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Tramp metal removal system cleans up dolomite reserves

Heavy-duty metal detectors and a suspended electromagnet, used to clean up aggregates, have been instrumental in removing ferrous and non-ferrous tramp metals from one of the world’s largest dolomite operations.

A sprawling 65ha quarry in York, Pennsylvania, is home to one of the world’s largest reserves of dolomite used in refractory and dolomitic products for lime, steel and cement.

Magnesita Refractories has operated this mine since 1950 and processes more than 60,000 tonnes per month of the mineral, composed of calcium magnesium carbonate.

When the aggregate is extracted in raw form, it contains numerous ferrous and non-ferrous metal fragments, enough to shut down expensive crushing equipment and cause innumerable downtime situations.

The solution for Magnesita was to install an Eriez model SE-7520 self-cleaning suspended electromagnet for tramp iron removal, and an Eriez model 1250 E-1 metal detector for additional ferrous and non-ferrous metal removal, providing an effective “double team” contaminant removal process, according to Magnesita’s project engineer John Dixon.


"Since we installed the metal detector and suspended electromagnet, we have had no crushers rebuilt because of tramp metal,"
John Dixon, Magnesita’s project engineer

Product technicians from Eriez and its local area sales representative agency PennQuip Inc, in tandem with a design and engineering team from Kemper Equipment, helped Magnesita select, install and test the equipment over a period of six months.

The result is that Magnesita has produced higher quality materials by achieving greater ferrous and non-ferrous metal removal than was possible with previous equipment.

Magnesita, a Brazilian company, operates 28 industrial and mining units, with 16 in Brazil, three in Germany, three in China, two in France and one each in Belgium, Taiwan, Argentina and the United States.

The total refractory production capacity is more than 1.4 million tonnes per year. Magnesita is the third largest producer of refractory products in the world and a leader in integrated solutions with refractory products.

Costly downtime

The York facility is particularly important because of its large, high quality dolomite reserves. In fact, Magnesita maintains an extensive research and development centre at this facility to meet the needs of the iron and steel industry.

According to Dixon, the process to approach the Eriez team began when expensive crushers were being damaged by undetected tramp metal. “The trigger for this project was the $[USD]750,000 [$AUD987,000] we spent on three crusher repairs for several years. We had to find a way to prevent that from happening in the future,” he said. “We called Eriez and Kemper and asked for a solution.”

The 1250 E-1 metal detector is inside the tunnel above a 76cm wide conveyor belt.
The 1250 E-1 metal detector is inside the tunnel above a 76cm wide conveyor belt.

The first phase involved choosing and installing the proper metal detector. Magnesita established several benchmarks and provided metal test cubes to ensure the Eriez Model 1250 E-1 metal detector with a 25cm (10”) high opening would perform to specifications. The test cubes included 16mm (5/8”) ferrous, 32mm (1.25”) stainless steel and 32mm manganese.

A “performance guarantee” was included in the contract, meaning if the metal detector did not perform at the quarry as specified during a one-month commissioning phase, Eriez and Kemper would remove it with a full refund.

Once in-house testing at Eriez was complete, the metal detector was installed and passed all performance tests, according to Dixon.

“Our old metal detector was outside the tunnel of the quarry, so we were getting false trips due to CB radios and handheld walkie talkies,” he said. “Even when we moved the old detector inside the tunnel, we were still getting interference. Eriez made a lot of recommendations to stop the false trips with the new unit.”

The new metal detector — located inside the tunnel — is on the 76cm (30”) wide number five conveyor belt at an incline of 30 degrees with a feed rate of 380 tonnes per hour. The belt travels at 164m (540 feet) per minute. Eriez recommended a flag marker system where a flag drops onto the belt within 61cm (24”) on either side of the tramp metal detected. After the flag drops, the conveyor coasts to a stop for quick metal removal.

Greater efficiency

The SE-7520 suspended electromagnet is above ground on the 91cm wide conveyor belt.
The SE-7520 suspended electromagnet is above ground on the 91cm wide conveyor belt.

Once officials at Magnesita were satisfied with the Eriez metal detector, the next phase involved the SE-7520 self-cleaning suspended electromagnet, now located above ground on the 91cm (36”) wide Q7 conveyor belt, about 91m from the metal detector, according to Dixon.

Magnesita was using an older manual cleaning-style, permanent suspended magnet. The newer Eriez electromagnetic unit operates at a much higher efficiency. This self-cleaning electromagnet has field strength 2.5 times greater than the older permanent magnet at the same cross-belt 25cm (10”) suspension height.

“Our older permanent magnet had enough strength to pull ferrous off the top of the burden surface, but it could not pull up the embedded material,” Dixon said. “Also, it was not a self-cleaning model, so material would accumulate on the magnet and require manual cleaning. We really needed a more powerful magnet to prevent any kind of tramp metal from going into our two crushers.

“The Eriez SE has the ability to pull out metal with greater force than our previous unit. The self-cleaning function has eliminated man hours to physically clean the magnet and the belt, which runs 119m (390 feet) per minute.”

Tramp metal removed by the SE is discharged into a hopper installed on a concrete pad.

“Since we installed the metal detector and suspended electromagnet, we have had no crushers rebuilt because of tramp metal,” Dixon said. “We gave Eriez and Kemper the thresholds we could not exceed in terms of maximum particle size, so we were confident the equipment would work once all the testing was complete.”

Meeting performance goals

Product technicians from Eriez and its subsidiaries helped Magnesita Refractories select, install and test the equipment over a six-month period.
Product technicians from Eriez and its subsidiaries helped Magnesita Refractories select, install and test the equipment over a six-month period.

Dan Sheakley, the operations manager for Kemper, attributed the successful outcome to testing the equipment in stages and monitoring the results.

“We created performance goals with the metal detector first, then went to stage two with the suspended magnet,” Sheakley said. “The end goal was to protect the equipment downstream throughout the plant.

“We can often do capacity guarantees, based on the type of equipment and application, but the performance guarantee on the metal detector was a unique situation. Since we knew Eriez had a testing facility to ensure the unit would operate correctly once installed at Magnesita, our ability to provide this type of guarantee was much easier.

Eriez customised the SE magnet to ensure the separated ferrous material would stay on the self-cleaning belt before being discharged into the hopper. It was a team effort.”

Eriez is recognised as a leading authority in separation technologies, metal detection, coarse particle flotation and vibratory feeders, and has applications in the mining, aggregate and recycling industries. The company manufactures and markets these products through 12 international facilities on six continents.

The Eriez Australia facility is based in Epping, Victoria.

Source: Eriez Australia




















Monday, 24 September, 2018 02:23pm
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