© 2015 information contained herein is proprietary and confidential to babcock power inc. all...

© 2015 Information contained herein is proprietary and confidential to Babcock Power Inc. All Rights Reserved 1

ONE SOURCE ONE PURPOSE MANY SOLUTIONS

Utility Users Group ConferenceAugust 5, 2015

Orange Beach, ALCraig Gillum

Riley Power Inc.Manager, Boiler Performance Engineering

Conversion of Coal-Fired Boilers to Natural Gas-Firing“Engineering Design”


Recent News


Conversion of Coal-Fired Boilers to Natural Gas-Firing

Phases of a NG Conversion Project1. Economics2. Permitting / Environmental3. Bid Process 4. Design

Engineering5. Construction6. Start-up7. Performance Results


NG Conversion

Design EngineeringFuel Combustion SystemBoiler PerformanceBoiler Auxiliary EquipmentBOP

Burner

Heat Transfer

Not “stand-alone” systems. All work together.

Fans


Design Engineering Up-Front Decisions by the Utility

1. Establish the Fuel Firing Matrix: • 100% Gas-Firing Only• Co-Fire NG and Coal• Dual-Fuel Capability (100% NG and 100%

Coal)

2. Establish Emissions Requirements:• Emissions drives Combustion System design

which in-turn impacts the Boiler Performance and Auxiliary Equipment Performance (Fans & AH).

NG Conversion Considerations


Up-Front Decisions by the Utility (cont.)

3. Establish Required Thermal Performance: • Capacity• Steam Temperature• Efficiency• Turndown range

4. Establish Design Constraints: • Pressure part modifications• FGR• Auxiliary equipment modifications

o Fanso Air heater

NG Conversion Considerations


Establish Fuel Firing

Matrix

Establish Emissions

Requirements

Combustion System

Design to Meet

Emissions

Evaluate Boiler

Performance

Evaluate Auxiliary

Equipment (Fans & AH)

Combustion System Design to Meet Emissions

Design Process


Combustion System Design Sequence(to meet emissions)

First:Analyze Burners Only

Second:Burners and Over-fire Air (OFA)

Third:Burners + OFA + Flue Gas Recirculation (FGR)

Typical Low NOx Combustion Design Process

Low NOx Coal FlameTflame ~ 3,000 – 3,300 [F]


Establish Fuel Firing

Matrix

Establish Emissions

Requirements

Add NG Combustion

System

OptionsAdd SNCR

or SCR

Evaluate Boiler

Performance

Evaluate Auxiliary

Equipment (Fans & AH)

If Combustion System Alone Cannot Meet Emissions; Added Emissions Control Equipment is Required.

Design Process

Combustion System Design to Meet Emissions


Indicative NOx & CO Emissions

Coal Burner retrofit w/NG Firing Capability

Emissions – Utility Boiler

NOx

(lb/mmbtu)CO

(ppm @ 3% O2)

Bituminous Coal w/OFA 0.27 – 0.32 <100

PRB Coal w/OFA 0.17 – 0.20 <300

NG w/OFA 0.22 – 0.30 <100

NG w/ OFA & FGR 0.09 – 0.15 <100

NG Burner Complete Replacement

Emissions – Utility Boiler

NOx

(lb/MMBtu)CO

(ppm @ 3% O2)

Burner 0.25 – 0.32 <100

Burner w/OFA 0.18 – 0.24 <100

Burner w/OFA + FGR 0.07 – 0.12 <100

Wall Fired NG Emissions


Indicative NOx & CO Emissions

T-Fired Burner w/NG Emissions – Utility Boiler

NOx

(lb/mmbtu)CO

(ppm @ 3% O2)

BNR Only 0.15 - 0.20 <150

BNR / SOFA 0.10 - 0.15 <150

BNR / SOFA / FGR 0.06 - 0.10 <150

Tangential Fired NG Emissions


Emissions Range is due to:

• Furnace Size Basket Area Heat Release(Hot box vs Cold Box)

• Retention Time Bnr & OFA to Furnace Exit(Tall vs short furnace)

• Furnace Depth Flame Length Control

• Burner Design Types of Air & Fuel Mixing

Natural Gas FlameTflame ~ 3,200 – 3,500 [F]


