A sewage treatment method and device

Abstract

The present invention discloses a method and device for purifying sewage, especially sewage from the papermaking industry. The method of the present invention is a treatment method using an MVR evaporation system. The device of the present invention uses a sewage treatment device of an MVR evaporator, including: a preheater connected to each other by pipelines in sequence, an MVR evaporator with an L-shaped stripping split welding line on the heat exchanger inside, a steam compressor of the MVR, a steam manifold, a heater, a water storage tank and a storage tank, a control system, etc. The present invention controls the supply of fresh steam to the area below the L-shaped weld in the evaporator according to the quality of the clean condensed water detected, and can accurately control the quality of the clean condensed water, thereby overcoming the problem in the prior art that the COD value of the condensed water obtained by secondary steam condensation is high and an additional treatment device needs to be set up, and can directly reach the secondary steam condensed water that meets the industrial emission standards.

Description

Technical Field

[0001] The present invention relates to a method and device for purifying sewage, especially sewage from the papermaking industry. The method of the present invention is a treatment method using an MVR evaporation system, and in the device of the present invention, an L-shaped stripping split welding line is provided on the inner heat exchanger of the MVR evaporator. Background Art

[0002] At present, evaporation process is the main measure for waste liquid treatment and recycling. This treatment method and process are widely used in daily production and life. Its purpose is basically to remove water from waste liquid, turn it into distilled water and reuse it in the production system, and at the same time increase the concentration of waste liquid to meet the requirements of subsequent processes. The overall goal is to produce clean distilled water in evaporation to meet the needs of production and life, and the remaining concentrated liquid is reasonably used to reduce pollutant emissions. Using MVR evaporator to treat sewage and waste liquid is a common method at this stage.

[0003] Chinese invention patent 201510525708.3 discloses an efficient and energy-saving sewage treatment method and device. The method and device of this patent utilize an MVR evaporator with an L-shaped weld bead and a stripping function to treat wastewater. Although this patent has a good treatment effect, the waste liquid always contains a certain proportion of other impurities, such as low-boiling organic matter and other condensable gases such as organic acids, alcohols, aldehydes, ethers, sulfides, etc. These gases are often separated from the solution along with water vapor during the evaporation process. When the secondary steam is condensed into water together, the COD value in the condensed water will be high, which does not meet the industrial emission standards and cannot be returned to the production system for reasonable use. To solve this problem, it is necessary to add corresponding treatment processes and equipment in the future. For example, a system and device for stripping the secondary steam is separately set up in the evaporation system to further treat the condensed water. This is an objective and realistic measure.

[0004] Secondly, the evaporation process is a process that requires relatively high energy utilization. How to improve the energy utilization in the evaporation process is also an issue that needs to be seriously addressed in this field.

[0005] At present, evaporators, especially plate-type falling film evaporators, are frequently used in the market. Their heat exchange elements are made of cold-rolled steel plates with surface treatment. After forming, they have a streamlined smooth surface with continuous undulations and unevenness. They are favored by the market and widely used because of their high heat exchange efficiency, low scaling, and convenient cleaning. During the operation process, steam enters the heat exchange element to participate in heat exchange, and the waste heat flows outside and is heated and then boils to produce secondary steam to meet the set process requirements. The steam entering the heat exchange element forms condensed water and is discharged from the condensed water pipeline. Other non-condensable gases and low-boiling organic matter are separated and discharged from the non-condensable gas pipeline. These process requirements require the setting of corresponding physical mechanisms to complete specific functions. In actual situations, the heat exchange elements are usually welded into heaters at a certain spacing and a certain number to ensure the required heat exchange area. The structure set on the heater for the heat exchange steam to enter is called a steam collecting box, and the structure for the condensed water to be discharged is called a liquid collecting box. Both headers have a gap opened on the edge of each heat exchange element, and are connected and welded together through thin strips to form a square box. The surface is blocked with a cover plate, and the inside of the square box is connected with each heat exchange element. Once the header is welded and closed, the internal situation cannot be observed. In actual operation, corrosion or scaling cannot be completely avoided, but the structure of the existing equipment cannot visually check the corrosion and scaling. The connecting bottom plate and the surrounding side plates that form the header are weak links. Slight vibrations during transportation or use may cause cracking of the welds and leakage, seriously affecting the normal use of the equipment. Once a problem occurs, the traditional structure can only cut a window for maintenance operations, and then re-weld the cut window after the maintenance is completed. This maintenance process is very difficult, takes a long time, and has a harsh working environment. At the same time, it will also cause safety hazards during operations after maintenance. Summary of the invention

[0006] The present invention provides a sewage treatment method and device which can solve the deficiencies of the prior art, use an MVR evaporation system to evaporate sewage, and can improve and control the quality of secondary steam condensate water.

[0007] Another object of the present invention is to solve the problem that it is inconvenient to inspect and repair the evaporator in the prior art.

