October 05, 2022, 11:44:59 AM
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Topic: Hydrogen-based economy?  (Read 143 times)

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Offline Enthalpy

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Hydrogen-based economy?
« on: October 01, 2022, 06:37:28 AM »
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!

Offline Enthalpy

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Re: Hydrogen-based economy?
« Reply #1 on: October 01, 2022, 09:31:07 AM »
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.

Offline Enthalpy

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Re: Hydrogen-based economy?
« Reply #2 on: October 01, 2022, 11:13:32 AM »
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.

Offline billnotgatez

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Re: Hydrogen-based economy?
« Reply #3 on: October 02, 2022, 01:20:14 AM »
Water vapor is the result of burning hydrogen.

I found these 2 quotes on the internet

Quote
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.

Quote
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.

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The global average carbon dioxide set a new record high in 2021: 414.72 parts per million.
« Last Edit: October 02, 2022, 01:35:19 AM by billnotgatez »

Offline Enthalpy

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Re: Hydrogen-based economy?
« Reply #4 on: Yesterday at 08:31:53 AM »
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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