Zero discharge system for shale gas flowback fluid

Abstract

The utility model provides a zero discharge system for shale gas flowback fluid. The zero discharge system comprises an adjusting tank 1, a sedimentation tank 2, a catalytic ozonation device 3, a BAF device 4, a membrane filtration device 5, a primary reverse osmosis device 6, a secondary reverse osmosis device 7, an electrocatalytic oxidation device 8 and an evaporation device 9. Shale gas flow-back fluid wastewater is treated by the adjusting tank, so that the water quality is stable; the sedimentation tank is used for removing oil, calcium and magnesium ions and suspended matters to prevent the membrane from scaling; the catalytic ozonation device improves the biodegradability of the wastewater and assists the BAF device to operate; the BAF device is used for removing residual COD, TN and TP and reducing organic matter pollution; the first-stage reverse osmosis device and the second-stage reverse osmosis device remove pollutants such as salt and COD, and water produced by the second-stage reverse osmosis device meets production requirements; the electrocatalytic oxidation device is used for removing organic matters in the first-stage reverse osmosis concentrated water and reducing pollution and blockage of the steam compression device; and the steam compression device realizes evaporative crystallization of salt in the wastewater and reflux of condensed water, so that zero emission is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of wastewater treatment, in particular to a zero-emission system for shale gas flowback fluid. Background Art

[0002] Shale gas is an unconventional natural gas resource with huge geological reserves. my country has initially formed four major shale gas production areas (Fuling, Changning, Weiyuan, and Ordos), with a production capacity of more than 7 billion m 3 ·a -1 Due to the particularity of shale gas development, a large amount of fracturing fluid needs to be injected into the formation for hydraulic fracturing. The water used to prepare the fracturing fluid for each well is (3-4)×10 4 m 3 . Fracturing flowback fluid is very different from conventional mining wastewater. After the fracturing operation is completed, the wastewater discharged from the formation is a complex multiphase dispersion system containing suspended solids (rock fragments, ceramsite sand, gel residue and water-insoluble matter), crude oil, bacteria, inorganic matter and organic matter. Fracturing flowback fluid has the following characteristics: (1) complex composition, many types of pollutants and high content; (2) high COD, high chloride, high viscosity and high emulsification; (3) difficult to treat. If it is discharged into the water body or injected into the formation without treatment, it can cause serious pollution problems of the surface or underground environmental system.

[0003] In recent years, due to the strong oxidative ability of advanced oxidation technology (AOP), it can generate highly active free radicals (OH, O 2- 、SO4 2- The electrocatalytic oxidation process is widely used in various wastewater treatments to effectively degrade some refractory organic pollutants. Advanced oxidation technologies mainly include wet oxidation technology, Fenton oxidation technology, electrocatalytic oxidation technology, ozone oxidation technology, and photocatalytic oxidation technology. Compared with other advanced oxidation technologies, electrocatalytic oxidation technology has the advantages of low energy consumption, wide application range, simple operation, environmental friendliness, and no secondary pollution. Therefore, among advanced oxidation technologies, electrocatalytic oxidation technology (EAOP) is considered to be an efficient, environmentally friendly, and highly adaptable oxidation technology. There are two main electrocatalytic oxidation mechanisms: direct oxidation, which means that pollutants migrate to the two electrodes under the action of an electric field and are oxidized directly on the anode surface through electron transfer into easily degradable small molecules or simple inorganic substances; indirect oxidation, which means that under the action of a catalyst, the aqueous solution is electrolyzed to generate strong oxidizing substances such as hydroxyl radicals (OH). Strong oxidizing substances such as hydroxyl radicals (OH) can non-selectively degrade organic pollutants and ultimately completely decompose large molecular pollutants into carbon dioxide and water, achieving the purpose of pollutant mineralization. Utility Model Content

[0004] The main purpose of the utility model is to provide a zero-emission system for shale gas flowback fluid.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A zero-discharge system for shale gas flowback fluid, comprising a regulating tank, a sedimentation tank, an ozone catalytic oxidation device, a BAF device, a membrane filtration device, a primary reverse osmosis device, a secondary reverse osmosis device, an electrocatalytic oxidation device, and an evaporation device;

