A plate column (or tray column) is equipment used in

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

to carry out

unit operation In chemical engineering and related fields, a unit operation is a basic step in a process. Unit operations involve a physical change or chemical transformation such as separation, crystallization, evaporation, filtration, polymerization, isomeriza ...

s where it is necessary to transfer mass between a liquid phase and a gas phase. In other words, it is a particular gas-liquid contactor. The peculiarity of this gas-liquid contactor is that the gas comes in contact with liquid through different stages; each stage is delimited by two plates (except the stages at the top and bottom of the column). Some common applications of plate columns are

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

, gas-liquid absorption and liquid-liquid extraction. In general, plate columns are suitable for both continuous and batch operations.

Fluid dynamics

The feed to the column can be liquid, gas or gas and liquid at

equilibrium Equilibrium may refer to: Film and television * ''Equilibrium'' (film), a 2002 science fiction film * '' The Story of Three Loves'', also known as ''Equilibrium'', a 1953 romantic anthology film * "Equilibrium" (''seaQuest 2032'') * ''Equilibr ...

. Inside the column there are always two phases: one gas phase and one liquid phase. The liquid phase flows downward through the column via gravity, while the gas phase flows upward. These two phases come in contact in correspondence of holes, valves or bubble caps that fill the area of the plates. Gas moves to the higher plate through these devices, while the liquid moves to the lower plate through a downcomer. The liquid is collected to the bottom of the column and it undergoes

evaporation Evaporation is a type of vaporization that occurs on the Interface (chemistry), surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evapora ...

through a

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 distillat ...

, while the gas is collected to the top and it undergoes

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...

through a condenser. The liquid and gas produced at the top and at the bottom are in general recirculated. In the simplest case, there are just one feed stream and two product streams. In the case of the

fractionating column A fractionating column or fractional column is equipment used in the distillation of liquid mixtures to separate the mixture into its component parts, or fractions, based on their differences in volatility. Fractionating columns are used in small ...

, there are instead many product streams.

Notes

Bibliography

* Robert Perry, Don W. Green, Perry's Chemical Engineers' Handbook, 8th ed., McGraw-Hill, 2007. * *

Fluid dynamics

Notes

Bibliography

See also