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SNCR processes for NOx reduction in coal-fired furnaces
16 Fuel science and technology (fundamental science, analysis, instrumentation) cycle. Numerical experiments show an improved energy cycle compared with the loading patterns generated by engineer expertise and genetic algorithms.
04/01596 CELLO: an advanced LBIC measurement technique for solar cell local characterization Carstensen, J. et al. Solar Energy Materials and Solar Cells, 2003, 76, (4), 599-611. An advanced light beam-induced current measurement for solar cell local characterization, called CELLO, has been developed and tested on mono- and multi-crystalline Si solar cells. A solar cell is illuminated at near 1.5 AM light intensity, and is additionally subjected to intensity modulated scanning local illumination by a focused IR-laser. The linear response (current or potential) of the solar cell is measured for various fixed global conditions (different preset voltage or current values) during scanning. A large number of independent data with high spatial resolution are obtained. Applying an advanced fitting procedure to these data yields a set of local parameters for each point on the solar cell. This gives information on the spatial distribution of the photo current, the series and shunt resistance, the lateral diffusion of minority carriers, the quality of the back surface field, and even allows the calculation of local I V curves. The theoretical and experimental approach to this technique will be discussed, and the applicability of this new solar cell characterization tool will be demonstrated.
04/01597 Change in viscosity of softening coal upon heating with its liquid content. Part h linear relationship between logarithm of viscosity and liquid fraction Hayashi, J.-I. et al. Fuel, 2003, 82, (t4), 1735-1741. A variable-force-loading needle penetrometry and a proton magnetic resonance analysis were performed for in situ measurements of shearrate-independent viscosity of softening coal pellet upon heating, 7, and the fraction of mobile hydrogen existing in the liquid phase, 0~h, respectively. During isothermal heating of the pellet at temperature in a range from 680 to 730 K, ~mh changed with time via a maximum while ~7 did inversely. At every temperature examined, the time for the maximum ~mh coincided with that for the minimum 71. This result qualitatively validated the experimental definition of the liquid fraction in the softening coal as a liquid/solid suspension by ~br~h- Further analysis of the results revealed that the logarithm of ~7, which changes in a rang e from 10 l° to 104 Pa s upon isothermal heating, is correlated linearly with the liquid fraction ranging from 0.1 to 0.5. For each of the pellets made of two different coals, it was found that the logarithm and ~mh varied being governed by a single linear relationship upon both isothermal heating and non-isothermal heating. Such a single relationship, which was valid over a temperature range from 600 to 800 K, suggested fairly small temperature dependency of the viscosity of liquid in the softening coal.
04•01598 Change in viscosity of softening coal upon heating with its liquid content, Part II, Examination of rheological property and phase structure of softening coal Hayashi, J.-I. et al. Fuel, 2003, 82, (14), 1743-1750. The phase structure of softening coal upon heating is discussed based on the relationship between the shear-rate-independent viscosity (r/) and the fraction of liquid (41) reported in the first part of this series paper, as well as results of previous studies on rheologieal property and physical structure of softening coal. Firstly, the existing models that assume softening coal to be a suspension of 'rigid' solid particles are examined focusing on their applicability to description of the observed of 1og(~7)-61 relationship. The examination reveals that none of the models can describe the particular features the log(~/)-~a relationship: linearity and insignificant sensitivity to temperature Apparent success of the existing models is attributed to problems such as no or inappropriate experimental definition of the liquid fraction as well as unsuitable estimation or measurement of the viscosity. Secondly, it is demonstrated that the linear logQ/)-~l relationship is explained best by considering that the softening coal is a suspension of 'deformable' solid. Thirdly, further examination of the new suspension model draws the following characteristics of the phase structure of the softening coal. The so-called plastic domain in the softening coal consists of the liquid phase, optically isotropic solid phase and anisotropic mesophaselike spherules. The isotropic solid phase and the anisotropic phase, both of which are detected as the solid by 1H-NMR, would have very similar viscosities so that their influences on the viscosity of the plastic domain are undistinguishable. The plastic domain is suspended with coarse grains of minerals and inert organics, while they are not responsible for the change in the viscosity of the whole softening coal upon heating. The viscosity is mainly a function of the solid/liquid fractions in the plastic domain.
04101599 Comparison of hypothetical LNG and fuel oil fires on water Lehr, W, and Simecek-Beatty, D. Journal of Hazardous Materials, 2004, 107, (1-2), 3-9.
