CO2 methanation in a shell and tube reactor CFD simulations: high temperatures mitigation analysis

CO2 methanation is gaining increasing interest in the last years as a way of storage of the energy surplus produced by renewable energy sources. Shell and tube reactors are among the most widespread type of methanation reactors. One-dimensional pseudo-homogenous/heterogeneous models and CFD (Computational Fluid Dynamics) models using some simplifications, as imposed heat exchange coefficients and constant coolant temperatures, have been applied up to now to study the problem. In this article those simplifications have been removed and the CO2 methanation in a cooled multi-tubular catalyst reactor has been investigated through 3D CFD simulations, using a commercial software and a porous model. Nitrogen and oil cooling have been studied and the results have been compared. The goal is to identify suitable solutions that allow the use of gas cooling, while maintaining low temperature levels and high conversions. The oil cooling case has been also analyzed for comparison and in the perspective of a future system upgrade. After a validation of the model using the available experimental data, a sensitivity analysis has been conducted for what concerns coolant and reactants temperatures and flow rates, catalyst load and operating pressure in the tubes. Strategies for the high temperatures mitigation in the reactive zones have been evaluated and discussed. In particular the proposed technique of catalyst uneven distribution has revealed to be very effective. The model has proved to be very useful for a detailed analysis of the phenomenon and for obtaining essential data that resulted difficult to measure by experimentation.