Carbon Deposition in Methane Reformer 1

[gregq8]

Dear All,

The feed to a methane reformer unit comprises of H2, C1, C2, C3 etc. As the SG of the feed increases, carbon deposition in the feed convection heater tubes as well as in the primary reformer catalyst tubes occurs. To prevent carbon deposition from occuring the steam to carbon ratio of the feed is increased. This has a large impact on plant operation!

Please would somebody let me know if there is a reliable method(s) for predicting if carbon deposition will occur as a function of feed composition, temperature and pressure?

Many thanks

Greg

 

[bardideh]

Bardideh(Chemical)
S/C ratio in the primary reformer is largely related to the composition of the reformer outlet and the design consideration such as heath content of the reformed gas.
I have experience in the ammonia plant and I faced few carbon deposit problem due to change of composition of the feed gas. When you have heavier feed gas compare to the design especially for increase of c2,c3,c4 you should increase steam/carbon ratio and the best way to be safe is the design S/C and close attention to the condition of reformer tubes .I think you can not stand to any formula for the right S/C ratio other than design value

 

[anjana]

Dear gregq8,

S/C ratio can be predicted using catalyst run data collected over a period of time.Try to make co-rellation( regression analysis) of S/C ratio with reformer operating parameters. I am sure you will surely find out best fit equation to predict S/C ratio.

 

[jcaiken]

It is not clear what the feedstock is - natural gas, LPG, refinery gases, naphtha etc. but increases in SG suggests that you may be producing methane from a range of heavier feeds rather than reforming natural gas to syn gas?

The carbon / steam ratio is critical in methane reforming processes and should be maintained above the minimum specified for the reformer.
The carbon deposition reactions (e.g. Bouduard reaction 2CO <=> CO2 + C) are avoided by using steam to preferentially shift (CO + H2O <=> CO2 + H2) and methanate (CO + 3H2 <=> CH4 + H2O) the CO. The equilibrium balance for each of these reactions varies with temperature but they are well documented. They can be modelled in process simulators such as Hysys etc. The potential for carbon deposition from any feed can be assessed by balancing the equilibria at the appropriate temperature.

Feedstock cracking in the heater is a different problem. If it is a liquid feed is it prone to thermal cracking & polymerisation? Could local hot-spots have developed within the heater? Could the heater carbon be depositing on the reformer catalyst? The ammount of steam required to prevent carbon laydown in the heater my be considerably more than in the reformer.

 

[ratchadas]

One thing to be reminded, the catalyst poison breaks through the treating section such as sulfur, Cl , can leads to unpredictable situation even the S/C ratio is compensated.

 

[mraptor]

Dear Gregg 8
As S/C ratio increases carbon deposition reduces. But higher S/C ratio needs more fuel at same tube outlet temperature and same H2 production. In terms of operating cost S/C ratio should be increased after executing various solution like removing thermal cracking before and inside refomer.

Regards;