water treatment applications

separating oily suspensions with low suspended solids content

In this case, the industrial machines used are called disc centrifuges (figure 44).

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These are vertical shaft, rotating machines that are capable for creating very high centrifugal fields (3,000 to 8,000 g). These units can be used with two sediment extraction systems:

• continuous output through nozzles (Ø 1 to 2 mm in diameter ): the effluent must not contain too much suspended solids (sediment volume below 2-3%) and especially no coarse particles (fine screening is essential);

• intermittent output via the restricted opening of the entire lower chamber (these machines are called: autocleaner bowl machines). They can process oily suspensions that have a higher suspended solids content (up to 5 or 6% sediment volume) but at moderate throughput rates.

Setting these clarifiers can sometimes be quite a delicate matter when the effluent quality (oil content) fluctuates. In effect, the financial appeal of this process depends on recycling the oils recovered so that they can be re-used; therefore, we need both an oil that does not have an aqueous phase and also an aqueous phase that does not have a very high oil content (maximum recovery).

This system finds its most widespread application in the treatment of wastewater produced by the automotive industry (soluble oils), steel mills, agri-food industries…

separating sludge-laden suspensions that have a high oil content

When the amount of sediment becomes too great (6-15% by volume), we can use 3-phase, horizontal shaft, cylindrical-conical continuous clarifiers: solid/water/oil.

Preheating up to 90°C and an appropriate treatment may often be required.

Separation reliability and regularity can only be ensured when these suspensions have relatively stable physical-chemical properties.

It should be noted that constructors are now developing machines that have a liquid ring that can be modified while the machine is running, thereby making oil/water recovery easily adjustable.

Applications: refineries, for instance.

cycloning used to separate out high granulometry, heavy particles

Cycloning also uses the centrifugal effect induced as the liquid arrives at a tangent into a fixed cylindrical-conical chamber. Acceleration levels are low but enough for separating out dense, granular particles (see section hydrocyclone).