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.