2. THEORETICAL FOUNDATIONS
2.4. Columns filling
In columns filling mass transfer is done continuously. These columns are also called packed columns. The filler tower is the most common that consists of a cylindrical casing which contains the inert material inside. This inert material is what is called padding.
The main purpose of padding is to provide a wider contact surface between the vapour and the extractor liquid , thus making the increase turbulence and thus improve their effectiveness.
There are many ways of filling and different dimensions. if the volume is large (5-20cm) can be placed in an orderly manner or messy if the filling volum is small (5-50mm). Generally are usually used Rasching ring large 5-8cm in diameter and placed in an orderly manner. As we increase the size of filler, the efficiency of mass transfer was reduced and therefore increase the pressure drop. In conclusion, in order to determine the optimal size of the landfill must take into account two factors:
- The selection of filler material.
- The ordering of the material inert, the filler.
Figure 2.11: Outline column gas absorption and filling.
Source: www.ocwus.us.es
The characteristics of the filling are:
- Must be chemically inert.
- They have a high degree of mechanical strength.
- They allow the passage of the two currents appropriate.
- Must allow good contact between the two phases.
- Must be low cost.
Most fillings are made of cheap material, inert and lightweight.
Example: clay, graphite, porcelain ... so can be used as regular or irregular shapes. The fillings that are ordered within the column and have relatively large dimensions, show channels interrupted by the bed and create pressure drops lower than those the filling placed at random, where the gas is often forced to change speed and direction.
Figure 2.12: Filling a column.
Source: http://materias.fi.uba.ar.pdf
The application features:
They have a continuous contact with the gas.
- Small diameter gas.
- Used when there is corrosive compounds in the gas mixture. And when there are sparkling liquid.
- Applies in cases where there are sudden changes in temperature.
- Should be used when working with low pressures.