The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Yunhan Xiao - One of the best experts on this subject based on the ideXlab platform.
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intensification of high density cfb by Standpipe aeration under elevated pressure
Chemical Engineering and Processing, 2020Co-Authors: Yunhan XiaoAbstract:Abstract The computational particle fluid dynamics approach is applied to investigate the effect of aeration scheme on gas-solid flow characteristics in a pressurized high-density circulating fluidized bed. The simulated pressure profiles in both riser and Standpipe agree well with experimental data under pressurized conditions. Two types of aeration schemes are proposed, and their effects on the solids circulation behavior under different pressures are compared. It is found that a small increase of the Standpipe aeration and the turning aeration can obviously increase the solids circulation rate. With the increase of solids circulation rate, there is no distinct interface between the packed bed and the free moving region under high pressure, while alternatively a dense transition region emerges. The Standpipe aeration makes the pressure gradient distribution in the packed bed more uniform. The falling particles in the bottom region of the Standpipe are fluidized and the frictional resistance is reduced, which is beneficial for particles being transported through the valve by the turning aeration.
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three dimensional full loop simulation of a high density cfb with Standpipe aeration experiments
Powder Technology, 2017Co-Authors: Xiang Xu, Yunhan XiaoAbstract:Three-dimensional full-loop simulation of a high-density circulating fluidized bed (HDCFB) is conducted using the multiphase particle-in-cell (MP-PIC) method. The computational results are in good agreement with the experimental data of pressure distribution and solids circulation rate under different aeration conditions of the Standpipe. The main feature of gas-solid flow in the riser is qualitatively predicted, with coexistence of the developed flow in the upper region and the acceleration flow in the lower region. The flow regime in the Standpipe is mainly concurrent downward gas-solid flow in the close packing region. Due to the influence of the aeration gas, the pressure gradient presents a wave variation along the height of Standpipe. The predicted solids residence time distribution in the Standpipe exhibits a feature of early peak with an extended tail, indicating that the solids flow is not uniform in the Standpipe.
Lawrence J Shadle - One of the best experts on this subject based on the ideXlab platform.
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Standpipe models for diagnostics and control of a circulating fluidized bed
Powder Technology, 2013Co-Authors: Christopher J Ludlow, Rupen Panday, Lawrence J ShadleAbstract:Abstract Two models for a Circulating Fluidized Bed (CFB) Standpipe were formulated, implemented and validated to estimate critical CFB operational parameters. The first model continuously estimates Standpipe bed height using incremental pressure measurements within the Standpipe. The second model estimates variations in the void fraction along the Standpipe using the Ergun equation in conjunction with the overall pressure drop across the bed, solids circulation rate and the Standpipe aeration flows introduced at different locations of the pipe. The importance of different Standpipe parameters obtained from these models is discussed in terms of successful operation of the overall CFB system. Finally, the applications of these models are shown in improving the solids circulation rate measurement and in calculating riser inventory.
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Evaluations of wall shear stress in the Standpipe of a circulating fluidized bed
2008Co-Authors: E.r. Monazam, Lawrence J ShadleAbstract:Shear stress was obtained in the Standpipe of a Circulating Fluidized Bed (CFB) for a light cork particles under a variety of flow conditions. The shear stress data were estimated using incremental gas phase pressure drop readings, and an estimate of the bed height to predict the hydrostatic pressure drop [(dp/dy) = ρs (1-e) g+4τsw/D]. In addition, we have also obtained data on aeration rate in the Standpipe, particle circulation rate and riser gas flow rate. Analysis of the results using a one-dimensional momentum equation reveal that the observed forced per unit area may be attributed to wall friction. The resulting shear stress demonstrates that as the aeration air in the Standpipe was increased the shear at the wall was decreased. An attempt was made to model solids friction factor as a function of particle velocity and it was compared to the other literature correlations.
