[Enthalpy]

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.

[Enthalpy]

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.

==========

A pipeline for gaseous hydrogen is intuitively better than trains, except maybe if the train lane exists but not the pipeline.

==========

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

[Enthalpy]

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 - A380 - Dreamlifter - C-5 Galaxy - C-17 Globemaster - AN-225
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

[Enthalpy]

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 αC_L=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, αC_L=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 6×30MW_e 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 6×23MW_e 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
Thoughts about flight motors, hydrogen and more at
  scienceforums
Waveforms to drive fast electric motors there
  scienceforums
Aluminium wires
  scienceforums - scienceforums

Marc Schaefer, aka Enthalpy

[Enthalpy]

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 1/10^th 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.

[Enthalpy]

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 - chemicalforums

Zeroavia has flown a Dornier 228 with hydrogen and fuel cells in the cabin
  Cnn
They would fit in the nacelles of a Dornier 328
  scienceforums
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
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?

[Enthalpy]

[...] 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

[Enthalpy]

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

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 - 09 Nov 2022 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.

[Enthalpy]

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
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

[Enthalpy]

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.

[Enthalpy]

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.

[Enthalpy]

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 - chemicalforums

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

[Enthalpy]

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

[Enthalpy]

I put figures on a sunlight-to-electricity plant here on 05 Mar 2023
  chemicalforums
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 - de.wiki

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
• 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

[Enthalpy]

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.