Supercritical fluid in power generation
The efficiency of a heat engine is ultimately dependent on the temperature difference between heat source and sink (Carnot cycle). To improve efficiency of power stations the operating temperature must be raised. Using water as the working fluid, this takes it into supercritical conditions. Efficiencies can be raised from about 39% for subcritical operation to about 45% using current technology. Supercritical water reactors (SCWRs) are promising advanced nuclear systems that offer similar thermal efficiency gains. Carbon dioxide can also be used in supercritical cycle nuclear power plants, with similar efficiency gains. Many coal-fired supercritical steam generators are operational all over the world, and have enhanced the efficiency of traditional steam-power plants.
Australian Renewable Energy Agency (ARENA). Let's see what the first Abbott budget had to offer up on this matter:
> Finance Minister Mathias Cormann confirmed yesterday that the Australian Renewable Energy Agency (ARENA) will be discontinued in the 2014-15 Budget.
Fun times, Australia. What fun!
To gut their funding is really very depressing.
$200 million annually in profit by 2017 for the government through investment in renewables. But making money from renewable energy is, one should remember, 'utterly offensive':
The CEFC is a commercial investment in actual rollouts of renewable energy with a 7% return on investment. The Abbott government, however, says 'bugger that, we hate evil renewable-tainted money' (or something like that) and is currently looking forward to passing legislation to abolish the CEFC as one of the first things the new Senate will do once the new Senate meets in about two weeks' time.
Note also that, if it weren't for that the $200 million might well grow to $520 million pretty handily - they've got $10 billion in applications:
> The Portfolio Budget Statement does not include the significantly higher positive contribution to the Budget the CEFC would make if it was able to continue to carry out its investment function over the forward estimates period. Were it to do so, the CEFC would deliver a net cash surplus (profit) for the Government of more than $520 million, net of operating costs.
This government is committed to throwing away $500 million and more for taxpayers in money companies are willing to borrow and pay back - with interest - to roll out renewable energy schemes.
It's like "Dear government, if you give us x amount of money, this lender over there will give us 2x of money, and I'll pay you back both, with interest. This is for us to change all the lighting across this huge area to use a third of the energy.", and the government saying, instead of "let's have a look at your business case and assure everyone this is a sound investment for us and your claim actually checks out and we'll all make money" a "lol, no".
I'm genuinely scared for the future of Australia, and I honestly don't know if I'll go back to raise a family (as I always thought I would)
Please, please, don't let him screw it up as badly has he's trying.
This is why they are shutting down much of the funding into alternatives. Even parts which are already making money, or saving money. Not including research like this which could be world changing. It's not even bucket loads of money in many cases.
Note that it is winter in Australia at the moment. There is a lot more heat and sun in the summer.
There is a small window of 10-20 years left to sell the shit out of coal before it becomes redundant. Germany already had a day in May producing 75% of its electricity needs from renewable resource power generation. So much that producers of electricity had to pay money to put electricity into the grid. The record the year before was about 60%.
He is also in the pocket of Rupert Murdoch who he met (along with many mining executives) whilst in the US. It is a real tragedy to see such worldwide talents like the CSIRO go unappreciated.
If there ever was a case for a corporate groomed politician, he's it. I struggle to believe his self-indulgent conservative ideology could explain the breadth of the changes he is attempting to make. It's like he's thrown it all out there and is hoping some will slip through while everyone is focusing on the big ticket items.
Supercritical steam is useful for fossil fuel generation because it is relatively easy to make closed off systems which can withstand high temperatures/pressures. The optimum for solar power might lie at the much lower temperature. Why? Because the cost of solar array as a function of desired temperature rises much faster than that of a fossil fuel generator.
"So instead of relying on burning coal to produce supercritical steam, this method demonstrates that the power plants of the future could be using the zero emission energy of the sun to reach peak efficiency levels – and at a cheaper price."
They also say that it is not ready to be used commercially. But this organisation is quite good at making things commercially viable. Rather than just doing research for tax breaks.
From one of the researchers:
“Steam flowed at around 330kg/hr , which equates to a little over 300kW of adsorbed solar energy. The experiments were designed to represent a single element of large scale design, so scale up is related more to multiplicity than redefining heat and mass fluxes.”
