| 1. |
- Davidsson, Kent, 1967, et al.
(författare)
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Potassium, chlorine, and sulfur in ash, particles, deposits, and corrosion during wood combustion in a circulating fluidized-bed boiler
- 2007
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 21:1, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the addition of chlorine and/or sulfur to the fuel on fly ash composition, deposit formation, and superheater corrosion has been studied during biomass combustion in a circulating fluidized-bed boiler. The chlorine (HCl (aq)) and sulfur (SO2 (g)) were added in proportions of relevance for the potassium chemistry. The composition of the bottom and the fly ashes was analyzed. Gas and particle measurements were performed downstream of the cyclone before the convection pass and the flue gas composition was recorded in the stack with a series of standard instruments and an FTIR analyzer. At the position downstream of the cyclone, a deposit probe was situated, simulating a superheater tube. Deposits on the probe and initial corrosion were examined. It is concluded that addition of sulfur and chlorine increases the formation of submicron particles leading to deposition of potassium sulfate and chloride. The results compare well with earlier work based on laboratory-scale experiments concerning effects of chlorine and sulfur on potassium chemistry.
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| 2. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
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Chlorine interactions with water ice studied by molecular beam techniques.
- 2006
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Ingår i: The journal of physical chemistry. B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:46, s. 23497-501
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of chlorine interactions with ice at temperatures between 103 and 165 K have been studied using molecular beam techniques. The Cl(2) trapping probability is found to be unity at thermal incident energies, and trapping is followed by rapid desorption. The residence time on the surface is less than 25 microg at temperatures above 135 K and approaches 1 s around 100 K. Rate constants for desorption are determined for temperatures below 135 K. The desorption kinetics follow the Arrhenius equation, and activation energies of 0.24 +/- 0.03 and 0.31 +/- 0.01 eV, with corresponding preexponential factors of 10(12.08+/-1.19) and 10(16.52+/-0.38) s(-1), are determined. At least two different Cl(2) binding sites are concluded to exist on the ice surface. The observed activation energies are likely to be the Cl(2)-ice binding energies for these states, and the Cl(2)-surface interactions are concluded to be stronger than earlier theoretical estimates. The surface coverage of Cl(2) on ice under stratospheric conditions is estimated to be negligible, in agreement with earlier work.
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| 3. |
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| 4. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of ammonia clusters studied by storage ring experiments
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:19, s. 194306-
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination of ammonia cluster ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for dissociative recombination of H+(NH3)(2), H+(NH3)(3), D+(ND3)(2), and D+(ND3)(3) in the collision energy range of 0.001-27 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 1000 K are calculated from the experimental data and compared with earlier results. The fragmentation patterns for the two ions H+(NH3)(2) and D+(ND3)(2) show no clear isotope effect. Dissociative recombination of X+(NX3)(2) (X=H or D) is dominated by the product channels 2NX(3)+X [0.95 +/- 0.02 for H+(NH3)(2) and 1.00 +/- 0.02 for D+(ND3)(2)]. Dissociative recombination of D+(ND3)(3) is dominated by the channels yielding three N-containing fragments (0.95 +/- 0.05).
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| 5. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of H+(H2O)3 and D+(D2O)3 water cluster ions with electrons: Cross sections and branching ratios
- 2007
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127, s. 194301-194309
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination (DR) of the water cluster ions H+(H2O)3 and D+(D2O)3 with electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, absolute DR cross sections have been measured for H+(H2O)3 in the energy range of 0.001–0.8 eV, and relative cross sections have been measured for D+(D2O)3 in the energy range of 0.001–1.0 eV. The DR cross sections for H+(H2O)3 are larger than previously observed for H+(H2O)n (n=1,2), which is in agreement with the previously observed trend indicating that the DR rate coefficient increases with size of the water cluster ion. Branching ratios have been determined for the dominating product channels. Dissociative recombination of H+(H2O)3 mainly results in the formation of 3H2O+H (probability of 0.95±0.05) and with a possible minor channel resulting in 2H2O+OH+H2 (0.05±0.05). The dominating channels for DR of D+(D2O)3 are 3D2O+D (0.88±0.03) and 2D2O+OD+D2 (0.09±0.02). The branching ratios are comparable to earlier DR results for H+(H2O)2 and D+(D2O)2, which gave 2X2O+X (X=H,D) with a probability of over 0.9.
