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03289 Sulfur capture under periodically changing oxidizing and reducing conditions in PFBC
04 By-products
related to fuels
oxygen complexes of higher thermal stability were left on the surface. Hence, the more thermally stable carbon-oxygen complexes are assumed to play an important role in the enhancement of the reaction rate by activating the neighbouring carbon atoms. 00103284 Reducing dioxin formation through coal co-firing Raghunathan, K. et al. Proc. Int. Conf. Incinerrrtion Therm. Treat. Technology, 1997, 373-378. It has already been established in past bench- and pilot-scale studies that the presence of SOz inhibits formation of polychlorinated dibenzo-pdioxins/ dibenzofurans (PCDD/F). The inhibition mechanism appears to be a combination of sulfur poisoning of the copper catalyst and gas-phase depletion of CIz through reaction with SOa. This leads to the possibility that co-firing waste combustors with high-sulfur coal can control PCDDiF formation. A commercial, densified, refuse-derived fuel (dRDF) was cofired with high-sulfur Illinois No. 6 coal in a 2 million Btuih (0.6 MW) stoker combustor. Additional parameters varied in the tests included dRDF feed rate, HCI concentration, sorbent injection, and flue gas quench rate. Flue gas was sampled for PCDD/F at 3 locations at nominal temperatures of 600, 300, and 150”. Most PCDD/F formation occurred at 600-300”, within -0.5 s. Results also showed that coal co-firing substantially inhibited PCDD/F formation. Injection of hydrated lime sorbent also effectively reduced PCDDIF formation. Other parameters affecting PCDDiF formation include combustion quality, dRDF feed rate, and HCI concentration. 00103285 Seasonality of carbon emissions from biomass burning in a Zambian savanna Hoffa, E. A. et al. J. Geophys. Res., /Amos./, 1999, 104. (Dl I), 1384113853. A study was carried out in Western Province, Zambia, into the seasonal trends in carbon emissions from savanna fires from early June to early August of 1996 (the early dry season). The objective was to determine the effect of fuel moisture content on combustion factors and modified combustion efficiency (the ratio of the molecular concentration of CO2 released to the molecular concentration of CO and CO*). Early dry season biomass burning may emit fewer emission products of complete combustion (e.g. COa) and more products of incomplete combustion (e.g. CO). Thirteen sites were burned between June and August of 1996, six in a Miombo woodland and seven in a Dambo grassland. Fires were lit in each ecosystem as the fuels dried so as to monitor changes in fire behaviour as the dry season progressed. Moisture content of green grass decreased from 127-69% in the Dambo and from 119-33% in the Miombo through the length of the study. Combustion factors (CF, the percentage of fuel consumed) increased from 44%-98% in the Dambo and from l-47% in the Miombo. Results indicate that combustion factors and combustion efficiency values follow seasonal trends correlating to metrics of vegetation moisture content, which may alter the type and quantity of carbon emissions. Global estimates of carbon flux in the subtropics and the amount of products of incomplete combustion per unit area burned should include incorporation of seasonal dynamics of the fire regime. Separation and characterization of the isotropic 00103286 phase and co-existing mesophase in thermally treated coal-tar pitches Blanco, C. Carbon, 2000, 38, (8), 1169-l 176. The isotropic and anisotropic phases which co-exist in thermally treated coal-tar pitches (lo-65 ~01% mesophase) were separated by pitch filtration. Optical microscopy showed that the filtrates were 100% isotropic, while the filtration residues had mesophase contents between 75 and 87 ~01%. The values of the characteristic parameters of the thermally treated pitches calculated from those of the fractions were in close agreement with the experimental values, indicating that the phases did not alter during the separation process. Comparison of the properties of the fractions showed that the anisotropic phases had a higher degree of polymerization than the isotropic phases, as reflected by the higher C/H atomic ratio, toluene and N-methyl-2-pyrrolidone insoluble content and carbon yield. Moreover, the effects of thermal treatment on the evolution of each phase were also studied. An increase in the degree of polymerization was observed in both phases. 