Anticorrosive and deoxidizing composite agent for geothermal well recharge water and preparation method thereof

Abstract

The application relates to the technical field of water treatment agents, and particularly discloses a corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water and a preparation method thereof. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water is prepared from the following raw materials in parts by weight: 30-40 parts of double-modified sodium sulfite, 10-20 parts of an inhibitor, 8-15 parts of a scale inhibitor, 5-10 parts of aminotri (methylene) phosphonic acid, 5-10 parts of hydroxyethyldiphosphonic acid, 3-8 parts of polyethylene glycol monomethyl ether acrylate and 40-50 parts of deionized water; the double-modified sodium sulfite is obtained by sequentially modifying sodium sulfite with a silane coupling agent and acrylic acid. The corrosion-preventing and oxygen-removing composite agent has the advantages of stable oxygen-removing efficiency and is capable of simultaneously improving the corrosion-preventing and scale-inhibiting functions on the basis of ensuring stable oxygen-removing efficiency, and is fully suitable for the complex working condition requirements of geothermal well recharge.

Description

Technical Field

[0001] This application relates to the field of water treatment agents, and more specifically, it relates to a composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water and its preparation method. Background Technology

[0002] Geothermal resources, as a clean and renewable new energy source, are increasingly widely used in urban heating, industrial production, and other fields. The closed-loop operation of geothermal well extraction and reinjection is the core key to achieving sustainable utilization of geothermal resources. Taking a mid-temperature hydrothermal geothermal field, characterized by layered fractured reservoirs controlled by fault structures, as an example, its geothermal heating projects generally adopt an "extraction-heat exchange-reinjection" operation mode. After energy exchange between geothermal water and heating medium water at a heat exchange station, the geothermal water is mechanically pressurized and reinjected into the underground reservoir. It is required that the extraction and reinjection volumes remain balanced to achieve 100% reinjection. During this process, the reinjection water must meet specific water quality requirements, and its stability directly affects the unobstructed flow of the reinjection wells, the permeability of the reservoir, and the long-term safe operation of the geothermal extraction system.

[0003] During heat exchange and transportation, geothermal well reinjection water is prone to a series of water quality problems due to factors such as temperature changes, pressure fluctuations, and contact with air. Among these, dissolved oxygen corrosion and scale formation caused by unstable water quality, leading to increased pipeline resistance, are the main bottlenecks restricting the efficient operation of geothermal reinjection systems. Dissolved oxygen reacts with reinjection pipelines and downhole metal components to form corrosion products, which not only shorten equipment lifespan but may also enter the geothermal reservoir with the reinjection water, clogging fissures and reducing reservoir permeability. Simultaneously, calcium and magnesium ions in the reinjection water are easily precipitated under temperature and pressure changes, forming scale, further exacerbating pipeline blockage and reducing heat transfer efficiency. To address these issues, existing technologies often employ the addition of anti-corrosion and deoxygenating composite agents to treat the reinjection water. The deoxygenating components in these agents reduce the dissolved oxygen content in the water, the corrosion inhibitors suppress metal corrosion, and the scale inhibitors stabilize ions in the water, thereby ensuring the stable operation of the reinjection system.

[0004] In related technologies, patent application CN103922491A discloses an energy-saving scale inhibitor, descaling, and corrosion-preventing composite agent for steam boilers and its preparation method. The raw materials include: 15-35 parts lignin, 5-20 parts sodium alginate, 0.5-2.5 parts sodium humate, 1.5-3.5 parts sodium tannate, 1.5-3.5 parts modified starch, 2.5-5.5 parts ethylene glycol derivative, 2.5-5.5 parts sodium hydroxide, and 5-17 parts trisodium phosphate. Mixing these components yields the composite agent for steam boilers, which can reduce boiler blowdown rate, effectively prevent scale formation, dissolve old scale in the system and convert it into sludge, which is then removed through blowdown. The sludge remains fluid and will not clog instruments and valves, thus preventing any ongoing corrosion in the system.

[0005] However, the aforementioned composite agents still suffer from insufficient stability in deoxygenation efficiency in practical applications, particularly in the complex operating conditions of geothermal well reinjection. During geothermal well reinjection, the water body undergoes rapid temperature changes during the heat exchange stage and drastic pressure fluctuations during pressurization reinjection. Furthermore, due to sealing limitations, the water body is repeatedly exposed to air during transportation and pressurization, leading to a continuous introduction of dissolved oxygen. The deoxygenation components of these composite agents are highly sensitive to temperature and pressure; sudden temperature and pressure changes accelerate their chemical decomposition, reducing the activity of the effective components. Simultaneously, impurities such as calcium and magnesium ions in the reinjection water interfere with the normal deoxygenation reaction, further weakening the deoxygenation effect. In summary, the composite agents in these technologies struggle to maintain a stable residual oxygen concentration in the complex environment of geothermal well reinjection, characterized by large temperature and pressure fluctuations and continuous introduction of dissolved oxygen. Corrosion risks persist, resulting in insufficient stability in deoxygenation efficiency and failing to guarantee the long-term safe operation of the reinjection system. Summary of the Invention

[0006] In order to effectively improve the oxygen removal efficiency and stability of anti-corrosion and deoxygenating agents, this application provides an anti-corrosion and deoxygenating composite agent for geothermal well reinjection water and its preparation method.