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experimentally measured shear stress in the Standpipe of a circulating fluidized bed
Aiche Journal, 2005Co-Authors: Angela Sarra, Aubrey L Miller, Lawrence J ShadleAbstract:Shear stress measurements were obtained in the Standpipe of a circulating fluidized bed (CFB) for 230-μm coke breeze particles under a variety of flow conditions. These data were combined with incremental gas-phase pressure drop readings, and an estimate of the bed weight to predict the solids-phase pressure drop. It was determined that the wall shear stress and solids-phase pressure drop are significant portions of the momentum balance and cannot be neglected when modeling frictional flow behavior of Geldart type B powders in a Standpipe using the conservation of linear momentum. The combined magnitude of the axial solids-phase pressure drop and wall shear stress exceeded 48% of the total forces in the mixture momentum balance for a Standpipe. However, tests indicated that the influence of the wall shear stress and axial solids pressure in the mixture momentum balance may be assumed to be negligible once minimum fluidization has been exceeded. Under packed Standpipe flow conditions most literature applications treat the wall shear stress as being directly proportional to the axial solids pressure divided by a proportionality factor that does not change with solids flow rate. This assumed constant is the product of the Janssen coefficient and coefficient of friction or the stress ratio. However, shear stress measurements indicated that this proportionality factor experienced a large monotonic decrease from conditions of incipient flow, where it was at its maximum, to conditions of high volumetric fluxes, where it approached a much smaller constant value. Two packed-bed flow regimes were identified. They are the smooth flow regime, characterized as spanning from moderate to large solid volumetric flow rates, and a stick-slip regime characterized as spanning from incipient to moderate solid volumetric fluxes.
Prabir Basu - One of the best experts on this subject based on the ideXlab platform.
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Heat transfer in Standpipe of circulating fluidised bed boiler
Journal of The Energy Institute, 2009Co-Authors: Prabir Basu, Animesh Dutta, James Butler, A. LeonAbstract:AbstractThe paper presents experimental and theoretical investigations into heat transfer to cross- and vertical tubes in the Standpipe of a circulating fluidised bed (CFB) boiler. Two separate test rigs (one to study the heat transfer on the wall and the other to cross-tubes) were used for this study of heat transfer to moving packed beds in the Standpipe of a CFB. The height averaged heat transfer coefficient on the wall and the surface averaged heat transfer coefficient on the tubes are comparable at a given solid flux through the Standpipe. Heat transfer coefficient on the wall reduced from the top to the bottom, and the rate of decrease reduced with height as generally observed on the furnace wall of a CFB riser. Analysis of heat transfer around the tube showed that heat transfer is the lowest at the bottom of the tube due to the presence of an area of stagnant particles resembling a wake. Owing to the increased residence time of particles on the surface of larger diameter tubes, an increase in the t...
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an investigation on heat transfer to the Standpipe of a circulating fluidized bed boiler
Chemical Engineering Research & Design, 2003Co-Authors: Animesh Dutta, Prabir BasuAbstract:The paper reports an experimental and theoretical investigation on heat transfer to the walls of the Standpipe of a circulating fluidized bed boiler. The heat transfer was studied in a Standpipe test section, 1940 mm long and 100 mm square cross section. Solids used in this study were silica-alumina ceramic and sand with densities of 700 and 2564 kg/m 3 , and sizes of 130 and 266 μm, respectively. The results show that there are two distinct zones: dense and dilute. For both types of particles, the heat transfer is higher in the dense section. The heat transfer coefficient increases with increase in the solids circulation rate. For a given circulation rate, a finer particle yields higher heat transfer coefficient. The paper also presents a mechanistic model of heat transfer in the Standpipe. Heat transfer coefficients predicted by the proposed model agree well with the experimental data.
Chengchuan Zhou - One of the best experts on this subject based on the ideXlab platform.
