The solids flow in the riser of a Circulating Fluidised Bed (CFB) viewed by Positron Emission Particle Tracking (PEPT)

Abstract Circulating Fluidised Beds (CFB) are attracting increasing interest for both gas–solid and gas-catalytic reactions, although the operating modes in these two cases are completely different. In modelling CFBs as reactors, the solids residence time is an important parameter. Previous studies mostly assess operations at moderate values of the solids circulation rates (≤ 100 kg/m 2 s), whereas gas-catalytic reactions and e.g. biomass pyrolysis require completely different operating conditions. In the current work, Positron Emission Particle Tracking (PEPT) is used to study the movement and population density of particles in the CFB-riser. The PEPT results can be used to obtain: (i) the vertical particle movement and population density in a cross sectional area of the riser; (ii) the transport gas velocity ( U tr ) required in order to operate in a fully established circulation mode; (iii) the overall particle movement mode (core flow versus core/annulus flow); and (iv) the particle slip velocity ( U s ). Only in a core flow mode can the particle slip velocity be estimated from the difference between the superficial gas velocity ( U ) and the particle terminal velocity ( U t ). The slip velocity is lower than U  −  U t outside the core flow mode. To operate in core flow, the superficial gas velocity should exceed U tr by approximately 1 m/s and the solids circulation rate should exceed 200 kg/m 2 s.

[1]  Jan Baeyens,et al.  Overall solids movement and solids residence time distribution in a CFB-riser , 2000 .

[2]  D. J. Parker,et al.  Positron emission tomography for process applications , 1996 .

[3]  Xianfeng Fan,et al.  Labelling a single particle for positron emission particle tracking using direct activation and ion-exchange techniques , 2006 .

[4]  Hsiaotao Bi,et al.  Flow regime diagrams for gas-solid fluidization and upward transport , 1995 .

[5]  David Parker,et al.  Enhancing 18F uptake in a single particle for positron emission particle tracking through modification of solid surface chemistry , 2006 .

[6]  Rex B. Thorpe,et al.  Particle residence time distributions in circulating fluidised beds , 2003 .

[7]  Jesse Zhu,et al.  Distinctions between low density and high density circulating fluidized beds , 1995 .

[8]  P. Fowles,et al.  Developments in particle tracking using the Birmingham Positron Camera , 1997 .

[9]  Jamal Chaouki,et al.  Effets de differents parametres sur les vitesses de transition de la fluidisation en regime turbulent , 1995 .

[10]  M. R. Hawkesworth,et al.  Positron emission particle tracking - a technique for studying flow within engineering equipment , 1993 .

[11]  Hsiaotao Bi,et al.  Existence of Turbulent Regime in Gas-Solid Fluidization , 1992 .

[12]  S. D. Kim,et al.  Bed expansion characteristics and transition velocity in turbulent fluidized beds , 1990 .

[13]  Jamal Chaouki,et al.  Hydrodynamics of circulating fluidized bed risers: A review , 1995 .

[14]  P. Gayán,et al.  Transport velocities of coal and sand particles , 1993 .

[15]  J. Bridgwater,et al.  PEPT for agglomeration , 2004 .

[16]  Katia Tannous Contribution à l'étude hydrodynamique des lits fluidisés de grosses particules , 1993 .