Hydrocarbon condensate stabilizer system

[ttbaldy]

I have at the plant a stabilizer system that utilizes a 21 tray tower and reboiler. Every few months the reboiler is significantly fouled. even one time it was fouled so bad the tube bundle was enshrouded in junk and the tubes not visible. Has anyone had experience with something like this in the past? The fouling occurs directly on the tube wall at the hottest point and builds from there.

 

[SNORGY]

Has the "junk" been analyzed in a lab? Is it black or light gray? Is there a feed / bottoms exchanger and, if so, is there a way to assess which side of the feed / bottoms exchanger is fouling more than the other? It might help track the root cause to the point in the process where the problem is starting.