There are many variations and purposes for bed limiters and holddown devices. As the names imply, their general purpose is to hold packing, random or structured, in place within the process column. However, in some cases, holddowns are used as a platform to support and level a liquid distributor.
Both devices can be mechanical designed to withstand specified up-lift requirements.
The most cost-effective bed limiter for random packing is the holddown device which is made an integral part of the Orifice/Riser liquid distributor. Expanded metal or anti-migration bars are welded beneath the vapor risers to prevent movement of the random packing during normal operation and upset conditions. Integral bed limiters have the following beneficial features: