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INDUSTRIAL MINERALS JUNE 2016 • E&MJ; 57 www.e-mj.com tion comes from bore mining, with the rest produced by the continuous miners during entry development or borer panel setups. Normally, two continuous miner crews are assigned to entry development. The CM crews cut rectangular, 18-ft-wide entries to the height of the seam in patterns of three to seven entries. Pillar dimensions vary according to the type of mining and estimated working life of the entry; e.g., main development, CM advance/retreat and borer advance/ retreat. Standard pillar dimensions are 80 x 120 ft. Active mining areas gener- ally measure a mile in length by three rooms wide. Three CM crews handle stub- out development ahead of the three borer miners. The general plan for borer mining results in a herringbone pattern with long, thin pillars. The mine has 180 underground pro- duction, maintenance and utility work- ers, with production crews working 14 days within each 28-day cycle, on an alternating day-and-night shift schedule culminating in an eight-day break. About 40 workers are underground during each 12-hour shift. About 200 workers are in- volved in surface operations. Crews enter the mine from the No. 2 shaft in the main complex and then use a variety of diesel-powered pickups, personnel carriers and utility vehicles to reach their work areas. Visitors taking the 13-mile underground trip from the service shaft to the mining area fnd it easy to identify the various techniques used to drive main roadways over the four-and-a-half decades since the mine opened in 1968—early roadway cross sections are rectangular and rough-walled as a result of the drill-and-blast methods in use early on. These transition to rect- angular spaces with smoother walls as the mine switched to continuous miners of various types in the ensuing years. En- tries cut by the borer miners are smooth- walled and oval in shape, about 8 ft high. Throughout the mine, Jennmar 5-ft grout- ed roof bolts are installed on 4-ft centers for ground control. Production typically ranges between 13,000 and 15,000 t/d. At the work face, the borer miners advance at an average rate of 30 in./min, twin rotors turning at 17 rpm. Each borer is con- nected to a Joy 4FCT Flexible Conveyor Train—a continuous haulage system with variable-speed conveyor and powerful traction components that permit move- ment in concert with the borer miner, ca- pable of navigating curves while breaking lumps and handling up to 15 t/min of ma- terial fow. The FCT transfers the ore to the mine's main belt system, comprising 12 segments that transport the material 13 miles back through the mine to the No. 3 shaft for hoisting to the surface. The continuous miners feed shuttle cars that carry the ore to a main-line conveyor loading point. Each of the main conveyor segments employs a 54-in.-wide, four-ply belt mov- ing at 600 ft/min. Four 300-hp electric motors drive each main belt segment. At the termination point, the belt dumps ore into a storage bunker, from which it is transferred by a shunt belt to one of the hoist's 22-ton-capacity skips. A pro- ject is currently under way to increase the underground bunker capacity by 700-800 tons to better accommodate production variances. From Crusher to Crystals Tata uses the monohydrate process to produce soda ash from trona, believing it to be less energy-intensive and, in gen- eral, lower-cost overall than other meth- ods in use. In addition, the process only requires vessels made of mild steel, not of more expensive stainless steel. It is a multi-step operation that includes crush- ing, calcining, clarifcation, evaporation, centrifuging and drying before shipment. The mine's 5-million-plus t/y of ore pro- duction nets slightly more than 2 million t/y of fnished soda ash product. Run of mine ore is reduced to minus 0.5 in. by two-stage crushing, using a horizontal shaft impactor followed by a roll sizer. The crushed ore is sent to a calciner and heated to 165°C, then dis- solved in hot water and clarifed to remove insoluble materials such as shale. Evap- orators remove water from the fltered "liquor" to begin formation of monohy- drate soda ash crystals, and the resultant slurry is centrifuged for additional de- watering, with the liquor drawn from the centrifuges returned to the evapora- tors for additional product recovery. The soda ash crystals are then processed in rotary steam tube dryers to produce an hydrous soda ash. In the dryers, 400-psi steam heats the ash to 205°C. With both the evap- orators and rotary tube dryers being steam-heated and the plant itself pow- ered by electricity from on-site steam- driven generators, the facility needs substantial steam capability—and has it, producing up to 1.35 million lb/h of steam, mostly by burning coal supplied from Westmoreland Coal's nearby Kem- merer mine, supplemented by natural gas as needed. Paul Peterson, TCSAP vice president of manufacturing, said the company has committed $40 mil- lion to upgrade its emissions-control equipment to continue using coal under new emissions guidelines. Although Tata generates most of the 30 megawatts of power its facilities demand, it also buys electricity from the regional utility as needed, and sells its locally gener- ated power to the utility during non- peak periods. Peterson also noted that Tata recently made a substantial investment to install equipment for reclaiming and reprocess- ing its large tailings deposits, recovering additional soda ash, and converting the remaining tailings to a thickened paste for easier handling and less environmen- tal impact. The Green River operation ships the fnished anhydrous soda ash crystals primarily by unit train for export, with about 5% delivered by truck to domes- tic customers. One unit train, com- posed of 100 100-ton-capacity bulk railcars, is loaded daily, fve days a week, bound for ports on the U.S. West Coast. Along with Tronox and Ciner, Tata's products are handled by American National Soda Ash Corp., a company headquartered in Westport, Connecticut, which operates as the sales, marketing and logistics arm for the three producers. Martin Keighley is bullish on future prospects for the soda ash market, ex- plaining that total global market de- mand is estimated at 56 million mt/y, and in the U.S. apparent consump - tion increased for the second year in a row from 2013-2014, with the 2014- 2015 period expected to show 3% growth year-over-year. With at least 50 years of future production and business growth anticipated, Keighley is eager to see what effect emerging trends and market forces will have on the products and industrial processes that require its product.