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236 comments on Advice to Pres. Obama (#5): One Engineer's Advice for Energy Policy
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236 comments on Advice to Pres. Obama (#5): One Engineer's Advice for Energy Policy
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Thanks EP - you should write more often...;-)
I share your optimism on nuclear, if for no other reason than this is the only chance at replacing the coming decline in aggregate energy surplus. But as typically is the case when addressing one problem at a time (in this case energy), there is often a cost - in this case water. Currently a full 48% of the water use in the United States is devoted towards cooling of thermo-electric power plants ((another 34% (and 81% of fresh water) towards crop irrigation)). Unless new nuclear water consumption/withdrawal technologies accompany a nuclear scale up, we are going to have water limitations to power, as recently was the case in France. Also, the choice to move to electric vehicles, unless the electricity is largely generated from new sources will have big implications for water:
I agree with much in your letter, but engineering and efficiency alone will not be enough. We need systems thinking and reductions in consumption (that are not the result of a credit crisis), starting yesterday.
Nate:
With regard to your citation regarding increased water consumption and withdrawal:
http://pubs.acs.org/doi/pdf/10.1021/es0716195?cookieSet=1
I think it would be helpful to put the increase in context.
But from earlier in the same paper at page 4310:
and from the "Conclusions", also at page 4310:
The quote was directly from the papers abstract.
The tradeoffs and linkages between energy and water are among the most critical we face; but they are very complicated, and extend beyond just those two commodities (e.g. we could use more water for bioenergy if we used less for meat, etc.) I am painfully aware of how complicated the linkages are, as evidenced by my current 3rd rewrite on a paper on Energy and Water. As soon as possible I plan to devote an entire post to the issue -but my main point here is everytime we look to a supply side 'solution', we tend to make some other limiting input more limiting.
P.s. are you the TOD'er I went to U of Chicago with? I keep forgetting.
A large share of the publicized problems that the Atlanta area has had with water have to do with water usage for electricity.
One view now is that the estimates of water available for electric cooling were based on the assumption that Atlanta can be expected to get 50+ inches of rain a year--more than Seattle. Now there is some question whether the time period over which the 50+ inches assessment was taken was really representative. Maybe we should be expecting only about 40 inches of rain a year.
If this is the case, the problem is that the Southeast is already overbuilt for water-cooled electric power generating plants. All of the arguing about how much water Atlanta gets vs Florida vs Alabama basically has to do with how much water is available for electric power plants. It starts sounding a lot like the US Southwest.
Much thermal generation is near the sea/ocean since a lot of population is there as well. Once through cooling is no problem there, only a diffusor pipe system has to be built to mitigate local thermal pollution issues.
Anyways, for inland locations, dry cooling is a proven option available at a small increment in levelised cost. Historically little value was placed on water conservation, so most plants are wet cooled. Adding a tax on freshwater cooling (bigger in arid areas) is one solution.
However, a more productive option is to use CHP thermal desalination and water treatment plant, using the nuclear plant's turbine heat rejection. This both creates a lot of new freshwater supply (from eg sewage water, brakish water, salt water if a sea/ocean is nearby) while reducing cooling water use (because the CHP can be seen as increased efficiency). If no water supply is nearby (could be the case in arid areas where freshwater supply is most dire), other CHP uses can be devised, such as paper and pulp heat input, other chemical processes etc. etc. that can also greatly reduce cooling water use.
This is one problem that is easily solved, and that can actually reduce fuel use and imports even more in the process by reducing natural gas and oil that would otherwise be needed if CHP was not available. This all does require the right policy. So now that you're reading along, Barack... :)
Is it possible (reasonable) to go back and retrofit some existing power plants for dry cooling? It seems like both the Southwest and Southeast could use the additional water, if it were available.
Retrofitting is possible, however the plants electrical output would suffer. Thermodynamics of heat engines, of which steam turbines, diesel engines, and gas turbines are examples, state that the output is directly proportional to the heat flux times the difference between the input temperature and output temperature. For water it is difficult go higher than about 350º C on the hot end because of corrosion, high pressure and other engineering problems. On the low side we can go down to about 50º C if we can use cold sea water for cooling. For PWRs, (Pressurized Water Reactor) this limits us to about 34% efficiency. With a dry heat exchanger it would be difficult to get the low end temperature lower that about 110º C which would lower system efficiency to maybe 30%.
One large advantage of the LFTR and gas turbine is it can operate at between 650º- to 900º C on the hot end. With an air cooled heat exchanger on the low end running at 110º C we have an efficiency of over 50%, and lower cost.
