Converting (extracting) fuel from seawater? Really?

[LTLFTcomposite]

https://www.yahoo.com/news/us-navy-game-changer-converting-seawater-fuel-150544958.html" onclick="window.open(this.href);return false;

Any idea what they are talking about here?

 

[donald]

With enough energy (viz. an on-board nuclear reactor) you can split water and carbon dioxide into hydrogen and carbon monoxide. This is called 'syngas'. Then you can convert it into synthetic 'GTL' hydrocarbons by using Fischer Tropsch processes.

 

[klapauzius]

Which begs the question, where the nuclear reactor will go, on the tanker? Nothing really gained there, as ships would still have to dock for refueling (albeit you could "make" the fuel at sea, rather than having the tankers go back to refuel once in a while). Or on the ships themselves, in which case, you could power them directly??

Science journalism is so awful these days....
But at $3-$6 per gallon (as quoted in the article), this could certainly be a land-based technology to replace foreign oil imports eventually?
Would have the added benefit of turning clean, CO2 neutral nuclear power into dirty CO2 emissions...brilliant!

 

[donald]

Which begs the question, where the nuclear reactor will go, on the tanker?

On the aircraft carrier.

The 'conundrum' of nuclear powered carriers has always been that although they don't need fuel, their aircraft do, and so do the conventionally fuelled battle and support vessels that make up the battle-fleet (carriers never sail alone).

So it begs the question; why bother having a nuclear carrier if you have to send out fuel victualling to the battle fleet anyhow? But if you could instead make your own fuel with the carrier's nuclear power plant, the issue of sending out refuelling tankers goes away which is both a more secure solution and also validates the value of the nuclear carrier.

 

[LTLFTcomposite]

With enough energy (viz. an on-board nuclear reactor) you can split water and carbon dioxide into hydrogen and carbon monoxide. ...

So all that carbon dioxide being absorbed by the oceans is about to turn into a resource?

As I understand it, it isn't the carbon itself that is useful in today's world, it is the bond it has with hydrogen. So if there is a practical way to reform that bond, carbon becomes a renewable resource?

 

[donald]

As I understand it, it isn't the carbon itself that is useful in today's world, it is the bond it has with hydrogen. So if there is a practical way to reform that bond, carbon becomes a renewable resource?

Well, it becomes a viable 'energy vector' in that reducing CO2 to CO (the first step) is endothermic via a catalyst. You still need to put the energy in in the first place. There are a number of catalysts so far discovered that can do this, such as;

http://www.theengineer.co.uk/energy-and-environment/news/catalyst-converts-inert-carbon-dioxide-into-reactive-carbon-monoxide/1017950.article" onclick="window.open(this.href);return false;

Hydrogen can, as I am sure you know, be gained from water by electrolysis. Or [if you happen to have a high temperature nuclear reactor to hand] by thermal decomposition. Water begins to decompose around 2200C. You can also use thermolysis catalysts, such as iron oxide or the sulphur-iodine cycle, that allow thermal decomposition around 1000C.

Once you have a mix of hydrogen and CO, you bung them through another series of catalysts, following the F-T process.

Nature, as I am sure you know, uses a photosynthetic bio-catalyst called chlorophyll to split water but it is a bit slower than the Navy might want!

(There are also some anoxygenic bacteria that fix carbon directly from CO2 without O2 byproduct, but that's another story!....)

 

[LTLFTcomposite]

^ Isn't converting CO2 to CO the opposite of what catalytic converters in cars do?

 

[donald]

Yes. There is an oxidising catalyst to do this in a petrol powered ICE, for both CO and unburned hydrocarbons. But this is an exothermic catalysed reaction. Reducing catalysts generally need to have a power/thermal source as they tend to be endothermic.

There is also a reducing catalyst further down to reduce the NOx into N2 and O2. Different catalysts do different stuff.

 

[klapauzius]

Which begs the question, where the nuclear reactor will go, on the tanker?

On the aircraft carrier.

The 'conundrum' of nuclear powered carriers has always been that although they don't need fuel, their aircraft do, and so do the conventionally fuelled battle and support vessels that make up the battle-fleet (carriers never sail alone).

So it begs the question; why bother having a nuclear carrier if you have to send out fuel victualling to the battle fleet anyhow? But if you could instead make your own fuel with the carrier's nuclear power plant, the issue of sending out refuelling tankers goes away which is both a more secure solution and also validates the value of the nuclear carrier.

