Experimental and kinetics investigations of separated-gasification chemical looping combustion of char with an iron ore as the oxygen carrier

Abstract

This study presents the results obtained from a lab-scale two-stage reactor system to investigate the reaction characteristics and chemical kinetics of separated-gasification chemical looping combustion (SG-CLC) with a coal char as the fuel. The results have shown that there is huge mismatch of reaction rate between the slow gasification of char occurred in the gasification reactor (GR) and the rapid redox reactions of oxygen carrier (OC) and gasification products occurred in the reduction reactor (RR). Hence, the GR is recommended to be operated over 950 °C for a carbon conversion higher than 90% at the reaction time of 15 min, while 900 °C should be enough for the RR with an ideal gas combustion efficiency (>99%). Besides, the OC in SG-CLC shows favorable cycle stability, which can be attributed to the indirect mixing between the OC and char so that the attachment of potassium salt from the ash to the OC surface can be effectively avoided. In addition, the reaction kinetics models are determined to obtain the kinetics parameters of the char-fueled SG-CLC. The apparent activation energy is found to be 154.44, 149.79 and 161.42 kJ/mol for the first-order Kinetics Model, 2-D Contraction Model, and 3-D Contraction Model, respectively.