Method and device for treating produced water from a sulphur-containing gas field

Abstract

The present application relates to a treatment method and a treatment device for sulfur-containing gas field produced water, and belongs to the technical field of gas field produced water treatment. The treatment method for sulfur-containing gas field produced water provided by the present application first uses hydrogen peroxide to perform first oxidation treatment on the sulfur-containing gas field produced water, removes most of the sulfides in the produced water, and ensures that there is no residual hydrogen peroxide in the treated water; then uses water-soluble sodium hypochlorite to perform second oxidation treatment on the treated water, further removes the remaining sulfides completely, and simultaneously reduces COD cr and ammonia nitrogen, and ensures that there is no sodium hypochlorite in the purified water. The treatment method for sulfur-containing gas field produced water provided by the present application not only has strong on-site adaptability, but also has water quality of the purified water that is beneficial to subsequent deep treatment and resource recycling. The treatment method for sulfur-containing gas field produced water provided by the present application has the advantages of simple process, energy saving, time saving, and high efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a treatment method and device for high-sulfur gas field produced water, and belongs to the technical field of gas field produced water treatment. BACKGROUND

[0002] High-sulfur gas field produced water mainly includes formation water produced by high-sulfur gas wells, as well as sewage from gas well acidizing stimulation, acid cleaning of gas pipelines, gas well sulfur dissolution and plugging removal, batch treatment of gas pipelines, and sand flushing of ground containers, etc. The characteristics of high-sulfur gas field produced water are high sulfide content, high COD cr content, high ammonia nitrogen content, strong corrosiveness, high risk, and strong pollution. The quality of high-sulfur gas field produced water is complex and varies greatly, with a pH range of 2.0-13.0, a sulfide content range of 500-5000 mg / L, a COD cr content range of 1500-6000 mg / L, and an ammonia nitrogen content range of 100-800 mg / L.

[0003] For the treatment of high-sulfur gas field produced water, the traditional purpose is to remove the hazardous and toxic sulfide, and methods such as flashing, air flotation, and chemical oxidation are used for sulfide removal and purification. The treated water is then reinjected into deep formations for disposal. However, with increasingly stringent environmental requirements, more and more attention is being paid to reducing COD cr and ammonia nitrogen, thereby changing from reinjection after treatment to resource utilization after deep treatment.

[0004] Chinese patent document CN211339121U discloses a high-sulfur oil and gas field sewage treatment system, which uses a combination of pressure reduction flashing and chemical oxidation to remove hydrogen sulfide in the sewage, achieving the purposes of sulfur removal and sewage purification. Chinese patent document CN102863097B discloses a standard-compliant treatment and reinjection method for high-sulfur oil and gas field sewage containing sulfur. First, the high-sulfur sewage is subjected to air flotation pretreatment in a closed air flotation tank to remove oil, part of the suspended solids, and hydrogen sulfide gas phase substances in the sewage. Then, the air flotation pretreated sewage is pumped into a dosing device, and an oxidizing desulfurizer, a coagulant, and a flocculant are sequentially added and fully stirred for desulfurization and coagulation treatment. However, the above method cannot completely remove the sulfide in the sewage, and the sulfide content is reduced to 0 mg / L. Moreover, residual oxidizing desulfurizer remains in the treated produced water. If the sulfide in the sewage cannot be completely removed, the sulfide is prone to overflow, causing poisoning of personnel or triggering the hydrogen sulfide alarm system, which seriously affects safety production. If residual oxidizing desulfurizer remains, it significantly increases the corrosiveness of the water treatment system, and is also very unfavorable for subsequent deep treatment and resource utilization.

[0005] The Chinese patent document with the publication number CN107686196B discloses a resourceful treatment method for high-sulfur wastewater in oil and gas fields. The method uses negative pressure desulfurization, chemical catalytic oxidation, flocculation and sedimentation, organic membrane filtration, ozone catalytic oxidation, activated carbon adsorption, new electrodialyzer fractionation concentration, and crystallization technology to treat high-sulfur wastewater in oil and gas fields, realizing the resource utilization of high-sulfur wastewater in oil and gas fields. The Chinese patent document with the publication number CN108128983B discloses a deep purification treatment process for high-sulfur and high-salt produced water in gas fields. The high-sulfur produced water in gas fields enters a natural sedimentation unit, a flotation and coagulation sedimentation unit, an evaporation crystallization unit, a high-level oxidation unit, and a biochemical treatment unit in sequence. The effluent water quality meets the standard and is recycled. However, the chemical catalytic oxidation, ozone catalytic oxidation, activated carbon adsorption, high-level oxidation unit, and biochemical treatment unit in the above treatment methods all reduce COD cr and ammonia nitrogen, resulting in a long treatment process, high energy consumption, and low efficiency. SUMMARY

[0006] The present application aims to provide a treatment method for high-sulfur produced water in gas fields, which solves the problems of time-consuming, energy-consuming, and low efficiency in treating high-sulfur produced water in gas fields.

[0007] Another object of the present application is to provide a treatment device for high-sulfur produced water in gas fields.

[0008] To achieve the above object, the technical solution of the treatment method for high-sulfur produced water in gas fields of the present application is as follows:

[0009] A treatment method for high-sulfur produced water in gas fields, comprising the following steps:

[0010] (1) detecting whether the pH of the high-sulfur produced water in gas fields is 6.0-8.0, and if not, adjusting the pH of the high-sulfur produced water in gas fields to 6.0-8.0;

[0011] (2) using hydrogen peroxide to perform first oxidation treatment on the high-sulfur produced water in gas fields obtained in step (1), to obtain treated water with an oxidation-reduction potential of -200 mV to +200 mV;

[0012] (3) using water-soluble hypochlorite to perform second oxidation treatment on the treated water, to obtain purified water; the ratio of the molar amount of chlorine element in the water-soluble hypochlorite to the molar amount of sulfide in the treated water is (8-30):1.

