Influence of total pressures up to 80 bar on lignite char steam gasification using the KIVAN drop tube reactor

This study investigated the effects of total pressure of up to 80 bar on the gasification kinetics of lignite char under steam and established a kinetic model to predict reaction rates based on temperature, partial pressure and total pressure. Experimental data were collected from a pressurized drop tube furnace (KIVAN) at temperatures of 900–1050 °C, partial pressures of 5–20 bar, and total pressures of 20–80 bar, and compared with high-pressure thermobalance (TGA) experiments. Using the Random Pore Model (RPM) with the Arrhenius equation and the power law, kinetic parameters (E<inf>A</inf>, k<inf>0</inf>, n, Ψ) were derived. Both TGA (fixed bed) and KIVAN (entrained-flow) showed increased conversion and reaction rates with rising temperatures and H<inf>2</inf>O partial pressures, although the effect of temperature was found to be stronger. The gasification of HOK® under H<inf>2</inf>O was significantly slower in TGA than in KIVAN, approximately by a factor of 50. In KIVAN experiments, total pressure had little influence, with reaction rates remaining unaffected by total pressure variations. In contrast, TGA results showed a negative correlation due to heat and mass transfer limitations and inhibition. An overall kinetic with the kinetic parameters E<inf>A</inf> = 180 kJ/mol, k<inf>0</inf> = 2.18 × 10⁶ 1/s·barⁿ, n = 0.30 and Ψ = 2.0 was determined for the feedstock HOK® under the operating conditions investigated (p ≤ 80 bar, p<inf>H2O</inf> < 20 bar, T < 1050 °C). This kinetic model captured the experimental data with less than 5% error, validating intrinsic equations independent of total pressure for KIVAN.