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In our VDU furnace there are 4 cells & 1 coil/cell. In last few days suddenly few coils in cell 1,2 & 4 from the bottom started lifting up from the support inside radiation zone. Even few coils are floating continuously. While RCO entering the furnace pass4 comes first then 3,2 &1. What could be the reason?
 
Answers
28/07/2015 A: Sudhakara Babu Marpudi, Oman Refineries and Petroleum Industries Company, m_sudhakarababu@yahoo.com
Vertical coils are provided with guide supports at the bottom of the u bends. These supports hang freely thru the bottom plate of the furnace and guide the expansion of the tubes downwards so that the coil is firmly sitting on the U shaped anchor support provided in the arch section of the furnace. Some designers will provide a cap arrangement to these guide supports to prevent uncontrolled air ingress into the combustion zone (a energy optimization measure thru excess oxygen control). Over a period of time the caps get filled up with soot / refractory dust and block the down ward movement of the tube. So the tube expansion will continue towards the free space available at the arch section. Clearing the caps free of dust / soot periodically must resolve the problem.
27/07/2015 A: Saswat Panda, Reliance Industries Ltd, saswat.panda@ril.com
1. Pls open bottom cap of guide rod for suspected choking. Clean the guide rod for deposits is any and observe for change. In case of choking and restriction it may push the coil.
2. Whether hanger support is intact. In such case observe the tube from bottom inspection window. Whether there is bowing in tubes. This may also result into deformations.