Short version of the science: The heat is released via an exothermic chemical reaction between the Zeolite and water. However, unlike the one-time-use chemical-reaction heating pads you can buy in a pharmacy, this reaction is reversible, so you can "recharge" the Zeolite by heating it and removing the water as it is released in order to force the reaction to reverse itself. The reaction goes something like this:
Zeolite + water <-> Zeolite & water complex + HEAT
The reaction happens at the surface of the zeolite, so the storage capacity is proportional to the surface area of the pellet. If you make the pellet highly porous, this can be proportional to its volume.
I don't see how this can translate to the title "Zeolite retains heat indefinitely". After the cycle of heating and cooling has been repeated some finite number of times, parasitic heat loss to the environment will eventually remove all of the heat added at the beginning.
When you use water as a heat storage medium, you are storing the heat in the kinetic energy of the water molecules. In common parlance, you are increasing the temperature of the water. Obviously, over time the water's temperature will gradually revert to the ambient temperature, and you will lose all the heat you stored in it.
In contrast, when you store heat in Zeolite, you are not storing it as kinetic energy, you are driving an endothermic chemical reaction that stores the energy in high-energy chemical bonds. After you are done heating the Zeolite to "charge" it, it will return to the ambient temperature, but it still has (lots of) energy stored in the chemical bonds. This energy does not dissipate in the way that the kinetic energy of a high-temperature substance would. The energy can only be released by reversing the chemical reaction, so it is securely stored. You can then transport the Zeolite at ambient temperature to a location in need of heat, and then add water, which reverses the chemical reaction and releases the heat again.
So it doesn't actually store "heat", it takes in heat (i.e. molecular kinetic) energy and stores it in a different form (chemical bond energy).
I assume it means that, because it is stored in the chemical structure rather than actual heat, it's not leaking to the environment while the pellet is sitting on a shelf (if not exposed to the elements).
What they mean is that when the Zeolite is "heated", then it can be stored indefinitely without "cooling down". If you heat water and put it in a tank, it will lose its heat relatively quickly. The Zeolite stores the energy from heat in (stable) chemical bonds, so it won't lose energy over time.
You can heat Zeolite using solar power during the day and release the energy at night. Current thermal energy storage techniques use stuff like molten salt (http://en.wikipedia.org/wiki/Thermal_energy_storage), which is a lot harder to work with than pellets.
The article gives one example: you could charge them with waste heat at plants and factories, then transport them to homes and offices where (I suppose) they could be used for heating and hot water, at some later point in time.
This is a great application. It could be particularly useful in the New England states. Manufacturing could store their waste heat in the zeolite, and resell it to homes and businesses who can use it to heat up during the winter. It could be a major disruption to utility companies.
Water heater in your home. Deliver heat when needed by pouring water on stones, comes out hot. Doesn't have to keep water hot and ready; so probably save 90% of the energy currently leaked away due to Newton cooling (hot water heater cooling off all day while you're at work).
I think there's a saturated solution of sodium acetate inside. The metal clickie causes the solution to crystallize, which happens to happen exothermically.
They are a supersaturated Sodium acetate solution.
Liquids give off energy when they freeze and take energy in when they melt.
When you heat these and melt them they can stay stable as a saturated liquid until you create a small site for them to start freezing around - they then give off energy when they freeze. The 'clicker' is all that's required to localy concentrate it enough to form a single crystal seed to start the freezing
We use zeolite as a water scavenger in high vacuum systems, it's tremendously good at grabbing onto water BUT because it's so porous and very low thermal conductivity it's a real pain to heat it enough to get all the water out again.
We have a heater resistor at the bottom of a small can of this and the top of the pellets a few cm away is cool enough to touch.
You might do better with a microwave system but then the inefficiencies are going to hurt.
Why not use one of the many phase change salt solutions that are also used for rechargeable heater packs?
Is it such a major problem that it leads to major efficiency losses (measured as joules of output energy over joules of input energy required to "recharge")?
If you could figure out a good way to integrate the heating element and the the zeolite on a surface like a menger sponge you would have a very high surface area and good thermal response characteristics.
Surely a microwave oven is not 100% efficient in converting the input electrical energy into output heat in the object to be heated? I'm not sure how near 100% it is.
how is that stuff similar to the (salt?)-based cooling pads that you would crack to start the endothermic reaction, and then put in a freezer to "charge" them up?