This experiment was done so they could scale up production of power by just adding more of these.
In a heliostat-based configuration, I'd assume that it's just the cost of the target of the array of mirrors that increases, right?
Except the first, each of these is a very non linear. eg. taking reflectivity from 90 to 95 percent might double the cost. But then taking it to 97 might double the cost again.
If I were a betting man, I'd say this goes nowhere. I think PV has already won the "war" versus thermal unless someone can come up with a great solar -> syngas receiver.
Although there is also truth in that higher temp materials tend to be bad conductors. Tungsten is like what 4 times worse than copper as an engineering estimate? You don't use pure W or Cu anyway, but the general idea holds.
have a line that separates gas from liquid, but this line has a finite length. One endpoint is on the triple point (solid, liquid, gas coexist at one P,T) and the other is on the critical point. That's where the distinction between gas and liquid vanishes -- the viscosity, index of refraction, etc of one phase approach those of the other until differences vanish altogether at the critical point. It's a little arbitrary to say that steam at a given temperature or pressure is supercritical (there IS a rigorous definition, T>T_criticalpoint&&P>P_criticalpoint, I'm just saying that it's a bit arbitrary), but the gist of it is that you're in the part of the phase diagram where movement in the phase plane is going to avoid the gas/liquid transition. Nothing physical happens in a liquid->supercritical or supercritical->gas transition and there are no phase transitions in the supercritical region.
This is exploited for the production of aerogel. Normally you can't dry out a gel and have it retain its shape because the liquid/gas interface during evaporation/boiling has enough surface tension to tear apart the microstructure of the gel. But if you scoot around the liquid/gas transition in phase space (e.g. by heating past T_criticalpoint, lowering pressure below T_criticalpoint, cooling below T_criticalpoint, and finally releasing any lingering pressure, or in other words liquid->supercritical->gas) then you can get rid of the liquid without ever boiling/evaporating it -> no nasty surface tension to tear apart the microstructure!
Here is a video of CO2 being heated past the critical point. Since there is a gas-liquid equilibrium, the system will move more or less exactly along the curve separating gas from liquid until it "slips off the end" into the supercritical region:
EDIT: || -> && in the formal definition
EDIT2: linked a phase diagram for those who don't stare at them all day :)
In other words, you can smoothly transition from "liquid" to "gas" without needing to boil. The two states are a single phase.
That's still true. You can see the evidence in the video :)
But at every other point along the liquid->supercritical and gas->supercritical phase boundaries you are correct, the boundary is an arbitrary definition and not physical.
The temperature at which a substance freezes, melts, condenses, or boils is not fixed, but varies with pressure.
When a liquid crosses the "critical temperature" (at atmospheric pressure), it boils and becomes a gas with an obvious transition.
Less well known, when a liquid is subjected to pressure above the "critical pressure" (at a fixed temperature), it can actually become a compressible liquid.
The location on the graph where "critical temperature" and "critical pressure" meet is the "critical point" and that's where you can become supercritical. In that region, there is no difference between liquid and gas; there is no "boiling" or "condensing", because the substance effectively behaves like both at the same time. It has no surface tension, yet can dissolve things like a liquid solvent, but it can also diffuse through tiny holes like a gas.
Tiny variations in temperature or pressure can radically alter the density, allowing you to adjust for the exact behavior you want. Above the critical temperature, no amount of pressure can force the substance into liquid form, you can only solidify it. Some substances refuse to be made liquid or solid due to crazy critical temperature or pressure values required. Mixtures are another matter entirely, for example high pressure may force one component of a mixture to solidify and drop out of solution.
We think of matter as having "normal" properties because that's how it behaves at the earth's atmospheric pressure and temperature ranges but in reality the way we experience matter is just one of many different and just as crazy states.
To bring it back down to earth, the point of mentioning "supercritical steam" is that it means they can heat the water well above boiling by keeping it under high pressure. If they didn't, additional heat added to the water would just create more steam, not heat the water any further (and steam is vastly less efficient at absorbing heat than liquid water).