[0007] The water outlet of the regulating tank is connected to the sedimentation tank, the water outlet of the sedimentation tank is connected to the ozone catalytic oxidation device, the water outlet of the ozone catalytic oxidation device is connected to the BAF device, the water outlet of the BAF device is connected to the membrane filtration device, the water production port of the membrane filtration device is connected to the primary reverse osmosis device, the concentrated water port of the primary reverse osmosis device is connected to the electrocatalytic oxidation device, the water outlet of the electrocatalytic oxidation device is connected to the evaporation device, and the water production port of the primary reverse osmosis device is connected to the secondary reverse osmosis device.

[0008] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0009] As an optimal technical solution of the present utility model: the sedimentation tank is a high-density sedimentation tank.

[0010] As an optimal technical solution of the present utility model: the ozone catalytic oxidation device is a high-efficiency ozone catalytic oxidation device.

[0011] As a preferred technical solution of the present utility model: a hydrochloric acid adding port is provided on the water inlet tank of the ozone catalytic oxidation device.

[0012] As a preferred technical solution of the present invention: the membrane filtration device is an ultrafiltration device.

[0013] As a preferred technical solution of the present invention: the ultrafiltration device is a tubular ultrafiltration device, the membrane cutoff molecular weight of the tubular ultrafiltration membrane in the tubular ultrafiltration device is 10,000 Da, and the recovery rate is 95%.

[0014] As an optimal technical solution of the present invention: the evaporation device is one of a mechanical vapor recompression device, a thermal vapor recompression device, a mechanical vapor compression device, a thermal vapor compression device, and a multi-effect evaporation device.

[0015] As a preferred technical solution of the present invention: the sludge discharge port of the sedimentation tank, the sludge discharge port or the return sludge port of the BAF device, and the sludge discharge port of the membrane filtration device are respectively connected to the plate and frame filter press.

[0016] As a preferred technical scheme of the utility model: the first reverse osmosis device is SWRO reverse osmosis device.

[0017] As a preferred technical scheme of the utility model: the second reverse osmosis device is BWRO reverse osmosis device.

[0018] The utility model provides a kind of zero emission system for shale gas flowback fluid, with following beneficial effects: shale gas flowback fluid wastewater is collected and homogenization treatment is carried out by wastewater conditioning tank, so that the water quality of wastewater discharged in conditioning tank is stable;Oil, calcium magnesium ion and suspended solids in wastewater are removed by high-density sedimentation tank, to avoid the phenomenon of calcium magnesium scale on the rear end membrane;Small molecular organic matter in wastewater can be removed by ozone catalytic oxidation device, and macromolecular organic matter is degraded into small molecular organic matter, improve wastewater biodegradability, help the operation of subsequent BAF device;Residual COD, TN, TP in wastewater is removed by BAF, to reduce organic pollution in rear end;Salt, COD and other pollutants in wastewater are removed by first and second reverse osmosis devices, and second reverse osmosis water can meet the requirements of plant production water;Organic matter in first reverse osmosis concentrated water is removed by electro-catalytic oxidation device, to reduce the pollution of steam compression device caused by organic matter;Salt in wastewater is evaporated and crystallized by steam compression device, and condensate water is returned to the system, so as to achieve the purpose of zero emission. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Flow chart of the zero emission system for shale gas flowback fluid provided by the utility model;

[0020] In the figure: 1-conditioning tank;2-sedimentation tank;3-ozone catalytic oxidation device;4-BAF device;5-membrane filtration device;6-first reverse osmosis device;7-second reverse osmosis device;8-electro-catalytic oxidation device;9-steam compression device;10-plate-frame filter press. DETAILED DESCRIPTION

[0021] The utility model is further described in detail with reference to the drawings and specific embodiments.

