Anti-scale MVR (mechanical vapor recompression) evaporator

Abstract

The invention relates to the technical field of wastewater treatment equipment, and particularly provides an anti-scale MVR evaporator which comprises a falling-film evaporator, a separator, a compressor and a centrifugal machine, the falling-film evaporator comprises a distributor, a steam cavity and a falling-film pipe, the falling-film pipe penetrates through the steam cavity in the vertical direction, the distributor is arranged above the falling-film pipe, and the separator is arranged above the falling-film pipe. The distributor is used for distributing fed high-salinity wastewater, a gradient layer is arranged on the inner surface of the falling film tube, and the contact angle of the surface of the gradient layer is gradually increased from top to bottom. The technical effects of reducing the scaling rate and improving the heat transfer efficiency in the evaporation process of the high-salinity wastewater are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment equipment, and in particular to an anti-scaling MVR evaporator. Background Art

[0002] As the core equipment for high-salt wastewater treatment, the anti-scaling technology of MVR evaporators has always been a difficult point in the industry. In the prior art, scale inhibitors are generally added to inhibit the precipitation of salts. This solution requires continuous dosing of chemical agents, which poses an environmental risk and may affect the properties of the wastewater in the long term. Traditional mechanical cleaning requires shutdown maintenance, which is not only difficult to operate but also significantly reduces the wastewater treatment efficiency.

[0003] There are contradictions among the anti-scaling effect, energy efficiency, and environmental protection of the existing solutions. There is an urgent need for a passive anti-scaling MVR evaporator that does not require chemical intervention and can continuously inhibit scaling. Summary of the Invention

[0004] In view of this, the present invention proposes an anti-scaling MVR evaporator.

[0005] The technical solution of the present invention is realized as follows: The present invention provides an anti-scaling MVR evaporator, which includes a falling-film evaporator, a separator, a compressor, and a centrifuge. High-salt wastewater is fed from the top of the falling-film evaporator. The bottom side of the falling-film evaporator is connected to the feed port of the separator. The bottom discharge port of the separator and the bottom discharge port of the falling-film evaporator are both connected to the centrifuge. The steam outlet at the top of the separator is connected to the inlet of the compressor. The outlet of the compressor is connected to the inlet of the falling-film evaporator. It is characterized in that the falling-film evaporator includes a distributor, a steam chamber, and falling-film tubes. The falling-film tubes penetrate the steam chamber in the vertical direction. The distributor is arranged above the falling-film tubes and is used to distribute the fed high-salt wastewater. The inner surface of the falling-film tubes is provided with a gradient layer, and the contact angle of the surface of the gradient layer gradually increases from top to bottom.

[0006] In some embodiments, the gradient layer sequentially includes a main hydrophilic layer, a transition hydrophilic layer, a transition hydrophobic layer, and a main hydrophobic layer from top to bottom. Among them, the contact angle θ of the main hydrophilic layer is <10°, the contact angle θ of the transition hydrophilic layer is 10°-30°, the contact angle θ of the transition hydrophobic layer is 60°-90°, and the contact angle θ of the main hydrophobic layer is >110°. The main hydrophilic layer accounts for 20-30% of the length of the gradient layer, the transition hydrophilic layer accounts for 25-35% of the length of the gradient layer, the transition hydrophobic layer accounts for 20-30% of the length of the gradient layer, and the main hydrophobic layer accounts for 15-25% of the length of the gradient layer.

[0007] In some embodiments, the method for preparing the main hydrophilic layer includes: immersing the main hydrophilic layer region of the falling film tube made of titanium in the electrolyte and connecting it to the anode of the power supply, connecting the cathode of the power supply to a carbon rod immersed in the electrolyte, starting the pulsed power supply, performing electrolytic treatment and then cleaning and drying to obtain the main hydrophilic layer. The electrolyte contains 10 g / L of Na2SiO3 and 2 g / L of KOH.

[0008] In some embodiments, the electrolytic treatment conditions include: temperature of 25 - 30 °C, pulsed DC of 400 V, frequency of 1000 Hz, and electrolytic treatment for 10 - 20 min.

[0009] When the electrolysis time is within the range of 10 - 20 min, the uniformity of the nanopore structure (the porosity deviation detected by SEM < 5%) can meet the anti-scaling requirements.

