Cleaner Colorado conveyor

June 16, 2008 at 2:00 am | Posted in Power Plant | Leave a comment

Colorado Springs Utilities’ Martin Drake Plant, which has three units with a total capacity of 262 MW, recently joined the crowd by switching to Powder River Basin (PRB) coal. As you might expect, the move necessitated fuel blending to optimize performance and costs, plus changes to the plant’s coal-handling operation. Regarding the latter, the coal yard needed to be equipped with a second reclaim system—complete with a belt scale—to feed the PRB coal onto a new conveyor from which it would be metered into the local coal on an existing conveyor.

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The Salt Lake City office of the engineering firm Roberts & Schaefer was awarded the contract to develop the blending system. Their design called for the installation of a new pan feeder to transfer coal from the new reclaim system to a new belt conveyor that would load the PRB coal onto the existing boiler room feed conveyor (Figure 2).


2. Air suppresses dust. An air-supported belt conveyor improved the transportability of PRB coal at Colorado Springs Utilities’ Martin Drake Plant while minimizing fugitive dust (left). Currents of air passing through openings in the belt-support trough (right) make for a smoother ride and eliminate the need for conventional idlers.

Courtesy: Martin Engineering

Because the Martin Drake Plant is in downtown Colorado Springs, environmental protection was a high priority. The plant’s consulting engineer, Bill Nixon, knew that PRB coal is extremely friable and therefore more prone to create dust if not handled carefully. So he charged Roberts & Schaefer with developing a system that provided maximum control of fugitive airborne dust emissions from the coal-handling system.

“We knew that adding the western coal could create environmental problems if we weren’t careful,” Nixon explains. “So we were willing to look at an unconventional design to achieve the dust control we needed. I knew we would need something tightly sealed and controlled, and the totally enclosed, air-supported conveyor Roberts & Schaefer came up with looked to be a good solution.”

The air-supported belt conveyor relies on a current of air passing through openings in the belt support trough to eliminate the need for conventional idlers. Below the belt, this film of air supplies almost frictionless support for the belt when it is fully loaded.

Compared to conventional trough-idler conveyors, air-supported belt conveyors have many benefits in addition to lower auxiliary power costs and longer belt lives:

  • Because they have no carrying-side idlers, idler lubrication is not required.
  • Because the film of air makes for a smoother belt “ride,” spillage of coal and dust levels are reduced.
  • Because the air-supported conveyor system is fully enclosed, it acts as a self-contained plenum, allowing airborne particles to settle back onto the belt cargo.

To carry the PRB coal material from the new stockpile and place it on the existing conveyor, the Martin Drake plant installed a new, 80-foot-long, 35-degree trough belt conveyor. The first 60 feet serve as an air-supported conveyor plenum; for the final 20 feet the conveyor is supported by idlers, allowing use of a belt scale. Fed by a McClanahan drag chain feeder, the 30-inch-wide belt conveyor carries 120 tons per hour from the new stockpile’s reclaim into a transfer structure, where the material is loaded onto an existing conveyor to be moved to the crusher house.

Installation of the system was completed in November 2002, when initial unloaded runs were performed. The new reclaim system with the air-supported conveyor was put into daily operation in December 2002. Some adjustments were needed at start-up, explains Pete Page, coal handling section leader for the plant. “We had to do some tweaking at startup, such as adjusting the take-up to get belt tension right and changing the oil in the conveyor drive to cope with weather as cold as –5°F. Other than that, I’d say the startup was basically trouble-free.”

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