[holowoodman]

> Most uses of fossil fuels are very inefficient. For instance, when you step on the accelerator in your car, only around 30% of the energy in the fuel you use actually is being used to propel you forward. The majority of the energy is wasted as heat. In a power plant that's more like 70% being captured and going towards the goal (electricity generation).

Yes, but there are also future inefficient uses of renewables. E.g. when making iron, you heat the ore (iron oxides) with coke (refined sulfurless coal). The coke will provide extra heat and act as a reduction agent, separating the oxygen atoms from the iron oxides. Now you can do the same thing with hydrogen as the reduction agent to avoid producing CO2 and to avoid using fossil fuels. However, creating renewable hydrogen is atm only 30% efficient, storing and transporting it has losses. Even with possible improvements, that hydrogen will be a very inefficient and costly use of electricity, and at least half of it will always be wasted.

So in terms of total energy usage, making those kinds of industrial processes use hydrogen, we will have to at least double our electricity output. And a lot of that doubling will be wasted because of the inefficiency of electrolysis, as opposed to directly using coal or natural gas.

[xorcist]

The interesting bit about using H2 in industrial processes is that, while inefficient, it's also the school book example of variable loads. Solar and wind produces power extremely cheap but intermittent, so in a grid the push down prices when they produce the most. Variable loads can, at least in theory, be run when prices are the cheapest.

[Borg3]

Uh, can you provide any scientific papers that H2 can be used for Iron smelting? CO2 is very stable, even at high temperatures. Its hard to strip O2 from it (except photosintesis). Now, H2 itself is very violatile gas. When burn, it creates water. Water is not stable high temperatures. It become vapor and when temperature rise it can even break bond between H2 and O.

So, papers or are you hallucinating?

[nasmorn]

They are already building such plants. So I would assume they have a plan

But here is a paper - only the title is German the main part is English https://pure.unileoben.ac.at/files/1851525/AC06514880n01vt.p...

[holowoodman]

See https://en.wikipedia.org/wiki/Steelmaking#Hydrogen_direct_re... and linked sources.

[jijijijij]

Are you suggesting burning H2 will create water and enough energy to split the water in H2 and oxygen again, afterwards? That would be amazing news!

https://en.wikipedia.org/wiki/Steelmaking#Hydrogen_direct_re...

[holowoodman]

No, not at all. Coke or hydrogen always only provide additional heat, they are never the main source of heat. The main heat source can either be coal or an electric arc furnace. The coke or hydrogen are just necessary for the chemical reaction, and providing some heat is a side-effect.

[jijijijij]

Sorry, in face of OP’s tone I allowed myself some sarcasm. Obviously there needs to be additional energy. You’d have some equilibrium with those reactions and OP didn’t make any argument why that can’t be controlled in favor of reducing Fe2O3.

It’s also borderline unbelievable OP never heard of hydrogen in future steelmaking, if they are at all invested in the topic. You’d need a special kind of ignorance to think people are hugely throwing money at this, when the basic chemistry is infeasible.

[Borg3]

Yeah, I did not thats why I asked. Water and Steel doesnt like each other. But thanks for the info.. It seems it can be done in controlled way.

Now I wonder how cost effective it is :)

[holowoodman]

Well, actually, thermolysis for water occurs at 2200°C. Thermolysis of CO₂ starts at 1400°C, of CO at 3700°C. The melting point of iron is around 1500°C, similarly its oxides.

So water as a product is actually more stable than CO₂, and doesn't undergo thermolysis at the relevant temperatures for smelting iron. Whereas when going the CO₂ route, there is the risk of producing relevant amounts of CO, which is not as desirable and less efficient because it only absorbs half the oxygen.

Cost is a big question, but it will for sure be more expensive to use hydrogen. Back of the envelop calculation (250$/t coal price, need 1/3t of H_2 for the same effect, so H₂ may cost up to 750$/t, need 40kWh/kg for H₂ electrolysis at 100% efficiency) gives a breakeven electricity price of 1.875ct/kWh. While this happens from time to time due to overproduction, those prices will even out as soon as there is a market for that excess electricity through batteries, storage and electrolysis. Which means that cost-wise, the H₂ route will never be more effective than coal. To make it viable, coal use needs to be made more expensive through taxes and tariffs.

[jijijijij]

> Now I wonder how cost effective it is :)

I believe right now, it's expected to cost about 30% more. But we don't have an hydrogen economy yet, or 1000 years of experimentation as with carbon as reducing agent. There is probably still some room for innovation in material science for every part of the process.