Kentucky, USA-based Sterett Crane and Rigging used a Terex CC 2400-1 lattice boom crawler crane to replace lids on eight anaerobic digester tanks at the East and West Evansville wastewater treatment plants.
“Having sufficient space alone to bring in and assemble the crane was challenging enough,” said Matt Crisp, crawler crane fleet manager for Sterett, about the congested project site at the 34-year-old facilities.
“To remove the massive tank lids that weighed in excess of 250,000 pounds (113.4 tonnes) each, we needed to mobilise a crane that was small enough to fit into and manoeuvre in the tight area while, at the same time, offer the capacity to lift the heavy lids.”
Out of the dozens of crane options from Sterett’s fleet, the one crane stood out for this job – the Terex CC 2400-1 lattice boom crawler crane. With its 440 US ton (400 tonne) capacity, the Terex crane offered power to lift the heavy loads, and its Vario-Superlift structure feature proved to be the X-factor Sterett needed to manoeuvre about the site at full load.
The digester tank lids were being removed and relocated for sandblasting and refurbishment. Each tank lid weighed between 258,000 to 274,000 pounds (117 to 124.3 tonnes). The weight of the load required the CC 2400-1 to be rigged in its superlift configuration, but as the crane’s body swung the lids into position to lower them onto the concrete cribbing, the superlift tray had to manoeuvre past site barriers.
“The lids alone were 75 feet (22.9 metres) in diameter, and we had to rig to them at 16 points,” said Crisp. “The plan was to pick the lid at a 91 ft (27.7 m) radius, boom up, move the crane a short distance and then swing the ring into position for lowering it onto the cribbing. However, often a tank obstructed the path of the tray as we swung the load.”
The CC 2400-1 crane has variable tray positioning for the superlift structure that increases the crane’s flexibility for use in congested areas.
“The Vario-Superlift configuration on the CC 2400-1 crane offers a variable radius from 36 to 49.2 ft (11 to 15 m) during operation,” said Daiane Laidler, regional business manager at Terex Cranes.
“The Superlift can be configured with up to a 98.4 ft [30 m] mast and counterweight tray with a maximum weight of 529,200 lb [240 tonnes].”
For lifting the lids, the CC 2400-1 was configured with 137 ft (42 m) of main boom. Crew members added 264,500 lb (120 tonnes) of counterweight to the superstructure and additional 44,000 lb (20 tonnes) of central ballast. The crane was rigged with the full 98.4 ft (30 m) of Superlift mast, and the tray was loaded with 352,700 lb (160 tonnes) of counterweight.
Rigged and ready for the lifts, the CC 2400-1 operated atop timber planks to help spread the ground contact pressure of the crane load. The initial pick of the 10 ft (3 m) tall by 75 ft (22.9 m) diameter lids was made at the 91-ft (27.7) main boom radius, and the lid was lifted to a height of approximately 20 ft (6.1 m).
“At the beginning of the lift, the CC2400-1 crane’s Superlift tray was positioned at its maximum 49.2 ft [15 m] radius,” said Laidler.
Initially, the load was picked over the toes of the crawlers, and it was walked forward approximately 15 ft (4.6 m). The crane then rotated the lid to position it over concrete blocks that served as the platform for refurbishment.
“As we swung the crane, we transitioned the Superlift tray’s radius from 49.2 ft [15 m] to 36 ft [11 m] to pass by the tank at the rear of the crane,” explained Crisp. “After passing the obstruction, we extended the counterweight tray back to a 49.2 ft [15 m] radius to set the lid on the blocks. All this was done while under load without removing any counterweight.”