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Climate Change(d)?

steve_bank

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As a first order approximation ignoring the rest of the processes, calculate the energy needed to boil seawatre per liter at STP.

q = m*c*dt

q watts (dJ/dt)
m mass kg
c specific heat of seawater
dt temperature difference between seawater and boiling point


I leave it as an exercise for the student.
 

bilby

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As a first order approximation ignoring the rest of the processes, calculate the energy needed to boil seawatre per liter at STP.

q = m*c*dt

q watts (dJ/dt)
m mass kg
c specific heat of seawater
dt temperature difference between seawater and boiling point


I leave it as an exercise for the student.
Who the fuck boils seawater?

Modern desalination plants work by reverse osmosis. Water remains at ambient temperature throughout the process.
 

steve_bank

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OMG!!! I made a blunder. Not the first and not the last.
 

Jokodo

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As a first order approximation ignoring the rest of the processes, calculate the energy needed to boil seawatre per liter at STP.

q = m*c*dt

q watts (dJ/dt)
m mass kg
c specific heat of seawater
dt temperature difference between seawater and boiling point


I leave it as an exercise for the student.
Still the wrong unit.

Mass is kg.
Heat capacity is joules / (kelvins*kg)
Temperature difference is kelvins

All you end up with is joules, not joules over time. There is no time parameter in the input.
 

Politesse

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As drought lowers the levels of these two important rivers, salt incursion becomes more of a problem.
And the political lobby of the ag industry in the Valley counties is such that any conversation about calculated river management is political suicide. The farmers would happily see the San Joaquin and Sacramento rivers go completely dry over the summer rather than surrender any of their water rights.
Water politics goes back to the1 9th century does it not?
Water politics are more or less a constant in human history. But yes, often a particular problem in this conversation is that some of the stakeholders have grandfathered water rights that precede state law.
 

Politesse

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California has no need to be energy poor; Like Germany, their dependence upon imports for energy is entirely self inflicted and unnecessary.
We're not exactly dependent on imports, they're just cheaper and more commensurate with our ecological goals. But as we pay quite a lot for our energy as it is, relative to our neighbors, that's usually a strong consideration.

It's hard to make the case that the nation would be better off without those imports, either; if we just suddenly cut off the tap, it would be a disaster for the states we buy from. But I would like to see Californians use less energy in the first place, and especially California businesses.
 

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As a first order approximation ignoring the rest of the processes, calculate the energy needed to boil seawatre per liter at STP.

q = m*c*dt

q watts (dJ/dt)
m mass kg
c specific heat of seawater
dt temperature difference between seawater and boiling point


I leave it as an exercise for the student.
Huh? It takes more to vaporize than to raise it to the boiling point.
 

Loren Pechtel

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California has no need to be energy poor; Like Germany, their dependence upon imports for energy is entirely self inflicted and unnecessary.
We're not exactly dependent on imports, they're just cheaper and more commensurate with our ecological goals. But as we pay quite a lot for our energy as it is, relative to our neighbors, that's usually a strong consideration.

It's hard to make the case that the nation would be better off without those imports, either; if we just suddenly cut off the tap, it would be a disaster for the states we buy from. But I would like to see Californians use less energy in the first place, and especially California businesses.
Exporting the pollution is not a viable ecological solution. It's the usual way to make things "green" but it's actually not-green as you still have the same emissions and add the transport costs.
 

Politesse

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California has no need to be energy poor; Like Germany, their dependence upon imports for energy is entirely self inflicted and unnecessary.
We're not exactly dependent on imports, they're just cheaper and more commensurate with our ecological goals. But as we pay quite a lot for our energy as it is, relative to our neighbors, that's usually a strong consideration.

It's hard to make the case that the nation would be better off without those imports, either; if we just suddenly cut off the tap, it would be a disaster for the states we buy from. But I would like to see Californians use less energy in the first place, and especially California businesses.
Exporting the pollution is not a viable ecological solution. It's the usual way to make things "green" but it's actually not-green as you still have the same emissions and add the transport costs.
Relatively little of California's energy use comes from non-renewable resources, considering how much energy we use, even when imports are considered (it's not all coal); we're consistently ahead of our own goals on that. But, I do think there is room for further progress.
 

steve_bank

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A thought from the thread on German bird pests.

We label non human critters that foul the environment as pests.

Here in Seattle migrating Canadian Geese discovered open grass like golf courses. They foul lawns and lakes to the point where swimming is banned. They can take over a home lawn.

If we looked at humans as we do her species, might we be 'pests'?

Climate change to me is the result of our mytholgy as being apart and avove all others in the ecosystm.
 

Jimmy Higgins

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What about a farming tax? Almonds require obscene amounts of water. Why not provide a significant tax on top of it, so if the consumer really wants those almonds, they help fund the infrastructure that makes their growth in California possible?

Of course, nut growers would be against that.
 