00103287 Structure of melt-blown mesophase pitch-based carbon fiber Watanabe, F. et al. Carbon, 2000, 38, (5), 741-747. Mesophase pitch-based short carbon fibres prepared by the melt blown method exhibited diameters 6-16 pm distributed along the filament. The transverse surfaces of the thicker and thinner parts of the filament were very different. The thicker part showed a skin/core texture where very thick and long domains run parallel to the core while the thinner one had a PANAM texture where sets of straight domains run along the equator. Such unique shapes and textures were prepared through melt blown spinning and different extents of stabilization according to the diameter of the filament. Study on COP global recycling system M. et al. Greenhouse Gas Control Technol. Proc. Int. Conf. 4th, 1999, 433438. Edited by Ehasson B. et al. The ‘Project of chemical COz fixation and utilization using catalytic hydrogenation reaction’ has been developing a COz mitigation system since 1990. The concept of the system is comprised of the CO* separation/ 00/03288 Takeuchi,
370
Fuel and Energy Abstracts
November 2000
recovery via membrane separation in large amounts of CO2 emttted from stationary sources such as power stations, ironworks, chemical plants and so on, tanker transportation of the COz to a coast close to a desert, hydrogen production by water electrolysis generated by renewable energy, methanol synthesis from COz and hydrogen; and the transportation of the methanol produced to energy consumption site and/or as a chemical product. Analysis of conceptual designs and energy input for building plant, energy input for running plant has been conducted based on a case using this system for a 1000 MW power plant, followed by an evaluation of the material balance and energy balance. Results showed 467 tons/h of COz out of 778 tons/h of the total COz emissions could be recovered and 323 tons/h (2.4 million tons/y) of methanol could be produced. Energy efficiency, the COz reduction rate and the balance ratio of the energy of the system is respectively 38%, 40% and 2, assuming that (a) the primary energy was photovoltaic power generation, (b) the stationary COz emission source was a coal-fired power plant, and (c) the generation efficiency of the methanol power plant was 60%. It clearly revealed that this system would be effective to reduce COz emissions and to utilize renewable energy. Furthermore, on comparison with a methane convert system and a liquid hydrogen transportation system, this system displayed a higher energy efficiency. 00/03289 Sulfur capture under periodically changing oxidizing and reducing conditions in PFBC Zevenhoven, R. et al. Proc. Int. Con/Y Fluid. Bed Comhust., 1999, IOOO1018. A temperature optimum was found during in situ sulfur capture with a calcium-based sorbent in fluidized bed combustion (FBC) at atmospheric pressure and at -850”. The repeated decomposition of sulfated limestone during stages where the gas atmosphere surrounding the sorbent particle was not oxidizing but reducing and the identification of this explained thts maximum. Under pressurized (PFBC) conditions. an addttional aspect is the direct conversion of calcium carbonate (CaCOa) without the tntermediate calcium oxide (CaO) due to the partial pressure of carbon dioxide (COz). In this work it was evaluated how stable calcium sulfate (CaSOd) was in a gas atmosphere that periodically changed from oxidation to reduction and vice versa. Atmosphere as well as elevated pressures were considered. CaO or CaCO1, and/or calcium sulfide (CaS) was formed during the reduction stage. Using a pressurized thermogravimetric reactor (PTGR) a limestone was periodically sulfated under oxidizing conditions and decompound under reducmg conditions wtth carbon monoxide (CO), or with CO + Hz (hydrogen). Experiments at I and I5 bar were carried out, at temperatures from 850 to 950”, at CO and CO + Hz concentrations up to 4~01%. The experimental data were modelled using simple first order (parallel) reaction schemes that allowed for sorbent structure changes. This gave rate parameters for the sulfation and the decomposition reactions, and identified the decomposition products. It was found that I bar, CO in Hz gives a higher reductton of CaS04 than CO, at the same total concentratron The rate of decomposition increases faster with temperature than the sulfation, explaining the sulfatton efficiency maxtmum mentioned above. At I5 bar, a different picture