First of all thanks to all for participating in the discussion and sharing your expert views. It was indeed helpful.
To conclude this thread I would like to share the solution of the problem we implemented.
After detailed discussion with the LICENSOR, LICENSOR suggested there is accumulation of the contaminants(heavier components) in the bottom side of the reboiler. The solution suggested by LICENSOR is periodically draining out of the accumulated contaminants.
Regards
Jitender