| 11. |
- Palchonok, Gennadij, 1950, et al.
(författare)
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Estimates of turbulence effects in CFB boilers
- 1996
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Ingår i: Proc of the 5th International Conference on Circulating Fluidized Bed. ; 5, s. 440-445
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Konferensbidrag (refereegranskat)abstract
- A simplified physical model of turbulence in a circulating fluidized bed (CFB) combustor is presented. The existence of a dense bubbling bottom bed, a splash zone with pronounced clustering effects and a transport zone with predominantly disperse solids flow in the core is accounted for. The energy dissipation rate evaluated from the total energy supply and the macro-scale of the bubble-induced turbulence are used as defining parameters for order of magnitude estimates of turbulence effects in a 0.7 m wide cold rig and a 12 MW CFB boiler. The results obtained show a reasonable agreement with available experimental data.
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| 12. |
- Peirano, Eric, 1966, et al.
(författare)
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Estimates of turbulence mechanisms in circulating fluidized bed combustors
- 1998
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Ingår i: Powder Technology. - 1873-328X .- 0032-5910. ; 96:2, s. 90-105
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Tidskriftsartikel (refereegranskat)abstract
- Estimates of the characteristic time scales (particle relaxation time, eddy-particle interaction time, interparticle collision time), and the energy dissipation mechanisms are performed together with a turbulent kinetic energy budget, for a simple equilibrium shear flow with conditions similar to those of a circulating fluidized bed (CFB) combustor. Based on dimensional analysis, the influence of five parameters is investigated: the Eulerian integral length scale in the gas phase, the gas-particle density ratio, the mean velocity gradient, the particle diameter, and the particle volume fraction. The results show significant differences between particles of Geldart groups A and B regarding response to gas phase turbulence, transition from dense to dilute suspensions, pressure and temperature dependence, and also energy dissipation mechanisms.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Svensson, Anders, 1960, et al.
(författare)
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Bottom bed regimes in a circulating fluidized bed boiler
- 1996
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Ingår i: International Journal of Multiphase Flow. - 0301-9322. ; 22:6, s. 1187-1204
-
Tidskriftsartikel (refereegranskat)abstract
- This paper extends previous work on the fluidization regimes of the bottom bed of circulating flyidized bed (CFB) boilers. Pressure measurements were performed to obtain the time-average bottom bed voidage and to study the bed pressure fluctuations. The measurements were carried out in a 12 MWth CFB boiler operated at 850°C and also under ambient conditions (40°C). Two bubbling regimes were identified: a “single bubble regime” with large single bubbles present at low fluidization velocities, and, at high fluidization velocities, an “exploding bubble regime” with bubbles often stretching all the way from the air distributor to the surface of the bottom bed. The exploding bubble regime results in a high through-flow of gas, indirectly seen from the low average voidage of the bottom bed, which is similar to that of a stationary fluidized bed boiler, despite the higher gas velocities in the CFB boiler. Methods to determine the fluidization velocity at the transition from the single to the exploding bubble regime are proposed and discussed. The transition velocity increases with an increase in particle size and bed height.
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| 17. |
- Svensson, Anders, 1960, et al.
(författare)
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Fluidization regimes in non-slugging fluidized beds: the influence of pressure drop across the air distributor
- 1996
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Ingår i: Powder Technology. - 1873-328X .- 0032-5910. ; 86:3, s. 299-312
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present work is to study the influence of the pressure drop across the air distributor on the bubbling conditions of thebottom bed of circulating fluidized beds (CFB). The bottom bed is the dense bubbling zone just above the distributor. The experimental workwas carried out in a 12 MWm CFB boiler and in a cold CFR Three different distributions of the bubble flow in time and space, termedfluidization regimes, were identified in the cold CFB: the multiple bubble regime with many small bubbles evenly distributed in the bed; thesingle bubble regime, characterized by the presence of only one bubble at a time in the bed; and the exploding bubble regime with large,single, irregular voids stretching from the air distributor to the bed surface. These bubbling conditions were observed during variations in thegas velocity and the distributor pressure drop. A comparison with the 2 mz cross-section CFB boiler showed that the boiler always operatesin the single or in the exploding bubble regime, which indicates a bubble flow that is not continuous and not well distributed over the crosssectionof the bed. The conditions in the boiler are influenced by the relatively large area of gas passage and the low pressure drop of theboiler air distributor.
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| 18. |
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| 19. |
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| 20. |
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