[0010] In some embodiments, the method for preparing the transition hydrophilic layer includes: using a galvanometer scanning system to process a parallel micro-groove array in the transition hydrophilic layer region, making the direction of the micro-grooves form a 45° angle with the fluid flow direction, and performing cleaning and drying after treatment.

[0011] In some embodiments, the laser wavelength for processing is 1064 nm, the power is 200 W, the scanning speed is 50 mm / s, the line spacing is 20 μm, the width of the parallel micro-grooves is 20 μm, and the depth is 5 μm.

[0012] In some embodiments, the method for preparing the transition hydrophobic layer includes: first using a laser to process a micro-pit array on the surface of the transition hydrophobic layer region, then spraying perfluorooctyltriethoxysilane on the surface of the transition hydrophobic layer region, and then heating to 120 °C for baking treatment for 20 - 40 min.

[0013] In some embodiments, the laser power is 50 W, the diameter of the micro-pits is 5 - 10 μm, and the depth is 2 μm.

[0014] In some embodiments, the method for preparing the main hydrophobic layer includes: exposing the main hydrophobic layer region in the CVD reaction chamber and aligning it with the gas nozzle, heating to 250 °C, then introducing hexamethyldisilazane and carrier gas argon, performing deposition treatment for 2 h, and then annealing at 300 °C in vacuum for 1 h.

[0015] In some embodiments, the gas flow rate of hexamethyldisilazane is 20 sccm, and the argon flow rate is 50 sccm.

[0016] In the present invention, the main hydrophilic layer (θ < 10°) rapidly spreads the liquid film through the nanoporous structure to form a continuous liquid film with a thickness < 0.1 mm, avoiding the formation of hard scales such as CaSO4 and CaCO3 caused by local drying. The micro-groove structure (width 20 μm) of the transition hydrophilic layer (θ = 10° - 30°) induces turbulence and destroys the oriented growth of crystal nuclei. The micro-pits (diameter 5 - 10 μm) of the transition hydrophobic layer (θ = 60° - 90°) form an air film through the Cassie - Baxter effect, reducing the solid - liquid contact area. The nano - pillar array (height 500 nm) of the main hydrophobic layer (θ > 110°) triggers the droplet bouncing effect to peel off the initial soft scale.

[0017] The ultra - thin liquid film in the main hydrophilic region reduces the thermal resistance, the micro - grooves in the transition region enhance the turbulence, and the main hydrophobic region maintains stable heat transfer by suppressing excessive boiling.

[0018] First, the main hydrophilic layer is treated with high - energy PEO, then the transition region is processed by laser, and finally, low - temperature fluorination spraying and CVD deposition are carried out to avoid the destruction of the treated area by high - temperature processes.

[0019] The matching of the laser power (200 W) and the scanning speed (50 mm / s) ensures the consistency of the micro - groove depth (5 ± 0.5 μm), and the balance of the CVD deposition temperature (250 °C) and the precursor flow rate (20 sccm HMDSN) realizes the vertical growth of the nano - pillars.

[0020] The present invention has the following beneficial effects compared with the prior art:

[0021] Through the collaborative optimization of the four - region gradient wettability surface design and the partition preparation process, the present invention achieves the remarkable effects of significantly reducing the scaling rate and greatly improving the heat transfer efficiency during the evaporation of high - salt wastewater, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is a connection schematic diagram of the anti - scaling MVR evaporation system of the present invention;

[0024] Figure 2 It is a longitudinal sectional view of the falling - film tube in the anti - scaling MVR evaporation system of the present invention.

[0025] In the figure: 1 - falling film evaporator, 2 - separator, 3 - compressor, 4 - centrifuge, 11 - distributor, 12 - steam chamber, 13 - falling film tube, 14 - gradient layer, 141 - main hydrophilic layer, 142 - transition hydrophilic layer, 143 - transition hydrophobic layer, 144 - main hydrophobic layer. Specific Embodiments

[0026] The following will describe clearly and completely the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0027] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0028] It should be understood that the orientation or positional relationship indicated by terms such as "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present application.

[0029] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the embodiments of the present invention belong. If the definitions stated in this part are contrary to or inconsistent with the definitions stated in the patents, patent applications, published patent applications and other publications incorporated herein by reference, the definitions listed in this part shall prevail over the definitions incorporated herein by reference.