[0013] The treatment method of the sulfur-containing gas field produced water in the application first uses hydrogen peroxide to perform first oxidation treatment on the sulfur-containing gas field produced water with pH of 6.0-8.0, removes most of the sulfides in the produced water (sulfide removal rate is 85%-99%), and can ensure that there is no residual hydrogen peroxide in the treated water, then uses water-soluble sodium hypochlorite to perform second oxidation treatment on the treated water, which can further completely remove the remaining sulfides, and at the same time can reduce COD cr and ammonia nitrogen, and can ensure that there is no sodium hypochlorite in the purified water. Since there is no residual hydrogen peroxide in the treated water, the corrosion of the treated water on the equipment in the subsequent treatment process can be avoided. The treatment method of the sulfur-containing gas field produced water in the application not only has strong on-site adaptability, but also the quality of the purified water obtained is beneficial to the subsequent deep treatment and resource recycling. The treatment method of the sulfur-containing gas field produced water in the application has the advantages of simple process, energy saving, time saving and high efficiency.

[0014] In the application, the sulfide content is determined by methylene blue spectrophotometry (the specific determination method can refer to standard HJ 1226-2021), and the result is expressed in the form of mass-volume concentration of sulfur ions (S 2- ); the hydrogen peroxide content is determined by titanium salt colorimetry; the COD cr content is determined according to standard GB / T 31195-2014 “Chemical Oxygen Demand Determination of High Chlorine and High Ammonia Wastewater-Chloride Ion Correction Method”; and the ammonia nitrogen content is determined according to standard HJ 535-2009 “Water Quality Ammonia Nitrogen Measurement-Nessler Reagent Spectrophotometry”. It can be understood that after the content of sulfide (S 2- ) is determined, the amount of substance of sulfide (S 2- ) can be obtained by calculation.

[0015] Preferably, in step (1), whether the pH of the sulfur-containing gas field produced water is 6.5-7.5 is detected, if the pH does not meet the condition, the pH of the sulfur-containing gas field produced water is adjusted to 6.5-7.5, and then the first oxidation treatment is performed again. The pH of the produced water is 6.0-8.0, which can provide the most suitable pH condition for the first oxidation treatment.

[0016] Preferably, the pH of the sulfur-containing gas field produced water is adjusted by mixing a pH regulator with the sulfur-containing gas field produced water. Preferably, the pH regulator is selected from one or any combination of sodium hydroxide, calcium hydroxide, hydrochloric acid, and sulfuric acid. Preferably, the mass fraction of the hydrochloric acid is 10% to 35%. Further preferably, the mass fraction of the hydrochloric acid is 10% to 15%. Preferably, the mass fraction of the sulfuric acid is not less than 30%. Further preferably, the mass fraction of the sulfuric acid is 30% to 50%. Preferably, the sodium hydroxide is used in the form of a sodium hydroxide solution. Preferably, the mass fraction of the sodium hydroxide solution is 10% to 50%. Further preferably, the mass fraction of the sodium hydroxide solution is 10% to 20%. For example, the mass fraction of the sodium hydroxide solution is 20%. Preferably, the calcium hydroxide is used in the form of a calcium hydroxide dispersion. Preferably, the mass fraction of the calcium hydroxide dispersion is 10% to 30%. Further preferably, the mass fraction of the calcium hydroxide dispersion is 10% to 15%.

[0017] Preferably, the first oxidation treatment is performed for 0.5 to 2 hours at a temperature of 20 to 45°C. For example, the first oxidation treatment is performed for 0.5 hours at a temperature of 35.5°C. After the first oxidation treatment, the sulfide content of the high-sulfur gas field produced water can be reduced from 500 to 5000 mg / L to 10 to 100 mg / L, and the hydrogen peroxide content of the treated water is substantially 0 mg / L.

[0018] Preferably, in step (2), after the first oxidation treatment, the treated water has an oxidation-reduction potential of -200 mV to +100 mV. Further preferably, in step (2), after the first oxidation treatment, the treated water has an oxidation-reduction potential of -100 mV to +100 mV.

[0019] Preferably, the sulfide content of the treated water is 10 to 100 mg / L. It can be understood that when the sulfide content of the treated water is 10 to 100 mg / L, the hydrogen peroxide content of the treated water is substantially 0 mg / L. By adjusting the process parameters of the first oxidation treatment, the hydrogen peroxide and the sulfide in the produced water can react in a 1:1 molar ratio, thereby ensuring that the hydrogen peroxide is not left over and is not wasted. During the first oxidation treatment, the hydrogen peroxide and the sulfide undergo an oxidation-reduction reaction, and the product generated is elemental sulfur.

[0020] Preferably, the hydrogen peroxide is used in the form of hydrogen peroxide solution. Preferably, the mass fraction of the hydrogen peroxide solution is 20% to 70%. Further preferably, the mass fraction of the hydrogen peroxide solution is 20% to 50%. For example, the mass fraction of the hydrogen peroxide solution is 27.2%.

[0021] Preferably, the ratio of the molar amount of chlorine element in the water-soluble hypochlorite to the molar amount of sulfide in the treatment water is (15-20):1.

[0022] Preferably, the water-soluble hypochlorite is an alkali metal hypochlorite. For example, the water-soluble hypochlorite is sodium hypochlorite. Preferably, the water-soluble hypochlorite is used in the form of a water-soluble hypochlorite solution. Preferably, the mass fraction of the water-soluble hypochlorite in the water-soluble hypochlorite solution is 5%-15% in terms of chlorine element. Further preferably, the mass fraction of the water-soluble hypochlorite in the water-soluble hypochlorite solution is 8%-10% in terms of chlorine element. When the water-soluble hypochlorite solution is a sodium hypochlorite solution, generally, the volume of the sodium hypochlorite solution to be used per liter of treatment water is 5-25 mL, more preferably 8-15 mL.

