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01398 Nitric oxide destruction during coal and char oxidation under pulverized-coal combustion conditions
01 Solid fuels (preparation) of compounds. Infrared spectroscopic study revealed the release of easily removable sulfur compounds as the band intensities due to -S(O and -SO2 groups have declined considerably in their respective regions in the desulfurized coals. The degree of desulfurization is 28.5 wt% in the presence of naphthalene and 24.6 wt% in absence of naphthalene, both at 4 h and 50°C. The sulfur extrusion process is continuous and application of a first-order kinetic model produced specific rate constants of the desulfurization reaction in the two systems, at different temperatures, which falls in the range of (1.3-2.9)x10 -s s 1. The activation energy of the sulfur-loss1 reaction in the system containing naphthalene (26.8 kJ tool ) is about 12% lower than that of the system without naphthalene (30.6 kJ tool-l). The frequency factor of the sulfur removal reaction in the systems have been found to be in the range of 0.8-3.2 s 1, suggesting low amount of successful collisions and an associated type of reaction. The desulfurization reaction is nonspontaneous in nature, proceeds with the absorption of heat and there is reduction in the degree of disorderliness in the system as predicted by the transition state theory.
05/01395
Extent of lead in high sulphur Assam coals
Baruah, M. K. et al. Fuel Processing Technology, 2005, 86, (6), 731-734. This study has been undertaken to understand the precise nature of association of lead in high sulfur Assam coal. Sequential extraction of lead with ammonium acetate, HC1 and RuCI3 solutions have been carried out. RuC13 has been used as a suitable reagent for the extraction of lead. It is found that treatment of sample with CC14 increases the extraction of lead by RuC13 solution. The amount of lead in the coal studied varies between 43.2 and 50.4ppm. It has been found that lead is predominantly occurring in coals in association with organic matter and needs concerted attention to understand its bio-availability. The chemical principles involved therein are also discussed.
05/01396 Methane and carbon dioxide adsorptiondiffusion experiments on coal: upscaling and modeling Busch, A. et al. International Journal of Coal Geology, 2004, 60, (2-4), 151 168. Numerical modelling of the processes of CO2 storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO 2 and CH4 were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VRr=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to ~3 m m at temperatures of 45 and 32°C, using a volumetric experimental setup. CO2 sorption was consistently faster than CH4 sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than two with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions. Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO2 and CH4 that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated. Further, it was shown that an upscaling of the experimental and modelling results for CO2 and CH4 can be achieved by performing experiments on different grain size fractions under the same experimental conditions. In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.
05/01397 Microbial desulphurization of coal containing pyritic sulphur in a continuously operated bench scale coal slurry reactor Pandey, R. A. et al. Fuel, 2005, 84, (1), 81-87. Pre-combustion microbial desulfurization of coal containing total sulfur (3.90%) and pyritic sulfur (2.80%) has been evaluated in a coal slurry reactor. The coat slurry reactor operated at hydraulic retention time (HRT) of 96 h with a coal pulp density of 15 percent and remove 79 percent of pyritic sulfur and 76 percent of ash with an increase in the calorific value of coal from 4400 to 6800 kcal kg -1 at a pyritic load of 1.9 kg pyritic sulfur kg -1 MLSS d -1. The treated coal yield is 72 percent. The biochemical kinetic coefficients, viz. yield coefficient (Y) and decay coefficient (Kd) in the coal slurry reactor system are 0.178 and 0.007 d-l, respectively, while maximum growth rate (gm~×) and half saturation rate constant (Ks) are 0.025 h -1 and 0.220 g 1-~ as pyrite, respectively.
212
Fuel and Energy Abstracts
July 2005
05/01398 Nitric oxide destruction during coal and char oxidation under pulverized-coal combustion conditions Molina, A. et al. Combustion and Flame, 2004, 136, (3), 303 312. A modified drop-tube reactor that allows particle distribution over the reactor cross-sectional area, and oxidation of chars produced in situ, was used to study the conversion efficiency of char nitrogen to nitric oxide (c~ NO). The results confirm previous findings by other investigators that aNO decreases as the weight of char burned increases, a NO for coal was the same as (at 4% 02) or lower than (at 20% 02) that for an equal mass of char during oxidation. Since coal will yield approximately half its mass as fixed carbon, these results suggest that the local stoichiometry surrounding the particle is responsible for the observed reduction in a NO as sample size increases. The analysis of the exhaust gases showed increases in HCN concentration and a decrease in C O j C O ratio as sample size increased, suggesting that local stoichiometry influences c~ NO. Additional experiments showed that a NO decreased as the background NO concentration was increased, at rates that diminished as the oxygen concentration increased, independent of particle size. The steep reduction in NO production as the background NO concentration increased was explained by the destruction of NO in the gas phase.
