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

Abstract

The power‐to‐gas (PtG) process, enabling the long‐term indirect storage of electrical energy, includes the water electrolysis for hydrogen production and the subsequent hydrogenation of carbon dioxide in a methanation reactor. The dynamic operation of methanation reactors is favored to limit upstream storage capacities, but not fully understood thus far. Therefore, this contribution investigates the dynamic operation of a fixed‐bed recycle reactor during flow rate ramps with a variation of the ramp time. Load ramps of the volumetric flow rate lead to global maxima during the transition; for the methane content if the flow rate is decreased, and for the gas temperature if the flow rate is increased. Furthermore, the adaptation of the product recirculation during flow rate ramps is discussed at the end. The recycle ratio turns out to provide an additional degree of freedom for stabilizing the reactor behavior under fluctuating feed conditions.

Novel Multiplicity and Stability Criteria for Non-Isothermal Fixed-Bed Reactors

“…However, designing and operating polytropic fixed-bed reactors is a rather challenging task, due to a variety of possible physiochemical phenomena (e.g., runaway, parametric sensitivity), which can lead to performance losses or critical process failures (see e.g., Kreitz et al, 2019;Kiewidt and Thöming, 2019;Moioli et al, 2019;Theurich et al, 2019;Fache et al, 2020;Fischer and Freund, 2020;Zimmermann et al, 2020). Such instances correlate with features from systems theory, i.e., uniqueness, multiplicity, and stability.…”

Challenges and Opportunities to Enhance Flexibility in Design and Operation of Chemical Processes

“…Based on the described concept, various systematic investigations are performed with regard to the operating window, transient states, and start‐up. The results show on the one hand that adiabatic fixed‐bed reactors with product recycling can be applied in a wide operating window 44 and on the other hand that the system response to varying feeds is weakened by the recycling loop, making the system less sensitive to changes 45. At the same time, the recycling quantity represents a further degree of freedom for dynamic operation.…”

“…With regard to the operation of unit operations and chemical reactors, various approaches describe specific operation strategies to increase flexibility at the level of the individual equipment. Theurich et al [43][44][45] While many authors investigate single-pass or multistage reactors for CO 2 methanation, Theurich et al propose a single-stage, adiabatic fixed-bed reactor with a product recycle loop. Based on the described concept, various systematic investigations are performed with regard to the operating window, transient states, and start-up.…”

“…With regard to the operation of unit operations and chemical reactors, various approaches describe specific operation strategies to increase flexibility at the level of the individual equipment. Theurich et al 43–45 investigate the influence of product recycling in CO 2 methanation. While many authors investigate single‐pass or multistage reactors for CO 2 methanation, Theurich et al propose a single‐stage, adiabatic fixed‐bed reactor with a product recycle loop.…”

Influence of Power‐to‐Fuel Plant Flexibility Towards Power and Plant Utilization and Intermediate Hydrogen Buffer Size

“…Only a small number of studies have been devoted yet towards the investigation of the influence of flexibility on the output and utilization degree, which arises from certain assumptions. Some researchers have investigated the possibility of performing alternative processes for energy storage via molecules like methane (synthetic natural gas) under dynamic boundary conditions [9][10][11][12]; mostly catalyst stability and the challenges for describing the reactor system have been investigated there. Major obstacles are under-stoichiometric hydrogen supply in unsteady-state operation leading to catalyst deactivation.…”