Time Saving Detail in a Coking Cycles

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Figure 2-5 shows the valves used during the coking cycle. Prior to switching out of a coke drum, the process operators must be sure that the empty coke drum is truly empty. Trying to speed up the cycle by cutting hot feed (900°F) into a coke drum that is incompletely drained will cause a foamover.

Valves used during the coking cycle
Valves used during the coking cycle

The quick way to be sure that a coke drum is clear of liquid is to use a “tailpipe” thermocouple (Fig. 2-6). This temperature point is located between the coke drum bottom head and the condensate collection drum. When the coke drum is draining freely, the tailpipe temperature will be close to the coke drum temperature.

Thermocouple verifies drainage (courtesy Oil & Gas Journal).
Thermocouple verifies drainage (courtesy Oil & Gas Journal).

A cold tailpipe indicates a coke drum with liquid accumulated in the bottom head. About 30 minutes before switching time, the operating crew should verify that the tailpipe thermocouple is reading at least 370°F to 400°F.

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