How To Optimise Air Velocity In Pneumatic Conveying Systems?

A pneumatic conveying system is a simple technology that helps with the transportation of bulk material in the form of powders or granules. This transportation is done through the pipe by using airflow or gas. A variety of bulk materials from diverse industries can be conveyed with the use of this technology. 

It is a cost-effective way of handling the materials with a very minimised loss, for which the application of it is in high demand. In this article, you will learn a bit more about the use and function of pneumatic conveying systems. Following that, you will get insight into the optimisation of air velocity in the execution of pneumatic conveying. 

A] Understanding Air Flow Rates in Pneumatic Conveying

The pneumatic conveying flow rate of the air refers to that of the air mass or volumetric airflow. It is the air volume that passes through the specific cross-sectional area/unit of time. The mass rate of flow measures the air mass also passes through the same measurement.

For the pneumatic conveying systems to efficiently handle the material particles and keep them suspended while passing through pipelines, they will need sufficient air volume. In connection with the air volume is the optimal air flow rate, which needs to be adjusted as per the air volume in order to prevent particles from damaging the pipes. 

The flow rate of air in the pneumatic conveying system should also be in alignment with the air velocity for maintaining product quality. The ideal flow rate of the air will differ with respect to the product. If any change is made to the same, it will imply corresponding changes to the air volume, velocity and mass of the flow rate. 

The flow rate of air in the pneumatic systems is meant to directly impact the material that’s being conveyed. Alongside that, the components that come in contact with the same will also be affected. Therefore, to prevent both equipment and product degradation, it is crucial for you to get the rate of airflow right. 

B] What Are The Factors Influencing The Material Flow Rate of Air in Pneumatic Conveying?

The velocity of air in the pneumatic conveying system will directly affect the way materials get conveyed. Therefore, here are some of the factors that explain how air velocity affects materials and are responsible for influencing the air flow rate in pneumatic conveying applications:

1. Shape

Materials that consist of particles with bigger surface areas, such as cement, will require lower pneumatic conveying velocity. For you to compare, cement would need an air velocity of somewhere between 10 and 11 m/s. Fly ash, on the other hand, requires air velocity ranging from 11 to 12 m/s. Fly ash comes with a spherical shape, which increases the demand for air velocity. 

2. Size

The way air velocity affects materials with fine or granular particles is reflected in the higher air velocity values that are necessary to convey them. It typically ranges between 13 and 15 m/s. But this rate of flow can fluctuate, depending upon the width of particle size distribution. For instance, materials such as granular sugar will require higher air velocity for pneumatic conveying, somewhere around 16 m/s, because of its narrower size. 

3. Weight & Density

The materials with different weights and densities also get impacted with respect to air velocity. For instance, lighter materials have the tendency to degrade when they come across higher conveying air velocity through the pipelines. When you are conveying larger particles that are higher in weight or density, it would require higher velocities to move smoothly through the pipeline. Low air pressure in high-density material transportation cases might result in pressure loss or blockage. 

C] Why is Achieving the Ideal Flow Rate of Crucial Importance? 

The flow rate of air in the pneumatic system directly impacts the material that is being conveyed. Following that, the components that come in contact with the material also get affected equally. Therefore, to prevent the degradation of both equipment and products, it is important to set the airflow right. 

It is also mentioned if the airflow rate or velocity is implemented at high pressure, it will degrade or abrade the softer materials such as plastics. They will be cluttered within the internal walls of the pipes. This will be the outcome because the materials will be travelling too quickly by creating frictional heat. Thus, the material will melt. 

Thus, it leads to the formation of streamers or angel hairs, resulting in colour contamination and product degradation. And this will eventually clog the filters. In a different use case scenario, if the rate of velocity or airflow is less, the heavier particles will get destabilised and will step out of suspension while travelling through the pipelines. 

Due to such effects, the pneumatic conveying system will experience pressure losses and blocked pipelines. Therefore, maintaining the right flow rate for the pneumatic conveying system is quite important for enhancing productivity. And this can be done by implementing automated flow control systems. 

D] Tips to Optimise Air Velocity for Efficiency

Here are some of the tips for you to feasibly optimise the air velocity for increasing the efficiency of pneumatic conveying systems:

1. Calculate the Air Velocity

The minimum pneumatic conveying system calculations on air velocity are stated differently for varying materials. If you are transporting a very fine material, then the minimum air velocity should be 10 to 12 m/s; for fine material, it should be 14 to 16 m/s, and for coarse material, it should be 16 m/s or higher than that. Do your pneumatic conveyor calculation optimally, or take the help of experts.

2. Avoid Excessive Air Velocity

A safety margin of around 20% should be implemented upon the air velocity being used in the pneumatic conveying systems. This is the general recommendation, but the margin should not be too high, as the pressure drop and required energy might vary approximately with respect to the square of air velocity. 

3. Prevent Material Segregation

With the use of the lean-phase conveying approach, a lot of air gets mixed with the small powder quantity, which leads to increased air and powder velocity. Thus, the speed and volume of air are too high to keep the particles moving continuously within the suspension, increasing the chances of segregation. Setting up the constant air velocity in a pneumatic conveying system will repel segregation problems. 

4. Regular Maintenance and Monitoring

Regular maintenance and monitoring of the pneumatic conveying systems will save you from costly downtimes. It is quite essential for you to minimise the risks by all means possible. One of the best ways to do that is by monitoring the system periodically and giving it regular preventive maintenance. 

5. Consider the Pipe Diameter

The conveying pipe diameter directly affects the velocity of air. By reducing the diameter of the pipe, you can increase the volume of the flow rate and reduce the pressure. On the other hand, as the diameter increases, the flow rate also decreases by increasing the pressure. Thus, considering the pipe diameter would help you stabilise the air velocity in a pneumatic conveying system. 

Conclusion

Air velocity plays a very crucial role in promoting seamless material handling within pneumatic conveying systems. You need to set the right flow of air in order to ensure the material gets transported in the best condition as expected and the system stays operational without any blockages, pressure drops or downtimes. 

You need the best quality products, along with the right operational training, in order to efficiently run the conveying system. So, look out for the best pneumatic conveyor manufacturer in business to help you source the best machinery at a reasonable price and guide you with recommendations on optimising the air velocity for operations.