For the fifteen MSHA Northeast Mine Safety & Health Conference attendees who took the half-day Graymont (PA), Inc. tour on April 30, 2015, the experience was rewarding. From the underground mine tour that featured Graymont’s new primary crusher and conveyance system to the aboveground tour of their processing plant and kiln facilities, there was a lot to see in a short time. As we have experienced in the past, Graymont hospitality was unexcelled.
Once David Martin, Graymont’s Environmental/Safety Coordinator, prepared us with thorough safety instruction and the specifics of underground PPE, we boarded a bus chauffeured by Scott Schilling, Mine Engineer/Geologist and our tour guide in the mine. Heading underground, Schilling explained that Graymont installed MMD sizers underground as their primary and secondary crushers, along with associated conveying systems to the surface which eliminated the need for haul trucks to make the extensive round trips to the surface and return. Once we arrived at the new primary crusher, we had the opportunity to watch several loads of rock being dumped into the infeed where it moved steadily into the sizer before disappearing onto the conveyor for the trip to the surface. Schilling told us the haul truck cycle time is reduced to approximately five minutes instead of what once could take 20 minutes or more. As a result, the 773 CAT haulers have increased productivity with reduced cost.
As we traveled inside the mine, we passed several mined portals that had been closed to travel with earthen berms that indicated they were no longer active. In some instances, large curtains had been installed over the openings to help with ventilation airflow throughout the mine. Shilling said the mine pillars are on a 65-foot by 165-foot pattern with the ceilings reinforced with roof bolts. He noted that some of the benches within the portals are as much as 65-feet high at the face. He also said that at any given time, crews might be working any of 33 faces within the mine as a way to maintain consistent quality in the limestone they crush.
Once we returned to the surface, David Martin led the above ground tour, beginning with a stop at the control room of the two operating kilns, numbers 6 and 7. He said the new vertical kiln, currently being constructed alongside the other two kilns, will be designated Kiln #8.
As we walked between the kilns, moving on to the building that houses their electrical generation unit, Martin said that heat from Kiln 7 not only produces lime for their customers, the exhaust waste heat also is used to produce steam to power turbines to drive the 3.5 megawatt generator that supplies power to the electrical grid. He said that by making use of their available heat source, they are helping to offset the power needs of the quarry and lime plant at the same time.
Much of the processing plant is computer controlled. That allows Alan Breon, kiln operator, to monitor and control the plant from a hi-tech control room. With the addition of the new third kiln, the control room will be upgraded as well.
As material is conveyed from the primary crusher in the mine to the screen plant above ground, it arrives at the screen plant where it goes across a triple-deck vibratory screen before being conveyed to stockpiles for use as kiln. Material is constantly monitored with a Thermo Scientific Cross-belt Analyzer for purity. Stockpiles of three classes of material are identified as A, B and C grade material. The limestone for the rotary kilns is screened to 2 ¾ inches while the new vertical kiln that is being installed will have an infeed of 4 inch stone.
An interesting aspect of the Pleasant Gap facility is its source and discharge for water used in daily operations. In the 1980s and 1990s, dewatering the underground mine and water containment became a priority. It was during this time that a plan was developed to pipe the water from this facility to the head of Logan Branch, a stream 3 miles from the plant and the location of a PA Fish and Game Commission fish hatchery.
Underground, fresh water is pumped from the mine, into a 1 million gallon storage tank that is used to regulate the discharge to the creek. A portion of that water is retained for the daily needs of plant operations. That water is stored in a separate 250,000 gallon tank nearby. Depending on the time of year and the need for water at the plant, the water discharge is regulated in collaboration with the PA Fish and Game Commission so that Logan Branch has a regular supply of clean cold water.
As we concluded our tour, we finished by passing the coal stockpile where there are three kinds of coal on hand to blend for optimum heating BTUs. “We use King, Fisher and one other kind of low-sulfur coal,” said Martin as we head back to the office. “While we will be using more natural gas in the future because of its abundance here in Pennsylvania and the lower cost per BTU, coal has provided the high temperatures that we need to make the quality lime we require.” For more information on Graymont Lime and Stone Products, visit their website at www.graymont.com.