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Post by cyrilr on Jan 19, 2013 22:36:11 GMT 9.5
Edireland or anyone else - do you have technical references I can read about these SOFCs-in-reverse? It sounds like an important simplification in synfuel processing, but Googling finds a number of different techniques used and I don't know which one you're talking about here.
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Post by jagdish on Jan 20, 2013 2:07:35 GMT 9.5
Conversion of CO2 to fuels is always an inefficient use of energy. Energy conversion should always be to a more conveniently usable form. Any production of fuel should be from a form where some solar energy has already been put in preferably at no fossil energy cost. That means bio-wastes or plastic wastes. There is no point in throwing good energy after a not as good one form. Electricity is a good form of energy but it is wasteful to use it for heating effect where you can use directly produced heat. It is same for carbon fuel for burning, as hydrogen or any other input.
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Post by grlcowan on Jan 20, 2013 3:09:48 GMT 9.5
Edireland or anyone else - do you have technical references I can read about these SOFCs-in-reverse? It sounds like an important simplification in synfuel processing, but Googling finds a number of different techniques used and I don't know which one you're talking about here. In "Stabilization of STEP electrolyses in lithium-free molten carbonates" S. Licht has demonstrated the electrolysis of calcium carbonate:
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Post by Hank Roberts on Jan 20, 2013 4:29:21 GMT 9.5
I'm missing something important here. Why go after CO2 in seawater instead of CO2 from smokestacks on the coal plants? Can this process work directly on a coal power plant using electricity and heat from the coal power plant to capture the CO2 at the point of origin?
I know the Navy needs jet fuel at sea -- they can't capture the exhaust from what they're burning. But I don't understand capturing CO2 or anything else from a widely distributed dilute source instead of capturing it at the point of origin, when that's available.
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Post by cyrilr on Jan 20, 2013 4:33:02 GMT 9.5
I'm missing something important here. Why go after CO2 in seawater instead of CO2 from smokestacks on the coal plants? Can this process work directly on a coal power plant using electricity and heat from the coal power plant to capture the CO2 at the point of origin? I know the Navy needs jet fuel at sea -- they can't capture the exhaust from what they're burning. But I don't understand capturing CO2 or anything else from a widely distributed dilute source instead of capturing it at the point of origin, when that's available. It's simple, long term we don't want to lock ourselves into using coal, and there just isn't enough low impact sustainable biomass around. Short term, coal flue gas - or even better, natural gas flue gas, which is not contaminated with sulphur or heavy metal compounds - can be used to test the idea.
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Post by anonposter on Jan 20, 2013 14:45:31 GMT 9.5
Conversion of CO2 to fuels is always an inefficient use of energy. Energy conversion should always be to a more conveniently usable form. Any production of fuel should be from a form where some solar energy has already been put in preferably at no fossil energy cost. That means bio-wastes or plastic wastes. There is no point in throwing good energy after a not as good one form. Electricity is a good form of energy but it is wasteful to use it for heating effect where you can use directly produced heat. It is same for carbon fuel for burning, as hydrogen or any other input. There's not enough biomass for our needs. Maybe aviation could get by using only biofuels but if we can't make electric cars good enough then we're going to have to use synfuels. Besides, if energy is abundant and cheap (which it will be with fission) using it efficiently isn't a major concern.
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Post by Roger Clifton on Jan 20, 2013 18:44:26 GMT 9.5
Desalination by multi-stage-flash-distillation (MSF) seems to provide an easier way to extract CO2 from seawater than membrane methods.
In a scenario of MSF using exhaust heat from a thermal power station, seawater could be brought up to temperature under reduced pressure, when it would outgas CO2 and other dissolved gases.
From there it would be standard MSF, where the first stage is taken above normal boiling point under pressure. The boiloff is clean steam which then heats brine in the next stage at a lower temperature. A final stage of lowest temperature below normal boiling point might be (vacuum) pumped down for the last run of clean steam.
At ~50 mL/L of CO2 gas in seawater, that is still only ~100 g/kL, so the outgassing stage probably would have to aid the desalination to justify its inclusion in the desal train.
