Tight Condenser

20 March 2008

Southern Industrial completed a complicated rigging job as a subcontractor to Dresser Rand, which was performing a larger retrofit of a steam turbine plant at the University of North Carolina in Chapel Hill US. Southern Industrial has been an SC&RA member for more than 40 years and this was the company's first entry in the Rigging Job of the Year contest.

The task for Southern Industrial was to remove an existing condenser from its second floor location at the cogeneration plant and then to re-install a new replacement condenser in the same location. The original condenser weighed 60,000 pounds (27 tonnes) and was 20 feet long and eight feet in diameter (6 x 2.4 m). The replacement condenser weighed 80,000 pounds (36 tonnes) and was 24 feet long and nine feet in diameter (7.3 x 2.7 m).

What made the job so tedious were the tight quarters. The condenser sat in an alcove area that was 12 feet (3.7 m) above the floor of an adjacent and larger open bay area room. The ceiling height of the elevated alcove area was 13 feet (4 m), leaving very little headroom to operate. The alcove area was 12 feet above the main floor so the safety managers had to engineer a suitable plan. A cable safety barricade was installed at the opening of the alcove area and chokers were suspended from above the alcove to allow tie off in all areas of the alcove and the open bay area room. The elevated alcove area opened into the adjacent larger area room that was 22 feet wide, 40 feet long and 25 feet high (6.7 x 12 x 7.6 m).

Although much larger than the alcove, it was a challenge to get the condenser into and out of the open bay area. Its width and length did not allow much room for placement of gantries, forklifts, aerial work platforms or rigging equipment, and certain critical existing pipes and objects were in the way and could not be cut out or removed, rather they had to be “rigged around.”

The open bay area room was just high enough and wide enough, by millimetres in some places, for the manoeuvring and handling of the large condenser that would require rotating, lowering and extracting, and then reversing this procedure to install the new unit.

Making the job even more of a challenge, no work could be done from above, which would have been the preferred method. This eliminated the use of overhead cranes or overhead lifting systems for the transfer of the old condenser off the raised alcove area into the open bay area room.

The concrete floor above the work area was the actual turbine room with a ceiling above that, making roof penetrations impossible and unacceptable to the owner and the prime contractor. The condensers had to be rigged out and back in “the old fashioned way,” using jacks, beams, dollies, gantries, fabrication of a custom-built turntable and hard work and ingenuity from a crew of riggers and project supervision through to the chairman of the company.

To remove the original condenser from its second storey location, it first had to be jacked up using a 100 US ton (91 tonne) Lift Systems gantry to allow room to slide in two running beams to serve as tracks to dolly the condenser out into the open bay room. Although there was enough headroom above the condenser, the actual floor structure and pit opening under it made inserting the beams a challenge, requiring jacking, sliding, plates, cutting and come-alongs, which was described as “lots of bullwork.”

Once the beams were secured under the old condenser, the old unit was jacked up and placed on rollers for movement. Come-alongs were attached on each end of the condenser, one to pull and one to restrain the unit.

Since the condenser could not be grabbed from above, it had to be rolled out onto an elevated turntable platform fabricated for the job. The turntable was sitting on top of four pods of a 200 ton (181 tonne) Lift Systems gantry system. Paying special attention to safety, the old condenser was pulled out of its alcove and into the open bay area onto the suspended turntable, in a process again described as “old style rigging inch by inch.”

Once on the turntable, come alongs were attached to each end of the platform and at times to the unit itself to pull, work and turn the condenser 90 degrees so it could be lowered to the floor of the open bay area room. The turntable worked as planned, with the condenser turning into place with very little room to spare, by just 1 inch (25.4 mm) at one critical point.

Once at the right angle on the turntable, the condenser was lowered to the floor for final removal. To lower it to the floor, four pods of a 400 ton (363 tonne) Lift Systems gantry were positioned on each side of the old condenser, which was resting on top of the turntable held up by the 200 ton system. At this point, due to the width, length, and height of the open bay area room, the room was full of gantries, forklifts, aerial work platforms and the condenser. Space was so tight that one of the outside gantry pods had to be placed on cribbing to work on top of existing steam pipes that could not be cut away any lower.

Once all the equipment was in place, the condenser was grabbed from above with chokers suspended from the beams of the 400 ton gantry system, which then raised the condenser and turntable up together so that the 200 ton gantry system could be removed from below the turntable, thereby allowing the lowering of the combined condenser and turntable as one unit.

The turntable platform and condenser were then dollied to the far end of the room. The condenser was again rotated 90 degrees so it could be set on dollies and driven down the hall and out of the building. As if that was not enough, the entire process had to be carefully reversed to re-install the new replacement unit, which was larger and heavier.

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