MVR system for high-salt and high-cod wastewater treatment

Abstract

The utility model provides a kind of MVR system of high-salt high COD wastewater treatment, including the communication of crystallization evaporator, thick thickener, centrifuge and plate-and-frame filter press in proper order, the crystallization evaporator side is equipped with wastewater inlet pipe, bottom is equipped with liquid phase outlet pipe, top is equipped with gas phase outlet pipe;The gas phase outlet pipe is horizontally arranged, middle part is equipped with demister, demister below is equipped with bifurcation pipe and is connected with high concentration condensate tank, and the outlet end of the gas phase outlet pipe is connected with low concentration condensate tank.The utility model has the beneficial effect that: high-salt high COD wastewater is clarified and concentrated, to avoid insoluble organic matter, solid material such as silt into system.Similarly, increase the baffle in mother liquor tank, return waste brine to crystallization separation system, and the enriched organic phase is pressure filtered.Reduces the possibility of foaming and fouling, improves the thermal efficiency of the whole system.

Description

Technical Field

[0001] This utility model relates to the chemical industry, specifically to an MVR system for treating high-salt, high-COD wastewater. Background Technology

[0002] Wastewater from the agrochemical industry is complex in composition, with high COD levels. Besides pesticides, solvents, and intermediates, it also contains large amounts of one or more inorganic salts such as sodium chloride, sodium sulfate, and sodium acetate. During stripping and distillation, surfactants are generated, leading to increased foam layers. MVR (mechanical vapor recompression) evaporation and concentration technology is a highly efficient and energy-saving technology that recovers the latent heat of secondary steam through mechanical compression, achieving heat energy recycling and significantly reducing wastewater treatment costs for enterprises. MVR combined with crystallization centrifugation technology is the mainstream approach for treating high-salt, high-COD wastewater in the agrochemical industry. The foam generated by wastewater evaporation is highly hazardous. First, it leads to false liquid levels, reducing the effective volume of the equipment. For example, in a crystallization evaporator, the separation chamber volume increases by 30% compared to a non-foaming system. Second, it causes severe mist entrainment, resulting in liquid at the compressor inlet in the MVR system, affecting the compressor's normal operation. More seriously, the impact of foam bursting inside the compressor can cause pitting and honeycomb-like peeling on the inner wall of the equipment, similar to pump cavitation.

[0003] High-salt, high-COD wastewater undergoes evaporation and crystallization in a crystallizer. The mother liquor from the centrifuged crystallized slurry is then returned to the system for further evaporation. When this process accumulates to a certain point, the organic matter content can even exceed the inorganic salt content. This leads to an increase in the evaporation chamber temperature, causing the organic matter to easily decompose and generate gas at high temperatures. Small molecular components or coke adhere to the equipment and pipes. With prolonged operation, the gasification rate decreases, and system failure may even occur. The conventional approach is to repeat the evaporation process several times before sending the wastewater to a dryer for solidification.

[0004] Organic acids, alkalis, or salts in high-salt, high-COD wastewater often contain long carbon chains or aromatic rings. These hydrophobic groups give them hydrophilic-hydrophobic properties, allowing them to be directionally adsorbed at the gas-liquid interface, reducing surface tension and making them more stable foams compared to those formed by only hydrophilic inorganic salt solutions. Wastewater often contains small particles or droplets, such as those from pump sealing oil and lubricating grease, which lower the surface tension and make the wastewater prone to foaming. The crystal slurry at the bottom of the evaporator often adsorbs gases or vapors, initially acting as bubble nuclei. Under negative pressure, bubbles form. Because the pressure of smaller bubbles is greater than that of larger bubbles, they grow until buoyancy exceeds drag, gradually floating to the interface. Rising bubbles in the evaporator accumulate at the gas-liquid interface. Many bubbles aggregate to form spherical bubble aggregates of different sizes. More aggregates form a foam layer, which is carried to the gas phase pipe by secondary steam. In abnormal situations, the foam layer gradually rises to the gas phase outlet of the crystallizer, limiting evaporation capacity and causing COD in the condensate to exceed standards. Utility Model Content

