Bed Limiters are situated directly over a packed bed to preven the movement or discharge of the packings. They are particularly necessary in such cases where packings can experience uplift due to high gas loading or sporadic pressure surges. In addition, they can be used to separate packing of different sizes to avoid mixing of different packings within the column.

Bed limiters are designed in such a way that they do not disturb the steady state of the liquid distribution. Depending on the model, bed limiters either sit directly on top of the packed bed or are mechanically attached to the vessel wall. It is also possible to hang them directly from the liquid distributor and /or redistributor. Additionally, bed limiter can be integrated into the design of the liquid distributor or redistributor.

A variety of support grids are available to support the column packed bed, depending on the specific application and the column diameter. The support grid must be constructed in such a way that it minimally hinders gas and liquid flows.

Particularly between the packed bed and the support grid, the possibility of reduced hydraulic capacity exists.

Support grids must be adapted to:

• type of packing
• bed height
• liquid holdup
• additional weight caused by fouling
• design temperature for specific application

Support grids require a support ring and, depending on the diameter and/or the supporting loads, one or more internal support beams. If high gas velocities, pressure surges or flooding are a possibility, the bed support can be mechanically fastened to the support ring.

Flat Support Grid For Structured Packing

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The most straightforward design is the flat support grid which is used for small column diameters. The hydraulic conditions need to be taken into consideration as this type of support grid has a relatively low free cross-section. Flat support grids are available in ceramic and graphite materials in addition to metals and thermoplastics.

Hump Support For Random Packing

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Profile support grids using profile beams, offer a free cross section of 100% in relation to the entire column cross-section. Downcoming liquid flows separately from the up flowing gas stream, thus preventing the possibility of flooding, even at high hydraulic loadings. The height of the profile beams as well as the slot width ar a function of the parameters of a specific application