Chemical Forums
General Forums => Personal Blogs => Topic started by: Enthalpy on October 01, 2022, 06:37:28 AM
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Hello nice people!
Some 40 years ago, newspapers and a book claimed that hydrogen would be the energy vector of our societies, produced by renewables, to replace the consumption of fossil fuels.
This hasn't happened, but as hydrocarbons got more expensive than renewables even before the embargo against Russia, some politicians want to revive to old idea.
I claim that lithium batteries have killed hydrogen storage meanwhile, and that very few uses justify hydrogen. Opinions welcome!
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The most visible evolution is the electric car, more generally terrestrial transports.
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Around 2000, many car manufacturers had projects with gaseous hydrogen in pressure tanks, possibly aided by adsorption, and fuel cells to feed electric motors.
I know only of two (2) gaseous car models on the market and never saw them on the streets. As opposed, dozens of battery car models exist, and in Germany I see one or more battery car in every small street.
The range of battery small cars suffices for many uses but not all. Customers often have an additional gasoline or hybrid vehicle for longer trips, which still emits CO2. Agro-fuels for them?
Range improves with better regenerative braking, and from lower drag. The visionary Tesla did it brilliantly, some German companies make efforts, while the resigned French industry doesn't even try.
Range improves also with bigger batteries, which can exaggerate a bit further. Or they need more capacity per mass unit, which still improves. For instance a massive lithium electrode would weigh less than lithium atoms in a carrier electrode, if someone succeeds. Or do zinc+air, more generally air as a depolarizer, or other reactions provide alternatives? Or charging while moving?
The load time is a worry for long trips only. Supermarkets boast already loading stations. Tesla proposed loading stations at highway restaurants. We could have loading stations at highway rest parks, if bringing electricity there. And: there is no hard limit to the load time, which depends on an electrode area-to-volume ratio. The self-discharge worsens, but research can improve that. Or: replace the battery instead of loading it quickly. Postal services did replace the horses at the stations.
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Bigger terrestrial vehicles favor batteries even more as they use far less energy per mass unit. Trucks, trains run easily on a battery charge for a working day. Main obstacle: the operators pay little taxes on fossil fuels.
A truck consuming mean 100kW for 8h in a day needs 2.9GJ from 3.2t Li-ion battery, heavier than the Diesel+fuel. This takes an axle more or reduces the payload, but the mass ratio is much easier than for a small car. The truck could recharge at night in the equipped rest park. It's a matter of economy, not feasibility.
A 3MW locomotive consuming mean 1MW for 16h in a day needs 58GJ from a 87t fast-discharge Li-MnO2 battery, not the most compact. Fine: that's the mass of the 4-axle locomotive, sparing the cast iron added for adherence. A passenger train with distributed traction is even easier. No need for hydrogen-powered trains.
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Are electric boats interesting, despite the operators pay little taxes on fossil fuels?
Battery boats operate already for complete days, they cross bays and straights. Frequent accelerations and limited streamlining didn't stop them. Newspapers claim operation is cheaper. I believe easily that passengers favour the cleanliness.
Container ships as opposed couldn't navigate for long on batteries. Full 2×32MW for two weeks use 77TJ from 85 000 t of Li-MnO2 batteries in 165 000 t deadweight. Plus the unreasonable fast charge. They develop renewable fuels instead: ammonia, methanol, yuk. Methanol converts efficiently to ethylene in labs, I'd go further to tetradecene or trialkylamines with C+N around 14. Already palm oil fuel must be too expensive for boats.
The same 400m×59m×(14+73)m container ship with 32t of 60% efficient fuel cell would consume 1060t liquid H2 that fit in 15 000 m3, a D=31m sphere, easy. Here hydrogen makes sense.
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Water vapor is the result of burning hydrogen.
I found these 2 quotes on the internet
Water vapor is Earth's most abundant greenhouse gas. It's responsible for about half of Earth's greenhouse effect — the process that occurs when gases in Earth's atmosphere trap the Sun's heat. Greenhouse gases keep our planet livable.
At 30 °C (86 °F), for example, a volume of air can contain up to 4 percent water vapour. At -40 °C (-40 °F), however, it can hold no more than 0.2 percent. When a volume of air at a given temperature holds the maximum amount of water vapour, the air is said to be saturated.
As an aside here is another quote from the internet on carbon dioxide.
The global average carbon dioxide set a new record high in 2021: 414.72 parts per million.
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Hi billnotgatez, nice to read you!
The fate of the greenhouse gases in the atmosphere must be considered too.
- Additional water vapour rains down.
- Methane is destroyed over decades.
- Carbon dioxide isn't destroyed. Part of it is absorbed over time by vegetables and by the Ocean, but this too has limits and drawbacks.
Also: the proportion of human-produced carbon dioxide in the atmosphere is very significant. How small would be human contribution as compared to water evaporating naturally?
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What about electric planes?
========== Motors
Electric motors are very small and light if allowed to run fast, say 100m/s or more. Only the force costs materials and losses, speed is for free. Look
wikipedia (https://en.wikipedia.org/wiki/Turbo_generator) second picture: wikipedia (https://en.wikipedia.org/wiki/File:Turbogenerator01.jpg)
the HP stage pair is grey, the three parallel LP stage pairs are yellow, the alternator is red. Or check my estimates
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=736848) and around
a ring electric motor of Cu, Fe and optionally Nd-Fe-B as slow as the fan fits in the same volume as the turbofan and is 1/3 as light. A gear would squeeze the motor further.
Aeroplanes need no superconducting motors, simply because the motors are fast. Superconductors are dangerous: they can quench and explode, and have more failure modes while Cu+Fe motors are extremely reliable. I strongly believe superconducting motors for aircraft are wasted time and moneys.
