Pre-Assembly Puts Plant Upgrade in Ship Shape
In early March—amid subzero temperatures—project team members involved in environmental upgrades to a coal-fired generating plant in Michigan City, Ind., were waiting for the waters of Lake Michigan to warm up so they could resume barge shipments of preassembled components required to complete the dry flue-gas desulfurization of Northern Indiana Public Service Co.'s (NIPSCO) Unit 12. The $246-million project, sited near Lake Michigan's shoreline, reunites many of the firms involved in a similar undertaking at a NIPSCO plant in Wheatfield Ind., including Oakbrook Terrace, Ill.-based Graycor Industrial Constructors Inc., the project's mechanical contractor, and Chicago-based engineer Sargent & Lundy. This time, however, project particulars couldn't have been more different.
"While the Wheatfield station rests on 2,900 acres, our Michigan City station occupies only 114 acres," says Jason D. Klaich, director, major generation projects. "Of that, we have 31 acres for staging." It amounts to scant space for a project requiring nearly 300 tradesmen to install more than 30,000 lineal ft of pipe, 3,000 tons of ductwork plate and 4,000 tons of structural steel, all in support of erecting a pair of spray dryer absorbers, or scrubbers; a pair of pulse-jet filters, or baghouses; and pebble lime and hydrated lime silos, all critical to bringing Unit 12's sulfur-based emissions in accordance with federal regulations.
"From the outset, we looked for ways to facilitate economical construction at a site with little room for preassembly and the potential for weather delays, many from high winds that occur along the shoreline year-round," says Michael G. Vacek, senior project manager with Sargent & Lundy.
Hence the decision to preassemble components for circulating scrubber vessels, 24 baghouse modules, air slides and ductwork in a former 30,000-sq-ft dry storage facility some 20 miles from the site, then ship them via water on a 210-ft-long, 60-ft-wide barge, a solution that also allowed project team members to circumnavigate weight restrictions and other logistical challenges had components been shipped in smaller modules by truck.
The solution won instant approval from Worcester, Mass.-based supplier Babcock Power Environmental Inc., charged with supplying Unit 12's scrubbers, baghouses, lime silos and compressors, among other components. As a matter of routine, "we maximize shop fabrication and assembly based on shipping methods specified by clients," says Aires R. Pavao, Babcock project manager. "It's been our experience the approach reduces or eliminates fit-up issues in the field, accelerates the schedule and reduces overall project costs."
For Unit 12, fleets of trucks from numerous Babcock suppliers as far south as Texas fabricated and shipped components, each sized in accordance with varying load restrictions. Once components arrived in Port of Indiana, cranes placed some on outdoor fabrication tables and others on skates for preassembly within the fabrication facility.
Components for 45-ton, 60-ft-high, 30-ft-long, 20-ft-wide baghouse modules, for instance, arrived in C-sections—or halves—each hoisted onto a skate by a Manitowoc 4100 lattice-boom crawler crane.
In all, a team of 40 welders and mechanics preassembled 50% of components indoors and 50% outdoors, says Kevin Grooms, project director with Graycor. Due to space restrictions, crews worked outdoors to preassemble trios of circular steel components—with 30-ft-tall, 34-ft-dia cores, middles and tops for each of Unit 12's 90-ft-high reactor vessels.
Team members initially considered fabricating components in even larger assemblies at a shop further northeast, then shipping them across a greater expanse of water. Upon evaluating the additional engineering required, as well as the potential for disruptive lake conditions, planners subsequently reversed course, settling on Port of Indiana.
Supplemented with additional lighting, heating and outlets, the facility proved of sufficient height to accommodate the 60-ton hydraulic crane deployed to maneuver components, though adjustments to its entrance were required to facilitate ingress and egress.
As crews completed subassemblies, a self-propelled modular transporter—a remote-controlled assembly that Grooms likens to a 20-wheel semi-truck without the cab—transported them to the barge, where longshoremen utilized a 200-ton Manitowoc 4100 lattice-boom crawler crane to load them in place. Barges were met by another Manitowoc 4100 in Michigan City to unload components.
With the arrival of spring, Port of Indiana will commence shipment of ductwork to Michigan City, where sections will route boiler flue gas to scrubbers and baghouses for removal of sulfur dioxide, sulfur trioxide and other substances prior to routing it back to a chimney for release in the atmosphere.
Crews have not been completely idle as they await deliveries: About 280 workers were on site in late winter to complete construction of the baghouses and other assemblies shipped from Port of Indiana last summer and fall.
"We made 11 shipments from June to mid-November," Klaich says. Shipments were made in accordance with a "bottom-up" erection sequence and included virtually all scrubber and baghouse components.
"It's been akin to just-in-time delivery," says Grooms. "We're not stick-building over craftsmen's heads. That's where preassembly comes in."
Crews deployed a 600-ton Kobelco crawler crane to set circular cores, middles and tops weighing up to 70 tons within structural frames for reactor vessels, stacking one upon the other before crews proceeded with welds. Workers used the same crane to set baghouse modules within structural steel in early February.
Work is driving toward a delivery date of Sept. 4, when NIPSCO will suspend operations for 12 weeks to tie-in new components to existing ones, a period when crews will tear out ductwork feeding Unit 12's chimney and route new ductwork to scrubbers and baghouses and back.
"A lot of activities occur during a tie-in, and we're planning each in a very detailed manner," says Vacek. "This is going to be one very busy place."
"It's a narrow window," Grooms adds. "That's when we'll be bumping elbows to get it all done."
