Combustione ed ossicombustione industriale del carbone
1. PC firing
Leonardo Tognotti
University of Pisa, Italy&
International Flame Research Foundation
Corso di dottorato congiunto
Politecnico di Milano – Università di Napoli “Federico II”
Anacapri, Villa Orlandi, 5-9 Ottobre
Outline
The role of coal in the energy scenario
The drivers for innovation in clean coal
technologies
The processes associated with PC firing
Burners and boilers
Ash related problems
Comprehensive modelling of coal
combustion
The role of coal
38%
7%
25%
39%
24%
19%
6%
18%
6%17%
Primary energy demand Power generation
Coal covers approximately 1/4 of the world energy demand
Coal demand increases up to 40% in the power sector
Font: IEA World Energy Outlook 2004 and BP Statistical Review 2004
Oil
Natural gas
Nuclear
Coal
Hydro and other renewable
Fossil source: actual reservoirs
Developed
countries
R/P
192 years
Ge
ogra
ph
ical d
istr
ibu
tio
n
(%)
Transition
economiesMiddle East Other
developing
countries
R/P
67 years
R/P
41 years
To
tal re
se
rvo
irs
(GTe
p)
36%
11%5%
10%
6%
0%
35%
53%
19% 23%
35%
66%
484
158 157
0
100
200
300
400
500
Coal Gas Oil
0%
20%
40%
60%
80%
100%
Font: BP Statistical
Review 2004
Requirements for future power generation
The role of coal
Requirements for future power generation
Primary energy sources for electricity production
– Demand for new power plants until 2020:
– EU: 200 GW
– world: 2000 GW
• Developing countries: additional demand
• Europe: replacement
Huge investments are needed
in the next 20 years to replace
the aging infrastructure and to
continue BAU:
•1 000 billion euros in EU
•12 000 billion euros in the
world
0
1
2
3
4
5
6
20202000
40 %
13 %
29 %
12 %
43 %
10 %19 %
20 %
Prim
ary
energ
y (
Gto
e)
Nuclear
Oil
Gas
Coal
Renewables
Source: World Energy Outlook 2002
0
2
4
6
8
10
12
14
16
18
20
22
24
0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 >40Years
Pe
rce
nta
ge
of
Ins
talle
d C
co
al-
Fir
ed
Ca
pa
cit
y in
Eu
rop
e
0
20
40
60
80
100
120
140
160
180
200
Nu
mb
er
of
Pla
nts
37 % 63 %
Age of Coal-Fired Power Plants in Europe
Innovation is the most important instruments for long term
success of coal in power generation sector.
The main items are :
•Increase of efficiency.
•Abatement of pollutants.
•Reduction of CO2 emission.
•Social acceptance.
Sustainable coal: drivers
Increase of efficiency
Development of Coal Fired Power Stations
Today technology is proven for 280 bar, 600/610°C and is ready for 300 bar,
630/630°C. Japan has a competitive advantage of about 5 years on large “state-of-
the-art” installations.
Measures to improve efficiency
Condenser
pressureReheatingSteam
conditions
Stack gas
temperatureAir ratio40
41
42
43
44
45
46
Net
eff
icie
nc
y, %
(L
HV
)
1,25
1,15120°C
130°C25 MPa
540°C
30 MPa
600°C
Single
reheat
Double
reheat
0,0065
MPa
0,003 MPa
P.f. ultra-supercritical boilers,
CO2 emissions
200
400
600
800
1000
1200
25% 30% 35% 40% 45% 50% 55% 60%
Net efficiency, % (LHV)
CO
2 e
mis
sio
ns
g/k
Wh
Current average
EU countries
Plants to be
replaced
Average EU
countries 2010 Thermie
AD700
DC
O2
~ 3
0%
Source: PowerGen Europe 2003
New clean coal power Europe-wide and in the world
Power plant CompanyCapacity (MWe)
Steam temperature (°C)
Tsuruga 2 Hokoriku EPCo (J) 700 24.1 593/593 2000
Tachibana -wan 1&2 J-Power (J) 1050 x 2 24.6 600/610 2000/2001
