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PostPosted: Sep 03, 2009 8:51 am 
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Been knocking aorund a couple of ideas for a speech, and was wondering about the feasibility of refitting a current coal-fired steam-turbine plant with a nuclear heat source such as LFTR while also bringing in a brayton topping cycle, such as Kirk's beloved SCO2.

Would installing the extra turbine as an uprate make such a nuclear fired combined cycle arrangement more feasible than a new-build setup, since the coal-yard conversion already has the steam turbine in place?

Also, what sort of capacity would an SCO2 turbine hall fitting in a land footprint of 18m by 8m have? 250 MW? 1 GW? 2 GW?

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PostPosted: Sep 03, 2009 9:41 am 
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I think we have about 20 different threads, all on this same topic. I need to consolidate them.

Short answer, I don't think we have tight answers as to how a LFTR would couple to a coal plant. My personal preference is to bring a submersible LFTR near to the coal plant's riverine location and tie into the electrical grid and switching yard there, rather than try to reuse or requalify the steam turbines of the coal plant.


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PostPosted: Sep 03, 2009 10:44 am 
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fnord wrote:
......a brayton topping cycle, such as Kirk's beloved SCO2....
Supercritical CO2 isn't much good as a topping cycle. Its advantages over other brayton cycles come from exploiting the odd properties of CO2 near its critical temperature (31°C)at the bottom of the cycle

Luke


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PostPosted: Sep 03, 2009 1:01 pm 
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I have advocated and lobbied for a bare bones Lftr core whose interface to the old coal fired plant generator is precisely matched through the use of a molten salt interface comprised as follows: Sodium Nitrate NaNO3 60 % Potassium Nitrate KNO3 40 %. This salt mix can support a maximum salt temperature of 550C.

All the components of the old coal fired power plant are maintained except the coal fired boilers. There are two molten salt storage tanks provided, a cold tank and a hot tank, see diagram below. The cold tank provides the input molten salt feed into the Lftr; the hot tank stores the heat output interface of the Lftr. The coal fired boilers are replaced by a steam generator located inside the hot molten salt tank, see the diagram below.

Image

Water runs through the piping of the steam generator that converts the water to super heated steam compatible with the exact temperature and flow rate specifications required by the existing turboelectric generator sets that were supported by the old coal fired boiler house.

The molten salt interface provides the flexibility to match the heat flow rate, pressure, and temperature specifications of the existing coal fired plants generator sets. The hot molten salt storage tank receives either hot salt from the Lftr or cold salt from the cold salt tank to moderate the temperature of the super heated steam fed to the turboelectric generators

This approach will be the most attractive and economic repowering of existing coal fired coal facilities. There are a large number of these brand new plants recently placed in service throughout the world which have cost billions to construct. The utilities and governments who have made this large investment will look to recapture as much of it as possible.

The cost of such and molten salt/Lftr approach for a large coal fired plant repowering will be less then $100 million; this is far less the any CCS retrofit cost.


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PostPosted: Sep 03, 2009 6:41 pm 
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How big a coal fired boiler does your figure assume is being replaced? 100 MW? How would things shake out for a 200 MW unit?

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PostPosted: Oct 03, 2009 8:43 pm 
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The local coal burning power plant 10 miles from my home has two 750 MW generators. The plant was designed and built in the 70s and has been recently upgraded. Would a LFTR boiler replacement be a single reactor or multiple smaller units?

Can you speculate on the factor limiting the load following ability of such a coal plant with a nuclear thermal boiler replacement? Would load following be limited by the reactor or - as I suspect- by the thermal limitations of the turbine?
thanks


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PostPosted: Oct 03, 2009 10:46 pm 
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Given the FP scrubbing integral to the LFTR, the turbines would be the limiting factor. Xe, the main factor embuggerising thermal-spectrum load-following, is no longer significant.

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PostPosted: Oct 03, 2009 11:13 pm 
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About the only thing that would be an advantage in a coal to nuclear conversion is that you could probably use the switch-yard and transformers and your distribution lines are already in place.

Retrofitting anything is done as a last resort, because the process is an incubator for problems. In the case of a power plant it would probably be cheaper and easer to brown-field the site and start over.


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PostPosted: Oct 04, 2009 12:40 am 
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Coal2nuclear finds the fast reactor with small core size as the best replacement for the boiler:-
http://www.coal2nuclear.com/bn-800_reactor.htm
Only if a stable salt mixture could replace the sodium, I would agree heartily. Fast reactor could run on U238-Pu239 or Th-U233 cycle. Changeover from existing design to salt cooled one would require less new research and be ready quite early, even in my lifetime. The SNF from LWRs would turn into fuel stocks.
Would NaNO3-KNO3 mixture work?


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PostPosted: Oct 04, 2009 12:05 pm 
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DV82XL wrote:
About the only thing that would be an advantage in a coal to nuclear conversion is that you could probably use the switch-yard and transformers and your distribution lines are already in place.

Retrofitting anything is done as a last resort, because the process is an incubator for problems. In the case of a power plant it would probably be cheaper and easer to brown-field the site and start over.


I agree completely. I will add that transmission lines, especially the rights of way for their construction and expansion are indeed very very valuable in this NIMBY age. The only thing possible more difficult to build from a legal and political permitting perspective would be seawater intake and outfall conduits for ocean cooling to a coastal power plant.


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PostPosted: Oct 04, 2009 12:35 pm 
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Why it is more attractive to the owners of a coal fired power plant to discard the steam powered generators and their associated cooling systems than it is to match their steam interface to a nuclear heat source? To an industry outsider, this is not obvious. Is it just too hard to do? Is it beyond the state of the engineer’s art?

