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Piero Salatino, Osvalda SennecaPiero Salatino, Osvalda Senneca
DipartimentoDipartimento didi IngegneriaIngegneria ChimicaChimicaUniversitàUniversità deglidegli StudiStudi didi NapoliNapoli Federico IIFederico II
IstitutoIstituto di Ricerche sulla Combustione di Ricerche sulla Combustione ConsiglioConsiglio Nazionale delle Nazionale delle RicercheRicerche
PRINCIPI DI COMBUSTIONE E GASSIFICAZIONE DI SOLIDI
PRINCIPI DI COMBUSTIONE E GASSIFICAZIONE PRINCIPI DI COMBUSTIONE E GASSIFICAZIONE DI SOLIDIDI SOLIDI
Shrinkage,Secondary fragmentation
Swelling,Primary fragmentation
Size and morphological
changes
Thermal annealing(change of turbostratic carbon structure,
ash sintering/melting)
Oxidation by H2O, CO2, H2Oxidation by O2Coal depolymerization, Tar/gas release,
Metaplast cross-linking and resolidification
Chemical and microtextural
changes
Char gasificationChar combustionDevolatilization
OUTLINE OF THE STAGES OF COAL GASIFICATIONand related coal transformations
OUTLINE OF THE STAGES OF COAL GASIFICATIONOUTLINE OF THE STAGES OF COAL GASIFICATIONand related coal transformationsand related coal transformations
• Coal can be represented as reasonablyordered polyaromatic domains withamorphous aliphatic groups;
• Stage I of the coalification process movesfrom the nearly amorphous parent coalmaterial to yield ordered polycyclic lamellae(C%≅90), approaching a first coalificationpole;
• Stage II of the coalification process yieldscondensation of polyaromatic domains withhydrogen release approaching a second coalification pole;
PYROLYSIS VERSUS THERMAL ANNEALING:THE “TWO-COMPONENT” HYPOTHESIS
OF COAL STRUCTURE
PYROLYSIS VERSUS THERMAL ANNEALING:PYROLYSIS VERSUS THERMAL ANNEALING:THE THE ““TWOTWO--COMPONENTCOMPONENT”” HYPOTHESIS HYPOTHESIS
OF COAL STRUCTUREOF COAL STRUCTURE
Stage IStage II
van Krevelen diagram (taken from Hurt, 1998)
• Carbonization resembles (but does notreproduce) the coalification process, exhibiting a first and a secondcarbonization poles;
• Pyrolysis may be assumed as stage I of carbonization (C%<90);
• Thermal annealing represents stage II of the carbonization process, yieldingstacking and condensation of polyaromaticdomains with hydrogen release;
• Changes (sintering/melting) of mineral matter further add on the complexity of thethermally-activated transformations of coal.
after Fletcher (2005)
MODELLING DEVOLATILIZATION OF NON-SOFTENING COALS
MODELLING DEVOLATILIZATION MODELLING DEVOLATILIZATION OF NONOF NON--SOFTENING COALSSOFTENING COALS
FG DVC [Solomon & coworkers]
FLASHCHAIN [Niksa & coworkers]
CPD [Fletcher & coworkers]
Rates and yields of devolatilization products (char, tar, light gases) predicted accounting for: structural models of coal(assessed via NMR or inferred through elemental analysis), vapor pressure equilibria, kinetics of coal fragmentation, metaplastcross-linking and decomposition.
MODELLING THE CHEMISTRY OF COAL DEVOLATILIZATION: STRUCTURAL MODELS
MODELLING THE CHEMISTRY OF COAL MODELLING THE CHEMISTRY OF COAL DEVOLATILIZATION: STRUCTURAL MODELSDEVOLATILIZATION: STRUCTURAL MODELS
FRAGMENTATION OF THE COAL NETWORKDURING PRIMARY PYROLYSIS
FRAGMENTATION OF THE COAL NETWORKFRAGMENTATION OF THE COAL NETWORKDURING PRIMARY PYROLYSISDURING PRIMARY PYROLYSIS
after Fletcher (2005)
THE ROLE OF “METAPLASTS”THE ROLE OF THE ROLE OF ““METAPLASTSMETAPLASTS””
after Fletcher (2005)
DEVOLATILIZATION AT HIGH-PRESSUREDEVOLATILIZATION AT HIGHDEVOLATILIZATION AT HIGH--PRESSUREPRESSURE
after Yu et al. (2007)
after Suuberg (1977)
DEVOLATILIZATION AT HIGH-PRESSUREDEVOLATILIZATION AT HIGHDEVOLATILIZATION AT HIGH--PRESSUREPRESSURE
Retention and/or crosslinking
of tars
COAL SOFTENING AND “SWELLING”AT HIGH PRESSURE
COAL SOFTENING AND COAL SOFTENING AND ““SWELLINGSWELLING””AT HIGH PRESSUREAT HIGH PRESSURE
after Wall et al. (2002) after Zeng and Fletcher (2005)
• Smaller weight loss and comparativelyeven smaller tar yield as pressureincreases.