05/01399
Pressurised flash drying of Yallourn lignite
Ross, D. et al. Fuel, 2005, 84, (1), 47-52. A previously developed 1D model of lignite drying for pulverized lignite feeding into a conventional pulverized fuel boiler during the coal milling process is applied to lignite in an entrained flow configuration at elevated pressure. A combustor fired with diesel and air was used to produce a flue gas at 800°C and 10 atm to flash dry Yallourn lignite at a nominal feed rate of 725 kg/h along a 50 m duct. A coal feeder arrangement was also developed which provides a simple positive feeding device for feeding against a back pressure. The feeder takes as an input coal which is nominally <50 m m and discharges it as a finely divided product with a mean particle size of approximately 1.01.5 mm. The comparison between model predictions and measured temperature profiles for the flue gas and final moisture content of the dried coal product showed excellent agreement. Coal moisture was reduced from 67 wt% to between 30 and 40 wt%, depending upon on the coal feed rate and particle size. The small variation in the final outlet temperature observed between the model and experimental results is due to heat losses from the exposed duct work to the environment.
05•01400 Separation of drying and devolatilization during conversion of solid fuels Thunman, H. et al. Combustion and Flame, 2004, 137, (1-2), 242-250. A drying number, Dr, which is in effect a Damk6hler number, is derived to account for the separation of the drying and devolatilization processes of a solid fuel particle. This number is a qualitative measure of the relative times for drying and devolatJlization. It is intended tbr fuels entering an environment that has a considerably higher temperature than its saturation temperature. The number relates the kinetic rate of devolatilizatiou to the rate of evaporation, which is controlled by heat transfer to an evaporation front. The information given by the drying number is useful for choosing an appropriate model for the drying and the devolatilization of a fuel particle. For example, if the drying number is small, drying and devolatilization can be modelled separately; if it is around unity, a more detailed description is needed; and if it is very high, simplifications can be introduced, because drying and devolatilization then follow each other, and the rate of conversion of moisture and volatiles in a moist particle is given by the rate of evaporation. Experiments confirm that the drying number provides this information.
05•01401 Studies of inorganics added to low-rank coals for catalytic gasification Domazetis, G. et al. Fuel Processing Technology, 2005, 86, (5), 463-486. Inorganic complexes were added to low-rank coals by step-wise pH adjustment of a mixture of inorganic solution and brown coal while avoiding the formation of precipitates. The nature and amounts of the added inorganic depend on the pH of the coal/solution mixture and concentration of inorganic salts. The amount of hydroxide added for high loading of iron to coal is consistent with added multinuclear complexes. Computer generated models of brown coal with multi-iron species account for observed OH/Fe ratios. X-ray photoelectron spectroscopy (XPS) data for these samples are consistent with multiiron species in coal. Computer molecular modelling of two brown coal models with added inorganics shows monodentate carboxyl coordination to metals is sterically favoured. Mononuclear Fe(III) with bidentate carboxyl coordination form distorted structures and are energetically unfavoured. Modelling indicates significant reductions in partial charges on metal centres, consistent with a redistribution of electron density on complexation. Low temperature pyrolysis of brown coals with added inorganics provides increased yields of gases, no detectable tar and lower char, compared with acid washed coals.
05/01395
Extent of lead in high sulphur Assam coals
Baruah, M. K. et al. Fuel Processing Technology, 2005, 86, (6), 731-734. This study has been undertaken to understand the precise nature of association of lead in high sulfur Assam coal. Sequential extraction of lead with ammonium acetate, HC1 and RuCI3 solutions have been carried out. RuC13 has been used as a suitable reagent for the extraction of lead. It is found that treatment of sample with CC14 increases the extraction of lead by RuC13 solution. The amount of lead in the coal studied varies between 43.2 and 50.4ppm. It has been found that lead is predominantly occurring in coals in association with organic matter and needs concerted attention to understand its bio-availability. The chemical principles involved therein are also discussed.
05/01396 Methane and carbon dioxide adsorptiondiffusion experiments on coal: upscaling and modeling Busch, A. et al. International Journal of Coal Geology, 2004, 60, (2-4), 151 168. Numerical modelling of the processes of CO2 storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO 2 and CH4 were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VRr=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to ~3 m m at temperatures of 45 and 32°C, using a volumetric experimental setup. CO2 sorption was consistently faster than CH4 sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than two with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions. Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO2 and CH4 that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated. Further, it was shown that an upscaling of the experimental and modelling results for CO2 and CH4 can be achieved by performing experiments on different grain size fractions under the same experimental conditions. In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.
