Simulation-Based Evaluation of a Two-Stage Small-Scale Methanation Unit for Decentralized Applications

Abstract

The present work aims for a simulation-based evaluation of a two-stage methanation unit for the production of substitute natural gas (SNG) in decentralized small-scale applications with low complexity. Equilibrium calculations reveal a remarkable impact of CO 2 removal efficiency on final SNG composition with an optimum removal efficiency of 85% for the examined synthesis gas. The first methanation stage consists of a polytropic fixed-bed methanation reactor and is implemented as a one-dimensional pseudohomogeneous model in Aspen Plus TM with reaction kinetics from literature. The comparison of three different kinetic models reveals that reverse reaction of CO methanation has to be considered in the kinetic rate equations for appropriate modeling within a dynamic temperature range above 400 °C in case of polytropic reactors. The first methanation stage is examined with one kinetic model in terms of reactor geometry, varying GHSV and influence of the feed gas composition to determine limits in upscaling and avoidance of too high temperatures. A significant decrease of the reactor diameter favors the heat removal in case of polytropic reactor concept, whereas a higher GHSV causes higher outlet temperatures. The results show that an effective operation of the proposed methanation concept is limited by an appropriate heat removal.

Conversion of tars on solid oxide fuel cell anodes and its impact on voltages and current densities

“…In Figure , a C‐H‐O ternary diagram illustrates the issue. Ternary diagrams constitute a possibility for an intuitive illustration of several different processes, that is, SNG production or fuel cell operation . A producer gas composition from wood gasification was added to give an example how the ternary diagram can be used to predict safe operation domains.…”

Pushing the Limits of SNG Process Intensification: High GHSV Operation at Pilot Scale

“…Optimal temperature profiles along the catalyst bed enable smaller equipment volumes and thus intensification of the CO 2 methanation process . These temperature profiles can only be achieved by applying polytropic reactors, where the required heat to sustain the process remains in the reaction medium, and the excess of heat is taken away from the system using molten salt, water, air, or thermal oil − as cooling media. In brief, a polytropic reactor includes heat transfer systems, while adiabatic reactors do not.…”

Numerical Simulation of CO Methanation for the Production of Synthetic Natural Gas in a Fluidized Bed Reactor

“…The main issue is the strongly exothermic process during the reaction which leads to carbon particle formation on the surface of catalysts. 5 And the catalytic activity and stability will be significantly affected due to the increasing of temperature. 6 Hence, the removal of reaction heat is crucial for methanation.…”