Device and method for improving performance of water produced by treating shale gas through membrane distillation

Abstract

The invention discloses a device and method for improving the performance of shale gas produced water treated through membrane distillation, and relates to the technical field of shale gas produced water treatment.The device comprises a water collecting pond, a constant-level water pond, an oxidation pond, a heating water pond, a membrane distillation filter pond and a condensation recycling water pond, the condensation recycling water pond is connected with the membrane distillation filter pond, and the membrane distillation filter pond is connected with the heating water pond; the heating pool is connected with the oxidation pool, the oxidation pool is connected with the constant-level pool, the constant-level pool is connected with the water collecting pool, and the water collecting pool is connected with the water inlet lifting pump and the water inlet valve. According to the device and method for improving the performance of the shale gas produced water treated through membrane distillation, the membrane distillation membrane assembly is adopted as the last barrier for Fenton oxidation pretreatment, particulate matter, colloid, microorganisms and the like in water are intercepted, and the inflow water quality of the shale gas produced water treated through the follow-up process is guaranteed; meanwhile, in the stable membrane distillation operation process, a filter cake layer composed of inorganic salt, organic matter and microorganisms can be formed on the surface of the membrane, and part of the organic matter can be degraded and intercepted.

Description

Technical Field

[0001] This invention relates to the field of shale gas produced water treatment technology, and in particular to an apparatus and method for improving the performance of membrane distillation in treating shale gas produced water. Background Technology

[0002] The advent of horizontal drilling and hydraulic fracturing technologies has revolutionized shale gas extraction, unlocking the vast reserves of this resource. However, the hydraulic fracturing process requires the input of large amounts of fresh water, resulting in high-salinity wastewater, i.e., shale gas produced water. Throughout the extraction process, each horizontal well produces 5200-34900 m³ of produced water. 3 Shale gas produced water is a complex substance containing large amounts of suspended solids, cations, anions, organic matter, and naturally occurring radioactive materials. Improper treatment can pose serious threats to human health and aquatic ecosystems. Therefore, the urgent task is to develop efficient treatment technologies to achieve the sustainable reuse and zero-liquidity discharge of high-concentration industrial wastewater.

[0003] Membrane distillation, due to its superior separation performance and environmental friendliness, has become a promising solution for treating high-salinity wastewater such as shale gas produced water. However, the application of membrane distillation is hindered by membrane scaling and wetting, primarily caused by organic matter in shale gas produced water. Therefore, reducing the organic matter content in shale gas produced water is an ideal way to improve membrane distillation performance. Summary of the Invention

[0004] The purpose of this invention is to provide an apparatus and method for improving the performance of membrane distillation in treating shale gas produced water, and to solve the problems that the performance of membrane distillation is hindered by membrane scaling and membrane wetting, which leads to increased subsequent membrane maintenance costs.

[0005] To achieve the above objectives, the present invention provides an apparatus for improving the performance of membrane distillation in treating shale gas produced water, comprising a water collection tank, a constant-level water tank, an oxidation tank, a heating water tank, a membrane distillation filter, and a condensate recovery water tank. The condensate recovery water tank is connected to the membrane distillation filter, the membrane distillation filter is connected to the heating water tank, the heating water tank is connected to the oxidation tank, the oxidation tank is connected to the constant-level water tank, the constant-level water tank is connected to the water collection tank, and the water collection tank is connected to an inlet booster pump and an inlet valve.

[0006] Preferably, a constant-level water tank inlet is provided on one side wall of the constant-level water tank, and the constant-level water tank inlet is connected to the water collection tank outlet through a pipe. A constant-level water tank outlet is provided on the other side wall of the constant-level water tank, and a water level sensor is provided inside the constant-level water tank.

[0007] Preferably, the oxidation tank is equipped with oxidant and catalyst dosing pipelines and a stirring mechanism. An oxidation tank inlet is provided on one side wall of the oxidation tank, which is connected to the outlet of the constant-level water tank through the pipeline. An oxidation tank outlet is provided on the other side wall of the oxidation tank.