[0022] As Figure 1 shown, a zero emission system for shale gas flowback fluid includes conditioning tank 1, sedimentation tank 2, ozone catalytic oxidation device 3, BAF device 4, membrane filtration device 5, first reverse osmosis device 6, second reverse osmosis device 7, electro-catalytic oxidation device 8 and evaporation device 9;

[0023] The water outlet of the regulating tank 1 is connected to the sedimentation tank 2, the water outlet of the sedimentation tank 2 is connected to the ozone catalytic oxidation device 3, the water outlet of the ozone catalytic oxidation device 3 is connected to the BAF device 4, the water outlet of the BAF device 4 is connected to the membrane filtration device 5, the water production port of the membrane filtration device 5 is connected to the primary reverse osmosis device 6, the concentrated water port of the primary reverse osmosis device 6 is connected to the electrocatalytic oxidation device 8, the water outlet of the electrocatalytic oxidation device 8 is connected to the evaporation device 9, and the water production port of the primary reverse osmosis device 6 is connected to the secondary reverse osmosis device 7.

[0024] Sedimentation tank 2 is a high-density sedimentation tank, into which demulsifier, flocculant PAC, and coagulant aid PAM are added, and NaOH is used to adjust the pH to about 11.5.

[0025] The ozone catalytic oxidation device 3 is a high-efficiency ozone catalytic oxidation device. A hydrochloric acid feeding port is provided on the water inlet tank. The pH of the inlet water is controlled at about 7. The ozone dosage is 80 mg / L and the catalyst is Al2O3.

[0026] The filter material loaded in the BAF device 4 is ceramsite.

[0027] In this embodiment, the membrane filtration device 5 is an ultrafiltration device, which is a tubular ultrafiltration device. The membrane cutoff molecular weight of the tubular ultrafiltration membrane in the tubular ultrafiltration device is 10,000 Da, and the recovery rate is 95%.

[0028] The evaporation device 9 is one of a mechanical vapor recompression device (MVR), a thermal vapor recompression device (TVR), a mechanical vapor compression device, a thermal vapor compression device, and a multi-effect evaporation device (MEE). In this embodiment, the evaporation device 9 is a mechanical vapor recompression device (MVR).

[0029] The sedimentation tank 2 , the BAF device 4 , and the membrane filtration device 5 are also respectively connected to the inlet of the plate and frame filter press 10 .

[0030] The first-stage reverse osmosis device 6 is a SWRO reverse osmosis device, the inner membrane of which is a desalination membrane, the recovery rate is 80%, the pressure is 40-50 bar, and the average water production membrane flux is 15-16LMH.

[0031] The secondary reverse osmosis device 7 is a BWRO reverse osmosis device with a bitter-light membrane as the inner membrane, a recovery rate of 90%, a pressure of 20-30 bar, and an average water production membrane flux of 17-20 LMH.

[0032] The current of the electrocatalytic oxidation device 8 is 15A, the reaction time is 30min, and the added oxidant is 100mg / L sodium persulfate. The purpose is to slow down the organic fouling of the rear steam compression device 9. Due to the reverse osmosis concentration, the organic concentration in the reverse osmosis concentrated water will increase again.

[0033] Specifically, the above-mentioned zero-discharge system for shale gas flowback fluid is implemented through the following steps:

[0034] S1: The wastewater generated is collected in the regulating tank 1 and subjected to physical and chemical treatment in the sedimentation tank 2. A demulsifier is added to remove oil from the wastewater. NaOH, Na2CO3, flocculants and coagulants are added to remove calcium, magnesium ions and suspended solids in the wastewater. The sludge enters the plate and frame filter press 10 for treatment. The filter cake is dried and transported for external treatment. The filtrate is returned to the regulating tank 1.

[0035] S2: High-density produced water enters the ozone catalytic oxidation device 3, which is used to remove small molecular weight organic matter and degrade large molecular weight organic matter, thereby improving the biodegradability of the wastewater;

[0036] S3: The effluent from the ozone catalytic oxidation device 3 enters the BAF device 4, where it undergoes biochemical treatment. The biofilm attached to the ceramsite can remove organic matter, TN, and TP from the wastewater.