[0008] The method for treating sewage by using an MVR evaporator of the present invention comprises the following steps: preheating the sewage to be treated to a set temperature and then sending it into an MVR evaporator with a stripping function for evaporation and concentration; firstly, supplying fresh steam into the MVR evaporator so that the sewage is heated to a boiling point in the MVR evaporator to generate secondary steam; closing the supply of fresh steam, opening the steam compressor, and using mechanical work to pressurize and heat the secondary steam, and then sending it into a heater of the MVR evaporator, so that all heat exchange elements in the heater perform heat exchange with the sewage, so as to heat the sewage for evaporation, concentration and stripping; sewage in the MVR evaporator that reaches the concentration required by the process is to be subsequently treated; dirty condensed water and clean condensed water discharged from the MVR evaporator are respectively discharged into a dirty condensed water tank and a clean condensed water tank and then are respectively to be subsequently treated or used; the quality of the clean condensed water is detected during operation; when the quality of the clean condensed water is equal to or better than the design requirement, the operation is maintained; when the quality of the clean condensed water is lower than the design requirement, fresh steam is appropriately supplied into the MVR evaporator to improve the stripping effect, so that the quality of the clean condensed water is equal to or better than the design requirement again.

[0009] Preferably, in the method for treating sewage using an MVR evaporator of the present invention, the preheating of the sewage to be treated includes waste liquid preheating and steam preheating performed in sequence, wherein the waste liquid preheating uses the clean condensed water discharged from the clean condensed water tank as the preheating heat source for the sewage to be treated, and the steam preheating uses the non-condensable gas discharged from the MVR evaporator as the reheating heat source for the sewage to be treated after the waste liquid preheating.

[0010] Preferably, in the method of sewage treatment using an MVR evaporator of the present invention, the dirty condensed water discharged from the dirty condensed water tank is preheated and then sent to the upper part of a separately arranged distillation tower, and fresh steam is allowed to enter from the lower part of the distillation tower. The dirty condensed water in the distillation tower and the steam move in opposite directions and cross each other, so that the dirty condensed water in the distillation tower forms a top-down flow in the opposite direction to the steam. The dirty condensed water in the distillation tower becomes clean condensed water after the stripping and distillation stages. The secondary steam discharged from the top of the distillation tower is sent to the MVR evaporator for full utilization, and the quality of the condensed water after the tower is controlled by controlling the amount of fresh steam input into the distillation tower.

[0011] Preferably, in the method of treating sewage using an MVR evaporator of the present invention, the non-condensable gas discharged from the MVR evaporator undergoes heat exchange with the sewage during steam preheating, and the reflux condensed water generated is then sent to the top layer of the distillation tower, and after descending, it is mixed with the dirty condensed water discharged from the dirty condensed water tank and then preheated. The clean condensed water discharged from the distillation tower preheats the dirty condensed water discharged from the dirty condensed water tank, and then is mixed with the clean condensed water discharged from the clean condensed water tank and used as a preheating heat source for the sewage to be treated.

[0012] The above-mentioned methods of the present invention can make fuller use of the thermal energy of the system.

[0013] More preferably, in the method of sewage treatment using MVR evaporator of the present invention, a balanced heat exchanger is arranged outside the steam preheater for reheating the sewage to be treated after the waste liquid is preheated, the non-condensable gas generated after cooling of the balanced heat exchanger is emptied or waits for reprocessing, and the generated condensed water is finally sent to the top layer of the distillation tower, and the working pressure of the balanced heat exchanger is set to be slightly higher than the local atmospheric pressure. The adoption of this technical measure can make the whole process run effectively under a micro-pressure working environment without the need to set up a vacuum system separately, so it will be safer and more reliable.

[0014] The sewage treatment device using an MVR evaporator of the present invention comprises: a waste liquid storage tank, a waste liquid preheater, a steam preheater, an MVR evaporator with an L-shaped stripping splitting welding line on the internal heater, a steam compressor and a steam confluence tank which are sequentially connected by pipelines, a clean condensed water tank connected to the heating end of the waste liquid preheater and the clean condensed water discharge end of the MVR evaporator by pipelines, a dirty condensed water tank connected to the dirty condensed water discharge end of the MVR evaporator by pipelines, a reflux condensed water tank and a clean condensed water tank connected to the condensed water output end of the preheater by pipelines, a dirty condensed water tank connected to the discharge end of the dirty condensed water tank by pipelines, and a control device. A distillation tower is provided in the sewage treatment device, the steam inlet of the distillation tower is connected with fresh steam, the steam inlet of the MVR evaporator is connected with a steam manifold, the steam manifold is connected with a fresh steam source through a manifold fresh steam supply pipe with a manifold fresh steam control valve, and a steam and clean condensate header, a dirty condensate header and a non-condensable gas header are respectively provided at the lower, middle and upper parts of the heater of the MVR evaporator, wherein: the steam and clean condensate header is used for heat exchange steam entry and clean condensate discharge, and a manifold fresh steam control valve is provided on the pipeline between the fresh steam source and the steam entry end of the steam manifold, and the clean condensate discharge end on the steam and clean condensate header is connected with a clean condensate tank; the non-condensable gas header is used for discharging non-condensable gas containing organic matter and air, and the non-condensable gas header is connected with the heating end of the steam preheater;

[0015] The feed end and the discharge end of the waste liquid preheater are respectively connected to the water outlet end of the waste liquid storage tank and the feed end of the steam preheater for reheating the wastewater to be treated after the waste liquid has been preheated. The heating end of the waste liquid preheater is respectively connected to the condensate discharge end of the dirty condensate preheater and the water outlet end of the clean condensate tank. The condensate output end of the waste liquid preheater is connected to the clean condensate tank.