The Lower Mississippi River has no foreseeable heat sink issues. The volume of water is incredibly vast.
Just the shipping channel at New Orleans is 900' wide and 100' deep moving at several knots at the summer minimum. Add the water underneath the shipping channel and to the sides.
Alan
I was pretty sure 'frombigeasy' was refering to your hometown and not some techy organization that feels big things come easy (you do paint bright pictures with a broad brush). Always good to see someone give good information about a place they know well, thanks. :)
hit the key twice
Overall, excellent article. Kudos.
I tend to discount the difficulties of "water for power generation cooling" on the following grounds:
a) Much of the present water "used" for power plant cooling is not really used, simply heated slightly then returned to source immediately available for other uses. Distinction needs to be made.
b) For only a relatively small (approx. 2% for added blower input, 2% reduced overall plant efficiency) hit plants can switch to air cooling and eliminate water use almost entirely.
c) Most population concentrations live near enough to "essentially unlimited" ocean water sources to ignore the issue.
d) Coming technologies such as the "Vortex Engine" technology have a clear potential with relatively small R&D to both eliminate the cooling tower requirement altogether, and also to contribute an added 20% to the overall plant efficiency. Probably very cost-effective, esp. in dry areas. See Atmospheric Vortex Engine (AVE)
I realize I'm somewhat over-simplifying, but so is above (necessarily, as myself) in the limited space and time available.
The linked to paper (and indeed all papers addressing water limitation issues) distinguish between water consumption and withdrawals. Withdrawals are typically considered the diversion of freshwater from its natural hydrologic cycle, either at the surface or from below the ground, for anthropogenic purposes. Water consumed usually refers to water used in the energy production process that is either lost to a given watershed as steam or contaminated beyond cost-effective remediation.
Though energy from biomass is far more worrisome in its water impacts, the closures in Europe in 2006 and 2007 of nuclear plants due to heat/water limitations suggest this is not a trivial issue. Globally the current water stock in rivers is about 2000 km3; the anthropogenic water withdrawals from these rivers is 3800 km3/yr; and the global river discharge is 45,500 km3/yr -so clearly we can reuse this water many times over - (unlike energy) - but, as with energy, there are limits.
One of the advantages of molten-salt (and perhaps also metal-cooled) nuclear plants is that they can run hot enough to use gas turbines instead of steam turbines as the heat engines. If the designers are willing to accept lower efficiency1, open-cycle gas turbines using air are possible. This eliminates water as a coolant, and also eliminates the capital cost of condensers and cooling towers. (It also makes the design suitable for sites where there is no available water.)
GE's recent F-series intercooled gas turbines produce several hundred megawatts from a rather small package. A few similar units, with regenerators instead of heat-recovery steam generators and supplied heat from a molten salt or metal loop instead of combustion, would make a compact and innocuous generator system for a 1-GWe class reactor.
1 Nuclear fuel is so cheap that capital cost should probably be a greater concern. Just being able to eliminate both the sulfur/mercury emissions and water consumption of plants in the Southwest would be a major selling point.
There are potential advantages to that, as you mention. But don't get ahead of the facts now. For a given temperature, advanced steam cycles are more efficient than gas turbines. This is a big advantage too. Sure, regenerators increase efficiency, but they cost $$$ and adding more has diminishing returns. Sure, ultracritical can't be taken to really high temps, but it's still increasing incrementally, and anyway we may find that very high reactor temps are not optimal from a total cost and durability viewpoint.
Gas turbines excel at power density. Great for airplanes. Not hugely important for a stationary utility generator.
Gas turbines could be safer since the pressures in/around the reactor can be lowered, and possibly yielding a bigger power density. That could be a big advantage. But it's a matter of good design, and it's not like there would be a meltdown in the event of a major failure.
There is a difference between capital cost per unit of thermal output and capital cost per unit electrical output. Sometimes, increasing the net electrical efficiency can increase the cost per unit of thermal output, but decrease the cost per unit of electrical output. That last thing is what we're looking for. I think we may find that a rather high efficiency is optimal.
How high a temperature can they run at?
The Molten Salt Reactor Experiment ran at up to 650° C. If you look at the pictures, you'll see that it didn't take much of a radiator to dissipate 7.4 megawatts of heat at that temperature! I expect that the temperature was limited by the properties of the Hastelloy-N used to make the vessels, pipes and pumps, and increasing the temperature to the ~850° C needed to run a sulfur-iodine cycle for thermochemical hydrogen production would require some new materials science.