• Hindered tar release favours “metaplast” accumulation at moderately high pressureswhich, in turn, promotes coal softening and swelling.
• Secondary coking favoured by hindranceof tar vaporization and repolymerization of metaplasts.
COAL DEVOLATILIZATION AT HIGH PRESSURE: HIGHLIGHTS
COAL DEVOLATILIZATION AT HIGH COAL DEVOLATILIZATION AT HIGH PRESSURE: HIGHLIGHTSPRESSURE: HIGHLIGHTS
after Zeng & Fletcher (2005)
MODELLING DEVOLATILIZATION AT HIGH-PRESSUREMODELLING DEVOLATILIZATION AT HIGHMODELLING DEVOLATILIZATION AT HIGH--PRESSUREPRESSURE
MODELLING DEVOLATILIZATION OF SOFTENING COALS
MODELLING DEVOLATILIZATION MODELLING DEVOLATILIZATION OF SOFTENING COALSOF SOFTENING COALS
after Oh, Peters and Howard (1989)
after Yu et al. (2004)
MODELLING DEVOLATILIZATION OF SOFTENING COALS
MODELLING DEVOLATILIZATION MODELLING DEVOLATILIZATION OF SOFTENING COALSOF SOFTENING COALS
• Comprehensive models of devolatilization of non softeningcoals at atmospheric pressure are available, reasonably wellvalidated.
• Modelling of devolatilization at moderate/high pressure ismuch more immature and mostly qualitative.
• Additional focus is called on:– Plastic behaviour of softened coal– Enhanced metaplast cross-linking and resolidification– Coking during secondary pyrolysis
• Better assessment of the “memory” of devolatilization in charproperties:– Enhanced development of vescicular/cenospheric structures– Increased propensity to thermal annealing along with
gasification
MODELLING OF DEVOLATILIZATIONMODELLING OF DEVOLATILIZATIONMODELLING OF DEVOLATILIZATION
MODELLING PRIMARY FRAGMENTATION DURING DEVOLATILIZATION OF COALS
MODELLING PRIMARY FRAGMENTATION MODELLING PRIMARY FRAGMENTATION DURING DEVOLATILIZATION OF COALSDURING DEVOLATILIZATION OF COALS
PRIMARY FRAGMENTATION UNDER FBC CONDITIONS
PRIMARY FRAGMENTATION PRIMARY FRAGMENTATION UNDER FBC CONDITIONSUNDER FBC CONDITIONS
after Chirone and Massimilla (1989)
PRIMARY FRAGMENTATION IN PC FIRING (at atmospheric pressure)
PRIMARY FRAGMENTATION IN PC FIRING PRIMARY FRAGMENTATION IN PC FIRING (at atmospheric pressure)(at atmospheric pressure)
after Dacombe et al. (1999)
• There is a lack of primary fragmentation data and models suitable for application to high pressure.
• Smaller VM yield and larger coal plasticity duringpyrolysis might reduce the extent of primaryfragmentation, but experimental confirmation islacking.