========== Batteries
They are still heavy and demand special aeroplane design. This fits hobby or schooling use. Examples
(Fly 60+30mn) Pipistrel (https://www.pipistrel-aircraft.com/products/light-sport-microlight/alpha-electro/) - (paperwork) scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/page-2?do=findComment&comment=988839)
Airliners must carry many passengers and if needed divert to an airport 100nm away then wait 45min in the air. Batteries don't fit airliners presently. Much effort was already invested in batteries, so progress is probably expensive.
========== Hydrogen
Hydrogen provides more energy hence flight time and range than the same kerosene mass.
Light tanks store liquid hydrogen at atmospheric pressure. My paperwork:
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=738806) and elsewhere
I consider all designs around gaseous hydrogen under pressure inadequate for aircaft. Too heavy, too dangerous. Liquid hydrogen is a smaller explosion hazard
Part1 (https://www.youtube.com/watch?v=7bFJK5kU_UQ) – Part2 (https://www.youtube.com/watch?v=RNzjksIImb8) on Youtube
Fuel cells are 60% efficient, commercial hot SOFC were measured at 62% in 2018, with progress at limited cost
fuelcellsworks.com (https://fuelcellsworks.com/news/fuel-cell-system-breaks-efficiency-record/)
while the best gas turbine, terrestrial hence heavy, 10* as powerful as an airliner engine, converts 43% of the fuel energy into shaft energy
ge.com (https://www.ge.com/gas-power/products/gas-turbines/9ha)
and gas turbines take two decades and huge investment to gain 6 points efficiency.
I claim that consuming 1.5× as much hydrogen in a hydrogen turbine is nonsense. Hydrogen tanks are already bulky enough. Hydrogen has a cost. This development squanders moneys. Aircraft will fly with fuel cells.
This is even more true for cars. One company develops a hydrogen engine, despite fuel cells are fully operational for cars.
========== Uses
Fuel cells for the Toyota Mirai weigh 0.5kg/kW
wikipedia (https://en.wikipedia.org/wiki/Toyota_Mirai)
This is perfect for rotating-wing aircraft. Design examples with masses, still 1kg/kW there:
masses (https://www.scienceforums.net/topic/75102-electric-helicopter/?do=findComment&comment=747135) - sketch (https://www.scienceforums.net/topic/75102-electric-helicopter/?do=findComment&comment=748087) - masses (https://www.scienceforums.net/topic/75102-electric-helicopter/?do=findComment&comment=749812) - sketch (https://www.scienceforums.net/topic/75102-electric-helicopter/?do=findComment&comment=770514)
Electric motors being cheap and light, four rotors, or six or more for redundancy, are better than one or two with cyclic pitch.
Light hydrogen brings flight time and range. Kerosene lets operational copters fly for around 1h, too short for search, rescue and surveillance at sea and moutain, badly short for oil platform service or road rescue. Copters could be first to adopt hydrogen.
Hydrogen improves also light and business aircraft with present fuel cells
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=738661) - scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=738806)
Regional and cargo aircraft are slower, they need less power and live with present fuel cell performance
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=739458) (1kg/kW) - scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=1070457) (0.5kg/kW)
Long-haul airliners are faster, they need more power, but 0.5kg/kW plus the hydrogen, the tanks and the motors weigh a much at lift-off as the kerosene and the engines. Hydrogen fits under the wings
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=1147157) and next
Only supersonic planes fly badly at M1.3 with fuel cells, still 1kg/kW there
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=878522)
So even at 1000km/h, lighter fuel cells are no prerequisite to fly, they're only a strong wish. The automotive industry improved them enough for cars. Aeronautics can lighten them further. Fuel cells need area while the volume weighs, so improvement must be possible. Planes may have specific demands too. Less effort was invested in light fuel cells than in gas turbines, letting hope progress at limited cost. That is a useful research direction.
Aluminium cables work at high voltage lines. Aeronautics should make them operational in aircraft. Research topic.
And among the transports, aeronautics is the one that needs hydrogen rather than batteries, boats possibly too.
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I happened on this YOUTUBE on a facet of this topic
https://www.youtube.com/watch?v=M0fnEsz4Ks0 (https://www.youtube.com/watch?v=M0fnEsz4Ks0)
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Seems to be a catchy name for adsorption or for metal hydrides. Both are much heavier than liquid hydrogen if one includes the tanks.
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As some people imagine hydrogen as a general vector of energy, they would like solar cells to feed electrolysis. That's nonsense, I claim.
Typical solar cells are only 1/6 efficient. Their collecting area is expensive. Typical electrolysis is 70% efficient. From the costly area to the hydrogen, this would convert only 12% of the energy.
Compare with the Zn/ZnO or the FeO/Fe3O4 cycles. They use heat, say from a sunlight concentrator, and make hydrogen. They demonstrated 30% conversion two decades ago, with 60% as an easy target. That means a sunlight collector 5× smaller, made of cheap steel sheet mirrors, not of expensive semiconductors. Obvious choice.
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I've even read that such hydrogen imported from Namibia or the Arabic peninsula to northern Europe shall produce iron from ore.
If someone really wants to consume electricity to make iron, he shall electrolyse the ore, not go over hydrogen. OK, that's still research.
Hydrogen storage for dark days is worse than ore and iron storage, I say. Compare the temperatures, the volumes, the risks.
Transporting hydrogen rather than iron is uneconomic too. Several countries that export iron ore have plenty sunlight: Australia, Mauretania and more. Sunlight near the mine can first reduce the ore to FeO just by hea. Then make hydrogen from sunlight over the FeO/Fe3O4 cycle and use the gaseous hydrogen immediately and on site to reduce the FeO or the ore to iron. This consumes no water, it emits only oxygen, and lets transport only the iron, not the hydrogen nor the ore. Obvious choice again.
