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03916 Gas diffusion through the ash layer of coal particles during the combustion process
09
Combustion
(burners, combustion
systems)
95103915 Fractal and projected structure properties of soot aggregates Koylu, U. 0. et al., Combusrion & Flame, Mar. 1995, 100, (4), 621-633. The structure of soot aggregates was investigated, emphasizing the fractal properties as well as the relationships between the properties of actual and projected soot images. This information was developed by considering numerically simulated soot aggregates based on cluster-cluster aggregation as well as measured soot a gregates based on thermophoretic sampling and analysis by transmission ef ectron microscopy of soot for a variety of fuels (acetylene, propylene, ethylene, and propane) and both laminar and turbulent diffusion flame conditions. Gas diffusion through the ash layer of coal parti95103916 cles during the combustion process Yan, J. er al., Gongcheng Rewuli Xuebao, 1994, 15, (3), 341-344. (In Chinese) Describes gas diffusion throu h the ash layer on coal articles during combustion. A measurement met f od was proposed whrc.g can be used in the design studies of low-grade coal-fired flutdized-bed boilers. High temperature desulfurizatlon using fine sor95103917 bent particles under boiler injection conditions Ye, 2. et al., Fuel, May 1995, 74, (5), 743-750. The high temperature reaction of SO, and CaO was investigated in three reactors: a thermogravimetric reactor (TGA), a volumetric reactor and an entrained flow reactron. Several natural limestones with su er fine particles were used as sorbents. It was found that the reaction coul ct)be well characterized by a two-stage process. The initial stage was very fast and lasted about 0.1-0.4s. The chemical kinetics of the reaction were studied and modelled. In addition to other parameters, such as particle size and Braunauer-Emmett-Teller surface area, the pore volume located in the larger pores (~5.0 nm) was found to contribute somewhat to the high SO, removal and CaO conversion. At Ca/S=2 the SO, removal was more than 90%. 95103916 Ignition and combustion proper ies of pulverized coal suspended in iaminar upward flow unde d high heating rate condition Taniguchi, M. et al., Kagaku Kogaku Ronbunshu, 1994, 20, (6), 834-842. (In Japanese) Descrrbes observations of ignition and combustion behaviours for pulverized coal particles which were suspended in a laminar upward flow and heated by a single-pulse Nd:YAG laser to achieve surface temperature increases of approximately lo6 K/s. High-speed video observations revealed that brtuminous coal particles ignited heterogeneously l-2 ms after the laser ulse operation; this was followeed by the evolution of volatile materra,P s and their combustion in the gas phase. 95103919 Ignition problems In scramjet testing Mitani, T. Comb&on & Flame, May 1995, 101, (3), 347-359: Ignition of H, in heated air containing H,O radicals, and dust was investigated for scramjet testing. Using a reduced kinetit model for H,-0, sysiems, the effects of H$ a,nd radicals in nozzles are discussed in relatl’on- to engine testing with vrtratron heaters. Analysis using linearized rate-equations suggested that the addition of 0 atoms was 1.5 times more effective than the addition of H atoms for ignition. This result can be applied to the problem of premature ignition caused by residual radicals and to plasma-jet igniters. Thermal and chemical effects of dust, inevitable in storage air heaters, were studied next. The inhibition of ignition by dust may result, if the mass fraction of dust becomes IO--‘. 95103920 Images of the two-dimensional field and temperature gradients to quantify mixing rates within a non-premixed turbulent jet flame Everest, D. A. et al., Combustion & Flame, Apr. 1995, 101, (l), 58-68. The two-dimensional structure of the instantaneous temperature field and the temperature gradients were imaged in a turbulent iet flame using Planar Rayleigh ScatterTng. Two types of regions are observed: thin therm;1 layers in which temperature gradients are large and in which intense thermal mixing occurs, and broad homogeneous thermal zones in which temperature gradients are negligible. Many of the thermal gradient layers appear to be created by vortex motions, since the thin layers are parallel and are rolled up into spiral-shaped patterns. Flame-vortex interactions are shown which result in local flame extinction, and in some cases the vortices appear to penetrate through the viscous flame gases in the radial direction. An In-depth evaluation ofcombustion oerformance 95103921 predictors of aviation fuels sooting tendencies ’ Pande, S. G. and Hardy, D. R. Energy & Fuels, May-Jun. 1995, 9, (3) 448-457. The capabilities of combustion performance predictors to reliably predict the sooting tendencies of aviation fuels in jet combustion were evaluated. The test matrix included two primary fuel sets which were representative of current and future aviation fuels and combustor data, which consisted of radiation and soot data from two different combustors at specific levels of operation.
