Heavy duty belt presses operate according to the pressure filtration principle: two endless belts converge by being fed through a suitable frame and roller (with bearings) structure which must be sturdy for mineral applications where the material density, shear forces and abrasion attack are high and low residual moisture requires high belt tensions. Three distinctively different dewatering zones are defined: the gravity zone where the slurry is dewatered by gravity alone, the wedge zone, where the belts converge to form a wedge and pressure dewatering starts due to the resulting reduction in volume, and finally the press zone where the highest possible pressing pressure is applied to the filter cake gradually to obtain low residual moisture.
For optimal overall performance these zones ought to be synchronized carefully which is challenging for a given set-up, i.e., roll number and diameters und thus angle (or area) of contact, lengths of gravity and wedge zone, respectively, and converging angle of wedge zone. The only operating parameters left are the belt speed and tension that allow coping with varying throughput and slurry properties besides upstream slurry conditioning measures such as feed equalizing measures or control of filtration aids. While the belt speed is paramount for the throughput, belt tension and rollers, particularly the final roller diameter, are decisive for final cake dryness.
Tailings from lithium carbonate and coal were tested in laboratory were all three zones were simulated consecutively. Although laboratory results are not directly suitable for up-scaling, the trends are captured correctly and the scaling factors stem from large scale operation data. The flocculation screening revealed that...
Session: L11 - Discontinuous and Continuous Press Filters
Day: 14 March 2018
Time: 16:45 - 18:00 h