Method for improving operation load of evaporator system under high-silicon salt water

Abstract

The invention provides a method for improving the operation load of an evaporator system under high-silicon salt water. The evaporator system comprises a water inlet tank, a heat exchanger, a falling film tube and a steam compression system, and the mass concentration of silicon in the high-silicon saline water is larger than or equal to 400 mg / L. The method comprises the following steps that firstly, specific types of alkaline substances are continuously added into the falling film tube on line, the pH value and the retention time of water in the falling film tube are controlled, then adding of the alkaline substances is stopped, and the water content in the falling film tube is kept constant; specific types of acidic substances are added into the water inlet tank on line in batches, the pH value and the retention time of water in the water inlet tank are controlled, and adding of the acidic substances is stopped; and repeating the steps in sequence. According to the method, specific types of acidic substances and alkaline substances are periodically adopted, the pH range and the retention time are controlled, frequent shutdown is not needed, online cleaning of the evaporator is achieved, the operation load and efficiency are remarkably improved, the problem of frequent scaling under high-silicon salt water is effectively solved, and the maintenance cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for increasing the operating load of an evaporator system underwater using high-silicon salt water. Background Art

[0002] In the coal chemical and petroleum refining industries, salty wastewater treatment and sewage deep treatment are key steps to achieve environmentally friendly production and resource recycling. In traditional processes, after the above wastewater is anaerobic treated, the remaining high-salt wastewater (including circulating water discharge, desalted water discharge, and boiler discharge wastewater) needs to be further deep treated to ensure that the salt in the water is recovered and utilized to the greatest extent. The recycled water after deep treatment is usually re-transported to the circulating water and desalted water system for recycling, while the high-concentration salt water needs to be evaporated and concentrated, and finally sent to the evaporation pond for natural evaporation and crystallization.

[0003] In recent years, the water treatment technology of "zero discharge" pretreatment + double membrane (ultrafiltration + reverse osmosis) + falling film evaporation has attracted wide attention and application in the industry due to its stability and simplicity, and can achieve zero discharge of wastewater, and its market share has steadily increased. However, in actual operation, especially when treating concentrated brine containing high concentrations of silicon (such as 400 mg / L), the existing evaporation system faces serious scaling problems. Specifically, the design parameters of the falling film tube evaporator are usually suitable for lower silicon mass concentrations, such as 25 mg / L, but the silicon content in actual operation far exceeds the design value, resulting in rapid scaling of the falling film tube, the main body of the equipment, and the pipeline network of the key components of the evaporator, and a significant decrease in the amount of water and evaporation efficiency. More seriously, the current plate heat exchanger design is not suitable for long-term treatment of high-silicon wastewater, which further aggravates the operating load problem of the evaporator (such as: the evaporator operating load can only be maintained at about 40%), and cannot meet the operating load requirements of the device.

[0004] In the prior art, the descaling of evaporators, especially the scale treatment in high-silicon concentrated brine environment, usually involves the following methods, but all of them need to face the problem of equipment shutdown for cleaning, for example, high-pressure water jet cleaning: the scale is physically removed by high-pressure hydraulic impact on the surface of the evaporator. Although this method is effective, the evaporator needs to be completely stopped for manual or mechanical cleaning, and the high-pressure water flow may cause physical damage to the equipment. Chemical cleaning: the evaporator is soaked in a strong acid or strong alkali solution (such as hydrochloric acid, sulfuric acid, sodium hydroxide, etc.) to dissolve or decompose the scaling substances. Chemical cleaning usually requires shutdown, and the cleaning agent is introduced into the evaporator for circulation to chemically react with the scale layer to achieve the purpose of descaling. However, this method not only consumes a large amount of chemicals, but also has potential corrosion to the evaporator materials, and the treated waste liquid needs to be treated for environmental protection, which adds additional costs. Ultrasonic cleaning: the cavitation effect of ultrasound is used to break the scale layer and make it fall off the surface of the evaporator. Although ultrasonic cleaning does not require direct contact and reduces physical damage, the evaporator still needs to be shut down to ensure the safety of the operator and the cleaning effect. Bio-enzyme cleaning: Bio-enzyme preparations are used to remove organic scale through the biodegradation of enzymes. This method is environmentally friendly, but the efficiency is relatively low, and the processing capacity for inorganic silicates is limited. The evaporator also needs to be shut down to complete the entire cleaning process.