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Post by jagdish on Jan 21, 2013 11:21:26 GMT 9.5
A naval ship producing synfuel at sea would require energy to convert CO2 to fuel. It would have to come from its own nuclear reactor only. It would be being used already to run the ship. Smaller boats would best use batteries charged before release from the ship. The aircraft will be best catapulted from the deck using the ships power as they normally are on an aircraft carrier and can glide around. They could use the RTG engines used on satellites. Cheap Sr-90 is not in short supply. It can work only for a decade or so at good power as it has a half life of only 30 years against 90 yrs of Pu-238. For synfuel production on land, bio-waste or plastic waste would make a better carbon feed. Let the CO2 in the sea produce aquatic algae. Harvest it if you need it.
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Post by edireland on Jan 21, 2013 11:59:17 GMT 9.5
Try operating combat gliders from a flat top and you will have a lto of crashed gliders and no targets engaged. (Ditto RTGs aren't going to cut it to power aircraft in combat).
Electricity is and will be cheap. Liquid fuels and plastics are and will remain relatively expensive.
Converting the former, which we have in effectively limitless quantities, to the latter is a reasonable transacation. The efficiencies we can get (apparently 70% with high temperature electrolysis) should be sufficient.
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Post by anonposter on Jan 21, 2013 15:35:04 GMT 9.5
Try operating combat gliders from a flat top and you will have a lto of crashed gliders and no targets engaged. (Ditto RTGs aren't going to cut it to power aircraft in combat). lol To directly power aircraft with nuclear you'd need a very high power density reactor and you'd also have to forgo some radiation shielding (only give the crew compartment full shielding and rely on the inverse square law). You also need a big plane. Probably not practical (though if there were no in-flight refuelling long range bombers operating from remote sites in the desert could do it) and certainly not something you'd do on a flattop.
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Post by jagdish on Jan 22, 2013 14:53:02 GMT 9.5
RTG's are light enough to be carried on satellites and space crafts where the mass is at a premium. Synthetic fuels starting from CO2 are never going to be an energy efficient idea. It may be alright from coal/waste. When we have exhausted the oil, synthetic liquid fuels can be manufactured on shore and carried like the oil now. Best energy idea from the sea, not yet used, is floating generating plants in ocean currents. Better synthetic fuels could be not hydrocarbons but alcohols, ethers, aldehydes or ketones. they have lower calorific value due to oxygen carried in the molecules but burn better with no soot wastage.
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Post by anonposter on Jan 22, 2013 17:56:20 GMT 9.5
RTG's are light enough to be carried on satellites and space crafts where the mass is at a premium. For limited electrical power. Notice how those spacecraft still use chemical rockets (mainly hydrazine variants with nitrogen tetroxide) to manoeuvre? There was some research on RTG rockets using 210Po including testing but they only give a few Newton's of thrust and there's no way an aircraft could climb up from a carrier with 10 N thrust. Synthetic fuels starting from CO2 are never going to be an energy efficient idea. So? If you've got cheap abundant energy you won't care all that much. It may be alright from coal/waste. When we have exhausted the oil, synthetic liquid fuels can be manufactured on shore and carried like the oil now. It'd be acceptable if nuclear heat were used to run coal to liquid since the climate effects would then be no worse than oil and it'd open the possibility of upgrading it to get the carbon out of the atmosphere (possibly via the ocean). Better synthetic fuels could be not hydrocarbons but alcohols, ethers, aldehydes or ketones. they have lower calorific value due to oxygen carried in the molecules but burn better with no soot wastage. Ethers, aldehydes and ketones are hydrocarbons.
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Post by edireland on Jan 22, 2013 18:29:35 GMT 9.5
As a chemistry graduate I can confirm that ketones can produce soot just as well as anything else.
I have seen an acetone fire in a lab bay spewing out black smoke like anything.
And they aren't technically hydrocarbons since they also contain oxygen.
As to the "inefficiency" iof the process, efficiency is not the be all and end all, this converts surplus off peak electricity into handy liquid fuels, plastic and animal feed.
The average output of a two ESBWR plant replaces thousands of square kilometres of soybeans with a plantation of oil palms a tenth the size (to produce palm oil to replace the soy oil in various industrial processes).
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Post by Roger Clifton on Jan 23, 2013 18:23:32 GMT 9.5
Anon said: "there's no way (such) an aircraft could climb up from a carrier"
Heck, if you have a nuclear powered aircraft, why bother with the aircraft carrier?
Why not just leave it aloft? Remote piloting reduces the load it must carry and lengthens its mission into months. It may only have to carry cameras or scanners.
There must be plenty of problems that would welcome such a solution. Surveillance, weather, enviromental monitoring, disaster assessment. The recent expansions of economic zones mean the responsible nations need 24/7 monitoring for fishing vessels over vast areas of sea.
