Air drying system and method for drying compressed air using same

An air drying system includes a regeneration special dryer and at least one air dryer unit. The air dryer unit contains a pair of first and second air dryer dehumidification tanks in which a dehumidification process and a regeneration process are alternately performed; a main compressor to supply compressed wet air to an inlet line; a first direction switching valve unit configured to transfer the compressed wet air from the inlet line to first dehumidification tank performing dehumidification; a second direction switching valve unit configured to transfer the compressed dry air from the first dehumidification tank or transfer regeneration special dry air from a regeneration special dryer to second dehumidification tank performing the regeneration; a heating unit configured to heat the regeneration special dry air supplied from the regeneration special dryer; and a cooler configured to detach moisture from dehumidifying agent filled in the second dehumidification tank.