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Träfflista för sökning "AMNE:(TEKNIK OCH TEKNOLOGIER) ;pers:(Leckner Bo G 1936)"

Sökning: AMNE:(TEKNIK OCH TEKNOLOGIER) > Leckner Bo G 1936

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1.
  • Leckner, Bo G, 1936 (författare)
  • Fluid dynamic regimes in circulating fluidized bed boilers—A mini-review
  • 2022
  • Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 247
  • Tidskriftsartikel (refereegranskat)abstract
    • The fluid dynamics in the furnaces of large-scale circulating fluidized bed (CFB) boilers are surprisingly little known in contrast to the many laboratory studies made on conditions related to chemical reactors. Two areas are surveyed in the present work: the bottom bed and the upper dilute zone of a furnace. The bottom bed is considered bubbling, but the general opinion is that either it does not exist, or it is turbulent. The flow in the upper furnace is dilute phase transport, judging from regime maps, showing that the state of the flow is outside of the range of fast fluidization. However, this is also not generally accepted. Usually, the regime of fluidization in CFB boilers is said to be fast fluidization. In one work it is considered fast fluidization even though the authors agree that it is different from the general definition. In another investigation it is called entrained flow. Here, the conclusion is that the diversity of opinions should be resolved by further investigations with the aim of defining the conditions for the fluidized flow in furnaces, including the influence of particle size and density, fluidization velocity, gas properties, and effects from the furnace dimensions, if any.
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2.
  • Leckner, Bo G, 1936 (författare)
  • Fluidization Characteristics of Circulating Fluidized Bed Boilers
  • 2023
  • Ingår i: Chemie-Ingenieur-Technik. - : Wiley. - 0009-286X .- 1522-2640. ; 95:1-2, s. 32-39
  • Forskningsöversikt (refereegranskat)abstract
    • The fluidization in the furnace of circulating fluidized bed (CFB) boilers is described. Data have been obtained from a 12 MWth CFB boiler and from literature. The bottom bed is bubbling rather than fast or turbulently fluidized as is often assumed. There is an extended splash zone above this bed, in which particles are thrown up by the bubbles and fall back onto the bottom bed. Other particles are carried further into the transport zone, initially as a saturated gas flow, but some particles move into the wall layers and the density decays towards the exit. The density of the transport zone is low, and the circulation rate is relatively seen small. Therefore, this flow is in a state of dilute-phase transport and not in the fast fluidization regime, such as is often claimed.
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3.
  • Bergenblock, Tobias, 1972, et al. (författare)
  • Averaging of particle data from phase Doppler
  • 2006
  • Ingår i: International Journal of Multiphase Flow. ; 32, s. 248-268
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel post-processing algorithm is proposed to correct statistical bias observed in the treatment of time seriesobtained by a phase Doppler anemometer (PDA) at flow locations with variable particle velocity and concentration.Extensive properties of each validated particle are weighted with their inverse measuring (validation) volume to accountfor the procedure of particle sampling and fluctuations in the particle concentration. To compensate for the short characteristiclength of the validation volume, the properties of particles are expressed by properties of fields of particle groups,using a local averaging time. A window shift and a decorrelation scheme are applied on the fields to increase their frequencyresolution. This algorithm has been tested on numerical time series, provided by an Eulerian/Lagrangian code representinga gas/solids flow past a bluff body. Moments and spectral estimates of concentration and velocity of particlegroups were successfully validated by the numerical simulation using the PDA data algorithm and control volume averaging.The control volume was much larger than the PDA validation volume, but the centre positions of the two volumeswere identical.
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4.
  • Leckner, Bo G, 1936 (författare)
  • Heat and mass transfer to/from active particles in a fluidized bed - An analysis of the Baskakov-Palchonok correlation
  • 2021
  • Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 168
  • Tidskriftsartikel (refereegranskat)abstract
    • Heat and mass transfer to or from single active particles surrounded by inert (passive) particles in a fluidized bed has been investigated based on published correlations. Special emphasis is on the application of a proposal by Baskakov, further developed by Palchonok. This representation describes heat and mass transfer as a function of the size ratio of inert to active particles. Two limits have been chosen: the limit of small active particles, where the active and the inert particles are equal, and the limit of large active particles, where the influence of the size of the active particle has vanished. The presentation aims at finding a suitable relationship, describing the size ratio of inert to active particles on heat and mass transfer to/from particles in fluidized beds and to critically evaluate its usefulness. It seems that the agreement between available correlations is qualitative and only approximate estimations can be made. A generalized scheme for calculations is presented. The formulation is made for bubbling fluidization. A discussion is presented on its use in circulating fluidized bed applications for fuel conversion as well.
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5.
