Treatment method of high-salinity oil-containing wastewater
By monitoring the whiteness and chlorine concentration of inorganic salt products, the discharge of mother liquor is precisely controlled. Combined with the adjustment of pH value with alkaline substances and multi-effect evaporation for solid-liquid separation, the problem of oil and chlorine enrichment in high-salt and oily wastewater is solved, thereby improving the quality of inorganic salt products and the stability of the treatment process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-14
- Publication Date
- 2026-04-07
AI Technical Summary
When treating high-salt and oily wastewater, existing technologies lead to reduced evaporation efficiency and decreased inorganic salt quality due to the enrichment of oil and chlorine. Traditional discharge strategies are prone to resource waste or system collapse.
By monitoring the whiteness of inorganic salt products and the chlorine concentration of the mother liquor in the last-effect evaporator, the timing of mother liquor discharge is precisely controlled. Alkaline substances are added to adjust the pH value during the oil removal pretreatment of the mother liquor. Combined with multi-effect evaporation and solid-liquid separation technology, high-quality inorganic salt products are prepared.
This has improved the stability of inorganic salt product quality, reduced the production of defective products, increased evaporation efficiency and resource utilization, and ensured the continuity of the processing technology.
Smart Images
Figure CN121800360A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of wastewater treatment technology, specifically to a method for treating high-salt, oily wastewater. Background Technology
[0002] Hydrometallurgical wastewater commonly exhibits characteristics such as high salinity, high COD (Chemical Oxygen Demand), high chlorine, and high ammonia nitrogen. To fully recover and utilize the water and inorganic salt resources within it, the industry generally employs a "pretreatment + evaporation" process. For oily hydrometallurgical wastewater, the industry currently mainly uses resin degreasing and activated carbon degreasing for pretreatment, but a small amount of oil still remains. During the multi-effect evaporation treatment of this pretreated wastewater through an MVR (Mechanical Vapor Recompression) system, the following situations arise: First, the boiling point of oil is significantly higher than that of water, and the residual oil gradually accumulates in the water as evaporation proceeds; second, chloride ions in high-chlorine wastewater usually exist in the form of chloride salts (such as ammonium chloride), whose solubility is lower than that of sulfates, causing chlorine to also accumulate in the aqueous phase during evaporation. The continuous accumulation of oil and chlorine not only leads to an increase in the boiling point of the wastewater and a decrease in evaporation efficiency, but also seriously affects the quality of inorganic salts.
[0003] To ensure evaporation rate and the quality of produced inorganic salts, MVR systems need to periodically discharge mother liquor to reduce oil and chlorine content within the system. However, traditional discharge strategies are often based on fixed cycles or fuzzy experience, which can easily lead to two extremes: either excessively frequent discharge, resulting in resource waste and increased operating costs, or delayed discharge, causing system collapse and forcing shutdown for cleaning. Summary of the Invention
[0004] In view of this, the purpose of this application is to provide a method for treating high-salt and oily wastewater to solve the above-mentioned technical problems.
[0005] This application provides a method for treating high-salt oily wastewater, comprising: pre-treating the high-salt oily wastewater to obtain a pre-treated liquid; concentrating the pre-treated liquid through multi-effect evaporation to obtain a crystalline liquid; performing solid-liquid separation on the crystalline liquid and drying the separated crystals to obtain a first inorganic salt product; monitoring the whiteness of the first inorganic salt product and the chlorine concentration of the mother liquor in the last-effect evaporator, and discharging the mother liquor in the last-effect evaporator when the whiteness is less than 55% or the chlorine concentration is greater than 60 g / L.
[0006] In some optional embodiments, the method further includes: pre-treating the discharged mother liquor by removing oil and adding an alkaline substance to adjust the pH value to 3.0-4.5 to obtain a pre-treated mother liquor; evaporating and concentrating the pre-treated mother liquor to obtain a concentrated mother liquor; cooling and crystallizing the concentrated mother liquor to obtain a crystallized mother liquor; performing solid-liquid separation on the crystallized mother liquor and drying the separated crystals to obtain a second inorganic salt product.