[0008] Preferably, the outlet of the oxidation tank is connected to the inlet of the heating water tank, the inlet of the heating water tank is connected to the side wall of the heating water tank, and the heating water tank is equipped with a heating mechanism and a stirring mechanism.

[0009] Preferably, the membrane distillation filter includes an inlet water zone and a reclaimed water zone, the reclaimed water zone being connected to the condensate reclaimed water tank via the pipe, and the inlet water zone being connected to the heating water tank via the pipe.

[0010] Preferably, both the recycled water zone and the inlet water zone are provided with an inlet, an outlet, and a magnetically driven gear pump, with the magnetically driven gear pump installed on the pipe connected to the inlet.

[0011] Preferably, the condensate recovery tank is provided with a product water overflow tank, a product water collection tank and a condensate pipeline inside. The upper part of the condensate pipeline is connected to the condensation equipment, and the lower part of the condensate pipeline is connected to the product water overflow tank. An overflow plate is provided between the product water overflow tank and the product water collection tank.

[0012] Preferably, the membrane distillation filtration membrane is a hydrophobic membrane with a pore size of 0.1-5 μm.

[0013] A method of using an apparatus for improving the performance of membrane distillation in treating shale gas produced water includes the following steps:

[0014] Step 1: Shale gas produced water first enters the collection tank through the inlet booster pump and inlet valve, and then flows into the constant level water tank. The liquid level in the constant level water tank is maintained constant by feedback regulation through the water level sensor.

[0015] Step 2: Water from the constant-level water tank enters the oxidation tank through pipes. Oxidant and catalyst are added to the oxidation tank through oxidant and catalyst addition pipelines. The stirring mechanism stirs the oxidant and catalyst.

[0016] Step 3: The effluent from the oxidation tank enters the heating water tank. When the temperature in the heating water tank reaches 70°C and the temperature in the condensate recovery water tank reaches 20°C, the filtration system is activated.

[0017] Step 4: First, turn on the magnetic drive gear pump and the magnetic drive gear pump to fill the product water pipeline connected to the water inlet and water recycling zones with water to realize the membrane distillation process.

[0018] Step 5: The permeate from the pressure-driven membrane distillation filter enters the condensate recovery tank through the collection pipeline. The permeate overflowing from the condensate recovery tank through the outlet pipeline of the pressure-driven membrane distillation filter flows below the liquid level in the permeate overflow tank, then overturns the overflow plate and enters the permeate collection tank, and finally enters the subsequent process.

[0019] Preferably, in step three, the oxidant is cuprous oxide, and the catalyst is ferrous sulfate and hydrogen peroxide. The oxidant and catalyst can be added continuously or in a single addition. When added continuously, the concentrations of the catalyst and oxidant are 100-1500 mg / L and 30-700 mg / L, respectively; when added in a single addition, the concentrations are 200-3000 g / m³, respectively. 2 and, 60-1400g / m 2 .

[0020] Therefore, this invention employs the aforementioned apparatus and method for improving the performance of membrane distillation in treating shale gas produced water. The membrane distillation module serves as the final barrier in the Fenton oxidation pretreatment process, effectively trapping particulate matter, colloids, and microorganisms in the water, thus ensuring the quality of the influent for subsequent shale gas produced water treatment. Simultaneously, after the pressure-driven membrane filter stabilizes, a biologically active filter cake layer forms on the membrane surface, which can degrade and trap some organic matter. The oxidative action of the oxidant and catalyst is fully utilized; the free radical oxidation generated by the Fenton reaction activated by cuprous oxide and hydrogen peroxide can remove small-molecule organic pollutants in the water that reduce membrane distillation performance.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a device for improving the performance of membrane distillation in treating shale gas produced water according to the present invention;

[0023] Figure 2 The graph shows the flux and effluent conductivity of the membrane distillation process in an embodiment of the present invention.

