Method for recycling valuable elements in gas field water

Abstract

The invention relates to the technical field of gas field water resource development and comprehensive utilization, and particularly discloses a method for recycling valuable elements in gas field water, which comprises the following steps: S1, pretreating the gas field water; s2, the pretreated gas field water is subjected to hardness removal to remove magnesium ions and precipitable ions; s3, carrying out first-stage isothermal evaporation on the hardness-removed gas field water at 50-70 DEG C to concentrate valuable elements; s4, adsorbing and extracting lithium from the gas field water subjected to the first-stage isothermal evaporation concentration by adopting a lithium adsorbent; s5, acidizing the lithium extraction mother liquor, adjusting the pH value to 3.5-5, introducing chlorine gas to oxidize and blow off bromine, and introducing the bromine into a potassium hydroxide saturated solution to generate potassium bromide; s6, carrying out second-stage isothermal evaporation on the bromine extraction mother liquor at 50-70 DEG C, and crystallizing to separate out NaCl; s7, after a large amount of NaCl is separated out, mother liquor continues to be subjected to isothermal evaporation, and potassium mixed salt containing NaCl is separated out. According to the invention, recycling of valuable elements such as lithium, potassium and bromine is realized.

Description

Technical Field

[0001] The invention relates to the technical field of gas field water resource development and comprehensive utilization, and in particular to a method for recycling valuable elements in gas field water. Background Art

[0002] In the process of shale gas extraction, hydraulic fracturing technology is one of the necessary means to improve the recovery rate. During the hydraulic fracturing process, tens of thousands of cubic meters of water are injected into the well under high pressure to break the underground rock formation and release the gas in it; the water injected into the formation will be returned to the ground at different stages of shale gas production, that is, fracturing flowback fluid and produced water, collectively referred to as produced water (gas field water). Gas field water has a complex composition and contains a high concentration of suspended matter (including formation particles, etc.). It has the characteristics of high COD, high TDS and high TSS. There is a risk of polluting groundwater and surface water. If directly reused, these components will have an adverse effect on the resistance reduction, viscosity and other properties of the fracturing fluid. Inorganic components (Ca 2+ Mg 2+ , Sr 2+ , Ba 2+ The high-valent metal ions such as ions (such as ions of argon, etc.) not only affect the drag reduction rate of the drag reducing agent, but also easily cause problems such as scaling in pipelines and underground, thus affecting the shale gas production. In addition, most of the areas in my country with rich shale reserves are areas with severe seasonal water shortages. Shale gas extraction occupies a large amount of water resources, which will directly lead to a lack of water resources. Therefore, it is of great significance to develop economical, efficient and suitable technologies for treating gas field water, reduce the discharge of gas field water, and reduce the impact on the surrounding environment, in order to achieve the harmonious unity of efficient development of shale gas resources and environmental protection.

[0003] The general treatment technology of gas field water includes three methods: reinjection into the formation, reuse with qualified standards, and discharge with qualified standards. At present, the formation reinjection capacity is far from sufficient, and the cost of qualified discharge treatment is high. In order to reduce the pressure on water resources and save costs, the main treatment method of gas field water is to use the treated gas field water for compounding various liquids required by the well site. The reuse technology after appropriate treatment mainly includes conventional pretreatment technology and desalination technology. Desalination is a key step in the reuse and treatment of gas field water. The concentrated saline mother liquor in the desalination system is generally multi-effect evaporated into solid salt and piled up or treated as mixed industrial salt. Concentration further concentrates and enriches the valuable elements lithium, potassium, boron, and bromine in the produced water. At present, the valuable elements lithium, potassium, boron, and bromine in the saline mother liquor have not been extracted and utilized, resulting in waste of resources and environmental pollution. However, potassium, lithium, and bromine are far higher than the grades of their individual mining, and have very high development and utilization value. The gas field water is pretreated to remove suspended solids, organic matter, oil and other impurities. After evaporation and concentration using the natural gas separated from the gas field as a heat source, lithium, bromine and potassium resources can be gradually extracted through certain separation technologies. The condensed water produced during the evaporation process is mixed with the tail liquid after comprehensive utilization and reused, which not only solves the discharge pressure of the gas field water, but also realizes the comprehensive utilization of mineral resources, promotes the recycling of water resources, and ensures the continuous production of oil and gas fields while protecting the environment.

[0004] After pretreatment, the gas field water in the Sichuan Basin is chloride-type brine, which is very different from the carbonate-type and sulfate-type salt lake brine that has been successfully developed and utilized. Multiple sampling and analysis have proved that the magnesium-lithium ratio in the gas field water is relatively low, which is more conducive to the extraction and separation of lithium resources.

