This topic contains 4 replies, has 4 voices, and was last updated by Anonymous 16 years, 11 months ago.
August 9, 2005 at 11:07 pm #4321
Does anyone have an emergency procedure that deals with a coke drum foam-over? Prevention of a coke drum foam-over is one thing but after the coke drum foams over, what do you do? What if the foam-over is so heavy that it plugs the overhead vapor line and the relief valves? What do you do?
August 14, 2005 at 2:30 am #7747
Yes. Essentially, we ensure the maximum antifoam rate is going into the drum, and prepare to switch or bypass if necessary. We have never experienced a foamover severe enough to plug the overhead line or PRDs.
September 20, 2005 at 1:46 pm #7741
From the How to Coker Book
Actions to take (sequenced in order)
1. Check that the antifoam system is working, and increase its rate to four times the normal as a maximum. Cut out sludge injection if being used.
2. Raise combination tower pressure 3 5 psig to pressure up coke drum(s) and slow down the carryover.
3. Reduce the furnace charge 25 percent every five minutes until foaming subsides or until the minimum furnace charge rate is reached. (Increase furnace velocity steam when furnace charge rates approach 50 percent of capacity.)
4. Start or increase diluent into the tower bottom.
5. Switch out of the full drum as soon as the new drum is hot enough. (Make a smooth switch to avoid a combination tower upset, which could aggravate the situation.)
6. If a drum switch cannot be accomplished, trip the furnace and charge pump; or cut the furnace coil outlet temperature rapidly to 750 775°F, bypass the full drum, and put the unit on circulation. A temporary outage is preferable to the alternative of extended downtime for decoking.
September 20, 2005 at 1:51 pm #7740
From the ‘How to Coke Book’
Signs of foam
1. Early, unusual or sudden drum level detector activity by any one of the drum level detectors.
2. Unusual blips, sudden or even gradual increases in coke drum pressure (sign of liquid/foam carrying over and briefly restricting normal vapor flow).
3. Increase in wet gas production (causes higher drum velocities and foaming).
4. Sharp increase(s) in combination tower level.
5. Decrease in fresh feed when recycle coking (reductions caused by material entering the tower from the coke drum overhead line).
6. Decrease in combination tower chimney temperature (temperature will drop as less drum vapors and more heavy liquid enters the tower in its place).
December 6, 2005 at 9:54 pm #7705
Recently we have a foamover incident. That has caused a 10-day shutdown. Before the incident,
our practice is to switch the drum once the 3rd nuclear source level is exceeded. Then we would inject 7 tonnes/hr of steam into the coke drum and routed to Fractionator for 20 minutes. We have seen coke fines carried over into the fractionator. The question is that, should we reduce the steam rate to reduce amount of coke fines into fractionator? Our coke drum before-quench temperature is normally between 430- 445 C. At what rate shall be the max for the steamout rate as not to cause coke fine carry over?
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