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Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved1
IMPROVING NOx EMISSIONS FOR COAL PLANTS BY OPTIMISING AIR/FUEL BALANCE & PLANTS BY OPTIMISING AIR/FUEL BALANCE &
COMBUSTION CONTROL SYSTEM
C. Ellula, W. Hahna, D. Shemilta, A. Powellb, S. Willersb, S. Quarmbyb,
S. Lormorb & N. BusbybS. Lormor & N. Busby
Presented by : Dr Connie Ellul
EDF ENERGY UK, CENTRAL TECHNICAL ORGANIZATION &
COTTAM POWER STATION
ECCRIA CONFERENCE SHEFFIELD UNIVERSITY 5-7TH SEPTEMBER 2016
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved2
Challenges of NOChallenges of NOxx Reduction for Coal Reduction for Coal gg xxGenerators Generators
IED NOx/
Meeting l i l ti i
Coal Power Emissions Limits /
TNP Limits (340mg) Actual Emissions
B bbl
legislation requires further Boiler
Retrofit & SNCR/ SCR I t t
Generators have to consider the
viability for further iBubble SCR Investments investments
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved3
EDF Energy Cottam Power EDF Energy Cottam Power S iS iStationStation
Location :
North Nottinghamshire/ Lincolnshire
Operational Since 1966
No of Units : 4
Total Generated Load : 2100 MWeTotal Generated Load : 2100 MWe
Designed for British Bituminous Coals
4 Units Feeding a Communal Chimney
Biomass Co-firing Capability : Max 10 %
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved4
Boiler Properties Boiler Properties Boiler Properties Boiler Properties Type of Boiler John Thompson Design (circa 1960s)Assisted circulation, super and re-heated steam Assisted circulation, super and re heated steam circuits, with forced flow economiser & re-generative air heaters.Steam Properties E ti f 1 542214 k /h S h t Evaporation of 1,542214 kg/hr; Super heater outlet 165.5 bar; 568oCRe Heater steam flow 1,206556 kg/hr; 40.3 bar; 568oCType of Firing Front Wall Fired 32 Burners supplied by 4 mills and 8 exhaustersMaximum No of Burners 28 normally in serviceMaximum No of Burners 28 normally in serviceType of Burners - ICL 1st generation Low NOx burners Fuel Preparation Mill Type - Suction Tube Ball Mill No of Mills = 4 Exhausters Per Mill = 2
h f ll dExhausters for Full Load = 6 or 7
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved5
Low NOLow NO Combustion Work at Cottam Combustion Work at Cottam Low NOLow NOxx Combustion Work at Cottam Combustion Work at Cottam
Late 1990/2000 installation of 1st generation ICL Burners
Initial NOx
2007 - Rear & Side BOFA Ports Installed, 14 in total
600-550
2013 Installation of Zolobosslaser measurement system + laser measurement system + Siemens P3000 Optimizer Target NOx
<340 (Valid)
PF burner retrofit of 1 unit in 2014-2015
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved6
Introduction: NOIntroduction: NOxx Formation in Coal Boilers Formation in Coal Boilers xx
Thermal NOx
Highly dependant onHighly dependant on Temperature & Amount of Air - ( Easily Controlled)
P t NO Prompt NOx
Forms rapidly in the Flame zone not easily quenched
Fuel NOx
Rapid reaction between the N b d f l d A il blN2 bound fuel and Available Air - not easily quenched. Amount of Fuel NOx
Control Of NOx in Coal Boilers is Usually Achieved via
formed is specific coal type dependent
y• Controlling Gas Temperature • Operate at the optimum Residence
Time & • Turbulence
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved7
• Turbulence
Issues Faced in Controlling In NOIssues Faced in Controlling In NOxx for Power for Power Pl t G t Pl t G t Plant Generators Plant Generators Boiler Design, Technology &
l i ll d l Plant Start up vs NOxcontrol installed control methodology Available
500
550
600Plant Start-up vs NOx
Inconsistent coal supply
350
400
450
Load shifting - running from minimum to partial to base load - Lower & partial loads =
200
250
300
phigher NOx (higher XS O2)