[0005] At present, there are no reports or engineering cases on the comprehensive extraction and reuse of valuable elements lithium, potassium and bromine in gas field water at home and abroad. Therefore, it is necessary to design a method for comprehensive recovery and utilization of lithium, potassium and bromine in gas field water and realize the reuse of gas field water. Summary of the invention

[0006] The purpose of the present invention is to provide a method for recycling valuable elements in gas field water. The method realizes the recycling of valuable elements lithium, potassium and bromine by preparing lithium carbonate, sodium chloride, potassium chloride and potassium bromide, which not only solves the problems of effective utilization of gas field water and environmental pollution, but also creates certain economic value.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for recycling valuable elements in gas field water comprises the following steps:

[0009] S1. Pre-treat gas field water;

[0010] S2. Remove hardness from the pretreated gas field water: add sodium hydroxide to remove magnesium ions and sodium carbonate to remove divalent hardness ions that can be precipitated; divalent hardness ions that can be precipitated include calcium ions, barium ions and strontium ions, which greatly reduces the types of impurity ions in the gas field water;

[0011] S3. The gas field water after hardness removal is evaporated isothermally at 50-70°C until the evaporation rate is 40%-65% of the original gas field water, so that the valuable elements lithium, potassium and bromine are concentrated, and NaCl is not crystallized;

[0012] S4, the gas field water after isothermal evaporation and concentration is adsorbed and lithium extracted by a lithium adsorbent, the adsorption eluate is purified and concentrated, and then lithium is precipitated by sodium carbonate, and lithium carbonate and lithium extraction mother liquor are collected respectively;

[0013] S5, acidifying the lithium extraction mother liquor, adjusting the pH value to 3.5-5, introducing chlorine gas to oxidize and blow off bromine, introducing bromine into a saturated potassium hydroxide solution to generate potassium bromide, and collecting potassium bromide and bromine extraction mother liquor respectively;

[0014] S6, the bromine extraction mother liquor is subjected to two-stage isothermal evaporation at 50-70°C until the evaporation rate is 70%-95% of the original gas field water, and NaCl is crystallized;

[0015] S7. After a large amount of NaCl is precipitated, the mother liquor is further isothermally evaporated to precipitate potassium mixed salt containing NaCl, which is then purified by flotation to produce KCl.

[0016] The evaporation loss rate of the present invention is also called the evaporation rate. The evaporation rate of the water-containing product is calculated by the formula: (product weight before evaporation - product weight after evaporation) ÷ product weight before evaporation × 100%. The ratio of the weight of the evaporated water to the weight of the liquid before evaporation is called the evaporation loss rate.

[0017] Step S1 of the present invention can reduce sulfides, petroleum substances and suspended solids in gas field water through pretreatment, so as to clarify the gas field water and meet the requirements for extraction and separation of various elements in subsequent processes.

[0018] Step S2 of the present invention greatly reduces the types of impurity ions in the gas field water through hardness removal treatment, greatly simplifies the composition of the gas field water, and is conducive to the extraction of lithium, potassium and bromine in the gas field water. The amount of sodium hydroxide used in the process of adding sodium hydroxide to remove all magnesium ions is 110% to 150% of the theoretical amount; the amount of sodium carbonate used in the process of adding sodium carbonate to the gas field water after magnesium removal to remove divalent ions such as calcium is 105% to 130% of the theoretical amount.

[0019] In step S3 of the present invention, the evaporation loss rate of a section of isothermal evaporation is reasonably controlled to be 40% to 65% of the original gas field water, so that lithium, potassium and bromine in the gas field water are concentrated to a certain extent, and at the same time, sodium chloride solid is not crystallized and precipitated, thereby avoiding the entrainment loss of lithium resources.

[0020] In step S4 of the present invention, the lithium in the concentrated brine can be converted into lithium carbonate for recycling.

[0021] In step S5 of the present invention, bromine in the lithium extraction mother liquor can be converted into potassium bromide for recycling.

[0022] In step S6 of the present invention, by reasonably controlling the evaporation loss rate of the second-stage isothermal evaporation to be 70% to 95% of the original gas field water, a large amount of sodium chloride crystals can be precipitated, and potassium chloride is precipitated as little as possible, thereby improving the recovery of potassium in subsequent steps as much as possible.

[0023] In step S7 of the present invention, potassium ions can be converted into potassium chloride, thereby realizing the recovery of potassium.

[0024] The extraction order of valuable elements in the present invention is respectively lithium, bromine, sodium and potassium. Since the gas field water is weakly alkaline (9.5-11.5) after a period of isothermal evaporation and concentration, the optimal condition for the titanium-based lithium adsorbent to adsorb and extract lithium is alkaline, and the extraction and separation of bromine requires acidification of the brine. Therefore, the lithium element is first adsorbed and extracted, and then the gas field water is acidified to extract bromine. The separation and extraction of sodium and potassium adopts the evaporation crystallization method. In order to avoid the entrainment loss of lithium and bromine resources during the evaporation crystallization process, the separation of sodium and potassium is placed at the end.

[0025] Compared with the existing technology, the present invention abandons the traditional desalination technology. After the gas field water is pretreated, the double alkali method is first used to remove impurities before evaporation, which solves the scaling problem in the subsequent evaporation and concentration process, greatly reduces the types of impurity ions in the gas field water, greatly simplifies the composition of the gas field water, and is conducive to the extraction of lithium, potassium and bromine in the gas field water. The valuable elements lithium, potassium and bromine are concentrated and enriched by adopting the isothermal evaporation process, and then the lithium, bromine and potassium resources are gradually extracted by controlling the evaporation loss rate and pH value in the isothermal evaporation process and combining certain separation technologies, so that the separation and extraction efficiency of each element is optimized, especially the control of the conditions for lithium extraction by adsorption method, so that the extraction efficiency of lithium is greatly improved.

