Blowing Off Steam
There are things in life that have the “once-in-a-lifetime” label attached to them.
Jeff Hertz, project manager at Brentwood, Md.-based American Combustion Industries, proudly puts his involvement in a recent double boiler installation in that category.
Hertz was the project manager for ACI on a $3.38 million design-build contract to replace the steam generation system for the TC-7 Catapult at the Naval Aviation Warfare Center at the Naval Air Station Patuxent River (PAX), Md.
The PAX air station is one of only a few installations throughout the world where the Navy can run performance tests on aircraft carrier catapult operations on a land-based system with flight testing and engineering support resources that would not necessarily be available on an aircraft carrier that is docked or at sea.
“It was absolutely a once-in-a-lifetime project,” Hertz says. “It’s quite a thrill to see those jets.”
Located by the approach on runway 3-2 at Patuxent River, the catapult system is operated and maintained by the Navy, while the steam generation system is operated and maintained by civilian personnel.
“We test tomorrow’s aircraft today,” explains Jerry Girdlestone, the TC-7 Mark 7 site supervisor and a retired 25-year Navy veteran who worked with catapult, arresting gear and steam systems during his time in the Navy.
“These planes go all over the world to different ships. Before any new (type of) airplane gets shipped or after there is a modification to a type of airplane, we test it here. If it succeeds here on our tests, it will not have a problem out in the fleet. We put more pressure on it than it would normally get. We do faster launches. We want to get that g-force, which is the force of gravity or acceleration on a body, up and make sure the plane can survive out in the fleet.”
Pregame Warm-UpsACI was tasked with replacing two Foster-Wheeler D-Type watertube package 110,000-pound boilers (both installed in 1955) with two 2009 Babcock and Wilcox D-Type FM9-52 watertube package boilers. The boilers create steam, which drives the catapult’s launch system.
“The old boilers were bigger in size,” Girdlestone explains. “They were still operational, but we’d have something go wrong here, a valve or a line would blow there. With the age of the boilers, it was very hard to find replacement parts when something broke or wore out. It was just time to replace them.”
The new boilers are designed to match the 26,000-pounds-per-hour capacity of the old units. Each boiler is rated for a maximum working pressure of 825 pounds per square inch gauge with a normal operating pressure of 690 psig at 750 degrees F. Both boilers are equipped with superheaters to provide dry steam with 200 degrees of superheat to prevent condensate slugs that would develop in saturated steam with excessive load swings that are experienced as part of normal operation. Each new boiler is equipped with a factory-mounted Powerflame Vector burner with 33,600-Btu/hr. oil input and propane pilot ignition.
However, due to the heft of the boilers and the confined underground space the boilers are stored in, the project required a heavy dose of reconnaissance. The project’s design phase lasted more than six months.
ACI partnered with Elkridge, Md.-based Leach Wallace Associates (Charles Gonnerman was the lead engineer) on the project for consulting engineering and construction management services. They worked closely with boiler operators and plant support personnel to ensure the functionality of the new system would meet and exceed the functionality of the existing system, while also improving the performance of the existing system where possible.
“It was a good six months of just watching and learning from the guys on the site,” says Hertz, who points out ACI self-performed all ASME code welds on the project.
“Six months on a design-build process for a project this size is a long time. We learned how things operate and we asked questions to find out how we could improve the operation. We did not want to repeat any mistakes.”
The Opening ActThe project included two construction phases. The first phase featured the replacement of the existing boiler-feed system, while the final phase involved replacing the boilers themselves.
The new boiler-feed system was operational in just over six weeks once ACI was granted permission to begin demolition. The new system features a Watts 909 backflow preventer, a Kansas City tray-type deaerator to match boiler capacity, two Carver RS9 13-stage horizontal ring section pumps (with more than 1,000 psig head capability), two Aurora horizontal end suction booster pumps (to provide consistent suction pressure for the larger feed pumps) and a Water-EG custom resin softener system.