Conversion of Existing Coal-Fired Boilers

1) Wall-Fired : Typically associated w/Riley, Foster Wheeler

and B&W Boilers2) Tangential-Fired : CE/Alstom Boilers

Various Utility Firing Configurations

Each has their own characteristics on both the combustion and heating surface design


Wall FiredDual Fuel Coal/NG

Existing Burner Retrofit


Wall-Fired Furnace Example: 365 MW Unit – LNB & OFA – PRB Coal

CFD Model – Wire Frame

FEGT Plane

OFA Ports Plane

CO Emissions

CFD Furnace Modeling-Wall Fired Furnace Design

Temperature

Burners located on the Front and/or Rear Walls


Wall Fired - Dual Fuel - VS III® LNB for Coal and NG Gun Retrofit

Retractable main gas gun

Dual Fuel “Smart” Scanners

• Center fired gas gun with pneumatic retraction

• Dual head UV/IR flame scanners

CCV® Coal Nozzle

CCV® Coal Nozzle

Retractable Gas Gun


Wall Fired - Dual Fuel - Retrofit Option: Gas Ring Retrofit w/Existing Coal Burner

• RPI VS III® LNB or reuse existing burner air registers with components retrofit

• Coal

– CCV nozzle

– SA / TA diverters

• Gas

– Ring header with spuds

– Center fired gas gun

Gas Ring w/Spuds

CCV® Coal Nozzle


Wall Fired

NG Firing OnlyBurner Replacement


Wall Fired – Gas Only STS® Low NOx Gas Burner Replacement


Wall Fired – Gas Only - STS® Low NOx Gas Burner Utility Design

• Plug-in design• Burner capacity 30 to 250 MMBtu/hr heat

input• Low burner air pressure drop typically less

than 5” WC• Independent flow and swirl control for

flame shaping• Primary Air/ Secondary Air flow split

control to minimize NOx• Burner to burner air flow balancing biasing

capability to correct unbalanced windboxes• Automatic air shroud to control

Windbox/Furnace differential pressure• Ability to eliminate combustion induced

vibration with online adjustable gas canes• High mechanical reliability from proven

register design


STS ® LNB - Adjustable Gas Canes

• Tip position adjustment– Axial– Rotational

• Adjustable w/ burner online– Remove cap (14)– Loosen lock nut (5)– Turn drive nut (4)

• Field tuning adjustable for emissions & vibration


Tangentially Fired Dual Fuel

& Gas Only


Tangential -Fired Utility Furnace

Tangentially Fired Dual Fuel & Gas Only

CFD Model

Furnace Modeling

Corner Fired Circular RotationCorner Fuel & Air Ports


Tangentially Fired – Coal & Gas

• Install gas spuds in existing auxiliary air compartments

• Add igniters to aux air compartments or Side horn Ignitors

Coal compartments

Aux Air compartments w/ gas spuds & tips

Tangentially Fired Dual Fuel & Gas Retrofit


Tangentially Fired Dual Fuel & Gas Retrofit

Gas Spud(Stationary)

Gas Tip(Angle adjustable)

Gas Spuds


Over Fire Air(OFA)


OFA Systems

• Important design features from RPI study for EPRI

– Location– Uniform distribution– Penetration (adequate pressure and

velocity)– Mixing– Turndown (1/3, 2/3 area flow control

dampers)– Biasing capabilities

• Major components– Individual nozzles located above each

burner column– OFA ports use 1/3 - 2/3 nozzle design with

individual dampers with automatic control

OFA: Staged Combustion• % of Combustion Air Injected

Above the burners • Used for NOx Control


Separated OFA System Arrangement

SOFA Windbox

T-Fired Boiler


Flue Gas Recirculation

(FGR)



Flue gas recirculated back to the Furnace

• NOx Control: - FGR Through the Burners

• Steam Temp Control: - FGR Through the Furnace

Bottom

Flue Gas Recirculation (FGR)


Flue Gas Recirculation Systems

1. FGR from Economizer Exit2. FGR From Airheater Exit3. “Induced” FGR from ID Fan to FD Fan


Boiler Performance


Boiler Performance

SH / RH Steam Temperature

AH Exit flue gas temperature

Boiler Efficiency


Boiler Thermal Modeling

Two Main Types of Models:1. Theoretical Model

– Based on a Text Book Analysis2. Calibrated Model

– Based on Calibration to Actual Data

Uses– Predict Performance at New Physical

Operating Conditions– “What-If” Analysis– Sensitivity Analysis, “Bound the Solution”– Evaluate the Complete System “Big Picture”

Input Requirements– Detail Physical Arrangement– Design Operating Condition– Actual Data for Calibration


1. Furnace Exit Gas Temperature • Expect some change• Dependent on design coal

2. Surface Fouling Characteristics • Furnace & Convection surfaces are cleaner & more effective

3. Flue Gas Flows Produced• Coal firing excess air 18 – 24 % • NG firing excess air 8 – 10% • Overall NG firing flue gas flow reduce 7-12 %.

