Julie Gass, P.E., is a Lead Mechanical Process Engineer at Black & Veatch and an industry veteran with extensive experience in mechanical equipment in wastewater treatment plants. She also served on the American Society of Mechanical Engineers (ASME) Committee responsible for ASME PTC 13, Wire-to-Air Performance Test Code for Blower Systems, which is the performance test code published in October 2019 for all blower technologies. Blower & Vacuum Best Practices Magazine interviewed Gass to gain her views on aeration blowers, PTC 13, and the firm’s rigorous specification process to ensure treatment plants get the blower best suited for their application.
Good morning. Please describe Black & Veatch.
Black & Veatch is a global employee-owned engineering, procurement, consulting and construction company headquartered in Overland Park, Kansas. I work in our Water building, located in Kansas City, Missouri, which is about 15 minutes from our headquarters building. Black & Veatch was founded over 100 years ago in 1915 and is ranked as one of the world’s largest wastewater construction and engineering firms.
Black & Veatch’s design experience in the industry includes primary, secondary, and tertiary treatment; wet-weather flow treatment; effluent reuse; ozonation; ultraviolet disinfection; aerobic and anaerobic digestion; nutrient removal and recovery; and odor/air emissions control. We also have extensive experience in advanced process options, such as biological aerated filters, membrane bioreactors, moving bed biofilm reactors, and integrated fixed-film activated sludge. In addition, we excel in all aspects of biosolids management.
We engage with clients on all different types of projects, whether it’s stand-alone jobs, or designing, installing, and commissioning new or upgraded treatment facilities.
Julie Gass, Lead Mechanical Process Engineer, Black & Veatch.
How would you assess blower manufacturers’ ability to the meet the needs of wastewater treatment plants today?
In my view, blower manufacturers have been very responsive to the needs of treatment plant owners.
For example, gearless high-speed turbo blowers were one of the first technologies to offer better efficiency for small-to medium wastewater treatment plants when they first came out. Size classifications are rather arbitrary, but, in my mind, a small treatment plant is a facility that typically uses blowers that are each sized for 2,000 scfm or less. Medium-sized plants are operations with blowers from 2,000 to 10,000 scfm each. A larger plant is one with each blower sized for 10,000 scfm or more. The availability of gearless turbo blowers was significant because there weren’t too many choices for improved energy efficiency for these plants and they tended to rely on Positive Displacement (PD) or multistage centrifugal blowers.
In terms of newer technologies - like the gearless high-speed turbo blowers with non-contact bearings - they’re not perfect, but nothing ever is. We all know there were some issues with the early generations of blowers of this type. However, I have to give credit to the manufacturers. They’ve all made improvements and continue to make improvements in one way or another to ensure reliability and make customers happy. Some are focusing on improving Variable Frequency Drives (VFDs) and some are focusing on other parts of the machine. I think everyone is more focused on energy efficiency than even 10 years ago because, of course, electricity keeps going up in price.
On the topic of blower technologies, what determines whether a PD or centrifugal blower is best suited for a particular aeration application?
The biggest contributor to the machine’s discharge pressure requirement is the depth of the water level requiring aeration.
A PD blower is a good candidate for any application where the water level varies significantly because it will produce whatever pressure is required to overcome the backpressure of within the range of the machine. One example is an activated sludge processing using sequencing batch reactors (SBRs). We’ve also used high-speed turbos for SBRs and they have worked well. SBRs call for frequent starts and stops, which can be challenging for some gearless turbo air bearing machines.
In an aeration basin where you have more of a constant water level, it’s often better to go with a centrifugal blower, whether it’s an integrally geared, single-stage machine or a gearless turbo. While centrifugal machines have a pretty narrow pressure range, they are typically more efficient than PD machines. You can still install a centrifugal machine with some variation of water level, but that’s going to require more careful blower selection and more engineering.
It’s also not uncommon to see different blower technologies at the same treatment plant serving different processes, with the machine type being based on what best fits the process requirements.
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Have you seen plants where mixed technologies discharge air into a common header for activated sludge aeration?
We’ve done that before, and usually it’s a situation where a plant has an older blower technology in place and wants to add a new, more efficient technology to the mix without incurring the capital cost required to replace all of their blowers.
For example, take a plant that has a lot of older multistage centrifugal blowers. They really don’t have the capital to replace all units, yet they want something more efficient. We’ll look at the annual average airflow requirement, among other things, and say, “What if we put in a new technology to meet the annual average requirement by itself under normal conditions? And then, under those maximum conditions, you run the old and new technology in parallel?”
Of course, the older technology won’t be as efficient as the new blowers, but if you’re only running the older machines maybe one month out of the year in total it still gives the plant a lot of improvement in blower efficiency and power consumption. The plant can then quickly recover their capital outlay for the new machines in energy savings. We’ve done that on a few occasions.
Have you changed how you write specifications for blowers based on ongoing developments in blower technologies?
We continually revise our blower specifications. Available blowers change, we learn more about them, different features work well for some clients but not others, etc.
