secondary filtration, drying, and tertiary filtration in sequence to obtain a dry mixed gas. Step four: Perform pressure balancing on the dry mixed gas obtained in step three to obtain a stabilized mixed gas. Step 5: Cool the stabilized mixed gas obtained in Step 4 to obtain condensed liquid carbon dioxide and non-condensable gas, respectively. Step six: Separate the condensed liquid carbon dioxide and non-condensable gas obtained in step five to obtain liquid carbon dioxide and non-condensable gas. Step 7: The liquid carbon dioxide is subjected to flash evaporation by heating and depressurization to obtain purified liquid carbon dioxide and flash evaporated gas.

[0007] In step one, the high-pressure return gas mixture at the wellhead is filtered once to remove solid impurities and moisture from the return gas mixture, thus obtaining a high-pressure mixture gas after primary filtration.

[0008] The particle size of impurities in the high-pressure mixed gas after one filtration is ≤3μm.

[0009] In step two, the pressure of the high-pressure mixed gas after primary filtration is adjusted to 3 MPa using a pressure-reducing valve.

[0010] In step three, the depressurized mixed gas is subjected to secondary filtration, drying, and tertiary filtration in sequence to obtain a dry mixed gas. The third filter removes solid impurities and free oil and water from the depressurized gas mixture to obtain a second-filtered gas mixture. The second-filtered gas mixture is then dried using an adsorption dryer. Finally, the fourth filter removes molecular sieve dust from the dried gas mixture to obtain a dry gas mixture.

[0011] The impurity particle size in the mixed gas after secondary filtration is ≤1μm, and the oil content is ≤0.01PPM; the impurity particle size in the dried mixed gas is ≤1μm, and the oil content is ≤0.1PPM.

[0012] In step four, the dry mixed gas is subjected to pressure balancing treatment through the first buffer tank and the second buffer tank in sequence to obtain a pressure-stabilized mixed gas.

[0013] In step six, the non-condensable gas is depressurized, and the depressurized non-condensable gas is then subjected to combustion treatment, with the exhaust gas produced by combustion being discharged.

[0014] In step seven, the flash gas is collected and its pressure is stabilized, the stabilized flash gas is depressurized, and the depressurized flash gas is treated with flame retardant before being discharged into the air.

[0015] In step seven, the purified liquid carbon dioxide is transported to a carbon dioxide storage tank for storage via a drain pump.

[0016] The beneficial effects of this invention are: In this invention, the filter elements of the first and second filters are made of glass fiber. The first and second filters remove large particulate solid impurities and free oil and water from the gas, protecting the downstream molecular sieve and thus ensuring the service life of the adsorbent.

[0017] In this invention, by setting a first heater and a second heater, the pressure of the wellhead gas is prevented from being reduced through the first pressure regulating valve and the second pressure regulating valve. The condensate in the wellhead gas freezes and blocks the first pressure regulating valve, the second pressure regulating valve and the system pipeline. The frozen pipeline and valve are defrosted, and the defrosted liquid is discharged to the equipment and does not enter the recovery storage tank.

[0018] In this invention, the first flame arrester and the second flame arrester are installed at the vent to prevent the spread of flames from flammable gases and flammable liquid vapors, thus preventing backfire accidents.

[0019] In this invention, the medium heat exchanger of the refrigeration device adopts a tube bundle type air heat exchanger, which has high heat exchange efficiency and low pressure drop. Through heat exchange, the cooling capacity is utilized to the maximum extent, exchanging heat with the high-temperature wellhead gas at the inlet. This reduces the inlet temperature of the wellhead gas entering the heat exchanger to the lowest possible range. At the same time, it increases the outlet temperature, preventing condensation in the downstream pipelines due to excessively low outlet air temperature, thus protecting the pipelines from corrosion.

[0020] In this invention, the filter element of the fourth filter is made of glass fiber. The dried gas after passing through the adsorption-type drying device contains a certain amount of molecular sieve dust due to the pulverization of the desiccant. The fourth filter is used to filter and intercept this molecular sieve dust, ensuring that the maximum particle size in the exhaust gas is ≤1μm, effectively protecting downstream equipment. The pressure-reducing drying skid depressurizes the filtered gas returned from the wellhead to a pressure of 3MPa. Water vapor in the wellhead gas condenses and frosts after depressurization and cooling, potentially causing freezing and blockage of the pressure regulating valve and pipelines. The pressure-reducing drying skid is equipped with two pressure-reducing branches, one in use and one on standby, ensuring stable and continuous system operation. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of a carbon capture and recovery method for carbon dioxide fracturing backflow provided by the present invention.