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| 6. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Water Condensation on Graphite Studied by Elastic Helium Scattering and Molecular Dynamics Simulations
- 2007
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:42, s. 15258-15266
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Tidskriftsartikel (refereegranskat)abstract
- Formation of water/ice layers on graphite has been studied in the temperature range from 90 to 180 K by elastic helium scattering, light scattering, and molecular dynamics simulations. Combined helium- and light-scattering experiments show that an ice film that wets the graphite surface is formed at surface temperatures of 100-140 K, whereas three-dimensional ice structures are formed at 140-180 K. Desorption of adsorbed water molecules competes with water incorporation into the ice film, and the ice formation rate is strongly temperature dependent. At 150 K, ice-layer formation takes place at the same time scale as layer reconstruction, and its properties are sensitive to the water deposition rate. The experimental results are compared with kinetics models, and the Johnston-Mehl-Avrami-Kolmogorov model is concluded to well describe the ice-layer formation kinetics in the whole temperature range. Molecular dynamics simulations of water-cluster formation on graphite at 90-180 K show that water molecules and small clusters are highly mobile on the surface, which rapidly results in the nucleation of large and less mobile clusters on the surface. Clusters formed at low temperature tend to have the most molecules in direct contact with the uppermost graphite layer, while multilayer cluster structures are preferred at high temperatures. The results are discussed and compared with earlier studies of water ice formation on solid surfaces.
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| 7. |
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| 8. |
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| 9. |
- Gatari, Michael J, et al.
(författare)
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Inorganic and black carbon aerosol concentrations at a high altitude on Mt Kenya
- 2009
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Ingår i: X-Ray Spectrometry. - : Wiley. - 0049-8246 .- 1097-4539. ; 38:1, s. 26-36
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol samples were collected at an altitude of 3678 m on Mt Kenya in August 2001. A virtual impactor was used to collect particles in fine (aerodynamic diameter, da < 2.5 µm) and coarse (2.5 µm < da < 10 µm) size fractions. The samples were analyzed for particulate mass (PM), black carbon (BC) and 15 elements. The PM concentrations varied in the ranges 3.3 ± 1.1-7.8 ± 2.5 µg m-3 (in fine fraction) and 3.7 ± 1.2-9.6 ± 3.0 µg m-3 (in coarse fraction). The fine fraction was dominated by high concentrations of BC, S and K due to particles formed during biomass burning and sulfate particles from secondary processes in the atmosphere. The coarse fraction was dominated by high concentrations of Si, S, Cl, K, Ca and Fe indicative of the presence of soil dust particles. This was further verified by enrichment factors (EFs) calculated using the elemental content of the average crustal rock. Chemical mass balance (CMB) calculations indicated that the PM was largely attributable to biomass burning, mineral dust and sulfate, while contributions from anthropogenic sources were small. Source apportionment of elemental concentrations compared well with that of an earlier study on the southwestern slope of Mt Kenya, while PM and sulfate concentrations were comparable with those observed at high-altitude sites in North America and Europe. The observed concentrations were 5-50 times lower than those of urban Kenya.
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| 10. |
- Hak, Claudia S., 1976, et al.
(författare)
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A new approach to in-situ determination of roadside particle emission factors of individual vehicles under conventional driving conditions
- 2009
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 43:15, s. 2481-2488
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Tidskriftsartikel (refereegranskat)abstract
- A method for continuous on-road measurements of particle number emissions for both diesel- and petrol-fuelled vehicles is presented. The setup allows the determination of particle number emission factors on an individual vehicle basis by the simultaneous measurement of CO2 and particle concentrations. As an alternative to previous measurements on the kerbside, the sample is taken directly in the street, with the advantage of sampling in-situ within the exhaust plumes of passing vehicles, allowing the separation of the individual high-concentration plumes. The method was tested in two experiments that were conducted in the Gothenburg area. In the first study, which was performed at an urban roadside, we were able to determine particle emission factors from individual vehicles in a common car fleet passing the measurement site. The obtained emission factors were of the same order of magnitude (between 1.4 × 1012 and 1.8 × 1014 particles km−1) as values published in the recent literature for light duty vehicles. An additional on-road experiment was conducted at a rural road with four light duty reference vehicles (three of them petrol-powered and one diesel-powered) at driving speeds of 50 and 70 km h−1, realised with different engine speeds. The results of the traffic emission studies show that the method is applicable provided that instruments with an adequate dynamic range are used and that the traffic is not too dense. In addition, the variability in particle emissions for a specified driving condition was estimated.
