Through the input of heat,the molecular sieve is heated to such an extent that the adsorbed material leaves the pores. This type of regeneration can simply and reliably be adapted to the most varied operating situations
Diagram 6.4.8.1
As molecular sieves possess a relatively low thermal conductivity, heating the adsorber bed is best effected indirectly by means of a current of hot gas. This, at the same time, serves as flushing medium, removing the adsorbed material from the molecular sieve bed. The nature of the adsorbates and the product purity aimed at, are among the factors determining the temperature to which the molecular sieve bed has to be heated in order to effect regeneration. The product purity achieved by an adsorption installation based on a molecular sieve depends on the regeneration temperature and the adsorbate content of the flushing gas. In practice, temperatures between 180°C and 250°C are required. The heat allowance (see section 7.3) for adequate reactivation includes the following heat quantities:
- Heat requirement when heating and evaporating the adsorbate
- Heat capacity of the equipment, piping and of the adsorbent
- Desorption heat of the adsorbate
- Heat loss of the adsorption installation
In addition, the adsorber bed should be heated slowly only, so that maximum temperature of the regeneration gas is achieved only in the course of a period of one hour or more. Such slow heating favours the removal of reactive molecules at low temperatures, thus strongly diminishing the possibility of carbonisation or polymerisation. The heating phase during reactivation normally includes a cooling phase, in the course of which the bed is brought back to adsorption temperature. For this, the same gas current as for reactivation is usually employed, however, avoiding an input of heat.
