Pressure leaf filters provide wet filtration solutions for a number of industries, including alumina and waste water treatments. Essentially these filters are required to efficiently remove solid material and oils from fluids for the purposes of decontamination and purification.
1. How pressure leaf filters work
Pressure filters are composed of several screens made from either fine metal or plastic mesh or a cloth fabric, which are spaced apart in a filter vessel. The screens are used to trap solid matter and allow the liquid to pass through.
The filtration system does its job by purposefully allowing a build-up of the solid particles – known as a ‘filter cake’ – on the surface of screen. It is actually the cake itself which performs the filtration process while the screen acts as a support mechanism. As the cake builds up in layers it becomes thicker, enabling filtration of finer and finer particles.
In some cases where very fine particles require filtering, a pre-coat is applied to the screen, which then thickens even more as the sold filtered material builds up on top of it.
As might be expected the cake can eventually become so thick that filtering diminishes and back-pressure results – in which case it will need to be cleaned off. This can be done by various methods including blowing off by air or water or though shaking or spinning.
2. Considerations for pressure filters
There are several things to consider when it comes to pressure filters. These include:
- Corrosion resistance – it’s important that the screen frame and assembly parts are resistant to corrosion from both the liquid and solid materials.
- Screen hole size – screen holes need to be of the correct size to enable filter cake development. For instance if the holes are too large for the solid material, the filter cake will not be able to build up.
- Velocity – the speed of the flow needs to be low enough to prevent disturbance and dislodgement of the filter cake, but also able to be increased as the cake thickens in order to ensure filtration continues.
- Screen thickness and strength – this needs to be sufficient to resist chemical attack and force from back-pressure.
Using the right filter for the job is essential and requires a bit of a balancing act between enabling flow and cake development while reducing wear and tear of the filters.
3. Potential pitfalls and solutions
Problems in the use of pressure filters may result from inadequate cleaning, wear and tear or damage of the screens or fabric, and cake ‘touching’ between filter leaves if they are too closely spaced – which can result in reduced liquid flow.
Good care and maintenance of pressure filters is required to enable them to work as they should and keep them in good condition. This may include additional cleaning by mechanical or ultrasound methods (or chemicals in some cases) in order to dislodge old sediment. Damaged screens should be replaced as should any seals that are showing signs of leakage.
Solaft’s pressure filters
At Solaft we recognise the necessity for pressure filters to be durable and efficient and a good match for the stresses they are exposed to. Our Kelly Filters and Plate and Frame Filters are engineered to improve flow performance and cake release and recovering time after cleaning.
To find out more about pressure leaf filters and other wet filtration systems, don’t hesitate to contact our team at Solaft!