Hydrogen Production in Steam Gasification of Biomass with CaO as a CO_2 Absorbent

摘要

Characteristics of steam gasification of biomass for hydrogen production at ambient pressure in a laboratory-scale external circulating concurrent moving bed (ECCMB) system with CaO as a CO_2 absorbent were investigated. In this ECCMB system, steam gasification of biomass, in situ CO_2 capture, combustion of the produced char, and calcination of CaCO_3 can occur simultaneously. The experimental results verified that the in situ CO_2 capture was achieved with calcined limestone as a CO_2 absorbent, which increased the extent of the water-gas shift reaction and enhanced the yield of H_2. The H_2 content of 60-70 mol % in dry gas can be obtained at a steam/biomass weight ratio (S/B ratio) of 0.38-0.59 and a CO_2 absorbent/biomass weight ratio (A/B ratio) of 20 at the reactor temperature of 700-800 ℃. The results showed that the addition of a CaO-based CO_2 absorbent is a good solution to increase hydrogen content in dry gas from the ECCMB process. An irreversible deactivation of the CO_2 absorbent occurred in the cyclic carbonation/calcination because of the sinter of CO_2 absorbent particles and the formation of inorganic adhesions on the surface of the particles from the solid-solid reactions between biomass ash and CO_2 absorbent.