Blend rules

The Blend Rules page shows a list of properties for which a blend rule is associated, and lets you add and delete associations between properties and blend rules.

If you don't associate a blend rule with a property, the property is blended linearly.

Note: Blend rules must be published as global reference data before they can be used in a supply chain model. Blend rules are published from other components of AVEVA Unified Supply Chain, such as Assay or Process Model Manager.
To publish a new blend rule ask your AVEVA Unified Supply Chain administrator, or consult the documentation for the relevant product.

The table on the Blend Rules page shows each Property and the Blend Rule to which this is associated. Also shown are the Formula defining the blend rule and the corresponding unit of measure (UoM). These last two fields are part of the blend rule definition and cannot be modified in this page.

Associate a property with a blend rule

1. Do either of the following:

   • Click Add Blend Rule in the Blend Rules group of the Home ribbon tab.

   • Right-click anywhere on the table and choose Add Blend Rule from the context menu.

     A new row is added to the bottom of the table.

2. In the new row, choose the property you want to associate from the drop-down list in the Property column.

3. If more than one blend rule has been defined for the property, choose the blend rule you want to use from the drop-down list in the Blend Rule column.

Remove an association between a property and a blend rule

4. Select the rows corresponding to the associations you want to remove.

5. Do either of the following:

   • Click Delete Blend Rule in the Blend Rules group of the Home ribbon tab.

   • Right-click anywhere on the table and choose Delete Blend Rule from the context menu.

6. Click Yes in the confirmation dialog that appears. The selected rows are removed from the table.

About blend rules

For calculating the properties of blended products and blended streams, Network assumes that all properties blend linearly. That is, the value for a particular property of a blend is the average of the properties of the individual components, weighted by the amount of each component in the blend. This is true for many properties, such as sulfur and nickel.

However, for many properties (such as pour point) the values of the final property is not the linear combination of the individual component properties. Instead to calculate the property value of the final product a blending index is used. This transforms the original non-linear blending property value into a value that can be blended linearly. Blending indexes are derived through experimental measurement of the property for various blends in order to find a mathematical function that allows the property values to be blended linearly. These blending indices are well established for most properties and are used extensively throughout the refining sector.

During any simulation or optimization, Network assumes that every property without an associated blend index blends linearly. Therefore, by default, any reported property values is the weighted average of the component streams. The averaging takes place with respect to either weight or volume depending on the property. The blending basis is defined in the property reference data and published from tools such as Assay. Properties such as sulfur blend linearly by weight, so the weighted average with respect to weight yields is used. If the stream yields are expressed in volume terms, they are converted to their weight equivalent using their densities. Properties such as viscosity blend using an index with respect to volume yields, so the viscosity values in engineering space (for example cSt) are converted to blend index space and then blended linearly with respect to the volume yields (again converting from weight yields using density if necessary). Properties such as aromatics blend by weight or volume, so the necessary basis for any downstream calculation is used.

The Blend Rules chart plots your blend rule against a specific property over the blend range.

Note: For multi-plant cases, blend rules defined for an individual plant, in the Blend Rules page of the planning environment, take precedence over blend rules defined for the multi-plant case as a whole.