A method and device for treating die casting wastewater

Abstract

The application discloses a die-casting wastewater treatment method and device, which comprises an outer cylinder, a heating body, an inner cylinder, a feeding unit and a driving mechanism. The application is characterized in that specific structure micropores are arranged on the side wall of the inner cylinder and rotate at high speed, so that the die-casting wastewater is sprayed in the form of liquid drops or liquid films to the stepped heating body on the inner wall of the outer cylinder under the action of strong centrifugal force. The liquid is subjected to severe shearing when passing through the micropores, which not only greatly increases the specific surface area of the liquid, but also destroys the surface stable layer of the emulsified oil drops, so that the oil drops are coalesced, the water is rapidly evaporated, the processes of demulsification, oil-water separation and evaporation concentration are integrated in the same device and are simultaneously completed. Therefore, the treatment process is greatly shortened, the equipment floor area is reduced, and efficient and continuous oil removal and salt removal are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, and particularly relates to a die-casting wastewater treatment method and device. BACKGROUND

[0002] Die-casting industry is one of the core pillars of modern manufacturing industry, and is widely used in many key fields such as automobiles, electronics, aerospace, etc. However, the wastewater generated in its production process has become a major challenge for environmental governance due to its complex composition and high pollutant concentration. Such wastewater is usually rich in high-concentration emulsified oil, various high-molecular organic matter, and a large amount of dissolved salts, and the ratio of chemical oxygen demand to biochemical oxygen demand is often less than 0.25, showing poor biodegradability, which makes the treatment efficiency of traditional biological treatment methods, such as activated sludge method, very limited.

[0003] In the prior art, the industry usually adopts a step-by-step treatment strategy for oil-containing wastewater and high-salt wastewater. For emulsified oil pollution, common treatment methods include physical separation, chemical demulsification, biological degradation, and membrane separation, etc. Among them, chemical demulsification destroys the stability of emulsions by adding demulsifiers or adjusting pH value to separate oil and water, and then removes them by flotation or sedimentation. The treatment of high-salt wastewater generally relies on evaporation and concentration technology, among which mechanical vapor recompression technology is widely used due to its high energy efficiency and relatively low operating cost. This technology realizes the deep concentration of wastewater and the crystallization and precipitation of salts by compressing and heating the secondary steam for reuse, while recovering high-quality condensed water. These step-by-step treatment methods have been mature in their respective professional fields and have solved the problem of single pollutant treatment to a certain extent. SUMMARY

[0004] The present application overcomes the shortcomings of the prior art and provides a die-casting wastewater treatment method and device.

[0005] To achieve the above purpose, the technical solution adopted by the present application is as follows: a die-casting wastewater treatment device, comprising:

[0006] an outer cylinder having a heating body arranged inside;

[0007] an inner cylinder coaxially arranged inside the outer cylinder and rotationally connected thereto;

[0008] Among them, the side wall of the inner cylinder is provided with a plurality of micropores, and the micropores are used to make the die-casting wastewater pass through the micropores and be sprayed to the internal heating body of the outer cylinder in the form of droplets or liquid film when the inner cylinder rotates;

[0009] a feeding unit for conveying the die-casting wastewater to be treated to the inside of the inner cylinder;

[0010] and a driving mechanism connected with the inner cylinder body, used to drive the inner cylinder body to rotate at a preset rotating speed.

[0011] In a preferred embodiment of the present application, the heating body is installed on the inner wall of the outer cylinder body.

[0012] The heating body comprises a plurality of annular rings and a plurality of inclined plates connecting the annular rings; the annular rings are stacked layer by layer by the inclined plates, and the inner diameters of the annular rings gradually decrease from the bottom to the top of the outer cylinder body, forming a stepped heating body.

[0013] In a preferred embodiment of the present application, the angle between the inclined plate and the horizontal plane is 5-10°.

[0014] In a preferred embodiment of the present application, the micro-hole is composed of a circular hole and two rectangular strip holes connected on both sides of the circular hole.

[0015] The diameter of the circular hole ranges from 80 to 200 μm.

[0016] The length of the rectangular strip hole is 50-100 μm, and the width is 10-20 μm.

[0017] In a preferred embodiment of the present application, the outlet of the circular hole has a tangential angle, and the tangential angle ranges from 5 to 30°.

[0018] In a preferred embodiment of the present application, the inlet of the circular hole has a horn structure, and the inner diameter gradually decreases from the inlet to the outlet, forming a convergent-divergent structure of the jet hole.

[0019] In a preferred embodiment of the present application, the micro-holes are arranged in a spiral array along the axial and circumferential directions of the inner cylinder body.

[0020] In a preferred embodiment of the present application, the top of the inner cylinder body and the top of the outer cylinder body are provided with negative pressure holes, which are connected with the outside pump body to control the inner cylinder body and the outer cylinder body to be in the same negative pressure state.

[0021] The vaporized wastewater is collected through the negative pressure holes.

[0022] In a preferred embodiment of the present application, the cavity formed between the inner cylinder body and the outer cylinder body is a collection cavity for collecting the separated emulsified oil and the precipitated crystals.

[0023] A die casting wastewater treatment method using the die casting wastewater treatment device, comprising the following steps:

[0024] Step S1: delivering the die casting wastewater to be treated to the inside of the inner cylinder body through the feeding unit.