EDIT: upon further research, I find that "adsorption" is actually also a thing, but it appears that here they meant the traditional absorption. Adsorbtion definitely isn't a thing. Also it sounds like a baby trying to say "abortion," which is weird.
What possesses people to give things such similar names? And while we're at it, mathematicians: stop using variables that rhyme. Bs, Cs, Ds, Es, Ps, Zs, it makes my head hurt. Would it kill you to chuck an H or a Q in there? M and N, now thats just purely vindictive. How am I supposed to cope with that?
After writing this comment I think the spelling part of my brain is now fried forever. And to think I've been walking around merrily saying "absorbsion" all these years...
I learnt the verb "adsorb" in high school chemistry. Why is adsorption not a thing? (Although it does look like the article meant "absorption" and not "adsorption".)
Quote for those not in the know:
-----
<<<"Absorb" refers to a situation where something is taken into a medium, and disappears as a
consequence (from?). "Adsorb" refers to a situation where something gets stuck onto (to?)
the surface of a medium.
We would use "absorb" for when light is absorbed by a coloured or opaque object, or for when water is
soaked into a sponge, or even for when my students manage to "take in" some of what I am telling
them. It is an ordinary English word.
"Adsorb" is used for a very specific situation where molecules get stuck onto a surface. It does not
occur as a word in ordinary language, outside its scientific meaning. Adsorption is very important,
because many chemical reactions can go a lot faster when the reacting molecules are adsorbed at a
surface (reactions of hydrogen gas on the surface of nickel, for example), or chemical reactions can be
prevented by the presence of a barricading adsorbed layer on the surface (aluminium failing to react
with air, for example), or impurities can be removed from a solution by adsorbing them onto a finely
divided solid (activated charcoal for decolorizing solutions, or for medicinal use, for example).>>>
Now you can see why my brain was fried trying to type all that correctly. Not only do the phonemes sound the same, the letters are mirror images of each other. I think I now know how dyslexics must feel all the time.
Which makes a lot of the science understandable. I can't help thinking that by saying "OMG hard science, so here is a massively dumbed down version" they actually made crucial parts of the theory incomprehensible :)
Case in point being; adsorbtion explains later comments about why surface area is important.
How selective is the zeolite in what it absorbs? Could this be used for water purification? That is, if you let the zeolite absorb water from an impure source, move it to a clean container and heat it to release the water, is the water potable? Even if it selectively absorbs water to remove contaminants, does the zeolite itself make the water non-potable?
This reminds me of zeolite-water solar adsorption refrigeration:
This paper presents some of the experimental evaluations of a prototype solar refrigerator, based on an intermittent thermodynamic cycle of adsorption, using water as refrigerant and the mineral zeolite as adsorber. This system uses a mobile adsorber, which is regenerated out of the refrigeration cycle and no condenser is applied, because the solar regeneration is made in the ambient air For the regeneration, a SK14 solar cooker is considered. The cold chamber, with a capacity of 44 liters, is aimed for food and vaccine conservation. The objective is to analyze the advantages and disadvantages of the eventual use of this refrigerator in rural regions of Peru, where no electricity is available. On the bases of the results obtained, a new prototype of refrigerator for rural regions is designed, based on the same thermodynamic cycle, but including changes in design and operation.
During the day, solar energy is used to drive water out of the zeolite.
The dry zeolite is exposed to water under low-pressure causing the water
to evaporate and be adsorbed into the zeolite. The evaporative cooling
can be used to refrigerate food without electricity.
A German company with various zeolite refrigeration applications:
No, your conversion of ambient heat to drying the zeolite and the inverse release of heat when adding water; are both less than perfectly efficient. Entropy grows at each step. The retention of heat in the dried zeolite is not a conversion step, and the total entropy of the system doesn't change during that time.
Heat shield for spaceships? Imagine on re-entry the outside part is made of a layer of zeolite, heat builds up but is retained on the layer and water is released as vapours ( which can add an extra layer of shielding ).
While industrial applications of this is useful, I think it is far more useful to look at distributed manufacturing applications (such as RapRap + practical zeolite heat batteries).
I'd like to see some energy density numbers in units I can understand before I would jump up and down about this use.
