3 replies to this topic

[ELI]

Hello,

I am trying to design (with the software Pro/II) a methanator. First of all, I want to mention that this methanator is not a part of a ammonia process... I also already read all the topics there are here about methanation, but they didn't really help me.

I have two stream gases (mainly H2, CO, CO2, N2 and CH4). All sulfur remain traces were removed. I can also adjust the stream gases to have a stoichiometric ratio of 3*H2 for CO.

I was thinking about 2 or 3 methanation reactors with intermediate cooling. In the litterature, this is said that temperature rise of about 70 to 80ºC per mole% of CO converted in the feed gas. What does it really mean?

I decided the first reactor will have an inlet temperature of 400ºC and pressure of 25 bar. It is what seems most common in commercial processes. I have a total inlet stream of ~3000kgmol/hr (and I have a fraction converted of ~0.5 for CO. Is it realistic to think that temperature will increase of 300ºC in the first methanator?

My second and last methanator will have an inlet temperature of about 250ºC. I thougth the temperature of the second one will increase of about 200ºC and the last one of 150ºC...

I would also like to know if pressure will change during the methanation.

By the way, should I keep the N2 during the methanation? (I thought N2 could help to control the rises of temperature)

Regards,

Eli

P.S. Here's the approximate composition of the stream gases:
CO : 12%
N2 : 12%
CO2 : 13%
H2 : 41%
CH4 : 16%
H2O : 5%
and traces of O2 and C2H4

P.P.S. Sorry for my English, this is my second language...

[abhi_agrawa]

Eli,

The Methanation reaction is highly exothermic. So instead of going by the guideline, I'd suggest that you should do a heat and energy balance around the reactor and determine for yourself the temperature rise. Adding N2 will help as it will help to reduce the temperature rise, but on the other hand hand it will decrease the rate of reaction (as it will lower the partial pressure of the reactants) and hence more volume of catalyst will be required.

Hope this helps,
abhishek

[ELI]

Hello,

Thanks, but no, it doesn't really help me!

In fact, the problem is that I'm not sure to know how to do an energy and heat balance (this is my second year of Chemical Engineering) on a commercial scale. More, I don't really have books here and i cant ask some teachers (this is not a school project).

Anyway, thanks for the help, I'll try to do what I can...

[ELI]

Hi again!

I still need your help...

Suppose I have an inlet stream of 525kg-mol/hr and an outlet stream of 230 kg-mol/hr which it means that I have a fraction converted of about 56% in the methanation reaction. (there's not really any shift reaction in the first reactor)

Does it mean that temperature should rises of 0.56*75ºC = 45ºC? That's not a lot...