Product Wear assessment and predictions during Pneumatic Transport

Pneumatic Conveying Wear
Pneumatic conveying is generally used to convey materials from a single source such as a silo or a hopper to one or multiple destinations, over relatively long distances. During the conveying, the particles are carried on an airstream with a high velocity, throughout the system interacting with the pneumatic transport conveying system which consists of pipelines with many twists and turns.  As a consequence of the particle interaction with the conveying pipeline system, the impact of the material might lead to material wear. To assess the Pneumatic Conveying Wear. We first need to look at the air velocity, the number of bends, as well as the angle of the bends as well as the brittleness or hardness of the material. All these aspects combined are critical parameters to determine the possible wear on the material transported.

Pneumatic Conveying Particle Wear
Particle wear can easily occur in the material conveying process. And creates a number of potential hazards. The airborne fine particles that are released into the air as a result of the wear may be released into the atmosphere and can cause a potential health hazard as well as pose a potential explosion risk. Additional issues that may arise during the transport are of a production quality nature. The pneumatic transport wear may affect the materials applied coating or might change the particle size and shape, which may directly influence the product quality and production consistency. The most common cause of the wear during transportation can be found in the particle to particle impact and the particle to wall impact which most commonly occur in bends and transition areas within the lines.

Pneumatic Conveying Wear in powdered milk
One typical case of wear that has a huge impact on product quality is the handling of milk powder. During the conveying process, the powdered milk breaks at the bends and as a result might change the particle size distribution, which can cause several process issues such as packaging challenges, caking, and dissolution problems.

Figure 1: Particle size distribution result of milk powder under different air velocities by pneumatic conveying.

Figure 2 shows the particle size distribution results after applying different air velocities in the pneumatic conveying system. The red line is the original particle size of the material. After applying the different velocities, the particle sizes decreased to a certain extent.

We can thus conclude that there is a direct correlation between higher air velocity and material breakage.

Figure 3: Particle breakage of bio-granules (center) by different bend types in the pneumatic conveying system evidencing clearly more fines in the radius bend (right) compared to the mitered bend (left).

Another case that was relevant for us to examine is that of bio-granule products. It is a product that is known for its brittleness easily creating dust particles during the conveying process. We found, as shown in figure 2. that different bend types with varying radii’ created an increase in fine particles which leads to a higher risk of explosion hazards, which is regulated in ATEX.

How laboratory insights meet the practice of the industrial process
We are able to explore these situations and others because Delft Solids Solutions is capable of mimicking industrial conveying on a lab-scale, to quantitatively predict the wear of powder and granule particles. Our lab-scale pneumatic conveying system has a total pipeline length of 2 meters, we can apply a varying number of bends and bend types we are able to switch between 3, 6, and 9 bends, and two different bend types, offering different radius types bends as well as a mitered bend. During the conveying, different air pressures are applied throughout the system in order to reach particle velocities up to 20 m/s.

Delft Solids Solutions also offers repeated impact test
The repeated impact test is a technology developed to mimic the simulated wall impact by a repeated controlled constant velocity. The vertical particle box movement is to ensure that the particles collide with the wall, as shown in Figure 3, which mimics the bend impact from the pneumatic conveying system.

The repeat impact tester has its advantages. Only small amounts of sample material are required. Approximately between 1 and 2 grams of material will be tested, which is suitable for companies that are unable to provide larger amounts of sample material, such as pharma, for example, the costly nature of the material.

Figure 3: Schematic representation of CS-RIT and the mechanical mechanisms of CS-RIT.

Impact extrapolation
Due to the high frequency of the repeated impact test, it can easily reach thousands of collisions, which are equal to hundreds of bend simulations in the pneumatic conveying system. The repeated impact test is highly suitable for clients wanting to explore the impact of maximum collision within their production process.

The correlation between pneumatic conveying and repeated impact test results can be quantified by kinetic energy. The kinetic energy transfer table versus mass fraction in the diagram above as seen in figure 4 (see below) indicates that the particle wear during pneumatic conveying seems to have a satisfying correlation with the repeated impact test. By increasing the kinetic energy in both systems, the mass fraction results seem to be similar from 3 m/s to 9 m/s.Therefore, by using the repeated impact test, Delft Solids Solutions can simulate the extreme conveying situation up to thousands of collisions.