Desalination-Presentation - Dewvaporation Dewvaporation...

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Unformatted text preview: Dewvaporation Dewvaporation “Carrier-Gas Enhanced Atmospheric Gas Pressure Desalination” Pressure Noah Abbas and Kehinde Adesoye Outline Outline Existing Technologies Existing Reverse Osmosis Reverse Thermal Processes Thermal Dewvaporation Explanation Dewvaporation Mathematical Model Mathematical Cost Calculations Cost Desalination Desalination Process of purifying seawater Process A solution to water shortages around the world world Existing technologies Existing Reverse Osmosis Reverse Thermal Evaporation Dewvaporation Dewvaporation Factors of Comparison Factors Purity of water Purity Economics Economics Energy efficiency Energy Production rate Production Regional factors Regional Resources vary from region to region Resources Proximity to ocean Proximity Availability of fuel Availability Reverse Osmosis Reverse Most common in the USA USA Solvent forced through membrane membrane Energy consumption from pressure from Susceptible to fouling, scaling and degradation scaling Process of Reverse Osmosis Process Pressurized feed Applied pressure > Osmotic pressure Osmotic Semi-permeable Semi permeable membrane membrane Incomplete salt removal (different rates) (different Typical RO Plant Typical Membrane Module Saline Feed Pretreatment Post Treatment Pump Brine Pure Water Problems Problems Membrane fouling Membrane Caused by micro organisms and particles Caused Reduce water quality Reduce Add chemical e.g. chlorine Add Ultra-filtration of suspended solids Ultra Scaling Scaling Formation of salt precipitate e.g. CaCO3 Formation Reduces efficiency Reduces Add anti-scalant e.g. H2SO4 Add RO Statistics RO Operating costs Operating • 2.50 – 4.00 $/1000gal of product2 2.50 Energy requirements • 26 KWh/1000gal of product2 Capital cost for sea water desalination Capital • 4.00 - 10.00 $/gal-day2 4.00 Thermal Process Thermal (Evaporation) Phase separation Heat saline water/condense vapor water/condense Fresh water Heat Saline feed Reduce pressure Reduce Pretreatment Energy required for heat of vaporization of Large energy costs, less common in USA common Evaporation / Condensation Column Brine Multi Stage Flash Distillation Multi 80% of world’s thermal 80% thermal desalination product desalination Energy needed for heat Recycles heat Recycles Two heat sources for incoming saline feed incoming External External Heat of vaporization Heat Schematic of MSF Schematic Condensate Trays Heat Exchanger Tubes Additional heat Additional Saline Feed Pressure released in first chamber chamber Heat Vapor Water boils quickly quickly Evaporation and condensation condensation Pure Water Pump Waste Brine Problems Problems Scale formation Scale Extra heat transfer layer Extra Reduces heat transferred Reduces Reduces efficiency Reduces Erosion and Corrosion Erosion Use stainless steel Use Evaporation Statistics Evaporation Energy requirements • 56 KWh/1000gal of product2 Costs are very high Costs • Because of expensive energy, prices are in the Because range of $12 to $14 per 1000 gallons5 in USA range in • Only economically feasible in regions like the Only Middle East, where fuel is cheap and water is scarce scarce Dewvaporation Dewvaporation Developed by James Beckman Beckman Arizona State University Arizona Relies on air circulation Relies Air moves in a cycle Air Works to recycle heat Works Waste heat Waste Atmospheric pressure Atmospheric Dewvaporation Apparatus P u r e Air w a t e r Evaporating water Heat Condensing water Added heat (Qboiler) S a l i n e f e e d Saline feed Outlet Air Inlet Air Ambient Air Blower