[0007] The technical solution provided in this application for a composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water is as follows:

[0008] A composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water comprises the following raw materials in parts by weight:

[0009] 30-40 parts of double-modified sodium sulfite;

[0010] 10-20 parts corrosion inhibitor;

[0011] 8-15 parts scale inhibitor;

[0012] 5-10 parts of aminotrimethylenephosphonic acid;

[0013] 5-10 parts of hydroxyethylidene diphosphonic acid;

[0014] 3-8 parts of polyethylene glycol monomethyl ether acrylate;

[0015] 40-50 parts deionized water;

[0016] The double-modified sodium sulfite was obtained by sequentially modifying sodium sulfite with a silane coupling agent and acrylic acid.

[0017] By adopting the above technical solution, double-modified sodium sulfite is used as the main oxygen removal agent. Through sequential modification with silane coupling agent and acrylic acid, the environmental adaptability of traditional oxygen removal components is optimized at the molecular structure level, solving the key problems of existing oxygen removal components being sensitive to temperature and pressure changes and easily decomposing and failing. The pretreatment with silane coupling agent can form a stable coating layer on the surface of sodium sulfite, effectively resisting the damage of the core oxygen removal groups to sudden temperature and pressure changes; the organic long chains introduced by subsequent acrylic acid grafting further construct a steric hindrance effect, slowing down the oxidation and decomposition rate of the effective components, ensuring continuous oxygen removal activity throughout the entire process of geothermal reinjection heat exchange and pressurization.

[0018] The introduction of aminotrimethylenephosphonic acid (ATA) and hydroxyethylidene diphosphonic acid (HEDDI) specifically addresses the problem of impurities such as calcium and magnesium ions interfering with the deoxygenation reaction in recharge water. The combined system of ATA and HEDDI, through synergistic chelation, efficiently captures various interfering ions in the water, preventing them from reacting with the main deoxygenating agent to form precipitates or adsorbing onto the active sites of the deoxygenating agent, thus ensuring the smooth progress of the deoxygenation reaction. Compared to single anti-interference agents, this combined system can adapt to a wide range of pH fluctuations in recharge water, ensuring stable anti-interference performance under different water quality conditions, and providing a guarantee for the stability of deoxygenation efficiency from the perspective of the reaction environment.

[0019] The addition of polyethylene glycol monomethyl ether acrylate achieves the dual goals of component synergy and enhanced efficiency, further improving the overall stability of deoxygenation performance. On the one hand, it improves the dispersion compatibility of each functional component in water, avoiding localized deoxygenation efficiency attenuation caused by component stratification and antagonism. On the other hand, the hydrophilic groups in its molecular structure accelerate the reaction rate between the deoxygenating agent and continuously introduced dissolved oxygen, while simultaneously assisting in the construction of a dense protective film on the metal surface, ensuring corrosion prevention while avoiding interference with the deoxygenation reaction. The above-mentioned composite agent system has a scientifically proportioned composition, ensuring stable deoxygenation performance while simultaneously achieving synergistic enhancement of corrosion prevention and scale inhibition functions. It is fully adaptable to the complex operating conditions of geothermal well reinjection, effectively solving the shortcomings of existing agents that are unable to maintain a stable residual oxygen concentration and where corrosion risks persist.

[0020] Optionally, the double-modified sodium sulfite is prepared by the following method:

[0021] A1. Sodium sulfite is mixed with a silane coupling agent KH550 solution and stirred at 30-40℃ for 1-2 hours. After filtration and drying, pretreated sodium sulfite is obtained.

[0022] A2. Pretreated sodium sulfite is mixed with acrylic acid, and then ammonium persulfate initiator is added. The mixture is reacted at 65-85℃ for 3-4 hours. After cooling, filtration, washing and drying, double-modified sodium sulfite is obtained.