• The formation of vescicular/cenospheric chars at high pressure might shift fragmentation from the devolatilization stage (primary) to the chargasification stage (secondary fragmentation)
PRIMARY FRAGMENTATIONPRIMARY FRAGMENTATIONPRIMARY FRAGMENTATION
MODELLING COMBUSTION AND GASIFICATION OF CHAR
MODELLING COMBUSTION AND GASIFICATION MODELLING COMBUSTION AND GASIFICATION OF CHAROF CHAR
Reazioni di combustione e gassificazione del char
ReazioniReazioni didi combustionecombustione e e gassificazionegassificazione del chardel char
Le reazioni di combustione del char sono: 1. C + ½ O2 → CO ∆H = -26.4 kcal/mol 2. C + O2 → CO2 ∆H = -94.2 kcal/mol cui si affianca la reazione in fase omogenea 3. CO + ½ O2 = CO2 ∆H = -67.6 kcal/mol
Le reazioni di gassificazione del char sono: 4. C + H2O = CO + H2 ∆H = 32.2 kcal/mol 5. C + CO2 = 2 CO ∆H = 41.4 kcal/mol 6. C + 2 H2 = CH4 ∆H = -20.2 kcal/mol
Cui vanno associate le seguenti reazioni in fase gas: 7. CO + H2O = H2 + CO2 ∆H = -9.2 kcal/mol 8. CO + 3 H2 = CH4 + H2O ∆H = -52.4 kcal/mol 9.H2 + ½ O2 = H2O ∆H = -58.6 kcal/mol
after Kajitani et al. (2002)
CINETICA INTRINSECA:APPROCCIO LUMPED
CINETICA INTRINSECA:CINETICA INTRINSECA:APPROCCIO LUMPEDAPPROCCIO LUMPED
• Lo schema lumped è inadeguato in condizioni estreme• I dati di cinetica intrinseca sono molto scatterati ed incerti• Equazioni di bilancio di materia e di energia (il problema del
trasporto)• Interazione tra fenomeni puramente termici e reazioni
eterogenee
MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI
CHAR
MODELLI DI MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI COMBUSTIONE/GASSIFICAZIONE DI
CHARCHAR
48
2
7
26
2
5
42
23
22
2
12
2
)(
)(
)(
)(
,)(
)(,)(
)(
CHHC
COOC
HOCOHC
COOC
COOCCOC
CCOCOOC
OCCOCOOOC
OCOC
→+
→
+→+
→
+→+
+→
+→+
→+
combustion
gasification
CINETICA INTRISECA SEMIDETTAGLIATACINETICA INTRISECA SEMIDETTAGLIATACINETICA INTRISECA SEMIDETTAGLIATA
CH
'6OH6CO
'4CO47
CO417CO C
)z(Pk)z(Pk)z(Pk)z(Pkk
)z(Pk)1(kR
222
2
2 +++++=
γγγ
2kPk
PkkPkkR
3O1
O312O21
O
2
22
2
+⋅
⋅+⋅=
CH
'6OH6CO
'4CO47
OH617OH C
)z(Pk)z(Pk)z(Pk)z(Pkk
)z(Pk)1(kR
222
2
2 +++++=
γγγ
CINETICA INTRISECA SEMIDETTAGLIATACINETICA INTRISECA SEMIDETTAGLIATACINETICA INTRISECA SEMIDETTAGLIATA
• Lo schema lumped è inadeguato in condizioni estreme• I dati di cinetica intrinseca sono molto scatterati ed incerti• Equazioni di bilancio di materia e di energia (il problema del
trasporto)• Interazione tra fenomeni puramente termici e reazioni
eterogenee
MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI
CHAR
MODELLI DI MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI COMBUSTIONE/GASSIFICAZIONE DI
CHARCHAR
0.001
0.01
0.1
1
10
100
1000
0.0004 0.0005 0.0006 0.0007 0.0008 0.0009
1/T, K-1
t gas
if, s
Liu et al.
Kajitani et al.
