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SOLID ALUMINUM ALLOYS: A HIGH ENERGY DENSITY MATERIAL FOR SAFE ENERGY STORAGE, TRANSPORT, AND SPLITTING WATER TO MAKE HYDROGEN ON DEMAND
Outline
• Energy density and technology sustainability
• Brief history and technology overview
• What else we know about it
• Process flow and hydrogen delivery control
• Markets and applications
Energy density and technology sustainability
As hydrogen from splitting water:
• 1 Kg H2: 142 MJ = 39.4 kW-Hrs combustible energy
• 1 Kg Al* makes 111 gms. of hydrogen
• 1 Kg Al makes 4.4 kW-Hrs as H2 energy
• 1 gal (10 Kg) Al makes 44 kW-Hrs as hydrogen
• 1 gal. diesel: 37 kW-Hrs
• 1 gal. liq.hydrogen: 10 kW-Hrs
• As heat from splitting water:
• 1 Kg Al: 409 KJ x 1000/27 = 15.1 MJ = 4.2 kW-Hrs
* 1 Kg of water is converted by this process
Important facts about making aluminum
Bauxite ore mined and dressed to extract alumina
• Alumina is chemically purified to 4-9s purity
• Purified alumina is sized to a powder with a particle size of 120 micrometers
• If done by Alcoa in Australia it is shipped to one of their nine smelters around the world
• Batches of Al with customer specified impurities are made by electrolysis of high purity alumina
• Spent Al products are mostly sent to scrap yards
• Most of this scrap Al metal with impurities is currently not recycled because it’s cheaper to purify alumina than impure Al!
Technology Sustainability: large scale applications
World supply
• Al reserve in the planet’s crust: about 1013 Kg (as Al); 1.2 x 1012 Kg
of H2 made by splitting water = 5 x 1013 kWhrs of H2 energy
• Current worldwide annual Al production: 32 billion Kg from bauxite;
• 400 billion Kg of impure elemental Al available for recycling!
Large demand example: hybrid cars:
• If half of the impure “recyclable” Al was dedicated to split water, 50
billion Kg of H2 could be made = 200 billion kWhrs (@ $0.15/kWhr)
• This could power a 100 million, 50 kW hybrid cars 200 miles
What about infrastructure/supply chain/vehicle fuel insertion?
• Some components either do exist or are easily realized
• Fuel insertion: 2-filler ports, one for water and one for alloy pellets
both being hose delivered; spent fuel dumped into holding tanks
Brief history and technology overview
The Discovery
In 1968 Woodall discovered that aluminum (Al) dissolved in liquid gallium (Ga) just above room temperature would split water into hydrogen (H2) and aluminum oxide (alumina) plus heat via the reaction:
2Al + 3H20 --> 3H2 + Al203 + heat
How does it work?
• Aluminum loves oxygen
• As a result, a skin of alumina (Al203) forms on air-exposed pure Al and protects it from further rapid oxidation
• If this passivating oxide is disrupted, Al would react with water to produce hydrogen
• This can be done slightly above room temperature by dissolving Al into liquid gallium (Ga)
• When this liquid alloy contacts water, hydrogen is generated via Al in the Ga diffusing to the water-liquid metal interface where it splits water into hydrogen, alumina; the alumina is no longer protective
Where are we now?
• We can now make solid and bulk Al rich alloys (95 w% Al, 5 wt% Ga,In,Sn) that split water at temperatures between ice (0C) and steam (>100C) and make H2 on demand
•1st order projected materials cost of 20 cents per kilowatt hour of energy as combustible H2 and 10 cents per kilowatt hour of energy as heat plus combustible H2