Q & A > Question Details
We have a thermosyphon reboiler for Light kerosene stripper with LGO pump around as heating media. We have seen a significant reduction in the reboiler performance observed by reduced delta T across LGO Pump around. This has resulted problems in light kerosene flash point. We introduced stripping steam and somehow overcome the problems. We observed that there was gradual increase in delta T over a period of time across light kerosene side in the reboiler. Can anyone help us to explain this unusual phenomenon in LK reboiler? Can the dryness across light kerosene in the reboiler results higher delta T? Gamma scanning of the column was done and found normal. How can we predict the Thermosyphon Circulation rates? Can the high temperature of LGO pump around inlet to reboiler cause fouling on kerosene side? If it is fouling on the tubes, then there should be reduction in delta T across LK side. In fact we are seeing an increase in delta T across LK side of the reboiler.

 
Answers
16/05/2011 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
It could be a simple problem of in adequate inlet flow to the reboiler. Please maintain the stripper level from the current operating levels and observe the changes in the delta T across the reboiler inlet and outlet streams. Adequate head and consequent improved circulation volumes will help the thermosyphon reboliers perform better. Some strippers are designed in such a way that the reboiled material enters the same side of the baffle (located in the bottom of the stripper) or from which the reboiler inlet stream is with drawn on a location that distributes the reboiler outlet material either way. Although it may be theoretically correct that the reboiler outlet can be any where, it is better that the reboiler inlet and outlet streams are separated by the baffle so that the reboiled high flash material does not meet the low flash reboiler feed material again.
05/05/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Because it happened gradually, I would conclude, also, that fouling has occurred. Is it once-through thermosyphon or recirculating. If once-through, there may be too much leakage through the tray for adequate flow to the reboiler. Scans have been known to be misleading at times.
03/05/2011 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
You may be fouling. Previous respondent had good points on that.
Increasing T on LK side may indicate poor circulation and too much vapourization, which can also lead to fouling. A check of the hydraulics and heat transfer using HTRI is recommended to confirm.
03/05/2011 A: NS Murthy, Reliance Industries, ns.murthy@ril.com
Couple of suggestions.
1. Look at LK quality. High acidity and low Sulphur could induce corrosion products.
2. If slop being processed, look at fractions in LK region specially olefins, if any.
3. Run HTRI for HMB across shell and tube flows. If too high LMTD, try to restrict this as well.