Study of Unsteady‐State Operation of Methanation by Modeling and Simulation

Abstract

Methanation of CO under unsteady-state operation conditions was studied systematically based on a simplified mathematical model for an integral reactor using steady-state kinetics available in the literature. The inlet composition of CO and H 2 was changed stepwise and the step response of the system was monitored in order to study the dynamic behavior of the reactor. Furthermore, periodic changes were applied with different cycling times. It was observed that the time average reaction rate could not be improved by cycling the feed composition. Moreover, the reactor appears to be self-stabilizing, since the amplitude at the outlet is reduced, leading to a steady state for high cycling frequencies. The results allow conclusions on principles to design a methanation reactor for unsteadystate operation. However, it also becomes obvious that unsteady-state kinetics is mandatory in order to describe the experimental results obtained under dynamic conditions.

Transfer Functions for Periodic Reactor Operation: Fundamental Methodology for Simple Reaction Networks

“…The typical rigorous model consists of a nonlinear system of partial differential equations for describing the temporal and spatial profiles in the gas and catalyst phase [18], which cannot be described by simple TFs. However, the qss and rss regions could probably be distinguished based on results from numerical simulations or experiments, which allows designing the reactor and process to operate dynamically within these regions.…”

“…Of particular interest in this regard is the ability of the chemical reaction system to be operated dynamically, in order to avoid extensive storage for smoothing fluctuations [16,17]. As the fluctuations in composition and/or flow rate occur stochastically, a highly complex system behavior is expected [18]. Additionally, unsteady-state kinetics often differ from the steady-state ones [10], which probably leads to a nonlinear response of temporal and spatial concentration and temperature profiles with feedback on the kinetics.…”

Global Reaction Kinetics of CO and CO2 Methanation for Dynamic Process Modeling

“…Current dynamic simulations of CO and CO 2 methanation processes primarily refer to rates from Xu 23, e.g., 17, 31, and with less frequency to the rates determined by Kopyscinski 19, e.g., 32. However, a closer look at these models and reaction rates reveals a significant validity limitation concerning the methanation temperature.…”

Transient Flow Rate Ramps for Methanation of Carbon Dioxide in an Adiabatic Fixed‐Bed Recycle Reactor

“…Under isothermal conditions, the heat of reaction is not considered. Hence, the activator is not present in the system and the reactor exhibits a stable operation with damping behavior . The dynamic phenomena induced by DIFIs are the wrong‐way behavior, moving hot spots, and extinction waves.…”