2 replies to this topic

[talalja]

I am designing a stripper column for carbon capture plant using MEA, I reached to the point of calculating the height of the column which is basically Z=Hog * Nog, i managed to calculate the height of transfer unit my problem is in calculating the number of transfer unit using the logarithmic mean driving force which requires the VLE curve. All the data I found in literature are based on CO2 partial pressure Vs Loading, how can I generate equilibrium line bed on vapour fraction Vs. liquid fraction ? 

[Art Montemayor]

If you are designing a carbon capture unit, then you probably have to employ trays instead of a packed CO2 stripper with MEA because of the stripper size.

 

No one that I have ever known designs the MEA stripper using equilibrium calculations.  Use 15 trays.  This is based on empirical, actual field data which I can assure you is conservative.  Some engineering contractors employ upwards of 20-24 trays - presumably for insuring they meet contractual terms.

 

I don't believe anyone is capable of challenging the use of empirical design - which has been used since the MEA process was patented in 1930 - especially your profs.

[MrShorty]

All the data I found in literature are based on CO2 partial pressure Vs Loading, how can I generate equilibrium line bed on vapour fraction Vs. liquid fraction ?

Even though it may not actually change the final design you use, this is a calculation that I think you should be able to do -- this calculation to computer "partial pressure vs. CO2 loading" that is common in CO2 absorption literature to "vapor [mole] fraction y" and "liquid [mole] fraction x".

 

You have not explained why you are having difficulty with this calculation, so I will assume it is getting started.

 

For computing the liquid fraction, we use the basic definition of composition as mole fractions: x(i)=n(i)/n(total) where x(i) is the mole fraction of component i, n(i) is the number of moles of component i, and n(total) is the total moles in the solution (n(CO2)+n(H2O)+n(amine)+n(others)). Find each of those mole numbers and you have your mole fraction x.

 

For computing vapor fraction, we use the standard "Dalton's law" type equation. P(total)=P(CO2)+P(H2O)+P(amine)+P(other) where P(total) is the total pressure, and P(i) is the partial pressure of i. y(i) is then P(i)/P(total). Again, find all of the partial pressures, and you have y.