GE's latest gas turbines are running at ~1300° C turbine inlet temperature, so an air-cycle turbine fed from an MSR would be rather unchallenging from a technical standpoint.
The nuclear part is somewhat challenging at higher temperatures, especially with regards to durability over decades of use.
650°C is only 100 degrees above the typical operating temperature of a steam turbine. I am guessing that you could run a closed cycle gas turbine with this inlet temperature using coal as the energy source. I am not promoting more coal fired generation; I am just saying that it could be done if it was necessary. Presumably it is not done in practice because there is some kind of performance/cost penalty.
At the time of the experiment, no heat engines were available in the 650 degrees celcius range. This no doubt lessened the commercial interest in the MSR, along with little political backing it's no surprise that the experiment didn't lead to real reactor systems.
State of the art steam turbines operating at around 600 degrees C are more efficient than gas turbines at similar temperature. A huge amount of power is required to run the compressor in the gas turbine. Natural gas burning gas turbines are still very efficient because they are burning extremely hot, so as to get a high delta T. This is not optimal for a nuclear heat source, IMHO.
Nate -
The water issue is certainly non-trivial, but I think you would have to admit that it is largely a regional issue.
I don't see that water usage for nuclear power plants would be a deal-killer for most of the Northeast, Great Lakes Region, or on our most of our major rivers, such as the Mississippi or the Ohio. The Southwest is a whole other story, and probably the last thing the Colorado River basin needs is to add a large nuclear power plant. Parts of the Southeast could also be problematic.
One thing I do not have a handle on is the comparative water consumption of a nuclear power plant versus a coal-fired power plant of the exact same rated output. Let us assume that both have similar natural-convection cooling towers with the exact same evaporation and blow-down rates. The question I have is: Which one will consume the most water (by 'consumption' I mean water evaporated from the cooling tower, not gross water throughput)?
Unless I am missing something, I tend to think the water consumption of the two would be in the same range. Both operate a steam cycle in which cooling water is used for running the condensers. As far as reactor cooling goes, doesn't the heat transfer loop that furnishes heat to the steam generators accomplish just that, and isn't the reactor power level and amount of such cooling closely optimized for a given level of output so as not to waste reactor heat?
If indeed a nuclear power plant and a coal-fired power plant have similar water consumption, then it become less of a persuasive argument against nukes to say that they consume too much water.
Anybody else out there knowledgeable on this question?
I think you're "mostly right", eg. "a nuclear power plant and a coal-fired power plant have similar water consumption". No water is consumed in a nuclear power plant other than for cooling/condensing the steam after the turbine, just like in a coal plant. However, since overall thermal efficiency of a typical new nuclear power plant might be as much as 5% lower than a comparable coal plant, a cooling-tower-cooled nuclear plant will use perhaps (40/35 - 1) * 100 =approx 15% more cooling water.
lengould -
Thanks.
If indeed due to differences in thermal efficiencies a nuclear power plant results only slight more water consumption than a coal-fired one, then high water consumption is not a terribly valid argument against nukes, at least in comparison to coal-fired plants.
I wonder if some of these 'next generation' nuclear power cycles, as described in the lead article, will have thermal efficiencies equal to or somewhat better than coal-fired power plants.
And as pointed out in some other posts, it is possible to go to air cooling, though there is a significant penalty in doing so, both in terms of capital cost and energy consumption. However, if worse comes to worst, that may be a option in highly water constrained regions. As such, I don't think it's fair to try to write-off nuclear power solely on the water consumption issue.
The issue is mostly policy related. Putting a tax on cooling water would fix the issue, especially if combined with a guaranteed long lasting low investment tax and property tax rate on CHP as the business case for CHP uses would look much more attractive. (CHP saves cooling water by artificially increasing the efficiency of the cycle, reducing per kWh cooling water required).
The MSR is sited underground in deep holes and uses passive air cooling from the chimney effect to cool the reactor. The high operating temperature of the reactor and gas turboelectric generators support efficiency of 55% as opposed to 33% for coal and LWR plants.
The MSR that EP described is air cooled and uses no water. If MSRs replaced coal generation and light water reactors, there is no water problem.
Even light water reactors don't have to be a water problem. The Palo Verde Nuclear Power station in Arizona uses effluent from Phoenix for cooling. http://phoenix.about.com/cs/utilities/a/paloverde.htm
It's just a design issue, as in it is easier to put a power plant near to a river and use that for cooling, so that's what happened.