Tominaga et al., fast
Tominaga et al., slow
wen&chaung
boundary layer diffusion limit
@P=20bar; CO2=16%, H2O=50%, CO=H2=16%; dp=40µm
GASIFICATION TIME SCALESGASIFICATION TIME SCALESGASIFICATION TIME SCALES
rang
eof
res
iden
ce ti
mes
range of operating temperatures
• Lo schema lumped è inadeguato in condizioni estreme• I dati di cinetica intrinseca sono molto scatterati ed incerti• Equazioni di bilancio di materia e di energia (il problema del
trasporto)• Interazione tra fenomeni puramente termici e reazioni
eterogenee
MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI
CHAR
MODELLI DI MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI COMBUSTIONE/GASSIFICAZIONE DI
CHARCHAR
( )( )( )
( )εεερερρ
εεεε
−+=
−+=
−+=
−+=
1
1
1
1
sg
scgc
scgcc
sg
DDD
kkk
ccc
Solido pienoSv=1 cm2/g
Solido porosoSv=10-1000m2/g
Solido non poroso
1. Trasporto di materia per reagenti e prodotti attraverso lo strato limite gassoso 2. Trasporto di materia per reagenti e prodotti attraverso l’eventuale strato di
ceneri3. Reazione del gas sulla superficie del solido
Reagente gassoso A
Solido non poroso, ceneri incoerenti
( )
ASA
molg
AASAga
kcr
ScfL
DShk
rcckN
=
==
=−= ∞
"
"
)(Re,*
sm
moliA2
( )
ASA
molg
AASAog
kcr
ScfL
DShk
SrccSk
=
==
=−∞
"
"2
)(Re,*
Solido non poroso, ceneri coerenti
molg
g
g
gg
mol
g
DSc
Lv
D
LkSh
ρµµ
ρ
=
=
=
Re
In generale le reazioni eterogenee del tipo gas-solido sono caratterizzate da un network di processi chimici e fisici in serie-parallelo tra loro, ovvero:
1. Trasporto di materia per reagenti e prodotti attraverso lo strato limite gassoso 2. Trasporto di materia per reagenti e prodotti attraverso l’eventuale strato di ceneri3. Trasporto di materia all’interno dei pori del solido reagente4. Reazione del gas sulla superficie del solido
Solido poroso
Reagente gassoso A
Solido poroso
vAAA rxcDvct
c −∇⋅∇=⋅∇+∂
∂*
"AA rncD =⋅∇
A
z
y
Bilancio nella fase gas
Condizione al contorno sulla superficie solida
02 =∇ Ax
A
Ipotesi di unidimensionalità
vAA
eff kSrdz
cdD == "
2
2
)( ASAgA
eff cckdz
dcD −= ∞
z
y
Condizione al contorno sulla superficie solida
0=dz
dcD A
eff
A
3
2
223
2
][1
m
m
sm
mol
mm
mol
s
m =
Particella porosaipotesi di unidimensionalità
vAA
eff kSrdz
cdD == "
2
2
[ ]s
mDDeff
2
==τε
Dm=10-4-10-5 m2/sDK=10-6-10-7 m2/s
Datt=10-16-10-18 m2/s
323
33
2
223
2
1][
exp
exp
][][
m
mol
ssm
mol
cRT
Ekk
cRT
Ekk
sm
mol
m
m
sm
mol
mm
mol
s
m
Aov
nAov
=
−⋅=
−⋅=
==
k
)(
T
1
s
HDeff ∆−=β
Regime IIProfilo A”
Regime IProfilo A
>>1
Regime IIIProfilo C
<<1
>>1<<1Thiele
Biot/Sherwood( )
2
1
S
V 1
est
+⋅⋅=− n
D
Ck
eff
nAs
vϕ
eff
g
D
LkBi =
vseff
vA
eff
kHdz
Tdk
kdz
cdD
⋅∆−=
=
2
2
2
2
mol
g
D
LkSh=
Caso non isotermo
η<<1
η<0,5
η = 11/T
b II a
LnR
III I
Profili di concentrazione del reagente gassoso all’interno ed all’esterno di una
particella di char
Diagramma di Arrhenius
( )dX
XDXA
X
TkDShD
d
cdTcR
X
eash∫+
+
++
= ∞∞ *
0 )()(12
)(2
21
,,
αδα
( )[ ] ( ) ( )4412 ∞∞→→ −+−=∆−+∆ TTTT
d
NukHHR t
COCCOC σεαα
Apparent reaction kinetics for lumped kinetics(per unit external surface, linear kinetics, ϕ >>1):Apparent reaction kinetics for lumped kineticsApparent reaction kinetics for lumped kinetics
(per unit external surface, linear kinetics, (per unit external surface, linear kinetics, ϕ >>1):>>1):
• Lo schema lumped è inadeguato in condizioni estreme• I dati di cinetica intrinseca sono molto scatterati ed incerti• Equazioni di bilancio di materia e di energia (il problema del
trasporto)• Interazione tra fenomeni puramente termici e reazioni
eterogenee
MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI
CHAR