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

[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 creates additional pressure on environmental protection operations, affecting the stable operation and economic benefits of the factory. Summary of the invention

[0007] The main purpose of the present invention is to provide a method for increasing the operating load of an underwater evaporator system with high silicon salt water, so as to solve the problems in the prior art that the underwater evaporator system with high silicon salt water has a short operating cycle, low load, and needs to be shut down for cleaning after scaling.

[0008] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for increasing the operating load of an evaporator in high-silicon salt water is provided. The evaporator system includes a water inlet tank, a heat exchanger, a falling film tube and a steam compression system. In the high-silicon salt water, the mass concentration of silicon is ≥400 mg / L. The method includes the following steps: Step S1, adding alkaline substances to the falling film tube online and continuously, controlling the pH value of the water quality in the falling film tube to be 10-12, and maintaining it for 10-30 days, and stopping adding alkaline substances; Step S2, adding acidic substances to the water inlet tank online in batches, controlling the pH value of the water quality in the water inlet tank to be 1-4, and maintaining it for 0.5-2 days, and stopping adding acidic substances; repeating steps S1 and S2 in sequence; wherein the alkaline substances include 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.

[0009] Furthermore, in high-silicon brine, Ca 2+ The concentration is 10~400mg / L, Mg 2+ The concentration is 5~110mg / L, SO4 2- The concentration is ≤145266mg / L, Cl - The concentration is 25699~30687mg / L, NO3 - The concentration is 5984~7241mg / L, COD≤2100, and TDS is 210000~240000.

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

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

[0012] Furthermore, in step S1, the alkaline substance is added in the form of an alkaline solution, the concentration of the alkaline solution is 25-35 wt%, and the volume ratio of the alkaline solution to the high-silicon brine is 1:(150-160).

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

[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 the acidic substance is 1 to 2 times / 2 hours, and / or the total number of times the acidic substance is added is 5 to 20 times.

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

[0017] Further, 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 the present 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 retention time, thereby realizing online cleaning of the evaporator without frequent shutdowns, significantly improving the operating load and efficiency, effectively solving the problem of frequent underwater scaling of high-silicon salts, reducing maintenance costs, and promoting the continuity and economy of the industrial water treatment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0020] Figure 1 The schematic diagram of the process of the evaporator system of Example 1 of the present invention is shown.

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

[0022] 1. Water inlet tank; 2. Preheater; 3. Shell and tube heat exchanger; 4. Degasser; 5. Falling film tube; 6. Demister; 7. Steam compression system; 8. Circulation pump; 9. Distilled water tank;

[0023] A. High-silicon salt water; B. Alkaline substances; C. Acidic substances; D. Brine; E. Non-condensable gas; F. Steam; G. Soda-water mixture; H. Recycled water. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] As described in the background technology of the present invention, there are problems in the prior art such as short operating cycle, low load and need to be shut down for cleaning after scaling in the high-silicon brine underwater evaporator system. In particular, the evaporator falling film tubes and ancillary equipment pipelines are prone to scaling and clogging under high-silicon brine conditions, resulting in reduced system operating cycle and load, and the plate heat exchanger is not suitable for processing high-silicon brine, resulting in low operating load of the evaporator and the need to be shut down for cleaning after scaling. In order to solve the above problems, in a typical embodiment of the present invention, a method for increasing the operating load of an evaporator system underwater in high-silicon brine is provided, the evaporator system comprises an 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 ≥400 mg / L, and the method comprises the following steps: step S1, continuously adding alkaline substances to the pipeline of the falling film tube online, controlling the pH value of the water quality in the falling film tube to 10-12, and maintaining it for 10-30 days, and stopping adding the alkaline substances; step S2, adding acidic substances to the inlet tank online in batches, controlling the pH value of the water quality in the inlet tank to 1-4, and maintaining it for 0.5-2 days, and stopping adding the acidic substances; repeating steps S1 and S2 in sequence; wherein the alkaline substances include 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.

