Air Quality Monitor
Increasingly stringent government regulations for control
of the environment require industrial firms to install increasingly
sophisticated monitoring equipment for full compliance with smokestack
emission standards. One such advanced system is the Stak-Tracker
(Stak-Tracker is a trademark of General Electric Company) CEM
(Continuous Emission Monitor) Gas Analyzer, an air quality monitor
capable of separating the various gases in a bulk exhaust stream
and determining the amounts of individual gases present within
the stream.
A pair of industrial smokestacks equipped with GE Reuter-Stokes
Stak-Tracker gas analyzers; the Stak-Tracker equipment is shown
in closeup (below).
The Stak-Tracker is produced by GE Reuter-Stokes, Twinsburg,
Ohio, a subsidiary of General Electric Company, and is supported
by the GE Corporate Research & Development Center (GE CR&D),
Schenectady, New York. An important element of the Stak-Tracker
is a NASA-developed software package that made possible the system's
advanced analytical technique. This technique is the key to accurate
measurement of minute quantities of certain gases, such as nitric
oxide, carbon monoxide and sulphur dioxide, generated in new,
low-emission combustors.
Developed by Langley Research Center, the method of analysis
is a gas filter correlation technique; it measures the concentration
of an individual target gas within the bulk stream by determining
the degree to which molecules of that gas absorb an infrared
beam.
The Stak-Tracker directs an infrared beam across a smokestack
exhaust to a reflector and collects the reflected beam. The instrument
sends the beam through a dual filter assembly. The first filter
operates in the general wavelength range of the target gas. The
other filter, which oscillates in and out of the infrared beam,
is the target gas cell. When the cell filter is in the beam,
the beam is absorbed by the cell at the target gas' specific
wavelength before it goes through the smokestack exhaust. A detector
measures the ratio of the two signals, which serves as the basic
input that enables the patented analysis technique to provide
a measurement of the target gas concentration. The Stak-Tracker
can measure up to six gas components within three seconds.
Offering highly accurate measurements of pollutants for improved
compliance with environmental regulations, the system incorporates
software technology that originated at Langley Research Center.
In the early 1990s, when the GE CR&D was helping GE Reuter-Stokes
develop the system, it became apparent that there were no commercially-available
software tools for modeling the performance of sensitive pollution
monitors of this type. The developers, however, were aware that
Langley Research Center had designed a software system for a
Gas Filter Correlation Radiometer (GFCR) that seemed the answer
to the need.
Two GE CR&D scientists-Dr. Emily Shu of the Industrial
Electronics Laboratory and Dr. M. K. Cueman of the Manufacturing
Technology Laboratory-visited Langley's Atmospheric Research
Division and received detailed information on the GFCR software,
which is capable of calculating gas absorption even when the
gas is present in minute amounts, and which additionally can
separate the interference from a number of coexisting gases in
a stream. The visit led to a GE-NASA Space Act Agreement for
exchange of technical information relative to trace gas measurement.
Langley scientists shared their expertise in atmospheric research
and helped GE apply the GFCR code. The GFCR software was incorporated
into the calibration of the Stak-Tracker, and the software has
found additional use at GE CR&D for evaluating changes in
the instrument's design and solving other industrial problems.
Besides its utility as an aid to full compliance with environmental
regulations, the Stak-Tracker offers fast response for process
control applications and relatively low installation and maintenance
costs. It is applicable to gas turbines, gas, oil, or coal-fired
boilers, incinerators, dryers, scrubber controls, kilns and process
heaters used by the power, oil, pulp and paper, iron and steel,
non-ferrous metals, cement, glass and other industries.
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