Biomass gasification ash reutilization: Recirculation reusability and mechanism analysis

Area of Science:

• Chemical Engineering
• Environmental Science
• Energy Technology

Background:

• Biomass gasification is a key thermochemical conversion process.
• Ash disposal presents a significant challenge in biomass gasification.
• Recirculating gasification ash offers a potential solution for waste management and process improvement.

Purpose of the Study:

• To investigate the feasibility and impact of recirculating corn straw (CS) gasification ash.
• To analyze the effect of ash recirculation on syngas composition, heating value, and tar content.
• To determine the role of metal enrichment in ash recirculation's performance.

Main Methods:

• Corn straw (CS) gasification ash was recirculated for six cycles in a gasifier.
• Syngas composition (CO, H2), lower heating value (LHV), and tar content were analyzed.
• Metal content (K, Na, Ca, Mg, Fe) in recirculated ash was quantified.
• Grey relational analysis was employed to identify key influencing parameters.

Main Results:

• Ash recirculation significantly increased CO and H2 content and LHV of syngas, peaking within the first four cycles.
• Tar decomposition was enhanced, reducing tar content from 4.63 to 3.62 g/Nm3 after the first recirculation.
• Metal accumulation (K, Na, Ca, Mg, Fe) in ash correlated with performance improvements.
• SO2 capture was observed in the first two recirculation cycles due to CaO, but was limited by carbonation.

Conclusions:

• Recirculating biomass gasification ash is a feasible method for upgrading gasification performance.
• Metal enrichment, particularly potassium, is crucial for the observed improvements in syngas quality and tar reduction.
• The positive effects of ash recirculation are persistent up to a certain number of cycles, after which metal content stabilizes.