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OMG!!! I made a blunder. Not the first and not the last.
If by that you mean “I got caught out bloviating and big-noting myself as a great teacher and master of the Socratic Method, while in fact not knowing the first thing about the subject under discussion”, then yes, you made “a blunder”.
 

bilby

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California has no need to be energy poor; Like Germany, their dependence upon imports for energy is entirely self inflicted and unnecessary.
We're not exactly dependent on imports, they're just cheaper and more commensurate with our ecological goals. But as we pay quite a lot for our energy as it is, relative to our neighbors, that's usually a strong consideration.

It's hard to make the case that the nation would be better off without those imports, either; if we just suddenly cut off the tap, it would be a disaster for the states we buy from. But I would like to see Californians use less energy in the first place, and especially California businesses.
Exporting the pollution is not a viable ecological solution. It's the usual way to make things "green" but it's actually not-green as you still have the same emissions and add the transport costs.
Relatively little of California's energy use comes from non-renewable resources, considering how much energy we use, even when imports are considered (it's not all coal); we're consistently ahead of our own goals on that. But, I do think there is room for further progress.
“Renewable sources” are slightly less environmentally harmful than fossil fuels, but if you think they’re anywhere close to having as low an impact on the environment as the nuclear power plants California has been closing, then you are badly misinformed.
 

skepticalbip

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What about a farming tax? Almonds require obscene amounts of water. Why not provide a significant tax on top of it, so if the consumer really wants those almonds, they help fund the infrastructure that makes their growth in California possible?

Of course, nut growers would be against that.
Vegans would probably object too. It would make their almond milk much more expensive.

Which raises a side question. How do they milk almonds? Those teats have gotta be awfully small and I would imagine getting the milking stool under an almond must be tricky.
 

Jokodo

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As a first order approximation ignoring the rest of the processes, calculate the energy needed to boil seawatre per liter at STP.

q = m*c*dt

q watts (dJ/dt)
m mass kg
c specific heat of seawater
dt temperature difference between seawater and boiling point


I leave it as an exercise for the student.
Who the fuck boils seawater?

Modern desalination plants work by reverse osmosis. Water remains at ambient temperature throughout the process.

And even if you did boil it, you could significantly lower the requirement of energy by recuperating much of the condensation heat and with a clever anticurrent heat exchange piping.
 

Jimmy Higgins

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What about a farming tax? Almonds require obscene amounts of water. Why not provide a significant tax on top of it, so if the consumer really wants those almonds, they help fund the infrastructure that makes their growth in California possible?

Of course, nut growers would be against that.
Vegans would probably object too. It would make their almond milk much more expensive.
Vegans are used to things costing more. People with lactose issues would probably complain more.
Which raises a side question. How do they milk almonds? Those teats have gotta be awfully small and I would imagine getting the milking stool under an almond must be tricky.
Yes, that was funny the first 20,000 times it was said.
 

steve_bank

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It has been reported almond production is going down. It uses more water than most other agriculture.
 

Loren Pechtel

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What about a farming tax? Almonds require obscene amounts of water. Why not provide a significant tax on top of it, so if the consumer really wants those almonds, they help fund the infrastructure that makes their growth in California possible?

Of course, nut growers would be against that.
Vegans would probably object too. It would make their almond milk much more expensive.
Vegans are used to things costing more. People with lactose issues would probably complain more.
People with lactose issues can get the lactose-free milk.
 

Politesse

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California has no need to be energy poor; Like Germany, their dependence upon imports for energy is entirely self inflicted and unnecessary.
We're not exactly dependent on imports, they're just cheaper and more commensurate with our ecological goals. But as we pay quite a lot for our energy as it is, relative to our neighbors, that's usually a strong consideration.

It's hard to make the case that the nation would be better off without those imports, either; if we just suddenly cut off the tap, it would be a disaster for the states we buy from. But I would like to see Californians use less energy in the first place, and especially California businesses.
Exporting the pollution is not a viable ecological solution. It's the usual way to make things "green" but it's actually not-green as you still have the same emissions and add the transport costs.
Relatively little of California's energy use comes from non-renewable resources, considering how much energy we use, even when imports are considered (it's not all coal); we're consistently ahead of our own goals on that. But, I do think there is room for further progress.
“Renewable sources” are slightly less environmentally harmful than fossil fuels, but if you think they’re anywhere close to having as low an impact on the environment as the nuclear power plants California has been closing, then you are badly misinformed.
Don't worry, I've had conversations with many a nuclear nut over the years. I think of you guys as being a bit like pot adovcates. You know, the golden substance that solves all ills and whose alleged downsides are all propaganda by "the other side" who is trying to keep us down. It's not that you don't have a point of sorts, but nuclear power has costs and benefits like any other power source. I don't disagree that nuclear power should be a part of California's power grid, and contrary to what you seem to imply, it is and will continue to be for the indefinite future, even with our two current plants closed. As has been observed, we do business with other states also.
 

steve_bank

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California has no need to be energy poor; Like Germany, their dependence upon imports for energy is entirely self inflicted and unnecessary.
We're not exactly dependent on imports, they're just cheaper and more commensurate with our ecological goals. But as we pay quite a lot for our energy as it is, relative to our neighbors, that's usually a strong consideration.

