Method for increasing the operating load of an evaporator system under brines with high silicon content

Abstract

The application provides a method for improving the operation load of an evaporator system under high-silicon brine. The evaporator system comprises a water inlet tank, a heat exchanger, a falling film tube and a steam compression system, the mass concentration of silicon in the high-silicon brine is greater than or equal to 400 mg / L, and the method comprises the following steps: first, continuously adding a specific kind of alkaline substance in the falling film tube on line, controlling the pH value and the holding time of the water quality in the falling film tube, then stopping adding the alkaline substance, adding a specific kind of acidic substance in the water inlet tank on line in batches, controlling the pH value and the holding time of the water quality in the water inlet tank, and stopping adding the acidic substance; and the above steps are repeated in sequence. The application periodically uses specific kinds of acidic substances and alkaline substances, controls the pH value range and the holding time, does not need frequent shutdown, realizes the on-line cleaning of the evaporator, significantly improves the operation load and the efficiency, effectively solves the frequent scaling problem under high-silicon brine, and reduces the maintenance cost.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a method for increasing the operating load of an evaporator system under high-silica saline conditions. Background Technology

[0002] In the coal chemical and petroleum refining industries, saline wastewater treatment and advanced wastewater treatment are crucial steps in achieving environmentally friendly production and resource recycling. In traditional processes, after anaerobic treatment, the remaining high-salinity wastewater (including wastewater from circulating water systems, demineralized water systems, and boiler emissions) requires further advanced treatment to ensure maximum salt recovery and utilization. The treated reclaimed water is typically recycled back into the circulating water and demineralized water systems, while the high-concentration brine is concentrated through evaporation and then sent to an evaporation pond for natural crystallization.

[0003] In recent years, the "zero-discharge" water treatment technology combining pretreatment, dual membranes (ultrafiltration + reverse osmosis), and falling film evaporation has received widespread attention and application in the industry due to its stability, simplicity, and ability to achieve zero wastewater discharge, resulting in a steady increase in market share. However, in actual operation, especially when treating concentrated brine containing high concentrations of silicon (e.g., 400 mg / L), existing evaporation systems face serious scaling problems. Specifically, the design parameters of falling film evaporators are typically suitable for lower silicon concentrations, such as 25 mg / L, but in actual operation, the silicon content far exceeds the design value, leading to rapid scaling of key components such as the falling film tubes, the main body of the equipment, and the piping network, resulting in a significant decrease in flow rate and evaporation efficiency. More seriously, the current plate heat exchanger design is not suitable for long-term treatment of high-silica wastewater, which further exacerbates the evaporator's operating load problem (e.g., the evaporator operating load can only be maintained at around 40%), failing to meet the system's operating load requirements.

[0004] In existing technologies, evaporator descaling, especially in high-silica concentrated brine environments, typically involves the following methods, all of which require equipment shutdown for cleaning. For example, high-pressure water jet cleaning: physically removes scale by impacting the evaporator surface with high-pressure water. While effective, this method requires the evaporator to be completely shut down for manual or mechanical cleaning, and the high-pressure water jet may cause physical damage to the equipment. Chemical cleaning: soaking the evaporator in strong acid or alkali solutions (such as hydrochloric acid, sulfuric acid, sodium hydroxide, etc.) to dissolve or decompose the scale. Chemical cleaning usually requires shutdown, introducing the cleaning agent into the evaporator for circulation to chemically react with the scale layer to achieve descaling. However, this method not only consumes large amounts of chemicals but also has the potential to corrode the evaporator materials, and the treated wastewater requires environmentally friendly treatment, increasing additional costs. Ultrasonic cleaning: utilizing the cavitation effect of ultrasound to break up the scale layer and remove it from the evaporator surface. Although ultrasonic cleaning avoids direct contact and reduces physical damage, it still requires the evaporator to be shut down to ensure operator safety and cleaning effectiveness. Bio-enzyme cleaning: This method uses bio-enzyme preparations to remove organic scale through the biodegradation of enzymes. While environmentally friendly, this method is relatively inefficient and has limited capacity to handle inorganic silicates. It also requires the evaporator to be shut down to complete the entire cleaning process.

[0005] The common drawback of the above descaling methods is that they all require the evaporator to be shut down, which not only affects the continuity of production, but also increases operating costs and maintenance complexity. Especially in modern chemical industries that pursue "zero emissions" and maximize resource utilization, frequent shutdowns for cleaning have become a major obstacle to improving the operating efficiency and economic benefits of evaporators.

