RESEARCH ARTICLE

Modeling of solids segregation in circulating fluidized bed boilers

  • Xuan YAO 1 ,
  • Tao WANG 1 ,
  • Jia ZHAO 2 ,
  • Hairui YANG , 1 ,
  • Hai ZHANG 1
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  • 1. Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
  • 2. Department of Mathematics and Applied Science, School of Applied Science, University of Science and Technology Beijing, Beijing 100083, China

Received date: 08 Jan 2010

Accepted date: 09 Mar 2010

Published date: 05 Mar 2011

Copyright

2014 Higher Education Press and Springer-Verlag Berlin Heidelberg

Abstract

Segregation always occurs in a circulating fluidized bed (CFB) because of the wide distribution of particle size and density of the bed material. Terminal velocity has a significant influence on solids segregation; thus, it is convenient to describe the segregation tendency using single particle terminal velocity ut. This paper proposes a segregation model in CFB boilers based on the Cell Model. In each cell along the riser, varied-sized particles have different tendencies toward segregation; finer particles are carried out more easily, while coarser ones tend to sink into the cell. It is assumed that the average terminal velocity ut ¯, corresponding to the mean particle size in the cell, has a segregation index of x = 1.0 as the reference point. The segregation index of particles with higher terminal velocity is lower than 1.0, while that for finer particles is larger than 1.0. The empirical formulae of segregation parameters, namely x0 and k1, are derived by optimizing experimental data in published literature. The test result of ash size distribution in a 220 t/h CFB boiler validates the reasonableness of the model.

Cite this article

Xuan YAO , Tao WANG , Jia ZHAO , Hairui YANG , Hai ZHANG . Modeling of solids segregation in circulating fluidized bed boilers[J]. Frontiers in Energy, 2011 , 5(1) : 115 -119 . DOI: 10.1007/s11708-010-0103-0

Acknowledgements

This work was supported by the Hi-Tech Research and Development Program of China (No. 2009AA05Z302) and the National 11th-Five Year Plan (No. 2006BAD07A14-4).
Nomenclature
Asection area/ m2
dpparticle size/m
d ¯pmean particle size of all materials in the cell/m
d ¯p0mean particle size of all materials in the riser/m
d50cut size/m
d90critical size/m
Gscirculating rate/(kg·m-2·s-1)
icell number
jparticle size number
k1segregation ability/(m·s-1)
k2segregation ability/(m·s-1)
mjmass of size j particles/kg
mtotal mass in each cell
ugasgas velocity/(m·s-1)
utterminal velocity/(m·s-1)
utermaverage terminal velocity corresponding to d ¯p0 in riser/(m·s-1)
ut ¯average terminal velocity corresponding to d ¯p in cell i/(m·s-1)
Wdndownward flowing rate/(kg·s-1)
Wupupward flowing rate/(kg·s-1)
ξsegregation index
ϵvoidage
ρparticle density/(kg·m-3)
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