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Centrifuge Special Introduction | Horizontal Piston Discharge Centrifuge

Centrifuge Special Introduction | Horizontal Piston Discharge Centrifuge

Horizontal piston discharge centrifuge is a kind of automatic operation, continuous operation, pulsating discharge filter centrifuge, which completes the processes of feeding, separation, filter cake washing, drying and discharging at full speed. The biggest difference between horizontal piston discharge centrifuge and scraper discharge centrifuge is the discharging form. The discharging of piston discharge centrifuge is completed by the reciprocating motion of the piston. Working principle 01 After the rotating drum runs at full speed, the suspension enters the conical hopper installed on the pushing plate through the feeding pipe. Under the action of centrifugal force, the suspension enters the rotating drum evenly through the hopper. The filtrate is thrown out of the rotating drum through the screen gap and the filter holes on the rotating drum wall, and the solid phase is retained on the screen to form a cylindrical filter cake layer. The pushing plate reciprocates under the control of the hydraulic system. When the pushing plate moves forward, the filter cake layer is pushed forward for a certain distance. After the pushing plate moves backward, a new filter cake layer is formed on the empty screen. Due to the continuous reciprocating motion of the pushing plate, the filter cake layer is continuously pushed forward along the axis of the rotating drum wall and finally discharged from the rotating drum. It is discharged through the slag outlet of the casing. The liquid phase is collected in the casing and discharged through the discharge port at the bottom or side of the casing. If the filter cake needs to be washed in the machine, the washing liquid can be continuously sprayed onto the filter cake layer through the washing liquid pipe or other washing equipment, and the washing liquid and the separated liquid are discharged together from the discharge port. Structure type and operation method 02 The structural types of horizontal piston discharge centrifuges can be divided into: horizontal single-stage piston discharge centrifuge, horizontal double-stage piston discharge centrifuge and horizontal column/cone double-stage piston discharge centrifuge. To improve the separation effect of the piston discharge centrifuge, it is necessary to ensure the residence time of the separated materials in the rotating drum. Therefore, the rotating drum of the single-stage piston discharge centrifuge should have sufficient length. However, with the increase of the drum length, the resistance of pushing the filter cake layer also increases, and it is often due to the insufficient thickness of the filter cake layer that the material arches or accumulates, which destroys the separation, washing and normal discharging of the filter cake. In order to prevent the filter cake layer from producing the above phenomena, it is necessary to increase the thickness of the filter cake layer while increasing the length of the rotating drum, but this will reduce the dehydration and washing effect of the centrifuge, so the length of the rotating drum cannot be increased indefinitely. Horizontal double-stage piston discharge centrifuge has double-stage rotating drums, each of which can be shortened, while the total length of the two rotating drums is greater than that of the single-stage piston discharge centrifuge. Therefore, when ensuring the same filter cake residence time, the filter cake layer can be correspondingly thinned, and when the filter cake is pushed from the upper rotating drum to the lower rotating drum, it is loosened, which is conducive to improving the separation, dehydration and washing effect. Horizontal double-stage piston discharge centrifuge can effectively improve the separation factor of the centrifuge and improve the filtration driving force. Compared with horizontal single-stage piston discharge centrifuge, horizontal double-stage piston discharge centrifuge has the advantages of wide adaptability, low filter cake moisture content, sufficient washing and low unit energy consumption. The small rotating drum of the horizontal column/cone double-stage piston discharge centrifuge is cylindrical, and the large rotating drum, i.e., the secondary rotating drum, is column/cone shaped. When the filter cake removes part of the water in the first-stage rotating drum and enters the second-stage column/cone rotating drum, it is not only loosened, but also when the filter cake enters the conical part of the second-stage rotating drum, the filter cake layer becomes thinner with the increase of the radius, and the dehydration effect is better. In the separation process of this centrifuge, separation, dehydration and dehydration can be realized. Therefore, when the horizontal column/cone double-stage piston discharge centrifuge is used to separate the mixture of liquid and solid phases, the final filter cake moisture content is 2%~4% lower than that of the ordinary double-stage piston discharge centrifuge, and the output can be increased by 20%~30%, and the unit energy consumption is also correspondingly reduced. Model selection principles 03 ①Under the condition of determining the selection of filter centrifuge, if continuous operation and large output are required, horizontal piston discharge centrifuge should be selected. ②Materials with a mass fraction of 30%~80% can be selected for horizontal piston discharge centrifuge. The higher the solid content in the suspension, the greater the production capacity. In actual production, materials with low concentration can use pre-concentration equipment, such as cyclone separators, sedimentation tanks, thickeners, or add pre-concentration devices to the piston discharge centrifuge itself to meet the separation requirements of horizontal piston discharge centrifuge. ③The larger the particle size of the solid phase of the material processed by the horizontal piston discharge centrifuge, the better. The crystal particles are required to have a certain shape, and under the action of centrifugal force, they can maintain sufficient drainage channels. The horizontal piston discharge centrifuge requires that the average particle size of the material crystals should be greater than 180μm, and the material viscosity should be less than 0.1Pa·S. When high requirements are put forward for the moisture content of the filter cake or the washing of the filter cake, horizontal double-stage piston discharge centrifuge or column/cone double-stage piston discharge centrifuge can be selected. ④The possibility of crystal breakage in horizontal piston discharge centrifuge is relatively large. For products with strict requirements on crystal particle size and shape, the selection of this equipment should be carefully considered. ⑤Horizontal piston discharge centrifuge has certain requirements for the strength of the filter cake. When the consolidation strength of the filter cake layer is insufficient, the filter cake will bulge and accumulate, resulting in the failure of the equipment to operate normally. ⑥Double-stage piston discharge centrifuge is suitable for separating suspensions of medium-sized crystalline or short-fiber materials, especially those that need to be washed in the machine. The requirements for materials of horizontal double-stage piston discharge centrifuge are not as strict as those of single-stage piston discharge centrifuge, but the feeding concentration should be stable, the feeding should be uniform, and the average particle size of the solid phase is 0.1~3mm. ⑦Horizontal column/cone double-stage piston discharge centrifuge is suitable for separating materials separated by ordinary horizontal double-stage piston discharge centrifuge, and also suitable for separating fine crystalline particles. The requirements for feeding concentration and temperature are the same as those of horizontal single-stage and double-stage piston discharge centrifuges.

