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PostPosted: Jan 27, 2011 2:33 am 
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A bit of a belated question, but is the DME being discussed here dimethyl ether or dimethoxyethane? Either way, it might be a great fuel for a gas turbine, but it is a terrible fuel for a spark ignition engine due to a low octane number. Low octane is good for compression ignition engines, and the low molecular weight and high oxygen content will make soot formation due to incomplete combustion less likely, but is it compatible with high pressure fuel injection hardware?

As for bicarbonate in pop, there is very little of it. The pKa of carbonic acid is about 6 and a carbonated beverage has a pH of 4 or lower. This means 99+% of the dissolved CO2 is in non-deprotonated form (H2CO3 + dissolved CO2). The equilibrium CO2 : H2CO3 ratio is about 800, so almost all of the carbonation in pop is in the form of dissolved CO2. Shaking the pop is just speeding the rate at which that dissolved CO2 comes out of solution by providing more surface area. The "mentos trick" is an extreme example of the same principle. Ironically, adding dry ice will also decarbonate pop in a hurry.

For seawater, the pH is about 8, so 99% of the dissolved CO2 is in a deprotonated form (carbonate or bicarbonate). The 1% or so that is dissolved CO2 could probably be made to come out of solution reasonably quickly, but the very low equilibrium H2CO3 concentration will limit the rate at which the rest comes out of solution. In the same way as the classic elementary school baking soda volcano would be a bit underwhelming if you added water instead of vinegar, you would need to acidify the seawater to get a large fraction of the CO2 out. If your fuel supply ship can make substantial amounts of HCl and NaOH it might work, otherwise you're probably better off finding a good sorbent to pull CO2 from the air.


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PostPosted: Jan 27, 2011 4:43 am 
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NNadir,

The Navy has a bunch of Super Hornets, and will one day have a bunch of F-35s. These have to last for 40 years. It is definitely possible to swap their turbines for another set of similarly-sized turbines. In fact, that is likely during the life of these planes. So it is possible to swap to an engine burning something else.

What fuel would you propose? Please suggest something that does not decrease the range of the jet.

Titanium-48,

DME = Dimethyl ether.

Here is a link to a seawater vacuum deaerator. I think they are much more worried about removing oxygen than anything else, so perhaps this is not relevant.

If I understand correctly, one worry that oilfield operators have is that if they inject seawater into the reservoir in an attempt to force out oil, and that seawater includes oxygen, that microbes will grow down there, feeding off the oxygen and oil and producing crud that plugs up the reservoir. I'm amazed that microbes will grow at those pressures.

You are right that to extract the CO2 from the water, the oilfield guys add acid. HCl is made by electrolyzing brine. Does that mean I can acidify the incoming water by sticking in a pair of electrodes and running a current through them, and taking the lye off one and bypassing it around to neutralize the exit water? This sounds like a really power hungry idea.

David LeBlanc found this great MIT thesis on exactly this idea, written 16 years ago. One thing the author seems to have missed is that the energy used to pump the seawater, while not exactly recoverable, can be used to drive the ship forward. He also has not suggested the idea of sparging to increase HCO3 + H -> H2O + CO2. One thing that I certainly missed is that the same system that extracts CO2 also extracts desalinated water: he suggests 10x the rate of CO2. So, the nuclear fueller that produces 460 metric tons/day of fuel also produces 4600 metric tons/day of desalinated water. Some of that gets used to produce the hydrogen for the fuel, but the rest can be drinking and wash water, which presumably has some value to the fleet.

-Iain


Last edited by iain on Jan 28, 2011 1:53 pm, edited 2 times in total.

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PostPosted: Jan 27, 2011 5:13 am 
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If you just have to have floating factories for liquid fuel, you have to think comprehensively from the scratch.
1. A nuclear reactor as energy source.
2. Hydrogen from seawater.
3. Coal as reserve carbon stock.
4. Algae-culture for sustained capture of carbon and sunlight from air and sea.
Algae and coal can be converted to syngas and then on to Dimethyl ether or other liquid fuels.


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PostPosted: Jan 31, 2011 1:45 pm 
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Here's a summary of my findings so far:

The Navy SSG XIX study shows that in 2000 the Navy completed a study showing that a nuclear fueller would greatly increase the fighting power of the rest of the fleet. The gains come from not having to provide antisubmarine and antimissile defense to tankers shuttling from friendly ports to the fight zone, and from the ability to maneover the carrier group without regard to resupply. Resupply is still necessary (in a fight, ordance primarily), but because tonnage is down by 80%, existing supply vessels can sustain the fleet for 5x longer. In the campaign modelled, it looked like existing supply vessels were close to being able to sustain the fleet from arrival through strike phases, but I didn't see that point made in the paper. That study foundered on a source of carbon.

Kevin Terry's 1995 MIT masters thesis looked at the problem of the nuclear fueller and suggested stripping CO2 from the ocean. The thesis did not examine the problem of converting bicarbonate in the seawater to carbonic acid, without which the CO2 is not coming out of solution.

Titanium48 suggested the following process, which is actually in use today in seawater degas systems used on deep sea drilling platforms.