[0024] Figure Labels

[0025] 1. Water collection tank; 2. Constant-level water tank; 3. Oxidation tank; 4. Heating water tank; 5. Pressure-driven membrane distillation filter; 6. Condensate recovery water tank; 11. Water collection tank inlet; 12. Inlet valve; 13. Inlet booster pump; 14. Water collection tank outlet; 21. Constant-level water tank inlet; 22. Water level sensor; 23. Constant-level water tank outlet; 31. Oxidant and catalyst dosing pipeline; 32. Stirring mechanism; 33. Oxidation tank inlet; 34. Oxidation tank outlet; 41. Stirring mechanism one; 42. Heating mechanism; 43. Heating water tank inlet; 51. Inlet area; 52. Recovered water area; 53. Inlet; 54. Outlet; 55. Magnetic drive gear pump; 61. Condensate pipeline; 62. Condensation equipment; 63. Product water overflow tank; 64. Product water collection tank; 65. Outlet. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0028] Example

[0029] Please see Figures 1-2 The present invention provides an apparatus for improving the performance of membrane distillation in treating shale gas produced water, comprising a water collection tank 1, a constant water tank 2, an oxidation tank 3, a heating water tank 4, a pressure-driven membrane distillation filter 5, and a condensate recovery water tank 6.

[0030] A water inlet 11 is provided on the upper part of one side wall of the water collection tank 1, and a water outlet 14 is provided on the other side wall of the water collection tank 1. The water inlet 11 is connected to the water inlet pump 13 and the water inlet valve 12.

[0031] A water level sensor 22 is installed inside the constant level water tank 2. A constant level water tank inlet 21 is provided on one side wall of the constant level water tank 2, and a constant level water tank outlet 23 is provided on the other side wall of the constant level water tank 2. The water collection tank outlet 14 is connected to the constant level water tank inlet 21 through a pipe.

[0032] The oxidation tank 3 is equipped with oxidant and catalyst dosing pipelines 31 and a stirring mechanism 32. An oxidation tank inlet 33 and an oxidation tank outlet 34 are located on the upper side wall of the oxidation tank 3. The outlet 23 of the constant-level water tank is connected to the oxidation tank inlet 33 via a pipeline. The oxidant and catalyst are cuprous oxide, ferrous sulfate, and hydrogen peroxide, respectively. The cuprous oxide and hydrogen peroxide catalysts and oxidants used are inexpensive, readily available, and easy to store and manage, requiring no special treatment, making them suitable for engineering applications.

[0033] The heating water tank 4 is equipped with a stirring mechanism 41 and a heating mechanism 42. The upper side wall of the heating water tank 4 is provided with a heating water tank inlet 43. The oxidation tank outlet 34 is connected to the heating water tank inlet 43 through a pipe.

[0034] The pressure-driven membrane distillation filter 5 is internally divided into two parts: an inlet zone 51 and a recovery water zone 52. The inlet zone 51 is equipped with an inlet 53 and an outlet 54. A magnetically driven gear pump 55 circulates the heated water tank 4, inlet 53, and outlet 54. The recovery water zone 52 also has an inlet 53 and an outlet 54. A magnetically driven gear pump 55 circulates the condensate recovery water tank 6, inlet 53, and outlet 54. Using a pump-driven membrane filtration system offers advantages such as simple operation and maintenance, and high efficiency. The flux variation trend of the pressure-driven membrane filter is similar to that of the shale gas wastewater return flow, making it particularly suitable for the actual operation of shale gas produced water at mining sites.

[0035] Membrane distillation filtration uses flat sheet membranes or hydrophobic membranes, with the hydrophobic membrane having a pore size of 0.1-5 μm. The membrane material can be organic or inorganic; when using organic membranes, they are polyethersulfone (PES), polysulfone (PS), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polypropylene (PP), polyacrylonitrile (PAN), or cellulose acetate (CA); when using inorganic membranes, they are alumina (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), or silicon oxide (SiO2).

[0036] The condensate recovery water tank 6 is equipped with a condensate pipe 61 and connected to a condensate device 62. It also contains a product water overflow tank 63 and a product water collection tank 64, which are separated by an overflow plate in the middle. The lower part of the side wall of the condensate recovery water tank 6 is provided with an outlet 65, which is connected to the subsequent desalination process.

