The straightener is a particular kind of vane pack used to break the foam and calm the gas flow. This internal is often placed between a rectifier and vane pack separator or a wire mesh demister.
A secondary positive effect of the straightener is a primary coarse separation of the liquid droplets from the gas flow. Usually the diameter of the straightener is equal to the vessel diameter but the remaining characteristics (kind of vanes, thickness, pitch of the vane etc) can be designed according to the process.