Coking in stripper bottom line

[Anonymous]

Normally in FCCU coking found at the shell side of the debutanizer reboiler, but we are facing problem with stripper bottom to Debut feed line coking. If any one has experienced this kind of problem, share the root cause of it and corrective action for it. We found the coke in stripper bottom line in recent shutdown and identified the problem. Due to restriction of the flow to Debut we have to cut down the throughput. Following parameter may help you.   Parameters for stripper. Stripper top pressure : 16-16.3 Kg/cm2(g) Stripper bottom temp : 122-125 Deg C. Stripper bottom reboiler outlet temp : 122-125 Deg C. Stripper bottom reboiler Tubeside (Lighr Cycle oil) inlet temp : 200-206 Deg C.   I have dought about the stripper feed high sulphur or water carry over from HP separator. (OR pH of the water at HP separator boot might lower that 7.0.). We found higher chloride value in HP receiver boot water. Is it a root cause for it? Give your opinion for it.

[Anonymous]

Jigs1980:

Coking in the stripper bottoms to the debutanzer is very unlikely the cause of the line pluggage. It is more likely that the pluggage is due to Iron Sulfide scale that is entrained in sour water trapped in the stripper. At typical stripper operating pressure and temperatures any sour water carried into the stripper from the HP separator upstream will be trapped in the stripper. Here are my recommendations:

First, check the sour water level in the HP separator and make sure it’s in the boot and not above the draw nozzle to the stripper. Ensure that the HP separator sour water boot is functioning and that sour water is flowing out of the boot.

Second, if line pluggage becomes a chronic issue consider installing a sour water settler in the stripper reboiler circuit to remove any trapped water.

Good Luck.

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