Continuous Sulphur Dioxide Stack Monitoring
The continuous sulphur dioxide (SO2) stack monitoring system devised by Ed Adams,
Robin Rankine, Edward Hardy and Joseph Lukacs utilized spectroscopic technology employed by astronomers, and
direct recording by computers, to provide a continuous record of SO2 emissions from oil and natural
The monitoring system was a significant improvement over the old procedure, which involved
sending a technician up a smokestack to record the emission levels from an emissions detection station. That
particular system was prone to erroneous emissions reporting, and as government air quality standards became
more rigorous during the late 1960s, there was a need for another continuous monitoring system.
The detection apparatus was mounted on the refinery or plant stack, and used a tube and
thermocouple array to sample the stack emissions, while a Pitot tube (one tube set perpendicular to the flow,
the other set parallel) measured stack flow rates. The SO2 analyzer had a light source at one end,
with a photo multiplier at the other end.
As the light from the sample passed the spectroscope, it would give off light with the
characteristic absorption spectrum of SO2. The absorption spectrum helped measure the concentration
of sulphur dioxide in the plant, and these measurements were then fed to a computer processor to generate
continuous emission records.
The direct benefit of the continuous stack monitoring allows plant operators to monitor
SO2 emissions that comply with air quality regulations. Plant operators could also use the stack
monitoring system to track and improve their process efficiency, since the quantity and concentration of
SO2 gas released could indicate production problems or equipment malfunctions.
The continuous stack monitoring system was initially deployed in oil and sour gas refineries.
It has since been adapted for use in coal-fired generating stations and pulp and paper mills.
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