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Electricity storage over hydrogen means 70% inefficient electrolysis and 62% inefficient fuel cells, the cycle being 43% inefficient. Present lithium batteries do it with 92% cycle efficiency, at interesting cost. No brainer.
But useful research can be done over other storage methods. Flywheels, underwater air or vacuum, and hopefully more. Little has been done up to now, it needs no prior theoretical advances, so progress can be affordable there.
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While I have nothing against hydrogen in some uses, especially air transport, in other uses it's uncompetitive. I don't believe hydrogen will be a ubiquitious energy vector.
Marc Schaefer, aka Enthalpy
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Beyond the FeO to Fe reduction suggested above, hydrogen from sunlight over the FeO/Fe3O4 cycle might reduce more metals without emitting CO2. Heats of formation under normal conditions, that's improvable.
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From H2O FeO Ni2O3 Co3O4 CoO
To g H2 Fe 2Ni 3CoO Co
kJ/mol 242 272 3×163 177 238
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Mn, Mo are more doubtful.
Maybe some cycle among the oxides of Ni and Co produces hydrogen from sunlight too. It isn't required, since Fe isn't lost in the cycle.
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Concentrated sunlight making heat reduces ZnO to Zn and hopefully other metals too. Heats of formation under normal conditions, again.
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From ZnS ZnO Cu2S 2CuO Cu2O CuO SnO2 SnO PbO2 PbO Bi2O3
To Zn Zn 2Cu Cu2O 2Cu Cu SnO Sn PbO Pb 2Bi
kJ/mol 206 351 80 146 169 157 297 281 58 219 3×191
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ZnO reduction by heat provides very pure Zn through distillation, optionally as powder or grains.
S is volatile enough to leave the heated zone.
The above table is a first approach only. The ore, intermediates or the metal must be purified. Existing processes do that cheaply and massively.
Sunlight abounds at some mines, in the Atacama or southern USA.
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Zn can store and distribute sunlight as Zn batteries, notably zinc-air primary batteries.
Heat from concentrated sunlight reduces recycles ZnO to pure Zn available as powder making new batteries.
Zinc-air batteries bring 1700kJ/kg, better than 500kJ/kg for lithium secondary batteries (=accumulators)
wikipedia (https://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery)
This solves the range limit of electric cars. Replacing primary batteries avoids the charging time of accumulators. Discharge in 5h fits the range. Car batteries must improve the power density over button cells here.
Zinc-air batteries are still heavy for container ships. The same 64MW for 2 weeks take 45 000 t from 165 000 t deadweight.
The transport of the batteries consumes energy. Lorries, trains, boats outperform small cars.
The cycle is decently efficient: 1.35V is 74% of ZnO's ΔHf = -351kJ/kg = -1.83eV×2q while ZnO reduction exploits typically 40% of the sunlight input
wikipedia (https://en.wikipedia.org/wiki/Zinc%E2%80%93zinc_oxide_cycle)
The 30% round-trip is better than solar cells charging accumulators, and the collecting area is cheaper per surface unit. The ZnO reduction can probably improve.
A zinc-air battery comprises other parts which must be checked, refurbished, sometimes replaced and recycled, yes.
Marc Schaefer, aka Enthalpy
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A regional airliner can fly with zinc-air batteries, as their energy density exceeds that of lithium accumulators. Evaluated for 90mn flight at 540km/h and 10mn ground movements plus 160km to an alternate landing airport and 45mn wait there.
An existing frame design fails with batteries while it can fly with hydrogen and fuel cells, see there
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=1070457)
The same 17.9GJ need 10500kg of 1700kJ/kg zinc-air batteries but the Dornier 328-100 can only take off with 14000kg.
Zinc-air batteries can improve with the size and the necessity to save mass. Casing, insulator, gaskets... can shrink. Lighter cells were demonstrated. But a used anode weighs 1.24* more than fresh.
wikipedia (https://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery)
The solution is a adequate airplane design. Existing frames optimize the commercial operation with turboprop and kerosene. The example Dornier 320-100 has a lift-to-drag ratio around 10 while operational gliders have 60, and 25 still look like an optimized commercial aircraft. That would reduce the battery to 4200kg, less if the battery is optimized. Electric motors, especially if geared, save much of the 2*800kg turboprops. The frame would be designed with the battery mass in mind, typically with a wider wing. Materials improved also a lot over 40 years.
Concentrated sunlight can provide the heat that regenerates efficiently the Zn anodes from used ZnO, and the plane flies from solar energy.
Marc Schaefer, aka Enthalpy
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Maersk agreed with Spain to produce methanol from renewables to power its ships. From wind in Galicia and sunlight in Andalusia. Nice to see some people tackling the issue seriously!
Maersk (https://www.maersk.com/news/articles/2022/11/03/maersk-and-the-spanish-government-to-explore-large-scale-green-fuels-production) - Reuters (https://www.reuters.com/business/sustainable-business/maersk-agrees-project-with-spain-make-e-methanol-its-fleet-2022-11-03/) - Hydrogentoday (https://hydrogentoday.info/en/maersk-will-produce-green-methanol-in-spain/)
I'm less than enthusiastic about the process as described in the papers: wind or sunlight to electricity, electrolysis, react hydrogen with carbon dioxide. Each step is wasteful and may let abandon the project as soon as fossil fuels get affordable again.
Sunlight to hydrogen shouldn't pass over electricity. The Zn-ZnO and FeO/Fe3O4 cycles are better, as suggested here on 06 Nov 2022.
