Adsorption dryers of the closed loop design, Fig. 5.7.1.1, require two adsorbers for continuous operation. The vessels are interconnected by piping with, in each case, independent 4/2-way valves (item 1 and item 4), being the main valves for switch over from adsorption to regeneration.
Figure 5.7.1.1
In addition, two 3/2-way valves (item 5 and item 6) are integrated into the piping system, being linked via a shaft. The additional water cooled heat exchanger (item 7) with attached cyclone separator (item 8) is typical for this system. The link to the compressor is formed by two alternative connections fulfilling correspondingly different tasks. In order to dry compressed air, low temperatures are needed. In order to regenerate drying media, however, high temperatures are required. For this reason, the dryer possesses one connector each, for hot and cold compressed air. An entirely new aspect is caused by the technology of the process. Adsorption and regeneration take place under operating pressure. For this reason, components such as exhaust valve, relief valve, regeneration air line and silencer, needed for other drying systems, are not required. This leads to a layout of captivating simplicity and clarity. A further material difference, as compared with the adsorption dryer systems shown previously, can be seen from Fig. 5.7.1.2. Loading up and regeneration take place in countercurrent as before with the associated cooling operation, however, in the main direction of flow.
Figure 5.7.1.2
It is known from process technology that the required regeneration temperature depends on the dewpoint of the regeneration gas. The drier the gas used for regeneration, the lower the regeneration temperature which can expediently be used. With a dryer of closed loop design, the regeneration gas is relativel humid as compared with that in other drying systems. For this reason, closed loop systems always require a higher regeneration temperature in order to reach a specified pressure dewpoint, than is necessary with other designs of dryer. It is, therefore, barely possible to achieve pressure dewpoints below -30°C, even with continuously running operation. Lower pressure dewpoints call for an additional heater system. The interrelation between pressure dewpoint and compressor temperature is shown in diagram 5.7.1.
