Morphological Characteristics of Chars Obtained from Low-Temperature Pyrolysis of Pulverized Lignite

Staged coal conversion, with pyrolysis as its foundation, is one clean and effective coal usage technology. In this study, the structural and morphological characteristics of Ximeng lignite chars obtained from low-temperature pyrolysis during preheating in staged coal conversion are studied. The pulverized lignite was pyrolyzed under N-2 in a temperature range of 300-700 degrees C. Sieve analysis was used to investigate changes in char particle size. N-2 adsorption/desorption, and a scanning electron microscope (SEM) and Fourier transform infrared ( FTIR) spectroscopy were used to investigate changes in pore structure, surface morphology, and chemical structure of the char particles. The mechanisms of changes in particle size are discussed. Results suggest that the char particles have the trend of being smaller with increasing pyrolysis temperature. Changes in particle size, pore structure, and chemical structure at temperatures above 500 degrees C are more significant than those below 500 degrees C as a result of greater extent of pyrolysis and more vigorous condensation reactions at high temperatures. Specific surface area and pore volume increase with increasing pyrolysis temperature. More micropores are developed, and the number of mesopores with an average size smaller than 10 nm decreases as the temperature ranges up to 500 degrees C. Moreover, when the pyrolysis temperature increases above 500 degrees C, the specific surface area and pore volume increase sharply as a result of large number of pores and wide pore-size distribution. FTIR analysis shows that the aromaticity of char increases oxygen-containing functional groups, and aliphatic structures decrease as the pyrolysis temperature increases. (C) 2018 American Society of Civil Engineers.