Energy From Thorium Discussion Forum

It is currently Jan 20, 2018 4:03 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 24 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: May 25, 2016 2:26 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
So I have been wondering about thermal energy storage for nuclear reactors as a way to provide daily load shifting and also potentially, if they could be made cheap enough, for longer periods. [Weekday loads using weekend lulls or similar].

I decided that thermal energy storage using phase changes of various molten salts was probably the best bet, you can tailor your melting temperature range to the required input/output temperature and salts are generally quite cheap.
I decided, because they exist today and because its more challenging/interesting - to use LWR type reactors in the assumptions. With higher temperatures you can start to use cheaper salts but at a ~250C temperature your choices are much more limited.

First to be checked, was some form of solar salt variant based on Sodium and Potassium Nitrates. It does the job but is very expensive and doesn't have a huge energy capacity, if we assume heat being removed about 230C with a 25% cycle efficiency you end up with only ~10-15kWh/t of material expended. And at several hundred dollars per tonne it gets very expensive very quickly.
The salt ends up costing about $90/kWh(e) of storage, and whilst this does include the balance of plant it is obviously too expensive.

[I reason that with large enough reservoirs the cost will approach the cost of the heat storage medium]

So I went looking and finally found a ternary AlCl3-NaCl-KCl salt system that melts at roughly ~250C.
In molar terms it is 10AlCl3-50NaCl-40KCl, which translates to about 18% AlCl3, 40% NaCl and 42% KCl by mass.
It stores ~28kWh(e) [404MJ/thermal per tonne] per tonne of salt at 25% storage efficiency.
But the big thing about it is it is cheap. Very cheap.

I used prices:
$100/t for NaCl - this is going to relatively high grade so it can't be the really cheap stuff
$280/t for KCl
$700/t for AlCl3 - this is hard to make, it has to be produced by reaction of molten aluminium metal and chlorine, however I estimated this price because I was unable to find an open result, raw material inputs come to ~$600/t based on current Al and Cl costs.

This results in a cost that is dominated by AlCl3 and KCl (surprisingly in the former case considering how little is required). It comes out at roughly ~$280/t.
Which means the cost comes in as low as $10/kWh.
Obviously this is a limiting factor that includes no other equipment or the cost of the tank.
But still

$10/kWh is so low that storage for over a hundred hours of production might be feasible.
Going to higher temperatures would help, as it woudl enable a reduction in the aluminium chloride content, but either way it is very impressive.

A long way of my target of ~$1/kWh(e) though, which would enable seasonal thermal storage to be almost feasible. That would require cheap grade pure table salt, with huge temperatures, but one can dream.
It certainly seems competitive with pumped storage, either way.


Top
 Profile  
 
PostPosted: May 25, 2016 2:52 pm 
Offline
User avatar

Joined: Dec 22, 2015 8:40 pm
Posts: 356
Location: Florida
E Ireland, What a brilliant idea, may I say.

The Flibe Energy LFTR coolant salt emerges from the PHX at a temperature of 633C. Is your 10AlCl3-50NaCl-40KCl molar salt still a good choice at that temp? I apologize for not helping with the math, is that okay?

_________________
"Those who say it can’t be done are usually interrupted by others doing it."

—James Arthur Baldwin, American novelist, essayist, playwright, poet, and social critic


Top
 Profile  
 
PostPosted: May 25, 2016 3:15 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
No, it is designed to melt at 250C, but at that temperature we can go for other salt choices.
We want a combination that melts/sets at about the temperature at which the temperature storage is required.
So we can make use of the heat of fusion of the salt melting/freezing rather than simple sensible heat.

EDIT: That temperature is rather awkward because it would involve throwing away temperature advantage to use many salts, but is not quite high enough for the cheaper, high temperature selections. Best choice would be to use a melting point salt that is a eutectic of sodium and calcium chlorides in a roughly 1:2 mass split.
It melts at 500C though, but it is cheap enough that the loss of efficiency from throwing away 130 celsius might be worth it.

Bit confused how practical it is to make use of non eutectic mixtures, but you could reduce the calcium chloride content to increase the melting temperature.


Last edited by E Ireland on May 25, 2016 5:12 pm, edited 1 time in total.

