Applications-Nonwoven Spunlace Wastewater treatment

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What is spunlace nonwoven process?

The spunlaced nonwoven process is a process that uses water as a medium to convert energy so that the fibers in the fiber web are entangled and entangled with each other and reinforced. It consumes a lot of water. A 3.5 m wide production line generally requires 100 to 300 t/h of water, so the process water is recycled. At the same time, the water pressure is generated by the tiny pinholes of the water needle plate (the hole diameter of the water needle plate is generally 0.08 ~ 0.12 mm). The requirements for water quality, especially particulate matter in the water, are very high, so the production line's water treatment process and system accuracy are exceptionally high. Important.

The spun lace unit mainly comprises a water circulation system and a fiber mesh reinforcement system. The water circulation system mainly includes water filtration, pressurization, spun lace, recovery, and other devices. Filtration generally adopts multi-stage water filtration and applies different methods, and ultimately, impurities with diameters as small as 20 μm must be filtered out. Nowadays, the most mature method widely used and proven to be the best is air flotation + sand filtration + secondary filtration + safety filtration.

Why does spunlace nonwoven production use air flotation?

During the spun lace production process, when high-pressure water needles impact the fiber web, the fibers will fall off. The fibers will enter the water, and the various oils (auxiliary agents) and microorganisms in the water will affect the water quality, causing the water needle plate to be clogged, which will not only affect the production efficiency. It also affects the quality and appearance of the product, so the water circulation filtration system is an integral part of the spunlace process.

The circulation pump sends the recycled water after spun lace to the air flotation tank. After air flotation filtration, it is sent to the sand filter. The filtered water is then sent to the bag filter for fine filtration by the filtered water pump. After the above multi-stage filtration treatment, The water meets the requirements for the production process. It enters the water storage tank for recycling with the supplemented fresh water. In the entire water treatment process, air flotation plays a vital role in subsequent layers of filtration.

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Application of air flotation method in the production of spunlace nonwoven materials

Among the many air flotation methods, partial reflux dissolved air flotation is the most suitable process in water treatment. Partial reflux dissolved air flotation directly introduces all the fluid into the flocculation tank or flotation tank (when flocculation is not used). Part of the flotation water or filtered water is dissolved into the air under pressure until it is saturated and then circulated back to the air flotation tank. In the floating tank reaction area, the bubble release device instantly reduces the pressure, thereby forming many fine bubbles (20-100 μm in diameter). The bubbles are adsorbed by fibers, solids, and emulsified oil in the water in the reaction tank, forming foam, water, and particles (oil ) in a three-phase mixture that floats to the water's surface. Therefore, the air flotation method used in hydroentangling production belongs to the partial reflux dissolved air flotation method.

Schematic diagram of an efficient air flotation device used for circulating water treatment in the production of spunlace nonwoven materials

High-efficiency partial reflux dissolved air flotation composition

The high-efficiency air flotation device mainly consists of two parts:

(1) Pressurized dissolved air and release system, including pressurized air pump, water ejector, dissolved air tank, dissolved air pipe, high-efficiency air flotation nozzle, etc. The water ejector is drawn from the dissolved air tank or the adding water. The water from the outlet pipe of the pressure pump is used as injection water. Through the adjustment of the water inlet valve of the water ejector, an appropriate amount of air can be sucked into the dissolved air tank;

(2) Air flotation tank, including water inlet, adsorption, separation, slag scraping, drainage, and other parts.

Other supporting devices vary according to the water quality of the treated water. They mainly include sewage water pumps (depending on the head of the incoming water), coagulation reaction tanks, dispensing and dosing devices (depending on the water quality needs), and scum (oil) treatment plants.
Treatment device (post-treatment methods vary depending on water quality and user requirements).
The working principle of the high-efficiency air flotation device is through a pressurized dissolved air pump, the working water is pumped into the dissolved air tank, and the air is dissolved in the water in the tank. The form of bubbles is released, and numerous microbubbles adsorb, condense, and float to the water surface with the suspended solids in the water being treated. The slag scraping device scraps the floating solids (slag or oil), thereby purifying water quality. When the pressure is 0.3 MPa, the air in water at 20°C is 62 ml/L, while the solubility at normal pressure is 20 ml/L.

Application case

Case Studies-Nonwoven Spunlace Wastewater Treatment

The Hangzhou Nbond Nonwovens Co., Ltd project uses high-efficiency dissolved air flotation produced by our company for pretreatment to reduce the content of organic matter and suspended matter in the landfill leachate. After air flotation pretreatment, the suspended matter concentration removal rate reaches over 90%. The grease removal rate reaches over 95%, significantly reducing the burden of subsequent biochemical treatment.

Application of flotation agents and flocculants in hydroentanglement production

There are various pollutants in wastewater, including hydrophobic fibers (substances) and hydrophilic fibers (substances).

Hydrophobic substances are not easily wetted by water; they quickly air bubbles and float easily.

