Environment-friendly biological slime control method for conventional cooling tower

Abstract

The application provides an environment-friendly conventional cooling tower biological slime control method, and relates to a metal-organic composite material microbial electric coupling porous membrane structure. The structure comprises an activated carbon fiber felt anode and an air cathode, wherein the air cathode comprises porous PTFE as a diffusion layer, MnCo / NC nitrogen-doped bimetallic-based carbon composite organic material as a cathode catalyst layer, and porous carbon material as a base electrode. The anode and the air cathode are fixed as an integrated metal-organic composite material microbial electric coupling porous membrane structure by using a woven metal fiber mesh structure. The metal-organic composite material microbial electric coupling porous membrane structure is placed on the water surface of a conventional cooling tower bottom collecting pool, filters large-particle pollutants, adsorbs microorganisms in water, and inhibits the growth of algae in water. Through the removal of large-particle biological slime flocs, organic and inorganic pollutants and microorganisms in circulating cooling water, the application realizes the control of biological slime in a circulating cooling water pipe network.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical control of microorganisms in circulating cooling water, specifically involving a metal-organic composite microbial electrocoupling porous membrane structure for conventional cooling towers, located in the bottom water collection pool of the tower for adsorbing microorganisms, filtering microbial slime, and preventing algae growth. Background Technology

[0002] Due to the high temperature and unstable quality of circulating cooling water, microorganisms easily proliferate in cooling towers, resulting in the formation of biological slime. The main components of biological slime are various complex microorganisms such as algae, bacteria, fungi, and inorganic and organic impurities. Biological slime is a viscous, transparent substance that disperses in water in a flocculent form. The microorganisms in circulating cooling water mainly originate from two sources: first, the cooling tower requires the introduction of a large amount of air during the evaporation and heat exchange process, and microorganisms are carried into the cooling water along with the air; second, the makeup water of the cooling water system contains microorganisms, which also enter the cooling water system along with the makeup water.

[0003] Under sunlight, algae photosynthesize with carbon sources such as carbon dioxide and bicarbonate in the water, absorbing carbon as nutrients and releasing oxygen. Therefore, when algae proliferate in large quantities, the dissolved oxygen content in the water increases, promoting oxygen depolarization and accelerating the corrosion process. Large amounts of biological slime can clog cooling tower pipes, reduce cooling efficiency, and cause heat transfer efficiency and head loss when deposited in heat exchangers. Slime deposited on metal surfaces can cause severe under-deposit corrosion and also prevent corrosion and scale inhibitors from acting on the metal, thus hindering their effectiveness. Besides accelerating under-deposit corrosion, some bacteria in microbial slime can also directly corrode metals through their metabolic secretions. All these problems prevent the long-term safe operation of the circulating water system, affecting production and causing serious economic losses. Therefore, the harm caused by microorganisms is just as serious as that caused by scale and corrosion to cooling water systems; in fact, controlling the harm caused by microorganisms is arguably the most important of the three.

[0004] The most common method for controlling microorganisms is to add bactericides. However, bactericides are not environmentally friendly, can cause wastewater pollution to exceed standards, and are costly. Microorganisms can also develop resistance to the drugs. Even if bactericides are very effective, the sludge that is shed will still exist in the pipeline system. If it is not cleaned in time, it will cause pipeline blockage and accumulate in the coils and packing of condensers, heat exchangers, and cooling towers.

[0005] Conventional cooling towers: specifically referring to hyperbolic natural draft reinforced concrete wet cooling towers that use reclaimed water as circulating cooling water. Large power plants often use hyperbolic cooling towers, such as... Figure 2As shown. This type of cooling tower is mostly used in inland hydropower stations. The tower body is a hyperbolic, thin-walled, column- and beam-free spatial structure that facilitates natural ventilation, and is mostly made of reinforced concrete. The upper part of the cooling tower is the ventilation duct, which mainly includes the lower ring beam 5, the duct wall 6, and the tower top rigid ring 7. The lower ring beam 5 is located at the lower end of the ventilation duct shell. The self-weight of the duct and other loads it bears are transferred to the inclined support 8 through the lower ring beam 5, and then to the foundation. The duct wall 6 is the main part of the cooling tower ventilation duct. It is a tall, thin-shell structure that mainly bears wind loads and is very sensitive to wind. The tower top rigid ring 7 is located at the top of the shell and is a reinforcing hoop at the top of the shell, which enhances the rigidity and stability of the top of the shell. The height of the cooling tower is generally 75 to 150 meters, and the bottom diameter is 65 to 120 meters. The lower part of the cooling tower is equipped with a water distribution tank 9 and a water spray device 10, which are mostly made of PE or PVC materials. Below the water spray device 10 is the heat exchange packing 11. At the bottom of the tower is a water collection pool 12, typically a circular pool about 2 meters deep below ground level. Its function is to collect the cooling water after heat exchange and to store and regulate the water volume, achieving water conservation through circulation. However, continuous water replenishment is required based on the evaporation rate. The water spray device 10 is the main equipment for evaporative cooling. During operation, water flows downwards from the water distribution tank 9, while air enters from the side of the tower bottom, fully contacts the water, and then carries heat upwards. The cooling process is primarily evaporative cooling, with a small portion being convection cooling. Summary of the Invention

[0006] To address the well-known problem of microbial growth and biofilm formation in circulating cooling water, an environmentally friendly method for controlling biofilm in conventional cooling towers using a metal-organic composite microbial electrocoupling porous membrane structure is provided.

[0007] Environmentally friendly method for controlling biological slime in conventional cooling towers: A metal-organic composite microbial electrocoupling porous membrane structure is laid flat on the water surface of the collection tank at the bottom of the cooling tower. When cooling water is sprayed from the spray system, it concentrates on the membrane structure. First, it filters out large organic and inorganic impurities and suspended slime colloids dispersed in the circulating water, preventing them from clogging the pipes. Second, since most microorganisms are negatively charged, the membrane structure can adsorb suspended microorganisms in the circulating cooling water. Third, the most important element for the growth of algae, one of the main microorganisms promoting slime growth, is sunlight. The membrane structure can block light, reducing the growth of algae in the collection tank, thereby reducing the number of microorganisms, controlling the proliferation of biological slime, and preventing blockage of the circulating cooling water system. In addition, the membrane structure can enhance heat exchange efficiency without reducing the cooling tower drift rate and cooling capacity, and without reducing the standard cooling water flow rate.

[0008] Metal-organic composite microbial electrocoupling porous membrane structure: Microorganisms in the cooling water collection tank metabolize at the anode, oxidizing organic matter in the cooling water to generate electrons and protons. These electrons, generated in the respiratory chain, are then transferred to the anode via various pathways. Driven by the potential difference between the anode and cathode, the electrons travel through an external circuit to the cathode, where they combine with electron acceptors such as oxygen to complete a reduction reaction, thus forming an electric current. In this structure, machine-woven metal meshes are applied to both sides of the anode and cathode, with the edges connected by high-temperature pressing to fix the cathode and anode layers. Figure 3 As shown. The metal wire is made of copper wire with a diameter of 1mm and a square mesh shape with a side length of 10mm. This structure features clear mesh, a flat surface, high temperature resistance, wear resistance, and good conductivity. The anode is made of carbon fiber, and the cathode is an air cathode, forming a three-in-one composite structure. After the charged circuit is formed, since bacteria are mostly negatively charged, bacteria and other microorganisms in the cooling water will be gradually adsorbed onto the anode, thereby purifying the circulating cooling water.

[0009] Anode reaction: C6H 12 O6 + 6H2O → 6CO2 + 24H + +24e -

[0010] Cathode reaction: 24H + +24e - +6O2→12H2O

[0011] Anode material: Activated carbon fiber felt is used. Activated carbon fiber is a typical microporous carbon, with numerous micropores directly distributed on the fiber surface in a monodisperse manner. The abundant presence of micropores not only increases the specific surface area of ​​the activated carbon fiber but also increases its adsorption capacity. Micropores and mesopores play a decisive role in the adsorption process, while macropores mainly act as transport channels, delivering the adsorbate into the interior of the carbon fiber. Activated carbon fiber has broad adsorption spectrum and a large adsorption capacity. It exhibits rapid desorption and excellent purification effect.

