Microwave-assisted biomass pyrolysis polygeneration process using a scaled-up reactor: Product characterization, thermodynamic assessment and bio-hydrogen production

Recent investigations of microwave-heated biomass pyrolysis using laboratory scale reactors have proven thermodynamically superior to electrically-heated processes. Despite these promising results, microwave pyrolysis has not been implemented commercially. Further research into diverse feedstocks and scaled-up processes would encourage commercial investment. To accomplish this, present work examines the performance of scaled-up microwave pyrolysis using corn stalk, pinewood and algae biomasses. The results showed that the lower heating value (LHV) of pyrolytic gas increased with temperature. The LHV of three biomass samples ranged from 10.3 MJ Nm⁻³ to 17.6 MJ Nm⁻³, higher than the requirement for fuel gas in district heating. Importantly, corn stalk-derived pyrolysis gas reached a LHV of 17.6 MJ Nm⁻³ at 600 °C, higher than gas obtained from pulverized coal gasification. The HHV value of pinewood char was the highest of the solid products at three temperatures, reaching 27.3 MJ kg⁻¹, due to its high carbon and low oxygen contents. The energetic assessment showed that pyrolysis system efficiency (PSE) increased with temperature from augmentation of gas yields, compensating for declining char and oil yields. Corn stalk (63%) had the highest PSE at 600 °C. The exergetic efficiencies of three different biomass-based systems followed a similar trend. The exergy efficiency of each system was lower than its corresponding energy value, due to the difference in sensible heat values. The experimental results analysed through a hydrogen plant simulation, confirming that the greatest performance was achieved by utilizing algae (85 gH₂ kg algae⁻¹) as fuel, followed by pinewood (78 gH₂ kg pinewood⁻¹).