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For kbd512 re #350
Thank you for the reminder of the need to compare Apples to Apples.
I am calling for real numbers instead of hand waving in this forum.
The method reported for production of some result using a molecular jiggling method is one thing.
A method that produces the same exact result using another method can be compared to the first one.
Each method will have advantages and disadvantages.
One method will consume less energy than the other to produce a kilogram of product.
It seems possible to me that this forum is capable of placing into the public record information that is precise and actionable.
Update: I just renamed a topic in hopes our members will help to build up a collection of knowledge about CO2 in the Mars context.
https://newmars.com/forums/viewtopic.php?id=10930
If you have time, please create posts that contains all the information a person or group would need to implement one of the methods to work with CO2. Please keep each post tightly focused so that the reader can concentrate on one particular idea.
The jiggly method discovered by the folks at the university in South Wales might turn into an entire industry.
There are already entire industries developed or developing around carbon capture.
There are entire industries developed or developing around using pure carbon.
The NewMars environment can draw upon all existing resources and blend them into something a reader can use to solve a problem or create an entire infrastructure on Mars.
(th)
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Energy requirement, mass of equipment, plus foot print volume required to send to Mars.
Repairability risk of parts not mechanical.
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tahanson43206,
I went back and actually read all of the Nature article he posted most recently. I was wrong. That one is actually related to solid Carbon production, so I'll study it in greater detail. The prior articles he's posted were related to CO production, which is great if the goal is syngas for liquid fuel production, but not for elemental Carbon. I can easily understand why he places great emphasis on liquid fuel production, though, since those are the forms of energy we consume the most of. Nearly all of the machines that do the real work necessary for cities to exist are burning diesel or natural gas, so he would rightly view production of those fuels as of greater importance than coal, which remains relatively abundant. The problem, at least as I see it, is that even coal is finite. Our ability to completely replace extracted coal with pure Carbon from CO2 would mean as long as we have access to CO2 and thermal energy from sunlight to capture the CO2, our synthetic coal supply is functionally inexhaustible. Most of the nasty stuff in coal (Sulfur, heavy metals, and radioactive elements) would no longer be spewed into the air, either.
Here's a Science Direct article using a different Gallium alloy and ceramic catalyst that also requires no external energy input to drive the reaction:
Room-temperature CO2 conversion to carbon using liquid metal alloy catalysts without external energy input
Regardless, I think I'm on fairly stable scientific ground when I assert that any chemical process which does not require any kind of external energy input is likely to be more efficient than one which does require external energy inputs, provided that there's not some other kind of serious "gotcha", such as absurdly low selectivity or an unstable catalyst or extreme energy input to obtain the catalyst in usable form or to construct the chemical reactor device. If the chemical reactor to break CO2 into Carbon and Oxygen had to be made from pure Platinum, that might make the process economically infeasible, even if the tech worked exactly as advertised without using any energy input.
I can think of various other similar reactions requiring no energy input, though.
If you drop a chunk of Magnesium Oxide (MgO) into Fluorine, the Fluorine is so electro-negative that it will break the bond Oxygen has with Magnesium, strong as it is, without any energy input at all, creating MgF2 in the process. Similarly, Magnesium metal will immediately and rapidly generate Hydrogen gas when dropped into water without further energy input of any kind.
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For kbdt12 re #353
Thanks for going back to study the Nature article, and for reporting your findings.
Pure Carbon sure does sound (to me at least) like a valuable commodity.
It can be used as feed stock for all sorts of useful compounds, or it could just be burned in air as a convenient energy store all by itself.
On Mars it seems to me that CO and O2 are more attractive for transportation because they are so easy to make and so easy to use.
It very well might be desirable to make methane or even something as complex as gasoline for special missions, but the oxygen still has to be carried along.
I've set up a topic for collecting knowledge about working with Carbon. I hope that a few members will be inspired to create posts that would be useful to future readers.
