Introduction
Pressure filtration/expression is a process performed in many operations such as dewatering of sludge in waste water treatment [1], thickening of minerals and oil sands tailings in the mining industry [2, 3] and of coal reuse slurries [4], and expressing biological material in the food and beverage industry, such as sugar beet pulp or oil seeds. This paper deals with pressure filtration/expression in a membrane filter press, in which edible fat crystal aggregates, with a diameter of the order of 100 μm (see Figure 1), are separated from an oil-like mother liquor. Essentially, our pressure filtration consists of the same steps as the flexible‐membrane plate‐and‐frame filter press cycle shown in figure 1 of the paper by Stickland et al. [5]. In the application of current interest, a specific pressure-time profile is imposed with the view of optimizing or improving the filtration process in terms of filtration time and the final solid fat contents of the cake.
In a somewhat simplified version of this filtration process, a cake is compressed one-sided to force the liquid through a filter cloth at the other side. At the start of this pressure assisted filtration process, the cake consists of loosely packed porous crystal aggregates containing oil while surrounded by a continuous oil phase (see Figure 2). When the pressure is increased, the cake with the aggregates is compressed to force the oil out of the aggregates and to flow, along with the oil surrounding the aggregates, through the consolidating cake towards the filter cloth at the other end. This paper describes a novel model for describing this 1-D expression process in terms of temporally and spatially resolved porosities of aggregates and cake, resulting in a time-dependent oil flux through the cloth out of the cake.