Mea Absorption

A removal process consisting of absorption, desorption, heat exchangers and auxiliary equipment is shown in Figure 10. Absorption is traditionally performed in a column with plates, random packing or structured packing. CO2 containing gas flows upwards and the absorption liquid flows downwards. The solvent (rich amine) is pumped further through a heat exchanger to a separation column. The absorbed CO2 is regenerated in a separation (stripper) column. Heat is added to the reboiler and a condenser supplies reflux to the column. After the separator, the regenerated solvent (lean amine) is recirculated back to the absorption column and cooled in a heat exchanger and a cooler. The simplest and most used amine for CO2 removal is MEA (monoethanolamine).
MEA has a high CO2 capacity, MEA is a relatively cheap chemical, the toxicity is relatively low and the environmental effects are less questionable than for many other suggested amines because MEA occurs naturally in living organisms. The most important drawback using MEA is the resulting high energy consumption needed for separation. This is a side effect of the high absorption efficiency. Other problems with MEA are significant vapor losses and a high corrosion tendency. Another problem with amines in contact with exhaust gas is that it will have a tendency to degrade in presence of oxygen and other components like nitrogen oxides or Sulphur oxides. At low pressure, the driving force for separation is much lower than at high pressure, and this makes the CO2 removal more challenging. A water wash section is located at the top of the absorption column. From the top of the absorption section, there are traces of the solvent that should be avoided to be sent to the
The water is circulated by a pump and clean make-up water is added to the circulation. To avoid build-up of amines in the wash water, a small part flows to the main absorption section of the column. In the separator, the CO2 is stripped from the liquid into the gas. The CO2 gas flows upwards together with steam. Heat is added in the reboiler, and in the column top there is a cooler which condenses water which is returned as reflux to the column top. CO2 and some water vapor leave from the top of the separator. The lean amine from the bottom of the column is heat exchanged with rich amine from the absorption column and is returned to the absorption