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gas solid flow behavior in the Standpipe of a circulating fluidized bed with a loop seal
Energy & Fuels, 2011Co-Authors: Hairui Yang, Hai Zhang, Chengchuan ZhouAbstract:In this paper, the flow behavior of gas−solid flow in the Standpipe of a circulating fluidized bed (CFB) and its influence on the system pressure balance and hydrodynamic performance have been studied. A CFB apparatus with a square riser of 0.1 × 0.1 m in cross-section and 4.5 m in height and a Standpipe of 3.0 m in height and 0.08 m in diameter were established. The Standpipe connected the riser to a loop seal on one end and connected to the cyclone on the other end. The experimental results showed that the flow behavior in the Standpipe is not only strongly related to the particle holdup, the structure, and the aeration flow rate of the Standpipe and loop seal but also strongly coupled with the pressure drops of the rest of the parts of the CFB system. At fixed-bed inventory Mt and fluidizing gas velocity in the riser Ug, the solid circulating rate GS increases with the flow rate of aeration air Q in the loop seal. With an increasing GS, the pressure drop of the loop seal decreases, while both the press...
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Gas−Solid Flow Behavior in the Standpipe of a Circulating Fluidized Bed with a Loop Seal
Energy & Fuels, 2011Co-Authors: Hairui Yang, Hai Zhang, Chengchuan ZhouAbstract:In this paper, the flow behavior of gas−solid flow in the Standpipe of a circulating fluidized bed (CFB) and its influence on the system pressure balance and hydrodynamic performance have been studied. A CFB apparatus with a square riser of 0.1 × 0.1 m in cross-section and 4.5 m in height and a Standpipe of 3.0 m in height and 0.08 m in diameter were established. The Standpipe connected the riser to a loop seal on one end and connected to the cyclone on the other end. The experimental results showed that the flow behavior in the Standpipe is not only strongly related to the particle holdup, the structure, and the aeration flow rate of the Standpipe and loop seal but also strongly coupled with the pressure drops of the rest of the parts of the CFB system. At fixed-bed inventory Mt and fluidizing gas velocity in the riser Ug, the solid circulating rate GS increases with the flow rate of aeration air Q in the loop seal. With an increasing GS, the pressure drop of the loop seal decreases, while both the press...
Animesh Dutta - One of the best experts on this subject based on the ideXlab platform.
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Heat transfer in Standpipe of circulating fluidised bed boiler
Journal of The Energy Institute, 2009Co-Authors: Prabir Basu, Animesh Dutta, James Butler, A. LeonAbstract:AbstractThe paper presents experimental and theoretical investigations into heat transfer to cross- and vertical tubes in the Standpipe of a circulating fluidised bed (CFB) boiler. Two separate test rigs (one to study the heat transfer on the wall and the other to cross-tubes) were used for this study of heat transfer to moving packed beds in the Standpipe of a CFB. The height averaged heat transfer coefficient on the wall and the surface averaged heat transfer coefficient on the tubes are comparable at a given solid flux through the Standpipe. Heat transfer coefficient on the wall reduced from the top to the bottom, and the rate of decrease reduced with height as generally observed on the furnace wall of a CFB riser. Analysis of heat transfer around the tube showed that heat transfer is the lowest at the bottom of the tube due to the presence of an area of stagnant particles resembling a wake. Owing to the increased residence time of particles on the surface of larger diameter tubes, an increase in the t...
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an investigation on heat transfer to the Standpipe of a circulating fluidized bed boiler
Chemical Engineering Research & Design, 2003Co-Authors: Animesh Dutta, Prabir BasuAbstract:The paper reports an experimental and theoretical investigation on heat transfer to the walls of the Standpipe of a circulating fluidized bed boiler. The heat transfer was studied in a Standpipe test section, 1940 mm long and 100 mm square cross section. Solids used in this study were silica-alumina ceramic and sand with densities of 700 and 2564 kg/m 3 , and sizes of 130 and 266 μm, respectively. The results show that there are two distinct zones: dense and dilute. For both types of particles, the heat transfer is higher in the dense section. The heat transfer coefficient increases with increase in the solids circulation rate. For a given circulation rate, a finer particle yields higher heat transfer coefficient. The paper also presents a mechanistic model of heat transfer in the Standpipe. Heat transfer coefficients predicted by the proposed model agree well with the experimental data.