The Metcalf Energy Center (NG fueled 600MW) in San Jose, CA uses recycled water from the San Jose Sewage Treatment plant for cooling as another example of water reuse rather than using "new" water for plant cooling. This was a win-win solution as it reduced the amount of fresh water going into San Francisco Bay and did not impact local water supplies.
It has been claimed that air cooling erases the efficiency gains from supercritical steam at the Kogan Creek coal fired station in Queensland. The operators claimed a CO2 saving of 22% relative to pulverised coal but apparently omitted the power drain of the pumps and fans.
Note in heatwaves they just spray river water on the outside of the radiator. So much for water saving.
You could operate the system during a heat wave without water, but this requires extra redundancies like more powerful fans and pumps, and this also increases parasitic losses.
Again, the issue is too little or no tax on cooling water. It's too cheap to use water cooling. A high tax on cooling water (at least in arid areas) would spur deployment and development of CHP which is desirable.
Nate
heard you comment on obama's speech on the BBC world service just now...
good delivery... very serious and measured tone that carried a sense of "knowing expertise"
gravitas with out the panic cassandra stuff
get yourself on MSM more..
When a farmer withdraws 1,000,000 gallons of water from a river to irrigate corn for ethanol, none of it is returned, hopefully, because any return water would be contaminated with fertilizer, pesticide and top soil.
When a nuclear power plant withdraws 1,000,000 gallons of water from a river to cool its condensers, all 1,000,000 gallons is returned, actually slightly more because the water expands when heated, but the same mass. The river is slightly warmer as a result and over the next few days a small amount of water evaporates due to the temperature change, about one half gallon per kWh.
The average American lifestyle uses 1,550 watts, 37.2 kWh / day / per person.
If all that power came from nuclear with an average evaporation rate of 0.5 gal / kWh it would evaporate 18.6 gallons per day, 6,790 gal / year.
In year 2000 the U.S. consumed 408 billion gallons of water per day.
http://pubs.usgs.gov/circ/2004/circ1268/
Assuming a population of 295 million in 2000, that is an average of 1,380 gal / day / person, of which the nuclear share would be about 1.3% if it all came from nuclear. Fossil plants also consume water, so the difference between fossil and nuclear is much smaller.
Contrast that with corn ethanol which needs 10,000 gallons of water to produce the energy equivalent of 8 gallons of gasoline, page 54.
http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/DOE%20energy-wat...
Filling a 20 gallon tank with E-85 one time consumes enough water to make all of your electricity for two years with nuclear power.
But, many nuclear plants are located on coastlines and use the ocean as a heat sink which is effectively unlimited and consumes no fresh water. Plants located near the discharge of rivers don’t count since the water discharges into the ocean before it has time to evaporate. So the average evaporation rate for our nuclear plants is significantly less than calculated above.
If we mass produce floating nuclear plants they will use sea water for cooling and they can desalinate sea water. Also note on the chart, page 38 of the pdf, that dry nuclear is an option.
So why the big fuss about water consumption by nuclear plants?
How many people want to see their electric bill double to save ½ % on their water consumption?
Anti nuclear folks like to talk about water withdrawals, not water consumption, because most people do not understand the difference. It is deliberate obfuscation, and in my mind unethical.
By the way, hydro evaporates 9 times more water than nuclear, bottom of page 38.
Nukes do require a minimum river flow though.
Atlanta has seen it's stored water in a prolonged severe drought drained away to cool the Southern Co. nukes near Dothan Alabama. In this particular case it is many thousands of gallons/NW Georgia resident lost to nuclear power.
Alan
Only those built with once through cooling. Take a satellite trip down the Ohio River and see how many fossil and nuclear plants have cooling towers. If climate change reduces Georgia rainfall, cooling towers, canals or ponds can be retrofitted.
Citing water withdrawals of once through plants as a reason not to build nuclear, as if all nuclear plants need that much water, is misleading. Water issues are not a good reason to avoid nuclear power in the future.
Water issues are not a good reason to avoid nuclear power in the future.
When reactors have to be shut down on the hottest days of the year when A/Cs are at max and drought impacts river flows, then yes, water issues do come into play.
Only those built with once through cooling.
I understand that there are maximum discharge temperatures that are also a consideration.
If climate change reduces Georgia rainfall, cooling towers, canals or ponds can be retrofitted.
And what happens when those canals and ponds begin to look like Lake Lanier?
