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Titan: hydrocarbons & oxygen for burning 'em

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Sat, 2012-07-28 12:35
#1
jackgraham jackgraham's picture
Titan: hydrocarbons & oxygen for burning 'em
All right boffins, let's get this sorted!. So, our assumption that Titanians would figure out a way to burn hydrocarbons rests on ideas about how to exploit the chemistry of Titan promulgated by Robert Zubrin & other interplanetary colonization wonks. I'm more interested in getting it right than being right, so let's talk it out. (And Zubrin has led me wrong before, btw...) The notion is that you can start with "seed" fusion power, use electrolysis to free up hydrogen and oxygen from Titan's abundant water ice, and then burn hydrocarbons. It assumes that you get more energy back from burning methane (which when burnt yields energy comparable to gasoline) than you put into electrolyzing the water. As far as balancing out/recycling the chemicals you're left with after burning, I'd refer you to this article about how they do life support on the ISS today. Also, remember, they're growing a lot of plants, so the oxygen they need for life support can be recycled pretty efficiently. How these elements are used for power is a mixed bag, too, with varying efficiencies. The obvious use would be burning methane to generate electricity, but in the early days of the colony, they'd probably have been storing a lot of O2 to mix with methane for rocket propulsion, too. At any rate, agreed that you can't just show up on Titan and start burning hydrocarbons -- you need to have brought other power sources to kickstart the process. My assumptions about whether you can turn that into a self-sustaining cycle could be off, though. And there are a bunch of other things in the setting that break horribly if electrolysis isn't as efficient as we think it is. This is the most interesting energy-related topic since the huge arguments we had early on in design about He3 vs. other types of fusion. Interested to hear what people think.
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Sat, 2012-07-28 13:52
kindalas kindalas's picture
A few quick thoughts
The water cracking efficiency consideration goes out the window when you pause to consider that fusion reactors are immobile and very good at turning hydrogen (well D2) into Helium and usable energy. And that having a portable energy source that is compact (say a tank of O2) and having a 2nd fuel tank of methane on board is a lot simpler to have and use then requiring expensive nuclear batteries or hyper expensive fusion reactors on board a vehicle.
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Sat, 2012-07-28 14:31
crizh crizh's picture
Efficiency
Burning 1mol of Methane requires 2mol of Oxygen and releases 891kJ. Cracking water to produce Oxygen requires 572kJ/mol of Oxygen released. So we waste 253kJ/mol when burning Methane in Oxygen we've extracted from Water with a Fusion plant. That's pissing somewhere between a third and a quarter of all the energy we produce up against a wall. If we can manufacture any form of battery that is better than 75% efficient we are better off doing that than using precious Oxygen to burn Methane. We are nevertheless using Fusion as a Primary source of power. We are using Oxygen as a 'convenient' storage medium for that energy and Methane happens to be something that is lying around that allows us to easily release that energy. It's possible you might well burn small amounts of Methane to produce the Carbon Dioxide your going to need to grow plants inside your domes. Maybe you could use it for street lighting? My personal pet theory is that you would use your Fusion plants to crack water to create Oxygen to breathe and then you would use the released Hydrogen as a high density energy storage medium. Metallicise (sp?) it and sublimate it through nano-turbines to generate power as you need it. The released gas could either just be dumped into the atmosphere or pushed through a fuel-cell to get the last few drops of efficiency out of the system depending on circumstances.
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Sat, 2012-07-28 18:56
Arenamontanus Arenamontanus's picture
As the others have said, the
As the others have said, the process wastes energy. But it produces various convenient forms of energy storage: hydrocarbons that can be burned "indoors" to power vehicles or devices (fuel cells are nice an clean in EP - nanotech allows some amazingly clean combustion!) and oxygen that can be burned "outdoors". Considering that gasoline has energy density 47.2 MJ/kg while TNT just has 4.2 and lithium batteries just 1.8 (hydrogen at 700 atm is 123 MJ but is cumbersome to handle - and even worse, metallic hydrogen requires special tools) this is a very good form of energy storage. It is awesome to realize that when you tank your car, the hose is transmitting near a megawatt of power! So I think it makes sense to consider Titan to have an energy economy powered primarily by fusion, with energy delivered either as electricity or suitable high energy compounds.
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Sat, 2012-07-28 20:20
jackgraham jackgraham's picture
crizh wrote:Cracking water to
crizh wrote:
Cracking water to produce Oxygen requires 572kJ/mol of Oxygen released.
OK, so that's completely awful. Fortunately it's not a major plot point that a great many gamers will stop in the middle of their Firewall missions to debate, but it's going to bug _me_ now. :) Using methane + oxygen as energy storage, vehicle fuel, etc. (which was part of how it had been envisioned working anyway) seems to work out, though. I think over time we just change the references to the giant abandoned power plant out side Aarhus to a giant abandoned refinery, etc., and we're good to go. (Although now I wonder... what the hell are people in Aarhus driving? Cars with fusion reactors in the boot?)
