Co-gasification characteristics of Ca-rich sludge and Fe-rich sludge under CO2 atmosphere, and potential utilization of gasification residues as renewable catalyst in biomass pyrolysis

The co-gasification behaviors and performances of Ca-rich sludge (CS) and Fe-rich sludge (FS) were studied by thermogravimetric analyzer. The results showed that the comprehensive gasification index was highest at 40% CS ratio, which was 9.7 × 10−8 %2/(min2·°C3). The co-gasification resulted in more solid products generation due to that ash hindered contacts of gasifying agent and organics. By the sliding resistance furnace (SRF), in 80%CO2/20%N2, the evolution of gas compositions during the gasification process and impacts of different temperatures and blending ratios on co-gasification were evaluated. The evolution of gas compositions showed that the gas yields from CS gasification were higher than those from FS, and the interactions and ash catalytic effect during the co-gasification made the peak times earlier. The reaction temperatures and blending ratios had certain effects on the co-gasification process, affecting the mineral compositions and pores structures of sludge residues. Finally, considering the attributes of rich pores structure and Ca/Fe elements, the gasification residues can be used as ex-situ catalyst in the modification of biomass pyrolytic volatiles. Conducting the pyrolysis experiments by the SRF under N2 atmosphere, with adding gasification residues of sludge, the CO yield from biomass pyrolysis grew, but the yields of CO2, H2 and C2Hm reduced.