[0025] Step S2, under the action of the driving mechanism, the inner cylinder is rotated at high speed, so that the die casting wastewater is sprayed in the form of liquid drops or liquid films to the heating body of the outer cylinder under the action of centrifugal force;

[0026] Step S3, the emulsified oil is instantaneously demulsified, oil-water separation and water evaporation by the shearing effect of the micro-hole spraying, the centrifugal supergravity field effect and the thermal evaporation effect of the heating wall surface;

[0027] Wherein, the oil phase migrates and accumulates to the central axis area of the inner cylinder under the action of centrifugal force, part of the water phase is instantaneously evaporated after impacting the heating wall surface, the soluble salt is analyzed out, and the un-evaporated oil phase flows downward along the heating wall surface under the action of gravity and air flow;

[0028] Step S4, the separated salt crystals and the separated emulsified oil are collected in the collection cavity between the inner cylinder and the outer cylinder;

[0029] Step S5, the oil phase is concentrated in the center of the inner cylinder and is guided out, the water vapor is condensed and recovered at the top, and the separated salt is collected in the cavity between the inner cylinder and the outer cylinder.

[0030] The present application solves the defects in the background art, and has the following beneficial effects:

[0031] (1) The present application provides a die casting wastewater treatment method and device, by setting a micro-hole with a specific structure on the side wall of the inner cylinder and rotating it at high speed, the die casting wastewater is sprayed in the form of liquid drops or liquid films to the stepped heating body on the inner wall of the outer cylinder under the action of strong centrifugal force, the liquid is subjected to severe shearing when passing through the micro-hole, not only greatly increasing the specific surface area of the liquid, but also destroying the surface stable layer of the emulsified oil drops, making them coalesce, and accelerating the rapid evaporation of water, thereby integrating the processes of demulsification, oil-water separation and evaporation concentration in the same device simultaneously, greatly shortening the treatment process, reducing the equipment floor area, and realizing efficient and continuous oil removal and salt removal.

[0032] (2) The present application provides a die casting wastewater treatment method and device, which utilizes the centrifugal force generated by high-speed rotation to produce a super-strong gravity field, by strengthening the density difference between water and oil, the oil drops in the inner cylinder rapidly migrate radially in the centrifugal field and realize the relative layering of water-oil, the oil phase in water can quickly accumulate, and the water phase is concentrated in different layers, thereby accelerating the oil-water separation process, and at the same time, the oil-water liquid sprayed out of the inner cylinder continues to be affected by the super-strong gravity field and moves quickly in the centrifugal direction, realizing the rapid centripetal migration of oil drops and the radial separation of water phase in the spraying state, realizing two-stage separation of the wastewater in the inner cylinder, and improving the separation efficiency of oil phase and water phase, and shortening the treatment time.

[0033] (3) The application provides a die casting wastewater treatment method and device, through a micropore structure composed of a circular hole and two rectangular strip holes connected at two sides of the circular hole, asymmetric vortex is generated by flow separation of the rectangular strip holes to form high-frequency pulsating shear force, liquid sprayed out is stretched and sheared, thus, liquid droplets with large momentum are generated at the moment of spraying, and thin liquid film and fine mist droplets are synchronously formed, the interface area of the oil-water mixed liquid is doubled, mass transfer and heat transfer on the oil-water interface are strengthened, evaporation efficiency is greatly improved, and the high-frequency pulsating shear force at the outlet of the rectangular strip hole destroys the stable film layer of emulsified oil, so that the emulsified oil rapidly loses stability and coalescence migration occurs, thereby realizing rapid layering and complete demulsification in the liquid droplet flight and spreading process, and then the liquid droplets can uniformly spread and constantly refresh the heating surface after impacting the outer cylinder heating body, so that oil droplets and salt are prevented from forming covering deposition in a local area, and the long-term cleaning of the heat transfer surface is maintained.

[0034] (4) The application provides a die casting wastewater treatment method and device, a stepped heating body composed of multiple circular rings stacked by inclined sheets and gradually decreasing in inner diameter from bottom to top is arranged on the inner wall of an outer cylinder body, a continuous heating surface is divided into multiple independent annular evaporation areas, liquid droplets or liquid films sprayed out of the micropore of the inner cylinder body are limited to the annular surface of the stepped circular ring to evaporate, and residual emulsified oil drops from the annular surface of the circular ring to the collection cavity, the path of the emulsified oil sliding on the annular surface of the circular ring is reduced, mixing, rewrapping or forming of a continuous oil film of the residual oil of different liquid droplets in the sliding process is effectively avoided, mutual interference is avoided, and the oil-salt mixture is prevented from staying on the heating surface of the heating body for a long time to scale and coking, so that the cleaning state of the heating body is ensured, and the heat transfer resistance caused by the composite coverage of the oil film and the salt scale is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor;

[0036] Figure 1 is a perspective structure diagram of the preferred embodiment of the present application;

[0037] Figure 2 is a schematic diagram of a front view structure of the preferred embodiment of the present application;

[0038] Figure 3 is a schematic diagram of a front view structure of the preferred embodiment of the present application; Figure 2 is an enlarged schematic diagram of A in the embodiment of the present application;

[0039] Figure 4is a preferred embodiment of the present application Figure 2 Amplified schematic view at B in the figure

[0040] In the figure: 1, outer cylinder; 2, inner cylinder; 3, micropore; 4, circular ring; 5, inclined piece; 6, circular hole; 7, rectangular slot; 8, collection cavity. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0042] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a variety of ways beyond the specific details set forth herein, and the scope of the present application is not limited to the specific embodiments described below.

[0043] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the scope of protection of the present application. In addition, the terms "first", "second" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise specified and limited, the term "a plurality of" means two or more.

[0044] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0045] SUMMARY

[0046] For the complex wastewater containing high concentration of emulsified oil and high salt, the traditional step-by-step treatment mode usually means that a separate demulsification unit and evaporation concentration unit need to be set up, which not only leads to the increase of equipment floor area and investment cost, but also significantly lengthens the overall treatment process and reduces the system operation efficiency due to the complexity of the operation conditions of each unit and the material transfer, and there is a waste of repeated heating and cooling in energy consumption. Moreover, there is a fundamental conflict between the demulsification of emulsified oil and the evaporation of high-salt wastewater in thermodynamics and kinetics, so that simply connecting or combining them often fails to achieve the expected effect, and even may cause negative effects.

