| 1. |
- Ersoy, L., et al.
(author)
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Circulating fluidized bed hydrodynamics with air staging: an experimental study
- 2004
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In: Powder Technology. ; 145, s. 25-33
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Journal article (peer-reviewed)abstract
- The influence of secondary air injection (SA) on the hydrodynamics of circulating fluidized beds was studied in a 0.23-m ID riser. The secondary to primary air ratio, the vertical position, and the mode of injection (radial, tangential, and 45j entrance) are considered to be the key parameters of SA injection. It was found that the amount and location of SA have direct influence on the solids holdup and the segregation patterns in the riser. The SA divided the riser into two different flow zones: a dense turbulent zone below and a relatively dilute bed above the injection port. The mean solids velocity is found to be upwards with a greater magnitude in the center region. It is downwards with a smaller magnitude along the walls, suggesting core-annular flow structures for both above and below the SA injection region.
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| 2. |
- Koksal, M., et al.
(author)
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Effect of staged air on heat transfer in circulating fluidized beds
- 2008
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In: Applied Thermal Engineering. ; 28, s. 1008-1014
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Journal article (peer-reviewed)abstract
- The purpose of this work is to develop a model for bed-to-surface heat transfer in circulating fluidized bed (CFB) risers with secondary air (SA) injection. The heat transfer coefficient is correlated to cross-sectionally averaged solids hold-up. The average solids hold-up is correlated with the operating and design parameters of CFB risers with SA injection. The data used in developing the correlations cover a range of 2.0–8.6 m/s for superficial gas velocity, 5–100 kg/m2s for solids circulation rate, 0–0.6 for secondary to primary air ratio, and 60–300 lm for particle diameter (groups A and B). The predictions obtained with the correlations show good agreement with the experimental data. Furthermore, an experimental correlation, developed in our previous work for prediction of wall-to-bed heat transfer coefficient was used in a parametric study to investigate the effects of design and operating parameters on heat transfer.
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| 3. |
- Zhang, D., et al.
(author)
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Fluidization Characteristics of Rice Husk in a Bubbling Fluidized Bed
- 2006
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In: 19th International Conference on Fluidized Bed Combustion.
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Conference paper (peer-reviewed)abstract
- The fluidization characteristics of rice husk was investigated experimentally in a 0.17 m ID, 0.9 m high laboratory scale fluidized bed by analyses of mean bed pressure drop, pressure fluctuations, power spectrum of pressure fluctuations, and visual observation with a digital camera. The results show that pure rice husk (rp = kg/m3) cannot be fluidized uniformly due to the occurrence of severe channeling. One of the possible methods to facilitate fluidization is to mix rice husk with an easily fluidizable solid. In this study, mixing 700 mm glass bead particles (rp = 2500 kg/m3) with rice husk improved the fluidization characteristics significantly. The minimum fluidization velocity of the binary mixture decreased and approached to that of glass bead particles as the mass fraction of the rice husk in the mixture was decreased. Power spectrum of pressure fluctuations was used to determine the quality of fluidization and estimate the onset of fluidization for the rice husk-glass beads mixture. Furthermore, it was found that with intermittent (pulsed) supply of fluidization air, the fluidization characteristics of pure rice husk could be substantially enhanced. In a frequency range of 0-10 Hz, flow pulsation resulted in turbulent bed-like behavior with improved gas-solid contact.
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| 4. |
- Koksal, M., et al.
(author)
-
HEAT TRANSFER IN CIRCULATING FLUIDIZED BEDS WITH SECONDARY AIR INJECTION
- 2006
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In: International Heat Transfer Conference, IHTC-13. - 1567002250
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Conference paper (peer-reviewed)abstract
- In this study, we present an empirical model for bed-to-surface heat transfer in Circulating Fluidized Beds (CFB) with secondary air (SA) injection. The model is based on a correlation that relates the heat transfer coefficient to cross-sectionally averaged solids holdup. The average solids holdup was correlated with the operating and design parameters of CFBs with SA injection using three dimensionless parameters: Archimedes number, Gs/rp(U0-USA) and (1-HSA/Hr). The correlations were obtained using least square analysis for a wide range of data available in the literature as well as the data obtained in this study for two types of SA injectors: radial and tangential. The data used in developing the correlations cover a range of 2.0 to 8.6 m/s for superficial gas velocity, 5 to 100 kg/m2s for solids circulation rate, 0-0.6 for secondary to primary air ratio, and 60 to 300 mm for particle diameter (Groups A and B). The predictions obtained with the correlations show good agreement with the experimental data. Furthermore, an experimental correlation, developed in our previous work for prediction of wall-to-bed heat transfer coefficient in CFB risers operated with SA was used in a parametric study to investigate the effects of design and operating parameters on heat transfer. The results of the parametric study indicate that the heat transfer coefficient increases with increasing secondary air ratio, solids circulation rate, and height of secondary air injection port. The tangential SA injector was found to result in a significant increase in heat transfer coefficient compared with radial injector and non-SA operation due to increase in average solids holdup. This is consistent with the available data in the literature.
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| 5. |
- Koksal, M., et al.
(author)
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Thermal Aspects a Circulating Fluidized Bed with Air Staging
- 2005
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In: International Journal of Energy Research. - : John Wiley & Sons, Ltd.. - 0363-907X .- 1099-114X. ; 29:10, s. 923-935
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Journal article (peer-reviewed)abstract
- In this study, effects of air staging on wall-to-bed heat transfer were investigated in a laboratory scale circulating fluidized bed (0.23m ID, 7.6m high). The bed was operated under ambient conditions with silica sand particles (dp=89 mm, rp=2650 kgm_3). Two different designs of secondary air (SA) injectors were used for air staging: radial and tangential. Bed-to-wall heat transfer measurements were carried out at three elevations above the SA injection port. The results indicate that similar to non-SA operation, the heat transfer with air staging depends strongly on the cross-sectional average suspension density. Tangential secondary injection was found to increase the bed-to-wall heat transfer above the SA injection port significantly due to increased suspension density compared with non-SA operation.
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