05/01397 Microbial desulphurization of coal containing pyritic sulphur in a continuously operated bench scale coal slurry reactor Pandey, R. A. et al. Fuel, 2005, 84, (1), 81-87. Pre-combustion microbial desulfurization of coal containing total sulfur (3.90%) and pyritic sulfur (2.80%) has been evaluated in a coal slurry reactor. The coat slurry reactor operated at hydraulic retention time (HRT) of 96 h with a coal pulp density of 15 percent and remove 79 percent of pyritic sulfur and 76 percent of ash with an increase in the calorific value of coal from 4400 to 6800 kcal kg -1 at a pyritic load of 1.9 kg pyritic sulfur kg -1 MLSS d -1. The treated coal yield is 72 percent. The biochemical kinetic coefficients, viz. yield coefficient (Y) and decay coefficient (Kd) in the coal slurry reactor system are 0.178 and 0.007 d-l, respectively, while maximum growth rate (gm~×) and half saturation rate constant (Ks) are 0.025 h -1 and 0.220 g 1-~ as pyrite, respectively.
212
Fuel and Energy Abstracts
July 2005
05/01398 Nitric oxide destruction during coal and char oxidation under pulverized-coal combustion conditions Molina, A. et al. Combustion and Flame, 2004, 136, (3), 303 312. A modified drop-tube reactor that allows particle distribution over the reactor cross-sectional area, and oxidation of chars produced in situ, was used to study the conversion efficiency of char nitrogen to nitric oxide (c~ NO). The results confirm previous findings by other investigators that aNO decreases as the weight of char burned increases, a NO for coal was the same as (at 4% 02) or lower than (at 20% 02) that for an equal mass of char during oxidation. Since coal will yield approximately half its mass as fixed carbon, these results suggest that the local stoichiometry surrounding the particle is responsible for the observed reduction in a NO as sample size increases. The analysis of the exhaust gases showed increases in HCN concentration and a decrease in C O j C O ratio as sample size increased, suggesting that local stoichiometry influences c~ NO. Additional experiments showed that a NO decreased as the background NO concentration was increased, at rates that diminished as the oxygen concentration increased, independent of particle size. The steep reduction in NO production as the background NO concentration increased was explained by the destruction of NO in the gas phase.
05/01399
Pressurised flash drying of Yallourn lignite
Ross, D. et al. Fuel, 2005, 84, (1), 47-52. A previously developed 1D model of lignite drying for pulverized lignite feeding into a conventional pulverized fuel boiler during the coal milling process is applied to lignite in an entrained flow configuration at elevated pressure. A combustor fired with diesel and air was used to produce a flue gas at 800°C and 10 atm to flash dry Yallourn lignite at a nominal feed rate of 725 kg/h along a 50 m duct. A coal feeder arrangement was also developed which provides a simple positive feeding device for feeding against a back pressure. The feeder takes as an input coal which is nominally <50 m m and discharges it as a finely divided product with a mean particle size of approximately 1.01.5 mm. The comparison between model predictions and measured temperature profiles for the flue gas and final moisture content of the dried coal product showed excellent agreement. Coal moisture was reduced from 67 wt% to between 30 and 40 wt%, depending upon on the coal feed rate and particle size. The small variation in the final outlet temperature observed between the model and experimental results is due to heat losses from the exposed duct work to the environment.
05•01400 Separation of drying and devolatilization during conversion of solid fuels Thunman, H. et al. Combustion and Flame, 2004, 137, (1-2), 242-250. A drying number, Dr, which is in effect a Damk6hler number, is derived to account for the separation of the drying and devolatilization processes of a solid fuel particle. This number is a qualitative measure of the relative times for drying and devolatJlization. It is intended tbr fuels entering an environment that has a considerably higher temperature than its saturation temperature. The number relates the kinetic rate of devolatilizatiou to the rate of evaporation, which is controlled by heat transfer to an evaporation front. The information given by the drying number is useful for choosing an appropriate model for the drying and the devolatilization of a fuel particle. For example, if the drying number is small, drying and devolatilization can be modelled separately; if it is around unity, a more detailed description is needed; and if it is very high, simplifications can be introduced, because drying and devolatilization then follow each other, and the rate of conversion of moisture and volatiles in a moist particle is given by the rate of evaporation. Experiments confirm that the drying number provides this information.
05•01401 Studies of inorganics added to low-rank coals for catalytic gasification Domazetis, G. et al. Fuel Processing Technology, 2005, 86, (5), 463-486. Inorganic complexes were added to low-rank coals by step-wise pH adjustment of a mixture of inorganic solution and brown coal while avoiding the formation of precipitates. The nature and amounts of the added inorganic depend on the pH of the coal/solution mixture and concentration of inorganic salts. The amount of hydroxide added for high loading of iron to coal is consistent with added multinuclear complexes. Computer generated models of brown coal with multi-iron species account for observed OH/Fe ratios. X-ray photoelectron spectroscopy (XPS) data for these samples are consistent with multiiron species in coal. Computer molecular modelling of two brown coal models with added inorganics shows monodentate carboxyl coordination to metals is sterically favoured. Mononuclear Fe(III) with bidentate carboxyl coordination form distorted structures and are energetically unfavoured. Modelling indicates significant reductions in partial charges on metal centres, consistent with a redistribution of electron density on complexation. Low temperature pyrolysis of brown coals with added inorganics provides increased yields of gases, no detectable tar and lower char, compared with acid washed coals.