[0026] In summary, the present invention achieves the recovery and utilization of lithium, sodium, potassium and bromine in gas field water by obtaining the products of lithium carbonate, sodium chloride, potassium chloride and potassium bromide, and can improve the recovery rate of each valuable element by reasonably controlling the evaporation loss rate of the first isothermal evaporation and the evaporation loss rate of the second isothermal evaporation.

[0027] Furthermore, step S1 specifically includes the following steps:

[0028] S11, acidifying the gas field water, adjusting the pH value to 3-5, and stripping the gas field water after the pH is adjusted to remove hydrogen sulfide gas, which is absorbed by alkaline solution; specifically, the gas field water after the pH is adjusted is stripped with circulating gas in a stripping tower, and the stripped hydrogen sulfide gas is passed into an absorption tower of saturated sodium hydroxide solution to generate sodium sulfide, which is concentrated, crystallized and dried to obtain a sodium sulfide product;

[0029] S12, after the hydrogen sulfide is removed, the gas field water is treated by a flocculation sedimentation combined with filtration process to remove suspended solids, organic matter and a small amount of oil;

[0030] S13. The gas field water that has undergone sedimentation treatment is filtered through an organic membrane to remove organic matter and a small amount of oil.

[0031] Furthermore, in step S12, the flocculant for flocculation and sedimentation is polyaluminium chloride, and the addition amount is 20-50 mg / L; in step S12, the coagulant aid for flocculation and sedimentation is anionic polyacrylamide, with a molecular weight of 5 million to 8 million and an addition amount of 2-5 mg / L.

[0032] Furthermore, in step S13, the membrane material of the organic membrane is polytetrafluoroethylene, the membrane pore size is 0.1-0.25 μm, and the membrane flux is controlled at 300-500 L / m 2 ·h.

[0033] After the pretreatment in step S1, the sulfide in the gas field water is ≤5mg / L, petroleum is ≤3mg / L, suspended solids are ≤5mg / L, COD is ≤285mg / L, and the gas field water is clear, which meets the requirements of extraction and separation of various elements in subsequent processes.

[0034] Furthermore, in step S4, the lithium adsorbent is a titanium-based adsorbent.

[0035] The pH value of the gas field water in the first stage of evaporation and concentration is 9.5-11.5, and the lithium content has reached the concentration. Since the optimal adsorption condition of titanium-based adsorbents is alkaline and the adsorption capacity is large, the lithium extraction efficiency is greatly improved by using titanium-based adsorbents to extract lithium through adsorption. After purification and impurity removal, the desorption liquid is evaporated and concentrated to 10-30g / L. The amount of sodium carbonate added is 110%-140% of the theoretical amount, and a precipitation reaction occurs. After washing and drying, the lithium carbonate obtained meets the requirements of the national standard (GB / T23853-2009) for qualified products.

[0036] Furthermore, the specific process of step S5 is:

[0037] Dilute acid is added to the lithium extraction mother liquor for acidification treatment, and the pH value is adjusted to 3.5-5, and then chlorine is introduced for oxidation, and the amount of the introduced chlorine is 105%-130% of the theoretical amount. The oxidized liquid is sprayed and blown out by air in a blowing tower to obtain bromine-containing air and mother liquor after bromine blowing. The bromine-containing air is introduced into an absorption tower of a saturated potassium hydroxide solution, and the volume of the saturated potassium hydroxide solution is 105%-130% of the theoretical volume; potassium bromide is generated by reaction in the absorption tower, and the potassium bromide solution is concentrated, crystallized and dried to obtain a potassium bromide product.

[0038] Furthermore, in step S7, the evaporation rate is 70% to 95% of the original gas field water. At this evaporation rate, potassium mixed salt containing sodium chloride can be precipitated.

[0039] Furthermore, the method further comprises the following steps:

[0040] Industrial hydrochloric acid is added to the mother liquor after lithium extraction by adsorption to obtain crude boric acid, and the amount of industrial hydrochloric acid used is 100% to 120% of the theoretical amount of boric acid generated by the complete reaction of B2O3 in the mother liquor after lithium extraction by adsorption.

[0041] The main water quality characteristics of gas field water are: pH value 5.5-7.5, sulfide 20-500 mg / L, petroleum 10-100 mg / L, COD 30-10000 mg / L, suspended solids 30-500 mg / L, sodium ions 10000-100000 mg / L, lithium ions 30-300 mg / L, boron 200-600 mg / L, potassium ions 1000-10000 mg / L, bromide ions 200-2000 mg / L, calcium ions 150-15000 mg / L, magnesium ions 60-1000 mg / L, barium ions 30-2500 mg / L, strontium ions 60-2500 mg / L, and chloride ions 2000-170000 mg / L.

[0042] It can be seen that the gas field water contains not only lithium, bromine and potassium, but also boron. The present invention can also realize the recovery and utilization of boron.

[0043] The best conditions for titanium-based lithium adsorbents to adsorb and extract lithium are alkaline, and the extraction and separation of boron and bromine both require acidification of the brine. Therefore, the lithium element is first adsorbed and extracted, and then the gas field water is acidified to extract boron and bromine in turn, thereby achieving sharing of acidic conditions.

