An accurate measure

The International Fertilizer Development Center (IFDC) estimates that the lion’s share of the phosphoric acid mined globally (approximately 82%) is used to produce fertilizer. The remaining 18% is used in many other areas, for instance to produce feed phosphates, as well as pharmaceutical and food products. Phosphorus is crucial to global food security, especially when one considers that the UN is projecting the global population is to reach 9.6 billion by 2050.

World’s largest producer of phosphate ore

Only a few countries have the necessary raw material base for the production of phosphate-based fertilizers. One of the world’s largest producers of high-grade phosphate ore and nepheline concentrate recently began a search for a belt scale supplier. Given the nature of phosphate mining, the company had high requirements in terms of reliability and accuracy for the rugged and harsh applications involved. As with any mining process, high accuracy is important, as the ore is weighed to determine mine production rates. In particular, the company was looking to reduce maintenance time, its spare part inventory and modernise its production processes.

Siemens Milltronics MMI’s compact design and drop-in installation offer significant cost savings in harsh and rugged industrial environments.

Challenge

Conveyor belt scales continuously calculate bulk material flow rates by measuring belt load and speed. They can be installed in many locations throughout a mine or mineral processing operation for rate control, production and inventory monitoring. Proper selection is important because with increased accuracy comes higher costs.

In addition to high accuracy and reliability, the company had two specific requirements when it came to modernising and expanding its production operation. The first requirement was the safety of its staff – a paramount concern of the company. Personnel were always to be protected and never required to touch any moving parts of the conveyor. The second requirement was calibration of the belt scale without stopping the process. Proper calibration is like picking up the right tool for the right job. Without proper calibration, accuracy is certainly at risk.

Siemens tested the Milltronics belt scale systems at two mines on the vacuum filters and load mills. Tests were conducted over several months using a variety of calibration methods. The company needed to ensure accuracy and reliability even with uneven, heavy or light loading.

The Milltronics MWL weight lifter’s modular construction easily adapts to a wide range of conveyor widths.

Siemens’ solution

Belt scales work by responding to vertical forces, both desired and undesired. Many issues are a result of problems with the conveyor or improper commissioning. Careful evaluation of the application, proper installation, calibration and routine maintenance will result in many years of continuous and reliable service. A typical belt scale system includes a weighbridge structure supported on load cells, electronic integrator and a belt speed sensor.

Siemens offered the Milltronics MSI belt scale and the Milltronics MMI belt scale (a combination of two or more MSI belt scales operating in tandem). The compact design of the single-idler model facilitated quick and easy installation and reduced the amount of total weighing space required. A Sitrans WS300 speed sensor mounted on a self-cleaning bend pulley or a Milltronics RBSS return belt speed sensor, a calibration test chain and a Milltronics BW500 integrator completed Siemens’ belt scale system solution.

After testing a variety of systems from different suppliers, the company chose the Siemens Milltronics MSI and MMI belt scale solutions. These Milltronics belt scales fully meet its requirements for accuracy, easy maintenance, long-term stability and simple and fast methods of calibration.

The rugged design of the Milltronics RBSS speed sensor is ideal for rugged applications. The RBSS offers easy, low-cost installation, while providing accurate belt speed detection.

Improved performance without sacrificing safety

Milltronics MSI is a heavy-duty, high-accuracy, full-frame single-idler belt scale used for process and load-out control. Milltronics MSI provides continuous inline weighing on a variety of products in primary and secondary industries. It is proven in a range of tough applications, from extraction (in mines, quarries and pits) to power generation, iron and steel, food processing and chemicals. The MSI’s patented use of parallelogram-style load cells results in fast reaction to vertical forces, ensuring instant response to product loading. This enables it to provide outstanding accuracy and repeatability even with uneven loading and fast belt speeds – a key concern.

Similar to the MSI, the Milltronics MMI is a heavy-duty, high-accuracy scale with multiple idlers. It is suited for the harsh conditions encountered when mining nepheline.

The total belt scale system indicates flow rate, total weight, belt load and belt speed of bulk materials on a belt conveyor. Both the MSI and the MMI are installed in a simple drop-in operation and can be secured with just eight bolts and existing idler sets, secured to the dynamic beam. With no moving parts, maintenance is kept to a minimum with only periodic calibration checks as required.

An added benefit of the Siemens system is the Milltronics MWL. Milltronics MWL weight lifter is a mechanical calibration weight lifter for Siemens belt scales. The MWL mechanically raises and lowers the static weights and then stores the weights securely above the belt scale calibration arms. This allows the operator to lower and apply them safely without having to lean into the conveyor. Safe and easy application of belt scale reference weights with the MWL means that the personnel can remain outside the conveyor.

The two belt scale systems were installed on belts carrying nepheline ore before and after the secondary crusher. The first belt is 1600 mm wide, with a high feed rate of 3200 tph. The second belt is 1400 mm wide and has a feed rate of 500 tph. After the Siemens belt scales had been installed at the material dosing portion of the mill, the company noticed improved performance and higher quality of material components in the finished product. With the belt scales installed, the company’s inventories are now measured in real time, preventing costly inventory adjustments. They have been able to improve capacities and production infrastructure, while increasing output. And all of this has been achieved while keeping safety at the forefront.

Milltronics BW500 is a full feature integrator for use with both belt scales and weightfeeders. Belt load and speed signals are processed for accurate flow rate and totalised weight of bulk solids.

Author

Matt Morrissey, Siemens Canada.