Today, most modern compression stations are built to run continuously and their support systems are designed to accommodate the continuous operations of the system. Specifically, the jacket-water cooling, lube-oil cooling and after-cooler cooling are designed to constantly lower the temperature of each running unit, thereby keeping it in set optimal ranges.

However, these facilities are now occasionally being shut down. In such instances, two major problems can occur. The first issue pertains to cold starts, especially in the winter.

"It takes a lot of power to roll over that much cold steel," explains Steve Hockett, principal field project manager for a U.S.-based pipeline company. "Equipment becomes scored and things break. Also, it can take days to cold start a unit—despite the fact that demand calls for the gas to start running immediately."

The second issue is water condensation, which can form on the exterior and interior of compression units, both of which are unfavorable conditions, he says. "First, not only does external condensation cause paint to peel off and surfaces to rust, it also makes work areas and walkways wet and slippery, which are very unsafe conditions."

Second, internal condensation can cause rust to form on internal components that can mix with lube oil, which, in turn, causes a loss of lubrication to critical moving parts.

"To solve these cold start and offline maintenance issues, the compressor units need to be kept above the dew point temperature, which requires heat," says Hockett.

Hockett manages a large-diameter transmission pipeline that taps into supply regions in the Gulf of Mexico, Texas, Appalachia and Canada. The interstate natural gas pipeline system is capable of delivering natural gas to markets across the mid-West, mid-South and mid-Atlantic regions.

To keep the gas moving up the 14,000-mile pipeline system at 900 pounds per square inch of pressure (psi), the gas pressure has to be boosted at regular intervals. Therefore, compressor plants are implemented approximately every 100 miles to boost the gas pressure, giving it the necessary momentum to travel to the next station.

Fast fix

On September 17, 2010, Hockett was asked to install a jacket-water heating system at one of the pipeline's compression facilities in northern Kentucky. The facility was in need of a heating system and had to be up and running by no later than January 15, 2011.

"To meet this deadline, everything about a standard design-build project had to be expedited," Hockett says. As he began to research options for meeting this tight deadline, Hockett reached out to Bill Hunt, sales representative for James M. Pleasants Company. Hunt informed him that the company's packaged equipment branch, HYFAB, had the resources and expertise to complete the heating component of the project in the allotted time.

"When I first spoke with Bill and became aware of HYFAB's capabilities, I knew there was a chance we might be able to meet the project delivery date," says Hockett.

Condensing boiler choices

Historically, heat-system designs have used a traditional fire-tube boiler to provide the required Btu per hour to preheat the compressor horsepower. However, Hockett recognized that such systems were not the most efficient. His experience in building heat systems for other natural gas pumping facilities led him to the Power-Fin line of boilers, by Lochinvar LLC, based in Lebanon, Tennessee, which can have up to 87% thermal efficiency.

A HYFAB team member

A HYFAB-team member stands next to a shipping unit at headquarters in Greensboro, North Carolina.

A HYFAB-team member

However, as Hockett and Hunt started working with the HYFAB team to design the skid-mounted heat system for the northern Kentucky station, Hunt recommended the SYNC condensing boiler, also by Lochinvar, rather than the Power-Fin for this application.

"I have been working with these products, such as Power-Fin, for decades, but this was the first time I have specified the SYNC Boiler," says Hunt. "With its stainless steel heat exchanger and ability to handle low temperature applications, I knew it was a better choice for this project."

Hockett agrees, adding, "Rather than installing one 6 million Btu (MMBtu) per hour, 65% thermal-efficiency fire-tube boiler, which is traditionally used for this type of application, or building the system around the 87% thermal-efficiency Power-Fin, Bill helped us design this system around three 1.5 MMBtu per hour, 98% thermal-efficiency SYNC condensing boilers," explains Hockett.

"With condensing boilers of this caliber, we could maintain the optimal start temperature of between 80 to 100 degrees for the compressor horsepower and save about a third of the amount of the fuel traditionally used with the industry-standard fire-tube boiler. Also, with SYNC's on-board touchscreen and operating control, we could remove the exterior control and sequencing equipment, used in the past, to create a cleaner package with greater range of control."

System design

The system included three SBN1500 SYNC boilers, a system pump with variable-frequency drive, boiler pumps, an expansion tank, a glycol feed tank, hydronic heating-system accessories and all of the piping for the boiler room. The complete mechanical system was built on a skid and contained in a structure that was 15 feet long by 25 feet wide by 11.5 feet high.

Although the size of the package made it a challenge to ship as a complete unit, the HYFAB team—accompanied by a police escort from HYFAB headquarters in Greensboro, North Carolina, to northern Kentucky—successfully transported the system to the pre-poured pad at the compressor plant.

Upon delivery, the prefabricated package system was set in place by a crane for a quick installation. This marked the first time that the subject compressor plant had been taken completely offline since its construction in 1951, so minimizing downtime for the compressor plant was a top priority.

Once the equipment was installed, the contractor simply connected the natural gas fuel supply and brought the heating-water supply and return piping to the system. After wiring the electricity, the system was up and running.

"The installation was a very simple process," says Paul Worley, project manager for John Bouchard & Sons Co., the installing contractor based in Nashville, Tennessee. "The on-site team knew what they were doing, and the equipment couldn't have been easier to work with. All it took was a couple of quick connections to get the system started."

Consistent temperature management

The data for this remote-monitored system shows that the boiler system rapidly increased the compressor's jacket-water temperature upon implementation, even on a cold January day.

"Everyone on-site guessed it would take 24 hours to bring this system up to temperature, so it was a huge surprise when the boilers began to back down and modulate after just two hours," says Hunt.

"The installation and performance of the three SYNC units was everything I expected it to be, and more. Also, the control system is impressive to the end user. I can't tell you how many times I saw someone staring at the controls, just to see how much firing rate was required to heat the system."

The data continue to show consistent temperature management due to SYNC's internal cascading sequencer and each boiler's ability to modulate at 10:1 turndown to precisely match system demand. In fact, the three 1.5 MMBtu per hour condensing boilers, which were installed in place of one 6 MMBtu per hour fire-tube boiler, are operating daily with no more than two of the boilers, or 3 MMBtu per hour, running at any given time.

"The system is operating exactly as it was designed, and we couldn't be happier with the way it's working," says Mark Quillen, cross-functional technician and a 35-year veteran of the pipeline company.

As a result of the project, and the equipment chosen and installed, such as the installation of three boilers instead a single, larger boiler, the pipeline operator avoids the problem of having his entire jacket-water heating system shut down for maintenance or repairs, and also avoids the more critical problems of scoring or breaking equipment, and internal and external condensation damage.