Dynamic analysis of a flare network: Gas blow-by and depressurization system

Abstract

Flare network systems are essential in chemical plants to ensure process safety. In particular, the flare network system of offshore platforms is expected to play a critical role, mainly due to the isolated location from the onshore safety infrastructure and the compact structure of the platforms. However, owing to the spatial and weight limitations of the offshore platforms, it is important to reduce the pipe sizes used in the flare network, while also satisfying the installation codes and standards for such systems. In this study, flare network systems of the offshore platforms were designed and optimized based on dynamic simulation results. For this, two separate cases of “control valve fail-open” and “depressuring system” were considered. In the former scenario, we observed ‘gas blow-by’ due to the inlet of high-pressure gas into the low-pressure separator, caused by liquid disappearance in the high-pressure separator. Under the latter scenario, we analyzed whether the developed design of the flare networks satisfies the depressuring rate requirement from API Standard 521 and noticed potential extreme decline in temperature in a unit during the relieving condition. As a result, we developed a strategy to decrease depressuring rate in the unit. Lastly, we saved capital costs by reducing the pipe sizes based on the optimization results, obtained from the dynamic simulation analysis.