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PostPosted: Jan 24, 2011 9:41 am 
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Producing fuel at a base would not solve the problem that I understand they are concerned with, cutting the logistics chain to bring fuel to the front line, although it would avoid the use of oil which may be in short supply.


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PostPosted: Jan 24, 2011 4:29 pm 
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Iain,

Have you looked into producing Ammonia? No carbon feedstock required. We have several fans of this process around here, particularly Darryl Siemer formerly of INL. Not sure how advanced the processes are to produce it without using methane as the hydrogen source but there are one or more threads discussing this. Ammonia scares people a bit but can be used directly as a fuel stock.

David L.


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PostPosted: Jan 24, 2011 5:27 pm 
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iain wrote:
Tom,

Getting the carbon from seawater is an interesting idea. I get different numbers than you.

http://www.seafriends.org.nz/oceano/seawater.htm says there is 90 mg(CO2)/kg(seawater). So, 8 kg/s carbon is 29.3 kg/s CO2 is 326,000 kg/s of seawater, or 326 m^3/second.

That's like the flow through the prop! If we had a 6-meter diameter pipe, the fluid velocity would be 11.5 m/s and the flow kinetic power would be 21 megawatts, which is about what one of these ships puts out at cruise speed.

If we sucked all that water through a pipe 8 meters tall, so that the pressure at the top was perhaps 20 kPa absolute, we might boil out 80% of that CO2. What we'd actually get would be 194 kg/s of gas with about 15% CO2. At 20 kPa, this gas would be bulky, around 1000 m^3/s. So we'd have to seperate the gas and water, and then the gas would have to be recompressed to atmospheric pressure. I think this would take about 700 kilowatts. The water then gets exhausted out the back as a jet which pushes the ship forward. The gas goes through the rest of the Green Freedom process, now much smaller because just 200 m^3/s is being processed rather than 55,000 m^3/s. The difference in those two numbers is due to the way water dissolves CO2 more than O2 or N2, because most of the CO2 forms carbonic acid. We're using the surface area of the ocean to do our first stage air handling.

I like it.

-Iain

I like it!


Except that the water will only be spending a fraction of a second at low pressure and the CO2 - carbonic acid - bicarbonate - carbonate system will not come to equilibrium. The CO2 might come out of solution, but the bicarbonate will not. Maybe if you found a way to immobilize carbonic anhydrase in your column it might work.


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PostPosted: Jan 24, 2011 6:28 pm 
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David wrote:
Iain, Have you looked into producing Ammonia?


Yes. For the Navy, this is not good enough. Neither is DME.

The problem is that any of the NxHy molecules have half the energy per kg of JP-5. (Yes: hydrazine has half the energy density of JP-5! It's actually worse than ammonia!) That means a plane using the stuff has half the range. This seems terrible to me. It's not like the planes can be easily redesigned with larger gas tanks, either: this is a mature field and they are closely trading payload for performance. If they had to use ammonia, they would, and this would lead to larger tanks for sure, but also less performance. It seems very unlikely to me that they would trade this loss for the ability to avoid antisubmarine patrols over the tanker route, because they already live with the latter.

DME has about the same energy density as ammonia. Same problem, except DME has carbon, so you would have had to solve that problem.

Ammonia can solve the problem for the ships, but the jets burn as much fuel as the ships. We have to have a carbon source.

-Iain


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PostPosted: Jan 24, 2011 6:29 pm 
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Titanium48 wrote:
Except that the water will only be spending a fraction of a second at low pressure and the CO2 - carbonic acid - bicarbonate - carbonate system will not come to equilibrium. The CO2 might come out of solution, but the bicarbonate will not. Maybe if you found a way to immobilize carbonic anhydrase in your column it might work.


Ah shoot.

What's the equilibrium time constant on this system?

-Iain


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PostPosted: Jan 24, 2011 6:45 pm 
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Hang on a sec. This system gets close to equilibrium in my lungs when I'm not exercising hard. The blood residence time in my lung aveoli has got to be just seconds: I pump 5 liters/minute at rest, and have a total blood capacity of 5 liters. How much of that can be in my lungs? My forced vital capacity is about 6 liters, and it's hard for me to imagine that there is more than 500 ml of blood in there. So that says that blood resides in the aveoli for 6 seconds.

