Empirical equations were developed giving minimum air and power requirements for the vacuum and pressure transport of crushed coal through horizontal pipelines. The test system included 2-, 4-, 6-, and 8-in.-dia pipelines, each with a 200-ft straight section followed by three shorter runs connected by 90-deg bends of different radii. Air requirements were found to be a function of coal rate and specific gravity, pipe diameter and length, and the ratio of the cross-sectional area of the pickup section to that of the pipe. Although coal size was not a significant variable, the maximum size cannot exceed four-tenths the diameter of the pipe. The highest coal rate—55 tons per hr—was achieved in pressure operation with 1.35 specific, gravity coal transported through the 8-in.-dia pipeline. In this experiment with a pickup to pipe area ratio of 3 to 1, about 2200 actual cu ft per min of air at the pipeline entrance was required to keep the coal moving in full suspension with a 7.5-psi drop in pressure. The equations can be used to design horizontal pipeline systems operated under either vacuum or pressure with different types of pick-up devices and varying conditions of coal gravity and rate and pipe diameter and length. For example, assuming a pressure drop of 20 psi and a pickup to pipe area ratio of 3 to 1, 380 tons per hr of 5- by 0-in. coal (sp. gr. 1.40) could be transported through 1000 ft of straight 12-in.-dia pipe by 7300 actual cu ft per min (17,300 standard cu ft per min) at the pipeline entrance at the expense of 1080 theoretical horsepower.

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