Guest Author: Krystof Litomisky
Generally speaking, getting “good performance” from an industrial dust collection system is a matter of getting “enough” - enough air velocity at all drops such that waste material is reliably picked up, enough air velocity in the ducting system such that the waste material does not settle there, and so on.
There are, however, cases where more precision is needed - where the velocity needs to be in a very specific range, and both too much or too little presents a problem. These scenarios present interesting challenges.
Let’s look at an example.
The Challenge
Abrasive blasting (also known as sandblasting), is the process of directing a stream of abrasive material against a surface in order to smooth, roughen, shape, or clean it. The abrasive material can vary from metal shot (“shot blasting”), sand (“sandblasting”), glass beads, or can even be a non-abrasive material such as ice or dry ice.
The process generates dust that, if inhaled, poses a significant health hazard to humans. In addition, if not captured, such dust also poses a significant fire, deflagration, or explosion danger.
For this reason, it is absolutely critical that dust generated by this process be properly and reliably captured by the dust collection system. This is the lower bound - drop velocities must be at least at this value in order to reliably capture dust and eliminate the health and safety hazard posed by it.
The upper limit is given by the velocity at which the dust collection system begins to capture the shot material. If this happens, the shot material cannot be reused and will therefore need to be replaced - which can be very costly.
Thus, for abrasive blasting applications, drop velocities need to be above the velocity needed to reliably capture dust and contaminants, but below the velocity at which the dust collection system begins to capture the shot media. Let’s refer to this as the “target range”.
Depending on the application, the target range can be quite narrow. For example, for a specific shotblasting machine in an automotive manufacturing facility that generates fine & light metal dust, we have experimentally measured the target range to be 3,200 FPM to 3,500 FPM - quite narrow indeed.
A first pass at a solution is straightforward: let’s set up the system such that the drop velocity is in the middle of the range (3,350 FPM) and let it run.
The issue with this approach is that factors that influence the performance of the dust collection systems can change without intentional human input. For example, filter pressure losses change as the filter is used and the filter media becomes dirty. Other factors that may change the drop air velocities include the operation of summer/winter gates, or the addition (or removal) of other machines on the ducting system.
The target range for this particular machine is narrow - a drop pressure change of just 9% would move the operating point from one side of the range to the other. Any one of the above factors can cause such a change.
The most straightforward solution seems to be recalibrate our system periodically, including after every regular filter cleaning and maintenance and any system modifications. This solution, while plausible, is extremely time-consuming and error-prone.
Surely there must be a better way that leverages modern technology?
The Solution
That is exactly the question posed to us at Ecogate by a large manufacturer of automotive parts who uses shotblasting in their finishing process. The company had had issues with reliably maintaining the required drop velocities, and this had caused several fires in the facility.
Together, we quickly zeroed in on the key to success for this challenge: continually monitoring the drop velocities (rather than secondary signals such as fan motor frequency), adjusting system performance in real-time closed-loop regulation such that the drop velocities were in the target range, and reporting to the shotblast systems when it was safe to operate.
This is exactly the solution we have delivered.
We have installed an Ecogate intelligent automatic blast gate at each drop, which continually monitors the air velocity, pressure, and volume flowing through it.
The air velocity information for each drop is then fed to the central Ecogate greenBOX Master control unit. The greenBOX adjusts the speed of the dust collection system fan using a variable frequency drive (VFD) such that the desired air velocities are met at all workstations.
Thus, the system uses closed-loop regulation to provide the right air velocities at all drops.
The desired air velocity range is easily set by the end-user individually for each machine using the greenBOX controller’s touchscreen.
As an additional safety function, each automatic blast gate outputs a signal indicating when the air velocity passing through it is within the desired range. This signal is then used as an additional input for the shotblasting machine, indicating when it is safe to run.
The sequence of operations is as follows:
- A shotblasting machine indicates that it is ready to run and requests ventilation
- The Ecogate blast gate to this machine opens
- The greenBOX controller adjusts the dust collection system’s fan speed such that the drop air velocity is in the target range
- The Ecogate blast gate indicates that the air velocity is in the desired range
- The shotblasting machine reads the signal from the blast gate and commences shotblasting
The Results
The system has now been performing as designed for over three years.
The “air velocity is in the target range” signal provided by the Ecogate blast gate is used to indicate to the shotblasting machine when it is OK for it to run. By monitoring the direct indicator (the actual air velocity) rather than a secondary signal (such as “fan is running”), the system is robust with respect to external conditions, including changing filter pressure losses.
An additional benefit of the system as installed is dramatically reduced electricity use. This is because the system automatically closes blast gates to machines that indicate that they do not need ventilation. This reduces the total air volume at the fan, which in turn means that greenBOX control unit can slow down the fan speed using the installed variable frequency drive. Because fan power varies with the cube of the air volume (as described by the Affinity Laws), substantial energy savings are achieved even with a modest reduction in air volume.
This system as installed is a great example of how adding sensing capabilities and intelligent controls can dramatically improve the reliability and safety of industrial manufacturing processes.
Krystof Litomisky is the CEO at Ecogate, Inc., the maker of the world’s best industrial dust collection control system. Ecogate makes dust collection systems run better and safer while using significantly less electricity. For more information, visit Ecogate.com, or check out our 100-second video.
