The reboiler on a splitter column was experiencing problems on a major petrochemical refinery within Western Europe.
The pressure drop across the bottom section of the distillation column was surging periodically and problems were occurring around the temperature of the reboiler.
An initial TRU-SCAN®/Tru-Grid™ Scan of the column confirmed that the trays were in their correct location, although the loading on the bottom trays was much heavier than they were designed for. The liquid level in the base of the column was also higher than expected.
For the next stage of the investigation a series of densitometers were positioned a various locations: one below tray 1 (above the liquid in the base but below the vapour return); one between tray 1 and 2 and finally; one between tray 2 and 3. The density of the material at these points was measured over a period of time and the results indicated that the liquid in the base rose and then decreased, causing a rise in the traffic on both trays 1 and 2.
The liquid in the base of the column was rising to a level approaching the vapour return line and appeared to be “blowing” liquid from the base up the column. The only way the liquid in the base could be rising was due to a blockage at the exit (i.e. feed line to the reboiler)
A thorough investigation of the pipework leading into the
reboiler was carried using TRACERCO Diagnostics™
Scan. The results from the TRACERCO Diagnostics™
Scan confirmed the presence and location of deposits within
the pipeline, although not enough to totally starve the
reboiler it was enough to cause the liquid level to back
The column was shutdown and a new section of pipe was installed, clearing the blockage, allowing the liquid level in the base of the column to be maintained below the vapour return line. This resolved the high pressure drop and liquid surges up the column.
As well as investigating the process and mechanical integrity of columns, TRU-SCAN®/Tru-Grid™ Scan can be equally useful in determining the location and extent of blockages within pipework.