[0023] By adopting the above technical solution, a two-step preparation process for double-modified sodium sulfite was clarified, ensuring the stability and reliability of the modification effect and providing a core material basis for stable oxygen removal efficiency. This preparation method first achieves uniform coating of the sodium sulfite surface through silane coupling agent pretreatment, and then introduces functional long chains through acrylic acid grafting. The two-step reaction conditions are mild and controllable, avoiding problems such as insufficient modification and structural inhomogeneity caused by single or mixed modification. The double-modified sodium sulfite prepared by this method maintains stable resistance to temperature and pressure fluctuations and stable oxygen removal activity, effectively avoiding the problem of oxygen removal efficiency fluctuations caused by improper modification processes, and further enhancing the stability of the oxygen removal efficiency of double-modified sodium sulfite as a primary oxygen removal agent.

[0024] Optionally, in step A1, the mass concentration of the silane coupling agent KH550 solution is 10%-15%, and the mass ratio of sodium sulfite to the silane coupling agent KH550 solution is 1:(3-5).

[0025] By employing the above technical solution, and limiting the concentration of the silane coupling agent KH550 solution and the mass ratio of sodium sulfite to the solution, the modification effect in the pretreatment stage is ensured to be controllable. A suitable solution concentration ensures that the silane coupling agent is fully dispersed and forms a stable bond with the hydroxyl groups on the sodium sulfite surface, avoiding excessively thick coating layers due to excessively high concentrations, which would affect oxygen removal activity, or incomplete coating and insufficient resistance to temperature and pressure due to excessively low concentrations. A reasonable mass ratio ensures sufficient contact and reaction between sodium sulfite and the silane coupling agent, guaranteeing the structural stability of the pretreated sodium sulfite and laying a good foundation for the subsequent acrylic acid grafting reaction, thereby indirectly improving the efficiency and stability of the oxygen removal agent.

[0026] Optionally, in step A2, the mass ratio of the pretreated sodium sulfite to acrylic acid is 1:(0.5-0.8).

[0027] Optionally, the amount of ammonium persulfate initiator added is 0.8%-1.2% of the total mass of pretreated sodium sulfite and acrylic acid.

[0028] By adopting the above technical solution, an appropriate amount of initiator can effectively initiate the grafting reaction, ensuring a complete reaction and avoiding side reactions. Insufficient initiator will lead to incomplete grafting and difficulty in forming an effective steric hindrance effect. Excessive initiator may cause polymer crosslinking or damage the oxygen-scavenging active groups of sodium sulfite. This limitation ensures the controllability of the grafting reaction, thereby ensuring the stability of the structure and properties of the double-modified sodium sulfite and providing a process-level guarantee for stable oxygen scavenging efficiency.

[0029] Optionally, the corrosion inhibitor is a compound of molybdate and benzotriazole, wherein the mass ratio of molybdate to benzotriazole is (3-5):1.

[0030] By adopting the above technical solution, the compound system and ratio of the corrosion inhibitor were clearly defined, ensuring the anti-corrosion effect while avoiding interference from the corrosion inhibitor components on the stability of the deoxygenation efficiency. The compound system of molybdate and benzotriazole has a good synergistic anti-corrosion effect, forming a stable protective film on the metal surface and reducing the corrosion of metal components by dissolved oxygen. At the same time, this compound system has good compatibility with the dual-modified deoxygenating agent, will not react with the deoxygenating active components, and will not adsorb onto the deoxygenating active sites. A reasonable compound ratio can ensure high-efficiency anti-corrosion at a low dosage, avoiding water quality deterioration or deoxygenation reaction inhibition caused by excessive corrosion inhibitor, thereby ensuring the stable performance of deoxygenation efficiency.

[0031] Optionally, the molybdate is any one of sodium molybdate, potassium molybdate, or ammonium molybdate.

[0032] Optionally, the scale inhibitor is a compound of polyepoxysuccinic acid and hydrolyzed polymaleic anhydride, wherein the mass ratio of polyepoxysuccinic acid to hydrolyzed polymaleic anhydride is (1.5-2):1.

[0033] By adopting the above technical solution, the compound system of polyepoxysuccinic acid and hydrolyzed polymaleic anhydride exhibits highly efficient scale inhibition performance. It effectively inhibits the precipitation and scaling of calcium and magnesium ions in the reinjection water, preventing problems such as poor water flow and insufficient local deoxygenation caused by scale clogging pipes. This compound system has good compatibility with the deoxygenating agent and anti-interference additives, and will not react with the active deoxygenating components. Its scale inhibition effect keeps the pipes unobstructed, ensuring sufficient contact between the agent and the reinjection water, thereby guaranteeing a uniform and stable deoxygenation reaction and preventing localized attenuation of deoxygenation efficiency.

[0034] Optionally, the polyepoxysuccinic acid has a molecular weight of 400-800.

