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PostPosted: Oct 26, 2014 3:37 pm 
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Actually steam cycles are build commercially for steam temperatures of up to 600/620°C, 285 bar. This is the steel limitation. R&D around the world is developing steam turbines for 700/720° C, 350 bar. These turbines are based on nickel super alloys.

Some MSR concepts as the MSFR are designed for reactor outlet temperatures of 850°C and more.

Is there any R&D done on steam cycles and steam turbines at > 800°C??????
Which materials could be suitable, Mo-TZM, SSiC??

Holger


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PostPosted: Oct 26, 2014 7:45 pm 
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A combined cycle is the current answer to this problem.
http://en.wikipedia.org/wiki/Combined_cycle
It could be used for high temperature nuclear too.


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PostPosted: Oct 27, 2014 3:51 pm 
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Hi Jagdish... a combined cycles requires additional very large (gas - steam) hx and hence costs and efficiency is lower than that of a potential very high temperature steam turbine.

regards

Holger


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PostPosted: Oct 28, 2014 3:11 am 
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The materials challenge isn't worth the gain. Stick to what's on the market, 620C is plenty high enough if the MSR is not a paper reactor (ie not operating at 850C but <700C).


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PostPosted: Nov 01, 2014 2:22 am 
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How much is enough? I would say anything above 45% net efficiency is enough and that can be done with commercially available steam turbines available from multiple manufacturers. Moreover these are also proven in commercial service at steam temperatures up to 610C

The economic drivers work like this if the nuclear island is expensive then additional investment in a high efficiency power conversion island makes sense, but if the nuclear island is reasonably priced there's little to no benefit to pushing for extreme steam temperatures. In my opinion you switch to a CCGT model somewhere between 800 and 900C, up to that point stay with off the shelf steam turbine technology at 600/620C.

If you really want to push further, the next step in IMO would be to go to a double reheat, something like 285 Bar, 600/620/620C that should deliver a pinch more than 50% net efficiency.

To answer your initial post, aside from the Thermie 700 project I don't know of anyone looking at 700C or higher. As far as materials go, I don' think that Mo based alloys would work as they are easily oxidised.

Here is something to consider which plant makes more money, the plant that is 48% efficient and 97% available or the one that is 51% efficient and only 70% available?


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PostPosted: Nov 01, 2014 12:21 pm 
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Quote:
If you really want to push further, the next step in IMO would be to go to a double reheat, something like 285 Bar, 600/620/620C that should deliver a pinch more than 50% net efficiency.


So we can reach 50 % net efficiency with supercritical steam turbines at only 620 °C. I didn't know it, that's a good new for me. So the incentives to go further in temperatures are low.

In the far future, if we can have heat at more than 800°C with low pressure molten salts, we can maybe use first this heat for low pressure thermochemical processes (if corrosion's problems can be managed) and then use supercritical turbines at 620 °C (or 720 °C for nickel turbines) for producing electricity (or cogeneration of electricity and heat or desalinated water). This was proposed for the Very High Temperature Reactor which use helium as coolant, except that with molten salts we can have low pressure which facilitates things at these very high temperatures.


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PostPosted: Nov 01, 2014 2:17 pm 
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Its worth noting that if civilisation was to go entirely to nuclear (in the optimistic case of Norwegian levels of electricity consumption all round) using PWR or similar cycle reactors we would still have measurable global warming inducing radiative forcing from the collosal quantities of dispersed waste heat.
At that point there would be two options: massive carbon dioxide capture to reduce greenhouse forcing by a similar magnitude or adopting high temperature reactors with drastically reduced power outputs.

One unit of electricity generated in a PWR adds three units of heat to the environment in total.
One unit of electricity generated in a 50% efficient steam cycle adds only two units of heat.


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PostPosted: Nov 01, 2014 2:42 pm 
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Dear Lindsay,

600/620°C, 285 bar with 2 x overheating is offered for ex. by Siemens today.

