Control of a distillation column using virtual analyzer

Summary form only given. In many processes, especially distillation columns, feed composition changes can be a source of large disturbances that affect process operations. Feed composition changes affect the physical behavior of the process phenomenon, i.e., thermodynamics, vapor-liquid equilibrium, etc., and therefore, such disturbances tend to have a more pronounced impact on the operations, and typically, it takes more time to recover from such upsets. Often times, feed composition changes are not transient disturbances. They can be the result of changes made “on-purpose” to the front-end of the unit such as adjustments to reactor conditions, etc. Moreover, there is usually a significant deadtime associated with such disturbances. All of the above can pose a challenging control problem. The column operation can be adversely affected if the feed composition change is not anticipated properly and appropriate corrective action are not taken in a timely manner. The problem is complicated by the fact that online analyzers are rare in industrial practice partly due to analyzer reliability and maintenance issues, and partly due to the fact that online analysis of certain streams are difficult or cost prohibitive