Investigation on co-gasification performances of sewage sludge and polyolefins by thermogravimetric analyze and two-stage fixed bed reactor

Co-gasification of biomass with hydrogen-rich feedstock is a promising method to improve H₂ yield. Thus, in this work, co-gasification performances and corresponding promotion/inhibition effects of sewage sludge (SS) and three types of polyolefins (PE, PP and PS) were investigated in the thermogravimetric analyze and two-stage fixed bed reactor. Thermogravimetric experiments results indicated that with the addition of polyolefins, the initial temperature of blends progressively elevated, while its terminal temperature declined, suggesting that adding polyolefins facilitated the decomposition of samples. The thermal degradation of blends was distinguished into two stages, and in the first stage, a negative interaction was found at 25 % polyolefins mass ratio, but a positive interaction was occurred at 50 % and 75 % polyolefins mass ratios. Meanwhile, in the second stage, a negative interaction was obtained for blending with PE, whereas an opposite result was observed for blending with PP or PS. Therefore, temperature, feedstock and mixing ratio interacted on synergy effects between SS and polyolefins. Besides, two-stage fixed bed experiments results suggested that a higher gasification temperature was beneficial for the production of syngas, particularly the H₂ yield, and blending with polyolefins into SS enhanced the H₂ content, with PE performing best. The synergy interactions between SS and polyolefins accelerated the concentrations of H₂ and CH₄, while declining the C_nH_m yield, demonstrating a stronger re-cleavage of macromolecules. Furthermore, the low heat value of syngas and carbon conversion efficiency for all the samples separately elevated and reduced with rising gasification temperature and polyolefins mass ratios. At 800 °C, the highest gasification efficiency of samples could be achieved with the addition of 50 % PP or PS. This study provides a basis for the application of SS and polyolefins co-gasification.