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Making Jet Fuel From Seawater While at Sea

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Re: Making Jet Fuel From Seawater While at Sea

#31

Post by iwwr »

ta12121 wrote: post #20
sien wrote: post #16

This is a good reason why Tesla cars are folly. This is why electric vehicles won't work. I'll copy in most of a comment I made a few days back. Let's say tomorrow some grad student gets fusion going at a very low price. The best way to use this to power cars would be to use it to create a fuel with a high energy density. If you had 'free energy' you'd extract C02 from the atmosphere and turn it into a hydrocarbon. F…

No. Electrolysing water to make H2 and extracting CO2 from the environment, and then synthesizing hydrocarbons from them, is extremely energy inefficient. Sure, theoretically, it can be done, and maybe one day it could even be done efficiently. But Tesla is making battery-electric cars that work today . The military does not care about efficiency because they have nuclear reactors on their ships and their goal is to…

It's energy inefficient, but you're thinking in terms of energy scarcity we have today. What if we had 10x more electric energy capacity (most likely due to nuclear resurgence)?

Re: Making Jet Fuel From Seawater While at Sea

#32

Post by Roritharr »

Isn't this also heavily destructive to our ecosystem because they use the carbon trapped in the water and release it into our atmosphere? Didn't we want more trapped carbon than less?

I don't get why everyone finds this great since it takes a very long time for carbon in the atmosphere to get trapped in seawater.

Re: Making Jet Fuel From Seawater While at Sea

#33

Post by dalke »

sien wrote: post #16

This is a good reason why Tesla cars are folly. This is why electric vehicles won't work. I'll copy in most of a comment I made a few days back. Let's say tomorrow some grad student gets fusion going at a very low price. The best way to use this to power cars would be to use it to create a fuel with a high energy density. If you had 'free energy' you'd extract C02 from the atmosphere and turn it into a hydrocarbon. F…

"Let's say tomorrow some grad student gets fusion going at a very low price. The best way to use this to power cars would be to use it to create a fuel with a high energy density."

That is incorrect. If the fusion source is compact, and can produce a lot of instantaneous electrical power, and is quick to throttle up and down, then a "Back to the Future"-style Mr. Fusion would be the best way to power cars.

Energy density isn't the only factor. There's also a question of infrastructure. Electrical distribution has few moving parts, while extracting C02 from the atmosphere to make fuel and distributing the fuel has many more mechanical parts. A fusion plant which could produce 50 kW, weighed 2 tons, and could be installed in the back yard of a home would mean that a house could be off the grid and still have power left over to charge the car, while using intermediate hydrocarbon storage would mean trips to fill the car, or heating oil, or cooking gas.

So while I completely agree that airplanes will not be powered by batteries, I don't think that energy density is the only factor to consider in the economics equation.

Re: Making Jet Fuel From Seawater While at Sea

#34

Post by dalke »

ChuckMcM wrote: post #25
Sukotto wrote: post #12

Earlier quoted context omitted.

That's a great deal. Jet Fuel (Kerosene) closed at $3.135/gallon today[1]. And that doesn't include the cost of transporting it from the Gulf Coast to where your Navy needs it. [1] Sep 28, 2012: http://www.eia.gov/dnav/pet/pet_pri_spt_s1_d.htm

To be fair you have to subtract off Federal taxes which the government doesn't pay for the fuel it buys which brings it down closer to $2/gal.

That quoted price was the spot price. It doesn't include Federal or other taxes.

Let's suppose that it did include taxes. Federal tax for jet fuel for non-commercial-aviation use is 21.9¢/gal so even if the quoted price of $3.135/gal included federal tax, the without-tax price would still be $2.916/gal, which is a lot closer to $3/gal than $2/gal.

(Gas for commercial aviation use is also subject to the federal transportation tax and harder for me to figure out.)

Re: Making Jet Fuel From Seawater While at Sea

#35

Post by jordanb »

wamatt wrote: post #13

Very interesting. Can someone who knows about this stuff comment on whether the energy required to extract the H2 from the water, is more than the energy contained in the chemical bonds of the H2 itself? (assume both sides of the comparison contain equal number of molecules) I suspect it is.. otherwise they are potentially sitting on a much more important innovation, than mere jet fuel.

Consider it from the perspective of the conservation of energy:

2H2 + O2 = 2H2O + energy

The energy is on the right because the reaction is exothermic.

The opposite reaction must be endothermic and must have the same amount of energy on the left:

2H2O + energy = 2H2 + O2

Otherwise, energy isn't conserved.

Because nothing is 100% efficient, there's also energy lost to inefficiencies. So the answer to your question is that yes, you need more energy to make the second reaction happen than is stored in the chemical bond.

