Solar powered multi-stage natural vacuum low temperature desalination process

Presenters: Jeff Steinwinder & Edith Martinez-GuerraTeam Members: Hugo Guerra & Ben Spiller

Advisor: Dr. Veera Gnaneswar Gude

Mississippi Water Resources Conference April 5, 2016

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Outline1. Overview 2. Proposed System3. Material and Methods4. Experimental Data5. Results and Discussions6. Conclusions and Future Work

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Natural Desalination Desalination is an engineering

technique that essentially mimics the natural water cycle

Process is related to heating, evaporating and condensing the freshwater from the saline waters

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http://www.eduplace.com/kids/sla/graphics/sla_3d1.jpg

Desalination: an overview

Desalination◦ Producing freshwater through heat exchange or membrane

processes

Thermal and membrane technologies◦ Thermal include phase-change (evaporation –

condensation)◦ Membrane include physical separation

Energy supplied through heat and electricity depending on process◦ Fossil fuel sources or renewable energy such as solar

energy

Various saline water sources◦ Seawater and brackish ground water (2500-200,000 mg/L)

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http://water.usgs.gov/edu/graphics/desalinationprocess.gif

Desalination: an overview

Thermal Membrane

Reverse Osmosis and Electrodialysis

Processes are costly, energy intensive (prime electricity), maintenance and require professional workers to oversee daily functions.

Typically chosen for small, large-scale production

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Multi-stage flash distillation

Process yields low production rates and requires multiple stages.

Energy intensive but can be supplied from waste heat and process integration

Large-scale public integration

Desalination needs in USA

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http://droughtmonitor.unl.edu/data/pngs/20160329/20160329_usdm_home.png

http://www.kleinfelder.com/index.cfm/services/design-engineering/structural-engineering/carlsbad-desalination-plant/

Carlsbad Desalination Plant - Carlsbad, CA

Brackish Water Sources in the United States

7http://www.wrri.nmsu.edu/tbndrc/images/us-saline.gif

The Proposed System Solar Energy: low grade energy source ◦ High conversion efficiency; less heat losses

Low pressure/vacuum ◦ Creation of natural vacuum (evaporates water at low temperatures)

Multiple Stage System◦ 3 open boundary control volumes ◦ System works in parallel in terms of mass flow◦ Linear system in terms of heat exchange

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Heat Exchanger Stage 1 Stage 2 Stage 3

Flow of Usable Heat

Surroundings

Brine Water Tank

Fresh Water Tank

Saline Water Tank

HE

SC Panels

PV Panels

EC

EC

EC

Battery Bank/Data Logger

~ 10 m

Waterline

Waterline

Waterline

Thermocouple - -

Transducer - -

Pump - -

The Proposed System: Schematic

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The Proposed System: Construction Stage Construction◦ Plexiglas

◦ Predrilled and screwed

◦ Aluminum sheet separation

◦ Circulating pumps

Data Collector◦ Thermocouple

◦ Pressure Transducers

◦ Rain Collectors

• Solar Collectors• Installation and connection

• Wooden base frames

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Components: Evaporator/Condenser

Each stage contains an evaporator/condenser system Mass Conservation Heat Transfer Heat Losses and control

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Data Acquisition

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CR1000 dataloggers

PC200W software Thermocouples J

Pressure transducers (0-50psia) Rain gauge (tipping bucket)

12 V battery

Monitored Data Temperature◦ Water at each stage◦ Vapor at each stage

◦ Condenser at each stage◦ Incoming water- to coil

◦ Out of coil water

Fresh water quantity

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Temperature Results Condensation temperatures: 55, 65, and 75 °C◦ 10 hours of heat and 8 hours to cool down

Similar trend for other two stages

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Results

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Temperature and freshwater production profiles for the three-stage desalination unit at a hot water sourcetemperature of 65°C: (a) temperature profiles in stage 1 and (b) hourly freshwater production rates andcumulative volume in 10 hour heat supply window. (c) and (d) show for second stage.

Efficiency Results Energy Balance◦ Water into the coil- 150 kg/hr◦ 20 L of water in first stage

◦ 10 L of water in 2nd and 3rd stage◦ Latent heat for each stage

Water production in 1st stage:◦ 5, 10, 10.5 L/d approx. for 55, 65, and 75 °C

respectively

Results for 0. 3 m2 (lab-scale)

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Temperature (°C)

Efficiency (%)

Effluent (ml/hr)

55 45 120

65 55 230

75 58 250

Future Work Insulation for reactor and piping system Studies using solar collectors Natural vacuum

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Acknowledgements

U.S. Environmental Protection Agency Mr. Joe Ivy Civil and Environmental Engineering Department Ms. Crystal Byrd, Ms. Maria Solis, Ms. Monica Pistorius

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