what is called loading in a distillation column?

Answer 1

Too much vapour flow (velocity) upwards through a tray may cause entrainment/foaming. Too much liquid flow down the column may flood the downcomers and will reduce contact time with the vapour flow upwards. Consider the design liquid flow (in volume terms) and the design vapour flow in volume terms (allow for any change in pressure from design case) as 100% loading unless one has established by performance test or detailed calculation that the column has spare capacity.