“It’s not the auditor’s job to know and do everything,” explains David Emerson, Terex Roadbuilding’s director of product management. “There’s a talented team here to support him.”
A full day process, the onsite audit begins before the start of the day’s production and ends after the last load of hot mix has been delivered. The systematic process includes hundreds of component inspections from the conveyors and idle bearings to the drum mixer and storage silo. “I like to start at the cold-feed bins and work my way through the plant,” says Wilkins.
At the bins, he checks for adequate storage capacity and inspects the liners, dividers, extensions, vibrators and air cannon. According to Wilkins, “One of the most common recommendations at the bins is for a liner replacement.”
From there, the inspection covers the belts, belt wipers, idlers, and drives and continues through the aggregate and RAP screening and weighing systems. Moving forward, the auditor comes to the heart of the plant and one of the most critical inspection points, the drum mixer.
External drum inspections include the tire mounts and drive trunnion, chains, sprockets, and assembly as well as the drum auger, shell thickness and slinger feeder. Additionally, the auditor inspects the inside of the drum to look for, among other items, flight problems and liner wear.
With today’s rising natural gas and fuel oil costs, the exhaust gas analysis performed by the auditor offers a huge benefit for the producer. With this exam, exhaust temperatures are compared to mix temperatures. “We want to see the exhaust at or below mix temperatures,” comments Emerson. If exhaust temperatures are higher, fuel is being wasted.
Adjustments can be made to the burner and flights to correct this problem, which saves producers money every day the plant is running. According to Wilkins, “We have saved producers 5 to 10 percent in fuel costs alone with this analysis. With today’s high prices, this is significant.”
Another hot spot for inefficiencies is the baghouse. Auditors thoroughly comb through the bags to check for plugging and remaining service life. They also inspect airflow pressure along with the shell thickness, screw auger and hanger bearing performance. Emerson states that airflow problems are related to poor baghouse performance and achieving the right airflow can improve combustion efficiency by as much as 25 percent. Switching exhaust fan motors on the baghouse remains the biggest energy savings potential the auditors have uncovered to date. Most plants will have one or two 200 horsepower, constant-speed motors running at full tilt to power the fans. The installation of energy efficient, variable speed motors that run only as fast as and when necessary have generated significant savings for producers. At today’s energy prices, most operations can recover the cost of variable speed motor installation within a single season.
The audit concludes with detailed inspections of the rest of the plant components, including the controls package. “Control software is continuously being updated to help increase plant operating efficiency,” says Ken Cosby, Terex Roadbuilding’s manager of computer controls. “This is one of the first items outdated on a plant.”
Upon returning to the factory, the auditor shares his findings with a team of specialists that includes plant engineers, technicians, parts personnel and managers. In roughly a two-week time frame, the team analyzes the findings to develop a series of recommendations, a parts needs list and upgrade cost estimates. “All recommendations are based on the premise optimizing of plant production and maximizing uptime,” says Emerson.
The final recommendations are compiled into a 16-page report that is personally delivered to the customer. “This is probably the most important step in the audit program,” comments Wilkins. “Delivering the report in person allows us to answer any questions the customer may have and explain how we came to our conclusions.”