[0044] Furthermore, the heat source used in the first stage isothermal evaporation and the second stage isothermal evaporation is natural gas. Using the extracted and separated natural gas as a heat source for the first stage isothermal evaporation and the second stage isothermal evaporation concentration can reduce costs.

[0045] Furthermore, the condensed water generated during the last stage of evaporation and the second stage of evaporation is mixed with the potassium precipitation mother liquor and reused.

[0046] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0047] 1. The present invention can comprehensively utilize lithium, potassium and bromine in gas field water, produce lithium carbonate, sodium chloride, potassium chloride and potassium bromide products, and realize the recycling of gas field water by sequentially subjecting gas field water to acidification and oxidation, flocculation and sedimentation combined filtration, organic membrane filtration and other pretreatment technologies, adding double alkali method to remove impurities, one-stage isothermal evaporation and concentration, adsorption of lithium, chlorine oxidation to bromine, two-stage isothermal evaporation to extract sodium chloride and potassium chloride, and mixing old brine with evaporated condensed water for reuse after potassium extraction. This method can not only solve the problem of effective utilization of gas field water and environmental pollution, but also create certain economic value.

[0048] 2. The present invention reasonably controls the evaporation loss rate of the first stage isothermal evaporation and the evaporation loss rate of the second stage isothermal evaporation to optimize the separation and extraction efficiency of each element, thereby improving the recovery rate of each valuable element. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0050] Figure 1 This is a process flow chart of Examples 1 to 3 of the present invention. DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0052] Embodiment 1:

[0053] The main water quality characteristics of gas field brine in a certain area of ​​Sichuan Basin are: pH 6.73, sulfide 200mg / L, petroleum 30mg / L, COD 1000mg / L, suspended solids 300mg / L, sodium ions 31116.4mg / L, lithium ions 75.4mg / L, potassium ions 2870mg / L, bromide ions 715.4mg / L, calcium ions 1724.1mg / L, magnesium ions 249.4mg / L, barium ions 997.5mg / L, strontium ions 1084.4mg / L, and chloride ions 63254.5mg / L.

[0054] like Figure 1 As shown, the specific processing and extraction steps are as follows:

[0055] (1) The pH value of gas field water is adjusted to 4.5 by using hydrochloric acid, and the gas field water after pH adjustment is stripped by circulating gas in a stripping tower, and the hydrogen sulfide gas stripped is passed into an absorption tower of saturated sodium hydroxide solution to generate sodium sulfide, which is then concentrated, crystallized and dried to obtain a sodium sulfide product;

[0056] (2) After the removal of hydrogen sulfide, the gas field water enters the flocculation and sedimentation unit for flocculation and sedimentation. The flocculant is polyaluminium chloride, with a dosage of 30 mg / L, and the coagulant is polyacrylamide, with a molecular weight of 6 million and a dosage of 3 mg / L. The combined filtration process is used to remove suspended solids, organic matter and a small amount of oil. The flocculation sedimentation residue is solidified and then transported out for centralized treatment.

[0057] (3) After flocculation and sedimentation, the gas field water is filtered through an organic membrane made of polytetrafluoroethylene. The membrane pore size is 0.15 μm, and the membrane flux of the filtration unit is controlled at 350 L / m 2 ·h;

[0058] (4) After the pretreatment process of steps (1) to (3), the sulfide in the gas field water is ≤5 mg / L, the petroleum is ≤3 mg / L, the suspended solids are ≤5 mg / L, and the COD is ≤285 mg / L. The gas field water is clear and meets the requirements for extraction and separation of various elements in subsequent processes;

[0059] (5) adding sodium hydroxide to the pretreated gas field water to remove magnesium ions, wherein the molar ratio of sodium hydroxide to magnesium ions is 1.15:1, thereby obtaining gas field water after magnesium ions are removed;

[0060] (6) Sodium carbonate is added to the gas field water after magnesium ions are removed to remove divalent ions such as calcium (including barium ions and strontium ions). The molar ratio of sodium carbonate to divalent ions such as calcium is 1.2:1. Divalent ions such as calcium (including barium ions and strontium ions) are removed as much as possible, which greatly reduces the types of impurity ions in the gas field water and greatly simplifies the composition of brine;

[0061] (7) Using the extracted and separated natural gas as a heat source to carry out an isothermal (55°C) evaporation concentration of the impurity-removed brine to reduce costs. The evaporation loss rate is 60% of the original gas field water. The brine is concentrated to a certain extent, and the sodium chloride solid does not crystallize and precipitate, thus avoiding the loss of lithium resources;

[0062] (8) The pH value of the gas field water after the first stage of evaporation and concentration is 10, and the lithium content is concentrated. A titanium-based adsorbent is used to extract lithium by adsorption, and the lithium extraction rate reaches 92%. The desorbed liquid is purified and impurities are removed, and then evaporated and concentrated to 15 g / L. Sodium carbonate in an amount of 130% of the theoretical amount is added to cause a precipitation reaction. After washing and drying, the obtained lithium carbonate meets the index requirements of the national standard (GB / T23853-2009) or above.

