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Crushing consistency problems in phosphate

Since the mid-1960s a mine in Vernal, Utah, USA, has produced phosphate for agriculture fertiliser. The three ingredients used in the production of this fertiliser are ammonia, sulphur and phosphate ore.

In 2003 agribusiness and food group giant JR Simplot purchased the property and formed Simplot Phosphates.

Company officials had for more than a decade struggled with their ore crushing system. Their existing crusher crushed slabs of phosphate ore into inconsistently sized pieces that would often trip and cause delays on conveyor belts.

Some of the harder ore couldn’t be crushed with the existing machine and had to be set aside. Additionally, as the site’s face moved, haul distances increased, meaning higher fuel usage and greater wear and tear on trucks.

However, none of this was as time-consuming or frustrating as the daily need to maintain the existing feeder-breaker by replacing picks on the pick roll. One of the workers had to climb inside and replace whatever picks had been damaged daily, a process that rarely took less than an hour.

In addition to the time-consuming repairs on the interior pick rolls, the feeder-breaker was inefficient in consistently crushing material to the required size, resulting in oversized material and causing belt trips along the 3.2km conveyor system. Simplot also had power constraints that limited the site to 447kW for the system.

“The feeder-breaker we had was highly inefficient and high maintenance,” Simplot Phosphate’s maintenance supervisor Delrie Gale said. “The operation would have to slow down, and it was tough to stockpile enough inventory to keep up.”

Simplot officials knew they had to make a change. In early 2011 they turned to mineral processing equipment manufacturer McLanahan for a solution. McLanahan’s regional sales manager Jeff McGovern studied the problem and worked extensively with Simplot officials to change the crushing system.

“The problem is that feeder-breakers only crush in one dimension, and that created some problems on their 1067mm wide conveyance system,” McGovern said. “Our solution would have to address their needs, work within their energy requirements and meet their budget.”

After research and discussions with Simplot personnel, McLanahan proposed a 1829mm wide x 1143mm long apron feeder that fed into a hybrid 1219mm diameter x 1829mm long heavy-duty double roll crusher. This custom-engineered system incorporated the design features of a direct drive crusher sizer, along with the drive configuration of a heavy-duty double roll, ultimately saving 346kW to accommodate the limited power supply.

“We were trying to find a solution that would size the ore better, work with their operation and not trip the system,” McGovern said. “After reviewing the application, we found the right machines to get the job done in the parameters we had to follow.”

The skid-mounted design would also allow the crushing system to move with the face, decreasing haul times and distances. Best of all, the entire system would come in on time and under budget. In late 2011, the system was installed and commissioned for use in early 2012.

Successful outcome

Since its start-up the crushing station has made significant savings in energy use and resulted in less wear and tear on the machines.

The smaller, more consistent product allows Simplot to crush more ore in fewer work days.

The system crushes the phosphate ore into a more cubicle-shaped product – a consistent 203mm in size. This is in contrast to the old system, which had a 254mm range but created slabs that got caught in the system, requiring shutdowns. This more consistent feed from the McLanahan crushing station to the conveyor for further processing in a sag mill cuts down on the belt trips and downtime that occurred while the slabs were removed.

“With the help of McLanahan, our problem was solved,” Gale said. “We had a smoother, even flow material going down the conveyor belt. The mill had a smaller material to deal with and it went through our facility faster.”

Simplot was also able to reduce the crushing schedule from 14 days to 12 days with no loss in productivity.

The company uses the two days off as energy-saving days – lowering costs, slashing power usage and saving on wear and tear.

There is also much less maintenance required with the new system, as it only needs to be checked two or three times a week, not daily.

Gale said Simplot had seen a large decrease in time spent on maintenance. “As far as man hours, we changed picks every day, seven days a week,” he said. “We had to get down into the crusher every day for hours at a time. No one misses that.”

Gale said working with McLanahan on an ongoing basis helped the operation better anticipate and head off potential challenges that inevitably arise at a mining site.

“With McLanahan’s help, we are improving how the system works, making it a better machine, more refined,” Gale said.

“More consistent product flows down the conveyor belt and we’re seeing it in our mill.”  

Source: McLanahan Corporation

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