During the conveying, the particles are carried in 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 wear, one need to consider the air velocity (and associated with that the particle 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.
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 and thus its application. 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 typically occur in bends and transition areas within the lines.
Pneumatic conveying and 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 filling and packaging challenges, caking, and feel and look problems.
Figure 1 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 velocities and material breakdown.
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. Typically we switch between from 3, 6, and 9 bends, and two different bend types, offering different radius-type 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 only 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 large amounts of sample material due to limited availability in the early stage of product development or due to e.g. a costly or toxic nature of the material.
Kinetic energy extrapolation for actual product behaviour
The correlation between pneumatic conveying and repeated impact test results can be acquired by implementing the kinetic energy executed in the various tests. The mass fraction due to wear plotted versus the kinetic energy transferred as seen in Figure 4 indeed confirms that the particle wear during pneumatic conveying displays a decent correlation with repeated impact testing. By increasing the kinetic energy in both systems, the mass fraction results in this particular example follow a similar trend for particle velocities of 3 up to 9 m/s. As such, repeated impact testing is capable of predicting material behaviour under realistic transportation conditions.
Impact extrapolation for transportation process design and worst case scenarios
Due to the high frequency of the repeated impact test, it can easily reach thousands of collisions, which corresponds to an infinite number of bends in the pneumatic conveying system. The repeated impact test is thus highly suitable for customers interested in exploring a new transport line design or the impact of extreme conditions within their production process and want to learn of the impact of such process conditions on the product properties.
Therefore, by using the repeated impact testing approach, Delft Solids Solutions can simulate extreme conveying situations up to numerous collisions.
Delft Solids Solutions is a privately-held contract research organization working on research and characterization of solid materials. Topics include, but are not limited to, primary physical properties as porosity, pore volume, pore size, surface area, particle size, density of powders and granules. We also investigate related characteristics such ...