TY - GEN
T1 - CFB cyclones
T2 - 9th International Conference on Circulating Fluidized Beds, CFB 2008, in Conjunction with the 4th International VGB Workshop on Operating Experience with Fluidized Bed Firing Systems
AU - Chan, C. W.
AU - Seville, J. P.K.
AU - Fan, X.
AU - Dewil, R.
AU - Baeyens, J.
PY - 2008/1/1
Y1 - 2008/1/1
N2 - Cyclones are widely used in circulating fluidized beds (CFB), where they operate at high solids loading. The paper presents experimental results of DP measurements for a CFB cyclone, and views the real-time particle motion within the cyclone by positron emission particle tracking (PEPT). The pressure drop is a function of the solids loading (Cs), with an initial decrease, followed by a dominant increase at Cs in excess of ∼3 kg of solids per kg of air. The particle movement in the cyclone can elucidate this phenomenon. A total of 40 experiments were carried out using PEPT imaging. Cyclones normally operate in a stable particle movement mode, always with a spiral motion in the cylindrical part of the cyclone, followed either by a continued spiral in the cone (at Cs < ∼1) or by a pseudo-packed solids flow near the cone wall at higher Cs values. Unstable movement is seen within a narrow range of combined cyclone velocity (vc) and Cs, without formation of a wall film of particle aggregates. The occurrence of aggregates at high Cs is demonstrated by the nearly constant tangential velocity of the tracer particle, irrespective of the air flow rate and Cs: an increased air flow rate does not increase the tangential velocity of the particle. The stability of the vortices is related to the amount of solids hold-up in the cyclone, itself seen to increase with Cs value, to achieve a nearly constant value when Cs > 10. Knowing Cs and the hold-up in the cyclone, an average thickness of the solids film can be calculated: this film thickness firstly increases up to Cs values of ∼10 kg/kg, and thereafter remains fairly constant at 0.0175 m, irrespective of the air flow. This downwards moving layer reduces the actual "free" cross section of the cyclone, thus increasing the air velocity and the pressure drop, especially for small cyclones, as used in the present research. This effect will be negligible for larger cyclones where the influence of Cs is less pronounced and DP values are expected to remain in the decreasing part of the ΔP vs. vc relationship.
AB - Cyclones are widely used in circulating fluidized beds (CFB), where they operate at high solids loading. The paper presents experimental results of DP measurements for a CFB cyclone, and views the real-time particle motion within the cyclone by positron emission particle tracking (PEPT). The pressure drop is a function of the solids loading (Cs), with an initial decrease, followed by a dominant increase at Cs in excess of ∼3 kg of solids per kg of air. The particle movement in the cyclone can elucidate this phenomenon. A total of 40 experiments were carried out using PEPT imaging. Cyclones normally operate in a stable particle movement mode, always with a spiral motion in the cylindrical part of the cyclone, followed either by a continued spiral in the cone (at Cs < ∼1) or by a pseudo-packed solids flow near the cone wall at higher Cs values. Unstable movement is seen within a narrow range of combined cyclone velocity (vc) and Cs, without formation of a wall film of particle aggregates. The occurrence of aggregates at high Cs is demonstrated by the nearly constant tangential velocity of the tracer particle, irrespective of the air flow rate and Cs: an increased air flow rate does not increase the tangential velocity of the particle. The stability of the vortices is related to the amount of solids hold-up in the cyclone, itself seen to increase with Cs value, to achieve a nearly constant value when Cs > 10. Knowing Cs and the hold-up in the cyclone, an average thickness of the solids film can be calculated: this film thickness firstly increases up to Cs values of ∼10 kg/kg, and thereafter remains fairly constant at 0.0175 m, irrespective of the air flow. This downwards moving layer reduces the actual "free" cross section of the cyclone, thus increasing the air velocity and the pressure drop, especially for small cyclones, as used in the present research. This effect will be negligible for larger cyclones where the influence of Cs is less pronounced and DP values are expected to remain in the decreasing part of the ΔP vs. vc relationship.
UR - http://www.scopus.com/inward/record.url?scp=84904819248&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:84904819248
SN - 9783930400577
T3 - CFB 2008 - Proceedings of the 9th Int. Conference on Circulating Fluidized Beds, in Conjunction with the 4th International VGB Workshop "Operating Experience with Fluidized Bed Firing Systems"
BT - CFB 2008 - Proceedings of the 9th Int. Conference on Circulating Fluidized Beds, in Conjunction with the 4th International VGB Workshop "Operating Experience with Fluidized Bed Firing Systems"
PB - TuTech Innovation GmbH
Y2 - 13 May 2008 through 16 May 2008
ER -