A process for ammonia saturation of a solid material capable of absorbing and desorbing ammonia, the solid material being composed of solid particles and includes placing the solid material in contact with a cooled surface, with the solid material being disposed against the cooled surface in a thin layer having a thickness of less than 100 mm. The process further includes injecting a stream of gaseous ammonia to be in contact with the solid material, while the solid material is in contact with the cooled surface.