What Does Bed Expansion Mean?
Bed expansion is defined as the increase in the volume of a bed of ion exchange or filter media during upflow operations, such as during backwashing. It is caused by lifting and separation of the media. Usually, bed expansion is expressed as the percent of increase in bed depth. Bed expansion is also called Expanded Bed Adsorption (EBA).
Corrosionpedia Explains Bed Expansion
Once the adsorption step is completed, it is a standard industry practice to wash the ion exchange resin beds or the fluidized bed so that any remaining particulates at the bottom of the bed are flushed out. This is performed with the effluent flow in the reverse direction. This procedure is also called a backwash step. An effective backwash of a fluidized bed happens when a uniform flow of water is fed from the bottom of the bed in order to fluidize the resins and disengage any fine resin and suspended particulates around the resin bed. For the complete removal of left over resin particulates, the resin bed or fluidized bed can be expanded to 12 inches (30 cm) of the backwash collector at the top of the vessel as shown in the diagrams below.
We can calculate the percent expansion for an ion exchange vessel using the formula:
Percent Expansion = Fluidized Height / Settled Bed Depth x 100