A four-effect falling film evaporation device and method for wastewater containing organic matter and high concentration of sodium sulfate

Abstract

This invention relates to the fields of oil refining and chemical technology, and provides a four-effect falling film evaporation device and method for wastewater containing organic matter and high concentrations of sodium sulfate. It includes a feed tank, a plate heat exchanger, an oil removal tank, a first-effect heating chamber, a first-effect crystallizing evaporator, a second-effect heating chamber, a second-effect separation chamber, a first flash tank, a third-effect heating chamber, a third-effect separation chamber, a second flash tank, a fourth-effect heating chamber, a fourth-effect separation chamber, an indirect condenser, a vacuum unit, a condensate tank, a thickener, a centrifuge, a mother liquor tank, and a pump. This invention eliminates the need for an alkali storage tank, an alkali metering pump device, and an acid-base neutralization tank, avoiding alkali consumption, reducing equipment investment by more than 30%, saving land investment, and reducing engineering workload and labor intensity. The pH value of the material entering the four-effect falling film evaporator is maintained at an acidic level, reducing the formation of scale and viscous colloids, reducing the discharge of highly concentrated wastewater, lowering subsequent operating costs, maintaining an acidic environment, preventing scale formation, reducing maintenance costs, and improving efficiency and production capacity.

Description

Technical Field

[0001] This invention relates to the fields of oil refining and chemical technology, specifically to a four-effect falling film evaporation apparatus and method for wastewater containing organic matter and high concentrations of sodium sulfate. Background Technology

[0002] During the production process, oil refining and chemical enterprises will generate some wastewater with high concentrations of salt and organic matter. When the output is small, it is generally discharged directly into the wastewater treatment plant and mixed with other wastewater before undergoing pretreatment and biochemical degradation. However, when the output is high, the high-concentration wastewater with high salt and organic matter has an inhibitory and toxic effect on the biochemical treatment system. Not only can it not be effectively degraded, but it can also cause the entire wastewater treatment plant to malfunction. In this case, it is necessary to pretreat the high-concentration wastewater separately.

[0003] In the field of wastewater evaporation crystallization desalination equipment in the wastewater treatment industry, the four-effect falling film evaporation crystallization desalination device is currently the most widely used treatment technology. Four-effect falling film evaporation involves connecting several evaporators in series, allowing for multiple uses of steam heat energy, thereby improving heat energy utilization and reducing operating costs. In the four-effect evaporation process, the first evaporator (called the first effect) uses live steam as heating steam, while the other three (called the second, third, and fourth effects) use secondary steam from the previous effect as heating steam, thus significantly reducing the amount of live steam used.

[0004] The condensate after evaporation can be directly discharged into a wastewater treatment plant for further processing. This device mainly consists of an alkali neutralization system, a preheating system, an evaporation system, a vacuum system, a separation system, and a condensate system, making it one of the most advanced evaporators currently available. Both the second-effect to third-effect and third-effect to fourth-effect evaporators utilize natural feed flow. Forced circulation is used for crystallization and discharge within the first-effect crystallizing evaporator. By controlling the mother liquor circulation flow rate, the heat transfer coefficient and the supersaturation of the mixed liquor can be adjusted to ensure stable crystallization operation. The evaporated crystals are dehydrated by a centrifuge and then directly packaged and transported. The liquid discharged from the centrifuge is then returned to the first effect for repeated processing. The four-effect evaporator is a highly efficient multi-pass circulating evaporation device, primarily used for the treatment of soluble aqueous solutions, and is widely applicable to evaporation operations in chemical, light industrial, food, and metallurgical industries.

[0005] It has the advantages of high heat transfer efficiency, high operational flexibility, reliable operation, low evaporation temperature, low equipment corrosion, small temperature difference during circulation, easy scaling of heat exchange tubes, and long operation cycle.

[0006] However, it also has disadvantages such as high overall energy consumption, numerous auxiliary equipment, large consumption of auxiliary materials, low productivity, prominent pipe blockage and scaling, the need for regular and frequent cleaning, and high labor intensity. For wastewater containing soluble organic matter and extremely high salt content (such as wastewater from phenol and acetone production), as the quadruple-effect falling film evaporation continues, the concentration of the mother liquor increases continuously with the repeated circulation. This causes scaling and scaling to easily form on the heating tubes during the wastewater evaporation and concentration process, thus affecting the treatment effect and wasting energy. At the same time, due to the concentration and polymerization of one or more organic substances, a large amount of viscous colloids are formed in the mother liquor. These viscous colloids have high viscosity and are difficult to separate and dissolve under molecular polymerization. In addition, the temperature of the downstream material decreases, and after a period of operation, the viscous colloids and scale will adhere to the top of the quaternary heating chamber, causing the aperture of the quaternary heating chamber to gradually decrease. This results in a smaller material circulation volume in the quadruple-effect heating chamber and uneven distribution on the heat exchange tubes, affecting the material evaporation and concentration effect, reducing the operating cycle, and increasing maintenance costs. Summary of the Invention