  • Bergenblock, Tobias, 1972, et al. (författare)
  • Experimental estimation of particle flow fluctuations in dense unsteady two-phase flow using phase Doppler anemometry
  • 2007
  • Ingår i: International Journal of Multiphase Flow. ; 33, s. 849-872
  • Tidskriftsartikel (refereegranskat)abstract
    • A recently proposed and successfully validated post-processing algorithm is extended to treat particle data obtained by a phase Doppler anemometer (PDA) in dense, fluctuating, low-speed, two-phase flow. In such a flow, Doppler signals may be noisy and split, since particles have long residence times in the measurement volume. A novel time average based on the measured burst lengths is proposed to estimate the cross-sectional area of the measurement volume. This time average accounts for the possible split of a noisy Doppler burst, and it provides a more general description of the measurement volume than the conventional ensemble average. The extended post-processing algorithm was tested on experimental time series obtained in a circulating fluidized bed and the algorithm was compared to conventional treatment of the particle data by a commercial PDA processor. The conventional processing strongly overestimates the vertical mass flux integrated over the cross-section. In contrast, time-mean and fluctuations of mass flux, particle volume concentration, and particle velocity are reliably estimated employing the proposed algorithm, with continuity check parameters in succeeding particle data, as well as with a particle velocity filter to estimate the size of the probe volume, applying a two-component PDA in a three-dimensional flow.
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6.
  • Enwald, H., et al. (författare)
  • Simulation of the fluid dynamics of a bubbling fluidized bed. Experimental validation of the two-fluid model and evaluation of a parallel multiblock solver
  • 1999
  • Ingår i: Chemical Engineering Science. - 0009-2509. ; 54:3, s. 311-328
  • Tidskriftsartikel (refereegranskat)abstract
    • A mesh refinement study and validation of two-fluid model closures were carried out for a bubbling fluidized bed application. The mesh refinement study indicates that a higher degree of mesh refinement is required for atmospheric than for pressurized fluidization. Statistical bubble parameters (bubble frequency, mean bubble rise velocity, mean pierced bubble length and mean bubble volume fraction) were evaluated. The simulated statistical bubble quantities are computed from voidage signals derived from the transient multidimensional solution of two-fluid models. The algorithm for computing these quantities is taken directly from the evaluation program treating the measurement signals. To remedy the long simulation times required to obtain acceptable statistical values, a parallel version of the two-fluid model solver was developed, based on a domain decomposition method for distributed memory computers. A number of problems related to the parallelization are investigated. These are optimal treatment of velocity components on multi-block boundaries, frequency of data exchange at multi-block boundaries, local errors at multi-block boundaries and simulation time requirements.
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9.
  • Johansson, Andreas, et al. (författare)
  • Solids back-mixing in CFB boiler
  • 2007
  • Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 62, s. 561-573
  • Tidskriftsartikel (refereegranskat)abstract
    • The furnaces of circulating fluidized bed (CFB) boilers have substantially lower height-to-width ratios than most of the laboratory CFB risers from which experimental investigations on riser fluid dynamics are published. Therefore, it is uncertain whether literature expressions for prediction of the distribution of solids and the thickness of the wall layers, derived from investigations in laboratory units, are applicable to boilers. In this work, data from laboratory units are compared with boiler data, and the accuracy of literature expressions for prediction of solids distribution, solids flow and wall layer thickness is reviewed. It is found that the height-to-width ratio does have a significant impact on the flow properties. Correlations based on experiments in laboratory units show poor agreement when applied to boilers. Modifications of literature expressions for prediction of solids flow and solids distribution are proposed, and an improved expression is formulated for prediction of the thickness of the wall layer.
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10.
  • Leckner, Bo G, 1936 (författare)
  • Hundred years of fluidization for the conversion of solid fuels
  • 2022
  • Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 411
  • Tidskriftsartikel (refereegranskat)abstract
    • This is a summary of the development of conversion of solid fuels in fluidized bed during the hundred years that follow the first patent of Winkler in September 1922. The Winkler gasifiers and their followers are described first. Other fuel converters, such as boilers, appeared only in the 1960–70s and became of interest because of their expected environmental advantages. Initially, bubbling bed boilers were introduced, followed by circulating fluidized bed (CFB) boilers in the beginning of the 1980s. Now, CFB is the dominant technology. The entire development has not been conditioned by technological breakthroughs, but rather by the surrounding conditions: industrial demand, wars, environmental effects, availability and price of fuels. The recent development of the presently rather mature technology depends very much on the necessity to limit greenhouse gas accumulation in the atmosphere. Although fluidized bed technology offers solutions to reduce CO2 emissions, so far, no decisive line of application has been established for CO2 reduction, except for the use of biomass and waste.
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