Hydrogen can propel the boats directly, as noted here on 01 Oct 2022. Fuels cells are very efficient, a combined cycle should outperform the very best engines, while the conversion of hydrogen to methanol wastes energy. Hydrogen brings hazards, but methanol too. 2 months autonomy need 4240t liquid hydrogen that fit in D=49m for a ship 59m wide and 14+73m tall.
Or if really producing it, methanol can be transformed over dimethyl ether and ethylene to alkenes or trialkylamines around C+N=12 to supply the existing engines. Sunheat can regenerate the acid or zeolite. Safer fuels, save the mass of wasteful C-O and O-H.
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Wiki cites efficiencies of 30% (demonstrator), 40% (typical) or 60% (goal) from sunlight to hydrogen over the Zn-ZnO cycle. This includes the reduction of water (liquid -286kJ/mol) by ZnO production (-351kJ/mol), which is 82% efficient at best. So the production of Zn from sunlight is 37% or 74% efficient, not 30% or 60%.
How subtle are present demonstrators? The minimum radiative loss by a black body at 1800°C is only 1%. Upscaling must reduce the conduction losses. Heat exchanges by flowing the oxygen through fresh ZnO in opposite directions improves this loss. Hot Zn can preheat ZnO, over an intermediate fluid if needed. Possible waste heat can make some electricity.
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Can Zn reduce CO2 to CO and stop there, to avoid the complexity and losses of intermediate H2?
I couldn't evaluate the reaction with Propep nor Rpa, as they surprisingly ignore ZnO as a product. But this reaction must be well known.
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If making hydrogen from sunlight, we could store and transport the zinc and make hydrogen where and when needed. Produce Zn in Andalucia, ship it by train or boat to some foggy airport, produce and liquefy the hydrogen shortly before filling the aircraft.
Solid Zn takes 3× less volume than hydrogen, Zn powder about 1.5×. But it's 32× as heavy as hydrogen alone, around 16× as heavy as hydrogen in its tank. Paraffin that drowns Zn powder makes it some 15% heavier and much safer.
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The EU and Egypt announced yesterday an principle agreement to produce hydrogen from sunlight.
Marc Schaefer, aka Enthalpy
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To get rid of fossil fuels, some people revive the old idea of hydrogen as a vector to transport and store energy, but metal cycles are better. Zn-ZnO, FeO-Fe3O4, there are a dozen cycles. Most are meant to produce hydrogen, which isn't necessary, so more cycles are possible.
The cycles reduce the metal at the energy source and oxidize it at the consumer. The vector
- Is safe (can store in paraffin)
- Is dense
- Converts efficiently to electricity
- Offers an efficient cycle
Here are (upper) heating powers. The bulk density of ZnO powder is estimated. Zn and H2 convert well to electricity to run a heat pump, which doubles the heat in a house. Same advantage towards mechanical work, as engines convert 1/3 to 1/2 of the heat.
MJth/kg kg/m3 GJth/m3
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Fuel oil 46 860 40
Coal 34 800 31
Liq H2 142 71 10
Zn/ZnO 4.4 2800 12
Zeolite 0.33 1400 0.46
Molten salt 0.24 2000 0.48
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Solar thermal power plants that store heat from day to night exist in Spain. Zn-ZnO outperforms 25 to 50× the molten salts in that application, both for the energy density and through a conversion twice as efficient to electricity. The unconverted energy can feed a urban heat network.
Present research wants to heat houses in winter by summer sunheat stored as desiccated zeolite. Zn-ZnO outperforms zeolite 25 to 50× in that application too. Again, easy and efficient conversion to electricity is precious. I see the hot reduction temperature as a modest hurdle.
House delivery of Zn or FeO reduced at a central plant makes sense too. Lorries and storage need 3× to 1.5× as much room as for coal: realistic, better than zeolite. Alternative to the reduction at the house in summer.
Batteries (or fuel cells) exist in labs that consume only Zn and keep the other components. The unconverted energy can heat the house directly or warm the input of the heat pump. Batteries, supercapacitors can store excess electricity when more heat is briefly sought, water does the opposite.
Marc Schaefer, aka Enthalpy
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Re: production of water: Water is a big greenhouse gas... but our ability to emit water is microscopic compared to the amount already in the air. Also, per kg, water is a poor greenhouse gas compared to CO2.
I like the idea of metal redox... but like hydrogen is comes with some inherent fire risks, which are greater than hydrocarbon fuels (for instance finely divided Zn+H2O is bad news, and surface area is the name of the game for all these metal cycles)
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Agreed, Wildfyr!
I hope that between "burn in 0.1s" and "use in hours or months" there is some safe and useful Zn grain size. Zn-air batteries have already found a reasonable compromise. If the powder must be finer, storage in paraffin alleviates the risk, as is done with more active metals.
Metal cycles seduce me because every step looks reasonable and feasible. Reduction by mere heat (1800°C does need engineering), decent risk and volume for transport and storage, easy use even to make electricity, correct overall efficiency, fits many contexts.
When comparing with hydrogen economy, with zeolite energy storage, or molten salts heat storage, I feel metal cycles obviously better. Some nasty bits will emerge when exploring or engineering the idea, that belongs to the game.
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Bulky hydrogen is uneasy to move to an airport or other customers. Here an example by train.
Liquid at 20K, hydrogen can fill balloons of round section. Multilayer insulation in vacuum and polymer straps holding the balloon make evaporation minimal. Foam slows the evaporation if vacuum is lost, the overpressure vent can burn the hydrogen over a catalyst and cool the vapour. It needs a vacuum vessel.
One 19m wagon with Jakobs bogies carries 5.3t hydrogen. With end bogies, pantographs and transformers to feed the cryocoolers, one set of 9 wagons carries 48t or slightly more. A locomotive and 4 sets form a 740m train carrying only 200t, as much mechanical energy as 970t kerosene that fit in 15 four-axle wagons. Move 3× as many trains.
