Kyanite Mining Corp. is a family-owned and operated mining company that specializes in the extraction and beneficiation of kyanite (3Al2O3*3SiO2) and its calcined derivative, mullite. KMC ships both minerals worldwide for use as “super-duty” additives in a variety of ceramic and refractory products. Kyanite is used in these products because of it resistance to heat, abrasion and corrosive environments.
Raw kyanite ore is mined at Willis Mountain, located in central Virginia, and beneficiated at two primary facilities, the Willis Mountain and the East Ridge plants. The ore is excavated through the open pit method, crushed, ground in a wet slurry, washed, and the kyanite is then removed in a flotation process. The kyanite concentrate is then dried and the metallic impurities are removed with magnets. Finally the dry, purified kyanite is trucked to additional processing facilities where it is ground to different mesh sizes, warehoused, packaged and shipped. Almost 200 people work in this around-the-clock operation that has the capacity to produce over 150,000 tons of commercial grade kyanite concentrate a year.
Good Neighbor Policy: The drying of the partially purified wet kyanite concentrate produces stack emissions that, according to company Vice President Guy Dixon, were “often unsightly and sometimes smelled. Our company does business in rural Virginia and we all live and recreate around and sometimes on the mine property. Making sure that our plant was outfitted with world class pollution control equipment, and that you couldn’t see or smell our exhaust, was important to my family and our management team.”
As Environmental Director Todd Johnston put it, “We all live here. We have to eat in the same restaurants and shop at the same grocery store as every one else in this area.”
It was this kind of ethos that drove KMC to look for help in controlling its stack emissions. It was decided that the centerpiece of KMC’s plan would be the design, fabrication and installation of two air pollution control systems, supplied by the Clean Air Group.
The Clean Air’s pollution control systems are designed to control emission streams produced during the heat-treating phase of the beneficiation process. Initial diagnostics indicated that KMC’s process produces emissions that include solid particulate matter, SO2, H2SO4 mist, and condensable organics and inorganics. Preliminary investigations, consisting of engineering analysis and test samples taken prior to KMC’s existing scrubbers, quantified the amounts of sulfur oxide and particulate emissions from the two sources. The East Ridge fluid bed dryer, the larger of the two processing facilities, was shown to produce particulate emissions at 2790 mg/cf, and SO2 at 3580 ppm.
Both plants’ dryer systems operate on the same principle and produce similar products, although their primary means of drying the material are different. The East Ridge Plant utilizes a fluid-bed system followed by a rotary cooler; the Willis Mountain Plant dryes kyanite in a rotary kiln/dryer followed by a rotary cooler.
East Ridge dryer operator Doug Amos didn’t know what all the numbers meant, but he did know that sometimes he couldn’t even see the fluid bed dryer he was supposed to be operating from his control room.
“Every once in a while the stack would start emitting this blue, hazy looking smoke,” says Amos. Some employees and neighbors could even smell the exhaust several miles away and to the people of KMC, that was unacceptable.
The Solution: The East Ridge Plant’s scrubbing system consists of a rod deck scrubber followed by a wet ESP sized to accept 35,376 acfm at 447 F.
In this system, exhaust gasses are captured and treated in two phases. In the first phase, combustion gasses and particulates from the fluid bed are captured and treated by the scrubber and Condensing Wesp system, then emitted to the ambient air. In the second phase, emissions created from the cooling process are captured and routed through a second particulate scrubber and rod deck absorber to provide a clean, preheated gas stream. This gas is then routed back into the fluid-bed burner as combustion air. This closed loop system created around the plant’s cooler allows for the combustion of pollutants that cannot be removed by traditional scrubbing mechanisms.
Unlike many mining companies the people at KMC have built, fabricated and installed almost every single building and piece of stationary equipment on their property. They have their own construction crew and metal workers, and farming out the design and fabrication of these pollution control devices was very near a first for the company.
With installation of the new systems, stack opacity, which could reach 60 percent, was reduced to near zero. The chart shows preliminary test results: removal efficiencies of 99.6 percent for PM2.5, 99.4 percent for sulfur dioxide, 93 percent for acid mist and roughly 90 percent for condensed inorganic and organic material. Additionally, the WESP systems reduced NOx by about 50 percent, a collateral benefit of the integrated pollution control system without any additional cost impact.
Kyanite management is pleased with the system’s performance. Operational reliability is high due to no moving parts within the air pollution control systems. Discharge of collected contaminants within the slurries goes to a wastewater treatment facility. Additionally, the systems require minimal maintenance due to self-cleaning design features of the scrubber and condensing wet ESP.