[0022] Figure 2This is a schematic diagram of the process flow of a carbon dioxide fracturing backflow carbon capture and recovery device provided by the present invention.

[0023] The present invention will now be described in further detail with reference to the accompanying drawings.

[0024] In the figure, the attached figures are labeled as follows: 1. Wellhead return flow mixed gas interface; 2. First filter; 3. First pressure regulating valve; 4. First heater; 5. First gas-liquid separator; 6. Third filter; 7. Adsorption dryer; 8. Fourth filter; 9. First buffer tank; 10. Inlet pipe; 11. Second filter; 12. Second pressure regulating valve; 13. Second heater; 14. Carbon dioxide storage tank; 15. Second buffer tank; 16. Refrigeration unit; 17. Second gas-liquid separator; 18. First flash tank; 19. Third buffer tank; 20. Second flash tank; 21. Refrigerant storage tank; 22. Refrigeration unit; 3. Shell and tube heat exchanger; 24. First flow meter; 25. Electric valve A; 26. Valve A; 27. Valve B; 28. Electric valve B; 29. ​​Valve C; 30. Electric valve C; 31. First gas bypass; 32. Second gas bypass; 33. First pipeline; 34. Second pipeline; 35. Third pipeline; 36. Electric valve D; 37. Temperature sensor A; 38. Electric valve E; 39. Temperature sensor B; 40. Valve D; 41. Temperature sensor C; 42. Pressure sensor A; 43. Valve E; 44. Valve F; 45. Valve G; 46. Valve H; 4 7. First drying tank; 48. Second drying tank; 49. Electric valve F; 50. Electric valve G; 51. Electric valve H; 52. Electric valve I; 53. Safety valve A; 54. Manual valve; 55. First switching valve; 56. Second switching valve; 57. Temperature sensor D; 58. Pressure sensor B; 59. Safety valve B; 60. Electric valve J; 61. Check valve; 62. Carbon dioxide concentration sensor; 63. Valve I; 64. Valve J; 65. Valve K; 66. Temperature sensor E; 67. Electric valve K; 68. Electric valve L; 69. Pressure sensor C; 70. Temperature sensor F; 71. Third pressure regulating valve; 72. Temperature sensor G; 73. Electric valve M; 74. Check valve; 75. First flame arrester; 76. Fourth pressure regulating valve; 77. Electric valve N; 78. Second flame arrester; 79. Second flow meter; 80. Drain pump; 81. Electric valve O; 82. Electric valve P; 83. Safety valve C; 84. Pressure sensor D; 85. Drain valve A; 86. Electric valve Q; 87. Electric valve R; 88. Safety valve D; 89. Pressure sensor E; 90. Drain valve B; 91. Valve L; 92. Electric valve S; 93. Electric valve T. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0027] Example 1: To overcome the limitations of existing methods in handling, separating, and recovering carbon dioxide from mixed gases containing water and impurities under conditions of large fluctuations in inlet gas volume, this invention provides... Figures 1-2 The invention presents a carbon dioxide fracturing flowback carbon capture and recovery method. This invention can efficiently and cost-effectively process, separate, and liquefy carbon dioxide in mixed gases containing water and impurities under conditions of large fluctuations in gas intake. It is also suitable for harsh working conditions in oilfields, with a working temperature range of -20℃ to 35℃ and humidity of ≤90% (+20℃), and is suitable for all-weather outdoor operations.

[0028] A method for capturing and recovering carbon from carbon dioxide fracturing flowback, comprising the following steps: Step 1: The high-pressure flowback mixed gas at the wellhead is filtered once using a carbon dioxide fracturing flowback carbon capture and recovery device to obtain a high-pressure mixed gas after primary filtration. Step 2: Reduce the pressure of the high-pressure mixed gas after the first filtration in Step 1 to the set value, and control the temperature of the high-pressure mixed gas at the set value to obtain the depressurized mixed gas; Step 3: The depressurized mixed gas obtained in Step 2 is subjected to secondary filtration, drying, and tertiary filtration in sequence to obtain a dry mixed gas. Step four: Perform pressure balancing on the dry mixed gas obtained in step three to obtain a stabilized mixed gas. Step 5: Cool the stabilized mixed gas obtained in Step 4 to obtain condensed liquid carbon dioxide and non-condensable gas, respectively. Step six: Separate the condensed liquid carbon dioxide and non-condensable gas obtained in step five to obtain liquid carbon dioxide and non-condensable gas. Step 7: The liquid carbon dioxide is subjected to flash evaporation by heating and depressurization to obtain purified liquid carbon dioxide and flash evaporated gas.

