5 ms·

I worked on a mining project years ago where we had to dewater the mine of 90 degree Celsius water at 700L/s. Always wondered whether we can use it for energy…

by rmm 3y ago

I worked on a mining project years ago where we had to dewater the mine of 90 degree Celsius water at 700L/s. Always wondered whether we can use it for energy….

darig 3y ago
[dead]
zdragnar 3y ago
You could use it for district heating of buildings in winter, but that's about it. As the article mentions, you need to get above the phase transition between liquid and gas at high pressure (they mention 150c) to be able to reliably and quickly convert the thermal energy into kinetic, then into electrical inductance (gas expansion moving a turbine, moving a dynamo). Maybe if you went into business making pot roast, you could cook meat low and slow, or set up massive dehydrators. Running it under a shallow drying bed might make salt extraction from water evaporation faster, too. Sadly, none of those things tend to be very close to mines.
- angiosperm 3y ago
  There are fluids other than water that have usefully different boiling points. Problem is that mature turbines are designed for steam. Turbines for other fluids cannot approach their market volume.
  - pi-e-sigma 3y ago
    That's not true at all. If any other liquids were more useful they would have been used long time ago, even in places where the cost is not of primary concern, such as nuclear submarines.
    - angiosperm 3y ago
      Nuclear submarines have no use for a working fluid that boils below 100 C. Indeed, they pressurize the water so that the boiling point is well above that point, because they have no difficulty heating water well above that. Steam is used everywhere despite that it is quite corrosive, mainly because it is cheap.
      - pi-e-sigma 3y ago
        You clearly don't know what you are talking about. Water steam is a perfect medium for turbines because of its favorable thermodynamic properties, mainly high specific heat allowing water steam to absorb large amount of thermal energy. Also water steam is not corrosive because water itself is not corrosive. It's the dissolved minerals making it corrosive and that's why water used for turbines is purified first.
        angiosperm 3y ago
        Yet, steam turbines attached to nuke and coal plants spend 10-20% of their time offline, being overhauled mainly because of high-temperature/high-pressure steam's corrosiveness. Cold distilled water is not corrosive. Superheated steam, howsoever pure, little resembles cold liquid water in any detail. Furthermore, hot water will pick up minerals from whatever it runs through. Many materials that are not especially corrosive as cold liquids behave quite differently at extreme pressure and temperature. Water has uncommon valuable thermodynamic properties, but not uniquely so; its chief virtue is that it is good enough and cheap.
        pi-e-sigma 3y ago
        OK, give me an example of one such liquid from your list of 'many' that has all the desired properties of water and doesn't have any undesired, such as being a poison. You can't because there aren't any.
    - mr_toad 3y ago
      > That's not true at all. If any other liquids were more useful they would have been used long time ago, Gas turbines are common when power to weight is more important than cost.
xarope 3y ago
Sous Vide is 50-60'C? I use to scoff, but turkey sous vided is yummy
greesil 3y ago
Ideal thermodynamic efficiency is 1-Tcold/Thot in an absolute temperature scale. This means given a perfect mechanism to turn heat into work this is the upper bound of how much of the heat can be turned into useful work. Say ambient air is 20 deg C, with your 90 deg C heat source then you get 1-293/363 which is about 20%. So it's not to say you can't get work out of this system, but it's not great compared to having something nice and not. And even then, you can't push a turbine with a hot liquid so your energy extraction technique now gets complicated.
- this_was_posted 3y ago
  would it be possible to use a heat pump to increase the temperature to a more efficient range? Or would all of the efficiency gained be lost by operating the heat pump?
  - seiferteric 3y ago
    I have wondered about this as well... If your heat pump uses say 1kW, and they usually provide 4x-5x heat out, so say 5kW of heat out and your able to extract 50% of that as energy using say a turbine, you would get 2.5kW out? or maybe 1.5kW (subtracting the initial 1kW used to run it?) so maybe not great but maybe possible?
    - rcxdude 3y ago
      given perfect heat pumps/engines in that circumstance, you would get exactly as much energy out as you put in. Theoretically perfect heat engines are called 'reversable' for that reason: they give you the best possible exchange between heat and work. Said another way: heat pumps can give you 4-5x the heat out as work you put in precisely for the same reason you can't get much work out of that heat: the temperature increase is small. If you were to heat something up to a temperature where you could more efficiently extract work from it, it would require more energy to do so.
  - greesil 3y ago
    Yes you can use a heat pump, but that requires work to run. Think compressors and whatnot. So even with a perfectly efficient heat pump that limit still holds because you are using some of the energy gained from your new hot temperature to run the heat pump.
a2l 3y ago
With this perhaps? https://climeon.com/how-it-works/ https://climeon.com/how-it-works/

by rmm 3y ago

I worked on a mining project years ago where we had to dewater the mine of 90 degree Celsius water at 700L/s. Always wondered whether we can use it for energy….

