Abstract

Accurate and repeatable measurement of volumetric flow rates in iron ore processing plants is particularly difficult, which could be due to process variations and inefficiencies but also due to inappropriate instrumentation. Dense medium separation (DMS) is one of the techniques used in the iron ore beneficiation process. The dense or carrier medium used in these DMS plants is normally composed of material such as ferrosilicon (FeSi) but is occasionally based on a milled magnetite medium as the carrier. This magnetic carrier medium has been shown to undesirably influence the measurements provided by electromagnetic-based flowmeters. In the flotation processes, the entrained air bubbles also create problems for traditional flowmeters, including high noise levels, loss of signal, and offsets in flow rate readings. The transporting of the iron ore along the many pipeline routes within a plant can, due to the highly abrasive nature of the ore, abrade the pipeline wall and even destroy any in-line instruments and particularly in-line flowmeters such as electromagnetic flowmeters or differential pressure-based flowmeters. Coarse size fractions in slurry and even scats that get through holed screens can impact on inline instruments, creating breakage or unacceptable noise spikes in electromagnetic flowmeter signals.

These and other slurry measurement problems have now been overcome with the introduction of the latest generation of flowmeter technology—non-intrusive arraybased flowmeter technology. The sensor head (blanket) is wrapped around the outside of the pipe and never comes into direct contact with the slurry, thus tremendously increasing its reliability and eliminating any maintenance or replacement due to abraded or corroded sensors. It is a passive instrument, i.e. it does not induce any energy into the pipe, unlike the ultrasonic flowmeters which become increasingly unreliable as factors like slurry density and vary over time. It is not influenced by the slurry properties in the pipeline, so magnetic slurry or solids do not impact on the reliability of the measurement. This paper outlines the basics of this flowmeter technology, along with its applications in iron ore processing.