(55ai) Optimize Flare Design and Mitigate Flare Capacity Issues Using Dynamic Simulations

Flares are used to burn off-gases before they are released to atmosphere. Multiple relief devices can relieve in the event of global failure such as Total Power Failure, Cooling Water Failure etc which makes flare design for an emergency event a complex task. Due to lack of data or time pressure, designers often tend to make simplified conservative assumptions which can lead to overdesigning of new relief system. Overdesign has its own negative consequences in terms of performance and cost. Overestimation of required relief rate results in bigger PSVs and bigger headers for global scenarios. In addition to flare headers, these over-estimated relief rates have direct impact on sizing of effluent handling system components such as Knock Out (KO) Drums, KO pumps and Flare Stack. Experience shows that Dynamic simulations are rarely considered in new flare design mainly due to efforts involved and time constraints. Dynamic Simulation is a time dependent/transient analysis. Pressure relief is an unsteady process - Changes in flow rates, temperature, pressure, vapor-liquid ratio, physical properties, material composition cannot be captured in the conventional methods. This presentation talks about benefits of dynamic simulations in new flare design or how to address flare capacity issues due to feed rate increase, addition of relief valves within new units to the existing flare system etc. A case study is presented which talks about how Ingenero used dynamic simulations performed in HYSYS for power failure event (controlling event for flare header rating within this facility) to address flare capacity issues for an existing low-pressure system which got overloaded due to addition of new units and rate augmentation.