HYDROGEN QUESTION PLEASE CAN YOU HELP ME?

[Mechdod]

What is the specific Energy for hydrogen and how can i caculate the Mass of hydrogen required to produce electricity for a day at an Eff of about 90%

THANKS YOU R A STAR

 

[bonzoboy]

There are 3,412 Btu in each kW-hr. At 90% efficiency, you would need 3,412 Btu/0.90 of hydrogen for each kW-hr.

Hydrogen has 51,571 Btu/lb (LHV) and/or 235 Btu/scf. From; that you can determine how much hydrogen you need.

 

[Mechdod]

thnx

 

[mbeychok]

Mechdod and Bonzoboy:

I don't know where that 90 % efficiency came from. If Mechdod is talking about a conventional power plant in which a fuel is burned to produce steam and the steam is then used to drive a turbo-generator to produce electricity, such plants have an overall thermal efficiency of about 34-35 percent. Thus, they require about 10,000 Btu of combustible fuel per kw-hr of end product electricity ... whether that fuel is natural gas, oil, coal or hydrogen.

If the power plant uses a combined cycle (i.e., a gas turbine driving a generator, and the gas turbine's hot flue gas is used to generate steam to drive another generator), then the overall thermal effciiency is about 60 percent which means that the required fuel is about 5,700 Btu per kw-hr.

If the combined cycle is used to cogenerate electricity and heat (which is not what Mechdod asked about), then the overall thermal efficiency may approach about 85 percent.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[kenvlach]

From the location of the cross-listed thread:
Hydrogen and related fuel cell engineering Forum
thread804-148816
it may be a fuel cell question. Mechdod, please elaborate on how you intend to use the hydrogen.

 

[Mechdod]

What is the specific Energy for hydrogen and how can i caculate the Mass of hydrogen required to produce electricity for a day at an Eff of about 90%.(in a fuel cell vehicle)

''A fuel cell vehicle or fork lift consumes approximately 3kg - 5kg of H2 per day.''

 

[kenvlach]

Use the enthalpy of formation of water vapor:

[Δ]H_{f, H2O(g)} = -228.6 kJ/mole

from CRC Handbook of Chemistry and Physics.
A mole of H₂ is 2 grams, so multiply by 500 for

Energy per Kg of H₂: 114.3 MJ/Kg