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PostPosted: Aug 07, 2014 3:03 pm 
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Cyril R wrote:
I wouldn't bet my money on those loopholes. When it comes to court, antagonists will claim, rightfully, that a desal or floating reactor makes as much long lived waste as a power reactor, on a thermal power basis.



I'm not saying I would either, easier just to build in Arizona. But the law in California explicitly allows new reactors for research and desalination. So Berkeley could build an FHR.


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PostPosted: Aug 08, 2014 12:37 am 
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Gee whiz you guys can get off track pretty quickly.

Our perfect salt storage peaking MSR might look something like this.
Attachment:
CalISO Peaker Curve and Est Price.png
CalISO Peaker Curve and Est Price.png [ 46.05 KiB | Viewed 1476 times ]
The MW curve was set based on meeting the requirements of the 2020 CalISO curve while producing an average of 1000 MWe. The price curve was synthesised based on setting an average price of $50/MWh, and shaping based on MW curve which sort of makes sense. To get more MW the market price has to increase.

For these assumptions the uplift in revenue is about 23% compared to base loading against the same price curve. The bad news: by my extremely crude estimates the cost of a plant capable of delivering that output curve costs 47% more than the base load plant producing the same daily MWh output. So to a quick first estimate, it doesn't look economic to build that peaking function into your MSR NPP based on electricity prices alone.


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PostPosted: Aug 08, 2014 7:51 am 
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Looking at your curve it looks like a 1GWe plant would need a 3.3GWe-hr storage system to go with it to store energy during the day and release it in the evening. Let's assume a low thermal efficiency of 33% since this is a peaking plant and we really need to hold the capital costs down for the turbine. For just the heat store portion, based on Cyril's $5/KWth-hr, we'd be talking about $50M. This is the same number I came up with in my calculations so it seems at least reasonable. The key is that we are storing high temperature heat so we can have a 200 to 300 degree delta temp between the hot and cold salt. You still need to have the peaking turbine and generator and the transmission lines that only get used for a few hours a day.

Still doesn't make this good policy but it does look like something we could compete in once the natural gas glut here gets straightened out and natural gas prices pop up to a level that actually turns a profit for the oil companies.


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PostPosted: Aug 08, 2014 8:06 am 
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Lindsay wrote:
Gee whiz you guys can get off track pretty quickly.


Hmm I dunno Lindsay, seems pretty relevant to ask whether you are actually allowed to build this reactor in California.


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PostPosted: Aug 08, 2014 8:09 am 
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[quote="Lars"]Looking at your curve it looks like a 1GWe plant would need a 3.3GWe-hr storage system to go with it to store energy during the day and release it in the evening. Let's assume a low thermal efficiency of 33% since this is a peaking plant and we really need to hold the capital costs down for the turbine. For just the heat store portion, based on Cyril's $5/KWth-hr, we'd be talking about $50M. This is the same number I came up with in my calculations so it seems at least reasonable. The key is that we are storing high temperature heat so we can have a 200 to 300 degree delta temp between the hot and cold salt. You still need to have the peaking turbine and generator and the transmission lines that only get used for a few hours a day.[quote]

The suggested operating window for the binary nitrate "solar salt" or "draw salt", is 265C low, 565C high, this gives you the 300C you need.

By the way, the $5/kWth includes a salt-to-oil heat exchanger so is a close enough proxy for a salt steam generator.


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PostPosted: Aug 08, 2014 8:44 am 
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For the California example - what about attempting to inject steam into the Geysers field?
It should be able to soak up a few hundred megawatt hours at a time.


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PostPosted: Aug 08, 2014 8:50 am 
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E Ireland wrote:
For the California example - what about attempting to inject steam into the Geysers field?
It should be able to soak up a few hundred megawatt hours at a time.


What is the recovery efficiency of this? I imagine large losses to heating up porous rock.


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PostPosted: Aug 08, 2014 10:33 pm 
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Lars wrote:
Looking at your curve it looks like a 1GWe plant would need a 3.3GWe-hr storage system to go with it to store energy during the day and release it in the evening. Let's assume a low thermal efficiency of 33% since this is a peaking plant and we really need to hold the capital costs down for the turbine. For just the heat store portion, based on Cyril's $5/KWth-hr, we'd be talking about $50M. This is the same number I came up with in my calculations so it seems at least reasonable. The key is that we are storing high temperature heat so we can have a 200 to 300 degree delta temp between the hot and cold salt. You still need to have the peaking turbine and generator and the transmission lines that only get used for a few hours a day.