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Sat, 2012-07-28 21:58
crizh crizh's picture
Energy density
I liked that analysis. Bearing in mind that Methane requires that you bring along sufficient oxygen it works out at 11.14 MJ/kg. Not counting the mass of the tanks.... According to the main rule book EP batteries are 25 times better than the best tech we have now which makes them a minimum of 45 MJ/kg. Methane might still have the edge if you can use atmospheric Oxygen and you ignore the weight of the tanks required to keep it liquid. Seems like a lot of trouble to go to when you've got perfectly adequate technology that operates in the same ballpark and is probably a lot less risky. On the subject of Metallic Hydrogen, I understood that we were operating under an assumption that it has a Metastable form that drastically reduces the problems associated with storage. Certainly substantially less trouble than anti-matter. I've no knowledge really in the area but my wiki-fu suggests that densities of 2.5 GJ/kg or more are realistic. edit - Altered density of batteries in line with the figures Arenamontanus gave for Lithium. edit 2 - On back checking EP MH is kept meta-stable with Magnetic fields in a similar manner to storing AM. Assuming the same 10 to 1 ratio for containment your still looking at 250 MJ/kg. That's a fantastic power to weight ratio whilst still not being on the same planet as AM and so potentially perfectly safe. AM being in the range of 18 Million GJ/kg. (18 PetaJoules/kg)
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Sat, 2012-07-28 22:14
nick012000 nick012000's picture
Isn't the entire point of the
Isn't the entire point of the plutocrats how ridiculously wasteful their lifestyle is? I could totally see energy-inefficient methane-powered retro cars as a part of that.
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Sat, 2012-07-28 23:53
kindalas kindalas's picture
Don't forget
Don't forget the inherent inefficiencies of energy transfer and storage. Once you take into account the waste energy of say putting fusion reactor output into a battery. When compared to directly cracking water for oxygen (for methane burning and breathing) and hydrogen (which can be made into rocket fuel). Also consider turning CO2 and water vapour (exhaust gasses) back into 02, carbon and hydrogen using semi portable wind turbines. Sure batteries are practically mega capacitors in the EP setting, but the simplicity of using basic technology makes living on the frontier a lot safer when you consider the dangers of a busted black box device stranding a team in the murky soup that's Titan's atmosphere.
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Sun, 2012-07-29 02:37
crizh crizh's picture
Waste
I was also ignoring any inefficiencies involved in cracking water and storing the resulting gases, which I'm pretty sure are substantial. We're not talking about a bunch of rubes scrapping by with out dated tech here. We're talking about a group with the best kit transhumanity has to offer. You don't walk for 12 weeks across a frozen wasteland pissing into Disposable Absorption Containment Trunks.
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Sun, 2012-07-29 09:20
Xagroth Xagroth's picture
I think it is important to
I think it is important to notice that efficiency is not always an option: Passed Jupiter the sunlight is so dim it is almost useless (unless you happen to be a space weed... XD), and the problem with nuclear energy is that you need to bring there (or mine there) some elements to act as fuel. While it can be safely assumed that the first stages of colonization in Titan were not 100% efficient, so they might have burned a lot of methane losing 1/4 of the energy produced, I think this kind of stuff is important for the other, smaller habitats in Rimward. Because, essentially, when you have nothing else, you will end up using whatever you have, even if the output is only 5% of the total energy produced. Some energy beats no energy at all!
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Sun, 2012-07-29 10:59
Dr. Black Dr. Black's picture
No energy beats negativ energy
The problem, if I understand crizh right, is that you are get no energy in the process. It needs more energy to crack the water and produce oxygen than you got by burning the methane with the oxygen. This is only feasible if you have a other power source (like a fusion reactor) and want convert the energy in a transportable form. You did not get only 20 % or so of the produced energy, you have to inject more energy than you get out. Of course you produce hydrogen in this process, but I guess it is quite useless because it needs oxygen to be converted into energy.
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Sun, 2012-07-29 20:29
NewAgeOfPower NewAgeOfPower's picture
So, are we going to see
So, are we going to see massive ret-cons now? :D
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Sun, 2012-07-29 22:12
jackgraham jackgraham's picture
NewAgeOfPower wrote:So, are
NewAgeOfPower wrote:
So, are we going to see massive ret-cons now? :D
"Massive retcons" might be exaggerating it. What I'm taking away from this is that CH4 + electrolyzed O2 remains handy as a way of storing power -- especially for rocketry, which, unlike many of the battery/reactor-based alternatives mentioned, requires thrust mass. What we should probably be redacting, though, is any mention of hydrocarbons being used in stationary power plants. They should be described as refineries, not power generating stations. The figures Crizh brought rule the latter out.
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Mon, 2012-07-30 03:34
750 750's picture
Would it be possible to use
Would it be possible to use something other than Oxygen? https://en.wikipedia.org/wiki/Oxidizing_agent
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Mon, 2012-07-30 05:20
Arenamontanus Arenamontanus's picture
750 wrote:Would it be
750 wrote:
Would it be possible to use something other than Oxygen?
Oxygen is a very handy substance: there are a few others in the Titan environment, but I think it is the one that gives the most energy when oxidizing something. Carbon, nitrogen, and hydrogen, the most prevalent atoms, can react to each other. But a cursory check in my chemistry tables doesn't find any good high energy reactions that beat making carbon dioxide or water. Nitrogen compounds famously can become pretty energetic, but most work best when there is oxygen to oxidise remaining hydrogen and carbon.
