Air-operated double-diaphragm pumps can complement liquid-transfer applications.
It was around 70 years ago that the filter press—which was invented a century earlier in the United Kingdom—gained a foothold in industrial liquid-handling applications in the United States. By their design and operation, filter presses are used as a tool in separation processes, namely where solids must be removed from a liquid stream. The sludge that is separated as the solid-laden liquid moves through the filter press can be easily removed and disposed of. The cleaned liquid can then be moved to the next stage of the production process or recirculated back into the filter press for further processing. In this role, the filter press has performed admirably in industrial applications, but in recent times, enterprising manufacturers of consumables, some of which must be produced in hygienic/sanitary operating conditions, have found that filter presses can further optimize operations.
Waste Not, Want Not
Industrial water and wastewater are applications where filter presses have proven their worth from day one. This is an application where large volumes of solids and liquids need to be separated on a daily basis. The filter press works well for this application because of its method of operation. As the solid-laden slurry is pumped into the press, two chambers are filled, which facilitates the formation of thick slurry cakes. While the chambers fill, the pressure inside the system increases to the point that when the chambers reach capacity, the liquid is filtered out with the aid of streams of compressed air or water. This dewatering leaves behind solid slurry or sludge cakes that are ready for disposal.
An advantage in this cake-creation process for the operators of water/ wastewater plants is that instead of having to dispose of large amounts of wet slurry, the outcome is a flow of neutralized water and a small amount of cake, which reduces disposal costs.
To operate properly, filter presses require good filtration and constant system pressure so that the flakes that form the slurry cakes are not destroyed. This means that pressures of up to 100 pounds per square inch (7 bar) are generally required. The filter-press process in water/wastewater treatment also requires that various types of ancillary liquids be used. In many cases, these liquids—including things like milk of lime, which is abrasive, and a variety of alkalines—cannot be released into the environment. This necessitates the need for a reliably leak-free pumping technology that is compatible with a wide range of liquid types.
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