Experimental Research on the Production of Hydrogen-Rich Synthesis Gas via the Air-Gasification of Olive Pomace: A Comparison between an Updraft Bubbling Bed and a Downdraft Fixed Bed

Abstract

The present study compares the performance of bubbling-bed updraft and a fixed-bed downdraft gasification systems for producing hydrogen-rich (H2) syngas from olive pomace on a semi-industrial scale. The focus is on examining the effects of temperature and efficiency ratio (ER) on the composition, low heat value (LHV), carbon conversion efficiency (CCE), and cold gas efficiency (CGE) of the produced syngas. The results presented for the fixed bed show the concentration of H2 (15.6–16.52%), CGE (58.99–66.80%), CCE (69.07–71.86%), and LHV (4.82–5.70 MJ/Nm3). The CGE reaches a maximum of 66.80% at a temperature of 700 °C and an ER of 0.20, while the syngas yield (2.35 Nm3/kg) presents a maximum at a temperature 800 °C and an ER of 0.21, with a tendency to decrease with the increase in the temperature. For the bubbling fluidized bed, results were shown for the concentration of H2 (12.54–12.97%), CGE (70.48–89.51%), CCE (75.83–78.49%), and LHV (6.10–6.93 MJ/Nm3), where, at a temperature of 700 °C and an ER of 0.23, the CGE is 89.51% and the LHV is 6.93 MJ/Nm3, with a tendency to decrease with the increase in the temperature, while the maximum syngas yield (2.52 Nm3/kg) occurs at a temperature of 800 °C and an ER of 0.23. Comparing the two gasification processes, the fixed bed has a higher concentration of H2 at all the temperatures and ERs of the experiments; however, the bubbling fluidized bed has a higher CGE. These findings have implications for applications involving syngas, such as energy production and chemical synthesis, and can guide process optimization and enhance energy efficiency. The information obtained can also contribute to emission mitigation strategies and improvements in syngas-based synthesis reactors.