13 December 2001
Driving Doubled Cement Production
by Carl Tuch
Aiming to meet demand for consistent quality cement, Lone Star Industries expands Indiana plant— pioneering semidry process in U.S.
Powered by new drives and controls, Lone Star Industries, Inc. in June 2000 commissioned and started up a much expanded Greencastle, Ind., cement plant. The revamped facility, featuring a new semidry process being introduced to the U.S. for the first time, will nearly double its annual production—from 750,000 to 1.3 million tons.
"The semidry process not only allows us to double production but provides an environmentally sound alternative to achieving the stringent emission levels imposed by both federal and state regulations," said Dave Puzan, manager of the plant. The facility was recently acquired by Dyckerhoff AG but continues to be known as a Lone Star plant—and called by that name.
"It will be the first semidry production process in the U.S.," according to George Glassburn, electrical superintendent. The new type of production allows the plant to keep in place its wet feed process, including the slurry tanks (each with a 2 million gallon capacity), pumps, pipelines, "and all our experience of knowing how to make slurry," he noted.
Motors, Drives Critical
The need to maximize the plant's capacity and uptime requires electrical engineers and their suppliers to assure that all electrics work efficiently for round-the-clock production, emphasized Bob Brown, Greencastle electrical supervisor.
Motors and motor drives are absolutely critical to optimize uptime. "We have upgraded many of our electrical motors to higher-efficiency motors in the last decade," said Glassburn. "We have installed 40 variable frequency drives from ABB on key motors throughout the entire plant. These are key pieces of equipment that we cannot stand to have a failure with because any one piece in a sequence of electrical equipment can take us down."
The standard AC variable frequency drive (VFD) in the plant powers motors ranging from 3 horsepower (hp, feeder weights) up to 800 hp (the fan drawing air through the kiln into the stack). Six 150-hp drives control the slurry pumping stations and feed pumps into the kilns, while 600-hp drives power the primary air fan and baghouse cooler exhaust.
VFDs also control the primary OSEPA exhaust fan. OSEPA is the brand name for a high-efficiency separator from F. L. Smidth. Since 1993, a 300-hp drive, the first such unit manufactured by ABB, has controlled this motor/fan for more than 40,000 hours without a single incident or trip of the switch. A 200-hp drive controls the OSEPA separator in the finish mill.
Smaller motor controllers are used on fuel-feeding applications such as the alternate fuel pump and agitator, as well as the feeder from the primary rock crusher to the conveyor at the quarry site.
Load Sizing Helped
Correct load sizing has helped engineers at Greencastle simplify the variety of motor and drive models the plant needs. "We size motors to the largest horsepower an application requires, and then we slightly oversize the motor," noted Ross Tennis, chief electrician at the plant. That strategy allows Lone Star to specify the same motor to handle the variety of loads within a process, he said, such as feeder weights or slurry pumps.
The plant extends this specification strategy to the motor drives as well. "The same type of drives are used to control these motors across different functions," said Tennis. Such standardization, from a practical, operational point of view, provides multiple benefits, he said. Since the drives share a common operating platform, the electrical technicians can be trained once but operate drives throughout the plant—reducing training time and mistakes, he said.
"And because there's a set of like motors and like drives, it also reduces the number of spare parts you need," he noted. New AC drives, including ABB's AC 600 controllers, are also "smart," he said. "They are easy to install, set up and start up, and through features like direct torque control, they can sense what motors can and cannot do" (see sidebar).
To maintain uptime, a local supplier of parts, service, and new equipment is also critical, Lone Star managers said. The Greencastle plant relies on Indianapolis-based Scherer Industrial Group, Inc., a distributor that handles drive start-ups for the facility. "We don't energize until they check it," said Tennis. "That's my policy. If I put anything in, I won't energize it until the technician says it's hooked up right."
Uses Semidry Process
The Lone Star facility near Indianapolis is the only one of the company's five U.S. plants to have used a wet process (historically, U.S. cement plants have used either a wet or a dry process). The "semidry" process is a third type altogether. Good availability of relatively low-cost electricity, combined with efficient energy usage and the plant's ability to utilize alternate fuels for producing clinker, make the mill's products competitive with cement produced from dry process facilities.
