Drum without lifters

Drum Without Lifters and Without Discharge End Constriction, 202 Drum Without Lifters and With Discharge End Constriction, 204 Drum With Lifters, 204... 

FLOW OF HIGHLY SETTLING SLURRIES IN ROTARY DRUMS, 207 Drum With an Open-End Dishcarge and No Lifters, 207 Drums With an End-Constriction, 220 Drum Without Lifters, 220 Drum With Lifters, 231... 

There are two types of solids motion in a horizontal rotary drum longitudinal (axial) and transverse (radial). For a horizontal drum without lifters, solids transport in the axial direction occurs as a result of the difference in the bed height at the inlet and outlet ends of the drum. Afacan and Masliyah discussed various models to predict dry solids transport in rotary drums as a result of the bed height axial gradient [16]. 

Drum Without Lifters and Without Discharge End Constriction... 

The variation of solids fractional hold-up with drum speed is shown in Figure 5 for the case of a drum without lifters and with discharge end constriction. The variation is similar to that reported by Abouzeid and Fuerstenau [11,29]. The solids hold-up is much higher with the end constriction than with a free drum opening as shown in Figure 3. 

Figure 23. Effect of drum speed on bed frequency of oscillation for a drum without lifters.

Figure 28. Effect of slurry feed flow rate on slurry hold-up in a drum without lifters.

Nasr El-Din et al. [39] observed that at low rotational speeds, the solid particles were carried up the drum wall with the lifters and fell back to the bottom of the drum. As a result of the particles motion, mixing within the slurry bed and between the liquid and the slurry bed was significantly improved. At higher drum speeds, solids in the bed assumed a rolling motion and the slurry bed had a kidney shape. Unlike the drum without lifters, no slurry bed oscillation was observed for all the experiments conducted using the drum with lifters. The presence of the lifters prevented the downswing solids motion and, hence, prevented any oscillation from occurring. In essence, the lifters affected the radial motion of the solids bed drastically. 

Slurry Hold-up and Mean Solids Concentration. Figure 30 depicts the influence of the drum rotational speed on the slurry hold-up for slurry feed concentrations of 7.8%, 21.0%, and 45.9%. The slurry hold-up-drum speed relationship exhibited a minimum for all the feed solids concentrations examined. At low drum speeds, the slurry hold-up increased with the feed solids concentration. However, at high drum speeds the effect of the slurry feed solids concentration on the slurry holdup was less significant. The most important aspect of Figure 30 is that the lifters eliminated the abrupt changes in the slurry hold-up observed for the drum without lifters. 

The results shown in Figures 25 and 31 indicate that for a given Cp the mean solids concentration in the drum with lifters is lower than that for the drum without lifters. This trend is due to higher axial particle velocities encountered in drums with lifters. For the drum with lifters, the variation of the slurry mean solids concentration with the drum speed was much less pronounced than that observed for the drum without lifters. Also, the effect of Cp on the hold-up solids concentration was more pronounced for the drum with lifters. 

Effect of Feed Rate on Slurry Hold-up. Figure 33 shows the effect of the slurry feed rate on the slurry hold-up at drum speeds of 7 and 35 rpm for Cp = 21.1%. The slurry hold-up increased with the slurry feed flow rate. This trend is similar to that observed with the drum without lifters (Figure 28). However, the presence of lifters tended to decrease the slurry hold-up at a drum speed of 7 rpm. At a drum speed of 35 rpm, the effect of the lifters on the slurry hold-up was not significant. 

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