Enhanced Hydrogen Production from Steam Gasification of Coal with in-situ CO_2 Capture in a Pressurized Fluidized Bed

摘要

Steam gasification of a typical Chinese bituminous for hydrogen production in a lab-scale pressurized bubbling fluidized bed system with CaO as CO_2 sorbent was conducted over a temperature range of 660-750 °C whilst varying gasification pressure from atmospheric pressure to 4 bar. The production gas composition was examined and correlated to the critical gasification variables such as pressure (P), mole ratio of steam to carbon ([H_2O]/[C]), mole ratio of CaO to carbon ([CaO]/[C]) and temperature (T). The experimental results indicated that the H_2 yield is enhanced by the increasing temperature, pressure, [H_2O]/[C] and [CaO]/[C]. The presence of CaO sorbent transferred the CO_2 in the production gas to solid CaCO_3, thus shifted the reforming and water gas shift reactions beyond the reaction equilibrium restrictions and enhanced H_2 yield. H_2 concentration was as high as 78vol% (dry basis) under the condition of 750 °C, 4 bar, [Ca]/[C]=1 and [H_2O]/[C]=2, while the CO_2 (2.7 vol%) was almost in-situ captured by the CaO sorbent. This study demonstrated that CaO could be as a substantially excellent CO_2 sorbent for the pressurized steam gasification of bituminous coal. With the presence of CaO, H_2-rich syngas was obtained at relatively low temperature and pressure comparing with conventional steam gasification of coal.