Advanced Process Control
In day to day operations, engineers experience many challenges. Advanced Process Control is a low-cost tool that can help overcome these challenges:
- Producing a consistent product quality at a minimum cost with ever-changing process conditions and a given set of process limits.
- The performance of the process depends on operator experience.
- Environment regulations have a major impact on profit.
- Maximize production when high demand and good margins.
- Produce a predefined amount with minimal specific energy consumption when low demand and low margins.
- Find a trade-off between production and specific energy consumption when possible.
- Operators get extra administrative responsibilities, preventing them from focusing on the unit operations.
Advanced Process Control solution
The graph to the right shows an example of the effect on plant operation from installing an Advanced Process Control solution. In this particular case the example is shown for a single process variable.
Consider one variable that has a specific normal variation, and a high limit. In the first part of the graph, on the left side, the variable is shown with its normal variations. As a result of the variations in the variable, the operators tend to keep the average value of the parameter well below the limit, so that even with the relatively high variations in the variable, the value never exceeds the high limit.
By implementing APC application, the variance of the variable is greatly reduced. This is seen in the middle part of the graph. With this reduced variation, the average value of the variable can now safely be moved closer to the limit. Advanced Process Control solution will move the average value smoothly closer to the limit, if the optimization calculations conclude that bringing this variable closer to its limit will result in a more economical operation of the process.
The power of an Advanced Process Control solution lies not just in the reduction of the variation of key process parameters, but more in its ability to “think in a multivariable way”, i.e. truly optimize the process operation whilst taking all plant variables and all relationships in the process into account. As a result, the APC application will shift the entire operation closer to the most economical limits of the plant.
A practical APC example
In the figure is an APC example displayed. To the left the figure shows the “normal operation” of the plant away from the limitations, and the new operational region is displayed after commissioning an APC application.
During operation with APC, the process is operated closer to the most economical limitations, and the variability of the key parameters in the process is greatly reduced, as witnessed by the smaller size of the ellipse indicating the operational region with APC. The APC example shows a greatly reduced variance obviously directly relates to a more stable operation of the plant, typically leading to higher on-stream factors.