| 61. |
- Köhler, Anna, 1989, et al.
(författare)
-
Determination of the Apparent Viscosity of Dense Gas-Solids Emulsion by Magnetic Particle Tracking
- 2018
-
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.
|
|
| 62. |
- Köhler, Anna, 1989, et al.
(författare)
-
Experimental characterization of axial fuel mixing in fluidized beds by magnetic particle tracking
- 2016
-
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.
|
|
| 63. |
- Le, Anh Tuan, 1974, et al.
(författare)
-
Towards Future Electricity Networks – Meeting Strict CO2 Targets
- 2008
-
Ingår i: Smart Energy Strategies Conference, 2008, ETH Zurich, Switzerland.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper discusses challenges and possible pathways for the electricity networks up to the year 2050, assuming that strict CO2 emission targets are to be met. The analysis is based on input from an energy systems model which gives the development of the power generation system until the year 2050, meeting the EU 2020 CO2 target and a 60% CO2 reduction until the year 2050. The development of the power generation system is modeled by means of a techno-economic energy systems model which gives the technology mix until the year 2050 under assumptions on cost for various technologies and applying specific CO2 emission targets. Yet, for such modeling, the possibilities and barriers imposed by the electricity network is seldom included. This paper discusses a methodology to analyze the pathways for the electricity networks using the modeled pathways for the power generation system as input. The focus is on EU27.
|
|
| 64. |
|
|
| 65. |
- Leckner, Bo G, 1936, et al.
(författare)
-
Pressure fluctuations in gas fluidised beds
- 2001
-
Ingår i: 3rd Symp of South-East European Countries on Fluidized Bed i Energy Production, Chemical and Process Engineering and Ecology Sinaia, Romania, September 25-29, 2001 / Dragos, L., Inescu, G., Flueraru, C.. ; 125, s. 3-8
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
|
|
| 66. |
|
|
| 67. |
|
|
| 68. |
- Lind, Fredrik, 1978, et al.
(författare)
-
What is the efficiency of a biorefinery?
- 2012
-
Ingår i: Systems Perspectives on Biorefineries 2012. - 9789198030013 ; , s. 59-71
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
|
|
| 69. |
- Lyngfelt, Anders, 1955, et al.
(författare)
-
Dependence of Sulphur Capture Performance on Air Staging in a 12 MW Circulating Fluidised Bed Boiler
- 1993
-
Ingår i: Gas Cleaning at High Temperatures, Eds. R. Clift and J.P.K. Seville, Blackie Academic & Professional, Glasgow, ISBN 0 7514 0178 1.. - 0751401781 ; , s. 470-491
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Three cases of air staging were examined in a 12 MW circulating fluidised bed boiler: i) no staging, ii} normal staging and iii) intensified staging. The conditions inside the combustion chamber were investigated by zirconia cell measurements of the oxygen partial pressure, 0.35, 0.65 and 8 m above the bottom air distributor plate. A significant effect of the degree of staging was seen in the two lower locations: At 0.65 m height the fraction of time under substoichiometric conditions was low in the no-staging case (2-35%), at normal staging it was 70-90%, whereas at intensified staging it was 100Y.. At 0.35 m height, i.e. in the dense bed, a similar effect was seen, although the fraction of time under reducing conditions was lower. The fraction of time under reducing conditions was low in the top of the combustion chamber in all three cases . The increase in the fraction of time under reducing conditions with a higher degree of staging is associated with a decrease in sulphur capture. It is assumed that a release of SO2 from CaSO4 takes place during the transitions between oxidising and reducing conditions. Thus, the rapid alternations between oxidising and reducing conditions, as seen with the zirconia cell, offer an explanation of the reductive decomposition and, accordingly, of the dependence of sulphur capture on temperature and on the extent of staging.
|
|
| 70. |
|
|
