Modeling and control of the solar powered membrane distillation system

In many arid and semiarid regions desalination of sea and brackish water has become a necessity. It is commonly reported that the lack of fresh water will increase dramatically in the near future. It is known solar radiation can be transferred to thermal energy by collectors and used to solar thermal energy systems. There are many potentially commercial advantages to use seawater desalination systems driven by solar power. Membrane distillation (MD) is a thermal process in which only vapor molecules, driven by a difference in temperature, transport through porous hydrophobic membranes and condense on the opposite side. This work studies the dynamic modeling and process control of the solar powered membrane distillation system. Direct contact membrane distillation (DCMD) is considered in the proposed solar powered MD system. The mathematical models of solar collector, thermal storage tanks, heat exchanger, MD module and fresh water storage tank are built on MATLAB platform. The simulated dynamic characteristics of these units are compared with those shown in the literature. This study also presents two temperature control loops and determines the feasible PI controller parameters for the solar powered MD systems. According to surrounding climate data of Taipei and Kaohsiung cities of Taiwan reported in the literature, the simulation results demonstrate effective performance of the proposed control loops for the solar powered MD systems.