Decanters are a very efficient means of carrying out liquid-liquid extraction with a high solids content. GEA Westfalia Separator has developed a continuous
counter-current decanter specifically for such applications. The counter-current extraction decanter is a horizontal scroll-type centrifuge with a cylindrical conical solid-wall bowl. A scroll adapted to the bowl wall rotates with a differential speed inside the bowl.
These decanters are able to extract valuable substances directly out of the suspensions. A typical area of application for these machines is the extraction of antibiotics from fermentation solutions. The suspension to be extracted, e. g. fermentation broth, flows through the external centrally arranged inlet tube and is fed into the machine via distributor slots in the scroll of the bowl. The suspension then enters the counter-current extraction zone of the bowl, where it flows to the conical end of the bowl via the separating disc against the flow direction of the extraction agent (counter-current effect). The extracted suspension (raffinate) is discharged under gravity from the discharge of the machine. The sedimented solids are conveyed by the scroll which rotates at a differential speed in relation to the bowl, and are discharged under gravity together with the raffinate. The extraction agent (solvent) flows through the internal centrally arranged inlet tube into the distributor, where it enters the counter-current extraction zone through apertures. The extraction agent flows to the cylindrical end of the bowl against the flow direction of the suspension to be extracted, and is then discharged under pressure via the centripetal pump. Both phases, namely the extract and the raffinate, are first mixed and then flow through the clarifying zones to enable the phases to be separated efficiently. In order to permit safe operation in explosive surroundings, the decanter has been provided with a gas-tight design and can also be blanketed with inert gas.