[0006] Due to frequent scaling and clogging, the evaporator is forced to shut down 3 to 4 times a year for descaling, which not only increases the complexity and cost of equipment maintenance, but also puts additional pressure on environmental protection operations, affecting the stable operation and economic benefits of the factory. Summary of the Invention

[0007] The main objective of this invention is to provide a method for increasing the operating load of an evaporator system under high-silica saline conditions, in order to solve the problems of short operating cycles, low loads, and the need for shutdown and cleaning after scaling in existing high-silica saline evaporator systems.

[0008] To achieve the above objectives, according to one aspect of the present invention, a method for increasing the operating load of an evaporator under high-silica brine conditions is provided. The evaporator system includes an inlet tank, a heat exchanger, falling film tubes, and a vapor compression system. The high-silica brine has a silica concentration ≥400 mg / L. The method includes the following steps: Step S1, continuously adding an alkaline substance online to the falling film tubes, controlling the pH of the water in the falling film tubes to 10–12, and maintaining this pH for 10–30 days, then stopping the addition of the alkaline substance; Step S2, adding an acidic substance online in portions, controlling the pH of the water in the inlet tank to 1–4, and maintaining this pH for 0.5–2 days, then stopping the addition of the acidic substance; repeating steps S1 and S2 sequentially; wherein the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, and sodium bicarbonate; and the acidic substance includes one or more of citric acid, oxalic acid, and acetic acid.

[0009] Furthermore, in high-silica salt water, Ca 2+ The concentration is 10–400 mg / L, Mg 2+ The concentration is 5–110 mg / L, SO4 2- The concentration is ≤145266 mg / L, Cl - The concentration of NO3 was 25699–30687 mg / L. - The concentration ranged from 5984 to 7241 mg / L, with COD ≤ 2100 and TDS 210000 to 240000.

[0010] Furthermore, the method also includes the step of adding sulfuric acid to pretreat the high-silica brine.

[0011] Furthermore, the method also includes the step of adding sulfuric acid and adjusting the pH of the high-silica brine to 4-5 to pretreat the high-silica brine.

[0012] Further, in step S1, the alkaline substance is added in the form of an alkaline solution with a concentration of 25-35 wt% and a volume ratio of the alkaline solution to the high-silica salt water of 1:(150-160).

[0013] Furthermore, in step S1, an alkaline substance is added to the falling film tube to control the pH value of the water in the falling film tube to be 10.2 to 10.8.

[0014] Furthermore, in step S2, an acidic substance is added to the water inlet tank to control the pH value of the water in the water inlet tank to be 3-4.

[0015] Furthermore, in step S2, the frequency of adding acidic substances is 1 to 2 times / 2 hours, and / or the total number of times acidic substances are added is 5 to 20 times.

[0016] Furthermore, the operating temperature of the falling film tube is 80–120°C.

[0017] Furthermore, the operating load of the evaporator system is 88–120% of the design load; and / or, the thickness growth rate of the falling film tube is ≤2 μm / d.

[0018] By applying the technical solution of this invention, specific types of acidic substances (one or more of citric acid, oxalic acid, and acetic acid) and alkaline substances (one or more of sodium hydroxide, potassium hydroxide, and sodium bicarbonate) are periodically used to control the pH range and holding time, achieving online cleaning of the evaporator without frequent shutdowns. This significantly improves operating load and efficiency, effectively solves the problem of frequent scaling in high-silica saline water, reduces maintenance costs, and promotes the continuity and economy of industrial water treatment processes. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 A schematic flow diagram of the evaporator system according to Embodiment 1 of the present invention is shown.

[0021] The above figures include the following reference numerals:

[0022] 1. Inlet tank; 2. Preheater; 3. Shell-and-tube heat exchanger; 4. Deaerator; 5. Falling film tube; 6. Demister; 7. Vapor compression system; 8. Circulating pump; 9. Distilled water tank;