The issue that I have isn't that water issues are unimportant, but they are far less important than one might be led to believe. They're issues of concern to individual locations in the same way that geographic fault lines, hurricanes, infrastructure, and distance to market are. They aren't a singular concern unique to nuclear power and dont really merit discussion except on a case by case basis.
I agree, but a more focused concern of water availability will reduce the number of viable nuke sites even more.
One reason (among several) to build new nukes next to old nukes is site acceptability. Adding a new nuke near Dothan is likely to draw objections form Georgia, as one specific example.
Overall, there are wide areas of the USA where there are no acceptable nuke sites. A limitation that has to be seriously considered (and routinely overlooked) by advocates for a "Rush to Nuke".
Alan
If the new nukes are air-cooled, the objections may turn to praise; replacing existing water-cooled plants would not just save the water, it would prevent power shortages when water temperatures are too high.
FWIW, 650°C is roughly the temperature at the inlet of a diesel turbocharger. Open-cycle gas turbines are a definite possibility for high-temperature reactors (and play nicely with CAES).
Today's nukes would also be suitable for CAES. The rejected steam from the turbine outlet is over 160 degrees Celcius. Not as efficient as having very high grade heat, but it should do nicely, right?
Air cooling makes sense sometimes, but it's typically much better to find a use for the waste heat - CHP, the double edged blade. Desalination, district heating, domestic hot water, paper and pulp, various chemical processes, etc.
A fine engineer is he who turns a problem into a solution.
Most steam powerplants have turbine exhaust pressures well below atmospheric and send sub-saturated steam (some fraction of liquid water) to the condenser; the exhaust temperature is closer to 130°F, not 160°C.
We are not talking about the condensate that is already cooled from the condenser here.
An example of a modern efficient operating saturated steam cycle range would be from, say, 300 degrees Celcius down to 200 degrees Celcius. However, the lower pressure sections don't really get you that much power; steam is not very good at that under lower temperatures. An easy way to do a CAES heat diversion, then, would be to bleed off steam at some lower pressure part of the turbine (i.e. at a point where steam pressures are well above atmospheric), without too much electrical output losses.
It's painfully obvious that you have no idea what you're talking about.
Oh that's very enlightening. The only thing that's painfully obvious is that you don't have an argument, nor make even the slightest effort to try. Do you even understand the basics of CHP? Do you know what bleeding off steam means from a turbine section? I thought better of you.
http://www.warwickshire.gov.uk/Web/corporate/pages.nsf/Links/2E4F3CDA2F5DEA36802574870037D7AF/$file/Appendix+4.c+Combined+Heat+and+Power+potential.pdf
Take a look at table 1. Sacrificing a relatively small amount of electrical output gets you a large amount of heat available for the CAES system - and the heat input compared to electric CAES output is relatively small. Considering the relatively low cost of the CAES system, and the high value kWh electricity that the CAES system will deliver - nearly carbon free, clean, dispatchable electricity - this should make for an impressive business case.
Cyril, since you do not even try to understand the thermodynamics, you're just talking nonsense. I'd hoped to spare you this, but you don't know when to quit.
Quite. I've written on it before.
It's long been one of the standard methods of increasing the efficiency of steam-cycle plants; partially-expanded steam is tapped off and used to pre-heat boiler feed water, which is heat that does not need to be supplied by the boiler and is not rejected to the condenser. See Feedwater heater. I have done thermodynamic analyses of such systems, which you obviously have not.
Bleed steam has nothing whatsoever to do with CAES, which does not have a steam cycle.
Steam at 10 bar has a saturation temperature of about 180°C. A nuclear-driven CAES system will input heat to the turbine at over 600°C, and a gas-fired CAES system would probably operate at well over 1000°C; this is crucial, because the energy which can be recovered from a given amount of air is proportional to the absolute temperature (and expanding air cannot be allowed to drop below 0°C or the turbines will ice up). The waste-to-energy system you're using as a reference has a maximum electric thermal efficiency of 23.3% (refer back to column 1 of your Table 1, which you obviously did not understand); CAES systems on the drawing board are specced at 80% fuel-to-electric. There is no point bothering with a steam cycle at less than 1/3 the thermal efficiency when you can feed heat to the air cycle. It would be a waste of both energy and capital.
BTW, I note that you can't even provide a working link to your own reference. Here's a good one, for anyone who wants to check out the details.
The thing that you've made painfully obvious is that your intellect goes as far as recognizing acronyms beginning with "C", and loses the ability to make distinctions after that. Thermodynamics is beyond your ken, and probably always will be.
Show me which of my statements regarding thermodynamics was factually incorrect.
