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Old 11-04-2014, 16:17   #16
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Re: Fuel From Seawater

"A catalytic converter extracts carbon dioxide and hydrogen from water and converts the gases into liquid hydrocarbons at a 92 percent efficiency rate, and the resulting fuel can be used in ships’ existing engines."

So where will the ship get the energy to do the conversion at 92% efficiency?

Assume that quoted 1000 gallons an hour consumption equates to 20 NM of steaming. (The accuracy of that figure is immaterial to the discussion)

Do you take 1000 gallons of fuel and use this process to produce 920 gallons of new fuel to go 18.4 NM or just use the original fuel to go 20NM?
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Old 11-04-2014, 16:35   #17
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Re: Fuel From Seawater

This is a terrible development. If we burn all the seawater, where will we sail?
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Old 11-04-2014, 16:45   #18
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Re: Fuel From Seawater

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Originally Posted by Tscott8201 View Post
I give up. I'm not trying to make anyone look stupid. I found an article from multiple credible sources and posted it up here for discussion. I even did research on the admiral noted in the story. Everything seems legit. Also, I'm not uneducated myself. I'm an electrical engineer employed in my field so I too have some knowledge on the subject.

Tom
The technology is not in question, it is interesting, I read about it a month or so ago, reading technical papers on it.
I've been looking for a way to create liquid fuel from solar power for a while
so I can sit at port for a month and generate enough fuel for a passage, even if it is inefficient.
There have been lots of efforts to do this and doing it in a lab is not that hard, usually using some exotic materials and equipment that just don't make it practical, but it DOES MAKE HEADLINES and get you to click on the links!
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Old 11-04-2014, 16:47   #19
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Re: Fuel From Seawater

There's a lot better description of the process in the Navy's press release, here: Scale Model WWII Craft Takes Flight with Fuel From the Sea Concept

Note that it's not simple electrolysis. It's a two step process involving electrolytic cation exchange to extract the CO2 and H2, which are then converted to liquid hydrocarbons (fuel) in a catalytic reactor. The liquid hydrocarbon fuel was used to power an internal combustion engine in the demonstration.

What they don't explain is the energy balance, i.e., how much energy is required to produce a certain amount of fuel. Of course, if the process is run on a nuclear powered aircraft carrier, that becomes almost immaterial.
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Old 11-04-2014, 16:48   #20
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Re: Fuel From Seawater

Stu,

The power for the fuel generator is from the massive nuclear generators that power aircraft carriers.

The advantage is that IF this is installed on an air craft carrier they have found a way to convert electricity plus sea water into a liquid fuel with 90% efficiency. Great way to keep planes in the air, useless to almost anyone else. Of course since the cost per gallon is expected to be $3-$6/ gallon, it may make industrial sense for commercial airlines as well. This technology has no value for the recreational market.
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Old 11-04-2014, 16:49   #21
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Re: Fuel From Seawater

Extracting hydrogen from water is old news. Two problems remain insurmountable. The laws of thermodynamics and the loss of molar mass when you combust hydrogen which makes h2 an inefficient fuel compared to what we have now.

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Old 11-04-2014, 16:53   #22
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Re: Fuel From Seawater

leftbrain, you missed the substance of the report. Read the Navy's press release. I'd be interested in your take on it.
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Old 11-04-2014, 17:55   #23
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Re: Fuel From Seawater

They aren't combusting h2, they are combining it and co2 to make a hydrocarbon liquid fuel substitute for jet fuel.

Since air craft carriers have an effectively limitless fuel supply, this works for them. And if it works in other jet aircraft it may be a substitute for commercial jet liners at roughly similar prices.
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Old 11-04-2014, 18:25   #24
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Re: Fuel From Seawater

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Since air craft carriers have an effectively limitless fuel supply, this works for them. And if it works in other jet aircraft it may be a substitute for commercial jet liners at roughly similar prices.
Not exactly. The reactor on an aircraft carrier produces a finite amount of electrical power. On a Nimitz-Class carrier, the available electric power is 90%+ used. There is little to no available power for an operation like this. The upcoming Ford-Class however has much more powerful reactors and their anticipated load is only 50% of capacity or less. Whether this system is ever deployed on a carrier is a direct function of how much power it uses and how much power is available. We wont see this on a carrier anytime in the near future. It's a possibility on a Ford, a flat out impossibility on a Nimitz.

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Old 11-04-2014, 20:36   #25
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Re: Fuel From Seawater

Kevin,

90% of the power is spoken for but that assumes that the ship is steaming at top speed. Most of the time they operate at speeds far lower than this.

