Thermal Performance and Stability of CO ₂ -Rich Biogas Combustion in a Heat-Recuperated Radiant Porous Burner

High Resolution Image Download MS PowerPoint Slide Low-calorific-value biogas with high CO 2 content presents significant challenges for conventional combustion systems due to reduced flame stability, lower reaction temperatures and diminished thermal efficiency. Developing efficient technologies capable of directly utilizing CO 2 -rich biogas without costly upgrading processes is therefore essential for expanding its use in renewable heat generation. This study presents a combined experimental and numerical investigation of the effects of CO 2 -rich biogas composition and reactant preheating on the performance of a radiant porous burner equipped with an integrated heat recovery system. Biogas was simulated using CH 4 /CO 2 mixtures containing up to 65 vol % CO 2, and the burner was operated under ultralean conditions at an equivalence ratio of 0.50. The system consists of a two-layer porous medium and a radially integrated stainless-steel coil heat exchanger designed to enhance internal heat recirculation and promote reactant preheating. Flame stability limits, temperature profiles, outlet surface temperature, radiative efficiency and pollutant emissions were experimentally evaluated. In parallel, a thermodynamic model based on a global energy balance was applied to quantify energy losses relative to an ideal adiabatic system, while detailed kinetic simulations using the GRI-Mech 3.0 were conducted to assess adiabatic laminar flame speed and temperature. Increasing the CO 2 concentration reduced the burner stability range and shifted the reaction zone toward the outlet due to lower flame temperatures and slower reaction kinetics. Reactant preheating increased the inlet temperature to approximately 100 °C and expanded the stability range by up to 75% for the 50% CH 4 /50% CO 2 mixture, while also reducing CO emissions. The maximum CO emission index was 0.082 g kg –1, whereas NO emissions remained below detection limits. Energy losses ranged from 13 to 17%, with higher flow velocities primarily increasing exhaust-gas losses.