Catalytic gasification of Pakistani Lakhra and Thar lignite chars in steam gasification

The catalytic effects of different catalysts, i.e., 3%Ca, 5%Na-BL, and 3%Ca+5%Na-BL catalyst, on carbon conversion, gasification reaction rate constant, activation energy, and relative amount of harmful sulfur containing gases, were investigated by thermogravimetry in steam gasification under temperature 700°C to 900°C at ambient pressure for two Pakistani Lakhra (LKH) and Thar (THR) lignite chars. High carbon conversion can be obtained by direct gasification of both LKH and THR chars, but the gasification rate became much fast using BL catalyst. THR char with high ash content was easy to form some complex silicates during BL catalytic gasification, leading to a lower conversion than that of LKH char with low ash content. SO2 and H2S as sulfur-containing gases produced by char and BL itself in steam gasification can be captured by the existence of Ca mixed with BL, which is more effective at temperatures less than 900°C. The shrinking core model (SCM) can be considered as a better choice to correlate the relations between conversion and time and to estimate the reaction rate constant (k) under different temperatures. The reaction activation energy (Ea) and pre-exponential factor (A) were predicted based on Arrhenius equation. The reaction activation energy of 44.7 kJ/mol and 59.6 kJ/mol for LKH chars with BL+Ca and BL catalysts were much lower than 114.6 kJ/mol and 100.8 kJ/mol for THR chars with the same catalysts, respectively. They were also lower than 161.2 kJ/mol for LKH char and 124.8 kJ/mol for THR char without catalyst.