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Low Temperature Desalination: An Option forLow Temperature Desalination: An Option for Sustainability & Energy Savings
Veera Gnaneswar GudeNagamany NirmalakhandanShuguang DengShuguang Deng
New Mexico State University
Outline of the Presentation
1. Energy requirements for desalination2. New desalination technology3. Working principle4. Phase I: Theoretical studies5. Phase II: Pilot scale studies6. Phase III: Field scale studies7. Conclusions
New Mexico State University
Energy for DesalinationMinimum Theoretical Energy Requirement for Production of 1 kg of Freshwater is 2.5Minimum Theoretical Energy Requirement for Production of 1 kg of Freshwater is 2.5 kJ (Spiegler, 1977)
PMulti-Effect S l S ill
Multi Stage Flash Multi Effect
Di ill i MVC MED- Reverse EDProcess Solar Still (MESS)
Flash Distillation
(MSF)
Distillation (MED)
MVC MEDTVC
Reverse Osmosis ED
Thermal energy (kJ/kg) 1500 250-300 150-220 _ 220-240 _ _
Energy Requirements
( g)
Electrical energy
(kWh/m3)0 3.5-5 1.5-2.5 11-12 1.5-2 5-9 2.6-5.5
Total electric equivalent (kWh/m3)
0 15-25 8-20 11-12 21.5-22 5-9 2.6-5.5
GHG Emissions kg CO2/m3 Maximum value 0 24 19.2 11.5 21 8.6 5.3kg CO2/m
H2O
• 45 % of the unit desalinated water cost is due to the energy requirements in the process
New Mexico State University
Research Goals and Objectives
Phase I: Theoretical Studies
• Study New, energy-efficient, self-sustainable, low temperature desalination (LTD) system
• Study and evaluate the performance of LTD system using low grade solar/waste energy (heat rejected by refrigeration system)system)
• Application of renewable energy sources such as solar collectors Photovoltaics PV/T collectors and Geothermalcollectors, Photovoltaics, PV/T collectors and Geothermal water sources
New Mexico State University
New, Low-Temperature Desalination System
• Continuous process (Energy-efficient, lower specific energy requirement)
• Near vacuum pressures (natural means of gravity & barometric pressure head- Natural Vacuum)
• Lower temperature (40-50 0C < Conventional)
• Renewable/Low Grade energy Source dependent
• No mechanical pumping• No mechanical pumping
• No cooling
Thermodynamic JustificationGeneric Phase-Change Desalination ProcessGeneric Phase-Change Desalination Process
)( QhmhmmhmQhm
EoutEin
Thermodynamic Analysis (FLT)
)(
)]()([
)(
bss
Li
f
LLfbfsffiss
hhh
hhm
mm
QhmhmmhmQhm
)( Lbfs hhhm
Qi = variable kJ/hr, Fixed feed rate, 1 kg/hr Qi = 1000 kJ/hr, variable feed rate, kg/hr
2700 0
2750.0
2800.0
2850.0
2900.0
2950.0
uire
men
t (kJ
/kg 0.4
0.50.60.70 8 0 200
0.250
0.300
0.350
0.400
oduc
tion
Rat
ehr
)
1
1.5
2
2400.0
2450.0
2500.0
2550.0
2600.0
2650.0
2700.0
40 50 60 70 80 90 100
Spec
ific
Hea
t Req
u 0.8
0.000
0.050
0.100
0.150
0.200
50 60 70 80 90 100
Fres
hwat
er P
ro(k
g/h 2
2.5
3
3.5
440 50 60 70 80 90 100
Evaporation Temperature (Deg C)
50 60 70 80 90 100
Evaporation Temperature (Deg C)4.5
5
Physical Principle behind Natural VacuumPhysical Principle behind Natural Vacuum
T = 25ºCVP = 0.51 psi
T = 25ºCVP = 0.49 psi
T = 25ºCVP = 0.51 psi
T = 45ºCVP = 1.0 psi
Low
Barometrichead = ~ 10 m
Lowgradeheat
Freshwater Saline water Freshwater Saline water
New Mexico State University
Desalination Using Low Grade Waste HeatFl t l
Condenser, CONEvaporation
chamber, EC
Flat panelsolar collector
HE1
HE2 Lowgradeheat
Thermalenergystorage,
TES
Hot water storage
~ 10 m
Waste heatSolar energy
heatTES
Generator Auxiliary
energySolar energyProcess heat Cooling
load
Condenser
Evaporator
energy
Saline water Brine FreshwaterAbsorption refrigeration system, ARS
New Mexico State University
Summary of ResultsSummary of Results(Theoretical Study)
Energy Source Mode of operation
Heat energy required
(kJ/kg
Mechanical energy
required (kJ/k
Total Energy
required (kJ/koperation (kJ/kg
freshwater) (kJ/kg freshwater)
(kJ/kg freshwater)
ARS configuration Continuous 194 14 208configuration