Top
 Profile  
 
PostPosted: May 25, 2016 3:39 pm 
Offline
User avatar

Joined: Dec 22, 2015 8:40 pm
Posts: 356
Location: Florida
Thanks, E. I think I'm getting it.

Does your idea apply for the Flibe Energy LFTR (I'm referring to the EPRI Report from October 2015) where your thermal storage would be placed between the IHX and the PCS?

Sidenote: If I may, E, please briefly (re-)state your position on the Flibe Energy design. Thank you. Essayons!

_________________
"Those who say it can’t be done are usually interrupted by others doing it."

—James Arthur Baldwin, American novelist, essayist, playwright, poet, and social critic


Top
 Profile  
 
PostPosted: May 25, 2016 4:26 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
The thermal storage would be placed in parallel with the IHX and turbine plant.
There is little reason to move heat back into the reactor plant, since the storage system would need its own turbine set (if it is running it is likely the plant is already using its attached plant anyway).

That simplifies things a little with regards the design of the plant.

I see the LFTR design as an interesting engineering challenge, but as a Chemist by (primary) education, I take one look at the flow sheet and start to have nightmares. I like the DMSR better in that regard, simpler and still very good at conserving fissiles. AFter all there is no (major) shortage of uranium.
But I like advanced LWRs because they can start construction tommorow if someone opens their chequebook.

EDIT:
One advantage of the lower temperature is you can claim a bit of sensible heat in there, and settle for a easier to design, cheaper heat exchanger.


Top
 Profile  
 
PostPosted: May 26, 2016 3:08 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2231
E Ireland wrote:
So I have been wondering about thermal energy storage for nuclear reactors as a way to provide daily load shifting and also potentially, if they could be made cheap enough, for longer periods. [Weekday loads using weekend lulls or similar].

I decided that thermal energy storage using phase changes of various molten salts was probably the best bet, you can tailor your melting temperature range to the required input/output temperature and salts are generally quite cheap.
I decided, because they exist today and because its more challenging/interesting - to use LWR type reactors in the assumptions. With higher temperatures you can start to use cheaper salts but at a ~250C temperature your choices are much more limited.

First to be checked, was some form of solar salt variant based on Sodium and Potassium Nitrates. It does the job but is very expensive and doesn't have a huge energy capacity, if we assume heat being removed about 230C with a 25% cycle efficiency you end up with only ~10-15kWh/t of material expended. And at several hundred dollars per tonne it gets very expensive very quickly.
The salt ends up costing about $90/kWh(e) of storage, and whilst this does include the balance of plant it is obviously too expensive.

[I reason that with large enough reservoirs the cost will approach the cost of the heat storage medium]

So I went looking and finally found a ternary AlCl3-NaCl-KCl salt system that melts at roughly ~250C.
In molar terms it is 10AlCl3-50NaCl-40KCl, which translates to about 18% AlCl3, 40% NaCl and 42% KCl by mass.
It stores ~28kWh(e) [404MJ/thermal per tonne] per tonne of salt at 25% storage efficiency.
But the big thing about it is it is cheap. Very cheap.

I used prices:
$100/t for NaCl - this is going to relatively high grade so it can't be the really cheap stuff
$280/t for KCl
$700/t for AlCl3 - this is hard to make, it has to be produced by reaction of molten aluminium metal and chlorine, however I estimated this price because I was unable to find an open result, raw material inputs come to ~$600/t based on current Al and Cl costs.

This results in a cost that is dominated by AlCl3 and KCl (surprisingly in the former case considering how little is required). It comes out at roughly ~$280/t.
Which means the cost comes in as low as $10/kWh.
Obviously this is a limiting factor that includes no other equipment or the cost of the tank.
But still

$10/kWh is so low that storage for over a hundred hours of production might be feasible.
Going to higher temperatures would help, as it woudl enable a reduction in the aluminium chloride content, but either way it is very impressive.

A long way of my target of ~$1/kWh(e) though, which would enable seasonal thermal storage to be almost feasible. That would require cheap grade pure table salt, with huge temperatures, but one can dream.
It certainly seems competitive with pumped storage, either way.

NaCl-MgCl2 would be cheap, higher melting and more efficient.


Top
 Profile  
 
PostPosted: May 26, 2016 10:28 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
jagdish wrote:
NaCl-MgCl2 would be cheap, higher melting and more efficient.


