Studies on Vapour Absorption Heat Transformer based water distillation systems

Abstract

In recent years considerable attention has been given to reduce the use of fossil fuels for heating and cooling applications. The Vapour Absorption Heat Transformer (VAHT), being principally heat operated, is an useful tool to upgrade this low temperature rejected heat to the required heat energy at higher temperatures for useful applications. The desalination of seawater using Multi Effect Distillation (MED) is one such application which requires heat input at higher temperatures. Therefore, integrating the VAHT and the MED for the desalination of seawater can significantly contribute to improvements in energy consumption efficiencies and also to energy conservation. This thesis presents theoretical and experimental investigations on vapour absorption heat transformer based desalination systems using the MED. The analysis shows that between the specified range of operating conditions, the working fluid combination H2O - LiCl + LiNO3 yields the highest COP, while consuming the lowest specific thermal energy for water purification using the coupled system, followed by the H2O - LiBr, H2O - LiI, H2O - LiBr + LiNO3, H2O - LiBr + ZnBr2 + LiCl2 and H2O LiCl + CaCl2 + Zn(NO3)2 systems respectively. It is also found that the working fluid combination H2O - LiCl + CaCl2 + Zn (NO3)2 produces the highest distilled water output compared to the other combinations. The maximum COP of 0.38 has been realized at a heat source temperature of 80°C, condensing temperature of 25°C, with the GTL of 15°C. The distillate water is tested for its quality with respect to the electrical conductivity, pH, total dissolved solids, calcium, magnesium, etc. and it is found that the parameters are within the desired limits and suitable for drinking purposes. The feasibility of operating multi effect distillation combined with the vapour absorption heat transformer, using water - lithium bromide as the working fluid has been established for the distillation of seawater.