Desalination Presentation 3
25
Forward Osmosis Energy Use Comparisons to RO, MSF, MED R. McGinnis, J. McCutcheon M. Elimelech Dept. of Chemical Engineering Environmental Engineering Program Yale University NAMS 2007, Orlando, FL
-
Upload
hayehoyehu -
Category
Documents
-
view
443 -
download
1
Transcript of Desalination Presentation 3
Forward Osmosis Energy Use Comparisons to RO, MSF, MED
R. McGinnis, J. McCutcheon M. ElimelechDept. of Chemical EngineeringEnvironmental Engineering ProgramYale University
NAMS 2007, Orlando, FL
Outline• Overview of NH3 /CO2 FO
• Solute Removal / Recycle Methods
• Modeling Methods
• FO Energy Estimates
• Comparison to RO, MSF, MED
• Impact of Membrane Efficiency on Heat Use
The Ammonia-Carbon Dioxide FO Process
Reverse OsmosisSaline Water
Brine
Membrane
Product Water
HP Pump
EnergyRecovery
EnergyInput ( )πσΔ−Δ= PAJw
Forward Osmosis Process
EnergyInput
( )PAJw Δ−Δ= πσ0
Saline Water
Draw SolutionNH3 /CO2
ProductWater
Brine
Membrane
Draw Solute Recovery
Potential Benefits• Low Energy Costs
– Can use low temperature heat– Low cost of heat favors low total water costs
• Lower Energy Use than Other Thermal Methods– Phase change of solute, not solvent
• High Feedwater Recovery – No osmotic pressure limitation to recovery– Pretreatment to prevent scaling will be limiting factor
• Reduced Brine Discharge
• May be Effective for Difficult Feedwaters– FO uses so far: food concentration, landfill leachate treatment,
anaerobic sludge centrate treatment
Solute Removal / Recycle Methods
Seawater Distillation1≈=
steam
water
KgKgGOR
Image from Wikipedia
steam
water
KgKgGOR =
Multi-Stage Distillation
128−≈=steam
water
KgKgGOR
steam
water
KgKgGOR =
Image from Encarta Encyclopedia Online
MED DesalinationTemperature,
Pressure
Brine
Product Water
Feed
Energy
148−≈=steam
water
KgKgGOR
steam
water
KgKgGOR =
Forward Osmosis Process
DistillationColumn
Saline Water
Draw SolutionNH3 /CO2
ProductWater
Brine
Membrane
Draw Solute Recovery
Single Distillation Column
Reboiler
Column
Product Water
To Membrane System
From Membrane System
Heat Duty (Steam in, Condensate out)
Presenter
Presentation Notes
If steam temp is 40C, then bottom of reboiler operating at approx. 37C, depending on choice of temperature approach for heat exchange operations in FO plant
Multi-Stage Column Distillation
• Benefits from Heat Reuse Efficiencies of MSF / MED
• Reduces Quantity of Energy Required by 60-70%
• May use Higher Temperatures than MSF or MED (to increase range of increased efficiency)
Multiple Column OperationTemperature,
PressureFrom Membrane System
Reboiler
Reboiler
ColumnProduct Water
To Membrane System
ColumnProduct Water
To Membrane System
From Membrane System
Heat DutyFrom Membrane System
Multi-Stage Column Distillation (MSCD)
Product Water
Feed
Energy
Draw Solution
Temperature, Pressure
McGinnis, Elimelech, “Energy Requirements of Ammonia–Carbon Dioxide ForwardOsmosis Desalination”, Desalination, 207 (2007) 370-382.
Modeling Methods
• AspenTech Hysys Chemical Process Modeling Software
• OLI Electrolyte Property Database (high ionic strength)
• Draw Solution Concentrations Based on Experimental Flux Data
Hysys / OLI
50 100 150 200 2500
100
200
300
400 MED MSF FO MSCD
Hea
t Dut
y (M
J/m
3 )
Heat Temp. (oC)
Heat Duty versus Temperature of Heat
MED plot based on Performance Ratios (lbs water / 1000 BTU) of 8 - 14.73 for heat temperatures of 70-131 oC; MSF for GOR of 12 for 115 oC (from Morin, O.J., Design and Operating Comparison of MSF and MED Systems. Desalination,93(1-3) (1993) 69-109)
Electrical Power:MED = 1.60 kWh/m3
MSF = 2.65 kWh/m3
FO = 0.24 kWh/m3
0 50 100 150 200 25005
101520253035
GO
R
Heat Temp. (oC)
Heat Duty vs. Temp. of Heat
( ) ( )[ ](kJ/kg)FODuty Heat
(kJ/kg)35 @ water HsteamHGOR0C−
=steam
water
KgKgGOR =
Presenter
Presentation Notes
This GOR calculation assumes water returned at temperature of condenser. The enthalpy difference between hot water and 35C water increases as the temperature of the steam increases.
Equivalent WorkDecreasing Steam Pressure, Decreasing Ability to do Work
[ ] electurbineoutinC
waterequiv W
MJkWhEHH
GORmW +⎟
⎠⎞
⎜⎝⎛ ×××−⎟
⎟⎠
⎞⎜⎜⎝
⎛= −6
35
3
1077.2)(0
GOR =Kgwater
Kgsteam
LP Steam TurbineSteam In Steam Out
Condenser
Steam to Desalination Process
Mechanical work not done by steam
[ ] electurbineoutinC
waterequiv W
MJkWhEHH
GORmW +⎟
⎠⎞
⎜⎝⎛ ×××−⎟
⎟⎠
⎞⎜⎜⎝
⎛= −6
35
3
1077.2)(0
0 50 100 150 200 2500
1
2
3
Equi
v. W
ork
(kW
h/m
3 )
Heat Temp. (oC)
Equivalent Work vs Heat Temperature (FO MSCD)
RO
0
1
2
3
4
5
6
kW
h/m
3
MSF MED-TVC MED-LT RO FO-LT
Comparison of Desalination Technologies Based on Equivalent Work
Contribution fromElectrical Power
Draw Concentration vs. Energy Use
0.5 1.0 1.50
10
20
30
40 160 C 40-44C
GO
R
Draw Conc. (M)
Adapted from: McGinnis, Elimelech, “Energy Requirements of Ammonia–Carbon Dioxide Forward Osmosis Desalination”, Desalination, 207 (2007) 370-382.
0.5 1.0 1.50
1
2
3
4 160 C 40-44 C
Equ
iv. W
ork
(kW
h/m
3 )
Draw Conc (M)
Concluding Remarks• Availability of heat determines best
desalination method– If heat is available for cogeneration, FO is likely
preferable to RO in energy cost– If only electricity or fuel is available, RO is best
• Multiple columns useful to produce the most water yield for a given heat source
• FO membrane performance drives energy use of FO
Acknowledgements
• Funding by the Office of Naval Research
• Hydration Technologies
• Dow Filmtec
• Cascade Designs
