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Case 4 Liquid Hammer (Reference 7)

INSTALLATION A total air condenser condensing column overhead. Condenser length was 32 feet and the tubes were sloped 5-6 feet. Condensate was backed up from the accumulator drum to ensure there was a liquid level inside the tubes. This level varied according to the capacity requirements. Column pressure was controlled by a control valve in the line from the column to the condenser (Figure 8.2.4).

PROBLEM A liquid hammer that shook the whole unit occurred during startup.

CAUSE Under some conditions during startup, the control valve would completely shut. When this occurred, the air cooler quickly condensed all the vapor available downstream of the valve. This caused liquid to be drawn up from the accumulator drum, producing the liquid hammer.

SOLUTION The valve was modified so it would not complete shut. FROrt C0UMN

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CASE 5 Slug Flow in Risers (Reference 8; a similar experience is reported in Reference 9).

INSTALLATION Overhead from an atmospheric crude distillation column (Figure 8.2.5) was condensed using four condensers located below the reflux drum.

PROBLEM Sharp fluctuations were observed at low flow rates. Column pressure and accumulator level fluctuated. Fluctuations were caused by slug flow.

SOLUTION Change riser size to avoid slug flow; alternatively, use dual risers.

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