[0007] In some optional embodiments, the method further includes: monitoring the evaporation rate of the evaporator in the pretreated mother liquor evaporation process, and when the evaporation rate is less than 70% of the initial evaporation rate, discharging the mother liquor in the evaporator and returning it to the pretreated mother liquor preparation step.
[0008] In some alternative embodiments, after solid-liquid separation of the mother liquor containing crystals, the separated liquid is returned to the evaporator of the pretreated mother liquor evaporation process for further evaporation and concentration.
[0009] In some alternative embodiments, the method further includes preheating the pretreated mother liquor before evaporating and concentrating it.
[0010] In some alternative implementations, the oil removal pretreatment of the mother liquor is achieved through activated carbon adsorption.
[0011] In some alternative embodiments, the alkaline substance is one or more of ammonia, sodium hydroxide, or sodium carbonate.
[0012] In some alternative implementations, after solid-liquid separation of the crystalline liquid, the separated liquid is returned to the final-effect evaporator for further evaporation and concentration.
[0013] In some alternative embodiments, the method further includes preheating the pretreated liquid before concentrating it through multi-effect evaporation.
[0014] In some alternative implementations, the oil removal pretreatment of high-salt oily wastewater is achieved through activated carbon adsorption or resin adsorption.
[0015] Based on the above technical solution, the method for treating high-salt and oily wastewater provided in this application can accurately control the timing of discharge of the final-effect mother liquor by monitoring the whiteness of the first inorganic salt product and the chlorine concentration of the final-effect mother liquor, thereby enabling early prediction of the quality decline of the first inorganic salt product, reducing the output of unqualified products and improving the product qualification rate. Attached Figure Description
[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a schematic flowchart of a method for treating high-salt, oily wastewater provided in an embodiment of this application. Detailed Implementation
[0018] The specific embodiments of this application will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of this application, and not all of them. Based on the description of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.
[0019] like Figure 1 As shown, this embodiment provides a method for treating high-salt, oily wastewater, including the following steps: S1. Oil removal pretreatment is performed on high-salt and oily wastewater to obtain pretreated liquid.
[0020] In this step, oil removal pretreatment can be achieved through activated carbon adsorption or resin adsorption, depending on the wastewater volume and equipment maintenance status. Since resin adsorption has a higher oil removal efficiency and a lower risk of foreign matter introduction than activated carbon, resin oil removal is prioritized when the wastewater volume is within the resin adsorption capacity range, and activated carbon oil removal is discontinued. However, when the wastewater volume exceeds the upper limit of the resin adsorption capacity or the resin column is under maintenance, activated carbon oil removal is activated.
[0021] As an example, activated carbon is used for oil removal pretreatment of high-salt oily wastewater. Specifically, powdered activated carbon is added to the hydrometallurgical oily wastewater at a ratio of 5‰-7‰ for adsorption, and the mixture is stirred simultaneously. Then, a filter press is used to retain the activated carbon, which forms the purified liquid, i.e., the pretreated liquid.
[0022] S2. Preheat the pretreated liquid.
[0023] In this step, the pretreated liquid can exchange heat with the high-temperature condensate generated by the MVR evaporation system in the subsequent step through a plate heat exchanger to recover and utilize the waste heat in the high-temperature condensate. This can significantly reduce the temperature difference between the material entering the MVR evaporation system and the evaporation temperature, thereby reducing the external energy input required for the MVR system to reach boiling, effectively reducing the overall energy consumption of the subsequent MVR evaporation system, and saving operating costs.
[0024] S3. The pretreated liquid is concentrated by multi-effect evaporation to obtain a liquid containing crystals.
[0025] In this step, the multi-effect evaporation concentration of the pretreated liquid is usually a triple-effect evaporation concentration, which is achieved through an MVR evaporation system. This MVR evaporation system includes a first-effect evaporator, a second-effect evaporator, a third-effect evaporator, a first steam compressor, and a second steam compressor. The first-effect evaporator, the second-effect evaporator, and the third-effect evaporator are connected in series in the material flow path. The first-effect evaporator and the second-effect evaporator together with the first steam compressor form a first steam circulation loop, and the third-effect evaporator together with the second steam compressor form a second steam circulation loop.