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2023

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07

Comprehensive analysis of reverse osmosis membrane fouling and solutions

Comprehensive analysis of reverse osmosis membrane fouling and solutions

I. Reverse Osmosis Membrane Fouling 1. Damage to the performance of the reverse osmosis membrane, resulting in membrane fouling (1) Polyester material reinforced non-woven fabric, approximately 120μm thick; (2) Polysulfone material porous intermediate support layer, approximately 40μm thick; (3) Polyamide material ultra-thin separation layer, approximately 0.2μm thick. Based on its performance structure, the possible reasons for damage to the reverse osmosis membrane performance may include: (1) Non-standard maintenance of new reverse osmosis membranes; (2) Storage time exceeding 1 year under compliant maintenance; (3) Non-standard maintenance of reverse osmosis membranes in the shutdown state; (4) Ambient temperature below 5℃; (5) System operating under high pressure; (6) Improper shutdown operation. 2. Frequent changes in water quality resulting in membrane fouling Changes in raw water quality compared to the design water quality increase the pretreatment load. Due to the increase in inorganic substances, organic substances, microorganisms, particulate matter, and colloids in the influent, the probability of membrane fouling increases. 3. Untimely cleaning and incorrect cleaning methods resulting in membrane fouling During use, in addition to the normal attenuation of membrane performance, untimely cleaning and incorrect cleaning methods are also important factors leading to severe membrane fouling. 4. Incorrect addition of chemicals In the use of composite polyamide membranes, because polyamide membranes have poor resistance to residual chlorine, the incorrect addition of disinfectants such as chlorine during use, coupled with insufficient user attention to microbial prevention, easily leads to microbial contamination. 5. Membrane surface wear Membrane elements are blocked by foreign objects or the membrane surface is worn (such as sand grains), in which case the detection method should be used to detect the elements in the system, find the damaged elements, modify the pretreatment, and replace the membrane elements. II. Phenomena of Reverse Osmosis Membrane Fouling During reverse osmosis operation, due to the selective permeability of the membrane, certain solutes accumulate near the membrane surface, resulting in membrane fouling. Common fouling signs include: one is biological fouling (symptoms appear gradually) organic deposits are mainly living or dead microorganisms, hydrocarbon derivatives, natural organic polymers, and all carbon-containing substances. Initially manifested as increased desalination rate, increased pressure drop, and reduced water production. Then there is colloidal fouling (symptoms appear gradually) during membrane separation, the concentration of metal ions and changes in solution pH may cause metal hydroxide (mainly represented by Fe(OH)3) deposition, causing fouling. Initially manifested as a slight decrease in desalination rate, gradually increasing, and finally increased pressure drop and reduced water production. There is also particulate fouling. During the operation of the reverse osmosis system, if the security filter has problems, it will cause particulate matter to enter the system, causing particulate fouling of the membrane. Initially manifested as an increase in concentrate flow rate, little change in desalination rate in the initial stage, gradually decreasing water production, and a rapid increase in system pressure drop. Finally, there is also chemical scaling (symptoms appear quickly) when the feed water contains high concentrations of Ca2+, Mg2+, HCO3-, CO32-, SO42-, etc., CaCO3, CaSO4, MgCO3, etc., will be deposited on the membrane surface. It is manifested by a decrease in desalination rate, especially in the last section, and a decrease in water production. Membrane fouling is the main reason for the decrease in membrane permeation flux. This includes the blockage of membrane channels and macromolecular solutes, causing an increase in membrane filtration resistance; solute adsorption on the inner walls of the pores; and the formation of a gel layer on the membrane surface, increasing mass transfer resistance. The deposition of components in the membrane pores will cause the membrane pores to shrink or even become blocked, effectively reducing the effective area of the membrane. The additional resistance generated by the fouling layer formed by the deposition of components on the membrane surface may be much greater than the resistance of the membrane itself, making the permeation flux independent of the membrane's own permeability. This effect is irreversible and the degree of fouling is related to the membrane material, the solvent in the retained liquid, the concentration, properties, solution pH, ionic strength, charge composition, temperature, and operating pressure of macromolecular solutes, etc. When the fouling is severe, the membrane flux can decrease by more than 80%. In system operation, membrane fouling is a very thorny problem. Its occurrence causes a significant decrease in the removal