| 1. |
- Djerf, Tove, 1989, et al.
(författare)
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Solids circulation in circulating fluidized beds with low riser aspect ratio and varying total solids inventory
- 2016
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Ingår i: Fluidization XV (2016), Quebec, Canada.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents an experimental study with the aim tounderstand the relation between the flow conditions - the riser pressure drop and fluidization velocity - in a CFB riser and the net (external)solids flux (Gs [kg/m2s]), applying a riser geometry and overall flow conditions similar to CFB boilers.The experiments are carried out in a CFB unit operated under ambient conditions. The riser has a cross section of 0.7 m x 0.12 m and a height of 8.5 m, yielding a riser height-to-width aspect ratio of 10.6 (in the wide dimension), similar to that of CFB boilers. The unit is equipped with densely spaced pressure taps providing a fine resolution of the measured vertical pressure profile along the riser and an automatic system to accurately measure Gs. The experiments cover fluidization velocities of 0.3-7 m/s, riser pressure drops of 1.7-10.5 kPa and loopseal fluidization velocities of 0.12-0.54 m/s (secondary air flows are not considered). These ranges correspond to conditions both with and without a dense bottom region.The results show that Gs is determined by the solids concentration at the riser top, which depends riser pressure drop and fluidization velocity, and the backflow effect, which depends on the configuration and flow conditions of the loop seal and the exit region. For operating conditions with a dense bottom bed present, Gs is independent of riser pressure drop, whereas when operating without a dense bed an increase in riser pressure drop yields an increase in Gs.
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| 2. |
- Köhler, Anna, 1989, et al.
(författare)
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Determination of the Apparent Viscosity of Dense Gas-Solids Emulsion by Magnetic Particle Tracking
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- When designing fluidised bed units a key to ensure efficient conversion is proper control of the mixing of the fuel in both lateral and axial directions in the bed. In order to mechanistically describe the mixing of fuel particles in a fluidised bed, there is a need to determine the apparent viscosity of the gas-solids emulsion, which determines the drag on the fuel particles. In this work the apparent viscosity of a bed of spherical glass beads and air at minimum fluidisation was determined by means of the falling sphere method. Hereto the drag of the bed on a single immersed object was obtained by measuring the velocity of a negatively buoyant tracer with magnetic particle tracking (MPT). MPT allows for highly temporally and spatially resolved trajectories (10-3 s and 10-3 m, respectively) in all 3-dimensions. The bed consisted of glass beads with a narrow size distribution (215 to 250 μm) and tracers with a size from 5 to 20 mm and densities from 4340 to 7500 kg/m3 were used. Hence, the literature, which typically covers data for velocities lying within or just above the Stoke flow regime (0.002 < Re < 2.0) could be expanded to Re numbers (53 to 152) well within the transition flow regime. The drag and apparent viscosity was compared to different fluid models and agreed well with the Newtonian model, when taking into account possible effects of the bed walls. Comparing the drag coefficient of data of free falling spheres and data of spheres falling with controlled velocities, the latter showed a dependence on the product of tracer diameter and falling velocity, dput, while the former was constant over dput. This indicates the method with controlled falling velocities to be intrusive and influencing the result of the apparent viscosity of the bed. Using the free falling sphere method this work obtained an apparent viscosity of 0.24 Pa s, which is consistent with values found in earlier literature for an emulsion of air and sand of similar size and density.
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| 3. |
- Köhler, Anna, 1989, et al.
(författare)
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Experimental characterization of axial fuel mixing in fluidized beds by magnetic particle tracking
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A Magnetic Particle Tracking (MPT) system is applied to a bubbling fluidized bed to study how axial mixing and segregation of fuel are influenced by the fuel density and operational conditions (fluidization velocity, bed height and pressure drop across the gas distributor). The MPT system is used to determine the vertical distribution of the tracer particle in a fluid-dynamically down-scaled cold unit resembling a 0.74×0.74 m2 fluidized bed reactor operating at 800 °C. This work uses a tracer particle of 10 mm in diameter, corresponding to a fuel particle of 44 mm. Different tracer particles are applied with solids density representing biomass, biomass char and that of the average bulk. The MPT system yields a spatial accuracy in the order of 10-3 m and a time resolution of 10-3 s. For the operational range investigated, three fuel segregation regimes can be identified from the MPT measurements: 1) A flotsam regime which occurs at low fluidization velocities and for low density tracer particles, 2) A transition regime over which an increase in fluidization velocity results in that the presence of fuel particles at the bed surface decreases rapidly, and 3) A fully developed mixing regime in which the presence of tracer particle at the bed surface and the splash zone remains constant with fluidization velocity. The transition velocities between the regimes depend on bed height and density of the tracer particle.
