By Pete Massa, Public Service of Indiana, Lyndell Fuller, XMS Equipment,
Tim Buckley, Buckley Communications.
During the winter months, coal being transported by rail from the mine to Public Service of Indiana Power's (PSI) 1000 MW Cayuga plant often freezes. Traditionally, plant personnel used poles and long shovels to break up the five to six feet clumps of frozen coal as they traveled from the rail cars into hoppers and through mechanical feeders to the conveyors below. However, this process was slow, laborious and labor intensive. Breaking the frozen coal and cleaning up the spilled coal by hand also slowed the coal unloading process.
Although the mine applied anti-freeze in the rail cars and on the coal, this was not always adequate to compensate for snow and ice that accumulated before loading and during the 50 mile transit to the plant. At one time the plant's management had considered installing a mechanical "coal cracker." However, the cracker's cost and extra maintenance made the economics unacceptable. As a result, the plant continued to break up the frozen coal manually and accept the reduction in productivity for the few winter months of the year when freezing was a problem.
Nonetheless, Public Service of Indiana (PSI) was still interested in coming up with a long-term solution to the frozen coal. In 2000, PSI contacted Arizona-based XMS Equipment (formerly a subsidiary of Xtek, Inc., of Ohio) about designing a pair of modularized and portable crushers.
Unlike the coal cracker initially considered, where the rolls would be in contact with the coal throughout the year, the rollers of the portable crushers could be removed during the non-winter months. Removing the rollers when not required reduces wear. After putting the project out for bid, PSI awarded the contract to XMS Equipment for a cost of approximately $300,000. This did not include the cost of any electrical work.
Crusher installation: Photograph courtesy of XMS Equipment.
The coal-fired Cayuga plant has two 500 MW vintage 1970 Combustion Engineering boilers. Coal, 10,000 tons/load, is delivered to the plant by train. After arriving at the plant the coal is transferred to a 300 ton capacity hopper. From the hopper it is then transported to an in-plant bunker while the coal not required for immediate use is stored in a nearby open stockpile.
To break up the frozen chunks of coal as they drop from the hoppers onto the coal conveyors, the plant relied on four or five workers being paid overtime. Plant O&M costs increased, therefore, and there was also a potential loss of plant productivity. Another problem was that coal jamming in the mechanical feeders and transfer points caused wear and tear on the equipment. Depending upon the severity of the weather, the freezing problem could last for up to four months each year.
Design and Installation
As XMS and PSI discussed the engineering design for the installation of the portable crushers, there appeared to be two major obstacles to the project. First, the crushers themselves and the structural steel to build the support platform had to be small enough to fit through a 6 feet by 7 feet access hatchway in the unloading dock's cement slab. Once through the opening, the parts and steelwork would then have to be lowered and positioned in the hopper pit, 40 to 50 feet below the concrete slab. Another challenge was the platform and crushers had to be installed while the plant remained on-line. The date for final installation and startup was New Years Day, 2001.
In late fall of 2000 the structural steel was delivered to the site. Associated Steel Contractors, Inc., a subcontractor, took two months to install the structural steel columns, beams, work platform, catwalks and stairs.
Pit and crusher area: Photograph courtesy of XMS Equipment.
American Pulverizer, Saint Louis, supplied the two modular crushers. Because of the limited access and weight restrictions, the crushers were delivered disassembled. The heaviest part was about 6000 pounds.
A three-ton capacity hoist at the rail site lowered the parts and material to a concrete ledge 25 feet below the access opening of the hopper pit. A permanent monorail system, made from a 50-foot long I-beam, was constructed to transport the materials. The monorail was secured to the end walls of the hopper pit, about five feet below the roof and 20 feet above the work platform. It was also attached to the sides of the hoppers.
The construction crew loaded the materials onto a manually operated trolley hung from the monorail. This trolley moved the materials above the work area. Another hoist, mounted on the trolley, lowered the material into the work area below. Chain hoists and come-alongs were then used to move the material into position.
Monorail used for crusher installations. Photo courtesy of XMS Equipment.
Construction of the work platform, at the base of the hoppers, was started before the crushers arrived on-site. During this time the hoppers continued to be supported by the roof above. The platform was used to support the crushers and other materials during the construction phase. Twelve columns were installed to support the 50-foot long work platform.
A removable panel on the side of each hopper allowed access for installation of the crushers. The panel also allowed the steel roller drums, measuring five feet long and three feet in diameter, to be slid in and out as needed. The mechanical feeders, which are normally hung from the bottom of the hoppers, were permanently attached to the lower side of the work platform To reduce wear on the rollers, they can be removed during the summer months.
Construction of the platform was finished in December 2000, and over the Christmas and New Year's weekends, when coal shipments were idled, the crushers were installed and tested. When operating the crushers break the 5 feet to 6 feet frozen coal blocks into 3 to 4 inch chunks. Since installation of the crushers, safety has improved and overtime for breaking the frozen coal has been eliminated. In addition, the new crushers now allow the plant to operate at full design capacity.
Removing the crusher rolls in the summer is relatively quick and easy. After preparing the roller for removal, a one-horsepower electric drill activates a jackscrew that slides the 5000 lb roller out of the hopper chute along a five-foot track. It sets there until the winter months when the process is reversed and the rolls are re-installed. The process takes about four hours for each crusher. PSI schedules the changeovers in between coal deliveries, so there is no loss of production.
After taking care of the frozen coal in the hoppers and the coal feed system, PSI still had a problem with the coal freezing in the reclaim hoppers and the open coal storage area. A tunnel connects the ground level reclaim hoppers to the main plant. Although the bulldozers that pushed the coal into the reclaim hoppers did break up some of the frozen coal, manual labor was still necessary to breakup the remaining frozen chunks of coal.
Because there was not enough room to use the same type of crushers previously used, PSI asked XMS to come up with an alternative crusher. After evaluating the problem, two smaller 1000 ton/hr crushers from Gundlach were specified. However, unlike the previous crushers, which were designed to be removed when not required, the Gundlach rollers would remain in the coal feed year-round. Since the reclaim hoppers are only used intermittently, the crushers do not handle as much tonnage.
The most innovative aspect of this second crusher installation, however, was the placement of the crushers. Because there was little room in the hopper chute, the crushers were designed to be retrofitted inside the skirt-boards of the conveyors, just below the discharge of the mechanical feeders. Even though Gundlach had supplied crushers for this sort of application before, they had not been installed in this fashion. However, the existing skirtboards are exceptionally large so there was plenty of room.
Installation and testing was completed on the reclaim hopper crushers in February of 2001. According to PSI, the project has been successful and the utility is anticipating that freezing coal will no longer be a problem at the plant. The reclaim hopper crusher project cost PSI approximately $250,000.
Pete Massa is a senior engineer at PSI and he has more than 20 years' experience in the coal mining industry.
Lyndell Fuller is a system designer and sales manager for XMS Equipment and has over 30 years' experience in the design and management of process systems in materials handling applications.
Tim Buckley is an Oregon-based author and freelance writer. Among the businesses and industries he covers are mining, manufacturing, heavy equipment, materials handling and construction. He can be reached at firstname.lastname@example.org