The cake-forming filtration of suspensions, which includes the optional steps of washing and deliquoring of the filter cake, is a key method in solid-liquid separation. It is found in a wide range of industries where diverse continuous and batch filter apparatuses are used. Such fields include the chemical, petrochemical, food and beverages, pharmaceutical, pulp and paper, electronics, metallurgical, waste water industries just to name some. It is common for all filter apparatuses to have a filter area covered by a filter medium and the formation of a filter cake. The driving potential for the cake formation can be a gas pressure difference: vacuum (continuous vacuum belt, drum, disc and pan filters) or overpressure (continuous pressure drum and disc filters, pressure nutsche filters), a hydraulic overpressure (candle and pressure leaf filters, filter presses, filter press automats) or a centrifugal pressure (all types of batch and continuous filter centrifuges).

Depending on the suspension characteristics as well as the process requirements and plant specific restrictions, the selection of the proper filter apparatus and the determination of its optimal operational settings with minimal and systematic experimental effort is a real challenge for new projects. On the other hand, for running filter apparatuses, it is extremely important to troubleshoot and reliably determine the optimization potential as well as the quantification of the possible performance improvement by considering the use of another filter. Solutions for the aforementioned challenging tasks will be presented.

Simple, praxis friendly and half-empirical mathematical models for formation, washing and deliquoring (including squeezing) of the filter cake will be presented. Emphasis will be given to the model specific dimensionless kinetic parameters as well as to the model adaptation parameters, which are called the efficiency parameters. The efficiency parameters have a physical meaning and characterize mainly the cake structure for the given suspension and, strictly speaking for the given apparatus. How the use of the efficiency parameters enables the determination of scale -up factors for the main filter performance parameters (solids mass rate, cake moisture content and optionally the wash out content of the discharged cake) will be discussed. Furthermore, it will be explained, how the judgment of the performance of a given filter as well as the comparison of its performance with other filters can be done correctly by using the efficiency parameters and the kinetic parameters for each step. Finally, the importance of establishing a suspension typology and a common language among the filtration specialists in different companies and institutions will be emphasized.