[0035] By adopting the above technical solutions, polyepoxysuccinic acid within the aforementioned specific molecular weight range exhibits superior scale inhibition activity and dispersing performance, enabling more efficient stabilization of calcium and magnesium ions in water and preventing scale formation. Simultaneously, polyepoxysuccinic acid within this molecular weight range demonstrates better solubility and dispersibility in water, avoiding the formation of colloids or precipitates that could interfere with the deoxygenation reaction. Optimizing the molecular weight of the scale-inhibiting components ensures stable scale inhibition function, preventing deterioration of operating conditions due to poor scale inhibition and thus guaranteeing continuous and stable deoxygenation efficiency.

[0036] Secondly, this application provides a method for preparing a composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water, using the following technical solution:

[0037] A method for preparing a composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water includes the following steps:

[0038] Add aminotrimethylene phosphonic acid and hydroxyethylidene diphosphonic acid sequentially to deionized water and stir for 10-15 minutes until completely dissolved. Then add double-modified sodium sulfite and stir at room temperature for 20-30 minutes. Next, add corrosion inhibitor and scale inhibitor sequentially and stir for 25-35 minutes. Finally, add polyethylene glycol monomethyl ether acrylate, stir for 15-20 minutes, and filter to obtain a corrosion-preventing and oxygen-removing composite agent.

[0039] By adopting the above technical solution, the preparation method optimizes the feeding sequence and stirring conditions, ensuring thorough mixing and synergistic effects of each component, thereby improving the stability of the deoxygenation efficiency of the agent from the preparation stage. The entire preparation process is simple and controllable, effectively avoiding fluctuations in agent performance caused by uneven mixing and insufficient reaction, ensuring that the batch-produced agents can stably adapt to the complex working conditions of geothermal well reinjection and continuously exert stable deoxygenation efficiency.

[0040] In summary, this application has the following beneficial effects:

[0041] 1. This application precisely addresses the core problem of insufficient deoxygenation efficiency stability of existing agents in complex environments with large temperature and pressure fluctuations during geothermal well reinjection, continuous introduction of dissolved oxygen, and significant interference from impurities by constructing a core system of "dual-modified deoxygenating agent - composite anti-interference additive - synergistic enhancer". The dual-modified deoxygenating agent significantly improves the environmental adaptability of the deoxygenating components through molecular structure optimization, effectively resisting the damage to the core active groups caused by sudden temperature and pressure changes, slowing down the oxidation and decomposition rate, and ensuring continuous deoxygenation activity throughout the entire process; the composite anti-interference additive can efficiently capture interfering ions in the water, ensuring smooth deoxygenation reaction, while adapting to a wide range of pH fluctuations, providing environmental protection for stable deoxygenation efficiency; the synergistic enhancer optimizes the dispersion compatibility of each component, avoids local efficiency decay, accelerates the deoxygenation reaction rate, and assists in the construction of an anti-corrosion protective film. The entire system has achieved a breakthrough improvement in the stability of deoxygenation efficiency, while simultaneously taking into account the synergistic effects of corrosion prevention and scale inhibition. It has completely solved the shortcomings of existing agents in maintaining a stable residual oxygen concentration and the continuous existence of corrosion risks, and is fully adapted to the complex working conditions of geothermal well reinjection.

[0042] 2. The preferred design in this application, including the double-modified sodium sulfite preparation process and the compound system of corrosion inhibitor and scale inhibitor, further enhances the stability of deoxygenation efficiency. The two-step preparation process of double-modified sodium sulfite is mild and controllable, ensuring the uniformity and reliability of the modification effect and avoiding fluctuations in deoxygenation efficiency caused by insufficient modification or structural inhomogeneity, thus laying a material foundation for the stable performance of the core deoxygenation function. The optimized compound scheme of corrosion inhibitor and scale inhibitor, while ensuring corrosion and scale inhibition efficiency, maximizes the compatibility with the main deoxygenation agent and anti-interference additives, and will not interfere with the deoxygenation reaction process. These optimized designs, from the perspective of component performance optimization and system compatibility improvement, further avoid various risks that may lead to the decline of deoxygenation efficiency, enabling the agent to maintain a stable deoxygenation effect under different water quality and operating conditions, significantly enhancing the practicality and adaptability of the solution.

[0043] 3. The preparation method of this application ensures the stability of the deoxygenation efficiency of the reagent by scientifically optimizing the feeding sequence and stirring conditions from the production stage. This method adopts a feeding logic of "pretreatment with anti-interference additives first, then step-by-step addition of functional components, and finally synergistic enhancement," which can establish a stable reaction environment in advance and avoid reaction imbalance or precipitation caused by excessively high local concentrations of components. Mild stirring conditions and reasonable stirring time ensure that each functional component is fully dispersed and uniformly mixed, avoiding insufficient local deoxygenation efficiency due to uneven mixing. The entire preparation process is simple and controllable, effectively avoiding reagent performance differences caused by process fluctuations in batch production, ensuring that each batch of finished product can stably adapt to the complex working conditions of geothermal well reinjection, continuously exerting stable deoxygenation efficiency, and providing reliable reagent protection for the long-term safe operation of the geothermal reinjection system. Detailed Implementation

[0044] The present application will be further described in detail below with reference to the embodiments.