[0016] The discharge end of the MVR evaporator is connected to the feed end of the MVR evaporator by a circulating liquid pipeline with a circulating pump thereon, so as to form a circulation, the circulating liquid pipeline includes an evaporator circulating liquid outlet pipe and an evaporator circulating liquid inlet pipe respectively arranged upstream and downstream of the circulating pump, a feed control valve is arranged on the pipeline connecting the discharge end of the steam preheater with the evaporator circulating liquid outlet pipe, and a concentrated liquid discharge pipe is arranged on the evaporator circulating liquid outlet pipe, between the circulating pump and the feed control valve, the secondary steam output end of the MVR evaporator is connected to the upstream of the steam compressor by a secondary steam outlet pipe, and the heating end of the steam preheater is connected to the non-condensable gas discharge end of the MVR evaporator;

[0017] The non-condensable gas discharge end of the organic matter and air of the non-condensable gas header is connected to the heating end of the steam preheater through a non-condensable gas discharge pipe, and the dirty condensed water header is connected to the secondary steam end of the top of the distillation tower; the dirty condensed water discharge end of the dirty condensed water header is connected to the input end of the dirty condensed water tank through the evaporator dirty condensed water discharge pipe, and the output end of the steam compressor is connected to the steam manifold; the evaporator steam inlet pipe on the steam and clean condensed water header is connected to the steam manifold for heat exchange steam to enter, and the clean condensed water discharge end on the steam and clean condensed water header is connected to the heating end of the waste liquid preheater;

[0018] The discharge end of the dirty condensed water tank is connected to the dirty condensed water tank through a pipeline with a dirty condensed water pump provided thereon, and the discharge end of the dirty condensed water tank is connected to the dirty condensed water preheater through a pipeline with a dirty condensed water tank pump provided thereon;

[0019] The discharge end of the steam preheater is connected to the evaporator circulating liquid outlet pipe through an evaporator waste liquid feed pipe provided with a feed control valve, and the condensed water output end of the steam preheater is connected to the reflux condensed water tank;

[0020] The heating end of the distillation tower is connected to the fresh steam source through a fresh steam supply pipe for the distillation tower with a fresh steam control valve for the distillation tower. The rear condensate output end of the distillation tower is connected to the heating end of the dirty condensate preheater through a rear condensate pipe provided with a rear condensate pump. The dirty condensate inlet end of the distillation tower is connected to the discharge end of the dirty condensate preheater. The reflux condensate inlet end of the distillation tower is connected to the discharge end of the reflux condensate tank through a pipeline provided with a reflux condensate pump.

[0021] A liquid quality detection sensor is provided on the clean condensate discharge pipe connected to the lower area of ​​the L-shaped steam stripping split welding line on the heat exchange element of the heater in the MVR evaporator. The control device controls the opening of the fresh steam control valve of the junction tank according to the value detected by the liquid quality detection sensor.

[0022] Preferably, in the sewage treatment device using the MVR evaporator of the present invention, the exhaust end of the steam preheater is connected to the heating end of the balanced heat exchanger, the exhaust end of the balanced heat exchanger discharges the non-condensable gas generated after cooling, the condensate output end of the balanced heat exchanger is connected to the reflux condensate tank, and the working pressure of the balanced heat exchanger is set to be slightly higher than the local atmospheric pressure. This measure allows the device to operate effectively in a slightly positive pressure working environment, and no additional vacuum system is required.

[0023] More preferably, the sewage treatment device using the MVR evaporator of the present invention is provided with a maintenance manhole at the steam manifold tank. Through the provided maintenance manhole, maintenance personnel can conveniently and smoothly enter the steam manifold tank, and enter the steam header through the steam inlet pipe of the heater, so as to visually observe and check the internal conditions of the manifold tank and the intermittent evaporator, which is convenient for maintenance and repair.

[0024] The present invention appropriately controls the supply of fresh steam into the area below the L-shaped weld in the evaporator according to the quality of the clean condensed water detected therein. Since the fresh steam has higher temperature and pressure than the secondary steam from the steam compressor, it will improve the local stripping effect after entering the bottom of the heat exchange element, and can accurately control the quality of the clean condensed water, thereby overcoming the problem in the prior art that the COD value of the condensed water obtained by condensing the secondary steam is high and an additional treatment device needs to be set up, and the secondary steam condensate that meets the industrial emission standards can be directly obtained.

