Sesame and Broad Bean Stalks: Mixing Characteristics of Chips as a Biomass Fuel for Bubbling Fluidized Bed Combustor

2018 ◽  
Vol 16 (6) ◽  
Author(s):  
Saad A. El-Sayed ◽  
Amro A. El-baz ◽  
Emad H. Noseir
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Mass Fraction ◽  
Broad Bean ◽  
Sand Particle ◽  
Gas Velocity ◽  
Mixing Index ◽  
Bubbling Fluidized Bed ◽  
Superficial Gas Velocity ◽  
Fluidized Bed Combustor

Abstract Mixing and segregation characteristics of biomass particles are of practical importance because the in-bed combustion efficiency of volatile matter affects the vertical location of biomass in bubbling fluidized bed combustor. Sesame and broad bean stalk biomass materials mixed with sand used in this study. The superficial gas velocity, biomass chip length, sand particle size and mass fraction of biomass varied as experimental variables. The mixing and segregation behavior of mixtures were analyzed in terms of mixing index. It was found that the variability in the chip-shape made the sesame chips is quantitatively and qualitatively higher homogeneity and mixedness than the broad bean chips. The optimum overall mixing index for the sesame and the broad bean is around 0.96 and 0.84 at dimensionless superficial gas velocity (U/Umf) of 2.0 (1.40 m/sec) and 2.1 (1.25 m/sec), respectively. It was found that as the mean diameter increased and the sphericity decreased, the mixing quality decreased. The average sand particle size of 371 µm can keep good mixing with biomass chips of both materials, compared with average particle sizes of sand 550 and 700 µm. Increasing the initial biomass mass fraction yields a poor mixing of the investigated biomass stalks.

scholarly journals Particle-Scale Simulation of Solid Mixing Characteristics of Binary Particles in a Bubbling Fluidized Bed

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4442 ◽  
Author(s):  
Junjie Lin ◽  
Kun Luo ◽  
Shuai Wang ◽  
Liyan Sun ◽  
Jianren Fan
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Fluidized Bed ◽  
Critical Velocity ◽  
Superficial Velocity ◽  
Mixing Index ◽  
Mixing Behavior ◽  
Mixing Characteristics ◽  
Bubbling Fluidized Bed

The behavior of solid mixing dynamic is of profound significance to the heat transfer and reaction efficiencies in energy engineering. In the current study, the solid mixing characteristics of binary particles in the bubbling fluidized bed are further revealed at particle-scale. Specifically, the influences of gas superficial velocity, Sauter mean diameter (SMD) in the system and the range distribution of particle sizes on the performance of mixing index are quantitatively explored using a computational fluid dynamics-discrete element method (CFD-DEM) coupling model. The competition between solid segregation and the mixing of binary particles is deeply analyzed. There is a critical superficial velocity that maximizes the mixing index of the binary mixture in the bubbling fluidized bed. Solid mixing performs more aggressive when below the critical velocity, otherwise solid segregation overtakes mixing when above this critical velocity. Moreover, superficial velocity is a major factor affecting the mixing efficiency in the binary bubbling fluidized bed. Additionally, the mixing behavior is enhanced with the decrease of SMD while it is deteriorated in the binary system with a wide range of particle size distribution. Therefore, it is highly recommended to perform a binary particle system with smaller SMD and closer particle size distribution for the purpose of enhancing the mixing behavior. The significant understanding of mixing characteristics is expected to provide valuable references for the design, operation, and scale-up of binary bubbling fluidized bed.

Influence of Fluidization Velocity on Bed Defluidization in Fluidized Bed Combustors

2005 ◽  
Author(s):  
Mohammad R. Golriz ◽  
Morgan Eriksson ◽  
Marcus O¨hman ◽  
Anders Nordin ◽  
Rainer Backman
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Large Scale ◽  
Particle Diameter ◽  
Operating Conditions ◽  
Biomass Combustion ◽  
Gas Velocity ◽  
Fluidization Velocity ◽  
Significant Difference ◽  
Superficial Gas Velocity

Effects of superficial gas velocity and bed particle size on bed defluidization during biomass combustion were investigated. Sampled bed particles from four different large-scale circulating- and bubbling fluidized bed combustors, using biomass as fuel, were collected and analyzed. The bed particles from each fluidized bed unit were divided into small and large particle size fractions. The results indicate no significant difference in elemental compositions between small and large coated bed particles but the ratio of coating thickness to the mean particle diameter was higher for the small particles compared to the large ones. Controlled fluidized bed agglomeration tests revealed strong influence from fluidization velocity on initial defluidization temperatures at lower velocities, but little effect at higher velocities. Influence of bed particle size on initial defluidization temperature varied depending on operating conditions. Finally, a model based on viscous flow sintering is proposed for the relation between agglomeration temperature and superficial gas velocity. The model predictions are in good agreement with experimental data.

Characteristics of Mixing/Segregation in a Bubbling/Slugging Fluidized Bed with Binary Mixtures

2011 ◽  
Vol 396-398 ◽  
pp. 322-325 ◽  
Author(s):  
Heng Zhi Chen ◽  
Zheng Kui Guo
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Binary Mixtures ◽  
Fixed Bed ◽  
Size Difference ◽  
Gas Velocity ◽  
Carbon Particles ◽  
Fluidization Regime ◽  
Superficial Gas Velocity

Fluidization behavior of binary mixtures with titanic slag particles and carbon particles had been investigated. Three solids states in the bed: fixed bed, transient fluidization and steady fluidization, emerges as increasing gas velocity. The extent of segregation of solids mixture in transient fluidization regime depended on the size difference between jetsam particles and flotsam particles. The effects of flotsam particle size, initial jetsam concentration and the superficial gas velocity on the segregation of binary solids had been measured.

scholarly journals Limestone particle attrition and size distribution in a bench scale bubbling fluidized bed

2015 ◽  
Vol 17 (2) ◽  
pp. 236-247
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Fluidized Bed ◽  
Mass Fraction ◽  
Size Reduction ◽  
Particle Size Reduction ◽  
Bubbling Fluidized Bed ◽  
Cumulative Mass ◽  
Particle Attrition ◽  
Limestone Fines

<div> <p>Attrition of limestone particles in bubbling fluidized bed has significant influence on cyclic CO<sub>2</sub> capture ability of sorbents. The limestone particle attrition and size distribution characteristics were investigated experimentally in a bench scale fluidized bed. The effects of initial particle sizes, fluidized velocity, attrition time and temperature on limestone attrition characteristics were studied. An empirical fitting correlation was proposed to describe the relationship of cumulative mass fraction of limestone fines (<em>R</em>) and attrition time (<em>t</em>). The results show that the fines generation rate decreases and particle size reduction rate increases with increasing initial size. Chipping of large particle takes predominant position when fluidized velocity exceeds the minimum fluidization velocity resulting in more prominent reduction of particle size. After 4 hours attrition, particle size reduction and fines generation rate become constant. It is suggested that cumulative mass fraction of limestone fines (<em>R</em>) increases with attrition time with a function of decaying exponential correlation.</p> </div> <p>&nbsp;</p>

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