Hydrogen Facts

[Farrah Day]

Hydrogen Facts

I thought it might be a good idea to produce a Hydrogen Facts thread, which may be particularly useful for anyone interested in its use as a fuel.

This idea of this thread then is to provide a handy source of reference and somewhere that information gathered from numerous sources can  all be found in one place.

I've noticed over the years that there appears to be much confusion surrounding the energy released from combusting hydrogen, so thought that clearing this up would be a good starting point.  

Most of the confusion seems to arise because comparisons of energies released by various fuels is not always compared fairly, or indeed accurately. For example, comparing fuels by volumes can be very misleading, especially in the case of hydrogen due to its extremely low density.

The following table is known to be accurate, and gives a figure for the energy released when a mass of 1kg of the fuel is completely burned in oxygen.

Carbon, C (as in coal)    C(solid) + O2(gas) = CO2(gas)...................................................................................33,000kJ
Methane, CH4 (as in natural gas)    CH4(g) + 2O2(g) = CO2(g) + 2H2O(g).......................................................50,000kJ
Octane, C8H18 (as in petrol)    2C8H18(liquid) + 25O2(g) = 16CO2(g) + 18H2O(g............................................45,000kJ
Methanol, CH3OH   2CH3OH(liquid) + 3O2(g) = 2CO2(g) + 4H2O(g)...............................................................20,000kJ
Carbohydrates (sugars and starches).....products are CO2(g) and H2O(liquid).........................................average 17,000kJ
Animal Fats..........products are CO2(g) and H2O(liquid)......................................................variable, but typically 40,000kJ

Hydrogen, H2   2H2(g) + O2(g) = 2H2O(g)............................................................................................120,000kJ

So, if we are comparing energies released by mass, then hydrogen clearly possesses the greatest energy by far.

The problem is that hydrogen liquid has a low density, so as a fuel, larger volumes of it are required when compared to say petrol.

For example liquid hydrogen has a density of just 72 kilograms per cubic metre, petrol is around 737kg/m3 and water 1000kg/m3.

So while mass for mass hydrogen releases the greatest amount of energy upon combustion in oxygen, its low density means that volume for volume, around 4 times more liquid hydrogen would be needed to equal that of a given volume of petrol. Hence hydrogen, even in liquid state would require substantially greater volumes to be carried on board a vehicle in order to get it to travel for the same distance as a vehicle fueled with petrol.

Of course, when we are talking about powering a vehicle with liquid hydrogen as fuel, there is also the issue of not only producing the hydrogen initially, but also in compressing it into liquid state.

Here's an interesting piece I found:

Here's what Pimentel (1996, p. 211-212) has to say.

In terms of energy contained, 9.5 kg of hydrogen is equivalent to 25kg of gasoline ( Peschka 1987). Storing 25 kg of gasoline requires a tank with a mass of 17 kg, whereas the storage of 9.5 kg of hydrogen requires 55kg, (Peschka 1987). Part of the reason for this difference is that the volume of hydrogen fuel is about 4 times greater for the same energy content of gasoline. Although the hydrogen storage vessel is large, hydrogen burns 1.33 times more efficiently than gasoline in automobiles ( Bockris and Wass 1988). In tests a BMW 745h liquid-hydrogen test vehicle with a 75 kg tank and the energy equivalent of 40 liters of gasoline had a cruising range in traffic of 400 km, or a fuel efficiency of 10 km per liter ( Winter 1986).

Carrying liquid hydrogen around as a fuel has never really appealed to me due to the problems associated with it in liquid state. So whether it be used to drive and ICE or a hydrogen fuel cell to power an electric motor, the problem of carrying, storing and indeed refuelling are obstacles I feel too great to make it worth the effort. This of course is to say nothing of having to produce the hydrogen in the first place.

Now here's the thing, and the beauty of water. Any given volume of water - even though it contains the oxygen atom as well as hydrogen - actually contains more hydrogen than pure liquid hydrogen of an equal volume.  This for me is the real appeal of on-demand production of hydroxy from water.

Of course we are extremely hampered by the conservation of energy laws, but that is not to say that some laws cannot be rewritten if new information comes to light or new discoveries are made that perhaps question whether or not these laws truly take into account every factor.  By this I mean that some laws generally work great and calculations are accurate within most useable parameters, but the same law can fall apart under certain specific conditions whereby the physics we know seems to go out of the window. I believe Ohm's Law is one such case.  So there are always possibilities – always hope!

Interesting you-tube video detailing the amount of hydrogen (gas) required to run a vehicle:

http://www.youtube.com/watch?v=7qzrI20VPCw

Note: If anyone finds that I've provided incorrect figures anywhere, either through a typo or otherwise, please speak up and I'll correct any mistakes.


** rather than adding further new posts of information that may inevitably be lost between discussion posts, I will always update this first post in order to keep all the relevant information in one place and hence easy to find.

[iquant]

How about Ammonia (NH3) or Ammonia Borane H6NB based energy carriers? They store 3 and 6 times as much H2 as liquid h2 and release at relatively low pressure with heat.
Ammonia Borane makes for an interesting and efficient hydrogen carrier that can be safely handled without pressure in the form of pellets.
Ammonia is released on-demand by controlled thermal desorption..  Release H2 from ammonia by electrolysis with only a 5% overhead.

Once the hydrogen is expended the Ammonia Borane cartridge can be reprocessed and recharged...  Really a high density efficient hydrogen battery.

