Analysis of burner operation inside an enclosed ground flare

An industrial enclosed ground flare used as part of a large refinery project has been analyzed to assess combustion stability and performance under low and high flow conditions. This flare includes a large combustion chamber directly above the burner deck with Low Flow (LF) burners that fire up to 9 MMBtu/hr plus High Flow (HF) burners designed to fire at 8 to 45 MMBtu/hr. The LF burners operate with simple "diffusion" flames while the HF burners use "pre-mixed" flames designed to limit NOx emissions. During initial commissioning tests, the flare was operated over a range of process conditions. Testing results indicated the following: 1. Relative flow velocity through the burner throat was critical to maintaining a stable flame above the burner, 2. Burner placement inside the flare impacted flow profiles that led to asymmetric flow and produced low pressure fluctuations during normal operations, and 3. High frequency pressure fluctuations observed near the burner were attenuated and became low frequency fluctuations at the stack exit. This paper describes results of the CFD analysis of this enclosed flare that focused on flame stability and noise generation inside the flare during operation