[0047] The traditional step-by-step treatment not only needs to set up independent units, leading to large floor area, high investment and repeated energy consumption, but also has a fundamental conflict in process conditions. Efficient evaporation often requires a high temperature above 80℃, while the demulsification of emulsified oil is usually suitable for 50-70℃, and too high temperature will lead to the enhancement of the stability of emulsified system, the failure of demulsifier, and even the volatilization of light oil and the coking of heavy components, which seriously affects the heat transfer efficiency and the operation stability of the equipment. Therefore, the existing technology cannot reconcile the contradiction between the demulsification of emulsified oil and the evaporation of high-salt wastewater, and the treatment effect is often unsatisfactory.

[0048] The applicant found that by introducing a rotating spray and a supergravity field in the sleeved structure of the inner cylinder 2 and the outer cylinder 1, and combining the shear of the composite micropore 3 and the evaporation of the outer cylinder heating, the demulsification and evaporation processes are optimized. In the running process of the device, the wastewater is forced to be sprayed into droplets and liquid films under high-speed rotation through the composite micropore 3, which not only expands the oil-water interface area and destroys the emulsified stable layer, promotes the rapid separation of oil and water, but also realizes efficient evaporation and salt precipitation on the surface of the outer cylinder heating body, and the oil, water and salt phases complete separation and collection in one system.

[0049] As shown in Figure 1 and Figure 2 , a die-casting wastewater treatment device comprises:

[0050] an outer cylinder 1, which is provided with a heating body inside;

[0051] an inner cylinder 2, which is coaxially arranged inside the outer cylinder 1 and rotationally connected therewith;

[0052] wherein the side wall of the inner cylinder 2 is provided with a plurality of micropores 3, and the micropores 3 are used to make the die-casting wastewater pass through the micropores 3 and be sprayed into the inner heating body of the outer cylinder 1 in the form of droplets or liquid films when the inner cylinder 2 rotates;

[0053] a feeding unit for conveying the die-casting wastewater to be treated to the inside of the inner cylinder 2;

[0054] and a driving mechanism connected with the inner cylinder 2 for driving the inner cylinder 2 to rotate at a preset speed.

[0055] Specifically, the feeding unit is responsible for transporting the die-casting wastewater to be treated into the device, which can be composed of a screw pump or a diaphragm pump with variable frequency speed regulation function, for example, the flow range is 1 m 3 / h-10 m 3 / h, the lift is 10 m-30 m, the pump is connected with the water inlet in the middle of the inner cylinder 2 through the pipeline to ensure that the wastewater enters at a stable and controllable flow rate, and a flow sensor and a pre-filter can also be provided on the feeding pipeline to monitor the feeding amount and remove large particle impurities to protect the operation of the subsequent equipment.

[0056] The material of the outer cylinder 1 is preferably high-temperature-resistant and corrosion-resistant stainless steel, for example, selected from 316L stainless steel, to meet the challenges of high-temperature evaporation environment and corrosive wastewater.

[0057] It should be noted that the inner wall of the outer cylinder 1 is provided with a heating body, and there is an included angle between the inner wall of the outer cylinder 1 and the heating body, and the included angle is in the range of 1-5°. By using the design of the conical included angle, the liquid droplets or liquid films flowing and evaporating on the heating body can be effectively guided to flow downward, and the separated oil phase and concentrated salt phase can be collected along the wall surface into the collection cavity 8 between the inner cylinder 2 and the outer cylinder 1.

[0058] Preferably, the inner surface of the heating body is provided with a high-performance coating, such as polytetrafluoroethylene or silicon carbide coating. Such coating has excellent corrosion resistance, non-stick and anti-fouling ability, which can effectively prevent the deposition of oil and salt scale on the inner wall of the outer cylinder during the evaporation process, thereby maintaining the heat transfer efficiency and the long-term stable operation of the equipment.

[0059] The inner cylinder 2 is installed inside the outer cylinder 1 and is coaxially rotatably installed. The material of the inner cylinder 2 is preferably a high-strength corrosion-resistant alloy, for example, selected from nickel-based alloys such as Hastelloy C-276 or titanium alloys such as Gr2 titanium alloy, to ensure sufficient mechanical strength and long-term corrosion resistance in high-speed rotation and corrosive media. The wall thickness of the inner cylinder 2 is 2 mm-5 mm, which is used to withstand the centrifugal stress generated by high-speed rotation.

[0060] The heating body uses an electric heating band, and the driving mechanism is usually composed of an alternating current variable frequency motor, a reducer and a flexible coupling. By using a variable frequency speed regulator, the rotating speed of the inner cylinder 2 is controlled to be between 500 rpm and 5000 rpm.

[0061] Among them, the outer cylinder 1 and the inner cylinder 2 are dynamically sealed by a mechanical seal to prevent leakage of wastewater or water vapor. The mechanical seal preferably uses silicon carbide-graphite friction pair materials, so such materials have excellent corrosion resistance, wear resistance and self-lubricating properties, ensuring long-term sealing performance under high-temperature and high-speed operating conditions.

[0062] In the process of treating complex die-casting wastewater containing high concentration of emulsified oil and high salt, the die-casting wastewater needs to be fed into the inner cylinder 2 through the feeding unit, and the volume of the wastewater should be in the range of one third to two thirds of the volume of the inner cylinder 2, so as to facilitate the subsequent rotation to realize the supergravity field;

[0063] The inner cylinder 2 is driven to rotate by the driving mechanism. Since the surface of the inner cylinder 2 is provided with a plurality of micro-holes 3, during the rotation of the inner cylinder 2, a supergravity field, i.e. a radial centrifugal force field, is generated. The die-casting wastewater entering the inner cylinder 2 is forced to distribute radially under the action of the supergravity, and is extruded to the inner cylinder 2 under high pressure, and is sprayed onto the heating body through the micro-holes 3 on the inner cylinder 2;

[0064] The heating body is used to provide continuous heat input for the wastewater droplets or liquid film sprayed into the inside of the outer cylinder 1, so as to realize the rapid vaporization of water and the crystallization and precipitation of salt.

