IR-CFBC Boiler Design & Concept

Jayaraman Rajavel

Thermax Ltd., Pune

25th June 2010IR-CFBC Boiler Conference

Outline

� Concept of IR-CFBC boiler

� Comparison between CFBC and AFBC boiler technologies

� Features of IR-CFBC design� Comparison of various CFBC technologies

Fluidization concept

Fluidization concept

WHY CFBC BOILER ?

� HIGH THERMAL EFFICIENCY

� EFFECTIVE REDUCTION OF Sox EMISSIONS THROUGH LIME INJECTION

� REDUCTION OF NOX FORMATION BY REDUCED THERMAL NOX GENERATION

� REDUCED CO EMISSION LEVELS

� FUEL FLEXIBILITY

CFBC.PPT-8

Better combustion- Why?

� Uniform combustion temperature

� High Turbulence in bubbling bed zone� Higher Residence time

� Smaller fuel particles.

Emission…..

� Controlled combustion temperature � Sox control through Lime addition

� Nox control through lower operating temperature

� Staging of combustion

� Lower excess air utilization

Fuel Flexibility….

� COAL� LIGNITE� WASHERY REJECTS� CHAR� PETCOKE� BIOMASS � INDUSTRIAL REJECTS (CHAR ,ETP SLUDGE

ETC). � OIL� GAS

– Accepts wide range of fuels–Volatile matter, % 4 – 40

–Ash, % 0 – 70

–Heating value, Kcal/kg > 1500

–Moisture, % < 55

– Use of lower rank fuels reduces fuel costs

– Fuel flexibility - minimizes fuel supply uncertainties

– Ability to burn low cost and waste fuels

B&W IR-CFBC Boiler Fuel Flexible Technology

Difference between AFBC and CFBC

� Circulating bed, burning particles travel entire furnace

� Particle separation device ( U-beam , cyclone) is used, solids are recycled.

� No heating surfaces are provided in the bed ( which are prone for erosion)

Difference between AFBC and CFBC Design parameters

� Low temperature� High residence time� Air split� High heat transfer rate� Uniform furnace temperature� Low un-burnt carbon in ash� Bed material size� Lime stone size� Bed velocity

Internal Recirculation – Circulating Fluidized Bed Combustion Boiler

Boiler System Overview

B&W Internal Recirculation - Circulating Fluidized Bed Combustion Boilers

�A simplified approach to improved flexibility and reliability

�Design Features– High combustion

efficiency– Compact, economical

design– Higher reliability and

availability– Lower maintenance

costs– Reduced erosion– Fuel flexibility– Low emissions

U-Beam Separators

41

2

3FlueGas

&SolidFlow

FlueGas

�1. Sidewall� membrane panel

�2. U-beam - SS309H/ � SS310H/RA253MA

�3. Seal baffle

�4. Refractory

UU--BEAMS IN IRBEAMS IN IR --CFBC BOILERCFBC BOILER

U-Beam Separators

• SEGMENTAL “U” BEAMS

IR-CFBC U-Beam Segments

U-Beams

Water-cooled Support Tubes

Multicyclone Secondary Collector (Mechanical Dust Collector or MDC)

– Proven modular design– Predictable high

performance– Low maintenance

�Easy access�High hardness cyclone

tubes�No refractory

• High-hardness alloy casting

• Ceramic shape

Multicyclone Secondary Collector (Mechanical Dust Collector or MDC)

Overall Grade Separation Efficiency Comparison�B&W IR-CFBC Two Stage Solids Collection vs Hot Cyclone CFBC Collection

Particle Size, Micron

Effi

cien

cy, %

100

90

80

70

60

50

400 20 40 60 80 100 120

B&WIR-CFBC

Cyclone-BasedCFBC

B&W IR-CFBC Two-Staged Solids Separation System

�Benefits–High overall solid collection efficiency ~ More than 99.7%

–Precise furnace temperature control ~ By controlling solid recycle rate from the secondary collector

–Extended turndown ratio without use of auxiliary fuel (oil/gas) ~ 100% to 20% MCR

–Low auxiliary power requirements compared to cyclone-based CFBC technologies ~ 2-4” w.c. (50-100 mm w.c.)