Re: Making Jet Fuel From Seawater While at Sea

#36

Post by Dn_Ab »

sien wrote: post #16

This is a good reason why Tesla cars are folly. This is why electric vehicles won't work. I'll copy in most of a comment I made a few days back. Let's say tomorrow some grad student gets fusion going at a very low price. The best way to use this to power cars would be to use it to create a fuel with a high energy density. If you had 'free energy' you'd extract C02 from the atmosphere and turn it into a hydrocarbon. F…

Very good point. But it doesn't make Tesla cars a folly so much as put a strong constraint on their long term economic viability: the invention of fusion power or some other method of making energy abundant turned to making hydrocarbons effectively renewable. But that could be decades away, timeline of practical viability is effectively unknown. Considering how speculative this notion of really cheap energy is (for now), I still think Tesla is a good bet. On the event of the floor dropping off the prices in energy markets, there will be few that are dependent on large energy barriers to entry that will emerge unscathed.

It is also effectively win-win. If such a thing becomes possible the costs in much of production will cut very drastically and the potential of things now open would be just incredible. So much of expense is due to energy constraints.

Re: Making Jet Fuel From Seawater While at Sea

#37

Post by zmmz »

Roritharr wrote: post #32

Isn't this also heavily destructive to our ecosystem because they use the carbon trapped in the water and release it into our atmosphere? Didn't we want more trapped carbon than less? I don't get why everyone finds this great since it takes a very long time for carbon in the atmosphere to get trapped in seawater.

It's not that simple:

CO2 in atmosphere -> CO2 in water -> Ocean acidification[1] -> Change in ocean ecosystem

The oceans absorb OC2 from the atmosphere, which you could argue is good, but it is not without consequences. Putting CO2 in the water moves the problem from having it in the atmosphere elsewhere, but it's still a problem. In some ways then, this can be seen as a good thing, because it is undoing the effects that increased CO2 in the atmosphere has on the oceans. Obviously though, I doubt that its effects would be at all noticeable.

The wiki article already linked has a chapter called 'Possible Impact'.

1: http://en.wikipedia.org/wiki/Ocean_acidification

Re: Making Jet Fuel From Seawater While at Sea

#38

Post by confluence »

sien wrote: post #16

This is a good reason why Tesla cars are folly. This is why electric vehicles won't work. I'll copy in most of a comment I made a few days back. Let's say tomorrow some grad student gets fusion going at a very low price. The best way to use this to power cars would be to use it to create a fuel with a high energy density. If you had 'free energy' you'd extract C02 from the atmosphere and turn it into a hydrocarbon. F…

You are wrong.

Electric engines run at 92% efficiency. Car engines run at ~15%. So energy density need not reach equivalence.

That physicist is wrong too (Nobel prizes don't mean you aren't wrong - it just means people listen to you more) - jet engines on planes require oxygen to work - hence capped at ~10 km altitude with massive drag causing ineffecient travel.

10 years till battery tech reaches complete parity for lowest denominator cars, and 7 years before we start to see hyper sonic electric passenger jets being tested way up in the upper atmosphere (no oxygen needed, go as high and fast as you want - London - LA in a few hours - space views - cheap power).

Re: Making Jet Fuel From Seawater While at Sea

#39

Post by Roritharr »

zmmz wrote: post #37
Roritharr wrote: post #32

Isn't this also heavily destructive to our ecosystem because they use the carbon trapped in the water and release it into our atmosphere? Didn't we want more trapped carbon than less? I don't get why everyone finds this great since it takes a very long time for carbon in the atmosphere to get trapped in seawater.

It's not that simple: CO2 in atmosphere -> CO2 in water -> Ocean acidification[1] -> Change in ocean ecosystem The oceans absorb OC2 from the atmosphere, which you could argue is good, but it is not without consequences. Putting CO2 in the water moves the problem from having it in the atmosphere elsewhere, but it's still a problem. In some ways then, this can be seen as a good thing, because it is undoing the effects…

I'm not for putting more carbon into the oceans... just against taking the currently stored carbon out.

Re: Making Jet Fuel From Seawater While at Sea

#40

Post by dctoedt »

pixie_ wrote: post #5
landryraccoon wrote: post #4

Earlier quoted context omitted.

If it's an aircraft carrier, probably the nuclear power plant on board.

Yep, it's a pretty good use of 200MW of power when you're just sitting around in the ocean.

> when you're just sitting around in the ocean

Watch any of the documentary series about life aboard an aircraft carrier [1] and you'll see that there's essentially no "just sitting around in the ocean." But your main point is still accurate: If there's power available, putting it to work making jet fuel might be a good trade-off for the additional drain on the nuclear fuel.

[1] E.g., http://www.pbs.org/weta/carrier/

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