Development and experimental testing of a fixed bed adsorption system for deep dehumidification

Dehumidification of air is extremely important in several contexts. Elevated water vapor concentrations can create a variety of problems, including low thermal comfort, increased bacterial growth, and reduction of quality in daily products storage. In industrial contexts, it has an impact on production safety and product quality. For instance, lithium-ion battery production lines require a supply air with dew point of -10°C and below. In this context, there is a huge need of experimental proofs of devices that can achieve high dehumidification level, guaranteeing supply air with humidity ratio < 5 g/kg. The aim of the present work is to present the design and experimental realization of such a device. It includes 2 stages: an adsorption stage followed by a condensation stage. The adsorption stage consists of an air-water aluminium heat exchanger filled with a composite material composed by silica gel/CaCl2 25% realized by wet impregnation. The employed material has a cost lower than 2 €/kg and the production process can be easily scaled for large quantities. The condensation stage consists of an air-water aluminium heat exchanger connected to a reversible heat pump, which circulates water at temperatures of 2-15°C. The combination of both thermal and electric stages allowed reaching outlet air humidity ratio as low as 4 g/kg. A dedicated experimental campaign was carried out to evaluate the effect of air velocity, heat transfer fluid temperature in the condensation stage and adsorption temperature in the adsorption stage. Results showed that low air flow rates improve the adsorption capacity, whereas temperatures for adsorption and condensation lower than 12°C do not yield any significant improvement in the system performance.