In the recovery gas section of our UFCC unit seems that is having a fouling in the rectifier tower(tower before the debutanizer) reboiler. In the top of this tower is heavy fuel gas and the bottom is LPG and naphta. The reboiler is heated by main tower top pumparound. It seems that the fouling is in the process side from rectifier tower. Is it common this fouling in this kind of reboiler ? What is it this fouling (coke, gums, etc) ? Why has this fouling (process conditions) ?