Velocities in pipelines, typical

TABLE 6.2. Typical Velocities and Pressure Drops in Pipelines Karman s equation... 

As discussed in Sec, 6.13, the economic velocity in a pipeline is primarily dependent on the density of the fluid flowing. For long-distance natural-gas pipelines, the pressures are normally in the range of 500 to 1000 psia, so densities are of the order of 1 to 21bm/ft From Table 6.4 we can estimate the economic velocity at about 20ft/s, which is typical of these pipelines. Thus, this kind of flow does not really correspond to the subject of this section—high-velocity gas flow however, it fits in naturally here, after we have developed the equations for high-velocity gas flow. 

In a typical slurry pipeline design situation, the flowrates and solids concentrations are fixed by process material balances and equipment performance specifications. In these circumstances, a primary goal in design is selection of the optimum pipe diameter. For slurries in turbulent flow, the optimum transport condition almost invariably occurs when all the particles are suspended but moving at the lowest possible mean velocity. By operating the pipeline at the slurry deposition velocity, the frictional energy losses and wear are minimized and the whole of the pipe cross-section is available for flow. 

Fine mineral beneficiation plant tailings and concentrates are often transported in pipelines and low values of (d/D Co) occur frequently with these slurries because the median particle size is fine. Although it is now accepted that deposition velocities should be measured for these slurries, it is frequently not possible to obtain the relatively large quantities of slurry required for a full scale test. It is therefore necessary to scale-up the deposition velocities meeisured in smaller pipelines. In the next section some typical experimental results will be presented to illustrate the behaviour which may occur. 

Two typical sets of pressure measurement data for the vertically down and vertically up sections of pipeline are presented in Fig. 2. This shows the location of the pressure tappings and their proximity to the various bends in the pipeline. The data relate to the pneumatic conveying of a fine grade of pulverised fuel ash. Five different bulk particulate materials were investigated in the research programme, the other four being barytes, bentonite, cement and fluorspar. All five materials were capable of being conveyed in dense phase and hence at low velocity. 

The flow rate in a transportation pipeline has to be larger than the deposition velocity of the mineral particles in order to avoid solids segregation. Typical flow rates... 

The flow rate in a transportation pipeline has to be larger than the deposition velocity of the mineral particles in order to avoid the segregation of solids. Typical flow rates range from 1 to 2 m s for coal and oil sand froth pipelining to about 4ms for some heavy metal concentrates [2]. For mineral slurries, abrasion becomes a signiflcant concern at velocities above about 2.5 m s and a major problem above about 4.5 m s [2]. 

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