Common compressed heat dryers include freeze dryers and adsorption dryers. In compressed heat dryers ， freeze dryers can only treat the dew point temperature of compressed air to 3 ° C or so, while adsorption dryers can only be used when a lower dew point temperature is required. Depending on the regeneration method of the adsorption dryer, it can be divided into athermal regeneration dryer, microthermal regeneration dryer, blower heating regeneration dryer, and shrinkage regeneration dryer.

In compressed heat dryers ， Adsorption dryers generally adopt a double-tower structure, one for gas drying and one for adsorbent regeneration. Commonly used adsorption materials include activated alumina and molecular sieves. Activated alumina is very sensitive to the temperature of the working medium. When the ambient temperature of the adsorbent reaches 130 ℃ or more, the water content of the adsorbent is only 1% or so, and desorption is almost complete. However, at the same temperature, the water absorption rate of molecular sieves is higher than that of activated alumina, and the desorption is not as complete as activated alumina.

The regeneration process of the adsorbent is divided into four stages: heating - depressurization - cold blowing - pressure equalization. The adsorption tower and regeneration tower switch according to the dryer PLC control signals given.

High-temperature compressed air ( 110 ℃ or more) enters the dryer and flows directly into the regeneration tower. Because the high-temperature compressed air is unsaturated, it will evaporate the water stored in the adsorbent. The evaporated water is absorbed by the unsaturated high-temperature compressed air and then enters the subsequent cooler of the dryer, where it is cooled to 40 ℃ or so. At this time, the compressed air is supersaturated, and a large amount of liquid water is precipitated. The liquid water is discharged from the steam separator. The cooled compressed air enters the compressed heat dryer, and after reaching the dew point requirement, most of it is output to the compressed air network to supply the workshop and gas station, and a small part flows into the regeneration tower through the cooling tower. Adsorbent cold blowing control valve. This stage consumes about 2% of the total air volume. Since the compressed air used for cold blowing is dry compressed air, the adsorbent can undergo secondary desorption. After the cooling process, this part of the compressed air is discharged through the silencer.

Before switching, the regeneration tower and the adsorption tower need to go through a pressure equalization process, which is controlled by the PLC control program. Each switch means that the dryer has gone through a complete working cycle, and the control methods generally include dew point control and time control.

The compressed air entering and leaving the dryer is a continuous process, while the switching of the two towers of the compressed heat dryer is an intermittent process, so these two processes are not synchronized. During the cold blowing process of the regeneration tower, the high-temperature compressed air entering the compressed heat dryer must bypass and directly enter the aftercooler and steam-water separator, and then enter the compressed heat dryer. These processes must be implemented by the compressed heat dryer control program.