Two processes (with cooled and adiabatic fixed bed reactors) for direct biogas methanation were assessed using detailed balances and rate-based models. The simulations show that they are capable to produce synthetic natural gas (SNG) in one or two steps without further upgrading after the reactors. The sizes for cooled beds are smaller than for adiabatic reactors due to heat transfer that reduces the needs for recirculation and allows for more favorable temperature profiles; although a more complex heat exchanger systems is then required for cooling. Thus, the processes are compared to identify the most cost-effective operating conditions for each system, since all considered optimized systems can meet product specifications and technical aspects alone are not enough to decide which the most beneficial approach is. The economic analysis shows that the costs dominant come from biogas and hydrogen and total costs production of SNG (0.54-0.58 (sic)/Nm(SNG)(3)) is still high compared to natural gas. Cheap biogas and electricity may lead to more competitive SNG costs, while the methanation step can effectively remove the problems related to biogas or hydrogen uses at the same time that is a minor part of final costs. (c) 2020 Elsevier Ltd. All rights reserved.