[0023] A. High-silica brine; B. Alkaline substances; C. Acidic substances; D. Brine; E. Non-condensable gases; F. Vapor; G. A mixture of steam and water; H. Reclaimed water. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] As described in the background section of this invention, existing technologies suffer from problems such as short operating cycles, low loads, and the need for shutdown and cleaning after scaling in evaporator systems operating under high silica salt conditions. In particular, the evaporator falling film tubes and auxiliary equipment pipelines are prone to scaling and blockage under high silica salt conditions, leading to reduced system operating cycles and loads. Plate heat exchangers are not suitable for treating high silica salt conditions, resulting in low evaporator operating loads and the need for shutdown and cleaning after scaling. To address the aforementioned problems, in a typical embodiment of the present invention, a method for increasing the operating load of an evaporator system under high-silica brine conditions is provided. The evaporator system includes an inlet tank, a heat exchanger, a falling film tube, and a vapor compression system. The high-silica brine has a silica concentration ≥400 mg / L. The method includes the following steps: Step S1, continuously adding an alkaline substance online into the falling film tube to control the pH value of the water in the falling film tube to 10–12 and maintaining it for 10–30 days, then stopping the addition of the alkaline substance; Step S2, adding an acidic substance online in portions to the inlet tank to control the pH value of the water in the inlet tank to 1–4 and maintaining it for 0.5–2 days, then stopping the addition of the acidic substance; Steps S1 and S2 are repeated sequentially; wherein the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, and sodium bicarbonate; and the acidic substance includes one or more of citric acid, oxalic acid, and acetic acid.

[0026] In step S1 of this method, an alkaline substance (such as sodium hydroxide, potassium hydroxide, sodium bicarbonate, etc.) is added online into the falling film pipe to adjust the pH value of the water in the tank to a strongly alkaline condition of 10-12. Under such a pH environment, silicates and scale deposits such as CaSiO3, Na2SiO3, or MgSiO3 deposited on the surface of equipment such as the falling film pipe are converted into soluble forms and can enter the subsequent evaporation and crystallization process. With the long-term addition of alkaline substances, scale deposits such as silica gradually decrease or even disappear. Moreover, the silicates are not easy to form deposits on the surface of the falling film pipe, thereby inhibiting the formation of silica scale.

[0027] In step S2, acidic substances are added online to the inlet tank to adjust the pH of the water to an acidic level of 1-4. For example, in an acidic environment, carbonates in the scale, such as CaCO3, are converted into carbon dioxide and water, while alkaline substances, such as Mg(OH)2 and Ca(OH)2, are converted into soluble salts and peeled off from the surfaces of equipment such as falling film tubes, thereby restoring the heat exchange efficiency and hydrodynamic performance of the evaporator system. Regular acid washing not only removes existing scale but also prevents the formation of new scale, thus extending the continuous operating cycle of the evaporator system, reducing maintenance and cleaning frequency, lowering operating costs, and improving overall economic efficiency.

[0028] Furthermore, this application not only controls the pH range but also specifically limits the duration of pH maintenance. Maintaining water quality within a specific pH range for a certain period significantly affects the operating efficiency and maintenance cycle of the evaporator system. Specifically, maintaining a strongly alkaline pH of 10–12, by fully disrupting the chemical balance of silica scale formation, can significantly reduce clogging of the falling film tubes and effectively inhibit silicate scaling, thereby extending the equipment's trouble-free operating time. Meanwhile, periodically maintaining the water within an acidic pH range of 1–4 for several days, utilizing acidic substances, can fully and effectively remove deposited scale, effectively avoiding the high costs and environmental risks of high-pressure cleaning.

[0029] It should be noted that, regarding the type of alkaline substance, the inventors, through extensive experimental research, have particularly favored one or more of sodium hydroxide, potassium hydroxide, and sodium bicarbonate. Compared to calcium hydroxide, magnesium hydroxide, etc., the alkaline substance of this application has high solubility and strong alkalinity. It can not only rapidly raise the pH value of the solution to a specific range, quickly and efficiently dissolve scaling substances, and effectively inhibit the deposition of silicates on the surface of the falling film tube, thus significantly slowing down the scaling process, but also does not introduce ions that easily form scaling substances, thereby helping to reduce scaling formation. In addition, the alkaline substance of this application is low in cost and can gently maintain the equipment, extending its service life. By periodically adding specific types of alkaline substances, scaling problems in high-silica saline solutions can be effectively controlled, significantly increasing the operating load and cycle of the evaporator system, reducing maintenance costs, and providing strong technical support for achieving efficient and economical treatment of industrial wastewater.

