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Mist eliminators, or demisters, play an essential role in removing mists and other liquids generated during industrial and manufacturing processes. During these processes, droplets of water and other molecules may become trapped in the air or gas, resulting in entrapment.
As environmental protection regulations have increased, the use of mist eliminators has risen to meet these new requirements and reduce pollutants that gases may otherwise carry. Understanding how mist elimination works will help you choose a suitable mist eliminator for wet scrubber systems.
The wet scrubbing process is designed to remove solid or liquid particles from a gas stream. This is done by merging the gas stream with a liquid like water to control the particulate matter. In environments where machines are used, it is essential to use moisture eliminators and control systems.
For a wet scrubber to work effectively, inertia and dispersion must apply. Wet scrubbers incorporate mist eliminators that help manipulate the gas to control these particulates and remove them from the air.
The mist eliminator’s role is to remove liquid contaminants from gas streams. Eliminating these contaminants helps improve plant emissions, promote product integrity, prevent equipment corrosion and reduce possible employee health risks. The design of a wet scrubber incorporates mist eliminators to remove liquid droplets. Contaminants and pollutants can become trapped if gas and liquid streams make contact.
In combination with mist eliminators, wet scrubbers can remove both particulate matter and gases. Additionally, a wet scrubber’s ability to collect droplets is directly proportionate to how much power the scrubber receives and how well the mist eliminator functions per its design.
The three most common types of mist eliminators for wet scrubbers are mesh pads, vanes and fiber beds.
Wire mesh is the most common type of mist eliminator. They incur a low installation cost and provide high separation efficiency. These eliminators are usually made of several compressed layers of metal wire or thermoplastic held together by support grids. They can deliver great results in a variety of conditions, and you can set them up in vertical or horizontal airflow arrangements. Wire mesh mist eliminators work by dirty air being forced through the media, where the droplets coalesce and continue to push the now-clean air to the outlet. The droplets are removed from the dirty air by direct interception, inertial impaction and Brownian diffusion.
Brownian diffusion — or Brownian motion — occurs when particles and molecules bounce off one another in an airstream in an irregular motion rather than a straight line. The eliminator may use multiple layers of mesh wire filters to create multiple stages of droplet collection. When choosing a wire mesh eliminator, some variables to consider include surface area, mesh thickness, wire diameter and the surface tension between the captured liquid and fiber.
Vane eliminators, also known as chevron or baffle-type mist eliminators, are needed to remove larger droplets from gas streams. This type of mist eliminator uses inertial impact to separate particulate droplets from the airflow. Rows of parallel plates, or chevrons, are placed in a zigzag formation to attract droplets. There are plates in each of these rows that allow the gas to flow through once it is rid of the droplets. Vane mist eliminators can be used for vertical or horizontal airflow.
You can combine vane mist eliminators with wire mesh to provide a more efficient system for capturing particulates. The wire mesh serves as a precursor for the fine mist and forms large particulate droplets for the vane mist eliminator. When these are combined, you can expect improved performance and the benefits of each type of equipment to be optimized.
For industrial processes that generate finer particulate droplets, consider a fiber bed mist eliminator. These work very similar to wire mesh mist eliminators but are only built for horizontal gas streams.
Fiber bed mist eliminators are cylindrical. An inner and outer screen is rolled to form the cylinder, and plates or flanges are attached to either end for draining and mounting. This type of mist eliminator is best used for removing sub-micron particulates from gas streams.
Like mesh wire mist eliminators, the fiber bed type utilize Brownian diffusion to impinge the droplets onto the media before reaching the outlet. The air stream’s velocity and media density both play a factor in removing most contaminated droplets in this method.
Mist eliminators are a perfect addition to wet scrubbers and help enhance the cleaning of contaminated air. The three types of mist eliminators can be made to meet the specifications that you require for your wet scrubber system.
Mesh mist eliminators are relatively inexpensive and are efficient at removing small particles.
Filter bed mist eliminators filter smaller droplets extremely efficiently. Due to the large surface area of this type of mist eliminator, you can also filter a high volume of contaminated air.
Vane mist eliminators work across various applications, and the blade spacing can be adjusted for specific cases. You can arrange this type horizontally or vertically for high-capacity filtering. Out of the three mist eliminators, the vane-type creates the lowest pressure drop as gas is forced through.
If you’re unsure which type of mist eliminator would be best for your facility, or if you need a custom wet scrubber system engineered for a specialized application, MACH Engineering can help.
If you’re interested in learning more about mist eliminators, contact MACH Engineering. At MACH Engineering, we design state-of-the-art odor and emission control systems for specific industry applications. We use multiple construction materials, sizes and other elements to create the most effective possible solutions.
