Multi Product Blend Environment

The Multi Product Blend Environment allows a series of blends within the schedule to be optimized, allowing management of feasibility and optimality of several blends. Multi product blend optimization will attempt to ensure that all necessary specifications are met for the set of queued product blends, whilst also providing the optimal recipes based on user defined criteria for each blend.

Example: A refinery may produce gasoline from light naphtha, reformate and ethanol. Suppose the refinery produces two grades of gasoline, regular and premium.
When creating a sequence of blends, say two batches of regular gasoline, followed by a third batch of premium gasoline, it is important to ensure that it is possible to make each of these blends given the available components within the plant at the time of blending. For example, it would probably be necessary to hold some reformate back from the initial two blends in order to provide the extra octane required by the final premium gasoline batch. That is, if you used all the high octane reformate to make regular gasoline the third product blend would not be feasible as there would not be enough high octane blendstock.

The Multi Product Blend Environment manages these sequenced blend events allowing optimization across several blends to ensure feasibility based on the available blend components at the point of blending. The Multi Product Blend Environment builds on single blends (Product Blend Inspector) and allows a pre-defined set of single blends to be optimized across a time frame to improve blend feasibility and economics.

The following steps describe a typical workflow in the Multi Product Blend Environment.

1. Select the blends you want to work on

   Rather than working on all the blends in your schedule, you may want to work on blends within a given time period, or blends associated to one or more blenders. You can filter the blends included in the environment via the Filter group of the Home ribbon tab. See Filter Blends for more information.

2. Edit individual blends

   The Blends pane lists all the blends you are going to optimize, taking into account any filters you have set in the previous step. Click on a row to open the corresponding blend in the Single Blend Inspector pane. In this pane you can edit and even optimize the individual blend, as explained in Product Blends.

   Note that the Apply button is absent, unlike in the Single Blend Inspector you can open from the Tabular or Gantt panes. In the Multi Product Blend Environment, optimization results are applied via the Apply button in the Modelling group of the Home ribbon tab, as the final details of individual single blends are usually optimized as part of a holistic optimization across several blends, rather than on a single blend basis.

3. Edit blend constraints

   You can edit the constraint on each blend in the Constraints tab of the Single Blend Inspector pane. However, if you need to edit constraints on several blends it is be better to use the Blend Constraints pane, which lists the constraints on all the blends included in the environment.

   The grid columns are the same as in the Constraints tab of the Single Blend Inspector pane, except for the Blend column, which identifies the blend each constraint refers to.

4. Edit blender constraints

   In addition to constraints on blends, you can also set constraints on blenders. To do so, click Constraints in the Panes group of the Home ribbon tab. The Multi Blend Constraints pane opens.

   

   Delay between blends. You can force the optimizer to leave a minimum amount of time between the end date of a blend and the start date of the following blend in a given blender. Enter a value in the Settings - Delay column to specify a minimum delay for a blender. You can change the unit of measure using the drop-down menu in the column header. Note that values you have already entered are not converted when you change the unit of measure.

   After optimization, the delay is shown graphically in the Gantt chart.

   

   End of period blendability. This constraint allows you to specify that at the end of the optimization period there should be enough components to create the selected Grade in the specified Amount with the given Recipe. Selecting a grade in the table populates the Recipe drop-down menu with all the recipes previously stored against this grade. Click a column header to order the table rows according to the contents of that column. Click again to reverse the ordering. A small arrow in a column header shows that the rows are ordered according to the contents of the column.

   If you leave a grade as Empty but specify an amount, the optimizer will ensure that there is at least the specified amount of material left at the end of the period between all the components used by this blender.

5. Edit blend optimization settings

   Select the Blend Optimization check box in the Panes ribbon group to open the Blend Optimization Settings pane. From here you can change infeasibility breaker settings for the optimization of product blends.

   The Activity drop-down menu gives you three options on how infeasibility breakers are used during blend optimization:

   • Always: The optimization problem is always built including penalty functions to allow infeasibility breakers to be used. Adding this extra structure to the problem may cause small decreases in performance.

   • Only When Infeasible: The optimization problem is initially built with no infeasibility breakers included. If the resultant problem is infeasible, the problem is rebuilt including penalized infeasibility breakers and re-optimized to find a solution, which may involve activating one or more infeasibility breakers.

