Chutes are commonly adopted in conveying systems as a method of transferring bulk materials from one conveyor belt to another. Although widely used, a poorly designed chute or even the application of a chute out of its original design conditions (higher tonnage, different particle material, wet material, and so on) often lead to problems, which can result in lower productivity, increased maintenance costs, higher wear rates, or even shut downs.
Some of the most common chutes problems are plugging, excessive chute and/or belt wear, misalignment of belts due to uneven flow distribution, and exaggerated dust generation.
Of course, there are guidelines for designing chutes that attempt to avoid these issues and obtain a controlled flow of particles. But let’s face it: even a beautifully designed chute may become a bottleneck in the plant. Standard operating shifts–even small ones–like increases in production or changes to material compositions can cause a once perfectly operating chute to become a sudden problem.
Because there are many factors that affect how well a chute operates, engineers who design chutes often must consider some fairly tricky questions. For example:
What is the optimal angle to minimize the impact between the granular flow and the transfer geometry for this sticky material?
Will the addition of this deflector plate centralize the material load and reduce the belt mistracking and spillage?
How far can I increase the tonnage of this chute without leading to blockages? And how much should I increase the velocity of the receiving belt?
Is it possible to reduce the need for dust control by modifying this skirting design, including internal wear liners, or using some dust curtains staggered throughout the loading area?
Can I still use this chute originally designed to deal with dry materials to transfer this wetter-than-expected material without making further modifications?
Are there minor modifications that can be made easily in order to deal with this cohesive material?
How can DEM help?
Rocky DEM is a powerful tool that helps engineers design and/or optimize transfer chutes by simulating different scenarios, which reduces the costs of building and testing different configurations. As an example, Video 1 below shows a Rocky simulation of a shiftable chute discharging onto a conveyor belt.
Video 1: Rocky DEM simulation showing a shiftable chute discharging onto a conveyor belt
By doing some calibration tests in order to adjust the DEM parameters to best reflect your real-life material, you can pick the best candidate between different designs in order to avoid plugging or clogging, as seen in Video 2 below.
Video 2: Rocky DEM simulation showing a chute clogging
Adhesion and shape representation
Real-life particles aren’t perfect spheres. The come in convex and concave shapes. They can form agglomerates. They can stick to the chute walls or to the belts. The adhesion models available in Rocky DEM combined with its accurate shape representation allows the simulation of nearly any type of material handling environment. Video 3 below shows the transportation of wet, sticky ore particles through a chute.
Video 3: Rocky DEM simulation showing a transfer chute with wet, sticky material
Large tonnage? Small particles? Complex particle size distributions (PSDs)? Rocky DEM has the ability to perform large scale simulations significantly faster by utilizing parallel CPU and GPU processing. These abilities have overcome one of the main limitations in the wide application of DEM in chute design: computational cost. Figure 1 below shows the run-time comparison using CPU and GPU solvers when simulating one million particles. Video 4 shows the simulation used for this comparison, which includes both spherical and rounded polygons (with three, five, and seven corners) passing through a chute over 10 seconds.
(Nice, isn’t it? Wait until you see the new Multi-GPU abilities that are coming soon with Rocky 4!)
Figure 1: CPU vs. GPU run-time comparison for Rocky DEM simulation with 1 million particles
Customized and tailored for equipment designers
Moreover, Rocky DEM includes several post-processing options to help users extract as easily as possible the information needed from the simulation. For example, Video 5 shows how color mapping can be used to depict shear wear on a transfer chute, while Figure 2 shows how to analyze in graph form the average shear and impact intensity along the receiving belt width.
Video 5: Rocky DEM chute simulation showing shear wear
Figure 2: Average shear and impact intensity along the receiving belt width
Rocky and ANSYS Mechanical coupling
Last but not least, the integration between ANSYS Mechanical and Rocky DEM makes it possible to analyze the impact of particle flow upon the chute structure. In this way, users can optimize their chute designs not only to get the desired material flow but also to minimize deformation and stresses on the structure. Video 6 below shows an example of this coupling in action.
Video 6: Coupled Rocky DEM and ANSYS simulation showing the impact of particles upon a chute structure
Lucilla holds a BE (Chemical) undergraduate degree, an M.Sc. in Chemical Engineering and a Ph.D. in Nuclear engineering from the Federal University of Rio de Janeiro. She joined ESSS in 2008 and has spent 5 years focused on applying CFD to solve common engineering problems in the Oil and Gas industry, dealing with turbulent and multiphase flow simulations. Since 2013, she is an Application Engineer for Rocky DEM Business Unit, supporting users, working on consultancy projects and validating models implemented for the CFD-DEM coupling.