Harald Anlauf

Recent developments in research and machinery of solid-liquid separation processes

Separation of particles from liquids is an extremely widespread problem, which has to be solved under very different aspects in nearly all industrial production processes, in environmental protection, in water purification, and every day in our personal lives. The very different nature of separation problems has led to the development of a large number of mechanical separation principles. Although a lot of successful research work has been done in the past, there are still today many open questions left about process understanding and calculation. After a systematic view to the different physical principles of mechanical solid–liquid separation processes, some recent developments are discussed more in detail.

Avoiding filter cake cracking: Influence of consolidation on desaturation characteristics

ABSTRACT In cake filtration processes with an air-blowing step, cracking is an undesirable phenomenon as it leads to deterioration of the filtration process by highly increasing gas throughput. This leads to higher residual moisture if the pressure difference cannot be maintained and an increase in overall cost. Crack formation can be avoided by compacting the filter cake before desaturation. While this action will make the separation process applicable by highly reducing gas consumption, there are also potential negative effects. Compaction increases filter cake resistance and might therefore slow down desaturation kinetics. Therefore, the authors investigated how the filter cake characteristics governing desaturation change from the nonconsolidated to the consolidated state of the filter cake and compared these findings to the actual dewatering kinetics. The results showed that for the case where cracking could be oppressed, dewatering kinetics of the consolidated cake are actually faster than for the nonconsolidated cake, despite higher resistance of the consolidated cake. Thus, compaction is an appropriate action when dealing with filter cake cracking.

Filter cake compaction by oscillatory shear

ABSTRACT In cake filtration, low values of residual moisture are desirable. This can be achieved by filter cake compaction. The present work proposes a new method for filter cake compaction by applying oscillatory shear superimposed with normal pressure. An experimental setup for the application of oscillatory shear is presented and the influence of oscillation frequency and displacement as well as the number of cycles and the magnitude of superimposed normal pressure on the compaction behavior is investigated. It was found that the reduction of residual moisture with number of cycles follows an exponential decay law. The variation of displacement implies that displacement and oscillation frequency are not independent parameters, but the resulting mean shear rate determines the degree of compaction that can be reached. The compaction behavior with frequency or shear rate, respectively, was strongly influenced by the superimposed normal pressure. The effect of oscillatory shear on the compaction of the filter cake was compared to the compaction obtained by applying solely mechanical pressure. By applying oscillatory shear, a significant reduction of compaction pressure needed to obtain a certain value of residual moisture could be obtained.

Vibration-enhanced compaction of filter cakes and its influence on filter cake cracking

ABSTRACT Filter cake cracking is a common problem in cake filtration that can be avoided by compacting the filter cake prior to air-blowing. Here, we present a new method for compaction by applying vibration in the form of oscillatory shear. The shrinking and cracking behavior of the model material is analyzed by combining laser displacement measurements and image analysis. Then, the compaction results are presented and discussed regarding the process time and energy consumption. Finally, we show how compaction by oscillatory shear influences the cracking behavior of the filter cake. Significant reduction in cracking could be achieved.