[0029] This invention provides a carbon capture and recovery method for carbon dioxide fracturing backflow, which can achieve efficient and low-cost recovery of wellhead backflow gas with high carbon dioxide content. It is applicable to harsh working conditions in oilfields, with a working temperature range of -20℃ to 35℃ and humidity of ≤90% (+20℃), and is suitable for all-weather outdoor operations.

[0030] In this invention, the carbon dioxide fracturing backflow carbon capture and recovery device includes a decompression drying skid and a condensation flash skid. The carbon dioxide fracturing backflow carbon capture and recovery device is designed as a skid, and the equipment inside the device is prefabricated in the factory, reducing the amount of on-site work.

[0031] In this invention, the pressure-reducing drying skid depressurizes the filtered gas returned from the wellhead to a pressure of 3 MPa. The water vapor in the wellhead gas condenses and frosts after depressurization and cooling, potentially causing freezing and blockage of the pressure regulating valve and pipelines. The pressure-reducing drying skid is equipped with two pressure-reducing branches, one in operation and one as a backup, ensuring stable and continuous system operation. Pressure regulation range: 3-10 MPa; maximum flow rate: 2500 Nm³ / h; operating temperature: -40~50°C; adjustable ratio: 50:1.

[0032] After being filtered and depressurized, the gas enters the adsorption drying device 7, where its dew point temperature is dried to -35°C. During this process, the gas temperature rises by 5-10°C. Compressed air alternately passes through the first drying tank 47 and the second drying tank 48, with one tank operating while the other is regenerated with dried air. The operation of the two tanks is switched by controlling electric valves F49, G50, H51, I52, the first switching valve 55, and the second switching valve 56 to ensure continuous operation. The consumption of dried gas is approximately 20%. In this invention, the refrigeration device 16 maximizes the utilization of cooling capacity through heat exchange, exchanging heat with the high-temperature wellhead gas. This lowers the inlet temperature of the wellhead gas entering the heat exchanger to a minimum. Simultaneously, it raises the outlet temperature, preventing condensation in the downstream pipelines due to excessively low outlet air temperature and protecting the pipelines from corrosion. The first flash tank 18 and the second flash tank 20 purify the liquid. The purified liquid carbon dioxide, measured by the second flow meter 79, enters the carbon dioxide storage tank 14.

[0033] Example 2: Based on Example 1, in this embodiment, preferably, in step one, the high-pressure return mixed gas at the wellhead is filtered once to remove solid impurities and moisture from the return mixed gas, thereby obtaining a high-pressure mixed gas after one filtration.

[0034] Preferably, the particle size of impurities in the high-pressure mixed gas after primary filtration is ≤3μm.

[0035] Preferably, in step two, the pressure of the high-pressure mixed gas after primary filtration is adjusted to 3 MPa by a pressure-reducing valve.

[0036] Preferably, in step three, the method for obtaining a dry mixed gas by sequentially performing secondary filtration, drying, and tertiary filtration on the depressurized mixed gas is as follows: Preferably, the solid impurities and free oil and water in the depressurized mixed gas are filtered by the third filter 6 to obtain a mixed gas after secondary filtration; the mixed gas after secondary filtration is dried by the adsorption drying device 7; and the molecular sieve dust in the dried mixed gas is filtered and intercepted by the fourth filter 8 to obtain a dried mixed gas.

[0037] Preferably, the impurity particle size in the mixed gas after secondary filtration is ≤1μm and the oil content is ≤0.01PPM; the impurity particle size in the dried mixed gas is ≤1μm and the oil content is ≤0.1PPM.

[0038] Preferably, in step four, the dry mixed gas is subjected to pressure balancing treatment through the first buffer tank 9 and the second buffer tank 15 in sequence to obtain a pressure-stabilized mixed gas.

[0039] Preferably, in step six, the non-condensable gas is depressurized, and the depressurized non-condensable gas is then subjected to combustion treatment, with the exhaust gas produced by combustion being discharged.

[0040] Preferably, in step seven, the flash gas is collected and stabilized, the stabilized flash gas is depressurized, and the depressurized flash gas is treated with flame retardant before being discharged into the air.

