Q & A > Question Details
Decoking of the fired heater of VDU
During recent years , the skin temperature of one of the 4 coils developed a slightly higher skin temperature than the other 3 coils , the skin temperature is nearly 500 C , it is still in the safe range but we are now considering decoking to to remove any present coke during shutdown . Anyways , I am comparing SAD ( Steam Air Decoking ) to Pigging , There seem to be many hazards and incidents during SAD , i wonder if any of you witnessed any incidents with SAD ? ... Can anyone clarify the potential hazards and their severity ? do you recommend it or you recommend pigging ? ...... Thanks for your comments and replies in advance ....
 
Answers
05/09/2017 A: Mohamed Awad, AMOC, Egypt, Mohamed.awad@Ymail.com
Thanks for your valuable insights .... after a careful study, our department decided to use Pigging instead of SAD and we have just initiated an invitation to bid for hiring a specialized contractor during the next shutdown.
31/08/2017 A: S Sivasankaran SABANAYAGAM, CPCL, cpclsiva@yahoo.com
We have done SAD without any issue so far. However close monitoring is required while admitting air and it should be controlled properly
500 Deg C very normal temperature for VDU heaters.
31/08/2017 A: Dave Collings, Jacobs, dave.collings@jacobs.com
My impression is that you will find issues with steam-air decoking, pigging, and online spalling. All of these processes need to be monitored closely to make sure the procedure is done correctly and safely.
Years ago, I monitored a dozen or so steam-air decoking jobs at a Coker heater. I adjusted the air myself to optimize the process. My personal view is that steam-air decoking is easy to manage.
Have someone from Tru-Tec (or one of their competitors) on site to take thermometry measurements periodically during the process. Have an engineer or good operator monitor visually and adjust the air as needed to make the process go quickly while not exceeding max skin temperatures.
Steam-air decoking on a Coker heater took us about 2.5 days oil in to oil out. Pigging can be done in 2 days oil in to oil out. So, the steam-air decoking took longer.
18/08/2017 A: Muhammad Faisal, OQ integrated energy company (Oman), engr.faisalfraz@gmail.com
We have experienced of SAD & Pigging. Of course Pigging is preferred over SAD. If heater is equipped with SAD, try to utilize it first, major point to focus, carry out extended hours steam flow, while introduce air very slowly and at a low rate for extended period.
Decoking drum drain effluent water colour is main check whether the line is clear or not after applying air.
For Pigging, it involve s/d, specialised contractors (contract resources (CR)) available plus others to perform it safely & efficiently.
16/08/2017 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Pigging is generally preferred, but the large number of diameter changes in the tubes complicates the pigging process. If pigging is done too aggressively the pig can gouge the tubes. If the pigging is not aggressive enough skin temperature recovery will be incomplete.