Large spills of refined petroleum products have been an occasional occurrence over the past few decades. This has not been true for large spills of liquefied natural gas (LNG). This paper compares the likely similarities and differences between accidental releases from a ship of sizable quantities of these different hydrocarbon fuels, their subsequent spreading, and possible pool-fire behaviour. Quantitative estimates are made of the spread rate and maximum slick size, burn rate, and duration; effective thermal radiation; and subsequent soot generation.
04/01600 Complex permittivities and dielectric relaxation of granular activated carbons at microwave frequencies between 0,2 and 26 GHz Atwater, J. E. et al. Carbon, 2003, 41, (9), 1801 1807. Carbonaceous materials are amenable to microwave heating to varying degrees. The primary indicator of susceptibility is the complex permittivity (e*), of which the real component correlates with polarization and the imaginary term represents dielectric loss. For a given material, the complex permittivity is dependent upon both frequency and temperature. Here the complex permittivities of three activated carbons of diverse origin over the frequency range from 0.2 to 26 GHz were reported. Dielectric polarization-relaxation phenomena for these materials are also characterized. Measurements were made using a coaxial dielectric probe and vector network analyser based system across the temperature region between 22 and 190°C.
04/01601 Computational study of opposed-force-flow flame spread across propanol pools Kim, I. and Sirignano, W. A. Combustion and Flame, 2003, 132, (4), 611-627. Two-dimensional flame-spread across sub-flash-point propanol pools in opposed-forced airflow is investigated numerically for normal and zero gravities with finite-rate, one-step chemical kinetics, variable properties, and an adaptive finite-difference gridding scheme. Effects of air speed, liquid depth, and gravity on the characteristics of the flame-spread are examined with correct initial profiles for the gasphase velocity and the mass-fraction of fuel vapor before ignition. Some of the results are as follows: (1) 10-ram pools are deep enough to examine flame-spread rates on deep pools in the uniform regime and pulsation frequencies on deep pools in the pulsating regime; (2) the pseudo-uniform regime is found only in deep pools and not in shallow pools; (3) the effect of opposed-forced airflow on the flame-spread rate is different, depending on the regime for To, where To denotes the initial pool temperature. Effects of pool depth on the liquid phase are also investigated: there is only a surface-tension-driven flow in the liquid phase of shallow pools. Finally, the flame-spread regime is displayed as a function of initial pool temperature, air speed, pool depth, and gravity.
04/01602 Detailed modeling of hybrid reburn/SNCR processes for NOx reduction in coal-fired furnaces Hart, X. et al. Combustion and Flame, 2003, 132, (3), 37~386. Mechanism reduction has made the detailed kinetic modelling of combustion problems much easier; it also offers potential improvement of modelling accuracy and flexibility in comparison to global mechanisms. The present work applies mechanism reduction in conjunction with the CHEMKIN library and develops an automatic reduction programme code. Regarding the hybrid re-burn/selective non-catalytic reduction (SNCR) ('advanced re-burning') conditions in coal-fired furnaces and based on a full mechanism 'GADM98', a skeletal mechanism with 39 species, 105 reactions, and further a 10step/14-species reduced mechanism were established. The reduced mechanism was implemented into a 3D-combustion computational fluid dynamics (CFD) code. The eddy-dissipation-concept model was used to describe the influence of turbulence on the combustion chemistry. A large number of simulations for reburning and hybrid reburn/SNCR processes in a coal-fired reactor were executed; the predicted results were compared with experimental measurements. The reduced mechanism and the comprehensive modelling give quite satisfactory results over a wide range of mole ratios for /3 = [NH3]/ [NO] and air/fuel equivalence ratios Az in the reburn zone. From the modelling results, it was found that adding ammonia premixed with reburn fuel (CH4) effects no further reduction of NO× or even impairs the reduction efficiency compared to pure reburning, and in contrast, staged addition of ammonia downstream of the CH4 injection in the reburn zone provokes a significant further reduction of NOx over a wide range of parameters. According to the predictions, NOx-reduetion rates of 50-60% and of 70-80% can be achieved through pure reburning and hybrid reburn/SNCR approaches, respectively, at A2 = 0.95 and /3 = 1.5. Concerning the computational procedure, essential measures were taken to optimize convergence and computing time. The computing time with the present reduced mechanism is N2.5 times that with the traditional global mechanism for the same iteration number. Tabulation of the rate constants reduced the computing time of the reaction kinetics by ~50%.
