Quantifying ease of control for inherently safer process design and optimization
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2017 IChemE. Current inherently safer design strategies in the conceptual design stage focus on reducing the overall hazard of a process plant without considering the operability of the process. The process is first designed to be inherently safer with respect to a nominal, steady-state case. Then, after the process is designed, layers of protection are added and operability issues are addressed. However, this sequential design approach does not account for the impact of the design itself on the operability of the facility. A particular design may be safe with respect to its steady-state operation, but may suffer from operability issues. For example, an intensified process may contain less of a hazardous substance and thus be inherently less hazardous, but the design may restrict the controllability of the process, thus making the design have a higher risk and be more prone to loss. A considerable depth of research has been done to simultaneously optimize the design and control system of process plants, but no such approach has integrated inherent safety, only seeking to produce an economically optimal design rather than a safer one. The objective of this research is to implement a strategy to simultaneously design and control an inherently safer plant. The Parametric Optimization and Control (PAROC) framework will be used as a basis to simultaneously design the plant and the controller. Different inherently safer design indices will be integrated into PAROC, and the operability, safety, and economic profitability of the results will be compared. An extensive literature review identified metrics by which controllability of a process plant can be identified and optimized along with the design, as well as inherently safer design indices that can be implemented into the PAROC framework. These metrics and inherently safer design indices will be compared to create a new index for the integration of inherently safer design and control. With process systems and their dynamics becoming increasingly complex, consideration of operability issues in the design stage becomes even more necessary to prevent incidents. The integration of inherently safer design and control will substantially reduce operability issues that result from an uncontrollable process design and allow for greater tolerance and ease of control.