A wagon of uneasy design with rectangular 2.8m×4.0m section would carry 11.0t hydrogen instead, and a train 400t. I keep 200t in here under.
240 000 takeoffs/year with hydrogen from a medium-big airport need 2 000 000 t/year or 27 trains/day. Feasible with fast unloading.
The light and streamlined wagons could technically move at 200 or 320km/h.
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A pipeline for gaseous hydrogen is intuitively better than trains, except maybe if the train lane exists but not the pipeline.
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Trains move reduced and oxidized zinc more safely, and zinc can make electricity or hydrogen at the destination.
Many wagon design reach the track limit of 8t/m in the EU, so a 740m train moves 5600t. But 5600t ZnO have produced only 140t hydrogen per slow train.
Marc Schaefer, aka Enthalpy
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Planes can bring hydrogen to airports. They use existing runways, can be wider and taller than trains, and they move faster.
While other airplanes carry less volume or mass, the AN-225 has adequate shoulders
BelugaXL (https://en.wikipedia.org/wiki/Airbus_BelugaXL) - A380 (https://fr.wikipedia.org/wiki/Airbus_A380) - Dreamlifter (https://en.wikipedia.org/wiki/Boeing_Dreamlifter) - C-5 Galaxy (https://en.wikipedia.org/wiki/Lockheed_C-5_Galaxy) - C-17 Globemaster (https://en.wikipedia.org/wiki/Boeing_C-17_Globemaster_III) - AN-225 (https://en.wikipedia.org/wiki/Antonov_An-225_Mriya)
The AN-225 can carry 200t on its back, like 170t hydrogen in a 30t tank, and some 50t in its cargo hold. I'd prefer an adaptation to >250t on the back, where leaks are less dangerous.
The ellipsoidal external tank has L=48.3m D=10.6m and S=1130m2 per Knud Thomsen. Insulating foam for 20K exists, see Ariane V: 33mW/m/K and less at cold, 50kg/m3, so 0.2m weigh 11t and leak 52kW, which evaporates 0.4t/h at constant 20K or heats the hydrogen by 0.15K/h or 0.07bar/h at constant amount. Glass fabric in epoxy, or something more expensive, can make a sandwich, where 5+5mm weigh 20t. 1bar overpressure pulls one 5mm skin by 100MPa, so some overpressure can remain at altitude and stabilize the shape at varied ground altitudes.
If the tank isn't empty nor full, say to serve several airports, it needs partitions to immobilize the hydrogen. Maybe cones of similar sandwich material.
The only flying AN-225 was bombed, but Antonov will finish the other one. Once all flights sip hydrogen, a medium-big airport will need 27 loads a day like from trains, but an AN-225 can make two 1000+1000km rotations a day from a sunny (sol-zinc!) or windy production site. Meanwhile, one tank plane suffice, possibly shared among airports. Leasing an AN-225 at reported 30kusd/h costs 100kusd/200t or 0.5usd/kg, equivalent to 0.1usd/kg for kerosene.
Maybe a flotilla of AN-225 operates later, or bigger planes powered by hydrogen, until all airports have pipelines for gaseous hydrogen.
Marc Schaefer, aka Enthalpy
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Here's a plane designed to bring hydrogen to airports. Don't trust every pixel and digit of this draft, like the short horizontal stabilizer.
It consumes hydrogen to emit no carbon dioxide, and is as big as an A380. The 1008m2 wing has W/L=5.7 only, I take L/D=15 from the Spitfire. Winglets are desired, or maybe the chord splits near the tips and the elements spread as for eagles.
- At sea level and 820t, flaps achieve αCL=1.3 to stall at 100m/s=360km/h=195knots. The displayed blown flaps improve.
- At 8000m (0.526kg/m3), 820t and 200m/s=720km/h=389knots, αCL=0.76.
Three bodies are slimmer than one, they spread the weight over the runway and the wing. The gears retracted in the tanks drag less. A lifting body or a blended wing-body look worse.
The plane shall take-off or land at 820t. The displayed ellipsoidal tanks host 480t hydrogen if the rest is light enough. 0.2m foam as on Ariane V weigh 3×13t and can be the core of a sandwich as in the previous message. The heat leak evaporates half as much hydrogen as the fuel cells consume, so some liquid is removed too. Again, hours of heat leak have little effect on the pressure, or they waste little hydrogen.
The 6 ducted fans blow over D=3.75m, bigger than the Trent.
- At sea level, they accelerate 6×2131kg/s air from 0 to quiet 158m/s with 90% efficiency to push 6×337kN or 820t×0.25g like the A380 and An225.
- The 98% efficient electric motors obtain 6×30MWe from 3×30t fuel cells. 2kW/kg exist at the Toyota Mirai.
- At 8000m (0.526kg/m3), the fans accelerate 6×1511kg/s air from 200m/s to 260m/s to push 6×91kN for L/D=15 and 820t.
- The motors draw 6×23MWe at cruise speed, 77% of the peak power.
The fuel cells need over 6×13kg/s air, easy but must be done. The ducts around the fans can host the fuel cells. A bit of slowed air can flow radially over a short distance and much area to feed the cells, then the warmer vapour and depleted air expand for ramjet thrust.
The fans could reside at the bodies' aft to reduce the drag. They won't blow the flaps then, and the fuel cell must remain before the wing for equilibrium.
Powered wheels, easy with electricity, would taxi and accelerate the plane more efficiently than the fans alone do. Supercapacitors are bad but accumulators could store descent and braking energy to supplement the take-off and ascent.
