Modeling of solids segregation in circulating fluidized bed boilers
Received date: 08 Jan 2010
Accepted date: 09 Mar 2010
Published date: 05 Mar 2011
Copyright
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 , 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.
Key words: segregation; model; terminal velocity; circulating fluidized bed (CFB)
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
A | section area/ m2 |
dp | particle size/m |
mean particle size of all materials in the cell/m | |
mean particle size of all materials in the riser/m | |
d50 | cut size/m |
d90 | critical size/m |
Gs | circulating rate/(kg·m-2·s-1) |
i | cell number |
j | particle size number |
k1 | segregation ability/(m·s-1) |
k2 | segregation ability/(m·s-1) |
mj | mass of size j particles/kg |
m | total mass in each cell |
ugas | gas velocity/(m·s-1) |
ut | terminal velocity/(m·s-1) |
uterm | average terminal velocity corresponding to in riser/(m·s-1) |
average terminal velocity corresponding to in cell i/(m·s-1) | |
Wdn | downward flowing rate/(kg·s-1) |
Wup | upward flowing rate/(kg·s-1) |
ξ | segregation index |
ϵ | voidage |
ρ | particle density/(kg·m-3) |
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