A study on blowdown of pressurized vessel containing CO2/N2/H2S at cryogenic conditions

Abstract

At times, CO2 capture and sequestration from the gaseous mixture have to be done at high pressure and high concentration of CO2 in vessels and pipelines. During depressurization of CO2 mixture from high pressure vessel, the chances of solidification increase and the mixture undergo sudden complex phase behavior changes that can lead to accidental events. By avoiding solidification and controlling the complex phase transitions, the chances of accident and unscheduled breakdowns can be minimized. In this paper, a simulation study is presented for the depressurization of highly pressurized vessel containing the ternary mixture of CO2/N2/H2S. The simulation is performed over different blowdown valves with orifice sizes of 4.325 mm, 6.325 mm, and 8.325 mm using BLOWDOWN software package in Aspen HYSYS® V9 to predict the phase behavior of mixture and changes in the temperature and pressure. The results indicate that the chances of an accident are minimized by avoiding the solidification during depressurization process using blowdown valve with an orifice diameter of 4.325 mm.