Configure the operating parameters of your process units

Where a process unit requires further configuration to run, the Operating Parameters grid shows the parameters to be set.

To change the process unit for which operating parameters are shown, select the required Process Unit from the menu.

To change the process model parameters associated with the selected process unit, select the required Process Model from the menu.

See the following image for an example.

Reformer models often contain different operating modes corresponding to the differing degrees of severity with which the reformer is operated. Each mode differs in the final RON of the reformate produced, and by setting the target RON of the product the appropriate reformer Base + Delta model is used during optimization.

In the Lake Charles model the reformer can target the RON between 98 and 102.

See the following image for another example.

In the Lake Charles model the reformate splitter can have a swing cut between 80-100°C for the cut between light and heavy reformate. This can be included as an optimizable operating parameter in the run.

For each operating parameter you can enter a Min, Max or Fixed constraint. Any marginal value related to the constraint is shown in the Marginal ($/d/UoM) column.

You can also define the upper and lower boundaries for the value ranges triggering Warning and Error diagnostics. Cells in the Alert column show an amber disc if the solution value of the corresponding parameter is outside the range defined by Warning Min and Warning Max. A red disc is shown if the solution value is outside the range defined by Error Min and Error Max.

Operating parameters for multiple modes

Operating parameters are typically used to represent externally controlled settings for a process unit. Thus, in a single operating mode of a process unit, they are the same across all process models used to represent that process unit. If the process unit has more than one operating mode, the operating parameters can be different in each operating mode, while being the same within a single mode across all models.

For example, a distillate hydrotreater process unit might have two operating modes, low desulfurization and high desulfurization. The process unit itself contains two process models: one for straight run material and one for cracked material. These models each have operating parameters for sulfur target and reactor temperature. The straight run desulfurization model also has an extra parameter for catalyst activity.

In both desulfurization modes, the operating parameters are the same across the two process models. As the activity parameter is only relevant for the straight run model, it is not included in the other process model.

Fixed base constraints and marginal values

Suppose you have a process model with multiple bases, and you create a driver operating parameter with a fixed constraint at one end of the driver interpolation range.

For example, the next image shows a process model with two bases.

The Riser Temperature operating parameter is fixed at 990 F, which is one end of the interpolation range.

This results in either a zero marginal value or no marginal value at all, depending on the problem builder version. The reason is that the optimizer uses the base corresponding to the fixed constraint. The operating parameter becomes essentially redundant and is either ignored or not built at all. This has the advantage of reducing the size of the optimization problem.

If you need the marginal value for the operating parameter, you can add a small perturbation to the fixed constraint value, displacing it slightly from the base value. Alternatively, you can replace the fixed constraint with maximum and minimum constraints covering a very small range.

Edit operating parameters

Use the Operating Parameters Editor to set up and the operating parameters associated with a process model. To edit the operating parameters:

1. Enter a Name for the operating parameter.

2. Select a UoM Category for the operating parameter.

3. Enter a Default Value for the parameter and select the corresponding UoM.

   Note: When creating an operating parameter, if you enter a default value a Fixed constraint with the same value is automatically created. Remember to disable or delete the constraint if you want to use the default value as an initial guess for the optimization, rather than a fixed value.
   No fixed constraint is added when editing an existing operating parameter.

4. Enter a Valid Range for this operating parameter and choose its UoM. Any constraints you enter that violate this range will result in a warning diagnostic message during optimization. If you enter a fixed constraint outside the valid range, the constraint will be changed to a valid value during optimization.

5. Select Automatically add a corresponding variable if you want to add a matching driver or prediction. Choose either Driver or Prediction by clicking the corresponding option button.

   

   Note: It is important to set a valid range for the operating parameter. This range is used for bounding the possible value of the parameter during optimization. You can further restrict the bounds by entering a minimum and maximum within this valid range, but you cannot extend the operating range via constraints. You can also fix the operating parameter within this valid range.

Set targets for your operating parameters

Note: Targeting is only supported for Base + Delta models and related operating parameters. It is not possible to target operating parameters (that is, swing cuts) on distillation unit models.

When using simulation, normally all operational parameters of each process unit must be fixed. This is necessary to simulate the unit performance in the operational state that the simulation represents. However, it may be desired to vary these operational parameters during simulation to target some other property value.

The Target section of the Operating Parameters tab allows you to set a property target for each operating parameter. During simulation, the operating parameter is varied within its allowed range to meet this target.

To add a property target:

6. Click the Add button in the Target section.

7. Select the Variable to target.

8. Enter the property Value to target in the same unit of measure as the variable is defined.

Lock your operating parameters

Solution values can be locked during subsequent runs. This means that a solution value will not change in any subsequent run, even if other input to the run is changed.

Example: The flow of naphtha from a crude could be locked, and in subsequent runs it would not be able to change. Therefore, if a fixed swing cut point was changed and the model re-run, the crude blend would have to change in order to match the fixed flow rate.

Locking a solution value acts in a similar way to fixing the value. The advantage over fixing a value is that the lock can be clearly seen in the user interface, so it is simpler to distinguish true fixed values from those which are temporarily locked.

To lock one or more solution values, select the corresponding rows in the table and do either of the following:

• Click Lock Solution in the Behaviour group of the Home ribbon tab.

• Right-click on the table and choose Locking > Lock from the context menu.

To unlock one or more solution values, select them and either click Unlock Solution in the ribbon or choose Locking > Unlock from the context menu.