280
Fuel and Energy Abstracts
July 1995
95103922 The influence of air staging in the reduction of SO, by limestone in a fluldized bed combustor Khan, W. Z. and Gibbs, B. M. Fuel, Jun. 1995, 74, (6), 800-805. To meet the legislation on limiting NO,and SO, emission from large combustion plants, SO emissions may need to be reduced by about 6070%. The authors’ technique for achieving significant reduction in SO, emissions from combustion systems burning large coals utilizes limestone for in situ reduction of SO, in fluidized bed combustors. A recent technique for reducing NO, emissions combines staged combustion with ammonia injection. However, concern has arisen about the effect of low primary air:coal ratio, and hence low bed oxygen levels, on the rate of reaction between calcined limestone and SO, The naoer reoorts on the significance of air-staging on the reductions of‘SG, e&&ions 6y limestone in a fluidized bed combustor.
95103923 Influence of pressure on pyrolysis of coal Hill, R. J. er al., ACS Symp. Ser., 1994, 57b, 161-193. Discusses the influence of pressure on the gas, liquid and solid products of coal nvrolvsis. The startinn coal was Illinois No.6. a hinh volatile bitumi*,,,=‘,&t ‘,h+~;*~~ Ltie Argonne premium coal cofiection. Dry, confined pyrolysis was performed m sealed gold tubes at 300 and 340” and pressures ranging from 70 to 2000 bars for 72 h. Results show the rates of gas and liquid product generation and solid maturation are influenced by pressure.
95403924 Isothermal detonation Ershov, A. P. Combustion & Flame, May 1995, 101, (3) 339-346. A simple model of the fast convective waves in porous high explosives is proposed. The movement of the solid phase is neglected, and only gas phase equations are considered. The burning solid grains supply the gas influx into the pore space and produce considerable drag for the gas flow. Under realistic assumptions, the combustion zone is shown to be approximately isothermal. As a result, the energy equation can be avoided and the analysis becomes much simpler. The existence of stationary ChapmanJouget waves is shown. The Chapman-Jouget condition involves the isothermal sound velocity. Results agree qualitatively with the experimental data. The model is interesting as a limiting case of nonideal detonation with high momentum losses.
Kinetic modeling and sensitivity analysis for 95103925 B/H/O/C/F combination systems Brown. R. C. er al., Combusrion & Flame, Mav 1995. 101. (31 221-238. A kinetic model is presented to describe the high-temperature;.gas-phase B/H/O/C/F chemistry associated with fluoroamino/nitroamino/B(s) mixtures. The results of thermodynamic constant temperature and pressure calculations for a prototypical fluoroamino/nitroamino-based oxidrzer and solid boron are oresented to characterize the eauilibrium sneciation. Kev gas-phase reactants are selected and a reaction mechani’sm describing potential reaction pathways is formulated. Rate parameters for elementary reactions were obtained from published experimental/theoretical data or estimated using transition state arguments and scaling relations. 95103926 Laser ignition of levitated char particles Wong, B. A. et al., Energy & Fuels, May-Jun. 1995, 9, (3), 484-492. The temperature history of a char particle that was heated by a carbon dioxide laser to the ignition point was studied in the electrodynamic balante. The ignition characteristics of char articles are an important part of the overall coal combustion process, an B the aim of the research m this area is to improve efficiency and minimize waste products and pollution in current combustors. The exoeriments were conducted usine 158-210 micron diameter Spherocarb Garticles, and 200-300 micron diaketer char particles from a bituminous coal. Individual charged char particles were suspended in the electrodynamic balance and heated by a 420 ms pulse of radiation from a CO, laser at a heating rate of approximately 4.5 X 10’ K/s The temperature of the particle was measured with an optical pyrometer. A light scattering study of coal combustion in a 95103927 drop tube furnace Card, J. B. and Jones, A. R. Proc. 2nd Int. Symp. Environ. Biotechnol., Inst, of Chemical Eng., Rugby, UK, 1994, 2, 550-552. A light scattering technique originally reported by J. Card and A. Jones (1991) to discriminate betwen coal and fly ash in ash also operated successfully in real combustion situations. Further, the transition from coal to ash can be followed continuously, resulting in monitoring of combustion rates. Low-NO, combustion technology in pulverized coal 95103928 combustion Makino, H. and Kimoto, M. Kagaku Kogaku Ronbunshu, 1994, 20, (6), 747-754. (In Japanese) The concept of low-NOI combustion was introduced, and trends in research and development m this field were discussed, especially focusing on a method that used low-air-ratio combustion near the burner, and an intensification of the reduction flame.