[0063] (9) adding dilute hydrochloric acid to the lithium extraction mother liquor for acidification treatment, adjusting the pH value to 4, introducing chlorine gas, the amount of which is 103% of the theoretical amount, spraying the oxidizing liquid in a blowing tower and blowing out the air to obtain bromine-containing air and a bromine-blown mother liquor, and airtightly introducing the bromine-containing air into an absorption tower containing a saturated potassium hydroxide solution, the volume of which is 105% of the theoretical volume, evaporating and concentrating, centrifuging, and crystallizing and drying to obtain a potassium bromide product;

[0064] (10) using the extracted and separated natural gas as a heat source to perform two-stage isothermal (55° C.) evaporation concentration on the mother liquor after bromine extraction, and when the evaporation loss rate is 80% of the original gas field water, sodium chloride crystals begin to precipitate in large quantities, and when the evaporation loss rate reaches 93% of the original gas field water, the precipitated sodium chloride is separated to obtain a pure sodium chloride product;

[0065] (11) continuing to use the natural gas separated from the production as a heat source to isothermally (55° C.) evaporate and concentrate the mother liquor after sodium precipitation. When the evaporation loss rate is 96% of the original gas field water, potassium mixed salt containing sodium chloride begins to precipitate. When a large amount of solids are precipitated, flotation method is used to purify and produce potassium chloride;

[0066] (12) Finally, the condensed water produced during the first and second evaporation processes is mixed with the potassium precipitation mother liquor for reuse. The mixed solution meets the reuse standards for gas field water and is used to compound various liquids required by the well site.

[0067] Embodiment 2:

[0068] The main water quality characteristics of gas field brine in a certain area of ​​Sichuan Basin are: pH 6.72, sulfide 250mg / L, petroleum 40mg / L, COD 2000mg / L, suspended solids 350mg / L, sodium ions 34260mg / L, lithium ions 82.1mg / L, potassium ions 4165mg / L, bromide ions 851.1mg / L, calcium ions 1532mg / L, magnesium ions 291mg / L, barium ions 1356mg / L, strontium ions 1017mg / L, and chloride ions 54556.3mg / L.

[0069] like Figure 1 As shown, the specific processing and extraction steps are as follows:

[0070] (1) The pH value of gas field water is adjusted to 5 by using hydrochloric acid, and the gas field water after pH adjustment is stripped by using circulating gas in a stripping tower, and the hydrogen sulfide gas stripped is passed into an absorption tower of saturated sodium hydroxide solution to generate sodium sulfide, which is then concentrated, crystallized and dried to obtain a sodium sulfide product;

[0071] (2) After the removal of hydrogen sulfide, the gas field water enters the flocculation and sedimentation unit for flocculation and sedimentation. The flocculant is polyaluminium chloride, with a dosage of 35 mg / L, and the coagulant is polyacrylamide, with a molecular weight of 6.5 million and a dosage of 3.5 mg / L. The combined filtration process is used to remove suspended solids, organic matter and a small amount of oil. The flocculation sedimentation residue is solidified and then transported out for centralized treatment.

[0072] (3) After flocculation and sedimentation, the gas field water is filtered through an organic membrane made of polytetrafluoroethylene. The membrane pore size is 0.20 μm, and the membrane flux of the filtration unit is controlled at 400 L / m 2 ·h;

[0073] (4) After the pretreatment process of steps (1) to (3), the sulfide in the gas field water is ≤5 mg / L, the petroleum is ≤3 mg / L, the suspended solids are ≤5 mg / L, and the COD is ≤285 mg / L. The gas field water is clear and meets the requirements for extraction and separation of various elements in subsequent processes;

[0074] (5) adding sodium hydroxide to the pretreated gas field water to remove magnesium ions, wherein the molar ratio of sodium hydroxide to magnesium ions is 1.2:1, thereby obtaining gas field water after magnesium ions are removed;

[0075] (6) Sodium carbonate is added to the gas field water after magnesium ions are removed to remove divalent ions such as calcium (including barium ions and strontium ions). The molar ratio of sodium carbonate to divalent ions such as calcium is 1.3:1. Divalent ions such as calcium (including barium ions and strontium ions) are removed as much as possible, which greatly reduces the types of impurity ions in the gas field water and greatly simplifies the composition of brine;

[0076] (7) Using the extracted and separated natural gas as a heat source to carry out an isothermal (60°C) evaporation concentration of the impurity-removed brine to reduce costs. The evaporation loss rate is 50% of the original gas field water. The brine is concentrated to a certain extent, and the sodium chloride solid does not crystallize and precipitate, thereby avoiding the loss of lithium resources;

[0077] (8) The pH value of the gas field water after the first stage of evaporation and concentration is 10.5, and the lithium content is concentrated. A titanium-based adsorbent is used to extract lithium by adsorption, and the lithium extraction rate reaches 93%. The desorbed liquid is purified and impurities are removed, and then evaporated and concentrated to 24 g / L. Sodium carbonate in an amount of 120% of the theoretical amount is added to cause a precipitation reaction. After washing and drying, the obtained lithium carbonate meets the index requirements of the national standard (GB / T23853-2009) for qualified products;

