Case study: the effect of vapor blowby to the debutanizer column pressure relief valve (PRV) sizing

Gas or vapor blowby is a dynamic scenario whereby the vapor is being discharged via liquid outlet from the process component due to the multiple process failures such as control valve fail-open or blocked liquid outlet provided that the design pressure of downstream equipment is lower than the upstream pressure. The degree of fatality caused by failure to properly address a vapor blowby event, which is significant for a distillation column relief valve sizing may affects the plant performance, creates casualty and in worst case scenario loss of life. Therefore, this work was carried out in order to study the effect of vapor blowby to a distillation unit profile which are temperature, pressure and flow rate from its upstream column and its importance for a column relief device sizing. The work was simulated using Aspen HYSYS software focusing on debutanizer column under four different cases. From the result, it is confirmed that in order to adequately size a relief device and also cater for the possibility of a vapor blowby event, the relief valve should be sized for a two - phase flow condition.