Economic Analysis Economic The cost has two main components The Operational costs associated with the heat added added Heat required to created a larger temperature difference from dew formation to evaporation side side Cost associated with equipment Cost Modeled as a heat exchanger Modeled Differential Analysis Differential Heat Transfer Model Region 1 FDz G, GVz Region 1 Region 2 dWd G, GVz+dz FDz+dz Mass Balance: GVz = GVz + dz + dWd Heat Balance: Gha (T1 ) + GVhv (T1 ) = Gha (T + dT1 ) + GVhV (T + dT1 ) + ∆hvap dWd + hL (T1 − T2 ) dz Heat Transfer Model Heat Deriving Differential Equations Deriving Deriving Differential Equations (Continued) (Continued) Equations Used Equations Solving Differential Equation in Spreadsheet Spreadsheet Heating the Air Heating Heat needs to be added to achieve a temperature difference from dewvaporation to dewvaporation to evaporation side evaporation Can be added as steam Can Adding steam keeps air saturated Adding This made ∆T and G of the air stream above the and tower design parameters tower Q to achieve ∆T Humid Air G, GVsd 1 2 Dry Air 3 4 G, Humid Air GVse 5 Dry Air Results of Model Results G, GVsd 1 Humid Air 2 3 4 G, GVse 5 Dry Air T5 Model considered credible if temperature profile was appropriate appropriate Temperature of evaporation side air had to reach ambient air temperature (25ºC) at bottom of column temperature Air flow rate (G) had the most dramatic effect on product flow and heating requirements flow Temperature Profile Temperature Temperature Down the Tower 80.00 ∆T 70.00 Temperature (deg. C) 60.00 50.00 T Air Dewformation Side T Pure W ater Product 40.00 T Seawater/Brine T Air Evaporation Side 30.00 20.00 10.00 0.00 0 100 200 300 400 500 600 Distance from Tow er Top (cm) 700 800 Equipment Cost and Energy Cost Calculations Calculations Qboiler J/hour Operating Cost $/1000gallons FD gal/day FB gal/day FAC $ 290700 187.85 954.77 $1,557.14 $5.86 2000 581400 272.06 870.56 $1,665.91 $4.27 3 3000 872100 562.05 580.56 $1,725.26 $1.81 4 4000 1162800 749.33 393.29 $1,773.35 $1.30 5 5000 1453500 936.60 206.01 $1,830.24 $1.00 6 6000 1744200 1123.76 18.85 $1,867.10 $0.79 Design G mol/h 1 1000 2 Cost $/1000gallons Cost Costs $/1000gallons vs. Flow Rate 25.00 $/1000gallons 20.00 15.00 10.00 5.00 0.00 0 200 400 600 800 Flow Rate (gallons/day) 1000 1200 Equipment Cost and Energy Cost vs. Air Flow vs. Energy cost goes up sharply sharply Energy Cost Vs. Air Flow 1.00 0.90 Cost of Energy $/day 0.80 0.70 More air to heat More 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0 1000 2000 3000 4000 5000 6000 7000 Flow Rate of Air Mol/hr Equipment Cost vs. Air Flow Equipment cost increases increases 3500.00 Equipment Cost $ 3000.00 2500.00 2000.00 1500.00 1000.00 500.00 0.00 0 1000 2000 3000 4000 Air Flow Mol/hr 5000 6000 7000 More expensive blower blower Slightly higher tower Slightly Fixed Annualized Cost Fixed FAC vs. Air Flow 2000.00 1900.00 1800.00 1700.00 FAC $ 1600.00 1500.00 1400.00 1300.00 1200.00 1100.00 1000.00 0 1000 2000 3000 4000 5000 6000 Air Flow mol/hr 10 years of operation 10 Production of 200 to 1200 gal/day Production 7000 Conclusions Conclusions Dewvaporation iis on the low Dewvaporation s end of costs for current desalination technologies desalination Flow rates similar to Beckman’s had similar costs Beckman This is in the $1.70 to $3.70/1000gallon range $3.70/1000gallon Most effective in places like Arizona where the air is dry Arizona ...
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This note was uploaded on 08/31/2011 for the course CHE 4273 taught by Professor Staff during the Spring '10 term at Oklahoma State.

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