[0045] Preparation example of double-modified sodium sulfite

[0046] Preparation Example 1

[0047] The double-modified sodium sulfite was prepared by the following method:

[0048] A1. Mix 10 kg of sodium sulfite with 30 kg of 15% KH550 silane coupling agent solution, stir at 30°C for 1 h, filter and dry to obtain pretreated sodium sulfite.

[0049] A2. Mix 10 kg of pretreated sodium sulfite with 5 kg of acrylic acid, then add 0.12 kg of ammonium persulfate initiator, react at 65 °C for 3 h, cool and filter to obtain filter cake, wash repeatedly with deionized water 3 times, and then dry in a vacuum drying oven at 50 °C for 2 h to obtain double-modified sodium sulfite.

[0050] Preparation Example 2

[0051] The double-modified sodium sulfite was prepared by the following method:

[0052] A1. Mix 10 kg of sodium sulfite with 40 kg of 12% KH550 silane coupling agent solution, stir at 35°C for 1.5 h, filter and dry to obtain pretreated sodium sulfite.

[0053] A2. Mix 10 kg of pretreated sodium sulfite with 6.5 kg of acrylic acid, then add 0.17 kg of ammonium persulfate initiator, react at 75 °C for 3.5 h, cool and filter to obtain filter cake, wash repeatedly with deionized water 3 times, and then dry in a vacuum drying oven at 55 °C for 1.5 h to obtain double-modified sodium sulfite.

[0054] Preparation Example 3

[0055] The double-modified sodium sulfite was prepared by the following method:

[0056] A1. Mix 10 kg of sodium sulfite with 50 kg of 10% KH550 silane coupling agent solution, stir at 40°C for 1 h, filter and dry to obtain pretreated sodium sulfite.

[0057] A2. Mix 10 kg of pretreated sodium sulfite with 8 kg of acrylic acid, then add 0.22 kg of ammonium persulfate initiator, react at 85 °C for 3 h, cool and filter to obtain filter cake, wash repeatedly with deionized water 3 times, and then dry in a vacuum drying oven at 60 °C for 1 h to obtain double-modified sodium sulfite.

[0058] Preparation Example 4

[0059] Modified sodium sulfite was prepared using the following method:

[0060] 10 kg of sodium sulfite was mixed with 8 kg of acrylic acid, and then 0.22 kg of ammonium persulfate initiator was added. The mixture was reacted at 85 °C for 3 h. After cooling, the mixture was filtered to obtain a filter cake, which was washed three times with deionized water and then dried in a vacuum drying oven at 60 °C for 1 h to obtain modified sodium sulfite.

[0061] Example

[0062] Example 1

[0063] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water, the raw material components and dosages of which are shown in Table 1, wherein the double-modified sodium sulfite is selected from the double-modified sodium sulfite prepared in Preparation Example 1, the corrosion inhibitor is a compound obtained by compounding sodium molybdate and benzotriazole in a mass ratio of 3:1, and the scale inhibitor is a compound obtained by compounding polyepoxysuccinic acid and hydrolyzed polymaleic anhydride in a mass ratio of 1.5:1, wherein the molecular weight of polyepoxysuccinic acid is 400 and the molecular weight of hydrolyzed polymaleic anhydride is 500.

[0064] A method for preparing a composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water includes the following steps:

[0065] Aminotrimethylene phosphonic acid and hydroxyethylidene diphosphonic acid were added sequentially to deionized water and stirred for 10 minutes until completely dissolved. Then, double-modified sodium sulfite was added and stirred at room temperature for 20 minutes. Corrosion inhibitor and scale inhibitor were added sequentially and stirred for 25 minutes. Finally, polyethylene glycol monomethyl ether acrylate was added, stirred for 15 minutes, and then filtered to obtain a corrosion-preventing and oxygen-removing composite agent.

[0066] Example 2

[0067] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water, the raw material components and dosages of which are shown in Table 1, wherein the double-modified sodium sulfite is selected from the double-modified sodium sulfite prepared in Preparation Example 2, the corrosion inhibitor is a compound obtained by compounding sodium molybdate and benzotriazole in a mass ratio of 4:1, and the scale inhibitor is a compound obtained by compounding polyepoxysuccinic acid and hydrolyzed polymaleic anhydride in a mass ratio of 1.8:1, wherein the molecular weight of polyepoxysuccinic acid is 600 and the molecular weight of hydrolyzed polymaleic anhydride is 1000.

