|Filter press feed pumps|
ABEL piston diaphragm pumps have been used since the 1960s as filter press feeding pumps for chamber filter presses. Many thousands of these specially equipped piston diaphragm pumps have been in operation in a variety of industries since then. Chamber filter presses are mechanical dewatering devices, which consist of any number of equally-sized filter plates connected in series.
Most of the filter plates are made of plastic, some of cast iron. Sizes range from 400 x 400 mm to 2500 x 2500 mm. Stretched over the filter plates are special filter cloths, which are selected precisely for the medium to be filtered. The filter plates have a hole, often in the middle (also called core hole), through which the medium to be filtered is fed into the individual chambers (the spaces between two filter plates). In these spaces, the filter cakes build up on the filter cloths, while the liquid (filtrate) is discharged under control via special channels in the filter plates.
How to select the correct pump for filter press feed? The particular, demands on the feed pump result from the way the filter press works: At the beginning of the filtration process, a high flow rate is required from the feed pump, until the chambers between the filter plates gradually fill up with particulate matter resulting in what are called “filter cakes”. Due to the resultant increasing resistance to flow as the filter cake builds up, the pump’s discharge pressure rises, while simultaneously the flow rate must be reduced, because the intake capacity of the filter press falls.
ABEL piston diaphragm pumps can fulfil these demands for filter press feeding in various ways. Equipped with an analogue pressure sensor and a frequency converter, the initial flow rate, break-point and minimum flow rate can be easily set and, much more importantly, also varied, if need be. The analogue signal of the pressure sensor is sent directly to the frequency inverter. Therefore, a separate control for this regulating function is not required. This type of control scheme for filter press feed is energy-saving, and at the same time, allows for individual adjustment, even with changing slurries, to reach optimum filtration results. After all, the filtration properties of a suspension, i.e. the medium to be filtered, cannot always be improved, e.g. by appropriate conditioning with coagulation aids. This leaves only the filter cloths and the feeding pump for optimisation.
As the filter press chambers fill with solids, pressure increases, and the feed rate is reduced accordingly via pressure sensor control.
The filtration process controls the feeding pump.
This adaptability is a real plus compared to other types of feed pumps, whose pumping rate is, as a result of the pump's construction, dependent on counter pressure. Particularly when short filtration times and high solids content are important.
If, however, there is good reason for not using sensitive electronics, ABEL offers filter press feed pumps with an internal membrane stroke control. With this option, the pumping rate of the piston diaphragm pump under increasing counter-pressure is not achieved by stroke number reduction (via VFD), but rather mechanically by reducing the membrane stroke length. This is simple, long-term, and cost-effective alternative solution, particularly for small chamber filter presses, such as one often encounters in industrial applications under difficult conditions.
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