CN108218101B - Low-cost treatment and recycling method for high-salt-content gas field water - Google Patents

Low-cost treatment and recycling method for high-salt-content gas field water Download PDF

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CN108218101B
CN108218101B CN201611191060.1A CN201611191060A CN108218101B CN 108218101 B CN108218101 B CN 108218101B CN 201611191060 A CN201611191060 A CN 201611191060A CN 108218101 B CN108218101 B CN 108218101B
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wastewater
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gas field
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张杨
谭明
刘茹
孙小寒
史元腾
张宇菲
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Qingdao Institute of Bioenergy and Bioprocess Technology of CAS
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Abstract

The invention belongs to an electrodialysis desalination technology, and particularly relates to a low-cost treatment and recycling method for high-salt-content gas field water. Separating the salt and COD wastewater in the wastewater by electrodialysis on the high-salt-content gas field water; performing double decomposition on the salt which is easy to scale in the wastewater by adopting nanofiltration-electrodialysis to generate soluble salt; or mixing salt in the wastewater by using divalent selective electrodialysis and concentrating; the salt water extracted by the various modes further adopts membrane distillation, mechanical steam recompression or multi-effect evaporation concentration crystallization to recover industrial salt, and the extracted COD wastewater is reused and discharged after COD is further removed by adopting a biochemical method. The process avoids the defects that the organic matter content of the salt recovered by directly adopting membrane distillation, mechanical vapor recompression or multi-effect evaporation concentration crystallization is high and the salt can not be sold, avoids the recovered salt from being mixed salt and becoming solid waste, and also avoids the defects that the stable operation of a biochemical system is influenced by overhigh salinity. The invention not only solves the problem of waste water, but also recycles water and salt in the waste water, and has great application potential.

Description

Low-cost treatment and recycling method for high-salt-content gas field water
Technical Field
The invention belongs to an electrodialysis desalination technology, and particularly relates to a low-cost treatment and recycling method for high-salt-content gas field water.
Background
Gas field water is formation water carried out of gas wells with natural gas during natural gas production and condensate water produced during gas collection and production. The composition of gas field water in different areas is very different, even if the same gas field is used, the water quality and the water quantity of the gas field water at different time are also very different, the mineralization degree is generally tens of thousands to hundreds of thousands mg/L, and the COD value is dozens to thousands of mg/L.
Gas field water reinjection is the main treatment method at present, and comprises units of coagulation, filtration and fine filtration. The gas field water reinjection well needs to have the following conditions: (1) the water storage space is large; the water is not blown to the ground after being injected; (3) ground cracks and holes develop and have good permeability; (4) the distance from the water outlet well is short, and the ground construction investment is small. It is becoming increasingly difficult to find suitable reinjection wells, especially for new production fields. Some researchers adopt combined processes of coagulating sedimentation, air flotation, filtration, catalytic oxidation, oxidation of potassium permanganate, sodium hypochlorite, Fenton and the like, adsorption, biological treatment and the like to treat gas field water, but at present, industrialization cannot be realized due to high cost or immature technology.
On the other hand, gas field water is a comprehensive liquid mineral resource, so that potential economic benefits are achieved, and a plurality of researchers develop gas field water comprehensive utilization technologies. With the development of scientific technology, more and more chemical elements in gas field water will be developed and utilized. The comprehensive utilization of gas field water in China is mainly evaporation salt production, including natural evaporation and heating evaporation (mechanical vapor recompression, multi-effect evaporation and the like), wherein the former produces a lot of waste salt, so that the environmental protection pressure is higher and higher, and the latter is difficult to adopt due to high investment cost and operation cost.
The Chinese patent with application number 201010148428.2 discloses an oil and gas field wastewater treatment method, which comprises the steps of firstly grinding, granulating and calcining a precious metal salt and a silicate mineral to prepare a catalyst, then adding the catalyst, ferrous sulfate or aluminum sulfate into wastewater to precipitate poly-iron or poly-aluminum, reducing 20-80 g/L of chloride ions to 500-1000 mg/L, and reducing more than 10 g/L of COD to 2 g/L.
The Chinese patent with application number 201110022282.1 discloses a method for desalting high-salinity wastewater of an oil and gas field in exploration, production and transportation of petroleum and natural gas, which comprises the steps of firstly removing hardness by adopting alkali and carbonate, then adding a flocculating agent to coagulate organic matters, then removing the organic matters and colloid by using ultrafiltration, and finally passing through a reverse osmosis membrane, wherein the filtered water is discharged after reaching the standard.