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

[0027] In step S2, the pH value of the water is adjusted to an acidic condition of 1 to 4 by adding an acidic substance online to the water inlet tank. Exemplarily, in an acidic environment, carbonates in the scale, such as CaCO3, are converted into carbon dioxide and water, and alkaline substances, such as Mg(OH)2 and Ca(OH)2, are converted into soluble salts and peeled off from the surface of the falling film tube and other equipment, thereby restoring the heat exchange efficiency and fluid dynamic performance of the evaporator system. Regular acid washing can not only remove the scale that has already formed, but also prevent the formation of new scale, thereby extending the continuous operation cycle of the evaporator system, reducing the maintenance and cleaning frequency, reducing operating costs, and improving overall economic benefits.

[0028] In addition, while controlling the pH range, the present application also specifically limits the holding time of the pH value. Keeping the water quality in a specific pH range for a certain period of time can significantly affect the operating efficiency and maintenance cycle of the evaporator system. Specifically, maintaining the pH value at a strong alkaline condition of 10 to 12 can significantly reduce the blockage of the falling film tube by fully destroying the chemical balance formed by silica scale, and can also effectively inhibit silicate scaling, which is beneficial to extend the trouble-free operation time of the equipment. Regularly maintaining the acidic pH range of 1 to 4 for several days and using acidic substances can fully and effectively remove the deposited scaling, effectively avoiding the high cost and environmental risks of high-pressure cleaning.

[0029] It should be noted that, regarding the types of alkaline substances, the inventors have conducted a large number of experimental studies and particularly preferred one or more of sodium hydroxide, potassium hydroxide and sodium bicarbonate. Compared to calcium hydroxide, magnesium hydroxide, etc., the alkaline substances of the present application have high solubility and strong alkalinity, can not only rapidly increase the pH value of the solution to a specific range, quickly and efficiently dissolve scaling substances, effectively inhibit the deposition of silicates on the surface of the falling film tube, and thus significantly slow down the scaling process, and do not introduce ions that are easy to generate scaling substances, thereby helping to reduce scaling substance generation, in addition, the alkaline substances of the present application are low in cost, and can also gently maintain equipment and extend the service life of the equipment. By periodically adding a specific type of alkaline substance, the scaling problem under high-silicon salt can be effectively controlled, the operating load and cycle of the evaporator system can be greatly improved, and the maintenance cost can be reduced, providing a strong technical guarantee for realizing efficient and economical treatment of industrial wastewater.

[0030] At the same time, the inventors also particularly preferred the type of acidic substance to be one or more of citric acid, oxalic acid and acetic acid. The addition of inorganic strong acid, such as HCl, not only introduces impurity ions that are easy to form precipitation, affecting the subsequent distillation and crystallization process, but also causes serious corrosion to the equipment; HF is extremely corrosive, the operating cost is too high, and F - It is not easy to remove in the subsequent desalination process and is not suitable for cleaning the evaporator system. In comparison, citric acid, oxalic acid and acetic acid have low corrosiveness and can effectively dissolve a variety of scaling substances, such as calcium and magnesium salts. At the same time, at a specific pH value, they can gently peel off silicate deposits to avoid significant damage to evaporator materials, especially metal surfaces. In addition, citric acid has good biodegradability and little impact on the environment, making the cleaning process more environmentally friendly.

[0031] In summary, the method of the present application periodically uses specific types of acidic and alkaline substances to control the pH range and retention time, which can achieve online cleaning of the evaporator without frequent shutdowns, significantly improve operating load and efficiency, effectively solve the problem of frequent underwater scaling of high-silica salts, reduce maintenance costs, and promote the continuity and economy of the industrial water treatment process.

[0032] In a preferred embodiment, in high silicon brine, Ca 2+ The concentration is 10~400mg / L, Mg 2+ The concentration is 5~110mg / L, SO4 2- The concentration is ≤145266mg / L, Cl - The concentration is 25699~30687mg / L, NO3 - The concentration is 5984-7241 mg / L, COD≤2100, and TDS is 210000-240000. The method of the present application is used to treat the above water quality. Based on the solubility product and surface activity mechanism, it can more effectively inhibit the formation of hard scale, reduce the adsorption of organic matter on the evaporator surface, ensure heat exchange efficiency, extend the equipment operation cycle, avoid frequent shutdowns for cleaning, and more effectively reduce the consumption of acidic and / or alkaline substances, significantly reducing maintenance costs and environmental pressures.