was seen. The reductive decomposition rate as well as the sulfation rate were slower, with CO as well as CO with small amounts of Hz as the reducing species. There was a significant effect of the water which was present in the gas at higher concentrations than Hz_ 00103290 Surface functionality and porosity of activated carbons obtained from chemical activation of wood Benaddi, H. et al. Carbon, 2000, 38, (5), 6699674. Mixtures of wood with either phosphoric acid or diammonium hydrogen phosphate [(NH4)aHP04] were heated under nitrogen or steam/nitrogen flows at temperatures between 300 and 500°C. As a result of these processes, activated carbons with various pore size distribution and surface properties were obtained. The samples were characterised using potentiometric titration and sorption of nitrogen at its boiling point. The results showed the significant influence of the nature of the activating agent and the atmosphere on the final properties of the materials. It was demonstrated that steam inhibits the incorporation of heteroatoms into the carbon matrix. Activation of wood in the presence of phosphoric acid together with steam gives carbon of high surface area (-1800 mz/g) with well-developed mesoporosity and an almost neutral surface. 00103291 TG-FTIR and isotopic studies on coke formation on zeolite catalyst during methanol to gasoline process Bauer, F. et crl. Mtrroporou~ Mesoporous Mater.. 1999, 29, (l-2). 10991 15. A thermobalance system coupled with an IR spectrometer was used to investigate the removal of carbonaceous deposits formed during the conversion of methanol to hydrocarbons on zeolite H-ZSM-5. Using different carrier gases, the effect of thermal treatment increased in the order helium < hydrogen < propane. Up to 20% of the total amount of coke was released by the treatment with propane. The coke remaining on the zeolite is hydrogen-deficient in nature, as shown by temperatureprogrammed oxidation. The interaction of coke with molecular hydrogen was studied by H/D exchange. Furthermore, no evidence of carboxylate-like bonds between coke species and the zeolite surface was found from isotope labelling. 00103292 The effect of flow pattern on adsorption of dimethyl methyl phosphonate in activated carbon beds and canisters Suzin, Y. Carbon, 2000, 38, (8), 1129-l 133.
related to fuels
oxygen complexes of higher thermal stability were left on the surface. Hence, the more thermally stable carbon-oxygen complexes are assumed to play an important role in the enhancement of the reaction rate by activating the neighbouring carbon atoms. 00103284 Reducing dioxin formation through coal co-firing Raghunathan, K. et al. Proc. Int. Conf. Incinerrrtion Therm. Treat. Technology, 1997, 373-378. It has already been established in past bench- and pilot-scale studies that the presence of SOz inhibits formation of polychlorinated dibenzo-pdioxins/ dibenzofurans (PCDD/F). The inhibition mechanism appears to be a combination of sulfur poisoning of the copper catalyst and gas-phase depletion of CIz through reaction with SOa. This leads to the possibility that co-firing waste combustors with high-sulfur coal can control PCDDiF formation. A commercial, densified, refuse-derived fuel (dRDF) was cofired with high-sulfur Illinois No. 6 coal in a 2 million Btuih (0.6 MW) stoker combustor. Additional parameters varied in the tests included dRDF feed rate, HCI concentration, sorbent injection, and flue gas quench rate. Flue gas was sampled for PCDD/F at 3 locations at nominal temperatures of 600, 300, and 150”. Most PCDD/F formation occurred at 600-300”, within -0.5 s. Results also showed that coal co-firing substantially inhibited PCDD/F formation. Injection of hydrated lime sorbent also effectively reduced PCDDIF formation. Other parameters affecting PCDDiF formation include combustion quality, dRDF feed rate, and HCI concentration. 