[0025] The second advantage of the present invention is that the condensed water after sewage treatment by the MVR evaporator is sent to the distillation tower. Similarly, fresh steam is introduced into the distillation tower to interact with the dirty condensed water. In the process of reverse cross movement with the fresh steam, the dirty condensed water becomes clean condensed water after the distillation stage, and there is no need to use a post-effect evaporator for treatment. This not only simplifies the process, but also reduces the cost of equipment.

[0026] When fresh steam needs to be supplied to the distillation tower and evaporator respectively, it will inevitably cause fluctuations in system pressure and heat, affecting the heat balance of the device. To solve this problem, the present invention sets a balanced heat exchanger, which is satisfactorily solved by controlling the amount of circulating cooling water supplied to the balanced heat exchanger and the return temperature of the circulating cooling water. In addition, by setting the working pressure of the balanced heat exchanger to be slightly higher than the local atmospheric pressure, the device of the present invention can be effectively operated in a slightly positive pressure working environment, and there is no need to set up a vacuum system separately.

[0027] The present invention provides a manhole on the steam manifold tank, which facilitates the inspection and maintenance of the equipment.

[0028] The present invention can maximize the use of the heat generated by the system, thereby greatly reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Attached Figure 1 Schematic diagram of the system in the present invention.

[0030] Attached Figure 2 This is a schematic diagram of the installation position of the evaporator, steam manifold and pipelines.

[0031] Attached Figure 3 Schematic diagram of the internal channel structure between the evaporator, steam manifold and manhole.

[0032] In the figure: 1 is a clean condensate tank pump; 2 is a clean condensate tank; 3 is a waste liquid feed pump; 4 is a waste liquid storage tank; 5 is a waste liquid collecting pipe; 6 is a dirty condensate tank; 7 is a dirty condensate preheater; 8 is a dirty condensate tank pump; 9 is a concentrated liquid discharge pump; 10 is a condensate pump after the tower; 11 is a distillation tower; 12 is a fresh steam pipe for the distillation tower; 13 is a fresh steam control valve for the distillation tower; 14 is a fresh steam main network; 15 is a secondary steam pipe at the top of the tower; 16 is a reflux condensate inlet pipe for the distillation tower; 17 is a dirty condensate inlet pipe for the distillation tower; 18 is a concentrated liquid discharge pipe; 19 is an evaporator circulating liquid inlet pipe; 20 is an evaporator circulating pump; 21 is an evaporator circulating liquid outlet pipe; 22 is an evaporator secondary steam outlet pipe; 23 is an MVR evaporator; 24 is a steam manifold; 25 is a fresh steam pipe for the manifold; 26 is the fresh steam control valve of the junction tank; 27 is the clean condensate discharge pipe; 28 is the clean condensate pump; 29 is the steam compressor; 30 is the evaporator waste liquid feed pipe; 31 is the clean condensate delivery pipe; 32 is the dirty condensate preheater clean condensate discharge pipe; 33 is the clean condensate mixing pipe; 34 is the clean condensate tank; 35 is the evaporator non-condensable gas discharge pipe; 36 is the evaporator dirty condensate discharge pipe; 37 is the dirty condensate pump; 38 is the dirty condensate delivery pipe; 39 is the steam preheater; 40 is the dirty condensate tank; 41 is the reflux condensate tank; 42 is the steam preheater feed pipe; 43 is the waste liquid preheater; 44 is Clean condensate tank inlet pipe; 45 is reflux condensate pump; 46 is circulating cooling water return pipe; 47 is steam preheater exhaust pipe; 48 is balanced heat exchanger; 49 is non-condensable gas exhaust port; 50 is cooling circulating water supply pipe; 51 is clean condensate delivery pipe; 52 is evaporator steam inlet pipe; 53 is steam manifold tank manhole; 54 is steam and clean condensate header; 55 is evaporator shell; 56 is dirty condensate header; 57 is non-condensable gas header; 58 is heater; 59 is MVR evaporator feed control valve; 60 is concentrated liquid discharge valve; 61 is L-shaped weld; 62 is condensate pipe after tower; 63 is liquid quality detection sensor. DETAILED DESCRIPTION

[0033] The accompanying drawing is a schematic diagram of an embodiment of the present invention, which is used for treating papermaking waste liquid. The following is an explanation in conjunction with the accompanying drawing.