Avedore 2 Energy E2 (DK) 410 30 580/600 2001
Hekinan 4&5 Chubo EPCo (J) 1000 x 2 24 568/593 2001 /2002
Tomatoh Atsuma 4 Hokkaido EPCo (J) 700 25 600/600 2002
Niederhaussem RWE (D) 965 27.5 580/600 2002
Isogo 1 J-Power (J) 60 0 24 600/610 2002
Reihoku 2 Kyushu EPCo (J) 700 24.1 600/600 2002
Hitachinaka Tokyo EPCo (J) 1000 24.5 600/600 2003
Maizuru 1 Ka n sai EPCo (J) 900 25.4 595/595 2004
Hirono 5 Tokyo EPCo (J) 600 25.4 600/600 2004
Genesee 3 EPCOR (CAN) 495 25 570/568 2005
Council Bluffs 4 Mid American Eco (USA) 790 25.3 566/593 2007
Yuhuan Huanen Pow. Int. (C ina ) 1000 x 4 25 600/600 2007
Weston 4 Wisconsin PServ. (USA) 530 25 585/585 2008
Torvaldaliga 2,3&4 Enel (I) 660 x 3 25 600/610 2008/2008/2009
Elm Road Wisconsin E Power (USA) 677 x 2 25.5 566/566 2008 /2009
Isogo 2 J-Power (J) 600 25 600/620 2009
Boa 2&3 Neurath RWE 2x1050 27.2 600/605 2009/2010
Walsum 10 Steag (D) 750 - 600/620 2010
Datteln 4 E.ON (D) 1100 25.5 600/620 2010
Boxberg R RWE 1x670 - - 2011
Hamm RWE 2x750 27.2 600/605 2011/2012
Moorburg Vattenfall 2x820 - - 2011/2012
Maasvlackte E.ON (D) 1100 25.5 600/620 2012
Steam pressure (MPa) Start-up
Enel Torrevaldaliga Nord power plant
First unit in service late 2008, will be the first 600°C SH unit in Europe.
Coal
storage
Boilers
Turbine
housing
Fabric filter
Wet FGD
State-of-the-art Performance
Efficiency (LHV, net) ~45%
PSH 242 bar
TSH (turbine inlet) 600°C
TRH (turbine inlet) 610°C
Cond. back pressure 0.042 bar
Very Low Emissions
(mg/Nm3 @ 6% O2)
SO2 100 (200)
NOx 100 (200)
Dust 15 (30)
( ) EU Directive 2001/80/EC
96/62/EC Ambient Air Quality Assessment and Management
99/30/EC Air quality standard for PM10, SO2, NOx e lead
00/69/EC Air quality standard for CO and Benzene
02/03/EC Air quality standard for Ozone
04/107/EC Air quality standards for Cd, As, Ni, benzo(a)P
Air Quality
Two wheel
veichles
97/24/EC
Incineration
00/76/EC
VOC
99/13/EC
IPPC
96/61/EC
Acidification
99/32/EC
01/80/EC (LCPs)
01/81/EC
Auto OIL
98/69/EC
98/70/EC
99/96/EC
Environmental drivers
Air quality management: European Legislation
SO2
NOx
PM
USA 609/EC USA 81/EC USAHawthorn
Japan3ten
0
200
400
600
800
1000
1200
1400
1600
1979 1988 1999-2000 2001 2001 2002 2010
ItalyTorre Nord
mg/N
m3, 6%
O2
Emissions: limit trends for coal power stations
Factors driving clean coal technology
Environmental issues
0
0,1
0,2
0,3
1980DM
12.7.90
EU
2000/76/EC
Hg
Cd+Tl
Present limits
0
100
200
300
VOC
Hg+Cd+TlNo
limits
Micropollutants: Heavy metals and fine particulate
Directive (2004/107/EC): Limit values of arsenic, cadmium, mercury, nickel and
polycyclic aromatic hydrocarbons in ambient air – link to PM10 and PM2.5
Factors driving clean coal technologies
Environmental issues
Processes associated with PC combustion
Fundamentals
Pollutant abatement
FF DeSOx
GGH
DeNOxBoiler
TSDFly ash
Liquid drain
Gypsum
LJ
ΔNOx = 30-70% ΔNOx = 80-90%
Δdust = 99,9%
ΔSOx = 97%
PC Boiler terminology
Coal Flames
Type 0 Type 1
Type 2
IFRF Aerodynamically Air-Staged Burners (AASB)
IFRF classification of Swirling Flames
Fricker and Leuckel, 1976
www.ifrf.net
Pulverised coal Burners
TEA-C
Low-NOX Burner
Secondary and tertiary air with
independent swirler
Fuels: NG, oil, coal
Coal burner technology
Low NOx burners
Burner Arrangements in PC Boilers
Tangential Burners for a PC Boiler
Advantages
- PC particles sweep around furnace volume, with longer
residence time.