The Chinese patent with application number of 201310273856.1 discloses a novel process for zero discharge of natural gas field development sewage, which comprises the steps of classifying the gas field sewage in detail, introducing the sewage containing COD into a biochemical treatment unit, introducing saline water into an electrodialysis unit, and introducing gas field water into a pretreatment unit; and the electrodialysis concentrated water and the gas field water treated by the pretreatment unit enter an evaporation crystallization unit for advanced treatment, and the crystallized salt is buried or recycled to realize zero emission.
The Chinese patent application No. 201510270918.2 discloses a treatment method of gas field water with high salt content, high ammonia nitrogen content and COD, which comprises the steps of firstly adding NaOH and sodium carbonate to precipitate calcium and magnesium ions, then removing ammonia nitrogen by fractional evaporation and oxidation, and finally removing COD by electrolytic catalytic oxidation.
The Chinese patent with application number of 201510553613.2 discloses a treatment system and a treatment process for recycling high-salt-content fracturing flow-back fluid and gas field water.
The invention discloses a Chinese patent with application number of 201510557355.5, and discloses a high-salt-content fracturing flow-back fluid and gas field water surface discharge system and a process.
In conclusion, the water mineralization of the gas field is very high, the COD value is dozens to thousands of mg/L, and a proper reinjection well is increasingly difficult to find; the evaporation crystallization is adopted to generate a large amount of mixed salt which can only be basically buried, the alkali, carbonate and sulfate are used for removing calcium and magnesium ions, the concentration of the calcium and magnesium ions is high, the yield is high, slag is too high, the mixed salt is difficult to use, the catalytic oxidation is carried out, and the oxidation of potassium permanganate, sodium hypochlorite, Fenton and the like faces too high cost. With the stricter and stricter requirements on environmental protection, the treatment of gas field water becomes a negative factor restricting the development of natural gas extraction enterprises, affects the development of new gas fields, and further affects the production of established gas fields.
Disclosure of Invention
In order to solve the problems existing in gas field water treatment, the invention provides a low-cost treatment and resource technology for high-salt-content gas field water by introducing an electrodialysis technology to separate salt from COD (chemical oxygen demand) in wastewater and separating the salt in the wastewater.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for treating high-salt-content gas field water at low cost and recycling the high-salt-content gas field water comprises the steps of separating salt in wastewater from COD wastewater through electrodialysis; performing double decomposition on the salt which is easy to scale in the wastewater by adopting nanofiltration-electrodialysis to generate soluble salt; or mixing salt in the wastewater by using divalent selective electrodialysis and concentrating; the salt water extracted by the various modes further adopts membrane distillation, mechanical steam recompression or multi-effect evaporation concentration crystallization to recover industrial salt, and the extracted COD wastewater is reused and discharged after COD is further removed by adopting a biochemical method.
The extracted COD wastewater is discharged after reaching standards after further removing COD by adopting a biochemical method, or returned to an electrodialysis device for recycling.
And the anion or cation exchange membrane adopted in the electrodialysis process is a homogeneous membrane or a heterogeneous membrane.
The high-salinity high-COD gas field water wastewater to be treated enters an electrodialysis diluting chamber in an electrodialysis mode, salt in the gas field water wastewater (diluting chamber) is desalted through an electrodialysis anion-cation exchange membrane under the action of an electric field, the salt water enters a concentration chamber with the conductivity of 100 mus/cm-80 ms/cm, and the salt in the wastewater and the COD wastewater are separated and treated. The electrodialysis is characterized in that anion-cation exchange membranes and cation-anion exchange membranes are alternately arranged to form a thick chamber and a thin chamber.
The gas field water wastewater with strong scaling tendency enters a nanofiltration membrane, SO that the wastewater is divided into a monovalent salt solution and a monovalent and divalent mixed salt solution, the two solutions respectively enter a dilute chamber of electrodialysis for further double decomposition, and SO is generated under the action of an electric field4 2-、S2-Binding of equi-scaling anions to sodium ions, Ca2+、Mg2+Combining the easy-scaling cations with chloride ions to generate soluble salt solution; so that the waste water is treated. The electrodialysis is characterized in that anion-cation exchange membranes and cation-anion exchange membranes are alternately arranged to form a thick chamber and a thin chamber.
