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PostPosted: Jun 25, 2014 10:14 am 
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https://www.youtube.com/watch?v=869aTKh9ZJY

Link is to Magdi Ragheb's talk at TEAC6 titled "Alternative Cooling Systems for Th-MSR Breeder Reactors." Magdi gave a brief overview of the Dissociating Gas and Kalina cycles, does anyone here know more about these designs? This was the first I had heard of either...

Kalina cycle is essentially the same as a Rankine cycle, only it uses two working fluids with different boiling points. The reference case uses 70% ammonia and 30% water (I believe the principle is applicable for any 2 fluids with an overlapping liquid phase). Spreading the phase change out along a wider temperature range improves efficiency and is well suited as a bottoming cycle (seems broader than that to me).
[url=en.wikipedia.org/wiki/Kalina_cycle]Wiki Kalina Cycle[/url]
Kalina Overview


I'm less clear on the dissociating gas cycle. IIUC the general principle is that certain molecules (e.g. nitrogen tetroxide, aluminum bromide) dissociate under heat, effectively doubling the amount of work possible per unit mass. Magdi proposes such a cycle for very high power-to-weight propulsion systems for nuclear submarines.


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PostPosted: Jun 25, 2014 4:47 pm 
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WEll the MSR concepts I saw are generating reactor outlet temperatures of 400 - 850 °C. These temperatures are very suitable for supercritical water, steam and supercritical CO2 systems.

Which benefits do you see for the Kalina process in the mentioned temperature range?
Which media would you choose within this temperature range?
Which dissolving gas or liquid do you see for a MSR?

Concerning the MSR subject...the coolant needs to be non-corrosive at the mentioned temperature range. It must not react with molten fluoride or chloride salts. It should have a high cv, low viscosity, not freeze. Ideally it should not be toxic.

Holger


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PostPosted: Jun 26, 2014 12:54 am 
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'..the coolant needs to be non-corrosive at the mentioned temperature range.... Ideally it should not be toxic.'
Unfortunately dinitrogen tetroxide is listed as both corrosive and highly toxic. Which didn't stop over twenty papers being written on using it as a coolant, mostly from Byelorussia, and all dated pre-Chernobyl.
http://link.springer.com/article/10.100 ... 482#page-1


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PostPosted: Jun 26, 2014 11:15 am 
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Here is Magdi's actual powerpoint presentation.

http://mragheb.com/Alternative%20Cooling%20Systems%20for%20the%20Thorium%20Fuel%20Cycle%20Molten%20Salt%20Breeder%20Reactor.pdf


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PostPosted: Jun 26, 2014 7:01 pm 
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Kalina can be very good for pulling out more heat from the low temperature heat source like geothermal hot water while using sensible pressures, but it has no benefits at MSR temperatures. My personal favourite for high temperature applications is mercury binary Rankine where liquid mercury is boiled and superheated, the vapour is passed through a topping turbine, then condensed in a steam generator that drives a large steam turbine, all this allowing the user to tap high temperature heat sources without resorting to extreme pressures. Someone actually built a demonstration unit, but had some difficulty keeping the mercury inside the system :cry:

One can do the same thing with a sodium/steam binary Rankine cycle as well, that's not so poisonous, and definitely more exciting. But far more reliable and boring is supercritical steam Rankine, but that currently tops out at 620C. If one has a heat source at 900C then CCGT cycles start to become very attractive and improve rapidly as temperature increases. If anyone has the need for such a device, please let me know or read up on the UC Berkeley work on NACC which is a CCGT derivative.

I have never seen a commercial power cycle based on the dissociation of a chemical compound, so I'm guessing that the benefits don't outweigh the risk and costs.

I will have a look at Magdi's presentation, sounds interesting.


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PostPosted: Jun 26, 2014 9:42 pm 
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Waiting for Lindsay's followup ... patiently ...


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PostPosted: Jun 26, 2014 11:50 pm 
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Re Kalina Magdi sums it up pretty well in the presentation.
Quote:
In low gas temperature heat recovery systems such as diesel engine exhaust or fired heater exhaust, the energy recovered from the hot gas stream is more significant and Kalina cycle output increases by 20 - 30 percent.

So it's not that the Kalina Cycle per se is more efficient, it is that in certain circumstances Kalina can capture more thermal energy from a low temperature source. But with MSR's we are dealing with a high temperature heat source, so there is no benefit to be had for that application.

Regarding the dissociating compounds, I was really keen to see the predicted cycle efficiency numbers, those are crucial for civilian nuclear power generation. High conversion efficiency is key. For military applications small sized equipment is very important and that is where steam systems are at a disadvantage.

It would be interesting to know how well this turbo machinery works in real life, one challenge I can think of is the migration of the compound into your turbine, plugging up the blades and nozzles. Steam turbines can suffer from this due to contaminated steam and the level of contamination may be very small, but the high mass flow in the turbine means that deposits can build up very quickly.


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PostPosted: Jul 22, 2014 4:51 am 
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What I find interesting is the heat rejection under pressure. That means a really compact LP turbine and condenser. Any idea as to the size of this advantage Lindsay? Definately looks like a noticeable advantage even if the efficiency improvement is marginal. Smaller equipment means reduced equipment cost but also reduced foundation, building, and seismic cost/security cost (those can be more expensive for an NPP than the turbine-generator itself!)

