Unsteady-state methanation of carbon dioxide in a fixed-bed recycle reactor - Experimental results for transient flow rate ramps

The utilization of fluctuating renewable electrical energy in chemical processes necessitates the dynamic operation of chemical reactors. One important example is the methanation reactor in the power-to-gas process, where the electrolysis of water is applied for the production of hydrogen, which can be converted into methane via hydrogenation of carbon oxides. The methanation step might be operated dynamically in order to reduce the storage capacity of hydrogen. Therefore, the unsteady-state behavior of the methanation is investigated in the present work. In particular a fixed-bed reactor with product recirculation is considered in terms of the system stability upon dynamic variations of the inlet flow rate. A systematic three-step study based on a steady-state parameter variation as well as load ramps with and without gas recycle was conducted on a lab-scale test facility. Focusing on a reactor system reaching chemical equilibrium, it was found that the reactor behavior is independent of the load change velocity in the investigated range. During the transient variation of the inlet volume flow rate, the temperature response inside the fixed-bed is decelerated compared to the concentration response. The adaption of the product recirculation allows to stabilize the bed temperature, which is unavoidable for a high conversion of carbon dioxide. (C) 2016 Published by Elsevier B.V.