[0026] During operation, the pretreated liquid, after preheating, first enters the first-effect evaporator for initial evaporation and concentration, during which condensate is generated simultaneously. Then, the pretreated liquid, after the first evaporation and concentration, enters the second-effect evaporator for a second evaporation and concentration, again during which condensate is generated. Finally, the pretreated liquid, after the second evaporation and concentration, enters the third-effect evaporator for a third evaporation and concentration, during which condensate is generated, crystals precipitate, and a solid-liquid ratio of 8%-15% is achieved.
[0027] S4. Perform solid-liquid separation on the liquid containing crystals, and dry the separated crystals to obtain the first inorganic salt product.
[0028] As an example, solid-liquid separation is performed on a liquid containing crystals. Specifically, the liquid containing crystals first undergoes preliminary solid-liquid separation through a thickener, and then enters a centrifuge for centrifugation to achieve secondary solid-liquid separation. The separated crystals, i.e., inorganic salts, are dried in a fluidized bed to form the first inorganic salt product; the separated liquid, i.e., the spin-off liquid, is returned to a triple-effect evaporator for further evaporation, concentration, and crystallization.
[0029] S5. Monitor the whiteness of the first inorganic salt product and the chlorine concentration of the mother liquor in the last-effect evaporator. When the whiteness of the product is less than 55% or the chlorine concentration of the mother liquor is greater than 60g / L, discharge the mother liquor in the last-effect evaporator.
[0030] In this step, because the separation of oil and chlorine from wastewater is relatively difficult during the evaporation process of the pretreated liquid in the MVR evaporation system, oil and chlorine will gradually accumulate in the last-effect evaporator. Therefore, the crystallized liquid obtained in step S4 still contains a small amount of oil (about 7 mg / L) and chlorine (about 1 g / L). When the oil accumulates to a certain extent, the quality of the first inorganic salt product will decrease significantly. Therefore, the discharge standard of the mother liquor in the last-effect evaporator is set as follows: the whiteness of the first inorganic salt product is less than 55% or the chlorine concentration of the mother liquor in the last-effect evaporator is greater than 60 g / L.
[0031] Under normal circumstances, because the whiteness of inorganic salt products is significantly affected by water quality, the whiteness of the first inorganic salt product will quickly fall below 55%. In this case, adjusting relevant parameters of the MVR evaporation system, such as the solid-liquid ratio in the final-effect evaporator and the discharge of mother liquor, can improve the whiteness of the first inorganic salt product. When the chlorine concentration of the mother liquor in the final-effect evaporator is >60g / L, adjusting the MVR evaporation system parameters will not provide significant improvement. At this point, the mother liquor in the final-effect evaporator must be completely drained, and the final-effect evaporator, salt leg slurry tank, post-spinning liquid tank, thickener, etc., must be cleaned.
[0032] The term "last-effect evaporator" refers to the last evaporator in a multi-effect evaporation system. As an example, the last-effect evaporator is the triple-effect evaporator in the aforementioned MVR evaporation system.
[0033] Regarding the determination of the whiteness of the first inorganic salt product, as an example, during the packaging process of the first inorganic salt product, a sample is taken every 4 hours. The sample is crushed by a patting machine and then placed on a whiteness meter to determine its whiteness.
[0034] As an example, regarding the determination of chlorine concentration in the mother liquor, during the operation of the MVR evaporation system, a sample of the material in the last-effect evaporator is taken every 12 hours and then sent to the laboratory for chlorine concentration determination by turbidimetric method.
[0035] S6. The discharged mother liquor is pretreated to remove oil, and an alkaline substance is added to adjust the pH value to 3.0-4.5 to obtain the pretreated mother liquor.
