Liquid Level in Reflux Accumulators

Liquid level in the reflux accumulator is normally far less troublesome than bottom liquid level. With an all-liquid top product, an overflowing accumulator will usually back up liquid into the condenser, flooding some tubes. This will reduce condensation and prevent further rise in liquid level. Often, column pressure will rise and the relief valve may possibly lift. With a vapor product, excessive accumulator 

Low accumulator liquid levels are likely to damage pumps and/or induce flow of vapor to downstream units. One case history of pump damage due to loss of reflux drum level has been described (237). 

When the reflux accumulator separates two liquid phases, excessive rise or fall of the interface level can carry over one phase into another, and/or reflux the column with the improper phase. In some situations, such carryover can be h2aardous. In one case (7), carryover of hydrofluoric acid into a propane product route from the reflux accumulator of an alkylation depropanizer caused multiple explosions in downstream equipment. The author is familiar with an almost identical incident that overpress u ed downstream equipment but stopped short of exploding. Refluxing an improper phase into a column can also be troublesome this is described in detail in Sec. 13.7. 

As with column bottom level, when an excessively high or low level can be hazardous, it is a good practice to install high-reliability level instrumentation including alarms, trips, and indicators, and to mount these as per Figs. 5.4 and 15.16. The trips usually switch off rotating machinery downstream of the accumulator and/or cut off product flow. 

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