Experimental and numerical investigation of sorption desalination demonstrators

Energy sustainability and freshwater production are two of the main challenges faced by modern society in order to ensure a good quality of life for humanity and to protect the planet. On one hand, the limited availability of currently exploitable energy resources combined with the urgent need to reduce the use of fossil fuels, has driven the need of renewable energy sources. However, this transition still faces various issues, including the mismatch between energy supply and demand which makes it necessary to store the energy produced. Thermochemical heat storage represents one of the most promising technologies, which base principle is to store energy through a chemical or physical reaction and then release it through the reverse reaction when required. On the other hand, in the current world the increased need for fresh water contrasts with the scarcity of this resource in many parts of the world. This issue results in the need to research new technlogies for fresh water production. The focus of this work is on an adsorption based desalination system, which could represent a combined response to the two issues. The adsorption is a process in which molecules of an adsorbate (water in this case) adhere to the surface of a solid or liquid material (silica gel). This reaction is spontaneous and involves heat release and the reverse physical reaction is named desorption and requires heat supply, allowing for a thermal energy storage cycle. On the other side, if the water vapour adsorbed comes from a salt water tank and the desorbed water is condensed in another separate container, the cycle allows for salt water desalination. The main goal of this thesis work is to experimentally and numerically analyze a system that uses such technology. From an experimental point of view, the main goals are to define a testing protocol and optimize system performance by changing its operating conditions, while from the numerical one, the goal is to develop a model that well simulates the system's behavior. Results are obtained testing a machine installed at the laboratories of the Politecnico di Torino and show that a good testing protocol was developed and production of water was increased from 0.2 to 2.1 liters per day per kg of silica. On the other hand a model utilizing the Linear Driving Force model for adsorption kinetics and a Dubinin-Astakhov Model for adsorption ishotherms was developed and system's specific parameters were tuned to well simulate the real behavior.