It's hard to make the case that the nation would be better off without those imports, either; if we just suddenly cut off the tap, it would be a disaster for the states we buy from. But I would like to see Californians use less energy in the first place, and especially California businesses.
Exporting the pollution is not a viable ecological solution. It's the usual way to make things "green" but it's actually not-green as you still have the same emissions and add the transport costs.
Relatively little of California's energy use comes from non-renewable resources, considering how much energy we use, even when imports are considered (it's not all coal); we're consistently ahead of our own goals on that. But, I do think there is room for further progress.
“Renewable sources” are slightly less environmentally harmful than fossil fuels, but if you think they’re anywhere close to having as low an impact on the environment as the nuclear power plants California has been closing, then you are badly misinformed.
Don't worry, I've had conversations with many a nuclear nut over the years. I think of you guys as being a bit like pot adovcates. You know, the golden substance that solves all ills and whose alleged downsides are all propaganda by "the other side" who is trying to keep us down. It's not that you don't have a point of sorts, but nuclear power has costs and benefits like any other power source. I don't disagree that nuclear power should be a part of California's power grid, and contrary to what you seem to imply, it is and will continue to be for the indefinite future, even with our two current plants closed. As has been observed, we do business with other states also.
Most definitely a big thumbs up.
 

lpetrich

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I'll calculate the energy input necessary to desalinate water.

First, desalination by boiling.

Water - Heat of Vaporization vs. Temperature
Water - Specific Heat vs. Temperature
Water - Saturation Pressure vs. Temperature

The specific heat of water is 4.18 joules/gram/kelvin (J/g/K) - From room temperature (20 C) to sea-level-pressure boiling point (100 C) is 334 J/g.

The heat of vaporization is much greater, 2256 J/g at 100 C at sea-level pressure (1.014 bar), while lower pressure makes it slightly higher: 2308 J/g at 80 C (0.4742 bar), 2358 J/g at 60 C (0.1995 bar), 2406 J/g at 40 C (0.0739 bar).

So it takes a *lot* of energy to boil water.
 

Jokodo

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I'll calculate the energy input necessary to desalinate water.

First, desalination by boiling.

Water - Heat of Vaporization vs. Temperature
Water - Specific Heat vs. Temperature
Water - Saturation Pressure vs. Temperature

The specific heat of water is 4.18 joules/gram/kelvin (J/g/K) - From room temperature (20 C) to sea-level-pressure boiling point (100 C) is 334 J/g.

The heat of vaporization is much greater, 2256 J/g at 100 C at sea-level pressure (1.014 bar), while lower pressure makes it slightly higher: 2308 J/g at 80 C (0.4742 bar), 2358 J/g at 60 C (0.1995 bar), 2406 J/g at 40 C (0.0739 bar).

So it takes a *lot* of energy to boil water.
In your kitchen, yes. In an industrial setting where saving energy is the key to commercial success, or to public approval, a *lot* of the energy can be recuperated by having a countercurrent piping for heat exchange and recuperating some of the heat of condensation. Your output isn't stream, your output is water at ambient temperature. The limiting factor is how efficiently the energy can be recovered, not how much you'd need for One gram in isolation.
 

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I'll now consider reverse osmosis, and its thermodynamic limit.

Desalination_system_with_efficiency_approaching_the_theoretical_limits.pdf

\( \displaystyle{ \frac{dW}{dn_{out}} = \Delta \mu = - R T \ln f } \)

The "mu" is something called "chemical potential", the amount of energy needed to add one molecule of something. W is the energy input, n(out) is amount of water out, R is the ideal gas constant, T is the temperature, and f is the ratio of n(water) to n(total) = n(water) + n(solute, what's dissolved). The n's are in moles (gram molecular weights, not the burrowing animals):

\( \displaystyle{ f = \frac{n_w}{n_w + n_s} } \)

Since n(solute) << n(water) for seawater and most brines, we can simplify the equation to

\( \displaystyle{ \frac{dW}{dn_w} = R T \frac{n_s}{n_w} } \)

We get a solution:

\( \displaystyle{ W = R T n_s \log \frac{n_i}{n_f} } \)

where n(i) and n(f) are the initial and amounts of source water.

I find from  Seawater that it contains 0.021 moles of dissolved ions for each mole of water, and I estimate that for extracting half of the original water, the thermodynamic limit is about 2 J/g.

In practice, however, reverse osmosis is much less efficient, typically 10% - 20%, meaning that it consumes 5 to 10 times that much energy.
 
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Swammerdami

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It has been reported almond production is going down. It uses more water than most other agriculture.

