Even with extensive time and effort dedicated to addressing issues and innovating in pneumatic conveying, new challenges and the reappearance of past ones constantly arise. Material properties such as cohesiveness, abrasiveness, and friability; particle shape; static buildup; and the use of grinding aids can have varying and unexpected impacts on pneumatic conveying, making it difficult to accurately design an effective system.
While it may not always provide a solution, recognizing and preparing for these potential obstacles is crucial in mitigating the challenges they can create in pneumatic conveying. Gain a deeper understanding of the complexities of pneumatic conveying by acknowledging and anticipating the various external factors and material properties that can impact its effectiveness. With recognition comes preparation, and with preparation comes improved success rates in addressing issues and innovating in this industry.
Material cohesiveness
Various materials are known for their cohesive properties. Small particles, especially those less than 5 microns, tend to stick together, causing issues with flow and fluidization. This problem is not limited to moist particles, as even dry particles can be attracted to each other and create blockages in conveying lines. These blockages can reduce the line’s diameter and decrease conveying capacity, resulting in increased pressure losses that may be difficult to manage.
Materials that contain fat or moisture are especially prone to cohesion, especially if they consist of fine particles. Conducting fluidization tests in the initial stages of system planning can help identify these issues and determine the best corrective measures. Humidity can also play a role in cohesion, causing problems in warm weather. While solutions exist, they may not always be perfect or cost-effective. Options such as using a dehumidifier or a closed loop conveying system can help address the issue. Another option would be to utilize ambient air that has been conditioned to remove excess moisture.
Improve the performance and productivity of your conveying system by addressing the common issue of particle cohesion. Materials with fat or moisture are particularly prone to this problem, especially when consisting of fine particles. Conducting fluidization tests during the initial stages of system planning can help identify these issues and determine the most effective corrective measures. In some cases, options such as using a dehumidifier or closed loop system may be necessary to ensure smooth material flow and prevent blockages. Don’t let cohesion hinder your system’s efficiency – plan and choose the best solutions for your specific materials.
Material abrasiveness and friability
Abrasive and friable materials can cause wear issues in conveying systems. While abrasive materials wear down the line, friable materials can also wear it down upon contact. Dealing with worn system components due to abrasive materials may not be very burdensome, but unexpected degradation of friable materials during conveying or material that is no longer in spec for downstream production can pose significant problems.
The effect of both abrasive and friable materials on conveying lines is unpredictable, making it difficult to estimate service life or the extent of material degradation even after running tests on a pilot-plant conveying loop. The unpredictable nature of abrasive and friable materials can lead to significant problems in conveying systems. These materials can cause unexpected and varying degrees of damage, making it challenging to estimate service life or the impact on downstream production.
As an industry expert, I know that dealing with worn system components due to these materials is a necessary burden, but the additional challenges they pose can be costly and time-consuming.
Particle shape
When designing a conveying system to handle materials, particle shape is a crucial factor in determining fluidity. The shape of particles can vary greatly, from smooth spheres to sharp cubes and flat platelets, each with its own unique drag coefficient. While we typically assume a spherical shape, other shapes such as flat platelets and stringy fibers present challenges and require a more conservative design. This results in a higher cost and slightly more power usage. Therefore, it is important to consider the impact of particle shape when planning a conveying system.
Static buildup
When a material, especially plastic, is not effectively moved by a conveying system, static electricity (electrostatic charge) may be the root cause. The first step to resolving this issue is to use a well-grounded system, although grounding alone cannot guarantee the absence of static problems. While summer humidity can sometimes minimize static buildup due to its higher conductivity, this is not always the case.
In one instance, a user attempted to increase the humidity levels in the conveying air by injecting water vapor during the summer, but this did not completely solve the problem and even caused further complications in winter. Some users have used test data to calculate the difference between the theoretical and actual static charge effects in their completed pneumatic conveying systems. However, accurately predicting this effect before constructing the system remains a challenge. To prevent static problems, properly grounding the system and removing sources of static buildup are effective precautions but may not eliminate the issue.
Grinding aids
Grinding aids are often added to materials in size-reduction applications to facilitate the process and reduce the amount of grinding power required. This is seen in one example where the addition of as little as 4 parts per million of grinding aid to Portland cement significantly decreases the power needed for grinding. In addition, grinding aids can also improve the performance of pneumatic conveying systems, increasing their capacity and decreasing the pressure in the conveying line.
This suggests that by incorporating small quantities of additives, it may be possible to enhance the flowability of a material and improve the throughput of the conveying system without impacting the final product. However, it should be noted that the inclusion or omission of even small amounts of additives can sometimes lead to unexpected results in a conveying system.