Ch i O ti i Mill 0
50
100
150
Changes in Operation i.e. Mill Switching or Type of Cold/ Warm/ Hot Startup
0 MW
NOx
NOx formation vs Load Curve at Start Up
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved8
x p
Effect of Boiler Cycling on NOEffect of Boiler Cycling on NOxxPerformance Performance Performance Performance Maximum NOx Peaks when
Load Shifting
Base Loading
Improving NOx Emissions / Smoothing the Peaks During 2 Shifting can have significant effects on the mean reported figures
InIn--House Methods for Improving NOHouse Methods for Improving NOInIn--House Methods for Improving NOHouse Methods for Improving NOxx
• Switching to a low NOx coal diet - burning high volatile coals • Improving combustion control & diagnostics
I i Ai & F l B l th f • Improving Air & Fuel Balance the furnace Mill Performance & PA: PF distributionReviewing Air Distribution in the Furnace Reviewing Air Distribution in the Furnace Reducing Furnace Air Leakage
Some of the latter can be improved on site without Some of the latter can be improved on site without significant investments compared to the cost of burner
retrofit + BOFA Retrofit + installation of SNCR /SCR
Effect of XS Air on Boiler Operation Effect of XS Air on Boiler Operation
Steam Temperature
& other Plant
Integrity g yIssues
Boiler Efficiency
Slagging & Fouling
XS Air
yg
NOx Performance
PA : PF mixing
Can Lead to Boilerto Boiler Damage
Typical Air Distribution in the Boiler Economiser XS O23% or More
Air From FD Fans
BOFA + Cooling Air C b i
Burner Level
Cooling Air Combustion Air
Air to BNRS Air to BOFA
Cooling Air
Air Leakage
Air can be redistributed by
Bzs = 1/less
Furnace
Air to BOFA
ychanging the Burner Zone
Stiochiometry & Amount of BOFA in the system + Improving
Furnace Leakage ?
in the system + Improving Leakage
What have we done ??? What have we done ???
Revisited the Air : Fuel B l i h SBalance in the System
lo Monitor Operational XS O2Levels
o Consider Effectiveness of Air Distribution in the System
Air - Gas Flow Diagram for Cottam as Originally Built
Measures to Improve NOMeasures to Improve NOxx at Cottam at Cottam
• Installation of the Zoloboss + P3000 Optimiser - improved O2/CO trim control + reduced total air through the burners
• Re-use & further investigation/adjustment of the original BOFA Ports
• Introduced Burner secondary air Staging to Improve NOx
• Reviewed & Investigated existing burner fixed air control adjustments
T t d th l li it f XS O ti t b l d ith t i • Tested the lower limits for XS O2 operation at base load - without causing any issues
• Reviewed and modified O2 Curves for various ramps & unit Loading Reviewed and modified O2 Curves for various ramps & unit Loading
• Reviewed Air : Fuel Requirement during start up & shutdown
• Reviewed & Tested Exhauster Purge Procedure to obtain reduced air flow purge which reduced temperature excursions when putting mills in mills service or
taking mills out of service
•
Impact of the Impact of the ZolobossZoloboss + P3000 System + P3000 System Laser Grid System is installed above
the BOFA Ports. The Laser Grid Maps and Reads O2, CO & Temperature 2 pthis information is sent to the P3000 optimiser which attempts to conduct local air/NOX balancing
The Siemens P3000 Optimizer is a software based system, utilising the so t a e based syste , ut s g t einformation from the Laser Grid + Other Boiler Operational Parameters to Perform continuous Combustion Optimisation
Each Unit has to have a series of Each Unit has to have a series of tests prior to the improvements. Gives greater understanding of combustion dynamics within the furnace dynamics within the furnace
Combustion Combustion Optimization Modules used by Optimization Modules used by Siemens P3000 ControllerSiemens P3000 ControllerSiemens P3000 ControllerSiemens P3000 Controller