DUH! You may have followed thermodynamics courses, yet you are not very good at listening. I was suggesting to use nuclear LWR and HWR cogeneration to supply CAES heat input. Then you say this:
So you do know what you're talking about - I knew that, but you were being deliberately obtuse and I had to call you on it.
So it is proportional. That means 180 degrees is still a large potential heat input. It depends on the cost which you've shown no detailed calculations on. Sure, parasitics will be higher if lower grade heat is used. But this is not huge and moreover is also a cost issue.
Nope; the LWR and HWR are already there. Paid for and delivering energy to the grid. That's what makes it so attractive to me if LWR cogeneration can be used for CAES heat input.
Don't know why that happened. It works if you copy paste it in your browser; clearly this is too much too ask. I get the feeling that you're really frustrated. Maybe you should get some coffee? Or did your cat die? Do you want to talk about it?
First you do not respond to my post - only with an ad hominem attack. This is not an intellectual response EP. Then when I call you out for that, you post more proof of not understanding what I said, and even now you dismiss a potentially powerfull CAES heat input (from existing nuclear technology) on a very thin analytical basis. Saying it is too expensive won't do. Show me accurate cost calculations why LWR steam bled off to supply CAES heat input replacing natural gas is uneconomical and/or does not supply enough heat. Since LFTR and high temperature nuclear in general is not widely available and has a risk of not being available for a long time, this is important. It is you who did not make distinctions.
Why would you say such a thing? It doesn't serve any purpose of debate, and is not a very scientific thing to say. Remember, you started the ad hominem attack; when you do that, do not be surprised when people respond negatively. What is your problem? You're not usually like this.
Now, let's keep it factual. Being mean doesn't help. Show me the cost calculations.
What are you wrong about? Just about everything.
Wrong; try 93° F and 0.8 PSIA.
More of the same.
Demonstrated to be nonsense above.
And this claim of yours is generally false:
Even at the reactor outlet temperature of ~550°F, the available heat would be insufficient. 1000°F is about the minimum for a serious gas turbine, and the hotter the better. If you understood thermodynamics, you'd be able to demonstrate this to your own satisfaction and drop the issue. Either you don't understand or you're trolling. The prescription is the same for both: shut up. TOD does ban trolls.
Bullshit. You were and are committing the fallacy of ambiguity, which is dishonest.
Another statement showing you have no grasp. 180°C is ~453 K, while you really need to hit about 820 K and would prefer to be well over 1000 K. You're talking around half the pressure-volume product, half the recoverable energy, twice the heat exchangers required to achieve it, around 1/4 or less of the heat transfer per mass of air...
Since you claim to be so smart, let's see you do an analysis of this issue. Assume air out of storage at 303 K and 50 bar, how much energy/kg of air could you get with heat at 453 K, 560 K and 920 K and isentropic expansion (γ=1.40)? How many reheats would you need for each input temp to avoid cooling below 273 K? What's the thermal efficiency of the three cycles?
You're talking about a wholesale re-engineering of the heat engine, for a purpose for which the reactor is ill-designed. This would be massively expensive. This is why I proposed doing it with a molten-salt reactor designed around an air-cycle gas turbine; most of the heat engine would already be handling air in the way required for CAES.
Clearly, you didn't try it. I did, and only got a partial URL.
BS is highly unscientific. It's a reaction to the BS you've been flooding this thread with, and you can stop right here, troll.
CAES- compressed air energy storage?
Yes. I'd link these things but I use the acronym so often it gets tiresome.
It's tough writing for a mixed audience. You may write about CAES every day of the week but I don't read about CAES that often.
So what's the advantage of storing energy as compressed air as opposed to keeping a couple tons of molten salt in insulated containers?
A short list off the top of my head:
One CAES study I saw posited several days of storage capacity, and it wouldn't be all that difficult to expand to weeks. Pumped hydro and other systems are limited to hours, and molten salts would be very expensive to expand beyond that (and would be very lossy due to heat conduction). CAES is a game-changer.
A CAES system operates partially as a heat engine itself, and usually outputs more energy than is input to the compressors.
Could you expand on that (no pun intended)? I know you don't mean a perpetual motion machine, but are you referring to the inclusion of natural gas, and not counting its input energy? Or are you implying that it is adiabatic?
Yes, I'm referring to the inclusion of fuel (natural gas isn't the only one that could be used). One CAES overview study I read included a system which had an electric output:input ratio of 1.33:1 and a gas-to-output efficiency of 80%.