[0078] (9) adding dilute hydrochloric acid to the lithium extraction mother liquor for acidification treatment, adjusting the pH value to 4.3, introducing chlorine gas in an amount of 107% of the theoretical amount, spraying the oxidizing liquid in a blowing tower and blowing out the air to obtain bromine-containing air and bromine-blown mother liquor, and air-sealing the bromine-containing air into an absorption tower of a saturated potassium hydroxide solution in an amount of 102% of the theoretical volume, evaporating and concentrating, centrifuging, and crystallizing and drying to obtain a potassium bromide product;

[0079] (10) using the extracted and separated natural gas as a heat source to perform two-stage isothermal (60° C.) evaporation concentration on the mother liquor after bromine extraction, and when the evaporation loss rate is 71% of the original gas field water, sodium chloride crystals begin to precipitate in large quantities, and when the evaporation loss rate reaches 85% of the original gas field water, the precipitated sodium chloride is separated to obtain a pure sodium chloride product;

[0080] (11) continuing to use the natural gas separated from the production as a heat source to isothermally (60° C.) evaporate and concentrate the mother liquor after sodium precipitation. When the evaporation loss rate is 90% of the original gas field water, potassium mixed salt containing sodium chloride begins to precipitate. When a large amount of solids are precipitated, flotation method is used to purify and produce potassium chloride;

[0081] (12) Finally, the condensed water produced during the first and second evaporation processes is mixed with the potassium precipitation mother liquor for reuse. The mixed solution meets the reuse standards for gas field water and is used to compound various liquids required by the well site.

[0082] Embodiment 3:

[0083] The main water quality characteristics of gas field brine in a certain area of ​​Sichuan Basin are: pH 6.52, sulfide 350mg / L, petroleum 50mg / L, COD 2500mg / L, suspended solids 400mg / L, sodium ions 33820mg / L, lithium ions 112.7mg / L, potassium ions 3254mg / L, bromide ions 945.2mg / L, calcium ions 1982mg / L, magnesium ions 252.4mg / L, barium ions 1775mg / L, strontium ions 1266mg / L, and chloride ions 59171mg / L.

[0084] like Figure 1 As shown, the specific processing and extraction steps are as follows:

[0085] (1) The pH value of gas field water is adjusted to 4.3 by using hydrochloric acid, and the gas field water after pH adjustment is stripped by using circulating gas in a stripping tower, and the hydrogen sulfide gas stripped is passed into an absorption tower of saturated sodium hydroxide solution to generate sodium sulfide, which is then concentrated, crystallized and dried to obtain a sodium sulfide product;

[0086] (2) After the removal of hydrogen sulfide, the gas field water enters the flocculation and sedimentation unit for flocculation and sedimentation. The flocculant is polyaluminium chloride, with a dosage of 40 mg / L, and the coagulant is polyacrylamide, with a molecular weight of 7 million and a dosage of 4 mg / L. The combined filtration process is used to remove suspended solids, organic matter and a small amount of oil. The flocculation sedimentation residue is solidified and then transported out for centralized treatment.

[0087] (3) After flocculation and sedimentation, the gas field water is filtered through an organic membrane made of polytetrafluoroethylene. The membrane pore size is 0.25 μm, and the membrane flux of the filtration unit is controlled at 450 L / m 2 ·h

[0088] (4) After the pretreatment process of steps (1) to (3), the sulfide in the gas field water is ≤5 mg / L, the petroleum is ≤3 mg / L, the suspended solids are ≤5 mg / L, and the COD is ≤285 mg / L. The gas field water is clear and meets the requirements for extraction and separation of various elements in subsequent processes;

[0089] (5) adding sodium hydroxide to the pretreated gas field water to remove magnesium ions, wherein the molar ratio of sodium hydroxide to magnesium ions is 1.1:1, thereby obtaining gas field water after magnesium ions are removed;

[0090] (6) Sodium carbonate is added to the gas field water after magnesium ions are removed to remove divalent ions such as calcium (including barium ions and strontium ions). The molar ratio of sodium carbonate to divalent ions such as calcium is 1.35:1. Divalent ions such as calcium (including barium ions and strontium ions) are removed as much as possible, which greatly reduces the types of impurity ions in the gas field water and greatly simplifies the composition of brine;

[0091] (7) Using the extracted and separated natural gas as a heat source to carry out an isothermal (63°C) evaporation concentration of the impurity-removed brine to reduce costs. The evaporation loss rate is 55% of the original gas field water. The brine is concentrated to a certain extent, and the sodium chloride solid does not crystallize and precipitate, thus avoiding the loss of lithium resources;

[0092] (8) The pH value of the gas field water after the first stage of evaporation and concentration is 11, and the lithium content is concentrated. A titanium-based adsorbent is used to extract lithium by adsorption, and the lithium extraction rate reaches 95%. The desorbed liquid is purified and impurities are removed, and then evaporated and concentrated to 25 g / L. Sodium carbonate in an amount of 110% of the theoretical amount is added to cause a precipitation reaction. After washing and drying, the obtained lithium carbonate meets the index requirements of the national standard (GB / T23853-2009) or above.

