(94b) A Dying Column, Hidden Damage And The Weeping Trap Syndrome

A deterioration in a petrochemicals column performance offered a challenging puzzle. Investigations were carried-out into the potential root causes, through data analysis and trials, all of which suggested a severe stage loss through the system - this was at odds with the column scan which showed much more restricted damage.  Opening the column showed extensive manway loss and panel damage, apparently confirming a simple explanation of poor manway installation. However detailed analysis of other causes led us to highlight a previously underestimated vulnerability with this kind of column named “Weeping Trap Syndrome” or WTS. Cases where the steady state load profiles in the column change severely tray to tray are most susceptible to WTS.  Whilst most trays are well loaded others are on the edge of weeping even at design.

Following this theory through, the loss of a few trays can have a significant overall stage loss as the low load front shifts down the column. For most towers the numbers of stages is a threshold function of rate - hit the right load to seal the trays and the stage count is fixed.  For a WTS column we postulate an odd feedback mechanism where the number of stages depends on both rate and the degree of separation you achieve.  This leads to potentially unworkable startups.