[0034] See attached Figure 1The device of the embodiment of the present invention comprises: a dirty condensate preheater 7, a waste liquid preheater 43, a steam preheater 39 and a balance heat exchanger 48 which are interconnected by pipelines, an MVR evaporator 23 with an L-shaped steam stripping splitting welding line on the internal heat exchanger, an MVR steam compressor 29, a steam manifold 24, a heater 58 in the MVR evaporator, a clean condensate tank 34, a dirty condensate tank 40, a reflux condensate tank 41, a clean condensate tank 2, a waste liquid storage tank 4 and a dirty condensate tank 6, as well as a distillation tower 11 and correspondingly arranged pumps and valves. The fresh steam supply pipe 12 of the distillation tower 11 of the present invention is connected to the fresh steam main pipe network 14, and a header is respectively arranged at the lower, middle and upper parts of the heater 58 of the MVR evaporator 23, wherein: the lower header is used for the heat exchange steam inlet to be connected to the steam manifold tank 24 through the evaporator steam inlet pipe 52, and the clean condensed water outlet is connected to the clean condensed water tank 34 through the clean condensed water outlet pipe 27. A manifold tank fresh steam control valve 26 is arranged in the manifold tank fresh steam supply pipeline 25 between the fresh steam source and the heat exchange steam inlet end of the lower header; the tower top secondary steam pipe 15 for secondary steam entry of the middle header is connected to the secondary steam outlet of the top of the distillation tower, and is connected to the dirty condensed water tank 40 through the evaporator dirty condensed water outlet pipe 36. The dirty condensate tank 40 is connected to the dirty condensate tank 6 by a dirty condensate delivery pipe 38 on which a dirty condensate pump 37 is provided for the discharge of dirty condensate; the upper header uses an evaporator non-condensable gas discharge pipe 35 to deliver non-condensable gas with organic matter and air to the heating end of the steam preheater 39 for reheating the preheated sewage to be treated. The discharge end and the feed end of the MVR evaporator 23 are connected by an evaporator circulating liquid inlet pipe 19 provided with an evaporator circulating pump 20 to form a circulation, and the secondary steam output end of the MVR evaporator 23 is connected to the upstream of the steam compressor 29 by a secondary steam outlet pipe 22, and a concentrated liquid discharge pipe 18 is provided between the evaporator circulating liquid inlet pipe 19 located upstream of the evaporator circulating pump 20 and the feed control valve 59 of the MVR evaporator, and the feed amount is controlled by the feed control valve 59. The present invention sets a bypass on the discharge pipeline (this point is not shown in the attached figure), which is connected to the evaporator itself. If the discharge concentration is low, the discharge will be refluxed to the evaporator through the bypass to continue to concentrate; if the discharge concentration reaches the design requirements, the bypass valve is closed and the discharge can be carried out according to the normal process. The feed end of the steam preheater 39 is connected to the discharge end of the waste liquid preheater 43 by the steam preheater feed pipe 42. The condensate output end of the steam preheater 39 is connected to the reflux condensate tank 41 by a pipeline. The exhaust end of the steam preheater 39 is connected to the heating end of the balance heat exchanger 48 by the steam preheater exhaust pipe 47, and the exhaust end of the balance heat exchanger 48 is emptied or connected to a separate treatment device. The condensate output end of the balance heat exchanger 48 is connected to the reflux condensate tank 41. During operation, the working pressure of the balance heat exchanger 48 should be set to be slightly higher than the local atmospheric pressure.The feed end and the discharge end of the waste liquid preheater 43 are respectively connected to the waste liquid storage tank 4 and the feed end of the steam preheater 39 for reheating the preheated wastewater to be treated. The condensate discharge end of the dirty condensate preheater 7 and the MVR evaporator clean condensate delivery pipe 31 are both connected to the clean condensate mixing pipe 33 connected to the heating end of the waste liquid preheater 43. The condensation end of the waste liquid preheater 43 and the clean condensate tank 2 are connected by the clean condensate tank inlet pipe 44. In this embodiment, the post-tower condensate output end of the distillation tower 11 is connected to the heating end of the dirty condensate preheater 7 through the post-tower condensate pipe 62 provided with the post-tower condensate pump 10, the dirty condensate inlet end of the distillation tower 11 is connected to the discharge end of the dirty condensate preheater 7, and the reflux condensate inlet end of the distillation tower 11 is connected to the discharge end of the reflux condensate tank 41 through a pipeline provided with a reflux condensate pump 45.

[0035] A liquid quality detection sensor 63 is provided in the lower area of ​​the L-shaped steam stripping separation welding line or the discharged clean condensed water pipeline of the MVR evaporator heat exchange element of this embodiment. The simplest method is to use a conductivity sensor. The device is provided with a control device that controls the opening, closing or opening size of the fresh steam control valve 26 of the junction tank according to the detection value of the liquid quality detection sensor.

[0036] In addition, the sewage treatment device of this embodiment is provided with a maintenance manhole at the steam confluence tank 24 .