[0065] Among them, in order to realize the spraying and dispersion of liquid, a plurality of micro-holes 3 are opened on the side wall of the inner cylinder 2. When the wastewater passes through the micro-holes 3 under high-speed rotation conditions, the liquid flow will be subjected to strong shear force and disturbance effect, and will be broken into countless small droplets or extremely thin liquid film, so as to be sprayed at high speed in the form of droplets or liquid film to the surface of the heating body of the outer cylinder 1;

[0066] Unlike the traditional whole liquid flow, the droplets and liquid film have extremely high specific surface area due to their small size, which significantly enlarges the interface area between oil and water, greatly improves the mass transfer and heat transfer rate, and at the same time, the stable structure of emulsified oil formed by surfactant and electric double layer is destroyed in the process of spraying and high-speed shearing of the micro-holes 3, and the emulsified oil droplets lose stability and coalesce, thereby accelerating the oil-water separation process.

[0067] In order to continuously supply wastewater to the inside of the inner cylinder 2, the device is also provided with a feeding unit which can stably transport the die-casting wastewater containing emulsified oil and high salt into the inner cylinder 2, so as to ensure the continuity and stability of the whole treatment process.

[0068] In addition, the inner cylinder 2 is connected with the external power device through the driving mechanism, and the driving mechanism can control the rotating speed of the inner cylinder 2, so as to adjust the size of the centrifugal force, and thereby realize the optimization of the droplet spraying state, the dispersion particle size and the separation effect.

[0069] When treating special corrosive wastewater, the inner cylinder 2 and the outer cylinder 1 can be made of nickel-based alloy with high temperature resistance and corrosion resistance, such as Inconel 625. Using nickel-based alloy as the material of the inner cylinder 2 and the outer cylinder 1 has excellent stability to sulfides and chlorides.

[0070] Before the inner cylinder 2 is used, the inner surface thereof is subjected to a composite treatment of mechanical polishing and electrochemical polishing, so that the surface roughness is less than or equal to 0.2 μm, thereby reducing the frictional resistance of the fluid flowing in the inner cylinder and effectively inhibiting the adhesion of oil and solid particles.

[0071] As shown in Figure 3 In the present application, the heating body is installed on the inner wall of the outer cylinder 1.

[0072] The heating body comprises a plurality of annular rings 4 and a plurality of inclined plates 5 connecting the annular rings 4; the annular rings 4 are stacked layer by layer by means of the inclined plates 5, and the inner diameters of the annular rings 4 gradually decrease from the bottom to the top of the outer cylinder, thereby forming a stepped heating body.

[0073] The stepped heating body divides the overall heating surface of the outer cylinder 1 into a plurality of relatively independent annular evaporation zones.

[0074] In the stacking structure, the inner diameters of the annular rings 4 gradually decrease from the bottom to the top of the outer cylinder 1, i.e., the inner diameter of the lower annular ring 4 is larger, and the inner diameter of the upper annular ring 4 is smaller, thereby forming a stepped structure in the space between the inner cylinder 2 and the outer cylinder 1. Through the stepped heating body, the liquid drops or liquid films ejected from the micro-holes 3 of the inner cylinder 2 are distributed in the respective annular evaporation zones to complete evaporation after impacting the heating surface, and do not continuously slide on the large-area heating surface.

[0075] It should be noted that after the liquid drops complete evaporation in the annular zone, the residual oil phase can drop to the collection cavity 8 between the inner cylinder 2 and the outer cylinder 1, and does not stay on the surface of the heating body for a long time, thereby avoiding the long oil flow path, oil coking and oil stain deposition.

[0076] The stepped annular rings 4 are independent of each other, so that the liquid drops in different zones do not interfere with each other, and the continuous oil film is prevented from being formed when a plurality of liquid drops slide down, thereby effectively reducing the risk of oil stain deposition and salt stain coking. Since the evaporation zone is divided into a plurality of small zones, the liquid drops in each zone are heated more uniformly, and the evaporation efficiency is significantly improved.

[0077] It should be noted that if the angle of the inclined plate 5 connecting the annular rings 4 is too small, such as the horizontal arrangement of the inclined plate 5 or the angle between the inclined plate 5 and the annular ring 4 is greater than 90°, the liquid drops are likely to stay or slowly slide along the surface of the inclined plate 5 after impacting, thereby causing the liquid drops to stay in the local area for a long time, and the residual oil or salt is easily deposited after being heated in the local area, thereby forming oil stains or scale, and affecting the cleanliness and heat transfer efficiency of the heating surface. Therefore, in the present application, the angle between the inclined plate 5 and the horizontal plane is 5-10°.

[0078] Specifically, when the liquid droplets or liquid film ejected from the micro-holes 3 of the inner cylinder 2 impact the heating body at high speed under the action of centrifugal force, they will evaporate in the respective corresponding annular evaporation areas, avoiding continuous sliding on the entire large-area heating surface, thereby greatly optimizing the uniformity of the liquid film spreading and the evaporation efficiency.

[0079] The inclination angle between the inclined piece 5 connected to the circular ring 4 and the horizontal plane ensures that the liquid droplets can smoothly flow down the surface of the inclined piece 5 after being ejected after impact, avoiding the liquid droplets from being retained or slowly sliding in a local area, thereby effectively preventing the liquid droplets from forming deposits after being heated for a long time in a local area, avoiding the formation of oil spots or fouling, and further maintaining the cleanliness of the heating surface and ensuring the heat transfer efficiency.

[0080] After the liquid droplets complete evaporation in the annular area, the remaining oil phase and concentrated liquid can naturally drip into the collection cavity 8 formed between the inner cylinder 2 and the outer cylinder 1, avoiding long-term residence on the heating body surface.