Still doesn't make this good policy but it does look like something we could compete in once the natural gas glut here gets straightened out and natural gas prices pop up to a level that actually turns a profit for the oil companies.
I get a little bit more at 4.7 GWhe, see revised chart. As for costs I arbitrarily to a salt price of $0.82/kg (simple hot and cold salt model with a 200C range) and doubled it to cover all the other bits and the $/kWh came to $19.52/kWh, that's the price that got included in the estimate for the peaking/storage MSR. I can see how with a thermocline you can get to $20/kWh, but I don't see how you can go from there to $5/kWh. What I haven't done is work out the relative economics of using a gas fired peaker, which is what commonly happens when you have big movements in demand and no hydro-electric power.
Attachment:
CalISO Peaker Curve, Storage and Est Price.png
CalISO Peaker Curve, Storage and Est Price.png [ 53 KiB | Viewed 1437 times ]


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PostPosted: Aug 08, 2014 10:57 pm 
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So for the MSR peaker with storage to work commercially you need a few things to go your way.

1 you need a power conversion system as cheap as an open cycle gas turbine.

2 you need high/higher natural gas prices.

3 the cost of thermal storage needs to be quite low

4 the conversion efficiency still needs to quite high to avoid having a large amount of storage and or a bigger reactor


Last edited by Lindsay on Aug 09, 2014 2:12 am, edited 1 time in total.

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PostPosted: Aug 09, 2014 1:10 am 
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Quote:
I can see how with a thermocline you can get to $20/kWh, but I don't see how you can go from there to $5/kWh.


Simple arithmetics. Starting from the Pacheco et al $20//kWh, then correcting for higher dT. (3x cost reduction). So you're into $7//kWh at that point. Scaleup (bigger tank) reduces cost of the tank and insulation. It also improves thermocline practical capacity (taller tank). In California everything is always more expensive so $5/kWh may not be feasible there.


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PostPosted: Aug 09, 2014 2:11 am 
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I still think that there are some important details missing, if using solar salt and a steam cycle (a very sensible combination) the cold salt has to be hotter than feedwater.

Example: Feedwater at 250C (pretty standard), implies a lowest salt temp ~280C, but then you top out at say 540C for the high temperature, so that's a 260C delta. 540C => 510C steam temp, so the conversion efficiency is lower than you would like, so you need more storage. If you need more storage, then achieving that low storage cost becomes even more important, but your reactor has to be bigger also, add more $. The more detail one looks at, the harder it it gets. Here's one more example, in order to get that 300C delta on the salt one might drop the feedwater temperature design point down to say 210C, but when we do that, the conversion efficiency drops also, so some of the gain from the bigger delta on the salt has to be given away.


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PostPosted: Aug 09, 2014 5:30 am 
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That's already considered in the figure. Here are Pacheco et al assumptions:

Tank delta T=84ºC, Mixed filler cost=$72/tonne, Salt cost=$0.45/kg, Tank cost =$155/m3, Thermocline practical capacity = 69%

If your salt tlow is 280C, you might use a 570C thigh for the salt. 290C dT, which gives (290/84) = 3.45x reduction in storage cost. Consider increased tank thickness (to resist creep) and insulation, and slight increase in HX cost (steam is higher pressure than oil), call that factor of 3 cost advantage.

It looks like efficiency is worth more than steam generator, so my guess is you end up with more aggressive pinch points.

Here's what I'm thinking. 250C feedwater to be standard, 540C steam or supercritical water. Heated by 270C cold salt, 570C hot salt stream. 20C difference on feedwater, 30C difference on steam, that seems plenty. Feedwater heaters usually only have 10C difference so maybe we can even make 560C steam from 570C salt.


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PostPosted: Aug 09, 2014 6:24 am 
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Hmm wait, I was wrong, the cost of the heat exchanger is greater than I thought, so the cost reduction is less. Looks like we'll have trouble getting that $5/kWh. $10-15 would be more like it, unless scaleup gets a really big cost reduction.

On that subject. The Pacheco 688 MWh thermal system is quite tiny. What kind of economy of scale do we get from a scaleup from 688 MWh to 6880 MWh?


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PostPosted: Aug 09, 2014 10:39 am 
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I think that there would be quite strong economies of scale, but I wouldn't want to predict them. I also think that you're on the right track to target the highest possible delta in salt temperature. A logical extension of that is to go for a phase changing salt for the thermal storage AND a large temperature delta. For example a certain mix of MgCl/KCl/NaCl has a mp of 380C, a latent heat of fusion of 400 kJ/kg. My concern is how does one manage the mechanical consequences of freezing and thawing.

Anyhoo if one could master the phase changing molten salt, maybe as a bunch of thinly clad engineered rocks for a thermocline design, the size of storage could much smaller, but that model sounds expensive.


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PostPosted: Aug 09, 2014 4:44 pm 
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Hrm well, having a liquid that can be pumped always seems a major advantage. And i like the idea of using cheap sand to replace most of the nitrate. So my preference is for thermocline. But even two tank systems look great if the dT is high. Two tank is lowest tech risk.


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