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| 11. |
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| 12. |
- Janhäll, Sara, 1965, et al.
(författare)
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Evolution of the urban aerosol during winter temperature inversion episodes
- 2006
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 40:28, s. 5355-5366
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Tidskriftsartikel (refereegranskat)abstract
- Winter temperature inversions are for Nordic urban sites a major cause for exceeding air-quality legislation thresholds for most primary pollutants. In this study, number particle size distributions have been measured and compared to other tracers for traffic emissions. Concentrations during winter days with and without morning temperature inversion were compared. Morning temperature inversion resulted in high concentrations of traffic-related pollutants, including CO, NO and NO2 together with ultrafine particles, while the pollution levels where considerably lower during mornings without temperature inversion. The specific time trends of NOx species could be well understood when considering the reaction with O-3. The two different particle measures used in this study, i.e. the number concentration of ultrafine particles (10-100 nm) and the mass of particles below 10 pm (PM10), both increased during morning rush hours. When the morning inversion broke up and ground-level air mixed with air aloft, the number of particles decreased more rapidly than PM10 concentrations. LIDAR measurements were used to follow the vertical distribution of particles, and they clearly showed how the mixing processes started after the morning inversion and resulted in rising of the inversion followed by a relatively well-mixed boundary layer with a height of I kin around 14:00. (c) 2006 Elsevier Ltd. All rights reserved.
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| 13. |
- Kotarba, A., et al.
(författare)
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In situ monitoring of bare and K-doped Mo2C catalysts surface depassivation based on emission of electrons and K+ ions
- 2006
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 252:12, s. 4129-4137
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Tidskriftsartikel (refereegranskat)abstract
- The method for in situ characterization of surface transformations on heterogeneous catalyst is described. The method is based on the measurements of thermal electron and ion emissions from the catalyst surface. It is demonstrated by investigating the depassivation process of undoped and K-doped Mo2C catalysts exposed to air after synthesis and use to identify characteristic steps of reduction-carburization by flowing CH4/H-2 gas mixture. The information obtained from thermal emission experiments is consistent with the methane consumption profile, which provided an independent observation of the recarburization step. (c) 2005 Published by Elsevier B.V.
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| 14. |
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| 15. |
- Olofson, K. Frans G., 1976, et al.
(författare)
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Arctic aerosol and clouds studied by bistatic lidar technique
- 2009
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Ingår i: Journal of Geophysical Research. - Washington, D.C. : American geophysical union. - 0148-0227 .- 2156-2202. ; 114, s. D18208-
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol and cloud studies were carried out with a polarimetric bistatic lidar setup at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in Andenes (69°N, 16E°), Norway. The measurements were performed from 10 to 23 October 2006 and covered altitudes between 1.5 and 11 km, corresponding to scattering angles between 130 and 170°. The degree of linear polarization, PL, calculated from the experiments was compared with light scattering calculations using Lorenz‐Mie theory for spherical particles, the T‐matrix approach for nonspherical rotationally symmetric particles, and a geometric optics ray‐tracing method. Average PL values between 0.61 and 0.72 were obtained for the background aerosol under cloud‐free conditions. The aerosol results may be qualitatively reproduced by standard aerosol types if a suitable combination of coarse‐ and fine‐mode spherical particles is assumed. The PL values obtained for thin and mildly opaque clouds were in the range from 0.21 to 0.38. These results were not well described by spherical particles, and the results for relatively small prolate and oblate particles studied with the T‐matrix method tended to be slightly higher than the experimental values. Geometric optics calculations for hexagonal column ice particles with surface roughness were able to reproduce the experimental cloud data. This does not rule out contributions from other types of particles, and particle orientation effects may also have influenced the results. We conclude that the experimental results are consistent with earlier in situ studies of cirrus clouds, and the further development and application of the bistatic lidar technique is discussed.