We stand behind the quality of our products and our service. For more information about the benefits of our mist elimination systems or to request a quote for a mist eliminator for a new or existing process tower, contact us using our online form.
Demister pad, also called mist pad, wire mesh demister, mesh mist eliminator, catching mist, mist eliminator, is used in gas entrained mist separation column to guarantee the filtering efficiency.
DPZ-01: Working principle of demister pad.
History of demister pad
The late fifties, the foreign used an apparatus which made of the special wrinkle woven mesh to remove inclusions of tiny liquid foam in the gas. Then it is found that is very efficient and the resistance is very small, which is unmatched by other gas-liquid separation device, so it is widely accepted and used in a wide range of applications.
Wire demister standard was formulated by the Ministry of Chemical Industry in China on December 20, 1982, the basic implementation of the Shanghai municipal government standards Q/YSZZ-88-91 wire mesh industry was in 1991, began to fully implement HG/T21618-1998 national unity standard after the year 1998. The new standard demisters are divided into HG5-1404-81 riser type, HG5-1405-81 necking type and HG5-1406-81 full bore wire mesh device.
Demister pad is commonly placed at the top of the packing tower, which can not only ensure the mass transfer efficiency, but also reduce the board spacing. Demister pad is widely used in chemical, petroleum, pharmaceutical, light industry, metallurgy and other industrial production in the vertical cylindrical equipment vapor-liquid separation device. It can also be used in the desulfurization and other productions to remove oil mist, toxic and poisonous gas.
Working principle of demister pad
When the gas with mist rises at a constant speed and passes through the wire mesh, the rising mist will collided with the mesh filament and attached to the surface filament due to the inertia effect. The mist will be diffuse on the filament surface and the droplet will follow along the filaments of the two wire intersection. The droplet will grow bigger and isolate from the filament until the droplets gravity exceeding gas rising force and liquid surface tension force while there is little gas passing through the demister pad.
Separate the gas in the droplets can improve the operating condition, optimize process indicators, reduce corrosion of the equipment, extend equipment life, increase the amount of processing and recovery of valuable materials, protect the environment, and decrease air pollution.
Contact us to discuss your requirements of mist eliminator pad for sale. Our experienced sales team can help you identify the options that best suit your needs.
DPZ-02: Round shape embedded demister pad.
DPZ-03: Circle shape embedded demister pad.
Features of demister pad
Selected wire mesh form
Selected demister pad forms have four categories: standard type, efficient type, high penetration type and shock absorber type.
Specifications of standard type demister pad Item Wire type Wire sizeDPZ-04: Flattened type standard demister pad.
DPZ-05: Ginning type standard demister pad.
Specifications of efficient type demister pad Item Wire type Wire sizeDPZ-06: Rectangular shape efficient demister pad.
DPZ-07: Round shape efficient demister pad.
Specifications of high-penetration type demister pad Item Wire type Wire sizeDPZ-08: High penetration type demister pad detail.
DPZ-09: High penetration type demister pad.
Specifications of shock absorber type demister pad Item Specification Filament specificationsDPZ-10: Shock absorber type demister pad detail.
DPZ-11: Shock absorber type demister pad.
Domestic standards
Wire mesh demister pad domestic standards are divided into HG5-1404 (1405, 1406) - 81, HG/T 21618-1998, HG/T 21586-98.
DPZ-12: SP type demister pad.
DPZ-13: DP type demister pad.
DPZ-14: HR/HP type demister pad.
Type Standard wire specification SP 0.1 mm + 0.03 mm × 0.4 mm DP 0.1 mm + 0.02 mm × 0.3 mm HR 0.23 mm + 0.03 mm × 0.4 mm. HP 0.1 mm + 0.03 mm × 0.4 mmMesh pad installation
There are two kinds of wire mesh demister pad, which are disk shaped demister pad and bar type demister pad.
According to different using condition, it can be divided into upload type and download type. When the opening is located in the above of the demister pad or when there is no opening but has flange, you should choose the upload demister pad.
When the opening is in the below of the demister pad, you should choose the download type demister pad.
DPZ-15: Upload type demister pad.
DPZ-16: Download type demister pad.
Schematic of demister pad
DPZ-17: Horizontal separation tower.
DPZ-18: Spherical separation tower.
DPZ-19: Scrubber.
DPZ-20: Distillation column.
DPZ-21: Vertical separation column.
DPZ-22: packed tower.
After using for a long time, the demister pad will clog or prone to flooding and the pressure drop will increase. All these because of the particles in the gas blocks the demister pad. So you need maintain the demister pad properly and regularly.
Maintenance method: clean the demister pad. As we all know, the dilute acid on the demister pad will shorten the service life of demister pad, so we should place the demister pad in the natural state or under the sunlight
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