[0068] A method for preparing a composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water includes the following steps:

[0069] Aminotrimethylene phosphonic acid and hydroxyethylidene diphosphonic acid were added sequentially to deionized water and stirred for 12 minutes until completely dissolved. Then, double-modified sodium sulfite was added and stirred at room temperature for 25 minutes. Corrosion inhibitor and scale inhibitor were added sequentially and stirred for 30 minutes. Finally, polyethylene glycol monomethyl ether acrylate was added, stirred for 18 minutes, and then filtered to obtain a corrosion-preventing and oxygen-removing composite agent.

[0070] Example 3

[0071] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water, the raw material components and dosages of which are shown in Table 1, wherein the double-modified sodium sulfite is selected from the double-modified sodium sulfite prepared in Preparation Example 3, the corrosion inhibitor is a compound obtained by compounding sodium molybdate and benzotriazole in a mass ratio of 5:1, and the scale inhibitor is a compound obtained by compounding polyepoxysuccinic acid and hydrolyzed polymaleic anhydride in a mass ratio of 2:1, wherein the molecular weight of polyepoxysuccinic acid is 800 and the molecular weight of hydrolyzed polymaleic anhydride is 1500.

[0072] A method for preparing a composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water includes the following steps:

[0073] Aminotrimethylene phosphonic acid and hydroxyethylidene diphosphonic acid were added sequentially to deionized water and stirred for 15 minutes until completely dissolved. Then, double-modified sodium sulfite was added and stirred at room temperature for 30 minutes. Corrosion inhibitor and scale inhibitor were added sequentially and stirred for 35 minutes. Finally, polyethylene glycol monomethyl ether acrylate was added, stirred for 20 minutes, and then filtered to obtain a corrosion-preventing and oxygen-removing composite agent.

[0074] Table 1. Raw material components and dosage (kg) of the anti-corrosion and oxygen-removing composite agents in Examples 1-3

[0075]

[0076] Example 4

[0077] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water differs from Example 1 in that the corrosion inhibitor in this example is a compound obtained by mixing potassium molybdate and benzotriazole in a mass ratio of 3:1.

[0078] Example 5

[0079] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water differs from Example 1 in that the corrosion inhibitor in this example is a compound obtained by mixing ammonium molybdate and benzotriazole in a mass ratio of 3:1.

[0080] Example 6

[0081] A composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water differs from Example 1 in that the corrosion inhibitor in this example is a single benzotriazole.

[0082] Example 7

[0083] A composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water differs from Example 1 in that the scale inhibitor in this example is a single hydrolyzed maleic anhydride.

[0084] Comparative Example

[0085] Comparative Example 1

[0086] An anti-corrosion composite agent was prepared according to Example 1 in the patent application document with publication number CN103922491A, entitled "An Energy-Saving Scale Inhibitor, Scale Remover and Corrosion Preventive Composite Agent for Steam Boilers and Its Preparation Method".

[0087] Comparative Example 2

[0088] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water differs from Example 1 in that an equal amount of modified sodium sulfite prepared in Preparation Example 4 is used in this comparative example to replace the double-modified sodium sulfite in the raw materials.

[0089] Comparative Example 3

[0090] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water differs from Example 1 in that an equal amount of unmodified sodium sulfite is used in this comparative example to replace the double-modified sodium sulfite in the raw materials.

[0091] Comparative Example 4

[0092] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water differs from Example 1 in that aminotrimethylene phosphonic acid is not added in this comparative example, and the difference is made up with hydroxyethylidene diphosphonic acid.

[0093] Comparative Example 5

[0094] A composite agent for corrosion prevention and deoxygenation of geothermal well reinjection water differs from Example 1 in that hydroxyethylidene diphosphonic acid is not added in this comparative example, and the difference is made up with aminotrimethylene phosphonic acid.

[0095] Performance testing

[0096] 1. Deoxygenation efficiency test (iodometric method, according to GB / T15456-2019)

[0097] Test water sample: Simulated geothermal reinjection water (containing 200 mg / L Ca2+, 80 mg / L Mg2+, pH 7.5, initial dissolved oxygen content 8.2 mg / L);

[0098] Test conditions: room temperature (25℃), normal pressure, and the dosage of the reagent was 50 mg / L (the conventional dosage for geothermal reinjection).

[0099] Operating procedure: Take 1000 mL of simulated water sample and place it in a beaker. Add the set dose of reagent, stir to dissolve, and start timing. Take a sample after 1 hour of reaction and determine the residual dissolved oxygen content in the water sample using the iodometric method.

[0100] Calculation method: Deoxygenation efficiency (%) = (initial dissolved oxygen content - residual dissolved oxygen content) / initial dissolved oxygen content × 100%, take the average value of 3 parallel tests.