And the high-salt low-COD gas field water wastewater enters a divalent selective electrodialysis diluting chamber, and the salt in the gas field water (diluting chamber) is subjected to the analysis and concentration of mixed salt through an ion exchange membrane of the electrodialysis and the divalent selective ion exchange membrane under the action of an electric field, so that the wastewater is treated. The divalent selective electrodialysis comprises 2n cation exchange membranes and n anion exchange membranes, wherein each cation exchange membrane comprises a cation exchange membrane and a divalent selective cation exchange membrane, or the 2n anion exchange membranes and the n cation exchange membranes are alternately arranged, and each anion exchange membrane comprises an anion exchange membrane and a divalent selective anion exchange membrane to form 2n dilute chambers and n concentrate chambers.
Applying voltage between two electrode plates of electrodialysis, wherein the voltage of single membrane is 0.1-5.0V, and the electrolyte in the two electrodes is Na with concentration of 0.01-2M2SO4A solution; the water inlet temperature of the electrodialysis thick chamber and the electrodialysis thin chamber is 10-60 ℃, and the flow rate is 1-100 cm/s.
The electrodialysis concentration chamber is tap water, regenerated water or low-concentration brine; wherein the conductivity of the inlet water of the concentration chamber is 100 mu s/cm-80 ms/cm. Wherein, when the water inlet of the electrodialysis concentration chamber is low-concentration brine, the concentration of the brine is lower than that of the corresponding gas field water to be treated.
In the electrodialysis process, the anion exchange membrane is quaternary ammonium type anion exchange membrane, the cation exchange membrane is sulfonic acid type cation exchange membrane, and the thickness of a divalent selective ion exchange membrane (commercially available) is about 0.05-0.75 mm, and the resistance is 0.5-40 omega.cm2(ii) a The thickness of the baffle plate and the flow channel is about 0.1-1 mm.
The invention has the following advantages:
the invention adopts electrodialysis technology to separate salt and COD, adopts nanofiltration-electrodialysis technology to double decompose salt which is easy to scale to generate soluble salt, adopts divalent selective electrodialysis to separate and concentrate mixed salt, further adopts membrane distillation, mechanical steam recompression or multi-effect evaporation concentration crystallization to extract salt water to recover industrial salt, and further adopts a biochemical method to further remove COD in the residual COD wastewater for recycling and discharging. The defects that natural evaporation, multi-effect evaporation and the like are adopted to obtain salt with high organic matter content, salt is mixed salt and cannot be sold to form solid waste, and the stable operation of a biochemical system is influenced due to overhigh salinity are avoided; the invention not only solves the problem of waste water, but also recycles water and salt in the waste water, has great application potential, and can realize industrial application.
Description of the drawings:
FIG. 1 is a diagram of the process for electrodialysis separation of salt and COD according to the present invention (CM and AM stand for cation and anion exchange membranes, respectively).
FIG. 2 is a flow diagram of a gas field water treatment process of the present invention. The extracted brine is further subjected to membrane distillation, mechanical steam recompression or multi-effect evaporation concentration crystallization to recover industrial salt, and the water is returned to the electrodialysis device for recycling; the COD wastewater is further discharged or recycled after COD is removed by a biochemical method.
FIG. 3 is a graph showing the relationship between (a) COD (b) conductivity and operation time in the field water (weak chamber) and the regenerated water (rich chamber) in accordance with example 1 of the present invention. The fresh room water is gas field water, the main components are NaCl and oil, and the concentrated room water is regenerated water.
FIG. 4 shows Na in the first concentrating chamber in (a) according to embodiment 2 of the present invention+With Ca2+(b) Cl in the second concentrating chamber-With SO4 2-And operating time (c) process flow diagram. The nanofiltration penetrating fluid enters an electrodialysis first diluting chamber (D1), and the main component is NaCl; the nanofiltration trapped fluid enters an electrodialysis second diluting chamber (D2) and mainly comprises NaCl and CaSO4(ii) a The inlet water of the first and second concentration chambers is regenerated water.
FIG. 5 shows Na in (a) a first diluting chamber, (b) a second diluting chamber and (c) a concentrating chamber in an embodiment 3 of the present invention+With Mg2+Concentration versus operating time. The first fresh room is filled with gas field water containing NaCl and MgCl as main components2(ii) a The second dilute chamber is filled with water and is NaCl water solution; the inlet water of the concentration chamber is regenerated water.