[0041] Preferably, in step seven, the purified liquid carbon dioxide is transported to the carbon dioxide storage tank 14 via the drain pump 80.

[0042] In this invention, the pressure-reducing drying skid includes a first filter 2, a first pressure regulating valve 3, a first heater 4, a first gas-liquid separator 5, a third filter 6, an adsorption drying device 7, a fourth filter 8, a first buffer tank 9, a second filter 11, a second pressure regulating valve 12, and a second heater 13.

[0043] like Figure 1As shown, one end of the intake pipe 10 is connected to the wellhead return mixed gas interface 1, and the other end of the intake pipe 10 is connected to the intake port of the first filter 2. The outlet of the first filter 2 is sequentially connected to the intake ports of the first pressure regulating valve 3, the first heater 4, the first gas-liquid separator 5, the third filter 6, the adsorption drying device 7, the fourth filter 8, and the first buffer tank 9. The first pressure regulating valve 3 is located above the first heater 4 and to one side of the first filter 2. The outlet of the first filter 2 is connected to one end of the first pressure regulating valve 3, and the other end of the first pressure regulating valve 3 is connected to the intake port of the first heater 4. The outlet of the first heater 4 is connected to the intake port of the first gas-liquid separator 5 through the first pipeline 33. The outlet of the first gas-liquid separator 5 is connected to the intake port of the third filter 6. The outlet of the third filter 6 is connected to the intake port of the adsorption drying device 7. The outlet of the adsorption drying device 7 is connected to the intake port of the fourth filter 8. The outlet of the fourth filter 8 is connected to the intake port of the first buffer tank 9.

[0044] The other end of the air inlet pipe 10 is connected to the air inlet of the second filter 11, the air outlet of the second filter 11 is connected to one end of the second pressure regulating valve 12, the other end of the second pressure regulating valve 12 is connected to the air inlet of the second heater 13, and the air outlet of the second heater 13 is connected to the air inlet of the first gas-liquid separator 5 through the second pipe 34.

[0045] In this invention, the filter elements of the first filter 2 and the second filter 11 are made of glass fiber. The first filter 2 and the second filter 11 remove large particulate solid impurities and free oil and water from the gas, protect the downstream molecular sieve, and thus ensure the service life of the adsorbent.

[0046] In this invention, by setting a first heater 4 and a second heater 13, the pressure of the wellhead gas is prevented from being reduced by the first pressure regulating valve 3 and the second pressure regulating valve 12. The condensate in the wellhead gas freezes and blocks the first pressure regulating valve 3, the second pressure regulating valve 12 and the system pipeline. The frozen pipeline and valve are defrosted, and the defrosted liquid is discharged to the equipment and does not enter the recovery storage tank.

[0047] In this invention, the filter element of the fourth filter 8 is made of glass fiber. The dried gas after passing through the adsorption drying device 7 contains a certain amount of molecular sieve dust due to the pulverization of the desiccant. The fourth filter 8 is used to filter and intercept the molecular sieve dust to ensure that the maximum particle size in the exhaust is ≤1μm, which can effectively protect the downstream equipment.

[0048] In this invention, the pressure-reducing drying skid depressurizes the filtered gas returned from the wellhead to a pressure of 3 MPa. The water vapor in the wellhead gas condenses and frosts after depressurization and cooling, potentially causing freezing and blockage of the pressure regulating valve and pipelines. This invention equips the pressure-reducing drying skid with two pressure-reducing branches, one in operation and one as a backup, ensuring stable and continuous system operation. Pressure regulation range: 3-10 MPa; maximum flow rate: 2500 Nm³ / h; operating temperature: -40~50°C; adjustable ratio: 50:1.

[0049] like Figure 2 As shown, in this invention, an electric valve A25 and a valve A26 are installed on the intake pipe 10. A valve B27 and an electric valve B28 are installed between the other end of the intake pipe 10 and the intake port of the first filter 2. A valve C29 and an electric valve C30 are installed between the other end of the intake pipe 10 and the intake port of the second filter 11. A first gas bypass 31 is connected in parallel between the intake port and the outlet port of the first filter 2. When the pressure of the backflow mixture in the intake pipe 10 is greater than the maximum operating pressure of the first filter 2, the backflow mixture enters the first pressure regulating valve 3 through the first gas bypass 31.

[0050] A second gas bypass 32 is connected in parallel between the inlet and outlet of the second filter 11. When the pressure of the backflow mixed gas in the inlet pipe 10 is greater than the maximum operating pressure of the second filter 11, the backflow mixed gas enters the second pressure regulating valve 12 through the first gas bypass 31.