Normally, when you boil water the vapourisation happens piecemeal. That's why you see bubbles rising to the surface. For supercritically heated water, the vapourisation is a runaway chain reaction, triggered by a reduction in pressure, so the whole body of water flashes into stream.
Edit: added note about reduction in pressure being the trigger.
You can note in this diagram that what you are describing is true whether or not the system is supercritical, and can be seen in how water will boil into steam when the pressure is decreased from atmospheric as well.
What you are describing is how higher pressures allow you to add energy to the water while it remains liquid, and how if you add enough energy it will overcome the enthalpy of vaporization and cause it to convert to steam as the pressure is reduced.
As I understand it, a container of boiling water will have liquid in the bottom half and steam in the top half. As the pressure and temperature rise, the steam/water goes supercritial, meaning the water/steam boundary disappears and the whole container becomes a homogenous mush of supercritical fluid.
Am I right in thinking that this supercritical fluid can flash into steam faster than a combination of water and steam? My thinking is that for a water/steam combination to convert into steam, the water molecules have to take the time to break their bonds and separate into a gas. For a supercritical fluid it's faster because there are no bonds to be broken?
I'd be grateful if you can correct the above, as I can learn something here.
The reason for that would be that there is a nucleation process in forming gas from liquid, which does take some time. Or at least more than not needing to do so.
There is some terminology you're using that bothers me, like "flash into steam" isn't really a good way to describe it. At that point you'd be better off describing it as "super pressurized steam" converting to "normal pressure steam" or something. It's just expanding, but there is no flash (which to implies a sudden change). It's gradually and continuously decreasing in density.
I think part of this may be confusion over how we overload the word "water" to mean "liquid water" as well as "water the chemical". I am meaning "water the chemical" which can be a solid, liquid, or gas. Steam is water that is a gas.
With a supercritical system, you can take liquid water, stay in the liquid state until the water becomes supercritical (where the liquid and gas phases are indistinguishable), and then move across a boundary from "liquid like" to "gas like", go back into a sub-critical state as gas, and never formally boil/flash/etc.
Physicists have made special engines that operate on this "super-critical" fluid, that only works above this temperature / pressure combination. For the first time ever, a solar-panel has achieved this critical mass of temperature and pressure, allowing solar-energy (in very hot regions) to take advantage of the same technology that makes conventional fossil fuels so efficient.
Supercritical steam is a special form of steam that can not be described as a gas or a liquid. It's somewhere between the two: molecules aren't bunched together in dense clusters that settle at the bottom of a container (as they are in a liquid), but they also aren't flying all over the place individually in a low density vapour (as they are in a gas).
How's that possible? Water molecules have relatively strong intermolecular attractive forces between neighbouring molecules. They like to stick together, even though there's no permanent connection between them. They are like mini-magnetised marbles. This explains why water has a much higher boiling point than most tri-atomic molecules.
When you increase the temperature of liquid water, the molecules in the liquid vibrate and move around within the liquid, and as you cross the boiling point, the vibration and movement of the molecules is so great that they are able to escape the pull of their attractive interactions with their neighbours en masse. When this happens, the molecules shoot off into the vapour, where there is an (almost) unlimited amount of space for them to shoot around in.
Now consider what happens when you do this at high pressure. High pressure essentially means that there are lots of molecules in the gas phase moving around really quickly. Now, when the temperature gets high enough that molecules have enough energy to overcome their attractive interactions with neighbouring molecules, they leave the pack: but this time with nowhere to go to. The pressure is so high in the 'gas' phase (i.e. there are so many other molecules up there) that they are forced to just bump around where the liquid was but at extremely high speeds. This type of behaviour is pretty difficult to distinguish from the behaviour in the high pressure 'gas' -- in fact, after the system has time to equilibriate, they are exactly the same.
Clearly then, the transition from 'liquid' to 'gas' at this point is pretty much indistinguishable. The liquid may begin to display the molecular kinetic behaviour of a gas, but the density stays the same.
The end result is: When the pressure and temperature is high enough, to onlookers it appears as if the entirety of the fluid is half way between a liquid and a gas, and is stable in that state. That's called a supercritical fluid.
For example: http://eurjmin.geoscienceworld.org/content/15/5/773/F3.large...
A straightforward way to distinguish between liquids and gasses is their density. Liquid water is a high density fluid and steam is low density fluid.
