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PostPosted: Feb 14, 2016 2:44 pm 
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Manufacturing portland cement requires temperatures around 1450 °C. From what I've read molten salt reactors can't supply this sort of temperature directly. I think the main reasons are to do with the boiling point of the salts and that reactivity declines as the salt gets hot beyond a certain temperature. One proposed solution is to take the heat available and then use an electric arc to boost it to the level required. I've been pondering a different solution. Could we run molten salt reactors a lot hotter if they were pressurised? In the same way they light water reactors operate above the boiling point of water by pressurising the water.


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PostPosted: Feb 14, 2016 4:01 pm 
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You could do a hybrid approach. Use natural gas and preheat the gas, the air, and the precursors of cement. Perhaps extract oxygen from the air and preheat that.

The hotter the reactor is, the more problems with corrosion, and strength of materials. So increasing temperatures is very difficult.

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PostPosted: Feb 14, 2016 4:13 pm 
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Quote:
Could we run molten salt reactors a lot hotter if they were pressurised?


You don't necessarily have to pressurize to run at 1450 °C. For example magnesium difluoride is very good neutronically and boils at 2260 °C at atmospheric pressure. I guess it is possible to find a combinaison of salts which stays liquid at 1450 °C and 1 bar.

Just being at 1450 °C and 1 bar will be a challenge on materials but it is maybe doable with current refractory alloys.


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PostPosted: Feb 14, 2016 7:12 pm 
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TerjeP wrote:
Manufacturing portland cement requires temperatures around 1450 °C.

Could we run molten salt reactors a lot hotter if they were pressurised?


The alloys I've seen proposed for LFTR and other MSRs have a melting point near or below that temperature. This might be considered an additional safety factor, the pipes will melt and the fuel will spill out before the salt reaches a temperature at which the really bad stuff boils away.

One example I found was Hastelloy C, it melts at 1350C. That is not sufficient. Flibe will boil at 1430C at atmospheric pressure, I can only assume you are correct that by pressurizing the reactor we could get hot enough but then we'd still have the problem of finding a material that can contain this.

I have a thought. A oxyhydrogen torch can reach 2800C. Use the MSR to drive a thermochemical water decomposition process, then use that oxyhydrogen gas to fuel the furnace. There are a number of thermochemical hydrogen production processes that will run at 500C or so, well within the capability of most any MSR design to date.

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PostPosted: Feb 15, 2016 4:06 am 
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TerjeP wrote:
Manufacturing portland cement requires temperatures around 1450 °C. From what I've read molten salt reactors can't supply this sort of temperature directly. I think the main reasons are to do with the boiling point of the salts and that reactivity declines as the salt gets hot beyond a certain temperature. One proposed solution is to take the heat available and then use an electric arc to boost it to the level required. I've been pondering a different solution. Could we run molten salt reactors a lot hotter if they were pressurised? In the same way they light water reactors operate above the boiling point of water by pressurising the water.


The current limitation is that of the metals. MSRs are proposing to use SS316 at temperatures below 700C, and this is the current limitation. Using SS316 this makes like a lot easier.

There would need to be more research (and qualification) on more exotic materials to raise this temperature. Up to 900C should be straight forward, but 1450C not so. And pressurising a MSR destroys a key benefit. Perhaps pebble bed HTRs would work better for 1450C.

However, for MSRs, the target - after electricity production of course - will be the 850C required for thermal decomposition of hydrogen.


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PostPosted: Feb 15, 2016 4:09 am 
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Kurt Sellner wrote:

I have a thought. A oxyhydrogen torch can reach 2800C. Use the MSR to drive a thermochemical water decomposition process, then use that oxyhydrogen gas to fuel the furnace. There are a number of thermochemical hydrogen production processes that will run at 500C or so, well within the capability of most any MSR design to date.


I thought about that, but:
- A high temperature (850C) MSR will be able to produce electricity at 50% efficiency
- It will also be able to produce hydrogen at a similar efficiency, and perhaps (with big assumptions) at a similar cost (which could make hydrocarbons at $50-60 per barrel).

Wouldn't it be easier, at a similar $/MWh cost, to use the electricity rather than the oxyhydrogen?


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PostPosted: Feb 15, 2016 8:16 am 
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Using electricity to reduce oxides of iron could make it costlier than copper!
The coal could be gasified by nuclear steam for reducing carbon and other uses as a fuel. This low nitrogen gas could be very efficient in reducing iron ore.


