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Jan 10, 2022

How automatic Larox® pressure filters can transform starch production

Using a Larox® PF filter has transformed many industrial processes, for example in fine chemicals, pigments, modified starch, and pharmaceutical fermentation broth. The primary dewatering mechanism is pressure filtration, in which a pressing force of up to 16 bar can be used. As a result, the energy consumption of the Larox® PF filter is significantly lower than that of centrifugal separators. The unique manner in which the cake is formed and subsequently sustained means that other operations, such as washing and drying, are as efficient and effective as possible.
Larox® PF filter
Larox® PF filter - Simpler designs, lower energy consumption and improved yield

The absence of a high-speed revolving mass or any continuously moving parts makes plant construction and machine maintenance simple. Pressure filters also consume less fresh water, use a lot less energy and provide a much higher starch recovery than centrifugal separators.

Larox® pressure filters can be applied to the following processing of starch from the following raw ingredients:

  • Corn (Maize)
  • Potato
  • Rice
  • Tapioca (Cassava)
  • Wheat

Automatic pressure filters such as Metso Outotec’s Larox® PF filter, process starch suspensions as follows:

Feeding

When the plate pack is closed, a set of chambers is formed and starch suspension enters these through feeding pipes. A filter cake builds up and filtrate passes through the filter cloth, support grid, and filtrate hoses. Because the cake is static and horizontal, it is extremely uniform and there are no misaligned forces to either deform it or cause cracks to form within it.

Feeding
Feeding

First pressing

The pressing medium enters the space behind the diaphragm under high pressure. The diaphragm squeezes the cake, forcing more liquid out.

First pressing
First pressing

Solids washing

After the pressing pressure is relieved, wash water enters the chamber through the same feed pipe as the suspension, filling the filter chamber while forcing the pressing medium out from behind the diaphragm. The water then passes through the filter cake solids, washing out impurities before exiting the filter chamber through the filter cloth to the filtrate collection line.

Solids washing
Solids washing

Second pressing

A second squeeze with the pressing diaphragm forces the wash water to pass uniformly through the cake. Because the cake is uniform and unstressed, this minimizes the presence of thin or thicker areas that may cause short circuiting or bypassing. This ensures the best possible cake washing and the lowest possible water consumption.

Second pressing
Second pressing

Solids drying

Compressed air enters the chamber through the feed port, pushes the diaphragm up, and passes through the cake in a uniform front in much the same way as the wash water. The airflow through the highly uniform cake reduces the residual moisture in the cake to the lowest possible level and also removes any remaining filtrate from the filtrate area.

Solids drying
Solids drying

Solids discharge and filter cloth washing

When the drying step is complete, all the filter chambers open up simultaneously. The filter cloth drive motor starts to move the endless filter cloth, discharging the solids from both sides of the filter. In this way, all of the starch is passing forward through the process at all times, with no material hold-up. At the same time, the filter cloth cleaning device washes both sides of the cloth in order to maintain a consistently high level of filtration efficiency and to remove any residual starch.

Solids discharge and filter cloth washing
Solids discharge and filter cloth washing

By using automatic pressure filters such as the Metso Outotec Larox® PF filter, you can increase production, reduce water and energy consumption verses centrifugal separators and improve start quality consistency.

See how much you can save with our starch value calculator
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