[0023] Preferably, the time of the second oxidation treatment is 0.5-1 h, and the temperature of the second oxidation treatment is 20-45℃. For example, the time of the second oxidation treatment is 0.5 h.

[0024] Preferably, the pH detection and adjustment of the sulfurous gas field produced water is automatically controlled. Preferably, in the first oxidation treatment, the oxidation-reduction potential is monitored, and the amount of hydrogen peroxide added is automatically controlled according to the oxidation-reduction potential.

[0025] Principle of reducing the content of sulfide, COD and ammonia nitrogen in the second treatment process cr and ammonia nitrogen in the second treatment process is as follows: by using the strong oxidizing property of hypochlorite, redox reactions with sulfide, macromolecular organic matter and ammonia nitrogen are simultaneously carried out, the sulfide is oxidized into sulfate, the macromolecular organic matter is oxidized into small molecular organic matter or carbon dioxide, and the ammonia nitrogen is oxidized into nitrogen oxide or nitrogen.

[0026] The technical scheme adopted by the sulfurous gas field produced water treatment device of the present application is as follows:

[0027] A sulfurous gas field produced water treatment device, comprising, in the direction of material flow, a pH detection and adjustment unit, a first oxidation unit and a second oxidation unit connected in sequence;

[0028] The pH detection and adjustment unit is used to detect the water quality and adjust the pH of the water to meet the requirements.

[0029] The first oxidation unit comprises a hydrogen peroxide feeding device, a first oxidation reaction device and an ORP monitor. The hydrogen peroxide feeding device is used to add hydrogen peroxide to the produced water, and the first oxidation reaction device is used to provide the produced water added with hydrogen peroxide for redox reaction to form treatment water. The ORP monitor is used to monitor the oxidation-reduction potential of the treatment water.

[0030] The second oxidation unit comprises a hypochlorite feeding device for adding hypochlorite into the treated water and a second oxidation reaction device for the treated water added with the hypochlorite to perform an oxidation-reduction reaction to form purified water.

[0031] The treatment device for the sulfur-containing produced water of a gas field has simple structure, can realize efficient treatment of the sulfur-containing produced water of a gas field, has strong on-site adaptability, and the purified water obtained by treatment is beneficial to subsequent deep treatment and resource recycling.

[0032] Preferably, the hydrogen peroxide feeding device comprises a hydrogen peroxide metering device for quantitatively adjusting the feeding amount of hydrogen peroxide. Preferably, the hydrogen peroxide metering device is a hydrogen peroxide metering pump. Preferably, the hydrogen peroxide metering pump is a variable frequency pump. Preferably, the hydrogen peroxide feeding device further comprises a hydrogen peroxide conveying pipeline, and the hydrogen peroxide metering device is arranged on the hydrogen peroxide conveying pipeline. Preferably, the hydrogen peroxide feeding device further comprises a hydrogen peroxide storage device, and a discharge port of the hydrogen peroxide storage device is connected with a liquid inlet of the hydrogen peroxide conveying pipeline.

[0033] Preferably, the hypochlorite feeding device comprises a hypochlorite metering device for quantitatively adjusting the feeding amount of hypochlorite. Preferably, the hypochlorite metering device is a hypochlorite solution metering pump. Preferably, the hypochlorite solution metering pump is a variable frequency pump. Preferably, the hypochlorite feeding device further comprises a hypochlorite solution conveying pipeline, and the hypochlorite metering device is arranged on the hypochlorite solution conveying pipeline. Preferably, the hypochlorite feeding device further comprises a hypochlorite solution storage device, and a discharge port of the hypochlorite solution storage device is connected with a liquid inlet of the hypochlorite solution conveying pipeline.

[0034] Preferably, the pH detection and adjustment unit comprises, in sequence in the material flow direction, a first pH detection device, a pH adjusting agent feeding device and a second pH detection device. The first pH detection device is used for on-line detection of the pH of the produced water. The pH adjusting agent feeding device is used for adding a pH adjusting agent into the produced water to adjust the pH of the produced water. The second pH detection device is used for detection of the pH of the produced water after the pH adjustment. Preferably, the pH adjusting agent feeding device comprises a pH adjusting agent metering device for quantitatively adjusting the feeding amount of the pH adjusting agent.

[0035] Preferably, the pH adjusting agent feeding device comprises an acid feeding device and a base feeding device. Preferably, the acid feeding device comprises an acid metering device for quantitatively adjusting the amount of acid feeding. Preferably, the base feeding device comprises a base metering device for quantitatively adjusting the amount of base feeding. Preferably, the acid metering device is an acid liquid metering pump. Preferably, the acid liquid metering pump is a variable frequency pump. Preferably, the acid feeding device further comprises an acid liquid conveying pipeline, and the acid metering device is arranged on the acid liquid conveying pipeline. Preferably, the acid feeding device further comprises an acid liquid storage device, and the discharge port of the acid liquid storage device is connected to the liquid inlet of the acid liquid conveying pipeline. Preferably, the base metering device is a base liquid metering pump. Preferably, the base liquid metering pump is a variable frequency pump. Preferably, the base feeding device further comprises a base liquid conveying pipeline, and the base metering device is arranged on the base liquid conveying pipeline. Preferably, the base feeding device further comprises a base liquid storage device, and the discharge port of the base liquid storage device is connected to the liquid inlet of the base liquid conveying pipeline.

[0036] Preferably, the pH adjusting unit further comprises a mixing device, which is arranged between the pH adjusting agent feeding device and the pH second detection device, and is a place for mixing the produced water to which the pH adjusting agent is added. Preferably, the lower part of the mixing device is provided with a liquid inlet, and the upper part is provided with a liquid outlet. Preferably, the pH adjusting unit further comprises a mixing liquid conveying pipeline for conveying the produced water to which the pH adjusting agent is added, and the liquid inlet of the mixing liquid conveying pipeline is connected to the liquid outlet of the mixing device.