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Mon, 2012-07-30 06:18
Decivre Decivre's picture
jackgraham wrote:What we
jackgraham wrote:
What we should probably be redacting, though, is any mention of hydrocarbons being used in stationary power plants. They should be described as refineries, not power generating stations. The figures Crizh brought rule the latter out.
I don't know, I could see hydrocarbons being an interesting form for solar power generators to convert drawn energy into. Unfortunately, Titan is too far away for that to be feasible. However, biological methane manufacturers are quite common on Earth. I wonder if it would be a possibility for the Titanian caribou to be used as a means of producing methane in ranches, which could then be used for energy purposes. Or other methods, such as bacteria or mold farms. Through water cracking, it's infeasible, but there are other ways to get your hydrocarbons.
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Mon, 2012-07-30 07:24
750 750's picture
Methane production is not the
Methane production is not the issue, the place has rivers off it forming naturally. The issue is that of finding something to burn/oxidize it with...
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Mon, 2012-07-30 08:39
Decivre Decivre's picture
750 wrote:Methane production
750 wrote:
Methane production is not the issue, the place has rivers off it forming naturally. The issue is that of finding something to burn/oxidize it with...
That makes it easier. Organisms are perfect for producing oxygen! Now to find something for them to metabolize….
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Mon, 2012-07-30 09:00
crizh crizh's picture
Something to Metabolize
Organisms are indeed good at releasing Oxygen from Oxides. All we would need would be an Oxides, water for example, and a source of free energy to power the reaction......
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Mon, 2012-07-30 16:05
NewtonPulsifer NewtonPulsifer's picture
Methane in the atmosphere of
Methane in the atmosphere of titan would help reduce the amount you'd need to carry in your tank. The atmosphere of Titan is 1.4% methane, 0.1-0.2%, and around 0.1% other (all flammable when you add an oxidizer). The atmosphere of titan is about 4.5 times thicker than earth at sea level, so you can get a bunch of atmosphere into your combustion engine or fuel cell that way (volumetric efficiency) (denser atmosphere plus lower temperature increases relative density of atmosphere). In addition, 1 mole of methane uses 2 moles of O2. So on earth if you're burning methane you need 2 moles of O2 per mole of methane. Other way around on titan, so having less in the atmosphere doesn't throw your ratio out of whack too badly. Also, having an atmosphere 4.5 times thicker means you need that much less lift for your aircraft, so you could get a lot of lift for a small lifting surface (wing). Insulation/heating would be a big deal/problem, though. 4.5 times thicker atmosphere at only 18.5 degrees Celcius above the temperature where the nitrogen in the atomosphere turns liquid would mean you lose heat really quickly. This is one reason you'd want to use a fuel cell or combustion engine - plenty of nice waste heat to warm the craft and the passengers. A battery plus electric motor could be too efficient. You'd end up wasting your charge just running a heating coil.
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Mon, 2012-07-30 18:23
crizh crizh's picture
Heating
You realize that a superconductor with 100 MJ in it and 100MJ worth of Oxygen (pretty trivially stored as a liquid on Titan, so that's one upside) to react with atmospheric Methane will both produce exactly the same amount of heating? You're going to need amazing insulation to prevent you turning into an instant popsicle which means that any waste heat your equipment produces is a bad thing. Your vehicle or dome will rapidly turn into an oven and you'll end up having to use the external atmosphere to bleed away the excess heat. So either your combustion engines are inside and produce waste heat you have to radiate away or you keep them outside where the waste heat is just waste. Either way it is waste and inefficiency. Once you've generated electricity from your fusion plant every transformative step you take that doesn't involve superconductors wastes some of it. Sticking it straight in superconducting batteries is the best and cheapest option unless there is another power storage method that is several orders of magnitude more 'power dense'. Like Antimatter. I was proposing Metallic Hydrogen as another potential storage medium but it might be only five times more effective than superconducting batteries. At that level you might find that an inefficient process for creating MH makes the whole idea moot. Although as MH might itself be a room temperature superconductor that might make storing it a lot easier than Antimatter. Although Metallic Antihydrogen might be worth investigating... [As an aside I was glancing at the rules for Antimatter rockets and noticed that they are just Metallic Hydrogen rockets with 1% AM added to the mix to boost thrust. I'm pretty sure that 1% is nonsense because that would increase thrust by a factor of 72,000 or thereabouts.]
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Tue, 2012-07-31 16:48
NewAgeOfPower NewAgeOfPower's picture
crizh wrote:
crizh wrote:
I was proposing Metallic Hydrogen as another potential storage medium but it might be only five times more effective than superconducting batteries. At that level you might find that an inefficient process for creating MH makes the whole idea moot. Although as MH might itself be a room temperature superconductor that might make storing it a lot easier than Antimatter. Although Metallic Antihydrogen might be worth investigating... [As an aside I was glancing at the rules for Antimatter rockets and noticed that they are just Metallic Hydrogen rockets with 1% AM added to the mix to boost thrust. I'm pretty sure that 1% is nonsense because that would increase thrust by a factor of 72,000 or thereabouts.]