FIG. 6 shows an example of the present invention, which can be applied industrially.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
The invention is further illustrated by the following examples, it is to be understood that the scope of the invention as claimed is not limited to the specific embodiments, and modifications made by researchers and technicians in accordance with the invention are also within the scope of the invention.
The electrodialysis process comprises the following steps: applying voltage between the two polar plates, wherein the voltage of the single membrane pair is 0.1-5.0V; introducing high-salt gas field water into electrodialysis fresh room, introducing tap water/regenerated water/low-concentration salt solution into concentration room to carry salt, and introducing Na into electrode room2SO4And (3) solution. Under the action of electric field, the salt in gas field water (dilute chamber) can be passed through anion-cation exchange membrane and fed into the running water/regenerated water/low-concentration salt solution chamber (concentrated chamber), and the COD in the gas field water can not be passed through the ion-exchange membrane due to that the oil is uncharged. The nanofiltration-electrodialysis process is that gas field water is divided into a monovalent salt solution and a monovalent and divalent mixed salt solution through nanofiltration, the monovalent salt solution enters a dilute chamber 1 for electrodialysis, the monovalent and divalent mixed salt solution enters a dilute chamber 2 for electrodialysis, and tap water/regenerated water/low-concentration salt solution is input into both the dense chambers 1 and 2. And (3) carrying out double decomposition on the easily-scaling salt under the action of an electric field to generate the easily-soluble salt. The divalent selective electrodialysis process is that gas field water enters a dilute chamber 1 of electrodialysis, a replacement salt solution enters a dilute chamber 2 of electrodialysis, and tap water/regenerated water/low-concentration salt solution is input into a dense chamber. Under the action of an electric field, the mixed salt is analyzed and concentrated. The process avoids the defects that the organic matter content of the salt recovered by directly adopting membrane distillation, mechanical vapor recompression or multi-effect evaporation concentration crystallization is high and the salt can not be sold, avoids the recovered salt from being mixed salt and becoming solid waste, and also avoids the defects that the stable operation of a biochemical system is influenced by overhigh salinity. The invention not only solves the problem of waste water, but also recycles water and salt in the waste water, and has great application potential.
It should be noted that during the electrodialysis operation, the anode membrane is more resistant to acid and alkali corrosion and oxidation than the cathode membrane, and in order to avoid damage of the electrode reaction to the anion exchange membrane, the membranes adjacent to the anode and cathode plates are all cation exchange membranes. In the following electrodialysers, the membranes adjacent to the anode and cathode plates are cation exchange membranes.
Example 1 (high salt high COD gas field water)
The gas field water comprises the following components: NaCl content 5.2 wt.%, COD 4600 mg/L.
The electrodialyzer comprises a pair of positive and negative polar plates, 2 anion exchange membranes, 3 cation exchange membranes, 2 separators between the cation exchange membranes and the polar plates, and 4 flow channels between the cation exchange membranes and the anion exchange membranes. The positive membrane is a sulfonic acid type homogeneous cation exchange membrane, the thickness is about 0.130 mm, and the resistance is 9.9 omega cm2The water content is 25%; the negative membrane is quaternary ammonium type homogeneous anion exchange membrane with thickness of about 0.150 mm and resistance of 11.6 omega cm2The water content is 35 percent; the area of a single membrane is about 0.03 m2. The thickness of the partition and the flow channel is about 0.5 mm in 0.1M Na2SO4The solution is polar liquid, a voltage of 1.12V is applied between two polar plates of the electrodialyzer, the single membrane pair voltage is 0.56V, and the current density is 180A/m2. The inlet water of the concentration chamber is regenerated water.
Passing the wastewater to be treated through the electrodialyzer dilute chamber at a feed temperature of 25 ℃ and a flow rate of 10 cm/s for repeated desalination treatment (the wastewater enters a wastewater storage tank after the electrodialysis treatment and circularly enters the electrodialyzer again); the experiment was stopped until the conductivity dropped below 1ms/cm, resulting in a conductivity of the desalted wastewater (dilute chamber) of 0.824 ms/cm and a COD of 5100 mg/L. The inlet water of the concentration chamber is regenerated water, the water temperature is 25 ℃, and the flow rate is 10 cm/s; the concentrated chamber receives the salt transferred from the dilute chamber to obtain saline water, the conductivity is about 234 ms/cm, and the COD is 123 mg/L. The relationship between the conductivity of (a) COD (b) and the operation time in the gas field water (dilute chamber) and the regenerated water (concentrated chamber) is shown in figure 3.