[0051] The air inlet of the first gas-liquid separator 5 is connected to the first pipeline 33 and the second pipeline 34 through the third pipeline 35. The first pipeline 33 is equipped with an electric valve D36 and a temperature sensor A37, the second pipeline 34 is equipped with an electric valve E38 and a temperature sensor B39, and the third pipeline 35 is equipped with a valve D40, a temperature sensor C41 and a pressure sensor A42.

[0052] A valve E43 is installed between the outlet of the first gas-liquid separator 5 and the inlet of the third filter 6; a valve F44 is installed between the outlet of the third filter 6 and the inlet of the adsorption dryer 7; a valve G45 is installed between the outlet of the adsorption dryer 7 and the inlet of the fourth filter 8; and a valve H46 is installed between the outlet of the fourth filter 8 and the inlet of the first buffer tank 9.

[0053] In this invention, the adsorption drying device 7 includes a first drying tank 47, a second drying tank 48, an electric valve F49, an electric valve G50, an electric valve H51, an electric valve I52, a safety valve A53, a manual valve 54, a first switching valve 55, and a second switching valve 56.

[0054] The inlet of the first drying tank 47 is connected to one end of electric valve F49 and one end of electric valve H51. The other end of electric valve F49 is connected to one end of electric valve G50. The other end of electric valve H51 is connected to one end of electric valve I52. The other ends of electric valve G50 and electric valve I52 are connected to the inlet of the second drying tank 48. The other ends of electric valve H51 and one end of electric valve I52 are connected to valve F44 and the air outlet of the third filter 6 in sequence. The other ends of electric valve F49 and one end of electric valve G50 are connected to safety valve A53.

[0055] The outlet of the first drying tank 47 is connected to one end of the manual valve 54 and one end of the first switching valve 55. The other end of the first switching valve 55 is connected to one end of the second switching valve 56. The other end of the second switching valve 56 and the other end of the manual valve 54 are connected to the outlet of the second drying tank 48. The other end of the first switching valve 55 and one end of the second switching valve 56 are connected in sequence to valve G45 and the air inlet of the fourth filter 8.

[0056] After being filtered and depressurized, the gas enters the adsorption drying unit 7, where its dew point temperature is dried to -35℃. During this process, the gas temperature rises by 5-10℃. Compressed air alternately passes through the first drying tank 47 and the second drying tank 48, with one tank operating while the other is regenerated with dried air. The operating states of the two tanks are switched by controlling electric valves F49, G50, H51, I52, the first switching valve 55, and the second switching valve 56 to ensure continuous operation. The consumption of dried gas is approximately 20%.

[0057] In this invention, both the first buffer tank 9 and the second buffer tank 15 are equipped with a temperature sensor D57, a pressure sensor B58, and a safety valve B59. The first buffer tank 9 is also equipped with a concentration detection branch, which includes an electric valve J60, a one-way valve 61, and a carbon dioxide concentration sensor 62 that are connected in sequence to the first buffer tank 9.

[0058] In this invention, the condensation flash skid includes a carbon dioxide storage tank 14, a second buffer tank 15, a first flow meter 24, a refrigeration device 16, a second gas-liquid separator 17, a first flash tank 18, and a third buffer tank 19. The outlet of the first buffer tank 9 is connected to the inlet of the second buffer tank 15, and the outlet of the second buffer tank 15 is connected to the heat exchange gas inlet of the refrigeration device 16. The first flow meter 24 is located between the outlet of the second buffer tank 15 and the heat exchange gas inlet of the refrigeration device 16. The heat exchange outlet of the refrigeration device 16 is connected to the inlet of the second gas-liquid separator 17. The liquid outlets of the first gas-liquid separator 5 and the second gas-liquid separator 17 are connected to the liquid inlet of the first flash tank 18, and the outlet of the first flash tank 18 is connected to the gas inlet of the third buffer tank 19.

[0059] In this invention, the refrigeration device 16 includes a refrigerant storage tank 21, a refrigeration unit 22, and a shell-and-tube heat exchanger 23. The refrigerant storage tank 21 delivers the refrigerant to the refrigeration unit 22 for compression. After compression, the refrigerant enters the shell-and-tube heat exchanger 23 and evaporates to absorb heat, exchanging heat with the gas inside the shell-and-tube heat exchanger 23, thereby lowering the gas temperature.