My turbulators are the topic of
scienceforums (https://www.scienceforums.net/topic/122584-vortex-generator/)
Thoughts about flight motors, hydrogen and more at
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/)
Waveforms to drive fast electric motors there
scienceforums (http://www.scienceforums.net/topic/110665-quasi-sine-generator/)
Aluminium wires
scienceforums (http://www.scienceforums.net/topic/82314-better-black-boxes-on-airliners/page-3?do=findComment&comment=804826) - scienceforums (http://www.scienceforums.net/topic/82314-better-black-boxes-on-airliners/page-3?do=findComment&comment=884494)
Marc Schaefer, aka Enthalpy
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The Toyota Mirai's fuel cell uses a polymer membrane electrolyte and operates around +120°C, so cooling uses many times more air than 13kg/s at each fan of the previous H2 lifter. Very preliminary estimates suggest 1/10th the main flux, an incentive to put the cells at the fans.
The losses at the fuel cells, like 40% becoming heat, make my previous proposal more interesting: slow down the secondary flux, cool (and feed) the fuel cells, expand the flux to accelerate it. Very preliminary estimates suggest the gain is equivalent to 70% fuel cell efficiency instead of 60%, wow.
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More and more people grasp that hydrogen and fuel cells will fly aeroplanes. Many companies develop the technology, some fly already.
I told already that a hydrogen turbine is a dead end, because fuel cells and electric motors are 1.5× as efficient, and the ratio will spread further
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=1147816) - chemicalforums (https://www.chemicalforums.com/index.php?topic=112014.msg395869#msg395869)
Zeroavia has flown a Dornier 228 with hydrogen and fuel cells in the cabin
Cnn (https://edition.cnn.com/travel/article/zeroavia-hydrogen-test-flight-climate/index.html)
They would fit in the nacelles of a Dornier 328
scienceforums (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=1070457)
but Zeroavia did a fantastic step. Engineering is harder than a naive drawing, and the Dornier 228 is the biggest to fly on hydrogen up to now. Kudos!
Even Airbus seem to slowly grasp that planes need hydrogen, not batteries, and used in fuel cells, not in turbofans
Cnn (https://edition.cnn.com/travel/article/airbus-fuel-cell-engine-rolls-royce-easyjet-engine-c2e-spc-intl/index.html)
Wow! Still recently, they were betting on the turbofans by Safran and Rolls-Royce. Have Airbus already understood that superconducting motors are superfluous and risky?
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[...] Slow down the secondary flux, cool (and feed) the fuel cells, expand the flux to accelerate it [...]
Here's an illustration and figures for a 30MW, 4m fan as the former H2 lifter uses. The PEFC fuel cells have a polymer electrolyte as for the Toyota Mirai, with exhaust under +140°C: I take +120°C. ΔHf=-286kJ/mol for H2O liq @298K.
I compute for air taken as an ideal diatomic gas. It mainly cools the cells, only 3% of the exhaust moles are H2O but these carry much vaporization heat, partly recovered at expansion, so misused Propep would compute better. Staying near the dew point gains efficiency.
On the sketch, the cooling flux has its own straightener and the stator blades are far. The stator blades could reside more forward and some or all cells behind them. The cooling air flows radially through the cells, with only 6m/s over the big area, and at a higher pressure that enable the expansion and bigger exhaust speed. Less area and a longer path are possible.
163kg/s of the 1250kg/s air are heated by the cells' losses and leave with 293m/s rather than 260m/s. 1.079× as much thrust for the same electric power, which saves 9t cells at the former H2 lifter. The efficiency improves as much, as if the cells improved from 60% to 65%.
The rotor could blow the cooling flux faster with a local blade angle, especially of the fluxes are separated early. This should increase the gain and remains very simple. Maybe future powerplants have some extra compressor and turbine around the cells to help move the main rotor.
If a fan without a duct holds at a pod, the cooling air can be taken at the pod's leading edge behind the tip of the blades. If a fan resides at a nacelle before a wing, the cooling air can be taken at the wing's leading edge behind the tip of the blades.
Marc Schaefer, aka Enthalpy
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Many projects in Europe want to reduce ore to iron and steel using hydrogen instead of coal. Said hydrogen being obtained from sunlight and wind and dams electricity, the process emits no CO2. Kudos, applause.
Bbc (https://www.bbc.com/news/business-64538296)
But... Coal is usually the cheapest source of energy. Electricity, a vector obtained from other sources, uses to be the most expensive one. Worse: sunlight to electricity generally uses expensive and inefficient solar cells, then electricity to hydrogen passes through inefficient electrolysis. That steel would be very expensive - Bbc:
"at least in the European context, their steel will be competitive"
Ever more protectionism, the bad policy that hampers the European companies using steel.
Repeating myself:
06 Nov 2022 (https://www.chemicalforums.com/index.php?topic=112014.msg396042#msg396042) - 09 Nov 2022 (https://www.chemicalforums.com/index.php?topic=112014.msg396070#msg396070) on chemicalforums
- If using electricity, electrolyse the ore, bypass lossy hydrogen. Still research.
- Australia, Brazil, South Africa, Iran, Kazakhstan... combine ore and sunlight. Reduce the ore to FeO by heat near the mines, this saves coal and transport.
- Later at these places, reduce FeO to Fe by H2 obtained from sunheat and the FeO/Fe3O4 cycle.
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Solar plants take much area, so what power does 1km2 with Zn-ZnO cycle produce? Other metal oxide cycles bring similar performance.
1km2 in Andalusia receives 1800GWh/year or mean 0.21GW. The tropics offer more. Some countries have free area and consumers.
Concentrators or solar cells don't catch all the incoming light. I neglect that here, not accurate, but at least the comparison is fair.
The reduction of ZnO to Zn shall be 74% efficient, as on 17 Nov 2022
chemicalforums (https://www.chemicalforums.com/index.php?topic=112014.msg396135#msg396135)
This is an estimated target. The few demonstrators achieved half that.
