Casey Shockey, President, Chief Engineering PLLC

Dust Safety Science is an organization dedicated to promoting awareness of combustible dust hazards and safety within the bulk solids handling industry. We're a proud member of this organization, and we've learned incredibly helpful information from leaders and members within the group that helps us ensure the safety of our customers.

One of my favorite resources is the Dust Safety Science Podcast, a weekly podcast hosted by Dr. Chris Cloney, Managing Director and Lead Researcher at DustEx Research. I was honored to have been featured in episode 94: Use of 3D Scanning in Processing Facilities. In this episode, we discuss the following topics:
​

• How does 3D scanning benefit processing facilities?
• How can it be used in facilities handling combustible dust?
• How can facilities prepare for a scan?

Listen to the full episode here:  ​https://dustsafetyscience.com/3d-scanning-casey-shockey/

Thank you again to Dr. Chris Cloney for having me on the podcast and for the great work he and his team are doing at Dust Safety Science. Make sure to check out dustsafetyscience.com for the latest and greatest in combustible dust research and safety advice, and contact me at casey@chiefengineering.us if you're interested in learning more about using 3D scanning in your facility.

Beau McLeod, P.E., Chief Engineering PLLC
Running a 100 horsepower motor for a year at full speed can be costly. Installing a variable frequency drive (VFD) can result in big savings, with payback periods often measured in months, particularly when utility company rebates are considered. A VFD controls the speed of a motor by varying the frequency and voltage of its power supply. Motors required to meet varying demand by operating with a throttled-down output are good candidates for VFD operation. Ultimately, three things help determine if a VFD is right for the application:

1. Operating conditions and characteristics. For new installations, the motor needs to meet the minimum and maximum performance requirements of the system.  To determine the system parameters, determine if the motor will run for long periods of time, if the system requires running at different speeds, or if the application requires constant torque. If the answer to any one of these questions is no, then a VFD may not be suitable for the application.
2. Installation cost. As a rule of thumb, the typical cost of adding a VFD to an applicable system is between $200-$500 per horsepower. The cost of adding a VFD to any system is significantly higher than other starting methods[AS1] . The capital cost of a VFD can determine the length of the payback period.
3. Cost savings. VFDs enable longer motor life and reduced maintenance expenses. Also, utility companies often offer rebates for VFD installations. Make sure to consider these cost savings benefits when determining if a VFD is the right choice.

Let’s use an example to determine if a VFD is suitable for a certain application. The following table shows input power percentage vs. flow percentage controlled by a VFD and an internal vane damper.

Now, let’s assume that the fan specifications include the following:

• 100 HP motor nameplate
• 95% efficient motor
• 20k cfm
• 19.5” w.g.
• 2295 operating hrs./yr. @ $.12/kWh
• 30,000 hour VFD service life
• $35,000 VFD capital cost.
  

Using the Affinity Laws for VFDs, the chart below shows the amount of savings that can be achieved with a VFD when the load is reduced. Using the fan specifications above, the average annual energy costs can be calculated for both a VFD and an internal vane damper configuration. At 80% reduced load, using a VFD requires much less horsepower to achieve the same airflow rate than utilizing a vane damper. This can lead to significant energy savings and a longer lifespan for the equipment.   

To determine if a VFD is financially feasible for the application, a detailed financial analysis will need to be performed to calculate the payback period to cover the initial cost of the equipment. According to the example above, if the application only utilizes an 80% airflow load every year, the VFD will have an annual energy savings of $6,704.10. By dividing those savings from the capital cost of the VFD itself ($35,000), the result is an approximately 5-year payback period. If the VFD service life is 25,000 hours and the fan is operating 2,295 hrs./yr., then the lifetime of the VFD will be approximately 11 years. In this case, a VFD does make sense for this application and will receive ~$40,225 in VFD savings ($6,704.10 x 6 yrs.) after capital costs have been recuperated.

Even though VFDs are expensive, they can be a huge money saving device served in the right application. So, are VFDs worth it? Yes, in the right circumstances. Follow the exercises above to determine if a VFD makes sense for your application. If you need help with an application regarding fan sizing and performance, contact a professional engineer at Chief Engineering or visit our website at www.chiefengineering.us.

Everything seems fine. Your systems are running smoothly, nothing looks broken or out of the ordinary. But lurking beyond eyesight, things like combustible dusts and condensates could be building up within your system. And when that happens, safety is jeopardized and employees’ lives are endangered. From flash fires to explosions, several deadly but preventable incidents have occurred across multiple industries due to dust accumulation (for a list of examples, check out this article from Nilfisk). Understanding the combination and characteristics of materials moving through your system and the necessary conveying velocities can help mitigate these risks and help you meet NFPA standards and OSHA regulations.  