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved16
Courtesy of Siemens
Results after installation of Results after installation of ZolobossZoloboss + P3000 + P3000
-25%
Testing carried out at base load •P3000 Siemens Fuel Air Balancing & Zoloboss in Service•P3000 Siemens BOFA control in service •Use of the Siemens P3000 resulted in an overall decrease of 25 % in NO•Use of the Siemens P3000 resulted in an overall decrease of 25 % in NOx( approximately 140 mg/Nm3 max NOx reduction)
Modification of the XS OModification of the XS O22
• Higher XS O2 levels can have an impact on boiler efficiency and in turn increases NOin-turn increases NOx
• Lower XS O2 levels decrease NOx, however give rise to Fire Side Corrosion Slagging Fouling high Corrosion , Slagging, Fouling, high CO and possible flame instability issues which can produce Carbon in Ash Tests for Decreasing XS O2 and Controlling Fixed Ash O2 & FD Fans Manually Same Operating Conditions
& Fuel
Global XS O2 was reduced by reconfiguring the O2 Load
Control Curve Compromise With CO & Flame
Stability Issues taken into account
Effect of BOFA Flow Effect of BOFA Flow • BOFA Flow was altered from
minimum to maximum available flow
Boiler Front
• Different flow combinations were tested including equal
SA SAwere tested including equal flows on 2 BOFA fans & max flow with 1 fan in service
• The effect of altering BOFA damper settings as left by the manufacturer was Investigated 14 BOFA Ports manufacturer was Investigated
• Modifications to the BOFA air t l t i t
BOFA Fan 1 BOFA Fan 2
control system requirements were implemented
Simplified Schematic Diagram of BOFA S d i d b b kSystem designed by Doosan Babcock at
Cottam
Effect of BOFA Increasing FlowEffect of BOFA Increasing FlowEffect of BOFA Increasing FlowEffect of BOFA Increasing Flow
600
500
600
400
300
Test 1Test 2 Test 3
200
Generated Load (MW) T1 NOX (mg/Nm3) T1
~ - 20 mg/Nm3
0
100( ) ( g )
Generated Load (MW) T2 NOX (mg/Nm3) T2
Generated Load (MW) T3 NOX (mg/Nm3) T3
Revisiting Burner Operation Revisiting Burner Operation g pg p Installation of Zoloboss & P3000
allowed the reduction of total air to the burners i.e. from100 %
Total Air Damper (SAD) Damper to the burners i.e. from100 %
open – to lower values
d d d
(SAD) Damper
Questioned and revisited SAD openings during start up, shutdown and lower loads
Furnace air staging control was adopted by setting dampers to adopted by setting dampers to impose further in–furnace air staging with BOFA in service
Further air control was implementd by reduced Damper
GA Drawing of ICL Cottam Burner
Opening at Lower Loads
Burner InBurner In--Furnace Staging Furnace Staging A Mill Biasing concept was implemented by adjusting the Secondary Air Damper Opening Adjustment for each burner in service irrespective of the random fuel
supply due to positioning of the burners
Lower Fuel:Air Ratio at the top
Fuel Lean Region Fuel Lean Region
supply due to positioning of the burners
R3
R4 Shorter Flames Shorter Flames
R2
R3Intermediate Intermediate
Region Region
R1
R2
Fuel Rich Region Fuel Rich Region Longer Flames Longer Flames R1
Higher Fuel:Air Ratio at the bottom
Longer Flames Longer Flames
bottom
Effect of Reducing Total Air from Burners Effect of Reducing Total Air from Burners 100 % Secondary Air Damper
Opening vs Windbox Press Control & SAD Opening
Structured Furnace Staging Effect
p g
500
600
500
600
400
Test 1
400
200
300Test 2
- 40 mg/Nm3 200
300
-20/-25 mg/Nm3
Test 1 Test 2
100 Generated Load ( MW) T1NOX Valid (mg/Nm3) T1Generated Load (MW) T2
100Generated Load (MW) T1NOX (Valid) (mg/Nm3) T1Generated Load (MW) T2
0
Generated Load (MW) T2NOX Valid (mg/Nm3) T2
Test 1 SAD Dampers – 100 % Open; XS O2 = 3.1 % ; BOFA Flow 30 kg/s
0
Generated Load (MW) T2NOX (Valid) (mg/Nm3) T2
