Hydrogen Power Production: Where To Make It?

Factual Questions
21

No it won’t. You see mechanical engines have a very poor speed-torque characteristics and much of the inefficiency of cars come when you change the speed. That is why you get a lower city mileage and high highway mileage. If you would ever look into a diesel locomotive, you’ll see that the engine drives a generator which in turn drives a motor. This way the speed (and power) control is easier and takes much less space and is more efficient.

And electrical systems are easier to optimize. You can very well increase decrease the voltage to the motor and use it to charge a battery, when you apply brakes. That is instead of converting all your car’s energy to heat when you brake, you store it in a battery.

**Electric motors are also not without their inefficiencies either. So I will need a cite for the 90% you quote for fuel cells. **

Sorry no quote, but we were dealing with the hypothetical case of using pure hydrogen for the fuel cells. Not using pure hydrogen but methanol gives a fuel cell efficiency of about 85% and motor efficiences are above 95%.

**You have neglected that method to produce hydrogen is only 65% efficient so we will need better accounting for the losses in the system before you can say it is more efficient. **

I had considered that into the overall efficiency. Note that 65% figure is the energy in - energy out efficiency. Which is not much meaningful when you consider that hydrogen maybe made from CH4 ( methane / natural gas) which could’nt be used in cars - US has large reserves of natural gas as compared to petroleum. Also less CO2 is released in burning CH4 than gasoline for the same amount of energy produced. Also part of the energy expended in making the hydrogen can come from lower grade fuels like fuel oil, coal, etc.

Also, many fuels like methanol, etc. can be used to make hydrogen. Again steam reforming is only one of the processes to make hydrogen- there are other processes too - like partial oxidation etc. Also the newer fuel cells can reform their own hydrogen, insitu, thereby boosting the overall efficiency.

** What kind of treatment is there for CO2? **

From here "Two promising chemical pathways are magnesium carbonate and CO2 clathrate, an ice-like material. Both provide quantum increases in volume density compared to gaseous CO2.

As an example of the potential of chemical pathways, the entire global emissions of carbon in 1990 could be contained as magnesium carbonate in a space 10 kilometers by 10 kilometers by 150 meters."

Having said that, the fuel cell technology is by no means mature enough to become economically attractive for atleast 10 more years unless the socio-political climate changed. Fuel Cells were there even before the first Internal Combustion came through. Fuel Cells will require setting up infrastructure (capital investments) and the oil lobby will also try to postpone it as much as possible.

22

Ummm…I doubt that hydrogen would be transported by truck or train.

Pipeline would seem to be the natural choice.

23

You’re wrong.

The “tank-to-wheel” efficiency of a vehicle powered by a fuel cell is not 90%. As described on this[sup]1[/sup] page, most fuel cells have a conversion efficiency of between 50% and 60% and a tank-to-wheel efficiency of between 36% and 38%. Vehicles powered by a gasoline internal combustion engine (ICE) have a tank-to-wheel efficiency of 18% to 19%, while diesel ICE’s have a tank-to-wheel efficiency of 22%.

So let’s assume we’re comparing a fuel-cell vehicle with a tank-to-wheel efficiency of 38% to a gasoline vehicle with a tank-to-wheel efficiency of 18%:

1.6 joules must be expended (by burning coal, oil, or whatever) to produce 1 joule of hydrogen, of which 0.38 joules will be used to turn the wheels of vehicle powered by a fuel cell. The overall efficiency is 24%.

0.353 joules must be expended (by burning coal, oil, or whatever) to produce 2.11 joule of gasoline, of which 0.38 joules will be used to turn the wheels of vehicle powered by an ICE. The overall efficiency is 108%.

Not only is the total efficiency of a gasoline internal combustion engine 4.5 times better than a fuel cell, but the power plant must expend approx. 4.5 times more energy to turn the wheels of a vehicle powered by a fuel cell vs. a gasoline vehicle.

Note that this is obviously a 1st-order analysis. One advantage of a fuel cell vehicle is much cleaner emissions. They also don’t heat up the environment as much. But it cannot be overlooked that the power plant must expend a hell of a lot more energy to turn the wheels of a fuel cell vehicle than a gasoline-powered vehicle.
[sup]1[/sup] [sub]Note that this analysis conveniently leaves out production efficiency.[/sub]

24

I expect that hydrogen embrittlement of the pipeline would complicate the design. ( alloy hydrogen brittle diffuse ) H[sub]2[/sub] molecles are small enough that they like to quantum-tunnel out of containers, or at least into the walls. That’s not good for the material properties of the containers.