IIUC there is still a slight gain in efficiency even at 550C steam, in the ballpark of 1-2% or so, but then again no one has ever made a Kalina cycle at that temperature.

The major thing that puts me off with Kalina is the limited number of installations and they are all small and low temperature. A large, high temperature Kalina would be unproven tech. One of the big advantages with ordinary steam Rankine or supercritical Rankine is the off the shelf, proven nature. Takes away a lot of project risk.


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PostPosted: Jul 23, 2014 7:42 am 
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It would be smaller, but whether is would be significantly cheaper that's hard to say. Low pressure condensers are not cheap, but they're not expensive either. With efficiencies of scale, making things smaller often only provides a percentage of the cost reduction that was expected. It does make shipping and handling easier however.


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PostPosted: Jul 23, 2014 9:46 am 
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Lindsay wrote:
It would be smaller, but whether is would be significantly cheaper that's hard to say. Low pressure condensers are not cheap, but they're not expensive either. With efficiencies of scale, making things smaller often only provides a percentage of the cost reduction that was expected. It does make shipping and handling easier however.


Seems like an advantage if we can avoid major vacuum equipment. I think the real cost advantage would come from if we can produce more on assembly lines with smaller and smaller equipment.


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PostPosted: Jul 26, 2014 12:26 am 
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Cyril R wrote:
Seems like an advantage if we can avoid major vacuum equipment. I think the real cost advantage would come from if we can produce more on assembly lines with smaller and smaller equipment.
Vacuum equipment for a STG is a pretty minor cost <5% of the condenser cost. Small is usually good, standard is ideal.


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PostPosted: Jul 26, 2014 9:14 am 
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Lindsay wrote:
Cyril R wrote:
Seems like an advantage if we can avoid major vacuum equipment. I think the real cost advantage would come from if we can produce more on assembly lines with smaller and smaller equipment.
Vacuum equipment for a STG is a pretty minor cost <5% of the condenser cost. Small is usually good, standard is ideal.


Agree, though reluctantly, and angrily. :evil: :lol:

Though on a more serious note, I was thinking of the operational problems induced by vacuum. Seawater or service water going into the vacuum condenser. Would be nice to avoid that. But maybe there are other ways to do this, such as Heller indirect dry cooling...


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PostPosted: Jul 26, 2014 12:13 pm 
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Cyril R wrote:
Though on a more serious note, I was thinking of the operational problems induced by vacuum. Seawater or service water going into the vacuum condenser. Would be nice to avoid that. But maybe there are other ways to do this, such as Heller indirect dry cooling...
Vacuum systems can be a real pain in the tail sometimes, but generally they run reliably for long periods. If you look at the power produced at that low pressure it is quite substantial, so the economic value of the extra generation typically drives you to run the system that provides the lowest possible condenser pressure, even if you have to alter the steam turbine design to make use of it.

I don't recall the specifics right now, but I do remember some steam plants in Scandinavia (I think) running once through seawater cooling at ~4.5C which were in their day the most efficient in the world partly because they designed the condensing, vacuum and steam turbine systems to run and use outrageously low condenser pressure (~2 kPaa I think, many steam plant run 5-7 kPaa) squeezing out more power and more efficiency for every kg/s of steam flow into that condenser. Or put another way they successfully reduced the temperature of cycle heat rejection to one of the lowest ever seen for a steam cycle, receiving a power and efficiency gain for their trouble. One of those cases where convenience and simplicity gets trumped by economics.


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PostPosted: Jul 26, 2014 12:31 pm 
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Lindsay wrote:
Cyril R wrote:
Though on a more serious note, I was thinking of the operational problems induced by vacuum. Seawater or service water going into the vacuum condenser. Would be nice to avoid that. But maybe there are other ways to do this, such as Heller indirect dry cooling...
Vacuum systems can be a real pain in the tail sometimes, but generally they run reliably for long periods. If you look at the power produced at that low pressure it is quite substantial, so the economic value of the extra generation typically drives you to run the system that provides the lowest possible condenser pressure, even if you have to alter the steam turbine design to make use of it.

I don't recall the specifics right now, but I do remember some steam plants in Scandinavia (I think) running once through seawater cooling at ~4.5C which were in their day the most efficient in the world partly because they designed the condensing, vacuum and steam turbine systems to run and use outrageously low condenser pressure (~2 kPaa I think, many steam plant run 5-7 kPaa) squeezing out more power and more efficiency for every kg/s of steam flow into that condenser. Or put another way they successfully reduced the temperature of cycle heat rejection to one of the lowest ever seen for a steam cycle, receiving a power and efficiency gain for their trouble. One of those cases where convenience and simplicity gets trumped by economics.


Ok, that's with conventional Rankine, but with Kaline it seems optimal heat reject pressure >>100 kPa.

Here's a reference where they consider 4-7 bar condenser pressure, even with a low heat sink temp of 5C, they are talking about 5.1 bar out of the turbine.

http://hal.archives-ouvertes.fr/docs/00 ... 02.006.pdf


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PostPosted: Jul 26, 2014 12:43 pm 
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Yes, Kalina and any organic binary cycle should excel with any low temperature heat sink.


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