(356d) Dynamic Simulation and Optimization for Flare System Design and Validation

The correct design of flare systems is a key aspect of the safety of process plants. The current industrial practice primarily focuses on the use of steady-state calculations based on the maximum relief flowrates that could originate from the various potential sources connected to the system. The underlying assumption and justification for this approach is that this would represent the most challenging situation that the system would ever have to handle.

In fact, it is relatively easy to envisage plausible combinations of events that would lead to worse situations, sometimes with serious safety-related implications. These more complex scenarios invariably arise from the dynamics of both the plant and the flare system, and are often associated with effects that relate not just to the pressures (e.g. flow reversal in parts of the flare system), but also to the temperatures of materials and equipment in the system (e.g. potential failures due to very low temperatures), and sometimes to the interactions between pressure, temperature and chemical composition (e.g. potential formation of solid phases in the flare system pipework). As a result, the analysis of such situations requires mathematical models that are not only dynamic, but also incorporate a degree of detail that is significantly higher than what is currently employed in such applications.

Even with the help of detailed dynamic models, the design of new flare systems or the validation of existing ones is hampered by the very large number of possible combinations of events that can potentially arise. Consequently, the identification of ?worst-case scenarios? via repeated dynamic simulations may be neither efficient nor reliable. A more systematic alternative is offered by the use of dynamic optimization techniques with suitably formulated objectives. If necessary, any scenarios that are identified in this manner can then be used in the context of a multiscenario optimization approach to suggest appropriate modifications to the existing flare system design.

In this paper, we describe an advanced system for flare system design and validation based on the above concepts and methodologies. The paper incorporates examples illustrating the key points made above.