Separator and Stabiliser

As I understand it, the separator releases (by flashing) hydrogen-rich gas to be recycled and exported. The stabilizer is a fractionating tower whose main purpose is to stabilize (i.e., debutanize) the reformate.

It can be nothing more than that.

The separator allows the stabilizer to be smaller because you have removed some gases that do not need to be "distilled". Think about this, if you raised the temperature in the separator 100 degress, some reformate would become gas and be lost. Likewise, if you cooled the separator 100 degress, you would feed the distillation tower with with more mass and its size (diameter and heat duty) would increase.

You can look at a separator before a tower as a 1 stage distillation tower to remove lighter ends before the next tower. You could even put 20 separators with heaters and coolers in series and end up with a distillation tower.