[0060] In this invention, the medium heat exchanger of the refrigeration device 16 adopts a tube bundle air heat exchanger, which has high heat exchange efficiency and low pressure drop. Through heat exchange, the cooling capacity is utilized to the maximum extent, exchanging heat with the high-temperature wellhead gas at the inlet. This reduces the inlet temperature of the wellhead gas entering the heat exchanger to the lowest possible range. At the same time, it increases the outlet temperature, preventing condensation in the downstream pipelines due to excessively low outlet air temperature, thus protecting the pipelines from corrosion.

[0061] A valve I63 is installed between the first flow meter 24 and the outlet of the second buffer tank 15. A valve J64 is installed between the first flow meter 24 and the heat exchange gas inlet of the refrigeration device 16. A valve K65 and a temperature sensor E66 are installed between the heat exchange outlet of the refrigeration device 16 and the inlet of the second gas-liquid separator 17.

[0062] The condenser flash skid also includes a second flash tank 20. The outlets of the first gas-liquid separator 5 and the second gas-liquid separator 17 are connected to the inlet of the second flash tank 20. The outlet of the second flash tank 20 is connected to the gas inlet of the third buffer tank 19. An electric valve K67 is installed between the outlet of the first gas-liquid separator 5 and the inlet of the first flash tank 18 and the inlet of the second flash tank 20. An electric valve L68, a pressure sensor C69, and a temperature sensor F70 are installed between the outlet of the second gas-liquid separator 17 and the inlet of the first flash tank 18 and the inlet of the second flash tank 20.

[0063] The condensation flash skid also includes a third pressure regulating valve 71, a temperature sensor G72, an electric valve M73, a check valve 74, and a first flame arrester 75. The outlet of the second gas-liquid separator 17 is sequentially connected to the third pressure regulating valve 71, the electric valve M73, the check valve 74, and the first flame arrester 75. The temperature sensor G72 is located between the third pressure regulating valve 71 and the electric valve M73. The gas separated by the second gas-liquid separator 17 passes sequentially through the third pressure regulating valve 71, the electric valve M73, the check valve 74, and the first flame arrester 75 before being discharged as exhaust gas. The first flame arrester 75 is located at the vent and is a safety device used to prevent the spread of flames from flammable gases and flammable liquid vapors, thus preventing backfire accidents.

[0064] The carbon dioxide fracturing backflow carbon capture and recovery unit also includes a fourth pressure regulating valve 76, an electric valve N77, and a second flame arrester 78. The outlet of the third buffer tank 19 is sequentially connected to the fourth pressure regulating valve 76, the electric valve N77, and the second flame arrester 78. The second flame arrester 78 is installed at the vent and is a safety device used to prevent the spread of flames from flammable gases and flammable liquid vapors, thereby preventing backfire accidents.

[0065] The condensation flash skid also includes a second flow meter 79 and a discharge pump 80. The outlets of the first flash tank 18 and the second flash tank 20 are connected to one end of the second flow meter 79, and the other end of the second flow meter 79 is connected to the inlet of the discharge pump 80. The outlet of the discharge pump 80 is connected to the carbon dioxide storage tank 14. The first flash tank 18 and the second flash tank 20 purify the liquid, and the purified liquid carbon dioxide enters the carbon dioxide storage tank 14 after being measured by the second flow meter 79.

[0066] The first flash tank 18 is equipped with an electric valve O81, an electric valve P82, a safety valve C83, a pressure sensor D84, and a vent valve A85. One end of the electric valve O81 is connected to the liquid outlet of the first gas-liquid separator 5 and the liquid outlet of the second gas-liquid separator 17. The other end of the electric valve O81 is connected to one end of the electric valve P82 and the liquid inlet of the first flash tank 18. The other end of the electric valve P82 is connected to one end of the safety valve C83. The other end of the safety valve C83 is connected to the gas outlet of the first flash tank 18.

[0067] The second flash tank 20 is equipped with electric valves Q86 and R87, a safety valve D88, a pressure sensor E89, and a vent valve B90. One end of electric valve Q86 is connected to one end of electric valve O81, the liquid outlet of the first gas-liquid separator 5, and the liquid outlet of the second gas-liquid separator 17. The other end of electric valve Q86 is connected to one end of electric valve R81 and the liquid inlet of the first flash tank 18. The other end of electric valve R87 is connected to one end of safety valve D88, and the other end of safety valve D88 is connected to the gas outlet of the first flash tank 18. The other end of electric valve P82, one end of safety valve C83, the other end of electric valve R87, one end of safety valve D88, valve L91, and the gas inlet of the third buffer tank 19 are connected in sequence.

