Second Opinion On Drive System Replacement Gives U.S. Agrichemical Big Results
Engineering consultants said the gear drive system couldn't be upgraded due to space
constraints. But, U.S. Agrichemical Project Engineer, P.K. Bhattacharjee, knew continual
maintenance costs and downtime on the aging system were becoming too costly. Bhattacharjee
knew he had to find a way to upgrade the 18-year-old drive system on the ammonium phosphate
granulator to increase production and prevent further losses.
"The old drive system served its purpose," said Bhattacharjee. "It was in service for 18
years. But, we were having big problems with maintenance and downtime related to the chain drive section of the system."
Located in Central Florida's phosphate-rich "Bone Valley," U.S. Agrichemical's Bartow,
Fla. facility produces granulated ammonium phosphate fertilizer for agricultural uses. The plant currently produces 800,000 tons of diammonium phosphate (DAP) annually. U.S. Agrichemical is a division of Sinochem American Holdings Inc., which is owned by China National.
Bhattacharjee noted that because the granulator drive is in the facility's main process stream, it is crucial to the operation. "If the granulator drive is down, it hurts our whole operation," said Bhattacharjee.
The production of DAP is a complex process that is interdependent upon each phase of the
operation. Raw phosphate rock is insoluble and chemical processes like adding sulfuric acid
are required to convert the rock into a useable form. After the phosphate is mined using a dragline, it is deposited into a pit where the spray from high-pressure water guns converts it into a watery mixture called slurry. The slurry is then pumped to the chemical plant for processing. After separating the phosphate from the slurry, the raw phosphate rocks are kept in storage before being made into fertilizer.
Controlled amounts of anhydrous ammonia and phosphoric acid are then mixed and combined with ammoniated phosphate fines. The anhydrous ammonia, phosphoric acid, and ammoniated phosphate fines are combined in a mixer and then sent to the granulator where it is shaped and sized. The granulator, a 15-foot (4.6 meter) diameter by 20-foot (6.1 meter) rotating drum, facilitates the granulation of the DAP. Next, the granulated product is dried, polished, and cooled further. X pounds of granules are produced hourly. Any downtime in this process can adversely affect production rates.
An Ailing Drive System
In service on the 18-year-old granulator drive system was a 150 horsepower (112 kW) AC
electric motor powering a parallel shaft gear drive with a chain sprocket mounted on the low-speed shaft. The other sprocket was mounted on a spur pinion shaft mounted in bearings. The spur pinion meshed with a spur ring gear flange mounted on the granulator.
Because of the dusty
environment in the plant, U.S. Agrichemical was having problems with chain
lubrication, stretching, breakage, and premature sprocket wear. This was
contributing to costly maintenance, downtime, and replacements parts
costs.
Finding a Way
Early in 1994, Bhattacharjee and Plant Manager Clarence Neff decided it was time to find a
way to upgrade and put the troublesome chain and sprocket drive out of its misery. This would
meet their production plans of increasing the granulator drive speed.
"We wanted a solution that would increase the speed of the drive system and eliminate the downtime we were experiencing - that was our main objective," said Bhattacharjee.
Bhattacharjee contacted local engineering consultants for a solution. When the engineering consultants said an upgrade was impossible due to space constraints, U.S. Agrichemical turned to the manufacturers of the enclosed gear drive that had given them 18 years of reliable service on the system - the Milwaukee-based Falk
drive.
"When Bhattacharjee notified me of the situation at U.S. Agrichemical, I was confident that we could work with them to provide a solution," said
the Tampa-based field engineer.
"When U.S. Agrichemical looked at trying to find an alternative to the chain and sprocket
component of the system, initially the consultants determined that you couldn't fit anything in the existing space because of the way the drive foundation and granulator were arranged."
After talking with Bhattacharjee and examining existing engineering drawings,
the account executive visited U.S. Agrichemical to take some field measurements. "While out in the field, we also
discovered that the drive system installed did not have the sufficient capacity to achieve the desired speed and horsepower that they needed for the operation upgrade."
The account executive called in Jay Carter of Motion Industries,
Inc., a local distributor familiar with U.S. Agrichemical's operation.
Together, they worked on providing a solution for the ailing granulator
drive.
Providing the Answer
The account executive was able to specify a drive system that eliminated the chain and sprocket drive, fit
within the space constraints, and exceeded the ratings for U.S. Agrichemical's granulator application.
"I wish we had called him in to review the problem from the very beginning," said Bhattacharjee. "We listened to the other guys for too long.
The company had the answer."
"I determined that we could fit in a 200 hp (149 kW) capacity Falk parallel shaft gear drive. While it was one size larger than they needed capacity-wise, the greater center distance between the input and output shaft allowed us sufficient clearance between the low-speed shaft, the pinion, and the trunnion
bearings that support the entire granulator. It was a tricky configuration."
The only other option for U.S. Agrichemical would have been to eliminate the entire three-foot tall, concrete foundation, relocate the wrap-around ring gear on the outside of the granulator, and start from scratch. Thanks to a second opinion, that didn't happen.
A parallel shaft gear drive with three reductions (24.9:1 ratio) was supplied to achieve the necessary output torque. The drive is powered by a 200 hp (149 kW), 1750 rpm Siemens AC electric motor driven through a Falk Steelflex? tapered grid coupling.
Like the high-speed shaft, the drive's low-speed shaft is also connected by a Steelflex tapered-grid coupling to the bearing mounted spur pinion shaft. The drive system upgrade allowed for a granulator drum increase of 7.5 rpm to 9.5 rpm. The drive system produces a total output torque of 179,303 in-lbs (20,259 Nm).
Providing an extra punch to the drive system upgrade was the surface-hardened gearing on the Falk drive. It allowed U.S. Agrichemical's upgrade to include more horsepower and higher
ratings in a smaller "package."
Falk's patented Magnum™ no-leak shaft bearing seals make the gear drive the right choice for service in the plant's dusty, granulator house environment. This seal keeps lubricating oil in and prohibits foreign particles from damaging bearings. An inner cage, with labyrinth axial and radial bush seals, prevents oil from leaving the drive.
"An oil drainback ensures an effective seal by returning any oil that gets beyond the bush
seal, back into the gear drive unit. Since there are no moving parts, this seal arrangement will last as long as the unit if properly maintained."
The gear drive also has purgeable grease chambers and an internal, continuous splash lubrication system that provides higher thermal ratings.
The main reason the old chain and sprocket assembly
became troublesome was that the extremely dirty environment made proper
lubrication difficult. Premature chain and sprocket wear was unavoidable.
By eliminating the chain and sprocket assembly and its lubrication
requirements and constructing a direct pinion drive configuration,
downtime and maintenance will be reduced.
Upgrading Nets Big Results
The new drive system is expected to improve production numbers at U.S. Agrichemical's DAP facility.
The drive upgrade allowed for a 50 hp (37 kW) motor gain and granulator speed increase of
27 percent. But most importantly, upgrading not only solved the problem of continual maintenance on the old drive system, but it also reduced costly downtime. Scheduled maintenance downtime is projected to be reduced by 50 percent over the previous drive system. "Although it is still early, we've already seen downtime reduced and there is no doubt in my mind that the drive upgrade will significantly reduce our downtime," added Neff.
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