The catalyst is chosen for its efficiency, its stability and selectivity. The required volume of catalyst is referred to as bed extending over a fixed height for a given reactor diameter.The catalyst loading diagram is the general scheme with the sequence of inert balls, and different types of catalyst, each one having its specific size and bulk density.The catalist layers can extend in one bed or several beds in a multi bed reactor, in such a way that several support grids have to be installed in the same reactor.Under axial flow operations, the support grid Assembly has to withstand vertical process loads. The grids have to be reinforced or supported by extra beams adding extra strength to the assembly.T or I shape beams can be used. T- beams generally are used for high design pressure allowing the possibility to immerge the important height of the web inside the bed above the grid. I- beams, on the contrary is more commonly used for lighter design pressure, allowing to position the beam below the grid.The support grid is installed on a ring integral to the pressure shell. It has to be built in sectors to enable its installation through the vessel manhole. Some processes require a locking system to secure the panels.A small gap is left with the inside of the vessel wall in order to allow differential thermal expansion and installation clearance and to handle manufacturing tolerances or out of roundness of the reactor itself.Rope packing for catalyst sealing.