Other kinds of additional constraints

An advantage of being able to define enforceable, arbitrary mathematical relationships between reconciled flows is that this permits you to force your plant balance to accommodate a known engineering relationship between flow rates. As we have seen, this relationship can pertain to components and enthalpy, but there are sometimes other relationships which, if taken into account during reconciliation, can increase the accuracy of the overall mass balance.

A simple example of another kind of additional constraint

Figure: A simple example of another kind of additional constraint

If we suppose the measurement of the “FEED” stream in the above example is redundant (could be inferred from other measurements), the reconciled mass quantity of this stream varies simply according to the measured value of the other streams.

Assume, however, that we also know that the mass flow rate of the overhead stream “OVHD” should be equal to 10% of the feed stream. The mass balance model alone does not guarantee this relationship since the reconciled mass will be calculated by the data reconciliation algorithm without regard for, or knowledge of, the relationship.

We can add an additional constraint, as below, that will act in addition to the mass balance constraint so that we get the expected results from data reconciliation: