A demister, also known as a mist eliminator, is a component used in gas cleaning systems to separate entrained liquid droplets from gas streams. It operates through impingement, centrifugal force, or filtration mechanisms, ensuring that the gas output is clean and preventing downstream equipment from damage caused by liquid carryover. This product is typically installed in vessels such as scrubbers, knock-out drums, or evaporators, where it captures droplets that would otherwise contaminate the gas or corrode piping and compressors. The demister is available in various configurations, including mesh pads, vane packs, and cyclonic separators, each suited to specific process conditions. The choice of material—stainless steel, polypropylene, or fiberglass—depends on the chemical compatibility and temperature requirements of the application. Key parameters to consider when selecting a demister include operating pressure, temperature, gas flow rate, removal efficiency, pressure drop, mist load, vessel diameter, material grade, and weight. For instance, the operating pressure range is 1.0–1.6 MPa, with a note that The operating temperature range is -40 to 120°C, above which material degradation may occur. Gas flow rates can vary from 1000 to 50000 m³/h, with higher flows requiring larger vessels. Removal efficiency is typically 99–99.9% for droplets larger than 5 μm. Pressure drop is low, between 0.1 and 0.5 kPa, but higher drops reduce efficiency. Mist load should be kept between 0.1 and 10 g/m³, as exceeding 10 g/m³ may cause flooding. Vessel diameter ranges from 300 to 3000 mm, with custom sizes available. Material grades include SS304 and SS316L, conforming to ASTM A240, for corrosion resistance. Weight ranges from 50 to 500 kg, depending on size and material. These values are reference ranges and must be verified for the specific model and application with the legal manufacturer or supplier. The demister is a critical component in chemical manufacturing, ensuring process reliability and product quality.
The demister operates by forcing gas streams containing liquid droplets through a mesh pad, vane pack, or cyclonic separator. As the gas flows through, droplets collide with the surfaces, coalesce into larger droplets, and then drain away by gravity. The clean gas passes through and exits the vessel. The mechanism relies on inertial impaction, where droplets, due to their higher density, deviate from the gas streamlines and impact the collecting surfaces. The efficiency of droplet removal depends on factors such as droplet size, gas velocity, and the geometry of the demister. For fine droplets, a mesh pad with high surface area is effective, while for larger droplets, vane packs or cyclones may be used. The pressure drop across the demister is minimal, ensuring energy efficiency. Proper design and selection are essential to achieve the desired removal efficiency without causing flooding or excessive pressure loss.
