Separator (process engineering)

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A separator (from Latin : separare = separate, separate), also known as a purifier , clarifier or decanter centrifuge , separates different phases of different densities from one another.

Working principle

Separators work on the principle of separation by means of centrifugal forces . Compared to a sedimentation tank , in which the downward acceleration of gravity acts on the phases, separators use centrifugal acceleration due to their rotation and thus increase the acceleration many times over. A prerequisite for a good separation of a mixture is that the individual phases of the mixture have different densities. Furthermore, the solids should have a large difference in density compared to the liquid or gaseous phases.

Separators are vertically mounted centrifuges and are usually built with overhead bearings. The power transmission to the spindle, and thus to the drum, can be carried out by three different types of drive, by means of helical gear , belt drive or direct drive via a special motor . When sealing the separators, a distinction is made between open, hydrohermetic (sealing of the product space) and fully hermetic (complete airtightness). The assignment depends on the type of fluid supply and drainage.

If one looks at the outflows of the liquid phases, one speaks of a continuous process , as these are continuously discharged from the separator drum. When it comes to solids discharge, a distinction is made between manual solids removal , automatic, intermittent solids discharge and continuous solids discharge. With all three solids discharge variants, two or three phase separations can be carried out. Due to the greatest density of the solids, they collect in the centrifugal field as an outermost ring, directly on the inner wall of the drum. The continuously operating centrifuge was invented by Gustav de Laval in 1878 .

With the solids-collecting separators, the separators must be stopped and opened at certain time intervals so that the solids can be removed manually. In separators with discontinuous, automatic solids discharge, the solids are also collected on the inside wall of the drum. The drum is opened briefly at full speed at adjustable time intervals via water hydraulics (lower picture, middle separator, dark gray slide bottom slides down). The solids are discharged using the existing kinetic energy and the drum is closed again.

In the case of separators with continuous solids discharge, one also speaks of nozzle separators, which are available in different designs for various tasks. With both the continuously and discontinuously discharging separators, a part of the liquid is always emptied (flushing effect). The liquid phase (s) is (are) either discharged from the separator without pressure or under pressure . One speaks here of peeling disks (grippers), which work like a stationary pump wheel while the liquid rotates.

Three solid discharge variants of a plate separator

When it comes to separation, one speaks of three different separation tasks:

  • During the clarification / clarification, a solid phase is separated from a liquid phase.
  • When separating two liquids (possibly also a solid phase ), a distinction is made as to whether the heavy phase or the light liquid phase predominates.
  • During purification, a heavy liquid phase is separated from a lighter liquid, for example fuel processing .
  • On the other hand, if the heavy liquid phase from which a light liquid phase is to be separated out predominates, this is referred to as a concentration

Types

Hydrocyclones

Separators :

  • Nozzle separators
  • Screw press separators
  • Chamber separators
  • Disc separators
  • Full-jacket plate separators

Decanter :

  • Two-phase decanter
  • Three-phase decanter

Centrifuges :

  • Three column centrifuges
  • Single buffer centrifuges
  • Vibrating vibrating centrifuges
  • Vibrating centrifuges (tumbling centrifuges)
  • Solid bowl peeler centrifuges
  • Solid bowl screw centrifuges
  • Tubular centrifuges
  • Sieve drum peeler centrifuges
  • Pusher centrifuges
  • Sieve screw centrifuges
  • Chip centrifuges
  • Inverting filter centrifuges
  • Universal centrifuges

application

Application in the chemical and biotechnological industry

Separators are used to clarify liquids or to separate liquids of different densities. They replace centrifuges as soon as the volume flows to be cleaned are too large for an economical batch process. Typical applications in biotechnology are the clarification of cell culture supernatants or fermenter broths as well as the separation of aqueous two-phase systems .

Application in the food industry

In a dairy in particular , separators are used to separate the milk either into skimmed milk and cream (cream), to remove impurities from the milk or to adjust the fat content of the milk (e.g. for drinking milk or cheese milk).

Use in combustion engines and in the lubricating oil circuit

The operation of a separator enables continuous operation of the lubricating oil (Lub Oil) from the commissioning of a ship to scrapping . An oil change, as is the case with other vehicles, would be a very costly affair with ship engines and the on-board machines to be lubricated because of the large oil volume required. Long-term use of the lubricating oil is only possible through uniform consumption and thus uniform addition in order to compensate for the chemical consumption of the lubricating oil additives. This process is called "freshening" the oil. A low consumption of the lubricating oil occurs through losses during cleaning through separation and through combustion in the engine (approx. 0.6 to 1 g / kWh). The lubricating oil does not age and is always in the best condition with the same viscosity if the separator is working properly .

Heavy oils (heavy fuel oil) as fuel for large diesel engines (> approximately 1 MW) contain solids and water additives and must also be continuously cleaned with separators. Due to the price advantages over other fuels, heavy oil is the main fuel in shipping and in large diesel engine power plants.

Up to certain generations of separators (up to around the mid-1990s), differently configured drums had to be used for both of the above-mentioned oils, which differ in their wear protection through special wear plates in the drum, so-called LO and HFO drums. Furthermore, in these drums, the separation zone had to be adjusted to the density of the medium to be separated using so-called "water or regulating disks" (until around 2005). Newer model generations solve both problems with higher quality materials for the drum and better control with continuous water detection on the light phase side (oil leakage).

The old method of using a purifier (for separating water) and a clarifier (for separating solids) in series when separating heavy oils in ship operations has not been followed for around 15 years. Modern heavy oil separators from all manufacturers now run problem-free in combined operation with continuous water and intermittent solids separation.

Other uses

Scheme of an industrial decanter (decanter centrifuge)

A decanter in the industrial sense (not to be confused with manual decanting , especially of wine) is another type of centrifuge. Here, the solid components of the materials to be separated are continuously removed from the centrifuge drum with a slower or faster running screw conveyor .

The decanter (decanter centrifuge) is usually used with a higher solids content (from around 3% in the feed). Solid / liquid separation takes place in the decanter centrifuge. Solids and liquids are continuously discharged. The 3-phase decanter is a further developed design. Here solids and two different, non-soluble liquids are separated from each other. There is also the option of separating two solids of different weights from one liquid (e.g. in the case of plastics recycling).

Areas of application for decanter centrifuges are e.g. B. Sewage sludge treatment, pharmaceuticals, paint sludge treatment. The dry matter content is concentrated to 5 to 8% and so the sludge volume is reduced by 90 to 95%. In the last few years the decanter in the field of sewage sludge dewatering has largely displaced other dewatering processes such as chamber filter presses and sieve belt filters and has made a major contribution to reducing the transport of undewatered sewage sludge ("sewage sludge tourism").

In the course of further technical development, the decanters themselves as well as the individual components are subject to ever increasing demands in terms of design, material, precision and performance. For this reason, certain core components, such as conical or cylindrical barrel shells, screw bodies, sealing covers, tubes, bushings or rings are produced using the centrifugal casting process, because the materials used (duplex steels, austenites, nickel-based alloys) offer optimum strength and a very high level of strength Corrosion resistance.

Web links

Individual evidence

  1. separators. Retrieved October 28, 2016 .
  2. Decanter for thickening sewage sludge