351 amanda hughes_icaer final


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351 amanda hughes_icaer final

  1. 1. Effects of Solar Energy Intermittency on a PV/Thermal Powered Membrane Distillation System Amanda J Hughes, Tapas K. Mallick and Tadhg S O’Donovan 4th ICAER 10-12th December 2013 IIT Bomday, Mumbai, India
  2. 2. Motivations and Aims 0.9 billion people without clean drinking water 0.8 billion without water and electricity 1.5 billion people without access to electricity - Provide a reliable and competitive means of water desalination that can be implemented in developing countries. -  Development of a membrane distillation system with concentrating photovoltaic/thermal energy source for seawater desalination .  
  3. 3. “Water, water, everywhere, Not any drop to drink.” –S. T. Coleridge
  4. 4. Solar based solutions are particularly suitable for desalination purposes, given the availability of such source in most of the water stressed areas (i.e. the more the water scarcity, the more the solar radiation)
  5. 5. Desalination Processes Thermal Membrane Electro Dialysis Reverse Osmosis Membrane distillation Solar stills MED MVC MSF
  6. 6. Membrane Distillation   What it is?   Thermally driven membrane separation process   Hydrophobic membranes allow pure water vapor to pass through, whilst salt is retained
  7. 7. Membrane Distillation Advantages   100% theoretical salt retention   Low operating temperature, 30-800c, when compared with conventional distillation   Reduced vapour space compared to conventional thermal processes, thus reduced plant volume.   Low operating pressure when compared with conventional pressure driven membrane processes   The membranes used in MD are tested against fouling and scaling.   Chemical feed water pre-treatment is not necessary.   System efficiency and high product water quality are almost independent from the salinity of the feed water.
  8. 8. Membrane Distillation • Problems • Membrane wetting • High thermal energy consumption • Low permeate flux capacity when compared with established membrane technologies. (MD capacity 1-10 m3/d compared with 100-1000 m3 for Wind-RO) This is still an emerging technology….
  9. 9. Developing a membrane module
  10. 10. Developing a membrane module Condensing plate Stainless steel end plate Distillate stream Membrane Cold Channel SEM Image of membrane Spacers Stainless steel end plate Hot Channel
  11. 11. Energy system Parabolic dish with a PV/thermal receiver Aperture area of 1m2 and a receiver area 0.002m2, giving a concentration ratio approximately 500×.   The photovoltaic cells have an efficiency of 36%   2 axis tracking required   Evacuated tube collectors • The evacuated tube collectors have an area of 5.7m2 and an efficiency of 65%
  12. 12. PV/T receiver – Temperature effect   PV absorbs a section of the solar spectrum, the rest is converted to heat   PV cells have a nominal operating temperature, usually around 250C   Any increase in temperature above this cause a decrease in efficiency of the PV.   0.4% per degree for silicon Heat collected from the PV cells will provide the driving force for membrane distillation
  13. 13. System overview
  14. 14. How does the membrane cope with a fluctuating power supply? •  Solar intensity is known to fluctuate throughout the day, subsequently so will the inlet seawater temperature of the MD unit. •  Transient operation will affect the quantity and quality of the distillate produced.
  15. 15. Temperatures from energy system Output temperatures from the energy system, calculated via a mathematical model
  16. 16. Geometry & Boundary Conditions of 3D Densely Packed Receiver Results from the distillate yield No Region Boundary condition 1 On top of cells Inflow heat flux as found from numerical model 2 Ambient Ambient temperature of 20-45oC The distillate surface 3 Cell’s flow 4 Sides of rate showed a cell time 5 Heat Sink delayed response to the solar PV receiver components 1: Frame fluctuations, due to 2: Cover glass 3: Al O ceramic the thermal mass of 4: Solar cells 1 5: Copper MD unit the plate 2 3 Surface to ambient radiation and natural convection Heat is conducted through the layers Surface to ambient radiation and convection 2 3 1 2 6: Aluminium heat sink 4 4 5 3 5 6
  17. 17. Conductivity of the distillate yield The distillate quality varied, but always remained well within the guidelines set by the World Health Organisation. The result show that there is nothing to rule out transient operation of the MD module
  18. 18. Discussion & Conclusions   A Membrane distillation module was developed at Heriot Watt   The system was tested under fluctuating operating conditions, as would be the case were it powered by a solar energy system.   The quantity of drinking water produced was greatly reduced when the power supply reduced, as is to be expected. A delay was seen in this effect due to thermal mass of the system.   The quality of the drinking water produced, its conductivity, remained within the safe drinking guidelines set by World Health Organisation, even during fluctuating operation… something not seen in a renewable energy powered membrane system to date!
  19. 19. Thank you for your attention ! Any Questions?