An aqua-ammonia absorption apparatus comprising an absorber assembly, a generator assembly, a condenser and an evaporator, the generator assembly comprising a boiler section, a solution-heated-desorber section, an adiabatic desorber or GAX desorber section, and a rectifier section, the interior space of at least one of said sections of said generator being substantially filled with structured packing material inert to an aqueous ammonia solution at generator temperatures.