Design of distillation trays for cyclic mass transfer

Conditions of realization cyclic mass transfer expressed two postulates: lack of outflow of liquids to the trays vapor admission; lack of mixing of liquids in adjacent trays upon outflow of liquid. This method of interaction phases increase in efficiency mass transfer as compared to the standard process.

The method interaction phases in the distillation column can be as follows: discrete feed of liquid and vapor; continuous supply of liquid and discrete steam; constant supply of fluid and continuous steam. These conditions can be achieved at both the distillation column and the level distillation trays.

First stage of development of column internals for cyclic mass transfer was by external mechanical drives that are associated with elements of thrust trays. Pilot scale development and research of this solution has led to the establishment of individual actuators on each tray. In this case we have alternately devastation (overflow) distillation trays from bottom to top of distillation column, by changing the free sectional trays. Unfortunately, this method has not received industrial implementation.

In the second stage of development for liquid overflow on the distillation tray began to use the kinetic energy of motion of vapor in the distillation column.
In case of cyclic steam flow, the steam flow acts as a control of liquid flows in the distillation column. The main element of such distillation trays are sluice chambers and valves. In this case, the liquid flow (feed, reflux, distillate and bottom product) moves in a continuous mode. Cyclic mass transfer operation consisting of two key parts: vapor flows goes through the distillation column and the stationary liquid stays on the trays, and this is called the vapor flow period, while the liquid flow period arises when vapor flow is stopped and the liquid holdup in sluice chambers, the vapor flow period starts and liquid from sluice chambers falls into the tray below. The design of Maleta distillation trays and two key parts of interactions you can see at the picture. Today, Maleta distillation trays works in stripping column, rectification column and tray dividing wall columns with a diameter ranging from 400 to 1700 mm.

All of the methods and design of a cyclic mass transfer operation has its advantages and disadvantages and can be used in industrial process, depending on the tasks for increasing mass transfer efficiency in distillation column.

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