Hydrocyclones for Solids Control: Desander vs. Desilter and How to Choose

 

Hydrocyclones for Desander, Desilter and How to Choose

Sand and drilled solids can quickly build up in a drilling fluid system if they are not removed at the right stage. Coarse sand is usually handled by a desander, while finer drilled solids may need a desilter further downstream.

Both machines use hydrocyclones, but they are designed for different parts of the solids load. Desanders normally use larger cones for coarse solids, while desilters use smaller cones for finer solids.

When selecting hydrocyclones for solids control, the practical questions are simple: What solids need to be removed? How much mud needs to be processed? What are the mud conditions, and what pressure is available at the cyclone inlet?

Hydrocyclones for Solids Control

The Difference Starts With the Solids

A desander is generally installed downstream of the shale shaker. The shaker removes the larger cuttings first, and the desander takes out sand-sized material that remains in the mud.

A desilter works further down the solids-size range. It is normally used after desanding when finer drilled solids are still present.

	Desander	Desilter
Main target	Coarse sand-sized solids	Fine drilled solids
Typical cyclone size	8–12 in.	3–5 in.
Common cyclone	8 in. / 10 in.	4 in.

Four-inch cones are common in desilters because smaller hydrocyclones are suited to finer separation. Larger 8-inch or 10-inch cones are commonly used for desanding and can handle more flow per cone.

These sizes are typical rather than fixed requirements. The right configuration depends on the cyclone design, operating conditions, and drilling fluid.

Why Desanders Use Larger Cones

Hydrocyclone diameter affects both capacity and separation.

Larger hydrocyclones generally handle more mud per cone and are used for coarser solids. Smaller cones handle less flow but are better suited to finer separation.

That is why desanders and desilters are built around different cyclone sizes rather than simply using the same cone throughout the mud system.

Feed pressure also matters. The pressure creates the swirling flow inside the cyclone, while mud density, viscosity and solids concentration can affect how the separation works.

A cyclone should therefore not be selected from its diameter alone. Its rated capacity needs to match the actual mud system and operating conditions.

Start With Flow Rate, Then Look at the Solids

Flow rate gives you the first indication of how many cones are needed.

As a simple sizing example, assume a drilling system handles 120 m³/h and one 4-inch hydrocyclone is rated at about 15 m³/h per cone under the specified operating conditions.

The basic calculation is:

120 ÷ 15 = 8 operating cones

This gives the starting number of operating cones. If the system needs to remain in service during maintenance, additional cone capacity may be included so one cone can be isolated without stopping the entire unit.

The final quantity should be based on the manufacturer's rated capacity and the actual operating conditions.

Once the required capacity is clear, look at the solids you need to remove. Coarse sand normally points toward a desander. If the coarse fraction has already been removed but finer drilled solids continue to accumulate, a desilter is more appropriate.

The Mud Matters Too

A hydrocyclone does not operate under the same conditions on every drilling site.

Mud density, viscosity and solids concentration can change as the formation and drilling conditions change. A heavily loaded or more viscous mud may therefore behave differently from a cleaner fluid at the same flow rate.

This is one reason two systems with the same flow rate may not require exactly the same cyclone configuration.

The equipment upstream matters as well. If large cuttings reach the hydrocyclone stage, they add unnecessary solids loading and can increase wear. The shale shaker should remove the larger cuttings before the mud reaches the hydrocyclones.

TR Shale Shaker

Feed pressure is another practical point to check. The pressure shown on the pump nameplate is not necessarily the pressure available at the hydrocyclone inlet. Pipe friction, valves, elevation changes and other restrictions can reduce it before the mud reaches the cyclone manifold.

For a new system, the feed pump, piping and hydrocyclone manifold should be considered together.

When One Separation Stage Isn't Enough

Some drilling systems need to control both coarse sand and finer drilled solids.

A mud cleaner combines desander and desilter hydrocyclones with an underflow vibrating screen. The hydrocyclones separate the solids from the drilling fluid, and the screen then recovers part of the drilling fluid from the cyclone underflow before the solids are discharged.

This can be useful when drilling-fluid loss is a concern. Instead of sending the entire cyclone underflow directly to waste, the screen provides another separation step.

The choice is therefore fairly practical:

Coarse sand → Desander

Fine drilled solids → Desilter

Both, with underflow screening → Mud Cleaner

TR Mud Cleaner

What Should You Check Before Ordering?

Before asking for a quotation, have the following information ready:

• Normal and maximum mud flow rate
• Target solids size
• Mud density and viscosity
• Solids concentration
• Available cyclone inlet pressure

Particle-size data is useful if it is available. It can show whether the main problem is coarse sand, fine drilled solids or a wider range of solids.

The existing solids control layout also matters. The hydrocyclone stage needs to work with the shale shaker, feed pump, piping and downstream equipment already in the system.

This information gives the supplier a much better basis for selecting the cyclone size and quantity than flow rate alone.

How TR Configures the Equipment

TR Solids Control manufactures desanders, desilters and mud cleaners for drilling fluid solids control, with cyclone configurations selected according to flow rate and the required separation stage.

Cyclone size and quantity are matched to the required capacity. Depending on the application, polyurethane or high-chrome cast iron hydrocyclones can be used. Individual isolation valves can also be included so a single cone can be taken out of service for inspection or replacement while the other cones remain in operation.

For example, a fine-solids application around 120 m³/h may use several 4-inch hydrocyclones. A system focused on coarse sand would normally use larger cones. Where both stages are required, the hydrocyclones can be integrated into a mud cleaner with an underflow screen.

Desander and desilter used in HDD Mud Recycling System

Questions About Desanders and Desilters

What is the difference between a desander and a desilter?

A desander uses larger hydrocyclones for coarse sand-sized solids. A desilter uses smaller cones for finer drilled solids.

What hydrocyclone size is common for desilting?

Four-inch hydrocyclones are widely used for drilling mud desilting. The number of cones depends on the required flow and operating conditions.

Can a desander and desilter be used together?

Yes. A mud cleaner combines both hydrocyclone stages with an underflow vibrating screen.

Which One Should You Choose?

Choose a desander when coarse sand-sized solids are the main concern.

Choose a desilter when finer drilled solids remain after the desanding stage.

Choose a mud cleaner when both stages are required and the cyclone underflow needs additional liquid recovery.

Start with the flow rate and solids you need to remove, then check the mud properties and available cyclone inlet pressure before finalising the equipment.

For hydrocyclones for solids control, the actual drilling conditions should determine the configuration—not cyclone diameter or catalogue capacity alone.