[0033] In a preferred embodiment, the method further comprises the step of adding sulfuric acid to pre-treat the high-silicon brine.

[0034] It should be noted that if too much sulfate ion is introduced, calcium sulfate scale may be formed, which is difficult to remove. In a preferred embodiment, the method further includes a step of adding sulfuric acid and adjusting the pH value of the high-silicon brine to 4-5 to pretreat the high-silicon brine.

[0035] In a preferred embodiment, in the high-silicon salt water, calcium silicate accounts for 30-40%, magnesium silicate accounts for 15-20%, calcium carbonate accounts for 10-20%, calcium sulfate accounts for 25-40%, and the mass concentration of silicon is ≥400 mg / L. The method of the present application is used to treat the above water quality, based on the dissolution equilibrium and chemical reaction mechanism, which can more effectively inhibit the formation of silicate scale and reduce Ca 2+ and Mg 2+ Related hard scale deposition ensures efficient heat exchange of the evaporator, significantly extends the operating cycle, avoids frequent shutdowns due to scaling, reduces operating and maintenance costs, and can also optimize the crystallization quality of brine after evaporation, creating favorable conditions for subsequent salt resource utilization, and achieving the dual goals of cost reduction and efficiency improvement and environmental protection in the process of chemical wastewater treatment.

[0036] In order to more effectively maintain the efficient and stable operation of the evaporation system, balance equipment protection and cost control, and be more conducive to reducing environmental pollution, in a preferred embodiment, in step S1, the alkaline substance exists in the form of an alkaline solution, the concentration of the alkaline solution is 25-35wt%, and the volume ratio of the alkaline solution to the high-silicon salt water is 1: (150-160). The above parameter design is based on the solubility change mechanism of silicates at different pH values. By introducing an appropriate amount of alkaline substances, the water pH can be more effectively adjusted to form a strong alkaline environment, significantly inhibit silicate scaling, and avoid equipment corrosion problems caused by excessive alkaline substances. However, if the alkali concentration is too high or the volume ratio is too much, it may cause accelerated corrosion of the evaporator equipment, reduced heat exchange efficiency, increased maintenance costs, and may cause environmental alkaline pollution, affecting the quality of the crystallized salt; while the alkali concentration is too low or the volume ratio is too little, it may not be able to effectively inhibit silicate scaling, affecting the operating load and efficiency of the evaporator, and may cause 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 in the falling film tube to be 10.2 to 10.8. Under the above conditions, it is possible to more accurately balance scaling inhibition and equipment corrosion risk, reduce excessive use of chemical agents, optimize heat exchange efficiency, reduce environmental pollution, and improve operational stability.

[0038] In a preferred embodiment, 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 to 4. Under the above conditions, it is possible to more effectively focus on the dissolution of scaling substances and reduce the overreaction of non-target substances, thereby reducing the risk of equipment corrosion, improving cleaning efficiency and safety, and moreover, it is more conducive to saving chemical agents, reducing the environmental impact after wastewater treatment, and achieving a more environmentally friendly and economical maintenance effect.

[0039] The frequency and number of times of acid addition directly affect the cleanliness and operating efficiency of the equipment. In a preferred embodiment, in step S2, the frequency of adding the acidic substance is 1 to 2 times / 2h, and / or the total number of times the acidic substance is added is 5 to 20 times. The above frequency can more effectively ensure continuous scale layer management and prevent scale accumulation from affecting heat exchange; the above number of times can avoid corrosion and waste of resources that may be caused by excessive cleaning. This can not only more effectively maintain the high-performance operation of the system and reduce sudden failures, but also further extend the life of the equipment and reduce maintenance costs.

[0040] In a preferred embodiment, the evaporator system also includes a pump, the inlet and outlet of the pump are connected to the falling film tube, driving the alkaline substance into the falling film tube. By using the pump to transport the alkaline substance, accurate addition can be achieved, the pH value can be effectively adjusted, and scaling can be inhibited; and / or, the operating temperature of the falling film tube is 80-120°C, under which conditions, a high-efficiency evaporation and crystallization process can be more preferably ensured, and energy utilization can be optimized; and / or, the heater is a shell and tube heater. Compared with a plate heat exchanger, a shell and tube heater can enhance the stability and efficiency of heat exchange while reducing the risk of clogging.

