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 Post subject: Re: LFTR and Water?
PostPosted: Sep 26, 2014 4:44 am 
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Cthorm wrote:
There are a couple of threads that have discussed similar ideas. The amount of water produced depends heavily on what desalination method you use. I'm not really sure if cogeneration makes much sense, unless you were to do it in a binary way (i.e. desal during the midday load lull, full power production otherwise). Reverse Osmosis looks like the most efficient method to use at 3-5.5 kWh/m^3.

A 500MWe plant could make as much as 90,000 cubic meters of desalinated water per hour, unless my math is badly off.

http://www.energyfromthorium.com/forum/viewtopic.php?f=2&t=4377&hilit=desalination

http://www.energyfromthorium.com/forum/viewtopic.php?f=7&t=4384&p=58518&hilit=desalination#p58518

http://www.energyfromthorium.com/forum/viewtopic.php?f=17&t=4425&p=59263&hilit=desalination#p59263


Could you share abit regarding the math you used to come up with 90,000m3 from a 500MWe plant? Very interested to plug some numbers myself.


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 Post subject: Re: LFTR and Water?
PostPosted: Sep 26, 2014 11:31 am 
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500MWe = 500x10^3KWe / 5.5kWe energy per m^3 = 90,909 cubic meters desal output

kwH/m^3:
Min 3.00
Avg 4.25
Max 5.50

Cubic Meters Desal Output per Hour by Plant Size (in MW) @ min, avg, max energy requirement:

30 10,000 7,059 5,455
100 33,333 23,529 18,182
500 166,667 117,647 90,909

(Output % to Desal 100%)


Last edited by MSJ on Oct 02, 2014 10:50 am, edited 2 times in total.

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 Post subject: Re: LFTR and Water?
PostPosted: Sep 26, 2014 3:44 pm 
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MSJ wrote:
500MWe = 500x10^3KWe / 5.5kwH energy per m^3 = 90,909 cubic meters desal output

kwH/m^3:
Min 3.00
Avg 4.25
Max 5.50

Cubic Meters Desal Output per Hour by Plant Size (in MW) @ min, avg, max energy requirement:

30 10,000 7,059 5,455
100 33,333 23,529 18,182
500 166,667 117,647 90,909

(Output % to Desal 100%)


Wait a sec you are using the energy figure from Reverse Osmosis, I'm assuming we are talking about potential desal from a LFTR using the waste heat from the power conversion system.

It would be missing the point if you took the electrical energy generated by a LFTR to conduct RO desal because the beauty of LFTR is that you can use the waste heat that would otherwise be discarded to the environment. Using the electricity is not only a tremendous opportunity cost but silly since you lose energy during the conversion from thermal to electrical, i.e. might as well just use the thermal energy straight.

The best thermal system for desal would probably be Multi-stage flash (MSF) which some figures cite as 23-25 kWh/m3

To calculate how much thermal energy a 500MWe LFTR produces, you convert it based on the efficiency of the conversion system, since LFTRs have superb efficiency of potentially 40-45%, taking a rough calc (500/0.40=1250) so a 500MWe LFTR produces 1250MWth outlet power.

Of course there is no way to actually harness all 1250MWth, unless your LFTR facility was a water producer and nothing else and even then there will be some losses.

There are 2 trains of thought here, one is that you have an in-line co-generation system that uses the thermal power left over after driving a generator, this is the more attractive option since you would have no opportunity cost; i.e. whether you do desal or not, your plant produces the same amount of energy.

Two is you have a parallel system, which revs up desal during off-peak or low load periods of the day, and shuts down or idles during peak periods.

Thoughts?


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 Post subject: Re: LFTR and Water?
PostPosted: Sep 26, 2014 6:55 pm 
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I'm reading up on desal process options / economics ..

My general sense is reverse osmosis has been the preferred method for some time, wordlwide, but I would like to know the math well enough to assess how using waste heat ("free" thermal energy) from molten salt reactor plants designed to cogenerate electricity and freshwater in variable proportion might make MSF or MED just as good or better than RO.

Posted the "easy math" earlier showing desal output that occurs if 100% of plant electric output were devoted to an RO desal process -- so you can see where the number mentioned before came from, this also provides sense of scale relating plant electric output to freshwater production.

It was never meant to assert that it's reasonable to build an MSR, and devote 100% of electrical power to desalinating seawater.

That being said -- during off peak electricity demand periods, alternate high value application(s) for electricity not needed by the grid is an enhancement to the value premise of an MSR, alongside any valued application (industrial process heat, district heat, etc) that runs concurrently alongside the plant primary purpose (generating safe, reliable, dispatchable and cheap electricity).

Here's the IAEA 2006 study on nuclear desalination options including RO, MSF, MED: http://www-pub.iaea.org/MTCD/publications/PDF/CMS-19_web.pdf

I was looking for a link to downloadable the IAEA DEEP 3.0 model because I'm curious to see how that model might work with cheap, higher temperature thermal inputs (from MSR). I thought I already had it but .. (rolls eyes) ..


