4 replies to this topic

[j_k]

What is typical specific natural gas consumption [(NG Feed+ NG Fuel)/Hydrogen; wt basis] for hydrogen generation unit?

[PingPong]

Depends on NG composition, on unit design, reformer outlet temperature, Steam/Carbon ratio, et cetera.

 

Assuming NG does not contain inerts, (NG Feed+ NG Fuel)/Hydrogen ratio is roughly 3.5 kg/kg.

[j_k]

Theoretically 1 mole of methane will give 4 moles of H2, then this ratio on weight basis is 2 (without considering fuel consumption )...

I am looking at the best number one can get based on experience of other refiners across world...

[PingPong]

All reactions in a hydrogen plant are limited by equilibria:

- not all CH4 is converted but part of it passes unreacted through the unit (depending on reformer heater outlet temperature and S/C ratio).

- not all reacted CH4 is converted into CO2 but part remains CO (depending on shift reactor temperature and S/C ratio).

 

Moreover: not all produced H2 is recovered as pure H2 product but 10 % is lost in the PSA tailgas (together with CO and CH4 slip).

 

As a result of all the above, 1 mol of CH4 feed will, in the real world, produce only about 3 mol H2 (instead of 4), say 2.7 kg NG feed / kg H2 product.

 

But natural gas is not pure CH4 (but also contains heavier hydrocarbons with lower H/C ratio) so say 2.8 kg NG feed / kg H2 product.

 

PSA tailgas is used as fuel, but on top of that is a consumption of say 0.6 kg NG fuel / kg H2 product.

 

One can of course spend a lot of plant investment cost trying to lower the 2.8 number, but one should realise that that results in less PSA tailgas, so the 0.6 number would then go up.

Edited by PingPong, 12 November 2014 - 06:31 AM.

[Himanshu Sharma]

Hey !

 

Pingpong added good details,in my experience the number is typically 3.3kg/kg for NG as Feed and tail gas used for firing in reformer.

 

Thanks and Regards

Himanshu