July 1, 2002 -- Flooding at AmerenUE's Sioux Plant, 30 miles up the Mississippi River from St. Louis, is always a concern for the plant's management.
Although the plant is on high ground, the plant can be isolated when the Mississippi River floods. When this happens the roads and the single rail line coming into the plant become impassible. As a result, coal trains cannot get in, and employees are forced to commute across the river by ferry from Alton, Illinois, a one-hour trip. A flood in 1993 isolated the Sioux Plant for 13 weeks.
Because of the flooding potential, AmerenUE's Sioux Plant has recently completed the installation of a new E-Crane barge unloading facility. Sioux plant's new barge unloading facility provides an alternate delivery route for coal. With the new barge unloading facility, the plant is no longer dependent on rail deliveries that can be interrupted by spring floods. In addition, with an annual capacity of 3.7 million tons of coal, the barge-unloading facility can support future increases in generating capacity.
The E-Crane equilibrium crane features a moving counterweight. As the arm extends out, the counterweight extends back. Likewise, as the arm moves in, the counterweight also moves in. At 75 percent of its maximum reach the E-crane, with a full payload, is in precise balance. Working with the arm either at maximum reach or nearly under the cab, the weight of the entire E-Crane, plus half of its payload, is balanced.
In operation, the E-Crane never has to lift anything heavier than half its payload of 12 cubic yards of coal. On the other hand, excavators and cable cranes have to lift the full payload, plus the weight of the boom and arm. They must also be counterbalanced for the most extreme anticipated condition.
The barge unloading system, equipped with a 24 cubic foot clamshell bucket, can reach out 86 feet horizontally. It is also able to continue unloading barges even when the river rises or falls 25 feet. The free-dig rate of the E-Crane is 1,800 tons/hr. Unloading a barge containing 1,500 tons of coal takes less than 90 minutes. However, because of the confined space within the barge and the need to unload the coal evenly, the barge must be moved frequently.
Unloading Barges at Sioux Plant
The barge unloading system is mounted on a 32-foot diameter cell. Basically the cell is an artificial island made by driving lengths of sheet steel into the riverbed, filling the resulting cell with rock, and capping it with concrete. Two additional cells were also constructed, one upriver and the other downriver. Four permanently moored barges form a dock between the center cell and the two other cells. The floating dock to which the barges are moored is allowed to rise and fall with the river.
A cable system controlled from the cab of the E-Crane moves two loaded barges back and forth along the dock for balanced unloading. As the barges are emptied they are moved to a transit area downriver. Fully loaded barges waiting to unload wait in a staging area upriver. The staging area can dock up to 55 barges.
Coal unloaded from the barges is dumped into a hopper. From the hopper the coal is transferred onto a 60-inch wide conveyer belt to the plant. Before reaching the plant's coal storage yard the conveyor passes over 600 feet of environmentally sensitive wetland, across the plant's cooling-water discharge canal and eventually to the plant - a total distance of about 2,200 feet.
To minimize environmental disturbances to the wetlands and the river, most of the equipment, including the barge unloader, was brought in by barge and erected using conventional cranes mounted on barges. Total construction time was less than a year.
The Selection Process
AmerenUE engineers looked at four alternatives for barge unloading-an excavation-type digger similar in operation to a backhoe, a conventional crane with the clamshell bucket suspended from cables, the E-Crane, and a continuous bucket unloader.
However, the largest excavation digger available and a conventional crane with a clamshell bucket only had a capacity to unload 2 million tons a year, not enough for the project. Although a continuous bucket unloader is capable of handling up to 6 million tons a year, its cost was found to be prohibitive.
After evaluating the different options the AmerenUE engineers proposed to purchase a hydraulic E-Crane. Nonetheless, before making the final decision, AmerenUE engineers decided to tour barge unloading facilities at three companies using the E-Crane.
According to Michael Lobbig, project director for AmerenUE, the E-Crane was chosen because it met all of the plant's requirements and nothing else really fit the criteria. AmerenUE expects the E-Crane will be cost-effective in terms of operation and maintenance.
The E-Crane only requires a 600 hp electric motor to drive its hydraulics. In operation the barge unloader at the Sioux plant is reported to be quick and smooth to operate. "I think the E-Crane could pick up a piece of cardboard," says Tom Meyer, project engineer, AmerenUE.
In full-scale tests conducted by AmerenUE, the barge unloader emptied the barges without any problems. The only manual labor required was to move small quantities of coal out of corners of the barge into areas the E-Crane could reach. E-Crane International-USA will perform annual inspections and maintenance under a service agreement with AmerenUE.
This article is scheduled to appear in Power Engineering Magazine, July 2002. To read the current issue of Power Engineering, visit http://pe.pennnet.com/Articles/Print_TOC.cfm?Section=Articles&SubSection=CurrentIssue.