25

Apples and Oranges. You can’t build a liquification factory right next to where you launch and control the shuttle. Nobody in the gov’t will give NASA sufficient funds to build such a plant anyway.

http://www.airproducts.com/ehs/MSDS/hydrogencompressed.doc

Under the transportation section it says nothing about requiring a HazMat liscence. Merely how to properly carry it. Liquefied is a different matter, but that’s not what you were saying.

26

Liquid Hydrogen is stored right in the shuttle which is launched. The quote was for making Hydrogen, not liquifying it. Besides, NASA already has its refrigeration liquification plant right there. You see any gas which is liquified needs to be refrigerated (either self refrigerated by venting - not possible here because hydrogen cannot be vented). So once NASA gets it hydrogen from Lousiana or wherever - it has to refrigerate it :). What is apples and what is oranges here - can you please explain ?

**http://www.airproducts.com/ehs/MSDS/hydrogencompressed.doc
Under the transportation section it says nothing about requiring a HazMat liscence. **

Read the MSDS Sheet and then go to http://hazmat.dot.gov/rules.htm and look for 173.2a(a). I cannot post the link directly so you’ll have to do that. Also look at this letter from DOT - here. You’ll see that even Hydrogen in Hydrides is given the highest applicable hazard class.

Thats a dream. :d Must make a few thermodymics guys turn in their grave. Check your calculations.

27

You’re wrong.

Let’s say I go in the woods and cut down a tree with a bow saw. And let’s assume I expend 30,000 joules (in muscle power) cutting up the wood. I then burn the wood, which provides 5,000,000 joules.

The overall efficiency is 16,666%.

Of course, I’m not counting the fact that the tree had to grow, sunlight was used, etc. But that’s O.K.; neither do we add up the energy required to “make” coal or oil. We do not care about the millions of years “making” it – we simply rip it out of the ground.

When we process coal or oil, the amount of energy we receive is much greater than the energy we expended processing it. In other words, the efficiency is over 100%. It must be that way, else we would never do it in the first place.

Do you now understand? If you’re nodding your head “Yes,” then go back and read my previous post. It will now make sense.

28

What in the hell are you talking about?

(If you haven’t noticed, you’re digging yourself a pretty big hole in this thread, andy_fl.)

Even though I’m “just” and electrical engineer, and despite the fact I’ve had quite a few beers at this point, I do know that a gas which is liquefied does not need to be refrigerated. For Christ’s sake, we have 2 dewers of liquid nitrogen back in our lab right now that are at (gasp!!) room temperature. Yea, sure, they’re under pressure in a closed container. But they’re certainly not refrigerated…

29

Yawn. Electrical Engineer - that explains it !

Dewars are small end user devices. Dewars are nothing but thermal insulation systems but even they cannot prevent heat from getting in completely, so they keep losing the resulting Nitrogen Vapor continously due to evaporation.

In an industrial setting its not economical to lose the vapor. So all industrial liquid gas storage systems are refrigerated. If you buy the large bottles of L Nitrogen to charge your dewars, you’ll see that those bottles have an internal coil through which the vaporizing nitrogen is flashed to refrigerate the LN. Adiabatic Expansion causes cooling for most gases.

Hydrogen cannot be vented straight to the atmosphere. I hope you know by now, why. So the systems will need to be refrigerated or the resulting hydrogen will need to be “flared”.

Incidentally, since you are an EE, and work with LN. Ask the safety guys to check the O2 level in your lab with the dewars. Low levels of O2 are a problem in rooms with LN dewars which are not well ventilated.

When it comes to automotive fuels, I leave the head nodding to electrical engineers. The efficiency of concern to experts in this field is ** Well to Wheel Efficiency **. You can define whatever efficiency you like for your amusement.

Even, more important than energy utilization is Anergy (Available Energy) utilization. If you remember, thermodynamics, 1 J of heat available at 1500 F can do a lot more work than 1 J of heat available at 500 F. Its not the heat available that is of primary concern, but how much work can that heat do. Its the quality of heat available.

From a thermodynamics point of view a gas turbine will be more efficient compared to the internal combustion engine simply because the temperature of combustion in the turbine is higher.

30

You’re simply incorrect, andy_fl. Most LN[sub]2[/sub] containers are not heavily insulated. There’s no reason for them to be. And how is one molecule of nitrogen going to be lost in a closed container?

Let me explain.

Let’s say I fill a vessel with (cold) LN[sub]2[/sub]. I then secure a tight lid to the vessel. What will happen?

