Скачать или смотреть Sludge Dewatering Unit with Decanter Centrifuge device at Water Treatment Plant

A centrifuge is a device which employs a high rotational speed to separate components of different densities. This becomes relevant in the majority of industrial jobs where solids, liquids and gases are merged into a single mixture and the separation of these different phases is necessary. A decanter centrifuge (also known as solid bowl centrifuge) separates continuously solid materials from liquids in slurry and therefore plays an important role in wastewater treatment, chemical, oil and food processing industries. There are several factors that affect the performance of a decanter centrifuge and some design heuristics to be followed which are dependent upon given applications. In oil well drilling fluid process, decanter centrifuge is the 5th purification equipment in whole mud system. Operating principle

The operating principle of a decanter centrifuge is based on separation via buoyancy. Naturally, a component with a higher density would fall to the bottom of a mixture, while the less dense component would be suspended above it. A decanter centrifuge increases the rate of settling through the use of continuous rotation, producing a g-force equivalent to between 1000 and 4000 G's. This reduces the settling time of the components by a large magnitude, whereby mixtures previously having to take hours to settle can be settled in a matter of seconds using a decanter centrifuge. This form of separation enables more rapid and controllable results.
How does it work

The original product is pumped into the decanter centrifuge through the feed pipe or inlet. The product goes through an inlet tube into a horizontal bowl which rotates. The bowl has is composed of a cylindrical part and a conical part. The separation takes place in the cylindrical part of the bowl. The fast rotation generate centrifugal forces up to 4000 x g. Under these forces the solid particles with higher density are collected and compacted on the wall of the bowl. A scroll (also screw or screw conveyor) rotates inside the bowl at a slightly different speed. This speed difference is called the differential speed. This way the scroll is transporting the settled particles along the cylindrical part of the bowl and up to the end conical part of the bowl. At the smallest end of the conical part of the bowl, the dewatered solids leave the bowl via discharge opening. The clarified liquid leaves through a paring disc (internal centripetal pump).[1] 3-phase separation with a decanter[2]

With a 3 phase decanter centrifuge it is possible to separate 3 phases from each other in one process step only. For example, two liquids which cannot be mixed because of different densities (e.g. oil and water) are separated from a solids phase. The heavy liquid (water) collects in the middle between the oil and the solids layer. Thus the two liquids separated from each other can be drawn off from decanter. The solids are transported via the scroll to the discharge openings as it happens also in 2-phase separation.

Typical applications of 3-phase separation are production of edible oils such as olive oil, oil sludge processing, the production of bio diesel etc.
Parameters and influencing factors of the separation[3]
Feed, throughput and residence time

Through the feed, the separation medium to be processed can be input into the centre of the infeed chamber of the scroll, where it is accelerated. The throughput will have an influence on the residence time.
Acceleration

The separation medium reaches its maximum speed in the decanter bowl, causing the solids to settle on the bowl inner diameter. A characteristic feature of the bowl is its cylindrical/conical shape.
Differential speed
There is a differential speed between the decanter bowl and the scroll, which is created by a gear unit on the industrial decanter centrifuges. The differential speed determines the solid content in the outfeed. Filling volume / Weir discs or overflow weir

Pond depth / Weir discs

The clarified liquid flows to the cylindrical end of the bowl in the decanter centrifuge, from where it runs out through openings in the bowl cover. These openings contain precisely adjustable weir discs/weir plates by means of which the pond depth in the bowl can be set. The weir discs determine the filling volume of the bowl.
Range of applications
The main application of decanter centrifuges is to separate large amounts of solids from liquids on a continuous basis. They are also used to wash and dry various solids in industry, such as polystyrene beads, clarify liquids and concentrate solids. Table 1.0 displays various examples of the utilisation of decanter centrifuges in various industries. Table 1.0: Industries with corresponding examples that use decanter centrifuges Industry Examples
Food processing

Edible animal fat
Animal protein
Protein recovery
Plant oils such as olive oil and vegetable oil
Wine (clarification)
Fruit, berries and vegetable juice
Soy protein