We like to do a lifecycle cost evaluation early in the design of a system to determine which technology will be the lowest lifecycle cost and then write our specification around the selected technology, as well as number and size of blowers. We’ve suggested our clients factor in the lifecycle cost of equipment, not just the capital costs by doing an evaluated bid. We’re doing that more and more because end users see the benefit as electricity costs continue to increase. This is especially important if one vendor’s blowers consume significantly less energy than another.
Of course, there are many complexities with performance specifications. One example is with non-contact bearing machines there are air bearing and magnetic bearing options. The challenge is that clients either want, or they’re required to have competition written in the spec, but there aren’t a lot of vendors with a long experience list with magnetic bearing machines. Our typical policy is for a new vendor or technology to have five years of operating experience before we name them in our spec, but we have not always lived by that because there are many unique situations where the process or building limitations will work only with a new technology. In that case, we explain the risks to our client and write the specification in a manner that helps mitigate risks to the extent possible.
Another development impacting specifications is ASME PTC 13, which would allow us to bid some type of rotary positive displacement blower against a gearless turbo machine, for example, if desired. PTC 13 by intent is technology-neutral, so energy use for any type of blower can be compared to any other type. In a case such as this, the layout would need to allow for either blower type being considered so it may not be practical or cost effective to bid multiple technologies in some cases.
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Speaking of PTC 13, congratulations to you and others on the PTC 13 Committee on your accomplishment.
I’m very happy to see PTC 13 published. I anticipate it will most commonly be used as a guide for an after-the-sale test to determine whether the manufacturer of the entire blower package has met power guarantees. If testing shows guarantees are not met, there are typically financial penalties written into the specification to protect the customer. That’s why it’s important to identify all of the components to be tested in the purchased blower package to be run at the manufacturer’s test facility.
With the older technologies, you would have a blower and a motor. Often, the blower didn’t even include special cooling equipment and the motor might be a NEMA premium efficiency motor for which efficiency requirements are well defined and established. With newer technologies, however, you have a lot of ancillary power consumers. As an example, a machine might have a high-speed permanent magnetic motor and the efficiencies of those vary from one manufacturer to another. It’s not as standardized as a NEMA-rated motor and then the VFD has to be specific for that type of high-speed motor so the power losses associated with it need to be considered, as well. And then you have things like harmonic filters, silencers, air filters, and the special cooling equipment I mentioned and so forth.
PTC 13 provides guidance for testing all the components of an entire packaged system and its overall energy consumption in order to get reliable and repeatable results. The older performance test code, PTC 10, was pretty much geared for constant-speed machines without all the ancillary electrical equipment in particular. Witnessed performance tests are important to verify performance and to detect any issues before machines get into the field where they’re more difficult to correct. Witnessing performance tests is especially important for large machines, new technology machines, or machines where the original equipment manufacturers have been bought out by a manufacturer who may be less familiar with the technology.
Will PTC 13 change the need for witnessed performance tests?
Years before PTC 13 existed, we typically only required witnessed performance tests on machines from 500 hp and above, due to the cost of testing and the percentage of the total equipment costs.
But we started recommending witness testing on smaller-size machines after the industry saw manufacturers buying other manufacturers with different technologies. We wanted to ensure these machines worked like they were supposed to work before they got in the field. Then, new technologies like gearless turbos came out. The manufacturers often did not yet have much of a knowledge base for how their machines would perform and there was not a standardized performance test code that addressed the technology. That’s when we pretty much said we’re going to recommend a witness performance test on gearless turbo machines regardless of the size, although there are some exceptions that.
I think the machine size at which we insist a witnessed performance test be performed will start to go back up again as we all become more confident with PTC 13, or maybe we see that a manufacturer has done ten projects and they’ve never failed a PTC 13 test. Obviously, PTC 13 just came out so that will be a few years down the road.
You mentioned the importance of knowing whether a technology is proven when writing specs. What else does Black & Veatch do to ensure things go well when specifying blowers?
As far as proving technology works in the field, we’ll check references by talking with plants who have had a certain technology installed for a period of time to see what their experience has been with it.
We also like to see manufacturers with their own Research & Development department rather than a company that just does “reverse engineering” of somebody else’s equipment design.
Another thing we do is carefully assess the experience of the systems integrator involved on the aeration controls. We used to allow aeration controls to go out to the low-bid integrator, but we’ve changed our approach. We want to see an experienced integrator on our projects. You might have an integrator who is good at programming PLCs, but what if they’ve never seen a wastewater treatment plant? That can cause problems.
We found the best way to ensure we get an experienced integrator on the project is to have the blower manufacturer responsible for the entire aeration control system. Many of the manufacturers now have controls people on staff to do that. If they don’t, we want to see if they have an established relationship with an experienced integrator. In some cases, the specification might list three integrators and require they use one of them without exception because we’ve had success with them. Aeration controls have become too important to rely on a firm without the proper level of experience in wastewater treatment applications because controls are also very important for the overall efficiency of the system.
Thank you for these insights.
All photos courtesy of Black & Veatch.
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