Normalisation

Base + Delta Models often required normalisation constraints to ensure conservation through the unit models. For example the sum of the output yields from a hydrotreater unit should be equal to the yield of the input feed (allowing for any loss). To ensure that a particular property is normalised through a unit the vectors for that property should sum to 0 during regression. Normalisation is used to ensure that particular properties are conserved during fitting.

With the use of Base + Delta models the mass balance must remain closed not only at base conditions, but also when deviating from the base. To achieve this, it must be ensured that the sum of all delta vectors on the weight yields equal zero, otherwise mass may be generated or lost unknowingly which will bias the LP solution. Even though all process models are perfectly mass balanced, with multivariable regression the sum of the yield delta vectors for a specific independent might not equate exactly to zero. Generally this occurs when any one of the yield vectors is forced to a different value.

By default the normalisation constraint ensures that the sum of the left-hand-side (LHS) vectors is equal to zero, thus ensuring conservation through the system. However, if required the applied constraint can be configured so the sum of the LHS vectors is equal to the sum of a set of right-hand-side vectors.

To apply a normalisation constraint:

1. Click Add next to the constraints list.

2. Enter a name and description for the new constraint.

3. Click Add next to the Sum of left-hand-side delta values list to add a new constraint.

4. Select the required output stream/property to which the constraint applies.

5. If required, click Add next to the Sum of right-hand-side delta values list to add the matching constraining property.

6. Select the stream/property to which the left-hand side value should match.