[0012] Cathode Material: An air cathode is used. Oxygen acts as the electron acceptor, and the reaction is completed in direct contact with the cathode. The air cathode mainly consists of three parts: a catalyst layer, a base electrode layer, and a diffusion layer. The diffusion layer is made of porous PTFE (polytetrafluoroethylene) and is located on the air side of the base electrode layer, promoting the arrival of oxygen from the air at the cathode reaction site for reduction. Oxygen from the air permeates through the waterproof diffusion layer to reach the catalyst layer, where it reacts with protons and electrons. The catalyst layer uses MOFs (Metal-organic frameworks). MOFs are 3D porous metal-organic framework materials formed by the self-assembly of metal clusters and organic ligands through covalent or ion-covalent coordination. These materials have advantages such as porosity, high specific surface area, surface functionalization, controllable size, and the presence of unsaturated active sites. This structure uses nitrogen-doped porous carbon-supported nickel-cobalt nanocomposite materials. Co nanoparticles can improve ORR activity, while Mn nanoparticles possess good OER performance and chemical stability. The base electrode layer uses porous carbon material. Compared with many electrode materials, porous carbon material has advantages such as low cost, high chemical stability, fast electronic response speed, high specific surface area, and adjustable pore structure. The honeycomb morphology structure with interconnected macropores can encapsulate microbial agents.

[0013] This invention is achieved through the following technical solution:

[0014] An environmentally friendly method for controlling biological slime in conventional cooling towers, the method comprising: placing a metal-organic composite microbial electrocoupling porous membrane structure in the water collection tank of a conventional cooling tower;

[0015] The metal-organic composite microbial electrocoupling porous membrane structure includes an anode layer and a cathode layer. The cathode layer includes a catalyst layer, a base electrode layer, and a diffusion layer. The catalyst layer and the diffusion layer are respectively coated on both sides of the base electrode layer. The anode layer and the cathode layer are fixed by means of metal wire weaving or hot pressing. The sides of the anode layer and the cathode layer coated with the catalyst layer are adjacent to each other.

[0016] Furthermore, the anode layer is made of activated carbon fiber felt, the diffusion layer is made of PTFE, the catalyst layer is made of MnCo / NC nitrogen-doped bimetallic carbon composite organic material, and the base electrode layer is made of porous carbon material with an internal honeycomb morphology structure of interconnected macropores.

[0017] Furthermore, the method for preparing the diffusion layer is as follows: 40% polytetrafluoroethylene emulsion is evenly brushed onto the base electrode layer. To prevent the coating from being applied to the other side, small air bubbles and polytetrafluoroethylene clumps remaining on the surface are removed. After the coating is air-dried for more than 10 minutes until the surface turns white, it is placed in a muffle furnace and dried at 360-380°C for more than 20 minutes. The above operation is repeated 4-5 times to form 4-5 dense diffusion layers.

[0018] Furthermore, the catalyst layer material is prepared by pyrolyzing the precursor MnCo-ZIF-67 nanocrystals at a high temperature of 800–850℃, with a heating rate of 5℃·min. -1 After holding at the temperature for 2 hours, it is cooled to room temperature along with the furnace.

[0019] Furthermore, the bimetallic MnCo-ZIF-67 nanocrystals were prepared using a conventional solution method. Zeolite-like imidazole framework materials (ZIFs) are a type of MOF, characterized by abundant pore structure, high specific surface area, high metal ion site density, and naturally occurring heteroatoms (N, S, P) in the ligands. ZIF-67, with Co as the metal center, is cross-linked with an organic imidazole ester to form a polyhedral framework structure. Because its organic ligand, 2-methylimidazolium, contains a large amount of nitrogen, it can be pyrolyzed at high temperature in an inert atmosphere to obtain nitrogen-doped Co-based porous carbon materials, which can then be used as electrocatalysts.

[0020] Further, the conventional solution method involves dissolving 12 mmol of 2-methylimidazole (2-MeIM) in 30 mL of methanol to form a homogeneous solution A; dissolving 3 mmol of cobalt nitrate hexahydrate and 1 mmol of manganese nitrate hexahydrate in 30 mL of methanol to form a homogeneous solution B; slowly pouring solution A into solution B and magnetically stirring at room temperature for 30 min; centrifuging to obtain a purple precipitate; washing three times with methanol; and drying at 60 °C for 12 h to obtain MnCo-ZIF-67.

