Using Particle Velocity Measurement to Supplement Static Pressure, Velocity Pressure and Total Pressure Calculations

Posted by Earl Parker on Mar 21, 2017 1:30:00 PM

The right measurements for effective management

When first studying up on the fundamentals of industrial dilute phase conveying, dust collection and other related systems, plant engineers might find themselves inundated with convoluted technical formulas and unfamiliar terminology. Often much of this proves to have little practical use with regards to their actual system and ends up confusing rather than simplifying efficient operations.

In our experience, we often encounter this issue when we discuss the benefits of monitoring particle velocity inside a dust collection system or bulk powder system. Because instruments have never been available to measure particle velocity, and air velocity measurement can disrupt the process and/or typically fail due to the presence of the particulate, many have learned to rely on calculations.

It's worth looking at how particle velocity monitoring instruments might provide practical supplement to calculations for static pressure, velocity pressure and total pressure to optimize system operation. So let’s consider briefly these terms and why we need not spend too much time focusing on them. 

Static Pressure, Velocity Pressure and Total Pressure in Dilute Phase Applications

One definition of these terms reads: “Velocity pressure is that pressure required to accelerate air from zero velocity to some velocity (V) and is proportional to the kinetic energy of the air stream. For example, when a fan is moving air through a duct system, two types of pressure are encountered: velocity pressure and static pressure. The sum of these pressures is referred to as total pressure.” 

Most often, velocity pressure in dust collection systems is not directly measured once the system is installed nor is it normally even calculated during design phase except on very complex systems. In contrast, static pressure plays a key role in proper functioning of the system and so is calculated during initial design as well as periodically after installation as part of certain troubleshooting procedures. The "static" measurement refers to the overall resistance to airflow created when air flows through a space. For example, as air moves through a duct the friction between the air and the duct creates resistance. In order to overcome this resistance, the fan must have sufficient pressure or vacuum power to move the air through the duct. When doing initial design of a system, static pressure must be carefully calculated so that an adequate fan/motor combination can be selected. Often airflow problems arise when the system ductwork is modified later without considering implications to the pressure required and adjusting the fan accordingly. 

How Might Particle Velocity Monitoring Instruments Help?

Application for particle velocity monitoringIn dilute phase conveying systems like pneumatic conveying and dust collection systems, particle velocity needs to stay at or above the minimum conveying velocity for the material (the velocity at which particles will be carried along suspended in the airstream). The best guess has traditionally been air velocity, but of course that's an approximation based on many assumptions. If the air velocity dips below the minimum covey velocity the dust/product will begin to settle and drop out of the airstream, building up in the ductwork eventually causes blockages making the problem even worse. Increasing the speed isn't necessarily the solution, however, since in many cases higher speeds lead to higher attrition, smearing and other complications.

The challenge process engineers have is that many things can affect air velocity (much less the particle velocity) within the system. These include upset conditions, increased differential pressure in the collector, buildup in the ductwork, temperature fluctuations, etc. When these cause the airflow to drop below the minimum conveying velocity problems ensue.

Everyone knows this - the problem is that there's never been a reliable way to monitor PARTICLE velocity in a closed system. Until now.

Now it's possible to directly monitor particle velocity in a conveying systems using Auburn Systems’ triboelectric technology. Having this data metric available can allow operators to make informed operation decisions and convert the art of velocity management to a straightforward science.

This offers broad potential savings in product attrition, system maintenance and unplanned downtime.

Conclusion

Should you concern yourself with learning the ins and outs of various calculated pressure measurements? They are important system design considerations, but of potentially greater value is the monitoring of particle velocity - and then, even using that data to directly control fan speed. 

Would you like to know more about how Auburn’s triboelectric technology provides such accuracy when reading particle velocity instead of theoretical velocity calculations? Click here to learn more about our triboelectric technology or click here for a product brochure on our new TRIBO.hs Model 5000 Velocity Monitor.

Want to kick around ideas for how particle velocity measurement might improve your operation? We're happy to jump on a call. 

Let's Talk!

Topics: Process Control