00103285 Seasonality of carbon emissions from biomass burning in a Zambian savanna Hoffa, E. A. et al. J. Geophys. Res., /Amos./, 1999, 104. (Dl I), 1384113853. A study was carried out in Western Province, Zambia, into the seasonal trends in carbon emissions from savanna fires from early June to early August of 1996 (the early dry season). The objective was to determine the effect of fuel moisture content on combustion factors and modified combustion efficiency (the ratio of the molecular concentration of CO2 released to the molecular concentration of CO and CO*). Early dry season biomass burning may emit fewer emission products of complete combustion (e.g. COa) and more products of incomplete combustion (e.g. CO). Thirteen sites were burned between June and August of 1996, six in a Miombo woodland and seven in a Dambo grassland. Fires were lit in each ecosystem as the fuels dried so as to monitor changes in fire behaviour as the dry season progressed. Moisture content of green grass decreased from 127-69% in the Dambo and from 119-33% in the Miombo through the length of the study. Combustion factors (CF, the percentage of fuel consumed) increased from 44%-98% in the Dambo and from l-47% in the Miombo. Results indicate that combustion factors and combustion efficiency values follow seasonal trends correlating to metrics of vegetation moisture content, which may alter the type and quantity of carbon emissions. Global estimates of carbon flux in the subtropics and the amount of products of incomplete combustion per unit area burned should include incorporation of seasonal dynamics of the fire regime. Separation and characterization of the isotropic 00103286 phase and co-existing mesophase in thermally treated coal-tar pitches Blanco, C. Carbon, 2000, 38, (8), 1169-l 176. The isotropic and anisotropic phases which co-exist in thermally treated coal-tar pitches (lo-65 ~01% mesophase) were separated by pitch filtration. Optical microscopy showed that the filtrates were 100% isotropic, while the filtration residues had mesophase contents between 75 and 87 ~01%. The values of the characteristic parameters of the thermally treated pitches calculated from those of the fractions were in close agreement with the experimental values, indicating that the phases did not alter during the separation process. Comparison of the properties of the fractions showed that the anisotropic phases had a higher degree of polymerization than the isotropic phases, as reflected by the higher C/H atomic ratio, toluene and N-methyl-2-pyrrolidone insoluble content and carbon yield. Moreover, the effects of thermal treatment on the evolution of each phase were also studied. An increase in the degree of polymerization was observed in both phases. 00103287 Structure of melt-blown mesophase pitch-based carbon fiber Watanabe, F. et al. Carbon, 2000, 38, (5), 741-747. Mesophase pitch-based short carbon fibres prepared by the melt blown method exhibited diameters 6-16 pm distributed along the filament. The transverse surfaces of the thicker and thinner parts of the filament were very different. The thicker part showed a skin/core texture where very thick and long domains run parallel to the core while the thinner one had a PANAM texture where sets of straight domains run along the equator. Such unique shapes and textures were prepared through melt blown spinning and different extents of stabilization according to the diameter of the filament. Study on COP global recycling system M. et al. Greenhouse Gas Control Technol. Proc. Int. Conf. 4th, 1999, 433438. Edited by Ehasson B. et al. The ‘Project of chemical COz fixation and utilization using catalytic hydrogenation reaction’ has been developing a COz mitigation system since 1990. The concept of the system is comprised of the CO* separation/ 00/03288 Takeuchi,
370
Fuel and Energy Abstracts
November 2000
recovery via membrane separation in large amounts of CO2 emttted from stationary sources such as power stations, ironworks, chemical plants and so on, tanker transportation of the COz to a coast close to a desert, hydrogen production by water electrolysis generated by renewable energy, methanol synthesis from COz and hydrogen; and the transportation of the methanol produced to energy consumption site and/or as a chemical product. Analysis of conceptual designs and energy input for building plant, energy input for running plant has been conducted based on a case using this system for a 1000 MW power plant, followed by an evaluation of the material balance and energy balance. Results showed 467 tons/h of COz out of 778 tons/h of the total COz emissions could be recovered and 323 tons/h (2.4 million tons/y) of methanol could be produced. Energy efficiency, the COz reduction rate and the balance ratio of the energy of the system is respectively 38%, 40% and 2, assuming that (a) the primary energy was photovoltaic power generation, (b) the stationary COz emission source was a coal-fired power plant, and (c) the generation efficiency of the methanol power plant was 60%. It clearly revealed that this system would be effective to reduce COz emissions and to utilize renewable energy. Furthermore, on comparison with a methane convert system and a liquid hydrogen transportation system, this system displayed a higher energy efficiency. 