Packed Tower Internals
Packed towers are designed on the basis of equal liquid and gas superficial velocity across the column cross section. The pressure drop across the packing provides a means for the upward flowing gas to become uniformly distributed across the column area. However, as the liquid flows down the packed bed by gravity it has poor cross mixing tendencies therefore it is important to ensure uniformed liquid distribution at the top of the packed bed. Distributors are internals which are installed above a packed be to provide a finite liquid distribution over the packed bed, it allows liquid to flow in discrete streams. This can be done with through orifices or V-weirs, located on/in the distributor. Distributors also provide a separate passage for the upward flowing gas.
Bed limiters and hold down plates are retaining devices used to prevent fluidisation of packing during operational upsets. Movement of packing can cause efficiency loss, therefore bed limiters are used for both random and structured packing. They are fastened to the column wall by means of support ring or bolting clips. They can also be suspended on tie rods from the liquid distributor.
Bed limiters rest directly on packing and can prevent ceramic packing from breaking up due to fluidisation when operated at high pressure drops or during surges. Bed limiters are designed to provide high open-area and reduce interference to liquid flow. They should be designed to withstand upward forces acting on the packed bed.
Packing Support Plate
Support plates are used to physically hold up the cumulative weight of the packing and the operating liquid hold-up in the packed bed. Support plates are shaped and designed to provide the maximum open area and minimal pressure drop. Factors that influence the choice and design of the support plate include the column diameter, design loads (mechanical and hydraulic), packing type, liquid hold up and system corrosively.
GLP packing support plates are designed to promote maximum capacity gas injection, with perforated beam design for optimal strength. These support plates are manufactured in sections to fit through vessel manways and can be manufactured from a wide range of materials.
A liquid distributor will not function properly if vapor is trapped in the liquid which creates uneven hydraulic head across the distributor. Flash feed devices separate the vapor in the feed so that only clear liquid is introduced onto the distributor.