Hurt, RH
1996
Nitrogen Release During Coal Combustion
Baxter, L.L.; Reginald, E.M.; Fletcher, T.H. and Hurt, R.H.
Energy & Fuels, 10:188-196. Funded by US Department of Energy/Sandia National Laboratories.
Experiments in entrained flow reactors at combustion temperatures are performed to resolve the rank dependence of nitrogen release on an elemental basis for a suite of 15 U.S. coals ranging from lignite to low-volatile bituminous. Data were obtained as a function of particle conversion, with overall mass loss up to 99% on a dry, ash-free basis. Nitrogen release rates are presented relative to both carbon loss and overall mass loss. During devolatilization, fractional nitrogen release from low-rank coals is much slower than fractional mass release and noticeably slower than fractional carbon release. As coal rank increases, fractional nitrogen release rate relative to that of carbon and mass increases, with fractional nitrogen release rates exceeding fractional mass and fractional carbon release rates during devolatilization for high-rank (low-volatile bituminous) coals. At the onset of combustion, nitrogen loss rates increase significantly. For all coals investigated, fractional nitrogen loss rates relative to those of mass and carbon pass through a maximum during the earliest stages of oxidation. The mechanism for generating this maximum is postulated to involve nascent thermal rupture of nitrogen-containing compounds and possible preferential oxidation of nitrogen sites. During later stages of oxidation, the fractional loss rate of nitrogen approaches that of carbon for all coals. Changes in the relative release rates of nitrogen compared to those of both overall mass and carbon during all stages of combustion are attributed to a combination of the chemical structure of coals, temperature histories during combustion, and char chemistry.
1993
Heat Transfer From a Molten Phase to an Immersed Coal Particle During Devolatilization
Hurt, R.H.; Fletcher, T.H. and Sampaio, R.S.
ASME Journal of Heat Transfer, 115:717-723, 1993. Funded by Sandia Technology Maturation Program.
In several development and commercial processes, coal particles come into direct contact with a high-temperature molten phase. These processes include molten carbonate coal gasification and bath smelting for the production of iron. Recently, real-time X-ray fluoroscopic images have been published that show volatile matter evolving rapidly from coal particles immersed in molten phases, displacing the surrounding melt and producing a periodic cycle of formation, rise, and detachment of gas cavities. The present work makes use of these observations to develop a model of heat transfer from the melt to particles undergoing gas evolution. The model is developed for the general case and applied to predict melt-particle heat transfer coefficients under conditions relevant to bath smelting processes. The model shows that the presence of the gas film can actually increase the overall heat transfer rate under certain conditions.
Hurt, RH
1996
Nitrogen Release During Coal Combustion
Baxter, L.L.; Reginald, E.M.; Fletcher, T.H. and Hurt, R.H.
Energy & Fuels, 10:188-196. Funded by US Department of Energy/Sandia National Laboratories.
Experiments in entrained flow reactors at combustion temperatures are performed to resolve the rank dependence of nitrogen release on an elemental basis for a suite of 15 U.S. coals ranging from lignite to low-volatile bituminous. Data were obtained as a function of particle conversion, with overall mass loss up to 99% on a dry, ash-free basis. Nitrogen release rates are presented relative to both carbon loss and overall mass loss. During devolatilization, fractional nitrogen release from low-rank coals is much slower than fractional mass release and noticeably slower than fractional carbon release. As coal rank increases, fractional nitrogen release rate relative to that of carbon and mass increases, with fractional nitrogen release rates exceeding fractional mass and fractional carbon release rates during devolatilization for high-rank (low-volatile bituminous) coals. At the onset of combustion, nitrogen loss rates increase significantly. For all coals investigated, fractional nitrogen loss rates relative to those of mass and carbon pass through a maximum during the earliest stages of oxidation. The mechanism for generating this maximum is postulated to involve nascent thermal rupture of nitrogen-containing compounds and possible preferential oxidation of nitrogen sites. During later stages of oxidation, the fractional loss rate of nitrogen approaches that of carbon for all coals. Changes in the relative release rates of nitrogen compared to those of both overall mass and carbon during all stages of combustion are attributed to a combination of the chemical structure of coals, temperature histories during combustion, and char chemistry.
1993
Heat Transfer From a Molten Phase to an Immersed Coal Particle During Devolatilization
Hurt, R.H.; Fletcher, T.H. and Sampaio, R.S.
ASME Journal of Heat Transfer, 115:717-723, 1993. Funded by Sandia Technology Maturation Program.
In several development and commercial processes, coal particles come into direct contact with a high-temperature molten phase. These processes include molten carbonate coal gasification and bath smelting for the production of iron. Recently, real-time X-ray fluoroscopic images have been published that show volatile matter evolving rapidly from coal particles immersed in molten phases, displacing the surrounding melt and producing a periodic cycle of formation, rise, and detachment of gas cavities. The present work makes use of these observations to develop a model of heat transfer from the melt to particles undergoing gas evolution. The model is developed for the general case and applied to predict melt-particle heat transfer coefficients under conditions relevant to bath smelting processes. The model shows that the presence of the gas film can actually increase the overall heat transfer rate under certain conditions.