During heating and pyrolysis, the morphology and size of incipient char particles can be affected by softening, swelling, fragmentation. While fragmentation of non-swelling coal is well addressed in the literature, effects associated with swelling and softening are still scarcely understood and modeled. Under pulverized fuel-fired (PF) conditions, softening and swelling of fuel particles result in the formation of spherical and often hollow char particles. In fluidized bed conditions the presence of sand in proximity of the particles may lead to more complex phenomena. The present work attempts to investigate the behavior of different carbon rich fuels in Fluidized Bed: 1. Auguste Victoria bituminous coal (Coal); 2. a bitumen used in the cement industry (Bit); 3. a solid waste coming from the refinery industry with high metal content (RW). Tests have been carried out in a laboratory scale Fluidized Bed Reactor (40 mm id) at temperatures of 600-850 °C. Quartz sand of 200-300 ?m has been used for the bed, fluidized by a gas flow of N2 or N2/air with a superficial velocity of 0.4 m/s. The reactor was equipped by on line gas analysers. Single particles were fed from the top of the reactor and residues were collected by a basket. Coal particles had irregular shape and size of 2-4 mm. Bitumen particles were spheres of d=4-10 mm. RW particles were 10x10 mm squares. In the case of coal, the heavy/tarry species formed in the early pyrolysis stages entrap sand particles and lead to the formation of hollow aggregates. The size of the cavity is comparable with the initial particle diameter. The outer shell is larger than the original particle. Char combustion rate is slowed down by mass transfer of oxygen through the sand-enriched shell. Upon heating Bit particles undergo fast pyrolysis and the small char residue (20 %w), in presence of oxygen burns simultaneously to volatiles. RW upon pyrolysis generates large round particles, which enclose quartz sand and large cavities. Combustion of such agglomerates requires again much longer time than volatiles release due to mass transfer effects. The properties of the fuel which may be at the origin of the observed behavior are discussed.
On the plastic behavior of carbonaceous fuels in Fluidized Beds
2019-01-01
Abstract
During heating and pyrolysis, the morphology and size of incipient char particles can be affected by softening, swelling, fragmentation. While fragmentation of non-swelling coal is well addressed in the literature, effects associated with swelling and softening are still scarcely understood and modeled. Under pulverized fuel-fired (PF) conditions, softening and swelling of fuel particles result in the formation of spherical and often hollow char particles. In fluidized bed conditions the presence of sand in proximity of the particles may lead to more complex phenomena. The present work attempts to investigate the behavior of different carbon rich fuels in Fluidized Bed: 1. Auguste Victoria bituminous coal (Coal); 2. a bitumen used in the cement industry (Bit); 3. a solid waste coming from the refinery industry with high metal content (RW). Tests have been carried out in a laboratory scale Fluidized Bed Reactor (40 mm id) at temperatures of 600-850 °C. Quartz sand of 200-300 ?m has been used for the bed, fluidized by a gas flow of N2 or N2/air with a superficial velocity of 0.4 m/s. The reactor was equipped by on line gas analysers. Single particles were fed from the top of the reactor and residues were collected by a basket. Coal particles had irregular shape and size of 2-4 mm. Bitumen particles were spheres of d=4-10 mm. RW particles were 10x10 mm squares. In the case of coal, the heavy/tarry species formed in the early pyrolysis stages entrap sand particles and lead to the formation of hollow aggregates. The size of the cavity is comparable with the initial particle diameter. The outer shell is larger than the original particle. Char combustion rate is slowed down by mass transfer of oxygen through the sand-enriched shell. Upon heating Bit particles undergo fast pyrolysis and the small char residue (20 %w), in presence of oxygen burns simultaneously to volatiles. RW upon pyrolysis generates large round particles, which enclose quartz sand and large cavities. Combustion of such agglomerates requires again much longer time than volatiles release due to mass transfer effects. The properties of the fuel which may be at the origin of the observed behavior are discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
