High temperature gas-cooled reactor for H2 Production question 1

[M98Ranger]

I have been reading that hydrogen production, when coupled to a high temperature gas-cooled reactor, can increase "typical electrolysis efficiencies" by "45% to 50%". The following question is meant to encite opining. Why isn't this fact being touted more, in so far as advertisement to the public is concerned? It seems that such a power source would virtually secure the future of hydrogen. Are there any blairing engineering problems that haven't been addressed as yet dealing with the production of hydrogen by this method (besides the obvious fact that nuclear waste and nuclear power (in fission reactions anyway) will always be inseparably connected?

 

[MikeHalloran]

Sounds like a load of hot gas to me.



Mike Halloran
Pembroke Pines, FL, USA

 

[moltenmetal]

What you meant to say is that you can use a nuclear reaction to produce hydrogen by means other than electrolysis, with (in theory) higher efficiency than could be obtained by electrolysis. Though none of the proposed schemes I've seen for this purpose are actually technically feasible, that doesn't mean that someone won't come up with a feasible scheme in the future.

So what? You can make electricity directly from nuclear reactors- established technology. But for some reason, we still perfer to mine and burn coal. Why do you think that is?

You can also make hydrogen by reforming any carbonaceous material, including fossil fuels, biomass etc. That's where the majority of the hydrogen now in use comes from, and is where any significant amount of hydrogen we wish to use in future will come from.

Even if you get a "high temperature gas cooled nuclear reactor" scheme to work, what have you solved by making hydrogen?

Hydrogen still suffers from the same problems that make it a very troublesome energy storage medium: it's only 75 kg/m3 as a LIQUID, which gives it an extremely low energy density per unit volume- and the practical energy storage inefficiency associated with liquid, high pressure or adsorbed (metal hydride) storage of hydrogen are quite large. And if you're thinking PEM fuelcells are the answer for the ultimate re-conversion of that hydrogen to electricity, don't forget that although they do not suffer from Carnot efficiency limitations, they are NOT 100% efficient by any stretch of the imagination! Not to mention their enormous cost...

Until all our stationary users of energy are converted over to renewables or nuclear, screwing around with hydrogen is a total waste of time at best and a harmful, expensive distraction at worst.

 

[M98Ranger]

moltenmetal said, "Though none of the proposed schemes I've seen for this purpose are actually technically feasible, that doesn't mean that someone won't come up with a feasible scheme in the future."

Just recently, Idaho National Laboratory was able to show that HTE (High Temperature Electrolysis) is what I would term technically feasible.(*

http://www.sciencedaily.com/releases/2008/09/080918170624.htm,

September 22, 2008)

Give or take a few weeks, full-scale HTE very well could have already occured allowing a miniature version of the system to be used in the production of 500 grams an hour (about .14 grams per second). With the same design a plant should produce around 2 grams a second, which is the energy equivalent according to science daily of 2 gallons (of petrol based fuel) a second. That is promising if you ask me. Of course there are significant hurdles to go over in order to get there. But (as with any significant technology) the problems just take time to understand and circumvent.


In my opinion, (with the current ideas that I have heard about), batteries will never be able to replace gasoline. They will definately supplement the use of gasoline, but barring some significant changes such as an ability to charge a battery in a matter of a few minutes, they will not be able to make fueling up as easy and economical (time-wise) as hydrogen will be.

Even with the obvious volumetric limitations that hydrogen pose, the energy is still there. In fact for the same 12 gallons gas energy equivalent in hydrogen you are talking about less than a third of the weight. I haven't done the math on it and I haven't really even done any ball park calculation on it, but I would be willing to bet that just based on the relative energy content of hydrogen versus regular gas, hydrogen would beat it considerably. And even with the added volume that hydrogen gives I beleive that the "added drag" is not going to over run the extra energy content inherent in hydrogen fuel.

Plus, really who is going to care that much about the size being to big? The most popular vehicles in america are not the small geo metros (even though I like that car a lot), they are the big Yukons and Ford and Dodge 4X4 trucks. Thus, I would say that size (whether or not something is compact) is not the determining issue. It is whether or not the thing can put out the kind of torque that feels adequate and whether or not fuel is "affordable" (whatever that means).