rate, water permeability, and membrane flux of the reverse osmosis device, while increasing the operating pressure of each section, increasing operating and maintenance costs, and seriously affecting the service life of the membrane and the development and utilization of reverse osmosis technology. III. Solutions 1. Improve pretreatment For each membrane device, people hope that it can play its role to the maximum extent, hoping for the highest desalination rate, the largest water permeability, and the longest possible lifespan. To achieve the above three points, the water quality is crucial. Therefore, the raw water entering the membrane device must have good pretreatment. Reasonable pretreatment is very important for the long-term safe operation of the reverse osmosis device. With pretreatment that meets the reverse osmosis feed water quality requirements, it is possible to ensure that the water production rate remains stable; the desalination rate remains at a certain value for a long time; the product water recovery rate can remain unchanged; the operating costs are minimized; and the membrane service life is longer, etc. Specifically, reverse osmosis pretreatment is to: (1) Prevent surface fouling of the membrane, i.e., prevent suspended impurities, microorganisms, colloidal substances, etc., from adhering to the membrane surface or blocking the water flow channels of the membrane elements. (2) Prevent scaling on the membrane surface. During the operation of the reverse osmosis device, due to water concentration, some sparingly soluble salts are deposited on the membrane surface, so it is necessary to prevent the formation of these sparingly soluble salts. (3) Ensure that the membrane is free from mechanical and chemical damage to ensure that the membrane has good performance and a sufficiently long service life. 2. Clean the membrane Even though the slurry undergoes various pretreatment measures, after long-term use, deposits and scaling may still occur on the membrane surface, causing the membrane pores to become blocked and the water production to decrease. Therefore, it is necessary to periodically clean the fouled membrane. However, the reverse osmosis membrane system cannot wait until the fouling is very serious before cleaning, as this will increase the cleaning difficulty, increase the number of cleaning steps, and prolong the cleaning time. It is necessary to correctly grasp the cleaning time and remove the fouling in time. Cleaning principles: Understand the characteristics of local water quality, perform chemical analysis of pollutants, and use the results to select the best cleaning agent and cleaning method to provide a basis for finding the best method under specific feed water conditions; Cleaning conditions: a. Product water volume is 5%-10% lower than normal. b. To ensure product water volume, the feed water pressure after temperature correction is increased by 10%-15%. c. The conductivity (salt content increase) of the permeate water increases by 5%-10%. d. Multi-stage RO system, the pressure drop in different stages increases significantly. Cleaning methods: First perform system backwashing; then perform negative pressure cleaning; perform mechanical cleaning if necessary; then perform chemical cleaning; ultrasonic cleaning is possible if conditions permit; online electric field cleaning is a good method, but it is expensive; because chemical cleaning has a better effect, other methods are somewhat difficult to implement, and although the names and methods of use of the chemicals provided by various suppliers are different, their principles are roughly the same. For example, our company currently uses membrane cleaning agents MC2 and MA10. Cleaning steps: Cleaning a single-stage system: (1) Prepare the cleaning solution; (2) Low-flow input of the cleaning solution; (3) Circulation; (4) Immersion; (5) High-flow pump circulation; (6) Rinsing; (7) Restart the system. Cleaning for specific pollutants includes: cleaning sulfate scale, cleaning carbonate scale, cleaning iron and manganese pollution, cleaning organic pollution, etc. III. Proper Maintenance of the Membrane Maintenance of new reverse osmosis membranes New reverse osmosis membrane elements are usually immersed in a 1% NaHSO3 and 18% glycerol aqueous solution and stored in sealed plastic bags. If the plastic bag is not broken, storage for about 1 year will not affect its lifespan and performance. When the plastic bag is opened, it should be used as soon as possible to avoid adverse effects on the elements due to the oxidation of NaHSO3 in the air. Therefore, the membrane should be opened before use as much as possible. During non-production periods, the maintenance of the reverse osmosis system is a relatively important issue. It can be carried out according to the following methods. (1) System shutdown for a short period (1-3 days): Before shutdown, first rinse the system at low pressure (0.2-0.4 MPa) and high flow rate (approximately equal to the system's water production), for 14-16 minutes; maintain the normal natural water flow and allow the water to flow into the concentrate channel. (2) System shutdown for more than one week (ambient temperature above 5℃): Before shutdown, first rinse the system at low pressure (0.2-0.4 MPa) and high