Inspiration and perspiration get the credit, but most innovations become reality thanks to the right tools and available resources. For instance, a new semi-dry process is nearly doubling capacity at Lone Star Industries' cement plant (Greencastle, Ind.) from 750,000 tons per year to 1.3 million tons to keep up with demand. However, several key ingredients were needed to make the process economically feasible.

"It's the first semi-dry cement production process in the U.S.," says George Glassburn, Lone Star's electrical superintendent. "This new process allows the plant to retain its wet-feed process, which includes two-million-gallon slurry tanks, pumps, pipelines, and all our knowledge about making slurry."

Availability of relatively low-cost electricity, using energy efficiently, and the plant's ability to use alternate fuels make Lone Star's products competitive with dry process facilities. However, this requires Lone Star's engineers to maximize capacity and uptime by managing and maintaining the plant's electric equipment, such as motors, drives, and controls, for efficient, round-the-clock operation. Their latest effort involves a $75 million capital improvement and retrofit program, which was completed in spring 2000, and included 40 ABB floor- and wall-mount variable frequency drives (VFDs) on key motors. Renovation mainly involved shortening the plant's 580-ft kiln to 255 ft and adding a 322-ft, one-stage preheater tower. The project was managed by Fuller Engineering and required six weeks of downtime.

Lone Star has upgraded many of its electrical motors to increase efficiency in the past decade because a failure of any one piece in its equipment sequence could halt the production process. The plant's standard ac VFDs power motors in the 3-800 hp range. VFDs also control the primary OSEPA exhaust fan, which uses a 300-hp drive from ABB that has logged more than 40,000 hours since 1993 without one incident or trip. The plant's new ac drives include ABB's AC 600 controller with DTC (direct torque control), which can sense a motor's capabilities without a feedback device.

To increase the shortened kiln's speed from 1 to 3 rpm, a new 900-hp dc motor and DCS 500 drive, both from ABB, were installed. For the first time, the plant also incorporated medium-voltage technology, which consists of a 5,000-hp ABB drive and motor to power the plant's ID fan in the one-stage preheater.

Correct load sizing helps Lone Star's engineers simplify the variety of motors and drive models used. "We size motors to the largest horsepower an application requires, and then we slightly oversize the motor," says Ross Tennis, chief electrician. "This allows us to specify the same motor to handle the variety of loads within a process, such as feeder weights or slurry pumps.

"Since the drives also have a common operating platform, technicians can be trained once, but they can operate drives throughout the plant, which cuts training time and minimizes mistakes. Common motors and drives also reduce the number of spare parts required."

Lone Star's managers add that the semi-dry process and their new equipment makes them optimistic that the plant will be able handle long-term increases in production capacity. They project the expansion will allow the plant to produce 4,000 tons per day (TPD) of clinker, up from about 2,160 TPD previously.

"By the time this plant is done, we're going to have more than 19,000 hp on line. That eats up kilowatts and costs money," says Mr. Glassburn. "In this business, if you can save 1% of consumption per year, that's a significant savings. And, if you can do it with a higher-efficiency motor—putting a VFD that controls a motor right up to the rpm you need—then you'll also save energy."

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