SpectraSensors Provides Tunable Diode Laser An Increasingly Vital Process Tool

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Fast and dependable, a variety of laser-based analyzers can help petrochemical and energy producers avoid problems that can corrupt processes and product quality.

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The ability to detect and measure the presence of moisture and problematic compounds in gas streams has become increasingly vital to the protection of process integrity, plant safety, the avoidance of pollution and preservation of plant infrastructure assets in refineries and chemical processing industries. Among the most significant of the technologies to advance such detection and measurement is the tunable diode laser (TDL) - based absorption spectroscopy gas analyzers.

This is an optical system that uses a laser to produce a specific wavelength of light tuned to an absorption line, the known light frequency of the "target" gases. The laser light stimulates vibrations and rotation in the molecule, resulting in energy absorption, thereby enabling the sensing of water vapor and other gasses. Gas concentration is calculated by measuring the difference in the amount of light received for each wavelength via the tunable diode laser (TDL) analyzer's built-in detector.

Categorically, the tunable diode laser (TDL) analyzer is a photometer. And while other types of photometers (e.g. infrared and ultraviolet) are used to detect contaminants in gas streams, they are generally considered less precise in measuring absorption bandwidth than TDL-based technology.

Essentially, there are two popular tunable diode laser (TDL) analyzer system designs in use: the "open path" type and the "extractive" type. Both systems use similar principles, however they vary significantly in applications.

Due to its condensed design, the extractive TDL analyzer offers several advantages. It is small enough to permit convenient installation virtually anywhere in a plant. The long optical path of the cell enables highly sensitive measurements of trace gases in small volumes. Because it is operating outside the stream being measured, the extractive TDL is not subjected to particulate matter flowing in the stream.

The development of today's extractive tunable diode laser (TDL) is the culmination of sophisticated research by NASA's Jet Propulsion Laboratory for use on Mars. This development has resulted in a spin-off company, SpectraSensors, Inc., which has fostered diverse applications ranging from atmospheric research to widening use by the refinery and chemical industries.

In the natural gas industry the SpectraSensors design has virtually become the industry standard in recent years. This industry is particularly concerned about the presence of moisture along with H2S and CO2 in pipeline systems. Not only are producers, transporters and users concerned about the presence of those contaminants in terms of natural gas tariffs, but they must also guard against the gathering of moisture into "slugs" that can destroy a million-dollar natural gas-powered turbine in seconds.

The use of TDL technology makes it possible to greatly alleviate the problems of using older probe technologies. Both open path and extractive configurations provide fast, accurate response with low maintenance. The advantage of the open path TDL system is the ability to monitor environmental pollutants combustion products in-situ at percent levels. The advantage of the extractive tunable diode laser (TDL) is its ability to measure trace levels for process control where fast response enables control not previously possible.

For information contact: Sam Miller, SpectraSensors, Inc., 11027 Arrow Route, Rancho Cucamonga, CA 91730; Email- smiller @ spectrasensors.com; Phone (909) 948-4106 / (800) 619-2861; Fax: (909) 948-4142; or visit the web site: http://www.spectrasensors.com

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HEATHER METCALFE

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