The cost of the coal fired boilers must be a small faction of the cost of a coal fired power plant. The cost to just replace this function with a small nuclear unit seems like a good deal for the plant operators.

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PostPosted: Oct 04, 2009 2:44 pm 
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Axil wrote:
Why it is more attractive to the owners of a coal fired power plant to discard the steam powered generators and their associated cooling systems than it is to match their steam interface to a nuclear heat source? To an industry outsider, this is not obvious. Is it just too hard to do? Is it beyond the state of the engineer’s art?


It is not beyond possibility, it is just generally too expensive to retrofit on a case-by-case bases. This is because validating solutions before implementing them are difficult. If you have a significant number of identical units to convert, you can afford to lose money on the first few developing a process. In the case of coal-to-nuclear every plant is unique enough that they have to be seen as separate problems.

The output of the steam generator would have to match the old one, the fittings would have to match, and these two by themselves mean that much of the project will have to be custom built, this is to say nothing about secondary containment which would have to be integrated into existing structures that may not have been designed for extra loading. It goes on and on, and inevitably at least half the problems will be from surprises that were not known during the initial evaluation, which will have a multiplying effect on their impact.

All in all such a project could turn into a nightmare eliminating any potential savings. More to the point the money will have retained someone like me to look over such a project and is likely to not want to invest in such a scheme.

And this is just the technical issues, we haven't even touched on the regulatory and legal ones that are certain to attend this sort of project.

In the long run brownfielding the site and starting from there is by far the better option.


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PostPosted: Jan 13, 2010 7:37 am 
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DV82XL wrote:
Axil wrote:
Why it is more attractive to the owners of a coal fired power plant to discard the steam powered generators and their associated cooling systems than it is to match their steam interface to a nuclear heat source? To an industry outsider, this is not obvious. Is it just too hard to do? Is it beyond the state of the engineer’s art?



All in all such a project could turn into a nightmare eliminating any potential savings. More to the point the money will have retained someone like me to look over such a project and is likely to not want to invest in such a scheme.

And this is just the technical issues, we haven't even touched on the regulatory and legal ones that are certain to attend this sort of project.

In the long run brownfielding the site and starting from there is by far the better option.


I agree, I have worked in generation development for many years now and while the idea of repowering some old steam turbine to give an extended life sounds good, once you start digging into the details it all starts to get too hard, too expensive or too unreliable. If you are going to plunk down multi millions of dollars for a nuclear conversion, you want it to work reliably for a very long time and be efficient. Retrofitting old coal units with a new nuclear powered steam generator is not likely to give you that result. It's not impossible, just unlikely. Normally the best route is to slot new equipment into an existing site, better performance, better reliability, something that you can rely on for 25 years or more if you do it right.


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PostPosted: Jan 04, 2014 4:36 pm 
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This is an old post.

Zimmer was a nuke plant turned into a coal plant.

Midland was a nuke plant turned into a gas plant.

NSP retrofitted a number of old coal plants to use gas. I worked on the installation of a turbine at one of them many years ago and was surprised that the coal boilers had been replaced with gas turbines combined with the steam turbine. The output was greater because they turned it into a combined cycle unit.

Transformers, turbines, condensers, pumps, controls and piping are all expensive. As has been noted, the external infrastructure is in place. Granted, it's not brand new and may not be state of the art, but it's there. It's licensed. The community is accustomed to its existence. There is a large footprint at coal plants. There would be room for one of these reactors. The electrical supply that serviced the boiler auxiliaries could be re-utilized. If the NRC could be sold on an easier licensing procedure, these seem to be a waiting opportunity.

Per Wikepedia, the large low sulfur coal fields only have about a 20 year life. There are many coal plants that burn Powder River Basin coal. The time frame seems perfect.

Boiler structures can be huge. They are in close proximity to the steam turbine. Molten salt reactors are supposed to be a smaller source of heat. They are a more dense form of generating heat. I could envision them fitting in that space. I've viewed a lot of internet videos touting how they are such a flexible solution to our energy problems. Has the whole thing been vaporware? This could be a ready market. Since none have been built other than an experimental unit in the 1960s, maybe their problems are actually insurmountable. Maybe you just can't build a molten salt to steam heat exchanger without "crapping" up the entire plant. (Tritium?)

Why not?


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PostPosted: Jan 04, 2014 4:55 pm 
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Any part of the plant where there is any chance of any (and I mean any) radioactivity must go through the NRC and certainly anything existing won't survive that scrutiny. So, if you want to reuse and add nuclear you must have an HX loop with no residual activation. Our molten salt fueled systems will have plenty of radioactivity in the primary salt so the first HX absolutely must be new. But beyond this the delayed neutrons will activate the secondary loop, so it too must be new including the secondary HX. So the smallest system I could imagine would include a secondary salt and the secondary salt to steam generator as new equipment. More likely though I would guess you will need a third loop of molten salt to provide the necessary fission product barrier redundancy. My guess is that we will also want to have this kind of system separation developed for industrial heat applications.

On the downside we incur the extra capital expense of extra HX's. For a steam application the extra loops have a benefit of reducing the max temperature to something the steam generators are happy with and providing some protection against salt freezing (repeating what I've heard here - I don't fully understand this). For industrial head applications the loss of max temp we get with each HX is a distinct disadvantage. But I think when we get to industrial heat applications we will want to avoid having the NRC looking at the industrial application at all so we will need to cleanly separate the functions and have the industrial heat applications in a separate building.


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