[0030] Furthermore, the inventors specifically selected one or more of citric acid, oxalic acid, and acetic acid as the acidic substance. The addition of strong inorganic acids, such as HCl, not only introduces impurity ions that easily form precipitates, affecting subsequent distillation and crystallization processes, but also causes severe corrosion to the equipment; while HF is extremely corrosive, has excessively high operating costs, and F... - It is difficult to remove in subsequent desalination processes and is not suitable for cleaning evaporator systems. In contrast, citric acid, oxalic acid, and acetic acid have low corrosiveness and can effectively dissolve various scaling substances, such as calcium and magnesium salts. At the same time, at a specific pH value, they can gently peel off silicate deposits, avoiding significant damage to evaporator materials, especially metal surfaces. Moreover, citric acid has good biodegradability and has little impact on the environment, making the cleaning process more environmentally friendly.

[0031] In summary, the method of this application periodically uses specific types of acidic and alkaline substances, controls the pH range and holding time, and can achieve online cleaning of the evaporator without frequent shutdowns, significantly improving operating load and efficiency, effectively solving the problem of frequent scaling in high silica salt water, reducing maintenance costs, and promoting the continuity and economy of industrial water treatment processes.

[0032] In a preferred embodiment, in a high-silica brine, Ca 2+ The concentration is 10–400 mg / L, Mg 2+ The concentration is 5–110 mg / L, SO4 2- The concentration is ≤145266 mg / L, Cl - The concentration of NO3 was 25699–30687 mg / L. - The concentration of the pollutants was 5984–7241 mg / L, COD ≤ 2100, and TDS 210000–240000. Using the method described in this application to treat the above-mentioned water quality, based on the solubility product and surface activity mechanism, can more effectively inhibit the formation of hard scale, while reducing the adsorption of organic matter on the evaporator surface, ensuring heat exchange efficiency, extending equipment operating cycles, avoiding frequent shutdowns for cleaning, and more effectively reducing the consumption of acidic and / or alkaline substances, significantly lowering maintenance costs and environmental pressure.

[0033] In a preferred embodiment, the method further includes the step of adding sulfuric acid to pretreat the high-silica brine.

[0034] It should be noted that if too many sulfate ions are introduced, calcium sulfate scale may form, which is difficult to remove. In a preferred embodiment, the method further includes adding sulfuric acid and adjusting the pH of the high-silica brine to 4-5 to pretreat the high-silica brine.

[0035] In a preferred embodiment, the high-silica brine contains, by weight percentage, 30-40% calcium silicate, 15-20% magnesium silicate, 10-20% calcium carbonate, and 25-40% calcium sulfate, with a silicon concentration ≥400 mg / L. Treating the aforementioned water quality using the method of this application, based on dissolution equilibrium and chemical reaction mechanisms, can more effectively inhibit the formation of silicate scale while reducing calcium content. 2+ and Mg 2+ The associated hard scale deposition ensures efficient heat exchange of the evaporator, significantly extends the operating cycle, avoids frequent shutdowns caused by scaling, reduces operating and maintenance costs, and can also optimize the crystallization quality of the brine after evaporation, creating favorable conditions for subsequent utilization of salt resources, and achieving the dual goals of cost reduction and efficiency improvement and environmental protection in the process of chemical wastewater treatment.

[0036] To more effectively maintain the efficient and stable operation of the evaporation system, balance equipment protection and cost control, and further reduce environmental pollution, in a preferred embodiment, the alkaline substance in step S1 exists in the form of an alkaline solution with a concentration of 25-35 wt% and a volume ratio of the alkaline solution to the high-silica brine of 1:(150-160). These parameters are designed based on the solubility variation mechanism of silicates at different pH values. By introducing an appropriate amount of alkaline substance, the pH of the water can be more effectively adjusted to create a strongly alkaline environment, significantly inhibiting silicate scaling while avoiding equipment corrosion problems caused by excessive alkaline substances. However, if the alkaline concentration is too high or the volume ratio is too high, it may accelerate the corrosion of the evaporator equipment, reduce heat exchange efficiency, increase maintenance costs, and potentially cause alkaline pollution in the environment, affecting the quality of the crystallized salt. Conversely, if the alkaline concentration is too low or the volume ratio is too low, it may not effectively inhibit silicate scaling, affecting the operating load and efficiency of the evaporator, potentially leading to frequent equipment shutdowns for cleaning, increasing operational instability and economic burden.

