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 Post subject: Steam bottoming cycles
PostPosted: Sep 02, 2014 7:46 am 
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I have been thinking a lot about UHVDC systems like the newly available 1100kV equipment from ABB - these will allow transmission over thousands of kilometres with relatively minor losses. (Extrapolating from 800kV data it appears that losses would be ~5.5% for four thousand kilometres).
Considering voltages are unlikely to stop there with the huge transport distances being looked at in India and China this means long distance transport of electricity will get ever easier.

This begs the question - now that our generators can be almost anywhere, why not position them where they can be most efficient? Relatively minor gains in efficiency would make up for losses, especially with VSC type inverters that will allow the UHVDC to be pushed further down the distribution chain.

One obvious way to make plants more efficient is to reduce the cold sink temperature.
Taking (for example) Churchill, MB - the most northerly location in North America with a railway connection to the main system and a deep water port, peak temperatures for seawater are roughly 10 Celsius - which should allow for relatively high efficiencies.

While summer peak air temperatures are in the ~20C range in the winter months the average high is -15C at best with typical temperatures in the -25C range. Would it be worthwhile adding some sort of organic bottom cycle to the system that would function in the winter to make use of this huge drop in air temperature? Perhaps using dry 'cooling' towers?
Considering it would operate for a large part of the year would it be able to make up for its increased capital cost and what sort of cycle would it use?


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PostPosted: Sep 02, 2014 1:02 pm 
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Quote:
why not position them where they can be most efficient? Relatively minor gains in efficiency would make up for losses


Transmission lines running at one third of that voltage cost a million dollars a mile to build. Adding a billion or so dollars to the cost of your electricity solution would swamp the benefits of locating the generation plant in an area of optimal cooling, especially if it as a high temperature reactor like a LFTR.

Also you take a hit on reliability, see http://retasite.wordpress.com/2011/07/30/tornadoes-topple-high-voltage-towers/
not to mention Hurricanes, and Blizzards. At least two blackouts in the northeastern US had long power transmission lines as a contributing factor and wether was not the major factor.


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PostPosted: Sep 02, 2014 1:41 pm 
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Tim Flavin wrote:
Transmission lines running at one third of that voltage cost a million dollars a mile to build. Adding a billion or so dollars to the cost of your electricity solution would swamp the benefits of locating the generation plant in an area of optimal cooling, especially if it as a high temperature reactor like a LFTR.


Cost data from 800kVdc projects indicate that for a 2000km transmission 6GWe scheme the total cost is roughly $2bn, with $1bn for the converter stations, $500m for 'Losses' and $500/kW for the lines.
Experience from previous projects indicate that converters for 1100kW will cost a similar amount, or less per kW than 800kV converters while reducing losses by something like half.
That takes us to $1.75bn for 2000km.
Another 2000km will cost us a further $250m for losses and $500m for lines.
That takes us to a project cost of $2.5bn for a six gigawatt connection.
That takes us to something like $420/kW - and that is conservative as you will gain generation due to the cooler temperatures and thus offset the losses.
That is hardly an enormous cost when we consider the costs of nuclear are unlikely to drop below $2500/kW in the forseable future.

It's not just optimal cooling that benefits from being out in the Canadian Arctic, it is just a sweetener, the best part is the fact that there are almost no NIMBYs for hundreds of miles in any direction.
A single 1100kV bipole will be able to transport 8-10GWe.
It may cost a lot but economies of scale are a massive factor in power transmission.

Tim Flavin wrote:
Also you take a hit on reliability, see http://retasite.wordpress.com/2011/07/30/tornadoes-topple-high-voltage-towers/
not to mention Hurricanes, and Blizzards. At least two blackouts in the northeastern US had long power transmission lines as a contributing factor and wether was not the major factor.

I have yet to see a transmission system that is invulnerable to overhead lines being brought down by wind - but when you have such huge economies of scale you can likely build a partially diverse routing now that we have HVDC circuit breakers.
Additionally these events, while headline grabbing, are far from common.


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PostPosted: Sep 02, 2014 2:01 pm 
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Technically feasible and may have a place one day to support a reactor park, but in economic terms it would be something to avoid. By making a bigger investment in the STG and condenser, you can extract more electric power from a given quantity of thermal power if you have low temperature cooling water. Balancing that would be the converter station and line losses tending to reduce that efficiency benefit; which still leaves you with the capital and operating costs of the HVDC tie including lease payments to affected land owners and all of that joyous hum-drum day to day stuff.

On a balanced economic assessment I don't think that the efficiency gain would pay for the transmission infrastructure, assuming that more conventional locations are available. That said MSR nuclear and HVDC back bones would be good together is getting access to closer sites became a problem.

The other thing to consider is if MSR's are as cheap as we believe they are, the economically rational thing to do is build a slightly bigger reactor and live with the lower conversion efficiency. Which is cheaper building a reactor 3-5% bigger or adding $500/kWe to the project cost? That's the key question.


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PostPosted: Sep 02, 2014 2:53 pm 
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Lindsay,

Disagree. They key question is not technical but political.
NIMBY, radiaphobia, evacuation plans, demagogues on the make, etc, etc.
If remote siting gets us over this hump,
then the tradeoff between colder water and transmission costs
is in the noise.

