Co-gasification of woody biomass and microalgae in a fluidized bed

• Increasing the mixing ratio of microalgal torrefied pellet in co-gasification, LHV of syngas first increases and then decreases.
• High-content ash in the microalgal torrefied pellet dominates the gasification products.
• The extreme higher amount of ash in microalgal torrefied pellet may cause sintering and agglomeration during gasification.

In this study, the microalgal (Spirulina platensis) torrefied pellet and woody biomass (Eucalyptus globulus) torrefied pellet were co-gasified in a 30 kW bubbling fluidized bed gasifier to investigate the effect of gasification temperature, equivalence ratio (ER), feedstock mixing ratio and steam injection on syngas compositions, the lower heating value (LHV), tar content, etc. Before feeding into the gasifier, the microalgal and woody biomass pellets were torrefied to increase the heating values.It can be found that the ash content of microalgal torrefied pellet is much higher than that of woody biomass torrefied pellet. Although ash compositions can act as catalysts to enhance the gasification reaction, the extreme higher amount of ash may cause sintering and agglomeration during gasification. From the above co-gasification experiments, the results show that CO and CO2 contents increase with increasing the ER, and CH4 and H2 show the contrary tendency. Increasing the mixing ratio of the microalgal torrefied pellet, H2, and CH4 contents first decrease and then increase slightly, but CO and LHV first increase and then decrease. Injecting steam can increase H2 and CO2 yields, but decrease CH4 and CO yields, and LHV. It can be found that the high-content ash in the microalgal torrefied pellet dominates the gasification products, and the results show the contrary tendency compared with gasification of woody biomass torrefied pellet.