New Thermocell Could Turn 'Waste Heat' Into Electricity

dryriver sends this quote from Phys.org: "Harvesting waste heat from power stations and even vehicle exhaust pipes could soon provide a valuable supply of electricity. A small team of Monash University researchers ... has developed an ionic liquid-based thermocell (abstract). Thermocell technology is based on harnessing the thermal energy from the difference in temperature between two surfaces and converting that energy into electricity. The new thermocell could be used to generate electricity from low grade steam in coal fired power stations at temperatures around 130C. This would be implemented by having the steam pass over the outer surface of the hot electrode to keep it hot while the other electrode is air or water cooled."

Thermoelectric Power

[Anonymous Coward]

Thermoelectric power has been around for a long time. There is, literally, nothing new about this. The efficiency is still not high enough to make it worthwhile for any sense of scale. They are better off using waste heat the way they currently do, to heat up the incoming cold fluids that get turned to steam through heat exchangers.

On cars, you do not get enough power out of the current materials to make it worthwhile.

Re:Cost/Benefit Analysis?

[icebike]

Net energy loss is what you already have today.

Drive your car down the road, and your exhaust is always hotter than the ambient.
Run your exhaust thru this device, and you can recapture some of that existing loss to power your car's Air Conditioning.

This isn't the only research looking for such technology:
http://phys.org/news/2011-05-high-performance-bulk-thermoelectrics.html [phys.org]

Re:Little known fact

[ShanghaiBill]

We already suffer a glut of energy [oregonlive.com]

A temporary and localized surplus is not what "glut" usually refers to. Hydro-power surpluses from spring rain have been around as long hydro-power. That is not proof that we have too much capacity.

Re:TAANSTAFL!

[fustakrakich]

I was under the impression that a Peltier could go both ways, and it uses the Seebeck effect for it

Re:TAANSTAFL!

[Antipater]

It's being circulated already in the power plant's existing cooling tower.

Re:TAANSTAFL!

[Anonymous Coward]

Exhaust from a steam turbines are on the order of 40-50 C. This works because the condenser actually operates in a vacuum (created from the thousand-fold volume decrease from steam to liquid water). And this makes more sense than wasting steam (since you would want to condense it anyways to save water).

Really, there is no magic technology with thermoelectrics. And with any heat engine, what matters is the delta-T and entropy. Unless you waste water, you are bound by the Carnot cycle. And anybody who has worked with steam knows that things like pulling extraction steam or main steam and using it in reheaters, as well as preheating your feedwater will give a shitload more efficiency gains than worrying about fucking with the ends of your LP turbines.

Re:Nuclear steam

[gewalker]

For efficient conversion of heat to you MUST have high temps. Modern pressurized water nuclear reactors run at about 150 atmospheres -- corresponding temperature of 315 C / 600 F. There is no way to avoid this with liquid water as the working fluid. Contain 150 atmosphere of pressure at all times dominates the design of the reactor. Some newer designs use different working fluid. E.g. a LFTR reactors (drawing board only) using a Brayton cycle based on helium or nitrogen gas and a 700 C temperature source -- no high pressure used in the the nuclear vessel.

Also look at the design of the power generation cycle in a power plant. There is a relatively small high-temperature turbine that generate 2/3 of the electricity and a much larger secondary turbine that generates 1/3 of the electricity. The lower-temp output of the first turbine is the input for the 2nd turbine.

Re:TAANSTAFL!

[Farmer Tim]

Let me introduce you to the convection cooled heatsink [jaycar.com.au]. No moving parts, powered entirely by the dissipated heat itself, it just has to have sufficient surface area for the job (and they scale up more easily than actively cooled systems).

Mod parent up

[Animats]

Right. What we have here is another crap materials science article. Somebody did something vaguely interesting at lab scale, and then issued a bullshit press release.

Trying to get the last remnants of recoverable energy out of a heat engine is an old game, going back to the reciprocating engine era. Basic steam engines had one cylinder running off boiler pressure. Double-expansion steam engines had a second cylinder running off the output of the first. The second cylinder is bigger and runs at lower pressure. Triple expansion steam engines had a third, even bigger cylinder. Some quadruple expansion engines were built, but this is a diminishing-returns thing, and triple expansion is about as far as it's worth going economically. Marine engines were often triple-expansion.

Large steam turbines do the same thing, with a succession of rotors of increasing size. Three to twelve stages have been used. Again, this is a diminishing returns thing. At some point the steam condenses to water, which you don't want to happen inside the turbine. Existing turbines get close to that limit. Some turbine plants have a partial vacuum going into the condenser to keep the steam as a gas below 100C. 90C exit temperatures are not uncommon. Almost all of the usable energy has been extracted with an exit temperature like that.

If this new thermoelectric thing is a better way to convert heat to electricity than a steam turbine, it should replace steam turbines, not just be used on the cold end of the system. An efficient solid-state way of converting heat to electrical energy would be valuable. All the existing thermoelectric devices have low efficiency compared to heat engines. Back around 2011, there were several startups [bloomberg.com] getting Federal grants for R&D into "heat harvesting". Commercial products were supposed to appear in 2012. Didn't happen.

Limits aside from heat extraction...

[Bugler412]

Commercial fossil power stations already drive their stack gas temperature about as low as practical via various heat capture methods, reheat systems, etc. The limiting factor generally is not recovering more energy from stack gasses but the desire to never drive the stack gas temperature below the dew point in that exhaust gas, doing so causes all sorts of negative chemical consequences for the stack itself, pollution control equipment, etc., increasing maintenance cost and reducing equipment life due to aggressive corrosion of stack components and structure. Plants I operated were strictly kept from dropping below dewpoint on the exhaust for this reason, not to mention temperature input constraints for effective operation of some pollution control equipment, you CAN recover more energy from stack gasses, but doing so hits a cost negative and reliability wall. Always remember that waste heat/energy for a utility station equates to large $$$, if there's a practical way to extract more energy from a given amount of fuel, they are likely there as quickly as they can implement it. But the carnot cycle and other less heat cycle related limitation put up a pretty tough barrier to going further, Perhaps this is useful for more "pure" exhaust gas or waste heat streams, but I don't see it happening for commercial fossil power stations

Re:Nuclear steam

[KonoWatakushi]

However, the carbon moderator core at over 600 C scares me. What if oxygen gets in there? Burning core, reminscent of Chernobyl. Very scary.

Contrary to what you might think, carbon is actually safer at those temperatures. Under neutron bombardment at low temperatures, the Wigner energy can build up, and that is the source of the problems. However, at the operating temperatures of molten salt reactors, solid graphite is quite safe. (You can purchase graphite crucibles good to 2500C.) There is further discussion here [energyfromthorium.com].