3966 forum posts
Allegedly 60-70% efficient
UK energy plant to use liquid air
|Martin Kyte||08/11/2020 16:19:41|
2132 forum posts
Souns like a plan. Bit like a big spring really.
|Jon Lawes||08/11/2020 16:52:16|
422 forum posts
What a great idea. Probably less efficient than batteries but does that matter? Less rare earth metals and such, batteries degrade over time, and as the article says, easily scaleable. If the plant needs more capacity, add some tanks!
I love seeing new technology like this emerge. Although I can't imagine its the first time its been tried
|duncan webster||08/11/2020 17:08:55|
2854 forum posts
I'm fairly sure you can't liquify air by compression alone, you have to cool it. This takes energy, and the heat extracted is thrown away. The energy might be going spare in the middle of the night, or it could be charging the fleets of electric vehicles we are going to have. To then get it back to a gas you have to heat it, so a heat source is needed.
I can see why the CEGB went for pumped storage
Edited By duncan webster on 08/11/2020 17:20:09
|Howard Lewis||08/11/2020 18:15:40|
|3797 forum posts|
Maybe the latent heat of evaporation, coming from the ambient air, will help to reduce global warming, as long as it does not produce a local ice age
3966 forum posts
Seems like a super simple way of storing excess energy to me
You can put it anywhere you like and tap/feed whatever you need from the grid, the main resource is steel
Overproduction can be managed and stored, great for off grid facilities
Just hope that the guys doing it aren't ex-British Leyland people...
|Clive Foster||08/11/2020 18:23:05|
|2475 forum posts|
Yep. Duncan has it.
Too much to hope that the BBC is actually aware of things like phase diagrams. Let alone what they mean.
You need cooling to liquify atmospheric gases (except carbon dioxide). Commonly called regenerative systems. Incoming gas at high pressure goes through a heat echanger and thence to a nozzle pointing at said heat exchanger. The expansion of the gas it rushes out of the nozzle cools it which in turn cools the heat exchanger so the gas passing through it is also cooled. After a while the heat exchanger is cold enough that liquid nitrogen comes out of the nozzle as well as cold gas.
Well thats the theory.
As anyone who has used small Joule-Thompson coolers to produce liquid nitrogen from high pressure nitrogen gas seriously frustrating) or high pressure air (seriously, seriously frustrating as in jumping up and down tearing your hair out screaming profanities) the real world is less than co-operative. Given half a chance the systems will ice up, stopping flow and basically sit there sticking its tongue out at you saying Nah, Nah, Nah until its warmed up enough to evaporate everything. Which takes a while and, given that you are trying to cool things down, warming up is counterproductive.
In practice its likely that only nitrogen will be used. The other gases being filtered out. Oxygen condenses a little before nitrogen so a mix could be used but care is needed to avoid cold spots where oxygen ice could form and block flow. Annoying with a small JT cooler, potentially lethal in an industrial scale system.
The efficiency figures are suspiciously high. Link implies an isothermal system efficiency of 60 to 70% which seems unlikely.
Need to start with around 3,500 psi to regeneratively liquify nitrogen. Compressing air is notoriously inefficient, be doing well to get 80% compressor efficiency. Lots of waste head to deal with as well as the noise from a big reciprocating compressor. Screw types can't deliver the pressures needed. So that's over half the quoted loss budget gone already.
Expansion ratio of nitrogen when it goes from liquid to gas is just under 700, under half that of water which is 1600 when going to wet steam. So output turbine performance may be compromised. Especially as there is no equivalent to superheating or other tricks to get more energy in. The output side is going to get very cold too. The energy to evaporate the liquid will come from the ambient surroundings. For all practical purposes the sytem analyses as a heat pump. All the output energy is drawn from the surroundings.
Frankly I'd be surprised if the calculated output stage isothermal efficiency were much over 60%.
Looks something of a fraud to me.
Edited By Clive Foster on 08/11/2020 18:24:17
Edited By Clive Foster on 08/11/2020 18:24:47
|2645 forum posts|
HIW is at the bottom of the story:
|Peter Bell||08/11/2020 20:18:40|
|330 forum posts|
Thanks for the explanation--its all new to me so I found it very interesting after finding it on the web. From the info the plant looks quite large at 50Mw so expect the compressor (or multiples) and cooling to be big. Is the compressor normally a 3 stage piston type? Seems frightening pressures to me!
Once the air is a liquid can it be stored in an insulated container and what would the pressure be?
5578 forum posts
When cooling the air as part of the liquefaction process you can use the heat produced in a community heating project for for greenhouses, and to warm it again in the morning you can sell the coldness to cool computers and offices or just use river water.
|old mart||08/11/2020 20:43:41|
|2237 forum posts|
We had liquid nitrogen at work in a small vertical dewar flask around 3 feet diameter by 5 foot 6 inches high. The take off pipe inside ran close to the bottom of the tank and the valve and flexible pipe was at the top. The nitrogen was always at its boiling point, but kept at about 20 psi. This was to make it self discharging when the outlet valve was turned on. There were two safety valves, one designed to periodically vent pressure over the 20 psi set, the other set slightly higher. There was also a safety burst disc, a concave thin stainless steel, about 3" diameter which if it started to blow out, came in contact with sharp cutters which would rupture it.
Our works manager came up to me one day and said he was taking the rep from the firms insurance company past the nitrogen tank when a sudden blast of gas made them jump. I said to him that the safety vent did that several times a day and not to worry.