[0037] In a preferred embodiment, in step S1, an alkaline substance is added to the falling film tube to control the pH value of the water inside the tube to be between 10.2 and 10.8. Under these conditions, scaling inhibition and equipment corrosion risk can be more accurately balanced, excessive use of chemical agents can be reduced, heat exchange efficiency can be optimized, environmental pollution can be reduced, and operational stability can be improved.

[0038] In a preferred embodiment, in step S2, an acidic substance is added to the inlet tank to control the pH value of the water in the inlet tank to 3-4. Under these conditions, the dissolution of scale can be more effectively focused, reducing the excessive reaction of non-target substances, thereby reducing the risk of equipment corrosion, improving cleaning efficiency and safety, and also saving chemical agents, reducing the environmental impact of wastewater treatment, and achieving a more environmentally friendly and economical maintenance effect.

[0039] The frequency and number of acid additions directly affect the cleanliness and operating efficiency of the equipment. In a preferred embodiment, in step S2, the acidic substance is added 1-2 times per 2 hours, and / or the total number of additions is 5-20 times. These frequencies more effectively ensure continuous scale management, preventing scale buildup from affecting heat exchange; these numbers avoid corrosion and resource waste that may result from over-cleaning. This not only more effectively maintains the system's high-performance operation and reduces sudden failures, but also further extends equipment lifespan and reduces maintenance costs.

[0040] In a preferred embodiment, the evaporator system further includes a pump, the inlet and outlet of which are connected to the falling film tubes to drive alkaline substances into the falling film tubes. By using a pump to deliver alkaline substances, precise dosing can be achieved, pH value can be effectively adjusted, and scaling can be inhibited. And / or, the operating temperature of the falling film tubes is 80–120°C, under which conditions can more effectively ensure a high-efficiency evaporation and crystallization process and optimize energy utilization. And / or, the heater is a shell-and-tube heater. Compared with plate heat exchangers, shell-and-tube heaters can enhance the stability and efficiency of heat exchange while reducing the risk of blockage.

[0041] Using the method of this application, the operating load can be significantly increased, the scaling rate can be effectively suppressed, and the need for frequent shutdowns for cleaning can be avoided. In a preferred embodiment, the operating load of the evaporator system is 88-120% of the design load; and / or, the thickness growth rate of the falling film tube is ≤2μm / d; and / or, using the method, it is not necessary to shut down the evaporator system.

[0042] In summary, the method described in this application not only enhances the stability and efficiency of the system and reduces maintenance costs, but also promotes continuous production, achieving a dual improvement in energy conservation, emission reduction, and economic benefits, and is of great value in ensuring the long-term efficient operation of equipment.

[0043] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0044] Example 1

[0045] See the flow diagram of the evaporator system. Figure 1 The evaporator system includes an inlet tank 1, a preheater 2, a shell-and-tube heat exchanger 3, a degasser 4, a falling film tube 5, a vapor compression system 6, a circulating pump 7, a demister 8, and a distilled water tank 9.

[0046] The components of high-silica saline solution A include: 190 mg / L of Ca. 2+ SO4 136540 mg / L 2+ 47 mg / L of Mg 2+ 27850 mg / L Cl - NO3 6122 mg / L - The silicon concentration was 450 mg / L, COD ≤ 2100, and TDS 220000.

[0047] High-silica brine is pretreated with concentrated sulfuric acid to adjust the pH of the influent to 4.5, preventing calcium carbonate scale buildup in the plate heat exchanger from clogging the water passages. The brine is then passed sequentially through influent tank 1, preheater 2, and shell-and-tube heat exchanger 3 (where high-temperature steam F provides heat to the brine and converts it into a steam-water mixture G), raising the water temperature to 98°C. It then enters degasser 4 to remove non-condensable gases E (including carbon dioxide) from the concentrate, followed by heat exchange and circulating evaporation concentration in vertical falling film tubes 5. During this process, the steam generated in the falling film tubes is pressurized by demister 6 and steam compression system 7 before entering distillation tank 9 and preheater 2 to recover heat. The generated reclaimed water H is reused in the system, while the concentrated brine D is used in subsequent processes for evaporation and crystallization.

