Fine silica from included quartz in pulverized-coal combustion

The Effect of Pressure on Ash Formation during Pulverized Coal Combustion

“…Large ash particles (>2 μm) correspond to ash resulting from mechanisms which include coal or char fragmentation, structural disintegration of the char, − coalescence of ash on the surface of a char particle or within the particle, ,− fragmentation of minerals due to inorganic reaction, ,, shedding of ash particles from the surface of chars during combustion, ,, and ash cenosphere formation . Fine ash particles (<2 μm), result from mechanisms that include vaporization, condensation and aggregation of volatile ash components, ,,,− chemical reaction of mineral grains, , convective transport of organically bound and possibly small-grained inorganic material away from coal particle during coal devolatilization, fragmentation of coal and char particles and excluded minerals due to thermal shock, ,, rapid evolution of gases during mineral decomposition, secondary fragmentation of char particles that produces very fine ash particle, ,, and ash cenosphere breakage to produce fine particles. , …”

“…However, char fragmentation occurs during coal combustion so that one coal particle may produce more than one ash particle. Char structure is believed to be a key parameter determining the char fragmentation and ash coalescence behavior. ,,, The combustion of synthetic char indicated that the macroporosity of the char is the key parameter when determining char fragmentation behavior under diffusion-controlled conditions . The results show macroporous Spherocarb doped with sodium silicate gave 75 ash particles greater that 1 μm in diameter per char particle, while nonmacroporous sucrose/carbon black char doped with sodium silicate yielded only 1 ash particle per char particle.…”

“…Mitchell 6 indicated that the fragmentation of synthetic char during burnout is percolative in nature, and fragmentation of char particles during devolatilisation is also percolative, with the extent of fragmentation increasing with coal volatile yield. It was also found that the fine silica present in coal particles transfers into a fine silica ash particle as a result of char fragmentation rather than fume formation …”

“…It was also found that the fine silica present in coal particles transfers into a fine silica ash particle as a result of char fragmentation rather than fume formation. 19 Char particles of different structural and morphological properties were also found to exhibit different fragmentation behavior, burnout history, and ash formation mechanisms. 7 Highly porous char particles fragment extensively and are burnt out during the early or middle combustion stages, producing fine ash particles.…”

Ash Liberation from Included Minerals during Combustion of Pulverized Coal: The Relationship with Char Structure and Burnout

“…The large size ash particles (>2 μm) are formed by mechanisms such as coal or char fragmentation and the structural disintegration of char, − coalescence of ash on the surface of a char particle or within a char particle, ,, fragmentation of minerals due to inorganic reaction, ,, shedding of ash particles from the surface of chars during combustion, ,,, and cenosphere formation . The small size mode, size less than 2 μm, is referred to as fine ash particles (including fume) and results from mechanisms such as ash species vaporization, condensation, and aggregation, ,,,− chemical reaction of mineral grains to form fume particles, , convective transport of organically bound and possibly small-grained inorganic material away from the coal particle during coal devolatilization, thermal shock of coal particle or excluded minerals, ,, rapid evolution of gases during mineral decomposition, char secondary fragmentation, and busting of cenosphere to produce fine particles. , …”