Q: What is ‘filtrate’?
A: The filtrate is the liquid which is separated from the solid-liquid suspension by the action of filtration.
Q: What is ‘filter cake’?
A: Filter cake is the solid which is separated from the solid-liquid suspension by the action of filtration.
Q: What is a rotary drum vacuum filter?
A: Quite simply, it is a multi-panel drum which is covered in a filter medium and partially immersed in a solid-liquid suspension. When vacuum is applied to the drum, the solids are retained on the filter medium whilst the liquid [filtrate] passes into the drum. The filtrate is removed from the drum via a special valve arrangement. By slowly rotating the drum, the filtered solids can be continuously removed from the filter medium.
Q: How fast does the drum rotate on a rotary drum vacuum filter?
A: Typical drum rotation speeds are between 0.1 and 1.0 rpm, although this range can be modified to suit the filtration characteristics of the suspension.
Q: How is the rotary drum vacuum filter area determined?
A: The filtration area can only be calculated once the filtration flux rate has been established for the suspension. The filtration flux rate is expressed as m3/m2/hr and is obtained by carrying out filtration tests on representative suspension samples.
Q: Do rotary drum vacuum filters require a lot of maintenance?
A: Generally, no. Provided that the filter is correctly lubricated, the slow drum rotation speed of the drum and gentle oscillation of the trough agitator means that component wear is minimal.
Q: What is an automatic tower press?
A: An automatic tower press is a vertical stack of filtration chambers. Through each chamber passes a continuous filter belt. The solid-liquid suspension is fed into each chamber where the filter cake is retained on the filter belt. The liquid [filtrate] passes through the filter belt and is discharged from the filter. To reduce the moisture in the filter cake, membranes in the filter chambers are inflated thereby squeezing the cake. Air drying is also used to reduce the filter cake moisture. The solids are discharged by expanding the vertical stack and advancing the filter belt.
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