Combustion
(burners, combustion
systems)
95103915 Fractal and projected structure properties of soot aggregates Koylu, U. 0. et al., Combusrion & Flame, Mar. 1995, 100, (4), 621-633. The structure of soot aggregates was investigated, emphasizing the fractal properties as well as the relationships between the properties of actual and projected soot images. This information was developed by considering numerically simulated soot aggregates based on cluster-cluster aggregation as well as measured soot a gregates based on thermophoretic sampling and analysis by transmission ef ectron microscopy of soot for a variety of fuels (acetylene, propylene, ethylene, and propane) and both laminar and turbulent diffusion flame conditions. Gas diffusion through the ash layer of coal parti95103916 cles during the combustion process Yan, J. er al., Gongcheng Rewuli Xuebao, 1994, 15, (3), 341-344. (In Chinese) Describes gas diffusion throu h the ash layer on coal articles during combustion. A measurement met f od was proposed whrc.g can be used in the design studies of low-grade coal-fired flutdized-bed boilers. High temperature desulfurizatlon using fine sor95103917 bent particles under boiler injection conditions Ye, 2. et al., Fuel, May 1995, 74, (5), 743-750. The high temperature reaction of SO, and CaO was investigated in three reactors: a thermogravimetric reactor (TGA), a volumetric reactor and an entrained flow reactron. Several natural limestones with su er fine particles were used as sorbents. It was found that the reaction coul ct)be well characterized by a two-stage process. The initial stage was very fast and lasted about 0.1-0.4s. The chemical kinetics of the reaction were studied and modelled. In addition to other parameters, such as particle size and Braunauer-Emmett-Teller surface area, the pore volume located in the larger pores (~5.0 nm) was found to contribute somewhat to the high SO, removal and CaO conversion. At Ca/S=2 the SO, removal was more than 90%. 95103916 Ignition and combustion proper ies of pulverized coal suspended in iaminar upward flow unde d high heating rate condition Taniguchi, M. et al., Kagaku Kogaku Ronbunshu, 1994, 20, (6), 834-842. (In Japanese) Descrrbes observations of ignition and combustion behaviours for pulverized coal particles which were suspended in a laminar upward flow and heated by a single-pulse Nd:YAG laser to achieve surface temperature increases of approximately lo6 K/s. High-speed video observations revealed that brtuminous coal particles ignited heterogeneously l-2 ms after the laser ulse operation; this was followeed by the evolution of volatile materra,P s and their combustion in the gas phase. 95103919 Ignition problems In scramjet testing Mitani, T. Comb&on & Flame, May 1995, 101, (3), 347-359: Ignition of H, in heated air containing H,O radicals, and dust was investigated for scramjet testing. Using a reduced kinetit model for H,-0, sysiems, the effects of H$ a,nd radicals in nozzles are discussed in relatl’on- to engine testing with vrtratron heaters. Analysis using linearized rate-equations suggested that the addition of 0 atoms was 1.5 times more effective than the addition of H atoms for ignition. This result can be applied to the problem of premature ignition caused by residual radicals and to plasma-jet igniters. Thermal and chemical effects of dust, inevitable in storage air heaters, were studied next. The inhibition of ignition by dust may result, if the mass fraction of dust becomes IO--‘. 95103920 Images of the two-dimensional field and temperature gradients to quantify mixing rates within a non-premixed turbulent jet flame Everest, D. A. et al., Combustion & Flame, Apr. 1995, 101, (l), 58-68. The two-dimensional structure of the instantaneous temperature field and the temperature gradients were imaged in a turbulent iet flame using Planar Rayleigh ScatterTng. Two types of regions are observed: thin therm;1 layers in which temperature gradients are large and in which intense thermal mixing occurs, and broad homogeneous thermal zones in which temperature gradients are negligible. Many of the thermal gradient layers appear to be created by vortex motions, since the thin layers are parallel and are rolled up into spiral-shaped patterns. Flame-vortex interactions are shown which result in local flame extinction, and in some cases the vortices appear to penetrate through the viscous flame gases in the radial direction. An In-depth evaluation ofcombustion oerformance 95103921 predictors of aviation fuels sooting tendencies ’ Pande, S. G. and Hardy, D. R. Energy & Fuels, May-Jun. 1995, 9, (3) 448-457. The capabilities of combustion performance predictors to reliably predict the sooting tendencies of aviation fuels in jet combustion were evaluated. The test matrix included two primary fuel sets which were representative of current and future aviation fuels and combustor data, which consisted of radiation and soot data from two different combustors at specific levels of operation.
