1. Experimental prototype of a desalination system with efficiency approaching the theoretical limit Philip Davies, Chioma Alatta, Kim Nguyen and James Wayman Sustainable Environment Research Group, Engineering and Applied Science
5th Oxford Water and Membranes Research Event: Water-energy-food nexus 30th June 2015

2. Outline Real vs. ideal SEC Need for high recovery desalination inland
Advantage batch RO over continuous or ‘closed-circuit’
Construction of prototype
Results
Driving from thermal power source
Conclusions and further work

3. Real vs. ideal Specific Energy Consumption
Specific Energy Consumption (SEC): a key performance indicator
Define: Energy Consumption Ratio= Real SEC
Ideal minimum SEC
Focus on inland brackish water system – high recovery
Energy Consumption Ratio
Seawater
3 – 5
Brackish water
>10
Reference: M. Li, B. Noh, Validation of model-based validation of brackish water
reverse osmosis (BWRO) desalination, Desalination, 304 (2012),

4. Saline aquifers may be far from sea
1000 km
International Groundwater Resource Assessment
Saline and brackish groundwater by genesis
Source UN-IGRAC

6. Batch is more efficient than continuous RO…
Force
Feed
Pressure varies with time (not distance)
Recirculation
Continuous
∞ stages to achieve theoretical minimum energy
Multistage continuous
As regards longitudinal concentration gradients, it is possible to overcome these by multi-staging. However, as explained here, multi-staging does not provide the perfect solution unless an infinite number of stages are used. Instead at Aston we are investigating a batch system to provide theoretically ideal SEC even when working at high recovery.
Theoretical minimum
achieved in 1 stage
Reproduced from Elimelech et al, Science 333, 712 (2011)

7. …especially at high recovery
Minimum
Continuous 1 stage + ERD
‘Closed-circuit desalination’
Continuous 2 stage + ERD
Use equations from Water paper
Batch RO
Qiu and Davies: Water, 4, (2012).
ERD: Energy Recovery Device

8. Formulae used Based on van’t Hoff law r – recovery ratio
Qiu and Davies: Water, 4, (2012).

9. Different to ‘closed-circuit desalination’
Mixing point avoided in our design
L. Szücz, A. Szücs, US Patent , 1991

10. Different to ‘closed-circuit desalination’
Batch (our design)
Closed circuit

11. Pressure Gauge / Flow Meter
Basic Layout
Water Filter
Bore Pump
Flow meter
Pressure Gauge
Concentrate Drain
Pressure Gauge / Flow Meter
Recirculation Pump
Air Release Valve
RO Module
Non- return valve
Non-return valve
Pressure vessel
Ball valve
Piston
Solar simulator

12. Pressure Gauge / Flow Meter
1. Pressurise
Water Filter
Bore Pump
Flow meter
Pressure Gauge
Concentrate Drain
Pressure Gauge / Flow Meter
Recirculation Pump
Air Release Valve
RO Module
Non- return valve
Non-return valve
High pressure water being used to drive process
Ball valve
Piston prevents mixing

13. Pressure Gauge / Flow Meter
2. Purge
Water Filter
Bore Pump
Flow meter
Pressure Gauge
Concentrate Drain
Pressure Gauge / Flow Meter
Recirculation Pump
Air Release Valve
RO Module
Non- return valve
Non-return valve
Pressure vessel
Ball valve
Piston
Feed water used to drive process in previous cycle, remains in vessel during purge process.

14. Pressure Gauge / Flow Meter
3. Refill
Water Filter
Bore Pump
Flow meter
Pressure Gauge
Concentrate Drain
Pressure Gauge / Flow Meter
Recirculation Pump
Air Release Valve
RO Module
Non- return valve
Non-return valve
Ball valve
Piston
Feed water now used to refill loop

15. 1. Pressurise (start again)
Water Filter
Bore Pump
Flow meter
Pressure Gauge
Concentrate Drain
Pressure Gauge / Flow Meter
Recirculation Pump
Air Release Valve
RO Module
Non- return valve
Non-return valve
Pressure vessel
Ball valve
Piston

16. Rig development Aims High recovery for inland use with brackish water
Energy efficiency (low SEC)
Try to use readily available components
Pressure exchanger and pressurised batch vessel integrated, made of standard RO pressure vessel
Developed by Aston MEng students in 6 months
Budget <£1500
[Imam Ahmad (6768) and Ibn Maajah (419)]
Allah Says in the Holy Quran Chapter 7 Surah Aaraaf verse 31:
يَا بَنِي آدَمَ خُذُوا زِينَتَكُمْ عِندَ كُلِّ مَسْجِدٍ وَكُلُوا وَاشْرَبُوا وَلَا تُسْرِفُوا ۚ إِنَّهُ لَا يُحِبُّ الْمُسْرِفِينَ
‘O children of Adam! Attend to your embellishments at every time of prayer, and eat and drink and be not extravagant; surely He does not love the extravagant’.
James
Kim
Chioma

17. Under construction

18. Compression springs
Micro switch
Piston and O-ring assembly
Sealing end cap
Hydraulic connection
Switch contact plate
Pressure Differential Sensor - Designed to electrically isolate bore pump at end of each pressurisation cycle

19. Electrical system

20. Pressure Differential Sensor - Circuitry

21. Solar Array Simulator
(Laboratory power supply to substitute use of a solar photovoltaic array)

22. Finished Feed water flow meter and pressure gauge RO membranes
Pressure vessel
Pressure differential sensor
Water filter
Water reservoir and bore pump
Recirculation pump
Ball valves
Concentrate outlet
Permeate outlet

23. Results: 3500 ppm feed, 60% recovery
Less pressure & flux, higher efficiency
Pressure (kPa)
osmotic
Permeate volume (m3)

24. Results: 3500 ppm feed, 70% recovery
Less pressure & flux, higher efficiency
osmotic
Pressure (kPa)
Real SEC
Ideal 1-stage+ERD
Note cycle time 4-10 min
Ideal SEC
Permeate volume (m3)

25. Results summary (3500 ppm feed)
Our system – measured
result based on hydraulic
energy

26. Results summary (5000 ppm feed)
(measured)
(measured)
Max pressure 1400 kPa
Max pressure 1440 kPa

27. Driving from thermal power source
Power piston
Pump piston
Coupling mechanism
Steam
Freshwater
Saline water
Membrane
Stirrer p p
pVn=const
pV=const V V

28. Linkage arrangement Steam in Power piston valve Steam out1 L O 2 q1 P
valve
Steam out
Expansion cylinder q2
Linkage arrangement
Concentrate
Davies, Desalination, 271, (2011)
Freshwater 5 M
Pump piston
Membrane module 4
Pump
cylinder
Feed pump
Saline groundwater in 3

29. Prototype for thermal power source
PhD students:
Clara Qiu
Opus Igobo
Isothermal Rankine Engine R245fa

30. Conclusions and further work
New design of PV-batch RO system for brackish water
Tested with NaCl solution up to 5000 ppm
SEC reduced to <2x ideal minimum (based on hydraulic energy)
Better than 1-stage+ERD at high recovery (70%)
Nothing in principle to stop it reaching the ideal minimum
This differs from conventional systems
Can also be designed for thermal power sources
Further work
Optimise pumps, membrane, module, spacers
Automate valves and start up (priming)
Improve pressure differential sensor
Connect to real solar panels
Test in field and commercialise

31. Thank you