COMBUSTION CONTROL IN
COAL AND GAS BOILERS
MOUNTING/INSTALLATION POSITIONS FOR COAL AND GAS FIRED BOILERS
O 2
SERVOTOUGH
Laser 3 Plus (TDL)
GAS
COMBUSTION
CO e
SERVOTOUGH
FluegasExact 2700
(Zirconia)
EMISSIONS
The biggest issue for coal boilers,
compared to gas-fired systems, is the
amount of dust produced. Coal dust can
obscure the beam in TDL analysis, and
SERVOTOUGH
FluegasExact 2700
KEY
COAL
CHALLENGES OF COAL
VS GAS BOILERS
SERVOTOUGH
FluegasExact 2700
O 2
O 2
CO
NH 3
SERVOTOUGH
Laser 3 Plus Ammonia
NH 3
SERVOTOUGH
FluegasExact 2700
SERVOTOUGH
FluegasExact 2700
O 2
SCR/SNCR
CO e
Low Very low
Speed of response Very fast Fast
Cross-interference None Limited to hydrocarbons/
high sulfur for COe versions
Maintenance Very low Low
Measurement principle Average across duct Spot measurement
Process temperature &
pressure External inputs required
for accurate measurement Independent
Measurement capability Single units required for
O 2 , CO & CO+CH 4 Combined O 2 & COe in
one unit
SERVOTOUGH
FluegasExact 2700
O 2
SERVOTOUGH
Laser 3 Plus Combustion
Installation Simple Simple
O 2
SERVOTOUGH
Laser 3 Plus Combustion
O 2
Laser 3 Plus Combustion
CO
Lifetime cost of ownership
SERVOTOUGH
FluegasExact 2700
SERVOTOUGH
O 2
ZIRCONIA
Laser 3 Plus Combustion
SERVOTOUGH
RADIANT
SECTION
These challenges make the placement of
the TDL and Zirconia analyzers key for
each type of boiler.
TDL
SERVOTOUGH
SAFETY
CO e
Temperatures can reach more than
1,000 o C in the radiant section and can fall
to less than 400 o C around the economizer,
affecting both analyzer types.
Emission levels of NOx are typically much
higher for coal-based boilers, due to the
nitrogen bound within the coal.
A COMPARISON OF TDL AND ZIRCONIA
TECHNOLOGIES FOR COMBUSTION CONTROL
CO e
Laser 3 Plus Ammonia
O 2
causes abrasion to the probe (for Zirconia
analyzers) or insertion tubes (for TDL).
ELECTROSTATIC
PRECIPITATION
(ESP)
GAS AIR
HEATER
CO+CH 4
CO
COAL ONLY
COMBUSTION CONTROL IN
COAL AND GAS BOILERS
In a coal-fired power plant, pre-heated
air and pulverized coal are fed to the
boiler where combustion takes place.
As combustion processes are by
nature variable and coal quality is
never consistent, variable amounts
of excess air are required to ensure
P08
complete combustion. Too much air,
and combustion efficiency will drop,
producing lower levels of CO but higher
levels of NOx toxic emission gases.
NOx emissions are also created at
higher temperatures as a by-product of
the combustion process where excess
nitrogen (N 2 ) in the air reacts with O 2 ,
as well as reacting with any elemental
nitrogen that may be resident in the fuel.
This temperature variation affects
the production of CO 2 , CO and NOx
differently, so by controlling the
combustion process the boiler efficiency
increases.
gas turbine
Recovering waste heat in a
e efficient
combined cycle is 50-75% mor
ors.
than using separate generat
BURNER MONITORING
Monitoring above the burners, in the
radiant section, can help detect any
burner issues. The correct product for this
challenging measurement will depend on
the fuel type, dust loading and process
temperature.
A SERVOTOUGH Laser 3 Plus can be
installed on the duct to measure O 2 and
another for CO for combustion control
purposes. While it provides a more sensitive
measurement by taking an average reading
across the duct, TDL is less effective at
detecting individual burner issues.
However, this averaging effect alleviates
issues associated with gas stratification in
the duct, and general burner issues can
be detected early.
SERVOTOUGH FluegasExact 2700 units can
be placed above each burner to measure
O 2 , for combustion control, and COe, for
direct detection of burner issues.
The SERVOTOUGH Laser 3 Plus
Combustion can also be used to detect
flame-out conditions in natural gas
fired boilers, using its dual CO+CH 4
measurement. Although it is very fast,
the extractive sampling technology of
the FluegasExact 2700 means it is not fast
enough to be used as a safety device.
P09