In this article we will see how a plate filter press works.
The plate filter press is an industrial machine that is used in various sectors to dehydrate dense fluids and sludge, by separating the solid part from the liquid one.
The origin of this machine dates back to around the mid-1800s in the UK, where a rudimentary kind of press was used to obtain vegetable oil from seeds. However, the first automatic horizontal filter press dates back to the 1950s.
The filter press works thanks to a series of porous plates, covered with drain fabric. The thick fluid or sludge is pumped between the plates and pressed, so that the liquid part passes through the fabric and the solid part is retained by the plates. At the end of the operation, the latter are opened to allow the unloading of the panel that they have formed.
Thus the filter pressing process works by leading to a volumetric reduction of fluid substances that contain suspended solid particles. This process allows us to obtain very dry sludge. It can be discontinuous (therefore not very productive) and require a lot of assistance, with an impact on labor costs.
In order to optimize the process and improve the work performance of the plate filter press, it is very important to choose the best pumps for the suction and introduction of sludge and dense fluids inside the filter press. The PEMO Pumps range offers a wide choice of vertical, horizontal, submersible or multistage pumps, which are adaptable to the needs of each sector.
It is also necessary to carry out a preventive treatment of the sludge, which usually takes place by using ferric chloride and aluminum hydrochloride or polyelectrolytes.
The work of the plate filter press finds its use in various industrial contexts, including:
- industrial and waste water treatment plants;
- chemical plants;
- mining and metallurgical sector;
- battery recycling sector;
- pharmaceutical sector;
- food industry.
Components of the filter press
If we analyze all filter press models by components, we see that they can differ in the level of automation required and other details, but they mainlly share the same basic structure, which determines how a plate filter press works.
in fact, all filter presses are made up of several components:
- a frame, formed by a movable head, a fixed head and a jack;
- several filter plates;
- hydraulic cylinder that moves the filter plates;
- hydraulic power unit which in turn activates the hydraulic cylinder;
- pump for feeding the sludge or thick fluid into the filter press.
Optional components can be added to this basic structure, depending on the type of process in which the plate filter press works and on the desired degree of automation.
Among these, depending on how our plate filter press works, we find:
- electrical panel for the control and management of the filter press cycles;
- framework for housing the pneumatic process valves;
- fixed safety guards;
- mobile safety guards or photoelectric barriers to make any intervention on the machine by operators safe;
- system for opening the filter plates;
- system for shaking the filter plates
and other components that may vary according to the sector in which the filter press operates.
Collection of sludge
The collection of the sludge takes place through a feed pump for filter press. To understand which type of pump to choose, it is necessary to understand well how the plate filter press works.
The pump plays a crucial role in the filtration and sludge collection process, even more crucial than that of the filter press itself. In fact, if a gasket breaks or if some automatic function is defective, it is still possible to complete the filtration, perhaps with a greater waste of time. Instead, there is no way to proceed with filtration if the pump is not working properly.
In dewatering and sludge collection plants, the applications of filter press feed pumps can be performed by:
- two elements in sequence;
- a single variable feed element.
In the first case, the collection and transit of sludge are managed by a centrifugal pump in the filling phase and a volumetric one for the final filtration phase.
The former are particularly suitable in the initial stage, which requires a high flow rate with low pressure values.
The main advantage of the second option is given by having to manage a single element, with a possible reduction in management costs.
How does the filtration process work inside a plate filter press?
It begins with the closure of the filter press through an oleodynamic system, which is composed of one or more thrust cylinders that align the plates (support of the filter cloths) and keep them close to each other by exerting a very strong pressure. This also guarantees tightness and counterthrust against the one exerted by the feed pump.
The sludge is pumped into the chambers that form between the plates. The liquid in which it is suspended is pushed through a series of cloths, which cover them and perform the filtration action.
The plates are configured to allow the entry of the sludge and the exit of the filtered liquid through a series of holes that are placed in the fixed head.
After checking the clean water flow and filtration pressure, the system signals that dehydration has been achieved. At this point the slurry feed pump is stopped, the pressure is discharged and the plates of the filter press are separated. In this way, they allow the dehydrated sludge to be released as a filtration cake (also called a panel).
Cleaning plates of the filter press
The cleaning of the filter press plates is necessary when the duration of the filtration cycles becomes excessive or the pressure in the initial stage of filtration is too high.
Compatibly with the characteristics of the plates of the filter press and with the frequency with which their cleaning is necessary, this can usually be done in two ways:
- using a pressure sprayer;
- performing an acid wash.
The use of a portable pressure sprayer, fed with cold water, has the advantage of not requiring the removal of the plates from the filter press.
However, it is necessary to be very careful when using this procedure, to prevent the filtering cloths from being damaged. In order to minimize the risk of accidentally cutting them, it is advisable to use a fan jet, staying a few meters from the surface to be cleaned. It is also better not to exceed the spray pressure.
The acid cleaning of the plates is generally performed by using hydrochloridic acid diluted from 3 to 5%, when there is no sludge inside the filter press. This is a particularly practical method when frequent cleaning of the filter press plates is required.
It works by flooding. The plates are closed together, by pressure, through the hydraulic cylinder which is mounted in the fixed head. Then the hydrochloric acid is added. All automatic valves are closed, to allow the acid to act on the filter cloths and free them from encrustations.
After washing, the acid comes out from special drain valves and is returned to the tank from which it was taken or placed in another tank to be refined and reused.
Why you should use Pemo pumps for the filter press
Now let’s focus on why to use Pemo pumps for the filter press.
As we have seen, the choice of an efficient pump is crucial to guarantee the optimal functioning of the filter press and the possibility of carrying out a complete filtration cycle. The operation of the filter press in itself may not be compromised by any defect in the machine or automation. But the entire filtration process cannot even begin if the feed pump malfunctions.
All thebasic models of the PEMO Pumps range can be adapted for this purpose. The different possible configurations are over three thousand, and this really allows you to face any activity and any need for handling sludge.
The models of high pressure pumps for filter presses that our company has developed for this purpose are over forty (in the versions with one, two or three stages, with flow rates up to 1,100 mc / hour and pressures up to 21 bar), and it is always possible to customize them according to the needs of the customer and the sector in which he operates.