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Decanter centrifuges

Lemitec decanter centrifuges of the MD series were developed specifically as two-phase decanter centrifuges for use in laboratories and pilot plants to enable small quantities of products to be processed at rates of between 1 L/h to 100 L/h in a continuous separation operation.

The minimum throughputs of industrial decanter centrifuges are generally far greater than the throughputs required for the quantities of products available in research laboratories. In the past, the processing stage of continuous separation therefore frequently had to be simulated with alternative batch-wise separation methods.

Applications
Lemitec decanter centrifuges are typically used in the food and fermentation industries, the chemical and pharmaceutical industries and in biotechnology. In addition to their use in R&D departments, Lemitec decanter centrifuges have also been successfully used over long periods in the production of high-quality products requiring material flows of less than 100 L/h.

Lemitec decanter centrifuges can also be used as measuring instruments to obtain data on the flow properties of individual product phases. The flow behaviour of the product stream and the change in the torque between the bowl and the scroll are displayed on the control panel of the decanter centrifuge as a function of the power consumption of the drive motors and recorded, thus enabling the flow behaviour to be evaluated for the purpose of modelling decanter applications.


Operating principle
The operating principle of decanter centrifuges is quite simple and has been known for over a century. The suspension to be separated is pumped into the bowl through an inlet tube (feed) and accelerated.



Separation process
The bowl comprises a cylindrical and a conical section and rotates at a speed appropriate for the separation operation. Centrifugal force causes the solids present in the suspension to be deposited on the wall of the bowl.


Solids discharge
The scroll, which has the same cylindrical/conical shape as the bowl, rotates at a slightly higher speed (differential speed) than the bowl. This causes the separated solids to be conveyed towards the narrow conical end of the bowl where they are expelled through outlets and discharged. The extent to which the solids are dewatered depends, amongst other things, on the length of time they are exposed to the centrifugal force in the bowl. The time taken for the solids to be conveyed through the bowl can be set as appropriate for the type of separation operation by altering the differential speed.


Liquid discharge
A weir disc that can be set exactly as required is fitted at the end of the cylindrical section of the bowl. The clarified liquid flows along the scroll thread to the cylindrical end of the bowl and out over the weir plate, after which it is collected in the casing and discharged. The depth of the clarified liquid in the bowl can be adjusted to exactly the level required by inserting different weir discs.


Control
The decanter centrifuge is controlled and monitored by means of a modern touch screen that also displays all important process parameters at a glance. The decanter centrifuge can be incorporated into a process control system via a variety of interfaces.

The acceleration (g) and the differential speed are also fully adjustable during operation and can be altered to suit the product behaviour.



Drive
The bowl and scroll are driven by two separately controlled servo-motors that are connected electronically. This means that there is no need to use a mechanical gear unit. The differential speed can therefore be set with a high degree of precision, irrespective of the range of speeds. The minimum differential speed is as low as 1 rpm.  As the bowl and scroll are not mechanically connected, Lemitec decanter centrifuges may also be used to determine the optimum or maximum separation parameters of individual products. The drive is switched off electrically without damaging the machine if the permitted operating parameters are exceeded, for example due to an excessive amount of torque between the bowl and the scroll.

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Lemitec decanter centrifuges

Fascinating centrifuges for your solid-liquid separation processes
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