Fuel and Energy Abstracts
May 2004 217
04/01596 CELLO: an advanced LBIC measurement technique for solar cell local characterization Carstensen, J. et al. Solar Energy Materials and Solar Cells, 2003, 76, (4), 599-611. An advanced light beam-induced current measurement for solar cell local characterization, called CELLO, has been developed and tested on mono- and multi-crystalline Si solar cells. A solar cell is illuminated at near 1.5 AM light intensity, and is additionally subjected to intensity modulated scanning local illumination by a focused IR-laser. The linear response (current or potential) of the solar cell is measured for various fixed global conditions (different preset voltage or current values) during scanning. A large number of independent data with high spatial resolution are obtained. Applying an advanced fitting procedure to these data yields a set of local parameters for each point on the solar cell. This gives information on the spatial distribution of the photo current, the series and shunt resistance, the lateral diffusion of minority carriers, the quality of the back surface field, and even allows the calculation of local I V curves. The theoretical and experimental approach to this technique will be discussed, and the applicability of this new solar cell characterization tool will be demonstrated.
04/01597 Change in viscosity of softening coal upon heating with its liquid content. Part h linear relationship between logarithm of viscosity and liquid fraction Hayashi, J.-I. et al. Fuel, 2003, 82, (t4), 1735-1741. A variable-force-loading needle penetrometry and a proton magnetic resonance analysis were performed for in situ measurements of shearrate-independent viscosity of softening coal pellet upon heating, 7, and the fraction of mobile hydrogen existing in the liquid phase, 0~h, respectively. During isothermal heating of the pellet at temperature in a range from 680 to 730 K, ~mh changed with time via a maximum while ~7 did inversely. At every temperature examined, the time for the maximum ~mh coincided with that for the minimum 71. This result qualitatively validated the experimental definition of the liquid fraction in the softening coal as a liquid/solid suspension by ~br~h- Further analysis of the results revealed that the logarithm of ~7, which changes in a rang e from 10 l° to 104 Pa s upon isothermal heating, is correlated linearly with the liquid fraction ranging from 0.1 to 0.5. For each of the pellets made of two different coals, it was found that the logarithm and ~mh varied being governed by a single linear relationship upon both isothermal heating and non-isothermal heating. Such a single relationship, which was valid over a temperature range from 600 to 800 K, suggested fairly small temperature dependency of the viscosity of liquid in the softening coal.
04•01598 Change in viscosity of softening coal upon heating with its liquid content, Part II, Examination of rheological property and phase structure of softening coal Hayashi, J.-I. et al. Fuel, 2003, 82, (14), 1743-1750. The phase structure of softening coal upon heating is discussed based on the relationship between the shear-rate-independent viscosity (r/) and the fraction of liquid (41) reported in the first part of this series paper, as well as results of previous studies on rheologieal property and physical structure of softening coal. Firstly, the existing models that assume softening coal to be a suspension of 'rigid' solid particles are examined focusing on their applicability to description of the observed of 1og(~7)-61 relationship. The examination reveals that none of the models can describe the particular features the log(~/)-~a relationship: linearity and insignificant sensitivity to temperature Apparent success of the existing models is attributed to problems such as no or inappropriate experimental definition of the liquid fraction as well as unsuitable estimation or measurement of the viscosity. Secondly, it is demonstrated that the linear logQ/)-~l relationship is explained best by considering that the softening coal is a suspension of 'deformable' solid. Thirdly, further examination of the new suspension model draws the following characteristics of the phase structure of the softening coal. The so-called plastic domain in the softening coal consists of the liquid phase, optically isotropic solid phase and anisotropic mesophaselike spherules. The isotropic solid phase and the anisotropic phase, both of which are detected as the solid by 1H-NMR, would have very similar viscosities so that their influences on the viscosity of the plastic domain are undistinguishable. The plastic domain is suspended with coarse grains of minerals and inert organics, while they are not responsible for the change in the viscosity of the whole softening coal upon heating. The viscosity is mainly a function of the solid/liquid fractions in the plastic domain.
04101599 Comparison of hypothetical LNG and fuel oil fires on water Lehr, W, and Simecek-Beatty, D. Journal of Hazardous Materials, 2004, 107, (1-2), 3-9.
