A comparison of graded PSD methods in slurry transport

Most methods for determining the hydraulic gradient of slurry transport are based on a single particle size. A few methods describe how to deal with a graded Particle Size Distribution (PSD). The way these methods deal with graded PSD's is very different. The original Durand/Condolios method defines an equivalent particle diameter, based on a weighted average of particle Froude numbers using the parallel resistor method. The heterogeneous Wilson model uses a power for the dependency of the hydraulic gradient on the line speed, where this power is smaller, the more graded the PSD. This power has a maximum of 1.7 for single sized particle solids and a minimum of 0.25 in the Wilson model. The Sellgren & Wilson 4 component model divides the PSD in 4 components based on particle size boundaries. For each particle size based component, the corresponding model is applied. These models are the homogeneous model for very small particles influencing the viscosity, the reduced Equivalent Liquid Model for small particles, the heterogeneous model for medium sized particles and the two-layer and three layer models for large particles. The 4th model considered is the Delft Head Loss & Limit Deposit Velocity Framework, dividing the PSD in fractions. The number of fractions is free to choose, but normally 9 is sufficient. First the carrier liquid properties are adjusted based on the fines fraction. Secondly the hydraulic gradient curve is determined for each fraction. These hydraulic gradient curves are added, multiplied with the fraction. The paper describes the 4 methods and gives pros and cons of each method. The 4 methods are compared with each other. © BHR Group Hydrotransport 20.