Droplet eliminator
A droplet separator (also aerosol , English demister ) is an apparatus for separating liquid drops from flowing gaseous media such as air or process gases .
Mode of action
Droplet separators use the higher inertia of liquid droplets compared to the lower inertia of the gas that carries them. For this purpose, the moist gas is passed through fixtures in which the direction of flow of the gas is deflected several times. The liquid droplets cannot follow these changes of direction, which is why they collide with the fixtures and settle there. With increasing deposition of the drops, they flow downwards. The liquid can then be collected in a collecting space.
Droplet eliminators are usually installed in the area of the device outlet. It is important how the liquid transported by the drops is diverted and collected, since a renewed transition of the liquid phase into the gas phase is to be prevented. The adherence of the droplets to the built-in components is referred to as “primary separation”, the drainage of the liquid film that forms as “secondary separation”.
Types
Very different types of droplet eliminators are used in practice. This depends in particular on the droplet size distribution in front of the separator, the droplet loading in the gas phase, the required separation performance, the permissible pressure loss and the solid content of the droplets. When selecting the material, it is important to ensure that there is no spread of harmful substances, such as B. by polychlorinated dibenzodioxins and dibenzofurans in plastic.
Wire mesh droplet eliminator
Wire mesh -Tropfenabscheider be made mesh-connected wires produced. The mesh size can be very different and is determined depending on the substances flowing through it. There are mesh sizes from 0.05 to 0.5 mm, but also versions of 1.5 mm or larger. The separation efficiency is increased by laying several layers of wire mesh on top of each other. Parcels with a height of 50 mm to 200 mm are common. Wire mesh droplet separators have a good separation efficiency, but they tend to clog due to solid caking.
Lamella separator
Deflection separators in the form of lamellar separators are composed of several sheets of metal arranged next to one another. These sheets are usually 20 mm to 40 mm apart and are wave-shaped. As a result of the wave shape in connection with the relatively small sheet metal spacing, there is a constant change in direction of the gas flow and thus the separation of the liquid droplets.
Lamella separators are often used in rectification columns .
Centrifugal separator
In a centrifugal separator , the gas flowing through the apparatus is set in rotation. The liquid droplets contained in the gas experience a very high acceleration due to the centrifugal force and are deposited on the wall of the centrifugal separator. Centrifugal separators basically behave in a similar way to liquid droplets as they do to dust . They are often installed downstream of venturi scrubbers .
Pourings
For beds are random body such. B. Raschig rings, arranged one above the other. These piles lie on a support grid that is provided with holes so that the gas can flow through it and the pile on it.
Applications
Gas scrubbing
During gas scrubbing, a gas (e.g. exhaust air from a combustion process) flows through an area that is constantly kept moist and in which solids and pollutants are absorbed by the scrubbing liquid (e.g. water). The gas also absorbs part of the liquid. In order to ensure that this gas leaves the apparatus dry, droplet separators are used in the area of the apparatus outlet. As a rule, gas washers are designed with droplet eliminators.
Air conditioners
In air conditioning systems, fresh or circulating air is conditioned, i. H. brought to a desired temperature and humidity. In many cases, water must be added to the air, which is usually done using finely divided nozzles. In order to prevent droplets from being discharged, which could lead to corrosion in the system, droplet separators are installed at the end of the humidification section.
literature
- VDI 3679 Part 3: 2010-6 wet separator; Droplet eliminators (wet separators; mist eliminators). Beuth Verlag, Berlin. ( Summary online , table of contents )
Individual evidence
- ↑ VDI 3679 Part 3: 2010-6 wet separator; Droplet eliminators (wet separators; mist eliminators). Beuth Verlag, Berlin, p. 27.
- ↑ Ulrich Glinka: On the trail - amendment of the guideline VD 3927 sheet 2. In: Hazardous substances - pure content. Air . 75, No. 1/2, 2015, ISSN 0949-8036 , pp. 41-46.
- ↑ a b VDI 3679 Part 3: 2010-6 wet separator; Droplet eliminators (wet separators; mist eliminators). Beuth Verlag, Berlin, p. 37.
- ^ Franz Joseph Dreyhaupt (ed.): VDI-Lexikon Umwelttechnik . VDI-Verlag, Düsseldorf 1994, ISBN 3-18-400891-6 , p. 1212.
- ↑ VDI 3676: 1999-09 Inertial Separators. Beuth Verlag, Berlin, p. 24.
- ↑ Armin Bürkholz: Cyclones as separators for mist droplets. In: Dust - cleanliness. Air . 38, No. 6, 1976, pp. 211-215.
- ^ Günter Baumbach: Air pollution control . 2nd Edition. Springer-Verlag, Berlin / Heidelberg / New York 1992, ISBN 3-540-55078-X , p. 325.
- ↑ Armin Bürkholz: Droplet Separation. VCH Verlagsgesellschaft, Weinheim 1989, ISBN 3-527-27865-6 , p. 123.
- ↑ VDI 3679 sheet 1: 2014-07 wet separator; Basics, waste gas cleaning of particulate matter (wet separators; Fundamentals, waste gas cleaning of particle collections). Beuth Verlag, Berlin, p. 13.
- ^ Matthias Stieß: Mechanische Verfahrenstechnik 2. Springer-Verlag, Berlin / Heidelberg / New York 1994, ISBN 3-540-55852-7 , p. 33.
- ↑ VDI 3679 Part 3: 2010-6 wet separator; Droplet eliminators (wet separators; mist eliminators). Beuth Verlag, Berlin, p. 48.