[0093] (9) adding dilute hydrochloric acid to the lithium extraction mother liquor for acidification treatment, adjusting the pH value to 4.5, introducing chlorine gas in an amount of 107% of the theoretical amount, spraying the oxidizing liquid in a blowing tower and blowing out the air to obtain bromine-containing air and bromine-blown mother liquor, and air-sealing the bromine-containing air into an absorption tower of a saturated potassium hydroxide solution in an amount of 110% of the theoretical volume, evaporating and concentrating, centrifuging, and crystallizing and drying to obtain a potassium bromide product;

[0094] (10) using the extracted and separated natural gas as a heat source to perform two-stage isothermal (63° C.) evaporation concentration on the mother liquor after bromine extraction, and when the evaporation loss rate is 75% of the original gas field water, sodium chloride crystals begin to precipitate in large quantities, and when the evaporation loss rate reaches 89% of the original gas field water, the precipitated sodium chloride is separated to obtain a pure sodium chloride product;

[0095] (11) continuing to use the natural gas separated from the production as a heat source to isothermally (63° C.) evaporate and concentrate the mother liquor after sodium precipitation. When the evaporation loss rate is 92% of the original gas field water, potassium mixed salt containing sodium chloride begins to precipitate. When a large amount of solids are precipitated, flotation method is used to purify and produce potassium chloride;

[0096] (12) Finally, the condensed water produced during the first and second evaporation processes is mixed with the potassium precipitation mother liquor for reuse. The mixed solution meets the reuse standards for gas field water and is used to compound various liquids required by the well site.

[0097] Embodiment 4:

[0098] This embodiment is based on Example 1, and is different from Example 1 in that this embodiment also recovers boron, specifically comprising the following steps:

[0099] Gas field brine from a certain area in the Sichuan Basin (the ion concentrations of the brine are shown in Table 1 below) was first subjected to a pretreatment process, wherein an acidification method was used to remove H2S gas, and a flocculation sedimentation combined filtration treatment process was used to remove suspended matter, organic matter and a small amount of oil. Organic matter and a small amount of oil were removed by organic membrane filtration, and the obtained clarified gas field water did not affect the subsequent separation and extraction of various ions. The specific process of the pretreatment was the same as in Example 1.

[0100] Table 1 Chemical composition of gas field water

[0101]

[0102] (1) adding sodium hydroxide to the pretreated gas field water to remove magnesium ions, wherein the molar ratio of sodium hydroxide to magnesium ions is 1.15:1, thereby obtaining gas field water after magnesium ions are removed;

[0103] (2) Sodium carbonate is added to the gas field water after magnesium ions are removed to remove divalent ions such as calcium (including barium ions and strontium ions). The molar ratio of sodium carbonate to divalent ions such as calcium is 1.1:1. Calcium ions (including barium ions and strontium ions) are removed as much as possible, which greatly reduces the types of impurity ions in the gas field water and greatly simplifies the composition of brine;

[0104] (3) Using the extracted and separated natural gas as a heat source to carry out an isothermal (55°C) evaporation concentration of the impurity-removed brine to reduce costs. The evaporation loss rate is 60% of the original gas field water. The brine is concentrated to a certain extent, and the sodium chloride solid does not crystallize and precipitate, thus avoiding the loss of lithium resources;

[0105] (4) The pH value of the gas field water after the first stage of evaporation and concentration is 10, and the lithium content is concentrated. A titanium-based adsorbent is used to extract lithium by adsorption, and the lithium extraction rate reaches 92%. The desorbed liquid is purified and impurities are removed, and then evaporated and concentrated to 15 g / L. Sodium carbonate in an amount of 130% of the theoretical amount is added to cause a precipitation reaction. After washing and drying, the obtained lithium carbonate meets the index requirements of the national standard (GB / T23853-2009) or above.

[0106] (5) adding industrial hydrochloric acid in an amount of 105% of the theoretical amount to the mother liquor after lithium extraction by adsorption, filtering and washing to obtain crude boric acid and bromine-containing mother liquor, at which the bromine concentration in the gas field water is 2.3 g / L;

[0107] (6) adding dilute hydrochloric acid to the boron extraction mother liquor for acidification treatment, adjusting the pH value to 4, introducing chlorine gas, the amount of chlorine gas being 103% of the theoretical amount, the oxidizing liquid being sprayed and blown out by air in a blow-out tower to obtain bromine-containing air and bromine-blown mother liquor, the bromine-containing air being sealed and introduced into an absorption tower of saturated potassium hydroxide solution, the volume of the saturated potassium hydroxide solution being 105% of the theoretical volume, reacting in the absorption tower to generate potassium bromide, concentrating the potassium bromide solution, crystallizing and drying to obtain a potassium bromide product;

[0108] (7) using the extracted and separated natural gas as a heat source to carry out two-stage isothermal (55° C.) evaporation concentration of the mother liquor after bromine extraction, and when the evaporation loss rate is 80% of the original gas field water, sodium chloride crystals begin to precipitate in large quantities, and when the evaporation loss rate reaches 93% of the original gas field water, the precipitated sodium chloride is separated to obtain a pure sodium chloride product;

[0109] (8) continuing to use the natural gas separated from the production as a heat source to isothermally (55° C.) evaporate and concentrate the mother liquor after sodium precipitation. When the evaporation loss rate is 96% of the original gas field water, potassium mixed salt containing sodium chloride begins to precipitate. When a large amount of solids are precipitated, flotation method is used to purify and produce potassium chloride;

[0110] (9) The old brine after potassium precipitation is returned to an isothermal evaporation stage for recycling, forming a cyclic closed-loop process.

