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AnonymousI would like share with this forum our recent incident in the DCU.
It happened when we shut down our DCU for cleaning the overhead line of the coke drum.
It happened when the contract worker was about finished with the cleaning work. The 4″ HCGO quench oil line was wating for him to connect to the 48″ overhead line. He stood in front of the 4″ opening nozzle on the overhead line.
Then, a sudden steam blow from the 4″ nozzle on the overhead line (48″) topple and scald the worker.
What is the root cause of this incident?
Why does steam still exist in the coke drum after three days of cleaning work?
Following is our inferential conclusion:
In order to avoid the plugging problem of the switch valve and isolation MOV, we do not stop the steam injection for these valves.
The injected steam condensed and accumulated backwardly in the overhead line.
As the overhead line is well insulated, the condensed liquid actually is a saturated boiling liquid. It could blow out at any time, especially when the liquid level is high.
From 4DrumCoker
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AnonymousI do not think that the condensate flashed. More than likely, steam entered the drum and lifted the condensate. There is also the possibility that there was residual steam condensate downstream in the vapor line, either upstream of the first steam-purged block valve or in the spool between the two block valves. Steam could have entered by that side (via the downstream valves or spool) and lifted condensate toward the depressurized coke drum.
Bottom line: This event points to the need to drain and isolate (using close blinds) coke drum piping that is to be opened for maintenance. Relying only on closure of the double block valves is not sufficient to prevent steam incursion into the piping system being repaired or maintenanced.
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Our standard practice does not allow us to open / enter any system without positive isolation. Basically, a schematic drg showing blinds is maintained along with a master list of blinds. This also helps when you are de-blinding before commissioning.
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AnonymousA similar incident happened several years back at a Coker in the southern US. The root cause was steam purge leakby into the overhead vapor line. The steam was condensing, and eventually accumulated a sufficient level to “burp” overhead into the piping. A contract worker was working at that location to hydroblast the vapor line, and was scalded when the hot water came out. The facility now opens drain valves on the vapor line to prevent a level from forming. Hope this helps. [;)]
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I think so, thank you to share it to us, I will have a try.
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