If you leave it sit long enough, the temperature of the LN[sub]2[/sub] must eventually come to equilibrium with the temperature of the outside (ambient) air. It has to. The LN[sub]2[/sub] remains liquid because the vessel is not allowing it to expand into a gas. (Pound-for-pound, gas requires much more volume than a liquid. LN[sub]2[/sub] expands more than 600 times in volume when transitioning from a liquid to a gas.) But there is a price to be paid: the pressure goes way up. In fact, if the vessel has weak walls it will explode. So you should only store LN[sub]2[/sub] in a container that’s designed for it, else you will have a bomb on your hands.

Now let’s say I want to cool something using LN[sub]2[/sub]. I stick a hose on the vessel and (carefully and slowly) allow it to vent. Some of the LN[sub]2[/sub] will begin to boil. When it boils it absorbs energy from its surroundings, and therefore the surroundings get cold. This is how LN[sub]2[/sub] cools things – allow it to boil (by venting it) and it will draw energy from its surroundings. It’s very simple.

31

A Dewar is a unique beast, because as you say, the liquid is kept under pressure.

So how do you transport hydrogen? It seems to me the options are as a high-pressure gas, as a high-pressure liquid, or a refrigerated liquid. Is that not correct?

None of those seem like a viable way of transporting hydrogen around the country. So it seems to me that the hydrogen will have to be bound into some sort of compound to stabilize it.

I don’t know if that’s a useful thing to have or not. Making the creation process biological doesn’t get you around the laws of thermodynamics. A creature that exhales hydrogen will still need food and energy. Most biological processes are reallly just solar energy collectors, and usually not very efficient ones. But still… If a genetically-engineered creature can be created that eats easy-to-provide raw resources, and can rapidly grow to cover large areas and start producing hydrogen in large quantities, we might have something useful. But my guess is that if you do the math, you’ll find out that the surface area and food requirements for enough bio-engineered creatures to create significant amounts of hydrogen will make the whole plan unworkable.

32

Man, you never give up :D. Here is a cross section of a dewar. It took a lot of research into making a dewar, it is very heavily insulated. Note that for liquified gases, not only conduction and convection losses come into play but even ** radiation ** losses are significant. Those surfaces inside are heavily polished to reduce radiation heat transfer.

Liquid Nitrogen will increase in volume to around 650 times when vaporized to room temperature. So the evaporated Liquid Nitrogen is let out - for evaporation losses read here . You’ll see that a 4 liter Dewar loses around 0.4 l per day - Around 10%.

Now read here as to what happens to the vaporized nitrogen - Quote from the page -
**Pressure Relief Devices ** - *Liquid helium dewars are designed with two over-pressure relief valves and an over- pressure rupture disk. The over- pressure reliefs are initiated at 0.5 PSI 10 PSI at room temperature, respectively. *

So hope that convinces you that your Dewar is venting that vapor.

33

Andy_fl: Let’s put an end to this, shall we? Because I think we’re (finally!) in agreement.

I believe we were confused on what a “dewar” is. (I think it was mostly my fault.) A dewar is a vessel that tries to keep liquid nitrogen cold. It is (obviously) very well insulated, and usually vented to some degree.

But liquid nitrogen does not need to be “kept cold” for storage or transportation if the proper vessel is used. In fact, I once used liquid nitrogen from a container that was sitting around for 6 months. It was still in its liquid state. The entire container + contents had to have been at room temperature. (Not even vacuum insulation is that good.) In fact, it would have been impossible for it not to be in its liquid state (assuming no leaks). When vented via insulated pipes, the liquid nitrogen simply boiled and got cold.

Here’s a synopsis of what goes on at the processing facility:

  1. Cool nitrogen to below its boiling point. It will turn into a liquid.
  2. Fill a very strong, un-insulated vessel with the liquid nitrogen.
  3. Close the container.
  4. Allow the vessel + contents (i.e. liquid nitrogen) to equilibrate at room temperature.
  5. The nitrogen is still in its liquid state. The pressure is very high. The nitrogen may now be stored indefinitely.

The liquid nitrogen is put on a truck and delivered to our lab. When it comes time that we want to cool something,

  1. Connect an insulated hose to the vessel.
  2. Slowly open the regulator valve.
  3. The liquid nitrogen will begin to boil.
  4. Cold liquid nitrogen will exit the hose.

The above scenario is basically what happens to every lab in our building that needs liquid nitrogen, though I have left out some details. If you think the above is impossible, I suggest you speak with a chemist.

34

Thanks Crafter, i agree with you except for minor details and I happen to know the details because I had designed air separation units for BOC and Praxair before. I happen to be a Chemical Engineer and no its not the same as a Chemist.

