Chemical looping staged conversion of microalgae with calcium ferrite as oxygen carrier: Pyrolysis and gasification characteristics

Abstract

Aiming to take full advantage of biomass featuring high volatiles and high oxygen content, we propose two chemical looping staged conversion (CLSC) schemes by decoupling pyrolysis and gasification into two distinct stages. In current work, the pyrolysis and gasification characteristics of microalgae Nannochloropsis sp. with calcium ferrite as oxygen carrier were performed by TG-FTIR analysis and experiments in a tubular reactor. Meanwhile, the gained bio-oils and gaseous products were analyzed using GC-MS and GC, respectively. The results suggested that both the oxidized and reduced calcium-ferrite oxygen carrier could enhance the quality of bio-oil in the pyrolysis stage by decreasing the oxygenated and nitrogenized compounds dramatically. Furthermore, the CO-rich or H2-rich syngas was generated in the gasification stage via the reactions between oxygen carrier and pyrolytic char. In the pyrolysis stage, the oxidized oxygen carrier facilitated the formation of chemicals (such as aromatics and alcohols), while the reduced oxygen carrier promoted the quality of bio-oil as the liquid fuel with the heating value high to 34.18 MJ/kg. Meanwhile, the content of H2 in pyrolytic gas was up to 50 %. In the gasification stage, CO-rich syngas was generated without the steam gasification agent, while H2-rich syngas was produced with the steam gasification agent. It proves that CLSC will provide a promising approach for high effective and clean utilization of biomass.