(155a) Silencing Deethanizer Reboiler Condensate Drum Hydraulic Hammer

A deethanizer reboiler condensate drum experienced hydraulic hammering when the reboiler operated at lower steam loads and when the column loads were reduced quickly. The condensate drum level indicator was unreliable and insensitive to the variations in level control valve opening. Condensate drum level control was poor and the control valve had to be operated on manual.

Surface temperature survey showed that the reboiler condensate was highly subcooled. 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. This explained why the liquid level was insensitive to the level valve opening. The hammering was due to the collapse of steam onto the subcooled condensate.

The problem was solved by restoring vapor space to the drum. This was achieved by relocating the condensate entry below the liquid level and adding a channel baffle to keep the subcooled condensate away from the drum liquid surface. The level measurement was modified to measure the level across the drum only and not both the drum and reboiler. Following the modifications, the hammering was entirely eliminated and good automatic level control was established.

Lessons learnt are that correct, inexpensive hydraulic design of a condensate pot is central to stable, trouble-free reboiler operation, and that contrary to recent published reports, correctly locating the condensate inlet to the drum is central to trouble-free operation.