[0036] In this step, the oil removal pretreatment is achieved through activated carbon adsorption. The alkaline substance is one or more of ammonia, sodium hydroxide, or sodium carbonate. The mother liquor contains a large amount of salt ((NH4)2SO4 approximately 400-500 g / L, Cl... - The concentration is approximately 35g / L-45g / L, with a high oil content and a low pH (approximately 1.5-2). After adjusting the pH to 3.0-4.5 with alkaline substances, the charge at the crystallization interface tends to balance, resulting in a moderate double-layer thickness. (NH4) + SO4² - Cl - The target ions are subject to less electrostatic repulsion and are more likely to approach the crystallization interface, thereby increasing the crystallization rate.
[0037] As an example, coal-based powdered activated carbon is added to the mother liquor at a ratio of 5‰-7‰, and ammonia water is added at the same time to adjust the pH value of the mother liquor to 3.0-4.5. The mixture is stirred and mixed simultaneously, and then the activated carbon is retained by a filter press to obtain the pretreated mother liquor.
[0038] S7. Preheat the pretreated mother liquor.
[0039] In this step, the pretreated liquid can exchange heat with the high-temperature condensate generated during the evaporation of the pretreated mother liquor in the subsequent step through a plate heat exchanger, so as to recover and utilize the waste heat in the high-temperature condensate, effectively reducing the overall energy consumption of the evaporator in the subsequent evaporation process of the pretreated mother liquor and saving operating costs.
[0040] S8. The pretreated mother liquor is concentrated by evaporation to obtain concentrated mother liquor.
[0041] In this step, the evaporation and concentration of the pretreated mother liquor is usually a single-effect evaporation and concentration, which is achieved by a single-effect evaporator, preferably a single-effect MVR evaporator; the solid-liquid ratio of the concentrated mother liquor is 20%-35%.
[0042] S9. Cool and crystallize the concentrated mother liquor to obtain a mother liquor containing crystals.
[0043] As an example, the concentrated mother liquor is cooled and crystallized. Specifically, the concentrated mother liquor enters the crystallization kettle, and circulating water is used to cool the crystallization kettle to promote the cooling and crystallization of the material inside the crystallization kettle, reducing the temperature of the material in the crystallization kettle to about 40°C.
[0044] S10. The mother liquor containing crystals is subjected to solid-liquid separation, and the separated crystals are dried to obtain the second inorganic salt product.
[0045] As an example, solid-liquid separation is performed on the mother liquor containing crystals. Specifically, the mother liquor containing crystals is centrifuged to achieve solid-liquid separation. The separated crystals, i.e., inorganic salts, are dried in a fluidized bed to form a second inorganic salt product; the separated liquid, i.e., the spin-off liquid, is returned to the evaporator in the pretreated mother liquor evaporation process for further evaporation, concentration, and crystallization.
[0046] S11. Monitor the evaporation rate of the evaporator in the evaporation process of the pretreated mother liquor. When the evaporation rate is less than 70% of the initial evaporation rate, discharge the mother liquor in the evaporator and return it to the preparation step of the pretreated mother liquor.
[0047] In this step, because it is relatively difficult to separate oil and other impurity ions from wastewater during the evaporation process of the mother liquor after pretreatment, oil and impurity ions will gradually accumulate in the evaporator of the mother liquor evaporation process after pretreatment. Therefore, the mother liquor containing crystals obtained in step S8 still contains oil and a large amount of chlorine (about 40g / L). When the oil accumulates to a certain extent, the evaporation rate of the evaporator is less than 70% of the initial evaporation rate, that is, it drops significantly. At this time, the mother liquor in the evaporator needs to be completely drained and cleaned. The discharged mother liquor is then returned to step S6 for further processing.
[0048] To operate two of the above-mentioned MVR evaporation systems, the discharge capacity of the triple-effect mother liquor from one MVR evaporation system is approximately 500 m³. 3Taking the cycle as an example, the discharge of the triple-effect mother liquor is about 133 m³ / d. Using the high-salt oily wastewater treatment method provided in this embodiment, the mother liquor treatment capacity can reach 89 m³ / d.
