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Cleaning the Coke Drum Vapor Lines Pays

How long is your plant willing to wait to clean (a.k.a. decoke, line mole, hydroblast, or– my personal favorite– “Clean the Donut”) the drum vapor line?

DOV Opening for Cleanout 6

DOV Opening for Cleanout 6

Determining the optimum frequency is site specific but when we look at some select factors, we often arrive at the same conclusion: you should be cleaning it more often than you are. This will pay significant dividends in the form of yield improvement.

New Delayed Cokers– like those by Bechtel, Amec Foster Wheeler or Lummus– are designed with a minimal pressure drop between the coke drum and the fractionator flash zone to increase liquid yields. In many cases, it is not uncommon to see vapor lines +24″. The typical design pressure drop is 2-5 psig only. However, in site performance assessments, it is common to see the dP exceeding 4-5 psig above the clean state.

This is costing real money!

Pressure vs Yield PetroSIM

Pressure vs Yield PetroSIM

Yes, finding the yield shift in the poor DCU material balance will be hard, but there is enough science to demonstrate it is real to keep the economics on solid ground. Based on the PetroSIM DCU model, each PSI is worth (-0.16 wt%) reduction in coke yield. These products will be distributed in the yields but most of the incremental molecules will be HCGO. Assuming your HCGO goes to either an FCC or HDC, the marginal value of the extra HCGO will be $5-20+/BBL. Assuming a margin of $10/bbl on a 50kbd coker, the value of cleaning the vapor line at 2 psig versus 5 psig over the clean state is: 3 psig > 240 bpd+ HCGO > 876k$/year!

I could be wrong, but I think you can pay the salaries for a lot of maintenance guys to do this cleaning more regularly with those profit margins. At one recent plant visit, I observed operators doing the donut cleaning without maintenance support. That was amazing! Just make sure you torque the bolts on the dollar plate properly, guys….

Here are some cleaning frequency recommendations with proven success:

Check out the recent presentation given at RefComm® Galveston 2018 by Sim Romero and Maria Aldescu about PetroSIM model results and new correlations.

For more information, feel free to contact me directly or visit

–Written by Evan Hyde, Director of Field Operations

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Posted by: Evan Hyde

Evan Hyde is the director of field services for He previously was president of C2 Nano Technology where they researched surface treatments to combat fouling & corrosion issues in cokers & other petrochemical process units. He was a Senior Engineering Advisor for Becht Engineering Co., Inc. and has consulted on processing improvement and reliability initiatives for coking clients around the world. Prior to joining Becht, Evan worked for ExxonMobil Research and Engineering, as a process engineer, with assignments in research, and troubleshooting for heavy oil upgrading equipment. He holds a B.S. of Chemical Engineering from Pennsylvania State University.