[0037] The embodiment of the present invention operates as follows:

[0038] The black liquor from papermaking pulp washing is collected in the waste liquid storage tank 4 by the waste liquid collection pipe 5. The waste liquid storage tank has a certain volume and can accommodate a certain amount of waste liquid, which plays a buffering and stabilizing role. That is, if there is a fault in the front section, the subsequent section can still work normally; if there is a problem in the subsequent section, the front section can still discharge the waste liquid continuously, avoiding unnecessary losses caused by frequent shutdowns. Turn on the waste liquid feed pump 3 to start feeding the system. The waste liquid first enters the waste liquid preheater 43 and exchanges heat with the clean condensed water generated by the system. The temperature of the clean condensed water decreases, the temperature of the waste liquid increases, and the heat in the system is effectively utilized. The waste liquid that has been preliminarily heated enters the steam preheater 39 through the steam preheater feed pipe 42. The evaporator non-condensable gas discharge pipe 35 carries steam, low-boiling organic matter, etc. that have not been fully utilized by the evaporator. In the steam preheater 39, it is fully heat-exchanged with the waste liquid, and the waste liquid is heated again, and the waste heat of the system is effectively utilized again. The waste liquid discharged from the steam preheater enters the evaporator 23 through the evaporator waste liquid feed pipe 30 to start the concentration and evaporation process.

[0039] When the waste liquid in the MVR evaporator 23 reaches the set liquid level and meets the working flow of the evaporator, the evaporator circulation pump 20 is turned on, and the waste liquid is discharged from the evaporator circulation liquid outlet pipe 21, sent out by the evaporator circulation pump 20, and enters the upper part of the MVR evaporator 23 after passing through the evaporator circulation liquid inlet pipe 19, and is evenly sprayed on the surface of the heater 58 to form a thin film and flow downward. The fresh steam control valve 26 of the junction tank is opened to supply fresh steam to the MVR evaporator 23. The waste liquid is continuously heated in the MVR evaporator 23 and then reaches the boiling point, boiling occurs and a large amount of secondary steam is emitted. At this time, the steam compressor 29 is turned on, and the fresh steam control valve 26 of the junction tank is closed. The secondary steam in the MVR evaporator 23 enters the steam compressor 29 through the evaporator secondary steam outlet pipe 22, and the steam pressure and steam temperature are increased by mechanical work, and then sent to the steam junction tank 24, and then enter the steam and clean condensate header 54 through the evaporator steam inlet pipe 52, and is evenly distributed to all heat exchange elements for heat exchange. At the bottom of the heater 58, steam carrying low-boiling-point and condensable organic matter moves upward from the bottom of the heat exchange element. Compared with other organic gases, the condensation of water vapor has a greater potential energy difference. Under this physical action, the water vapor first undergoes a phase change and is liquefied into clean condensed water, which flows out of the evaporator 23 through the clean condensed water discharge pipe 27 and enters the clean condensed water tank 34. The clean condensed water pump 28 then sends the waste liquid to the waste liquid preheater 43 to heat the waste liquid, which is then cooled and sent to the clean condensed water tank 2 for standby use. In this process, the COD index of the clean condensed water is obtained through the sensor 63.

[0040] Secondary steam is continuously generated in the evaporator, which is continuously heated and pressurized by the steam compressor and then sent into the evaporator. The concentration of the waste liquid increases in the steamer, and after meeting the process requirements, it is sent out by the concentrated liquid discharge pump 9 and used directly as an industrial product or as other process materials. New waste liquid is continuously added to the evaporator to ensure stable and continuous operation.

[0041] When the sensor 63 detects that the COD value of the clean condensed water flowing out of the clean condensed water discharge pipe 27 is high, the fresh steam control valve 26 of the manifold tank is controlled to open to an appropriate degree to supply an appropriate amount of fresh steam to the evaporator. Since the fresh steam has a higher temperature and pressure than the secondary steam from the steam compressor, it will form a local stripping effect after entering the bottom of the heat exchange element through the steam manifold tank 24, so the quality of the clean condensed water can be accurately controlled.

[0042] The steam continues to rise in the heater 58 and forms dirty condensate after entering the upper area of ​​the L-shaped weld of the heat exchange element. Low boiling point and condensable organic matter are mixed into the steam and discharged from the evaporator dirty condensate discharge pipe 36. It first flows by gravity into the dirty condensate tank 40 and is then sent by the dirty condensate pump 37 to the dirty condensate tank 6 for temporary storage.

[0043] The COD value of the condensed water stored in the dirty condensed water tank 6 is very high. It cannot be used directly or discharged directly. It must be cleaned in the next step. The dirty condensed water tank pump 8 first sends the dirty condensed water to the dirty condensed water preheater 7, and exchanges heat with the clean condensed water after the tower has been treated. The dirty condensed water is heated, which is conducive to a better stripping effect, and the clean condensed water after the tower is cooled, which is conducive to normal pressure storage. After the dirty condensed water leaves the dirty condensed water preheater 7, it is sent to the upper part of the distillation tower 11. Fresh steam enters from the lower part of the distillation tower 11. The dirty condensed water flows from top to bottom and crosses with the steam in the opposite direction. After the dirty condensed water passes through the distillation and distillation stages, it becomes clean condensed water. The fresh steam control valve 13 of the distillation tower adjusts the input amount of fresh steam to the distillation tower 11, and the condensed water after the tower presents different forms of quality.

