06 secondary air upgrades
TRANSCRIPT
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Secondary air system upgrades
Foster Wheeler Service Thailand boiler days
30-31 October 2014
Sami Marjeta, Technical Manager, FWST
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Typical air systems in FW CFB
Fuel quality and effect of high volatile fuel
Scope of SA modification
Case examples
3D combustion modeling capabilities
Content
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Not all Foster Wheeler CFB have upper secondary air
Background variation in air system configuration
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1 2 3 4
PA X X X X
UPA X - X -Lower SA X X X X
Upper SA - X X X
Tertiary air - - - X
1 Low volatile fuel CFB
2 Medium or high volatile fuel
CFB
3 Large variation in CFB fuel
volatile content
4 BFB
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Typical trend in many cases is that volatile content of the fuel mixture
increases from original design
Possible reasons:
Bio fuel burning starts or increases
Coal quality decreases i.e. gets younger Biomass quality development
Fuel quality development
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What was good 20 years ago, is not good anymore
More and more strict emission regulations demand optimized
combustion
Load variation demands
Base load plant can have to face load control requirements from
electrical or process network (example USA plants due to shahle gas)
Lower fuel heating value coupled with higher volatile content
increases furnace velocities
All sums up to higher elevation combustion zone in furnace
CO corrosion
Increased requirements for air feeding
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Typical scope
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Process assesment (what is the current process situation)
Process measurements
CFD modeling (standard air nozzle or 3D combustion modeling)
Engineering
Conceptual
Sizing of ducts, nozzles, fans
Layout
Detail
Modification
Final commissioning and tuning Underlined items are mandatory, but without detailed information, their
results may wary
Recommend to have all (if you save in modeling, you lose in
commissioing and tuning)
Scope
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Depending on how difficult the demand is
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Case examples
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Case E.ON Coal Fired CFB Boiler, Finland
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Problem
Erosion in furnace and in backpass
potential reason high flue gas velocities and understochiometric
conditions with local high temperatures
erosive ash and bed quality
Goals
Balancing horizontal O2-, CO- and temperature profiles in lower furnace
by secondary air nozzle modifications, location and type defined by CFD
modeling
Balancing horizontal O2-, CO- and temperature profiles by gas profile
measurements for minimizing afterburning in upper furnace
Decrease of fly ash unburned carbon
Decrease of erosion in backpass by Vortex killer fins in vortex finder
and flue gas guidance plates
Case E.ON Coal Fired CFB Boiler, Finland
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Number of problems, number of solutions...
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Makes an air vortex
Typically used above fuel feeding to
provide a shroud of air between CO
gas and membrane wall
Lower penetration than standardnozzle
Secondary Air Nozzle Type: Vortex Nozzle
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Old nozzles, air veloc ities > 100 m/s Vortex nozzles, air veloc ities< 60 m/s
Air nozzle Velocities
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Furnace Velocities
Old nozzles, air veloci ties > 100 m/s Vortex nozzles, air veloci ties< 60 m/s
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Results
Results after gas profile measurements and secondary air
improvements:
during winter 2004-2005 no tube leakages, earlier ~3 stops/winter
fly ash UBC decreased from 30 % to 12 %
back pass erosions was decreased
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Completed SA modification at NPS units 7-8
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Secondary air modification made to NPS PB#7 & 8:
Gas profile measurement showed CO rich zero O2-zones (=reductive
conditions causing corrosion-erosion phenomena) near side walls
Reductive conditions removed by secondary air nozzle relocations and
by adding new secondary air level
NPS secondary air modification
Introduction
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Fuel quality development
No antracite anymore
Younger bituminous coal
Biomass share increase
Original flue gas amount was less than today Higher furnace velocity
NPS secondary air modification
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Background
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The scope of changes (which nozzles blocked, where to put new
nozzles etc.) was selected based on operation experience, wall
thickness and gas profile measurement and experience.
No 3D combustion modeling was done
When the changes were implemented, gas profiles were measured
again and dampers adjusted
NPS secondary air modification
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Scope
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3D combustion and Glow units 1-2
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Based on 1 directional (vertical) furnace model
The model has been applied to hundreds of
different cases and the code has been
developed based on the validation tests
Typical model construction time 1 week
Modeling 1-2 weeks, depending on amount of
cases
1 calculation run, i.e. how about if we move this
SA nozzle a little bit?takes 2-3 hours
3D model details
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Furnace dimensions 13.2 m x 6.6 m x 32.8 m.
Mesh size 74 400 calculation cells.
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3D combustion model
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What can it do?
Can tell what is predicted flue gas component (SO2, CO, Nox, O2) in
each furnace location (X, Y, Z direction)
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3D combustion model
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It will tell you where to add air and how much to get rid of CO close
to walls
It can help in lowering emissions, limestone or NH3 consumption
Model is validated and fine tuned with profile measurements
Profile measurement
point i.e. Validation
point
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Unique FW capability
Field gas profile measuments coupled to highly developed
combustion computer model
Each gas component profile
3D Combustion modeling Glow 1-2
existing air
supplyproposed air
supply
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During the boiler lifetime, fuel variety can be significant
CFB design can be altered to better match new fuel properties
Grid changes
Air system changes
Fuel feeding changes
If there is a clear trend in fuel quality development, boiler capabilities
can be modified
There is a CFB for every fuel, but not all CFBs can burn any fuel!
Conclusion
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