Yes, that makes sense.
Do they have enough excess power to generate fuel as well? I cannot imagine this to be a very efficient process. At 10 kwh per liter and e.g. a 200MW plant ( not sure if that is realistic), the fuel generation would be 20000 liters/h at 100% conversion efficiency. Probably not enough to power even a small fleet and aircraft?

 

[AndyH]

Which begs the question, where the nuclear reactor will go, on the tanker?

On the aircraft carrier.

The 'conundrum' of nuclear powered carriers has always been that although they don't need fuel, their aircraft do, and so do the conventionally fuelled battle and support vessels that make up the battle-fleet (carriers never sail alone).

So it begs the question; why bother having a nuclear carrier if you have to send out fuel victualling to the battle fleet anyhow? But if you could instead make your own fuel with the carrier's nuclear power plant, the issue of sending out refuelling tankers goes away which is both a more secure solution and also validates the value of the nuclear carrier.

Yes, that makes sense.
Do they have enough excess power to generate fuel as well? I cannot imagine this to be a very efficient process. At 10 kwh per liter and e.g. a 200MW plant ( not sure if that is realistic), the fuel generation would be 20000 liters/h at 100% conversion efficiency. Probably not enough to power even a small fleet and aircraft?

No. Adding more generation takes up valuable space, adds more weight, and increases the already destructive tail of fuel for the reactors. The carrier is a warship and tankers are tankers - and it's still much simpler and less expensive to make fuel on land and transport it to the fleet.

It makes no sense unless we're on Water World, then all bets are off anyway.

 

[klapauzius]

No. Adding more generation takes up valuable space, adds more weight, and increases the already destructive tail of fuel for the reactors. The carrier is a warship and tankers are tankers - and it's still much simpler and less expensive to make fuel on land and transport it to the fleet.
It makes no sense unless we're on Water World, then all bets are off anyway.

Well, yes, 200 MW (which seems about right for an aircraft carrier) would mean devoting all power on board to making fuel...
But if you were to put this on a ship, a carrier with a big nuclear power plant is probably the place to put it.

I was wondering, in these modern times, are the oceans really that big that you need this kind of autonomy? With long range planes and missiles and ever more precise guidance systems, even the pacific ocean might be a relatively small pond...

But everyone loves the idea of making fuel from salt water...

 

[AndyH]

No. Adding more generation takes up valuable space, adds more weight, and increases the already destructive tail of fuel for the reactors. The carrier is a warship and tankers are tankers - and it's still much simpler and less expensive to make fuel on land and transport it to the fleet.
It makes no sense unless we're on Water World, then all bets are off anyway.

Well, yes, 200 MW (which seems about right for an aircraft carrier) would mean devoting all power on board to making fuel...
But if you were to put this on a ship, a carrier with a big nuclear power plant is probably the place to put it.

Again NO - the carrier is NOT the place to put it and that's why we don't. An aircraft carrier is a warship, not a fuel production facility or tanker. Everything on this vessel is tailored to do one thing - deliver air power where needed. It is NOT the place to make fuel.

I was wondering, in these modern times, are the oceans really that big that you need this kind of autonomy? With long range planes and missiles and ever more precise guidance systems, even the pacific ocean might be a relatively small pond...

Have you ever seen a missile that can jump in the water and save a human washed to sea by a tsunami? Or haul pallets of food and water? Or deliver doctors to a soccer field? Yes, we need this kind of autonomy.

 

[donald]

NO - the carrier is NOT the place to put it and that's why we don't. An aircraft carrier is a warship, not a fuel production facility or tanker. Everything on this vessel is tailored to do one thing - deliver air power where needed....

.... which involves filling those aircraft up with fuel. So you either have storage tanks, which will need refilling which takes the carrier off-line for a while, or you reduce your storage capacity and install fuel generation equipment.

The theory is not the problem, the issue is the mass and size of such equipment for a given productivity, and whether it would be compact and could be co-located in the hull. Given they are no where near bringing such equipment to fleet strength just yet, it is clearly a moot question right now.

 

[AndyH]

NO - the carrier is NOT the place to put it and that's why we don't. An aircraft carrier is a warship, not a fuel production facility or tanker. Everything on this vessel is tailored to do one thing - deliver air power where needed....