[0044] The condensate produced in the steam preheater 39 and the balance heat exchanger 48 has a very high COD value and a strong gas volatility, which is called reflux condensate. After entering the reflux condensate tank 41, it is directly sent to the topmost tray of the distillation tower 11 by the reflux condensate pump 45, flows from top to bottom, and then mixes with the dirty condensate, and moves in the opposite direction of the steam, and becomes relatively clean condensate after the distillation stage.

[0045] As the amount of fresh steam entering the distillation tower 11 and the evaporator 23 changes, the system will inevitably fluctuate and the heat balance will be affected. It will be controlled by the balancing heat exchanger 48 through the water supply volume of the cooling circulating water supply pipe 50 and the return water temperature of the circulating cooling water return pipe 46.

[0046] By opening the steam manifold tank manhole 53, one can enter the steam and clean condensate header 54 to clean the interior of the equipment and perform routine maintenance, which is very convenient and intuitive.

Claims

1. A method for treating sewage using an MVR evaporator, wherein the sewage to be treated is preheated to a set temperature and then sent to an MVR evaporator with a stripping function for evaporation and concentration, fresh steam is first supplied to the MVR evaporator so that the sewage is heated to a boiling point in the MVR evaporator to generate secondary steam, the fresh steam supply is turned off, and the steam compressor is turned on to use mechanical work to pressurize and heat the secondary steam and then send it to the heater of the MVR evaporator, so that all heat exchange elements in the heater exchange heat with the sewage to heat the sewage for evaporation, concentration and stripping, the sewage in the MVR evaporator that reaches the concentration required by the process is to be subsequently treated, and the dirty condensed water and clean condensed water discharged from the MVR evaporator are respectively discharged into a dirty condensed water tank and a clean condensed water tank and then are respectively to be subsequently treated or used, characterized in that: During operation, the quality of clean condensed water is tested. When the quality of clean condensed water is equal to or better than the design requirements, the operation is maintained. When the quality of clean condensed water is lower than the design requirements, fresh steam is appropriately supplied to the MVR evaporator to improve the stripping effect, so that the quality of clean condensed water is equal to or better than the design requirements again.

2. The method for treating sewage using an MVR evaporator according to claim 1, characterized in that: The preheating of the sewage to be treated includes waste liquid preheating and steam preheating performed in sequence. The waste liquid preheating uses the clean condensed water discharged from the clean condensed water tank as the preheating heat source for the sewage to be treated, and the steam preheating uses the non-condensable gas discharged from the MVR evaporator as the reheating heat source for the sewage to be treated after the waste liquid preheating.

3. The method for sewage treatment using an MVR evaporator according to claim 2, characterized in that: The dirty condensed water discharged from the dirty condensed water tank is preheated and then sent to the upper part of a separately set distillation tower, and fresh steam is allowed to enter from the lower part of the distillation tower. The dirty condensed water in the distillation tower crosses with the steam in the opposite direction, so that the dirty condensed water in the distillation tower forms a top-down flow in the opposite direction of the steam. The dirty condensed water in the distillation tower becomes clean condensed water after the stripping and distillation stages. The secondary steam discharged from the top of the distillation tower is sent to the MVR evaporator for full utilization. The quality of the condensed water after the tower is controlled by controlling the amount of fresh steam input into the distillation tower.

4. The method for sewage treatment using an MVR evaporator according to claim 3, characterized in that: The non-condensable gas discharged from the MVR evaporator undergoes heat exchange with the sewage during steam preheating, and the resulting reflux condensed water is then sent to the top layer of the distillation tower, and after descending, it is mixed with the dirty condensed water discharged from the dirty condensed water tank and then preheated. The clean condensed water discharged from the distillation tower preheats the dirty condensed water discharged from the dirty condensed water tank, and then is mixed with the clean condensed water discharged from the clean condensed water tank and used as a preheating heat source for the sewage to be treated.

5. The method for treating sewage using an MVR evaporator according to any one of claims 2 to 4, characterized in that: A balancing heat exchanger is arranged outside the steam preheater for reheating the wastewater to be treated after the waste liquid is preheated. The non-condensable gas generated after cooling of the balancing heat exchanger is discharged or awaits further treatment, and the generated condensed water is finally sent to the top layer of the distillation tower. The working pressure of the balancing heat exchanger is set to be slightly higher than the local atmospheric pressure.

