When Lone Star Industries, Indianapolis, decided to expand its cement plant in Greencastle, Ind., it set high goals for growth. Planning to nearly double the facility's production capacity from 750,000 tons per year to 1.3 million tons per year, this project was no small undertaking. According to George Glassburn, electrical superintendent, this will be the first semi-dry cement-making production process in the United States.
"The semi-dry process not only allows us to double production at the Greencastle facility (Photo 1), but provides an environmentally sound alternative to achieving the stringent emission levels imposed by both federal and state regulations," says Dave Puzan, plant manager.
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 use alternate fuels for producing clinker, make the mill's products competitive with cement produced from dry process facilities.
Local demand 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. Central Indiana's red-hot building construction and road construction markets fuel this demand.
Efficient Electric Is Critical to Uptime The need to maximize capacity and uptime for the plant challenges electrical engineers (and their suppliers) to use, manage, and maintain all the electrical equipment for efficient, round-the-clock production, says 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," says 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 that require from 3 hp (feeder weights) up 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 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, and the feeder from the primary rock crusher to the conveyor at the quarry site (Photo 2).
Correct sizing of loads helps the engineers 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, such as feeder weights or slurry pumps.
The plant also extends this specification strategy to the motor drives (Photo 3).
"The same type of drives are used to control these motors across different functions," says Tennis. Such standardization, from a practical, operational point of view, provides multiple benefits. Since the drives share a common operating platform, the electrical technicians can be trained once, and 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," notes Tennis. New AC drives, including ABB's AC 600 controllers, also are "smart," he says. "They are easy to install, setup 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 is also critical in the electrical chain to maintain uptime. 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," says Tennis. "That's my policy. If I put anything in, I won't energize it until the technician says it's hooked up right."
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," says 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 online," 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."
The speed of the shortened kiln at the Greencastle plant now increases three times, from 1 rpm to 3 rpm. It is being powered with a new 900 hp-DC motor and DCS 500 high-performance drive. For the first time, the plant also has 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 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 4,000 tons per day (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.