(Refractory highlighted in yellow)

Thin Cooled Refractory

Low gas velocity through U-beam collector significantly reduces need for refractory

Lower Furnace Refractory Construction

• Studs anchor and cool the thin layer of refractory

• Minimal refractory maintenance

Refractory – Reduced Diameter Zone

• Significant reduction in tube and refractory erosion at refractory interface

Pin studs & refractory highlighted in yellow

Typical Bubble Cap

Fluidizing air jets

BubbleCap Bed

CFBC Boiler Design ComparisonB&W IR-CFB Hot-Cyclone Integral Cyclone Cold-Cyclone

Solids Separation System Two-stage (100% Single-stage (100% Single-stage (100% Single-stage (100%efficiency for particles of efficiency for particles of efficiency for particles efficiency for particles ofd>80 micron*) d>100 micron) d>100 micron) d>100 micron)

* Recycling finer particles increases furnace heat transfer rate, improves combustion efficiency and limestone utilization.

Upper Furnace Density lb/ft 3 (kg/m 3) 0.7 – 1.0 0.5 – 0.7 0.5 – 0.7 0.3 – 0.5(11 – 16) (8 – 11) (8 – 11) (5 – 8)

Furnace Temperature Control Desired temperature can Temperature is pre- Temperature is pre- Lower bed temperaturebe maintained within +/- determined by furnace determined by furnace is controlled by adjusting10 F interval for wide range and heat exchanger and heat exchanger cold cyclone ash recycleof fuels and operating design along with fuel design along with fuel rate. Temperature span conditions by adjusting and limestone properties and limestone properties across furnace height issecondary recycle rate. and sizing. and sizing. up to 200 F.

Boiler Turndown Without 5 : 1 3.5 : 1 3.5 : 1 3.5 : 1Auxiliary Fuel

Refractory:Thickness, in. (mm) 0.6 – 2.0 (15 – 50) ~3 (~75) on studded tubes ~3 (~75) ~2 (~50)

8-12 (200-300) on casing

Covered Areas Lower furnace, U-beam Lower furnace, cyclone Lower furnace, cyclone Entire furnace, cyclonezone enclosure walls recycle loop (5 – 10 times recycle loop (3 – 5 times (3 – 4 times more than @

more than @ B&W CFB) more than @ B&W CFB) B&W CFB)

Hot-Temperature Expansion Joints None 3 – 5 per cyclone Number varies with arrangement None

Furnace Shaft Velocity 15 –18 16 – 18 16 – 18 13 – 15[Design Range] , ft/s (m/s) (4.9 – 5.5) (4.9 – 5.5) (4.9 – 5.5) (4.0 – 4.5)

Furnace Exit Velocity, ft/s (m/s) 21 – 23 75 – 85 75 – 85 N/A(6.4 – 9.8) (22 – 26) (22 – 26) N/A

High-Pressure Air Not required Required for J-valves Required for J-valves Required for siphons

Total Pressure Drop Across Solids 4 (1.0) 6 – 8 (1.5 – 2.0) ~6 (~1.5) 4 – 6 (1.0 – 1.5)Separator(s), in. wc (kPa) (U-beams + MDC)

Auxiliary Power Consumption Lower Higher Higher Moderate

IR-CFBC Features / Benefits

–High upper furnace heat transfer rate and precise furnace temperature control

AND

–Extended turndown ratio (no oil/gas) 100% to 20% MCR�Are both the result of the B&W IR-CFB two stage solids collection /

recycle system characteristics

–Low auxiliary power requirements�Due to low flue gas ∆P and no fluidizing blower

IR-CFB Features / Benefits

–Fast shut down / cool down�80%+ of bed material is drained during cooldown. Can shutdown / cool /

enter / re-start within a 24 hour period compared to 2 to 3 times longer for other CFB design types

