OT: Liquid air power storage

Water has a fairly high thermal capacity, thus can carry away a lot of heat without much temperature rise. Further, the input temperature of the fluid to be cooled will not be too much above 100C, and the water will be warmed to 30C or so, so the temperature difference is not large. Unlike liquid air, which will be at -200C. And you wouldn't want to use water to warm it, too much risk of it freezing. Using ambient air can be done but the volume of air will be large, due to its much lower (than water) thermal capacity.

i.e. about 1000 times as expensive as Lithium Ion batteries from Lidl?

See also:

Its that solid air I worry about myself.

Brian

And 100 percent of wind comes from politicians?

I cannot see any advantage in breaking up the grid since the whole point of it is that its a national grid, go five years down the road and each one will be using incompatible systems so when we really do need a national distribution it will be broken. Brian

On 08/11/2020 15:33, Tim Streater wrote: <snip>

Yep - although IIRC the Highview designers make the point that using air at about ambient pressue for warming and evaporation allows the use of simple and cheap pipes, pumps, and cold stores

The air will have to be cooled as well as compressed. Hard to see how that would be economically achieved

I thought the plan was to just do this when energy prices are low due (windy nights say) and then use it as a version of ?pump storage?. It?s about providing short term power when required.

Tim

If you consider that a gas turbine consists of a compressor then a burner and then a power turbine and uses much of it's output to run the compressor, feeding it with high pressure air means you no longer require the compressor stage, add some thermal input, like natural gas, and not only do you get power out but you increase the expansion considerably plus you have the hot exhaust to supply energy for the change in state from liquid to gas.

I never did really understand temperature changes on compression and expansion of real gases properly, but I am pretty sure you won't get all that much heat out of the expansion stage of liquid air. A conventional gas turbine exhaust is bloody hot because of all the energy you are releasing in the combustion chamber.

A bicycle pump gets hot when you are working hard, and none of that is latent heat of evaporation/condensation. I'd expect the final expansion stages of air out of a turbine to be getting cooler.

No, and that's because you have to put heat in. I take it, BTW, that you imagine fridges work by magic?

Correct, because nothing is evaporating or condensing. You are compressing the gas (air in teh tube) and so it heats up.

When you expand air through a pressure difference it does work, even if it is only pushing against atmospheric pressure with a nozzle, it also get cooler, when you compress air, as in your pump, you exert energy and simultaneously its temperature rises.

To change air from liquid to gas you first have to supply energy, at the boiling point of the liquid, latent heat, with no rise in temperature. Once it is a gas you expand it through a heat engine, probably a turbine, but in expanding and doing work against the turbine it loses temperature again, so it doesn't expand as much but also makes everything around the exhaust cold, this is why I suggested expanding ambient temperature compressed air through a series of turbines with heat exchangers between each stage running a generator in the tube to cool the tunnels.

To be efficient you need to expand the air through the biggest temperature difference between the high pressure part of the cycle and the low temperature exhaust part of the cycle, so best to put some heat energy in at the high pressure and expand it to as near ambient as you can get.

In practice the turbine exhaust is over 800c, hence combined cycle gas power plants raise steam and get more work out of the hot exhaust . Further heat energy can be recycled after the steam condenser by using this heat to vaporise the liquid at the start of the cycle.

Not adding any heat at the beginning of the expansion would mean the work lost to the environment during isothermal compression and liquefaction could never be recovered and would severely impact whole cycle efficiency.

A conventional

Yes this heat is put in at the highest pressure part of the cycle. the temperature at this stage is what limits a jet because the metal parts of the turbine would suffer loss of strength under the immense centrifugal forces, so extra air needs to be added to cool components and reduce combustion temperature below what it would be if fuel where burned perfectly, even to having to have hollow turbine blades cooled by compressed air.

The reciprocating engines don't suffer as much because they only contact burning gases for part of the cycle and all the components are able to lose heat through conduction, hence they can burn fuel in the perfect proportion of air.

It's a brilliant idea. All that heat absorbed in warming up the gas will help cool the planet and counteract the effect of CO2!

/sarc

Seriously though, the process can't be anything but hugely inefficient. Perhaps that doesn't matter if the electricity is surplus to immediate requirements and the wind generators would otherwise be throttled back, but the capital has to be paid for and I would think that would make the electricity very expensive, and unsaleable on the open market.

I assume this is a demonstration plant. The one thing it will demonstrate is the impracticability of it all.

A couple of articles:

The Grauniad article says the total cost will be £85M, so about ten times your figure for cost per kWh! The advantage claimed is that it uses well-established cryogenic techniques and can be built using readily available components and doesn't need vast amounts of scarce rare-earths.

Where have my sums gone wrong?

capacity of plant being built

grant £m8

so

capital cost per MWh is 8,000,000/250 = £32,000

and capital cost per kWh is 8,000,000/250/1000 = £32

Or if the capital cost is £m85 (which seems more reasonable) then £340 per kWh.

PS I think most accept that batteries will be cheaper (as well as more efficient and faster to respond to grid demands) with current battery costs. But one driver behind LAES is to avoid having too many eggs in one basket should supply chains for their raw materials become difficult. (No prizes for guessing who has been accumulating ownership.)