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tahanson43206,
If you have to carry the fuel and oxidizer with you, as you would on any planet except Earth, then pure Carbon doesn't require extra Oxygen atoms to combine with the Hydrogen atoms.
Kilograms of Pure Oxygen for Complete Combustion of 1kg of fuel:
Pure Carbon (32.8MJ/kg; 1kg powdered graphite = 1.05-1.15L; 28.52MJ/L): 2.67kg (2.34L); 3.49L ttl vol, 9.40MJ/L incl O2
Gasoline (44-46MJkg; 1kg = 1.2-1.4L; 32.86MJ/L): 2.3-2.7kg (2.37L); 3.77L ttl vol, 12.20MJ/L incl O2
Kerosene (43-46MJ/kg; 1kg = 1.25L; 36.8MJ/L): 2.93kg (2.57L); 3.82L ttl vol, 12.04MJ/L incl O2
Diesel (42-46MJ/kg; 1kg = 1.16-1.2L; 38.33MJ/L): 3.4kg (2.98L); 4.18L ttl vol, 11.00MJ/L incl O2
Methane (50-55.5MJ/kg; 1kg LCH4 = 2.36L; 23.52MJ/L): 4kg (3.51L); 5.87L ttl vol, 9.45MJ/L incl O2
Hydrogen (120-142MJ/kg; 1kg LH2 = 14.1L; 1L = 10.07MJ/L): 8kg (7.01L); 21.11L ttl vol, 6.73MJ/L incl O2
LOX is 1,141kg/m^3 or 1.141kg/L
What can we conclude from that?
1. LH2 is a pretty pedestrian fuel when you need to store the cryogenic oxidizer, too.
2. There's not much difference between pure Carbon powder and Methane, except that making Methane is a lot more difficult and requires a lot more energy and technology than bubbling collected CO2 through a column of liquid Gallium eutectic. You need equipment to collect both H2O and CO2, a Sabatier reactor, a reverse fuel cell, and a really good electrical power source.
3. You do get 17% to 30% more energy per total volume by combusting diesel / kerosene / gasoline, in comparison to Carbon powder, but if you thought making Methane was energy intensive, you're going to need to add a lot more energy-intensive equipment to your chemistry set, and of course, you only get that additional energy by combusting it using additional O2 mass, which means you need to make more O2 from some combination of H2O and CO2. It's a pretty safe bet that all those additional chemical reaction steps will cannibalize whatever gains a dense liquid hydrocarbon fuel provides.
4. The relative complexity of obtaining LCO2 feedstock, on Earth or Mars, is pretty low. It's everywhere in the atmosphere and in the oceans here on Earth. Mars helps us out a bit by having a nearly-pure CO2 atmosphere, but at absurdly low density. Speaking of absurdly low density, LH2 looks great, best of all fuels, except when you must consider the mass of the storage equipment, and then it doesn't look so hot.
5. Of all the fuels listed, and any other liquid hydrocarbon fuels that weren't, if you throw a kilogram of Carbon on the ground, here on Earth or on Mars, that same kilogram of pure Carbon fuel will still be there the next day. We can't make the same claim about any of those other fuels. Carbon doesn't require special storage of any kind. If storing a cryogenic oxidizer is a pain we'd rather not deal with, then why compound the problem with fuels which also have special storage requirements?
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For kbd512 re Post #355
Thank you for the overview of fuels, with details that should help a reader to compare them.
The single most important point in Post #355 (from my perspective) is the stability/storability of pure carbon.
A practical way of using pure carbon was pioneered by humans centuries ago... I'm thinking of steam but there are surely many other applications that NewMars members can think of, or modern search tools can help to identify them.
Steam might be adapted as a practical system for Mars. Water would be too precious to vent to the atmosphere, so water vapor would have to be collected after it is used. The cold atmosphere of Mars might allow for sufficient radiation of thermal energy, but that would mean a system to produce mechanical power would need an array of fins to condense the steam. That might be practical for a fixed installation. I suspect steam will not be used for transportation systems if competitive systems are available.
