Gas well operation wastewater resourceful treatment process and equipment

Abstract

The invention discloses a gas well operation wastewater resourceful treatment process and equipment, and belongs to the field of wastewater treatment. The process comprises the following steps: 1, lifting wastewater from a raw water regulating tank to a dosing tank through a raw water pump; 2, enabling the raw water obtained in the step 1 to enter a dosing tank and then overflow to a reaction tank for reaction; 3, conveying the raw water obtained in the step 2 from the buffer pool to a PEK organic tubular membrane system; 4, concentrated liquor separated by the PEK organic tubular membrane system enters a desliming system, and produced water obtained in the step 3 is conveyed to a nanofiltration membrane system; step 6, enabling the nanofiltration produced water obtained in the step 5 to pass through resin and a decarburization system; 7, conveying the produced water obtained in the step 6 to a high-pressure reverse osmosis system, and enabling the produced water to enter a secondary reverse osmosis system; 8, conveying the produced water in the step 7 to an activated carbon system for deep treatment; and 9, conveying the high-pressure reverse osmosis concentrated water obtained in the step 7 into an oxidation system to remove COD, and then feeding the high-pressure reverse osmosis concentrated water into an evaporative crystallization system.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, and in particular to a process and equipment for resource treatment of wastewater from gas well operations. Background Art

[0002] The relevant national policies on water conservation and emission reduction propose that we should adhere to the principle of water conservation and give priority to water conservation, regard water resources as the biggest rigid constraint, resolutely curb unreasonable water demand, carry out in-depth water conservation and water control to reduce the intensity of water resource development and utilization, and accelerate the formation of a water-saving production and lifestyle. We must insist on taking water conservation as the premise of water resource development, utilization, protection, allocation, and dispatch, and run through all areas of the entire process of economic and social development; we must insist on taking water resources as the biggest rigid constraint; we must adhere to the principle of water conservation and give priority to water conservation, and promote the transformation of water use from extensive to economical and intensive.

[0003] With the needs of my country's national construction and development, the exploitation and use of combustible gas resources such as natural gas, shale gas, and coalbed methane have been vigorously developed. With the development of the combustible gas industry, the amount of wastewater generated in gas well operations is increasing. If effective treatment methods are not adopted, the environmental pollution problem will become increasingly serious. At the same time, water resources in gas well concentration areas are scarce, and the reuse rate of water resources needs to be improved.

[0004] At present, the treatment process of gas well wastewater is mainly based on reinjection, and this type of treatment process will gradually be abandoned. In order to meet the needs of social development, the recycling and resource utilization of water resources is the general trend. At the same time, it can also solve the dilemma of water shortage in the process of gas well mining. Based on the above facts, efficient and low-cost solutions to the resource utilization of gas well operation wastewater have emerged. Advanced membrane filtration and evaporation crystallization technology are used to physically intercept different pollutants, obtain refined brine solution, and then evaporate and crystallize crystalline salt to realize wastewater resource utilization, greatly reduce the treatment process, and provide resource utilization to the greatest extent. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention proposes a process and equipment for resource-based treatment of wastewater from gas well operations.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] The first aspect of the present invention relates to a process for recycling wastewater from gas well operations, comprising the following steps:

[0008] Step 1: The wastewater is pumped from the raw water regulating tank to the dosing tank, and hardness removal, silicon removal or fluorine removal agents are added, and no auxiliary or flocculation agents are added;

[0009] Step 2: The raw water obtained in step 1 overflows into the reaction tank after entering the dosing tank for reaction;

[0010] Step 3: transport the raw water obtained in step 2 from the buffer tank to the PEK organic tubular membrane system for mud-water separation under alkaline conditions;

[0011] Step 4: The concentrated liquid separated by the PEK organic tubular membrane system in step 3 enters the desludging system. The final solids filtered out by the concentrated liquid pressure entering the desludging system enter the sludge treatment link. The clear liquid obtained by the desludging system is returned to the PEK organic tubular membrane system for circulation purification. The obtained clear liquid enters the clear liquid buffer tank. The final produced water obtained from the clear liquid buffer tank does not need to add any auxiliary or flocculating agents.

