Separator Functional Principle
The separator, or disc centrifuge, is a vertically arranged centrifuge. It is used for separating and clarifying liquids. In a disk stack separator, solid-liquid mixtures or liquid-liquid mixtures are separated by centrifugal force. Compared to a decanter centrifuge, the separator differs significantly in its technical design and application.
How Does a Separator Work?
A disk stack separator is based on the basic principle of sedimentation. In a solid/liquid mixture, the heavy solids collect on the bottom of the container. They sink due to gravity. (1) In a continuous solid/liquid separation system, not all the solid particles have sufficient time to settle on the bottom. They leave the system together with the liquid phase. The separation is not complete. To prevent this, several flat inserts are used in the form of vanes or plates. (2) The actual separation takes place in the space between the disks in the disk stack. The more vanes or disks there are, the larger the clarifying surface. In order to prevent clogging of the plates, the bottoms are not mounted horizontally, but rather tilted. The solid particles slide to the bottom. (3)
The separator principle can also be used to separate liquids of different densities, such as oil droplets in water or water droplets in oil.
Separation by gravity (1 G) is slow and for many industrial applications it is not efficient. Disk stack separators accelerate the separation process significantly. They use centrifugal force to separate the mixture of solid phase and liquid phase materials. The geometric surface (clarifying surface) and centrifugal acceleration are used to calculate the "equivalent clarifying surface," which is the measure of the efficiency of a separator.
The high G forces allow the separator to achieve high separation performance. Compared to a decanter, the separator operates at higher speeds and separates significantly finer solids (particles down to about 5 µm) from a liquid.
Disk Stack Separator Structure
The mixture to be separated is fed through a stationary infeed pipe (1) into the distributor of the rotating bowl (2) (the container that holds the liquid). There it accelerates to the circumferential speed of the separator bowl. It is important that no unnecessary shear forces occur during distribution of the mixture. Such forces could break up the fine particles or produce emulsions. Slots or holes are provided on the outer edge of the distributor foot through which the product to be separated enters the disk pack. The separation takes place within the disk pack of the separator (3). The solids push outwards and collect in the so-called solids space (4). The separated liquid phases flow through the disk pack into the upper part of the bowl, and then through an impeller (gripper) or a fixed weir (5). The configuration used depends on the application.
The collected solids run off through a separate outlet (solids discharge). Disk pack separators that have a self-cleaning bowl (continuous separators) and manual separators are available. In a separator with a self-cleaning bowl, the bowl has an opening mechanism through which the separated solids are discharged at regular intervals (6). In this case, the bowl consists of the bowl bottom part, where the hydraulic emptying mechanism is located, and the bowl cover.
Using the hydraulic ejection mechanism, the separator opens at the outermost part of the centrifuge housing where the solids collect. After the solid phase has run off, the separator closes again. This happens in a few tenths of a second.
The separator is typically driven by a V-belt or flat belt drive. This depends on the size of the separator. The drive motor is controlled by a variable frequency drive.
Applications of Separator Technology
Separators are perfect for separation tasks in which a high degree of selectivity is required or in which the separation of the finest particles is important. They are also used for separating solid/liquid mixtures having only a small difference in density. Disk stack separators have many applications that can be found in the most diverse branches of industry, for example:
- In the food and beverage sector
- In the grease and oil processing industry
- In the chemical, pharmaceutical, and biotechnology industries
- In the petroleum industry and energy production
- In environmental protection
Separators are mainly used for three different separation processes:
- As a clarifier for clarifying liquids. Clarification is the separation of finely distributed solid particles from a liquid. The separator is used for mixtures with a low solids content. If the mixture to be clarified contains a large quantity of solids, a decanter is a better choice. The clarification of turbidity from fruit juice is a typical example application for a separator.
- As a purifier/separator for separating liquids. This separates a liquid with a lower density from a liquid with a higher density. An example of this use is the separation of water from mineral oil. Solids can be separated out of such a mixture at the same time.
- For concentrating liquids. This involves the concentration of a light liquid from a heavy liquid. One example is the extraction of essential oil from water using the separator. The simultaneous separation of solids is possible.
Lebensmittel- und Bioverfahrenstechnik [Food and Bioprocess Engineering], H.G. Kessler