[0021] Furthermore, the catalyst layer is prepared by grinding MnCo / NC nitrogen-doped bimetallic carbon composite organic material for 30-35 minutes, weighing 40 mg of fine powder and placing it into a centrifuge tube, then adding 400 μL of ethanol, 100 μL of distilled water, and 25 μL of Nafion solution, and ultrasonically vibrating until the catalyst is evenly diffused in the solution, then coating it on the other side of the base electrode layer, and drying it at room temperature for 24 hours to form a dense catalyst layer.

[0022] The advantages of this invention over the prior art are:

[0023] 1. Filtering slime flocs, organic and inorganic impurities, and metals. In this method, the porous membrane electrode structure made of organic composite carbon material can filter large particles of biological slime flocs, as well as organic and inorganic impurities in the cooling water sprayed from the spray device. This reduces the nutrients required for microbial growth in the circulating cooling water collection tank, thereby reducing the number of microorganisms in the collection tank and preventing the formation of biological slime in the pipe network.

[0024] 2. In this method, the metal-organic composite microbial electrocoupling porous membrane structure can spontaneously adsorb microorganisms. Charged microorganisms in the water are adsorbed into the microporous structure of the anode through electrochemical action, without the need for an external power source. The entire circuit can be considered a battery structure, with the microorganisms generating their own electricity. The microorganisms adsorbed in the anode are desorbed and removed using a saturated activated carbon ultrasonic regeneration method. The working mechanism involves generating high-energy cavitation bubbles in the solution through ultrasonic cavitation. The high-pressure impact energy generated by the bursting of these bubbles effectively separates the organic matter attached to the activated carbon surface through pyrolysis and oxidation.

[0025] 3. With the present invention, the circulating cooling water does not need to be filtered through a separate bypass. The porous membrane electrode structure of organic composite carbon material is simply placed on the surface of the water in the cooling tower's water collection pool, which is easy to implement and saves energy.

[0026] 4. This invention can effectively inhibit the growth of algae in the cooling tower water collection pool. The porous membrane electrode structure of metal-organic composite material is located on the water surface of the water collection pool, which can effectively block the sunlight entering from the air inlet of the cooling tower, so that the algae in the water collection pool lose the necessary conditions for growth, thereby inhibiting the growth of algae.

[0027] 5. This invention can effectively reduce microorganisms and biological slime in circulating cooling water, thereby reducing the amount and frequency of bactericide use in existing processes, and greatly reducing the pollution of water bodies by sewage discharged from the pipeline network.

[0028] 6. The air cathode electrode material in this invention exhibits excellent performance. Compared to traditional materials, MOFs possess significantly larger specific surface area, porosity, and pore volume. Their structure and size are adjustable; MOF materials of different sizes can be obtained by changing the preparation temperature. The pore structure is relatively regular and possesses a certain degree of rigidity. They are low-cost and simple to prepare using convenient hydrothermal or ultrasonic methods. They can be functionalized; by adding different functional groups, MOF materials with varying properties can be obtained, containing abundant metal active sites.

[0029] 7. In this invention, the MOF material is a MnCo / NC nitrogen-doped bimetallic carbon composite organic material. The kinetics of oxygen evolution and oxygen reduction reaction (OER / ORR) inherent in the air cathode are faster than those of ordinary electrodes, with higher energy density and good stability. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the membrane structure of the present invention;

[0031] Figure 2 This is a schematic diagram of a conventional hyperbolic cooling tower structure;

[0032] Among them, 1-diffusion layer, 2-basic electrode layer, 3-catalyst layer, 4-anode layer, 5-lower ring beam, 6-cylinder wall, 7-tower top rigid ring, 8-inclined support column, 9-water distribution tank, 10-water spraying device, 11-heat exchange packing, 12-water collection tank;

[0033] Figure 3 This is a schematic diagram of the metal mesh fixing cathode layer and anode layer of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0035] Example 1:

