# Settling Slurries

Saltation/Blockage Warning When designing slurry flow systems, FluidFlow will enunciate a warning notifying the designer that line blockage may occur if the calculated line velocity is below the slurry deposition velocity. This helps the engineer develop an efficient operating system. Figure 1 provides an overview of the flow regime associated with a given point on a system resistance curve. Figure 1: Slurry Pipe Resistance Curve. Based on the above illustration, we can see that as flow rate/velocity decreases, the flow regime moves from pseudo-homogeneous to heterogeneous suspension (no deposition), through sliding bed and ending up with a stationary bed/blocked pipe. When designing a slurry system, it is recommended that we review the minimum transport velocities at all anticipated flow rates and particle concentrations. The pump suction pipe is usually the largest diameter and as such, often presents a likely location for sanding. A slurry system is partially self-limiting as, when the effective area of the pipework decreases, the velocity is forced to increase. If a slurry system has solved such that the duty point is positioned to the left of the curve apex (deposition point), the system is likely to operate as a sliding bed which increases pie wear and energy costs. In a worst case scenario the system can also develop a pipe blockage. It is therefore good practice to develop a plant which operates to the right hand side of this apex point. Users can quickly compare deposition velocities with actual line velocities and study the resistance chart for each pipe which allows us to develop more efficient systems. Liu Dezhong When modelling slurry flow systems using the Liu Dezhong correlation, a value for Cvd Deposition Velocity may not appear on the Results table. This can occur if the Liu Dezhong method establishes that the slurry you are modelling is in fact, non-Newtonian, non-settling slurry in which case, there is no associated deposition velocity. If this is the case, we would recommend obtaining rheology data for the slurry. This will help characterize the slurry accurately allowing you to select the most appropriate modelling approach. If you wish, you can review the particle sizes defined for the slurry at the system inlet boundary and increase the portion/percentage of the larger particle sizes defined at the inlet boundary. When you recalculate the model, you may then see a result displayed on the Results table for deposition velocity as the properties of the slurry will have changed from non-settling to settling due to the higher concentration of larger particle sizes. The pipe resistance curve will also have changed accordingly. If your model has solved with Liu Dezhong and without a value for deposition velocity, the Results table for a pipe will appear as per Figure 2. As we can see, the fluid phase is described as non-Newtonian. Figure 2: Liu Dezhong Correlation - values for deposition velocity not displayed.