(147e) Develop Distillation Controls during Process Design Phase

Charles D. Herzog

Retired Chemical Engineer

Address basic process control issues during engineering design phase to increase system capacity and improve on-spec performance.

View process control as a life-cycle discipline, rather than an activity that begins after startup.

Summary:

Designing a distillation system to consistently achieve a given on-spec capacity involves more than the traditional activities of sizing equipment and pipe. Other factors determine actual performance in the presence of feed changes, equipment constraints, uncontrolled disturbances, and periodic analyzer downtime.

Analysis of these factors during process design phase leads to improvements that reduce variation of primary product composition. Reduced variation allows the composition operating target to be shifted toward the product spec. This decreases heat and reflux requirements per unit feed, leading to increased capacity and reduced energy consumption.

These design-phase opportunities are missed if process control engineering is deferred until after startup.

This paper discusses some of the specific ways to achieve improved performance, including:

• Selecting a composition operating target during design phase
• Identifying low-cost capital improvements to reduce variation of product composition
• Designing regulatory process control strategy to prioritize the primary product
• Adding a redundant analyzer or inferential composition model for analyzer-down periods

Please Note:

This material was presented at Southwest Process Technology Conference in 2019, and the full article was published in CEP magazine in Feb 2021 issue. This presentation was included in the program for the 2022 Spring Meeting, but I had to cancel due to a medical issue. The material is still relevant to all distillation systems.

Email: chasherz@aol.com