Q & A > Question Details
we are suffering coke formation inside our VDU heater, considering high tube hardness we can't preform steam air decoking, the other alternatives are pigging and chemical cleaning. Any advice about the difference between these methods, concerning risks, operation, concerns, disadvantages?
03/12/2015 A: Gamal Abou Senna, Alexandria Mineral Oils Co. (AMOC), gamal@amocalex.com
Acids utilized in chemical cleaning are weak acids and their effectiveness on coke removal is very slow because the formed coke includes inorganic compounds, so to save time the mechanical cleaning by pigging is preferable.
10/11/2015 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Chemical cleaning of coke would be a very difficult task. It would probably take a strong acid to digest the coke as coke is not normally going to respond to traditional solvents. Pigging vacuum heaters can be challenging because of the changing tube diameters. I'm not sure why having hard tubes would prevent you from steam air decoking. I have not heard that one before.
10/11/2015 A: Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
Firstly chemicals will not remove hard, bonded, inert hydrocarbon Coke formation.
Providing tubes are piggable and not overly restricted by the Coke then studded pigging is viable.
There are about 15 studded pigging companies globally.
Occasionally pigs have been know to score the tubes which cannot then be undone so take care.
Scoring means that the pig will follow the grooves and no longer effectively de-coke.
Super high polymerised water jetting is a safe but slower alternative but it requires small access ports on every other bend.
Online live mechanical decoking @ 450 deg C, although quite a new technology, is potentially possible, dependent on the design by tubetech.com.
As an aside and in order to achieve maximum heater efficiency; Robotic Convection Bank cleaning (external finned tube surfaces is adviseable. This minimises hotspots and future internal Coke formation as well keeping stack temperatures down, not least reduced energy costs and longer run times and of course asset life.