There is line on the phase diagram that separates the liquid field from the vapour field. On that line is the only place on the diagram where liquid and vapour can coexist, i.e. where boiling can occur. It happens to be the case that the surface of the earth is in the liquid field, but within vicinity of that line, so if you heat some water up, you can watch it boil. However, at ~250°C, you need to be at a pressure of ~4 MPa to observe boiling. At those conditions the density of the liquid will be ~0.8 g/cc and the vapour ~0.2 g/cc.
The liquid-vapour phase boundary (the boiling curve) terminates at the critical point (647 K and 22.064 MPa). Above the critical point H2O is supercritical. On inspection of the phase diagram we see isochores radiating out from the critical point. Above the critical point the density of water can vary smoothly as a function of P and T, and there is no boiling, condensation, etc.
I don't know anything about power generation, but presumably when you can maintain temperatures higher than the T of the critical point, you don't have to worry about losing energy to phase changes.
Its more efficient in driving steam engines and turbines
A big gain is your stereotypical turbine blade doesn't like condensing conditions. Supercritical can't condense by definition, so its inherently good. Water droplets literally wear away the blade. Kinda sucks. They're expensive. So those expensive little things last longer if superheated steam is used. Its not so much that you can't make a condensing turbine, its that a condensing turbine will be less financially / economically efficient, its going to have to be much bigger and stronger for a given power output. Also the flow of steam is very predictable and constant, but once you start condensing no one really knows how it'll put vibration loads on, which can break the blades and wear out the bearings. Its false economy to use saturated or "wet" steam in a turbine to save money, usually.
You can add a reheat stage to the middle of a turbine to prevent condensation. Of course that costs money and maint labor and energy. You can see the appeal of just using higher quality steam and avoiding all that. Sometimes you just have to eat the losses. Especially with nukes, they have relatively wet steam, well compared to coal plants anyway.
Note that what some people call a condensing turbine doesn't involve condensation in the blades, at least not intentionally LOL. Its just a turbine with a huge condenser on the output instead of using a small condenser with an intermediate stage of process heat. Process heat is like, here's cruddy wet steam, but its hot, so how about using it in the office radiators, or to help heat preheat cooking ovens or something. Its hot by human standards but by power generation standards its only lukewarm and no longer economically useful to generate electricity. Its useless on the turbine floor, but perhaps a neighboring bread bakery would pay real money for it.
For wind and solar to be economically competitive with coal / gas / nuclear they have to be at price parity including 24+hrs storage. This isn't going to happen any time soon without massive government incentive.
Professor Barry Brook of Adelaide University has been blogging about this for a good few years now. We need to think critically about 'sustainable energy'. I encourage you all to read his blog , particularly the TCASE  (Thinking Critically About Sustainable Energy) series.
Let's level the playing field: ultimately there are only two good metrics worth considering a) life-time cost per kWh and b) life-time CO2 emissions per kWh --- but to level the playing field you need to consider each generating technology on a base-load comparison. It's no good comparing a 1GW gas plant and a 1GW nameplate solar installation because the sun only shines about 6.5hrs per day averaged throughout the year in, say, Adelaide for example, so you typically need to over-build solar by a factor of 4 and then add storage. When you do that the life-time cost and life-time CO2 emissions aren't so crash got because of the massive amounts of energy intensive stainless steel, steel, and concrete required, plus new transmission lines.
If you want to see a real-world example of how wind does work, check the UK National Grid Status site  - the wind hasn't been blowing in the UK for weeks, presently their 8GW of installed wind is generating 0.82GW electricity.
The data speaks for itself, look at the graphs. A vote for wind / solar is a vote for new gas _because_ gas is easily load following. Of course, the gas plant owners don't like that because when the wind blows their plants sit idle.
The whole renewable energy push is an expensive mess. I've commented elsewhere on HN about this, so I'll stop repeating myself now.
So what ? ALL energy production is. But I would rather take a clean, renewable source of energy over the polluting coal/gas or the unsafe nuclear kinds.
And a country like Australia would be amazing for renewables provided we could have a country wide power grid. It is windy almost every day in say Fremantle and likewise sunny almost every day in many northern/central areas.