CO and O2 in gaseous form appear to me to by far the most practical energy storage systems for Mars.
I'll come back to re-read your post to see if you included that fundamental pairing in your study.
I'd like see this forum show practical designs for machinery for Mars, and those designs can include all the fuel combinations you listed and any that you omitted for reasons of space or time.
For twenty plus years this forum has accumulated high level 30,000 foot visions of what might be done on Mars. A few members have published the equivalent of practical suggestions, but those are not cataloged for easy lookup.
We only have a few members active in this epoch. I've described a project that will require a lot of thought and effort. With any luck at all we may attract new members who would be willing to help to build up a repository of knowledge.
The people who are going to explore and develop Mars are alive today. The Mars Society itself is providing opportunities for those individuals to publish and present work they've done to prepare for Mars. This forum has the potential to provide a gathering place for those individuals and others to work together to build teams that will transfer easily to missions, companies or organizations.
An example of the kind of practical knowledge I would like to see in this forum would be a series on CO and O2 that would include everything a planner/funder would need to create a family of transportation vehicles and related support services for Mars. The series would include specifications for extracting CO2 from the atmosphere and making CO and O2. the series would include specifications for storing the output at the manufacturing site and delivering quantities to distribution centers. The series would include design of vehicles of various kinds, including the 10 ton trucks that SpaceNut has shown us recently, and all manner of other useful vehicles. I can imagine this collection as part of the Projects category that SpaceNut created, with as many topics as are needed to organize the knowledge so it is easy to find and to use.
It should be obvious, but just in case someone is reading this for the first time, every vehicle and every power production machine that uses CO and O2 on Mars ** will ** require tanks for both fuel and oxidizer, just as any chemical rocket does on Earth today.
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tahanson43206,
Elemental Carbon and "CO", which is Carbon Monoxide, are two different chemicals with different properties. Elemental Carbon is a solid. It does not require a pressurized storage tank for bulk storage. Coal, which is mostly elemental Carbon, can be stored on the ground outside in the elements, because it's a solid. Carbon Monoxide and Carbon Dioxide are gases or liquids, dependent upon pressure and temperature, which does require pressurized storage tanks. Carbon Monoxide and Carbon Dioxide will both "freeze solid" when you get them cold enough, but again, you have to keep them cold, which generally implies a pressurized storage tank and cryocooler. Elemental Carbon, on the other hand, is a solid and remains a solid until it's combusted, which then forms Carbon Monoxide (partial combustion) or Carbon Dioxide (complete combustion).
Martian nights are so cold that Carbon Dioxide can and frequently does become a solid near the planet's surface, similar to water vapor becoming "frost" on cold nights here on Earth. For Carbon Monoxide to freeze, it has to be cooled to cryogenic temperatures well below what the ambient Martian environment provides at its North and South poles during the night. The described "freezing effect" is sufficient that frozen CO2, aka "dry ice", can be collected from the surface of Mars at night, even near the Martian equator during summer, for very modest energy expenditure. The dry ice is fed into an empty pressure tank, which then creates liquid CO2 (LCO2) after the tank is sealed and begins to pressurize as heat is applied. An electric heating element inside the tank would add heat to cause the dry ice to become LCO2 or SCO2. LCO2 is a dense liquid that's easy to pump, unlike dry ice. Adding a little bit more pressure using a bit more heat transforms the LCO2 into supercritical CO2 (SCO2), which does not require any pumping power to transfer the batch of collected CO2 from Storage Bottle A to Storage Bottle B, because supercritical fluids flow like gases. While LCO2 can also flow (expand) without pumping power if pressure is slowly released, so that it does not re-freeze from expanding too fast and isn't allowed to expand so much that it becomes a gas again, the speed of the flow is much more pronounced in SCO2, so tank fill / transfer operations can be very fast. For our purposes, though, LCO2 flow speeds are likely to be completely acceptable and required pumping power is very modest.