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 Post subject: Re: LFTR and Water?
PostPosted: Sep 26, 2014 11:17 pm 
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Ah I see, well yes RO is the preferred method precisely because of its low energy requirements, the most efficient of all the choices of RO processes, but the reason for that is because it isn't a thermal methodology and cannot be employed with LFTRs unless you intend to use the electrical output to power it.

But yes, I think it's a worthwhile exercise to determine precisely how much potential production and what kind of methodology should be employed with LFTRs


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 Post subject: Re: LFTR and Water?
PostPosted: Sep 27, 2014 12:37 am 
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http://www.forbes.com/sites/amorylovins ... -takeover/
The waste nuclear heat could be used for micropower which could then be used for desalination or other uses including the operation/safety of the plant itself.


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 Post subject: Re: LFTR and Water?
PostPosted: Sep 27, 2014 9:41 am 
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bensoon wrote:


To calculate how much thermal energy a 500MWe LFTR produces, you convert it based on the efficiency of the conversion system, since LFTRs have superb efficiency of potentially 40-45%, taking a rough calc (500/0.40=1250) so a 500MWe LFTR produces 1250MWth outlet power.

Of course there is no way to actually harness all 1250MWth, unless your LFTR facility was a water producer and nothing else and even then there will be some losses.



Well, a typical LFTR or any flouride MSR can be easily efficient in the range of 45-50%, say 47%, even using current, state of the art, super critical steam technology - obviously, you're going to lose some of that high efficiency using low temp heat (say, at a temp of 100-150 °C) in cogeneration mode, i.e. power plus heat. So, rather than having a single ~ 1110 MW th plant producing 500 MWe of electric power only, we can have a plant producing, for example, ~ 385-425 MWe of electricity together with ~ 640-680 MWth of low temp heat, from which we could even produce at its peak 65 milion m^3 per year of fresh water (@ 65 kWh of heat per tonn) or about 10^4 m^3/hour (this is optmistically assuming all the heat goes into water distillation)

Quote:
The best thermal system for desal would probably be Multi-stage flash (MSF) which some figures cite as 23-25 kWh/m3




Maybe my infos are a bit outdated, but as far I remember the best thermal distillation process like MED or MSF uses at least 55 to 75 thermal kWh per cubic meter of fresh water, while your figures seem to me incredibly lower


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 Post subject: Re: LFTR and Water?
PostPosted: Sep 28, 2014 11:56 pm 
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Alex P wrote:
bensoon wrote:


To calculate how much thermal energy a 500MWe LFTR produces, you convert it based on the efficiency of the conversion system, since LFTRs have superb efficiency of potentially 40-45%, taking a rough calc (500/0.40=1250) so a 500MWe LFTR produces 1250MWth outlet power.

Of course there is no way to actually harness all 1250MWth, unless your LFTR facility was a water producer and nothing else and even then there will be some losses.



Well, a typical LFTR or any flouride MSR can be easily efficient in the range of 45-50%, say 47%, even using current, state of the art, super critical steam technology - obviously, you're going to lose some of that high efficiency using low temp heat (say, at a temp of 100-150 °C) in cogeneration mode, i.e. power plus heat. So, rather than having a single ~ 1110 MW th plant producing 500 MWe of electric power only, we can have a plant producing, for example, ~ 385-425 MWe of electricity together with ~ 640-680 MWth of low temp heat, from which we could even produce at its peak 65 milion m^3 per year of fresh water (@ 65 kWh of heat per tonn) or about 10^4 m^3/hour (this is optmistically assuming all the heat goes into water distillation)

Quote:
The best thermal system for desal would probably be Multi-stage flash (MSF) which some figures cite as 23-25 kWh/m3




Maybe my infos are a bit outdated, but as far I remember the best thermal distillation process like MED or MSF uses at least 55 to 75 thermal kWh per cubic meter of fresh water, while your figures seem to me incredibly lower


Yes, the wiki pages do state that the energy requirements of MED/MSF are between 50-110 kWh/m^3. The 23-25 figures come from some other assertions, but in anycase, taking a best case and worst case scenario would allow us to understand the economics in either case.


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 Post subject: Re: LFTR and Water?
PostPosted: Sep 30, 2014 12:49 am 
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Thermal energy is essentially waste and electrical energy input should be considered. Multi-effect distillation and RO are both economical in electrical energy.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 01, 2014 12:40 pm 
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I think there is a real problem here of not looking outside the box.

Possibilities....

Making desal from the waste heat is possible...only in exactly in two states: California and Texas. In no place is this needed in terms of the US. What does this mean, it means that Texas is likely the only place for this to happen unless LFTR can win over the population...when and if it is *actually* deployed...which certainly is at least 10 years away and 10,000 miles away, in China. I don't see it being deployed commercially for desal for at least 15 years and likely 20 as Kirk on another thread suggested. But that's the political paradigm, lets examine the tech.

Where I disagree with Kirk and other others going back year is that a LFTR should be set up to produce electricity with desal as the co-gen byproduct of the higher-than-LWR (or other Rankine turbines) outlet temps from the Brayton Cycle GT used to power the generator. As Kirk has explained the use of flash distillers can be used with great efficiency. And should be. But why restrict it to this waste heat?