.... which involves filling those aircraft up with fuel. So you either have storage tanks, which will need refilling which takes the carrier off-line for a while, or you reduce your storage capacity and install fuel generation equipment.

What you're missing is that the carrier already has some storage - it has the storage necessary to perform their worldwide mission.

We have ten Nimitz-class aircraft carriers in the US Navy. Each carries 80 aircraft. Carriers don't travel alone, they travel as part of a carrier group that includes resupply craft for the entire group. Other ships in the group have turbine-powered aircraft that require fuel. It is much, much, much more efficient and much, much, much less expensive to resupply the fleet from a dedicated vessel rather than increase the size, complexity, and cost of every vessel with a flight deck or helipad.

You cannot 'reduce storage capacity' and still launch aircraft in a fire fight because when the excrement impacts the rotating air movement device you're burning jet fuel orders of magnitude faster than the synfuel plant can produce it. An F-18 burns around 4000 lbs per hour (about 600 gallons) on average...

 

[klapauzius]

Have you ever seen a missile that can jump in the water and save a human washed to sea by a tsunami? Or haul pallets of food and water? Or deliver doctors to a soccer field? Yes, we need this kind of autonomy.

Now that would be something fun. I recall a number of sci-fi stories involving intelligent bombs (e.g. Dark Star...), but I think the application was mostly
destructive (despite being smart).

Sorry, I was thinking of our military hardware being mostly used to destroy enemies?

For civilian uses, the current system with refueling tankers would work just fine?
But you think they will build nuclear powered tankers?

I would find the other civilian application, i.e. fuel generation from nukes, probably more curious than the military use. Depending on cost and efficiency, that might have some far reaching application....
Is the process Co2 neutral?
Or would this be another way to say turn otherwise "clean" fissile materials into extra CO2?

 

[Nubo]

You cannot 'reduce storage capacity' and still launch aircraft in a fire fight because when the excrement impacts the rotating air movement device you're burning jet fuel orders of magnitude faster than the synfuel plant can produce it. An F-18 burns around 4000 lbs per hour (about 600 gallons) on average...

But, would it not still be worthwhile to have ability to generate fuel, as a contingency? Sure, other means may be more efficient and cheaper, but if our group/fleet/world is really in a bad situation, isn't some fuel better than no fuel? If the plant could generate enough fuel for a sortie over the course of a day or two, for example? Realistic?

 

[klapauzius]

You cannot 'reduce storage capacity' and still launch aircraft in a fire fight because when the excrement impacts the rotating air movement device you're burning jet fuel orders of magnitude faster than the synfuel plant can produce it. An F-18 burns around 4000 lbs per hour (about 600 gallons) on average...

But, would it not still be worthwhile to have ability to generate fuel, as a contingency? Sure, other means may be more efficient and cheaper, but if our group/fleet/world is really in a bad situation, isn't some fuel better than no fuel? If the plant could generate enough fuel for a sortie over the course of a day or two, for example? Realistic?

Assuming you could turn ALL power into fuel, which would be the hypothetical , but never achievable upper limit, 200 MW would make 20000 l per hour, which would be enough, based on a burn rate of 2000 l/h, to power 10 planes for one h.In practice that number would be closer to 1.
1 out of 80 seems insignificant. So what is the military application for this?

 

[LTLFTcomposite]

Well they did make it sound like a breakthrough. Do we know they haven't come up with something nobody thought of?

Setting aside disdain for hydrocarbons and liquid fuels, is it possible the guy who invented the solar panel didn't have the last good idea?

 

[klapauzius]

Well they did make it sound like a breakthrough. Do we know they haven't come up with something nobody thought of?

Setting aside disdain for hydrocarbons and liquid fuels, is it possible the guy who invented the solar panel didn't have the last good idea?

I dont think its this vs. that technology...certainly there is not a limit on good ideas out there still to be discovered.
Liquid fuels, due to their incredible energy density, are still very useful, especially in military applications, where it would be pretty tough to replace them...

 

[donald]

Until there is working, mature equipment fit for fitment into the bowels of a hull, it is pure speculation as to what is or is not possible or appropriate.

The point a few of the posts are missing is that the US Navy HAS been actively researching this and pressing ahead with it, so clearly THEY believe there is a good reason to do it and have been making the degree of progress they want to towards whatever goals they have chosen, so any arm-chair theorists saying otherwise are talking out of their hats.