Kinetics of Char and Catalyzed Char Gasification at High Steam Partial Pressures with or without H₂ for Chemical Looping Coal Combustion

Abstract

Effects of high H₂ and H₂O (steam) partial pressure (H₂ from 0 to 1.2 MPa, H₂O from 2 to 1.2 MPa) on gasification rates of coal char and Ca-loaded coal char were investigated by using a thermogravimetric apparatus with the temperature range 923 K to 1,173 K. The gasification rate increased rapidly as the H₂ partial pressure was reduced in the reaction gases. The presence of H₂ gas strongly inhibited the char steam gasification rate. However, the gasification rate of Ca-loaded coal char was much higher than that of coal char, and the inhibition by H₂ of the gasification rate was smaller for Ca-loaded coal char than for coal char. The Langmuir–Hinshelwood model was used to analyze the effects of the H₂O and H₂ partial pressures on char and Ca-loaded coal char gasification rates. The temperature-dependent activation energies k_a, k_b, and k_c in the Langmuir–Hinshelwood model were obtained from experimental data and were used to simulate gasification rates for char and Ca-loaded coal char over a wide range of temperatures and P_H2/P_H2O ratios. The effects of H₂ partial pressure were greater (smaller) for Ca-loaded coal char than for char at 1,173 K (1,023 K).