0.15GW Zn make electricity in a battery (which is still research). A zinc-air battery provides 1.45V while Zn->ZnO packs 351kJ/mol=1.82V, so this 80% efficient step leaves 0.12GW electricity. A power plant takes 8.3km2 to deliver mean 1GW electricity.
The same plant can also distribute ≤0.09GW heat. Or rather, recycle the high-temperature heat at some process step to provide more Zn. Or use the heat in a combined cycle to make more electricity. 40% of 0.05GW heat provide 0.02GW electricity more and let distribute 0.07GW heat.
Zn flexibly produces H2 or electricity. 0.15GW Zn provide 0.12GW = 27kt/year H2 from 1km2.
The plant can also ship Zn to customers rather than H2.
Zn storage produces electricity on demand. From day to night, 14h×0.11GW fit in 16kt Zn or 4.4dam3, a heap 10m tall, 20m wide and 44m long. Even 7 days ×0.15GW need only 73dam3 or 20m×40m×180m. This heap costs only ground area.
========== Compare with engine
Heat storage at moderate temperature prevents a combined cycle, so the engine shall obtain mean 40% = 0.084GW electricity. It can also distribute 0.13GW heat.
To provide electricity at night, the plant must store 0.21GW×73%×14h=7.8TJ heat in 26kt melting salt (300kJ/kg). The salts are cheap if they're little processed ore, like chlorides. Storage for a few days is feasible and demonstrated.
========== Compare with solar cells
The same area costs much more than concentrators, which are little more than steel sheet.
They convert about 19% of sunlight. 1km2 provides mean 0.040GW electricity and no heat.
Storage does cost and has a limited capacity, with Li batteries being the present main choice. The same 14×0.11GW from day to night take 7700× Powerpack 2 storing 200kWh each. They weigh 12.5kt too but cost 0.4G€ while a Zn heap is nearly for free. If serving for 20 years, they add 34€/MWh to the stored electricity fraction. A week storage remains too expensive.
========== Compare with solar cells and electrolysis
Demonstrated PEM cells are up to 80% efficient presently, so the output is around 0.032GW = 7.2kt/year H2 from 1km2.
Storage and transport are possible but less convenient than with Zn.
In the least inefficient later use of H2, fuel cells recover ≈62% = 0.020GW electricity from 1km2.
Such a meaningless cascade of losses is just the worst possible combination among renewables. No idea why everybody concentrates on this.
========== Compare with nuclear and electrolysis
Nuclear electricity is almost twice as expensive as renewables under realistic conditions. EDF get guaranteed 92.50gbp/MWh for the EPR at Hinckley Point while the providers-operators of offshore wind parks got 55gbp/MWh.
Nuclear is an even worse way to hydrogen than solar cells and electrolysis.
========== Others
More radical processes convert sunlight or sunheat to hydrogen, welcome. I ignore how efficient and proven they are.
Marc Schaefer, aka Enthalpy
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Many Boeing 474 and Airbus 380 are being retired presently, so they would make cheap H2 transporters.
Their cabin volume limits the transport capacity, but maybe they can receive an external tank on added shoulders, similarly to the Antonov 225 depicted here on 18 Dec 2022? The A380 was tested to land much more mass than its rating, and 2000km need little kerosene mass. If the wing can't lift so much hydrogen at the center, added pylons or trusses might spread the force outwards on the wing.
The Dreamlifter, Beluga XL and others got a cheaper faster certification because they modified only the cabin.
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The B747 and A380 could also get a wider and taller upper body like the Dreamlifter and BelugaXL did. The tail then keeps some efficiency. Several sleek tanks under the wing would complete the volume and spread the load.
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Hey chemists, ideas needed!
Leaks of natural gas make catastrophic explosions. Usually, gas+air deflagrate (wooff, where the heat propagates the combustion), but sometimes they detonate (peng, the shock wave does it), which is more destructive.
It will worsen if we replace natural gas by hydrogen that detonates nearly always. Ethylene willingly detonates too. Ethane is more calm.
So can you propose a gaseous fuel as calm as possible? Easily mass-produced, CO2 neutral, etc. Ethane is just one possibility, isobutane can be better. I suppose N2, CO2, some air can be added to match the heating power of natural gas and keep the burners tuned.
chemicalforums (https://www.chemicalforums.com/index.php?topic=111032.msg392960#msg392960) - chemicalforums (https://www.chemicalforums.com/index.php?topic=111032.msg392998#msg392998)
Or can you propose a phlegmatizer added to the natural gas ersatz that prevents detonation and slow down deflagrations? Maybe a compound that interrupts the free radical chain. Halons are excluded, but ethers and aromatics (alas in big proportion) do it for high-octane gasoline. Toluene, ethers, tert-butyldimethylamine, tert-butylformate, formic acid, 1,4-cyclohexadiene, cyclobutene, cyclooctatetraene...? Has isobutene any merit here? Or a compound that releases CO in the flame? Known reaction poisons?
Comments, opinions, suggestions, remarks...?
Cheers!
Marc Schaefer, aka Enthalpy
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I could misuse CPropepShell to compute the secondary flux that cools and feeds the fuel cells as I proposed here on
Jan 16, 2023 and Jan 22, 2023
I only don't dare to tell you how :-[.
Updated figures. Still 30MW electricity, 60% efficient cells, 353g/s H2, but with water's vaporization enthalpy, and the expansion modeled by Propep.
- The secondary air flux is 98.5kg/s (not 163kg/s).
- Expansion from 55kPa to 36kPa accelerates it to 303m/s.
- 303m/s instead of 260m/s (primary flux) gain 4.2kN or 5.6% thrust.
- Other cooling methods could have completely lost 19.7kN or 26% thrust at the secondary.