It is noted these rockets are heavily modified and are unable to operate without Antimatter- perfectly reasonable and not nonsense ;p It is unknown what properties Metallic Hydrogen possesses at STP; it is quite likely it isn't even stable at STP. I agree, once you have superconducting batts, using chemical power storage is ALMOST nonsense... almost. A superconducting battery probably is dramatically more complex than your average fuel cell... And requires very rare resources (especially on metal-poor Titan) whereas your fuel cell can be simplified dramatically, and if one is willing to tolerate inefficiencies requires practically no rare elements at all!
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Tue, 2012-07-31 18:17
ProxyKlee ProxyKlee's picture
Methanotrophs
What about using nitrates as oxidizers for methane? If archaea microbes can do anaerobic oxidation of methane (AOM) in vivo couldn't transhumans do it in vitro? Nitrifying bacteria in human waste recycling systems could produce the nitrates. However, I don't know what is exactly needed to get methane and nitrate to react outside of a biological system. It might be more difficult or inefficient than the current issue of burning methane on Titan.
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Tue, 2012-07-31 19:19
crizh crizh's picture
NewAgeOfPower wrote:
NewAgeOfPower wrote:
It is noted these rockets are heavily modified and are unable to operate without Antimatter
Uh, where? I did some poking about and I think the energy density of the fuel in the Space Shuttle's booster rockets is about a sixth of that of TNT. If you were to mix it with 1% AM as it came out the thrusters you could reduce the boosters down to something 15mm long by 1.2mm in diameter. (My engineering skills are non-existent but I'm pretty sure that's in the ball park. Fuel at .73MJ/kg mixed with 1% of fuel at 18000000 GJ/kg. That's like 10 zeros of difference right there.) ---- That's kinda what I meant about MH being a potential room temperature superconductor. You wouldn't need to come up with some elaborate way of extracting stored power from the MH itself. You could just make superconducting batteries out of it, no exotic elements required... And no, from what I've read fuel cells are a pain in the arse. If you could make a superconducting battery out of plain old Hydrogen it would be spectacularly simpler. You could probably exploit quantum-locking to make magnetic stabilization of the MH self-sustaining and very low overhead.
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Tue, 2012-07-31 19:35
crizh crizh's picture
ProxyKlee wrote:What about
ProxyKlee wrote:
What about using nitrates as oxidizers for methane? If archaea microbes can do anaerobic oxidation of methane (AOM) in vivo couldn't transhumans do it in vitro? Nitrifying bacteria in human waste recycling systems could produce the nitrates. However, I don't know what is exactly needed to get methane and nitrate to react outside of a biological system. It might be more difficult or inefficient than the current issue of burning methane on Titan.
Is producing Nitrates not going to have an energy cost? If bacteria make them they still have to get the energy from somewhere, which in human habitats is going to eventually turn out to be a fusion plant of some description. Unless there are vast amounts of Nitrate lying around on Titan, which I don't think there are, then you have the same problem, any energy you extract from the system is energy you had to put into it in the first place to create one of the reactants.
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Tue, 2012-07-31 22:33
NewAgeOfPower NewAgeOfPower's picture
crizh wrote:NewAgeOfPower
crizh wrote:
NewAgeOfPower wrote:
It is noted these rockets are heavily modified and are unable to operate without Antimatter
Uh, where? I did some poking about and I think the energy density of the fuel in the Space Shuttle's booster rockets is about a sixth of that of TNT. If you were to mix it with 1% AM as it came out the thrusters you could reduce the boosters down to something 15mm long by 1.2mm in diameter. (My engineering skills are non-existent but I'm pretty sure that's in the ball park. Fuel at .73MJ/kg mixed with 1% of fuel at 18000000 GJ/kg. That's like 10 zeros of difference right there.) ---- That's kinda what I meant about MH being a potential room temperature superconductor. You wouldn't need to come up with some elaborate way of extracting stored power from the MH itself. You could just make superconducting batteries out of it, no exotic elements required...
Is Metallic Hydrogen a room temp superconductor or not? The Authors probably have decided it is not. Yes. This is why courier boats can approach 1% the speed of light- their drives are absurdly efficient compared to standard plasma/fusion torches.
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Wed, 2012-08-01 05:33
crizh crizh's picture
Superconductor
I don't think the dev's have decided one way or the other, I'd love to hear their opinions. From what I've read it seems pretty likely that MH is superconductive all the way up to around 290K which would make for some pretty cool tech. Obviously I'm just spit balling here, throwing out interesting ideas that I think would be cool not trying to tell other people what cannon ought to be. ---- On the subject of the anti-matter that was exactly my point. Anti-matter drives are absurdly efficient. What I was trying to say was that 1% seems too big a number. It's a minor issue but for accuracies sake it needs to be much, much smaller than that. Maybe I don't know what I'm talking about, sometimes I find myself thinking round in circles and talking myself out of a position. That table just makes my head hurt, it's so badly wrong, every time I look at that page I tie myself in mental knots trying to extract some sort of sense out of it. I'm a big fan of Traveller:New Era's Fire, Fusion and Steel design supplement, which frankly makes me a ridiculous nerd, but once you're used to designing firearms and vehicles using real equations of motion it becomes difficult to look at something that isn't 'real' without wincing. edit Sorry, forgot. What was the source for the 'heavily modified' thing?
