Large-particle hydrotransport flow phenomena are analyzed. These include particle suspension mechanisms, relative in situ slip between phases, and shear between separated solid/liquid flow regions. These phenomena are related to the mechanistic force balance modeling approach to predicting nominal and minimum horizontal pipeline transport conditions. Results of four series of tests in a 35 m-long, 0.165 m-diameter plexiglass pipeline are presented. These tests were designed to investigate isolated flow phenomena related to lower limits of operation of large-particle transport. They included measurements of the particle size dependence and flow geometry dependence on interfacial friction factors, initiation of plug flow motion, and plugging tendencies of flow through upward-turning elbows. Numerous flow phenomena and parameter dependencies are included in analysis of predictions made using the force balance modeling approach. Comparisons with data are made where possible and a step-by-step solution procedure is presented. Results show agreement with some data sets and disagreement with others. Most available data, however, are neither extensive enough nor accurate enough to form complete conclusions as to the minimum operating conditions predicted with the force balance modeling approach. Additional data from a systematic experimental program in a once-through pipeline system are necessary to further verify the modeling approach. A limited qualitative analysis of methods proposed to unplug large particle pipelines is presented. Methods assessed include pulsed air injection, vibration augmentation, friction reducing surfactant injection, and mechanical or hydraulic boring machinery. Advantages and disadvantages of each method are assessed qualitatively. Laboratory and field testing are required to determine applications.
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