The adsorption dryer regenerated by means of heat undergoes this regeneration with the help of a purge of already dried air accompanied by a simultaneous supply of heat. The external layout is roughly similar to that of adsorption dryers with heatless regeneration, but a direct acting electrical source of heat is utilised and this supports the regeneration to optimum effect. This decisive characteristic calls for differentiating considerations from the process technology point of view. With heat regenerated adsorption dryers, possessing a regeneration air system complete with a heater built into the adsorber, the heat of regeneration is fed directly into the drying medium by the heater. Optimum heat transfer efficiency depends on the system, as only small losses occur in the course of the transfer of heat from the heating system to the drying material. In contrast to the dryer with heatless regeneration, the charging process does not have to be interrupted at brief intervals for secondary reasons of process balance. Corresponding to thermal separating processes, the following knowledge is required in order to design an adsorption system:
- Adsorbate/adsorbent balance in the light of thermal adsorption processes
- Kinetics of adsorption and desorption
- Mass and energy requirements of adsorption
- Permissible flow velocities and pressure losses
- Dimensioning of the adsorbent layers
Adsorption media must fulfil the following requirements:
- High selectivity for the component to be separated
- High readiness to be desorbed after being charged
- High adsorbing capacity even in the face of low concentrations
- Mechanical robustness against changes in temperature
- Gas and steam permeability during adsorption and desorption
- Chemical resistance against gases and water vapour
The following sections explain individual special aspects of thermal separating processes.