6. A sewage treatment device using an MVR evaporator, comprising: a waste liquid storage tank, a waste liquid preheater, a steam preheater, an MVR evaporator with an L-shaped stripping splitting welding line on the internal heater, a steam compressor and a steam confluence tank connected in sequence by pipelines, a clean condensed water tank connected to the heating end of the waste liquid preheater and the clean condensed water discharge end of the MVR evaporator by pipelines, a dirty condensed water tank connected to the dirty condensed water discharge end of the MVR evaporator by pipelines, a reflux condensed water tank and a clean condensed water tank connected to the condensed water output end of the preheater by pipelines, a dirty condensed water tank connected to the discharge end of the dirty condensed water tank by pipelines, and a control device, The invention is characterized in that a distillation tower is arranged in the sewage treatment device, the steam inlet of the distillation tower is connected with the fresh steam, the steam inlet of the MVR evaporator is connected with the steam manifold, the steam manifold is connected with the fresh steam source by a fresh steam supply manifold with a manifold fresh steam control valve, and a steam and clean condensate manifold, a dirty condensate manifold and a non-condensable gas manifold are arranged at the lower part, the middle part and the upper part of the heater of the MVR evaporator respectively, wherein: the steam and clean condensate manifold is used for the entry of heat exchange steam and the discharge of clean condensate, and a manifold fresh steam control valve is arranged on the pipeline between the fresh steam source and the steam entry end of the steam manifold, and the clean condensate discharge end on the steam and clean condensate manifold is connected with the clean condensate tank; the non-condensable gas manifold is used for discharging non-condensable gas containing organic matter and air, and the non-condensable gas manifold is connected with the heating end of the steam preheater; The feed end and the discharge end of the waste liquid preheater are respectively connected to the water outlet end of the waste liquid storage tank and the feed end of the steam preheater for reheating the wastewater to be treated after the waste liquid has been preheated. The heating end of the waste liquid preheater is respectively connected to the condensate discharge end of the dirty condensate preheater and the water outlet end of the clean condensate tank. The condensate output end of the waste liquid preheater is connected to the clean condensate tank. The discharge end of the MVR evaporator is connected to the feed end of the MVR evaporator by a circulating liquid pipeline with a circulating pump thereon, so as to form a circulation, the circulating liquid pipeline includes an evaporator circulating liquid outlet pipe and an evaporator circulating liquid inlet pipe respectively arranged upstream and downstream of the circulating pump, a feed control valve is arranged on the pipeline connecting the discharge end of the steam preheater with the evaporator circulating liquid outlet pipe, and a concentrated liquid discharge pipe is arranged on the evaporator circulating liquid outlet pipe, between the circulating pump and the feed control valve, the secondary steam output end of the MVR evaporator is connected to the upstream of the steam compressor by a secondary steam outlet pipe, and the heating end of the steam preheater is connected to the non-condensable gas discharge end of the MVR evaporator; The non-condensable gas discharge end of the organic matter and air of the non-condensable gas header is connected to the heating end of the steam preheater through a non-condensable gas discharge pipe, and the dirty condensed water header is connected to the secondary steam end of the top of the distillation tower; the dirty condensed water discharge end of the dirty condensed water header is connected to the input end of the dirty condensed water tank through the evaporator dirty condensed water discharge pipe, and the output end of the steam compressor is connected to the steam manifold; the evaporator steam inlet pipe on the steam and clean condensed water header is connected to the steam manifold for heat exchange steam to enter, and the clean condensed water discharge end on the steam and clean condensed water header is connected to the heating end of the waste liquid preheater; The discharge end of the dirty condensed water tank is connected to the dirty condensed water tank through a pipeline with a dirty condensed water pump provided thereon, and the discharge end of the dirty condensed water tank is connected to the dirty condensed water preheater through a pipeline with a dirty condensed water tank pump provided thereon; The discharge end of the steam preheater is connected to the evaporator circulating liquid outlet pipe through an evaporator waste liquid feed pipe provided with a feed control valve, and the condensed water output end of the steam preheater is connected to the reflux condensed water tank; The heating end of the distillation tower is connected to the fresh steam source through a fresh steam supply pipe for the distillation tower with a fresh steam control valve for the distillation tower. The rear condensate output end of the distillation tower is connected to the heating end of the dirty condensate preheater through a rear condensate pipe provided with a rear condensate pump. The dirty condensate inlet end of the distillation tower is connected to the discharge end of the dirty condensate preheater. The reflux condensate inlet end of the distillation tower is connected to the discharge end of the reflux condensate tank through a pipeline provided with a reflux condensate pump. A liquid quality detection sensor is provided on the clean condensate discharge pipe connected to the lower area of ​​the L-shaped steam stripping split welding line on the heat exchange element of the heater in the MVR evaporator, and the control device controls the opening of the fresh steam control valve of the junction tank according to the value detected by the liquid quality detection sensor.

7. The sewage treatment device using the MVR evaporator according to claim 6, characterized in that: The exhaust end of the steam preheater is connected to the heating end of the balancing heat exchanger. The exhaust end of the balancing heat exchanger discharges the non-condensable gas generated after cooling. The condensate output end of the balancing heat exchanger is connected to the reflux condensate tank. The working pressure of the balancing heat exchanger is set to be slightly higher than the local atmospheric pressure.

8. The sewage treatment device using the MVR evaporator according to claim 6 or 7, characterized in that: A maintenance manhole is provided at the steam manifold, through which maintenance personnel can enter the steam and clean condensate headers via the steam inlet pipe of the MVR evaporator heater.

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