Non-aquaeous expansion medium for a reactor

[christian everett]

I wanted to ask whether it might be feasible and advantageous to use an expansion medium other that water to go from liquid to vapor to turn a turbine to generate electicity in a reactor.

Because of water's very high specific heat and heat of vaporiaztion, would it be possible find another substane that would go from liquid to gas using much less energy for the same volume and pressure of vapor.

 

[dRic2]

Water is the cheapest thing you can get... I think it all come to this, in my opinion.

 

[christian everett]

The non-aquaeous expansion medium could be recycled in a closed loop after being heated by the molten sodium loop...by cooling back to the liquid phase with another loop, which could be water...

In this way the input and output temperature could be regulated so that a change of a few tens degrees or even less could change the medium from liquid to gas and back again, instead of heating water at ambient temperatures, about 70 F, to form steam under pressure, about 750 F, which is then discarded.

 

[dRic2]

Depending on the type of reactor water has also other important features (like moderator). I don't know much about new generations of nuclear reactors (neither about older ones to be honest ), but it is hard to imagine some other material with the same properties as water, but cheaper. Also recycling is not always so cheap...

I will look something online, but I think the only way we still produce power is to use water to generate steam... I didn't know about molten sodium loop reactors, but in the end it seems they still use water.

 

[jrmichler]

Google is your friend. Try search terms steam cycle nuclear power plant or steam cycle power plant. This is one good hit, although it's not complete on its own: https://ocw.mit.edu/courses/nuclear...ing-2008/lecture-notes/MIT22_091S08_lec08.pdf.

Pay particular attention to the need for superheat with a steam turbine. Also to the effect of steam pressure and condenser pressure on the thermal efficiency. And even the effect of feedwater heaters on efficiency.

Then, if you still want to look at alternative fluids, note that a usable heat transfer fluid must meet a number of requirements. It must not chemically break down. It must not react with any materials used in the piping, valves, heat exchangers, etc. It must be available and affordable. The pressure-temperature curve needs to be within a reasonable range. And it must have properties that result in overall advantage over water. At a minimum, it must result in better efficiency.

 

[christian everett]

It probably wouldn't be very difficult to find a material with a better pressure/temperature curve than water.

Energy would have to be expended to inject the condensed liquid back into the expnsion chamber, but maybe a thousand times as much energy would be generated when the material turns back into vapor.

Even an azeotrope, binary or tertiary with water might be advantageous over pure H2O.

 

[Chestermiller]

Another consideration is environmental safety. If water escapes the system into the environment, it doesn't pose much of a hazard, but other substances would be much more dangerous.

 

[christian everett]

So I'm not getting an answer to my question here.

 

[gmax137]

So I'm not getting an answer to my question here.

I'm not sure what you are expecting. So why don't you pick a substance, work through the thermodynamics, and tell us how / why it is better than using water?

 

[anorlunda]

Because of water's very high specific heat and heat of vaporiaztion, would it be possible find another substane that would go from liquid to gas using much less energy for the same volume and pressure of vapor.

Before concluding that this alternate substance cycle is actually better, you have to examine how much energy it gives up in the turbine, how much in the condenser and feedwater heaters. In other words, a complete heat balance for the entire cycle, not just the evaporation part. Temperatures and pressures are significant also, not just energy.

 

[trurle]

It probably wouldn't be very difficult to find a material with a better pressure/temperature curve than water.

Energy would have to be expended to inject the condensed liquid back into the expnsion chamber, but maybe a thousand times as much energy would be generated when the material turns back into vapor.

Even an azeotrope, binary or tertiary with water might be advantageous over pure H2O.

You are likely looking for the Kalina cycle.
https://en.wikipedia.org/wiki/Kalina_cycle