[0048] The falling film tube is connected to the inlet and outlet of the circulating pump 8. Alkaline substance B (sodium hydroxide aqueous solution, concentration 25wt%, volume ratio of sodium hydroxide to high-silica brine 1:150) is added through the liquid alkali addition point at the outlet of the circulating pump to control the pH of the falling film tube at 10.5–10.7 for 30 days, ensuring a continuously strong alkaline environment within the vertical falling film tube. Subsequently, the addition of alkaline substance is stopped, and acidic substance C (citric acid, 0.2 tons each time, added once every 2 hours, for a total of 10 times) is added to clean the evaporation system, controlling the water pH at 3.5–3.8, and then the addition of acidic substance is stopped.

[0049] Repeat the above operations.

[0050] Example 2

[0051] The only difference from Example 1 is:

[0052] An alkaline substance (sodium hydroxide aqueous solution, concentration 25wt%, volume ratio of sodium hydroxide to high silica brine 1:150) was added to control the pH of the falling film tube at 11.4–12 and maintain this state for 10 days, ensuring a consistently strong alkaline environment within the vertical falling film tube. Subsequently, the addition of the alkaline substance was stopped, and an acidic substance (citric acid, 0.2 tons each time, added once every 2 hours, for a total of 10 times) was added to clean the evaporation system, controlling the water pH at 3.5–3.8. The addition of the acidic substance was then stopped.

[0053] Repeat the above operations.

[0054] Example 3

[0055] The only difference from Example 1 is:

[0056] An alkaline substance (sodium hydroxide aqueous solution, concentration 25wt%, volume ratio of sodium hydroxide to high silica brine 1:150) was added to control the pH of the falling film tube at 10.5–10.7 for 30 days, ensuring a consistently strong alkaline environment within the vertical falling film tube. Subsequently, the addition of the alkaline substance was stopped, and an acidic substance (citric acid, added once every 2 hours, 0.2 tons each time, for a total of 20 times) was added to clean the evaporation system, controlling the water pH at 1.3–2. The addition of the acidic substance was then stopped.

[0057] Repeat the above operations.

[0058] Example 4

[0059] The only difference from Example 1 is:

[0060] Add alkaline substances to control the pH of the falling film tube at 10.2–10.4 and maintain this level for 30 days. Then, stop adding alkaline substances and add acidic substances (citric acid, 0.2 tons each time, once every 2 hours, for a total of 10 times) to clean the evaporation system, controlling the water pH at 3.5–3.8, and then stop adding acidic substances.

[0061] Example 5

[0062] The only difference from Example 1 is:

[0063] Add an alkaline substance (sodium hydroxide aqueous solution, concentration 25wt%, volume ratio to high-silica brine 1:150) to control the pH of the falling film tube at 10.5–10.7 and maintain this state for 30 days, ensuring a continuously strong alkaline environment within the vertical falling film tube. Then, stop adding the alkaline substance and add an acidic substance (citric acid, added twice every 2 hours, 0.2 tons each time, for a total of 10 times) to clean the evaporation system, controlling the water pH at 3–3.4. Stop adding the acidic substance then. Repeat the above operation.

[0064] Example 6

[0065] The only difference from Example 1 is:

[0066] The alkaline substance is a 25 wt% potassium hydroxide aqueous solution, with a volume ratio of 1:150 to the high-silica brine. The alkaline substance is added to control the pH of the falling film tube at 10.5–10.7 and maintain this state for 30 days, ensuring a consistently strong alkaline environment within the vertical falling film tube. Subsequently, the addition of the alkaline substance is stopped, and an acidic substance (citric acid, 0.2 tons each time, added once every 2 hours, for a total of 10 times) is added to clean the evaporation system, controlling the water pH at 3.5–3.8. The addition of the acidic substance is then stopped. This process is repeated.

[0067] Example 7

[0068] The only difference from Example 1 is:

[0069] The alkaline substance is a sodium bicarbonate aqueous solution with a concentration of 35 wt%, a water temperature of 35℃, and a volume ratio of 1:160 to the high-silica brine. The alkaline substance is added to control the pH of the falling film tube at 10.5–10.7 and maintain this state for 30 days, ensuring a consistently strong alkaline environment within the vertical falling film tube. Subsequently, the addition of the alkaline substance is stopped, and an acidic substance (citric acid, 0.2 tons each time, added once every 2 hours, for a total of 10 times) is added to clean the evaporation system, controlling the water pH at 3.5–3.8. The addition of the acidic substance is then stopped. This process is repeated.

