SC&RA Job of the year: Installing a conveyor section at a Florida, US coal plant
By D.Ann Shiffler22 April 2010
Crane Rental Corporation applied extreme rigging creativity to install a long, heavy conveyor section over an intake canal at a coal plant in Florida.
Using a rare rigging technique and a broad range of lifting and transportation equipment, Crane Rental Corporation successfully installed a 150-foot long conveyor section weighing 240,000 pounds across a 240-foot wide intake canal at a coal-fired power plant in Florida.
The plant, which has a 1,900 megawatt output and serves 667,000 customers, needed to add a rail-car unloading facility and conveyor system to feed its four coal units. From the rail spur, the conveyor runs west, along the north bank of the intake canal for the power plant, which is south of the canal. The conveyor would have to cross the intake canal.
Crane Rental's team considered the choices for accomplishing the job. One option was to place two large cranes on each shoreline, assemble the conveyor on a barge, and then push the barge in proximity of the two cranes on shore, and then lift and set in place the conveyor system. Another option was to place a large crane on a barge and place the conveyor on another barge and perform the setting from the barge-mounted crane. Both these options were deemed too risky and expensive.
Crane Rental proposed the idea of using a gantry system and conveyor section on a single barge. While complicated, this system would work beautifully, after much planning, engineering and research. Crane Rental had to control hazards such as tidal variances, waterflow and wind. In its research, the company determined they could plan for these forces and the job would be a success.
Initial questions had to be answered. What type and size of barge should be used? What stroke do the gantry legs need? What's the water intake schedule of the plant? What kind of kite effect would the conveyor section have?
Crane Rental called on 2DM Associates, a consulting engineering firm based in Houston, and hydraulic gantry manufacturer J&R Engineering, based in Mukwonago, WI to help answer these questions. The company also called other industry contacts for their ideas and input.
The best fit was a 180-foot by 50-foot ABS certified barge. Crane Rental's 700-ton "Lift-N-Lock" gantry, built by J&R Engineering, was selected due to the stroke required to set the high side of the conveyor. Calculations were performed to determine the amount of drag on the barge due to tidal flow and the demands of the intake pumps for the operating plant. Wind computations were developed to determine the allowable amount of wind speed to and to factor in the kite effect of the conveyor.
Ballast computations were also issued to determine the amount of water required to level the barge after loading. Fresh water was required for ballasting and two ballasting pumps were onboard and available to transfer water as needed. All components on the barge had to have 100 percent securing devices to prevent movement due to wave action.
During the mobilization of the barge, Crane Rental supplied its 550-ton Grove AT to set the two cantilever sections and one additional section of conveyor over the water at both sides of the canal. Crane Rental's 240-ton Grove AT was used to assist with the construction of the conveyor and the erection of the gantry system on the barge.
As the mobilization plan was being put into motion, Hurricane Ida was churning in the Gulf and flirting with an easterly turn. Wind speeds were calculated as well as tidal surge. The barge was moved further off shore to insure it wouldn't be blown free of its moorings. Thankfully Ida took another course.
A fall protection plan was implemented and a safety boat was deployed to monitor activities and transport workers on and off the barge. Life vests were required and special life vests were acquired to allow for use of body harnesses when needed. Daily planning meetings insured a safe work environment. Special containment barriers were installed to retain any unforeseen hydraulic spills associated with the onboard equipment.
With weather clear and the assembly completed on deck, the decision was made to proceed with the lift. First, four dead men weighing 50,000 pounds each were placed on the north and south shorelines to tie the barge off and to use for final positioning.
Two tugboats and crews moved the barge to a close proximity of its final position. The barge was walked into position with only 2 feet of clearance. Slowly tugging the barge within 8 inches of final position, the lines were secured and the spuds set.
At last, with the barge secured in place, approval was given to make the lift. The 700-ton gantry system and power links slowly raised the conveyor system without a hitch. All that needed to be done was the bolt up.
Pressure gauges installed on each gantry leg were monitored during the connection phase. Six tides and 48 hours later the bolt-up connections were complete, and the gantry system was lowered for disassembly. After confirmation the connections were properly made, and the structure was stable, Crane Rental crews loaded up its equipment and went home. Crane Rental had approximately 1,600 man hours on the task, which was completed with no incidents or accidents.