flow rate (approximately equal to the system's water production), for 14-16 minutes; perform chemical cleaning according to the methods for chemical cleaning of the system in the reverse osmosis system operating instructions; after the chemical cleaning is completed, rinse the reverse osmosis membrane clean; prepare a 0.5% formalin solution, input it into the system at low pressure, and circulate for 10 minutes; close all system valves and seal; if the system is shut down for more than 10 days, the formalin solution must be replaced every 10 days. (3) Ambient temperature below 5℃: Before shutdown, first rinse the system at low pressure (0.2-0.4 MPa) and high flow rate (approximately equal to the system's water production), for 14-16 minutes; where conditions permit, the ambient temperature can be raised to above 5℃, and then the system can be maintained according to method 1; if there are no conditions to raise the ambient temperature, then: low pressure (0.1 MPa), flow rate is 1/3 of the system's water production, long flow to prevent the reverse osmosis membrane from being frozen, and ensure that the system runs for 2 hours every day; after cleaning the reverse osmosis membrane according to methods (2) and (3) in 1, remove the reverse osmosis membrane, move it to a place where the ambient temperature is greater than 5℃, and immerse it in a prepared 0.5% formalin solution, turning it over every two days; the water in the system pipes should be drained to prevent damage to the system due to freezing. IV. Avoid Operation of the Membrane Under High Pressure Residual gas remains in the system during startup and shutdown, causing the system to operate under high pressure. The pressure gauges before and after the filter in the system are used to monitor the pressure drop of the filter element, while the primary and final pressure gauges are used to monitor the pressure drop of the RO membrane module. Adjust the feed water valve and concentrate water valve to ensure operating pressure and recovery rate. If the water production flow rate or total flow rate decreases during operation, or if the pressure difference between the primary and intermediate stages increases significantly compared to the initial pressure difference during operation (using the initial operating data of the new reverse osmosis membrane module as the standard), the system needs to be rinsed or cleaned to ensure the performance and safety of the membrane module. (1) After the equipment is drained, when restarting, the gas is not completely discharged before rapid pressurization operation. The remaining air should be discharged under system pressure before gradually increasing the pressure. (2) When the joint between the pretreatment equipment and the high-pressure pump is poorly sealed or leaking (especially when the micrometer filter and the subsequent pipeline are leaking), when the pretreatment water supply is insufficient, such as when the micrometer filter is blocked, some air will be sucked in due to the vacuum at the poorly sealed location. The micrometer filter should be cleaned or replaced to ensure that the pipeline does not leak. (3) Whether the operation of each pump is normal, whether the flow rate is the same as the specified value, and compare it with the pump operation curve to determine the operating pressure. V. Pay Attention to Shutdown Operations (1) Rapid depressurization during shutdown without thorough rinsing. Since the concentration of inorganic salts on the concentrate side of the membrane is higher than that of the raw water, it is easy to scale and foul the membrane. When preparing to shut down, gradually reduce the pressure to about 3 bar and rinse with pretreated water for 14-16 minutes. (2) Adding chemical reagents when preparing to shut down will cause the reagents to remain in the membrane and membrane shell, causing membrane fouling and affecting the service life of the membrane. It should be stopped.

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2023

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07

Beijing plans to liberalize the government pricing of reclaimed water: users of reclaimed water will not pay water resource taxes and sewage treatment fees.

Beijing plans to liberalize the government pricing of reclaimed water: users of reclaimed water will not pay water resource taxes and sewage treatment fees.

13

2023

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07

【Dry Goods】A Comprehensive Analysis of Lithium Extraction Technology

【Dry Goods】A Comprehensive Analysis of Lithium Extraction Technology

11

2023

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07

This article thoroughly explains the methods for budgeting the costs of wastewater treatment plants

This article thoroughly explains the methods for budgeting the costs of wastewater treatment plants

06

2023

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07

What salinity level constitutes high-salinity wastewater? Below what salinity level can biological treatment be applied?

What salinity level constitutes high-salinity wastewater? Below what salinity level can biological treatment be applied?

05

2023

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07

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