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Renewable Energy Open Lab RMIT University 2
Demand for fresh water and electricity: Combined Desalination and Power generation system Presenter: Abhijit Date Energy Conservation And Renewable Energy Group (Energy CARE Group) School of Aerospace Mechanical and Manufacturing Engineering Email : abhijit.date@rmit.edu.au
Energy demand 4
Fresh water availability Glaciers and Icecaps 5
Land Salinity Issue In many areas around Australia the aquifer is getting salty. Picture from salt effect area in northern Victoria 6
Land Salinity Issue Many areas of formerly productive land are suffering from rising salinity levels around the world. Picture of a Salt lake in the northern Victoria 7
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Desalination / Distillation methods Distillation Multi-stage flash distillation (MSF) Multiple-effect distillation (MED) Vapor-compression (VC) Membrane processes Reverse osmosis (RO) Membrane distillation (MD) Freezing desalination Single stage humidification-dehumidification (HDH) Multiple-effect humidification (MEH) Seawater greenhouse 9
Multi-stage flash distillation plants produce 85% Multiple-effect distillation (MED ME) Adapted from Lubna K. Hamdan (2008) 10
Reverse Osmosis Pressure Membrane Saline water Fresh water Salt 11
Low temperature heat engines Organic Rankine Cycle heat engines are most commonly used for power generation from low temperature heat source. Expander / Turbine m hot _ water 10kg/ Q Utilised Hot water s In (95) º C Hot water out (90) º C 2 Heat Exchanger 1 Saturated Vapour at (90) º C 2 Organic working fluid (Binary) Sub cooled Liquid 3 Pump Saturated Mixture at (35) º C Pump Condenser 3 4 Saturated or sub cooled Liquid at (35) º C Cold water Out Cold water In (30-20) º C T T 104.2 9590 kw m hot _ water cp water In exit 210 12
Combined Desalination and Power generation system (Direct Trilateral cycle) Vacuum tank Cooling water Vacuum Non condensable gas Condenser Electric Generator Water Vapour (35 C) Reaction Turbine Fresh Water Q Utilised Hot saline water (95 C, 3% salt) m hot _ water 10kg/ s Brine (35 C) T T 104.2 9535 kw m hot _ water cp water In exit 2520 13
Hero's - Simple reaction steam turbine Barkers water turbine 14
Trilateral cycle: Two phase simple reaction turbine V a V r T h exit exit, P, v exit exit, Diverging section of the nozzle Throat of the nozzle A throat R A exit Inlet U,T shaft Hot saline water enters the turbine T, P in in m in h, v, in High velocity mixture Exit U R; V V U; T mv R; V r A W exit shaft v o. mv. m o a 2 2 R 2( h 2 2 R 2( h. mv r exit in in h h exit exit ) ) shaft a 2 2 R 2( h 2 2 T mr R 2( h h ) R shaft. in exit in h exit ) overall W Q shaft Extractable Turbine. m R nozzle. W mc 2 2 R 2( h p. shaft mc ( T p ( T in Va m 2 in T in T 2 exit ) h exit exit ) ) R 15
Theoretical Predictions Tin 95 C ; Texit 35 C ; m 4kg/ s; isentropic 50%; Q Supplied / utilised 1MW 16
Shaft Power (kw) Theoretical Predictions Tin 95 C ; Texit 35 C ; m 4kg/ s; isentropic 50%; Q Supplied / utilised 1MW Rotational Speed (rpm) 17
Investigation of the optimum length of diverging section of the two phase flow stationary nozzle Computational analysis Experimental analysis 18
Pressure (kpa) Investigation of the optimum length of diverging section of the two phase flow stationary nozzle 500 Ohta Nozzle B 100 450 90 400 80 350 300 250 200 70 60 50 40 Pressure (kpa) 150 30 100 20 50 Throat 10 0 0-30 0 30 60 90 120 Nozzle Length (mm) 19
Combined Desalination and Power generation system (Stage 1: Design) Flashing tank Brine tank Custom made coil condenser 25mm tube diameter 12 branches Each branch about 10 m length Fresh water tank Total cooling capacity of about 100kW @120L/min cooling water flow rate and 12C T 20
Stage 1: CDP system in operation Hot water supplied at 98 C, 35 C turbine outlet and 0.3kg/s inlet mass flow. Produced 400W peak electrical power at 3500-4000rpm and 0.03kg/s fresh water 21
Combined Desalination and Power generation system Stage 2: Design Vacuum vessel Vacuum Non condensable gas Flashing Tank Reaction Turbine Brine Condenser Electric generator Hot saline water (65 C +, 3% salt) Fresh Water Cooling water 22
