Slug catcher is designed to accommodate slug volume created by change in flow rate of two-phase fluid so that downstream equipment handle stable flow of fluid. Slug catcher is commonly provided in upstream oil & gas processing facilities to handle reservoir fluid coming from oil wells.
Slug volume is a function of change in liquid hold-up volume. The liquid hold-up fraction is ratio of liquid volume in a pipe line to total pipe line volume. As liquid hold-up decreases with increase in gas flow rate, there is a decrease in liquid holdup volume when total two phase fluid rate increases. The difference between initial and final liquid hold-up volume is released over a time period, which is liquid residence time and equal to final liquid holdup volume divided by final liquid volumetric flow rate. Thus, there is increase in total liquid flow rate during the transition period (liquid residence time). After the transition period, liquid flow rate stabilizes to equilibrium flow rate.
During transition period, total liquid volumetric flow rate is sum of equilibrium flow rate and the additional flow rate due to reduction in liquid holdup volume. The excess of this flow rate over what can be handled at receiving end of the pipe line gives rise to slug volume i.e. slug volume is excess flow rate multiplied by liquid residence time. A slug catcher which in essence is a liquid-vapor separator should be provided with additional liquid holdup (between normal liquid level and high liquid level) equivalent to slug volume.
About Author: Satyendra Kumar Singh, B.Tech. (Chemical Technology) + M.B.A., is proprietor of Satsha Management Services-an award winning design engineering and management consulting company (www.satshamanagement.com). He possesses approximately 30 years’ experience in engineering consultancy in process and energy industries. Satyendra has authored several papers on energy, business and management, which have been published in some renowned journals/magazines such as ‘Chemical Engineering’, ‘Process Worldwide’, ‘Modern Manufacturing India’. He may be reached at satyendra.singh@satshamanagement.com, Ph. +919811293605.