[0007] To address the problems existing in the background art, the present invention provides a four-effect falling film evaporation device and method for wastewater containing organic matter and high concentration of sodium sulfate, comprising a feed tank, a plate heat exchanger, an oil removal tank, a first-effect heating chamber, a first-effect crystallizing evaporator, a second-effect heating chamber, a second-effect separation chamber, a first flash tank, a third-effect heating chamber, a third-effect separation chamber, a second flash tank, a fourth-effect heating chamber, a fourth-effect separation chamber, an indirect condenser, a vacuum unit, a condensate tank, a thickener, a centrifuge, a mother liquor tank, and a pump.

[0008] The raw material liquid enters the feed storage tank directly without alkali neutralization. After being preheated by the plate heat exchanger, it enters the first-effect heating chamber, the second-effect heating chamber, the third-effect heating chamber, and the fourth-effect heating chamber for heating in sequence. After passing through the first-effect crystallizing evaporator, the oil and liquid are separated. The oil and viscous colloidal organic matter are separated and enter the oil storage tank. The liquid passes through the thickener and forms crystal salts. After being dehydrated by the centrifuge, it is discharged. The concentrated liquid discharged from the centrifuge enters the mother liquor tank and is then pumped back to the first-effect heating chamber for repeated circulation.

[0009] Boiler steam enters the shell side of the first-effect heating chamber. The condensate, after preheating the raw liquid, returns to the boiler. The secondary steam evaporated from the first-effect heating chamber enters the shell side of the second-effect heating chamber as heating steam. After condensation in the second-effect separation chamber, the condensate enters the second-effect heating chamber for flash evaporation. The secondary steam evaporated from the second-effect heating chamber serves as heating steam for the third-effect heating chamber. After condensation in the third-effect separation chamber, the condensate enters the third-effect heating chamber for flash evaporation. The secondary steam evaporated from the third-effect heating chamber serves as heating steam for the fourth-effect heating chamber. After condensation in the fourth-effect separation chamber, the condensate enters the fourth-effect heating chamber for flash evaporation. The steam evaporated from the fourth-effect heating chamber is condensed by an indirect condenser, and the non-condensable gases are discharged by the vacuum unit.

[0010] In the preferred embodiment, the first-effect crystallizing evaporator is equipped with a three-phase cyclone separator, connecting and fixing plates, an oil drain port, and a first-effect material inlet. There are four connecting and fixing plates. The three-phase cyclone separator is installed inside the top wall of the first-effect crystallizing evaporator through the four connecting plates. The four connecting plates are installed evenly and symmetrically.

[0011] In the preferred embodiment, a 50mm gap is maintained between the outer wall of the three-phase cyclone separator and the inner wall of the single-effect crystallizing evaporator, and the inlet of the three-phase cyclone separator enters the feed inlet of the single-effect crystallizing evaporator tangentially along the periphery.

[0012] In the preferred embodiment, the liquid level in the first-effect crystallizing evaporator is controlled above the material inlet of the first-effect evaporator, the oil drain pipe is installed 10mm above the normal liquid level in the first-effect crystallizing evaporator, the pipe diameter is selected as DN40mm, and the end of the oil drain pipe is connected to the oil remover.

[0013] In the preferred embodiment, stainless steel coalescing packing is installed inside the oil tank for oil-water separation.

[0014] In a preferred embodiment, the top of the four-effect heating chamber is equipped with three layers of perforated plates, which are welded to the shell. The perforated plates are provided with perforated plate holes, and adjacent perforated plate holes are installed in a staggered manner.

[0015] In a preferred embodiment, the aperture of the stencil is 6 mm.

[0016] The beneficial effects achieved by this invention are as follows:

[0017] 1. This invention eliminates the need for alkali storage tanks, alkali metering pumps, and acid-base neutralization tanks, avoiding alkali consumption, reducing equipment investment by more than 30%, saving land investment, avoiding data waste, and reducing engineering workload and labor intensity. The pH value of the material entering the four-effect falling film evaporator is kept acidic, reducing the formation of scale and viscous colloids, reducing the discharge of high-concentration wastewater, reducing subsequent operating costs, while maintaining an acidic environment to prevent scale formation, reduce maintenance costs, and improve efficiency and production capacity.

