In the mining industry, hydrocyclones are mineral processing equipment used in slurry pulps to separate coarse and fine particles according to their size and density. From Wikipedia:

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.

I connected with Emerson’s Cristián Doerr in the Mining Center of Excellence about Hydrocyclone Optimizer technology to improve separation efficiency and increase reliability.

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.

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