[0030] Unless otherwise specified, the methods used in the following embodiments are all conventional methods. The materials, reagents and instruments used, unless otherwise specified, are all conventional materials, reagents and instruments in the art, and those skilled in the art can obtain them through commercial channels.

[0031] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed individually. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range. In the specification and claims of this application, range limitations can be combined and / or interchanged, and if not otherwise stated, these ranges include all sub-ranges contained therein.

[0032] As Figure 1-2 shown, the scale-inhibiting MVR evaporator of the present invention includes: a falling film evaporator 1, a separator 2, a compressor 3, and a centrifuge 4. High-salt wastewater is fed from the top of the falling film evaporator 1. The bottom side of the falling film evaporator 1 communicates with the feed port of the separator 2. The bottom discharge port of the separator 2 and the bottom discharge port of the falling film evaporator 1 both communicate with the centrifuge 4. The steam outlet at the top of the separator 2 communicates with the air inlet of the compressor 3. The air outlet of the compressor 3 communicates with the air inlet of the falling film evaporator 1. It is characterized in that the falling film evaporator 1 includes a distributor 11, a steam chamber 12, and falling film tubes 13. The falling film tubes 13 penetrate the steam chamber 12 in the vertical direction. The distributor 11 is arranged above the falling film tubes 13. The distributor 11 is used to distribute the fed high-salt wastewater. A gradient layer 14 is provided on the inner surface of the falling film tubes 13, and the contact angle of the surface of the gradient layer 14 gradually increases from top to bottom.

[0033] The gradient layer 14 sequentially includes a main hydrophilic layer 141, a transition hydrophilic layer 142, a transition hydrophobic layer 143, and a main hydrophobic layer 144 from top to bottom. Among them, the contact angle θ of the main hydrophilic layer 141 < 10°, the contact angle θ of the transition hydrophilic layer 142 = 10° - 30°, the contact angle θ of the transition hydrophobic layer 143 = 60° - 90°, the contact angle θ of the main hydrophobic layer 144 > 110°. The main hydrophilic layer 141 accounts for 20 - 30% of the length of the gradient layer 14, the transition hydrophilic layer 142 accounts for 25 - 35% of the length of the gradient layer 14, the transition hydrophobic layer 143 accounts for 20 - 30% of the length of the gradient layer 14, and the main hydrophobic layer 144 accounts for 15 - 25% of the length of the gradient layer 14.

[0034] Example 1

[0035] This example provides a solution for a four-region gradient wettability falling film tube

[0036] 1. Materials and Equipment

[0037] Substrate: TA2 industrial pure titanium tube (Φ25×6000mm, wall thickness 2mm)

[0038] Equipment: PEO power supply (400V / 20A), fiber laser processing machine (1064nm), CVD tube furnace

[0039] 2. Preparation steps

[0040] Step 1: Treatment of the main hydrophilic layer

[0041] Cover the non-treatment area with a mask (the length ratio of the main hydrophilic layer is 25%).

[0042] Electrolyte: 10g / L Na2SiO3 + 2g / L KOH, constant temperature at 25℃.

[0043] PEO treatment: 400V pulsed DC, frequency 1000Hz, time 15min.

[0044] Ultrasonic cleaning (deionized water, 5min), dried with nitrogen.

[0045] Step 2: Treatment of the transition hydrophilic layer

[0046] Laser parameters: 1064nm, 200W, 50mm / s, line spacing 20μm.

[0047] Process 45° oblique microgrooves (width 20μm, depth 5μm), length ratio 30%.

[0048] Step 3: Treatment of the transition hydrophobic layer

[0049] Laser process micro-pits (50W, diameter 5 - 10μm, depth 2μm), length ratio 25%.

[0050] Spray 5wt% perfluorooctyltriethoxysilane (spraying pressure 0.3MPa).

[0051] Bake at 120℃ for 30min to form a fluorinated coating.

[0052] Step 4: Treatment of the main hydrophobic layer

[0053] CVD deposition: 250℃, HMDSN 20sccm + Ar 50sccm, time 2h.

[0054] Vacuum annealing: 300℃, 1h.

