Synthetic Gas Production from Biogas Reforming by Non-Thermal Plasma

Abstract

This research focused on upgrading biogas to synthetic gas for various applications by using non-thermal, gliding arc plasma.A box shaped gliding arc plasma reactor was designed and built to increase reaction zone and provide smooth flow profiles at gas outlet and to prevent dead spots at the corner of the reactor. The optimum gap distance of electrodes was at 4 mm. Simulated biogas was generated by mixing CH4andCO2at different fractions.Objectives of this research were to experimentallyinvestigate factors affecting production of synthetic gas, andto numericallysimulatesynthetic gas productionusing gliding arc plasma. The experiments were divided into 3 main parts, dry reforming, partial oxidation, and multistage reforming reactors. In the gliding arc plasma dry reforming process, effects of biogas composition, power input and biogas flow rate were studied. It was found that high conversion, yield and selectivity were obtained at biogas composition of CH4:CO2 = 50:50. When power input was increased from 100 to 600 W, conversion, yield and selectivity were increased. However, at high power input, coke formation occurred at the electrodes. This can present serious problem for reforming operation. In the later experiments, low power input of 100 W was used for biogas reforming to avoid coke formation. With respect to biogas flow rate, it was found that at high flow rate, synthetic gas production was decreased due to shorter reaction times in the reactor. The optimum flow rate on gliding arc reforming reactor was 1 L/min. Adding air to biogas reforming process was found to enable increased synthetic gas production. However, synthetic gas production showed some limitations, depending on composition of biogas. The maximum production was obtained at biogas composition CH4:CO2 = 90:10 and air of 60 % by volume. Disadvantage of adding air was higher operating temperature than the dry reforming process. Temperature of air addition operation was about 120 to 380 ˚C, depending on the amount of added air. Alternative way to increase synthetic gas production was with a multistage reactor. In this process, connecting reactors in series was employed. Synthetic gas production was increased, while energy consumption was not much different. The optimum condition was to add air for increased synthetic gas production for biogas composition at CH4:CO2 = 50:50 Plasma reforming simulation was alsoperformed, based on available kinetic parameters from literature. It was preceded using COMSOL Multiphysics software. Synthetic gas production was found to increase due to reforming reaction, enabled by the presence of active species in the plasma. Results from the experiment compared qualitatively well with the model. However, difference in magnitude from over-prediction was obtained due to the fact that other reactions and gas products may involve in the process.