[0012] Step 5: The final produced water obtained in step 3 is adjusted to pH < 7 and then transported to the nanofiltration membrane system; the nanofiltration concentrated water and crystallization mother liquor are desalted and dried;

[0013] Step 6: The nanofiltration product water obtained in step 5 is passed through the resin and decarbonization system;

[0014] Step 7: The produced water obtained in step 6 is transported to a high-pressure reverse osmosis system to concentrate sodium chloride to a mass concentration of more than 12%. The operating pressure of the high-pressure reverse osmosis is greater than 8MPa. The produced water enters a secondary reverse osmosis system. The operating pressure of the secondary reverse osmosis is greater than 4MPa. The secondary reverse osmosis concentrated water is returned to step 6;

[0015] Step 8: The produced water from step 7 is transported to the activated carbon system for deep treatment, discharge or reuse;

[0016] Step nine: The high-pressure reverse osmosis concentrated water from step seven is transported to the oxidation system to remove COD and then enters the evaporation crystallization system to evaporate and crystallize sodium chloride crystals; the crystallization mother liquor and nanofiltration concentrated water enter the mixed salt drying system.

[0017] The second aspect of the present invention relates to a gas well operation wastewater resource treatment device, comprising:

[0018] Raw water regulating tank;

[0019] Dosing tank, used to collect raw water and dosing softening treatment;

[0020] PEK organic tubular membrane system for mud-water separation;

[0021] Desludging system, used to desludify muddy water filtered by PEK organic tubular membrane system;

[0022] Nanofiltration membrane system, used for nanofiltration treatment of the clear liquid obtained from the PEK organic tubular membrane system;

[0023] A resin and decarbonization system, used for performing resin dehardening and decarbonization processes on the produced water of the nanofiltration membrane system;

[0024] Reverse osmosis system, used to concentrate and desalinate the produced water from the resin and decarbonation system;

[0025] A secondary reverse osmosis system for secondary treatment of the produced water of the reverse osmosis system;

[0026] An activated carbon system, used to remove COD and ammonia nitrogen from the produced water of the secondary reverse osmosis system;

[0027] Catalytic oxidation system, used to remove COD from the concentrate of the reverse osmosis system;

[0028] And, an evaporation crystallization system is used to evaporate and crystallize the produced water of the catalytic oxidation system to obtain sodium chloride crystals.

[0029] Furthermore, the final water quality reaches: TDS <100ppm, COD <30ppm, ammonia nitrogen <1ppm, meeting the surface four-category emission standards.

[0030] Furthermore, the PEK organic tubular membrane is a PEK (polyether ketone) material separation membrane with a membrane pore size of 5nm to 0.2μm. It utilizes the screening principle of the membrane and the chemical resistance and wear resistance of the PEK material to achieve the ultimate mud-water separation effect.

[0031] Furthermore, the entire treatment process including dosing, reaction, membrane filtration, desludging, crystallization and drying does not require the addition of any coagulant or flocculating agent.

[0032] Furthermore, the recovery rate of produced water through the PEK organic tubular membrane system and desludging for circulation purification exceeds 99%.

[0033] Furthermore, the entire treatment including reaction, ultrafiltration membrane filtration and desludging process is carried out under strong alkaline conditions (pH>11).

[0034] Furthermore, the entire treatment process consumes less reagents and reduces carbon emissions.

[0035] Furthermore, the nanofiltration membrane system removes most of the COD and secondary anions, reduces the processing volume of the crystallization mother liquor and the operating cost of the oxidation unit, and at the same time, improves the quality of the crystallized salt of sodium chloride and the recovery rate of the crystallized salt.

