The unique hydraulic characteristics of materials to be transported by slurry pipeline require that laboratory tests be performed to establish definitive design parameters. An overview of the relevant material characteristics, how they are determined In the laboratory, and their application to basic hydraulic design are presented. The programs incorporating this data and their application to the hydraulic design of slurry systems are discussed as well as system operation limitations and specific physical design characteristics.
A large variety of solid bulk materials are transported in slurry form, including iron concentrate, coal, phosphate concentrate, copper concentrate, nickel, and limestone. The material properties which affect slurry pipeline design (particle size distribution, solid specific gravity, particle shape, and hardness) vary between applications, even when like commodities are transported. A prerequisite to detailed design of any slurry pipeline system is a definition of the hydraulic behavior of the material to be transported. This paper summarizes the analytical procedure utilized by Bechtel Petroleum, Inc. in the design of slurry pipeline systems. No attempt is made in this paper to present the equations used in the analysis. Only pertinent parameters are explained, and the solutions to particular design problems are presented.
Slurry systems pose additional design considerations beyond the usual trade off between pipe size and pumping equipment associated with gas or liquids pipelines. These include:
Influence of Particle Size Distribution Selection of the particle size distribution (size consist) is an optimization procedure in which conflicting priorities are balanced. A high content of fine particles will tend to produce a stable slurry suitable for long-distance transport. The fine particles help to suspend the coarser fractions, allowing lower operating velocities accompanied by savings in friction losses and pump horsepower.
Slope Limitations Due to the settling characteristics of slurries, the maximum slope in a slurry pipeline is usually limited by the angle at which solids slide to low points in the pipe after shutdown. This angle is determined in the laboratory, by observing the angle at which settled slurry begins to slide in a transparent tube, and by observing the angle of repose when slurry settles in a tube set at predetermined angle(s).
Abrasiveness of the Slurry Slurry piping systems must be designed to prevent erosion of the pipe walls. At high velocities (above about 8 feet per second) or when operating at velocities below that required to maintain the particles in a relatively homogeneous suspension, pipe wear is typically rapid. Pipe wear is virtually eliminated when all particles are suspended at moderate velocities. In some applications, such as tailings disposal lines or short coarse slurry lines, the coarse particles cannot be suspended at moderate velocities. In these instances, the pipe should be lined with an abrasion-resistant material, such as ceramic basalt or elastomeric compounds such as high-density polyethylene or polyurethane. Wear problems preclude the use of control valves in slurry service. To control the flow in slurry transportation systems, variable speed pumps are utilized.
