Low-cost thermal desalination technology for emergency conditions

The aim of this thesis is to build a low-cost technology to desalinate seawater using as low renewable energy as possible. The prototype will utilize membrane distillation technology, a thermally driven process predominantly employed for desalination, to address water needs in emergency situations where access to electricity is limited, such as following an earthquake or hurricane. First, a totally passive prototype of this technology, originally designed at Politecnico di Torino, was developed to better understand its working principles. A passive system operates without any active components, such as moving parts like pumps or heating elements, thus eliminating the need for any electrical power. In this case, the only energy required is derived from the sun, which is utilized to heat the water. This first implementation was built using larger membrane area (from a 12 cm by 12 cm square to a 20 cm by 20 cm square) to assess the feasibility of scale up. After testing this first prototype, the main engineering limitations to further scaling up were highlighted, and design improvements implemented. Therefore, the second release of this technology included an air gap membrane distillation configuration, instead of the direct contact one adopted in the first prototype, In the first configuration the feedwater is used as a cooling stream to recover the latent heat of condensation from the permeate; in the second one the feed and cooling stream are decoupled to increase the driving force and so the distillate flux. Such a new solution unlocked an easier scale up, at the cost of adding simple active components like pumps. Both prototypes were tested in the lab by using an electrical resistance to simulate the heat from the sun, and performance recorded achieving a productivity of 1L/(m^2h) at 55°C and 1.2L/(m^2h) at 60°C with the second configuration of the air gap prototype.. Then, an energy analysis was done to better understand the efficiency of the modules themselves and of the system, comparing the efficiency of both tested prototypes. Finally, an economic and scale up analysis were carried out.