[0036] Furthermore, the process flow places the resin de-hardening and decarbonization system before the reverse osmosis system and after the nanofiltration membrane system. Since COD and the amount of secondary ions are reduced, the consumption of resin regeneration agents and the installed power of the decarbonization equipment are reduced.

[0037] Furthermore, the high-pressure reverse osmosis system can concentrate the content of sodium chloride to more than 12% at an operating pressure of more than 8 MPa.

[0038] Furthermore, the two-stage reverse osmosis system can ensure that the total system desalination rate is greater than 99.7% and the total recovery rate is greater than 80%.

[0039] Furthermore, the crystallized salt output rate of the evaporation crystallization system is greater than 95%, and the quality of the crystallized salt meets the requirements of first-class industrial crystallized salt dry salt.

[0040] Furthermore, the softening or silicon removal agent includes: one or a combination of sodium hydroxide, calcium oxide, calcium hydroxide, calcium chloride, magnesium hydroxide, sodium carbonate, magnesium chloride, sodium aluminate, and sodium sulfate.

[0041] Beneficial effects of the present invention:

[0042] 1. The characteristics of the present invention are simple processing flow, few types of reagents, small amount of addition, small equipment footprint, low operating cost, stable water output, and full automatic control;

[0043] 2. The present invention is particularly suitable for the treatment of wastewater with high hardness, high mineralization, high COD, high silicon and oil;

[0044] 3. The organic tubular ultrafiltration membrane used in the present invention is a PEK organic tubular membrane. The PEK tubular ultrafiltration membrane has the characteristics of acid and alkali resistance, COD resistance, oil resistance, good hydrophilicity, large flux, long cleaning cycle, no need for backwashing, etc. The pore size has different specifications of 5nm to 0.2μm, and has many advantages as a sludge-water separation with high sludge concentration and high organic matter;

[0045] 4. The process of the present invention adopts a pretreatment process of pretreatment + membrane filtration (PEK organic tubular membrane). After softening + ultrafiltration membrane (PEK organic tubular ultrafiltration membrane) treatment, the produced water can enter NF, RO, and evaporation for deep treatment. As a pretreatment process to ensure the water quality of NF, RO, and evaporation water. The process has stable water quality, low operating cost, high system automation, integrated equipment and long service life.

[0046] 5. The continuous concentration design adopted in the present invention ensures the stable operation of the system, the stability of the produced water quality and the strong ability to cope with the impact of the incoming water quality and water volume.

[0047] 6. The GTRO technology in the process of the present invention uses low operating pressure to recover high-concentration sodium chloride, provides the concentration of sodium chloride, reduces the amount of water inlet for evaporation and crystallization, and reduces the energy consumption and operating cost of the entire process. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be further described below in conjunction with the accompanying drawings.

[0049] Figure 1 The present invention is a flow chart of a process for resource recovery treatment of wastewater from gas well operations. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] In some embodiments of the present invention, a process for recycling wastewater from gas well operations is disclosed, such as Figure 1 As shown, the process of the present invention is carried out according to the following steps:

[0052] Step 1: The wastewater is lifted from the raw water regulating tank to the gel breaking and flotation tank through the raw water pump. When the raw water enters the dosing tank, no more coagulants or flocculation agents are added to reduce the raw water viscosity and petroleum, and remove suspended oil;

[0053] Step 2: The raw water obtained in step 1 enters the dosing and reaction tank, the pH is greater than 11, and the reaction is 1 to 4 hours. The dosing types are lime, liquid alkali, and soda ash, and no other coagulants or flocculation agents are added;

[0054] Step 3: Send the raw water obtained in step 2 to the tubular membrane inlet pool for buffering to ensure the stability of the water inlet of the subsequent system;

