Coal and mineral mining as well as cement operations need to analyze the bulk materials that are flowing through their production process. Minute-by-minute online analysis of ores, concentrates and various raw materials allows accurate high frequency process control to reduce process upsets, increase throughput and maintain quality all while extending mine life.
Crossbelt online elemental analyzers provide a means for reliable and accurate online analysis of bulk raw materials, including cement, coal, and minerals. These analyzers utilize Prompt gamma neutron activation analysis (PGNAA) or pulsed fast thermal neutron activation (PFTNA) technology, which are non-contact, non-destructive analytical techniques. PGNAA analyzers are situated directly on the conveyor belt and penetrate the entire raw material cross-section, providing minute-by-minute, uniform measurement of the entire material stream, not just a sample.
Thus, before installing crossbelt analyzers, one should consider the belt conveyors that are being used, because the material from which they are made and how they are set up could affect the accuracy of the analysis as well as the ease of use of the equipment.
One point to remember is that accommodations should be made for the return conveyor to pass beneath the analyzer. This typically means that the distance between the delivery strand of the conveyor and the return strand of the conveyor may need to be increased in the vicinity of the analyzer installation location.
Here are some other points to remember:
- Overhead Clearance — There should be enough clearance available to lift certain components in place with a mechanical lifting device.
- Horizontal Clearance — There should be enough horizontal clearance, at least on one side and ideally on both sides, to install and remove the detectors and isotope sources safely.
- Elevated Installations — If there is less shielding under the conveyer than on the sides or above it, it will be located close to the ground. Therefore, elevated installations require restricted personnel access beneath the analyzer. The details and size of the restricted area should adhere to the manufacturer’s specifications.
- Sloped Belt Installations — Installations on sloped conveyer belts require special attention to the rigging during installation.
In addition, the conveyer belt should be fabricated from rubber without metal cable reinforcement or any chlorine content, as this could potentially have adverse effects on analysis if not known prior. Vulcanized splices are strongly recommended over mechanical splices to prevent damage to the analyzer.
The shield assembly tunnel may be damaged from an overloaded or untrained conveyer belt. Controlling the material profile and training the conveyer belt are important.
Note that material belt loading affects performance in two ways.
- Overloading can cause physical damage with unpredictable results to the analyzer.
- Low belt loading can reduce the number of measurable gamma ray events since less mass is available to emit gamma rays. A lower gamma ray count rate results in reduced repeatability performance, while measurement accuracy is affected to a much lesser extent. Keeping periods of low belt loading as short as possible is therefore important for consistently good analysis results.
Lastly, make sure there are Conveyor Belt Safety Switches installed that activate an alarm when potentially hazardous conditions occur. A conveying system is constantly moving and contains bouncing rocks, minerals, and other materials. Inevitably a hazard will arise out of those conditions. Conveyor protection switches for bulk monitoring systems are used for position information, control signals, and to identify potentially hazardous situations with your process equipment.