Nitpick: While almonds use VERY much water per gram of shelled product, that really isn't the proper measure. Water per unit of food "value" would make more sense; simplest is to define the food's "value" as its selling price. Almonds are expensive.

The water cost of almonds is still high even when measured that way, but less exaggeratedly so. I think citrus fruits also have high water cost per dollar of food "value."
 

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It has been reported almond production is going down. It uses more water than most other agriculture.

Nitpick: While almonds use VERY much water per gram of shelled product, that really isn't the proper measure. Water per unit of food "value" would make more sense; simplest is to define the food's "value" as its selling price. Almonds are expensive.

The water cost of almonds is still high even when measured that way, but less exaggeratedly so. I think citrus fruits also have high water cost per dollar of food "value."
Citrus in California, but probably not as much citrus in Florida.
 

steve_bank

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It has been reported almond production is going down. It uses more water than most other agriculture.

Nitpick: While almonds use VERY much water per gram of shelled product, that really isn't the proper measure. Water per unit of food "value" would make more sense; simplest is to define the food's "value" as its selling price. Almonds are expensive.

The water cost of almonds is still high even when measured that way, but less exaggeratedly so. I think citrus fruits also have high water cost per dollar of food "value."


We are fiddling aka nitpicking while Rome burns. The story that Emporer Nero was playing a fiddle whie a fire raged.
 

Swammerdami

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We are fiddling aka nitpicking while Rome burns. The story that Emporer Nero was playing a fiddle whie a fire raged.

You must not get around. I am certainly aware of the Nero story: It was I who introduced it recently in another thread as evidence for an historic Jesus Christ — Whether or not he fiddled, historians attest that Nero blamed the fire on Chrestians.

If the Christians were a significant religious heresy in the Roman capital barely 2 decades after the Crucifixion, one infers that that sect or sects caught on quickly, even before the alleged writings of Paul or proto-Mark. That is certainly incompatible with the notion that Jesus of Nazareth was a fiction developed in the 2nd century. AFAICT, mythicists are reduced to complaining that Chrestians/Chrstians and Christians are spelled differently; and then postulating the two (English transcriptions?) to be different. Talk about grasping at straws.
 

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For evaporation desalination, one can avoid heating the water by boiling it at room temperature, while keeping it warm with a heat exchanger that would be supplied by additional water. From that Engineering Toolbox calculator, I find 30 C: 0.0425 bar, 20 C: 0.023 bar, 10 C 0.0123 bar, 0 C 0.0061 bar. So one will need some strong air pumps, strong enough to make a soft vacuum.

Microsoft PowerPoint - SWRO-and-energy-consumption-KV_5-4-20_dv - Read-Only - energy-recovery-presentation-2020-water-forum.pdf

Page 8:
  • 1970: Multistage Flash -- low-pressure evaporation
  • 1982: Membrane Technology -- reverse osmosis
  • 2002: Membrane Technology Improvement -- more RO
  • 2005: Renewable Energies -- to power the desalination
My comments are after the --'s.

From Page 18 is energy consumption (kWh/m^3):
  • Multistage Flash Evaporation -- 1970: 25, 1978: 19, 1987: 14
  • Reverse Osmosis -- 1988: 13, 1990: 8, 1993: 6, 1998: 5, 2000: 4, 2003: 3.5, 2005: 3, 2010: 2.5, 2020: 2
1 kWh/m^3 = 3.6 J/g

So one can do as good as 7 J/g at the present day.

For low-pressure evaporation, a plausible lower limit can be found with the help of the ideal gas law: for 1 mole of water, R*T or 135 J/g.
 

steve_bank

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We are fiddling aka nitpicking while Rome burns. The story that Emporer Nero was playing a fiddle whie a fire raged.

You must not get around. I am certainly aware of the Nero story: It was I who introduced it recently in another thread as evidence for an historic Jesus Christ — Whether or not he fiddled, historians attest that Nero blamed the fire on Chrestians.

If the Christians were a significant religious heresy in the Roman capital barely 2 decades after the Crucifixion, one infers that that sect or sects caught on quickly, even before the alleged writings of Paul or proto-Mark. That is certainly incompatible with the notion that Jesus of Nazareth was a fiction developed in the 2nd century. AFAICT, mythicists are reduced to complaining that Chrestians/Chrstians and Christians are spelled differently; and then postulating the two (English transcriptions?) to be different. Talk about grasping at straws.
You da man!

Fiddle dee dee.

Holy crap man. It was just a commnet about how we are all gong about busness as usual while climate worsens. At least over the image of Nero is or used to be a comm metaphor.
 

Loren Pechtel

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For evaporation desalination, one can avoid heating the water by boiling it at room temperature, while keeping it warm with a heat exchanger that would be supplied by additional water. From that Engineering Toolbox calculator, I find 30 C: 0.0425 bar, 20 C: 0.023 bar, 10 C 0.0123 bar, 0 C 0.0061 bar. So one will need some strong air pumps, strong enough to make a soft vacuum.

