Effects of quicklime conditioning on the volatile reforming and tar elimination performance of sewage sludge pyrochar

Abstract

The pyrochar of sewage sludge can be exploited for catalytic tar reforming since the developed pore structure and high metal content. However, Fe in the raw sludge tends to form Fe-S and Fe-P during pyrolysis, which inhibits catalytic activity of pyrochar. Here, the wet sludge was conditioned with quicklime, and the pyrochar was used to reform sewage sludge pyrolysis volatiles. The results showed that H2 generation from pyrochar reforming increased by 55.2% after conditioning. In addition, the tar elimination achieved the highest ratio (79.6%) compared with unconditioned char and quicklime, while PAHs and N-compounds were concentrated in tar with the relative content 46.9% and 37.1% due to the significant removal of other tar compounds such as oxygenates. During pyrolysis, a proportion of added CaO captured P and S anions which favored the formation of Ca2Fe2O5 and Fe-O, while the remaining CaO (21.9%) was highly dispersed on pyrochar. This promoted both the catalytic tar cracking effects and the CO2 absorption of the char. These findings provide a novel method to produce H2-rich gas from sewage sludge pyrolysis with less tar yield.