Accurate production rate measurement in a potash mine

Potash is the common name given to potassium carbonate and various mined and manufactured salts that contain the element potassium in water-soluble form. Potassium occurs abundantly in nature, being the 7th most common element in the earth's crust.

Potash has been used since antiquity in the manufacture of glass, soap, and soil fertilizer. Potash is important for agriculture because it improves water retention, yield, nutrient value, taste, colour, texture and disease resistance of food crops. It has wide application to fruit and vegetables, rice, wheat and other grains, sugar, corn, soybeans, palm oil and cotton, all of which benefit from the nutrient's quality enhancing properties. Although potash is used in over 150 countries it is only produced in 12.

The potash market has been experiencing rapid growth in the last decade primarily due to more demand for food, fiber and feed. This trend has been reinforced by increased demand for biofuels. The current potash market is estimated at 50 million tons annually, and is projected to grow at a rate of 3-4%.

A leading global producer and distributor of potash and phosphate for industrial use, operates 16 phosphate rock mines and plants, five potash production facilities, and one nitrogen production facility. In 2006 revenues for this producer exceeded $5.3 billion.

Challenge

At one of their mines in Canada, this producer needed to weigh raw potash ore on a conveyor suspended from the mine ceiling. High accuracy is important, as the ore is weighed to determine mine production rates. The potential belt scale design would need the capability to accurately weigh on a suspended, 48-inch belt conveyor carrying 2,800 short tonnes per hour at 600 feet per minute. A further challenge was posed by the support method of the conveyor, which creates dynamic forces that can affect the accuracy and repeatability of the belt scale.

Solution

Siemens engineers evaluated the application to ensure dynamic forces caused by the suspension of the conveyor would not influence the belt scale measurement. A 48" (122 cm) Milltronics MSI belt scale was installed with a Milltronics BW500 integrator, and a Milltronics MD-36A speed sensor attached to a 60-inch bend pulley.

Milltronics MSI is a single-idler belt scale ideal for critical process measurement. It is ideal for use on applications with fast-moving belts, short idler spacing, and light or uneven belt loading. The Milltronics MSI provides accuracy of ± 0.5% of totalized rate throughout a 5 to 1 turn down ratio. It has stainless steel parallelogram load cells with 300% overload protection that provide instant response to vertical loading, eliminating any dynamic forces generated by the horizontal movement of the belt. Strong static beam support also compensates for any dynamic forces created by the suspension of the conveyor. With belt speeds up to 5 m/s (1000 fpm) the Milltronics MSI handles mine production rates quickly and efficiently.

The Milltronics BW500 integrator provides the data processing capability and ease of use required for this challenging application. This microprocessor-based integrator monitors rate, load, totalized weight, and speed, and offers communications with many industry standard protocols.

Benefits

Since the installation of the Milltronics MSI belt scale, BW500 integrator, and MD-36A speed sensor, reliable weighing results have been achieved, leading to accurate mine production indication.

Because most belt scales in the market need two to four idlers to achieve similar reliable results in rugged applications, the single-idler Milltronics MSI and BW500 cost 20-25% less. Also Milltronics MSI and BW500 shipping packages weigh up to three times less than the average beltscale package, resulting in lower shipping costs.

Special equipment to move and install the BW500/MSI scale is not required. There is less down time required for installation as the belt scale is designed to Conveyor Equipment Manufacturer Association (CEMA) standards, allowing for simple drop-in installation with no conveyor modification required. The stainless steel triple beam load cell design makes the MSI suited for the harshest mine conditions, with high moisture and corrosion resistance, and suitability for ore of all sizes. With fewer idlers and fewer surfaces for product build-up, maintenance costs are lower.

As with any proper belt scale installation, precise alignment is required, but this procedure is simplified using the MSI's independent weighbridge. Because static test weights are used for routine calibration, the use of a roller test chain is not required, saving significant cost and hassle.

For this mining company, the Milltronics MSI/BW500 package offers an economical and reliable solution for measuring mine production. A long-time customer of Siemens Milltronics, they will continue to place orders for Milltronics weighing and level products.

Siemens Process Instrumentation
Century House
Bridgwater Road
Worcester
Worcestershire
WR4 9ZQ
UK

T: 01905 450500
F: 01905 450501