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| 16. |
- Olofson, K. Frans G., 1976, et al.
(författare)
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Bistatic lidar measurements of clouds in the Nordic Arctic region
- 2008
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165 .- 1539-4522. ; 47:26, s. 4777-4786
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Tidskriftsartikel (refereegranskat)abstract
- Cloud studies were carried out with a polarimetric bistatic lidar setup at the Arctic Lidar Observatory for Middle Atmosphere Research in Andenes (69 degrees N, 16 degrees E), Norway. Measurements were performed at altitudes between 1.5 and 10.5 km, corresponding to scattering angles between 130 degrees and 170 degrees. The geometry, not restricted to the parallel or perpendicular laser polarization directions, gave a well-defined scattering angle, which together with polarization characterization, was used to investigate the scattering particles. The principles of the technique and the first results are presented together with an evaluation of the capabilities.
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| 17. |
- Olofson, K. Frans G., 1976, et al.
(författare)
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Urban aerosol evolution and particle formation during wintertime temperature inversions
- 2009
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 43, s. 340-346
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol temporal and spatial distributions during wintertime temperature inversions in Gothenburg, Sweden, have been characterized by ground-based and airborne particle measurements combined with lidar measurements. Ground inversions frequently developed during evenings and nights with stable cold conditions, and the low wintertime insolation often resulted in near neutral boundary layer conditions during day-time. Under these conditions ground level aerosol concentrations peaked during morning rush hours and often remained relatively high throughout the day due to inefficient ventilation. The particle number concentrations decreased slowly with increasing altitude within the boundary layer, and measurements slightly above the boundary layer suggested limited entrainment of polluted air into the free troposphere. High concentrations of ultrafine particles were observed throughout the boundary layer up to altitudes of 1100 m, which suggested that nucleation took place within the residual layer during the night and early morning. Recently formed particles were also observed around midday when the layer near ground was ventilated by mixing into the boundary layer, which indicated that ultrafine particles were either transported down from the residual layer to ground level or formed when the polluted surface layer mixed with the cleaner air above.
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| 18. |
- Omrane, Alaa, et al.
(författare)
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Surface temperature of decomposing construction materials studied by laser-induced phosphorescence
- 2005
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Ingår i: Fire and Materials. - : Wiley. - 0308-0501 .- 1099-1018. ; 29:1, s. 39-51
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of surface temperature and mass loss of decomposing construction materials during rapid pyrolysis are presented. Experiments have been performed With samples of low-density fiberboard. medium-density fiberboard,. particleboard and poly(methyl methacrylate) in a single particle reactor at temperatures between 300degrees and 600degreesC. Ultraviolet laser light was used to excite micrometer-Sized thermographic phosphor particles that Were deposited on the investigated materials. and the temperature was obtained from temporally resolved measurements of the laser-induced emission. The wood-based materials show a similar behavior, with small differences being attributed to differences in material properties. The surface temperature rapidly increases to about 400degreesC When a particle is introduced to the hot reactor. The initial phase is followed by rapid decomposition during Which the surface temperature is 380degrees-540degreesC. The heating rate is slowed down during the rapid pyrolysis. and again increases as the remaining char is heated to the reactor temperature. The poly (methyl methacrylate), however. melts and at high temperatures can be characterized as a liquid with a boiling point of about 40degreesC. Thermographic phosphors are concluded to be suitable for high precision remote measurements of the surface temperature of decomposing construction materials, and possibilities for further studies and developments of the technique are discussed. Copyright paired right arrows 2004 John Wiley Sons. Ltd.
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| 19. |
- Petrignani, Annemieke, et al.
(författare)
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Dissociative recombination of the weakly bound NO-dimer cation: cross sections and three-body dynamics.
