Application of modified olivine to a two-stage gasification process to evaluate the effects on hydrogen generation and retention of heavy metals

Abstract

An environmentally-friendly and efficient waste-to-energy and heavy metal retention system was successfully developed in this study. The natural resource-olivine was applied to be the bed material of second-stage gasifier, and the effects of second-stage gasifier temperature, and steam/biomass ratio on the hydrogen (H2) production ratio of syngas and heavy metal retention were discussed in detail. The optimal hydrogen production ratio (30.3%) was achieved when second-stage temperature, steam/biomass ratio (S/B ratio) were respectively controlled at 900 °C, and 0.25. The characterization analysis results evidenced that the Fe and Mg from pristine olivine and calcined olivine can facilitate the waste-to-hydrogen during the gasification reaction. Moreover, the NiO and Ni loaded on the surface of the calcine olivine could not only facilitate the water–gas shift reaction for H2 production, but also provide strong binding sites for the linkage of ether and cleavage of the C–O bond, leading to formation of CH4. The formed CH4 would be further dissociated over the metallic Ni/olivine, resulting in a significantly improved H2 production efficiency. In general, the order based on the H2 ratio of the syngas at the second-stage was calcined Ni-loaded olivine > calcined olivine > olivine; the heavy metal retention efficiency of three bed materials was in the order of Cu > Pb > Zn.