[0081] The coating coated on the heating body is preferably selected from polytetrafluoroethylene or silicon carbide material.

[0082] The polytetrafluoroethylene coating has excellent chemical inertness, extremely low surface energy, and non-stick properties, which can effectively prevent the deposition of oil and salt on the heating surface during high-temperature evaporation.

[0083] The silicon carbide coating has extremely high hardness, wear resistance, excellent thermal conductivity, and corrosion resistance, providing longer service life and more stable heat transfer performance under extreme working conditions.

[0084] The coating thickness is usually controlled between 100 μm and 300 μm, ensuring good adhesion and functionality. The heating body uses an electric heating band as a heat source, and the electric heating band is wound outside the heating body. By controlling the power of the electric heating band, such as adjustable to 10 kW-500 kW, the surface temperature of the heating body can be precisely adjusted to meet different wastewater treatment needs.

[0085] As shown in Figure 4 In the present application, the micro-holes 3 are composed of a circular hole 6 and two rectangular strip holes 7 connected on both sides of the circular hole 6;

[0086] The diameter of the circular hole 6 ranges from 80 μm to 200 μm;

[0087] The outlet of the circular hole 6 has a tangential angle, and the tangential angle ranges from 5° to 30°;

[0088] The inlet of the circular hole 6 has a flared structure, and the inner diameter gradually decreases from the inlet to the outlet, forming a converging-diverging structure of the ejection hole.

[0089] The number density of the plurality of micro-holes 3 on the inner cylinder 2 is 100-500 per square centimeter to ensure that a sufficient number of spray points are provided on the limited surface area to maximize the shearing and atomization of the wastewater.

[0090] When the wastewater passes through the circular hole 6 with a flared entrance under pressure, the fluid is initially accelerated and focused to form a high-speed jet, which is immediately divided and guided by the two-sided rectangular strip holes 7, the flow lines change sharply, and flow separation occurs at the sharp edges of the strip holes, generating asymmetric vortices.

[0091] The use of a flared entrance serves as a streamlined guide and initial acceleration, smoothly converting the pressure energy of the fluid into kinetic energy. The fluid is accelerated through the throat of the circular hole 6, and finally sprayed out of the composite outlet formed by the circular hole 6 and the two-sided strip holes, with a converging-diverging flow channel design to reduce energy loss.

[0092] Regarding the composite structure of the micro-holes 3, the circular hole 6 produces a relatively symmetric and stable jet, which is immediately disturbed and modulated by the two-sided rectangular strip holes 7 at the outlet, destroying the symmetry of the flow and generating asymmetric vortices at the sharp edges of the rectangular strip holes 7 and the outlet.

[0093] The use of rectangular strip holes 7 generates flow separation to form asymmetric vortices, creating high-frequency pulsating shear forces that stretch and shear the sprayed liquid, resulting in the formation of both large-diameter droplets with high momentum and thin liquid films and fine mist droplets simultaneously at the moment of spraying, greatly increasing the interfacial area of the oil-water mixture and strengthening mass and heat transfer across the oil-water interface, thereby significantly improving evaporation efficiency.

[0094] The high-frequency pulsating shear force at the outlet of the rectangular strip holes 7 destroys the stable film layer of the emulsified oil, causing the emulsified oil to rapidly destabilize and coalesce, thereby achieving rapid separation and complete demulsification during the droplet flight and spreading process, and further allowing the droplets to uniformly spread and constantly refresh the heated surface after impacting the outer cylinder heating body, avoiding the formation of localized coverage and deposition of oil droplets and salt, and maintaining the long-term cleanliness of the heat transfer surface.

[0095] It should be noted that the design of the micro-holes 3 produces a nearly cylindrical liquid beam through the circular hole, which, in combination with the rectangular strip holes 7, causes the sprayed liquid to initially take the form of a thin fan-shaped liquid film rather than a liquid column that requires impact to spread.

[0096] The use of the initial thin liquid film with a large initial specific surface area allows it to have extremely high heat and mass transfer efficiency before impacting the heated wall, and the strip-shaped liquid film itself is more unstable and more prone to spontaneous fragmentation into smaller and more uniform droplets, further increasing the total evaporation area and greatly enhancing the evaporation process.

[0097] Considering that the flux of single round hole 6 will decrease sharply once it is partially blocked by fibers or soft particles, the micro-hole 3 structure provides redundant flow paths, so that even if the main channel of round hole 6 is partially blocked, the fluid can still pass through the strip hole on one side or both sides, at the same time, the unstable flow field and vortex generated in the hole have a strong scouring effect on the potential blockage, which gives the micro-hole 3 certain self-cleaning ability, thereby reducing the pretreatment requirements and maintenance frequency.

[0098] In the present application, the length of the rectangular strip hole 7 is 50-100 μm, and the width is 10-20 μm.

[0099] Considering that if the micro-hole 3 is arranged in axial parallel or circumferential ring, the liquid flow sprayed from the inner cylinder will form several discrete and strip-shaped impact areas on the inner wall of the outer cylinder, resulting in uneven heating of the heating surface, fluctuation of evaporation efficiency, and inability of the liquid film to form a coherent cover on the wall surface.

[0100] Therefore, the present application adopts a spiral array arrangement, so that when the inner cylinder body 2 rotates, the spray trajectory of the micro-hole 3 forms a continuous, uniform and non-overlapping coverage area on the inner wall of the outer cylinder, ensuring that the entire effective area of the heating body is fully utilized, avoiding the formation of local overheating or dry areas, thereby significantly improving the uniformity and overall efficiency of evaporation and concentration.

[0101] At the same time, the spiral array structure actively guides and optimizes the flow path and residence time of the fluid in the outer cylinder, and this arrangement makes the droplets sprayed from different axial heights and different circumferential phases form an orderly, spiral propulsion type flow pattern in the centrifugal field.