To achieve similar performance, I need an outgassing tank to hold 2000 metric tons of seawater 8 meters above the ocean surface before it goes back down again. Yes, that's big. But the ship is going to weigh 50,000 metric tons, so it's not horrible.

Keep it coming, btw. I need to finish today, this is great criticism.

-Iain


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PostPosted: Jan 24, 2011 7:08 pm 
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The uncatalysed rate constant ranges from 10 to 40 s-1 over the temperature range of 15°C to 30°C for the reaction H2CO3 --> H2O + CO2. At ocean pH the H2CO3 concentration is very low as the majority of the carbon is in the form of bicarbonate.

Reference
Alan L. Soli, Robert H. Byrne, CO2 system hydration and dehydration kinetics and the equilibrium CO2/H2CO3 ratio in aqueous NaCl solution, Marine Chemistry, Volume 78, Issues 2-3, May 2002, Pages 65-73, ISSN 0304-4203, DOI: 10.1016/S0304-4203(02)00010-5.
(http://www.sciencedirect.com/science/ar ... ee7bea64c4)


In your lungs the reaction is much faster due to the enzyme carbonic anhydrase, some forms of which are essentially diffusion limited. This increases the rate constant to as much as 10^6 s-1.


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PostPosted: Jan 25, 2011 12:10 am 
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Your assumption of aircraft fuel use being dominate may not be valid in the future. See this link
http://www.strategypage.com/dls/article ... 2-2011.asp

In short smart bombs allow a single aircraft to do the work of many. Also for various reasons manned naval aircraft might well be replaced by pilotless UAVs which will be smaller and use much less fuel. Already there is talk of moving to smaller aircraft carriers as a result.

In any event interesting project you are working on.


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PostPosted: Jan 25, 2011 1:19 am 
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Okay, at 10 hertz the H2CO3 --> H2O + CO2 reaction is definitely fast enough.

I'll note that when I open a bottle of soda, there is a satisfying whoosh of bubbles, which I presume is the H2CO3, followed by a period of an hour or more where little bubbles stream to the surface from small imperfections in the glass container. These bubbles grow considerably from when they leave the glass side to when they reach the liquid/air surface, during which trip their surrounding absolute pressure decreases imperceptably. I suppose this is HCO3, and the minor irregularities in the glass surface and bubble surface catalyze the conversion to H2CO3 and thence to CO2 + H2O.

If I shake up that bottle of soda, there is another whoosh of bubbles. It seems like there are many things that catalyze the conversion of H + HCO3 to H2CO3.

What do you suppose would happen if I sparged the rising seawater with a small amount of gas recycled from the top of the degas vessel? Among other things, the rising bubbles would make the rising water column buoyant relative to the falling water column. That's going to create a pressure difference I can use to pump the water. I'm not suggesting I've found a perpetual motion machine, but it does sound like a substantial amount of the energy used to degas the water can be recovered to propel the ship forward.

In fact, I can drop the absolute static pressure of the water by accelerating it rather than by lifting it, which keeps the water lower in the hull. Now I can hold a larger volume of water at low pressure, which gives the bubbles more time to sparge the HCO3 out.

-Iain


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PostPosted: Jan 25, 2011 4:01 am 
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Iain, have you looked at a two step process where you first make a lower alcohol and then convert higher alkanes using zeolites? This is high energy density fuel similar to exisiting fuels (gasoline, diesel, kerosene), and you lose only ~10% of your HHV in the zeolites.


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PostPosted: Jan 25, 2011 9:08 am 
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There's a big difference in pH between carbonated beverages and seawater. In the former, most of the carbon is in the form of dissolved CO2 (equilibrium constant for the reaction H2CO3 --> H2O + CO2 is about 800), which can be released quite quickly. In seawater, most of the CO2 is in the form of bicarbonate, with a very low equilibrium concentration of H2CO3.


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PostPosted: Jan 26, 2011 12:35 am 
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Seems the price of gasoline is raising in the US and this might be a time to promote nuclear powered fuel. The common man if presented a gasoline equivalent gallon might promote the idea if he can see it coming right to his pocket at the pump.

What would be the cost per gallon if one were to use .05 kwh nuclear power to produce gasoline from coal or natural gas?


