Novel Approaches to Solar Thermal Desalination for Islands Leon Awerbuch, President, LET/IDA Past President, Dean IDA Desalination Academy IRENA - MARTINIQUE CONFERENCE ON ISLAND ENERGY TRANSITIONS: PATHWAYS FOR ACCELERATED UPTAKE OF RENEWABLES Martinique, 22-24 June 2015
This presentations reviews use of Novel Thermal Hybrid systems in combination with solar energy. Nanofiltration Softening Membranes with Multi Effect Distillation solutions, which will be able to operate with low temperature solar thermal energy, like solar pond both with pure water or salinity gradient and using low temperature geothermal resource as well as coupled with more conventional lower temperature concentrated solar Parabolic Trough Collectors or Solar Dual purpose power and desalination solutions.
MED Technology today uses relatively low temperature, which can effectively provided by many different solar solutions without generating electric power: Today MED plants design are limited to a TBT only of 64 to 75º C. The MED specific power consumption is between 0.9-1.8 kwh/ton of distillate depending on feed solution and significantly lower than MSF requirements of typical 3,5-4 kwh/ton of product. Low-cost, high-efficiency form of solar water heating and trough CSP receiver, already in the development, to produce relatively low temperature heat source needed for desalination.
Sketch: Nano-filtration as a pre-treatment for MED INTERNATIONAL DESALINATION ASSOCIATION The challenge is coupling of solar energy to MED thermal desalination plants
Solar Pond Salinity and Temperature Profiles
TIGI s Honeycomb Collector is the revolutionary, new and most cost effective type of solar thermal collector available for demanding applications. It is highly efficient and cost effective, outperforming all other available collectors particularly in high temperature hot water applications. The result was the development and manufacturing of transparent insulation and implementation of solar ponds covered with a new type of solar-thermal collector that could preheat large amounts of water to close to boiling temperatures with unprecedented efficiency. At the heart of the Honeycomb Collector is a polymer-made layer of transparent insulation (TI). The TI honeycomb substance is transparent to solar irradiation, allowing for energy to enter the collector and heat the absorber plate. However, it creates a layer of air that cannot circulate, thus dramatically reducing losses related to convection the major reason for energy losses and lower efficiency of flat plate collectors at high temperature differentials. In addition, the polymer blocks back radiation in the infrared, thus further reducing energy losses.
Producing Hot Water for MED Desalination TIGI s Honeycomb Collector Substitute the heat sink for MED-NF and return the 70.3 deg C to Tigi even if some loss of efficiency.
Benefits of Nanofiltration PREFERENTIALLY REMOVES SCALING (DIVALENT) IONS ALLOWS HIGHER TOP BRINE TEMPERATURE FOR MSF (121 vs. 110 C AND FOR MED (100 vs. 63-75 C) Higher Temperature Range Increases Production and Efficiency Reduced Capital Costs Reduced Operating Costs
NF SOFTENING SYSTEM Softened feed to high temp. MED effects Reject from softening to outfall or low tem. effects Seawater to NF softening Seawater from intake to final condenser Process and apparatus for partial blending of softened feed to high temperature effects of MED in order to increase TBT
NF-MED desalination with Solar Pond
Solar Pond coupled with NF-MED Advanced Solar Desalination with solar pond using 18 effects MED hybridized with Nanofiltration NF to soften feed for the hottest groups will decrease the specific thermal energy consumption to 168.2 kj/kg or PR=13.8, never before achieved without thermocompression TVC with heat input at 90 ºC. We have design a full size commercial unit of 25,000 m3/day with 20 effects desalination plant with thermal energy consumption to 137.6 kj/kg or PR=16.25.
Conclusions Technologies are made available that can reduce dependence on fossil energy for desalination. We foresee use of renewable energy: wind, solar, geothermal, ocean power to achieve reduction incarbon footprint and cost of desalinated water. New technologies can reduce energy use and reduce cost of desalinated water. The integrated hybrids could one of the approaches. Application of hybrid NF-MED and RO couple with solar energy like solar ponds offers great opportunity. There will be a great incentive for their development by the public and private sectors