1. Mohammed Abdulla Sunday, December 19, 2010
Desalination
Mohammed Abdulla
Sunday, December 19, 2010

2. Outlines Salinity Desalination Processes Desalination Barriers.
Abu Dhabi Solar Desalination Plant.
Useful Resources.
First of all I will define the main term in desalination which is salinity.

3. Desalination Plants Rejection
1. Salinity
Salinity
Concentration of salt in water measured in grams per liter or parts per thousand.
Fresh Water
Brackish Water
Saline Water
Brine
Less than 0.5 g/l
Desalinated Water
g/l
Underground Water
30-50 g/l
Sea Water
More than 50 g/l
Desalination Plants Rejection
Based on the salinity, water is divided into four parts.

4. 2. Desalination Processes
Mainly, we have two inputs, and two outputs.
Now, lets sea what the separation process could be?

5. 2. Desalination Processes
Separation Processes
Thermal
Multi Stage Flash
Multiple Effect Evaporation
Freezing
Humidification-Dehumidification
Membrane
Reverse Osmosis
Electro-Dialysis

6. Specific Heat Capacity
2.1 Thermal Desalination
Specific Heat Capacity
Heat required to raise a unit mass by a unit temperature at constant volume or pressure (J/kg.°C).
Sensible Heat
Latent Heat
Heat added or removed and causes change in temperature.
Heat added or removed and causes change in phase.
I would like to review some thermodynamics terminologies as they are essential in thermal desalination.
Water Vapor
Water Steam
Gas phase of water.
Water vapor at high pressure and temperature.

7. Water Saturation Pressure
2.1 Thermal Desalination
Water Saturation Pressure
Pressure at which water changes its phase at certain temperature.
In thermal desalination, we always need vapor. In order to keep the water vapor, its pressure should always be below the saturation pressure.
This will become clear when we come to the thermal processes.

8. 2.1.1 Multi Stage Flash
Most widely, 60% in the world. It consists mainly of several stage depending on the capacity of the plant, condensers, and heater.
Moving forward in the consecutive stages, the temperature decreases.

9. 2.1.1 Multi Stage Flash
Demister is like a mesh that separates brine droplets from fresh water vapor.
Part of the feed water is for cooling and is rejected after condenser because this is a single stage that is not able to handle all the feedwater.
The most challenging part in thermal desalination is the accurate control of temperature, pressure, brine level, vibration, insulation,
This is very simple. You can do something like this in your project prviding heating water from solar panels.
(El-Dessouky & Ettouney, 2002)

10. 2.1.2 Multiple Effect Evaporation

11. 2.1.2 Multiple Effect Evaporation
(El-Dessouky & Ettouney, 2002)

12. 2.2 Membrane Desalination (Reverse Osmosis)
Osmosis (Natural Osmosis)
Water movement through a membrane from low salinity side to the high salinity side.

13. 2.2 Membrane Desalination (Reverse Osmosis)

14. 2.2 Membrane Desalination (Reverse Osmosis)

15. 2.2 Membrane Desalination (Reverse Osmosis)
Tampa Bay RO Desalination Plant, Florida, US, 2007

16. 3. Desalination Barriers
Energy Consumption
Cost
Scaling
Environment Impact
Main desalination barriers are energy consumption, cost, scaling, and environmental impact.

17. 3.1 Energy Consumption
Multi Stage Flash & Multiple Effect Evaporation (Thermal)
Reverse Osmosis (Membrane)
10 – 200 kWh/m³
1 – 10 kWh/m³
Steam Turbines
Gas Turbines
Steam and Gas Turbines
Power (MW) to Water (MIGD) Ratio
5 : 1
10 : 1
15 : 1
Water desalination plants usually exist in conjunction with power generation plants. One reason is to reduce energy consumption significantly specially for thermal desalination. Also, when building new city they first build desalination and power plants together. If they want water more than power, they will get steam turbines. If they want

18. 3.1 Energy Consumption
This is a desalination plant that consists of both thermal and membrane desalination.

19. 3.2 Cost
(Semiat, 2000)

20. 3.3 Scaling What is scaling?
The accumulation of salt particles on the desalination plant components.
How to minimize scaling?
Addition of chemicals, like Polyphosphate.
Accumulation over condensers, evaporators.
Act as thermal insulation and decreases efficiency.

21. 3.4 Environmental Impact Energy consumption and carbon footprint.
Rejection of brine back into sea.
Brine is hot and has high salinity. It could destroy marine life. Should be diluted and cooled down before rejection.

22. 4. Abu Dhabi Solar Desalination Plant
Built in It consists mainly of a solar collector field, heat accumulator tanks, and evaporator.
Evacuated tube flat plate collectors. They want this plant to run for 24 hours and to minimize the temperature flactuation, so they added heat accumulator tanks.
Most solar desalination plants use vertical MEE because
(El-Nashar, 2008)

23. 5. Useful Resources
Fundamentals of Salt Water Desalination, by El-Dessouky & Ettouney
Thermal analysis, mass balance, energy balance, efficiencies, ratios.
Desalination Research Progress, by Delgado & Moreno
Renewable energies and desalination.
Multiple Effect Distillation of Seawater Using Solar Energy, by El-Nashar
Solar desalination plant in Abu-Dhabi.