Q ) Why expansion bellow is provided in  between ash hopper and vessel in big ash handling plant?

Ans - Expansion below are used  to provide isolation from vibrators which are mounted on the surface of the vessel to remove the fly ash contents before it's temperature decreases to prevent solidification of fly ash on the walls of vessel.

FOR DETAIL CLARIFICATION PLEASE REFER TO - http://mbl.in/ash_handling_pressure_pneumatic_conveying_system.html