Desulfurization

[BZLAM21]

Hello all,

Can some one help me to calculate the quantity of hydrogen necessary for the desulfurization of natural gas knowing that :
gas flow=217 kg/h
Total sulphur content (ppmw)=40
Required toal sulphur (ppmw)=1
Is there a good practice wich help to minimise the consumption of H2 knowing that there is a shortage of H2.

NBurpose of desulfurization is to prepare the feed for steam reforming.

Best regards.

 

[georgeverghese]

Typically, desulphurisation of trace amounts of H2S in nat gas (in pretreatment for steam reforming) is done by passing the gas over a bed of Girdler catalyst whose active component is ZnO. The bed is kept hot to enable a fast reaction. No H2 required.
ZnO + H2S = ZnS + H2O

 

[BZLAM21]

Hi,
Yes i agree this is the second step but i was talking about total sulphur eg:
CH3SH+H2=CH4+H2S
H2S++ZNO=ZNS+H2O
So first equation need H2 .
Kind regards.

 

[georgeverghese]

Calcs tell me the quantity of H2 required, (for 217 kg/hr of nat gas with 40ppmw of sulphur as CH3-SH) for stoichiometric completion of reaction 1 is 5.4e-4 kg/hr
Adding 100 % excess H2 to ensure completion of reaction, H2 required is 0.0011kg/hr or 0.013Sm3/hr.
Are you using some catalyst to speed up reaction 1 ?

 

[BZLAM21]

Hi,
Thank you for response georgeverghese.
Yes we will use a catalyst.
Could you plesase explain hiw did you calculate the quantity of H2.
Kind regards.

 

[georgeverghese]

Total sulphur in feed gas = 40e-6 x 217 = 8.68e-3kg/hr, which is attributable to the sulphur in CH3SH - sulphur atomic weight = 32
CH3SH mol wt = 48
Quantity of CH3SH in feedgas = (8.68e-3/32) x 48 = 0.013kg/hr
So, from the reaction, 48kg of CH3SH reacts with 2kg of H2
H2 required for stoichiometric completion of reaction 1 = (0.013/48) x 2 = 5.4e-4kg/hr
Add 100% excess H2 to ensure completion of reaction at sufficient speed = 5.4e-4 x 2 = 0.0011kg/hr
1kgmole = 23.645sm3, so this is = 0.0011 x 23.645 = 0.013Sm3/hr

From this article, with Ni-Mo catalyst for reaction 1, it seems 100% excess H2 is adequate

https://patents.google.com/patent/US4460553A/en