[0036] An environmentally friendly method for controlling biofilm in conventional cooling towers includes a metal-organic composite microbial electrocoupling porous membrane structure. This structure comprises, from bottom to top, an anode layer 4 and a cathode layer. The anode layer 4 is made of activated carbon fiber felt. The cathode layer, from bottom to top, comprises three layers: a catalyst layer 3, a base electrode layer 2, and a diffusion layer 1. The diffusion layer 1 is made of PTFE. The catalyst layer 3 is made of MnCo / NC nitrogen-doped bimetallic carbon composite organic material. The base electrode layer 2 is made of porous carbon material with an internal honeycomb structure featuring interconnected macropores. The cathode catalyst layer 3 is attached to one side of the cathode base electrode layer 2 by brushing, and the diffusion layer 1 is attached to the other side of the base electrode layer 2 by brushing. After brushing, the anode layer 4 and the cathode layer are fixed by wire weaving or hot pressing. The membrane structure can be prepared into several 2m*1m rectangles according to the size of the water collection tank 12 and laid flat on the water surface of the water collection tank 12 at the bottom of the conventional cooling tower. The thickness of the anode layer 4 is 5mm, and the thickness of the cathode base layer is 5mm.

[0037] The diffusion layer 1 is prepared by: uniformly brushing 40% polytetrafluoroethylene emulsion onto the base electrode layer 2, preventing it from being applied to the other side, removing small air bubbles and polytetrafluoroethylene clumps remaining on the surface, air-drying the coating for more than 10 minutes until the surface turns white, placing it in a muffle furnace to dry at 360-380°C for more than 20 minutes, repeating the above operation 4-5 times to form 4-5 dense diffusion layers 1.

[0038] The MnCo / NC nitrogen-doped bimetallic carbon composite organic material was prepared by high-temperature pyrolysis of the precursor MnCo-ZIF-67 nanocrystals at 800–850 °C, with a heating rate of 5 °C·min. -1 After holding at the temperature for 2 hours, it is cooled to room temperature along with the furnace.

[0039] The bimetallic MnCo-ZIF-67 nanocrystals were prepared by a conventional solution method. Zeolite-like imidazole framework materials (ZIFs) are a type of MOF, characterized by abundant pore structures, high specific surface area, high metal ion site density, and naturally occurring heteroatoms (N, S, P) in the ligands. ZIF-67, in particular, uses Co as the metal center and crosslinks with an organic imidazole ester to form a polyhedral framework structure. Because its organic ligand, 2-methylimidazolium, contains a large amount of nitrogen, it can be pyrolyzed at high temperatures in an inert atmosphere to obtain nitrogen-doped Co-based porous carbon materials, which can then be used as electrocatalysts.

[0040] The conventional solution method involves dissolving 12 mmol of 2-methylimidazole (2-MeIM) in 30 mL of methanol to form a homogeneous solution (denoted as solution A); and dissolving 3 mmol of cobalt nitrate hexahydrate and 1 mmol of manganese nitrate hexahydrate in 30 mL of methanol to form a homogeneous solution (denoted as solution B). Solution A is then slowly poured into solution B and magnetically stirred at room temperature for 30 min. The mixture is centrifuged to obtain a purple precipitate, which is washed three times with methanol and finally dried at 60 °C for 12 h to obtain MnCo-ZIF-67.

[0041] The catalyst layer 3 material, MnCo / NC nitrogen-doped bimetallic carbon composite organic material, is coated by grinding the cathode catalyst for about 30 minutes, weighing 40 mg of fine powder and placing it in a centrifuge tube, then adding 400 μL of ethanol, 100 μL of distilled water, and 25 μL of Nafion solution, and ultrasonically vibrating until the catalyst is evenly diffused in the solution. The coating is then applied to the other side of the cathode base electrode layer 2 and dried at room temperature for 24 hours to form a dense catalyst layer 3.