Just some quick numbers, and I am not sure about all the numbers...

The 1000' 90,000 ton (loaded) cargo carriers operating on the Great Lakes with 19,500 bhp has a max speed of 16.5kn. While the 1090' 100,000 ton Nimitz class has 260,000 shp but a top speed of over 30kn.

However the Nimitz carriers typically operate at far less than 30kn so that the other ships in the carrier fleet can keep up. This leaves a huge amount of reserve power that can be repurposed to fuel production when operating at less than full speed.


Even assuming only 10% of installed power could be repurposed to fuel production that still leaves 19.3 megawatts of power that could be repurposed.

I am really bad at these conversions, so I probably got it wrong... But my back of the napkin math indicates this would result in about 8,500gallons/hr production.
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Old 11-04-2014, 20:58   #26
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Re: Fuel From Seawater

Trust me, I'm going off of memory myself here. My concern would be what impact this would have in combat operations. For flight ops, the carrier normally steams at 30kts+. And during combat, the ship may stay at that speed for 18 hours a day (that's just a guess). Unfortunately, this is exactly when this capability is most needed. What I would worry about is this: what if the carrier was in the middle of making fuel at say 18kts. When for whatever reason flank speed was immediately needed. What would be the effect on the fuel plant? Could it be shut down in seconds without adverse consequences or would it require a lengthy shutdown that would negatively impact the ships top speed during that time?

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Old 11-04-2014, 21:10   #27
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Re: Fuel From Seawater

Pretty funny thread.

For most (not quite all), please go study chemistry and refining for a few years and then come back.

An interesting parlor trick, but Ill bet my boat that this is green posturing and amounts to noise. Would they develop some minor shipboard JP capability? Possibly, but I doubt it, since the cost is probably an order of magnitude higher than quoted.

(I'm in the refining field)
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Old 11-04-2014, 21:55   #28
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Re: Fuel From Seawater

Don't know if the catalyst is new, but here's our last discussion.



US Navy turning seawater into Jet Fuel


In the thread is a nice paper:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA539765

In the paper they say the fuel will cost $5 -$6 per gallon.

In the paper also:

synthesis of 100,000 gallons/day of jet fuel, then we would need 246,102 kWhr/hr or simply 246 MWhr/hr.
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Old 12-04-2014, 01:16   #29
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Re: Fuel From Seawater

Thin water,

What difference does the cost make? This is the military remember.

I had to look it up, but the Nimitz class carried 3.5 million gallons of avgas when full. Even a 40,000 gallon/day production capacity would appreciably increase their fuel capability.


From what I have seen (and understand, say 5% of what I have read) no one is expecting this to be ready for prime time in the near future. Like many DARPA type projects it has huge potential upside, but little immediate practical value.

Assuming the numbers actually work as published, it really could be competitive on the market. AvGas is running $5.75 a gallon, so if they hit the numbers that PopSci indicated of $3-6 a gallon it could make commercial sense.
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Old 12-04-2014, 02:13   #30
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Re: Fuel From Seawater

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I admit I didn't read this article, but I don't really see the need too.
My job as a Turbine Engine test engineer for the Boeing Company here in Everett Washington for the last 7 years gives me enough information to know how turbine engines run

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This is a terrible development. If we burn all the seawater, where will we sail?
Quote:
Originally Posted by Hud3 View Post
There's a lot better description of the process in the Navy's press release, here: Scale Model WWII Craft Takes Flight with Fuel From the Sea Concept

Note that it's not simple electrolysis. It's a two step process involving electrolytic cation exchange to extract the CO2 and H2, which are then converted to liquid hydrocarbons (fuel) in a catalytic reactor. The liquid hydrocarbon fuel was used to power an internal combustion engine in the demonstration.

What they don't explain is the energy balance, i.e., how much energy is required to produce a certain amount of fuel. Of course, if the process is run on a nuclear powered aircraft carrier, that becomes almost immaterial.
Quote:
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Pretty funny thread.

For most (not quite all), please go study chemistry and refining for a few years and then come back.

An interesting parlor trick, but Ill bet my boat that this is green posturing and amounts to noise. Would they develop some minor shipboard JP capability? Possibly, but I doubt it, since the cost is probably an order of magnitude higher than quoted.

(I'm in the refining field)
Too many good posts to quote, all with the same theme... Relative energy in/out, thermo laws, etc...

I can make fire with 2 sticks... is it efficient and practical?
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