And that aircraft carrier may appreciate having an eye aloft for the whole of their journey too.
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Post by edireland on Jan 24, 2013 16:49:10 GMT 9.5
Nuclear powered aircraft have all sorts of servicing problems unfortunately, such as weight restrictions requiring the reactosr to be unshielded except for a crew protection shadow shield.
This means the entire airframe becomes too hot for ground crew to safely approach which makes servicing an absolute nightmare.
As to fast reactors using oceanic uranium recovery and air capture synthetic hydrocarbons.... has any thought been given to the effects on society of energy/fuel/plastics/animal feed protein prices effectively coming to a dead stop in real terms?
They should never rise by greater than the rate of inflation again, and probably should drop as we get better at building fast reactors and chemical plants, so this has got to have some interesting social effects.
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Post by anonposter on Jan 24, 2013 17:36:28 GMT 9.5
Nuclear powered aircraft have all sorts of servicing problems unfortunately, such as weight restrictions requiring the reactosr to be unshielded except for a crew protection shadow shield. This means the entire airframe becomes too hot for ground crew to safely approach which makes servicing an absolute nightmare. As I understand it the US ANP proposal wasn't for it to be completely unshielded expect for the crew, just for only the crew compartment to have enough shielding to be safe to occupy when the reactor is running and the rest of it would be safe to approach if the reactor were shut down (though you'd have to get ground crew well away when you start it up, probably have to towed out to the end of the runway, then the reactor started once everyone got clear). As to fast reactors using oceanic uranium recovery and air capture synthetic hydrocarbons.... has any thought been given to the effects on society of energy/fuel/plastics/animal feed protein prices effectively coming to a dead stop in real terms? They should never rise by greater than the rate of inflation again, and probably should drop as we get better at building fast reactors and chemical plants, so this has got to have some interesting social effects. That's what has historically happened to food prices, I would say that the results have been good, though there will be people who don't consider it such a good thing (namely those whose business model is based on the prices going up).
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Post by Roger Clifton on Jan 24, 2013 18:42:27 GMT 9.5
Well, how much shielding would a nuclear pilotless aircraft need? That depends on how much neutron spill...
An ocean-patrolling surveillance drone needs enough power to fly faster than high altitude winds, say 100 knots. That suggests a wing size and design like a Cessna 150, of 75 kW motive power.
If a nuke replaced the combustion chamber in a turboprop engine of say 1:4 efficiency, it would need maybe 600 kW of heat at take off (from an empty airstrip!). That indicates a reactor rather than an isotope. Even after gliding in to land, FP decay heat may require the core being pulled out immediately after landing.
Considering that Pu239 must be >10 kg, reactor grade Pu would need a core of the order of 200 kg. Just the engine itself might consume half a tonne of lift. That doesn't leave much lift for shielding. Some token to reduce noise in the electronics perhaps, but it seems that a nuclear aircraft would have to be unshielded.
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Post by Roger Clifton on Jan 27, 2013 9:08:40 GMT 9.5
Well, all right, a flying reactor is a bit er, fanciful. However, if we can sketch such a lightweight design as a hot-air turbine, we can more easily conceive of transportable nuclear power systems.
If a power plant can be readily moved from one job to another, it can be hired rather than bought.
Remote mine sites come to mind. Any large diesel consumer for that matter.
Wheel-in-wheel-out gas turbines would have competition, at least until the gas pipeline arrived.
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Post by edireland on Jan 27, 2013 20:22:23 GMT 9.5
I think HVDC Light is going to cause more trouble for small gas turbines and low speed diesels than modular reactors really.
The lines are sufficiently cheap to lay (overland you need a plough and that is about it) and the power electronics can be fit inside a few shipping containers for transport with all the iffy calibration already done.
It means almost anywhere can be brought on-grid at a reasonable cost (including off shore gas platforms in the North Sea now - see Troll A)
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Post by David B. Benson on Jan 28, 2013 7:54:37 GMT 9.5
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Post by edireland on Jan 28, 2013 9:46:16 GMT 9.5
Indeed, Siemens refer to it as HVDC "Plus"..... I just prefer ABBs trade name, it sounds much better than the generic "Voltage Source Converter HVDC"
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Post by JeremyRG on Jan 28, 2013 18:19:21 GMT 9.5
Impressive work, John. Certainly beats capture from ambient air. But I think synfuel from high temperature atomic-powered cement kilns (+ e.g. sulfur-iodine) has to come first, as that's a serious source of emissions currently, it's concentrated, relatively clean, and the right order of magnitude to cover aviation. Thoughts as to the relative costs for capture from limestone kilning vs. sea water?