[0018] 2. The equipment structure has been optimized, improving the ability to remove organic matter, reducing the production of highly enriched wastewater, and reducing subsequent treatment costs; the working efficiency of the centrifuge has been improved, and operating costs have been reduced.

[0019] 3. A three-phase cyclone separator is installed in the single-effect crystallization evaporation chamber to improve the removal rate of organic matter, accelerate the evaporation and concentration of materials, and improve the material treatment effect.

[0020] 4. An oil drain pipe is installed at the top of the feed inlet in the single-effect crystallization evaporation chamber to reduce the oil content of the material entering the thickener and improve the separation effect of the centrifuge.

[0021] 5. The diameter of the perforated plate in the quadruple heating chamber has been changed from 3mm to 6mm, which reduces the clogging of the perforated plate, reduces the failure rate of the circulating pump in the quadruple heating chamber, and reduces the maintenance frequency; it also increases the flow rate of circulating materials and accelerates the evaporation of materials. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 This is a schematic diagram of a single-effect crystallization evaporator;

[0024] Figure 3 This is a schematic diagram of the oil removal tank.

[0025] Figure 4 This is a schematic diagram of the structure of a four-effect heating chamber;

[0026] Figure 5 yes Figure 4 Schematic diagram of the middle perforated plate structure.

[0027] Numbering on the map:

[0028] 1. Feed tank; 2. Plate heat exchanger; 3. Oil removal tank; 4. First-effect heating chamber; 5. First-effect crystallizing evaporator; 6. Second-effect heating chamber; 7. Second-effect separation chamber; 8. First flash tank; 9. Third-effect heating chamber; 10. Third-effect separation chamber; 11. Second flash tank; 12. Fourth-effect heating chamber; 13. Fourth-effect separation chamber; 14. Indirect condenser; 15. Vacuum unit; 16. Condensate tank; 17. Thickener; 18. Centrifuge; 19. Mother liquor tank; 20. Pump; 1-2. Three-phase cyclone separator; 1-3. Connecting and fixing plate; 1-5. Oil outlet; 1-6. First-effect material inlet; 2-3. Stainless steel coalescing packing; 3-2. Strainer plate; 3-3. Strainer plate hole. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see Figures 1 to 5This invention provides a technical solution: a four-effect falling film evaporation device and method for wastewater containing organic matter and high concentration of sodium sulfate, comprising a feed tank 1, a plate heat exchanger 2, an oil removal tank 3, a first-effect heating chamber 4, a first-effect crystallization evaporator 5, a second-effect heating chamber 6, a second-effect separation chamber 7, a first flash tank 8, a third-effect heating chamber 9, a third-effect separation chamber 10, a second flash tank 11, a fourth-effect heating chamber 12, a fourth-effect separation chamber 13, an indirect condenser 14, a vacuum unit 15, a condensate tank 16, a thickener 17, a centrifuge 18, a mother liquor tank 19, and a pump 20.

[0031] The raw material liquid enters the feed storage tank 1 directly without alkali neutralization. After being preheated by the plate heat exchanger 2, it enters the first-effect heating chamber 4, the second-effect heating chamber 6, the third-effect heating chamber 9, and the fourth-effect heating chamber 12 for heating in sequence. After passing through the first-effect crystallizing evaporator 5, the oil and liquid are separated. The oil and viscous colloidal organic matter are separated and enter the oil storage tank. The liquid passes through the thickener 17 and forms crystal salt. After being dehydrated by the centrifuge 18, it is discharged. The concentrated liquid discharged from the centrifuge 18 enters the mother liquor tank 19 and is then pumped back to the first-effect heating chamber 4 by the pump 20 for repeated circulation.

[0032] Boiler steam enters the shell side of the first-effect heating chamber 4. The condensate, after preheating the raw liquid, returns to the boiler. The secondary steam evaporated from the first-effect heating chamber 4 enters the shell side of the second-effect heating chamber 6 as the heating steam for the second-effect heating chamber 6. After condensation in the second-effect separation chamber 7, the condensate enters the second-effect heating chamber 6 for flash evaporation. The secondary steam evaporated from the second-effect heating chamber 6 serves as the heating steam for the third-effect heating chamber 9. After condensation in the third-effect separation chamber 10, the condensate enters the third-effect heating chamber 9 for flash evaporation. The secondary steam evaporated from the third-effect heating chamber 9 serves as the heating steam for the fourth-effect heating chamber 12. After condensation in the fourth-effect separation chamber 13, the condensate enters the fourth-effect heating chamber 12 for flash evaporation. The steam evaporated from the fourth-effect heating chamber 12 is condensed by the indirect condenser 14, and the non-condensable gases are discharged by the vacuum unit 15.