Jack


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PostPosted: Sep 02, 2014 4:57 pm 
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djw1

The green comunists that block nuclear power in favor of their middle age wind mills would block the transmission lines as well.

Russia offered German utilities to build some new nuclear in Kaliningrad (Koenigsberg) and to transfer the electricity thru VHVDC lines beneath the baltic sea to Germany. As soon as it was published green company`s as Greenpeace attacked the utilities until it was stopped.


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PostPosted: Sep 02, 2014 6:49 pm 
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djw1 wrote:
Lindsay,

Disagree. They key question is not technical but political.
NIMBY, radiaphobia, evacuation plans, demagogues on the make, etc, etc.
If remote siting gets us over this hump,
then the tradeoff between colder water and transmission costs
is in the noise.

Jack
No, I think that we agree, the biggest challenges are political/people based and remote siting may be one of the techniques to used to help placate opposition and get new NPP's built, but it's not really dealing with the problem which is rooted in the FUD surrounding most things nuclear.


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PostPosted: Sep 02, 2014 7:01 pm 
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I assume there is no way to make use of the almost absurdly low air temperatures during the winter?
Would the equipment to take advantage be too expensive and complex to operate?

I imagine there might be some issues with the water intakes from the bay freezing if the design was not careful.
(Probably a second set of outfalls next to the intakes through which some of the outlet water can be cycled to make sure the intakes stay above freezing).

What's the lowest condenser temperature you know of having been used in service?


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PostPosted: Sep 03, 2014 3:03 am 
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Some powerplants very up north use hybrid cooling, air in winter, water in summer. Sometimes necessary to deal with freezing issues in the intake water.

For a working fluid and cycle, maybe Kalina is suitable. The ammonia mixture reduces the freezing point and the condenser is more compact with heat rejection under pressure rather than vacuum. Not sure if you get that much higher power output though. Hard to beat a bog standard superheat or supercritical steam cycle.

Here's what I worry about. People really don't like to work in nasty cold places in the middle of nowhere. Generally you have to pay them 100% or even 200% more just to work in your nasty location. Then if you have to fly them in and out with helicopters, that costs even more.

Labor cost is really important, even for modular reactors quite a bit of site works and operations, inspectors, security etc are needed. If you pay 2-3x more for that then this could easily sink the concept economically. There just wouldn't be a way to compete with a gas turbine plant that is only a few km from its major load centers and has access to large labor pools in a pleasant environment.

I like the idea though, build a large reactor park away from population centers. But maybe make it a more pleasant location, not 2000 km away but say 100 km. So people can drive there from a city 100 km away for example. I would look for industrial centers some distance from cities.


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PostPosted: Sep 03, 2014 6:25 am 
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Churchill has a railway with, admittedly slow, passenger trains and an airport with a 2800m Asphalt runway. Might be able to get people in from say Winnipeg easily.


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PostPosted: Sep 03, 2014 11:47 am 
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E Ireland wrote:
Churchill has a railway with, admittedly slow, passenger trains and an airport with a 2800m Asphalt runway. Might be able to get people in from say Winnipeg easily.


People really don't like to commute more than 2 hours. Speaking for myself, even 1 hour is annoying if its a daily trip.


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PostPosted: Sep 03, 2014 1:07 pm 
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How many staff do you need for something like ~30,000MWe of plant?
That is the bottom end of what we would be looking at.


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PostPosted: Sep 03, 2014 1:27 pm 
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A todays nuclear power plant has a staff of 300 + 200 contractors working for security and whatever. During the planned outages about 400 - 600 additional workers get in to make maintenance and repair work.

As economics of nuclear power plants improve with the size I would install for the 30000MWe 10 x 3000MWe large MCFR plus a reprocessing unit for them. All in all I would estimate it would require some 4000+ men.

But back to the points mentioned by Lindsay 2% additional nuclear heat might not really increase the cost of a new reactor. You can run the pumps a bit faster and get easily 2% more power to compensate the lower efficiency of a warmer cooling water. I would place the reactors at the Atlantic between New York and Philadelphia or at the Great Lakes close to the demand.

Today there are no strong connections between the electrical grids in North America. VHVDC lines could help to equalize demand and increase the potential % of base load hence make more nuclear economic.


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PostPosted: Sep 03, 2014 2:46 pm 
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Problem is you will never get the permissions to build a complex there.

Up in the Arctic you can build a complex that sprawls over a huge area and not even have a problem with someone complaining that their house will be compulsorily purchased.
And the Greens will have trouble claiming that a Chernobyl esque accident would cause absurd amounts of property damage.
I wonder how much the total value of all the property up there actually is.

And that is another benefit of these huge lines.
Baseload that is unused in the winter in Winnipeg can be used in summer in Los Angeles and things like that.


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PostPosted: Sep 03, 2014 4:42 pm 
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A nuclear power plant requires a high capital investment while operation costs are low. Thus it is used for base load only. That means the potential is 50% of the electricity demand or 10% of the total end energy demand. That`s it.

A UHVDC overlay grid over north america could increase the baseload fraction of the electricity demand. Poeple in New York wake up some hours earlier than in LA. In the North the electricity demand is high in winter while it is the opposite in the south. It could reduce the required reserve capacity. It would allow to build bigger more economic units.


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