European companies like Siemens are looking for a competitive advantage against their Asian competitors despite of their cost disadvantages. The 700/720°C technology is one of the fields of development. The EU and Germany spend a lot of R&D on this technology. In Germany 20.000h component tests are ongoing in the Sholven coal power plant.

I assume that the 700/720°C, 350 bar technology could be commercially available within 10 - 15 years from today. The first movers might face a learning curve but don`t you think that it will become similar reliable as todays technology some years later?

Don`t you think that utilities faced with high coal prices and the CO2 climate hoax (media pressure, CO2 certificates....) will aim for that?

The question is will this development will move ahead to 800°C???


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PostPosted: Nov 02, 2014 9:13 am 
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I'm totally with steam turbine expert Lindsay on this one. Just look at the most succesful turbine used in modern coal plants and copy that verbatim.

Once coal plants switch to the super duper steam cycles and there's a decade or so of good experience with then we just switch to that. This would be normally in line with MSR development, start with lower temperature design and let technology evolve to higher temperatures, more reheat and whatnot when this becomes available and is well tested in other sectors.

Gas turbines aren't much use, they cost a lot and they need to drive a lot of compressor work that makes them inefficient. If you have a 1000 degree plus reactor then look into it, but in my opinion a 1000 degree reactor is not feasible, I think even 700C is pushing things since the MSRE operated at 650C.

Likely a supercritical CO2 cycle will eventually be used for MSRs because of the cost advantages and simplicity over Rankine.

Currently limits are creep and corrosion especially for supercritical designs. Much more expensive alloys are already available that could make you a 700 degree C steam turbine but the cost is so much higher than lower alloy steels and you run into supply chain issues if you use enormous amounts of superalloy.

In MSRs things are much worse because you now need an alloy that can take 800-900C salt or so on one side, and 700C steam on the other, that is currently not feasible with any alloy.


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PostPosted: Nov 03, 2014 4:35 pm 
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Cyril R wrote:
I'm totally with steam turbine expert Lindsay on this one. Just look at the most succesful turbine used in modern coal plants and copy that verbatim.

Once coal plants switch to the super duper steam cycles and there's a decade or so of good experience with then we just switch to that. This would be normally in line with MSR development, start with lower temperature design and let technology evolve to higher temperatures, more reheat and whatnot when this becomes available and is well tested in other sectors.

Gas turbines aren't much use, they cost a lot and they need to drive a lot of compressor work that makes them inefficient. If you have a 1000 degree plus reactor then look into it, but in my opinion a 1000 degree reactor is not feasible, I think even 700C is pushing things since the MSRE operated at 650C.

Likely a supercritical CO2 cycle will eventually be used for MSRs because of the cost advantages and simplicity over Rankine.

Currently limits are creep and corrosion especially for supercritical designs. Much more expensive alloys are already available that could make you a 700 degree C steam turbine but the cost is so much higher than lower alloy steels and you run into supply chain issues if you use enormous amounts of superalloy.

In MSRs things are much worse because you now need an alloy that can take 800-900C salt or so on one side, and 700C steam on the other, that is currently not feasible with any alloy.


This. MSRs have enough technological risk as it is, there is no reason to take on more for incremental improvements in power conversion efficiency. One step at a time.


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PostPosted: Nov 04, 2014 1:28 am 
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HolgerNarrog wrote:
Dear Lindsay,

600/620°C, 285 bar with 2 x overheating is offered for ex. by Siemens today.

...The question is will this development will move ahead to 800°C???
That is exactly my point for suggesting double reheat, because we can do it today with a very acceptable risk profile. 350 bar and 700C is very challenging, the combination of pressure AND temperature makes it very challenging, dealing with one or the other is not so bad, but both at once is too much IMO.

Personally I don't think that 350 bar 700C will become commercial anytime soon and I see even more challenges with trying to move to 800C. I don't see that happening at all, but one should never say never.


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