4. SH / RH Steam Temperatures• Typically SH / RH temperatures reduce (10-60 JF)• Temperature or spray will reduce• Depends on original coal characteristics and amount of radiant surface

Note: Adding FGR for NOx control can improve steam temperatures.

NG Firing Facts Concerning Boiler Performance


Boiler Performance Firing Natural Gas

Con’t.

5. If Flue Gas Recirculation (FGR) is Used for NOx Control.• Flue gas flow rate will increase 5 – 20% (as required for NOx control)• Increases SH / RH steam temperatures and increasing LTSH tube metals.

6. Economizer exit and AH exit gas temperatures• Typically Flue Gas Temperatures decrease• Note: AH performance changes with the elimination of coal pulverizer

tempering air.

7. SH / RH Tube Metals• SH / RH Tube metal temperatures typically do not change firing NG except:• First bundle out of furnace• When FGR is used. FGR increases the convective pass heat absorption that in-turn

increases the LTSH temperature (before spray).

8. Boiler Efficiency• Boiler efficiency firing NG reduces by 3 – 5% due to the increased Hydrogen (H2)

moisture loss.


Furnace PerformanceFurnace Exit Gas Temperature

Furnace Exit Gas Temperature (FEGT)

• Flame Characteristics

• Furnace Cleanliness

• Furnace Size

Circulation• Slight change in

heat absorption profile

• No Change in boiler circulation

Bituminous Coal

Bituminous Coal - Severe Slagging

Bituminous Coal - Low Slagging

PRB Coal

Natural Gas

Furnace Area Heat Release

Gas

Tem

pera

ture


Change in Convective Heat Transfer

Fr. Sc

rn

Fin. S

H

Rear. Sc

rnSc

rn 1

Fin. R

H

LTSH

4

LTSH

3

LTSH

2

LTSH

1

Upper Eco

n

Lower E

con

Boiler O

ut

0.000.100.200.300.400.500.600.700.800.901.00

Coal Base

Nat. Gas

Nat. Gas w/ FGR

Nor

mal

ized

Gas

Ent

halp

y

• Due to changes in radiant absorption and gas temperature and flow, heat transfer in convection sections will typically decrease.

• FGR is one way to increase the convection by increasing gas flow.


PRB Bituminous Natural Gas

H2O 29.34 2.9 0C 48.43 80.31 73.21

H2 3.57 4.47 23.2

O2 12.62 2.85 0.45

N2 0.71 1.38 3.14S 0.25 1.54 0

Ash 5.08 6.55 0Total 100 100 100

HHV (BTU/lb) 8,223 14,100 22,738

Efficiency (%) 84.35 89.45 83.70Fuel Flow (pph) 713,930 391,068 259,166Flue Gas Flow 6,018,886 5,457,221 4,985,251

Qout.steam (KBTU/hr) 4,951,890 4,932,326 4,932,371

Fuel Analysis Comparison


Conversion of Existing Coal-Fired BoilersBoiler Efficiency Changes

• Highly dependent on existing fuel characteristics• In general, a decrease in boiler efficiency of more than 5% can occur.• 1:1 change in unit heat rate with change in boiler efficiency

η = 89.45% η = 84.27% η = 83.79%(-5.7% ∆η from Bit.)(-0.5% ∆η from PRB)


NERC GADS Lost Generation Data

Coal Gas0

10,00020,00030,00040,00050,00060,00070,00080,00090,000

Boiler Tube Leaks

Boiler Tube Leaks

Boiler Fuel Supply To Bunker Boiler Fuel Supply From Bunkers T Boiler Piping SystemBoiler Internals And Structures Slag And Ash Removal Boiler Tube LeaksBoiler Tube Fireside Slagging Or Miscellaneous Boiler Tube Problem Boiler Air And Gas SystemsBoiler Control Systems Boiler Overhaul And Inspections Boiler Water ConditionBoiler Design Limitations Miscellaneous (Boiler)