[0042] After the cooling tower uses the metal-organic composite microbial electrocoupling porous membrane structure of the present invention, the COD of the cooling water in the water collection tank 12 is reduced. Cr From 1.0×10 2 Reduced to 0.3×10 2 Below these parameters, the removal rate is greater than 70%; turbidity is maintained below 3 NTU; and the microbial adhesion rate is ≤10 mg / (cm³). 2 (month); biological slime content ≤2.5ml / m 3 Total heterotrophic bacteria count ≤ 1×10 5The concentrations per mL were all below the levels specified in GB50050—2007 "Design Code for Industrial Circulating Cooling Water Treatment" and DB37 / T1575-2010 "Water Quality Standard for Circulating Cooling Water in Power Plants".

[0043] The algae and moss on the inner wall of the collection tank 12 were significantly reduced, the rate of biological slime deposition inside the condenser and heat exchanger was slowed down, and at the same time the amount of drug added was reduced to less than 30% of the original amount. The water quality can be maintained at the same level as before the application of the metal-organic composite microbial electrocoupled porous membrane structure of this invention, thus reducing the pollution of the environment by drugs in the discharged wastewater.

Claims

1. An environmentally friendly method for controlling biological slime in conventional cooling towers, characterized in that: The method is as follows: a metal-organic composite microbial electrocoupling porous membrane structure is placed in the water collection tank of a conventional cooling tower; The metal-organic composite microbial electrocoupling porous membrane structure includes an anode layer and a cathode layer. The cathode layer includes a catalyst layer, a base electrode layer, and a diffusion layer. The catalyst layer and diffusion layer are respectively coated on both sides of the base electrode layer. The anode layer and cathode layer are fixed by means of metal wire weaving or hot pressing. The sides of the anode layer and cathode layer coated with the catalyst layer are adjacent. The anode layer is made of activated carbon fiber felt, the diffusion layer is made of PTFE, the catalyst layer is made of MnCo / NC nitrogen-doped bimetallic carbon composite organic material, and the base electrode layer is made of porous carbon material with an internal honeycomb morphology structure of interpenetrating macropores.

2. The method for controlling biological slime in an environmentally friendly conventional cooling tower according to claim 1, characterized in that: The diffusion layer is prepared by uniformly brushing 40% polytetrafluoroethylene emulsion onto the base electrode layer. To prevent the coating from being applied to the other side, small air bubbles and polytetrafluoroethylene clumps on the surface are removed. After the coating has been air-dried for more than 10 minutes until the surface turns white, it is placed in a muffle furnace and dried at 360~380℃ for more than 20 minutes. The above operation is repeated 4~5 times to form 4~5 dense diffusion layers.

3. The method for controlling biological slime in an environmentally friendly conventional cooling tower according to claim 1, characterized in that: The catalyst layer material is prepared by pyrolyzing the precursor MnCo-ZIF-67 nanocrystals at a high temperature of 800~850℃, with a heating rate of 5℃·min. -1 After holding at the temperature for 2 hours, it is cooled to room temperature with the furnace.

4. The method for controlling biological slime in an environmentally friendly conventional cooling tower according to claim 3, characterized in that: The MnCo-ZIF-67 nanocrystals were prepared by a conventional solution method.

5. The method for controlling biological slime in an environmentally friendly conventional cooling tower according to claim 4, characterized in that: The conventional solution method involves dissolving 12 mmol of 2-methylimidazole (2-MeIM) in 30 mL of methanol to form a homogeneous solution A; dissolving 3 mmol of cobalt nitrate hexahydrate and 1 mmol of manganese nitrate hexahydrate in 30 mL of methanol to form a homogeneous solution B; slowly pouring solution A into solution B and magnetically stirring at room temperature for 30 min; centrifuging to obtain a purple precipitate; washing three times with methanol; and drying at 60 °C for 12 h to obtain MnCo-ZIF-67.

6. The method for controlling biological slime in an environmentally friendly conventional cooling tower according to claim 1, characterized in that: The catalyst layer is prepared by grinding MnCo / NC nitrogen-doped bimetallic carbon composite organic material for 30-35 min, weighing 40 mg of fine powder and placing it into a centrifuge tube, then adding 400 µL of ethanol, 100 µL of distilled water and 25 µL of Nafion solution, and ultrasonically vibrating until the catalyst is evenly diffused in the solution. The catalyst is then coated on the other side of the base electrode layer and dried at room temperature for 24 h to form a dense catalyst layer.

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