[0101] Experimental results: see Table 2.

[0102] 2. Deoxygenation stability test (simulated cyclic operating condition test)

[0103] Experimental setup: A circulating temperature and pressure fluctuation simulation device (including an aeration unit, a temperature and pressure control unit, and a circulating pump, with an effective volume of 5L) was used.

[0104] Test water sample: Simulated geothermal reinjection water used in the deoxygenation efficiency test;

[0105] Simulated operating conditions: continuous aeration (aeration rate 0.5L / min, simulating continuous introduction of dissolved oxygen) + cyclic temperature and pressure fluctuations (temperature 25℃→80℃→25℃, pressure 0.1MPa→1.0MPa→0.1MPa, one cycle every 4 hours, cumulative operation 24 hours), reagent dosage 50mg / L;

[0106] Operating steps: Add 5L of simulated water sample and the set dosage of reagent to the device, start the device, and take samples at 0h (initial), 4h, 8h, 12h and 24h respectively to determine the residual dissolved oxygen content;

[0107] Evaluation index: Maximum fluctuation of residual dissolved oxygen (ΔDO, mg / L) within 24 hours. The smaller the fluctuation, the better the oxygen removal stability.

[0108] Experimental results: see Table 2.

[0109] 3. Decomposition rate detection of active ingredients under varying temperature and pressure (ion chromatography)

[0110] Target of testing: The core oxygen-removing component in the reagent (active sulfite ions of double-modified sodium sulfite);

[0111] Test conditions: A high-pressure reactor was used to simulate temperature and pressure fluctuations (temperature 25℃→80℃→25℃, pressure 0.1MPa→1.0MPa→0.1MPa, heat and pressure maintained for 12h), and the reagent concentration was 50mg / L (dissolved in simulated geothermal reinjection water).

[0112] Operating procedures: Determine the content of active sulfite in the reagent before (initial) and after the test (ion chromatography: eluent is a mixture of NaHCO3 and Na2CO3, flow rate 1.0 mL / min).

[0113] Calculation method: Decomposition rate (%) = (Initial active sulfite content - Active sulfite content after experiment) / Initial active sulfite content × 100%.

[0114] Experimental results: see Table 2.

[0115] 4. Metal corrosion rate test (drop loss method, according to GB / T18175-2014)

[0116] Test piece material: Q235 carbon steel (common material for geothermal reinjection pipes), size 50mm×25mm×2mm, weighed after pretreatment (accurate to 0.0001g).

[0117] Test conditions: Simulated working conditions for deoxygenation stability testing (24h circulating temperature and pressure fluctuations + continuous aeration), reagent dosage 50mg / L, test piece fully immersed in water sample;

[0118] Operating procedures: After the test, remove the test piece, remove the corrosion products, dry it, weigh it, and calculate the corrosion rate;

[0119] Calculation method: Corrosion rate (mm / a) = (8.76 × 10) 4 ×Δm) / (S×ρ×t), where Δm is the weight loss of the sample (g), and S is the surface area of ​​the sample (cm²). 2 ), ρ is the density of carbon steel (7.85 g / cm³). 3 ), where t is the test time (h).

[0120] Experimental results: see Table 2.

[0121] Table 2 Experimental Results

[0122]

[0123] As shown in Table 2, the composite agent provided in this application maintains good performance in terms of oxygen removal efficiency, oxygen removal stability, and active ingredient stability, as detailed below:

[0124] Deoxygenation efficiency and stability: The deoxygenation efficiencies of Examples 1-5 were all above 95%, and the maximum fluctuation of residual dissolved oxygen over 24 hours was below 0.35 mg / L, significantly better than Comparative Example 1 (deoxygenation efficiency 80.2%, dissolved oxygen fluctuation 1.85 mg / L), Comparative Example 2 (deoxygenation efficiency 92.1%, dissolved oxygen fluctuation 0.86 mg / L), and Comparative Example 3 (deoxygenation efficiency 88.5%, dissolved oxygen fluctuation 1.23 mg / L). This demonstrates that the "dual-modified deoxygenating agent + composite anti-interference additive" system of this application can rapidly and efficiently remove oxygen, and can stably maintain a low residual oxygen concentration under geothermal reinjection conditions of continuous aeration and temperature and pressure fluctuations, solving the core problem of insufficient stability in the deoxygenation efficiency of existing agents.