[0049] In contrast, the discharge standard for the mother liquor in the triple-effect evaporator in step S5 is set to periodic discharge, and the addition of alkaline substances in step S6 is cancelled. Similarly, with two sets of the above-mentioned MVR evaporation systems in operation, the discharge volume of the triple-effect mother liquor from one MVR evaporation system is approximately 500 m³. 3 Taking the cycle as an example, if the mother liquor of the triple-effect effluent is discharged at a cycle of about 10 days, the mother liquor treatment volume is about 53 m³ / d, which is significantly different from the discharge volume of about 133 m³ / d of the triple-effect effluent. The mother liquor will accumulate severely, affecting the continuity of the high-salt and oily wastewater treatment process.
[0050] In summary, the high-salt oily wastewater treatment method provided in this application, by monitoring the whiteness of the first inorganic salt product and the chlorine concentration of the final-effect mother liquor, precisely controls the timing of the discharge of the final-effect mother liquor, enabling early prediction of the quality decline of the first inorganic salt product, thereby reducing the output of unqualified products and improving the product qualification rate; adding alkaline substances to adjust the pH in the oil removal pretreatment stage of the mother liquor can accelerate the crystallization rate and significantly increase the mother liquor treatment volume; by increasing the mother liquor treatment volume, the difference between it and the discharge volume of the final-effect mother liquor can be narrowed, effectively alleviating the problem of mother liquor accumulation, thereby improving the continuity of the high-salt oily wastewater treatment process.
[0051] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application.
Claims
1. A method for treating high-salt, oily wastewater, characterized in that, include: Oil removal pretreatment was performed on high-salt oily wastewater to obtain pretreated liquid; The pretreated liquid was concentrated by multi-effect evaporation to obtain a liquid containing crystals; The crystalline liquid is subjected to solid-liquid separation, and the separated crystals are dried to obtain the first inorganic salt product; Monitor the whiteness of the first inorganic salt product and the chlorine concentration of the mother liquor in the last-effect evaporator. When the whiteness is less than 55% or the chlorine concentration is greater than 60 g / L, discharge the mother liquor in the last-effect evaporator.
2. The method for treating high-salt, oily wastewater according to claim 1, characterized in that, Also includes: The discharged mother liquor is subjected to oil removal pretreatment, and an alkaline substance is added to adjust the pH value to 3.0-4.5 to obtain the pretreated mother liquor; The pretreated mother liquor was concentrated by evaporation to obtain concentrated mother liquor; The concentrated mother liquor is cooled and crystallized to obtain a mother liquor containing crystals; The mother liquor containing crystals is subjected to solid-liquid separation, and the separated crystals are dried to obtain a second inorganic salt product.
3. The method for treating high-salt, oily wastewater according to claim 2, characterized in that, Also includes: Monitor the evaporation rate of the evaporator in the pretreated mother liquor evaporation process. When the evaporation rate is less than 70% of the initial evaporation rate, discharge the mother liquor in the evaporator and return it to the pretreated mother liquor preparation step.
4. The method for treating high-salt, oily wastewater according to claim 2, characterized in that, After solid-liquid separation of the crystallized mother liquor, the separated liquid is returned to the evaporator of the pretreated mother liquor evaporation process for further evaporation and concentration.
5. The method for treating high-salt, oily wastewater according to claim 2, characterized in that, Also includes: Before evaporating and concentrating the pretreated mother liquor, the pretreated mother liquor is preheated.
6. The method for treating high-salt, oily wastewater according to claim 2, characterized in that, The oil removal pretreatment of the mother liquor is achieved through activated carbon adsorption.
7. The method for treating high-salt, oily wastewater according to claim 2, characterized in that, The alkaline substance is one or more of ammonia, sodium hydroxide, or sodium carbonate.
8. The method for treating high-salt, oily wastewater according to claim 1, characterized in that, After solid-liquid separation of the crystalline liquid, the separated liquid is returned to the final-effect evaporator for further evaporation and concentration.
9. The method for treating high-salt, oily wastewater according to claim 1, characterized in that, Also includes: The pretreated liquid is preheated before being concentrated by multi-effect evaporation.
10. The method for treating high-salt, oily wastewater according to claim 1, characterized in that, The oil removal pretreatment of the high-salt, oily wastewater is achieved through activated carbon adsorption or resin adsorption.