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PostPosted: Jan 26, 2011 1:18 pm 
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Cyril,

The attached review paper suggests methanol-to-gasoline conversion loses 10% of the high heating value, which agrees with your figure. It also suggests a "wind to tank" efficiency of 46% for CO2 capture, H2 electrolysis, and methanol generation. Combine the two and we get 41% efficiency.

Ida-Russkie,

If input electricity is $0.05/kWh, then the energy content of the synthetic gasoline is $1.52.

Assume $2B capex, 7% interest, 40 year depreciation, and $0.01 cent/kWh opex for a plant that can take 4 GW(e) and convert it to 3150 metric tons/day of gasoline (1.15 million gallons/day). That's 87 cents/gallon.

Total is $2.39/gallon. I wonder what the cost of gasoline ex-refinery is.

Titanium48,

I really appreciate your help. Do you think that a carbonated soda, left out for 10 minutes, has much dissolved CO2? Wouldn't the remainder have to be bicarbonate?

Because, if I take a soda, leave it out, and then shake it: voom, out comes a whole lot of bubbles.

I guess I need to go find out if someone has done the experiments on bicarbonate -> CO2 rates at the surface of liquid as opposed to the bulk of the liquid.

-Iain


Attachments:
Lotus_PARC_SOFT_SAE_PFL_2009_1.pdf [1.62 MiB]
Downloaded 106 times


Last edited by iain on Jan 27, 2011 1:25 am, edited 1 time in total.
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PostPosted: Jan 26, 2011 3:14 pm 
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http://tonto.eia.doe.gov/dnav/pet/pet_pri_top.asp

has a big list of links to current prices for several petroleum products.

The current Nymex futures price for regular gasoline is 2.34 per gallon. so the 2.39 is close
to today's prices.


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PostPosted: Jan 26, 2011 10:47 pm 
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David wrote:
Iain,

Have you looked into producing Ammonia? No carbon feedstock required. We have several fans of this process around here, particularly Darryl Siemer formerly of INL. Not sure how advanced the processes are to produce it without using methane as the hydrogen source but there are one or more threads discussing this. Ammonia scares people a bit but can be used directly as a fuel stock.

David L.


Ammonia is the worst hydrogen carrier imaginable, not only because of its obvious health characteristics, but because of the N2O problem.

Any ammonia that leaks - and it will leak, just like methane leaks - will cause further accumulation of nitrous oxide in the atmosphere.

This is a already very serious environmental issue, and anyone who looks at it will see that N2O is going to make CFC's look like a cakewalk.

If there is a large ammonia leak, you are going to read about it in the newspapers, people hospitalized, blinded, and permanently disabled and, most assuredly, killed.

If DME leaks, you're going to read, um, nothing most likely, because it's going to be very much like a hairspray can.

Because of our population, we must make ammonia - for fertilzer - but to everytime I read about it as a fuel, I want to scream.

A DME comparison to gasoline is rather like a CFL bulb comparison to an incandescent. Everybody likes the devil we know, because we, um, know it. An incandescent bulb is not intrinsically superior to a CFL. Had the CFL been invented before the incandescent, and people tried to push incandescents for some reason - say, mercury problems - I assure you that you'd hear loud vociferous complaints from people who said they just had to have the CFL.

Everyone wants to compare DME's properties to gasoline as if gasoline were ideal. Gasoline's and other petroleum based fuels debits are far greater than their positives actually, and the only thing to recommend them is that they're familiar. This is not the same as saying they're good. Energy/mass density is not the only issue with transportable fluid phased fuels. An optimization vector has many other dimensions.

The only thing that makes me want to scream worse than the idea of ammonia, is the idea of making petroleum like fuels (alkanes) with nuclear energy. Can it be done? Sure. Should it be done because it can be done. My personal vote is a strong resounding "no." Petroleum is a disaster, and has been a disaster since the early 20th century, when Japan bombed Pearl Harbor on a matter that was actually intimately involved with alkanes, if you really look into it. (I always find it ironic in a strange way that the Arizona is still leaking oil into Pearl Harbor.)

Of course, nuclear alkanes are different than petroleum alkanes, but that doesn't address even a fraction of the problem. As things stand now, two million people die each year from air pollution. The only fluid fuel I know that is both liqufiable and completely free of air pollution issues is DME.

I really think that in any sustainable combinatorial optimization problem, DME is such a superior fuel that I can't even imagine that's it's debatable.


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