MODELLI DI MODELLI DI COMBUSTIONE/GASSIFICAZIONE DI COMBUSTIONE/GASSIFICAZIONE DI
CHARCHAR
Shrinkage,Secondary fragmentation
Swelling,Primary fragmentation
Size and morphological
changes
Thermal annealing(change of turbostratic carbon structure,
ash sintering/melting)
Oxidation by H2O, CO2, H2Oxidation by O2Coal depolymerization, Tar/gas release,
Metaplast cross-linking and resolidification
Chemical and microtextural
changes
Char gasificationChar combustionDevolatilization
INTERAZIONE TRA FENOMENI PURAMENTE TERMICI E REAZIONI ETEROGENEE
INTERAZIONE TRA FENOMENI PURAMENTE INTERAZIONE TRA FENOMENI PURAMENTE TERMICI E REAZIONI ETEROGENEETERMICI E REAZIONI ETEROGENEE
FRAMMENTAZIONE SECONDARIAFRAMMENTAZIONE SECONDARIAFRAMMENTAZIONE SECONDARIA
After Wall et al. (2002)
after Kang et al. 1992
PERCOLAZIONEPERCOLAZIONEPERCOLAZIONE
PERCOLAZIONEPERCOLAZIONEPERCOLAZIONE
after Miccio, Salatino and Tina, 2000
increasing burn-off
PyrolysisPyrolysisCHARCHAR
GASIFICATIONGASIFICATIONPRODUCTSPRODUCTS
COALCOAL
HeterogeneousHeterogeneous gasificationgasification reactionsreactions
INTERAZIONE TRA FENOMENI PURAMENTE TERMICI E REAZIONI ETEROGENEEL’APPROCCIO CLASSICO
INTERAZIONE TRA FENOMENI PURAMENTE TERMICI E INTERAZIONE TRA FENOMENI PURAMENTE TERMICI E REAZIONI ETEROGENEEREAZIONI ETEROGENEELL’’APPROCCIO CLASSICOAPPROCCIO CLASSICO
PyrolysisPyrolysis
“YOUNG”YOUNG”CHARCHAR
GASIFICATIONGASIFICATIONPRODUCTSPRODUCTS
COALCOAL ““ ANNEALED”ANNEALED”CHARCHAR
AnnealingAnnealing
Purely thermally activated processes
HeterogeneousHeterogeneous gasificationgasification reactionsreactions
Interazione tra fenomeni puramente termici e reazioni eterogenee
L’approccio classico
Interazione tra fenomeni puramente termici e reazioni Interazione tra fenomeni puramente termici e reazioni eterogeneeeterogenee
LL’’approccioapproccio classicoclassico
PyrolysisPyrolysis
“YOUNG”YOUNG”CHARCHAR
GASIFICATIONGASIFICATIONPRODUCTSPRODUCTS
COALCOAL ““ ANNEALED”ANNEALED”CHARCHAR
AnnealingAnnealing
Purely thermally activated processes
HeterogeneousHeterogeneous gasificationgasification reactionsreactions
Interazione tra fenomeni puramente termici e reazioni eterogenee
L’approccio classico
Interazione tra fenomeni puramente termici e reazioni Interazione tra fenomeni puramente termici e reazioni eterogeneeeterogenee
LL’’approccioapproccio classicoclassico
volatile matter release
annealing
pyrolysis
stacking of graphene layers
change of carbon hybridization
course of heat-treatment, ξξξξ
crystallite growth
heterogeneous oxidation inhibited
heterogeneousoxidation
active
ξξξξ*
release of interlayer defects
release of in-plane defects
volatile matter release
annealing
pyrolysis
stacking of graphene layers
change of carbon hybridization
course of heat-treatment, ξξξξ
crystallite growth
heterogeneous oxidation inhibited
heterogeneousoxidation
active
ξξξξ*
release of interlayer defects
release of in-plane defects
after Senneca and Salatino, 2002
PYROLISI/ THERMAL ANNEALINGPYROLISI/ THERMAL ANNEALINGPYROLISI/ THERMAL ANNEALING
after Marsh and Griffiths (1982)
THERMAL ANNEALINGTHERMAL ANNEALINGTHERMAL ANNEALING
after Shim and Hurt, 2000
C-O2
A B
C D
0.05µm 0.05µm
0.05µm
0.05µm
900°C for 1 minin nitrogen
1350°C for 30 min in nitrogen
1165°C for 30 min in nitrogen
1165°C for 1 min in nitrogen after char oxidation
ORDINE CRISTALLOGRAFICO E TRATTAMENTO TERMICO
ORDINE CRISTALLOGRAFICO E ORDINE CRISTALLOGRAFICO E TRATTAMENTO TERMICOTRATTAMENTO TERMICO
Number distribution of angular orientations of frin ges in char samples subjected to different heat treatments.
