Silencing Hydraulic Hammer in Deethanizer Reboiler Condensate Drum

摘要

Braskem’s deethanizer reboiler condensate drum experienced hydraulic hammering when thereboiler operated at lower steam loads and when the column loads were reduced quickly. Thecondensate drum level indicator was unreliable and insensitive to the variations in level controlvalve opening. Condensate drum level control was poor, and the control valve had to be operatedon manual.Surface temperature survey showed that the reboiler condensate was highly subcooled. Thesubcooling is attributed to generous sizing of the reboiler and to an undersized condensate drainline. Analysis in terms of vapor pressure led to the conclusion that due to the subcooled liquid,the condensate drum did not operate like a normal drum with a normal vapor space. Thisexplained why the liquid level was insensitive to the level valve opening. The hammering wasdue to the collapse of steam onto the subcooled condensate.The problem was solved by keeping the subcooled condensate away from the drum liquidsurface, thereby restoring vapor space to the drum. This was achieved by relocating thecondensate entry below the liquid level and adding a channel baffle to keep the subcooledcondensate down in the drum. The level measurement was modified to measure the level acrossthe drum only and not both the drum and reboiler. Following the modifications, the hammeringwas entirely eliminated and good automatic level control was established.Lessons learnt are that correct, inexpensive hydraulic design of a condensate pot is central tostable, trouble-free reboiler operation, and that contrary to recent published reports, correctlylocating the condensate inlet to the drum is central to trouble-free operation.