Circulating Fluidised Bed Technology

for Indian and other coals

Dr John Topper

IEA Clean Coal Centre, London

STEP-TREC Programme,Trichy,

December, 2013

Introduction

• Pulverised coal combustion provides over 90%

of global coal capacity

• CFBC technology offers greater fuel flexibility

and low cost emissions reduction

• Recent development of large, super-critical

boilers make CFBC a viable alternative for utility

power projects

Overview of PCC

• Coal is pulverised finely enough to ignite in a flame

(>1300˚C)

• State-of-the-art USC plants up to 47% efficient

• Problems with large deviation from design coal, or

high ash content (slagging and fouling)

Overview of CFBC

• High pressure air suspends solid fuel in a fluid-like state

• Particles escaping the furnace are returned by cyclones

• Low temperature combustion (800–900˚C) over a longer

residence time

• Low NOx, simple deSOx by limestone addition to furnace

Growth in boiler capacity

• First utility CFB boiler in 1985

• Similar rate of scale-up to PCC

• 800 MW CFB boilers commercially available

0

200

400

600

800

1000

1200

1400

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Un

it s

ize

, MW

PCC CFBC

Utility-scale CFBC plants

Northside

Lagisza SC

Samcheok SC

Gardanne

Sulcis

Baima

Baima SC

1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016

200

250

300

350

400

450

500

550

600

650

Year commissioned

Gro

ss e

lect

ical

ou

tpu

t, M

We

Foster Wheeler

Alstom

Harbin

Dongfang

BHEL - CFB Boilers – Experience

CFBC Boilers - 26Nos (18 In

Operation)

Less than 30 Mwe - 5

30 to 70 Mwe - 6

>70 to 135 MWe - 11

250 MWe - 4

BHEL – CFBC Technology Development

2007

1995

2006

1x125 MW (405 t/h) Rajastan Lignite based Power Plant for RVUNL

2004

3 x 275 t/h Pet Coke Fired Boilers for BORL

CFB Market Expanded in Utility Segment with 6 more 125MW

orders secured

First export order to PT IBR, Indonesia - 1x120

t/h coal fired boiler

2005

2008

175 t/h Boiler for Sinarmas Pulp & Paper Ltd firing coal & 2x125 MW

(390 t/h) Gujarat Lignite based Power Plant for GIPCL

2012

Export order received from Koniambo 2x

135MW & PT MSW 2x 126tph coal fired boiler

250 MW (845 t/h) Neyveli Lignite based Power Plant for NLC

commissioned

Performance of BHEL CFB Boilers – SLPP Units

Year 2012 - 13

Particulars Units 1&2 3&4

Availability Factor % 92.29 90.79

PLF % 83.86 80.86

Generation MU 1836.6 1770.89

• 1&2 Units Commissioned in 1999

• 3&4 Units Commisioned in 2010

• One of the best performing lignite

power plants

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

1999 2000 2001 2002 2003 2004 2005 2006

SLPP Boiler Availability

Unit #1 Boiler

Unit #2 Boiler

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

1999 2000 2001 2002 2003 2004 2005 2006

SLPP Continous Operation in Hours

Unit #1 Continuous Run

Unit #2 Continuous Run

Lagisza, Poland:

• First SC CFB, 460 MW unit

operating since 2009

• Local bituminous coal

Supercritical CFBC

Baima, China:

• 600 MW, largest in the world

• Trial operation April 2013

• Local high-ash anthracite

Ultra-supercritical CFBC

Samcheok Green Energy Centre, South Korea:

• 4 x 550 MW ultra-supercritical CFB boilers

scheduled for start-up in 2015

• Four more to follow

• Wide range of imported coal possible, up to 20%

biomass

Growth in CFBC market share

CFBC represents ~5–7% of global

coal capacity and is projected to

grow at over 12% per year.

Motivating factors:

• Response to stricter emissions

limits

• Exploiting cheaper fuels or using

poorer quality coal available (high

ash, waste coal, petcoke, lignite)

• Flexibility to international market

Efficiency

Combustion efficiency:

• Problems with high residual carbon have been

experienced for some fuels in CFBC

Boiler efficiency:

• In-furnace desulphurisation allows lower boiler

exit temperature without risk of acid corrosion

Thermal efficiency:

• Fluidising air fans consume more power than

wet FGD and pulverisers

• Supercritical steam has allowed a significant

gain in CFBC efficiency

0

2

4

6

8

10

12

Au

x. p

ow

er,

%Auxiliary power consumption

• Fan power can be

reduced by optimising

fluidisation state

• Requires control of fuel

size distribution

0

2

4

6

8

10

12

Normal Novel

Be

d p

ress

ure

dro

p, k

Pa

Coarse

Fine

2.3% points saved PCC w/ FGD

Load following

• Lower ramp rates in CFBC due to thermal inertia

of bed material: 2–4% MCR/min compared to 5%

MCR/min in PCC

• Hot or warm restarts easier in CFBC but cold

starts difficult

• Lower minimum loads without oil support

achievable for low volatile matter coal

• Transients and low loads detrimental to deSOx

Ash-related operational issues

• Very high ash coal can be used in CFBC as low

temperatures reduce slagging and fouling

• Bed agglomeration still a problem

• Erosion damage also a major concern

• Initially poor reliability for several utility CFB

boilers, particularly in China

Agglomeration

Erosion

Availability

CFB Boiler Initial

availability,

%

Availability/

(reliability)

2012, %

Northside 59 (2004) (99)

Gardanne 87 -

Spurlock 1 (Alstom) 92 -

Foster Wheeler

bituminous average

- (98.5)

Foster Wheeler

lignite average

- (98.3)

China 300 MW

average

78 87

SO2 emissions: PCC options

Wet FGD

Spray-dryer FGD

Emissions: NOx

• CFBC produces around 60% of PCC NOx

• SNCR is often added to meet limits

SCR SNCR CFBC + SNCR

Ammonia

use

Low High Moderate

Operating

cost

£ ££ £

Capital cost ££££ £ £

• The 550 MW boilers at

Samcheok will use SCR to

meet 50 ppm limit. May be

necessary for larger boilers.

SCR

SNCR

Emissions: Nitrous oxide

• CFBC produces high levels of N2O, over 300

times the greenhouse effect of CO2

• Potential for regulation

• Could be abated with SNCR/SCR or afterburning

Ash recycle

CFBC ash:

• High levels of lime and anhydrite

• Self-cementing, but can expand on hydration

• Not approved for use in concrete (principal PCC

fly ash use)

• Mostly used in mine reclamation: neutralising

acid soil or sealing-off acid drainage

Oxide (%) CFBC bed ash PCC fly ash

Silica 12.77 52.75

Alumina 5.25 22.94

Iron oxide 3.15 14.92

Lime 48.23 2.67

SO3

27.83 0.64

Acid mine drainage

Ash

CFBC ash applications:

• Lower grade construction applications (soil

stabilisation, road base, flowable fill)

• Waste stabilisation

• Agriculture

Quantity of ash is higher due to limestone.

PCC with wet FGD produces two saleable

byproducts: coal ash and gypsum.

Biomass cofiring

• CFBC widely used for biomass firing and

cofiring in Sweden and Finland

• Most large CFB produced by Foster

Wheeler offer 10–20% cofiring capability

• Coarser fuel feed acceptable

• Less problem with slagging

• Agro-wastes can also cause problems

for CFBC (agglomeration)

Virginia City CFB

Drax

Developments in Oxy-CFB technology

A simplified flow diagram of an oxy-CFB combustion process

Oxyfuel combustion

Possible advantages of CFBC for oxyfuel combustion:

• Heat transfer from circulating solids allows higher

oxygen concentrations: smaller boiler

• Positive boiler pressure reduces air ingress

• Lower excess air reduces oxygen demand per kW

• No new burner design required

CIUDEN

Capital costs

• Estimates of CFBC capital costs are beginning

to approach those of PCC.

• CFB boiler equipment is still more expensive,

but can be balanced by lack of FGD equipment,

SCR, and coal pulverisers.

PCC CFBC

Boiler ($/kW) 506 (w/ SCR) 678

FGD ($/kW) 297 0

Contingencies ($/kW) 204 311

Total plant cost ($/kW) 1879 1932

O&M ($/MWh) 14.1 14.4

LCOE ($/MWh) 73 78

Summary

• CFBC has achieved competitive efficiency and

costs

• Some fuel flexibility may be sacrificed for high

efficiency and reliability

• Strict emissions standards could make CFBC of

high sulphur coal less competitive

• CFBC ash markets limited

• High potential for biomass and oxyfuel

• Future growth depends on adoption of SC CFBC

in China; and India?

THE END

THANK YOU ALL FOR LISTENING

john.topper@iea-coal.org

Acknowledgements to Toby Lockwood and Qian Zhu of IEA

Clean Coal Centre who have both produced reports on CFBC on

which this presentation is based