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.