Thermo-hydraulic modeling of flow in flare systems

Abstract

Flare systems play a major role in the safety of Oil and Gas installations by serving as outlets for emergency pressure relief in case of process upsets. Accurate and reliable estimation of system thermo-hydraulic parameters, especially system back-pressure is critical to the integrity of a flare design. FlareNet (Aspen Flare System Analyzer Version 7) is a steady state simulation tool tailored for flare system design and has found common use today. But design based on steady state modeling tends to be over conservative, due to the transient nature of the pressure relief processes in a flare system. In this work an evaluation is done to see if OLGA (Version 7.1.1), a dynamic tool but not tailored for the high velocity flow common to flare systems, may be used for reliable dynamic modeling of a flare system. Simulations are run both in FlareNet and OLGA for a simple pipe system representing part of a flare network under steady state conditions. A comparison of the results from FlareNet and OLGA shows that OLGA estimates lie within acceptable ranges for subsonic flow. Observed differences in estimated back pressure are thoroughly analyzed, and reasons for such differences are stated. Recommendation is made that OLGA may be used for dynamic modeling of flare systems with reliable results that give a more realistic characterization of the processes taking place during pressure relief.