Microsoft PowerPoint - SWRO-and-energy-consumption-KV_5-4-20_dv - Read-Only - energy-recovery-presentation-2020-water-forum.pdf

Page 8:
  • 1970: Multistage Flash -- low-pressure evaporation
  • 1982: Membrane Technology -- reverse osmosis
  • 2002: Membrane Technology Improvement -- more RO
  • 2005: Renewable Energies -- to power the desalination
My comments are after the --'s.

From Page 18 is energy consumption (kWh/m^3):
  • Multistage Flash Evaporation -- 1970: 25, 1978: 19, 1987: 14
  • Reverse Osmosis -- 1988: 13, 1990: 8, 1993: 6, 1998: 5, 2000: 4, 2003: 3.5, 2005: 3, 2010: 2.5, 2020: 2
1 kWh/m^3 = 3.6 J/g

So one can do as good as 7 J/g at the present day.

For low-pressure evaporation, a plausible lower limit can be found with the help of the ideal gas law: for 1 mole of water, R*T or 135 J/g.
I'm curious if you could make a practical desalinator with a vacuum pump:

Take say 20 meters of pipe, stick the bottom 5 meters into the ocean, connect the top to a vacuum pump. The pump should suck water vapor + dissolved gases and you should be able to get some of the power needed to run it from the heating as you compress that back to sea level pressure.

(For efficiency I would think you would want a big open flat area at the point where the water was evaporating and a separate discharge pipe that goes deeper into the ocean--you would need a pump to start it but I'm not sure it would require continued use as the discharge water is denser, once started there would be a natural flow, but I don't know if it would be enough to be useful.)
 

steve_bank

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Freeze dried coffee. Or freeze dried solids from salt water?


Lowering the pressure lowers the boiling point. I'd guess you would need a filter
 

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You lower the pressure, that leads to evaporation... but how do you get the water out? So great, you have water vapor and a surface with solids... but how do you get the vapor somewhere else to consolidate back into liquid? Being a vacuum, you can't move push or manipulate where it goes. And the volume of vapor will be notable compared to the volume of the liquid.
 

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You lower the pressure, that leads to evaporation... but how do you get the water out? So great, you have water vapor and a surface with solids... but how do you get the vapor somewhere else to consolidate back into liquid? Being a vacuum, you can't move push or manipulate where it goes. And the volume of vapor will be notable compared to the volume of the liquid.
You compress the chamber after removing the solids? Know I don't know if that's energy efficient, and I'm definitely not saying it is, but where did a filter come in?
 

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You lower the pressure, that leads to evaporation... but how do you get the water out? So great, you have water vapor and a surface with solids... but how do you get the vapor somewhere else to consolidate back into liquid? Being a vacuum, you can't move push or manipulate where it goes. And the volume of vapor will be notable compared to the volume of the liquid.
You compress the chamber after removing the solids? Know I don't know if that's energy efficient, and I'm definitely not saying it is, but where did a filter come in?
Presumably some of the solids would present as a dust or film on the surface the water was on, so removal isn't going to be simple.

The vacuum idea sounded great until I gave it a little thought and then the idea kind of falls apart. You need to be able to cover the solids, drop the water out of the vacuum, but that'd require something large and mechanical. Moving the tanks isn't feasible and you can't move the "air".
 

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Why are we brainstorming ideas for how to desalinate seawater, when it is an already mature technology whereby the factory gate wholesale price of the finished commodity is around $0.0009 per litre?

Reverse osmosis works very well on industrial scales, and has been doing so for many decades now.

In the context of a discussion on the dangers of any given coastal region “running out of water”, this sets a ceiling on the actual cost of water for residents of that region; They literally cannot run out of water as long as they can afford $0.0009 per litre (for regions away from the coast, a small additional cost for pumping and infrastructure would also be needed).

They might run out of water at the current price point, which is presumably lower than $0.0009/l, but I am struggling to see that as any kind of disaster.

California is amongst the wealthiest regions of the wealthiest nation in the history of the world. They are not going to run out of water, and they can easily afford to supply it to anyone and everyone at a cost that is utterly trivial to any resident who can afford food.

Any Californian state, county, or city authority could also easily afford to supply desalinated water free at point of use to residences, and recoup the costs of doing so either through local taxes, or by having industrial, commercial and agricultural bulk water users pay a few cents per cubic metre to subsidise that service. But that would be communism and would collapse civilisation, so I won’t suggest it.

If anyone thinks that boiling or vacuum distillation of seawater can compete with reverse osmosis, they are of course welcome to establish their own competitive drinking water supply company.
 

Loren Pechtel

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You lower the pressure, that leads to evaporation... but how do you get the water out? So great, you have water vapor and a surface with solids... but how do you get the vapor somewhere else to consolidate back into liquid? Being a vacuum, you can't move push or manipulate where it goes. And the volume of vapor will be notable compared to the volume of the liquid.
The water will condense on it's own as it cools down after coming out of the vacuum pump.

