Typical cyclone feed pump layout. Photo: Schurco Slurry

In the production of aggregates, sand and gravel for road construction, construction or other applications, the raw materials are mined from deposits of advanced materials mixed with other unwanted materials and debris. 

Physical separation must be performed to extract marketable materials from unwanted by-products. Depending on the sediment, material manufacturers can use a variety of physical separation methods.

In the process of this physical separation, fine and ultra-fine materials may be produced or already existing and entrained with raw materials. In these cases, a washing process takes place-and often additional separation of these fine powders may be required to extract these fine powders and mix them with marketable products, while still meeting the various specifications of each product, Or condense these fine powders and throw them away for fines in trash pools or dumps.

A common method of separating these washed fines from waste or product streams is to use hydrocyclones.

Cyclone separators, like centrifugal pumps, have a curve that controls their performance.

There is a relative defined pressure drop within a certain volume flow range through the cyclone separator, and the separation performance of the cyclone separator depends on the pressure drop.

Essentially, the pressure of the fluid entering the cyclone generates centrifugal force to separate the solid and liquid phases in the device, so that heavier particles are thrown out from the central axis and flow in a spiral motion against the cone of the cyclone. , And was dragged into the undercurrent of the whirlwind. The lighter and more fluid part of the flow is guided to the central axis of the cyclone separator and spirals upwards into the overflow.

This classification occurs in the "separation zone", which is the cone-shaped part of the device, located under the vortex detector in the top/headbox section. A variety of design principles are used in the cyclone separator and separator to realize various cutting of the medium. There are cyclone separators and separator performance curves-a bit like a pump curve, where the pressure drop through the cyclone separator is defined by various parameters inherent to the cyclone separator/separator and the pump that feeds it.

Schematic diagram of hydrocyclone. Photo: Schurco Slurry

Centrifugal slurry pumps are an excellent solution for various applications where solids are moved by hydraulic transport-cyclone separation is one of them.

The design of the mud pump should reach the total head of the cyclone separator, plus the calculated or predicted pressure drop of the cyclone separator to obtain the required flow rate and cutting volume. Making the cut and maintaining a good separation largely depends on maintaining the specified pressure drop.

Then, the control of the pump becomes critical to maintaining this pressure. As variable frequency drives (also called inverters, VFDs or VSDs) become cheaper and more common in the industry, they are more and more frequently used in cyclone/separator feed applications Slurry pump.

In order to maintain the best performance at the separation point (cyclone/separator), it is recommended to control the pump speed through a VFD based on the feedback from the pressure sensor that measures the inlet pressure of the cyclone/separator.

It is understood that steady state is the goal of any continuous operation, but in practice, it is difficult to achieve it through variable product feeding and other non-steady state processes around the factory or factory. Operating the pump in this manner may cause an imbalance in the tank level because the pump speed will change to achieve a single pressure set point at the cyclone/separator. But this can be designed around sufficient make-up water at the pump sump.

When the process medium delivered to the sump is lower than the design parameters, product dilution may occur in the sump, but the unit operation—centrifuging the heavier and lighter media at the cyclone or separator—will remain at Design point.

Generally speaking, if the centrifugal pump feeds the cyclone separator or separator, the control point of the system should be centered on the performance of the cyclone separator. The performance of the pump must be maintained by ensuring that a sufficient and constant flow is provided to the pump through the hopper.

Nevertheless, if the liquid level control of the feed hopper controls the pump speed, thereby controlling the flow and head (pressure) of the cyclone separator, the cyclone performance may be affected.

If the performance of the cyclone is affected, first confirm that no foreign matter enters the pump, pipe or the cyclone itself. After confirming the mechanical integrity of all equipment in the system, please contact the pump manufacturer to provide all information related to your system, including:

• Pump model • Speed ​​(or pulley size and motor nameplate speed) • Installed motor power • Pump outlet and working point cyclone header pressure • Motor ampere consumption at working point • (if present) VFD operation plan (input / Output)

Armed with this information, the pump manufacturer should be able to help diagnose and resolve cyclone separator performance issues, which may require additional dialogue with the cyclone separator manufacturer.

Almost all applications using heavy-duty centrifugal slurry pumps can achieve stable and reliable cyclone/separator performance. With the correct data, operators can get the performance they want from their system and hopefully ensure higher reliability of all related equipment.

Will Pierce is the vice president of engineering for Schurco Slurry.

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