1 title of presentation © 1 january 2015 edf energy plc ... ellul … · challenges of no x...

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


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


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 %


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


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


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


• 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


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


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 )



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


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


1 title of presentation © 1 january 2015 edf energy plc ... ellul … · challenges of no x...

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