NG Conversion

RecommendationPerform an

“Up-Front Engineering Study”Benefits• More in depth analysis• Evaluates Alternatives (“What if” analysis)• Considers both Technical and Financial Aspects• Evaluates the Total System (load range, effects on other equipment)• Establishes a Better Project Plan• Better Defines Project Costs and Reduces Risks• Reduces Project “Surprises” • Reduces Disagreements and Misunderstandings• Typically “In the Long Run”, Saves Money $$


Key Take-Away

Every Boiler is Different

Front End Feasibility Study is Best

Overall Performance Impact is Highly Dependent on Base Fuel

Boiler Efficiency Decrease

Aux. Power Load Decrease

May Require Design Change to Address Convective Changes

Potential for Increased Flexibility


Questions&

Thank You


45

Extra Sides for Reference



• Boiler efficiency is a 1:1 inverse relationship to unit heat rate. – 1% decrease in boiler efficiency is a 1% increase in heat rate.

• Steam temperature will effect heat rate also.

Unit Net Heat Rate

• Gas Firing results in a net decrease of auxiliary power– Mill power– I.D. Fan Power– SOx Removal Systems– ESP Power


Conversion of Existing Coal-Fired BoilersBurner Ignitor Systems

Classification Class I Class III Class III Special

Ignition of Main Burner

Ignite or support Small ignitor for gas and oil burners under prescribed

light-off conditions

Provides direct spark ignition to ignite main burner

Heat Input >10% burner heat input < 4% burner heat input Only spark for ignition

Continuous Operation

Yes Not permissible No

Trial for Ignition Period

10 – 15 s for gas & oils 10 – 15 s for gas & oils 10 – 15 s for gas & oils

Extended Operating Range

Support combustion of the main flames

Cannot be used to support ignition or extend the

turndown range

Cannot be used to support ignition or extend the

turndown range

Flame Detection One detector to prove either the ignitor or main flame.

One detector required for main burner and ignitor

Only require main flame detector

Master Fuel Trip (MFT) Requirement

Does not require MFTRequires 1-minute delay

before restart

Does not require MFTRequires 1-minute delay

before restart

Failure of first burner to light requires MFT


Background

• Natural Gas-Firing – No SOx emissions– Virtually no PM– ~1/3 the NOx emissions of coal

w/FGR– 50-80% less CO2 than coal


Manually Adjustable Secondary Air Swirl Vanes

Automatic Modulating Total Air flow Control Shroud

Manual Control of the Primary and Secondary Air Flow Split

Air Flow Measurement

High level of NOx reduction

Superior mechanical reliability

Monitoring of burner temperatures

STS® Low NOx Gas Burner – Industrial Design


Burner capacity 40 to 250 mmBtu/hr

heat input

NOx reductions up to 60% from uncontrolled NOx

Independent air flow and swirl control

Low CO emissions

Low burner air pressure drop typically less than 5 iwc

Burner to burner air flow balancing biasing capability to correct unbalanced windboxes

High mechanical reliability from proven register design

Can be retrofitted to wall-fired applications without modification of burner throat tube opening

Can be adapted to accommodate existing windbox openings

Flame shaping capability

STS® Low NOx Gas Burner – Industrial Desi RPI STS® Burner Technology for Industrial Design


Boiler Efficiency

39%

28%

30%

1%1%2%

PRB Fuel (18% XSA)

59%

2%

33%

1% 1% 3%

Bituminous Fuel (20 % XSA)

30%

67%

1%2%

Natural Gas Fuel (10 % XSA)

Dry Flue Gas LossMoist. (Liquid) in Fuel Loss Water from Hydrogen CombustionAir Moisture Loss Unburned Carbon Loss Radiation Loss

Ƞ= 84.35% Ƞ= 89.45% Ƞ= 83.70%


21.1%

3.6%

69.7%

1.2% 0.2% 4.3%

Bituminous Fuel (20 % XSA)

14.0% 2.0%

70.8%

1.2% 12.0%

Natural Gas Fuel (10 % XSA)

CO2

O2

N2

Ar

SO2

H2O

21.1%

3.1%

66.2%

1.1%0.1%

8.4%

PRB Fuel (18% XSA)

© 2015 information contained herein is proprietary and confidential to babcock power inc. all...

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