Mathermatical Calculations Used Within Dixon Ring Characterisation
Dixon Ring is made by woven wire mesh to manfuacturer pioneering fitlers, to serve a niche market in a vast range of application
When Dixon ring were first manufactured 65 years ago, Dr Dixon used a split pin t owind the mesh around forming the dixon ring shape. However this was extremely slow and laborious and the real potential for Dixon ring was not initially found.
The reason Dixon ring have made a return, over 50 years later, is due to their superior efficieny compared to other random packing including pall ring and intalox saddle.
Now we will quantify the performance of Dixon rings and compare them to competitor column packings.
One of the main quantities that performance of column packings is compared on is Mass transfer efficiency. This piece of work shows how once the results are obtained from testing in a counter current water/carbon dioxide setup (figure 2), using maths the optimum condidtions and the performance at optimum conditions of carbon dioxide absorption by water can be found.
The table below shows a sample of results obtained from testing using the ring shown in figure 2.
Description of condition
|
pH start
|
pH after 60 seconds
|
pH change per minute
|
CO2 absorbed per minute
|
Water0.5 l/min CO2 2 l/min
|
6.72
|
4.76
|
1.96
|
364.8
|
Water0.5 l/min CO2 4 l/min
|
6.76
|
4.65
|
2.11
|
515.3
|
Water0.5 l/min CO2 8 l/min
|
6.79
|
4.67
|
2.12
|
527.3
|
Water0.5 l/min CO2 10 l/min
|
6.70
|
4.69
|
2.01
|
409.32
|
Water0.5 l/min CO2 14 l/min
|
6.80
|
4.94
|
1.86
|
289.77
|
This data was plotted in Microsoft Excel to produce a surface plot shown, as shown in figure 3, to easily iew the optimum conditions.
The purpos of this work, as well as finding the optimum conditions for absorption of carbon dioxixde was to actually work out the efficiency of absorption.
As pure carbon dioxide gas was used the concentration of initial inputted gas was easily calculated as follows:
Carbon dioxide is formed from the consituent elements one carbon atom and two oxygen atoms.
The molar mass which can easily be read off the periodic table for carbon is 12.01 and oxygen is 16.00.
Therefore the total molecular weight of a carbon dioxide molecule is 40.01 grams/mol.
The density of carbon dioxide gas at standard temperature and pressure (1 atmospere 273.15K.) is 1.97 grams/litre.
Rerranging the formula Density=Mass/Volume
to give Mass=Density*Volume
Then the mass of one litre of carbon dioxide can be calculated.
Mass=1.97*1=1.97 g.
From this the number of moles can be calculated using the formula
Moles=Mass/Molecular weight
=1.97/44.01
=0.04643857 per litre.
This calculation can be checked because at standard temperature and pressure a mole of any gas occupies 22.4 litres.
1 litre=1/22.4 moles= 0.044642857 moles.
This indicates that the calculation is correct.
We now know the total moles of carbon dioxide flowing though the column, we now need to calculate the amount of carbon dioxide absorbed.
Using the calculations above we curretly have an absorption measured in parts per million.