[0041] The method of the present application can significantly increase the operating load, effectively inhibit the scaling rate, and avoid the need for frequent shutdowns for cleaning. 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, the method is used without the need to shut down the evaporator system.

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

[0043] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0044] Example 1

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

[0046] The components of high-silicon salt water A include: 190 mg / L of Ca 2+ , 136540mg / L SO4 2+ , 47mg / L Mg 2+ , 27850mg / L Cl - , 6122mg / L NO3 - , among which, the mass concentration of silicon is 450 mg / L, COD≤2100, and TDS is 220000.

[0047] Concentrated sulfuric acid is used to pre-treat the high-silicon brine, and the pH value of the inlet water is adjusted to 4.5 to prevent the calcium carbonate scale of the inlet plate heat exchanger from clogging the water passage of the heat exchanger. The high-silicon concentrated brine then passes through the inlet tank 1, preheater 2, and shell-and-tube heat exchanger 3 in sequence (the high-temperature steam F provides heat to the brine and converts it into a steam-water mixture G). At this time, the water temperature rises to 98°C, and then enters the degasser 4 to remove the non-condensable gas E (including carbon dioxide) in the concentrated water, and then enters the vertical falling film tube 5 for heat exchange, cyclic evaporation and concentration. In this process, the steam generated in the falling film tube is pressurized by the demister 6 and the steam compression system 7, and then enters the distilled water tank 9 and the preheater 2 to recover heat. The generated regenerated water H enters the system for reuse, and the concentrated brine D enters the subsequent process for evaporation and crystallization.

[0048] The falling film tube is connected to the inlet and outlet of the circulation pump 8. Alkaline substance B (sodium hydroxide aqueous solution, with a concentration of 25wt%, and a volume ratio of 1:150 to high-silicon brine) is added through the liquid alkali addition point at the outlet of the circulation pump to control the pH of the falling film tube at 10.5-10.7 and maintain it for 30 days to make the vertical falling film tube continuously present strong alkalinity. Subsequently, the addition of alkaline substances is stopped, and acidic substances C (citric acid, 0.2 tons each time, the addition frequency is 1 time / 2h, and a total of 10 times) are added to clean the evaporation system, and the water quality pH value is controlled at 3.5-3.8, and the addition of acidic substances is stopped.

[0049] Repeat the above operation in a loop.

[0050] Example 2

[0051] The only difference from Example 1 is:

[0052] Add alkaline substances (sodium hydroxide aqueous solution, with a concentration of 25wt%, and a volume ratio of 1:150 to high-silicon brine) to control the pH of the falling film tube at 11.4-12, and maintain it for 10 days to make the vertical falling film tube continue to show strong alkalinity. Subsequently, stop adding alkaline substances, add acidic substances (citric acid, 0.2 tons each time, adding frequency is 1 time / 2h, a total of 10 times) to clean the evaporation system, control the water quality pH value at 3.5-3.8, and stop adding acidic substances.

[0053] Repeat the above operation in a loop.

[0054] Example 3

[0055] The only difference from Example 1 is:

[0056] Add alkaline substances (sodium hydroxide aqueous solution, with a concentration of 25wt%, and a volume ratio of 1:150 to high-silicon brine) to control the pH of the falling film tube at 10.5-10.7 and maintain it for 30 days to make the vertical falling film tube continuously show strong alkalinity. Subsequently, stop adding alkaline substances and add acidic substances (citric acid, adding frequency is 1 time / 2h, 0.2 tons each time, and adding 20 times in total) to clean the evaporation system, control the water quality pH value at 1.3-2, and stop adding acidic substances.

[0057] Repeat the above operation in a loop.

[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 keep it for 30 days. Then, stop adding alkaline substances and add acidic substances (citric acid, 0.2 tons each time, adding frequency is 1 time / 2h, adding 10 times in total) to clean the evaporation system, control the pH value of water quality at 3.5-3.8, and stop adding acidic substances.

