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Power from liquid air

Helios
Work is starting in Manchester on MW scale liquid air to power system , designed by a inventor not from a university or academic institution , basic principals seem to be electricity is used to liquify air down to -197oC and the heat from this stored at around 110oC , the liquid air is held in cryogenic tanks and then when needed to generate electricity, the hot side is used to heat the liquid air , expanding it by 700 times in volume , this expansion then drives turbine and gen set.


At 20 yrs expected life of plant , no harmful emissions and ability to be a cheaper alternative to most battery technologies ,it looks a really interesting choice for eco thinkers and inventor did really interesting thing of storing the heat from compression , i like it had ability to use other heat sources also,, quoted efficiency is 60% which perhaps needs to improve because in one way its consuming electricity , however its biggest marketing aspect is that it can use surplus (mostly night time) cheap electricity, which is interesting as this electricity must be really cheap if your plant in one way is losing 40% of iit every cycle, whilst I dont think the media have been duped in giving it so much praise , one remark i herd is why not give people cheap night time electricity or isn,t this a device for making cheap electricity more costly ??? 


that aside i do see some uses for liquid air , be useful in some off grid scenarios , in a simpler format , could certainly heat a home at night , maybe an air conditioner supplimentary heat energy source ??  


only data i cant find is how many kw it takes to make a kg of liquid air ??? if any one knows
  • Former Community Member
    0 Former Community Member
    The market and technologies for energy storage are interesting,. For more data on liquid air and some comparisons see. https://kth.diva-portal.org/smash/get/diva2:1216213/FULLTEXT01.pdf and take a look at Highview Power website https://highviewpower.com/faq/  They are leading the way with projects such as https://finance.yahoo.com/news/highview-power-breaks-ground-250mwh-090000321.html


    In the UK, and other countries, there are times where electricity generation from renewable sources exceeds demand. This energy is wasted via a process call curtailment. For example see https://www.evwind.es/2020/07/05/wind-energy-expanded-19-in-2019-with-around-60-gw-of-new-capacity/75563  During these time wholesale electricity prices may be zero of even negative. This is one motivation for energy storage, even if it is not near 100% efficient. Pumped hydro systems are viable at 75% round trip efficiency for example in UK https://en.wikipedia.org/wiki/Dinorwig_Power_Station Other ractors are also impotant, particularly capital and operating costs.


    Andrew

    www.sygensys.com
  • 0
    Some more background reading here
    article

    A kilo of air is approx one cubic metre at room temperature and reduces to approx 1,2 litres of liquid at  77 K, the boiling point of liquid nitrogen - as oxygen has a higher boiling point and iar is mostly N2 anyway  the nitrogen temp, and molecular mass is normally assumed.


    To liquefy nitrogen  needs you to cool the air  by 220 degrees at  ~1 joule per gram per degree you might think this is mere 220kJ, plus a vaporisation energy of a further 180kJ  (based on 5000 Joules/mol where 1 mol is 28g). However  the second law of thermodynamics kicks in, even before you allow for real efficiency, so  to pump out 400kJ or between 2 masses 220degrees apart at  77K  and say 350K , will need  4.5 times as much energy - so your high temp heat-sink  receives 1800kJ, and you need to put in something closer to 2200kJ.

    Some but not all of these factors work in reverse getting the liquid back to gas again and getting the energy out.   You may be storing energy as "cold", but you could have to store or use quite a bit more as "hot". The key here to efficiency is not to waste the heat.

    In reality the whole cycle of putting energy in and getting it back again is perhaps only 30-50% efficient, but if the alternative is to set your wind turbines to idle, then saving half of something free is better than saving none, and in such cases when losses are not so important, storage makes sense. to compare  facilities using pumped water electric storage like Dinorwig electric mountain

    are typically quoted as 75% efficient. Unlike water, air tanks do not rely on the right geography. There are very small installations that use the waste cold gas from the turbines to operate refrigerated storage as well as generate electricity
    experiments on lorries are encouraging.



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    only data i cant find is how many kw it takes to make a kg of liquid air ??? if any one knows


    The specific heat capacity of air is around 1 kJ/kg.K, but I can’t tell you the latent heat of vaporisation off the top of my head and you’d have to account for all the moisture as well.


    What I *can* say is that the same principle is used in Air Separation Units, and I did some assessment work for one which was being moved from literally right next door to a coal-fired power station which was being decommissioned to a site in a different part of the country where it could be hooked up to an EHV substation.


    Obviously the idea is that the process is reversible like pumped hydro, batteries and so on, and while the efficiency you quote there is worse than either of the other examples, it doesn’t need a handy mountain to build it inside of like pumped hydro.  I’m not so sure what the advantage over a battery would be though - I did wonder whether footprint might be the answer, but apparently you can fit a 1 MW supercapacitor in a shipping container so I doubt it’s that...???


  • 0
    thanks thats a good way of working it out , I havent done it yet but if done by electricty I think about 2.5kw per kg . your right it does have better efficiency where it can access high heat , but I dont believe this 60% figure as its shown for this site , expect 50% in this configuration , ,just wonder how it will fair in 30oC although might be good for hot deserts by using spent air for air conditioning ????
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    Thanks Chris B ,I think its 2.5kw of electricity per kg , but its a curious figure not to be able to find on internet when you can find hydrogen easily , yes i am quite looking forward to MW scale capacitiors should be quite interesting , also may be able to get much more out of electric car , but poor old grid is creaking at the seems , there will be a place somewhere where some poor person plugs in to charge and they just happen to be the load that trips it out .I reckon in 10yrs time peak winter demands of 70000mw will be seen and no one will have thought how we are going to do it .
  • 0
    I suspect an attraction is that unlike batteries, you can use this with synchronous generation, real spinning copper and steel, with the load/frequency/phase relationships we need to keep the grid control stable. Also it sounds like the sort of thing that is more like engine making, and does not need large volumes of exotic chemicals, and can be done in a way that works for 50-100  years, more like a traditional power station, rather than needing a new battery every decade or so.
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    Himapj1  yes this turbo machinery argument is quite interesting , depends whether electrons are pushed down a cable or drawn down a cable, however i must admit that if the theory was true the electric car would be in a lot of trouble, either that or only houses on hills with car pointing downhill....? , if he could have attained 90% efficiency he would have probably cleaned up.

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