[0037] Preferably, the produced water conveying pipeline, the acid liquid conveying pipeline, the first mixed liquid conveying pipeline, the base liquid conveying pipeline, the second mixed liquid conveying pipeline and the mixing device are sequentially connected in series.

[0038] Preferably, the pH first detection device is arranged on the produced water conveying pipeline, and the pH second detection device is arranged on the mixing liquid conveying pipeline.

[0039] Preferably, the lower part of the first oxidation reaction device is provided with a liquid inlet, and the upper part is provided with a treated water outlet. Preferably, the mixing liquid conveying pipeline and the hydrogen peroxide conveying pipeline are connected to the first mixed material conveying pipeline, and the liquid outlet of the first mixed material conveying pipeline is connected to the liquid inlet of the first oxidation reaction device. In order to timely detect the oxidation-reduction potential of the treated water in the first oxidation reaction device, the ORP monitor is arranged at the upper part of the first oxidation reaction device, and the liquid surface position detected by the ORP monitor is lower than the treated water outlet.

[0040] Preferably, the lower part of the second oxidation reaction device is provided with a liquid inlet, and the upper part is provided with a purified water outlet. Preferably, the sulfur-containing gas field produced water treatment device further comprises a treated water conveying pipeline, the liquid inlet of the treated water conveying pipeline being connected with the treated water outlet of the first oxidation reaction device. Preferably, the treated water conveying pipeline is connected with the hypochlorite solution conveying pipeline and the second mixed material conveying pipeline, and the liquid outlet of the second mixed material conveying pipeline is connected with the liquid inlet of the second oxidation reaction device.

[0041] Preferably, the sulfur-containing gas field produced water treatment device further comprises a purified water conveying pipeline, the liquid inlet of the purified water conveying pipeline being connected with the purified water outlet of the second oxidation reaction device.

[0042] Preferably, the sulfur-containing gas field produced water treatment device further comprises a PLC control unit, the PLC control unit being connected with the first pH detection device, the pH regulator feeding device, the second pH detection device, the hydrogen peroxide feeding device and the ORP monitor respectively to realize automatic control operation.

[0043] Preferably, the PLC control unit comprises a PLC first control module and a PLC second control module, the PLC first control module being connected with the first pH detection device, the acid metering device, the alkali metering device and the second pH detection device respectively, and the PLC second control module being connected with the hydrogen peroxide metering device and the ORP monitor respectively.

[0044] When the first pH detection device detects that the pH of the produced water is less than 6.5, the PLC first control module outputs a feedback signal to start the alkali metering pump connected with the alkali storage device to add alkali and increase the pH of the mixed liquid.

[0045] When the first pH detection device detects that the pH of the produced water is greater than 7.5, the PLC first control module outputs a feedback signal to start the acid metering pump connected with the acid storage device to add acid and reduce the pH of the mixed liquid.

[0046] In order to more accurately control the pH of the produced water, when the first pH detection device detects that the pH of the produced water is less than 6.5 and the second pH detection device detects that the pH of the mixed liquid is less than 6.0, the PLC first control module outputs a feedback signal to increase the frequency of the alkali metering pump connected with the alkali storage device to increase the amount of alkali added; when the first pH detection device detects that the pH of the produced water is less than 6.5 and the second pH detection device detects that the pH of the mixed liquid is greater than 8.0, the PLC first control module outputs a feedback signal to reduce the frequency of the alkali metering pump connected with the alkali storage device to reduce the amount of alkali added.

[0047] When the pH first detection device detects that the pH of the produced water is greater than 7.5 and the pH second detection device detects that the pH of the mixed liquid is greater than 8.0, the PLC first control module outputs a feedback signal to increase the frequency of the acid liquid metering pump connected with the acid liquid storage device, thereby increasing the amount of acid liquid feeding; when the pH first detection device detects that the pH of the produced water is greater than 7.5 and the pH second detection device detects that the pH of the mixed liquid is less than 6.0, the PLC first control module outputs a feedback signal to decrease the frequency of the acid liquid metering pump connected with the acid liquid storage device, thereby decreasing the amount of acid liquid feeding.

[0048] If the measurement value of the ORP monitor is less than -200 mV, the PLC second control module outputs a feedback signal to increase the frequency of the hydrogen peroxide metering pump connected with the hydrogen peroxide storage device, thereby increasing the amount of hydrogen peroxide feeding.

[0049] If the measurement value of the ORP monitor is greater than +200 mV, the PLC second control module outputs a feedback signal to decrease the frequency of the hydrogen peroxide metering pump connected with the hydrogen peroxide storage device, thereby decreasing the amount of hydrogen peroxide feeding. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 A schematic diagram of the produced water treatment device for the sulfur-containing gas field of Example 1; wherein the reference signs are as follows: 1-mixing tank, 2-first oxidation reactor, 3-second oxidation reactor, 4-acid liquid storage tank, 5-alkali liquid storage tank, 6-hydrogen peroxide storage tank, 7-hypochlorite solution storage tank, 8-acid liquid metering pump, 9-alkali liquid metering pump, 10-hydrogen peroxide metering pump, 11-hypochlorite solution metering pump, 12-pH first online monitor, 13-pH second online monitor, 14-ORP monitor, 15-produced water conveying pipeline, 16-mixed liquid conveying pipeline, 17-treated water conveying pipeline, 18-purified water conveying pipeline, 19-PLC first control module, 20-PLC second control module, 21-acid liquid conveying pipeline, 22-first mixed liquid conveying pipeline, 23-alkali liquid conveying pipeline, 24-first mixed material conveying pipeline, 25-second mixed liquid conveying pipeline, 26-hydrogen peroxide conveying pipeline, 27-hypochlorite solution conveying pipeline and 28-second mixed material conveying pipeline. DETAILED DESCRIPTION

[0051] The technical solutions of the present application will be further described below in combination with specific examples.