[0061] Example 5

[0062] The only difference from Example 1 is:

[0063] Add alkaline substances (sodium hydroxide aqueous solution, with a concentration of 25wt%, and a volume ratio of 1:150 to high-silicon brine), control the pH of the falling film tube at 10.5-10.7, and maintain it for 30 days, so that the vertical falling film tube continues to show strong alkalinity. Subsequently, stop adding alkaline substances, add acidic substances (citric acid, adding frequency is 2 times / 2h, 0.2 tons each time, adding 10 times in total) to clean the evaporation system, control the water quality pH value at 3-3.4, and stop adding acidic substances. Repeat the above operation.

[0064] Example 6

[0065] The only difference from Example 1 is:

[0066] The alkaline substance is a potassium hydroxide aqueous solution with a concentration of 25wt% and a volume ratio of 1:150 to the high-silicon brine. Add the alkaline substance to control the pH of the falling film tube at 10.5-10.7 and maintain it for 30 days so that the vertical falling film tube continues to be strongly alkaline. Subsequently, stop adding the alkaline substance and add the acidic substance (citric acid, 0.2 tons each time, the frequency of addition is 1 time / 2h, and a total of 10 times) to clean the evaporation system, control the water quality pH value at 3.5-3.8, and stop adding the acidic substance. Repeat the above operation.

[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 35wt%, a water temperature of 35°C, and a volume ratio of 1:160 to the high-silicon brine. Add the alkaline substance to control the pH of the falling film tube at 10.5-10.7 and maintain it for 30 days to make the vertical falling film tube continuously show strong alkalinity. Subsequently, stop adding the alkaline substance and add the acidic substance (citric acid, 0.2 tons each time, the frequency of addition is 1 time / 2h, and a total of 10 times) to clean the evaporation system, control the water quality pH value at 3.5-3.8, and stop adding the acidic substance. Repeat the above operation.

[0070] Example 8

[0071] The only difference from Example 1 is:

[0072] Add alkaline substances (sodium hydroxide aqueous solution, with a concentration of 25wt%, and a volume ratio of 1:150 to high-silicon brine), control the pH of the falling film tube at 10.5-10.7, and maintain it for 30 days, so that the vertical falling film tube continues to show strong alkalinity. Subsequently, stop adding alkaline substances, add acidic substances (oxalic acid, 0.16 tons each time, adding frequency is 1 time / 2h, a total of 10 times) to clean the evaporation system, control the water quality pH value at 3.5-3.8, and stop adding acidic substances. Repeat the above operation.

[0073] Example 9

[0074] The only difference from Example 1 is:

[0075] Add alkaline substances (sodium hydroxide aqueous solution, with a concentration of 25wt%, and a volume ratio of 1:150 to high-silicon brine), control the pH of the falling film tube at 10.5-10.7, and maintain it for 30 days, so that the vertical falling film tube continues to show strong alkalinity. Subsequently, stop adding alkaline substances, add acidic substances (acetic acid, 0.4 tons each time, adding frequency is 1 time / 2h, a total of 10 times) to clean the evaporation system, control the water quality pH value at 3.5-3.8, and stop adding acidic substances. Repeat the above operation.

[0076] Example 10

[0077] The only difference from Example 1 is:

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

[0079] Embodiment 11

[0080] The only difference from Example 1 is:

[0081] The components of high-silicon salt water A include: 400 mg / L of Ca 2+ , 119870mg / L SO4 2+ , 5mg / L Mg 2+ , 25699mg / L Cl - , 5984mg / L NO3 - , among which, the mass 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 adding alkaline substances, add acidic substance HF (0.2 tons each time, adding frequency is 1 time / 2h, adding 10 times in total) to clean the evaporation system, control the pH value of water quality at 3.5-3.8, and stop adding acidic substances.

[0085] Experiments have shown that the overall evaporator descaling effect is not obvious, the overall water inlet load has not increased significantly, and it also causes equipment corrosion. The introduction of fluoride ions seriously affects the subsequent salt separation and crystallization treatment effect, has a greater 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] The acidic substance was replaced with HCl. After the addition of alkaline substances was stopped, the acidic substance HCl was added (0.2 tons each time, the frequency of addition was 1 time / 2h, and a total of 10 times) to clean the evaporation system, the pH value of the water quality was controlled at 3.5-3.8, and the addition of acidic substances was stopped.