[0055] Step 4: Send the raw water obtained in step 3 to the PEK organic tubular membrane system for mud and water separation under strong alkaline conditions (pH greater than 11), and the clear liquid enters the ultrafiltration clear liquid buffer tank. The water quality of the produced water reaches: SS ≤ 0.5 mg / L, total hardness ≤ 50 mg / L, SDI 15 ≤3, total silicon ≤5mg / L;

[0056] Step 5: The concentrated liquid separated by the PEK organic tubular membrane system in step 3 enters the desludging system. The final solid filtered out by the concentrated liquid entering the desludging system enters the sludge treatment link. The clear liquid obtained by the desludging system is returned to the PEK organic tubular membrane system. The PEK organic tubular membrane system and the desludging are circulated and purified, and finally the clear liquid enters the ultrafiltration clear liquid buffer tank.

[0057] Step 6: Send the produced water obtained in step 4 to the nanofiltration membrane system. The nanofiltration membrane system adopts a continuous concentration design, and the single-stage recovery rate is greater than 95%. A small amount of concentrated liquid is dried to remove salt. The nanofiltration produced water is mainly sodium chloride solution. The COD of the nanofiltration produced water is less than 200 mg / L, and the divalent anion is less than 100 ppm.

[0058] Step 7: Send the produced water obtained in step 6 to the resin and decarbonization system. The produced water after hardness removal and decarbonization enters the intermediate buffer tank. The water quality requirements of the produced water are total hardness <1ppm and total alkalinity <50ppm.

[0059] Step 8: Send the produced water obtained in step 7 to the GTRO system and the secondary RO system. The sodium chloride concentration in the GTRO concentrate is greater than 12%. The GTRO produced water enters the secondary RO system. The secondary RO concentrated water flows back to the GTRO raw water. The secondary RO produced water has TDS less than 100ppm, COD less than 30ppm, and ammonia nitrogen less than 1ppm.

[0060] Step 9: Send the produced water obtained in step 8 to the activated carbon system to ensure that the produced water quality TDS <100ppm, COD <30ppm, ammonia nitrogen <1ppm, meet the four types of surface emission standards, and meet the standards for discharge or reuse.

[0061] Step 10: The concentrated liquid obtained in step 8 is sent to the catalytic oxidation system to further remove COD, and the COD of the produced water is less than 150ppm, thereby ensuring the quality and resource utilization rate of the crystallized salt.

[0062] Step 11: Send the produced water obtained in step 10 to the evaporation crystallization system to crystallize qualified sodium chloride industrial salt. The product meets the requirements of industrial crystallized salt dry salt first-grade product. The evaporated condensed water enters the secondary RO water production pool.

[0063] Step 12: Mix the crystallization mother liquor produced in step 11 and the concentrated liquid of the nanofiltration membrane system and send them to the salt drying system. The solids produced will be handled by a qualified unit, and the produced water will enter the secondary RO water production pool.

[0064] Step 13: The cleaning water and recycled water of all the above systems are returned to the raw water regulating tank.

[0065] In the embodiments of the present invention, the functions and specifications of the membrane system used can refer to the following configuration:

[0066] PEK organic tubular membrane system, wherein the PEK tubular membrane is a PEK (polyether ketone) material separation membrane with a membrane pore size of 5nm to 0.2μm.

[0067] Nanofiltration membrane system: The nanofiltration membrane is a polyamide separation membrane with a roll or disc tube structure and a molecular weight cutoff of 150-800Da.

[0068] Resin hardness removal system: the resin is a macroporous weak acid cationic resin or a chelating resin.

[0069] High-pressure reverse osmosis membrane system: The nanofiltration membrane is a polyamide separation membrane with a roll or disc-tube structure. The operating pressure is >8MPa and the desalination rate is >90%.

[0070] Secondary RO system: The nanofiltration membrane is a polyamide separation membrane with a roll or disc tube structure. The operating pressure is >4MPa and the desalination rate is >99.5%.

[0071] In order to better implement the present invention, the following examples are given to further illustrate the present invention, but the present invention is not limited to the following examples.