[0102] It can guide the salt crystals, concentrated droplets and separated oil phase generated during the evaporation process to move orderly along the predetermined path to the collection area, effectively reducing the dead zone and short circuit phenomenon of the fluid in the cavity, preventing the backmixing of separated materials, thereby promoting more thorough separation and more efficient collection of oil, water and salt three-phase on a macroscopic level.

[0103] The arrangement of micro-hole 3 adopts a spiral arrangement to ensure that the wastewater can form a uniform and continuous liquid film cover when sprayed to the heating surface position of the heating body, avoiding local dry areas or excessive liquid film thickness, thereby optimizing the heat and mass transfer efficiency.

[0104] The spiral angle of the spiral array is usually set to be between 15-30°, and the center distance of adjacent micro-holes 3 is about 3-5 times the diameter of the hole.

[0105] It should be noted that, considering that the root cause of the scaling and plugging problem of the traditional evaporator in treating oily high-salt wastewater is the standing and hysteresis, the wastewater slowly flows or relatively stationary evaporates on the heating surface, causing the dissolved salt to rise in concentration as the water evaporates, eventually oversaturating and precipitating, and firmly adhering to the wall to form hard and heat-insulating scale, at the same time, the oil in the wastewater is easy to oxidize, polymerize and entangle with the salt to form viscous sludge, and then carbonize into hard coke scale.

[0106] Once such a scale layer is formed, it is extremely difficult to remove, which can seriously reduce the heat transfer efficiency and increase the energy consumption, and the equipment must be shut down for chemical or mechanical cleaning.

[0107] And the physical peeling and inhibition realized by the continuous high-speed impact of the liquid droplets;

[0108] Specifically, the liquid droplets sprayed from the micropores 3 of the inner cylinder 2 are not soft droplets, but droplet groups with high kinetic energy driven by centrifugal force, which continuously and uniformly impact the entire surface of the heating body;

[0109] The continuous impact of liquid droplets with high kinetic energy on the heating body continuously scours the surface of the heating body, making it difficult for precipitated crystalline particles to find stable attachment points;

[0110] Even if there is initial adhesion, subsequent droplet scouring on the surface of the heating body can scour and peel the deposits on the surface of the heating body.

[0111] At the same time, by the structural arrangement of the stepped heating body, the continuous heating surface is divided into a plurality of independent annular steps, and after the liquid undergoes brief evaporation on each step, it does not stay indefinitely, but directly drips from the edge of the ring 4 step to the collection cavity 8 between the inner cylinder 2 and the outer cylinder 1 under the action of gravity, ensuring that the residence time of the liquid on the surface of the heating body is controlled within a short time range, avoiding excessive concentration and stagnation in local areas, thereby structurally eliminating the occurrence of serious scaling and oil coking.

[0112] In the present application, the top of the inner cylinder 2 and the outer cylinder 1 is provided with a negative pressure hole, which is communicated with the outside pump body through the negative pressure hole, so that the inner cylinder 2 and the outer cylinder 1 are in the same negative pressure state;

[0113] And the vaporized wastewater is collected through the negative pressure hole.

[0114] In the present application, the cavity formed between the inner cylinder 2 and the outer cylinder 1 is a collection cavity 8 for collecting precipitated crystals and separated emulsified oil.

[0115] Example 1:

[0116] Experiments were conducted using a die-casting wastewater treatment device designed and manufactured in accordance with the present application.

[0117] Outer cylinder 1: made of 316L austenitic stainless steel, inner diameter 600 mm, height 2500 mm.

[0118] Heating body: heating tape, inner wall coated with a 50-micron-thick PTFE-based composite anti-fouling coating, surface roughness Ra value 0.2 μm.

[0119] Inner cylinder 2: made of duplex stainless steel 2205, outer diameter 400 mm, height 2000 mm.

[0120] Heating temperature of heating body: 80-95℃.

[0121] Drive mechanism 4: variable frequency motor, inner cylinder 2 rotation speed set to 2800 RPM.

[0122] Feeding mechanism 5: feeding flow rate set to 800 L / h.

[0123] Example 2:

[0124] Generally the same structure as Example 1, except that the micropore 3 structure is a circular hole 6, and the rectangular strip holes 7 on both sides are removed.

[0125] Comparative Example 1:

[0126] Traditional multi-effect evaporator combined with chemical demulsification pretreatment.

[0127] Composed of a chemical demulsification tank, a sedimentation tank, and a three-effect falling film evaporator.

[0128] Chemical demulsification unit: chemical demulsification using polyacrylamide PAM and polyaluminum chloride PAC. Dosage is 500 ppm and 1000 ppm, respectively. After demulsification, settle for 1 hour.

[0129] Three-effect falling film evaporator: total heat transfer area equivalent to the evaporation area of Example 1. Steam heating is used, with a temperature difference between effects controlled at 10-15℃, and a maximum heating temperature of 110℃.

[0130] Scraping: no scraping mechanism is provided, and only stop and clean when the heat transfer surface is scaled and the efficiency is reduced.

[0131] Experimental conditions:

[0132] Wastewater to be treated: emulsified wastewater from a certain automobile parts manufacturer, initial oil content 12000 mg / L, COD 25000 mg / L, SS 3000 mg / L, pH 7.5, conductivity 15000 μS / cm.

[0133] Continuous running time: 500 hours.

[0134] Results of Example 1 experiment:

[0135] In the 500 hours of continuous operation, the device showed highly stable and efficient treatment performance.

[0136] Oil phase separation rate: The purity of the oil phase collected through the separated oil phase outlet reached more than 95%, and the pre-separated oil phase of the inner cylinder 2 accounted for 25% of the total oil. The oil content in the condensed water was 4±0.5 mg / L, and the total oil removal rate reached 99.96±0.02%.

