Keep Drain Free to Shorten Coking Cycle

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One of the frequent causes of extended coke drum cycles is the difficulty in filling the drum with cooling water. Once feed is switched out of a coke drum, the coke tends to settle back and partially plug the feed nozzle in the bottom head. This effect is especially pronounced when shot (i.e., BB-size pellet) coke is produced because of charging a low-gravity feed. Not only is the time required to fill the drum with water extended, but it becomes difficult to drain the drum.

To keep the feed nozzle open during a switch, a small amount of steam must be cracked into the drum that is being taken off-line. By the time the feed has been diverted from a full drum, the flow of steam should be several thousand pounds per hour. In practice, the steam flow is adjusted to maintain the pressure in the feed line several psi above the pressure in the bottom of the coke drum.

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