Drum with 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... 

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. 

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. 

Figure 31. Effect of drum speed on slurry mean solids concentration in a drum with lifters.

To examine the effect of the fluid flow rate on the solids hold-up for the drum with lifters, the solids hold-up is plotted in Figure 34 as a function of the solids... 

Figure 33. Effect of slurry feed flow rate on slurry hold-up In a drum with lifters.

Drum Separators Very coarse solids, up to 0.3 m (12 in), are often processed in a drum separator of the type shown in Fig. 19-32. This is similar to a ball-mill shell with lifters permanently attached to the wall. Medium and feed enter at one end, and the float product flows out through the discharge trunnion, while the sink is lifted by the rotation of the drum to a stationary launder, through which it is flushed out. Modifications of this type include division oithe shell into two compartments, which permits simultaneous operation at two different pulp densities resulting in various grades of products. The two-compartment revolving drum is illustrated in Fig. 19-32. 

For given F, drum geometry and material properties. Equation 9 is used to evaluate P, which is then used to evaluate the fractional hold-up, H. Equation 9 is applicable to inclined drums with no end constriction and no lifters. 

Drum Without Lifters and With 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 7 displays the effect of the drum speed on the solids fractional hold-up for a drum fitted with lifters, but with no discharge end constriction. At the same solids feed rate and drum speed, the presence of the lifters increases the drum solids hold-up (Figures 3 and 7). 

Figure 7. Variation of soiids fractional hold-up with drum speed (with lifters and no end constriction). Solids feed rate, (kg/s) , 6.3 x 10 , 12.5 X 10-3 21.3 x IQ- <), 30.3 x IQ- .

Langrish [45] conducted a thorough study on using Equation 3 to predict Matched and Sheikh [46] hold-up data. The latter authors used a rotary drum fitted with lifters. 

In the previous section, the flow of a sand-water slurry in a horizontal drum with an open-end discharge was reviewed. Slurry hold-up was found to be a function of particle size, drum speed, feed flow rate, and composition. The experimental results also showed relatively low slurry hold-up and poor radial (transverse) mixing inside the drum. To overcome these problems for the case of dry solids, an end-constriction and lifters are normally used. The effects of such additions on the slurry hold-up and mean residence times of solids and fluid phases will be discussed in the next section. 

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. 

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. 

Flow of slurries in rotary drums depends on, among other factors, slurry settling characteristics. For the case of highly settling slurries flowing in a rotary drum with open-end and no lifters, these conclusions were obtained ... 

European machines in particular are operated with very low water levels in order to save energy and water. It is therefore important to ensure that the laundry load is soaked in water or suds as quickly as possible so that dry textiles do not rub unnecessarily against the drum or the rubber seal. This is achieved in European machines by constructional features that improve water absorption, shown in Fig. 3.3, such as lifter bars, circulation (jet) systems or direct injection. 

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