Powdered solid fuels burned by external combustion engines, such as SCO2 gas turbines, can have the solid fuel fed into the combustion chamber using CO2 gas to "fluidize" the powder. SCO2 gas turbines are external rather than internal combustion engines. The heat from burning this "synthetic coal" is indirectly fed into the SCO2 working fluid that drives the power turbine. Hot exhaust CO2 is recirculated into the combustion chamber to moderate the temperatures produced by combusting synthetic coal / elemental Carbon. The Allam-Fetvedt cycle burns coal powder or natural gas in an external combustion chamber that drives a SCO2 power turbine via a heat exchanger loop (exactly like a refrigerant loop) that carries hot expanding SCO2 through the power turbine, then back to a pump to repressurize the SCO2, and finally back through the burner. 95% of the gas fed into the combustion chamber is CO2, the remainder being pure O2 and coal powder or natural gas. The hot section of this "engine" is effectively a blow torch adding heat to a thermal power transfer fluid (SCO2) with density more closely comparable to liquid water than steam / water vapor. The 95% CO2 "atmosphere" in the combustion chamber is put there to soak up additional heat to dump into the working fluid and pumps responsible for SCO2 repressurization. This is the penultimate "lean burn" combustion engine. It does have a cold side heat sink, because like every other heat engine it has to, but it's as miserly as it possibly can be with the fuel and oxidizer.
The reason we would want SCO2 gas turbines for land vehicles is their incredible power density per unit weight and volume, as well as their ability to operate at extreme temperatures and pressures. The kerosene burning AGT-1500 conventional gas turbine that powers our M1 tank produces about 1,500hp (~1MW) and is so large that a relatively strong adult cannot pick up the turbine wheel (the rotating assembly that compresses air and expands combusted exhaust gases) with both hands because it's so large and heavy. The AGT-1500 engine's dry weight is 1,134kg, so about as heavy as a subcompact car. That same person can easily pick up a 1MW SCO2 turbine rotor with one hand, since it readily fits in the palm of their hand. The power density of the rotating machinery in a SCO2 gas turbine is "extremely extreme", meaning 1MW/kg and 10MW/L. Only nuclear thermal rocket engine core power density surpasses SCO2 gas turbine rotor power density. Large commercial nuclear reactors fall in the range of 100-200kW/L. There is no other kind of rotating or reciprocating engine with SCO2 turbine power density. The RS-25's high pressure Hydrogen turbopump's power density is about 33.8kW/kg, so even the most powerful rocket engine turbopumps, which are a type of conventional gas turbine used to force-feed propellants into liquid rocket engines, have a power density 10X lower than SCO2 gas turbines. However, SCO2 gas turbines also require other attached equipment such as heat exchangers and combustors, so overall power density is much lower than turbine rotor power density alone would suggest. However, power density for a full ceramic composite SCO2 gas turbine / heat exchanger / combustor package is on-par with a rocket engine turbopump. Since a rocket engine turbopump is only designed to feed propellants into a combustion chamber, that makes the SCO2 gas turbine more useful for powering non-rocket vehicles, particularly heavy ground vehicles like mining equipment.
For a mining truck, a SCO2 turbine would generate electricity used to drive electric motors directly powering the wheels, eliminating a lot of the heavy rotating machinery connected to the diesel piston engine of a more conventionally powered mining truck. If something happens to the engine or drive train of a conventional mining truck, that truck is a paperweight until the component is replaced. SCO2 would make the critical components compact and light enough that multiple engines could be carried for redundancy. A 10MW diesel engine weighs tens of tons, so there's only space and weight allocation for one of those diesel engines in the mining truck. A Mars mining truck could have quadruple redundant 10MW SCO2 turbine engines, but all four engines wouldn't come close to the weight and bulk of a mere 1MW diesel engine. Since solid Carbon isn't as energy dense as diesel fuel, the extra space and mass could be occupied by larger fuel and oxidizer tanks.
