The mixture [slurry pulp] is injected into the hydrocyclone in such a way as to create the vortex and, depending upon the relative densities of the two phases, the centrifugal acceleration will cause the dispersed phase to move away from or towards the central core of the vortex.
Coarse particles exit the bottom of the device (underflow) while fine particles are carried by the central air column and exit at the top (overflow). In metal processing applications, the product stream is the overflow (fine particles) and is typically sent to flotation circuits. In coal and iron processing, the product stream is the underflow (coarse particles), as fines are separated from the final product as a means of quality control.
Cristián noted that under certain conditions roping and plugging can occur where the hydrocyclones ceases to classify the particles. The shapes of the discharge are visibly different than normal operating conditions.
The roping condition occurs when the amount of solids in the underflow increases to such a point that its discharge velocity is limited, resulting in the accumulation of coarse solids in the separation chamber. This mass passes through the vortex, causing the inner air core to collapse and the discharge at the apex to take the form of a solid stream (rope) consisting of coarse material with high solids density. Roping conditions reduce recovery rates and efficiency in metals processing and lead to quality losses in coal & iron processing.
If not corrected in time the flow may clog and stop—a plugging condition which can result in contamination and downstream processing efficiency losses. Plugging occurs when the bottom aperture completely plugs forcing the materials overhead. In metals processing applications plugging reduces recovery efficiency, can cause flotation cell damage and reduce overall availability in order to clean the flotation cells. For coal and iron processing, similarly recovery efficiency is affected along with possible damage to the hydrocyclones and downstream equipment.
To avoid these conditions and operate productively and reliably, the Mining Center of Excellence team developed Hydrocyclone Optimizer technology. This control & optimization application addresses the problems associated with roping, plugging and undesired particle classification. It characterizes the different operating parameters of each cyclone. Having this information per cyclone allows the execution of efficient control strategies.
When the information is only per battery, you are not able to see which are the poor performing cyclones in a battery, based on particle size distribution, mass flows and densities of solids in the pulps transferred by the vortex and apex, in addition to their circulating loads. The application displays this information in real-time to the plant operator.
The solution uses two non-invasive, externally-mounted vibration sensors on each cyclone of a classification battery with the wired sensors placed in the vortex and apex areas and transmit the energy signals generated by the process. These vibration signals are processed first in a multi-channel Emerson AMS 6500 machinery health monitor and then in an expert system that resides either in a DeltaV Ethernet I/O card (EIOC) or a DeltaV PK Controller where roping and plugging conditions can be accurately identified.
In addition to the vibration characteristics, the expert system also incorporates key process variables from the plant’s PI historian (expert system also pull data out from plant existing PLC or DCS) and provides real-time particle size distribution data to the operator.
This solution helps reduce process downtime, increase recovery, avoid quality penalties, improve production efficiency, and lower operations costs by providing early recognition of misclassification conditions.
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