Transient Ignition of Multi-Tip Ground Flares

Paper from the AFRC 2018 conference titled Transient Ignition of Multi-Tip Ground Flares

Multi-Point Ground Flares (MPGF) represent a special class of flares capable of processing significant quantities of flare gas in flare fields which includes hundreds of burners surrounded by a complex wind fence that limits radiation to surrounding equipment and improves safety for plant personnel. A detailed computational fluid dynamics (CFD) model of an MPGF has been developed using a proprietary flare modeling tool called C3d. This tool has been used to simulate the ignition phenomena for several MPGFs for flare gas flow rates between hundreds to 1000 tons or more per hour (TPH).; Simulation results have been directly compared to operating test data for an elevated multipoint methane flare for calibration. Results demonstrate the ability of C3d to replicate the measured flame spread rate and reproduce the measured pressure wave generated during the ignition event. Based on this validation, the tool has been used to conduct over sixty separate simulations to investigate the ignition behavior for this multi-point elevated flare. Results from these simulations clearly show the critical effect of ignition delay on the magnitude of the pressure wave generated on ignition. The main conclusion drawn from this analysis is that the ignition system's reliability to quickly ignite the flare gas above the flare tip is critical to safe operation. Predictions show that a 0.6 second ignition delay results in a significant pressure wave generated during flare ignition. Simulations at maximum flow rate (1350 TPH) exhibit explosive tendencies with pressure waves greater than one atmosphere. This confirms the conclusion that the flare must be operated with a continuous pilot to avoid and type of ignition delay. These results underscore the importance of the API recommended practice of continuous pilot operation for all large scale gas flares.; The application of this tool to MPGF has demonstrated its ability to cause ignition in adjacent unignited rows due to wind effects. The tool is capable of predicting pressure wave events in these unignited row scenarios. Such effects can be important when pilots may be extinguished and combustible hydrocarbons are released to the atmosphere in a well-mixed and highly combustible state. Such gas clouds could be ignited remotely and create large pressure waves capable of damaging surrounding plant equipment and injuring plant personnel.