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| 4. |
- Martinez Castilla, Guillermo, 1993, et al.
(författare)
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Calcium looping for combined CO 2 capture and thermochemical energy storage
- 2023
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Ingår i: Circular Economy Processes for CO2 Capture and Utilization: Strategies and Case Studies. - 9780323956680 ; , s. 119-162
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The carbonation of calcium oxide (CaO) has been extensively investigated concerning the separation of CO2 from gaseous streams. The carbonation reaction is of special interest in postcombustion processes for the capture of CO2 since the produced calcium carbonate (CaCO3) can be calcined in a separate reactor to generate a stream of pure CO2 for sequestration and storage. The cycle, which consists of carbonation and calcination reactions, involves considerable heat of reaction, rendering the process relevant not only for CO2 capture but also for energy storage purposes in the form of thermochemical energy storage (TCES). Energy storage is envisioned as an important flexibility measure to increase the penetration of variable renewable electricity (VRE), thereby increasing the value of VRE due to the reduced share of generation that needs to be curtailed. In this chapter, the general characteristics of the calcium looping process for both CO2 capture and energy storage are presented. Thereafter, the process that combines these two features is described, focusing on its layout specifications, associated opportunities and challenges, and the most recent advances toward its development.
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| 5. |
- Pallarès, David, 1975, et al.
(författare)
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Fluidized bed technologies for near-zero emission combustion and gasification
- 2013
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Ingår i: Woodhead Publishing Ltd. Eds.. - 0857095412 ; , s. 690-
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Fluidized bed combustion (FBC) is an advanced technique for fuel flexible, high efficiency and low emission power generation. In these systems fuels are combusted as a fluidized bed suspended by jets of air with sorbents that remove harmful emissions such as NOx and SOx. CO2 capture can also be incorporated. This book provides an overview of this important area. Opening chapters provide an introduction to fluidization science and technology. Following sections review the fundamentals of fluidized bed combustion and gasification and advances in these areas. The final part focuses on emerging CO2 capture technologies. - See more at: http://www.woodheadpublishing.com/en/book.aspx?bookID=2643#sthash.vj8iFmQR.dpuf
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| 6. |
- Pallarès, David, 1975, et al.
(författare)
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Modeling of fluidized bed combustion processes
- 2013
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Ingår i: Fluidized Bed Technologies for Near-Zero Emission Combustion and Gasification. - : Elsevier. - 9780857095411 ; , s. 524-578
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter provides an overview of the aims, principles, and limitations of the different types of modeling used for fluidized bed combustion (FBC) systems with a focus on macroscopic modeling, which is currently considered the most suitable modeling approach for FBC units of industrial scale. Sub-models for the different regions characterizing FBC units are described, with emphasis on the most critical in-furnace phenomena. Guidelines and examples are given of how different sub-models can be linked into a comprehensive process model for FBC units.
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| 7. |
- Sette, Erik, 1984, et al.
(författare)
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3-dimensional particle tracking in a fluid-dynamically downscaled fluidized bed using magneto resistive sensors
- 2015
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Ingår i: The 8th International Symposium on Coal Combustion.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a measurement technique for continuous tracking of particles in 3-dimensional bubbling fluidized beds operated according to scaling laws. By applying Glicksman’s full set of scaling laws to both bulk solids and tracer particle the bed is assumed to be fluid-dynamically similar to a combustor operated at 900 °C with the tracer particle corresponding to a fuel particle with properties similar to anthracite coal. Two different gas distributors with varying pressure drop are used to investigate the influence of bed design on fuel mixing.Flow structures formed around rising gas bubbles, so called bubble paths, are identified and the tracer particle traverses the entire bed for a gas distributor yielding a high pressure drop. For a gas distributor yielding a low pressure drop flow structures are less pronounced and the tracer particle is not circulating the entire bed.
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| 8. |
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| 9. |
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