Base + delta model

A Base + Delta model is a linear representation of a refinery process unit. A reference point is chosen based on a typical feed and operating conditions which provides the base for the unit output's yields and properties. Delta vectors are then constructed which represent linear changes in output yields and properties based on changes in the input feed composition.

If a particular variable has a highly non-linear response several different models may be required to represent the process unit in different sets of circumstances.