23-08-2012, 03:59 PM
Multi-interface Level Sensors and New Development in Monitoring and Control of Oil Separators
[attachment=32540]
Abstract:
In the oil industry, huge saving may be made if suitable multi-interface level
measurement systems are employed for effectively monitoring crude oil separators and
efficient control of their operation. A number of techniques, e.g. externally mounted
displacers, differential pressure transmitters and capacitance rod devices, have been
developed to measure the separation process with gas, oil, water and other components.
Because of the unavailability of suitable multi-interface level measurement systems, oil
separators are currently operated by the trial-and-error approach. In this paper some
conventional techniques, which have been used for level measurement in industry, and new
development are discussed.
Keywords: Level sensor, multi-interface measurement, electrical capacitance tomography
(ECT).
Sensors 2006, 6 381
Introduction
Measurement of liquid level in storage and processing vessels, tanks, wells, reservoirs and hoppers
is commonly needed. There is a great diversity of situations, which require level measurement, ranging
from pure water to viscous, sticky and corrosive fluids. The environment for level sensors varies from
vacuum to high pressure and from below zero Celsius degree to high temperature. Because of the
involvement of different situations, many types of level sensors have been developed.
Nowadays, the control strategies in use with crude oil separators are simple due to the difficulties in
finding suitable multi-interface level measurement systems. Accurate measurement of multi-interface
levels in crude oil separators is regarded as a challenge for hydrocarbon processing. A number of
different methods have been developed, e.g. externally mounted displacers, differential pressure
transmitters, ultrasonic transducers, single-electrode and multi-electrode capacitance sensors. The
methods used in the oil industry for measuring the interfaces in crude oil separators are limited because
of the request on high reliability, variety of fluids, harsh environments and intrinsic safety issues. It is
particularly important for the offshore oil companies to deal with this problem because crude oil from
undersea contains a huge amount of water, which should be separated on site to avoid the additional
transportation cost. Therefore, it is necessary to investigate suitable sensors for an accurate and reliable
measurement of different interface levels.
A crude oil separator (see Figure 1) normally contains gas, oil, water, emulsion and sludge. Due to
the limited space in an offshore platform, effective monitoring and efficient control of crude oil
separators would result in huge savings to the oil companies and reduce environmental pollution.
Some other applications of multi-interface level measurement systems are petrol/kerosene storage
tanks in petrol stations and fuel storage tanks in airports. For these applications an ideal multi-interface
level measurement system should have the following characteristics:
(1) Accurately locating interfaces between different materials, e.g. gas-oil, oil-emulsion and
emulsion-water,
(2) Low maintenance cost,
(3) Self-cleaning,
(4) Intrinsically safe.
Figure 1. Conventional oil separator.
Sensors 2006, 6 382
Level measurement techniques
The operation of an oil separator relies on the measurement of interfaces between different
materials. If a conventional capacitance level sensor with only a single-electrode is used, two main
problems are encountered: (1) Temperature compensation is required because the capacitance
measurement is greatly affected by temperature, and (2) it is unable to measure more than one
interface. Research has been carried out to investigate multi-interface level measurement systems.
Externally mounted displacers
Externally mounted displacers are commonly used for the interface level measurement [1]. This
technique makes use of the difference in densities between two types of liquid being measured, e.g. oil
and water. A displacer used for oil/water interface measurement must have a density between the
densities of oil and water.
As the interface moves up and down in a separator, the position of displacer is mechanically
transferred to a read-out system (see Figure 2). Using two different displacers with different densities,
both the oil/gas and water/oil interfaces can be measured. However, the presence of an emulsion layer
will disturb the measurement and also the foam thickness cannot be measured by this technique.
[attachment=32540]
Abstract:
In the oil industry, huge saving may be made if suitable multi-interface level
measurement systems are employed for effectively monitoring crude oil separators and
efficient control of their operation. A number of techniques, e.g. externally mounted
displacers, differential pressure transmitters and capacitance rod devices, have been
developed to measure the separation process with gas, oil, water and other components.
Because of the unavailability of suitable multi-interface level measurement systems, oil
separators are currently operated by the trial-and-error approach. In this paper some
conventional techniques, which have been used for level measurement in industry, and new
development are discussed.
Keywords: Level sensor, multi-interface measurement, electrical capacitance tomography
(ECT).
Sensors 2006, 6 381
Introduction
Measurement of liquid level in storage and processing vessels, tanks, wells, reservoirs and hoppers
is commonly needed. There is a great diversity of situations, which require level measurement, ranging
from pure water to viscous, sticky and corrosive fluids. The environment for level sensors varies from
vacuum to high pressure and from below zero Celsius degree to high temperature. Because of the
involvement of different situations, many types of level sensors have been developed.
Nowadays, the control strategies in use with crude oil separators are simple due to the difficulties in
finding suitable multi-interface level measurement systems. Accurate measurement of multi-interface
levels in crude oil separators is regarded as a challenge for hydrocarbon processing. A number of
different methods have been developed, e.g. externally mounted displacers, differential pressure
transmitters, ultrasonic transducers, single-electrode and multi-electrode capacitance sensors. The
methods used in the oil industry for measuring the interfaces in crude oil separators are limited because
of the request on high reliability, variety of fluids, harsh environments and intrinsic safety issues. It is
particularly important for the offshore oil companies to deal with this problem because crude oil from
undersea contains a huge amount of water, which should be separated on site to avoid the additional
transportation cost. Therefore, it is necessary to investigate suitable sensors for an accurate and reliable
measurement of different interface levels.
A crude oil separator (see Figure 1) normally contains gas, oil, water, emulsion and sludge. Due to
the limited space in an offshore platform, effective monitoring and efficient control of crude oil
separators would result in huge savings to the oil companies and reduce environmental pollution.
Some other applications of multi-interface level measurement systems are petrol/kerosene storage
tanks in petrol stations and fuel storage tanks in airports. For these applications an ideal multi-interface
level measurement system should have the following characteristics:
(1) Accurately locating interfaces between different materials, e.g. gas-oil, oil-emulsion and
emulsion-water,
(2) Low maintenance cost,
(3) Self-cleaning,
(4) Intrinsically safe.
Figure 1. Conventional oil separator.
Sensors 2006, 6 382
Level measurement techniques
The operation of an oil separator relies on the measurement of interfaces between different
materials. If a conventional capacitance level sensor with only a single-electrode is used, two main
problems are encountered: (1) Temperature compensation is required because the capacitance
measurement is greatly affected by temperature, and (2) it is unable to measure more than one
interface. Research has been carried out to investigate multi-interface level measurement systems.
Externally mounted displacers
Externally mounted displacers are commonly used for the interface level measurement [1]. This
technique makes use of the difference in densities between two types of liquid being measured, e.g. oil
and water. A displacer used for oil/water interface measurement must have a density between the
densities of oil and water.
As the interface moves up and down in a separator, the position of displacer is mechanically
transferred to a read-out system (see Figure 2). Using two different displacers with different densities,
both the oil/gas and water/oil interfaces can be measured. However, the presence of an emulsion layer
will disturb the measurement and also the foam thickness cannot be measured by this technique.