00/03289 Sulfur capture under periodically changing oxidizing and reducing conditions in PFBC Zevenhoven, R. et al. Proc. Int. Con/Y Fluid. Bed Comhust., 1999, IOOO1018. A temperature optimum was found during in situ sulfur capture with a calcium-based sorbent in fluidized bed combustion (FBC) at atmospheric pressure and at -850”. The repeated decomposition of sulfated limestone during stages where the gas atmosphere surrounding the sorbent particle was not oxidizing but reducing and the identification of this explained thts maximum. Under pressurized (PFBC) conditions. an addttional aspect is the direct conversion of calcium carbonate (CaCOa) without the tntermediate calcium oxide (CaO) due to the partial pressure of carbon dioxide (COz). In this work it was evaluated how stable calcium sulfate (CaSOd) was in a gas atmosphere that periodically changed from oxidation to reduction and vice versa. Atmosphere as well as elevated pressures were considered. CaO or CaCO1, and/or calcium sulfide (CaS) was formed during the reduction stage. Using a pressurized thermogravimetric reactor (PTGR) a limestone was periodically sulfated under oxidizing conditions and decompound under reducmg conditions wtth carbon monoxide (CO), or with CO + Hz (hydrogen). Experiments at I and I5 bar were carried out, at temperatures from 850 to 950”, at CO and CO + Hz concentrations up to 4~01%. The experimental data were modelled using simple first order (parallel) reaction schemes that allowed for sorbent structure changes. This gave rate parameters for the sulfation and the decomposition reactions, and identified the decomposition products. It was found that I bar, CO in Hz gives a higher reductton of CaS04 than CO, at the same total concentratron The rate of decomposition increases faster with temperature than the sulfation, explaining the sulfatton efficiency maxtmum mentioned above. At I5 bar, a different picture was seen. The reductive decomposition rate as well as the sulfation rate were slower, with CO as well as CO with small amounts of Hz as the reducing species. There was a significant effect of the water which was present in the gas at higher concentrations than Hz_ 00103290 Surface functionality and porosity of activated carbons obtained from chemical activation of wood Benaddi, H. et al. Carbon, 2000, 38, (5), 6699674. Mixtures of wood with either phosphoric acid or diammonium hydrogen phosphate [(NH4)aHP04] were heated under nitrogen or steam/nitrogen flows at temperatures between 300 and 500°C. As a result of these processes, activated carbons with various pore size distribution and surface properties were obtained. The samples were characterised using potentiometric titration and sorption of nitrogen at its boiling point. The results showed the significant influence of the nature of the activating agent and the atmosphere on the final properties of the materials. It was demonstrated that steam inhibits the incorporation of heteroatoms into the carbon matrix. Activation of wood in the presence of phosphoric acid together with steam gives carbon of high surface area (-1800 mz/g) with well-developed mesoporosity and an almost neutral surface. 00103291 TG-FTIR and isotopic studies on coke formation on zeolite catalyst during methanol to gasoline process Bauer, F. et crl. Mtrroporou~ Mesoporous Mater.. 1999, 29, (l-2). 10991 15. A thermobalance system coupled with an IR spectrometer was used to investigate the removal of carbonaceous deposits formed during the conversion of methanol to hydrocarbons on zeolite H-ZSM-5. Using different carrier gases, the effect of thermal treatment increased in the order helium < hydrogen < propane. Up to 20% of the total amount of coke was released by the treatment with propane. The coke remaining on the zeolite is hydrogen-deficient in nature, as shown by temperatureprogrammed oxidation. The interaction of coke with molecular hydrogen was studied by H/D exchange. Furthermore, no evidence of carboxylate-like bonds between coke species and the zeolite surface was found from isotope labelling. 00103292 The effect of flow pattern on adsorption of dimethyl methyl phosphonate in activated carbon beds and canisters Suzin, Y. Carbon, 2000, 38, (8), 1129-l 133.