Lease Automatic
Custody Transfer
LACT Units
LACT Units
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Requirements of a LACT unit
– Control operation of the system
– Accurately measure the quantity transferred
– Monitor the crude oil quality and prevent transfer of
non-merchantable oil
– Obtain a representative sample
– Provide facilities for periodic proving
LACT Units
 Control Functions of a LACT unit
– Detects level in the lease tank and starts and stops the
pump which forces oil through the LACT unit
– Shuts down flow if rate is out of the desired range for
accurate meter operation
– Shuts down flow once the maximum allowable oil has
been transferred
– Operates the solenoid which extracts a sample
proportional to flow
– Diverts flow back to the tank when S&W content is too
high
– Actuate alarms as required
LACT Units
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Components of a LACT unit
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Charge/Transfer Pump
S&W Monitor
Diverter Valve
Strainer/Air Eliminator
Sample System
Flow Meter
Meter Prover Loop
Back Pressure Valve
Check Valve
Control Panel
LACT Units
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Typical LACT configuration
LACT Units
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Why Coriolis Meters?
– Multi-variable Measurement
• Mass, Volume, Density, Temperature  Reduces cost of ownership
– Non-intrusive measurement
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Displaces mechanical meters
• No moving parts
• Measures slurries nor damaged by slugs of air
• No straight pipe runs required
– Maintenance
• No mechanical parts to wear
• Reduced calibration
– Accuracy
• High turndown ratio
• Better than 0.15% accuracy on volume flow
LACT Units
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Charge/Transfer Pump
– The pump should produce a non-pulsating flow for the
LACT unit at a pressure compatible with the pipeline
carrier
– Centrifugal pumps are typically used for LACT units
requiring medium to high volumes at low pressure.
• If high discharge pressure is required, a positive displacement
pump can act as a booster pump.
– Flow rate, pressure required and fluid properties
determine the size of the pump.
LACT Units

S&W Probe
– S & W probes determine free water and sediment
content in crude oil by typically measuring the
dielectric constant which is the ability of the fluid to act
as an insulator.
– The dielectric constant of oil is higher than that of
water.
LACT Units
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S&W Monitor
– Solid state circuitry detects changes in the
dielectric constant with sensitivity that can
detect 0.1% of 1%S&W content.
– An adjustable time delay and fail-safe relays
operate the divert valve over a selectable
setting of 0-3% S&W.
– The monitor diverts flow back to a retreating
facility and returns the LACT to normal
operation as determined by the allowable
S&W setting.
LACT Units

Divert Valve
– Divert valves have the
primary function to fail
closed when any of the
following occurs:
• Excess S&W
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Loss of power
Loss of supply pressure
Low level in the lease tank
Meter failure condition
LACT Units
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Strainer
– Strainers are installed
upstream of the flowmeter to
protect the meter and the
other elements of the4
system from being damaged
by foreign materials such as
pipe scale, pebbles, and
large debris that may be
entrained.
LACT Units

Air Eliminator
– Why use an air
eliminator?
• Large amounts of free air
compromises meter
accuracy and can lead to
overspeeding of mechanical
type meters.
• To insure accurate liquid
measurement, it is
necessary to remove all
vapor and free all entrained
air from the system.
LACT Units

Deaerator
– Float operated valve principle
– High capacity air elimination
– Vertical tank facilitates installation
– Wide variety of materials and
pressure ratings
– Various venting and connection
applications
– Low maintenance
LACT Units
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Sample System
– The components which
make up a typical system
include
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Static mixer
Sample probe
Extraction device
Sample Receiver/Mixer
LACT Units
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Static Mixer
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The optional static mixer is
installed upstream of the
sample probe.
Rigid elements split,
rearrange, and recombine
component streams into
smaller and smaller layers
until one homogeneous
stream exits.
LACT Units
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Sample Probe
– The sample probe extends into the center third of the
pipe facing the flow.
– The sample probe is installed in a horizontal position
in a vertical run of pipe.
– The extraction device is pulsed by the meter to extract
a fixed quantity of sample during normal operation of
the LACT unit.
LACT Units

Sample Receiver
– The sample container is sized to allow adequate
storage during the total transfer period.
– The fluid is stored under pressure and the container
is vapor tight to prevent evaporation.
– The fluid is tested at the end of the period to
determine the quality for custody transfer/net
volume calculations.
LACT Units

Centrifuge Tube
– Centrifuge tubes hold the
sample and the appropriate
solvent or demulsifier if
necessary.
– The tube is heated to a
specified temperature and
rotated in a centrifuge for a
specific amount of time at a
specific speed. The S&W is
forced to the bottom of the
tube where the amount is read
on the scale.
LACT Units

Hydrometer
– Hydrometers are utilized to
prove the output of a
densitometer or to obtain the
gravity of a sample.
 Accurate temperature
measurement is important.
 If light ends escape from your
sample, your hydrometer
reading will not match your
densitometer reading.
LACT Units
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Temperature Averager
– Temperature averagers
provide a true average of
the process temperature
based on volume or time.
– Average temperature is
utilized for calculation of
net volume during a batch
cycle, such as the end of
the month.
LACT Units
 The LACT Controller
provides:
– Local totalization
– High speed pulse output for
proving
– Two scaled pulse outputs
for remote monitoring and
pacing of the sample
system
– Three analog outputs for
flow rate, temperature and
density
LACT Units

Meter Proving Loop
LACT Units
Back Pressure Valve
The
purpose of the back
pressure valve is to maintain a
constant pressure on the
flowmeter to prevent cavitation
and to control flow rate if a
centrifugal pump is used.
The
back pressure setting
should always be above the
vapor pressure of the fluid.
LACT Units