UFC 3 -430-11
14 February 2001
When practical obtain the analyzer from the manufacturer completely
packaged in a housing, wired, piped and with the sample system installed. Specify the
analyzer to be free standing unless it is mounted on the equipment.
5-2.13.2 Oxygen Analyzer. Oxygen analyzers in a boiler plant are used for oxygen
measurement to provide an indication of excess air in the flue gas. Use the analyzer for
alarms and trim. Do not use it as the sole instrument for the control of combustion air.
Probe location is not critical for forced draft type or pressurized boilers since
leakage is flue gas out of the boiler. Probe location is critical, however, for balanced
draft boilers (which have induced draft fans), since leakage is typically tramp air into the
boiler from flue ductwork. Locate the oxygen probe so as to keep the effect of tramp air
on the oxygen reading at a minimum. This usually entails locating the probe as close to
the furnace as practical.
5-2.13.3 Combustibles Analyzer. Combustibles analyzers in a boiler plant are used
for carbon monoxide measurement, hydrogen measurement or both to provide an
indication of incomplete combustion in the flue gas. Use the analyzer for alarms and
trim. Do not use it as the sole instrument for the control of combustion air.
5-2.13.3.1
Carbon Monoxide Analyzer. Carbon monoxide (CO) analyzers used in a
boiler plant may utilize a catalytic element, wet electrochemical cell, or non-dispersive
infrared absorption.
Install the CO analyzer in a clean gas stream that is downstream of the
particulate removal system.
A CO analyzer permits firing at lower oxygen levels than without it. A
minimum air requirement is established by decreasing oxygen in the stack gas until a
large increase in the CO reading occurs. A CO analyzer is also useful in boiler start-
up. During start-up monitor the CO analyzer closely for unsafe firing conditions. Hi gh
CO readings indicate incomplete combustion, which implies potentially unsafe
conditions in the furnace.
5-2.13.3.2
on line monitors that employ a catalytic element.
Like the CO a nalyzer, a Hydrogen analyzer permits firing at lower oxygen
levels than without it. A minimum air requirement is established by decreasing oxygen
in the stack gas until a large increase in the H2 reading occurs. A H2 analyzer is also
useful in boiler start-up. During start-up monitor the H2 analyzer closely for unsafe firing
unsafe conditions in the furnace.
5-2.13.4 Stack Opacity Analyzer. Stack opacity analyzers are used in a boiler plant
to monitor particulate emissions. Their main use is in coal and heavy oil fired boilers.
Stack opacity monitors are generally not required for gas fired boilers, however, state
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