Flue Gas Analysis As A Furnace Diagnostic Tool Doug Simmers- Worldwide Product Manager Rosemount Analytical

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Flue Gas Analysis As A Furnace Diagnostic
ToolDoug Simmers- Worldwide Product Manager
Rosemount Analytical


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Contents

• Overview of traditional applications for
  combustion flue gas analyzers
• Traditional analyzer technologies
• New measurement goals
• Analyzer applications to detect furnace anomalies
  
• New analyzer developments

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Traditional Application of Flue Gas Analyzers-
Optimize Fuel/Air Ratios
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Determining CO Breakthrough- how low can your O2
go
Traditional Application of Flue Gas Analyzers-
Optimize Fuel/Air Ratios
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Traditional Application of Flue Gas Analyzers-
Optimize Fuel/Air Ratios
The point of CO breakthrough changes with firing
rate. Higher firing rates induce greater
turbulence in the burner(s), providing better
mixing of fuel and air, and a lower possible
excess O2 setpoint. This curve should be
re-established periodically, but more often is
not.
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New Measurement Goals-Staged Combustion for NOx
Reduction
Not enough O2 to react into NOx
Excess air flow quenches the flame, Lowering
reaction temperatures below That required to make
NOx
Flue gas O2 setpoints may be shifted up or down,
based on minimizing the amount of NOx and CO
produced at the burner
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New Application- Flue Gas Recirculation
Controlling Final O2 Entering The Wildbox
Flue Gas
3 O2
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New Measurement Goals-Slag Prevention
Ash fusion temperatures vary with flue gas O2
levels
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Application Overview- Large, Multi-burner
Furnaces


Probes
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Typical flue gas Analyzers
Point Measurements
Averaging, Line-of-sight Measurements
In Situ O2 Probe
Spectroscopy IR for CO Laser IR for CO and
O2 (NOx is also possible)
Extractive O2/ combustibles system
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Typical flue gas Analyzers In Situ Oxygen Probe

• Zirconium Oxide Fuel cell technology is
  commonly used
• Output is inverse, and logarithmic.
• Cell generates its own signal, which increases
  at the low O2 levels commonly experienced in
  combustion processes.
• Accuracy actually improves at lower O2 levels.
• No sampling system required.
• Passive diffusion- filters last a long time
  before plugging in high particulate applications
• Speed of response is fast.
• Cost effective
• Sensing cells are robust.
• Operate well at elevated temperatures
• Sulfur resistance is good.
• Cell life can easily exceed 3-5 years.

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Typical flue gas Analyzers
Point measurements
Averaging, line-of-sight measurements
In Situ O2 Probe
Spectroscopy IR for CO Laser IR for CO and
O2 (NOx is also possible)
Extractive O2/ combustibles system
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Typical flue gas Analyzers Close-Coupled
Extractive (no sample conditioning)

• Same ZrO2 Oxygen sensor
• Calorimetric combustibles sensor
• Detects CO breakthrough, but cannot resolve fine
  PPM CO levels
• May require frequent maintenance in high
  particulate applications (coal, biofuels, garbage
  incineration, etc.)

OCX 8800 Launch Presentation July 09, 2009 //
Slide 13
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Typical flue gas Analyzers
Point measurements
Averaging, line-of-sight measurements
In Situ O2 Probe
Spectroscopy IR for CO Laser IR for CO and
O2 (NOx is also possible)
Extractive O2/ combustibles system
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Typical flue gas Analyzers IR or Laser
Spectroscopy for CO

• Most implementations are across-stack, or
  line-of sight.
• Averages across the flue duct.
• Difficult to challenge with a known calibration
  gas.
• CO is a good absorber of IR energy _at_ about 470nm
  wave number
• CO as well as O2 and NOx can be reliably detected
  with tunable diode laser systems.

Typical Installation
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Historical Progression of Point O2 AnalysisIn
Large Multi-Burner Furnaces

• Early years- 1970-1980- a single O2 Probe per
  flue gas duct is sufficient- placement is
  somewhere near the middle
• Confused- 1985- a second O2 probe is added, to
  get a better average for fuel/air ratio
  adjustment
• The two probes rarely agree, so operators trust
  the readings from neither probe.
• After many calibrations, its understood that
  both probes are telling the truth, and
  significant stratification exists in the ductwork
• 1990- More probes are added in order to again
  get a better O2 average
• More stratification is witnessed by the
  operators, and more confusion ensues
• Probes that are particularly out of the norm are
  often removed from the average (exactly the wrong
  thing to do)!