[0052] First, the specific implementation of the produced water treatment device for the sulfur-containing gas field of the present application is as follows:

[0053] Example 1

[0054] The schematic diagram of the structure of the produced water treatment device for the sulfur-containing gas field of the present embodiment is as follows: Figure 1As shown, the system comprises a produced water conveying pipeline 15, a first pH on-line monitor 12, an acid liquid storage tank 4, an acid liquid metering pump 8, an acid liquid conveying pipeline 21, a first mixed liquid conveying pipeline 22, an alkali liquid storage tank 5, an alkali liquid metering pump 9, an alkali liquid conveying pipeline 23, a second mixed liquid conveying pipeline 25, a mixing tank 1, a mixed liquid conveying pipeline 16, a second pH on-line monitor 13, a hydrogen peroxide storage tank 6, a hydrogen peroxide conveying pipeline 26, a hydrogen peroxide metering pump 10, a first mixed material conveying pipeline 24, a first oxidation reactor 2, a treated water conveying pipeline 17, a hypochlorite solution storage tank 7, a hypochlorite solution conveying pipeline 27, a hypochlorite solution metering pump 11, a second mixed material conveying pipeline 28, a second oxidation reactor 3, a purified water conveying pipeline 18, a PLC first control module 19 and a PLC second control module 20.

[0055] The first pH on-line monitor 12 is arranged on the produced water conveying pipeline 15 and used to detect the pH of the produced water in the produced water conveying pipeline 15. The acid liquid storage tank 4 is connected with the acid liquid conveying pipeline 21, and the acid liquid metering pump 8 is arranged on the acid liquid conveying pipeline 21. The acid liquid metering pump 8 is a variable frequency pump. The produced water conveying pipeline 15 and the acid liquid conveying pipeline 21 are merged and connected with the first mixed liquid conveying pipeline 22. The alkali liquid storage tank 5 is connected with the alkali liquid conveying pipeline 23, and the alkali liquid metering pump 9 is arranged on the alkali liquid conveying pipeline 23. The alkali liquid metering pump 9 is a variable frequency pump. The first mixed liquid conveying pipeline 22 is merged with the alkali liquid conveying pipeline 23 and connected with the second mixed liquid conveying pipeline 25.

[0056] The mixing tank 1 is provided with a liquid inlet at the lower part and a liquid outlet at the upper part. The liquid outlet of the second mixed liquid conveying pipeline 25 is connected with the liquid inlet of the mixing tank 1. The liquid outlet of the mixing tank 1 is connected with the liquid inlet of the mixed liquid conveying pipeline 16. The second pH on-line monitor 13 is arranged on the mixed liquid conveying pipeline 16 and used to detect the pH of the mixed liquid.

[0057] The hydrogen peroxide storage tank 6 is connected with the hydrogen peroxide conveying pipeline 26, and the hydrogen peroxide metering pump 10 is arranged on the hydrogen peroxide conveying pipeline 26. The hydrogen peroxide metering pump 10 is a variable frequency pump. The mixed liquid conveying pipeline 16 and the hydrogen peroxide conveying pipeline 26 are merged and connected with the first mixed material conveying pipeline 24.

[0058] The first oxidation reactor 2 is provided with a liquid inlet at the lower part and a treated water outlet and an ORP monitor 14 at the upper part. The liquid surface position that can be detected by the ORP monitor 14 is lower than the treated water outlet. The liquid inlet of the first oxidation reactor 2 is connected with the liquid outlet of the first mixed material conveying pipeline 24, and the liquid outlet of the first oxidation reactor 2 is connected with the liquid inlet of the treated water conveying pipeline 17.

[0059] The hypochlorite solution storage tank 7 is connected with a hypochlorite solution conveying pipeline 27, and a hypochlorite solution metering pump 11 is arranged on the hypochlorite solution conveying pipeline 27. The hypochlorite solution metering pump 11 is a variable frequency pump. The treated water conveying pipeline 17 and the hypochlorite solution conveying pipeline 27 are merged and connected with a second mixed material conveying pipeline 28.

[0060] The lower part of the second oxidation reactor 3 is provided with an inlet, and the upper part is provided with a purified water outlet. The inlet of the second oxidation reactor 3 is connected with the outlet of the second mixed material conveying pipeline 28, and the purified water outlet of the second oxidation reactor 3 is connected with the inlet of the purified water conveying pipeline 18.

[0061] The PLC first control module 19 is connected with the pH first on-line monitor 12, the acid liquid metering pump 8, the alkali liquid metering pump 9 and the pH second on-line monitor 13, respectively. When the pH first on-line monitor 12 detects that the pH of the produced water is less than 6.5, the PLC first control module 19 outputs a feedback signal to start the alkali liquid metering pump 9 connected with the alkali liquid storage tank 5 to add alkali liquid and increase the pH of the mixed liquid. When the pH first on-line monitor 12 detects that the pH of the produced water is greater than 7.5, the PLC first control module 19 outputs a feedback signal to start the acid liquid metering pump 8 connected with the acid liquid storage tank 4 to add acid liquid and reduce the pH of the mixed liquid. When the pH first on-line monitor 12 detects that the pH of the produced water is less than 6.5 and the pH second on-line monitor 13 detects that the pH of the mixed liquid is less than 6.0, the PLC first control module 19 outputs a feedback signal to increase the frequency of the alkali liquid metering pump 9 connected with the alkali liquid storage tank 5 to increase the amount of alkali liquid. When the pH first on-line monitor 12 detects that the pH of the produced water is less than 6.5 and the pH second on-line monitor 13 detects that the pH of the mixed liquid is greater than 8.0, the PLC first control module 19 outputs a feedback signal to reduce the frequency of the alkali liquid metering pump 9 connected with the alkali liquid storage tank 5 to reduce the amount of alkali liquid. When the pH first on-line monitor 12 detects that the pH of the produced water is greater than 7.5 and the pH second on-line monitor 13 detects that the pH of the mixed liquid is greater than 8.0, the PLC first control module 19 outputs a feedback signal to increase the frequency of the acid liquid metering pump 8 connected with the acid liquid storage tank 4 to increase the amount of acid liquid. When the pH first on-line monitor 12 detects that the pH of the produced water is greater than 7.5 and the pH second on-line monitor 13 detects that the pH of the mixed liquid is less than 6.0, the PLC first control module 19 outputs a feedback signal to reduce the frequency of the acid liquid metering pump 8 connected with the acid liquid storage tank 4 to reduce the amount of acid liquid.

