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Comment by kragen

7 months ago

Steam engines currently power most of the world's electrical grid. The main reason for this is that, completely contrary to what you said, they are more efficient and more reliable than diesel engines. (Electric motors of course are not a heat engine at all and so are not comparable.)

Steam engines used to be very inefficient, in part because the underlying thermodynamic principles were not understood, but also because learning to build safe ones (largely a question of metallurgy) took a long time. Does that mean that designing them before those principles were known was "not engineering"? That seems like obvious nonsense to me.

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kragen

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PaulHoule  7 months ago

Steam engines are thoroughly obsolete in the developed world where there are natural gas pipeline networks.

People quit building coal burning power plants in North America at the same time they quit burning nuclear power plants for the same reason. The power density difference between gas turbines and steam turbines is enough that the capital cost difference is huge. It would be hard to afford steam turbines if the heat was free.

Granted people have been building pulverized coal burning power plants in places like China where they'd have to run efficient power plants on super-expensive LNG. They thought in the 1970s it might be cheaper to gasify coal and burn it in a gas turbine but it's one of those technologies that "just doesn't work".

Nuclear isn't going to be affordable unless they can perfect something like

https://www.powermag.com/what-are-supercritical-co2-power-cy...

If you count the cost of the steam turbine plus the steam generators plus the civil works to enclose those, nuclear just can't be competitive.

  • kragen  7 months ago

    There is some truth in what you say. Though steam engines still power most of the power grid (especially in the "developed world") their capital costs are indeed too high to be economically competitive.

    However, there are also some errors.

    In 02022 24% of total US electrical power generation capacity was combined-cycle gas turbines (CCGT), https://www.eia.gov/todayinenergy/detail.php?id=54539 which run the exhaust from a gas turbine through a boiler to run a steam turbine, thus increasing the efficiency by 50–60%. So in fact a lot of gas turbines are installed together with a comparable-capacity steam turbine, even today.

    Syngas is not a technology that "just doesn't work". It's been in wide use for over two centuries, though its use declined precipitously in the 20th century with the advent of those natural-gas pipeline networks. The efficiency of the process has improved by an order of magnitude since the old gasworks you see the ruins of in many industrial cities. As you say, though, that isn't enough to make IGCC plants economically competitive.

    The thing that makes steam engines economically uncompetitive today is renewable energy. Specifically, the precipitous drop in the price of solar power plants, especially PV modules, which are down to €0.10 per peak watt except in the US, about 15% of their cost ten years ago. This combines with rapidly dropping prices for batteries and for power electronics to undercut even the capex of thermal power generation rather badly, even (as you say) if the heat was free, whereas typically the fuel is actually about half the cost. I don't really understand what the prospects are for dramatically cheaper steam turbines, but given that the technology is over a century old, it seems likely that its cost will continue to improve only slowly.