• Improved coal particle burnout;
• Fuel-rich zone in inner region, surrounded by O2-rich SA
outer
• Low NOx: By detaching high T & high O2, two necessary
conditions for NOx;
• Oxidizing atmosphere along furnace water-wall (reducing
one is very corrosive)
Low-NOx combustion: in-furnace measures
SECONDARYAIR
PRIMARYAIR
TERTIARYAIR
DNOx 40%
LNB
LEAN
RICH
DNOx 50%
OFA
FLEAN
RICH
LEAN
DNOx 70%
Reburning
F
F
Burners and OFA
Ash related problems
Why?
• Slagging, fouling and corrosion
most important single reason
for unscheduled shut downs of boilers
• Fireside deposits on heat exchanger tubes
- decreased heat transfer to steam/water side
- increased pressure drop in fluegas channel
- corrosion of heat exchanger tubes
• Emission problem
Trace elements, health risk
Mechanisms of slagging and fouling
Ash Formation
• Fuel
• Furnace
Transportation mechanisms
• Particle size
• Flow field
Deposit formation (adhesion,
densification)
• Chemistry
• Temperature vs time1 Fuel
2
Combustionwith ashformation
4Depositformation
3Transportto wall
Melting
Includedminerals
Organic
Fragmentation
Vaporization
Nucelation
< 1 m > 1 m Fly ash
Extraneousminerals
Diffusion - Impaction
Deposit
- porous
- molten
700
750
800
850
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
1450
1500
1550
tem
pe
ratu
re [
°C]
softening to hemispherical (ST-HT) hemispherical to fluid (HT-FT)
european
hard coal
wood
samplesdifferent straw samples
energy
crop
36 samples
miscanthus
sinensis
standard
deviation
and mean
value
Ash Fusion Characteristics
Comprehensive coal combustion modelling
The framework is based on CFD using numerical solutions of
multidimensional, differential equations for conservation of
mass, energy, and momentum.
Other submodels are coupled within this framework to
account for gaseous species mixing and chemical reactions,
solid fuel particle devolatilization and char oxidation, and
radiant energy transport.
A comprehensive model must balance submodel
sophistication with computational practicality.
Much of the research in this field is aimed at both improved
solution techniques, and new or more “efficient” submodels
able to provide practical engineering solutions.
Comprehensive modeling of PC firing systems:
sub-models
Coal ignition/flame sub-model• Coal particle trajectories
• Devolatilisation
• Homogeneous combustion chemistry
• Burner aerodynamics and heat transfer
Char burnout sub-model
Ash partitioning sub-model• Deposition
• Trace metals
Heat transfer sub-model• Radiant zone
• Convection zone
Combustion by-products• NOx, SOx, Hg chemistry
Integrated furnace model Calculation of heat transfer, species, temperature
profiles in all furnace zones
The approach
FINAL APPLICATION
SCALING UP, KNOW HOW
CFDTESTING AT THE
PILOT SCALE
FLUID-DYNAMIC TESTS
COMBUSTION TESTS
LAB ANALYSIS
SUBMODELSDEVO, COMB, RADIATION
SEMI INDUSTRIAL/
FULL SCALE
TESTSSCALING UP, KNOW HOW
INDUSTRIAL PROBLEMPHISICAL MODEL DESIGN
SCALING DOWN
Essential feature: validation
Validation is an essential part of development of any
mathematical model
Collection of in-flame data- semi-industrial tests
“Ad hoc” experiments for sub-models
(coal combustion: Isothermal Plug Flow Reactor for
high temperature kinetics)
• Thermo Gravimetric Analysis
• Hot Wire Mesh systems
• Single particle methods (different suspension
methods- aerodyn., captive, electrodynamic)
• Drop tubes, plug flow reactors
• Lab scale Fluidised Beds
• .......................................................
• Chemical and physical analysis of fuel and products
• (Ex. Elemental/proximate analysis, chemical
fractionation, FTIR, SEM, NMR, surface areas,
• ......Grindability test and Index, ash melting tests
Fuel characterisation: Methodologies/apparata
Isothermal Plug Flow Reactor “IPFR”
IPFR is a drop tube reactor which is usedfor the characterization of solid fuels(i.e coals, biomass etc.).
Five principal sections:
i) gas pre-heater
ii) vertical reactor
iii) particles injection
iv) quench
v) particles collection system
Vertical
Reactor
Gas pre-heater
Quench
Particles
injeion
Particles collection system
N2 , CO2, Air
Length 4.5 m
Diameter 0.15 m
Min operating T 700 °C
Max operating T 1400 °C
Min residence time 5 ms
Max residence time 1500 ms
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 50 100 150 200 250 300 350
time (ms)
Devo
lati
lizati
on
co
nvers
ion
(%
)
