The Use of Capsules for Solids Transmission in Pipelines

Abstract

Investigations are being carried out at the Research Council of Alberta intothe possibility of using long-distance pipelines to move commodities in theform of long trains of cylinders or spheres. One of the most interestingdiscoveries of the laboratory investigations of this type of transport is thatthese forms, called capsules, with diameters close to that of the inside of thepipe, nearly always move faster than the average liquid velocity in the pipe.The reason for this is that the capsules occupy a region in the pipe where theliquid velocities are higher than the average liquid velocity. The density ofthe capsules has surprisingly little effect on their velocity relative to theliquid. The added pressure gradient in a pipeline due to the presence of acapsule train is proportional to the volumetric concentration of the capsulesand increases with capsule density, but does not increase or decreaseappreciably with liquid velocity. One important advantage that capsuletransport has over slurry transport is that pumping power is generally lower -except for slurries with very small particle sizes. Theoretical studies havebeen made, and numerical analyses have been used to predict the behaviour ofcapsules transported by a liquid in a pipeline. The experimental results thusfar have been obtained with laboratory-scale pipelines. Scaleup experiments arein progress to enable predictions to be made about the performance of capsulesin commercial lines. Introduction Pipelines have been used for several decades to move liquids over longdistances. The low cost of long-distance transport of liquids and gases bypipeline, which approaches that of surface transport by water, has in recentyears accounted for the construction of a large number of slurry pipelines in Europe and the Americas - ref. (1) to (9) - conveying a great variety ofdifferent materials. Further development of solids pipelining is foreseen, particularly in the United States and Canada, where railway freight rates oftenfar exceed production costs and tend to exclude western producers from nationalas well as international markets (2).