Stepped-diameter pipelines

Some examples of long-distance stepped-diameter pipeline systems include 100 t h1 of fly ash over 1.5 km (Wypych, 1995b) and 24 t h1 of pulverized coal over 1.8 km (Wypych et al., 1990). Some of the different pipeline configurations considered for the latter are repeated in Table 3 below. Note  

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Stepped-diameter pipelines to minimize pressure drop, velocity, wear and power consumption. 

For the general purpose of minimizing air flow, transport velocity, wear and power, the fluidized dense-phase mode of flow is preferred for long-distance applications. Efficient blow tank feeders, rotary-screw compressors, refrigerated dryers and stepped-diameter pipelines also are recommended. For products that are not suited to fluidized dense-phase, the possible modes of flow include dilute-phase (suspension flow) or bypass conveying (Wypych, 1995a). 

Using the above models and method of feeding, the following optimal operating conditions were predicted for the extreme case of maximum pipeline length and maximum throughput. Note, a stepped-diameter pipeline was selected to minimize pressure drop, air mass flow rate and hence, conveying air velocities. 

Conveying of solids over long distances up to a few thousand feet encoimters different phenomena owing to the gas expansion of that distance. The gas expansion caused the gas and solid velocities to increase and thus affect the attrition of the particles and the erosion of the pipeline, both of which increase to the nth power with velocity, where n ranges from 2.5 to 5.0. To slow the particles down, one can step the pipeline to larger diameters to decrease the velocities. Another technique developed in our laboratories is to use a flow economizer, which effectively takes gas from the system in a prescribed fashion to reduce the gas velocity. Figure 4 shows a schematic of the flow economizer tested in our laboratory. This unit withdraws a prescribed amount of air at critical points in the transport line. 

Therefore, for the three conveyors selected in the previous step, the pipeline diameters are 76 mm or 102 mm (PIAB 2006). 

Based on the above mentioned, the programme of theoretical and experimental investigation of the main parameters of coal-methanol (or its water solution) mixture pipeline transport should be opened. As the first step of the programme the comparison of power consumption (dependency of hydraulic gradient I on slurry flow velocity V and solid concentration Cs) for the pipeline transport of coal-water mixture and coal-methanol solution mixture was realised. The special laboratory measurements were made to define unknown input data of semi-empirical relationships, i.e. the limit volumetric concentration Cm and the coefficient of mechanical friction of coal in the water or water-methanol solution ka. The resultant comparison of the hydraulic gradient I of the coal-water and coal-methanol solution mixture flow is presented in Figure 2, where density of coal was pc = 1480 kg/m3, diameter of the pipe was D = 0.103 mm, the maximal grain size of coal dmax was less than 0.25 mm, volumetric concentration - C = 20 %. 

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