Is there anyone knowledgeable who can explain the structure, materials, technical specifications, and so on of mist foam collectors?

There are three mechanisms by which mist collectors work: 1. Inertial collision – mist droplets larger than three micrometers collide with the fiber surface, separate from the airflow, and are captured by the fiber bed. 2. Fog droplets with a diameter of 0–0.3 micrometers can be captured through direct interception. 3. Brownian diffusion: Extremely tiny fog particles undergo random thermal motion due to collisions with gas molecules. The Brownian motion of fog droplets with a diameter of 0.1 micrometers is 10 times greater than that of droplets with a diameter of 1 micrometer, which **increases the likelihood of them colliding with fibers**.

This post was last edited by luoli519 on 2016-7-13 11:38. A foam catcher is also known as a demister. Demisters, which are commonly used in industry for the separation of gas and liquid phases by removing bubbles and mist, can be roughly divided into fiber mesh demisters, baffle demisters, swirl plate demisters, vane-type demisters, multi-factor swirl sub- and mother demisters, as well as combined devices. Fiber mesh type demisters, whether using composite glass fiber or metal fiber meshes, essentially belong to the traditional barrier-type demisting internals technology; little technological advancement has taken place since their use began in the early 20th century. It primarily relies on the pores formed by the interweaving and \"bridging\" of screen fiber filaments to block and intercept liquid droplets and mists within a certain size range, thereby achieving separation. However, the pores formed by the interbridging of fiber filaments are distributed in a small Gaussian pattern; while small-sized liquid droplets and mist particles are trapped and separated by the smaller pore sizes, larger-sized droplets are able to pass through the larger pores and escape. Therefore, traditional perforated baffle-type demisters find it difficult to achieve highly efficient separation of liquid droplets and mists of specified sizes. In addition, the flow channels of screen-type demisters are prone to being clogged by solid particles and gels that can be carried by air currents, which leads to a rapid decline in separation efficiency, high operating pressure drops, limited operational flexibility, and the risk of metal fibers being eroded and broken. As a result, it is necessary to regularly maintain and replace the internal components of screen demisters, resulting in high costs for operation and maintenance. However, due to limitations in the understanding of defoaming separation technologies, screen-type defoamers are widely used across various industries. They are not suitable for applications with high liquid content in the gas stream and unstable operating conditions, nor for use in situations where the gas stream contains solid particles, gels, or liquid droplets. To address the shortcomings of screen-type demisters, such as frequent clogging, short operational life, and difficulties in operation and maintenance when used to remove foam from air streams containing solid particles, gels, and liquid droplets, baffle-type demisters and swirl plate demisters were introduced abroad in the mid-20th century. Baffle plates, also known as Chevron plates, have a lower separation efficiency compared to mesh separators. However, their advantages include resistance to clogging by solid particles, lower pressure drop, longer operational life, lower operating and maintenance costs, and no need to replace internal components. The swirl plate demister is based on the Chevron baffle; through simple modifications, it replaces the multiple momentum changes in the flow channels of the original baffle with a single large swirl, making its production and installation simpler and more convenient ； However, the separation efficiency did not improve substantially. Baffle and swirl plate demisters do not escape the control mechanism based on gravity separation; as a result, the airflow still flows vertically, with gravity acting downward to separate the gas phase. Furthermore, due to the lack of sufficiently accurate fluid dynamics modeling for separation techniques at that time, these techniques relied on basic empirical designs; there was a shortage of model data to guide the scaling up of fluid conditions, leading to continuous issues with such empirical scaling. Abroad, it is basically used only for demisting in evaporation crystallizers for saline-alkaline solutions, as well as for rough separation in the lime-based flue gas desulfurization process in FGD power plants ； For applications requiring quantitative and efficient separation, baffle demisters and swirl plate demisters are not recommended. The vane-type demister separator, which comes after baffle plates and swirl plates, aims primarily to maintain the advantages of those plates while continuously narrowing the gap in separation efficiency compared to barrier-type demisters. The main focus is on continuously improving the dynamics of its internal microfluidic channels, in order to achieve efficient and stable quantitative separation performance, a wider operating range, and reduced space requirements for installation. Currently, the fifth-generation technology at the highest technical level is the feather-leaf type high-efficiency gas-liquid demisting and defoaming separator. Its secondary microchannels and short-path structures force the airflow to flow horizontally; when separating and removing tiny droplets, the