Sizing of safety valves and connected inlet and outlet lines for gas/liquid two-phase flow

摘要

Under the auspices of the International Standards Organisation (ISO) a working group of the Technical Committee 185 entitled "Flashing liquids in safety devices" is developing a draft for the sizing safety relief valves in two-phase gas/liquid flow. Extracts from the current draft proposal will be presented in the following and is open for discussion. The sizing method within the ISO draft standard is primarily based on the DIERS methodology. Herewith, the flow through the safety valve is assumed to be homogeneously mixed and both phases are assumed to be in thermodynamic equilibrium. Particularly for low mass flow qualities at the entrance of the safety valve, this method can oversize the safety valve and any connected vent-lines and separators. The original method is therefore extended to account for thermodynamic non-equilibrium (boiling delay).