Post on 08-Apr-2018
transcript
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
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
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