[0037] S4: The effluent from the BAF device 4 enters the membrane filtration device 5 to remove small suspended solids in the wastewater. After meeting the reverse osmosis water inlet requirements, it enters the primary reverse osmosis device 6 for treatment. The water produced by the primary reverse osmosis device 6 enters the secondary reverse osmosis device 7. The water produced by the secondary reverse osmosis device 7 can be reused, and the concentrated water returns to the water inlet tank of the primary reverse osmosis 6;

[0038] S5: The concentrated water from the first-stage reverse osmosis device 6 enters the electrocatalytic oxidation device 8 to remove some organic matter, alleviating the blockage of organic matter in the rear-end steam compression device 9. The condensed water from the steam compression device 9 enters the water inlet tank of the second-stage reverse osmosis device 7, and the evaporated salt is transported out for treatment.

[0039] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Within the spirit of the present invention and the scope of protection of the claims, any modifications, equivalent replacements, improvements, etc. made to the present invention shall fall within the scope of protection of the present invention.

Claims

1. A zero-discharge system for shale gas flowback fluid, characterized by: It comprises a regulating tank (1), a sedimentation tank (2), an ozone catalytic oxidation device (3), a BAF device (4), a membrane filtration device (5), a primary reverse osmosis device (6), a secondary reverse osmosis device (7), an electrocatalytic oxidation device (8) and an evaporation device (9); The water outlet of the regulating tank (1) is connected to the sedimentation tank (2), the water outlet of the sedimentation tank (2) is connected to the ozone catalytic oxidation device (3), the water outlet of the ozone catalytic oxidation device (3) is connected to the BAF device (4), the water outlet of the BAF device (4) is connected to the membrane filtration device (5), the water production port of the membrane filtration device (5) is connected to the primary reverse osmosis device (6), the concentrated water outlet of the primary reverse osmosis device (6) is connected to the electrocatalytic oxidation device (8), the water outlet of the electrocatalytic oxidation device (8) is connected to the evaporation device (9), and the water production port of the primary reverse osmosis device (6) is connected to the secondary reverse osmosis device (7).

2. The zero-discharge system for shale gas flowback fluid according to claim 1, characterized in that: The sedimentation tank (2) is a high-density sedimentation tank.

3. The zero-discharge system for shale gas flowback fluid according to claim 1, characterized in that: The ozone catalytic oxidation device (3) is a high-efficiency ozone catalytic oxidation device.

4. The zero-discharge system for shale gas flowback fluid according to claim 1 or 3, characterized in that: The water inlet tank of the ozone catalytic oxidation device (3) is provided with a hydrochloric acid feeding port.

5. The zero-discharge system for shale gas flowback fluid according to claim 1, characterized in that: The membrane filtration device (5) is an ultrafiltration device.

6. The zero-discharge system for shale gas flowback fluid according to claim 5, characterized in that: The ultrafiltration device is a tubular ultrafiltration device. The membrane cutoff molecular weight of the tubular ultrafiltration membrane in the tubular ultrafiltration device is 10,000 Da, and the recovery rate is 95%.

7. The zero-discharge system for shale gas flowback fluid according to claim 1, characterized in that: The evaporation device (9) is one of a mechanical steam recompression device, a thermal steam recompression device, a mechanical steam compression device, a thermal steam compression device, and a multi-effect evaporation device.

8. The zero-discharge system for shale gas flowback fluid according to claim 1, characterized in that: The sludge discharge port of the sedimentation tank (2), the sludge discharge port or the return sludge port of the BAF device (4), and the sludge discharge port of the membrane filtration device (5) are respectively connected to the plate and frame filter press (10).

9. The zero-discharge system for shale gas flowback fluid according to claim 1, characterized in that: The primary reverse osmosis device (6) is a SWRO reverse osmosis device.

10. The zero-discharge system for shale gas flowback fluid according to claim 1, characterized in that: The secondary reverse osmosis device (7) is a BWRO reverse osmosis device.

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