Study of Dynamic Sealing Characteristics in an Elevated Flare

Elevated flare is currently the most widely used flare systems in refineries and petrochemical, natural gas and coal gasification industries. Waste gases from upstream process must be burnt before releasing to the atmosphere. The emissions of combustible exhaust gases usually have large turndown ratios. The size of the flare is designed according to the maximum discharge condition. However, in the case of small flow rates, combustion can be highly unstable which affects the safety of the system. In practice, a dynamic seal is often installed on the flare header to prevent oxygen penetration. Inert gas is purged into the system to maintain a micro-positive pressure inside the flare header. Typically, the appropriate purge gas rate is decided on engineering experience which may not be able to ensure the operation safety. In this study, we carried out numerical simulations and experiments to investigate the fluid dynamics and oxygen concentration within a flare model. Typical working conditions are tested in experiment for validation purpose. The safe and economical purging speed is explored as well as the influencing factors to provide calculation methods and basis for the dynamic seal design. (paper)