The value of the water is determined by society due to it's scarcity. Middle east nations actually use direct burning of natural gas into various forms of distillers including flash distillers. No power generation needed. Why can't a LFTR do the same with its inventory of molten salt the *primary* purpose, or the *only* purpose of this imagined LFTR would be to produce huge quantities of water using high temperature industrial process heat where ALL the energy created in the reactor is used to break seawater into potable water? Why not? No expensive GT and generator, just some big-ass heat exchangers to boil water to make fresh potable water?

More: why not use, especially on larger LFTRs, say of the 600MW to 1600MW variety (and this includes the already agreed upon use of flash distillers for the exhaust heat) a similar set up where by load on the generator is controlled by regulated leak off heat on the primary or secondary heat to a desal boiler. As load goes up in the day, the leak off is restricted and water production stops. At night, it can go full blast. Again, this helps in load control for the generation.

Lastly, the same, via load control for a 100% thorium power grid, be used this way OR by siphoning generated power to RO facilities anywhere on the grid that potable water is need near a coast line? Again, we need to think of all possible configurations for the use of the heat generated by such a reactor as a LFTR.

David Walters

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 Post subject: Re: LFTR and Water?
PostPosted: Oct 01, 2014 2:02 pm 
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dwalters wrote:
I think there is a real problem here of not looking outside the box.

Possibilities....

Making desal from the waste heat is possible...only in exactly in two states: California and Texas. In no place is this needed in terms of the US. What does this mean, it means that Texas is likely the only place for this to happen unless LFTR can win over the population...when and if it is *actually* deployed...which certainly is at least 10 years away and 10,000 miles away, in China. I don't see it being deployed commercially for desal for at least 15 years and likely 20 as Kirk on another thread suggested. But that's the political paradigm, lets examine the tech.

Where I disagree with Kirk and other others going back year is that a LFTR should be set up to produce electricity with desal as the co-gen byproduct of the higher-than-LWR (or other Rankine turbines) outlet temps from the Brayton Cycle GT used to power the generator. As Kirk has explained the use of flash distillers can be used with great efficiency. And should be. But why restrict it to this waste heat?

The value of the water is determined by society due to it's scarcity. Middle east nations actually use direct burning of natural gas into various forms of distillers including flash distillers. No power generation needed. Why can't a LFTR do the same with its inventory of molten salt the *primary* purpose, or the *only* purpose of this imagined LFTR would be to produce huge quantities of water using high temperature industrial process heat where ALL the energy created in the reactor is used to break seawater into potable water? Why not? No expensive GT and generator, just some big-ass heat exchangers to boil water to make fresh potable water?

More: why not use, especially on larger LFTRs, say of the 600MW to 1600MW variety (and this includes the already agreed upon use of flash distillers for the exhaust heat) a similar set up where by load on the generator is controlled by regulated leak off heat on the primary or secondary heat to a desal boiler. As load goes up in the day, the leak off is restricted and water production stops. At night, it can go full blast. Again, this helps in load control for the generation.

Lastly, the same, via load control for a 100% thorium power grid, be used this way OR by siphoning generated power to RO facilities anywhere on the grid that potable water is need near a coast line? Again, we need to think of all possible configurations for the use of the heat generated by such a reactor as a LFTR.

David Walters


For the use case you've outlined I think the IMSR is the most practical choice. Single fluid reduces the proliferation potential (however dubious that argument is), and the design is already optimized for low-touch operation and providing process heat.

While we're peering outside the box, the concept can go far further than desal water. You could treat a huge bulk of waste water, or incinerate solid wastes for extra power. Make concrete. Run a metals recycling plant/smelter.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 01, 2014 4:20 pm 
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You don't have to think very far out of the box. That newly made fresh water will need to be pumped uphill away from the ocean. The LFTR could be used to make steam to directly drive a pump (like a Terry turbine) and pump that fresh water right into the reservoir. Using steam to pump water is definitely a mature technology. (deep within the box.)


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 01, 2014 8:46 pm 
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Cthorm wrote:
Single fluid reduces the proliferation potential (however dubious that argument is)


Very dubious argument. Any uranium-fueled MSR produces chemically-separable plutonium. I don't see any advantage, besides the US already has nuclear weapons. We can't "proliferate"...we already have them.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 02, 2014 1:29 am 
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Very true. The anti-proliferation argument is only to discourage (and hinder by sanctions) others to acquire useful technology.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 02, 2014 2:03 am 
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bensoon wrote:
Yes, the wiki pages do state that the energy requirements of MED/MSF are between 50-110 kWh/m^3. The 23-25 figures come from some other assertions, but in anycase, taking a best case and worst case scenario would allow us to understand the economics in either case.

Please remember that factors like temperature differences have as much effect of the efficiency of desalination as they do with electricity generation. Saying something uses 50-110 kWh/m^3 of thermal energy tells you nothing if you don't know the quality of the heat. 5.5kWh of electricity made with 100C steam will consume similar large quantities of thermal energy.

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