Dewvaporation Dewvaporation Carrier Carrier- -Gas Enhanced - - PowerPoint PPT Presentation

Dewvaporation Dewvaporation

“ “Carrier Carrier-

• Gas Enhanced Atmospheric

Gas Enhanced Atmospheric Pressure Desalination Pressure Desalination” ”

Outline Outline

• Existing Technologies

Existing Technologies

• Reverse Osmosis

Reverse Osmosis

• Thermal Processes

Thermal Processes

• Dewvaporation

Dewvaporation Explanation Explanation

• Mathematical Model

Mathematical Model

• Cost Calculations

Cost Calculations

Desalination Desalination

• Process of purifying seawater

Process of purifying seawater

• A solution to water shortages around the

A solution to water shortages around the world world

• Existing technologies

Existing technologies

• Reverse Osmosis

Reverse Osmosis

• Thermal Evaporation

Thermal Evaporation

• Dewvaporation

Dewvaporation

Factors of Comparison Factors of Comparison

• Purity of water

Purity of water

• Economics

Economics

• Energy efficiency

Energy efficiency

• Production rate

Production rate

• Regional factors

Regional factors

• Resources vary from region to region

Resources vary from region to region

• Proximity to ocean

Proximity to ocean

• Availability of fuel

Availability of fuel

Reverse Osmosis Reverse Osmosis

• Most common in the

Most common in the USA USA

• Solvent forced through

Solvent forced through membrane membrane

• Energy consumption

Energy consumption from pressure from pressure

• Susceptible to fouling,

Susceptible to fouling, scaling and degradation scaling and degradation

Process of Reverse Osmosis Process of Reverse Osmosis

• Pressurized feed

Pressurized feed

• Applied pressure >

Applied pressure > Osmotic pressure Osmotic pressure

• Semi

Semi-

• permeable

permeable membrane membrane

• Incomplete salt removal

Incomplete salt removal (different rates) (different rates)

Typical RO Plant Typical RO Plant

Membrane Module Pump Brine Pretreatment Post Treatment Saline Feed Pure Water

Problems Problems

• Membrane fouling

Membrane fouling

• Caused by micro organisms and particles

Caused by micro organisms and particles

• Reduce water quality

Reduce water quality

• Add chemical e.g. chlorine

Add chemical e.g. chlorine

• Ultra

Ultra-

• filtration of suspended solids

filtration of suspended solids

• Scaling

Scaling

• Formation of salt precipitate e.g. CaCO

Formation of salt precipitate e.g. CaCO3

3

• Reduces efficiency

Reduces efficiency

• Add anti

Add anti-

• scalant

scalant e.g. H e.g. H2

2SO

SO4

4

RO Statistics RO Statistics

• Operating costs

Operating costs

• 2.50

2.50 – – 4.00 $/1000gal of product 4.00 $/1000gal of product2

2

• Energy requirements

Energy requirements

• 26 KWh/1000gal of product

26 KWh/1000gal of product2

2

• Capital cost for sea water desalination

Capital cost for sea water desalination

• 4.00

4.00 -

• 10.00 $/gal

10.00 $/gal-

• day

day2

2

Thermal Process Thermal Process (Evaporation) (Evaporation)

• Phase separation

Phase separation

• Heat saline

Heat saline water/condense vapor water/condense vapor

• Reduce pressure

Reduce pressure

• Energy required for heat

Energy required for heat

• f vaporization
• f vaporization
• Large energy costs, less

Large energy costs, less common in USA common in USA

Evaporation / Condensation Column Brine Fresh water Pretreatment Saline feed Heat

Multi Stage Flash Distillation Multi Stage Flash Distillation

• 80% of world

80% of world’ ’s thermal s thermal desalination product desalination product

• Energy needed for heat

Energy needed for heat

• Recycles heat

Recycles heat

• Two heat sources for

Two heat sources for incoming saline feed incoming saline feed

• External

External

• Heat of vaporization

Heat of vaporization

Schematic of MSF Schematic of MSF

• Additional heat

Additional heat

• Pressure

Pressure released in first released in first chamber chamber

• Water boils

Water boils quickly quickly

• Evaporation and

Evaporation and condensation condensation

Heat Vapor Saline Feed Pure Water Waste Brine Pump Condensate Trays Heat Exchanger Tubes

Problems Problems

• Scale formation

Scale formation

• Extra heat transfer layer

Extra heat transfer layer

• Reduces heat transferred

Reduces heat transferred

• Reduces efficiency

Reduces efficiency

• Erosion and Corrosion

Erosion and Corrosion

• Use stainless steel

Use stainless steel

Evaporation Statistics Evaporation Statistics

• Energy requirements

Energy requirements

• 56 KWh/1000gal of product

56 KWh/1000gal of product2

2

• Costs are very high

Costs 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 gallons range of $12 to $14 per 1000 gallons5