And impossible to melt using LWR steam.
The whole purpose of the exercise was to determine if a low cost phase change material for LWR steam existed.
And it does.
And NaCl-MgCl2 is likely crushed by NaCl2-CaCl2 in the economic respect, calcium chloride is a waste product from the Solvay process. MgCl2 is not available is such quantities at such low prices.


Top
 Profile  
 
PostPosted: May 26, 2016 11:42 am 
Offline
User avatar

Joined: Dec 22, 2015 8:40 pm
Posts: 356
Location: Florida
Thank you, E, for replying to my side note. You're a chemist also. Interesting.

In parallel. Of course. Can you give me an example of a chemical industrial flow sheet that is a "nightmare" and that industry supplies millions of tons of product to market?

E, do you have an aversion to identity? Or is it a secret, in which case your answer will be silence.

_________________
"Those who say it can’t be done are usually interrupted by others doing it."

—James Arthur Baldwin, American novelist, essayist, playwright, poet, and social critic


Top
 Profile  
 
PostPosted: May 26, 2016 2:11 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
No, my surname is literally Ireland. I can see why that would look rather strange.

There are many evil-looking chemical flow sheets that produce lots of products in industry, for example isomerisation units in oil refineries contain large quantities of either fuming sulphuric acid or even hydrofluoric acid, and operate across the world.
It is just a matter of this process never having been attempted on a large scale before, and the fact that if anything goes wrong fixing it would be horrifyingly difficult to fix because everything is so radioactive you can never go near it ever.


Top
 Profile  
 
PostPosted: May 26, 2016 2:31 pm 
Offline
User avatar

Joined: Dec 22, 2015 8:40 pm
Posts: 356
Location: Florida
Thank you, E, for your perspective. It's very good and wise.

And I agree with the hazard concerns (not the least of which includes nonproliferation security) of integrating a chemical processor into a thorium burner that is based on molten 7LiF-BeF2.

I believe that a qualified plan can be arranged to thoroughly quantify and safeguard each and every operating requirement to meet the most rigorous multiple-phase licensing process for the Flibe Energy design that essentially resumes and completes the work initiated under Dr. Alvin Weinberg at Oak Ridge since the 1970s when the ORNL MSBR program was shut down.

Given passage of the pending legislation with DOE funding and support through the GAIN program, Flibe could initiate such a licensing plan that will have a robust set of contingencies for each and every critical element of the machine.

_________________
"Those who say it can’t be done are usually interrupted by others doing it."

—James Arthur Baldwin, American novelist, essayist, playwright, poet, and social critic


Top
 Profile  
 
PostPosted: May 26, 2016 3:01 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
Given that summer time lectricity generation capacity is not very valuable in the UK, with peak demand occuring in the winter even now - a trend that is likely to increase if electric heating is extensively adopted in every house - I have been trying to find things for reactors to do in the summer, so as to reduce the effective cost of wintertime generating capacity by at least partially amortising its ongoing capital costs away.
One is essentially to take over all salt production by simply using multi effect evaporators coupled to the reactor plants in the summer when the power they would be generating is near worthless.
Another is to charge up giant salt tanks, which unfortunately requires either very high temperatures or very expensive "lakes" of molten salt.

But I continue to look for processes that are heavily energy dependent but have little fixed infrastructure, so that a reduced capacity factor of only running for a few months of the year in the summer can be balanced out by very low energy costs.

EDIT:

Assuming you draw the heat out of the CaCl2-NaCl salt storage at 500C with a 600C salt peak temperature you can get another ~100kJ/kg out of the salt storage by cooling it before it starts to solidify, so if you stick it in a thermocline style tank with heating at the bottom and steam generators at the top you can significantly increase the amount of energy stored.
This case has intrigued me enough that I will run some more calculations on efficiencies and get back to the thread with them sometime tomorrow.


Top
 Profile  
 
PostPosted: May 27, 2016 9:53 am 
Offline
User avatar

Joined: Dec 22, 2015 8:40 pm
Posts: 356
Location: Florida
E Ireland wrote:
". . . with heating at the bottom and steam generators at the top you can significantly increase the amount of energy stored."
E, what about supercritical CO2 at that top?

