A desander is a vital component of the mining and drilling process. Desander is a solid control device with a series of hydro cyclones that separates sand and silt from the rig’s drilling fluid. The desander is fixed at the top of the sludge tank, just after the shale shaker and the degasser, and before the desilter. As they are usually installed at the wellhead in the oil and gas field, they are also known as wellhead desander. Wellhead desanders are produced in both ASME and API design ratings as per requirement.
Desanders are basically solid control devices. Cyclonic desander and desilters use a centrifugal force to separate solids from liquids. There are no rotating components. Centrifugal force is created by turning the head of a centrifugal pump into a high-speed rotating flow inside a cone.
Solids are concentrated near the cone wall in proportion to their mass and exit as underflow at the bottom of the cone. Clean liquids and fine solids return from the overflow at the top of the cone.
Demineralization and sand removal hydro-cyclones are simple mechanical devices with no moving parts, but they facilitate the solids sedimentation process. Drilling mud laden with solids is drawn into the body of the hydro-cyclone and the iatrogenic force of the flow separates the heavy solids from the lighter solids. The heavier solids are discharged at the lowest point (underflow) of the hydro-cyclone and the lighter solids at the highest point (overflow). Solids removal is dependent on feed particle size, liquid concentration, liquid feed pressure (as a function of liquid density), and hydro-cyclone size.
Desanders remove abrasive solids from drilling fluids that vibrators can’t remove. In general, the diameter of the solids separated by the desander is 45 µm to 74 µm and the diameter of the decanter is 15 µm to 44 µm.
Working of Desander
When the drilling fluid reaches the dead grinder, it enters through a pressurized pipe and hits the dead grinder cone first. The way this cone turns the liquid is similar to the flow of water in a sink, except the walls of the desander cone are porous to filter out sand particles.
Desanders have no moving parts and particle removal is accomplished solely by gravity and pressure. Desanders are generally not large tools, about the size of a bathtub for small jobs, and rarely larger than the average car. When the liquid reaches the small end of the cone, it is pushed out of the tube and proceeds to the next step in the purification process.
This type of work is commonly used in the oil industry. Desander is also used in other industries, primarily related to the drilling and extraction of materials such as natural gas. Companies that manage lakes and dams can use desalters and desilters to keep water flowing and remove contaminants.
Types of Desanders
- Desander of simple cycloning: These are good for sandy or slightly sandy soils. After the sludge has passed through a screening stage to remove oversize, it is fed to a cyclone separator.
- Desander of double cycloning: Similar to a single cyclone, with the difference that the sludge pass twice through the cyclone so as to separate the finest sand and silt even.
Feature of Desanders
- Cyclonic desanders and decanters have no moving parts and are extremely reliable solids removal devices when properly operated and maintained.
- Customized cone configurations.
- The material of the hydrocyclone is polyurethane, which makes it lightweight and durable.
- Victaulic clamp connects indoor and outdoor cables for easy removal.
- Skids mounted with ring bolts welded to the frame.
Selection of Desanders
The parameters that must be looked upon while selecting a desander for the specific application are:
- The Crude oil quality.
- External pipe outer diameter and the working pressure of the pipeline.
- Efficiency and accuracy of Separation.
- Operating parameters.
- Desander size requirements
- Wear resistance and anti-aging properties.
- Service life.
Advantages of Desanders
Hydrocyclones for desanders and demineralizers in drilling are used to remove sand and silt particles from drilling fluids that have passed through oil and gas vibrating screens. The main advantages of installing a desander are:
- Preventing solid build-up in equipment and pipelines.
- Elimination of fine chips
- Large capacity with a relatively simple structure
- No rotating parts
- Easy to use
- Low downtime and maintenance
- Protecting downstream equipment from wear and damage
