Absorber Column Dimensions

By: Jessica Narku-Tetteh

When designing an absorber column to achieve the maximum efficiency, two things need to be determined, the diameter and the height of the column. In lame man’s terms, the diameter refers to how fat the column whereas the height refers to how tall the column will be. For starters, diameter relates to capacity, whereas height relates to the absorption rate.

In the reaction between amine and CO2, which is typically a gas-liquid phase reaction, enough contact time must be allowed for the liquid and gas to be able to interact sufficiently with each other in order for the reaction to proceed. Thus, this means that the absorber has to have sufficient height in order for the liquid amine to flow down in a manner that will allow enough time for the up flowing gas to contact it. The height of the column determines how long the liquid and gas flows stay in the column for the reaction to proceed. If the column is too short the reaction time will be short. As such, there will be very little reaction going on and as a result the absorber efficiency will decrease. The absorber efficiency refers to how much CO2 has been removed; essentially it is the CO2 capture efficiency of the process.

Let’s talk about the column diameter. The diameter determines how much gas and liquid the column will allow in order to operate efficiently. So essentially the size of the column determines the allowable gas and liquid flow rate. If you design a column that has a very small diameter, it will be difficult to run the process at high gas flow rates. If these gas flows are allowed in such a scenario, there will be a high pressure drop in the column and this will result in liquid hold up and ultimately flood the column. Column flooding is undesirable, because it results in significant solvent losses and also reduces the CO2 capture efficiency.

If your column is tall but has a very small diameter, you will gain on the reaction kinetics, however you lose on capacity, could have flooding issues and consequently will affect your capture efficiency. If you have a column with a big diameter, but too short, you will avoid flooding issues but you lose on the kinetics, which will also affect your CO2 capture efficiency. So, you need to get these parameters right in your design.