Particle Morphology Evolution and Its Enhancement for Lignite Gasification in Supercritical Water

Supercritical water gasification is a promising technology for the clean and efficient conversion of lignite particles. The particle morphology evolution has not yet been investigated for its impact on gasification. We monitor the evolution of the sphericity (C-s) and local surface sharpness (sigma(p)*) of three-dimensional (3D) irregular lignite particles during gasification by 3D optical measurement. The particle morphology is found to mainly shift from structures with high sharpness (sigma(p)* > 0.10) to low sharpness (sigma(p)* < 0.10). High-sharpness structure decreases in the pyrolysis reaction, regenerates in the gasification reaction, and consumes at the end of the reaction. Local structure with high sharpness promotes particle conversion up to 86.21% due to the enhanced heat and mass transfer. The optimum particle morphology of C-s < 0.74 and size D-0 < 1.5 mm are identified, which yield the average mass conversion of around 79.12% without a catalyst. We obtain the reaction activation energy E-a = 17.20 +/- 6.45 kJmol(-1) under 550-650 degrees C while 162.70 +/- 8.42 kJmol(-1) under 650-750 degrees C from the particle mass evolution.