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Fri, 2012-08-03 02:09
NewAgeOfPower NewAgeOfPower's picture
1% is fine. You still have to
1% is fine. You still have to cart around 99% of your Reaction mass. Just because a drive has an ISP 10 times greater than the next drive doesn't make it impossible, or even extremely complex (other than AM production/storage/transport). If MH was room temp superconducting = canon, then there wouldn't be a need for the Methane-Fueled Aircars (Sunward, Canon) or this entire discussion we're having here. I'm sure there are other instances of Hydrocarbon-fuel usage in other books, this is the one I thought of immediately.
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Fri, 2012-08-03 07:12
crizh crizh's picture
Confession
I admit I have pretty much ignored Mars as part of the setting because it bores me. Actually I'm not exactly excited about the entire Inner System. However, the point of this thread is should such things exist in canon at all? Methane fueled aircars are just as much rubbish as Titan's Methane power generation network. Mars is still 60 years from having a breathable atmosphere. The difference between turbines and rockets is that turbines require a certain minimum percentage of atmospheric Oxygen to operate. As the vast majority of Mars still doesn't have any and the areas that do may not have sufficient burning Methane doesn't seem like an optimal method of 'storing' energy. As batteries are more efficient than that particular form of stored chemical energy by AF10 it strikes me as lunacy to be wasting as precious a resource as Oxygen on an attempt to be cool. They've got an entire planet to blanket in Oxygen, I'm sure they've got better things to do than waste it on outmoded methods of energy storage.
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Fri, 2012-08-03 12:15
NewAgeOfPower NewAgeOfPower's picture
So we're agreed that an 1% AM
So we're agreed that an 1% AM torch is just a matter of gross structural engineering (once you have the AM production/storage/transport down...)? IIRC, the authors waved Methane-burning cars off as artificial ecological engineering, by attempting to increase the greenhouse effect on Mars through incentives for creating CO2.
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Sat, 2012-08-04 08:35
crizh crizh's picture
Greenhouse
Is Methane not a better greenhouse gas than CO2? You would be better just releasing the Methane... Edit 72x stronger according to Wikipedia....
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Sat, 2012-08-04 10:32
NewAgeOfPower NewAgeOfPower's picture
crizh wrote:Is Methane not a
crizh wrote:
Is Methane not a better greenhouse gas than CO2? You would be better just releasing the Methane... Edit 72x stronger according to Wikipedia....
LOL! Maybe they dislike the air smelling weird? Or that Methane, unlike C02 disintegrates more rapidly as Oxygen levels are increased (which will be going through the roof as terraforming proceeds?)
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Sat, 2012-08-04 10:53
Decimator Decimator's picture
Methane doesn't actually have
Methane doesn't actually have an odor. The stink of natural gas isn't natural gas at all, it's Methanethiol, an additive so people can smell the gas and not get blowed up.
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Sat, 2012-08-04 10:55
NewAgeOfPower NewAgeOfPower's picture
Decimator wrote:Methane doesn
Decimator wrote:
Methane doesn't actually have an odor. The stink of natural gas isn't natural gas at all, it's Methanethiol, an additive so people can smell the gas and not get blowed up.
Thanks, Decimator. I learn something new every day. I just got School'd... no, I just got Decimated. :D
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Sat, 2012-08-04 11:03
crizh crizh's picture
Nothing of the sort
It's not like that though. We're coming together here as a community to try and create a shared vision of how this particular future might operate as accurately as possible. Almost everything that Arenamontanus posts makes me feel both incredibly stupid and significantly more informed.
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Sat, 2012-08-04 16:01
Arenamontanus Arenamontanus's picture
crizh wrote:Almost everything
crizh wrote:
Almost everything that Arenamontanus posts makes me feel both incredibly stupid and significantly more informed.
Aww, thanks! :-) (Of course, now I need to say something smart and informative... hmm, extracting energy from quantum entanglement? http://www.technologyreview.com/view/428670/entangled-particles-break-cl... - no, it is not going to be a viable power source for a car.)
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Sat, 2012-08-04 18:47
athanasius athanasius's picture
why burn?
there is a problem linked with combustion in space, a combustion engine is competing with humans for oxigen use. By EP seetting a big issure is life support for overcrowd habitble space, if you burn something you are stealing brethable... Methane is a primary source of useful carbon for structural nanutube an other diamondoids, the excess H can be conserved for reaction mass for rockets and biological use. Titanians have also good resources for thinking abouth Carbon Nitrogen Oxigen catalized HH fusion, openig a market for He3 export and unlimited energy (for more about CNO cicle http://en.wikipedia.org/wiki/CNO_cycle)
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Sun, 2012-08-05 02:13
NewAgeOfPower NewAgeOfPower's picture
crizh wrote:It's not like
crizh wrote:
It's not like that though. We're coming together here as a community to try and create a shared vision of how this particular future might operate as accurately as possible. Almost everything that Arenamontanus posts makes me feel both incredibly stupid and significantly more informed.
LOL. I'm making a joke with Decimator's name... it's too easy to make a cheesy joke.