[0005] To address the issue of reduced wastewater treatment capacity caused by foaming and scaling in MVR systems, and to ensure stable system operation, consistent condensate and waste salt discharge, and compliance with relevant standards; This utility model provides an MVR system for treating high-salt, high-COD wastewater, comprising a crystallizer evaporator, a thickener, a centrifuge, and a plate and frame filter press connected in sequence. The crystallizer evaporator has a wastewater inlet pipe on its side, a liquid phase outlet pipe at its bottom, and a gas phase outlet pipe at its top. The gas phase outlet pipe is horizontally arranged, with a demister in the middle. Below the demister, there is a branch pipe connecting to a high-concentration condensate tank, and the outlet end of the gas phase outlet pipe connects to a low-concentration condensate tank.

[0006] As a preferred embodiment, the wastewater inlet pipe is connected to a wastewater settling container. The wastewater settling container is equipped with an upper inclined plate group to increase the clarification area and a lower inclined plate group to increase the adhesion area. The outlet of the wastewater settling container inlet pipe is located between the upper and lower inclined plate groups. Multiple liquid outlet pipes are provided on the side of the wastewater settling container, located above the upper inclined plate group and below the lower inclined plate group respectively, and connected to the wastewater inlet pipe. A sludge removal pipe is provided at the bottom of the wastewater settling container.

[0007] As a preferred embodiment, a reboiler is installed on the wastewater inlet pipe, live steam is introduced into the reboiler's heat medium inlet pipe, the gas phase outlet pipe is connected to the reboiler's heat medium inlet pipe, and a compressor is installed at the outlet of the gas phase outlet pipe.

[0008] As a preferred embodiment, the crystallizing evaporator is provided with a reflux pipe connected to the feed inlet of the reboiler.

[0009] As a preferred embodiment, a hydrocyclone assembly for pretreatment is provided between the crystallizer evaporator and the thickener. The lower port of the hydrocyclone assembly is connected to the feed tank in the middle of the thickener, and the waste liquid is distributed by the distribution head in the middle of the hydrocyclone assembly.

[0010] As a preferred embodiment, a centrifugal mother liquor tank is provided between the centrifuge and the plate and frame filter press. The centrifugal mother liquor tank is equipped with baffles and is a horizontal tank with a flat bottom and an elliptical head. A long glass sight glass and a density meter are provided on the flat bottom.

[0011] As a preferred embodiment, the solid phase outlet pipe of the plate and frame filter press is equipped with a drum dryer, and the liquid phase outlet pipe is connected to a centrifugal mother liquor tank for reflux.

[0012] The beneficial effects of this utility model are as follows: 1. This invention clarifies and concentrates high-salt, high-COD wastewater, preventing insoluble organic matter, silt, and other solid materials from entering the system. Similarly, a baffle is added to the mother liquor tank to return the waste brine to the crystallization separation system, while the enriched organic phase is filtered. This reduces the possibility of foaming and scaling, and improves the overall thermal efficiency of the system.

[0013] 2. This invention applies foam separation technology to an evaporation crystallization system. The foam liquid, which has adsorbed organic matter, is collected in a high-concentration condensate tank. After secondary steam compression, it is sent to a reboiler for condensation, and the condensate enters a low-concentration condensate tank. These components then flow into different equipment at the wastewater treatment plant, achieving a separation of clean and polluted water. As surfactants are extracted along with the bubbles, accumulation in the crystallizing evaporator is avoided, reducing the foam layer height and ultimately improving the evaporation crystallization processing capacity.

[0014] 3. This utility model adds a hydrocyclone group before the conventional combination of thickener and horizontal centrifuge, which further reduces the fine salt particles entrained in the mother liquor. At the same time, it can reduce the operating power of centrifugation and reduce the operating costs of slurry centrifugation and mother liquor drying. Attached Figure Description

[0015] To make the content of this utility model easier to understand, the present utility model will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a schematic diagram of the structure of the present invention.

