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Desander Hydrocyclones enable sand and solids to be efficiently and reliably
separated from produced water, condensate and/or gas streams. They have
proven to be a valuable part of many oil and gas production facilities by
providing:
- High efficiency solids removal
- A compact, small footprint
- Cost-effective protection
against erosion damage
- No moving parts, minimal
maintenance
- Highly consistent performance
Description
Desander Cyclones are static cyclone separators commonly used for continuous
sand and solids removal[KS1] from produced water, condensate
or gas streams. They are supplied either as single-liner units, or as
multiple-liner configurations inside vessels.
The cyclone liner size and type selected is dependent on the process fluid,
temperature, pressure and the concentration and type of solids present in the
liquid (water or oil) or gas stream.
Small Diameter (2”/50mm), High Efficiency Desander Cyclones are typically made
of ceramic materials to provide excellent erosion resistance. Larger units
may be specially lined with stainless steel to provide enhanced erosion
protection.
Operating
Principles
Desander Cyclones are pressure driven separators that require a pressure drop
across the unit to cause the solids to separate from the water. The inlet
stream (containing solids) enters the cyclone through a tangential Inlet
Section under pressure, where it is forced into a spiral motion by the
cyclone’s internal profile. The internal cone shape makes the spinning
accelerate, which generates high centrifugal forces, causing the denser
solids particles to move to the outer wall of the cyclone while the water/oil/gas
is displaced to the central core.
Solids continue to spiral down along the outer wall of the conical section
inside the cyclone to the outlet or underflow, where they exit. It is
typical to collect the solids in a closed underflow container or vessel, and
periodically dump these solids.
De-sanded water/oil/gas in the central core section reverses direction and is
forced out through the central Vortex Finder at the top of the cyclone, which
serves as the overflow.
  Schematic of a Desander Vessel
Technical
Factors involved in the selection of a Desander Cyclone:
- Desired particle size removal
(in micron)
- Temperature/Viscosity of the water/liquid
- Liquid density
- Solids density
- Volume to be treated
- Available pressure/pressure
drop to drive the cyclone
Particle Size Removal
The rule in selecting a Desander Cyclone size is that smaller cyclones remove
smaller particles. This is illustrated in the Cyclone Sizing graph below.
This
graph shows how the removal of solids of a specific particle size determines
the size (diameter) of the cyclone required to result in ~98% removal of
particles that size and larger. This size is designated as the “D98.”
Temperature/Viscosity
The temperature of the water/liquids is very important. A higher temperature
reduces liquid viscosity, which improves separation by reducing the drag
forces on the particles.
Liquid Density
Water density is ~1.0, although it varies slightly according to temperature,
salt concentrations, etc. Oil can vary from 0.6 - 0.99 S.G.
Solids Density
The solids density seen in production fluids typical has a density of ~2.2 -
2.65 S.G. This density directly effects separation potential as higher
density solids are more easily separated. There can be a range of different
types of solids with a range of densities, although there is typically one
major component.
Pressure drop
Cyclones can be installed to operate at any pressure. They use pressure as
the energy for separation. The pressure drop (across the cyclone) required
for solids removal is 15 – 70 psi. (1.0 – 4.8 Bar). This range provides optimal
performance while also minimising erosion and pressure loss.
The following graph depicts water capacity for cyclone diameter:
Product
Range
Process Group provides a range of cyclone sizes to suit the requirements of
common applications, which usually require one of two options:
- FINE particle separation:
removes solids down to ~ 10-20 micron (1”-2”/25-50 mm diameter).
- COARSE solids separation:
removes solids >50 micron (4”-30”/100-750 mm diameter).
Applications
- Removal of abrasive solids
from process piping to minimise maintenance on pumps, control valves and
other process equipment.
- Sand removal from process to
minimise Separator sand build-up, to improve Separator efficiency (more
residence time), and to reduce or eliminate shut down maintenance to
remove sand, etc.
- Solids removal for water re-injection
to prevent formation blockage and damage to pumps.
- Removal heavy metals from
process liquids (condensate and/or water) to comply with environmental
or sales requirements.
Desander
Cyclone Installation
The photo below shows a Vessel (with 50 mm Ceramic Cyclones), and a Solids
Accumulator Vessel.
The Solids Accumulator vessel (underneath) is useful at pressures >100
psi/7 Bar, as it allows safe dumping of solids to the atmosphere. The
Accumulator Vessel can be isolated from the Desander Vessel, and remains on
line and continues to collect solids, when the Accumulator Vessel is isolated
for solids emptying. This affords continuous solids collection and the
periodic dumping of solids without ever having to shut the Desander system
down.
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