Absorption is a process that separates gas mixtures by selectively dissolving one or more gas components into a liquid solvent. It is commonly used to remove impurities from gas streams. There are two main types of absorption processes: physical and chemical. Absorption equipment includes tray towers, packed columns, spray towers, and bubble columns. Tray towers contain a series of metal trays that facilitate countercurrent contact between the rising gas and falling liquid. Design considerations for absorption systems include flow rates, recovery levels, operating conditions, equipment selection, and the number of theoretical equilibrium stages required. The graphical equilibrium-stage method can be used to calculate stage requirements for tray towers based on equilibrium relationships and material balances.