May 18, 2007

Aluminum instead of gasoline to power cars

There is a proposal to use aluminum to power cars instead of gasoline. The plan is to use pellets of aluminum to generate hydrogen as needed to power a fuel cell. The aluminum gets converted to alumina in the process. The alumina can be recycled from aluminum to alumina. Based on the info the mileage is 1 mile per pound of aluminum.

This is a poor proposal. If we scale it up to all cars we would be moving 140 million tons of aluminum per week to and from cars and charging facilities. To get the aluminum part of the system cost competitive with gasoline we need expensive fuel cells. It would be better to get plug in hybrids and transition to all electrical.

There was also a storage system breakthrough for holding gases of most any kind. It stores a target of 180 times the volume at about 500psi. The gas storage system is based on corn cobs turned into brickets.

A midsize car with a full tank of aluminum-gallium pellets, which amounts to about 350 pounds of aluminum, could take a 350-mile trip and it would cost $60, assuming the alumina is converted back to aluminum on-site at a nuclear power plant."

If I put gasoline in a tank, I get six kilowatt hours per pound, or about two and a half times the energy than I get for a pound of aluminum. So I need about two and a half times the weight of aluminum to get the same energy output, but I eliminate gasoline entirely, and I am using a resource that is cheap and abundant in the United States. If only the energy of the generated hydrogen is used, then the aluminum-gallium alloy would require about the same space as a tank of gasoline, so no extra room would be needed, and the added weight would be the equivalent of an extra passenger, albeit a pretty large extra passenger."

For 800 million cars one would need 140 million tons of aluminum for full tanks for all cars. So the actual amount of aluminum/alumina in a system of rotating material some in tanks, some being charged) would need to be three to five times as much, but their can be home or "gas station" recharging. Ideally you do not want to be transporting a lot of alumina/aluminum back and forth large distances to centralized recharging stations. If we did then the recharging stations should be in every city, town, community.

About 27 million tons of aluminum are produced each per year The aluminum is not consumed in the proposed process but is transmuted into alumina.

There are globally 23 billion tons of bauxite reserves

Aluminum production is energy intensive process but it would only be done once. Then the aluminum would be part of a closed loop process to make hydrogen in cars and then get recharged and stripped of the extra oxygen.

Aluminium electrolysis with the Hall-Héroult process consumes a lot of energy, but alternative processes were always found to be less viable economically and/or ecologically. The world-wide average specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram of aluminium produced from alumina. (52 to 56 MJ/kg). The most modern smelters reach approximately 12.8 kW·h/kg (46.1 MJ/kg). Reduction line current for older technologies are typically 100 to 200 kA. State-of-the-art smelters operate with about 350 kA. Trials have been reported with 500 kA cells.

Recovery of the metal via recycling has become an important facet of the aluminium industry. Recycling involves melting the scrap, a process that uses only five percent of the energy needed to produce aluminium from ore.[8] Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverage cans brought it to the public consciousness.

Fuel cells are still over $3000/kw If I need fuel cells to allow me to go 80 miles in one hour. Then the fuel cell would need to provide 200 kWh. So the fuel cells still look too expensive. If it was part of hybrid system then hydrogen fuel cell part could be shrunk. The costs of this approach would need to be reduced for all components for it to be viable.

How much water is needed to provide the hydrogen for the alumina to convert?

The most accurate way to determine this would be to use the gas law. Start with the amount of hydrogen needed and then convert to the equivalent amount of water.

I will shortcut this and use the standard that 180 times the volume of the gas tank is needed. A site with possibly useful conversion rates on hydrogen from water 34 pounds of hydrogen has the energy content of 15 gallons of gasoline

1.2 tablespoons (one mole of water) makes 22.42 liters of H2 gas and
11.21 liters of O2 gas.

250 liters of gas to fill a 60 gallon tank.
11 tablespoons to fill the tank but multiply by 180 concentration.

256 tablespoons to a gallon
So about 8 gallons of water to equal a 15 gallon gas tank.


Dezakin said...

Sheesh, what a bad idea.

You could just make synthetic gasoline or diesel fuel from hydrogen and CO2. It gives better energy density and doesnt require totally new infrastructure.

DV8 2XL said...

What I'd like to know is how they plan to keep the powder dry when shipping and storing. Even a bit of moisture would run the risk of a dangerous build-up of hydrogen gas