[0037] The Fenton oxidation technology described above for improving the performance of shale gas produced water through membrane distillation is carried out according to the following steps:

[0038] Step 1: Shale gas produced water first enters the collection tank 1 through the booster pump 13 and the inlet valve 12, and then flows into the constant level water tank 2. The liquid level in the constant level water tank 2 is maintained constant by feedback regulation through the water level sensor 22.

[0039] Step 2: Water in constant-temperature water tank 2 enters oxidation tank 3 through pipes. At the same time, oxidant and catalyst (cuprous oxide and hydrogen peroxide, etc.) are added to oxidation tank 3 through oxidant and catalyst addition pipeline 31. The oxidant and catalyst enhance the removal effect of pollutants in the filtered water under the stirring action of stirring mechanism 32.

[0040] The catalyst and oxidant can be added continuously or in a single dose. When added continuously, the concentrations of the catalyst and oxidant are 100-1500 mg / L and 30-700 mg / L (influent volume), respectively. When added in a single dose, the concentrations are 200-3000 g / m³, respectively. 2 and 60-1400g / m 2 (Unit membrane area).

[0041] Step 3: The effluent from oxidation tank 3 enters heating water tank 4. When the heating temperature reaches 70℃, the temperature in condensate recovery water tank 6 reaches 20℃, and the filtration system is activated.

[0042] Step 4: When starting the filter, first turn on the magnetic drive gear pump 55 to fill the product water pipeline connected to the inlet water zone 51 and the recovery water zone 52 with water to realize the membrane distillation process; the product water of the pressure-driven membrane distillation filter 5 enters the condensate recovery water tank 6 through the water collection pipeline, and the product water overflow tank 63 in the condensate recovery water tank 6 of the pressure-driven membrane distillation filter is below the liquid level, then it flips over the overflow plate and enters the product water collection tank 64, and finally enters the subsequent process.

[0043] The purpose of evacuating the pressure-driven membrane distillation filter 5 before startup is to remove air from the water collection pipeline and ensure that the pipeline is filled with liquid. The permeate flux of the membrane in the pressure-driven membrane distillation filter 5 is calculated using the flow sensor on the water collection pipeline and the membrane area.

[0044] Using produced water from a shale gas well in the Sichuan Basin as raw water, and a mixture of cuprous oxide and hydrogen peroxide (1:1) as catalyst and oxidant, 100-1500 mg / L and 30-700 mg / L (adsorption tank volume) were added in a single application. A PVDF flat sheet membrane with a pore size of 0.45 μm was used in the membrane distillation system. Experimental results showed that, without additives and with different dosages of oxidant and catalyst, the normalized flux increased from 0.465 to 0.503, 0.681, and 0.908, respectively, while the permeate conductivity decreased from 70.56 μS / cm to 55.74, 45.06, and 43.15 μS / cm, respectively. Figure 2 As shown.

[0045] Therefore, this invention employs the aforementioned apparatus and method for improving the performance of shale gas produced water treatment via membrane distillation. The membrane distillation module serves as the final barrier in the Fenton oxidation pretreatment process, intercepting particulate matter, colloids, and microorganisms in the water, thus ensuring the quality of the influent water for subsequent shale gas produced water treatment. Simultaneously, during stable operation of the membrane distillation, a filter cake layer composed of inorganic salts, organic matter, and microorganisms forms on the membrane surface. This filter cake layer can degrade and retain some organic matter. The water tank and membrane filter used are characterized by their small footprint and modular design, allowing them to be manufactured as mobile purification units, facilitating installation and transportation.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A device for improving the performance of membrane distillation in treating shale gas produced water, characterized in that: It includes a water collection tank, a constant-level water tank, an oxidation tank, a heating water tank, a membrane distillation filter, and a condensate recovery water tank. The condensate recovery water tank is connected to the membrane distillation filter, the membrane distillation filter is connected to the heating water tank, the heating water tank is connected to the oxidation tank, the oxidation tank is connected to the constant-level water tank, the constant-level water tank is connected to the water collection tank, and the water collection tank is connected to the inlet lift pump and the inlet valve.