The question is the energy used by this process.
 

Loren Pechtel

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Presumably some of the solids would present as a dust or film on the surface the water was on, so removal isn't going to be simple.

The vacuum idea sounded great until I gave it a little thought and then the idea kind of falls apart. You need to be able to cover the solids, drop the water out of the vacuum, but that'd require something large and mechanical. Moving the tanks isn't feasible and you can't move the "air".

The surface of the water will boil. Why would the solids come up with the steam?
 

steve_bank

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Is the implication that a vacuum is the same quality as distilled water?


Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property that is driven by chemical potential differences of the solvent, a thermodynamic parameter. Reverse osmosis can remove many types of dissolved and suspended chemical species as well as biological ones (principally bacteria) from water, and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective", this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as solvent molecules, e.g., water, H2O) to pass freely.[1]

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (high water potential), through a membrane, to an area of high solute concentration (low water potential). The driving force for the movement of the solvent is the reduction in the Gibbs free energy of the system when the difference in solvent concentration on either side of a membrane is reduced, generating osmotic pressure due to the solvent moving into the more concentrated solution. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications.

Reverse osmosis differs from filtration in that the mechanism of fluid flow is by osmosis across a membrane. The predominant removal mechanism in membrane filtration is straining, or size exclusion, where the pores are 0.01 micrometers or larger, so the process can theoretically achieve perfect efficiency regardless of parameters such as the solution's pressure and concentration. Reverse osmosis instead involves solvent diffusion across a membrane that is either nonporous or uses nanofiltration with pores 0.001 micrometers in size. The predominant removal mechanism is from differences in solubility or diffusivity, and the process is dependent on pressure, solute concentration, and other conditions.[2]

Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other effluent materials from the water molecules.[3]

Drinking water purification​


Around the world, household drinking water purification systems, including a reverse osmosis step, are commonly used for improving water for drinking and cooking.

Such systems typically include a number of steps:


  • a sediment filter to trap particles, including rust and calcium carbonate
  • optionally, a second sediment filter with smaller pores
  • an activated carbon filter to trap organic chemicals and chlorine, which will attack and degrade certain types of thin-film composite membrane
  • a reverse osmosis filter, which is a thin-film composite membrane
  • optionally, an ultraviolet lamp for sterilizing any microbes that may escape filtering by the reverse osmosis membrane
  • optionally, a second carbon filter to capture those chemicals not removed by the reverse osmosis membrane

In some systems, the carbon prefilter is omitted, and a cellulose triacetate membrane is used. CTA (cellulose triacetate) is a paper by-product membrane bonded to a synthetic layer and is made to allow contact with chlorine in the water. These require a small amount of chlorine in the water source to prevent bacteria from forming on it. The typical rejection rate for CTA membranes is 85–95%.

The cellulose triacetate membrane is prone to rotting unless protected by chlorinated water, while the thin-film composite membrane is prone to breaking down under the influence of chlorine. A thin-film composite (TFC) membrane is made of synthetic material, and requires chlorine to be removed before the water enters the membrane. To protect the TFC membrane elements from chlorine damage, carbon filters are used as pre-treatment in all residential reverse osmosis systems. TFC membranes have a higher rejection rate of 95–98% and a longer life than CTA membranes.

Portable reverse osmosis water processors are sold for personal water purification in various locations. To work effectively, the water feeding to these units should be under some pressure (280 kPa (40 psi) or greater is the norm).[10] Portable reverse osmosis water processors can be used by people who live in rural areas without clean water, far away from the city's water pipes. Rural people filter river or ocean water themselves, as the device is easy to use (saline water may need special membranes). Some travelers on long boating, fishing, or island camping trips, or in countries where the local water supply is polluted or substandard, use reverse osmosis water processors coupled with one or more ultraviolet sterilizers.

In the production of bottled mineral water, the water passes through a reverse osmosis water processor to remove pollutants and microorganisms. In European countries, though, such processing of natural mineral water (as defined by a European directive[11]) is not allowed under European law. In practice, a fraction of the living bacteria can and do pass through reverse osmosis membranes through minor imperfections, or bypass the membrane entirely through tiny leaks in surrounding seals. Thus, complete reverse osmosis systems may include additional water treatment stages that use ultraviolet light or ozone to prevent microbiological contamination.

Membrane pore sizes can vary from 0.1 to 5,000 nm depending on filter type. Particle filtration removes particles of 1 µm or larger. Microfiltration removes particles of 50 nm or larger. Ultrafiltration removes particles of roughly 3 nm or larger. Nanofiltration removes particles of 1 nm or larger. Reverse osmosis is in the final category of membrane filtration, hyperfiltration, and removes particles larger than 0.1 nm.[12]

Energy


It takes most reverse osmosis plants about three to 10 kilowatt-hours of energy to produce one cubic meter of freshwater from seawater. Traditional drinking water treatment plants typically use well under 1 kWh per cubic meter.May 15, 2015

How much does membrane desalination cost?


