Hydrogen-Rich Gas Production from Steam Gasification of Bio-char in the Presence of CaO

The steam gasification of bio-char to produce hydrogen-rich gas with CaO as in-bed catalyst is experimentally investigated in a fluidized bed reactor. The purpose of the study is twofold: (1) evaluate the optimal operating conditions of catalytic gasification for hydrogen-rich gas production, by examining catalyst activity and steam flowrate; (2) optimize the process by investigating the potential for reducing the gasification temperature. Results reveal that increasing the CaO/wood mass ratio from 0 to 1.0 is effective for both H2 improvement and tar reduction; this is attributed to enhanced CO2 absorption and reforming reactions. Increasing the steam flowrate is beneficial towards H2 production via the water gas shift reactions. A maximum H2 concentration is achieved at a steam flowrate of 160 g/h; however, excessive steam injection will lead to an opposite effect, due to decreased available heat. The reaction temperature should be balanced between the gasification performance and CaO carbonation ability, and the optimal temperature is found to be 700 °C in this study. Comparing the results with non-catalytic high-temperature gasification, 50% CaO addition at 700 °C could reach as high H2 yield as that gasified at 800 °C without catalyst. Meanwhile, the use of CaO also optimizes the gasification performance with a much higher H2 concentration, a higher H2/CO ratio and reduced tar yield. Therefore, it is concluded that 50% CaO addition as catalyst at 700 °C is effective to reduce the steam gasification reaction temperature by 14% (ca. 100 °C).