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Post by Roger Clifton on Jan 29, 2013 8:18:52 GMT 9.5
A key value of a transportable reactor is that it is removable, essential for miners and military, and valuable for any expanding industry remote from the main grid.
Mine sites close suddenly when prices drop. If the lessor can quickly move the power plant to an operation elsewhere, it never need miss a mortgage payment.
Feasibility of a mining operation is constrained by the availability of power, water and transport. With plentiful power on site, there is no need for a power line, gas line, or even water pipeline. With increased processing of the ore on site, the demand on roads is reduced. It the operator can extract C1 or C2 liquids via CO2 during desalination, the logistics on transport fuel have been reduced too.
In Australia and Canada, the mining industry is a significant political consideration for a government trying to introduce a carbon price. With a reactor on site, a heavy-diesel user has an alternative, reducing exposure to the carbon price. In politically unstable areas in Africa, a nuke removes fuel vulnerability. In Indonesia and the Philippines, island communities could be brought into the developing world.
Dollar cost? Perhaps a prototype would be developed by the military, for their remote camps. A mass-produced version of an air-cooled reactor could supply power to industries and communities over very large areas away from the main grids. That is, over most of the Earth's surface.
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Post by edireland on Jan 29, 2013 10:16:10 GMT 9.5
If we assume the cement kiln operates with similar costs in all fields apart from energy as normal cement kilns and can produce product of similar or superior quality (As it should) then the only excess cost is the cost of electricity compared to the cost of the coal normally used.
A modern coal fired kiln consumes roughly 100kg of coal per tonne of product cement and produces roughly 920kg of carbon dioxide per tonne in total, of which approximatley 500kg is produced by the calcining of calcium carbonate.
100kg of coal has an energy value of approximately 2.4GJ, which is equivalent to roughly 667kWh which at the price of five cents per kWh equals some $33.50/tonne of clinker
$33.50 for 500kg of carbon dioxide means a total price per tonne, in excess of the conventional cement price (100kg at $70/t for high rank coal means $14 of coal replaced per tonne of carbon dioxide) of approximately $53/t
Assuming you can sustain 5 cents/kWh and that the price of high rank coal remains in a similar order of magnitude to $70/t. (This is the approximate price for Central Appalachia low Sulfur coal)
This figure obviously excludes cleaning the carbon dioxide. But assuming you strike some kind of electric arc this should not be a problem as the gas with be almost entirely carbon dioxide. (You might also be able to use simple resistive heating with "Kanthal" or Molybdenum disilicide heating elements that may be able to be made sufficiently high melting to survive the temperature required)
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Post by engineerpoet on Feb 4, 2013 11:48:10 GMT 9.5
do you have technical references I can read about these SOFCs-in-reverse? These are just another application of oxygen-ion membranes, which are usually some sort of stabilized zirconia. The archetypical application is the automotive exhaust oxygen sensor. If you pump electricity through one, you can move oxygen from the negative side to the positive side. If one side has steam and CO2 on it and a catalyst which allows them to dissociate into CO+O and H2+O, the O can be converted to O-- and pumped away.
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Post by engineerpoet on Feb 4, 2013 12:17:57 GMT 9.5
I have gone over the Navy paper and it doesn't look as good to me as it seems to to others.
The tests run so far took 6.22 volts at 0.94 amps, processing seawater at 0.1 mg/ml and 140 ml/minute. At 95% recovery of the freed CO2, I calculate an energy input of 1160 kJ/mol of CO2. The energy required to electrolyze water to H2 is only 285.8 kJ/mol (minimum), so in this case the extraction of CO2 from seawater costs roughly as much as the hydrogen needed to react with it (CO2 + 3 H2 -> CH2 + 2 H2O). In a word, not cheap.
I've found a paper claiming that potassium carbonate absorption only requires 44 kJ/mol of CO2. This is not something you can do on an aircraft carrier, but it's far better than the electrolysis of seawater.
Regardless, synthetic fuels are not going to be cheap. Maybe we're better off with beamed power and unmanned, nuclear-powered towplanes for trans-oceanic flights.