[0062] The PLC second control module 20 is connected with the hydrogen peroxide metering pump 10 and the ORP monitor 14 respectively. If the measured value of the ORP monitor 14 is less than -200 mV, the PLC second control module 20 outputs a feedback signal to increase the frequency of the hydrogen peroxide metering pump 10 connected with the hydrogen peroxide storage tank 6, thereby increasing the dosage of hydrogen peroxide.

[0063] If the measured value of the ORP monitor 14 is greater than +200 mV, the PLC second control module outputs a feedback signal to reduce the frequency of the hydrogen peroxide metering pump 10 connected with the hydrogen peroxide storage tank 6, thereby reducing the dosage of hydrogen peroxide.

[0064] The pH first online monitor 12 is a pH first detection device, and the pH second online monitor 13 is a pH second detection device; the acid liquid metering pump 8 is an acid metering device, and the acid liquid storage tank 4 is an acid liquid storage device; the alkali liquid storage tank 5 is an alkali metering device, and the alkali liquid storage tank 5 is an alkali liquid storage device. The acid liquid storage tank 4, the acid liquid metering pump 8 and the acid liquid conveying pipeline 21 constitute an acid feeding device; the alkali liquid storage tank 5, the alkali liquid metering pump 9 and the alkali liquid conveying pipeline 23 constitute an alkali feeding device; and the acid feeding device and the alkali feeding device constitute a pH regulator feeding device. The mixing tank 1 is a mixing device. The pH first detection device, the pH regulator feeding device, the mixing device and the pH second detection device constitute a pH adjustment unit.

[0065] The hydrogen peroxide storage tank 6 is a hydrogen peroxide storage device, and the hydrogen peroxide metering pump 10 is a hydrogen peroxide metering device. The hydrogen peroxide storage tank 6, the hydrogen peroxide conveying pipeline 26 and the hydrogen peroxide metering pump 10 constitute a hydrogen peroxide feeding device. The first oxidation reactor 2 is a first oxidation reaction device, and the first oxidation reaction device and the hydrogen peroxide feeding device constitute a first oxidation unit.

[0066] The hypochlorite solution storage tank 7 is a hypochlorite solution storage device, and the hypochlorite solution metering pump 11 is a hypochlorite metering device. The hypochlorite solution storage tank 7, the hypochlorite solution conveying pipeline 27 and the hypochlorite solution metering pump 11 constitute a hypochlorite feeding device. The second oxidation reactor 3 is a second oxidation reaction device. The hypochlorite feeding device and the second oxidation reaction device constitute a second oxidation unit.

[0067] The PLC second control module 19 and the PLC second control module 20 constitute a PLC control unit.

[0068] The treatment methods of the sulfur-containing produced water in Examples 2-8 and the comparative examples below use the treatment device for the sulfur-containing produced water in Example 1 to purify the sulfur-containing produced water.

[0069] Second, the specific implementation of the treatment method for the sulfur-containing produced water in the present application is as follows:

[0070] Example 2

[0071] The treatment method of the produced water of the sulfur-containing gas field in this embodiment specifically comprises the following steps:

[0072] The pH regulator is added into the produced water of the sulfur-containing gas field, and then the produced water containing the pH regulator enters a mixing tank for mixing to obtain a mixed liquid. Then, hydrogen peroxide is added into the mixed liquid to obtain a first mixed liquid. The first mixed liquid enters a first oxidation reactor for first oxidation treatment to obtain treated water. Finally, sodium hypochlorite solution is added into the treated water to obtain a second mixed liquid. The second mixed liquid enters a second oxidation reactor for second oxidation treatment to obtain purified water.

[0073] In this embodiment, the pH of the produced water of the sulfur-containing gas field is 5.54, the sulfide content is 840.1 mg / L, the temperature is 35.5℃, the pH regulator used is a sodium hydroxide solution with a mass fraction of 20%, the mass fraction of hydrogen peroxide in the hydrogen peroxide used is 27.2%, and the mass fraction of sodium hypochlorite in the sodium hypochlorite solution is 8.78% in terms of chlorine element.

[0074] The hydrogen peroxide used corresponds to 3.31 g per liter of the mixed liquid, the pH of the mixed liquid is 6.55, the ratio of the molar amount of hydrogen peroxide in the hydrogen peroxide added per liter of the mixed liquid to the molar amount of sulfide per liter of the produced water is 1.07:1, the first oxidation treatment time is 0.5 h, the ORP value of the treated water obtained is +58.1 mV, and the sulfide content in the treated water is 57.8 mg / L.

[0075] The volume of the sodium hypochlorite solution used corresponds to 8.28 mL per liter of the treated water, i.e., the ratio of the molar amount of chlorine element in the sodium hypochlorite solution added per liter of the treated water to the molar amount of sulfide per liter of the treated water is 14.5:1, and the second oxidation treatment time is 0.5 h.

[0076] Example 3

[0077] The treatment method of the produced water of the sulfur-containing gas field in this embodiment is different from the treatment method of the produced water of the sulfur-containing gas field in Example 2 only in that, in this embodiment, the hydrogen peroxide used corresponds to 3.86 g per liter of the mixed liquid, the pH of the mixed liquid is 8.0, the ratio of the molar amount of hydrogen peroxide in the hydrogen peroxide added per liter of the mixed liquid to the molar amount of sulfide per liter of the produced water is 1.25:1, the first oxidation treatment time is 0.5 h, and the ORP value of the treated water obtained is -192.7 mV.