2. The apparatus for improving the performance of membrane distillation in treating shale gas produced water according to claim 1, characterized in that: A constant-level water tank inlet is provided on one side wall of the constant-level water tank, and the constant-level water tank inlet is connected to the water collection tank outlet through a pipe. A constant-level water tank outlet is provided on the other side wall of the constant-level water tank, and a water level sensor is provided inside the constant-level water tank.

3. The apparatus for improving the performance of membrane distillation in treating shale gas produced water according to claim 2, characterized in that: The oxidation tank is equipped with oxidant and catalyst dosing pipelines and a stirring mechanism. An oxidation tank inlet is provided on one side wall of the oxidation tank, which is connected to the outlet of the constant-level water tank through the pipeline. An oxidation tank outlet is provided on the other side wall of the oxidation tank.

4. The apparatus for improving the performance of membrane distillation in treating shale gas produced water according to claim 3, characterized in that: The outlet of the oxidation tank is connected to the inlet of the heating water tank, and the inlet of the heating water tank is connected to the side wall of the heating water tank. The heating water tank is equipped with a heating mechanism and a stirring mechanism.

5. The apparatus for improving the performance of membrane distillation in treating shale gas produced water according to claim 4, characterized in that: The membrane distillation filter includes an inlet water zone and a reclaimed water zone. The reclaimed water zone is connected to the condensate reclaimed water tank via the pipe, and the inlet water zone is connected to the heating water tank via the pipe.

6. The apparatus for improving the performance of membrane distillation in treating shale gas produced water according to claim 5, characterized in that: Both the recycled water zone and the inlet water zone are equipped with an inlet, an outlet, and a magnetically driven gear pump. The magnetically driven gear pump is installed on the pipe connected to the inlet water.

7. The apparatus for improving the performance of membrane distillation in treating shale gas produced water according to claim 6, characterized in that: The condensate recovery tank is equipped with a product water overflow tank, a product water collection tank and a condensate pipeline. The upper part of the condensate pipeline is connected to the condensation equipment, and the lower part of the condensate pipeline is connected to the product water overflow tank. An overflow plate is provided between the product water overflow tank and the product water collection tank.

8. The apparatus for improving the performance of membrane distillation in treating shale gas produced water according to claim 7, characterized in that: The membrane distillation filtration membrane is a hydrophobic membrane with a pore size of 0.1-5μm.

9. A method of using the apparatus for improving the performance of shale gas produced water treatment using membrane distillation as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Shale gas produced water first enters the collection tank through the inlet booster pump and inlet valve, and then flows into the constant level water tank. The liquid level in the constant level water tank is maintained constant by feedback regulation through the water level sensor. Step 2: Water from the constant-level water tank enters the oxidation tank through pipes. Oxidant and catalyst are added to the oxidation tank through oxidant and catalyst addition pipelines. The stirring mechanism stirs the oxidant and catalyst. Step 3: The effluent from the oxidation tank enters the heating water tank. When the temperature in the heating water tank reaches 70°C and the temperature in the condensate recovery water tank reaches 20°C, the filtration system is activated. Step 4: First, turn on the magnetic drive gear pump to fill the product water pipeline connected to the inlet water area and the recycled water area with water to realize the membrane distillation process. Step 5: The permeate from the pressure-driven membrane distillation filter enters the condensate recovery tank through the collection pipeline. The permeate overflowing from the condensate recovery tank through the outlet pipeline of the pressure-driven membrane distillation filter flows below the liquid level in the permeate overflow tank, then overturns the overflow plate and enters the permeate collection tank, and finally enters the subsequent process.

10. The method of using the apparatus for improving the performance of shale gas produced water by membrane distillation according to claim 9, characterized in that: In step three, the oxidant is cuprous oxide, and the catalysts are ferrous sulfate and hydrogen peroxide. The oxidant and catalyst can be added continuously or in a single addition. When added continuously, the concentrations of the catalyst and oxidant are 100-1500 mg / L and 30-700 mg / L, respectively. When added in a single addition, the concentrations are 200-3000 g / m³, respectively. 2 and 60-1400g / m 2 .

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