Closed air circulation sludge dryer

The invention discloses a closed air circulation sludge dryer, which comprises a sludge drying box, a condenser, a heat exchange device, a closed air circulation loop, a waste heat source and a chiller, wherein the closed air circulation loop is communicated with the sludge drying box, the condenser and the heat exchange device; the waste heat source is used for supplying heat energy to the heat exchange device; the chiller is used for removing heat energy produced by the condenser; the sludge drying box produces air which contains water; and the air which contains water is subjected to temperature reduction and dehumidification by the condenser and heated by the heat exchange device and enters the sludge drying box to take the water in the sludge drying box away, so that the air which contains water is produced again and can be recycled.