The conductivity of the wastewater in the dilute chamber decreased from 78 to 0.824 ms/cm and the COD increased from 4600 to 5100 mg/L, because sodium ions migrate from the dilute chamber to the dense chamber through the cation membrane in the form of hydrated ions, resulting in a reduction of the water content in the dilute chamber of about 10%; while the conductivity of the dense chamber brine increased from 1.2 to 234 ms/cm (15.5 wt.%), the COD increased from 0 to 123 mg/L. The obtained brine is directly fed into an evaporative crystallizer for crystallization to obtain NaCl industrial salt, the purity of the NaCl industrial salt is more than 99.1 percent, and the industrial salt meets the standard of high-grade refined industrial salt-industrial dry salt (GB/T5462-; the COD wastewater has extremely low salt content and can be subjected to biochemical treatment.
Example 2 (high salt easy scaling gas field water, nanofiltration-electrodialysis)
The gas field water comprises the following components: NaCl content 5.8 wt.%, CaSO4The content was 1.36 g/L.
The operating pressure of the nanofiltration membrane separator is 12 bar, and the effective membrane area is 214.5 cm2The recovery rate was about 76%. The gas field water was nanofiltered to become a retentate and a permeate with the compositions shown in table 1.
The electrodialyzer comprises a pair of positive and negative polar plates, 10 anion exchange membranes, 11 cation exchange membranes, 2 separators between the cation exchange membranes and the polar plates, and 20 flow channels between the cation exchange membranes and the anion exchange membranes. The positive membrane is a sulfonic acid type homogeneous cation exchange membrane, the thickness is about 0.130 mm, and the resistance is 9.9 omega cm2The water content is 25%; the negative membrane is quaternary ammonium type homogeneous anion exchange membrane with thickness of about 0.150 mm and resistance of 11.6 omega cm2The water content is 35 percent; the area of a single membrane is about 0.03 m2. The thickness of the partition and the flow channel is about 0.5 mm in 0.1M Na2SO4The solution is polar liquid, 5.6V voltage is applied between two polar plates of the electrodialyzer, the single membrane pair voltage is 0.56V, and the current density is 60A/m2. The inlet water of the concentration chamber is regenerated water.
After passing the gas field water through a nanofiltration membrane separator at a feed temperature of 25 ℃ and a flow rate of 80L/h, the permeate enters a first electrodialysis weak chamber (D1), the retentate enters a second electrodialysis weak chamber (D2), the regenerated water enters first and second concentration chambers (C1 and C2), and D1 and D2 undergo double decomposition in C1 and C2; the circulation operation is carried out until the conductivity of the effluent water of C1 and C2 is reduced to below 1ms/cm, and the experiment is stopped. The conductivity of the gas field water penetrating liquid in D1 is reduced from 204 to 0.89 ms/cm, and the conductivity of the gas field water retaining liquid in D2 is reduced from 204 to 0.93 ms/cm. The inlet water of the concentration chamber is regenerated water, the water temperature is 25 ℃, the flow rate is 10 cm/s, and the conductivity of the regenerated water in C1 and C2 is increased from 1.2 to 204 ms/cm. Referring to FIG. 4, (a) Na in the first concentrating chamber+With Ca2+(b) Cl in the second concentrating chamber-With SO4 2-And operating time. The nanofiltration penetrating fluid enters an electrodialysis first diluting chamber (D1), and the main component is NaCl; the nanofiltration trapped fluid enters an electrodialysis second diluting chamber (D2) and mainly comprises NaCl,CaSO4(ii) a The inlet water of the first and second concentration chambers is regenerated water.
The C1 saline water obtained above is CaCl2Mixing with NaCl solution (concentration of 4.55 g/L and 138.7 g/L), evaporating at high temperature for crystallization to obtain NaCl crystal, cooling for crystallization to obtain CaCl2A crystal; c2 the saline solution is Na2SO4Mixing with NaCl solution (concentration of 5.84 g/L and 143.5 g/L respectively), evaporating at higher temperature for crystallization to obtain NaCl crystal, cooling for crystallization to obtain Na2SO4And (4) crystals.