[0111] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0112] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and the like cited in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of the relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

Claims

1. A method for recycling valuable elements in gas field water, characterized in that: The following steps are involved: S1. Pre-treat gas field water; S2, removing hardness from the pretreated gas field water: adding sodium hydroxide to remove magnesium ions and sodium carbonate to remove precipitable divalent hardness ions; S3. The gas field water after hardness removal is evaporated isothermally at 50-70°C until the evaporation rate is 40%-65% of the original gas field water, so that the valuable elements lithium, potassium and bromine are concentrated, and NaCl is not crystallized; S4, the gas field water after isothermal evaporation and concentration is adsorbed and lithium extracted by a lithium adsorbent, the adsorption eluate is purified and concentrated, and then lithium is precipitated by sodium carbonate, and lithium carbonate and lithium extraction mother liquor are collected respectively; S5, acidifying the lithium extraction mother liquor, adjusting the pH value to 3.5-5, introducing chlorine gas to oxidize and blow off bromine, introducing bromine into a saturated potassium hydroxide solution to generate potassium bromide, and collecting potassium bromide and bromine extraction mother liquor respectively; S6, the bromine extraction mother liquor is subjected to two-stage isothermal evaporation at 50-70°C until the evaporation rate is 70%-95% of the original gas field water, and NaCl is crystallized; S7. After a large amount of NaCl is precipitated, the mother liquor is further isothermally evaporated to precipitate potassium mixed salt containing NaCl, which is then purified by flotation to produce KCl.

2. A method for recycling valuable elements in gas field water according to claim 1, characterized in that: Step S1 specifically includes the following steps: S11, acidifying the gas field water, adjusting the pH value to 3-5, and stripping the gas field water after pH adjustment to remove hydrogen sulfide gas, which is absorbed by alkaline solution; S12, after the hydrogen sulfide is removed, the gas field water is treated by a flocculation sedimentation combined with filtration process to remove suspended solids, organic matter and a small amount of oil; S13. The gas field water that has undergone sedimentation treatment is filtered through an organic membrane to remove organic matter and a small amount of oil.

3. A method for recycling valuable elements in gas field water according to claim 2, characterized in that: In step S12, the flocculant for flocculation and sedimentation is polyaluminium chloride, and the addition amount is 20-50 mg / L.

4. A method for recycling valuable elements in gas field water according to claim 2, characterized in that: In step S12, the coagulant aid for flocculation and sedimentation is anionic polyacrylamide with a molecular weight of 5 million to 8 million and a dosage of 2 to 5 mg / L.

5. A method for recycling valuable elements in gas field water according to claim 2, characterized in that: In step S13, the membrane material of the organic membrane is polytetrafluoroethylene, the membrane pore size is 0.1-0.25 μm, and the membrane flux is controlled at 300-500 L / m 2 ·h.

6. A method for recycling valuable elements in gas field water according to claim 1, characterized in that: In step S2, the amount of sodium hydroxide used in the process of adding sodium hydroxide to remove all magnesium ions is 110% to 150% of the theoretical amount; the amount of sodium carbonate used in the process of adding sodium carbonate to the gas field water after magnesium removal to remove divalent ions such as calcium is 105% to 130% of the theoretical amount.

7. A method for recycling valuable elements in gas field water according to claim 1, characterized in that: In step S4, the lithium adsorbent is a titanium-based adsorbent.

8. The method for recycling valuable elements in gas field water according to claim 1, characterized in that: The specific process of step S5 is: Dilute acid is added to the lithium extraction mother liquor for acidification treatment, and the pH value is adjusted to 3.5-5, and then chlorine gas is introduced for oxidation. The oxidized liquid is blown out by air in a blowing tower after spraying to obtain bromine-containing air and mother liquor after bromine blowing. The bromine-containing air is introduced into an absorption tower of saturated potassium hydroxide solution; potassium bromide is generated by reaction in the absorption tower, and the potassium bromide solution is concentrated, crystallized and dried to obtain a potassium bromide product.

9. A method for recycling valuable elements in gas field water according to claim 1, characterized in that: In step S7, the evaporation rate is 70% to 95% of the original gas field water.

10. The method for recycling valuable elements in gas field water according to claim 1, characterized in that: The following steps are also included: Add industrial hydrochloric acid to the mother liquor after lithium extraction by adsorption to obtain crude boric acid.

11. A method for recycling valuable elements in gas field water according to any one of claims 1 to 10, characterized in that: The heat source used in the first stage isothermal evaporation and the second stage isothermal evaporation is natural gas.

12. A method for recycling valuable elements in gas field water according to any one of claims 1 to 10, characterized in that: The condensed water generated during the last stage of evaporation and the second stage of evaporation is mixed with the potassium precipitation mother liquor and reused.

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