[0070] Example 8

[0071] The only difference from Example 1 is:

[0072] Add an alkaline substance (sodium hydroxide aqueous solution, concentration 25 wt%, volume ratio to high-silica brine 1:150) to control the pH of the falling film tube at 10.5–10.7 and maintain this state for 30 days, ensuring a continuously strong alkaline environment within the vertical falling film tube. Then, stop adding the alkaline substance and add an acidic substance (oxalic acid, 0.16 tons each time, once every 2 hours, for a total of 10 times) to clean the evaporation system, controlling the water pH at 3.5–3.8. Stop adding the acidic substance then. Repeat the above operation.

[0073] Example 9

[0074] The only difference from Example 1 is:

[0075] Add an alkaline substance (sodium hydroxide aqueous solution, concentration 25wt%, volume ratio to high-silica brine 1:150) to control the pH of the falling film tube at 10.5–10.7 and maintain this state for 30 days, ensuring a consistently strong alkaline environment within the vertical falling film tube. Then, stop adding the alkaline substance and add an acidic substance (acetic acid, 0.4 tons each time, once every 2 hours, for a total of 10 times) to clean the evaporation system, controlling the water pH at 3.5–3.8. Stop adding the acidic substance then. Repeat the above operation.

[0076] Example 10

[0077] The only difference from Example 1 is:

[0078] The components of high-silica saline solution A include: 10 mg / L of Ca. 2+ SO4 145266 mg / L 2+ 110 mg / L of Mg 2+ 30687 mg / L Cl - NO3 7241 mg / L- The concentration of silicon is >400 mg / L, COD ≤2100, and TDS is 210000.

[0079] Example 11

[0080] The only difference from Example 1 is:

[0081] The components of high-silica saline solution A include: 400 mg / L of Ca. 2+ SO4 119870 mg / L 2+ 5 mg / L Mg 2+ 25699 mg / L Cl - NO3 5984 mg / L - The concentration of silicon is >400 mg / L, COD ≤2100, and TDS is 240000.

[0082] Comparative Example 1

[0083] The only difference from Example 1 is:

[0084] After stopping the addition of alkaline substances, add acidic substance HF (0.2 tons each time, once every 2 hours, for a total of 10 times) to clean the evaporation system, control the pH value of the water at 3.5-3.8, and then stop adding acidic substances.

[0085] Experiments have shown that the overall evaporator has an insignificant descaling effect, and the overall influent load has not been significantly improved. At the same time, it causes equipment corrosion, introduces fluoride ions, seriously affects the subsequent salt separation and crystallization treatment effect, has a significant impact on the fluoride ion removal section, and increases the operating load of this work order.

[0086] Comparative Example 2

[0087] The only difference from Example 1 is:

[0088] Replace the acidic substance with HCl. After stopping the addition of alkaline substances, add the acidic substance HCl (0.2 tons each time, once every 2 hours, for a total of 10 times) to clean the evaporation system and control the pH value of the water at 3.5-3.8. Then stop adding the acidic substance.

[0089] Experiments have shown that while the evaporator achieves descaling, the introduction of chloride ions accelerates the corrosion rate of equipment and facilities. Evaporator systems often utilize stainless steel and duplex steel, which are susceptible to intergranular corrosion from chloride ions, hindering system operation. Furthermore, the introduction of chloride ions significantly impacts the freeze-crystallization stage in the subsequent salt separation process, disrupting the chloride-sulfate ratio and affecting subsequent salt separation efficiency. Therefore, this substance is not feasible in this system.

[0090] Comparative Example 3

[0091] The only difference from Example 1 is:

[0092] After adding alkali, control the pH to a weakly alkaline range of 9-10.

[0093] Analysis shows that when the pH is in the weakly alkaline range of 9 to 10, it is difficult for silicates in the water to form a molten state, making it difficult to remove silica, calcium and other scale deposits from the falling film tube. As a result, the overall influent load of the evaporator tends to decrease, the scaling rate increases to an average of 15 μm / d, and the descaling effect is not obvious.

[0094] Comparative Example 4

[0095] The only difference from Example 1 is:

[0096] After adding acid, control the pH to a weakly acidic range of 4 to 6.

[0097] Analysis shows that when the pH is in the weakly alkaline range of 4 to 6, the reaction effect of calcium carbonate and magnesium hydroxide formed in the water is not obvious. The silicate substances in the water prevent these substances from reacting, and the acidity is insufficient to achieve the removal effect. The overall influent load of the evaporator does not change significantly compared with normal operation. After adding acid to adjust, when the strong alkaline conditions are restored, the evaporator operating load does not change significantly.