[0055] 3. Performance testing

[0056] Scaling test: Treat high-salt wastewater, wastewater Cl - concentration 18%, Ca 2+5000 mg / L, flow rate 1.5 m / s, temperature 80 °C, continuous operation for 72 hours. The scaling rate was tested by the weighing method and reached 2.0 g / m 2 ·h.

[0057] Scaling thickness: SEM showed that the scaling layer in the main hydrophobic region was only 38 μm, while that of the traditional tube was 320 μm.

[0058] Scaling morphology: XRD analysis showed that the scaling layer was loose CaSO4·2H2O.

[0059] Heat transfer test: Under the same working conditions, the measured heat transfer coefficient K = 2870 W / m 2 ·°C.

[0060] Example 2

[0061] The difference between this example and Example 1 is that the length ratios of the main hydrophilic layer, transition hydrophilic layer, transition hydrophobic layer, and main hydrophobic layer are 20%, 30%, 25%, and 25% respectively.

[0062] The scaling rate of this example was 2.1 g / m 2 ·h, and the heat transfer coefficient was 2850 W / m 2 ·°C.

[0063] Example 3

[0064] The difference between this example and Example 1 is that the length ratios of the main hydrophilic layer, transition hydrophilic layer, transition hydrophobic layer, and main hydrophobic layer are 30%, 35%, 20%, and 15% respectively.

[0065] The scaling rate of this example was 2.5 g / m 2 ·h, and the heat transfer coefficient was 2700 W / m 2 ·°C.

[0066] Example 4

[0067] The difference between this example and Example 1 is that the length ratios of the main hydrophilic layer, transition hydrophilic layer, transition hydrophobic layer, and main hydrophobic layer are 25%, 30%, 22%, and 23% respectively.

[0068] The scaling rate of this example was 2.3 g / m 2 ·h, and the heat transfer coefficient was 2800 W / m 2 ·°C.

[0069] Comparative Example 1

[0070] Based on Example 1, this comparative example used full-tube PEO treatment, and the inner wall of the full tube was treated according to the treatment method of the main hydrophilic layer in Example 1.

[0071] The scaling rate of this comparative example was 8.7 g / m2 ·h, with a heat transfer coefficient of 2100 W / m 2 ·°C.

[0072] Comparative Example 2

[0073] Based on Example 1, this comparative example uses full-tube CVD treatment, and the inner wall of the full tube is treated according to the treatment method of the main hydrophobic layer in Example 1.

[0074] The fouling rate of this comparative example is 5.2 g / m 2 ·h, with a heat transfer coefficient of 1900 W / m 2 ·°C.

[0075] Comparative Example 3

[0076] Based on Example 1, this comparative example reverses the process sequence of the transition hydrophobic layer, specifically including spraying 5wt% perfluorooctyltriethoxysilane (spraying pressure 0.3 MPa) first, and then laser processing micro-pits (50 W, diameter 5 - 10 μm, depth 2 μm), with a length ratio of 25%.

[0077] The contact angle θ of the transition hydrophobic layer in this comparative example is 85°. The fouling rate is 4.8 g / m 2 ·h.

[0078] In the above Example 1, the fouling layer on the surface of the main hydrophobic layer is loose, with a thickness of 38 μm, while in Comparative Example 1, the surface is hydrophilic, forming a dense fouling layer with a thickness reaching 320 μm. After reversing the process sequence of the transition hydrophobic layer in Comparative Example 3, the peeled thickness of the fouling layer of its transition hydrophobic layer reaches 210 μm.

[0079] After running for 500 h in Example 1, the heat transfer coefficient can still be maintained at greater than 2500 W / m 2 ·°C, and in Comparative Example 1, it drops to 1600 W / m after running for 200 h 2 ·°C.

[0080] Comparative Example 4

[0081] Using a commercially available scale inhibitor (Senas SN-203, dosage 50 mg / L)

[0082] The fouling rate is 6.8 g / m 2 ·h, with a heat transfer coefficient of 2300 W / m 2 ·°C.