5 in USA

in 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 scarce scarce

Dewvaporation Dewvaporation

• Developed by James

Developed by James Beckman Beckman

• Arizona State University

Arizona State University

• Relies on air circulation

Relies on air circulation

• Air moves in a cycle

Air moves in a cycle

• Works to recycle heat

Works to recycle heat

• Waste heat

Waste heat

• Atmospheric pressure

Atmospheric pressure

Dewvaporation Apparatus

P u r e w a t e r S a l i n e f e e d Inlet Air Ambient Air Outlet Air Added heat (Qboiler) Heat Condensing water Saline feed Air Evaporating water

Blower

Economic Analysis Economic Analysis

• The cost has two main components

The cost has two main components

• Operational costs associated with the heat

Operational costs associated with the heat added added

• 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 side side

• Cost associated with equipment

Cost associated with equipment

• Modeled as a heat exchanger

Modeled as a heat exchanger

Differential Analysis Differential Analysis

Heat Transfer Model Region 1

d dz z z

dW GV GV + =

+

dz T T hL dW h dT T GVh dT T Gh T GVh T Gh

d vap V a v a

) ( ) ( ) ( ) ( ) (

2 1 1 1 1 1

− + ∆ + + + + = +

Mass Balance: Heat Balance: dWd G, GVz G, GVz+dz FDz FDz+dz Region 1 Region 2

Heat Transfer Model Heat Transfer Model

Deriving Differential Equations Deriving Differential Equations

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

Equations Used Equations Used

Solving Differential Equation in Solving Differential Equation in Spreadsheet Spreadsheet

Heating the Air Heating the Air

• Heat needs to be added to achieve a

Heat needs to be added to achieve a temperature difference from temperature difference from dewvaporation dewvaporation to to evaporation side evaporation side

• Can be added as steam

Can be added as steam

• Adding steam keeps air saturated

Adding 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 parameters tower design parameters

1 2 3 4 5 Q to achieve T G, GVs

e

G, GVs

d

Humid Air Dry Air Humid Air Dry Air

Results of Model Results of Model

• Model considered credible if temperature profile was

Model considered credible if temperature profile was appropriate appropriate

• Temperature of evaporation side air had to reach ambient air

Temperature of evaporation side air had to reach ambient air temperature (25 temperature (25º ºC) at bottom of column C) 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 requirements flow and heating requirements

1 Humid Air 2 3 4 5 Dry Air G, GVs

e

G, GVs

d

T5

Temperature Profile Temperature Profile

Temperature Down the Tower

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 100 200 300 400 500 600 700 800 Distance from Tower Top (cm) Temperature (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 Calculations Calculations

$0.79 $1,867.10 18.85 1123.76 1744200 6000 6 $1.00 $1,830.24 206.01 936.60 1453500 5000 5 $1.30 $1,773.35 393.29 749.33 1162800 4000 4 $1.81 $1,725.26 580.56 562.05 872100 3000 3 $4.27 $1,665.91 870.56 272.06 581400 2000 2 $5.86 $1,557.14 954.77 187.85 290700 1000 1 Operating Cost $/1000gallons FAC $ FB gal/day FD gal/day Qboiler J/hour G mol/h Design

Cost $/1000gallons Cost $/1000gallons

Costs $/1000gallons vs. Flow Rate

0.00 5.00 10.00 15.00 20.00 25.00 200 400 600 800 1000 1200 Flow Rate (gallons/day) $/1000gallons

Equipment Cost and Energy Cost Equipment Cost and Energy Cost

• vs. Air Flow
• vs. Air Flow
• Energy cost goes up

Energy cost goes up sharply sharply

• More air to heat

More air to heat

• Equipment cost

Equipment cost increases increases

• More expensive

More expensive blower blower

• Slightly higher tower

Slightly 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 1000 2000 3000 4000 5000 6000 7000 Flow Rate of Air Mol/hr Cost of Energy $/day

Equipment Cost vs. Air Flow

0.00 500.00 1000.00 1500.00 2000.00 2500.00 3000.00 3500.00 1000 2000 3000 4000 5000 6000 7000 Air Flow Mol/hr Equipment Cost $

Fixed Annualized Cost Fixed Annualized Cost

FAC 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 1000 2000 3000 4000 5000 6000 7000 Air Flow mol/hr FAC $

• 10 years of operation

10 years of operation

• Production of 200 to 1200 gal/day

Production of 200 to 1200 gal/day

Conclusions Conclusions

• Dewvaporation

Dewvaporation is on the low is on the low end of costs for current end of costs for current desalination technologies desalination technologies

• Flow rates similar to

Flow rates similar to Beckman Beckman’ ’s had similar costs s 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 dry Arizona where the air is dry