Adiabatic CAES would beat those figures handily. I'm trying to find the time to look at the potential of near-isothermal compression for the first stage, which might also be a game-changer.
I'd be curious to see that study; did the cavern have a higher starting temperature than ambient air? Was this averaged over a year's time of charging/discharging? There has to be some reason for having a higher output vs. input energy. And it's not clear how the gas efficiency was determined.
I'm all for CAES, btw, just curious how many sites would achieve this level of performance, and for how long.
There's no mystery. The compressed-air input isn't included in the gas-to-electric figure, but it takes a bit of digging into the report to get all the figures together to calculate exactly what comes from what. The overall efficiency (output vs. electric+gas inputs) is around fifty percent, IIRC (the storage of air at near-ambient temperature loses a lot of compression energy, which has to be made up before expansion - that's what the fuel is for).
The overall efficiency (output vs. electric+gas inputs) is around fifty percent
Ok, that makes sense now.
If the heat generated during compression can be stored (that is, the adiabatic variant), the total efficiency could be in the 70-80% range and perhaps even better.
But don't take my word for it. Someone recently told me thermodynamics is beyond my ken.
If one could insulate the cave/reservoir, then it might be more adiabatic. Otherwise, the thermal conductivity of the rock mass (virtually infinite) will draw heat energy out at some rate and dissipate it.
The heat capacity of the earth may be effectively infinite, but the thermal conductivity is not and it becomes less significant as the system gets larger. Hot-water storage for concentrating solar thermal plants has been suggested using lined rock caverns without insulation. The rate of heat loss to the rock (presumably after an initial heating period, which is a one-time cost) is low enough that it's not worth the cost of insulation.
A regenerator has a thermal gradient from the hot side to the cold side. If insulation is an issue, one possibility is to put the hot side in the middle of a volume and the cold side at the edges. The heat would have to move through the colder areas before it could escape, and this heat would be the first to be removed from the regenerator when air was withdrawn.
I don't think the guys ordering a brand new nuclear reactor are worried about the cost of salt. Even tons of it. Air isn't free at my corner gas station. Compressed air has costs involved.
All a nuclear reactor produces is heat. If the air compression took mechanical or electrical energy, that means at some point there was a lossy heat engine producing the mechanical energy. Molten salt energy hasn't gone through the lossy heat engine yet. You use the phrase "back to mechanical energy". The energy was never mechanical in the first place. Losses due to heat conduction can be arbitrarily small just by piling on more insulation.
I know of two utility scale CAES in the USA (you mention the one in Alabama.) They've built a commercial scale prototype and they aren't going forward. The cure is evidently worse than the disease at least at this point in time. Nobody doubts storing energy as compressed air is "proven technology".
Anyways, I don't have a dog in this hunt and don't really care if the future is CAES or not.
What kind of salt are you talking about? If it's got isotopically-purified 7LiF in it, it's going to be expensive.
It really doesn't make sense to store nuclear heat anyway, since you can make it 24/7. That's more for concentrating solar.
For the compressing. The atmosphere is free, and isn't depleted or appreciably altered by people compressing air and letting it out again. Water's often not so easily available.
The beauty of air as a medium for storing e.g. wind energy is that it holds mechanical energy, not heat energy. You have losses but the medium is so cheap that your system cost is determined mostly by the power capacity of the system and only slightly by the amount of energy stored.
The wind energy was. This discussion of CAES is in the context of a hybrid wind/nuclear system with storage. The nuclear energy would be applied to the reheat of stored air before expansion.
I don't have a dog in this hunt either, but if people are complaining that the grid can't run on base-load nuclear and un-schedulable wind, CAES is a way to match supply and demand. (It would also allow major power lines to go out for significant periods with minimal effect on the system; the ability to store energy on one side and release storage on the other make such events far less troublesome.)
Ok, hybrid wind-nuclear system. I missed that. The low grade heat from somewhere in the steam turbine is used to heat the compressed air which is where the synergy comes in. So the air is compressed by windmills.
The CAES is used for load following and the nuke is always on. So the steam has to cooled whether the CAES is discharging or not. I guess we can heat a nearby river for that.
Ok, we need a site with 1) huge salt caverns, 2) excellent wind, 3) running water 4) High voltage grid connection. Are there any likely candidates in the USA?
You really need high-grade heat. MSR or HTGR heat would do, PWR/BWR heat would be marginal (and stick you with two different power systems).
The air is compressed using whatever power source is in surplus. The compressors are electric and don't care where the power is coming from.