For a frame of reference, the typical annualized costs for seawater desalination projects vary widely from US $2.00/1,000 gallons (kgal) to $12.00/kgal.



Membranes.
RO membranes are typically either cellulose acetate or polysulfone coated with aromatic polyamides3. NF membranes are made from cellulose acetate blends or polyamide composites like the RO membranes, or they could be modified forms of UF membranes such as sulfonated polysulfone10.



I am weak in chemistry so I won't wade through it.
 

lpetrich

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I added J/g values to kWh/m^3 values in ()'s, to see how close one can get to the thermodynamic limit.
  • Multistage Flash Evaporation -- 1970: 25 (90), 1978: 19 (68), 1987: 14 (50)
  • Reverse Osmosis -- 1988: 13 (47), 1990: 8 (29), 1993: 6 (22), 1998: 5 (18), 2000: 4 (14), 2003: 3.5 (13), 2005: 3 (11), 2010: 2.5 (9), 2020: 2 (7)


Water use in California
(2019 June)

It reports water volumes in millions of acre-feet. 1 acre-foot is 1233.48 cubic meters. 1 million acre-feet = 1.23348 cubic kilometers
  • Agriculture: 31 maf/yr = 38 km^3/yr = 1200 m^3/s = 8.4 gigawatts at 7 J/g
  • Urban uses: 7.9 maf/yr = 9.7 km^3/yr = 300 m^3/s = 2.2 gigawatts at 7 J/g
So California's agriculture uses 4 times as much water as what California's citizens use directly. I think that that state needs to invest heavily in low-flow irrigation, like drip irrigation, and also in salt-tolerant crop plants.

From https://www.energy.gov/sites/prod/files/2015/05/f22/CA-Energy Sector Risk Profile.pdf (2015), CA's annual consumption of electricity is 259.5 terawatt-hours per year or 29 gigawatts.

So it could be done.
 

steve_bank

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Some yeras back I wraced a segment on low water toilets. A professor was conrcted to build a toiet for 3rd wprd cuntries.

He invnetd a super slippery surface with fine slippery threads. He had to createa faux poop to test it.

The amount of wtaer a tliet flushes depnds on how slippery the surface is.

Something newer.


Scientists develop spray-on slippery toilet coating to stop poo sticking – video

Ian Sample Science editor

@iansample
Mon 18 Nov 2019 11.11 ESTLast modified on Mon 18 Nov 2019 14.50 EST

The toilet brush need never leave its holder again. Scientists have created a super-slippery coating that helps usher excrement on its way without leaving traces behind.
The spray-on coating, which is slipperier than Teflon, reduces adhesion of even tenacious faeces by up to 90%, tests suggest, so far less water is needed to flush them away and leave the toilet clean.



Toilet tech is no longer the oft-overlooked subject it once was, and much of that is thanks to the Gates Foundation, which has made helping the 3.5 billion people lacking access to clean toilets one of its main missions. But how does one test the durability of potential cost-effective commodes? By using fake poop, of course.


During the Gates Foundation's 2012 Reinvent the Toilet Fair—a competition that encouraged local inventors to create inexpensive and hygienic waterless toilets—organizers obviously couldn't ask all the participants to fill their toilets with round after round of test poops. Instead, the Gates Foundation looked to the engineered excrement of Maximum Performance, a company whose sole mission is to create the best damn fake poop this world has to offer.
 

skepticalbip

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Some yeras back I wraced a segment on low water toilets. A professor was conrcted to build a toiet for 3rd wprd cuntries.

He invnetd a super slippery surface with fine slippery threads. He had to createa faux poop to test it.

The amount of wtaer a tliet flushes depnds on how slippery the surface is.

Older technology was much more efficient as far as water use. They called them outhouses and they used no water. 😉
 

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Some yeras back I wraced a segment on low water toilets. A professor was conrcted to build a toiet for 3rd wprd cuntries.

He invnetd a super slippery surface with fine slippery threads. He had to createa faux poop to test it.

The amount of wtaer a tliet flushes depnds on how slippery the surface is.

Older technology was much more efficient as far as water use. They called them outhouses and they used no water. 😉
That worked well enough when 80 per cent of the population lives in rural settings. Not so much in countries where 80+ per cent is urbanised.

Highrise_Building_in_Hongkong.jpg
 

steve_bank

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For evaporation desalination, one can avoid heating the water by boiling it at room temperature, while keeping it warm with a heat exchanger that would be supplied by additional water. From that Engineering Toolbox calculator, I find 30 C: 0.0425 bar, 20 C: 0.023 bar, 10 C 0.0123 bar, 0 C 0.0061 bar. So one will need some strong air pumps, strong enough to make a soft vacuum.