[0072] Embodiment 1:

[0073] In this embodiment, an example of gas well operation wastewater treatment of a certain oil and gas company in Shaanxi using the above embodiment is disclosed, and the water quality is as follows:

[0074] Table 4.4-2 Category I raw water: Water quality of gas field fracturing flowback fluid

[0075] Number sequence project Fracturing flowback fluid (mg / L) Drilling wastewater (mg / L) 1 pH 5-10 5-10 2 Dissolved oxygen ≤1.44 ≤0.68 3 Chemical oxygen demand ≤8000 ≤8000 4 BOD ≤2100 ≤2100 5 Ammonia nitrogen ≤136 ≤136 6 Total Phosphorus ＜0.1 trace 7 Total Nitrogen ≤408 ≤408 8 copper trace ≤0.01 9 Zinc trace ≤0.088 10 Fluoride ≤5.51 ≤5.2 11 selenium trace ≤0.602(ug / L) 12 arsenic ≤0.731(ug / L) ≤3.88(ug / L) 13 lead trace ≤0.327 14 mercury ≤0.464(ug / L) ≤0.723(ug / L) 15 cadmium ≤0.026 ≤0.076 16 Hexavalent Chromium trace ≤1.14 17 Cyanide trace ≤0,915 18 Petroleum ≤1 ≤1 19 TDS ≤20000 ≤20000 20 SS ≤50 ≤100

[0076] Table 4.4-3 Second category raw water: mud filtrate water quality

[0077]

[0078] Table 4.4-4 Water quality of the third category raw water: mud filtrate and fracturing flowback fluid mixture

[0079]

[0080] After the operating wastewater is lifted from the regulating tank, it is first pre-treated by gel breaking, flotation, etc., and then passed through the dosing softening system. It is clarified and impurities removed by the alkali-resistant PEK tubular ultrafiltration membrane (UF1). The hardness of the produced water is less than 50mg / L (calcium and magnesium ions ≤10mg / L). The concentrated water containing sludge is directly dehydrated by plate and frame filter press. After dehydration, the mud cake enters the landfill and the filtrate returns to the front softening reaction tank (the actual tubular membrane recovery rate is nearly 100%, and only the concentrated slag brings out a small amount of water). The PEK tubular ultrafiltration membrane system has a primary water recovery rate of more than 90%. The tubular membrane produced water enters the nanofiltration membrane system after the pH is adjusted. The nanofiltration membrane concentrated water is desalted and dried. The nanofiltration membrane produced water resin is de-hardened and decarbonized before entering the reverse osmosis membrane system. The high-pressure reverse osmosis membrane GTRO1 system has a recovery rate of 70%. After the GTRO1 produced water passes through the secondary RO desalination, the produced water is 14m 3 / hAfter activated carbon treatment, the secondary RO concentrated water is returned to the GTRO1 raw water. The final water quality meets the water replenishment requirements of "Urban Wastewater Recycling-Industrial Water Quality" (GB / T19923-2024) and is reused in industrial production. High-pressure reverse osmosis concentrated water 5m 3 / h, TDS is about 120000ppm. After catalytic oxidation, most of the COD is removed to the concentrated salt evaporation and crystallization system at the back end. After evaporation and crystallization, it can reach the first-class standard of refined industrial salt and industrial dry salt in "Industrial Salt" (GB / T5462-2015). This process is used to achieve zero liquid discharge, and the final crystallized salt is uniformly entrusted for processing.