That said, there is a lot still to be done. I think I mentioned that earlier in my post. And to answer your comment/question, "But for some reason, we still perfer to mine and burn coal. Why do you think that is?"... people still "prefer" carbon based fuel creation because it is 1) prevalent, 2) people already are familiar with the methods to mine it, and

3) in order to move from carbon-based to a hydrogen economy there is going to be a lot of job displacement. Job displacement is not pleasant for anyone. Initially, the actual job "loss" is going to come from oversees in other countries that we get oil from. They will take the hit and we will have obtained their carbon based energy production jobs. However, as we start moving to a hydrogen based economy, (and after our oil reliance is decreased significantly), the jobs will have to shift from carbon based to hydrogen here in the United States. In the long run we will see many more jobs created in the US then are "lost" due to change in our energy infrastructure. Much more of our money will stay in the United States increasing our standard of living. That does nothing to ease the pain of the people who have to retrain or move to a different industry in order to make ends meet. Change is tough all the way around, but I think that everyone can see that the alternative to change is a lot worse. We can change with the times or else we can get ran over and end up eating dust economically.

 

[moltenmetal]

The processes I was talking about were direct chemical conversion methods which directly using high temperature heat from nukers- without the need to make electricity first with its associated heat engine-related thermodynamic losses. None of these high temperature energy cycles would seem to be at all feasible for a wide variety of very practical reasons, mostly associated with materials of contruction.

These Idaho folks are running a solid oxide fuelcell backwards essentially, electrolyzing 800 C steam to produce hydrogen and oxygen. That begs the question: why bother, if you've made the electricity already?!!

They waste 100% of the oxygen they produce by sweeping it away into an "air stream". Although oxygen isn't a fuel, it takes serious energy to produce pure oxygen from air. Thinking about the process properly, wasting the oxygen is equvalent to throwing fully half the energy you've used right into the garbage.

Electrolysis of LIQUID water is already ~ 60% efficient, and you get both hydrogen AND oxygen as pure products you can sell. Why bother with the SOFC?

Nice research project, I guess. But I wouldn't be hinging my hopes of a fossil fuel-free future on this one.

Hydrogen's not just "big"- it's extraordinarily energy-inefficient to store in quantities suitable for use in transportation applications. You MUST store it either as a very high pressure compressed gas or as a cryo liquid. Hydrogen compression wastes a huge amount of energy which is difficult at best to recover to any useful purpose. The stored pressure energy in the tank is extraordinarily difficult to recover as useful work by the vehicle. The only way you can make a fuelcell vehicle look energetically attractive is if you forget about this very real energy loss entirely. Storing H2 as a cryogenic liquid is even worse, involving enormous energy waste to make the liquid, plus huge standby losses due to venting to keep it that cold.

Yes, hydrogen has a three-fold higher energy content per unit mass than gasoline. But even as a cryogenic liquid (70 kg/m3 at -252 C, which is only 21 K) it doesn't approach the energy content per unit VOLUME you get out of liquid methane (422 kg/m3 at a balmy -161 C ) or propane (582 kg/m3 at -42 C) much less gasoline (~800 kg/m3 at room temperature).

http://en.wikipedia.org/wiki/Image:Energy_Density.PNG

People like to burn coal not primarily because of the "comfort" reasons you've given, but because it's cheap- cheap to produce, transport, store and use. It's cheap primarily because we've assessed no cost to dumping sh*t into the atmosphere. Fix that problem and you can START to make sensible energy policy.

Stationary users of energy are still at least 60% of the energy market, and right now a very significant fraction of those stationary energy users are running on fossil-derived energy. In 2004, ~2 of the ~3.3 TW of energy used were derived from sources other than oil- and not all of the oil the US consumes is used for making gasoline and diesel fuel. Tackling those stationary energy uses with renewables and nuclear makes vastly greater sense than bothering with finding gasoline substitutes. But for some reason, people have gasoline on the brain...

 

[owg]

I estimate the energy density of two hypothetical automotive fuels as follows. Each vehicle has a 1 cubic foot fuel tank. One contains liquid hydrogen and one contains Iso-octane as a proxy for gasoline.

The Hydrogen car has 214,432 BTU net on board
The "gasoline" car has 793,897 BTU net on board

The hydrogen car would have extra weight since it has to contain and cool the liquid hydrogen.

I think these numbers are correct give or take a few percent. Please feel free to check and correct them if necessary.

HAZOP at

http://www.curryhydrocarbons.ca

 

[M98Ranger]

OWG

Your numbers seem pretty plausible without going over them. However, as I stated before, mass for mass hydrogen has more energy content than gasoline. Once people understand that a bigger volume doesn't necessarily mean larger weight I think people will be alright with it. At least I hope so.