[0137] Water recovery rate: The condensed water production rate was 87.7±0.8%. The COD of the condensed water was 42±1 mg / L, the SS was 9.2±0.4 mg / L, the conductivity was lower than 100 µS / cm, and the pH value was 6.8-7.2, which could be directly reused for production or as municipal miscellaneous water.

[0138] Salt recovery: The salt content in the 25 discharge of the concentrated liquid and salt slurry outlet reached more than 50%, mainly inorganic salt crystals, which could be further recovered.

[0139] Energy consumption: The average energy consumption was 0.55 kWh / L of treated water.

[0140] Scaling situation: During the 500 hours of operation, the heat transfer coefficient of the inner wall of the outer cylinder 1 only decreased by 4.24±0.34%, and the scraper cleaning mechanism effectively inhibited the accumulation of scaling. There was no shutdown cleaning due to scaling.

[0141] Floor area: The floor area of the device was about 5m 2 .

[0142] Results of Example 2 experiment:

[0143] In the 500 hours of continuous operation, the device showed highly stable and efficient treatment performance.

[0144] Oil phase separation rate: The purity of the oil phase collected through the separated oil phase outlet reached more than 95%, and the pre-separated oil phase of the inner cylinder 2 accounted for 25% of the total oil. The oil content in the condensed water was 4±0.5 mg / L, and the total oil removal rate reached 99.96±0.02%.

[0145] Water recovery rate: The condensed water production rate was 87.7±0.8%. The COD of the condensed water was 42±1 mg / L, the SS was 9.2±0.4 mg / L, the conductivity was lower than 100 µS / cm, and the pH value was 6.8-7.2, which could be directly reused for production or as municipal miscellaneous water.

[0146] Salt recovery: The salt content in the concentrated liquid and the salt slurry outlet 25 discharge reached more than 50%, mainly inorganic salt crystals, which can be further recovered.

[0147] Energy consumption: The average energy consumption is 0.62 kWh / L of treated water.

[0148] Fouling: During the 500-hour operation, the heat transfer coefficient of the inner wall of the outer cylinder 1 only decreased by 5.03±0.22%, and the scraping mechanism effectively inhibited the accumulation of fouling. There was no shutdown cleaning due to fouling.

[0149] Floor area: The floor area of the device is about 5m 2 .

[0150] Experimental results of Comparative Example 1:

[0151] During the 500-hour operation, the system showed obvious deficiencies in treatment efficiency and stability.

[0152] Oil separation rate: After chemical demulsification and sedimentation, the oil content of the pretreated wastewater was still as high as 800-1500 mg / L. The oil content in the condensate water from the evaporator was 37±12 mg / L, and the total oil removal rate was about 99.60±0.04%.

[0153] Water recovery rate: The condensate water production rate was 78.4±0.3%. The COD of the condensate water was 157±12 mg / L, the SS was 35±4 mg / L, the conductivity was 150-300 µS / cm, and the pH value was greatly affected by the chemical agent.

[0154] Salt recovery: The salt content in the concentrated liquid was about 30%, and the concentration ratio was limited due to the problem of fouling.

[0155] Energy consumption: The average energy consumption is 0.95 kWh / L of treated water.

[0156] Fouling: After about 120 hours of operation, the heat transfer surface of the evaporator began to show obvious fouling, and the heat transfer coefficient decreased by 24.3±0.7%. In order to maintain the treatment efficiency, it had to be cleaned every 150-200 hours, and each cleaning took about 8-12 hours, which seriously affected the continuous production. The amount of cleaning agent used was large.

[0157] Floor area: The total floor area of the chemical demulsification unit, the sedimentation tank and the three-effect evaporator is about 15m 2 .

[0158] The performance indicators of Example 1 and Comparative Example are quantitatively compared to clearly show the technical advantages of the present application, as shown in Table 1.

[0159] Table 1:

[0160]

[0161] In summary, comparative example 1, example 2, and comparative example 1 can draw that example 1 has the best treatment effect on die casting wastewater, mainly because the centrifugal force generated by high-speed rotation generates an ultra-strong gravity field, which enhances the density difference between water and oil, makes the oil droplets in the inner cylinder 2 rapidly migrate radially in the centrifugal field and realize the relative stratification of water-oil, the oil phase in water can quickly gather, and the water phase is concentrated in different levels, thereby accelerating the oil-water separation process, and at the same time, the oil-water liquid sprayed out of the inner cylinder 2 continues to be affected by the ultra-strong gravity field and moves quickly in the centrifugal direction, realizing the rapid centripetal migration of oil droplets and the radial separation of water phase in the spraying state. Through two-stage separation of the wastewater in the inner cylinder 2, the separation efficiency of the oil phase and the water phase is improved;

[0162] The rectangular strip hole 7 generates flow separation to generate asymmetric vortex flow, forming high-frequency pulsating shear force, stretching and shearing the sprayed liquid, so that both large-particle-size droplets with large momentum and thin liquid film and fine mist droplets are formed synchronously at the moment of spraying, the interface area of the oil-water mixture is doubled, the mass transfer and heat transfer on the oil-water interface are strengthened, the evaporation efficiency is greatly improved, and the high-frequency pulsating shear force at the outlet of the rectangular strip hole 7 destroys the stable film layer of the emulsified oil, making the emulsified oil quickly lose stability and migrate, so that rapid stratification and complete demulsification are realized during the flight and spreading of the droplets, and then the droplets can uniformly spread and constantly refresh the heating surface after impacting the outer cylinder heating body, avoiding the formation of local covering deposition of oil droplets and salt, and keeping the heat transfer surface clean for a long time.

