The adsorption dryer regenerated by heat (Fig. 5.5.1.1) with external heater and blower consists of two adsorbers complete with a sieve bottom and dust sieve. The adsorbers are interconnected by piping at the inlet and outlet, complete with the required valves. Significant additional dryer components can be detected if one makes comparisons with the adsorption dryers so far described:
Figure 5.5.1.1
Two 4/2-way valves (item 1) are fitted in combination, actuated by a pneumatic drive via a common hinged shaft. The external heater (item 9), installed on the outlet side, is linked via a flexible connection to the External and sound attenuated blower, mounted in line with the heater (item 8) Adsorption is carried out at operating pressure from bottom to top. Regeneration, on the other hand, by countercurrent and without pressure, with heated blower air. The exhaust valve (item 6) is open during regeneration, closed during pressure build-up after regeneration. Adsorption dryers with external heat regeneration are designed for pressure dewpoints of -25°C. The rule regarding dwell times of adequate length for the reliable achievement of the pressure dewpoints applies to this design of dryer in equal measure. With the help of blower regeneration, pressure dew points of -55°C can be reached in continuous operation.
Suitable heating capacity and dwell times for low pressure dewpoints call for a relatively large outlay in device size, adsorption medium and energy use. Depending on the pressure dewpoint, different cooling and purge air quantities are required, in turn depending on the heat requirement. The drying medium used in heat regenerated adsorption is a silica gel combination of water resisting material on the inlet side, and molecular sieve drying material on the outlet side. The silica gel combination is used for inlet temperatures of up to 40°C and pressure dewpoints down to -40°C. Molecular sieves find their application at higher inlet temperatures up to 45°C and lower pressure dewpoints down to about -55°C. The electrical control system which processes valve functions and other signals such as regeneration temperature, heating time, cooling and purging phase as well as pressure build-up, has to be compact. For this reason, programmable logic controllers represent modern state of the art for this type of dryer. These types of controller offer the simultaneous advantage of being able to fit additional components and also unlimited possibilities of adaptation to particular operating situations. As a point of principle, one should consider insulation of the adsorbers by means of mineral or slag wool or other material. This, firstly for reasons of radiated energy saving, secondly as protection against touching. Adsorption dryers of this type are constructed up to performances up to 50 000 m3/h and even higher. For certain sizes of installation, transport in sub assemblies is necessary. For smaller outputs, the system is mounted on a basic frame as a compact unit.