[0016] The numbers in the attached diagram are: 1. Reboiler; 3. Crystallizing evaporator; 31. Wastewater inlet pipe; 32. Liquid phase outlet pipe; 33. Gas phase outlet pipe; 34. Demister; 35. Reflux pipe; 5. Hydrocyclone assembly; 6. Thickener; 7. Centrifuge; 8. Centrifugal mother liquor tank; 10. Plate and frame filter press; 11. Drum dryer; 12. Compressor; 13. High-concentration condensate tank; 14. Low-concentration condensate tank; 16. Wastewater settling container; 161. Upper inclined plate assembly; 162. Lower inclined plate assembly. Detailed Implementation

[0017] To illustrate the features of this utility model, the following description, in conjunction with the accompanying drawings and embodiments, will further explain this utility model.

[0018] Example 1: Please see Figure 1 This utility model provides an MVR system for treating high-salt, high-COD wastewater, the specific structure of which is described below: The system comprises a crystallizing evaporator 3, a thickener 6, a centrifuge 7, and a plate and frame filter press 10, connected sequentially along the processing flow. The crystallizing evaporator 3 is a vertical design, 2.5 meters in diameter and 6 meters high. It has a wastewater inlet pipe 31 with a diameter of 150 mm on its side; a liquid phase outlet pipe 32 at the bottom; and a gas phase outlet pipe 33 with a diameter of 200 mm at the top. The gas phase outlet pipe 33 is horizontally positioned, with a demister 34 installed in its middle. A branch pipe below the demister connects to a high-concentration condensate tank 13. The outlet end of the gas phase outlet pipe 33 is connected to a low-concentration condensate tank 14.

[0019] The wastewater inlet pipe 31 is first connected to a wastewater settling container 16. Inside this container are an upper inclined plate assembly 161 to increase the clarification area and a lower inclined plate assembly 162 to increase the adhesion area, with a 100 mm gap between the two sets of inclined plates. The outlet of the wastewater inlet pipe is located between the upper and lower inclined plate assemblies. Two discharge pipes are located on the side of the wastewater settling container 16, one above the upper inclined plate assembly and the other below the lower inclined plate assembly, converging and connecting to the wastewater inlet pipe 31. A 200 mm diameter sludge removal pipe is located at the bottom of the wastewater settling container 16.

[0020] Before the wastewater enters the crystallizing evaporator 3, a reboiler 1 is installed in the pipeline. Live steam at a pressure of 0.4 MPa is introduced into the heat medium inlet pipe of the reboiler 1. The vapor phase outlet pipe 33 at the top of the crystallizing evaporator 3 is pressurized by a 110 kW compressor 12 and also connected to the heat medium inlet pipe of the reboiler 1 to provide it with heat energy. In addition, the crystallizing evaporator 3 is also equipped with a return pipe 35 connected to the feed inlet of the reboiler 1 for material circulation.

[0021] Between the crystallizer evaporator 3 and the thickener 6, a hydrocyclone group 5 consisting of four hydrocyclones connected in parallel is installed for pretreatment of the crystal slurry. The lower inlet of the hydrocyclone group 5 is connected to the feed tank in the middle of the thickener 6, and the waste liquid is evenly distributed through the middle distribution head.

[0022] The thickener 6 has its slurry outlet at the bottom connected to a centrifuge 7. The liquid outlet of the centrifuge 7 is connected to a 5-cubic-meter centrifugal mother liquor tank 8. This tank is a horizontal tank with a flat bottom and an elliptical head, and is equipped with baffles inside. A 1.2-meter-long glass sight glass and an online density meter are installed on its flat bottom.

