Conveying line inlet air velocity

Data obtained with cement and analysed in terms of an equivalent length of straight horizontal pipeline are presented in Fig. 13. This is for 90° bends having a bend diameter D, to pipe bore d, ratio of 24 1 in 53 mm bore pipeline in horizontal plane. Almost identical results were obtained when a similar analysis was carried out for the conveying of barytes. A simple correlation in terms of the conveying line inlet air velocity was not expected, but it was not possible to determine any effect of the position of the bends in the pipeline. Data obtained with barytes and analysed in terms of a pressure drop across a bend are presented in Fig. 14. Once again, almost identical results were obtained for the conveying of cement. These data are for the same bends reported in Fig. 13. 

A conveying line inlet air velocity, Ci, will need to be specified for the given material and conveying conditions, and a pipeline bore, d, will also need to be evaluated. By re-arranging the above equations and substituting for constants (including R) and free air conditions it can be shown that ... 

For the cement the increase in power with increase in pipeline bore can also be explained in terms of velocity profiles, but in this case it is values of conveying line inlet air velocity that are relevant. Since cement is capable of being conveyed in dense phase, the relationship between minimum velocity and solids loading ratio, as shown in Figure 4.41, dictates. In an 81 mm bore pipeline the inlet velocity is only 4.2 m/s, since the solids loading ratio is 109. In the 200 mm bore pipeline the solids loading ratio is reduced to 14 and so the inlet air velocity is 12.0 m/s. 

If data on minimum conveying air velocities is to be used in the design process, such as that shown in Figure 4.41, it would generally be recommended that a 20% margin be allowed for the value of conveying line inlet air velocity to be employed ... 

Conv ng line inlet and outlet air velocities have also been added for completeness, and from this it will be seen that the pressure minimum point occurs at a conveying line inlet air velocity of about 10 m/s, over the entire pressure range. The maximum value of solids loading ratio of only 30 is typical for the low velocity dense phase conveying of this type of material, because of its extremely high value of penneability. 

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