[0163] A die casting wastewater treatment method using a die casting wastewater treatment device, comprising the following steps:

[0164] Step S1, delivering the die casting wastewater to be treated to the inside of the inner cylinder through the feeding unit;

[0165] Step S2, rotating the inner cylinder at high speed under the action of the driving mechanism, so that the die casting wastewater is sprayed into droplets or liquid film to the heating body of the outer cylinder under the action of centrifugal force;

[0166] Step S3, instantaneous demulsification of emulsified oil, oil-water separation, and water evaporation by the shearing effect of micro-hole spraying, the centrifugal ultra-gravity field effect, and the thermal evaporation effect of the heating wall surface;

[0167] Among them, the oil phase migrates and gathers to the central axis area of the inner cylinder under the action of centrifugal force, part of the water phase is instantaneously evaporated after impacting the heating wall surface, the dissolved salt is analyzed out, and the oil phase that has not evaporated flows downward along the heating wall surface under the action of gravity and air flow;

[0168] Step S4, the separated salt crystals and emulsified oil are collected in the collecting cavity between the inner cylinder and the outer cylinder;

[0169] Step S5, the oil phase is gathered in the center of the inner cylinder and is guided out, the water vapor is condensed and recovered at the top, and the separated salt is collected in the cavity between the inner cylinder and the outer cylinder.

[0170] In use, the die casting wastewater to be treated is delivered to the inside of the inner cylinder through the feeding unit, and the inner cylinder is rotated at high speed under the action of the driving mechanism, so that the die casting wastewater is sprayed into droplets or liquid membranes to the heating body of the outer cylinder under the action of centrifugal force, the emulsified oil is instantaneously demulsified, oil and water are separated, and water is evaporated through the shearing effect of the micro-hole spraying, the effect of centrifugal supergravity field, and the thermal evaporation effect of the heating wall surface, the oil phase that is not evaporated flows downward along the heating wall surface under the action of gravity and air flow; the separated salt crystals and emulsified oil are collected in the collecting cavity between the inner cylinder and the outer cylinder, the oil phase is gathered in the center of the inner cylinder and is guided out, the water vapor is condensed and recovered at the top, and the separated salt is collected in the cavity between the inner cylinder and the outer cylinder.

[0171] The above is based on the ideal embodiment of the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims

1. A die casting wastewater treatment device characterized by comprising: The application relates to a centrifugal evaporation device for pressure casting wastewater treatment. The device comprises: an outer cylinder provided with a heating body inside; an inner cylinder coaxially arranged inside the outer cylinder and rotationally connected with the outer cylinder; wherein the side wall of the inner cylinder is provided with a plurality of micropores, the micropores are used for spraying the pressure casting wastewater in the form of liquid droplets or liquid films to the heating body inside the outer cylinder when the inner cylinder rotates; the heating body is mounted on the inner wall of the outer cylinder, and an included angle exists between the inner wall of the outer cylinder and the heating body, the included angle ranges from 1 to 5 degrees; the heating body comprises a plurality of annular rings and a plurality of inclined plates connecting the annular rings; the annular rings are stacked layer by layer through the inclined plates, the inner diameters of the annular rings gradually decrease from the bottom to the top of the outer cylinder, and the heating body is formed in a stepped mode; the included angle between the inclined plate and the horizontal plane ranges from 5 to 10 degrees; the micropore is composed of a circular hole and two rectangular strip holes connected on both sides of the circular hole; the diameter of the circular hole ranges from 80 to 200 microns; the length of the rectangular strip hole ranges from 50 to 100 microns, and the width ranges from 10 to 20 microns; the outlet of the circular hole has a tangential angle, and the tangential angle ranges from 5 to 30 degrees; the inlet of the circular hole has a horn mouth structure, the inner diameter of the horn mouth structure gradually decreases from the inlet to the outlet, and the circular hole is formed in a convergent-divergent structure; a feeding unit is arranged for conveying the pressure casting wastewater to be treated to the inside of the inner cylinder; 2. A die casting wastewater treatment device according to claim 1, characterized in that: and a driving mechanism is arranged for driving the inner cylinder to rotate at a preset rotating speed.

3. A die casting wastewater treatment device according to claim 1, characterized in that: The micropores are arranged in a spiral array along the axial direction and the circumferential direction of the inner cylinder. The top of the inner cylinder and the top of the outer cylinder are both provided with a negative pressure hole, the negative pressure hole is connected with an external pump body, and the inner cylinder and the outer cylinder are controlled to be in the same negative pressure state; 4. A die casting wastewater treatment device according to claim 1, characterized in that: and the vaporized wastewater is collected through the negative pressure hole.

5. A method for treating die casting wastewater using the die casting wastewater treatment apparatus according to claim 4, characterized by, The cavity formed between the inner cylinder and the outer cylinder is a collection cavity for collecting the separated emulsified oil and the precipitated crystals. The application further discloses a pressure casting wastewater treatment method. The method comprises the following steps: S1, conveying the pressure casting wastewater to be treated to the inside of the inner cylinder through the feeding unit; S2, driving the inner cylinder to rotate at a high speed under the action of the driving mechanism, and spraying the pressure casting wastewater to the heating body of the outer cylinder in the form of liquid droplets or liquid films under the action of the centrifugal force through the micropores; S3, instantaneously breaking the emulsified oil, separating the oil and water and evaporating the water through the shearing effect of the micropore spraying, the centrifugal supergravity field effect and the thermal evaporation effect of the heating wall surface; wherein the oil phase migrates and gathers to the central axis area of the inner cylinder under the action of the centrifugal force, part of the water phase is instantaneously evaporated after impacting the heating wall surface, the soluble salt is precipitated, and the unevaporated oil phase flows along the heating wall surface downward under the action of the gravity and the air flow; S4, collecting the precipitated salt crystals and the separated emulsified oil in the collection cavity between the inner cylinder and the outer cylinder; S5, gathering the oil phase in the center of the inner cylinder and leading out, condensing and recycling the water vapor at the top, and collecting the precipitated salt in the cavity between the inner cylinder and the outer cylinder.

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