ACI elected to provide soft-start capabilities for the 75-horsepower, 3,500-rpm boiler feed pumps to reduce energy consumption at startup and to extend the life of the pump motors. ACI also elected to provide a closed-loop bearing cooling system to reduce wastewater flow.
Logistical PlanningACI had two 30-day periods in which to remove the two old boilers and install the new models. The first boiler was removed and installed starting in November 2008.
“Those were two 30-day periods where we could not fly,” Girdlestone says. “But we knew that six months in advance, so there was no loss of projects.”
The roof hatches to the mechanical room that stores the boilers had to be removed in order for the extraction and installation process to occur.
“The boilers are two stories down, so we had to do it in pieces,” Girdlestone says. “It’s a tight fit coming down. There’s less than a foot of room on each side.”
A 300-ton crane rigged the existing boilers in one piece and set the new boilers, which weigh 75,000 pounds apiece. Each extraction and installation process was scheduled for the same day the new boiler arrived from the Babcock and Wilcox factory in West Point, Miss.
“The crane had to be in the runway and it was blocking airspace,” Girdlestone says. “The less we had to use it the better. That’s why we waited until the new boiler was here.”
Being on an airbase also required special approvals for the crane.
“The physical rigging of the boilers was tricky. We welded lifting eyes on the drums to satisfy safety requirements,” Hertz says. “We had to coordinate with flight operations and with the Federal Aviation Administration. We had to coordinate with base security and get permits to get around the Beltway (an interstate highway that surrounds Washington and its inner suburbs in Maryland and Virginia).
“This was a lift that could not have been done without that type of crane. We coordinated closely with Crane Service Co. (ACI’s rigging subcontractor) to make sure there was nothing that could hold up the boiler lifts. Everything had to be perfect to get those boilers on the base and in place. There were quite a few people involved to make this happen, and we had to do this twice.”
In terms of efficiency, Hertz notes one of the boilers left the Babcock and Wilcox plant on a Monday, was at the base the following Wednesday and was lifted into the mechanical room Thursday.
Getting Down To BusinessOnce the first new boiler was set and the roof hatch was replaced and sealed, ACI prepared the unit for operation. A new Twin City BCS SWSI induced draft fan was installed along with a new ABB variable-frequency drive. ACI also installed a lower drum heating coil to reduce startup stress and operator overtime for startup and shutdown operations of the new unit.
“The boilers are the same capacity as the old ones, but they are much friendlier to operate,” Girdlestone says. “The valves are opened by push-button. The main isolation valves are manual, but everything else is push-button control.”
Hertz says another major point of emphasis was making sure all boiler controls were tested and configured to the highest possible standards.
“The controls are a little complicated,” Hertz states. “It’s a unique operation there. You’ve got a fluctuation in pressure when that catapult launches. The pressure drops all the way through the system. We wanted to make sure the control system worked properly. We had our own combustion control techs who spent quite a few hours fine-tuning the boilers.
“One of the things we provided that they didn’t have a lot of were alarms for when there is low or high water. That could damage the boiler. For instance, it takes five minutes from when a plane takes off to when the system is ready to launch a second plane. The boiler has at least a several-minute purge period before it lights up again. We wouldn’t have satisfied the contract if we didn’t control the pressures properly.”
The PostscriptThe project, which concluded last November, required only a minimum of change proposals (3 percent increase in contract value through change orders). ACI was the recipient of a safety contractor of the year honor for having no lost time on the job due to injury - more than 19,000 man-hours of labor were performed.
“This was a year-and-a-half project and we had no lost time, including subcontractors, on a very complicated and technical project,” Hertz says.
Girdlestone says in a normal year, the catapult launches 120 planes (and traps 300 more, though the TC-7 steam catapult is not used in recovery of the aircraft), thus making sure the right boilers were selected was of chief importance. Girdlestone notes numerous boiler models were rejected before ACI presented the Babcock and Wilcox model.
“ACI does this for a living,” he says. “They chose the boiler and sent me the info and I read up on it. It had all the criteria. I knew we would be all right. Our goal is to get at least another 50 years out of them.”