- 2005
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:19
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination (DR) of the dimer ion (NO)(2) (+) has been studied at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm. The experiments were aimed at determining details on the strongly enhanced thermal rate coefficient for the dimer, interpreting the dissociation dynamics of the dimer ion, and studying the degree of similarity to the behavior in the monomer. The DR rate reveals that the very large efficiency of the dimer rate with respect to the monomer is limited to electron energies below 0.2 eV. The fragmentation products reveal that the breakup into the three-body channel NO+O+N dominates with a probability of 0.69+/-0.02. The second most important channel yields NO+NO fragments with a probability of 0.23+/-0.03. Furthermore, the dominant three-body breakup yields electronic and vibrational ground-state products, NO(upsilon=0)+N((4)S)+O((3)P), in about 45% of the cases. The internal product-state distribution of the NO fragment shows a similarity with the product-state distribution as predicted by the Franck-Condon overlap between a NO moiety of the dimer ion and a free NO. The dissociation dynamics seem to be independent of the NO internal energy. Finally, the dissociation dynamics reveal a correlation between the kinetic energy of the NO fragment and the degree of conservation of linear momentum between the O and N product atoms. The observations support a mechanism in which the recoil takes place along one of the NO bonds in the dimer.
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| 20. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
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Formation of Adsorbed Layers by Deposition of Dinitrogen Pentoxide, Nitric Acid, and Water on Graphite
- 2009
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Ingår i: J. Phys. Chem. C. - : American Chemical Society (ACS). ; 113, s. 7728-7734
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Tidskriftsartikel (refereegranskat)abstract
- The formation of adsorbed layers of dinitrogen pentoxide, nitric acid, and water on graphite has been studied by molecular beam and light-scattering techniques. The desorption kinetics of N2O5 on graphite were described by the Arrhenius equation with an activation energy of 0.24 ± 0.03 eV and a pre-exponential factor of 2.3 × 10(10 ± 0.73) s−1, and N2O5 is concluded to bind more strongly than H2O to the graphite surface. Elastic helium scattering and light scattering were used to probe the formation of adlayers on the surface. Adsorption of pure N2O5 resulted in formation of thin adlayers at temperatures below 160 K. In coadsorption experiments N2O5 was concluded to facilitate the formation of thick N2O5−H2O ice layers at 155 K. In a similar way coadsorption of HNO3 and H2O resulted in the formation of thick adlayers at 170 K. N2O5 and HNO3 both bind more strongly than water to the graphite surface and are concluded to facilitate nucleation and growth of ice.
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| 21. |
- Suter, Martina, 1966, et al.
(författare)
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Argon collisions with amorphous water ice surfaces
- 2006
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Ingår i: Chemical Physics. ; 326:2-3, s. 281-288
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of argon atom collisions with amorphous ice surfaces are investigated using molecular beam techniques and molecular dynamics simulations. The formation of an amorphous ice layer on top of crystalline ice at 110 K is shown to have a strong influence on Ar scattering. Compared to crystalline ice, trapping followed by desorption is favoured over inelastic scattering, and a strongly enhanced emission of argon in the backward direction is observed. Molecular dynamics simulation with different types of amorphous and crystalline surfaces are consistent with the experimental data and show that large scale corrugation is required to reproduce the experimental findings. It is concluded that argon scattering can be used to probe changes in surface structure on the nanometer length-scale, while it is relatively insensitive to changes on the molecular level, and it thereby complements other techniques for studies of structural changes of ice surfaces. (c) 2006 Elsevier B.V. All rights reserved.
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| 22. |
- Suter, Martina, 1966, et al.
(författare)
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Formation of water-ammonia ice on graphite studied by elastic helium scattering
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 445, s. 208-212
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Tidskriftsartikel (refereegranskat)abstract
- Helium and light scattering experiments have been performed to study the formation of water–ammonia ice layers on graphite at 110–160 K. Ice formation is mainly governed by the partial water pressure, but the presence of ammonia enhances the formation rate and influences the layer properties. Ice formed at temperatures <140 K wets the surface, while ice formed at higher temperatures does not. At temperatures around 140 K ammonia destabilizes the two-dimensional ice layers and a dewetting transition is observed at a surface coverage of 90–95%.
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| 23. |
- Suter, Martina, 1966, et al.
(författare)
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Surface properties of water ice at 150-191 K studied by elastic helium scattering.