Anyway, I think I made my point about the various common forms and phases of Carbon and Carbon-Oxygen gases, as well as how we might use them on Mars in a more practical manner than any other fuel. We would definitely like to have Carbon-Hydrogen fuels if we can synthesize or extract them in useful quantities, but synthesizing and storing them is significantly more challenging. There's no way around that. If conventional gasoline or kerosene synthesis proves to be a "bridge too far" until the colony is more highly developed, we now have a simpler and less energy-intensive alternative that wasn't available before- fewer energy sinks, fewer pieces of equipment, fewer people to operate it, and fewer failure modes. Here on Earth we have easy access to enormous amounts of liquid water that simply doesn't exist anywhere else, so far as we know. Even if we find ice, we still have to extract, melt, purify, and transport the water. Since transportation cost will remain an issue for quite some time, why complicate fuel synthesis when you don't have to? The benefits of adding Hydrogen to Carbon are marginal when you have to expend additional energy to make the Hydrogen and attach it to the Carbon. The entire purpose behind creating chemical energy stores is to use them for other useful work unrelated to dumping energy back into the energy generating and storage systems. This is merely another way of saying that we don't create energy storage products to justify creating additional infrastructure required to create more of said energy products, because we know that energy invested into energy storage is always a losing proposition, unsustainable past the point where energy must be devoted to other uses such as purifying drinking water, food, shelter, clothing, etc. If obtaining 1kg of Uranium to fission in a reactor required expending the energy equivalent of 10kg of Uranium, then there would never be a commercial electric power plant powered by a fission reactor. That's effectively what Hydrogen synthesis entails on Mars. The only rational reason we would want to do something like that was if a Hydrogen powered rocket was the only feasible way to leave the surface of Mars to come back to Earth. Powering someone's personal car or home that way makes even less sense- something to be done only in the complete absence of more energy-input-favorable alternatives.
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For kbd512 re Post #357
This post seems (as I read it) to contain numerous points in support of using solid carbon as a chemical energy storage material in combination with oxygen.
I think that there might be enough knowledge in existence today to guide a person or a group toward design and construction of a practical combination of chemical processing services to supply the carbon and oxygen for a transportation or work system.
This forum is as good a place as any for a repository of that knowledge.
I am in favor of this repository, and willing to support a NewMars member who would like to build it.
Such a repository would NOT consist of hand waving or Rosy Scenarios. It would consist of proven examples of each technology, and exact steps needed to replicate whatever it is on Mars.
This forum has been in the fantasy business for two decades and unless something changes it will continue creating exciting visions for entertainment.
I consider CO and O2 to be chemicals that will inevitably become major players in the transportation and energy storage infrastructure on Mars, so I would like to see a knowledge repository in which their production and use are clearly defined so that a person or a group can replicate them on Mars.
A far more technically sophisticated individual or group might well elect to pursue the many advantages you've laid out, so a repository supporting an advanced technology would surely be of value.
(th)
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To make carbon monoxide, carbon must be burned in an atmosphere with limited oxygen. This releases about 20% of the heat released by complete combustion. The process that Kbd512 has described produces particles of carbon. So that is what we start with. Carbon monoxide has important uses of its own. One such use is the production of reduced iron. Making strong engineering bricks is another use we have noted. But it is a precursor to other more convenient fuels. For example:
CO + H2O + heat = CO2 + H2
2H2 + CO = CH3OH.
This is methanol. It is a clean burning liquid fuel that doesn't freeze until -97°C. We could store it in tanks on Mars with very little pressurisation. By using the appropriate catalyst, methanol can form dimethyl ether:
2CH3OH = H20 + H3C-O-CH3.
Dimethyl ether has been considered as a diesel substitute. It would make an energy dense rocket fuel that is less volatile than methane.
Last edited by Calliban (Yesterday 16:21:50)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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