Assessment of Adsorbents for Drying by Experiments and Dynamic Simulations

In order to slow down global warming, greenhouse gas emissions must be reduced. Human-caused greenhouse gas emissions come primarily from consumption of fossil energy. In order to reduce the consumption of fossil energy, the demand is rising for energy-efficient technologies. One promising energy-efficient technology is the adsorption dishwasher that was commercialized recently. The use of adsorbents enabled the adsorption dishwasher to save 25% of energy compared to a conventional dishwasher. To increase the savings and to further enhance the entire process, the adsorption dishwasher should be improved. The improvement should foremost focus on the adsorbents, since adsorbents are the key of this energy-efficient technology.

This thesis therefore assesses adsorbents for the application in an adsorption dishwasher. The assessment is carried out both experimentally and theoretically. Theoretical investigations are divided in 3 stages of complexity:

Stage 1 is a static analysis that is used to determine the required minimum mass of adsorbent. Stage 2 is a simple dynamic model that is used to determine the drying times. This simple 2-stage theoretical investigation method is applicable for any drying process in order to estimate the suitability of adsorbents. As a parameter study, adsorbents out of 3 material classes are evaluated regarding drying time and adsorbent mass required for the application in an adsorption dishwasher . The trade-off between drying time and adsorbent mass is discussed by employing the Pareto-frontier.

Based on the results of the simple 2-stage theoretical investigations, suitable commercially available adsorbents are investigated experimentally. Evaluation criteria of the experimental investigations are working capacity, pressure drop over the adsorbent bed and dehumidification rate. Based on these 3 criteria, the most suitable commercially available adsorbents are identified.

Finally, to assess adsorbents considering all dynamic interactions within the adsorption dishwasher, a theoretical investigation is conducted as Stage 3. Stage 3 is a complex dynamic model of the adsorption dishwasher including all its components. The tradeoff between drying time, adsorbent mass and energy consumption is discussed by employing the resulting Pareto-frontiers.

In summary, this thesis presents methods for characterisation of desiccants. By using these methods, more suitable adsorbents are found for use in the dishwasher application.