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32 / March 2020 powderbulk.com Figure 4a. also shows the impact on power con- sumption across the various lengths. When conveying material a shorter distance, naturally we expect the power consumption to decrease because less work is being done on the material as the material is of a less-difficult duty. However, with the statically operated systems, the power usage at the shorter distances doesn't drop significantly. Despite conveying only 25 percent of the distance, the system still uses more than 65 percent of the power. The blower still generates as much, if not more, air volume and only the pressure is reduced. With the dynamic velocity controls, the blower power drops to 40 percent for the shortest distance. The blower vol- ume and pressure are both dramatically reduced, so the conveying is inherently more efficient. In Figure 4b., the distance is held constant while the conveying rate is varied. A similar pattern emerges where the lower conveying rate produces 10 to 12 percent greater velocities in the underfed statically controlled systems, but with the dynamically con- trolled system, the velocity can be kept fairly constant. Likewise, the conveying rate reduction only produced modest reductions in energy consumption until the dynamic controls were employed. Figure 4b. also shows a unique aspect of the dynamically controlled system. If we look at the rate reduction case and continue with it down to no rate, the benefits will become greater unto the endpoint. the blower speed adjusted itself with a velocity-control algorithm. A sample of the results from the exper- iments are shown in Figures 4a. and 4b. to clearly demonstrate the relationship between system variables. In Figure 4a., the conveying rate was held constant while the distance was reduced across three lengths. For the standard dilute phase, the blower speed was set consistent with typical design using 3,997 fpm effective air velocity and then held constant throughout. As the distance gets shorter, representing a different, closer destination, the effective air velocity creeps up as there is less compression on the blower. We see an 18 percent velocity increase at mid-distance and more than a 40 percent increase at the nearest distance. With the static velocity control, the initial blower speed and effective air velocity can be reduced from the standard 3,787 fpm for the farthest destination. However, without additional blower setpoints for each destination, we still see the velocity increase by similar percentages as the standard dilute phase. Finally, with the use of dynamic velocity control, we are able to operate the system at 3,619 fpm for the longest pipe length (farthest distance). Then at the closer destinations, we get nominally the same effec- tive air velocity for all three conditions. This shows that the dynamically controlled system manages the velocity, while the statically controlled system experiences signif- icant velocity increases. 8 metric t/h Equivalent length Feet 850 460 200 Standard dilute phase Blower speed RPM 3500 3500 3500 Effective velocity FPM 3997 4720 5700 Blower power HP 46 37 31 Static velocity control Blower speed RPM 3300 3300 3300 Effective velocity FPM 3787 4417 5240 Blower power HP 41 32 27 Dynamic velocity control Blower speed RPM 3150 2710 2370 Effective velocity FPM 3619 3609 3658 Blower power HP 39 24 15 460 equivalent feet Convey rate metric t/h 8 5 0 Standard dilute phase Blower speed RPM 3000 3000 3000 Effective velocity FPM 3982 4488 5672 Blower power HP 28 24 18 Static velocity control Blower speed RPM 2800 2800 2800 Effective velocity FPM 3747 4131 5348 Blower power HP 25 21 15 Dynamic velocity control Blower speed RPM 2670 2400 1790 Effective velocity FPM 3491 3537 3666 Blower power HP 24 16 5 FIGURE 4 a. Constant rate for variable distance b. Constant distance for variable rate