Enhanced Sewage Sludge Gasification by Bauxite-Modified Carbide Slag for Hydrogen-Rich Syngas Production with In Situ CO2 Capture

Calcium-looping gasification is attractive to dispose massive sewage sludge for hydrogen-rich syngas with in situ CO2 capture but still challenged by apparent drop of CO2 sorbent reactivity, sorbent attrition, and uncertainty of sorbent performance during multi-cycle gasification. Herein, bauxite-modified carbide slag is prepared as a cheap CaO-based CO2 sorbent by a simple mechanical mixing method. Based on physical and chemical characterization as well as thermogravimetric analyses, it is found that the bauxite-modified carbide slag (CS) contained the inert component of mayenite, which is beneficial to improve pore characteristic and promote stability and mechanical strength of sorbent during multi-cycle CO2 capture. Fluidized bed gasification tests verify that adding carbide slag increases H-2 yield and efficiency of sewage sludge gasification. Moreover, appropriate increase in reaction temperature and steam flow rate enhances sewage sludge gasification with bauxite-modified carbide slag. During multi-cycle fluidized bed gasification, modified carbide slag CS-5 (with 5 wt% bauxite) presents more stable performance and better anti-attrition characteristic in comparison to carbide slag without modification. After five cycles of fluidized bed gasification, the yield and concentration of H-2 are increased while the fraction of fine particles produced by attrition is largely decreased for CS-5 in comparison to ordinary carbide slag.

Automated summary

Bauxite-modified carbide slag is a cheap CaO-based CO2 sorbent that improves the performance of calcium-looping gasification for hydrogen-rich syngas with in situ CO2 capture. It enhances pore properties, stability, and mechanical strength of the sorbent during multi-cycle CO2 capture.