For a sustainable world, aim high and try some abandoned technology: the airship. It could be the latest, coolest way to deliver the hydrogen economy.
LONDON, 7 August, 2019 − The airship could be on the way back. Tomorrow’s fuel could be delivered at all-but zero carbon cost by the ultimate in high-technology supertankers: vast dirigibles, sailing round the world at stratospheric heights on the jet stream.
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Enormous balloons or airships more than two kilometres in length, laden with hydrogen and an additional burden of cargo could, according to new calculations, circumnavigate the northern hemisphere in 16 days. They could, on route, deliver their heavy goods, and at the same time transfer 60% or even 80% of their hydrogen in gas form.
And then, the holds empty, the same airship could float back home in the same direction on the jet stream with the remaining hydrogen to provide the necessary lift, for another trip.
Transport accounts for almost a quarter of all greenhouse gas emissions generated by humankind: marine cargo delivery accounts for at least 3% and is projected to grow.
“Cheap and clean transportation of hydrogen would be convenient for the implementation of a global hydrogen economy. This would ultimately promote sustainable development on a global scale”
But as city authorities and inventive motor engineers and laboratory ingenuity around the world have already demonstrated, hydrogen can serve as a combustion fuel. And as solar and windpower investors have already found, surplus renewable energy can be stored as hydrogen, if the unwanted power is used to apply electrolysis to water. And that could be a cue for the return of the airship.
Dirigible development more or less ceased in 1937, when the Hindenburg caught fire and crashed in New Jersey: hydrogen is highly flammable. But a new study of the possibilities of lighter-than-air machines in the journal Energy Conversion and Management: X suggests that safety is now less of a problem.
With advances in computing and communications in the last eight decades, and vastly more accurate weather observation systems, such ships could be fuelled, flown, guided, landed and emptied entirely by robotic control. In effect, the hydrogen would provide the lift, the permanent stratospheric winds would provide the propulsion; in emergency the cargo would also provide the additional fuel.
Julian Hunt of the International Institute for Applied Systems Analysis in Austria and colleagues did the sums.
Big is beautiful
The Hindenburg class airship was 245 metres in length. Tomorrow’s hydrogen bulk carriers could be ten times that. Big here is beautiful: a tenfold increase in length would yield a thousandfold increase in volume at the cost of only a hundredfold of the fabric in which the hydrogen is enclosed.
One of those 2.4km giants could be loaded with 3,280 tonnes of hydrogen, lift it to 15km, and glide with the jet stream on a one-way route around the hemisphere. Assuming such a behemoth could make 25 deliveries a year, a fleet of 1,125 lighter-than-air supertankers could deliver enough energy stored in the form of hydrogen to account for a tenth of the global electricity consumption.
The combination of vast bulk carrier (the same cargo could also be transported in a monster balloon, the scientists argue) and a free ride at high altitude carries additional possibilities, they say. Hydrogen to be liquefied must reach a temperature of minus 253°C. Temperatures in the stratosphere can get as low as minus 70°C: altitude makes the process more economical because the fuel would already be at minus 60°C when it landed.
Hydrogen can also be used as fuel for landing and lift-off and course changes, but a big enough airship could also carry solar arrays to exploit the available sunlight. Hydrogen when burned to produce power also delivers nine times its weight as water: sprays of water at high altitude could be used to trigger the complex process that ends in rainfall over drought-stricken farmlands.
Slow but sure
But the researchers see the real bonus simply as a delivery system for hydrogen without the need to liquefy it (a process that consumes about 30% of the available energy of the hydrogen). Delivery might be slow compared to air freight, and always be in the direction west-to-east, but it would outpace most marine shipping – and a dirigible could load at, and deliver directly to, regions far from the coast: from Denver in the US to Islamabad in Pakistan, the researchers instance.
There are problems to overcome: wind and storm stresses could create real problems for structures of such size. Descent and landing could be problematic. But lighter-than-air travel comes with its own economies. Dirigibles are already being revived for a number of commercial uses.
And that’s not all a really vast airship could offer: a dirigible could deliver supplies to space, to be fired into the emptiness by pressure gun. Or a doughnut-shaped airship in the stratosphere could support a spaceship at its centre of gravity, to become the launch pad for its final lift-off.
Above all, the authors say, “cheap and clean transportation of hydrogen would be convenient for the implementation of a global hydrogen economy. This would ultimately support the widespread adoption of intermittent renewable energy technologies, such as solar and wind, and promote sustainable development on a global scale.” − Climate News Network
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