Make hydrochloric acid and lye:
H2O + NaCl => HCl + NaOH - 57.1 kJ/mol

Mobilize CO2 in seawater by mixing with HCl:
HCl + HCO3 => Cl- + H2CO3

Then get rid of the byproduct NaOH
Cl- + NaOH => NaCl + OH-

You end up with an ejected stream of alkaline water (adding 2.4 mmol/kg OH-). This is not surprising, since CO2 dissolution is making the ocean acidic on a global scale. Stripping large amounts of CO2 locally makes a locally concentrated alkaline output, which then gets diluted as it mixes with the surrounding seawater.

The energy and space requirements of seawater CO2 stripping in this manner do not appear to be a problem. Here are the chemical requirements:

NaCl + H2O => NaOH + HCl - 57.1 kJ/mol(C) (Brine Electrolysis to make acid)
3H2O(g) => 3H2(g) + 1.5O2(g) - 857.4 kJ/mol(C) (Water electrolysis to make hydrogen)
CO2(g) + 3H2(g) => CH3OH(g) + H2O(g) - 207.0 kJ/mol(C) (Methanol synthesis)
10CH3OH(g) + H2(g) => C10H22(g) + 10H2O(g) + 61.8 kJ/mol(C) (Mobil Methanol To Gasoline process)

Add to this chemical energy a substantial amount of mechanical pumping energy, primarily used to move seawater, compress stripped gas back to atmospheric pressure, and compress CO2 and hydrogen for methanol synthesis.

The electrolysis energy above is electricity, of course.

Methanol synthesis via the ICI process happens at 575 K and 50 to 100 bar pressure. Even though the chemistry is endothermic, this process rejects excess heat when the reactants are compressed. The compression energy is probably not recoverable on board a ship, not least because there will be a bunch of product separation work that will use that pressure.

The reat rejected from the MTG process is also probably not recoverable on a ship.

The Lotus paper claims atmosphere+electricity to oil can be done at 40% efficiency, which means 1470 kJ/mol(C), which seems reasonable given the numbers above. This doesn't count the cost of the air moving and water pumping, but CO2 from seawater would replace that with the cost of brine electrolysis and ship propulsion. If we assume the brine electrolysis step is 70% efficient, and so add 82 kJ/mol(C), we're up to 1552 kJ/mol(C), or 111 megajoules/kg of diesel output.

Ships producing 500 metric tons of fuel per day would require 650 megawatts electric to drive the chemistry, and another 50 megawatts for ship propulsion and hotel loads.

Westinghouse is supposedly ready to sign contracts to build the first U.S. AP1000s for $4/watt overnight costs, so I will assume this reactor can be built for $5/watt overnight cost. I will further suppose that the chemical plant can be built for $2/watt overnight, and that the rest of the ship comes to $500 million. That comes to $5.4 billion per ship, overnight cost.

I think the fifth ship like this should take two years from purchase order to initial criticality. I do not understand how the financing costs can get large as the overnight costs in five or so years, as I see quoted for land-based reactors. I think finance charges should be something like $400M.

So, if the ship gets 80% capacity factor, capex cost is 7%, it is paid off over 30 years, and fuel+O&M costs are 30 $/MWh (2.5x Palo Verde's costs, assuming the synthesis plant and the ship are costlier than the reactor), then the fuel cost is $11.46/gallon, about 4.2x what the Navy pays now. The majority of the cost is the capital expenditure.

A fighting carrier task force would require 4 of these ships, and the Navy as a whole would require 11, for a program cost of $60 billion. The fuellers would offset approximately $1.6 billion/year of fuel costs (which is not the primary point of the program). For comparison, the Arleigh Burke guided missile destroyer program, with 55 ships, cost about $43 billion.

I think that's about as far as I can analyze this. The economics of making oil from nuclear power don't look good to me, but the military value might be outstanding if $60B of ships can double the fighting power of the existing ships. This might make a lot of sense when the Navy is being asked to downsize, although I'm sure they'd rather build ships which fight directly.


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PostPosted: Jan 31, 2011 8:27 pm 
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Thanks for the summary Iain. Any thoughts on what could be a best case scenario to produce liquid fuels from CO2 in general?

I found some interesting economic data from this site

http://www.chemlink.com.au/gtl.htm

I think from the late 90s but they make it sound not very expensive to convert coal or methane to gasoline etc. For example they quote capital costs of equipment at 20 to 30k$ per barrel a day capacity. Your case of 500 tonnes a day (roughly 4000 barrels a day) is only 100 M$ (only 0.15$/watt, far lower than the 2$/W you estimated). They also list a O&M cost of only 5$ a barrel for methane to gasoline (and only 5$/barrel natural gas costs at 0.5$/MMBtu). Not sure how much the complexity and cost change of the chemical side of things by going all the way from CO2 to gasoline but would be very interesting to get an estimate of productions costs in the overall nuclear to liquid fuel picture.

