Amine strippers use heat and steam to reverse the chemical reactions with CO2 and H2S, The steam acts as a stripping gas to remove the CO2 and H2S from the liquid solution and to carry these gases to the overhead. To promote mixing of the solution and the steam, the stripper is a trayed or packed tower with packing normally used for small diameter columns.
The typical stripper consists of a tower operating at 10-20 psig with 20 trays, a reboiler, and an overhead condenser. The rich amine feed is introduced on the third or fourth tray from the top. The lean amine is removed at the bottom of the stripper and acid gases are removed from the top.
Liquid flow rates are greatest near the bottom tray of the tower where the liquid from the bottom tray must provide the lean-amine flow rate from the tower plus enough water to provide the steam generated by the reboiler. The lean-amine circulation rate is known, and from the reboiler duty, pressure, and temperature, the amount of steam generated and thus the amount of water can be calculated.
The vapor flow rate within the tower must be studied at both ends of the stripper. The higher of these vapor rates should be used to size the tower for vapor. At the bottom of the tower the vapor rate equals the amount of steam generated in the reboiler. Near the top of the tower the vapor rate equals the steam rate overhead plus the acid-gas rate. The steam overhead can be calculated from the steam generated in the reboiler by subtracting the amount of steam condensed by raising the lean amine from its inlet temperature to the reboiler temperature and the amount of steam condensed by vaporizing the acid gases.
For most field gas units it is not necessary to specify a stripper size. Vendors have standard design amine circulation packages for a given amine circulation rate, acid-gas loading, and reboiler. These concepts can be used in a preliminary check of the vendor’s design. However, for detailed design and specification of large units, a process simulation computer model should be used.