Thermoshipon reboiler return line should have one one bend or more than that is acceptable?
How many bend(elbow) and how much length of bend is acceptable?
There is no "rule of thumb" about changes to the design of these important process return lines..
Your question is really about the return line maximum pressure drop, which should have been considered during the equipment layout stage of the project..... Are you trying to relocate the Thermosiphon reboiler from an existing position ?
Bends are okay, but there should be no low point pockets in reboiler 2 phase return line, and line should slope continuously down to column product sump.