If the reactor is running on an open-cycle gas turbine, there's no steam. Air comes in, is compressed, heated, expanded and exhausted. If there's surplus power, there's a cooling and storage stage between compression and heating.
It's easier than that.
Grid power is the sine qua non.
Yes; However thats only the salt in the core. Salt for thermal transfer doesn't require isotopic purity.
Other advantages are:
- CAES is proven (Germany and Alabama have been operating a large system for years). It uses very conventional turbomachinery, the labor and expertise are largely available. Solution mined salt caverns is the same - salt mining industry. In the case of the Norton CAES facility being constructed right now, an existing mine is being used.
- CAES uses very little materials per unit of capacity and energy stored, compared to other bulk energy storage options, and it uses almost all commodities like steel.
Regarding heat storage, a long term attractive option for CAES is to store the heat generated during compression, to be used for reheating on expansion during discharge. This will make CAES a true storage option, as normally natural gas or other fuels would have to be used to get the heat in the expansion stage. So CAES and heat storage may not be mutually exclusive in the future; developments in large scale heat storage could benefit CAES with heat storage. However, going for combined heat and power (from eg nuclear and geothermal plants) may also prove to be an attractive option, as that avoids the cost and issues with storing the heat. Theoretically, storing the heat is ideal, but economics and practical issues are important.
Reactors do not have to be shutdown on the hottest days of the year. Cooling towers are an option. For a 100 year heat wave it might make more sense to wave the temperature limits than build a cooling tower that may only be needed for a few weeks in the 60 year life of the plant. These issues are the same for other heat sources.
Over the entire U.S., wind power dropped 20% below average during July and August of 2006, while Electricity consumption for the nation jumped 20% above average. Nuclear power plants normally run at 100% year round, yet production was 10% above average during July and August because they schedule refueling and maintenance outages for spring and fall when demand is low. Windfarms often perform maintenance in the summer to minimize production losses.
In California, windmill output at the time of peak demand dropped below 4% of data plate rating for seven days during the heat wave of 2006. Counting on wind power for baseload capacity during a heat wave could be deadly.
With a cooling tower water requirements are reduces by a factor of 100. Most likely other issues will dominate at that point. As a last resort we could cut back on biofuel production a tiny bit.
A more focused concern of water availability will dramatically reduce the number of viable sites for growing biofuel. Pumping an ancient aquifer to make ethanol is insane.
Adding a new nuclear plant at Dothan that includes cooling towers for both plants could reduce water withdrawals of that site by 98%.
“Zogby Poll: 67% Favor Building New Nuclear Power Plants in U.S.”
http://www.zogby.com/news/ReadNews.cfm?ID=1515
“More than three times as many strongly supported nuclear energy than strongly opposed it. Two thirds of self-described environmentalists favor it”
“In mid 2007 a survey of 1150 people living within 16 km of nuclear power plants in the USA, but without any personal involvement with them, showed very strong support for new nuclear plants. Over 90% thought nuclear energy was important for future supply, 82% favoured it now, 77% said that new plants should definitely be built and 71% said they would accept a new plant near them.”
http://www.world-nuclear.org/info/inf41.html#opinion
People who live near existing nuclear plants are more supportive than average Americans. Some of the new construction will be on existing nuclear sites, like the two plants in Texas.
Evidence please.
Adding a new nuclear plant at Dothan that includes cooling towers for both plants could reduce water withdrawals of that site by 98%.
As long as a nuke operates near Dothan, a minimum flow in the Chattahoochee River is required, The existing plants should go off-line circa 2040. A new reactor is likely to extend that to 2080 or so.
I think Georgia would object to another nuke at that site.
Evidence ?
1) The multi-year process to qualify a new nuke site (geology, hydrology, evacuation routes & capacity, soil stability among other factors that can disqualify a site for a new nuke).
2) AFAIK, only two new sites (one in Idaho, the other West Texas) are being considered for new nukes. All others at old sites.
3) No new nukes on Long Island, Oahu, very large areas of California, between Memphis & St. Louis, south of New Orleans, near Yellowstone, in or near large cities, etc. All areas where NRC rules would almost certainly ban a new nuke.
Alan
Even cooling towers require a certain level of water. Why are they on the Ohio River and not some creek ?
Cooling is a parasitic loss of electricity, the more power used to pump water & air, the less power for society.
Alan
CHP is one of the best solutions, since you can use wet cooling because a lot less cooling water is required, and a societal useful purpose is found for the rejected heat. Turn a minor problem into a major solution.