Several actions can prevent dust accumulation incidents from happening:

• Performing a hazard analysis or study of the system
• Increasing the design duct velocities
• Testing and validating the system before commissioning
• Gathering historical data and testing the materials to understand the necessary requirements, including conveying velocities, for the highest level of safety

 
Ductwork accumulation occurs based on insufficient conveying velocities in the ductwork system. Typically, poor ductwork sizing, expansions without the provision of additional airflow, capped branch lines, and improper modifications to the ductwork system can cause insufficient conveying velocities. In many cases, our team has seen instances where a machine center will have a small connection stub that is connected to an expansion fitting. For example, a table saw might have a two-inch diameter connection and then a fitting is added to increase that diameter to a larger, more readily available size such as a four-inch diameter. The increase in diameter reduces the ductwork velocity of the air stream through the downstream fittings. This reduction in airflow can cause a loss of momentum that leads to the dust falling out of suspension and settling in the bottom of the ductwork. In some cases, we have seen two-inch diameter connections expanded multiple times up to a six-inch diameter line downstream of the connection to the machine. In every case, a simple inspection of the ductwork showed that material had packed and plugged the ductwork allowing no airflow to the connection point and reduced conveying velocities downstream of the plugged ductwork. These situations can be hazardous and should be corrected immediately to meet NFPA and OHSA compliance standards.
 
Accumulations due to low ductwork velocities are typically seen at expansions, elbows, and in the worst case, through the entire ductwork system. Common ways of combatting these situations are to size the system’s blower to provide adequate airflow and pressure to keep the ductwork velocities at acceptable levels, or, if possible, increase the speed of the existing blower. Typically, the latter is not possible due to the size and class of the blower selected for the original design. You can also change the connection size or hood to allow consistent velocities without the need for an expansion fitting. Ductwork branch lines that are no longer needed should remain open and the airflow intake should be metered into the ductwork system to ensure the acceptable ductwork velocities are maintained. For larger ductwork modifications, consult an experienced engineer to obtain proper and compliant ductwork modification for the section or area in need of adjustment.
 
If your team needs help modifying or identifying issues with your dust collection system, call our team. We’re experienced, licensed, and ready to assist.
 
Chief Engineering, PLLC
901-574-3403
 
 

Casey Shockey, P.E., Chief Engineering PLLC

Working for years as an engineer in the traditional design-bid-build process taught me a valuable lesson: bringing contractors and the construction team in after the design is finished could be very costly to my clients. Over time, I learned to bring more people into the beginning of the process – the clients and contractors from the fabrication and installation side were now able to add valuable input into the design.  I soon realized that I was moving away from traditional design processes and toward the design-build methodology, which benefits both the client and the team responsible for design and construction.

From reduced project duration and cost to better results, here are some of the biggest pros I’ve found by moving to the design-build method of working:
 
It’s much faster than traditional construction methods.
 
Design-build projects, on average, are delivered 33 percent faster with 12 percent quicker construction speed than traditional design-bid-build methods.[1] Overlapping project phases shorten a project’s speed to market and enable collaboration among all of the project’s key players, especially between engineers and the construction team. Because the designers and the builders are working as a team from the beginning, any changes in the scope of the project have a much smaller impact to the overall timeline and budget compared to the three separate phases in the design-bid-build process.
 
Design-build saves money (and headaches).
 
When project stakeholders follow the design-bid-build process, the initial price estimate and the final project price might substantially differ to the detriment of the client. In this traditional method, the construction pricing doesn’t occur until the design work is 100% complete, leaving time for an increase in interest rates and material costs. In short, there’s rarely a reliable maximum price for the client. This risk is greatly mitigated for companies that choose the design-build methodology because the construction planning and pricing happens simultaneously with the design work. Cost escalation becomes less of a problem for the client, budgets become more certain, and predicting an accurate maximum price for the entire project is easier for the design-build team. And, the client has a single contract to manage for true turnkey project execution.
 
It generates high quality, innovative solutions.
 
The quality of work can drastically increase when a client, engineers, contractors, and construction crews work as a unified team. The team works together during the design phase, ensuring construction is considered before the plans are finalized. The collaboration in this process powers innovation – now, because multiple teams are participating in the design phase, solutions can be more customized to the client’s needs. The construction team better understands requirements within the design, resulting in a high quality product that better meets the client’s expectations.
 
At Chief Engineering, our team is constantly looking for ways to deliver high quality products to our customers, and the design-build process has enabled us to provide turnkey services to consistently meet or exceed expectations. We’re also looking beyond the construction phase to protect the client’s system, providing maintenance and reliability solutions to help reduce unscheduled system downtime. Learn more about the design-build methodology from the Design Build Institute of America’s Design Build Done Right Primer.
                                                                                          
[1] Design-Build Institute of America: https://dbia.org/what-is-design-build/