Abstract

A disk and doughnut type tubular reactor is presented as a design solution for biogas upgrading via CO2 methanation. To address the design problem related to hot spot control and SNG quality, a four step CFD methodology is proposed. Model validation is tackled by splitting the simulation domain into two sub systems characterized by the main phenomena of interest: Chemical kinetics and heat transfer. Benchmarking test problems results from the developed CFD methodology agreed well with the experimental and correlation data, giving a maximum error of 8.5% and 10% for the chemical reaction and heat transfer models, respectively. The proposed methodology was used to investigate the effect of two commercially available coolants (thermal oil and molten salts) on overall reactor performance through a parametric study involving four coolant flow rates. Although molten salts did show higher heat transfer coefficients at lower coolant rates (82%, its use increment five times the amount of pumping power required with respect to thermal oil in all cases. Flow field conditions prompted by the Disk and Doughnut design, ensure uniform cooling among tubes, and maximize heat transfer at hot spot. Finally, a basic design configuration is presented to produce SNG from a decentralized biogas source.