Manufacturers improve wear and throughput
By Steve Fiscor, Editor-in-Chief
Large surface coal mines rely on primary crushers to provide a consistent product. Unlike their bituminous counterparts that screen and wash coal, the mines extracting subbituminous coal and lignite are only looking to reduce the size of Run of Mine (RoM) coal, and they are moving extremely high volumes. For them, screens are devices that are used in the sampling process.
These crushers have to be robust and dependable. If the primary crusher is down, the entire coal handling network is impacted. Thousands of tons per hour translates to tens of thousands of tons per day and hundreds of thousands of dollars. This is the mining business, however, and things happen. Spotting a front-end loader tooth in the bed of 240-ton haul truck before it dumps into a hopper is difficult, something akin to the proverbial needle in a haystack. The damage that metal could inflict on a machine reducing feed to minus 2 in. will be noticeable.
Many of the primary crushers that have been installed in North American surface coal operations have now been running for about 30 years or more. Many of those that have been working in the Powder River Basin (PRB) have been crushing 20 to 30 million tons per year (tpy) or more. Similarly, the units handling lignite in North Dakota and Texas have been working just about as long and nearly as hard.
To gain some perspective on the situation, Coal Age spoke to two leading crusher manufacturers. TerraSource Global has been crushing RoM coal in the PRB with its breakers since the late 1970s. MMD began marketing the sizer to the coal business in the late 1980s and operators have embraced the technology. The machines they installed for large surface applications are completely different. Yet, they achieve similar results.
HIGH-CAPACITY ROLL CRUSHERS
The large surface mines in the West scoop up the coal, then crush it and ship it. The crushers range from 2,000 tph to 6,000 tph, breaking 48-in. lumps down to 2- x 0-in. Mines these days want higher capacity and longer wear life, explained Phil Schaefer, TerraSource Global’s regional sales manager for the western U.S. and Canada. “Many of the TerraSource units originally installed in the PRB are still operating,” Schaefer said. “A few of the machines met their life expectancy and they have been replaced with new TerraSource units that will last another 30 years. More will need to be replaced soon.”
The standard-issue TerraSource unit for the PRB was the Gundlach 8000 series breaker with four 80-in. rolls that would crush 48-in. RoM coal to 95% passing 2- x 0-in. at 3,300 tph. It is being replaced by the 5000 series, designed to crush subbituminous coal to 95% passing 2- x 0-in. at 6,000 tph. “The biggest challenge with a crusher of this size is feeding it properly and then promptly removing the coal,” Schaefer said.
The technology has not changed that much. The basic principles of the roll crusher remain the same. What has changed is the configuration of the housing and its approach toward eliminating environmental impacts. The 8000 series — the first model in the PRB — was a carriage-mounted breaker with four rolls and two stages of crushing all in one machine, Schaefer explained. TerraSource redesigned these large crushers and they became known as the 5000 series crusher. “The componentry is pretty much the same,” Schaefer said. “It’s the way the housing is designed.” The housing has been improved to control fugitive dust.
Steel, or what the professionals refer to as “noncrushables,” is another area for concern on these high-capacity systems. “TerraSource uses the