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Post at 29 Aug 2017

Allen-Bradley variable frequency drives help mines reduce energy consumption and lower unplanned downtime

Background

Families and businesses across the Western plains rely on energy that orginates from a coal mine in Wyoming. Every year the mine delivers roughly six million tons of coal by train to member utilities to generate electricity. This electricity heats homes, operates plants and keeps those must-have digital devices powered up.

That power begins with raw coal that’s mined from the two separate surface mines by huge dragline excavators and then dropped into dump trucks. The trucks unload their black cargo into crushers that break it down into small pieces. From there, the crushed coal moves on to conveyor belts to storage silos. The conveyor network forms the “circulatory system” of the operation, delivering coal from the crushers to the prep-plant where it is washed and filtered. Then it moves to storage silos and soon after, to the rails cars. The conveyors are propelled by powerful motors that move the coal more than a 1,000 feet per minute.

Challenge

The original conveyor system was built in the early 1980s, and the equipment was far from optimal. The system consumed vast amounts of electricity, was unreliable and created a deafening noise, especially during hard stops and starts. When transporting 2,250 tons of coal an hour, 24 hours a day, the operation needs reliable equipment to ensure the people who depend on the coal get it when they need it. Reliability was becoming even more of a concern with the construction of an onsite utility plant that would depend on the smooth flow of coal.

To become more energy-efficient and reduce operating costs, the mine’s team analyzed electrical usage. First, they scrutinized the equipment that drives conveyor belts. The hydraulic system used to operate the motors on the conveyor belts was mechanically based and therefore experienced lots of wear, driving up maintenance costs. The fluid-coupling device, part of the hydraulic system, was temperamental, and it caused a lot of downtime on the conveyor, along with being loud, unreliable and an energy hog. The high pressure and heat associated with the hydraulic system also presented safety risks to maintenence personnel. The engineering team knew the fluid-coupling device should go and that automation would be the critical player in delivering the solutions and the results desired.

Results
  • Saved an estimated $3,000 per month by controlling motors with variable frequency drives
  • Reduced maintenance costs compared to previous system
  • Reduced energy consumption has resulted in a more sustainable mining operation
  • Reduced noise by 15 decibels
  • Reduced high heat and pressure