New life for an old quarry
By Kerry Clines, Senior Editor
TXI’s Bridgeport Stone operation is located in North Central Texas on top of a large limestone deposit that has kept the Dallas/Fort Worth area supplied with aggregate since the middle of the last century. “TXI bought the plant in 1953,” says Gary Allen, general operations manager for TXI.
More than 50 years of continuous growth brought 50 years of technology advances, but it also brought 50 years of inefficiencies that needed to be addressed.
“The primary crusher had a separate control building, the sand plant had a separate control building, the concrete products plant had a separate control building, and the asphalt products plant had a separate control building,” says Todd Lacey, plant manager at Bridgeport Stone.
If the plant was to stay productive and competitive, something needed to change.
Automating the plant
“We felt like we were leaving a lot of money on the table with the facility as it was,” Allen says. So, two years ago, rather than tear everything down and start all over with a new plant, the entire operation was automated.
“We turned it on April 26, 2008,” Allen says. “We upgraded and automated the whole thing so we could run the entire plant out of one central location. We targeted the efficiencies and throughputs, and ultimately lowered our energy consumption by 25 percent.”
With all the individual operations running in a coordinated fashion and being controlled from one central location, the company was able to balance and fine tune the entire operation for optimum performance and production.
“The timing actually was great,” Allen says, “because the economy turned about the same time these improvements were completed, enabling us to operate more cost-effectively at a time when it was needed the most. Had the automation not been completed, continuing operational challenges and inefficiency would have made these last two years much more difficult. The results have exceeded our expectations, and, while it has taken us some time to get everything refined, it has really come together well.”
Before the plant was automated, one person was required in each control tower along with two ground hands to run each of the individual operations.
Instead of labor, the plant now has 15 cameras in strategic locations throughout the operation. The cameras are monitored and controlled by two operators in the central control room. “This is the heart of it all,” Lacey says. “We have people on the ground that can check things out, but for the most part, the two people in the control room run it all. One operator monitors the asphalt products plant, concrete products plant, and sand plant. The other operates the primary crushers, scrubbers, split bin, and the road base plant. They can speed the operation up or slow it down to optimize the production flow, and if you want to know what’s going on in the plant, you call them. It’s nice to go to one place and get every answer you need.”
The cameras can even be monitored and controlled from home, Lacey adds with a laugh, “but we try not to do it too often — it can become addictive, and we have to be careful.”
In addition to automation, Bridgeport Stone did several other things to streamline its operation and improve its bottom line.
About a year ago, the plant began using tire chains on its wheel loaders. This has not only saved valuable time that might be consumed changing and repairing tires, but has also saved money. “If the tires didn’t have the chains on,” Lacey says, “out of four available tires on a wheel loader, we probably would have replaced two by now. Wheel loader tires are about $100,000 for a set of four, so the numbers speak for themselves.”
Along with this significant change, Bridgeport Stone installed upgrades to the major motors and pumps throughout the operation. The plant was able to reduce energy consumption by installing variable frequency drives on each of its crushers, which are some of the largest electricity-consuming units in the operation.
The facility’s water pumps were automated as well. “Two years ago, we ran five pumps at 350 horsepower each,” Allen says, “now we only run three.” Instead of leaving a 350-horsepower pump running all the time so the water truck can fill up, the company installed an automated, and much smaller, 40-horsepower pump. When the water truck drives under the spout, the pump turns on automatically, the water truck fills its tank, and then the pump turns off. And if the plant isn’t running, everything is turned off. “We only want to use the power that is required at the time,” Allen says.
The company also took advantage of the slowdown in business to improve its quality control. “At our quality control lab, we run an average of 850 samples a year,” Lacey says. “As the economy continued to slow, we looked at how to better utilize TXI’s technical resources at Bridgeport Stone. Enhancing our quality control was an ideal fit.” Samples are pulled from every stockpile and every 10th railcar after being loaded, so the employees know if there’s a problem with the material before the train leaves the plant. This increased sample frequency has allowed Bridgeport Stone to improve the quality of the material it ships while also providing important feedback to the operations to further optimize production.
