Raschig ring
Encyclopedia
Raschig rings are pieces 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 or metal and provide a large surface area within the volume of the column for interaction between liquid and gas or vapour. Raschig rings are named after their inventor, the German chemist Friedrich Raschig.
They form what is now known as random packing, and enabled Raschig to perform distillations of much greater efficiency than his competitors using fractional distillation
columns with trays.
In a distillation column, the reflux
or condensed vapour runs down the column, covering the surfaces of the rings, while vapour from the reboiler
goes up the column. As the vapour and liquid pass each other countercurrently in a small space, they tend towards equilibrium. Thus less volatile material tends to go downwards, more volatile material upwards.
They are also used for devices where gas and liquid are put in contact for purposes of gas absorption, stripping or chemical reaction, and as a support for biofilm
s in biological reactors.
Raschig rings made from borosilicate glass
are sometimes employed in the handling of nuclear materials, where they are used inside vessels and tanks containing solutions of fissile material, for example solutions of enriched uranyl nitrate
, acting as neutron absorbers and preventing a potential criticality accident
.
Packed bed
In chemical processing, a packed bed is a hollow tube, pipe, or other vessel that is filled with a packing material. The packing can be randomly filled with small objects like Raschig rings or else it can be a specifically designed structured packing...
within columns for distillations and other chemical engineering
Chemical engineering
Chemical engineering is the branch of engineering that deals with physical science , and life sciences with mathematics and economics, to the process of converting raw materials or chemicals into more useful or valuable forms...
processes. They are usually ceramic or metal and provide a large surface area within the volume of the column for interaction between liquid and gas or vapour. Raschig rings are named after their inventor, the German chemist Friedrich Raschig.
They form what is now known as random packing, and enabled Raschig to perform distillations of much greater efficiency than his competitors using fractional distillation
Fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
columns with trays.
In a distillation column, the reflux
Reflux
Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations...
or condensed vapour runs down the column, covering the surfaces of the rings, while vapour from the reboiler
Reboiler
Reboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns. They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation....
goes up the column. As the vapour and liquid pass each other countercurrently in a small space, they tend towards equilibrium. Thus less volatile material tends to go downwards, more volatile material upwards.
They are also used for devices where gas and liquid are put in contact for purposes of gas absorption, stripping or chemical reaction, and as a support for biofilm
Biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...
s in biological reactors.
Raschig rings made from borosilicate glass
Borosilicate glass
Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common glass...
are sometimes employed in the handling of nuclear materials, where they are used inside vessels and tanks containing solutions of fissile material, for example solutions of enriched uranyl nitrate
Uranyl nitrate
Uranyl nitrate is a water soluble yellow uranium salt. The yellow-green crystals of uranium nitrate hexahydrate are triboluminescent.Uranyl nitrate can be prepared by reaction of uranium salts with nitric acid...
, acting as neutron absorbers and preventing a potential criticality accident
Criticality accident
A criticality accident, sometimes referred to as an excursion or a power excursion, is an accidental increase of nuclear chain reactions in a fissile material, such as enriched uranium or plutonium...
.