(I'm not saying you're wrong so much as saying I can't provide evidence you're right, and I'm hoping someone else can. Or at least tell us what exactly "the heat storage capability of water" is such that something can have 4 times as much. Please hold wild-assed guesses, please, I can compute the energy difference between two temperatures of water for a given volume as well as the next guy, but what temperatures, or is that even the right question? I'm looking for someone who knows.)
The relevant number for water at 25C is 4.184 joules per gram. But this isn't a strict apples to apples comparison: if you heat and cool zeolite in a vacuum chamber, it'll have a pathetic specific heat. (Like perlite, another foamed mineral, which has a specific heat of something like 0.1) That's because there's a chemical reaction taking place, not pure dumb-matter heating or cooling.
Meanwhile, the energy density of a lithium ion battery is 720 joules per gram, and the energy density of gasoline is 47,200 joules per gram. This does not "solve" energy storage, in any way, shape, or form.
Someone downmodded you because you messed up your units.
It's 4.184 joules per gram Kelvin. Meaning it stores that much energy for each dress of heat you add to it. If you take water from near freezing to boiling that's 100 degrees of storage - meaning 418.4 joules per gram - which is much more reasonable.
And there is no reason you have to stop at boiling. Storing something at 500 degrees is not impractical, so assuming starting at 20 degrees (room temperature) you can store over 2000 joules per gram. And there are plenty of materials that can handle even higher temperatures.
And that's a big part of my question... given that in the abstract water can store any amount of heat (between absolute 0 and the point at which we can no longer call it "water" due to being a plasma of some form), what exactly does it mean for this material to be able to store 4 times as much?
I'm sure there's an answer, because I'm sure the journalist got that number from somewhere, but I lack the connections to know where to begin finding this information.
The specific heat is the energy needed to raise the temperature per mass. So for water it takes 4.184 joules per gram to raise the temperature by 1 kelvin. So if you heated water to 75 degrees you would have put in about 205 joules per gram. You then have to deal with conductive losses and the efficiency of a heat engine.
This is not directly comparable to the energy density of gasoline or a lithium ion battery which use chemical reactions to store the energy. So you can turn almost 100% of the energy in a lithium ion battery into useful work but if you put the equivalent number of joules into heating an object you wouldn't get close unless you have a handy 0 kelvin object.
Fair point. Although the exact energy per volume is a less important measure, given that we know the ballpark, than the energy stored per energy invested, and the maximum storage available when considered as a commodity in the market and resource availability.
Not exactly but its a good start. But some interesting ideas come to mind. Using a conveyor to carry Zeolite to the top of a CSP plant and take the resulting stuff down to the reservevoir where its dumped into steam generators for turbines. If it replaced molten sodium as the working 'fluid' then that would make construction of such plants somewhat less challenging from an engineering perspective.
I miss the days when this stuff would show up in the Edmund Scientifics catalog.
Not exactly because it doesn't change the design space of CSP, it just offers up a different heat storage mechanism.
To put it differently, if heat storage was the only problem with CSP, and there is already a heat storage solution available (liquid salt) then Zeolite isn't solving a known 'problem'.
You don't need 'indefinite' heat storage for CSP, you really only need a couple of days worth, and we have that already.
It might be interesting to look at the total economic cost of heating these things up in one place, transporting them, and then generating power there. However the heat capacity, even at 4x that of water, means that you've a constant stream of train cars dumping 'charged' pellets into your power plant. While another constant stream is carrying 'spent' pellets back to be recharged. Not to mention that for all of this to work you need to adsorb water so you end up effectively pumping water in the return path. In a CSP setup without a lot of water (say in the desert) this means you need some sort of vapor recovery mechanism to minimize the loss of water.
Was thinking of it more as an urban/industrial thing.
Makes sense if you have to do power storage with this technology to do a lot of it at the street level if you can, rather than on the power generation site, as it gives you multiple redundancy and you have to supply cities with water anyway.
So when you have excess electrical power you dry pellets.
When you want power you give them water vapour which then gives you heat, which can give you motive power from heat engines, and from that electricity from induction generators.
All three of which are needed in a typical urban environment, so you are not having to convert all the way back to electric for a large percentage of the power used.
Now I know that this is not by any stretch the most thermodynamically efficient arrangement, but I suspect that it could be a relatively cheap and very robust approach that could store a hell of a lot of energy in a widely distributed network.