Solar collectors Batch 3118 4.1 3122.1PV/T collectors Batch 3118 4 3122
GeothermalGeothermal source* Continuous 2934 144 3078
New Mexico State University
Research Goals and ObjectivesResearch Goals and Objectives
Phase II: Pilot Scale StudiesD l d D h f ibili f l• Develop and Demonstrate the feasibility of low temperature desalination unit in continuous mode of operation using the power from electric grid
• Demonstrate the feasibility of low temperature desalination unit using renewable energy sources (direct solar and photovoltaic
) th h il t l t denergy) through pilot scale study
• Feasibility study of reclaiming potable quality water from the ffl f l (Ci f L C NM) beffluent of wastewater treatment plant (City of Las Cruces, NM) by
LTD system
New Mexico State University
Experimental SetupLTD P NMSU Objectives:Objectives:
•• To demonstrate the feasibility of To demonstrate the feasibility of LTD system using Renewable LTD system using Renewable
LTD Process at NMSU
energyenergy•• To study use of Different To study use of Different
Combinations of EnergyCombinations of Energy
Method:Method:•• Heat source: Solar/Photovoltaic Heat source: Solar/Photovoltaic
EnergyEnergyEnergyEnergy•• Withdrawal rate: 0.250 kg/hrWithdrawal rate: 0.250 kg/hr•• Open top during Day timeOpen top during Day time•• Evaporation temperatures: 45Evaporation temperatures: 45--6060 00CCEvaporation temperatures: 45Evaporation temperatures: 45 60 60 CC•• Summer conditionsSummer conditions
New Mexico State University
Experimental Results60
Temperature Profiles
20
30
40
50
erat
ure(
deg
C)
0
10
20
0:00:00 4:48:00 9:36:00 14:24:00 19:12:00 0:00:00
Tem
pe
Tambient TcondenserTevaporator Tvapor
400
500
1000
1200Wload Wbat Wpv Ws
Time(hours)
Energy Profiles
0
100
200
300
Ene
rgy
(W)
400
600
800
1000
Inso
latio
n(W
/m^2
)
-300
-200
-1000:00 4:48 9:36 14:24 19:12 0:00
Time(hours)0
200
400
Sola
r Prototype Prototype Des@LTDes@LT Unit powered by RESUnit powered by RES
New Mexico State University
Experimental Study - Phase II: Summary
Thermodynamic Benefits R d d St t ti R d d
250
300
350
min
utes
)
Thermodynamic Benefits • Reduced Start up time, Reduced response time for Freshwater demand
50
100
150
200
Star
t up
time
(m • Reduced Specific Energy Requirements by LTD systems
040 45 50 55 60 65
Evaporation temperature (Deg C)
3750g)
Experiment DescriptionMode of
Operation
Specific Energy Requirement
(kJ/kg)
Case 1 Utilization of direct solar energy Batch 4157
3500
3550
3600
3650
3700
Req
uire
men
t (kJ
/kg Case 1 Utilization of direct solar energy Batch 4157
Case 2 Utilization of direct solar energy with a reflector Batch 3118
Case 3Solar energy during sunlight hours, photovoltaic energy during non sunlight hours
Continuous 2926
3250
3300
3350
3400
3450
Spec
ific
Ener
gy R during non-sunlight hours
Case 4Solar and photovoltaic energy
together Batch 3325
40 45 50 55 60 65
Saline water evaporation temperature (Deg C)
New Mexico State University
Wastewater Effluent Reclamation
Parameter
Test 1 Test 2
Before After % Before After % Before After Reduction Before After Reduction
BOD (mg/L) 11 7 36.4 10 6 40
TDS (mg/L) 935 68 92.7 783 54 93.1( g )
TSS (mg/L) 5.1 0.5 90.2 8 1 87.5
Nitrate/Nitrite (as N-mg/L) 2.4 0.1 95.8 0.4 0.1 75.0g
Ammonia (as N-mg/L) 26.13 0.5 98.1 22.68 3.27 85.6
pH 7.1 7.1 0.0 7.6 7.6 0
Coliform (cfu) 77 0 100 55 0 100
New Mexico State University
Phase III: Field Studies
Objectives:
• To demonstrate low temperature desalination (LTD) unit at freshwater production rates (75-100 gal/d)
• To demonstrate two-stage low temperature desalination unit
• To study the process variables such as heat and mass transfer coefficients, areas, scaling and fouling issues
• To determine the specific energy requirements for a two-stage low temperature desalination (LTD) process
New Mexico State University
Multi-effect LTD Process Configuration
Stage # 1 Stage # 2 Stage # 3