- 2006
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:17
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Tidskriftsartikel (refereegranskat)abstract
- A highly surface sensitive technique based on elastic scattering of low-energy helium atoms has been used to probe the conditions in the topmost molecular layer on ice in the temperature range of 150-191 K. The elastically scattered intensity decreased slowly as the temperature was increased to about 180 K, followed by a rapid decrease at higher temperatures. An effective surface Debye temperature of 185+/-10 K was calculated from the data below 180 K. The changes in the ice surface above 180 K are interpreted as the onset of an anomalous enhancement of the mean square vibrational amplitude for the surface molecules and/or the onset of a limited amount of disorder in the ice surface. The interpretation is consistent with earlier experimental studies and molecular dynamics simulations. The observed changes above 180 K can be considered as the first sign of increased mobility of water molecules in the ice surface, which ultimately leads to the formation of a quasiliquid layer at higher temperatures. A small shift and broadening of the specular peak was also observed in the range of 150-180 K and the effect is explained by the inherent corrugation of the crystalline ice surface. The peak shift became more pronounced with increasing temperature, which indicates that surface corrugation increases as the temperature approaches 180 K. The results have implications for the properties and surface chemistry of atmospheric ice particles, and may contribute to the understanding of solvent effects on the internal molecular motion of hydrated proteins and other organic structures such as DNA.
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| 24. |
- Svane, Maria, 1957, et al.
(författare)
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Cesium as a tracer for alkali processes in a circulating fluidized bed reactor
- 2006
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 20:3, s. 979-985
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Tidskriftsartikel (refereegranskat)abstract
- Addition of cesium salt has been used to study the removal rate, transport, and fate of alkali components during combustion of a mixture of wood chips and pellets in a 12-MW circulating fluidized bed (CFB) reactor. The alkali concentration in the flue gas was monitored with a recently developed aerosol mass spectrometer to provide on-line measurements of alkali-containing submicron particles. Cs2CO3 was fed with the fuel during a 5.5-h period, and the Cs concentration in the flue gas and in ash samples was followed for 70 h. Cesium addition resulted in a 1000-fold increase in Cs concentrations, followed by a slow decay of the concentrations during the following days. Cs was concluded to bind strongly to the fluidized bed material and to be removed with the bed ash or by slow release to the gas phase. The apparent rate coefficient for Cs removal from the bed was approximately 0.03 h(-1). After 70 h, 33 +/- 10% of the added cesium had been removed with the bottom ash, 7 +/- 5% with secondary cyclone ash, and 45 +/- 10% with the bag-house filter ash. About 15% of the Cs remained in the facility at this time, either bound to the fluidized bed material or as deposits on surfaces. Cesium compounds released from the bed participate in the formation of new particles that are efficiently collected by the bag-house filters. A minor Cs fraction also condenses on fly ash particles that are removed by the secondary cyclone. The study shows that the results of cesium addition can be followed in detail under typical operation conditions, and the potential of the tracer method for studies of transformations and fate of alkali compounds in commercial scale boilers is discussed.
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| 25. |
- Svane, Maria, 1957, et al.
(författare)
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On-line alkali analysis of individual aerosol particles in urban air
- 2005
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 39:36, s. 6919-6930
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Tidskriftsartikel (refereegranskat)abstract
- On-line measurements of individual alkali-containing submicron particles in ambient air have been performed at two urban sites in Goteborg, on the west coast of Sweden. Results obtained with a recently developed particle beam mass spectrometer are presented. This instrument combines an optimized particle inlet with mass spectrometric techniques and detection of particle-bound alkali metal is based on surface ionization technique. The concentrations of Na and K in submicron particles were followed over periods of a few weeks. Mass concentrations of alkali in ambient air varied in the range 0.02-100 ng m(-3) during the measurement periods depending on air mass history, wind direction, season, and contributions from local sources. The number of alkali-containing particles varied between 0.1 and 100 cm(-3). Most detected individual particles contained a relatively small amount of Na, and few particles had sufficient Na content to be identified as pure sea-salt particles. The detected aerosol was concluded to be dominated by emissions from combustion of biomass and fossil fuels, with a significant contribution from sea-salt particles only during intrusion of marine air. This conclusion was supported by backward air mass trajectories and calculated K/Na weight ratios that generally agreed well with earlier measurements in urban environments. (c) 2005 Elsevier Ltd. All rights reserved.
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