A Chemist at the very best will know the composition of the nitrogen or ways to analyze it, but will know almost nothing about the double/triple column cryogenic distillation units used to make nitrogen or the storage systems.

Nitrogen and Liquid Nitrogen is widely made by air liquifaction followed by distillation. (There were older systems where the oxygen from the air was removed by combustion or things like that). Purer grades are obtained by PSA (pressure swing adsorption).

Another point to note is that to liquify Nitrogen by pressure, you need to be below the Critical Temperature (not the same as boiling temperature). Above Critical Temperature, you cannot liquify Nitrogen no matter how much pressure you apply. Also, Critical Pressure is the pressure below which you cannot liquify Nitrogen no matter how much cold you make it.
When you say it does not have to be a cold vessel, you’re partially right. Because, you see there is energy in that Liquified Nitrogen, and part of that energy is used to self refrigerate. You sacrifice a part of that Liquid Nitrogen to refrigerate the remaining. If you see inside the Nitrogen tanker, you’ll probably see the cooling mechanism.

No matter how you store the Liquid Nitrogen, there will be heat loss and consequently vaporization. A common way to reduce vaporization is to take the vapors and throttle them and pass the resulting cooler vapour to again cool the contents before venting it off to the atmosphere.

35

Why not? A waste oxygen line that injects the o2 into a large chimney of some sort with outside air blowing through to dilute it? Assuming you didnt want to capture the o2 for other uses (medical, welding, etc)

36

mmm O2 causes things to burn. Even a small amount of grease in the pipe will ignite almost violently in pure O2.

37

Yeah, as soon as they rub the magic battery lamp and get a lightweight battery, with massive capacity and a recharge time of only a few minutes instead of the hours it takes now. :rolleyes: The automakers have all pretty much cut their funding for electric car research and are pouring billions into hydrogen fuel cell research. Sooner or later, you’ll be driving a fuel cell car. You may not be pouring hydrogen into the tank, it may be gasoline or methane, but the internal combustion engine’s days are numbered, and as of right now, the only thing that looks like it’ll have a shot at replacing it is the fuel cell car.

All the talk of the dangers of hydrogen kill me. Folks, do you think gasoline is safe? As has been pointed out, there’s more energy in a cubic foot of gasoline, than there is in a cubic foot of hydrogen! So, IOW, you’re currently riding around in a car that has a bigger bomb in it than a hydrogen powered car would have! You’ve just gotten used to how gasoline behaves, and so, since you’ve been dealing with it all your lives, you think of it as “safe.” The same way people thought lead paint was “safe,” until someone began to notice that kids were eating it and having developmental problems.

As for home based hydrogen production, I can’t see that happening. The folks selling the hydrogen economy are as guilty as hyperbole as the folks pushing the dot coms a few years back. “Oh yeah!” they say, “You’ll be able to plug your hydrogen powered car into the power grid at night and have it generate electricity that you can sell back to the electric companies and use it to make your car payment!” :rolleyes: Yeah, right. First of all, the only way home production of hydrogen becomes economically viable is whenever they come up with cheap, high efficient solar cells. That’s not going to happen any time soon, I’m sure. Second, there’s no way it’ll ever be profitable for the hydrogen consumer to be able to sell power that he generates from his hydrogen powered car to the electric companies. They’ll have economies of scale working on their side, and if everyone’s doing it, why the heck would one need an electric company to begin with?

38

Not only that, but there’s more hydrogen in gasoline than in liquid hydrogen…

39

correct me if i’m way off base, but the only viable options for hydrogen production in the long] run would be a large amount of nuclear power plants, controlled fusion if the technology ever becomes mature or a giant solar panel orbiting the sun(although I always wondered how one would get energy from there to earth, radio waves? laser?).

40

Huh, why doesn’t someone investigate the use of short chain hydrocarbons as an alternative to these bulky, expensive, tempermental metallic hydrides we keep hearing are the next great thing in hydrogen storage ? Oh, wait, that’d be gasoline wouldn’t it ? :smack:
In regard to the difficulties of safely disposing of O[sub]2[/sub], it’s important to realize just how much oxygen will be generated by the electrolytic process. For every gallon of water electrolyzed, you will get ~64 cubic feet of pure O[sub]2[/sub] (4X4X4 feet at stp). That’s a lot of oxygen. When you combine that volume with O[sub]2[/sub]'s reactivity and the fact that it is heavier than air and likes to pool in low spots, you end up with a massive disposal problem. If everyone in a good size town were to power their cars with electrolytic hydrogen, you’d likely have to contend with clouds of waste oxygen flowing down the streets and incinerating the low lying areas. -Well, maybe not quite that bad, but still a matter for concern.