Investigation of brown coal gasification residues using light microscopy

• Published in: Fuel (Guildford) 1996, Vol.75 (6), p.775-779
• Main Authors: Shibaoka, M., Ohtsuka, Y., Wornat, M.J., Thomas, C.G.
• Format: Article
• Language: English
• Subjects: Applied sciences; Brown coal; brown coal gasification; catalytic effects; Energy; Exact sciences and technology; Fuels; optical microscopy; Processing; Wood. Peat. Brown coal
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/0016-2361(95)00288-X

In order to determine the effect of calcium on the gasification behaviour of brown coal, raw and calcium-exchanged brown coal particles were subjected to partial steam gasification (55–81%) in a bench-scale fluidized bed reactor operating at selected temperatures in the range 598 to 802°C and at 1.1 MPa. Morphological and reflectance analyses of the collected gasification char residues reveal that calcium inhibits the development of plasticity during brown coal gasification. Examination of gasification residues of raw coal particles shows that preferential gasification occurs within the particle interior and the char particles display a wide distribution of reflectance values—a result of the broad range of residence times of particles in the fluidized bed reactor. In contrast, the calcium-loaded coal shows no preference for gasification within the particle interior and displays a narrower distribution of reflectance values. These observations stem from the catalytic effect of calcium, which speeds the gasification reaction, allowing char particles to quickly attain their ultimate reflectance values. Char reflectance appears to be a good indicator of the progress of the steam gasification and pyrolysis reactions: it increases as pyrolysis proceeds, signifying an increase in aromaticity of the residual char; it decreases as gasification proceeds, signifying a loss of carbon density.