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SAS assesses safety impact of ignition delay with CFD

In order to assess the safety implications of ignition  delay on an elevated multi-point flare, SAS used a proprietary flare modeling tool and then developed it to simulate precisely the ignition phenomena of the Statoil flare burning gas at a rate of 350 tons per hour.

With the CFD model fine-tuned to accurately reflect  actual flare performance, CFD specialists at SAS were able to replicate the measured flame spread rate and reproduce the measured pressure wave generated during the ignition event.  Based on this verification, SAS' CFD tool was then used to conduct over sixty separate simulations to investigate the ignition behavior of the flare. 

Results from these simulations clearly showed the critical effects of ignition delay on the magnitude of the pressure wave generated during ignition.  The main conclusion drawn from this analysis was that the ignition system’s reliability to quickly ignite the flare gas above the flare tip was critical to its safe operation.

In fact results showed  that a delay of between 0.3 seconds to 0.6 seconds had a major impact on the magnitude of the pressure wave generated during flare ignition. This proved to be of particular importance  given that these results were based on a low flow rate, approximately one-tenth of full flare operating conditions. 

At higher flow rates, it was observed that a pressure wave capable of damaging equipment and injuring plant personnel may be possible.  Consequently,  additional work was carried out to assess the explosion potential.  

SAS' CFD tool was also used to evaluate and identify more efficient and reliable ignition techniques to reduce the explosion risk caused by excessive flare gas accumulation above the flare tip.