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where is the number of theoretical plates (also called the "plate count"), H is the total bed height and HETP is the height equivalent to a theoretical plate. The material in packed beds can either be random dumped packing (1-3" wide) such as Raschig rings or structured sheet metal.
In 1943 Dr Olaf George Dixon of ICI applied for a patent of a new product for column distillation. [1] He used stainless steel mesh instead of sheet steel in the Lessing ring in order to improve the pressure drop of the packed column (in fact, they were called "wire gauze Lessing rings" in a 1949 publication [2]).
A Raschig ring is a piece of tube, approximately equal in length and diameter, used in large numbers as a packed bed within columns for distillations and other chemical engineering processes. They are usually ceramic, metal, or glass and provide a large surface area within the volume of the column for interaction between liquid and gas vapours.
A larger surface area allows more cycles, improving separation. This is the rationale for a Vigreux column or a packed fractionating column. Spinning band distillation achieves the same outcome by using a rotating band within the column to force the rising vapors and descending condensate into close contact, achieving equilibrium more quickly.
where: = (), = = (), is the modified Reynolds number, is the packed bed friction factor,; is the pressure drop across the bed,; is the length of the bed (not the column), is the equivalent spherical diameter of the packing,
A packed bed used to perform separation processes, such as absorption, stripping, and distillation is known as a packed column. [1] Columns used in certain types of chromatography consisting of a tube filled with packing material can also be called packed columns and their structure has similarities to packed beds.
For a packed column, the cross-sectional area of the column exit flow path is usually taken as 0.6 times the cross-sectional area of the column. Alternatively, the linear velocity can be taken as the ratio of the column length to the dead time. If the mobile phase is a gas, then the pressure correction must be applied.
Random column packing is the practice of packing a distillation column with randomly fitting filtration material in order to optimize surface area over which reactants can interact while minimizing the complexity of construction of such columns. Random column packing is an alternative to structured column packing.