Breathing easy at greater depths
Three leaders in the mining industry–Robinson Industries, Inc., Inco Ltd. and The Hatch Group–recently joined forces to upgrade the exhaust system for the deepest nickel mine in the world.
Inco decided in 1998 to extend its Sudbury, Ont.-based Creighton mine to 2,493-m depth. Before it could begin revamping its oldest operating mine, Inco needed to design the appropriate ventilation system. The existing system was old and lacked adequate capacity.
Due to the size and complexity of the project, Inco needed a premier custom-fan manufacturer and an engineering and project-management company.
The Inco ventilation department developed a comprehensive specification used not only for bidding and vendor selection but also for the design and selection of the fans. The specification, following Air Movement & Control Association International Inc. (AMCA) standards, identified the required testing and analysis to be used by the vendors during design and fabrication.
Inco selected Robinson to design and manufacture the fan because of Robinson’s laboratory capabilities, reputation for strict testing standards, and ability to custom engineer and manufacture fans.
To manage the project, including the removal of old fans, and installation of new fans, foundations and electrical equipment, Inco choose Hatch as the EPCM based on its expertise in ventilation, civil, electrical, mechanical, instrumentation and controls. The project schedule was revealed in March 2000.
At the time of the project, the Creighton mine’s main exhaust was a concrete-lined, 6.4-m shaft extending 1,829 m below the surface, with connections to the workings on the 1,646- and 1,158-m levels. The shaft terminates on surface in a concrete plenum with three parallel connections, one to each fan.
The existing No.11 shaft axial flow exhaust fans were approximately 20 years old and lacked the capacity to provide the required flow and pressure to reach a depth of 2,493 m.
Inco identified two key challenges: selecting the proper fan type; and determining the most efficient fan arrangement. Also, the project would have to be implemented without interrupting current mine production.
To minimize interference of mine operations, the existing, three-finger concrete plenum would be used. This would allow one fan to be installed at a time, so the other two fans could continue operating.
The new fans would be designed to fit into the three-parallel-fan configuration already in place, with significant ducting and foundation modifications required for each installation.
Because of the increased depth, the new fans needed to supply a substantial increase in air volume and pressure. In consultation with Hatch and Robinson, Inco selected three double-width, double-inlet (DWDI), high-efficiency airfoil-type centrifugal fans. The parties based their decision on similar installations and discussions with other users.
Due to the various depths at which the mine operates, the specifications called for Robinson to equip the centrifugal fans with variable frequency drives (VFDs). The VFDs allow operators to adjust the fan operating speed, ensuring optimum efficiency for the constantly changing mine system resistance and performance requirements of the fans.
It was vital that design and implementation of the new ventilation system first be evaluated based on performance and stability of the proposed parallel, centrifugal fan installation. The entire fan installation, including the inlet ducting and existing concrete plenum, needed to be free from aerodynamically- and mechanically-induced vibration.
To meet the rigorous requirements of the fan specifications, Robinson employed a number of analyses and approaches:
* computational fluid dynamics (CFD) analysis;
* physical model testing; and
* finite element analysis (FEA) rotor stress and modal analyses and rotordynamics analyses
To minimize disruption of the mine operation, Robinson engineers worked closely with Inco and Hatch to ensure that construction of each new foundation and installation of each new fan and inlet ducting would occur while any combination of two new or existing fans were running. Robinson created a detailed schedule for its scope of work, which was integrated with and linked to the main schedule established by the Hatch team. Hatch modeled all equipment and structures to achieve three objectives: reduce project cost, improve layout and enhance input from operations.
Scope, schedule and cost were the three major factors for determining the success of this project–and all three were met.
The basic objective of the Creighton exhaust fan upgrade project was to remove the existing fans and install new fans that would allow mining operations to reach the specified depths. This objective was achieved, with the third and final fan commissioned a few days ahead of the November 12, 2001 target. In addition, the entire Creighton mine project was completed approximately 2% under-budget.
Teams from Inco, Robinson and Hatch convened at Creighton’s No.11 shaft for fan start-up of each new fan unit. Once coupled, each fan was started and ramped up to a nominal speed between 300 and 400 rpm, and a Robinson field service technician verified mechanical operation through a series of vibration analyses and mechanical checks. Field air performance testing to AMCA 203 verified the actual, installed operating fan performance and static efficiency.
The main commissioning period was completed within two weeks for each fan. Since completion of commissioning, all three centrifugal fans and motor/VFD combinations have operated in a satisfactory and trouble-free manner according to specification.
Jay Henderson is vice-president of marketing for Robinson Industries, and can be reached at 724-452-6121 or [email protected].
Cory McPhee is manager, external relations for Inco, and can be reached at [email protected].
Tom Reid is director, global communications for Hatch, and can be reached at or [email protected].