Hydrogen production from agricultural biomass wastes gasification in a fluidized bed with calcium oxide enhancing

The enhancing effect of calcium oxide (CaO) addition on steam gasification of four typical Chinese agricultural biomass wastes for H2 production has been investigated in an atmospheric fluidized bed reactor under different conditions. The result indicates that CaO acts both a CO2 absorbent and a catalyst in the gasification process. Its addition significantly increased the concentration and yield of H2 and simultaneously decreased the content of CO and CO2 in the product gas. At lower temperature (550-650 °C), the CO2 absorption enhancing effect of CaO greatly promoted the gasification process to produce a product gas with high content of H2 and low CO and CO2. While at higher temperature (700-800 °C), the catalytic effect of CaO became significant, the cracking of pyrolytic volatiles and steam gasification of volatiles and char as well as WGS reaction were intensified, which also caused the increase in H2 yield in spite of the decrease in H2 concentration. The increases of molar ratio of CaO-C (CaO/C, 0-2) and mass ratio of steam to biomass (S/B, 0.8-2) were both beneficial for H2 production process. CaO addition showed limited effect on CH4 and C2+ even at high temperature and high mass ratio of steam to biomass. The type of biomasses is closely associated with H2 yield, which is closely related to the volatile and C content of biomass materials.