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 CO2 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 PIus (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 degrees 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.