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All
Flowmeter Studies
Articles
on Optical Flow Metering
Optical
flow metering is an emerging technology for natural gas and flare
measurement. It uses optical laser technology to measure the actual speed
of particles rather than the speed of sound through a medium (as in
ultrasonic flowmeters) and conductivity
(as in mass thermal flowmeters).
Commercial
instruments are essentially optical transit time velocity meters, which rely
on optical scintillation technology. They measure the speed of particles
that accompany natural and industrial gases flow through a flare pipe. As
they pass through a laser beam, these particles cause laser light to
scatter and generate a pulse signal. The speed of the particles is
determined by measuring the time between signals from the known distance
between two photodetectors.
Optical
flowmeter (OFM) companies claim their technology offers unmatched
effectiveness for flare measurement.
This is good news for the environment and the oil & gas
industry, which sees potential profits go out the pipe every year. The
amount of flared gas in 2006 was valued around $40 billion, up 14% from
2004, according to a World Bank-financed study. Flaring dropped
significantly in Norway and Canada, which have developed flare metering
initiatives.
Optical
flowmeters are designed for flare and biogas applications with highly
variable flow rates and a wide range of pipe diameters, including
smokestacks, ducts, vents, and other confined spaces.
Global construction of pipelines is expected to place a high demand
worldwide as China begins a rapid program of gas pipeline infrastructure
construction.
Photon
Control, a leader in the field, is also developing a line of optical flow
meters to measure flow rates of gases and clear liquids in process control
and custody transfer applications. This market worldwide is estimated at 7
billion dollars per year and growing. Optical
Scientific Inc. is also a leader in optical flow.
Advantages
of optical flowmeters vs. ultrasonic flowmeters:
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Better
turndown ratio, even under less-than-ideal environmental conditions
– 1000:1 for OFM vs. 5000:1 for ultrasonic
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Measures
any process temperature, while conventional ultrasonic meters cannot
measure flare gases above 150o
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Accuracy
and performance unaffected by pipe vibration and acoustic noise
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Direct
measurement of the particle speed, rather than the speed of sound
through a material, so measurement is less affected by variable flow
conditions
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Single
installation point for simplicity of installation and maintenance
Advantages
of optical flowmeters vs. thermal mass flowmeters
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More
accurate data because measurement is independent of the gas
composition. (With thermal mass meters measure the flare gas thermal
conductivity, accuracy can be poor in flares that contain a mixture of
gases, flares with unknown moisture or CO2 content and flares that
have been contaminated by other substances
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Inherently
more resistant to contamination and fouling
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Outward
error signaling makes sure problems are immediately detected
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