MULTI‐EFFECT EVAPORATION PROCESS CONFIGURATION
Stage # 1 Stage # 2 Stage # 3P1, T1 P2, T2 P3, T3
Vapor VaporVapor
Water vapor
Water vapor
Condenser
Hot water
Recycle ne
W W
HotWater fresh
Bri
Freshwater
Brine Brine
Freshwater
Seaw
ater
Seaw
ater
Seaw
ater
Water Tank
sea
brine
fresh water
P1 > P2 > P3; T1 >T2 >T3
S sea water
NMSU
Two-stage LTD ProcessStage #1
Stage #2Condenser
Source Characteristics:• Seawater direct from ocean• TDS ~ 22000 ppmpp• Temperature: 10-15 0C• Hot water source: boiler
powered by electric grid
NMSU
powered by electric grid
Temperature and Pressure Profiles
-210
-200
160
180
-240
-230
-220
100
120
140
n H
G)
ure
(F)
-270
-260
-250
60
80
100
Pres
sure
(in
Tem
pera
tu
R1 W t R1 R2 W t
-300
-290
-280
0
20
40
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
R1 Water R1 vapor R2 WaterR2 Vapor HW in HW outF1 P1 P2
09:5
2:22
10:0
2:22
10:1
2:22
10:2
2:22
10:3
2:22
10:4
2:22
10:5
2:22
11:0
2:22
11:1
2:22
11:2
2:22
11:3
2:22
11:4
2:22
11:5
2:22
12:0
2:22
12:1
2:22
12:2
2:22
12:3
2:22
12:4
2:22
12:5
2:22
13:0
2:22
13:1
2:22
13:2
2:22
13:3
2:22
13:4
2:22
13:5
2:22
14:0
2:22
14:1
2:22
14:2
2:22
14:3
2:22
14:4
2:22
14:5
2:22
15:0
2:22
15:1
2:22
Time 8/27/08
NMSU
Temperature & 60
70
80
120
140
160
180
l/min
)
F) pEnergy Profiles
30
40
50
60
80
100
120
wat
er fl
ow (g
al
Tem
pera
ture
(F
HW inHW outF1
0
10
20
0
20
40
22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22
Hot
3
r)
09:5
2:2
10:0
7:2
10:2
2:2
10:3
7:2
10:5
2:2
11:0
7:2
11:2
2:2
11:3
7:2
11:5
2:2
12:0
7:2
12:2
2:2
12:3
7:2
12:5
2:2
13:0
7:2
13:2
2:2
13:3
7:2
13:5
2:2
14:0
7:2
14:2
2:2
14:3
7:2
14:5
2:2
15:0
7:2
Time
1 5
2
2.5
uction
rate (gal/hr Evaporation tank 1
Evaporation tank 22-Stage Freshwater Production Profiles
0.5
1
1.5
reshwater produ(75-90 gal/d)
0
1 2 3 4 5 6
F
Time (hours)
Product Water Quality
Sample TDS (ppm)Conductivity
(µS)pH
Feed water 22500 32150 7.8Fresh water 155 185 7.6
USEPA standard < 500 6.5-8.5Feed water 22800 32600 7.8Fresh water 71 145 7.5
USEPA standard < 500 6.5-8.5Feed water 22600 32200 7.8Fresh water 54 113 7.5
USEPA standard < 500 6.5-8.5
Feed water 22300 31800 7.8Fresh water 45 82 7.4
USEPA standard < 500 6.5-8.5
NMSU
Advantages of Low Temperature Desalination
• Thermodynamic efficiency– lower heat fluxes/temperature differentials; better thermal
efficiency lower heat losses to the environmentefficiency, lower heat losses to the environment
• Low corrosion and scaling rate– safe to use plastic pipes & aluminum plates; – temperatures well below the saturation limits of problem scalants
• Flexibility and reliability short start up less time for heating up freshwater demand– short start-up, less time for heating up, freshwater demand
– solid construction, proven equipment, low maintenance
Low energy costs:Low energy costs: enables use of low cost heat sources which would otherwiseenables use of low cost heat sources which would otherwiseLow energy costs: Low energy costs: enables use of low cost heat sources which would otherwise enables use of low cost heat sources which would otherwise be lost to environmentbe lost to environmentex: stack gases, cooling water streams and low pressure exhaust steamex: stack gases, cooling water streams and low pressure exhaust steam
Conclusions• Experimental studies demonstrate the feasibility of using direct
solar energy and photovoltaic energy• Lower energy: Specific energy requirements for single effect• Lower energy: Specific energy requirements for single effect
is 2926 kJ/kg• Two-stage LTD process successfully demonstrated• Two-stage energy requirements about 1600 kJ/kg• The system does not require any mechanical pumping except
occasional removal of accumulated gasesg• High quality distillate (TDS < 50 ppm)• High exergy efficiency (quality of energy completely utilized)
l i fi i i b h d• Multistage configuration can improve both energy and economic budget of the process