The surface of particles with strong hydrophilicity is hydrophilic, easy to be wetted by water, and challenging to adhere to bubbles for flotation.

Therefore, it is necessary to hydrophobicize them, add chemicals to interact with the particle surface, and reduce the particle-aqueous solution interface. Particle-air interface free energy improving floatability. This kind of agent that can enhance the palatability of particles is called a flotation agent. Flotation agents are generally organic substances containing hydrophilic (polar) and hydrophobic (non-polar) groups, such as stearic acid, fatty acids, salts, amines, etc. Taking stearic acid (C₁₇H₃₅COOH) as an example, -C₁₇H₃₅ is a hydrophobic group, and -COOH is a hydrophilic group. The hydrophilic group can be selectively adsorbed on the surface of suspended particles.

In contrast, the hydrophobic group faces towards the outside, thereby converting the hydrophilic particle surface into a hydrophobic surface and adhering to the air bubbles. Therefore, stearic acid can reduce the wettability of the particle surface, increase the floatability index of suspended particles, and improve the ability of particles to adhere to the bubble surface. Usually, the flocculation process of colloid particles aggregating with each other through the action of a double electric layer and the flocculation process of colloid particles bonding with each other through the adsorption and bridging effect of high molecular polymer are collectively called flocculation. Flocculants are substances that can make colloidal particles in water stick to each other. Flocculants destroy the stability of colloids and promote flocculation. They are divided into inorganic flocculants and organic flocculants.

The organic flocculant often used in hydroentanglement production is polyacrylamide, a high-polymerization polymer flocculant. It has the characteristics of fast coagulation speed, low dosage, and large and challenging floc particles. It is often combined with iron salts. , aluminum salt combined. Commonly used inorganic flocculants are mostly aluminum salts, among which poly aluminum chloride has a strong adsorption capacity for suspended solids in water and has strong adaptability to high turbidity water, industrial wastewater, organic sewage, special water with radioactive substances, etc. There is no need to add other additives, and its water purification effect is 4 to 6 times that of aluminum sulfate and 3 to 5 times that of crystalline aluminum chloride (aluminum trichloride). The degree of water pollution in hydroentanglement filtration is relatively low, so crystallized aluminum chloride (trichloride) is often used.

The amount of flocculant added is mainly determined by the different products. Usually, when producing sanitary materials, the dripping amount is more significant than that of conventional products due to stricter product requirements. The amount of flocculation added is also substantial when producing pure cotton and wood pulp composite products because there are more fiber scraps and other impurities, and the product quality requirements are high. At the same time, the amount of fresh water added to the circulating water is increased to ensure the circulating water. Microbiological indicators and prevent the water needle plate from being blocked.

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Advantages of air flotation in spunlace production

It has been measured that the water turbidity before air flotation filtration is 30°, the water turbidity after air flotation filtration is about 2°, and the turbidity is significantly reduced.

As the first filtration method of the spunlaced circulating water filtration system, air flotation filtration, on the one hand, improves the water purification effect of the entire filtration system and reduces the amount of freshwater added; on the other hand, the reduction in turbidity minimizes the impact on the water needle plate It prevents the water needle plate from being clogged and causing water needles to cross, resulting in dense lines, which significantly improves the surface smoothness and mechanical strength of spunlace products.

Air flotation technology reduces production costs, improves product quality, saves water resources, and has good economic and social benefits.

In the process of processing circulating water for spun lace, the high-efficiency air flotation nozzle designed based on the "differential energy dissipation and gas release principle" can produce microbubbles with a diameter of about one μm, a density that is more than 1,000 times higher than conventional ones, and good uniformity. The dissolved gas utilization rate is close to 100%. High-efficiency Dissolved Air Flotation has a solid ability to eliminate oil stains and emulsions. The chemical oxygen demand (COD) removal rate is 50. 5%, the tar removal rate is 59. 6%, and the tar recovery volume is more significant than 100 t/a.

In spun lace production, air flotation has the above technical advantages and high economic benefits. The application of circulating water saves water resources, reduces costs, and speeds up production.

Conclusion

(1) As a long-standing and mature solid-liquid separation technology, air flotation is widely used in life and production. Its application in many fields has achieved remarkable results and is an important water treatment method.

(2) Air flotation is used in hydroentangling production and is irreplaceable as the first treatment method in the circulating water filtration system. After air flotation filtration, a large amount of fiber debris, fine particles, and other impurities in the circulating water are removed, which significantly improves the water quality, reduces the load of subsequent filtration processes, and improves the efficiency of the circulating water filtration system.

(3) Flotation agents and flocculants are essential additives in air flotation technology. Their additional amount is related to the fiber properties, length, oil content of spun lace processing, the amount of fiber shed during spun lace and the spunlace process, etc.

(4) Using air flotation technology improves the quality of spun lace products, reduces economic losses, reduces the chance of water needle plate clogging, speeds up production, saves water resources and energy, and improves the purification of the filtration system. Ability lowers production costs and has good economic and social benefits.

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