280
Fuel and Energy Abstracts
July 1995
95103922 The influence of air staging in the reduction of SO, by limestone in a fluldized bed combustor Khan, W. Z. and Gibbs, B. M. Fuel, Jun. 1995, 74, (6), 800-805. To meet the legislation on limiting NO,and SO, emission from large combustion plants, SO emissions may need to be reduced by about 6070%. The authors’ technique for achieving significant reduction in SO, emissions from combustion systems burning large coals utilizes limestone for in situ reduction of SO, in fluidized bed combustors. A recent technique for reducing NO, emissions combines staged combustion with ammonia injection. However, concern has arisen about the effect of low primary air:coal ratio, and hence low bed oxygen levels, on the rate of reaction between calcined limestone and SO, The naoer reoorts on the significance of air-staging on the reductions of‘SG, e&&ions 6y limestone in a fluidized bed combustor.
95103923 Influence of pressure on pyrolysis of coal Hill, R. J. er al., ACS Symp. Ser., 1994, 57b, 161-193. Discusses the influence of pressure on the gas, liquid and solid products of coal nvrolvsis. The startinn coal was Illinois No.6. a hinh volatile bitumi*,,,=‘,&t ‘,h+~;*~~ Ltie Argonne premium coal cofiection. Dry, confined pyrolysis was performed m sealed gold tubes at 300 and 340” and pressures ranging from 70 to 2000 bars for 72 h. Results show the rates of gas and liquid product generation and solid maturation are influenced by pressure.
95403924 Isothermal detonation Ershov, A. P. Combustion & Flame, May 1995, 101, (3) 339-346. A simple model of the fast convective waves in porous high explosives is proposed. The movement of the solid phase is neglected, and only gas phase equations are considered. The burning solid grains supply the gas influx into the pore space and produce considerable drag for the gas flow. Under realistic assumptions, the combustion zone is shown to be approximately isothermal. As a result, the energy equation can be avoided and the analysis becomes much simpler. The existence of stationary ChapmanJouget waves is shown. The Chapman-Jouget condition involves the isothermal sound velocity. Results agree qualitatively with the experimental data. The model is interesting as a limiting case of nonideal detonation with high momentum losses.
Kinetic modeling and sensitivity analysis for 95103925 B/H/O/C/F combination systems Brown. R. C. er al., Combusrion & Flame, Mav 1995. 101. (31 221-238. A kinetic model is presented to describe the high-temperature;.gas-phase B/H/O/C/F chemistry associated with fluoroamino/nitroamino/B(s) mixtures. The results of thermodynamic constant temperature and pressure calculations for a prototypical fluoroamino/nitroamino-based oxidrzer and solid boron are oresented to characterize the eauilibrium sneciation. Kev gas-phase reactants are selected and a reaction mechani’sm describing potential reaction pathways is formulated. Rate parameters for elementary reactions were obtained from published experimental/theoretical data or estimated using transition state arguments and scaling relations. 95103926 Laser ignition of levitated char particles Wong, B. A. et al., Energy & Fuels, May-Jun. 1995, 9, (3), 484-492. The temperature history of a char particle that was heated by a carbon dioxide laser to the ignition point was studied in the electrodynamic balante. The ignition characteristics of char articles are an important part of the overall coal combustion process, an B the aim of the research m this area is to improve efficiency and minimize waste products and pollution in current combustors. The exoeriments were conducted usine 158-210 micron diameter Spherocarb Garticles, and 200-300 micron diaketer char particles from a bituminous coal. Individual charged char particles were suspended in the electrodynamic balance and heated by a 420 ms pulse of radiation from a CO, laser at a heating rate of approximately 4.5 X 10’ K/s The temperature of the particle was measured with an optical pyrometer. A light scattering study of coal combustion in a 95103927 drop tube furnace Card, J. B. and Jones, A. R. Proc. 2nd Int. Symp. Environ. Biotechnol., Inst, of Chemical Eng., Rugby, UK, 1994, 2, 550-552. A light scattering technique originally reported by J. Card and A. Jones (1991) to discriminate betwen coal and fly ash in ash also operated successfully in real combustion situations. Further, the transition from coal to ash can be followed continuously, resulting in monitoring of combustion rates. Low-NO, combustion technology in pulverized coal 95103928 combustion Makino, H. and Kimoto, M. Kagaku Kogaku Ronbunshu, 1994, 20, (6), 747-754. (In Japanese) The concept of low-NOI combustion was introduced, and trends in research and development m this field were discussed, especially focusing on a method that used low-air-ratio combustion near the burner, and an intensification of the reduction flame.