The production process
Production begins with a bang. The quarry shots are highly coordinated at Bridgeport Stone to ensure maximum yield while effectively controlling any non-productive variability. “The protocol, when you shoot the shot, is absolute,” Lacey says. “We go through a rigorous process. We don’t have any deviation. You can shoot a thousand times and never have a problem, but we don’t take any chances. It just takes that one time.”
As in most operations, digital caps are used so that they can be armed with a computer and patterned to create the exact shot the operation wants. “We keep eight milliseconds of delay between blast holes and utilize seismograph reports to maintain optimum timing between rows,” Lacey says.
The goal of the blast is to get the shot fine enough so that 75 percent of the material passes straight through at the primary crushing plant. The primary is set up with two side-by-side, identical jaw crushers, providing the capacity to accommodate two 100-ton haul trucks dumping simultaneously. Once the material goes through the primary crusher, any oversize material will be retained on the top deck and then be routed to the cone crusher to be crushed again.
“If we choose to do so, there’s a conveyor that kicks out on one side so we can produce 12-inch rip rap product,” Lacey says. “To summarize, the primary crusher process can produce 12-inch rip rap, along with 5-inch by 2-inch material passing straight through, while anything over 5-inch is routed to the cone crusher to get processed one more time.”
Once the material is crushed, it is sized and sent on to the appropriate stockpiles, which are located at the base plant, sand plant, concrete products plant, or the asphalt products plant, where the material is ready for loadout.
“Our road base business had declined until early 2010, but demand has steadily increased over the last six months,” Lacey says. “As the sale of key products slumped during the economic downturn, the plant had more time to improve our road base process. We had some surplus equipment available to dedicate to this line of business, so we modified it and installed an additional stacker to create the automated base plant. Now we have the capacity to meet our business demand. We were less committed from a system standpoint before, and these changes have allowed us to better compete in an important market.”
Finished product is transported by both truck and rail. “Probably 25 percent of what we ship goes out by rail,” Allen says. “We have initiated a program to operate the train locomotives ourselves at the plant site, which has significantly — and safely — improved loadout efficiency. The railroad personnel pull the train in and get off, while we take control of the locomotive and load the train. After loading is complete, we contact them and tell them to come get it. We train our people — all personnel who operate the rail equipment complete a certification program to be qualified to operate the locomotives.” Once the trains are loaded and ready to go, they wait for what is known as the “rock window,” which opens after the Dallas/Fort Worth-area commuter traffic completes operations for the day.
Highway trucks handle all the local shipments. Loading takes place from 4:30 a.m. to midnight, but some trucks arrive at the plant as early as 2 a.m. to be the first in line. “We load trucks 5½ days a week, 20 hours a day,” Lacey says.
When it began operation in the “1950’s,” Bridgeport Stone was capable of producing approximately 300,000 tons per year. Currently, with the automation and other upgrades that TXI has made to optimize the process, the plant can now produce in excess of 8 million tons per year. Not bad for a 50-plus-year-old plant.
Bridgeport Stone currently runs two shifts with a third shift reserved for maintenance.
“With the downturn in the economy, employees are currently working 40 hours a week,” Lacey says. “That’s down significantly from what they used to work. You really need four shifts to go 24/7/365. Before, we were doing it with two shifts, which, in retrospect, was not the optimum way to staff this plant. One thing our automation projects have allowed us to do during this downturn is to re-evaluate our staffing, improve our quality, and better plan for the time when higher levels of demand return to this marketplace.”
When business does pick up, as it surely will, Lacey plans to hire more employees as needed, but he has also challenged everyone currently on staff to maximize productivity.
“We currently have reserves capable of supporting this operation for many decades,” Lacey adds. “With these reserves and the level of technology in place today, we can continue to operate this plant for many years to come. But as newer technologies become available and continual optimization of the plant is required, it will likely bring more upgrades to Bridgeport Stone in the near future.” AM
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