Packed column versus Tray column

Selection of plate column or packed column can be done on the following basis:

Plate columns

  • Column Diameter is more than Packed column. So it’s very expensive.
  • Because of liquid loop on sieve tray pressure drop is very high. So because of pressure drop bottom temperature increases and ultimately heat load increase.
  • For smaller diameter cartridge tray to be used which is difficult to install as compare to packed column.
  • If suspended solid particle more than tray column is useful than packed columns to avoid chocking. TSS to be removed through manhole in trays column and cleaning procedure is easy.
  • Plate columns can handle wide range of gas and liquid flow rates.
  • When the liquid cause fouling or deposition of solids, even though the tray is blocked up, it is easier to clean it and manholes can be provided over the plate.
  • Tray columns are particularly applicable for high pressure columns, where pressure drop is not an important consideration and gas purity specifications can readily be attained with about 20 trays.
  • Trays handle solids much more easily than packing. Solids tend to accumulate in packing voids. There are fewer locations on trays where solids can be deposited. Cleaning trays is much easier than cleaning packing’s.
  • Plate columns are normally suitable for fouling liquids or laden with solids. They are easier to clean and could handle substantial temperature variation during operation
  • Foaming system reduces the performance of plate columns. Anti foaming agents can be made use of to suppress the foam.
  • Liquid hold up is very high. Therefore pressure drop is very high.
  • For corrosive liquids, cost of plate column is too high due to use of corrosion resistant material.
  • Supporting structure required is costly.
  • Columns with diameter less than 1 m (3 ft) are difficult to access from inside to install and maintain the trays. “Cartridge” trays or an oversized diameter are often used. Either option is expensive. Cartridge trays also run into problems with sealing to the tower wall and matching tower to tray hardware . Packing is normally a cheaper and more desirable alternative
  • The random packing appears to have the highest capacity and efficiency with conventional trays just slightly behind. Structured packing has the least capacity and efficiency.

Packed column

  • Column diameter is less than tray column, so it is cheaper than tray column.
  • Column height is reduced because more number of theoretical stages in packed column than tray column.
  • Flooding factor is more than tray column, so we get more capacity than tray column.
  • Void fraction is more than mass transfer area also more and avoid foaming.
  • For smaller diameter we can give redistributors which avoid channeling and we get more efficiency than tray column.
  • Packed columns are more suitable for low capacity operations.
  • Packed columns are particularly useful in the field of vacuum distillation. Here column pressure drop is of paramount importance to minimize the pressure and temperature at the bottom of the column.
  • Pressure drop per unit length is less in packed column.
  • Packed column provides continuous contact between the vapor and liquid phases.
  • Packed columns are suitable for handling foaming system.
  • Total weight of packed column is less due to use of low weight and high capacity packing.
  • Packing is also preferred for columns where pressure drop and possible foam formation are important considerations.
  • Packing should not be used in Stripper column which can readily Solidifying can lead to plugging of the packing.
  • Vacuum systems. Packing pressure drop is much lower than that of trays because the packing open area approaches the tower cross-sectional area.
  • the tray liquid head, which incurs substantial pressure drop (typically about 50 mm of the liquid per tray), is absent in packing.
  • tray pressure drop is of the order of 10 mbar per theoretical stage, compared to 3 to 4 mbar per theoretical stage with random packing’s.