[edit] looked into this a bit, and the temperature rise you tend to be able to achieve from adsorption in zeolite is not going to be enough to do anything much more than direct heating, from what I can find. On reflection, that should have been fairly obvious. Sulk. ;)
No need to sulk :-) there are fun things you can do. So lets say you have this huuuuuge pile of zeolite, you put it in your back yard during the summer and dry it out, then you store it in your shed during the winter and use it to warm the house rather than gas, or wood, or electicity. Many climes are wet during the winter and dry during the summer so this works out well for the adsorbtion requirements, and you don't get the air quality guys on your case for burning wood in the winter time. That is a difference if these things can hold their energy potential for the 9 months between summer and winter.
Probably not. It's important to distinguish the storage of heat and power because the efficiency of converting heat into electrical power depends on how big the temperature difference between your heat source and ambient temperature is.
The easiest way to understand this is the formula for Carnot efficiency: 1-(Ambient temp/Heat temp) which is the maximum theoretical efficiency that can be extracted from a heat engine to do useful work (eg. produce electrical power)
So I don't know how fast this Zeolite releases heat, but let's say it does so gradually so that your working fluid only ever gets to 90 degrees C or 363K. The maximum Carnot efficiency on a 20 degree C (293K) day would be 1-(293/363) or around 19%. And that's the theoretical max - a practical engine would be much lower.
So if the Zeolite can release its heat fairly quickly at a much higher temp it could be useful for power generation, but basically it's more likely to be useful for releasing low level heat again when it's needed.
Until I had a proper look at this, for some reason I thought you might be able to crank much higher temperature differentials out of the process.
Still, I prefer finding out that I am dreaming and being wildly optimistic, than to never bother dreaming or being wildly optimistic in the first place.
Let's do some math here, shall we. Oil has an energy density of 45MJ/kg. Water has a specific heat of about 4.2 J per gramm-Celsius. So if ambient=20C and heated water=100C we have 4.2*80 ~= 340 J/gramm => 340kJ/kg. These zeolites are claimed to have 4 times that capacity => 1.3MJ/kg.
Now we have yet another effect: The mass density of these zeolite balls is probably WAY below that of oil. Let's be generous and say it's a factor of 2. That means we would need 70 times the shipping volume of oil tankers to replace oil as our primary energy source. House tanks would need 70 times the volume. Car tanks would need 70 times the volume. Let's put it another way: For every liter of oil you use to transport them, you would need more than 70 liters of these transported JUST TO BREAK EVEN. I therefore heavily question whether this is useful even for the applications they claim. If anything they would have to be used very locally, not much more than the range we have today with isolated water pipers for transporting heat.
So yeah. These funny balls might be interesting for SOME applications, but they're far from being efficient enough for mass adoption.
The amount of energy you can store in this type of interaction is not very significant compared to other forms of solar storage. Batteries are one class of storage methods, but what's even better is to use solar energy to split water molecules and store it in molecular hydrogen and oxygen (H2 and O2). These can be recombined in a fuel cell to produce water (with no loss in molecules) and produce electricity. A much, much greater energy density, far greater than any existing battery would be in such devices.
Water-Splitting using natural sunlight is a difficult problem and many research groups at top institutions are working on it. The best known group in this field is Prof. Daniel Nocera at MIT. His research is being commercialized by the company Sun Catalytix and there are plenty of YouTube videos of him speaking and explaining his research. There are other research groups as well. The vision for the future is a distributed electrical grid. Each home or building would have a reactor on top that would contain a water-splitting catalyst producing hydrogen and oxygen gas, which can be stored indefinitely under pressure and then released into a fuel-cell device that would recombine to form water (that can be placed into the reactor) and electricity (for consumption). This would be an efficient way to capture much more of the sun's energy than current photovoltaics and is an entirely closed cycle.
On a similar theme, I really like the work of Dr. Lonnie Johnson, better known for designing the supersoaker, on his weird cross between a heat engine and a fuel-cell that he calls a JTEC;
That rather depends on how hot they get when you add water to them. Unless they get very, very hot indeed you're going to get rubbish thermodynamic efficiency generating electricity with them. I think these will be more useful for storing low temperature heat energy.
Zeolite + water <-> Zeolite & water complex + HEAT
The reaction happens at the surface of the zeolite, so the storage capacity is proportional to the surface area of the pellet. If you make the pellet highly porous, this can be proportional to its volume.