The axial distribution of the cross-sectionally averaged voidage in fast fluidized beds

Bai, Dingrong; Ye, Jin; Yu, Z.M.; Zhu, Jesse

doi:10.1016/0032-5910(92)88003-z

Cited by 180 publications

(107 citation statements)

References 1 publication

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“…It has been reported that a sharper riser exit geometry (e.g. L-shaped or T-shaped) increases the solids holdup in the top region of the riser due to particle reflux (Bai, Jin et al 1992;Martin, Derouin et al 1992;Zhou, Grace et al 1994;Pugsley, Lapointe et al 1997;Wu, Jiang et al 2010), but not for a more gradual exit geometry restriction such as a rounded bend (Lim, Zhu et al 1995) consistent with this study. Based solely on the exit geometry, the rounded elbow used in this work was not expected to culminate in strong reflux of solids at the top of the riser.…”

supporting

confidence: 81%

“…The y-axis represents dimensionless height along the riser (h/H), and the x-axis represents ΔP/Δh. For the large glass material depicted in Figure 148a, an increase in ΔP/Δh is observed at the topmost position of the riser; this phenomenon is known as 'reflux' and is due to the effect of the exit geometry (Bai, Jin et al 1992;Martin, Derouin et al 1992;Zhou, Grace et al 1994;Pugsley, Lapointe et al 1997). Interestingly, the higher ΔP/Δh at the top of the riser is more attenuated for the lower U s conditions, implying that back-mixing may be more dependent on U s than G s .…”

Section: Figure 147 Schematic Of Differences In Particle Trajectory mentioning

confidence: 99%

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Development, Verification, and Validation of Multiphase Models for Polydisperse Flows

Hrenya¹,

Cocco²,

Fox³

et al. 2011

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This report describes in detail the technical findings of the DOE Award entitled "Development, Verification, and Validation of Multiphase Models for Polydisperse Flows." The focus was on high-velocity, gas-solid flows with a range of particle sizes. A complete mathematical model was developed based on first principles and incorporated into MFIX. The solid-phase description took two forms: the Kinetic Theory of Granular Flows (KTGF) and Discrete Quadrature Method of Moments (DQMOM). The gas-solid drag law for polydisperse flows was developed over a range of flow conditions using Discrete Numerical Simulations (DNS). These models were verified via examination of a range of limiting cases and comparison with Discrete Element Method (DEM) data. Validation took the form of comparison with both DEM and experimental data. Experiments were conducted in three separate circulating fluidized beds (CFB's), with emphasis on the riser section. Measurements included bulk quantities like pressure drop and elutriation, as well as axial and radial measurements of bubble characteristics, cluster characteristics, solids flux, and differential pressure drops (axial only). Monodisperse systems were compared to their binary and continuous particle size distribution (PSD) counterparts. The continuous distributions examined included Gaussian, lognormal, and NETLprovided data for a coal gasifier.FINAL TECHNICAL 4 DE-FC26-07NT43098 5 EXECUTIVE SUMMARYThis report is the final technical report for the award DE-FC26-07NT43098 entitled "Development, Verification, and Validation of Multiphase Models for Polydisperse Flows." Below is a summary of work completed under the grant for each of the major goals. Goal I: Continuum Theory for Solid PhaseTwo separate and complementary continuum theories were derived to model polydisperse solids: the kinetic theory of granular flow (KTGF) and the discrete quadrature method of moments (DQMOM). Both theories are based on first principles with no adjustable parameters. The polydisperse KTGF and DQMOM were then encoded in MFIX, and underwent a wide range of verification testing to ensure, to the best possible extent, that no coding errors were present. These verification tests included both granular and gas-solid flows, including cases where an analytical solution and/or DEM (discrete element method) data and/or simple test cases. For the case of KTGF, another set of constitutive equations were derived which rigorously incorporated the gas phase for a simplified case of monodisperse systems at low Reynolds numbers. This derivation used the acceleration model developed in Task 2 from direct numerical simulations (DNS) in the starting kinetic equation, and indicated the effect of the fluid phase on the resulting constitutive relations. Goal II: Improved Gas-Particle Drag Laws -effect of particle size distributionIn this portion of the effort, two types of direct numerical simulations (DNS) were used to extract the drag force experienced by particles in a polydisperse suspension. These two methods, na...

