The flow characteristics such as the beds of bubbling, turbulent, fast and dilute phase have been studied in a vertical transport line (7.8 cm-I.D. × 600 cm-height) in order to determine the hydrodynamic properties of a fluidized bed precalciner.
The cement raw meals ($bar{d}$_p=23.6㎛) have been transported by compressed air at various flow regimes.
The effects of gas velocity and solid recirculating rate on the pressure drop, bed homogeneity and gas backmixing have been determined.
The slug breakdown velocity, $V_c$, from which bubbling and turbulent beds are divided, has been determined by measuring the fluctuations of pressure drop across the distributor at wide range of air velocities. Capacitance probe has been employed in order to measure the bed homogeneity. The degree of gas backmixing was measured using steady-state tracer ($CO_2$) injection technique in bubbling and turbulent beds.
The transport velocity, boundary between turbulent and fast beds, has been determined from the data of pressure drop at various air velocities, particle recirculating rates, and the time of fluidized bed disappearance.
From the present study, the slug breakdown and transport velocities are found to be 39 cm/sec, and 180-200 cm/sec, respectively.
The bed homogeniety of turbulent bed increased with increasing gas velocity. In this regard, the bed homogeniety of turbulent bed is superior than that of bubbling bed conditions. However, the extent of gas backmixing is found to be less in the turbulent bed.
From the analysis of the present data, the following equations are proposed in order to construct a flow regime diagram in the vertical transport line;
1. Boundary between packed bed and slugging dense phase flows (bubbling bed).
$R = 1388.9 (1-(1/747 V_g^+))$
2. Boundary between slugging dense phase and non-slugging dense phase flows (turbulent or fast beds)
$R = 520.8 (1-0.486/V_g^+)$
3. Boundary between non-slugging dense phase and dilute phase flow.
$R = 64.6 (1-0.97/V_g^+)$
