Lignite-char gasification mechanism in mixed atmospheres of steam and CO2 at different pressures

Gasification characteristics of lignite-char with steam, CO2 and their mixture in a pressurized fixed bed (PFB) reactor were investigated at different pressures (0.10 ~ 2.0 MPa, N2 as dilute gas). The results show that char-gasification mechanism in the mixture of steam and CO2 are connected with relative partial pressures of two reactant gases. A turning value of steam partial pressure is found in char gasification, when the steam partial pressure is lower than the value, the char gasification rate firstly increase and then drops with CO2 partial pressure increase; whereas, when the steam partial pressure is higher than the value, the increase of CO2 partial pressure results in char gasification rate decrease. The reaction mechanism of lignite-char gasification in the mixture of steam and CO2 is closely related to the total pressure: under lower pressures, it is consistent with the separate reactive site reaction mechanism; while under higher pressures, it approaches to the common reactive site reaction mechanism.