Liquid Air

Discussion in 'The Science Forum' started by jonwilly, Oct 5, 2012.

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  1. Imagine you have an energy grid, that is all the houses and businesses which required electricity.

    To meet demand you have a number of resorces, Fossil (to burn) and Renewable (wind/water/solar/etc).

    At the heart of the Grid are Base Load power stations, things like coal, oil and nuclear. Once you set these things running its not efficient to turn them off, you can turn it down but it is still possible that supply exceeds demand or demand exceeds supply.

    With the renewables, if you are relying on them to cover base demand and the sun goes in or the wind drops then you need things called peaking stations which can be gas fired jet engines that can fire up quickly and meet demand.

    So thats the basics for balance of power in a grid, at night when most are asleep, the excess power can be used at a low cost to pump water up to a reservoir where it is stored, during the day when there is a peak (or you want to sell electricity your water falling through turbines creates at more than the price you paid for the elctricity to pump it up there) the reservoir opens and you generation electricity. This is know as pumped storage.

    Up until now, I beleive apart from batteries this is the only viable way of storing excess but doesnt help if you dont have water and mountains.

    But now they are suggesting you can use the excess to create compressed air which can be stored and then released to create wind when there is no wind to power wind turbines.

    I suppose its good if you are using excess renewables to store the energy, but pumped storage is more robbing peter to pay paul, its about supply and demand rather than free electricity from green sources but hey, better than just wasting it I suppose if you are creating it anyway.
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  2. They are not talking about compressed air, but air cooled to the point where the gases condense into liquid. Liquid nitrogen can be stored very easily in what are essentially thermos flasks (dewars) and there are self-pressurising versions of this where heat from the environment is used to pressurise an enclosed volume of liquid nitrogen. The bulk of the nitrogen remains a liquid, and the pressure is determined by the temperature of the nitrogen (Boyle's law and Charles' law). Looking at an enthalpy diagram of nitrogen, it seems that they will only acheive a useable pressure of 30Bar/450psi, which is quite a low pressure with which to drive a turbine.
  3. Gents my Physics stopped a 'O' level GCE.
    The subject is Liquid Air.
    I do not know if it is a practical proposition.
    Just hoping for enlightenment.

  4. My fault, I assumed you compressed it not cooled it to a liquid, sorry john, i thought you were talking about the 'wrong time' electricity rather than the chemistry/physics of turning air liquid.

    If you turn it liquid by removing the Carbon Dioxide, and then you 'vent' the Carbon Dioxide, doesnt that make it a polluter and therefore not at all green?
  5. No, as you will eventually vent the rest of the air, making that part of the process carbon neutral. Whether the whole process has a carbon cost or not depends on where the energy to cool the air in the first place comes from.
  6. Certainly sounds more environmentally friendly over the course of life than using batteries.
  7. Read it the other day. I think the ImechE's 70% efficiency estimate is rather optimistic. The other problem of course is that liquid gas can't be stored indefinitely. There will come a point that the pressure in the tank will approach the limit of the safety valves and the tank need blown down to operating pressure.

    Otherwise crack on, more work for me.
  8. Batteries, both in their production and their disposal, are quite polluting. The upside is their portability and in the case of rechargeable ones, the abilty to recharge them. That said, though, even 'green' forms of energy cause pollution in the production, upkeep, and disposal of the equipment, wind turbines for example. In this proposed system, there would have to be some form of turbine, and there would be some environmental cost in the whole life of each one.
  9. Not true.
  10. Indeed, my point was just that - at a guess - the production and disposal of such a system should be somewhat less polluting than making batteries, as turbines/tanks/etc are made of fairly easily re-recyclable materials.
  11. I should have read more than the first report, its not driving a turbine its moving a piston, sorry for misleading.

    On the other point of carbon, the report mentions that it is more efficient when used attached to a power station as a heat source and yet it would be created by wind turbines working at green energy to make it, brown energy to convert it.

    If you are creating heat, and therefore generating electricity anyway, what is the addional liquid air worth compared to the expense of maintaining it?

    It sounds like a proposition that could use wrong time green electricity to create electricity at the right time, but im not convinced it is a practicle proposition to the worlds energy problems or viable finacially which is all that seems to matter.
  12. really? If there's no draw on a cryo tank for a protracted amount of time then pressure in the tank doesn't increase. I better go tell my employers they're doing it wrong.

    Edit. They'll be delighted we don't need to Install any more alarm panels. The failure rate on the new mk2 medaes ones is astounding.
  13. I don't know about you, but I've had a tank full of liquid nitrogen (we're talking a few thousand litres) sat for weeks on end with no appreciable rise in pressure. Yes, if you wait long enough, then the nitrogen will absorb enough heat to cause a pressure rise that will approach that of the mwp of the container, but the intent is to store it for only a short time until required for use.
  14. However....

    What if the answer to energy was balanced self sustainability, as well as those solar panels on your roof you have a windmill and water tanks in your roof and pipes buried deep underground in every new house.

    When you are at work or asleep or its raining, the sun/wind are either creating liquid air or pumping water into your roof tanks or they are being by the rain.

    When you are home and its dark with no wind, the liquid air is warmed by underground heat transfer to create electricity at a rate you need it and finally as a back up the water tanks empty through small turbines creating electricity.

    You could add a bank of batteries in a deep cellar for those long winters.