ATCO, a gas distribution company that supplies more than 1.1 million customers across Alberta, Canada, through a network of transmission and distribution systems, was having noise, reliability and maintenance issues at its high-pressure natural-gas letdown sites. At its Whitemud Gate Station, for example, the existing installation of booted regulators produced an unacceptable amount of noise for nearby condominium complexes' residents.
This user-case-study presentation of the solution to these problems, utilizing Fisher EZH and FL bootless regulators, won best-in-conference accolades at the 2019 Emerson Global Users Exchange in Nashville, Tennessee.
The solution that ATCO created with the help of Spartan Controls in Alberta, Canada, resulted in extremely safe, reliable and quiet operation at numerous distribution stations, while reducing maintenance costs.
Chris Yin, facilities engineer at ATCO, designs natural-gas regulating stations that reduce high-pressure gas from outside the city to low-pressure gas inside the city. This ensures the customers have safe and reliable gas delivered to their homes. Yin is in charge of capital-improvement projects under the Urban Pipeline Replacement (UPR) program. The goal of the UPR program is to reduce the high-pressure gas that is currently inside the city to low-pressure gas. This includes installing new equipment to ensure the system is adequate for the future.
"Of all the design considerations, noise gave us the biggest issue." ATCO’s Chris Yin (right) together Eric Kaert of Spartan Controls explained how the Canadian natural gas distribution company successfully mitigated auditory emissions at the Whitemud Gate Station at the 2019 Emerson Global Users Exchange.
"Much of our work at ATCO revolved around changing from boot to bootless regulators," said Eric Kaert, gas utilities specialist at Spartan Controls. "A boot-style regulator works by adjusting the loading pressure and adding force on top of the boot (diaphragm) pushing it down to block the port, stopping gas flow. As the pressure is relieved downstream, the pressure on the diaphragm is reduced, allowing it to raise the supply gas flow downstream, increasing pressure.
One of the draws of a boot-style regulator is that the boot is in the main flow of the gas stream. "All of the main flow is through and around the diaphragm, which causes the pressure drop," said Kaert. "So you have a piece of rubber, the seal, in the gas stream handling the pressure drop. At some point, the diaphragm will wear and ultimately fail. Typically it fails open, allowing full pressure downstream, requiring over-pressure devices to operate. The key point is that the throttling-and-control element is a piece of rubber."
On the other hand, a bootless regulator is more like a control valve. "A plug and a seat in the regulator do the throttling with the diaphragm above, outside the flow of gas—it doesn't see any of the main flow of gas—it just sees the loading pressure," said Kaert. "It's more like a valve and actuator. The pressure occurs across the plug and elastomer seat, and, even if that wears away, there is still a metal backing that can control the pressure."
The bootless regulator is also more accurate and requires less differential pressure to operate. "The diaphragm area is much larger on a bootless regulator,” said Kaert. "With the same change in pressure affecting a much larger area, it has much greater accuracy.”
The boot-style regulator is lower in cost and weighs less than the bootless-style, and the bootless-style has a higher initial capital cost, is heavier and appears to be more complex,” explained Kaert. "However, when we show maintenance and operators the valve and they get to take it apart, they are no longer concerned with complexity," he said.
When the team designed the UPR stations, there were design considerations that had to be addressed. "Of all the design considerations, noise gave us the biggest issue," said Yin. "Whitemud Gate Station is a success story about how bootless regulators helped us eliminate noise issues at a station near customers."
The government picked out the Whitemud Gate Station location within a transportation utilities corridor. "Usually we can pick locations that are far away from residences," said Yin. "Unfortunately, in this case we were given the Whitemud location and had to work with it. A condominium complex was located immediately to the north of the site. It was extremely close, and we foresaw noise issues but were asked to do our best."
In 2017, ATCO designed the station with a gas inlet pressure of 290 psig to 580 psig. The gas moves through the station, that includes a line heater to preheat the gas and is regulated down to an outlet pressure of 80 psig with a peak load of 1.7 million standard cubic feet per hour (scfh).
"The station components consist of two parallel piping runs," explained Yin. "The top one is the main run, and the bottom run is the alternate run. Each run has a monitor and a worker regulator. The wide-open monitor regulators are acting as a safety guard. Downstream are the workers that cut the pressure down to 80 psig."
Originally, Yin chose 6-inch boot regulators. "We finished the design and installed the system just before winter," he said. "We monitored for a few weeks without any concerns, and then winter hit. As the temperature dropped, gas demand ramped up causing a lot of gas flow. A few weeks later we received noise complaints from the residents. We took measurements at the site and found readings as high as 117 A-weighted decibels (dBA)—very loud. It was a huge safety concern and a big nuisance for the customers."
We reached out to Spartan Controls, and it determined the noise was coming from the boot regulators, continued Yin. "The design of the boot-regulator flow path caused the gas to be more turbulent and therefore noisy. That, combined with the noise of the boot movement itself, caused a lot of noise," he said.
Spartan Controls specified a Fisher Class 600 RF 6-by-12-inch FL SRSII bootless regulator because of its straight-through design that reduced the turbulence and related noise. The solution required piping modifications and a downstream spacer for ease of maintenance.
"With the new bootless regulator installed, there was a huge reduction in the sound level," said Yin. "We had the noise level checked again, and the new regulator brought the sound level down to about 85 dBA from 117 dBA. To this day, we have had no further complaints of noise from the station. Replacing the regulators was enough."
Before the bootless regulators were installed, ATCO planned to install noise curtains and pipe lagging for noise attenuation in the next four stations, just in case. However, since the bootless regulators solved the noise problem, it scrapped that idea, which actually saved $90,000 CAD per site.
"Overall, Whitemud was a huge success story, and we have plans to use the Fisher FLs at our next four big UPR stations," said Yin. "Not only do the FLs attenuate the noise, these bootless regulators are more reliable and require little maintenance, compared to boot regulators. The long-term/lifetime costs must be considered. Considering boot replacement cost per year to the much-longer-life bootless regulator replacement cost per year, the bootless solution provided an estimated savings of $650,000 to $1,300,000 CAD per year at ATCO."
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