Mechanical solid-liquid separation by cake filtration - Mechanical deliquoring of incompressible filter cakes by undersaturation using a gas pressure difference
The standard provides a basis for quantitative statements about the mechanical deliquorability of incompressible filter cakes by means of gas differential pressure. It continues VDI 2762 Part 2, where the formation of such filter cakes out of a suspension is described. Corresponding to the typical technical applications, the gas pressure difference is limited upwards to approx. 0,6 MPa. The filter cake is formed out of a homogeneously mixed suspension on the surface of a porous filter media (cf. VDI 2762 Part 2) and is fully saturated with liquid at the beginning of the deliquoring process. The deliquoring of the filter cake takes place exclusively by displacement. The gas displaces liquid out of the pore, if the magnitude of the gas pressure difference applied to the cake exceeds the effective capillary pressure inside the pore. Decisive for the deliquoring is the magnitude of the pressure difference applied to the filter cake, which can be generated against the ambient pressure either by an underpressure behind the filter media or an overpressure above the cake. This is the reason why in the experimental part of this standard the range of vacuum filtration is covered by appropriate experiments in a pressure filter cell.