David LeBlanc


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PostPosted: Feb 01, 2011 3:14 am 
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David,

A gallon of gasoline has 129 megajoules or about 36 kWh. At 5 cents/kWh, a perfect system could produce gasoline from CO2 and water for $1.80 plus capex+O&M. If the Lotus paper is right, realizable systems could do it for $4.50 plus capex+O&M. I don't see this coming down a lot, and I suspect capex will always be really large.

So, for this specialized application, I can see liquid fuel synthesis being useful. But in general, I don't see it as promising. I think the Navy thing is interesting because these are much bigger reactors than they currently have, and they are not propulsion reactors. Note that Naval Reactors has built 31 subs and three aircraft carriers in the last 20 years, with six different evolutionary reactor designs (Ohio class (S8G), Los Angeles class (S6G), Seawolf class (S6W), Virginia Class (S9G), Nimitz (A4W) and Gerald Ford (A1B)), built by three different manufacturers.

Clearly, the Navy has no difficulty designing and building nuclear powerplants. And, they have decent production volume.

It's fun to speculate that if the Navy were to build 11 700 MW(e) reactors, and deliberately designed those reactors to have more publicly releasable designs, that the company that built them might be allowed to build land based versions as well. This might potentially lower the cost for the Navy, and at the right price it would be great for our economy. I don't think that the Navy would have any difficulties getting their reactor designed and built, and presumably many copies of a working reactor would help the NRC understand the safety aspects.

The DOE has a mandate to reduce their carbon emissions, and the DOD is considering doing the same. If the DOD adopts the same goal as the DOE, they will need 7 gigawatts of zero-CO2 land-based electricity. There's another 10 units right there. They could base one or even two in Pearl Harbor, for instance. There is a clause in the Hawaiian constitution that says that any power reactor or waste disposal on the island requires a 2/3 approving vote by both houses of the legislature. As a military unit, the fuel might conceivably be disposed in WIPP, and it's not clear that the legislature has a say in what gets installed on the base. Presumably a fair number of Hawaiians would welcome a substantial drop in their electric bill.

I've been looking at vacuum maglevs pretty carefully for the last few months, and I'm no longer concerned that we need to make liquid fuel for airplanes. Trains can be electrified, and I think that a car-carrying vacuum maglev system for major routes could make battery electric vehicles desirable and affordable.

In summary at this point I don't think synthetic liquid fuels are either necessary or desirable.


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PostPosted: Feb 01, 2011 8:28 pm 
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There is nothing to stop the navy from putting more then one reactor of smaller size on their fueler ships. If the navy is trained and used to using a certain size.


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PostPosted: Feb 02, 2011 7:37 am 
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A much cheaper initial starter for tube delivery of goods would be this proposal:
http://nextbigfuture.com/2010/12/foodtu ... et-of.html

'The Foodtubes group wants to put goods in metal capsules 2 meters (6 feet) long, which are shifted through underground polyethylene tubes at speeds of up to 60 miles per hour, directed by linear induction motors and routed by intelligent software to their destinations.'

Since damage to the roads rises at the third power of axle weight this should enable massive savings in highway repair costs apart from those on fuel.
A single truck can do 8,000 times the damage of a car.


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PostPosted: Feb 02, 2011 7:41 am 
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I can't work out too much about what is proposed here for ammonia production and use - the details are pretty skimpy:
'http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10693646

'Fleming's most tangible contribution has been a small, cheap processing plant that converts hydrogen and nitrogen into ammonia using a compression and decompression system. It promises on-site production of hydrogen-carrying liquid fuel, solving the problem of storing and distributing (with considerable energy loss) a highly explosive gas from large and expensive centralised plants. "Ammonium can be liquefied, produces no carbon or solid deposits and can burn in internal combustion engines carrying a reasonable amount of hydrogen."

Based on an electrolyser he devised for potential use in gas fireplaces, the processor offers huge cost savings in the production of hydrogen using electricity. The processor costs US$200 ($267) (compared with around $130,000 using large-scale conventional models) and is predicted to produce fuel for about US27c a litre (36c) before taxes.'


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PostPosted: Feb 06, 2011 3:24 pm 
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27 cents per liter of what? Hydrogen gas? At what pressure?

-Iain


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PostPosted: Feb 06, 2011 4:29 pm 
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The US government is now distributing a $billion in loan guarantees to companies that develop and field biomass fuels that can be used in exiting US fuel infrastructure.

Non conforming fuels may be interesting from a technical standpoint, but they won’t fly politically.

The US government wants business as usual: gasoline, diesel, jet fuel in the biomass to fuel conversion process.

_________________
The old Zenith slogan: The quality goes in before the name goes on.


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PostPosted: Mar 13, 2011 1:35 am 
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iain wrote:
27 cents per liter of what? Hydrogen gas? At what pressure?

-Iain


per liter of liquid anhydrous ammonia.

He needs to sell a complete system to farmers and ranchers including a windmill generator with anhydrous ammonia production. The farmer will use ammonia for fertilizer and as fuel in dual fuel engines, diesel and/or ammonia.

With a side benefit of producing electricity for personal use or sale of excess electricity to the local utility. The ammonia can also be used in a fuel cell to produce electricity when the wind is not blowing.


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