Application of the model
The interest of companies is in producing a high edible fat content in a
period as short as possible. This translates into questions as to which
final pressure level, which pressure-time profile (including the option
of increasing pressure in steps) and which duration of the process are
optimum. The expression model reported in this paper could be helpful in
deciding on these issues. To illustrate the potential of the model, we
investigated the effect of varying the constant rate of pressure
increase on the eventual solid fat content, the final pressure level
being kept the same.
Figure 11 illustrates, for various rates of pressure increase, how solid
fat content increases in time due to a decrease ine 2 denoting pore volume (or aggregate oil) per
solid fat volume which is constant over time. Eqs. (1.11) and (1.12)
tell us that the decrease in e 2 depends on the
gradient in e 1. A slower pressure increase
implies that it takes longer for the gradient ine 1 to vanish and for the filter cake to obtain an
equilibrium state. It also takes longer to reach the final pressure
level partly because the squeezing and the oil separation set in later
in time, but it results in a higher solid fat content (some 2%). In
spite of the limitations and uncertainties of our 1-D filtration model,
these results at least suggest our model may successfully be used for
ranking process options. We like to emphasize that our experience with
tests in a pilot-plant scale membrane filter press suggest that such a
ranking exercise is harder, and more expensive, on the basis of tests,
due to inevitable slight variations between tests in slurry composition
and properties, a range of equipment and operational issues discussed
earlier, and the relatively large uncertainties in the measurements.