The Flibe Energy LFTR PHX is at 633C. The CaCl2-NaCl can be supplied from sea salt from direct thermal oceanic desal for fresh water and water management. A bank of LFTRs would supply both electrical and thermal desal and salt for the thermal batteries.

(My nickname is "Dreamer" as a side note.)
E Ireland wrote:
"This case has intrigued me enough that I will run some more calculations on efficiencies and get back to the thread with them sometime tomorrow."
Thank you for running the calcs, E. This case is more than intriguing. The UK isn't the only area with such circumstances.

_________________
"Those who say it can’t be done are usually interrupted by others doing it."

—James Arthur Baldwin, American novelist, essayist, playwright, poet, and social critic


Top
 Profile  
 
PostPosted: May 27, 2016 9:45 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
Tim Meyer wrote:
E Ireland wrote:
". . . with heating at the bottom and steam generators at the top you can significantly increase the amount of energy stored."
E, what about supercritical CO2 at that top?

The Flibe Energy LFTR PHX is at 633C. The CaCl2-NaCl can be supplied from sea salt from direct thermal oceanic desal for fresh water and water management. A bank of LFTRs would supply both electrical and thermal desal and salt for the thermal batteries.

(My nickname is "Dreamer" as a side note.)
E Ireland wrote:
"This case has intrigued me enough that I will run some more calculations on efficiencies and get back to the thread with them sometime tomorrow."
Thank you for running the calcs, E. This case is more than intriguing. The UK isn't the only area with such circumstances.


I make the latent heat of fusion of the 67CaCl2-33NaCl (mass) mixture is roughly 335MJ/tonne.
If we assume 500C heat can produce ~480C steam or something with about 40% efficiency overall.
That leads to ~37kWh(e) per tonne.

100C of superheat would give you ~1*100MJ/t - so about 100MJ/t.
So that takes us up to 435MJ/t total - which gives us 48kWh(e)/tonne.

Price of the salts:
NaCl $100/t - 330kg/t
CaCl2 $200/t - 670kg/t

Overall price is ~$167/t
Which takes us to about ~$3.48/kWh(e).


Top
 Profile  
 
PostPosted: May 28, 2016 9:37 am 
Offline
User avatar

Joined: Dec 22, 2015 8:40 pm
Posts: 356
Location: Florida
E Ireland wrote:
. . . my target of ~$1/kWh(e) though, which would enable seasonal thermal storage to be almost feasible. . . . but one can dream. It certainly seems competitive with pumped storage, either way.
I'm a dreamer, too.

E Ireland wrote:
Which takes us to about ~$3.48/kWh(e).

$3.48/kWh(e) ~ $1.00/kWh(e); 67CaCl2-33NaCl (mass) - pretty close, right?

You say 500C. The FE LFTR PHX is at 633C. That works? (Apologize for my mental deficiency.) Also, you're staying with steam. I asked about sCO2 for the more efficient Brayton Cycle. Is that useful?

_________________
"Those who say it can’t be done are usually interrupted by others doing it."

—James Arthur Baldwin, American novelist, essayist, playwright, poet, and social critic


Top
 Profile  
 
PostPosted: May 28, 2016 9:54 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
Tim Meyer wrote:
$3.48/kWh(e) ~ $1.00/kWh(e); 67CaCl2-33NaCl (mass) - pretty close, right?


Tim Meyer wrote:
You say 500C. The FE LFTR PHX is at 633C. That works? (Apologize for my mental deficiency.) Also, you're staying with steam. I asked about sCO2 for the more efficient Brayton Cycle. Is that useful?

Because I am proposing phase change salt, and that is the highest melting relatively cheap eutectic available that still melts below 633C. You could get a few extra degrees by going to more expensive salts but I don't think its worth it.
You do however store a bit more heat by heating the molten salt up to ~600C after melting it.

I am a little iffy about supercritical carbon dioxide, but I suppose its plausible, mainly I have been attempting to use proven technologies for everything I can.
It is also worth noting that we can't have fancy pumped heat excahngers because of the phase change we have, [unless we discharge a partially frozen slurry from them? Where is Cyril R when we need him?).
Our heat exchangers are reduced to plates/pipes across the top of the tank.
It turns out at this temperature range supercritical carbon dioxide is of similar performance to a steam turbine, Carbon dioxide only really becomes useful at higher temperatures.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 24 posts ]  Go to page 1, 2  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group