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Fluorine recovery

When concentrating phosphoric acid, silicon tetrafluoride (SiF4) and fluorhydric acid (HF) evaporate. If emitted into the atmosphere randomly, these molecules can be harmful to the environment. If the SiF4 content is high, the emissions can cause scaling in the condensers and the cooling sections of the concentration units.

These products are captured using absorption towers. In these towers, the SiF4 and the HF are absorbed into a fluosilicic acid (FSA). This solution can be neutralized or used as a raw material for the production of fluorine products.


The Prayon design has the following characteristics :

Small plot area

Our fluorine absorption technology is much more compact than that of other companies. The absorption tower is very compact and contains only one nozzle. The gas and liquid flows run co-currently to avoid droplets of gas forming that are then difficult to separate. The small plot area required by our technology means that it is easy to install in existing units and reduces investment costs.

Low friction loss

For fluosilicic acid to be suitable for sale, it must have an extremely low P2O5 content. All the drops of acid that are entrained during evaporation have to be separated before reaching the absorption tower. This separation is carried out in the Praysep droplet separator (equipment combining confidential expertise supplied by PROFILE).

This separator is also used after the absorption tower stage to trap drops of fluosilicic acid (FSA) which might pollute the cooling water in the condensers.

The Praysep separator consists of a static propeller which centrifuges the gases; the drops are then captured in the grooves in the body of the machine. In contrast to other systems, there is less friction loss, which makes such separators easy to use in existing systems, and means that smaller vacuum systems can be installed.

High absorption yield

Absorption is carried out in batches. Compared to a continuous system, this means yield can be increased by as much as 10%. Where a substantial concentration of fluosilicic acid (more than 22% H2SiF6) and a high yield is required, two absorption towers may be used together. Such a configuration is recommended when the phosphoric acid has a concentration of up to 42-46% P2O5.

Unlikely to suffer scaling

All equipment and operating processes have been designed to keep maintenance costs as low as possible. The nozzles (equipment incorporating confidential expertise supplied by PROFILE) have been designed to keep scaling to a minimum. On the other hand, the Praysep droplet separators are washed automatically on a regular basis to ensure that they remain clean. These characteristics mean that the system can remain in operation for longer periods.

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Prayon Technologies (PRT)
144, rue J. Wauters
4480 Engis
Tel: +32 4 273 93 41
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