–Low Maintenance Costs�No refractory maintenance, no hot expansion joints, no fluidized sealing

system, low furnace exit velocity, low gas velocity in convective heating surfaces

FEATURES OF INTERNAL RECIRCULATION CFB

INTERNAL RECIRCULATION - MORE THAN 95 % BY U - BEAMS

U-BEAMS OF SS 309H / SS253 MA MATERIAL - NO MAINTENANCE

HIGH TEMP WITHSTAND CAPACITY ( 940deg.C)

LESS REFRACTORY WORK (Only 15% as - ALLOWS QUICK START UP

compared to cyclone design CFB) - LESS OIL CONSUMPTION

WITH CYCLONE DESIGN CFB’s

LOWER POWER CONSUMPTION - Draft loss across U-BEAMS - 1 INCH

- Draft loss across CYCLONE - >5 INCH

LOW GAS VELOCITY - IN U-BEAM AREA 5 TO 6 m /s

- CYCLONE INLET 20 TO 25 m / s

CONTROLLED EXTERNAL FLY ASH RECYCLE - FASTER LOAD RESPONSE

WITHIN +/- 15 DEG.C FROM TOP - FURNACE TEMP. IS MAINTAINED TO BOTTOM OF

FURNACE

WATER NOT REQUIRED FOR - FD AIR COOLES BED ASH IN FLUID BED BED ASH

COOLING COOLER

GAS RECIRCUL. NOT REQUIRED - PARTICULATE COLLECTION EFF. OF U-BEAMS

IMPROVES AT PART LOADS

ROOTS BLOWER NOT REQUIRED - FUEL IS INJECTED TO FURNACE WITH FD AIR

PRESSURE

ADVANTAGE OF CFBC BOILER FROM TBW

� HIGH INTERNAL CIRCULATIONImproved furnace performanceHigh operating efficiency

� LOW EXTERNAL CIRCULATIONNo J valve / L valveFiner control on performance

� COMPACT PRIMARY COLLECTORSmall footprint areaBoiler plant size reduced

� NO THICK REFRACTORYQuick start up

� TOP SUPPORTED INTEGRATED UNITNo hot expansion jointsReduced maintenance

� UNIFORM LOW VELOCITY IN FURNACE & SUPERHEATERReduces potential for erosionReduced maintenance

CFBC.PPT-7

LOWER MAINTENANCE - HIGH AVAILABILITY - BETTER RELIABILITY

• LESS USE OF REFRACTORY (TYPICALLY 75 TONS VS 450) (NO THICK REFRACTORY)

• FLUID BED ASH COOLER - NO MOVING PARTS

• AIR -SWEPT COAL FEEDER- NO MOVING PARTS

• METAL COATING / RDZ FOR REFRACTORY INTERFACE- COUNTERS EROSION

• BETTER S/H SUPPORT SYSTEM USED FOR ENHANCED RELIABILITY - NO SLINGER TUBES PRONE TO

EROSION

• DENSE STUDS PATTERN (96 per Ft2)- BETTER HEAT TRANSFER - BETTER REFRACTORY ADHERENCE

• NO REFRACTORY LINED DIP - LEG, ‘J’, ‘L’ VALVE HIGH MAINTENANCE ITEM ELIMINATED

• TRADITIONAL PENDANT VERTICAL LEG SUPERHEATER - NO FOULING

• NO SOOT BLOWERS REQUIRED - LESS MAINTENANCE -SAVING IN BLOW STEAM

• LOW GAS VELOCITY IN CONVECTION PASS. NO EROSION OF PRESSURE PARTS

• LOW GAS VELOCITY AND IN-LINE ARRANGEMENT OF ECONOMISER AND AIR HEATER TUBES REDUCED

EROSION POTENTIAL

• ASH RECYCLE SYSTEM (MDC) GIVES FASTER LOAD CHANGE RESPONSE.

• LOWEST NOX EMISSION LEVEL IN THE INDUSTRY -<100 PPM

THANKS