As of now, the issues of hydrogen as an energy carrier are fairly straight forward and outlined pretty well by Moltenmetal. The main weakness I see is the fact that hydrogen takes energy to be created. Natural gas and oil is a lot less energy intensive to get to the end use. That is fact. Near-term no doubt we are going to go lean heavy on hybrid technology (diesel and gasoline). But I don't see how we can rely on batteries so far as convenience is concerned and so therefore there has to be a gasoline equivalent such as hydrogen on the list as a choice for alternative energy. I don't see how we can get by (in leau of current ideas/technology) without it.

Perhaps having spare batteries in the car is an option. However, batteries are like 5 grand or so a piece, so if you want an extra battery than you have to pay a considerable amount extra. That begs to question whether or not the 5 grand extra could pay for the "lost energy" in the production and compression of hydrogen into a useable form? And then you would be able to fuel up much more quickly.

I absolutely agree about the fact that our stationary energy needs to be largely supplanted by Nuclear and renewable sources of power. I kind of feel gasoline and the autonomy it gives us to go where we want to when we want to has become part of our culture. I think that is the main push behind the "alternative gasoline" movement.

Thanks for a good blog. You all had very good points that you touched upon.

 

[owg]

M98Ranger - You are correct about the extra weight of gasoline. My 1 cubic foot or 6.2 imperial gallons of gasoline would weigh an extra 40 pounds approx compared to the same volume of hydrogen liquid. I recall my fifties UK car had a 7 gallon tank so that may be a reasonable capacity for the highly efficient cars of the future.

HAZOP at

http://www.curryhydrocarbons.ca

 

[moltenmetal]

M98Ranger: the key problem in my view is not so much the energy it takes to generate the hydrogen in the first place: it's the energy required to transport and store it in sufficient quantity (in ENERGY on board terms, the only ones that ultimately matter for a transportation application). Hydrogen for transport applications is technological nonsense- UNTIL the dream day that we have huge amounts of renewable electrical generation in place that we don't know what else to do with.

The "extended range electric" concept is a good one for personal cars. Batteries sufficient for say 60 miles per charge, plus a gas engine for extended range. Something like 80% of fuel consumption can be dealt with via this concept, leaving gasoline for the long trips or travel into remote locations that it's ideal for. But if we pick up the slack in the electrical grid by building more coal fired powerplants, we're no further ahead- in fact in greenhouse gas and toxic atmospheric pollutant terms it probably puts us behind where we are right now.

 

[M98Ranger]

moltenmetal: I guess I kind of coupled all of the energy required to get the hydrogen to its end use "hydrogen generation", that wasn't exactly correct. I agree with your analysis. Really the order that things have to happen in general is,

1) We have to add a substantial portion of Nuclear and Renewables to expand our "stationary energy" infrastructure.

2) While this is happening, gasoline and more and more hybrids will keep us traveling where we want when we want.

3) Storage, Transportation, and hydrogen production coupled with nuclear has to be figured in order to acheive the end result of a possible zero CO2 emissions with fuel cell usage.

4) By that point people will be able to travel as far as they want for a "reasonable" price by either doing shorter travel with a hybrid (100 miles 'ish) or..... longer, heavier hauls(Trucks, trailers/SUVs, etc., traveling whatever distance) with a fuel cell vehicle.

 

[25362]

Why is it that experts don't advise expanding long-range mass transportation systems to reduce the "per capita" cost of moving around ?

 

[moltenmetal]

"Experts" do recommend such. Politicians know that there's more political benefit in selling the imaginary technological fix to these problems than there is in telling people that they'll have to change their lifestyles.

 

[ad101]

Going back to original question somewhat...High temperature gas cooled reactors aren't available yet! That's a generation IV design that needs alot of development to become reality. The reason you can yield hydrogen is because of the very high outlet temperatures of up to ~950C and is really just a CHP operation utilising the heat for the conversion process.

Long way to go there...lots of PWR's in between!

 

[EdStainless]

The issues that I see around the use of hydrogen as a fuel are similar to ones concerning the entire electrical grid, we need an economic incentive to change our load patterns.
If I could buy wind generated power at night (when it is almost all being made) for 1/10 the price of coal power during the day you bet that my house would have a chilled brine tank for 'cold storage' instead of a conventional air conditioner.
But in most locals residential users are not even offered time of day based rates.
A similar pattern holds true for cars. There is no economic penalty to owning a car with very long range. Most days I drive less than 60 mi total.
What I really want is a small hatchback that burns CNG. A small tank that would get me 150 mi would be fine and room for two men and their golf clubs. While the CO2 from this car would only be slightly less than gas it would be much cleaner in other respects. And it would meet 90% of my needs. It is also practical, now who will build it????

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