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Post by edireland on Feb 5, 2013 23:02:16 GMT 9.5
Actually with achieved efficiencies and offpeak power we could end up with cheaper than fuels are today.
And I'd like to see you tow a passenger plane at 600 knots, and how would it ascend to cruise altitude? You would have to fit engines to it anyway at which point I am not really sure its worth it.
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Post by engineerpoet on Feb 6, 2013 1:44:43 GMT 9.5
Actually with achieved efficiencies and offpeak power we could end up with cheaper than fuels are today. Color me doubtful. The sheer quantity of power required is going to require massive capital investment, and more efficient options will get there first; the PHEV is already in the marketplace, with a "fuel" cost of well under a dollar per gallon-equivalent. And I'd like to see you tow a passenger plane at 600 knots, and how would it ascend to cruise altitude? You would have to fit engines to it anyway at which point I am not really sure its worth it. It would need engines anyway, in case the towplane had a failure; fuel on board would be needed to get to the nearest landing site. But trans-oceanic flights do not travel at 600 kt (cruising speeds are around 500 kt or a bit under), and it would probably make sense to reduce speed to Mach 0.7 or less to get better dynamics. Would you rather take 20% longer to get there, or not be able to afford it?
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Post by edireland on Feb 6, 2013 9:54:42 GMT 9.5
Actually with achieved efficiencies and offpeak power we could end up with cheaper than fuels are today. Color me doubtful. The sheer quantity of power required is going to require massive capital investment, and more efficient options will get there first; the PHEV is already in the marketplace, with a "fuel" cost of well under a dollar per gallon-equivalent. And I'd like to see you tow a passenger plane at 600 knots, and how would it ascend to cruise altitude? You would have to fit engines to it anyway at which point I am not really sure its worth it. It would need engines anyway, in case the towplane had a failure; fuel on board would be needed to get to the nearest landing site. But trans-oceanic flights do not travel at 600 kt (cruising speeds are around 500 kt or a bit under), and it would probably make sense to reduce speed to Mach 0.7 or less to get better dynamics. Would you rather take 20% longer to get there, or not be able to afford it? Judging by the fact that we still don't have a working aircraft reactor (the ones trialed in the 60s would only possibly work if the entire thing was unshielded, which would rapidly make the entire airframe far too hot for aircrew to approach even when teh reactors were cold... which makes maintenance rather... interesting) if synthetic fuels are really as expensive as you claim they would be then it would be better just to do the crossing in a 40+ knot nuclear ocean liner. (Plymouth to Labrador or something, with High Speed rail the rest of the way for an Atlantic Crossing). Additionally, SOECs don't have "huge capital costs"... since by the very nature of the high temperature process they don't require that many very expensive materials in the construction of the equipment (the cells are made of things like alumina and silica and activated with nickel, not fancy platinoids). And once you have syngas it has been shown that the remaining equipment adds something less than $40/bbl to the price of the fuel. (Using plants such as Pearl GTL and the New Zealand prototype MTO plant as an example). It is really suprisingly cheap when you can run your equipment ~8-10hrs a day every day on electricity priced at ~1-2 US cents/kWh and stockpile the methanol/syngas for use during the peak periods. Even if you have to run the plant at reduced output during the day to keep it "ticking over". PHEVs are rather troublesome in that they have all the problems associated with EVs at the present time, relating to rapidly decaying battery capacity and the like. While they have important benefits in terms of air quality thanks to beter control of the conventional engine, they do not offer that great a reduction in fuel consumption. Its no suprise that the "PHEV" with the best sales record is the Toyota Prius Plug-In, which happens to be the one with the smallest battery pack. And how will this world without this process being affordable produce all its plastics and advanced petrochemical derived medicines? Fuel is just the tip of the iceberg
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Post by Michael Tobis on Feb 6, 2013 10:58:44 GMT 9.5
It makes very little difference whether carbon is removed from the air or from the upper ocean. The exchanges between them are rapid compared to anthropogenic emissions. Indeed this fact is often misused to obfuscate public conversation about the carbon cycle. It detracts from the credibility of the article for me that this question is framed as a tradeoff between acidification and climate forcing.
There is indeed a sort of a balance between the two effects, such that if one is worse than expected the other will likely be a bit less severe. But that tradeoff is nature's doing, not ours. The time scales are such that anthropogenic withdrawal of carbon from either reservoir will have approximately the same effect.
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