   • Never: The optimization problem does not include infeasibility breakers. If the problem is infeasible, the optimization will typically fail to converge.

     You can also enable or disable infeasibility penalties for the following two categories by selecting or deselecting the corresponding check boxes:

   • General Constraint Infeasibility Penalty: This is the cost of violating a constraint on a blend by one unit, in whatever units the constraint is defined.

   • Specification Violation Penalty: This is the cost of violating a blend specification by one unit.

     The default penalty is 100 M$ per unit. You can change this value in the text boxes for both penalties.

     The controls found in this window are also in the Product Blend Optimization tab of the Settings page in the main scheduling environment.

     Settings between the tab and the window are synchronized according to the following rules:

   • If you modify a setting in the Product Blend Optimization tab, this will be reflected in the Blend Optimization Settings window after you click the Refresh button in the Modelling group of the Home ribbon tab in the Multi Product Blend Environment.

   • If you modify a setting in the Blend Optimization Settings window, this will be reflected in the Product Blend Optimization tab after you click the Apply button in the Modelling group of the Home ribbon tab in the Multi Product Blend Environment.

6. Optimize the blends

   

   Click Optimize in the Modelling group of the Home ribbon tab.

   Select the Blend Weighting check box to force the optimizer to take into account the Weighting factor for each blend in the Blends pane. In case the Weighting column is not shown in the Blends pane, right click on a column header and choose Show Weightings from the context menu.

   The Multi Product Blend Environment attempts to find a feasible solution for the total set of blends, which also optimizes each single blend according to the optimization conditions defined for that blend.

7. Check optimization results

   Open the Diagnostics pane to inspect any information, warning and error messages generated during the optimization.

   

   Use the Single Blend Inspector pane to inspect the changes made by the optimization to each blend. If necessary, make adjustments to the individual single blends to further constrain or re-define them.

   Review the final blend details on the Gantt pane. Where appropriate, adjust the start and end times of the blends as necessary. If adjusting blends using the Gantt pane, take care that the correct blend details are updated.

   Open the Metrics pane to inspect a number of quantities useful to evaluate the results of the optimization. These are a subset of the quantities shown in the Solution Metrics pane of the planning environment.

   

   You can customize the Multi Blend Metrics pane in various ways.

   Customizing columns. Click and drag column headers to change the order of the columns. Click the Customize Columns icon () to open an empty window in which you can drag column headers from the table to remove the corresponding columns. You can then drag the headers back to the table at a later moment if you want to restore the columns.

   Ordering contents. Click a column header to order the table rows according to the contents of that column. Click again to reverse the ordering. A small arrow in a column header shows that the rows are odererd according to the contents of the column.

   Filtering. There are two ways to filter rows in the table:

   • Click the Filter icon () to show a text field where you can enter a keyword. Only rows where the keyword appears will be shown, with the keyword highlighted.

   • Click the small filter icon that appears when you hover the mouse pointer over a column header. A menu appears, showing several options to filter rows according to the contents of the column. Note that this is a column-specific filter, while the keywords entered via the Filter icon apply to all columns.

8. Re-optimize if necessary

   After adjusting the single blends it may be necessary to re-optimize the multi-blend sequence.

   Tip: When re-optimizing, you can prevent one or more blends from changing by selecting the appropriate check boxes in the Fixed column of the Blends pane.

   You can vary parameters and re-optimize multiple times, and then compare the optimizations in the Optimization History pane.

   

   The Optimization History pane lists past optimization runs and shows some key statistics for each, such as the time taken, the blend margin value, the number of warnings and errors. It allows you to test different optimizations and quickly compare and re-run them later.

   To restore the Multi Blend Environment to the settings of a given optimization run, select the corresponding row in the Optimization History pane and click Restore. To delete an optimization run, select it and click Delete.

   Warning: The list of past optimization runs is deleted when you close the Multi Blend Environment.

9. Apply results to schedule

   

   Apply the final blend details to the schedule by clicking Apply in the Modelling group of the Home ribbon tab. Existing activities in the schedule will be updated with the new details (new rates, start and end times and so on) and new activities will be created where necessary.