Biological computing aids mining industry with real time estimate of
particle size distribution
are not clear, but the computer does not care.
is largely about taking big pieces of blasted rock and crushing and grinding
them into fine powder. Only after the host rock is pulverized can the desired
mineral particles be separated. Grinding mills are expensive to operate
and maintian, so it is undesirable to grind the ore finer than required
for efficient mineral extraction. A common method to continously and
automatically separate the material that is fine enough from that requiring
more grinding is to pump the rock and water slurry through one or many hydrocyclones.
A hydrocyclone is a particle size classifier which has no internal moving
parts yet using centrifigal fields and vortices is able to split the feed
entering the unit into an overflow stream of small light particles and an
underflow stream of larger, heavy particles. The overflow stream leaves
the grinding circuit for further processing and the grinding mill operator
wants a continuous measurement of the finished particle size - in the range
of 150-170 microns. Seven thousand metric tons per hour of rock may
pass through a bank of parallel operating cyclones, yet the mining industry
lacks a reliable online method of measuring the size of particles exiting
are used throughout the mining industry to classify
Simple schematic of a closed loop continuous milling
circuit. The ore is mixed with
the grinding mill. The ground rock slurry is
pumped through the hydrocyclone where the finer
particles are removed
and the coarser particles
returned to the
Drawing by Keith Palchikoff
photos from Fort Knox
Trying to Sample Mud is Not Easy
This is an onstream particle size
analyzer which uses an onboard
computer to sequence slurry samples
through automated calipers. The slurry passes between the calipers which
open and close hundreds of times per minute. After two minutes, the average
of the measurements are reported as a % Passing 100 mess. This is the percentage
of particles that would pass through a screen mesh with 100 holes per inch
- this is a common US mining particle size measurement.
The machine has been out of service for two years because of ongoing high
maintenance and constant repairs - trying to sample mud is not easy
. It is estimated to cost $100,000 per year to maintain a particle analyzer.
Enter the Soft Sensor
A neural network based
model of hydrocyclone performance.
A Soft Sensor is a software based virtual analyzer which uses secondary
physical measurements of key state variables as inputs to a runtime process
model and produces an inferred measurement of the desired variable. No more
expensive hardware based analyzer to unplug. All that is
required is a reliable and practical model of cyclone performance.
Unfortunately, the physics of
particle behavior in a cyclone are not easily explained and is an area
of active scientific research.
The internal forces in a cyclone may be difficult or impractical to accurately
model based on first principles and solutions to partial differential equations.
However, a numerical modelling technique
based on the way the human brain learns complicated relationships, has
been successfully used to model and predict the particle size produced by
an operating cyclone.