Valve positioning control for process through put maximization

The application of a valve positioning controller (VPC) on top of a basic regulatory plant-wide control structure for maximizing the process through-put to increase plant profitability is demonstrated. The input to the VPC is a measurement of the bottleneck constraint and its output is the set-point of the through-put manipulator. The hydrodealkylation (HDA) of toluene to benzene process is used as an example case study with the feed hydrogen compressor and the furnace considered as bottleneck constraints that limit production. Results show that the automatic adjustment of the through-put manipulator allows the process to be operated close to (or at) the bottleneck constraint. De-rating of the plant through-put due to the possibility of disturbances is then avoided resulting in enhanced through-puts and plant operating profit. The increase in the through-put and plant profit over the de-rated operation is quantified with respect to variation in the magnitude of the principal disturbance that causes the bottleneck constraint to be hit. Results show that significant enhancement of more than 10% increase operating profit can be achieved. VPC is thus demonstrated to be a simple and effective means for increasing plant profitability by maximizing through-put.

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