Calculating Hydrocyclone Performance in Sand Washing Plants

Alan Bennetts
By: Alan Bennetts October 12, 2020
Measuring Hydrocyclone performance is important for the success of your plant. Here's why and how to calculate Hydrocyclone performance.

Running a plant is a business and you want to succeed. A plant is most successful when all the equipment is operating correctly and efficiently. 

But without measuring the performance, improvement is difficult and impossible to show. 

Still not convinced?

Imagine trying to drive a long distance with your eyes closed. Chances are you would not get to where you want to go and your car would be wrecked. 

That is what it is like trying to operate a plant without measuring the performance. You would not know what you were doing correctly and, perhaps more importantly, what you were doing wrong.  

A Hydrocyclone, also known as a cyclone, can be the center of a simple wash plant or just part of a more complex system, but a poor performing unit can throw everything off.  

How to calculate cyclone performance

To calculate at the performance of a Hydrocyclone, you have to know what to measure. Three areas require measurement: 

  • The feed
  • The underflow 
  • The overflow

Each of these areas has specific metrics that are important to record.  

Feed

In the case of a sand plant, the solids are the main concern, so the tons per hour (tph) and the particle size gradation are the key components in all those areas. 

The inlet pressure for the feed relates to the cut point. The Hydrocyclone will not operate as desired if the pressure is not correct.

This is a simple item to monitor and compare against a desired pressure. There’s not a lot to calculate unless you go back to the proprietary calculation to get an exact cut point. This is an important data point to watch and understand when monitoring the performance of a Hydrocyclone, and many issues can be traced back to this indicator.

Underflow and overflow

Hydrocyclones are engineered to do a solids split based on particle size. The coarser/larger particles tend to be sent to the underflow, while the finer/smaller particles are carried to the overflow.  

To determine how good of a split your Hydrocyclone makes, it is necessary to do a solids balance based on gradation.

The gradation of each of the three areas (feed, underflow and overflow) is needed to determine part of the picture of what is happening with the Hydrocyclone. Knowing the gradation of the feed lets you know what is possible. The gradation of the overflow and the underflow lets you know what you have going where. 

Knowing the tph of each of the three streams allows you to do a mass split. The specific gravity (S.G) of the solids and liquids should be known. The tph of solids, gallons per minute of slurry and percent solids by weight are the three key data points needed for a material balance, but if you have two of them, you can calculate the third.

mass-split.jpg?mtime=20201007160433#asset:51151

A sample mass split.

The last part of the picture is adding in the flow rate to allow for a liquids split.

Once you have all of the gradations, tph and flow rate, you can calculate the performance of the cyclone and examine for areas of improvement by looking at a material balance.  

Material-balance.jpg?mtime=20201007155519#asset:51146

A sample material balance.

Taking a sample

Talking about the numbers is usually a whole lot easier than actually getting the sample from the Hydrocyclone. 

Automatic sampling can be used to get the solids, but taking timed samples on all points (feed, underflow and overflow) is the most comprehensive approach to get the full material balance. Flow meters and density gauges on all points (feed, underflow and overflow) would be great but not practical.

This means having good sampling points around the Hydrocyclone is necessary, which is something most installations do not think of until it is too late.  

A word of advice for anyone doing a new installation: plan for sampling and build it into the plant. If sampling is added in upfront, it is easier in the long run to monitor, correct and improve the operation. A little spent upfront will provide a payback in the end.

How to correct cyclone performance issues

As mentioned before, Hydrocyclones are simple. Once a mechanical issue has been ruled out, there are only so many things that can be adjusted.  

Adjusting the pressure

First and foremost is changing the pressure. An increase in pressure will force more solids into the underflow. A lower inlet pressure allows more material into the overflow. Adjustments in the pressure change your cut point (d50) as shown in the d50 chart below.

d50-chart.png?mtime=20201007154327#asset:51142

This d50 chart shows the probability of a particle ending up in the underflow.

All Hydrocyclones will have some fine material reporting to the underflow because there will always be some water reporting to the underflow. Adjusting the apex smaller will decrease the amount of water but also increase the chance of roping the underflow. Roping compromises the performance of the Hydrocyclone and causes it to act more like a traditional pipe tee than a classifier. 

roping-vs-ideal-cyclone-underflow.png?mtime=20191007081012#asset:44571

Roping (shown on the left) alongside ideal Hydrocyclone underflow (right).

The Separator™ configuration of the Hydrocyclone removes the highest amount of water from the underflow, thereby decreasing the fines bypass. 

The other side of bypass happens when coarse particles report to the overflow. Fixing this issue could be as easy as adjusting the d50 in the fines direction by raising the pressure. 

Increasing the pressure can be done a number of ways, including with a higher flow rate or by changing the vortex finder to a smaller size. Note: when changing the vortex finder, it is normally a good idea to adjust the apex liner due to the increased solids reporting to the underflow.

Non-pressure-related issues

If the situation does not allow for a change in pressure, it is best to bring in the Hydrocyclone manufacturer to explore additional options. These options generally require some physical changes to the Hydrocyclone beyond replacing the vortex finder and may alter the Hydrocyclone’s installation footprint.

No matter what you are trying to improve on your Hydrocyclone's performance, it starts with being able to measure the three points: feed, overflow and underflow. Calculating Hydrocylone performance necessitates good sampling to give you an accurate measure of the feed, overflow and underflow. The better the information, the better the analysis and the better the improvement. 

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Tags: Washing and Classifying, Aggregates, Minerals
Alan Bennetts

Alan is the Global Product Manager for Washing and Classifying at McLanahan Corporation. He provides leadership, direction and oversight to the evaluation, design, development, engineering, training and support needed for McLanahan’s extensive washing and classifying equipment line. Alan has nearly 25 years of experience in the mineral and aggregate industry, having served in a wide array of roles with equipment manufacturers and mining companies throughout the United States. Alan is a 1996 graduate of the University of Montana, where he received his Bachelor of Science degree in metallurgical engineering.