Angle of orientation, deg
0 20 40 60 80 100 120 140 160 180
Num
ber
dist
ribut
ion,
%
0
5
10
15
20
25
30
900°C 1min
Angle of orientation, deg
0 20 40 60 80 100 120 140 160 180
Num
ber
dist
ribut
ion,
%
0
5
10
15
20
25
30
900°C 1min 1165°C 30min
Angle of orientation, deg
0 20 40 60 80 100 120 140 160 180
Num
ber
dist
ribut
ion,
%
0
5
10
15
20
25
30
900°C 1min 1165°C 30min
1350°C 30min
Angle of orientation, deg
0 20 40 60 80 100 120 140 160 180
Num
ber
dist
ribut
ion,
%
0
5
10
15
20
25
30
900°C 1min 1165°C 30min
1350°C 30min1165°C 30min with 1 oxygen pulse1165°C 30 min after char oxidation
ORDINE CRISTALLOGRAFICO E TRATTAMENTO TERMICO
ORDINE CRISTALLOGRAFICO E ORDINE CRISTALLOGRAFICO E TRATTAMENTO TERMICOTRATTAMENTO TERMICO
HT W/Ochar preoxidation
HT withchar preoxidation
INTERAZIONE TRA OSSIDAZIONE E ANNEALING INTERAZIONE TRA OSSIDAZIONE E ANNEALING INTERAZIONE TRA OSSIDAZIONE E ANNEALING
)E(FF
d)(RT
EexpAexp
F
F
RT
EexpFA
dt
dF
F,D
t
0
F,DD
0
F,DD
=
−⋅−=
−⋅⋅−=
∫ θθ
MODELLI DI THERMAL ANNEALINGDAEM model di Suuberg (1991)
MODELLI DI THERMAL ANNEALINGMODELLI DI THERMAL ANNEALINGDAEM model DAEM model didi SuubergSuuberg (1991)(1991)
( ) ( )[ ] )1n(1dd
0
tRTEexpA1n1RR
RR −−
∞
∞ −−+=−−
ξ annealing progress variable (0:young char; 1: annealed char)R reactivity of the heat treated charRo reactivity of the “young” charR∞ reactivity of the “fully annealed” charT heat treatment temperaturet time of heat treatment
( ) )RT/Eexp(Ak1kdt
ddd
n −⋅=−⋅= ξξ
MODELLI DI THERMAL ANNEALINGLa legge di potenza di Salatino e Senneca (1999)
MODELLI DI THERMAL ANNEALINGMODELLI DI THERMAL ANNEALINGLa La leggelegge didi potenzapotenza didi Salatino e Senneca (1999)Salatino e Senneca (1999)
MODELLI DI THERMAL ANNEALING“Diffusion” model di Bhatia et al. (2004)MODELLI DI THERMAL ANNEALINGMODELLI DI THERMAL ANNEALING“Diffusion” model “Diffusion” model didi Bhatia et al. (2004)Bhatia et al. (2004)
Senneca & Salatino, Combustion Flame 144 578 (2006)
Le scale temporaliLe scale temporaliLe scale temporali
Cy Ak
→ CA (1)
Cy* Ak
→ CA* (2)
2 Cy* + O2
y1
→ 2 Cy*(O) (3)
2 CA* + O2
A1
→ 2 CA*(O) (4)
Cy + O2 +Cy*(O) y2
→ CO2 + Cy*(O) (5)
Cy + C*y(O) y3
→ CO + Cy* (6)
CA + O2 +CA*(O) A2
→ CO2 + CA*(O) (7)
CA + CA*(O) A3
→ CO + CA* (8)
Un modello che include cinetica semidettagliata e thermal annealing
Un modello che include cinetica Un modello che include cinetica semidettagliatasemidettagliata e e thermalthermal annealingannealing
1/T [1/K]
0,0003 0,0004 0,0005 0,0006 0,0007 0,0008 0,0009 0,0010 0,0011
ln r
[1/s
]
-6
-4
-2
0
2
4
senza annealing (caso base)rid = 10rid = 100 (caso base)rid = 1000
Un modello che include cinetica semidettagliata e thermal annealing
Un modello che include cinetica Un modello che include cinetica semidettagliatasemidettagliata e e thermalthermal annealingannealing