[0089] Experiments have shown that the evaporator descaling effect is achieved, but the introduction of chloride ions accelerates the corrosion rate of equipment and facilities. The evaporator system is mostly made of stainless steel and duplex steel. Chloride ions cause intergranular corrosion of these materials, which is not conducive to system operation. At the same time, the introduction of chloride ions has a greater impact on the freezing crystallization stage in the subsequent salt separation crystallization stage, destroying the ratio of chlorine and sulfate in the system and affecting the subsequent salt separation effect. This substance is not feasible in this system.

[0090] Comparative Example 3

[0091] The only difference from Example 1 is:

[0092] After adding alkali, the pH is controlled to be in the weak alkaline range of 9 to 10.

[0093] Analysis shows that when the pH is within the weak alkaline range of 9 to 10, it is difficult for the silicates in the water to form a molten state, and it is difficult to peel off the silicon, calcium and other scaling substances on the falling film tubes. The overall water inlet load of the evaporator tends to decrease, and the scaling rate will increase, averaging 15μm / d, and the descaling effect is not obvious.

[0094] Comparative Example 4

[0095] The only difference from Example 1 is:

[0096] After adding acid, the pH is controlled to be in the weak acid range of 4 to 6.

[0097] Analysis shows that when the pH is in the weak 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 the reaction of such substances. The acidity is insufficient and the removal effect cannot be achieved. The overall water inlet load of the evaporator does not change significantly compared to normal operation. After acid addition and adjustment, when the strong alkaline conditions are restored, the operating load of the evaporator does not change significantly.

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

[0099] Test method:

[0100] COD test: Test according to GB-T 15456-2008 "Determination of Chemical Oxygen Demand (COD) in Industrial Circulating Cooling Water".

[0101] TDS test: Test according to GB57492006 "Sanitary Standard for Drinking Water".

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

[0103] Table 1

[0104]

[0105] It can be seen from the above that compared with the comparative example, the embodiment of the present invention periodically uses 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 retention time, which can ensure the stable operation of the device, no load attenuation, and intact equipment and facilities without damage, and can also save operating consumption and costs to the greatest extent, which is conducive to the stable operation of the device.

[0106] In addition, it can be seen that when the 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 only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for increasing the operating load of an evaporator system in a high-silicon-salt underwater environment, wherein the evaporator system comprises a water inlet tank, a heat exchanger, a falling film tube and a steam compression system, characterized in that: The mass concentration of silicon in the high-silicon brine is ≥400 mg / L, and the method comprises the following steps: Step S1, continuously adding alkaline substances into the falling film tube online, controlling the pH value of the water in the falling film tube to be 10 to 12, and maintaining the pH value for 10 to 30 days, and then stopping adding the alkaline substances; Step S2, adding acidic substances to the water inlet tank in batches online, controlling the pH value of the water in the water inlet tank to be 1 to 4, and maintaining it for 0.5 to 2 days, and then stopping adding the acidic substances; Repeat the step S1 and the step S2 in sequence; Wherein, the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide and sodium bicarbonate; The acidic substance includes one or more of citric acid, oxalic acid and acetic acid.

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

3. The method according to claim 1 or 2, characterized in that: The method further comprises the step of adding sulfuric acid to pre-treat the high-silicon brine.

4. The method according to any one of claims 1 to 3, characterized in that The method further comprises the step of adding sulfuric acid and adjusting the pH value of the high-silicon salt water to 4-5 to pretreat the high-silicon salt water.

5. The method according to any one of claims 1 to 4, characterized in that In the step S1, The alkaline substance is added in the form of an alkaline solution, the concentration of the alkaline solution is 25-35 wt %, and the volume ratio of the alkaline solution to the high-silicon salt water is 1:(150-160).

6. The method according to any one of claims 1 to 5, characterized in that In the step S1, The alkaline substance is added into 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 any one of claims 1 to 6, characterized in that In the step S2, The acidic substance is added into the water inlet tank to control the pH value of the water in the water inlet tank to be 3-4.

8. The method according to any one of claims 1 to 7, characterized in that In the step S2, The frequency of adding the acidic substance is 1 to 2 times / 2 hours, and / or the total number of adding the acidic substance is 5 to 20 times.

9. The method according to any one of claims 1 to 8, characterized in that The operating temperature of the falling film tube is 80-120°C.

10. The method according to any one of claims 1 to 9, 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 ≤2 μm / d.

Images