[0033] The single-effect crystallizing evaporator 5 is internally equipped with a three-phase cyclone separator 1-2, connecting and fixing plates 1-3, an oil drain port 1-5, and a single-effect material inlet 1-6. Four connecting and fixing plates 1-3 are provided. The three-phase cyclone separator 1-2 is installed inside the top wall of the single-effect crystallizing evaporator 5 via these four connecting plates, which are evenly and symmetrically installed. A 50mm gap is maintained between the outer wall of the three-phase cyclone separator 1-2 and the inner wall of the single-effect crystallizing evaporator 5. The inlet of the three-phase cyclone separator 1-2 enters the feed inlet of the single-effect crystallizing evaporator 5 tangentially along its perimeter. The liquid level inside the single-effect crystallizing evaporator 5 is controlled above the single-effect material inlet 1-6. The oil drain pipe is installed 10mm above the normal liquid level in the single-effect crystallizing evaporator 5, with a pipe diameter of DN40mm. The end of the oil drain pipe is connected to an oil separator. The oil separator tank 3 is equipped with stainless steel coalescing packing 2-3 for oil-water separation. The top of the quadruple-effect heating chamber 12 is equipped with three layers of perforated plates 3-2, which are welded to the shell. The perforated plates 3-2 are provided with perforated plate holes 3-3, and adjacent perforated plate holes 3-3 are staggered. The diameter of the perforated plate holes 3-3 is 6mm.

[0034] The wastewater treated by this invention mainly comes from the neutralization and oxidation units of the phenol workshop. The wastewater is discharged continuously from the device, with a volume of approximately 23 m³. 3 The wastewater has a pH of 3-5 and contains a large amount of Na2SO4, with an instantaneous Na2SO4 content of 70,000 ppm and an average concentration of about 40,000 ppm. The wastewater enters the acid-base adjustment tank via a DN100 pipeline, where alkali is added to adjust the pH to around 7. This invention, while adhering to the traditional treatment system consisting of an alkali neutralization system, preheating system, evaporation system, vacuum system, separation system, and condensate system, eliminates the need for an alkali neutralization system. The wastewater from the device directly enters the feed storage tank 1, and the effluent from the feed storage tank 1 is directly pumped by the booster pump 20 into the quadruple-effect falling film evaporator.

[0035] When the pH is low, i.e., when the acidity is strong, the acid does not easily dissociate into negatively charged anions. The scale-forming cations, however, can exist in a highly soluble ionic state under the influence of hydrated hydrogen ions. When the pH rises to a certain level, the hydrogen ion concentration in the water decreases, and the acid easily dissociates into negatively charged anions. Furthermore, the hydrated hydrogen ions surrounding the metal ions are neutralized by hydroxide ions. When the product of the anion concentration and the metal ion concentration reaches a certain value (called the ion product), insoluble scale precipitates are formed. The wastewater from the phenol plant has a pH of 3-5. The traditional process involves adding a NaOH solution with a concentration not exceeding 10% to the wastewater to adjust the pH to around 7 before it enters the quadruple-effect falling film evaporation process. At this point, the material's pH is neutral and gradually becomes alkaline as it evaporates and concentrates. Therefore, the calcium and magnesium salts in the material have a very strong tendency to form scale, which easily leads to scaling on the heat exchange tubes and perforated plates 3-2, and shortens the operating cycle. If the pH is 3-5, it is acidic and scale is not easily formed. Heat exchange tubes and sluice plates are less prone to scaling and have a longer operating cycle, which not only reduces the number of shutdowns for maintenance and labor intensity, but also improves processing efficiency.

[0036] During evaporation, the material's pH is acidic, which effectively controls foaming in the separation chamber, increases the evaporation rate of secondary steam, improves thermal energy utilization, lowers the material temperature, and slows down the formation of large amounts of viscous colloids from the concentration and polymerization of organic matter in the material under high-temperature conditions. This reduces the production of enriched wastewater and extends the operating cycle of the four-effect falling film evaporator. The wastewater from the phenol unit has a pH of 3-5. After adding alkali to adjust the pH to around 7 before entering the four-effect falling film evaporator, the non-acidic material produces a large amount of foam in the separation chamber, hindering the rapid evaporation of secondary steam and resulting in a higher material temperature within the separation chamber, making it easier for organic matter to polymerize into viscous colloids. The enriched wastewater needs to be discharged from the mother liquor tank 19 every 10-15 days; otherwise, the normal operation of the four-effect falling film evaporator will be affected. Wastewater from the phenol plant with a pH of 3-5 directly enters the quadruple-effect falling film evaporator. The mother liquor of the enriched wastewater is discharged only once every 30-40 days. The discharge time is extended by 2-3 times compared to adding alkali for neutralization, which not only improves equipment efficiency but also reduces labor intensity and subsequent treatment costs for the enriched wastewater. This invention eliminates the need to add alkali, thereby reducing the amount of alkali used for evaporation and avoiding resource waste.

