Efficient type of steam condenser for water desalination of solar thermal energy in remote arid areas and islands

Abstract

Comparison of material usage and cost of two types of cross-flow steam condensers is reported in this study which can be used for water desalination in conjunction with a parabolic trough solar energy concentrator plant. Traditional shell and tube condensers (where steam flows inside the tubes) and surface condensers (where steam flows in the shell and cooling water flows in the tubes) are considered in this study. It has been found that the energy production from the PTC of dimensions 4.5 m × 4.8 m with an aperture area of 21.6 m2 was 19.4 kW. It has been calculated that the distilled water production capacity of the solar energy harnessing system per day is 55.6 l, assuming solar irradiance to be 0.9 kW m-2 and the efficiency of solar energy harnessing system as 50% if the sun is available for four hours. The cooling water input temperature was assumed to be 30 °C. The minimum length required for a SS 304 tube of Ø 9.5 mm was 7.16 m for the traditional condenser and 1.30 m for the surface condenser. The efficiency of the traditional condenser reduced due to the formation of a condensed water layer on the surface of the tube, as it acts as a thermal barrier. However, in the surface condenser, efficiency was enhanced due to easy condensation while increasing the system pressure. Further, efficiency is enhanced due to density separation of wet vapour by changing the flow direction near the wet sump. Fabrication cost and maintenance cost are also found to be less in the surface condenser. As such, it can be concluded that use of surface condenser is the most cost effective method, which uses a smaller amount of material making the condenser smaller and lighter.