[0098] The scaling conditions of the evaporator systems prepared in the above embodiments and comparative examples are shown in Table 1.

[0099] Test method:

[0100] COD test: The test shall be conducted in accordance with GB-T 15456-2008 "Determination of Chemical Oxygen Demand (COD) in Industrial Circulating Cooling Water".

[0101] TDS test: The test was conducted in accordance with GB5749-2006 "Standards for Drinking Water Quality".

[0102] Operating load: Under actual water intake conditions, an online flow meter is used to measure the evaporator inlet water load in real time.

[0103] Table 1

[0104]

[0105] As can be seen from the above, compared with the comparative example, the embodiments of the present invention periodically use specific types of acidic substances (one or more of citric acid, oxalic acid and acetic acid) and alkaline substances (one or more of sodium hydroxide, potassium hydroxide and sodium bicarbonate) to control the pH range and the holding time. This can ensure stable operation of the device, no load decay, and intact and undamaged equipment and facilities. It can also save operating consumption and costs to the greatest extent, which is conducive to the stable operation of the device.

[0106] Furthermore, it can be seen that when all process parameters are within the preferred range of the present invention, the operating load of the evaporator system is higher and the scaling thickness growth rate of the falling film tube is slower.

[0107] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for increasing the operating load of an evaporator system under high-silica saline conditions, characterized in that, The evaporator system includes an inlet tank, a preheater, a heat exchanger, a degasser, a falling film tube, a demister, a vapor compression system, a circulating pump, and a distilled water tank. The high-silica brine contains silicon with a mass concentration ≥400 mg / L. The method includes the following steps: In step S0, the high-silica brine is passed sequentially through the inlet tank, preheater, heat exchanger, and degasser, and then enters the falling film tube for heat exchange and circulating evaporation and concentration to form steam and concentrate. The steam passes sequentially through the demister and steam compression system before entering the distilled water tank and preheater to recover heat. The concentrate is circulated under the action of the circulating pump. The falling film tube is connected to the inlet and outlet of the circulating pump. Step S1: Continuously add alkaline substances online into the falling film tube through the liquid alkali dosing point at the outlet of the circulating pump, control the pH value of the water in the falling film tube to 10~12, maintain it for 10~30 days, and then stop adding the alkaline substances. Step S2: Add acidic substances online in batches to the water inlet tank to control the pH value of the water in the water inlet tank to 1~4 and maintain it for 0.5~2 days, then stop adding the acidic substances; Repeat steps S1 and S2 in sequence; The alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, and sodium bicarbonate. The acidic substances include one or more of citric acid, oxalic acid, and acetic acid.

2. The method according to claim 1, characterized in that, The concentration of Ca 2+ in the high-silicon brine is 10-400 mg / L, the concentration of Mg 2+ is 5-110 mg / L, the concentration of SO4 2- is ≤145266 mg / L, the concentration of Cl - is 25699-30687 mg / L, the concentration of NO3 - is 5984-7241 mg / L, COD is ≤2100, and TDS is 210000-240000.

3. The method according to claim 1 or 2, characterized in that, The method further includes the step of adding sulfuric acid to pretreat the high-silica brine.

4. The method according to claim 1, characterized in that, The method further includes the step of adding sulfuric acid and adjusting the pH of the high-silica brine to 4-5 to pretreat the high-silica brine.

5. The method according to claim 1, characterized in that, In step S1 The alkaline substance is added in the form of an alkaline solution with a concentration of 25-35 wt% and a volume ratio of the alkaline solution to the high-silica salt water of 1:(150-160).

6. The method according to claim 1, characterized in that, In step S1 The alkaline substance is added to the falling film tube to control the pH value of the water in the falling film tube to be 10.2~10.

8.

7. The method according to claim 1, characterized in that, In step S2 The acidic substance is added to the water inlet tank to control the pH value of the water in the water inlet tank to 3-4.

8. The method according to claim 1, characterized in that, In step S2 The acidic substance is added 1 to 2 times per 2 hours, and / or the total number of times the acidic substance is added is 5 to 20 times.

9. The method according to claim 1, characterized in that, The operating temperature of the falling film tube is 80~120℃.

10. The method according to claim 1, characterized in that, The operating load of the evaporator system is 88-120% of the design load; and / or, The thickness growth rate of the falling film tube is ≤2μm / d.

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