Nagle, J., Strickland-Constable, R.F., Oxidation of carbon between 1000-2000°C, Proc. of Fifth Conf. Carbon, Vol. 1,
Macmillan, p.154 (1962)
GASIFICATION:TECHNOLOGY SURVEY
GASIFICATION:GASIFICATION:TECHNOLOGY SURVEYTECHNOLOGY SURVEY
gaseous fuels
hydrogenation
oxidation
slow pyrolysis
fast pyrolysis
steam reforming
Flow Regime moving bed fluidized bed entrained flow
Fuel type solids solids solids or liquids
fuel particle size 5 - 50 mm 0.5 - 5 mm < 500 microns
residence time 15 - 30 min 5 - 50 s 1 - 10 s
oxidizer air/oxygen air/oxygen oxygen
temperature at the exhaust
400 - 500 ºC 700 – 900 ºC 900 – 1400 ºC
ash handling slagging and non-slagging non-slagging always slagging
commercial technologies
Lurgi dry-ash (non-slagging), BGL (slagging)
GTI U-Gas, HT Winkler, KRW
GE Energy, Shell, Prenflo, ConocoPhillips, Noell
"moving" beds are mechanically stirred, fixed
beds are not
bed temperature lower than ash melting point
not suitable for high ash fuels
countercurrent flow suitable for high-ash fuelsnot suitable for poorly
grindable fuels
Note: The "transport" gasifier flow regime is between fluidized and entrained and can be air- or oxygen-blown.
Note
Oxygen Blown
• Entrained Flow– Texaco– E-GAS– Shell– Prenflo– Noell
• Fluidized Bed– HT Winkler– Foster Wheeler
• Moving Bed– British Gas Lurgi– Sasol– Lurgi
• Transport Reactor– Kellogg
Air Blown
• Fluidized Bed– HT Winkler– IGT “Ugas”– KRW– Foster Wheeler
• Spouted Bed– British Coal– Foster Wheeler
• Entrained Flow– Mitsubishi
• Transport Reactor– Kellogg
• Hybrid – Foster Wheeler– British Coal– ENERCON– FERCO/Silva
Slurry vs Dry
• Dry Feed Gasifier coupled with Waste Heat recoveryBoiler, (Shell gasification technology)
• Slurry Feed Gasifier coupled with Water Quench, (Texacogasification technology
DFG-WHB
SFG-WQ
DFGSFG
Slurry vs Dry
Syngas composition from entrained flow gasifiers
Availability of big IGCC plants:the learning curve
Availability of big IGCC plants:Availability of big IGCC plants:the learning curvethe learning curve
fuel pre-heating
gasifying agents pre-
heating
coaloxygensteam
DEVO sub-model(CPD Db)
COMBUSTIONsub-model (PFR)
GASIFICATIONsub-model (PFR)
.
.
i-th QUENCH(MIXER)
i-th HEATRECOVERY
.
.SEPARATION
syngas
waste water
slag
3 steps of quench / heat recovery
quench water
hot water
LP steam
pressurized water
HP hot water
material streams
heat streams
fuel pre-heating
biomass
DEVO sub-model(CHL Db)
COOLING SCREEN
COOLING JACKET
A “CHALLENGING” SYSTEMThe entrained flow gasifier
drying/devolatilizationswelling & primary fragmentation
particle-to-wall migration& slag buildup
gasification of suspended charsecondary fragmentation
wall gasification of char
VM and char combustion
ENTRAINED FLOW GASIFICATION: PHENOMENOLOGICAL HIGHL IGHTS