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Tue, 2012-08-07 01:32
NewtonPulsifer NewtonPulsifer's picture
crizh wrote:You realize that
crizh wrote:
You realize that a superconductor with 100 MJ in it and 100MJ worth of Oxygen (pretty trivially stored as a liquid on Titan, so that's one upside) to react with atmospheric Methane will both produce exactly the same amount of heating?
Sure. We have from pg. 300 a descripton of battery tech of "room-temperature superconductors with 25 times the capacity of the best batteries in common use in the early 21st century." I took that to mean my 31 gram NiMH AA battery (holds 3 watt-hours) would hold 75 watt-hours in my EP universe. Maybe 2.5 kilowatt hours in a 1 kilogram pack. Call it 8 megajoules per kilogram. Gasoline is about 45 megajoules per kilogram, methane is 55.6 megajoules per kilogram. Carnot efficiency for say a continuous detonation engine can reach 84%, which is probably an 80% or so thermodynamic efficiency at a 1950 degree celcius hot side temperature and -179 degree celsius cold side temperature. So that's 16% waste energy. Not a bank breaker I'd say. So normally in an oxygen rich atmosphere there's a fuel vs battery energy density advantage of almost 7 to 1 against these superconducting batteries. Unfortunately, on Titan you need to carry much of your own liquid oxygen, and mass-wise you need 4 times as much oxygen as methane. So our advantage is quite a bit smaller if you carry your own methane and oxygen - 1.4 to 1. Although you're likely to not need to carry the methane - turns out the Huygens probe data shows methane at more like 3.5%, Wikipedia's data is outdated. Still, 1.75 to 1 isn't a huge improvement.
crizh wrote:
You're going to need amazing insulation to prevent you turning into an instant popsicle which means that any waste heat your equipment produces is a bad thing. Your vehicle or dome will rapidly turn into an oven and you'll end up having to use the external atmosphere to bleed away the excess heat. So either your combustion engines are inside and produce waste heat you have to radiate away or you keep them outside where the waste heat is just waste. Either way it is waste and inefficiency.
So, yes, we're wasting 16% with heat engines external to the passenger/pilot area. We can even have a relatively crappy insulation (so remarkably good instead of amazing) in our craft because we can move some waste heat to the passenger/pilot compartment. This reduces cost and engineering complexity. And you can dispense with an advanced airlock (heatlock?). It's okay if you let some heat out when you exit the craft. Also, potential top speed is better for a continuous detonation engine (multi-mach) vs. an electric turboprop (probably mach 0.9). Why is this a big deal? The speed of sound is 60 percent less on Titan than on Earth. If time=money the faster craft might be cheaper, even if its fuel costs are higher.
crizh wrote:
Once you've generated electricity from your fusion plant every transformative step you take that doesn't involve superconductors wastes some of it. Sticking it straight in superconducting batteries is the best and cheapest option unless there is another power storage method that is several orders of magnitude more 'power dense'.
I think wasting 16% is fine. I realize there's some more efficiency wastage on top of that, as there's a cost to separate oxygen from water ice. It's still not a big deal. People buy vehicles nowadays with big differences in energy.fuel efficiency because some customers care about it more than others. It may not matter for certain types of vehicles, and the battery design would be better. This is especially true of ground vehicles. Aircraft carry total fuel load as much higher percentage of their mass vs. cars. This makes the battery mass disadvantage more of a problem. Not a big deal if 2% of your ground car is fuel vs. 14% for batteries. But if your aircraft is 40% fuel mass at 1 tonne, an equivalent switch to batteries for a titan aircraft would add 750kg (at least, because you might need more superstructure to support the weight, which means even more weight, which means you need more batteries because you're hauling more weight, etc. in a vicious cycle) and probably limit your top speed to .54 mach (Earth) while the heat engine aircraft can probably top out at mach 3.0 (Earth).
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Tue, 2012-08-07 01:57
NewtonPulsifer NewtonPulsifer's picture
athanasius wrote:there is a
athanasius wrote:
there is a problem linked with combustion in space, a combustion engine is competing with humans for oxigen use. By EP seetting a big issure is life support for overcrowd habitble space, if you burn something you are stealing brethable...
Ventilation rate is the key here. Carbon dioxide scrubbing is simple. On the space station, they use a regenerable system made of metal oxide. Just heat it after it reacts with the CO2 to release the O2. So its like running your car engine in a closed garage=bad. If there's big enough open areas with lots of air movement you're just fine. You'd want to have oxygen sensors scattered around so you don't get CO2 "hot spots", but it's doable to have oxygen using engines on habs at least. On a hab there'd probably be an extra tax on fuels that need oxygen to cover the scrubbing cost, so it probably wouldn't make financial sense. So batteries. I know in some sci-fi movies like Total Recall they made it out like oxygen was somehow expensive and your life support bill would be ruinous. It just isn't, though. If you have a nuclear power plant it is a drop in the bucket. Sure, a hab may have a hard limit on how much CO2 they can scrub depending on their scrubber design, but it's a very short term problem (doesn't take long to asphyxiate, of course). Its easy to add CO2 scrubbing capacity if you can fabricate even simple devices. You could even rapidly electrolyze water in a demand pinch. Real easy.