Take a look at http://www.amminex.net/index.php?option=com_content&task=view&id=61&Itemid=132

[Farrah Day]

Hi  iq

The problem as I see it with ammonia or a similar derivative is that you have to produce the ammonia in the first place which is a task in itself. By contrast, water as the fuel carrier is readily available in abundance.

There was a thread over on Mystic Murakami's forum some time ago,

http://www.energeticforum.com/renewable-energy/5247-ionization-water-fuel-26.html

whereby he was claiming that the key to on-demand fuel from for an ICE was creating ammonia from water and ionised nitrogen and then combusting that. And to forget all about hydrogen itself as the fuel.  The only problem - and something I continually argued about, until he banned me - was that he seemed blind to the fact that the amount of ammonia produced would only ever be proportional to the amount of hydrogen being produced. And as hydrogen would always be the fuel, why bother going to all the trouble and effort creating ammonia when you already had the hydrogen in the first place.  Mind you, he's a complete dick so it was like talking to a brick wall.

Anyway, I guess my point is that if you have ammonia or another hydrogen rich compound on hand, then great, but if you've got to produce it in the first place then it's really not so great. 

It's like the use of metal hydrides as a fuel carrier. At some point you have to replenish the hydrogen, which of course means that you will once again have to produce it in the first place.

[Room3327]

Hydrogen Facts

I thought it might be a good idea to produce a Hydrogen Facts thread, which may be particularly useful for anyone interested in its use as a fuel.

This idea of this thread then is to provide a handy source of reference and somewhere that information gathered from numerous sources can  all be found in one place.

I've noticed over the years that there appears to be much confusion surrounding the energy released from combusting hydrogen, so thought that clearing this up would be a good starting point. 

Most of the confusion seems to arise because comparisons of energies released by various fuels is not always compared fairly, or indeed accurately. For example, comparing fuels by volumes can be very misleading, especially in the case of hydrogen due to its extremely low density.

The following table is known to be accurate, and gives a figure for the energy released when a mass of 1kg of the fuel is completely burned in oxygen.

Carbon, C (as in coal)    C(solid) + O2(gas) = CO2(gas)...................................................................................33,000kJ
Methane, CH4 (as in natural gas)    CH4(g) + 2O2(g) = CO2(g) + 2H2O(g).......................................................50,000kJ
Octane, C8H18 (as in petrol)    2C8H18(liquid) + 25O2(g) = 16CO2(g) + 18H2O(g............................................45,000kJ
Methanol, CH3OH   2CH3OH(liquid) + 3O2(g) = 2CO2(g) + 4H2O(g)...............................................................20,000kJ
Carbohydrates (sugars and starches).....products are CO2(g) and H2O(liquid).........................................average 17,000kJ
Animal Fats..........products are CO2(g) and H2O(liquid)......................................................variable, but typically 40,000kJ

Hydrogen, H2   2H2(g) + O2(g) = 2H2O(g)............................................................................................120,000kJ

So, if we are comparing energies released by mass, then hydrogen clearly possesses the greatest energy by far.

The problem is that hydrogen liquid has a low density, so as a fuel, larger volumes of it are required when compared to say petrol.

For example liquid hydrogen has a density of just 72 kilograms per cubic metre, petrol is around 737kg/m3 and water 1000kg/m3.

So while mass for mass hydrogen releases the greatest amount of energy upon combustion in oxygen, its low density means that volume for volume, around 4 times more liquid hydrogen would be needed to equal that of a given volume of petrol. Hence hydrogen, even in liquid state would require substantially greater volumes to be carried on board a vehicle in order to get it to travel for the same distance as a vehicle fueled with petrol.

Of course, when we are talking about powering a vehicle with liquid hydrogen as fuel, there is also the issue of not only producing the hydrogen initially, but also in compressing it into liquid state.

Here's an interesting piece I found:

Carrying liquid hydrogen around as a fuel has never really appealed to me due to the problems associated with it in liquid state. So whether it be used to drive and ICE or a hydrogen fuel cell to power an electric motor, the problem of carrying, storing and indeed refuelling are obstacles I feel too great to make it worth the effort. This of course is to say nothing of having to produce the hydrogen in the first place.

Now here's the thing, and the beauty of water. Any given volume of water - even though it contains the oxygen atom as well as hydrogen - actually contains more hydrogen than pure liquid hydrogen of an equal volume.  This for me is the real appeal of on-demand production of hydroxy from water.

Of course we are extremely hampered by the conservation of energy laws, but that is not to say that some laws cannot be rewritten if new information comes to light or new discoveries are made that perhaps question whether or not these laws truly take into account every factor.  By this I mean that some laws generally work great and calculations are accurate within most useable parameters, but the same law can fall apart under certain specific conditions whereby the physics we know seems to go out of the window. I believe Ohm's Law is one such case.  So there are always possibilities – always hope!

Interesting you-tube video detailing the amount of hydrogen (gas) required to run a vehicle:

http://www.youtube.com/watch?v=7qzrI20VPCw

Note: If anyone finds that I've provided incorrect figures anywhere, either through a typo or otherwise, please speak up and I'll correct any mistakes.


** rather than adding further new posts of information that may inevitably be lost between discussion posts, I will always update this first post in order to keep all the relevant information in one place and hence easy to find.

Very interesting Farrah, I did not know that volume for volume water holds more hydrogen then pure liquid hydrogen. Why would anyone want to start with anything else?

[Farrah Day]

Very interesting Farrah, I did not know that volume for volume water holds more hydrogen then pure liquid hydrogen. Why would anyone want to start with anything else?

Hi Room.

Yes, not a lot of people know this, but it sure adds to the appeal of water as a stable and user friendly energy carrier.