[0125] Decomposition rate of active ingredients: The decomposition rate of active ingredients in Examples 1-5 was less than 4%, while the decomposition rate of Comparative Example 3 (unmodified) reached 18.7%, and that of Comparative Example 1 reached 25.3%. This indicates that the dual modification treatment (silane coupling agent pretreatment + acrylic acid grafting) can significantly improve the resistance to temperature and pressure fluctuations of the scavenging agent, reduce the decomposition of active ingredients, and provide a material basis for the stability of scavenging. The decomposition rate of Comparative Examples 4-5 was slightly higher than that of the Examples, indicating that the use of aminotrimethylene phosphonic acid and hydroxyethylidene diphosphonic acid as anti-interference agents can reduce the damage of impurities to active ingredients and further improve stability.

[0126] Corrosion rate: The corrosion rates of Examples 1-5 were all below 0.03 mm / a, far superior to Comparative Example 1 (0.215 mm / a), Comparative Example 2 (0.082 mm / a), and Comparative Example 3 (0.136 mm / a). This verifies that the present application can effectively inhibit metal corrosion by stabilizing oxygen removal efficiency, solving the defect of existing agents that cause persistent corrosion risk due to unstable oxygen removal. The corrosion rates of Examples 6-7 (single corrosion inhibitor / scale inhibitor) were slightly higher than those of Examples 1-5, indicating that the synergistic effect of the combined corrosion inhibitor and scale inhibitor can further enhance the anti-corrosion effect.

[0127] Example 3 exhibits the best performance across all metrics (deoxygenation efficiency 98.2%, dissolved oxygen fluctuation 0.18 mg / L, decomposition rate 2.1%, corrosion rate 0.019 mm / a). This is because it uses the highest amount of double-modified sodium sulfite and has a better ratio of corrosion inhibitor and scale inhibitor, indicating that optimizing the component dosage in this application can further improve performance. Examples 4-5 (using different molybdates) show performance similar to Example 1, demonstrating that the preferred molybdate types in this application are all compatible with the system, ensuring stable performance.

[0128] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A composite agent for corrosion prevention and oxygen removal in geothermal well reinjection water, characterized in that, The raw materials include the following weight parts: 30-40 parts of double modified sodium sulfite; 10-20 parts of corrosion inhibitor; 8-15 parts of scale inhibitor; 5-10 parts of amino trimethylene phosphonic acid; 5-10 parts of hydroxyethylidene diphosphonic acid; 3-8 parts of polyethylene glycol monomethyl ether acrylate; 40-50 parts of deionized water; The double modified sodium sulfite is obtained by sequentially modifying sodium sulfite with silane coupling agent and acrylic acid: A1, sodium sulfite is mixed with silane coupling agent KH550 solution, stirred at 30-40℃ for 1-2h, filtered and dried to obtain pretreated sodium sulfite; A2, the pretreated sodium sulfite is mixed with acrylic acid, then ammonium persulfate initiator is added, and the mixture is reacted at 65-85℃ for 3-4h, cooled, filtered, washed, and dried to obtain double modified sodium sulfite.

2. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water according to claim 1, characterized in that: In step A1, the mass concentration of the silane coupling agent KH550 solution is 10%-15%, and the mass ratio of sodium sulfite to silane coupling agent KH550 solution is 1:(3-5).

3. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water according to claim 2, characterized in that: In step A2, the mass ratio of pretreated sodium sulfite to acrylic acid is 1:(0.5-0.8).

4. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water according to claim 3, characterized in that: The addition amount of the ammonium persulfate initiator is 0.8%-1.2% of the total mass of pretreated sodium sulfite and acrylic acid.

5. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water according to claim 3, characterized in that: The corrosion inhibitor is a complex of molybdate and benzotriazole, and the mass ratio of molybdate to benzotriazole is (3-5):

1.

6. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water according to claim 5, characterized in that: The molybdate is any one of sodium molybdate, potassium molybdate, and ammonium molybdate.

7. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water according to claim 1, characterized in that: The scale inhibitor is a complex of polyepoxysuccinic acid and hydrolyzed polymaleic anhydride, and the mass ratio of polyepoxysuccinic acid to hydrolyzed polymaleic anhydride is (1.5-2):

1.

8. The corrosion-preventing and oxygen-removing composite agent for geothermal well recharge water according to claim 7, characterized in that: The molecular weight of the polyepoxysuccinic acid is 400-800.

9. A method for preparing the corrosion-preventing and oxygen-removing composite agent for geothermal well reinjection water according to any one of claims 1-8, characterized in that, The method includes the following steps: Amino trimethylene phosphonic acid and hydroxyethylidene diphosphonic acid are sequentially added to deionized water, stirred for 10-15min until completely dissolved, then double modified sodium sulfite is added, stirred at room temperature for 20-30min, then corrosion inhibitor and scale inhibitor are sequentially added, stirred for 25-35min; finally, polyethylene glycol monomethyl ether acrylate is added, stirred for 15-20min, then filtered to obtain the corrosion and oxygen removal composite agent.

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