[0078] Example 4

[0079] The difference between the treatment method of the sulfur-containing gas field produced water of the present embodiment and the treatment method of the sulfur-containing gas field produced water of embodiment 2 is that, in the present embodiment, 3.55 g of hydrogen peroxide is used per liter of mixed solution, the pH of the mixed solution is 6.0, the ratio of the molar amount of hydrogen peroxide in the hydrogen peroxide used per liter of mixed solution to the molar amount of sulfide in the produced water per liter is 1.15:1, and the ORP value of the treated water is +97.2 mV.

[0080] Embodiment 5

[0081] The difference between the treatment method of the sulfur-containing gas field produced water of the present embodiment and the treatment method of the sulfur-containing gas field produced water of embodiment 2 is that, in the present embodiment, 5.13 mL of sodium hypochlorite solution is used per liter of treated water, i.e., the ratio of the molar amount of chlorine in the sodium hypochlorite solution added per liter of treated water to the molar amount of sulfide in the treated water per liter is 8.96:1.

[0082] Embodiment 6

[0083] The difference between the treatment method of the sulfur-containing gas field produced water of the present embodiment and the treatment method of the sulfur-containing gas field produced water of embodiment 2 is that, in the present embodiment, 10.87 mL of sodium hypochlorite solution is used per liter of treated water, i.e., the ratio of the molar amount of chlorine in the sodium hypochlorite solution added per liter of treated water to the molar amount of sulfide in the treated water per liter is 18.99:1.

[0084] Embodiment 7

[0085] The difference between the treatment method of the sulfur-containing gas field produced water of the present embodiment and the treatment method of the sulfur-containing gas field produced water of embodiment 2 is that, in the present embodiment, 14.35 mL of sodium hypochlorite solution is used per liter of treated water, i.e., the ratio of the molar amount of chlorine in the sodium hypochlorite solution added per liter of treated water to the molar amount of sulfide in the treated water per liter is 25.06:1.

[0086] Embodiment 8

[0087] The difference between the treatment method of the sulfur-containing gas field produced water of the present embodiment and the treatment method of the sulfur-containing gas field produced water of embodiment 2 is that, in the present embodiment, 16.96 mL of sodium hypochlorite solution is used per liter of treated water, i.e., the ratio of the molar amount of chlorine in the sodium hypochlorite solution added per liter of treated water to the molar amount of sulfide in the treated water per liter is 29.62:1.

[0088] Comparative Example

[0089] The difference between the treatment method of the sulfur-containing gas field produced water of the present comparative example and the treatment method of the sulfur-containing gas field produced water of Example 2 is that, in the present comparative example, the volume of the sodium hypochlorite solution used per liter of the treated water is 19.13 mL, i.e., the ratio of the molar amount of chlorine element in the sodium hypochlorite solution added per liter of the treated water to the molar amount of sulfides in the treated water is 33.42:1.

[0090] Experimental Example 1

[0091] In order to investigate the influence of the pH of the mixed solution in the first oxidation treatment on the first oxidation treatment, the sulfide content, residual hydrogen peroxide content, COD cr and ammonia nitrogen content of the treated water obtained in Examples 2-4 are listed in Table 1.

[0092] Table 1 Sulfide content, residual hydrogen peroxide content, COD cr and ammonia nitrogen content of the treated water obtained in Examples 2-4

[0093]

[0094] The results show that, when the pH of the mixed solution is 8.0, the sulfide removal rate of the first oxidation treatment is 88.3%, which is still relatively high; however, the ratio of the sulfide reduction amount to the hydrogen peroxide consumption amount is only 70.6%. The residual hydrogen peroxide content is still 0 mg / L, and the COD cr and ammonia nitrogen results are not much different from those of Example 2. Therefore, when the pH of the mixed solution is increased to 8.0, the ratio of the sulfide reduction amount to the hydrogen peroxide consumption amount in the first oxidation treatment process decreases by about 15%, indicating that the utilization rate of hydrogen peroxide decreases.

[0095] When the pH of the mixed solution is 6.0, the sulfide removal rate of the first oxidation treatment is as high as 91.8%, but the residual hydrogen peroxide content is 28.7 mg / L, and the COD cr and ammonia nitrogen results are not much different from those of Example 2. Therefore, when the pH of the mixed solution is decreased to 6.0, a small amount of hydrogen peroxide remains.

[0096] Experimental Example 2

[0097] In order to investigate the influence of the addition amount of the sodium hypochlorite solution in the second oxidation treatment on the results of the second oxidation treatment, the sulfide content, residual hydrogen peroxide content, COD cr and ammonia nitrogen content of the purified water obtained in Examples 2, 5-8 and the comparative example are listed in Table 2.

[0098] Table 2 Sulfide content, residual hydrogen peroxide content, COD cr and ammonia nitrogen content of the purified water obtained in Examples 2, 5-8 and the comparative example

[0099]

[0100]

[0101] The results show that the sulfide content of the purified water obtained in Example 2 is 0 mg / L, achieving complete removal of sulfide; the sodium hypochlorite content is 0 mg / L, which can effectively reduce the corrosiveness of the wastewater. And can realize the synchronous reduction of COD cr and ammonia nitrogen, the removal rates are 15.3% and 38.0% respectively, which is beneficial to the downstream deep treatment resource utilization.

[0102] The sulfide content of the purified water obtained in Example 5 is 0 mg / L, achieving precise sulfur removal; and can realize the synchronous reduction of COD cr and ammonia nitrogen, the removal rates are 10.3% and 31.2% respectively, but the COD cr removal rate is low.

