Desalination Presentation - University of Oklahoma

DewvaporationDewvaporation““CarrierCarrier--Gas Enhanced Atmospheric Gas Enhanced Atmospheric

Pressure DesalinationPressure Desalination””

Noah Abbas and Kehinde Adesoye

OutlineOutline

�� Existing TechnologiesExisting Technologies�� Reverse OsmosisReverse Osmosis

�� Thermal ProcessesThermal Processes

�� DewvaporationDewvaporation ExplanationExplanation

�� Mathematical ModelMathematical Model

�� Cost CalculationsCost Calculations

DesalinationDesalination

�� Process of purifying seawaterProcess of purifying seawater

�� A solution to water shortages around the A solution to water shortages around the worldworld

�� Existing technologiesExisting technologies�� Reverse OsmosisReverse Osmosis

�� Thermal Evaporation Thermal Evaporation

�� DewvaporationDewvaporation

Factors of ComparisonFactors of Comparison

�� Purity of waterPurity of water

�� EconomicsEconomics�� Energy efficiencyEnergy efficiency

�� Production rateProduction rate

�� Regional factorsRegional factors�� Resources vary from region to regionResources vary from region to region

�� Proximity to oceanProximity to ocean

�� Availability of fuelAvailability of fuel

Reverse OsmosisReverse Osmosis

�� Most common in the Most common in the USAUSA

�� Solvent forced through Solvent forced through membranemembrane

�� Energy consumption Energy consumption from pressurefrom pressure

�� Susceptible to fouling, Susceptible to fouling, scaling and degradationscaling and degradation

Process of Reverse OsmosisProcess of Reverse Osmosis

�� Pressurized feed Pressurized feed

�� Applied pressure > Applied pressure > Osmotic pressureOsmotic pressure

�� SemiSemi--permeable permeable membranemembrane

�� Incomplete salt removal Incomplete salt removal (different rates)(different rates)

Typical RO PlantTypical RO Plant

MembraneModule

Pump

Brine

PretreatmentPost

Treatment

Saline Feed Pure Water

ProblemsProblems

�� Membrane foulingMembrane fouling�� Caused by micro organisms and particlesCaused by micro organisms and particles�� Reduce water qualityReduce water quality�� Add chemical e.g. chlorineAdd chemical e.g. chlorine�� UltraUltra--filtration of suspended solidsfiltration of suspended solids

�� ScalingScaling�� Formation of salt precipitate e.g. CaCOFormation of salt precipitate e.g. CaCO33

�� Reduces efficiencyReduces efficiency�� Add antiAdd anti--scalantscalant e.g. He.g. H22SOSO44

RO StatisticsRO Statistics

�� Operating costsOperating costs•• 2.50 2.50 –– 4.00 $/1000gal of product4.00 $/1000gal of product22

�� Energy requirements Energy requirements •• 26 KWh/1000gal of product26 KWh/1000gal of product22

�� Capital cost for sea water desalinationCapital cost for sea water desalination•• 4.00 4.00 -- 10.00 $/gal10.00 $/gal--dayday22

Thermal ProcessThermal Process(Evaporation)(Evaporation)

�� Phase separation Phase separation

�� Heat saline Heat saline water/condense vaporwater/condense vapor

�� Reduce pressureReduce pressure

�� Energy required for heat Energy required for heat of vaporizationof vaporization

�� Large energy costs, less Large energy costs, less common in USAcommon in USA

Evaporation / Condensation Column

Brine

Fresh water

Pretreatment

Saline feed

Heat

Multi Stage Flash DistillationMulti Stage Flash Distillation

�� 80% of world80% of world’’s thermal s thermal desalination productdesalination product

�� Energy needed for heat Energy needed for heat

�� Recycles heatRecycles heat

�� Two heat sources for Two heat sources for incoming saline feedincoming saline feed�� ExternalExternal

�� Heat of vaporizationHeat of vaporization

Schematic of MSFSchematic of MSF

�� Additional heatAdditional heat

�� Pressure Pressure released in first released in first chamberchamber

�� Water boils Water boils quicklyquickly

�� Evaporation and Evaporation and condensationcondensation

Heat Vapor

SalineFeed

PureWater

WasteBrine

Pump

Condensate Trays

Heat Exchanger

Tubes

ProblemsProblems

�� Scale formationScale formation�� Extra heat transfer layerExtra heat transfer layer

�� Reduces heat transferredReduces heat transferred

�� Reduces efficiencyReduces efficiency

�� Erosion and CorrosionErosion and Corrosion�� Use stainless steelUse stainless steel

Evaporation StatisticsEvaporation Statistics

�� Energy requirements Energy requirements •• 56 KWh/1000gal of product56 KWh/1000gal of product22

�� Costs are very highCosts are very high•• Because of expensive energy, prices are in the Because of expensive energy, prices are in the

range of $12 to $14 per 1000 gallonsrange of $12 to $14 per 1000 gallons5 5 in USAin USA

•• Only economically feasible in regions like the Only economically feasible in regions like the Middle East, where fuel is cheap and water is Middle East, where fuel is cheap and water is scarcescarce

DewvaporationDewvaporation

�� Developed by James Developed by James BeckmanBeckman

�� Arizona State UniversityArizona State University

�� Relies on air circulationRelies on air circulation�� Air moves in a cycleAir moves in a cycle