First built in 1918 and growing to a five-kiln facility, Lone Star resited the Greencastle mill in 1969 nearer a quarry on its limestone-rich, 1,320-acre property. The site boasts one of the largest inland U.S. kilns: 580 feet long.
Lone Star added a packaging operation at the original plant site in 1943 and, via compressed air, continues to transport cement underground from the current plant to the packaging facility approximately 1 mile away.
Product in High Demand
Local demand from the central Indiana's building construction and road construction markets for the mill's Type III, Type I, masonry, and Portland lime blend cement continues to stretch the mill's capacity—a trend that drove Lone Star's decision to invest more than $75 million in capital improvement projects for its plant in 1999 and 2000.
Operating around the clock, 15% to 20% of the Greencastle plant's production is Type III (premium), which requires fine grinding on one of the plant's two finish mills. Type I cement makes up the balance of the plant's production, with 95% of all production shipped bulk (truck, rail). The remaining 5% is bagged for local retail distribution.
Retrofit of the plant to the new semidry process has included shortening the kiln to 255 feet and adding a 322-foot, one-stage preheater tower, complete with an in-line calciner, a dual dedusting cyclone, and a hammer mill dryer.
"Slurry now is being atomized in the hammer mill dryer and moves through the dedusting cyclone's calciner and the first-stage cyclone before being fed into the kiln," said Tim Menke, production manager for the plant. "We are burning two-thirds of the total fuel at the preheater end to dry the slurry—and calcination of the feed—rather than having the entire heat transfer process occur inside the kiln."
The turnkey project is being handled by contractor Fuller Engineering.
Demand beyond capacity is a constant reminder of what's most important at Greencastle, said Glassburn. "It's a triangle. You want production, you want quality—and you want them accomplished safely." Consistent product "day in, day out" is critical, he said. "That's your No. 1 goal."
A concrete mix for a contractor that sets up on time, gets hard and strong, "and will be the same color from pour to pour, especially on the same job" is a very good definition of what quality is, he noted.
Planned Maintenance, Service
Another key to the plant's success is extensive planning for maintenance and service throughout the year. "We know that a little bit of preventive maintenance goes a long way in providing us that uptime," said Glassburn. "We schedule our downtimes, pick and choose them sparingly throughout the year, and plan our work. That includes getting in a maximum of maintenance and service routines for the electrical equipment in the shortest possible time," he said.
This kind of smart management within a cement processing plant is focused on both trouble-free uptime and energy use as efficient as possible to contain costs. "By the time this plant is done, we're going to have over 19,000 hp online," noted Glassburn.
"That eats up kilowatts and costs you money, even here, where we enjoy competitively priced electricity. If you save 1% of your consumption a year, that is a significant savings. If you do that with a higher-efficiency motor, putting in a VFD that controls a motor right to the rpm you need, that saves energy."
The speed of the shortened kiln at the Greencastle plant now increases three times, from 1 to 3 rpm. It's being powered with a new 900-hp DC motor and DCS 500 high-performance drive. For the first time, the plant has also installed medium voltage technology for a 5,000-hp drive and motor to power the new ID fan in the one-stage preheater.
Such equipment, combined with the new semidry process at the mill, makes managers optimistic about the mill's increased production capacity. They project that the expansion will allow the mill to produce 4,000 tons per day of clinker, as designed.
Infrastructure improvements remain strong and will continue to drive demand. "The federal government is helping drive the strong building economy by approving the TEA-21 bill, too, which provides funds for an infrastructure rebuild of Indiana state highways over six years," noted Puzan.
Lone Star has viewed the timing to be right for increasing capacity. The Greencastle facility will be a long-term producer, with the largest (and lowest-cost) plant in the market—able to address the needs of a thriving economy. MC
Carl Tuch is regional manager, ABB Inc., Automation Technology Products division, Drives & Power Electronics. Contact him at tel: (262) 785-3200 or (315) 635-9880.