So that's why someone aked me on an other forum. - The added thrust is equivalent to 63% rather than 60% efficient cells.
Marc Schaefer, aka Enthalpy
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I put figures on a sunlight-to-electricity plant here on 05 Mar 2023
chemicalforums (https://www.chemicalforums.com/index.php?topic=112014.msg397511#msg397511)
that concentrates sunheat to make metallic zinc, stores it cheaply, and converts it to electricity in a zinc-air cell.
- As said, the plant can produce electricity when needed, smoothening its own production and the consumption of its customers.
- Better: this plant can smoothen the production of other plants and the consumption of their customers, taking the present role of dams. Rather than from 70% to 130% of the mean production, the output varies then from 0% to 200% for instance. More Zn storage and more powerful zinc-air cells suffice, the concentrator area remains identical. Perfect combination with wind turbines on a European country scale!
- Could the output vary from -100% to +300% to mimic storage by pumps and turbines between two lakes? Yes, but the conversion of excess electricity to metallic zinc over heat may be 74% efficient, zinc to electricity 80% and the round trip only 59%. I prefer 92% in batteries if that were necessary.
========== About sunheat to zinc
- It is the beginning of the sol-zinc process, also called Zn-ZnO cycle.
- Sol-zinc then makes hydrogen from the metallic zinc and recycles the zinc oxide.
- The proposed plant can also output hydrogen, if some zinc is not converted to electricity.
- Zinc can also be distributed to other users.
- Heat is available at varied steps.
The process isn't old, but electricity rather than hydrogen was already described, check the German page
en.wiki (https://en.wikipedia.org/wiki/Zinc%E2%80%93zinc_oxide_cycle) - de.wiki (https://de.wikipedia.org/wiki/Solzinc-Verfahren)
De.wiki cites only the development at Paul Scherrer Institut and the demonstrator at Weizmann Institute of Science, with observed 30% and hoped 60% efficiency towards hydrogen. I deduce 37% and 74% towards zinc. En.wiki cites 40% towards hydrogen, possibly from other teams.
I hope quick progress from affordable research because the topic is recent. Decomposition by heat suggests a reliable process that improves by scaling up and resembles existing zinc production.
========== About zinc to electricity
- Zinc-air cells where only zinc is replenished are called mechanically recharged, or zinc-air fuel cell
wikipedia (https://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery#Mechanical_recharge) - They were investigated decades ago and fell out of fashion.
- I ignore how close they were to cells operable in a full-scale power plant.
Marc Schaefer, aka Enthalpy
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Fuels cells pass the air through fine channels. This let Toyota build lighter cells for their Mirai. But fuel cells may be more sensitive to dust than turboprop and piston engines are.
Obviously Toyota solved this, supposedly with a filter. Fuel cell airplanes should keep this air filter or build a better one.
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Zinc-air fuel cells are well alive! Also called "mechanically recharged", they store zinc powder separately from the cell that converts it into electricity. For instance that Canadian company
zinc8energy (https://www.zinc8energy.com/technology)
markets electricity storage, about home-size but scalable, with a "zinc regenerator", a "storage tank" and a "fuel power stack".
This is perfect for wind energy. But if sunlight provides the energy, covering km2 with expensive solar cells to lose 80% in the conversion is plain bad. We must obviously use the sol-zinc process to produce efficiently metallic Zn from a cheap concentrator area. If this process hasn't progressed, it must receive much moneys, work, ambition, vision - more so because zinc-to-electricity has progressed.
==========
By the way, many people find alternatives to lithium for utility-scale storage. Iron-air batteries make big demos
innovationorigins (https://innovationorigins.com/en/iron-air-grid-battery-is-going-to-make-real-impact-first-gigasite-under-construction/)
10MW 1GWh, wow.
A Chinese maker markets a car with a sodium battery.
Anybody still caring about the availability of lithium and cobalt?
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Fast electric machines use carbon fibres, typically to hold the magnets at the rotor against the centrifugal force. But meanwhile PBO fibres like Zylon outperform carbon and would increase the rotation speed or reduce the gap on the magnetic path, very nice.
wikipedia (https://en.wikipedia.org/wiki/Zylon) - toyobo.co.jp (https://www.toyobo.co.jp/e/seihin/kc/pbo)
A report of superior performance to reinforce 80T magnetic coils, a use nearly identical to fast electric machines:
Huang et al, Mechanical properties of Zylon/epoxy composite
Huang coiled impregnated fibres in-situ with pre-tension and obtained from the composite nearly the fibres' strength. I believe it's simpler than the separate sleeve of carbon fibres.
PBO fibres isolate, carbon fibres don't. This shouldn't change much. Nd magnets conduct anyway.
Huang obtained 2.9GPa tensile strength from a composite and even more with increased pre-tension. Waaah !
Marc Schaefer, aka Enthalpy
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Ever more projects and companies do what I had described. I proposed among others to retrofit existing airplanes with hydrogen nacelles integrating propellers, electric motors, fuel cells and liquid hydrogen tanks, much smaller than the opponents claim
Piaggio 180 (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=738806) -
Atr72 (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=739458) - Dornier 328 (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=1070457) -
Boeing 737 (https://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=1147157) - Dhc615 water bomber (https://www.chemicalforums.com/index.php?topic=113163.msg399116#msg399116)
This company does offer a conversion kit, notably for the Atr72, but it delivers the liquid hydrogen in tanks ready to load in the adapted aircraft, so the airports need no adaptation
Universal Hydrogen (https://hydrogen.aero/) - Get orders (https://hydrogen.aero/press-releases/universal-hydrogen-celebrates-250th-order-for-its-hydrogen-regional-aircraft-products/)
Interesting idea! But I'd put the tanks in the nacelles, not in the hold.