Biomass gasification ash reutilization: Recirculation reusability and mechanism analysis.

[Display omitted] • Metals, especially K, got enriched in ash as ash recirculation was performed. • Ash showed recirculation reusability in CO and H 2 generation, and tar removal. • The positive effect increased in the first four recirculation, and then kept steady. • The positive effect of recirculation highly depended on the metals content in ash. • Ash showed an ability in capturing SO 2 during its recirculation. A biomass gasification ash disposal method, recirculating it to gasification process, was proposed in this work. The recirculation reusability was analyzed via reusing corn straw (CS) gasification ash for six recirculation in a gasifier. Metals, especially K, got enriched in ash during ash recirculation. Under the 1st ash recirculation, CO content, H 2 content and lower heating value of gas products increased from 16.02 to 19.97 vol%, from 11.30 to 15.72 vol%, from 5.38 to 6.47 MJ/Nm3, respectively. Moreover, it also exhibited an ability in tar decomposition, resulting in a tar reduction (4.63 g/Nm3 for raw CS gasification and 3.62 g/Nm3 for 1st ash recirculation). These positive effects gradually increased during the first four ash recirculation. The positive effects highly depended on the accumulation of metals (K, Na, Ca, Mg, and Fe) in ash. The positive effect did not increase as the fifth and sixth ash recirculation were conducted, resulting from the constant metals content in ash. Grey relational analysis showed that the total content of these metals was the most significant influencing parameter, followed by K content, water-soluble K content, Ca content, respectively. Moreover, pollutant SO 2 could be captured by CaO during ash recirculation. This reaction competed with simultaneous CaO carbonation reaction, while it was inferior to the latter. Thus, only the first and second ash recirculation exhibited satisfactory ability in SO 2 capture. In summary, ash recirculation in gasification process was feasible for upgrading gasification performance and its effect was persistent. [ABSTRACT FROM AUTHOR]