Combined dryer adopting the latest development of the drying process is different from the process of freezing dryer in tandem with drain machine, which is summarized as follows: compressed air sent by air compressor from the rear cooler, which firstly exchanges heat with the dried low- temperature compressed air and lower the temperature in the heat exchanger, and then enter evaporator to be lowered to about 2. In this dew point, the most liquid water in compressed air was discharged, and the compressed air of minimal moisture enter absorption tower to further dry water. Finally the low temperature dry compressed air enter heat exchanger to cool the hot and humid air. At the same time, its own increasing temperature can prevent condensation of compressed air transmission pipe wall. Using a small portion of the compressed air which has been warmed up as regenerated air of adsorbent, improving the regeneration efficiency and lower energy consumption, meeting low dew point(-70 -- -80) industry use.