�� Works to recycle heatWorks to recycle heat

�� Waste heatWaste heat

�� Atmospheric pressureAtmospheric pressure

Dewvaporation Apparatus

Pure

water

Saline

feed

Inlet Air

Ambient Air

Outlet Air

Added heat(Qboiler)

Heat

Condensing water

Saline feed

Air

Evaporating water

Blower

Economic AnalysisEconomic Analysis

�� The cost has two main componentsThe cost has two main components

�� Operational costs associated with the heat Operational costs associated with the heat addedadded�� Heat required to created a larger temperature Heat required to created a larger temperature

difference from dew formation to evaporation difference from dew formation to evaporation sideside

�� Cost associated with equipmentCost associated with equipment�� Modeled as a heat exchangerModeled as a heat exchanger

Differential AnalysisDifferential Analysis

Heat Transfer Model Region 1

ddzzz dWGVGV += +

dzTThLdWhdTTGVhdTTGhTGVhTGh dvapVava )()()()()( 211111 −+∆++++=+

Mass Balance:

Heat Balance:

dWd

G, GVz

G, GVz+dz

FDz

FDz+dz

Region 1 Region 2

Heat Transfer ModelHeat Transfer Model

Deriving Differential EquationsDeriving Differential Equations

Deriving Differential Equations Deriving Differential Equations (Continued)(Continued)

Equations UsedEquations Used

Solving Differential Equation in Solving Differential Equation in SpreadsheetSpreadsheet

Heating the AirHeating the Air�� Heat needs to be added to achieve a Heat needs to be added to achieve a

temperature difference from temperature difference from dewvaporationdewvaporation to to evaporation sideevaporation side�� Can be added as steamCan be added as steam�� Adding steam keeps air saturatedAdding steam keeps air saturated

�� This made This made ∆∆T and G of the air stream above the T and G of the air stream above the tower design parameterstower design parameters

1 2 3 4 5

Q to achieve ∆T G,

GVse

G, GVs

d

Humid Air

Dry Air

Humid Air

Dry Air

Results of ModelResults of Model

�� Model considered credible if temperature profile was Model considered credible if temperature profile was appropriateappropriate�� Temperature of evaporation side air had to reach ambient air Temperature of evaporation side air had to reach ambient air

temperature (25temperature (25ººC) at bottom of columnC) at bottom of column

�� Air flow rate (G) had the most dramatic effect on product Air flow rate (G) had the most dramatic effect on product flow and heating requirementsflow and heating requirements

1 Humid Air

2 3 4 5 Dry Air

G, GVs

e

G, GVs

d

T5

Temperature ProfileTemperature Profile

Temperature Down the Tower

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

0 100 200 300 400 500 600 700 800

Distance from Tower Top (cm)

Tem

per

atu

re (

deg

. C

)

T Air Dewformation Side

T Pure Water Product

T Seawater/Brine

T Air Evaporation Side

∆T

Equipment Cost and Energy Cost Equipment Cost and Energy Cost CalculationsCalculations

$0.79$1,867.1018.851123.76174420060006

$1.00$1,830.24206.01936.60145350050005

$1.30$1,773.35393.29749.33116280040004

$1.81$1,725.26580.56562.0587210030003

$4.27$1,665.91870.56272.0658140020002

$5.86$1,557.14954.77187.8529070010001

Operating Cost $/1000gallons

FAC $FB gal/dayFD gal/dayQboiler

J/hourG mol/hDesign

Cost $/1000gallonsCost $/1000gallons

Costs $/1000gallons vs. Flow Rate

0.00

5.00

10.00

15.00

20.00

25.00

0 200 400 600 800 1000 1200

Flow Rate (gallons/day)

$/10

00g

allo

ns

Equipment Cost and Energy Cost Equipment Cost and Energy Cost vs. Air Flowvs. Air Flow

�� Energy cost goes up Energy cost goes up sharplysharply�� More air to heatMore air to heat

�� Equipment cost Equipment cost increasesincreases�� More expensive More expensive

blowerblower�� Slightly higher towerSlightly higher tower

Energy Cost Vs. Air Flow

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 1000 2000 3000 4000 5000 6000 7000

Flow Rate of Air Mol/hr

Co

st o

f E

ner

gy

$/d

ay

Equipment Cost vs. Air Flow

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

0 1000 2000 3000 4000 5000 6000 7000

Air Flow Mol/hr

Eq

uip

men

t C

ost

$

Fixed Annualized CostFixed Annualized CostFAC vs. Air Flow

1000.00

1100.00

1200.00

1300.00

1400.00

1500.00

1600.00

1700.00

1800.00

1900.00

2000.00

0 1000 2000 3000 4000 5000 6000 7000

Air Flow mol/hr

FA

C $

�� 10 years of operation10 years of operation

�� Production of 200 to 1200 gal/dayProduction of 200 to 1200 gal/day

ConclusionsConclusions

�� DewvaporationDewvaporation is on the low is on the low end of costs for current end of costs for current desalination technologiesdesalination technologies�� Flow rates similar to Flow rates similar to

BeckmanBeckman’’s had similar costss had similar costs

�� This is in the $1.70 to This is in the $1.70 to $3.70/1000gallon range$3.70/1000gallon range

�� Most effective in places like Most effective in places like Arizona where the air is dryArizona where the air is dry