Last edited by jagdish on Feb 19, 2016 2:31 am, edited 1 time in total.

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PostPosted: Feb 17, 2016 4:07 pm 
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I have been thinking about this for a long time.

The easiest solution appears to be substitute the flame torch in the rotary kiln with a molybdenum disillicide or similar resistive heating element.
Most of the equipment can remain the same, however the heat exchangers would have to be modified as less gas would be flowing through them as there would be no combustion products or nitrogen in the output gas stream, it would be near pure carbon dioxide.


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PostPosted: Feb 17, 2016 11:08 pm 
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alexterrell wrote:
Kurt Sellner wrote:

I have a thought. A oxyhydrogen torch can reach 2800C. Use the MSR to drive a thermochemical water decomposition process, then use that oxyhydrogen gas to fuel the furnace. There are a number of thermochemical hydrogen production processes that will run at 500C or so, well within the capability of most any MSR design to date.


I thought about that, but:
- A high temperature (850C) MSR will be able to produce electricity at 50% efficiency
- It will also be able to produce hydrogen at a similar efficiency, and perhaps (with big assumptions) at a similar cost (which could make hydrocarbons at $50-60 per barrel).

Wouldn't it be easier, at a similar $/MWh cost, to use the electricity rather than the oxyhydrogen?


It would be interesting to see the outcome of comparing the two processes. One thing that concerns me is that we've been making high temperature furnaces fired with combustible gasses for a very long time but I'm not aware of resistive heating at such temperatures being used very often. We'll heat metals to much higher temperatures with electricity but that is because the electricity passes through what is effectively the heating element, turning it to liquid. We don't want a liquid heating element in this case and the material that we want to heat does not conduct electricity very well. E Ireland does show we have materials that we might use to reach these temperatures but I just don't know enough about it. My brother in law does work on industrial furnaces but I don't recall any he's worked on that reach temperatures like this, I'll pick his brain on this when I see him again.

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PostPosted: Feb 18, 2016 5:32 am 
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An oxyhydrogen torch might also have issues because in a conventional furnace the flame is radiatively coupled to the material in the furnace.

An oxygen-hydrogen flame is not very luminous, as we see in LOX/LH2 rocket launches.


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PostPosted: Feb 18, 2016 9:45 am 
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Fused quartz furnaces reach very high temps using resistive bands and tungsten carbide for crucibles.


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PostPosted: Mar 02, 2016 5:36 pm 
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One way can be by heating compressed air with a molten salt reactor, use natural gas to achieve gas turbine temperature conditions, generate electricity at very high efficiency and add extra natural gas to reheat the exhaust gases up to the cement reaction temperature.


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PostPosted: Mar 02, 2016 6:16 pm 
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The solar thermal electrochemical process could be modified to use the thermal energy of the nuclear reactor and nuclear produced energy to electrochemically break down the calcium carbonate. The production of a co product (graphite/carbon nanotubes) could make the production more economically viable.

http://phys.org/news/2012-04-solar-thermal-cement-carbon-dioxide.html


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PostPosted: Mar 02, 2016 6:17 pm 
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Not portland cement but still useful.


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PostPosted: Mar 06, 2016 1:36 pm 
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michaelw wrote:
The solar thermal electrochemical process could be modified to use the thermal energy of the nuclear reactor and nuclear produced energy to electrochemically break down the calcium carbonate. The production of a co product (graphite/carbon nanotubes) could make the production more economically viable.

http://phys.org/news/2012-04-solar-thermal-cement-carbon-dioxide.html


The main problem with STEP is that it's so "politically correct" (offers a solar-powered solution to almost all problems) is that people, especially the government's science funding & climate science gurus, are dazzled by it. The Editors & reviewers of some of our most prestigious technical journals seem to be similarly afflicted.

I had a recent opportunity to take a close look at one such proposal because I was trying (and did) to dream up a practical way to use a nuclear renaissance's cheap power to accomplish something important that couldn't be done otherwise (a "killer app") - remove a significant amount of the excess carbon dioxide we've dumped into the atmosphere.

To try to put things into proper perspective that paper utilized readily available information & simple ball park calculations to compare how much power/energy would be needed by some of the proposals I'd read about, one of which was STEP. (That approach to paper-writing seems to offend lots of people including the aforementioned journal Editors )

Anyway, I'll post it here - the stuff about STEP is in pp3-4.

It would be a similarly impractical way to make lime (or "cement").


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CO2 basalt geo...post2ndNature rejection.doc [1.4 MiB]
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