MIST ELIMINATORS

Description

Mist eliminators are used to separate small droplets of liquid (mist) from gas streams. They are incorporated into most designs of wet scrubbers, such as venturi and plate scrubbers. There are three basic designs of mist eliminator - crimped wire eliminators, fibrous packing eliminators and baffle spray eliminators.

Mist eliminators trap the mist droplets through inertial impaction. The contaminated gas stream is forced to change direction as it passes through the eliminator and the droplets, which have a greater mass and momentum than the gas medium, are forced to impact upon the eliminator surfaces.

Fibrous packing eliminators are constructed from randomly packed plastic or glass fibres while crimped wire eliminators are constructed from layers of uniformly arranged wires. They can both be operated either dry or sprayed with a small amount of scrubbing liquid. In dry operation they are analogous to bag filters. Irrigated mist eliminators are similar in operation to packed towers and as such will remove some trace gases, such as hydrochloric acid, and low levels of particulate material. In both cases, the mist itself or the scrubbing liquid drips into a collection vessel.

Baffle spray eliminators are constructed from a series of vanes arranged in zigzag or s-shape formations, or combinations of both. The vanes create turbulence within the gas flow that causes mist droplets to impact onto the vanes, coalesce and drip into a collection vessel.

Application

Baffle spray eliminators are suitable for large mist droplets of approximately 50 µm diameter. Crimped wire eliminators are suitable for smaller droplets of, say, 15 µm, and fibrous packing eliminators can be used to separate mists of 2-5 µm with an efficiency of 98%.

Irrigated fibrous packed eliminators are also used to separate organic and acidic components from gas streams with lower airflows. Mist eliminators are incorporated into most designs of wet scrubbers, such as venturi and impingement scrubbers.

Sizing

The selection and subsequent efficiency of mist eliminators depends on the size and density of the mist droplets and the velocity of the gas throughput. A typical fibrous packing eliminator system designed to cope with 40,000 m3/hour could require a 75 kW fan to move the gas through the system.