Hydrocyclone Harmony

Ensuring maximum efficiency from your sand washing plant

By Ben Winter, design engineer, CDE Global

When considering hydrocyclone-based sand washing plants there are several factors which should be considered to ensure minimum plant wear.

The benefits of replacing inefficient bucket-wheel systems with hydrocyclone washing plants have been well documented. However, these operational efficiencies can be further enhanced by considering a number of key factors that can help reduce operating costs.

Vertical vs inclined cyclones

Plants which include an inclined hydrocyclone configuration generate excess wear on one side of the cyclone resulting in increased costs for spare parts and unnecessary plant downtime. This can be avoided by employing a plant with a vertical hydrocyclone arrangement.

Consideration should also be given to the extent of the rubber lining within the hydrocyclone, as this is key to ensuring maximum wear resistance. CDE’s experience of sand washing around the world has led to the conclusion that a cyclone lined with 10mm of rubber offers the best solution.

Cyclone discharge and feedbox

A large rubber-lined feed box positioned to ensure the cyclone underflow is discharged across the full width of the dewatering screen will maximize the screening area and ensure high-efficiency dewatering of the sand. It is also helpful if this feed box can be opened in order to monitor the cyclone discharge on to the dewatering screen.

If the feed box is too small it will result in excess wear in the feed box itself as well as on the dewatering screen. This will occur because all of the discharge impacts on the centre of the screen rather than being spread across its full width.

Also, discharging the cyclone underflow on to the centre of the screen means that the full screening area is not being utilized, which results in the sand product having a higher moisture content than should be the case.

Dewatering screen

While polyurethane screen media is generally accepted as the only sensible choice for sand washing plants, it is important to consider the type of polyurethane selected as well as the set-up of the screening panels.

Often, it is assumed that all polyurethane is of the same quality no matter which supplier it comes from, but this is not the case. There are many polyurethane screen-media suppliers in the market and the products they offer are all different.

Consider, too, how the dewatering screen panels will be secured in place. When using panels that have to be bolted into position it is important to take into account the reduction in screening area that this causes, as well as the increase in maintenance downtime when the panels need to be replaced. By selecting modular, non-bolted panels, maintenance time can be significantly reduced.

Another factor to consider is the wear protection offered to the screen. For example, are polyurethane side panels included to offer this additional protection? Given its wear-resistance properties, polyurethane is, once again, the best option here.

Finally, as with any dewatering operation, the longer the material can be held on the screen the more efficient the dewatering process will be. It is important that design of the sand washing plant ensures this objective is being met. The introduction of a dam bar at the end of the dewatering screen can help allow this to happen. Sand washing plants that do not have a means of retaining the sand on the screen for the longest possible time will deliver washed sand with a higher moisture content than should be the case.

Rubber springs

It is important to consider the means by which the vibration from the screen is transferred to the material, to ensure it is dewatered most effectively. Typically, rubber springs transfer 10–15% more energy to the screen than systems which employ steel springs. This results in better dewatering of the material and also helps protect the screen frame from vibration that is likely to lead to plant failure.

Systems that employ steel springs tend to transfer a lot of vibration to the screen frame compared with rubber springs. In CDE’s experience, more often than not this results in damage to the frame, which means increased costs and downtime.

Slurry pump protection

Protecting the slurry pump in the sump area reduces the risk of damage to the pump and, ultimately, plant failure due to the ingress of rogue aggregates from the sand washing phase. Although only a small measure, it can offer significant advantages for operators.

Plants that include an integrated pump ensure that the pump is protected from damage by rogue aggregates by means of a polyurethane pump protection mat with a 20mm aperture.

Matching cyclone and dewatering screen specs

Matching the capacity of the cyclone to the dewatering screen specifications ensures optimum performance of the sand washing plant. If the screen is too small to manage the volume of material coming from the cyclone, the result is excess wear on the screen. This, in turn, can lead to cracking of the screen due to overloading. It also means the sand is not being dewatered as effectively as it should be.

Float system

The purpose of the float is to maintain the required level within the sump even if there are variations in the slurry feed rate. This also ensures the sump never overflows leading to the loss of fine sand to ponds. Vertical float systems are much more robust than other types. 

Summary

Important considerations when using a hydrocyclone system include:

• Maximizing the rubber lining within the hydrocyclone; this is a key factor in ensuring maximum wear resistance.
• Positioning a feed box to ensure the cyclone underflow is discharged across the full width of the dewatering screen; this maximizes the screening area.
• The longer the material can be held on the screen, the more efficient the dewatering process will be; consider a dam bar at the end of the screen to aid this.
• It is important to consider the type of polyurethane that is selected as well as the set-up of the screening panels.
• Matching the capacity of the cyclone to the dewatering screen will ensure optimum performance of the sand washing plant.