Variable types

Several different variable types are available for use in calculations.

For each variable, you can define a name, a description and a symbol (see: Variable Names and Symbols). You can also choose a unit of measure from the UoM drop-down list, except for variables of type Constant. Most variable types require you to enter additional information, which is described in the remainder of this section.

The available variable types are the following:

• Constant: A fixed numerical value. This is useful if you have to use the same value in different places, or to make the meaning of the value clear to other users, since you can associate a name and a description to it.

• Period Duration: The current period duration, as defined on the Inventories page.

• Flow: The flow through a Pipe originating from a particular Asset, in a specific Mode or in all modes. To select the asset, choose the correct Asset Type first. You can choose among three flow types: the Total Flow of the pipe, the flow of a Feedstock or the flow of a Traded Material associated with the selected stream.

• Property: The value of the specified Property of a stream flowing in a given Pipe originating from an Asset, either in a particular Mode or in all modes. To select the asset, choose the correct Asset Type first.

• Global Parameter: The value of a global parameter defined in the case. If the global parameter is of type Multi-Period, you can choose between its Opening and Closing value.

• Operating Parameter: The value of an Operating Parameter associated with a Mode of a Process Unit in a particular Model.

• Purchase or Sale Flow: The amount of a particular material either bought or sold. You can choose between two options:

  • A particular Traded Material. If the material has more than one price, you can limit the amount to a particular Tranche (see: Sales, Tranches, Markets and Supplies).

  • A particular Utility.

    Warning: Purchase or sale flow variables are not supported in multi-plant or multi-period models. Within a multi-plant or multi-period model the purchase or sale happens outside the plant, and so the value for the variable cannot be determined from the purchase/sale amount. To obtain this information, use instead a flow variable and restrict the amount to a particular traded material.

• Purchase or Sale Price: The price of a particular material either bought or sold. From the Filter drop-down list choose between Crude and Import, then select the Tranche whose price you want to associate to the variable.

• Sale Property: The value of a Property measured on the sales from a Traded Material or a particular Tranche. You can choose the Any value for the traded material or tranche, to include all sales or all tranches of a particular traded material.

  Warning: Sale property variables are not supported in multi-plant or multi-period models, since the sale does not occur directly within the plant. Instead, use a flow property for the relevant blender or manifold output.

• Material Count: The number of traded materials flowing through a pipe to an asset, in a given mode or in all modes. To select the asset, choose the correct Asset Type first.

  This variable type is useful to limit the number of traded materials flowing to a particular asset. For example, you may wish to limit the number of types of crude oils flowing into a distillation unit in a single operating mode for scheduling reasons.

• Purchase Count: The total number of purchase of a particular Material Type. This is similar to the Material Count variable type, but it refers to the flowsheet as a whole, while Material Count limits the number of materials flowing to a particular asset.

• Blend Matrix: The flow of a Component entering a Blender and ending up in a given blend Product.

• Inventory Amount: The Opening or Final amount of a particular Inventory.

• Inventory Property: The value of a Property in either the Opening or Final stage of a particular Inventory.

• Group Flow: The total flow of material in all the members of a purchase or sale group.

• Group Property: The weighted average of a property for all the members of a purchase or sale group.

• Economic Objective: The value of the economic objective function.