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Tue, 2012-08-07 10:42
crizh crizh's picture
On the contrary...
NewtonPulsifer wrote:
I took that to mean my 31 gram NiMH AA battery (holds 3 watt-hours) would hold 75 watt-hours in my EP universe. Maybe 2.5 kilowatt hours in a 1 kilogram pack. Call it 8 megajoules per kilogram. Gasoline is about 45 megajoules per kilogram, methane is 55.6 megajoules per kilogram.
I'm basing my arguments on substantially different numbers. Arenamontanus gave a figure of 1.8MJ/kg for modern lithium batteries. I could only substantiate 1.6 or so but I've only got access to Wikipedia as a source. Using 1.8 as the basis for 10AF batteries we are looking at a figure of 45MJ/kg. Tanks of liquid Oxygen that we react with atmospheric Methane works out at 13.92MJ/kg. That's ignoring the weight of the tanks, conversion engines and any inefficiency losses. If there was a power density advantage to burning Oxygen I'd be the first to be proposing it as a more sensible tech for EP. The delta between mean atmospheric temperature on Titan and what is good for people is so great that I don't see you being able to reduce your insulation requirements much regardless of how much waste heat you produce. I suspect you need to be living in a virtual vacuum flask or be leaking so much energy to the environment that you've got bigger problems than what sort of energy storage paradigm you are going to be using. It's been twenty years since I did any chemistry so I'm no expert but I'm pretty sure that you're going to need to warm your Oxygen and Methane up to normal temperatures to properly react them together. There is a good use for any waste heat but I wouldn't be surprised if the waste heat won't be enough. I suppose if I put my mind to it I could work out how much energy it would take to do that. That process alone might eat substantial portions of the useful work you can get out of the reaction. Forget that. It's about 295kJ/kg I think. Hardly significant. Unless my maths sucks.... No more than 2% so easily covered by waste heat.
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Tue, 2012-08-07 11:37
NewtonPulsifer NewtonPulsifer's picture
crizh wrote:NewtonPulsifer
crizh wrote:
NewtonPulsifer wrote:
I took that to mean my 31 gram NiMH AA battery (holds 3 watt-hours) would hold 75 watt-hours in my EP universe. Maybe 2.5 kilowatt hours in a 1 kilogram pack. Call it 8 megajoules per kilogram. Gasoline is about 45 megajoules per kilogram, methane is 55.6 megajoules per kilogram.
I'm basing my arguments on substantially different numbers. Arenamontanus gave a figure of 1.8MJ/kg for modern lithium batteries. I could only substantiate 1.6 or so but I've only got access to Wikipedia as a source. Using 1.8 as the basis for 10AF batteries we are looking at a figure of 45MJ/kg.
I'd 100% agree with you if the book had "room-temperature superconductors with 25 times the capacity of the best batteries in [s]common use in[/s] the early 21st century." The best battery in my house is a lithium polymer in my phone and one of my laptops. It is certainly not something I can pick up at the local superstore so I'd hesitate to call it "common", it is custom/special order (and built-in). I'd say the calculation should be based on an interchangeable battery you can pick up at Walmart. And to me that would be stretching it, as even Walmart sells very niche batteries (not at all commonly used). Even then the Li-Ion cell phone batteries available at Walmart tend to only beat the NiMH total energy density by maybe 25% (say a user replaceable cell phone battery); their big advantage is they have triple the voltage (3.6v vs 1.2v). So our separate EP universes definitely have different assumptions on just how good these batteries are. Looks like this thread has turned into a more general "energy storage" discussion. I apologize if this is too much of a threadjack.
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Tue, 2012-08-07 12:24
crizh crizh's picture
Mmmmm
I just ripped the battery out of my wife's HTC Bravo. It's 30g and 5.18 Wh. That translates to 15.54MJ/kg by 10AF. That's 11% better than Oxygen ignoring any inefficiency from combustion etc. I'm pretty sure the battery in the Bravo is far from state of the art in the consumer space. edit Of course 'early' could easily be construed as meaning anything up to 2033 but that's kind of pushing it a bit.
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Tue, 2012-08-07 14:37
NewAgeOfPower NewAgeOfPower's picture
The thing is, electrical
The thing is, electrical-mechanical conversion easily exceeds 95% efficiency, while chemical-mechanical conversion is often under 30% efficiency. Of course, combined cycle powerplants can achieve over 70% efficiency, but that is still quite some loss...
