Limestone quarry – Mass flow measurement on a conveyor belt

Lime and limestone products are used in many areas of industry. Lime is known mainly as a key additive in steel production. However, lime and limestone products are also indispensable in drinking water treatment, in clarification plants, in agriculture, in the construction industry and in flue gas cleaning. The raw material is extracted as limestone rock in quarries. Nearly 30,000 tons of it are mined and processed every day in a large lime plant on the Rhine river. In the quarry, the blasted rock is loaded onto dump trucks with power shovels or wheel loaders and transported to the primary crushing station. The rock is supplied to the two large gyratory crushers via tipping hoppers and comminuted to a grain size that can be transported by a conveyor belt. The belt runs at a speed of 3.2 m/s and transports up to 3,600 tons per hour. The 1 km-long, 2 m-wide conveyor belt connects the primary crushing station in the quarry with the rock washer. In subsequent production steps the rock is washed, sorted by grain size and further processed in various ways. At the end of the production process, fired and unfired products for a variety of applications are stored or readied for shipment.

To regulate the primary crusher, the operator needs accurate, and above all reliable, mass flow measurement. Strong vibration, dirt, noise, moisture and dust make the measurement extremely difficult. The company had been using a mechanical belt scale to measure the flow rate. But the rough ambient conditions often falsified the measured values. The radiation-based measuring system WEIGHTRAC measures the mass flow on the conveyor belt continuously and contactlessly. The required belt speed is determined by the process control system. To ensure uniform throughput, the measurement data from WEIGHTRAC is used to control the output of the primary crusher. The detected material quantities can also be summed in the process control system. WEIGHTRAC is maintenance free and can be easily mounted on existing conveyor belts  The robust and reliable measuring system ensures smooth operation in the downstream production processes and makes it possible to optimize plant efficiency.

User benefits

• Optimization of transport capacity through precise flow measurement
• Maintenance free thanks to non-contact measuring principle
• Unaffected by environmental influences - reliable quantity measurement
• Long service life thanks to robust measuring system
• Simple installation on existing conveyors