June 18, 2016 at 9:49 pm #21874
In our DCU we have procedure of handling tarry drum by steam quenching (by MP steam, pressure 10kg/cm2) the tarry drum for prolonged period, 16hrs+ depending upon duration of tarry material and then following normal queching procedure (slow water quenching then fast water quenching). But we don’t have any procudure for handling tarry drum along with steam failure.Can anyone help. Do any other refinery have different methods for handling tarry drum?
June 27, 2016 at 9:15 pm #21884
Tarry drums are a complicated question. First, we must clarify why it was a tarry drum…..
1. low heater COT for some time?
2. Low drum vapor (DOV) temp for some time?
3. Short run drum (<4h), never reached DOV temp
Second and possibly separately, what is the cause of the steam failure? Power failure or other? Are you able to get water into the drum without steam stripping?
All of these scenarios could be handled differently by its own separate procedure. Sorry, not the clearest answer but each scenario is different. We recommend you think through each scenario completely and have a plan.
June 28, 2016 at 5:37 am #21885
Tarry drum is due to short run length.
The scenario is simultaneous power and steam failure which is a possibility and even though after recovery of power after an hour or so, steam recovery takes enough time.
Getting water into drum without steam stripping can be possible only after power recovery. But it is said that one should not get water into unconverted VR/ partially converted VR.
A more detailed description about my question could be that since due to short run length the materials inside drum would still be pitch like material. After power and steam failure, even though transfer line would be flushed by available steam header pressure, but as soon the steam pressure would fall down, the resid material from the drum would roll back into transfer line. Now if steam recovery takes enough time the resid material would plug/choke the transfer line completely and this scenario could be really dangerous and tedious to deal with.
How to mitigate from this kind of situation
February 27, 2017 at 9:03 pm #24927
You are correct in saying that this scenario could be very dangerous. This was the case at the Equilon Anacortes Coker in 1998. They unheaded the drum without quenching with water and the resulting incident caused 6 fatal injuries. There have been a number of presentations on this incident and there are always multiple factors that contribute to fatal injuries.
As a way to prevent the same sort of incident, water quenching the coke drum before deheading to removed the stored energy is imperative. If the feed line is plugged and steam and water are not able to enter the drum through the normal flow paths, add water to the top of the drum. Cover the coke bed with water and let the water boil away. Do this as many times as required to keep the water level over the top of the coke/tar.
The slide gates used for bottom heads from DeltaValve or Z&J make opening the bottom head from a remote location possible. An exclusion zone should be set up around the pit where the coke/water mixture will be routed when the bottom head is opened up. If the coke drum quench water is not completely drained, the potential for a flood of water into the pit is possible, so keep the area around the pit clear of personnel.
If you do not have slide gates for bottom heads, this complicates the draining of the drum and removing coke. Frank Tracy of P66 made a good presentation on this subject at the 2016 Galveston Coking.com conference.
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