Kinetic Study of Subcritical Steam Gasification of Coal Using Calcium-Based Carbon Dioxide Sorbent

The subcritical steam gasification of coal was performed with a calcium-based CO2 sorbent (Ca(OH)2) in a laboratory-scale batch reactor to examine the gasification kinetics with respect to the effects of partial pressure of steam and coal quality. The study was intended to support the hydrogen production by a reaction-integrated novel gasification (HyPr-RING) process in which coal is gasified with subcritical steam in a fluidized bed containing Ca(OH)2. Conducting subcritical steam gasification at 600–727 °C and 3–20 MPa produced zero emissions of CO2 because the rate of CO2 sorption by Ca(OH)2 was faster than that of CO2 generation by gasification. The gasification reaction mechanism was represented by a parallel first-order reaction model of the components of volatiles and char in coal. Hydrogen was mainly produced via tar from volatiles. The optimal partial pressure of steam preferred for hydrogen generation was 3 MPa, rather than 20 MPa. More volatiles in coal increased hydrogen yield in the gasification, a trend that could be estimated by analysis of its kinetics.