separated particles are quickly carried through these short-path channels, thereby separating them from the clean airflow and directing them into separate channels. This approach eliminates the reliance on gravity-based separation mechanisms in the separation process, and it no longer depends on Stokes’ laws and related formulas, which are based on gravity separation, to determine the size of particles that settle due to gravity within the airflow. For example, the liquid droplets of a certain size separated by the wire mesh demister fall back into the rising airflow. Whether these droplets can break free from the action of the airflow and settle in the liquid collection area at the bottom of the demister for final separation depends on Stokes’ law and related principles based on gravitational settling. Similarly, the liquid droplets of a certain size separated by the baffle plates and swirl plates fall back into the rising airflow. Whether these droplets of a certain size can break free from the airflow and settle into the liquid collection area at the bottom of the demister also depends on Stokes’ law and related principles based on gravitational settling. Through decades of meticulous research abroad, sufficient and precise fluid dynamics separation technology models have been developed for vane-type demisters. The separation calculation and design system platform is based on conditions that closely resemble those in actual operations, providing accurate data guidance for scaling up fluid conditions; this approach overcomes the problem of empirical scaling that has long plagued screen-type, baffle-type, and swirl plate-type demisters. The feather-leaf type high-efficiency gas-liquid demisting and defoaming separator has surpassed traditional mesh-type demisters in terms of quantitative separation efficiency and operational flexibility. However, in high-pressure and ultra-high-pressure operating conditions where the pressure exceeds 10 MPaG, the gas phase is highly compressed, resulting in a significant increase in its density; this **reduces the density difference between the gas and liquid phases, which has a negative impact on the efficiency of gas-liquid demisting and separation. Especially in ammonia synthesis plants, the density of liquid ammonia is usually lower than that of most liquids, further reducing the density difference between the gas phase and the liquid phase. The separation performance of the aforementioned gas-liquid demisting and defoaming device makes it difficult to meet the requirements of advanced separation processes. Thus, the multi-factor cyclone parent-child separator was developed. The multi-factor swirl parent-separator uses an array of micro-swirls within the parent unit as independent micro-separators. The air flow elements along with the liquid droplets they carry rotate at high speeds within a cyclone separator with a very small rotational radius, thereby creating a vector separation field that is dozens or even hundreds of times stronger than that achieved by gravitational separation ； Efficient collisions occur between the micro-elements, as well as between the liquid droplets and foam particles, and between these particles and the inner wall of the swirler, enabling them to coalesce into larger liquid droplets ； The enlarged liquid droplets, after being forced to separate from the airflow by strong centrifugal force, collide at high speed with the inner wall of the swirl element, where they wet and spread out to form a large surface liquid film ； The tiny liquid droplets carried in the airflow are continuously captured by the high surface free energy of the liquid film when they collide at high speed with this film, thus forming a continuous stream of liquid that is separated and collected from the tail end of the swirler. To achieve efficient gas-liquid demisting and defoaming in feed gas streams containing large amounts of liquid, under conditions of high or ultra-high pressure, it is necessary to use a combination of vaned high-efficiency separation elements and multi-factor cyclone parent/child separation elements. The former serves as a primary unit to remove most of the liquid present in the gas stream, ensuring that the amount of liquid in the gas flowing into the secondary multi-factor cyclone parent/child separation elements meets the requirements needed for its efficient and stable operation; together, these elements facilitate demisting and defoaming. I hope that by drawing on my many years of experience in the design and application of efficient foreign separation technologies and equipment for gas-liquid, gas-solid, gas-liquid-solid, gas-liquid-liquid, and liquid-liquid separations, this post can be useful for communication among my colleagues. You can also visit http://bbs.hcbbs.com/thread-1354813-1-1.html for more information.

Currently, the water mist collectors used in the chlor-alkali industry are mostly candle-type, and they come in both domestic and imported versions. Domestic ones generally need to be replaced once a year, as their demisting efficiency is poor; imported collectors, on the other hand, can last for 5 to 10 years. The filtering layer in these collectors is usually made of specially treated glass fiber, while polypropylene fiber is used when alkalinity is present. These collectors are held in place by frames made of 316L material. Their demisting efficiency is 100% for particles larger than 1 um, and 99.5% for particles smaller than 1 um. The dimensions of imported demisting collectors are generally the same: 26 inches * 120 inches