Constraints on cut boundaries

• Implicit and explicit constraints. Depending on the Flexibility of Movement setting, the optimiser will move the IBP or FBP boundary of the target cut. The boundary being moved cannot cross other cut boundaries. This is known as an implicit constraint. For example, if the Kerosene FBP boundary of 250.0° C is being moved, it cannot go above 350.0° C (the FBP of the adjacent Diesel cut) or below 145° C (the IBP of the Kerosene cut).
  Of course you can still define explicit constraints on the cut boundary, as you would for any other property of the cut. For example, you could constrain the Kerosene FBP to be below 300° C or above 200° C. Select the Initial Boiling Point and Final Boiling Point properties to set explicit constraints on cut boundaries.

• Constraints on IBP and FBP cannot be violated. The optimiser will always choose the solution that respects all implicit and explicit constraints on cut boundaries, even if this means violating all other constraints.

• You cannot have constraints on both IBP and FBP. If you set Flexibility of Movement to End of Cut, you can set additional constraints on the cut FBP (or on the IBP of the adjacent cut) to override the implicit constraints. However, you cannot set constraints on the IBP of the cut: only one cut boundary can move during optimisation.
  For example, if you choose to move the Kerosene FBP, the IBP must remain fixed at 145° C and you cannot define constraints on it. Similarly, if you move the IBP, you cannot define constraints on the FBP.

Within the constraints described in this section, cut boundaries are moved by the optimiser so that the following conditions are fulfilled:

1. The highest number of property constraints (excluding those on IBP and FBP) is fulfilled.

2. The yield of the target cut is minimised or maximised, depending on the Yield Target setting.