Published in American Longwall Magazine
THE Bridger opencut coal mine is located 35 miles east of Rock Springs, Wyoming and services the Jim Bridger power plant. With an annual consumption of about nine million tons of coal, the four-unit complex is one of the largest coal-fired power plants in the West. Each power unit has the capacity to produce 530,000kW.
Since mining began 30 years ago, over 170Mt of low-sulfur fuel has been trucked or delivered by conveyor belt to the plant.
PacifiCorp operates the plant and mine, and owns a two-thirds share of both, with the remaining portion owned by Idaho Power.
With surface reserves nearing exhaustion, recent exploration at the minesite identified an underground reserve containing about 100Mt of mineable coal from 250-900ft in depth.
After gaining a jump on permitting time through the renegotiation of the mine boundary, initial mine development to establish underground entry from a highwall started in May this year. This included highwall stabilization and the start of excavation for a three portal entry. Driveage to develop six entry mains started in September and will be the main focus until May next year.
The mine is currently using one DBT 25M continuous miner unit supported by two Joy 10SC32 shuttle cars, with a second miner unit scheduled to come on stream in September 2005. The second unit will parallel the first which will be starting development of the first gateroads of the first panel.
The coal seam averages 11ft in thickness increasing to 18ft in some places. Gateroad entries will go in at 9ft in height with top coal left in the roof for support.
Development of the first panel is expected to take about 13 months, running through to about October/November 2006.
“We’ll test the longwall first panel at a width of 750ft because of the soft ground conditions,” said Carl Pollastro, director, technical services and project development for Interwest Mining Company, a subsidiary of PacifiCorp.
“We have extremely soft siltstone and sandstone with both roof and coal around 1500psi. The floor is the hardest at around 2000psi.”
Roof support is expected to require higher than normal density bolting with entries narrowed to a maximum of 17-18ft with large support pillars.
The longwall will cut at a maximum cutting height of 12ft and a minimum of 7.5ft.
Once initial mains development is completed by May next year, permanent structure for the mains will be installed to include a 72in mains belt rated at 6000 tons per hour and a 60in section belt rated at 4000tph.
The mine currently transports coal over six miles of overland belt to the power plant. An additional three and a half miles will be required to connect the underground mine with the plant.
“The overland belt connection will be put in during the next construction season starting April and we aim to have that done by September,” Pollastro said. “We’ll also start putting in highwall facilities which will consist of a ventilation shaft and a permanent blowing system, substation, and high pressure water system.”
Longwall mining is expected to begin around January 2007 following surface compatibility and installation of the longwall equipment in November/December.
PacifiCorp has meanwhile negotiated an amendment to the surface mine contract for the new underground operation with the union which represents the mine’s surface workforce.
“With that in place we have the responsibility to utilize and retrain some of the surface people for underground positions,” Pollastro said.
“In this first round of hiring we’ve recruited people from everywhere from New Mexico, Utah, Colorado, to Wyoming. Right now in the first year we have 35 people made up of about 70% from the outside and 30% from within the company.”
About 75 people will be employed indefinitely in surface reclamation operations. Highwall mining began a year ago and will continue for the 20 year mine life at a production rate of about one million tons per annum.
PacifiCorp, through subsidiary Energy West Mining Company, also runs the Deer Creek longwall mine in Utah, where until recently Pollastro had worked for 23 years in a variety of management positions, including mine manger and manager of technical services and administration.
It will be a tight schedule to make the January 2007 start-up date but Pollastro is excited about the opportunity.
“It’s interesting to be able to start with a fresh page. If anything’s to blame it’s your fault.”
