Scrubber

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A gas scrubber ( English scrubber ) wet scrubber or absorber is a procedural apparatus , in which a gas stream is brought into contact with a liquid stream to accommodate components of the gas stream in the liquid. The passing components of the gas flow can be solid, liquid or gaseous substances. Pure solvents such as water , but also suspensions such as milk of lime ( flue gas desulphurisation ), can be used as washing liquid . Gas scrubbers can be used for dedusting and separating harmful gases at the same time. As a rule, a droplet separator has to be connected downstream.

construction

Gas scrubbing flow diagram (in general)

In many designs, the gas scrubber is divided into six areas. From the bottom up, they have the following task:

  • The scrubbing liquid collects in the sump of the gas scrubber and is fed back into the scrubber circuit or withdrawn,
  • in the gas inlet , the gas is given up and achieved by appropriate flow guide (z. B. by internals) a uniform application of the inner space,
  • The components in the gas flow are washed out in the contact section ,
  • In the washing liquid feed , the washing liquid is applied and distributed,
  • In the droplet separator entrained components of the washing liquid are separated and
  • the cleaned gas stream leaves the gas scrubber in the head .

Designs

Gas scrubbers can be differentiated according to various criteria. Distinguishing features are among others

  • the possible presence of fixtures and the question of whether they are movable or static,
  • the energy input to generate a large specific surface area of ​​the scrubbing liquid (whether through the scrubbing liquid, the gas or moving fixtures),
  • the specific need for washing liquid,
  • the fluidic conception.

The most well-known types of gas scrubber include:

There are also special shapes that are often modifications of the above-mentioned designs or are combined with other processes. These include so-called condensation and ionization scrubbers.

Working principle

The aim of the washer operation is to generate the largest possible liquid surface for the best possible mass transfer. This can be done by creating bubbles or drops or by sprinkling solid surfaces. The use of energy is necessary to generate an enlarged liquid surface. This can be introduced in the form of pressure loss in the flowing gas, such as in the case of a venturi scrubber, in the form of kinetic energy of the scrubbing liquid (jet scrubber) or via movable internals (rotary scrubber).

If drops are generated, they take on the speed of the surrounding gas comparatively quickly.

Special features of absorption

The approaches of Raoult and Henry can be used for the theoretical description of the absorption processes. The gas scrubber works in a similar way to the rectification column through repeated mixing and separating processes of the liquid and gaseous phases with the formation of phase equilibria. Liquid and gas phases can be conducted in cocurrent, cross or countercurrent in the absorber.

The efficiency of the gas scrubber is determined by

  1. the contact time,
  2. Surface of the washing liquid,
  3. the diffusion path in the gas phase,
  4. the difference in concentration between gas phase and liquid phase or
  5. an admixed chemical that acts as a reaction partner for the absorbed substance.

The efficiency can therefore be increased by

  1. a longer length of stay,
  2. Maximizing the surface of the washing solution through the use of special nozzles , fixtures and packing or
  3. a decrease in the concentration in the liquid phase due to more washing liquid or a chemical reaction.

When gases are absorbed, the release of heat is to be expected. With higher pollutant gas concentrations, this fact must be taken into account when designing the scrubber. Chemical reactions of the gas components with the scrubbing liquid can lead to encrustations on surfaces and fixtures. When using nozzles such. B. with the spray washer, they are likely to clog. To avoid additional emissions , the scrubbing liquid should have a low vapor pressure .

Special features of solid or liquid components in the gas

Wet separators for separating particles emerged from the further development of inertial force separators . With washers that work with droplet generation, the droplets produced are usually significantly larger than the particles to be separated and can be separated comparatively easily using a droplet separator at the device outlet.

The dust separation performance essentially depends on the energy used. Venturi scrubbers show a high pressure loss, but are able to separate particles with a diameter of 0.5 µm to an extent of more than 99%. The disadvantage of dust separation is the formation of sludge, which can, however, be processed. Another variable that influences the dust separation performance is the amount of washing liquid used. This cannot be reduced at will, since otherwise its property as a Newtonian fluid is lost and the gas scrubber can no longer work stably.

application areas

Areas of application for gas scrubbers include:

Gas scrubbers have a high level of operational reliability. They are particularly suitable when there is a risk of flying sparks, fire or explosion. Aerosol formation by the washing liquid can be disadvantageous .

literature

  • VDI 3679 Part 1: 2014-07 wet separator; Basics, waste gas cleaning of particulate matter (wet separators; Fundamentals, waste gas cleaning of particle collections) . Beuth Verlag, Berlin. ( Summary and table of contents online ).

Web links

Commons : Scrubber  - collection of images, videos and audio files

Individual evidence

  1. ↑ VDI 3679 Part 3: 2010-6 wet separator; Droplet eliminators (wet separators; mist eliminators) . Beuth Verlag, Berlin. P. 3.
  2. ^ A b c Karl Georg Schmidt: Wet washing devices from the point of view of the operating man. In: Dust: magazine for dust hygiene, dust technology, keeping the air clean, radioactive suspended matter . 24, No. 11, 1964, ISSN  0949-8036 , pp. 485-491.
  3. ↑ a b Matthias Stieß: Mechanical Process Engineering 2 . Springer-Verlag Berlin, Heidelberg, New York 1994, ISBN 3-540-55852-7 , pp. 32-35.
  4. ↑ 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. 44.
  5. ^ A b Klaus Holzer: Experience with wet-working dust collectors in the chemical industry . In: Dust - cleanliness. Air . 34, No. 10, 1974, ISSN  0949-8036 , pp. 361-365.
  6. ↑ 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. 42.
  7. ^ A b Ekkehard Weber: Status and goal of basic research in wet dedusting . In: Dust - cleanliness. Air . 29, No. 7, 1969, ISSN  0949-8036 , pp. 272-277.
  8. ↑ VDI 3679 sheet 2: 2014-07 wet separator; Waste gas cleaning by absorption (scrubbers) . Beuth Verlag, Berlin. P. 10.
  9. ↑ a b VDI 3679 sheet 2: 2014-07 wet separator; Waste gas cleaning by absorption (scrubbers) . Beuth Verlag, Berlin. P. 29.
  10. ↑ VDI 3679 sheet 2: 2014-07 wet separator; Waste gas cleaning by absorption (scrubbers) . Beuth Verlag, Berlin. P. 32.
  11. ↑ VDI 3679 sheet 2: 2014-07 wet separator; Waste gas cleaning by absorption (scrubbers) . Beuth Verlag, Berlin. P. 7.
  12. ↑ Michal Dylag, Janusz Krawczyk, Jerzy Rosiński: Reduction of the water consumption in the dedusting. In: Hazardous substances - cleanliness. Air . 58, No. 1/2, 1998, ISSN  0949-8036 , pp. 41-49.
  13. ↑ 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. 46.
  14. ↑ VDI 3927 sheet 2: 2015-05 exhaust gas cleaning; Reduction of inorganic and organic trace substances in waste gases from combustion processes (flue gases) (Waste gas cleaning; Reduction of inorganic and organic trace species in combustion flue gases) . Beuth Verlag, Berlin. P. 79.
  15. ↑ Crystec Technology Trading GmbH: The use of gas scrubbers in the semiconductor industry . Retrieved December 31, 2010.
  16. ↑ VDI 3679 sheet 4: 2014-10 wet separator; Waste gas cleaning by oxidative gas scrubbing (wet separators) . Beuth Verlag, Berlin, p. 9.