[0081] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0082] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A process for recycling wastewater from gas well operations, characterized in that: The following steps are involved: Step 1: The wastewater is pumped from the raw water regulating tank to the dosing tank, and hardness removal, silicon removal or fluorine removal agents are added; Step 2: The raw water obtained in step 1 overflows into the reaction tank after entering the dosing tank for reaction; Step 3: transport the raw water obtained in step 2 from the buffer tank to the PEK organic tubular membrane system for mud-water separation under alkaline conditions; Step 4: The concentrated liquid separated by the PEK organic tubular membrane system in step 3 enters the desludging system. The final solids filtered out by the concentrated liquid pressure entering the desludging system enter the sludge treatment link. The clear liquid obtained by the desludging system is returned to the PEK organic tubular membrane system for circulation and purification. The obtained clear liquid enters the clear liquid buffer tank, and the final produced water is obtained from the clear liquid buffer tank; Step 5: The final produced water obtained in step 3 is adjusted to pH < 7 and then transported to the nanofiltration membrane system; the nanofiltration concentrated water and crystallization mother liquor are desalted and dried; Step 6: The nanofiltration product water obtained in step 5 is passed through the resin and decarbonization system; Step 7: The produced water obtained in step 6 is transported to a high-pressure reverse osmosis system to concentrate sodium chloride to a mass concentration of more than 12%. The operating pressure of the high-pressure reverse osmosis is greater than 8MPa. The produced water enters a secondary reverse osmosis system. The operating pressure of the secondary reverse osmosis is greater than 4MPa. The secondary reverse osmosis concentrated water is returned to step 6. Step 8: The produced water from step 7 is transported to the activated carbon system for deep treatment, discharge or reuse; Step nine: The high-pressure reverse osmosis concentrated water from step seven is transported to the oxidation system to remove COD and then enters the evaporation crystallization system to evaporate and crystallize sodium chloride crystals; the crystallization mother liquor and nanofiltration concentrated water enter the mixed salt drying system.

2. The process for recycling gas well operation wastewater according to claim 1, characterized in that: The tubular membrane in the PEK organic tubular membrane system is a separation membrane made of polyetherketone, and the membrane pore diameter is 5nm to 0.2μm.

3. The process for recycling gas well operation wastewater according to claim 1, characterized in that: The alkaline condition in step 3 is PH>11.

4. The process for recycling gas well operation wastewater according to claim 1, characterized in that: The desludging system adopts a plate and frame filter press.

5. The process for recycling gas well operation wastewater according to claim 1, characterized in that: The dosing pool in step 2 is added with lime, liquid alkali and soda ash.

6. The process for recycling gas well operation wastewater according to claim 1, characterized in that: The process from the raw water regulating tank to the dosing tank also includes gel breaking and flotation treatment.

7. A gas well operation wastewater resource treatment equipment, characterized in that: include: Raw water regulating tank; Dosing tank, used to collect raw water and dosing softening treatment; PEK organic tubular membrane system for mud-water separation; Desludging system, used to desludify muddy water filtered by PEK organic tubular membrane system; Nanofiltration membrane system, used for nanofiltration treatment of the clear liquid obtained from the PEK organic tubular membrane system; A resin and decarbonization system, used for performing resin dehardening and decarbonization processes on the produced water of the nanofiltration membrane system; Reverse osmosis system, used to concentrate and desalinate the produced water from the resin and decarbonation system; A secondary reverse osmosis system for secondary treatment of the produced water of the reverse osmosis system; An activated carbon system, used to remove COD and ammonia nitrogen from the produced water of the secondary reverse osmosis system; Catalytic oxidation system, used to remove COD from the concentrate of the reverse osmosis system; And, an evaporation crystallization system is used to evaporate and crystallize the produced water of the catalytic oxidation system to obtain sodium chloride crystals.

8. The gas well operation wastewater resource treatment equipment according to claim 7 is characterized in that: The tubular membrane in the PEK organic tubular membrane system is a separation membrane made of polyetherketone, and the membrane pore diameter is 5nm to 0.2μm.

9. The gas well operation wastewater resource treatment equipment according to claim 7, characterized in that: The desludging system adopts a plate and frame filter press.

10. The gas well operation wastewater resource treatment equipment according to claim 7, characterized in that: A gel-breaking flotation treatment system is also provided between the raw water regulating tank and the dosing tank.

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