[0068] An electric valve S92 is installed between the liquid outlet of the first flash tank 18 and the second flow meter 79, and an electric valve T93 is installed between the liquid outlet of the second flash tank 20 and the second flow meter 79.

[0069] The first gas-liquid separator 5 and the second gas-liquid separator 17 are adsorption-type gas-liquid separators with a separation efficiency of ≥98%. When gas carrying mist rises through the wire mesh at a certain speed, the mist collides with the fine wire mesh filaments due to the inertia of the rising mist and adheres to the surface of the filaments. The diffusion of the mist on the surface of the filaments and the gravitational settling of the mist cause the mist to form larger droplets that flow along the filaments to the junction of the two filaments. The wettability of the filaments, the surface tension of the liquid, and the capillary action of the filaments cause the droplets to grow larger and larger until the accumulated droplets are large enough that their own gravity exceeds the resultant force of the rising force of the gas and the surface tension of the liquid. At this point, the droplets separate from the filaments and fall, achieving deep separation of droplets from the gas.

[0070] This invention employs the carbon dioxide fracturing flowback carbon capture and recovery method provided by the aforementioned carbon dioxide fracturing flowback carbon capture and recovery device, the specific steps of which are as follows: S0. The multiphase flow mixture returned from the wellhead is initially filtered by a three-phase separator. The liquid phase is discharged to the collection tank through the blowdown pipe, the solid phase is collected as a whole, and the gas phase is connected to the carbon capture and recovery device.

[0071] S1. Perform a primary filtration process on the high-pressure return gas mixture at the wellhead to remove large particulate impurities from the return gas, obtaining a primary filtered high-pressure mixture gas. This includes the following steps: The high-pressure return gas mixture from the wellhead is filtered through either the first filter 2 or the second filter 11 to remove solid impurities and moisture, resulting in a high-pressure mixture gas after primary filtration. The impurity particle size in the high-pressure mixture gas after primary filtration is ≤3μm; primary filtration is coarse filtration, removing large-diameter impurity particles.

[0072] S2. Reduce the pressure of the high-pressure mixed gas after primary filtration to a set value, and control the temperature of the high-pressure mixed gas at a set value to obtain the depressurized mixed gas, including the following steps: The pressure of the high-pressure mixed gas after primary filtration is reduced to the set value (3MPa) by the first pressure regulating valve 3 or the second pressure regulating valve 12, and the temperature is controlled above 5℃ to obtain the depressurized mixed gas.

[0073] S3. The liquid carbon dioxide and the depressurized mixed gas are separated by the first gas-liquid separator 5 to obtain the depressurized mixed gas.

[0074] S4. The depressurized mixed gas is subjected to secondary filtration, heating and drying, and tertiary filtration in sequence to obtain a dry mixed gas, including the following steps: S41. The solid impurities and free oil and water in the depressurized mixed gas are filtered through the third filter 6 to obtain a mixed gas after secondary filtration. The particle size of the impurities in the mixed gas after secondary filtration is ≤1μm, and the oil content is ≤0.01PPM.

[0075] S42. The mixed gas after secondary filtration is dried by the adsorption drying device 7.

[0076] S43. The molecular sieve dust in the dried mixed gas is filtered and intercepted by the fourth filter 8 to obtain a dry mixed gas. The impurity particle size in the dry mixed gas is ≤1μm and the oil content is ≤0.1PPM.

[0077] S5. The dry mixed gas is subjected to pressure balancing treatment through the first buffer tank 9 and the second buffer tank 15 in sequence to obtain a stable mixed gas.

[0078] S6. The regulated mixed gas is cooled by a refrigeration device to obtain condensed liquid carbon dioxide and non-condensable gas.

[0079] The mixture after pressure stabilization is mainly composed of methane and CO2. The basic principle of the condensation method is that the condensation point of CO2 is different from that of methane. After pressurization and cooling, CO2 condenses into liquid, while methane remains a gas. Through gas-liquid separation, CO2 and methane are separated.

[0080] S7. The condensed liquid carbon dioxide and non-condensable gas are separated by the second gas-liquid separator 17 to obtain liquid carbon dioxide and non-condensable gas.