[0037] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for operating a four-effect falling film evaporator for wastewater containing organic matter and high concentrations of sodium sulfate, characterized in that, It includes a feed tank (1), a plate heat exchanger (2), an oil removal tank (3), a first-effect heating chamber (4), a first-effect crystallizing evaporator (5), a second-effect heating chamber (6), a second-effect separation chamber (7), a first flash tank (8), a third-effect heating chamber (9), a third-effect separation chamber (10), a second flash tank (11), a fourth-effect heating chamber (12), a fourth-effect separation chamber (13), an indirect condenser (14), a vacuum unit (15), a condensate tank (16), a thickener (17), a centrifuge (18), a mother liquor tank (19), and a pump (20). The raw material liquid enters the feed storage tank (1) directly without alkali neutralization. After being preheated by the plate heat exchanger (2), it enters the second-effect heating chamber (6), the third-effect heating chamber (9), and the fourth-effect heating chamber (12) for heating in sequence. After passing through the first-effect crystallizing evaporator (5), the oil and liquid are separated. The oil and viscous colloidal organic matter enter the oil storage tank after separation. After passing through the thickener (17), the liquid forms crystal salts, which are dehydrated by the centrifuge (18) and discharged. The concentrated liquid discharged by the centrifuge (18) enters the mother liquor tank (19) and is then pumped back to the first-effect heating chamber (4) by the pump (20) for repeated circulation. Boiler steam enters the shell side of the first-effect heating chamber (4). After condensation, the condensate preheats the raw liquid and returns to the boiler. The secondary steam evaporated from the first-effect heating chamber (4) enters the shell side of the second-effect heating chamber (6) as the heating steam for the second-effect heating chamber (6). After condensation in the second-effect separation chamber (7), the condensate enters the second-effect heating chamber (6) for flash evaporation. The secondary steam evaporated from the second-effect heating chamber (6) serves as the heating steam for the third-effect heating chamber (9). After condensation in the third-effect separation chamber (10), the condensate enters the third-effect heating chamber (9) for flash evaporation. The secondary steam evaporated from the third-effect heating chamber (9) serves as the heating steam for the fourth-effect heating chamber (12). After condensation in the fourth-effect separation chamber (13), the condensate enters the fourth-effect heating chamber (12) for flash evaporation. The steam evaporated from the fourth-effect heating chamber (12) is condensed by the indirect condenser (14), and the non-condensable gases are discharged by the vacuum unit (15). The first-effect crystallizing evaporator (5) is equipped with a three-phase cyclone separator (1-2), a connecting fixing plate (1-3), an oil drain (1-5), and a first-effect material inlet (1-6). There are four connecting fixing plates (1-3). The three-phase cyclone separator (1-2) is installed inside the top wall of the first-effect crystallizing evaporator (5) through four connecting plates. The four connecting plates are evenly and symmetrically installed. A 50mm gap is maintained between the outer wall of the three-phase cyclone separator (1-2) and the inner wall of the single-effect crystallizer (5). The inlet of the three-phase cyclone separator (1-2) enters the feed inlet of the single-effect crystallizer (5) tangentially along the periphery. The liquid level in the first-effect crystallizing evaporator (5) is controlled above the material inlet (1-6) of the first-effect evaporator. The oil drain pipe is installed at a level 10 mm above the normal liquid level of the first-effect crystallizing evaporator (5). The pipe diameter is selected as DN40 mm. The end of the oil drain pipe is connected to the oil remover. The oil removal tank (3) is equipped with stainless steel coalescing packing (2-3) for oil-water separation; The top of the four-effect heating chamber (12) is equipped with three layers of perforated plates (3-2). The perforated plates (3-2) are welded to the shell. The perforated plates (3-2) are provided with perforated plate holes (3-3). Adjacent perforated plate holes (3-3) are installed in a staggered manner. The diameter of the perforation (3-3) in the sprue plate is 6 mm.

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