When the expansion of Lone Star Industries' Greencastle, Ind. cement plant was completed in early June 2000, the facility was distinguished by how it has nearly doubled its production capacity, from 750,000 to 1.3 million tpy.

"The semi-dry process not only allows us to double production at the Greencastle facility, but provides an environmentally sound alternative to achieving the stringent emission levels imposed by both federal and state regulations," said Dave Puzan, plant manager.

First semi-dry process "It is the first semi-dry production process in the country," according to George Glassburn, electrical superintendent for the plant. 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-gal. capacity), pumps, pipelines, "and all our experience of knowing how to make slurry," he noted.

Recently acquired by Dyckerhoff AG, Lone Star's facility near Indianapolis is the only one of the company's five U.S. plants to use a wet process. 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 re-sited the Greencastle mill in 1969 nearer to the quarry on its limestone-rich, 1,320-acre property. The site boasts one of the largest inland U.S. kilns, at 580 ft 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.

In high demand Local demand from the central Indiana's building construction and road construction markets for the mill's Type-III, Type-1, 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-and 95% of all production is shipped bulk (truck or rail), with the remaining 5% bagged for local retail distribution.

Retrofit of the plant to the new semi-dry process has included shortening the kiln to 255 ft, adding a 322-ft, one-stage preheater tower, complete with an in-line calciner, a dual de-dusting cyclone, and a hammermill dryer. "Slurry is being atomized in the hammermill dryer, and moves through the de-dusting cyclone's calciner and the first-stage cyclone before being fed into the kiln," according to 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, with the expected downtime scheduled to last about six weeks.

Demand-beyond-capacity is a constant reminder of what is most important at Greencastle, according to 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 number one 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.

Efficient electrics critical to uptime The need to maximize capacity and uptime for the plant challenges electrical engineers (and their suppliers) to utilize, manage and maintain all the electrics for efficient, round-the-clock production, according to Bob Brown, electrical supervisor at Greencastle.

Motors and motor drives are absolutely critical in optimizing uptime. "We have upgraded many of our electrical motors to higher-efficiency motors in the last decade," said Glassburn. "We 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 in the plant powers motors that range from requiring 3 hp (feeder weights) to 800 hp (the ID 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 (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). And 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.

Correct sizing of loads has helped the 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," notes 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. That reduces training time and minimizes mistakes. "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, also are "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."

A local supplier of parts, service, and new equipment also is critical in the electrical chain to maintain uptime, according to Lone Star managers. The Greencastle plant relies on Indianapolis-based Scherer Industrial Group, Inc., a distributor that handles drive start-ups for the facility.

Maximize downtime 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."

This kind of smart management within a cement processing plant is focused both on trouble-free uptime and using energy as efficiently as possible to contain costs. "By the time this plant is done, we're going to have over 19,000 hp on line," notes 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."

All on the upside The speed of the shortened kiln at the Greencastle plant will increase three times, from 1 to 3 rpm. It is powered with a new 900-hp DC motor and DCS 500 high-performance drive, both from ABB. For the first time, the plant also is installing medium-voltage technology for a 5,000-hp ABB drive and motor to power the new ID fan in the one-stage preheater.

Such equipment, combined with the new semi-dry process at the mill, makes managers optimistic about the mill's increased production capacity. They project that the expansion will now allow the mill to produce as much as 4,000 tpd of clinker, as designed.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.

This article was adapted from material provided by ABB.