What is a Mist Eliminator?
When designed correctly a standard mist eliminator collects essentially 100% of all liquid particles 10 microns and larger. They are used in the recovery of valuable products, to abate the emissions from chemical and refining processes, to meet industrial air pollution regulations, and to collect and remove fine liquid droplets in a vapor streams which otherwise may cause downstream corrosion of valuable equipment.
Utilizing mesh or plate surfaces to separate mist droplets from the gas stream through impingement. As the vapor moves through the demister, the inertia of the droplets causes them to contact the mesh surface, coalesce, and drain as larger droplets. The large surface area coupled with a small volume allows for the collection of liquid without impeding the gas flow.
Typically used to reduce the time needed to separate a liquid droplet size and therefore reduce the volume and cost of separator equipment, they are often used where vapor quality is critical with regard to entrained liquids, separator equipment costs are high or when space or weight savings are advantageous particularly inside a vessel.
Available in just about any size or shape and in a wide range of metals, fibers, plastics, and exotic alloys for maximum corrosion resistance, mist eliminator types include, mesh and coalescer pads, vane packs, insertion type Mist Fix and sub-micron fiber-beds . Each type is a distinct product, used in differing applications to achieve the basic job of demisting a vapor.
When determining which style of mesh is to be used the following should be considered:
1. The flow rate and properties of the process gas.
2. The flow rate and properties of the process liquid.
3. The minimum micron size and efficiency of the liquid particles that are to be removed.
4. The potential for clogging due to a viscous fluid.
Sizing and selecting mist eliminators requires analysis of the following:
1. The vapor velocity system limit for gravity separation defined by the Sounders-Brown equation.
2. The vapor velocity at which re-entrainment occurs.
3. The degree of separation required.
4. The pressure drop across the mist eliminator and from the entrance and exit of the vessel
5. Volume required for slug capacity