TABLE 1 composition of the materials before and after nanofiltration treatment
Composition/ppm Nanofiltration feed Nanofiltration permeate Nanofiltration retentate
Ca
2+ 400 8 1641
Na+ 22800 12768 54568
Cl- 35141 19679 84104
SO4 2- 960 19 3939
Example 3 (Low COD a divalent ion wastewater)
The gas field water comprises the following components: NaCl content 6.6 wt.%, MgCl2Content 3.9 wt.%.
The electrodialyzer comprises a pair of positive and negative polar plates, 11 cation exchange membranes, 11 divalent selective cation exchange membranes, 10 anion exchange membranes, 2 clapboards between the ion exchange membranes and the polar plates, 11 flow channels between the cation exchange membranes and the divalent selective cation exchange membranes, 10 flow channels between the divalent selective cation exchange membranes and the anion exchange membranes, and 10 flow channels between the cation exchange membranes and the anion exchange membranes. The positive membrane is a heterogeneous cation exchange membrane with a thickness of about 0.40 mm and a resistance of 30 omega cm2The water content is 40 percent; a divalent selective cation exchange membrane is a commercial product, and has a thickness of about 0.2 mm and a resistance of about 6 Ω -cm2(ii) a The negative membrane is a quaternary ammonium type heterogeneous anion exchange membrane, the thickness is about 0.45 mm, and the resistance is 31.6 omega-cm2The water content is 40 percent; the area of a single membrane is about 0.03 m2. The thickness of the partition and the flow channel is about 0.5 mm in 0.1M Na2SO4The solution is polar liquid, a voltage of 20V is applied between two electrodialyzed polar plates, the voltage of a single membrane pair is 2.0V, and the current density is 100A/m2
The wastewater to be treated passes through the electrodialysis first dilute chamber (D1) at the feeding temperature of 25 ℃ and the flow rate of 10 cm/s, the NaCl solution enters the electrodialysis second dilute chamber (D2), the regenerated water enters the concentrate chamber (C), and the experiment is stopped until the conductivity is reduced to below 1 ms/cm. The gas field water conductivity in the first dilute chamber decreased from 165.3 to 0.99 ms/cm; the aqueous NaCl solution in the second diluting chamber is gradually replaced by MgCl2Aqueous solution, conductivity from103 becomes 104 ms/cm. The inlet water of the concentration chamber is regenerated water, the water temperature is 25 ℃, the flow rate is 10 cm/s, the outlet water is NaCl aqueous solution, and the conductivity is increased from 1.2 to 164.5 ms/cm. See FIG. 5 for Na in (a) first fade chamber (b) second fade chamber (c) dense chamber+With Mg2+Concentration versus operating time.
The brine obtained from the second dilute chamber and the concentrated chamber directly enters an evaporative crystallizer for crystallization to obtain MgCl2And NaCl industrial salt with purity of 63% and 97.7% respectively, which meets the white industrial magnesium chloride standard (QB/T2605-.
Example 4 (Industrial example)
The gas field water comes from a gas well of a certain oil and gas company and mainly comprises the following components: 6.6 wt.% NaCl content, CaCl2The content is 3.88 wt.%, COD is 4600 mg/L, SO4 2-、S2-The contents of Fe and Ni are very low.
The electrodialyzer comprises a pair of positive and negative polar plates, 200 anion exchange membranes, 201 cation exchange membranes, 201 divalent selective cation exchange membranes, 2 separators between the cation exchange membranes and the polar plates, 201 flow channels between the cation exchange membranes and the divalent selective cation exchange membranes, 200 flow channels between the divalent selective cation exchange membranes and the anion exchange membranes, and 200 flow channels between the cation exchange membranes and the anion exchange membranes. The positive membrane is a sulfonic acid type homogeneous cation exchange membrane, the thickness is about 0.130 mm, and the resistance is 9.9 omega cm2The water content is 25%; a divalent selective cation exchange membrane is a commercial product, and has a thickness of about 0.15 mm and a resistance of about 2.5 Ω -cm2(ii) a The negative membrane is a quaternary ammonium type homogeneous anion exchange membrane, the thickness of the negative membrane is about 0.150 mm, and the resistance is 11.6 omega-cm2The water content is 35 percent; the area of a single membrane is about 0.8 m2. The thickness of the partition and the flow channel is about 0.5 mm in 0.1M Na2SO4The solution is polar liquid, 110V voltage is applied between two polar plates of the electrodialyzer, the single membrane pair voltage is 0.55V, and the current density is 180A/m2
Passing the gas field water through electrodialysis at a feed temperature of 25 deg.C and a flow rate of 10 cm/sA diluting chamber (D1), the salt solution enters an electrodialysis second diluting chamber (D2), the regenerated water enters a concentrating chamber (C), and the effluent water of the D1, the D2 and the C chamber is collected. The gas field water conductivity in the first dilute chamber decreased from 158.4 to 0.95 ms/cm; the salt solution in the second dilute chamber is gradually replaced by MgCl2Aqueous solution, conductivity changed from 63 to 67 ms/cm. The inlet water of the concentration chamber is regenerated water, the water temperature is 25 ℃, the flow rate is 10 cm/s, the outlet water is NaCl aqueous solution, the conductivity is increased from 1.2 to 155 ms/cm, and the process flow is shown in figure 6.
