| The measuring of combustion gas temperature
via infrared radiation has never been as reliable as with
Heitronics' new KT19.69. KT19.69 measures infrared emissions
from hot gases in a very narrow spectral response, which
lies somewhere between 4 to 5 microns. This "proprietary"
spectral response was determined during extensive incinerator
trials. As of today, many installations have been made on
both incinerator and fossil fuel fired boilers.
Theory Background
All matter above zero Kelvin emits infrared radiation.
Solid matter, such as steel, bricks, etc. emit and reflect
infrared radiation. Solids such as glass can not only emit
and reflect infrared radiation but can also transmit. Hot
combustion gas reflects a negligible amount of infrared
radiation and leaves us to deal with emissions and transmission.
The infrared radiation pyrometer KT19.69 is a passive
device which receives infrared radiation from within its
optical field of view. It requires the width of the gas
stream to be great enough in dimension and in radiation
intensity to make the measurement. Consider the following:
If the human eye were to view a clean and clear glass
window pane, and if there were no surface light reflections,
we would not "see" the glass itself. Now imagine looking
at a 25 ft. thick glass object similar to a decorative glass
block window which contains irregularities on its surface
and within its mass. You will now see the glass and very
little of what is behind it.
KT19.69's proprietary narrow spectral band lies between
4 to 5 microns, the region of the infrared spectrum where
carbon monoxide and carbon dioxide give off significant
levels of radiation. Since the burning of all fossil fuels
and trash give off carbon monoxide and carbon dioxide, KT19.69
is an excellent choice for large scale boilers.
Because combustion gases are semi-transparent, KT19.69
receives infrared radiation from a "stacked-column" of gas
molecules oriented towards the center of the gas stream.
Hotter gases are proportionately favored more than cooler
gases which makes the "end" of the stacked column (the end
farthest from the pyrometer) favored more than the near
side. Another way to describe this is to say that at some
distance, there is an extinguished depth of penetration;
a point where the pyrometer can "see" no further.
The maximum penetration into a natural gas combustion
stream would be about 25 ft. and occurs when making the
minimum 600°F reading. The extinguished depth would
be less than 10 ft. when making 2200°F readings from
a coal fired burner. In general, higher temperatures and
greater concentrations of combustion by-products or particulates
in the gas stream will reduce the penetration of measurement
into the gas.
One of the key features offered by KT19.69's proprietary
spectral response is that it sees through the cooler gases
which skirt the boiler perimeter, thus placing the measurement
within the gas stream where temperatures are more representative
of the whole and in a region which is less prone to inherent
temperature fluctuations.
Hardware Summary
KT19.69 includes a water/dust proof housing capable of
being exposed to ambient temperatures from 32 to 300°F.
(Air or water cooling is required for ambients above 140°F.)
To facilitate mounting and to shed the ambient temperature
load, a unique hardware assembly has been created. A pipe
flange, sized from 3" or greater, is required to fix the
pyrometer assembly to the outside of the boiler. A non-porous
thermal insulation spacer and spacer tube reduces conductive
heat. A shield helps reduce radiant heat. The coolable housing
of KT19.69 is available to shed the balance of conductive
and radiant heat, as well as ambient convective heat or
sun loading. Requests for custom modification to the hardware
assembly are welcome.
A blast gate valve will serve to shut off near to 100%
of potential escaping gases while checking the pyrometer's
optics for cleanliness. A cover cap held by a stainless
steel chain, is available for covering the open assembly
when the pyrometer is removed, as an added level of safety.
An air purge fitting shall accept a suggested 5 to 10
psi instrument air to keep the built-in sapphire window
clean. The sapphire window serves to protect the pyrometer's
calcium fluoride lens from dirt and thermal shock should
hot gases back-up into the hardware assembly. A planned
maintenance schedule should include a check of the two optical
components at least on a monthly basis initially, and then
longer if normal operating conditions allow. During critical
boiler start-up conditions, it is suggested to check these
optical components before firing because a dirty window
or lens will produce a lower than actual reading.
KT19 Performance Features
KT19.69 is a highly stable and well featured pyrometer.
General specifications are given on the KT19 Series Brochure.
The KT19's long-term stability is better than 0.0001 of
the reading in Kelvins/month (e.g. better than 3°F per
year when making 2000°F readings).
The standard signal processing of incoming radiation effectively
averages the turbulent gas temperature radiation when setting
response time to 10 seconds. Thus the need for external
rolling average signal processing is not a requirement.
Actual field results when comparing KT19.69 readings with
thermocouples have shown ±18°F agreement when
making 1000°F measurements.
The reading that KT19.69 makes is available simultaneously
in three formats; 1) local display on its housing, 2) via
1 of the 4 selectable and span programmable analog outputs
like linear 4 to 20mA, 3) via RS232 or with an optional
external RS422 converter.
Benefits of using KT19.69
During boiler start-up, it is often desired to confirm
that there is steam flow through the boiler tubes before
exceeding a lower critical limit near 1000°F. This ability
may help prevent boiler tube fracture of temporarily non-flowing
tubes, provided a required operating procedure is followed.
When a utility boiler is on-line, the temperature reading
can be used to trim burners to help balance boiler temperature
and be used to reduce excessive fuel consumption when electric
demand reduces.
For incinerator applications, a minimum acceptable operating
temperature can be monitored for environmental requirements,
in addition to trimming burners.
When burning coal, an upper temperature limit can be monitored
to help reduce fusion related maintenance and down time. |
