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Gas-tight decanter

Compact unit for applications exposed to the risk of explosion
Gas-tight decanter

Specially developed for applications exposed to the risk of explosion in the chemical and pharmaceutical industries, the gas-tight decanter is suitable for clarifying and extraction processes. High flexibility and simple adaptation to specific process conditions are provided by the two-gear drive and the Varipond system.

Jens Bühring

As a flat-cone machine, the CE 345 gas-tight decanter is a typical clarifying de-canter for solid/liquid processes. It is primarily used for separating solids from media that are exposed to the risk of explosion, such as in plant extraction from alcohol or organic solvents, xanthane production or the production of oil additives as well as in the biodiesel segment. The aim is to achieve maximum dry matter with the help of a flat conical angle and the relatively wide drying zone.
The CE 346 steep-cone decanter, on the other hand, is an extraction decanter that is used, amongst other things, for treating three-phase mixtures, such as an aqueous fermentation broth plus solvent, in order to remove water and solids (the heavy phase) from the light solvent phase (the valuable product). The steep angle of the cone is ideal for this type of liquid/liquid/solid extraction process. The production of antibiotics and hormone substances or biopolymers from fermentation processes are examples of this machine’s potential applications. The decanter itself operates in accordance with the direct extraction principle, which combines the mixing and separating stages in a single piece of equipment, developed by GEA Westfalia Separator.
Advanced technology
The relatively small machine size of the CE 345 and 346 focuses specifically on maximum performance, improved separating efficiency, minimum energy consumption, a reduced number of components, compact design, ease of access and optimal service. The CE generation has a very small footprint and is readily acces-sible as a result of the pedestal bearing concept – a particular advantage from the point of view of maintenance. The entire bowl chamber can be accessed freely; the rotor can be simply taken out of the frame if necessary and replaced by a spare rotor, for instance. If CIP cleaning is not possible, the rotor can also be cleaned outside the housing without any problems. And if the machine is used to process aggressive products, it can be inspected easily for wear and tear or corrosion.
Two-gear drive
The gas-tight decanter additionally features a two-gear drive. The major advantage of this drive type is that the differential speed is adapted automatically and extremely precisely as a function of the scroll torque – and thus as a function of the solids content in the bowl.
The speed difference between the bowl and the scroll is essential for conveying the solids along the bowl axis. At the same time, it also defines the solids content in the bowl. This has to be maintained at a constant level within tight limits, because an optimal dry-matter content cannot be achieved if the solids content is inadequate. On the other hand, if the solids content is too high, the remaining overflow height for the discharging liquid is too low and the clarifying efficiency deteriorates accordingly.
This is not the only challenge, however. A significantly fluctuating solids content in the feed can likewise result in an exces-sively high scroll torque. This is the outcome if the differential speed is not high enough to ensure that the solids separated in the bowl are discharged from it sufficiently fast. With unregulated decanters, therefore, this speed value must be adjusted so that problems are ruled out even in worst-case conditions. Unfortunately, this simultaneously prevents the decanter from performing optimally.
The situation is entirely different with a two-gear drive, which enables the differential speed to be matched smoothly to the specific solids load of the product. The speed difference is adjusted as a function of the torque generated by the product between the scroll and the bowl by means of an electronic module that can be adapted to the product in question. Maximum dewatering and separating efficiency can thus be achieved regardless of any fluctuations in the feed.
Varipond system
The Westfalia Separator Varipond system has also been installed in the gas-tight de-canter. It enables the pond depth in the decanter – and hence the quality of separation – to be optimised without having to shut down the decanter especially for this purpose.
Varipond takes account of the fact that a correct pond depth within the decanter is extremely important for efficient operation. It frequently happens that the permissible pond depth range is very narrow and consequently has to be adjusted regularly to reflect changes in the feed.
This is exactly the task that is carried out by the Varipond system. It provides the operator with an opportunity to alter the pond depth – an important parameter for influencing the separating zone between the heavy and light phases – without interrupting production.
A so-called Varipond disc dips into the clarified light phase directly in front of the regulating ring. This disc forms a hermetic chamber (Varipond chamber) together with the centripetal pump, to which pres-sure can be applied through a hole in the feed tube. Since the liquid level between the Varipond disc and the regulating ring is defined by the overflow diameter, overpressure in the Varipond chamber has the effect of enlarging the pond depth in the decanter bowl in accordance with the principle of communicating tubes. As a result, the separating zone between the light and heavy phases is displaced outwards.
The tried-and-tested Varipond system has been running successfully in permanent industrial applications for many years. The process operator benefits from a tool that permits the purity of the heavy and light phases to be adjusted precisely. This is indispensable for efficient and cost-saving decanter operation, particularly in case of changing feed conditions.
A further advantage of Varipond – particularly with gas-tight decanters – is that it requires no mechanically moving parts for adjusting the pond depth externally. This is a major improvement, because such parts are complicated, sensitive to dirt and have to be additionally sealed.
Package unit
The machine can be preassembled as a package unit on a frame together with the complete peripheral equipment. This results in savings not only in terms of space but also with regard to handling, cleaning and maintenance. The machine is blanketed with nitrogen in order to comply with explosion protection regulations. The nitrogen blanketing equipment is likewise a part of the package, as is an operating console. The control cabinet itself has to be installed outside the hazardous area. The machine is thus a fully functional, gas-tight entity for areas in which there is a risk of explosion; it complies with the Atex standard and bears the CE conformity marking.
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