Background:

Cake filtration is a widely used process to separate solids from liquid in various sectors, including mining industry or wastewater treatment. After cake formation, a porous particle structure exists which is completely filled with liquid. To remove the remaining liquid from the filter cake, mechanical deliquoring measures can be used as an alternative to thermal drying. Since mechanical deliquoring requires 100 to 1000 times less energy than thermal drying, it is reasonable to mechanically remove the liquid from the filter cake to the maximum possible extent.

Aim:

A conventional post-deliquoring method is desaturation, where further liquid is driven out of the cake pores by a gas differential pressure. Especially for fine, compressible filter cakes, this leads to cake shrinkage, which benefits crack formation. The lower flow resistance of the cracks in the filter cake causes a higher gas throughput at constant pressure difference and, hence, higher operating costs. In the worst case, a significant drop of the pressure difference occurs, which reduces the achievable residual moisture of the filter cake. So it is the goal of the investigation to show that vibration of a filter cake helps to consolidate the cake structure to ensure an efficient deliquoring and washing.

Methods:

Starting with previous investigations on vibration compaction perpendicular to the filtrate flow^] have been carried out on a discontinuous laboratory scale. For cake filtration in industrial applications is preferably realized in continuous filtration apparatuses such as Horizontal Vacuum Belt Filters (HVBF) to achieve high throughputs. Therefore, it is essential to verify the applicability of this technique for additional mechanical deliquoring of compressible filter cakes in an existing continuous filtration apparatus. This talk will address the transfer and scale-up of the method to an existing indexing HVBF. For this purpose, a novel modular unit for vibration compaction has been developed and will be presented.

Results:

After implementing the vibration module on the indexing HVBF, the compaction and mechanical deliquoring effect of the module on an industrially relevant slurry was investigated for different frequencies and vibration times in the continuous pilot-scale apparatus. An important aspect is particle segregation which has significant impacts on cake formation such as a longer cake formation time compared to homogeneous cakes. The talk addresses the impact of this effect on vibration compaction. Thus, dewatering results of homogeneous and segregated cakes made of the same material with a broad particle size distribution are compared. Although cake deliquoring is achievable despite particle segregation, vibration compaction is more effective for homogeneous cakes. The reason is that ...