Executive Summary : | Around 10,000 tons of oil is required every year to produce 1000 m3/day of desalinated water. Most of the conventional desalination plants operated by fossil fuel has contributed to green-house gas (GHG) emissions. This project attempts to explore alternate way for powering desalination units by renewable energy such as indirect solar desalination. A need is felt to develop a solar energy supported desalination unit which uses a nanofluid as the thermic fluid in MSF (Multistage Flash Distillation). However the stability of such nanofluids without clogging is a prime concern for maintaining their thermal conductivity for a longer time span. To overcome this the proposal intends to conjugate different functionalized MWCNTs (Multi Walled Carbon Nanotube) with either HBA (Hydrogen Bond Acceptor) or HBD (Hydrogen Bond Donor) molecules due to their extended π-electron clouds. The base fluids thus proposed are Deep Eutectic Solvents(DES) or Mixtures which essentially are combination of HBD and HBA. Presently such conjugation helps in faster heat transition and better stability in the matrix due to their interactions with the medium. This project thus attempts to design DES as base fluid along with graphene coated carbon nanotube and functionalized MWCNTs as nanoparticles.Initially the dispersion stability of these nanoparticles will be studied by TEM, centrifuging, dynamic light scattering and zeta potential. After a thorough evaluation of thermophysical properties of nanofluids,the flow characteristics of these nanofluids shall be ascertained in a forced convection setup under turbulent regime.
Thereafter these nanofluids shall be evaluated in a multistage flash (MSF). The fabrication shall consist of two sections namely (a) heat rejection and (b) heat recovery is undertaken. The heat rejection refer to the transfer of a large fraction of heat from the heat exchanger through nanofluid to the preheated seawater. This preheated seawater shall then transfer the heat to the incoming low temperature seawater within the heat rejection section. The heat recovery section here refers to the preheating of cold seawater with the residual heat of the seawater which is obtained from the heat rejection section. The entire process shall be simulated in ASPENone 8.8 so that the appropriate counter current heat exchanger and column can be designed. It shall operate by passing the hot brine or seawater through two vacuum stages, in which the brine or seawater undergoes flashing at a predecided temperature and pressure. This shall result in a distillate and also transfer the heat to the incoming sea feed water flowing inside the condenser tubes. Both the rejection and recovery section shall be connected via an orifice so that the flashing brine is pulled along by the increasing vacuum.Finally the Gained Output Ratio (GOR) along with the inbuilt ASPEN Process Economic Analyzer (APEA) in ASPENOne8.8 suite of programs shall be used to evaluate the economics of the process. |