Microsoft PowerPoint - SWRO-and-energy-consumption-KV_5-4-20_dv - Read-Only - energy-recovery-presentation-2020-water-forum.pdf

Page 8:
  • 1970: Multistage Flash -- low-pressure evaporation
  • 1982: Membrane Technology -- reverse osmosis
  • 2002: Membrane Technology Improvement -- more RO
  • 2005: Renewable Energies -- to power the desalination
My comments are after the --'s.

From Page 18 is energy consumption (kWh/m^3):
  • Multistage Flash Evaporation -- 1970: 25, 1978: 19, 1987: 14
  • Reverse Osmosis -- 1988: 13, 1990: 8, 1993: 6, 1998: 5, 2000: 4, 2003: 3.5, 2005: 3, 2010: 2.5, 2020: 2
1 kWh/m^3 = 3.6 J/g

So one can do as good as 7 J/g at the present day.

For low-pressure evaporation, a plausible lower limit can be found with the help of the ideal gas law: for 1 mole of water, R*T or 135 J/g.
You're thinking like an engineer! :D
 

Loren Pechtel

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Some yeras back I wraced a segment on low water toilets. A professor was conrcted to build a toiet for 3rd wprd cuntries.

He invnetd a super slippery surface with fine slippery threads. He had to createa faux poop to test it.

The amount of wtaer a tliet flushes depnds on how slippery the surface is.

Older technology was much more efficient as far as water use. They called them outhouses and they used no water. 😉

Not a good idea unless you have a lot of land to act like a septic system leech field.
 

skepticalbip

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Some yeras back I wraced a segment on low water toilets. A professor was conrcted to build a toiet for 3rd wprd cuntries.

He invnetd a super slippery surface with fine slippery threads. He had to createa faux poop to test it.

The amount of wtaer a tliet flushes depnds on how slippery the surface is.

Older technology was much more efficient as far as water use. They called them outhouses and they used no water. 😉

Not a good idea unless you have a lot of land to act like a septic system leech field.
A septic system needs water. Outhouses don't.

It is a matter of setting priorities, save water or eliminate stench. Steve was worried about water use. Cities like Paris and London were awfully smelly places before there were flush toilets but, with no flush toilets and sewer systems, their water use was minimal.
 

steve_bank

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I suppose a hole in the ground could be called technology. Just don't eat the yellow snow.

It is interesting in all of Star Trek TV I never once saw somebody take a restroom break.

It really comes down to there are too many people.

After fasting for 40 days an 40 nights and taking a dose of peyote I had a vision. Eventually nature will reduce population. The Great Spirit has spoken.

A report from Lebanon said that with the wheat crisis people there are on the verge of starvation. Same reports from other places.
 

bilby

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Some yeras back I wraced a segment on low water toilets. A professor was conrcted to build a toiet for 3rd wprd cuntries.

He invnetd a super slippery surface with fine slippery threads. He had to createa faux poop to test it.

The amount of wtaer a tliet flushes depnds on how slippery the surface is.

Older technology was much more efficient as far as water use. They called them outhouses and they used no water. 😉

Not a good idea unless you have a lot of land to act like a septic system leech field.
A septic system needs water. Outhouses don't.

It is a matter of setting priorities, save water or eliminate stench. Steve was worried about water use. Cities like Paris and London were awfully smelly places before there were flush toilets but, with no flush toilets and sewer systems, their water use was minimal.
Their cholera and dysentery levels were pretty spectacular though.

Saving water is easy when you’re dead.
 

bilby

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It really comes down to there are too many people.
No, there fucking aren’t.

That comment is directly on a par with “It really comes down to there are too many Jews” - it’s the inevitable precursor to attempts to change the world for the worse.

I wish people would learn to be equally as embarrassed to say either thing in public. But for some reason, genocide is fine as long as you are indiscriminate about who else you want to eliminate.
 

thebeave

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Some yeras back I wraced a segment on low water toilets. A professor was conrcted to build a toiet for 3rd wprd cuntries.

He invnetd a super slippery surface with fine slippery threads. He had to createa faux poop to test it.

The amount of wtaer a tliet flushes depnds on how slippery the surface is.

Older technology was much more efficient as far as water use. They called them outhouses and they used no water. 😉

Not a good idea unless you have a lot of land to act like a septic system leech field.
A septic system needs water. Outhouses don't.

It is a matter of setting priorities, save water or eliminate stench. Steve was worried about water use.
I always got a kick out the fact that they call the outhouse
I suppose a hole in the ground could be called technology. Just don't eat the yellow snow.

It is interesting in all of Star Trek TV I never once saw somebody take a restroom break.

It really comes down to there are too many people.

After fasting for 40 days an 40 nights and taking a dose of peyote I had a vision. Eventually nature will reduce population. The Great Spirit has spoken.

A report from Lebanon said that with the wheat crisis people there are on the verge of starvation. Same reports from other places.
Even more impressive is that there wasn't even a toilet in the kids' bathroom on The Brady Bunch. For 6 kids no less! Makes you wonder what sort food Alice was cooking up that enables you from ever having to relieve yourself.
 
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