Performance of dewatering in mining operations

Siobhan Doyle

Dr Alexis Speck, Bernhard Salbaum and Uwe Gradl compare mechanical and thermal cake drying.

Within solid-liquid separation with filter presses there is quite often a special task to gain a certain purity of the filtrate and the cake. In many cases, a very low residual moisture content is required. With the existing filtration methods often, an additional dryer must be used to achieve solid concentrations above 40%. Different efficient processes in a filter press are available to increase the dry solids content.

1. Mechanical High Pressure Drying in a Filter Press (DHC-Process)

This process works with membrane and combination plates, squeezing the filter cake with high pressure and displacing liquid from the filter cake. The limitation of this process is the compressibility of the cake to a maximum of 40-50% dry solids content.

2. Thermal Vacuum Drying in a Filter Press (DHV- Process)

This process uses the mechanical drying according to item 1. above, but with low pressure. The additional application of temperature and vacuum evaporates the remaining liquid in the heated cake. The limitation mentioned above does not exist anymore and a dry solid content close to 100% can be achieved.

Figure 1: Example of sludge dewatering with JVK TCM/TCC plates.

An example of an effective vacuum drying process for communal sewage sludge with a high organic content. The process steps come from a sewage sludge with additional biologic treatment (polymer conditioning), first with a squeezing pressure of up to 40 bar followed by a vacuum drying time of 150 minutes. The finished drying process with the same sludge, a high sand content and no treatment at all is also illustrated.

Figure 2: Example of a process diagram for a TCC/TCM drying system

In this filter process, a TCC plate related to steam of 110°C and the TCM plate was used with hot water of 75°C. A dry solid concentration (green) of almost 100% was reached using only a constant vacuum (blue). The squeezing pressure of the TCM plates was sequentially set up and the TCC pressure was also constant due to a permanent heating flow.

Dr Alexis Speck, Bernhard Salbaum and Uwe Gradl are with JVK Filtration Systems.

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