Combined Desalination and Power generation system Stage 2: Design 23
Combined Desalination and Power generation system Stage 2: Design 24
Combined Desalination and Power generation system Stage 2: Design 25
Vacuum (5kPa, Abs) Atmospheric pressure Hot saline water 26
Rotary mechanical seal Vacuum (5kPa, Abs) Atmospheric pressure Braking pulley Hot saline water Rotary mechanical seal 27
Vacuum (5kPa Abs) Rotary mechanical seal Atmospheric pressure 28
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Turbine 1 Turbine 2 32
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Experimental technique and results T 95 C ; T 35 C ; m 0.4kg s in exit / Dynamic _ frictional _ torque _ T Shaft _ Power _ W shaft Useful o _ Mechanical _ d I dt Acceleration Power I mass _ moment _ of _ inertia T O Frictional _ power _ loss d dt Deceleration 34
Experimental results Tin 95 C ; Texit 35 C ; m 0.4kg/ s 35
Experimental results Tin 95 C ; Texit 35 C ; m 0.4kg/ s Turbine _1 Turbine _ 2 max_ isentropic max_ isentropic 9% 17% 36
Turbine 3: 300 mm diameter turbine with circular cross-section nozzle and throat diameter 2mm 37
2 u R 2 w Optimum shape of the curved nozzle at different rotational speeds with Computational minimum Fluid fluid Dynamics separation Analysis 2 2 w u 2uw cos 0 R R R u w the the is inside is of local is is is local local rotating local rotor local angle the of rotor direction centripetal centripetal radius radius tan gential relative the nozzle between rotating and of of of fluid the normal the the accleration accleration 2uw acceleration due to R dw acceleration of the dt curvature velocity rotor velocity nozzle local nozzle in coriolis fluid to of of radius relative effect streamwise motion Diverging section of the nozzle u - Local tangential velocity of rotor Centripetal acceleration Throat of the nozzle Coriolis acceleration Hot saline water enters the turbine Centripetal acceleration in relative motion High velocity mixture 38 Acceleration of fluid stream
Gross Shaft Power (Watts) Experimental results: 300 mm diameter turbine with circular cross-section nozzle and throat diameter 2mm Temperature ( C) or Flow rate of feed water (lit/min) Gross shaft power T3-WP Nozzle exit temperature - T3-WP Supply Temp - T3-WP Feed water flow rate 1500 100 1400 1300 90 1200 80 1100 1000 70 900 60 800 700 50 600 40 500 400 30 300 20 200 100 10 0 0 250 275 300 325 350 375 400 425 450 Angular speed (rad/s) 39
Isentropic efficiency (%) Shaft Power (W) Experimental results 300 mm diamter turbine with circular cross-section nozzle and throat diameter 2mm 60% Isentropic efficiency Shaft Power 1,500 50% 1,250 40% 1,000 30% 750 20% 500 10% 250 0% 0 250 275 300 325 350 375 400 425 450 Angular speed (rad/s) 40
Desalination / Distillation method Energy Type Specific energy Multi-stage flash distillation (MSF) Mainly thermal 55-80kWh/m³ fresh water Distillation Multiple-effect distillation (MED) Mainly thermal 50-70kWh/m³ fresh water Vapor-compression (VC) Electrical 8-12 kwh/m³ fresh water Membrane Reverse osmosis (RO) (without ER) 4% salt Electrical 6-8 kwh/m³ fresh water Membrane distillation (MD) 0.5% salt Electrical 5-6 kwh/m³ fresh water Freezing desalination Electrical 10-12 kwh/m³ fresh water Single stage humidification-dehumidification (HDH) (Low capital cost) Multiple-effect humidification (MEH) Seawater greenhouse (main produce food) Combined desalination and power generation (CDP) produces electricity + fresh water 10-15 kwh of electrical energy produced / m³ fresh water Mainly thermal Mainly thermal Mainly thermal Mainly thermal 500-600kWh/m³ fresh water 80-200kWh/m³ fresh water 700-800 kwh/m³ fresh water 350-500 kwh /m³ fresh water Part reference: Akili D. Khawajia, Advances in seawater desalination technologies Desalination 221 (2008) 47 69 41
Potential thermal energy sources Waste heat below 100 C Boiler bleed off Furnace exhaust Solar thermal Concentrating type collectors Evacuated tube solar collectors Solar ponds Geothermal Hydro thermals Hot dry rock 42
CDP with Solar Pond concept and performance Heat exchanger 43
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Thank you Questions 45