Once you tally up life-time CO2 emissions for solar & wind, including storage, new transmission lines, and loses for 3000km long transmission lines, neither of them stack up very well compared to, say, gas or nuclear.
And saying "nuclear is unsafe" is nonsense. Nuclear kills fewer people per unit of electricity produced than even roof-top solar , including the deaths from Chernobyl and the deaths from the evacuation of the area surrounding Fukushima Daiichi. (I say "deaths from the evacuation" because, as yet, no one has died as a direct result of the core melt downs ).
Saying things like "nuclear is unsafe because of Chernobyl / Three Mile Island / Fukushima" is like saying "Air travel is unsafe because of the Hindenburg disaster".
Burning coal for electricity has released in to the environment more radioactive material than nuclear power ever will. It's the only current technology base-load capable electricity generator that has a completely closed fuel cycle.
Additionally, we need to move away from saying things like "Australia would be amazing for" this or that technology. Aside from the evidence pointing toward 'renewables' being a dumb idea environmentally and economically (just look at the real world data), if China and India and the USA don't do anything about their emissions Australia might as well not even bother. If Australia doesn't do anything about transport (14%) , direct fuel combustion (15%) , and agricultural, emissions (15.9%) , we might as well not even bother. Electricity production emissions account for 36%  of Australia's GHG emissions.
Edit: I'd like to see some sources for your claims wrt the footprint of renewables, I haven't been able to find anything which supports your position.
The Thinking Critically About Sustainable Energy series from bravenewclimate.com - TCASE 4  in particular. It references this  document form The University of Sydney for wind, and this one  for solar. TCASE 5  looks wave power, and TCASE 7  investigates scaling up Andasol 1 to baseload.
I also recommend reading the comments sections of those blog posts, there's some good quality discussion there.
The "nuclear is bad beacuse meltdown" and "nuclear is bad beacuse bombs" tropes have been dealt with extensively elsewhere. Both are hyped up FUD. We're still waiting for Godzilla, or some green-glowing-three-eyed-monster to appear.
Peak oil is too. Eventually costs will go up and as they do if your market doesn't have any viable substitutes what will happen?
Electricity has about doubled in price since I first started paying my own bills.
This has has precisely little, if any, impact on how much people drive and how much electricity they use. Vehicles become more efficient, people install reverse cycle air cons, wages rise.
Now, I'm not suggesting this can go on forever, it likely can't, but we have been told to panic about Peak Oil for a good 40 years, and is still hasn't happened. I'm not sure feeling anxious about Peak Oil is going to help. If anything, it tends to make a lot of people, especially young people I talk to, apathetic about the world.
What will happened after we run out of oil and coal? Or after we burn enough of it to make this planet unpleasant to live on? We will adapt or die. Let's hope we adapt before that happens. I'm not convinced that's going to happen, people seem to be attracted to crises - they're a damn good motivator.
Anecdotally this isn't really true either. The peak for air conditioning is usually later in the afternoon since it takes a while for the sun to heat up the area from the cool of the night.
John Oliver on Tony Abbott
This guy man. I don't even know what to do about it.
In particular, though, don't tell Abbott voters how terrible they are for voting for him. People will get defensive and actually strengthen their views under criticism. (http://youarenotsosmart.com/2011/06/10/the-backfire-effect/)
It struck me how tiny the amount of money involved here is. Let's say this engineering effort was a one one-thousandth step along the way to developing the technology into a major energy alternative. Then that would be, what, $5B?
Perhaps I'm overestimating the significance of this discovery.
Reading through http://en.wikipedia.org/wiki/Supercritical_steam_generator indicates that Benson boilers are more fuel efficient (and perhaps less prone to explosion), but reduction in amount of fossil fuels used to turn a turbine seems to be sort of a moot point here.
Would super critical steam generation mean a solar plant can produce more electricity? Or that a supercritical steam generating solar plant is cheaper to operate?
This should indicate that for a given amount of sunlight (or fossil fuels in a conventional power plant), a greater amount of electricity can be created.
So not 'more electricity' since the sun is functionally unlimited, but 'more electricity per square foot' or 'more electricity per heliostat' or what have you.