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supporting

confidence: 81%

Section: Figure 147 Schematic Of Differences In Particle Trajectory mentioning

confidence: 99%

Development, Verification, and Validation of Multiphase Models for Polydisperse Flows

Hrenya¹,

Cocco²,

Fox³

et al. 2011

View full text Add to dashboard Cite

show abstract

“…This solids volume concentration was higher than that in the bottom dense region of typical CFBs ($0.2) and that in the ''DSU'' (0.15-0.25) as reported by Issangya et al, 6 Grace et al, 18 Pärssinen and Zhu, 21 Louge and Chang, 28 and Malcus et al 29 This highdensity uniform axial solids distribution in the C-TFB was a significant advantage over conventional CFB, which have a substantial variation in cross-sectional averaged solids concentration with a dense phase at the bottom and a relatively dilute region towards the top. 5,12 The axial uniform flow structure should lead to both uniform solid-gas contact efficiency and uniform suspension-to-wall heat transfer throughout bed height.…”

Section: Axial Solids Distribution Profilesmentioning

confidence: 99%

“…In addition, the independent control of gas and solids retention times provides the reactor more flexibility in operation. Previous experiments have clearly demonstrated that CFB is hydrodynamically characterized by an extremely nonuniform flow structure, with a dense bottom region and dilute upper region in the axial direction [4][5][6] and a ''core-annulus'' flow structure in the radial direction. [7][8][9] This nonuniform flow structure and relatively dilute solids concentration (usually less than 10%) result in many disadvantages, such as the serious gas by-passing through the core dilute region and extensive backmixing of solids in the wall region, consequently resulting in lower gross gas-solids contact efficiency and poor selectivity of chemical reactions.…”

Section: Conventional Fluidized Bedmentioning

confidence: 99%

Gas‐solids flow structures in a novel circulating‐turbulent fluidized bed

He-hua

Zhu

2008

AIChE Journal

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in Wiley InterScience (www.interscience.wiley.com).In this article a novel circulating-turbulent fluidized bed (C-TFB) featured by high solids holdup and high gross solids circulation has been introduced and tested. The purpose of the new design was to integrate conventional circulating and turbulent fluidized beds into a unique high-density fluidization system for more efficient gas-solid contact and significantly reduced solids backmixing. The hydrodynamic characteristics of the C-TFB were analyzed in terms of differential pressure, solids concentration, particle velocity, and local solids flux distributions. An axial homogeneous flow structure was easily obtained with cross-sectional average solids volume concentrations higher than 0.25 throughout the entire C-TFB. At all measuring positions there was no net downflow of solids and a good gas-solid mixing was observed.

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“…The gas-solid flow above the dense bed is known as fast fluidization [11]. Previous studies have shown that the axial profile of particle concentration is influenced by many factors, including the superficial gas velocity, the bed inventory, the solid circulation rate and the bed geometric structure [12][13][14]. As the flow resistance is relatively small in loop seals and the furnace height is usually higher than the transport disengaging height (TDH), the geometric structure usually has a minor impact on the gas-solid flow in CFB boilers.…”

Section: Fluidization State Theory Analysismentioning

confidence: 99%

Progress of circulating fluidized bed combustion technology in China: a review

Cai

Lyu

et al. 2017

Clean Energy

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Circulating fluidized bed (CFB) technology plays an important role in the utilization of low-grade coal in China. This article reviews CFB combustion technology development in China and summarizes recent achievements. Since 1990 Chinese engineers and researchers have been undertaking work to improve CFB boiler technology. A completely novel CFB boiler design theory was developed and used in the domestic manufacturing of CFB boilers with various capacities. China is the largest supplier and customer of CFB boilers in the world due to the widespread use of CFB boilers. In 2007, the lower energy consumption CFB technology was successfully developed by re-specifying the fluidization state, which reduced the power consumption of forced fans and solved the potential erosion problems on the water wall. Afterwards, in order to increase the electric power generation efficiency, the supercritical CFB (SCCFB) boiler was developed and the first 600 MW SCCFB boiler was demonstrated and put into commercial operation in 2013. The success of the technology is evident with over 80 SCCFB boilers on order with capacities of 350 MW to 660 MW. Chinese scientists and engineers are also developing technology to lower the emissions of CFB combustion to meet the requirements of China's strict emission regulations. This emission reduction is through high-efficiency desulfurization by limestone injection into the furnace and low NO x combustion, ultra-low emission of SO 2 and NO x in the furnace can be realized by improving the bed quality and increasing the solid circulation rate. There is currently further research and design development being undertaken to develop a 660 MW ultra-supercritical CFB (USCCFB) boiler. The new boiler is expected to be operational before 2020 resulting in higher efficiency and lower energy consumption and emissions.

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The axial distribution of the cross-sectionally averaged voidage in fast fluidized beds

Cited by 180 publications

References 1 publication

Development, Verification, and Validation of Multiphase Models for Polydisperse Flows

Development, Verification, and Validation of Multiphase Models for Polydisperse Flows

Gas‐solids flow structures in a novel circulating‐turbulent fluidized bed

Progress of circulating fluidized bed combustion technology in China: a review

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