Edited By old mart on 08/11/2020 20:45:08
3966 forum posts
Thing is, efficiency really matters with finite resources like 100 tons of oil etc
But this is sun based renewables energy, so the resource is effectively infinite
So even if the efficiency isn't great, it's still better than what we've got as far as sustainability is concerned
|Mark Rand||08/11/2020 23:09:11|
|927 forum posts|
Just a small point:- liquid gas production plants use turbocompressors, with axial flow compressors, heat extraction, then axial flow turbines to expand the gas, cool it and feed power back to the compressors. This is more efficient than the free expansion in the Joule Thompson system.
Having said that, you still need to supply the heat that you rejected back to the liquified air/nitrogen in order to get meaningful output from the gas at the consumer end. You also need a plant that's got reaonable efficiency in extracting what's left of the usable energy at the consumer end. 75% cycle efficiency? Not convinced.
As a datum, AEI/GEC machines Rugby supplied what were the world's largest synchronous motors at 29,000hp for an oxygen liquifaction plant for a steel mill in the mid '70s...
If the plant stores the rejected heat in a usable form to help to re-gasify the air I'll believe that it's meaningful.
Edited By Mark Rand on 08/11/2020 23:18:26
997 forum posts
The plant to compress and cool the air will be incredibly noisy, we had a fractional distillation plant when I was in the Falklands, same process but was to produce liquid oxygen for use in the aircraft breathing systems. I remember in the 60’s in Sharjah, now the Emirates, we had an experimental rig that compressed and cooled gaseous oxygen from high pressure cylinders to convert to liquid oxygen again for aircraft system use. That was also incredibly noisy but due to the size of the plant , which worked 24 hours a day, only managed to produce about a litre a week which although it proved the equipment worked , the amount was not a useable quantity because each aircraft required a few litres every time it flew.
|J Hancock||09/11/2020 08:37:10|
|480 forum posts|
Which all nicely ignores the fact that there is NEVER a time when the output of renewables exceeds the
demand on the Grid.
|J Hancock||09/11/2020 08:45:35|
|480 forum posts|
Should have added a 'PS' !
It was good to see that inessential ' blackstuff ' providing 2.5% to the grid on a damp November weekend.
4899 forum posts
That sounds like they are not compressing it at all -- just cyrogenically freezing it to minus 196 degrees then using ambient heat to expand it to power a turbine. But who knows if the journalits have that quite right?
"Highview's liquid-air technology uses electricity to cool air down to -196°C, shrinking its volume by a factor of 700, which is then stored in low-pressure vacuum-insulated steel tanks — the kind that houses liquefied natural gas. When this cryogenically frozen air is exposed to ambient temperatures, it turns back into a gas and rapidly expands, with the rush of air from this 700-fold expansion directly driving an electricity-generating turbine. "
The artist's impression of the plant appears to show a bank of standard type air cooling towers in the foreground, as seen on many air-con or fridge plants. So there would be heat dumped overboard but probably still more efficient than building dams and pipelines and pumping water uphill etc in pumped hydro systems.
Edited By Hopper on 09/11/2020 10:22:56
|Peter Sansom||09/11/2020 11:53:35|
|79 forum posts|
Sounds like the first stage of of an Air Separation Unit, also known as an Oxygen plant for Oxygen and Nitrogen.
To separate Oxygen, Nitrogen and Argon from the air the first stage is is to liquify the air. This is done by compressing the with usually a large turbo compressor, removing all water, cooling with regenerative cooling then expansion. In large scale plants that separate Oxygen and Nitrogen they are usually producing large quantities of Oxygen and Nitrogen as a gas and after putting the liquid air in a distillation column, the separated products are used for the regenerative cooling. Only small quantities of Liquid Oxygen and Nitrogen are produced.
I cannot see a Liquid Air storage plant having a high enough efficiency to be commercially viable.
|1011 forum posts|
Although this concept is strange, with the surrounding air or water acting as the heat source and the working fluid the sink, it appears to me thermodynamically sound. It contravenes neither of the laws of thermodynamics.
However I would not invest any money in it. I cannot see a simple, cheap and easy way to get energy from it. Is it going to be a two stage system where you get energy from the liquid and gas or just a single stage system using just the gas? I am not a metallurgist but I recall that lots of metals don't like very cold temperatures.
I would invest in a liquid sodium liquid chlorine energy storage system.
6469 forum posts
The BBC article and other accounts I found on the web are technically poor - journalism. Of course it will work and could be very useful.
It's a bad mistake to compare this technology with fossil fuels. We happen to live at a time when fossil fuels were cheap and plentiful and perhaps are convinced it will last forever. The horrid truth is the party is coming to an end. Fossil fuels are a limited resource, about half of it has been burnt already and demand is rising rapidy. It's 2020, not 1955!
The outcome is predictable. Fossil fuel prices are going to rise until most people can't afford them. Think about a world in which a litre of petrol costs twenty times as much as it does today. Or more.
So unless the country wants to go down the toilet here's an urgent need to establish alternative sources of energy. Renewable energy is clean and free, but there's a catch : it only generates when Mother Nature is in the mood. So there has to be a way of storing most renewable energy, which is what this system does.
Although it makes little sense to burn coal in order to store energy# like this, using spare solar and wind energy to do the same is perfectly reasonable. It's a different system obeying different economic rules. Using renewable energy requires different technical solutions, not what worked well in the past.
# But see Dinorweg, which was originally used to overcome the inability of coal powered generating stations to slow down overnight.
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