darig 3y ago

[dead]

zdragnar 3y ago

You could use it for district heating of buildings in winter, but that's about it. As the article mentions, you need to get above the phase transition between liquid and gas at high pressure (they mention 150c) to be able to reliably and quickly convert the thermal energy into kinetic, then into electrical inductance (gas expansion moving a turbine, moving a dynamo). Maybe if you went into business making pot roast, you could cook meat low and slow, or set up massive dehydrators. Running it under a shallow drying bed might make salt extraction from water evaporation faster, too. Sadly, none of those things tend to be very close to mines.

angiosperm 3y ago
There are fluids other than water that have usefully different boiling points. Problem is that mature turbines are designed for steam. Turbines for other fluids cannot approach their market volume.
- pi-e-sigma 3y ago
  That's not true at all. If any other liquids were more useful they would have been used long time ago, even in places where the cost is not of primary concern, such as nuclear submarines.
  - angiosperm 3y ago
    Nuclear submarines have no use for a working fluid that boils below 100 C. Indeed, they pressurize the water so that the boiling point is well above that point, because they have no difficulty heating water well above that. Steam is used everywhere despite that it is quite corrosive, mainly because it is cheap.
    - pi-e-sigma 3y ago
      You clearly don't know what you are talking about. Water steam is a perfect medium for turbines because of its favorable thermodynamic properties, mainly high specific heat allowing water steam to absorb large amount of thermal energy. Also water steam is not corrosive because water itself is not corrosive. It's the dissolved minerals making it corrosive and that's why water used for turbines is purified first.
      - angiosperm 3y ago
        Yet, steam turbines attached to nuke and coal plants spend 10-20% of their time offline, being overhauled mainly because of high-temperature/high-pressure steam's corrosiveness. Cold distilled water is not corrosive. Superheated steam, howsoever pure, little resembles cold liquid water in any detail. Furthermore, hot water will pick up minerals from whatever it runs through. Many materials that are not especially corrosive as cold liquids behave quite differently at extreme pressure and temperature. Water has uncommon valuable thermodynamic properties, but not uniquely so; its chief virtue is that it is good enough and cheap.
        pi-e-sigma 3y ago
        OK, give me an example of one such liquid from your list of 'many' that has all the desired properties of water and doesn't have any undesired, such as being a poison. You can't because there aren't any.
  - mr_toad 3y ago
    > That's not true at all. If any other liquids were more useful they would have been used long time ago, Gas turbines are common when power to weight is more important than cost.

xarope 3y ago

Sous Vide is 50-60'C? I use to scoff, but turkey sous vided is yummy

greesil 3y ago

Ideal thermodynamic efficiency is 1-Tcold/Thot in an absolute temperature scale. This means given a perfect mechanism to turn heat into work this is the upper bound of how much of the heat can be turned into useful work. Say ambient air is 20 deg C, with your 90 deg C heat source then you get 1-293/363 which is about 20%. So it's not to say you can't get work out of this system, but it's not great compared to having something nice and not. And even then, you can't push a turbine with a hot liquid so your energy extraction technique now gets complicated.

this_was_posted 3y ago
would it be possible to use a heat pump to increase the temperature to a more efficient range? Or would all of the efficiency gained be lost by operating the heat pump?
- seiferteric 3y ago
  I have wondered about this as well... If your heat pump uses say 1kW, and they usually provide 4x-5x heat out, so say 5kW of heat out and your able to extract 50% of that as energy using say a turbine, you would get 2.5kW out? or maybe 1.5kW (subtracting the initial 1kW used to run it?) so maybe not great but maybe possible?
  - rcxdude 3y ago
    given perfect heat pumps/engines in that circumstance, you would get exactly as much energy out as you put in. Theoretically perfect heat engines are called 'reversable' for that reason: they give you the best possible exchange between heat and work. Said another way: heat pumps can give you 4-5x the heat out as work you put in precisely for the same reason you can't get much work out of that heat: the temperature increase is small. If you were to heat something up to a temperature where you could more efficiently extract work from it, it would require more energy to do so.
- greesil 3y ago
  Yes you can use a heat pump, but that requires work to run. Think compressors and whatnot. So even with a perfectly efficient heat pump that limit still holds because you are using some of the energy gained from your new hot temperature to run the heat pump.

a2l 3y ago

With this perhaps? https://climeon.com/how-it-works/ https://climeon.com/how-it-works/