[0083] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An anti-scaling MVR evaporator, comprising: A film evaporator (1), a separator (2), a compressor (3) and a centrifuge (4); high-salt wastewater is fed from the top of the falling film evaporator (1); the bottom side of the falling film evaporator (1) is connected to the feed port of the separator (2); the bottom discharge port of the separator (2) and the bottom discharge port of the falling film evaporator (1) are both connected to the centrifuge (4); the steam outlet at the top of the separator (2) is connected to the air inlet of the compressor (3); the air outlet of the compressor (3) is connected to the falling film evaporator (4); The falling film evaporator (1) is connected to the air inlet of the device (1), characterized in that the falling film evaporator (1) comprises a distributor (11), a steam chamber (12) and a falling film tube (13), the falling film tube (13) vertically penetrates the steam chamber (12), the distributor (11) is arranged above the falling film tube (13), the distributor (11) is used to distribute the feed high-salt wastewater, and the inner surface of the falling film tube (13) is provided with a gradient layer (14), and the contact angle of the surface of the gradient layer (14) gradually increases from top to bottom.

2. The anti-scaling MVR evaporator according to claim 1, characterized in that: The gradient layer (14) comprises, from top to bottom, a main hydrophilic layer (141), a transitional hydrophilic layer (142), a transitional hydrophobic layer (143) and a main hydrophobic layer (144), wherein the contact angle θ of the main hydrophilic layer (141) is less than 10°, the contact angle θ of the transitional hydrophilic layer (142) is 10°-30°, the contact angle θ of the transitional hydrophobic layer (143) is 60°-90°, the contact angle θ of the main hydrophobic layer (144) is greater than 110°, the main hydrophilic layer (141) accounts for 20-30% of the length of the gradient layer (14), the transitional hydrophilic layer (142) accounts for 25-35% of the length of the gradient layer (14), the transitional hydrophobic layer (143) accounts for 20-30% of the length of the gradient layer (14), and the main hydrophobic layer (144) accounts for 15-25% of the length of the gradient layer (14).

3. The anti-scaling MVR evaporator according to claim 2, characterized in that: The preparation method of the main hydrophilic layer (141) comprises: immersing the main hydrophilic layer (141) area of ​​the titanium falling film tube (13) into an electrolyte and connecting it to a power anode, connecting a power cathode to a carbon rod and immersing it in the electrolyte, starting a pulse power supply, and then washing and drying after electrolysis treatment to obtain the main hydrophilic layer, wherein the electrolyte contains 10 g / L Na2SiO3 and 2 g / L KOH.

4. The anti-scaling MVR evaporator according to claim 3, characterized in that: The electrolytic treatment conditions include: temperature of 25-30° C., 400 V pulsed DC, frequency of 1000 Hz, and electrolytic treatment for 10-20 minutes.

5. The anti-scaling MVR evaporator according to claim 2, characterized in that: The preparation method of the transitional hydrophilic layer (142) comprises: using a galvanometer scanning system to process a parallel micro-groove array in the transitional hydrophilic layer (142) region, so that the direction of the micro-groove forms an angle of 45° with the flow direction of the fluid, and cleaning and drying after processing.

6. The anti-scaling MVR evaporator according to claim 5, characterized in that: The processing laser wavelength is 1064nm, the power is 200W, the scanning speed is 50mm / s, the line spacing is 20μm, the parallel micro-groove width is 20μm, and the depth is 5μm.

7. The anti-scaling MVR evaporator according to claim 2, characterized in that: The preparation method of the transition hydrophobic layer (143) comprises: firstly processing a micro-pit array on the surface of the transition hydrophobic layer (143) region with a laser, then spraying perfluorooctyl triethoxysilane on the surface of the transition hydrophobic layer (143) region, and then heating to 120° C. and baking for 20-40 minutes.

8. The anti-scaling MVR evaporator according to claim 7, characterized in that: The laser power was 50 W, the diameter of the micro-pits was 5-10 μm, and the depth was 2 μm.

9. The anti-scaling MVR evaporator according to claim 2, characterized in that: The preparation method of the main hydrophobic layer (144) comprises: exposing the main hydrophobic layer (144) area in a CVD reaction chamber and aligning it with a gas nozzle, heating it to 250°C, introducing hexamethyldisilazane and carrier gas argon, depositing it for 2 hours, and then annealing it at 300°C in vacuum for 1 hour.

10. The anti-scaling MVR evaporator according to claim 9, characterized in that: The gas flow rate of hexamethyldisilazane was 20 sccm, and the gas flow rate of argon was 50 sccm.

Images