Gasification characteristics of a simulated waste under separate and mixed atmospheres of steam and CO2

Downdraft gasifier is attractive for small-scale solid waste treatment, but the gasification characteristics are worthy of deep research. In this study, a two-stage continuous feeding apparatus was developed to examine the effect of moisture content of the mixed feedstock on co-gasification. Furthermore, considering the effect of CO2 from flue gas, the gasification experiments were carried out when CO2 participated in the gasification alone or in a mixed atmosphere of CO2 and steam. The pyrolysis residue plays an essential role in the gasification with steam, which can improve the syngas yield, especially the H2 yield reaches 0.345 m3/kg when steam and feedstock mass ratio (S/F) is 0.8. CO2 is inferior to steam in promoting H2 formation. But when CO2 and feedstock mass ratio (C/F) rises from 0.74 to 1.48, the gas yield increases from 60.52% to 77.15%, and the yields of tar and residue cut down correspondingly. CO2 is still an alternative gasifying agent, which can partially substitute steam in the gasification process. However, when CO2 coexists with a small amount of steam (S/F = 0.4), introducing excessive CO2 (C/F = 1.48) will intensify the competition between steam and CO2.