Demister Filter BOLL & KIRCH

Demister Filter

Reliable gas filtration

Demisters (droplet separators) serve to separate droplets of liquid from flowing gaseous media and are used to filter gas. The demister acts as a pre-separator when the liquefied gas is highly contaminated. Solids can only be separated to a certain extend in the liquid. This is where duplex filters come into play. Furthermore, demisters are extremely sensitive to changes in the operating conditions, such as pressure or the volumetric flow rate.

The cyclone, like the demister, is used as pre-separator when the gas is expected to be highly contaminated by liquid and solid particles. The cyclone separates high solids content as well as high moisture content. The separation efficiency is based on centrifugal force, which carries the particles to the outer wall of the cyclone.

Mode of function


In demisters, the separation mechanism is primarily responsible for any sluggishness. Efficient separation is achieved by repeatedly diverting the flow of gas through the demister. During the droplet separation process, the droplets flow through the wire mesh. The moment of inertia causes them to crash against the wire surface and then collect at crossover points in the wire mesh. The accumulated droplets of liquid then form larger drops and travel downward, where they collect at the base.

The demister’s design depends on operating conditions such as the volumetric flow rate, in addition to the type of particle, the medium being separated, and the separation performance.


To separate even the smallest and lightest particles, a fast rotating gas flow is necessary. This is supplied by the special introduction of the gas into the cyclone. Once separated by centrifugal force, the particles run down the inner wall of the cyclone into a collection zone. Because of the separation principle, the separation efficiency of the cyclone depends on the operating conditions. Widely varying operating conditions lead to varying separation efficiencies. Due to the required high gas velocity, a relatively high pressure loss has to be accepted.

Areas of application

Droplet separators are used in chemical and petrochemical plants, in the offshore sector, in cooling towers, in environmental engineering, in evaporative condensers, and in power plants; anywhere drops need to be reliably separated from flows of gas. Droplet separators not only improve process safety and increase the efficiency of gas scrubbing, they also contribute significantly to protecting the environment.


  • Simplex: BFB-CY and BFD-CYD