Moisture Measurement in Mineral Processes
The measurement of any analyte should provide valuable information to the plant, and the moisture measurement is no different. Moisture measurement can assist in several ways to increase understanding of plant and financial parameters and to stabilise operations.
Value moisture measurements are present in several sectors of plant operations
- Metallurgical Accounting
- Contractual compliance
- Energy optimisation
- Process Optimisation
- SHEQ – Dust suppression
Metallurgical Accounting
There are often unaccounted losses between the Run of Mine (ROM) supply of dry tons and process plant production of concentrate.
Varying moisture content of the ore supplied may often contribute to this phenomenon, and proper moisture measurement may assist with understanding any discrepancies in accounting.
A 6-idler belt scale installed between the crusher and mill typically provides the RoM values. This measurement would probably be sufficient if the moisture content were predominately stable. However, even small changes in moisture can create a significant accounting "error"
Consider the example of an Iron Ore mine with the following supply characteristics.
For the example, we will only work with Average Tons per hour(mph) = 5000 and moisture content expressed as an % of the total weight.
If the actual moisture content is 3 %, instead of an anticipated 1%, over a year, the process plant would have received 864 000 fewer dry tons than the mine reported providing.
It clearly illustrates that a Belt Scale alone does not provide enough information to account for discrepancies between RoM and production tallies accurately; and that moisture measurement is essential.
Contractual Compliance: Transportable Moisture Limit (TML)
Liquefaction of mineral ores is the process where, in some scenarios, moist sediment loses its strength due to strong shaking and starts to react more like a fluid. Cargoes at risk of liquefaction contain at least some fine particles and some moisture, although they need not be visibly wet in appearance. ( Dr Martin Jonas)
Liquefaction may lead to cargo shift and loss of stability; and has been the cause of several tragic accidents.
For shipping in marine vessels, the Bulk Cargo Code adopts the Transportable Moisture Limit (TML) to regulate the maximum moisture content of a cargo deemed safe for carriage by sea in ships.
Compliance relies on reliable measurement and certification of moisture by shippers. Sample testing is required but may not be enough to ensure compliance. Consider the scenario where samples are taken and tested before a significant rain downpour occurs during open conveyor loading. Online monitoring of moisture content is, therefore, essential to ensure that actual moisture content complies with TML.
In the following articles, we will examine the value of moisture measurement in
- Energy optimisation
- Process Optimisation
- SHEQ – Dust suppression
And finally, we will focus on the technologies available for Moisture measurement
References
https://www.gard.no/Content/20651223/Cargo%20liquefaction%20January%202014.pdf