Question

What are the equations and parameters needed for a methanation reactor design?

Answer 1

The methanation system is requried for conversion of CO2 & CO to CH4 in the ammonia process.

The treated process gas from CO2 Absorber Overhead Knockout Drum is preheated from 50 °C to 316 °C in the Methanator Feed / Effluent Exchanger

where remaining carbon oxides combine with hydrogen over a nickel catalyst to form

methane and water:

CO2 + 4 H2 ⇔ CH4 + 2 H2O

CO + 3 H2 ⇔ CH4 + H2O

The methanation reactions are highly exothermic and could potentially overheat . This could occur if an upset in the shift (LTS/HTS) or carbon dioxide removal systems causes a breakthrough of carbon monoxide or carbon dioxide to methanation.

The exothermic methanation reactions cause a temperature rise across methenator. At end-

of-run of the LTS catalyst, the feed to methanator will contain about 0.35 mol% carbon monoxide and about 500 ppmv carbon dioxide. However, when the LTS catalyst is fresh, the carbon monoxide content will be lower, resulting in less temperature rise across methanation.

The methanation reactions go almost to completion. The total amount of carbon oxides in the effluent from methanation is <5 ppmv, and the outlet methane content at design conditions (EOR) is 2.29 mol%.

Parameters are requried such as , composition of process gas, Temperature, Pressure, flowrate of process gas.