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Average O2 for Fuel/Air Ratio Control Predictive
Maintenance Tool

• Seeking out stratification- Rather than avoid
  stratification, plant operators are more and more
  trying to determine what flue gas stratification
  is telling them.
• Balancing Burners
• Detecting Burner Fouling
• Poor coal distribution/roping
• Mill to mill variations

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Focusing In On The Real Process(es)
Each burner and coal mill constitutes a separate
process of its own
The furnace is an envelope
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Burner Diagnostics-Analyzer Placement Is
Important

• Burner columns are easier to identify with a
  wall-fired furnace
• Corner to corner variations in a tangentially
  fired furnace are harder to discern

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Changing Measurement Locations

• Coal-fired boilers
• Most boiler manufacturers provide testing ports
  after the economizer, hopper, which are often
  utilized for permanently mounted analyzers.
• An upstream location ahead of the economizer has
  advantages
• Large particle ash, or popcorn ash is less
  prominent- abrasion on probes is less.
• Stratification is greater, burner column by
  burner column

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Fine Tuning Probe Placement With Variable
Insertion
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Variable Insertion Probe- looking for the ideal
measuring point.
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Furnace Diagnostics- Detecting Air Leaks

• Air Heater Seal Leakage- the delta O2 before and
  after an air heater helps determine seal leakage

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Furnace Diagnostics- Flue duct seal leaks are
indicated by outer probes reading higher
Furnace Diagnostics- Detecting Air Leaks
3.4
3.4
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Furnace Diagnostics- Beyond Total Furnace Average
Duct averages can shift left or right with ID fan
load changes
Duct A Average
Duct B Average
Mill average- Burners fed from common pulverizer
mills may show similar readings when
mill/classifier problems arise.
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Furnace Diagnostics- Soot Blow Problems/Tube
breaks

• O2 readings will be affected by the dilution of
  water entering in the furnace
• O2 dry O2 wet (1/1-H2O
• Soot blow/water lance
• Tube breaks

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Duct Burners for Combined Cycle Combustion
Turbines
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Duct Burners Increase Steam Production, But Now
O2 Can Be Controlled To A More Efficient Level.
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New Developments In ZrO2-Getting New Information
From AReliable Sensor Technology
Recovering from process upsets- A ZrO2 sensor
that measures the level of O2 deficiency during
reducing events.
Zero O2
O2 range is depressed -2 to 10
During process upsets into reducing conditions,
the operator can see the level of O2 deficiency,
and see if his corrections are adequate
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New Developments In ZrO2-Getting New Information
From AReliable Sensor Technology
New ZrO2 probe sensor that measures CO
breakthrough.
O2 Probes
CO Probe
Boiler load (megawatts)
IR CO analyzer
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Summary

• Flue gas analysis has historically provided a
  good tool for optimizing fuel/air ratios in large
  furnaces
• Analyzers help achieve new goals such as NOx
  reduction and slag reduction.
• Multi-burner furnaces often have significant flue
  gas stratification, which is often a cause for
  operator concern
• Stratification profiles provide a great
  diagnostic of upstream processes at the burners
  and pulverizers
• The furnace is just an envelope for the process
  each burner is its own process.
• Point measurements provide good granularity of
  upstream burner columns, but more instruments are
  required in order to get a good average
• Line-of-sight measurements are inherently
  averaging, so fewer are required to get a good
  total average, but stratification is masked
• New developments in CO measurements will improve
  NOx reduction, combustion efficiency, and burner
  diagnostics.

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Thank You- Questions?
Chris Morrissey- S. California Sales
Engineer Chris.Morrissey_at_emerson.com (951)
285-1629 Chris Lesser- RM Regional Sales
Manager chris.lesser_at_emerson.com (303)
883-7180 Dave Anderson- Marketing
Manager dave.anderson_at_emerson.com (949)
322-8178 Doug Simmers- Worldwide Product
Manager doug.simmers_at_emerson.com [phone]