Fluctuating wind and solar energy can be used to produce hydrogen by water electrolysis and subsequently for the synthetic natural gas production via methanation in the power-to-gas process. This paper investigates the unsteady-state operation of the methanation in an adiabatic and cooled fixed-bed reactor, respectively, with product recirculation by simulation of a one-dimensional fixedbed reactor model. The results show that adiabatic fixed-bed reactors with product recirculation can operate in a wide range of partial and excess load. The recirculation of product gas cools the adiabatic fixedbed reactor effectively and an optimal recycle ratio for the highest methane productivity exists. Cooled reactors are very sensitive to load changes of the volumetric flow rate and thus less flexible. However, the recycle of product gas allows reducing the sensitivity for a more stable operation under fluctuating feed conditions. The start-up time of cooled fixed-bed reactors is considerably lower. In summary, the flexibility of the dynamic methanation is enhanced in a loop-reactor arrangement.
For the design and optimization of methfanation processes detailed modeling and simulation work is advisable. However, only a few kinetics published in literature rely on wide temperature and pressure ranges, which are prevalent at modern methanation applications with dynamic operation. Especially the simulation‐based design of methanation processes with commercial catalysts is difficult due to legal restrictions regarding the publication of kinetic data of those catalysts. In this work, rate equations for the dynamic modeling and simulation of methanation processes operating with commercial Ni/Al2O3 catalysts are selected, adapted, and tested in a dynamic reactor model. The results suggest that the catalyst's nickel content is an indicator for the choice of a rate equation. Testing of the equations in a reactor model meets published data for CO and CO2 methanation and own measurements.
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