[TheForge] Hydrogen storage

[James Binnion]

On May 8, 2006, at 7:36 PM, Demon Buddha wrote:

> Can it not be safely kept in liquified form?
>

Depends on your definition of safely. To my knowledge all  
refrigerated liquid gases are stored in dewars that continuously vent  
the gas as it boils off. If I understand it correctly this is due to  
the imperfect nature of the insulation of the dewar. If one did not  
allow this constant venting then the dewar would rupture from the  
pressure of the expanding gas. Dewars for gases like liquid hydrogen  
cannot stand much in the way of pressure due to the brittle nature of  
the tank materials at these low temperatures (just about any material  
is brittle at these temperatures). So I would not want to step into  
my garage and flick on the light switch after my cars tank full of  
liquid hydrogen was venting in it over night. I am also less than  
eager to be in an accident with a tank full of liquid hydrogen in my  
vehicle.

But with a lot of engineering ways can probably be found to safely  
store the hydrogen. Bruce mentioned metal hydrides as a possible  
storage method. I am a little dubious about the practicality of  
hydrides as they can store at most  5-7% by weight hydrogen (by  
heating the hydride to 250C or greater to release the H2) and more  
reasonably 1-2% by weight at room temperature. So you will need a  
hell of a lot of metal hydride mass to store a reasonable amount of  
hydrogen.  That 1 lb of hydrogen would need 50-100 lbs of metal  
hydride mass to  store it. Twenty six pounds of hydrogen is about  
equivalent to 15 gallons of gas so you would need somewhere between  
1000-3000 lbs of metal hydrides to store it. I think a lead acid  
battery electric would probably be more practical, it certainly is a  
more mature technology.


James Binnion
jbin at well.com