Compressed air dryers are used to remove water and other contaminants from compressed air.  Compressed air dryers use technologies such as refrigeration, desiccant adsorption, and membrane filtration to remove contaminants, particularly water, from the air.   Major groupings include refrigerant (which removes the water by cooling the air) force condensation, and desiccant (which adsorbs the water in the air with granular material such as activated alumina, silica gel and molecular sieves).  Other technologies include membrane and in-line compressed air dryers. The air can be dried in single or multiple stages to prevent tool corrosion and other problems associated with water.