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Old 05-25-2021, 02:11 AM   #5 (permalink)
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I had an extra tab open so I tried the Search function. Fruitlessly. There was some University research gone commercial about extracting and storing the heat and using it to warm the decompressed air.

But I did find this article via DDG: History and Future of the Compressed Air Economy:Historical compressed air systems hold the key to the design of a low-tech, low-cost, robust, sustainable and relatively energy efficient energy storage medium.
First Lesson: Avoid Energy Conversions
I've always thought wind powered compressed air is very elegant. The compressed air network in Paris spanned 25 kilometers.
Second Lesson: Use Heat and Cold for Other Purposes

Today, most CAES engineers are focused on further improving efficiency by using the waste heat of compression to reheat the compressed air upon expansion. This method is called “Advanced Adiabatic CAES” (AA-CAES) or “fuelless CAES” and removes the need to reheat with natural gas as in the standard “diabatic” CAES. The technology is expected to reach an overall efficiency of roughly 70%, bringing it closer to the efficiency of chemical batteries and pumped hydropower storage plants. 7
This is what the research I'd seen was about. But there's a necessary link between where the air is compressed and expended. Not so hot for moving vehicles.
Third Lesson: Improve the Air Compressor
This part I thought was cool. I've seen homemade trompes on Youtube made from 2-liter bottles:
Once again, it pays to look to the past for inspiration. Surprisingly, the holy grail of “isothermal” air compression – in which no waste heat is produced at all – was found at least 400 years ago. The hydraulic air compressor – or “trompe”, as it was originally known – was an Italian invention first mentioned by name in 1588, but possibly already known in Antiquity.

From the 1600s onwards, dozens of “trompes” furnished a continuous air blast to early iron and brass-smelting furnaces in the French/Spanish Pyrenees. 2628 Compared to a waterwheel running a wooden piston compressor, it was roughly three times more efficient, allowing higher iron production with less water power resources.

Over a 33-year period starting in 1896, eighteen gigantic hydraulic air compressors were built, mostly in the US, Canada, Germany and Sweden. In the largest of these installations, which were partly or completely built underground, water and air fell through pipes and shafts – hewn out of the rocks – which could be more than 100 metres deep and up to 4 metres wide. The delivery pressure amounted to 8 bar and the power output could reach 3,000 kilowatts.
That's 3 Megawatts from falling water!
Conclussion: a realization that smacks you upside the head

"Anything is a smoke machine if you use it wrong enough" --AvE
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