[0103] The sulfide content of the purified water obtained in Example 6 is 0 mg / L, also achieving precise sulfur removal; and can realize the synchronous reduction of COD cr and ammonia nitrogen, the removal rates are 19.2% and 56.9% respectively, and the ammonia nitrogen removal rate is high.

[0104] The sulfide content of the purified water obtained in Example 7 is 0 mg / L, achieving precise sulfur removal; and can realize the synchronous reduction of COD cr and ammonia nitrogen, the removal rates are 21.6% and 72.0% respectively. It shows that with the increase of sodium hypochlorite dosage, the ammonia nitrogen removal rate is further significantly improved.

[0105] The sulfide content and sodium hypochlorite content of the purified water obtained in Example 8 are both 0 mg / L, also achieving precise sulfur removal; and can realize the synchronous reduction of COD cr and ammonia nitrogen, the removal rates are 26.2% and 79.8% respectively, and the ammonia nitrogen removal rate is high.

[0106] The sulfide content of the purified water obtained in the comparative example is 0 mg / L, but the sodium hypochlorite content reaches 51.3 mg / L, and there is residual sodium hypochlorite; still synchronously reduces COD cr and ammonia nitrogen, the removal rates are 26.0% and 80.5% respectively. But sodium hypochlorite will increase the corrosiveness of the wastewater, and also seriously affect the biochemical unit in the subsequent resource treatment.

Claims

1. A method of treating a sour gas field produced water, characterized in that, The method comprises the following steps: (1) detecting whether the pH of the produced water from the sulfur-containing gas field is 6.0-8.0, and adjusting the pH of the produced water from the sulfur-containing gas field to 6.0-8.0 if the pH does not meet the requirement; (2) performing first oxidation treatment on the produced water from the sulfur-containing gas field obtained in step (1) by using hydrogen peroxide to obtain treated water with an oxidation-reduction potential of -200 mV to +97.2 mV; (3) performing second oxidation treatment on the treated water by using water-soluble sodium hypochlorite, and synchronously performing oxidation-reduction reactions with sulfides, macromolecular organic substances and ammonia nitrogen by using the strong oxidizing property of the sodium hypochlorite to obtain purified water; the molar ratio of chlorine in the water-soluble sodium hypochlorite to sulfides in the treated water is (8-30):

1.

2. The method of treating a sour gas field produced water as claimed in claim 1, characterized in that, The first oxidation treatment is performed for 0.5-2 hours at a temperature of 20-45°C.

3. The method of treating a sulfur-containing gas field produced water of claim 2, wherein, The second oxidation treatment is performed for 0.5-1 hour at a temperature of 20-45°C.

4. The method of treating a sulfur-bearing gas field produced water as described in claim 1 wherein, The hydrogen peroxide is used in the form of hydrogen peroxide water, and the mass fraction of the hydrogen peroxide water is 20%-70%.

5. The method of treating a sulfur-bearing gas field produced water as described in claim 1 wherein, The water-soluble sodium hypochlorite is sodium hypochlorite, and the water-soluble sodium hypochlorite is used in the form of a water-soluble sodium hypochlorite solution, and the mass fraction of the water-soluble sodium hypochlorite in the water-soluble sodium hypochlorite solution is 5%-15% in terms of chlorine.

6. The method of treatment of sulphur-containing gas field produced water according to any one of claims 1 to 5, wherein, The pH of the produced water from the sulfur-containing gas field is detected and adjusted automatically, and the oxidation-reduction potential is monitored during the first oxidation treatment, and the amount of hydrogen peroxide added is automatically controlled according to the oxidation-reduction potential.

7. An apparatus for treating a sulfur-containing produced water from a gas field, characterized in that, The pH detection and adjustment unit, the first oxidation unit and the second oxidation unit are connected in sequence in the material flow direction. The pH detection and adjustment unit is used for detecting the quality of the inlet water and adjusting the pH of the inlet water to meet the requirement. The first oxidation unit comprises a hydrogen peroxide feeding device, a first oxidation reaction device and an ORP monitor, the hydrogen peroxide feeding device is used for adding hydrogen peroxide to the produced water, the first oxidation reaction device is used for performing oxidation-reduction reaction on the produced water added with hydrogen peroxide to form treated water with an oxidation-reduction potential of -200 mV to +97.2 mV, and the ORP monitor is used for monitoring the oxidation-reduction potential of the treated water. The second oxidation unit comprises a sodium hypochlorite feeding device and a second oxidation reaction device, the sodium hypochlorite feeding device is used for adding sodium hypochlorite to the treated water, and oxidation-reduction reactions are synchronously performed with sulfides, macromolecular organic substances and ammonia nitrogen by using the strong oxidizing property of the sodium hypochlorite, and the second oxidation reaction device is used for performing oxidation-reduction reaction on the treated water added with sodium hypochlorite to form purified water.

8. The apparatus for treatment of sulphur-containing gas field produced water according to claim 7, characterised in that, The pH detection and adjustment unit comprises a first pH detection device, a pH adjuster feeding device and a second pH detection device connected in sequence in the material flow direction, the first pH detection device is used for detecting the pH of the produced water on line, the pH adjuster feeding device is used for adding a pH adjuster to the produced water to adjust the pH of the produced water, and the second pH detection device is used for detecting the pH of the produced water after the pH is adjusted.

9. The apparatus for treatment of sulphur-containing gas field produced water according to claim 7 or 8, characterised in that, The lower part of the first oxidation reaction device is provided with a liquid inlet, and the upper part is provided with a treated water outlet; the ORP monitor is arranged on the first oxidation reaction device, and the liquid surface position detected by the ORP monitor is lower than the treated water outlet.

10. The apparatus for treatment of sulphur-containing gas field produced water of claim 8, wherein, The device for treating the produced water of the sulfur-containing gas field further comprises a PLC control unit connected with the pH first detection device, the pH regulator feeding device, the pH second detection device, the hydrogen peroxide feeding device and the ORP monitor respectively to realize automatic control operation.

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