Tunable syngas production from two-stage sorption-enhanced steam gasification of sewage sludge

Syngas, a mixture of hydrogen (H₂) and carbon monoxide (CO), has attracted increasing attention since it is a versatile and flexible platform feedstock for the production of value-added chemicals and fuels via Fischer-Tropsch synthesis. Syngas production from biomass gasification has been widely investigated, while the lack of tunable H₂/CO ratio in the syngas limits the direct industrial application of biomass-derived syngas. By incorporation of steam gasification into the first stage of the two-stage sorption-enhanced steam gasification (SESG) of sewage sludge (SS), the H₂/CO ratio of produced syngas is tunable from 0.9 to 4.7 by controlling the CaO and steam contents. The SS sample with a CaO/SS mass ratio of 3:7 produces an H₂-rich gas stream (72.2 vol% purity) at the first stage (550 °C) and CO-rich gas stream (60.5 vol% purity) at the subsequent second stage (750 °C), providing a new promising approach to directly integrate the two-stage SESG of biomass with the syngas application where H₂ and CO could be mixed in desirable ratios for the downstream synthesis of value-added chemicals and fuels. The high distribution of carbon and hydrogen in the tar indicates that the two-stage SESG has a great potential to promote the decomposition of tar for enhanced syngas production.