Test 1 SAD Dampers – WP Control; XS O2 = 2%; BOFA Flow 60 kg/s% ; BOFA Flow 30 kg/s
Test 2 SAD Dampers – WP Control; XS O2 = 3.1% BOFA Flow 30 kg/s
BOFA Flow 60 kg/sTest 2
SAD DAMPERS – Fxd Staging; XS O2 = 2%; BOFA Flow 60 kg/s
Changes Changes toto Burner Hardware Burner Hardware
Air leakage & maldistribution of air within the Windbox can of air within the Windbox can occur Due to automated & local
d tti i SA & TA damper settings – i.e. SA & TA dampers
Changes made due to BOFA Faulty / Jammed Fixed SA/TA Damper Settings g
and other equipment which uses Secondary Air
p g
Detailed Total Air Damper Detailed, Total Air Damper Investigations & Windbox Inspections
were carried out to determine actual the damper settings the damper settings
Changed to an adjustable one
Effect of NOEffect of NO on Low Load Testing on Low Load Testing Effect of NOEffect of NOxx on Low Load Testing on Low Load Testing
NOx
Load
Lower NOx values obtained as a result of the
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved25
implemented changes
Discussion & Lessons Learnt Discussion & Lessons Learnt
Consistent monitoring of Boiler Performance is a must (XS O2 & CO Levels) especially When your plant is only partially controlled ( i.e.
ll ll d b h d hManually Controlled by the operator + pre-programmed in the DCS). This often requires frequent education and monitoring for the operations staff
Maintaining a constant O2 level (within operational limits) - has resulted in a substantial decrease in NOx
Understanding O /CO stratification issues due to transient/partial Understanding O2/CO stratification issues due to transient/partial loading, especially mill configuration changes
Comparing control system transients such a windbox pressure control (by closing & opening) SADs during transients can increase NOx when compared to conventional fixed SAD settings
Excessive Air was being used during transient loads which lead to Excessive Air was being used during transient loads which lead to higher NOx
ConclusionsConclusions
Observations from investigation work demonstrated to us that Air : Fuel Balance control is crucial when controlling NOBalance control is crucial when controlling NOx
Introduction of Novel Diagnostic techniques such as Zoloboss + P3000 System aided decreased NOx
O d h b i i d bli h l O l hi O2 Load curve has been revisited to establish lower NOx value - this was conducted within safe minimum flame stability limits
Structured in Furnace Staging + BOFA gave the lowest NOx result No Impact on Flame quality noted with the new SAD setting combination
for the range of coals burnt Increase in CO emissions , has been noticed, however the CIA values were , ,
still within acceptable limits and below 7 No signs of elevated S/H & R/H temperatures or Fireside Corrosion Additional modification to improve high temperature spikes during mill Additional modification to improve high temperature spikes during mill
purge start up/shut down has proven successful and temperature spikes avoided
Further Work Further Work Further Work …. Further Work ….
• Conducting further investigation on mill performance • Understanding stratification differences between the
boilers • Comparing & Matching Fixed Damper Settings for the
remaining unmodified 2 units
Acknowledgements Acknowledgements Acknowledgements Acknowledgements
The presenter & authors would like to acknowledge Cottam Operations Performance Boiler Maintenance & Cottam Operations, Performance, Boiler Maintenance &
Engineering teams + Siemens, for the fruitful discussions & invaluable assistance during these trial periods g p
EDF ENERGY UK COAL GENERATION EDF ENERGY UK COAL GENERATION
CELEBRATING 50 YEARSCELEBRATING 50 YEARSCELEBRATING 50 YEARS CELEBRATING 50 YEARS
Title of Presentation © 1 January 2015 EDF Energy plc. All rights Reserved30