Dynamic one-dimensional model for biological methanation in a stirred tank reactor

In this study, a dynamic model for a continuously stirred biomethanation reactor was developed with novel approach that combines semi-fundamental modeling of gas-liquid mass transfer, hydrodynamics, and biological reactions. The model was validated against existing experimental data and used in a sensitivity analysis of critical parameters, a scale-up study of a biomethanation reactor, and process dynamics studies. In each of the varying operational conditions, the model reproduced the trends observed in the experimental studies. The sensitivity analysis showed that biological parameters have a minimal effect on methane production. Conversely, the model is very sensitive to the gas-liquid mass transfer properties, such as the geometry of the impeller and reactor. The scaled-up study of biomethanation reactors with a CH4 production capacity of 56-508 Nm3/h revealed that the required stirring power is 0.7-1.1% from the electrolyzer power and decreases as the size of the reactor increases. High output quality (∼98%) of the methane could be reached in each of the studied cases, and the overall efficiency of the power-to-methane process was roughly 50%. Dynamic simulations showed that the modeled process is tolerant to large gradients in the input parameters. After correctly setting the reactor- and process-specific parameters, the model can be used to perform scaled-up and dynamic studies of various reactor designs and different biomass solutions.