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Tue, 2012-08-07 22:54
NewtonPulsifer NewtonPulsifer's picture
Carnot efficiency is the
Carnot efficiency is the theory that determines the theoretical maximum efficiency of a heat engine (like a steam, gasoline piston, turbine, or thermoelectric device). It goes up the greater the difference between the hot side and the cold size. So for combustion engines the hotter the boom and the colder the air, the more efficient it is. 30% thermodynamic efficiency is about right for a gasoline engine running on earth. The Audi 3L diesel engine was 47% thermodynamically efficient. That same car running at -179C would be like 62% efficient, but of course the Audi would be as brittle as glass at that temperature :) If you could get the heat of the engine combustion increased without melting it by using exotic materials (do-able now but unfeasibly expensive) with things like ceramic engines, you can improve even further. Then if you throw things in like combustion technologies that only exist in the lab right now (like detonation wave engines - sort of like the scramjet version of a turbine) things get even better. I guess my point is things are very likely to improve with regards to combustion engines in the next 100+ years. We're at maybe 55% of carnot efficiency now with diesel engines (maybe 66% for stirling engines), but could reach 84-90% in the future with better technology. Even just being able to use the advanced materials readily available in Eclipse Phase one could build a much better combustion engine just using 2012 tech by going much hotter on the combustion. Anyway, reaching 80%+ efficiency on Titan using a heat engine is do-able using Eclipse Phase level tech, partly because Titan is so dang cold. EDIT Top speed is still going to be a struggle vs. combustion engine with a battery powered aircraft.
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Tue, 2012-08-07 22:50
NewtonPulsifer NewtonPulsifer's picture
Cracking Nitrous Oxide ice instead of Water?
You know, one way to have a sort of "fossil fuel" industry on Titan is to use Nitrous Oxide ice. You mine it. It may not be super common, but even if you found an area with 1% Nitrous Oxide you could strip mine it. I have no idea how much energy it takes to disassociate the oxygen from the Nitrous Oxide, but its got to be less than cracking water. The catalytic converters in our cars do it. You just need high heat and the catalyst. Well, high enough heat alone will do it. Anybody know how much energy it takes to crack Nitrous Oxide?
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Wed, 2012-08-08 04:11
NewAgeOfPower NewAgeOfPower's picture
NewtonPulsifer wrote:
NewtonPulsifer wrote:
Even just being able to use the advanced materials readily available in Eclipse Phase one could build a much better combustion engine just using 2012 tech by going much hotter on the combustion. Anyway, reaching 80%+ efficiency on Titan using a heat engine is do-able using Eclipse Phase level tech, partly because Titan is so dang cold.
I remember first grinding out Carnot mathematics in highschool, AP Physics. Anyways, yes, on Titan, efficiency could certainly be dramatically higher than on Earth- however, many materials that could be used to build such an engine might be incredibly rare on Titan...
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Wed, 2012-08-08 13:43
crizh crizh's picture
Higher efficiency
Is it cold enough for efficiency to reach 112%? edit You can read that as 143% if you include the amount of energy wasted cracking the water in the first place. That is assuming that cracking water is 100% efficient. edit 2 This is a stupid argument. It is 14% more efficient to carry both the liberated Hydrogen and Oxygen from cracking water than it is to carry just the Oxygen and react it with atmospheric Methane. And that is still no more efficient than batteries.
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Wed, 2012-08-08 14:10
athanasius athanasius's picture
NewtonPulsifer wrote:I have
NewtonPulsifer wrote:
I have no idea how much energy it takes to disassociate the oxygen from the Nitrous Oxide, but its got to be less than cracking water.
This idea is good, N2O3 or similar nitrous oxide are very rich of energy and are used for boosting combustion. If you can find a lot of them you can create a fossil fuel industry on Titan! I think is a poor buisnes, having He^3 and D you change the enrgy equation shifting from chemical energy to nuclear energy, with a lot of energy is possible to create very energy rich compounds for storage and more "convertion friendly" as methanol: [url]http://en.wikipedia.org/wiki/Reformed_methanol_fuel_cell[/url] [url]http://en.wikipedia.org/wiki/Methanol[/url] This kind of fuels are used for fuel cell tipe energy conversion, even today we can attain 90% efficency with some variant so i don't see a brooming car on Titan for mass transport but a much less funny electric rover (Apollo11 like) or an enclosed version. EP nuclear battery are a more expensive solution but a veicle can have unlimited range, for paranoid maximum energy efficency searcher like me you can combine the two usinf methanol as energy accumulator for capture the excess energy when you are not driving and take the thermal for wharming the veicle (if possible make the hull with a peltier cell and recover some of that precious therma energy ;) ) Today the CH4 H2O economy is very interesting because we can't have a more efficent energy source (no fusion) and nuclear battery are very long lasting but power/mass inefficient.
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Sat, 2012-08-11 18:32
NewtonPulsifer NewtonPulsifer's picture
Nitrous Oxide viability
Just wanted to update - nitrous oxide nets 82.05kJ (kilojoules) per mol when decomposed. Similary Nitrogen Dioxide, Nitrogen Monoxide, and Nitric Oxide all are net positive.Wikipedia Standard Enthalpy Change of Formation So it is an energy source one could "mine" on Titan that would require no energy input to "crack". Assuming there's a profit in collecting it, it could be Titan's version of "fossil fuels". It would be solid (ice) at ambient temperatures on Titan, as well as dissolved in liquid water under the crust. It will decompose exothermically into nitrogen and oxygen in the presence of heat (catalysts can lower the temperature and speed up the rate), so you don't need any other fuel in a pinch. Ideally, one would react the liberated oxygen with methane/ethane (available in rivers and giants lakes of it on Titan) to get even more energy.
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Sat, 2012-08-11 19:47
crizh crizh's picture
Good
All we need now is some evidence of the existence of major deposits of NOx or similar compounds on Titan...
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