When a 2003 fire broke out on a conveyor system at the regional trash authority plant in Portsmouth, Virginia, it ignited a series of events and equipment upgrades that made maintenance easier and more cost-effective.
“The main conveyor going across the street caught fire on a Saturday, and it burned about two-thirds of the conveyor and the plant’s communication lines,” explains Steven Rawlings, account representative at Motion Industries, a subcontractor at the site. “They had to put an emergency bid procedure in to rebuild that entire conveyor.”
The conveyor feeds an incinerator/boiler facility across the street that produces steam used for operations at the naval shipyard in Portsmouth. From the dumping point, after sizing, picking and shredding, trash gets conveyed to the incinerator/boiler facility on a long inclined belt conveyor that enters the incinerator approximately 90 ft above the ground.
During the next several years, the plant replaced four conveyor assemblies and has 10 more scheduled over the next three years.
“Right now we have drives that are outdated, so we’re going to update everything,” explains Tom DeLoatche, maintenance supervisor at the plant, now called Wheelabrator Portsmouth, a Waste Management company. “We had some ideas, and we went to Steve at Motion Industries. The existing drive had a corrugated belt that slipped. We were talking about a few different ideas, and we looked at the alternatives.”
The existing gearboxes had been in place since the 1980s. “They’re chain driven, which poses a safety hazard,” says DeLoatche. “That’s another reason we wanted to change — to get rid of the pinchpoints.”
The plant has three lines, and they generally run two, says Rawlings. “The plant processes more than 2,000 tons of trash daily,” he says.
When the change was made, the plant wanted to increase steam production for the shipyard. This meant trash flow to the facility had to increase. However, because of space constraints, the conveyor size couldn’t be increased. This left increasing the conveyor speed as the only practical solution.
The existing conveyor drive was an inline arrangement that included a 60-hp motor, a gear reducer and a cogged belt connection to the conveyor head pulley. Upgrading the inline arrangement to achieve the necessary speed increase would involve larger drive components, larger reducer and chain guards, larger base platform and associated supporting structure, and time for fabrication and installation on the retrofit.
Motion Industries consulted Chris Wood at SEW-Eurodrive, who recommended a right-angle, hollow-shaft, compact gear reducer mounted directly to the conveyor head pulley shaft. “We remanufactured the conveyor head pulley, as opposed to the upper inline drive structure,” explains Wood. “We were able to mount the motor, high-speed coupling and gear reducer on a swing base and then slide the whole assembly onto the head pulley shaft. By shaft mounting the reducer onto the head pulley, a torque arm bracket was the only part that had to be fabricated.”
[pullquote]Rather than attempting to upsize the existing inline drive arrangement, the direct drive approach Wood suggested proved to be more efficient and saved installation time, which was a big factor in the project. “A shaft-mounted drive was a good solution,” says Rawlings. “The SEW unit was quick and easy to install onto the conveyor head pulley shaft. SEW had a quick ship, easier installation and was able to deliver more quickly than other companies who submitted bids.”
The project team coordinated with the plant’s maintenance organization to make the transition as seamlessly as possible. “The new drive was installed during a scheduled maintenance shutdown and didn’t interfere with normal operations,” says Wood. “Direct driving the conveyor boosted efficiency by 15% to 20%, which meant a 100-hp motor was sufficient to do the job. A more efficient drive arrangement allowed us to use the smaller motor. Maintenance issues and costs associated with the chain drive were also eliminated.”
The new drive has cut the maintenance time by 50% to 60%, says DeLoatche. “We do predictive and preventive maintenance monthly, semiannually or annually, depending on the equipment,” he explains. “We have 13 maintenance technicians, along with me and another supervisor.”
The implementation has been so successful that the plant is replicating the assembly over the remainder of its metal pan style low speed conveyors.
“In these applications, we’ll require a little more downtime upfront,” explains DeLoatche. “We’re replacing the whole head assembly, shaft and bearings. These are a little bit tighter to get to. This is downtime we budgeted for this year and are scheduling for the next year, as long as our gearboxes hold out there.”
The plant runs a metal pan conveyor through the plant at 8 rpm on the head sprockets, explains Rawlings. “The three conveyors that will be changed this year are feeding directly into the shredder,” he says. “Three shredders, one on each line, each drop under the floor level, and that’s where Conveyor 32 picks it up. Then Conveyor 33 takes it across the street. This place is designed with 80-ft-long trommels that screens the trash to size it. A few years ago, they decided, due to extensive wear and increased maintenance, they wanted to rip those trommels out and replace them with conveyors. In the end, they’ll have the same conveyors throughout, so they’ll have limited spares. They have three lines, and they generally run two.
They liked it so much that the second installation, Conveyor 32, was installed as a duplicate of Conveyor 33. They put it in the underground conveyor that feeds the big conveyor. They’ll be able to move all the material through their shredders with one gearbox and have a spare.”
Conveyor 33 had an inline gearbox with a chain drive. “It broke a lot,” explains Rawlings. “Ten years later, they put a big wide belt on it so they didn’t have to lubricate it, but it still needed a lot of maintenance. This new one has only had one leaky seal, and that’s it. You basically go up there and check the oil and make sure it’s not running hot. All these other gearboxes we’re replacing are these inline gearboxes with a chain guard. It’s such a big chain that it’s about a six-hour job to change the chain out.”