Tailings Dam Deposition (Cyclones)

[dainebryce]

I am busy with a research project to determine why our cyclones are supplying the wrong split! Our design is based on 16% underflow but we are only getting 11.8%. Can anybody with more experience help with some options as to why this could happen, so that i could look into with more depth and try to fix this problem?

Another question, if they asked me to do a grading on the slurry, what would this mean? And what results would the grading give me?

 

[oldestguy]

Can't help oh the cylone, but the word grading usually means determining the percentage of each particle size in the whole mass. In your case it probably means a mechanical analysis-via sieves of different opening sizes. It usually is then presented in the form of a chart relating particle size to percent of total. A geotechnical materials lab probably is where youn eed to take your sample for the test.

 

[dainebryce]

Great stuff, thank you for that, if the particles would be too small for a sieve, are there other forms of grading tests? The particle sizes are between 75 and 25 microns

 

[oldestguy]

Typically materials this size, such as silts or clays are "measured' using the hydrometer test. This test removes surface tension and other factors that may have particles clinging together (using dispersion agents) and then observes how they settle out in water. The density of the water and settling material at the hydrometer core elevation is then converted to percentage of the total mass, as would be done with the sieve test. To be accurate the specific gravity of the materials must be known. A test for specific gravity is usually done by the same lab. One method is with a pycnometer (a known volume flask), knowing temperature, etc. These tests are all standardized by ASTM.

Giving the sample to the lab ans asking for the gradation should get you the answer you want.

 

[itdepends]

Another method is using laser diffraction. There are commercial instruments available for that. Screen out the larger sizes (+150um) using a screen if necessary and then laser size the remainder.

Your cyclone will have a D50 cut size- when operating at design this will be the size of particles where 50% report to the overflow and 50% report to the underflow. Lower underflow densities can be caused by your material being finer than the cyclone was designed for (i.e. business as usual).

If you're going to size the material- get a representative sample of the overflow and underflow so that you can calculate the cut size for your cyclone and plot a tromp curve.

You can increase your underflow density by
Increasing your cyclone operating pressure (more flow per cyclone)
Decreasing your spigot size (that's the opening at the bottom)
Increasing the slurry density feeding the cyclone
Decreasing your cyclone diameter

Note cyclone spigots are one of the highest wear items and it's not uncommon for the outlet/spigot size to increase as they wear.

What happens to the cyclone overflow from this system? Changes made to the cyclone underflow will impact on the overflow.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"