[0081] S8. Liquid carbon dioxide is heated and depressurized by flash evaporation in the first flash tank 18 or the second flash tank 20 to obtain purified liquid carbon dioxide and flash gas. The purified liquid carbon dioxide is then reused.

[0082] The main purpose of flash evaporation is to further purify liquid CO2 for easier use.

[0083] S9. The non-condensable gas is depressurized by the third pressure regulating valve 71. The depressurized non-condensable gas is then subjected to combustion treatment, and the exhaust gas produced by combustion is discharged.

[0084] The non-condensable gases are mainly methane, which is treated by combustion, and the treated exhaust gas is discharged directly.

[0085] S10. The flash gas is collected and stabilized by the third buffer tank 19. The pressure of the stabilized flash gas is reduced by the fourth pressure regulating valve 76. The reduced-pressure flash gas is then discharged after being flame-retarded by the second flame arrester 78.

[0086] S11. The purified liquid carbon dioxide is pumped to the carbon dioxide storage tank 14 by the drain pump 80.

[0087] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0088] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0089] The examples above are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention fall within the scope of protection of the present invention. Device structures and method steps not described in detail in this invention are prior art and will not be further described in this invention.

Claims

1. A method for capturing and recovering carbon from carbon dioxide fracturing flowback, characterized in that: The specific steps are as follows: Step 1: The high-pressure flowback mixed gas at the wellhead is filtered once using a carbon dioxide fracturing flowback carbon capture and recovery device to obtain a high-pressure mixed gas after primary filtration. Step 2: Reduce the pressure of the high-pressure mixed gas after the first filtration in Step 1 to the set value, and control the temperature of the high-pressure mixed gas at the set value to obtain the depressurized mixed gas; Step 3: The depressurized mixed gas obtained in Step 2 is subjected to secondary filtration, drying, and tertiary filtration in sequence to obtain a dry mixed gas. Step four: Perform pressure balancing on the dry mixed gas obtained in step three to obtain a stabilized mixed gas. Step 5: Cool the stabilized mixed gas obtained in Step 4 to obtain condensed liquid carbon dioxide and non-condensable gas, respectively. Step six: Separate the condensed liquid carbon dioxide and non-condensable gas obtained in step five to obtain liquid carbon dioxide and non-condensable gas. Step 7: The liquid carbon dioxide is subjected to flash evaporation by heating and depressurization to obtain purified liquid carbon dioxide and flash evaporated gas.

2. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 1, characterized in that: In step one, the high-pressure return gas mixture at the wellhead is filtered once to remove solid impurities and moisture from the return gas mixture, thus obtaining a high-pressure mixture gas after primary filtration.

3. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 1, characterized in that: The particle size of impurities in the high-pressure mixed gas after one filtration is ≤3μm.

4. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 1, characterized in that: In step two, the pressure of the high-pressure mixed gas after primary filtration is adjusted to 3 MPa using a pressure-reducing valve.

5. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 1, characterized in that: In step three, the depressurized mixed gas is subjected to secondary filtration, drying, and tertiary filtration in sequence to obtain a dry mixed gas. The solid impurities and free oil and water in the depressurized mixed gas are filtered by the third filter (6) to obtain the mixed gas after secondary filtration; the mixed gas after secondary filtration is dried by the adsorption drying device (7). The molecular sieve dust in the dried mixed gas is filtered and intercepted by the fourth filter (8) to obtain a dry mixed gas.

6. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 5, characterized in that: The impurity particle size in the mixed gas after secondary filtration is ≤1μm, and the oil content is ≤0.01PPM; the impurity particle size in the dried mixed gas is ≤1μm, and the oil content is ≤0.1PPM.

7. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 1, characterized in that: In step four, the dry mixed gas is subjected to pressure balancing treatment through the first buffer tank (9) and the second buffer tank (15) in sequence to obtain a stable mixed gas.

8. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 1, characterized in that: In step six, the non-condensable gas is depressurized, and the depressurized non-condensable gas is then subjected to combustion treatment, with the exhaust gas produced by combustion being discharged.

9. The method for capturing and recovering carbon from carbon dioxide fracturing flowback according to claim 1, characterized in that: In step seven, the flash gas is collected and its pressure is stabilized, the stabilized flash gas is depressurized, and the depressurized flash gas is treated with flame retardant before being discharged into the air.

10. The method of using the carbon dioxide fracturing flowback carbon capture and recovery method according to claim 1, characterized in that: In step seven, the purified liquid carbon dioxide is transported to the carbon dioxide storage tank (14) via a drain pump (80).

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