An alkanolamine gas treatment unit system that may comprise an absorber column, a regenerator column, and a once-through natural circulation vertical thermosyphon reboiler comprising a reboiler tube and a shell. The reboiler may be a steam driven one having a process side and a shell side, wherein the process side is inside the reboiler tube, the process side of the reboiler and the regenerator column are in fluid communication with one another, an inner surface of the reboiler tube, on the process side, has a surface roughness of 0.06 μm or greater, the shell side of the reboiler is in fluid communication to a steam source, and the regenerator column and the absorber column are in fluid communication with one another. An absorbent regenerator system that may comprise the regenerator column and the once-through natural circulation vertical thermosyphon reboiler.