The COD wastewater obtained from the first diluting chamber enters a biochemical pool; directly feeding the brine obtained in the second diluting chamber into an evaporative crystallizer for crystallization to obtain CaCl2Industrial salt, purity>94 percent and meets the I-type anhydrous calcium chloride standard (GB/T26520-; the brine obtained in the concentration chamber is evaporated and crystallized to obtain NaCl industrial salt which meets the standard of high-grade refined industrial salt-industrial dry salt (GB/T5462-.

Claims (5)

1. A low-cost treatment and recycling method for high-salt-content gas field water is characterized by comprising the following steps: separating the brine and the COD wastewater in the wastewater by electrodialysis on the high-salt-content gas field water; further adopting membrane distillation, mechanical steam recompression or multi-effect evaporation concentration crystallization to recover industrial salt from the brine extracted from the wastewater, and further removing COD from the extracted COD wastewater by adopting a biochemical method for recycling and discharging;
when the high-salt-content gas field water is the gas field water wastewater to be treated and easy to scale, the wastewater enters a nanofiltration membrane, SO that the wastewater is divided into a monovalent salt solution and a monovalent and divalent mixed salt solution, the two solutions respectively enter different dilute chambers of electrodialysis for further double decomposition, and anions SO easy to scale are easy to scale under the action of an electric field4 2-、S2-Cation Ca combined with sodium ion and easy to scale2+、Mg2+Combined with chloride ions to generate soluble salt solution; treating the wastewater;
when the high-salt-content gas field water is high-salt low-COD gas field water wastewater, the wastewater enters a first dilute chamber of divalent selective electrodialysis, a replacement salt solution enters a second dilute chamber of the divalent selective electrodialysis, tap water or regenerated water is input into a dense chamber, the wastewater enters a dilute chamber of the divalent selective electrodialysis, and under the action of an electric field, salt in the wastewater is subjected to analysis and concentration by an ion exchange membrane of the electrodialysis and a divalent selective ion exchange membrane, so that the wastewater is treated;
the divalent selective electrodialysis is characterized in that 2n cation exchange membranes and n anion exchange membranes are alternately arranged, each cation exchange membrane comprises an electrodialysis cation exchange membrane and a divalent selective cation exchange membrane, or the 2n anion exchange membranes and the n cation exchange membranes are alternately arranged, each anion exchange membrane comprises an electrodialysis anion exchange membrane and a divalent selective anion exchange membrane, and n first fade chambers, n second fade chambers and n concentration chambers are formed.
2. The method for low-cost treatment and reclamation of high-salinity gas field water according to claim 1, wherein the method comprises the following steps: the extracted COD wastewater is discharged after reaching standards after further removing COD by adopting a biochemical method, or returned to an electrodialysis device for recycling.
3. The method for low-cost treatment and reclamation of high-salinity gas field water according to claim 1, wherein the method comprises the following steps: and the anion or cation exchange membrane adopted in the electrodialysis process is a homogeneous membrane or a heterogeneous membrane.
4. The method for low-cost treatment and reclamation of high-salinity gas field water according to claim 1, wherein the method comprises the following steps: applying voltage between two electrode plates of electrodialysis, the voltage of single membrane is 0.1-5.0V, and the electrolyte in the two electrode plates is Na with concentration of 0.01-2M2SO4And (3) solution.
5. The method for low-cost treatment and reclamation of high-salinity gas field water according to claim 1, wherein the method comprises the following steps: the conductivity of the inlet water of the concentration chamber is 100 mu s/cm-80 ms/cm.
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