[0023] The solid phase separated by centrifuge 7, along with the concentrated slurry at the bottom of centrifugal mother liquor tank 8, enters plate and frame filter press 10 for deep dewatering. The solid phase outlet of plate and frame filter press 10 is connected to a drum dryer 11 to dry the filter cake produced. The liquid phase outlet pipe of plate and frame filter press 10 is connected back to centrifugal mother liquor tank 8 to achieve mother liquor reflux.

[0024] This system efficiently recovers heat energy through mechanical vapor recompression technology and, combined with a multi-stage solid-liquid separation unit, achieves the reduction and resource recovery of high-salt, high-COD wastewater.

[0025] The above embodiments and accompanying drawings are only used to illustrate the technical solutions of this utility model and are not intended to limit this utility model. This utility model has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of this utility model do not depart from the spirit of this utility model and should also fall within the protection scope of the claims of this utility model. Other related technical structures not disclosed in detail in this utility model are existing technologies in the art.

Claims

1. An MVR system for treating high-salt, high-COD wastewater, characterized in that: The system includes a crystallizer evaporator (3), a thickener (6), a centrifuge (7), and a plate and frame filter press (10) connected in sequence. The crystallizer evaporator (3) has a wastewater inlet pipe (31) on its side, a liquid phase outlet pipe (32) at its bottom, and a gas phase outlet pipe (33) at its top. The gas phase outlet pipe (33) is horizontally arranged and has a demister (34) in the middle. A branch pipe is provided below the demister (34) to connect to a high-concentration condensate tank (13). The outlet end of the gas phase outlet pipe (33) is connected to a low-concentration condensate tank (14).

2. The MVR system for treating high-salt, high-COD wastewater according to claim 1, characterized in that: The wastewater inlet pipe (31) is connected to the wastewater settling container (16). The wastewater settling container (16) is provided with an upper inclined plate group (161) to increase the clarification area and a lower inclined plate group (162) to increase the adhesion area. The outlet position of the inlet pipe of the wastewater settling container (16) is located between the upper inclined plate group (161) and the lower inclined plate group (162). The side of the wastewater settling container (16) is provided with multiple liquid outlet pipes located above the upper inclined plate group (161) and below the lower inclined plate group (162) and connected to the wastewater inlet pipe (31). The bottom of the wastewater settling container (16) is provided with a sludge removal pipe.

3. The MVR system for treating high-salt, high-COD wastewater according to claim 1, characterized in that: A reboiler (1) is installed on the wastewater inlet pipe (31). Live steam is introduced into the heat medium inlet pipe of the reboiler (1). The gas phase outlet pipe (33) is connected to the heat medium inlet pipe of the reboiler (1). A compressor (12) is installed at the outlet of the gas phase outlet pipe (33).

4. The MVR system for treating high-salt, high-COD wastewater according to claim 3, characterized in that: The crystallizing evaporator (3) is provided with a reflux pipe (35) connected to the feed inlet of the reboiler (1).

5. The MVR system for treating high-salt, high-COD wastewater according to claim 1, characterized in that: A hydrocyclone assembly (5) for pretreatment is provided between the crystallizer evaporator (3) and the thickener (6). The lower port of the hydrocyclone assembly (5) is connected to the feed tank in the middle of the thickener (6), and the waste liquid is distributed by the distribution head in the middle of the hydrocyclone assembly (5).

6. The MVR system for treating high-salt, high-COD wastewater according to claim 1, characterized in that: A centrifugal mother liquor tank (8) is provided between the centrifuge (7) and the plate and frame filter press (10). A baffle is provided inside the centrifugal mother liquor tank (8). The centrifugal mother liquor tank (8) is a horizontal tank with a flat bottom and an elliptical head. A long glass sight glass and a density meter are provided on the flat bottom.

7. The MVR system for treating high-salt, high-COD wastewater according to claim 6, characterized in that: The solid phase outlet pipe of the plate and frame filter press (10) is equipped with a drum dryer (11), and the liquid phase outlet pipe is connected to the centrifugal mother liquor tank (8) for reflux.

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