Apparatus and method for slack flow elimination in a slurry pipeline

A method of operating a pipeline for transporting a first liquid between an upstream end and a downstream end of the pipeline at or below the design capacity of the pipeline over terrain of varying elevation comprising the steps of alternatingly stocking the upstream end of the pipeline with the first liquid and then with a second liquid, the liquids having differing specific gravities;

• pressurizing the stocked liquids sufficiently to overcome static pressure heads due to elevational differences over the length of the pipeline and due to friction losses of the liquids flowing through the pipeline and to maintain the entire cross-section of the pipeline substantially filled with liquid;
• sensing the pressure of the liquids in the pipeline at at least one relative high point of the pipeline;
• and generating a back pressure in the pipeline at a point downstream of the high point when an interface between the liquids is in the vicinity of the high point and the liquid pressure at the high point drops below a predetermined value;
• whereby an increased liquid velocity downstream of the high point and a resulting partial filling of the pipeline with liquid downstream of the high point are prevented, and resulting abrasion of the pipeline by the liquid is reduced.

A method of transporting through a pipeline a slurry having a relatively high specific gravity and including suspended abrasive particles at a capacity below the design capacity of the pipeline, the pipeline extending over terrain of varying elevation and including at least one relatively high point in the pipeline followed by a downgrade portion of the pipeline, the method comprising the steps of pressurizing the slurry sufficiently to pump it through the pipeline from an upstream end to a downstream end at a sufficiently low flow rate so that the average speed of the slurry permits the formation of a substantially stationary liquid boundary covering the interior wall of the pipeline to reduce abrasion of the pipeline wall by flowing particles;

• intermittently substituting a liquid for the slurry being pumped through the pipeline, the liquid having a lesser specific gravity than the slurry;
• sensing the liquid pressure at the high point at least when an interface between a downstream liquid batch and an upstream slurry batch is at or downstream of the high point;
• and increasing the flow resistance encountered by the liquid and the slurry at a control station downstream of the downgrade portion when the sensed pressure at said high point is at or below a predetermined value sufficiently to increase the sensed pressure above the predetermined value;
• whereby an increase in the flow rate of the slurry downstream of the high point and a penetration of the protective boundary by slurry particles are prevented and a resulting abrasion of the pipeline wall by the particles is reduced.