Large spills of refined petroleum products have been an occasional occurrence over the past few decades. This has not been true for large spills of liquefied natural gas (LNG). This paper compares the likely similarities and differences between accidental releases from a ship of sizable quantities of these different hydrocarbon fuels, their subsequent spreading, and possible pool-fire behaviour. Quantitative estimates are made of the spread rate and maximum slick size, burn rate, and duration; effective thermal radiation; and subsequent soot generation.
04/01600 Complex permittivities and dielectric relaxation of granular activated carbons at microwave frequencies between 0,2 and 26 GHz Atwater, J. E. et al. Carbon, 2003, 41, (9), 1801 1807. Carbonaceous materials are amenable to microwave heating to varying degrees. The primary indicator of susceptibility is the complex permittivity (e*), of which the real component correlates with polarization and the imaginary term represents dielectric loss. For a given material, the complex permittivity is dependent upon both frequency and temperature. Here the complex permittivities of three activated carbons of diverse origin over the frequency range from 0.2 to 26 GHz were reported. Dielectric polarization-relaxation phenomena for these materials are also characterized. Measurements were made using a coaxial dielectric probe and vector network analyser based system across the temperature region between 22 and 190°C.
04/01601 Computational study of opposed-force-flow flame spread across propanol pools Kim, I. and Sirignano, W. A. Combustion and Flame, 2003, 132, (4), 611-627. Two-dimensional flame-spread across sub-flash-point propanol pools in opposed-forced airflow is investigated numerically for normal and zero gravities with finite-rate, one-step chemical kinetics, variable properties, and an adaptive finite-difference gridding scheme. Effects of air speed, liquid depth, and gravity on the characteristics of the flame-spread are examined with correct initial profiles for the gasphase velocity and the mass-fraction of fuel vapor before ignition. Some of the results are as follows: (1) 10-ram pools are deep enough to examine flame-spread rates on deep pools in the uniform regime and pulsation frequencies on deep pools in the pulsating regime; (2) the pseudo-uniform regime is found only in deep pools and not in shallow pools; (3) the effect of opposed-forced airflow on the flame-spread rate is different, depending on the regime for To, where To denotes the initial pool temperature. Effects of pool depth on the liquid phase are also investigated: there is only a surface-tension-driven flow in the liquid phase of shallow pools. Finally, the flame-spread regime is displayed as a function of initial pool temperature, air speed, pool depth, and gravity.
04/01602 Detailed modeling of hybrid reburn/SNCR processes for NOx reduction in coal-fired furnaces Hart, X. et al. Combustion and Flame, 2003, 132, (3), 37~386. Mechanism reduction has made the detailed kinetic modelling of combustion problems much easier; it also offers potential improvement of modelling accuracy and flexibility in comparison to global mechanisms. The present work applies mechanism reduction in conjunction with the CHEMKIN library and develops an automatic reduction programme code. Regarding the hybrid re-burn/selective non-catalytic reduction (SNCR) ('advanced re-burning') conditions in coal-fired furnaces and based on a full mechanism 'GADM98', a skeletal mechanism with 39 species, 105 reactions, and further a 10step/14-species reduced mechanism were established. The reduced mechanism was implemented into a 3D-combustion computational fluid dynamics (CFD) code. The eddy-dissipation-concept model was used to describe the influence of turbulence on the combustion chemistry. A large number of simulations for reburning and hybrid reburn/SNCR processes in a coal-fired reactor were executed; the predicted results were compared with experimental measurements. The reduced mechanism and the comprehensive modelling give quite satisfactory results over a wide range of mole ratios for /3 = [NH3]/ [NO] and air/fuel equivalence ratios Az in the reburn zone. From the modelling results, it was found that adding ammonia premixed with reburn fuel (CH4) effects no further reduction of NO× or even impairs the reduction efficiency compared to pure reburning, and in contrast, staged addition of ammonia downstream of the CH4 injection in the reburn zone provokes a significant further reduction of NOx over a wide range of parameters. According to the predictions, NOx-reduetion rates of 50-60% and of 70-80% can be achieved through pure reburning and hybrid reburn/SNCR approaches, respectively, at A2 = 0.95 and /3 = 1.5. Concerning the computational procedure, essential measures were taken to optimize convergence and computing time. The computing time with the present reduced mechanism is N2.5 times that with the traditional global mechanism for the same iteration number. Tabulation of the rate constants reduced the computing time of the reaction kinetics by ~50%.
Fuel and Energy Abstracts
May 2004 217