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

QQ

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